Babcock &   Wilcox Co. Steam, Its Generation and Use 
 
 
 THE EARLY HISTORY OF THE GENERATION AND USE OF STEAM 
 While the time of man's first knowledge and use of the expansive force 
 of the vapor of water is unknown, records show that such knowledge 
 existed earlier than 150 B. C. In a treatise of about that time entitled 
 "Pneumatica", Hero, of Alexander, described not only existing devices of 
 his predecessors and contemporaries but also an invention of his own 
 which utilized the expansive force of steam for raising water above its 
 natural level. He clearly describes three methods in which steam might 
 be used directly as a motive of power; raising water by its elasticity, 
 elevating a weight by its expansive power and producing a rotary motion 
 by its reaction on the atmosphere. The third method, which is known as 
 "Hero's engine", is described as a hollow sphere supported over a 
 caldron or boiler by two trunnions, one of which was hollow, and 
 connected the interior of the sphere with the steam space of the 
 caldron. Two pipes, open at the ends and bent at right angles, were 
 inserted at opposite poles of the sphere, forming a connection between 
 the caldron and the atmosphere. Heat being applied to the caldron, the 
 steam generated passed through the hollow trunnion to the sphere and 
 thence into the atmosphere through the two pipes. By the reaction 
 incidental to its escape through these pipes, the sphere was caused to 
 rotate and here is the primitive steam reaction turbine. 
   
 Hero makes no suggestions as to application of any of the devices he 
 describes to a useful purpose. From the time of Hero until the late 
 sixteenth and early seventeenth centuries, there is no record of 
 progress, though evidence is found that such devices as were described 
 by Hero were sometimes used for trivial purposes, the blowing of an 
 organ or the turning of a skillet. 
   
 Mathesius, the German author, in 1571; Besson, a philosopher and 
 mathematician at Orleans; Ramelli, in 1588; Battista Delia Porta, a 
 Neapolitan mathematician and philosopher, in 1601; Decause, the French 
 engineer and architect, in 1615; and Branca, an Italian architect, in 
 1629, all published treatises bearing on the subject of the generation 
 of steam. 
   
 To the next contributor, Edward Somerset, second Marquis of Worcester, 
 is apparently due the credit of proposing, if not of making, the first 
 useful steam engine. In the "Century of Scantlings and Inventions", 
 published in London in 1663, he describes devices showing that he had in 
 mind the raising of water not only by forcing it from two receivers by 
 direct steam pressure but also for some sort of reciprocating piston 
 actuating one end of a lever, the other operating a pump. His 
 descriptions are rather obscure and no drawings are extant so that it is 
 difficult to say whether there were any distinctly novel features to his 
 devices aside from the double action. While there is no direct authentic 
 record that any of the devices he described were actually constructed, 
 it is claimed by many that he really built and operated a steam engine 
 containing pistons. 
   
 In 1675, Sir Samuel Moreland was decorated by King Charles II, for a 
 demonstration of "a certain powerful machine to raise water." Though 
 there appears to be no record of the design of this machine, the 
 mathematical dictionary, published in 1822, credits Moreland with the 
 first account of a steam engine, on which subject he wrote a treatise 
 that is still preserved in the British Museum. 
 Dr. Denys Papin, an ingenious Frenchman, invented in 1680 "a steam 
 digester for extracting marrowy, nourishing juices from bones by 
 enclosing them in a boiler under heavy pressure," and finding danger 
 from explosion, added a contrivance which is the first safety valve on 
 record. 
   
 The steam engine first became commercially successful with Thomas 
 Savery. In 1699, Savery exhibited before the Royal Society of England 
 (Sir Isaac Newton was President at the time), a model engine which 
 consisted of two copper receivers alternately connected by a three-way 
 hand-operated valve, with a boiler and a source of water supply. When 
 the water in one receiver had been driven out by the steam, cold water 
 was poured over its outside surface, creating a vacuum through 
 condensation and causing it to fill again while the water in the other 
 reservoir was being forced out. A number of machines were built on this 
 principle and placed in actual use as mine pumps. 
   
 The serious difficulty encountered in the use of Savery's engine was the 
 fact that the height to which it could lift water was limited by the 
 pressure the boiler and vessels could bear. Before Savery's engine was 
 entirely displaced by its successor, Newcomen's, it was considerably 
 improved by Desaguliers, who applied the Papin safety valve to the 
 boiler and substituted condensation by a jet within the vessel for 
 Savery's surface condensation. 
   
 In 1690, Papin suggested that the condensation of steam should be 
 employed to make a vacuum beneath a cylinder which had previously been 
 raised by the expansion of steam. This was the earliest cylinder and 
 piston steam engine and his plan took practical shape in Newcomen's 
 atmospheric engine. Papin's first engine was unworkable owing to the 
 fact that he used the same vessel for both boiler and cylinder. A small 
 quantity of water was placed in the bottom of the vessel and heat was 
 applied. When steam formed and raised the piston, the heat was withdrawn 
 and the piston did work on its down stroke under pressure of the 
 atmosphere. After hearing of Savery's engine, Papin developed an 
 improved form. Papin's engine of 1705 consisted of a displacement 
 chamber in which a floating diaphragm or piston on top of the water kept 
 the steam and water from direct contact. The water delivered by the 
 downward movement of the piston under pressure, to a closed tank, flowed 
 in a continuous stream against the vanes of a water wheel. When the 
 steam in the displacement chamber had expanded, it was exhausted to the 
 atmosphere through a valve instead of being condensed. The engine was, 
 in fact, a non-condensing, single action steam pump with the steam and 
 pump cylinders in one. A curious feature of this engine was a heater 
 placed in the diaphragm. This was a mass of heated metal for the purpose 
 of keeping the steam dry or preventing condensation during expansion. 
 This device might be called the first superheater. 
   
 Among the various inventions attributed to Papin was a boiler with an 
 internal fire box, the earliest record of such construction. 
   
 While Papin had neglected his earlier suggestion of a steam and piston 
 engine to work on Savery's ideas, Thomas Newcomen, with his assistant, 
 John Cawley, put into practical form Papin's suggestion of 1690. Steam 
 admitted from the boiler to a cylinder raised a piston by its expansion, 
 assisted by a counter-weight on the other end of a beam actuated by the 
 piston. The steam valve was then shut and the steam condensed by a jet 
 of cold water. The piston was then forced downward by atmospheric 
 pressure and did work on the pump. The condensed water in the cylinder 
 was expelled through an escapement valve by the next entry of steam. 
 This engine used steam having pressure but little, if any, above that of 
 the atmosphere. 
 In 1711, this engine was introduced into mines for pumping purposes. 
 Whether its action was originally automatic or whether dependent upon 
 the hand operation of the valves is a question of doubt. The story 
 commonly believed is that a boy, Humphrey Potter, in 1713, whose duty it 
 was to open and shut such valves of an engine he attended, by suitable 
 cords and catches attached to the beam, caused the engine to 
 automatically manipulate these valves. This device was simplified in 
 1718 by Henry Beighton, who suspended from the bottom, a rod called the 
 plug-tree, which actuated the valve by tappets. By 1725, this engine was 
 in common use in the collieries and was changed but little for a matter 
 of sixty or seventy years. Compared with Savery's engine, from the 
 aspect of a pumping engine, Newcomen's was a distinct advance, in that 
 the pressure in the pumps was in no manner dependent upon the steam 
 pressure. In common with Savery's engine, the losses from the alternate 
 heating and cooling of the steam cylinder were enormous. Though 
 obviously this engine might have been modified to serve many purposes, 
 its use seems to have been limited almost entirely to the pumping of 
 water. 
   
 The rivalry between Savery and Papin appears to have stimulated 
 attention to the question of fuel saving. Dr. John Allen, in 1730, 
 called attention to the fact that owing to the short length of time of 
 the contact between the gases and the heating surfaces of the boiler, 
 nearly half of the heat of the fire was lost. With a view to overcoming 
 this loss at least partially, he used an internal furnace with a smoke 
 flue winding through the water in the form of a worm in a still. In 
 order that the length of passage of the gases might not act as a damper 
 on the fire, Dr. Allen recommended the use of a pair of bellows for 
 forcing the sluggish vapor through the flue. This is probably the first 
 suggested use of forced draft. In forming an estimate of the quantity of 
 fuel lost up the stack, Dr. Allen probably made the first boiler test. 
   
 Toward the end of the period of use of Newcomen's atmospheric engine, 
 John Smeaton, who, about 1770, built and installed a number of large 
 engines of this type, greatly improved the design in its mechanical 
 details. 
 The improvement in boiler and engine design of Smeaton, Newcomen and 
 their contemporaries, were followed by those of the great engineer, 
 James Watt, an instrument maker of Glasgow. In 1763, while repairing a 
 model of Newcomen's engine, he was impressed by the great waste of steam 
 to which the alternating cooling and heating of the engine gave rise. 
 His remedy was the maintaining of the cylinder as hot as the entering 
 steam and with this in view he added a vessel separate from the 
 cylinder, into which the steam should pass from the cylinder and be 
 there condensed either by the application of cold water outside or by a 
 jet from within. To preserve a vacuum in his condenser, he added an air 
 pump which should serve to remove the water of condensation and air 
 brought in with the injection water or due to leakage. As the cylinder 
 no longer acted as a condenser, he could maintain it at a high 
 temperature by covering it with non-conducting material and, in 
 particular, by the use of a steam jacket. Further and with the same 
 object in view, he covered the top of the cylinder and introduced steam 
 above the piston to do the work previously accomplished by atmospheric 
 pressure. After several trials with an experimental apparatus based on 
 these ideas, Watt patented his improvements in 1769. Aside from their 
 historical importance, Watt's improvements, as described in his 
 specification, are to this day a statement of the principles which guide 
 the scientific development of the steam engine. His words are: 
   
    "My method of lessening the consumption of steam, and 
    consequently fuel, in fire engines, consists of the following 
    principles: 
   
    "First, That vessel in which the powers of steam are to be 
    employed to work the engine, which is called the cylinder in 
    common fire engines, and which I call the steam vessel, must, 
    during the whole time the engine is at work, be kept as hot as 
    the steam that enters it; first, by enclosing it in a case of 
    wood, or any other materials that transmit heat slowly; 
    secondly, by surrounding it with steam or other heated bodies; 
    and, thirdly, by suffering neither water nor any other substance 
    colder than the steam to enter or touch it during that time. 
   
    "Secondly, In engines that are to be worked wholly or partially 
    by condensation of steam, the steam is to be condensed in 
    vessels distinct from the steam vessels or cylinders, although 
    occasionally communicating with them; these vessels I call 
    condensers; and, whilst the engines are working, these 
    condensers ought at least to be kept as cold as the air in the 
    neighborhood of the engines, by application of water or other 
    cold bodies. 
   
    "Thirdly, Whatever air or other elastic vapor is not condensed 
    by the cold of the condenser, and may impede the working of the 
    engine, is to be drawn out of the steam vessels or condensers by 
    means of pumps, wrought by the engines themselves, or otherwise. 
   
    "Fourthly, I intend in many cases to employ the expansive force 
    of steam to press on the pistons, or whatever may be used 
    instead of them, in the same manner in which the pressure of the 
    atmosphere is now employed in common fire engines. In cases 
    where cold water cannot be had in plenty, the engines may be 
    wrought by this force of steam only, by discharging the steam 
    into the air after it has done its office.... 
   
    "Sixthly, I intend in some cases to apply a degree of cold not 
    capable of reducing the steam to water, but of contracting it 
    considerably, so that the engines shall be worked by the 
    alternate expansion and contraction of the steam. 
   
    "Lastly, Instead of using water to render the pistons and other 
    parts of the engine air and steam tight, I employ oils, wax, 
    resinous bodies, fat of animals, quick-silver and other metals 
    in their fluid state." 
   
 The fifth claim was for a rotary engine, and need not be quoted here. 
   
 The early efforts of Watt are typical of those of the poor inventor 
 struggling with insufficient resources to gain recognition and it was 
 not until he became associated with the wealthy manufacturer, Mattheu 
 Boulton of Birmingham, that he met with the success upon which his 
 present fame is based. In partnership with Boulton, the business of the 
 manufacture and the sale of his engines were highly successful in spite 
 of vigorous attacks on the validity of his patents. 
   
 Though the fourth claim of Watt's patent describes a non-condensing 
 engine which would require high pressures, his aversion to such practice 
 was strong. Notwithstanding his entire knowledge of the advantages 
 through added expansion under high pressure, he continued to use 
 pressures not above 7 pounds per square inch above the atmosphere. To 
 overcome such pressures, his boilers were fed through a stand-pipe of 
 sufficient height to have the column of water offset the pressure within 
 the boiler. Watt's attitude toward high pressure made his influence felt 
 long after his patents had expired. 
 In 1782, Watt patented two other features which he had invented as early 
 as 1769. These were the double acting engine, that is, the use of steam 
 on both sides of the piston and the use of steam expansively, that is, 
 the shutting off of steam from the cylinder when the piston had made but 
 a portion of its stroke, the power for the completion of the stroke 
 being supplied by the expansive force of the steam already admitted. 
   
 He further added a throttle valve for the regulation of steam admission, 
 invented the automatic governor and the steam indicator, a mercury steam 
 gauge and a glass water column. 
   
 It has been the object of this brief history of the early developments 
 in the use of steam to cover such developments only through the time of 
 James Watt. The progress of the steam engine from this time through the 
 stages of higher pressures, combining of cylinders, the application of 
 steam vehicles and steamboats, the adding of third and fourth cylinders, 
 to the invention of the turbine with its development and the 
 accompanying development of the reciprocating engine to hold its place, 
 is one long attribute to the inventive genius of man. 
   
 While little is said in the biographies of Watt as to the improvement of 
 steam boilers, all the evidence indicates that Boulton and Watt 
 introduced the first "wagon boiler", so called because of its shape. In 
 1785, Watt took out a number of patents for variations in furnace 
 construction, many of which contain the basic principles of some of the 
 modern smoke preventing furnaces. Until the early part of the nineteenth 
 century, the low steam pressures used caused but little attention to be 
 given to the form of the boiler operated in connection with the engines 
 above described. About 1800, Richard Trevithick, in England, and Oliver 
 Evans, in America, introduced non-condensing, and for that time, high 
 pressure steam engines. To the initiative of Evans may be attributed the 
 general use of high pressure steam in the United States, a feature which 
 for many years distinguished American from European practice. The demand 
 for light weight and economy of space following the beginning of steam 
 navigation and the invention of the locomotive required boilers designed 
 and constructed to withstand heavier pressures and forced the adoption 
 of the cylindrical form of boiler. There are in use to-day many examples 
 of every step in the development of steam boilers from the first plain 
 cylindrical boiler to the most modern type of multi-tubular locomotive 
 boiler, which stands as the highest type of fire-tube boiler 
 construction. 
   
 The early attempts to utilize water-tube boilers were few. A brief 
 history of the development of the boilers, in which this principle was 
 employed, is given in the following chapter. From this history it will 
 be clearly indicated that the first commercially successful utilization 
 of water tubes in a steam generator is properly attributed to George H. 
 Babcock and Stephen Wilcox. 
 
 
 
 BRIEF HISTORY OF WATER-TUBE BOILERS 
 As stated in the previous chapter, the first water-tube boiler was built 
 by John Blakey and was patented by him in 1766. Several tubes 
 alternately inclined at opposite angles were arranged in the furnaces, 
 the adjacent tube ends being connected by small pipes. The first 
 successful user of water-tube boilers, however, was James Rumsey, an 
 American inventor, celebrated for his early experiments in steam 
 navigation, and it is he who may be truly classed as the originator of 
 the water-tube boiler. In 1788 he patented, in England, several forms of 
 boilers, some of which were of the water-tube type. One had a fire box 
 with flat top and sides, with horizontal tubes across the fire box 
 connecting the water spaces. Another had a cylindrical fire box 
 surrounded by an annular water space and a coiled tube was placed within 
 the box connecting at its two ends with the water space. This was the 
 first of the "coil boilers". Another form in the same patent was the 
 vertical tubular boiler, practically as made at the present time. 
 The first boiler made of a combination of small tubes, connected at one 
 end to a reservoir, was the invention of another American, John Stevens, 
 in 1804. This boiler was actually employed to generate steam for running 
 a steamboat on the Hudson River, but like all the "porcupine" boilers, 
 of which type it was the first, it did not have the elements of a 
 continued success. 
 Another form of water tube was patented in 1805 by John Cox Stevens, a 
 son of John Stevens. This boiler consisted of twenty vertical tubes, 1¼ 
 inches internal diameter and 40½ inches long, arranged in a circle, the 
 outside diameter of which was approximately 12 inches, connecting a 
 water chamber at the bottom with a steam chamber at the top. The steam 
 and water chambers were annular spaces of small cross section and 
 contained approximately 33 cubic inches. The illustration shows the cap 
 of the steam chamber secured by bolts. The steam outlet pipe "A" is a 
 pipe of one inch diameter, the water entering through a similar aperture 
 at the bottom. One of these boilers was for a long time at the Stevens 
 Institute of Technology at Hoboken, and is now in the Smithsonian 
 Institute at Washington. 
 About the same time, Jacob Woolf built a boiler of large horizontal 
 tubes, extending across the furnace and connected at the ends to a 
 longitudinal drum above. The first purely sectional water-tube boiler 
 was built by Julius Griffith, in 1821. In this boiler, a number of 
 horizontal water tubes were connected to vertical side pipes, the side 
 pipes were connected to horizontal gathering pipes, and these latter in 
 turn to a steam drum. 
   
 In 1822, Jacob Perkins constructed a flash boiler for carrying what was 
 then considered a high pressure. A number of cast-iron bars having 1½ 
 inches annular holes through them and connected at their outer ends by a 
 series of bent pipes, outside of the furnace walls, were arranged in 
 three tiers over the fire. The water was fed slowly to the upper tier by 
 a force pump and steam in the superheated state was discharged to the 
 lower tiers into a chamber from which it was taken to the engine. 
 The first sectional water-tube boiler, with a well-defined circulation, 
 was built by Joseph Eve, in 1825. The sections were composed of small 
 tubes with a slight double curve, but being practically vertical, fixed 
 in horizontal headers, which headers were in turn connected to a steam 
 space above and a water space below formed of larger pipes. The steam 
 and water spaces were connected by outside pipes to secure a circulation 
 of the water up through the sections and down through the external 
 pipes. In the same year, John M'Curdy of New York, built a "Duplex Steam 
 Generator" of "tubes of wrought or cast iron or other material" arranged 
 in several horizontal rows, connected together alternately at the front 
 and rear by return bends. In the tubes below the water line were placed 
 interior circular vessels closed at the ends in order to expose a thin 
 sheet of water to the action of the fire. 
 In 1826, Goldsworthy Gurney built a number of boilers, which he used on 
 his steam carriages. A number of small tubes were bent into the shape of 
 a "U" laid sidewise and the ends were connected with larger horizontal 
 pipes. These were connected by vertical pipes to permit of circulation 
 and also to a vertical cylinder which served as a steam and water 
 reservoir. In 1828, Paul Steenstrup made the first shell boiler with 
 vertical water tubes in the large flues, similar to the boiler known as 
 the "Martin" and suggesting the "Galloway". 
   
 The first water-tube boiler having fire tubes within water tubes was 
 built in 1830, by Summers & Ogle. Horizontal connections at the top and 
 bottom were connected by a series of vertical water tubes, through which 
 were fire tubes extending through the horizontal connections, the fire 
 tubes being held in place by nuts, which also served to make the joint. 
 Stephen Wilcox, in 1856, was the first to use inclined water tubes 
 connecting water spaces at the front and rear with a steam space above. 
 The first to make such inclined tubes into a sectional form was Twibill, 
 in 1865. He used wrought-iron tubes connected at the front and rear with 
 standpipes through intermediate connections. These standpipes carried 
 the system to a horizontal cross drum at the top, the entrained water 
 being carried to the rear. 
   
 Clarke, Moore, McDowell, Alban and others worked on the problem of 
 constructing water-tube boilers, but because of difficulties of 
 construction involved, met with no practical success. 
 It may be asked why water-tube boilers did not come into more general 
 use at an early date, that is, why the number of water-tube boilers 
 built was so small in comparison to the number of shell boilers. The 
 reason for this is found in the difficulties involved in the design and 
 construction of water-tube boilers, which design and construction 
 required a high class of engineering and workmanship, while the plain 
 cylindrical boiler is comparatively easy to build. The greater skill 
 required to make a water-tube boiler successful is readily shown in the 
 great number of failures in the attempts to make them. 
   
 
 
 
 REQUIREMENTS OF STEAM BOILERS 
 Since the first appearance in "Steam" of the following "Requirements of 
 a Perfect Steam Boiler", the list has been copied many times either word 
 for word or clothed in different language and applied to some specific 
 type of boiler design or construction. In most cases, although full 
 compliance with one or more of the requirements was structurally 
 impossible, the reader was left to infer that the boiler under 
 consideration possessed all the desirable features. It is noteworthy 
 that this list of requirements, as prepared by George H. Babcock and 
 Stephen Wilcox, in 1875, represents the best practice of to-day. 
 Moreover, coupled with the boiler itself, which is used in the largest 
 and most important steam generating plants throughout the world, the 
 list forms a fitting monument to the foresight and genius of the 
 inventors.  
 
 
 
 REQUIREMENTS OF A PERFECT STEAM BOILER 
 1st. Proper workmanship and simple construction, using materials which 
 experience has shown to be the best, thus avoiding the necessity of 
 early repairs. 
   
   
 2nd. A mud drum to receive all impurities deposited from the water, and 
 so placed as to be removed from the action of the fire. 
   
   
 3rd. A steam and water capacity sufficient to prevent any fluctuation in 
 steam pressure or water level. 
   
   
 4th. A water surface for the disengagement of the steam from the water, 
 of sufficient extent to prevent foaming. 
   
   
 5th. A constant and thorough circulation of water throughout the boiler, 
 so as to maintain all parts at the same temperature. 
   
   
 6th. The water space divided into sections so arranged that, should any 
 section fail, no general explosion can occur and the destructive effects 
 will be confined to the escape of the contents. Large and free passages 
 between the different sections to equalize the water line and pressure 
 in all. 
   
   
 7th. A great excess of strength over any legitimate strain, the boiler 
 being so constructed as to be free from strains due to unequal 
 expansion, and, if possible, to avoid joints exposed to the direct 
 action of the fire. 
   
   
 8th. A combustion chamber so arranged that the combustion of the gases 
 started in the furnace may be completed before the gases escape to the 
 chimney. 
   
   
 9th. The heating surface as nearly as possible at right angles to the 
 currents of heated gases, so as to break up the currents and extract the 
 entire available heat from the gases. 
   
   
 10th. All parts readily accessible for cleaning and repairs. This is a 
 point of the greatest importance as regards safety and economy. 
   
   
 11th. Proportioned for the work to be done, and capable of working to 
 its full rated capacity with the highest economy. 
   
   
 12th. Equipped with the very best gauges, safety valves and other 
 fixtures. 
   
   
 The exhaustive study made of each one of these requirements is shown by 
 the following extract from a lecture delivered by Mr. Geo. H. Babcock at 
 Cornell University in 1890 upon the subject: 
   
 
 
 
 THE CIRCULATION OF WATER IN STEAM BOILERS 
 You have all noticed a kettle of water boiling over the fire, the fluid 
 rising somewhat tumultuously around the edges of the vessel, and 
 tumbling toward the center, where it descends. Similar currents are in 
 action while the water is simply being heated, but they are not 
 perceptible unless there are floating particles in the liquid. These 
 currents are caused by the joint action of the added temperature and two 
 or more qualities which the water possesses. 
   
 1st. Water, in common with most other substances, expands when heated; a 
 statement, however, strictly true only when referred to a temperature 
 above 39 degrees F. or 4 degrees C., but as in the making of steam we 
 rarely have to do with temperatures so low as that, we may, for our 
 present purposes, ignore that exception. 
   
 2nd. Water is practically a non-conductor of heat, though not entirely 
 If ice-cold water was kept boiling at the surface the heat would not 
 
 penetrate sufficiently to begin melting ice at a depth of 3 inches in 
 less than about two hours. As, therefore, the heated water cannot impart 
 its heat to its neighboring particles, it remains expanded and rises by 
 its levity, while colder portions come to be heated in turn, thus 
 setting up currents in the fluid. 
   
 Now, when all the water has been heated to the boiling point 
 corresponding to the pressure to which it is subjected, each added unit 
 of heat converts a portion, about 7 grains in weight, into vapor, 
 greatly increasing its volume; and the mingled steam and water rises 
 more rapidly still, producing ebullition such as we have noticed in the 
 kettle. So long as the quantity of heat added to the contents of the 
 kettle continues practically constant, the conditions remain similar to 
 those we noticed at first, a tumultuous lifting of the water around the 
 edges, flowing toward the center and thence downward; if, however, the 
 fire be quickened, the upward currents interfere with the downward and 
 the kettle boils over (Fig. 1). 
 If now we put in the kettle a vessel somewhat smaller (Fig. 2) with a 
 hole in the bottom and supported at a proper distance from the side so 
 as to separate the upward from the downward currents, we can force the 
 fires to a very much greater extent without causing the kettle to boil 
 over, and when we place a deflecting plate so as to guide the rising 
 column toward the center it will be almost impossible to produce that 
 effect. This is the invention of Perkins in 1831 and forms the basis of 
 very many of the arrangements for producing free circulation of the 
 water in boilers which have been made since that time. It consists in 
 dividing the currents so that they will not interfere each with the 
 other. 
 But what is the object of facilitating the circulation of water in 
 boilers? Why may we not safely leave this to the unassisted action of 
 nature as we do in culinary operations? We may, if we do not care for 
 the three most important aims in steam-boiler construction, namely, 
 efficiency, durability, and safety, each of which is more or less 
 dependent upon a proper circulation of the water. As for efficiency, we 
 have seen one proof in our kettle. When we provided means to preserve 
 the circulation, we found that we could carry a hotter fire and boil 
 away the water much more rapidly than before. It is the same in a steam 
 boiler. And we also noticed that when there was nothing but the 
 unassisted circulation, the rising steam carried away so much water in 
 the form of foam that the kettle boiled over, but when the currents were 
 separated and an unimpeded circuit was established, this ceased, and a 
 much larger supply of steam was delivered in a comparatively dry state. 
 Thus, circulation increases the efficiency in two ways: it adds to the 
 ability to take up the heat, and decreases the liability to waste that 
 heat by what is technically known as priming. There is yet another way 
 in which, incidentally, circulation increases efficiency of surface, and 
 that is by preventing in a greater or less degree the formation of 
 deposits thereon. Most waters contain some impurity which, when the 
 water is evaporated, remains to incrust the surface of the vessel. This 
 incrustation becomes very serious sometimes, so much so as to almost 
 entirely prevent the transmission of heat from the metal to the water. 
 It is said that an incrustation of only one-eighth inch will cause a 
 loss of 25 per cent in efficiency, and this is probably within the truth 
 in many cases. Circulation of water will not prevent incrustation 
 altogether, but it lessens the amount in all waters, and almost entirely 
 so in some, thus adding greatly to the efficiency of the surface. 
 A second advantage to be obtained through circulation is durability of 
 the boiler. This it secures mainly by keeping all parts at a nearly 
 uniform temperature. The way to secure the greatest freedom from unequal 
 strains in a boiler is to provide for such a circulation of the water as 
 will insure the same temperature in all parts. 
   
 3rd. Safety follows in the wake of durability, because a boiler which is 
 not subject to unequal strains of expansion and contraction is not only 
 less liable to ordinary repairs, but also to rupture and disastrous 
 explosion. By far the most prolific cause of explosions is this same 
 strain from unequal expansions. 
 Having thus briefly looked at the advantages of circulation of water in 
 steam boilers, let us see what are the best means of securing it under 
 the most efficient conditions We have seen in our kettle that one 
 essential point was that the currents should be kept from interfering 
 with each other. If we could look into an ordinary return tubular boiler 
 when steaming, we should see a curious commotion of currents rushing 
 hither and thither, and shifting continually as one or the other 
 contending force gained a momentary mastery. The principal upward 
 currents would be found at the two ends, one over the fire and the other 
 over the first foot or so of the tubes. Between these, the downward 
 currents struggle against the rising currents of steam and water. At a 
 sudden demand for steam, or on the lifting of the safety valve, the 
 pressure being slightly reduced, the water jumps up in jets at every 
 portion of the surface, being lifted by the sudden generation of steam 
 throughout the body of water. You have seen the effect of this sudden 
 generation of steam in the well-known experiment with a Florence flask, 
 to which a cold application is made while boiling water under pressure 
 is within. You have also witnessed the geyser-like action when water is 
 boiled in a test tube held vertically over a lamp (Fig. 3). 
 If now we take a U-tube depending from a vessel of water (Fig. 4) and 
 apply the lamp to one leg a circulation is at once set up within it, and 
 no such spasmodic action can be produced. Thus U-tube is the 
 representative of the true method of circulation within a water-tube 
 boiler properly constructed. We can, for the purpose of securing more 
 heating surface, extend the heated leg into a long incline (Fig. 5), 
 when we have the well-known inclined-tube generator. Now, by adding 
 other tubes, we may further increase the heating surface (Fig. 6), while 
 it will still be the U-tube in effect and action. In such a construction 
 the circulation is a function of the difference in density of the two 
 columns. Its velocity is measured by the well-known Torricellian 
 formula, V = (2gh)^{½}, or, approximately V = 8(h)^{½}, h being measured 
 in terms of the lighter fluid. This velocity will increase until the 
 rising column becomes all steam, but the quantity or weight circulated 
 will attain a maximum when the density of the mingled steam and water in 
 the rising column becomes one-half that of the solid water in the 
 descending column which is nearly coincident with the condition of half 
 steam and half water, the weight of the steam being very slight compared 
 to that of the water. 
 It becomes easy by this rule to determine the circulation in any given 
 boiler built on this principle, provided the construction is such as to 
 permit a free flow of the water. Of course, every bend detracts a little 
 and something is lost in getting up the velocity, but when the boiler is 
 well arranged and proportioned these retardations are slight. 
   
 Let us take for example one of the 240 horse-power Babcock & Wilcox 
 boilers here in the University. The height of the columns may be taken 
 as 4½ feet, measuring from the surface of the water to about the center 
 of the bundle of tubes over the fire, and the head would be equal to 
 this height at the maximum of circulation. We should, therefore, have a 
 velocity of 8(4½)^{½} = 16.97, say 17 feet per second. There are in this 
 boiler fourteen sections, each having a 4-inch tube opening into the 
 drum, the area of which (inside) is 11 square inches, the fourteen 
 aggregating 154 square inches, or 1.07 square feet. This multiplied by 
 the velocity, 16.97 feet, gives 18.16 cubic feet mingled steam and water 
 discharged per second, one-half of which, or 9.08 cubic feet, is steam. 
 Assuming this steam to be at 100 pounds gauge pressure, it will weigh 
 0.258 pound per cubic foot. Hence, 2.34 pounds of steam will be 
 discharged per second, and 8,433 pounds per hour. Dividing this by 30, 
 the number of pounds representing a boiler horse power, we get 281.1 
 horse power, about 17 per cent, in excess of the rated power of the 
 boiler. The water at the temperature of steam at 100 pounds pressure 
 weighs 56 pounds per cubic foot, and the steam 0.258 pound, so that the 
 steam forms but 1/218 part of the mixture by weight, and consequently 
 each particle of water will make 218 circuits before being evaporated 
 when working at this capacity, and circulating the maximum weight of 
 water through the tubes. 
 It is evident that at the highest possible velocity of exit from the 
 generating tubes, nothing but steam will be delivered and there will be 
 no circulation of water except to supply the place of that evaporated. 
 Let us see at what rate of steaming this would occur with the boiler 
 under consideration. We shall have a column of steam, say 4 feet high on 
 one side and an equal column of water on the other. Assuming, as before, 
 the steam at 100 pounds and the water at same temperature, we will have 
 a head of 866 feet of steam and an issuing velocity of 235.5 feet per 
 second. This multiplied by 1.07 square feet of opening by 3,600 seconds 
 in an hour, and by 0.258 gives 234,043 pounds of steam, which, though 
 only one-eighth the weight of mingled steam and water delivered at the 
 maximum, gives us 7,801 horse power, or 32 times the rated power of the 
 boiler. Of course, this is far beyond any possibility of attainment, so 
 that it may be set down as certain that this boiler cannot be forced to 
 a point where there will not be an efficient circulation of the water. 
 By the same method of calculation it may be shown that when forced to 
 double its rated power, a point rarely expected to be reached in 
 practice, about two-thirds the volume of mixture of steam and water 
 delivered into the drum will be steam, and that the water will make 110 
 circuits while being evaporated. Also that when worked at only about 
 one-quarter its rated capacity, one-fifth of the volume will be steam 
 and the water will make the rounds 870 times before it becomes steam. 
 You will thus see that in the proportions adopted in this boiler there 
 is provision for perfect circulation under all the possible conditions 
 of practice. 
 In designing boilers of this style it is necessary to guard against 
 having the uptake at the upper end of the tubes too large, for if 
 sufficiently large to allow downward currents therein, the whole effect 
 of the rising column in increasing the circulation in the tubes is 
 nullified (Fig. 7). This will readily be seen if we consider the uptake 
 very large when the only head producing circulation in the tubes will be 
 that due to the inclination of each tube taken by itself. This objection 
 is only overcome when the uptake is so small as to be entirely filled 
 with the ascending current of mingled steam and water. It is also 
 necessary that this uptake should be practically direct, and it should 
 not be composed of frequent enlargements and contractions. Take, for 
 instance, a boiler well known in Europe, copied and sold here under 
 another name. It is made up of inclined tubes secured by pairs into 
 boxes at the ends, which boxes are made to communicate with each other 
 by return bends opposite the ends of the tubes. These boxes and return 
 bends form an irregular uptake, whereby the steam is expected to rise to 
 a reservoir above. You will notice (Fig. 8) that the upward current of 
 steam and water in the return bend meets and directly antagonizes the 
 upward current in the adjoining tube. Only one result can follow. If 
 their velocities are equal, the momentum of both will be neutralized and 
 all circulation stopped, or, if one be stronger, it will cause a back 
 flow in the other by the amount of difference in force, with practically 
 the same result. 
 In a well-known boiler, many of which were sold, but of which none are 
 now made and a very few are still in use, the inventor claimed that the 
 return bends and small openings against the tubes were for the purpose 
 of "restricting the circulation" and no doubt they performed well that 
 office; but excepting for the smallness of the openings they were not as 
 efficient for that purpose as the arrangement shown in Fig. 8. 
 Another form of boiler, first invented by Clarke or Crawford, and lately 
 revived, has the uptake made of boxes into which a number, generally 
 from two to four tubes, are expanded, the boxes being connected together 
 by nipples (Fig. 9). It is a well-known fact that where a fluid flows 
 through a conduit which enlarges and then contracts, the velocity is 
 lost to a greater or less extent at the enlargements, and has to be 
 gotten up again at the contractions each time, with a corresponding loss 
 of head. The same thing occurs in the construction shown in Fig. 9. The 
 enlargements and contractions quite destroy the head and practically 
 overcome the tendency of the water to circulate. 
   
 A horizontal tube stopped at one end, as shown in Fig. 10, can have no 
 proper circulation within it. If moderately driven, the water may 
 struggle in against the issuing steam sufficiently to keep the surface 
 covered, but a slight degree of forcing will cause it to act like the 
 test tube in Fig. 3, and the more there are of them in a given boiler 
 the more spasmodic will be its working. 
   
 The experiment with our kettle (Fig. 2) gives the clue to the best means 
 of promoting circulation in ordinary shell boilers. Steenstrup or 
 "Martin" and "Galloway" water tubes placed in such boilers also assist 
 in directing the circulation therein, but it is almost impossible to 
 produce in shell boilers, by any means the circulation of all the water 
 in one continuous round, such as marks the well-constructed water-tube 
 boiler. 
   
 As I have before remarked, provision for a proper circulation of water 
 has been almost universally ignored in designing steam boilers, 
 sometimes to the great damage of the owner, but oftener to the jeopardy 
 of the lives of those who are employed to run them. The noted case of 
 the Montana and her sister ship, where some $300,000 was thrown away in 
 trying an experiment which a proper consideration of this subject would 
 have avoided, is a case in point; but who shall count the cost of life 
 and treasure not, perhaps, directly traceable to, but, nevertheless, due 
 entirely to such neglect in design and construction of the thousands of 
 boilers in which this necessary element has been ignored? 
   
   
 In the light of the performance of the exacting conditions of present 
 day power-plant practice, a review of this lecture and of the foregoing 
 list of requirements reveals the insight of the inventors of the Babcock 
 & Wilcox boiler into the fundamental principles of steam generator 
 design and construction. 
   
 Since the Babcock & Wilcox boiler became thoroughly established as a 
 durable and efficient steam generator, many types of water-tube boilers 
 have appeared on the market. Most of them, failing to meet enough of the 
 requirements of a perfect boiler, have fallen by the wayside, while a 
 few failing to meet all of the requirements, have only a limited field 
 of usefulness. None have been superior, and in the most cases the most 
 ardent admirers of other boilers have been satisfied in looking up to 
 the Babcock & Wilcox boiler as a standard and in claiming that the newer 
 boilers were "just as good." 
   
 Records of recent performances under the most severe conditions of 
 services on land and sea, show that the Babcock & Wilcox boiler can be 
 run continually and regularly at higher overloads, with higher 
 efficiency, and lower upkeep cost than any other boiler on the market. 
 It is especially adapted for power-plant work where it is necessary to 
 use a boiler in which steam can be raised quickly and the boiler placed 
 on the line either from a cold state or from a banked fire in the 
 shortest possible time, and with which the capacity, with clean feed 
 water, will be largely limited by the amount of coal that can be burned 
 in the furnace. 
   
 The distribution of the circulation through the separate headers and 
 sections and the action of the headers in forcing a maximum and 
 continuous circulation in the lower tubes, permit the operation of the 
 Babcock & Wilcox boiler without objectionable priming, with a higher 
 degree of concentration of salts in the water than is possible in any 
 other type of boiler. 
   
 Repeated daily performances at overloads have demonstrated beyond a 
 doubt the correctness of Mr. Babcock's computation regarding the 
 circulating tube and header area required for most efficient 
 circulation. They also have proved that enlargement of the area of 
 headers and circulating tubes beyond a certain point diminishes the head 
 available for causing circulation and consequently limits the ability of 
 the boiler to respond to demands for overloads. 
   
 In this lecture Mr. Babcock made the prediction that with the 
 circulating tube area proportioned in accordance with the principles 
 laid down, the Babcock & Wilcox boiler could be continuously run at 
 double its nominal rating, which at that time was based on 12 square 
 feet of heating surface per horse power. This prediction is being 
 fulfilled daily in all the large and prominent power plants in this 
 country and abroad, and it has been repeatedly demonstrated that with 
 clean water and clean tube surfaces it is possible to safely operate at 
 over 300 per cent of the nominal rating. 
   
 In the development of electrical power stations it becomes more and more 
 apparent that it is economical to run a boiler at high ratings during 
 the times of peak loads, as by so doing the lay-over losses are 
 diminished and the economy of the plant as a whole is increased. 
   
 The number and importance of the large electric lighting and power 
 stations constructed during the last ten years that are equipped with 
 Babcock & Wilcox boilers, is a most gratifying demonstration of the 
 merit of the apparatus, especially in view of their satisfactory 
 operation under conditions which are perhaps more exacting than those of 
 any other service. 
   
 Time, the test of all, results with boilers as with other things, in the 
 survival of the fittest. When judged on this basis the Babcock & Wilcox 
 boiler stands pre-eminent in its ability to cover the whole field of 
 steam generation with the highest commercial efficiency obtainable. Year 
 after year the Babcock & Wilcox boiler has become more firmly 
 established as the standard of excellence in the boiler making art. 
   
 
 
 
 EVOLUTION OF THE BABCOCK & WILCOX WATER-TUBE BOILER 
 Quite as much may be learned from the records of failures as from those 
 of success. Where a device has been once fairly tried and found to be 
 imperfect or impracticable, the knowledge of that trial is of advantage 
 in further investigation. Regardless of the lesson taught by failure, 
 however, it is an almost every-day occurrence that some device or 
 construction which has been tried and found wanting, if not worthless, 
 is again introduced as a great improvement upon a device which has shown 
 by its survival to be the fittest. 
   
 The success of the Babcock & Wilcox boiler is due to many years of 
 constant adherence to one line of research, in which an endeavor has 
 been made to introduce improvements with the view to producing a boiler 
 which would most effectively meet the demands of the times. During the 
 periods that this boiler has been built, other companies have placed on 
 the market more than thirty water-tube or sectional water-tube boilers, 
 most of which, though they may have attained some distinction and sale, 
 have now entirely disappeared. The following incomplete list will serve 
 to recall the names of some of the boilers that have had a vogue at 
 various times, but which are now practically unknown: Dimpfel, Howard, 
 Griffith & Wundrum, Dinsmore, Miller "Fire Box", Miller "American", 
 Miller "Internal Tube", Miller "Inclined Tube", Phleger, Weigant, the 
 Lady Verner, the Allen, the Kelly, the Anderson, the Rogers & Black, the 
 Eclipse or Kilgore, the Moore, the Baker & Smith, the Renshaw, the 
 Shackleton, the "Duplex", the Pond & Bradford, the Whittingham, the 
 Bee, the Hazleton or "Common Sense", the Reynolds, the Suplee or Luder, 
 the Babbit, the Reed, the Smith, the Standard, etc., etc. 
   
 It is with the object of protecting our customers and friends from loss 
 through purchasing discarded ideas that there is given on the following 
 pages a brief history of the development of the Babcock & Wilcox boiler 
 as it is built to-day. The illustrations and brief descriptions indicate 
 clearly the various designs and constructions that have been used and 
 that have been replaced, as experience has shown in what way improvement 
 might be made. They serve as a history of the experimental steps in the 
 development of the present Babcock & Wilcox boiler, the value and 
 success of which, as a steam generator, is evidenced by the fact that 
 the largest and most discriminating users continue to purchase them 
 after years of experience in their operation. 
 No. 1. The original Babcock & Wilcox boiler was patented in 1867. The 
 main idea in its design was safety, to which all other features were 
 sacrificed wherever they conflicted. The boiler consisted of a nest of 
 horizontal tubes, serving as a steam and water reservoir, placed above 
 and connected at each end by bolted joints to a second nest of inclined 
 heating tubes filled with water. The tubes were placed one above the 
 other in vertical rows, each row and its connecting end forming a single 
 casting. Hand-holes were placed at each end for cleaning. Internal tubes 
 were placed within the inclined tubes with a view to aiding circulation. 
   
 No. 2. This boiler was the same as No. 1, except that the internal 
 circulating tubes were omitted as they were found to hinder rather than 
 help the circulation. 
   
 Nos. 1 and 2 were found to be faulty in both material and design, cast 
 metal proving unfit for heating surfaces placed directly over the fire, 
 as it cracked as soon as any scale formed. 
   
 No. 3. Wrought-iron tubes were substituted for the cast-iron heating 
 tubes, the ends being brightened, laid in moulds, and the headers cast 
 on. 
   
 The steam and water capacity in this design were insufficient to secure 
 regularity of action, there being no reserve upon which to draw during 
 firing or when the water was fed intermittently. The attempt to dry the 
 steam by superheating it in the nest of tubes forming the steam space 
 was found to be impracticable. The steam delivered was either wet, dry 
 or superheated, according to the rate at which it was being drawn from 
 the boiler. Sediment was found to lodge in the lowermost point of the 
 boiler at the rear end and the exposed portions cracked off at this 
 point when subjected to the furnace heat. 
 No. 4. A plain cylinder, carrying the water line at its center and 
 leaving the upper half for steam space, was substituted for the nest of 
 tubes forming the steam and water space in Nos. 1, 2 and 3. The sections 
 were made as in No. 3 and a mud drum added to the rear end of the 
 sections at the point that was lowest and farthest removed from the 
 fire. The gases were made to pass off at one side and did not come into 
 contact with the mud drum. Dry steam was obtained through the increase 
 of separating surface and steam space and the added water capacity 
 furnished a storage for heat to tide over irregularities of firing and 
 feeding. By the addition of the drum, the boiler became a serviceable 
 and practical design, retaining all of the features of safety. As the 
 drum was removed from the direct action of the fire, it was not 
 subjected to excessive strain due to unequal expansion, and its 
 diameter, if large in comparison with that of the tubes formerly used, 
 was small when compared with that of cylindrical boilers. Difficulties 
 were encountered in this boiler in securing reliable joints between the 
 wrought-iron tubes and the cast-iron headers. 
 No. 5. In this design, wrought-iron water legs were substituted for the 
 cast-iron headers, the tubes being expanded into the inside sheets and a 
 large cover placed opposite the front end of the tubes for cleaning. The 
 tubes were staggered one above the other, an arrangement found to be 
 more efficient in the absorption of heat than where they were placed in 
 vertical rows. In other respects, the boiler was similar to No. 4, 
 except that it had lost the important element of safety through the 
 introduction of the very objectionable feature of flat stayed surfaces. 
 The large doors for access to the tubes were also a cause of weakness. 
   
 An installation of these boilers was made at the plant of the Calvert 
 Sugar Refinery in Baltimore, and while they were satisfactory in their 
 operation, were never duplicated. 
 No. 6. This was a modification of No. 5 in which longer tubes were used 
 and over which the gases were caused to make three passes with a view of 
 better economy. In addition, some of the stayed surfaces were omitted 
 and handholes substituted for the large access doors. A number of 
 boilers of this design were built but their excessive first cost, the 
 lack of adjustability of the structure under varying temperatures, and 
 the inconvenience of transportation, led to No. 7. 
 No. 7. In this boiler, the headers and water legs were replaced by 
 T-heads screwed to the ends of the inclined tubes. The faces of these Ts 
 were milled and the tubes placed one above the other with the milled 
 faces metal to metal. Long bolts passed through each vertical section of 
 the T-heads and through connecting boxes on the heads of the drums 
 holding the whole together. A large number of boilers of this design 
 were built and many were in successful operation for over twenty years. 
 In most instances, however, they were altered to later types. 
 Nos. 8 and 9. These boilers were known as the Griffith & Wundrum type, 
 the concern which built them being later merged in The Babcock & Wilcox 
 Co. Experiments were made with this design with four passages of the 
 gases across the tubes and the downward circulation of the water at the 
 rear of the boiler was carried to the bottom row of tubes. In No. 9 an 
 attempt was made to increase the safety and reduce the cost by reducing 
 the amount of steam and water capacity. A drum at right angles to the 
 line of tubes was used but as there was no provision made to secure dry 
 steam, the results were not satisfactory. The next move in the direction 
 of safety was the employment of several drums of small diameter instead 
 of a single drum. 
 This is shown in No. 10. A nest of small horizontal drums, 15 inches in 
 diameter, was used in place of the single drum of larger diameter. A set 
 of circulation tubes was placed at an intermediate angle between the 
 main bank of heating tubes and the horizontal drums forming the steam 
 reservoir. These circulators were to return to the rear end of the 
 circulating tubes the water carried up by the circulation, and in this 
 way were to allow only steam to be delivered to the small drums above. 
 There was no improvement in the action of this boiler over that of No. 
 9. 
   
 The four passages of the gas over the tubes tried in Nos. 8, 9 and 10 
 were not found to add to the economy of the boiler. 
 No. 11. A trial was next made of a box coil system, in which the water 
 was made to transverse the furnace several times before being delivered 
 to the drum above. The tendency here, as in all similar boilers, was to 
 form steam in the middle of the coil and blow the water from each end, 
 leaving the tubes practically dry until the steam found an outlet and 
 the water returned. This boiler had, in addition to a defective 
 circulation, a decidedly geyser-like action and produced wet steam. 
 All of the types mentioned, with the exception of Nos. 5 and 6, had 
 between their several parts a large number of bolted joints which were 
 subjected to the action of the fire. When these boilers were placed in 
 operation it was demonstrated that as soon as any scale formed on the 
 heating surfaces, leaks were caused due to unequal expansion. 
   
 No. 12. With this boiler, an attempt was made to remove the joints from 
 the fire and to increase the heating surface in a given space. Water 
 tubes were expanded into both sides of wrought-iron boxes, openings 
 being made for the admission of water and the exit of steam. Fire tubes 
 were placed inside the water tubes to increase the heating surface. This 
 design was abandoned because of the rapid stopping up of the tubes by 
 scale and the impossibility of cleaning them. 
 No. 13. Vertical straight line headers of cast iron, each containing two 
 rows of tubes, were bolted to a connection leading to the steam and 
 water drum above. 
 No. 14. A wrought-iron box was substituted for the double cast-iron 
 headers. In this design, stays were necessary and were found, as always, 
 to be an element to be avoided wherever possible. The boiler was an 
 improvement on No. 6, however. A slanting bridge wall was introduced 
 underneath the drum to throw a larger portion of its heating surface 
 into the combustion chamber under the bank of tubes. 
   
 This bridge wall was found to be difficult to keep in repair and was of 
 no particular benefit. 
 No. 15. Each row of tubes was expanded at each end into a continuous 
 header, cast of car wheel metal. The headers had a sinuous form so that 
 they would lie close together and admit of a staggered position of the 
 tubes when assembled. While other designs of header form were tried 
 later, experience with Nos. 14 and 15 showed that the style here adopted 
 was the best for all purposes and it has not been changed materially 
 since. The drum in this design was supported by girders resting on the 
 brickwork. Bolted joints were discarded, with the exception of those 
 connecting the headers to the front and rear ends of the drums and the 
 bottom of the rear headers to the mud drum. Even such joints, however, 
 were found objectionable and were superseded in subsequent construction 
 by short lengths of tubes expanded into bored holes. 
 No. 16. In this design, headers were tried which were made in the form 
 of triangular boxes, in each of which there were three tubes expanded. 
 These boxes were alternately reversed and connected by short lengths of 
 expanded tubes, being connected to the drum by tubes bent in a manner to 
 allow them to enter the shell normally. The joints between headers 
 introduced an element of weakness and the connections to the drum were 
 insufficient to give adequate circulation. 
 No. 17. Straight horizontal headers were next tried, alternately shifted 
 right and left to allow a staggering of tubes. These headers were 
 connected to each other and to the drums by expanded nipples. The 
 objections to this boiler were almost the same as those to No. 16. 
 Nos. 18 and 19. These boilers were designed primarily for fire 
 protection purposes, the requirements demanding a small, compact boiler 
 with ability to raise steam quickly. These both served the purpose 
 admirably but, as in No. 9, the only provision made for the securing of 
 dry steam was the use of the steam dome, shown in the illustration. This 
 dome was found inadequate and has since been abandoned in nearly all 
 forms of boiler construction. No other remedy being suggested at the 
 time, these boilers were not considered as desirable for general use as 
 Nos. 21 and 22. In Europe, however, where small size units were more in 
 demand, No. 18 was modified somewhat and used largely with excellent 
 results. These experiments, as they may now be called, although many 
 boilers of some of the designs were built, clearly demonstrated that the 
 best construction and efficiency required adherence to the following 
 elements of design: 
   
   
 1st. Sinuous headers for each vertical row of tubes. 
   
   
 2nd. A separate and independent connection with the drum, both front and 
 rear, for each vertical row of tubes. 
 3rd. All joints between parts of the boiler proper to be made without 
 bolts or screw plates. 
   
   
 4th. No surfaces to be used which necessitate the use of stays. 
   
   
 5th. The boiler supported independently of the brickwork so as to allow 
 freedom for expansion and contraction as it is heated or cooled. 
   
   
 6th. Ample diameter of steam and water drums, these not to be less than 
 30 inches except for small size units. 
   
   
 7th. Every part accessible for cleaning and repairs. 
   
   
 With these points having been determined, No. 20 was designed. This 
 boiler had all the desirable features just enumerated, together with a 
 number of improvements as to detail of construction. The general form of 
 No. 15 was adhered to but the bolted connections between sections and 
 drum and sections and mud drum were discarded in favor of connections 
 made by short lengths of boiler tubes expanded into the adjacent parts. 
 This boiler was suspended from girders, like No. 15, but these in turn 
 were carried on vertical supports, leaving the pressure parts entirely 
 free from the brickwork, the mutually deteriorating strains present 
 where one was supported by the other being in this way overcome. 
 Hundreds of thousands of horse power of this design were built, giving 
 great satisfaction. The boiler was known as the "C. I. F." (cast-iron 
 front) style, an ornamental cast-iron front having been usually 
 furnished. 
 The next step, and the one which connects the boilers as described above 
 to the boiler as it is built to-day, was the design illustrated in No. 
 These boilers were known as the "W. I. F." style, the fronts 
 
 furnished as part of the equipment being constructed largely of wrought 
 iron. The cast-iron drumheads used in No. 20 were replaced by 
 wrought-steel flanged and "bumped" heads. The drums were made longer and 
 the sections connected to wrought-steel cross boxes riveted to the 
 bottom of the drums. The boilers were supported by girders and columns 
 as in No. 20. 
 No. 22. This boiler, which is designated as the "Vertical Header" type, 
 has the same general features of construction as No. 21, except that the 
 tube sheet side of the headers is "stepped" to allow the headers to be 
 placed vertically and at right angles to the drum and still maintain the 
 tubes at the angle used in Nos. 20 and 21. 
 No. 23, or the cross drum design of boiler, is a development of the 
 Babcock & Wilcox marine boiler, in which the cross drum is used 
 exclusively. The experience of the Glasgow Works of The Babcock & 
 Wilcox, Ltd., with No. 18 proved that proper attention to details of 
 construction would make it a most desirable form of boiler where 
 headroom was limited. A large number of this design have been 
 successfully installed and are giving satisfactory results under widely 
 varying conditions. The cross drum boiler is also built in a vertical 
 header design. 
   
 Boilers Nos. 21, 22 and 23, with a few modifications, are now the 
 standard forms. These designs are illustrated, as they are constructed 
 to-day, on pages 48, 52, 54, 58 and 60. 
   
 The last step in the development of the water-tube boiler, beyond which 
 it seems almost impossible for science and skill to advance, consists in 
 the making of all pressure parts of the boiler of wrought steel, 
 including sinuous headers, cross boxes, nozzles, and the like. This 
 construction was the result of the demands of certain Continental laws 
 that are coming into general vogue in this country. The Babcock & Wilcox 
 Co. have at the present time a plant producing steel forgings that have 
 been pronounced by the _London Engineer_ to be "a perfect triumph 
 of the forgers' art". 
   
 The various designs of this all wrought-steel boiler are fully 
 illustrated in the following pages. 
   
 
 
 
 THE BABCOCK & WILCOX BOILER 
 The following brief description of the Babcock & Wilcox boiler will 
 clearly indicate the manner in which it fulfills the requirements of the 
 perfect steam boiler already enumerated. 
   
 The Babcock & Wilcox boiler is built in two general classes, the 
 longitudinal drum type and the cross drum type. Either of these designs 
 may be constructed with vertical or inclined headers, and the headers in 
 turn may be of wrought steel or cast iron dependent upon the working 
 pressure for which the boiler is constructed. The headers may be of 
 different lengths, that is, may connect different numbers of tubes, and 
 it is by a change in the number of tubes in height per section and the 
 number of sections in width that the size of the boiler is varied. 
   
 The longitudinal drum boiler is the generally accepted standard of 
 Babcock & Wilcox construction. The cross drum boiler, though originally 
 designed to meet certain conditions of headroom, has become popular for 
 numerous classes of work where low headroom is not a requirement which 
 must be met. 
   
 LONGITUDINAL DRUM CONSTRUCTION--The heating surface of this type of 
 boiler is made up of a drum or drums, depending upon the width of the 
 boiler extending longitudinally over the other pressure parts. To the 
 drum or drums there are connected through cross boxes at either end the 
 sections, which are made up of headers and tubes. At the lower end of 
 the sections there is a mud drum extending entirely across the setting 
 and connected to all sections. The connections between all parts are by 
 short lengths of tubes expanded into bored seats. 
 The drums are of three sheets, of such thickness as to give the required 
 factor of safety under the maximum pressure for which the boiler is 
 constructed. The circular seams are ordinarily single lap riveted though 
 these may be double lap riveted to meet certain requirements of pressure 
 or of specifications. The longitudinal seams are properly proportioned 
 butt and strap or lap riveted joints dependent upon the pressure for 
 which the boilers are built. Where butt strap joints are used the straps 
 are bent to the proper radius in an hydraulic press. The courses are 
 built independently to template and are assembled by an hydraulic 
 forcing press. All riveted holes are punched one-quarter inch smaller 
 than the size of rivets as driven and are reamed to full size after the 
 plates are assembled. All rivets are driven by hydraulic pressure and 
 held until black. 
 The drumheads are hydraulic forged at a single heat, the manhole opening 
 and stiffening ring being forged in position. Flat raised seats for 
 water column and feed connections are formed in the forging. 
   
 All heads are provided with manholes, the edges of which are turned 
 true. The manhole plates are of forged steel and turned to fit manhole 
 opening. These plates are held in position by forged-steel guards and 
 bolts. 
   
 The drum nozzles are of forged steel, faced, and fitted with taper 
 thread stud bolts. 
 Cross boxes by means of which the sections are attached to the drums, 
 are of forged steel, made from a single sheet. 
   
 Where two or more drums are used in one boiler they are connected by a 
 cross pipe having a flanged outlet for the steam connection. 
 The sections are built of 4-inch hot finished seamless open-hearth steel 
 tubes of No. 10 B. W. G. where the boilers are built for working 
 pressures up to 210 pounds. Where the working pressure is to be above 
 this and below 260 pounds, No. 9 B. W. G. tubes are supplied. 
 The tubes are expanded into headers of serpentine or sinuous form, which 
 dispose the tubes in a staggered position when assembled as a complete 
 boiler. These headers are of wrought steel or of cast iron, the latter 
 being ordinarily supplied where the working pressure is not to exceed 
 160 pounds. The headers may be either vertical or inclined as shown in 
 the various illustrations of assembled boilers. 
 Opposite each tube end in the headers there is placed a handhole of 
 sufficient size to permit the cleaning, removal or renewal of a tube. 
 These openings in the wrought steel vertical headers are elliptical in 
 shape, machine faced, and milled to a true plane back from the edge a 
 sufficient distance to make a seat. The openings are closed by inside 
 fitting forged plates, shouldered to center in the opening, their 
 flanged seats milled to a true plane. These plates are held in position 
 by studs and forged-steel binders and nuts. The joints between plates 
 and headers are made with a thin gasket. 
 In the wrought-steel inclined headers the handhole openings are either 
 circular or elliptical, the former being ordinarily supplied. The 
 circular openings have a raised seat milled to a true plane. The 
 openings are closed on the outside by forged-steel caps, milled and 
 ground true, held in position by forged-steel safety clamps and secured 
 by ball-headed bolts to assure correct alignment. With this style of 
 fitting, joints are made tight, metal to metal, without packing of any 
 kind. 
 Where elliptical handholes are furnished they are faced inside, closed 
 by inside fitting forged-steel plates, held to their seats by studs and 
 secured by forged-steel binders and nuts. 
   
 The joints between plates and header are made with a thin gasket. 
 The vertical cast-iron headers have elliptical handholes with raised 
 seats milled to a true plane. These are closed on the outside by 
 cast-iron caps milled true, held in position by forged-steel safety 
 clamps, which close the openings from the inside and which are secured 
 by ball-headed bolts to assure proper alignment. All joints are made 
 tight, metal to metal, without packing of any kind. 
   
 The mud drum to which the sections are attached at the lower end of the 
 rear headers, is a forged-steel box 7¼ inches square, and of such length 
 as to be connected to all headers by means of wrought nipples expanded 
 into counterbored seats. The mud drum is furnished with handholes for 
 cleaning, these being closed from the inside by forged-steel plates with 
 studs, and secured on a faced seat in the mud drum by forged-steel 
 binders and nuts. The joints between the plates and the drum are made 
 with thin gaskets. The mud drum is tapped for blow-off connection. 
   
 All connections between drums and sections and between sections and mud 
 drum are of hot finished seamless open-hearth steel tubes of No. 9 
 W. G. 
 
   
 Boilers of the longitudinal drum type are suspended front and rear from 
 wrought-steel supporting frames entirely independent of the brickwork. 
 This allows for expansion and contraction of the pressure parts without 
 straining either the boiler or the brickwork, and also allows of 
 brickwork repair or renewal without in any way disturbing the boiler or 
 its connections. 
 CROSS DRUM CONSTRUCTION--The cross drum type of boilers differs from the 
 longitudinal only in drum construction and method of support. The drum 
 in this type is placed transversely across the rear of the boiler and is 
 connected to the sections by means of circulating tubes expanded into 
 bored seats. 
   
 The drums for all pressures are of two sheets of sufficient thickness to 
 give the required factor of safety. The longitudinal seams are double 
 riveted butt strapped, the straps being bent to the proper radius in an 
 hydraulic press. The circulating tubes are expanded into the drums at 
 the seams, the butt straps serving as tube seats. 
   
 The drumheads, drum fittings and features of riveting are the same in 
 the cross drum as in the longitudinal types. The sections and mud drum 
 are also the same for the two types. 
   
 Cross drum boilers are supported at the rear on the mud drum which rests 
 on cast-iron foundation plates. They are suspended at the front from a 
 wrought-iron supporting frame, each section being suspended 
 independently from the cross members by hook suspension bolts. This 
 method of support is such as to allow for expansion and contraction 
 without straining either the boiler or the brickwork and permits of 
 repair or renewal of the latter without in any way disturbing the boiler 
 or its connections. 
   
 The following features of design and of attachments supplied are the 
 same for all types. 
   
 FRONTS--Ornamental fronts are fitted to the front supporting frame. 
 These have large doors for access to the front headers and panels above 
 the fire fronts. The fire fronts where furnished have independent frames 
 for fire doors which are bolted on, and ashpit doors fitted with blast 
 catches. The lugs on door frames and on doors are cast solid. The faces 
 of doors and of frames are planed and the lugs milled. The doors and 
 frames are placed in their final relative position, clamped, and the 
 holes for hinge pins drilled while thus held. A perfect alignment of 
 door and frame is thus assured and the method is representative of the 
 care taken in small details of manufacture. 
   
 The front as a whole is so arranged that any stoker may be applied with 
 but slight modification wherever boilers are set with sufficient furnace 
 height. 
 In the vertical header boilers large wrought-iron doors, which give 
 access to the rear headers, are attached to the rear supporting frame. 
 FITTINGS--Each boiler is provided with the following fittings as part of 
 the standard equipment: 
   
 Blow-off connections and valves attached to the mud drum. 
   
 Safety valves placed on nozzles on the steam drums. 
   
 A water column connected to the front of the drum. 
   
 A steam gauge attached to the boiler front. 
   
 Feed water connection and valves. A flanged stop and check valve of 
 heavy pattern is attached directly to each drumhead, closing 
 automatically in case of a rupture in the feed line. 
   
 All valves and fittings are substantially built and are of designs which 
 by their successful service for many years have become standard with The 
 Babcock & Wilcox Co. 
   
 The fixtures that are supplied with the boilers consist of: 
   
 Dead plates and supports, the plates arranged for a fire brick lining. 
   
 A full set of grate bars and bearers, the latter fitted with expansion 
 sockets for side walls. 
   
 Flame bridge plates with necessary fastenings, and special fire brick 
 for lining same. 
   
 Bridge wall girder for hanging bridge wall with expansion sockets for 
 side walls. 
   
 A full set of access and cleaning doors through which all portions of 
 the pressure parts may be reached. 
   
 A swing damper and frame with damper operating rig. 
   
 There are also supplied with each boiler a wrench for handhole nuts, a 
 water-driven turbine tube cleaner, a set of fire tools and a metal steam 
 hose and cleaning pipe equipped with a special nozzle for blowing dust 
 and soot from the tubes. 
   
 Aside from the details of design and construction as covered in the 
 foregoing description, a study of the illustrations will make clear the 
 features of the boiler as a whole which have led to its success. 
   
 The method of supporting the boiler has been described. This allows it 
 to be hung at any height that may be necessary to properly handle the 
 fuel to be burned or to accommodate the stoker to be installed. The 
 height of the nest of tubes which forms the roof of the furnace is thus 
 the controlling feature in determining the furnace height, or the 
 distance from the front headers to the floor line. The sides and front 
 of the furnace are formed by the side and front boiler walls. The rear 
 wall of the furnace consists of a bridge wall built from the bottom of 
 the ashpit to the lower row of tubes. The location of this wall may be 
 adjusted within limits to give the depth of furnace demanded by the fuel 
 used. Ordinarily the bridge wall is the determining feature in the 
 locating of the front baffle. Where a great depth of furnace is 
 necessary, in which case, if the front baffle were placed at the bridge 
 wall the front pass of the boiler would be relatively too long, a 
 patented construction is used which maintains the baffle in what may be 
 considered its normal position, and a connection made between the baffle 
 and the bridge wall by means of a tile roof. Such furnace construction 
 is known as a "Webster" furnace. 
   
 [Illustration: Longitudinal Drum Boiler--Front View] 
   
 A consideration of this furnace will clearly indicate its adaptability, 
 by reason of its flexibility, for any fuel and any design of stoker. The 
 boiler lends itself readily to installation with an extension or Dutch 
 oven furnace if this be demanded by the fuel to be used, and in general 
 it may be stated that a satisfactory furnace arrangement may be made in 
 connection with a Babcock & Wilcox boiler for burning any fuel, solid, 
 liquid or gaseous. 
   
 The gases of combustion evolved in the furnace above described are led 
 over the heating surfaces by two baffles. These are formed of cast-iron 
 baffle plates lined with special fire brick and held in position by tube 
 clamps. The front baffle leads the gases through the forward portion of 
 the tubes to a chamber beneath the drum or drums. It is in this chamber 
 that a superheater is installed where such an apparatus is desired. The 
 gases make a turn over the front baffle, are led downward through the 
 central portion of the tubes, called the second pass, by means of a 
 hanging bridge wall of brick and the second baffle, around which they 
 make a second turn upward, pass through the rear portion of the tubes 
 and are led to the stack or flue through a damper box in the rear wall, 
 or around the drums to a damper box placed overhead. 
   
 The space beneath the tubes between the bridge wall and the rear boiler 
 wall forms a pocket into which much of the soot from the gases in their 
 downward passage through the second pass will be deposited and from 
 which it may be readily cleaned through doors furnished for the purpose. 
   
 The gas passages are ample and are so proportioned that the resistance 
 offered to the gases is only such as will assure the proper abstraction 
 of heat from the gases without causing undue friction, requiring 
 excessive draft. 
 The method in which the feed water is introduced through the front 
 drumhead of the boiler is clearly seen by reference to the illustration. 
 From this point of introduction the water passes to the rear of the 
 drum, downward through the rear circulating tubes to the sections, 
 upward through the tubes of the sections to the front headers and 
 through these headers and front circulating tubes again to the drum 
 where such water as has not been formed into steam retraces its course. 
 The steam formed in the passage through the tubes is liberated as the 
 water reaches the front of the drum. The steam so formed is stored in 
 the steam space above the water line, from which it is drawn through a 
 so-called "dry pipe." The dry pipe in the Babcock & Wilcox boiler is 
 misnamed, as in reality it fulfills none of the functions ordinarily 
 attributed to such a device. This function is usually to restrict the 
 flow of steam from a boiler with a view to avoid priming. In the Babcock 
 & Wilcox boiler its function is simply that of a collecting pipe, and as 
 the aggregate area of the holes in it is greatly in excess of the area 
 of the steam outlet from the drum, it is plain that there can be no 
 restriction through this collecting pipe. It extends nearly the length 
 of the drum, and draws steam evenly from the whole length of the steam 
 space. 
 The large tube doors through which access is had to the front headers 
 and the doors giving such access to the rear headers in boilers of the 
 vertical header type have already been described and are shown clearly 
 by the illustrations on pages 56 and 74. In boilers of the inclined 
 header type, access to the rear headers is secured through the chamber 
 formed by the headers and the rear boiler wall. Large doors in the sides 
 of the setting give full access to all parts for inspection and for 
 removal of accumulations of soot. Small dusting doors are supplied for 
 the side walls through which all of the heating surfaces may be cleaned 
 by means of a steam dusting lance. These side dusting doors are a 
 patented feature and the shutters are self closing. In wide boilers 
 additional cleaning doors are supplied at the top of the setting to 
 insure ease in reaching all portions of the heating surface. 
   
 The drums are accessible for inspection through the manhole openings. 
 The removal of the handhole plates makes possible the inspection of each 
 tube for its full length and gives the assurance that no defect can 
 exist that cannot be actually seen. This is particularly advantageous 
 when inspecting for the presence of scale. 
   
 The materials entering into the construction of the Babcock & Wilcox 
 boiler are the best obtainable for the special purpose for which they 
 are used and are subjected to rigid inspection and tests. 
   
 The boilers are manufactured by means of the most modern shop equipment 
 and appliances in the hands of an old and well-tried organization of 
 skilled mechanics under the supervision of experienced engineers. 
   
 
 
 
 ADVANTAGES OF THE BABCOCK & WILCOX BOILER 
 The advantages of the Babcock & Wilcox boiler may perhaps be most 
 clearly set forth by a consideration, 1st, of water-tube boilers as a 
 class as compared with shell and fire-tube boilers; and 2nd, of the 
 Babcock & Wilcox boiler specifically as compared with other designs of 
 water-tube boilers. 
   
 
 
 
 WATER-TUBE _VERSUS_ FIRE-TUBE BOILERS 
 Safety--The most important requirement of a steam boiler is that it 
 shall be safe in so far as danger from explosion is concerned. If the 
 energy in a large shell boiler under pressure is considered, the thought 
 of the destruction possible in the case of an explosion is appalling. 
 The late Dr. Robert H. Thurston, Dean of Sibley College, Cornell 
 University, and past president of the American Society of Mechanical 
 Engineers, estimated that there is sufficient energy stored in a plain 
 cylinder boiler under 100 pounds steam pressure to project it in case of 
 an explosion to a height of over 3½ miles; a locomotive boiler at 125 
 pounds pressure from one-half to one-third of a mile; and a 60 
 horse-power return tubular boiler under 75 pounds pressure somewhat over 
 a mile. To quote: "A cubic foot of heated water under a pressure of from 
 60 to 70 pounds per square inch has about the same energy as one pound 
 of gunpowder." From such a consideration, it may be readily appreciated 
 how the advent of high pressure steam was one of the strongest factors 
 in forcing the adoption of water-tube boilers. A consideration of the 
 thickness of material necessary for cylinders of various diameters under 
 a steam pressure of 200 pounds and assuming an allowable stress of 
 12,000 pounds per square inch, will perhaps best illustrate this point. 
 Table 1 gives such thicknesses for various diameters of cylinders not 
 taking into consideration the weakening effect of any joints which may 
 be necessary. The rapidity with which the plate thickness increases with 
 the diameter is apparent and in practice, due to the fact that riveted 
 joints must be used, the thicknesses as given in the table, with the 
 exception of the first, must be increased from 30 to 40 per cent. 
   
 In a water-tube boiler the drums seldom exceed 48 inches in diameter and 
 the thickness of plate required, therefore, is never excessive. The 
 thinner metal can be rolled to a more uniform quality, the seams admit 
 of better proportioning, and the joints can be more easily and perfectly 
 fitted than is the case where thicker plates are necessary. All of these 
 points contribute toward making the drums of water-tube boilers better 
 able to withstand the stress which they will be called upon to endure. 
   
 The essential constructive difference between water-tube and fire-tube 
 boilers lies in the fact that the former is composed of parts of 
 relatively small diameter as against the large diameters necessary in 
 the latter. 
   
 The factor of safety of the boiler parts which come in contact with the 
 most intense heat in water-tube boilers can be made much higher than 
 would be practicable in a shell boiler. Under the assumptions considered 
 above in connection with the thickness of plates required, a number 10 
 gauge tube (0.134 inch), which is standard in Babcock & Wilcox boilers 
 for pressures up to 210 pounds under the same allowable stress as was 
 used in computing Table 1, the safe working pressure for the tubes is 
 870 pounds per square inch, indicating the very large margin of safety 
 of such tubes as compared with that possible with the shell of a boiler. 
   
        TABLE 1 
   
 PLATE THICKNESS REQUIRED 
 FOR VARIOUS CYLINDER 
        DIAMETERS 
   
    ALLOWABLE STRESS, 
    12000 POUNDS PER 
      SQUARE INCH, 
    200 POUNDS GAUGE 
 PRESSURE, NO JOINTS 
   
 +---------+-----------+ 
 |Diameter | Thickness | 
 |Inches   | Inches   | 
 +---------+-----------+ 
 |     4   |   0.033   | 
 |   36   |   0.300   | 
 |   48   |   0.400   | 
 |   60   |   0.500   | 
 |   72   |   0.600   | 
 |   108   |   0.900   | 
 |   120   |   1.000   | 
 |   144   |   1.200   | 
 +---------+-----------+ 
   
 A further advantage in the water-tube boiler as a class is the 
 elimination of all compressive stresses. Cylinders subjected to external 
 pressures, such as fire tubes or the internally fired furnaces of 
 certain types of boilers, will collapse under a pressure much lower than 
 that which they could withstand if it were applied internally. This is 
 due to the fact that if there exists any initial distortion from its 
 true shape, the external pressure will tend to increase such distortion 
 and collapse the cylinder, while an internal pressure tends to restore 
 the cylinder to its original shape. 
   
 Stresses due to unequal expansion have been a fruitful source of trouble 
 in fire-tube boilers. 
   
 In boilers of the shell type, the riveted joints of the shell, with 
 their consequent double thickness of metal exposed to the fire, gives 
 rise to serious difficulties. Upon these points are concentrated all 
 strains of unequal expansion, giving rise to frequent leaks and 
 oftentimes to actual ruptures. Moreover, in the case of such rupture, 
 the whole body of contained water is liberated instantaneously and a 
 disastrous and usually fatal explosion results. 
   
 Further, unequal strains result in shell or fire-tube boilers due to the 
 difference in temperature of the various parts. This difference in 
 temperature results from the lack of positive well defined circulation. 
 While such a circulation does not necessarily accompany all water-tube 
 designs, in general, the circulation in water-tube boilers is much more 
 defined than in fire-tube or shell boilers. 
   
 A positive and efficient circulation assures that all portions of the 
 pressure parts will be at approximately the same temperature and in this 
 way strains resulting from unequal temperatures are obviated. 
   
 If a shell or fire-tubular boiler explodes, the apparatus as a whole is 
 destroyed. In the case of water-tube boilers, the drums are ordinarily 
 so located that they are protected from intense heat and any rupture is 
 usually in the case of a tube. Tube failures, resulting from blisters or 
 burning, are not serious in their nature. Where a tube ruptures because 
 of a flaw in the metal, the result may be more severe, but there cannot 
 be the disastrous explosion such as would occur in the case of the 
 explosion of a shell boiler. 
   
 To quote Dr. Thurston, relative to the greater safety of the water-tube 
 boiler: "The stored available energy is usually less than that of any of 
 the other stationary boilers and not very far from the amount stored, 
 pound for pound, in the plain tubular boiler. It is evident that their 
 admitted safety from destructive explosion does not come from this 
 relation, however, but from the division of the contents into small 
 portions and especially from those details of construction which make it 
 tolerably certain that any rupture shall be local. A violent explosion 
 can only come from the general disruption of a boiler and the liberation 
 at once of large masses of steam and water." 
   
 Economy--The requirement probably next in importance to safety in a 
 steam boiler is economy in the use of fuel. To fulfill such a 
 requirement, the three items, of proper grate for the class of fuel to 
 be burned, a combustion chamber permitting complete combustion of gases 
 before their escape to the stack, and the heating surface of such a 
 character and arrangement that the maximum amount of available heat may 
 be extracted, must be co-ordinated. 
   
 Fire-tube boilers from the nature of their design do not permit the 
 variety of combinations of grate surface, heating surface, and 
 combustion space possible in practically any water-tube boiler. 
   
 In securing the best results in fuel economy, the draft area in a boiler 
 is an important consideration. In fire-tube boilers this area is limited 
 to the cross sectional area of the fire tubes, a condition further 
 aggravated in a horizontal boiler by the tendency of the hot gases to 
 pass through the upper rows of tubes instead of through all of the tubes 
 alike. In water-tube boilers the draft area is that of the space outside 
 of the tubes and is hence much greater than the cross sectional area of 
 the tubes. 
   
 Capacity--Due to the generally more efficient circulation found in 
 water-tube than in fire-tube boilers, rates of evaporation are possible 
 with water-tube boilers that cannot be approached where fire-tube 
 boilers are employed. 
   
 Quick Steaming--Another important result of the better circulation 
 ordinarily found in water-tube boilers is in their ability to raise 
 steam rapidly in starting and to meet the sudden demands that may be 
 thrown on them. 
   
 In a properly designed water-tube boiler steam may be raised from a cold 
 boiler to 200 pounds pressure in less than one-half hour. 
   
 For the sake of comparison with the figure above, it may be stated that 
 in the U. S. Government Service the shortest time allowed for getting up 
 steam in Scotch marine boilers is 6 hours and the time ordinarily 
 allowed is 12 hours. In large double-ended Scotch boilers, such as are 
 generally used in Trans-Atlantic service, the fires are usually started 
 24 hours before the time set for getting under way. This length of time 
 is necessary for such boilers in order to eliminate as far as possible 
 excessive strains resulting from the sudden application of heat to the 
 surfaces. 
   
 Accessibility--In the "Requirements of a Perfect Steam Boiler", as 
 stated by Mr. Babcock, he demonstrates the necessity for complete 
 accessibility to all portions of the boiler for cleaning, inspection and 
 repair. 
   
 Cleaning--When the great difference is realized in performance, both as 
 to economy and capacity of a clean boiler and one in which the heating 
 surfaces have been allowed to become fouled, it may be appreciated that 
 the ability to keep heating surfaces clean internally and externally is 
 a factor of the highest importance. 
   
 Such results can be accomplished only by the use of a design in boiler 
 construction which gives complete accessibility to all portions. In 
 fire-tube boilers the tubes are frequently nested together with a space 
 between them often less than 1¼ inches and, as a consequence, nearly the 
 entire tube surface is inaccessible. When scale forms upon such tubes it 
 is impossible to remove it completely from the inside of the boiler and 
 if it is removed by a turbine hammer, there is no way of knowing how 
 thorough a job has been done. With the formation of such scale there is 
 danger through overheating and frequent tube renewals are necessary. 
   
 [Illustration: Portion of 29,000 Horse-power Installation of Babcock & 
 Wilcox Boilers in the L Street Station of the Edison Electric 
 Illuminating Co. of Boston, Mass. This Company Operates in its Various 
 Stations a Total of 39,000 Horse Power of Babcock & Wilcox Boilers] 
   
 In Scotch marine boilers, even with the engines operating condensing, 
 complete tube renewals at intervals of six or seven years are required, 
 while large replacements are often necessary in less than one year. In 
 return tubular boilers operated with bad feed water, complete tube 
 renewals annually are not uncommon. In this type of boiler much sediment 
 falls on the bottom sheets where the intense heat to which they are 
 subjected bakes it to such an excessive hardness that the only method of 
 removing it is to chisel it out. This can be done only by omitting tubes 
 enough to leave a space into which a man can crawl and the discomforts 
 under which he must work are apparent. Unless such a deposit is removed, 
 a burned and buckled plate will invariably result, and if neglected too 
 long an explosion will follow. 
   
 In vertical fire-tube boilers using a water leg construction, a deposit 
 of mud in such legs is an active agent in causing corrosion and the 
 difficulty of removing such deposit through handholes is well known. A 
 complete removal is practically impossible and as a last resort to 
 obviate corrosion in certain designs, the bottom of the water legs in 
 some cases have been made of copper. A thick layer of mud and scale is 
 also liable to accumulate on the crown sheet of such boilers and may 
 cause the sheet to crack and lead to an explosion. 
   
 The soot and fine coal swept along with the gases by the draft will 
 settle in fire tubes and unless removed promptly, must be cut out with a 
 special form of scraper. It is not unusual where soft coal is used to 
 find tubes half filled with soot, which renders useless a large portion 
 of the heating surface and so restricts the draft as to make it 
 difficult to burn sufficient coal to develop the required power from 
 such heating surface as is not covered by soot. 
   
 Water-tube boilers in general are from the nature of their design more 
 readily accessible for cleaning than are fire-tube boilers. 
   
 Inspection--The objections given above in the consideration of the 
 inability to properly clean fire-tube boilers hold as well for the 
 inspection of such boilers. 
   
 Repairs--The lack of accessibility in fire-tube boilers further leads to 
 difficulties where repairs are required. 
   
 In fire-tube boilers tube renewals are a serious undertaking. The 
 accumulation of hard deposit on the exterior of the surfaces so enlarges 
 the tubes that it is oftentimes difficult, if not impossible, to draw 
 them through the tube sheets and it is usually necessary to cut out such 
 tubes as will allow access to the one which has failed and remove them 
 through the manhole. 
   
 When a tube sheet blisters, the defective part must be cut out by 
 hand-tapped holes drilled by ratchets and as it is frequently impossible 
 to get space in which to drive rivets, a "soft patch" is necessary. This 
 is but a makeshift at best and usually results in either a reduction of 
 the safe working pressure or in the necessity for a new plate. If the 
 latter course is followed, the old plate must be cut out, a new one 
 scribed to place to locate rivet holes and in order to obtain room for 
 driving rivets, the boiler will have to be re-tubed. 
   
 The setting must, of course, be at least partially torn out and 
 replaced. 
   
 In case of repairs, of such nature in fire-tube boilers, the working 
 pressure of such repaired boilers will frequently be lowered by the 
 insurance companies when the boiler is again placed in service. 
   
 In the case of a rupture in a water-tube boiler, the loss will 
 ordinarily be limited to one or two tubes which can be readily replaced. 
 The fire-tube boiler will be so completely demolished that the question 
 of repairs will be shifted from the boiler to the surrounding property, 
 the damage to which will usually exceed many times the cost of a boiler 
 of a type which would have eliminated the possibility of a disastrous 
 explosion. In considering the proper repair cost of the two types of 
 boilers, the fact should not be overlooked that it is poor economy to 
 invest large sums in equipment that, through a possible accident to the 
 boiler may be wholly destroyed or so damaged that the cost of repairs, 
 together with the loss of time while such repairs are being made, would 
 purchase boilers of absolute safety and leave a large margin beside. The 
 possibility of loss of human life should also be considered, though this 
 may seem a far cry from the question of repair costs. 
   
 Space Occupied--The space required for the boilers in a plant often 
 exceeds the requirements for the remainder of the plant equipment. Any 
 saving of space in a boiler room will be a large factor in reducing the 
 cost of real estate and of the building. Even when the boiler plant is 
 comparatively small, the saving in space frequently will amount to a 
 considerable percentage of the cost of the boilers. Table 2 shows the 
 difference in floor space occupied by fire-tube boilers and Babcock & 
 Wilcox boilers of the same capacity, the latter being taken as 
 representing the water-tube class. This saving in space will increase 
 with the size of the plant for the reason that large size boiler units 
 while common in water-tube practice are impracticable in fire-tube 
 practice. 
   
                   TABLE 2 
   
          COMPARATIVE APPROXIMATE FLOOR 
        SPACE OCCUPIED BY BABCOCK & WILCOX 
              AND H. R. T. BOILERS 
   
 +------------+----------------+---------------+ 
 |Size of unit|Babcock & Wilcox|   H. R. T.   | 
 |Horse Power |Feet and Inches |Feet and Inches| 
 +------------+----------------+---------------+ 
 |   100     |   7 3 × 19 9 | 10 0 × 20 0 | 
 |   150     |   7 10 × 19 9 | 10 0 × 22 6 | 
 |   200     |   9 0 × 19 9 | 11 6 × 23 10 | 
 |   250     |   9 0 × 19 9 | 11 6 × 23 10 | 
 |   300     | 10 2 × 19 9 | 12 0 × 25 0 | 
 +------------+----------------+---------------+ 
   
 
 
 
 BABCOCK & WILCOX BOILERS AS COMPARED WITH OTHER WATER-TUBE DESIGNS 
 It must be borne in mind that the simple fact that a boiler is of the 
 water-tube design does not as a necessity indicate that it is a good or 
 safe boiler. 
   
 Safety--Many of the water-tube boilers on the 
 market are as lacking as are fire-tube boilers in the positive 
 circulation which, as has been demonstrated by Mr. Babcock's lecture, is 
 so necessary in the requirements of the perfect steam boiler. In boilers 
 using water-leg construction, there is danger of defective circulation, 
 leaks are common, and unsuspected corrosion may be going on in portions 
 of the boiler that cannot be inspected. Stresses due to unequal 
 expansion of the metal cannot be well avoided but they may be minimized 
 by maintaining at the same temperature all pressure parts of the boiler. 
 The result is to be secured only by means of a well defined circulation. 
   
 The main feature to which the Babcock & Wilcox boiler owes its safety is 
 the construction made possible by the use of headers, by which the water 
 in each vertical row of tubes is separated from that in the adjacent 
 rows. This construction results in the very efficient circulation 
 produced through the breaking up of the steam and water in the front 
 headers, the effect of these headers in producing such a positive 
 circulation having been clearly demonstrated in Mr. Babcock's lecture. 
 The use of a number of sections, thus composed of headers and tubes, has 
 a distinct advantage over the use of a common chamber at the outlet ends 
 of the tubes. In the former case the circulation of water in one 
 vertical row of tubes cannot interfere with that in the other rows, 
 while in the latter construction there will be downward as well as 
 upward currents and such downward currents tend to neutralize any good 
 effect there might be through the diminution of the density of the water 
 column by the steam. 
   
 Further, the circulation results directly from the design of the boiler 
 and requires no assistance from "retarders", check valves and the like, 
 within the boiler. All such mechanical devices in the interior of a 
 boiler serve only to complicate the design and should not be used. 
   
 This positive and efficient circulation assures that all portions of the 
 pressure parts of the Babcock & Wilcox boiler will be at approximately 
 the same temperature and in this way strains resulting from unequal 
 temperatures are obviated. 
   
 Where the water throughout the boiler is at the temperature of the steam 
 contained, a condition to be secured only by proper circulation, danger 
 from internal pitting is minimized, or at least limited only to effects 
 of the water fed the boiler. Where the water in any portion of the 
 boiler is lower than the temperature of the steam corresponding to the 
 pressure carried, whether the fact that such lower temperatures exist as 
 a result of lack of circulation, or because of intentional design, 
 internal pitting or corrosion will almost invariably result. 
   
 Dr. Thurston has already been quoted to the effect that the admitted 
 safety of a water-tube boiler is the result of the division of its 
 contents into small portions. In boilers using a water-leg construction, 
 while the danger from explosion will be largely limited to the tubes, 
 there is the danger, however, that such legs may explode due to the 
 deterioration of their stays, and such an explosion might be almost as 
 disastrous as that of a shell boiler. The headers in a Babcock & Wilcox 
 boiler are practically free from any danger of explosion. Were such an 
 explosion to occur, it would still be localized to a much larger extent 
 than in the case of a water-leg boiler and the header construction thus 
 almost absolutely localizes any danger from such a cause. 
   
 Staybolts are admittedly an undesirable element of construction in any 
 boiler. They are wholly objectionable and the only reason for the 
 presence of staybolts in a boiler is to enable a cheaper form of 
 construction to be used than if they were eliminated. 
   
 In boilers utilizing in their design flat-stayed surfaces, or staybolt 
 construction under pressure, corrosion and wear and tear in service 
 tends to weaken some single part subject to continual strain, the result 
 being an increased strain on other parts greatly in excess of that for 
 which an allowance can be made by any reasonable factor of safety. Where 
 the construction is such that the weakening of a single part will 
 produce a marked decrease in the safety and reliability of the whole, it 
 follows of necessity, that there will be a corresponding decrease in the 
 working pressure which may be safely carried. 
   
 In water-leg boilers, the use of such flat-stayed surfaces under 
 pressure presents difficulties that are practically unsurmountable. Such 
 surfaces exposed to the heat of the fire are subject to unequal 
 expansion, distortion, leakage and corrosion, or in general, to many of 
 the objections that have already been advanced against the fire-tube 
 boilers in the consideration of water-tube boilers as a class in 
 comparison with fire-tube boilers. 
 Aside from the difficulties that may arise in actual service due to the 
 failure of staybolts, or in general, due to the use of flat-stayed 
 surfaces, constructional features are encountered in the actual 
 manufacture of such boilers that make it difficult if not impossible to 
 produce a first-class mechanical job. It is practically impossible in 
 the building of such a boiler to so design and place the staybolts that 
 all will be under equal strain. Such unequal strains, resulting from 
 constructional difficulties, will be greatly multiplied when such a 
 boiler is placed in service. Much of the riveting in boilers of this 
 design must of necessity be hand work, which is never the equal of 
 machine riveting. The use of water-leg construction ordinarily requires 
 the flanging of large plates, which is difficult, and because of the 
 number of heats necessary and the continual working of the material, may 
 lead to the weakening of such plates. 
   
 In vertical or semi-vertical water-tube boilers utilizing flat-stayed 
 surfaces under pressure, these surfaces are ordinarily so located as to 
 offer a convenient lodging place for flue dust, which fuses into a hard 
 mass, is difficult of removal and under which corrosion may be going on 
 with no possibility of detection. 
   
 Where stayed surfaces or water legs are features in the design of a 
 water-tube boiler, the factor of safety of such parts must be most 
 carefully considered. In such parts too, is the determination of the 
 factor most difficult, and because of the "rule-of-thumb" determination 
 frequently necessary, the factor of safety becomes in reality a factor 
 of ignorance. As opposed to such indeterminate factors of safety, in the 
 Babcock & Wilcox boiler, when the factor of safety for the drum or drums 
 has been determined, and such a factor may be determined accurately, the 
 factors for all other portions of the pressure parts are greatly in 
 excess of that of the drum. All Babcock & Wilcox boilers are built with 
 a factor of safety of at least five, and inasmuch as the factor of the 
 safety of the tubes and headers is greatly in excess of this figure, it 
 applies specifically to the drum or drums. This factor represents a 
 greater degree of safety than a considerably higher factor applied to a 
 boiler in which the shell or any riveted portion is acted upon directly 
 by the fire, or the same factor applied to a boiler utilizing 
 flat-stayed surface construction, where the accurate determination of 
 the limiting factor of safety is difficult, if not impossible. 
   
 That the factor of safety of stayed surfaces is questionable may perhaps 
 be best realized from a consideration of the severe requirements as to 
 such factor called for by the rules and regulations of the Board of 
 Supervising Inspectors, U. S. Government. 
   
 In view of the above, the absence of any stayed surfaces in the Babcock 
 & Wilcox boiler is obviously a distinguishing advantage where safety is 
 a factor. It is of interest to note, in the article on the evolution of 
 the Babcock & Wilcox boiler, that staybolt construction was used in 
 several designs, found unsatisfactory and unsafe, and discarded. 
   
 Another feature in the design of the Babcock & Wilcox boiler tending 
 toward added safety is its manner of suspension. This has been indicated 
 in the previous chapter and is of such nature that all of the pressure 
 parts are free to expand or contract under variations of temperature 
 without in any way interfering with any part of the boiler setting. The 
 sectional nature of the boiler allows a flexibility under varying 
 temperature changes that practically obviates internal strain. 
   
 In boilers utilizing water-leg construction, on the other hand, the 
 construction is rigid, giving rise to serious internal strains and the 
 method of support ordinarily made necessary by the boiler design is not 
 only unmechanical but frequently dangerous, due to the fact that proper 
 provision is not made for expansion and contraction under temperature 
 variations. 
   
 Boilers utilizing water-leg construction are not ordinarily provided 
 with mud drums. This is a serious defect in that it allows impurities 
 and sediment to collect in a portion of the boiler not easily inspected, 
 and corrosion may result. 
   
 Economy--That the water-tube boiler as a class lends itself more readily 
 than does the fire-tube boiler to a variation in the relation of grate 
 surface, heating surface and combustion space has been already pointed 
 out. In economy again, the construction made possible by the use of 
 headers in Babcock & Wilcox boilers appears as a distinct advantage. 
 Because of this construction, there is a flexibility possible, in an 
 unlimited variety of heights and widths that will satisfactorily meet 
 the special requirements of the fuel to be burned in individual cases. 
   
 An extended experience in the design of furnaces best suited for a wide 
 variety of fuels has made The Babcock & Wilcox Co. leaders in the field 
 of economy. Furnaces have been built and are in successful operation for 
 burning anthracite and bituminous coals, lignite, crude oil, gas-house 
 tar, wood, sawdust and shavings, bagasse, tan bark, natural gas, blast 
 furnace gas, by-product coke oven gas and for the utilization of waste 
 heat from commercial processes. The great number of Babcock & Wilcox 
 boilers now in satisfactory operation under such a wide range of fuel 
 conditions constitutes an unimpeachable testimonial to the ability to 
 meet all of the many conditions of service. 
   
 The limitations in the draft area of fire-tube boilers as affecting 
 economy have been pointed out. That a greater draft area is possible in 
 water-tube boilers does not of necessity indicate that proper advantage 
 of this fact is taken in all boilers of the water-tube class. In the 
 Babcock & Wilcox boiler, the large draft area taken in connection with 
 the effective baffling allows the gases to be brought into intimate 
 contact with all portions of the heating surfaces and renders such 
 surfaces highly efficient. 
   
 In certain designs of water-tube boilers the baffling is such as to 
 render ineffective certain portions of the heating surface, due to the 
 tendency of soot and dirt to collect on or behind baffles, in this way 
 causing the interposition of a layer of non-conducting material between 
 the hot gases and the heating surfaces. 
   
 In Babcock & Wilcox boilers the standard baffle arrangement is such as 
 to allow the installation of a superheater without in any way altering 
 the path of the gases from furnace to stack, or requiring a change in 
 the boiler design. In certain water-tube boilers the baffle arrangement 
 is such that if a superheater is to be installed a complete change in 
 the ordinary baffle design is necessary. Frequently to insure 
 sufficiently hot gas striking the heating surfaces, a portion is 
 by-passed directly from the furnace to the superheater chamber without 
 passing over any of the boiler heating surfaces. Any such arrangement 
 will lead to a decrease in economy and the use of boilers requiring it 
 should be avoided. 
   
 Capacity--Babcock & Wilcox boilers are run successfully in every-day 
 practice at higher ratings than any other boilers in practical service. 
 The capacities thus obtainable are due directly to the efficient 
 circulation already pointed out. Inasmuch as the construction utilizing 
 headers has a direct bearing in producing such circulation, it is also 
 connected with the high capacities obtainable with this apparatus. 
   
 Where intelligently handled and kept properly cleaned, Babcock & Wilcox 
 boilers are operated in many plants at from 200 to 225 per cent of their 
 rated evaporative capacity and it is not unusual for them to be operated 
 at 300 per cent of such rated capacity during periods of peak load. 
   
 Dry Steam--In the list of the requirements of the perfect steam boiler, 
 the necessity that dry steam be generated has been pointed out. The 
 Babcock & Wilcox boiler will deliver dry steam under higher capacities 
 and poorer conditions of feed water than any other boiler now 
 manufactured. Certain boilers will, when operated at ordinary ratings, 
 handle poor feed water and deliver steam in which the moisture content 
 is not objectionable. When these same boilers are driven at high 
 overloads, there will be a direct tendency to prime and the percentage 
 of moisture in the steam delivered will be high. This tendency is the 
 result of the lack of proper circulation and once more there is seen the 
 advantage of the headers of the Babcock & Wilcox boiler, resulting as it 
 does in the securing of a positive circulation. 
   
 In the design of the Babcock & Wilcox boiler sufficient space is 
 provided between the steam outlet and the disengaging point to insure 
 the steam passing from the boiler in a dry state without entraining or 
 again picking up any particles of water in its passage even at high 
 rates of evaporation. Ample time is given for a complete separation of 
 steam from the water at the disengaging surface before the steam is 
 carried from the boiler. These two features, which are additional causes 
 for the ability of the Babcock & Wilcox boiler to deliver dry steam, 
 result from the proper proportioning of the steam and water space of the 
 boiler. From the history of the development of the boiler, it is evident 
 that the cubical capacity per horse power of the steam and water space 
 has been adopted after numerous experiments. 
   
 That the "dry pipe" serves in no way the generally understood function 
 of such device has been pointed out. As stated, the function of the "dry 
 pipe" in a Babcock & Wilcox boiler is simply that of a collecting pipe 
 and this statement holds true regardless of the rate of operation of the 
 boiler. 
   
 In certain boilers, "superheating surface" is provided to "dry the 
 steam," or to remove the moisture due to priming or foaming. Such 
 surface is invariably a source of trouble unless the steam is initially 
 dry and a boiler which will deliver dry steam is obviously to be 
 preferred to one in which surface must be supplied especially for such 
 purpose. Where superheaters are installed with Babcock & Wilcox boilers, 
 they are in every sense of the word superheaters and not driers, the 
 steam being delivered to them in a dry state. 
   
 The question has been raised in connection with the cross drum design of 
 the Babcock & Wilcox boiler as to its ability to deliver dry steam. 
 Experience has shown the absolute lack of basis for any such objection. 
 The Babcock & Wilcox Company at its Bayonne Works some time ago made a 
 series of experiments to see in what manner the steam generated was 
 separated from the water either in the drum or in its passage to the 
 drum. Glass peepholes were installed in each end of a drum in a boiler 
 of the marine design, at the point midway between that at which the 
 horizontal circulating tubes entered the drum and the drum baffle plate. 
 By holding a light at one of these peepholes the action in the drum was 
 clearly seen through the other. It was found that with the boiler 
 operated under three-quarter inch ashpit pressure, which, with the fuel 
 used would be equivalent to approximately 185 per cent of rating for 
 stationary boiler practice, that each tube was delivering with great 
 velocity a stream of solid water, which filled the tube for half its 
 cross sectional area. There was no spray or mist accompanying such 
 delivery, clearly indicating that the steam had entirely separated from 
 the water in its passage through the horizontal circulating tubes, which 
 in the boiler in question were but 50 inches long. 
   
 [Illustration: Northwest Station of the Commonwealth Edison Co., 
 Chicago, Ill. This Installation Consists of 11,360 Horse Power of 
 Babcock & Wilcox Boilers and Superheaters, Equipped with Babcock & 
 Wilcox Chain Grate Stokers] 
   
 These experiments proved conclusively that the size of the steam drums 
 in the cross drum design has no appreciable effect in determining the 
 amount of liberating surface, and that sufficient liberating surface is 
 provided in the circulating tubes alone. If further proof of the ability 
 of this design of boiler to deliver dry steam is required, such proof is 
 perhaps best seen in the continued use of the Babcock & Wilcox marine 
 boiler, in which the cross drum is used exclusively, and with which 
 rates of evaporation are obtained far in excess of those secured in 
 ordinary practice. 
   
 Quick Steaming--The advantages of water-tube boilers as a class over 
 fire-tube boilers in ability to raise steam quickly have been indicated. 
   
 Due to the constant and thorough circulation resulting from the 
 sectional nature of the Babcock & Wilcox boiler, steam may be raised 
 more rapidly than in practically any other water-tube design. 
   
 In starting up a cold Babcock & Wilcox boiler with either coal or oil 
 fuel, where a proper furnace arrangement is supplied, steam may be 
 raised to a pressure of 200 pounds in less than half an hour. With a 
 Babcock & Wilcox boiler in a test where forced draft was available, 
 steam was raised from an initial temperature of the boiler and its 
 contained water of 72 degrees to a pressure of 200 pounds, in 12½ 
 minutes after lighting the fire. The boiler also responds quickly in 
 starting from banked fires, especially where forced draft is available. 
   
 In Babcock & Wilcox boilers the water is divided into many small streams 
 which circulate without undue frictional resistance in thin envelopes 
 passing through the hottest part of the furnace, the steam being carried 
 rapidly to the disengaging surface. There is no part of the boiler 
 exposed to the heat of the fire that is not in contact with water 
 internally, and as a result there is no danger of overheating on 
 starting up quickly nor can leaks occur from unequal expansion such as 
 might be the case where an attempt is made to raise steam rapidly in 
 boilers using water leg construction. 
   
 Storage Capacity for Steam and Water--Where sufficient steam and water 
 capacity are not provided in a boiler, its action will be irregular, the 
 steam pressure varying over wide limits and the water level being 
 subject to frequent and rapid fluctuation. 
   
 Owing to the small relative weight of steam, water capacity is of 
 greater importance in this respect than steam space. With a gauge 
 pressure of 180 pounds per square inch, 8 cubic feet of steam, which is 
 equivalent to one-half cubic foot of water space, are required to supply 
 one boiler horse power for one minute and if no heat be supplied to the 
 boiler during such an interval, the pressure will drop to 150 pounds per 
 square inch. The volume of steam space, therefore, may be over rated, 
 but if this be too small, the steam passing off will carry water with it 
 in the form of spray. Too great a water space results in slow steaming 
 and waste of fuel in starting up; while too much steam space adds to the 
 radiating surface and increases the losses from that cause. 
   
 That the steam and water space of the Babcock & Wilcox boiler are the 
 result of numerous experiments has previously been pointed out. 
   
 Accessibility--Cleaning. That water-tube boilers are more accessible as 
 a class than are fire-tube boilers has been indicated. All water-tube 
 boilers, however, are not equally accessible. In certain designs, due to 
 the arrangement of baffling used it is practically impossible to remove 
 all deposits of soot and dirt. Frequently, in order to cheapen the 
 product, sufficient cleaning and access doors are not supplied as part 
 of the boiler equipment. The tendency of soot to collect on the crown 
 sheets of certain vertical water-tube boilers has been noted. Such 
 deposits are difficult to remove and if corrosion goes on beneath such a 
 covering the sheet may crack and an explosion result. 
   
 [Illustration: Rear View--Longitudinal Drum Vertical Header Boiler, 
 Showing Access Doors to Rear Headers] 
   
 It is almost impossible to thoroughly clean water legs internally, and 
 in such places also is there a tendency to unsuspected corrosion under 
 deposits that cannot be removed. 
   
 In Babcock & Wilcox boilers every portion of the interior of the heating 
 surfaces can be reached and kept clean, while any soot deposited on the 
 exterior surfaces can be blown off while the boiler is under pressure. 
   
 Inspection--The accessibility which makes possible the thorough cleaning 
 of all portions of the Babcock & Wilcox boiler also provides a means for 
 a thorough inspection. 
   
 Drums are accessible for internal inspection by the removal of the 
 manhole plates. Front headers may be inspected through large doors 
 furnished for the purpose. Rear headers in the inclined header designs 
 may be inspected from the chamber formed by such headers and the rear 
 wall of the boiler. In the vertical header designs rear tube doors are 
 furnished, as has been stated. In certain designs of water-tube boilers 
 in order to assure accessibility for inspection of the rear ends of the 
 tubes, the rear portion of the boiler is exposed to the atmosphere with 
 resulting excessive radiation losses. In other designs the means of 
 access to the rear ends of the tubes are of a makeshift and 
 unworkmanlike character. 
   
 By the removal of handhole plates, all tubes in a Babcock & Wilcox 
 boiler may be inspected for their full length either for the presence of 
 scale or for suspected corrosion. 
   
 Repairs--In Babcock & Wilcox boilers the possession of great strength, 
 the elimination of stresses due to uneven temperatures and of the 
 resulting danger of leaks and corrosion, the protection of the drums 
 from the intense heat of the fire, and the decreased liability of the 
 scale forming matter to lodge on the hottest tube surfaces, all tend to 
 minimize the necessity for repairs. The tubes of the Babcock & Wilcox 
 boiler are practically the only part which may need renewal and these 
 only at infrequent intervals When necessary, such renewals may be made 
 cheaply and quickly. A small stock of tubes, 4 inches in diameter, of 
 sufficient length for the boiler used, is all that need be carried to 
 make renewals. 
   
 Repairs in water-leg boilers are difficult at best and frequently 
 unsatisfactory when completed. When staybolt replacements are necessary, 
 in order to get at the inner sheet of the water leg, several tubes must 
 in some cases be cut out. Not infrequently a replacement of an entire 
 water leg is necessary and this is difficult and requires a lengthy 
 shutdown. With the Babcock & Wilcox boiler, on the other hand, even if 
 it is necessary to replace a section, this may be done in a few hours 
 after the boiler is cool. 
   
 In the case of certain staybolt failures the working pressure of a 
 repaired boiler utilizing such construction will frequently be lowered 
 by the insurance companies when the boiler is again placed in service. 
 The sectional nature of the Babcock & Wilcox boiler enables it to 
 maintain its original working pressure over long periods of time, almost 
 regardless of the nature of any repair that may be required. 
   
 [Illustration: 1456 Horse-power Installation of Babcock & Wilcox Boilers 
 at the Raritan Woolen Mills, Raritan, N. J. The First of These Boilers 
 were Installed in 1878 and 1881 and are still Operated at 80 Pounds 
 Pressure] 
   
 Durability--Babcock & Wilcox boilers are being operated in every-day 
 service with entirely satisfactory results and under the same steam 
 pressure as that for which they were originally sold that have been 
 operated from thirty to thirty-five years. It is interesting to note in 
 considering the life of a boiler that the length of life of a Babcock & 
 Wilcox boiler must be taken as the criterion of what length of life is 
 possible. This is due to the fact that there are Babcock & Wilcox 
 boilers in operation to-day that have been in service from a time that 
 antedates by a considerable margin that at which the manufacturer of any 
 other water-tube boiler now on the market was started. 
   
 Probably the very best evidence of the value of the Babcock & Wilcox 
 boiler as a steam generator and of the reliability of the apparatus, is 
 seen in the sales of the company. Since the company was formed, there 
 have been sold throughout the world over 9,900,000 horse power. 
   
 A feature that cannot be overlooked in the consideration of the 
 advantages of the Babcock & Wilcox boiler is the fact that as a part of 
 the organization back of the boiler, there is a body of engineers of 
 recognized ability, ready at all times to assist its customers in every 
 possible way. 
   
 
 
 
 HEAT AND ITS MEASUREMENT 
 The usual conception of heat is that it is a form of energy produced by 
 the vibratory motion of the minute particles or molecules of a body. All 
 bodies are assumed to be composed of these molecules, which are held 
 together by mutual cohesion and yet are in a state of continual 
 vibration. The hotter a body or the more heat added to it, the more 
 vigorous will be the vibrations of the molecules. 
   
 As is well known, the effect of heat on a body may be to change its 
 temperature, its volume, or its state, that is, from solid to liquid or 
 from liquid to gaseous. Where water is melted from ice and evaporated 
 into steam, the various changes are admirably described in the lecture 
 by Mr. Babcock on "The Theory of Steam Making", given in the next 
 chapter. 
   
 The change in temperature of a body is ordinarily measured by 
 thermometers, though for very high temperatures so-called pyrometers are 
 used. The latter are dealt with under the heading "High Temperature 
 Measurements" at the end of this chapter. 
   
 [Illustration: Fig. 11] 
   
 By reason of the uniform expansion of mercury and its great 
 sensitiveness to heat, it is the fluid most commonly used in the 
 construction of thermometers. In all thermometers the freezing point and 
 the boiling point of water, under mean or average atmospheric pressure 
 at sea level, are assumed as two fixed points, but the division of the 
 scale between these two points varies in different countries. The 
 freezing point is determined by the use of melting ice and for this 
 reason is often called the melting point. There are in use three 
 thermometer scales known as the Fahrenheit, the Centigrade or Celsius, 
 and the Réaumur. As shown in Fig. 11, in the Fahrenheit scale, the space 
 between the two fixed points is divided into 180 parts; the boiling 
 point is marked 212, and the freezing point is marked 32, and zero is a 
 temperature which, at the time this thermometer was invented, was 
 incorrectly imagined to be the lowest temperature attainable. In the 
 centigrade and the Réaumur scales, the distance between the two fixed 
 points is divided into 100 and 80 parts, respectively. In each of these 
 two scales the freezing point is marked zero, and the boiling point is 
 marked 100 in the centigrade and 80 in the Réaumur. Each of the 180, 100 
 or 80 divisions in the respective thermometers is called a degree. 
   
 Table 3 and appended formulae are useful for converting from one scale 
 to another. 
   
 In the United States the bulbs of high-grade thermometers are usually 
 made of either Jena 58^{III} borosilicate thermometer glass or Jena 
 16^{III} glass, the stems being made of ordinary glass. The Jena 
 16^{III} glass is not suitable for use at temperatures much above 850 
 degrees Fahrenheit and the harder Jena 59^{III} should be used in 
 thermometers for temperatures higher than this. 
   
 Below the boiling point, the hydrogen-gas thermometer is the almost 
 universal standard with which mercurial thermometers may be compared, 
 while above this point the nitrogen-gas thermometer is used. In both of 
 these standards the change in temperature is measured by the change in 
 pressure of a constant volume of the gas. 
   
 In graduating a mercurial thermometer for the Fahrenheit scale, 
 ordinarily a degree is represented as 1/180 part of the volume of the 
 stem between the readings at the melting point of ice and the boiling 
 point of water. For temperatures above the latter, the scale is extended 
 in degrees of the same volume. For very accurate work, however, the 
 thermometer may be graduated to read true-gas-scale temperatures by 
 comparing it with the gas thermometer and marking the temperatures at 25 
 or 50 degree intervals. Each degree is then 1/25 or 1/50 of the volume 
 of the stem in each interval. 
   
 Every thermometer, especially if intended for use above the boiling 
 point, should be suitably annealed before it is used. If this is not 
 done, the true melting point and also the "fundamental interval", that 
 is, the interval between the melting and the boiling points, may change 
 considerably. After continued use at the higher temperatures also, the 
 melting point will change, so that the thermometer must be calibrated 
 occasionally to insure accurate readings. 
   
                      TABLE 3 
   
          COMPARISON OF THERMOMETER SCALES 
   
 +---------------+----------+----------+----------+ 
 |               |Fahrenheit|Centigrade| Réaumur | 
 +---------------+----------+----------+----------+ 
 |Absolute Zero | -459.64 | -273.13 | -218.50 | 
 |               |   0     | -17.78 | -14.22 | 
 |               |   10     | -12.22 |   -9.78 | 
 |               |   20     |   -6.67 |   -5.33 | 
 |               |   30     |   -1.11 |   -0.89 | 
 |Freezing Point |   32     |   0     |   0     | 
 |Maximum Density|         |         |         | 
 | of Water     |   39.1   |   3.94 |   3.15 | 
 |               |   50     |   10     |   8     | 
 |               |   75     |   23.89 |   19.11 | 
 |               | 100     |   37.78 |   30.22 | 
 |               | 200     |   93.33 |   74.67 | 
 |Boiling Point | 212     | 100     |   80     | 
 |               | 250     | 121.11 |   96.89 | 
 |               | 300     | 148.89 | 119.11 | 
 |               | 350     | 176.67 | 141.33 | 
 +---------------+----------+----------+----------+ 
   
 F = 9/5C+32° = 9/4R+32° 
   
 C = 5/9(F-32°) = 5/4R 
   
 R = 4/9(F-32°) = 4/5C 
   
 As a general rule thermometers are graduated to read correctly for total 
 immersion, that is, with bulb and stem of the thermometer at the same 
 temperature, and they should be used in this way when compared with a 
 standard thermometer. If the stem emerges into space either hotter or 
 colder than that in which the bulb is placed, a "stem correction" must 
 be applied to the observed temperature in addition to any correction 
 that may be found in the comparison with the standard. For instance, for 
 a particular thermometer, comparison with the standard with both fully 
 immersed made necessary the following corrections: 
   
 _Temperature_ _Correction_ 
      40°F         0.0 
    100           0.0 
    200           0.0 
    300           +2.5 
    400           -0.5 
    500           -2.5 
   
 When the sign of the correction is positive (+) it must be added to the 
 observed reading, and when the sign is a negative (-) the correction 
 must be subtracted. The formula for the stem correction is as follows: 
   
 Stem correction = 0.000085 × n (T-t) 
   
 in which T is the observed temperature, t is the mean temperature of the 
 emergent column, n is the number of degrees of mercury column emergent, 
 and 0.000085 is the difference between the coefficient of expansion of 
 the mercury and that in the glass in the stem. 
   
 Suppose the observed temperature is 400 degrees and the thermometer is 
 immersed to the 200 degrees mark, so that 200 degrees of the mercury 
 column project into the air. The mean temperature of the emergent column 
 may be found by tying another thermometer on the stem with the bulb at 
 the middle of the emergent mercury column as in Fig. 12. Suppose this 
 mean temperature is 85 degrees, then 
   
 Stem correction = 0.000085 × 200 × (400 - 85) = 5.3 degrees. 
   
 As the stem is at a lower temperature than the bulb, the thermometer 
 will evidently read too low, so that this correction must be added to 
 the observed reading to find the reading corresponding to total 
 immersion. The corrected reading will therefore be 405.3 degrees. If 
 this thermometer is to be corrected in accordance with the calibrated 
 corrections given above, we note that a further correction of 0.5 must 
 be applied to the observed reading at this temperature, so that the 
 correct temperature is 405.3 - 0.5 = 404.8 degrees or 405 degrees. 
   
 [Illustration: Fig. 12] 
   
 [Illustration: Fig. 13] 
   
 Fig. 12 shows how a stem correction can be obtained for the case just 
 described. 
   
 Fig. 13 affords an opportunity for comparing the scale of a thermometer 
 correct for total immersion with one which will read correctly when 
 submerged to the 300 degrees mark, the stem being exposed at a mean 
 temperature of 110 degrees Fahrenheit, a temperature often prevailing 
 when thermometers are used for measuring temperatures in steam mains. 
   
 Absolute Zero--Experiments show that at 32 degrees Fahrenheit a perfect 
 gas expands 1/491.64 part of its volume if its pressure remains constant 
 and its temperature is increased one degree. Thus if gas at 32 degrees 
 Fahrenheit occupies 100 cubic feet and its temperature is increased one 
 degree, its volume will be increased to 100 + 100/491.64 = 100.203 cubic 
 feet. For a rise of two degrees the volume would be 100 + (100 × 2) / 
 491.64 = 100.406 cubic feet. If this rate of expansion per one degree 
 held good at all temperatures, and experiment shows that it does above 
 the freezing point, the gas, if its pressure remained the same, would 
 double its volume, if raised to a temperature of 32 + 491.64 = 523.64 
 degrees Fahrenheit, while under a diminution of temperature it would 
 shrink and finally disappear at a temperature of 491.64 - 32 = 459.64 
 degrees below zero Fahrenheit. While undoubtedly some change in the law 
 would take place before the lower temperature could be reached, there is 
 no reason why the law may not be used within the range of temperature 
 where it is known to hold good. From this explanation it is evident that 
 under a constant pressure the volume of a gas will vary as the number of 
 degrees between its temperature and the temperature of -459.64 degrees 
 Fahrenheit. To simplify the application of the law, a new thermometric 
 scale is constructed as follows: the point corresponding to -460 degrees 
 Fahrenheit, is taken as the zero point on the new scale, and the degrees 
 are identical in magnitude with those on the Fahrenheit scale. 
 Temperatures referred to this new scale are called absolute temperatures 
 and the point -460 degrees Fahrenheit (= -273 degrees centigrade) is 
 called the absolute zero. To convert any temperature Fahrenheit to 
 absolute temperature, add 460 degrees to the temperature on the 
 Fahrenheit scale: thus 54 degrees Fahrenheit will be 54 + 460 = 514 
 degrees absolute temperature; 113 degrees Fahrenheit will likewise be 
 equal to 113 + 460 = 573 degrees absolute temperature. If one pound of 
 gas is at a temperature of 54 degrees Fahrenheit and another pound is at 
 a temperature of 114 degrees Fahrenheit the respective volumes at a 
 given pressure would be in the ratio of 514 to 573. 
   
 [Illustration: Ninety-sixth Street Station of the New York Railways Co., 
 New York City, Operating 20,000 Horse Power of Babcock & Wilcox Boilers. 
 This Company and its Allied Companies Operate a Total of 100,000 Horse 
 Power of Babcock & Wilcox Boilers] 
   
 British Thermal Unit--The quantitative measure of heat is the British 
 thermal unit, ordinarily written B. t. u. This is the quantity of heat 
 required to raise the temperature of one pound of pure water one degree 
 at 62 degrees Fahrenheit; that is, from 62 degrees to 63 degrees. In the 
 metric system this unit is the _calorie_ and is the heat necessary 
 to raise the temperature of one kilogram of pure water from 15 degrees 
 to 16 degrees centigrade. These two definitions lead to a discrepancy of 
 0.03 of 1 per cent, which is insignificant for engineering purposes, and 
 in the following the B. t. u. is taken with this discrepancy ignored. 
 The discrepancy is due to the fact that there is a slight difference in 
 the specific heat of water at 15 degrees centigrade and 62 degrees 
 Fahrenheit. The two units may be compared thus: 
   
 1 Calorie = 3.968 B. t. u.       1 B. t. u. = 0.252 Calories. 
   
 _Unit_       _Water_     _Temperature Rise_ 
 1 B. t. u.   1 Pound     1 Degree Fahrenheit 
 1 Calorie   1 Kilogram   1 Degree centigrade 
   
 But 1 kilogram = 2.2046 pounds and 1 degree centigrade = 9/5 degree 
 Fahrenheit. 
   
 Hence 1 calorie = (2.2046 × 9/5) = 3.968 B. t. u. 
   
   
 The heat values in B. t. u. are ordinarily given per pound, and the heat 
 values in calories per kilogram, in which case the B. t. u. per pound 
 are approximately equivalent to 9/5 the calories per kilogram. 
   
 As determined by Joule, heat energy has a certain definite relation to 
 work, one British thermal unit being equivalent from his determinations 
 to 772 foot pounds. Rowland, a later investigator, found that 778 foot 
 pounds were a more exact equivalent. Still later investigations indicate 
 that the correct value for a B. t. u. is 777.52 foot pounds or 
 approximately 778. The relation of heat energy to work as determined is 
 a demonstration of the first law of thermo-dynamics, namely, that heat 
 and mechanical energy are mutually convertible in the ratio of 778 foot 
 pounds for one British thermal unit. This law, algebraically expressed, 
 is W = JH; W being the work done in foot pounds, H being the heat in 
 t. u., and J being Joules equivalent. Thus 1000 B. t. u.'s would be 
 
 capable of doing 1000 × 778 = 778000 foot pounds of work. 
   
 Specific Heat--The specific heat of a substance is the quantity of heat 
 expressed in thermal units required to raise or lower the temperature of 
 a unit weight of any substance at a given temperature one degree. This 
 quantity will vary for different substances For example, it requires 
 about 16 B. t. u. to raise the temperature of one pound of ice 32 
 degrees or 0.5 B. t. u. to raise it one degree, while it requires 
 approximately 180 B. t. u. to raise the temperature of one pound of 
 water 180 degrees or one B. t. u. for one degree. 
   
 If then, a pound of water be considered as a standard, the ratio of the 
 amount of heat required to raise a similar unit of any other substance 
 one degree, to the amount required to raise a pound of water one degree 
 is known as the specific heat of that substance. Thus since one pound of 
 water required one B. t. u. to raise its temperature one degree, and one 
 pound of ice requires about 0.5 degrees to raise its temperature one 
 degree, the ratio is 0.5 which is the specific heat of ice. To be exact, 
 the specific heat of ice is 0.504, hence 32 degrees × 0.504 = 16.128 
 t. u. would be required to raise the temperature of one pound of ice 
 
 from 0 to 32 degrees. For solids, at ordinary temperatures, the specific 
 heat may be considered a constant for each individual substance, 
 although it is variable for high temperatures. In the case of gases a 
 distinction must be made between specific heat at constant volume, and 
 at constant pressure. 
   
 Where specific heat is stated alone, specific heat at ordinary 
 temperature is implied, and _mean_ specific heat refers to the average 
 value of this quantity between the temperatures named. 
   
 The specific heat of a mixture of gases is obtained by multiplying the 
 specific heat of each constituent gas by the percentage by weight of 
 that gas in the mixture, and dividing the sum of the products by 100. 
 The specific heat of a gas whose composition by weight is CO_{2}, 13 per 
 cent; CO, 0.4 per cent; O, 8 per cent; N, 78.6 per cent, is found as 
 follows: 
   
 CO_{2} :   13 × 0.217 = 2.821 
 CO     : 0.4 × 0.2479 = 0.09916 
 O     :   8 × 0.2175 = 1.74000 
 N     : 78.6 × 0.2438 = 19.16268 
                          -------- 
        100.0           23.82284 
   
 and 23.8228 ÷ 100 = 0.238 = specific heat of the gas. 
   
   
 The specific heats of various solids, liquids and gases are given in 
 Table 4. 
   
 Sensible Heat--The heat utilized in raising the temperature of a body, 
 as that in raising the temperature of water from 32 degrees up to the 
 boiling point, is termed sensible heat. In the case of water, the 
 sensible heat required to raise its temperature from the freezing point 
 to the boiling point corresponding to the pressure under which 
 ebullition occurs, is termed the heat of the liquid. 
   
 Latent Heat--Latent heat is the heat which apparently disappears in 
 producing some change in the condition of a body without increasing its 
 temperature If heat be added to ice at freezing temperature, the ice 
 will melt but its temperature will not be raised. The heat so utilized 
 in changing the condition of the ice is the latent heat and in this 
 particular case is known as the latent heat of fusion. If heat be added 
 to water at 212 degrees under atmospheric pressure, the water will not 
 become hotter but will be evaporated into steam, the temperature of 
 which will also be 212 degrees. The heat so utilized is called the 
 latent heat of evaporation and is the heat which apparently disappears 
 in causing the substance to pass from a liquid to a gaseous state. 
   
                               TABLE 4 
   
                  SPECIFIC HEATS OF VARIOUS SUBSTANCES 
 +--------------------------------------------------------------------+ 
 |                               SOLIDS                               | 
 +-------------------------------+----------------+-------------------+ 
 |                               | Temperature[2]|                   | 
 |                               |   Degrees     |     Specific     | 
 |                               |   Fahrenheit   |       Heat       | 
 +-------------------------------+----------------+-------------------+ 
 | Copper                       |     59-460     |       .0951       | 
 | Gold                         |     32-212     |       .0316       | 
 | Wrought Iron                 |     59-212    |       .1152       | 
 | Cast Iron                     |     68-212     |       .1189       | 
 | Steel (soft)                 |     68-208     |       .1175       | 
 | Steel (hard)                 |     68-208     |       .1165       | 
 | Zinc                        |     32-212     |       .0935       | 
 | Brass (yellow)               |     32         |       .0883       | 
 | Glass (normal ther. 16^{III}) |     66-212     |       .1988       | 
 | Lead                         |     59         |       .0299       | 
 | Platinum                     |     32-212     |       .0323       | 
 | Silver                       |     32-212     |       .0559       | 
 | Tin                           |   -105-64     |       .0518       | 
 | Ice                           |               |       .5040       | 
 | Sulphur (newly fused)         |               |       .2025       | 
 +-------------------------------+----------------+-------------------+ 
 |                               LIQUIDS                             | 
 +-------------------------------+----------------+-------------------+ 
 |                               | Temperature[2]|                   | 
 |                               |   Degrees     |   Specific       | 
 |                               |   Fahrenheit |     Heat         | 
 +-------------------------------+----------------+-------------------+ 
 | Water[3]                     |     59         |     1.0000       | 
 | Alcohol                       |     32         |       .5475       | 
 |                              |   176         |       .7694       | 
 | Mercury                       |     32         |       .03346     | 
 | Benzol                       |     50         |       .4066       | 
 |                               |   122         |       .4502      | 
 | Glycerine                     |     59-102     |       .576       | 
 | Lead (Melted)                 | to 360         |       .0410       | 
 | Sulphur (melted)             |   246-297     |       .2350       | 
 | Tin (melted)                 |              |       .0637       | 
 | Sea Water (sp. gr. 1.0043)   |     64         |       .980       | 
 | Sea Water (sp. gr. 1.0463)   |     64         |       .903       | 
 | Oil of Turpentine             |     32         |       .411       | 
 | Petroleum                     |     64-210     |       .498       | 
 | Sulphuric Acid               |     68-133     |       .3363       | 
 +-------------------------------+----------------+-------------------+ 
 |                               GASES                              | 
 +--------------------------+---------------+--------------+----------+ 
 |                         |               |   Specific   | Specific | 
 |                         | Temperature[2]|   Heat at   | Heat at | 
 |                          |   Degrees     |   Constant   | Constant | 
 |                         | Fahrenheit   |   Pressure   | Volume | 
 +--------------------------+---------------+--------------+----------+ 
 | Air                     |   32-392     |     .2375   |   .1693 | 
 | Oxygen                   |   44-405     |     .2175   |   .1553 | 
 | Nitrogen                 |   32-392     |     .2438   |   .1729 | 
 | Hydrogen                 |   54-388     |   3.4090   | 2.4141 | 
 | Superheated Steam       |              | See table 25 |         | 
 | Carbon Monoxide         |   41-208     |     .2425   |   .1728 | 
 | Carbon Dioxide           |   52-417     |     .2169   |   .1535 | 
 | Methane                 |   64-406     |     .5929   |   .4505 | 
 | Blast Fur. Gas (approx.) |     ...       |     .2277   |   ...   | 
 | Flue gas (approx.)       |     ...       |     .2400   |   ...   | 
 +--------------------------+---------------+--------------+----------+ 
   
 Latent heat is not lost, but reappears whenever the substances pass 
 through a reverse cycle, from a gaseous to a liquid, or from a liquid to 
 a solid state. It may, therefore, be defined as stated, as the heat 
 which apparently disappears, or is lost to thermometric measurement, 
 when the molecular constitution of a body is being changed. Latent heat 
 is expended in performing the work of overcoming the molecular cohesion 
 of the particles of the substance and in overcoming the resistance of 
 external pressure to change of volume of the heated body. Latent heat of 
 evaporation, therefore, may be said to consist of internal and external 
 heat, the former being utilized in overcoming the molecular resistance 
 of the water in changing to steam, while the latter is expended in 
 overcoming any resistance to the increase of its volume during 
 formation. In evaporating a pound of water at 212 degrees to steam at 
 212 degrees, 897.6 B. t. u. are expended as internal latent heat and 
 72.8 B. t. u. as external latent heat. For a more detailed description 
 of the changes brought about in water by sensible and latent heat, the 
 reader is again referred to the chapter on "The Theory of Steam Making". 
   
 Ebullition--The temperature of ebullition of any liquid, or its boiling 
 point, may be defined as the temperature which exists where the addition 
 of heat to the liquid no longer increases its temperature, the heat 
 added being absorbed or utilized in converting the liquid into vapor. 
 This temperature is dependent upon the pressure under which the liquid 
 is evaporated, being higher as the pressure is greater. 
   
                TABLE 5 
   
 BOILING POINTS AT ATMOSPHERIC PRESSURE 
   
 +---------------------+--------------+ 
 |                     |   Degrees   | 
 |                     | Fahrenheit | 
 +---------------------+--------------+ 
 | Ammonia            |     140     | 
 | Bromine           |     145     | 
 | Alcohol           |     173     | 
 | Benzine           |     212     | 
 | Water             |     212     | 
 | Average Sea Water |     213.2   | 
 | Saturated Brine   |     226     | 
 | Mercury           |     680     | 
 +---------------------+--------------+ 
   
 Total Heat of Evaporation--The quantity of heat required to raise a unit 
 of any liquid from the freezing point to any given temperature, and to 
 entirely evaporate it at that temperature, is the total heat of 
 evaporation of the liquid for that temperature. It is the sum of the 
 heat of the liquid and the latent heat of evaporation. 
   
 To recapitulate, the heat added to a body is divided as follows: 
   
 Total heat = Heat to change the temperature + heat to overcome the 
              molecular cohesion + heat to overcome the external pressure 
              resisting an increase of volume of the body. 
   
 Where water is converted into steam, this total heat is divided as 
 follows: 
   
 Total heat = Heat to change the temperature of the water + heat to 
              separate the molecules of the water + heat to overcome 
              resistance to increase in volume of the steam, 
            = Heat of the liquid + internal latent heat + external 
             latent heat, 
            = Heat of the liquid + total latent heat of steam, 
            = Total heat of evaporation. 
   
 The steam tables given on pages 122 to 127 give the heat of the liquid 
 and the total latent heat through a wide range of temperatures. 
   
 Gases--When heat is added to gases there is no internal work done; hence 
 the total heat is that required to change the temperature plus that 
 required to do the external work. If the gas is not allowed to expand 
 but is preserved at constant volume, the entire heat added is that 
 required to change the temperature only. 
   
 Linear Expansion of Substances by Heat--To find the increase in the 
 length of a bar of any material due to an increase of temperature, 
 multiply the number of degrees of increase in temperature by the 
 coefficient of expansion for one degree and by the length of the bar. 
 Where the coefficient of expansion is given for 100 degrees, as in Table 
 6, the result should be divided by 100. The expansion of metals per one 
 degree rise of temperature increases slightly as high temperatures are 
 reached, but for all practical purposes it may be assumed to be constant 
 for a given metal. 
   
                                TABLE 6 
   
          LINEAL EXPANSION OF SOLIDS AT ORDINARY TEMPERATURES 
   
 (Tabular values represent increase per foot per 100 degrees increase 
              in temperature, Fahrenheit or centigrade) 
   
 +-------------------+--------------+----------------+----------------+ 
 |                   | Temperature |               |               | 
 |                  | Conditions[4]|Coefficient per |Coefficient per | 
 |   Substance       | Degrees     | 100 Degrees   | 100 Degrees   | 
 |                   | Fahrenheit   | Fahrenheit     | Centigrade     | 
 +-------------------+--------------+----------------+----------------+ 
 |Brass (cast)       | 32 to 212   |   .001042     |   .001875     | 
 |Brass (wire)       | 32 to 212   |   .001072     |   .001930     | 
 |Copper             | 32 to 212   |   .000926     |   .001666     | 
 |Glass (English     |            |               |               | 
 |flint)             | 32 to 212   |   .000451     |   .000812     | 
 |Glass (French     |             |               |               | 
 |flint)             | 32 to 212   |   .000484     |   .000872     | 
 |Gold               | 32 to 212   |   .000816     |   .001470     | 
 |Granite (average) | 32 to 212   |   .000482     |   .000868     | 
 |Iron (cast)       |     104     |   .000589     |   .001061     | 
 |Iron (soft forged) | 0 to 212   |   .000634     |   .001141     | 
 |Iron (wire)       | 32 to 212   |   .000800     |   .001440     | 
 |Lead               | 32 to 212   |   .001505     |   .002709     | 
 |Mercury           | 32 to 212   |   .009984[5] |   .017971     | 
 |Platinum          |     104     |   .000499     |   .000899     | 
 |Limestone         | 32 to 212   |   .000139     |   .000251     | 
 |Silver             |     104     |   .001067     |   .001921     | 
 |Steel (Bessemer   |             |               |              | 
 |rolled, hard)     | 0 to 212   |   .00056     |   .00101     | 
 |Steel (Bessemer   |             |               |               | 
 |rolled, soft)     | 0 to 212   |   .00063     |   .00117     | 
 |Steel (cast,       |            |               |               | 
 |French)           |     104     |   .000734     |   .001322     | 
 |Steel (cast       |             |               |               | 
 |annealed, English) |     104     |   .000608     |   .001095     | 
 +-------------------+--------------+----------------+----------------+ 
   
 High Temperature Measurements--The temperatures to be dealt with in 
 steam-boiler practice range from those of ordinary air and steam to the 
 temperatures of burning fuel. The gases of combustion, originally at the 
 temperature of the furnace, cool as they pass through each successive 
 bank of tubes in the boiler, to nearly the temperature of the steam, 
 resulting in a wide range of temperatures through which definite 
 measurements are sometimes required. 
   
 Of the different methods devised for ascertaining these temperatures, 
 some of the most important are as follows: 
   
    1st. Mercurial pyrometers for temperatures up to 1000 degrees 
    Fahrenheit. 
   
    2nd. Expansion pyrometers for temperatures up to 1500 degrees 
    Fahrenheit. 
   
    3rd. Calorimetry for temperatures up to 2000 degrees Fahrenheit. 
   
    4th. Thermo-electric pyrometers for temperatures up to 2900 
    degrees Fahrenheit. 
   
    5th. Melting points of metal which flow at various temperatures 
    up to the melting point of platinum 3227 degrees Fahrenheit. 
   
    6th. Radiation pyrometers for temperatures up to 3600 degrees 
    Fahrenheit. 
   
    7th. Optical pyrometers capable of measuring temperatures up to 
    12,600 degrees Fahrenheit.[6] For ordinary boiler practice 
    however, their range is 1600 to 3600 degrees Fahrenheit. 
   
 [Illustration: 228 Horse-power Babcock & Wilcox Boiler, Installed at the 
 Wentworth Institute, Boston, Mass.] 
   
 Table 7 gives the degree of accuracy of high temperature measurements. 
   
                      TABLE 7 
   
    ACCURACY OF HIGH TEMPERATURE MEASUREMENTS[7] 
   
 +------------------------+------------------------+ 
 |       Centigrade       |       Fahrenheit       | 
 +-------------+----------+-------------+----------+ 
 |             | Accuracy |             | Accuracy | 
 | Temperature | Plus or | Temperature | Plus or | 
 |   Range     | Minus   |   Range     | Minus   | 
 |             | Degrees |             | Degrees | 
 +-------------+----------+-------------+----------+ 
 |   200- 500 |   0.5   |   392- 932 |   0.9   | 
 |   500- 800 |   2     |   932-1472 |   3.6   | 
 |   800-1100 |   3     | 1472-2012 |   5.4   | 
 | 1100-1600 |   15     | 2012-2912 |   27     | 
 | 1600-2000 |   25     | 2912-3632 |   45     | 
 +-------------+----------+-------------+----------+ 
   
   
 Mercurial Pyrometers--At atmospheric pressure mercury boils at 676 
 degrees Fahrenheit and even at lower temperatures the mercury in 
 thermometers will be distilled and will collect in the upper part of the 
 stem. Therefore, for temperatures much above 400 degrees Fahrenheit, 
 some inert gas, such as nitrogen or carbon dioxide, must be forced under 
 pressure into the upper part of the thermometer stem. The pressure at 
 600 degrees Fahrenheit is about 15 pounds, or slightly above that of the 
 atmosphere, at 850 degrees about 70 pounds, and at 1000 degrees about 
 300 pounds. 
   
 Flue-gas temperatures are nearly always taken with mercurial 
 thermometers as they are the most accurate and are easy to read and 
 manipulate. Care must be taken that the bulb of the instrument projects 
 into the path of the moving gases in order that the temperature may 
 truly represent the flue gas temperature. No readings should be 
 considered until the thermometer has been in place long enough to heat 
 it up to the full temperature of the gases. 
   
   
 Expansion Pyrometers--Brass expands about 50 per cent more than iron and 
 in both brass and iron the expansion is nearly proportional to the 
 increase in temperature. This phenomenon is utilized in expansion 
 pyrometers by enclosing a brass rod in an iron pipe, one end of the rod 
 being rigidly attached to a cap at the end of the pipe, while the other 
 is connected by a multiplying gear to a pointer moving around a 
 graduated dial. The whole length of the expansion piece must be at a 
 uniform temperature before a correct reading can be obtained. This fact, 
 together with the lost motion which is likely to exist in the mechanism 
 connected to the pointer, makes the expansion pyrometer unreliable; it 
 should be used only when its limitations are thoroughly understood and 
 it should be carefully calibrated. Unless the brass and iron are known 
 to be of the same temperature, its action will be anomalous: for 
 instance, if it be allowed to cool after being exposed to a high 
 temperature, the needle will rise before it begins to fall. Similarly, a 
 rise in temperature is first shown by the instrument as a fall. The 
 explanation is that the iron, being on the outside, heats or cools more 
 quickly than the brass. 
   
   
 Calorimetry--This method derives its name from the fact that the process 
 is the same as the determination of the specific heat of a substance by 
 the water calorimeter, except that in one case the temperature is known 
 and the specific heat is required, while in the other the specific heat 
 is known and the temperature is required. The temperature is found as 
 follows: 
   
 A given weight of some substance such as iron, nickel or fire brick, is 
 heated to the unknown temperature and then plunged into water and the 
 rise in temperature noted. 
   
 If X = temperature to be measured, w = weight of heated body in pounds, 
 W = weight of water in pounds, T = final temperature of water, t = 
 difference between initial and final temperatures of water, s = known 
 specific heat of body. Then X = T + Wt ÷ ws 
   
 Any temperatures secured by this method are affected by so many sources 
 of error that the results are very approximate. 
   
 Thermo-electric Pyrometers--When wires of two different metals are 
 joined at one end and heated, an electromotive force will be set up 
 between the free ends of the wires. Its amount will depend upon the 
 composition of the wires and the difference in temperature between the 
 two. If a delicate galvanometer of high resistance be connected to the 
 "thermal couple", as it is called, the deflection of the needle, after a 
 careful calibration, will indicate the temperature very accurately. 
   
 In the thermo-electric pyrometer of Le Chatelier, the wires used are 
 platinum and a 10 per cent alloy of platinum and rhodium, enclosed in 
 porcelain tubes to protect them from the oxidizing influence of the 
 furnace gases. The couple with its protecting tubes is called an 
 "element". The elements are made in different lengths to suit 
 conditions. 
   
 It is not necessary for accuracy to expose the whole length of the 
 element to the temperature to be measured, as the electromotive force 
 depends only upon the temperature of the juncture at the closed end of 
 the protecting tube and that of the cold end of the element. The 
 galvanometer can be located at any convenient point, since the length of 
 the wires leading to it simply alter the resistance of the circuit, for 
 which allowance may be made. 
   
 The advantages of the thermo-electric pyrometer are accuracy over a wide 
 range of temperatures, continuity of readings, and the ease with which 
 observations can be taken. Its disadvantages are high first cost and, in 
 some cases, extreme delicacy. 
   
 Melting Points of Metals--The approximate temperature of a furnace or 
 flue may be determined, if so desired, by introducing certain metals of 
 which the melting points are known. The more common metals form a series 
 in which the respective melting points differ by 100 to 200 degrees 
 Fahrenheit, and by using these in order, the temperature can be fixed 
 between the melting points of some two of them. This method lacks 
 accuracy, but it suffices for determinations where approximate readings 
 are satisfactory. 
   
 The approximate melting points of certain metals that may be used for 
 determinations of this nature are given in Table 8. 
   
 Radiation Pyrometers--These are similar to thermo-electric pyrometers in 
 that a thermo-couple is employed. The heat rays given out by the hot 
 body fall on a concave mirror and are brought to a focus at a point at 
 which is placed the junction of a thermo-couple. The temperature 
 readings are obtained from an indicator similar to that used with 
 thermo-electric pyrometers. 
   
 Optical Pyrometers--Of the optical pyrometers the Wanner is perhaps the 
 most reliable. The principle on which this instrument is constructed is 
 that of comparing the quantity of light emanating from the heated body 
 with a constant source of light, in this case a two-volt osmium lamp. 
 The lamp is placed at one end of an optical tube, while at the other an 
 eyepiece is provided and a scale. A battery of cells furnishes the 
 current for the lamp. On looking through the pyrometer, a circle of red 
 light appears, divided into distinct halves of different intensities. 
 Adjustment may be made so that the two halves appear alike and a reading 
 is then taken from the scale. The temperatures are obtained from a table 
 of temperatures corresponding to scale readings. For standardizing the 
 osmium lamp, an amylacetate lamp, is provided with a stand for holding 
 the optical tube. 
   
                TABLE 8 
   
 APPROXIMATE MELTING POINTS OF METALS[8] 
   
 +-----------------+------------------+ 
 |   Metal       |   Temperature   | 
 |                 |Degrees Fahrenheit| 
 +-----------------+------------------+ 
 |Wrought Iron     |       2737       | 
 |Pig Iron (gray) |     2190-2327   | 
 |Cast Iron (white)|       2075       | 
 |Steel           |     2460-2550   | 
 |Steel (cast)     |       2500       | 
 |Copper           |       1981       | 
 |Zinc             |       786       | 
 |Antimony         |       1166       | 
 |Lead            |       621       | 
 |Bismuth         |       498       | 
 |Tin             |       449       | 
 |Platinum         |       3191       | 
 |Gold             |       1946       | 
 |Silver           |       1762       | 
 |Aluminum         |       1216       | 
 +-----------------+------------------+ 
   
   
 Determination of Temperature from Character of Emitted Light--As a 
 further means of determining approximately the temperature of a furnace, 
 Table 9, compiled by Messrs. White & Taylor, may be of service. The 
 color at a given temperature is approximately the same for all kinds of 
 combustibles under similar conditions. 
   
                        TABLE 9 
   
    CHARACTER OF EMITTED LIGHT AND CORRESPONDING 
              APPROXIMATE TEMPERATURE[9] 
   
 +--------------------------------------+-----------+ 
 |     Character of Emitted Light     |Temperature| 
 |                                     | Degrees | 
 |                                     | Fahrenheit| 
 +--------------------------------------+-----------+ 
 |Dark red, blood red, low red         |   1050   | 
 |Dark cherry red                       |   1175   | 
 |Cherry, full red                     |   1375   | 
 |Light cherry, bright cherry, light red|   1550   | 
 |Orange                               |   1650   | 
 |Light orange                         |   1725   | 
 |Yellow                               |   1825   | 
 |Light yellow                         |   1975   | 
 |White                                 |   2200   | 
 +--------------------------------------+-----------+ 
   
 
 
 
 THE THEORY OF STEAM MAKING 
 [Extracts from a Lecture delivered by George H. Babcock, at Cornell 
 University, 1887[10]] 
   
   
 The chemical compound known as H_{2}O exists in three states or 
 conditions--ice, water and steam; the only difference between these 
 states or conditions is in the presence or absence of a quantity of 
 energy exhibited partly in the form of heat and partly in molecular 
 activity, which, for want of a better name, we are accustomed to call 
 "latent heat"; and to transform it from one state to another we have 
 only to supply or extract heat. For instance, if we take a quantity of 
 ice, say one pound, at absolute zero[11] and supply heat, the first 
 effect is to raise its temperature until it arrives at a point 492 
 Fahrenheit degrees above the starting point. Here it stops growing 
 warmer, though we keep on adding heat. It, however, changes from ice to 
 water, and when we have added sufficient heat to have made it, had it 
 remained ice, 283 degrees hotter or a temperature of 315 degrees 
 Fahrenheit's thermometer, it has all become water, at the same 
 temperature at which it commenced to change, namely, 492 degrees above 
 absolute zero, or 32 degrees by Fahrenheit's scale. Let us still 
 continue to add heat, and it will now grow warmer again, though at a 
 slower rate--that is, it now takes about double the quantity of heat to 
 raise the pound one degree that it did before--until it reaches a 
 temperature of 212 degrees Fahrenheit, or 672 degrees absolute (assuming 
 that we are at the level of the sea). Here we find another critical 
 point. However much more heat we may apply, the water, as water, at that 
 pressure, cannot be heated any hotter, but changes on the addition of 
 heat to steam; and it is not until we have added heat enough to have 
 raised the temperature of the water 966 degrees, or to 1,178 degrees by 
 Fahrenheit's thermometer (presuming for the moment that its specific 
 heat has not changed since it became water), that it has all become 
 steam, which steam, nevertheless, is at the temperature of 212 degrees, 
 at which the water began to change. Thus over four-fifths of the heat 
 which has been added to the water has disappeared, or become insensible 
 in the steam to any of our instruments. 
   
 It follows that if we could reduce steam at atmospheric pressure to 
 water, without loss of heat, the heat stored within it would cause the 
 water to be red hot; and if we could further change it to a solid, like 
 ice, without loss of heat, the solid would be white hot, or hotter than 
 melted steel--it being assumed, of course, that the specific heat of the 
 water and ice remain normal, or the same as they respectively are at the 
 freezing point. 
   
 After steam has been formed, a further addition of heat increases the 
 temperature again at a much faster ratio to the quantity of heat added, 
 which ratio also varies according as we maintain a constant pressure or 
 a constant volume; and I am not aware that any other critical point 
 exists where this will cease to be the fact until we arrive at that very 
 high temperature, known as the point of dissociation, at which it 
 becomes resolved into its original gases. 
   
 The heat which has been absorbed by one pound of water to convert it 
 into a pound of steam at atmospheric pressure is sufficient to have 
 melted 3 pounds of steel or 13 pounds of gold. This has been transformed 
 into something besides heat; stored up to reappear as heat when the 
 process is reversed. That condition is what we are pleased to call 
 latent heat, and in it resides mainly the ability of the steam to do 
 work. 
   
 [Graph: Temperature in Fahrenheit Degrees (from Absolute Zero) 
 against Quantity of Heat in British Thermal Units] 
   
 The diagram shows graphically the relation of heat to temperature, the 
 horizontal scale being quantity of heat in British thermal units, and 
 the vertical temperature in Fahrenheit degrees, both reckoned from 
 absolute zero and by the usual scale. The dotted lines for ice and water 
 show the temperature which would have been obtained if the conditions 
 had not changed. The lines marked "gold" and "steel" show the relation 
 to heat and temperature and the melting points of these metals. All the 
 inclined lines would be slightly curved if attention had been paid to 
 the changing specific heat, but the curvature would be small. It is 
 worth noting that, with one or two exceptions, the curves of all 
 substances lie between the vertical and that for water. That is to say, 
 that water has a greater capacity for heat than all other substances 
 except two, hydrogen and bromine. 
   
 In order to generate steam, then, only two steps are required: 1st, 
 procure the heat, and 2nd, transfer it to the water. Now, you have it 
 laid down as an axiom that when a body has been transferred or 
 transformed from one place or state into another, the same work has been 
 done and the same energy expended, whatever may have been the 
 intermediate steps or conditions, or whatever the apparatus. Therefore, 
 when a given quantity of water at a given temperature has been made into 
 steam at a given temperature, a certain definite work has been done, and 
 a certain amount of energy expended, from whatever the heat may have 
 been obtained, or whatever boiler may have been employed for the 
 purpose. 
   
 A pound of coal or any other fuel has a definite heat producing 
 capacity, and is capable of evaporating a definite quantity of water 
 under given conditions. That is the limit beyond which even perfection 
 cannot go, and yet I have known, and doubtless you have heard of, cases 
 where inventors have claimed, and so-called engineers have certified to, 
 much higher results. 
   
 The first step in generating steam is in burning the fuel to the best 
 advantage. A pound of carbon will generate 14,500 British thermal units, 
 during combustion into carbonic dioxide, and this will be the same, 
 whatever the temperature or the rapidity at which the combustion may 
 take place. If possible, we might oxidize it at as slow a rate as that 
 with which iron rusts or wood rots in the open air, or we might burn it 
 with the rapidity of gunpowder, a ton in a second, yet the total heat 
 generated would be precisely the same. Again, we may keep the 
 temperature down to the lowest point at which combustion can take place, 
 by bringing large bodies of air in contact with it, or otherwise, or we 
 may supply it with just the right quantity of pure oxygen, and burn it 
 at a temperature approaching that of dissociation, and still the heat 
 units given off will be neither more nor less. It follows, therefore, 
 that great latitude in the manner or rapidity of combustion may be taken 
 without affecting the quantity of heat generated. 
   
 But in practice it is found that other considerations limit this 
 latitude, and that there are certain conditions necessary in order to 
 get the most available heat from a pound of coal. There are three ways, 
 and only three, in which the heat developed by the combustion of coal in 
 a steam boiler furnace may be expended. 
   
 1st, and principally. It should be conveyed to the water in the boiler, 
 and be utilized in the production of steam. To be perfect, a boiler 
 should so utilize all the heat of combustion, but there are no perfect 
 boilers. 
   
 2nd. A portion of the heat of combustion is conveyed up the chimney in 
 the waste gases. This is in proportion to the weight of the gases, and 
 the difference between their temperature and that of the air and coal 
 before they entered the fire. 
   
 3rd. Another portion is dissipated by radiation from the sides of the 
 furnace. In a stove the heat is all used in these latter two ways, 
 either it goes off through the chimney or is radiated into the 
 surrounding space. It is one of the principal problems of boiler 
 engineering to render the amount of heat thus lost as small as possible. 
   
 The loss from radiation is in proportion to the amount of surface, its 
 nature, its temperature, and the time it is exposed. This loss can be 
 almost entirely eliminated by thick walls and a smooth white or polished 
 surface, but its amount is ordinarily so small that these extraordinary 
 precautions do not pay in practice. 
   
 It is evident that the temperature of the escaping gases cannot be 
 brought below that of the absorbing surfaces, while it may be much 
 greater even to that of the fire. This is supposing that all of the 
 escaping gases have passed through the fire. In case air is allowed to 
 leak into the flues, and mingle with the gases after they have left the 
 heating surfaces, the temperature may be brought down to almost any 
 point above that of the atmosphere, but without any reduction in the 
 amount of heat wasted. It is in this way that those low chimney 
 temperatures are sometimes attained which pass for proof of economy with 
 the unobserving. All surplus air admitted to the fire, or to the gases 
 before they leave the heating surfaces, increases the losses. 
   
 We are now prepared to see why and how the temperature and the rapidity 
 of combustion in the boiler furnace affect the economy, and that though 
 the amount of heat developed may be the same, the heat available for the 
 generation of steam may be much less with one rate or temperature of 
 combustion than another. 
   
 Assuming that there is no air passing up the chimney other than that 
 which has passed through the fire, the higher the temperature of the 
 fire and the lower that of the escaping gases the better the economy, 
 for the losses by the chimney gases will bear the same proportion to the 
 heat generated by the combustion as the temperature of those gases bears 
 to the temperature of the fire. That is to say, if the temperature of 
 the fire is 2500 degrees and that of the chimney gases 500 degrees above 
 that of the atmosphere, the loss by the chimney will be 500/2500 = 20 
 per cent. Therefore, as the escaping gases cannot be brought below the 
 temperature of the absorbing surface, which is practically a fixed 
 quantity, the temperature of the fire must be high in order to secure 
 good economy. 
   
 The losses by radiation being practically proportioned to the time 
 occupied, the more coal burned in a given furnace in a given time, the 
 less will be the proportionate loss from that cause. 
   
 It therefore follows that we should burn our coal rapidly and at a high 
 temperature to secure the best available economy. 
   
 
 
 
 PROPERTIES OF WATER 
 Pure water is a chemical compound of one volume of oxygen and two 
 volumes of hydrogen, its chemical symbol being H_{2}O. 
   
 The weight of water depends upon its temperature. Its weight at four 
 temperatures, much used in physical calculations, is given in Table 10. 
   
                    TABLE 10 
   
          WEIGHT OF WATER AT TEMPERATURES 
          USED IN PHYSICAL CALCULATIONS 
   
 +---------------------------+----------+----------+ 
 |   Temperature Degrees   |Weight per|Weight per| 
 |       Fahrenheit        |Cubic Foot|Cubic Inch| 
 |                           | Pounds | Pounds | 
 +---------------------------+----------+----------+ 
 |At 32 degrees or freezing |         |         | 
 | point at sea level       | 62.418 | 0.03612 | 
 |At 39.2 degrees or point of|         |         | 
 | maximum density         | 62.427 | 0.03613 | 
 |At 62 degrees or standard |         |         | 
 | temperature             | 62.355 | 0.03608 | 
 |At 212 degrees or boiling |         |         | 
 | point at sea level       | 59.846 | 0.03469 | 
 +---------------------------+----------+----------+ 
   
 While authorities differ as to the weight of water, the range of values 
 given for 62 degrees Fahrenheit (the standard temperature ordinarily 
 taken) being from 62.291 pounds to 62.360 pounds per cubic foot, the 
 value 62.355 is generally accepted as the most accurate. 
   
 A United States standard gallon holds 231 cubic inches and weighs, at 62 
 degrees Fahrenheit, approximately 8-1/3 pounds. 
   
 A British Imperial gallon holds 277.42 cubic inches and weighs, at 62 
 degrees Fahrenheit, 10 pounds. 
   
 The above are the true weights corrected for the effect of the buoyancy 
 of the air, or the weight in vacuo. If water is weighed in air in the 
 ordinary way, there is a correction of about one-eighth of one per cent 
 which is usually negligible. 
   
                TABLE 11 
   
 VOLUME AND WEIGHT OF DISTILLED WATER AT 
        VARIOUS TEMPERATURES[12] 
   
 +-----------+---------------+----------+ 
 |Temperature|Relative Volume|Weight per| 
 | Degrees | Water at 39.2 |Cubic Foot| 
 | Fahrenheit| Degrees = 1 | Pounds | 
 +-----------+---------------+----------+ 
 |   32     |   1.000176   | 62.42   | 
 |   39.2   |   1.000000   | 62.43   | 
 |   40     |   1.000004   | 62.43   | 
 |   50     |   1.00027     | 62.42   | 
 |   60     |   1.00096     | 62.37   | 
 |   70     |   1.00201     | 62.30   | 
 |   80     |   1.00338     | 62.22   | 
 |   90     |   1.00504     | 62.11   | 
 |   100     |   1.00698     | 62.00   | 
 |   110     |   1.00915     | 61.86 | 
 |   120     |   1.01157     | 61.71   | 
 |   130     |   1.01420     | 61.55   | 
 |   140     |   1.01705     | 61.38   | 
 |   150     |   1.02011     | 61.20   | 
 |   160     |   1.02337     | 61.00   | 
 |   170     |   1.02682     | 60.80   | 
 |   180     |   1.03047     | 60.58   | 
 |   190     |   1.03431     | 60.36   | 
 |   200     |   1.03835     | 60.12   | 
 |   210     |   1.04256     | 59.88   | 
 |   212     |   1.04343     | 59.83   | 
 |   220     |   1.0469     | 59.63   | 
 |   230     |   1.0515     | 59.37   | 
 |   240     |   1.0562     | 59.11   | 
 |   250     |   1.0611     | 58.83   | 
 |   260     |   1.0662     | 58.55   | 
 |   270     |   1.0715     | 58.26   | 
 |   280     |   1.0771     | 57.96   | 
 |   290     |   1.0830     | 57.65   | 
 |   300     |   1.0890     | 57.33   | 
 |   310     |   1.0953     | 57.00   | 
 |   320     |   1.1019     | 56.66   | 
 |   330     |   1.1088     | 56.30   | 
 |   340     |   1.1160     | 55.94   | 
 |   350     |   1.1235     | 55.57  | 
 |   360     |   1.1313     | 55.18   | 
 |   370     |   1.1396     | 54.78   | 
 |   380     |   1.1483     | 54.36   | 
 |   390     |   1.1573     | 53.94   | 
 |   400     |   1.167       | 53.5   | 
 |   410     |   1.177       | 53.0   | 
 |   420     |   1.187       | 52.6   | 
 |   430     |   1.197       | 52.2   | 
 |   440     |   1.208       | 51.7   | 
 |   450     |   1.220       | 51.2   | 
 |   460     |   1.232       | 50.7   | 
 |   470     |   1.244       | 50.2   | 
 |   480     |   1.256       | 49.7   | 
 |   490     |   1.269       | 49.2   | 
 |   500     |   1.283       | 48.7   | 
 |   510     |   1.297       | 48.1   | 
 |   520     |   1.312       | 47.6   | 
 |   530     |   1.329       | 47.0   | 
 |   540     |   1.35      | 46.3   | 
 |   550     |   1.37       | 45.6   | 
 |   560     |   1.39       | 44.9   | 
 +-----------+---------------+----------+ 
   
 Water is but slightly compressible and for all practical purposes may be 
 considered non-compressible. The coefficient of compressibility ranges 
 from 0.000040 to 0.000051 per atmosphere at ordinary temperatures, this 
 coefficient decreasing as the temperature increases. 
   
 Table 11 gives the weight in vacuo and the relative volume of a cubic 
 foot of distilled water at various temperatures. 
   
 The weight of water at the standard temperature being taken as 62.355 
 pounds per cubic foot, the pressure exerted by the column of water of 
 any stated height, and conversely the height of any column required to 
 produce a stated pressure, may be computed as follows: 
   
 The pressure in pounds per square foot = 62.355 × height of column in 
 feet. 
   
 The pressure in pounds per square inch = 0.433 × height of column in 
 feet. 
   
 Height of column in feet = pressure in pounds per square foot ÷ 62.355. 
   
 Height of column in feet = pressure in pounds per square inch ÷ 0.433. 
   
 Height of column in inches = pressure in pounds per square inch × 27.71. 
   
 Height of column in inches = pressure in ounces per square inch × 1.73. 
   
 By a change in the weights given above, the pressure exerted and height 
 of column may be computed for temperatures other than 62 degrees. 
   
 A pressure of one pound per square inch is exerted by a column of water 
 2.3093 feet or 27.71 inches high at 62 degrees Fahrenheit. 
   
 Water in its natural state is never found absolutely pure. In solvent 
 power water has a greater range than any other liquid. For common salt, 
 this is approximately a constant at all temperatures, while with such 
 impurities as magnesium and sodium sulphates, this solvent power 
 increases with an increase in temperature. 
   
                            TABLE 12 
   
          BOILING POINT OF WATER AT VARIOUS ALTITUDES 
   
 +--------------+----------------+-------------+---------------+ 
 |Boiling Point | Altitude Above | Atmospheric |   Barometer   | 
 |   Degrees   |   Sea Level   | Pressure   |   Reduced   | 
 | Fahrenheit |     Feet     | Pounds per | to 32 Degrees | 
 |             |               | Square Inch |   Inches     | 
 +--------------+----------------+-------------+---------------+ 
 |     184     |     15221     |   8.20     |     16.70     | 
 |     185     |     14649     |   8.38     |     17.06     | 
 |     186     |     14075     |   8.57     |     17.45     | 
 |     187     |     13498     |   8.76     |     17.83    | 
 |     188     |     12934     |   8.95     |     18.22     | 
 |     189     |     12367     |   9.14     |     18.61     | 
 |     190     |     11799     |   9.34     |     19.02     | 
 |     191     |     11243     |   9.54     |     19.43    | 
 |     192     |     10685     |   9.74     |     19.85     | 
 |     193     |     10127     |   9.95     |     20.27     | 
 |     194     |     9579     |   10.17     |     20.71     | 
 |     195     |     9031     |   10.39     |     21.15    | 
 |     196     |     8481     |   10.61     |     21.60     | 
 |     197     |     7932     |   10.83     |     22.05     | 
 |     198     |     7381     |   11.06     |     22.52     | 
 |     199     |     6843     |   11.29     |     22.99    | 
 |     200     |     6304     |   11.52     |     23.47     | 
 |     201     |     5764     |   11.76     |     23.95     | 
 |     202     |     5225     |   12.01     |     24.45     | 
 |     203     |     4697     |   12.26     |     24.96    | 
 |     204     |     4169     |   12.51     |     25.48     | 
 |     205     |     3642     |   12.77     |     26.00     | 
 |     206     |     3115     |   13.03     |     26.53     | 
 |     207     |     2589     |   13.30     |     27.08    | 
 |     208     |     2063     |   13.57     |     27.63     | 
 |     209     |     1539     |   13.85     |     28.19     | 
 |     210     |     1025     |   14.13     |     28.76     | 
 |     211     |       512     |   14.41     |     29.33    | 
 |     212     |   Sea Level   |   14.70     |     29.92     | 
 +--------------+----------------+-------------+---------------+ 
   
 Sea water contains on an average approximately 3.125 per cent of its 
 weight of solid matter or a thirty-second part of the weight of the 
 water and salt held in solution. The approximate composition of this 
 solid matter will be: sodium chloride 76 per cent, magnesium chloride 10 
 per cent, magnesium sulphate 6 per cent, calcium sulphate 5 per cent, 
 calcium carbonate 0.5 per cent, other substances 2.5 per cent. 
 The boiling point of water decreases as the altitude above sea level 
 increases. Table 12 gives the variation in the boiling point with the 
 altitude. 
   
 Water has a greater specific heat or heat-absorbing capacity than any 
 other known substance (bromine and hydrogen excepted) and its specific 
 heat is the basis for measurement of the capacity of heat absorption of 
 all other substances. From the definition, the specific heat of water is 
 the number of British thermal units required to raise one pound of water 
 one degree. This specific heat varies with the temperature of the water. 
 The generally accepted values are given in Table 13, which indicates the 
 values as determined by Messrs. Marks and Davis and Mr. Peabody. 
   
                        TABLE 13 
   
      SPECIFIC HEAT OF WATER AT VARIOUS TEMPERATURES 
   
 +----------------------+--------------------------------+ 
 |   MARKS AND DAVIS   |           PEABODY             | 
 |   From Values of   |         From Values of         | 
 | Barnes and Dieterici |     Barnes and Regnault       | 
 +-----------+----------+---------------------+----------+ 
 |Temperature| Specific |     Temperature     | Specific | 
 +-----------+   Heat   +----------+----------+   Heat   | 
 | Degrees   |         | Degrees | Degrees |         | 
 |Fahrenheit |         |Centigrade|Fahrenheit|         | 
 +-----------+----------+----------+----------+----------+ 
 |     30   | 1.0098 |   0     |   32   | 1.0094 | 
 |     40   | 1.0045 |   5     |   41   | 1.0053 | 
 |     50   | 1.0012 |   10     |   50   | 1.0023 | 
 |     55   | 1.0000 |   15     |   59   | 1.0003 | 
 |     60   | 0.9990 |   16.11 |   61   | 1.0000 | 
 |     70   | 0.9977 |   20     |   68   | 0.9990 | 
 |     80   | 0.9970 |   25     |   77   | 0.9981 | 
 |     90   | 0.9967 |   30     |   86   | 0.9976 | 
 |   100   | 0.9967 |   35     |   95   | 0.9974 | 
 |   110   | 0.9970 |   40     |   104   | 0.9974 | 
 |   120   | 0.9974 |   45     |   113   | 0.9976 | 
 |   130   | 0.9979 |   50     |   122   | 0.9980 | 
 |   140   | 0.9986 |   55     |   131   | 0.9985 | 
 |   150   | 0.9994 |   60     |   140   | 0.9994 | 
 |   160   | 1.0002 |   65     |   149   | 1.0004 | 
 |   170   | 1.0010 |   70     |   158   | 1.0015 | 
 |   180   | 1.0019 |   75     |   167   | 1.0028 | 
 |   190   | 1.0029 |   80     |   176   | 1.0042 | 
 |   200   | 1.0039 |   85     |   185   | 1.0056 | 
 |   210   | 1.0052 |   90     |   194   | 1.0071 | 
 |   220   | 1.007   |   95     |   203   | 1.0086 | 
 |   230   | 1.009   | 100     |  212   | 1.0101 | 
 +-----------+----------+----------+----------+----------+ 
   
 In consequence of this variation in specific heat, the variation in the 
 heat of the liquid of the water at different temperatures is not a 
 constant. Table 22[13] gives the heat of the liquid in a pound of water 
 at temperatures ranging from 32 to 340 degrees Fahrenheit. 
   
 The specific heat of ice at 32 degrees is 0.463. The specific heat of 
 saturated steam (ice and saturated steam representing the other forms in 
 which water may exist), is something that is difficult to define in any 
 way which will not be misleading. When no liquid is present the specific 
 heat of saturated steam is negative.[14] The use of the value of the 
 specific heat of steam is practically limited to instances where 
 superheat is present, and the specific heat of superheated steam is 
 covered later in the book. 
   
 
 
 
 BOILER FEED WATER 
 All natural waters contain some impurities which, when introduced into a 
 boiler, may appear as solids. In view of the apparent present-day 
 tendency toward large size boiler units and high overloads, the 
 importance of the use of pure water for boiler feed purposes cannot be 
 over-estimated. 
   
 Ordinarily, when water of sufficient purity for such use is not at hand, 
 the supply available may be rendered suitable by some process of 
 treatment. Against the cost of such treatment, there are many factors to 
 be considered. With water in which there is a marked tendency toward 
 scale formation, the interest and depreciation on the added boiler units 
 necessary to allow for the systematic cleaning of certain units must be 
 taken into consideration. Again there is a considerable loss in taking 
 boilers off for cleaning and replacing them on the line. On the other 
 hand, the decrease in capacity and efficiency accompanying an increased 
 incrustation of boilers in use has been too generally discussed to need 
 repetition here. Many experiments have been made and actual figures 
 reported as to this decrease, but in general, such figures apply only to 
 the particular set of conditions found in the plant where the boiler in 
 question was tested. So many factors enter into the effect of scale on 
 capacity and economy that it is impossible to give any accurate figures 
 on such decrease that will serve all cases, but that it is large has 
 been thoroughly proven. 
   
 While it is almost invariably true that practically any cost of 
 treatment will pay a return on the investment of the apparatus, the fact 
 must not be overlooked that there are certain waters which should never 
 be used for boiler feed purposes and which no treatment can render 
 suitable for such purpose. In such cases, the only remedy is the 
 securing of other feed supply or the employment of evaporators for 
 distilling the feed water as in marine service. 
   
                               TABLE 14 
   
    APPROXIMATE CLASSIFICATION OF IMPURITIES FOUND IN FEED WATERS 
              THEIR EFFECT AND ORDINARY METHODS OF RELIEF 
   
 +-----------------------+--------------+-----------------------------+ 
 | Difficulty Resulting | Nature of   | Ordinary Method of         | 
 | from Presence of     | Difficulty   | Overcoming or Relieving     | 
 +-----------------------+--------------+-----------------------------+ 
 | Sediment, Mud, etc.   | Incrustation | Settling tanks, filtration, | 
 |                      |             | blowing down.               | 
 |                       |             |                             | 
 | Readily Soluble Salts | Incrustation | Blowing down.               | 
 |                       |             |                            | 
 | Bicarbonates of Lime, | Incrustation | Heating feed. Treatment by | 
 | Magnesia, etc.       |             | addition of lime or of lime | 
 |                       |             | and soda. Barium carbonate. | 
 |                      |             |                             | 
 | Sulphate of Lime     | Incrustation | Treatment by addition of   | 
 |                       |             | soda. Barium carbonate.     | 
 |                       |             |                            | 
 | Chloride and Sulphate | Corrosion   | Treatment by addition of   | 
 | of Magnesium         |             | carbonate of soda.         | 
 |                       |             |                             | 
 | Acid                 | Corrosion  | Alkali.                     | 
 |                       |             |                             | 
 | Dissolved Carbonic   | Corrosion   | Heating feed. Keeping air   | 
 | Acid and Oxygen       |             | from feed. Addition of     | 
 |                      |             | caustic soda or slacked     | 
 |                       |             | lime.                       | 
 |                       |             |                             | 
 | Grease               | Corrosion   | Filter. Iron alum as       | 
 |                       |             | coagulent. Neutralization   | 
 |                       |             | by carbonate of soda. Use   | 
 |                       |             | of best hydrocarbon oils.   | 
 |                       |             |                             | 
 | Organic Matter       | Corrosion   | Filter. Use of coagulent.   | 
 |                       |             |                             | 
 | Organic Matter       | Priming     | Settling tanks. Filter in  | 
 | (Sewage)             |             | connection with coagulent. | 
 |                       |             |                             | 
 | Carbonate of Soda in | Priming     | Barium carbonate. New feed | 
 | large quantities     |             | supply. If from treatment, | 
 |                       |             | change.                     | 
 +-----------------------+--------------+-----------------------------+ 
   
 It is evident that the whole subject of boiler feed waters and their 
 treatment is one for the chemist rather than for the engineer. A brief 
 outline of the difficulties that may be experienced from the use of poor 
 feed water and a suggestion as to a method of overcoming certain of 
 these difficulties is all that will be attempted here. Such a brief 
 outline of the subject, however, will indicate the necessity for a 
 chemical analysis of any water before a treatment is tried and the 
 necessity of adapting the treatment in each case to the nature of the 
 difficulties that may be experienced. 
   
 Table 14 gives a list of impurities which may be found in boiler feed 
 water, grouped according to their effect on boiler operation and giving 
 the customary method used for overcoming difficulty to which they lead. 
   
   
 Scale--Scale is formed on boiler heating surfaces by the depositing of 
 impurities in the feed water in the form of a more or less hard adherent 
 crust. Such deposits are due to the fact that water loses its soluble 
 power at high temperatures or because the concentration becomes so high, 
 due to evaporation, that the impurities crystallize and adhere to the 
 boiler surfaces. The opportunity for formation of scale in a boiler will 
 be apparent when it is realized that during a month's operation of a 100 
 horse-power boiler, 300 pounds of solid matter may be deposited from 
 water containing only 7 grains per gallon, while some spring and well 
 waters contain sufficient to cause a deposit of as high as 2000 pounds. 
   
 The salts usually responsible for such incrustation are the carbonates 
 and sulphates of lime and magnesia, and boiler feed treatment in general 
 deals with the getting rid of these salts more or less completely. 
   
                          TABLE 15 
   
        SOLUBILITY OF MINERAL SALTS IN WATER (SPARKS) 
 IN GRAINS PER U. S. GALLON (58,381 GRAINS), EXCEPT AS NOTED 
   
 +------------------------------+------------+-------------+ 
 |Temperature Degrees Fahrenheit| 60 Degrees | 212 Degrees | 
 +------------------------------+------------+-------------+ 
 |Calcium Carbonate             |   2.5     |   1.5     | 
 |Calcium Sulphate             | 140.0     | 125.0     | 
 |Magnesium Carbonate           |   1.0     |   1.8     | 
 |Magnesium Sulphate           | 3.0 pounds | 12.0 pounds | 
 |Sodium Chloride               | 3.5 pounds | 4.0 pounds | 
 |Sodium Sulphate              | 1.1 pounds | 5.0 pounds | 
 +------------------------------+------------+-------------+ 
   
            CALCIUM SULPHATE AT TEMPERATURE ABOVE 
                  212 DEGREES (CHRISTIE) 
   
 +------------------------------+----+----+-------+----+---+ 
 |Temperature degrees Fahrenheit|284 |329 |347-365| 464|482| 
 |Corresponding gauge pressure | 38 | 87 |115-149| 469|561| 
 |Grains per gallon             |45.5|32.7| 15.7 |10.5|9.3| 
 +------------------------------+----+----+-------+----+---+ 
   
 Table 15 gives the solubility of these mineral salts in water at various 
 temperatures in grains per U. S. gallon (58,381 grains). It will be seen 
 from this table that the carbonates of lime and magnesium are not 
 soluble above 212 degrees, and calcium sulphate while somewhat insoluble 
 above 212 degrees becomes more greatly so as the temperature increases. 
   
 Scale is also formed by the settling of mud and sediment carried in 
 suspension in water. This may bake or be cemented to a hard scale when 
 mixed with other scale-forming ingredients. 
   
   
 Corrosion--Corrosion, or a chemical action leading to the actual 
 destruction of the boiler metal, is due to the solvent or oxidizing 
 properties of the feed water. It results from the presence of acid, 
 either free or developed[15] in the feed, the admixture of air with the 
 feed water, or as a result of a galvanic action. In boilers it takes 
 several forms: 
   
 1st. Pitting, which consists of isolated spots of active corrosion which 
 does not attack the boiler as a whole. 
   
 2nd. General corrosion, produced by naturally acid waters and where the 
 amount is so even and continuous that no accurate estimate of the metal 
 eaten away may be made. 
   
 3rd. Grooving, which, while largely a mechanical action which may occur 
 in neutral waters, is intensified by acidity. 
   
 Foaming--This phenomenon, which ordinarily occurs with waters 
 contaminated with sewage or organic growths, is due to the fact that the 
 suspended particles collect on the surface of the water in the boiler 
 and render difficult the liberation of steam bubbles arising to that 
 surface. It sometimes occurs with water containing carbonates in 
 solution in which a light flocculent precipitate will be formed on the 
 surface of the water. Again, it is the result of an excess of sodium 
 carbonate used in treatment for some other difficulty where animal or 
 vegetable oil finds its way into the boiler. 
   
 Priming--Priming, or the passing off of steam from a boiler in belches, 
 is caused by the concentration of sodium carbonate, sodium sulphate or 
 sodium chloride in solution. Sodium sulphate is found in many southern 
 waters and also where calcium or magnesium sulphate is precipitated with 
 soda ash. 
   
 Treatment of Feed Water--For scale formation. The treatment of feed 
 water, carrying scale-forming ingredients, is along two main lines: 1st, 
 by chemical means by which such impurities as are carried by the water 
 are caused to precipitate; and 2nd, by the means of heat, which results 
 in the reduction of the power of water to hold certain salts in 
 solution. The latter method alone is sufficient in the case of certain 
 temporarily hard waters, but the heat treatment, in general, is used in 
 connection with a chemical treatment to assist the latter. 
   
 Before going further into detail as to the treatment of water, it may be 
 well to define certain terms used. 
   
 _Hardness_, which is the most widely known evidence of the presence in 
 water of scale-forming matter, is that quality, the variation of which 
 makes it more difficult to obtain a lather or suds from soap in one 
 water than in another. This action is made use of in the soap test for 
 hardness described later. Hardness is ordinarily classed as either 
 temporary or permanent. Temporarily hard waters are those containing 
 carbonates of lime and magnesium, which may be precipitated by boiling 
 at 212 degrees and which, if they contain no other scale-forming 
 ingredients, become "soft" under such treatment. Permanently hard waters 
 are those containing mainly calcium sulphate, which is only precipitated 
 at the high temperatures found in the boiler itself, 300 degrees 
 Fahrenheit or more. The scale of hardness is an arbitrary one, based on 
 the number of grains of solids per gallon and waters may be classed on 
 such a basis as follows: 1-10 grain per gallon, soft water; 10-20 grain 
 per gallon, moderately hard water; above 25 grains per gallon, very hard 
 water. 
   
 _Alkalinity_ is a general term used for waters containing compounds with 
 the power of neutralizing acids. 
   
 _Causticity_, as used in water treatment, is a term coined by A. McGill, 
 indicating the presence of an excess of lime added during treatment. 
 Though such presence would also indicate alkalinity, the term is 
 arbitrarily used to apply to those hydrates whose presence is indicated 
 by phenolphthalein. 
   
 Of the chemical methods of water treatment, there are three general 
 processes: 
   
 1st. Lime Process. The lime process is used for waters containing 
 bicarbonates of lime and magnesia. Slacked lime in solution, as lime 
 water, is the reagent used. This combines with the carbonic acid which 
 is present, either free or as carbonates, to form an insoluble 
 monocarbonate of lime. The soluble bicarbonates of lime and magnesia, 
 losing their carbonic acid, thereby become insoluble and precipitate. 
   
 2nd. Soda Process. The soda process is used for waters containing 
 sulphates of lime and magnesia. Carbonate of soda and hydrate of soda 
 (caustic soda) are used either alone or together as the reagents. 
 Carbonate of soda, added to water containing little or no carbonic acid 
 or bicarbonates, decomposes the sulphates to form insoluble carbonate of 
 lime or magnesia which precipitate, the neutral soda remaining in 
 solution. If free carbonic acid or bicarbonates are present, bicarbonate 
 of lime is formed and remains in solution, though under the action of 
 heat, the carbon dioxide will be driven off and insoluble monocarbonates 
 will be formed. Caustic soda used in this process causes a more 
 energetic action, it being presumed that the caustic soda absorbs the 
 carbonic acid, becomes carbonate of soda and acts as above. 
   
 3rd. Lime and Soda Process. This process, which is the combination of 
 the first two, is by far the most generally used in water purification. 
 Such a method is used where sulphates of lime and magnesia are contained 
 in the water, together with such quantity of carbonic acid or 
 bicarbonates as to impair the action of the soda. Sufficient soda is 
 used to break down the sulphates of lime and magnesia and as much lime 
 added as is required to absorb the carbonic acid not taken up in the 
 soda reaction. 
   
 All of the apparatus for effecting such treatment of feed waters is 
 approximately the same in its chemical action, the numerous systems 
 differing in the methods of introduction and handling of the reagents. 
   
 The methods of testing water treated by an apparatus of this description 
 follow. 
   
 When properly treated, alkalinity, hardness and causticity should be in 
 the approximate relation of 6, 5 and 4. When too much lime is used in 
 the treatment, the causticity in the purified water, as indicated by the 
 acid test, will be nearly equal to the alkalinity. If too little lime is 
 used, the causticity will fall to approximately half the alkalinity. The 
 hardness should not be in excess of two points less than the alkalinity. 
 Where too great a quantity of soda is used, the hardness is lowered and 
 the alkalinity raised. If too little soda, the hardness is raised and 
 the alkalinity lowered. 
   
 Alkalinity and causticity are tested with a standard solution of 
 sulphuric acid. A standard soap solution is used for testing for 
 hardness and a silver nitrate solution may also be used for determining 
 whether an excess of lime has been used in the treatment. 
   
 Alkalinity: To 50 cubic centimeters of treated water, to which there has 
 been added sufficient methylorange to color it, add the acid solution, 
 drop by drop, until the mixture is on the point of turning red. As the 
 acid solution is first added, the red color, which shows quickly, 
 disappears on shaking the mixture, and this color disappears more slowly 
 as the critical point is approached. One-tenth cubic centimeter of the 
 standard acid solution corresponds to one degree of alkalinity. 
 Causticity: To 50 cubic centimeters of treated water, to which there has 
 been added one drop of phenolphthalein dissolved in alcohol to give the 
 water a pinkish color, add the acid solution, drop by drop, shaking 
 after each addition, until the color entirely disappears. One-tenth 
 cubic centimeter of acid solution corresponds to one degree of 
 causticity. 
   
 The alkalinity may be determined from the same sample tested for 
 causticity by the coloring with methylorange and adding the acid until 
 the sample is on the point of turning red. The total acid added in 
 determining both causticity and alkalinity in this case is the measure 
 of the alkalinity. 
   
 Hardness: 100 cubic centimeters of the treated water is used for this 
 test, one cubic centimeter of the soap solution corresponding to one 
 degree of hardness. The soap solution is added a very little at a time 
 and the whole violently shaken. Enough of the solution must be added to 
 make a permanent lather or foam, that is, the soap bubbles must not 
 disappear after the shaking is stopped. 
   
 Excess of lime as determined by nitrate of silver: If there is an excess 
 of lime used in the treatment, a sample will become a dark brown by the 
 addition of a small quantity of silver nitrate, otherwise a milky white 
 solution will be formed. 
   
 Combined Heat and Chemical Treatment: Heat is used in many systems of 
 feed treatment apparatus as an adjunct to the chemical process. Heat 
 alone will remove temporary hardness by the precipitation of carbonates 
 of lime and magnesia and, when used in connection with the chemical 
 process, leaves only the permanent hardness or the sulphates of lime to 
 be taken care of by chemical treatment. 
   
                      TABLE 16 
   
    REAGENTS REQUIRED IN LIME AND SODA PROCESS 
      FOR TREATING 1000 U. S. GALLONS OF WATER 
 PER GRAIN PER GALLON OF CONTAINED IMPURITIES[16] 
   
 +-----------------------+-----------+-----------+ 
 |                       | Lime[17] | Soda[18] | 
 |                       |   Pounds |   Pounds | 
 +-----------------------+-----------+-----------+ 
 | Calcium Carbonate   |   0.098   |   ...   | 
 | Calcium Sulphate     |   ...   |   0.124   | 
 | Calcium Chloride     |   ...   |   0.151   | 
 | Calcium Nitrate     |   ...   |   0.104   | 
 | Magnesium Carbonate |   0.234   |   ...   | 
 | Magnesium Sulphate   |   0.079   |   0.141   | 
 | Magnesium Chloride   |   0.103   |   0.177   | 
 | Magnesium Nitrate   |   0.067   |   0.115   | 
 | Ferrous Carbonate   |   0.169   |   ...   | 
 | Ferrous Sulphate     |   0.070   |   0.110   | 
 | Ferric Sulphate     |   0.074   |   0.126   | 
 | Aluminum Sulphate   |   0.087   |   0.147   | 
 | Free Sulphuric Acid |   0.100   |   0.171   | 
 | Sodium Carbonate     |   0.093   |   ...   | 
 | Free Carbon Dioxide |   0.223   |   ...   | 
 | Hydrogen Sulphite   |   0.288   |   ...   | 
 +-----------------------+-----------+-----------+ 
   
 The chemicals used in the ordinary lime and soda process of feed water 
 treatment are common lime and soda. The efficiency of such apparatus 
 will depend wholly upon the amount and character of the impurities in 
 the water to be treated. Table 16 gives the amount of lime and soda 
 required per 1000 gallons for each grain per gallon of the various 
 impurities found in the water. This table is based on lime containing 90 
 per cent calcium oxide and soda containing 58 per cent sodium oxide, 
 which correspond to the commercial quality ordinarily purchasable. From 
 this table and the cost of the lime and soda, the cost of treating any 
 water per 1000 gallons may be readily computed. 
   
 Less Usual Reagents--Barium hydrate is sometimes used to reduce 
 permanent hardness or the calcium sulphate component. Until recently, 
 the high cost of barium hydrate has rendered its use prohibitive but at 
 the present it is obtained as a by-product in cement manufacture and it 
 may be purchased at a more reasonable figure than heretofore. It acts 
 directly on the soluble sulphates to form barium sulphate which is 
 insoluble and may be precipitated. Where this reagent is used, it is 
 desirable that the reaction be allowed to take place outside of the 
 boiler, though there are certain cases where its internal use is 
 permissible. 
   
 Barium carbonate is sometimes used in removing calcium sulphate, the 
 products of the reaction being barium sulphate and calcium carbonate, 
 both of which are insoluble and may be precipitated. As barium carbonate 
 in itself is insoluble, it cannot be added to water as a solution and 
 its use should, therefore, be confined to treatment outside of the 
 boiler. 
   
 Silicate of soda will precipitate calcium carbonate with the formation 
 of a gelatinous silicate of lime and carbonate of soda. If calcium 
 sulphate is also present, carbonate of soda is formed in the above 
 reaction, which in turn will break down the sulphate. 
   
 Oxalate of soda is an expensive but efficient reagent which forms a 
 precipitate of calcium oxalate of a particularly insoluble nature. 
   
 Alum and iron alum will act as efficient coagulents where organic matter 
 is present in the water. Iron alum has not only this property but also 
 that of reducing oil discharged from surface condensers to a condition 
 in which it may be readily removed by filtration. 
   
 Corrosion--Where there is a corrosive action because of the presence of 
 acid in the water or of oil containing fatty acids which will decompose 
 and cause pitting wherever the sludge can find a resting place, it may 
 be overcome by the neutralization of the water by carbonate of soda. 
 Such neutralization should be carried to the point where the water will 
 just turn red litmus paper blue. As a preventative of such action 
 arising from the presence of the oil, only the highest grades of 
 hydrocarbon oils should be used. 
   
 Acidity will occur where sea water is present in a boiler. There is the 
 possibility of such an occurrence in marine practice and in stationary 
 plants using sea water for condensing, due to leaky condenser tubes, 
 priming in the evaporators, etc. Such acidity is caused through the 
 dissociation of magnesium chloride into hydrochloride acid and magnesia 
 under high temperatures. The acid in contact with the metal forms an 
 iron salt which immediately upon its formation is neutralized by the 
 free magnesia in the water, thereby precipitating iron oxide and 
 reforming magnesium chloride. The preventive for corrosion arising from 
 such acidity is the keeping tight of the condenser. Where it is 
 unavoidable that some sea water should find its way into a boiler, the 
 acidity resulting should be neutralized by soda ash. This will convert 
 the magnesium chloride into magnesium carbonate and sodium chloride, 
 neither of which is corrosive but both of which are scale-forming. 
   
 The presence of air in the feed water which is sucked in by the feed 
 pump is a well recognized cause of corrosion. Air bubbles form below the 
 water line and attack the metal of the boiler, the oxygen of the air 
 causing oxidization of the boiler metal and the formation of rust. The 
 particle of rust thus formed is swept away by the circulation or is 
 dislodged by expansion and the minute pit thus left forms an ideal 
 resting place for other air bubbles and the continuation of the 
 oxidization process. The prevention is, of course, the removing of the 
 air from the feed water. In marine practice, where there has been 
 experienced the most difficulty from this source, it has been found to 
 be advantageous to pump the water from the hot well to a filter tank 
 placed above the feed pump suction valves. In this way the air is 
 liberated from the surface of the tank and a head is assured for the 
 suction end of the pump. In this same class of work, the corrosive 
 action of air is reduced by introducing the feed through a spray nozzle 
 into the steam space above the water line. 
   
 Galvanic action, resulting in the eating away of the boiler metal 
 through electrolysis was formerly considered practically the sole cause 
 of corrosion. But little is known of such action aside from the fact 
 that it does take place in certain instances. The means adopted as a 
 remedy is usually the installation of zinc plates within the boiler, 
 which must have positive metallic contact with the boiler metal. In this 
 way, local electrolytic effects are overcome by a still greater 
 electrolytic action at the expense of the more positive zinc. The 
 positive contact necessary is difficult to maintain and it is 
 questionable just what efficacy such plates have except for a short 
 period after their installation when the contact is known to be 
 positive. Aside from protection from such electrolytic action, however, 
 the zinc plates have a distinct use where there is the liability of air 
 in the feed, as they offer a substance much more readily oxidized by 
 such air than the metal of the boiler. 
   
 Foaming--Where foaming is caused by organic matter in suspension, it may 
 be largely overcome by filtration or by the use of a coagulent in 
 connection with filtration, the latter combination having come recently 
 into considerable favor. Alum, or potash alum, and iron alum, which in 
 reality contains no alumina and should rather be called potassia-ferric, 
 are the coagulents generally used in connection with filtration. Such 
 matter as is not removed by filtration may, under certain conditions, be 
 handled by surface blowing. In some instances, settling tanks are used 
 for the removal of matter in suspension, but where large quantities of 
 water are required, filtration is ordinarily substituted on account of 
 the time element and the large area necessary in settling tanks. 
   
 Where foaming occurs as the result of overtreatment of the feed water, 
 the obvious remedy is a change in such treatment. 
   
 Priming--Where priming is caused by excessive concentration of salts 
 within a boiler, it may be overcome largely by frequent blowing down. 
 The degree of concentration allowable before priming will take place 
 varies widely with conditions of operation and may be definitely 
 determined only by experience with each individual set of conditions. It 
 is the presence of the salts that cause priming that may result in the 
 absolute unfitness of water for boiler feed purposes. Where these salts 
 exist in such quantities that the amount of blowing down necessary to 
 keep the degree of concentration below the priming point results in 
 excessive losses, the only remedy is the securing of another supply of 
 feed, and the results will warrant the change almost regardless of the 
 expense. In some few instances, the impurities may be taken care of by 
 some method of water treatment but such water should be submitted to an 
 authority on the subject before any treatment apparatus is installed. 
 Boiler Compounds--The method of treatment of feed water by far the most 
 generally used is by the use of some of the so-called boiler compounds. 
 There are many reliable concerns handling such compounds who 
 unquestionably secure the promised results, but there is a great 
 tendency toward looking on the compound as a "cure all" for any water 
 difficulties and care should be taken to deal only with reputable 
 concerns. 
   
 The composition of these compounds is almost invariably based on soda 
 with certain tannic substances and in some instances a gelatinous 
 substance which is presumed to encircle scale particles and prevent 
 their adhering to the boiler surfaces. The action of these compounds is 
 ordinarily to reduce the calcium sulphate in the water by means of 
 carbonate of soda and to precipitate it as a muddy form of calcium 
 carbonate which may be blown off. The tannic compounds are used in 
 connection with the soda with the idea of introducing organic matter 
 into any scale already formed. When it has penetrated to the boiler 
 metal, decomposition of the scale sets in, causing a disruptive effect 
 which breaks the scale from the metal sometimes in large slabs. It is 
 this effect of boiler compounds that is to be most carefully guarded 
 against or inevitable trouble will result from the presence of loose 
 scale with the consequent danger of tube losses through burning. 
   
 When proper care is taken to suit the compound to the water in use, the 
 results secured are fairly effective. In general, however, the use of 
 compounds may only be recommended for the prevention of scale rather 
 than with the view to removing scale which has already formed, that is, 
 the compounds should be introduced with the feed water only when the 
 boiler has been thoroughly cleaned. 
   
 
 
 
 FEED WATER HEATING AND METHODS OF FEEDING 
 Before water fed into a boiler can be converted into steam, it must be 
 first heated to a temperature corresponding to the pressure within the 
 boiler. Steam at 160 pounds gauge pressure has a temperature of 
 approximately 371 degrees Fahrenheit. If water is fed to the boiler at 
 60 degrees Fahrenheit, each pound must have 311 B. t. u. added to it to 
 increase its temperature 371 degrees, which increase must take place 
 before the water can be converted into steam. As it requires 1167.8 
 t. u. to raise one pound of water from 60 to 371 degrees and to 
 
 convert it into steam at 160 pounds gauge pressure, the 311 degrees 
 required simply to raise the temperature of the water from 60 to 371 
 degrees will be approximately 27 per cent of the total. If, therefore, 
 the temperature of the water can be increased from 60 to 371 degrees 
 before it is introduced into a boiler by the utilization of heat from 
 some source that would otherwise be wasted, there will be a saving in 
 the fuel required of 311 ÷ 1167.8 = 27 per cent, and there will be a net 
 saving, provided the cost of maintaining and operating the apparatus for 
 securing this saving is less than the value of the heat thus saved. 
   
 The saving in the fuel due to the heating of feed water by means of heat 
 that would otherwise be wasted may be computed from the formula: 
   
                        100 (t - t_{i}) 
 Fuel saving per cent = ---------------     (1) 
                        H + 32 - t_{i} 
   
 where, t = temperature of feed water after heating, t_{i} = temperature 
 of feed water before heating, and H = total heat above 32 degrees per 
 pound of steam at the boiler pressure. Values of H may be found in Table 
 Table 17 has been computed from this formula to show the fuel saving 
 
 under the conditions assumed with the boiler operating at 180 pounds 
 gauge pressure. 
   
                        TABLE 17 
   
 SAVING IN FUEL, IN PER CENT, BY HEATING FEED WATER 
                GAUGE PRESSURE 180 POUNDS 
   
 +-----------+-----------------------------------------+ 
 | Initial | Final Temperature--Degrees Fahrenheit | 
 |Temperature|-----+-----+-----+-----+-----+-----+-----| 
 | Fahrenheit| 120 | 140 | 160 | 180 | 200 | 250 | 300 | 
 +-----------+-----+-----+-----+-----+-----+-----+-----+ 
 |     32   | 7.35| 9.02|10.69|12.36|14.04|18.20|22.38| 
 |     35   | 7.12| 8.79|10.46|12.14|13.82|18.00|22.18| 
 |     40   | 6.72| 8.41|10.09|11.77|13.45|17.65|21.86| 
 |     45   | 6.33| 8.02| 9.71|11.40|13.08|17.30|21.52| 
 |     50   | 5.93| 7.63| 9.32|11.02|12.72|16.95|21.19| 
 |     55   | 5.53| 7.24| 8.94|10.64|12.34|16.60|20.86| 
 |     60   | 5.13| 6.84| 8.55|10.27|11.97|16.24|20.52| 
 |     65   | 4.72| 6.44| 8.16| 9.87|11.59|15.88|20.18| 
 |     70   | 4.31| 6.04| 7.77| 9.48|11.21|15.52|19.83| 
 |     75   | 3.90| 5.64| 7.36| 9.09|10.82|15.16|19.48| 
 |     80   | 3.48| 5.22| 6.96| 8.70|10.44|14.79|19.13| 
 |     85   | 3.06| 4.80| 6.55| 8.30|10.05|14.41|18.78| 
 |     90   | 2.63| 4.39| 6.14| 7.89| 9.65|14.04|18.43| 
 |     95   | 2.20| 3.97| 5.73| 7.49| 9.25|13.66|18.07| 
 |   100   | 1.77| 3.54| 5.31| 7.08| 8.85|13.28|17.70| 
 |   110   | .89| 2.68| 4.47| 6.25| 8.04|12.50|16.97| 
 |   120   | .00| 1.80| 3.61| 5.41| 7.21|11.71|16.22| 
 |   130   |     | .91| 2.73| 4.55| 6.37|10.91|15.46| 
 |   140   |     | .00| 1.84| 3.67| 5.51|10.09|14.68| 
 |   150   |     |     | .93| 2.78| 4.63| 9.26|13.89| 
 |   160   |     |     | .00| 1.87| 3.74| 8.41|13.09| 
 |   170   |     |     |     | .94| 2.83| 7.55|12.27| 
 |   180   |     |     |    | .00| 1.91| 6.67|11.43| 
 |   190   |     |     |     |     | .96| 5.77|10.58| 
 |   200   |     |     |     |     | .00| 4.86| 9.71| 
 |   210   |     |     |     |     |     | 3.92| 8.82| 
 +-----------+-----+-----+-----+-----+-----+-----+-----+ 
   
 Besides the saving in fuel effected by the use of feed water heaters, 
 other advantages are secured. The time required for the conversion of 
 water into steam is diminished and the steam capacity of the boiler 
 thereby increased. Further, the feeding of cold water into a boiler has 
 a tendency toward the setting up of temperature strains, which are 
 diminished in proportion as the temperature of the feed approaches that 
 of the steam. An important additional advantage of heating feed water is 
 that in certain types of heaters a large portion of the scale forming 
 ingredients are precipitated before entering the boiler, with a 
 consequent saving in cleaning and losses through decreased efficiency 
 and capacity. 
   
 In general, feed water heaters may be divided into closed heaters, open 
 heaters and economizers; the first two depend for their heat upon 
 exhaust, or in some cases live steam, while the last class utilizes the 
 heat of the waste flue gases to secure the same result. The question of 
 the type of apparatus to be installed is dependent upon the conditions 
 attached to each individual case. 
   
 In closed heaters the feed water and the exhaust steam do not come into 
 actual contact with each other. Either the steam or the water passes 
 through tubes surrounded by the other medium, as the heater is of the 
 steam-tube or water-tube type. A closed heater is best suited for water 
 free from scale-forming matter, as such matter soon clogs the passages. 
 Cleaning such heaters is costly and the efficiency drops off rapidly as 
 scale forms. A closed heater is not advisable where the engines work 
 intermittently, as is the case with mine hoisting engines. In this class 
 of work the frequent coolings between operating periods and the sudden 
 heatings when operation commences will tend to loosen the tubes or even 
 pull them apart. For this reason, an open heater, or economizer, will 
 give more satisfactory service with intermittently operating apparatus. 
   
 Open heaters are best suited for waters containing scale-forming matter. 
 Much of the temporary hardness may be precipitated in the heater and the 
 sediment easily removed. Such heaters are frequently used with a reagent 
 for precipitating permanent hardness in the combined heat and chemical 
 treatment of feed water. The so-called live steam purifiers are open 
 heaters, the water being raised to the boiling temperature and the 
 carbonates and a portion of the sulphates being precipitated. The 
 disadvantage of this class of apparatus is that some of the sulphates 
 remain in solution to be precipitated as scale when concentrated in the 
 boiler. Sufficient concentration to have such an effect, however, may 
 often be prevented by frequent blowing down. 
   
 Economizers find their largest field where the design of the boiler is 
 such that the maximum possible amount of heat is not extracted from the 
 gases of combustion. The more wasteful the boiler, the greater the 
 saving effected by the use of the economizer, and it is sometimes 
 possible to raise the temperature of the feed water to that of high 
 pressure steam by the installation of such an apparatus, the saving 
 amounting in some cases to as much as 20 per cent. The fuel used bears 
 directly on the question of the advisability of an economizer 
 installation, for when oil is the fuel a boiler efficiency of 80 per 
 cent or over is frequently realized, an efficiency which would leave a 
 small opportunity for a commercial gain through the addition of an 
 economizer. 
   
 From the standpoint of space requirements, economizers are at a 
 disadvantage in that they are bulky and require a considerable increase 
 over space occupied by a heater of the exhaust type. They also require 
 additional brickwork or a metal casing, which increases the cost. 
 Sometimes, too, the frictional resistance of the gases through an 
 economizer make its adaptability questionable because of the draft 
 conditions. When figuring the net return on economizer investment, all 
 of these factors must be considered. 
   
 When the feed water is such that scale will quickly encrust the 
 economizer and throw it out of service for cleaning during an excessive 
 portion of the time, it will be necessary to purify water before 
 introducing it into an economizer to make it earn a profit on the 
 investment. 
   
 From the foregoing, it is clearly indicated that it is impossible to 
 make a definite statement as to the relative saving by heating feed 
 water in any of the three types. Each case must be worked out 
 independently and a decision can be reached only after an exhaustive 
 study of all the conditions affecting the case, including the time the 
 plant will be in service and probable growth of the plant. When, as a 
 result of such study, the possible methods for handling the problem have 
 been determined, the solution of the best apparatus can be made easily 
 by the balancing of the saving possible by each method against its first 
 cost, depreciation, maintenance and cost of operation. 
   
 Feeding of Water--The choice of methods to be used in introducing feed 
 water into a boiler lies between an injector and a pump. In most plants, 
 an injector would not be economical, as the water fed by such means must 
 be cold, a fact which makes impossible the use of a heater before the 
 water enters the injector. Such a heater might be installed between the 
 injector and the boiler but as heat is added to the water in the 
 injector, the heater could not properly fulfill its function. 
   
                                  TABLE 18 
   
                      COMPARISON OF PUMPS AND INJECTORS 
 _________________________________________________________________________ 
 |                            |                     |                   | 
 |     Method of Supplying     |                     |                   | 
 |     Feed-water to Boiler     | Relative amount of | Saving of fuel over| 
 | Temperature of feed-water as | coal required per   | the amount required| 
 | delivered to the pump or to | unit of time, the   | when the boiler is | 
 | injector, 60 degrees Fahren- | amount for a direct-| fed by a direct-   | 
 | heit. Rate of evaporation of | acting pump, feeding| acting pump without| 
 | boiler, to pounds of water   | water at 60 degrees | heater             | 
 | per pound of coal from and   | without a heater,   |     Per Cent       | 
 | at 212 degrees Fahrenheit   | being taken as unity|                   | 
 |______________________________|_____________________|____________________| 
 |                             |                     |                   | 
 | Direct-acting Pump feeding   |                     |                   | 
 | water at 60 degrees without |                     |                    | 
 | a heater                     |       1.000       |         .0       | 
 |                             |                     |                   | 
 | Injector feeding water at   |                     |                   | 
 | 150 degrees without a heater |         .985       |         1.5       | 
 | Injector feeding through a   |                     |                   | 
 | heater in which the water is |                     |                   | 
 | heated from 150 to 200       |                    |                   | 
 | degrees                     |         .938       |         6.2       | 
 |                             |                     |                   | 
 | Direct-acting Pump feeding   |                     |                   | 
 | water through a heater in   |                     |                   | 
 | which it is heated from 60   |                     |                   | 
 | to 200 degrees               |         .879       |       12.1       | 
 |                            |                     |                   | 
 | Geared Pump run from the     |                     |                   | 
 | engine, feeding water       |                     |                   | 
 | through a heater in which it |                     |                   | 
 | is heated from 60 to 200     |                     |                   | 
 | degrees                     |         .868       |       13.2       | 
 |______________________________|_____________________|____________________| 
   
 The injector, considered only in the light of a combined heater and 
 pump, is claimed to have a thermal efficiency of 100 per cent, since all 
 of the heat in the steam used is returned to the boiler with the water. 
 This claim leads to an erroneous idea. If a pump is used in feeding the 
 water to a boiler and the heat in the exhaust from the pump is imparted 
 to the feed water, the pump has as high a thermal efficiency as the 
 injector. The pump has the further advantage that it uses so much less 
 steam for the forcing of a given quantity of water into the boiler that 
 it makes possible a greater saving through the use of the exhaust from 
 other auxiliaries for heating the feed, which exhaust, if an injector 
 were used, would be wasted, as has been pointed out. 
   
 In locomotive practice, injectors are used because there is no exhaust 
 steam available for heating the feed, this being utilized in producing a 
 forced draft, and because of space requirements. In power plant work, 
 however, pumps are universally used for regular operation, though 
 injectors are sometimes installed as an auxiliary method of feeding. 
   
 Table 18 shows the relative value of injectors, direct-acting steam 
 pumps and pumps driven from the engine, the data having been obtained 
 from actual experiment. It will be noted that when feeding cold water 
 direct to the boilers, the injector has a slightly greater economy but 
 when feeding through a heater, the pump is by far the more economical. 
   
 Auxiliaries--It is the general impression that auxiliaries will take 
 less steam if the exhaust is turned into the condensers, in this way 
 reducing the back pressure. As a matter of fact, vacuum is rarely 
 registered on an indicator card taken from the cylinders of certain 
 types of auxiliaries unless the exhaust connection is short and without 
 bends, as long pipes and many angles offset the effect of the condenser. 
 On the other hand, if the exhaust steam from the auxiliaries can be used 
 for heating the feed water, all of the latent heat less only the loss 
 due to radiation is returned to the boiler and is saved instead of being 
 lost in the condensing water or wasted with the free exhaust. Taking 
 into consideration the plant as a whole, it would appear that the 
 auxiliary machinery, under such conditions, is more efficient than the 
 main engines. 
   
 
 
 
 STEAM 
 When a given weight of a perfect gas is compressed or expanded at a 
 constant temperature, the product of the pressure and volume is a 
 constant. Vapors, which are liquids in aeriform condition, on the other 
 hand, can exist only at a definite pressure corresponding to each 
 temperature if in the saturated state, that is, the pressure is a 
 function of the temperature only. Steam is water vapor, and at a 
 pressure of, say, 150 pounds absolute per square inch saturated steam 
 can exist only at a temperature 358 degrees Fahrenheit. Hence if the 
 pressure of saturated steam be fixed, its temperature is also fixed, and 
 _vice versa_. 
   
 Saturated steam is water vapor in the condition in which it is generated 
 from water with which it is in contact. Or it is steam which is at the 
 maximum pressure and density possible at its temperature. If any change 
 be made in the temperature or pressure of steam, there will be a 
 corresponding change in its condition. If the pressure be increased or 
 the temperature decreased, a portion of the steam will be condensed. If 
 the temperature be increased or the pressure decreased, a portion of the 
 water with which the steam is in contact will be evaporated into steam. 
 Steam will remain saturated just so long as it is of the same pressure 
 and temperature as the water with which it can remain in contact without 
 a gain or loss of heat. Moreover, saturated steam cannot have its 
 temperature lowered without a lowering of its pressure, any loss of heat 
 being made up by the latent heat of such portion as will be condensed. 
 Nor can the temperature of saturated steam be increased except when 
 accompanied by a corresponding increase in pressure, any added heat 
 being expended in the evaporation into steam of a portion of the water 
 with which it is in contact. 
   
 Dry saturated steam contains no water. In some cases, saturated steam is 
 accompanied by water which is carried along with it, either in the form 
 of a spray or is blown along the surface of the piping, and the steam is 
 then said to be wet. The percentage weight of the steam in a mixture of 
 steam and water is called the quality of the steam. Thus, if in a 
 mixture of 100 pounds of steam and water there is three-quarters of a 
 pound of water, the quality of the steam will be 99.25. 
   
 Heat may be added to steam not in contact with water, such an addition 
 of heat resulting in an increase of temperature and pressure if the 
 volume be kept constant, or an increase in temperature and volume if the 
 pressure remain constant. Steam whose temperature thus exceeds that of 
 saturated steam at a corresponding pressure is said to be superheated 
 and its properties approximate those of a perfect gas. 
   
 As pointed out in the chapter on heat, the heat necessary to raise one 
 pound of water from 32 degrees Fahrenheit to the point of ebullition is 
 called the _heat of the liquid_. The heat absorbed during ebullition 
 consists of that necessary to dissociate the molecules, or the _inner 
 latent heat_, and that necessary to overcome the resistance to the 
 increase in volume, or the _outer latent heat_. These two make up the 
 _latent heat of evaporation_ and the sum of this latent heat of 
 evaporation and the heat of the liquid make the _total heat_ of the 
 steam. These values for various pressures are given in the steam tables, 
 pages 122 to 127. 
   
 The specific volume of saturated steam at any pressure is the volume in 
 cubic feet of one pound of steam at that pressure. 
   
 The density of saturated steam, that is, its weight per cubic foot, is 
 obviously the reciprocal of the specific volume. This density varies as 
 the 16/17 power over the ordinary range of pressures used in steam 
 boiler work and may be found by the formula, D = .003027p^{.941}, which 
 is correct within 0.15 per cent up to 250 pounds pressure. 
   
 The relative volume of steam is the ratio of the volume of a given 
 weight to the volume of the same weight of water at 39.2 degrees 
 Fahrenheit and is equal to the specific volume times 62.427. 
   
 As vapors are liquids in their gaseous form and the boiling point is the 
 point of change in this condition, it is clear that this point is 
 dependent upon the pressure under which the liquid exists. This fact is 
 of great practical importance in steam condenser work and in many 
 operations involving boiling in an open vessel, since in the latter case 
 its altitude will have considerable influence. The relation between 
 altitude and boiling point of water is shown in Table 12. 
   
 The conditions of feed temperature and steam pressure in boiler tests, 
 fuel performances and the like, will be found to vary widely in 
 different trials. In order to secure a means for comparison of different 
 trials, it is necessary to reduce all results to some common basis. The 
 method which has been adopted for the reduction to a comparable basis is 
 to transform the evaporation under actual conditions of steam pressure 
 and feed temperature which exist in the trial to an equivalent 
 evaporation under a set of standard conditions. These standard 
 conditions presuppose a feed water temperature of 212 degrees Fahrenheit 
 and a steam pressure equal to the normal atmospheric pressure at sea 
 level, 14.7 pounds absolute. Under such conditions steam would be 
 generated _at_ a temperature of 212 degrees, the temperature 
 corresponding to atmospheric pressure at sea level, _from_ water at 212 
 degrees. The weight of water which _would_ be evaporated under the 
 assumed standard conditions by exactly the amount of heat absorbed by 
 the boiler under actual conditions existing in the trial, is, therefore, 
 called the equivalent evaporation "from and at 212 degrees." 
   
 The factor for reducing the weight of water actually converted into 
 steam from the temperature of the feed, at the steam pressure existing 
 in the trial, to the equivalent evaporation under standard conditions is 
 called the _factor of evaporation._ This factor is the ratio of the 
 total heat added to one pound of steam under the standard conditions to 
 the heat added to each pound of steam in heating the water from the 
 temperature of the feed in the trial to the temperature corresponding to 
 the pressure existing in the trial. This heat added is obviously the 
 difference between the total heat of evaporation of the steam at the 
 pressure existing in the trial and the heat of the liquid in the water 
 at the temperature at which it was fed in the trial. To illustrate by an 
 example: 
   
 In a boiler trial the temperature of the feed water is 60 degrees 
 Fahrenheit and the pressure under which steam is delivered is 160.3 
 pounds gauge pressure or 175 pounds absolute pressure. The total heat of 
 one pound of steam at 175 pounds pressure is 1195.9 B. t. u. measured 
 above the standard temperature of 32 degrees Fahrenheit. But the water 
 fed to the boiler contained 28.08 B. t. u. as the heat of the liquid 
 measured above 32 degrees Fahrenheit. Therefore, to each pound of steam 
 there has been added 1167.82 B. t. u. To evaporate one pound of water 
 under standard conditions would, on the other hand, have required but 
 970.4 B. t. u., which, as described, is the latent heat of evaporation 
 at 212 degrees Fahrenheit. Expressed differently, the total heat of one 
 pound of steam at the pressure corresponding to a temperature of 212 
 degrees is 1150.4 B. t. u. One pound of water at 212 degrees contains 
 180 B. t. u. of sensible heat above 32 degrees Fahrenheit. Hence, under 
 standard conditions, 1150.4 - 180 = 970.4 B. t. u. is added in the 
 changing of one pound of water into steam at atmospheric pressure and a 
 temperature of 212 degrees. This is in effect the definition of the 
 latent heat of evaporation. 
   
 Hence, if conditions of the trial had been standard, only 970.4 B. t. u. 
 would be required and the ratio of 1167.82 to 970.4 B. t. u. is the 
 ratio determining the factor of evaporation. The factor in the assumed 
 case is 1167.82 ÷ 970.4 = 1.2034 and if the same amount of heat had been 
 absorbed under standard conditions as was absorbed in the trial 
 condition, 1.2034 times the amount of steam would have been generated. 
 Expressed as a formula for use with any set of conditions, the factor 
 is, 
   
    H - h 
 F = -----     (2) 
    970.4 
   
 Where H = the total heat of steam above 32 degrees Fahrenheit from steam 
          tables, 
      h = sensible heat of feed water above 32 degrees Fahrenheit from 
          Table 22. 
   
 In the form above, the factor may be determined with either saturated or 
 superheated steam, provided that in the latter case values of H are 
 available for varying degrees of superheat and pressures. 
   
 Where such values are not available, the form becomes, 
   
    H - h + s(t_{sup} - t_{sat}) 
 F = ----------------------------     (3) 
                970.4 
   
 Where             s = mean specific heat of superheated steam at the 
                      pressure existing in the trial from saturated 
                      steam to the temperature existing in the trial, 
            t_{sup} = final temperature of steam, 
            t_{sat} = temperature of saturated steam, corresponding to 
                     pressure existing, 
 (t_{sup} - t_{sat}) = degrees of superheat. 
   
 The specific heat of superheated steam will be taken up later. 
   
 Table 19 gives factors of evaporation for saturated steam boiler trials 
 to cover a large range of conditions. Except for the most refined work, 
 intermediate values may be determined by interpolation. 
   
 Steam gauges indicate the pressure above the atmosphere. As has been 
 pointed out, the atmospheric pressure changes according to the altitude 
 and the variation in the barometer. Hence, calculations involving the 
 properties of steam are based on _absolute_ pressures, which are equal 
 to the gauge pressure plus the atmospheric pressure in pounds to the 
 square inch. This latter is generally assumed to be 14.7 pounds per 
 square inch at sea level, but for other levels it must be determined 
 from the barometric reading at that place. 
   
 Vacuum gauges indicate the difference, expressed in inches of mercury, 
 between atmospheric pressure and the pressure within the vessel to which 
 the gauge is attached. For approximate purposes, 2.04 inches height of 
 mercury may be considered equal to a pressure of one pound per square 
 inch at the ordinary temperatures at which mercury gauges are used. 
 Hence for any reading of the vacuum gauge in inches, G, the absolute 
 pressure for any barometer reading in inches, B, will be (B - G) ÷ 2.04. 
 If the barometer is 30 inches measured at ordinary temperatures and not 
 corrected to 32 degrees Fahrenheit and the vacuum gauge 24 inches, the 
 absolute pressure will be (30 - 24) ÷ 2.04 = 2.9 pounds per square inch. 
   
                                TABLE 19 
   
                        FACTORS OF EVAPORATION 
                CALCULATED FROM MARKS AND DAVIS TABLES 
   
 ______________________________________________________________________ 
 |       |                                                             | 
 |Feed   |                                                             | 
 |Temp- |                                                             | 
 |erature|                                                              | 
 |Degrees|                   Steam Pressure by Gauge                   | 
 |Fahren-|                                                             | 
 |heit   |                                                             | 
 |_______|______________________________________________________________| 
 |       |       |       |       |       |       |       |       | 
 |       |   50 |   60 |   70 |   80 |   90 |   100 |   110 | 
 |_______|________|________|________|________|________|________|________| 
 |       |       |       |       |       |       |       |       | 
 |   32 | 1.2143 | 1.2170 | 1.2194 | 1.2215 | 1.2233 | 1.2233 | 1.2265 | 
 |   40 | 1.2060 | 1.2087 | 1.2111 | 1.2131 | 1.2150 | 1.2168 | 1.2181 | 
 | 50 | 1.1957 | 1.1984 | 1.2008 | 1.2028 | 1.2047 | 1.2065 | 1.2079 | 
 |   60 | 1.1854 | 1.1881 | 1.1905 | 1.1925 | 1.1944 | 1.1961 | 1.1976 | 
 |   70 | 1.1750 | 1.1778 | 1.1802 | 1.1822 | 1.1841 | 1.1859 | 1.1873 | 
 |   80 | 1.1649 | 1.1675 | 1.1699 | 1.1720 | 1.1738 | 1.1756 | 1.1770 | 
 |   90 | 1.1545 | 1.1572 | 1.1596 | 1.1617 | 1.1636 | 1.1653 | 1.1668 | 
 | 100 | 1.1443 | 1.1470 | 1.1493 | 1.1514 | 1.1533 | 1.1550 | 1.1565 | 
 | 110 | 1.1340 | 1.1367 | 1.1391 | 1.1411 | 1.1430 | 1.1448 | 1.1462 | 
 | 120 | 1.1237 | 1.1264 | 1.1288 | 1.1309 | 1.1327 | 1.1345 | 1.1359 | 
 | 130 | 1.1134 | 1.1161 | 1.1185 | 1.1206 | 1.1225 | 1.1242 | 1.1257 | 
 | 140 | 1.1031 | 1.1058 | 1.1082 | 1.1103 | 1.1122 | 1.1139 | 1.1154 | 
 | 150 | 1.0928 | 1.0955 | 1.0979 | 1.1000 | 1.1019 | 1.1036 | 1.1051 | 
 | 160 | 1.0825 | 1.0852 | 1.0876 | 1.0897 | 1.0916 | 1.0933 | 1.0948 | 
 | 170 | 1.0722 | 1.0749 | 1.0773 | 1.0794 | 1.0813 | 1.0830 | 1.0845 | 
 | 180 | 1.0619 | 1.0646 | 1.0670 | 1.0691 | 1.0709 | 1.0727 | 1.0741 | 
 | 190 | 1.0516 | 1.0543 | 1.0567 | 1.0587 | 1.0606 | 1.0624 | 1.0638 | 
 | 200 | 1.0412 | 1.0439 | 1.0463 | 1.0484 | 1.0503 | 1.0520 | 1.0535 | 
 | 210 | 1.0309 | 1.0336 | 1.0360 | 1.0380 | 1.0399 | 1.0417 | 1.0432 | 
 |_______|________|________|________|________|________|________|________| 
 ______________________________________________________________________ 
 |       |                                                             | 
 |Feed   |                                                             | 
 |Temp- |                                                             | 
 |erature|                                                             | 
 |Degrees|                   Steam Pressure by Gauge                   | 
 |Fahren-|                                                              | 
 |heit   |                                                             | 
 |_______|______________________________________________________________| 
 |       |       |       |       |       |       |       |       | 
 |       |   120 |   130 |   140 |   150 |   160 |   170 |   180 | 
 |_______|________|________|________|________|________|________|________| 
 |       |       |       |       |       |       |       |       | 
 |   32 | 1.2280 | 1.2292 | 1.2304 | 1.2314 | 1.2323 | 1.2333 | 1.2342 | 
 |   40 | 1.2196 | 1.2209 | 1.2221 | 1.2231 | 1.2241 | 1.2250 | 1.2259 | 
 |   50 | 1.2093 | 1.2106 | 1.2117 | 1.2128 | 1.2137 | 1.2147 | 1.2156 | 
 |   60 | 1.1990 | 1.2003 | 1.2014 | 1.2025 | 1.2034 | 1.2044 | 1.2053 | 
 |   70 | 1.1887 | 1.1900 | 1.1911 | 1.1922 | 1.1931 | 1.1941 | 1.1950 | 
 |   80 | 1.1785 | 1.1797 | 1.1809 | 1.1819 | 1.1828 | 1.1838 | 1.1847 | 
 |   90 | 1.1682 | 1.1695 | 1.1706 | 1.1717 | 1.1725 | 1.1735 | 1.1744 | 
 | 100 | 1.1579 | 1.1592 | 1.1603 | 1.1614 | 1.1623 | 1.1633 | 1.1642 | 
 | 110 | 1.1477 | 1.1489 | 1.1500 | 1.1511 | 1.1520 | 1.1530 | 1.1539 | 
 | 120 | 1.1374 | 1.1386 | 1.1398 | 1.1408 | 1.1418 | 1.1427 | 1.1436 | 
 | 130 | 1.1271 | 1.1284 | 1.1295 | 1.1305 | 1.1315 | 1.1324 | 1.1333 | 
 | 140 | 1.1168 | 1.1181 | 1.1192 | 1.1203 | 1.1212 | 1.1221 | 1.1230 | 
 | 150 | 1.1065 | 1.1078 | 1.1089 | 1.1099 | 1.1109 | 1.1118 | 1.1127 | 
 | 160 | 1.0962 | 1.0975 | 1.0986 | 1.0997 | 1.1006 | 1.1015 | 1.1024 | 
 | 170 | 1.0859 | 1.0872 | 1.0883 | 1.0893 | 1.0903 | 1.0912 | 1.0921 | 
 | 180 | 1.0756 | 1.0768 | 1.0780 | 1.0790 | 1.0800 | 1.0809 | 1.0818 | 
 | 190 | 1.0653 | 1.0665 | 1.0676 | 1.0687 | 1.0696 | 1.0706 | 1.0715 | 
 | 200 | 1.0549 | 1.0562 | 1.0573 | 1.0584 | 1.0593 | 1.0602 | 1.0611 | 
 | 210 | 1.0446 | 1.0458 | 1.0469 | 1.0480 | 1.0489 | 1.0499 | 1.0508 | 
 |_______|________|________|________|________|________|________|________| 
 ______________________________________________________________________ 
 |       |                                                            | 
 |Feed   |                                                             | 
 |Temp- |                                                             | 
 |erature|                                                             | 
 |Degrees|                  Steam Pressure by Gauge                   | 
 |Fahren-|                                                             | 
 |heit   |                                                             | 
 |_______|______________________________________________________________| 
 |       |       |       |       |       |       |       |       | 
 |       |   190 |   200 |   210 |   220 |   230 |   240 |   250 | 
 |_______|________|________|________|________|________|________|________| 
 |       |        |       |       |       |       |       |       | 
 |   32 | 1.2350 | 1.2357 | 1.2364 | 1.2372 | 1.2378 | 1.2384 | 1.2390 | 
 |   40 | 1.2267 | 1.2274 | 1.2282 | 1.2289 | 1.2295 | 1.2301 | 1.2307 | 
 |   50 | 1.2164 | 1.2171 | 1.2178 | 1.2186 | 1.2192 | 1.2198 | 1.2204 | 
 |   60 | 1.2061 | 1.2068 | 1.2075 | 1.2083 | 1.2089 | 1.2095 | 1.2101 | 
 |   70 | 1.1958 | 1.1965 | 1.1972 | 1.1980 | 1.1986 | 1.1992 | 1.1998 | 
 |   80 | 1.1855 | 1.1863 | 1.1869 | 1.1877 | 1.1883 | 1.1889 | 1.1895 | 
 |   90 | 1.1750 | 1.1760 | 1.1766 | 1.1774 | 1.1780 | 1.1786 | 1.1792 | 
 | 100 | 1.1650 | 1.1657 | 1.1664 | 1.1671 | 1.1678 | 1.1684 | 1.1690 | 
 | 110 | 1.1547 | 1.1554 | 1.1562 | 1.1569 | 1.1575 | 1.1581 | 1.1587 | 
 | 120 | 1.1444 | 1.1452 | 1.1459 | 1.1466 | 1.1472 | 1.1478 | 1.1484 | 
 | 130 | 1.1341 | 1.1349 | 1.1356 | 1.1363 | 1.1369 | 1.1375 | 1.1381 | 
 | 140 | 1.1239 | 1.1246 | 1.1253 | 1.1260 | 1.1266 | 1.1272 | 1.1278 | 
 | 150 | 1.1136 | 1.1143 | 1.1150 | 1.1157 | 1.1163 | 1.1169 | 1.1176 | 
 | 160 | 1.1033 | 1.1040 | 1.1047 | 1.1054 | 1.1060 | 1.1066 | 1.1073 | 
 | 170 | 1.0930 | 1.0937 | 1.0944 | 1.0951 | 1.0957 | 1.0963 | 1.0969 | 
 | 180 | 1.0826 | 1.0834 | 1.0841 | 1.0848 | 1.0854 | 1.0860 | 1.0866 | 
 | 190 | 1.0723 | 1.0730 | 1.0737 | 1.0745 | 1.0751 | 1.0757 | 1.0763 | 
 | 200 | 1.0620 | 1.0627 | 1.0634 | 1.0641 | 1.0647 | 1.0653 | 1.0660 | 
 | 210 | 1.0516 | 1.0523 | 1.0530 | 1.0538 | 1.0544 | 1.0550 | 1.0556 | 
 |_______|________|________|________|________|________|________|________| 
   
 The temperature, pressure and other properties of steam for varying 
 amounts of vacuum and the pressure above vacuum corresponding to each 
 inch of reading of the vacuum gauge are given in Table 20. 
   
                                TABLE 20 
   
        PROPERTIES OF SATURATED STEAM FOR VARYING AMOUNTS OF VACUUM 
                  CALCULATED FROM MARKS AND DAVIS TABLES 
 ______________________________________________________________________ 
 |       |         |         |           |       |       |         | 
 |       |         |         | Heat of | Latent | Total |         | 
 |       |         | Temp- | the Liquid| Heat   | Heat   |         | 
 |       |         | erature |   Above   | Above | Above |Density or| 
 |       | Absolute | Degrees |   32 De- | 32 De- | 32 De- |Weight per| 
 | Vacuum | Pressure | Fahren- |   grees   | grees | grees |Cubic Foot| 
 |Ins. Hg.| Pounds | heit   | B. t. u. |B. t. u.|B. t. u.| Pounds | 
 |________|__________|_________|___________|________|________|__________| 
 |       |         |         |           |       |       |         | 
 |   29.5 |   .207 |   54.1 |   22.18 | 1061.0 | 1083.2 | 0.000678 | 
 |   29   |   .452 |   76.6 |   44.64 | 1048.7 | 1093.3 | 0.001415 | 
 |   28.5 |   .698 |   90.1 |   58.09 | 1041.1 | 1099.2 | 0.002137 | 
 |   28   |   .944 |   99.9 |   67.87 | 1035.6 | 1103.5 | 0.002843 | 
 |   27   |   1.44   | 112.5 |   80.4   | 1028.6 | 1109.0 | 0.00421 | 
 |   26   |   1.93   | 124.5 |   92.3   | 1022.0 | 1114.3 | 0.00577 | 
 |   25   |   2.42   | 132.6 |   100.5   | 1017.3 | 1117.8 | 0.00689 | 
 |   24   |   2.91   | 140.1 |   108.0   | 1013.1 | 1121.1 | 0.00821 | 
 |   22   |   3.89   | 151.7 |   119.6   | 1006.4 | 1126.0 | 0.01078 | 
 |   20   |   4.87   | 161.1 |   128.9   | 1001.0 | 1129.9 | 0.01331 | 
 |   18   |   5.86   | 168.9 |   136.8   | 996.4 | 1133.2 | 0.01581 | 
 |   16   |   6.84   | 175.8 |   143.6   | 992.4 | 1136.0 | 0.01827 | 
 |   14   |   7.82   | 181.8 |   149.7   | 988.8 | 1138.5 | 0.02070 | 
 |   12   |   8.80   | 187.2 |   155.1   | 985.6 | 1140.7 | 0.02312 | 
 |   10   |   9.79   | 192.2 |   160.1   | 982.6 | 1142.7 | 0.02554 | 
 |   5   | 12.24   | 202.9 |   170.8   | 976.0 | 1146.8 | 0.03148 | 
 |________|__________|_________|___________|________|________|__________| 
   
 From the steam tables, the condensed Table 21 of the properties of steam 
 at different pressures may be constructed. From such a table there may 
 be drawn the following conclusions. 
   
                      TABLE 21 
   
            VARIATION IN PROPERTIES OF 
            SATURATED STEAM WITH PRESSURE 
 ___________________________________________________ 
 |         |           |         |       |       | 
 | Pressure |Temperature | Heat of | Latent | Total | 
 | Pounds | Degrees   | Liquid | Heat | Heat   | 
 | Absolute | Fahrenheit |B. t. u. |B. t. u.|B. t. u.| 
 |__________|____________|_________|________|________| 
 |         |           |         |       |       | 
 |   14.7   |   212.0   | 180.0 | 970.4 | 1150.4 | 
 |   20.0   |   228.0   | 196.1 | 960.0 | 1156.2 | 
 | 100.0   |   327.8   | 298.3 | 888.0 | 1186.3 | 
 | 300.0   |   417.5   | 392.7 | 811.3 | 1204.1 | 
 |__________|____________|_________|________|________| 
   
 As the pressure and temperature increase, the latent heat decreases. 
 This decrease, however, is less rapid than the corresponding increase in 
 the heat of the liquid and hence the total heat increases with an 
 increase in the pressure and temperature. The percentage increase in the 
 total heat is small, being 0.5, 3.1, and 4.7 per cent for 20, 100, and 
 300 pounds absolute pressure respectively above the total heat in one 
 pound of steam at 14.7 pounds absolute. The temperatures, on the other 
 hand, increase at the rates of 7.5, 54.6, and 96.9 per cent. The 
 efficiency of a perfect steam engine is proportional to the expression 
 (t - t_{1})/t in which t and t_{1} are the absolute temperatures of the 
 saturated steam at admission and exhaust respectively. While actual 
 engines only approximate the ideal engine in efficiency, yet they follow 
 the same general law. Since the exhaust temperature cannot be lowered 
 beyond present practice, it follows that the only available method of 
 increasing the efficiency is by an increase in the temperature of the 
 steam at admission. How this may be accomplished by an increase of 
 pressure is clearly shown, for the increase of fuel necessary to 
 increase the pressure is negligible, as shown by the total heat, while 
 the increase in economy, due to the higher pressure, will result 
 directly from the rapid increase of the corresponding temperature. 
   
              TABLE 22 
   
      HEAT UNITS PER POUND AND 
 WEIGHT PER CUBIC FOOT OF WATER 
 BETWEEN 32 DEGREES FAHRENHEIT AND 
        340 DEGREES FAHRENHEIT 
 _________________________________ 
 |           |         |          | 
 |Temperature|Heat Units| Weight | 
 | Degrees |   per   |   per   | 
 | Fahrenheit| Pound   |Cubic Foot| 
 |___________|__________|__________| 
 |           |         |         | 
 |     32   |   0.00 |   62.42 | 
 |     33   |   1.01 |   62.42 | 
 |     34   |   2.01 |   62.42 | 
 |     35   |   3.02 |   62.43 | 
 |     36   |   4.03 |   62.43 | 
 |     37   |   5.04 |   62.43 | 
 |     38   |   6.04 |   62.43 | 
 |     39   |   7.05 |   62.43 | 
 |     40   |   8.05 |   62.43 | 
 |    41   |   9.05 |   62.43 | 
 |     42   |   10.06 |   62.43 | 
 |     43   |   11.06 |   62.43 | 
 |     44   |   12.06 |   62.43 | 
 |     45   |   13.07 |   62.42 | 
 |     46   |   14.07 |   62.42 | 
 |     47   |   15.07 |   62.42 | 
 |     48   |   16.07 |   62.42 | 
 |     49   |   17.08 |   62.42 | 
 |     50   |   18.08 |   62.42 | 
 |     51   |   19.08 |   62.41 | 
 |     52   |   20.08 |   62.41 | 
 |     53   |   21.08 |   62.41 | 
 |     54   |   22.08 |   62.40 | 
 |     55   |   23.08 |   62.40 | 
 |     56   |   24.08 |   62.39 | 
 |     57   |   25.08 |   62.39 | 
 |     58   |   26.08 |   62.38 | 
 |     59   |   27.08 |   62.37 | 
 |     60   |   28.08 |   62.37 | 
 |     61   |   29.08 |   62.36 | 
 |     62   | 30.08 |   62.36 | 
 |     63   |   31.07 |   62.35 | 
 |     64   |   32.07 |   62.35 | 
 |     65   |   33.07 |   62.34 | 
 |     66   |   34.07 |   62.33 | 
 |     67   |   35.07 |   62.33 | 
 |     68   |   36.07 |   62.32 | 
 |     69   |   37.06 |   62.31 | 
 |     70   |   38.06 |   62.30 | 
 |     71   |   39.06 |   62.30 | 
 |     72   |   40.05 |   62.29 | 
 |     73   |   41.05 |   62.28 | 
 |     74   |   42.05 |   62.27 | 
 |     75   |   42.05 |   62.26 | 
 |     76   |   44.04 |   62.26 | 
 |     77   |   45.04 |   62.25 | 
 |     78   |   46.04 |   62.24 | 
 |     79   |   47.04 |   62.23 | 
 |     80   |   48.03 |   62.22 | 
 |     81   |   49.03 |   62.21 | 
 |     82   |   50.03 |   62.20 | 
 |     83   |   51.02 |   62.19 | 
 |     84   |   52.02 |   62.18 | 
 |     85   |   53.02 |   62.17 | 
 |     86   |   54.01 |   62.16 | 
 |     87   |   55.01 |   62.15 | 
 |     88   |   56.01 |   62.14 | 
 |     89   |   57.00 |   62.13 | 
 |     90   |   58.00 |   62.12 | 
 |     91   |   59.00 |   62.11 | 
 |     92   |   60.00 |   62.09 | 
 |     93   |   60.99 |   62.08 | 
 |     94   |   61.99 |   62.07 | 
 |     95   |   62.99 |   62.06 | 
 |     96   |   63.98 |   62.05 | 
 |     97   |   64.98 |   62.04 | 
 |     98   |   65.98 |   62.03 | 
 |     99   |   66.97 |   62.02 | 
 |   100   |   67.97 |   62.00 | 
 |   101   |   68.97 |   61.99 | 
 |   102   |   69.96 |   61.98 | 
 |   103   |   70.96 |   61.97 | 
 |   104   |   71.96 |   61.95 | 
 |  105   |   72.95 |   61.94 | 
 |   106   |   73.95 |   61.93 | 
 |   107   |   74.95 |   61.91 | 
 |   108   |   75.95 |   61.90 | 
 |   109   |   76.94 |   61.88 | 
 |   110   |   77.94 |   61.86 | 
 |   111   |   78.94 |   61.85 | 
 |   112   |   79.93 |   61.83 | 
 |   113   |   80.93 |   61.82 | 
 |   114   |   81.93 |   61.80 | 
 |   115   |   82.92 |   61.79 | 
 |   116   |   83.92 |   61.77 | 
 |   117   |   84.92 |   61.75 | 
 |   118   |   85.92 |   61.74 | 
 |   119   |   86.91 |   61.72 | 
 |   120   |   87.91 |   61.71 | 
 |   121   |   88.91 |   61.69 | 
 |   122   |   89.91 |   61.68 | 
 |   123   |   90.90 |   61.66 | 
 |   124   |   91.90 |   61.65 | 
 |   125   |   92.90 |   61.63 | 
 |   126   | 93.90 |   61.61 | 
 |   127   |   94.89 |   61.59 | 
 |   128   |   95.89 |   61.58 | 
 |   129   |   96.89 |   61.56 | 
 |   130   |   97.89 |   61.55 | 
 |   131   |   98.89 |   61.53 | 
 |   132   |   99.88 |   61.52 | 
 |   133   | 100.88 |   61.50 | 
 |   134   | 101.88 |   61.49 | 
 |   135   | 102.88 |   61.47 | 
 |   136   | 103.88 |   61.45 | 
 |   137   | 104.87 |   61.43 | 
 |   138   | 105.87 |   61.41 | 
 |   139   | 106.87 |   61.40 | 
 |   140   | 107.87 |   61.38 | 
 |   141   | 108.87 |   61.36 | 
 |   142   | 109.87 |   61.34 | 
 |   143   | 110.87 |   61.33 | 
 |   144   | 111.87 |   61.31 | 
 |   145   | 112.86 |   61.29 | 
 |   146   | 113.86 |   61.27 | 
 |   147   | 114.86 |   61.25 | 
 |   148   | 115.86 |   61.24 | 
 |   149   | 116.86 |   61.22 | 
 |   150   | 117.86 |   61.20 | 
 |   151   | 118.86 |   61.18 | 
 |   152   | 119.86 |   61.16 | 
 |   153   | 120.86 |   61.14 | 
 |   154   | 121.86 |   61.12 | 
 |   155   | 122.86 |   61.10 | 
 |   156   | 123.86 |   61.08 | 
 |   157   | 124.86 |   61.06 | 
 |   158   | 125.86 |   61.04 | 
 |   159   | 126.86 |   61.02 | 
 |   160   | 127.86 |   61.00 | 
 |   161   | 128.86 |   60.98 | 
 |   162   | 129.86 |   60.96 | 
 |   163   | 130.86 |   60.94 | 
 |   164   | 131.86 |   60.92 | 
 |   165   | 132.86 |   60.90 | 
 |   166   | 133.86 |   60.88 | 
 |   167   | 134.86 |   60.86 | 
 |   168   | 135.86 |   60.84 | 
 |  169   | 136.86 |   60.82 | 
 |   170   | 137.87 |   60.80 | 
 |   171   | 138.87 |   60.78 | 
 |   172   | 139.87 |   60.76 | 
 |   173   | 140.87 |   60.73 | 
 |   174   | 141.87 |   60.71 | 
 |   175   | 142.87 |   60.69 | 
 |   176   | 143.87 |   60.67 | 
 |   177   | 144.88 |   60.65 | 
 |   178   | 145.88 |   60.62 | 
 |   179   | 146.88 |   60.60 | 
 |   180   | 147.88 |   60.58 | 
 |   181   | 148.88 |   60.56 | 
 |   182   | 149.89 |   60.53 | 
 |   183   | 150.89 |   60.51 | 
 |   184   | 151.89 |   60.49 | 
 |   185   | 152.89 |   60.47 | 
 |   186   | 153.89 |   60.45 | 
 |   187   | 154.90 |   60.42 | 
 |   188   | 155.90 |   60.40 | 
 |   189   | 156.90 |   60.38 | 
 |   190   | 157,91 |   60.36 | 
 |   191   | 158.91 |   60.33 | 
 |   192   | 159.91 |   60.31 | 
 |   193   | 160.91 |   60.29 | 
 |   194   | 161.92 |   60.27 | 
 |   195   | 162.92 |   60.24 | 
 |   196   | 163.92 |   60.22 | 
 |   197   | 164.93 |   60.19 | 
 |   198   | 165.93 |   60.17 | 
 |   199   | 166.94 |   60.15 | 
 |   200   | 167.94 |   60.12 | 
 |   201   | 168.94 |   60.10 | 
 |   202   | 169.95 |   60.07 | 
 |   203   | 170.95 |   60.05 | 
 |   204   | 171.96 |   60.02 | 
 |   205   | 172.96 |   60.00 | 
 |   206   | 173.97 |   59.98 | 
 |   207   | 174.97 |   59.95 | 
 |   208   | 175.98 |   59.93 | 
 |   209   | 176.98 |   59.90 | 
 |   210   | 177.99 |   59.88 | 
 |   211   | 178.99 |   59.85 | 
 |   212   | 180.00 |   59.83 | 
 |   213   | 181.0   |   59.80 | 
 |   214   | 182.0   |   59.78 | 
 |   215   | 183.0   |   59.75 | 
 |   216   | 184.0   |   59.73 | 
 |   217   | 185.0   |   59.70 | 
 |   218   | 186.1   |   59.68 | 
 |   219   | 187.1   |   59.65 | 
 |   220   | 188.1   |   59.63 | 
 |   221   | 189.1   |   59.60 | 
 |   222   | 190.1   |   59.58 | 
 |   223   | 191.1   |   59.55 | 
 |   224   | 192.1   |   59.53 | 
 |   225   | 193.1   |   59.50 | 
 |   226   | 194.1   |   59.48 | 
 |   227   | 195.2   |   59.45 | 
 |   228   | 196.2   |   59.42 | 
 |   229   | 197.2   |   59.40 | 
 |   230   | 198.2   |   59.37 | 
 |   231   | 199.2   |   59.34 | 
 |   232   | 200.2   |   59.32 | 
 |  233   | 201.2   |   59.29 | 
 |   234   | 202.2   |   59.27 | 
 |   235   | 203.2   |   59.24 | 
 |   236   | 204.2   |   59.21 | 
 |   237   | 205.3   |   59.19 | 
 |   238   | 206.3   |   59.16 | 
 |   239   | 207.3   |   59.14 | 
 |   240   | 208.3   |   59.11 | 
 |   241   | 209.3   |   59.08 | 
 |   242   | 210.3   |   59.05 | 
 |   243   | 211.4   |   59.03 | 
 |   244   | 212.4   |   59.00 | 
 |   245   | 213.4   |   58.97 | 
 |   246   | 214.4   |   58.94 | 
 |   247   | 215.4   |   58.91 | 
 |   248   | 216.4   |   58.89 | 
 |   249   | 217.4   |   58.86 | 
 |   250   | 218.5   |   58.83 | 
 |   260   | 228.6   |   58.55 | 
 |   270   | 238.8   |   58.26 | 
 |   280   | 249.0   |   57.96 | 
 |   290   | 259.3   |   57.65 | 
 |   300   | 269.6   |   57.33 | 
 |   310   | 279.9   |   57.00 | 
 |   320   | 290.2   |   56.66 | 
 |   330   | 300.6   |   56.30 | 
 |   340   | 311.0   |   55.94 | 
 |___________|__________|__________| 
   
 The gain due to superheat cannot be predicted from the formula for the 
 efficiency of a perfect steam engine given on page 119. This formula is 
 not applicable in cases where superheat is present since only a 
 relatively small amount of the heat in the steam is imparted at the 
 maximum or superheated temperature. 
   
 The advantage of the use of high pressure steam may be also indicated by 
 considering the question from the aspect of volume. With an increase of 
 pressure comes a decrease in volume, thus one pound of saturated steam 
 at 100 pounds absolute pressure occupies 4.43 cubic feet, while at 200 
 pounds pressure it occupies 2.29 cubic feet. If then, in separate 
 cylinders of the same dimensions, one pound of steam at 100 pounds 
 absolute pressure and one pound at 200 pounds absolute pressure enter 
 and are allowed to expand to the full volume of each cylinder, the 
 high-pressure steam, having more room and a greater range for expansion 
 than the low-pressure steam, will thus do more work. This increase in 
 the amount of work, as was the increase in temperature, is large 
 relative to the additional fuel required as indicated by the total heat. 
 In general, it may be stated that the fuel required to impart a given 
 amount of heat to a boiler is practically independent of the steam 
 pressure, since the temperature of the fire is so high as compared with 
 the steam temperature that a variation in the steam temperature does not 
 produce an appreciable effect. 
   
 The formulae for the algebraic expression of the relation between 
 saturated steam pressures, temperatures and steam volumes have been up 
 to the present time empirical. These relations have, however, been 
 determined by experiment and, from the experimental data, tables have 
 been computed which render unnecessary the use of empirical formulae. 
 Such formulae may be found in any standard work of thermo-dynamics. The 
 following tables cover all practical cases. 
   
 Table 22 gives the heat units contained in water above 32 degrees 
 Fahrenheit at different temperatures. 
   
 Table 23 gives the properties of saturated steam for various pressures. 
   
 Table 24 gives the properties of superheated steam at various pressures 
 and temperatures. 
   
 These tables are based on those computed by Lionel S. Marks and Harvey 
 Davis, these being generally accepted as being the most correct. 
 
   
                                TABLE 23 
   
                    PROPERTIES OF SATURATED STEAM 
   
                    REPRODUCED BY PERMISSION FROM 
              MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" 
              (Copyright, 1909, by Longmans, Green & Co.) 
 ____________________________________________________________________ 
 |Pressure,| Temper- |Specific Vol-|Heat of   |Latent Heat|Total Heat| 
 | Pounds |ature De-| ume Cu. Ft. |the Liquid,| of Evap., |of Steam, | 
 |Absolute |grees F. | per Pound | B. t. u. | B. t. u. | B. t. u. | 
 |_________|_________|_____________|___________|___________|__________| 
 |   1     | 101.83 |   333.0     |   69.8   | 1034.6   | 1104.4 | 
 |   2     | 126.15 |   173.5     |   94.0   | 1021.0   | 1115.0 | 
 |   3     | 141.52 |   118.5     |   109.4   | 1012.3   | 1121.6 | 
 |   4     | 153.01 |   90.5     |   120.9   | 1005.7   | 1126.5 | 
 |   5     | 162.28 |   73.33   |   130.1   | 1000.3   | 1130.5 | 
 |   6     | 170.06 |   61.89   |   137.9   |  995.8   | 1133.7 | 
 |   7     | 176.85 |   53.56   |   144.7   |   991.8   | 1136.5 | 
 |   8     | 182.86 |   47.27   |   150.8   |   988.2   | 1139.0 | 
 |   9     | 188.27 |   42.36   |   156.2   |   985.0   | 1141.1 | 
 | 10     | 193.22 |   38.38   |   161.1   |   982.0   | 1143.1 | 
 | 11     | 197.75 |   35.10   |   165.7   |   979.2   | 1144.9 | 
 | 12     | 201.96 |   32.36   |   169.9   |   976.6   | 1146.5 | 
 | 13     | 205.87 |   30.03   |   173.8   |   974.2   | 1148.0 | 
 | 14     | 209.55 |   28.02   |   177.5   |   971.9   | 1149.4 | 
 | 15     | 213.0   |   26.27   |   181.0   |   969.7   | 1150.7 | 
 | 16     | 216.3   |   24.79   |   184.4   |   967.6   | 1152.0 | 
 | 17     | 219.4   |   23.38   |   187.5   |   965.6   | 1153.1 | 
 | 18     | 222.4   |   22.16   |   190.5   |   963.7   | 1154.2 | 
 | 19     | 225.2   |   21.07   |   193.4   |   961.8   | 1155.2 | 
 | 20     | 228.0   |   20.08   |   196.1   |   960.0   | 1156.2 | 
 | 22    | 233.1   |   18.37   |   201.3   |   956.7   | 1158.0 | 
 | 24     | 237.8   |   16.93   |   206.1   |   953.5   | 1159.6 | 
 | 26     | 242.2   |   15.72   |   210.6   |   950.6   | 1161.2 | 
 | 28     | 246.4   |   14.67   |   214.8   |   947.8   | 1162.6 | 
 | 30     | 250.3   |   13.74   |   218.8   |   945.1   | 1163.9 | 
 | 32     | 254.1   |   12.93   |   222.6   |   942.5   | 1165.1 | 
 | 34     | 257.6   |   12.22   |   226.2   |   940.1   | 1166.3 | 
 | 36     | 261.0   |    11.58   |   229.6   |   937.7   | 1167.3 | 
 | 38     | 264.2   |   11.01   |   232.9   |   935.5   | 1168.4 | 
 | 40     | 267.3   |   10.49   |   236.1   |   933.3   | 1169.4 | 
 | 42     | 270.2   |   10.02   |   239.1   |   931.2   | 1170.3 | 
 | 44     | 273.1   |     9.59   |   242.0   |   929.2   | 1171.2 | 
 | 46     | 275.8   |     9.20   |   244.8   |   927.2   | 1172.0 | 
 | 48     | 278.5   |     8.84   |   247.5   |   925.3   | 1172.8 | 
 | 50     | 281.0   |     8.51   | 250.1   |   923.5   | 1173.6 | 
 | 52     | 283.5   |     8.20   |   252.6   |   921.7   | 1174.3 | 
 | 54     | 285.9   |     7.91   |   255.1   |   919.9   | 1175.0 | 
 | 56     | 288.2   |     7.65   |   257.5   |   918.2   | 1175.7 | 
 | 58   | 290.5   |     7.40   |   259.8   |   916.5   | 1176.4 | 
 | 60     | 292.7   |     7.17   |   262.1   |   914.9   | 1177.0 | 
 | 62     | 294.9   |     6.95   |   264.3   |   913.3   | 1177.6 | 
 | 64     | 297.0   |     6.75   |   266.4   |   911.8   | 1178.2 | 
 | 66     | 299.0   |     6.56   |   268.5   |   910.2   | 1178.8 | 
 | 68     | 301.0   |     6.38   |   270.6   |   908.7   | 1179.3 | 
 | 70     | 302.9   |     6.20   |   272.6   |   907.2   | 1179.8 | 
 | 72     | 304.8   |    6.04   |   274.5   |   905.8   | 1180.4 | 
 | 74     | 306.7   |     5.89   |   276.5   |   904.4   | 1180.9 | 
 | 76     | 308.5   |     5.74   |   278.3   |   903.0   | 1181.4 | 
 | 78     | 310.3   |     5.60   |   280.2   |   901.7   | 1181.8 | 
 | 80     | 312.0   |     5.47   |   282.0   |   900.3   | 1182.3 | 
 | 82     | 313.8   |     5.34   |   283.8   |   899.0   | 1182.8 | 
 | 84     | 315.4   |     5.22   |   285.5   |   897.7   | 1183.2 | 
 | 86     | 317.1   |     5.10   |   287.2   |   896.4   | 1183.6 | 
 | 88     | 318.7   |     5.00   |   288.9   |   895.2   | 1184.0 | 
 | 90     | 320.3   |     4.89   |   290.5   |   893.9   | 1184.4 | 
 | 92     | 321.8   |     4.79   |   292.1   |   892.7   | 1184.8 | 
 | 94     | 323.4   |     4.69   |   293.7   |   891.5   | 1185.2 | 
 | 96     | 324.9   |     4.60   |   295.3   |   890.3   | 1185.6 | 
 | 98     | 326.4   |     4.51   |   296.8   |   889.2   | 1186.0 | 
 | 100     | 327.8   |     4.429   |   298.3   |   888.0   | 1186.3 | 
 | 105     | 331.4   |     4.230   |   302.0   |   885.2   | 1187.2 | 
 | 110     | 334.8   |     4.047   |   305.5   |   882.5   | 1188.0 | 
 | 115     | 338.1   |     3.880   |   309.0   |   879.8   | 1188.8 | 
 | 120     | 341.3   |     3.726   |   312.3   |   877.2   | 1189.6 | 
 | 125     | 344.4   |     3.583   |   315.5   |   874.7   | 1190.3 | 
 | 130     | 347.4   |     3.452   |   318.6   |   872.3   | 1191.0 | 
 | 135     | 350.3   |     3.331   |   321.7   |   869.9   | 1191.6 | 
 | 140     | 353.1   |     3.219   |   324.6   |   867.6   | 1192.2 | 
 | 145     | 355.8   |     3.112   |   327.4   |   865.4   | 1192.8 | 
 | 150     | 358.5   |     3.012   |   330.2   |   863.2   | 1193.4 | 
 | 155     | 361.0   |     2.920   |   332.9   |   861.0   | 1194.0 | 
 | 160     | 363.6   |     2.834   |   335.6   |   858.8   | 1194.5 | 
 | 165     | 366.0   |     2.753   |   338.2   |   856.8   | 1195.0 | 
 | 170     | 368.5   |     2.675   |   340.7   |   854.7   | 1195.4 | 
 | 175     | 370.8   |     2.602   |   343.2   |   852.7   | 1195.9 | 
 | 180     | 373.1   |     2.533   |   345.6   |   850.8   | 1196.4 | 
 | 185     | 375.4   |     2.468   |   348.0   |   848.8   | 1196.8 | 
 | 190     | 377.6   |     2.406   |   350.4   |   846.9  | 1197.3 | 
 | 195     | 379.8   |     2.346   |   352.7   |   845.0   | 1197.7 | 
 | 200     | 381.9   |     2.290   |   354.9   |   843.2   | 1198.1 | 
 | 205     | 384.0   |     2.237   |   357.1   |   841.4   | 1198.5 | 
 | 210     | 386.0   |     2.187   |   359.2   |   839.6   | 1198.8 | 
 | 215     | 388.0   |     2.138   |   361.4   |   837.9   | 1199.2 | 
 | 220     | 389.9   |     2.091   |   363.4   |   836.2   | 1199.6 | 
 | 225     | 391.9   |     2.046   |   365.5   |   834.4   | 1199.9 | 
 | 230     | 393.8   |     2.004   |   367.5   |   832.8   | 1200.2 | 
 | 235     | 395.6   |     1.964   |   369.4   |   831.1   | 1200.6 | 
 | 240     | 397.4   |     1.924   |   371.4   |   829.5   | 1200.9 | 
 | 245     | 399.3   |     1.887   |   373.3   |   827.9   | 1201.2 | 
 | 250     | 401.1   |     1.850   |   375.2   |   826.3   | 1201.5 | 
 |_________|_________|_____________|___________|___________|__________| 
   
 [Illustration: Portion of 6100 Horse-power Installation of Babcock & 
 Wilcox Boilers Equipped with Babcock & Wilcox Chain Grate Stokers at the 
 Campbell Street Plant of the Louisville Railway Co., Louisville, Ky. 
 This Company Operates a Total of 14,000 Horse Power of Babcock & Wilcox 
 Boilers] 
   
                              TABLE 24 
   
                 PROPERTIES OF SUPERHEATED STEAM 
   
                    REPRODUCED BY PERMISSION FROM 
            MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" 
            (Copyright, 1909, by Longmans, Green & Co.) 
 __________________________________________________________________ 
 |       |         |                                               | 
 |       |         |             Degrees of Superheat             | 
 |Pressure|         |_______________________________________________| 
 | Pounds |Saturated|       |      |       |       |       |       | 
 |Absolute| Steam |   50 | 100 | 150 | 200 | 250 | 300 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 162.3 | 212.3 | 262.3 | 312.3 | 362.3 | 412.3 | 462.3 | 
 |   5   v|   73.3 | 79.7 | 85.7 | 91.8 | 97.8 | 103.8 | 109.8 | 
 |       h| 1130.5 |1153.5 |1176.4 |1199.5 |1222.5 |1245.6 |1268.7 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 193.2 | 243.2 | 293.2 | 343.2 | 393.2 | 443.2 | 493.2 | 
 | 10   v|   38.4 | 41.5 | 44.6 | 47.7 | 50.7 | 53.7 | 56.7 | 
 |       h| 1143.1 |1166.3 |1189.5 |1212.7 |1236.0 |1259.3 |1282.5 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 213.0 | 263.0 | 313.0 | 363.0 | 413.0 | 463.0 | 513.0 | 
 | 15   v|   26.27 | 28.40| 30.46| 32.50| 34.53| 36.56| 38.58| 
 |       h| 1150.7 |1174.2 |1197.6 |1221.0 |1244.4 |1267.7 |1291.1 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 228.0 | 278.0 | 328.0 | 378.0 | 428.0 | 478.0 | 528.0 | 
 | 20   v|   20.08 | 21.69| 23.25| 24.80| 26.33| 27.85| 29.37| 
 |       h| 1156.2 |1179.9 |1203.5 |1227.1 |1250.6 |1274.1 |1297.6 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |      t| 240.1 | 290.1 | 340.1 | 390.1 | 440.1 | 490.1 | 540.1 | 
 | 25   v|   16.30 | 17.60| 18.86| 20.10| 21.32| 22.55| 23.77| 
 |       h| 1160.4 |1184.4 |1208.2 |1231.9 |1255.6 |1279.2 |1302.8 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 250.4 | 300.4 | 350.4 | 400.4 | 450.4 | 500.4 | 550.4 | 
 | 30   v|   13.74 | 14.83| 15.89| 16.93| 17.97| 18.99| 20.00| 
 |       h| 1163.9 |1188.1 |1212.1 |1236.0 |1259.7 |1283.4 |1307.1 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 259.3 | 309.3 | 359.3 | 409.3 | 459.3 | 509.3 | 559.3 | 
 | 35   v|   11.89 | 12.85| 13.75| 14.65| 15.54| 16.42| 17.30| 
 |       h| 1166.8 |1191.3 |1215.4 |1239.4 |1263.3 |1287.1 |1310.8 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 267.3 | 317.3 | 367.3 | 417.3 | 467.3 | 517.3 | 567.3 | 
 | 40   v|   10.49 | 11.33| 12.13| 12.93| 13.70| 14.48| 15.25| 
 |       h| 1169.4 |1194.0 |1218.4 |1242.4 |1266.4 |1290.3 |1314.1 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 274.5 | 324.5 | 374.5 | 424.5 | 474.5 | 524.5 | 574.5 | 
 | 45   v|   9.39 | 10.14| 10.86| 11.57| 12.27| 12.96| 13.65| 
 |       h| 1171.6 |1196.6 |1221.0 |1245.2 |1269.3 |1293.2 |1317.0 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 281.0 | 331.0 | 381.0 | 431.0 | 481.0 | 531.0 | 581.0 | 
 | 50   v|   8.51 |   9.19|   9.84| 10.48| 11.11| 11.74| 12.36| 
 |       h| 1173.6 |1198.8 |1223.4 |1247.7 |1271.8 |1295.8 |1319.7 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 287.1 | 337.1 | 387.1 | 437.1 | 487.1 | 537.1 | 587.1 | 
 | 55   v|   7.78 |   8.40|   9.00|   9.59| 10.16| 10.73| 11.30| 
 |       h| 1175.4 |1200.8 |1225.6 |1250.0 |1274.2 |1298.1 |1322.0 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 292.7 | 342.7 | 392.7 | 442.7 | 492.7 | 542.7 | 592.7 | 
 | 60   v|   7.17 |   7.75|   8.30|   8.84|   9.36|   9.89| 10.41| 
 |       h| 1177.0 |1202.6 |1227.6 |1252.1 |1276.4 |1300.4 |1324.3 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 298.0 | 348.0 | 398.0 | 448.0 | 498.0 | 548.0 | 598.0 | 
 | 65   v|   6.65 |   7.20|  7.70|   8.20|   8.69|   9.17|   9.65| 
 |       h| 1178.5 |1204.4 |1229.5 |1254.0 |1278.4 |1302.4 |1326.4 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 302.9 | 352.9 | 402.9 | 452.9 | 502.9 | 552.9 | 602.9 | 
 | 70   v|   6.20 |   6.71|   7.18|   7.65|   8.11|   8.56|   9.01| 
 |       h| 1179.8 |1205.9 |1231.2 |1255.8 |1280.2 |1304.3 |1328.3 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 307.6 | 357.6 | 407.6 | 457.6 | 507.6 | 557.6 | 607.6 | 
 | 75   v|   5.81 |   6.28|   6.73|   7.17|   7.60|   8.02|   8.44| 
 |       h| 1181.1 |1207.5 |1232.8 |1257.5 |1282.0 |1306.1 |1330.1 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 312.0 | 362.0 | 412.0 | 462.0 | 512.0 | 562.0 | 612.0 | 
 | 80   v|   5.47 |   5.92|   6.34|   6.75|   7.17|   7.56|   7.95| 
 |       h| 1182.3 |1208.8 |1234.3 |1259.0 |1283.6 |1307.8 |1331.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 316.3 | 366.3 | 416.3 | 466.3 | 516.3 | 566.3 | 616.3 | 
 | 85   v|   5.16 |   5.59|   6.99|   6.38|   6.76|   7.14|   7.51| 
 |       h| 1183.4 |1210.2 |1235.8 |1260.6 |1285.2 |1309.4 |1333.5 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 320.3 | 370.3 | 420.3 | 470.3 | 520.3 | 570.3 | 620.3 | 
 | 90   v|   4.89 |   5.29|   5.67|   6.04|   6.40|   6.76|   7.11| 
 |       h| 1184.4 |1211.4 |1237.2 |1262.0 |1286.6 |1310.8 |1334.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 324.1 | 374.1 | 424.1 | 474.1 | 524.1 | 574.1 | 624.1 | 
 | 95   v|   4.65 |   5.03|   5.39|   5.74|   6.09|   6.43|   6.76| 
 |       h| 1185.4 |1212.6 |1238.4 |1263.4 |1288.1 |1312.3 |1336.4 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 327.8 | 377.8 | 427.8 | 477.8 | 527.8 | 577.8 | 627.8 | 
 | 100   v|   4.43 |   4.79|   5.14|   5.47|   5.80|   6.12|   6.44| 
 |       h| 1186.3 |1213.8 |1239.7 |1264.7 |1289.4 |1313.6 |1337.8 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 331.4 | 381.4 | 431.4 | 481.4 | 531.4 | 581.4 | 631.4 | 
 | 105   v|   4.23 |   4.58|   4.91|   5.23|   5.54|   5.85|   6.15| 
 |       h| 1187.2 |1214.9 |1240.8 |1265.9 |1290.6 |1314.9 |1339.1 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 334.8 | 384.8 | 434.8 | 484.8 | 534.8 | 584.8 | 634.8 | 
 | 110   v|   4.05 |   4.38|   4.70|   5.01|   5.31|   5.61|   5.90| 
 |       h| 1188.0 |1215.9 |1242.0 |1267.1 |1291.9 |1316.2 |1340.4 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 338.1 | 388.1 | 438.1 | 488.1 | 538.1 | 588.1 | 638.1 | 
 | 115   v|   3.88 |   4.20|   4.51|   4.81|   5.09|   5.38|   5.66| 
 |       h| 1188.8 |1216.9 |1243.1 |1268.2 |1293.0 |1317.3 |1341.5 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 341.3 | 391.3 | 441.3 | 491.3 | 541.3 | 591.3 | 641.3 | 
 | 120   v|   3.73 |   4.04|   4.33|   4.62|   4.89|   5.17|   5.44| 
 |       h| 1189.6 |1217.9 |1244.1 |1269.3 |1294.1 |1318.4 |1342.7 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 344.4 | 394.4 | 444.4 | 494.4 | 544.4 | 594.4 | 644.4 | 
 | 125   v|   3.58 |   3.88|   4.17|   4.45|  4.71|   4.97|   5.23| 
 |       h| 1190.3 |1218.8 |1245.1 |1270.4 |1295.2 |1319.5 |1343.8 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 347.4 | 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | 
 | 130   v|   3.45 |   3.74|   4.02|   4.28|   4.54|   4.80|   5.05| 
 |       h| 1191.0 |1219.7 |1246.1 |1271.4 |1296.2 |1320.6 |1344.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 350.3 | 400.3 | 450.3 | 500.3 | 550.3 | 600.3 | 650.3 | 
 | 135   v|   3.33 |   3.61|   3.88|   4.14|   4.38|   4.63|   4.87| 
 |       h| 1191.6 |1220.6 |1247.0 |1272.3 |1297.2 |1321.6 |1345.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 353.1 | 403.1 | 453.1 | 503.1 | 553.1 | 603.1 | 653.1 | 
 | 140   v|   3.22 |   3.49|   3.75|   4.00|   4.24|   4.48|   4.71| 
 |       h| 1192.2 |1221.4 |1248.0 |1273.3 |1298.2 |1322.6 |1346.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 355.8 | 405.8 | 455.8 | 505.8 | 555.8 | 605.8 | 655.8 | 
 | 145   v|   3.12 |   3.38|   3.63|   3.87|   4.10|   4.33|   4.56| 
 |       h| 1192.8 |1222.2 |1248.8 |1274.2 |1299.1 |1323.6 |1347.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 358.5 | 408.5 | 458.5 | 508.5 | 558.5 | 608.5 | 658.5 | 
 | 150   v|   3.01 |   3.27|   3.50|   3.75|   3.97|   4.19|   4.41| 
 |       h| 1193.4 |1223.0 |1249.6 |1275.1 |1300.0 |1324.5 |1348.8 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 361.0 | 411.0 | 461.0 | 511.0 | 561.0 | 611.0 | 661.0 | 
 | 155   v|   2.92 |   3.17|   3.41|   3.63|   3.85|   4.06|   4.28| 
 |       h| 1194.0 |1223.6 |1250.5 |1276.0 |1300.8 |1325.3 |1349.7 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 363.6 | 413.6 | 463.6 | 513.6 | 563.6 | 613.6 | 663.6 | 
 | 160   v|   2.83 |   3.07|   3.30|   3.53|   3.74|   3.95|   4.15| 
 |       h| 1194.5 |1224.5 |1251.3 |1276.8 |1301.7 |1326.2 |1350.6 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 366.0 | 416.0 | 466.0 | 516.0 | 566.0 | 616.0 | 666.0 | 
 | 165   v|   2.75 |   2.99|   3.21|   3.43|   3.64|   3.84|   4.04| 
 |       h| 1195.0 |1225.2 |1252.0 |1277.6 |1302.5 |1327.1 |1351.5 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 368.5 | 418.5 | 468.5 | 518.5 | 568.5 | 618.5 | 668.5 | 
 | 170   v|   2.68 |   2.91|   3.12|   3.34|   3.54|   3.73|   3.92| 
 |       h| 1195.4 |1225.9 |1252.8 |1278.4 |1303.3 |1327.9 |1352.3 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 370.8 | 420.8 | 470.8 | 520.8 | 570.8 | 620.8 | 670.8 | 
 | 175   v|   2.60 |   2.83|   3.04|   3.24|   3.44|   3.63|   3.82| 
 |       h| 1195.9 |1226.6 |1253.6 |1279.1 |1304.1 |1328.7 |1353.2 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 373.1 | 423.1 | 473.1 | 523.1 | 573.1 | 623.1 | 673.1 | 
 | 180   v|   2.53 |   2.75|   2.96|   3.16|   3.35|   3.54|   3.72| 
 |       h| 1196.4 |1227.2 |1254.3 |1279.9 |1304.8 |1329.5 |1353.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 375.4 | 425.4 | 475.4 | 525.4 | 575.4 | 625.4 | 675.4 | 
 | 185   v|   2.47 |   2.68|   2.89|   3.08|   3.27|   3.45|  3.63| 
 |       h| 1196.8 |1227.9 |1255.0 |1280.6 |1305.6 |1330.2 |1354.7 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 377.6 | 427.6 | 477.6 | 527.6 | 577.6 | 627.6 | 677.6 | 
 | 190   v|   2.41 |   2.62|   2.81|   3.00|   3.19|   3.37|   3.55| 
 |       h| 1197.3 |1228.6 |1255.7 |1281.3 |1306.3 |1330.9 |1355.5 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 379.8 | 429.8 | 479.8 | 529.8 | 579.8 | 629.8 | 679.8 | 
 | 195   v|   2.35 |  2.55|   2.75|   2.93|   3.11|   3.29|   3.46| 
 |       h| 1197.7 |1229.2 |1256.4 |1282.0 |1307.0 |1331.6 |1356.2 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 381.9 | 431.9 | 481.9 | 531.9 | 581.9 | 631.9 | 681.9 | 
 | 200   v|   2.29 |   2.49|   2.68|   2.86|   3.04|   3.21|   3.38| 
 |       h| 1198.1 |1229.8 |1257.1 |1282.6 |1307.7 |1332.4 |1357.0 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 384.0 | 434.0 | 484.0 | 534.0 | 584.0 | 634.0 | 684.0 | 
 | 205   v|   2.24 |   2.44|   2.62|   2.80|   2.97|   3.14|   3.30| 
 |       h| 1198.5 |1230.4 |1257.7 |1283.3 |1308.3 |1333.0 |1357.7 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 386.0 | 436.0 | 486.0 | 536.0 | 586.0 | 636.0 | 686.0 | 
 | 210   v|   2.19 |   2.38|   2.56|   2.74|   2.91|   3.07|   3.23| 
 |       h| 1198.8 |1231.0 |1258.4 |1284.0 |1309.0 |1333.7 |1358.4 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 388.0 | 438.0 | 488.0 | 538.0 | 588.0 | 638.0 | 688.0 | 
 | 215   v|   2.14 |   2.33|   2.51|   2.68|   2.84|   3.00|   3.16| 
 |       h| 1199.2 |1231.6 |1259.0 |1284.6 |1309.7 |1334.4 |1359.1 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 389.9 | 439.9 | 489.9 | 539.9 | 589.9 | 639.9 | 689.9 | 
 | 220   v|   2.09 |   2.28|   2.45|   2.62|   2.78|   2.94|   3.10| 
 |       h| 1199.6 |1232.2 |1259.6 |1285.2 |1310.3 |1335.1 |1359.8 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 391.9 | 441.9 | 491.9 | 541.9 | 591.9 | 641.9 | 691.9 | 
 | 225   v|   2.05 |   2.23|   2.40|   2.57|   2.72|   2.88|   3.03| 
 |       h| 1199.9 |1232.7 |1260.2 |1285.9 |1310.9 |1335.7 |1360.3 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 393.8 | 443.8 | 493.8 | 543.8 | 593.8 | 643.8 | 693.8 | 
 | 230   v|   2.00 |   2.18|   2.35|   2.51|   2.67|   2.82|   2.97| 
 |       h| 1200.2 |1233.2 |1260.7 |1286.5 |1311.6 |1336.3 |1361.0 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 395.6 | 445.6 | 495.6 | 545.6 | 595.6 | 645.6 | 695.6 | 
 | 235   v|   1.96 |   2.14|   2.30|   2.46|   2.62|   2.77|   2.91| 
 |       h| 1200.6 |1233.8 |1261.4 |1287.1 |1312.2 |1337.0 |1361.7 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | 697.4 | 
 | 240   v|   1.92 |   2.09|   2.26|   2.42|   2.57|   2.71|   2.85| 
 |       h| 1200.9 |1234.3 |1261.9 |1287.6 |1312.8 |1337.6 |1362.3 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 399.3 | 449.3 | 499.3 | 549.3 | 599.3 | 649.3 | 699.3 | 
 | 245   v|   1.89 |   2.05|   2.22|   2.37|   2.52|   2.66|   2.80| 
 |       h| 1201.2 |1234.8 |1262.5 |1288.2 |1313.3 |1338.2 |1362.9 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 401.0 | 451.0 | 501.0 | 551.0 | 601.0 | 651.0 | 701.0 | 
 | 250   v|   1.85 |   2.02|   2.17|   2.33|   2.47|   2.61|   2.75| 
 |       h| 1201.5 |1235.4 |1263.0 |1288.8 |1313.9 |1338.8 |1363.5 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
 |       t| 402.8 | 452.8 | 502.8 | 552.8 | 602.8 | 652.8 | 702.8 | 
 | 255   v|   1.81 |   1.98|   2.14|  2.28|   2.43|   2.56|   2.70| 
 |       h| 1201.8 |1235.9 |1263.6 |1289.3 |1314.5 |1339.3 |1364.1 | 
 |________|_________|_______|_______|_______|_______|_______|_______| 
   
   
 t = Temperature, degrees Fahrenheit. 
 v = Specific volume, in cubic feet, per pound. 
 h = Total heat from water at 32 degrees, B. t. u. 
   
 [Graph: Temperature of Steam--Degrees Fahr. 
 against Temperature in Calorimeter--Degrees Fahr. 
   
 Fig. 15. Graphic Method of Determining Moisture Contained in Steam from 
 Calorimeter Readings] 
   
 
 
 
 MOISTURE IN STEAM 
 The presence of moisture in steam causes a loss, not only in the 
 practical waste of the heat utilized to raise this moisture from the 
 temperature of the feed water to the temperature of the steam, but also 
 through the increased initial condensation in an engine cylinder and 
 through friction and other actions in a steam turbine. The presence of 
 such moisture also interferes with proper cylinder lubrication, causes a 
 knocking in the engine and a water hammer in the steam pipes. In steam 
 turbines it will cause erosion of the blades. 
   
 The percentage by weight of steam in a mixture of steam and water is 
 called the _quality of the steam_. 
   
 The apparatus used to determine the moisture content of steam is called 
 a calorimeter though since it may not measure the heat in the steam, the 
 name is not descriptive of the function of the apparatus. The first form 
 used was the "barrel calorimeter", but the liability of error was so 
 great that its use was abandoned. Modern calorimeters are in general of 
 either the throttling or separator type. 
   
 Throttling Calorimeter--Fig. 14 shows a typical form of throttling 
 calorimeter. Steam is drawn from a vertical main through the sampling 
 nipple, passes around the first thermometer cup, then through a 
 one-eighth inch orifice in a disk between two flanges, and lastly around 
 the second thermometer cup and to the atmosphere. Thermometers are 
 inserted in the wells, which should be filled with mercury or heavy 
 cylinder oil. 
 The instrument and all pipes and fittings leading to it should be 
 thoroughly insulated to diminish radiation losses. Care must be taken to 
 prevent the orifice from becoming choked with dirt and to see that no 
 leaks occur. The exhaust pipe should be short to prevent back pressure 
 below the disk. 
   
 When steam passes through an orifice from a higher to a lower pressure, 
 as is the case with the throttling calorimeter, no external work has to 
 be done in overcoming a resistance. Hence, if there is no loss from 
 radiation, the quantity of heat in the steam will be exactly the same 
 after passing the orifice as before passing. If the higher steam 
 pressure is 160 pounds gauge and the lower pressure that of the 
 atmosphere, the total heat in a pound of dry steam at the former 
 pressure is 1195.9 B. t. u. and at the latter pressure 1150.4 B. t. u., 
 a difference of 45.4 B. t. u. As this heat will still exist in the steam 
 at the lower pressure, since there is no external work done, its effect 
 must be to superheat the steam. Assuming the specific heat of 
 superheated steam to be 0.47, each pound passing through will be 
 superheated 45.4/0.47 = 96.6 degrees. If, however, the steam had 
 contained one per cent of moisture, it would have contained less heat 
 units per pound than if it were dry. Since the latent heat of steam at 
 160 pounds gauge pressure is 852.8 B. t. u., it follows that the one per 
 cent of moisture would have required 8.5 B. t. u. to evaporate it, 
 leaving only 45.4 - 8.5 = 36.9 B. t. u. available for superheating; 
 hence, the superheat would be 36.9/0.47 = 78.5 degrees, as against 96.6 
 degrees for dry steam. In a similar manner, the degree of superheat for 
 other percentages of moisture may be determined. The action of the 
 throttling calorimeter is based upon the foregoing facts, as shown 
 below. 
   
 Let     H = total heat of one pound of steam at boiler pressure, 
        L = latent heat of steam at boiler pressure, 
        h = total heat of steam at reduced pressure after passing 
            orifice, 
    t_{1} = temperature of saturated steam at the reduced pressure, 
    t_{2} = temperature of steam after expanding through the orifice 
            in the disc, 
      0.47 = the specific heat of saturated steam at atmospheric pressure, 
        x = proportion by weight of moisture in steam. 
   
 The difference in B. t. u. in a pound of steam at the boiler pressure 
 and after passing the orifice is the heat available for evaporating the 
 moisture content and superheating the steam. Therefore, 
   
 H - h = xL + 0.47(t_{2} - t_{1}) 
   
       H - h - 0.47(t_{2} - t_{1}) 
 or x = ---------------------------     (4) 
                    L 
   
 Almost invariably the lower pressure is taken as that of the atmosphere. 
 Under such conditions, h = 1150.4 and t_{1} = 212 degrees. The formula 
 thus becomes: 
   
    H - 1150.4 - 0.47(t_{2} - 212) 
 x = ------------------------------     (5) 
                  L 
   
 For practical work it is more convenient to dispense with the upper 
 thermometer in the calorimeter and to measure the pressure in the steam 
 main by an accurate steam pressure gauge. 
   
 A chart may be used for determining the value of x for approximate work 
 without the necessity for computation. Such a chart is shown in Fig. 15 
 and its use is as follows: Assume a gauge pressure of 180 pounds and a 
 thermometer reading of 295 degrees. The intersection of the vertical 
 line from the scale of temperatures as shown by the calorimeter 
 thermometer and the horizontal line from the scale of gauge pressures 
 will indicate directly the per cent of moisture in the steam as read 
 from the diagonal scale. In the present instance, this per cent is 1.0. 
   
 Sources of Error in the Apparatus--A slight error may arise from the 
 value, 0.47, used as the specific heat of superheated steam at 
 atmospheric pressure. This value, however is very nearly correct and any 
 error resulting from its use will be negligible. 
   
 There is ordinarily a larger source of error due to the fact that the 
 stem of the thermometer is not heated to its full length, to an initial 
 error in the thermometer and to radiation losses. 
   
 With an ordinary thermometer immersed in the well to the 100 degrees 
 mark, the error when registering 300 degrees would be about 3 degrees 
 and the true temperature be 303 degrees.[19] 
   
 The steam is evidently losing heat through radiation from the moment it 
 enters the sampling nipple. The heat available for evaporating moisture 
 and superheating steam after it has passed through the orifice into the 
 lower pressure will be diminished by just the amount lost through 
 radiation and the value of t_{2}, as shown by the calorimeter 
 thermometer, will, therefore, be lower than if there were no such loss. 
 The method of correcting for the thermometer and radiation error 
 recommended by the Power Test Committee of the American Society of 
 Mechanical Engineers is by referring the readings as found on the boiler 
 trial to a "normal" reading of the thermometer. This normal reading is 
 the reading of the lower calorimeter thermometer for dry saturated 
 steam, and should be determined by attaching the instrument to a 
 horizontal steam pipe in such a way that the sampling nozzle projects 
 upward to near the top of the pipe, there being no perforations in the 
 nozzle and the steam taken only through its open upper end. The test 
 should be made with the steam in a quiescent state and with the steam 
 pressure maintained as nearly as possible at the pressure observed in 
 the main trial, the calorimeter thermometer to be the same as was used 
 on the trial or one exactly similar. 
   
 With a normal reading thus obtained for a pressure approximately the 
 same as existed in the trial, the true percentage of moisture in the 
 steam, that is, with the proper correction made for radiation, may be 
 calculated as follows: 
   
 Let T denote the normal reading for the conditions existing in the 
 trial. The effect of radiation from the instrument as pointed out will 
 be to lower the temperature of the steam at the lower pressure. Let 
 x_{1} represent the proportion of water in the steam which will lower 
 its temperature an amount equal to the loss by radiation. Then, 
   
        H - h - 0.47(T - t_{1}) 
 x_{1} = ----------------------- 
                    L 
   
 This amount of moisture, x_{1} was not in the steam originally but is 
 the result of condensation in the instrument through radiation. Hence, 
 the true amount of moisture in the steam represented by X is the 
 difference between the amount as determined in the trial and that 
 resulting from condensation, or, 
   
 X = x - x_{1} 
   
    H - h - 0.47(t_{2} - t_{1})   H - h - 0.47(T - t_{1}) 
 = --------------------------- - ----------------------- 
                  L                       L 
   
    0.47(T - t_{2}) 
 = ---------------     (6) 
            L 
   
 As T and t_{2} are taken with the same thermometer under the same set of 
 conditions, any error in the reading of the thermometers will be 
 approximately the same for the temperatures T and t_{2} and the above 
 method therefore corrects for both the radiation and thermometer errors. 
 The theoretical readings for dry steam, where there are no losses due to 
 radiation, are obtainable from formula (5) by letting x = 0 and solving 
 for t_{2}. The difference between the theoretical reading and the normal 
 reading for no moisture will be the thermometer and radiation correction 
 to be applied in order that the correct reading of t_{2} may be 
 obtained. 
   
 For any calorimeter within the range of its ordinary use, such a 
 thermometer and radiation correction taken from one normal reading is 
 approximately correct for any conditions with the same or a duplicate 
 thermometer. 
   
 The percentage of moisture in the steam, corrected for thermometer error 
 and radiation and the correction to be applied to the particular 
 calorimeter used, would be determined as follows: Assume a gauge 
 pressure in the trial to be 180 pounds and the thermometer reading to be 
 295 degrees. A normal reading, taken in the manner described, gives a 
 value of T = 303 degrees; then, the percentage of moisture corrected for 
 thermometer error and radiation is, 
   
      0.47(303 - 295) 
 x = ---------------- 
          845.0 
   
 = 0.45 per cent. 
   
 The theoretical reading for dry steam will be, 
   
        1197.7 - 1150.4 - 0.47(t_{2} - 212) 
    0 = ------------------------------------ 
                        845.0 
   
 t_{2} = 313 degrees. 
   
 The thermometer and radiation correction to be applied to the instrument 
 used, therefore over the ordinary range of pressure is 
   
        Correction = 313 - 303 = 10 degrees 
   
 The chart may be used in the determination of the correct reading of 
 moisture percentage and the permanent radiation correction for the 
 instrument used without computation as follows: Assume the same trial 
 pressure, feed temperature and normal reading as above. If the normal 
 reading is found to be 303 degrees, the correction for thermometer and 
 radiation will be the theoretical reading for dry steam as found from 
 the chart, less this normal reading, or 10 degrees correction. The 
 correct temperature for the trial in question is, therefore, 305 
 degrees. The moisture corresponding to this temperature and 180 pounds 
 gauge pressure will be found from the chart to be 0.45 per cent. 
 There are many forms of throttling calorimeter, all of which work upon 
 the same principle. The simplest one is probably that shown in Fig. 14. 
 An extremely convenient and compact design is shown in Fig. 16. This 
 calorimeter consists of two concentric metal cylinders screwed to a cap 
 containing a thermometer well. The steam pressure is measured by a gauge 
 placed in the supply pipe or other convenient location. Steam passes 
 through the orifice A and expands to atmospheric pressure, its 
 temperature at this pressure being measured by a thermometer placed in 
 the cup C. To prevent as far as possible radiation losses, the annular 
 space between the two cylinders is used as a jacket, steam being 
 supplied to this space through the hole B. 
   
 The limits of moisture within which the throttling calorimeter will work 
 are, at sea level, from 2.88 per cent at 50 pounds gauge pressure and 
 7.17 per cent moisture at 250 pounds pressure. 
   
 Separating Calorimeter--The separating calorimeter mechanically 
 separates the entrained water from the steam and collects it in a 
 reservoir, where its amount is either indicated by a gauge glass or is 
 drained off and weighed. Fig. 17 shows a calorimeter of this type. The 
 steam passes out of the calorimeter through an orifice of known size so 
 that its total amount can be calculated or it can be weighed. A gauge is 
 ordinarily provided with this type of calorimeter, which shows the 
 pressure in its inner chamber and the flow of steam for a given period, 
 this latter scale being graduated by trial. 
   
 The instrument, like a throttling calorimeter, should be well insulated 
 to prevent losses from radiation. 
   
 While theoretically the separating calorimeter is not limited in 
 capacity, it is well in cases where the percentage of moisture present 
 in the steam is known to be high, to attach a throttling calorimeter to 
 its exhaust. This, in effect, is the using of the separating calorimeter 
 as a small separator between the sampling nozzle and the throttling 
 instrument, and is necessary to insure the determination of the full 
 percentage of moisture in the steam. The sum of the percentages shown by 
 the two instruments is the moisture content of the steam. 
   
 The steam passing through a separating calorimeter may be calculated by 
 Napier's formula, the size of the orifice being known. There are 
 objections to such a calculation, however, in that it is difficult to 
 accurately determine the areas of such small orifices. Further, small 
 orifices have a tendency to become partly closed by sediment that may be 
 carried by the steam. The more accurate method of determining the amount 
 of steam passing through the instrument is as follows: 
 A hose should be attached to the separator outlet leading to a vessel of 
 water on a platform scale graduated to 1/100 of a pound. The steam 
 outlet should be connected to another vessel of water resting on a 
 second scale. In each case, the weight of each vessel and its contents 
 should be noted. When ready for an observation, the instrument should be 
 blown out thoroughly so that there will be no water within the 
 separator. The separator drip should then be closed and the steam hose 
 inserted into the vessel of water at the same instant. When the 
 separator has accumulated a sufficient quantity of water, the valve of 
 the instrument should be closed and the hose removed from the vessel of 
 water. The separator should be emptied into the vessel on its scale. The 
 final weight of each vessel and its contents are to be noted and the 
 differences between the final and original weights will represent the 
 weight of moisture collected by the separator and the weight of steam 
 from which the moisture has been taken. The proportion of moisture can 
 then be calculated from the following formula: 
   
    100 w 
 x = -----     (7) 
    W - w 
   
 Where x = per cent moisture in steam, 
      W = weight of steam condensed, 
      w = weight of moisture as taken out by the separating 
          calorimeter. 
   
 Sampling Nipple--The principle source of error in steam calorimeter 
 determinations is the failure to obtain an average sample of the steam 
 delivered by the boiler and it is extremely doubtful whether such a 
 sample is ever obtained. The two governing features in the obtaining of 
 such a sample are the type of sampling nozzle used and its location. 
   
 The American Society of Mechanical Engineers recommends a sampling 
 nozzle made of one-half inch iron pipe closed at the inner end and the 
 interior portion perforated with not less than twenty one-eighth inch 
 holes equally distributed from end to end and preferably drilled in 
 irregular or spiral rows, with the first hole not less than one-half 
 inch from the wall of the pipe. Many engineers object to the use of a 
 perforated sampling nipple because it ordinarily indicates a higher 
 percentage of moisture than is actually present in the steam. This is 
 due to the fact that if the perforations come close to the inner surface 
 of the pipe, the moisture, which in many instances clings to this 
 surface, will flow into the calorimeter and cause a large error. Where a 
 perforated nipple is used, in general it may be said that the 
 perforations should be at least one inch from the inner pipe surface. 
   
 A sampling nipple, open at the inner end and unperforated, undoubtedly 
 gives as accurate a measure as can be obtained of the moisture in the 
 steam passing that end. It would appear that a satisfactory method of 
 obtaining an average sample of the steam would result from the use of an 
 open end unperforated nipple passing through a stuffing box which would 
 allow the end to be placed at any point across the diameter of the steam 
 pipe. 
   
 Incidental to a test of a 15,000 K. W. steam engine turbine unit, Mr. 
 G. Stott and Mr. R. G. S. Pigott, finding no experimental data 
 
 bearing on the subject of low pressure steam quality determinations, 
 made a investigation of the subject and the sampling nozzle illustrated 
 in Fig. 18 was developed. In speaking of sampling nozzles in the 
 determination of the moisture content of low pressure steam, Mr. Pigott 
 says, "the ordinary standard perforated pipe sampler is absolutely 
 worthless in giving a true sample and it is vital that the sample be 
 abstracted from the main without changing its direction or velocity 
 until it is safely within the sample pipe and entirely isolated from the 
 rest of the steam." 
 It would appear that the nozzle illustrated is undoubtedly the best that 
 has been developed for use in the determination of the moisture content 
 of steam, not only in the case of low, but also in high pressure steam. 
   
 Location of Sampling Nozzle--The calorimeter should be located as near 
 as possible to the point from which the steam is taken and the sampling 
 nipple should be placed in a section of the main pipe near the boiler 
 and where there is no chance of moisture pocketing in the pipe. The 
 American Society of Mechanical Engineers recommends that a sampling 
 nipple, of which a description has been given, should be located in a 
 vertical main, rising from the boiler with its closed end extending 
 nearly across the pipe. Where non-return valves are used, or where there 
 are horizontal connections leading from the boiler to a vertical outlet, 
 water may collect at the lower end of the uptake pipe and be blown 
 upward in a spray which will not be carried away by the steam owing to a 
 lack of velocity. A sample taken from the lower part of this pipe will 
 show a greater amount of moisture than a true sample. With goose-neck 
 connections a small amount of water may collect on the bottom of the 
 pipe near the upper end where the inclination is such that the tendency 
 to flow backward is ordinarily counterbalanced by the flow of steam 
 forward over its surface; but when the velocity momentarily decreases 
 the water flows back to the lower end of the goose-neck and increases 
 the moisture at that point, making it an undesirable location for 
 sampling. In any case, it should be borne in mind that with low 
 velocities the tendency is for drops of entrained water to settle to the 
 bottom of the pipe, and to be temporarily broken up into spray whenever 
 an abrupt bend or other disturbance is met. 
 Fig. 19 indicates certain locations of sampling nozzles from which 
 erroneous results will be obtained, the reasons being obvious from a 
 study of the cuts. 
   
 Before taking any calorimeter reading, steam should be allowed to flow 
 through the instrument freely until it is thoroughly heated. The method 
 of using a throttling calorimeter is evident from the description of the 
 instrument given and the principle upon which it works. 
 
 
 
 SUPERHEATED STEAM 
 Superheated steam, as already stated, is steam the temperature of which 
 exceeds that of saturated steam at the same pressure. It is produced by 
 the addition of heat to saturated steam which has been removed from 
 contact with the water from which it was generated. The properties of 
 superheated steam approximate those of a perfect gas rather than of a 
 vapor. Saturated steam cannot be superheated when it is in contact with 
 water which is also heated, neither can superheated steam condense 
 without first being reduced to the temperature of saturated steam. Just 
 so long as its temperature is above that of saturated steam at a 
 corresponding pressure it is superheated, and before condensation can 
 take place that superheat must first be lost through radiation or some 
 other means. Table 24[20] gives such properties of superheated steam for 
 varying pressures as are necessary for use in ordinary engineering 
 practice. 
   
 Specific Heat of Superheated Steam--The specific heat of superheated 
 steam at atmospheric pressure and near saturation point was determined 
 by Regnault, in 1862, who gives it the value of 0.48. Regnault's value 
 was based on four series of experiments, all at atmospheric pressure and 
 with about the same temperature range, the maximum of which was 231.1 
 degrees centigrade. For fifty years after Regnault's determination, this 
 value was accepted and applied to higher pressures and temperatures as 
 well as to the range of his experiments. More recent investigations have 
 shown that the specific heat is not a constant and varies with both 
 pressure and the temperature. A number of experiments have been made by 
 various investigators and, up to the present, the most reliable appear 
 to be those of Knoblauch and Jacob. Messrs. Marks and Davis have used 
 the values as determined by Knoblauch and Jacob with slight 
 modifications. The first consists in a varying of the curves at low 
 pressures close to saturation because of thermodynamic evidence and in 
 view of Regnault's determination at atmospheric pressure. The second 
 modification is at high degrees of superheat to follow Holborn's and 
 Henning's curve, which is accepted as authentic. 
   
 For the sake of convenience, the mean specific heat of superheated steam 
 at various pressures and temperatures is given in tabulated form in 
 Table 25. These values have been calculated from Marks and Davis Steam 
 Tables by deducting from the total heat of one pound of steam at any 
 pressure for any degree of superheat the total heat of one pound of 
 saturated steam at the same pressure and dividing the difference by the 
 number of degrees of superheat and, therefore, represent the average 
 specific heat starting from that at saturation to the value at the 
 particular pressure and temperature.[21] Expressed as a formula this 
 calculation is represented by 
   
          H_{sup} - H_{sat} 
 Sp. Ht. = -----------------     (8) 
          S_{sup} - S_{sat} 
   
 Where H_{sup} = total heat of one pound of superheated steam at any 
                 pressure and temperature, 
      H_{sat} = total heat of one pound of saturated steam at same 
                pressure, 
      S_{sup} = temperature of superheated steam taken, 
      S_{sat} = temperature of saturated steam corresponding to the 
               pressure taken. 
   
                            TABLE 25 
   
              MEAN SPECIFIC HEAT OF SUPERHEATED STEAM 
              CALCULATED FROM MARKS AND DAVIS TABLES 
 _______________________________________________________________ 
 |Gauge   |                                                    | 
 |Pressure |             Degree of Superheat                     | 
 |         |_____________________________________________________| 
 |         | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 
 |_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| 
 | 50     | .518| .517| .514| .513| .511| .510| .508| .507| .505| 
 | 60     | .528| .525| .523| .521| .519| .517| .515| .513| .512| 
 | 70     | .536| .534| .531| .529| .527| .524| .522| .520| .518| 
 | 80     | .544| .542| .539| .535| .532| .530| .528| .526| .524| 
 | 90     | .553| .550| .546| .543| .539| .536| .534| .532| .529| 
 | 100     | .562| .557| .553| .549| .544| .542| .539| .536| .533| 
 | 110     | .570| .565| .560| .556| .552| .548| .545| .542| .539| 
 | 120     | .578| .573| .567| .561| .557| .554| .550| .546| .543| 
 | 130     | .586| .580| .574| .569| .564| .560| .555| .552| .548| 
 | 140     | .594| .588| .581| .575| .570| .565| .561| .557| .553| 
 | 150     | .604| .595| .587| .581| .576| .570| .566| .561| .557| 
 | 160     | .612| .603| .596| .589| .582| .576| .571| .566| .562| 
 | 170     | .620| .612| .603| .595| .588| .582| .576| .571| .566| 
 | 180     | .628| .618| .610| .601| .593| .587| .581| .575| .570| 
 | 190     | .638| .627| .617| .608| .599| .592| .585| .579| .574| 
 | 200     | .648| .635| .624| .614| .605| .597| .590| .584| .578| 
 | 210     | .656| .643| .631| .620| .611| .602| .595| .588| .583| 
 | 220     | .664| .650| .637| .626| .616| .607| .600| .592| .586| 
 | 230     | .672| .658| .644| .633| .622| .613| .605| .597| .591| 
 | 240     | .684| .668| .653| .640| .629| .619| .610| .602| .595| 
 | 250     | .692| .675| .659| .645| .633| .623| .614| .606| .599| 
 |_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| 
 |Gauge   |                                                    | 
 |Pressure |             Degree of Superheat                     | 
 |         |-----------------------------------------------------| 
 |         | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 225 | 250 | 
 |---------+-----+-----+-----+-----+-----+-----+-----+-----+-----| 
 | 50     | .504| .503| .502| .501| .500| .500| .499| .497| .496| 
 | 60     | .511| .509| .508| .507| .506| .504| .504| .502| .500| 
 | 70     | .516| .515| .513| .512| .511| .510| .509| .506| .504| 
 | 80     | .522| .520| .518| .516| .515| .514| .513| .511| .508| 
 | 90     | .527| .525| .523| .521| .519| .518| .517| .514| .510| 
 | 100     | .531| .529| .527| .525| .523| .522| .521| .517| .513| 
 | 110     | .536| .534| .532| .529| .528| .526| .525| .520| .517| 
 | 120     | .540| .537| .535| .533| .531| .529| .528| .523| .519| 
 | 130     | .545| .542| .539| .537| .535| .533| .531| .527| .523| 
 | 140     | .550| .547| .544| .541| .539| .536| .534| .530| .526| 
 | 150     | .554| .550| .547| .544| .542| .539| .537| .533| .529| 
 | 160     | .558| .554| .551| .548| .545| .543| .541| .536| .531| 
 | 170     | .562| .558| .555| .552| .549| .546| .544| .538| .533| 
 | 180     | .566| .561| .558| .555| .552| .549| .546| .540| .536| 
 | 190     | .569| .565| .562| .558| .555| .552| .549| .543| .538| 
 | 200     | .574| .569| .566| .562| .558| .555| .552| .546| .541| 
 | 210     | .578| .573| .569| .565| .561| .558| .555| .549| .543| 
 | 220     | .581| .577| .572| .568| .564| .561| .558| .551| .545| 
 | 230     | .585| .580| .575| .572| .567| .564| .561| .554| .548| 
 | 240     | .589| .584| .579| .575| .571| .567| .564| .556| .550| 
 | 250     | .593| .587| .582| .577| .574| .570| .567| .559| .553| 
 |_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| 
   
 Factor of Evaporation with Superheated Steam--When superheat is present 
 in the steam during a boiler trial, where superheated steam tables are 
 available, the formula for determining the factor of evaporation is that 
 already given, (2),[22] namely, 
   
                        H - h 
 Factor of evaporation = ----- 
                          L 
   
 Here H = total heat in one pound of superheated steam from the table, 
 h and L having the same values as in (2). 
   
 Where no such tables are available but the specific heat of superheat is 
 known, the formula becomes: 
   
                        H - h + Sp. Ht.(T - t) 
 Factor of evaporation = ---------------------- 
                                  L 
   
 Where H = total heat in one pound of saturated steam at pressure 
          existing in trial, 
      h = sensible heat above 32 degrees in one pound of water at the 
          temperature entering the boiler, 
      T = temperature of superheated steam as determined in the trial, 
      t = temperature of saturated steam corresponding to the boiler 
          pressure, 
 Sp. Ht. = mean specific heat of superheated steam at the pressure and 
          temperature as found in the trial, 
      L = latent heat of one pound of saturated steam at atmospheric 
          pressure. 
   
 Advantages of the Use of Superheated Steam--In considering the saving 
 possible by the use of superheated steam, it is too often assumed that 
 there is only a saving in the prime movers, a saving which is at least 
 partially offset by an increase in the fuel consumption of the boilers 
 generating steam. This misconception is due to the fact that the fuel 
 consumption of the boiler is only considered in connection with a 
 definite weight of steam. It is true that where such a definite weight 
 is to be superheated, an added amount of fuel must be burned. With a 
 properly designed superheater where the combined efficiency of the 
 boiler and superheater will be at least as high as of a boiler alone, 
 the approximate increase in coal consumption for producing a given 
 weight of steam will be as follows: 
   
 _Superheat_     _Added Fuel_ 
 _Degrees_       _Per Cent_ 
    25               1.59 
    50               3.07 
    75               4.38 
    100               5.69 
    150               8.19 
    200             10.58 
   
 These figures represent the added fuel necessary for superheating a 
 definite weight of steam to the number of degrees as given. The standard 
 basis, however, of boiler evaporation is one of heat units and, 
 considered from such a standpoint, again providing the efficiency of the 
 boiler and superheater is as high, as of a boiler alone, there is no 
 additional fuel required to generate steam containing a definite number 
 of heat units whether such units be due to superheat or saturation. That 
 is, if 6 per cent more fuel is required to generate and superheat to 100 
 degrees, a definite weight of steam, over what would be required to 
 produce the same weight of saturated steam, that steam when superheated, 
 will contain 6 per cent more heat units above the fuel water temperature 
 than if saturated. This holds true if the efficiency of the boiler and 
 superheater combined is the same as of the boiler alone. As a matter of 
 fact, the efficiency of a boiler and superheater, where the latter is 
 properly designed and located, will be slightly higher for the same set 
 of furnace conditions than would the efficiency of a boiler in which no 
 superheater were installed. A superheater, properly placed within the 
 boiler setting in such way that products of combustion for generating 
 saturated steam are utilized as well for superheating that steam, will 
 not in any way alter furnace conditions. With a given set of such 
 furnace conditions for a given amount of coal burned, the fact that 
 additional surface, whether as boiler heating or superheating surface, 
 is placed in such a manner that the gases must sweep over it, will tend 
 to lower the temperature of the exit gases. It is such a lowering of 
 exit gas temperatures that is the ultimate indication of added 
 efficiency. Though the amount of this added efficiency is difficult to 
 determine by test, that there is an increase is unquestionable. 
   
 Where a properly designed superheater is installed in a boiler the 
 heating surface of the boiler proper, in the generation of a definite 
 number of heat units, is relieved of a portion of the work which would 
 be required were these heat units delivered in saturated steam. Such a 
 superheater needs practically no attention, is not subject to a large 
 upkeep cost or depreciation, and performs its function without in any 
 way interfering with the operation of the boiler. Its use, therefore 
 from the standpoint of the boiler room, results in a saving in wear and 
 tear due to the lower ratings at which the boiler may be run, or its use 
 will lead to the possibility of obtaining the same number of boiler 
 horse power from a smaller number of boilers, with the boiler heating 
 surface doing exactly the same amount of work as if the superheaters 
 were not installed. The saving due to the added boiler efficiency that 
 will be obtained is obvious. 
   
 Following the course of the steam in a plant, the next advantage of the 
 use of superheated steam is the absence of water in the steam pipes. The 
 thermal conductivity of superheated steam, that is, its power to give up 
 its heat to surrounding bodies, is much lower than that of saturated 
 steam and its heat, therefore, will not be transmitted so rapidly to the 
 walls of the pipes as when saturated steam is flowing through the pipes. 
 The loss of heat radiated from a steam pipe, assuming no loss in 
 pressure, represents the equivalent condensation when the pipe is 
 carrying saturated steam. In well-covered steam mains, the heat lost by 
 radiation when carrying superheated steam is accompanied only by a 
 reduction of the superheat which, if it be sufficiently high at the 
 boiler, will enable a considerable amount of heat to be radiated and 
 still deliver dry or superheated steam to the prime movers. 
   
 It is in the prime movers that the advantages of the use of superheated 
 steam are most clearly seen. 
   
 In an engine, steam is admitted into a space that has been cooled by the 
 steam exhausted during the previous stroke. The heat necessary to warm 
 the cylinder walls from the temperature of the exhaust to that of the 
 entering steam can be supplied only by the entering steam. If this steam 
 be saturated, such an adding of heat to the walls at the expense of the 
 heat of the entering steam results in the condensation of a portion. 
 This initial condensation is seldom less than from 20 to 30 per cent of 
 the total weight of steam entering the cylinder. It is obvious that if 
 the steam entering be superheated, it must be reduced to the temperature 
 of saturated steam at the corresponding pressure before any condensation 
 can take place. If the steam be superheated sufficiently to allow a 
 reduction in temperature equivalent to the quantity of heat that must be 
 imparted to the cylinder walls and still remain superheated, it is clear 
 that initial condensation is avoided. For example: assume one pound of 
 saturated steam at 200 pounds gauge pressure to enter a cylinder which 
 has been cooled by the exhaust. Assume the initial condensation to be 20 
 per cent. The latent heat of the steam is given up in condensation; 
 hence, .20 × 838 = 167.6 B. t. u. are given up by the steam. If one 
 pound of superheated steam enters the same cylinder, it would have to be 
 superheated to a point where its total heat is 1199 + 168 = 1367 
 t. u. or, at 200 pounds gauge pressure, superheated approximately 325 
 
 degrees if the heat given up to the cylinder walls were the same as for 
 the saturated steam. As superheated steam conducts heat less rapidly 
 than saturated steam, the amount of heat imparted will be less than for 
 the saturated steam and consequently the amount of superheat required to 
 prevent condensation will be less than the above figure. This, of 
 course, is the extreme case of a simple engine with the range of 
 temperature change a maximum. As cylinders are added, the range in each 
 is decreased and the condensation is proportionate. 
   
 The true economy of the use of superheated steam is best shown in a 
 comparison of the "heat consumption" of an engine. This is the number of 
 heat units required in developing one indicated horse power and the 
 measure of the relative performance of two engines is based on a 
 comparison of their heat consumption as the measure of a boiler is based 
 on its evaporation from and at 212 degrees. The water consumption of an 
 engine in pounds per indicated horse power is in no sense a true 
 indication of its efficiency. The initial pressures and corresponding 
 temperatures may differ widely and thus make a difference in the 
 temperature of the exhaust and hence in the temperature of the condensed 
 steam returned to the boiler. For example: suppose a certain weight of 
 steam at 150 pounds absolute pressure and 358 degrees be expanded to 
 atmospheric pressure, the temperature then being 212 degrees. If the 
 same weight of steam be expanded from an initial pressure of 125 pounds 
 absolute and 344 degrees, to enable it to do the same amount of work, 
 that is, to give up the same amount of heat, expansion then must be 
 carried to a point below atmospheric pressure to, say, 13 pounds 
 absolute, the final temperature of the steam then being 206 degrees. In 
 actual practice, it has been observed that the water consumption of a 
 compound piston engine running on 26-inch vacuum and returning the 
 condensed steam at 140 degrees was approximately the same as when 
 running on 28-inch vacuum and returning water at 90 degrees. With an 
 equal water consumption for the two sets of conditions, the economy in 
 the former case would be greater than in the latter, since it would be 
 necessary to add less heat to the water returned to the boiler to raise 
 it to the steam temperature. 
   
 The lower the heat consumption of an engine per indicated horse power, 
 the higher its economy and the less the number of heat units must be 
 imparted to the steam generated. This in turn leads to the lowering of 
 the amount of fuel that must be burned per indicated horse power. 
   
 With the saving in fuel by the reduction of heat consumption of an 
 engine indicated, it remains to be shown the effect of the use of 
 superheated steam on such heat consumption. As already explained, the 
 use of superheated steam reduces condensation not only in the mains but 
 especially in the steam cylinder, leaving a greater quantity of steam 
 available to do the work. Furthermore, a portion of the saturated steam 
 introduced into a cylinder will condense during adiabatic expansion, 
 this condensation increasing as expansion progresses. Since superheated 
 steam cannot condense until it becomes saturated, not only is initial 
 condensation prevented by its use but also such condensation as would 
 occur during expansion. When superheated sufficiently, steam delivered 
 by the exhaust will still be dry. In the avoidance of such condensation, 
 there is a direct saving in the heat consumption of an engine, the heat 
 given up being utilized in the developing of power and not in changing 
 the condition of the working fluid. That is, while the number of heat 
 units lost in overcoming condensation effects would be the same in 
 either case, when saturated steam is condensed the water of condensation 
 has no power to do work while the superheated steam, even after it has 
 lost a like number of heat units, still has the power of expansion. The 
 saving through the use of superheated steam in the heat consumption of 
 an engine decreases demands on the boiler and hence the fuel consumption 
 per unit of power. 
   
 Superheated Steam for Steam Turbines--Experience in using superheated 
 steam in connection with steam turbines has shown that it leads to 
 economy and that it undoubtedly pays to use superheated steam in place 
 of saturated steam. This is so well established that it is standard 
 practice to use superheated steam in connection with steam turbines. 
 Aside from the economy secured through using superheated steam, there is 
 an important advantage arising through the fact that it materially 
 reduces the erosion of the turbine blades by the action of water that 
 would be carried by saturated steam. In using saturated steam in a steam 
 turbine or piston engine, the work done on expanding the steam causes 
 condensation of a portion of the steam, so that even were the steam dry 
 on entering the turbine, it would contain water on leaving the turbine. 
 By superheating the steam the water that exists in the low pressure 
 stages of the turbine may be reduced to an amount that will not cause 
 trouble. 
   
 Again, if saturated steam contains moisture, the effect of this moisture 
 on the economy of a steam turbine is to reduce the economy to a greater 
 extent than the proportion by weight of water, one per cent of water 
 causing approximately a falling off of 2 per cent in the economy. 
   
 The water rate of a large economical steam turbine with superheated 
 steam is reduced about one per cent, for every 12 degrees of superheat 
 up to 200 degrees Fahrenheit of superheat. To superheat one pound of 
 steam 12 degrees requires about 7 B. t. u. and if 1050 B. t. u. are 
 required at the boiler to evaporate one pound of the saturated steam 
 from the temperature of the feed water, the heat required for the 
 superheated steam would be 1057 degrees. One per cent of saving, 
 therefore, in the water consumption would correspond to a net saving of 
 about one-third of one per cent in the coal consumption. On this basis 
 100 degrees of superheat with an economical steam turbine would result 
 in somewhat over 3 per cent of saving in the coal for equal boiler 
 efficiencies. As a boiler with a properly designed superheater placed 
 within the setting is more economical for a given capacity than a boiler 
 without a superheater, the minimum gain in the coal consumption would 
 be, say, 4 or 5 per cent as compared to a plant with the same boilers 
 without superheaters. 
   
 The above estimates are on the basis of a thoroughly dry saturated steam 
 or steam just at the point of being superheated or containing a few 
 degrees of superheat. If the saturated steam is moist, the saving due to 
 superheat is more and ordinarily the gain in economy due to superheated 
 steam, for equal boiler efficiencies, as compared with commercially dry 
 steam is, say, 5 per cent for each 100 degrees of superheat. Aside from 
 this gain, as already stated, superheated steam prevents erosion of the 
 turbine buckets that would be caused by water in the steam, and for the 
 reasons enumerated it is standard practice to use superheated steam for 
 turbine work. The less economical the steam motor, the more the gain due 
 to superheated steam, and where there are a number of auxiliaries that 
 are run with superheated steam, the percentage of gain will be greater 
 than the figures given above, which are the minimum and are for the most 
 economical type of large steam turbines. 
   
 An example from actual practice will perhaps best illustrate and 
 emphasize the foregoing facts. In October 1909, a series of comparable 
 tests were conducted by The Babcock & Wilcox Co. on the steam yacht 
 "Idalia" to determine the steam consumption both with saturated and 
 superheated steam of the main engine on that yacht, including as well 
 the feed pump, circulating pump and air pump. These tests are more 
 representative than are most tests of like character in that the saving 
 in the steam consumption of the auxiliaries, which were much more 
 wasteful than the main engine, formed an important factor. A résumé of 
 these tests was published in the Journal of the Society of Naval 
 Engineers, November 1909. 
   
 The main engines of the "Idalia" are four cylinder, triple expansion, 
 11-1/2 × 19 inches by 22-11/16 × 18 inches stroke. Steam is supplied by 
 a Babcock & Wilcox marine boiler having 2500 square feet of boiler 
 heating surface, 340 square feet of superheating surface and 65 square 
 feet of grate surface. 
   
 The auxiliaries consist of a feed pump 6 × 4 × 6 inches, an independent 
 air pump 6 × 12 × 8 inches, and a centrifugal pump driven by a 
 reciprocating engine 5-7/16 × 5 inches. Under ordinary operating 
 conditions the superheat existing is about 100 degrees Fahrenheit. 
   
 Tests were made with various degrees of superheat, the amount being 
 varied by by-passing the gases and in the tests with the lower amounts 
 of superheat by passing a portion of the steam from the boiler to the 
 steam main without passing it through the superheater. Steam temperature 
 readings were taken at the engine throttle. In the tests with saturated 
 steam, the superheater was completely cut out of the system. Careful 
 calorimeter measurements were taken, showing that the saturated steam 
 delivered to the superheater was dry. 
   
 The weight of steam used was determined from the weight of the condensed 
 steam discharge from the surface condenser, the water being pumped from 
 the hot well into a tank mounted on platform scales. The same 
 indicators, thermometers and gauges were used in all the tests, so that 
 the results are directly comparable. The indicators used were of the 
 outside spring type so that there was no effect of the temperature of 
 the steam. All tests were of sufficient duration to show a uniformity of 
 results by hours. A summary of the results secured is given in Table 26, 
 which shows the water rate per indicated horse power and the heat 
 consumption. The latter figures are computed on the basis of the heat 
 imparted to the steam above the actual temperature of the feed water 
 and, as stated, these are the results that are directly comparable. 
   
                                TABLE 26 
   
                         RESULTS OF "IDALIA" TESTS 
 _______________________________________________________________________ 
 |                               |       |       |       |       |       | 
 |Date                   1909   |Oct. 11|Oct. 14|Oct. 14|Oct. 12|Oct. 13| 
 |_______________________________|_______|_______|_______|_______|_______| 
 |Degrees of superheat Fahrenheit|   0   | 57   | 88   | 96   | 105   | 
 |Pressures, pounds per} Throttle| 190   | 196   | 201   | 198   | 203   | 
 |square inch above   } First  |       |       |       |       |       | 
 |Atmospheric Pressure } Receiver| 68.4 | 66.0 | 64.3 | 61.9 | 63.0 | 
 |                     } Second |       |       |       |       |       | 
 |                     } Receiver|   9.7 |   9.2 |   8.7 |   7.8 |   8.4 | 
 |Vacuum, inches                 | 25.5 | 25.9 | 25.9 | 25.4 | 25.2 | 
 |Temperature, Degrees Fahrenheit|       |       |       |       |       | 
 |               } Feed         | 201   | 206   | 205   | 202   | 200   | 
 |               } Hot Well     | 116   | 109.5 | 115   | 111.5 | 111   | 
 |                               |       |       |       |       |       | 
 |Revolutions per minute         |       |       |       |       |       | 
 |             {Air Pump       | 57   | 56   | 53   | 54   | 45   | 
 |             {Circulating Pump| 196   | 198   | 196   | 198   | 197   | 
 |             {Main Engine     | 194.3 | 191.5 | 195.1 | 191.5 | 193.1 | 
 |Indicated Horse Power,         |       |       |       |       |       | 
 |           Main Engine         | 512.3 | 495.2 | 521.1 | 498.3 | 502.2 | 
 |Water per hour, total pounds   |9397   |8430   |8234   |7902   |7790   | 
 |Water per indicated           |       |       |       |       |       | 
 |       Horse Power, pounds   | 18.3 | 17.0 | 15.8 | 15.8 | 15.5 | 
 |B. t. u. per minute per       |       |       |       |       |       | 
 |       indicated Horse Power | 314   | 300   | 284   | 286   | 283   | 
 |Per cent Saving of Steam       | ...   |   7.1 | 13.7 | 13.7 | 15.3 | 
 |Percent Saving of Fuel         |       |       |       |       |       | 
 |               (computed)     | ...   |   4.4 |   9.5 |   8.9 |   9.9 | 
 |_______________________________|_______|_______|_______|_______|_______| 
   
 The table shows that the saving in steam consumption with 105 degrees of 
 superheat was 15.3 per cent and in heat consumption about 10 per cent. 
 This may be safely stated to be a conservative representation of the 
 saving that may be accomplished by the use of superheated steam in a 
 plant as a whole, where superheated steam is furnished not only to the 
 main engine but also to the auxiliaries. The figures may be taken as 
 conservative for the reason that in addition to the saving as shown in 
 the table, there would be in an ordinary plant a saving much greater 
 than is generally realized in the drips, where the loss with saturated 
 steam is greatly in excess of that with superheated steam. 
   
 The most conclusive and most practical evidence that a saving is 
 possible through the use of superheated steam is in the fact that in the 
 largest and most economical plants it is used almost without exception. 
 Regardless of any such evidence, however, there is a deep rooted 
 conviction in the minds of certain engineers that the use of superheated 
 steam will involve operating difficulties which, with additional first 
 cost, will more than offset any fuel saving. There are, of course, 
 conditions under which the installation of superheaters would in no way 
 be advisable. With a poorly designed superheater, no gain would result. 
 In general, it may be stated that in a new plant, properly designed, 
 with a boiler and superheater which will have an efficiency at least as 
 high as a boiler without a superheater, a gain is certain. 
   
 Such a gain is dependent upon the class of engine and the power plant 
 equipment in general. In determining the advisability of making a 
 superheater installation, all of the factors entering into each 
 individual case should be considered and balanced, with a view to 
 determining the saving in relation to cost, maintenance, depreciation 
 etc. 
   
 In highly economical plants, where the water consumption for an 
 indicated horse power is low, the gain will be less than would result 
 from the use of superheated steam in less economical plants where the 
 water consumption is higher. It is impossible to make an accurate 
 statement as to the saving possible but, broadly, it may vary from 3 to 
 5 per cent for 100 degrees of superheat in the large and economical 
 plants using turbines or steam engines, in which there is a large ratio 
 of expansion, to from 10 to 25 per cent for 100 degrees of superheat for 
 the less economical steam motors. 
   
 Though a properly designed superheater will tend to raise rather than to 
 decrease the boiler efficiency, it does not follow that all superheaters 
 are efficient, for if the gases in passing over the superheater do not 
 follow the path they would ordinarily take in passing over the boiler 
 heating surface, a loss may result. This is noticeably true where part of 
 the gases are passed over the superheater and are allowed to pass over 
 only a part or in some cases none of the boiler heating surface. 
   
 With moderate degrees of superheat, from 100 to 200 degrees, where the 
 piping is properly installed, there will be no greater operating 
 difficulties than with saturated steam. Engine and turbine builders 
 guarantee satisfactory operation with superheated steam. With high 
 degrees of superheat, say, over 250 degrees, apparatus of a special 
 nature must be used and it is questionable whether the additional care 
 and liability to operating difficulties will offset any fuel saving 
 accomplished. It is well established, however, that the operating 
 difficulties, with the degrees of superheat to which this article is 
 limited, have been entirely overcome. 
   
 The use of cast-iron fittings with superheated steam has been widely 
 discussed. It is an undoubted fact that while in some instances 
 superheated steam has caused deterioration of such fittings, in others 
 cast-iron fittings have been used with 150 degrees of superheat without 
 the least difficulty. The quality of the cast iron used in such fittings 
 has doubtless a large bearing on the life of such fittings for this 
 service. The difficulties that have been encountered are an increase in 
 the size of the fittings and eventually a deterioration great enough to 
 lead to serious breakage, the development of cracks, and when flanges 
 are drawn up too tightly, the breaking of a flange from the body of the 
 fitting. The latter difficulty is undoubtedly due, in certain instances, 
 to the form of flange in which the strain of the connecting bolts tended 
 to distort the metal. 
   
 The Babcock & Wilcox Co. have used steel castings in superheated steam 
 work over a long period and experience has shown that this metal is 
 suitable for the service. There seems to be a general tendency toward 
 the use of steel fittings. In European practice, until recently, cast 
 iron was used with apparently satisfactory results. The claim of 
 European engineers was to the effect that their cast iron was of better 
 quality than that found in this country and thus explained the results 
 secured. Recently, however, certain difficulties have been encountered 
 with such fittings and European engineers are leaning toward the use of 
 steel for this work. 
   
 The degree of superheat produced by a superheater placed within the 
 boiler setting will vary according to the class of fuel used, the form 
 of furnace, the condition of the fire and the rate at which the boiler 
 is being operated. This is necessarily true of any superheater swept by 
 the main body of the products of combustion and is a fact that should be 
 appreciated by the prospective user of superheated steam. With a 
 properly designed superheater, however, such fluctuations would not be 
 excessive, provided the boilers are properly operated. As a matter of 
 fact the point to be guarded against in the use of superheated steam is 
 that a maximum should not be exceeded. While, as stated, there may be a 
 considerable fluctuation in the temperature of the steam as delivered 
 from individual superheaters, where there are a number of boilers on a 
 line the temperature of the combined flow of steam in the main will be 
 found to be practically a constant, resulting from the offsetting of 
 various furnace conditions of one boiler by another. 
   
 
 
 
 PROPERTIES OF AIR 
 Pure air is a mechanical mixture of oxygen and nitrogen. While different 
 authorities give slightly varying values for the proportion of oxygen 
 and nitrogen contained, the generally accepted values are: 
   
    By volume, oxygen 20.91 per cent, nitrogen 79.09 per cent. 
    By weight, oxygen 23.15 per cent, nitrogen 76.85 per cent. 
   
 Air in nature always contains other constituents in varying amounts, 
 such as dust, carbon dioxide, ozone and water vapor. 
   
 Being perfectly elastic, the density or weight per unit of volume 
 decreases in geometric progression with the altitude. This fact has a 
 direct bearing in the proportioning of furnaces, flues and stacks at 
 high altitudes, as will be shown later in the discussion of these 
 subjects. The atmospheric pressures corresponding to various altitudes 
 are given in Table 12. 
   
 The weight and volume of air depend upon the pressure and the 
 temperature, as expressed by the formula: 
   
 Pv = 53.33 T     (9) 
   
 Where P = the absolute pressure in pounds per square foot, 
      v = the volume in cubic feet of one pound of air, 
      T = the absolute temperature of the air in degrees Fahrenheit, 
 53.33 = a constant for air derived from the ratio of pressure, volume 
          and temperature of a perfect gas. 
   
 The weight of one cubic foot of air will obviously be the reciprocal of 
 its volume, that is, 1/v pounds. 
   
                  TABLE 27 
   
          VOLUME AND WEIGHT OF AIR 
          AT ATMOSPHERIC PRESSURE 
          AT VARIOUS TEMPERATURES 
 _______________________________________ 
 |             |            |           | 
 |             |   Volume   |           | 
 | Temperature | One Pound | Weight One | 
 | Degrees   |     in     | Cubic Foot | 
 | Fahrenheit | Cubic Feet | in Pounds | 
 |_____________|____________|____________| 
 |             |            |           | 
 |     32     |   12.390   | .080710   | 
 |     50     |   12.843   | .077863   | 
 |     55     |   12.969   | .077107   | 
 |     60     |   13.095   | .076365   | 
 |     65     |   13.221   | .075637   | 
 |     70     |   13.347   | .074923   | 
 |     75     |   13.473   | .074223   | 
 |     80     |   13.599   | .073535   | 
 |     85     |   13.725   | .072860   | 
 |     90     |   13.851   | .072197   | 
 |     95     |   13.977   | .071546   | 
 |     100     |   14.103   | .070907   | 
 |     110     |   14.355   | .069662   | 
 |     120     |   14.607   | .068460   | 
 |     130     |   14.859   | .067299   | 
 |     140     |   15.111   | .066177   | 
 |     150     |   15.363   | .065092   | 
 |     160     |   15.615   | .064041   | 
 |     170     |   15.867   | .063024   | 
 |     180     |   16.119   | .062039   | 
 |     190     |   16.371   | .061084   | 
 |     200     |   16.623   | .060158   | 
 |     210     |   16.875   | .059259   | 
 |     212     |   16.925   | .059084   | 
 |     220     |   17.127   | .058388   | 
 |     230     |   17.379   | .057541   | 
 |     240     |   17.631   | .056718   | 
 |     250     |   17.883   | .055919   | 
 |     260     |   18.135   | .055142   | 
 |     270     |   18.387   | .054386   | 
 |     280     |   18.639   | .053651   | 
 |     290     |   18.891   | .052935   | 
 |     300     |   19.143   | .052238   | 
 |     320     |   19.647   | .050898   | 
 |     340     |   20.151   | .049625   | 
 |     360     |   20.655   | .048414   | 
 |    380     |   21.159   | .047261   | 
 |     400     |   21.663   | .046162   | 
 |     425     |   22.293   | .044857   | 
 |     450     |   22.923   | .043624   | 
 |     475     |   23.554   | .042456   | 
 |     500     |   24.184   | .041350   | 
 |     525     |   24.814   | .040300   | 
 |     550     |   25.444   | .039302   | 
 |     575     |   26.074   | .038352   | 
 |     600     |   26.704   | .037448   | 
 |     650     |   27.964   | .035760   | 
 |     700     |   29.224   | .034219   | 
 |     750    |   30.484   | .032804   | 
 |     800     |   31.744   | .031502   | 
 |     850     |   33.004   | .030299   | 
 |_____________|____________|____________| 
   
 Example: Required the volume of air in cubic feet under 60.3 pounds 
 gauge pressure per square inch at 115 degrees Fahrenheit. 
   
 P = 144 (14.7 + 60.3) = 10,800. 
   
 T = 115 + 460 = 575 degrees. 
   
          53.33 × 575 
 Hence v = ----------- = 2.84 cubic feet, and 
            10,800 
   
                        1   1 
 Weight per cubic foot = - = ---- = 0.352 pounds. 
                        v   2.84 
   
 Table 27 gives the weights and volumes of air under atmospheric pressure 
 at varying temperatures. 
   
 Formula (9) holds good for other gases with the change in the value of 
 the constant as follows: 
   
 For oxygen 48.24, nitrogen 54.97, hydrogen 765.71. 
   
 The specific heat of air at constant pressure varies with its 
 temperature. A number of determinations of this value have been made and 
 certain of those ordinarily accepted as most authentic are given in 
 Table 28. 
   
                           TABLE 28 
   
                      SPECIFIC HEAT OF AIR 
          AT CONSTANT PRESSURE AND VARIOUS TEMPERATURES 
 ______________________________________________________________ 
 |                         |               |                   | 
 |  Temperature Range   |               |                   | 
 |_________________________|_______________|____________________| 
 |           |           |               |                   | 
 | Degrees   | Degrees   | Specific Heat |     Authority     | 
 | Centigrade | Fahrenheit |               |                   | 
 |____________|____________|_______________|____________________| 
 |           |           |               |                   | 
 | -30- 10   | -22- 50   |     0.2377   | Regnault          | 
 |   0-100   | 32- 212   |     0.2374   | Regnault           | 
 |   0-200   | 32- 392   |     0.2375   | Regnault           | 
 | 20-440   | 68- 824   |     0.2366   | Holborn and Curtis | 
 | 20-630   | 68-1166   |     0.2429   | Holborn and Curtis | 
 | 20-800   | 68-1472   |     0.2430   | Holborn and Curtis | 
 |   0-200   | 32- 392   |     0.2389   | Wiedemann         | 
 |____________|____________|_______________|____________________| 
   
 This value is of particular importance in waste heat work and it is 
 regrettable that there is such a variation in the different experiments. 
 Mallard and Le Chatelier determined values considerably higher than any 
 given in Table 28. All things considered in view of the discrepancy of 
 the values given, there appears to be as much ground for the use of a 
 constant value for the specific heat of air at any temperature as for a 
 variable value. Where this value is used throughout this book, it has 
 been taken as 0.24. 
   
 Air may carry a considerable quantity of water vapor, which is 
 frequently 3 per cent of the total weight. This fact is of importance in 
 problems relating to heating drying and the compressing of air. Table 29 
 gives the amount of vapor required to saturate air at different 
 temperatures, its weight, expansive force, etc., and contains sufficient 
 information for solving practically all problems of this sort that may 
 arise. 
   
                                    TABLE 29 
   
    WEIGHTS OF AIR, VAPOR OF WATER, AND SATURATED MIXTURES OF AIR AND VAPOR 
                           AT DIFFERENT TEMPERATURES, 
      UNDER THE ORDINARY ATMOSPHERIC PRESSURE OF 29.921 INCHES OF MERCURY 
   
 Column Headings: 
 1: Temperature Degrees Fahrenheit 
 2: Volume of Dry Air at Different Temperatures, the Volume at 32 Degrees 
    being 1.000 
 3: Weight of Cubic Foot of Dry Air at the Different Temperatures Pounds 
 4: Elastic Force of Vapor in Inches of Mercury (Regnault) 
 5: Elastic Force of the Air in the Mixture of Air and Vapor in Inches of 
    Mercury 
 6: Weight of the Air in Pounds 
 7: Weight of the Vapor in Pounds 
 8: Total Weight of Mixture in Pounds 
 9: Weight of Vapor Mixed with One Pound of Air, in Pounds 
 10: Weight of Dry Air Mixed with One Pound of Vapor, in Pounds 
 11: Cubic Feet of Vapor from One Pound of Water at its own Pressure in 
    Column 4 
 ____________________________________________________________________________ 
 |   |     |     |     |                                             |     | 
 |   |     |     |     |           Mixtures of Air Saturated         |     | 
 |   |     |     |     |                 with Vapor                 |     | 
 |___|_____|_____|______|______________________________________________|______| 
 |   |     |     |     |     |Weight of Cubic Foot |       |       |     | 
 |   |     |     |     |     | of the Mixture of |       |       |     | 
 |   |     |     |     |     |   Air and Vapor   |       |       |     | 
 |   |     |     |     |     |_____________________|       |       |     | 
 |   |     |     |     |     |     |      |       |       |       |     | 
 | 1 | 2 | 3 | 4   | 5   | 6 |   7   |   8   |   9   |   10   | 11 | 
 |___|_____|_____|______|______|_____|_______|_______|________|________|______| 
 |   |     |     |     |     |     |       |       |       |       |     | 
 | 0| .935|.0864| .044|29.877|.0863|.000079|.086379| .00092|1092.4 |     | 
 | 12| .960|.0842| .074|29.849|.0840|.000130|.084130| .00155| 646.1 |     | 
 | 22| .980|.0824| .118|29.803|.0821|.000202|.082302| .00245| 406.4 |     | 
 | 32|1.000|.0807| .181|29.740|.0802|.000304|.080504| .00379| 263.81 |3289 | 
 | 42|1.020|.0791| .267|29.654|.0784|.000440|.078840| .00561| 178.18 |2252 | 
 |   |     |     |     |     |     |       |       |       |       |     | 
 | 52|1.041|.0776| .388|29.533|.0766|.000627|.077227| .00810| 122.17 |1595 | 
 | 62|1.061|.0761| .556|29.365|.0747|.000881|.075581| .01179| 84.79 |1135 | 
 | 72|1.082|.0747| .785|29.136|.0727|.001221|.073921| .01680| 59.54 | 819 | 
 | 82|1.102|.0733| 1.092|28.829|.0706|.001667|.072267| .02361| 42.35 | 600 | 
 | 92|1.122|.0720| 1.501|28.420|.0684|.002250|.070717| .03289| 30.40 | 444 | 
 |   |     |     |     |     |     |       |       |       |       |     | 
 |102|1.143|.0707| 2.036|27.885|.0659|.002997|.068897| .04547| 21.98 | 334 | 
 |112|1.163|.0694| 2.731|27.190|.0631|.003946|.067046| .06253| 15.99 | 253 | 
 |122|1.184|.0682| 3.621|26.300|.0599|.005142|.065042| .08584| 11.65 | 194 | 
 |132|1.204|.0671| 4.752|25.169|.0564|.006639|.063039| .11771|   8.49 | 151 | 
 |142|1.224|.0660| 6.165|23.756|.0524|.008473|.060873| .16170|   6.18 | 118 | 
 |   |     |     |     |     |     |       |       |       |       |     | 
 |152|1.245|.0649| 7.930|21.991|.0477|.010716|.058416| .22465|   4.45 | 93.3| 
 |162|1.265|.0638|10.099|19.822|.0423|.013415|.055715| .31713|   3.15 | 74.5| 
 |172|1.285|.0628|12.758|17.163|.0360|.016682|.052682| .46338|   2.16 | 59.2| 
 |182|1.306|.0618|15.960|13.961|.0288|.020536|.049336| .71300|   1.402| 48.6| 
 |192|1.326|.0609|19.828|10.093|.0205|.025142|.045642| 1.22643|   .815| 39.8| 
 |   |     |     |     |     |     |       |       |       |       |     | 
 |202|1.347|.0600|24.450| 5.471|.0109|.030545|.041445| 2.80230|   .357| 32.7| 
 |212|1.367|.0591|29.921| 0.000|.0000|.036820|.036820|Infinite|   .000| 27.1| 
 |___|_____|_____|______|______|_____|_______|_______|________|________|______| 
   
 Column 5 = barometer pressure of 29.921, minus the proportion of this 
 due to vapor pressure from column 4. 
   
 
 
 
 COMBUSTION 
 Combustion may be defined as the rapid chemical combination of oxygen 
 with carbon, hydrogen and sulphur, accompanied by the diffusion of heat 
 and light. That portion of the substance thus combined with the oxygen 
 is called combustible. As used in steam engineering practice, however, 
 the term combustible is applied to that portion of the fuel which is dry 
 and free from ash, thus including both oxygen and nitrogen which may be 
 constituents of the fuel, though not in the true sense of the term 
 combustible. 
   
 Combustion is perfect when the combustible unites with the greatest 
 possible amount of oxygen, as when one atom of carbon unites with two 
 atoms of oxygen to form carbon dioxide, CO_{2}. The combustion is 
 imperfect when complete oxidation of the combustible does not occur, or 
 where the combustible does not unite with the maximum amount of oxygen, 
 as when one atom of carbon unites with one atom of oxygen to form carbon 
 monoxide, CO, which may be further burned to carbon dioxide. 
   
 Kindling Point--Before a combustible can unite with oxygen and 
 combustion takes place, its temperature must first be raised to the 
 ignition or kindling point, and a sufficient time must be allowed for 
 the completion of the combustion before the temperature of the gases is 
 lowered below that point. Table 30, by Stromeyer, gives the approximate 
 kindling temperatures of different fuels. 
   
                TABLE 30 
   
 KINDLING TEMPERATURE OF VARIOUS FUELS 
   
 ____________________________________ 
 |                 |                 | 
 |                 |   Degrees       | 
 |                |   Fahrenheit     | 
 |_________________|__________________| 
 |                 |                 | 
 | Lignite Dust   |   300           | 
 | Dried Peat     |   435           | 
 | Sulphur         |   470           | 
 | Anthracite Dust |   570           | 
 | Coal           |   600           | 
 | Coke           |   Red Heat       | 
 | Anthracite     |   Red Heat, 750 | 
 | Carbon Monoxide |   Red Heat, 1211 | 
 | Hydrogen       |   1030 or 1290   | 
 |_________________|__________________| 
   
   
 Combustibles--The principal combustibles in coal and other fuels are 
 carbon, hydrogen and sulphur, occurring in varying proportions and 
 combinations. 
   
 Carbon is by far the most abundant as is indicated in the chapters on 
 fuels. 
   
 Hydrogen in a free state occurs in small quantities in some fuels, but 
 is usually found in combination with carbon, in the form of 
 hydrocarbons. The density of hydrogen is 0.0696 (Air = 1) and its weight 
 per cubic foot, at 32 degrees Fahrenheit and under atmospheric pressure, 
 is 0.005621 pounds. 
   
 Sulphur is found in most coals and some oils. It is usually present in 
 combined form, either as sulphide of iron or sulphate of lime; in the 
 latter form it has no heat value. Its presence in fuel is objectionable 
 because of its tendency to aid in the formation of clinkers, and the 
 gases from its combustion, when in the presence of moisture, may cause 
 corrosion. 
   
 Nitrogen is drawn into the furnace with the air. Its density is 0.9673 
 (Air = 1); its weight, at 32 degrees Fahrenheit and under atmospheric 
 pressure, is 0.07829 pounds per cubic foot; each pound of air at 
 atmospheric pressure contains 0.7685 pounds of nitrogen, and one pound 
 of nitrogen is contained in 1.301 pounds of air. 
   
 Nitrogen performs no useful office in combustion and passes through the 
 furnace without change. It dilutes the air, absorbs heat, reduces the 
 temperature of the products of combustion, and is the chief source of 
 heat losses in furnaces. 
   
 Calorific Value--Each combustible element of gas will combine with 
 oxygen in certain definite proportions and will generate a definite 
 amount of heat, measured in B. t. u. This definite amount of heat per 
 pound liberated by perfect combustion is termed the calorific value of 
 that substance. Table 31, gives certain data on the reactions and 
 results of combustion for elementary combustibles and several compounds. 
   
                                  TABLE 31 
   
                  OXYGEN AND AIR REQUIRED FOR COMBUSTION 
   
                      AT 32 DEGREES AND 29.92 INCHES 
   
 Column headings: 
   
 1: Oxidizable Substance or Combustible 
 2: Chemical Symbol 
 3: Atomic or Combining Weight 
 4: Chemical Reaction 
 5: Product of Combustion 
 6: Oxygen per Pound of Column 1 Pounds 
 7: Nitrogen per Pound of Column 1. 3.32[23] × O Pounds 
 8: Air per Pound of Column 1. 4.32[24] × O Pounds 
 9: Gaseous Product per Pound of Column 1[25] + Column 8 Pounds 
 10: Heat Value per Pound of Column 1 B. t. u. 
 11: Volumes of Column 1 Entering Combination Volume 
 12: Volumes of Oxygen Combining with Column 11 Volume 
 13: Volumes of Product Formed Volume 
 14: Volume per Pound of Column 1 in Gaseous Form Cubic Feet 
 15: Volume of Oxygen per Pound of Column 1 Cubic Feet 
 16: Volume of Products of Combustion per Pound of Column 1 Cubic Feet 
 17: Volume of Nitrogen per Pound of Column 1 3.782[26] × Column 15 Cubic 
    Feet 
 18: Volume of Gas per pound of Column 1 = Column 10 ÷ Column 17 Cubic 
    Feet 
   
                                  BY WEIGHT 
 ________________________________________________________________________ 
 |               |       |   |               |                 |       | 
 |       1       |   2   | 3 |       4       |       5       |   6   | 
 |________________|_______|____|________________|_________________|_______| 
 |               |       |   |               |                |       | 
 | Carbon         | C     | 12 | C+2O = CO_{2} | Carbon Dioxide | 2.667 | 
 | Carbon         | C     | 12 | C+O = CO       | Carbon Monoxide | 1.333 | 
 | Carbon Monoxide| CO   | 28 | CO+O = CO_{2} | Carbon Dioxide | .571 | 
 | Hydrogen       | H     | 1 | 2H+O = H_{2}O | Water           | 8     | 
 |               |       |   / CH_{4}+4O =   | Carbon Dioxide        | 
 | Methane       | CH_{4}| 16 |               |                 | 4     | 
 |               |       |    CO_{2}+2H_{2}O | and Water       /       | 
 | Sulphur       | S     | 32 | S+2O = SO_{2} | Sulphur Dioxide | 1     | 
 |________________|_______|____|________________|_________________|_______| 
   
 ________________________________________________________ 
 |               |      |       |       |       |       | 
 |       1       |   2   |   7   |   8   |   9   | 10   | 
 |________________|_______|_______|_______|_______|_______| 
 |               |       |       |       |       |       | 
 | Carbon         | C     | 8.85 | 11.52 | 12.52 | 14600 | 
 | Carbon         | C     | 4.43 | 5.76 | 6.76 | 4450 | 
 | Carbon Monoxide| CO   | 1.90 | 2.47 | 3.47 | 10150 | 
 | Hydrogen       | H     | 26.56 | 34.56 | 35.56 | 62000 | 
 |               |       |       |       |       |       | 
 | Methane       | CH_{4}| 13.28 | 17.28 | 18.28 | 23550 | 
 |               |       |       |       |       |       | 
 | Sulphur       | S     | 3.32 | 4.32 | 5.32 | 4050 | 
 |________________|_______|_______|_______|_______|_______| 
   
   
                           BY VOLUME 
   
 ________________________________________________________________ 
 |                 |       |     |   |               |       | 
 |       1       |   2   | 11 | 12 |       13       |   14   | 
 |_________________|________|______|____|________________|________| 
 |                 |       |     |   |               |       | 
 | Carbon         | C     | 1C   | 2 | 2CO_{2}       | 14.95 | 
 | Carbon         | C     | 1C   | 1 | 2CO           | 14.95 | 
 | Carbon Monoxide | CO    | 2CO | 1 | 2CO_{2}       | 12.80 | 
 | Hydrogen       | H     | 2H   | 1 | 2H_{2}O       | 179.32 | 
 | Methane         | CH_{4} | 1C4H | 4 | 1CO_{2} 2H_{2}O| 22.41 | 
 | Sulphur         | S     | 1S   | 2 | 1SO_{2}       |   5.60 | 
 |_________________|________|______|____|________________|________| 
   
 _____________________________________________________________ 
 |                 |       |       |       |       |       | 
 |       1       |   2   | 15   |   16   |   17   |   18   | 
 |_________________|________|_______|________|________|________| 
 |                 |       |       |       |       |       | 
 | Carbon         | C     | 29.89 | 29.89 | 112.98 | 142.87 | 
 | Carbon         | C     | 14.95 | 29.89 | 56.49 | 86.38 | 
 | Carbon Monoxide | CO     | 6.40 | 12.80 | 24.20 | 37.00 | 
 | Hydrogen       | H     | 89.66 | 179.32 | 339.09 | 518.41 | 
 | Methane         | CH_{4} | 44.83 | 67.34 | 169.55 | 236.89 | 
 | Sulphur         | S     | 11.21 | 11.21 | 42.39 | 53.60 | 
 |_________________|________|_______|________|________|________| 
   
 It will be seen from this table that a pound of carbon will unite with 
 2-2/3 pounds of oxygen to form carbon dioxide, and will evolve 14,600 
 t. u. As an intermediate step, a pound of carbon may unite with 1-1/3 
 
 pounds of oxygen to form carbon monoxide and evolve 4450 B. t. u., but 
 in its further conversion to CO_{2} it would unite with an additional 
 1-1/3 times its weight of oxygen and evolve the remaining 10,150 
 t. u. When a pound of CO burns to CO_{2}, however, only 4350 B. t. u. 
 
 are evolved since the pound of CO contains but 3/7 pound carbon. 
   
 Air Required for Combustion--It has already been shown that each 
 combustible element in fuel will unite with a definite amount of oxygen. 
 With the ultimate analysis of the fuel known, in connection with Table 
 31, the theoretical amount of air required for combustion may be readily 
 calculated. 
   
 Let the ultimate analysis be as follows: 
   
              _Per Cent_ 
 Carbon         74.79 
 Hydrogen         4.98 
 Oxygen           6.42 
 Nitrogen         1.20 
 Sulphur         3.24 
 Water           1.55 
 Ash             7.82 
                ------ 
                100.00 
   
 When complete combustion takes place, as already pointed out, the carbon 
 in the fuel unites with a definite amount of oxygen to form CO_{2}. The 
 hydrogen, either in a free or combined state, will unite with oxygen to 
 form water vapor, H_{2}O. Not all of the hydrogen shown in a fuel 
 analysis, however, is available for the production of heat, as a portion 
 of it is already united with the oxygen shown by the analysis in the 
 form of water, H_{2}O. Since the atomic weights of H and O are 
 respectively 1 and 16, the weight of the combined hydrogen will be 1/8 
 of the weight of the oxygen, and the hydrogen available for combustion 
 will be H - 1/8 O. In complete combustion of the sulphur, sulphur 
 dioxide SO_{2} is formed, which in solution in water forms sulphuric 
 acid. 
   
 Expressed numerically, the theoretical amount of air for the above 
 analysis is as follows: 
   
 0.7479 C × 2-2/3         = 1.9944 O needed 
 (           0.0642 ) 
 ( 0.0498 - -------) H × 8 = 0.3262 O needed 
 (             8   ) 
 0.0324 S × 1             = 0.0324 O needed 
                              ------ 
                    Total   2.3530 O needed 
   
 One pound of oxygen is contained in 4.32 pounds of air. 
   
 The total air needed per pound of coal, therefore, will be 2.353 × 4.32 
 = 10.165. 
   
 The weight of combustible per pound of fuel is .7479 + .0418[27] + .0324 
 + .012 = .83 pounds, and the air theoretically required per pound of 
 combustible is 10.165 ÷ .83 = 12.2 pounds. 
   
 The above is equivalent to computing the theoretical amount of air 
 required per pound of fuel by the formula: 
   
                                    (   O) 
 Weight per pound = 11.52 C + 34.56 (H - -) + 4.32 S     (10) 
                                    (   8) 
   
 where C, H, O and S are proportional parts by weight of carbon, 
 hydrogen, oxygen and sulphur by ultimate analysis. 
   
 In practice it is impossible to obtain perfect combustion with the 
 theoretical amount of air, and an excess may be required, amounting to 
 sometimes double the theoretical supply, depending upon the nature of 
 the fuel to be burned and the method of burning it. The reason for this 
 is that it is impossible to bring each particle of oxygen in the air 
 into intimate contact with the particles in the fuel that are to be 
 oxidized, due not only to the dilution of the oxygen in the air by 
 nitrogen, but because of such factors as the irregular thickness of the 
 fire, the varying resistance to the passage of the air through the fire 
 in separate parts on account of ash, clinker, etc. Where the 
 difficulties of drawing air uniformly through a fuel bed are eliminated, 
 as in the case of burning oil fuel or gas, the air supply may be 
 materially less than would be required for coal. Experiment has shown 
 that coal will usually require 50 per cent more than the theoretical net 
 calculated amount of air, or about 18 pounds per pound of fuel either 
 under natural or forced draft, though this amount may vary widely with 
 the type of furnace, the nature of the coal, and the method of firing. 
 If less than this amount of air is supplied, the carbon burns to 
 monoxide instead of dioxide and its full heat value is not developed. 
   
 An excess of air is also a source of waste, as the products of 
 combustion will be diluted and carry off an excessive amount of heat in 
 the chimney gases, or the air will so lower the temperature of the 
 furnace gases as to delay the combustion to an extent that will cause 
 carbon monoxide to pass off unburned from the furnace. A sufficient 
 amount of carbon monoxide in the gases may cause the action known as 
 secondary combustion, by igniting or mingling with air after leaving the 
 furnace or in the flues or stack. Such secondary combustion which takes 
 place either within the setting after leaving the furnace or in the 
 flues or stack always leads to a loss of efficiency and, in some 
 instances, leads to overheating of the flues and stack. 
   
 Table 32 gives the theoretical amount of air required for various fuels 
 calculated from formula (10) assuming the analyses of the fuels given in 
 the table. 
   
 The process of combustion of different fuels and the effect of variation 
 in the air supply for their combustion is treated in detail in the 
 chapters dealing with the various fuels. 
   
                            TABLE 32 
   
              CALCULATED THEORETICAL AMOUNT OF AIR 
              REQUIRED PER POUND OF VARIOUS FUELS 
   
 ____________________________________________________________ 
 |               |Weight of Constituents in One |Air Required| 
 |     Fuel       |Pound Dry Fuel               |per Pound   | 
 |               |______________________________|of Fuel     | 
 |               | Carbon | Hydrogen| Oxygen   |Pounds     | 
 |               | Per Cent| Per Cent| Per Cent |           | 
 |________________|_________|_________|__________|____________| 
 |Coke           | 94.0   |   .   |   .     | 10.8     | 
 |Anthracite Coal | 91.5   |   3.5   |   2.6   | 11.7     | 
 |Bituminous Coal | 87.0   |   5.0   | 4.0   | 11.6     | 
 |Lignite         | 70.0   |   5.0   | 20.0   |   8.9     | 
 |Wood           | 50.0   |   6.0   | 43.5   |   6.0     | 
 |Oil             | 85.0   | 13.0   |   1.0   | 14.3     | 
 |________________|_________|_________|__________|____________| 
   
 
 
 
 ANALYSIS OF FLUE GASES 
 The object of a flue gas analysis is the determination of the 
 completeness of the combustion of the carbon in the fuel, and the amount 
 and distribution of the heat losses due to incomplete combustion. The 
 quantities actually determined by an analysis are the relative 
 proportions by volume, of carbon dioxide (CO_{2}), oxygen (O), and 
 carbon monoxide (CO), the determinations being made in this order. 
   
 The variations of the percentages of these gases in an analysis is best 
 illustrated in the consideration of the complete combustion of pure 
 carbon, a pound of which requires 2.67 pounds of oxygen,[28] or 32 cubic 
 feet at 60 degrees Fahrenheit. The gaseous product of such combustion 
 will occupy, when cooled, the same volume as the oxygen, namely, 32 
 cubic feet. The air supplied for the combustion is made up of 20.91 per 
 cent oxygen and 79.09 per cent nitrogen by volume. The carbon united 
 with the oxygen in the form of carbon dioxide will have the same volume 
 as the oxygen in the air originally supplied. The volume of the nitrogen 
 when cooled will be the same as in the air supplied, as it undergoes no 
 change. Hence for complete combustion of one pound of carbon, where no 
 excess of air is supplied, an analysis of the products of combustion 
 will show the following percentages by volume: 
   
                              _Actual Volume_ 
                          _for One Pound Carbon_     _Per Cent_ 
                                _Cubic Feet_           _by Volume_ 
 Carbon Dioxide                     32         =       20.91 
 Oxygen                              0         =         0.00 
 Nitrogen                           121         =       79.09 
                                    ---                 ------ 
 Air required for one pound Carbon 153         =       100.00 
   
 For 50 per cent excess air the volume will be as follows: 
   
    153 × 1½ = 229.5 cubic feet of air per pound of carbon. 
   
                _Actual Volume_ 
            _for One Pound Carbon_   _Per Cent_ 
                  _Cubic Feet_         _by Volume_ 
 Carbon Dioxide        32         =     13.91 } 
 Oxygen               16         =       7.00 } = 20.91 per cent 
 Nitrogen             181.5       =     79.09 
                      -----             ------ 
                      229.5       =     100.00 
   
 For 100 per cent excess air the volume will be as follows: 
   
    153 × 2 = 306 cubic feet of air per pound of carbon. 
   
                _Actual Volume_ 
              _for One Pound Carbon_   _Per Cent_ 
                  _Cubic Feet_         _by Volume_ 
 Carbon Dioxide         32         =     10.45 } 
 Oxygen                 32         =     10.45 } = 20.91 per cent 
 Nitrogen             242         =     79.09 
                      ---               ------ 
                      306         =     100.00 
   
 In each case the volume of oxygen which combines with the carbon is 
 equal to (cubic feet of air × 20.91 per cent)--32 cubic feet. 
   
 It will be seen that no matter what the excess of air supplied, the 
 actual amount of carbon dioxide per pound of carbon remains the same, 
 while the percentage by volume decreases as the excess of air increases. 
 The actual volume of oxygen and the percentage by volume increases with 
 the excess of air, and the percentage of oxygen is, therefore, an 
 indication of the amount of excess air. In each case the sum of the 
 percentages of CO_{2} and O is the same, 20.9. Although the volume of 
 nitrogen increases with the excess of air, its percentage by volume 
 remains the same as it undergoes no change while combustion takes place; 
 its percentage for any amount of air excess, therefore, will be the same 
 after combustion as before, if cooled to the same temperature. It must 
 be borne in mind that the above conditions hold only for the perfect 
 combustion of a pound of pure carbon. 
   
 Carbon monoxide (CO) produced by the imperfect combustion of carbon, 
 will occupy twice the volume of the oxygen entering into its composition 
 and will increase the volume of the flue gases over that of the air 
 supplied for combustion in the proportion of 
   
      100 + ½ the per cent CO 
 1 to ----------------------- 
                100 
   
 When pure carbon is the fuel, the sum of the percentages by volume of 
 carbon dioxide, oxygen and one-half of the carbon monoxide, must be in 
 the same ratio to the nitrogen in the flue gases as is the oxygen to the 
 nitrogen in the air supplied, that is, 20.91 to 79.09. When burning 
 coal, however, the percentage of nitrogen is obtained by subtracting the 
 sum of the percentages by volume of the other gases from 100. Thus if an 
 analysis shows 12.5 per cent CO_{2}, 6.5 per cent O, and 0.6 per cent 
 CO, the percentage of nitrogen which ordinarily is the only other 
 constituent of the gas which need be considered, is found as follows: 
   
 100 - (12.5 + 6.5 + 0.6) = 80.4 per cent. 
   
 The action of the hydrogen in the volatile constituents of the fuel is 
 to increase the apparent percentage of the nitrogen in the flue gases. 
 This is due to the fact that the water vapor formed by the combustion of 
 the hydrogen will condense at a temperature at which the analysis is 
 made, while the nitrogen which accompanied the oxygen with which the 
 hydrogen originally combined maintains its gaseous form and passes into 
 the sampling apparatus with the other gases. For this reason coals 
 containing high percentages of volatile matter will produce a larger 
 quantity of water vapor, and thus increase the apparent percentage of 
 nitrogen. 
   
   
 Air Required and Supplied--When the ultimate analysis of a fuel is 
 known, the air required for complete combustion with no excess can be 
 found as shown in the chapter on combustion, or from the following 
 approximate formula: 
   
    Pounds of air required per pound of fuel = 
   
          (C       O   S) 
    34.56 (- + (H - -) + -)[29]     (11) 
          (3       8   8) 
   
 where C, H and O equal the percentage by weight of carbon, hydrogen and 
 oxygen in the fuel divided by 100. 
   
 When the flue gas analysis is known, the total, amount of air supplied 
 is: 
   
    Pounds of air supplied per pound of fuel = 
   
                N 
    3.036 (-----------) × C[30]     (12) 
            CO_{2} + CO 
   
 where N, CO_{2} and CO are the percentages by volume of nitrogen, carbon 
 dioxide and carbon monoxide in the flue gases, and C the percentage by 
 weight of carbon which is burned from the fuel and passes up the stack 
 as flue gas. This percentage of C which is burned must be distinguished 
 from the percentage of C as found by an ultimate analysis of the fuel. 
 To find the percentage of C which is burned, deduct from the total 
 percentage of carbon as found in the ultimate analysis, the percentage 
 of unconsumed carbon found in the ash. This latter quantity is the 
 difference between the percentage of ash found by an analysis and that 
 as determined by a boiler test. It is usually assumed that the entire 
 combustible element in the ash is carbon, which assumption is 
 practically correct. Thus if the ash in a boiler test were 16 per cent 
 and by an analysis contained 25 per cent of carbon, the percentage of 
 unconsumed carbon would be 16 × .25 = 4 per cent of the total coal 
 burned. If the coal contained by ultimate analysis 80 per cent of carbon 
 the percentage burned, and of which the products of combustion pass up 
 the chimney would be 80 - 4 = 76 per cent, which is the correct figure 
 to use in calculating the total amount of air supplied by formula (12). 
   
 The weight of flue gases resulting from the combustion of a pound of dry 
 coal will be the sum of the weights of the air per pound of coal and the 
 combustible per pound of coal, the latter being equal to one minus the 
 percentage of ash as found in the boiler test. The weight of flue gases 
 per pound of dry fuel may, however, be computed directly from the 
 analyses, as shown later, and the direct computation is that ordinarily 
 used. 
   
 The ratio of the air actually supplied per pound of fuel to that 
 theoretically required to burn it is: 
   
          N 
 3.036(---------)×C 
      CO_{2}+CO 
 ------------------     (13) 
      C       O 
 34.56(- + H - -) 
      3       8 
   
 in which the letters have the same significance as in formulae (11) and 
 (12). 
   
 The ratio of the air supplied per pound of combustible to the amount 
 theoretically required is: 
   
          N 
 ------------------     (14) 
 N - 3.782(O - ½CO) 
   
 which is derived as follows: 
   
 The N in the flue gas is the content of nitrogen in the whole amount of 
 air supplied. The oxygen in the flue gas is that contained in the air 
 supplied and which was not utilized in combustion. This oxygen was 
 accompanied by 3.782 times its volume of nitrogen. The total amount of 
 excess oxygen in the flue gases is (O - ½CO); hence N - 3.782(O - ½CO) 
 represents the nitrogen content in the air actually required for 
 combustion and N ÷ (N - 3.782[O - ½CO]) is the ratio of the air supplied 
 to that required. This ratio minus one will be the proportion of excess 
 air. 
   
 The heat lost in the flue gases is L = 0.24 W (T - t)     (15) 
   
 Where L = B. t. u. lost per pound of fuel, 
      W = weight of flue gases in pounds per pound of dry coal, 
      T = temperature of flue gases, 
      t = temperature of atmosphere, 
    0.24 = specific heat of the flue gases. 
   
 The weight of flue gases, W, per pound of carbon can be computed 
 directly from the flue gas analysis from the formula: 
   
 11 CO_{2} + 8 O + 7 (CO + N) 
 ----------------------------     (16) 
      3 (CO_{2} + CO) 
   
 where CO_{2}, O, CO, and N are the percentages by volume as determined 
 by the flue gas analysis of carbon dioxide, oxygen, carbon monoxide and 
 nitrogen. 
   
 The weight of flue gas per pound of dry coal will be the weight 
 determined by this formula multiplied by the percentage of carbon in the 
 coal from an ultimate analysis. 
   
 [Graph: Temperature of Escaping Gases--Deg. Fahr. 
 against Heat carried away by Chimney Gases--In B.t.u. 
 per pound of Carbon burned.[31] 
   
 Fig. 20. Loss Due to Heat Carried Away by Chimney Gases for Varying 
 Percentages of Carbon Dioxide. Based on Boiler Room Temperature = 80 
 Degrees Fahrenheit. Nitrogen in Flue Gas = 80.5 Per Cent. Carbon 
 Monoxide in Flue Gas = 0. Per Cent] 
   
 Fig. 20 represents graphically the loss due to heat carried away by dry 
 chimney gases for varying percentages of CO_{2}, and different 
 temperatures of exit gases. 
   
 The heat lost, due to the fact that the carbon in the fuel is not 
 completely burned and carbon monoxide is present in the flue gases, in 
 t. u. per pound of fuel burned is: 
 
   
              (   CO     ) 
 L' = 10,150 × (-----------)     (17) 
              (CO + CO_{2}) 
   
 where, as before, CO and CO_{2} are the percentages by volume in the 
 flue gases and C is the proportion by weight of carbon which is burned 
 and passes up the stack. 
   
 Fig. 21 represents graphically the loss due to such carbon in the fuel 
 as is not completely burned but escapes up the stack in the form of 
 carbon monoxide. 
   
 [Graph: Loss in B.T.U. per Pound of Carbon Burned[32] 
 against Per Cent CO_{2} in Flue Gas 
   
 Fig. 21. Loss Due to Unconsumed Carbon Contained in the 
 CO in the Flue Gases] 
   
 Apparatus for Flue Gas Analysis--The Orsat apparatus, illustrated in 
 Fig. 22, is generally used for analyzing flue gases. The burette A is 
 graduated in cubic centimeters up to 100, and is surrounded by a water 
 jacket to prevent any change in temperature from affecting the density 
 of the gas being analyzed. 
   
 For accurate work it is advisable to use four pipettes, B, C, D, E, the 
 first containing a solution of caustic potash for the absorption of 
 carbon dioxide, the second an alkaline solution of pyrogallol for the 
 absorption of oxygen, and the remaining two an acid solution of cuprous 
 chloride for absorbing the carbon monoxide. Each pipette contains a 
 number of glass tubes, to which some of the solution clings, thus 
 facilitating the absorption of the gas. In the pipettes D and E, copper 
 wire is placed in these tubes to re-energize the solution as it becomes 
 weakened. The rear half of each pipette is fitted with a rubber bag, one 
 of which is shown at K, to protect the solution from the action of the 
 air. The solution in each pipette should be drawn up to the mark on the 
 capillary tube. 
   
 The gas is drawn into the burette through the U-tube H, which is filled 
 with spun glass, or similar material, to clean the gas. To discharge any 
 air or gas in the apparatus, the cock G is opened to the air and the 
 bottle F is raised until the water in the burette reaches the 100 cubic 
 centimeters mark. The cock G is then turned so as to close the air 
 opening and allow gas to be drawn through H, the bottle F being lowered 
 for this purpose. The gas is drawn into the burette to a point below the 
 zero mark, the cock G then being opened to the air and the excess gas 
 expelled until the level of the water in F and in A are at the zero 
 mark. This operation is necessary in order to obtain the zero reading at 
 atmospheric pressure. 
   
 The apparatus should be carefully tested for leakage as well as all 
 connections leading thereto. Simple tests can be made; for example: If 
 after the cock G is closed, the bottle F is placed on top of the frame 
 for a short time and again brought to the zero mark, the level of the 
 water in A is above the zero mark, a leak is indicated. 
   
 [Illustration: Fig. 22. Orsat Apparatus] 
   
 Before taking a final sample for analysis, the burette A should be 
 filled with gas and emptied once or twice, to make sure that all the 
 apparatus is filled with the new gas. The cock G is then closed and the 
 cock I in the pipette B is opened and the gas driven over into B by 
 raising the bottle F. The gas is drawn back into A by lowering F and 
 when the solution in B has reached the mark in the capillary tube, the 
 cock I is closed and a reading is taken on the burette, the level of the 
 water in the bottle F being brought to the same level as the water in A. 
 The operation is repeated until a constant reading is obtained, the 
 number of cubic centimeters being the percentage of CO_{2} in the flue 
 gases. 
   
 The gas is then driven over into the pipette C and a similar operation 
 is carried out. The difference between the resulting reading and the 
 first reading gives the percentage of oxygen in the flue gases. 
   
 The next operation is to drive the gas into the pipette D, the gas being 
 given a final wash in E, and then passed into the pipette C to 
 neutralize any hydrochloric acid fumes which may have been given off by 
 the cuprous chloride solution, which, especially if it be old, may give 
 off such fumes, thus increasing the volume of the gases and making the 
 reading on the burette less than the true amount. 
   
 The process must be carried out in the order named, as the pyrogallol 
 solution will also absorb carbon dioxide, while the cuprous chloride 
 solution will also absorb oxygen. 
   
 As the pressure of the gases in the flue is less than the atmospheric 
 pressure, they will not of themselves flow through the pipe connecting 
 the flue to the apparatus. The gas may be drawn into the pipe in the way 
 already described for filling the apparatus, but this is a tedious 
 method. For rapid work a rubber bulb aspirator connected to the air 
 outlet of the cock G will enable a new supply of gas to be drawn into 
 the pipe, the apparatus then being filled as already described. Another 
 form of aspirator draws the gas from the flue in a constant stream, thus 
 insuring a fresh supply for each sample. 
   
 The analysis made by the Orsat apparatus is volumetric; if the analysis 
 by weight is required, it can be found from the volumetric analysis as 
 follows: 
   
 Multiply the percentages by volume by either the densities or the 
 molecular weight of each gas, and divide the products by the sum of all 
 the products; the quotients will be the percentages by weight. For most 
 work sufficient accuracy is secured by using the even values of the 
 molecular weights. 
   
 The even values of the molecular weights of the gases appearing in an 
 analysis by an Orsat are: 
   
 Carbon Dioxide   44 
 Carbon Monoxide 28 
 Oxygen           32 
 Nitrogen         28 
   
 Table 33 indicates the method of converting a volumetric flue gas 
 analysis into an analysis by weight. 
   
                                TABLE 33 
   
     CONVERSION OF A FLUE GAS ANALYSIS BY VOLUME TO ONE BY WEIGHT 
   
 Column Headings: 
   
 A: Analysis by Volume Per Cent 
 B: Molecular Weight 
 C: Volume times Molecular Weight 
 D: Analysis by Weight Per Cent 
 _____________________________________________________________________ 
 |                       |       |           |       |               | 
 |         Gas           |   A   |     B     |   C   |       D       | 
 |________________________|_______|___________|________|_______________| 
 |                       |      |           |       |               | 
 |                       |       |           |       |               | 
 |                       |       |           |       | 536.8         | 
 | Carbon Dioxide CO_{2} | 12.2 | 12+(2×16) | 536.8 | ------ = 17.7 | 
 |                       |       |           |       | 3022.8       | 
 |                       |       |           |       |               | 
 |                       |       |           |       | 11.2         | 
 | Carbon Monoxide CO     |   .4 | 12+16   |   11.2 | ------ =   .4 | 
 |                       |       |           |       | 3022.8       | 
 |                       |       |           |       |               | 
 |                       |       |           |       | 220.8         | 
 | Oxygen         O     |   6.9 |   2×16   | 220.8 | ------ = 7.3 | 
 |                       |       |           |       | 3022.8       | 
 |                       |       |           |       |               | 
 |                       |       |         |       | 2254.0       | 
 | Nitrogen       N     | 80.5 |   2×14   | 2254.0 | ------ = 74.6 | 
 |                       |       |           |       | 3022.8       | 
 |________________________|_______|___________|________|_______________| 
 |                        |       |           |       |               | 
 | Total                 | 100.0 |           | 3022.8 |         100.0 | 
 |________________________|_______|___________|________|_______________| 
   
 Application of Formulae and Rules--Pocahontas coal is burned in the 
 furnace, a partial ultimate analysis being: 
   
                        _Per Cent_ 
 Carbon                   82.1 
 Hydrogen                   4.25 
 Oxygen                     2.6 
 Sulphur                   1.6 
 Ash                       6.0 
 t. u., per pound dry 14500 
 
   
 The flue gas analysis shows: 
   
                _Per Cent_ 
   
 CO_{2}             10.7 
 O                   9.0 
 CO                 0.0 
 N (by difference) 80.3 
   
 Determine: The flue gas analysis by weight (see Table 33), the amount of 
 air required for perfect combustion, the actual weight of air per pound 
 of fuel, the weight of flue gas per pound of coal, the heat lost in the 
 chimney gases if the temperature of these is 500 degrees Fahrenheit, and 
 the ratio of the air supplied to that theoretically required. 
   
 Solution: The theoretical weight of air required for perfect combustion, 
 per pound of fuel, from formula (11) will be, 
   
          (.821           .026   .016) 
 W = 34.56 (---- + (.0425 - ----) + ----) = 10.88 pounds. 
          ( 3               8       8 ) 
   
 If the amount of carbon which is burned and passes away as flue gas is 
 80 per cent, which would allow for 2.1 per cent of unburned carbon in 
 terms of the total weight of dry fuel burned, the weight of dry gas per 
 pound of carbon burned will be from formula (16): 
   
    11 × 10.7 + 8 × 9.0 + 7(0 + 80.3) 
 W = --------------------------------- = 23.42 pounds 
                3(10.7 + 0) 
   
 and the weight of flue gas per pound of coal burned will be .80 × 23.42 
 = 18.74 pounds. 
   
 The heat lost in the flue gases per pound of coal burned will be from 
 formula (15) and the value 18.74 just determined. 
   
 Loss = .24 × 18.74 × (500 - 60) = 1979 B. t. u. 
   
 The percentage of heat lost in the flue gases will be 1979 ÷ 14500 = 
 13.6 per cent. 
   
 The ratio of air supplied per pound of coal to that theoretically 
 required will be 18.74 ÷ 10.88 = 1.72 per cent. 
   
 The ratio of air supplied per pound of combustible to that required will 
 be from formula (14): 
   
          .803 
 ------------------------- = 1.73 
 .803 - 3.782(.09 - ½ × 0) 
   
 The ratio based on combustible will be greater than the ratio based on 
 fuel if there is unconsumed carbon in the ash. 
   
   
 Unreliability of CO_{2} Readings Taken Alone--It is generally assumed 
 that high CO_{2} readings are indicative of good combustion and hence of 
 high efficiency. This is true only in the sense that such high readings 
 do indicate the small amount of excess air that usually accompanies good 
 combustion, and for this reason high CO_{2} readings alone are not 
 considered entirely reliable. Wherever an automatic CO_{2} recorder is 
 used, it should be checked from time to time and the analysis carried 
 further with a view to ascertaining whether there is CO present. As the 
 percentage of CO_{2} in these gases increases, there is a tendency 
 toward the presence of CO, which, of course, cannot be shown by a CO_{2} 
 recorder, and which is often difficult to detect with an Orsat 
 apparatus. The greatest care should be taken in preparing the cuprous 
 chloride solution in making analyses and it must be known to be fresh 
 and capable of absorbing CO. In one instance that came to our attention, 
 in using an Orsat apparatus where the cuprous chloride solution was 
 believed to be fresh, no CO was indicated in the flue gases but on 
 passing the same sample into a Hempel apparatus, a considerable 
 percentage was found. It is not safe, therefore, to assume without 
 question from a high CO_{2} reading that the combustion is 
 correspondingly good, and the question of excess air alone should be 
 distinguished from that of good combustion. The effect of a small 
 quantity of CO, say one per cent, present in the flue gases will have a 
 negligible influence on the quantity of excess air, but the presence of 
 such an amount would mean a loss due to the incomplete combustion of the 
 carbon in the fuel of possibly 4.5 per cent of the total heat in the 
 fuel burned. When this is considered, the importance of a complete flue 
 gas analysis is apparent. 
   
 Table 34 gives the densities of various gases together with other data 
 that will be of service in gas analysis work. 
   
                              TABLE 34 
   
 DENSITY OF GASES AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE 
                    ADAPTED FROM SMITHSONIAN TABLES 
   
 +----------+----------+--------+---------+----------+---------------+ 
 |         |         |       |         |         |   Relative   | 
 |         |         |       | Weight |         |   Density,   | 
 |         |         |       |   of   | Volume | Hydrogen = 1 | 
 |         |         |Specific|One Cubic|   of   +-------+-------+ 
 | Gas     | Chemical |Gravity | Foot   |One Pound |       |Approx-| 
 |         | Symbol | Air=1 | Pounds |Cubic Feet| Exact | imate | 
 +----------+----------+--------+---------+----------+-------+-------+ 
 |Oxygen   |   O     | 1.053 | .08922 | 11.208 | 15.87 | 16   | 
 |Nitrogen |   N     | 0.9673 | .07829 | 12.773 | 13.92 | 14   | 
 |Hydrogen |   H     | 0.0696 | .005621 | 177.90   | 1.00 |   1   | 
 |Carbon   |         |       |         |         |      |       | 
 | Dioxide | CO_{2} | 1.5291 | .12269 | 8.151   | 21.83 | 22   | 
 |Carbon   |         |       |         |         |       |       | 
 | Monoxide |   CO     | 0.9672 | .07807 | 12.809   | 13.89 | 14   | 
 |Methane   | CH_{4} | 0.5576 | .04470 | 22.371   | 7.95 |   8   | 
 |Ethane   |C_{2}H_{6}| 1.075 | .08379 | 11.935   | 14.91 | 15   | 
 |Acetylene |C_{2}H_{2}| 0.920 | .07254 | 13.785   | 12.91 | 13   | 
 |Sulphur   |         |       |         |         |       |       | 
 | Dioxide | SO_{2} | 2.2639 | .17862 | 5.598   | 31.96 | 32   | 
 |Air       |   ...   | 1.0000 | .08071 | 12.390   | ... | ... | 
 +----------+----------+--------+---------+----------+-------+-------+ 
   
 [Illustration: 1942 Horse-power Installation of Babcock & Wilcox Boilers 
 and Superheaters in the Singer Building, New York City] 
   
 
 
 
 CLASSIFICATION OF FUELS 
 (WITH PARTICULAR REFERENCE TO COAL) 
   
   
 Fuels for steam boilers may be classified as solid, liquid or gaseous. 
 Of the solid fuels, anthracite and bituminous coals are the most common, 
 but in this class must also be included lignite, peat, wood, bagasse and 
 the refuse from certain industrial processes such as sawdust, shavings, 
 tan bark and the like. Straw, corn and coffee husks are utilized in 
 isolated cases. 
   
 The class of liquid fuels is represented chiefly by petroleum, though 
 coal tar and water-gas tar are used to a limited extent. 
   
 Gaseous fuels are limited to natural gas, blast furnace gas and coke 
 oven gas, the first being a natural product and the two latter 
 by-products from industrial processes. Though waste gases from certain 
 processes may be considered as gaseous fuels, inasmuch as the question 
 of combustion does not enter, the methods of utilizing them differ from 
 that for combustible gaseous fuel, and the question will be dealt with 
 separately. 
   
 Since coal is by far the most generally used of all fuels, this chapter 
 will be devoted entirely to the formation, composition and distribution 
 of the various grades, from anthracite to peat. The other fuels will be 
 discussed in succeeding chapters and their combustion dealt with in 
 connection with their composition. 
   
 Formation of Coal--All coals are of vegetable origin and are the remains 
 of prehistoric forests. Destructive distillation due to great pressures 
 and temperatures, has resolved the organic matter into its invariable 
 ultimate constituents, carbon, hydrogen, oxygen and other substances, in 
 varying proportions. The factors of time, depth of beds, disturbance of 
 beds and the intrusion of mineral matter resulting from such 
 disturbances have produced the variation in the degree of evolution from 
 vegetable fiber to hard coal. This variation is shown chiefly in the 
 content of carbon, and Table 35 shows the steps of such variation. 
   
                    TABLE 35 
   
      APPROXIMATE CHEMICAL CHANGES FROM WOOD 
            FIBER TO ANTHRACITE COAL 
   
 +----------------------+-------+--------+-------+ 
 |Substance             |Carbon |Hydrogen|Oxygen | 
 +----------------------+-------+--------+-------+ 
 |Wood Fiber            | 52.65 | 5.25 | 42.10 | 
 |Peat                 | 59.57 | 5.96 | 34.47 | 
 |Lignite               | 66.04 | 5.27 | 28.69 | 
 |Earthy Brown Coal     | 73.18 | 5.68 | 21.14 | 
 |Bituminous Coal       | 75.06 | 5.84 | 19.10 | 
 |Semi-bituminous Coal | 89.29 | 5.05 | 5.66 | 
 |Anthracite Coal       | 91.58 | 3.96 | 4.46 | 
 +----------------------+-------+--------+-------+ 
   
 Composition of Coal--The uncombined carbon in coal is known as fixed 
 carbon. Some of the carbon constituent is combined with hydrogen and 
 this, together with other gaseous substances driven off by the 
 application of heat, form that portion of the coal known as volatile 
 matter. The fixed carbon and the volatile matter constitute the 
 combustible. The oxygen and nitrogen contained in the volatile matter 
 are not combustible, but custom has applied this term to that portion of 
 the coal which is dry and free from ash, thus including the oxygen and 
 nitrogen. 
   
 The other important substances entering into the composition of coal are 
 moisture and the refractory earths which form the ash. The ash varies in 
 different coals from 3 to 30 per cent and the moisture from 0.75 to 45 
 per cent of the total weight of the coal, depending upon the grade and 
 the locality in which it is mined. A large percentage of ash is 
 undesirable as it not only reduces the calorific value of the fuel, but 
 chokes up the air passages in the furnace and through the fuel bed, thus 
 preventing the rapid combustion necessary to high efficiency. If the 
 coal contains an excessive quantity of sulphur, trouble will result from 
 its harmful action on the metal of the boiler where moisture is present, 
 and because it unites with the ash to form a fusible slag or clinker 
 which will choke up the grate bars and form a solid mass in which large 
 quantities of unconsumed carbon may be imbedded. 
   
 Moisture in coal may be more detrimental than ash in reducing the 
 temperature of a furnace, as it is non-combustible, absorbs heat both in 
 being evaporated and superheated to the temperature of the furnace 
 gases. In some instances, however, a certain amount of moisture in a 
 bituminous coal produces a mechanical action that assists in the 
 combustion and makes it possible to develop higher capacities than with 
 dry coal. 
   
 Classification of Coal--Custom has classified coals in accordance with 
 the varying content of carbon and volatile matter in the combustible. 
 Table 36 gives the approximate percentages of these constituents for the 
 general classes of coals with the corresponding heat values per pound of 
 combustible. 
   
                            TABLE 36 
   
            APPROXIMATE COMPOSITION AND CALORIFIC VALUE 
        OF GENERAL GRADES OF COAL ON BASIS OF COMBUSTIBLE 
   
 +-------------------+----------------------------+--------------+ 
 |   Kind of Coal   | Per Cent of Combustible   |   B. t. u.   | 
 |                   +------------+---------------+ Per Pound of | 
 |                   |Fixed Carbon|Volatile Matter| Combustible | 
 +-------------------+------------+---------------+--------------+ 
 |Anthracite         |97.0 to 92.5| 3.0 to 7.5 |14600 to 14800| 
 |Semi-anthracite   |92.5 to 87.5| 7.5 to 12.5 |14700 to 15500| 
 |Semi-bituminous   |87.5 to 75.0| 12.5 to 25.0 |15500 to 16000| 
 |Bituminous--Eastern|75.0 to 60.0| 25.0 to 40.0 |14800 to 15300| 
 |Bituminous--Western|65.0 to 50.0| 35.0 to 50.0 |13500 to 14800| 
 |Lignite           | Under 50 |   Over 50   |11000 to 13500| 
 +-------------------+------------+---------------+--------------+ 
   
   
 Anthracite--The name anthracite, or hard coal, is applied to those dry 
 coals containing from 3 to 7 per cent volatile matter and which do not 
 swell when burned. True anthracite is hard, compact, lustrous and 
 sometimes iridescent, and is characterized by few joints and clefts. Its 
 specific gravity varies from 1.4 to 1.8. In burning, it kindles slowly 
 and with difficulty, is hard to keep alight, and burns with a short, 
 almost colorless flame, without smoke. 
   
   
 Semi-anthracite coal has less density, hardness and luster than true 
 anthracite, and can be distinguished from it by the fact that when newly 
 fractured it will soot the hands. Its specific gravity is ordinarily 
 about 1.4. It kindles quite readily and burns more freely than the true 
 anthracites. 
   
   
 Semi-bituminous coal is softer than anthracite, contains more volatile 
 hydrocarbons, kindles more easily and burns more rapidly. It is 
 ordinarily free burning, has a high calorific value and is of the 
 highest order for steam generating purposes. 
   
   
 Bituminous coals are still softer than those described and contain still 
 more volatile hydrocarbons. The difference between the semi-bituminous 
 and the bituminous coals is an important one, economically. The former 
 have an average heating value per pound of combustible about 6 per cent 
 higher than the latter, and they burn with much less smoke in ordinary 
 furnaces. The distinctive characteristic of the bituminous coals is the 
 emission of yellow flame and smoke when burning. In color they range 
 from pitch black to dark brown, having a resinous luster in the most 
 compact specimens, and a silky luster in such specimens as show traces 
 of vegetable fiber. The specific gravity is ordinarily about 1.3. 
   
 Bituminous coals are either of the caking or non-caking class. The 
 former, when heated, fuse and swell in size; the latter burn freely, do 
 not fuse, and are commonly known as free burning coals. Caking coals are 
 rich in volatile hydrocarbons and are valuable in gas manufacture. 
   
 Bituminous coals absorb moisture from the atmosphere. The surface 
 moisture can be removed by ordinary drying, but a portion of the water 
 can be removed only by heating the coal to a temperature of about 250 
 degrees Fahrenheit. 
   
 Cannel coal is a variety of bituminous coal, rich in hydrogen and 
 hydrocarbons, and is exceedingly valuable as a gas coal. It has a dull 
 resinous luster and burns with a bright flame without fusing. Cannel 
 coal is seldom used for steam coal, though it is sometimes mixed with 
 semi-bituminous coal where an increased economy at high rates of 
 combustion is desired. The composition of cannel coal is approximately 
 as follows: fixed carbon, 26 to 55 per cent; volatile matter, 42 to 64 
 per cent; earthy matter, 2 to 14 per cent. Its specific gravity is 
 approximately 1.24. 
   
 Lignite is organic matter in the earlier stages of its conversion into 
 coal, and includes all varieties which are intermediate between peat and 
 coal of the older formation. Its specific gravity is low, being 1.2 to 
 1.23, and when freshly mined it may contain as high as 50 per cent of 
 moisture. Its appearance varies from a light brown, showing a distinctly 
 woody structure, in the poorer varieties, to a black, with a pitchy 
 luster resembling hard coal, in the best varieties. It is non-caking and 
 burns with a bright but slightly smoky flame with moderate heat. It is 
 easily broken, will not stand much handling in transportation, and if 
 exposed to the weather will rapidly disintegrate, which will increase 
 the difficulty of burning it. 
   
 Its composition varies over wide limits. The ash may run as low as one 
 per cent and as high as 50 per cent. Its high content of moisture and 
 the large quantity of air necessary for its combustion cause large stack 
 losses. It is distinctly a low-grade fuel and is used almost entirely in 
 the districts where mined, due to its cheapness. 
   
 Peat is organic matter in the first stages of its conversion into coal 
 and is found in bogs and similar places. Its moisture content when cut 
 is extremely high, averaging 75 or 80 per cent. It is unsuitable for 
 fuel until dried and even then will contain as much as 30 per cent 
 moisture. Its ash content when dry varies from 3 to 12 per cent. In this 
 country, though large deposits of peat have been found, it has not as 
 yet been found practicable to utilize it for steam generating purposes 
 in competition with coal. In some European countries, however, the peat 
 industry is common. 
   
 Distribution--The anthracite coals are, with some unimportant 
 exceptions, confined to five small fields in Eastern Pennsylvania, as 
 shown in the following list. These fields are given in the order of 
 their hardness. 
   
 Lehigh or Eastern Middle Field 
 Green Mountain District 
 Black Creek District 
 Hazelton District 
 Beaver Meadow District 
 Panther Creek District[33] 
   
 Mahanoy or Western Field[34] 
 East Mahanoy District 
 West Mahanoy District 
   
 Wyoming or Northern Field 
 Carbondale District 
 Scranton District 
 Pittston District 
 Wilkesbarre District 
 Plymouth District 
   
 Schuylkill or Southern Field 
 East Schuylkill District 
 West Schuylkill District 
 Louberry District 
   
 Lykens Valley or Southwestern Field 
 Lykens Valley District 
 Shamokin District[35] 
   
 Anthracite is also found in Pulaski and Wythe Counties, Virginia; along 
 the border of Little Walker Mountain, and in Gunnison County, Colorado. 
 The areas in Virginia are limited, however, while in Colorado the 
 quality varies greatly in neighboring beds and even in the same bed. An 
 anthracite bed in New Mexico was described in 1870 by Dr. R. W. Raymond, 
 formerly United States Mining Commissioner. 
   
 Semi-anthracite coals are found in a few small areas in the western part 
 of the anthracite field. The largest of these beds is the Bernice in 
 Sullivan County, Pennsylvania. Mr. William Kent, in his "Steam Boiler 
 Economy", describes this as follows: "The Bernice semi-anthracite coal 
 basin lies between Beech Creek on the north and Loyalsock Creek on the 
 south. It is six miles long, east and west, and hardly a third of a mile 
 across. An 8-foot vein of coal lies in a bed of 12 feet of coal and 
 slate. The coal of this bed is the dividing line between anthracite and 
 semi-anthracite, and is similar to the coal of the Lykens Valley 
 District. Mine analyses give a range as follows: moisture, 0.65 to 1.97; 
 volatile matter, 3.56 to 9.40; fixed carbon, 82.52 to 89.39; ash, 3.27 
 to 9.34; sulphur, 0.24 to 1.04." 
   
 Semi-bituminous coals are found on the eastern edge of the great 
 Appalachian Field. Starting with Tioga and Bradford Counties of northern 
 Pennsylvania, the bed runs southwest through Lycoming, Clearfield, 
 Centre, Huntingdon, Cambria, Somerset and Fulton Counties, Pennsylvania; 
 Allegheny County, Maryland; Buchannan, Dickinson, Lee, Russell, Scott, 
 Tazewell and Wise Counties, Virginia; Mercer, McDowell, Fayette, Raleigh 
 and Mineral Counties, West Virginia; and ending in northeastern 
 Tennessee, where a small amount of semi-bituminous is mined. 
   
 The largest of the bituminous fields is the Appalachian. Beginning near 
 the northern boundary of Pennsylvania, in the western portion of the 
 State, it extends southwestward through West Virginia, touching Maryland 
 and Virginia on their western borders, passing through southeastern 
 Ohio, eastern Kentucky and central Tennessee, and ending in western 
 Alabama, 900 miles from its northern extremity. 
   
 The next bituminous coal producing region to the west is the Northern 
 Field, in north central Michigan. Still further to the west, and second 
 in importance to the Appalachian Field, is the Eastern Interior Field. 
 This covers, with the exception of the upper northern portion, nearly 
 the entire State of Illinois, southwest Indiana and the western portion 
 of Kentucky. 
   
 The Western Field extends through central and southern Iowa, western 
 Missouri, southwestern Kansas, eastern Oklahoma and the west central 
 portion of Arkansas. The Southwestern Field is confined entirely to the 
 north central portion of Texas, in which State there are also two small 
 isolated fields along the Rio Grande River. 
   
 The remaining bituminous fields are scattered through what may be termed 
 the Rocky Mountain Region, extending from Montana to New Orleans. A 
 partial list of these fields and their location follows: 
   
 Judith Basin               Central Montana 
 Bull Mountain Field       Central Montana 
 Yellowstone Region         Southwestern Montana 
 Big Horn Basin Region     Southern Montana 
 Big Horn Basin Region     Northern Wyoming 
 Black Hills Region         Northeastern Wyoming 
 Hanna Field               Southern Wyoming 
 Green River Region         Southwestern Wyoming 
 Yampa Field               Northwestern Colorado 
 North Park Field           Northern Colorado 
 Denver Region             North Central Colorado 
 Uinta Region               Western Colorado 
 Uinta Region               Eastern Utah 
 Southwestern Region       Southwestern Utah 
 Raton Mountain Region     Southern Colorado 
 Raton Mountain Region     Northern New Mexico 
 San Juan River Region      Northwestern New Mexico 
 Capitan Field             Southern New Mexico 
   
 Along the Pacific Coast a few small fields are scattered in western 
 California, southwestern Oregon, western and northwestern Washington. 
   
 Most of the coals in the above fields are on the border line between 
 bituminous and lignite. They are really a low grade of bituminous coal 
 and are known as sub-bituminous or black lignites. 
   
 Lignites--These resemble the brown coals of Europe and are found in the 
 western states, Wyoming, New Mexico, Arizona, Utah, Montana, North 
 Dakota, Nevada, California, Oregon and Washington. Many of the fields 
 given as those containing bituminous coals in the western states also 
 contain true lignite. Lignite is also found in the eastern part of Texas 
 and in Oklahoma. 
   
 Alaska Coals--Coal has been found in Alaska and undoubtedly is of great 
 value, though the extent and character of the fields have probably been 
 exaggerated. Great quantities of lignite are known to exist, and in 
 quality the coal ranges in character from lignite to anthracite. There 
 are at present, however, only two fields of high-grade coals known, 
 these being the Bering River Field, near Controllers Bay, and the 
 Matanuska Field, at the head of Cooks Inlet. Both of these fields are 
 known to contain both anthracite and high-grade bituminous coals, though 
 as yet they cannot be said to have been opened up. 
   
 Weathering of Coal--The storage of coal has become within the last few 
 years to a certain extent a necessity due to market conditions, danger 
 of labor difficulties at the mines and in the railroads, and the 
 crowding of transportation facilities. The first cause is probably the 
 most important, and this is particularly true of anthracite coals where 
 a sliding scale of prices is used according to the season of the year. 
 While market conditions serve as one of the principal reasons for coal 
 storage, most power plants and manufacturing plants feel compelled to 
 protect their coal supply from the danger of strikes, car shortages and 
 the like, and it is customary for large power plants, railroads and coal 
 companies themselves, to store bituminous coal. Naval coaling stations 
 are also an example of what is done along these lines. 
   
 Anthracite is the nearest approach to the ideal coal for storing. It is 
 not subject to spontaneous ignition, and for this reason is unlimited in 
 the amount that may be stored in one pile. With bituminous coals, 
 however, the case is different. Most bituminous coals will ignite if 
 placed in large enough piles and all suffer more or less from 
 disintegration. Coal producers only store such coals as are least liable 
 to ignite, and which will stand rehandling for shipment. 
   
 The changes which take place in stored coal are of two kinds: 1st, the 
 oxidization of the inorganic matter such as pyrites; and 2nd, the direct 
 oxidization of the organic matter of the actual coal. 
   
 The first change will result in an increased volume of the coal, and 
 sometimes in an increased weight, and a marked disintegration. The 
 changes due to direct oxidization of the coal substances usually cannot 
 be detected by the eye, but as they involve the oxidization of the 
 carbon and available hydrogen and the absorption of the oxygen by 
 unsaturated hydrocarbons, they are the chief cause of the weathering 
 losses in heat value. Numerous experiments have led to the conclusion 
 that this is also the cause for spontaneous combustion. 
   
 Experiments to show loss in calorific heat values due to weathering 
 indicate that such loss may be as high as 10 per cent when the coal is 
 stored in the air, and 8.75 per cent when stored under water. It would 
 appear that the higher the volatile content of the coal, the greater 
 will be the loss in calorific value and the more subject to spontaneous 
 ignition. 
   
 Some experiments made by Messrs. S. W. Parr and W. F. Wheeler, published 
 in 1909 by the Experiment Station of the University of Illinois, 
 indicate that coals of the nature found in Illinois and neighboring 
 states are not affected seriously during storage from the standpoint of 
 weight and heating value, the latter loss averaging about 3½ per cent 
 for the first year of storage. They found that the losses due to 
 disintegration and to spontaneous ignition were of greater importance. 
 Their conclusions agree with those deduced from the other experiments, 
 viz., that the storing of a larger size coal than that which is to be 
 used, will overcome to a certain extent the objection to disintegration, 
 and that the larger sizes, besides being advantageous in respect to 
 disintegration, are less liable to spontaneous ignition. Storage under 
 water will, of course, entirely prevent any fire loss and, to a great 
 extent, will stop disintegration and reduce the calorific losses to a 
 minimum. 
   
 To minimize the danger of spontaneous ignition in storing coal, the 
 piles should be thoroughly ventilated. 
   
 Pulverized Fuels--Considerable experimental work has been done with 
 pulverized coal, utilizing either coal dust or pulverizing such coal as 
 is too small to be burned in other ways. If satisfactorily fed to the 
 furnace, it would appear to have several advantages. The dust burned in 
 suspension would be more completely consumed than is the case with the 
 solid coals, the production of smoke would be minimized, and the process 
 would admit of an adjustment of the air supply to a point very close to 
 the amount theoretically required. This is due to the fact that in 
 burning there is an intimate mixture of the air and fuel. The principal 
 objections have been in the inability to introduce the pulverized fuel 
 into the furnace uniformly, the difficulty of reducing the fuel to the 
 same degree of fineness, liability of explosion in the furnace due to 
 improper mixture with the air, and the decreased capacity and efficiency 
 resulting from the difficulty of keeping tube surfaces clean. 
   
 Pressed Fuels--In this class are those composed of the dust of some 
 suitable combustible, pressed and cemented together by a substance 
 possessing binding and in most cases inflammable properties. Such fuels, 
 known as briquettes, are extensively used in foreign countries and 
 consist of carbon or soft coal, too small to be burned in the ordinary 
 way, mixed usually with pitch or coal tar. Much experimenting has been 
 done in this country in briquetting fuels, the government having taken 
 an active interest in the question, but as yet this class of fuel has 
 not come into common use as the cost and difficulty of manufacture and 
 handling have made it impossible to place it in the market at a price to 
 successfully compete with coal. 
   
 Coke is a porous product consisting almost entirely of carbon remaining 
 after certain manufacturing processes have distilled off the hydrocarbon 
 gases of the fuel used. It is produced, first, from gas coal distilled 
 in gas retorts; second, from gas or ordinary bituminous coals burned in 
 special furnaces called coke ovens; and third, from petroleum by 
 carrying the distillation of the residuum to a red heat. 
   
 Coke is a smokeless fuel. It readily absorbs moisture from the 
 atmosphere and if not kept under cover its moisture content may be as 
 much as 20 per cent of its own weight. 
   
 Gas-house coke is generally softer and more porous than oven coke, 
 ignites more readily, and requires less draft for its combustion. 
   
 
 
 
 THE DETERMINATION OF HEATING VALUES OF FUELS 
 The heating value of a fuel may be determined either by a calculation 
 from a chemical analysis or by burning a sample in a calorimeter. 
   
 In the former method the calculation should be based on an ultimate 
 analysis, which reduces the fuel to its elementary constituents of 
 carbon, hydrogen, oxygen, nitrogen, sulphur, ash and moisture, to secure 
 a reasonable degree of accuracy. A proximate analysis, which determines 
 only the percentage of moisture, fixed carbon, volatile matter and ash, 
 without determining the ultimate composition of the volatile matter, 
 cannot be used for computing the heat of combustion with the same degree 
 of accuracy as an ultimate analysis, but estimates may be based on the 
 ultimate analysis that are fairly correct. 
   
 An ultimate analysis requires the services of a competent chemist, and 
 the methods to be employed in such a determination will be found in any 
 standard book on engineering chemistry. An ultimate analysis, while 
 resolving the fuel into its elementary constituents, does not reveal how 
 these may have been combined in the fuel. The manner of their 
 combination undoubtedly has a direct effect upon their calorific value, 
 as fuels having almost identical ultimate analyses show a difference in 
 heating value when tested in a calorimeter. Such a difference, however, 
 is slight, and very close approximations may be computed from the 
 ultimate analysis. 
   
 Ultimate analyses are given on both a moist and a dry fuel basis. 
 Inasmuch as the latter is the basis generally accepted for the 
 comparison of data, it would appear that it is the best basis on which 
 to report such an analysis. When an analysis is given on a moist fuel 
 basis it may be readily converted to a dry basis by dividing the 
 percentages of the various constituents by one minus the percentage of 
 moisture, reporting the moisture content separately. 
   
        _Moist Fuel_   _Dry Fuel_ 
   
 C         83.95         84.45 
 H          4.23         4.25 
 O           3.02         3.04 
 N           1.27         1.28 
 S           .91           .91 
 Ash         6.03         6.07 
                        ------ 
                        100.00 
   
 Moisture     .59           .59 
          ------ 
          100.00 
   
 Calculations from an Ultimate Analysis--The first formula for the 
 calculation of heating values from the composition of a fuel as 
 determined from an ultimate analysis is due to Dulong, and this formula, 
 slightly modified, is the most commonly used to-day. Other formulae have 
 been proposed, some of which are more accurate for certain specific 
 classes of fuel, but all have their basis in Dulong's formula, the 
 accepted modified form of which is: 
   
 Heat units in B. t. u. per pound of dry fuel = 
   
                      O 
 14,600 C + 62,000(H - -) + 4000 S     (18) 
                      8 
   
 where C, H, O and S are the proportionate parts by weight of carbon, 
 hydrogen, oxygen and sulphur. 
   
 Assume a coal of the composition given. Substituting in this formula 
 (18), 
   
 Heating value per pound of dry coal 
   
                          (       .0304) 
 = 14,600 × .8445 + 62,000 (.0425 - -----) + 4000 × .0091 = 14,765 B. t. u. 
                          (         8 ) 
   
 This coal, by a calorimetric test, showed 14,843 B. t. u., and from a 
 comparison the degree of accuracy of the formula will be noted. 
   
 The investigation of Lord and Haas in this country, Mabler in France, 
 and Bunte in Germany, all show that Dulong's formula gives results 
 nearly identical with those obtained from calorimetric tests and may be 
 safely applied to all solid fuels except cannel coal, lignite, turf and 
 wood, provided the ultimate analysis is correct. This practically limits 
 its use to coal. The limiting features are the presence of hydrogen and 
 carbon united in the form of hydrocarbons. Such hydrocarbons are present 
 in coals in small quantities, but they have positive and negative heats 
 of combination, and in coals these appear to offset each other, 
 certainly sufficiently to apply the formula to such fuels. 
   
 High and Low Heat Value of Fuels--In any fuel containing hydrogen the 
 calorific value as found by the calorimeter is higher than that 
 obtainable under most working conditions in boiler practice by an amount 
 equal to the latent heat of the volatilization of water. This heat would 
 reappear when the vapor was condensed, though in ordinary practice the 
 vapor passes away uncondensed. This fact gives rise to a distinction in 
 heat values into the so-called "higher" and "lower" calorific values. 
 The higher value, _i. e._, the one determined by the calorimeter, is the 
 only scientific unit, is the value which should be used in boiler 
 testing work, and is the one recommended by the American Society of 
 Mechanical Engineers. 
   
 There is no absolute measure of the lower heat of combustion, and in 
 view of the wide difference in opinion among physicists as to the 
 deductions to be made from the higher or absolute unit in this 
 determination, the lower value must be considered an artificial unit. 
 The lower value entails the use of an ultimate analysis and involves 
 assumptions that would make the employment of such a unit impracticable 
 for commercial work. The use of the low value may also lead to error and 
 is in no way to be recommended for boiler practice. 
   
 An example of its illogical use may be shown by the consideration of a 
 boiler operated in connection with a special economizer where the vapor 
 produced by hydrogen is partially condensed by the economizer. If the 
 low value were used in computing the boiler efficiency, it is obvious 
 that the total efficiency of the combined boiler and economizer must be 
 in error through crediting the combination with the heat imparted in 
 condensing the vapor and not charging such heat to the heat value of the 
 coal. 
   
 Heating Value of Gaseous Fuels--The method of computing calorific values 
 from an ultimate analysis is particularly adapted to solid fuels, with 
 the exceptions already noted. The heating value of gaseous fuels may be 
 calculated by Dulong's formula provided another term is added to provide 
 for any carbon monoxide present. Such a method, however, involves the 
 separating of the constituent gases into their elementary gases, which 
 is oftentimes difficult and liable to simple arithmetical error. As the 
 combustible portion of gaseous fuels is ordinarily composed of hydrogen, 
 carbon monoxide and certain hydrocarbons, a determination of the 
 calorific value is much more readily obtained by a separation into their 
 constituent gases and a computation of the calorific value from a table 
 of such values of the constituents. Table 37 gives the calorific value 
 of the more common combustible gases, together with the theoretical 
 amount of air required for their combustion. 
   
                                TABLE 37 
   
              WEIGHT AND CALORIFIC VALUE OF VARIOUS GASES 
            AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE 
        WITH THEORETICAL AMOUNT OF AIR REQUIRED FOR COMBUSTION 
   
 +---------------+----------+------+-----+------+----------+-----------+ 
 |     Gas     | Symbol |Cubic |B.t.u|B.t.u.|Cubic Feet|Cubic Feet | 
 |               |         | Feet | per | per | of Air | of Air   | 
 |               |         |of Gas|Pound|Cubic | Required | Required | 
 |               |         | per |     | Foot |per Pound | Per Cubic | 
 |               |         |Pound |     |     | of Gas |Foot of Gas| 
 +---------------+----------+------+-----+------+----------+-----------+ 
 |Hydrogen       |   H     |177.90|62000| 349 | 428.25 |   2.41   | 
 |Carbon Monoxide|   CO   | 12.81| 4450| 347 |   30.60 |   2.39   | 
 |Methane       |CH_{4}   | 22.37|23550| 1053 | 214.00 |   9.57   | 
 |Acetylene     |C_{2}H_{2}| 13.79|21465| 1556 | 164.87 |   11.93   | 
 |Olefiant Gas   |C_{2}H_{4}| 12.80|21440| 1675 | 183.60 |   14.33   | 
 |Ethane         |C_{2}H_{6}| 11.94|22230| 1862 | 199.88 |   16.74   | 
 +---------------+----------+------+-----+------+----------+-----------+ 
   
 In applying this table, as gas analyses may be reported either by weight 
 or volume, there is given in Table 33[36] a method of changing from 
 volumetric analysis to analysis by weight. 
   
   
 Examples: 
   
   
 1st. Assume a blast furnace gas, the analysis of which in percentages by 
 weight is, oxygen = 2.7, carbon monoxide = 19.5, carbon dioxide = 18.7, 
 nitrogen = 59.1. Here the only combustible gas is the carbon monoxide, 
 and the heat value will be, 
   
 0.195 × 4450 = 867.75 B. t. u. per pound. 
   
 The _net_ volume of air required to burn one pound of this gas will be, 
   
 0.195 × 30.6 = 5.967 cubic feet. 
   
   
 2nd. Assume a natural gas, the analysis of which in percentages by 
 volume is oxygen = 0.40, carbon monoxide = 0.95, carbon dioxide = 0.34, 
 olefiant gas (C_{2}H_{4}) = 0.66, ethane (C_{2}H_{6}) = 3.55, marsh gas 
 (CH_{4}) = 72.15 and hydrogen = 21.95. All but the oxygen and the carbon 
 dioxide are combustibles, and the heat per cubic foot will be, 
   
 From CO         = 0.0095 × 347 =   3.30 
      C_{2}H_{4} = 0.0066 × 1675 = 11.05 
      C_{2}H_{6} = 0.0355 × 1862 = 66.10 
      CH_{4}     = 0.7215 × 1050 = 757.58 
      H         = 0.2195 × 349 = 76.61 
                                  ------ 
 t. u. per cubic foot 914.64 
 
   
 The _net_ air required for combustion of one cubic foot of the gas will 
 be, 
   
 CO         = 0.0095 × 2.39 = 0.02 
 C_{2}H_{4} = 0.0066 × 14.33 = 0.09 
 C_{2}H_{6} = 0.0355 × 16.74 = 0.59 
 CH_{4}     = 0.7215 × 9.57 = 6.90 
 H           = 0.2195 × 2.41 = 0.53 
                                ---- 
 Total net air per cubic foot 8.13 
   
 Proximate Analysis--The proximate analysis of a fuel gives its 
 proportions by weight of fixed carbon, volatile combustible matter, 
 moisture and ash. A method of making such an analysis which has been 
 found to give eminently satisfactory results is described below. 
   
 From the coal sample obtained on the boiler trial, an average sample of 
 approximately 40 grams is broken up and weighed. A good means of 
 reducing such a sample is passing it through an ordinary coffee mill. 
 This sample should be placed in a double-walled air bath, which should 
 be kept at an approximately constant temperature of 105 degrees 
 centigrade, the sample being weighed at intervals until a minimum is 
 reached. The percentage of moisture can be calculated from the loss in 
 such a drying. 
   
 For the determination of the remainder of the analysis, and the heating 
 value of the fuel, a portion of this dried sample should be thoroughly 
 pulverized, and if it is to be kept, should be placed in an air-tight 
 receptacle. One gram of the pulverized sample should be weighed into a 
 porcelain crucible equipped with a well fitting lid. This crucible 
 should be supported on a platinum triangle and heated for seven minutes 
 over the full flame of a Bunsen burner. At the end of such time the 
 sample should be placed in a desiccator containing calcium chloride, and 
 when cooled should be weighed. From the loss the percentage of volatile 
 combustible matter may be readily calculated. 
   
 The same sample from which the volatile matter has been driven should be 
 used in the determination of the percentage of ash. This percentage is 
 obtained by burning the fixed carbon over a Bunsen burner or in a muffle 
 furnace. The burning should be kept up until a constant weight is 
 secured, and it may be assisted by stirring with a platinum rod. The 
 weight of the residue determines the percentage of ash, and the 
 percentage of fixed carbon is easily calculated from the loss during the 
 determination of ash after the volatile matter has been driven off. 
   
 Proximate analyses may be made and reported on a moist or dry basis. The 
 dry basis is that ordinarily accepted, and this is the basis adopted 
 throughout this book. The method of converting from a moist to a dry 
 basis is the same as described in the case of an ultimate analysis. A 
 proximate analysis is easily made, gives information as to the general 
 characteristics of a fuel and of its _relative_ heating value. 
   
 Table 38 gives the proximate analysis and calorific value of a number of 
 representative coals found in the United States. 
   
                                  TABLE 38 
   
 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN COALS 
   
 ____________________________________________________________________________ 
    |       |               |               |               |             | 
    |       |               |               |               |             | 
 No. | State |     County     |   Field, Bed   |     Mine     |   Size     | 
    |       |               |   or Vein     |               |             | 
    |       |               |               |               |             | 
    |       |              |               |               |             | 
 ____|_______|________________|________________|_______________|_____________| 
    |       |                                                 |             | 
    |       |                   ANTHRACITES                  |             | 
 ____|_______|_________________________________________________|_____________| 
    |       |               |               |               |             | 
 1 | Pa.   | Carbon         | Lehigh         | Beaver Meadow |            | 
 2 | Pa.   | Dauphin       | Schuylkill     |               | Buckwheat   | 
 3 | Pa.   | Lackawanna     | Wyoming       | Belleview     | No. 2 Buck. | 
 4 | Pa.   | Lackawanna     | Wyoming       | Johnson       | Culm.       | 
 5 | Pa.   | Luzerne       | Wyoming       | Pittston     | No. 2 Buck. | 
 6 | Pa.   | Luzerne       | Wyoming       | Mammoth       | Large       | 
 7 | Pa.   | Luzerne       | Wyoming       | Exeter       | Rice       | 
 8 | Pa.   | Northumberland | Schuylkill     | Treverton     |             | 
 9 | Pa.   | Schuylkill     | Schuylkill     | Buck Mountain |             | 
 10 | Pa.   | Schuylkill     |               | York Farm     | Buckwheat   | 
 11 | Pa.   |               |               | Victoria      | Buckwheat   | 
 12 | Pa.   | Carbon         | Lehigh         | Lehigh &     | Buck. & Pea | 
    |       |               |               | Wilkes C. Co. |             | 
 13 | Pa.   | Carbon         | Lehigh         |               | Buckwheat   | 
 14 | Pa.   | Lackawanna     |               |Del. & Hud. Co.| No. 1 Buck. | 
 ____|_______|________________|________________|_______________|_____________| 
    |       |                                                 |             | 
    |       |                SEMI-ANTHRACITES               |             | 
 ____|_______|_________________________________________________|_____________| 
    |       |               |               |               |             | 
 15 | Pa.   | Lycoming       | Loyalsock     |               |             | 
 16 | Pa.   | Sullivan       |               | Lopez         |             | 
 17 | Pa.   | Sullivan       | Bernice       |               |             | 
 ____|_______|________________|________________|_______________|_____________| 
    |       |                                                 |             | 
    |       |                 SEMI-BITUMINOUS                 |             | 
 ____|_______|_________________________________________________|_____________| 
    |     |               |               |               |             | 
 18 | Md.   | Alleghany     | Big Vein,     |               |             | 
    |       |               | George's Crk. |               |             | 
 19 | Md.   | Alleghany     | George's Creek |               |             | 
 20 | Md.   | Alleghany     | George's Creek |               |             | 
 21 | Md.   | Alleghany     | George's Creek | Ocean No. 7   | Mine run   | 
 22 | Md.   | Alleghany     | Cumberland     |              |             | 
 23 | Md.   | Garrett       |               | Washington   | Mine run   | 
    |       |               |               | No. 3         |             | 
 24 | Pa.   | Bradford       |               | Long Valley   |             | 
 25 | Pa.   | Tioga         |               | Antrim       |             | 
 26 | Pa.   | Cambria       | "B" or Miller | Soriman Shaft |             | 
    |       |               |               | C. Co.       |             | 
 27 | Pa.   | Cambria       | "B" or Miller | Henrietta     |             | 
 28 | Pa.   | Cambria       | "B" or Miller | Penker       |             | 
 29 | Pa.   | Cambria       | "B" or Miller | Lancashire   |             | 
 30 | Pa.   | Cambria       | Lower          | Penn. C. & C. | Mine run   | 
    |       |               | Kittanning     | Co. No. 3     |             | 
 31 | Pa.   | Cambria       | Upper         | Valley       | Mine run   | 
    |       |               | Kittanning     |               |            | 
 32 | Pa.   | Clearfield     | Lower         | Eureka       | Mine run   | 
    |       |               | Kittanning     |               |             | 
 33 | Pa.   | Clearfield     |               | Ghem         | Mine run   | 
 34 | Pa.   | Clearfield     |               | Osceola       |             | 
 35 | Pa.   | Clearfield     | Reynoldsville |               |             | 
 36 | Pa.   | Clearfield     | Atlantic-     |               | Mine run   | 
    |       |               | Clearfield     |               |             | 
 37 | Pa.   | Huntington     | Barnet & Fulton| Carbon       | Mine run   | 
 38 | Pa.   | Huntington     |               | Rock Hill     | Mine run   | 
 39 | Pa.   | Somerset       | Lower         | Kimmelton     | Mine run   | 
    |       |               | Kittanning     |               |             | 
 40 | Pa.   | Somerset       | "C" Prime Vein | Jenner       | Mine run   | 
 ____|_______|________________|________________|_______________|_____________| 
   
 _____________________________________________________________________ 
    |                                       |       |             | 
    |     Proximate Analysis (Dry Coal)     |B. t. u.|             | 
 No. |________________________________________| Per   |             | 
    |         |         |       |         | Pound | Authority   | 
    | Moisture | Volatile | Fixed | Ash   | Dry   |             | 
    |         | Matter | Carbon |         | Coal |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
    |         |         |       |         |       |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 1 |   1.50   |   2.41   | 90.30 |   7.29 |       | Gale         | 
 2 |   2.15   | 12.88   | 78.23 |   8.89 | 13137 | Whitham     | 
 3 |   8.29   |   7.81   | 77.19 | 15.00 | 12341 | Sadtler     | 
 4 | 13.90   | 11.16   | 65.96 | 22.88 | 10591 | B. & W. Co. | 
 5 |   3.66   |   4.40   | 78.96 | 16.64 | 12865 | B. & W. Co. | 
 6 |   4.00   |   3.44   | 90.59 |   5.97 | 13720 | Carpenter   | 
 7 |   0.25   |   8.18   | 79.61 | 12.21 | 12400 | B. & W. Co. | 
 8 |   0.84   |   6.73   | 86.39 |   6.88 |       | Isherwood   | 
 9 |         |   3.17   | 92.41 |   4.42 | 14220 | Carpenter   | 
 10 |   0.81   |   5.51   | 75.90 | 18.59 | 11430 |             | 
 11 |   4.30   |   0.55   | 86.73 | 12.72 | 12642 | B. & W. Co. | 
 12 |   1.57   |   6.27   | 66.53 | 27.20 | 12848 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 13 |         |   5.00   | 81.00 | 14.00 | 11800 | Carpenter   | 
 14 |   6.20   |         |       | 11.60 | 12100 | Denton       | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |            | 
    |         |         |       |         |       |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 15 |   1.30   |   8.72   | 84.44 |   6.84 |       |             | 
 16 |   5.48   |   7.53   | 81.00 | 11.47 | 13547 | B. & W. Co. | 
 17 |   1.29   |   8.21   | 84.43 |   7.36 |       |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
    |         |         |       |         |       |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |       |       |             | 
 18 |   3.50   | 21.33   | 72.47 |   6.20 | 14682 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 19 |   3.63   | 16.27   | 76.93 |   6.80 | 14695 | B. & W. Co. | 
 20 |   2.28   | 19.43   | 77.44 |   6.13 | 14793 | B. & W. Co. | 
 21 |   1.13   |         |       |         | 14451 | B. & W. Co. | 
 22 |   1.50   | 17.26   | 76.65 |   6.09 | 14700 |             | 
 23 |   2.33   | 14.38   | 74.93 | 10.49 | 14033 | U. S. Geo. S.| 
    |         |         |       |         |       | [37]         | 
 24 |   1.55   | 20.33   | 68.38 | 11.29 | 12965 |             | 
 25 |   2.19   | 18.43   | 71.87 |   9.70 | 13500 |             | 
 26 |   3.40   | 20.70   | 71.84 |   7.46 | 14484 | N. Y. Ed. Co.| 
    |         |         |       |         |       |             | 
 27 |   1.23   | 18.37   | 75.28 |   6.45 | 14770 | So. Eng. Co. | 
 28 |   3.64   | 21.34   | 70.48 |   8.18 | 14401 | B. & W. Co. | 
 29 |   4.38   | 21.20   | 70.27 |   8.53 | 14453 | B. & W. Co. | 
 30 |   3.51   | 17.43   | 75.69 |   6.88 | 14279 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 31 |   3.40   | 14.89   | 75.03 | 10.08 | 14152 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 32 |   5.90   | 16.71   | 77.22 |   6.07 | 14843 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 33 |   3.43   | 17.53   | 69.67 | 12.80 | 13744 | B. & W. Co. | 
 34 |   1.24   | 25.43   | 68.56 |   6.01 | 13589 | B. & W. Co. | 
 35 |   2.91   | 21.55   | 69.03 |   9.42 | 14685 | B. & W. Co. | 
 36 |   1.55   | 23.36   | 71.15 |   5.94 | 13963 | Whitham     | 
    |         |         |       |         |       |             | 
 37 |   4.50   | 18.34   | 73.06 |   8.60 | 13770 | B. & W. Co. | 
 38 |   5.91   | 17.58   | 73.44 |   8.99 | 14105 | B. & W. Co. | 
 39 |   3.09   | 17.84   | 70.47 | 11.69 | 13424 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 40 |   9.37   | 16.47   | 75.76 |   7.77 | 14507 | P. R. R.     | 
 ____|__________|__________|________|_________|________|______________| 
   
 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN 
 COALS--Continued 
   
 ____________________________________________________________________________ 
    |       |               |               |               |             | 
    |       |              |               |               |             | 
 No. | State |     County     |   Field, Bed   |     Mine     |   Size     | 
    |       |               |   or Vein     |               |             | 
    |       |               |                |               |             | 
    |       |               |               |               |             | 
 ____|_______|________________|________________|_______________|_____________| 
    |       |               |               |              |             | 
 41 | W. Va.| Fayette       | New River     | Rush Run     | Mine run   | 
 42 | W. Va.| Fayette       | New River     | Loup Creek   |             | 
 43 | W. Va.| Fayette       | New River     |               | Slack       | 
 44 | W. Va.| Fayette       | New River     |               | Mine run   | 
 45 | W. Va.| Fayette       | New River     | Rush Run     | Mine run   | 
 46 | W. Va.| McDowell       | Pocahontas     | Zenith       | Mine run   | 
    |       |              | No. 3         |               |             | 
 47 | W. Va.| McDowell       | Tug River     | Big Sandy     | Mine run   | 
 48 | W. Va.| Mercer         | Pocahontas     | Mora         | Lump       | 
 49 | W. Va.| Mineral       | Elk Garden     |               |             | 
 50 | W. Va.| McDowell       | Pocahontas     | Flat Top     | Mine run   | 
 51 | W. Va.| McDowell       | Pocahontas     | Flat Top     | Slack       | 
 52 | W. Va.| McDowell       | Pocahontas     | Flat Top     | Lump        | 
 ____|_______|________________|________________|_______________|_____________| 
    |       |                                                 |             | 
    |       |                 BITUMINOUS                     |             | 
 ____|_______|_________________________________________________|_____________| 
    |       |               |               |               |             | 
 53 | Ala. | Bibb           | Cahaba         | Hill Creek   | Mine run   | 
 54 | Ala. | Jefferson     | Pratt         | Pratt No. 13 |             | 
 55 | Ala. | Jefferson     | Pratt         | Warner       | Mine run   | 
 56 | Ala. | Jefferson     |               | Coalburg     | Mine run   | 
 57 | Ala. | Walker         | Horse Creek   | Ivy C. & I.   | Nut         | 
    |       |               |               | Co. No. 8     |             | 
 58 | Ala. | Walker         | Jagger         | Galloway C.   | Mine run   | 
    |       |               |               | Co. No. 5     |             | 
 59 | Ark. | Franklin       | Denning       | Western No. 4 | Nut         | 
 60 | Ark. | Sebastian     | Jenny Lind     | Mine No. 12   | Lump       | 
 61 | Ark. | Sebastian     | Huntington     | Cherokee     | Mine run   | 
 62 | Col. | Boulder      | South Platte   | Lafayette     | Mine run   | 
 63 | Col. | Boulder       | Laramie       | Simson       | Mine run   | 
 64 | Col. | Fremont       | Canon City     | Chandler     | Nut and     | 
    |       |               |               |               | Slack       | 
 65 | Col. | Las Animas     | Trinidad       | Hastings     | Nut         | 
 66 | Col. | Las Animas     | Trinidad       | Moreley       | Slack       | 
 67 | Col. | Routt         | Yampa         | Oak Creek     |            | 
 68 | Ill. | Christian     | Pana           | Penwell Col. | Lump       | 
 69 | Ill. | Franklin       | No. 6         | Benton       | Egg         | 
 70 | Ill. | Franklin       | Big Muddy     | Zeigler       | ¾ inch     | 
 71 | Ill. | Jackson       | Big Muddy     |               |             | 
 72 | Ill. | La Salle       | Streator       |               |             | 
 73 | Ill. | La Salle       | Streator       | Marseilles   | Mine run   | 
 74 | Ill. | Macoupin       | Nilwood       | Mine No. 2   | Screenings | 
 75 | Ill. | Macoupin       | Mt. Olive     | Mine No. 2   | Mine run   | 
 76 | Ill. | Madison       | Belleville     | Donk Bros.   | Lump       | 
 77 | Ill. | Madison       | Glen Carbon   |              | Mine run   | 
 78 | Ill. | Marion         |               | Odin         | Lump       | 
 79 | Ill. | Mercer         | Gilchrist     |               | Screenings | 
 80 | Ill. | Montgomery     | Pana or No. 5 | Coffeen       | Mine run   | 
 81 | Ill. | Peoria         | No. 5         | Empire       |             | 
 82 | Ill. | Perry         | Du Quoin       | Number 1     | Screenings | 
 ____|_______|________________|________________|_______________|_____________| 
   
 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN 
 COALS--Continued 
   
 _____________________________________________________________________ 
    |                                       |       |             | 
    | Proximate Analysis (Dry Coal)         |B. t. u.|             | 
 No. |________________________________________| Per   |             | 
    |         |         |       |         | Pound | Authority   | 
    | Moisture | Volatile | Fixed | Ash   | Dry   |             | 
    |         | Matter | Carbon |         | Coal |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 41 |   2.14   | 22.87   | 71.56 |   5.57 | 14959 | U. S. Geo. S.| 
 42 |   0.55   | 19.36   | 78.48 |   2.16 | 14975 | Hill         | 
 43 |   6.66   | 20.94   | 73.16 |   5.90 | 14412 | B. & W. Co. | 
 44 |   2.16   | 17.82   | 75.66 |   6.52 | 14786 | B. & W. Co. | 
 45 |   0.94   | 22.16   | 75.85 |   1.99 | 15007 | B. & W. Co. | 
 46 |   4.85   | 17.14   | 76.54 |   6.32 | 14480 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 47 |   1.58   | 18.55   | 76.44 |   4.91 | 15170 | U. S. Geo. S.| 
 48 |   1.74   | 18.55   | 75.15 |   6.30 | 15015 | U. S. Geo. S.| 
 49 |   2.10   | 15.70   | 75.40 |   8.90 | 14195 | B. & W. Co. | 
 50 |   0.52   | 24.02   | 74.59 |   1.39 | 14490 | B. & W. Co. | 
 51 |   3.24   | 15.33   | 77.60 |   7.07 | 14653 | B. & W. Co. | 
 52 |   3.63   | 16.03   | 78.04 |   5.93 | 14956 | B. & W. Co. | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
    |         |          |       |         |       |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 53 |   6.19   | 28.58   | 55.60 | 15.82 | 12576 | B. & W. Co. | 
 54 |   4.29   | 25.78   | 67.68 |   6.54 | 14482 | B. & W. Co. | 
 55 |   2.51   | 27.80   | 61.50 | 10.70 | 13628 | U. S. Geo. S.| 
 56 |   0.94   | 31.34   | 65.65 |   3.01 | 14513 | B. & W. Co. | 
 57 |   2.56   | 31.82   | 53.89 | 14.29 | 12937 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 58 |   4.83   | 34.65   | 51.12 | 14.03 | 12976 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 59 |  2.22   | 12.83   | 75.35 | 11.82 |       | U. S. Geo. S.| 
 60 |   1.07   | 17.04   | 74.45 |   8.51 | 14252 | U. S. Geo. S.| 
 61 |   0.97   | 19.87   | 70.30 |   9.83 | 14159 | U. S. Geo. S.| 
 62 | 19.48   | 38.80   | 49.00 | 12.20 | 11939 | B. & W. Co. | 
 63 | 19.78   | 44.69   | 48.62 |   6.69 | 12577 | U. S. Geo. S.| 
 64 |   9.37   | 38.10   | 51.75 | 10.15 | 11850 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 65 |   2.15   | 31.07   | 53.40 | 15.53 | 12547 | B. & W. Co. | 
 66 |   1.88   | 28.47   | 55.58 | 15.95 | 12703 | B. & W. Co. | 
 67 |   6.67   | 42.91   | 55.64 |   1.45 |       | Hill         | 
 68 |   8.05   | 43.67   | 49.97 |   6.36 | 10900 | Jones        | 
 69 |   8.31   | 34.52   | 54.05 | 11.43 | 11727 | U. S. Geo. S.| 
 70 | 13.28   | 31.97   | 57.37 | 10.66 | 12857 | U. S. Geo. S.| 
 71 |   4.85   | 31.55   | 62.19 |   6.26 | 11466 | Breckenridge | 
 72 |   8.40   | 41.76   | 51.42 |   6.82 | 11727 | Breckenridge | 
 73 | 12.98   | 43.73   | 49.13 |   7.14 | 10899 | B. & W. Co. | 
 74 | 13.34   | 34.75   | 44.55 | 20.70 | 10781 | B. & W. Co. | 
 75 | 13.54   | 41.28   | 46.30 | 12.42 | 10807 | U. S. Geo. S.| 
 76 | 13.47   | 38.69   | 48.07 | 13.24 | 12427 | U. S. Geo. S.| 
 77 |   9.78   | 38.18   | 51.52 | 10.30 | 11672 | Bryan       | 
 78 |   6.20   | 42.91   | 49.06 |   8.03 | 11880 | Breckenridge | 
 79 |   8.50   | 36.17   | 41.64 | 22.19 | 10497 | Breckenridge | 
 80 | 11.93   | 34.05   | 49.85 | 16.10 | 10303 | U. S. Geo. S.| 
 81 | 17.64   | 31.91   | 46.17 | 21.92 | 10705 | B. & W. Co. | 
 82 |   9.81   | 33.67   | 48.36 | 17.97 | 11229 | B. & W. Co. | 
 ____|__________|__________|________|_________|________|______________| 
   
 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN 
 COALS--Continued 
   
 ____________________________________________________________________________ 
    |       |               |              |               |             | 
    |       |               |               |               |             | 
 No. | State |     County     |   Field, Bed   |     Mine     |   Size     | 
    |       |               |   or Vein     |               |             | 
    |       |               |               |               |             | 
    |       |               |               |               |             | 
    |_______|________________|________________|_______________|_____________| 
    |      |               |               |               |             | 
 83 | Ill. | Perry         | Du Quoin       | Willis       | Mine run   | 
 84 | Ill. | Sangamon       |               | Pawnee       | Slack       | 
 85 | Ill. | St. Clair     | Standard       | Nigger Hollow | Mine run   | 
 86 | Ill. | St. Clair     | Standard       | Maryville     | Mine run   | 
 87 | Ill. | Williamson     | Big Muddy     | Daws         | Mine run   | 
 88 | Ill. | Williamson     | Carterville   | Carterville   |             | 
    |       |               | or No. 7       |               |             | 
 89 | Ill. | Williamson     | Carterville   | Burr         | Nut, Pea   | 
    |       |               | or No. 7       |               | and Slack   | 
 90 | Ind. | Brazil         | Brazil         | Gartside     | Block       | 
 91 | Ind. | Clay           |               | Louise       | Block       | 
 92 | Ind. | Green         | Island City   |               | Mine run   | 
 93 | Ind. | Knox           | Vein No. 5     | Tecumseh     | Mine run   | 
 94 | Ind. | Parke         | Vein No. 6     | Parke Coal Co.| Lump       | 
 95 | Ind. | Sullivan       | Sullivan No. 6 | Mildred       | Washed     | 
 96 | Ind. | Vigo           | Number 6       | Fontanet     | Mine run   | 
 97 | Ind. | Vigo           | Number 7       | Red Bird     | Mine run   | 
 98 | Iowa | Appanoose     | Mystic         | Mine No. 3   | Lump       | 
 99 | Iowa | Lucas         | Lucas         | Inland No. 1 | Mine run   | 
 100 | Iowa | Marion         | Big Vein       | Liberty No. 5 | Mine run   | 
 101 | Iowa | Polk           | Third Seam     | Altoona No. 4 | Lump       | 
 102 | Iowa | Wapello       | Wapello       |               | Lump       | 
 103 | Kan. | Cherokee       | Weir Pittsburgh| Southwestern | Lump       | 
    |       |               |               | Dev. Co.     |             | 
 104 | Kan. | Cherokee       | Cherokee       |               | Screenings | 
 105 | Kan. | Cherokee      | Cherokee       |               | Lump       | 
 106 | Kan. | Linn           | Boicourt       |               | Lump       | 
 107 | Ky.   | Bell           | Straight Creek | Str. Ck. C. & | Mine run   | 
    |       |               |               | C. Co.       |             | 
 108 | Ky.   | Hopkins       | Bed No. 9     | Earlington   | Lump       | 
 109 | Ky.   | Hopkins       | Bed No. 9     | Barnsley     | Mine run   | 
 110 | Ky.   | Hopkins       | Vein No. 14   | Nebo         |Pea and Slack| 
 111 | Ky.   | Johnson       | Vein No. 1     | Miller's Creek| Mine run   | 
 112 | Ky.   | Mulenburg     | Bed No. 9     | Pierce       |Pea and Slack| 
 113 | Ky.   | Pulaski       |               | Greensburg   |             | 
 114 | Ky.   | Webster       | Bed No. 9     |               |Pea and Slack| 
 115 | Ky.   | Whitley       |               | Jellico       |Nut and Slack| 
 116 | Mo.   | Adair         |               | Danforth     | Mine run   | 
 117 | Mo.   | Bates         | Rich Hill     | New Home     | Mine run   | 
 118 | Mo.   | Clay           | Lexington     | Mo. City Coal |             | 
    |       |               |               | Co.           |             | 
 119 | Mo.   | Lafayette     | Waverly       | Buckthorn    |             | 
 120 | Mo.   | Lafayette     | Waverly       | Higbee       |             | 
 121 | Mo.   | Linn           | Bevier         | Marceline     |             | 
 122 | Mo.   | Macon         | Bevier         | Northwest     |             | 
  |       |               |               | Coal Co.     |             | 
 123 | Mo.   | Morgan         | Morgan Co.     | Morgan Co.   | Mine run   | 
    |       |               |               | Coal Co.     |             | 
 124 | Mo.   | Putnam        | Mendotta       | Mendotta No. 8|             | 
 125 | N.Mex.| McKinley       | Gallup         | Gibson       |Pea and Slack| 
 ____|_______|________________|________________|_______________|_____________| 
   
 ______________________________________________________________________ 
    |                                       |       |             | 
    |     Proximate Analysis (Dry Coal)     |B. t. u.|             | 
 No. |________________________________________| Per   |             | 
    |         |          |       |         | Pound | Authority   | 
    | Moisture | Volatile | Fixed | Ash   | Dry   |             | 
    |         | Matter | Carbon |         | Coal |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 83 |   7.22   | 33.06   | 53.97 | 12.97 | 11352 | U. S. Geo. S.| 
 84 |   4.81   | 41.53   | 39.62 | 18.85 | 10220 | Jones       | 
 85 | 14.39   | 32.90   | 44.84 | 22.26 | 11059 | B. & W. Co. | 
 86 | 15.71   | 38.10   | 41.10 | 20.80 | 10999 | B. & W. Co. | 
 87 |   8.17   | 34.33   | 52.50 | 13.17 | 12643 | U. S. Geo. S.| 
 88 |   4.66   | 35.65   | 56.86 |   7.49 | 12286 | Univ. of Ill.| 
    |         |         |       |         |       |             | 
 89 | 11.91   | 33.70   | 55.90 | 10.40 | 12932 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 90 |   2.83   | 40.03   | 51.97 |   8.00 | 13375 | Stillman     | 
 91 |   0.83   | 39.70   | 52.28 |   8.02 | 13248 | Jones       | 
 92 |   6.17   | 35.42   | 53.55 | 11.03 | 11916 | Dearborn     | 
 93 | 10.73   | 35.75   | 54.46 |   9.79 | 12911 | B. & W. Co. | 
 94 | 10.72   | 44.02   | 46.33 |   9.65 | 11767 | U. S. Geo. S.| 
 95 | 16.59   | 42.17   | 48.44 |   9.59 | 13377 | U. S. Geo. S.| 
 96 |   2.28   | 34.95   | 50.50 | 14.55 | 11920 | Dearborn     | 
 97 | 11.62   | 41.17   | 46.76 | 12.07 | 12740 | U. S. Geo. S.| 
 98 | 13.48   | 39.40   | 43.09 | 17.51 | 11678 | U. S. Geo. S.| 
 99 | 16.01   | 37.82   | 46.24 | 15.94 | 11963 | U. S. Geo. S.| 
 100 | 14.88   | 41.53   | 39.63 | 18.84 | 11443 | U. S. Geo. S.| 
 101 | 12.44   | 41.27   | 40.86 | 17.87 | 11671 | U. S. Geo. S.| 
 102 |   8.69   | 36.23   | 43.68 | 20.09 | 11443 | U. S. Geo. S.| 
 103 |   4.31   | 33.88   | 53.67 | 12.45 | 13144 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 104 |  6.16   | 35.56   | 46.90 | 17.54 | 10175 | Jones       | 
 105 |   1.81   | 34.77   | 52.77 | 12.46 | 12557 | Jones       | 
 106 |   4.74   | 36.59   | 47.07 | 16.34 | 10392 | Jones       | 
 107 |   2.89   | 36.67   | 57.24 |   6.09 | 14362 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 108 |   6.89   | 40.30   | 55.16 |   4.54 | 13381 | St. Col. Ky. | 
 109 |   7.92   | 40.53   | 48.70 | 10.77 | 13036 | U. S. Geo. S.| 
 110 |   8.02   | 31.91   | 54.02 | 14.07 | 12448 | B. & W. Co. | 
 111 |   5.12   | 38.46   | 58.63 |   2.91 | 13743 | U. S. Geo. S.| 
 112 |   9.22   | 33.94   | 52.18 | 13.88 | 12229 | B. & W. Co. | 
 113 |   2.80   | 26.54   | 63.58 |   9.88 | 14095 | N. Y. Ed. Co.| 
 114 |   7.30   | 31.08   | 60.72 |   8.20 | 13600 | B. & W. Co. | 
 115 |   3.82   | 31.82   | 58.78 |   9.40 | 13175 | B. & W. Co. | 
 116 |   9.00   | 30.55   | 46.26 | 23.19 |   9889 | B. & W. Co. | 
 117 |   7.28   | 37.62   | 43.83 | 18.55 | 12109 | U. S. Geo. S.| 
 118 | 12.45   | 39.39   | 48.47 | 12.14 | 12875 | Univ. of Mo. | 
    |         |         |       |         |       |             | 
 119 |   8.58   | 41.78   | 45.99 | 12.23 | 12735 | Univ. of Mo. | 
 120 | 10.84   | 31.72   | 55.29 | 12.99 | 12500 | Univ. of Mo. | 
 121 |   9.45   | 36.72   | 52.20 | 11.08 | 13180 | Univ. of Mo. | 
 122 | 13.09   | 37.83   | 42.95 | 19.22 | 11500 | U. S. Geo. S.| 
    |         |         |       |         |        |             | 
 123 | 12.24   | 45.69   | 47.98 |   6.33 | 14197 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 124 | 20.78   | 39.36   | 50.00 | 10.64 | 12602 | U. S. Geo. S.| 
 125 | 12.17   | 36.31   | 51.17 | 12.52 | 12126 | B. & W. Co. | 
 ____|__________|__________|________|_________|________|______________| 
   
 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN 
 COALS--Continued 
   
 ____________________________________________________________________________ 
    |       |               |               |               |             | 
    |       |               |               |               |             | 
 No. | State |     County     |   Field, Bed   |     Mine     |   Size     | 
    |       |               |   or Vein     |               |             | 
    |       |               |               |               |             | 
    |       |               |               |               |             | 
    |_______|________________|________________|_______________|_____________| 
    |       |               |               |               |             | 
 126 | Ohio | Athens         | Hocking Valley | Sunday Creek | Slack       | 
 127 | Ohio | Belmont       | Pittsburgh     | Neff Coal Co. | Mine run   | 
    |       |               | No. 8         |               |             | 
 128 | Ohio | Columbiana     | Middle         | Palestine     |             | 
    |       |               | Kittanning     |              |             | 
 129 | Ohio | Coshocton     | Middle         | Morgan Run   | Mine run   | 
    |       |               | Kittanning     |               |             | 
 130 | Ohio | Guernsey       | Vein No. 7     | Little Kate   |             | 
 131 | Ohio | Hocking       | Hocking Valley |               | Lump       | 
 132 | Ohio | Hocking       | Hocking Valley |               |             | 
 133 | Ohio | Jackson       | Brookville     | Superior     | Mine run   | 
    |       |              |               | Coal Co.     |             | 
 134 | Ohio | Jackson       | Lower         | Superior     | Mine run   | 
    |       |               | Kittanning     | Coal Co.     |             | 
 135 | Ohio | Jackson       | Quakertown   | Wellston     |             | 
 136 | Ohio | Jefferson     | Pittsburgh     | Crow Hollow   | ¾ inch     | 
    |       |               | or No. 8       |               |             | 
 137 | Ohio | Jefferson     | Pittsburgh     | Rush Run No. 1| ¾ inch     | 
    |       |               | or No. 8       |               |             | 
 138 | Ohio | Perry         | Hocking       | Congo         |             | 
 139 | Ohio | Stark         | Massillon     |               | Slack       | 
 140 | Ohio | Vinton         | Brookville     | Clarion       | Nut and     | 
    |       |               | or No. 4       |               | Slack       | 
 141 | Okla. | Choctaw       | McAlester     | Edwards No. 1 | Mine run   | 
 142 | Okla. | Choctaw       | McAlester     | Adamson       | Slack       | 
 143 | Okla. | Creek         |               | Henrietta     | Lump and   | 
    |       |               |               |               | Slack       | 
 144 | Pa.   | Allegheny     | Pittsburgh     |              | Slack       | 
    |       |               | 3rd Pool       |               |             | 
 145 | Pa.   | Allegheny     | Monongahela   | Turtle Creek |             | 
 146 | Pa.   | Allegheny     | Pittsburgh     | Bertha       | ¾ inch     | 
 147 | Pa.   | Cambria       |               | Beach Creek   | Slack       | 
 148 | Pa.   | Cambria       | Miller         | Lincoln       | Mine run   | 
 149 | Pa.   | Clarion       | Lower Freeport |               |             | 
 150 | Pa.   | Fayette       | Connellsville |               | Slack       | 
 151 | Pa.   | Greene         | Youghiogheny   |               | Lump       | 
 152 | Pa.   | Greene         | Westmoreland   |               | Screenings | 
 153 | Pa.   | Indiana       |                | Iselin       | Mine run   | 
 154 | Pa.   | Jefferson     |               | Punxsutawney | Mine run   | 
 155 | Pa.   | Lawrence       | Middle         |               |             | 
    |       |               | Kittanning     |               |            | 
 156 | Pa.   | Mercer         | Taylor         |               |             | 
 157 | Pa.   | Washington     | Pittsburgh     | Ellsworth     |             | 
 158 | Pa.   | Washington     | Youghiogheny   | Anderson     | ¾ inch     | 
 159 | Pa.   | Westmoreland   | Pittsburgh     | Scott Haven   | Lump       | 
 160 | Tenn. | Campbell       | Jellico       |               |             | 
 161 | Tenn. | Claiborne     | Mingo         |               |             | 
 162 | Tenn. | Marion         |                | Etna         |             | 
 163 | Tenn. | Morgan         | Brushy Mt.     |               |             | 
 164 | Tenn. | Scott         | Glen Mary No. 4| Glen Mary     |             | 
 165 | Tex. | Maverick       |               | Eagle Pass   |             | 
 166 | Tex. | Paolo Pinto   |               | Thurber       | Mine run   | 
 167 | Tex. | Paolo Pinto   |               | Strawn       | Mine run   | 
 168 | Va.   | Henrico       |               | Gayton       |           | 
 ____|_______|________________|________________|_______________|_____________| 
   
 _____________________________________________________________________ 
    |                                       |       |             | 
    |     Proximate Analysis (Dry Coal)     |B. t. u.|             | 
 No. |________________________________________| Per   |             | 
    |         |         |       |         | Pound | Authority   | 
    | Moisture | Volatile | Fixed | Ash   | Dry   |             | 
    |         | Matter | Carbon |         | Coal |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 126 | 12.16   | 34.64   | 53.10 | 12.26 | 12214 |             | 
 127 |   5.31   | 38.78   | 52.22 |   9.00 | 12843 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 128 |   2.15   | 37.57   | 51.80 | 10.63 | 13370 | Lord & Haas | 
    |         |        |       |         |       |             | 
 129 |         | 41.76   | 45.24 | 13.00 | 13239 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 130 |   6.19   | 33.02   | 59.96 |   7.02 | 13634 | B. & W. Co. | 
 131 |   6.45   | 39.12   | 50.08 | 10.80 | 12700 | Lord & Haas | 
 132 |   2.60   | 40.80   | 47.60 | 11.60 | 12175 | Jones       | 
 133 |   7.59   | 38.45   | 43.99 | 17.56 | 11704 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 134 |   8.99   | 41.43   | 50.06 |   8.51 | 13113 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 135 |   3.38   | 35.26   | 54.18 |   7.56 | 12506 | Hill         | 
 136 | 4.04   | 40.08   | 52.27 |   9.65 | 13374 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 137 |   4.74   | 36.08   | 54.81 |   9.11 | 13532 | U. S. Geo. S.| 
    |         |         |       |         |      |             | 
 138 |   6 41   | 38.33   | 46.71 | 14.96 | 12284 | B. & W. Co. | 
 139 |   6.67   | 40.02   | 46.46 | 13.52 | 11860 | B. & W. Co. | 
 140 |   2.47   | 42.38   | 50.39 |   6.23 | 13421 | U. S. Geo. S.| 
    |         |        |       |         |       |             | 
 141 |   4.79   | 39.18   | 49.97 | 10.85 | 13005 | U. S. Geo. S.| 
 142 |   4.72   | 28.54   | 58.17 | 13.29 | 12105 | B. & W. Co. | 
 143 |   7.65   | 36.77   | 50.14 | 13.09 | 12834 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 144 |   1.77   | 32.06   | 57.11 | 10.83 | 13205 | Carpenter   | 
    |         |         |       |         |       |             | 
 145 |   1.75   | 36.85   | 53.94 |  9.21 | 13480 | Lord & Haas | 
 146 |   2.61   | 35.86   | 57.81 |   6.33 | 13997 | U. S. Geo. S.| 
 147 |   3.01   | 32.87   | 55.86 | 11.27 | 13755 | B. & W. Co. | 
 148 |   5.39   | 30.83   | 61.05 |   8.12 | 13600 | B. & W. Co. | 
 149 |   0.54   | 35.93   | 57.66 |   6.41 | 13547 |             | 
 150 |   1.85   | 28.73   | 63.22 |   7.95 | 13775 | Whitham     | 
 151 |   1.25   | 32.60   | 54.70 | 12.70 | 13100 | B. & W. Co. | 
 152 | 11.12   | 31.67   | 55.61 | 12.72 | 13100 | P. R. R.     | 
 153 |   2.70   | 29.33   | 63.56 |   7.11 | 14220 | B. & W. Co. | 
 154 |   3.38   | 29.33   | 64.93 |   5.73 | 14781 | B. & W. Co. | 
 155 |   0.70   | 37.06   | 56.24 |   6.70 | 13840 | Lord & Haas | 
    |         |        |       |         |       |             | 
 156 |   4.18   | 32.19   | 55.55 | 12.26 | 12820 | B. & W. Co. | 
 157 |   2.46   | 35.35   | 58.46 |   6.19 | 14013 | U. S. Geo. S.| 
 158 |   1.00   | 39.29   | 54.80 |   5.91 | 13729 | Jones      | 
 159 |   4.06   | 32.91   | 59.78 |   7.31 | 13934 | B. & W. Co. | 
 160 |   1.80   | 37.76   | 62.12 |   1.12 | 13846 | U. S. Navy   | 
 161 |   4.40   | 34.31   | 59.22 |   6.47 |       | U. S. Geo. S.| 
 162 |   3.16   | 32.98   | 56.59 | 10.43 |       |             | 
 163 |   1.77   | 33.46   | 54.73 | 11.87 | 13824 | B. & W. Co. | 
 164 |   1.53   | 40.80   | 56.78 |   2.42 | 14625 |Ky. State Col.| 
 165 |   5.42   | 33.73   | 44.89 | 21.38 | 10945 | B. & W. Co. | 
 166 |   1.90   | 36.01   | 49.09 | 14.90 | 12760 | B. & W. Co. | 
 167 |   4.19   | 35.40   | 52.98 | 11.62 | 13202 | B. & W. Co. | 
 168 |   0.82   | 17.14   | 74.92 |   7.94 | 14363 | B. & W. Co. | 
 ____|__________|__________|________|_________|________|______________| 
   
 APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN 
 COALS--Continued 
   
 ____________________________________________________________________________ 
    |       |               |               |               |            | 
    |       |               |               |               |             | 
 No. | State |     County     |   Field, Bed   |     Mine     |   Size     | 
    |       |               |   or Vein     |               |             | 
    |       |              |               |               |             | 
    |       |               |               |               |             | 
    |_______|________________|________________|_______________|_____________| 
    |       |               |                |               |             | 
 169 | Va.   | Lee           | Darby         | Darby         | 1½ inch     | 
 170 | Va.   | Lee           | McConnel       | Wilson       | Mine run   | 
 171 | Va.   | Wise           | Upper Banner   | Coburn        | 3½ inch     | 
 172 | Va.   | Rockingham     |               | Clover Hill   |             | 
 173 | Va.   | Russel         | Clinchfield   |               |             | 
 174 | Va.   |               | Monongahela   | Bernmont     |             | 
 175 | W. Va.| Harrison       | Pittsburgh     | Ocean         | Mine run   | 
 176 | W. Va.| Harrison       |               | Girard       | Nut, Pea   | 
    |       |               |               |               | and Slack   | 
 177 | W. Va.| Kanawha      | Winifrede     | Winifrede     |             | 
 178 | W. Va.| Kanawha       | Keystone       | Keystone     | Mine run   | 
 179 | W. Va.| Logan         | Island Creek   |               |Nut and Slack| 
 180 | W. Va.| Marion         | Fairmont       | Kingmont     |             | 
 181 | W. Va.| Mingo         | Thacker       | Maritime     |             | 
 182 | W. Va.| Mingo         | Glen Alum     | Glen Alum     | Mine run   | 
 183 | W. Va.| Preston       | Bakerstown     |               |            | 
 184 | W. Va.| Putnam         | Pittsburgh     | Black Betsy   | Bug dust   | 
 185 | W. Va.| Randolph       | Upper Freeport | Coalton       | Lump and Nut| 
 ____|_______|________________|________________|_______________|_____________| 
    |       |                                                 |             | 
    |       |           LIGNITES AND LIGNITIC COALS           |             | 
 ____|_______|_________________________________________________|_____________| 
    |       |               |                |               |             | 
 186 | Col. | Boulder       |               | Rex           |             | 
 187 | Col. | El Paso       |               | Curtis       |             | 
 188 | Col. | El Paso       |               | Pike View     |             | 
 189 | Col. | Gunnison       | South Platte   | Mt. Carbon   |             | 
 190 | Col. | Las Animas     |               | Acme         |             | 
 191 | Col. |               | Lehigh         |               |             | 
 192 |N. Dak.| McLean         |               | Eckland       | Mine run   | 
 193 |N. Dak.| McLean         |               | Wilton       | Lump       | 
 194 |N. Dak.| McLean         |               | Casino       |             | 
 195 |N. Dak.| Stark        | Lehigh         | Lehigh       | Mine run   | 
 196 |N. Dak.| William       | Williston     |               | Mine run   | 
 197 |N. Dak.| William       | Williston     |               | Mine run   | 
 198 | Tex. | Bastrop       | Bastrop       | Glenham       |             | 
 199 | Tex. | Houston       | Crockett       |               |             | 
 200 | Tex. | Houston       |               | Houston C. & |             | 
    |       |               |               | C. Co.       |            | 
 201 | Tex. | Milam         | Rockdale       | Worley       |             | 
 202 | Tex. | Robertson     | Calvert       | Coaling No. 1 |             | 
 203 | Tex. | Wood           | Hoyt           | Consumer's   |             | 
    |     |               |               | Lig. Co.     |             | 
 204 | Tex. | Wood           | Hoyt           |               |             | 
 205 | Wash. | King           |               | Black Diamond |             | 
 206 | Wyo. | Carbon         | Hanna         |               | Mine run   | 
 207 | Wyo. | Crook         | Black Hills   | Stilwell Coal |             | 
    |       |               |               | Co.           |             | 
 208 | Wyo. | Sheridan       | Sheridan       | Monarch       |             | 
 209 | Wyo. | Sweetwater     | Rock Spring   |               | Screenings | 
 210 | Wyo. | Uinta         | Adaville       | Lazeart       |             | 
 ____|_______|________________|________________|_______________|_____________| 
   
 _____________________________________________________________________ 
    |                                       |       |             | 
    | Proximate Analysis (Dry Coal)         |B. t. u.|             | 
 No. |________________________________________| Per   |             | 
    |         |         |       |         | Pound | Authority   | 
    | Moisture | Volatile | Fixed | Ash   | Dry   |             | 
    |         | Matter | Carbon |         | Coal |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 169 |   4.35   | 38.46   | 56.91 |   4.63 | 13939 | U. S. Geo. S.| 
 170 |   3.35   | 36.35   | 57.88 |   5.77 | 13931 | U. S. Geo. S.| 
 171 |   3.05   | 32.65   | 62.73 |   4.62 | 14470 | U. S. Geo. S.| 
 172 |         | 31.77   | 57.98 | 10.25 | 13103 |             | 
 173 |   2.00   | 35.72   | 56.12 |   8.16 | 14200 |             | 
 174 |         | 32.00   | 59.90 |   8.10 | 13424 | Carpenter   | 
 175 |   2.47   | 39.35   | 52.78 |   7.87 | 14202 | U. S. Geo. S.| 
 176 |         | 36.66   | 57.49 |   5.85 | 14548 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 177 |   1.05   | 32.74   | 64.38 |   2.88 | 14111 | Hill         | 
 178 |   2.21   | 33.29   | 58.61 |   8.10 | 14202 | U. S. Geo. S.| 
 179 |   1.12   | 38.61   | 55.91 |   5.48 | 14273 | Hill         | 
 180 |   1.90   | 35.31   | 57.34 |   7.35 | 14198 | U. S. Geo. S.| 
 181 |   0.68   | 31.89   | 63.48 |   4.63 | 14126 | Hill         | 
 182 |   3.02   | 33.81   | 59.45 |   6.74 | 14414 | U. S. Geo. S.| 
 183 |   4.14   | 29.09   | 63.50 |   7.41 | 14546 | U. S. Geo. S.| 
 184 |   7.41   | 32.84   | 53.96 | 13.20 | 12568 | B. & W. Co. | 
 185 |   2.11   | 29.57   | 59.93 | 10.50 | 13854 | U. S. Geo. S.| 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |            | 
    |         |         |       |         |       |             | 
 ____|__________|__________|________|_________|________|______________| 
    |         |         |       |         |       |             | 
 186 | 16.05   | 42.12   | 47.97 |   9.91 | 10678 | B. & W. Co. | 
 187 | 23.25   | 42.11   | 49.38 |   8.51 | 11090 | B. & W. Co. | 
 188 | 23.77   | 48.70   | 41.47 |   9.83 | 10629 | B. & W. Co. | 
 189 | 20.38   | 46.38   | 47.50 |   6.12 |       |             | 
 190 | 16.74   | 47.90   | 44.60 |   7.50 |       |Col. Sc. of M.| 
 191 | 18.30   | 45.29   | 44.67 | 10.04 |       |             | 
 192 | 29.65   | 45.56   | 47.05 |   7.39 | 10553 | Lord         | 
 193 | 35.96   | 49.84   | 38.05 | 12.11 | 11036 | U. S. Geo. S.| 
 194 | 29.65   | 46.56   | 38.70 | 14.74 |       | Lord         | 
 195 | 35.84   | 43.84   | 39.59 | 16.57 | 10121 | U. S. Geo. S.| 
 196 | 41.76   | 39.37   | 48.09 | 12.54 | 10121 | B. & W. Co. | 
 197 | 42.74   | 40.83   | 47.79 | 11.38 | 10271 | B. & W. Co. | 
 198 | 32.77   | 42.76   | 36.88 | 20.36 |   8958 | B. & W. Co. | 
 199 | 23.27   | 40.95   | 38.37 | 20.68 | 10886 | U. S. Geo. S.| 
 200 | 31.48   | 46.93   | 34.40 | 18.87 | 10176 | B. & W. Co. | 
    |         |         |       |         |       |             | 
 201 | 32.48   | 43.04   | 41.14 | 15.82 | 10021 | B. & W. Co. | 
 202 | 32.01   | 43.70   | 43.08 | 13.22 | 10753 | B. & W. Co. | 
 203 | 33.98   | 46.97   | 41.40 | 11.63 | 10600 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 204 | 30.25   | 43.27   | 41.46 | 15.27 | 10597 |             | 
 205 |   3.71   | 48.72   | 46.56 |   4.72 |       | Gale         | 
 206 |   6.44   | 51.32   | 43.00 |   5.68 | 11607 | B. & W. Co. | 
 207 | 19.08   | 45.21   | 46.42 |   8.37 | 12641 | U. S. Geo. S.| 
    |         |         |       |         |       |             | 
 208 | 21.18   | 51.87   | 40.43 |   7.70 | 12316 | U. S. Geo. S.| 
 209 |   7.70   | 38.57   | 56.99 |   4.44 | 12534 | B. & W. Co. | 
 210 | 19.15   | 45.50   | 48.11 |   6.39 |   9868 | U. S. Geo. S.| 
 ____|__________|__________|________|_________|________|______________| 
 TABLE 39 
   
    SHOWING RELATION BETWEEN PROXIMATE AND ULTIMATE ANALYSES OF COAL 
   
 ========================================================================= 
 |                   |           |                         | Common in | 
 |                   |           |                         |Proximate &| 
 |                   | Proximate |                          | Ultimate | 
 |                   | Analysis |     Ultimate Analysis   | Analysis | 
 |--------------------|-----------|--------------------------|-----------| 
 |   |       |       | V   |     |     | H |     | N |   |     | M | 
 |   |       |       | o   |     |     | y |     | i | S |     | o | 
 |   |       |       | l M |   C | C | d | O | t | u |     | i | 
 | S |       |       | a a | F a | a | r | x | r | l |     | s | 
 | t |       |       | t t | i r | r | o | y | o | p |     | t | 
 | a | Field |       | i t | x b | b | g | g | g | h | A | u | 
 | t | or   |       | l e | e o | o | e | e | e | e | s | r | 
 | e | Bed   | Mine | e r | d n | n | n | n | n | r | h | e | 
 |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |   |       |Icy Coal|     |     |     |   |     |   |   |     |     | 
 |   |       | & Iron |     |     |     |   |     |   |   |     |     | 
 |   | Horse | Co.   |     |     |     |   |     |   |   |     |     | 
 |Ala| Creek | No. 8 |31.81|53.90|72.02|4.78| 6.45|1.66| .80|14.29| 2.56| 
 |---|----------------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |   |       |Central |     |     |     |   |     |   |   |     |     | 
 |   |       |C. & C. |     |     |     |   |     |   |   |     |     | 
 |   | Hunt- | Co.   |     |     |     |   |     |   |   |     |     | 
 |Ark|ington | No. 3 |18.99|67.71|76.37|3.90| 3.71|1.49|1.23|13.30| 1.99| 
 |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |   | Pana | Clover |     |     |     |   |     |   |   |     |     | 
 |   | or   | Leaf, |     |     |     |   |     |   |   |     |     | 
 |Ill| No. 5 | No. 1 |37.22|45.64|63.04|4.49|10.04|1.28|4.01|17.14|13.19| 
 |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |   |No. 5, |       |     |     |     |   |     |   |   |     |     | 
 |   |Warrick|       |     |     |     |   |     |   |   |     |     | 
 |Ind| Co. |Electric|41.85|44.45|68.08|4.78| 7.56|1.35|4.53|13.70| 9.11| 
 |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |   |No. 11,| St.   |     |     |     |   |     |   |   |     |     | 
 |   |Hopkins|Bernard,|     |     |     |   |     |   |   |     |     | 
 |Ky | Co. | No. 11 |41.10|49.60|72.22|5.06| 8.44|1.33|3.65| 9.30| 7.76| 
 |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |   |"B" or |       |     |     |     |   |     |   |   |     |     | 
 |   |Lower |      |     |     |     |   |     |   |   |     |     | 
 |   |Kittan-| Eureka,|     |     |     |   |     |   |   |     |     | 
 |Pa | ning | No. 31 |16.71|77.22|84.45|4.25| 3.04|1.28| .91| 6.07| .56| 
 |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |   |Indiana|       |     |     |     |   |     |   |   |     |     | 
 |Pa | Co. |       |29.55|62.64|79.86|5.02| 4.27|1.86|1.18| 7.81| 2.90| 
 |---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| 
 |W. | Fire | Rush   |     |     |     |   |     |   |   |     |     | 
 |Va | Creek | Run   |22.87|71.56|83.71|4.64| 3.67|1.70| .71| 5.57| 2.14| 
 ========================================================================= 
   
 Table 39 gives for comparison the ultimate and proximate analyses of 
 certain of the coals with which tests were made in the coal testing 
 plant of the United States Geological Survey at the Louisiana Purchase 
 Exposition at St. Louis. 
   
 The heating value of a fuel cannot be directly computed from a proximate 
 analysis, due to the fact that the volatile content varies widely in 
 different fuels in composition and in heating value. 
   
 Some methods have been advanced for estimating the calorific value of 
 coals from the proximate analysis. William Kent[38] deducted from 
 Mahler's tests of European coals the approximate heating value dependent 
 upon the content of fixed carbon in the combustible. The relation as 
 deduced by Kent between the heat and value per pound of combustible and 
 the per cent of fixed carbon referred to combustible is represented 
 graphically by Fig. 23. 
   
 Goutal gives another method of determining the heat value from a 
 proximate analysis, in which the carbon is given a fixed value and the 
 heating value of the volatile matter is considered as a function of its 
 percentage referred to combustible. Goutal's method checks closely with 
 Kent's determinations. 
   
 All the formulae, however, for computing the calorific value of coals 
 from a proximate analysis are ordinarily limited to certain classes of 
 fuels. Mr. Kent, for instance, states that his deductions are correct 
 within a close limit for fuels containing more than 60 per cent of fixed 
 carbon in the combustible, while for those containing a lower 
 percentage, the error may be as great as 4 per cent, either high or low. 
   
 While the use of such computations will serve where approximate results 
 only are required, that they are approximate should be thoroughly 
 understood. 
   
 Calorimetry--An ultimate or a proximate analysis of a fuel is useful in 
 determining its general characteristics, and as described on page 183, 
 may be used in the calculation of the approximate heating value. Where 
 the efficiency of a boiler is to be computed, however, this heating 
 value should in all instances be determined accurately by means of a 
 fuel calorimeter. 
   
 [Graph: B.T.U. per Pound of Combustible 
 against Per Cent of Fixed Carbon in Combustible 
   
 Fig. 23. Graphic Representation of Relation between Heat Value Per Pound 
 of Combustible and Fixed Carbon in Combustible as Deduced by Wm. Kent.] 
   
 In such an apparatus the fuel is completely burned and the heat 
 generated by such combustion is absorbed by water, the amount of heat 
 being calculated from the elevation in the temperature of the water. A 
 calorimeter which has been accepted as the best for such work is one in 
 which the fuel is burned in a steel bomb filled with compressed oxygen. 
 The function of the oxygen, which is ordinarily under a pressure of 
 about 25 atmospheres, is to cause the rapid and complete combustion of 
 the fuel sample. The fuel is ignited by means of an electric current, 
 allowance being made for the heat produced by such current, and by the 
 burning of the fuse wire. 
   
 A calorimeter of this type which will be found to give satisfactory 
 results is that of M. Pierre Mahler, illustrated in Fig. 24 and 
 consisting of the following parts: 
   
 A water jacket A, which maintains constant conditions outside of the 
 calorimeter proper, and thus makes possible a more accurate computation 
 of radiation losses. 
   
 The porcelain lined steel bomb B, in which the combustion of the fuel 
 takes place in compressed oxygen. 
   
 [Illustration: Fig. 24. Mahler Bomb Calorimeter] 
   
 The platinum pan C, for holding the fuel. 
   
 The calorimeter proper D, surrounding the bomb and containing a definite 
 weighed amount of water. 
   
 An electrode E, connecting with the fuse wire F, for igniting the fuel 
 placed in the pan C. 
   
 A support G, for a water agitator. 
   
 A thermometer I, for temperature determination of the water in the 
 calorimeter. The thermometer is best supported by a stand independent of 
 the calorimeter, so that it may not be moved by tremors in the parts of 
 the calorimeter, which would render the making of readings difficult. To 
 obtain accuracy of readings, they should be made through a telescope or 
 eyeglass. 
   
 A spring and screw device for revolving the agitator. 
   
 A lever L, by the movement of which the agitator is revolved. 
   
 A pressure gauge M, for noting the amount of oxygen admitted to the 
 bomb. Between 20 and 25 atmospheres are ordinarily employed. 
   
 An oxygen tank O. 
   
 A battery or batteries P, the current from which heats the fuse wire 
 used to ignite the fuel. 
   
 This or a similar calorimeter is used in the determination of the heat 
 of combustion of solid or liquid fuels. Whatever the fuel to be tested, 
 too much importance cannot be given to the securing of an average 
 sample. Where coal is to be tested, tests should be made from a portion 
 of the dried and pulverized laboratory sample, the methods of obtaining 
 which have been described. In considering the methods of calorimeter 
 determination, the remarks applied to coal are equally applicable to any 
 solid fuel, and such changes in methods as are necessary for liquid 
 fuels will be self-evident from the same description. 
   
 Approximately one gram of the pulverized dried coal sample should be 
 placed directly in the pan of the calorimeter. There is some danger in 
 the using of a pulverized sample from the fact that some of it may be 
 blown out of the pan when oxygen is admitted. This may be at least 
 partially overcome by forming about two grams into a briquette by the 
 use of a cylinder equipped with a plunger and a screw press. Such a 
 briquette should be broken and approximately one gram used. If a 
 pulverized sample is used, care should be taken to admit oxygen slowly 
 to prevent blowing the coal out of the pan. The weight of the sample is 
 limited to approximately one gram since the calorimeter is proportioned 
 for the combustion of about this weight when under an oxygen pressure of 
 about 25 atmospheres. 
   
 A piece of fine iron wire is connected to the lower end of the plunger 
 to form a fuse for igniting the sample. The weight of iron wire used is 
 determined, and if after combustion a portion has not been burned, the 
 weight of such portion is determined. In placing the sample in the pan, 
 and in adjusting the fuse, the top of the calorimeter is removed. It is 
 then replaced and carefully screwed into place on the bomb by means of a 
 long handled wrench furnished for the purpose. 
   
 The bomb is then placed in the calorimeter, which has been filled with a 
 definite amount of water. This weight is the "water equivalent" of the 
 apparatus, _i. e._, the weight of water, the temperature of which would 
 be increased one degree for an equivalent increase in the temperature of 
 the combined apparatus. It may be determined by calculation from the 
 weights and specific heats of the various parts of the apparatus. Such a 
 determination is liable to error, however, as the weight of the bomb 
 lining can only be approximated, and a considerable portion of the 
 apparatus is not submerged. Another method of making such a 
 determination is by the adding of definite weights of warm water to 
 definite amounts of cooler water in the calorimeter and taking an 
 average of a number of experiments. The best method for the making of 
 such a determination is probably the burning of a definite amount of 
 resublimed naphthaline whose heat of combustion is known. 
   
 The temperature of the water in the water jacket of the calorimeter 
 should be approximately that of the surrounding atmosphere. The 
 temperature of the weighed amount of water in the calorimeter is made by 
 some experimenters slightly greater than that of the surrounding air in 
 order that the initial correction for radiation will be in the same 
 direction as the final correction. Other experimenters start from a 
 temperature the same or slightly lower than the temperature of the room, 
 on the basis that the temperature after combustion will be slightly 
 higher than the room temperature and the radiation correction be either 
 a minimum or entirely eliminated. 
   
 While no experiments have been made to show conclusively which of these 
 methods is the better, the latter is generally used. 
   
 After the bomb has been placed in the calorimeter, it is filled with 
 oxygen from a tank until the pressure reaches from 20 to 25 atmospheres. 
 The lower pressure will be sufficient in all but exceptional cases. 
 Connection is then made to a current from the dry batteries in series so 
 arranged as to allow completion of the circuit with a switch. The 
 current from a lighting system should not be used for ignition, as there 
 is danger from sparking in burning the fuse, which may effect the 
 results. The apparatus is then ready for the test. 
   
 Unquestionably the best method of taking data is by the use of 
 co-ordinate paper and a plotting of the data with temperatures and time 
 intervals as ordinates and abscissae. Such a graphic representation is 
 shown in Fig. 25. 
   
 [Graph: Temperature--° C. against Time--Hours and Minutes 
   
 Fig. 25. Graphic Method of Recording Bomb Calorimeter Results] 
   
 After the bomb is placed in the calorimeter, and before the coal is 
 ignited, readings of the temperature of the water should be taken at one 
 minute intervals for a period long enough to insure a constant rate of 
 change, and in this way determine the initial radiation. The coal is 
 then ignited by completing the circuit, the temperature at the instant 
 the circuit is closed being considered the temperature at the beginning 
 of the combustion. After ignition the readings should be taken at 
 one-half minute intervals, though because of the rapidity of the 
 mercury's rise approximate readings only may be possible for at least a 
 minute after the firing, such readings, however, being sufficiently 
 accurate for this period. The one-half minute readings should be taken 
 after ignition for five minutes, and for, say, five minutes longer at 
 minute intervals to determine accurately the final rate of radiation. 
   
 Fig. 25 shows the results of such readings, plotted in accordance with 
 the method suggested. It now remains to compute the results from this 
 plotted data. 
   
 The radiation correction is first applied. Probably the most accurate 
 manner of making such correction is by the use of Pfaundler's method, 
 which is a modification of that of Regnault. This assumes that in 
 starting with an initial rate of radiation, as represented by the 
 inclination of the line AB, Fig. 25, and ending with a final radiation 
 represented by the inclination of the line CD, Fig. 25, that the rate of 
 radiation for the intermediate temperatures between the points B and C 
 are proportional to the initial and final rates. That is, the rate of 
 radiation at a point midway between B and C will be the mean between the 
 initial and final rates; the rate of radiation at a point three-quarters 
 of the distance between B and C would be the rate at B plus 
 three-quarters of the difference in rates at B and C, etc. This method 
 differs from Regnault's in that the radiation was assumed by Regnault to 
 be in each case proportional to the difference in temperatures between 
 the water of the calorimeter and the surrounding air plus a constant 
 found for each experiment. Pfaundler's method is more simple than that 
 of Regnault, and the results by the two methods are in practical 
 agreement. 
   
 Expressed as a formula, Pfaundler's method is, though not in form given 
 by him: 
   
      _                 _ 
      |   R' - R         | 
 C = N|R + ------ (T" - T)|     (19) 
      |_   T' - T       _| 
   
 Where C = correction in degree centigrade, 
      N = number of intervals over which correction is made, 
      R = initial radiation in degrees per interval, 
      R' = final radiation in degrees per interval, 
      T = average temperature for period through which initial radiation 
            is computed, 
      T" = average temperature over period of combustion[39], 
      T' = average temperature over period through which final radiation 
            is computed.[39] 
   
 The application of this formula to Fig. 25 is as follows: 
   
 As already stated, the temperature at the beginning of combustion is the 
 reading just before the current is turned on, or B in Fig. 25. The point 
 C or the temperature at which combustion is presumably completed, should 
 be taken at a point which falls well within the established final rate 
 of radiation, and not at the maximum temperature that the thermometer 
 indicates in the test, unless it lies on the straight line determining 
 the final radiation. This is due to the fact that in certain instances 
 local conditions will cause the thermometer to read higher than it 
 should during the time that the bomb is transmitting heat to the water 
 rapidly, and at other times the maximum temperature might be lower than 
 that which would be indicated were readings to be taken at intervals of 
 less than one-half minute, _i. e._, the point of maximum temperature 
 will fall below the line determined by the final rate of radiation. With 
 this understanding AB, Fig. 25, represents the time of initial 
 radiation, BC the time of combustion, and CD the time of final 
 radiation. Therefore to apply Pfaundler's correction, formula (19), to 
 the data as represented by Fig. 25. 
   
 N = 6, R = 0, R' = .01, T = 20.29, T' = 22.83, 
   
      20.29 + 22.54 + 22.84 + 22.88 + 22.87 + 22.86 
 T" = --------------------------------------------- = 22.36 
                            6 
   
      _                             _ 
      |       .01 - 0                 | 
 C = 6|0 + -------------(22.36 - 20.29)| 
      |_   22.85 - 20.29             _| 
   
 = 6 × .008 = .048 
   
 Pfaundler's formula while simple is rather long. Mr. E. H. Peabody has 
 devised a simpler formula with which, under proper conditions, the 
 variation from correction as found by Pfaundler's method is negligible. 
   
 It was noted throughout an extended series of calorimeter tests that the 
 maximum temperature was reached by the thermometer slightly over one 
 minute after the time of firing. If this period between the time of 
 firing and the maximum temperature reported was exactly one minute, the 
 radiation through this period would equal the radiation per one-half 
 minute _before firing_ plus the radiation per one-half minute _after the 
 maximum temperature is reached_; or, the radiation through the one 
 minute interval would be the average of the radiation per minute before 
 firing and the radiation per minute after the maximum. A plotted chart 
 of temperatures would take the form of a curve of three straight lines 
 (B, C', D) in Fig. 25. Under such conditions, using the notation as in 
 formula (19) the correction would become, 
   
    2R + 2R' 
 C = ------- + (N - 2)R', or R + (N - 1)R'     (20) 
      2 
   
 This formula may be generalized for conditions where the maximum 
 temperature is reached after a period of more than one minute as 
 follows: 
   
 Let M = the number of intervals between the time of firing and the 
 maximum temperature. Then the radiation through this period will be an 
 average of the radiation for M intervals before firing and for M 
 intervals after the maximum is recorded, or 
   
    MR + MR'             M         M 
 C = ------- + (N - M)R' = - R + (N - -)R'     (21) 
        2                 2         2 
   
 In the case of Mr. Peabody's deductions M was found to be approximately 
 2 and formula (21) becomes directly, C = R + (N - 1)R' or formula (20). 
   
 The corrections to be made, as secured by the use of this formula, are 
 very close to those secured by Pfaundler's method, where the point of 
 maximum temperature is not more than five intervals later than the point 
 of firing. Where a longer period than this is indicated in the chart of 
 plotted temperatures, the approximate formula should not be used. As the 
 period between firing and the maximum temperature is increased, the 
 plotted results are further and further away from the theoretical 
 straight line curve. Where this period is not over five intervals, or 
 two and a half minutes, an approximation of the straight line curve may 
 be plotted by eye, and ordinarily the radiation correction to be applied 
 may be determined very closely from such an approximated curve. 
   
 Peabody's approximate formula has been found from a number of tests to 
 give results within .003 degrees Fahrenheit for the limits within which 
 its application holds good as described. The value of M, which is not 
 necessarily a whole number, should be determined for each test, though 
 in all probability such a value is a constant for any individual 
 calorimeter which is properly operated. 
   
 The correction for radiation as found on page 188 is in all instances to 
 be added to the range of temperature between the firing point and the 
 point chosen from which the final radiation is calculated. This 
 corrected range multiplied by the water equivalent of the calorimeter 
 gives the heat of combustion in calories of the coal burned in the 
 calorimeter together with that evolved by the burning of the fuse wire. 
 The heat evolved by the burning of the fuse wire is found from the 
 determination of the actual weight of wire burned and the heat of 
 combustion of one milligram of the wire (1.7 calories), _i. e._, 
 multiply the weight of wire used by 1.7, the result being in gram 
 calories or the heat required to raise one gram of water one degree 
 centigrade. 
   
 Other small corrections to be made are those for the formation of nitric 
 acid and for the combustion of sulphur to sulphuric acid instead of 
 sulphur dioxide, due to the more complete combustion in the presence of 
 oxygen than would be possible in the atmosphere. 
   
 To make these corrections the bomb of the calorimeter is carefully 
 washed out with water after each test and the amount of acid determined 
 from titrating this water with a standard solution of ammonia or of 
 caustic soda, all of the acid being assumed to be nitric acid. Each 
 cubic centimeter of the ammonia titrating solution used is equivalent to 
 a correction of 2.65 calories. 
   
 As part of acidity is due to the formation of sulphuric acid, a further 
 correction is necessary. In burning sulphuric acid the heat evolved per 
 gram of sulphur is 2230 calories in excess of the heat which would be 
 evolved if the sulphur burned to sulphur dioxide, or 22.3 calories for 
 each per cent of sulphur in the coal. One cubic centimeter of the 
 ammonia solution is equivalent to 0.00286 grams of sulphur as sulphuric 
 acid, or to 0.286 × 22.3 = 6.38 calories. It is evident therefore that 
 after multiplying the number of cubic centimeters used in titrating by 
 the heat factor for nitric acid (2.65) a further correction of 
 6.38 - 2.65 = 3.73 is necessary for each cubic centimeter used in 
 titrating sulphuric instead of nitric acid. This correction will be 
 3.73/0.297 = 13 units for each 0.01 gram of sulphur in the coal. 
   
 The total correction therefore for the aqueous nitric and sulphuric acid 
 is found by multiplying the ammonia by 2.65 and adding 13 calories for 
 each 0.01 gram of sulphur in the coal. This total correction is to be 
 deducted from the heat value as found from the corrected range and the 
 amount equivalent to the calorimeter. 
   
 After each test the pan in which the coal has been burned must be 
 carefully examined to make sure that all of the sample has undergone 
 complete combustion. The presence of black specks ordinarily indicates 
 unburned coal, and often will be found where the coal contains bone or 
 slate. Where such specks are found the tests should be repeated. In 
 testing any fuel where it is found difficult to completely consume a 
 sample, a weighed amount of naphthaline may be added, the total weight 
 of fuel and naphthaline being approximately one gram. The naphthaline 
 has a known heat of combustion, samples for this purpose being 
 obtainable from the United States Bureau of Standards, and from the 
 combined heat of combustion of the fuel and naphthaline that of the 
 former may be readily computed. 
   
 The heat evolved in burning of a definite weight of standard naphthaline 
 may also be used as a means of calibrating the calorimeter as a whole. 
   
 
 
 
 COMBUSTION OF COAL 
 The composition of coal varies over such a wide range, and the methods 
 of firing have to be altered so greatly to suit the various coals and 
 the innumerable types of furnaces in which they are burned, that any 
 instructions given for the handling of different fuels must of necessity 
 be of the most general character. For each kind of coal there is some 
 method of firing which will give the best results for each individual 
 set of conditions. General rules can be suggested, but the best results 
 can be obtained only by following such methods as experience and 
 practice show to be the best suited to the specific conditions. 
   
 The question of draft is an all important factor. If this be 
 insufficient, proper combustion is impossible, as the suction in the 
 furnace will not be great enough to draw the necessary amount of air 
 through the fuel bed, and the gases may pass off only partially 
 consumed. On the other hand, an excessive draft may cause losses due to 
 the excess quantities of air drawn through holes in the fire. Where coal 
 is burned however, there are rarely complaints from excessive draft, as 
 this can be and should be regulated by the boiler damper to give only 
 the draft necessary for the particular rate of combustion desired. The 
 draft required for various kinds of fuel is treated in detail in the 
 chapter on "Chimneys and Draft". In this chapter it will be assumed that 
 the draft is at all times ample and that it is regulated to give the 
 best results for each kind of coal. 
   
   
                              TABLE 40 
   
                        ANTHRACITE COAL SIZES 
   
 _________________________________________________________________ 
 |                           |                 |                 | 
 |                           |                 | Testing Segments | 
 |                           |   Round Mesh   | Standard Square | 
 |                           |                 |       Mesh       | 
 |       Trade Name         |__________________|__________________| 
 |                           |         |       |         |       | 
 |                          | Through | Over | Through | Over | 
 |                           | Inches | Inches | Inches | Inches | 
 |___________________________|_________|________|_________|________| 
 |                           |         |       |         |       | 
 | Broken                   | 4-1/2 | 3-1/4 | 4     | 2-3/4 | 
 | Egg                       | 3-1/4 | 2-3/8 | 2-3/4 | 2     | 
 | Stove                     | 2-3/8 | 1-5/8 | 2     | 1-3/8 | 
 | Chestnut                 | 1-5/8 |   7/8 | 1-3/8 |   3/4 | 
 | Pea                       |   7/8 |   5/8 |   3/4 |   1/2 | 
 | No. 1 Buckwheat           |   5/8 |   3/8 |   1/2 |   1/4 | 
 | No. 2 Buckwheat or Rice   |   3/8 |   3/16 |   1/4 |   1/8 | 
 | No. 3 Buckwheat or Barley |   3/16 | 3/32 |   1/8 |   1/16 | 
 |___________________________|_________|________|_________|________| 
   
 Anthracite--Anthracite coal is ordinarily marketed under the names and 
 sizes given in Table 40. 
   
 The larger sizes of anthracite are rarely used for commercial steam 
 generating purposes as the demand for domestic use now limits the 
 supply. In commercial plants the sizes generally found are Nos. 1, 2 and 
 3 buckwheat. In some plants where the finer sizes are used, a small 
 percentage of bituminous coal, say, 10 per cent, is sometimes mixed with 
 the anthracite and beneficial results secured both in economy and 
 capacity. 
   
 Anthracite coal should be fired evenly, in small quantities and at 
 frequent intervals. If this method is not followed, dead spots will 
 appear in the fire, and if the fire gets too irregular through burning 
 in patches, nothing can be done to remedy it until the fire is cleaned 
 as a whole. After this grade of fuel has been fired it should be left 
 alone, and the fire tools used as little as possible. Owing to the 
 difficulty of igniting this fuel, care must be taken in cleaning fires. 
 The intervals of cleaning will, of course, depend upon the nature of the 
 coal and the rate of combustion. With the small sizes and moderately 
 high combustion rates, fires will have to be cleaned twice on each 
 eight-hour shift. As the fires become dirty the thickness of the fuel 
 bed will increase, until this depth may be 12 or 14 inches just before a 
 cleaning period. In cleaning, the following practice is usually 
 followed: The good coal on the forward half of the grate is pushed to 
 the rear half, and the refuse on the front portion either pulled out or 
 dumped. The good coal is then pulled forward onto the front part of the 
 grate and the refuse on the rear section dumped. The remaining good coal 
 is then spread evenly over the whole grate surface and the fire built up 
 with fresh coal. 
   
 A ratio of grate surface to heating surface of 1 to from 35 to 40 will 
 under ordinary conditions develop the rated capacity of a boiler when 
 burning anthracite buckwheat. Where the finer sizes are used, or where 
 overloads are desirable, however, this ratio should preferably be 1 to 
 25 and a forced blast should be used. Grates 10 feet deep with a slope 
 of 1½ inches to the foot can be handled comfortably with this class of 
 fuel, and grates 12 feet deep with the same slope can be successfully 
 handled. Where grates over 8 feet in depth are necessary, shaking grates 
 or overlapping dumping grates should be used. Dumping grates may be 
 applied either for the whole grate surface or to the rear section. Air 
 openings in the grate bars should be made from 3/16 inch in width for 
 No. 3 buckwheat to 5/16 inch for No. 1 buckwheat. It is important that 
 these air openings be uniformly distributed over the whole surface to 
 avoid blowing holes in the fire, and it is for this reason that 
 overlapping grates are recommended. 
   
 No air should be admitted over the fire. Steam is sometimes introduced 
 into the ashpit to soften any clinker that may form, but the quantity of 
 steam should be limited to that required for this purpose. The steam 
 that may be used in a steam jet blower for securing blast will in 
 certain instances assist in softening the clinker, but a much greater 
 quantity may be used by such an apparatus than is required for this 
 purpose. Combustion arches sprung above the grates have proved of 
 advantage in maintaining a high furnace temperature and in assisting in 
 the ignition of fresh coal. 
   
 Stacks used with forced blast should be of such size as to insure a 
 slight suction in the furnace under any conditions of operation. A blast 
 up to 3 inches of water should be available for the finer sizes supplied 
 by engine driven fans, automatically controlled by the boiler pressure. 
 The blast required will increase as the depth of the fuel bed increases, 
 and the slight suction should be maintained in the furnace by damper 
 regulation. 
   
 The use of blast with the finer sizes causes rapid fouling of the 
 heating surfaces of the boiler, the dust often amounting to over 10 per 
 cent of the total fuel fired. Economical disposal of dust and ashes is 
 of the utmost importance in burning fuel of this nature. Provision 
 should be made in the baffling of the boiler to accommodate and dispose 
 of this dust. Whenever conditions permit, the ashes can be economically 
 disposed of by flushing them out with water. 
   
 Bituminous Coals--There is no classification of bituminous coal as to 
 size that holds good in all localities. The American Society of 
 Mechanical Engineers suggests the following grading: 
   
   
 _Eastern Bituminous Coals_-- 
   
 (A) Run of mine coal; the unscreened coal taken from the mine. 
   
 (B) Lump coal; that which passes over a bar-screen with openings 1¼ 
    inches wide. 
   
 (C) Nut coal; that which passes through a bar-screen with 1¼-inch 
    openings and over one with ¾-inch openings. 
   
 (D) Slack coal; that which passes through a bar-screen with ¾-inch 
    openings. 
   
   
 _Western Bituminous Coals_-- 
   
 (E) Run of mine coal; the unscreened coal taken from the mine. 
   
 (F) Lump coal; divided into 6-inch, 3-inch and 1¼-inch lump, according 
    to the diameter of the circular openings over which the respective 
    grades pass; also 6 × 3-inch lump and 3 × 1¼-inch lump, according as 
    the coal passes through a circular opening having the diameter of 
    the larger figure and over that of the smaller diameter. 
   
 (G) Nut coal; divided into 3-inch steam nut, which passes through an 
    opening 3 inches diameter and over 1¼ inches; 1¼ inch nut, which 
    passes through a 1¼-inch diameter opening and over a ¾-inch 
    diameter opening; ¾-inch nut, which passes through a ¾-inch 
    diameter opening and over a 5/8-inch diameter opening. 
   
 (H) Screenings; that which passes through a 1¼-inch diameter opening. 
   
   
 As the variation in character of bituminous coals is much greater than 
 in the anthracites, any rules set down for their handling must be the 
 more general. The difficulties in burning bituminous coals with economy 
 and with little or no smoke increases as the content of fixed carbon in 
 the coal decreases. It is their volatile content which causes the 
 difficulties and it is essential that the furnaces be designed to 
 properly handle this portion of the coal. The fixed carbon will take 
 care of itself, provided the volatile matter is properly burned. 
   
 Mr. Kent, in his "Steam Boiler Economy", described the action of 
 bituminous coal after it is fired as follows: "The first thing that the 
 fine fresh coal does is to choke the air spaces existing through the bed 
 of coke, thus shutting off the air supply which is needed to burn the 
 gases produced from the fresh coal. The next thing is a very rapid 
 evaporation of moisture from the coal, a chilling process, which robs 
 the furnace of heat. Next is the formation of water-gas by the chemical 
 reaction, C + H_{2}O = CO + 2H, the steam being decomposed, its oxygen 
 burning the carbon of the coal to carbonic oxide, and the hydrogen being 
 liberated. This reaction takes place when steam is brought in contact 
 with highly heated carbon. This also is a chilling process, absorbing 
 heat from the furnaces. The two valuable fuel gases thus generated would 
 give back all the heat absorbed in their formation if they could be 
 burned, but there is not enough air in the furnace to burn them. 
 Admitting extra air through the fire door at this time will be of no 
 service, for the gases being comparatively cool cannot be burned unless 
 the air is highly heated. After all the moisture has been driven off 
 from the coal, the distillation of hydrocarbons begins, and a 
 considerable portion of them escapes unburned, owing to the deficiency 
 of hot air, and to their being chilled by the relatively cool heating 
 surfaces of the boiler. During all this time great volumes of smoke are 
 escaping from the chimney, together with unburned hydrogen, 
 hydrocarbons, and carbonic oxide, all fuel gases, while at the same time 
 soot is being deposited on the heating surface, diminishing its 
 efficiency in transmitting heat to the water." 
   
 To burn these gases distilled from the coal, it is necessary that they 
 be brought into contact with air sufficiently heated to cause them to 
 ignite, that sufficient space be allowed for their mixture with the air, 
 and that sufficient time be allowed for their complete combustion before 
 they strike the boiler heating surfaces, since these surfaces are 
 comparatively cool and will lower the temperature of the gases below 
 their ignition point. The air drawn through the fire by the draft 
 suction is heated in its passage and heat is added by radiation from the 
 hot brick surfaces of the furnace, the air and volatile gases mixing as 
 this increase in temperature is taking place. Thus in most instances is 
 the first requirement fulfilled. The element of space for the proper 
 mixture of the gases with the air, and of time in which combustion is to 
 take place, should be taken care of by sufficiently large combustion 
 chambers. 
   
 Certain bituminous coals, owing to their high volatile content, require 
 that the air be heated to a higher temperature than it is possible for 
 it to attain simply in its passage through the fire and by absorption 
 from the side walls of the furnace. Such coals can be burned with the 
 best results under fire brick arches. Such arches increase the 
 temperature of the furnace and in this way maintain the heat that must 
 be present for ignition and complete combustion of the fuels in 
 question. These fuels too, sometimes require additional combustion 
 space, and an extension furnace will give this in addition to the 
 required arches. 
   
 As stated, the difficulty of burning bituminous coals successfully will 
 increase with the increase in volatile matter. This percentage of 
 volatile will affect directly the depth of coal bed to be carried and 
 the intervals of firing for the most satisfactory results. The variation 
 in the fuel over such wide ranges makes it impossible to definitely 
 state the thickness of fires for all classes, and experiment with the 
 class of fuel in use is the best method of determining how that 
 particular fuel should be handled. The following suggestions, which are 
 not to be considered in any sense hard and fast rules, may be of service 
 for general operating conditions for hand firing: 
   
 Semi-bituminous coals, such as Pocahontas, New River, Clearfield, etc., 
 require fires from 10 to 14 inches thick; fresh coal should be fired at 
 intervals of 10 to 20 minutes and sufficient coal charged at each firing 
 to maintain a uniform thickness. Bituminous coals from Pittsburgh Region 
 require fires from 4 to 6 inches thick, and should be fired often in 
 comparatively small charges. Kentucky, Tennessee, Ohio and Illinois 
 coals require a thickness from 4 to 6 inches. Free burning coals from 
 Rock Springs, Wyoming, require from 6 to 8 inches, while the poorer 
 grades of Montana, Utah and Washington bituminous coals require a depth 
 of about 4 inches. 
   
 In general as thin fires are found necessary, the intervals of firing 
 should be made more frequent and the quantity of coal fired at each 
 interval smaller. As thin fires become necessary due to the character of 
 the coal, the tendency to clinker will increase if the thickness be 
 increased over that found to give the best results. 
   
 There are two general methods of hand firing: 1st, the spreading method; 
 and 2nd, the coking method. 
 In the spreading method but little fuel is fired at one time, and is 
 spread evenly over the fuel bed from front to rear. Where there is more 
 than one firing door the doors should be fired alternately. The 
 advantage of alternate firing is the whole surface of the fire is not 
 blanketed with green coal, and steam is generated more uniformly than if 
 all doors were fired at one time. Again, a better combustion results due 
 to the burning of more of the volatile matter directly after firing than 
 where all doors are fired at one time. 
   
 In the coking method, fresh coal is fired at considerable depth at the 
 front of the grate and after it is partially coked it is pushed back 
 into the furnace. The object of such a method is the preserving of a bed 
 of carbon at the rear of the grate, in passing over which the volatile 
 gases driven off from the green coal will be burned. This method is 
 particularly adaptable to a grate in which the gases are made to pass 
 horizontally over the fire. Modern practice for hand firing leans more 
 and more toward the spread firing method. Again the tendency is to work 
 bituminous coal fires less than formerly. A certain amount of slicing 
 and raking may be necessary with either method of firing, but in 
 general, the less the fire is worked the better the results. 
   
 Lignites--As the content of volatile matter and moisture in lignite is 
 higher than in bituminous coal, the difficulties encountered in burning 
 them are greater. A large combustion space is required and the best 
 results are obtained where a furnace of the reverberatory type is used, 
 giving the gases a long travel before meeting the tube surfaces. A fuel 
 bed from 4 to 6 inches in depth can be maintained, and the coal should 
 be fired in small quantities by the alternate method. Above certain 
 rates of combustion clinker forms rapidly, and a steam jet in the ashpit 
 for softening this clinker is often desirable. A considerable draft 
 should be available, but it should be carefully regulated by the boiler 
 damper to suit the condition of the fire. Smokelessness with hand firing 
 with this class of fuel is a practical impossibility. It has a strong 
 tendency to foul the heating surfaces rapidly and these surfaces should 
 be cleaned frequently. Shaking grates, intelligently handled, aid in 
 cleaning the fires, but their manipulation must be carefully watched to 
 prevent good coal being lost in the ashpit. 
   
 Stokers--The term "automatic stoker" oftentimes conveys the erroneous 
 impression that such an apparatus takes care of itself, and it must be 
 thoroughly understood that any stoker requires expert attention to as 
 high if not higher degree than do hand-fired furnaces. 
   
 Stoker-fired furnaces have many advantages over hand firing, but where a 
 stoker installation is contemplated there are many factors to be 
 considered. It is true that stokers feed coal to the fire automatically, 
 but if the coal has first to be fed to the stoker hopper by hand, its 
 automatic advantage is lost. This is as true of the removal of ash from 
 a stoker. In a general way, it may be stated that a stoker installation 
 is not advantageous except possibly for diminishing smoke, unless the 
 automatic feature is carried to the handling of the coal and ash, as 
 where coal and ash handling apparatus is not installed there is no 
 saving in labor. In large plants, however, stokers used in conjunction 
 with the modern methods of coal storage and coal and ash handling, make 
 possible a large labor saving. In small plants the labor saving for 
 stokers over hand-fired furnaces is negligible, and the expense of the 
 installation no less proportionately than in large plants. Stokers are, 
 therefore, advisable in small plants only where the saving in fuel will 
 be large, or where the smoke question is important. 
   
 Interest on investment, repairs, depreciation and steam required for 
 blast and stoker drive must all be considered. The upkeep cost will, in 
 general, be higher than for hand-fired furnaces. Stokers, however, make 
 possible the use of cheaper fuels with as high or higher economy than is 
 obtainable under operating conditions in hand-fired furnaces with a 
 better grade of fuel. The better efficiency obtainable with a good 
 stoker is due to more even and continuous firing as against the 
 intermittent firing of hand-fired furnaces; constant air supply as 
 against a variation in this supply to meet varying furnace conditions in 
 hand-fired furnaces; and the doing away to a great extent with the 
 necessity of working the fires. 
   
 Stokers under ordinary operating conditions will give more nearly 
 smokeless combustion than will hand-fired furnaces and for this reason 
 must often be installed regardless of other considerations. While a 
 constant air supply for a given power is theoretically secured by the 
 use of a stoker, and in many instances the draft is automatically 
 governed, the air supply should, nevertheless, be as carefully watched 
 and checked by flue gas analyses as in the case of hand-fired furnaces. 
   
 There is a tendency in all stokers to cause the loss of some good fuel 
 or siftings in the ashpit, but suitable arrangements may be made to 
 reclaim this. 
   
 In respect to efficiency of combustion, other conditions being equal, 
 there will be no appreciable difference with the different types of 
 stokers, provided that the proper type is used for the grade of fuel to 
 be burned and the conditions of operation to be fulfilled. No stoker 
 will satisfactorily handle all classes of fuel, and in making a 
 selection, care should be taken that the type is suited to the fuel and 
 the operating conditions. A cheap stoker is a poor investment. Only the 
 best stoker suited to the conditions which are to be met should be 
 adopted, for if there is to be a saving, it will more than cover the 
 cost of the best over the cheaper stoker. 
   
 Mechanical Stokers are of three general types: 1st, overfeed; 2nd, 
 underfeed; and 3rd, traveling grate. The traveling grate stokers are 
 sometimes classed as overfeed but properly should be classed by 
 themselves as under certain conditions they are of the underfeed rather 
 than the overfeed type. 
   
 Overfeed Stokers in general may be divided into two classes, the 
 distinction being in the direction in which the coal is fed relative to 
 the furnaces. In one class the coal is fed into hoppers at the front end 
 of the furnace onto grates with an inclination downward toward the rear 
 of about 45 degrees. These grates are reciprocated, being made to take 
 alternately level and inclined positions and this motion gradually 
 carries the fuel as it is burned toward the rear and bottom of the 
 furnace. At the bottom of the grates flat dumping sections are supplied 
 for completing the combustion and for cleaning. The fuel is partly 
 burned or coked on the upper portion of the grates, the volatile gases 
 driven off in this process for a perfect action being ignited and burned 
 in their passage over the bed of burning carbon lower on the grates, or 
 on becoming mixed with the hot gases in the furnace chamber. In the 
 second class the fuel is fed from the sides of the furnace for its full 
 depth from front to rear onto grates inclined toward the center of the 
 furnace. It is moved by rocking bars and is gradually carried to the 
 bottom and center of the furnace as combustion advances. Here some type 
 of a so-called clinker breaker removes the refuse. 
   
 Underfeed Stokers are either horizontal or inclined. The fuel is fed 
 from underneath, either continuously by a screw, or intermittently by 
 plungers. The principle upon which these stokers base their claims for 
 efficiency and smokelessness is that the green fuel is fed under the 
 coked and burning coal, the volatile gases from this fresh fuel being 
 heated and ignited in their passage through the hottest portion of the 
 fire on the top. In the horizontal classes of underfeed stokers, the 
 action of a screw carries the fuel back through a retort from which it 
 passes upward, as the fuel above is consumed, the ash being finally 
 deposited on dead plates on either side of the retort, from which it can 
 be removed. In the inclined class, the refuse is carried downward to the 
 rear of the furnace where there are dumping plates, as in some of the 
 overfeed types. 
   
 Underfeed stokers are ordinarily operated with a forced blast, this in 
 some cases being operated by the same mechanism as the stoker drive, 
 thus automatically meeting the requirements of various combustion rates. 
   
 Traveling Grates are of the class best illustrated by chain grate 
 stokers. As implied by the name these consist of endless grates composed 
 of short sections of bars, passing over sprockets at the front and rear 
 of the furnace. Coal is fed by gravity onto the forward end of the 
 grates through suitable hoppers, is ignited under ignition arches and is 
 carried with the grate toward the rear of the furnace as its combustion 
 progresses. When operated properly, the combustion is completed as the 
 fire reaches the end of the grate and the refuse is carried over this 
 rear end by the grate in making the turn over the rear sprocket. In some 
 cases auxiliary dumping grates at the rear of the chain grates are used 
 with success. 
   
 Chain grate stokers in general produce less smoke than either overfeed 
 or underfeed types, due to the fact that there are no cleaning periods 
 necessary. Such periods occur with the latter types of stokers at 
 intervals depending upon the character of the fuel used and the rate of 
 combustion. With chain grate stokers the cleaning is continuous and 
 automatic, and no periods occur when smoke will necessarily be produced. 
   
 In the earlier forms, chain grates had an objectionable feature in that 
 the admission of large amounts of excess air at the rear of the furnace 
 through the grates was possible. This objection has been largely 
 overcome in recent models by the use of some such device as the bridge 
 wall water box and suitable dampers. A distinct advantage of chain 
 grates over other types is that they can be withdrawn from the furnace 
 for inspection or repairs without interfering in any way with the boiler 
 setting. 
   
 This class of stoker is particularly successful in burning low grades of 
 coal running high in ash and volatile matter which can only be burned 
 with difficulty on the other types. The cost of up-keep in a chain 
 grate, properly constructed and operated, is low in comparison with the 
 same cost for other stokers. 
   
 The Babcock & Wilcox chain grate is representative of this design of 
 stoker. 
   
 Smoke--The question of smoke and smokelessness in burning fuels has 
 recently become a very important factor of the problem of combustion. 
 Cities and communities throughout the country have passed ordinances 
 relative to the quantities of smoke that may be emitted from a stack, 
 and the failure of operators to live up to the requirements of such 
 ordinances, resulting as it does in fines and annoyance, has brought 
 their attention forcibly to the matter. 
   
 The whole question of smoke and smokelessness is to a large extent a 
 comparative one. There are any number of plants burning a wide variety 
 of fuels in ordinary hand-fired furnaces, in extension furnaces and on 
 automatic stokers that are operating under service conditions, 
 practically without smoke. It is safe to say, however, that no plant 
 will operate smokelessly under any and all conditions of service, nor is 
 there a plant in which the degree of smokelessness does not depend 
 largely upon the intelligence of the operating force. 
   
 [Illustration: Fig. 26. Babcock & Wilcox Boiler and Superheater Equipped 
 with Babcock & Wilcox Chain Grate Stoker. This Setting has been 
 Particularly Successful in Minimizing Smoke] 
   
 When a condition arises in a boiler room requiring the fires to be 
 brought up quickly, the operatives in handling certain types of stokers 
 will use their slice bars freely to break up the green portion of the 
 fire over the bed of partially burned coal. In fact, when a load is 
 suddenly thrown on a station the steam pressure can often be maintained 
 only in this way, and such use of the slice bar will cause smoke with 
 the very best type of stoker. In a certain plant using a highly volatile 
 coal and operating boilers equipped with ordinary hand-fired furnaces, 
 extension hand-fired furnaces and stokers, in which the boilers with the 
 different types of furnaces were on separate stacks, a difference in 
 smoke from the different types of furnaces was apparent at light loads, 
 but when a heavy load was thrown on the plant, all three stacks would 
 smoke to the same extent, and it was impossible to judge which type of 
 furnace was on one or the other of the stacks. 
   
 In hand-fired furnaces much can be accomplished by proper firing. A 
 combination of the alternate and spreading methods should be used, the 
 coal being fired evenly, quickly, lightly and often, and the fires 
 worked as little as possible. Smoke can be diminished by giving the 
 gases a long travel under the action of heated brickwork before they 
 strike the boiler heating surfaces. Air introduced over the fires and 
 the use of heated arches, etc., for mingling the air with the gases 
 distilled from the coal will also diminish smoke. Extension furnaces 
 will undoubtedly lessen smoke where hand firing is used, due to the 
 increase in length of gas travel and the fact that this travel is 
 partially under heated brickwork. Where hand-fired grates are 
 immediately under the boiler tubes, and a high volatile coal is used, if 
 sufficient combustion space is not provided the volatile gases, 
 distilled as soon as the coal is thrown on the fire, strike the tube 
 surfaces and are cooled below the burning point before they are wholly 
 consumed and pass through as smoke. With an extension furnace, these 
 volatile gases are acted upon by the radiant heat from the extension 
 furnace arch and this heat, together with the added length of travel 
 causes their more complete combustion before striking the heating 
 surfaces than in the former case. 
   
 Smoke may be diminished by employing a baffle arrangement which gives 
 the gases a fairly long travel under heated brickwork and by introducing 
 air above the fire. In many cases, however, special furnaces for smoke 
 reduction are installed at the expense of capacity and economy. 
   
 From the standpoint of smokelessness, undoubtedly the best results are 
 obtained with a good stoker, properly operated. As stated above, the 
 best stoker will cause smoke under certain conditions. Intelligently 
 handled, however, under ordinary operating conditions, stoker-fired 
 furnaces are much more nearly smokeless than those which are hand fired, 
 and are, to all intents and purposes, smokeless. In practically all 
 stoker installations there enters the element of time for combustion, 
 the volatile gases as they are distilled being acted upon by ignition or 
 other arches before they strike the heating surfaces. In many instances 
 too, stokers are installed with an extension beyond the boiler front, 
 which gives an added length of travel during which, the gases are acted 
 upon by the radiant heat from the ignition or supplementary arches, and 
 here again we see the long travel giving time for the volatile gases to 
 be properly consumed. 
   
 To repeat, it must be emphatically borne in mind that the question of 
 smokelessness is largely one of degree, and dependent to an extent much 
 greater than is ordinarily appreciated upon the handling of the fuel and 
 the furnaces by the operators, be these furnaces hand fired or 
 automatically fired. 
   
 
 
 
 SOLID FUELS OTHER THAN COAL AND THEIR COMBUSTION 
 Wood--Wood is vegetable tissue which has undergone no geological change. 
 Usually the term is used to designate those compact substances 
 familiarly known as tree trunks and limbs. When newly cut, wood contains 
 moisture varying from 30 per cent to 50 per cent. When dried for a 
 period of about a year in the atmosphere, the moisture content will be 
 reduced to 18 or 20 per cent. 
   
                          TABLE 41 
   
 ULTIMATE ANALYSES AND CALORIFIC VALUES OF DRY WOOD (GOTTLIEB) 
   
 _______________________________________________________ 
 |       |       |     |     |       |     |         | 
 | Kind   |       |     |     |       |     | B. t. u.| 
 | of   |   C   | H   | N   |   O   | Ash | per   | 
 | Wood   |       |     |     |       |     | Pound   | 
 |________|_______|______|______|_______|______|_________| 
 |       |       |     |     |       |     |         | 
 | Oak   | 50.16 | 6.02 | 0.09 | 43.36 | 0.37 | 8316   | 
 | Ash   | 49.18 | 6.27 | 0.07 | 43.91 | 0.57 | 8480   | 
 | Elm   | 48.99 | 6.20 | 0.06 | 44.25 | 0.50 | 8510   | 
 | Beech | 49.06 | 6.11 | 0.09 | 44.17 | 0.57 | 8391   | 
 | Birch | 48.88 | 6.06 | 0.10 | 44.67 | 0.29 | 8586   | 
 | Fir   | 50.36 | 5.92 | 0.05 | 43.39 | 0.28 | 9063   | 
 | Pine   | 50.31 | 6.20 | 0.04 | 43.08 | 0.37 | 9153   | 
 | Poplar | 49.37 | 6.21 | 0.96 | 41.60 | 1.86 | 7834[40]| 
 | Willow | 49.96 | 5.96 | 0.96 | 39.56 | 3.37 | 7926[40]| 
 |________|_______|______|______|_______|______|_________| 
   
 Wood is usually classified as hard wood, including oak, maple, hickory, 
 birch, walnut and beech; and soft wood, including pine, fir, spruce, 
 elm, chestnut, poplar and willow. Contrary to general opinion, the heat 
 value per pound of soft wood is slightly greater than the same value per 
 pound of hard wood. Table 41 gives the chemical composition and the heat 
 values of the common woods. Ordinarily the heating value of wood is 
 considered equivalent to 0.4 that of bituminous coal. In considering the 
 calorific value of wood as given in this table, it is to be remembered 
 that while this value is based on air-dried wood, the moisture content 
 is still about 20 per cent of the whole, and the heat produced in 
 burning it will be diminished by this amount and by the heat required to 
 evaporate the moisture and superheat it to the temperature of the gases. 
 The heat so absorbed may be calculated by the formula giving the loss 
 due to moisture in the fuel, and the net calorific value determined. 
   
 In designing furnaces for burning wood, the question resolves itself 
 into: 1st, the essential elements to give maximum capacity and 
 efficiency with this class of fuel; and 2nd, the construction which will 
 entail the least labor in handling and feeding the fuel and removing the 
 refuse after combustion. 
   
 Wood, as used commercially for steam generating purposes, is usually a 
 waste product from some industrial process. At the present time refuse 
 from lumber and sawmills forms by far the greater part of this class of 
 fuel. In such refuse the moisture may run as high as 60 per cent and the 
 composition of the fuel may vary over wide ranges during different 
 portions of the mill operation. The fuel consists of sawdust, "hogged" 
 wood and slabs, and the percentage of each of these constituents may 
 vary greatly. Hogged wood is mill refuse and logs that have been passed 
 through a "hogging machine" or macerator. This machine, through the 
 action of revolving knives, cuts or shreds the wood into a state in 
 which it may readily be handled as fuel. 
   
 Table 42 gives the moisture content and heat value of typical sawmill 
 refuse from various woods. 
   
                                TABLE 42 
   
            MOISTURE AND CALORIFIC VALUE OF SAWMILL REFUSE 
 _____________________________________________________________________ 
 |                     |                       |         |           | 
 |                     |                       | Per Cent | B. t. u. | 
 |   Kind of Wood     |   Nature of Refuse   | Moisture | per Pound | 
 |                    |                       |         | Dry Fuel | 
 |_____________________|_______________________|__________|____________| 
 |                     |                       |         |           | 
 | Mexican White Pine | Sawdust and Hog Chips |   51.90 |   9020     | 
 | Yosemite Sugar Pine | Sawdust and Hog Chips |   62.85 |   9010     | 
 | Redwood 75%,       | Sawdust, Box Mill     |         |           | 
 |   Douglas Fir 25%   |   Refuse and Hog     |   42.20 |   8977[41] | 
 | Redwood             | Sawdust and Hog Chips |   52.98 |   9040[41] | 
 | Redwood             | Sawdust and Hog Chips |   49.11 |   9204[41] | 
 | Fir, Hemlock,       |                       |         |           | 
 |   Spruce and Cedar | Sawdust               |   42.06 |   8949[41] | 
 |_____________________|_______________________|__________|____________| 
   
 It is essential in the burning of this class of fuel that a large 
 combustion space be supplied, and on account of the usually high 
 moisture content there should be much heated brickwork to radiate heat 
 to the fuel bed and thus evaporate the moisture. Extension furnaces of 
 the proper size are usually essential for good results and when this 
 fuel is used alone, grates dropped to the floor line with an ashpit 
 below give additional volume for combustion and space for maintaining a 
 thick fuel bed. A thick fuel bed is necessary in order to avoid 
 excessive quantities of air passing through the boiler. Where the fuel 
 consists of hogged wood and sawdust alone, it is best to feed it 
 automatically into the furnace through chutes on the top of the 
 extension. The best results are secured when the fuel is allowed to pile 
 up in the furnace to a height of 3 or 4 feet in the form of a cone under 
 each chute. The fuel burns best when not disturbed in the furnace. Each 
 fuel chute, when a proper distance from the grates and with the piles 
 maintained at their proper height, will supply about 30 or 35 square 
 feet of grate surface. While large quantities of air are required for 
 burning this fuel, excess air is as harmful as with coal, and care must 
 be taken that such an excess is not admitted through fire doors or fuel 
 chutes. A strong natural draft usually is preferable to a blast with 
 this fuel. The action of blast is to make the regulation of the furnace 
 conditions more difficult and to blow over unconsumed fuel on the 
 heating surfaces and into the stack. This unconsumed fuel settling in 
 portions of the setting out of the direct path of the gases will have a 
 tendency to ignite provided any air reaches it, with results harmful to 
 the setting and breeching connection. This action is particularly 
 objectionable if these particles are carried over into the base of a 
 stack, where they will settle below the point at which the flue enters 
 and if ignited may cause the stack to become overheated and buckle. 
   
 Whether natural draft or blast is used, much of the fuel is carried onto 
 the heating surfaces and these should be cleaned regularly to maintain a 
 good efficiency. Collecting chambers in various portions of the setting 
 should be provided for this unconsumed fuel, and these should be kept 
 clean. 
   
 With proper draft conditions, 150 pounds of this fuel containing about 
 30 to 40 per cent of moisture can be burned per square foot of grate 
 surface per hour, and in a properly designed furnace one square foot of 
 grate surface can develop from 5 to 6 boiler horse power. Where the wood 
 contains 50 per cent of moisture or over, it is not usually safe to 
 figure on obtaining more than 3 to 4 horse power per square foot of 
 grate surface. 
   
 Dry sawdust, chips and blocks are also used as fuel in many wood-working 
 industries. Here, as with the wet wood, ample combustion space should be 
 supplied, but as this fuel is ordinarily kiln dried, large brickwork 
 surfaces in the furnace are not necessary for the evaporation of 
 moisture in the fuel. This fuel may be burned in extension furnaces 
 though these are not required unless they are necessary to secure an 
 added furnace volume, to get in sufficient grate surface, or where such 
 an arrangement must be used to allow for a fuel bed of sufficient 
 thickness. Depth of fuel bed with the dry fuel is as important as with 
 the moist fuel. If extension furnaces are used with this dry wood, care 
 must be taken in their design that there is no excessive throttling of 
 the gases in the furnace, or brickwork trouble will result. In Babcock & 
 Wilcox boilers this fuel may be burned without extension furnaces, 
 provided that the boilers are set at a sufficient height to provide 
 ample combustion space and to allow for proper depth of fuel bed. 
 Sometimes this is gained by lowering the grates to the floor line and 
 excavating for an ashpit. Where the fuel is largely sawdust, it may be 
 introduced over the fire doors through inclined chutes. The old methods 
 of handling and collecting sawdust by means of air suction and blast 
 were such that the amount of air admitted through such chutes was 
 excessive, but with improved methods the amount of air so admitted may 
 be reduced to a negligible quantity. The blocks and refuse which cannot 
 be handled through chutes may be fired through fire doors in the front 
 of the boiler, which should be made sufficiently large to accommodate 
 the larger sizes of fuel. As with wet fuel, there will be a quantity of 
 unconsumed wood carried over and the heating surfaces must be kept 
 clean. 
   
 In a few localities cord wood is burned. With this as with other classes 
 of wood fuel, a large combustion space is an essential feature. The 
 percentage of moisture in cord wood may make it necessary to use an 
 extension furnace, but ordinarily this is not required. Ample combustion 
 space is in most cases secured by dropping the grates to the floor line, 
 large double-deck fire doors being supplied at the usual fire door level 
 through which the wood is thrown by hand. Air is admitted under the 
 grates through an excavated ashpit. The side, front and rear walls of 
 the furnace should be corbelled out to cover about one-third of the 
 total grate surface. This prevents cold air from laneing up the sides of 
 the furnace and also reduces the grate surface. Cord wood and slabs form 
 an open fire through which the frictional loss of the air is much less 
 than in the case of sawdust or hogged material. The combustion rate with 
 cord wood is, therefore, higher and the grate surface may be 
 considerably reduced. Such wood is usually cut in lengths of 4 feet or 4 
 feet 6 inches, and the depth of the grates should be kept approximately 
 5 feet to get the best results. 
   
 Bagasse--Bagasse is the refuse of sugar cane from which the juice has 
 been extracted by pressure between the rolls of the mill. From the start 
 of the sugar industry bagasse has been considered the natural fuel for 
 sugar plantations, and in view of the importance of the industry a word 
 of history relative to the use of this fuel is not out of place. 
   
 When the manufacture of sugar was in its infancy the cane was passed 
 through but a single mill and the defecation and concentration of the 
 saccharine juice took place in a series of vessels mounted one after 
 another over a common fire at one end and connected to a stack at the 
 opposite end. This primitive method was known in the English colonies as 
 the "Open Wall" and in the Spanish-American countries as the "Jamaica 
 Train". 
   
 The evaporation and concentration of the juice in the open air and over 
 a direct fire required such quantities of fuel, and the bagasse, in 
 fact, played such an important part in the manufacture of sugar, that 
 oftentimes the degree of extraction, which was already low, would be 
 sacrificed to the necessity of obtaining a bagasse that might be readily 
 burned. 
   
 The furnaces in use with these methods were as primitive as the rest of 
 the apparatus, and the bagasse could be burned in them only by first 
 drying it. This naturally required an enormous quantity of handling of 
 the fuel in spreading and collecting and frequently entailed a shutting 
 down of the mill, because a shower would spoil the supply which had been 
 dried. 
   
 The difficulties arising from the necessity of drying this fuel caused a 
 widespread attempt on the part of inventors to the turning out of a 
 furnace which would successfully burn green bagasse. Some of the designs 
 were more or less clever, and about the year 1880 several such green 
 bagasse furnaces were installed. These did not come up to expectations, 
 however, and almost invariably they were abandoned and recourse had to 
 be taken to the old method of drying in the sun. 
   
 From 1880 the new era in the sugar industry may be dated. Slavery was 
 almost universally abolished and it became necessary to pay for labor. 
 The cost of production was thus increased, while growing competition of 
 European beet sugar lowered the prices. The only remedy for the new 
 state of affairs was the cheapening of the production by the increase of 
 extraction and improvement in manufacture. The double mill took the 
 place of the single, the open wall method of extraction was replaced by 
 vacuum evaporative apparatus and centrifugal machines were introduced to 
 do the work of the great curing houses. As opposed to these 
 improvements, however, the steam plants remained as they started, 
 consisting of double flue boilers externally fired with dry bagasse. 
   
 On several of the plantations horizontal multitubular boilers externally 
 fired were installed and at the time were considered the acme of 
 perfection. Numerous attempts were made to burn the bagasse green, among 
 others the step grates imported from Louisiana and known as the Leon 
 Marie furnaces, but satisfactory results were obtained in none of the 
 appliances tried. 
   
 The Babcock & Wilcox Co. at this time turned their attention to the 
 problem with the results which ultimately led to its solution. Their New 
 Orleans representative, Mr. Frederick Cook, invented a hot forced blast 
 bagasse furnace and conveyed the patent rights to this company. This 
 furnace while not as efficient as the standard of to-day, and expensive 
 in its construction, did, nevertheless, burn the bagasse green and 
 enabled the boilers to develop their normal rated capacity. The first 
 furnace of this type was installed at the Southwood and Mt. Houmas 
 plantations and on a small plantation in Florida. About the year 1888 
 two furnaces were erected in Cuba, one on the plantation Senado and the 
 other at the Central Hormiguero. The results obtained with these 
 furnaces were so remarkable in comparison with what had previously been 
 accomplished that the company was overwhelmed with orders. The expense 
 of auxiliary fuel, usually wood, which was costly and indispensable in 
 rainy weather, was done away with and as the mill could be operated on 
 bagasse alone, the steam production and the factory work could be 
 regulated with natural increase in daily output. 
   
 Progress and improvement in the manufacture itself was going on at a 
 remarkable rate, the single grinding had been replaced by a double 
 grinding, this in turn by a third grinding, and finally the maceration 
 and dilution of the bagasse was carried to the extraction of practically 
 the last trace of sugar contained in it. The quantity of juice to be 
 treated was increased in this way 20 or 30 per cent but was accompanied 
 by the reduction to a minimum of the bagasse available as a fuel, and 
 led to demands upon the furnace beyond its capacity. 
   
 With the improvements in the manufacture, planters had been compelled to 
 make enormous sacrifices to change radically their systems, and the 
 heavy disbursement necessary for mill apparatus left few in a financial 
 position to make costly installations of good furnaces. The necessity of 
 turning to something cheap in furnace construction but which was 
 nevertheless better than the early method of burning the fuel dry led to 
 the invention of numerous furnaces by all classes of engineers 
 regardless of their knowledge of the subject and based upon no 
 experience. None of the furnaces thus produced were in any sense 
 inventions but were more or less barefaced infringements of the patents 
 of The Babcock & Wilcox Co. As the company could not protect its rights 
 without hurting its clients, who in many cases against their own will 
 were infringing upon these patents, and as on the other hand they were 
 anxious to do something to meet the wants of the planters, a series of 
 experiments were started, at their own rather than at their customers' 
 expense, with a view to developing a furnace which, without being as 
 expensive, would still fulfill all the requirements of the manufacturer. 
 The result was the cold blast green bagasse furnace which is now 
 offered, and it has been adopted as standard for this class of work 
 after years of study and observation in our installations in the sugar 
 countries of the world. Such a furnace is described later in considering 
 the combustion of bagasse. 
   
 Composition and Calorific Value of Bagasse--The proportion of fiber 
 contained in the cane and density of the juice are important factors in 
 the relation the bagasse fuel will have to the total fuel necessary to 
 generate the steam required in a mill's operation. A cane rich in wood 
 fiber produces more bagasse than a poor one and a thicker juice is 
 subject to a higher degree of dilution than one not so rich. 
   
 Besides the percentage of bagasse in the cane, its physical condition 
 has a bearing on its calorific value. The factors here entering are the 
 age at which the cane must be cut, the locality in which it is grown, 
 etc. From the analysis of any sample of bagasse its approximate 
 calorific value may be calculated from the formula, 
   
                              8550F + 7119S + 6750G - 972W 
 t. u. per pound bagasse = ----------------------------     (22) 
 
                                          100 
   
 Where F = per cent of fiber in cane, S = per cent sucrose, G = per cent 
 glucose, W = per cent water. 
   
 This formula gives the total available heat per pound of bagasse, that 
 is, the heat generated per pound less the heat required to evaporate its 
 moisture and superheat the steam thus formed to the temperature of the 
 stack gases. 
   
 Three samples of bagasse in which the ash is assumed to be 3 per cent 
 give from the formula: 
   
 F = 50     S and G = 4.5 W = 42.5 B. t. u. = 4183 
 F = 40     S and G = 6.0 W = 51.0 B. t. u. = 3351 
 F = 33.3   S and G = 7.0 W = 56.7 B. t. u. = 2797 
   
 A sample of Java bagasse having F = 46.5, S = 4.50, G = 0.5, W = 47.5 
 gives B. t. u. 3868. 
   
 These figures show that the dryer the bagasse is crushed, the higher the 
 calorific value, though this is accompanied by a decrease in sucrose. 
 The explanation lies in the fact that the presence of sucrose in an 
 analysis is accompanied by a definite amount of water, and that the 
 residual juice contains sufficient organic substance to evaporate the 
 water present when a fuel is burned in a furnace. For example, assume 
 the residual juice (100 per cent) to contain 12 per cent organic matter. 
 From the constant in formula, 
   
 12×7119             (100-12)×972 
 ------- = 854.3 and ------------ = 855.4. 
 100                  100 
   
 That is, the moisture in a juice containing 12 per cent of sugar will be 
 evaporated by the heat developed by the combustion of the contained 
 sugar. It would, therefore, appear that a bagasse containing such juice 
 has a calorific value due only to its fiber content. This is, of course, 
 true only where the highest products of oxidization are formed during 
 the combustion of the organic matter. This is not strictly the case, 
 especially with a bagasse of a high moisture content which will not burn 
 properly but which smoulders and produces a large quantity of products 
 of destructive distillation, chiefly heavy hydrocarbons, which escape 
 unburnt. The reasoning, however, is sufficient to explain the steam 
 making properties of bagasse of a low sucrose content, such as are 
 secured in Java, as when the sucrose content is lower, the heat value is 
 increased by extracting more juice, and hence more sugar from it. The 
 sugar operations in Java exemplify this and show that with a high 
 dilution by maceration and heavy pressure the bagasse meets all of the 
 steam requirements of the mills without auxiliary fuel. 
   
 A high percentage of silica or salts in bagasse has sometimes been 
 ascribed as the reason for the tendency to smoulder in certain cases of 
 soft fiber bagasse. This, however, is due to the large moisture content 
 of the sample resulting directly from the nature of the cane. Soluble 
 salts in the bagasse has also been given as the explanation of such 
 smouldering action of the fire, but here too the explanation lies solely 
 in the high moisture content, this resulting in the development of only 
 sufficient heat to evaporate the moisture. 
   
                                TABLE 43 
   
                ANALYSES AND CALORIFIC VALUES OF BAGASSE 
 +---------------------------------------------------------------------+ 
 |+----------+--------+-------+-------+-------+-------+-------+-------+| 
 ||         |       |       |       |       |       |       |B.t.u. || 
 ||         |       |       |       |       |       |       | per || 
 || Source |Moisture|   C   |   H   |   O   |   N   | Ash | Pound || 
 ||         |       |       |       |       |       |       | Dry || 
 ||         |       |       |       |       |       |       |Bagasse|| 
 |+----------+--------+-------+-------+-------+-------+-------+-------+| 
 ||Cuba     | 51.50 | 43.15 | 6.00 | 47.95 |       | 2.90 | 7985 || 
 ||Cuba     | 49.10 | 43.74 | 6.08 | 48.61 |       | 1.57 | 8300 || 
 ||Cuba     | 42.50 | 43.61 | 6.06 | 48.45 |       | 1.88 | 8240 || 
 ||Cuba     | 51.61 | 46.80 | 5.34 | 46.35 |       | 1.51 |       || 
 ||Cuba     | 52.80 | 46.78 | 5.74 | 45.38 |       | 2.10 |       || 
 ||Porto Rico| 41.60 | 44.28 | 6.66 | 47.10 | 0.41 | 1.35 | 8359 || 
 ||Porto Rico| 43.50 | 44.21 | 6.31 | 47.72 | 0.41 | 1.35 | 8386 || 
 ||Porto Rico| 44.20 | 44.92 | 6.27 | 46.50 | 0.41 | 1.90 | 8380 || 
 ||Louisiana | 52.10 |       |       |       |       | 2.27 | 8230 || 
 ||Louisiana | 54.00 |       |       |       |       |       | 8370 || 
 ||Louisiana | 51.80 |      |       |       |       |       | 8371 || 
 ||Java     |       | 46.03 | 6.56 | 45.55 | 0.18 | 1.68 | 8681 || 
 |+----------+--------+-------+-------+-------+-------+-------+-------+| 
 +---------------------------------------------------------------------+ 
   
 Table 43 gives the analyses and heat values of bagasse from various 
 localities. Table 44 gives the value of mill bagasse at different 
 extractions, which data may be of service in making approximations as to 
 its fuel value as compared with that of other fuels. 
   
                              TABLE 44 
   
    VALUE OF ONE POUND OF MILL BAGASSE AT DIFFERENT EXTRACTIONS 
   
 1: Per Cent Extraction of Weight of Cane 
 2: Per Cent Moisture in Bagasse 
 3: Per Cent in Bagasse 
 4: Fuel Value, B. t. u. 
 5: Per Cent in Bagasse 
 6: Fuel Value, B. t. u. 
 7: Per Cent in Bagasse 
 8: Fuel Value, B. t. u. 
 9: Total Heat Developed per Pound of Bagasse 
 10: Heat Required to Evaporate Moisture[42] 
 11: Heat Available for Steam Generation 
 12: Pounds of Bagasse Equivalent to one Pound of Coal of 14,000 B. t. u. 
   
 +----------------------------------------------------------------+ 
 |+---+-----+----------+---------+---------+----------------+----+| 
 ||   |     |         |         |         |B.t.u. Value per|   || 
 ||   |     |   Fiber | Sugar   |Molasses |Pound of Bagasse|   || 
 ||   |     +-----+----+----+----+----+----+-----+----+-----+   || 
 ||   |     |     |   |   |   |   |   |     |   |     |   || 
 || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 || 
 |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| 
 || BASED UPON CANE OF 12 PER CENT FIBER AND JUICE CONTAINING   || 
 ||18 PER CENT OF SOLID MATTER. REPRESENTING TROPICAL CONDITIONS || 
 |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| 
 ||75 |42.64|48.00|3996|6.24|451 |3.12|217 |4664 |525 |4139 |3.38|| 
 ||77 |39.22|52.17|4343|5.74|414 |2.87|200 |4958 |483 |4475 |3.13|| 
 ||79 |35.15|57.14|4757|5.14|371 |2.57|179 |5307 |433 |4874 |2.87|| 
 ||81 |30.21|63.16|5258|4.42|319 |2.21|154 |5731 |372 |5359 |2.61|| 
 ||83 |24.12|70.59|5877|3.53|256 |1.76|122 |6255 |297 |5958 |2.35|| 
 ||85 |16.20|80.00|6660|2.40|173 |1.20| 83 |6916 |200 |6716 |2.08|| 
 |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| 
 || BASED UPON CANE OF 10 PER CENT FIBER AND JUICE CONTAINING   || 
 ||15 PER CENT OF SOLID MATTER. REPRESENTING LOUISIANA CONDITIONS|| 
 |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| 
 ||75 |51.00|40.00|3330|6.00|433 |3.00|209 |3972 |678 |3294 |4.25|| 
 ||77 |48.07|43.45|3617|5.66|409 |2.82|196 |4222 |592 |3630 |3.86|| 
 ||79 |44.52|47.62|3964|5.24|378 |2.62|182 |4524 |548 |3976 |3.52|| 
 ||81 |40.18|52.63|4381|4.73|342 |2.36|164 |4887 |495 |4392 |3.19|| 
 ||83 |35.00|58.82|4897|4.12|298 |2.06|143 |5436 |431 |5005 |2.80|| 
 ||85 |28.33|66.67|5550|3.33|241 |1.67|116 |5907 |349 |5558 |2.52|| 
 |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| 
 +----------------------------------------------------------------+ 
   
 Furnace Design and the Combustion of Bagasse--With the advance in sugar 
 manufacture there came, as described, a decrease in the amount of 
 bagasse available for fuel. As the general efficiency of a plant of this 
 description is measured by the amount of auxiliary fuel required per ton 
 of cane, the relative importance of the furnace design for the burning 
 of this fuel is apparent. 
   
 In modern practice, under certain conditions of mill operation, and with 
 bagasse of certain physical properties, the bagasse available from the 
 cane ground will meet the total steam requirements of the plant as a 
 whole; such conditions prevail, as described, in Java. In the United 
 States, Cuba, Porto Rico and like countries, however, auxiliary fuel is 
 almost universally a necessity. The amount will vary, depending to a 
 great extent upon the proportion of fiber in the cane, which varies 
 widely with the locality and with the age at which it is cut, and to a 
 lesser extent upon the degree of purity of the manufactured sugar, the 
 use of the maceration water and the efficiency of the mill apparatus as 
 a whole. 
 Experience has shown that this fuel may be burned with the best results 
 in large quantities. A given amount of bagasse burned in one furnace 
 between two boilers will give better results than the same quantity 
 burned in a number of smaller furnaces. An objection has been raised 
 against such practice on the grounds that the necessity of shutting down 
 two boiler units when it is necessary for any reason to take off a 
 furnace, requires a larger combined boiler capacity to insure continuity 
 of service. As a matter of fact, several small furnaces will cost 
 considerably more than one large furnace, and the saving in original 
 furnace cost by such an installation, taken in conjunction with the 
 added efficiency of the larger furnace over the small, will probably 
 more than offset the cost of additional boiler units for spares. 
   
 The essential features in furnace design for this class of fuel are 
 ample combustion space and a length of gas travel sufficient to enable 
 the gases to be completely burned before the boiler heating surfaces are 
 encountered. Experience has shown that better results are secured where 
 the fuel is burned on a hearth rather than on grates, the objection to 
 the latter method being that the air for combustion enters largely 
 around the edges, where the fuel pile is thinnest. When burned on a 
 hearth the air for combustion is introduced into the furnace through 
 several rows of tuyeres placed above and symmetrically around the 
 hearth. An arrangement of such tuyeres over a grate, and a proper 
 manipulation of the ashpit doors, will overcome largely the objection to 
 grates and at the same time enable other fuel to be burned in the 
 furnace when necessary. This arrangement of grates and tuyeres is 
 probably the better from a commercially efficient standpoint. Where the 
 air is admitted through tuyeres over the grate or hearth line, it 
 impinges on the fuel pile as a whole and causes a uniform combustion. 
 Such tuyeres connect with an annular space in which, where a blast is 
 used, the air pressure is controlled by a blower. 
   
 All experience with this class of fuel indicates that the best results 
 are secured with high combustion rates. With a natural draft in the 
 furnace of, say, three-tenths inch of water, a combustion rate of from 
 250 to 300 pounds per square foot of grate surface per hour may be 
 obtained. With a blast of, say, five-tenths inch of water, this rate can 
 be increased to 450 pounds per square foot of grate surface per hour. 
 These rates apply to bagasse as fired containing approximately 50 per 
 cent of moisture. It would appear that the most economical results are 
 secured with a combustion rate of approximately 300 pounds per square 
 foot per hour which, as stated, may be obtained with natural draft. 
 Where a natural draft is available sufficient to give such a rate, it is 
 in general to be preferred to a blast. 
   
 Fig. 27 shows a typical bagasse furnace with which very satisfactory 
 results have been obtained. The design of this furnace may be altered to 
 suit the boilers to which it is connected. It may be changed slightly in 
 its proportions and in certain instances in its position relative to the 
 boiler. The furnace as shown is essentially a bagasse furnace and may be 
 modified somewhat to accommodate auxiliary fuel. 
   
 The fuel is ignited in a pit A on a hearth which is ordinarily 
 elliptical in shape. Air for combustion is admitted through the tuyeres 
 B connected to an annular space C through which the amount of air is 
 controlled. Above the pit the furnace widens out to form a combustion 
 space D which has a cylindrical or spherical roof with its top 
 ordinarily from 11 to 13 feet above the floor. The gases pass from this 
 space horizontally to a second combustion chamber E from which they are 
 led through arches F to the boiler. The arrangement of such arches is 
 modified to suit the boiler or boilers with which the furnace is 
 operated. A furnace of such design embodies the essential features of 
 ample combustion space and long gas travel. 
   
 The fuel should be fed to the furnace through an opening in the roof 
 above the pit by some mechanical means which will insure a constant fuel 
 feed and at the same time prevent the inrush of cold air into the 
 furnace. 
   
 This class of fuel deposits a considerable quantity of dust, which if 
 not removed promptly will fuse into a hard glass-like clinker. Ample 
 provision should be made for the removal of such dust from the furnace, 
 the gas ducts and the boiler setting, and these should be thoroughly 
 cleaned once in 24 hours. 
   
 Table 45 gives the results of several tests on Babcock & Wilcox boilers 
 using fuel of this character. 
   
                                TABLE 45 
   
          TESTS OF BABCOCK & WILCOX BOILERS WITH GREEN BAGASSE 
 ____________________________________________________________________ 
 | Duration of Test           | Hours   | 12 | 10 | 10 | 10 | 
 | Rated Capacity of Boiler   |Horse Power| 319 | 319 | 319 | 319 | 
 | Grate Surface             |Square Feet| 33 | 33 | 16.5 | 16.5 | 
 | Draft in Furnace           | Inches   | .30 | .28 | .29 | .27 | 
 | Draft at Damper           | Inches   | .47 | .45 | .46 | .48 | 
 | Blast under Grates         | Inches   | ... | ... | ... | .34 | 
 | Temperature of Exit Gases | Degrees F.| 536 | 541 | 522 | 547 | 
 |                   /CO_{2} | Per Cent | 13.8 | 12.6 | 11.7 | 12.8 | 
 | Flue Gas Analysis { O     | Per Cent | 5.9 | 7.6 | 8.2 | 6.9 | 
 |                   CO     | Per Cent | 0.0 | 0.0 | 0.0 | 0.0 | 
 | Bagasse per Hour as Fired | Pounds   | 4980 | 4479 | 5040 | 5586 | 
 | Moisture in Bagasse       | Per Cent |52.39 |52.93 |51.84 |51.71 | 
 | Dry Bagasse per Hour       | Pounds   | 2371 | 2108 | 2427 | 2697 | 
 | Dry Bagasse per Square Foot|           |     |     |     |     | 
 | of Grate Surface per Hour| Pounds   | 71.9 | 63.9 |147.1 |163.4 | 
 | Water per Hour from and at |           |     |     |     |     | 
 |   212 Degrees             | Pounds   |10141 | 9850 |10430 |11229 | 
 | Per Cent of Rated Capacity |           |    |     |     |     | 
 |   Developed               | Per Cent | 92.1 | 89.2 | 94.7 |102.0 | 
 |____________________________|___________|______|______|______|______| 
   
 Tan Bark--Tan bark, or spent tan, is the fibrous portion of bark 
 remaining after use in the tanning industry. It is usually very high in 
 its moisture content, a number of samples giving an average of 65 per 
 cent or about two-thirds of the total weight of the fuel. The weight of 
 the spent tan is about 2.13 times as great as the weight of the bark 
 ground. In calorific value an average of 10 samples gives 9500 B. t. u. 
 per pound dry.[43] The available heat per pound as fired, owing to the 
 great percentage of moisture usually found, will be approximately 2700 
 t. u. Since the weight of the spent tan as fired is 2.13 as great as 
 
 the weight of the bark as ground at the mill, one pound of ground bark 
 produces an available heat of approximately 5700 B. t. u. Relative to 
 bituminous coal, a ton of bark is equivalent to 0.4 ton of coal. An 
 average chemical analysis of the bark is, carbon 51.8 per cent, hydrogen 
 6.04, oxygen 40.74, ash 1.42. 
   
 Tan bark is burned in isolated cases and in general the remarks on 
 burning wet wood fuel apply to its combustion. The essential features 
 are a large combustion space, large areas of heated brickwork radiating 
 to the fuel bed, and draft sufficient for high combustion rates. The 
 ratings obtainable with this class of fuel will not be as high as with 
 wet wood fuel, because of the heat value and the excessive moisture 
 content. Mr. D. M. Meyers found in a series of experiments that an 
 average of from 1.5 to 2.08 horse power could be developed per square 
 foot of grate surface with horizontal return tubular boilers. This horse 
 power would vary considerably with the method in which the spent tan was 
 fired. 
   
 
 
 
 LIQUID FUELS AND THEIR COMBUSTION 
 Petroleum is practically the only liquid fuel sufficiently abundant and 
 cheap to be used for the generation of steam. It possesses many 
 advantages over coal and is extensively used in many localities. 
   
 There are three kinds of petroleum in use, namely those yielding on 
 distillation: 1st, paraffin; 2nd, asphalt; 3rd, olefine. To the first 
 group belong the oils of the Appalachian Range and the Middle West of 
 the United States. These are a dark brown in color with a greenish 
 tinge. Upon their distillation such a variety of valuable light oils are 
 obtained that their use as fuel is prohibitive because of price. 
   
 To the second group belong the oils found in Texas and California. These 
 vary in color from a reddish brown to a jet black and are used very 
 largely as fuel. 
   
 The third group comprises the oils from Russia, which, like the second, 
 are used largely for fuel purposes. 
   
 The light and easily ignited constituents of petroleum, such as naphtha, 
 gasolene and kerosene, are oftentimes driven off by a partial 
 distillation, these products being of greater value for other purposes 
 than for use as fuel. This partial distillation does not decrease the 
 value of petroleum as a fuel; in fact, the residuum known in trade as 
 "fuel oil" has a slightly higher calorific value than petroleum and 
 because of its higher flash point, it may be more safely handled. 
 Statements made with reference to petroleum apply as well to fuel oil. 
   
 In general crude oil consists of carbon and hydrogen, though it also 
 contains varying quantities of moisture, sulphur, nitrogen, arsenic, 
 phosphorus and silt. The moisture contained may vary from less than 1 to 
 over 30 per cent, depending upon the care taken to separate the water 
 from the oil in pumping from the well. As in any fuel, this moisture 
 affects the available heat of the oil, and in contracting for the 
 purchase of fuel of this nature it is well to limit the per cent of 
 moisture it may contain. A large portion of any contained moisture can 
 be separated by settling and for this reason sufficient storage capacity 
 should be supplied to provide time for such action. 
   
 A method of obtaining approximately the percentage of moisture in crude 
 oil which may be used successfully, particularly with lighter oils, is 
 as follows. A burette graduated into 200 divisions is filled to the 100 
 mark with gasolene, and the remaining 100 divisions with the oil, which 
 should be slightly warmed before mixing. The two are then shaken 
 together and any shrinkage below the 200 mark filled up with oil. The 
 mixture should then be allowed to stand in a warm place for 24 hours, 
 during which the water and silt will settle to the bottom. Their 
 percentage by volume can then be correctly read on the burette 
 divisions, and the percentage by weight calculated from the specific 
 gravities. This method is exceedingly approximate and where accurate 
 results are required it should not be used. For such work, the 
 distillation method should be used as follows: 
   
 Gradually heat 100 cubic centimeters of the oil in a distillation flask 
 to a temperature of 150 degrees centigrade; collect the distillate in a 
 graduated tube and measure the resulting water. Such a method insures 
 complete removal of water and reduces the error arising from the slight 
 solubility of the water in gasolene. Two samples checked by the two 
 methods for the amount of moisture present gave, 
   
    _Distillation_       _Dilution_ 
      _Per Cent_         _Per Cent_ 
          8.71               6.25 
          8.82               6.26 
   
                                                TABLE 46 
   
                             COMPOSITION AND CALORIFIC VALUE OF VARIOUS OILS 
   
 +-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ 
 |       Kind of Oil       | %C | %H | %S |   %O   |S.G.|FP | %H2O |Btu |Authority              | 
 +-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ 
 |California, Coaling     |     |     |   |       |.927|134|       |17117|Babcock & Wilcox Co.   | 
 |California, Bakersfield |     |     |   |      |.975|   |       |17600|Wade                   | 
 |California, Bakersfield |     |     |1.30|       |.992|   |       |18257|Wade                   | 
 |California, Kern River   |     |     |   |       |.950|140|       |18845|Babcock & Wilcox Co.   | 
 |California, Los Angeles |     |     |2.56|       |   |   |       |18328|Babcock & Wilcox Co.   | 
 |California, Los Angeles |     |     |   |       |.957|196|       |18855|Babcock & Wilcox Co.   | 
 |California, Los Angeles |     |     |   |       |.977|   | .40   |18280|Babcock & Wilcox Co.   | 
 |California, Monte Christo|     |     |   |       |.966|205|       |18878|Babcock & Wilcox Co.   | 
 |California, Whittier     |     |     | .98|       |.944|   |1.06   |18507|Wade                  | 
 |California, Whittier     |     |     | .72|       |.936|   |1.06   |18240|Wade                   | 
 |California               |85.04|11.52|2.45| .99[44]|   |   |1.40   |17871|Babcock & Wilcox Co.   | 
 |California               |81.52|11.51| .55|6.92[44]|   |230|       |18667|U.S.N. Liquid Fuel Board| 
 |California               |     |     | .87|       |   |   | .95   |18533|Blasdale               | 
 |California               |     |     |   |       |.891|257|       |18655|Babcock & Wilcox Co.   | 
 |California               |     |     |2.45|       |.973|   |1.50[45]|17976|O'Neill                 | 
 |California               |     |     |2.46|       |.975|   |1.32   |18104|Shepherd               | 
 |Texas, Beaumont         |84.6 |10.9 |1.63|2.87   |.924|180|       |19060|U.S.N. Liquid Fuel Board| 
 |Texas, Beaumont         |83.3 |12.4 | .50|3.83   |.926|216|       |19481|U.S.N. Liquid Fuel Board| 
 |Texas, Beaumont         |85.0 |12.3 |1.75| .92[44]|   |   |       |19060|Denton                | 
 |Texas, Beaumont         |86.1 |12.3 |1.60|       |.942|   |       |20152|Sparkes                 | 
 |Texas, Beaumont         |     |     |   |       |.903|222|       |19349|Babcock & Wilcox Co.   | 
 |Texas, Sabine           |     |    |   |       |.937|143|       |18662|Babcock & Wilcox Co.   | 
 |Texas                   |87.15|12.33|0.32|       |.908|370|       |19338|U. S. N.               | 
 |Texas                   |87.29|12.32|0.43|       |.910|375|       |19659|U. S. N.               | 
 |Ohio                     |83.4 |14.7 |0.6 |1.3     |   |   |       |19580|                       | 
 |Pennsylvania             |84.9 |13.7 |   |1.4     |.886|   |       |19210|Booth                   | 
 |West Virginia           |84.3 |14.1 |   |1.6     |.841|   |       |21240|                       | 
 |Mexico                   |     |     |   |       |.921|162|       |18840|Babcock & Wilcox Co.   | 
 |Russia, Baku             |86.7 |12.9 |   |       |.884|   |       |20691|Booth                   | 
 |Russia, Novorossick     |84.9 |11.6 |   |3.46   |   |   |       |19452|Booth                   | 
 |Russia, Caucasus         |86.6 |12.3 |   |1.10   |.938|   |       |20138|                       | 
 |Java                     |87.1 |12.0 |   | .9     |.923|   |       |21163|                       | 
 |Austria, Galicia         |82.2 |12.1 |5.7 |       |.870|   |       |18416|                       | 
 |Italy, Parma             |84.0 |13.4 |1.8 |       |.786|   |       |     |                        | 
 |Borneo                   |85.7 |11.0 |   |3.31   |   |   |       |19240|Orde                   | 
 +-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ 
   
 %C     = Per Cent Carbon 
 %H     = Per Cent Hydrogen 
 %S     = Per Cent Sulphur 
 %O     = Per Cent Oxygen 
 S.G.   = Specific Gravity 
 FP     = Degrees Flash Point 
 %H_{2}O = Per Cent Moisture 
 Btu     = B. t. u. Per Pound 
   
 Calorific Value--A pound of petroleum usually has a calorific value of 
 from 18,000 to 22,000 B. t. u. If an ultimate analysis of an average 
 sample be, carbon 84 per cent, hydrogen 14 per cent, oxygen 2 per cent, 
 and assuming that the oxygen is combined with its equivalent of hydrogen 
 as water, the analysis would become, carbon 84 per cent, hydrogen 13.75 
 per cent, water 2.25 per cent, and the heat value per pound including 
 its contained water would be, 
   
 Carbon       .8400 × 14,600 = 12,264 B. t. u. 
 Hydrogen     .1375 × 62,100 = 8,625 B. t. u. 
                             ------[**Should be .1375 x 62,000 = 8,525] 
                        Total 20,889 B. t. u.[**Would be Total = 20,789] 
   
 The nitrogen in petroleum varies from 0.008 to 1.0 per cent, while the 
 sulphur varies from 0.07 to 3.0 per cent. 
   
 Table 46, compiled from various sources, gives the composition, 
 calorific value and other data relative to oil from different 
 localities. 
   
 The flash point of crude oil is the temperature at which it gives off 
 inflammable gases. While information on the actual flash points of the 
 various oils is meager, it is, nevertheless, a question of importance in 
 determining their availability as fuels. In general it may be stated 
 that the light oils have a low, and the heavy oils a much higher flash 
 point. A division is sometimes made at oils having a specific gravity of 
 0.85, with a statement that where the specific gravity is below this 
 point the flash point is below 60 degrees Fahrenheit, and where it is 
 above, the flash point is above 60 degrees Fahrenheit. There are, 
 however, many exceptions to this rule. As the flash point is lower the 
 danger of ignition or explosion becomes greater, and the utmost care 
 should be taken in handling the oils with a low flash point to avoid 
 this danger. On the other hand, because the flash point is high is no 
 justification for carelessness in handling those fuels. With proper 
 precautions taken, in general, the use of oil as fuel is practically as 
 safe as the use of coal. 
   
 Gravity of Oils--Oils are frequently classified according to their 
 gravity as indicated by the Beaume hydrometer scale. Such a 
 classification is by no means an accurate measure of their relative 
 calorific values. 
   
 Petroleum as Compared with Coal--The advantages of the use of oil fuel 
 over coal may be summarized as follows: 
   
 1st. The cost of handling is much lower, the oil being fed by simple 
 mechanical means, resulting in, 
   
 2nd. A general labor saving throughout the plant in the elimination of 
 stokers, coal passers, ash handlers, etc. 
   
 3rd. For equal heat value, oil occupies very much less space than coal. 
 This storage space may be at a distance from the boiler without 
 detriment. 
   
 4th. Higher efficiencies and capacities are obtainable with oil than 
 with coal. The combustion is more perfect as the excess air is reduced 
 to a minimum; the furnace temperature may be kept practically constant 
 as the furnace doors need not be opened for cleaning or working fires; 
 smoke may be eliminated with the consequent increased cleanliness of the 
 heating surfaces. 
   
 5th. The intensity of the fire can be almost instantaneously regulated 
 to meet load fluctuations. 
   
 6th. Oil when stored does not lose in calorific value as does coal, nor 
 are there any difficulties arising from disintegration, such as may be 
 found when coal is stored. 
   
 7th. Cleanliness and freedom from dust and ashes in the boiler room with 
 a consequent saving in wear and tear on machinery; little or no damage 
 to surrounding property due to such dust. 
   
 The disadvantages of oil are: 
   
 1st. The necessity that the oil have a reasonably high flash point to 
 minimize the danger of explosions. 
   
 2nd. City or town ordinances may impose burdensome conditions relative 
 to location and isolation of storage tanks, which in the case of a plant 
 situated in a congested portion of the city, might make use of this fuel 
 prohibitive. 
   
 3rd. Unless the boilers and furnaces are especially adapted for the use 
 of this fuel, the boiler upkeep cost will be higher than if coal were 
 used. This objection can be entirely obviated, however, if the 
 installation is entrusted to those who have had experience in the work, 
 and the operation of a properly designed plant is placed in the hands of 
 intelligent labor. 
   
                                TABLE 47 
   
                    RELATIVE VALUE OF COAL AND OIL FUEL 
   
 +------+--------+-------+-----------------------------------------------+ 
 |Gross | Net   | Net |         Water Evaporated from and at         | 
 |Boiler| Boiler |Evap- |   212 Degrees Fahrenheit per Pound of Coal   | 
 |Effic-|Effici- |oration+-----+-----+-----+-----+-----+-----+-----+-----+ 
 | iency|ency[46]| from |     |     |     |     |     |     |     |     | 
 | with | with |and at |     |     |     |     |     |     |     |     | 
 | Oil | Oil   | 212 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 
 | Fuel | Fuel |Degrees|     |     |     |     |     |     |     |     | 
 |     |       |Fahren-|     |     |     |     |     |     |     |     | 
 |     |       | heit +-----+-----+-----+-----+-----+-----+-----+-----+ 
 |     |       | per |                                              | 
 |     |       | Pound |   Pounds of Oil Equal to One Pound of Coal   | 
 |     |       |of Oil |                                               | 
 +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ 
 | 73 |   71  | 13.54 |.3693|.4431|.5170|.5909|.6647|.7386|.8124|.8863| 
 | 74 |   72   | 13.73 |.3642|.4370|.5099|.5827|.6556|.7283|.8011|.8740| 
 | 75 |   73   | 13.92 |.3592|.4310|.5029|.5747|.6466|.7184|.7903|.8621| 
 | 76 |   74   | 14.11 |.3544|.4253|.4961|.5670|.6378|.7087|.7796|.8505| 
 | 77 |   75   | 14.30 |.3497|.4196|.4895|.5594|.6294|.6993|.7692|.8392| 
 | 78 |   76   | 14.49 |.3451|.4141|.4831|.5521|.6211|.6901|.7591|.8281| 
 | 79 |   77   | 14.68 |.3406|.4087|.4768|.5450|.6131|.6812|.7493|.8174| 
 | 80 |   78   | 14.87 |.3363|.4035|.4708|.5380|.6053|.6725|.7398|.8070| 
 | 81 |   79   | 15.06 |.3320|.3984|.4648|.5312|.5976|.6640|.7304|.7968| 
 | 82 |   80   | 15.25 |.3279|.3934|.4590|.5246|.5902|.6557|.7213|.7869| 
 | 83 |   81   | 15.44 |.3238|.3886|.4534|.5181|.5829|.6447|.7125|.7772| 
 +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ 
 |     |       | Net |                                               | 
 |     |       |Evap- |                                               | 
 |      |       |oration|                                               | 
 |     |       | from |                                               | 
 |     |       |and at |                                               | 
 |     |       | 212 |   Barrels of Oil Equal to One Ton of Coal   | 
 |     |       |Degrees|                                               | 
 |     |       |Fahren-|                                               | 
 |     |       | heit |                                              | 
 |     |       | per |                                               | 
 |     |       |Barrel |                                               | 
 |     |       |of Oil |                                               | 
 +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ 
 | 73 |   71   | 4549 |2.198|2.638|3.077|3.516|3.955|4.395|4.835|5.275| 
 | 74 |   72   | 4613 |2.168|2.601|3.035|3.468|3.902|4.335|4.769|5.202| 
 | 75 |   73   | 4677 |2.138|2.565|2.993|3.420|3.848|4.275|4.703|5.131| 
 | 76 |   74   | 4741 |2.110|2.532|2.954|3.376|3.798|4.220|4.642|5.063| 
 | 77 |   75   | 4807 |2.082|2.498|2.914|3.330|3.746|4.162|4.578|4.994| 
 | 78 |   76   | 4869 |2.054|2.465|2.876|3.286|3.697|4.108|4.518|4.929| 
 | 79 |   77   | 4932 |2.027|2.433|2.838|3.243|3.649|4.054|4.460|4.865| 
 | 80 |   78   | 4996 |2.002|2.402|2.802|3.202|3.602|4.003|4.403|4.803| 
 | 81 |   79   | 5060 |1.976|2.371|2.767|3.162|3.557|3.952|4.348|4.743| 
 | 82 |   80   | 5124 |1.952|2.342|2.732|3.122|3.513|3.903|4.293|4.683| 
 | 83 |   81   | 5187 |1.927|2.313|2.699|3.085|3.470|3.856|4.241|4.627| 
 +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ 
 Many tables have been published with a view to comparing the two fuels. 
 Such of these as are based solely on the relative calorific values of 
 oil and coal are of limited value, inasmuch as the efficiencies to be 
 obtained with oil are higher than that obtainable with coal. Table 47 
 takes into consideration the variation in efficiency with the two fuels, 
 but is based on a constant calorific value for oil and coal. This table, 
 like others of a similar nature, while useful as a rough guide, cannot 
 be considered as an accurate basis for comparison. This is due to the 
 fact that there are numerous factors entering into the problem which 
 affect the saving possible to a much greater extent than do the relative 
 calorific values of two fuels. Some of the features to be considered in 
 arriving at the true basis for comparison are the labor saving possible, 
 the space available for fuel storage, the facilities for conveying the 
 oil by pipe lines, the hours during which a plant is in operation, the 
 load factor, the quantity of coal required for banking fires, etc., etc. 
 The only exact method of estimating the relative advantages and costs of 
 the two fuels is by considering the operating expenses of the plant with 
 each in turn, including the costs of every item entering into the 
 problem. 
   
 Burning Oil Fuel--The requirements for burning petroleum are as follows: 
   
 1st. Its atomization must be thorough. 
   
 2nd. When atomized it must be brought into contact with the requisite 
 quantity of air for its combustion, and this quantity must be at the 
 same time a minimum to obviate loss in stack gases. 
   
 3rd. The mixture must be burned in a furnace where a refractory material 
 radiates heat to assist in the combustion, and the furnace must stand up 
 under the high temperatures developed. 
   
 4th. The combustion must be completed before the gases come into contact 
 with the heating surfaces or otherwise the flame will be extinguished, 
 possibly to ignite later in the flue connection or in the stack. 
   
 5th. There must be no localization of the heat on certain portions of 
 the heating surfaces or trouble will result from overheating and 
 blistering. 
   
 The first requirement is met by the selection of a proper burner. 
   
 The second requirement is fulfilled by properly introducing the air into 
 the furnace, either through checkerwork under the burners or through 
 openings around them, and by controlling the quantity of air to meet 
 variations in furnace conditions. 
   
 The third requirement is provided for by installing a furnace so 
 designed as to give a sufficient area of heated brickwork to radiate the 
 heat required to maintain a proper furnace temperature. 
   
 The fourth requirement is provided for by giving ample space for the 
 combustion of the mixture of atomized oil and air, and a gas travel of 
 sufficient length to insure that this combustion be completed before the 
 gases strike the heating surfaces. 
   
 The fifth requirement is fulfilled by the adoption of a suitable burner 
 in connection with the furnace meeting the other requirements. A burner 
 must be used from which the flame will not impinge directly on the 
 heating surface and must be located where such action cannot take place. 
 If suitable burners properly located are not used, not only is the heat 
 localized with disastrous results, but the efficiency is lowered by the 
 cooling of the gases before combustion is completed. 
   
 Oil Burners--The functions of an oil burner is to atomize or vaporize 
 the fuel so that it may be burned like a gas. All burners may be 
 classified under three general types: 1st, spray burners, in which the 
 oil is atomized by steam or compressed air; 2nd, vapor burners, in which 
 the oil is converted into vapor and then passed into the furnace; 3rd, 
 mechanical burners, in which the oil is atomized by submitting it to a 
 high pressure and passing it through a small orifice. 
   
 Vapor burners have never been in general use and will not be discussed. 
   
 Spray burners are almost universally used for land practice and the 
 simplicity of the steam atomizer and the excellent economy of the better 
 types, together with the low oil pressure and temperature required makes 
 this type a favorite for stationary plants, where the loss of fresh 
 water is not a vital consideration. In marine work, or in any case where 
 it is advisable to save feed water that otherwise would have to be added 
 in the form of "make-up", either compressed air or mechanical means are 
 used for atomization. Spray burners using compressed air as the 
 atomizing agent are in satisfactory operation in some plants, but their 
 use is not general. Where there is no necessity of saving raw feed 
 water, the greater simplicity and economy of the steam spray atomizer is 
 generally the most satisfactory. The air burners require blowers, 
 compressors or other apparatus which occupy space that might be 
 otherwise utilized and require attention that is not necessary where 
 steam is used. 
   
 Steam spray burners of the older types had disadvantages in that they 
 were so designed that there was a tendency for the nozzle to clog with 
 sludge or coke formed from the oil by the heat, without means of being 
 readily cleaned. This has been overcome in the more modern types. 
   
 Steam spray burners, as now used, may be divided into two classes: 1st, 
 inside mixers; and 2nd, outside mixers. In the former the steam and oil 
 come into contact within the burner and the mixture is atomized in 
 passing through the orifice of the burner nozzle. 
 In the outside mixing class the steam flows through a narrow slot or 
 horizontal row of small holes in the burner nozzle; the oil flows 
 through a similar slot or hole above the steam orifice, and is picked up 
 by the steam outside of the burner and is atomized. Fig. 28 shows a type 
 of the Peabody burner of this class, which has given eminent 
 satisfaction. The construction is evident from the cut. It will be noted 
 that the portions of the burner forming the orifice may be readily 
 replaced in case of wear, or if it is desired to alter the form of the 
 flame. 
   
 Where burners of the spray type are used, heating the oil is of 
 advantage not only in causing it to be atomized more easily, but in 
 aiding economical combustion. The temperature is, of course, limited by 
 the flash point of the oil used, but within the limit of this 
 temperature there is no danger of decomposition or of carbon deposits on 
 the supply pipes. Such heating should be done close to the boiler to 
 minimize radiation loss. If the temperature is raised to a point where 
 an appreciable vaporization occurs, the oil will flow irregularly from 
 the burner and cause the flame to sputter. 
   
 On both steam and air atomizing types, a by-pass should be installed 
 between the steam or air and the oil pipes to provide for the blowing 
 out of the oil duct. Strainers should be provided for removing sludge 
 from the fuel and should be so located as to allow for rapid removal, 
 cleaning and replacing. 
   
 Mechanical burners have been in use for some time in European countries, 
 but their introduction and use has been of only recent occurrence in the 
 United States. Here as already stated, the means for atomization are 
 purely mechanical. The most successful of the mechanical atomizers up to 
 the present have been of the round flame type, and only these will be 
 considered. Experiments have been made with flat flame mechanical 
 burners, but their satisfactory action has been confined to instances 
 where it is only necessary to burn a small quantity of oil through each 
 individual burner. 
   
 This system of oil burning is especially adapted for marine work as the 
 quantity of steam for putting pressure on the oil is small and the 
 condensed steam may be returned to the system. 
   
 The only method by which successful mechanical atomization has been 
 accomplished is one by which the oil is given a whirling motion within 
 the burner tip. This is done either by forcing the oil through a passage 
 of helical form or by delivering it tangentially to a circular chamber 
 from which there is a central outlet. The oil is fed to these burners 
 under a pressure which varies with the make of the burner and the rates 
 at which individual burners are using oil. The oil particles fly off 
 from such a burner in straight lines in the form of a cone rather than 
 in the form of a spiral spray, as might be supposed. 
   
 With burners of the mechanical atomizing design, the method of 
 introducing air for combustion and the velocity of this air are of the 
 greatest importance in securing good combustion and in the effects on 
 the character and shape of the flame. Such burners are located at the 
 front of the furnace and various methods have been tried for introducing 
 the air for combustion. Where, in the spray burners, air is ordinarily 
 admitted through a checkerwork under the burner proper, with the 
 mechanical burner, it is almost universally admitted around the burner. 
 Early experiments with these air distributors were confined largely to 
 single or duplicate cones used with the idea of directing the air to the 
 axis of the burner. A highly successful method of such air introduction, 
 developed by Messrs. Peabody and Irish of The Babcock & Wilcox Co., is 
 by means of what they term an "impeller plate". This consists of a 
 circular metal disk with an opening at the center for the oil burner and 
 with radial metal strips from the center to the periphery turned at an 
 angle which in the later designs may be altered to give the air supply 
 demanded by the rate of combustion. 
   
 The air so admitted does not necessarily require a whirling motion, but 
 experiments show that where the air is brought into contact with the oil 
 spray with the right "twist", better combustion is secured and lower air 
 pressures and less refinement of adjustment of individual burners are 
 required. 
   
 Mechanical burners have a distinct advantage over those in which steam 
 is used as the atomizing agent in that they lend themselves more readily 
 to adjustment under wider variations of load. For a given horse power 
 there will ordinarily be installed a much greater number of mechanical 
 than steam atomizing burners. This in itself is a means to better 
 regulation, for with the steam atomizing burner, if one of a number is 
 shut off, there is a marked decrease in efficiency. This is due to the 
 fact that with the air admitted under the burner, it is ordinarily 
 passing through the checkerwork regardless of whether it is being 
 utilized for combustion or not. With a mechanical burner, on the other 
 hand, where individual burners are shut off, air that would be admitted 
 for such burner, were it in operation, may also be shut off and there 
 will be no undue loss from excess air. 
   
 Further adjustment to meet load conditions is possible by a change in 
 the oil pressure acting on all burners at once. A good burner will 
 atomize moderately heavy oil with an oil pressure as low as 30 pounds 
 per square inch and from that point up to 200 pounds or above. The 
 heating of the oil also has an effect on the capacity of individual 
 burners and in this way a third method of adjustment is given. Under 
 working conditions, the oil pressure remaining constant, the capacity of 
 each burner will decrease as the temperature of the oil is increased 
 though at low temperatures the reverse is the case. Some experiments 
 with a Texas crude oil having a flash point of 210 degrees showed that 
 the capacity of a mechanical atomizing burner of the Peabody type 
 increased from 80 degrees Fahrenheit to 110 degrees Fahrenheit, from 
 which point it fell off rapidly to 140 degrees and then more slowly to 
 the flash point. 
   
 The above methods, together with the regulation possible through 
 manipulation of the boiler dampers, indicate the wide range of load 
 conditions that may be handled with an installation of this class of 
 burners. 
   
 As has already been stated, results with mechanical atomizing burners 
 that may be considered very successful have been limited almost entirely 
 to cases where forced blast of some description has been used, the high 
 velocity of the air entering being of material assistance in securing 
 the proper mixture of air with the oil spray. Much has been done and is 
 being done in the way of experiment with this class of apparatus toward 
 developing a successful mechanical atomizing burner for use with natural 
 draft, and there appears to be no reason why such experiments should not 
 eventually produce satisfactory results. 
   
 Steam Consumption of Burners--The Bureau of Steam Engineering, U. S. 
 Navy, made in 1901 an exhaustive series of tests of various oil burners 
 that may be considered as representing, in so far as the performance of 
 the burners themselves is concerned, the practice of that time. These 
 tests showed that a burner utilizing air as an atomizing agent, required 
 for compressing the air from 1.06 to 7.45 per cent of the total steam 
 generated, the average being 3.18 per cent. Four tests of steam 
 atomizing burners showed a consumption of 3.98 to 5.77 per cent of the 
 total steam, the average being 4.8 per cent. 
   
 Improvement in burner design has largely reduced the steam consumption, 
 though to a greater degree in steam than in air atomizing burners. 
 Recent experiments show that a good steam atomizing burner will require 
 approximately 2 per cent of the total steam generated by the boiler 
 operated at or about its rated capacity. This figure will decrease as 
 the capacity is increased and is so low as to be practically negligible, 
 except in cases where the question of loss of feed water is all 
 important. There are no figures available as to the actual steam 
 consumption of mechanical atomizing burners but apparently this is small 
 if the requirement is understood to be entirely apart from the steam 
 consumption of the apparatus producing the forced blast. 
   
 Capacity of Burners--A good steam atomizing burner properly located in a 
 well-designed oil furnace has a capacity of somewhat over 400 horse 
 power. This question of capacity of individual burners is largely one of 
 the proper relation between the number of burners used and the furnace 
 volume. In some recent tests with a Babcock & Wilcox boiler of 640 rated 
 horse power, equipped with three burners, approximately 1350 horse power 
 was developed with an available draft of .55 inch at the damper or 450 
 horse power per burner. Four burners were also tried in the same furnace 
 but the total steam generated did not exceed 1350 horse power or in this 
 instance 338 horse power per burner. 
   
 From the nature of mechanical atomizing burners, individual burners have 
 not as large a capacity as the steam atomizing class. In some tests on a 
 Babcock & Wilcox marine boiler, equipped with mechanical atomizing 
 burners, the maximum horse power developed per burner was approximately 
 Here again the burner capacity is largely one of proper relation 
 
 between furnace volume and number of burners. 
   
 Furnace Design--Too much stress cannot be laid on the importance of 
 furnace design for the use of this class of fuel. Provided a good type 
 of burner is adopted the furnace arrangement and the method of 
 introducing air for combustion into the furnace are the all important 
 factors. No matter what the type of burner, satisfactory results cannot 
 be secured in a furnace not suited to the fuel. 
   
 The Babcock & Wilcox Co. has had much experience with the burning of oil 
 as fuel and an extended series of experiments by Mr. E. H. Peabody led 
 to the development and adoption of the Peabody furnace as being most 
 eminently suited for this class of work. Fig. 29 shows such a furnace 
 applied to a Babcock & Wilcox boiler, and with slight modification it 
 can be as readily applied to any boiler of The Babcock & Wilcox Co. 
 manufacture. In the description of this furnace, its points of advantage 
 cover the requirements of oil-burning furnaces in general. 
   
 The atomized oil is introduced into the furnace in the direction in 
 which it increases in height. This increase in furnace volume in the 
 direction of the flame insures free expansion and a thorough mixture of 
 the oil with the air, and the consequent complete combustion of the 
 gases before they come into contact with the tube heating surfaces. In 
 such a furnace flat flame burners should be used, preferably of the 
 Peabody type, in which the flame spreads outward toward the sides in the 
 form of a fan. There is no tendency of the flames to impinge directly on 
 the heating surfaces, and the furnace can handle any quantity of flame 
 without danger of tube difficulties. The burners should be so located 
 that the flames from individual burners do not interfere nor impinge to 
 any extent on the side walls of the furnace, an even distribution of 
 heat being secured in this manner. The burners are operated from the 
 boiler front and peepholes are supplied through which the operator may 
 watch the flame while regulating the burners. The burners can be 
 removed, inspected, or cleaned and replaced in a few minutes. Air is 
 admitted through a checkerwork of fire brick supported on the furnace 
 floor, the openings in the checkerwork being so arranged as to give the 
 best economic results in combustion. 
 With steam atomizing burners introduced through the front of the boiler 
 in stationary practice, it is usually in the direction in which the 
 furnace decreases in height and it is with such an arrangement that 
 difficulties through the loss of tubes may be expected. With such an 
 arrangement, the flame may impinge directly upon the tube surfaces and 
 tube troubles from this source may arise, particularly where the feed 
 water has a tendency toward rapid scale formation. Such difficulties may 
 be the result of a blowpipe action on the part of the burner, the over 
 heating of the tube due to oil or scale within, or the actual erosion of 
 the metal by particles of oil improperly atomized. Such action need not 
 be anticipated, provided the oil is burned with a short flame. The 
 flames from mechanical atomizing burners have a less velocity of 
 projection than those from steam atomizing burners and if introduced 
 into the higher end of the furnace, should not lead to tube difficulties 
 provided they are properly located and operated. This class of burner 
 also will give the most satisfactory results if introduced so that the 
 flames travel in the direction of increase in furnace volume. This is 
 perhaps best exemplified by the very good results secured with 
 mechanical atomizing burners and Babcock & Wilcox marine boilers in 
 which, due to the fact that the boilers are fired from the low end, the 
 flames from burners introduced through the front are in this direction. 
   
 Operation of Burners--When burners are not in use, or when they are 
 being started up, care must be taken to prevent oil from flowing and 
 collecting on the floor of the furnace before it is ignited. In starting 
 a burner, the atomized fuel may be ignited by a burning wad of oil-soaked 
 waste held before it on an iron rod. To insure quick ignition, the steam 
 supply should be cut down. But little practice is required to become an 
 adept at lighting an oil fire. When ignition has taken place and the 
 furnace brought to an even heat, the steam should be cut down to the 
 minimum amount required for atomization. This amount can be determined 
 from the appearance of the flame. If sufficient steam is not supplied, 
 particles of burning oil will drop to the furnace floor, giving a 
 scintillating appearance to the flame. The steam valves should be opened 
 just sufficiently to overcome this scintillating action. 
   
 Air Supply--From the nature of the fuel and the method of burning, the 
 quantity of air for combustion may be minimized. As with other fuels, 
 when the amount of air admitted is the minimum which will completely 
 consume the oil, the results are the best. The excess or deficiency of 
 air can be judged by the appearance of the stack or by observing the 
 gases passing through the boiler settings. A perfectly clear stack 
 indicates excess air, whereas smoke indicates a deficiency. With 
 properly designed furnaces the best results are secured by running near 
 the smoking point with a slight haze in the gases. A slight variation in 
 the air supply will affect the furnace conditions in an oil burning 
 boiler more than the same variation where coal is used, and for this 
 reason it is of the utmost importance that flue gas analysis be made 
 frequently on oil-burning boilers. With the air for combustion properly 
 regulated by adjustment of any checkerwork or any other device which may 
 be used, and the dampers carefully set, the flue gas analysis should 
 show, for good furnace conditions, a percentage of CO_{2} between 13 and 
 14 per cent, with either no CO or but a trace. 
   
 In boiler plant operation it is difficult to regulate the steam supply 
 to the burners and the damper position to meet sudden and repeated 
 variations in the load. A device has been patented which automatically 
 regulates by means of the boiler pressure the pressure of the steam to 
 the burners, the oil to the burners and the position of the boiler 
 damper. Such a device has been shown to give good results in plant 
 operation where hand regulation is difficult at best, and in many 
 instances is unfortunately not even attempted. 
   
 Efficiency with Oil--As pointed out in enumerating the advantages of oil 
 fuel over coal, higher efficiencies are obtainable with the former. With 
 boilers of approximately 500 horse power equipped with properly designed 
 furnaces and burners, an efficiency of 83 per cent is possible or making 
 an allowance of 2 per cent for steam used by burners, a net efficiency 
 of 81 per cent. The conditions under which such efficiencies are to be 
 secured are distinctly test conditions in which careful operation is a 
 prime requisite. With furnace conditions that are not conductive to the 
 best combustion, this figure may be decreased by from 5 to 10 per cent. 
 In large properly designed plants, however, the first named efficiency 
 may be approached for uniform running conditions, the nearness to which 
 it is reached depending on the intelligence of the operating crew. It 
 must be remembered that the use of oil fuel presents to the careless 
 operator possibilities for wastefulness much greater than in plants 
 where coal is fired, and it therefore pays to go carefully into this 
 feature. 
   
 Table 48 gives some representative tests with oil fuel. 
   
                                  TABLE 48 
   
            TESTS OF BABCOCK AND WILCOX BOILERS WITH OIL FUEL 
   
 _______________________________________________________________________ 
 |                             |             |             |             | 
 |                             |Pacific Light|Pacific Light|Miami Copper | 
 |                             | and Power | and Power |   Company   | 
 | Plant                       |   Company   |   Company   |             | 
 |                             |Los Angeles, |             |   Miami,   | 
 |                            |   Cal.     |Redondo, Cal.|   Arizona   | 
 |_____________________________|_____________|_____________|_____________| 
 |                 |         |             |             |             | 
 | Rated Capacity   | Horse   |            |             |             | 
 |   of Boiler     | Power   |     467     |     604     |     600     | 
 |__________________|__________|_____________|_____________|_____________| 
 |                 |         |     |     |     |     |     |    | 
 | Duration of Test | Hours   | 10 | 10 |   7 |   7 | 10 |   4 | 
 |                 |         |     |     |     |     |     |     | 
 | Steam Pressure   |         |     |     |     |     |     |     | 
 |   by Gauge       | Pounds   | 156.4| 156.9| 184.7| 184.9| 183.4| 189.5| 
 |                 |         |     |     |     |     |     |     | 
 | Temperature of   | Degrees |     |     |     |     |     |     | 
 |   Feed Water     |   F.   | 62.6| 61.1| 93.4| 101.2| 157.7| 156.6| 
 |                 |         |     |     |     |     |     |     | 
 | Degrees of       | Degrees |     |     |     |     |     |     | 
 |   Superheat     |   F.   |     |     | 83.7| 144.3| 103.4| 139.6| 
 |                 |        |     |     |     |     |     |     | 
 | Factor of       |         |     |     |     |     |     |     | 
 |   Evaporation   |         |1.2004|1.2020|1.2227|1.2475|1.1676|1.1886| 
 |                 |         |     |     |     |     |     |     | 
 | Draft in Furnace | Inches   | .02 | .05 | .014| .19 | .12 | .22 | 
 |                 |         |     |     |     |     |     |     | 
 | Draft at Damper | Inches   | .08 | .15 | .046| .47 | .19 | .67 | 
 |                 |         |     |     |     |     |     |     | 
 | Temperature of   | Degrees |     |     |     |     |     |     | 
 |   Exit Gases     |   F.   | 438 | 525 | 406 | 537 | 430 | 612 | 
 |         _       |         |     |     |     |     |     |     | 
 | Flue   | CO_{2} | Per Cent |     |     | 14.3 | 12.1 |     |     | 
 | Gas     | O     | Per Cent |     |     | 3.8 | 6.8 |     |     | 
 | Analysis|_CO     | Per Cent |     |     | 0.0 | 0.0 |     |     | 
 |                  |         |     |     |     |     |     |     | 
 | Oil Burned       |         |     |     |     |     |     |     | 
 |   per Hour       | Pounds   | 1147 | 1837 | 1439 | 2869 | 1404 | 3214 | 
 |                 |         |     |     |      |     |     |     | 
 | Water Evaporated |         |     |     |     |     |     |     | 
 |   per Hour from |         |     |     |     |     |     |     | 
 |   from and at   | Pounds   | 18310| 27855| 22639| 40375| 21720| 42863| 
 |   212 Degrees   |         |     |     |     |     |     |     | 
 |                 |         |     |     |     |     |     |     | 
 | Evaporation from |         |     |     |     |     |     |     | 
 |   and at 212     |         |     |    |     |     |     |     | 
 |   Degrees per   | Pounds   | 15.96| 15.16| 15.73| 14.07| 15.47| 13.34| 
 |   Pound of Oil   |         |     |     |     |     |     |     | 
 |                 |         |     |     |     |     |     |     | 
 | Per Cent of     |         |     |     |     |     |     |     | 
 |   Rated Capacity | Pounds   | 113.6| 172.9| 108.6| 193.8| 104.9| 207.1| 
 |   Developed     |         |     |     |     |     |     |     | 
 |                 |         |      |     |     |     |     |     | 
 | B. t. u. per     |         |     |     |     |     |     |     | 
 |   Pound of Oil   | B. t. u. | 18626| 18518| 18326| 18096| 18600| 18600| 
 |                 |         |     |     |     |     |     |    | 
 | Efficiency       | Per Cent | 83.15| 79.46| 83.29| 76.02| 80.70| 69.6 | 
 |__________________|__________|______|______|______|______|______|______| 
   
 Burning Oil in Connection with Other Fuels--Considerable attention has 
 been recently given to the burning of oil in connection with other 
 fuels, and a combination of this sort may be advisable either with the 
 view to increasing the boiler capacity to assist over peak loads, or to 
 keep the boiler in operation where there is the possibility of a 
 temporary failure of the primary fuel. It would appear from experiments 
 that such a combination gives satisfactory results from the standpoint 
 of both capacity and efficiency, if the two fuels are burned in separate 
 furnaces. Satisfactory results cannot ordinarily be obtained when it is 
 attempted to burn oil fuel in the same furnace as the primary fuel, as 
 it is practically impossible to admit the proper amount of air for 
 combustion for each of the two fuels simultaneously. The Babcock & 
 Wilcox boiler lends itself readily to a double furnace arrangement and 
 Fig. 30 shows an installation where oil fuel is burned as an auxiliary 
 to wood. 
 Water-gas Tar--Water-gas tar, or gas-house tar, is a by-product of the 
 coal used in the manufacture of water gas. It is slightly heavier than 
 crude oil and has a comparatively low flash point. In burning, it should 
 be heated only to a temperature which makes it sufficiently fluid, and 
 any furnace suitable for crude oil is in general suitable for water-gas 
 tar. Care should be taken where this fuel is used to install a suitable 
 apparatus for straining it before it is fed to the burner. 
   
 
 
 
 GASEOUS FUELS AND THEIR COMBUSTION 
 Of the gaseous fuels available for steam generating purposes, the most 
 common are blast furnace gas, natural gas and by-product coke oven gas. 
   
 Blast furnace gas, as implied by its name, is a by-product from the 
 blast furnace of the iron industry. This gasification of the solid fuel 
 in a blast furnace results, 1st, through combustion by the oxygen of the 
 blast; 2nd, through contact with the incandescent ore (Fe_{2}O_{3} + C 
 = 2 FeO + CO and FeO + C = Fe + CO); and 3rd, through the agency of 
 CO_{2} either formed in the process of reduction or driven from the 
 carbonates charged either as ore or flux. 
   
 Approximately 90 per cent of the fuel consumed in all of the blast 
 furnaces of the United States is coke. The consumption of coke per ton 
 of iron made varies from 1600 to 3600 pounds per ton of 2240 pounds of 
 iron. This consumption depends upon the quality of the coal, the nature 
 of the ore, the quality of the pig iron produced and the equipment and 
 management of the plant. The average consumption, and one which is 
 approximately correct for ordinary conditions, is 2000 pounds of coke 
 per gross ton (2240 pounds) of pig iron. The gas produced in a gas 
 furnace per ton of pig iron is obtained from the weight of fixed carbon 
 gasified, the weight of the oxygen combined with the material of charge 
 reduced, the weight of the gaseous constituents of the flux and the 
 weight of air delivered by the blowing engine and the weight of volatile 
 combustible contained in the coke. Ordinarily, this weight of gas will 
 be found to be approximately five times the weight of the coke burned, 
 or 10,000 pounds per ton of pig iron produced. 
   
 With the exception of the small amount of carbon in combination with 
 hydrogen as methane, and a very small percentage of free hydrogen, 
 ordinarily less than 0.1 per cent, the calorific value of blast furnace 
 gas is due to the CO content which when united with sufficient oxygen 
 when burned under a boiler, burns further to CO_{2}. The heat value of 
 such gas will vary in most cases from 85 to 100 B. t. u. per cubic foot 
 under standard conditions. In modern practice, where the blast is heated 
 by hot blast stoves, approximately 15 per cent of the total amount of 
 gas is used for this purpose, leaving 85 per cent of the total for use 
 under boilers or in gas engines, that is, approximately 8500 pounds of 
 gas per ton of pig iron produced. In a modern blast furnace plant, the 
 gas serves ordinarily as the only fuel required. Table 49 gives the 
 analyses of several samples of blast furnace gas. 
   
                              TABLE 49 
   
                TYPICAL ANALYSES OF BLAST FURNACE GAS 
   
 +----------------------------------------------------------------+ 
 |+-----------------------+------+----+-----+----+------+--------+| 
 ||                       |CO_{2}| O | CO | H |CH_{4}|   N   || 
 |+-----------------------+------+----+-----+----+------+--------+| 
 ||Bessemer Furnace       | 9.85|0.36|32.73|3.14| .. |53.92   || 
 ||Bessemer Furnace       | 11.4 | .. |27.7 |1.9 | 0.3 |58.7   || 
 ||Bessemer Furnace       | 10.0 | .. |26.2 |3.1 | 0.2 |60.5   || 
 ||Bessemer Furnace       | 9.1 | .. |28.7 |2.7 | 0.2 |59.3   || 
 ||Bessemer Furnace       | 13.5 | .. |25.2 |1.43| .. |59.87   || 
 ||Bessemer Furnace[47]   | 10.9 | .. |27.8 |2.8 | 0.2 |58.3   || 
 ||Ferro Manganese Furnace| 7.1 | .. |30.1 | .. | .. |62.8[48]|| 
 ||Basic Ore Furnace     | 16.0 |0.2 |23.6 | .. | .. |60.2[48]|| 
 |+-----------------------+------+----+-----+----+------+--------+| 
 +----------------------------------------------------------------+ 
   
 Until recently, the important consideration in the burning of blast 
 furnace gas has been the capacity that can be developed with practically 
 no attention given to the aspect of efficiency. This phase of the 
 question is now drawing attention and furnaces especially designed for 
 good efficiency with this class of fuel are demanded. The essential 
 feature is ample combustion space, in which the combustion of gases may 
 be practically completed before striking the heating surfaces. The gases 
 have the power of burning out completely after striking the heating 
 surfaces, provided the initial temperature is sufficiently high, but 
 where the combustion is completed before such time, the results secured 
 are more satisfactory. A furnace volume of approximately 1 to 1.5 cubic 
 feet per rated boiler horse power will give a combustion space that is 
 ample. 
   
 Where there is the possibility of a failure of the gas supply, or where 
 steam is required when the blast furnace is shut down, coal fired grates 
 of sufficient size to get the required capacity should be installed. 
 Where grates of full size are not required, ignition grates should be 
 installed, which need be only large enough to carry a fire for igniting 
 the gas or for generating a small quantity of steam when the blast 
 furnace is shut down. The area of such grates has no direct bearing on 
 the size of the boiler. The grates may be placed directly under the gas 
 burners in a standard position or may be placed between two bridge walls 
 back of the gas furnace and fired from the side of the boiler. An 
 advantage is claimed for the standard grate position that it minimizes 
 the danger of explosion on the re-ignition of gas after a temporary 
 stoppage of the supply and also that a considerable amount of dirt, of 
 which there is a good deal with this class of fuel and which is 
 difficult to remove, deposits on the fire and is taken out when the 
 fires are cleaned. In any event, regardless of the location of the 
 grates, ample provision should be made for removing this dust, not only 
 from the furnace but from the setting as a whole. 
   
 Blast furnace gas burners are of two general types: Those in which the 
 air for combustion is admitted around the burner proper, and those in 
 which this air is admitted through the burner. Whatever the design of 
 burner, provision should be made for the regulation of both the air and 
 the gas supply independently. A gas opening of .8 square inch per rated 
 horse power will enable a boiler to develop its nominal rating with a 
 gas pressure in the main of about 2 inches. This pressure is ordinarily 
 from 6 to 8 inches and in this way openings of the above size will be 
 good for ordinary overloads. The air openings should be from .75 to .85 
 square inch per rated horse power. Good results are secured by inclining 
 the gas burners slightly downward toward the rear of the furnace. Where 
 the burners are introduced over coal fired grates, they should be set 
 high enough to give headroom for hand firing. 
   
 Ordinarily, individual stacks of 130 feet high with diameters as given 
 in Kent's table for corresponding horse power are large enough for this 
 class of work. Such a stack will give a draft sufficient to allow a 
 boiler to be operated at 175 per cent of its rated capacity, and beyond 
 this point the capacity will not increase proportionately with the 
 draft. When more than one boiler is connected with a stack, the draft 
 available at the damper should be equivalent to that which an individual 
 stack of 130 feet high would give. The draft from such a stack is 
 necessary to maintain a suction under all conditions throughout all 
 parts of the setting. If the draft is increased above that which such a 
 stack will give, difficulties arise from excess air for combustion with 
 consequent loss in efficiency. 
   
 A poor mixing or laneing action in the furnace may result in a pulsating 
 effect of the gases in the setting. This action may at times be remedied 
 by admitting more air to the furnace. On account of the possibility of a 
 pulsating action of the gases under certain conditions and the puffs or 
 explosions, settings for this class of work should be carefully 
 constructed and thoroughly buckstayed and tied. 
   
 Natural Gas--Natural gas from different localities varies considerably 
 in composition and heating value. In Table 50 there is given a number of 
 analyses and heat values for natural gas from various localities. 
   
 This fuel is used for steam generating purposes to a considerable extent 
 in some localities, though such use is apparently decreasing. It is best 
 burned by employing a large number of small burners, each being capable 
 of handling 30 nominal rated horse power. The use of a large number of 
 burners obviates the danger of any laneing or blowpipe action, which 
 might be present where large burners are used. Ordinarily, such a gas, 
 as it enters the burners, is under a pressure of about 8 ounces. For the 
 purpose of comparison, all observations should be based on gas reduced 
 to the standard conditions of temperature and pressure, namely 32 
 degrees Fahrenheit and 14.7 pounds per square inch. When the temperature 
 and pressure corresponding to meter readings are known, the volume of 
 gas under standard conditions may be obtained by multiplying the meter 
 readings in cubic feet by 33.54 P/T, in which P equals the absolute 
 pressure in pounds per square inch and T equals the absolute temperature 
 of the gas at the meter. In boiler testing work, the evaporation should 
 always be reduced to that per cubic foot of gas under standard 
 conditions. 
   
                              TABLE 50 
   
          TYPICAL ANALYSES (BY VOLUME) AND CALORIFIC VALUES OF NATURAL 
                          GAS FROM VARIOUS LOCALITIES 
   
 +----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ 
 |Locality of Well| H |CH_{4}| CO |CO_{2}| N | O | Heavy |H_{2}S|B. t. u.| 
 |               |     |     |     |     |     |   |Hydro- |     | per   | 
 |               |     |     |     |     |     |   |carbons|     | Cubic | 
 |               |     |     |     |     |     |   |       |     | Foot | 
 |               |     |     |     |     |     |   |       |     |Calcul- | 
 |               |     |     |     |     |     |   |       |     |ated[49]| 
 |----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ 
 |Anderson, Ind. | 1.86|93.07| 0.73| 0.26| 3.02|0.42| 0.47 | 0.15 | 1017 | 
 |Marion, Ind.   | 1.20|93.16| 0.60| 0.30| 3.43|0.55| 0.15 | 0.20 | 1009 | 
 |Muncie, Ind.    | 2.35|92.67| 0.45| 0.25| 3.53|0.35| 0.25 | 0.15 | 1004 | 
 |Olean, N. Y.   |     |96.50| 0.50|     |     |2.00| 1.00 |     | 1018 | 
 |Findlay, O.     | 1.64|93.35| 0.41| 0.25| 3.41|0.39| 0.35 | 0.20 | 1011 | 
 |St. Ive, Pa.   | 6.10|75.54|Trace| 0.34|     |   | 18.12 |     | 1117 | 
 |Cherry Tree, Pa.|22.50|60.27|     | 2.28| 7.32|0.83| 6.80 |     |   842 | 
 |Grapeville, Pa. |24.56|14.93|Trace|Trace|18.69|1.22| 40.60 |     |   925 | 
 |Harvey Well,   |     |     |     |     |     |   |      |     |       | 
 | Butler Co., Pa.|13.50|80.00|Trace| 0.66|     |   | 5.72 |     |   998 | 
 |Pittsburgh, Pa. | 9.64|57.85| 1.00|     |23.41|2.10| 6.00 |     |   748 | 
 |Pittsburgh, Pa. |20.02|72.18| 1.00| 0.80|     |1.10| 4.30 |     |   917 | 
 |Pittsburgh, Pa. |26.16|65.25| 0.80| 0.60|     |0.80| 6.30 |     |   899 | 
 +----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ 
 When natural gas is the only fuel, the burners should be evenly 
 distributed over the lower portion of the boiler front. If the fuel is 
 used as an auxiliary to coal, the burners may be placed through the fire 
 front. A large combustion space is essential and a volume of .75 cubic 
 feet per rated horse power will be found to give good results. The 
 burners should be of a design which give the gas and air a rotary motion 
 to insure a proper mixture. A checkerwork wall is sometimes placed in 
 the furnace about 3 feet from the burners to break up the flame, but 
 with a good design of burner this is unnecessary. Where the gas is 
 burned alone and no grates are furnished, good results are secured by 
 inclining the burner downward to the rear at a slight angle. 
   
 By-product Coke Oven Gas--By-product coke oven gas is a product of the 
 destructive distillation of coal in a distilling or by-product coke 
 oven. In this class of apparatus the gases, instead of being burned at 
 the point of their origin, as in a beehive or retort coke oven, are 
 taken from the oven through an uptake pipe, cooled and yield as 
 by-products tar, ammonia, illuminating and fuel gas. A certain portion 
 of the gas product is burned in the ovens and the remainder used or sold 
 for illuminating or fuel purposes, the methods of utilizing the gas 
 varying with plant operation and locality. 
   
 Table 51 gives the analyses and heat value of certain samples of 
 by-product coke oven gas utilized for fuel purposes. 
   
 This gas is nearer to natural gas in its heat value than is blast 
 furnace gas, and in general the remarks as to the proper methods of 
 burning natural gas and the features to be followed in furnace design 
 hold as well for by-product coke oven gas. 
   
                    TABLE 51 
   
          TYPICAL ANALYSES OF BY-PRODUCT 
                  COKE OVEN GAS 
   
 +----------------------------------------------+ 
 |+------+-------------------------------------+| 
 ||CO_{2}| O |CO |CH_{4}| H | N |B.t.u. per|| 
 ||     |     |   |     |   |   |Cubic Foot|| 
 |+------+-----+---+------+----+----+----------+| 
 || 0.75 |Trace|6.0|28.15 |53.0|12.1|   505   || 
 || 2.00 |Trace|3.2|18.80 |57.2|18.0|   399   || 
 || 3.20 | 0.4 |6.3|29.60 |41.6|16.1|   551    || 
 || 0.80 | 1.6 |4.9|28.40 |54.2|10.1|   460   || 
 |+------+-----+---+------+----+----+----------+| 
 +----------------------------------------------+ 
   
 The essential difference in burning the two fuels is the pressure under 
 which it reaches the gas burner. Where this is ordinarily from 4 to 8 
 ounces in the case of natural gas, it is approximately 4 inches of water 
 in the case of by-product coke oven gas. This necessitates the use of 
 larger gas openings in the burners for the latter class of fuel than for 
 the former. 
   
 By-product coke oven gas comes to the burners saturated with moisture 
 and provision should be made for the blowing out of water of 
 condensation. This gas too, carries a large proportion of tar and 
 hydrocarbons which form a deposit in the burners and provision should be 
 made for cleaning this out. This is best accomplished by an attachment 
 which permits the blowing out of the burners by steam. 
   
 
 
 
 UTILIZATION OF WASTE HEAT 
 While it has been long recognized that the reclamation of heat from the 
 waste gases of various industrial processes would lead to a great saving 
 in fuel and labor, the problem has, until recently, never been given the 
 attention that its importance merits. It is true that installations have 
 been made for the utilization of such gases, but in general they have 
 consisted simply in the placing of a given amount of boiler heating 
 surface in the path of the gases and those making the installations have 
 been satisfied with whatever power has been generated, no attention 
 being given to the proportioning of either the heating surface or the 
 gas passages to meet the peculiar characteristics of the particular 
 class of waste gas available. The Babcock & Wilcox Co. has recently gone 
 into the question of the utilization of what has been known as waste 
 heat with great thoroughness, and the results secured by their 
 installations with practically all operations yielding such gases are 
 eminently successful. 
   
                        TABLE 52 
   
            TEMPERATURE OF WASTE GASES FROM 
             VARIOUS INDUSTRIAL PROCESSES 
   
 +-----------------------------------------------------+ 
 |+-----------------------------------+---------------+| 
 ||Waste Heat From                   |Temperature[50]|| 
 ||                                   |   Degrees     || 
 |+-----------------------------------+---------------+| 
 ||Brick Kilns                       | 2000-2300   || 
 ||Zinc Furnaces                     | 2000-2300   || 
 ||Copper Matte Reverberatory Furnaces| 2000-2200   || 
 ||Beehive Coke Ovens                | 1800-2000   || 
 ||Cement Kilns                       | 1200-1600[51]|| 
 ||Nickel Refining Furnaces           | 1500-1750   || 
 ||Open Hearth Steel Furnaces         | 1100-1400   || 
 |+-----------------------------------+---------------+| 
 +-----------------------------------------------------+ 
   
 The power that can be obtained from waste gases depends upon their 
 temperature and weight, and both of these factors vary widely in 
 different commercial operations. Table 52 gives a list of certain 
 processes yielding waste gases the heat of which is available for the 
 generation of steam and the approximate temperature of such gases. It 
 should be understood that the temperatures in the table are the average 
 of the range of a complete cycle of the operation and that the minimum 
 and maximum temperatures may vary largely from the figures given. 
   
 The maximum available horse power that may be secured from such gases is 
 represented by the formula: 
   
        W(T-t)s 
 P. = -------     (23) 
 
        33,479 
   
   
 Where W = the weight of gases passing per hour, 
      T = temperature of gases entering heating surface, 
      t = temperature leaving heating surface, 
      s = specific heat of gases. 
   
 The initial temperature and the weight or volume of gas will depend, as 
 stated, upon the process involved. The exit temperature will depend, to 
 a certain extent, upon the temperature of the entering gases, but will 
 be governed mainly by the efficiency of the heating surfaces installed 
 for the absorption of the heat. 
   
 Where the temperature of the gas available is high, approaching that 
 found in direct fired boiler practice, the problem is simple and the 
 question of design of boiler becomes one of adapting the proper amount 
 of heating surface to the volume of gas to be handled. With such 
 temperatures, and a volume of gas available approximately in accordance 
 with that found in direct fired boiler practice, a standard boiler or 
 one but slightly modified from the standard will serve the purpose 
 satisfactorily. As the temperatures become lower, however, the problem 
 is more difficult and the departure from standard practice more radical. 
 With low temperature gases, to obtain a heat transfer rate at all 
 comparable with that found in ordinary boiler practice, the lack of 
 temperature must be offset by an added velocity of the gases in their 
 passage over the heating surfaces. In securing the velocity necessary to 
 give a heat transfer rate with low temperature gases sufficient to make 
 the installation of waste heat boilers show a reasonable return on the 
 investment, the frictional resistance to the gases through the boiler 
 becomes greatly in excess of what would be considered good practice in 
 direct fired boilers. Practically all operations yielding waste gases 
 require that nothing be done in the way of impairing the draft at the 
 furnace outlet, as this might interfere with the operation of the 
 primary furnace. The installation of a waste heat boiler, therefore, 
 very frequently necessitates providing sufficient mechanical draft to 
 overcome the frictional resistance of the gases through the heating 
 surfaces and still leave ample draft available to meet the maximum 
 requirements of the primary furnace. 
   
 Where the temperature and volume of the gases are in line with what are 
 found in ordinary direct fired practice, the area of the gas passages 
 may be practically standard. With the volume of gas known, the draft 
 loss through the heating surfaces may be obtained from experimental data 
 and this additional draft requirement met by the installation of a stack 
 sufficient to take care of this draft loss and still leave draft enough 
 for operating the furnace at its maximum capacity. 
   
 Where the temperatures are low, the added frictional resistance will 
 ordinarily be too great to allow the draft required to be secured by 
 additional stack height and the installation of a fan is necessary. Such 
 a fan should be capable of handling the maximum volume of gas that the 
 furnace may produce, and of maintaining a suction equivalent to the 
 maximum frictional resistance of such volume through the boiler plus the 
 maximum draft requirement at the furnace outlet. Stacks and fans for 
 this class of work should be figured on the safe side. Where a fan 
 installation is necessary, the loss of draft in the fan connections 
 should be considered, and in figuring conservatively it should be 
 remembered that a fan of ample size may be run as economically as a 
 smaller fan, whereas the smaller fan, if overloaded, is operated with a 
 large loss in efficiency. In practically any installation where low 
 temperature gas requires a fan to give the proper heat transfer from the 
 gases, the cost of the fan and of the energy to drive it will be more 
 than offset by the added power from the boiler secured by its use. 
 Furthermore, the installation of such a fan will frequently increase the 
 capacity of the industrial furnace, in connection with which the waste 
 heat boilers are installed. 
   
 In proportioning heating surfaces and gas passages for waste heat work 
 there are so many factors bearing directly on what constitutes the 
 proper installation that it is impossible to set any fixed rules. Each 
 individual installation must be considered by itself as well as the 
 particular characteristics of the gases available, such as their 
 temperature and volume, and the presence of dust or tar-like substances, 
 and all must be given the proper weight in the determination of the 
 design of the heating surfaces and gas passages for the specific set of 
 conditions. 
   
 [Graph: Per Cent of Water Heating Surface passed over by Gases/Per Cent 
 of the Total Amount of Steam Generated in the Boiler 
 against Temperature in Degrees Fahrenheit of Hot Gases Sweeping Heating 
 Surface 
   
 Fig. 31. Curve Showing Relation Between Gas Temperature, Heating Surface 
 passed over, and Amount of Steam Generated. Ten Square Feet of Heating 
 Surface are Assumed as Equivalent to One Boiler Horse Power] 
   
 Fig. 31 shows the relation of gas temperatures, heating surface passed 
 over and work done by such surface for use in cases where the 
 temperatures approach those found in direct fired practice and where the 
 volume of gas available is approximately that with which one horse power 
 may be developed on 10 square feet of heating surface. The curve assumes 
 what may be considered standard gas passage areas, and further, that 
 there is no heat absorbed by direct radiation from the fire. 
   
 Experiments have shown that this curve is very nearly correct for the 
 conditions assumed. Such being the case, its application in waste heat 
 work is clear. Decreasing or increasing the velocity of the gases over 
 the heating surfaces from what might be considered normal direct fired 
 practice, that is, decreasing or increasing the frictional loss through 
 the boiler will increase or decrease the amount of heating surface 
 necessary to develop one boiler horse power. The application of Fig. 31 
 to such use may best be seen by an example: 
   
 Assume the entering gas temperatures to be 1470 degrees and that the 
 gases are cooled to 570 degrees. From the curve, under what are assumed 
 to be standard conditions, the gases have passed over 19 per cent of 
 the heating surface by the time they have been cooled 1470 degrees. 
 When cooled to 570 degrees, 78 per cent of the heating surface has been 
 passed over. The work done in relation to the standard of the curve is 
 represented by (1470 - 570) ÷ (2500 - 500) = 45 per cent. (These 
 figures may also be read from the curve in terms of the per cent of the 
 work done by different parts of the heating surfaces.) That is, 78 per 
 cent - 19 per cent = 59 per cent of the standard heating surface has 
 done 45 per cent of the standard amount of work. 59 ÷ 45 = 1.31, which 
 is the ratio of surface of the assumed case to the standard case of the 
 curve. Expressed differently, there will be required 13.1 square feet 
 of heating surface in the assumed case to develop a horse power as 
 against 10 square feet in the standard case. 
   
 The gases available for this class of work are almost invariably very 
 dirty. It is essential for the successful operation of waste-heat 
 boilers that ample provision be made for cleaning by the installation of 
 access doors through which all parts of the setting may be reached. In 
 many instances, such as waste-heat boilers set in connection with cement 
 kilns, settling chambers are provided for the dust before the gases 
 reach the boiler. 
   
 By-passes for the gases should in all cases be provided to enable the 
 boiler to be shut down for cleaning and repairs without interfering with 
 the operation of the primary furnace. All connections from furnace to 
 boilers should be kept tight to prevent the infiltration of air, with 
 the consequent lowering of gas temperatures. 
   
 Auxiliary gas or coal fired grates must be installed to insure 
 continuity in the operation of the boiler where the operation of the 
 furnace is intermittent or where it may be desired to run the boiler 
 with the primary furnace not in operation. Such grates are sometimes 
 used continuously where the gases available are not sufficient to 
 develop the required horse power from a given amount of heating surface. 
   
 Fear has at times been expressed that certain waste gases, such as those 
 containing sulphur fumes, will have a deleterious action on the heating 
 surface of the boiler. This feature has been carefully watched, however, 
 and from plants in operation it would appear that in the absence of 
 water or steam leaks within the setting, there is no such harmful 
 action. 
   
 
 
 
 CHIMNEYS AND DRAFT 
 The height and diameter of a properly designed chimney depend upon the 
 amount of fuel to be burned, its nature, the design of the flue, with 
 its arrangement relative to the boiler or boilers, and the altitude of 
 the plant above sea level. There are so many factors involved that as 
 yet there has been produced no formula which is satisfactory in taking 
 them all into consideration, and the methods used for determining stack 
 sizes are largely empirical. In this chapter a method sufficiently 
 comprehensive and accurate to cover all practical cases will be 
 developed and illustrated. 
   
 Draft is the difference in pressure available for producing a flow of 
 the gases. If the gases within a stack be heated, each cubic foot will 
 expand, and the weight of the expanded gas per cubic foot will be less 
 than that of a cubic foot of the cold air outside the chimney. 
 Therefore, the unit pressure at the stack base due to the weight of the 
 column of heated gas will be less than that due to a column of cold air. 
 This difference in pressure, like the difference in head of water, will 
 cause a flow of the gases into the base of the stack. In its passage to 
 the stack the cold air must pass through the furnace or furnaces of the 
 boilers connected to it, and it in turn becomes heated. This newly 
 heated gas will also rise in the stack and the action will be 
 continuous. 
   
 The intensity of the draft, or difference in pressure, is usually 
 measured in inches of water. Assuming an atmospheric temperature of 62 
 degrees Fahrenheit and the temperature of the gases in the chimney as 
 500 degrees Fahrenheit, and, neglecting for the moment the difference in 
 density between the chimney gases and the air, the difference between 
 the weights of the external air and the internal flue gases per cubic 
 foot is .0347 pound, obtained as follows: 
   
 Weight of a cubic foot of air at 62 degrees Fahrenheit = .0761 pound 
 Weight of a cubic foot of air at 500 degrees Fahrenheit = .0414 pound 
                                             ------------------------ 
                                              Difference = .0347 pound 
   
 Therefore, a chimney 100 feet high, assumed for the purpose of 
 illustration to be suspended in the air, would have a pressure exerted 
 on each square foot of its cross sectional area at its base of .0347 × 
 100 = 3.47 pounds. As a cubic foot of water at 62 degrees Fahrenheit 
 weighs 62.32 pounds, an inch of water would exert a pressure of 62.32 ÷ 
 12 = 5.193 pounds per square foot. The 100-foot stack would, therefore, 
 under the above temperature conditions, show a draft of 3.47 ÷ 5.193 or 
 approximately 0.67 inches of water. 
   
 The method best suited for determining the proper proportion of stacks 
 and flues is dependent upon the principle that if the cross sectional 
 area of the stack is sufficiently large for the volume of gases to be 
 handled, the intensity of the draft will depend directly upon the 
 height; therefore, the method of procedure is as follows: 
   
   
 1st. Select a stack of such height as will produce the draft required by 
 the particular character of the fuel and the amount to be burned per 
 square foot of grate surface. 
   
   
 2nd. Determine the cross sectional area necessary to handle the gases 
 without undue frictional losses. 
   
   
 The application of these rules follows: 
   
 Draft Formula--The force or intensity of the draft, not allowing for the 
 difference in the density of the air and of the flue gases, is given by 
 the formula: 
   
                / 1     1  
 D = 0.52 H × P |--- - -----|     (24) 
                 T   T_{1}/ 
   
 in which 
   
 D     = draft produced, measured in inches of water, 
 H     = height of top of stack above grate bars in feet, 
 P     = atmospheric pressure in pounds per square inch, 
 T     = absolute atmospheric temperature, 
 T_{1} = absolute temperature of stack gases. 
   
 In this formula no account is taken of the density of the flue gases, it 
 being assumed that it is the same as that of air. Any error arising from 
 this assumption is negligible in practice as a factor of correction is 
 applied in using the formula to cover the difference between the 
 theoretical figures and those corresponding to actual operating 
 conditions. 
   
 The force of draft at sea level (which corresponds to an atmospheric 
 pressure of 14.7 pounds per square inch) produced by a chimney 100 feet 
 high with the temperature of the air at 60 degrees Fahrenheit and that 
 of the flue gases at 500 degrees Fahrenheit is, 
   
                      / 1     1  
 D = 0.52 × 100 × 14.7 | --- - --- | = 0.67 
                       521   961 / 
   
 Under the same temperature conditions this chimney at an atmospheric 
 pressure of 10 pounds per square inch (which corresponds to an altitude 
 of about 10,000 feet above sea level) would produce a draft of, 
   
                    / 1     1  
 D = 0.52 × 100 × 10 | --- - --- | = 0.45 
                     521   961 / 
   
 For use in applying this formula it is convenient to tabulate values of 
 the product 
   
                    / 1     1  
          0.52 × 14.7|--- - -----| 
                     T   T_{1}/ 
   
 which we will call K, for various values of T_{1}. With these values 
 calculated for assumed atmospheric temperature and pressure (24) becomes 
   
 D = KH.     (25) 
   
 For average conditions the atmospheric pressure may be considered 14.7 
 pounds per square inch, and the temperature 60 degrees Fahrenheit. For 
 these values and various stack temperatures K becomes: 
   
 _Temperature Stack Gases_       _Constant K_ 
              750                 .0084 
              700                 .0081 
              650                 .0078 
              600                 .0075 
              550                 .0071 
              500                 .0067 
              450                 .0063 
              400                 .0058 
              350                 .0053 
   
 Draft Losses--The intensity of the draft as determined by the above 
 formula is theoretical and can never be observed with a draft gauge or 
 any recording device. However, if the ashpit doors of the boiler are 
 closed and there is no perceptible leakage of air through the boiler 
 setting or flue, the draft measured at the stack base will be 
 approximately the same as the theoretical draft. The difference existing 
 at other times represents the pressure necessary to force the gases 
 through the stack against their own inertia and the friction against the 
 sides. This difference will increase with the velocity of the gases. 
 With the ashpit doors closed the volume of gases passing to the stack 
 are a minimum and the maximum force of draft will be shown by a gauge. 
   
 As draft measurements are taken along the path of the gases, the 
 readings grow less as the points at which they are taken are farther 
 from the stack, until in the boiler ashpit, with the ashpit doors open 
 for freely admitting the air, there is little or no perceptible rise in 
 the water of the gauge. The breeching, the boiler damper, the baffles 
 and the tubes, and the coal on the grates all retard the passage of the 
 gases, and the draft from the chimney is required to overcome the 
 resistance offered by the various factors. The draft at the rear of the 
 boiler setting where connection is made to the stack or flue may be 0.5 
 inch, while in the furnace directly over the fire it may not be over, 
 say, 0.15 inch, the difference being the draft required to overcome the 
 resistance offered in forcing the gases through the tubes and around the 
 baffling. 
   
 One of the most important factors to be considered in designing a stack 
 is the pressure required to force the air for combustion through the bed 
 of fuel on the grates. This pressure will vary with the nature of the 
 fuel used, and in many instances will be a large percentage of the total 
 draft. In the case of natural draft, its measure is found directly by 
 noting the draft in the furnace, for with properly designed ashpit doors 
 it is evident that the pressure under the grates will not differ 
 sensibly from atmospheric pressure. 
   
 Loss in Stack--The difference between the theoretical draft as 
 determined by formula (24) and the amount lost by friction in the stack 
 proper is the available draft, or that which the draft gauge indicates 
 when connected to the base of the stack. The sum of the losses of draft 
 in the flue, boiler and furnace must be equivalent to the available 
 draft, and as these quantities can be determined from record of 
 experiments, the problem of designing a stack becomes one of 
 proportioning it to produce a certain available draft. 
   
 The loss in the stack due to friction of the gases can be calculated 
 from the following formula: 
   
            f W² C H 
 [Delta]D = --------     (26) 
              A³ 
   
 in which 
   
 [Delta]D = draft loss in inches of water, 
        W = weight of gas in pounds passing per second, 
        C = perimeter of stack in feet, 
        H = height of stack in feet, 
        f = a constant with the following values at sea level: 
            .0015 for steel stacks, temperature of gases 600 degrees 
              Fahrenheit. 
            .0011 for steel stacks, temperature of gases 350 degrees 
              Fahrenheit. 
            .0020 for brick or brick-lined stacks, temperature of gases 
              600 degrees Fahrenheit. 
            .0015 for brick or brick-lined stacks, temperature of gases 
              350 degrees Fahrenheit. 
        A = Area of stack in square feet. 
 This formula can also be used for calculating the frictional losses for 
 flues, in which case, C = the perimeter of the flue in feet, H = the 
 length of the flue in feet, the other values being the same as for 
 stacks. 
   
 The available draft is equal to the difference between the theoretical 
 draft from formula (25) and the loss from formula (26), hence: 
   
                                f W² C H 
 d^{1} = available draft = KH - --------     (27) 
                                  A³ 
   
 Table 53 gives the available draft in inches that a stack 100 feet high 
 will produce when serving different horse powers of boilers with the 
 methods of calculation for other heights. 
   
                                  TABLE 53 
   
                              AVAILABLE DRAFT 
   
    CALCULATED FOR 100-FOOT STACK OF DIFFERENT DIAMETERS ASSUMING STACK 
 TEMPERATURE OF 500 DEGREES FAHRENHEIT AND 100 POUNDS OF GAS PER HORSE POWER 
   
          FOR OTHER HEIGHTS OF STACK MULTIPLY DRAFT BY HEIGHT ÷ 100 
   
 +-----+-------------------------------------------------------------------+ 
 |Horse|                                                                  | 
 |Power|                   Diameter of Stack in Inches                   | 
 +-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 
 |     |36 |42 |48 |54 |60 |66 |72 |78 |84 |90 |96 |102|108|114|120|132|144| 
 +-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 
 | 100 |.64|   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 
 | 200 |.55|.62|   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 
 | 300 |.41|.55|.61|   |   |   |   |   |   |   |   |   |   |   |   |   |   | 
 | 400 |.21|.46|.56|.61|   |   |   |   |   |   |   |   |   |   |   |   |   | 
 | 500 |   |.34|.50|.57|.61|   |   |   |   |   |   |   |   |   |   |   |   | 
 | 600 |   |.19|.42|.53|.59|   |   |   |   |   |   |   |   |   |   |   |   | 
 | 700 |   |   |.34|.48|.56|.60|.63|   |   |   |   |   |   |   |   |   |   | 
 | 800 |   |   |.23|.43|.52|.58|.61|.63|   |   |   |   |   |   |   |   |   | 
 | 900 |   |   |   |.36|.49|.56|.60|.62|.64|   |   |   |   |   |   |   |   | 
 |1000 |   |   |   |.29|.45|.53|.58|.61|.63|.64|   |   |   |   |   |   |   | 
 |1100 |   |   |   |   |.40|.50|.56|.60|.62|.63|.64|   |   |   |   |   |   | 
 |1200 |   |   |   |   |.35|.47|.54|.58|.61|.63|.64|.65|   |   |   |   |   | 
 |1300 |   |   |   |   |.29|.44|.52|.57|.60|.62|.63|.64|.65|   |   |   |   | 
 |1400 |   |   |   |   |   |.40|.49|.55|.59|.61|.63|.64|.65|.65|   |   |   | 
 |1500 |   |   |   |   |   |.36|.47|.53|.58|.60|.62|.63|.64|.65|.65|   |   | 
 |1600 |   |   |   |   |   |.31|.43|.52|.56|.59|.62|.63|.64|.65|.65|   |   | 
 |1700 |   |   |   |   |   |   |.41|.50|.55|.58|.61|.62|.64|.64|.65|   |   | 
 |1800 |   |   |   |   |   |   |.37|.47|.54|.57|.60|.62|.63|.64|.65|   |   | 
 |1900 |   |   |   |   |   |   |.34|.45|.52|.56|.59|.61|.63|.64|.64|   |   | 
 |2000 |   |   |   |   |   |   |   |.43|.50|.55|.59|.61|.62|.63|.64|   |   | 
 |2100 |   |   |   |   |   |   |   |.40|.49|.54|.58|.60|.62|.63|.64|   |   | 
 |2200 |   |   |   |   |   |   |   |.38|.47|.53|.57|.59|.61|.62|.64|   |   | 
 |2300 |   |   |   |   |   |   |   |.35|.45|.52|.56|.59|.61|.62|.63|   |   | 
 |2400 |   |   |   |   |   |   |   |.32|.43|.50|.55|.58|.60|.62|.63|   |   | 
 |2500 |   |   |   |   |   |   |   |   |.41|.49|.54|.57|.60|.61|.63|   |   | 
 |2600 |   |   |   |   |   |   |   |   |   |.47|.53|.56|.59|.61|.62|.64|.65| 
 |2700 |   |   |   |   |   |   |   |   |   |.45|.52|.55|.58|.60|.62|.64|.65| 
 |2800 |   |   |   |   |   |   |   |   |   |.44|.59|.55|.58|.60|.61|.64|.65| 
 |2900 |   |   |   |   |   |   |   |   |   |.42|.49|.54|.57|.59|.61|.63|.65| 
 |3000 |   |   |   |   |   |   |   |   |   |.40|.48|.53|.56|.59|.61|.63|.64| 
 |3100 |   |   |   |   |   |   |   |   |   |.38|.47|.52|.56|.58|.60|.63|.64| 
 |3200 |   |   |   |   |   |   |   |   |   |   |.45|.51|.55|.58|.60|.63|.64| 
 |3300 |   |   |   |   |   |   |   |   |   |   |.44|.50|.54|.57|.59|.62|.64| 
 |3400 |   |   |   |   |   |   |   |   |   |   |.42|.49|.53|.56|.59|.62|.64| 
 |3500 |   |   |   |   |   |   |   |   |   |   |.40|.48|.52|.56|.58|.62|.64| 
 |3600 |   |   |   |   |   |   |   |   |   |   |   |.47|.52|.55|.58|.61|.63| 
 |3700 |   |   |   |   |   |   |   |   |   |   |   |.45|.51|.55|.57|.61|.63| 
 |3800 |   |   |   |   |   |   |   |   |   |   |   |.44|.50|.54|.57|.61|.63| 
 |3900 |   |   |   |   |   |   |   |   |   |   |   |.43|.49|.53|.56|.60|.63| 
 |4000 |   |   |   |   |   |   |   |   |   |   |   |.42|.48|.52|.56|.60|.62| 
 |4100 |   |   |   |   |   |   |   |   |   |   |   |.40|.47|.52|.55|.60|.62| 
 |4200 |   |   |   |   |   |   |   |   |   |   |   |.39|.46|.51|.55|.59|.62| 
 |4300 |   |   |   |   |   |   |   |   |   |   |   |   |.45|.50|.54|.59|.62| 
 |4400 |   |   |   |   |   |   |   |   |   |   |   |   |.44|.49|.53|.59|.62| 
 |4500 |   |   |   |   |   |   |   |   |   |   |   |   |.43|.49|.53|.58|.61| 
 |4600 |   |   |   |   |   |   |   |   |   |   |   |   |.42|.48|.52|.58|.61| 
 |4700 |   |   |   |   |   |   |   |   |   |   |   |   |.41|.47|.51|.57|.61| 
 |4800 |   |   |   |   |   |   |   |   |   |   |   |   |.40|.46|.51|.57|.60| 
 |4900 |   |   |   |   |   |   |   |   |   |   |   |   |   |.45|.50|.57|.60| 
 |5000 |   |   |   |   |   |   |   |   |   |   |   |   |   |.44|.49|.56|.60| 
 +-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 
   
 FOR OTHER STACK TEMPERATURES ADD OR DEDUCT BEFORE MULTIPLYING BY 
 HEIGHT ÷ 100 AS FOLLOWS[52] 
   
 For 750 Degrees F. Add .17 inch. 
 For 700 Degrees F. Add .14 inch. 
 For 650 Degrees F. Add .11 inch. 
 For 600 Degrees F. Add .08 inch. 
 For 550 Degrees F. Add .04 inch. 
 For 450 Degrees F. Deduct .04 inch. 
 For 400 Degrees F. Deduct .09 inch. 
 For 350 Degrees F. Deduct .14 inch. 
   
 [Graph: Horse Power of Boilers against Diameter of Stack in Inches 
   
 Fig. 33. Diameter of Stacks and Horse Power they will Serve 
   
 Computed from Formula (28). For brick or brick-lined stacks, increase 
 the diameter 6 per cent] 
   
 Height and Diameter of Stacks--From this formula (27) it becomes evident 
 that a stack of certain diameter, if it be increased in height, will 
 produce the same available draft as one of larger diameter, the 
 additional height being required to overcome the added frictional loss. 
 It follows that among the various stacks that would meet the 
 requirements of a particular case there must be one which can be 
 constructed more cheaply than the others. It has been determined from 
 the relation of the cost of stacks to their diameters and heights, in 
 connection with the formula for available draft, that the minimum cost 
 stack has a diameter dependent solely upon the horse power of the 
 boilers it serves, and a height proportional to the available draft 
 required. 
   
 Assuming 120 pounds of flue gas per hour for each boiler horse power, 
 which provides for ordinary overloads and the use of poor coal, the 
 method above stated gives: 
   
 For an unlined steel stack-- 
   
 diameter in inches = 4.68 (H. P.)^{2/5}     (28) 
   
 For a stack lined with masonry-- 
   
 diameter in inches = 4.92 (H. P.)^{2/5}     (29) 
   
 In both of these formulae H. P. = the rated horse power of the boiler. 
   
 From this formula the curve, Fig. 33, has been calculated and from it 
 the stack diameter for any boiler horse power can be selected. 
   
 For stoker practice where a large stack serves a number of boilers, the 
 area is usually made about one-third more than the above rules call for, 
 which allows for leakage of air through the setting of any idle boilers, 
 irregularities in operating conditions, etc. 
   
 Stacks with diameters determined as above will give an available draft 
 which bears a constant ratio of the theoretical draft, and allowing for 
 the cooling of the gases in their passage upward through the stack, this 
 ratio is 8. Using this factor in formula (25), and transposing, the 
 height of the chimney becomes, 
   
   
    d^{1} 
 H = -----     (30) 
    .8 K 
   
 Where H = height of stack in feet above the level of the grates, 
 d^{1} = available draft required, 
      K = constant as in formula. 
   
 Losses in Flues--The loss of draft in straight flues due to friction and 
 inertia can be calculated approximately from formula (26), which was 
 given for loss in stacks. It is to be borne in mind that C in this 
 formula is the actual perimeter of the flue and is least, relative to 
 the cross sectional area, when the section is a circle, is greater for a 
 square section, and greatest for a rectangular section. The retarding 
 effect of a square flue is 12 per cent greater than that of a circular 
 flue of the same area and that of a rectangular with sides as 1 and 1½, 
 15 per cent greater. The greater resistance of the more or less uneven 
 brick or concrete flue is provided for in the value of the constants 
 given for formula (26). Both steel and brick flues should be short and 
 should have as near a circular or square cross section as possible. 
 Abrupt turns are to be avoided, but as long easy sweeps require valuable 
 space, it is often desirable to increase the height of the stack rather 
 than to take up added space in the boiler room. Short right-angle turns 
 reduce the draft by an amount which can be roughly approximated as equal 
 to 0.05 inch for each turn. The turns which the gases make in leaving 
 the damper box of a boiler, in entering a horizontal flue and in turning 
 up into a stack should always be considered. The cross sectional areas 
 of the passages leading from the boilers to the stack should be of ample 
 size to provide against undue frictional loss. It is poor economy to 
 restrict the size of the flue and thus make additional stack height 
 necessary to overcome the added friction. The general practice is to 
 make flue areas the same or slightly larger than that of the stack; 
 these should be, preferably, at least 20 per cent greater, and a safe 
 rule to follow in figuring flue areas is to allow 35 square feet per 
 1000 horse power. It is unnecessary to maintain the same size of flue 
 the entire distance behind a row of boilers, and the areas at any point 
 may be made proportional to the volume of gases that will pass that 
 point. That is, the areas may be reduced as connections to various 
 boilers are passed. 
 With circular steel flues of approximately the same size as the stacks, 
 or reduced proportionally to the volume of gases they will handle, a 
 convenient rule is to allow 0.1 inch draft loss per 100 feet of flue 
 length and 0.05 inch for each right-angle turn. These figures are also 
 good for square or rectangular steel flues with areas sufficiently large 
 to provide against excessive frictional loss. For losses in brick or 
 concrete flues, these figures should be doubled. 
   
 Underground flues are less desirable than overhead or rear flues for the 
 reason that in most instances the gases will have to make more turns 
 where underground flues are used and because the cross sectional area of 
 such flues will oftentimes be decreased on account of an accumulation of 
 dirt or water which it may be impossible to remove. 
   
 In tall buildings, such as office buildings, it is frequently necessary 
 in order to carry spent gases above the roofs, to install a stack the 
 height of which is out of all proportion to the requirements of the 
 boilers. In such cases it is permissible to decrease the diameter of a 
 stack, but care must be taken that this decrease is not sufficient to 
 cause a frictional loss in the stack as great as the added draft 
 intensity due to the increase in height, which local conditions make 
 necessary. 
   
 In such cases also the fact that the stack diameter is permissibly 
 decreased is no reason why flue sizes connecting to the stack should be 
 decreased. These should still be figured in proportion to the area of 
 the stack that would be furnished under ordinary conditions or with an 
 allowance of 35 square feet per 1000 horse power, even though the cross 
 sectional area appears out of proportion to the stack area. 
   
 Loss in Boiler--In calculating the available draft of a chimney 120 
 pounds per hour has been used as the weight of the gases per boiler 
 horse power. This covers an overload of the boiler to an extent of 50 
 per cent and provides for the use of poor coal. The loss in draft 
 through a boiler proper will depend upon its type and baffling and will 
 increase with the per cent of rating at which it is run. No figures can 
 be given which will cover all conditions, but for approximate use in 
 figuring the available draft necessary it may be assumed that the loss 
 through a boiler will be 0.25 inch where the boiler is run at rating, 
 0.40 inch where it is run at 150 per cent of its rated capacity, and 
 0.70 inch where it is run at 200 per cent of its rated capacity. 
   
 Loss in Furnace--The draft loss in the furnace or through the fuel bed 
 varies between wide limits. The air necessary for combustion must pass 
 through the interstices of the coal on the grate. Where these are large, 
 as is the case with broken coal, but little pressure is required to 
 force the air through the bed; but if they are small, as with bituminous 
 slack or small sizes of anthracite, a much greater pressure is needed. 
 If the draft is insufficient the coal will accumulate on the grates and 
 a dead smoky fire will result with the accompanying poor combustion; if 
 the draft is too great, the coal may be rapidly consumed on certain 
 portions of the grate, leaving the fire thin in spots and a portion of 
 the grates uncovered with the resulting losses due to an excessive 
 amount of air. 
   
 [Graph: Force of Draft between Furnace and Ash Pit--Inches of Water 
 against Pounds of Coal burned per Square Foot of Grate Surface per Hour 
   
 Fig. 34. Draft Required at Different Combustion Rates for Various Kinds 
 of Coal] 
   
 Draft Required for Different Fuels--For every kind of fuel and rate of 
 combustion there is a certain draft with which the best general results 
 are obtained. A comparatively light draft is best with the free burning 
 bituminous coals and the amount to use increases as the percentage of 
 volatile matter diminishes and the fixed carbon increases, being highest 
 for the small sizes of anthracites. Numerous other factors such as the 
 thickness of fires, the percentage of ash and the air spaces in the 
 grates bear directly on this question of the draft best suited to a 
 given combustion rate. The effect of these factors can only be found by 
 experiment. It is almost impossible to show by one set of curves the 
 furnace draft required at various rates of combustion for all of the 
 different conditions of fuel, etc., that may be met. The curves in Fig. 
 34, however, give the furnace draft necessary to burn various kinds of 
 coal at the combustion rates indicated by the abscissae, for a general 
 set of conditions. These curves have been plotted from the records of 
 numerous tests and allow a safe margin for economically burning coals of 
 the kinds noted. 
   
 Rate of Combustion--The amount of coal which can be burned per hour per 
 square foot of grate surface is governed by the character of the coal 
 and the draft available. When the boiler and grate are properly 
 proportioned, the efficiency will be practically the same, within 
 reasonable limits, for different rates of combustion. The area of the 
 grate, and the ratio of this area to the boiler heating surface will 
 depend upon the nature of the fuel to be burned, and the stack should be 
 so designed as to give a draft sufficient to burn the maximum amount of 
 fuel per square foot of grate surface corresponding to the maximum 
 evaporative requirements of the boiler. 
   
 Solution of a Problem--The stack diameter can be determined from the 
 curve, Fig. 33. The height can be determined by adding the draft losses 
 in the furnace, through the boiler and flues, and computing from formula 
 (30) the height necessary to give this draft. 
   
 Example: Proportion a stack for boilers rated at 2000 horse power, 
 equipped with stokers, and burning bituminous coal that will evaporate 8 
 pounds of water from and at 212 degrees Fahrenheit per pound of fuel; 
 the ratio of boiler heating surface to grate surface being 50:1; the 
 flues being 100 feet long and containing two right-angle turns; the 
 stack to be able to handle overloads of 50 per cent; and the rated horse 
 power of the boilers based on 10 square feet of heating surface per 
 horse power. 
   
 The atmospheric temperature may be assumed as 60 degrees Fahrenheit and 
 the flue temperatures at the maximum overload as 550 degrees Fahrenheit. 
 The grate surface equals 400 square feet. 
   
                                   2000 × 34½ 
 The total coal burned at rating = ---------- = 8624 pounds. 
                                      8 
   
 The coal per square foot of grate surface per hour at rating = 
   
 8624 
 ---- = 22 pounds. 
 400 
   
 For 50 per cent overload the combustion rate will be approximately 60 
 per cent greater than this or 1.60 × 22 = 35 pounds per square foot of 
 grate surface per hour. The furnace draft required for the combustion 
 rate, from the curve, Fig. 34, is 0.6 inch. The loss in the boiler will 
 be 0.4 inch, in the flue 0.1 inch, and in the turns 2 × 0.05 = 0.1 inch. 
 The available draft required at the base of the stack is, therefore, 
   
        _Inches_ 
 Boiler   0.4 
 Furnace 0.6 
 Flues   0.1 
 Turns   0.1 
          --- 
 Total 1.2 
   
 Since the available draft is 80 per cent of the theoretical draft, this 
 draft due to the height required is 1.2 ÷ .8 = 1.5 inch. 
   
 The chimney constant for temperatures of 60 degrees Fahrenheit and 550 
 degrees Fahrenheit is .0071 and from formula (30), 
   
      1.5 
 H = ----- = 211 feet. 
    .0071 
   
 Its diameter from curve in Fig. 33 is 96 inches if unlined, and 102 
 inches inside if lined with masonry. The cross sectional area of the 
 flue should be approximately 70 square feet at the point where the total 
 amount of gas is to be handled, tapering to the boiler farthest from the 
 stack to a size which will depend upon the size of the boiler units 
 used. 
   
 Correction in Stack Sizes for Altitudes--It has ordinarily been assumed 
 that a stack height for altitude will be increased inversely as the 
 ratio of the barometric pressure at the altitude to that at sea level, 
 and that the stack diameter will increase inversely as the two-fifths 
 power of this ratio. Such a relation has been based on the assumption of 
 constant draft measured in inches of water at the base of the stack for 
 a given rate of operation of the boilers, regardless of altitude. 
   
 If the assumption be made that boilers, flues and furnace remain the 
 same, and further that the increased velocity of a given weight of air 
 passing through the furnace at a higher altitude would have no effect on 
 the combustion, the theory has been advanced[53] that a different law 
 applies. 
   
 Under the above assumptions, whenever a stack is working at its maximum 
 capacity at any altitude, the entire draft is utilized in overcoming the 
 various resistances, each of which is proportional to the square of the 
 velocity of the gases. Since boiler areas are fixed, all velocities may 
 be related to a common velocity, say, that within the stack, and all 
 resistances may, therefore, be expressed as proportional to the square 
 of the chimney velocity. The total resistance to flow, in terms of 
 velocity head, may be expressed in terms of weight of a column of 
 external air, the numerical value of such head being independent of the 
 barometric pressure. Likewise the draft of a stack, expressed in height 
 of column of external air, will be numerically independent of the 
 barometric pressure. It is evident, therefore, that if a given boiler 
 plant, with its stack operated with a fixed fuel, be transplanted from 
 sea level to an altitude, assuming the temperatures remain constant, the 
 total draft head measured in height of column of external air will be 
 numerically constant. The velocity of chimney gases will, therefore, 
 remain the same at altitude as at sea level and the weight of gases 
 flowing per second with a fixed velocity will be proportional to the 
 atmospheric density or inversely proportional to the normal barometric 
 pressure. 
   
 To develop a given horse power requires a constant weight of chimney gas 
 and air for combustion. Hence, as the altitude is increased, the density 
 is decreased and, for the assumptions given above, the velocity through 
 the furnace, the boiler passes, breeching and flues must be 
 correspondingly greater at altitude than at sea level. The mean 
 velocity, therefore, for a given boiler horse power and constant weight 
 of gases will be inversely proportional to the barometric pressure and 
 the velocity head measured in column of external air will be inversely 
 proportional to the square of the barometric pressure. 
   
 For stacks operating at altitude it is necessary not only to increase 
 the height but also the diameter, as there is an added resistance within 
 the stack due to the added friction from the additional height. This 
 frictional loss can be compensated by a suitable increase in the 
 diameter and when so compensated, it is evident that on the assumptions 
 as given, the chimney height would have to be increased at a ratio 
 inversely proportional to the square of the normal barometric pressure. 
   
 In designing a boiler for high altitudes, as already stated, the 
 assumption is usually made that a given grade of fuel will require the 
 same draft measured in inches of water at the boiler damper as at sea 
 level, and this leads to making the stack height inversely as the 
 barometric pressures, instead of inversely as the square of the 
 barometric pressures. The correct height, no doubt, falls somewhere 
 between the two values as larger flues are usually used at the higher 
 altitudes, whereas to obtain the ratio of the squares, the flues must be 
 the same size in each case, and again the effect of an increased 
 velocity of a given weight of air through the fire at a high altitude, 
 on the combustion, must be neglected. In making capacity tests with coal 
 fuel, no difference has been noted in the rates of combustion for a 
 given draft suction measured by a water column at high and low 
 altitudes, and this would make it appear that the correct height to use 
 is more nearly that obtained by the inverse ratio of the barometric 
 readings than by the inverse ratio of the squares of the barometric 
 readings. If the assumption is made that the value falls midway between 
 the two formulae, the error in using a stack figured in the ordinary way 
 by making the height inversely proportional to the barometric readings 
 would differ about 10 per cent in capacity at an altitude of 10,000 
 feet, which difference is well within the probable variation of the size 
 determined by different methods. It would, therefore, appear that ample 
 accuracy is obtained in all cases by simply making the height inversely 
 proportional to the barometric readings and increasing the diameter so 
 that the stacks used at high altitudes have the same frictional 
 resistance as those used at low altitudes, although, if desired, the 
 stack may be made somewhat higher at high altitudes than this rule calls 
 for in order to be on the safe side. 
   
 The increase of stack diameter necessary to maintain the same friction 
 loss is inversely as the two-fifths power of the barometric pressure. 
   
 Table 54 gives the ratio of barometric readings of various altitudes to 
 sea level, values for the square of this ratio and values of the 
 two-fifths power of this ratio. 
   
                                  TABLE 54 
   
                 STACK CAPACITIES, CORRECTION FACTORS FOR 
                                ALTITUDES 
   
 _______________________________________________________________________ 
 |               |           |                 |       |               | 
 |   Altitude   |           |       R       |       |   R^{2/5}     | 
 | Height in Feet | Normal   | Ratio Barometer |       | Ratio Increase | 
 |     Above     | Barometer |     Reading     |   R² |   in Stack   | 
 |   Sea Level   |           | Sea Level to   |       |   Diameter   | 
 |               |           |   Altitude     |       |               | 
 |________________|___________|_________________|_______|________________| 
 |               |           |                 |       |               | 
 |        0     |   30.00   |     1.000     | 1.000 |     1.000     | 
 |     1000     |   28.88   |     1.039     | 1.079 |     1.015     | 
 |     2000     |   27.80   |     1.079     | 1.064 |     1.030     | 
 |     3000     |   26.76   |     1.121     | 1.257 |     1.047     | 
 |     4000     |   25.76   |     1.165     | 1.356 |     1.063     | 
 |     5000     |   24.79   |     1.210     | 1.464 |     1.079     | 
 |     6000     |   23.87   |     1.257     | 1.580 |     1.096     | 
 |     7000     |   22.97   |     1.306     | 1.706 |     1.113     | 
 |     8000     |   22.11   |     1.357     | 1.841 |     1.130     | 
 |     9000     |   21.28   |     1.410     | 1.988 |     1.147     | 
 |     10000     |   20.49   |     1.464     | 2.144 |     1.165     | 
 |________________|___________|_________________|_______|________________| 
   
 These figures show that the altitude affects the height to a much 
 greater extent than the diameter and that practically no increase in 
 diameter is necessary for altitudes up to 3000 feet. 
   
 For high altitudes the increase in stack height necessary is, in some 
 cases, such as to make the proportion of height to diameter 
 impracticable. The method to be recommended in overcoming, at least 
 partially, the great increase in height necessary at high altitudes is 
 an increase in the grate surface of the boilers which the stack serves, 
 in this way reducing the combustion rate necessary to develop a given 
 power and hence the draft required for such combustion rate. 
   
                                TABLE 55 
   
                      STACK SIZES BY KENT'S FORMULA 
   
                ASSUMING 5 POUNDS OF COAL PER HORSE POWER 
   
   
 ____________________________________________________________________ 
 |     |     |                                              |       | 
 |     |     |           Height of Stack in Feet           |Side of| 
 |     |     |______________________________________________|Equiva-| 
 | Dia- | Area |   |   |   |   |   |   |   |   |   |   | lent | 
 | meter|Square| 50| 60| 70| 80 | 90 | 100| 110| 125| 150| 175|Square | 
 |Inches| Feet |___|___|___|____|____|____|____|____|____|____| Stack | 
 |     |     |                                             |Inches | 
 |     |     |           Commercial Horse Power           |       | 
 |______|______|______________________________________________|_______| 
 |     |     |   |   |   |   |   |   |   |   |   |   |       | 
 | 33 | 5.94|106|115|125| 133| 141| 149|   |   |   |   |   30 | 
 | 36 | 7.07|129|141|152| 163| 173| 182|   |   |   |   |   32 | 
 | 39 | 8.30|155|169|183| 196| 208| 219| 229| 245|   |   |   35 | 
 | 42 | 9.62|183|200|216| 231| 245| 258| 271| 289| 316|   |   38 | 
 | 48 | 12.57|246|269|290| 311| 330| 348| 365| 389| 426| 460|   43 | 
 | 54 | 15.90|318|348|376| 402| 427| 449| 472| 503| 551| 595|   48 | 
 | 60 | 19.64|400|437|473| 505| 536| 565| 593| 632| 692| 748|   54 | 
 | 66 | 23.76|490|537|580| 620| 658| 694| 728| 776| 849| 918|   59 | 
 | 72 | 28.27|591|646|698| 747| 792| 835| 876| 934|1023|1105|   64 | 
 | 78 | 33.18|700|766|828| 885| 939| 990|1038|1107|1212|1310|   70 | 
 | 84 | 38.48|818|896|968|1035|1098|1157|1214|1294|1418|1531|   75 | 
 |______|______|___|___|___|____|____|____|____|____|____|____|_______| 
 |     |     |                                             |       | 
 |     |     |           Height of Stack in Feet           |Side of| 
 |     |     |______________________________________________|Equiva-| 
 | Dia- | Area |   |     |     |     |     |     |     |     | lent | 
 | meter|Square| 100| 110 | 125 | 150 | 175 | 200 | 225 | 250 |Square | 
 |Inches| Feet |____|_____|_____|_____|_____|_____|_____|_____| Stack | 
 |     |     |                                             |Inches | 
 |     |     |           Commercial Horse Power           |       | 
 |______|______|______________________________________________|_______| 
 |     |     |   |     |     |     |     |     |     |     |       | 
 | 90 | 44.18|1338| 1403| 1496| 1639| 1770| 1893| 2008| 2116|   80 | 
 | 96 | 50.27|1532| 1606| 1713| 1876| 2027| 2167| 2298| 2423|   86 | 
 | 102 | 56.75|1739| 1824| 1944| 2130| 2300| 2459| 2609| 2750|   91 | 
 | 108 | 63.62|1959| 2054| 2190| 2392| 2592| 2770| 2939| 3098|   98 | 
 | 114 | 70.88|2192| 2299| 2451| 2685| 2900| 3100| 3288| 3466| 101 | 
 | 120 | 78.54|2438| 2557| 2726| 2986| 3226| 3448| 3657| 3855| 107 | 
 | 126 | 86.59|2697| 2829| 3016| 3303| 3568| 3814| 4046| 4265| 112 | 
 | 132 | 95.03|2970| 3114| 3321| 3637| 3929| 4200| 4455| 4696| 117 | 
 | 144 |113.10|3554| 3726| 3973| 4352| 4701| 5026| 5331| 5618| 128 | 
 | 156 |132.73|4190| 4393| 4684| 5131| 5542| 5925| 6285| 6624| 138 | 
 | 168 |153.94|4878| 5115| 5454| 5974| 6454| 6899| 7318| 7713| 150 | 
 |______|______|____|_____|_____|_____|_____|_____|_____|_____|_______| 
   
 Kent's Stack Tables--Table 55 gives, in convenient form for approximate 
 work, the sizes of stacks and the horse power of boilers which they will 
 serve. This table is a modification of Mr. William Kent's stack table 
 and is calculated from his formula. Provided no unusual conditions are 
 encountered, it is reliable for the ordinary rates of combustion with 
 bituminous coals. It is figured on a consumption of 5 pounds of coal 
 burned per hour per boiler horse power developed, this figure giving a 
 fairly liberal allowance for the use of poor coal and for a reasonable 
 overload. When the coal used is a low grade bituminous of the Middle or 
 Western States, it is strongly recommended that these sizes be increased 
 materially, such an increase being from 25 to 60 per cent, depending 
 upon the nature of the coal and the capacity desired. For the coal 
 burned per hour for any size stack given in the table, the values should 
 be multiplied by 5. 
   
 A convenient rule for large stacks, 200 feet high and over, is to 
 provide 30 square feet of cross sectional area per 1000 rated horse 
 power. 
   
 Stacks for Oil Fuel--The requirements of stacks connected to boilers 
 under which oil fuel is burned are entirely different from those where 
 coal is used. While more attention has been paid to the matter of stack 
 sizes for oil fuel in recent years, there has not as yet been gathered 
 the large amount of experimental data available for use in designing 
 coal stacks. 
   
 In the case of oil-fired boilers the loss of draft through the fuel bed 
 is partially eliminated. While there may be practically no loss through 
 any checkerwork admitting air to the furnace when a boiler is new, the 
 areas for the air passage in this checkerwork will in a short time be 
 decreased, due to the silt which is present in practically all fuel oil. 
 The loss in draft through the boiler proper at a given rating will be 
 less than in the case of coal-fired boilers, this being due to a 
 decrease in the volume of the gases. Further, the action of the oil 
 burner itself is to a certain extent that of a forced draft. To offset 
 this decrease in draft requirement, the temperature of the gases 
 entering the stack will be somewhat lower where oil is used than where 
 coal is used, and the draft that a stack of a given height would give, 
 therefore, decreases. The factors as given above, affecting as they do 
 the intensity of the draft, affect directly the height of the stack to 
 be used. 
   
 As already stated, the volume of gases from oil-fired boilers being less 
 than in the case of coal, makes it evident that the area of stacks for 
 oil fuel will be less than for coal. It is assumed that these areas will 
 vary directly as the volume of the gases to be handled, and this volume 
 for oil may be taken as approximately 60 per cent of that for coal. 
   
 In designing stacks for oil fuel there are two features which must not 
 be overlooked. In coal-firing practice there is rarely danger of too 
 much draft. In the burning of oil, however, this may play an important 
 part in the reduction of plant economy, the influence of excessive draft 
 being more apparent where the load on the plant may be reduced at 
 intervals. The reason for this is that, aside from a slight decrease in 
 temperature at reduced loads, the tendency, due to careless firing, is 
 toward a constant gas flow through the boiler regardless of the rate of 
 operation, with the corresponding increase of excess air at light loads. 
 With excessive stack height, economical operation at varying loads is 
 almost impossible with hand control. With automatic control, however, 
 where stacks are necessarily high to take care of known peaks, under 
 lighter loads this economical operation becomes less difficult. For this 
 reason the question of designing a stack for a plant where the load is 
 known to be nearly a constant is easier than for a plant where the load 
 will vary over a wide range. While great care must be taken to avoid 
 excessive draft, still more care must be taken to assure a draft suction 
 within all parts of the setting under any and all conditions of 
 operation. It is very easily possible to more than offset the economy 
 gained through low draft, by the losses due to setting deterioration, 
 resulting from such lack of suction. Under conditions where the suction 
 is not sufficient to carry off the products of combustion, the action of 
 the heat on the setting brickwork will cause its rapid failure. 
 It becomes evident, therefore, that the question of stack height for 
 oil-fired boilers is one which must be considered with the greatest of 
 care. The designer, on the one hand, must guard against the evils of 
 excessive draft with the view to plant economy, and, on the other, 
 against the evils of lack of draft from the viewpoint of upkeep cost. 
 Stacks for this work should be proportioned to give ample draft for the 
 maximum overload that a plant will be called upon to carry, all 
 conditions of overload carefully considered. At the same time, where 
 this maximum overload is figured liberally enough to insure a draft 
 suction within the setting under all conditions, care must be taken 
 against the installation of a stack which would give more than this 
 maximum draft. 
   
                        TABLE 56 
   
                STACK SIZES FOR OIL FUEL 
   
      ADAPTED FROM C. R. WEYMOUTH'S TABLE (TRANS. 
 S. M. E. VOL. 34) 
 
   
 +----------------------------------------------------+ 
 |+--------+-----------------------------------------+| 
 ||       | Height in Feet Above Boiler Room Floor || 
 ||Diameter+------+------+------+-----+--------------+| 
 || Inches |   80 |   90 | 100 | 120 | 140 | 160 || 
 |+--------+------+------+------+------+------+------+| 
 ||   33   | 161 | 206 | 233 | 270 | 306 | 315 || 
 ||   36   | 208 | 253 | 295 | 331 | 363 | 387 || 
 ||   39   | 251 | 303 | 343 | 399 | 488 | 467 || 
 ||   42   | 295 | 359 | 403 | 474 | 521 | 557 || 
 ||   48   | 399 | 486 | 551 | 645 | 713 | 760 || 
 ||   54   | 519 | 634 | 720 | 847 | 933 | 1000 || 
 ||   60   | 657 | 800 | 913 | 1073 | 1193 | 1280 || 
 ||   66   | 813 | 993 | 1133 | 1333 | 1480 | 1593 || 
 ||   72   | 980 | 1206 | 1373 | 1620 | 1807 | 1940 || 
 || 84   | 1373 | 1587 | 1933 | 2293 | 2560 | 2767 || 
 ||   96   | 1833 | 2260 | 2587 | 3087 | 3453 | 3740 || 
 || 108   | 2367 | 2920 | 3347 | 4000 | 4483 | 4867 || 
 || 120   | 3060 | 3660 | 4207 | 5040 | 5660 | 6160 || 
 |+--------+------+------+------+------+------+------+| 
 +----------------------------------------------------+ 
   
 Figures represent nominal rated horse power. Sizes as given good for 50 
 per cent overloads. 
   
 Based on centrally located stacks, short direct flues and ordinary 
 operating efficiencies. 
   
 Table 56 gives the sizes of stacks, and horse power which they will 
 serve for oil fuel. This table is, in modified form, one calculated by 
 Mr. C. R. Weymouth after an exhaustive study of data pertaining to the 
 subject, and will ordinarily give satisfactory results. 
   
 Stacks for Blast Furnace Gas Work--For boilers burning blast furnace 
 gas, as in the case of oil-fired boilers, stack sizes as suited for coal 
 firing will have to be modified. The diameter of stacks for this work 
 should be approximately the same as for coal-fired boilers. The volume 
 of gases would be slightly greater than from a coal fire and would 
 decrease the draft with a given stack, but such a decrease due to volume 
 is about offset by an increase due to somewhat higher temperatures in 
 the case of the blast furnace gases. 
   
 Records show that with this class of fuel 175 per cent of the rated 
 capacity of a boiler can be developed with a draft at the boiler damper 
 of from 0.75 inch to 1.0 inch, and it is well to limit the height of 
 stacks to one which will give this draft as a maximum. A stack of proper 
 diameter, 130 feet high above the ground, will produce such a draft and 
 this height should ordinarily not be exceeded. Until recently the 
 question of economy in boilers fired with blast furnace gas has not been 
 considered, but, aside from the economical standpoint, excessive draft 
 should be guarded against in order to lower the upkeep cost. 
   
 Stacks should be made of sufficient height to produce a draft that will 
 develop the maximum capacity required, and this draft decreased 
 proportionately for loads under the maximum by damper regulation. The 
 amount of gas fed to a boiler for any given rating is a fixed quantity 
 and if a draft in excess of that required for that particular rate of 
 operation is supplied, economy is decreased and the wear and tear on the 
 setting is materially increased. Excess air which is drawn in, either 
 through or around the gas burners by an excessive draft, will decrease 
 economy, as in any other class of work. Again, as in oil-fired practice, 
 it is essential on the other hand that a suction be maintained within 
 all parts of the setting, in this case not only to provide against 
 setting deterioration but to protect the operators from leakage of gas 
 which is disagreeable and may be dangerous. Aside from the intensity of 
 the draft, a poor mixture of the gas and air or a "laneing" action may 
 lead to secondary combustion with the possibility of dangerous 
 explosions within the setting, may cause a pulsating action within the 
 setting, may increase the exit temperatures to a point where there is 
 danger of burning out damper boxes, and, in general, is hard on the 
 setting. It is highly essential, therefore, that the furnace be properly 
 constructed to meet the draft which will be available. 
   
 Stacks for Wood-fired Boilers--For boilers using wood as fuel, there is 
 but little data upon which to base stack sizes. The loss of draft 
 through the bed of fuel will vary over limits even wider than in the 
 case of coal, for in this class of fuel the moisture may run from 
 practically 0.0 per cent to over 60 per cent, and the methods of 
 handling and firing are radically different for the different classes of 
 wood (see chapter on Wood-burning Furnaces). As economy is ordinarily of 
 little importance, high stack temperatures may be expected, and often 
 unavoidably large quantities of excess air are supplied due to the 
 method of firing. In general, it may be stated that for this class of 
 fuel the diameter of stacks should be at least as great as for coal-fired 
 boilers, while the height may be slightly decreased. It is far the best 
 plan in designing a stack for boilers using wood fuel to consider each 
 individual set of conditions that exist, rather than try to follow any 
 general rule. 
   
 One factor not to be overlooked in stacks for wood burning is their 
 location. The fine particles of this fuel are often carried unconsumed 
 through the boiler, and where the stack is not on top of the boiler, 
 these particles may accumulate in the base of the stack below the point 
 at which the flue enters. Where there is any air leakage through the 
 base of such a stack, this fuel may become ignited and the stack burned. 
 Where there is a possibility of such action taking place, it is well to 
 line the stack with fire brick for a portion of its height. 
   
 Draft Gauges--The ordinary form of draft gauge, Fig. 35, which consists 
 of a U-tube, containing water, lacks sensitiveness in measuring such 
 slight pressure differences as usually exist, and for that reason gauges 
 which multiply the draft indications are more convenient and are much 
 used. 
 An instrument which has given excellent results is one introduced by Mr. 
 H. Barrus, which multiplies the ordinary indications as many times as 
 
 desired. This is illustrated in Fig. 36, and consists of a U-tube made 
 of one-half inch glass, surmounted by two larger tubes, or chambers, 
 each having a diameter of 2½ inches. Two different liquids which will 
 not mix, and which are of different color, are used, usually alcohol 
 colored red and a certain grade of lubricating oil. The movement of the 
 line of demarcation is proportional to the difference in the areas of 
 the chambers and the U-tube connecting them. The instrument is 
 calibrated by comparison with the ordinary U-tube gauge. 
   
 In the Ellison form of gauge the lower portion of the ordinary U-tube 
 has been replaced by a tube slightly inclined to the horizontal, as 
 shown in Fig. 37. By this arrangement any vertical motion in the 
 right-hand upright tube causes a very much greater travel of the liquid 
 in the inclined tube, thus permitting extremely small variation in the 
 intensity of the draft to be read with facility. 
 The gauge is first leveled by means of the small level attached to it, 
 both legs being open to the atmosphere. The liquid is then adjusted 
 until its meniscus rests at the zero point on the left. The right-hand 
 leg is then connected to the source of draft by means of a piece of 
 rubber tubing. Under these circumstances, a rise of level of one inch in 
 the right-hand vertical tube causes the meniscus in the inclined tube to 
 pass from the point 0 to 1.0. The scale is divided into tenths of an 
 inch, and the sub-divisions are hundredths of an inch. 
   
 The makers furnish a non-drying oil for the liquid, usually a 300 
 degrees test refined petroleum. 
   
 A very convenient form of the ordinary U-tube gauge is known as the 
 Peabody gauge, and it is shown in Fig. 38. This is a small modified 
 U-tube with a sliding scale between the two legs of the U and with 
 connections such that either a draft suction or a draft pressure may be 
 taken. The tops of the sliding pieces extending across the tubes are 
 placed at the bottom of the meniscus and accurate readings in hundredths 
 of an inch are obtained by a vernier. 
   
 
 
 
 EFFICIENCY AND CAPACITY OF BOILERS 
 Two of the most important operating factors entering into the 
 consideration of what constitutes a satisfactory boiler are its 
 efficiency and capacity. The relation of these factors to one another 
 will be considered later under the selection of boilers with reference 
 to the work they are to accomplish. The present chapter deals with the 
 efficiency and capacity only with a view to making clear exactly what is 
 meant by these terms as applied to steam generating apparatus, together 
 with the methods of determining these factors by tests. 
   
 Efficiency--The term "efficiency", specifically applied to a steam 
 boiler, is the ratio of heat absorbed by the boiler in the generation of 
 steam to the total amount of heat available in the medium utilized in 
 securing such generation. When this medium is a solid fuel, such as 
 coal, it is impossible to secure the complete combustion of the total 
 amount fed to the boiler. A portion is bound to drop through the grates 
 where it becomes mixed with the ash and, remaining unburned, produces no 
 heat. Obviously, it is unfair to charge the boiler with the failure to 
 absorb the portion of available heat in the fuel that is wasted in this 
 way. On the other hand, the boiler user must pay for such waste and is 
 justified in charging it against the combined boiler and furnace. Due to 
 this fact, the efficiency of a boiler, as ordinarily stated, is in 
 reality the combined efficiency of the boiler, furnace and grate, and 
   
    Efficiency of boiler,}   Heat absorbed per pound of fuel 
      furnace and grate } = -------------------------------     (31) 
                              Heat value per pound of fuel 
   
   
 The efficiency will be the same whether based on dry fuel or on fuel as 
 fired, including its content of moisture. For example: If the coal 
 contained 3 per cent of moisture, the efficiency would be 
   
        Heat absorbed per pound of dry coal × 0.97 
        ------------------------------------------ 
          Heat value per pound of dry coal × 0.97 
   
 where 0.97 cancels and the formula becomes (31). 
   
 The heat supplied to the boiler is due to the combustible portion of 
 fuel which is actually burned, irrespective of what proportion of the 
 total combustible fired may be.[54] This fact has led to the use of a 
 second efficiency basis on combustible and which is called the 
 efficiency of boiler and furnace[55], namely, 
   
    Efficiency of boiler and furnace[55] 
   
      Heat absorbed per pound of combustible[56] 
    = --------------------------------------     (32) 
        Heat value per pound of combustible 
   
   
 The efficiency so determined is used in comparing the relative 
 performance of boilers, irrespective of the type of grates used under 
 them. If the loss of fuel through the grates could be entirely overcome, 
 the efficiencies obtained by (31) and (32) would obviously be the same. 
 Hence, in the case of liquid and gaseous fuels, where there is 
 practically no waste, these efficiencies are almost identical. 
   
 As a matter of fact, it is extremely difficult, if not impossible, to 
 determine the actual efficiency of a boiler alone, as distinguished from 
 the combined efficiency of boiler, grate and furnace. This is due to the 
 fact that the losses due to excess air cannot be correctly attributed to 
 either the boiler or the furnace, but only to a combination of the 
 complete apparatus. Attempts have been made to devise methods for 
 dividing the losses proportionately between the furnace and the boiler, 
 but such attempts are unsatisfactory and it is impossible to determine 
 the efficiency of a boiler apart from that of a furnace in such a way as 
 to make such determination of any practical value or in a way that might 
 not lead to endless dispute, were the question to arise in the case of a 
 guaranteed efficiency. From the boiler manufacturer's standpoint, the 
 only way of establishing an efficiency that has any value when 
 guarantees are to be met, is to require the grate or stoker manufacturer 
 to make certain guarantees as to minimum CO_{2}, maximum CO, and that 
 the amount of combustible in the ash and blown away with the flue gases 
 does not exceed a certain percentage. With such a guarantee, the 
 efficiency should be based on the combined furnace and boiler. 
   
 General practice, however, has established the use of the efficiency 
 based upon combustible as representing the efficiency of the boiler 
 alone. When such an efficiency is used, its exact meaning, as pointed 
 out on opposite page, should be realized. 
   
 The computation of the efficiencies described on opposite page is best 
 illustrated by example. 
   
 Assume the following data to be determined from an actual boiler trial. 
   
 Steam pressure by gauge, 200 pounds. 
 Feed temperature, 180 degrees. 
 Total weight of coal fired, 17,500 pounds. 
 Percentage of moisture in coal, 3 per cent. 
 Total ash and refuse, 2396 pounds. 
 Total water evaporated, 153,543 pounds. 
 Per cent of moisture in steam, 0.5 per cent. 
 Heat value per pound of dry coal, 13,516. 
 Heat value per pound of combustible, 15,359. 
   
 The factor of evaporation for such a set of conditions is 1.0834. The 
 actual evaporation corrected for moisture in the steam is 152,775 and 
 the equivalent evaporation from and at 212 degrees is, therefore, 
 165,516 pounds. 
   
 The total dry fuel will be 17,500 × .97 = 16,975, and the evaporation 
 per pound of dry fuel from and at 212 degrees will be 165,516 ÷ 16,975 = 
 9.75 pounds. The heat absorbed per pound of dry fuel will, therefore, be 
 9.75 × 970.4 = 9461 B. t. u. Hence, the efficiency by (31) will be 9461 
 ÷ 13,516 = 70.0 per cent. The total combustible burned will be 16,975 
 - 2396 = 14,579, and the evaporation from and at 212 degrees per pound 
 of combustible will be 165,516 ÷ 14,579 = 11.35 pounds. Hence, the 
 efficiency based on combustible from (32) will be (11.35 × 97.04) ÷ 
 15,359 = 71.79.[**should be 71.71] 
   
 For approximate results, a chart may be used to take the place of a 
 computation of efficiency. Fig. 39 shows such a chart based on the 
 evaporation per pound of dry fuel and the heat value per pound of dry 
 fuel, from which efficiencies may be read directly to within one-half of 
 one per cent. It is used as follows: From the intersection of the 
 horizontal line, representing the evaporation per pound of fuel, with 
 the vertical line, representing the heat value per pound, the efficiency 
 is read directly from the diagonal scale of efficiencies. This chart may 
 also be used for efficiency based upon combustible when the evaporation 
 from and at 212 degrees and the heat values are both given in terms of 
 combustible. 
   
 [Graph: Evaporation from and at 212° per Pound of Dry Fuel 
 against B.T.U. per Pound of Dry Fuel 
   
 Fig. 39. Efficiency Chart. Calculated from Marks and Davis Tables 
   
 Diagonal Lines Represent Per Cent Efficiency] 
   
 Boiler efficiencies will vary over a wide range, depending on a great 
 variety of factors and conditions. The highest efficiencies that have 
 been secured with coal are in the neighborhood of 82 per cent and from 
 that point efficiencies are found all the way down to below 50 per cent. 
 Table 59[57] of tests of Babcock & Wilcox boilers under varying 
 conditions of fuel and operation will give an idea of what may be 
 obtained with proper operating conditions. 
   
 The difference between the efficiency secured in any boiler trial and 
 the perfect efficiency, 100 per cent, includes the losses, some of which 
 are unavoidable in the present state of the art, arising in the 
 conversion of the heat energy of the coal to the heat energy in the 
 steam. These losses may be classified as follows: 
   
 1st. Loss due to fuel dropped through the grate. 
   
 2nd. Loss due to unburned fuel which is carried by the draft, as small 
 particles, beyond the bridge wall into the setting or up the stack. 
   
 3rd. Loss due to the utilization of a portion of the heat in heating the 
 moisture contained in the fuel from the temperature of the atmosphere to 
 212 degrees; to evaporate it at that temperature and to superheat the 
 steam thus formed to the temperature of the flue gases. This steam, of 
 course, is first heated to the temperature of the furnace but as it 
 gives up a portion of this heat in passing through the boiler, the 
 superheating to the temperature of the exit gases is the correct degree 
 to be considered. 
   
 4th. Loss due to the water formed and by the burning of the hydrogen in 
 the fuel which must be evaporated and superheated as in item 3. 
   
 5th. Loss due to the superheating of the moisture in the air supplied 
 from the atmospheric temperature to the temperature of the flue gases. 
   
 6th. Loss due to the heating of the dry products of combustion to the 
 temperature of the flue gases. 
   
 7th. Loss due to the incomplete combustion of the fuel when the carbon 
 is not completely consumed but burns to CO instead of CO_{2}. The CO 
 passes out of the stack unburned as a volatile gas capable of further 
 combustion. 
   
 8th. Loss due to radiation of heat from the boiler and furnace settings. 
   
 Obviously a very elaborate test would have to be made were all of the 
 above items to be determined accurately. In ordinary practice it has 
 become customary to summarize these losses as follows, the methods of 
 computing the losses being given in each instance by a typical example: 
   
 (A) Loss due to the heating of moisture in the fuel from the atmospheric 
 temperature to 212 degrees, evaporate it at that temperature and 
 superheat it to the temperature of the flue gases. This in reality is 
 the total heat above the temperature of the air in the boiler room, in 
 one pound of superheated steam at atmospheric pressure at the 
 temperature of the flue gases, multiplied by the percentage of moisture 
 in the fuel. As the total heat above the temperature of the air would 
 have to be computed in each instance, this loss is best expressed by: 
   
 Loss in B. t. u. per pound = W(212-t+970.4+.47(T-212))     (33) 
   
 Where   W = per cent of moisture in coal, 
          t = the temperature of air in the boiler room, 
          T = temperature of the flue gases, 
        .47 = the specific heat of superheated steam at the atmospheric 
              pressure and at the flue gas temperature, 
    (212-t) = B. t. u. necessary to heat one pound of water from the 
              temperature of the boiler room to 212 degrees, 
      970.4 = B. t. u. necessary to evaporate one pound of water at 212 
              degrees to steam at atmospheric pressure, 
 .47(T-212) = B. t. u. necessary to superheat one pound of steam at 
              atmospheric pressure from 212 degrees to temperature T. 
   
 [Illustration: Portion of 15,000 Horse-power Installation of Babcock & 
 Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at 
 the Northumberland, Pa., Plant of the Atlas Portland Cement Co. This 
 Company Operates a Total of 24,000 Horse Power of Babcock & Wilcox 
 Boilers in its Various Plants] 
   
 (B) Loss due to heat carried away in the steam produced by the burning 
 of the hydrogen component of the fuel. In burning, one pound of hydrogen 
 unites with 8 pounds of oxygen to form 9 pounds of steam. Following the 
 reasoning of item (A), therefore, this loss will be: 
   
 Loss in B. t. u. per pound = 9H((212-t)+970.4+.47(T-212))     (34) 
   
 where H = the percentage by weight of hydrogen. 
   
 This item is frequently considered as a part of the unaccounted for 
 loss, where an ultimate analysis of the fuel is not given. 
   
 (C) Loss due to heat carried away by dry chimney gases. This is 
 dependent upon the weight of gas per pound of coal which may be 
 determined by formula (16), page 158. 
   
 Loss in B. t. u. per pound = (T-t)×.24×W. 
   
 Where T and t have values as in (33), 
   
 .24 = specific heat of chimney gases, 
   
 W = weight of dry chimney gas per pound of coal. 
   
 (D) Loss due to incomplete combustion of the carbon content of the fuel, 
 that is, the burning of the carbon to CO instead of CO_{2}. 
   
                                10,150 CO 
 Loss in B. t. u. per pound = C×---------     (35) 
                               CO_{2}+CO 
   
 C = per cent of carbon in coal by ultimate analysis, 
   
 CO and CO_{2} = per cent of CO and CO_{2} by volume from flue gas 
 analysis. 
   
 10,150 = the number of heat units generated by burning to CO_{2} one 
 pound of carbon contained in carbon monoxide. 
   
 (E) Loss due to unconsumed carbon in the ash (it being usually assumed 
 that all the combustible in the ash is carbon). 
   
 Loss in B. t. u. per pound = 
 per cent C × per cent ash × B. t. u. per pound of combustible in the ash 
 (usually taken as 14,600 B. t. u.)     (36) 
   
 The loss incurred in this way is, directly, the carbon in the ash in 
 percentage terms of the total dry coal fired, multiplied by the heat 
 value of carbon. 
   
 To compute this item, which is of great importance in comparing the 
 relative performances of different designs of grates, an analysis of the 
 ash must be available. 
   
 The other losses, namely, items 2, 5 and 8 of the first classification, 
 are ordinarily grouped under one item, as unaccounted for losses, and 
 are obviously the difference between 100 per cent and the sum of the 
 heat utilized and the losses accounted for as given above. Item 5, or 
 the loss due to the moisture in the air, may be readily computed, the 
 moisture being determined from wet and dry bulb thermometer readings, 
 but it is usually disregarded as it is relatively small, averaging, say, 
 one-fifth to one-half of one per cent. Lack of data may, of course, make 
 it necessary to include certain items of the second and ordinary 
 classification in this unaccounted for group. 
   
                        TABLE 57 
   
              DATA FROM WHICH HEAT BALANCE 
                  (TABLE 58) IS COMPUTED 
   
 +------------------------------------------------------+ 
 |+----------------------------------------------------+| 
 ||Steam Pressure by Gauge, Pounds               | 192 || 
 ||Temperature of Feed, Degrees Fahrenheit       | 180 || 
 ||Degrees of Superheat, Degrees Fahrenheit     |115.2|| 
 ||Temperature of Boiler Room, Degrees Fahrenheit| 81 || 
 ||Temperature of Exit Gases, Degrees Fahrenheit | 480 || 
 ||Weight of Coal Used per Hour, Pounds         | 5714|| 
 ||Moisture, Per Cent                           | 1.83|| 
 ||Dry Coal Per Hour, Pounds                     | 5609|| 
 ||Ash and Refuse per Hour, Pounds               | 561|| 
 ||Ash and Refuse (of Dry Coal), Per Cent       |10.00|| 
 ||Actual Evaporation per Hour, Pounds           |57036|| 
 ||           .- C, Per Cent                     |78.57|| 
 ||           | H, Per Cent                     | 5.60|| 
 ||Ultimate   | O, Per Cent                    | 7.02|| 
 ||Analysis -+ N, Per Cent                     | 1.11|| 
 ||Dry Coal   | Ash, Per Cent                   | 6.52|| 
 ||           '- Sulphur, Per Cent               | 1.18|| 
 ||Heat Value per Pound Dry Coal, B. t. u.       |14225|| 
 ||Heat Value per Pound Combustible, B. t. u.   |15217|| 
 ||Combustible in Ash by Analysis, Per Cent     | 17.9|| 
 ||           .- CO_{2}, Per Cent               |14.33|| 
 ||Flue Gas -+ O, Per Cent                     | 4.54|| 
 ||Analysis   | CO, Per Cent                    | 0.11|| 
 ||           '- N, Per Cent                     |81.02|| 
 |+----------------------------------------------+-----+| 
 +------------------------------------------------------+ 
   
 A schedule of the losses as outlined, requires an evaporative test of 
 the boiler, an analysis of the flue gases, an ultimate analysis of the 
 fuel, and either an ultimate or proximate analysis of the ash. As the 
 amount of unaccounted for losses forms a basis on which to judge the 
 accuracy of a test, such a schedule is called a "heat balance". 
   
 A heat balance is best illustrated by an example: Assume the data as 
 given in Table 57 to be secured in an actual boiler test. 
   
 From this data the factor of evaporation is 1.1514 and the evaporation 
 per hour from and at 212 degrees is 65,671 pounds. Hence the evaporation 
 from and at 212 degrees per pound of dry coal is 65,671÷5609 = 11.71 
 pounds. The efficiency of boiler, furnace and grate is: 
   
 (11.71×970.4)÷14,225 = 79.88 per cent. 
   
 The heat losses are: 
   
 (A) Loss due to moisture in coal, 
   
 = .01831 ((212-81)+970.4+.47(480-212)) 
 = 22. B. t. u., 
 = 0.15 per cent. 
   
 (B) The loss due to the burning of hydrogen: 
   
 = 9×.0560((212-81)+970.4+.47(480-212)) 
 = 618 B. t. u., 
 = 4.34 per cent. 
   
 (C) To compute the loss in the heat carried away by dry chimney gases 
 per pound of coal the weight of such gases must be first determined. 
 This weight per pound of coal is: 
   
 (11CO_{2}+8O+7(CO+N)) 
 (-------------------)C 
 (   3(CO_{2}+CO)   ) 
   
 where CO_{2}, O, CO and H are the percentage by volume as determined by 
 the flue gas analysis and C is the percentage by weight of carbon in the 
 dry fuel. Hence the weight of gas per pound of coal will be, 
   
 (11×14.33+8×4.54+7(0.11+81.02)) 
 (-----------------------------)×78.57 = 13.7 pounds. 
 (       3(14.33+0.11)       ) 
   
 Therefore the loss of heat in the dry gases carried up the chimney = 
   
 13.7×0.24(480-81) = 1311 B. t. u., 
                  = 9.22 per cent. 
   
 (D) The loss due to incomplete combustion as evidenced by the presence 
 of CO in the flue gas analysis is: 
   
    0.11 
 ----------×.7857×10,150 = 61. B. t. u., 
 14.33+0.11             = .43 per cent. 
   
 (E) The loss due to unconsumed carbon in the ash: 
   
 The analysis of the ash showed 17.9 per cent to be combustible matter, 
 all of which is assumed to be carbon. The test showed 10.00 of the total 
 dry fuel fired to be ash. Hence 10.00×.179 = 1.79 per cent of the total 
 fuel represents the proportion of this total unconsumed in the ash and 
 the loss due to this cause is 
   
 1.79 per cent × 14,600 = 261 B. t. u., 
                      = 1.83 per cent. 
   
 The heat absorbed by the boilers per pound of dry fuel is 11.71×970.4 = 
 11,363 B. t. u. This quantity plus losses (A), (B), (C), (D) and (E), or 
 11,363+22+618+1311+61+261 = 13,636 B. t. u. accounted for. The heat 
 value of the coal, 14,225 B. t. u., less 13,636 B. t. u., leaves 589 
 t. u., unaccounted for losses, or 4.15 per cent. 
 
   
 The heat balance should be arranged in the form indicated by Table 58. 
   
                                  TABLE 58 
   
                              HEAT BALANCE 
   
 T. U. PER POUND DRY COAL 14,225 
 
   
 +----------------------------------------------------------------------+ 
 |+--------------------------------------------------------------------+| 
 ||                                                 |B. t. u.|Per Cent|| 
 |+--------------------------------------------------+--------+--------+| 
 ||Heat absorbed by Boiler                           | 11,363 | 79.88 || 
 ||Loss due to Evaporation of Moisture in Fuel       |     22 |   0.15 || 
 ||Loss due to Moisture formed by Burning of Hydrogen|   618 |   4.34 || 
 ||Loss due to Heat carried away in Dry Chimney Gases|   1311 |   9.22 || 
 ||Loss due to Incomplete Combustion of Carbon       |     61 |   0.43 || 
 ||Loss due to Unconsumed Carbon in the Ash         |  261 |   1.83 || 
 ||Loss due to Radiation and Unaccounted Losses     |   589 |   4.15 || 
 |+--------------------------------------------------+--------+--------+| 
 ||Total                                             | 14,225 | 100.00 || 
 |+--------------------------------------------------+--------+--------+| 
 +----------------------------------------------------------------------+ 
   
 Application of Heat Balance--A heat balance should be made in connection 
 with any boiler trial on which sufficient data for its computation has 
 been obtained. This is particularly true where the boiler performance 
 has been considered unsatisfactory. The distribution of the heat is thus 
 determined and any extraordinary loss may be detected. Where accurate 
 data for computing such a heat balance is not available, such a 
 calculation based on certain assumptions is sometimes sufficient to 
 indicate unusual losses. 
   
 The largest loss is ordinarily due to the chimney gases, which depends 
 directly upon the weight of the gas and its temperature leaving the 
 boiler. As pointed out in the chapter on flue gas analysis, the lower 
 limit of the weight of gas is fixed by the minimum air supplied with 
 which complete combustion may be obtained. As shown, where this supply 
 is unduly small, the loss caused by burning the carbon to CO instead of 
 to CO_{2} more than offsets the gain in decreasing the weight of gas. 
   
 The lower limit of the stack temperature, as has been shown in the 
 chapter on draft, is more or less fixed by the temperature necessary to 
 create sufficient draft suction for good combustion. With natural draft, 
 this lower limit is probably between 400 and 450 degrees. 
   
 Capacity--Before the capacity of a boiler is considered, it is necessary 
 to define the basis to which such a term may be referred. Such a basis 
 is the so-called boiler horse power. 
   
 The unit of motive power in general use among steam engineers is the 
 "horse power" which is equivalent to 33,000 foot pounds per minute. 
 Stationary boilers are at the present time rated in horse power, though 
 such a basis of rating may lead and has often led to a misunderstanding. 
 _Work_, as the term is used in mechanics, is the overcoming of 
 resistance through space, while _power_ is the _rate_ of work or the 
 amount done per unit of time. As the operation of a boiler in service 
 implies no motion, it can produce no power in the sense of the term as 
 understood in mechanics. Its operation is the generation of steam, which 
 acts as a medium to convey the energy of the fuel which is in the form 
 of heat to a prime mover in which that heat energy is converted into 
 energy of motion or work, and power is developed. 
   
 If all engines developed the same amount of power from an equal amount 
 of heat, a boiler might be designated as one having a definite horse 
 power, dependent upon the amount of engine horse power its steam would 
 develop. Such a statement of the rating of boilers, though it would 
 still be inaccurate, if the term is considered in its mechanical sense, 
 could, through custom, be interpreted to indicate that a boiler was of 
 the exact capacity required to generate the steam necessary to develop a 
 definite amount of horse power in an engine. Such a basis of rating, 
 however, is obviously impossible when the fact is considered that the 
 amount of steam necessary to produce the same power in prime movers of 
 different types and sizes varies over very wide limits. 
   
 To do away with the confusion resulting from an indefinite meaning of 
 the term boiler horse power, the Committee of Judges in charge of the 
 boiler trials at the Centennial Exposition, 1876, at Philadelphia, 
 ascertained that a good engine of the type prevailing at the time 
 required approximately 30 pounds of steam per hour per horse power 
 developed. In order to establish a relation between the engine power and 
 the size of a boiler required to develop that power, they recommended 
 that an evaporation of 30 pounds of water from an initial temperature of 
 100 degrees Fahrenheit to steam at 70 pounds gauge pressure be 
 considered as _one boiler horse power_. This recommendation has been 
 generally accepted by American engineers as a standard, and when the 
 term boiler horse power is used in connection with stationary 
 boilers[58] throughout this country,[59] without special definition, it 
 is understood to have this meaning. 
   
 Inasmuch as an equivalent evaporation from and at 212 degrees Fahrenheit 
 is the generally accepted basis of comparison[60], it is now customary 
 to consider the standard boiler horse power as recommended by the 
 Centennial Exposition Committee, in terms of equivalent evaporation from 
 and at 212 degrees. This will be 30 pounds multiplied by the factor of 
 evaporation for 70 pounds gauge pressure and 100 degrees feed 
 temperature, or 1.1494. 30 × 1.1494 = 34.482, or approximately 34.5 
 pounds. Hence, _one boiler horse power is equal to an evaporation of 
 34.5 pounds of water per hour from and at 212 degrees Fahrenheit_. The 
 term boiler horse power, therefore, is clearly a measure of evaporation 
 and not of power. 
   
 A method of basing the horse power rating of a boiler adopted by boiler 
 manufacturers is that of heating surfaces. Such a method is absolutely 
 arbitrary and changes in no way the definition of a boiler horse power 
 just given. It is simply a statement by the manufacturer that his 
 product, under ordinary operating conditions or conditions which may be 
 specified, will evaporate 34.5 pounds of water from and at 212 degrees 
 per definite amount of heating surface provided. The amount of heating 
 surface that has been considered by manufacturers capable of evaporating 
 34.5 pounds from and at 212 degrees per hour has changed from time to 
 time as the art has progressed. At the present time 10 square feet of 
 heating surface is ordinarily considered the equivalent of one boiler 
 horse power among manufacturers of stationary boilers. In view of the 
 arbitrary nature of such rating and of the widely varying rates of 
 evaporation possible per square foot of heating surface with different 
 boilers and different operating conditions, such a basis of rating has 
 in reality no particular bearing on the question of horse power and 
 should be considered merely as a convenience. 
   
 The whole question of a unit of boiler capacity has been widely 
 discussed with a view to the adoption of a standard to which there would 
 appear to be a more rational and definite basis. Many suggestions have 
 been offered as to such a basis but up to the present time there has 
 been none which has met with universal approval or which would appear 
 likely to be generally adopted. 
   
 With the meaning of boiler horse power as given above, that is, a 
 measure of evaporation, it is evident that the capacity of a boiler is a 
 measure of the power it can develop expressed in boiler horse power. 
 Since it is necessary, as stated, for boiler manufacturers to adopt a 
 standard for reasons of convenience in selling, the horse power for 
 which a boiler is sold is known as its normal rated capacity. 
   
 The efficiency of a boiler and the maximum capacity it will develop can 
 be determined accurately only by a boiler test. The standard methods of 
 conducting such tests are given on the following pages, these methods 
 being the recommendations of the Power Test Committee of the American 
 Society of Mechanical Engineers brought out in 1913.[61] Certain changes 
 have been made to incorporate in the boiler code such portions of the 
 "Instructions Regarding Tests in General" as apply to boiler testing. 
 Methods of calculation and such matter as are treated in other portions 
 of the book have been omitted from the code as noted. 
 OBJECT 
 
   
   
 Ascertain the specific object of the test, and keep this in view not 
 only in the work of preparation, but also during the progress of the 
 test, and do not let it be obscured by devoting too close attention to 
 matters of minor importance. Whatever the object of the test may be, 
 accuracy and reliability must underlie the work from beginning to end. 
   
 If questions of fulfillment of contract are involved, there should be a 
 clear understanding between all the parties, preferably in writing, as 
 to the operating conditions which should obtain during the trial, and as 
 to the methods of testing to be followed, unless these are already 
 expressed in the contract itself. 
   
 Among the many objects of performance tests, the following may be noted: 
   
    Determination of capacity and efficiency, and how these compare 
    with standard or guaranteed results. 
   
    Comparison of different conditions or methods of operation. 
   
    Determination of the cause of either inferior or superior 
    results. 
   
    Comparison of different kinds of fuel. 
   
    Determination of the effect of changes of design or proportion 
    upon capacity or efficiency, etc. 
   
   
   
 PREPARATIONS 
 
   
   
 _(A) Dimensions:_ 
   
 Measure the dimensions of the principal parts of the apparatus to be 
 tested, so far as they bear on the objects in view, or determine these 
 from correct working drawings. Notice the general features of the same, 
 both exterior and interior, and make sketches, if needed, to show 
 unusual points of design. 
   
    The dimensions of the heating surfaces of boilers and 
    superheaters to be found are those of surfaces in contact with 
    the fire or hot gases. The submerged surfaces in boilers at the 
    mean water level should be considered as water-heating surfaces, 
    and other surfaces which are exposed to the gases as 
    superheating surfaces. 
   
   
 _(B) Examination of Plant:_ 
   
 Make a thorough examination of the physical condition of all parts of 
 the plant or apparatus which concern the object in view, and record the 
 conditions found, together with any points in the matter of operation 
 which bear thereon. 
   
    In boilers, examine for leakage of tubes and riveted or other 
    metal joints. Note the condition of brick furnaces, grates and 
    baffles. Examine brick walls and cleaning doors for air leaks, 
    either by shutting the damper and observing the escaping smoke 
    or by candle-flame test. Determine the condition of heating 
    surfaces with reference to exterior deposits of soot and 
    interior deposits of mud or scale. 
   
    See that the steam main is so arranged that condensed and 
    entrained water cannot flow back into the boiler. 
   
 If the object of the test is to determine the highest efficiency or 
 capacity obtainable, any physical defects, or defects of operation, 
 tending to make the result unfavorable should first be remedied; all 
 foul parts being cleaned, and the whole put in first-class condition. 
 If, on the other hand, the object is to ascertain the performance under 
 existing conditions, no such preparation is either required or desired. 
   
   
 _(C) General Precautions against Leakage:_ 
   
 In steam tests make sure that there is no leakage through blow-offs, 
 drips, etc., or any steam or water connections of the plant or apparatus 
 undergoing test, which would in any way affect the results. All such 
 connections should be blanked off, or satisfactory assurance should be 
 obtained that there is leakage neither out nor in. This is a most 
 important matter, and no assurance should be considered satisfactory 
 unless it is susceptible of absolute demonstration. 
   
   
   
 FUEL 
 
   
   
 Determine the character of fuel to be used.[62] For tests of maximum 
 efficiency or capacity of the boiler to compare with other boilers, the 
 coal should be of some kind which is commercially regarded as a standard 
 for the locality where the test is made. 
   
    In the Eastern States the standards thus regarded for 
    semi-bituminous coals are Pocahontas (Va. and W. Va.) and New 
    River (W. Va.); for anthracite coals those of the No. 1 
    buckwheat size, fresh-mined, containing not over 13 per cent ash 
    by analysis; and for bituminous coals, Youghiogheny and 
    Pittsburgh coals. In some sections east of the Allegheny 
    Mountains the semi-bituminous Clearfield (Pa.) and Cumberland 
    (Md.) are also considered as standards. These coals when of good 
    quality possess the essentials of excellence, adaptability to 
    various kinds of furnaces, grates, boilers, and methods of 
    firing required, besides being widely distributed and generally 
    accessible in the Eastern market. There are no special grades of 
    coal mined in the Western States which are widely and generally 
    considered as standards for testing purposes; the best coal 
    obtainable in any particular locality being regarded as the 
    standard of comparison. 
   
 A coal selected for maximum efficiency and capacity tests, should be the 
 best of its class, and especially free from slagging and unusual 
 clinker-forming impurities. 
   
 For guarantee and other tests with a specified coal containing not more 
 than a certain amount of ash and moisture, the coal selected should not 
 be higher in ash and in moisture than the stated amounts, because any 
 increase is liable to reduce the efficiency and capacity more than the 
 equivalent proportion of such increase. 
   
 The size of the coal, especially where it is of the anthracite class, 
 should be determined by screening a suitable sample. 
   
   
   
 APPARATUS AND INSTRUMENTS[63] 
 
   
   
 The apparatus and instruments required for boiler tests are: 
   
    (A) Platform scales for weighing coal and ashes. 
   
    (B) Graduated scales attached to the water glasses. 
   
    (C) Tanks and platform scales for weighing water (or water 
    meters calibrated in place). Wherever practicable the feed water 
    should be weighed, especially for guarantee tests. The most 
    satisfactory and reliable apparatus for this purpose consists of 
    one or more tanks each placed on platform scales, these being 
    elevated a sufficient distance above the floor to empty into a 
    receiving tank placed below, the latter being connected to the 
    feed pump. Where only one weighing tank is used the receiving 
    tank should be of larger size than the weighing tank, to afford 
    sufficient reserve supply to the pump while the upper tank is 
    filling. If a single weighing tank is used it should preferably 
    be of such capacity as to require emptying not oftener than 
    every 5 minutes. If two or more are used the intervals between 
    successive emptyings should not be less than 3 minutes. 
   
    (D) Pressure gauges, thermometers, and draft gauges. 
   
    (E) Calorimeters for determining the calorific value of fuel and 
    the quality of steam. 
   
    (F) Furnaces pyrometers. 
   
    (G) Gas analyzing apparatus. 
   
   
   
 OPERATING CONDITIONS 
 
   
   
 Determine what the operating conditions and method of firing should be 
 to conform to the object in view, and see that they prevail throughout 
 the trial, as nearly as possible. 
   
    Where uniformity in the rate of evaporation is required, 
    arrangement can be usually made to dispose of the steam so that 
    this result can be attained. In a single boiler it may be 
    accomplished by discharging steam through a waste pipe and 
    regulating the amount by means of a valve. In a battery of 
    boilers, in which only one is tested, the draft may be regulated 
    on the remaining boilers to meet the varying demands for steam, 
    leaving the test boiler to work under a steady rate of 
    evaporation. 
   
   
   
 DURATION 
 
   
   
 The duration of tests to determine the efficiency of a hand-fired 
 boiler, should be 10 hours of continuous running, or such time as may be 
 required to burn a total of 250 pounds of coal per square foot of grate. 
   
 In the case of a boiler using a mechanical stoker, the duration, where 
 practicable, should be at least 24 hours. If the stoker is of a type 
 that permits the quantity and condition of the fuel bed at beginning and 
 end of the test to be accurately estimated, the duration may be reduced 
 to 10 hours, or such time as may be required to burn the above noted 
 total of 250 pounds per square foot. 
   
    In commercial tests where the service requires continuous 
    operation night and day, with frequent shifts of firemen, the 
    duration of the test, whether the boilers are hand fired or 
    stoker fired, should be at least 24 hours. Likewise in 
    commercial tests, either of a single boiler or of a plant of 
    several boilers, which operate regularly a certain number of 
    hours and during the balance of the day the fires are banked, 
    the duration should not be less than 24 hours. 
   
    The duration of tests to determine the maximum evaporative 
    capacity of a boiler, without determining the efficiency, should 
    not be less than 3 hours. 
   
   
   
 STARTING AND STOPPING 
 
   
   
 The conditions regarding the temperature of the furnace and boiler, the 
 quantity and quality of the live coal and ash on the grates, the water 
 level, and the steam pressure, should be as nearly as possible the same 
 at the end as at the beginning of the test. 
   
 To secure the desired equality of conditions with hand-fired boilers, 
 the following method should be employed: 
   
    The furnace being well heated by a preliminary run, burn the 
    fire low, and thoroughly clean it, leaving enough live coal 
    spread evenly over the grate (say 2 to 4 inches),[64] to serve 
    as a foundation for the new fire. Note quickly the thickness of 
    the coal bed as nearly as it can be estimated or measured; also 
    the water level,[65] the steam pressure, and the time, and 
    record the latter as the starting time. Fresh coal should then 
    be fired from that weighed for the test, the ashpit throughly 
    cleaned, and the regular work of the test proceeded with. Before 
    the end of the test the fire should again be burned low and 
    cleaned in such a manner as to leave the same amount of live 
    coal on the grate as at the start. When this condition is 
    reached, observe quickly the water level,[65] the steam 
    pressure, and the time, and record the latter as the stopping 
    time. If the water level is not the same as at the beginning a 
    correction should be made by computation, rather than by feeding 
    additional water after the final readings are taken. Finally 
    remove the ashes and refuse from the ashpit. In a plant 
    containing several boilers where it is not practicable to clean 
    them simultaneously, the fires should be cleaned one after the 
    other as rapidly as may be, and each one after cleaning charged 
    with enough coal to maintain a thin fire in good working 
    condition. After the last fire is cleaned and in working 
    condition, burn all the fires low (say 4 to 6 inches), note 
    quickly the thickness of each, also the water levels, steam 
    pressure, and time, which last is taken as the starting time. 
    Likewise when the time arrives for closing the test, the fires 
    should be quickly cleaned one by one, and when this work is 
    completed they should all be burned low the same as the start, 
    and the various observations made as noted. In the case of a 
    large boiler having several furnace doors requiring the fire to 
    be cleaned in sections one after the other, the above directions 
    pertaining to starting and stopping in a plant of several 
    boilers may be followed. 
   
 To obtain the desired equality of conditions of the fire when a 
 mechanical stoker other than a chain grate is used, the procedure should 
 be modified where practicable as follows: 
   
    Regulate the coal feed so as to burn the fire to the low 
    condition required for cleaning. Shut off the coal-feeding 
    mechanism and fill the hoppers level full. Clean the ash or dump 
    plate, note quickly the depth and condition of the coal on the 
    grate, the water level,[66] the steam pressure, and the time, 
    and record the latter as the starting time. Then start the 
    coal-feeding mechanism, clean the ashpit, and proceed with the 
    regular work of the test. 
   
    When the time arrives for the close of the test, shut off the 
    coal-feeding mechanism, fill the hoppers and burn the fire to 
    the same low point as at the beginning. When this condition is 
    reached, note the water level, the steam pressure, and the time, 
    and record the latter as the stopping time. Finally clean the 
    ashplate and haul the ashes. 
   
    In the case of chain grate stokers, the desired operating 
    conditions should be maintained for half an hour before starting 
    a test and for a like period before its close, the height of the 
    throat plate and the speed of the grate being the same during 
    both of these periods. 
   
   
   
 RECORDS 
 
   
   
 A log of the data should be entered in notebooks or on blank sheets 
 suitably prepared in advance. This should be done in such manner that 
 the test may be divided into hourly periods, or if necessary, periods of 
 less duration, and the leading data obtained for any one or more periods 
 as desired, thereby showing the degree of uniformity obtained. 
   
 Half-hourly readings of the instruments are usually sufficient. If there 
 are sudden and wide fluctuations, the readings in such cases should be 
 taken every 15 minutes, and in some instances oftener. 
   
    The coal should be weighed and delivered to the firemen in 
    portions sufficient for one hour's run, thereby ascertaining the 
    degree of uniformity of firing. An ample supply of coal should 
    be maintained at all times, but the quantity on the floor at the 
    end of each hour should be as small as practicable, so that the 
    same may be readily estimated and deducted from the total 
    weight. 
   
    The records should be such as to ascertain also the consumption 
    of feed water each hour and thereby determine the degree of 
    uniformity of evaporation. 
   
   
   
 QUALITY OF STEAM[67] 
 
   
   
 If the boiler does not produce superheated steam the percentage of 
 moisture in the steam should be determined by the use of a throttling or 
 separating calorimeter. If the boiler has superheating surface, the 
 temperature of the steam should be determined by the use of a 
 thermometer inserted in a thermometer well. 
   
 For saturated steam construct a sampling pipe or nozzle made of one-half 
 inch iron pipe and insert it in the steam main at a point where the 
 entrained moisture is likely to be most thoroughly mixed. The inner end 
 of the pipe, which should extend nearly across to the opposite side of 
 the main, should be closed and interior portion perforated with not less 
 than twenty one-eighth inch holes equally distributed from end to end 
 and preferably drilled in irregular or spiral rows, with the first hole 
 not less than half an inch from the wall of the pipe. 
   
    The sampling pipe should not be placed near a point where water 
    may pocket or where such water may effect the amount of moisture 
  contained in the sample. Where non-return valves are used, or 
    there are horizontal connections leading from the boiler to a 
    vertical outlet, water may collect at the lower end of the 
    uptake pipe and be blown upward in a spray which will not be 
    carried away by the steam owing to a lack of velocity. A sample 
    taken from the lower part of this pipe will show a greater 
    amount of moisture than a true sample. With goose-neck 
    connections a small amount of water may collect on the bottom of 
    the pipe near the upper end where the inclination is such that 
    the tendency to flow backward is ordinarily counterbalanced by 
    the flow of steam forward over its surface; but when the 
    velocity momentarily decreases the water flows back to the lower 
    end of the goose-neck and increases the moisture at that point, 
    making it an undesirable location for sampling. In any case it 
    must be borne in mind that with low velocities the tendency is 
    for drops of entrained water to settle to the bottom of the 
    pipe, and to be temporarily broken up into spray whenever an 
    abrupt bend or other disturbance is met. 
   
 If it is necessary to attach the sampling nozzle at a point near the end 
 of a long horizontal run, a drip pipe should be provided a short 
 distance in front of the nozzle, preferably at a pocket formed by some 
 fitting and the water running along the bottom of the main drawn off, 
 weighed, and added to the moisture shown by the calorimeter; or, better, 
 a steam separator should be installed at the point noted. 
   
 In testing a stationary boiler the sampling pipe should be located as 
 near as practicable to the boiler, and the same is true as regards the 
 thermometer well when the steam is superheated. In an engine or turbine 
 test these locations should be as near as practicable to throttle valve. 
 In the test of a plant where it is desired to get complete information, 
 especially where the steam main is unusually long, sampling nozzles or 
 thermometer wells should be provided at both points, so as to obtain 
 data at either point as may be required. 
   
   
   
 SAMPLING AND DRYING COAL 
 
   
   
 During the progress of test the coal should be regularly sampled for the 
 purpose of analysis and determination of moisture. 
   
 Select a representative shovelful from each barrow-load as it is drawn 
 from the coal pile or other source of supply, and store the samples in a 
 cool place in a covered metal receptacle. When all the coal has thus 
 been sampled, break up the lumps, thoroughly mix the whole quantity, and 
 finally reduce it by the process of repeated quartering and crushing to 
 a sample weighing about 5 pounds, the largest pieces being about the 
 size of a pea. From this sample two one-quart air-tight glass fruit 
 jars, or other air-tight vessels, are to be promptly filled and 
 preserved for subsequent determinations of moisture, calorific value, 
 and chemical composition. These operations should be conducted where the 
 air is cool and free from drafts. 
   
 [Illustration: 3460 Horse-power Installation of Babcock & Wilcox Boilers 
 at the Chicago, Ill., Shops of the Chicago and Northwestern Ry. Co.] 
   
 When the sample lot of coal has been reduced by quartering to, say, 100 
 pounds, a portion weighing, say, 15 to 20 pounds should be withdrawn for 
 the purpose of immediate moisture determination. This is placed in a 
 shallow iron pan and dried on the hot iron boiler flue for at least 12 
 hours, being weighed before and after drying on scales reading to 
 quarter ounces. 
   
 The moisture thus determined is approximately reliable for anthracite 
 and semi-bituminous coals, but not for coals containing much inherent 
 moisture. For such coals, and for all absolutely reliable determinations 
 the method to be pursued is as follows: 
   
    Take one of the samples contained in the glass jars, and subject 
  it to a thorough air drying, by spreading it in a thin layer and 
    exposing it for several hours to the atmosphere of a warm room, 
    weighing it before and after, thereby determining the quantity 
    of surface moisture it contains.[68] Then crush the whole of it 
    by running it through an ordinary coffee mill or other suitable 
    crusher adjusted so as to produce somewhat coarse grains (less 
    than 1/16 inch), thoroughly mix the crushed sample, select from 
    it a portion of from 10 to 50 grams,[69] weigh it in a balance 
    which will easily show a variation as small as 1 part in 1000, 
    and dry it for one hour in an air or sand bath at a temperature 
    between 240 and 280 degrees Fahrenheit. Weigh it and record the 
    loss, then heat and weigh again until the minimum weight has 
    been reached. The difference between the original and the 
    minimum weight is the moisture in the air-dried coal. The sum of 
    the moisture thus found and that of the surface moisture is the 
    total moisture. 
   
   
   
 ASHES AND REFUSE 
 
   
   
 The ashes and refuse withdrawn from the furnace and ashpit during the 
 progress of the test and at its close should be weighed so far as 
 possible in a dry state. If wet the amount of moisture should be 
 ascertained and allowed for, a sample being taken and dried for this 
 purpose. This sample may serve also for analysis and the determination 
 of unburned carbon and fusing temperature. 
   
 The method above described for sampling coal may also be followed for 
 obtaining a sample of the ashes and refuse. 
   
   
   
 CALORIFIC TESTS AND ANALYSES OF COAL 
 
   
   
 The quality of the fuel should be determined by calorific tests and 
 analysis of the coal sample above referred to.[70] 
   
   
   
 ANALYSES OF FLUE GASES 
 
   
   
 For approximate determinations of the composition of the flue gases, the 
 Orsat apparatus, or some modification thereof, should be employed. If 
 momentary samples are obtained the analyses should be made as frequently 
 as possible, say, every 15 to 30 minutes, depending on the skill of the 
 operator, noting at the time the sample is drawn the furnace and firing 
 conditions. If the sample drawn is a continuous one, the intervals may 
 be made longer. 
   
   
   
 SMOKE OBSERVATIONS[71] 
 
   
   
 In tests of bituminous coals requiring a determination of the amount of 
 smoke produced, observations should be made regularly throughout the 
 trial at intervals of 5 minutes (or if necessary every minute), noting 
 at the same time the furnace and firing conditions. 
   
   
   
 CALCULATION OF RESULTS 
 
   
   
 The methods to be followed in expressing and calculating those results 
 which are not self-evident are explained as follows: 
   
    (A) _Efficiency._ The "efficiency of boiler, furnace and 
    grate" is the relation between the heat absorbed per pound of 
    coal fired, and the calorific value of one pound of coal. 
   
    The "efficiency of boiler and furnace" is the relation between 
    the heat absorbed per pound of combustible burned, and the 
    calorific value of one pound of combustible. This expression of 
    efficiency furnishes a means for comparing one boiler and 
    furnace with another, when the losses of unburned coal due to 
    grates, cleanings, etc., are eliminated. 
   
    The "combustible burned" is determined by subtracting from the 
    weight of coal supplied to the boiler, the moisture in the coal, 
    the weight of ash and unburned coal withdrawn from the furnace 
    and ashpit, and the weight of dust, soot, and refuse, if any, 
    withdrawn from the tubes, flues, and combustion chambers, 
    including ash carried away in the gases, if any, determined from 
    the analysis of coal and ash. The "combustible" used for 
    determining the calorific value is the weight of coal less the 
    moisture and ash found by analysis. 
   
    The "heat absorbed" per pound of coal, or combustible, is 
    calculated by multiplying the equivalent evaporation from and at 
    212 degrees per pound of coal or combustible by 970.4. 
   
 Other items in this section which have been treated elsewhere are: 
   
    (B) Corrections for moisture in steam. 
   
    (C) Correction for live steam used. 
   
    (D) Equivalent evaporation. 
   
    (E) Heat balance. 
   
    (F) Total heat of combustion of coal. 
   
    (G) Air for combustion and the methods recommended for 
    calculating these results are in accordance with those described 
    in different portions of this book. 
   
   
   
 DATA AND RESULTS 
 
   
   
 The data and results should be reported in accordance with either the 
 short form or the complete form, adding lines for data not provided for, 
 or omitting those not required, as may conform to the object in view. 
   
   
   
 CHART 
 
   
   
 In trials having for an object the determination and exposition of the 
 complete boiler performance, the entire log of readings and data should 
 be plotted on a chart and represented graphically. 
   
   
   
 TESTS WITH OIL AND GAS FUELS 
 
   
   
 Tests of boilers using oil or gas for fuel should accord with the rules 
 here given, excepting as they are varied to conform to the particular 
 characteristics of the fuel. The duration in such cases may be reduced, 
 and the "flying" method of starting and stopping employed. 
   
    The table of data and results should contain items stating 
    character of furnace and burner, quality and composition of oil 
    or gas, temperature of oil, pressure of steam used for 
    vaporizing and quantity of steam used for both vaporizing and 
    for heating. 
   
              TABLE DATA AND RESULTS OF EVAPORATIVE TEST 
                        SHORT FORM, CODE OF 1912 
   
 1 Test of.................boiler located at................................ 
        to determine...............conducted by.............................. 
 2 Kind of furnace.......................................................... 
 3 Grate surface.................................................square feet 
 4 Water-heating surface.........................................square feet 
 5 Superheating surface..........................................square feet 
 6 Date..................................................................... 
 7 Duration............................................................hours 
 8 Kind and size of coal.................................................... 
   
 AVERAGE PRESSURES, TEMPERATURES, ETC. 
   
 9 Steam pressure by gauge............................................pounds 
 10 Temperature of feed water entering boiler.........................degrees 
 11 Temperature of escaping gases leaving boiler......................degrees 
 12 Force of draft between damper and boiler...........................inches 
 13 Percentage of moisture in steam, 
      or number degrees of superheating..................per cent or degrees 
   
 TOTAL QUANTITIES 
   
 14 Weight of coal as fired[72]........................................pounds 
 15 Percentage of moisture in coal...................................per cent 
 16 Total weight of dry coal consumed..................................pounds 
 17 Total ash and refuse...............................................pounds 
 18 Percentage of ash and refuse in dry coal.........................per cent 
 19 Total weight of water fed to the boiler[73]........................pounds 
 20 Total water evaporated, corrected for moisture in steam............pounds 
 21 Total equivalent evaporation from and at 212 degrees...............pounds 
   
 HOURLY QUANTITIES AND RATES 
   
 22 Dry coal consumed per hour.........................................pounds 
 23 Dry coal per square feet of grate surface per hour.................pounds 
 24 Water evaporated per hour corrected for quality of steam...........pounds 
 25 Equivalent evaporation per hour from and at 212 degrees............pounds 
 26 Equivalent evaporation per hour from and at 212 degrees 
      per square foot of water-heating surface........................pounds 
   
 CAPACITY 
   
 27 Evaporation per hour from and at 212 degrees (same as Line 25).....pounds 
 28 Boiler horse power developed (Item 27÷34½).............boiler horse power 
 29 Rated capacity, in evaporation from and at 212 degrees per hour....pounds 
 30 Rated boiler horse power...............................boiler horse power 
 31 Percentage of rated capacity developed...........................per cent 
   
 ECONOMY RESULTS 
   
 32 Water fed per pound of coal fired (Item 19÷Item 14)................pounds 
 33 Water evaporated per pound of dry coal (Item 20÷Item 16)...........pounds 
 34 Equivalent evaporation from and at 212 degrees per pound 
      of dry coal (Item 21÷Item 16)...................................pounds 
 35 Equivalent evaporation from and at 212 degrees per pound 
      of combustible [Item 21÷(Item 16-Item 17)]......................pounds 
   
 EFFICIENCY 
   
 36 Calorific value of one pound of dry coal.........................B. t. u. 
 37 Calorific value of one pound of combustible......................B. t. u. 
   
                                            (     Item 34×970.4) 
 38 Efficiency of boiler, furnace and grate (100 × -------------)....per cent 
                                           (         Item 36   ) 
   
                                    (     Item 35×970.4) 
 39 Efficiency of boiler and furnace (100 × -------------)...........per cent 
                                    (         Item 37   ) 
   
 COST OF EVAPORATION 
   
 40 Cost of coal per ton of......pounds delivered in boiler room......dollars 
 41 Cost of coal required for evaporating 1000 pounds of water 
      from and at 212 degrees........................................dollars 
 
 
 
 THE SELECTION OF BOILERS WITH A CONSIDERATION OF THE FACTORS DETERMINING SUCH SELECTION 
 The selection of steam boilers is a matter to which the most careful 
 thought and attention may be well given. Within the last twenty years, 
 radical changes have taken place in the methods and appliances for the 
 generation and distribution of power. These changes have been made 
 largely in the prime movers, both as to type and size, and are best 
 illustrated by the changes in central station power-plant practice. It 
 is hardly within the scope of this work to treat of power-plant design 
 and the discussion will be limited to a consideration of the boiler end 
 of the power plant. 
   
 As stated, the changes have been largely in prime movers, the steam 
 generating equipment having been considered more or less of a standard 
 piece of apparatus whose sole function is the transfer of the heat 
 liberated from the fuel by combustion to the steam stored or circulated 
 in such apparatus. When the fact is considered that the cost of steam 
 generation is roughly from 65 to 80 per cent of the total cost of power 
 production, it may be readily understood that the most fruitful field 
 for improvement exists in the boiler end of the power plant. The 
 efficiency of the plant as a whole will vary with the load it carries 
 and it is in the boiler room where such variation is largest and most 
 subject to control. 
   
 The improvements to be secured in the boiler room results are not simply 
 a matter of dictation of operating methods. The securing of perfect 
 combustion, with the accompanying efficiency of heat transfer, while 
 comparatively simple in theory, is difficult to obtain in practical 
 operation. This fact is perhaps best exemplified by the difference 
 between test results and those obtained in daily operation even under 
 the most careful supervision. This difference makes it necessary to 
 establish a standard by which operating results may be judged, a 
 standard not necessarily that which might be possible under test 
 conditions but one which experiment shows can be secured under the very 
 best operating conditions. 
   
 The study of the theory of combustion, draft, etc., as already given, 
 will indicate that the question of efficiency is largely a matter of 
 proper relation between fuel, furnace and generator. While the 
 possibility of a substantial saving through added efficiency cannot be 
 overlooked, the boiler design of the future must, even more than in the 
 past, be considered particularly from the aspect of reliability and 
 simplicity. A flexibility of operation is necessary as a guarantee of 
 continuity of service. 
   
 In view of the above, before the question of the selection of boilers 
 can be taken up intelligently, it is necessary to consider the subjects 
 of boiler efficiency and boiler capacity, together with their relation 
 to each other. 
   
 The criterion by which the efficiency of a boiler plant is to be judged 
 is the cost of the production of a definite amount of steam. Considered 
 in this sense, there must be included in the efficiency of a boiler 
 plant the simplicity of operation, flexibility and reliability of the 
 boiler used. The items of repair and upkeep cost are often high because 
 of the nature of the service. The governing factor in these items is 
 unquestionably the type of boiler selected. 
   
 The features entering into the plant efficiency are so numerous that it 
 is impossible to make a statement as to a means of securing the highest 
 efficiency which will apply to all cases. Such efficiency is to be 
 secured by the proper relation of fuel, furnace and boiler heating 
 surface, actual operating conditions, which allow the approaching of the 
 potential efficiencies made possible by the refinement of design, and a 
 systematic supervision of the operation assisted by a detailed record of 
 performances and conditions. The question of supervision will be taken 
 up later in the chapter on "Operation and Care of Boilers". 
   
 The efficiencies that may be expected from the combination of 
 well-designed boilers and furnaces are indicated in Table 59 in which 
 are given a number of tests with various fuels and under widely 
 different operating conditions. 
   
 It is to be appreciated that the results obtained as given in this table 
 are practically all under test conditions. The nearness with which 
 practical operating conditions can approach these figures will depend 
 upon the character of the supervision of the boiler room and the 
 intelligence of the operating crew. The size of the plant will 
 ordinarily govern the expense warranted in securing the right sort of 
 supervision. 
   
 The bearing that the type of boiler has on the efficiency to be expected 
 can only be realized from a study of the foregoing chapters. 
   
 Capacity--Capacity, as already defined, is the ability of a definite 
 amount of boiler-heating surface to generate steam. Boilers are 
 ordinarily purchased under a manufacturer's specification, which rates a 
 boiler at a nominal rated horse power, usually based on 10 square feet 
 of heating surface per horse power. Such a builders' rating is 
 absolutely arbitrary and implies nothing as to the limiting amount of 
 water that this amount of heating surface will evaporate. It does not 
 imply that the evaporation of 34.5 pounds of water from and at 212 
 degrees with 10 square feet of heating surface is the limit of the 
 capacity of the boiler. Further, from a statement that a boiler is of a 
 certain horse power on the manufacturer's basis, it is not to be 
 understood that the boiler is in any state of strain when developing 
 more than its rated capacity. 
   
 Broadly stated, the evaporative capacity of a certain amount of heating 
 surface in a well-designed boiler, that is, the boiler horse power it is 
 capable of producing, is limited only by the amount of fuel that can be 
 burned under the boiler. While such a statement would imply that the 
 question of capacity to be secured was simply one of making an 
 arrangement by which sufficient fuel could be burned under a definite 
 amount of heating surface to generate the required amount of steam, 
 there are limiting features that must be weighed against the advantages 
 of high capacity developed from small heating surfaces. Briefly stated, 
 these factors are as follows: 
   
 1st. Efficiency. As the capacity increases, there will in general be a 
 decrease in efficiency, this loss above a certain point making it 
 inadvisable to try to secure more than a definite horse power from a 
 given boiler. This loss of efficiency with increased capacity is treated 
 below in detail, in considering the relation of efficiency to capacity. 
   
 2nd. Grate Ratio Possible or Practicable. All fuels have a maximum rate 
 of combustion, beyond which satisfactory results cannot be obtained, 
 regardless of draft available or which may be secured by mechanical 
 means. Such being the case, it is evident that with this maximum 
 combustion rate secured, the only method of obtaining added capacity 
 will be through the addition of grate surface. There is obviously a 
 point beyond which the grate surface for a given boiler cannot be 
 increased. This is due to the impracticability of handling grates above 
 a certain maximum size, to the enormous loss in draft pressure through a 
 boiler resulting from an attempt to force an abnormal quantity of gas 
 through the heating surface and to innumerable details of design and 
 maintenance that would make such an arrangement wholly unfeasible. 
   
 3rd. Feed Water. The difficulties that may arise through the use of poor 
 feed water or that are liable to happen through the use of practically 
 any feed water have already been pointed out. This question of feed is 
 frequently the limiting factor in the capacity obtainable, for with an 
 increase in such capacity comes an added concentration of such 
 ingredients in the feed water as will cause priming, foaming or rapid 
 scale formation. Certain waters which will give no trouble that cannot 
 be readily overcome with the boiler run at ordinary ratings will cause 
 difficulties at higher ratings entirely out of proportion to any 
 advantage secured by an increase in the power that a definite amount of 
 heating surface may be made to produce. 
   
 Where capacity in the sense of overload is desired, the type of boiler 
 selected will play a large part in the successful operation through such 
 periods. A boiler must be selected with which there is possible a 
 furnace arrangement that will give flexibility without undue loss in 
 efficiency over the range of capacity desired. The heating surface must 
 be so arranged that it will be possible to install in a practical 
 manner, sufficient grate surface at or below the maximum combustion rate 
 to develop the amount of power required. The design of boiler must be 
 such that there will be no priming or foaming at high overloads and that 
 any added scale formation due to such overloads may be easily removed. 
 Certain boilers which deliver commercially dry steam when operated at 
 about their normal rated capacity will prime badly when run at overloads 
 and this action may take place with a water that should be easily 
 handled by a properly designed boiler at any reasonable load. Such 
 action is ordinarily produced by the lack of a well defined, positive 
 circulation. 
   
 Relation of Efficiency and Capacity--The statement has been made that in 
 general the efficiency of a boiler will decrease as the capacity is 
 increased. Considering the boiler alone, apart from the furnace, this 
 statement may be readily explained. 
   
 Presupposing a constant furnace temperature, regardless of the capacity 
 at which a given boiler is run; to assure equal efficiencies at low and 
 high ratings, the exit temperature in the two instances would 
 necessarily be the same. For this temperature at the high rating, to be 
 identical with that at the low rating, the rate of heat transfer from 
 the gases to the heating surfaces would have to vary directly as the 
 weight or volume of such gases. Experiment has shown, however, that this 
 is not true but that this rate of transfer varies as some power of the 
 volume of gas less than one. As the heat transfer does not, therefore, 
 increase proportionately with the volume of gases, the exit temperature 
 for a given furnace temperature will be increased as the volume of gases 
 increases. As this is the measure of the efficiency of the heating 
 surface, the boiler efficiency will, therefore, decrease as the volume 
 of gases increases or the capacity at which the boiler is operated 
 increases. 
   
 Further, a certain portion of the heat absorbed by the heating surface 
 is through direct radiation from the fire. Again, presupposing a 
 constant furnace temperature; the heat absorbed through radiation is 
 solely a function of the amount of surface exposed to such radiation. 
 Hence, for the conditions assumed, the amount of heat absorbed by 
 radiation at the higher ratings will be the same as at the lower ratings 
 but in proportion to the total absorption will be less. As the added 
 volume of gas does not increase the rate of heat transfer, there are 
 therefore two factors acting toward the decrease in the efficiency of a 
 boiler with an increase in the capacity. 
   
                                TABLE 59 
   
          TESTS OF BABCOCK & WILCOX BOILERS WITH VARIOUS FUELS 
   
 ______________________________________________________________________ 
 |Number|                           |               |         | Rated | 
 | of |     Name and Location     | Kind of Coal | Kind of | Horse | 
 | Test |         of Plant         |               | Furnace |Power of| 
 |     |                           |               |         | Boiler | 
 |     |                           |               |         |       | 
 |______|___________________________|________________|_________|________| 
 |     |Susquehanna Coal Co.,      |No. 1 Anthracite|Hand     |       | 
 |   1 |Shenandoah, Pa.           |Buckwheat       |Fired   |   300 | 
 |______|___________________________|________________|_________|________| 
 |     |Balbach Smelting &         |No. 2 Buckwheat |Wilkenson|      | 
 |   2 |Refining Co., Newark, N. J.|and Bird's-eye | Stoker |   218 | 
 |______|___________________________|________________|_________|________| 
 |     |H. R. Worthington,         |No. 2 Anthracite|Hand     |       | 
 |   3 |Harrison N. J.            |Buckwheat       |Fired   |   300 | 
 |______|___________________________|________________|_________|________| 
 |     |Raymond Street Jail,       |Anthracite Pea |Hand     |       | 
 |   4 |Brooklyn, N. Y.           |               |Fired   |   155 | 
 |______|___________________________|________________|_________|________| 
 |     |R. H. Macy & Co.,         |No. 3 Anthracite|Hand     |       | 
 |   5 |New York, N. Y.           |Buckwheat       |Fired   |   293 | 
 |______|___________________________|________________|_________|________| 
 |     |National Bureau of         |Anthracite Egg |Hand     |       | 
 |   6 |Standards, Washington, D.C.|               |Fired   |   119 | 
 |______|___________________________|________________|_________|________| 
 |     |Fred. Loeser & Co.,       |No. 1 Anthracite|Hand     |       | 
 |   7 |Brooklyn, N. Y.           |Buckwheat       |Fired   |   300 | 
 |______|___________________________|________________|_________|________| 
 |     |New York Edison Co.,      |No. 2 Anthracite|Hand     |       | 
 |   8 |New York City             |Buckwheat       |Fired   |   374 | 
 |______|___________________________|________________|_________|________| 
 |     |Sewage Pumping Station,   |Hocking Valley |Hand     |       | 
 |   9 |Cleveland, O.             |Lump, O.       |Fired   |   150 | 
 |______|___________________________|________________|_________|________| 
 |     |Scioto River Pumping Sta., |Hocking Valley, |Hand     |       | 
 | 10 |Cleveland, O.             |O.             |Fired   |   300 | 
 |______|___________________________|________________|_________|________| 
 |     |Consolidated Gas & Electric|Somerset, Pa.   |Hand     |       | 
 | 11 |Co., Baltimore, Md.       |               |Fired   |   640 | 
 |______|___________________________|________________|_________|________| 
 |     |Consolidated Gas & Electric|Somerset, Pa.   |Hand     |       | 
 | 12 |Co., Baltimore, Md.       |               |Fired   |   640 | 
 |______|___________________________|________________|_________|________| 
 |     |Merrimac Mfg. Co.,         |Georges Creek, |Hand     |       | 
 | 13 |Lowell, Mass.             |Md.             |Fired   |   321 | 
 |______|___________________________|________________|_________|________| 
 |     |Great West'n Sugar Co.,   |Lafayette, Col.,|HandFired|       | 
 | 14 |Ft. Collins, Col.         |Mine Run       |Extension|   351 | 
 |______|___________________________|________________|_________|________| 
 |     |Baltimore Sewage Pumping   |New River       |Hand     |       | 
 | 15 | Station                 |               |Fired   |   266 | 
 |______|___________________________|________________|_________|________| 
 |     |Tennessee State Prison,   |Brushy Mountain,|Hand     |       | 
 | 16 |Nashville, Tenn.           |Tenn.           |Fired   |   300 | 
 |______|___________________________|________________|_________|________| 
 |     |Pine Bluff Corporation,   |Arkansas Slack |Hand     |       | 
 | 17 |Pine Bluff, Ark.           |                |Fired   |   298 | 
 |______|___________________________|________________|_________|________| 
 |     |Pub. Serv. Corporation     |Valley, Pa.,   |Roney   |       | 
 | 18 |of N. J., Hoboken         |Mine Run       |Stoker   |   520 | 
 |______|___________________________|________________|_________|________| 
 |     |Pub. Serv. Corporation     |Valley, Pa.,   |Roney   |       | 
 | 19 |of N. J., Hoboken         |Mine Run       |Stoker   |   520 | 
 |______|___________________________|________________|_________|________| 
 |     |Frick Building,           |Pittsburgh Nut |American |       | 
 | 20 |Pittsburgh, Pa.           |and Slack       |Stoker   |   300 | 
 |______|___________________________|________________|_________|________| 
 |      |New York Edison Co.,       |Loyal Hanna, Pa.|Taylor   |       | 
 | 21 |New York City             |               |Stoker   |   604 | 
 |______|___________________________|________________|_________|________| 
 |     |City of Columbus, O.,     |Hocking Valley, |Detroit |       | 
 | 22 |Dept. Lighting             |O.             |Stoker   |   300 | 
 |______|___________________________|________________|_________|________| 
 |     |Edison Elec. Illum. Co.,   |New River       |Murphy   |       | 
 | 23 |Boston, Mass.             |               |Stoker   |   508 | 
 |______|___________________________|________________|_________|________| 
 |     |Colorado Springs &         |Pike View, Col.,|Green Chn|       | 
 | 24 |Interurban Ry., Col.       |Mine Run       |Grate   |   400 | 
 |______|___________________________|________________|_________|________| 
 |     |Pub. Serv. Corporation     |Lancashire, Pa. |B&W.Chain|       | 
 | 25 |of N. J., Marion           |               |Grate   |   600 | 
 |______|___________________________|________________|_________|________| 
 |     |Pub. Serv. Corporation     |Lancashire, Pa. |B&W.Chain|       | 
 | 26 |of N. J., Marion           |               |Grate   |   600 | 
 |______|___________________________|________________|_________|________| 
 |     |Erie County Electric Co., |Mercer County, |B&W.Chain|       | 
 | 27 |Erie, Pa.                 |Pa.             |Grate   |   508 | 
 |______|___________________________|________________|_________|________| 
 |    |Union Elec. Lt. & Pr. Co., |Mascouth, Ill. |B&W.Chain|       | 
 | 28 |St. Louis, Mo.             |               |Grate   |   508 | 
 |______|___________________________|________________|_________|________| 
 |     |Union Elec. Lt. & Pr. Co., |St. Clair       |B&W.Chain|       | 
 | 29 |St. Louis, Mo.             |County, Ill.   |Grate   |   508 | 
 |______|___________________________|________________|_________|________| 
 |     |Commonwealth Edison Co.,   |Carterville,   |B&W.Chain|       | 
 | 30 |Chicago, Ill.             |Ill., Screenings|Grate   |   508 | 
 |______|___________________________|________________|_________|________| 
   
 ________________________________________________________________ 
 |Number|Grate |Dura-|Steam |Temper-|Degrees|Factor|     Draft   | 
 | of |Surf. | tion|Pres. | ature | Super | of | In   | At | 
 | Test |Square|Test | By | Water | -heat |Evapo-|Furnace|Boiler| 
 |     | Feet |Hours|Gauge |Degrees|Degrees|ration|Inches |Damper| 
 |     |     |     |Pounds| Fahr. | Fahr. |     |Upr/Lwr|Inches| 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 |   1 | 84 | 8 | 68 | 53.9 |       |1.1965| +.41 | .21 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     | +.65 |     | 
 |   2 | 51.6 | 7 | 136.3| 203 | 150 |1.1480|   .47 | .56 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 |   3 | 67.6 | 8 | 139 | 139.6 | 139 |1.1984| .70 | .96 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 |   4 | 40 | 8 | 110.2| 137 |       |1.1185| .33 | .43 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 |   5 | 59.5 | 10 | 133.2| 75.2 |       |1.1849| .19 | .40 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 |   6 | 26.5 | 18 | 132.1| 70.5 |       |1.1897| .33 |     | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     | +.51 |     | 
 |   7 | 48.9 | 7 | 101. | 121.3 |       |1.1333| -.20 | .30 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |      |       |     |       |     | 
 |   8 | 59.5 | 6 | 191.8| 88.3 |       |1.1771| .50 |     | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 |   9 | 27 | 24 | 156.3| 58   |       |1.2051| .10 | .24 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 10 |     | 24 | 145 | 75   |       |1.1866| .26 | .46 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 11 | 118 | 8 | 170 | 186.1 | 66.7 |1.1162| .34 | .42 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 12 | 118 | 7.92| 173 | 180.2 | 75.2 |1.1276| .44 | .58 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 13 | 52 | 24 | 75 | 53.3 |       |1.1987| .25 | .35 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 14 | 59.5 | 8 | 105 | 35.8 |      |1.2219| .17 | .38 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 15 | 59.5 | 24 | 170.1| 133 |       |1.1293| .12 | .43 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 16 | 51.3 | 10 | 105 | 75.1 |       |1.1814| .21 | .42 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 17 | 59.5 | 8 | 149.2| 71   |       |1.1910| .35 | .59 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 18 | 103.2| 10 | 133.2| 65.3 | 65.9 |1.2346| .05 | .49 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 19 | 103.2| 9 | 139 | 64   | 80.2 |1.2358| .18 | .57 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 20 | 53 | 9 | 125 | 76.6 |       |1.1826| +1.64 | .64 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 21 | 75 | 8 | 198.5| 165.1 | 104 |1.1662| +3.05 | .60 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |     |       |     |       |     | 
 | 22 |     | 9 | 140 | 67   | 180 |1.2942| .22 | .35 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 23 | 90 |16.25| 199 | 48.4 | 136.5 |1.2996| .23 | 1.27 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 24 | 103 | 8 | 129 | 56   |       |1.2002| .23 | .30 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     | +.52 |     | 
 | 25 | 132 | 8 | 200 | 57.2 | 280.4 |1.3909| +.19 | .52 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     | +.15 |     | 
 | 26 | 132 | 8 | 199 | 60.7 | 171.0 |1.3191| .04 | .52 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |      |     | 
 | 27 | 90 | 8 | 120 | 69.9 |       |1.1888| .31 | .58 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 28 | 103.5| 8 | 180 | 46   | 113 |1.2871| .62 | 1.24 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 29 | 103.5| 8 | 183 | 53.1 | 104 |1.2725| .60 | 1.26 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 |     |     |     |     |       |       |     |       |     | 
 | 30 | 90 | 7 | 184 | 127.1 | 180 |1.2393| .68 | 1.15 | 
 |______|______|_____|______|_______|_______|______|_______|______| 
 ______________________________________________________________ 
 |Number|Temper-|                     Coal                     | 
 | of | ature | Total | Moist-| Total |Ash and| Total |DryCoal| 
 | Test |FlueGas|Weight:| ure | dry | Refuse|Combus-|/sq.ft.| 
 |     |Degrees| Fired | Per | Coal | Per | tible | Grate | 
 |     | Fahr. |Pounds | Cent | Pounds| Cent | Pounds|/Hr.Lb.| 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   1 |      | 11670 | 4.45 | 11151 | 26.05 | 8248 | 16.6 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   2 | 487 | 8800 | 7.62 | 8129 | 29.82 | 5705 | 19.71 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   3 | 559 | 10799 | 6.42 | 10106 | 20.02 | 8081 | 21.77 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |      |       |       |       |       |       |       |       | 
 |   4 | 427 | 5088 | 4.00 | 4884 | 19.35 | 3939 | 15.26 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   5 | 414 | 9440 | 2.14 | 9238 | 11.19 | 8204 | 15.52 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   6 | 410 | 8555 | 3.62 | 8245 | 15.73 | 6948 | 17.28 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   7 | 480 | 7130 | 7.38 | 6604 | 18.35 | 5392 | 19.29 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   8 | 449 | 7500 | 2.70 | 7298 | 27.94 | 5259 | 14.73 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |      |       | 
 |   9 | 410 | 15087 | 7.50 | 13956 | 11.30 | 12379 | 21.5 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 10 | 503 | 29528 | 7.72 | 27248 |       |       | 24.7 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 11 | 487 | 20400 | 2.84 | 19821 | 7.83 | 18269 | 21.00 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 12 | 494 | 21332 | 2.29 | 20843 | 8.23 | 19127 | 22.31 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 13 | 516 | 24584 | 4.29 | 23529 | 7.63 | 21883 | 18.85 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 14 | 523 | 15540 | 18.64 | 12643 |       |       | 28.59 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 15 | 474 | 18330 | 2.03 | 17958 | 16.36 | 16096 | 12.57 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 16 | 536 | 12243 | 2.14 | 11981 |       |       | 23.40 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |      |       |       |       |       | 
 | 17 | 534 | 10500 | 3.04 | 10181 |       |       | 21.40 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 18 | 458 | 18600 | 3.40 | 17968 | 18.38 | 14665 | 17.41 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 19 | 609 | 23400 | 2.56 | 22801 | 16.89 | 18951 | 24.55 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 20 | 518 | 10500 | 1.83 | 10308 | 12.22 | 9048 | 21.56 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 21 | 536 | 25296 | 2.20 | 24736 |       |       | 41.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 22 | 511 | 14263 | 8.63 | 13032 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 23 | 560 | 39670 | 4.22 | 37996 | 4.32 | 36355 | 25.98 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 24 | 538 | 23000 | 23.73 | 17542 |       |       | 21.36 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |    |       |       |       |       |       |       |       | 
 | 25 | 590 | 32205 | 4.03 | 30907 | 15.65 | 26070 | 29.26 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 26 | 529 | 24243 | 4.09 | 23251 | 12.33 | 20385 | 22.01 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 27 | 533 | 22328 | 4.42 | 21341 | 16.88 | 17739 | 29.64 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 28 | 523 | 32163 | 13.74 | 27744 |       |       | 33.50 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 29 | 567 | 36150 | 14.62 | 30865 |       |       | 37.28 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |      |       | 
 | 30 |       | 30610 | 11.12 | 27206 | 14.70 | 23198 | 43.20 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
   
 ______________________________________________________________ 
 |Number|         Water         |       |   Flue Gas Analysis   | 
 | of |Actual | Equiv.|ditto /|% Rated|CO_{2} |   O   | CO   | 
 | Test |Evapor-|Evap. @|sq.ft. |Cap'ty.| Per | Per | Per | 
 |     | ation |>=212° |Heating|Develpd| Cent | Cent | Cent | 
 |     |/Hr.Lb.|/Hr.Lb.|Surface|PerCent|      |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   1 | 10268 | 12286 | 4.10 | 118.7 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   2 | 8246 | 9466 | 4.34 | 125.7 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |      |       |       |       | 
 |   3 | 9145 | 10959 | 3.65 | 105.9 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   4 | 5006 | 5599 | 3.61 | 104.7 | 12.26 | 7.88 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   5 | 7434 | 8809 | 3.06 | 87.2 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   6 | 2903 | 3454 | 2.91 | 84.4 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   7 | 7464 | 8459 | 2.82 | 81.7 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   8 | 9164 | 10787 | 2.88 | 83.5 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 |   9 | 4374 | 5271 | 3.51 | 101.8 | 11.7 | 7.3 | 0.07 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 10 | 8688 | 10309 | 3.44 | 99.6 | 12.9 | 5.0 | 0.2 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |      |       |       |       |       |       |       | 
 | 11 | 24036 | 26829 | 4.19 | 121.5 | 12.5 | 6.4 | 0.5 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 12 | 25313 | 28544 | 4.46 | 129.3 | 13.3 | 5.1 | 0.5 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 13 | 9168 | 10990 | 3.42 | 99.3 | 9.6 | 8.8 | 0.4 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 14 | 11202 | 13689 | 3.91 | 113.5 | 9.1 | 9.9 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 15 | 7565 | 8543 | 3.21 | 93.1 | 10.71 | 9.10 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |      | 
 | 16 | 9512 | 11237 | 3.74 | 108.6 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 17 | 9257 | 11025 | 3.70 | 107.2 |       |       |      | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 18 | 15887 | 19614 | 3.77 | 108.7 | 11.7 | 7.7 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 19 | 21320 | 26347 | 5.06 | 146.7 | 11.9 | 7.8 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |      |       | 
 | 20 | 9976 | 11978 | 3.93 | 112.0 | 11.3 | 7.5 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 21 | 28451 | 33066 | 5.47 | 158.6 | 12.3 | 6.4 | 0.7 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 22 | 10467 | 13526 | 4.51 | 130.7 | 11.9 | 7.2 | 0.04 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 23 | 20700 | 26902 | 5.30 | 153.5 | 11.1 |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |      |       |       |       | 
 | 24 | 14650 | 17583 | 4.40 | 127.4 |       |       |       | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 25 | 28906 | 40205 | 6.70 | 194.2 | 10.5 | 8.3 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 26 | 23074 | 30437 | 5.07 | 147.0 | 10.1 | 9.0 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 27 | 20759 | 24678 | 4.85 | 140.8 | 10.1 | 9.1 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |      |       |       |       |       | 
 | 28 | 21998 | 28314 | 5.67 | 161.5 | 8.7 | 10.6 | 0.0 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 29 | 24386 | 31031 | 6.11 | 177.1 | 8.9 | 10.7 | 0.2 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       |       | 
 | 30 | 30505 | 37805 | 7.43 | 215.7 | 10.4 | 9.4 | 0.2 | 
 |______|_______|_______|_______|_______|_______|_______|_______| 
   
 _______________________________________________________ 
 |Number| Proximate Analysis Dry Coal | Equiv.|Combnd.| 
 | of |Volatl.| Fixed | Ash |B.t.u./|Evap. @|Efficy.| 
 | Test |Matter |Carbon | Per | Pound |>=212°/|Boiler | 
 |     | Per | Per | Cent | Dry | Pound |& Grate| 
 |     | Cent | Cent |       | Coal |DryCoal|PerCent| 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   1 |       |       | 26.05 | 11913 | 8.81 | 71.8 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   2 |       |       |       | 11104 | 8.15 | 72.1 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   3 | 5.55 | 80.60 | 13.87 | 12300 | 8.67 | 68.4 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   4 | 7.74 | 77.48 | 14.78 | 12851 | 9.17 | 69.2 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   5 |       |       |       | 13138 | 9.53 | 69.6 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   6 | 6.13 | 84.86 | 9.01 | 13454 | 9.57 | 69.0 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   7 |       |       |       | 12224 | 8.97 | 71.2 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   8 | 0.55 | 86.73 | 12.72 | 12642 | 8.87 | 68.1 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 |   9 | 39.01 | 48.08 | 12.91 | 12292 | 9.06 | 71.5 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 10 | 38.33 | 46.71 | 14.96 | 12284 | 9.08 | 71.7 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 11 | 19.86 | 73.02 | 7.12 | 14602 | 10.83 | 72.0 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 12 | 20.24 | 72.26 | 7.50 | 14381 | 10.84 | 73.2 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 13 |       |       |       | 14955 | 11.21 | 72.7 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 14 | 39.60 | 54.46 | 5.94 | 11585 | 8.66 | 72.5 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 15 | 17.44 | 76.42 | 5.84 | 15379 | 11.42 | 72.1 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 16 | 33.40 | 54.73 | 11.87 | 12751 | 9.38 | 71.4 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 17 | 15.42 | 62.48 | 22.10 | 12060 | 8.66 | 69.6 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 18 | 14.99 | 75.13 | 9.88 | 14152 | 10.92 | 74.88 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 19 | 14.40 | 74.33 | 11.27 | 14022 | 10.40 | 71.97 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 20 | 32.44 | 56.71 | 10.85 | 13510 | 10.30 | 74.6 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 21 | 19.02 | 72.09 | 8.89 | 14105 | 10.69 | 73.5 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 22 | 32.11 | 53.93 | 13.96 | 12435 | 9.41 | 73.4 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 23 | 19.66 | 75.41 | 4.93 | 14910 | 11.51 | 74.9 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 24 | 43.57 | 46.22 | 10.21 | 11160 | 8.02 | 69.7 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 25 | 22.84 | 69.91 | 7.25 | 13840 | 10.41 | 72.6 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 26 | 32.36 | 60.67 | 6.97 | 14027 | 10.47 | 72.1 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 27 | 33.26 | 54.03 | 12.71 | 12742 | 9.25 | 70.4 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 28 | 28.96 | 46.88 | 24.16 | 10576 | 8.16 | 74.9 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 29 | 36.50 | 41.20 | 22.30 | 10849 | 8.04 | 71.9 | 
 |______|_______|_______|_______|_______|_______|_______| 
 |     |       |       |       |       |       |       | 
 | 30 |       |       | 10.24 | 13126 | 9.73 | 71.9 | 
 |______|_______|_______|_______|_______|_______|_______| 
 This increase in the efficiency of the boiler alone with the decrease in 
 the rate at which it is operated, will hold to a point where the 
 radiation of heat from the boiler setting is proportionately large 
 enough to be a governing factor in the total amount of heat absorbed. 
   
 The second reason given above for a decrease of boiler efficiency with 
 increase of capacity, viz., the effect of radiant heat, is to a greater 
 extent than the first reason dependent upon a constant furnace 
 temperature. Any increase in this temperature will affect enormously the 
 amount of heat absorbed by radiation, as this absorption will vary as 
 the fourth power of the temperature of the radiating body. In this way 
 it is seen that but a slight increase in furnace temperature will be 
 necessary to bring the proportional part, due to absorption by 
 radiation, of the total heat absorbed, up to its proper proportion at 
 the higher ratings. This factor of furnace temperature more properly 
 belongs to the consideration of furnace efficiency than of boiler 
 efficiency. There is a point, however, in any furnace above which the 
 combustion will be so poor as to actually reduce the furnace temperature 
 and, therefore, the proportion of heat absorbed through radiation by a 
 given amount of exposed heating surface. 
   
 Since it is thus true that the efficiency of the boiler considered alone 
 will increase with a decreased capacity, it is evident that if the 
 furnace conditions are constant regardless of the load, that the 
 combined efficiency of boiler and furnace will also decrease with 
 increasing loads. This fact was clearly proven in the tests of the 
 boilers at the Detroit Edison Company.[74] The furnace arrangement of 
 these boilers and the great care with which the tests were run made it 
 possible to secure uniformly good furnace conditions irrespective of 
 load, and here the maximum efficiency was obtained at a point somewhat 
 less than the rated capacity of the boilers. 
   
 In some cases, however, and especially in the ordinary operation of the 
 plant, the furnace efficiency will, up to a certain point, increase with 
 an increase in power. This increase in furnace efficiency is ordinarily 
 at a greater rate as the capacity increases than is the decrease in 
 boiler efficiency, with the result that the combined efficiency of 
 boiler and furnace will to a certain point increase with an increase in 
 capacity. This makes the ordinary point of maximum combined efficiency 
 somewhat above the rated capacity of the boiler and in many cases the 
 combined efficiency will be practically a constant over a considerable 
 range of ratings. The features limiting the establishing of the point of 
 maximum efficiency at a high rating are the same as those limiting the 
 amount of grate surface that can be installed under a boiler. The 
 relative efficiency of different combinations of boilers and furnaces at 
 different ratings depends so largely upon the furnace conditions that 
 what might hold for one combination would not for another. 
   
 In view of the above, it is impossible to make a statement of the 
 efficiency at different capacities of a boiler and furnace which will 
 hold for any and all conditions. Fig. 40 shows in a general form the 
 relation of efficiency to capacity. This curve has been plotted from a 
 great number of tests, all of which were corrected to bring them to 
 approximately the same conditions. The curve represents test conditions. 
 The efficiencies represented are those which may be secured only under 
 such conditions. The general direction of the curve, however, will be 
 found to hold approximately correct for operating conditions when used 
 only as a guide to what may be expected. 
   
 [Graph: Combined Efficiency of Boiler and Furnace Per Cent 
 against Per Cent of Boiler's Rated Capacity Developed 
   
 Fig. 40. Approximate Variation of Efficiency with Capacity under Test 
 Conditions] 
   
 Economical Loads--With the effect of capacity on economy in mind, the 
 question arises as to what constitutes the economical load to be 
 carried. In figuring on the economical load for an individual plant, the 
 broader economy is to be considered, that in which, against the boiler 
 efficiency, there is to be weighed the plant first cost, returns on such 
 investment, fuel cost, labor, capacity, etc., etc. This matter has been 
 widely discussed, but unfortunately such discussion has been largely 
 limited to central power station practice. The power generated in such 
 stations, while representing an enormous total, is by no means the 
 larger proportion of the total power generated throughout the country. 
 The factors determining the economic load for the small plant, however, 
 are the same as in a large, and in general the statements made relative 
 to the question are equally applicable. 
   
 The economical rating at which a boiler plant should be run is dependent 
 solely upon the load to be carried by that individual plant and the 
 nature of such load. The economical load for each individual plant can 
 be determined only from the careful study of each individual set of 
 conditions or by actual trial. 
   
 The controlling factor in the cost of the plant, regardless of the 
 nature of the load, is the capacity to carry the maximum peak load that 
 may be thrown on the plant under any conditions. 
   
 While load conditions, do, as stated, vary in every individual plant, in 
 a broad sense all loads may be grouped in three classes: 1st, the 
 approximately constant 24-hour load; 2nd, the steady 10 or 12-hour load 
 usually with a noonday period of no load; 3rd, the 24-hour variable 
 load, found in central station practice. The economical load at which 
 the boiler may be run will vary with these groups: 
   
 1st. For a constant load, 24 hours in the day, it will be found in most 
 cases that, when all features are considered, the most economical load 
 or that at which a given amount of steam can be produced the most 
 cheaply will be considerably over the rated horse power of the boiler. 
 How much above the rated capacity this most economic load will be, is 
 dependent largely upon the cost of coal at the plant, but under ordinary 
 conditions, the point of maximum economy will probably be found to be 
 somewhere between 25 and 50 per cent above the rated capacity of the 
 boilers. The capital investment must be weighed against the coal saving 
 through increased thermal efficiency and the labor account, which 
 increases with the number of units, must be given proper consideration. 
 When the question is considered in connection with a plant already 
 installed, the conditions are different from where a new plant is 
 contemplated. In an old plant, where there are enough boilers to operate 
 at low rates of capacity, the capital investment leads to a fixed 
 charge, and it will be found that the most economical load at which 
 boilers may be operated will be lower than where a new plant is under 
 consideration. 
   
 2nd. For a load of 10 or 12 hours a day, either an approximately steady 
 load or one in which there is a peak, where the boilers have been banked 
 over night, the capacity at which they may be run with the best economy 
 will be found to be higher than for uniform 24-hour load conditions. 
 This is obviously due to original investment, that is, a given amount of 
 invested capital can be made to earn a larger return through the higher 
 overload, and this will hold true to a point where the added return more 
 than offsets the decrease in actual boiler efficiency. Here again the 
 determining factors of what is the economical load are the fuel and 
 labor cost balanced against the thermal efficiency. With a load of this 
 character, there is another factor which may affect the economical plant 
 operating load. This is from the viewpoint of spare boilers. That such 
 added capacity in the way of spares is necessary is unquestionable. 
 Since they must be installed, therefore, their presence leads to a fixed 
 charge and it is probable that for the plant, as a whole, the economical 
 load will be somewhat lower than if the boilers were considered only as 
 spares. That is, it may be found best to operate these spares as a part 
 of the regular equipment at all times except when other boilers are off 
 for cleaning and repairs, thus reducing the load on the individual 
 boilers and increasing the efficiency. Under such conditions, the added 
 boiler units can be considered as spares only during such time as some 
 of the boilers are not in operation. 
   
 Due to the operating difficulties that may be encountered at the higher 
 overloads, it will ordinarily be found that the most economical ratings 
 at which to run boilers for such load conditions will be between 150 and 
 175 per cent of rating. Here again the maximum capacity at which the 
 boilers may be run for the best plant economy is limited by the point at 
 which the efficiency drops below what is warranted in view of the first 
 cost of the apparatus. 
   
 3rd. The 24-hour variable load. This is a class of load carried by the 
 central power station, a load constant only in the sense that there are 
 no periods of no load and which varies widely with different portions of 
 the 24 hours. With such a load it is particularly difficult to make any 
 assertion as to the point of maximum economy that will hold for any 
 station, as this point is more than with any other class of load 
 dependent upon the factors entering into the operation of each 
 individual plant. 
   
 The methods of handling a load of this description vary probably more 
 than with any other kind of load, dependent upon fuel, labor, type of 
 stoker, flexibility of combined furnace and boiler etc., etc. 
   
 In general, under ordinary conditions such as appear in city central 
 power station work where the maximum peaks occur but a few times a year, 
 the plant should be made of such size as to enable it to carry these 
 peaks at the maximum possible overload on the boilers, sufficient margin 
 of course being allowed for insurance against interruption of service. 
 With the boilers operating at this maximum overload through the peaks a 
 large sacrifice in boiler efficiency is allowable, provided that by such 
 sacrifice the overload expected is secured. 
 Some methods of handling a load of this nature are given below: 
   
 Certain plant operating conditions make it advisable, from the 
 standpoint of plant economy, to carry whatever load is on the plant at 
 any time on only such boilers as will furnish the power required when 
 operating at ratings of, say, 150 to 200 per cent. That is, all boilers 
 which are in service are operated at such ratings at all times, the 
 variation in load being taken care of by the number of boilers on the 
 line. Banked boilers are cut in to take care of increasing loads and 
 peaks and placed again on bank when the peak periods have passed. It is 
 probable that this method of handling central station load is to-day the 
 most generally used. 
   
 Other conditions of operation make it advisable to carry the load on a 
 definite number of boiler units, operating these at slightly below their 
 rated capacity during periods of light or low loads and securing the 
 overload capacity during peaks by operating the same boilers at high 
 ratings. In this method there are no boilers kept on banked fires, the 
 spares being spares in every sense of the word. 
   
 A third method of handling widely varying loads which is coming somewhat 
 into vogue is that of considering the plant as divided, one part to take 
 care of what may be considered the constant plant load, the other to 
 take care of the floating or variable load. With such a method that 
 portion of the plant carrying the steady load is so proportioned that 
 the boilers may be operated at the point of maximum efficiency, this 
 point being raised to a maximum through the use of economizers and the 
 general installation of any apparatus leading to such results. The 
 variable load will be carried on the remaining boilers of the plant 
 under either of the methods just given, that is, at the high ratings of 
 all boilers in service and banking others, or a variable capacity from 
 all boilers in service. 
   
 The opportunity is again taken to indicate the very general character of 
 any statements made relative to the economical load for any plant and to 
 emphasize the fact that each individual case must be considered 
 independently, with the conditions of operations applicable thereto. 
   
 With a thorough understanding of the meaning of boiler efficiency and 
 capacity and their relation to each other, it is possible to consider 
 more specifically the selection of boilers. 
   
 The foremost consideration is, without question, the adaptability of the 
 design selected to the nature of the work to be done. An installation 
 which is only temporary in its nature would obviously not warrant the 
 first cost that a permanent plant would. If boilers are to carry an 
 intermittent and suddenly fluctuating load, such as a hoisting load or a 
 reversing mill load, a design would have to be selected that would not 
 tend to prime with the fluctuations and sudden demand for steam. A 
 boiler that would give the highest possible efficiency with fuel of one 
 description, would not of necessity give such efficiency with a 
 different fuel. A boiler of a certain design which might be good for 
 small plant practice would not, because of the limitations in 
 practicable size of units, be suitable for large installations. A 
 discussion of the relative value of designs can be carried on almost 
 indefinitely but enough has been said to indicate that a given design 
 will not serve satisfactorily under all conditions and that the 
 adaptability to the service required will be dependent upon the fuel 
 available, the class of labor procurable, the feed water that must be 
 used, the nature of the plant's load, the size of the plant and the 
 first cost warranted by the service the boiler is to fulfill. 
   
                                                                  TABLE 60 
   
                                    ACTUAL EVAPORATION FOR DIFFERENT PRESSURES AND TEMPERATURES OF FEED 
                       WATER CORRESPONDING TO ONE HORSE POWER (34½ POUNDS PER HOUR FROM AND AT 212 DEGREES FAHRENHEIT) 
   
 ----------------------------------------------------------------------------------------------------------------------------------------- 
 Temperature|                                                                                                                             | 
    of     |                                         Pressure by Gauge--Pounds per Square Inch                                        | 
    Feed   |                                                                                                                             | 
 Degrees |                                                                                                                            | 
 Fahrenheit | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 210 | 220 | 230 | 240 | 250 | 
 -----------+-----------------------------------------------------------------------------------------------------------------------------| 
 32       |28.41|28.36|28.29|28.24|28.20|28.16|28.13|28.09|28.07|28.04|28.02|27.99|27.97|27.95|27.94|27.92|27.90|27.89|27.87|27.86|27.83| 
 40       |28.61|28.54|28.49|28.44|28.40|28.35|28.32|28.29|28.26|28.23|28.21|28.18|28.16|28.14|28.12|28.11|28.09|28.07|28.06|28.05|28.03| 
 50       |28.85|28.79|28.73|28.68|28.64|28.60|28.56|28.53|28.50|28.47|28.45|28.43|28.40|28.38|28.36|28.35|28.33|28.31|28.30|28.28|28.27| 
 60       |29.10|29.04|28.98|28.93|28.88|28.84|28.81|28.77|28.74|28.72|28.69|28.67|28.65|28.62|28.60|28.59|28.57|28.55|28.54|28.52|28.51| 
 70       |29.36|29.29|29.23|29.18|29.14|29.09|29.06|29.02|28.99|28.96|28.94|28.92|28.89|28.87|28.85|28.83|28.82|28.80|28.78|28.77|28.76| 
 80      |29.62|29.55|29.49|29.44|29.39|29.35|29.31|29.27|29.24|29.22|29.19|29.17|29.14|29.12|29.10|29.08|29.07|29.05|29.03|29.02|29.00| 
 90       |29.88|29.81|29.75|29.70|29.65|29.61|29.57|29.53|29.50|29.47|29.45|29.42|29.40|29.38|29.36|29.34|29.32|29.30|29.29|29.27|29.25| 
 100       |30.15|30.08|30.02|29.96|29.91|29.87|29.83|29.80|29.76|29.73|29.71|29.68|29.66|29.63|29.61|29.60|29.58|29.56|29.54|29.53|29.51| 
 110       |30.42|30.35|30.29|30.23|30.18|30.14|30.10|30.06|30.03|30.00|29.97|29.95|29.92|29.90|29.88|29.86|29.84|29.82|29.81|29.79|29.77| 
 120       |30.70|30.63|30.56|30.51|30.46|30.41|30.37|30.33|30.30|30.27|30.24|30.22|30.19|30.17|30.15|30.13|30.11|30.09|30.07|30.06|30.04| 
 130       |30.99|30.91|30.84|30.79|30.73|30.69|30.65|30.61|30.57|30.54|30.52|30.49|30.47|30.44|30.42|30.40|30.38|30.36|30.35|30.33|30.31| 
 140       |31.28|31.20|31.13|31.07|31.02|30.97|30.93|30.89|30.86|30.83|30.80|30.77|30.75|30.72|30.70|30.68|30.66|30.64|30.62|30.61|30.59| 
 150       |31.58|31.49|31.42|31.36|31.31|31.26|31.22|31.18|31.14|31.11|31.08|31.06|31.03|31.01|30.98|30.96|30.94|30.92|30.91|30.89|30.87| 
 160       |31.87|31.79|31.72|31.66|31.61|31.56|31.51|31.47|31.44|31.40|31.37|31.35|31.32|31.29|31.27|31.25|31.23|31.21|31.19|31.18|31.16| 
 170       |32.18|32.10|32.02|31.96|31.91|31.86|31.81|31.77|31.73|31.70|31.67|31.64|31.62|31.59|31.57|31.54|31.52|31.50|31.49|31.47|31.46| 
 180       |32.49|32.41|32.33|32.27|32.22|32.16|32.12|32.08|32.04|32.00|31.97|31.95|31.92|31.89|31.87|31.84|31.82|31.80|31.79|31.77|31.75| 
 190       |32.81|32.72|32.65|32.59|32.53|32.47|32.43|32.38|32.35|32.32|32.29|32.26|32.23|32.20|32.17|32.15|32.13|32.11|32.09|32.07|32.05| 
 200       |33.13|33.05|32.97|32.91|32.85|32.79|32.75|32.70|32.66|32.63|32.60|32.57|32.54|32.51|32.49|32.46|32.44|32.42|32.40|32.38|32.36| 
 210       |33.47|33.38|33.30|33.24|33.18|33.13|33.08|33.03|32.99|32.95|32.92|32.89|32.86|32.83|32.81|32.79|32.76|32.74|32.72|32.70|32.68| 
 ----------------------------------------------------------------------------------------------------------------------------------------- 
   
 The proper consideration can be given to the adaptability of any boiler 
 for the service in view only after a thorough understanding of the 
 requirements of a good steam boiler, with the application of what has 
 been said on the proper operation to the special requirements of each 
 case. Of almost equal importance to the factors mentioned are the 
 experience, the skill and responsibility of the manufacturer. 
   
 With the design of boiler selected that is best adapted to the service 
 required, the next step is the determination of the boiler power 
 requirements. 
   
 The amount of steam that must be generated is determined from the steam 
 consumption of the prime movers. It has already been indicated that such 
 consumption can vary over wide limits with the size and type of the 
 apparatus used, but fortunately all types have been so tested that 
 manufacturers are enabled to state within very close limits the actual 
 consumption under any given set of conditions. It is obvious that 
 conditions of operation will have a bearing on the steam consumption 
 that is as important as the type and size of the apparatus itself. This 
 being the case, any tabular information that can be given on such steam 
 consumption, unless it be extended to an impracticable size, is only of 
 use for the most approximate work and more definite figures on this 
 consumption should in all cases be obtained from the manufacturer of the 
 apparatus to be used for the conditions under which it will operate. 
   
 To the steam consumption of the main prime movers, there is to be added 
 that of the auxiliaries. Again it is impossible to make a definite 
 statement of what this allowance should be, the figure depending wholly 
 upon the type and the number of such auxiliaries. For approximate work, 
 it is perhaps best to allow 15 or 20 per cent of the steam requirements 
 of the main engines, for that of auxiliaries. Whatever figure is used 
 should be taken high enough to be on the conservative side. 
   
 When any such figures are based on the actual weight of steam required, 
 Table 60, which gives the actual evaporation for various pressures and 
 temperatures of feed corresponding to one boiler horse power (34.5 
 pounds of water per hour from and at 212 degrees), may be of service. 
   
 With the steam requirements known, the next step is the determination of 
 the number and size of boiler units to be installed. This is directly 
 affected by the capacity at which a consideration of the economical load 
 indicates is the best for the operating conditions which will exist. The 
 other factors entering into such determination are the size of the plant 
 and the character of the feed water. 
   
 The size of the plant has its bearing on the question from the fact that 
 higher efficiencies are in general obtained from large units, that labor 
 cost decreases with the number of units, the first cost of brickwork is 
 lower for large than for small size units, a general decrease in the 
 complication of piping, etc., and in general the cost per horse power of 
 any design of boiler decreases with the size of units. To illustrate 
 this, it is only necessary to consider a plant of, say, 10,000 boiler 
 horse power, consisting of 40-250 horse-power units or 17-600 
 horse-power units. 
   
 The feed water available has its bearing on the subject from the other 
 side, for it has already been shown that very large units are not 
 advisable where the feed water is not of the best. 
   
 The character of an installment is also a factor. Where, say, 1000 horse 
 power is installed in a plant where it is known what the ultimate 
 capacity is to be, the size of units should be selected with the idea of 
 this ultimate capacity in mind rather than the amount of the first 
 installation. 
   
 Boiler service, from its nature, is severe. All boilers have to be 
 cleaned from time to time and certain repairs to settings, etc., are a 
 necessity. This makes it necessary, in determining the number of boilers 
 to be installed, to allow a certain number of units or spares to be 
 operated when any of the regular boilers must be taken off the line. 
 With the steam requirements determined for a plant of moderate size and 
 a reasonably constant load, it is highly advisable to install at least 
 two spare boilers where a continuity of service is essential. This 
 permits the taking off of one boiler for cleaning or repairs and still 
 allows a spare boiler in the event of some unforeseen occurrence, such 
 as the blowing out of a tube or the like. Investment in such spare 
 apparatus is nothing more nor less than insurance on the necessary 
 continuity of service. In small plants of, say, 500 or 600 horse power, 
 two spares are not usually warranted in view of the cost of such 
 insurance. A large plant is ordinarily laid out in a number of sections 
 or panels and each section should have its spare boiler or boilers even 
 though the sections are cross connected. In central station work, where 
 the peaks are carried on the boilers brought up from the bank, such 
 spares are, of course, in addition to these banked boilers. From the 
 aspect of cleaning boilers alone, the number of spare boilers is 
 determined by the nature of any scale that may be formed. If scale is 
 formed so rapidly that the boilers cannot be kept clean enough for good 
 operating results, by cleaning in rotation, one at a time, the number of 
 spares to take care of such proper cleaning will naturally increase. 
   
 In view of the above, it is evident that only a suggestion can be made 
 as to the number and size of units, as no recommendation will hold for 
 all cases. In general, it will be found best to install units of the 
 largest possible size compatible with the size of the plant and 
 operating conditions, with the total power requirements divided among 
 such a number of units as will give proper flexibility of load, with 
 such additional units for spares as conditions of cleaning and insurance 
 against interruption of service warrant. 
   
 In closing the subject of the selection of boilers, it may not be out of 
 place to refer to the effect of the builder's guarantee upon the 
 determination of design to be used. Here in one of its most important 
 aspects appears the responsibility of the manufacturer. Emphasis has 
 been laid on the difference between test results and those secured in 
 ordinary operating practice. That such a difference exists is well known 
 and it is now pretty generally realized that it is the responsible 
 manufacturer who, where guarantees are necessary, submits the 
 conservative figures, figures which may readily be exceeded under test 
 conditions and which may be closely approached under the ordinary plant 
 conditions that will be met in daily operation. 
   
 
 
 
 OPERATION AND CARE OF BOILERS 
 The general subject of boiler room practice may be considered from two 
 aspects. The first is that of the broad plant economy, with a suggestion 
 as to the methods to be followed in securing the best economical results 
 with the apparatus at hand and procurable. The second deals rather with 
 specific recommendations which should be followed in plant practice, 
 recommendations leading not only to economy but also to safety and 
 continuity of service. Such recommendations are dictated from an 
 understanding of the nature of steam generating apparatus and its 
 operation, as covered previously in this book. 
   
 It has already been pointed out that the attention given in recent years 
 to steam generating practice has come with a realization of the wide 
 difference existing between the results being obtained in every-day 
 operation and those theoretically possible. The amount of such attention 
 and regulation given to the steam generating end of a power plant, 
 however, is comparatively small in relation to that given to the balance 
 of the plant, but it may be safely stated that it is here that there is 
 the greatest assurance of a return for the attention given. 
   
 In the endeavor to increase boiler room efficiency, it is of the utmost 
 importance that a standard basis be set by which average results are to 
 be judged. With the theoretical efficiency obtainable varying so widely, 
 this standard cannot be placed at the highest efficiency that has been 
 obtained regardless of operating conditions. It is better set at the 
 best obtainable results for each individual plant under its conditions 
 of installation and daily operation. 
   
 With an individual standard so set, present practice can only be 
 improved by a systematic effort to approach this standard. The degree 
 with which operating results will approximate such a standard will be 
 found to be directly proportional to the amount of intelligent 
 supervision given the operation. For such supervision to be given, it is 
 necessary to have not only a full realization of what the plant can do 
 under the best operating conditions but also a full and complete 
 knowledge of what it is doing under all of the different conditions that 
 may arise. What the plant is doing should be made a matter of continuous 
 record so arranged that the results may be directly compared for any 
 period or set of conditions, and where such results vary from the 
 standard set, steps must be taken immediately to remedy the causes of 
 such failings. Such a record is an important check in the losses in the 
 plant. 
   
 As the size of the plant and the fuel consumption increase, such a check 
 of losses and recording of results becomes a necessity. In the larger 
 plants, the saving of but a fraction of one per cent in the fuel bill 
 represents an amount running into thousands of dollars annually, while 
 the expense of the proper supervision to secure such saving is small. 
 The methods of supervision followed in the large plants are necessarily 
 elaborate and complete. In the smaller plants the same methods may be 
 followed on a more moderate scale with a corresponding saving in fuel 
 and an inappreciable increase in either plant organization or expense. 
   
 There has been within the last few years a great increase in the 
 practicability and reliability of the various types of apparatus by 
 which the records of plant operation may be secured. Much of this 
 apparatus is ingenious and, considering the work to be done, is 
 remarkably accurate. From the delicate nature of some of the apparatus, 
 the liability to error necessitates frequent calibration but even where 
 the accuracy is known to be only within limits of, say, 5 per cent 
 either way, the records obtained are of the greatest service in 
 considering relative results. Some of the records desirable and the 
 apparatus for securing them are given below. 
 Inasmuch as the ultimate measure of the efficiency of the boiler plant 
 is the cost of steam generation, the important records are those of 
 steam generated and fuel consumed Records of temperature, analyses, 
 draft and the like, serve as a check on this consumption, indicating the 
 distribution of the losses and affording a means of remedying conditions 
 where improvement is possible. 
   
 Coal Records--There are many devices on the market for conveniently 
 weighing the coal used. These are ordinarily accurate within close 
 limits, and where the size or nature of the plant warrants the 
 investment in such a device, its use is to be recommended. The coal 
 consumption should be recorded by some other method than from the 
 weights of coal purchased. The total weight gives no way of dividing the 
 consumption into periods and it will unquestionably be found to be 
 profitable to put into operation some scheme by which the coal is 
 weighed as it is used. In this way, the coal consumption, during any 
 specific period of the plant's operation, can be readily seen. The 
 simplest of such methods which may be used in small plants is the actual 
 weighing on scales of the fuel as it is brought into the fire room and 
 the recording of such weights. 
   
 Aside from the actual weight of the fuel used, it is often advisable to 
 keep other coal records, coal and ash analyses and the like, for the 
 evaporation to be expected will be dependent upon the grade of fuel used 
 and its calorific value, fusibility of its ash, and like factors. 
   
 The highest calorific value for unit cost is not necessarily the 
 indication of the best commercial results. The cost of fuel is governed 
 by this calorific value only when such value is modified by local 
 conditions of capacity, labor and commercial efficiency. One of the 
 important factors entering into fuel cost is the consideration of the 
 cost of ash handling and the maintenance of ash handling apparatus if 
 such be installed. The value of a fuel, regardless of its calorific 
 value, is to be based only on the results obtained in every-day plant 
 operation. 
   
 Coal and ash analyses used in connection with the amount of fuel 
 consumed, are a direct indication of the relation between the results 
 being secured and the standard of results which has been set for the 
 plant. The methods of such analyses have already been described. The 
 apparatus is simple and the degree of scientific knowledge necessary is 
 only such as may be readily mastered by plant operatives. 
   
 The ash content of a fuel, as indicated from a coal analysis checked 
 against ash weights as actually found in plant operation, acts as a 
 check on grate efficiency. The effect of any saving in the ashes, that 
 is, the permissible ash to be allowed in the fuel purchased, is 
 determined by the point at which the cost of handling, combined with the 
 falling off in the evaporation, exceeds the saving of fuel cost through 
 the use of poorer coal. 
   
 Water Records--Water records with the coal consumption, form the basis 
 for judging the economic production of steam. The methods of securing 
 such records are of later introduction than for coal, but great advances 
 have been made in the apparatus to be used. Here possibly, to a greater 
 extent than in any recording device, are the records of value in 
 determining relative evaporation, that is, an error is rather allowable 
 provided such an error be reasonably constant. 
   
 The apparatus for recording such evaporation is of two general classes: 
 Those measuring water before it is fed to the boiler and those measuring 
 the steam as it leaves. Of the first, the venturi meter is perhaps the 
 best known, though recently there has come into considerable vogue an 
 apparatus utilizing a weir notch for the measuring of such water. Both 
 methods are reasonably accurate and apparatus of this description has an 
 advantage over one measuring steam in that it may be calibrated much 
 more readily. Of the steam measuring devices, the one in most common use 
 is the steam flow meter. Provided the instruments are selected for a 
 proper flow, etc., they are of inestimable value in indicating the steam 
 consumption. Where such instruments are placed on the various engine 
 room lines, they will immediately indicate an excessive consumption for 
 any one of the units. With a steam flow meter placed on each boiler, it 
 is possible to fix relatively the amount produced by each boiler and, 
 considered in connection with some of the "check" records described 
 below, clearly indicate whether its portion of the total steam produced 
 is up to the standard set for the over-all boiler room efficiency. 
   
 Flue Gas Analysis--The value of a flue gas analysis as a measure of 
 furnace efficiency has already been indicated. There are on the market a 
 number of instruments by which a continuous record of the carbon dioxide 
 in the flue gases may be secured and in general the results so recorded 
 are accurate. The limitations of an analysis showing only CO_{2} and the 
 necessity of completing such an analysis with an Orsat, or like 
 apparatus, and in this way checking the automatic device, have already 
 been pointed out, but where such records are properly checked from time 
 to time and are used in conjunction with a record of flue temperatures, 
 the losses due to excess air or incomplete combustion and the like may 
 be directly compared for any period. Such records act as a means for 
 controlling excess air and also as a check on individual firemen. 
   
 Where the size of a plant will not warrant the purchase of an expensive 
 continuous CO_{2} recorder, it is advisable to make analyses of samples 
 for various conditions of firing and to install an apparatus whereby a 
 sample of flue gas covering a period of, say, eight hours, may be 
 obtained and such a sample afterwards analyzed. 
   
 Temperature Records--Flue gas temperatures, feed water temperatures and 
 steam temperatures are all taken with recording thermometers, any number 
 of which will, when properly calibrated, give accurate results. 
   
 A record of flue temperatures is serviceable in checking stack losses 
 and, in general, the cleanliness of the boiler. A record of steam 
 temperatures, where superheaters are used, will indicate excessive 
 fluctuations and lead to an investigation of their cause. Feed 
 temperatures are valuable in showing that the full benefit of the 
 exhaust steam is being derived. 
   
 Draft Regulation--As the capacity of a boiler varies with the combustion 
 rate and this rate with the draft, an automatic apparatus satisfactorily 
 varying this draft with the capacity demands on the boiler will 
 obviously be advantageous. 
   
 As has been pointed out, any fuel has some rate of combustion at which 
 the best results will be obtained. In a properly designed plant where 
 the load is reasonably steady, the draft necessary to secure such a rate 
 may be regulated automatically. 
   
 Automatic apparatus for the regulation of draft has recently reached a 
 stage of perfection which in the larger plants at any rate makes its 
 installation advisable. The installation of a draft gauge or gauges is 
 strongly to be recommended and a record of such drafts should be kept as 
 being a check on the combustion rates. 
   
 An important feature to be considered in the installing of all recording 
 apparatus is its location. Thermometers, draft gauges and flue gas 
 sampling pipes should be so located as to give as nearly as possible an 
 average of the conditions, the gases flowing freely over the ends of the 
 thermometers, couples and sampling pipes. With the location permanent, 
 there is no security that the samples may be considered an average but 
 in any event comparative results will be secured which will be useful in 
 plant operation. The best permanent location of apparatus will vary 
 considerably with the design of the boiler. 
   
 It may not be out of place to refer briefly to some of the shortcomings 
 found in boiler room practice, with a suggestion as to a means of 
 overcoming them. 
   
 1st. It is sometimes found that the operating force is not fully 
 acquainted with the boilers and apparatus. Probably the most general of 
 such shortcomings is the fixed idea in the heads of the operatives that 
 boilers run above their rated capacity are operating under a state of 
 strain and that by operating at less than their rated capacity the most 
 economical service is assured, whereas, by determining what a boiler 
 will do, it may be found that the most economical rating under the 
 conditions of the plant will be considerably in excess of the builder's 
 rating. Such ideas can be dislodged only by demonstrating to the 
 operatives what maximum load the boilers can carry, showing how the 
 economy will vary with the load and the determining of the economical 
 load for the individual plant in question. 
   
 2nd. Stokers. With stoker-fired boilers, it is essential that the 
 operators know the limitations of their stokers as determined by their 
 individual installation. A thorough understanding of the requirements of 
 efficient handling must be insisted upon. The operatives must realize 
 that smokeless stacks are not necessarily the indication of good 
 combustion for, as has been pointed out, absolute smokelessness is 
 oftentimes secured at an enormous loss in efficiency through excess air. 
   
 Another feature in stoker-fired plants is in the cleaning of fires. It 
 must be impressed upon the operatives that before the fires are cleaned 
 they should be put into condition for such cleaning. If this cleaning is 
 done at a definite time, regardless of whether the fires are in the best 
 condition for cleaning, there will be a great loss of good fuel with the 
 ashes. 
   
 3rd. It is necessary that in each individual plant there be a basis on 
 which to judge the cleanliness of a boiler. From the operative's 
 standpoint, it is probably more necessary that there be a thorough 
 understanding of the relation between scale and tube difficulties than 
 between scale and efficiency. It is, of course, impossible to keep 
 boilers absolutely free from scale at all times, but experience in each 
 individual plant determines the limit to which scale can be allowed to 
 form before tube difficulties will begin or a perceptible falling off in 
 efficiency will take place. With such a limit of scale formation fixed, 
 the operatives should be impressed with the danger of allowing it to be 
 exceeded. 
   
 4th. The operatives should be instructed as to the losses resulting from 
 excess air due to leaks in the setting and as to losses in efficiency 
 and capacity due to the by-passing of gases through the setting, that 
 is, not following the path of the baffles as originally installed. In 
 replacing tubes and in cleaning the heating surfaces, care must be taken 
 not to dislodge baffle brick or tile. 
   
 [Illustration: 2000 Horse-power Installation of Babcock & Wilcox 
 Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the 
 Sunnyside Plant of the Pennsylvania Tunnel and Terminal Railroad Co., 
 Long Island City, N. Y.] 
   
 5th. That an increase in the temperature of the feed reduces the amount 
 of work demanded from the boiler has been shown. The necessity of 
 keeping the feed temperature as high as the quantity of exhaust steam 
 will allow should be thoroughly understood. As an example of this, there 
 was a case brought to our attention where a large amount of exhaust 
 steam was wasted simply because the feed pump showed a tendency to leak 
 if the temperature of feed water was increased above 140 degrees. The 
 amount wasted was sufficient to increase the temperature to 180 degrees 
 but was not utilized simply because of the slight expense necessary to 
 overhaul the feed pump. 
   
 The highest return will be obtained when the speed of the feed pumps is 
 maintained reasonably constant for should the pumps run very slowly at 
 times, there may be a loss of the steam from other auxiliaries by 
 blowing off from the heaters. 
   
 6th. With a view to checking steam losses through the useless blowing of 
 safety valves, the operative should be made to realize the great amount 
 of steam that it is possible to get through a pipe of a given size. 
 Oftentimes the fireman feels a sense of security from objections to a 
 drop in steam simply because of the blowing of safety valves, not 
 considering the losses due to such a cause and makes no effort to check 
 this flow either by manipulation of dampers or regulation of fires. 
   
 The few of the numerous shortcomings outlined above, which may be found 
 in many plants, are almost entirely due to lack of knowledge on the part 
 of the operating crew as to the conditions existing in their own plants 
 and the better performances being secured in others. Such shortcomings 
 can be overcome only by the education of the operatives, the showing of 
 the defects of present methods, and instruction in better methods. Where 
 such instruction is necessary, the value of records is obvious. There is 
 fortunately a tendency toward the employment of a better class of labor 
 in the boiler room, a tendency which is becoming more and more marked as 
 the realization of the possible saving in this end of the plant 
 increases. 
   
 The second aspect of boiler room management, dealing with specific 
 recommendations as to the care and operation of the boilers, is dictated 
 largely by the nature of the apparatus. Some of the features to be 
 watched in considering this aspect follow. 
   
 Before placing a new boiler in service, a careful and thorough 
 examination should be made of the pressure parts and the setting. The 
 boiler as erected should correspond in its baffle openings, where 
 baffles are adjustable, with the prints furnished for its erection, and 
 such baffles should be tight. The setting should be so constructed that 
 the boiler is free to expand without interfering with the brickwork. 
 This ability to expand applies also to blow-off and other piping. After 
 erection all mortar and chips of brick should be cleaned from the 
 pressure parts. The tie rods should be set up snug and then slacked 
 slightly until the setting has become thoroughly warm after the first 
 firing. The boiler should be examined internally before starting to 
 insure the absence of dirt, any foreign material such as waste, and 
 tools. Oil and paint are sometimes found in the interior of a new boiler 
 and where such is the case, a quantity of soda ash should be placed 
 within it, the boiler filled with water to its normal level and a slow 
 fire started. After twelve hours of slow simmering, the fire should be 
 allowed to die out, the boiler cooled slowly and then opened and washed 
 out thoroughly. Such a proceeding will remove all oil and grease from 
 the interior and prevent the possibility of foaming and tube 
 difficulties when the boiler is placed in service. 
   
 The water column piping should be examined and known to be free and 
 clear. The water level, as indicated by the gauge glass, should be 
 checked by opening the gauge cocks. 
   
 The method of drying out a brick setting before placing a boiler in 
 operation is described later in the discussion of boiler settings. 
   
 A boiler should not be cut into the line with other boilers until the 
 pressure within it is approximately that in the steam main. The boiler 
 stop valve should be opened very slowly until it is fully opened. The 
 arrangement of piping should be such that there can be no possibility of 
 water collecting in a pocket between the boiler and the main, from which 
 it can be carried over into the steam line when a boiler is cut in. 
   
 In regular operation the safety valve and steam gauge should be checked 
 daily. In small plants the steam pressure should be raised sufficiently 
 to cause the safety valves to blow, at which time the steam gauge should 
 indicate the pressure at which the valve is known to be set. If it does 
 not, one is in error and the gauge should be compared with one of known 
 accuracy and any error at once rectified. 
   
 In large plants such a method of checking would result in losses too 
 great to be allowed. Here the gauges and valves are ordinarily checked 
 at the time a boiler is cut out, the valves being assured of not 
 sticking by daily instantaneous opening through manipulation by hand of 
 the valve lever. The daily blowing of the safety valve acts not only as 
 a check on the gauge but insures the valve against sticking. 
   
 The water column should be blown down thoroughly at least once on every 
 shift and the height of water indicated by the glass checked by the 
 gauge cocks. The bottom blow-offs should be kept tight. These should be 
 opened at least once daily to blow from the mud drum any sediment that 
 may have collected and to reduce the concentration. The amount of 
 blowing down and the frequency is, of course, determined by the nature 
 of the feed water used. 
   
 In case of low water, resulting either from carelessness or from some 
 unforeseen condition of operation, the essential object to be obtained 
 is the extinguishing of the fire in the quickest possible manner. Where 
 practicable, this is best accomplished by the playing of a heavy stream 
 of water from a hose on the fire. Another method, perhaps not so 
 efficient, but more generally recommended, is the covering of the fire 
 with wet ashes or fresh fuel. A boiler so treated should be cut out of 
 line after such an occurrence and a thorough inspection made to 
 ascertain what damage, if any, has been done before it is again placed 
 in service. 
   
 The efficiency and capacity depend to an extent very much greater than 
 is ordinarily realized upon the cleanliness of the heating surfaces, 
 both externally and internally, and too much stress cannot be put upon 
 the necessity for systematic cleaning as a regular feature in the plant 
 operation. 
   
 The outer surfaces of the tubes should be blown free from soot at 
 regular intervals, the frequency of such cleaning periods being 
 dependent upon the class of fuel used. The most efficient way of blowing 
 soot from the tubes is by means of a steam lance with which all parts of 
 the surfaces are reached and swept clean. There are numerous soot 
 blowing devices on the market which are designed to be permanently fixed 
 within the boiler setting. Where such devices are installed, there are 
 certain features that must be watched to avoid trouble. If there is any 
 leakage of water of condensation within the setting coming into contact 
 with the boiler tubes, it will tend toward corrosion, or if in contact 
 with the heated brickwork will cause rapid disintegration of the 
 setting. If the steam jets are so placed that they impinge directly 
 against the tubes, erosion may take place. Where such permanent soot 
 blowers are installed, too much care cannot be taken to guard against 
 these possibilities. 
   
 Internally, the tubes must be kept free from scale, the ingredients of 
 which a study of the chapter on the impurities of water indicates are 
 present in varying quantities in all feed waters. Not only has the 
 presence of scale a direct bearing on the efficiency and capacity to be 
 obtained from a boiler but its absence is an assurance against the 
 burning out of tubes. 
   
 In the absence of a blow-pipe action of the flames, it is impossible to 
 burn a metal surface where water is in intimate contact with that 
 surface. 
   
 In stoker-fired plants where a blast is used, and the furnace is not 
 properly designed, there is a danger of a blow-pipe action if the fires 
 are allowed to get too thin. The rapid formation of steam at such points 
 of localized heat may lead to the burning of the metal of the tubes. 
   
 Any formation of scale on the interior surface of a boiler keeps the 
 water from such a surface and increases its tendency to burn. Particles 
 of loose scale that may become detached will lodge at certain points in 
 the tubes and localize this tendency at such points. It is because of 
 the danger of detaching scale and causing loose flakes to be present 
 that the use of a boiler compound is not recommended for the removal of 
 scale that has already formed in a boiler. This question is covered in 
 the treatment of feed waters. If oil is allowed to enter a boiler, its 
 action is the same as that of scale in keeping the water away from the 
 metal surfaces. 
 It has been proven beyond a doubt that a very large percentage of tube 
 losses is due directly to the presence of scale which, in many 
 instances, has been so thin as to be considered of no moment, and the 
 importance of maintaining the boiler heating surfaces in a clean 
 condition cannot be emphasized too strongly. 
   
 The internal cleaning can best be accomplished by means of an air or 
 water-driven turbine, the cutter heads of which may be changed to handle 
 various thicknesses of scale. Fig. 41 shows a turbine cleaner with 
 various cutting heads, which has been found to give satisfactory 
 service. 
   
 Where a water-driven turbine is used, it should be connected to a pump 
 which will deliver at least 120 gallons per minute per cleaner at 150 
 pounds pressure. This pressure should never be less than 90 pounds if 
 satisfactory results are desired. Where an air-driven turbine is used, 
 the pressure should be at least 100 pounds, though 150 pounds is 
 preferable, and sufficient water should be introduced into the tube to 
 keep the cutting head cool and assist in washing down the scale as it is 
 chipped off. 
   
 Where scale has been allowed to accumulate to an excessive thickness, 
 the work of removal is difficult and tedious. Where such a heavy scale 
 is of sulphate formation, its removal may be assisted by filling the 
 boiler with water to which there has been added a quantity of soda ash, 
 a bucketful to each drum, starting a low fire and allowing the water to 
 boil for twenty-four hours with no pressure on the boiler. It should be 
 cooled slowly, drained, and the turbine cleaner used immediately, as the 
 scale will tend to harden rapidly under the action of the air. 
   
 Where oil has been allowed to get into a boiler, it should be removed 
 before placing the boiler in service, as described previously where 
 reference is made to its removal by boiling out with soda ash. 
   
 Where pitting or corrosion is noted, the parts affected should be 
 carefully cleaned and the interior of the drums should be painted with 
 white zinc if the boiler is to remain idle. The cause of such action 
 should be immediately ascertained and steps taken to apply the proper 
 remedy. 
   
 When making an internal inspection of a boiler or when cleaning the 
 interior heating surfaces, great care must be taken to guard against the 
 possibility of steam entering the boiler in question from other boilers 
 on the same line either through the careless opening of the boiler stop 
 valve or some auxiliary valve or from an open blow-off. Bad accidents 
 through scalding have resulted from the neglect of this precaution. 
   
 Boiler brickwork should be kept pointed up and all cracks filled. The 
 boiler baffles should be kept tight to prevent by-passing of any gases 
 through the heating surfaces. 
   
 Boilers should be taken out of service at regular intervals for cleaning 
 and repairs. When this is done, the boiler should be cooled slowly, and 
 when possible, be allowed to stand for twenty-four hours after the fire 
 is drawn before opening. The cooling process should not be hurried by 
 allowing cold air to rush through the setting as this will invariably 
 cause trouble with the brickwork. When a boiler is off for cleaning, a 
 careful examination should be made of its condition, both external and 
 internal, and all leaks of steam, water and air through the setting 
 stopped. If water is allowed to come into contact with brickwork that is 
 heated, rapid disintegration will take place. If water is allowed to 
 come into contact with the metal of the boiler when out of service, 
 there is a likelihood of corrosion. 
   
 If a boiler is to remain idle for some time, its deterioration may be 
 much more rapid than when in service. If the period for which it is to 
 be laid off is not to exceed three months, it may be filled with water 
 while out of service. The boiler should first be cleaned thoroughly, 
 internally and externally, all soot and ashes being removed from the 
 exterior of the pressure parts and any accumulation of scale removed 
 from the interior surfaces. It should then be filled with water, to 
 which five or six pails of soda ash have been added, a slow fire started 
 to drive the air from the boiler, the fire drawn and the boiler pumped 
 full. In this condition it may be kept for some time without bad 
 effects. 
   
 If the boiler is to be out of service for more than three months, it 
 should be emptied, drained and thoroughly dried after being cleaned. A 
 tray of quick lime should be placed in each drum, the boiler closed, the 
 grates covered and a quantity of quick lime placed on top of the 
 covering. Special care should be taken to prevent air, steam or water 
 leaks into the boiler or onto the pressure parts to obviate danger of 
 corrosion. 
   
 
 
 
 BRICKWORK BOILER SETTINGS 
 A consideration of the losses in boiler efficiency, due to the effects 
 of excess air, clearly indicates the necessity of maintaining the brick 
 setting of a boiler tight and free from air leaks. In view of the 
 temperatures to which certain portions of such a setting are subjected, 
 the material to be used in its construction must be of the best 
 procurable. 
   
 Boiler settings to-day consist almost universally of brickwork--two 
 kinds being used, namely, red brick and fire brick. 
   
 The red brick should only be used in such portions of the setting as are 
 well protected from the heat. In such location, their service is not so 
 severe as that of fire brick and ordinarily, if such red brick are 
 sound, hard, well burned and uniform, they will serve their purpose. 
   
 The fire brick should be selected with the greatest care, as it is this 
 portion of the setting that has to endure the high temperatures now 
 developed in boiler practice. To a great extent, the life of a boiler 
 setting is dependent upon the quality of the fire brick used and the 
 care exercised in its laying. 
   
 The best fire brick are manufactured from the fire clays of 
 Pennsylvania. South and west from this locality the quality of fire clay 
 becomes poorer as the distance increases, some of the southern fire 
 clays containing a considerable percentage of iron oxide. 
   
 Until very recently, the important characteristic on which to base a 
 judgment of the suitability of fire brick for use in connection with 
 boiler settings has been considered the melting point, or the 
 temperature at which the brick will liquify and run. Experience has 
 shown, however, that this point is only important within certain limits 
 and that the real basis on which to judge material of this description 
 is, from the boiler man's standpoint, the quality of plasticity under a 
 given load. This tendency of a brick to become plastic occurs at a 
 temperature much below the melting point and to a degree that may cause 
 the brick to become deformed under the stress to which it is subjected. 
 The allowable plastic or softening temperature will naturally be 
 relative and dependent upon the stress to be endured. 
   
 With the plasticity the determining factor, the perfect fire brick is 
 one whose critical point of plasticity lies well above the working 
 temperature of the fire. It is probable that there are but few brick on 
 the market which would not show, if tested, this critical temperature at 
 the stress met with in arch construction at a point less than 2400 
 degrees. The fact that an arch will stand for a long period under 
 furnace temperatures considerably above this point is due entirely to 
 the fact that its temperature as a whole is far below the furnace 
 temperature and only about 10 per cent of its cross section nearest the 
 fire approaches the furnace temperature. This is borne out by the fact 
 that arches which are heated on both sides to the full temperature of an 
 ordinary furnace will first bow down in the middle and eventually fall. 
   
 A method of testing brick for this characteristic is given in the 
 Technologic Paper No. 7 of the Bureau of Standards dealing with "The 
 testing of clay refractories with special reference to their load 
 carrying capacity at furnace temperatures." Referring to the test for 
 this specific characteristic, this publication recommends the following: 
 "When subjected to the load test in a manner substantially as described 
 in this bulletin, at 1350 degrees centigrade (2462 degrees Fahrenheit), 
 and under a load of 50 pounds per square inch, a standard fire brick 
 tested on end should show no serious deformation and should not be 
 compressed more than one inch, referred to the standard length of nine 
 inches." 
   
 In the Bureau of Standards test for softening temperature, or critical 
 temperature of plasticity under the specified load, the brick are tested 
 on end. In testing fire brick for boiler purposes such a method might be 
 criticised, because such a test is a compression test and subject to 
 errors from unequal bearing surfaces causing shear. Furthermore, a 
 series of samples, presumably duplicates, will not fail in the same way, 
 due to the mechanical variation in the manufacture of the brick. Arches 
 that fail through plasticity show that the tensile strength of the brick 
 is important, this being evidenced by the fact that the bottom of a 
 wedge brick in an arch that has failed is usually found to be wider than 
 the top and the adjacent bricks are firmly cemented together. 
   
 A better method of testing is that of testing the brick as a beam 
 subjected to its own weight and not on end. This method has been used 
 for years in Germany and is recommended by the highest authorities in 
 ceramics. It takes into account the failure by tension in the brick as 
 well as by compression and thus covers the tension element which is 
 important in arch construction. 
   
 The plastic point under a unit stress of 100 pounds per square inch, 
 which may be taken as the average maximum arch stress, should be above 
 2800 degrees to give perfect results and should be above 2400 degrees to 
 enable the brick to be used with any degree of satisfaction. 
   
 The other characteristics by which the quality of a fire brick is to be 
 judged are: 
   
 Fusion point. In view of the fact that the critical temperature of 
 plasticity is below the fusion point, this is only important as an 
 indication from high fusion point of a high temperature of plasticity. 
   
 Hardness. This is a relative quality based on an arbitrary scale of 10 
 and is an indication of probable cracking and spalling. 
   
 Expansion. The lineal expansion per brick in inches. This characteristic 
 in conjunction with hardness is a measure of the physical movement of 
 the brick as affecting a mass of brickwork, such movement resulting in 
 cracked walls, etc. The expansion will vary between wide limits in 
 different brick and provided such expansion is not in excess of, say, 
 .05 inch in a 9-inch brick, when measured at 2600 degrees, it is not 
 particularly important in a properly designed furnace, though in general 
 the smaller the expansion the better. 
   
 Compression. The strength necessary to cause crushing of the brick at 
 the center of the 4½ inch face by a steel block one inch square. The 
 compression should ordinarily be low, a suggested standard being that a 
 brick show signs of crushing at 7500 pounds. 
   
 Size of Nodules. The average size of flint grains when the brick is 
 carefully crushed. The scale of these sizes may be considered: Small, 
 size of anthracite rice; large, size of anthracite pea. 
   
 Ratio of Nodules. The percentage of a given volume occupied by the flint 
 grains. This scale may be considered: High, 90 to 100 per cent; medium, 
 50 to 90 per cent; low, 10 to 50 per cent. 
   
 The statement of characteristics suggested as desirable, are for arch 
 purposes where the hardest service is met. For side wall purposes the 
 compression and hardness limit may be raised considerably and the 
 plastic point lowered. 
   
 Aside from the physical properties by which a fire brick is judged, it 
 is sometimes customary to require a chemical analysis of the brick. Such 
 an analysis is only necessary as determining the amount of total basic 
 fluxes (K_{2}O, Na_{2}O, CaO, MgO and FeO). These fluxes are ordinarily 
 combined into one expression, indicated by the symbol RO. This total 
 becomes important only above 0.2 molecular equivalent as expressed in 
 ceramic empirical formulae, and this limit should not be exceeded.[75] 
   
 From the nature of fire brick, their value can only be considered from a 
 relative standpoint. Generally speaking, what are known as first-grade 
 fire brick may be divided into three classes, suitable for various 
 conditions of operation, as follows: 
   
 Class A. For stoker-fired furnaces where high overloads are to be 
 expected or where other extreme conditions of service are apt to occur. 
   
 Class B. For ordinary stoker settings where there will be no excessive 
 overloads required from the boiler or any hand-fired furnaces where the 
 rates of driving will be high for such practice. 
   
 Class C. For ordinary hand-fired settings where the presumption is that 
 the boilers will not be overloaded except at rare intervals and for 
 short periods only. 
   
 Table 61 gives the characteristics of these three classes according to 
 the features determining the quality. This table indicates that the 
 hardness of the brick in general increases with the poorer qualities. 
 Provided the hardness is sufficient to enable the brick to withstand its 
 load, additional hardness is a detriment rather than an advantage. 
   
                                  TABLE 61 
   
                  APPROXIMATE CLASSIFICATION OF FIRE BRICK 
   
 ________________________________________________________________________ 
 |                     |               |               |               | 
 | Characteristics     |     Class A   |     Class B   |     Class C   | 
 |_____________________|________________|________________|________________| 
 |                     |               |               |               | 
 | Fuse Point, Degrees | Safe at Degrees| Safe at Degrees| Safe at Degrees| 
 |   Fahrenheit       |   3200-3300   |   2900-3200   |   2900-3000 | 
 |                     |               |               |               | 
 | Compression Pounds |   6500-7500   |   7500-11,000 |   8500-15,000 | 
 |                     |               |               |               | 
 | Hardness Relative   |      1-2     |       2-4     |       4-6     | 
 |                     |               |               |               | 
 | Size of Nodules     |     Medium     |   Medium to   |Medium to Large | 
 |                     |               | Medium Large |              | 
 |                     |               |               |               | 
 | Ratio of Nodules   |     High     | Medium to High |   Medium Low   | 
 |                     |               |               |   to Medium   | 
 |_____________________|________________|________________|________________| 
   
 An approximate determination of the quality of a fire brick may be made 
 from the appearance of a fracture. Where such a fracture is open, clean, 
 white and flinty, the brick in all probability is of a good quality. If 
 this fracture has the fine uniform texture of bread, the brick is 
 probably poor. 
   
 In considering the heavy duty of brick in boiler furnaces, experience 
 shows that arches are the only part that ordinarily give trouble. These 
 fail from the following causes: 
   
 Bad workmanship in laying up of brick. This feature is treated below. 
   
 The tendency of a brick to become plastic at a temperature below the 
 fusing point. The limits of allowable plastic temperature have already 
 been pointed out. 
   
 Spalling. This action occurs on the inner ends of combustion arches 
 where they are swept by gases at a high velocity at the full furnace 
 temperature. The most troublesome spalling arises through cold air 
 striking the heated brickwork. Failure from this cause is becoming rare, 
 due to the large increase in number of stoker installations in which 
 rapid temperature changes are to a great degree eliminated. Furthermore, 
 there are a number of brick on the market practically free from such 
 defects and where a new brick is considered, it can be tried out and if 
 the defect exists, can be readily detected and the brick discarded. 
   
 Failures of arches from the expansive power of brick are also rare, due 
 to the fact that there are a number of brick in which the expansion is 
 well within the allowable limits and the ease with which such defects 
 may be determined before a brick is used. 
   
 Failures through chemical disintegration. Failure through this cause is 
 found only occasionally in brick containing a high percentage of iron 
 oxide. 
   
 With the grade of brick selected best suited to the service of the 
 boiler to be set, the other factor affecting the life of the setting is 
 the laying. It is probable that more setting difficulties arise from the 
 improper workmanship in the laying up of brick than from poor material, 
 and to insure a setting which will remain tight it is necessary that the 
 masonry work be done most carefully. This is particularly true where the 
 boiler is of such a type as to require combustion arches in the furnace. 
   
 Red brick should be laid in a thoroughly mixed mortar composed of one 
 volume of Portland cement, 3 volumes of unslacked lime and 16 volumes of 
 clear sharp sand. Not less than 2½ bushels of lime should be used in the 
 laying up of 1000 brick. Each brick should be thoroughly embedded and 
 all joints filled. Where red brick and fire brick are both used in the 
 same wall, they should be carried up at the same time and thoroughly 
 bonded to each other. 
   
 All fire brick should be dry when used and protected from moisture until 
 used. Each brick should be dipped in a thin fire clay wash, "rubbed and 
 shoved" into place, and tapped with a wooden mallet until it touches the 
 brick next below it. It must be recognized that fire clay is not a 
 cement and that it has little or no holding power. Its action is that of 
 a filler rather than a binder and no fire-clay wash should be used which 
 has a consistency sufficient to permit the use of a trowel. 
   
 All fire-brick linings should be laid up four courses of headers and one 
 stretcher. Furnace center walls should be entirely of fire brick. If the 
 center of such walls are built of red brick, they will melt down and 
 cause the failure of the wall as a whole. 
   
 Fire-brick arches should be constructed of selected brick which are 
 smooth, straight and uniform. The frames on which such arches are built, 
 called arch centers, should be constructed of batten strips not over 2 
 inches wide. The brick should be laid on these centers in courses, not 
 in rings, each joint being broken with a bond equal to the length of 
 half a brick. Each course should be first tried in place dry, and 
 checked with a straight edge to insure a uniform thickness of joint 
 between courses. Each brick should be dipped on one side and two edges 
 only and tapped into place with a mallet. Wedge brick courses should be 
 used only where necessary to keep the bottom faces of the straight brick 
 course in even contact with the centers. When such contact cannot be 
 exactly secured by the use of wedge brick, the straight brick should 
 lean away from the center of the arch rather than toward it. When the 
 arch is approximately two-thirds completed, a trial ring should be laid 
 to determine whether the key course will fit. When some cutting is 
 necessary to secure such a fit, it should be done on the two adjacent 
 courses on the side of the brick away from the key. It is necessary that 
 the keying course be a true fit from top to bottom, and after it has 
 been dipped and driven it should not extend below the surface of the 
 arch, but preferably should have its lower ledge one-quarter inch above 
 this surface. After fitting, the keys should be dipped, replaced 
 loosely, and the whole course driven uniformly into place by means of a 
 heavy hammer and a piece of wood extending the full length of the keying 
 course. Such a driving in of this course should raise the arch as a 
 whole from the center. The center should be so constructed that it may 
 be dropped free of the arch when the key course is in place and removed 
 from the furnace without being burned out. 
 Care of Brickwork--Before a boiler is placed in service, it is essential 
 that the brickwork setting be thoroughly and properly dried, or 
 otherwise the setting will invariably crack. The best method of starting 
 such a process is to block open the boiler damper and the ashpit doors 
 as soon as the brickwork is completed and in this way maintain a free 
 circulation of air through the setting. If possible, such preliminary 
 drying should be continued for several days before any fire is placed in 
 the furnace. When ready for the drying out fire, wood should be used at 
 the start in a light fire which may be gradually built up as the walls 
 become warm. After the walls have become thoroughly heated, coal may be 
 fired and the boiler placed in service. 
   
 As already stated, the life of a boiler setting is dependent to a large 
 extent upon the material entering into its construction and the care 
 with which such material is laid. A third and equally important factor 
 in the determining of such life is the care given to the maintaining of 
 the setting in good condition after the boiler is placed in operation. 
 This feature is discussed more fully in the chapter dealing with general 
 boiler room management. 
   
 Steel Casings--In the chapter dealing with the losses operating against 
 high efficiencies as indicated by the heat balance, it has been shown 
 that a considerable portion of such losses is due to radiation and to 
 air infiltration into the boiler setting. These losses have been 
 variously estimated from 2 to 10 per cent, depending upon the condition 
 of the setting and the amount of radiation surface, the latter in turn 
 being dependent upon the size of the boiler used. In the modern efforts 
 after the highest obtainable plant efficiencies much has been done to 
 reduce such losses by the use of an insulated steel casing covering the 
 brickwork. In an average size boiler unit the use of such casing, when 
 properly installed, will reduce radiation losses from one to two per 
 cent., over what can be accomplished with the best brick setting without 
 such casing and, in addition, prevent the loss due to the infiltration 
 of air, which may amount to an additional five per cent., as compared 
 with brick settings that are not maintained in good order. Steel plate, 
 or steel plate backed by asbestos mill-board, while acting as a 
 preventative against the infiltration of air through the boiler setting, 
 is not as effective from the standpoint of decreasing radiation losses 
 as a casing properly insulated from the brick portion of the setting by 
 magnesia block and asbestos mill-board. A casing which has been found to 
 give excellent results in eliminating air leakage and in the reduction 
 of radiation losses is clearly illustrated on page 306. 
   
 Many attempts have been made to use some material other than brick for 
 boiler settings but up to the present nothing has been found that may be 
 considered successful or which will give as satisfactory service under 
 severe conditions as properly laid brickwork. 
   
 
 
 
 BOILER ROOM PIPING 
 In the design of a steam plant, the piping system should receive the 
 most careful consideration. Aside from the constructive details, good 
 practice in which is fairly well established, the important factors are 
 the size of the piping to be employed and the methods utilized in 
 avoiding difficulties from the presence in the system of water of 
 condensation and the means employed toward reducing radiation losses. 
   
 Engineering opinion varies considerably on the question of material of 
 pipes and fittings for different classes of work, and the following is 
 offered simply as a suggestion of what constitutes good representative 
 practice. 
   
 All pipe should be of wrought iron or soft steel. Pipe at present is 
 made in "standard", "extra strong"[76] and "double extra strong" 
 weights. Until recently, a fourth weight approximately 10 per cent 
 lighter than standard and known as "Merchants" was built but the use of 
 this pipe has largely gone out of practice. Pipe sizes, unless otherwise 
 stated, are given in terms of nominal internal diameter. Table 62 gives 
 the dimensions and some general data on standard and extra strong 
 wrought-iron pipe. 
   
                              TABLE 62 
   
            DIMENSIONS OF STANDARD AND EXTRA STRONG[76] 
                    WROUGHT-IRON AND STEEL PIPE 
   
 _______________________________________________________________ 
 |         |                         |                         | 
 |         |         Diameter         |     Circumference       | 
 |         |__________________________|__________________________| 
 |         |       |                 |       |                 | 
 |         |External|   Internal     |External|   Internal     | 
 |         |Standard|_________________|Standard|_________________| 
 |         | and   |       |       | and   |       |       | 
 | Nominal | Extra |Standard| Extra | Extra |Standard| Extra | 
 | Size   | Strong |       | Strong | Strong |       | Strong | 
 |_________|________|________|________|________|________|________| 
 |         |       |       |       |       |       |       | 
 |     1/8 |   .405 |   .269 |   .215 | 1.272 |   .848 |   .675 | 
 |     1/4 |   .540 |   .364 |   .302 | 1.696 | 1.144 |   .949 | 
 |     3/8 |   .675 |   .493 |   .423 | 2.121 | 1.552 | 1.329 | 
 |     1/2 |   .840 |   .622 |   .546 | 2.639 | 1.957 | 1.715 | 
 |     3/4 | 1.050 |   .824 |   .742 | 3.299 | 2.589 | 2.331 | 
 |   1     | 1.315 | 1.049 |   .957 | 4.131 | 3.292 | 3.007 | 
 |   1-1/4 | 1.660 | 1.380 | 1.278 | 5.215 | 4.335 | 4.015 | 
 |   1-1/2 | 1.900 | 1.610 | 1.500 | 5.969 | 5.061 | 4.712 | 
 |   2     | 2.375 | 2.067 | 1.939 | 7.461 | 6.494 | 6.092 | 
 |   2-1/2 | 2.875 | 2.469 | 2.323 | 9.032 | 7.753 | 7.298 | 
 |   3     | 3.500 | 3.068 | 2.900 | 10.996 | 9.636 | 9.111 | 
 |   3-1/2 | 4.000 | 3.548 | 3.364 | 12.566 | 11.146 | 10.568 | 
 |   4     | 4.500 | 4.026 | 3.826 | 14.137 | 12.648 | 12.020 | 
 |   4-1/2 | 5.000 | 4.506 | 4.290 | 15.708 | 14.162 | 13.477 | 
 |   5     | 5.563 | 5.047 | 4.813 | 17.477 | 15.849 | 15.121 | 
 |   6     | 6.625 | 6.065 | 5.761 | 20.813 | 19.054 | 18.099 | 
 |   7     | 7.625 | 7.023 | 6.625 | 23.955 | 22.063 | 20.813 | 
 |   8     | 8.625 | 7.981 | 7.625 | 27.096 | 25.076 | 23.955 | 
 |   9   | 9.625 | 8.941 | 8.625 | 30.238 | 28.089 | 27.096 | 
 | 10     | 10.750 | 10.020 | 9.750 | 33.772 | 31.477 | 30.631 | 
 | 11     | 11.750 | 11.000 | 10.750 | 36.914 | 34.558 | 33.772 | 
 | 12     | 12.750 | 12.000 | 11.750 | 40.055 | 37.700 | 36.914 | 
 |_________|________|________|________|________|________|________| 
   
   
 __________________________________________________________ 
 |         |                     |       |                 | 
 |         |                     | Length |                 | 
 |        |       Internal     |   of   | Nominal Weight | 
 |         |     Transverse     |Pipe in |   Pounds per   | 
 |         |         Area       |Feet per|     Foot       | 
 |         |_____________________| Square |_________________| 
 |         |        |         |Foot of |       |       | 
 | Nominal | Standard | Extra   |External|Standard| Extra | 
 | Size   |         | Strong |Surface |       | Strong | 
 |_________|__________|__________|________|________|________| 
 |         |         |         |       |       |       | 
 |     1/8 |   .0573 |   .0363 | 9.440 |   .244 |   .314 | 
 |     1/4 |   .1041 |   .0716 | 7.075 |   .424 |   .535 | 
 |     3/8 |   .1917 |   .1405 | 5.657 |   .567 |   .738 | 
 |     1/2 |   .3048 |   .2341 | 4.547 |  .850 | 1.087 | 
 |     3/4 |   .5333 |   .4324 | 3.637 | 1.130 | 1.473 | 
 |   1     |   .8626 |   .7193 | 2.904 | 1.678 | 2.171 | 
 |   1-1/4 |   1.496 |   1.287 | 2.301 | 2.272 | 2.996 | 
 |   1-1/2 |   2.038 |   1.767 | 2.010 | 2.717 | 3.631 | 
 |   2     |   3.356 |   2.953 | 1.608 | 3.652 | 5.022 | 
 |   2-1/2 |   4.784 |   4.238 | 1.328 | 5.793 | 7.661 | 
 |   3     |   7.388 |   6.605 | 1.091 | 7.575 | 10.252 | 
 |   3-1/2 |   9.887 |   8.888 |   .955 | 9.109 | 12.505 | 
 |   4    | 12.730 | 11.497 |   .849 | 10.790 | 14.983 | 
 |   4-1/2 | 15.961 | 14.454 |   .764 | 12.538 | 17.611 | 
 |   5     | 19.990 | 18.194 |   .687 | 14.617 | 20.778 | 
 |   6     | 28.888 | 26.067 |   .577 | 18.974 | 28.573 | 
 |   7     | 38.738 | 34.472 |   .501 | 23.544 | 38.048 | 
 |   8     | 50.040 | 45.664 |   .443 | 28.544 | 43.388 | 
 |   9     | 62.776 | 58.426 |   .397 | 33.907 | 48.728 | 
 | 10     | 78.839 | 74.662 |   .355 | 40.483 | 54.735 | 
 | 11     | 95.033 | 90.763 |   .325 | 45.557 | 60.075 | 
 | 12     | 113.098 | 108.43   |   .299 | 49.562 | 65.415 | 
 |_________|__________|__________|________|________|________| 
   
 Dimensions are nominal and except where noted are in inches. 
   
 In connection with pipe sizes, Table 63, giving certain tube data may be 
 found to be of service. 
   
                                  TABLE 63 
   
        TUBE DATA, STANDARD OPEN HEARTH OR LAP WELDED STEEL TUBES 
   
 +-----+--+----+-----+------+------+------+------+-------+-------+-------+ 
 |S E D|B | T | I D |Circumference| Transverse |Square |Length |Nominal| 
 |i x i|. | h | n i |             |   Area     | Feet |in Feet|Weight | 
 |z t a|W | i | t a |             |Square Inches| of   | per |Pounds | 
 |e e m|. | c | e m +------+------+------+------+ Exter |Square | per | 
 | r e| | k | r e |Exter-|Inter-|Exter-|Inter-| -nal |Foot of| Foot | 
 | n t|G | n | n t | nal | nal | nal | nal |Surface| Exter |       | 
 | a e|a | e | a e |     |     |     |     | per | -nal |       | 
 | l r|u | s | l r |     |     |     |     |Foot of|Surface|       | 
 |     |g | s |     |     |     |     |     |Length |       |       | 
 |     |e |   |     |     |     |     |     |       |       |       | 
 +-----+--+----+-----+------+------+------+------+-------+-------+-------+ 
 |1-1/2|10|.134|1.232| 4.712| 3.870|1.7671|1.1921| .392 | 2.546 | 1.955 | 
 |1-1/2| 9|.148|1.204| 4.712| 3.782|1.7671|1.1385| .392 | 2.546 | 2.137 | 
 |1-1/2| 8|.165|1.170| 4.712| 3.676|1.7671|1.0751| .392 | 2.546 | 2.353 | 
 | 2 |10|.134|1.732| 6.283| 5.441|3.1416|2.3560| .523 | 1.909 | 2.670 | 
 | 2 | 9|.148|1.704| 6.283| 5.353|3.1416|2.2778| .523 | 1.909 | 2.927 | 
 | 2 | 8|.165|1.670| 6.283| 5.246|3.1416|2.1904| .523 | 1.909 | 3.234 | 
 |3-1/4|11|.120|3.010|10.210| 9.456|8.2958|7.1157| .850 | 1.175 | 4.011 | 
 |3-1/4|10|.134|2.982|10.210| 9.368|8.2958|6.9840| .850 | 1.175 | 4.459 | 
 |3-1/4| 9|.148|2.954|10.210| 9.280|8.2958|6.8535| .850 | 1.175 | 4.903 | 
 | 4 |10|.134|3.732|12.566|11.724|12.566|10.939| 1.047 | .954 | 5.532 | 
 | 4 | 9|.148|3.704|12.566|11.636|12.566|10.775| 1.047 | .954 | 6.000 | 
 | 4 | 8|.165|3.670|12.566|11.530|12.566|10.578| 1.047 | .954 | 6.758 | 
 +-----+--+----+-----+------+------+------+------+-------+-------+-------+ 
   
 Dimensions are nominal and except where noted are in inches. 
   
 Pipe Material and Thickness--For saturated steam pressures not exceeding 
 160 pounds, all pipe over 14 inches should be 3/8 inch thick O. D. pipe. 
 All other pipe should be standard full weight, except high pressure 
 feed[77] and blow-off lines, which should be extra strong. 
   
 For pressures above 150 pounds up to 200 pounds with superheated steam, 
 all high pressure feed and blow-off lines, high pressure steam lines 
 having threaded flanges, and straight runs and bends of high pressure 
 steam lines 6 inches and under having Van Stone joints should be extra 
 strong. All piping 7 inches and over having Van Stone joints should be 
 full weight soft flanging pipe of special quality. Pipe 14 inches and 
 over should be 3/8 inch thick O. D. pipe. All pipes for these pressures 
 not specified above should be full weight pipe. 
   
 Flanges--For saturated steam, 160 pounds working pressure, all flanges 
 for wrought-iron pipe should be cast-iron threaded. All high pressure 
 threaded flanges should have the diameter thickness and drilling in 
 accordance with the "manufacturer's standard" for "extra heavy" flanges. 
 All low pressure flanges should have diameter, thickness and drilling in 
 accordance with "manufacturer's standard" for "standard flanges." 
   
 The flanges on high pressure lines should be counterbored to receive 
 pipe and prevent the threads from shouldering. The pipe should be 
 screwed through the flange at least 1/16 inch, placed in machine and 
 after facing off the end one smooth cut should be taken over the face of 
 the flange to make it square with the axis of the pipe. 
   
 [Illustration: 2000 Horse-power Installation of Babcock & Wilcox Boilers 
 and Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers at 
 the Kentucky Electric Co., Louisville, Ky.] 
   
 For pressures above 160 pounds, where superheated steam is used, all 
 high pressure steam lines 4 inches and over should have solid rolled 
 steel flanges and special upset lapped joints. In the manufacture of 
 such joints, the ends of the pipe are heated and upset against the face 
 of a holding mandrel conforming to the shape of the flange, the lapped 
 portion of the pipe being flattened out against the face of the mandrel, 
 the upsetting action maintaining the desired thickness of the lap. When 
 cool, both sides of the lap are faced to form a uniform thickness and an 
 even bearing against flange and gasket. The joint, therefore, is a 
 strictly metal to metal joint, the flanges merely holding the lapped 
 ends of the pipe against the gasket. 
   
 A special grade of soft flanging pipe is selected to prevent breaking. 
 The bending action is a severe test of the pipe and if it withstands the 
 bending process and the pressure tests, the reliability of the joint is 
 assured. Such a joint is called a Van Stone joint, though many 
 modifications and improvements have been made since the joint was 
 originally introduced. 
   
 The diameter and thickness of such flanges should be special extra 
 heavy. Such flanges should be turned to diameter, their fronts faced and 
 the backs machined in lieu of spot facing. 
   
 In lines other than given for pressures over 150 pounds, all flanges for 
 wrought-iron pipe should be threaded. All threaded flanges for high 
 pressure superheated lines 3½ inches and under should be "semi-steel" 
 extra heavy. Flanges for other than steam lines should be manufacturer's 
 standard extra heavy. 
   
 Welded flanges are frequently used in place of those described with 
 satisfactory results. 
   
 Fittings--For saturated steam under pressures up to 160 pounds, all 
 fittings 3½ inches and under should be screwed. Fittings 4 inches and 
 over should have flanged ends. Fittings for this pressure should be of 
 cast iron and should have heavy leads and full taper threads. Flanged 
 fittings in high pressure lines should be extra heavy, and in low 
 pressure lines standard weight. Where possible in high pressure flanges 
 and fittings, bolt surfaces should be spot faced to provide suitable 
 bearing for bolt heads and nuts. 
   
 Fittings for superheated steam up to 70 degrees at pressures above 160 
 pounds are sometimes of cast iron.[78] For superheat above 70 degrees 
 such fittings should be "steel castings" and in general these fittings 
 are recommended for any degree of superheat. Fittings for other than 
 high pressure work may be of cast iron, except where superheated steam 
 is carried, where they should be of "wrought steel" or "hard metal". 
 Fittings 3½ inches and under should be screwed, 4 inches and over 
 flanged. 
   
 Flanges for pressures up to 160 pounds in pipes and fittings for low 
 pressure lines, and any fittings for high pressure lines should have 
 plain faces, smooth tool finish, scored with V-shaped grooves for rubber 
 gaskets. High pressure line flanges should have raised faces, projecting 
 the full available diameter inside the bolt holes. These faces should be 
 similarly scored. 
   
 All pipe ½ inch and under should have ground joint unions suitable for 
 the pressure required. Pipe ¾ inch and over should have cast-iron 
 flanged unions. Unions are to be preferred to wrought-iron couplings 
 wherever possible to facilitate dismantling. 
   
 Valves--For 150 pounds working pressure, saturated steam, all valves 2 
 inches and under may have screwed ends; 2½ inches and over should be 
 flanged. All high pressure steam valves 6 inches and over should have 
 suitable by-passes. All valves for use with superheated steam should be 
 of special construction. For pressures above 160 pounds, where the 
 superheat does not exceed 70 degrees, valve bodies, caps and yokes are 
 sometimes made of cast iron, though ordinarily semi-steel will give 
 better satisfaction. The spindles of such valves should be of bronze and 
 there should be special necks with condensing chambers to prevent the 
 superheated steam from blowing through the packing. For pressures over 
 160 pounds and degrees of superheat above 70, all valves 3 inches and 
 over should have valve bodies, caps and yokes of steel castings. 
 Spindles should be of some non-corrosive metal, such as "monel metal". 
 Seat rings should be removable of the same non-corrosive metal as should 
 the spindle seats and plug faces. 
   
 All salt water valves should have bronze spindles, sleeves and packing 
 seats. 
   
 The suggestions as to flanges for different classes of service made on 
 page 311 hold as well for valve flanges, except that such flanges are 
 not scored. 
   
 Automatic stop and check valves are coming into general use with boilers 
 and such use is compulsory under the boiler regulations of certain 
 communities. Where used, they should be preferably placed directly on 
 the boiler nozzle. Where two or more boilers are on one line, in 
 addition to the valve at the boiler, whether this be an automatic valve 
 or a gate valve, there should be an additional gate valve on each boiler 
 branch at the main steam header. 
   
 Relief valves should be furnished at the discharge side of each feed 
 pump and on the discharge side of each feed heater of the closed type. 
   
 Feed Lines--Feed lines should in all instances be made of extra strong 
 pipe due to the corrosive action of hot feed water. While it has been 
 suggested above that cast-iron threaded flanges should be used in such 
 lines, due to the sudden expansion of such pipe in certain instances 
 cast-iron threaded flanges crack before they become thoroughly heated 
 and expand, and for this reason cast-steel threaded flanges will give 
 more satisfactory results. In some instances, wrought-steel and Van 
 Stone joints have been used in feed lines and this undoubtedly is better 
 practice than the use of cast-steel threaded work, though the additional 
 cost is not warranted in all stations. 
   
 Feed valves should always be of the globe pattern. A gate valve cannot 
 be closely regulated and often clatters owing to the pulsations of the 
 feed pump. 
   
 Gaskets--For steam and water lines where the pressure does not exceed 
 160 pounds, wire insertion rubber gaskets 1/16 inch thick will be found 
 to give good service. For low pressure lines, canvas insertion black 
 rubber gaskets are ordinarily used. For oil lines special gaskets are 
 necessary. 
   
 For pressure above 160 pounds carrying superheated steam, corrugated 
 steel gaskets extending the full available diameter inside of the bolt 
 holes give good satisfaction. For high pressure water lines wire 
 inserted rubber gaskets are used, and for low pressure flanged joints 
 canvas inserted rubber gaskets. 
   
 Size of Steam Lines--The factors affecting the proper size of steam 
 lines are the radiation from such lines and the velocity of steam within 
 them. As the size of the steam line increases, there will be an increase 
 in the radiation.[79] As the size decreases, the steam velocity and the 
 pressure drop for a given quantity of steam naturally increases. 
   
 There is a marked tendency in modern practice toward higher steam 
 velocities, particularly in the case of superheated steam. It was 
 formerly considered good practice to limit this velocity to 6000 feet 
 per minute but this figure is to-day considered low. 
   
 In practice the limiting factor in the velocity advisable is the 
 allowable pressure drop. In the description of the action of the 
 throttling calorimeter, it has been demonstrated that there is no loss 
 accompanying a drop in pressure, the difference in energy between the 
 higher and lower pressures appearing as heat, which, in the case of 
 steam flowing through a pipe, may evaporate any condensation present or 
 may be radiated from the pipe. A decrease in pipe area decreases the 
 radiating surface of the pipe and thus the possible condensation. As the 
 heat liberated by the pressure drop is utilized in overcoming or 
 diminishing the tendency toward condensation and the heat loss through 
 radiation, the steam as it enters the prime mover will be drier or more 
 highly superheated where high steam velocities are used than where they 
 are lower, and if enough excess pressure is carried at the boilers to 
 maintain the desired pressure at the prime mover, the pressure drop 
 results in an actual saving rather than a loss. The whole is analogous 
 to standard practice in electrical distributing systems where generator 
 voltage is adjusted to suit the loss in the feeder lines. 
   
 In modern practice, with superheated steam, velocities of 15,000 feet 
 per minute are not unusual and this figure is very frequently exceeded. 
   
 Piping System Design--With the proper size of pipe to be used 
 determined, the most important factor is the provision for the removal 
 of water of condensation that will occur in any system. Such 
 condensation cannot be wholly overcome and if the water of condensation 
 is carried to the prime mover, difficulties will invariably result. 
 Water is practically incompressible and its effect when traveling at 
 high velocities differs little from that of a solid body of equal 
 weight, hence impact against elbows, valves or other obstructions, is 
 the equivalent of a heavy hammer blow that may result in the fracture of 
 the pipe. If there is not sufficient water in the system to produce this 
 result, it will certainly cause knocking and vibration in the pipe, 
 resulting eventually in leaky joints. Where the water reaches the prime 
 mover, its effect will vary from disagreeable knocking to disruption. 
 Too frequently when there are disastrous results from such a cause the 
 boilers are blamed for delivering wet steam when, as a matter of fact, 
 the evil is purely a result of poor piping design, the most common cause 
 of such an action being the pocketing of the water in certain parts of 
 the piping from whence it is carried along in slugs by the steam. The 
 action is particularly severe if steam is admitted to a cold pipe 
 containing water, as the water may then form a partial vacuum by 
 condensing the steam and be projected at a very high velocity through 
 the pipes producing a characteristic sharp metallic knock which often 
 causes bursting of the pipe or fittings. The amount of water present 
 through condensation may be appreciated when it is considered that 
 uncovered 6-inch pipe 150 feet long carrying 3600 pounds of high 
 pressure steam per hour will condense approximately 6 per cent of the 
 total steam carried through radiation. It follows that efficient means 
 of removing condensation water are absolutely imperative and the 
 following suggestions as to such means may be of service: 
   
 The pitch of all pipe should be in the direction of the flow of steam. 
 Wherever a rise is necessary, a drain should be installed. All main 
 headers and important branches should end in a drop leg and each such 
 drop leg and any low points in the system should be connected to the 
 drainage pump. A similar connection should be made to every fitting 
 where there is danger of a water pocket. 
   
 Branch lines should never be taken from the bottom of a main header but 
 where possible should be taken from the top. Each engine supply pipe 
 should have its own separator placed as near the throttle as possible. 
 Such separators should be drained to the drainage system. 
   
 Check valves are frequently placed in drain pipes to prevent steam from 
 entering any portion of the system that may be shut off. 
   
 Valves should be so located that they cannot form water pockets when 
 either open or closed. Globe valves will form a water pocket in the 
 piping to which they are connected unless set with the stem horizontal, 
 while gate valves may be set with the spindle vertical or at an angle. 
 Where valves are placed directly on the boiler nozzle, a drain should be 
 provided above them. 
   
 High pressure drains should be trapped to both feed heaters and waste 
 headers. Traps and meters should be provided with by-passes. Cylinder 
 drains, heater blow-offs and drains, boiler blow-offs and similar lines 
 should be led to waste. The ends of cylinder drains should not extend 
 below the surface of water, for on starting up or on closing the 
 throttle valve with the drains open, water may be drawn back into the 
 cylinders. 
   
                                TABLE 64 
   
            RADIATION FROM COVERED AND UNCOVERED STEAM PIPES 
   
      CALCULATED FOR 160 POUNDS PRESSURE AND 60 DEGREES TEMPERATURE 
   
 +---------------------------------------------------------------------+ 
 |+------+---------------------------+----+----+----+-----+-----+-----+| 
 ||     |                           |   |   |   |     |     |     || 
 || Pipe |                          |1/2 |3/4 | 1 |1-1/4|1-1/2|     || 
 ||Inches|   Thickness of Covering   |inch|inch|inch|inch |inch |Bare || 
 |+------+---------------------------+----+----+----+-----+-----+-----+| 
 ||     |B. t. u. per lineal foot   |   |   |   |     |     |     || 
 ||     | per hour                 |149 |118 | 99 | 86 | 79 | 597 || 
 ||     |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour                 |240 |190 |161 | 138 | 127 | 959 || 
 ||   2 |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour per one degree |   |   |   |     |     |     || 
 ||     | difference in temperature|.770|.613|.519|.445 |.410 |3.198|| 
 |+------+---------------------------+----+----+----+-----+-----+-----+| 
 ||     |B. t. u. per lineal foot   |   |   |   |     |     |     || 
 ||     | per hour                 |247 |193 |160 | 139 | 123 |1085 || 
 ||     |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour                 |210 |164 |136 | 118 | 104 | 921 || 
 ||   4 |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour per one degree |   |   |   |     |     |     || 
 ||     | difference in temperature|.677|.592|.439|.381 |.335 |2.970|| 
 |+------+---------------------------+----+----+----+-----+-----+-----+| 
 ||     |B. t. u. per lineal foot   |   |   |   |     |     |     || 
 ||     | per hour                 |352 |269 |221 | 190 | 167 |1555 || 
 ||     |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour                 |203 |155 |127 | 110 | 96 | 897 || 
 ||   6 |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour per one degree |   |   |   |     |     |     || 
 ||     | difference in temperature|.655|.500|.410|.355 |.310 |2.89 || 
 |+------+---------------------------+----+----+----+-----+-----+-----+| 
 ||     |B. t. u. per lineal foot   |   |   |   |     |     |     || 
 ||     | per hour                 |443 |337 |276 | 235 | 207 |1994 || 
 ||     |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour                 |196 |149 |122 | 104 | 92 | 883 || 
 ||   8 |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour per one degree |   |   |   |     |     |     || 
 ||     | difference in temperature|.632|.481|.394|.335 |.297 |2.85 || 
 |+------+---------------------------+----+----+----+-----+-----+-----+| 
 ||     |B. t. u. per lineal foot   |   |   |   |     |     |     || 
 ||     | per hour                 |549 |416 |337 | 287 | 250 |2468 || 
 ||     |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour                 |195 |148 |120 | 102 | 89 | 877 || 
 || 10 |B. t. u. per square foot   |   |   |   |     |     |     || 
 ||     | per hour per one degree |   |   |   |     |     |     || 
 ||     | difference in temperature|.629|.477|.387|.329 |.287 |2.83 || 
 |+------+---------------------------+----+----+----+-----+-----+-----+| 
 +---------------------------------------------------------------------+ 
   
 Covering--Magnesia, canvas covered. 
   
 For calculating radiation for pressure and temperature other than 160 
 pounds, and 60 degrees, use B. t. u. figures for one degree difference. 
   
 Radiation from Pipes--The evils of the presence of condensed steam in 
 piping systems have been thoroughly discussed above and in some of the 
 previous articles. Condensation resulting from radiation, while it 
 cannot be wholly obviated, can, by proper installation, be greatly 
 reduced. 
   
 Bare pipe will radiate approximately 3 B. t. u. per hour per square foot 
 of exposed surface per one degree of difference in temperature between 
 the steam contained and the external air. This figure may be reduced to 
 from 0.3 to 0.4 B. t. u. for the same conditions by a 1½ inch insulating 
 covering. Table 64 gives the radiation losses for bare and covered pipes 
 with different thicknesses of magnesia covering. 
   
 Many experiments have been made as to the relative efficiencies of 
 different kinds of covering. Table 65 gives some approximately relative 
 figures based on one inch covering from experiments by Paulding, 
 Jacobus, Brill and others. 
   
              TABLE 65 
   
            APPROXIMATE 
      EFFICIENCIES OF VARIOUS 
        COVERINGS REFERRED TO 
          BARE PIPES 
 +--------------------------------+ 
 |+-------------------+----------+| 
 ||   Covering       |Efficiency|| 
 |+-------------------+----------+| 
 ||Asbestocel         |   76.8   || 
 ||Gast's Air Cell   |   74.4   || 
 ||Asbesto Sponge Felt|   85.0   || 
 ||Magnesia           |   83.5   || 
 ||Asbestos Navy Brand|   82.0   || 
 ||Asbesto Sponge Hair|   86.0   || 
 ||Asbestos Fire Felt |   73.5   || 
 |+-------------------+----------+| 
 +--------------------------------+ 
   
 Based on one-inch covering. 
   
 The following suggestions may be of service: 
   
 Exposed radiating surfaces of all pipes, all high pressure steam 
 flanges, valve bodies and fittings, heaters and separators, should be 
 covered with non-conducting material wherever such covering will improve 
 plant economy. All main steam lines, engine and boiler branches, should 
 be covered with 2 inches of 85 per cent carbonate of magnesia or the 
 equivalent. Other lines may be covered with one inch of the same 
 material. All covering should be sectional in form and large surfaces 
 should be covered with blocks, except where such material would be 
 difficult to install, in which case plastic material should be used. In 
 the case of flanges the covering should be tapered back from the flange 
 in order that the bolts may be removed. 
   
 All surfaces should be painted before the covering is applied. Canvas is 
 ordinarily placed over the covering, held in place by wrought-iron or 
 brass bands. 
   
 Expansion and Support of Pipe--It is highly important that the piping be 
 so run that there will be no undue strains through the action of 
 expansion. Certain points are usually securely anchored and the 
 expansion of the piping at other points taken care of by providing 
 supports along which the piping will slide or by means of flexible 
 hangers. Where pipe is supported or anchored, it should be from the 
 building structure and not from boilers or prime movers. Where supports 
 are furnished, they should in general be of any of the numerous sliding 
 supports that are available. Expansion is taken care of by such a method 
 of support and by the providing of large radius bends where necessary. 
   
 It was formerly believed that piping would actually expand under steam 
 temperatures about one-half the theoretical amount due to the fact that 
 the exterior of the pipe would not reach the full temperature of the 
 steam contained. It would appear, however from recent experiments that 
 such actual expansion will in the case of well-covered pipe be very 
 nearly the theoretical amount. In one case noted, a steam header 293 
 feet long when heated under a working pressure of 190 pounds, the steam 
 superheated approximately 125 degrees, expanded 8¾ inches; the 
 theoretical amount of expansion under the conditions would be 
 approximately 9-35/64 inches. 
   
 
 
 
 FLOW OF STEAM THROUGH PIPES AND ORIFICES 
 Various formulae for the flow of steam through pipes have been advanced, 
 all having their basis upon Bernoulli's theorem of the flow of water 
 through circular pipes with the proper modifications made for the 
 variation in constants between steam and water. The loss of energy due 
 to friction in a pipe is given by Unwin (based upon Weisbach) as 
   
                  f 2 v² W L 
        E_{f} = ----------     (37) 
                      gd 
   
 where E is the energy loss in foot pounds due to the friction of W units 
 of weight of steam passing with a velocity of v feet per second through 
 a pipe d feet in diameter and L feet long; g represents the acceleration 
 due to gravity (32.2) and f the coefficient of friction. 
   
 Numerous values have been given for this coefficient of friction, f, 
 which, from experiment, apparently varies with both the diameter of pipe 
 and the velocity of the passing steam. There is no authentic data on the 
 rate of this variation with velocity and, as in all experiments, the 
 effect of change of velocity has seemed less than the unavoidable errors 
 of observation, the coefficient is assumed to vary only with the size of 
 the pipe. 
   
 Unwin established a relation for this coefficient for steam at a 
 velocity of 100 feet per second, 
   
            /     3  
      f = K| 1 + --- |     (38) 
                 10d / 
   
 where K is a constant experimentally determined, and d the internal 
 diameter of the pipe in feet. 
   
 If h represents the loss of head in feet, then 
   
   
                        f 2 v² W L 
          E_{f} = Wh = ----------     (39) 
                            gd 
   
                        f 2 v² L 
                and h = --------     (40) 
                           gd 
   
 If D represents the density of the steam or weight per cubic foot, and p 
 the loss of pressure due to friction in pounds per square inch, then 
   
                    hD 
                p = ---     (41) 
                    144 
   
 and from equations (38), (40) and (41), 
   
                    D v² L     /     3  
                p = -------- × K | 1 + --- |     (42) 
                    72 g d          10d / 
   
 To convert the velocity term and to reduce to units ordinarily used, let 
 d_{1} the diameter of pipe in inches = 12d, and w = the flow in pounds 
 per minute; then 
   
                    [pi] / d_{1} 
          w = 60v × --- | ---- |^{2} D 
                      4    12 / 
   
                  9.6 w 
      and v = -------------- 
             [pi] d_{1}^2 D 
   
   
 Substituting this value and that of d in formula (42) 
   
                  /     3.6    w^{2} L 
    p = 0.04839 K | 1 + ----- | -----------     (43) 
                       d_{1} / D d_{1}^{5} 
   
 Some of the experimental determinations for the value of K are: 
    K = .005 for water (Unwin). 
    K = .005 for air (Arson). 
    K = .0028 for air (St. Gothard tunnel experiments). 
    K = .0026 for steam (Carpenter at Oriskany). 
    K = .0027 for steam (G. H. Babcock). 
   
 The value .0027 is apparently the most nearly correct, and substituting 
 in formula (43) gives, 
   
                  /     3.6    w^{2} L 
      p = 0.000131 | 1 + ---- | -----------     (44) 
                       d_{1}/ D d_{1}^{5} 
   
   
              /   pDd_{1}^{5}    
      w = 87 | -------------- |^{½}     (45) 
              | /     3.6    | 
              | | 1 + ---- | L | 
                    d_{1}/   / 
   
 Where w = the weight of steam passing in pounds per minute, 
      p = the difference in pressure between the two ends of the pipe in 
          pounds per square inch, 
      D = density of steam or weight per cubic foot,[80] 
 d_{1} = internal diameter of pipe in inches, 
      L = length of pipe in feet. 
   
                                          TABLE 66 
   
                               FLOW OF STEAM THROUGH PIPES 
 +---------------------------------------------------------------------------------------+ 
 |Initl|Diameter[81] of Pipe in Inches,         Length of Pipe = 240 Diameters         | 
 |Gauge|---------------------------------------------------------------------------------+ 
 |Press| ¾ | 1 | 1½ | 2 | 2½ | 3 |   4 | 5 | 6 | 8 | 10 | 12 | 15 | 18 | 
 |Pound|---------------------------------------------------------------------------------+ 
 |/SqIn|     Weight of Steam per Minute, in Pounds, With One Pound Loss of Pressure     | 
 +-----+---------------------------------------------------------------------------------+ 
 |   1 |1.16|2.07| 5.7|10.27|15.45|25.38| 46.85| 77.3|115.9|211.4| 341.1| 502.4| 804|1177| 
 | 10 |1.44|2.57| 7.1|12.72|19.15|31.45| 58.05| 95.8|143.6|262.0| 422.7| 622.5| 996|1458| 
 | 20 |1.70|3.02| 8.3|14.94|22.49|36.94| 68.20|112.6|168.7|307.8| 496.5| 731.3|1170|1713| 
 | 30 |1.91|3.40| 9.4|16.84|25.35|41.63| 76.84|126.9|190.1|346.8| 559.5| 824.1|1318|1930| 
 | 40 |2.10|3.74|10.3|18.51|27.87|45.77| 84.49|139.5|209.0|381.3| 615.3| 906.0|1450|2122| 
 | 50 |2.27|4.04|11.2|20.01|30.13|49.48| 91.34|150.8|226.0|412.2| 665.0| 979.5|1567|2294| 
 | 60 |2.43|4.32|11.9|21.38|32.19|52.87| 97.60|161.1|241.5|440.5| 710.6|1046.7|1675|2451| 
 | 70 |2.57|4.58|12.6|22.65|34.10|56.00|103.37|170.7|255.8|466.5| 752.7|1108.5|1774|2596| 
 | 80 |2.71|4.82|13.3|23.82|35.87|58.91|108.74|179.5|269.0|490.7| 791.7|1166.1|1866|2731| 
 | 90 |2.83|5.04|13.9|24.92|37.52|61.62|113.74|187.8|281.4|513.3| 828.1|1219.8|1951|2856| 
 | 100 |2.95|5.25|14.5|25.96|39.07|64.18|118.47|195.6|293.1|534.6| 862.6|1270.1|2032|2975| 
 | 120 |3.16|5.63|15.5|27.85|41.93|68.87|127.12|209.9|314.5|573.7| 925.6|1363.3|2181|3193| 
 | 150 |3.45|6.14|17.0|30.37|45.72|75.09|138.61|228.8|343.0|625.5|1009.2|1486.5|2378|3481| 
 +---------------------------------------------------------------------------------------+ 
   
 This formula is the most generally accepted for the flow of steam in 
 pipes. Table 66 is calculated from this formula and gives the amount of 
 steam passing per minute that will flow through straight smooth pipes 
 having a length of 240 diameters from various initial pressures with one 
 pound difference between the initial and final pressures. 
   
 To apply this table for other lengths of pipe and pressure losses other 
 than those assumed, let L = the length and d the diameter of the pipe, 
 both in inches; l, the loss in pounds; Q, the weight under the 
 conditions assumed in the table, and Q_{1}, the weight for the changed 
 conditions. 
   
 For any length of pipe, if the weight of steam passing is the same as 
 given in the table, the loss will be, 
   
              L 
        l = ----     (46) 
            240d 
   
 If the pipe length is the same as assumed in the table but the loss is 
 different, the quantity of steam passing per minute will be, 
   
          Q_{1} = Ql^{½}     (47) 
   
 For any assumed pipe length and loss of pressure, the weight will be, 
   
                  /240dl 
          Q_{1} = Q|-----|^{½}     (48) 
                   L / 
   
                                          TABLE 67 
   
                                  FLOW OF STEAM THROUGH PIPES 
                                    LENGTH OF PIPE 1000 FEET 
   
 +--------------------------------------------------++----------------------------------------+ 
 | Discharge in Pounds per Minute corresponding to ||         Drop in Pressure in           | 
 |   Drop in Pressure on Right for Pipe Diameters   || Pounds per Square Inch corresponding | 
 |               in Inches in Top Line             ||     to Discharge on Left: Densities   | 
 |                                                 || and corresponding Absolute Pressures | 
 |                                                 ||   per Square Inch in First Two Lines   | 
 +--------------------------------------------------++----------------------------------------+ 
 |             Diameter[82]--Discharge             ||         Density--Pressure--Drop       | 
 +--------------------------------------------------++----------------------------------------+ 
 | 12 | 10 | 8 | 6 |   4 | 3 | 2½| 2 | 1½| 1 ||.208 |.230|.284|.328|.401|.443|.506|.548| 
 | In | In | In | In | In | In | In | In | In | In || 90 | 100| 125| 150| 180| 200| 230| 250| 
 +--------------------------------------------------++-------+--------------------------------+ 
 |2328|1443| 799| 371|123. |55.9|28.8|18.1|6.81|2.52||18.10|16.4|13.3|11.1|9.39|8.50|7.44|6.87| 
 |2165|1341| 742| 344|114.6|51.9|27.6|16.8|6.52|2.34||15.60|14.1|11.4|9.60|8.09|7.33|6.41|5.92| 
 |1996|1237| 685| 318|106.0|47.9|26.4|15.5|6.24|2.16||13.3 |12.0|9.74|8.18|6.90|6.24|5.47|5.05| 
 |1830|1134| 628| 292| 97.0|43.9|25.2|14.2|5.95|1.98||11.1 |10.0|8.13|6.83|5.76|5.21|4.56|4.21| 
 |1663|1031| 571| 265| 88.2|39.9|24.0|12.9|5.67|1.80|| 9.25|8.36|6.78|5.69|4.80|4.34|3.80|3.51| 
 |1580| 979| 542| 252| 83.8|37.9|22.8|12.3|5.29|1.71|| 8.33|7.53|6.10|5.13|4.32|3.91|3.42|3.16| 
 |1497| 928| 514| 239| 79.4|35.9|21.6|11.6|5.00|1.62|| 7.48|6.76|5.48|4.60|3.88|3.51|3.07|2.84| 
 |1414| 876| 485| 226| 75.0|33.9|20.4|10.9|4.72|1.53|| 6.67|6.03|4.88|4.10|3.46|3.13|2.74|2.53| 
 |1331| 825| 457| 212| 70.6|31.9|19.2|10.3|4.43|1.44|| 5.91|5.35|4.33|3.64|3.07|2.78|2.43|2.24| 
 |1248| 873| 428| 199| 66.2|23.9|18.0|9.68|4.15|1.35|| 5.19|4.69|3.80|3.19|2.69|2.44|2.13|1.97| 
 |1164| 722| 400| 186| 61.7|27.9|16.8|9.03|3.86|1.26|| 4.52|4.09|3.31|2.78|2.34|2.12|1.86|1.72| 
 |1081| 670| 371| 172| 57.3|25.9|15.6|8.38|3.68|1.17|| 3.90|3.53|2.86|2.40|2.02|1.83|1.60|1.48| 
 | 998| 619| 343| 159| 52.9|23.9|14.4|7.74|3.40|1.08|| 3.32|3.00|2.43|2.04|1.72|1.56|1.36|1.26| 
 | 915| 567| 314| 146| 48.5|21.9|13.2|7.10|3.11|0.99|| 2.79|2.52|2.04|1.72|1.45|1.31|1.15|1.06| 
 | 832| 516| 286| 132| 44.1|20.0|12.0|6.45|2.83|0.90|| 2.31|2.09|1.69|1.42|1.20|1.08|.949|.877| 
 | 748| 464| 257| 119| 39.7|18.0|10.8|5.81|2.55|0.81|| 1.87|1.69|1.37|1.15| .97|.878|.769|.710| 
 | 665| 412| 228| 106| 35.3|16.0| 9.6|5.16|2.26|0.72|| 1.47|1.33|1.08|.905|.762|.690|.604|.558| 
 | 582| 361| 200|92.8| 30.9|14.0| 8.4|4.52|1.98|0.63|| 1.13|1.02|.828|.695|.586|.531|.456|.429| 
 +--------------------------------------------------++----------------------------------------+ 
   
 To get the pressure drop for lengths other than 1000 feet, multiply by 
 lengths in feet ÷ 1000. 
   
 Example: Find the weight of steam at 100 pounds initial gauge pressure, 
 which will pass through a 6-inch pipe 720 feet long with a pressure drop 
 of 4 pounds. Under the conditions assumed in the table, 293.1 pounds 
 would flow per minute; hence, Q = 293.1, and 
   
                _       _ 
              | 240×6×4 | 
 Q_{1} = 293.1 | ------- |^{½}       = 239.9 pounds 
               |_ 720×12_| 
   
 Table 67 may be frequently found to be of service in problems involving 
 the flow of steam. This table was calculated by Mr. E. C. Sickles for a 
 pipe 1000 feet long from formula (45), except that from the use of a 
 value of the constant K = .0026 instead of .0027, the constant in the 
 formula becomes 87.45 instead of 87. 
   
 In using this table, the pressures and densities to be considered, as 
 given at the top of the right-hand portion, are the mean of the initial 
 and final pressures and densities. Its use is as follows: Assume an 
 allowable drop of pressure through a given length of pipe. From the 
 value as found in the right-hand column under the column of mean 
 pressure, as determined by the initial and final pressures, pass to the 
 left-hand portion of the table along the same line until the quantity is 
 found corresponding to the flow required. The size of the pipe at the 
 head of this column is that which will carry the required amount of 
 steam with the assumed pressure drop. 
   
 The table may be used conversely to determine the pressure drop through 
 a pipe of a given diameter delivering a specified amount of steam by 
 passing from the known figure in the left to the column on the right 
 headed by the pressure which is the mean of the initial and final 
 pressures corresponding to the drop found and the actual initial 
 pressure present. 
   
 For a given flow of steam and diameter of pipe, the drop in pressure is 
 proportional to the length and if discharge quantities for other lengths 
 of pipe than 1000 feet are required, they may be found by proportion. 
   
                              TABLE 68 
   
                  FLOW OF STEAM INTO THE ATMOSPHERE 
 __________________________________________________________________ 
 |           |             |           |            |             | 
 | Absolute | Velocity   |   Actual   | Discharge | Horse Power | 
 | Initial   | of Outflow | Velocity | per Square | per Square | 
 | Pressure | at Constant | of Outflow | Inch of   |   Inch of   | 
 | per Square |   Density   | Expanded | Orifice   | Orifice if | 
 |   Inch   | Feet per   | Feet per | per Minute | Horse Power | 
 |   Pounds   |   Second   |   Second   |   Pounds   | = 30 Pounds | 
 |           |             |           |           | per Hour   | 
 |____________|_____________|____________|____________|_____________| 
 |           |             |           |           |             | 
 |   25.37   |     863     |   1401   |   22.81   |     45.6   | 
 |   30.     |     867     |   1408   |   26.84   |    53.7   | 
 |   40.     |     874     |   1419   |   35.18   |     70.4   | 
 |   50.     |     880     |   1429   |   44.06   |     88.1   | 
 |   60.     |     885     |   1437   |   52.59   |   105.2   | 
 |   70.     |     889     |   1444    |   61.07   |   122.1   | 
 |   75.     |     891     |   1447   |   65.30   |   130.6   | 
 |   90.     |     895     |   1454   |   77.94   |   155.9   | 
 |   100.     |     898     |   1459   |   86.34   |   172.7   | 
 |   115.     |    902     |   1466   |   98.76   |   197.5   | 
 |   135.     |     906     |   1472   |   115.61   |   231.2   | 
 |   155.     |     910     |   1478   |   132.21   |   264.4   | 
 |   165.     |     912     |   1481   |   140.46   |   280.9   | 
 |   215.     |     919     |   1493   |   181.58   |   363.2   | 
 |____________|_____________|____________|____________|_____________| 
   
   
 Elbows, globe valves and a square-ended entrance to pipes all offer 
 resistance to the passage of steam. It is customary to measure the 
 resistance offered by such construction in terms of the diameter of the 
 pipe. Many formulae have been advanced for computing the length of pipe 
 in diameters equivalent to such fittings or valves which offer 
 resistance. These formulae, however vary widely and for ordinary 
 purposes it will be sufficiently accurate to allow for resistance at the 
 entrance of a pipe a length equal to 60 times the diameter; for a right 
 angle elbow, a length equal to 40 diameters, and for a globe valve a 
 length equal to 60 diameters. 
   
 The flow of steam of a higher toward a lower pressure increases as the 
 difference in pressure increases to a point where the external pressure 
 becomes 58 per cent of the absolute initial pressure. Below this point 
 the flow is neither increased nor decreased by a reduction of the 
 external pressure, even to the extent of a perfect vacuum. The lowest 
 pressure for which this statement holds when steam is discharged into 
 the atmosphere is 25.37 pounds. For any pressure below this figure, the 
 atmospheric pressure, 14.7 pounds, is greater than 58 per cent of the 
 initial pressure. Table 68, by D. K. Clark, gives the velocity of 
 outflow at constant density, the actual velocity of outflow expanded 
 (the atmospheric pressure being taken as 14.7 pounds absolute, and the 
 ratio of expansion in the nozzle being 1.624), and the corresponding 
 discharge per square inch of orifice per minute. 
   
 Napier deduced an approximate formula for the outflow of steam into the 
 atmosphere which checks closely with the figures just given. This 
 formula is: 
   
    pa 
 W = ----     (49) 
      70 
   
 Where W = the pounds of steam flowing per second, 
      p = the absolute pressure in pounds per square inch, 
 and a = the area of the orifice in square inches. 
   
 In some experiments made by Professor C. H. Peabody, in the flow of 
 steam through pipes from ¼ inch to 1½ inches long and ¼ inch in 
 diameter, with rounded entrances, the greatest difference from Napier's 
 formula was 3.2 per cent excess of the experimental over the calculated 
 results. 
   
 For steam flowing through an orifice from a higher to a lower pressure 
 where the lower pressure is greater than 58 per cent of the higher, the 
 flow per minute may be calculated from the formula: 
   
 W = 1.9AK ((P - d)d)^{½}     (50) 
   
 Where W = the weight of steam discharged in pounds per minute, 
      A = area of orifice in square inches, 
      P = the absolute initial pressure in pounds per square inch, 
      d = the difference in pressure between the two sides in pounds 
          per square inch, 
      K = a constant = .93 for a short pipe, and .63 for a hole in a 
          thin plate or a safety valve. 
   
 
 
 
 HEAT TRANSFER 
 The rate at which heat is transmitted from a hot gas to a cooler metal 
 surface over which the gas is flowing has been the subject of a great 
 deal of investigation both from the experimental and theoretical side. A 
 more or less complete explanation of this process is necessary for a 
 detailed analysis of the performance of steam boilers. Such information 
 at the present is almost entirely lacking and for this reason a boiler, 
 as a physical piece of apparatus, is not as well understood as it might 
 This, however, has had little effect in its practical development 
 
 and it is hardly possible that a more complete understanding of the 
 phenomena discussed will have any radical effect on the present design. 
   
 The amount of heat that is transferred across any surface is usually 
 expressed as a product, of which one factor is the slope or linear rate 
 of change in temperature and the other is the amount of heat transferred 
 per unit's difference in temperature in unit's length. In Fourier's 
 analytical theory of the conduction of heat, this second factor is taken 
 as a constant and is called the "conductivity" of the substance. 
 Following this practice, the amount of heat absorbed by any surface from 
 a hot gas is usually expressed as a product of the difference in 
 temperature between the gas and the absorbing surface into a factor 
 which is commonly designated the "transfer rate". There has been 
 considerable looseness in the writings of even the best authors as to 
 the way in which the gas temperature difference is to be measured. If 
 the gas varies in temperature across the section of the channel through 
 which it is assumed to flow, and most of them seem to consider that this 
 would be the case, there are two mean gas temperatures, one the mean of 
 the actual temperatures at any time across the section, and the other 
 the mean temperature of the entire volume of the gas passing such a 
 section in any given time. Since the velocity of flow will of a 
 certainty vary across the section, this second mean temperature, which 
 is one tacitly assumed in most instances, may vary materially from the 
 first. The two mean temperatures are only approximately equal when the 
 actual temperature measured across the section is very nearly a 
 constant. In what follows it will be assumed that the mean temperature 
 measured in the second way is referred to. In English units the 
 temperature difference is expressed in Fahrenheit degrees and the 
 transfer rate in B. t. u.'s per hour per square foot of surface. Pecla, 
 who seems to have been one of the first to consider this subject 
 analytically, assumed that the transfer rate was constant and 
 independent both of the temperature differences and the velocity of the 
 gas over the surface. Rankine, on the other hand, assumed that the 
 transfer rate, while independent of the velocity of the gas, was 
 proportional to the temperature difference, and expressed the total 
 amount of heat absorbed as proportional to the square of the difference 
 in temperature. Neither of these assumptions has any warrant in either 
 theory or experiment and they are only valuable in so far as their use 
 determine formulae that fit experimental results. Of the two, Rankine's 
 assumption seems to lead to formulae that more nearly represent actual 
 conditions. It has been quite fully developed by William Kent in his 
 "Steam Boiler Economy". Professor Osborne Reynolds, in a short paper 
 reprinted in Volume I of his "Scientific Papers", suggests that the 
 transfer rate is proportional to the product of the density and velocity 
 of the gas and it is to be assumed that he had in mind the mean 
 velocity, density and temperature over the section of the channel 
 through which the gas was assumed to flow. Contrary to prevalent 
 opinion, Professor Reynolds gave neither a valid experimental nor a 
 theoretical explanation of his formula and the attempts that have been 
 made since its first publication to establish it on any theoretical 
 basis can hardly be considered of scientific value. Nevertheless, 
 Reynolds' suggestion was really the starting point of the scientific 
 investigation of this subject and while his formula cannot in any sense 
 be held as completely expressing the facts, it is undoubtedly correct to 
 a first approximation for small temperature differences if the additive 
 constant, which in his paper he assumed as negligible, is given a 
 value.[83] 
   
 Experimental determinations have been made during the last few years of 
 the heat transfer rate in cylindrical tubes at comparatively low 
 temperatures and small temperature differences. The results at different 
 velocities have been plotted and an empirical formula determined 
 expressing the transfer rate with the velocity as a factor. The exponent 
 of the power of the velocity appearing in the formula, according to 
 Reynolds, would be unity. The most probable value, however, deduced from 
 most of the experiments makes it less than unity. After considering 
 experiments of his own, as well as experiments of others, Dr. Wilhelm 
 Nusselt[84] concludes that the evidence supports the following formulae: 
   
                    _               _ 
      [lambda]_{w} | w c_{p} [delta] | 
 a = b ------------ | --------------- |^{u} 
        d^{1-u}   |_   [lambda]   _| 
   
    Where a is the transfer rate in calories per hour per square meter 
              of surface per degree centigrade difference in temperature, 
            u is a physical constant equal to .786 from Dr. Nusselt's 
              experiments, 
            b is a constant which, for the units given below, is 15.90, 
            w is the mean velocity of the gas in meters per second, 
        c_{p} is the specific heat of the gas at its mean temperature 
              and pressure in calories per kilogram, 
      [delta] is the density in kilograms per cubic meter, 
    [lambda] is the conductivity at the mean temperature and pressure in 
              calories per hour per square meter per degree centigrade 
              temperature drop per meter, 
 [lambda]_{w} is the conductivity of the steam at the temperature of the 
              tube wall, 
            d is the diameter of the tube in meters. 
   
 If the unit of time for the velocity is made the hour, and in the place 
 of the product of the velocity and density is written its equivalent, 
 the weight of gas flowing per hour divided by the area of the tube, this 
 equation becomes: 
   
                        _          _ 
          [lambda]_{w} |   Wc_{p}   | 
 a = .0255 ------------ | --------- |^{.786} 
            d^{.214}   |_ A[lambda] _| 
   
 where the quantities are in the units mentioned, or, since the constants 
 are absolute constants, in English units, 
   
           a is the transfer rate in B. t. u. per hour per square foot 
              of surface per degree difference in temperature, 
            W is the weight in pounds of the gas flowing through the tube 
              per hour, 
            A is the area of the tube in square feet, 
            d is the diameter of the tube in feet, 
        c_{p} is the specific heat of the gas at constant pressure, 
    [lambda] is the conductivity of the gas at the mean temperature and 
              pressure in B. t. u. per hour per square foot of surface 
              per degree Fahrenheit drop in temperature per foot, 
 [lambda]_{w} is the conductivity of the steam at the temperature of the 
              wall of the tube. 
   
 The conductivities of air, carbonic acid gas and superheated steam, as 
 affected by the temperature, in English units, are: 
   
 Conductivity of air               .0122 (1 + .00132 T) 
 Conductivity of carbonic acid gas .0076 (1 + .00229 T) 
 Conductivity of superheated steam .0119 (1 + .00261 T) 
   
 where T is the temperature in degrees Fahrenheit. 
   
 Nusselt's formulae can be taken as typical of the number of other 
 formulae proposed by German, French and English writers.[85] Physical 
 properties, in addition to the density, are introduced in the form of 
 coefficients from a consideration of the physical dimensions of the 
 various units and of the theoretical formulae that are supposed to 
 govern the flow of the gas and the transfer of heat. All assume that the 
 correct method of representing the heat transfer rate is by the use of 
 one term, which seems to be unwarranted and probably has been adopted on 
 account of the convenience in working up the results by plotting them 
 logarithmically. This was the method Professor Reynolds used in 
 determining his equation for the loss in head in fluids flowing through 
 cylindrical pipes and it is now known that the derived equation cannot 
 be considered as anything more than an empirical formula. It, therefore, 
 is well for anyone considering this subject to understand at the outset 
 that the formulae discussed are only of an empirical nature and 
 applicable to limited ranges of temperature under the conditions 
 approximately the same as those surrounding the experiments from which 
 the constants of the formula were determined. 
   
 It is not probable that the subject of heat transfer in boilers will 
 ever be on any other than an experimental basis until the mathematical 
 expression connecting the quantity of fluid which will flow through a 
 channel of any section under a given head has been found and some 
 explanation of its derivation obtained. Taking the simplest possible 
 section, namely, a circle, it is found that at low velocities the loss 
 of head is directly proportional to the velocity and the fluid flows in 
 straight stream lines or the motion is direct. This motion is in exact 
 accordance with the theoretical equations of the motion of a viscous 
 fluid and constitutes almost a direct proof that the fundamental 
 assumptions on which these equations are based are correct. When, 
 however, the velocity exceeds a value which is determinable for any size 
 of tube, the direct or stream line motion breaks down and is replaced by 
 an eddy or mixing flow. In this flow the head loss by friction is 
 approximately, although not exactly, proportional to the square of the 
 velocity. No explanation of this has ever been found in spite of the 
 fact that the subject has been treated by the best mathematicians and 
 physicists for years back. It is to be assumed that the heat transferred 
 during the mixing flow would be at a much higher rate than with the 
 direct or stream line flow, and Professors Croker and Clement[86] have 
 demonstrated that this is true, the increase in the transfer being so 
 marked as to enable them to determine the point of critical velocity 
 from observing the rise in temperature of water flowing through a tube 
 surrounded by a steam jacket. 
   
 The formulae given apply only to a mixing flow and inasmuch as, from 
 what has just been stated, this form of motion does not exist from zero 
 velocity upward, it follows that any expression for the heat transfer 
 rate that would make its value zero when the velocity is zero, can 
 hardly be correct. Below the critical velocity, the transfer rate seems 
 to be little affected by change in velocity and Nusselt,[87] in another 
 paper which mathematically treats the direct or stream line flow, 
 concludes that, while it is approximately constant as far as the 
 velocity is concerned in a straight cylindrical tube, it would vary from 
 point to point of the tube, growing less as the surface passed over 
 increased. 
   
 It should further be noted that no account in any of this experimental 
 work has been taken of radiation of heat from the gas. Since the common 
 gases absorb very little radiant heat at ordinary temperatures, it has 
 been assumed that they radiate very little at any temperature. This may 
 or may not be true, but certainly a visible flame must radiate as well 
 as absorb heat. However this radiation may occur, since it would be a 
 volume phenomenon rather than a surface phenomenon it would be 
 considered somewhat differently from ordinary radiation. It might apply 
 as increasing the conductivity of the gas which, however independent of 
 radiation, is known to increase with the temperature. It is, therefore, 
 to be expected that at high temperatures the rate of transfer will be 
 greater than at low temperatures. The experimental determinations of 
 transfer rates at high temperatures are lacking. 
   
 Although comparatively nothing is known concerning the heat radiation 
 from gases at high temperatures, there is no question but what a large 
 proportion of the heat absorbed by a boiler is received direct as 
 radiation from the furnace. Experiments show that the lower row of tubes 
 of a Babcock & Wilcox boiler absorb heat at an average rate per square 
 foot of surface between the first baffle and the front headers 
 equivalent to the evaporation of from 50 to 75 pounds of water from and 
 at 212 degrees Fahrenheit per hour. Inasmuch as in these experiments no 
 separation could be made between the heat absorbed by the bottom of the 
 tube and that absorbed by the top, the average includes both maximum and 
 minimum rates for those particular tubes and it is fair to assume that 
 the portion of the tubes actually exposed to the furnace radiations 
 absorb heat at a higher rate. Part of this heat was, of course absorbed 
 by actual contact between the hot gases and the boiler heating surface. 
 A large portion of it, however, must have been due to radiation. Whether 
 this radiant heat came from the fire surface and the brickwork and 
 passed through the gases in the furnace with little or no absorption, or 
 whether, on the other hand, the radiation were absorbed by the furnace 
 gases and the heat received by the boiler was a secondary radiation from 
 the gases themselves and at a rate corresponding to the actual gas 
 temperature, is a question. If the radiations are direct, then the term 
 "furnace temperature", as usually used has no scientific meaning, for 
 obviously the temperature of the gas in the furnace would be entirely 
 different from the radiation temperature, even were it possible to 
 attach any significance to the term "radiation temperature", and it is 
 not possible to do this unless the radiations are what are known as 
 "full radiations" from a so-called "black body". If furnace radiation 
 takes place in this manner, the indications of a pyrometer placed in a 
 furnace are hard to interpret and such temperature measurements can be 
 of little value. If the furnace gases absorb the radiations from the 
 fire and from the brickwork of the side walls and in their turn radiate 
 heat to the boiler surface, it is scientifically correct to assume that 
 the actual or sensible temperature of the gas would be measured by a 
 pyrometer and the amount of radiation could be calculated from this 
 temperature by Stefan's law, which is to the effect that the rate of 
 radiation is proportional to the fourth power of the absolute 
 temperature, using the constant with the resulting formula that has been 
 determined from direct experiment and other phenomena. With this 
 understanding of the matter, the radiations absorbed by a boiler can be 
 taken as equal to that absorbed by a flat surface, covering the portion 
 of the boiler tubes exposed to the furnace and at the temperature of the 
 tube surface, when completely exposed on one side to the radiations from 
 an atmosphere at the temperature in the furnace. With this assumption, 
 if S^{1} is the area of the surface, T the absolute temperature of the 
 furnace gases, t the absolute temperature of the tube surface of the 
 boiler, the heat absorbed per hour measured in B. t. u.'s is equal to 
   
      _                     _ 
      | / T        / t    | 
 1600 | |----|^{4} - |----|^{4}| S^{1} 
      |_1000/       1000/   _| 
   
 In using this formula, or in any work connected with heat transfer, the 
 external temperature of the boiler heating surface can be taken as that 
 of saturated steam at the pressure under which the boiler is working, 
 with an almost negligible error, since experiments have shown that with 
 a surface clean internally, the external surface is only a few degrees 
 hotter than the water in contact with the inner surface, even at the 
 highest rates of evaporation. Further than this, it is not conceivable 
 that in a modern boiler there can be much difference in the temperature 
 of the boiler in the different parts, or much difference between the 
 temperature of the water and the temperature of the steam in the drums 
 which is in contact with it. 
   
 If the total evaporation of a boiler measured in B. t. u.'s per hour is 
 represented by E, the furnace temperature by T_{1}, the temperature of 
 the gas leaving the boiler by T_{2}, the weight of gas leaving the 
 furnace and passing through the setting per hour by W, the specific heat 
 of the gas by C, it follows from the fact that the total amount of heat 
 absorbed is equal to the heat received from radiation plus the heat 
 removed from the gases by cooling from the temperature T_{1} to the 
 temperature T_{2}, that 
   
          _                     _ 
          | / T        / t    | 
 E = 1600 | |----|^{4} - |----|^{4}| S^{1} + WC(T_{1} - T_{2}) 
          |_1000/       1000/   _| 
   
 This formula can be used for calculating the furnace temperature when E, 
 t and T_{2} are known but it must be remembered that an assumption 
 which is probably, in part at least, incorrect is implied in using it or 
 in using any similar formula. Expressed in this way, however, it seems 
 more rational than the one proposed a few years ago by Dr. Nicholson[88] 
 where, in place of the surface exposed to radiation, he uses the grate 
 surface and assumes the furnace gas temperature as equal to the fire 
 temperature. 
   
 If the heat transfer rate is taken as independent of the gas temperature 
 and the heat absorbed by an element of the surface in a given time is 
 equated to the heat given out from the gas passing over this surface in 
 the same time, a single integration gives 
   
                            Rs 
 (T - t) = (T_{1} - t) e^{- --} 
                            WC 
   
 where s is the area of surface passed over by the gases from the furnace 
 to any point where the gas temperature T is measured, and the rate of 
 heat transfer is R. As written, this formula could be used for 
 calculating the temperature of the gas at any point in the boiler 
 setting. Gas temperatures, however, calculated in this way are not to be 
 depended upon as it is known that the transfer rate is not independent 
 of the temperature. Again, if the transfer rate is assumed as varying 
 directly with the weight of the gases passing, which is Reynolds' 
 suggestion, it is seen that the weight of the gases entirely disappears 
 from the formula and as a consequence if the formula was correct, as 
 long as the temperature of the gas entering the surface from the furnace 
 was the same, the temperatures throughout the setting would be the same. 
 This is known also to be incorrect. If, however, in place of T is 
 written T_{2} and in place of s is written S, the entire surface of the 
 boiler, and the formula is re-arranged, it becomes: 
   
                _           _ 
      WC       | T_{1} - t | 
 R = --- Log[89]| --------- | 
      S         |_ T_{2} - t _| 
   
 This formula can be considered as giving a way of calculating an average 
 transfer rate. It has been used in this way for calculating the average 
 transfer rate from boiler tests in which the capacity has varied from an 
 evaporation of a little over 3 pounds per square foot of surface up to 
 15 pounds. When plotted against the gas weights, it was found that the 
 points were almost exactly on a line. This line, however, did not pass 
 through the zero point but started at a point corresponding to 
 approximately a transfer rate of 2. Checked out against many other 
 tests, the straight line law seems to hold generally and this is true 
 even though material changes are made in the method of calculating the 
 furnace temperature. The inclination of the line, however, varied 
 inversely as the average area for the passage of the gas through the 
 boiler. If A is the average area between all the passes of the boiler, 
 the heat transfer rate in Babcock & Wilcox type boilers with ordinary 
 clean surfaces can be determined to a rather close approximation from 
 the formula: 
   
                  W 
 R = 2.00 + .0014 - 
                  A 
   
 The manner in which A appears in this formula is the same as it would 
 appear in any formula in which the heat transfer rate was taken as 
 depending upon the product of the velocity and the density of the gas 
 jointly, since this product, as pointed out above, is equivalent to W/A. 
 Nusselt's experiments, as well as those of others, indicate that the 
 ratio appears in the proper way. 
   
 While the underlying principles from which the formula for this average 
 transfer rate was determined are questionable and at best only 
 approximately correct, it nevertheless follows that assuming the 
 transfer rate as determined experimentally, the formula can be used in 
 an inverse way for calculating the amount of surface required in a 
 boiler for cooling the gases through a range of temperature covered by 
 the experiments and it has been found that the results bear out this 
 assumption. The practical application of the theory of heat transfer, as 
 developed at present, seems consequently to rest on these last two 
 formulae, which from their nature are more or less empirical. 
   
 Through the range in the production of steam met with in boilers now in 
 service which in the marine type extends to the average evaporation of 
 12 to 15 pounds of water from and at 212 degrees Fahrenheit per square 
 foot of surface, the constant 2 in the approximate formula for the 
 average heat transfer rate constitutes quite a large proportion of the 
 total. The comparative increase in the transfer rate due to a change in 
 weight of the gases is not as great consequently as it would be if this 
 constant were zero. For this reason, with the same temperature of the 
 gases entering the boiler surface, there will be a gradual increase in 
 the temperature of the gases leaving the surface as the velocity or 
 weight of flow increases and the proportion of the heat contained in the 
 gases entering the boiler which is absorbed by it is gradually reduced. 
 It is, of course, possible that the weight of the gases could be 
 increased to such an amount or the area for their passage through the 
 boiler reduced by additional baffles until the constant term in the heat 
 transfer formula would be relatively unimportant. Under such conditions, 
 as pointed out previously, the final gas temperature would be unaffected 
 by a further increase in the velocity of the flow and the fraction of 
 the heat carried by the gases removed by the boiler would be constant. 
 Actual tests of waste heat boilers in which the weight of gas per square 
 foot of sectional area for its passage is many times more than in 
 ordinary installations show, however, that this condition has not been 
 attained and it will probably never be attained in any practical 
 installation. It is for this reason that the conclusions of Dr. 
 Nicholson in the paper referred to and of Messrs. Kreisinger and Ray in 
 the pamphlet "The Transmission of Heat into Steam Boilers", published by 
 the Department of the Interior in 1912, are not applicable without 
 modification to boiler design. 
   
 In superheaters the heat transfer is effected in two different stages; 
 the first transfer is from the hot gas to the metal of the superheater 
 tube and the second transfer is from the metal of the tube to the steam 
 on the inside. There is, theoretically, an intermediate stage in the 
 transfer of the heat from the outside to the inside surface of the tube. 
 The conductivity of steel is sufficient, however, to keep the 
 temperatures of the two sides of the tube very nearly equal to each 
 other so that the effect of the transfer in the tube itself can be 
 neglected. The transfer from the hot gas to the metal of the tube takes 
 place in the same way as with the boiler tubes proper, regard being paid 
 to the temperature of the tube which increases as the steam is heated. 
 The transfer from the inside surface of the tube to the steam is the 
 inverse of the process of the transfer of the heat on the outside and 
 seems to follow the same laws. The transfer rate, therefore, will 
 increase with the velocity of the steam through the tube. For this 
 reason, internal cores are quite often used in superheaters and actually 
 result in an increase in the amount of superheat obtained from a given 
 surface. The average transfer rate in superheaters based on a difference 
 in mean temperature between the gas on the outside of the tubes and the 
 steam on the inside of the tubes is if R is the transfer rate from the 
 gas to the tube and r the rate from the tube to the steam: 
   
      Rr 
    ----- 
  R + r 
   
 and is always less than either R or r. This rate is usually greater than 
 the average transfer rate for the boiler as computed in the way outlined 
 in the preceding paragraphs. Since, however, steam cannot, under any 
 imagined set of conditions, take up more heat from a tube than would 
 water at the same average temperature, this fact supports the contention 
 made that the actual transfer rate in a boiler must increase quite 
 rapidly with the temperatures. The actual transfer rates in superheaters 
 are affected by so many conditions that it has not so far been possible 
 to evolve any formula of practical value. 
   
 
 
 
 INDEX Pg 1 
 Absolute pressure                                               117 
 Absolute zero                                                   80 
 Accessibility of Babcock & Wilcox boiler                         59 
 Acidity in boiler feed water                                   106 
 Actual evap. corresponding to boiler horse power               288 
 Advantages of Babcock & Wilcox boilers                           61 
 Stoker firing                                                195 
 Water tube over fire tube boilers                             61 
 Air, composition of                                             147 
 In boiler feed water                                         106 
 Properties of                                                 147 
 Required for combustion                                 152, 156 
 Specific heat of                                             148 
 Supplied for combustion                                      157 
 Vapor in                                                     149 
 Volume of                                                     147 
 Weight of                                                     147 
 Alkalinity in boiler feed water                                103 
 Testing feed for                                             103 
 Altitude, boiling point of water at                             97 
 Chimney sizes corrected for                                   248 
 Alum in feed water treatment                                   106 
 S. M. E. code for boiler testing                             267 
 
 Analyses, comparison of proximate and ultimate                 183 
 Proximate coal, and heating values                           177 
 Analysis, coal, proximate, methods of                           176 
 Coal, ultimate                                               173 
 Determination of heating value from                           173 
 Analysis, Flue gas                                              155 
 Flue gas, methods of                                         160 
 Flue gas, object of                                           155 
 Anthracite coal                                                 166 
 Combustion rates with                                        246 
 Distribution of                                               167 
 Draft required for                                           246 
 Firing                                                       190 
 Grate ratio for                                              191 
 Semi                                                         166 
 Sizes of                                                     190 
 Steam as aid to burning                                       191 
 Thickness of fires with                                       191 
 Arches, fire brick, as aid to combustion                       190 
 Fire brick, for                                               304 
 Fire brick, laying                                           305 
 Automatic stokers, advantages of                               195 
 Overfeed                                                     196 
 Traveling grate                                               197 
 Traveling grate, Babcock & Wilcox                            194 
 Underfeed                                                     196 
 Auxiliaries, exhaust from, in heating feed water               113 
 Superheated steam with                                       142 
 Auxiliary grates, with blast furnace gas                       228 
 With oil fuel                                                 225 
 With waste heat                                               235 
 Babcock, G. H., lecture on circulation of water in Boilers       28 
 Lecture on theory of steam making                             92 
 Babcock & Wilcox Co., Works at Barberton, Ohio                   7 
 Works at Bayonne, N. J.                                         6 
 Babcock & Wilcox boiler, accessibility of                       59 
 Advantages of                                                 61 
 Circulation of water in                                   57, 66 
 Construction of                                               49 
 Cross boxes                                                  50 
 Cross drum                                                     53 
 Cross drum, dry steam with                                     71 
 Drumheads                                                     49 
 
 
 
 INDEX Pg 2 
 Drums                                                        49 
 Durability                                                     75 
 Evolution of                                                   39 
 Fittings                                                       55 
 Fixtures                                                      55 
 Fronts                                                         53 
 Handhole fittings                                         50, 51 
 Headers                                                   50, 51 
 Inclined header, wrought steel                                 54 
 Inspection                                                     75 
 Life of                                                       76 
 Materials entering into the construction of                  59 
 Mud drums                                                     51 
 Path of gases in                                               57 
 Path of water in                                               57 
 Rear tube doors of                                        53, 74 
 Repairs                                                       75 
 Safety of                                                     66 
 Sections                                                       50 
 Set for utilizing waste heat                                 236 
 Set with Babcock & Wilcox chain grate stoker                   12 
 Set with bagasse furnace                                     208 
 Set with Peabody oil furnace                                 222 
 Supports, cross drum                                           53 
 Supports, longitudinal drum                                   52 
 Tube doors                                                     53 
 Vertical header, cast iron                                    58 
 Vertical header, wrought steel                                 48 
 Babcock & Wilcox chain grate stoker                             194 
 Babcock & Wilcox superheater                                   136 
 Bagasse, composition of                                        206 
 Furnace                                                       209 
 Heat, value of                                               206 
 Tests of Babcock & Wilcox boilers with                       210 
 Value of diffusion                                            207 
 Barium carbonate in feed water treatment                       106 
 Barium hydrate in feed water treatment                         106 
 Barrus draft gauge                                             254 
 Bituminous coal, classification of                             167 
 Combustion rates with                                         246 
 Composition of                                               177 
 Distribution of                                               168 
 Firing methods                                               193 
 Semi                                                         166 
 Sizes of                                                     191 
 Thickness of fire with                                        193 
 Blast furnace gas, burners for                                 228 
 Combustion of                                                 228 
 Composition of                                               227 
 Stacks for                                                    228 
 Boiler, Blakey's                                                 23 
 Brickwork, care of                                           307 
 Circulation of water in steam                                 28 
 Compounds                                                    109 
 Development of water tube                                     23 
 Eve's                                                         24 
 Evolution of Babcock & Wilcox                                 39 
   
 
 
 
 INDEX Pg 3 
 Fire tube, compared with water tube                           61 
 Guerney's                                                     24 
 Horse power                                                   263 
 Loads, economical                                            283 
 Perkins'                                                       24 
 Room piping                                                   108 
 Room practice                                                 297 
 Rumsey's                                                      23 
 Stevens', John                                                 23 
 Stevens', John Cox                                             23 
 Units, number of                                             289 
 Units, size of                                                289 
 Wilcox's                                                       25 
 Woolf's                                                       23 
 Boilers, capacity of                                           278 
 Care of                                                       291 
 Efficiency of                                                 256 
 Horse power of                                               265 
 Operation of                                                  291 
 Requirements of steam                                         27 
 Testing                                                       267 
 Boiling point                                                   86 
 Of various substances                                        86 
 Of water as affected by altitude                               97 
 Brick, fire                                                     304 
 Arches                                                       305 
 Classification of                                            304 
 Compression of                                               303 
 Expansion of                                                 303 
 Hardness of                                                   303 
 Laying up                                                     305 
 Nodules, ratio of                                             303 
 Nodules, size of                                             303 
 Plasticity of                                                302 
 Brick, red                                                     302 
 Brickwork, care of                                             307 
 British thermal unit                                             83 
 Burners, blast furnace gas                                      228 
 By-product coke oven gas                                     231 
 Natural gas                                                   231 
 Oil                                                           217 
 Oil, capacity of                                              221 
 Oil, mechanical atomizing                                     219 
 Oil, operation of                                             223 
 Oil, steam atomizing                                         218 
 Oil, steam consumption of                                     220 
 Burning hydrogen, loss due to moisture formed in               261 
 By-product coke oven gas burners                               231 
 By-product coke oven gas, combustion of                         231 
 By-product coke oven gas, composition and heat value of         231 
 Calorie                                                         83 
 Calorific value (see Heat value). 
 Calorimeter, coal, Mahler bomb                                 184 
 Mahler bomb, method of correction                             187 
 Mahler bomb, method of operation of                           185 
 Calorimeter, steam, compact type of throttling                 132 
 Correction for                                               131 
   
 
 
 
 INDEX Pg 4 
 Location of nozzles for                                       134 
 Normal reading                                               131 
 Nozzles                                                       134 
 Separating                                                    133 
 Throttling                                                   129 
 Capacity of boilers                                       264, 278 
 As affecting economy                                         276 
 Economical loads                                              283 
 With bagasse                                                 210 
 With blast furnace gas                                       228 
 With coal                                                     280 
 With oil fuel                                                224 
 Capacity of natural gas burners                                 229 
 Capacity of oil burners                                         221 
 Carbon dioxide in flue gases                                   154 
 Unreliability of readings taken alone                         162 
 Carbon, fixed                                                   165 
 Incomplete combustion of, loss due to                         158 
 Monoxide, heat value of                                      151 
 Monoxide, in flue gases                                       155 
 Unconsumed in ash, loss due to                               261 
 Care of boilers when out of service                             300 
 Casings, boilers                                                307 
 Causticity of feed water                                       103 
 Testing for                                                   105 
 Celsius thermometer scale                                       79 
 Centigrade thermometer scale                                     79 
 Chain grate stoker, Babcock & Wilcox                           194 
 Chemicals required in feed water treatment                     105 
 Chimney gases, losses in                                   158, 159 
 Chimneys (see Draft). 
 Correction in dimensions for altitude                         248 
 Diameter of                                                   243 
 Draft available from                                         241 
 Draft loss in                                                239 
 For blast furnace gas                                         253 
 For oil fuel                                                 251 
 For wood fuel                                                 254 
 Height of                                                    243 
 Horse power they will serve                                   250 
 Circulation of water in Babcock & Wilcox boilers           57, 66 
 Of water in steam boilers                                     28 
 Results of defective                                 62, 66, 67 
 Classification of coals                                         166 
 Fire brick                                                   304 
 Feed water difficulties                                      100 
 Fuels                                                         165 
 Cleaners, turbine tube                                         299 
 Cleaning, ease of, Babcock & Wilcox boilers                     73 
 Closed feed water heaters                                      111 
 Coal, Alaska                                                   169 
 Analyses and heat value                                       177 
 Analysis, proximate                                           176 
 Analysis, ultimate                                            173 
 Anthracite                                                   166 
 Bituminous                                                   167 
 Cannel                                                       167 
   
 
 
 
 INDEX Pg 5 
 Classification of                                       165, 166 
 Combustion of                                                 190 
 Comparison with oil                                           214 
 Consumption, increase due to superheat                        139 
 Distribution of                                               167 
 Formation of                                                 165 
 Lignite                                                       167 
 Records                                                      293 
 Semi-anthracite                                               166 
 Semi-bituminous                                               166 
 Sizes of anthracite                                           190 
 Sizes of bituminous                                          191 
 Code of A. S. M. E. for boiler testing                         267 
 Coefficient of expansion of various substances                   87 
 Coke                                                           171 
 Oven gas, by-product, burners                                 231 
 Oven gas, by-product, combustion of                           231 
 Oven gas, by-product, composition and heat value of           231 
 Coking method of firing                                         195 
 Color as indication of temperature                               91 
 Combination furnaces                                           224 
 Combustible in fuels                                           150 
 Combustion                                                      150 
 Air required for                                         152, 156 
 Air supplied for                                             157 
 Combustion of coal                                             190 
 Of gaseous fuels                                              227 
 Of liquid fuels                                               212 
 Of solid fuels other than coal                               201 
 Composition of bagasse                                         205 
 Blast furnace gas                                             227 
 By-product coke oven gas                                     231 
 Coals                                                         177 
 Natural gas                                                   229 
 Oil                                                           213 
 Wood                                                         201 
 Compounds, boiler                                               109 
 Compressibility of water                                        97 
 Compression of fire brick                                       303 
 Condensation, effect of superheated steam on                   140 
 In steam pipes                                               313 
 Consumption, heat, of engines                                  141 
 Correction, stem, for thermometers                               80 
 For normal reading in steam calorimeter                       131 
 For radiation, bomb calorimeter                               187 
 Corrosion                                                101, 106 
 Coverings, pipe                                                 315 
 Cross drum, Babcock & Wilcox boiler                   52, 53, 60 
 Dry steam with                                                 71 
 Draft area as affecting economy in Babcock & Wilcox boilers     70 
 Available from chimneys                                       241 
 Draft loss in chimneys                                         239 
 Loss in boilers                                              245 
 Loss in flues                                                 243 
 Loss in furnaces                                             245 
 Draft required for anthracite                                   246 
 Required for various fuels                                    246 
   
 
 
 
 INDEX Pg 6 
 Drums, Babcock & Wilcox, cross                                   53 
 Cross, boxes                                                   50 
 Heads                                                         49 
 Longitudinal                                                  49 
 Manholes                                                       49 
 Nozzles on                                                     50 
 Dry steam in Babcock & Wilcox boilers                           71 
 Density of gases                                               147 
 Steam                                                         115 
 Dulong's formula for heating value                             173 
 Ebullition, point of                                            86 
 Economizers                                                     111 
 Efficiency of boilers, chart of                                 258 
 Combustible basis                                             256 
 Dry coal basis                                                256 
 Increase in, due to superheaters                             139 
 Losses in (see Heat balance)                                 259 
 Testing                                                       267 
 Test _vs._ operating                                          278 
 Variation in, with capacity                                   284 
 With coal                                                     288 
 With oil                                                     224 
 Ellison draft gauge                                             254 
 Engine, Hero's                                                   13 
 Engines, superheated steam with                                 141 
 Equivalent evaporation from and at 212 degrees                 116 
 Eve's boiler                                                     24 
 Evolution of Babcock & Wilcox boiler                             39 
 Exhaust steam from auxiliaries                                 113 
 Expansion, coefficient of                                      87 
 Of fire brick                                                 303 
 Of pipe                                                       315 
 Pyrometer                                                     89 
 Factor of evaporation                                          117 
 Fahrenheit thermometer scale                                     79 
 Fans, use of, in waste heat work                               233 
 Feed water, air in                                             106 
 As affecting capacity                                         279 
 Boiler                                                       100 
 Feed water heaters, closed                                     111 
 Economizers                                                   111 
 Open                                                         111 
 Feed water heating, methods of                                 111 
 Saving by                                                     110 
 Feed water, impurities in                                      100 
 Lines                                                         312 
 Method of feeding                                             110 
 Feed water treatment                                           102 
 Chemical                                                      102 
 Chemical, lime and soda process                               102 
 Chemical, lime process                                       102 
 Chemical, soda process                                       102 
 Chemicals used in lime and soda process                       105 
 Combined heat and chemical                                   105 
 Heat                                                         102 
 Less usual reagents                                           106 
 Firing, advantages of stoker                                   195 
   
 
 
 
 INDEX Pg 7 
 Methods for anthracite                                       190 
 Bituminous                                                   193 
 Lignite                                                      195 
 Fittings, handhole in Babcock & Wilcox boilers             50, 51 
 Pipe                                                         311 
 Superheated steam                                             145 
 With Babcock & Wilcox boilers                                55 
 Fixtures with Babcock & Wilcox boilers                           55 
 Flanges, pipe                                                   309 
 Flow of steam into pressure above atmosphere                   317 
 Into the atmosphere                                          328 
 Through orifices                                             317 
 Through pipes                                                 317 
 Flue gas analysis                                               155 
 Conversion of volumetric to weight                           161 
 Methods of making                                             160 
 Object of                                                     155 
 Orsat apparatus                                              159 
 Flue gas, composition of                                       155 
 Losses in                                               158, 159 
 Weight per pound of carbon in fuel                           158 
 Weight per pound of fuel                                      158 
 Weight resulting from combustion                             157 
 Foaming                                                   102, 107 
 Fuel analysis, proximate                                       176 
 Ultimate                                                      173 
 Fuel calorimeter, Mabler bomb                                   184 
 Tests, method of making                                         186 
 Fuels, classification of                                       165 
 Gaseous, and their combustion                                 227 
 Fuels, liquid, and their combustion                             212 
 Solid, coal                                                   190 
 Solid, other than coal                                       201 
 Furnace, bagasse                                               209 
 Blast furnace gas                                             228 
 By-product coke oven gas                                     231 
 Combination wood and oil                                      225 
 Efficiency of                                                 283 
 Natural gas                                                   229 
 Peabody oil                                                   222 
 Webster                                                      55 
 Wood burning                                             201, 202 
 Galvanic action                                                 107 
 Gas, blast furnace, burners                                     228 
 Combustion of                                                228 
 Composition of                                               227 
 Gas, by-product coke oven, burners                             231 
 Combustion of                                                 231 
 Composition of and heat value                                 231 
 Gas, natural, burners                                           229 
 Combustion of                                                 229 
 Composition and heat value of                                229 
 Gases, chimney, losses in                                 158, 159 
 Density of                                                   163 
 Flue (see Flue gases). 
 Path of in Babcock & Wilcox boilers                           57 
 Waste (see Waste heat)                                       232 
 
 
 
 INDEX Pg 8 
 Gaskets                                                         312 
 Gauges, draft, Barrus                                           254 
 Ellison                                                       255 
 Peabody                                                       255 
 U-tube                                                       254 
 Gauges, vacuum                                                 117 
 Grate ratio for anthracite                                    191 
 Gravity of oils                                                 214 
 Grooving                                                       102 
 Guerney's boiler                                                 24 
 Handhole fittings for Babcock & Wilcox boilers             50, 51 
 Handholes in Babcock & Wilcox boilers                       50, 51 
 Hardness of boiler feed water                                   102 
 Permanent                                                     102 
 Temporary                                                    102 
 Testing for                                                   105 
 Hardness of fire brick                                         303 
 Heat and chemical methods of treating feed water               105 
 And its measurement                                           79 
 Balance                                                       262 
 Consumption of engines                                       141 
 Latent                                                        84 
 Of liquid                                                     120 
 Sensible                                                       84 
 Specific (see Specific heat)                                   83 
 Total                                                          86 
 Transfer                                                     323 
 Heat value of bagasse                                           205 
 By-product coke oven gas                                     231 
 Coal                                                        177 
 Heat value of fuels, determination of                           173 
 Determination of Kent's approximate method                   183 
 High and low                                                 174 
 Heat value of natural gas                                       229 
 Oil                                                           215 
 Wood                                                         201 
 Heat waste (see Waste heat)                                    232 
 Heaters, feed water, closed                                     111 
 Economizers                                                   111 
 Open                                                         111 
 Heating feed water, saving by                                  110 
 Hero's engine                                                   13 
 High and low heat value of fuels                               174 
 High pressure steam, advantages of use of                       119 
 High temperature measurements, accuracy of                       89 
 Horse power, boiler                                             265 
 Evaporation (actual) corresponding to                         288 
 Rated boiler                                                 265 
 Stacks for various, of boilers                               250 
 Hydrogen in flue gases                                         156 
 Ice, specific heat of                                           99 
 "Idalia", tests with superheated steam on yacht                143 
 Impurities in boiler feed water                                 100 
 Incomplete combustion of carbon, loss due to                   158 
 Injectors, efficiency of                                       112 
 Relative efficiency of, and pumps                            112 
 Iron alum in feed water treatment                               106 
   
 
 
 
 INDEX Pg 9 
 Kent, Wm., determination of heat value from analysis           183 
 Stack table                                                   250 
 Kindling point                                                150 
 Latent heat                                                 84, 115 
 Laying of fire brick                                           305 
 Red brick                                                     305 
 Lignite, analyses of                                           181 
 Combustion of                                                 195 
 Lime and soda treatment of boiler feed                         102 
 Used in chemical treatment of feed                           105 
 Lime treatment of boiler feed water                             102 
 Liquid fuels and their combustion                               212 
 Loads, economical boiler                                       283 
 Losses due to excess air                                      158 
 Due to unburned carbon                                       158 
 Due to unconsumed carbon in the ash                           261 
 Losses in efficiency (see Heat balance). 
 In flue gases                                           158, 159 
 Low water in boilers                                           298 
 Melting points of metals                                         91 
 Mercurial pyrometers                                             89 
 Moisture in coal, determination of                              176 
 In fuels, losses due to                                       259 
 In steam, determination of                                   129 
 Mud drum of Babcock & Wilcox boiler                             51 
 Napier's formula for flow of steam                             321 
 Natural gas, burners for                                       229 
 Combustion of                                                 229 
 Composition and heat value of                                 229 
 Nitrate of silver in testing feed water                         105 
 Nitrogen, as indication of excess air                           157 
 In air                                                       147 
 In flue gases                                               157 
 Nodules, fire brick, ratio of                                   303 
 Size of                                                       303 
 Normal reading, throttling calorimeter                         131 
 Nozzles, steam sampling for calorimeter                        134 
 Location of                                                   134 
 Oil fuel, burners (see Burners). 
 Capacity with                                                 224 
 Combustion of                                                 217 
 Comparison with coal                                         214 
 Composition and heat value of                                 213 
 Efficiency with                                               224 
 Furnaces for                                                221 
 Gravity of                                                   214 
 In combination with other fuels                               224 
 Stacks for                                                   251 
 Tests with                                                  224 
 Open hearth furnace, Babcock & Wilcox boiler set 
 for utilizing waste heat from                                 236 
 Open heaters, feed water                                       111 
 Operation of boilers                                            291 
 Optical pyrometers                                               91 
 Orsat apparatus                                                 160 
 Oxalate of soda in feed water treatment                         106 
 Oxygen in air                                                  147 
   
 
 
 
 INDEX Pg 10 
 Flue gases                                                   155 
 Peabody draft gauge                                             255 
 Formulae for coal calorimeter correction                     188 
 Furnace for oil fuel                                     221, 222 
 Oil burner                                                   218 
 Peat                                                           167 
 Perkins' boiler                                                24 
 Pfaundler's method of coal calorimeter radiation correction     187 
 Pipe coverings                                                 315 
 Data                                                         308 
 Expansion of                                                  315 
 Pipe fittings                                                   311 
 Flanges                                                       309 
 Flow of steam through                                         317 
 Radiation from bare and covered                               314 
 Sizes                                                         312 
 Supports for                                                 315 
 Piping, boiler room                                             308 
 Pitting                                                        102 
 Plant records, coal                                             293 
 Draft                                                         294 
 Temperature                                                  294 
 Water                                                         293 
 Plasticity of fire brick                                       302 
 Pressed fuels                                                   171 
 Priming in boilers                                              102 
 Methods of treating for                                       107 
 Properties of water                                             96 
 Proximate analyses of coal                                     177 
 Proximate analysis                                              173 
 Method of making                                             176 
 Pulverized fuels                                               170 
 Pump, efficiency of feed                                       112 
 Pyrometers, expansion                                           89 
 Mercurial                                                     89 
 Optical                                                       91 
 Radiation                                                     90 
 Thermo-electric                                               90 
 Quality of steam                                               129 
 Radiation correction for coal calorimeter                 187, 188 
 Correction for steam calorimeter                              131 
 Effect of superheated steam on                               140 
 From pipes                                                   314 
 Losses in efficiency due to                                   307 
 Pyrometers                                                    90 
 Ratio of air supplied to that required for combustion           157 
 Reagents, less usual in feed treatment                         106 
 Records, plant, coal                                           293 
 Draft                                                        294 
 Temperature                                                   294 
 Water                                                         293 
 Requirements of steam boilers                                   27 
 As indicated by evolution of Babcock & Wilcox                 45 
 Rumsey's boiler                                                 23 
 Safety of Babcock & Wilcox boilers                               66 
 Salts responsible for scale                                    101 
 Solubility of                                                 101 
   
 
 
 
 INDEX Pg 11 
 Sampling coal                                                   271 
 Nozzles for steam                                             134 
 Nozzles for steam, location of                                134 
 Steam                                                         134 
 Steam, errors in                                             135 
 Saturated air                                                   149 
 Saving by heating feed                                         110 
 With superheat in "Idalia" tests                             143 
 With superheat in prime movers                           140, 142 
 Scale (see Thermometers)                                       101 
 Sea water, composition of                                       97 
 Sections, Babcock & Wilcox boiler                               50 
 Selection of boilers                                           277 
 Sensible heat                                                  84 
 Separating steam calorimeter                                   132 
 Sizes of anthracite coal                                       190 
 Bituminous coal                                               191 
 Smoke, methods of eliminating                                  197 
 Smokelessness, relative nature of                               197 
 With hand-fired furnaces                                     199 
 With stoker-fired furnaces                                   199 
 Soda, lime and, treatment of feed                               103 
 Oxalate of, in treatment of feed                             106 
 Removal of scale aided by                                     300 
 Silicate of, in treatment of feed                             106 
 Treatment of boiler feed                                     103 
 Space occupied by Babcock & Wilcox boilers                       66 
 Specific heat                                                   83 
 Specific heat of air                                            148 
 Ice                                                           99 
 Saturated steam                                               99 
 Specific heat of superheated steam                             137 
 Various solids, liquids and gases                            85 
 Water                                                         99 
 Spreading method of firing                                     193 
 Stacks and draft (see Chimneys)                                 237 
 Stacks for blast furnace gas                                    228 
 Oil fuel                                                     251 
 Wood                                                     202, 254 
 Stayed surfaces, absence of, in Babcock & Wilcox boilers         69 
 Difficulties arising from use of                               67 
 Steam                                                           115 
 As aid to combustion of anthracite                           191 
 As aid to combustion of lignite                               195 
 Consumption of prime movers                                   289 
 Density of                                                   115 
 Flow of, into atmosphere                                     320 
 Flow of, into pressure above atmosphere                      318 
 Flow of, through pipes                                       317 
 High pressure, advantage of                                   119 
 History of generation and use of                               13 
 Making, theory of                                            92 
 Moisture in                                                   129 
 Properties of, for vacuum                                     119 
 Properties of saturated                                       122 
 Properties of superheated                                     125 
 Quality of                                                   129 
 
 
 
 INDEX Pg 12 
 Saturated                                                     115 
 Specific heat of saturated                                     99 
 Specific heat of superheated                                 137 
 Specific volume of                                           115 
 Superheated                                                   137 
 Superheaters (see Superheated steam). 
 Steaming, quick, with Babcock & Wilcox boilers                   73 
 Stem Correction, thermometer                                     80 
 Stevens, John, boiler                                           23 
 Stevens, John Cox, boiler                                       23 
 Stokers, automatic, advantages of                               195 
 Babcock & Wilcox chain grate                                 194 
 Overfeed                                                     196 
 Smokelessness with                                            199 
 Traveling grate                                               197 
 Underfeed                                                     196 
 Superheated steam                                               137 
 Additional fuel for                                          139 
 Effect on condensation                                       140 
 Effect on radiation                                           140 
 Fittings for use with                                         145 
 "Idalia" tests with                                           143 
 Specific heat of                                             137 
 Variation in temperature of                                   145 
 With turbines                                                 142 
 Superheater, Babcock & Wilcox                                   136 
 Effect of on boiler efficiency                               139 
 Supports, Babcock & Wilcox boiler                           52, 53 
 Tan bark                                                        210 
 Tar, water gas                                                 225 
 Temperature, accuracy of high, measurements                     89 
 As indicated by color                                         91 
 Of waste gases                                                232 
 Records                                                       294 
 Test conditions _vs._ operating conditions                     278 
 Testing, boiler, A. S. M. E. code for                           267 
 Tests of Babcock & Wilcox boilers with bagasse                 210 
 Coal                                                         280 
 Oil                                                           224 
 Theory of steam making                                           92 
 Thermo-electric pyrometers                                       90 
 Thermometer scale, celsius                                       79 
 Thermometer scale, centigrade                                   76 
 Fahrenheit                                                    79 
 Réaumur                                                       79 
 Thermometer scales, comparison of                               80 
 Conversion of                                                 80 
 Thermometer stem correction for                                80 
 Thermometers, glass for                                         79 
 Throttling calorimeter                                         129 
 Total heat                                                 86, 115 
 Treatment of boiler feed water (see Feed water)                 102 
 Chemicals used in                                             105 
 Less usual reagents in                                       106 
 Tube data                                                       309 
 Doors in Babcock & Wilcox boilers                             53 
 Tubes in Babcock & Wilcox boilers                             50 
   
 
 
 
 INDEX Pg 13 
 Ultimate analyses of coal                                       183 
 Analysis of fuels                                            173 
 Unaccounted losses in efficiency                               261 
 Unconsumed carbon in ash                                       261 
 Units, boiler, number of                                       289 
 Size of                                                      289 
 Units, British thermal                                           83 
 Unreliability of CO_{2} readings alone                         162 
 Vacuum gauges                                                   117 
 Properties of steam for                                      119 
 Valves used with superheated steam                             312 
 Variation in properties of saturated steam                     119 
 Superheat from boilers                                       145 
 Volume of air                                                   147 
 Water                                                         96 
 Volume, specific, of steam                                     115 
 Waste heat, auxiliary grates with boilers for                   235 
 Babcock & Wilcox boilers set for use with                     236 
 Boiler design for                                             233 
 Curve of temperature, heat absorption, and heating surface   235 
 Draft for                                                    233 
 Fans for use with                                             233 
 Power obtainable from                                         232 
 Temperature of, from various processes                       232 
 Utilization of                                                232 
 Water, air in boiler feed                                       106 
 Boiling points of                                             97 
 Compressibility of                                             97 
 Water feed, impurities in                                       100 
 Methods of feeding to boiler                                 132 
 Saving by heating                                             110 
 Treatment (see Feed water). 
 Water-gas tar                                                  225 
 Heat of the liquid                                           120 
 Path of, in Babcock & Wilcox boilers                           57 
 Properties of                                                 96 
 Records                                                      293 
 Specific heat of                                               99 
 Volume of                                                     96 
 Weight of                                                 96, 120 
 Watt, James                                                     17 
 Weathering of coal                                             169 
 Webster furnace                                                 55 
 Weight of air                                                  147 
 Wilcox boiler                                                   25 
 Wood, combustion of dry                                         202 
 Wet                                                           203 
 Composition and heat value of                                201 
 Furnace design for                                           201 
 Moisture in                                                   201 
 Sawmill refuse                                               202 
 Woolf s boiler                                                  24 
 Zero, absolute                                                   81 
   
 
 
 
 FOOTNOTES Pg 14 
 [Footnote 1: See discussion by George H. Babcock, of Stirling's paper on 
 "Water-tube and Shell Boilers", in Transactions, American Society of 
 Mechanical Engineers, Volume VI., Page 601.] 
   
 [Footnote 2: When one temperature alone is given the "true" specific 
 heat is given; otherwise the value is the "mean" specific heat for the 
 range of temperature given.] 
   
 [Footnote 3: For variation, see Table 13.] 
   
 [Footnote 4: Where range of temperature is given, coefficient is mean 
 over range.] 
   
 [Footnote 5: Coefficient of cubical expansion.] 
   
 [Footnote 6: Le Chatelier's Investigations.] 
   
 [Footnote 7: Burgess-Le Chatelier.] 
   
 [Footnote 8: For accuracy of high temperature measurements, see Table 
 7.] 
   
 [Footnote 9: Messrs. White & Taylor Trans. A. S. M. E., Vol. XXI, 1900.] 
   
 [Footnote 10: See Scientific American Supplement, 624, 625, December, 
 1887.] 
   
 [Footnote 11: 460 degrees below the zero of Fahrenheit. This is the 
 nearest approximation in whole degrees to the latest determinations of 
 the absolute zero of temperature] 
   
 [Footnote 12: Marks and Davis] 
   
 [Footnote 13: See page 120.] 
   
 [Footnote 14: See Trans., A. S. M. E., Vol. XIV., Page 79.] 
   
 [Footnote 15: Some waters, not naturally acid, become so at high 
 temperatures, as when chloride of magnesia decomposes with the formation 
 of free hydrochloride acid; such phenomena become more serious with an 
 increase in pressure and temperature.] 
   
 [Footnote 16: L. M. Booth Company.] 
   
 [Footnote 17: Based on lime containing 90 per cent calcium oxide.] 
   
 [Footnote 18: Based on soda containing 58 per cent sodium oxide.] 
   
 [Footnote 19: See Stem Correction, page 80.] 
   
 [Footnote 20: See pages 125 to 127.] 
   
 
 
 
 FOOTNOTES Pg 15 
 [Footnote 21: The actual specific heat at a particular temperature and 
 pressure is that corresponding to a change of one degree one way or the 
 other and differs considerably from the average value for the particular 
 temperature and pressure given in the table. The mean values given in 
 the table give correct results when employed to determine the factor of 
 evaporation whereas the actual values at the particular temperatures and 
 pressures would not.] 
   
 [Footnote 22: See page 117.] 
   
 [Footnote 23: Ratio by weight of O to N in air.] 
   
 [Footnote 24: 4.32 pounds of air contains one pound of O.] 
   
 [Footnote 25: Per pound of C in the CO.] 
   
 [Footnote 26: Ratio by volume of O to N in air.] 
   
 [Footnote 27: Available hydrogen.] 
   
 [Footnote 28: See Table 31, page 151.] 
   
 [Footnote 29: This formula is equivalent to (10) given in chapter on 
 combustion. 34.56 = theoretical air required for combustion of one pound 
 of H (see Table 31).] 
   
 [Footnote 30: For degree of accuracy of this formula, see Transactions, 
 S. M. E., Volume XXI, 1900, page 94.] 
 
   
 [Footnote 31: For loss per pound of coal multiply by per cent of carbon 
 in coal by ultimate analysis.] 
   
 [Footnote 32: For loss per pound of coal multiply by per cent of carbon 
 in coal by ultimate analysis.] 
   
 [Footnote 33: The Panther Creek District forms a part of what is known 
 as the Southern Field; in the matter of hardness, however, these coals 
 are more nearly akin to Lehigh coals.] 
   
 [Footnote 34: Sometimes called Western Middle or Northern Schuylkill 
 Field.] 
   
 [Footnote 35: Geographically, the Shamokin District is part of the 
 Western Middle Mahanoy Field, but the coals found in this section 
 resemble more closely those of the Wyoming Field.] 
   
 [Footnote 36: See page 161.] 
   
 [Footnote 37: U. S. Geological Survey.] 
   
 [Footnote 38: See "Steam Boiler Economy", page 47, First Edition.] 
   
 [Footnote 39: To agree with Pfaundler's formula the end ordinates should 
 be given half values in determining T", _i. e._, T" = ((Temp. at B + 
 Temp. at C) ÷ 2 + Temp. all other ordinates) ÷ N] 
   
 [Footnote 40: B. t. u. calculated.] 
   
 [Footnote 41: Average of two samples.] 
   
 
 
 
 FOOTNOTES Pg 16 
 [Footnote 42: Assuming bagasse temperature = 80 degrees Fahrenheit and 
 exit gas temperature = 500 degrees Fahrenheit.] 
   
 [Footnote 43: Dr. Henry C. Sherman. Columbia University.] 
   
 [Footnote 44: Includes N.] 
   
 [Footnote 45: Includes silt.] 
   
 [Footnote 46: Net efficiency = gross efficiency less 2 per cent for 
 steam used in atomizing oil. 
   
 Heat value of oil = 18500 B. t. u. 
   
 One ton of coal weighs 2000 pounds. One barrel of oil weighs 336 pounds. 
 One gallon of oil weighs 8 pounds.] 
   
 [Footnote 47: Average of 20 samples.] 
   
 [Footnote 48: Includes H and CH_{4}.] 
   
 [Footnote 49: B. t. u. approximate. For method of calculation, see page 
 175.] 
   
 [Footnote 50: Temperatures are average over one cycle of operation and 
 may vary widely as to maximum and minimum.] 
   
 [Footnote 51: Dependant upon length of kiln.] 
   
 [Footnote 52: Results secured by this method will be approximately 
 correct.] 
   
 [Footnote 53: See "Chimneys for Crude Oil", C. R. Weymouth, Trans. 
 S. M. E., Dec. 1912.] 
 
   
 [Footnote 54: To determine the portion of the fuel which is actually 
 burned, the weight of ashes should be computed from the total weight of 
 coal burned and the coal and ash analyses in order to allow for any ash 
 that may be blown away with the flue gases. In many cases the ash so 
 computed is considerably higher than that found in the test.] 
   
 [Footnote 55: As distinguished from the efficiency of boiler, furnace 
 and grate.] 
   
 [Footnote 56: To obtain the efficiency of the boiler as an absorber of 
 the heat contained in the hot gases, this should be the heat generated 
 per pound of combustible corrected so that any heat lost through 
 incomplete combustion will not be charged to the boiler. This, however, 
 does not eliminate the furnace as the presence of excess air in the 
 gases lowers the efficiency and the ability to run without excess air 
 depends on the design and operation of the furnace. The efficiency based 
 on the total heat value per pound of combustible is, however, ordinarily 
 taken as the efficiency of the boiler notwithstanding the fact that it 
 necessarily involves the furnace.] 
   
 [Footnote 57: See pages 280 and 281.] 
   
 
 
 
 FOOTNOTES Pg 17 
 [Footnote 58: Where the horse power of marine boilers is stated, it 
 generally refers to and is synonymous with the horse power developed by 
 the engines which they serve.] 
   
 [Footnote 59: In other countries, boilers are ordinarily rated not in 
 horse power but by specifying the quantity of water they are capable of 
 evaporating from and at 212 degrees or under other conditions.] 
   
 [Footnote 60: See equivalent evaporation from and at 212 degrees, page 
 116.] 
   
 [Footnote 61: The recommendations are those made in the preliminary 
 report of the Committee on Power Tests and at the time of going to press 
 have not been finally accepted by the Society as a whole.] 
   
 [Footnote 62: This code relates primarily to tests made with coal.] 
   
 [Footnote 63: The necessary apparatus and instruments are described 
 elsewhere. No definite rules can be given for location of instruments. 
 For suggestions on location, see A. S. M. E. Code of 1912, Appendix 24. 
 For calibration of instruments, see Code, Vol. XXXIV, Trans., 
 S. M. E., pages 1691-1702 and 1713-14.] 
 
   
 [Footnote 64: One to two inches for small anthracite coals.] 
   
 [Footnote 65: Do not blow down the water-glass column for at least one 
 hour before these readings are taken. An erroneous indication may 
 otherwise be caused by a change of temperature and density of the water 
 within the column and connecting pipe.] 
   
 [Footnote 66: Do not blow down the water-glass column for at least one 
 hour before these readings are taken. An erroneous indication may 
 otherwise be caused by a change of temperature and density of the water 
 within the column and connecting pipe.] 
   
 [Footnote 67: For calculations relating to quality of steam, see page 
 129.] 
   
 [Footnote 68: Where the coal is very moist, a portion of the moisture 
 will cling to the walls of the jar, and in such case the jar and fuel 
 together should be dried out in determining the total moisture.] 
   
 [Footnote 69: Say ½ ounce to 2 ounces.] 
   
 [Footnote 70: For methods of analysis, see page 176.] 
   
 [Footnote 71: For suggestions relative to Smoke Observations, see 
 S. M. E. Code of 1912, Appendix 16 and 17.] 
 
   
 [Footnote 72: The term "as fired" means actual condition including 
 moisture, corrected for estimated difference in weight of coal on the 
 grate at beginning and end.] 
   
 [Footnote 73: Corrected for inequality of water level and steam pressure 
 at beginning and end.] 
   
 
 
 
 FOOTNOTES Pg 18 
 [Footnote 74: See Transactions, A. S. M. E., Volume XXXIII, 1912.] 
   
 [Footnote 75: For methods of determining, see Technologic Paper No. 7, 
 Bureau of Standards, page 44.] 
   
 [Footnote 76: Often called extra heavy pipe.] 
   
 [Footnote 77: See Feed Piping, page 312.] 
   
 [Footnote 78: See Superheat Chapter, page 145.] 
   
 [Footnote 79: See Radiation from Steam Lines, page 314.] 
   
 [Footnote 80: D, the density, is taken as the mean of the density at the 
 initial and final pressures.] 
   
 [Footnote 81: Diameters up to 5 inches, inclusive, are _actual_ 
 diameters of standard pipe, see Table 62, page 308.] 
   
 [Footnote 82: Diameters up to 4 inches, inclusive, are _actual_ internal 
 diameters, see Table 62, page 308.] 
   
 [Footnote 83: H. P. Jordan, "Proceedings of the Institute of Mechanical 
 Engineers", 1909.] 
   
 [Footnote 84: "Zeitschrift des Vereines Deutscher Ingenieur", 1909, page 
 1750.] 
   
 [Footnote 85: Heinrich Gröber--Zeit. d. Ver. Ing., March 1912, December 
 Leprince-Ringuet--Revue de Mecanique. July 1911. John Perry--"The 
 
 Steam Engine". T. E. Stanton--Philosophical Transactions, 1897. Dr. 
 T. Nicholson--Proceedings Institute of Engineers & Shipbuilders in 
 
 Scotland, 1910. W. E. Dally--Proceedings Institute of Mechanical 
 Engineers, 1909.] 
   
 [Footnote 86: Proceedings Royal Society, Vol. LXXI.] 
   
 [Footnote 87: Zeitschrift des Vereines Deutscher Ingenieur, 1910, page 
 1154.] 
   
 [Footnote 88: Proceedings Institute of Engineers and Shipbuilders, 
 1910.] 
   
 [Footnote 89: Natural or Hyperbolic Logarithm.] 
   
 
 
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