Laboratory manual of inorganic preparations
■w ss ' /// > Jy ■ c> v s . > 1- * ri "o $ ■*.<* .- ^ ^. ' ** % V *> •#N , ^ V^ ClV ^ v^ V •♦ \V V » 0 7 ^ ^^ </- tl -. ,0o. ^ X a> ^ - I), = ■■. ^ > '^^ ^ LABORATORY MANUAL OF Inorganic Preparations H. T. VULTE, PH. D., F. C S. INSTRUCTOR IN CHEMISTRY, COLUMBIA UNIVERSITY, AND LECTURER IN- DOMESTIC SCIENCE, TEACHERS' COLLEGE, N. Y. AND GEORGE M S. NEUSTADT INSTRUCTOR IN CHEMICAL ANALYSIS, COOPER UNION. N. Y. THIRD EDITION NEW YORK GEO. GOTTSBERGER PECK, Publisher 117 CHAMBERS STREET I902 THE LIBRARY ®F CONGRESS, Two Copies Receive© APR, If 1902 COPYWSHT SNTRV CLASS CtOfXa No. i o r-i i COPY S. I Entered according to Act of Congress, in the year i8qs, By GEO. GOTTSBERGER PECK, In the Office of the Librarian of Congress, at Washington, D. C. Entered according to Act of Congress, in the year 1902, Bv GEO. GOTTSBERGER PECK, In the Office of the Librarian of Congress, at Washington, D. C. PREFACE The study of inorganic chemistry naturally precedes that of organic, and in a certain way this plan is carried out in a com- plete chemical course. The study of the organic branch, how- ever, proceeds on a much more logical plan than that usually adopted in inorganic work; one of the chief advantages being the practice to which the student is introduced very early in his course. The following work is synthetic, and shows how compounds, often very complex in character, rare in occur- rence or expensive in preparation, may be produced from simple substances, or from those which are comparatively plenty and cheap, and at the same time the bye products may be saved. Such a course of study is also of great value in inorganic work, but should precede and lead up to, and not follow organic chem- istry. However, a contrary plan seems to have been followed, for while we have various works on organic preparations, there are none, so far as the authors know, in the inorganic branch of the subject (at least not in English), excepting the works on Elementary Chemistry; and where these treat of the subject in laboratory practice, the methods are those which cannot be recommended as the best and most economical. In many laboratories the waste of material is greater than the use. Students are apt to acquire the idea that after a certain re- sult has been produced the rest of the material is worthless, and in consequence much loss occurs from throwing away valuable material which can be recovered or used with little trouble or expense. It is not a very difficult operation to purify the various commercial salts, converting them into C. P. reagents, and in the operation the student cannot help acquiring facts which are directly and forcibly brought to his knowledge. Too much reli- ance is usually placed on the so-called C. P. chemicals in com- mon use. Many are high-priced and apt to deteriorate in the IV PREFACE. packages. There is no reason why the student should not pre- pare many of these, unless it be that he does not always know where to look for the necessary information. The book is designed to meet a long felt want in the inor- ganic laboratory, in training the student to prepare his own reagents and to test them for the customary impurities. The methods are largely those in commercial use, and should prove of value to those studying Applied Chemistry. The works of Fresenius, Erdmann and others, as well as the various chemical journals for some years past, have been carefully searched, and such information as was thought valuable has been collected and arranged in order, beginning with the simplest operations and gradually increasing in difficulty as the student acquires skill in his work. As far as possible, references to the original articles have been given. October, 1895. PREFACE TO SECOND EDITION. In this new edition, the number of small errors in the first edition, almost unavoidable in such a case, have been corrected, and a number of minor improvements have been made. All suggestions for alterations which have reached us since the publication of the first edition, have been carefully considered, and wherever it was possible and consistent with our endeavor to maintain unchanged the general scope and character of the book, the changes have been made. The favorable reception with which the first edition was received, both by journals of acknowledged authority, and by chemists of extended experience in this class of work, both in this country and abroad, has shown that the work is not without usefulness in the field for which it was designated. THE AUTHORS. Columbia University, 1897. PREFACE TO THIRD EDITION. In presenting the third edition of this work a number of minor improvements have been made, and the part dealing with volumetric analysis has been entirely rewritten. All suggestions that have reached us since the publication of the second edition have been considered and acted upon when thought advisable. We beg to thank our numerous friends for the favorable reception accorded the first two editions of this work, and trust that this new edition will be as acceptable as the two former. THE AUTHORS, Columbia University, Feb.. 1902, LABORATORY MANUAL OF INORGANIC PREPARATIONS, WATER. H20. Pure water is obtained by distilling spring water from a copper still with head and condenser made of pure tin.* The distillation is carried to about three-fourths of the quantity operated upon. If it is desired to have the distilled water perfectly tree trom carbonic acid and am- monium carbonate, the portions passing over first must be rejected. In the larger chemical laboratories, distilled water is obtained from the steam apparatus which serves for drying, etc. Rain water collected in the open air may in many cases be substituted for distilled water. It must be colorless, odorless, and tasteless, and should not leave the smallest residue when evaporated in a platinum vessel. It should not be changed by ammonium sulphide (copper, lead, iron), nor rendered turbid by baryta water (carbonic acid). No cloudiness should be caused even after long standing by the addition of ammonium oxalate, of barium chloride and hydrochloric acid (sul- * Glass retorts with ordinary condensers may be used when small quantities of water are required. 2 LABORATORY MANUAL OF phuric acid), of silver nitrate and nitric acid (chlorides), or of mercuric chloride and sodium carbonate (ammonia). We use water principally as a simple solvent for a great variety of substances. AMMONIUM— FREE WATER. If the ordinary distilled water gives a reaction for am- monia with Nessler's reagent, it should be treated with sodium carbonate, about one gram to the litre, boiled until one-fourth has been evaporated and then distilled. Ammonium free water may also be prepared by dis- tilling water made slightly acid with sulphuric acid. WATER FREE FROM ORGANIC MATTER AND AMMONIA.* About 15-20 litres of ordinary distilled water, to which about 1 gram, of potassium hydrate and 0.2 gram, of potassium permanganate have been added are maintained at about iOO° C. for twenty-four hours under an inverted condenser, after which the condenser is reversed and the water distilled off, discarding the first portions. Apply Nessler's test to the distillate from time to time, until 100 c.c. show no coloration and collect that which comes over subsequently, stopping 500 c.c. short of dryness. As an additional precaution the water thus obtained may be acidified with sulphuric acid and re-distilled. For preparing distilled water, the ordinary tin lined copper still and block tin condenser may be used, or a more economical way is to make use of the well known Domestic Water Still, (Fig. 1). This piece of apparatus * Water Analysis, Frankland, p. 113. INORGANIC PREPARATIONS. yields a good quality of product, with a minimum ex- penditure of heat and condenser water, and is moreover very compact. Fig. l. Water free from organic matter and ammonium, which is indispensable in water analysis and the preparation of many standard solutions such as potassium permanganate, argentic nitrate etc., is best prepared in the apparatus shown in. Fig 2, which consists of a glass-stoppered flask with side-neck tube. The end of the side-neck tube is turned vertically downward, being thrust deeply into the tin tube of the condenser, and held in place there by a short piece of rubber tubing. The three-eighth inch block tin pipe forming the condenser-tube is bent zigzag instead of in the conven- LABORATORY MANUAL OF tional helix. This affords a more even flow of the distillate. The cylindrical copper jacket containing the water for cool- ing is about four inches in diameter, and fifteen inches long. The disk closing the lower end is arched upward so that in Fig. 2. case the condenser " sweats " from the use of very cold water, the drip from the outside can not contaminate the distillate. The lower end of the tin tube is cut aslant for the more certain delivery of the distillate. INORGANIC PREPARATIONS. ETHYL ALCOHOL. C2H5.OH. Two sorts of alcohol are used in chemical analy- sis, viz. : 1st, Commercial " 95 per cent, alcohol," which really contains 93 to 94 per cent, of alcohol by weight ; and 2d, absolute alcohol. The latter may be prepared most conveniently by placing in a flask or tin can 800 grams of good quick-lime in coarse powder or small lumps, adding 1 litre of" 95 per cent, alcohol," connecting the vessel with the lower end of a Liebig condenser, and keeping its contents boiling on a water bath for an hour. The can is then connected to the upper end of a dry conden- ser, and the dehydrated alcohol distilled off into a bottle for use.* Pure alcohol must completely volatilize, and ought not to leave a smell of fusel-oil when rubbed between the hands ; nor should it alter the color of moist blue or red litmus paper. When kindled, it must burn with a faint bluish, barely preceptible flame. Commercial Alcohol invariably contains aldehyde and if kept in tin cans stannic oxide as well; such alcohol can- not be used for the preparation of alcoholic potash solutions, argentic nitrate or for Hiibl's iodo-mercuric chloride solution. For such purposes either of the two following methods may be used. A convenient amount of the alcohol to be purified is shaken with pulverized potassium permanganate until it assumes a decided color. It is then allowed to stand for * Erlenmeyer ; J. Lawrence Smith. 6 LABORATORY MANUAL OF some hours, until the permanganate has been decomposed and brown manganese oxide is deposited. A pinch of pulverized calcium carbonate is then added, and the alcohol distilled at the rate of about 50 c. c. in 20 minutes from a flask provided with a Wurtz tube or one of the Lebel- Heninger pattern. The distillate is tested frequently until about ioc. c. thereof, when boiled with 1 c. c. of strong (syrup) solution of caustic soda or potash, gives no percept- ible yellow coloration on standing for 20 minutes or half an hour. What distills over after that time is preserved for use. The first distillates may be added to the small amount remaining in the distilling flask (which should not be driven down to the complete dryness), and a fresh portion of puri- fied alcohol recovered. The rationale of the proceeding appears to be that the permanganate oxidizes and destroys chiefly the fusel- oil, furfurol and other compounds of that nature, the acids resulting from the reaction are neutralized by the calcium carbonate added before distillation, and by distilling slowly the aldehyde at least is concentrated in the first portions of the distillate. Distillation of alcohol contain- ing caustic potash or soda seemed to cause a constant formation of aldehyde. The alcohol thus purified is per- fectly neutral, and gives most satisfactory results when used as a solvent for caustic alkalies or silver nitrate, the solutions remaining as colorless as distilled water, even after boiling and standing indefinitely, if properly pro- tected from dust and other external influences.* Jour. Am. Chem. Soc. — E. Waller. INORGANIC PREPARATIONS. The second method consists in distilling the alcohol with some caustic potash in the presence of a large quantity of non-volatile fatty acid ; either oleic or stearic is gener- ally used, the process is simple and the result good. OXYGEN. 02. The compressed gas put up in steel cylinders is sufficiently pure for most purposes, but when not avail- able the gas maybe readily prepared by heating a mixture of equal parts of potassium chlorate and manganese di- oxide, in a copper retort, or better, in an apparatus similar to fig. 3. UM 3 Fig. 3. Oxygen gas made in this way is liable to contain chlorine or oxides of chlorine and carbon dioxide, it is purified by washing with potassium hydrate and dried by passing through concentrated sulphuric acid. Oxygen may also be prepared by treating sodium dioxide Na302 with dilute acid, either hydrochloric or sulphuric. 8 LABORATORY MANUAL OF Na202 f 2HC1 = O + 2NaCl + HgO, great heat is evolved in this reaction and the operation must be conducted with care; it is however an excellent way to oxidize solutions, in which case the solution is made acid and the sodium dioxide dropped in and well stirred until the desired effect has been produced. In the wet way oxygen is produced by treating "Chloride of Lime " Ca(C10)2,CaCl3 in disc form, in a Kipp's Apparatus with a mixture of I litre of hydrogen dioxide and 53 c. c. nitric acid com. Sp. Gr. 1.265. The same pre- cautions for purification are necessary as in the case of manganese dioxide and potassium chlorate. To prepare oxygen, cubes consisting of a mixture of 2 parts of barium dioxide, 1 part of manganese dioxide and 1 part of plaster are used with hydrochloric acid (sp. gr. 1. 12) diluted with an equal volume of water. The oxy- gen evolved contains traces of chlorine and must there- fore be washed with an alkali* It can also be prepared by adding potassium perman- ganate to hydrogen peroxide made alkaline with ammonia. t Oxygen is a colorless gas, and without odor. It is liquified with difficulty, requiring a pressure of 320 atmos- pheres at 212° F. Oxygen is remarkable for the wide range of its chemical attraction for other elementary bodies with all of which it is capable of entering into combi- nation except one, namely fluorine. * G. Neumann, Ber. 20, 1584. f C. F. Gohring, Chem. Zeit. 12, 1659. INORGANIC PREPARATIONS. HYDROGEN. H2. Hydrogen is best prepared from granulated zinc and dilute sulphuric acid (i litre acid, 5 litres water) in Kipp's Apparatus ; the zinc should not be too pure or the supply of gas will be slow and feeble. In any case it is well to add a small amount of copper sulphate solution, just sufficient to produce a thin coat of copper on the zinc, oi a piece of platinum foil maybe used in place of the copper sulphate ; in this latter case it is better to amalgamate the zinc, by first treating with dilute sulphuric acid and then adding mercury and shaking, or by simply treating the zinc with a strong solution of mercuric nitrate containing free nitric acid. A granulated alloy of tin and zinc, containing about 83 per cent, of the latter, prepared by adding zinc to molten tin as long as it dissolves, is recommended for use in Kipp's apparatus. The pieces retain their shape and size after all the zinc is dissolved out, and therefore have no tendency to fall through into the lower bulb.* Hydrogen may also be prepared by sodium amalgam with dilute acids. Hydrogen gas prepared by the action of zinc and acid is never pure, but may contain hydrocarbons, hydrogen sulphide, sulphur dioxide, etc. The very small amount of arsenic generally present, as AsH3, may be neglected. The other impurities are re- moved by first passing the gas through a solution of * J. Habermann, Zeit. Anal. Chem. 28, IO LABORATORY MANUAL OF potassium permanganate in order to oxidize hydrocarbons, hydrogen sulphide, etc., then through solution of potassium hydrate to absorb carbon dioxide, sulphur dioxide, etc., and finally through concentrated sulphuric acid and calcium chloride to remove water. Hydrogen is a colorless, odorless and tasteless gas, is highly combustible, burning with a very hot but slightly luminous flame, and when mixed with air or free oxygen, explodes with violence. NITROGEN. N2. This gas is seldom used, but when required may be readily prepared by heating equal parts of concentrated aqueous solutions of ammonium chloride and potassium or sodium nitrite. N H4 CI + KN03 = N3 + KC1 + 2H20. The operation is conducted in a spacious flask, the evolved gas mixed with steam, ammonium chloride, and pos- sibly some oxides of nitrogen, is cooled washed with water and dried over sulphuric acid. Nitrogen prepared in this way contains no argon. Nitrogen is a colorless, odorless and tasteless gas, and is a non-supporter of combustion. CHLORINE AND CHLORINE WATER. Cl2. Chlorine is prepared by mixing 18 parts of common salt in lumps with 15 parts of finely pulverized good man- INORGANIC PREPARATIONS. II ganese dioxide, free from calcium carbonate ; put the mix- ture in a flask, pour a completely cooled mixture of 45 parts of concentrated sulphuric acid and 21 parts of water upon it, and shake the flask : a uniform and continuous evolution of chlorine gas will soon begin, which, when slackening may be easily increased again by the application of a gentle heat. This method of WlGGERS is excellent, and can be highly recommended. Conduct the chlorine gas evolved first through a flask containing a little water, then into a bottle filled with cold water, and continue the process until the fluid is saturated. Where it is desired to obtain chlorine water quite free from bromine, the washing flask is changed after about one-half of the chlorine has been expelled, and the gas which now passes over is conducted into a fresh bottle filled with water. If the chlorine water is to be quite free from hydrochloric acid, the gas must be passed through a U tube containing manganese dioxide. The chlorine water must be protected from the action of light ; since, if this precaution is neglected, it speedily suf- fers complete decomposition, being converted into dilute hydrochloric acid, with evolution of oxygen (resulting from the decomposition of water). Smaller quantities, intended for use in the laboratory, are best kept in a stoppered bottle protected by a case of pasteboard. Chlorine water which has lost its strong peculiar odor is unfit for use. CHLORINE FROM CHLORIDE OF LIME IN KIPP'S APPA- RATUS. Dry chloride of lime is intimately mixed with plaster and moistened to such a degree that it can only with diffi- culty be rolled into balls between the fingers. It is made 12 LABORATORY MANUAL OF homogeneous by powdering in an iron mortar and beaten into an iron frame 10-12 m.m. high by means of an iron mallet. It is then covered with a piece of oilcloth and submitted to great pressure. The plate of chloride of lime is then cut into cubes while still in the frame and dried as quickly as possible at 200 C. The cubes are then preserved in well-closed vessels. It is used in a Kipp's apparatus with hydrochloric acid (sp. gr. 1.124) diluted with an equal volume of water. The acid must be free from sul- phuric acid.* When chlorine is generated from bleaching powder and hydrochloric acid in a Kipp's apparatus, it is advisable, af- ter using the apparatus, to blow in a little air, otherwise a slow but continuous action takes place, owing to the ab- sorption of the chlorine by the acid.f APPARATUS FOR A CONSTANT SUPPLY OF CHLORINE. I. Manganese dioxide is used in fragments the size of peas, and is placed in a two-necked bottle, at the bottom of which there is a layer of broken glass or pumice. This stands in a water bath. Hydrochloric acid is supplied from a reservoir at a higher level by a tube reaching to the bottom of the layer of glass, a T-piece and stopcocks allowing the same tube to serve for the removal of the manganese solution. The corks should be soaked in par- affin. Suitable drying apparatus can be attached and will not require replenishing for a long time. The chlorine begins to come off when the temperature of the bath reaches 50° C, and by means of a stopcock on the outlet its * C. Winkler, Ber. 20, 184. f C. Winkler, Ber. 22, 1076. INORGANIC PREPARATIONS. I 3 rate is completely under control. The evolution can speedily be arrested by closing the stopcock at the outlet of the drying apparatus and emptying the water bath. The apparatus is then left full of chlorine, and is ready at any moment to give supply of the gas completely free from oxygen.* II. From sodium chloride, pyrolusite, and sulphuric acid. — It is usually supposed that in this reaction the whole of the chlorine is evolved in the free state; detailed experi- ments have, however, shown that this is not the case, but that the reaction which takes place is as follows : 4NaCl + Mn02 + 3H2S04 = 2NaHS04 f- Na2S04 4- MnCl2+ 2H20 + Cl2. The necessary proportions are, therefore, 5 parts of pyrolusite, 1 1 parts salt, and 14 parts of sulphuric acid diluted with an equal volume of water. III. From pyrolusite, hydrochloric and sulphuric acids. — The instructions usually given for the preparation of chlorine by this method are to take 1 part of pyrolusite, 2 of hydrochloric acid of sp. gr. 1.14, and 1 part of sulphuric acid mixed with an equal bulk of water, the reaction being supposed to take place according to the equation: Mn02 + 2HC1 + H2S04 = MnS04 + 2H20 + Cl2. As in the foregoing case this equation is quite incorrect, only 65 per cent, of the chlorine being obtained in the free state. * A. Vosmaer, Zeit. Anal. Chem., 27, 638. 14 LABORATORY MANUAL OF CHLORINE FOR LABORATORY PURPOSES. When hydrochloric acid of sp. gr. i.i, heated to about 8o° C, is allowed to come slowly in contact with pieces of potassium chlorate which have been previously fused, a steady evolution of gas takes place. Under these condi- tions, about 82 to 85 per cent, of the gas is chlorine, the re- mainder being chlorine dioxide. Another 10 per cent, of the dioxide may be decomposed by passing the evolved gas through a saturated hydrochloric acid solution of man- ganous chloride at 900 C. If the gas is wanted absolutely pure, the gas, after passing through the manganous chlor- ide, may be passed through a combustion tube filled with asbestos and heated to redness. Care must be taken to have the acid hot, and not to allow the action to become rapid, or the proportion of chlorine dioxide may become much increased and explosion occur. 1 gram of potas- sium chlorate yields about half a litre of chlorine. If a Kipp or some similar constant gas-generating ap- paratus is employed, and the acid heated by a steam jacket or by standing the generator in hot water, this method forms a convenient constant chlorine apparatus for laboratory use.* Chlorine is a heavy greenish, yellowish gas, having a strong and suffocating odor, and if inhaled in sufficient quantities is capable of producing suffocation. Free chlorine gas is readily detected by its color and odor. * F. A. Gooch and D. A. Kreider, Zeit. Anorg. Chem. , 7, 17. INORGANIC PREPARATIONS. HYDROCHLORIC ACID, OR HYDROGEN CHLORIDE. HC1. Pour a cooled mixture of seven parts of concen- trated sulphuric acid and two parts of water over four parts of sodium chloride in a retort; expose the re- tort, with slightly raised neck, to the heat of a sand-bath until the evolution of gas ceases; conduct the evolved gas, by means of a bent tube, into a flask containing six parts of water, and take care to keep this vessel constantly cool. To prevent the gas from receding the tube ought to dip but about one line into the water of the flask. When the operation is terminated, try the specific gravity of the acid produced, and dilute with water until it marks from 1. 1 1 to 1. 12. If you wish to ensure the absolute purity of the acid, and its perfect freedom from every trace of arsenic and chlorine, you must take care to free the sulphuric acid intended to be used in the process from arsenic and the oxygen compounds of nitrogen, according to the directions (see sulphuric acid, page 22.) A pure acid may also be prepared cheaply from the crude hydrochloric acid of com- merce by diluting the latter to a specific gravity of 1.12 and distilling the fluid with addition of some chloride of sodium. Or you may put the acid into the retort in the concentrated form, placing 60 parts of water into the receiver for every 100 parts of concentrated acid, and not luting the receiver to the retort. If the crude acid contains chlorine this should be removed first by cautious addition of solution of sulphur dioxide, before proceeding to the distillation; if, 1 6 LABORATORY MANUAL OF on the other hand, it contains sulphur dioxide, this is re- moved in the same way by cautious addition of some chlorine water. Hydrochloric acid not unfrequently con- tains arsenious chloride, owing to the presence of arsenic in the sulphuric acid employed. To free it from this im- purity, the acid is mixed with twice its volume of water, hydrogen sulphide is conducted into it, the mixture allowed to stand at rest for some time, the clear fluid then decanted from the sulphur and arsenious sulphide, and heated, to ex- pel the hydrogen sulphide. Hydrochloric acid must be perfectly colorless and leave no residue upon evaporation. If it turns yellow on evaporation, ferric chloride is present. It must not im- part a blue tint to a solution of potassium iodide mixed with starch paste (chlorine or ferric chloride), nor discolor a fluid made faintly blue with iodized starch (sulphur dioxide). Barium chloride ought not to produce a pre- cipitate in the highly diluted acid (sulphuric acid). Hy- drogen sulphide must leave the diluted acid unaltered (ar- senic). After neutralization with ammonia, ammonium sulphide must produce no change in it (iron, thallium). It can also be prepared by distilling a mixture of cone. sulphuric and hydrochloric acids; this latter method is bet- ter where gaseous hydrochloric acid is needed. METHODS FOR OBTAINING CONSTANT STREAMS OF HY- DROGEN CHLORIDE, AMMONIA AND NITROGEN. Hydrogen chloride can be generated in a Kipp's ap- paratus by the action of ordinary sulphuric acid on carnal- lite ; ammonia gas by allowing a solution of ammonia to react with solid potassium hydroxide. When the ma- INORGANIC PREPARATIONS. 17 terials are exhausted, the solution of potash which is formed may be used for ordinary laboratory purposes after it has been boiled to expel ammonia. To prepare nitrogen in Kipp's apparatus, it is best to employ cubes containing chloride of lime made according to Winkler's method (page 11); these are treated with a mixture of equal volumes of ammonia and water. The resulting gas contains suspended ammonium chloride and other impurities, which may be removed by passing it through water, potash and sulphuric acid.* Fig. 4. NITRIC ACID, or HYDROGEN NITRATE. HNO3 or N02OH. Prepared by slowly distilling a mixture of 5 parts of sodium nitrate and 3 parts of cone, sulphuric acid, in an apparatus as shown in Fig. 4 ; the product is usually not By G. Neumann, (J. pr. Chem. [2] 37, 342-345). I 8 LABORATORY MANUAL OF sufficiently concentrated, and must be redistilled with five times its volume of cone, sulphuric acid in an apparatus similiar to the above. If the product is colored yellow or red by dissolved oxides of nitrogen, it may be rendered color- less by blowinga current of dry air through the acid for some minutes. Concentrated nitric acid 1.53 spcific gravity has a strong affinity for water and must be kept closely stop- pered. The sudden frothing which frequently takes place when nitric acid is prepared from sodium nitrate and sulphuric acid is explained on the assumption that the first portions pass over at 840 C, and that the heating mustbe commenced cautiously, and the temperature only allowed to rise after the first reaction abates. After the temperature has risen above 1090 C, no acid passes over until the temperature 1 1 70 C. is reached, when the last portions pass over. The latter acid has a sp. gr. 1.42, and corresponds with the hydrate, HN03 -f- 2H30,' which distills at 120 to 12 1° C. without decomposition.* Another method of preparation is to heat crude nitric acid of commerce, as free as possible from chlorine, and of a specific gravity of at least 1.3 1 in a glass retort to boiling, with addition of some potassium nitrate ; let the distillate run into a receiver kept cool, and try from time to time whether after dilution it still continues to precipi- tate or cloud solution of silver nitrate. As soon as this ceases to be the case, change the receiver, and distill until a trifling quantity only remains in the retort. Dilute the distillate with water until the specific gravity is 1.2. * By C. W. Volney, J. Amer. Chem. Soc. 13, 246-251. INORGANIC PREPARATIONS. 19 Another method is to dilute crude nitric acid of com- merce of about 1.38 specific gravity with two-fifths of its weight of water, and add solution of silver nitrate as long as a precipitate of silver chloride continues to form ; then add a further slight excess of solution of silver nitrate, let the precipitate subside, decant the perfectly clear super- natant acid into a retort or an alembic with ground head ; add some potassium nitrate free from chlorine, and distill until only a small quantity remains, taking care to attend to the proper cooling of the fumes distilling over. Dilute the distillate, if necessary, with water until it has a specific gravity of 1.2. Pure nitric acid must be colorless and leave no residue upon evaporation on platinum foil. Solution of silver nitrate or of barium nitrate must not cause the slightest turbidity in it. Dilute the acid with water before adding these reagents, as otherwise nitrates will pre- cipitate. Silver should be tested for by hydrochloric acid. NITROUS OXIDE. N30. Five parts of stannous chloride, 10 parts of hydrochloric acid sp. gr. 1.2 1, and 0.9 part of nitric acid sp. gr. 1.38, are heated to boiling, when the evolution of nitrous oxide commences, and continues to be evolved quite regularly and in a pure state. The above proportions of ingredients should be adhered to, as otherwise the gas is evolved ir- regularly, and even with violent explosions.* G. Campori, Ann. Chine. Pharm., 8, 253. 20 LABORATORY MANUAL OF It can also be prepared from a mixture of ammonium sulphateand sodium nitrate, kept at 1020 C. for 2 to 3 hours, undergoing in great partdecomposition into sodium sulphate and ammonium nitrate. If, however, it is rapidly raised to a higher temperature, nitrous oxide begins to be evolved atiio° C.,and comes off with some rapidity at 115 to 1200 C. During the heating up a little ammonia is evolved, and the longer the mixture is kept at about 104 to 1 io° C. the more ammonia is lost. If, then, the two salts have been mixed in molecular proportions, the deficiency in the ammonia leads to the evolution of some of the higher oxides of nitro- gen towards the end of the reaction. This may be remedied by increasing the proportion of ammonium sulphate, the mixture, with an additional 5 per cent, of that salt, affording a larger yield of nitrous oxide than would be obtained from the equivalent quantity of ammonium nitrate. The gas is evolved with regularity, whereas ammonium nitrate, raised to 1 1 5Q C, decomposes with a rapidity, accelerating towards explosive violence.* NITRIC OXIDE. NO. A Woulff's bottle, fitted with a funnel and delivery tube, is filled loosely with strips of copper, and then one- third with a cold saturated solution of sodium nitrate. Strong sulphuric acid is added more or less rapidly, ac- cording to the amount of gas required. The evolution of gas is very regular, and may be kept up for hours.f * By W. Smith, J0 Soc. Chem. Ind., 11,867; 12, 10. f By H. Kaemmerer, Ber. 18, 3064-3066. INORGANIC PREPARATIONS. 21 Nitric oxide may also be prepared from a mixture of solutions of potassium ferrocyanide and potassium nitrite added gradually from a stoppered funnel to a flask contain- ing acetic acid ; the contents of the flask must be vigor- ously shaken during the operation.* Another method is to add a strong solution of sodium nitrite to a solution of ferrous chloride or sulphate in hydrochloric acid. If the sodium nitrite contains car- bonate, it should be removed by precipitation with calcium chloride. f In order to obtain this gas in a very pure condition, the reaction which takes place in a Lunge's nitrometer is employed; namely, treating mercury with a mixture of sulphuric acid and nitric acid. The purity of the gas is placed beyond question by the results obtained on leading it over glowing copper; the increase in weight of the metal, giving the weight of oxygen, w"hilst the gas evolved, which is collected and measured, gives the weight of nitrogen. In the reaction between copper and nitric oxide, which is attended by the liberation of much heat, the metal is quantitatively converted into cuprous oxide.f NITROGEN TETROXIDE. N204. 200 grams arsenious acid in pieces the size of a pea are placed in a tubulated retort with bent neck, 200 grams nitric acid 1.38 sp.gr. poured over it, and very moderately * By C. M. Van Deventer, Ber. 26, 589-593. f By J. Thiele, Annalen, 253, 146. X By F. Enrich, Monatsch., 13, 73-77. 22 LABORATORY MANUAL OF warmed. The evolved gas passes into an empty wash- bottle, is then dried by a tube filled with calcium nitrate and is finally conducted into a wide combustion-tube which is surrounded by a freezing mixture of ice and common salt. A dark-green liquid condenses in this tube. Dry oxygen gas is conducted into it until the liquid has changed to a pure yellow, then the tube is sealed. The arsenic trioxide reduces the nitric acid passing into arsenic acid. In drying the gases calcium chloride must not be used, as they would be contaminated with chlorine, nor sulphuric acid, as it absorbs the gases. The condensed mixture of nitrogen trioxide and tetroxide is transformed by oxygen into pure tetroxide.' The liquid should show a sp. gr. of 1.45 and boil at 25 to 260 C. On cooling rapidly it should congeal to a colorless crystal mass, which melts at about 120 C. SULPHURIC ACID or HYDROGEN SULPHATE. H3S04 or S03(OH)2. a. Concentrated pure sulphuric acid. b, Concentrated sulphuric acid of commerce. c Common dilute sulphuric acid. The following method may be recommended for preparing chemically pure sulphuric acid : a. Mix 1,000 grams of ordinary concentrated sulphuric acid and 3 grams of ammonium sulphate in a porcelain dish, and heat till copious fumes of S03 begin to escape, in order to destroy the oxides of nitrogen which are present. After cooling, add 4 or 5 grams of powdered manganese dioxide, and heat to boiling while stirring, in INORGANIC PREPARATIONS. 23 order to convert any arsenious acid into arsenic acid. When cool pour off the clear fluid by means of a long funnel tube into a retort coated with clay. The retort should not be more than half full, and is to be heated directly over charcoal. To prevent bumping, rest the retort on an inverted crucible cover, so that the sides may be more heated than the bottom. The neck of the retort must reach so far into the receiver that the acid, distilling over, drops directly into the body. To cool the receiver by means of water is unnecessary and even dangerous. To prevent the receiver from coming into actual contact with the hot neck of the retort, some asbestos in large fibres is placed between them. When about 10 or 15 grams has been drawn over, change the receiver and slowly distil off three-fourths of the contents of the retort. This method depends upon the fact discovered by Bussy and Buignet, that on distilling sulphuric acid, which contains arsenic in the form of arsenic acid, an arsenic-free distillate is obtained. b. Pour into 4 parts of water 1 part of concentrated sulphuric acid, and conduct into the mixture for some time a slow stream of hydrogen sulphide, keeping the fluid heated to yo° C. Let the mixture stand at rest for several days, then decant the clear supernatant fluid from the precipitate, which consists of sulphur, lead sulphide, per- haps also arsenic sulphide, and heat the decanted fluid in a tubulated retort with upturned neck and open tubulature until sulphuric acid fumes escape with the aqueous vapor. The acid so purified is fit for many purposes of chemical analysis ; if it is desired, however, to free it also from non-volatile substances, it may be distilled 24 LABORATORY MANUAL OF from a coated retort as in a. As soon as the drops in the neck of the retort become oily, the receiver is changed, and the concentrated acid which then passes over is kept in a separate vessel. c. Common dilute sulphuric acid. — Add to 5 parts of water in a thin glass or porcelain dish gradually, with constant stirring, 1 part of concentrated sulphuric acid. The lead sulphate which seperates is allowed to subside, and the clear fluid finally decanted. Pure sulphuric acid must be colorless; when a colorless solution of ferrous sulphate is poured upon it in a test tube, no brown tint must mark the plane of contact of the two fluids (nitric acid, nitrous acid); when diluted with twenty parts of water it must not impart a blue tint to a solution of potassium iodide mixed with starch paste (nitrous acid). Mixed with pure zinc and water, it yields hydrogen gas, which, on being passed through a red- hot tube, should not deposit the slightest trace of arsenic. It should leave no residue upon evaporation on platinum, and must remain perfectly clear upon dilu- tion with four or five parts of alcohol (lead, iron, calcium). The presence of small quantities of lead is detected most easily by adding some hydrochloric acid to the sulphuric acid in a test tube. If the plane of contact is marked by turbidity (lead chloride), lead is present. Sulphurous acid is discovered by the odor after shaking the acid in a half-filled bottle. INORGANIC PREPARATIONS. 25 HYDROGEN SULPHIDE. HYDROSULPHURIC ACID. SULPHURETTED HYDROGEN. H3S. Hydrogen sulphide is usually evolved from iron sulphide, which is broken into small lumps and then treated with dilute sulphuric or hydrochloric acid. Fused iron sulphide may be purchased cheaply, or may be made by heating iron turnings or I to I ^ inch iron nails, in a covered Hessian crucible to a white heat, and then adding Fig. 6. small lumps of roll-sulphur until the entire contents of the crucible are in fusion. As soon as this is the case, pour the fused mass upon sand, or into an old Hessian crucible. Or make a hole in the bottom of the crucible, when the iron sulphide will run through as fast as it forms, and may 26 LABORATORY MANUAL OF be received in a shovel placed in the ash-pit. Or intro- duce an intimate mixture of thirty parts of iron filings and twenty-one parts of flowers of sulphur in small portions into a red-hot crucible, awaiting always the incandescence of the portion last introduced before proceeding to the addition of a fresh one. When you have thus put the mixture into the crucible, cover the latter closely, and expose it to a more intense heat, sufficient to make the iron sulphide fuse more or less, then allow the crucible to cool and break the sulphide in small pieces. The iron sulphide is then placed in a Kipp's apparatus, (Fig. 6,) and the gas is generated by the action of dilute sulphuric or hydrochloric acids. HYDROGEN SULPHIDE FREE FROM ARSENIC. Calcium sulphide (prepared by igniting a mixture of plaster of Paris and coal) yields the pure gas when treated with dilute hydrochloric acid. To evolve the gas in a regular stream, a mixture of calcium sulphide, with one- fourth of its weight of plaster of Paris and enough water to make a cream, is poured into shallow paper trays. As soon as it has set, the cake is cut up into blocks, which are dried at a gentle heat. They may be used in Kipp's apparatus.* Another method is to use barium sulphate (powdered barytes) mixed with 25 per cent, of ground coal and 20 per cent, of common salt. The dampened mixture is rammed into a clay crucible, which, after drying and closing with a luted cover, is heated for several hours * R. Fresenius, Zeit. Anal. Chem. 26, 339. INORGANIC PREPARATIONS. 2J at an incipient white heat. The product is in hard com- pact masses which dissolve completely in dilute hydro- chloric acid with a steady evolution of hydrogen sul- phide.* HYDROGEN SULPHIDE FREED FROM HYDROGEN ARSENIDE. This method is based on the fact that hydrogen arsen- ide reacts violently with iodine at ordinary temperature, arsenious iodide and hydrogen iodide being formed. A narrow tube, 30 to 40 cm. long, is loosely filled with coarsely powdered, air-dried iodine interspersed with glass wool; 2 or 3 grams of iodine will remove every trace of ar- senic from hydrogen sulphide prepared from the ordinary impure materials, by passing over it for several days. In purifying hydrogen, the latter is subsequently passed over glass wool wetted with potassium iodide solution and then through aqueous potash. f Free hydrogen sulphide in quantity is readily detected by its odor, and its blackening effect upon paper moist- ened with lead acetate solution. SULPHUR DIOXIDE. so2. Prepared by gently heating in a flask scrap copper with concentrated, sulphuric acid Cu 4- 2H2S04 = SOg + 2H20 + CuS04. It can be absorbed in water and used as a solution of sul- phurous acid or absorbed in caustic alkalies forming * C. Winkler, Zeit. Anal. Chem. 27, 26. f O. Jacobsen, Ber. 20, 1999. 28 LABORATORY MANUAL OF bisulphites which may be again used to generate sulphur dioxide by the action of cone, sulphuric acid. Prepared in this way, however, it is liable to contain sulphuric acid which is not readily removed. Sulphur dioxide is now obtainable in liquified condition and as such is used for disinfecting and freezing purposes. 