None
In the calcium found in the boiled water the greater part of the strontium and barium present are, as a rule, found also, while smaller quantities will have been precipitated as carbonates on boiling, in consequence of the double decomposition (which may be considered as very probable) between calcium bicarbonate (in water containing sodium chloride) and the barium and strontium sulphates, with the formation of barium and strontium carbonates, calcium sulphate, and carbonic acid. The quantity of calcium remaining in solution appears on this account to be slightly larger than it actually is. If all the barium and strontium originally present in the water is deducted, as is usually done, from the calcium found in the water after boiling (and containing the stron- tium and barium), a slight error is evidently introduced because of the inequality of the atomic weights, for, properly speaking, only so much of the strontium and barium contained in the boiled water should be deducted from or added to the calcium as is equiv- alent to the strontium or barium separated by boiling. To avoid this small error, there but remains to determine the strontium and barium in the calcium (containing the strontium and barium) obtained from the boiled water, and to deduct the § 211.] MODIFICATIONS REQUIRED WITH SALINE WATERS. 271 weight found from that of the calcium + strontium + barium obtained from the boiled water, while, on the other hand, the weight of the calcium equivalent to the small quantities of stron- tium and barium separated as carbonates with calcium carbonate on boiling is added to the weight of the calcium thus found. These quantities are determined by subtracting the strontium and barium found hi the boiled water from the total weights originally found. These slight corrections are scarcely worth considering, how- ever, because magnesium bicarbonate is decomposed by calcium sulphate on boiling (see foot-note, p. 269). 3. DETERMINATION OF THE IODINE AND BROMINE. In the case of alkaline waters, the evaporation of large volumes of the mineral water, as described in § 209, 6, may be effected without any addition and without fear of any loss of bromine or iodine. The like certainty is not afforded, however, in the case of non-alkaline waters, because portions of these halogens may be volatilized by the decomposition of magnesium bromide and iodide. It becomes necessary, hence, to add to the non-alkaline water sufficient perfectly pure sodium carbonate (it is best to use such as has been repeatedly boiled with alcohol) until the liquid is strongly alkaline before evaporating. The determination of the iodine, bromine, etc., is then carried out as detailed in § 209, 6. 4. DETERMINATION OF THE BARIUM AND STRONTIUM. The behavior of the mineral water on boiling affords no suffi- ciently satisfactory conclusion regarding the forms of the com- pounds in which the barium and strontium are present in saline waters. As a rule, portions of the barium and strontium are found in the precipitate, whereas other portions remain dissolved, and according as one or the other appears to be larger in quantity (a spectroscopic examination will afford an approximate idea), it is usual to calculate the two bases either as sulphates or carbonates. On account of the different methods of arranging the results, the analyses of mineral waters are not comparable; I consider it would be best to calculate the barium and strontium in saline waters as 272 ANALYSIS OF WATER. [§ 212- sulphates. These are more soluble in water containing sodium chloride than in pure water, hence their occurrence (especially that of the barium sulphate) in solution is not at all astonishing, and their partial separation as carbonates on boiling the water is ex- plained by the double decomposition between the calcium bicar- bonate and the sulphates, to form calcium sulphate, and barium jind strontium carbonates, as already noticed, § 211/2. 5. DETERMINATION OF THE AMMONIA, AND DETECTION AND DETERMINATION OF THE VOLATILE ORGANIC ACIDS. Attention has already been drawn ( § 209, 8 and 11) to the slight modifications in BOUSSINGAULT'S method, to be employed in de- termining the ammonia, and in evaporating the mineral water for the detection and determination of the volatile organic acids, when the water contains no sodium bicarbonate. REMARKS ON THE ANALYSIS OF SULPHUR WATER. § 212. It has already been noted (§ 208, 8) in what forms sulphur may be found in sulphur waters; also the methods best adapted for determining the free hydrogen sulphide as well as that combined with a metallic sulphide in the form of a sulpho salt; also the sulphur present as mono- and disulphide, and that present as thiosulphate. The few additional observations made by others as well as by myself may be here added. 1. The determination of the sulphuric acid cannot be effected in the usual manner, as the hydrogen sulphide is constantly under- going oxidation by the atmospheric air, which hence introduces serious errors. The determination is made as in § 167 (247). 2. The total quantity of the sulphur, whether combined with oxygen, hydrogen, or metal, is determined, by way of control, by conducting air-free chlorine gas into a measured volume of water, which is then acidulated with hydrochloric acid, concentrated, and the sulphuric acid formed precipitated with barium chloride. § 212.] REMARKS ON THE ANALYSIS OF SULPHUR WATER. 273 3. The behavior of waters containing free hydrogen sulphide differs of course from that of waters containing metallic sulphides, or sulpho salts (hepatic waters). As an example of the former kind may be mentioned the Weilbach water, which contains in the form of hydrogen sulphide all the sulphur not combined with oxygen. The water smells strongly of hydrogen sulphide, and on being shaken in a half-filled bottle disengages hydrogen sul- phide and carbonic acid ; on passing a current of hydrogen through it, it almost completely loses its hydrogen sulphide. When kept in a bottle containing also air, it soon deposits sulphur, the liquid becoming turbid, while the odor of hydrogen sulphide constantly diminishes ; by the further action of the air, the precipitated sul- phur is oxidized (to sulphuric acid) and as a rule dissolves, leaving the water as clear as at first. The Stachelberg water, analyzed by SIMMLER,* will serve as an example of the latter kind of water. It has but a slight odor (in winter almost none at all) of hydrogen sulphide, renders red litmus paper perfectly blue in the course of one minute, but has no effect on turmeric paper; manganous chloride causes in it a flesh-colored precipitate, ferrous sulphate a black one, while sodium nitroprussiate develops a reddish-violet color. If a bottle be filled with the water, this soon becomes slightly cloudy; but within five minutes the water becomes clear again, and then has a distinctly yellowish tinge; by the further action of air, and after repeated tur- bidity and clearing, the water becomes deep yellow in color, due to the formation of disulphate. With full access of air, a copious deposit of sulphur forms, with the simultaneous formation of sodium thiosulphate. The cause of the different behavior of the two kinds of water becomes at once apparent when we consider the different pro- portion in which the sulphur, in combination with hydrogen or metals, bears to the free carbonic acid in the two waters. In the case of the Weilbach water this proportion is 1:24, while in the Stachelberg water it is 1:2. Were a current of carbonic acid passed into the latter, it would convert the hepatic water into one * Journ. f. prakt. Chem., LXXI, 1. 274 ANALYSIS OF WATER. [§ 213. containing free hydrogen sulphide, because carbonic acid expels hydrogen sulphide from sodium sulphide or sodium sulphydrate, as, on the other hand, hydrogen sulphide expels carbonic acid from sodium bicarbonate. Owing to the slight difference of affinity, the action depends upon the amount of either of the compounds present; the greater the quantity of free carbonic acid present in a water containing sodium carbonate, the smaller will be the quantity of combined hydrogen sulphide and the greater that of free hydrogen sulphide. The temperature also has some influence on this point; for instance in the cold sodium bicarbonate may be present beside sodium sulphide, whereas at a higher temperature sodium monocarbonate will be formed with evolution of hydrogen sulphide. Sulphur waters which contain no alkali bicarbonate, and which hence ac- quire no alkaline reaction on being boiled, are to be considered as simple solutions of hydrogen sulphide, like, for instance, the sulphur water analyzed by A. and H. STRECKER.* 2. CALCULATION, CONTROL, AND ARRANGEMENT OF THE RE- SULTS OF ANALYSES OF MINERAL WATERS. §213. The results of the analyses performed as described in 1 are ob- tained by direct experiment, and are altogether independent of any theoretical considerations regarding the manner in which the various constituents are combined or associated with each other As the theoretical views may change according as chemical science develops, it becomes absolutely necessary, in reporting the analyses of waters, to give the direct results and also the methods by which they were obtained. The analysis is then of service for all time, as it at least gives the data for determining whether the composi- tion of the water is constant or not. So far as the principles are concerned, according to which the acids and bases are as a rule associated hypothetically to form salts, it is assumed that the bases and acids are combined accord- * Annal. d. Chem. u. Pharm., xcv, 175. § 213.] RESULTS OF ANALYSES OF MINERAL WATERS. 275 ing to their respective affinities, i.e., the strongest base is assumed to be combined with the strongest acid, etc., due attention being also paid, however, to the greater or less solubility of the salts, which, as is well known, exercise a considerable influence on the manifestations of the force of affinity. For instance, it is assumed that, when calcium, potassium, and sulphuric acid are found in water that has been boiled, the sulphuric acid is combined with the calcium, etc. It cannot be denied, however, that there is thus introduced the possible variation due to the personal views of the analyst, and that consequently different reports may be calculated from the results of the same direct experiments. It would be very advantageous to have a general understand- ing regarding the arrangement of the results of analyses, because otherwise the comparison of two mineral waters is effected with the greatest difficulty; it cannot be expected, however, that such an understanding will be soon arrived at, but so long as it is want- ing, the comparison of two mineral waters can only be made with regard to the immediate and direct results of the analyses. On one point, however, an agreement should at once be arrived at, and that is to put down all the salts in the anhydrous condition. In order to more clearly show the principles which serve as a basis of the most correct arrangement of the results of analyses, as also the method whereby the results may be controlled, I cite as an example the Elisabethenquelle at Homburg v. d. Hohe, which was analyzed by me. This water is saline; it has been se- lected because its calculation is somewhat complicated. In the case of alkaline waters the calculation is simpler, as in these the alkaline earths are usually calculated as carbonates or bicarbonates. ANALYSIS OF THE WATER OF THE ELISABETHENQUELLE AT HOMBURG, v. D. HOHE. a. Direct Results of the Analysis. The numbers express the mean of two or three concordant experiments and give the weight in grammes of substance in 1000 grammes of the water! 1. Silver chloride, bromide and iodide together 28-97763 2. Bromide and iodine — a. Bromine 0-002486 Corresponding with silver bromide 0 • 00584 276 ANALYSIS OF WATER. [§ 213. b. Iodine 0-0000285 Corresponding with silver iodide 0-000053 3. Chlorine — Silver chloride, bromide and iodide 28-97763 Deduct— Silver bromide 0-00584 Silver iodide .. . 0-00005 0-00589 Remainder, silver chloride 28-97174 Corresponding with chlorine 7 • 16264 4. Sulphuric acid 0-01796 5. Carbonic acid (total) 3-32925 6. Silicic acid 0-02635 7. Ferrous oxide 0-01438 8. Lime and strontia together, expressed as carbonates 2- 15835 9. Magnesia (total) 0-32129 10. Lime and strontia * retained in solution after boiling the water, expressed as carbonates 0 • 64633 11. Lime precipitated on boiling — Total lime + strontia, expressed as carbonates 2-15885 Lime and strontia retained in solution on boiling, ex- 3 carbonates. . 0-64633 The remainder= 1 • 51252 Gives in form of carbonate the amount of lime precipi- tated on boiling ; this corresponds with lime 0 • 84701 12. Lime retained in solution after boiling — Sum of the lime and strontia retained in solution, ex- pressed as carbonates 0 • 64633 Deduct the strontia (see 13), which calculated into car- bonate = 0-01428 Remainder= 0-63205 Which corresponds with lime 0-35395 13. Baryta, strontia, and manganous oxide — a. Baryta 0-00066 6. Strontia 0-01002 c. Manganous oxide 0 • 00094 14. Phosphoric acid 0-00043 15. Lithia . 0-00764 Corresponding with lithium chloride 0-02163 16. Sodium chloride + potassium chloride + lithium chloride. 10-22880 17. Potash 0-21876 Corresponding with potassium chloride 0 • 34627 * All the strontia was retained in solution , the trace of baryta which was within the limits of the experimental error in the lime determination was neglected in Miscalculation. § 213-] RESULTS OF ANALYSES OF MINERAL WATERS, 277 18. Soda- Sum of the chlorides of sodium, potassium and lithium . 10 • 22880 Deduct— Potassium chloride 0-34627 Lithium chloride 0-02163 0-36790 Remainder, sodium chloride 9-86090 Which corresponds with soda 5-22899 19. Ammonium oxide 0-010655 20. Total of fixed constituents 13-18438 21. Specific gravity 1-01140 at 19-5° The following substances were present in unweighable amounts, viz., caesia, rubidia, alumina, nickelous oxide, cobaltous oxide, oxide of copper, teroxide of antimony, arsenic acid, boric acid, fluorine, nitric acid, volatile organic acids, non-volatile organic matter, nitrogen, light carburetted hy- drogen, hydrogen sulphide. b. Calculation. a. Barium sulphate — Baryta present (13) 0-00066 Combines with sulphuric acid 0 • 00034 To form barium sulphate 0-00100 6. Strontium sulphate — Strontia present (13) 0-01002 Combines with sulphuric acid 0-00774 To form strontium sulphate 0-01776 c. Calcium sulphate — Sulphuric acid present (4) 0-01796 Of this is combined — With barium 0-00034 With strontium . . . 0-00774. . 0-00808 The remainder 0-00988 Combines with calcium 0 • 00692 To form calcium sulphate 0-01680 d. Magnesium bromide — Bromine present (2) 0-002486 Combines with magnesium 0 • 000373 To form magnesium bromide 0-002859 e. Magnesium iodide — Iodide present 0-0000285 Combines with magnesium 0-OOC0027 To form magnesium iodide 0-0000312 278 ANALYSIS OF WATER. [§ 213. /. Calcium chloride — Lime present in boiled water (12) 0-35395 Of this is combined with sulphuric acid (c) 0 • 00692 The remainder 0-34703 Corresponds with calcium 0-24788 Which combines with chlorine 0-43949 To form calcium chloride 0-68737 g. Potassium chloride — Potassa present (17) 0-21876 Corresponds with potassium 0- 18161 Which combines with chlorine 0-16466 To form potassium chloride 0 • 34627 h. Lithium chloride 0 • 00764 Lithia present (15) 0 • 00356 Corresponds with lithium 0-01807 Which combines with lithium 0-02163 i. Ammonium chloride — Ammonium oxide present (19) 0-01065 Corresponds with ammonium 0. 00737 Which combines with chlorine. 0-01452 To form ammonium chloride 0-02189 k. Sodium chloride — Soda present (18) 5-22899 Corresponds with sodium 3 • 87957 Which combines with chlorine. 5-98133 To form sodium chloride 9 • 86090 1. Magnesium chloride — Chlorine present (3) 7-16264 Of this is combined — With calcium 0-43949 With potassium 0-16466 With lithium 0-01807 With ammonium 0-01452 With sodium., .5-98133.. 6-61807 Remainder 0. 54457 Which combines with magnesium 0-18429 • To form magnesium chloride 0-72886 m. Calcium phosphate — Phosphoric acid present (14). 0. 00043 Combines with lime (3 eq.) 0-00051 To form basic calcium phosphate 0-00094 § 213.] RESULTS OF ANALYSES OF MINERAL WATERS. 279 n. Calcium carbonate — Calcium present in precipitate obtained by boil- ing (11) 0-84701 Of this is combined with phosphoric acid (ra). 0-00051 The remainder 0-84650 Combines with carbonic acid 0-66511 To form calcium monocarbonate 1-51161 o. Magnesium carbonate — Total magnesia (9) 0-32129 Corresponds with magnesium 0-19277 Of which is combined — With bromine (d) 0-000373 With iodine (e) 0-000003 With chlorine (0 0-184290 0-18467 The remainder 0.00810 Corresponds to magnesium 0-01350 Which combines with carbonic acid 0 • 01485 To form magnesium monocarbonate 0-02835 p. Ferrous carbonate — Ferrous oxide present (7) 0-01438 Combines with carbonic acid 0* 00879 To form ferrous carbonate 0-02317 q. Manganous carbonate — Manganous oxide present (13) 0-00094 Combines with carbonic acid. 0-00058 To form manganous carbonate 0 • 00152 r. Silicic acid — Silicic acid present (6) 0-02635 s. c. Comparison of the Total Quantity of Fixed Constituents Found Directly with the Sum of the Several Constituents. The several determinations have given — Barium sulphate 0-00100 Strontium sulphate 0-01776 Calcium sulphate 0-01680 Magnesium bromide 0-00286 Magnesium iodide 0-00003 Calcium chloride 0-68737 Potassium chloride 0-34627 Lithium chloride 0-02163 Ammonium chloride 0-02189 Sodium chloride 9-86090 Magnesium chloride 0 • 72886 Calcium phosphate 0-00094 Calcium carbonate 1 • 51161 Magnesium carbonate 0-02835 Ferric oxide * 0.01598 Manganese protosesquioxide * 0-00101 Silicic acid.. . 0-02635 13-28961 The residue dried at 180° 13-18438 An accurate agreement between these figures cannot be ex- pected, particularly in the case of a water like the above; in fact, were they to agree, we could conclude that the analysis was in- correct. The causes of the difference are manifest, although they can scarcely be expressed numerically. In the first place the ammonium chloride and calcium carbonate decompose each other during the evaporation, calcium chloride and ammonium carbonate being formed, the latter escaping; then the magnesium chloride, bromide, and iodide become basic with loss of a portion of their respective hydrogen acids; furthermore, silicic acid expels carbonic acid from carbonates during evaporation. It will be seen that all these causes tend in one direction, 'i.e., to cause the sum of the severally determined constituents to be higher than that of the residue obtained on evaporation. A more accurate control is obtained by treating the evapora- tion-residue with sulphuric acid (p. 245), and comparing the resi- due of the sulphates (the iron is present as ferric oxide) with the * These compounds are here put down in the condition in which they are present in the residue dried at 180°. § 213.J RESULTS OF ANALYSES OF MINERAL WATERS. 281 sum of the fixed alkalies, alkaline earths, and manganese calculated as sulphates, plus the ferric oxide and silicic acid, also any alumina or aluminium phosphate, should such be present, as well as — in the case of alkaline waters — any additional phosphoric acid as sodium pyrophosphate (in saline waters as calcium phosphate), and subtracting from the sum the quantity of sodium sulphate (as calcium sulphate) corresponding with sodium pyrophosphate (or calcium phosphate). As an example I give here the control relating to my analysis of the Kranchen water at Ems.* The residue obtained on evaporating with sulphuric acid and gently igniting is compared with the sum of the several constitu- ents calculated as sulphates, or oxides, both results being expressed in parts per thousand. Found soda 1 • 355391, calculated as sodium sulphate 3 • 102042 Found potassa 0-019891, calculated as potassium sulphate 0-036773 Found lithia 0-001029, calculated as lithium sulphate 0-003769 Found lime 0-084068, calculated as calcium sulphate 0-204165 Found strontia 0 • 001266, calculated as strontium sulphate 0 • 002245 Found baryta 0-0006513, calculated as barium sulphate. 0-000992 Found magnesia 0-064683, calculated as magnesium sul- phate 0-194050 Found ferrous oxide 0-000895, calculated as ferric oxide. 0-000994 Found manganous oxide 0-0000773, calculated as man- ganous sulphate 0-000164 Found silicic acid and calculated as such 0-049741 Found aluminium phosphate 0-000116 Found residual phosphoric acid 0-000637, calculated as sodium pyrophosphate . 0 . 001367 Total 3-596418 Deduct sodium sulphate for sodium phosphate 0-001459 Residual sulphates, etc 3 • 594959 Found directly 3 . 594699 d. Arrangement of Results. The results are best arranged in a manner to show the number of parts of the constituents .per thousand (or 1,000,000) parts of water (or grains per gallon, see pp. 215, 216). * Jahrbucher des nassauischen Sereins fur Naturkunde, Jahrgang 27 and 28, pp. 114 et seq. ANALYSIS OF WATER. [§ 213. The following are the heads under which the several constituents are best classified : a. Present in weighable quantity. b. Present in unweighable quantity. Regarding carbonates, it is a question whether they should be put down as neutral salts, calculating the excess of carbonic acid partly as bicarbonates and partly as free acid, or calculating the whole as bicarbonates, the excess of carbonic acid being then con- sidered as being present in the free state. Sometimes one way; sometimes the other, is adopted. I usually report analyses in both ways, in order to facilitate the comparison of the results with those of the analysis of other similar springs. It is usual to give the volume of the carbonic acid (and of gases generally) in c.c. per litre (or cubic inches per gallon), calculated to the temperature of the spring and the normal pressure (760 mm.). As further examples of the methods of calculating, controlling, and reporting the results of analyses of mineral waters the follow- ing memoirs are cited : 1. Analysis of the Kochbrunnen of Wiesbaden (saline thermal spring). 2. Analysis of the mineral springs of Ems (thermal alkaline springs). 3. Analysis of the springs of Schlangenbad (thermal springs holding only an extremely small quantity of solid constituents in solution). 4. Analysis of the mineral springs of Langenschwalbach (alkaline chaly- beate springs, abounding in carbonic acid). 5. Analysis of the Weilbach sulphuretted spring (cold sulphuretted spring). 6. Analysis of the mineral spring of Geilnau (alkaline chalybeate spring, abounding in carbonic acid). 7. Analysis of the new soda spring of Weilbach (alkaline spring contain- ing much lithia). 8. Analysis of the mineral spring at Niederselters (alkaline spring abound- ing in carbonic acid). 9. Analysis of the mineral spring at Fachingen (very rich in bicarbonate of soda). All these papers are comprised in one work, entitled "Chemische Untersuchung der wichtigsten Mineralwasser des Herzogthums Nassau, von Professor Dr. R. FRESENIUS" (C. W. KREIDEL, Wies- baden). They will also be found in the " Jahrbiichern des Nassau- ischen Naturhistorischen Vereins." § 213.] RESULTS OF ANALYSES OF MINERAL WATERS. 283 Nos. 1 and 2 contain a detailed description of the methods em- ployed in the examination of the muddy ochreous deposits and solid sinter deposits of the springs in question. Nos. 4, 5, and 6 are also published in the "Journal fiir praktische Chemie," Band 64, 70, 72. The student may also consult the author's "Analyses of the Homburg Mineral Springs" (KREIDEL, Wiesbaden) — these springs abound in carbonic acid, contain iron, and are very saline — and 1 ' Analysis of the Mineral Springs at Wildungen " (MITTLER, Arol- sen) — this water abounds in carbonic acid, is more or less alkaline and chalybeate, and contains much alkaline earthy bicarbonate. The following are examples of analyses of mineral waters more recently made by the author: Trinkquelle, Badequelle, and Helenenquelle at Pyrmont 1 (chalybeate springs containing much sulphate of lime). Trinkquelle at Driburg (chalybeate spring containing much sulphate of lime), Herster mineral spring (earthy mineral spring), also Satzer sulphuretted mud spring.2 Tonnissteiner Heilbrunnen (containing alkaline salts and very rich in carbonate of magnesia), and Tonnissteiner Stahlbrunnen.3 Lamscheider mineral spring 4 (alkaline salts). Augustaquelle, Victoriaquelle, Romerquelle, fresh examination of the Kranchen, Fiirstenbrunnen, Kesselbrunnen, and the new Badequelle at Ems,5 Stahlbrunnen at Homburg, v. d. H.' Carlsquelle at Bad Helmstedt 7 (chalybeate spring). Deutsch-Kreutzer Sauerbrunnen at Oedenburg 8 (alkaline salts). New Selser springs at Grosskarben 9 (earthy salts). Grindbrunnen at Frankfort-on-the-Maine 10 (containing alkaline sul- phides). Mineral spring at Birresborn n (alkaline salts). Mineral spring at Neudorf in Bohemia 12 (alkaline and iron salts). Thermal spring at Assmannshausen 13 (alkaline salts, rich in lithia). Mineral spring at Biskirchen 14 (alkaline salts). Wappenquelle at Ems 15 (alkaline thermal spring). Thermal brine spring at Werne.16 1 A. SPEYER, Arolsen, 1865. 2 C. W. KREIDEL, Wiesbaden, 1866. 3 Ibid., 1869. 4 Ibid., 1869. 6 Ibid., 1865, 1869, 1870, 1872. 6 Ibid., 1872. 7 Ibid., 1873. *Ibid., 1874. »Ibid., 1874. 10 C. NAUMANN, Frankfort-on-the-Maine, 1874. 11 C. W. KREIDEL, Wiesbaden, 1876. 12 Ibid., 1876. 13 Ibid., 1876. u Ibid., 1876. 15 Ibid., 1876. 16 Ibid., 1877. 284: DETERMINATION OF COMMERCIAL VALUES. [§ 214, II. ANALYSES OF SUCH PRODUCTS AS ARE FRE- QUENTLY THE OBJECT OF CHEMICAL IN- VESTIGATION, WITH PROCESSES FOR DETER- MINING THEIR COMMERCIAL VALUE. 1. DETERMINATION OF FREE ACID (ACIDIMETRY). A. DETERMINATION BY SPECIFIC GRAVITY. §214. As the relation between the specific gravity of an aqueous liquid or acid and the quantity of real acid present in the liquid is known, as the result of exact experiments which have been tabu- lated, it is frequently only necessary to ascertain the specific gravity of a liquid in order to ascertain its acid strength. Care must, however, be taken that the acids be free or almost free from other soluble substances. In the case of volatile acids (and most of the common ones are volatile — sulphuric, hydrochloric, nitric, acetic), any non-volatile substances may be usually readily de- tected by evaporating a small sample of the acid in a small plati- num or porcelain dish and observing whether it leaves a fixed residue. The determination of the specific gravity is effected either by weighing equal volumes of acid and water and comparing the weights (pp. 208 and 209),* or by means of a good hydrometer. Care must be taken to make the determination at the temperature to which the tables are calculated. The following tables give the relationship between the specific gravity and acid content of sulphuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, tartaric acid, and citric acid: * Zeitschr. /. analyt. Ghent., ix, 233 and 344. § 214.] ACIDIMETRY. 285 TABLE la. Showing the percentages of Acid (H,SO4) and Anhydride (SO3) corresponding to various specific gravities of aqueous Sulphuric Acid by BINEAU; calculated for 15° by OTTO. Specific ' gravity. Percentage of H^SO4. Percentage of SO3. Specific gravity. Percentage of H2S04. Percentage of S03. 1-8426 100 81-63 •398 50 40-81 1-842 99 80-81 •3886 49 40-00 1-8406 98 80-00 •379 48 39-18 1-840 97 79-18 •370 47 38-36 1-8384 96 78-36 -361 46 37-55 1-8376 95 77-55 -351 45 36-73 1-8356 94 76-73 -342 44 35-82 1-834 93 75-91 •333 43 35-10 1-831 92 75-10 •324 42 34-28 1-827 91 74-28 •315 41 33-47 1-822 90 73-47 •306 40 32-65 1-816 89 72-65 -2976 39 31-83 1-809 88 71-83 •289 38 31-02 1-802 87 71-02 1-281 37 30-20 -794 86 70-10 1-272 36 29-38 •786 85 69-38 1-264 35 28-57 ' -777 84 68-57 1-256 34 27-75 •767 83 67-75 1-2476 33 26-94 .756 82 66-94 1-239 32 26-12 •745 81 66-12 1-231 31 25-30 •734 80 65-30 1-223 30 * 24-49 • 722 79 64-48 1-215 29 23-67 •710 78 63-67 1-2066 28 22-85 •698 77 62-85 1-198 27 22-03 •686 76 62-04 1-190 26 21-22 1-675 75 61-22 1-182 25 20-40 1-663 74 60-40 1-174 24 19-58 1-651 73 59-59 1-167 23 18-77 1-639 72 58-77 1-159 22 17-95 1-627 71 57-95 1-1516 21 17-14 1-615 70 57-14 1-144 20 16-32 1-604 69 56-32 1-136 19 15-51 1-592 68 55-59 1-129 18 14-69 1-580 67 54-69 1-121 17 13-87 1-568 66 53-87 1-1136 16 13-06 1-557 65 53-05 1-106 15 12-24 •545 64 52-24 1-098 14 11-42 •534 63 51-42 •091 13 10-61 •523 62 50-61 •083 12 9-79 •512 61 49-79 •0756 11 8-98 •501 60 48-98 •068 10 8-16 •490 59 48-16 •061 9 7-34 •480 58 47-34 •0536 8 6-53 •469 57 46-53 •0464 7 5-71 •4586 56 45-71 1-039 6 4-89 1-448 55 44-89 . 1-032 5 4-08 1-438 54 44-07 1-0256 4 3-26 1-428 53 43-26 1-190 3 2-445 1-418 52 42-45 1-013 2 1-63 1-408 51 41-63 1-0064 1 0-816 286 DETERMINATION OF COMMERCIAL VALUES. [§ 214. TABLE 16. Showing the quantity of add in mixtures of sulphuric acid and water at each degree BATJME from 0 to 66, with the corresponding specific gravities at 15°, by J. KOLB.* Degree BAUME, Sp.gr. 80s. H2S04. Degree BAUME. Sp.gr. S04. HaSO,. 0 1-000 0-7 0-9 34 1-308 32-8 40-2 1 1-007 1-5 1-9 35 1-320 33-9 41-6 2 1-014 2-3 2-8 36 1-332 35-1 43-0 3 1-022 3-1 3-8 37 1-345 36-2 44-4 4 -029 3-9 4-8 38 1-357 37-2 45-5 5 -037 4-7 5-8 39 1-370 38-3 46-9 6 •045 5-6 6-8 40 1-383 39-5 48-3 7 . -052 6-4 7-8 41 1-397 40-7 49-8 8 •060 7-2 8-8 42 1-410 41-8 51-2 9 -067 8-0 9-8 43 1-424 42-9 52-8 10 -075 8-8 10-8 44 1-438 44-1 54-0 11 •083 9-7 11-9 45 1-453 45-2 55-4 12 -091 10-6 13-0 46 1-468 46-4 56-9 13 -100 11-5 14-1 47 1-483 47-6 58-3 14 -108 12-4 15 -.2 48 1-498 48-7 59-6 15 -116 13-2 16-2 49 1-514 49-8 61-0 16 •125 14-1 17-3 50 1-530 51-0 62-5 17 -134 15-1 18-5 51 -540 52-2 64-0 18 •142 16-0 19-6 52 •563 53-5 65-5 19 •152 17-0 20-8 53 •580 54-9 67-0 20 -162 18-0 22-2 54 •597 56-0 68-6 21 -171 19-0 23-3 55 •615 57-1 70-0 22 -180 20-0 24-5 56 •634 58-4 71-6 23 -190 21-1 25-8 57 -652 59-7 73-2 24 -200 22-1 27-1 58 -671 61-0 74-7 25 -210 23-2 28-4 59 -691 62-4 76-4 26 -220 24-2 29-6 60 •711 63-8 78-1 27 -231 25-3 31-0 61 •732 65-2 79-9 28 -241 26-3 32-2 62 •753 66-7 81-7 29 •252 27-3 33-4 63 •774 68-7 84-1 30 • 263 28-3 34-7 64 •796 70-6 86-5 31 1-274 29-4 36-0 65 •819 73-2 89-7 32 1-285 30-5 37-4 66 •842 81 -G 100-0 33 1-297 31-7 38-8 *Politechn. CentralbL, 1873, 826; DINGLER'S Polyt. Journ., ccrx, 268; Zeitschr. /. analyt. Chem., xn, 333. KOLB'S results agree with BINEAU'S (Table la) very closely, although not absolutely. With reference to BAUME'S degrees it should be observed that the zero is determined in pure water at 15°, and the degree 66° B. in pure hydrated sulphuric acid of 1-842 specific gravity. § 214.] ACIDIMETRY. 287 TABLE Ha. Showing the percentages of Anhydrous Add (HC1) corresponding to various specific gravities of aqueous solutions of Hydrochloric Acid, by URE. Tempera- ture 15°. Specific gravity. Percentage of hydrochloric-acid gas (HC1). Specific gravity. Percentage of hydrochloric-acid gas (HC1). 1-2000 40-777 1-1000 20-388 I - 1982 40-369 1-0980 i9-980 1-1964 39-961 1-0960 19-572 1 - 1946 39-554 1-0939 19-165 1 • 1928 39-146 1-0919 18-757 1-1910 38-738 1-0899 18-349 1 • 1893 38-330 1-0879 17-941 1 • 1875 37-923 1-0859 17-534 1 • 1857 37-516 1-0838 17-126 1 - 1846 37-108 1-0818 16-718 1 - 1822 36-700 1-0798 16-310 1-1802 36-292 1-0778 15-902 1-1782 35-884 -0758 15-494 1-1762 35-476 -0738 15-087 1-1741 35-068 •0718 14-679 1-1721 34-660 •0697 14-271 1-1701 34-252 •0677 13-863 1-1681 33-845 1-0657 13-456 1-1661 33-437 1-0637 13-049 1-1641 33-029 1-0617 12^641 1-1620 32-621 1-0597 12-233 1-1599 32-213 1-0577 11-825 1-1578 31-805 1-0557 11-418 1-1557 31-398 •0537 11-010 1-1537 30-990 •0517 10-602 1-1515 30-582 -0497 10-194 1 • 1494 30-174 •0477 9-786 1 • 1473 29-767 •0457 9-379 • 1452 29-359 •0437 8-971 •1431 28-951 •0417 8-563 •1410 28-544 •0397 8-155 -1389 28-136 1-0377 7-747 -1369 27-728 1-0357 7-340 -1349 27-321 1-0337 6-932 -1328 26-913 1-0318 6-524 •1308 26-505 1-0298 6-116 •1287 26-098 1-0279 5-709 1 • 1267 25-690 -0259 5-301 1-1247 25-282 1-0239 4-893 1-1226 24-874 -0220 4-486 1-1205 24-466 -0200 4-078 1-1185 24-058 •0180 3-670 1-1164 23-650 •0160 3-262 1-1143 23-242 -0140 2-854 1-1123 22-834 1-0120 2-447 1-1102 22-426 1-0100 2-039 1-1082 22-019 1-0080 1-631 1-1061 21-611 1-0060 1-124 1-1041 21-203 1-0040 0-816 1-1020 20-796 1-0020 0-408 288 DETERMINATION OF COMMERCIAL VALUES. [§ 214. TABLE 116. Showing the amount of acid in aqueous Hydrochloric Acid at each degree BAUMK, from 0 to 25-5, with the corresponding specific gravity at 15° C., by J. KOLB.* 100 parts contain: 100 parts contain: Degree BAUME. Specific gravity. Hydro- chloric- Hydro- chloric- Degree BAUMK. Specific gravity. Hydro- chloric- Hydro- chloric- acid gas acid gas acid gas acid gas at 0° C. at 15° C. at 0° C. at 15° C. 0 1-000 0-0 0-1 17 1-134 25-2 26-6 1 1-007 1-4 1-5 18 1-143 27-0 28-4 2 •014 2-7 2-9 19 1-152 28-7 30-2 3 •022 4-2 4-5 19-5 1-157 29-7 31-2 4 •029 5-5 5-8 20 1-161 30-4 32-0 5 •036 6-9 7-3 20-5 1-166 31-4 33-0 6 •044 8-4 8-9 21 1-171 32-3 33-9 7 •052 9-9 10-4 21-5 1-175 33-0 34-7 8 •060 11-4 12-0 22 1-180 34-1 35-7 9 •067 12-7 13-4 22-5 1-185 35-1 36-8 10 •075 14-2 15-0 23 1-190 36-1 37-9 11 •083 15-7 16-5 23-5 1-195 37-1 39-0 12 •091 17-2 18-1 24 1-199 38-0 39-8 13 1-100 18-9 19-9 24-5 1-205 39-1 41-2 14 1-108 20-4 21-5 25 1-210 40-2 42-4 15 1-116 21-9 23-1 25-5 1-212 41-7 42-9 16 1-125 23-6 24-8 * Compt. rend., LXXIV, 337; Zeitschr. /. . Chem., xi, 339. § 214.] ACIDIMETRY. TABLE III. 289 Showing the percentages corresponding with various specific gravities of aqueous Nitric Acid, both hydrated and anhydrous, by J. KOLB.* 100 parts contain: Sp. gr. 100 parts contain: Sp. gr. HNOg N203 at 0° at 15° HNO3 N^Os at 0° at 15° 100-00 85-71 •559 1-530 58-88 50-47 1-387 1-368 99-84 85-57 -559 1-530 58-00 49-71 1-382 •363 99-72 85-47 •558 1-530 57-00 48-86 1-376 •358 99-52 85-30 •557 1-529 56-10 48-08 1-371 •353 97-89 83-90 •551 1-523 55-00 47-14 1-365 •346 97-00 83-14 •548 1-520 54-00 46-29 1-359 •341 96-00 82-28 1-544 1-516 53-81 46-12 1-358 •339 95-27 81-66 1-542 1-514 53-00 45-40 1-353 •335 94-00 80-57 1-537 1-509 52-33 44-85 1-349 •331 93-01 79-72 1-533 1-506 50-99 43-70 1-341 •323 92-00 78-85 -529 •503 49-97 42-83 1-334 •317 91-00 78-00 -526 •499 49-00 42-00 1-328 •312 90-00 77-15 -522 •495 48-00 41-14 1-321 •304 89-56 76-77 •521 •494 47-18 40-44 1-315 •298 88-00 75-43 •514 •488 46-64 39-97 1-312 •295 87-45 74-95 •513 1-486 45-00 38-57 1-300 •284 86-17 73-86 1-507 1-482 43-53 37-31 1-291 •274 85-00 72-86 1-503 1-478 42-00 36-00 1-280 -264 84-00 72-00 1-499 1-474 41-00 35-14 1-274 •257 83-00 71-14 1-495 1-470 40-00 34-28 1-267 •251 82-00 ' 70-28 1-492 1-467 39-00 33-43 1-260 •244 80-96 ! 69-39 1-488 1-463 37-95 32-53 1-253 •237 80-00 68-57 1-484 1-460 36-00 30-86 1-240 •225 79-00 ! 67-71 1-481 1-456 35-00 29-29 1-234 •218 77-66 66-56 1-476 1-451 33-86 29-02 1-226 •211 76-00 65-14 1-469 1-445 32-00 27-43 1-214 •198 75-00 64-28 1-465 1-442 31-00 26-57 1-207 •192 74-01 63-44 1-462 1-438 30-00 25-71 1-200 •185 73-00 62-57 1-457 •435 29-00 24-85 -194 •179 72-39 62-05 1-455 •432 28-00 24-00 •187 •172 71-24 61-06 •450 •429 27-00 23-14 •180 •166 69-96 60-00 •444 •423 25-71 22-04 •171 •157 69-20 59-31 •441 •419 23-00 19-71 •153 •138 68-00 58-29 •435 •414 20-00 17-14 •132 •120 67-00 57-43 •430 •410 17-47 14-97 •115 •105 66-00 56-57 1-425 •405 15-00 12-85 •099 •089 65-07 55-77 1-420 •400 13-00 11-14 •085 •077 64-00 54-85 1-415 1-395 11-41 9-77 •075 •067 63-59 54-50 1-413 1-393 7-22 6-62 .050 •045 62-00 53-14 1-404 1-386 4-00 3-42 •026 •022 61-21 52.46 1-400 1-381 2-00 1-71 •013 •010 60-00 51-43 1-393 1-374 0-00 0-00 1-000 0-999 59-59 51-08 1-391 1-372 i * Ann. chim. phys. [4] x, 140; Zeitschr. /. analyt. Chem., v, 449. 290 DETERMINATION OF COMMERCIAL VALUES. [§ 214. TABLE IV. Showing the percentages of Anhydrous Acid corresponding with various specific gravities of aqueous Phosphoric Acid, by J. WATTS.* Sp. gr. at 15-5° C. Percentage of P2OS. Sp. gr. at 15-5° C. Percentage of P206. Sp. gr. at 15-5° C. Percentage of P206. •508 49-60 1-328 36-15 -144 17-89 •492 48-41 1-315 34-82 -136 16-95 •476 47-10 1-302 33-49 •124 15-64 -464 45-63 1-293 32-71 -113 14-33 •453 45-38 •285 31-94 •109 13 25 •442 44-13 •276 31-03 •095 12-18 •434 43-95 •268 30-13 1-081 10-44 1-426 43-28 •257 29-16 1-073 9-53 1-418 42-61 •247 28-24 1-066 8-62 1-408 41-60 •236 27-30 1-056 7-39 1-392 40-86 •226 26-36 1-047 6-17 1-384 40-12 •211 24-79 1-031 4-15 1-376 39-66 1-197 23-23 1-022 3-03 1-369 39-21 1-185 22-07 1-014 1-91 1-356 38-00 1-173 20-91 1-006 0-79 1-347 37-37 1-162 19-73 1-339 36-74 1-153 18-81 * Journ. Chem. Soc., xix, 499; Journ. f. prakt. Chem., ci, 59; Zeitschr. /. analyt. Chem., vii, 357. § 214.] ACIDIMETRY. 291 TABLE V. Showing the percentages of Hydrated Acetic Acid corresponding with various specific gravities of aqueous Acetic Acid, by A. C. OUDEMANS.* Percent- age of hydrated acetic acid. Specific gravity at 15° C. Specific gravity at 20° C. Percentage of hydrated acetic acid. Specific gravity at 15° C. Specific gravity at 20° C. 0 0-9992 0-9983 51 1-0623 1-0583 1 •0007 0-9997 52 1-0631 1-0590 2 •0022 1-0012 53 1-0638 1-0597 3 •0037 1-0026 54 1-0646 1-0604 4 •0052 1-0041 55 1-0653 1-0611 5 •0067 1-0055 56 1-0660 1-0618 6 •0083 1-0069 57 1-0666 •0624 7 1-0098 1-0084 58 1-0673 •0630 8 1-0113 1-0098 59 •0679 •0636 9 1-0127 1-0112 60 •0685 •0642 10 1-0142 1-0126 61 •0691 -0648 11 1-0157 1-0140 62 •0697 •0653 12 1-0171 1-0154 63 •0702 •0658 13 1-0185 -0168 64 •0707 •0663 14 1-0200 •0181 65 •0712 1-0667 15 1-0214 •0195 66 •0717 1-0671 16 1-0228 •0208 67 -0721 1-0675 17 -0242 -0222 68 1-0725 1-0679 18 •0256 •0235 69 1-0729 1-06S3 19 •0270 •0248 70 1-0733 1-0686 20 •0284 •0261 71 1-0737 1-0689 21 -0298 •0274 72 1-0740 1-0691 22 •0311 •0287 73 1-0742 1-0693 23 •0324 •0299 74 1-0744 1-0695 24 •0337 -0312 75 1-0746 1-0697 25 •0350 •0324 76 1-0747 1-0699 26 •0363 •0336 77 1-0748 1-0700' 27 •0375 1-0348 78 1-0748 1-0700 28 •0388 1-0360 79 1-0748 1-0700 29 •0400 1-0372 80 1-0748 1-0699 30 -0412 1-0383 81 1-0747 1-0698 31 •0424 1-0394 82 1-0746 1-0696 32 1-0436 1-0405 83 1-0744 1-0694 33 1-0447 1-0416 84 1-0742 1-0691 34 1-0459 1-0426 85 1-0739 1-0688 • 35 1-0470 1-0437 86 1-0736 •0684 , 36 1-0481 1-0448 87 1-0731 1-0679 37 1-0492 1-0458 88 1-0726 •0674 38 1-0502 1-0468 89 1-0720 •0668 39 1-0513 1-0478 90 •0713 •0660 40 1-0523 1-0488 91 •0705 •0652 41 1-0533 1-0498 92 -0696 •0643 42 1-0543 1-0507 93 -0686 -0632 43 •0552 1-0516 94 -0674 -0620 44 •0562 1-0525 95 •0660 •0606 45 •0571 •0534 96 •0644 •0589 46 •0580 •0543 97 •0625 •0570 47 •0589 •0551 98 •0604 •0549 48 •0598 •0559 99 •0580 •0525 49 •0607 •0567 100 •0553 •0497 50 -0615 •0575 * "The Specific Gravity of Acetic Acid and Mixtures of the Acid with Water.1 COHEN & SON, Bonn, 1866; Zeitschr. f. analyt. Chem., v, 453. M, 292 DETERMINATION OF COMMERCIAL VALUES. [§ 214. TABLE VI. Showing the percentages of crystallized Tartaric and Citric Acids corresponding with various specific gravities of aqueous solutions of the acids, by GERLACH.* Percent- age by weight in the solution. Crystallized tartaric acid, specific TI^ Crystallized citric acid, specific gravity at 15°. Percent- age by weight in the solution.. Crystallized tartaric acid, specific gravity at 15°. Crystallized citric acid, specific gravity at 15°. 1 •0045 1-0037 34 1-1726 1-1422 2 •0090 1-0074 35 1-1781 1-1467 3 •0136 1-0111 36 1-1840 1-1515 4 •0179 1-0149 37 1-1900 1-1564 5 •0224 1-0186 38 1-1959 1-1612 6 •0273 1-0227 39 1-2019 1-1661 7 • 0322 1-0268 40 1-2078 1-1709 8 •0371 1-0309 41 1-2138 1-1756 9 •0420 1-0350 42 1-2198 1-1814 10 1-0469 1-0392 43 1-2259 1-1851 11 1-0517 1-0431 44 1-2317 1-1899 12 1-0565 1-0470 45 1-2377 1 • 1947 13 1-0613 1-0509 46 1-2441 1-1998 14 1-0661 1-0549 47 •2504 1-2050 15 1-0709 1-0588 48 •2568 1-2103 16 1-0761 1-0632 49 •2632 1-2153 17 1-0813 1-0675 50 -2696 1-2204 18 1-0865 1-0718 51 -2762 1-2257 19 1-0917 1-0762 52 -2828 1-2307 20 1-0969 1-0805 53 •2894 1-2359 21 1 - 1020 1-0848 54 -2961 1-2410 22 1-1072 1-0889 55 -3027 1-2462 23 1-1124 1-0930 56 -3093 1-2514 24 1-1175 1.0972 57 •3159 1-2572 25 •1227 1-1014 58 1-2627 26 •1282 1 - 1060 59 1-2683 27 •1338 1-1106 60 1-2738 28 •1393 1-1152 61 1-2794 29 •1449 1-1198 62 1-2849 30 •1505 1 - 1244 63 1-2904 31 -1560 1-1288 64 1-2960 32 •1615 1 • 1333 65 1-3015 33 -1670 1-1378 66 1-3071 Zeitschr. /. analyt. Chem., viu, 295. In all cases in which the determination of the specific gravity fails to attain the end in view, or which demand particular accuracy, the volumetric method described under B is employed. § 215.] ACIDIMETRY. 293 B. ESTIMATION BY SATURATION WITH AN ALKALINE FLUID OP KNOWN STRENGTH.* §215. This method requires — 1. A dilute acid of known strength. Sulphuric or hydrochloric acid may be used. Nitric and oxalic acids are less frequently employed. 2. An alkaline fluid of known strength. I. PREPARATION OF THE SOLUTIONS. 1. The acid should be of such strength that 1000 c.c. at 17-5° ( = 14° R.) will contain the exact equivalent number (H= 1-008) of grammes of the acid, e.g., 49-043 of sulphuric acid, 36-458 hydrochloric acid, 63-024 oxalic acid, etc. Acids of this strength we term normal acids; equal volumes of them have equal power to saturate alkalies. As a rule normal sulphuric or hydrochloric acid is used, or, as recommended by MOHR, normal oxalic acid. 2. For the alkali solution a caustic-soda lye is used of such strength that one volume will suffice to neutralize one volume of normal acid, so that on mixing the two last drops the soda solu- tion imparts a blue color to the acid solution faintly reddened by litmus. A soda solution of such strength is termed a normal soda solution, and 1000 c.c. saturate one equivalent of any monobasic acid expressed in grammes. Various methods may be used for preparing normal acids; of these the most serviceable (a), in which pure anhydrous sodium carbonate is used for standardizing, is available for all acids, while the others (6) can be employed only for the valuation of individual normal acids. The manner of preparing the normal soda solution will be described under both a and b. * According to NICHOLSON and PRICE (Chem. Gaz., 1856, p. 30) the com- mon method of acidimetry is not suited for determining free acetic acid, on account of the alkaline reaction of neutral sodium acetate; however, OTTO (Annal. d. Chem. u. Pharm., en, 69) has clearly demonstrated that the error arising from this is so inconsiderable that it may safely be disregarded. 294 DETERMINATION OF COMMERCIAL VALUES. [§ 215. a. GENERAL METHODS (BY NEUTRALIZATION). 1. Requisites. a. Pure sodium carbonate, to be used as a standard. This is most easily prepared from the purest commercial sodium bicarbon- ate. Powder it, pack it firmly in a funnel in which a small filter has been placed, level the surface and place on it several layers of filter paper, and pour on small quantities of cold, distilled water, continuing the washing until the liquid passing through no longer shows traces of sulphuric acid or chlorine. Then dry the washed salt and heat it (best in a platinum dish) to convert the bicarbonate into anhydrous carbonate. This is then powdered and preserved for use. Before weighing off, moderately heat a suitable quantity in a platinum crucible for a long time and introduce the still hot powder into a dry, well-closed tube, which is to be preserved under a desiccator. /?. The alkali solution. Caustic-soda solution is used for this purpose. It is sufficient for the purpose if it has a specific gravity of from 1 • 046 to 1 • 048, as determined by the hydrometer, when the litre will contain somewhat more than one equivalent of Na2O, i.e., from 32 to 34 grammes. The use of the hydrometer can be avoided if a soda solution of approximately correct strength is at hand, by making a rough determination and then diluting the so- lution so that from 19 to 19 -5 c.c. will be required to saturate 20 c.c. normal acid. If it is desired to expel carbonic acid from a con- centrated soda solution containing some sodium carbonate, dilute the solution suitably, heat to boiling, add milk-of-lime, boil, cool somewhat, and fill into flasks, in which allow to settle. Close the flask with a perforated stopper bearing a bulb-tube containing soda- lime (Fig. 99, p. 298). When perfectly clear siphon off the solu- tion into another flask. 7-. A dilute acid, each litre of which contains somewhat more than one combining equivalent of the acid (H = 1-008) expressed in grammes; e.g., each litre will contain 41 to 42 grammes of anhydrous sulphuric acid, 37 to 39 grammes of hydrochloric acid, etc. It is sufficient to determine the strength of the acid by means. § 215.] ACIDIMLTRY. 295 of the hydrometer; and the following may be taken as the limits of the specific gravities at 15°: Dilute sulphuric acid 1 • 032 to 1 • 033 1 ' hydrochloric acid 1 • 018 to 1 • 019 " nitric acid 1-037 to 1-038 d. As tincture of litmus is frequently so alkaline as to require a notable quantity of acid to redden it, the excess of acid must be neutralized, so that on dilution with water the tincture will be violet-colored, and will be reddened by a trace of acid and rendered blue by a minimum of alkali ( § 65, 2). Regarding the special kinds of tincture of litmus and other indicators* used for ascertaining the neutrality-point of liquid, see § 215, 6. The requisites being at hand, we proceed — 1 . To accurately determine the acid content of the dilute acid. 2. To dilute the acid to normal strength. 3. To dilute the soda solution to normal strength. 2. Accurate Determination of the Acid Content. a. Fill one pinch-cock burette with the dilute acid (1,70, an^ a second one with the alkali (1, /?), both to the zero-point. Then run 20 c.c. of the acid into a beaker containing about 100 c.c. water, color it slightly red with litmus tincture, and run in the soda solu- tion until the liquid becomes just distinctly blue. If the point has not been exactly hit, add more acid, and then soda solution, until the point is accurately reached. After a few minutes read off the height in both burettes, and thus ascertain the relation of the soda solution to the acid. Let us assume we had used 19-5 c.c. of the soda solution to 20 c.c. of the acid. 