LIBRARY V X\i * F THE UNIVERSITY OF CALIFORNIA. Class m Works of ALFRED I. COHN PUBLISHED BY JOHN WILEY & SONS. Indicators and Test-papers. Their Source, Preparation, Application, and Tests for Sensitiveness. With Tabular Summary of the Applica- tion of Indicators. Second Edition. Revised and En- larged, i 2mo, ix -f-26? pages. Cloth, $2.00. Tests and Reagents, Chemical and Microscopical, known by their Authors' Names: together with an Index of Subjects. 8vo, iii-H83 pages. Cloth, $3 oo. Fresenius' Quantitative Chemical Analysis. New Authorized Translation of the latest German Edition. In two volumes. By Alfred I. Cohn. Recalculated on the basis of the latest atomic weights, and also greatly amplified by the translator. 8vo, 2vols., upwards of 2000 pages, 280 figures. Cloth, $12.50. QUANTITATIVE CHEMICAL ANALYSIS BY THE LATE DE. C. KEMIGIUS FRESENIUS PRIVY AULIC COUNSELLOR; DIRECTOR OF THE CHEMICAL LABORATORY AT WIESBADEN AUTHORIZED TRANSLATION OF THE GREATLY AMPLIFIED AND REVISED SIXTH GERMAN EDITION BY ALEBED I. COHN AUTHOR OF "INDICATORS AND TEST-PAPERS," AND "TESTS AND REAGENTS. 1 " MEMBER OF THE AMERICAN CHEMICAL SOCIETY; SOCIETY OF CHEMICAL INDUSTRY: VEREIN DEOTSCHER CHEMIKER: ETC. NEW YORK JOHN WILEY & SONS 43-45 EAST NINETEENTH STREET 1904 < 9 C^~~ GtNERAL : > Copyright, 1903, BY ALFRED I. COHN. ROBERT DRUMMOND. PRINTER, NEW YORK. CONTENTS. PART I. GENERAL. DIVISION I. THE EXECUTION OF ANALYSIS. SECTION VI. PACK 1 ORGANIC ANALYSIS, 171 I I. Qualitative examination of organic substances, 172 4 1. Testing for nitrogen 4 2. Testing for sulphur 5 3. Testing for phosphorus 7 4. Testing for iodine, bromine, and chlorine 7 5. Testing for inorganic substances g IL Determination of the elements in organic substances, 173 9 A. Analysis of substances containing carbon and hydrogen only, or carbon, hydrogen, and oxygen 11 a. Solid substances ., 12 a. Readily combustible and non-volatile 12 Combustion with cupric oxide 12 1. LIEBIG'S method, 174 12 (1) Apparatus and preparation required 12 (2) Performance of the analytical process 22 2. BUNSEN'S modification of LIEBIG'S method, 175 30 ft. Difficultly combustible non-volatile substances 33 (1) Combustion with lead chromate, 176 33 (2) Combustion with cupric oxide and potassium chlorate or perchlorate, 177 36 (3) Combustion with cupric oxide and oxygen, 178. ... 37 f. Hygroscopic or volatile compounds, or such as undergo changes when heated at 100, 179 44 6. Fluid bodies 46 a. Volatile liquids, 180 46 3. Non-volatile liquids, 181 49 Supplement to A, 174- 181 51-5, Modified apparatus, 182 51 v L02 VI CONTENTS. PACT! 1. For connecting the chloride of calcium tube to the com- bustion tube 51 2. For. the absorption of water 51 3. For the absorption of carbonic acid 53 B. Analysis of compounds, containing carbon, hydrogen, oxygen, and nitrogen 56 a. Determination of the carbon and hydrogen in nitrogenous sub- stances, 183 56 b. Determination of nitrogen in organic compounds 58 a. Determination of the nitrogen by volume 58 1. Relative determination of the nitrogen by volume, 184 59 aa. LIEBIG'S method 59 66. BUNSEN'S method 62 cc. MARCHAND'S method modified by GOTTLIEB 65 2. Absolute determination of nitrogen by volume, 185. .. 66 aa. DUMAS' method 66 66. SIMPSON'S method 69 cc. W. GIBBS' method 74 P. Determination of nitrogen by conversion into ammonia. Method of VARRENTRAPP-WILL, 186 82 Y. PELIGOT'S modification of VARRENTRAPP- WILL'S method, 187 91 C. Analysis of organic substances containing sulphur, 188 95 I. Methods in the dry way 96 1. Method suitable for determining sulphur in non- volatile substances poor in sulphur 96 2. Method adapted for non-volatile or difficultly volatile substances containing more than 5 per cent, sulphur. . 97 3. Method adapted for volatile and non- volatile substances 98 4. Method adapted for solid and liquid volatile compounds . 99 5. Methods based upon combustion in oxygen gas 100 6. Method of determining sulphur in coal and coke 115 II. Methods in the wet way 116 D. Determination of phosphorous in organic substances, 1C9. . . . 120 E. Analysis of organic compounds containing chlorine, bromine, and iodine, 190 121 I. Methods in the dry way 123 II. Methods in the wet way 126 F. Analysis of organic substances containing inorganic compounds, 191 129 Supplement to 174-191, 192 131 A. Methods for the direct estimation of oxygen, 192 131 a. BAUMHAUER'S method 131 6. STROMEYER'S method 135 c. MITSCHERLICH'S method 137 d. LADENBURG'S method 139 CONTENTS. V PAGE e. MAUMENE'S method 139 /. CRETIER'S method 140 B. Methods of organic analysis which differ from the ordinary pro- cess, without including a direct estimation of oxygen 140 a. CLOEZ' method 140 6. WARREN'S method 145 c. Method of WHEELER, F. SCHULZE, and T. SCHLOSING 145 d. ULLGREN'S modification of BRUNNER'S method 145 HI. Determination of the equivalent of organic compounds. . 145 1. From its combination with acids, bases, etc., 193 146 2. Determination of the vapor density of the compound, 194 147 A. DUMAS' process 147 B. HOFMANN'S process 151 C. GRABOWSKI and LANDOLT'S processes 155 D. BUNSEN'S process 156 E. Process of DEVILLE and TROOST 156 3. From its products of decomposition, 195 157 DIVISION II. CALCULATION OF ANALYSIS. I. Calculation of the constituent sought from the compound obtained in the analytical process, and conversion of the result in per cents. , 196. 158 1. When the substance sought has been separated in the free state 158 a. Solid, liquid, and gaseous substances which have been determined by weighing, 197 158 b. Gases which have been determined by measuring, 198 159 2. When the substance sought has been separated in com- bination, 199 164 3. Calculation of the results of indirect analysis, 200 166 SUPPLEMENT TO I. I. Remarks on loss and excess in analyses, and on taking the mean, 201 168 II. Deduction of empirical formulas. 202 170 HI. Deduction of rational formulas, 203 173 IV. Calculation of the vapor density of volatile substances, 204 177 CONTENTS. . PART II. SPECIAL. PAGE I. ANALYSIS OF WATER. A. Examination of potable water, 205 185 I. The water is clear 185 II. The water is not clear 214 Appendix to A., Estimation of hardness 215 B. Analysis of Mineral waters, 206 221 1. The analytical process 222 A. Operations at the spring or well 222 I. Apparatus and other requisites, 207 222 II. Special analytical processes, 208 224 B. Operations in the laboratory 242 I. Qualitative analysis 242 II. Quantitative analysis, 209 242 Examination of the dissolved gases, 210. . . . 265 Modifications required in the case of saline waters, 211. 268 Remarks on the analysis of sulphuretted waters, 212 ... 272 2. Calculation, control, and arrangement of the results of analyses of mineral waters, 213 274 II. ANALYSIS OF SOME TECHNICAL PRODUCTS AND MINERALS, WITH PRO- CESSES FOR DETERMINING THEIR COMMERCIAL VALUE 284 1. Determination of free acid acidimetry 284 A. Estimation by specific gravity, 214 284 B. Estimation by saturation of the acid with an alkaline liquid of known strength, 215 293 C. KIEFER'S modification of B, 216 315 D. Estimation by weighing the carbonic acid expelled by the free acid from sodium bicarbonate, 217 316 E. Methods relating to particular acids 317 2. Determination of free alkali and of alkali carbonate alkalimetry. . 319 A. Determination of potassa, soda, or ammonia, potassium car- bonate, or sodium carbonate from the specific gravity of their solutions, 218 319 B. Determination of the total amount of carbonated and caustic alkali present in a substance 323 I. Volumetric methods methods of titration 323 a. DESCROIZILLES and GAY-LUSSAC'S method slightly modi- fied, 219 323 b. MOHR'S method, 220 329 II. Gravimetric method of FRESENIUS and WILL, 221 331 (225 341 CONTENTS. IX MOB C. Determination of the caustic alkali which is present along with the carbonate, 222 332 Determination of sodium carbonate in presence of potassium carbonate 333 3. Estimation of alkaline earths by the alkalimetric method, 223 334 4. The most important technical potash compounds 336 A. Potash or pearlash, 224 336 B. Potassium chloride ) C. Potassium sulphate D. Potassium nitrate, 226 ._ 346 E. Analysis of gunpowder (Appendix to D.), I 227 349 F. Potassium bitartrate (tartar), 228 357 5. Sodium compounds 360 A. Soda, 229 360 B. Sodium chloride (common salt) , 230 371 C. Sodium sulphate (salt-cake), 231 373 6. Barium compounds 375 Heavy spar (Barium sulphate), 232 375 7. Calcium compounds 376 A. Calcium phosphate (phosphorite). See V. Analysis of manures 376 B. Chlorinated Lime, 233 376 A. PENOT'S method 379 B. MOHR'S modification of PENOT'S method 381 C. lodometric methods 382 D. OTTO'S method 383 C. Calcium acetate, 234 387 D. Analysis of limestones, dolomites, marls, cements, etc., 235. 393 8. Aluminium compounds 403 A. Clays. (See silicon compounds, 238, p. 413.) B. Aluminium sulphate, 236 403 9. Silicon compounds 405 A. Analysis of native, and more particularly of mixed silicates, 237. 405 B. Analysis of clays, 238 413 10. Chromium compounds. Analysis of chrome iron ore, 239 421 11. Zinc compounds 428 A. Calamine B. Electric calamine i * C. Zinc blende, 241 430 D Zinc ores generally 435 I. Volumetric determination of zinc, 242 435 II. Electrolytic determination of zinc in zinc ores, 243 .... 448 E. Metallic zinc, 244 450 F. Zinc dust, 245 452 12. Manganese compounds 456 A. Black oxide of manganese, 246 456 CONTENTS. PAGE I. Drying the sample 457 II. Determination of the manganese dioxide present, 247. . . 458 III. Determination of moisture in manganese, 248 468 IV. Determination of the amount of hydrochloric acid required for the complete decomposition of the manganese ore, 249 469 B. Manganese ores generally. Determination of their metallic manganese content, 250 470 Electrolytic determination 472 13. Nickel compounds 474 A. Nickel ores, "nickelstein," and other intermediate products of nickel manufacture, 251 474 B. Commercial metallic nickel, 252 483 14. Iron compounds 486 A. Iron ores 486 I. Methods for complete analysis, 253 486 a. Hematite 488 b. Brown iron ore (limonite) 488 c. Bog iron ore 493 d. Magnetic iron ore 494 e. Spathic iron ore 494 II. Determination of the iron in iron ores, 254 495 1. Volumetric methods 495 2. Gravimetric methods 499 B. Analysis of various kinds of iron 501 I. Cast iron, 255 501 II. Steel and wrought iron 548 C. Pyrites, 256 553 15. Uranium compounds, 257 567 16. Silver compounds, 258 568 A. Silver ores 568 B. Silver alloys 569 17. Lead compounds 574 A. Galena, 259 574 B. Varieties of metallic lead 584 C. Oxides and salts of lead 597 18. Mercury compounds, 260 601 A. Mercury ores 601 B. Metallic mercury 602 19. Copper compounds 605 A. Copper ores, 261 605 Electrolytic determination of copper 61 1 3. Other methods of determining copper 624 B. Varieties of copper 633 I. Cement copper, 262 633 II. Coarse copper, refined copper, 263 636 CONTENTS. XI C. Copper alloys, 264 , 655 I. Brass 655 II. Nickel coinage metal 659 III. German silver (Argentan) 660 20. Bismuth compounds, 265 661 A. Ores of bismuth 661 B. Bismuth alloys 665 C. Bismuth salts 666 21. Antimony compounds, 266 669 A. Antimony ores 669 B. Antimony alloys 674 22. Tin compounds, 267 675 A. Tin ores 675 I. Tinstone 675 II. Tin pyrites 676 B. Varieties of tin 677 C. Alloys of tin 680 I. Alloys consisting chiefly of copper and tin (bronzes, etc.) . . 680 II. Alloys consisting chiefly of lead and tin (solders) 683 III. Alloys consisting chiefly of antimony and tin (pewters) 685 IV. Alloys used for bearings (bearing metal) 686 D. Preparations of tin 689 23. Arsenic compounds, 268 690 Detection and estimation of arsenic in organic matter, 268a. . . 693 24. Phosphorus compounds, 269 700 25. Sulphur compounds, 270 703 A. Commercial sulphur 703 B. Fuming sulphuric acid 706 26. Nitrogen compounds, 271 710 A "Nitrose" 710 B. Chamber acid, etc 715 27 Carbon compounds, 272 717 A. Graphite 717 B. Coal and coke 721 28. Hydrogen compounds, 273 728 Hydrogen peroxide 728 SUPPLEMENT TO DIVISION II. L Determination of grape sugar (dextrose}, fruit sugar (levulose), in- vert-sugar, maltose, milk sugar, cane sugar (saccharose), starch, and dextrin. . 730 A. Methods based upon the reduction of cupric oxide to cuprous oxide, 274 732 B= Methods based upon the reduction of mercury compounds, 275 749 i CONTENTS. PAGE C. Methods based upon the decomposition of sugar by alco- holic fermentation, 276 754 D. Determination of cane sugar, dextrin, and starch, 277 . . 757 1. Cane sugar 757 2. Dextrin and starch 760 II. Determination of alcohol, 278 763 III. Determination of tannin 767 A. LOWENTHAL'S method, 279 767 B. HAMMER'S method, 280 775 C. Gravimetric modification of HAMMER'S method, 281 780 D. Other methods for estimating the tanning principle 780 IV. Estimation of anthracene, 282 785 HI. ESTIMATION OF THE INORGANIC CONSTITUENTS OF PLANTS, 283 ... 787 A. Ash analysis 789 I. Preparation of the ash, 284 790 II. Analysis of the ash, 285 798 a. Qualitative analysis. 799 b. Quantitative analysis 800 a. Ashes in which the carbonates of the alkalies or alkaline earths predominate, and in which all the phosphoric acid may be assumed to be combined with ferric oxide, 286 800 /?. Ashes decomposable by hydrochloric acid, and in which a further quantity of phosphoric acid is present above that combined with iron, 287 806 f. Ashes not decomposed by hydrochloric acid, 288 .... 808 B. Supplementary determination of certain other inorganic substances in plants, 289 810 C. Arrangement of the results, 290 813 IV. ANALYSIS OF SOILS, 291 815 A. Collecting the Sample, 292 816 B. Mechanical Analysis, 293 817 a. Purely mechanical method, 294 819 6. SCHLGSING'S method, 295 824 C. Chemical analysis, 296 825 1. Determination of the moisture 827 2. Determination of the chemically combined water 827 3. Estimation of the substances soluble in water, 297 827 4. Estimation of the substances soluble in hydrochloric acid, 298 831 5. Examination of that portion of the earth insoluble in cold hydrochloric acid, 299 835 CONTENTS. Xiii PAGE 6. Examination of the residue insoluble in sulphuric acid, 300 836 7. Determination of the carbon contained in organic com- pounds, 301 837 a. Determination of the total organically combined carbon. 838 b. Determination of humus 840 c. Determination of waxy and resinous substances 842 8. Determination of the nitrogenous constituents of the soil, 302. . . '. 842 a. Determination of nitric acid 842 6. Determination of ammonia 842 c. Determination. of the nitrogen in organic compounds. .. 846 9. Supplementary determinations, 303 847 10. Statement of the results, 304 848 V. ANALYSIS or MANURES 850 A. General, 305. 850 B. Sampling, 306 851 C. Analysis of manures the value of which depends entirely or almost entirely upon their phosphoric acid content 853 I. Those containing the whole of the phosphoric acid in the form of compounds insoluble in water, 307 853 1. Determination of the moisture 854 2. Estimation of the phosphoric acid 854 a. Dissolving the substance, 308 854 6. The determination 856 a. Molybdenum method, 309 856 /?. GLASER'S method, 310 860 II. Manures containing phosphoric acid partly in the form of water-soluble compounds, 311 862 1. Determination of the moisture 863 2. Determination of the phosphoric acid 863 a. Determination of the phosphoric acid hi the three con- ditions in which it may occur in superphosphate 863 a. Determination of the water-soluble phosphoric acid, 312 863 aa. Preparation of the solution 863 66. Determining the content of the solution, 313 . . 864 aa. Gravimetric method 864 pp. Volumetric uranium method 864 ff. Acidimetric method, 314 866 /?. Determination of the "reverted," and of the unat- tacked phosphoric acid, 315 869 6. Shortened methods of determining the values of super- phosphate 870 CONTENTS. PAGE a. Determination of "soluble" phosphoric acid, 316 . . 870 ft. Determination of the citrate-soluble phosphoric acid, 317 871 c. Determination of the total phosphoric acid in super- phosphates, 318 873 D. Analysis of manures, the value of which depends wholly or almost wholly upon their potassium content, 319 873 E. Analysis of manures, the value of which depends solely or nearly altogether upon the nitrogen they contain 875 I. Chili saltpetre, 320 875 II. Ammonium salts 883 a. Distillation method, 322 883 6. Azotimetric method, 322 835 III. Substances containing nitrogen organically combined. . . . 894 a. Modified VARRENTRAPP-WILL method, 323 894 6. KJELDAHL'S method, 324 897 a. KJELDAHL'S original method, 325 899 p. Modifications of KJELDAHL'S method, 326 902 F. Analysis of manures containing two or more manurial substances 907 I. Usual mode of procedure, 327. 908 1. Determination of the water 908 2. Total fixed constituents 908 3. Constituents both soluble and insoluble in water 908 4. Fixed constituents singly 908 5. Total carbon 909 6. Sulphur compounds 909 7. Total nitrogen, 328 909 a. Preparatory treatment 910 6. The analytical process 910 a. DUMAS' method 910 ft. JODLBAUER'S modification of KJELDAHL'S method. 910 f. VARRENTRAPP-WILL' s method and its modifications 911 8. Nitrogen in its different forms of combination, 329. . . . 914 a. In ammoniacal compounds 914 ft. In the form of nitric acid 914 f. In organic combination 915 IL Analysis of commercial manures 916 1. Bone preparations, 330 916 a. Bone meal 917 b. Animal charcoal or bone black 918 c. Bone ash 920 d. Precipitated calcium phosphate from bones 920 e. Superphosphate from bone 920 2. Guano (Peruvian guano), 331 921 a. Crude guano 921 b. Decomposed guano 925 CONTENTS. XV 3. Fish guano, "granat" guano, horn-meal, tendon-meal, and flesh-meal manure, 332 926 4. Mixed manures, 333 926 VI. ANALYSIS OF ATMOSPHERIC AIR 928 A. Determination of the water and carbonic acid 929 I. BRUNNER'S method, 334 929 II. PETTERSSON'S method, 335 932 B. Determination of carbonic acid alone 938 I. PETTENKOFER'S original process, 336 938 II. Modification of PETTENKOFER'S process 941 1. SONDEN'S modification, 337 941 2. SPRING and ROLAND'S modification, 338 942 3. Modifications in the manner of titrating the baryta water, 339 945 III. Process proposed by MOHR, and employed by HLASIWETZ and v. GILM, 340 946 C. Determination of oxygen and nitrogen, 341 948 PART III. EXERCISES FOR PRACTICE 953 A. Simple determinations in the gravimetric way, intended to teach the student the more common analytical operations 955 B. Complete analysis of salts in the gravimetric way; calculation of the formulae from the results obtained 964 C. Separation of two bases or two acid radicals from each other, and determinations hi the volumetric way 969 D. Analysis of alloys, minerals, industrial products, etc., in the gravi- metric and volumetric way 976 E. Determination of the solubility of salts 981 F. Determination of the solubility of gases hi liquids, and analysis of gaseous mixtures 982 G. Organic analysis, and determinations of the equivalents of organic compounds; also analyses hi which organic analysis has to be employed 984 ANALYTICAL EXPERIMENTS 985 XVi CONTENTS. APPENDIX I. PAGE OFFICIAL METHODS OF ANALYSIS ADOPTED BY THE ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS 1017 I. Methods for the analysis of fertilizers 1017 1. Preparation of sample 1017 2. Determination of moisture 1017 3. Determination of phosphoric acid 1017 a. Gravimetric method 1017 b. Optional volumetric method 1020 4. Determination of nitrogen 1021 a. KJELDAHL method 1021 b. GUNNING method. 1024 c. KJELDAHL method modified to include the nitrogen of nitrates 1024 d. GUNNING method modified to include the nitrogen of nitrates 1025 e. Absolute or cupric-oxide method 1025 /. Ruffle method 1027 g. Soda-lime method 1028 h. Magnesium oxide method 1029 i. ULSCH method modified by STREET 1029 j. Zinc-iron method 1030 5. Determination of potash 1030 a. LINDO-GLADDING method 1030 &. Optional method 1031 c. Factors 1032 II. Methods for the analysis of foods 1032 1. Preparation of sample 1032 2. Determination of moisture 1032 3. Determination of ash 1032 4. Determination of ether extract 1033 . a. Preparation of anhydrous ether 1033 b. Determination 1033 5. Determination of crude protein 1033 6. Determination of albuminoid nitrogen by STUTZER'S method 1033 7. Determination of crude fibre and carbohydrates 1034 8. Official methods for the determination of carbohydrates in grains and by-product cattle foods 1034 a. Determination of reducing sugars (estimated as dex- trose) 1034 6. Determination of sucrose 1034 c. Determination of starch in commercial starches and potatoes 1034 d. Diastase method for starch. . .1034 CONTENTS. XVU PAGE e. Provisional methods for the determination of pento- sans by means of phloroglucin 1035 /. Method for estimating galactan 1036 g. Determination of crude fibre 1036 HE. Methods for the determination of soluble carbohydrates 1037 1. Determination of water 1037 a. By drying 1037 (1) In sugars 1037 (2) In massecuites, molasses, honeys, and other liquid and semi-liquid products 1037 (3) Provisional method for drying molasses with quartz sand 1037 6. Aerometric methods 1038 2. Ash 1040 a. Determination of ash 1040 b. Quantitative analysis of the ash 1041 3. Determination of nitrogen 1041 4. Determination of reducing sugars 1042 a. Preparation of reagents 1042 6. Volumetric methods 1042 c. Gravimetric methods 1044 5. Determination of sucrose 1049 a. Optfcal methods 1049 6. Optical methods by inversion 1050 6. Determination of lactose 1051 a. Optical method for the determination of lactose in milk 1051 b. SOXHLET'S method using alkaline copper solution 1052 IV. Methods for the analysis of dairy products. .' 1054 1. Butter analysis 1054 a. Preparation of sample 1054 6. Determination of water 1054 c. Determination of ether extract 1054 d. Determination of casein, ash, and chlorine 1054 e. Determination of salt 1054 /. Determination of volatile acids 1055 LEFFMANN-BEAM method 1057 g. Determination of soluble and insoluble acids 1059 h. Determination of saponification equivalent 1060 i. Determination of the refractive index 1061 /. Determination of iodine absorption-number 1063 k. Determination of specific gravity 1065 1. Determination of melting-point 1066 m. Microscopic examination 1068 2. Milk analysis 1068 a. Determination of water . 1068 xviii CONTENTS. PAGE b. Determination of fat 1069 c. Determination of total nitrogen 1069 d. Determination of ash 1070 e. Determination of sugar 1070 3. Cheese analysis 1070 a. Preparation of sample 1070 b. Determination of water 1071 c. Determination of fat 1071 d. Determination of nitrogen 1071 e. Determination of ash 1071 /. Determination of other constituents 1072 g. Provisional method for the determination of acidity in cheese 1072 V. Methods for the analysis of fermented and distilled liquors 1072 1. Determination of specific gravity 1072 2. Determination of alcohol 1072 a. In fermented liquors 1072 b. In distilled liquors 1072 3. Determination of extract 1078 a. In distilled liquors, dry wines, beers, ales, etc 1078 b. In sweet wines 1078 4. Determination of total acidity 1078 5. Determination of volatile acids 1078 6. Determination of glycerin 1078 a. In dry wines 1078 b. In sweet wines 1078 7. Determination of reducing sugars 1078 8. Polarization 1078 a. In white wines 1078 b- In red wines 1079 c. In sweet wines 1079 d. Application of analytical methods 1079 9. Determination of tannin and coloring matter 1081 10. Determination of potassium bitartrate 1082 11. Determination of tartaric acid 1082 12. Determination of tartaric, malic, and succinic acids 1083 13 Detection of coloring matter 1084 14. Determination of ash 1085 15. Determination of potash 1085 16 Determination of sulphurous acid 1085 17. Detection of salicylic acid 1085 18, Detection of gum and dextrin 1086 19 Determination of fusel oil 1086 20. Determination of aldehydes ; 1087 21. Determination of ethereal salts. . . 1088 CONTENTS. XIX PAGE VI. Methods for the analysis of soils 1088 1. Preparation of sample 1088 2. Determination of moisture 1089 3. Determination of volatile matter 1089 4. Determination of acid-soluble materials 1089 a. Acid digestion of the soil 1089 6. Determination of ferric oxide, alumina, and phos- phoric acid, collectively 1090 c. Determination of manganese 1090 d. Determination of calcium 1091 e. Determination of magnesium 1091 /. Determination of ferric oxide 1091 g. Determination of phosphoric acid 1092 h. Provisional method for determining available phos- phoric acid 1092 t. Provisional method for determination of more active forms of phosphoric acid in soils 1093 j. Determination of sulphuric acid 1093 k. Determination of potash and soda 1094 5. Determination of acid-insoluble materials 1094 6. Determination of total alkalies 1094 7. Identification of lithium, caesium, and rubidium 1095 8. Determination of total nitrogen 1095 9. Determination of carbon dioxide 1095 10. Determination of humus 1095 11. Determination of humus nitrogen 1095 12. Statements of results 1096 VII. Methods for the analysis of ashes 1096 1. Preparation of the ash 1096 2. Solution and determination of carbon, sand, and silica 1097 3. Determination of manganese, calcium, and magnesium 1097 4. Determination of phosphoric acid 1098 5. Determination of sulphuric acid and alkalies 1 098 6. Determination of carbon dioxide . 1098 7. Determination of chlorine 1098 VIII. Methods for the analysis of tanning materials 1099 1. Preparation of sample 1099 2. Quantity of material 1099 3. Moisture 1099 4. Total solids 1099 5. Soluble solids 1099 6. Non-tannins 1099 7. Tannins 1 1 00 8. Testing hide powder 1100 9. Testing non-tannin filtrate 1 100 XX CONTENTS. APPENDIX II. PAGE SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS 1101 PART I. Introduction 1101 I. Importance of complete analysis 1101 II. Object and scope of the treatise 1106 III. Statement of analyses 1107 IV. Time needed for analysis 1109 V. Two useful aids in chemical manipulation 1109 VI. Limits of allowable error 1111 VII. Quality of reagents 1111 VIII. Preliminary qualitative analysis 1112 PART II. Methods 1112 I. Introductory remarks 1112 II. Specific gravity 1113 III. Preparation of sample for analysis 1116 IV. Water-hygroscopic, zeolitic, crystal 1117 Apparatus for direct determination of water at dif- ferent temperatures 1121 V. Water total or combined 1122 Arguments against "loss" on ignition method 1122 Direct weighing of the water without use of absorption tubes PENFIELD'S methods 1122 VI. Silica, separation from alumina, etc 1131 Alternative methods of decomposition 1131 Decomposition of refractory silicates by hydrochloric acid under pressure 1132 Boric-oxide method of JANNASCH and HEIDENREICH. . 1132 Sodium-carbonate method 1134 Subsequent treatment 1135 VII. Metals precipitable by hydrogen sulphide 1137 VIII. Aluminium. Total iron 1137 Indirect method for aluminium 1137 Precipitation of aluminium, iron, etc 1138 Ignition of precipitate 1139 Estimation of iron in the alumina precipitate, etc 1140 Determination of the true value for ferric iron 1141 Methods aiming at the more or less direct estimation of aluminium after first removing iron as sulphide ... 1 141 By extraction with a fixed caustic alkali 1142 Direct precipitation of alumina 1143 IX. Manganese, nickel, cobalt, copper, zinc 1143 Manganese and zinc 1143 Nickel, cobalt, and copper 1144 X. Calcium and strontium (barium) 1144 CONTENTS. Xxi PAGE Separation of strontium (barium) from calcium by ether-alcohol 1145 Behavior of barium 1145 Separation of barium from strontium 1146 XI. Magnesium 1146 Precipitation 1146 Methods of collecting and igniting the precipitate. . . . 1148 Contamination by and removal of barium and calcium 1149 XII. Titanium 1149 Colorimetric estimation with hydrogen peroxide (WEL- LER'S method) 1149 Alternative mode of preparing the solution 1150 Colorimetric apparatus and its use 1151 GOOCH'S gravimetric method 1152 GOOCH'S method not directly applicable to rocks con- taining zirconium 1154 Superiority of Colorimetric and GOOCH methods over older ones , 1154 BASKERVILLE 's method 1154 XIII. Barium (zirconium, total sulphur) 1155 XIV. Zirconium 1156 HILLEBRAND'S method 1156 Other methods of separating zirconium 1158 XV. Rare earths other than zirconia 1158 XVI. Phosphorus 1159 Procedure when material is ample 1159 Procedure when material is scanty 1159 XVII. Chromium 1160 Gravimetric method 1160 Colorimetric method 1161 XVIII. Vanadium (chromium) and molybdenum 1162 Distribution of vanadium and molybdenum 1162 Description of method 1163 Application of the method in presence of relatively much chromium 1 165 Condition of vanadium in rocks 1167 XIX. Ferrous iron 1 168 Comparison of sealed -tube and hydrofluoric -acid methods comparative worthlessness of the former in rock analysis 1168 Modified MITSCHERLICH method 1170 Hydrofluoric-acid method 1171 PRATT' s modification of the hydrofluoric-acid method. 1173 Influence of sulphides, vanadium, and carbonaceous matter on the determination of ferrous iron by the hydrofluoric-acid method 1173 XX11 CONTENTS. PAGE Uncertainties of the ferrous-iron determination 1175 XX. Alkalies 1175 LAWRENCE-SMITH method 1175 Lithium 1178 GOOCH method for separating lithium 1178 Separation of alkalies by other methods 1179 XXI. Carbon dioxide. Carbon 1180 XXII. Chlorine 1182 XXIII. Fluorine 1182 XXIV. Sulphur 1184 XXV. Boron 1185 XXVI. Nitrogen 1186 XXVII. Special operations 1187 Detection of nepheline in presence of olivine 1187 Estimation of soluble silica 1187 XXVIII. Estimation of minute traces of certain constituents. . .1188 TABLES FOR THE CALCULATION OF ANALYSES 1190 et seq. Table I. Equivalents of the elements 1190 Table II. Composition of the bases and oxygen acids 1191 Table III. Reduction of compounds found, to constituents sought, by simple multiplication or division 1195 Table IV. Amount of the constituent sought for every unit of weight of the compound found 1197 et seq. Table V. International atomic weights, 1903 1211 Table VI. Specific and absolute weights of some gases 1212 Table VII. Comparison of degrees of the mercurial thermometer with those of the air- or hydrogen-thermometer 1213 INDEX.. . 1215 QUANTITATIVE ANALYSIS, SECTION VI. ORGANIC ANALYSIS. 171. ORGANIC compounds contain comparatively but few of the ele- ments. A small number of them consist simply of 2 elements, viz., C and H; the greater number contain 3 elements, viz., as a rule, C, H, and O; most of the rest 4 elements, viz., generally, C, H, O, and N; a small number 5 elements, viz., C, H, O, N, and S; and a few elements, viz., C, H, O, N, S, and P. This applies to all the natural organic compounds which have as yet come under our notice. But we may artificially prepare organic compounds containing other elements besides those enu- merated; thus we know many organic substances which contain chlorine, iodine, or bromine; others which contain arsenic, anti- mony, tin, zinc, platinum, iron, cobalt, etc.; and it is quite impos- sible to say which of the other elements may not be similarly 2 ORGANIC ANALYSIS. [ 17l capable of becoming more remote constituents of organic com- pounds (constituents of organic radicals). With these compounds we must not confound those in which organic acids are combined with inorganic bases, or organic bases with inorganic acids, such as tartrate of lead, for instance, silicic ether, borate of morphine, etc.; since in such bodies any of the elements may of course occur. Organic compounds may be analyzed either with a view simply to resolve them into their proximate constituents; thus, for in- stance, a gum-resin into resin, gum, and ethereal oil; or the analy- sis may have for its object the determination of the ultimate con- stituents (the elements) of the substance. The simple resolution of organic compounds into their proximate constituents is effected by methods perfectly similar to those used in the analysis of inorganic compounds; that is, the operator endeavors to sepa- rate (by solvents, application of heat, etc.) the individual constitu- ents from one another, either directly or after having converted them into appropriate forms. We disregard here altogether this kind of organic analysis of which the methods must be nearly as numerous and varied as the cases to which they are applied and proceed at once to treat of the second kind, which may be called the ultimate analysis of organic bodies. The ultimate analysis of organic bodies (here termed simply organic analysis] has for its object, as stated above, the determi- nation of the elements contained in organic substances. It teaches us how to isolate these elements or to convert them into com- pounds of known composition, to separate the new compounds formed from one another, and to calculate from their several weights, or volumes, the quantities of the elements. Organic analysis, therefore, is based upon the same principles upon which rest most of the methods of separating and determining inorganic compounds. The conversion of most organic substances into distinctly characterized and readily separable products the weights of which can be accurately determined, offers no great difficulties, and organic analysis is therefore usually one of the more easy tasks 171.] ORGANIC ANALYSIS. 3 of analytical chemistry; and as, from the limited number of the elements which constitute organic bodies, there is necessarily a great sameness in the products of their decomposition, the analyti- cal process is always very similar, and a few methods suffice for all cases. It is principally ascribable to this latter circumstance that organic analysis has so speedily attained its present high degree of perfection the constant examination and improvement of a few methods by a great number of chemists could not fail to produce this result. An organic analysis may have for its object either simply to ascertain the relative quantities of the constituent elements of a substance thus, for instance, woods may be analyzed to ascertain, their heating power, fats to ascertain their illuminating power or to determine not only the relative quantities of the constituent elementary atoms, but also the number of atoms of carbon, hydro- gen, oxygen, etc., which constitute 1 molecule of the analyzed compound. In scientific investigations we have invariably the latter object in view, although we are not yet able to achieve it in all cases. These two objects cannot well be attained by one opera- tion; each requires a distinct process. The methods by which we ascertain the proportions of the con- stituent elements of organic compounds may be called collectively the ultimate analysis of organic bodies, in a more restricted sense; whilst the methods which reveal to us the absolute number of elementary atoms constituting the molecule of the analyzed com- pound may be. styled the determination of the molecular weight of organic bodies. The success of an organic analysis depends both upon the. method and its execution. The latter requires patience, circum- spection, and skill; whoever is moderately endowed with these gifts will soon become a proficient in this branch. The selection of the method depends upon the knowledge of the constituents of the substance, and the method selected may require certain modifi- cations, according to the properties and state of aggregation of the same. Before we can proceed, therefore, to describe the various, methods applicable in the different cases that may occur, we have 4 ORGANIC ANALYSIS. [ 172. first to occupy ourselves here with the means of testing organic bodies qualitatively. [. QUALITATIVE EXAMINATION OF ORGANIC BODIES. 172. It is not necessary for the correct selection of the proper method to know all the elements of an organic compound, since, for instance, the presence or absence of oxygen makes not the slightest difference to the method. But with regard to other ele- ments, such as nitrogen, sulphur, phosphorus, chlorine, iodine, bromine, etc., and also the various metals, it is absolutely indis- pensable that the operator should know positively whether either of them is present. This may be ascertained in the following manner: 1. Testing for Nitrogen. Substances containing a tolerably large amount of nitrogen evolve upon combustion, or when intensely heated, the well-known odor of singed hair or feathers. No further test is required if this smell is distinctly perceptible; otherwise one of the following experiments is resorted to: a. The substance is mixed with potassium hydroxide in powder or with soda-lims ( 66, 4) and the mixture heated in a test-tube. If the substance contains nitrogen, ammonia will be evolved, which .may be readily detected by its odor and reaction, and by the formation of white fumes with volatile acids. Should these reactions fail to afford positive certainty, every doubt may be removed by the following experiment: Heat a somewhat larger portion of the substance in a short tube, with an excess of soda- lime, and conduct the products of the combustion into dilute "hydrochloric acid; evaporate the acid on the water-bath, dissolve the residue in a little water, add platinic chloride to the solution, evaporate nearly to dryness on a water-bath and treat the residue Avith alcohol. If the residue dissolves and leaves no precipitate 172.] QUALITATIVE EXAMINATION OF ORGANIC BODIES. 5 of ammonium platinic chloride, the substance may be considered free from nitrogen. b. LASSAIGNE has proposed another method, which is based upon the property of potassium to form potassium cyanide when ignited with a nitrogenous organic substance. The following is the best mode of performing the experiment: Heat the substance under examination in a test-tube, with a small lump of potassium, and after the complete combustion of the potassium, treat the residue with a little water (cautiously); filter the solution, add 2 drops of solution of ferrous sulphate con- taining some ferric sulphate, digest the mixture a short time, and add hydrochloric acid in excess. The formation of a blue or bluish-green precipitate or coloration proves the presence of nitrogen. Both methods are delicate : a is the more commonly employed,, and suffices in almost all cases; b does not answer so well in the case of alkaloids containing oxygen (e.g., morphine, brucine). c. In organic substances containing oxides of nitrogen, the presence of nitrogen cannot be detected with certainty by either a or 6, but it may be readily discovered by heating the substance in a tube, when red acid fumes, imparting a blue tint to potassium- iodide starch paper, will be evolved, accompanied often by deflagration. 2. Testing for Sulphur. a. Solid substances are fused with about 12 parts of pure po- tassium hydroxide and 6 parts of potassium nitrate, or they are intimately mixed with some pure potassium nitrate and sodium carbonate; potassium nitrate is then heated to fusion in a porce- lain crucible, and the mixture gradually added to the fusing mass. The mass is allowed to cool, then dissolved in water, and the solu- tion tested with barium chloride after acidifying with hydrochloric acid. Special care must be taken that the reagents be free from sulphuric acid. The sulphur compounds present in coal gas may even give rise to error, hence in exact experiments the fusion muF^r be effected over an alcohol lamp. 6. Fluids are treated with fuming nitric acid free from sulphuria 6 ORGANIC ANALYSIS. [ 172. &cid, or with a mixture of nitric acid and potassium chlorate, at first in the cold, finally with application of heat; the solution is tested as in a. c. On heating a small quantity of a dry organic compound {containing sulphur) with a small fragment of sodium in a glass tube sealed at one end, the sulphur is converted into sodium sul- phide, which dissolves on treating the fragments cf the lower part of the tube with water, and may be detected by one of the methods detailed under d (SCHONN *). d. As the methods a, 6, and c serve simply to indicate the pres- ence of sulphur in a general way, but afford no information regard- ing the state or form in which that element may be present, I add here another method, which serves to detect only the sulphur in the non-oxidized state in organic compounds. Boil the substance with strong solution of potassa and evapo- rate nearly to dryness. Dissolve the residue in a little water, and bring the solution into a flask, Fig. 1, provided with a loosely-fitting stopper, through which passes a funnel tube reaching nearly to the bottom of the flask. Suspend from the lower surface of the stopper within the flask a strip of paper dipped first in lead-acetate, then in ammonium-carbonate solution. Add slowly dilute sulphuric acid through the funnel tube, c, and observe whether the lead paper, b, be- comes brown ; or test the first alkaline solution with a solution of lead oxide in soda lye, or by means of a polished surface of silver, or by nitroprusside of sodium, or by just acidi- fying the dilute solution with hydrochloric acid and adding a few drops of a mixture of ferric chloride and potassium ferricyanide (see "Qual. Anal.," 187, WELLS' translation, published by JOHN WILFT & SONS, New York). FIG. 1. * Zeitschr. f. analyt. Chem., viu, 52. 172.] QUALITATIVE EXAMINATION OF ORGANIC BODIES. 7 3. Testing for Phosphorus. The methods described in 2, a and b, may likewise serve for phosphorus. The solutions obtained are tested for phosphoric acid with magnesium sulphate, ammonium chloride, and ammonia; or with ferric chloride, with addition of sodium acetate; or best with solution of ammonium molybdate in nitric acid (comp. "Qual. Anal.")- I n method 6, the greater part of the excess of nitric acid must first be removed by evaporation. b. In some cases the following method by SCHONN * may be advantageously employed: Carbonize the organic matter in a covered crucible, powder the charred mass and mix it with half its volume of magnesium powder, introduce the mixture into the lower part of a thin-walled glass tube sealed at the lower end, and heat quite strongly while shaking the tube, so as to avoid having the mixture driven out. If the substance contained phosphorus, the upper part of the tube will appear luminous in the dark, and at times some yellow or amorphous phosphorus will be observed oii the sides. The remainder of the phosphorus will be in the residue as magnesium phosphide. On breaking off the lower end of the tube, moistening the contents with a little water, and heating, hydrogen phosphide develops, and is recognized by its characteristic odor. 4. Testing for Iodine, Bromine, and Chlorine. As regards the testing of organic substances for iodine, bromine, or chlorine, I refer to 190. I give here only two methods which suffice for most cases. a. Sprinkle the organic substance, if dry, on the bottom of a test-tube heated to redness. Iodine may be frequently recognized by the color of the vapor. On introducing the inverted tube into a larger one containing a little water and ammonia, hydriodic, hydrobromic, or hydrochloric acid may be detected in the liquid after a time, by the usual methods (see "Qual. Anal."). In the case of a liquid organic substance, fill into a small bulb-tube such as is used in organic analysis ( 180), insert the open and down- * Zeitschr. f. analyt. Chem., VTII, 55. 8 ORGANIC ANALYSIS. [ 172. wardly directed tube in a test-tube, ignite the bottom of the latter, and then cause some of the liquid to flow out by warming the bulb (ERLENMEYER *). 6. BEILSTEIN f ignites some powdered cupric oxide in the loop of a platinum wire, moistens with water, and ignites again. If the flame remains uncolored, the cupric oxide is eligible for use. Some of the substance to be tested is now taken up with the cupric oxide and held in the flame of a bunsen-burner near the lower and inner margin. The carbon burns first, but immediately after- wards the characteristic blue or green color is seen if chlorine, bromine, or iodine is present (see "Qual. Anal."). 5. Testing for Inorganic Substances. A portion of the substance is heated on platinum foil, to see whether or not a residue remains. When acting upon difficultly combustible substances, the process may be accelerated by heating the spot which the substance occupies on the platinum foil to the most intense redness, by directing the flame of the blow-pipe upon it from below. Occasionally complete combustion is best effected by adding mercuric oxide to the residue left on ignition, and re- igniting. The residue is then examined by the usual methods. That volatile metals in volatile organic compounds e.g., arsenic in cacodyl cannot be detected by this method need hardly be mentioned. These preliminary experiments should never be omitted, since neglect in this respect may give rise to very great errors. Thus, for instance, taurin, a substance in which a large proportion of sulphur was afterwards found to exist, had originally the formula C 4 N 2 H 14 10 assigned to it. The preliminary examination of organic substances for chlorine, bromine, and iodine is generally unneces- sary, as these elements do not occur in native organic compounds, and as their presence in compounds artificially produced by the action of the halogens requires generally no further proof. Should it, however, be desirable to ascertain positively whether a substance * Zeitschr. f. analyt. Chem., iv, 137. Mbid., xn, 95. 173.] ELEMENTS IN ORGANIC BODIES. 9 does or does not contain chlorine, iodine, or bromine, this may be done by the methods given in 190. II. DETERMINATION OP THE ELEMENTS IN ORGANIC BODIES.* 173. It is not my intention to detail the history of the development of organic analysis; I shall confine myself to a description of those methods which are considered to be the best, and shall not touch upon the others. The more simple methods, which usually are followed by the student in the study of organic analysis, I shall describe fully; the more complicated ones will be treated of more briefly, since the chemist who uses them is presupposed to possess a more advanced knowledge of the general manipulations of organic analysis. In the selection of the methods, consideration has also been paid to the varied requirements of the purely experimental as well as practical operator, since it is evident that methods based upon the use of complicated apparatus may be most suitable for laboratories wherein organic analyses are daily made, without being adapted for those chemists who make such an analysis only occa- sionally. For the latter those methods requiring simple apparatus are naturally the most suitable. Since the accuracy of the results depends just as much upon the proper construction and arrangement of the apparatus as upon the execution of the method itself, I would lay special stress upon the fact that equal care must be bestowed upon both; and that the rules here given may not be deviated from without impunity, as they are the results of long experience and numberless experi- ments on the part of the most distinguished chemists. In order to afford a clear survey over the extensive subject, the matter to be treated of is presented here in tabular form, show- ing the order in which the different methods are treated. * For Prof. WARREN'S admirable methods we must refer to his original papers in Am. Journ. Sci., 2d ser., xxxvin, 387, XLI, 40, and XLII, 156. 10 ORGANIC ANALYSIS. [ 173. A. SUBSTANCES CONSISTING OF CARBON AND HYDROGEN, OR OF CARBON, HYDROGEN, AND OXYGEN. a. Solid bodies. a. Readily combustible, non-volatile bodies. Com- bustion with cupric oxide. 1. LIEBIG'S Method, 174. 2. BUNSEN'S Modification, 175. ft. Difficultly combustible, non- volatile bodies. 1. Combustion with lead chromate (and potas- sium bichromate), 176. 2. Combustion with cupric oxide and potassium chlorate or perchlorate, 177. 3. Combustion with cupric oxide and oxygen gas, 178. 7*. Volatile bodies, or such as undergo alteration at 100, 179. 5. Liquid bodies. a. Volatile, 180. P. Non-volatile, 181. Supplement to A (174-182), 182. Modified apparatus. B. COMPOUNDS CONSISTING OF CARBON, HYDROGEN, OXYGEN, AND NITROGEN. a. Estimation of Carbon and Hydrogen, 183. b. Estimation of Nitrogen. a. From the volume. 1. Relative Method, 184. aa. According to LIEBIG. bb. According to BUNSEN. cc. According to MARCHAND and GOTTLIEB. 2. Absolute nitrogen estimation, 185. aa. According to DUMAS. bb. According to SIMPSON. ^. Estimation of nitrogen by conversion into ammonia, according to VARRENTRAPP and WILL, 186. 173.] ELEMENTS IN ORGANIC BODIES. 11 ;-. PELIGOT'S modification of VARRENTRAPP-WILL'S method, 186. C. ANALYSIS OF ORGANIC COMPOUNDS CONTAINING SULPHUR, 188. D. ESTIMATION OF PHOSPHORUS IN ORGANIC COMPOUNDS, 189. E. ANALYSIS* OF ORGANIC COMPOUNDS CONTAINING CHLORINE, BROMINE, OR IODINE, 190. F. ANALYSIS OF ORGANIC COMPOUNDS CONTAINING INORGANIC SUBSTANCES, 191. Supplement to 174-191. Direct estimation of oxygen in organic substances, and methods of organic analysis differing from those ordinarily used, 192. A, ANALYSIS OF COMPOUNDS WHICH CONSIST SIMPLY OF CARBON AND HYDROGEN, OR OF CARBON, HYDROGEN, AND OXYGEN. The principle of the method which serves to effect the quanti- tative analysis of such compounds, and which was first proposed in its present form by LIEBIG, is exceedingly simple. The sub- stance is burned to carbonic acid and water; these products are separated from each other and weighed, and the carbon of the substance is calculated from the weight of the carbon dioxide, the hydrogen from that of the water. If the sum of the carbon and hydrogen is equal to the original weight of the substance, the substance contains no oxygen ; if it is less than the weight of the substance, the difference expresses the amount of oxygen present.* The combustion is effected either by igniting the organic sub- stance with oxygenized bodies which readily part with their oxy- gen (cupric oxide, lead chromate, etc.) or at the expense both of free and combined oxygen. * The methods proposed for directly estimating oxygen in organic sub- stances have so far had no important influence on organic analysis. They will be described in 192. 112 ORGANIC ANALYSIS. [ 174. a. SOLID BODIES. a. Readily combustible, non-volatile bodies (e.g., sugar, starch, tartaric acid, etc.).* COMBUSTION WITH CUPRIC OXIDE. 1. LIEBIG'S METHOD. 174. I. APPARATUS AND PREPARATIONS REQUIRED FOR THE ANALYSIS. 1. THE SUBSTANCE. This must be most finely pulverized and perfectly pure and dry ; for the method of drying, I refer to 26. Substances which on drying in the air are liable to change, must be heated in a current of dry carbon dioxide or of hydrogen (RocH- LEDER f). 2. A TUBE IN WHICH TO WEIGH THE SUBSTANCE. A small, perfectly dry glass tube, 4 to 5 cm. long and about 1 cm. bore, Fig. 2. It should be provided either with a light ground-glass stopper or with a cork wrapped in tin foil. The weight of the tube with its stopper must be accurately known to 0.01 grm. It is advisable -to keep the tube, together with the substance, in the drying closet until the analysis is undertaken. It is either laid on the balance or placed in a small foot made of tin, Fig. 3. 3. THE COMBUSTION TUBE. A tube of difficultly fusible glass (potassa glass), about 2 mm. thick in the glass, about 90 cm. in length, and from 12 to 14 mm. inner diameter * It need scarcely be mentioned that readily combustible substances may be treated also by the methods given for difficultly combustible substances; and in fact these latter methods, because of the greater certainty afforded as regards completeness of combustion of the carbon, are generally preferred nowadays to the older methods, which are distinguished by their simplicity. f Zeitschr. /. Analyt. Chem., vi, 235. 174.] COMBUSTION WITH CUPRIC OXIDE. 13 is first cleaned with paper or linen tied to the end of a wire or string, then softened in the middle before a glass-blower's lamp, while being constantly rotated, drawn out as represented in Fig. 4, FIG. 4. and finally apart at 6. The fine points of the two pieces are then sealed and thickened a little in the flame, and the sharp edges of the open ends, a and c, are slightly rounded by fusion, care being taken to leave the aperture perfectly round. The posterior part of the tube should be shaped as shown in Fig. 5, and not as in Fig. 6. FIG. 5. FIG. 6. Two perfect combustion tubes are thus produced. The one intended for immediate use is cleaned with linen or paper attached to a piece of wire, and then thoroughly dried. This is effected either by laying the tube, with a piece of paper twisted over its mouth, for some time on a sand-bath, with occasional removal of the air from it by suction, with the aid of a glass tube, or (rapidly) by moving the tube to and fro over the flame of a gas or spirit lamp, heating its entire length, and continually removing the hot air by suction through the small glass tube (Fig. 7). The suction FIG. 7. may be most conveniently effected by the water-pump, but failing this, with the mouth. 14 ORGANIC ANALYSIS. [ 174. The combustion tube, when quite dry, is closed air-tight with a cork and kept in a warm place until required for use. In default of glass tubes possessed of the proper degree of infusibility, thin brass or copper foil, or brass gauze, is rolled round the tube, and iron wire coiled round it. 4. THE POTASH BULBS (Fig. 8). This apparatus, devised by LIEBIG, is filled, to the extent indicated in the engraving, with a clear solution of caustic potassa of 1-27 sp. gr. (66, 6*). The introduction of the potassa solution into the apparatus is effected by plunging the end a into a beaker or dish into which a little of fc FIG. 8. FIG. 9. the solution has been poured out, and applying suction to 6, best and safest by means of a caoutchouc tube, as in Fig. 9. The two ends are then wiped perfectly dry with twisted slips of paper, and the outside of the apparatus with a clean cloth. f 5. THE CALCIUM-CHLORIDE TUBE. Fig. 10 shows the simplest and original form. It is filled in the following manner: In the first place, the aperture a of the tube b a is loosely stopped with a small cotton plug extending about 1 cm. into the tube; this is effected by introducing a loose cotton plug into c and applying a sudden * If the potassa solution is pure, i.e., if it is free or nearly free from alu- mina and silica, a much more concentrated solution may be employed without danger of its frothing. J. LOWE (Zeitschr. f. analyt. Chem., ix, 220) rec- ommends a solution prepared by dissolving 1 part of good potassium hydroxide (containing 80 per cent. KOH) in 1 part of water. Potash bulbs filled with this solution may be used for a number of combustions without requiring refilling. + For other potash bulbs which may replace the LIEBIG bulbs, see 182, 174.] COMBUSTION WITH CUPRIC OXIDE. 15 and energetic suction at b. The bulb is then filled with lumps of calcium chloride (66, 7, a), and the tube c d up to e with smaller FIG. 10. FIG. 11. FIG. 12. fragments, intermixed with coarse powder of the same substance; a loose cotton plug is then inserted and the tube finally closed with a perforated cork into which a small glass tube is fitted; the pro- truding part of the cork is cut off and the cut surface covered over with sealing-wax; the edge of the little tube fg, Fig. 11, is slightly rounded by fusion at g. The tube illustrated in Fig. 12 is still more convenient to use, as a considerable quantity of water condenses hi the empty bulb a, and at the close of the experiment may be poured out. The oper- ator is thus enabled to test it as to reaction, etc., and also to use the same tube far oftener without fresh filling than when using a tube not provided with an empty bulb. Another form of tube, more convenient for weighing, is that of MARCHAND, Fig. 13. In this also the bulb a next to the com- bustion tube remains empty. VOLHARD * recommends the form shown in Fig. 14 as avoiding the use of perforated stoppers. Finally the two last forms may be combined, as shown in Fig. 14 (H. FRESENIUS f). In order to be quite certain that the calcium-chloride tubes absorb water only, and not small quantities of carbonic acid besides (as the salt usually has a slightly alkaline reaction), conduct through the filled tubes a slow stream of dry carbonic-acid gas * Annal. der Chem., CLXXVT, 339.; Zeitschr. f. analyt. Chem., xiv, 333. t Zeitschr. f. analyt. Chem., xiv, 334. 16 ORGANIC ANALYSIS. [ 174. and follow by a current of dry air until the carbonic-acid gas has been completely expelled from the tubes. 6. A SMALL TUBE OF VULCANIZED INDIA-RUBBER. This must be so narrow that it can only be pushed with difficulty over the tube g of the calcium-chloride tube on the one hand, and over the end a of the potash bulbs on the other hand; in which case there is r; FIG. 13. FIG. 14. FIG. 15. no need of binding with silk cord. If the rubber tube should be a little too wide, it must be tied round with silk cord or with ignited piano wire. It is self-evident that the narrow end g of the calcium-chloride tube should be of the same width as the tube a of the potash bulbs. The india-rubber tube is purified from any adherent sulphur and dried in the water-bath previous to use. 7. CORKS. These should be soft and smooth, and as free as possible from visible pores. A cork should be selected which, after careful squeezing, fits perfectly tight and screws with some diffi- culty to one-third of its length, at the most, into the mouth of the combustion tube; a perfectly smooth and round hole, into which the end b a of the calcium-chloride tube must fit perfectly air- tight, is then carefully bored through the axis of the cork. The cork is then kept for an hour or two in the water-bath. It is advisable always to have two corks of this description ready. Instead of ordinary corks, caoutchouc stoppers may be used with great advantage, according to SONNENSCHEIN,* who recommends them as being durable, tight-fitting, and non-hygroscopic, f They are now frequently used instead of corks. * Journ. f. prakt. Chem., LXVII, 153. f Cornp. DIBBITS, Zeitschr, /. analyt. Chem., xv, 157. 174.] COMBUSTION WITH CUPRIC OXIDE. 17 8. A MIXING MORTAR. A porcelain mortar of greater width than depth and provided with a lip. It should not be glazed inside, and it should be free from indentations and cracks. Before use it should be cleaned by washing with water; it is then set aside in a warm place to dry until required. 9. A SUCTION TUBE. The best form for this is shown in Fig. 16. The aperture a is closed by a cork into the perforation of which the tube b of the potash bulb is fitted. A caoutchouc tube, however, may FIG. 16. also be made to serve well.* 10. A GLASS TUBE, open at both ends and about 60 cm. long, and wide enough to be pushed over the tail of the combustion tube ; it is supported in place by a filter-stand, f 11. A SHEET OF GLAZED PAPER with cut edges. 12. CUPRIC OXIDE. A Hessian crucible of about 100 c.c. capacity is nearly filled with copper oxide prepared as directed in 66, 1 ; the crucible is covered with a well-fitting overlapping lid and heated to dull redness with charcoal, or in a suitable gas- furnace; 1 it is then allowed to cool, so that by the time the cupric oxide is required for use, the hand can only just bear contact with it. * An aspirator is nowadays generally used instead of the mouth, which was formerly used for effecting suction. t This tube is now generally replaced by a system of tubes containing soda-lime and calcium chloride. t If the copper scales employed in making the copper oxide contain lime, digest them first, for some time, with water and a little nitric acid, then wash and treat them, either immediately or after ignition in a muffie, with chlo- rine-free nitric acid. Copper oxide containing copper chloride is best purified, according to E. ERLENMEYER, by igniting first in a current of moist air and then, when the vapors no longer redden litmus paper, in a current of dry air, by which treatment all the nitrogen oxides present are also removed. Copper oxide perfectly free from injurious impurities may also be obtained by dissolving galvanically precipitated copper in perfectly pure nitric acid, evaporating, and igniting the cupric nitrate (C. REISCHAUER, Zeitschr. f. analyt. Chem., n, 197. J. LOWE, ibid., ix, 217). 18 ORGANIC ANALYSIS. [ 174. 13. AN AIR-PUMP WITH CALCIUM-CHLORIDE TUBE. See Fig. 24. For the manner of performing an organic analysis without this apparatus, see 176, 178, and 179. 14. HOT SAND. This is taken either from the sand-bath, or it must be specially heated for the purpose. Its temperature should be above 100, but not so high as to singe paper. 15. A WOODEN TROUGH for the sand. See Fig. 24. 16. A COMBUSTION FURNACE. Some time ago the only one used was LIEBIG'S, in which char- coal is the fuel. Recently gas combustion furnaces have been introduced into most laboratories, because they are more cleanly and convenient. a. LIEBIG'S combustion furnace is of sheet iron. It has the form of a long box, open at the top and behind. It serves to heat the combustion tube with red-hot charcoal. Fig. 17 represents the furnace as seen from the top. It is from 50 to 60 cm. long, and from 7 to 8 deep; the bottom, which, by cutting small slits in the sheet iron, is converted into a grating, has a width of about 7 cm. The side walls are inclined slightly outward, so that at the top they stand about 12 cm. apart. A series of upright pieces of strong sheet iron, having the form shown in D, Fig. 18, and riveted on the bottom of the furnace at intervals of about 5 cm., serves to support the combustion tube. They must be of exactly corresponding height with the round aperture in the front piece of the furnace (Fig. 18, A). w FIG. 18. FIG. 19. This aperture must be sufficiently large to admit the com- bustion tube easily. Of the two screens used, one has the form shown in Fig. 19, the other is a single plate precisely like the end piece of the furnace (Fig. 18). The openings cut into the screens must be sufficiently large to receive the combustion tube without 174.] COMBUSTION WITH CUPRIC OXIDE. 19 difficulty. The furnace is placed upon two bricks resting upon a flat surface, and is slightly raised at the farther end by insert- ing a piece of wood between the supports (see Fig. 26). The apertures of the grating at the anterior end of the furnace must not be blocked up by the supporting bricks. In cases where the combustion tubes are of good quality, the furnace may be raised by introducing a little iron rod between the furnace and the sup- porting brick. Placing the tube in a gutter of Russia sheet iron tends greatly to preserve it, but contact of the glass and iron must be prevented by an intervening layer of asbestos. A charcoal furnace with a regulator for the air access has been recommended by GAWALOWSKI.* b. Gas combustion furnaces of the most varied descriptions have been proposed.! Fig. 20 represents one form that is fre- quently employed, t The apparatus consists of two parts, the system of burners and the stand. The former consists of 15 to 25 BUNSEN burners, each of which is provided with a separate cock and a ring for regulating the air access. The burners are screwed on to a tube 48 to 78 cm. long and 25 mm. wide, connected with the gas-supply tube. The orifices of the burner tubes are flattened to form slits. The iron stand shown in Fig. 20 is that *Zeitschr. f. analyt. Chem., xiv, 309. f Compare the papers by v. BAUMHAUER (Annal. d. Chem. u. Pharm., xc, 21). HOFMANN (ibid., xc, 235). SONNENSCHEIN (Journ. f. prakt. Chem., LV, 478). MAGNUS (ibid., LX, 32). WETHERILL (LiEBio-Kopp's Jahresb., 1855, 828). PEBAL (Annal. d. Chem. u. Pharm., xcv, 24) J. LEHMANN (ibid., en, 180). v. BABO (Ber. uber die Verhandl. der Gesellsch. /. Beforderung der Naturw. zu Freiburg in Br., 1857, Nos. 22 and 23). HEINTZ (Pogg. Annal., cm, 142). G. J. MULDER (Scheik. Verhandl. en Onderzaek, n decl. 2, stuk. Ondez. 289). A. W. HOFMANN (Annal. d. Chem. u. Pharm., cvii, 37). BERTHELOT (Compt. Rend., XLVIII, 469). ERLEN- MEYER (Annal. d. Chem. u. Pharm., cxxxix, 17; and Zeitschr. f. analyt. Chem., vi. 110). LEOPOLDER (Zeitschr. f. analyt Chem., vm, 198). DONNY (ibid., cxvin, 200). GLASER (Annal. d. Chem. u. Pharm., Suppl., vii, 213; also Zeitschr. f. analyt. Chem., ix, 932). + Comp. also the Preisverzeichniss der BUNSEN'SCHEN Apparate vom Universitdtsmechanikus DESAGA in Heidelberg, 1873, p. 36. 20 ORGANIC ANALYSIS. [ 174. devised by v. BABO and improved by ERLENMEYER.* The flames enter through a slit-shaped opening, surround the combustion tube, and escape above also through a slit. The combustion tube is laid upon magnesia or asbestos in a sheet-iron trough, or in a fire- FIG. 20. clay trough in which LOWE recommends a number of small per- forations to be made. LOWE f also covers the tube with a fire- clay channel, so that the glass tube is completely surrounded by fire-clay. The heat is confined and reverberated by the fire-clay tiles, which, placed on each side, form a dome. The tiles on one side are immovably fastened; those on the other side are movable. The tube on which the burners are screwed, and also the channels in which the fire-clay tiles are supported, may be raised or lowered to enable the distance between the combustion tube and the burners to be regulated. HEINTZ'S apparatus has also been highly lauded. It is illustrated in HUGERSHOFF'S FIG. 21. price-list (Leipzig, 1874, p. 55). I have had no personal experience with it. A. W. HOFMANN'S J furnace, much used in England, * Annal. d. Chem. u. Pharm., cxxxix. 70; Zeitschr f. analyt Chem., vi, 110. f Zeitschr. f. analyt. Chem., ix, 222. J Annal. cL Chem. u. Pharm., evil, 39. 174.] COMBUSTION WITH CUPRIC OXIDE. 21 differs materially from the above. It yields excellent service, although with a greater gas consumption. Its arrangement is shown in Fig. 21 and Fig. 22. FIG. 22. Into the brass tube a, about 90 cm. long and 2 cm. wide , Fig. 21, connected with the gas-supply tube, there are screwed 30 to 34 tubes, b, each provided with an air-regulator, stop-cock, and carry- ing a cross-tube, c c. Each of these crossrtubes bears 5 ordinary fish-tail burners, each consuming 4 cubic feet of gas per hour, and over which a corresponding number of clay burners may be placed. These clay burners, d d, are simply well-burnt, hollow cylinders of pipe-clay or similar material, 8-5 cm. high, 2 cm. external, and 1 cm. internal diameter. They are closed at the top, and the side walls are perforated with numerous small pin-holes. A cylinder of the above dimensions has 10 rows of 15 perforations each. The middle row of burners are only 4- 5 cm. high and have 70 to 80 per- forations; it serves as a support for the combustion tube, /, which is thus bedded in a clay channel. Stability is imparted to the entire system of burners by a stout iron frame, g g, resting on two cast-iron feet, h h, screwed into an iron plate, i. The iron frame, g g, is in addition provided with a groove in which the clay side plates, k k, are movable. These plates are of the same height as the burners, but as they are supported on the frame, they overtop the burners by about 1 5 cm. The side plates, I, are likewise of clay, and are movable. The whole apparatus is figured in Fig. 22. In the fore part of the apparatus to which the potash bulbs are 22 ORGANIC ANALYSIS. [ 174. affixed, the side and top plates are left off in order to give a view of the clay burners in position. During the combustion all the burners are to be inclosed, as shown at the other end of the apparatus. The most suitable dis- tance between the individual burners is 3 mm. As it is important, in order to maintain a constant temperature, that the distance between the several burner-arms be perfectly equal, their distance from each other is more especially assured by corresponding holes in the iron frame, g g, Fig. 21. In conclusion I also mention here the gas furnace constructed on DONNY'S principle by C. GLASER in conjunction with KEKULE. This furnace, like HOFMANN'S, saves the combustion tubes, but consumes even more gas than ERLENMEYER'S. Its characteristic feature is that the combustion tube is borne by a number of iron supports pierced with holes covered by perforated clay covers. The hot combustion gases which first heat the iron supports of the tube are compelled to pass through both systems of perfora- tions, hence the tube is heated on all sides, even from above. Since the iron supports are movable, the heat may be lessened somewhat by separating the supports slightly. The furnace is made by C. GERHARDT, of Bonn. As this furnace is particularly serviceable in analyses requiring a current of oxygen, the detailed description will be given in 178. II. PERFORMANCE OF THE ANALYTICAL PROCESS. a. Weigh first the potash apparatus, then the calcium-chloride tube. Introduce about 0-35-0-6 grm. of the substance under examination (more or less, according as it is rich or poor in oxygen) into the weighing tube,* which must be no longer warm, and weigh the latter accurately with its contents after inserting the stopper. The weight of the empty tube with its stopper being approximately known, it is easy to take the right quantity of substance required for the analysis. Close the tube then with a smooth cork. * Care must be taken that no particles of the substance adhere to the sides of the tube, at least not at the top. 174.] COMBUSTION WITH CUPRIC OXIDE. 23 b. The filling of the combustion tube is now effected as follows : Spread the sheet of glazed paper on a clean table and place on it the still rather warm mortar. Rinse both the mortar and the still warm combustion tube with a little of the warm cupric oxide, which is then emptied out (and put by), and the tube filled up to the mark b, Fig. 23, with cupric oxide directly from the FIG. 23. crucible, using either the tube itself as a shovel or by aid of a small warm copper funnel and a German-diver spoon. A portion of the cupric oxide is now transferred from the tube to the mortar, and the substance to be analyzed added, taking care to thoroughly shake out the last particles from the small tube in which it was weighed by tapping it, then re-stopper the tube and lay it aside carefully, as it must be re- weighed. Now mix the substances in the mortar intimately by diligent trituration, avoiding too strong pressure, however; then add almost all the cupric oxide in the tube, leaving a layer of only about 3 to 4 cm., and mix again inti- mately. Now remove the pestle from the mortar after freeing it from particles of the mixture by tapping it, and transfer the mix- ture to the tube, using the latter as a scoop. The remainder in the mortar is poured out on a piece of smooth cardboard and likewise transferred to the tube. Then rinse the mortar out with a new small portion of cupric oxide which in turn is brought into the tube until the latter is filled up about to the mark a, Fig. 23, and finally fill with pure cupric oxide to within 3 or 4 cm. of the mouth, in which then place a plug of copper turnings oxidized by ignition in air, and lastly stopper temporarily with a cork. The filling of the tube is effected over the glazed paper so that should any of the mixture be spilled it may be readily recovered.* * In G. J. MULDER'S laboratory I saw the filling: accomplished differently, yet not less satisfactorily. The mixture, prepared in a small copper mortar, was transferred by means of a smooth, warm, copper funnel into the com- bustion tube, which was held upright in a retort holder, the operation being performed easily and rapidly. The anterior part of the tube is filled with 24 ORGANIC ANALYSIS. [ 174, c. A few gentle taps on the table will generally suffice to shake together the contents of the tube, so as to completely clear the tail from oxide of copper and leave a free passage for the evolved gas from end to end, as shown in the cut, Fig. 24. Should this FIG. 24. fail, as will occasionally happen, owing to malformation of the tail, the object in view may be attained by striking the mouth of the tube several times against the side of a table. Now place the tube in the wooden trough D, Fig. 24, and connect it by means of a cork with the calcium-chloride tube B, which is in turn connected with an air-pump. Next completely cover the tube throughout its length with hot sand, after which pump out the air slowly (if the pumping is quickly and incautiously done some of the mixture will be drawn over into the calcium-chloride tube) ; now open the cock a and allow a fresh supply of air (dried by its passage through the calcium-chloride tube) to enter, and again pump put as before, a layer of at least 2 dm. of granular cupric oxide well packed, and the cany- ing away of any particles by gas was prevented by a plug of copper turnings. Comp. Zeitschr. /. analyt. Chem., i, 7. 174.] COMBUSTION WITH CUPRIC OXIDE. 25 repeating the process some 10 or 12 times, thus insuring perfect removal of any moisture which the cupric oxide may have taken up during the operation of mixing. If a water air-pump is used insert between it and the calcium-chloride tube B a fork-shaped tube, Fig. 25, connecting a with the calcium-chloride tube and the end b with the pump, while c is closed by means of a short rubber tube provided with a a pinch-cock. After each exhaustion admit air FIG. 25. through c. d. Connect the end b (Fig. 26) of the weighed calcium-chloride tube with the combustion tube by means of a dried perforated cork, lay the furnace upon its supports, with a slight inclination forward, and place the combustion tube hi it; connect the end of the calcium-chloride tube, by means of a vulcanized india- PIG. 26. rubber tube, with the end ra of the potash apparatus, and, if neces- sary, secure the connection with silk cord, taking care to press the joint of the two thumbs close together whilst tightening the cords, since otherwise , should one of the cords happen to give way, the whole apparatus might be broken. Rest the potash appara- tus upon a folded piece of cloth. Fig. 26 shows the whole arrange- ment. e. To ascertain whether the joinings of the apparatus fit air- tight, put a piece of wood about the thickness of a finger (s), or a cork, or other body of the kind, under the bulb r of the potash apparatus, so as to raise that bulb slightly (see Fig. 26). Heat the bulb ra, by holding a piece of red-hot charcoal near it, until a certain amount of air is driven out of the apparatus; then remove 26 OKGANIC ANALYSIS. [ 174. the piece of wood (s), and allow the bulb m to cool. The solution of potassa will now rise into the bulb m,. filling it more or less; if the liquid in m preserves, for the space of a few minutes, the same level which it has assumed after the perfect cooling of the bulb, the joinings may be considered perfect; should the fluid, on the other hand, gradually regain its original level in both limbs of the apparatus, this is a positive proof that the joinings are not air- tight. (The few minutes which elapse between the two observa- tions may be advantageously employed in reweighing the little tube in which the substance intended for analysis was originally weighed.) /. Let the mouth of the combustion tube project 3 to 4 cm. beyond the furnaee; suspend the single screen over the anterior end of the furnace, as a protection to the cork; put the double screen over the combustion tube about two inches farther on (see Fig. 26), replace the little piece of wood (s) under r, and put small pieces of red-hot charcoal first under that portion of the tube which is separated by the screen; surround this portion gradually altogether with ignited charcoal, and let it get red-hot; * then shift the screen an inch farther back, surround the newly exposed por- tion of the tube also with ignited charcoal, and let it get red-hot; and proceed in this manner slowly and gradually extending the application of heat to the tail of the tube, taking care to wait always until the last exposed portion is red-hot before shifting the screen, and also to maintain the whole of the exposed portion of the tube before the screen in a state of ignition, and the projecting part of it so hot that the fingers can hardly bear the shortest con- tact with it. The whole process requires generally from f to 1 hour. It is quite superfluous, and even injudicious, to fan the charcoal constantly ; this should be done however when the process is draw- ing to an end, as we shall immediately have occasion to notice. The liquid in the potash bulbs is gradually displaced from the bulb m upon the application of heat to the anterior portion of the combustion tube, owing simply to the expansion of the heated air. * In using a gas furnace the individual burners are of course lit one after another. 174.] COMBUSTION WITH CUPRIC OXIDE. 27 As soon as the heat reaches the cupric oxide, which was used to rinse out the mortar, a little carbonic acid and aqueous vapor are evolved which drive out the air in the apparatus and force it through the potash bulbs in the form of large bubbles. The evolution of gas proceeds with greater briskness, however, when the heat begins to reach the actual mixture; the first bubbles are only partly absorbed, as the carbonic acid contains still an admixture of air; but those which follow are so completely absorbed by the potassa that only a solitary air-bubble escapes from time to time through the liquid. The process should be conducted in a manner to make the gas-bubbles follow each other at intervals of from J to 1 second. Fig. 27 shows the proper posi- a tion of the potash bulbs during the opera- tion. It will be seen from this that an air- bubble entering through m passes first into the bulb 6, thence to c, from c to d, and passing over the solution in the latter escapes finally into the bulb /, through the fluid which just covers the mouth of the tube e. g. When the tube is in its whole length surrounded with red- hot charcoal, and the evolution of gas has relaxed, fan the burning charcoal gently with a piece of cardboard. When the evolution of gas has entirely ceased, adjust the position of the potash bulbs to a level, remove the charcoal from the farther end of the tube, and place the screen before the tail. The ensuing cooling of the tube on the one hand, and the absorption of the carbonic acid in the potash bulbs on the other, cause the solution of potassa in the latter to recede, slowly at first, but with increased rapidity from the moment the liquid reaches the bulb m. (If you have taken care to adjust the position of the potash bulbs correctly you need not fear that the contents of the latter will recede to the calcium- chloride tube.) When the bulb m is about half filled with solution of potassa, break off the point of the combustion tube with a pair of pliers or scissors, whereupon the fluid in the potash bulbs will 28 ORGANIC ANALYSIS. [ 174. immediately resume its level. Restore the potash bulbs once more to their original oblique position, and place the glass tube mentioned in 174, 10, over the tail, supporting it against the arm of a filter- stand ; wait a few minutes so that the carbonic acid in the calcium- chloride tube and combustion tube may be absorbed by the potassa, and then slowly draw air through the potash bulbs, by means of a suction tube or rubber tube, until the bubbles last coming through no longer diminish in size. The arrangement of the apparatus at this point is shown in Fig. 28. It is better to employ a small aspi- FIG. 28. rator (Fig. 28) instead of sucking with the mouth. You then know the volume of air that has passed through the apparatus. LIEBIG directed to draw not more air through than a volume equal to the capacity of the calcium-chloride tube, say about 80 to 100 c.c. Nor may more be safely drawn through if the simple LIEBIG'S arrangement be used, as otherwise notable errors would be intro- duced. This terminates the analytical process. Disconnect the potash bulbs and remove the calcium-chloride tube, together with the cork, which must not be charred, from the combustion tube; re- move the cork also from the calcium-chloride tube, and place the latter upright, with the bulb upwards. After the lapse of half an 174.] COMBUSTION WITH CUPRIC OXIDE. 29 hour,* weigh the potash bulbs and the calcium-chloride tube, and then calculate the results obtained. They are generally very satis- factory. As regards the carbon, they are rather somewhat too low (about 0-1 per cent.) than too high. The carbon determination, indeed, is not free from sources of error; but none of these inter- fere materially with the accuracy of the results, and the deficiency arising from the one is partially balanced by the excess arising from the other. In the first place, the air which passes through the solution of potassa during the combustion, and finally during the process of aspiration, carries away with it a minute amount of moisture. The loss arising from this cause is increased if the evolution of gas proceeds very briskly, since this tends to heat the solution of potassa ; and also if nitrogen or oxygen passes through the potash bulbs (compare 178 and 186). This may be reme- died, however, by fixing to the exit end of the latter a tube filled with small fragments of potassa, or one-half filled with soda-lime and the other half with calcium chloride, the end containing soda- lime being connected with the potash apparatus, which is always weighed along with the appended tube. In the second place, traces of carbonic acid from the atmosphere are carried into the potash apparatus during the final aspiration ; this may be avoided by connecting the tail of the combustion tube during the aspiration with a tube filled with potassa crushed to small lumps, by means of a flexible tube. In the third place, it may happen in the analy- sis of substances containing a considerable proportion of water or hydrogen, that the carbonic acid is not completely dried in passing through the calcium chloride; this may be avoided by using an apparatus filled with sulphuric acid instead of the calcium-chloride tube, or, in conjunction with this latter, a U-tube filled with frag- ments of pumice-stone and H 2 SO 4 ; but usually a calcium-chloride tube, if filled for about 12 cm. of its length with not too coarsely * LOWE considers half an hour's cooling insufficient, at least when using his concentrated potash in the bulbs. According to him the weight of the apparatus becomes constant only after 2 to 3 hours. The open ends of the apparatus are kept closed during the cooling (but not while weighing) by means of short pieces of rubber tubing and pieces of glass rod. 30 ORGANIC ANALYSIS. [ 175. granulated calcium chloride, will suffice, provided the combustion is not pushed too rapidly. Finally, if the mixture was not suffi- ciently intimate, traces of carbon will remain unconsumed. It is therefore better to complete the combustion in oxygen gas. The hydrogen is usually too high averaging from 0-1 to 0-15 per cent. ; it is due chiefly to the fact that the final air drawn into the apparatus conveys a little moisture into the calcium-chloride tube; this may, however, be easily avoided by connecting a tube filled with potassa with the tail of the combustion before applying suction. I would particularly remark, however, that in most cases it is altogether unnecessary to make the operation still more com- plicated in order to avoid these sources of error, more particularly since their influence on the results is perfectly well known from the numerous experiments made. 2. BUNSEN'S MODIFICATION OF LIEBIG'S METHOD.* 175. In this modification (which is to be preferred when analyzing very hygroscopic substances, or such as may not be mixed with warm cupric oxide without danger) the cupric oxide is allowed to cool in a closed tube or stoppered flask, and the mixing of the substance with the cupric oxide is effected in the combustion tube itself, and not in a mortar, thus effectually guarding the cupric oxide from taking up any atmospheric moisture and rendering the exhaustion of the tube unnecessary. The dried substance is weighed in a tube of thin glass 20 cm. long and about 7 mm. diame- ter, one end being sealed and the other end closed by a smooth cork during the operation of weighing. Besides this tube, BUNSEN'S method requires a combustion tube, potash bulbs, calcium-chloride tube, rubber tubes, suction tube, perforated cork, combustion furnace, and cupric oxide (see 174). In addition to these there is required a wide glass tube * KOLBB, Handworterbuch der Chemie, Supplements, 186. A. STRECKER, ibid., 2d ed., i, 852. 175.] BUNSEN'S MODIFICATION OF LIEBIG'S METHOD. 31 sealed at one end, or a FLASK (Fig. 29), in which the freshly-ignited cupric oxide is allowed to cool, and from which it is trans- ferred to the combustion tube, secure from the possible absorption of moisture from the air. The freshly-ignited and still quite hot cupric oxide is transferred direct from the crucible to this filling tube, or flask, which is then closed air-tight with a cork. It saves time to fill in at once a sufficient quantity of oxide to last for several analyses. If the cork fits tight, the contents will remain several days fit for use, even though a portion FlG - 29 - has been taken out, and the tube repeatedly opened. The filling of the combustion tube is effected as follows: The perfectly dry tube is rinsed with some cupric oxide; a layer of the oxide about 13 cm. long is introduced into the posterior end of the combustion tube by inserting the latter into the filling tube or flask containing the cupric oxide (Fig. 30), holding both tubes in an oblique direc- tion and giving a few gentle taps. FIG. 30. Shortly before, the cork-stoppered tube with the substance must be accurately weighed. From the tube containing the sub- stance next remove the cork cautiously, to prevent the slightest loss of substance; insert the open end of the tube as deep as possi- ble into the combustion tube and pour from it the requisite quan- tity of substance by giving it a few turns, pressing the rim all the while gently against the upper side of the combustion tube, to prevent its coming into contact with the powder already poured out; the two tubes are, in this manipulation, held slightly inclined, as in Fig. 31. When a sufficient quantity of the substance has been thus transferred from the weighing to the combustion tube, the latter is restored to the horizontal position, which gives to the former a gentle inclination with the closed end downwards. If the little tube is now slowly withdrawn, with a few turns, the powder near 32 ORGANIC ANALYSIS. [ 175. the border of the opening falls back into it, leaving the opening free for the cork. The tube is then immediately corked and weighed, the combustion tube also being meanwhile kept closed with a cork. The difference between the two weighings shows the quantity of substance transferred from the weighing to the combustion tube. The latter is then again opened and a quantity FIG. 31. of oxide of copper equal to the first transferred to it from the filling tube, or flask, taking care to rinse down with this the parti- cles of the substance still adhering to the sides of the tube. There is now in the hind part of the tube a layer of cupric oxide about 20 cm. long, with the substance in the middle. The next operation is the mixing: this is performed with the aid of the polished brass or iron wire (Fig. 32), having a ring for a handle and a single corkscrew turn at the other, which should taper smoothly to a point. This wire is pushed down to within 3 to 4 cm. of the end and rapidly moved about in all directions until the mixture is complete and uniform, the tube being held nearly horizontal. A few minutes only suffice to effect so perfect a mix- ture that, in the case of pulverulent substances that do not cake, the eye can no longer distinguish the smallest particles. The combustion is then effected as in 174. Cupric oxide is then poured in to within 5 to 6 cm. of the open end and the tube is corked. {Completion of *hc Combustion by Oxygen Gas. To insure the oxidation of the last traces of carbon and to leave the cupric oxide ready for use again, it is advisable to finish the combustion in a 176.] COMBUSTION WITH LEAD CHROMATE, ETC. 33 stream of oxygen. For this purpose the tail of the combustion tube must be made rather stout and long. When the potash-lye recedes, slip tightly over the suitably cooled tail a caoutchouc tube connected with a source of pure and dry 0x3 gen gas, nip off the tip within this tube by help of a pliers, and cautiously let FIG. 32. on the oxygen until the reduced copper is oxidized and the gas traverses the potash bulbs. Then replace the stream of oxygen by one of pure and dry air, to remove all oxygen from the bulbs. To prevent loss by evaporation from the potash-lye, append to the potash bulb the additional absorbing apparatus above mentioned (in 174). The oxygen and purified air are supplied as in the process described in 178.] /?. Difficultly Combustible Non-volatile Bodies e.g., Resinous and Extractive Matters, Coal, etc. If substances of this kind are treated according to 174 and 175, small particles of carbon are likely to escape combustion. In order to avoid this the following methods are employed, which may, of course, be also used for readily combustible substances. 1. COMBUSTION WITH LEAD CHROMATE, OR WITH LEAD CHROMATE AND POTASSIUM BICHROMATE, OR WITH POTASSIUM CHRO- MATE AND CUPRIC OXIDE. 176. This is not only a good method for the analysis of compounds mentioned in 174, but is especially resorted to in the analysis of salts of organic acids with alkalies or alkali-earth metals (as the chromic acid completely displaces carbonic acid from their car- bon atss), and of bodies containing sulphur, chlorine, bromine, or 34 ORGANIC ANALYSIS. [ 176- iodine, and also for the combustion of substances containing car- bon in a difficultly oxidizable form e.g., graphite. Of the apparatus, etc., enumerated in 174, all are required ex- cept cupric oxide, which is here replaced by lead chromate ( 66, 2). A narrow combustion tube may be selected, as lead chromate contains- a much larger amount of available oxygen in an equal volume than cupric oxide. A quantity of the chromate, more than sufficient to fill the combustion tube, is heated in a platinum or porcelain dish over a gas or BERZELIUS lamp, until it begins to turn brown; before filling it into the tube, it is allowed to cool down to 100, and even below. The process is conducted like the one described in 174. It was formerly believed that when using lead chromate the exhaustion of the warmed tube could be omitted, as the lead chro- mate was considered to be not at all hygroscopic, or at least far less so than cupric oxide. Since ERDMANN * has shown, how- ever, that this opinion is unfounded, and that lead chromate takes up moisture just as rapidly as does cupric oxide, there is no longer any ground for neglecting the exhaustion. If the substance analyzed contains a large proportion of sulphur, use a rather long combustion tube (60-70 cm.) and place in front of the mixture 10-20 cm. pure lead chromate, which should be kept only at a dull-red heat during the combustion (CARIUS). One of the principal advantages which lead chromate has over cupric oxide as an oxidizing agent being its property of fusing at a high heat, the temperature must, in the last stage of the process of combustion, be raised (by fanning the charcoal, etc.) sufficiently high to completely fuse the contents of the tube as far as the substance extends. To heat the anterior end of the tube to the same degree of intensity would be injudicious, since the lead chromate in that part would thereby lose all porosity, and thus also the power of effecting the combustion of the products of decomposition which may have escaped oxidation in the other parts of the tube. * Journ. f. prakt. Chem., LXXXI, 180. 176.] COMBUSTION WITH CUPRIC OXIDE, ETC. 35 As the lead chromate, even in powder, is, on account of its. density, by no means all that could be desired in this latter respect, it is preferable, instead of filling with lead chromate, to fill the anterior part of the tube with coarsely pulverized strongly ignited cupric oxide, or with copper turnings which have been superficially oxidized by ignition in a muffle or in a crucible with access of air. In the case of very difficultly combustible substances e.g., graphite it is desirable that the mass should not only readily cake, but also, in the last stage of the process, give out a little more oxygen than is given out by lead chromate. It is therefore advisable in such cases to add to the latter one-tenth of its weight of fused and powdered potassium dichromate. With the aid of this addition, complete oxidation of even very difficultly com- bustible bodies may be effected (LIEBIG).* Good results may also be obtained with cupric oxide and potas- sium dichromate. GINTL f recommends the following process, which is very similar to that of BUNSEX : Introduce into the com- bustion tube, first, a layer of coarse cupric oxide 6 cm. long, then 3 cm. of potassium dichromate (which has first been fused, then powdered, and preserved from contact with air), then the sub- stance, and finally another layer of 3 cm. of cupric oxide. Mix the substances by aid of the wire, taking care, however, that 3 cm. of cupric oxide remain at the end of the tube perfectly free from, chromate. Now fill up the tube fully with cupric oxide as usual and proceed with the combustion. As the potassa-lye towards the end takes up oxygen, a little more air, free from carbonic acid and moisture, must be drawn through the apparatus at the close of the operation. Further, the exit of the potash bulbs must be connected with a tube filled two-thirds with soda-lime and one- third with calcium chloride, and which is weighed with the potash bulbs. * Experiments regarding this excellent method have been published by MAYER (Annal. d. Chem. u. Pharm., xcv, 204). f Zeitschr. /. analyt. Chem. vii, 302. 36 ORGANIC ANALYSIS. [ 177. 2. COMBUSTION WITH CUPRIC OXIDE AND POTASSIUM CHLORATE OR PERCHLORATE. 177. This method requires all the apparatus enumerated in 174 or 175, and in addition, a small quantity of potassium chlorate which is freed from water by heating it until it fuses, and then, after it has cooled, reducing it to a coarse powder and preserving it in a warm place until required for use. The process is the same as in 174 or 175, excepting that the layer of cupric oxide in the posterior end of the tube is somewhat longer (5 cm.), and is mixed by agitation with about one-eighth (3 to 4 grm.) of potassium chlorate. After this introduce 2 cm. of pure cupric oxide and then the substance to be analyzed. When, in heating the tube, the part of the tube containing the potassium chlorate is approached, the greatest caution must be exercised in applying the hot charcoal or in turning on the gas at the stop-cocks, so that the potassium chlorate will be only very gradually decom- posed; if this caution be neglected, a violent rush of gas may drive out some of the potassa solution and entirely spoil the analysis. The oxygen evolved from the potassium chlorate drives out all -the carbonic acid in the tube, effects the combustion of all tmconsumed particles of carbon, arid oxidizes the reduced copper. Oxygen gas cannot therefore pass through potash bulbs until all oxidizable substances in the tube have been oxidized. If, towards the last, much gas passes through the potash bulbs tinabsorbed, it is unnecessary to break off the point and draw air through the tube, since the latter will contain only oxygen, and neither carbonic acid nor moisture. Air dried and free from car- Iconic acid must, however, be drawn through the calcium-chloride tube and potash bulbs, otherwise these would be weighed full of oxygen. The decomposition of potassium chlorate is somewhat violent, as is well known. The perchlorate obtained by heating the chlo- rate decomposes much more quietly, however, and may be em- ployed instead of the chlorate, as first recommended by BUNSEN, 178.] COMBUSTION WITH CUPRIC OXIDE AND OXYGEN. 37 The perchlorate, while still hot and in a fused state, is introduced into the posterior end of the tube, followed by a loose plug of re- cently ignited asbestos ; the tube is then filled as usual. If BUN- SEX'S method of mixing, as given in 175, is followed, a plug of asbestos must always be used, even when using potassium chlorate, so that on mixing the substance may not come into immediate contact with the salt yielding the oxygen. As the dry oxygen passing through the potassa-lye carries off some moisture from the latter, the exit tube of the potash bulbs should be connected with a small tube, filled two-thirds with soda- lime and one-third with calcium chloride; the connection may be- made by means of a cork or a short piece of rubber tubing, and should be weighed with the bulbs. The increase of weight of the? bulbs and this tube indicate the carbonic acid absorbed. 3. COMBUSTION* WITH CUPRIC OXIDE AND OXYGEN. 178. Many chemists effect combustion with cupric oxide in a cur- rent of oxygen supplied by a gasometer. HESS, DUMAS and STAS, ERDMANN and MARCHAND, PIRIA, STRECKER, WOHLER, LOWE, GLASER, and others have proposed methods based upon this principle, which they employ not only for the analysis of diffi- cultly combustible bodies, but also to effect the determination of the carbon and hydrogen in organic substances in general. These processes, besides the others, have been used in my laboratory for years. As these methods require, besides a gasometer filled with oxygen, arrangements for perfectly drying the oxygen and free- ing it from carbonic acid, it may be readily seen that the appara- tus required is far more complicated than is that used ir the simple LIEBIG or BUXSEN method. They are to be recommended espe- cially only when a large number of ultimate analyses are to be made, as well as in the analysis of substances which cannot be reduced to powder, and which consequently cannot be intimately mixed with the cupric oxide. For heating the combustion tube, HESS, as well as ERDMAXXT 38 ORGANIC ANALYSIS. [ 178. and MARCHAND, used alcohol, but since gas has come into general use for heating purposes, the older forms of furnaces have been entirely superseded. The heating may also be conveniently effected by means of the charcoal furnace shown in Fig. 17, p. 18, but in this case the furnace should be 70 to 80 cm. long. The various methods of heating have no influence on the operation itself or on the accuracy of the results, provided the heating can be regulated at will and increased to the intensity necessary. The combustion with the aid of oxygen can be carried out in two ways, according as the substance is mixed with cupric oxide FIG. 33. or not. The latter method, in which the substance is placed in a boat inserted into the combustion tube, is the most convenient of all the methods, because in it the combustion tube, after the analysis is finished, is immediately ready for a second analysis. This method is described under a; the other method, that in which the substance is mixed with cupric oxide, is described under 6. 178.] COMBUSTION WITH CUPRIC OXIDE AND OXYGEN. 39 Many forms of apparatus have been devised for drying and puri- fying the air and oxygen which are used in the process. Fig. 33 shows one which is durable and efficient. The bulb tube entering the bottle d is connected with the gasometer by means of a rubber tube. The bottle d is half filled with concentrated sulphuric .acid, through which the gas or air passes in bubbles and enters the bottom of the cylinder c. The lower half of this cylinder is filled with fragments of fused potash, the upper half with calcium chloride, which is separated from the potash by a layer of asbestos. Glass tubes provided with glass stop-cocks enter the top of each cylin- der through rubber stoppers, and are connected by means of strong rubber tubes to the two limbs of the forked tube b, so that a regu- lated current of either air or oxygen can be made to enter the combustion tube through a at will. a. Combustion in a Boat. As in this method it is of especial value to be able to use the same tube for a number of combustions, it is advantageous to use a gas furnace which does not destroy the tube too rapidly, e.g., such a one as GLASER'S improved DONNY'S furnace, or that of HOFMANN. Fig. 34 shows the entire furnace as described by GLASER.* The ends of the furnace consist of two upright iron supports screwed to an iron plate and carrying two parallel iron bands. Directly over the latter two iron rods are fixed into the upright supports. The tiles are provided with grooves at both top and bottom, and may be readily put in place or removed from between the bands and rods, and serve, as seen in Fig. 35, as supports for the iron sections which, when placed together, form the trough for the reception of the combustion tube. One of these sections is shown at the right in Fig. 34. The flames from the gas burners beneath the iron sections heat these first; a part of the hot gases passes through the apertures * AnnaL der Chem. u. Pharm., Supplementband, vil, 213; also Zeitschr. /. analyt. Chem., ix, 392. The apparatus is furnished by MARQUART (G. GERHARDT), of Bonn. 40 ORGANIC ANALYSIS. [ 178. 178-] COAiBLSilON \ViiH CUPR1C OXIDE AND OXYGEN. 41 in the sides of the iron sections, meets over the combustion tube, and then escapes through apertures in the clay covers (Fig. 35). The shape of this cover is such as to concentrate the heat upon the glass tube. By this arrangement the important result is secured in that the tube is heated both from above and the sides, as in the LIEBIG charcoal fumace. (In ordinary combustions the iron sections are not placed close together, but two or three of the sections are separated at the place where the substance mixed with the FlG - 35 - cupric oxide is. In proportion as the combustion proceeds these sections may be readily pushed together by means of a pair of tongs, while the combustion tube, which rests in a channel of wire gauze, is held fast with one hand.) The combustion tube, Fig. 36, is open at both ends. From a 12cm > to b it is filled with oxidized copper turnings and granulated cupric oxide, kept together by plugs made of copper gauze at a and 6.* b c contains an oxidized copper spiral made from rolled copper gauze. (In the analysis of substances containing chlorine, bro- mine, or nitrogen, the spiral is replaced by spiral of metallic copper; see below.) The platinum boat containing the substance is placed at a d; finally, at d e is placed a metallic copper spiral secured to a wire. The combustion tube is laid in a trough of wire gauze placed in the bed of the furnace, first removing three of the iron sections from the place under the platinum boat. The fore part of the tube is now connected with an unweighed calcium-chloride tube by means of a perforated rubber stopper; the other end is * LOWE (Zeitschr. f. analyt. Chem., ix, 218) uses, instead of these, hemi- spheres of rather coarse-meshed platinum gauze the convex surfaces of which are turned toward the absorption apparatus. 42 ORGANIC ANALYSIS. [ 178. connected with the purifying and drying apparatus and gasometers. a and a A of the purifying and drying apparatus contain potassa solution, a being connected by d with the oxygen gasometer, and ttj by di with the air gasometer, b and ^ are two-thirds filled with soda-lime, the upper third being filled with calcium chloride. The U-tube c c, through which oxygen or air passes into the combustion tube, contains calcium chloride; it is connected with the combus- tion tube by means of a glass tube g, provided with a glass stop- cock, and the rubber tube /. In order to obviate all possibility of a diffusion of the gaseous BBga , ^a-s -, combustion-products of the sub- stance into the drying tubes, LOWE * interposes between the calcium-chloride tube of the drying apparatus and the combustion tube a mercury valve, as shown in Fig. 37. Air or oxygen enters FlG - 37 - at a and exits at b. In the point of the tube c is placed a little mercury into which the tube a, drawn out to a fine point, dips. The rubber stopper closing c is covered with a gelatin solution to insure its being air-tight. Before beginning an analysis, first heat the entire tube in the combustion furnace from end to end, while a slow current of dry air is passed through it, and then allow it to cool while the air is still passing through; then remove the posterior copper spiral, insert the platinum boat containing the substance to be analyzed, replace the spiral, place in position the iron disc seen in Fig. 34 (or one of clay LOWE), and connect the fore part of the com- bustion tube with the absorption apparatus. The guard tube (of which the bulb and half the tube are filled with calcium chloride, the other half of the tube being filled with soda-lime) is not weighed ; it is connected with the aspirator B by means of a glass tube pro- vided with a stop-cock. The aspirator consists of a tubulated glass bell-jar standing in a vessel filled with water. The stop- * Zeitschr. f. analyt. Chem., xi, 407. 178.] COMBUSTION WITH CUPRIC OXIDE AND OXYGEN. 43 cock is opened and the water aspirated up into the jar until the difference in level is about 12 to 15 cm. This aspirator, first de- scribed by PIRIA *, serves to counterbalance the pressure in the combustion tube caused by the potash bulbs, and affords, besides, a convenient means of testing the air-tightness of the apparatus. When everything has thus been made ready, close the glass cock of the drying apparatus, open that of the aspirator, and heat the fore part of the combustion tube, and the copper spiral in the hinder end, to low redness; then open the cock of the drying appa- ratus and allow to pass in a very slow current of oxygen gas, which will be entirely absorbed by the copper spiral in d e, and is only intended to prevent the products of combustion from entering the hinder part of the tube. The substance is now heated, according to its volatility, either by heat applied directly or by radiant heat, the temperature being easily regulated by removing or replacing the movable clay covers. When nothing more remains in the platinum boat but carbon, allow the copper spiral in d e to cool, and let a stronger current of oxygen gas pass through, which completes the combustion and converts the reduced copper into cupric oxide again. This oxida- tion is completed by the current of air which is next passed through the apparatus and drives out the oxygen from the latter. Now turn off the gas, close the cock of the aspirator and disconnect the latter from the absorption apparatus, allow this to become perfectly cold, and weigh. The method devised by CLOEZ will be detailed in a special paragraph, 192. b. Combustion of the Substance Mixed with Cupric Oxide. This method requires a tube about 50 cm. long, sealed behind, and drawn out as in Fig. 38. The operations are at first almost exactly the same as in BUN- SEN'S method ( 175). First fill the hind part of the tube with ignited granular cupric oxide from a to b, then fill the space 6 to c with the substance and ignited powdered cupric oxide, mixed * Cimento, v, 321 ; Jahresber. v. KOPP u. WILL, 1857, 573. 44 ORGANIC ANALYSIS. [ 179. by means of the wire; from c to d fill with ignited granular cupric oxide, and finally insert a spiral of ignited copper gauze in the place from d to e. After the weighed absorption apparatus is now connected with the tube, the combustion is effected as usual, beginning at the fore part of the tube and proceeding to the hinder end, but before reaching the mixture of the substance and cupric oxide heat the part a b to low redness to burn any products of distillation that may have passed to the hinder end. When the entire tube is at a low red heat and the evolution of gas has ceased, let the hinder end of the tube cool scmewhat so that the point may be comfortably handled, and slip one end of a rubber tube over it, connecting the other end with the calcium-chloride tube, c c, of the purifying and drying apparatus, Fig. 34. Now break off the point of the combustion tube within the rubber tubing and com- plete the combustion in a slow current of oxygen, displace the oxygen by a slow current of air, allow the apparatus to cool, and then weigh the absorption apparatus. y. Hygroscopic or Volatile Substances, or Bodies undergoing Alteration at 100 (losing Water, for instance). 179. aa. Hygroscopic substances, if burnt by any of the methods above described, are very apt to yield too high a hydrogen content. STEIN * hence recommends the following process for their analysis : The method is that detailed in 178, a. The portion of the tube in which the platinum boat containing the substance is situated is unsupported by any part of the trough or wire gauze,- in order * Zeitschr. f. analyt. Chem., v, 33. 179.] COMBUSTION WITH CUPRIC OXIDE AND OXYGEN. 45 to prevent any heat conduction. The substance is weighed in the boat after being simply dried in the air or in the exsiccator. Heat the tube first, then cool, and test as to ite tightness, after which insert the boat, light one or two burners some 9 to 12 cm. behind the boat, and pass a slow current of dry air over the sub- stance heated in this manner. Usually some water shows itself in the calcium chloride very soon, but it disappears after a tune and does not again appear even if the air-current is heated somewhat more strongly and the bulb of the calcium-chloride tube is cooled by means of ether. Now remove the absorption tube, and while it is being weighed, pass a slow current of cold, dry air through the apparatus. The weight of the potash bulbs with the potash or soda-lime tube will show whether any decomposition of the substance has occurred; the increase of weight gives the water content. On repeating the drying in a current of warm air and again weighing the calcium-chloride tube, the operator ascertains with certainty whether the substance has been completely dried. As soon as this point is reached, begin the combustion of the now thoroughly dried substance. In cases where a higher temperature is required in order to expel chemically combined water, STEIN suspends a piece of copper foil by four thin wires between the burners and the tube at the spot where the boat is, places a thermometer between, and lights a burner under the foil. The temperature in the tube is, of course, somewhat lower than that indicated by the thermometer. After the drying is completed, the foil may be readily removed by loosen- ing the wires. bb. Volatile Substances, or such as Undergo Alteration at 100, e.g., lose Water. If such substances are treated as in 174, a portion of the sub- stance or some water would escape on mixing the substance with the warm cupric oxide and exhausting the tube surrounded by the hot sand; and the results could not possibly be accurate. On the other hand, were the mixing done in the cold, the mixture would absorb moisture. 46 ORGANIC ANALYSIS. [ 180. The process is hence conducted either according to 175 or as directed in 178. Ignited chromate of lead, cooled in a closed tube, may also be employed as oxidizing agent, the mixing being effected in the combus- tion tube by means of a wire. b. FLUID BODIES. a. Volatile Liquids (e.g., ethereal oils, alcohol, etc.). 180. 1. The analysis of organic volatile fluids re- quires the objects enumerated in 174. The ra combustion tube should be somewhat longer than there mentioned; it should have a length of 50 or 60 cm., according as the substance is less or more volatile. If the combustion is not to be effected in a current of oxygen, as in 178, a, the process then requires also a flask to hold the cupric oxide, as in 175. The process requires besides several small glass bulbs for the reception of the liquid to be analyzed. These bulbs are made in the following manner: A glass tube, about 30 cm. long and about 8 mm. wide, is drawn out as shown in Fig. 39, fused off at a, and A expanded into a bulb, as shown in Fig. 40. The bulbed part is then cut off at ft. Another bulb is then made in the same way, and a third and fourth, etc., as long as sufficient length of tube is left to secure the .bulb from being reached by the moisture of the mouth. Two of these bulbs are accurately weighed; they are then filled with the liquid to be analyzed, closed by fusion f and weighed again. The filling is effected by slightly heating the bulb over a lamp and immersing the point into the liquid to be analyzed, part of which will now, upon cooling, enter the bulb. If the fluid is highly volatile, the portion entering the FIG. 40. FIG. 39. 180.] COMBUSTION WITH CUPRIC OXIDE AND OXYGEN. 47 still warm bulb is converted into vapor, which expels the fluid again; but the moment the vapor is recondensed, the bulb fills the more completely. If the liquid is of a less volatile nature, a small portion only will enter at first; in such cases the bulb is heated again, to convert what has entered into vapor, and the point is then again immersed into the fluid, which will now readily enter and fill the bulb. The excess of fluid is ejected from the neck of the little tube by a sudden jerk ; the point of the capillary neck is then sealed in a blowpipe flame. The combustion tube is now prepared for the process by introducing into it from the filling tube or flask ( 175) a layer of cupric oxide occupying about 6 cm. in length. The middle of the neck of one of the bulbs is slightly scratched with a file, the pointed end is quickly broken off, and the bulb and end are dropped into the combustion tube (see Fig. 41). Another layer of cupric oxide, about 6 to 9 cm. long, is then filled in, and the other bulb introduced in the same manner as the first. The tube is finally nearly filled with cupric oxide. A few gentle taps upon the table suffice to clear a free passage for the gases evolved. (It is ad- visable to place in the anterior half of the com- bustion tube small lumps of cupric oxide (comp. 66, 1), or superficially oxidized copper turnings, which will permit the free passage of the gases, even with a narrow channel, or no channel at all; since with a wide channel there is the risk of vapors passing unconsumed through the tube.) The combustion of highly volatile substances demands great care, and requires, certain modifica- tions of the common method. The operation is begun by heating to redness the anterior half of the tube, which is separated from the rest by a screen, or in the case of highly volatile substances, by two screens; ignited charcoal is then placed behind the tube to heat the tail and prevent the condensation of vapor hi that part. A piece of red-hot charcoal is now applied to that part of the tube which is occupied by the first bulb; this 48 ORGANIC ANALYSIS. [ 180. causes the efflux and evaporation of the contents of the latter; the vapor passing over the cupric oxide suffers combustion, and thus the evolution of gas commences, which is then maintained by heating very gradually the first, and after this the second bulb; it is better to conduct the operation too slowly than too quickly. Sudden heating of the bulbs would at once cause such an impetuous rush of gas as to eject the fluid from the potash bulbs. The tube is finally in its entire length surrounded with ignited charcoal and the rest of the operation conducted in the usual way. If the air drawn through the apparatus tastes of the analyzed substance, this is a sure sign that complete combustion has not been effected. 2. In the combustion of liquids of high boiling point and abounding in carbon, e.g., ethereal oils, unconsumed carbon is apt to deposit on the completely reduced copper near the substance; it is therefore advisable to distribute the quantity intended for analysis (about 0-4 grm.) in 3 bulbs, separated from each other in the tube by layers of cupric oxide. 3. In the combustion of less volatile liquids, it is advisable to empty the bulbs of their contents before the combustion begins: this is effected by connecting the filled tube with an exhausting syringe and rarefying the air in the tube by a single pull of the handle; this will suffice to expand the air-bubble in each bulb sufficiently to eject the oily liquid from it, which is then absorbed by the cupric oxide. 4. If, as frequently happens, there is reason to apprehend that the cupric oxide may not suffice to effect the complete combustion of the carbon, the process is terminated in a stream of oxygen gas which, as in 178, b, is finally passed through the red-hot tube shown in Fig. 38, or which is evolved from some potassium chlo- rate or perchlorate placed in the hinder end of the tube (see 177). 5. If it is intended to effect the combustion in the apparatus described in 178, a (using a boat and oxygen gas), place the bulb or bulbs, with their points broken off, in the boat in the tube pre- viously prepared, heat first the anterior end of the tube, then the hinder end, and thus burn the evaporated substance in a slow current of air. Oxygen is then passed through, and finally air. 181.] COMBUSTION WITH CUPRIC OXIDE AND OXYGEN. 49 This method requires great care with very volatile liquids, as, e.g., ether, on account of the explosions which may take place. ft. Non-volatile Liquids (e.g., fatty oils). 181. The combustion of non -volatile liquids is effected either, 1, with lead chromate, or cupric oxide with potassium chlorate or per- chlorate, or completed in a current of oxygen according to 178, b; or, 2, in 'the apparatus described in 178, a. 1. The operation is conducted in general as directed, 176, 177, or 178, b. The substance is weighed in a small tube placed for that purpose in a tin foot (see Fig. 42), and the mixing effected as follows: Introduce into the combustion tube first a layer, about 6 cm. long, of chromate of lead or of cupric oxide, with or without potassium chlorate ac- cording to circumstances; then drop in the small cylinder with the substance and let the oil completely run out into the tube ; make it spread about in various ~ FIG. 42. directions, taking care, however, to leave the upper side (intended for the channel) and the fore part, to the extent of J or J of the length of the tube, entirely clean. Fill the tube now nearly with chromate of lead or cupric oxide which has previously been cooled in the filling tube or flask taking care that the little cylin- der which contained the oil be completely filled with the oxidizing agent. Place the tube in hot sand, which, imparting a high degree of fluidity to the oil, leads to the perfect absorption of the latter by the oxidizing agent, exhaust if necessary, and proceed with the combustion in the usual way. It is advisable to select a tolerably long tube. Chromate of lead is usually to be preferred. If it is used, a very intense heat, sufficiently strong to fuse the contents of the tube, is cautiously applied in the last stage of the pro- cess. Solid fats or waxy substances which, not being reducible to powder, cannot be mixed with the oxidizing agent in the usual 50 ORGANIC ANALYSIS. [ 181. way, are treated like fatty oils. They are fused in a small weighed glass boat, made of a tube divided lengthwise, Fig. 43; when cold, the little boat with its contents is weighed and then dropped into the combustion tube, which has been previously filled to the extent of about 6 cm. with chromate of lead or with cupric oxide (mixed, according to circumstances, with potassium chlorate). The substance is then fused by the application of heat and made to spread about in the tube in the same manner as is done with fatty oils, the rest of the operation also being conducted oxactly as in the latter case. If chromate of lead is employed, it will be found advantageous to add some potassium dichromate ( 176). If cupric oxide be used, finish in a stream of oxygen. 2. If it is intended to effect the combustion of fatty substances or other bodies of the kind in a tray, in a current of oxygen gas, by means of the apparatus described in 178, a, the substance is weighed in a porcelain, copper, or platinum boat, which is in- serted into the tube prepared as usual. The combustion must be conducted with great care. As soon as the cupric oxide in the anterior and the copper roll in the posterior parts of the tube are red-hot, establish a slow current of oxygen and apply a piece of red-hot charcoal or a hot tile to the part occupied by the sub- stance. The volatile products generated by the dry distillation of the substance burn at the expense of the cupric oxide. When it is perceived that the surface layer of the cupric oxide is reduced, the application of heat to the substance is suspended for a time and resumed only after the reduced copper is reoxi- dized in the stream of oxygen gas. Care is finally taken to insure the complete combustion of the carbon remaining in the boat. 182.] MODIFIED APPARATUS. 51 Supplement to A, 174-181.* 182. MODIFIED APPARATUS. 1. For Connecting the Calcium-chloride Tube with the Com- bustion Tube. As is well known, BERZELIUS, unlike LIEBIG, did not connect the combustion tube with the calcium-chloride tube by means of a cork, but drew the fore end out into a long point, which was first bent upwards in an obtuse angle, then downwards, and connected by means of a rubber bandage with a peculiarly shaped calcium- chloride tube, into the bulb of which it projected. This arrange- ment was, however, inconvenient when the tubes were to be charged at the mouth. A similar arrangement was later recommended by LOWE f for tubes open behind. He draws out the anterior end to a not too thin or narrow point, which is slightly bent near its orifice, and fixes it by means of a perforated rubber stopper into the side tubulure of a U-shaped calcium-chloride tube bulb. LOWE extols this form of joint because it does not loosen as the tube expands, as is usually the case, but on the contrary it becomes tighter. AL. MITSCHERLICH % also draws out the front end of the combustion tube straight and fixes the point by means of a short section of rubber tubing into the water-absorption apparatus (a tube filled with phosphoric anhydride). 2. For the Absorption of Water. As is well known, calcium chloride is not capable of completely drying moist gases, but is surpassed in this respect, according to the author's experiments, by concentrated sulphuric acid; this hi turn is surpassed, although only to a very slight extent, || by * The methods of estimating oxygen directly, and detailed under this head in the previous edition, are here discussed in 192. f Zeitschr. f. analyt. Chem., ix, 218. J Elementaranal. durch Quecksilberoxyd, Berlin, Mittler u. Sohn, 1875. Zeitschr. f. analyt. Chem., iv, 177. || Compare DIBBITS, ibid., xv, 154. 52 ORGANIC ANALYSIS. [ 182. phosphoric anhydride. Many chemists hence replace the calcium- chloride tube by one containing sulphuric acid. For this purpose email U-tubes having the forms shown in Figs. 13, 14, and 15 answer. The tubes are filled with pieces of ignited pumice-stone or glass moistened with pure concentrated sulphuric acid. SCHROT- TER * recommends the form shown in Fig. 44. Both tubes contain pumice-stone moistened with sulphuric acid, and a small quantity of the acid is also introduced into the bulb. I would point out that when sulphuric acid is used for absorbing the water generated during the combustion, it must also be used for drying FIG. 44. the oxygen and air passed through the apparatus, because if air dried by calcium chloride is passed into the tube and exits through sulphuric acid, or vice versa, small errors will result (compare the author's experiments, loc. tit., 182; also DIE- BITS, loc. tit., 145). That sulphuric acid is likely to retain carbonic acid, as HLASIWETZ f believes to have found, is not to be feared (compare the author's experminets, loc. tit., 183). Tubes filled with phosphoric anhydride are also very well adapted for absorbing moisture, and have been recently strongly recommended by AL. MITSCHERLK& (loc. tit.). The tube used by him has the form shown in Fig. 45. It has a bore of 15 mm. and a length of 200 mm. The phosphoric anhydride is confined between two asbestos plugs and must not contain the slightest trace of admixed phosphorus. If, during the analysis, a notable quan- tity of water has been taken up, and if there is any possibility that chlorine, hydrochloric acid, carbonic acid, etc., may have been absorbed, these may be expelled by finally heating the tube only to such a point that moist filter-paper hisses when applied to it. It will then retain only the water. * Zeitschr. /. analyt. Chem., vm, 199. f Chem. CentralbL, 1856, 517. 182.] MODIFIED APPARATUS. 53 The wide end of the phosphoric-anhydride tube is, as above mentioned, connected with the drawn-out end of the combustion tube. 3. Far the Absorption of Carbonic Add. a. LIEBIG'S potash bulbs have been variously modified. GEISS- LER'S apparatus, Fig. 46, stands without support, and affords greater certainty of action in that the gas passes thrice through the potassa solution and renders ejection of the latter almost impossible. The filling and emptying of the apparatus is very simple. In filling, a is dipped into the potassa solution and suction applied to b; in emptying, simply blow into 6. One ob- jection to the GEISSLER apparatus is that the potassa solution in the three bulbs does not communicate; hence potassium bicar- bonate is very prone to form in the first bulb and stop the tube. On this account the GEISSLER apparatus requires refilling much more frequently than LIEBIG'S (J. LOWE *). FIG. 46. FIG. 47. Fig. 47 shows E. MITSCHERLICH'S apparatus slightly modified by AL. MITSCHERLICH. a b is first filled with pieces of potassa, and b c then filled with phosphoric anhydride, with a plug of asbestos at b and c. c is now pushed over a short piece of rubber tubing slipped over a small glass tube, and the apparatus then filled with potassa solution to such a height that, when the apparatus is held in a slanting position, the gas passing through will force some of the solution into the top bulb. DE KoxiNCKf modifies E. MITSCHERLICH'S apparatus by bending the tubes connecting the bulbs and letting them enter the bulbs laterally. * Zeitschr. f. analyt. Chem., vii, 224. f Ibid., ix, 481. 54 ORGANIC ANALYSIS. [ 182. MODIFIED APPARATUS FOR THE ABSORPTION OF CARBONIC ACID, b. G. J. MULDER * has replaced the potash bulbs altogether by a totally different absorption apparatus, in which soda-lime is used instead of potassa solution. The calcium-chloride tube is imme- diately connected with the sys- tem of U-tubes, Fig. 48; a con- tains small pieces of glass, 6 to 10 drops concentrated sulphuric acid, and at the top asbestos plugs, b is filled to J with granu- lated soda-lime (say 20 grm.), the remaining -J (in the 2d limb) contains calcium chloride (say 3 grm.). Lastly, c is filled with lumps of potassa. a and b are FIG. 48. weighed together, c serves as a guard to b } and is not weighed. The sulphuric-acid tube serves to show the rate of the evolution of gas; it contains enough sul- phuric acid when the lower part is just stopped up. If the process goes on properly, the weight of the tube does not increase more than 0.001 grm.; generally the increment is unweighable. If the tube is closed with caoutchouc caps after use, it may be used over and over again. The sulphuric acid possesses the advantage over other fluids that it indicates whether the combustion was complete or not; for in the first case it remains colorless, in the second it be- comes brown from the escaping hydrocarbons, and then the results cannot be expected to be perfectly accurate. From experiments made by me, it would appear that the in- crease in the sulphuric-acid tube is due to the fact that the air dried only by passage through calcium chloride still yields a trace of moisture to sulphuric acid. The sulphuric-acid tube may be quite readily dispensed with, and all the advantages it offers may be obtained by using SCHROTTER'S sulphuric-acid tube, Fig. 44, for absorbing moisture. The absorption of the carbonic acid by * Zeitschr. /. analyt. Chem., i, 2. $ 182.J MODIFIED APPARATUS. 55 the soda-lime tube is as rapid as it is complete; even when a stream of carbonic acid is passing, with ten times the rapidity usual in organic analysis, no trace of the acid makes its escape. The absorption of the carbonic acid is attended with warming of the soda-lime; if any water evaporates from the soda-lime, it is re- tained by the calcium chloride in the second limb. The corks of the absorption tubes are, like the others, coated with sealing-wax. A filled soda-lime tube weighs about 40 grm. The first time it is used alone; the second time the same tube is used, but as a pre- cautionary measure a second similarly rilled and separately weighed tube is placed in front of it. The second tube rarely increases in weight, and unless it does, the first tube can be used a third tune, but of course in connection with the second. If the second tube has gained in the third operation, the first tube is rejected at the fourth operation, and the second is now used alone, etc. If after the combustion a stream of oxygen is transmitted through the combustion tube, the tubes are of course at the end full of oxygen. If, then, care be taken that the tubes are full of oxygen before weighing, the trouble of the final transmission of air may be saved. For weighing, MULDER closes the ends of the glass tubes with caps made from india-rubber tubing. According to DIBBITS,* however, this is not to be recommended. MULDER'S absorption apparatus is peculiarly suitable when the carbonic acid is mixed with another gas. It insures complete absorption, precludes the evaporation of any water, and offers perfect security in case of the sudden occurrence of a too rapid evolution of gas. If it be desired to proceed strictly according to theory when using a sulphuric-acid tube for absorbing moisture, the fore part of the soda-lime tube must be connected with a small sulphuric- acid tube, which is to be weighed with it, to remove any trace of moisture that may not have been absorbed by the soda-lime and calcium chloride. Instead of soda-lime, KREUSLER f recommends * Zeitschr. f. analyt. Chem., xv, 157. f Ibid., v, 216. 56 ORGANIC ANALYSIS. [ 183. barium hydroxide, which also absorbs carbonic acid most com- pletely. B. ANALYSIS OF COMPOUNDS CONSISTING OF CARBON, HYDROGEN, OXYGEN, AND NITROGEN. The principle of the analysis of such compounds is in general this : In one portion the carbon and .the hydrogen are determined .as carbonic acid and water respectively; in another portion the nitrogen is determined either in the gaseous form, or as ammonium platinic chloride, or by determining volumetrically the ammonia formed from the nitrogen; the oxygen is calculated from the loss. As the presence of nitrogen exercises a certain influence upon the estimation of carbon and hydrogen, we have here to consider not only the method of determining the nitrogen, but also the modifications which the presence of the nitrogen renders necessary in the usual method of determining the carbon and hydrogen. a. DETERMINATION OF THE CARBON AND HYDROGEN IN NITROG- ENOUS SUBSTANCES. 183. 1. When nitrogenous substances are ignited with cupric oxide or with lead chromate, a portion of the nitrogen present escapes in the gaseous form, together with the carbonic acid and aqueous vapor; whilst another portion, minute indeed, still, in bodies abounding in oxygen, not quite insignificant, is converted into nitric-oxide gas, which is subsequently transformed wholly or partially into nitrous or hyponitric acid by the air in the apparatus. The application of the methods described in 174, etc., in the analysis of nitrogenous substances would accordingly give too much carbon; since the potash bulbs would retain, besides the carbonic acid, also the nitrous acid formed and a portion of the nitric oxide (which in the presence of potassa decomposes slowly into nitrous acid and nitrous oxide). This defect may be remedied either by intimately mixing, slowly burning, and, when possible, avoiding the use of any potassium chromate or chlorate (because when 183.] DETERMINATION OF CARBON AND HYDROGEN. 57 using these and burning rapidly the evolution of nitric oxide is much greater than when employing cupric oxide alone and slowly burning), or by selecting a combustion tube about 12-15 cm. longer than those commonly employed, filling this in the usual way, but finishing with a loose layer, about 9-12 cm. long, of clean, fine copper turnings (66, 5), or a compact roll of copper wire gauze. The roll of copper gauze in front of the oxide should not be previously oxidized (as is recommended for substances free from nitrogen, chlorine, and bromine), but should be in the metallic state.* The process is commenced by heating these copper turnings to redness, in which state they are maintained during the whole course of the operation. These are the only modifications required to adapt the methods above described for the analysis of nitrogenous substances. The use of the metallic copper depends upon its property of decomposing, when in a state of intense ignition, all the oxides of nitrogen into oxygen, with which it combines, and into pure nitrogen gas. As the metal exercises this action only when in a state of intense ignition, care must be taken to maintain the anterior part of the tube in that state throughout the process, and that the operation is not conducted too rapidly.f As metallic copper recently reduced retains hydrogen gas, and, when kept for some time, aqueous* vapor condensed on the surface, the copper turnings intended for the process must be introduced into the tube hot as they come from the drying closet (which is heated to 100). v. LIEBIG recommends to compress the hot turnings in a tube into a cylindrical form, to facilitate their rapid introduction into the combustion tube. Spirals of copper gauze are, however, more convenient. 2. If it is intended to burn nitrogenous bodies in the apparatus described in 178, a, a combustion tube, about 80 cm. long, must * The copper turnings or gauze cannot be replaced by the metallic powder obtained by the reduction of the oxide with hydrogen, as this obstinately retains hydrogen and consequently decomposes appreciable quantities of carbonic acid with formation of carbonic oxide. SCHROTTER, LAUTEMANN, Journ. f. prakt. Chem., LXXVII, 316. t Compare THORPE, Journ. Chem. Soc., 1866, xix, 359; Chem. Centrafol., 1867, 205; Zeitschr. /. analyt. Chem., v, 413. 58 ORGANIC ANALYSIS. [ 183. be used, and the fore part filled, for a length of 15-18 cm., with clean copper turnings or a copper-gauze spiral of similar length. Care must be taken to keep at least the anterior half of the roll from oxidizing, both during the ignition in the current of air and during the actual process of combustion. When the operation is terminated, and the oxidation of the metallic copper is visibly progressing, the oxygen is turned off, and the cock of the air gaso- meter opened a little instead, to let the tube cool in a slow stream of atmospheric air. 3. Since the metallic copper is usually oxidized during each combustion and must be reduced again, STEIN * uses silver instead of copper (turnings of finest silver thread). Silver has the addi- tional advantage that -it retains also chlorine. According to the investigations of CALBERLA, silver at a red heat reduces oxides of nitrogen completely, while it does not exercise the least influence on carbonic acid. b. NITROGEN DETERMINATION IN ORGANIC COMPOUNDS. As already indicated, two essentially different methods are in use for effecting the determination of the nitrogen in organic com- pounds, viz., the nitrogen is either separated in the pure form and its volume measured, or it is converted into ammonia, and this is determined either as ammonium platinic chloride, or platinum, or volumetrically by neutralization. a. Determination of Nitrogen from the Volume. The many methods recommended for effecting this purpose may be arranged under two heads. The object of the one is to collect all the nitrogen contained in a weighed portion of the sub- stance. In the other, only the relative proportion between the carbonic acid and nitrogen evolved is determined, and from this the quantity of nitrogen is calculated, which requires that the quantity of carbon contained in the substance must be previously known. The methods based upon the first-named principle are termed absolute or quantitative; those based on the latter are desig- nated as relative or qualitative. I have selected from both classes * Zeitschr. f. analyt. Chem., vin, 83. 184.] NITROGEN DETERMINATION. 59 those methods which are more easily carried out and which afford the most accurate results. 1. RELATIVE DETERMINATION OF NITROGEN FROM THE VOLTJM?. 184. da. LIEBIG'S Method.* This method is applicable only to substances which do not con- tain too small a quantity of nitrogen compared with their carbon content (see also below). It requires 6 to 8 accurately graduated strong glass tubes, each about 30 cm. long and 15 mm. bore; also a tall cylinder of strong glass widened at the top (Fig. 50). Into the sealed hinder end of a 60-cm. combustion tube in- troduce a 6-cm. layer of cupric oxide, then an intimate mixture of 0-5 grm.t of the very finely powdered substance with sufficient cupric oxide to about half fill the tube, next another layer of the pure cupric oxide, and finally enough copper turnings or a copper- gauze spiral to fill the remaining space ( 66, 5) of at least 12 cm. Connect the tube so prepared with the delivery tube, place it in the combustion furnace, and heat the anterior part to bright red- ness (which must be maintained during the entire operation), while that part of the tube in which the substance is contained is pro- tected from the heat by a screen, which is shifted back 3 cm. at a time as the heat is gradually advanced toward the tail end of the tube. When about one-fourth of the substance has been decom- posed, and the combustion products have almost completely dis- placed the atmospheric air in the tube, invert one of the graduated tubes filled with mercury % over the mouth of the delivery tube which dips into mercury, let it fill three-fourths with the gas, then remove it from the mercury trough so that the rest of the mercury may run out, and observe whether the gas has acquired any color, looking through the tube lengthwise. If not the slightest redness is observable, the operator may be certain that the gas contains * Handbook of Organic Analysis, 2d ed., p. 66. t The weight need not be more accurately known. J In order to fill a tube so that no air-bubbles will be left in it, pour the mercury into a funnel the stem of which reaches to the bottom of the tube, place a finger over the orifice, and invert the tube, manipulating so that the small bubbles may unite with the large one, and finally fill completely full. 60 ORGANIC ANALYSIS. [ 184. no admixed nitric oxide. (This test must be repeated near the middle and at the end of the operation in order to be absolutely certain that no nitric oxide is present in any of the tubes.) After this preliminary test, fill the graduated tubes one after another (Fig. 49), while the heating is slowly and uniformly continued. FIG. 49. This operation requires a stand capable of receiving and holding 6 to 8 tubes,* or an assistant must hold the tubes. The tubes should be marked in the order in which they were filled. When all the tubes are filled, the gaseous mixture in each is determined in the following manner: First immerse the tube fully in the mercury contained in the cylinder, Fig. 50, so that the temperature of the gases may be uniform and correspond with that of the mercury; next raise the tube until the mercury stands exactly at the same level inside and outside the tube, and note the volume (13, Vol. I). A small quantity of potassa solution is now introduced into the tube by cautiously blowing into the pipette, Fig. 51, which is filled with the potassa solution, and the lower end of which is bent up- wards and inserted into the tube. The absorption of the car- bonic acid is facilitated, after removing the pipette, by moving * Such a stand is figured and described in "Das Chem. Laboratorium zu Giessen," von J. P. HOFMANN, Heidelberg, 1842. 184.J NITROGEN DETERMINATION. 61 the firmly held tube up and down in the mercury, while pressing its mouth firmly against the side of the cylinder; finally, again completely immerse the tube, raise until the mer- cury level is restored, and read off the volume. (The pressure exerted by the small column of potassa solution may be entirely disregarded.) The difference between the volume found on the second reading (nitrogen) and the x IG. oL . volume first noted (nitrogen -f carbonic-acid gas) gives the carbonic-acid gas present. When the gaseous contents of one tube have been thus ascertained, purify the mercury by washing it with water acidulated with a little hydrochloric acid, then with pure water and blotting-paper, and proceed with the next tube. As a rule, the results obtained from the individual tubes agree quite closely; in many cases, however, where, for instance, the nitrogenous substance decomposes into decomposition products of varying volatility before combustion is complete, notable differences are observed in the individual tubes. As a rule, the arithmetical mean is taken as correct, and may be considered the more reliable the less the differences between the individual tubes. Should the first tubes, however, give a decidedly larger volume of nitrogen than those filled later, it may be assumed that the air had not been completely expelled when the first tubes were filled; in this case these tubes are not taken into account. The relative proportion of carbonic-acid gas to nitrogen ex- presses directly, and without requiring further calculation, the proportion between the equivalents of carbonic-acid gas and nitro- gen, since 1 eq. of carbon combines with 2 eq. of oxygen without in any way changing the volume of the latter, and hence gives 2 volumes of carbonic-acid gas; 1 eq. of nitrogen gives similarly 2 volumes of nitrogen gas. Suppose the proportion of carbonic-acid gas to nitrogen gas had been found to be as 4 : 1, then the compound would have contained for every equivalent of nitrogen, 14-04, 4 eq. of carbon = 4X 12 = 48. If, therefore, we had found in 100 parts of analyzed substance 52 parts of carbon, the substance would have contained 15-21 parts of nitrogen, since 48 : 14-04 :: 52 :z=15-21. The method of estimating nitrogen above described possesses 62 ORGANIC ANALYSIS. [ 184. one inherent source of error, in that the air is not completely ex- pelled from the combustion tube, and this always gives too high a nitrogen content. This error, however, leaves no doubt as to the correctness of the proportion if the volume of nitrogen is con- siderable. For instance, had the proportion been found to be 1:4-1, it would be at once evident that the correct ratio would be 1:4. Where the nitrogen content is relatively small, however, the results may be rendered erroneous by this error, and experience has shown that the method is not applicable in cases where the substance contains less than 1 eq. of nitrogen to 8 eq. of carbon. bb. BUNSEN'S Method.* This method gives more accurate results, but requires more time and trouble, and demands greater skill than that described under aa. First draw out one end of a tube of strong, difficu tly fusible 3, about 38 cm. long and 2 cm. wide, as shown in Fig. 52, A, then narrow the part a as in Fig. 52,5. This latter manipulation is .necessary in order to enable the tube to resist the pressure exerted by the gas within the tube during ignition. The part drawn out must be particularly stout. After the tubes have been scrupulously cleaned, introduce an intimate mixture of about 5 grm. of loose ignited cupric oxide with 0-03 to 0-05 grm. of the substance to be analyzed (and which need not be more accurately weighed), PIG. 52. and also a small quantity of clean copper turn- ings (66, 5). Now draw out the other end about 17 to 20 cm. from the already narrowed part, and just as was done before. Volatile fluids are best introduced in capillary tubes sealed at one or both ends. The tube, as shown in Fig. 53, is now connected at one end with the bulb B half filled with sulphuric acid, by which the hydrogen gas generated in A is dried; the other end is connected * See KOLBE'S paper on the subject in the Handworterbuch der Chemie, Supplemente zur ersten Auflage, S. 200. 184.] NITROGEN DETERMINATION. 63 with the hand air-pump, the cock of which, p, is open, and through which the hydrogen escapes. When the hydrogen has passed through the apparatus long enough to have rendered certain the expulsion of all the ah- in it, close the cock p, open A, compress c with a screw pinch-cock, rapidly draw up the piston of the air-pump and immediately FIG. 53. close the cock s. The hydrogen in the tube is by this procedure rarefied, and the tube may now be fused and sealed at d with the blowpipe without fear of any swelling. Now exhaust as completely as possible and fuse and seal the tube at b also. As a tube so prepared would inevitably swell and blow out from the pressure of the evolved gases on being heated to redness in the usual manner, it is inclosed in a strong sheet-iron mold shown in Fig. 54. This mold is made in two parts which accurately fit each other and afford a cylindrical cavity 30 cm. long and 5 to 6 cm. in diame- ter. Fill the two halves with freshly prepared plaster-of-Paris, to which has been added a handful of cut cow's hair, press the com- bustion tube into middle of one of the halves, cover it with the other as soon as the plaster begins to set, and clamp the two halves together by means of small iron wedges, as shown in Fig. 55. Each 64 ORGANIC ANALYSIS. L 184. half of the mold is provided with 10 to 12 holes for the escape of aqueous vapors, etc. After the plaster has set completely, slowly heat the mold in a suitable furnace to a dull redness. As soon as the odor of burnt FIG. 54. hair has diminished, and the mold entirely surrounded by live coal is at a red heat throughout, cover the coal with ashes, and con- tinue the heat thus for half an hour longer. After cooling, care- FIG. 55. fully remove the tube; it must look dull and opaque and must have a blistered surface an evidence that it had been completely softened by the heat. If too much substance is employed, or if the temperature was too high, the tube will frequently be found to have blown out or swelled in some part. The point of the tube is broken off under mercury in such a manner that the gaseous contents are received in a graduated tube filled with mercury and into which a drop of water has been introduced ( 16) ; the already moist gas is hereby fully saturated with aqueous vapor. It is unnecessary to introduce the entire gaseous content of the com- bustion tube into the measuring tube, but it is advisable to have as large a volume of gas as possible for the subsequent analysis. Now make notes of the barometric and thermometric readings 184.] NITROGEN DETERMINATION. 65 and the height of the column of mercury in the graduated tube, and introduce a moistened ball of potassa fused on the end of an iron or platinum wire to absorb the carbonic-acid gas. Remove this ball and introduce a second and dry ball, to completely dry the residual nitrogen, and then measure the latter. Reduce the volume to the same temperature, pressure, and dryness and thus ascertain the relative proportion of carbonic-acid gas to nitrogen, and consequently also the ratio of carbon to nitrogen in the analyzed substance. cc. MARCHAXD'S * process, modified by GOTTLIEB.! Draw out the hinder end of a long combustion tube to an open point, then introduce an asbestos plug, then the mixture of 0-1 to 0- 12 grm. of the substance with a large quantity of cupric oxide, then a 6-cm. layer of pure cupric oxide, next 12 to 14 cm. of copper turnings, and finally 6 cm. of coarsely powdered fuced calcium chloride. Now connect the anterior end of the tube with a delivery tube bent at right angles and the descending limb of which is 80 cm. long, and pass a current of dry hydrogen gas for two hours through the apparatus by the drawn-out point. Towards the end the tip of the delivery tube must dip into a trough of mercury. Now fuse and seal the hinder end, heat the pure cupric oxide (the oxygen of which combines with the hydrogen, thus creating a vacuum), invert a measuring cylinder filled with mercury over the end of the delivery tube and proceed to effect the combustion. 90 to 100 c.c. of gas are obtained, and of this about one-half is taken for the analysis, the remainder being used for testing for nitric-oxide gas. The results obtained by GOTTLIEB exhibit a very satisfactory degree of accuracy.:]: dd. In SIMPSON'S method the combustion is carried out with a mixture of cupric and mercuric oxides. For details, see the original memoir. * Journ. /. prakt. Chem., XLI, 177. f Annal. d. Chem. u. Pharm., LXXVIII, 241. % HEINTZ'S method for the absolute estimation of nitrogen is based on the same principle (Journ. f. prakt. Chem., LV, 229). Annal. d. Chem. u. Pharm., xcrv, 64. 66 ORGANIC ANALYSIS. [ 185. 2. ABSOLUTE NITROGEN DETERMINATION FROM THE VOLUME. 185. act. DUMAS' Method. This method is applicable to all organic nitrogenous compounds. It requires a graduated glass cylinder of about 200 c.c. capacity, and which may be closed by ground-glass plate. The combustion tube is about 70 to 80 cm. long and is sealed off round at one end. Into it introduce a layer of 12 to 15 cm. of pure dried sodium bicarbonate, then 4 cm. of cupric oxide, next a very intimate mixture of the weighed substance (0-3 to 0-6 grm., or in case of substances poor in nitrogen, still more) with cupric oxide, next the oxide that has served to rinse out the mortar, followed by a layer of pure cupric oxide, and finally a 15-cm. layer of metallic copper in the form of a wire spiral, roll of thin sheet copper, or copper turnings.* Make a channel along the top of the FIG. 56. tube by gentle tapping, and connect the tube with the bent delivery tube, cf, Fig. 56, then place in the furnace. Now gradually heat * MELSENS (Annal. d. Chem. u. Pharm., LX, 115) recommends tubes of 1-1 to 1-25 meters length, and fills them thus: Sodium bicarbonate, 10 cm.; coarse cupric oxide, 20 cm. ; the substance first triturated with finely pow- dered cupric oxide, then mixed with coarser oxide, 30 cm.; coarse oxide, 30 cm.; metallic copper, 20 cm. STROMEYER recommends adding sodium carbonate to the cupric oxide in order to prevent the formation of nitrogen oxides from the first (Annal. d. Chem. u. Pharm., cxvu, 250). 185.] NITROGEN DETERMINATION. 67 to redness the farther end of the tube for a length of about 6 cm., while the other parts are protected from the heat by a screen. The sodium bicarbonate is decomposed by the heat, and the evolved carbonic-acid gas drives out and displaces the 'ah* in the tube. When the evolution of gas has proceeded for some time, immerse the end of the bent delivery tube under mercury, invert over it a test-tube filled with potassa solution, and advance the heat a little farther towards the fore part of the tube. If the gas bubbles entering the cylinder are completely absorbed by the solution of potassa, this is a proof that the air is thoroughly expelled from the tube. But should this not be the case, the evolution of carbonic acid must be continued until the desired point is attained. Now invert the graduated cylinder, f filled with mercury and J with con- centrated solution of potassa, over the end of the delivery tube, with the aid of a ground-glass plate,* and proceed with the com- bustion in the usual way, heating first the anterior end of the tube to redness and advancing gradually towards the farther end. In the last stage of the process the remainder of the sodium bicar- bonate is decomposed, so that the whole of the nitrogen gas which still remains in the tube is forced into the cylinder by the carbonic acid evolved. Wait now until the volume of the gas in the cylinder no longer decreases, even upon shaking the latter (consequently, until the whole of the carbonic acid has been absorbed), then place the cylinder in a large and deep glass vessel filled with water, the transport from the mercurial trough to this vessel being effected by keeping the aperture closed with a small dish filled with mercury, or better, an iron cap with sheet-iron strips f riveted (not soldered) * The following is the best way of filling the cylinder and inverting it over the opening of the bent delivery tube : The mercury is introduced at first, and the air-bubbles which adhere to the walls of the vessel are removed in the usual way. The solution of potassa is then poured in, leaving the top of the cylinder free to the extent of about 5 mm. ; this is cautiously filled up to the brim with pure water and the ground-glass plate slid over it. The cylinder is now inverted and the opening placed under the mercury in the trough; the glass plate is then withdrawn from under the cylinder. In this manner the operation may be performed easily and without soiling the fingers with the potassa solution. f REICHARDT, Zeitschr. /. analyt. Chem., v, 67. 68 ORGANIC ANALYSIS. [ 185. to it (Fig. 57). The mercury and the solution of potassa sink to the bottom and are replaced by water. Immerse the cylinder, then raise it again until the water is inside and outside on an exact level; read off the volume of the gas and note the temperature of the water and the state of the barometer; calculate the weight of the nitrogen gas from its volume, after reduction to the normal temperature and pressure, and with due regard to the tension of the aqueous vapor (comp. "Calcula- tion of Analyses").* The results are generally some- what too high, viz., by about 2 to 5 per cent. ; this is owing to the circumstance that even long-continued transmission of carbonic acid through the tube fails to expel every trace of atmospheric air adhering to the cupric oxide, and that frequently the nitrogen contains a small quantity of admixed nitric oxide (see below). It is highly advisable before making any nitrogen determina- tions with this method to subject a non-nitrogenous substance, e.g., sugar, to the same process. The analyst thereby acquaints himself with the extent of the error to which he will be exposed. In such .an experiment the quantity of unabsorbed gas should not exceed 1 or 1-5 c.c. To insure complete combustion of difficultly combustible bodies, STRECKER f recommends the addition of arsenous oxide in powder to the cupric oxide with which the substance is to be mixed ; the arsenous oxide is volatilized by the action of the heat, the fumes burning the whole of the carbon like a current of oxygen. The arsenous oxide sublimes in the anterior part of the tube, and arsenic remains in the copper. This method has also been modified in various ways. THUDICHUM and WANKLYN J recommend an intimate mixture of 5 parts anhydrous sodium carbonate and 13 parts of fused potassium dichromate, in powder form, for evolving carbonic-acid * BROWN has given tables for simplifying the calculation (Zeitschr. f. .analyt. Chem., iv, 450). f Handworterbuch der Chem., 2. AufL, I, 878. J Journ. Chem. Soc., xxn, 293. 185.] NITROGEN DETERMINATION. 69 gas. This mixture has the advantage of containing no water. These authors further consider it necessary to adopt FRANKLAND'S* proposal and determine the nitric oxide usually present in small quantity in the nitrogen. This is accomplished by first reading off the volume, then admitting a small quantity of oxygen, removing the excess of the latter not used up in oxidizing the nitric oxide by means of potassium pyrogallate, and then again reading off the volume. The difference gives the nitric-oxide gas; the residue is pure nitrogen. One volume of nitric oxide contains volume of nitrogen. Finally, measurement over mercury rather than water is preferred, because water by reason of the slight quantity of air it contains gives rise to small errors. L. KESSLER f advises collecting the gases in a sulphur-free india-rubber bag containing a little potassa solution and to then transfer them to the graduated tube. Instead of evolving the carbonic acid in the tube itself, it may be generated in a special apparatus. The combustion tube must in such a case, however, be open behind and be provided with a mercury valve shown in Fig. 37, p. 42, interposed between it and the delivery tube, which must also bear a glass or rubber stop- cock. The carbonic-acid apparatus must not allow the escape of the gas when the cock is closed, and must deliver the gas at a tension sufficient to readily overcome the pressure of the mercury in the valve. bb. SIMPSON'S Method. J The principle of this method, which may be applied to the analysis of all nitrogenous substances, and which affords accurate results also in the case of difficultly combustible compounds, is the same as that of DUMAS' method, but the process embodies several characteristic differences. The carbonic-acid gas which serves to expel and displace the air in the tube is generated from manganous carbonate; the combustion is effected by a mixture of cupric and mercuric oxides; the free oxygen gas is removed by * Phil. Transact., CXLVII, 62; also Zeitschr. f. analyt. Chem., VTII, 490. t Compt. rend., LXXIV, 683; Zeitschr. f. analyt. Chem., xi, 445. J Annal. d. Chem. u. Pharm., xcv, 74. 70 ORGANIC ANALYSIS. [ 185. means of copper in a state of ignition, and the gaseous mixture is received in a special apparatus in which the carbonic-acid gas is removed by means of potassa solution, and the nitrogen is then transferred to a graduated tube to be measured over mercury. Select a strong combustion tube about 80 cm. long, and close one end by fusion. Then introduce a mixture of 12 grm. man- ganous carbonate, dried at 100, with 2 grm. mercuric oxide. (The addition of the mercuric oxide insures against the possible forma- tion of any carbonic-oxide gas that might otherwise develop from the acidulated admixture of organic matter.) 3 cm. distant from this mixture insert a plug of recently ignited asbestos, so that on placing the tube in a horizontal position a sufficiently large canal may form; next introduce 1 grm. of mercuric oxide. Now mix the accurately weighed substance (about 0-5 to 0-6 grm.) with 45 times its weight of a mixture of 4 parts freshly ignited cupric oxide and 5 parts mercuric oxide (this mixture having been pre- viously prepared and dried), and introduce the mixture without loss into the combustion tube. Next rinse out the mixing mortar with some clean cupric oxide and some of the mixed cupric and mercuric oxides, and transfer these likewise to the tube. An asbestos plug is finally inserted, about 30 cm. distant from the first plug, in order that the mixture may not form too thick a layer, but should leave a canal of ample height; the plug, further, is intended to remove any particles of the mixture that may have adhered to the fore part of the glass tube, and to push them to the rear. Next fill in a layer of 6 to 9 cm. with pure cupric oxide, insert another asbestos plug, and fill in 20 to 24 cm. with metallic copper (obtained by reducing granular cupric oxide by hydrogen at a relatively low temperature).* The fore part of the tube is now drawn out and connected by means of a small rubber tube with a delivery tube the lower end of which is bent at right angles and dips into the mercury in a trough. When a canal has been made by tapping the tube, place the latter in the combustion furnace and prepare the apparatus * Regarding the modifications required in the process of filling when fluids are to be analyzed, see the original paper (loc. cit., p. 83). 185.] NITROGEN DETERMINATION. 71 FIG. 58. shown in Fig. 58 for the reception of the gases. This apparatus should have a capacity of about 200 c.c. and should be of sufficiently strong glass. The upper part should have an external diameter of 7 to 8 mm. Slip a stout piece of rubber tubing 5 cm. long over the point, leaving a piece of tubing pro- ject about 3 cm., and tie it securely with silk cord; then insert into the projecting rubber tube a piece of glass rod 15 mm. long and of the same diameter as the rubber tube, until it touches the point of the vessel; finally, insert in the rubber tube still left free a very narrow delivery tube of the same external diameter as the glass rod, and fasten it securely by tying, after which also tie cord around the part occupied by the glass rod, thus assuring an air-tight closure of the vessel. To ascertain whether the vessel is actually air-tight, partly fill it with mercury, invert it in the trough, and observe whether the mercury level falls. If the joints are found to be tight, fill the vessel with mercury and 16 to 17 c.c. of concentrated potassa solution, invert it in the trough, and secure it as shown in Fig. 59. FIG. 59. Now screen off the hinder half of manganous carbonate by means of a screen, and heat it for a few minutes with a few pieces 72 ORGANIC ANALYSIS. [ 185.. of red-hot charcoal,* until the carbonic-acid gas evolved has com- pletely expelled all the air from this part of the tube, remove the heat from the hinder end and gradually heat to redness the other half of the manganous carbonate as well as the copper and cupric oxide in the fore part of the tube. That part of the tube contain- ing the mixture must be protected from the heat by screens. As soon as the evolution of carbon dioxide ceases, insert the end of the delivery tube (which from the beginning had dipped into the mercury) into the orifice of the gas apparatus, but without lifting it above the surface of the mercury, and now heat the mix- ture, begininng at the fore end and slowly proceeding to the hinder. During the entire combustion the fore part of the tube, as well as that containing the exhausted manganous carbonate, must be maintained at a red heat. When the combustion is at an end, decompose the manganous carbonate behind the screen to drive out all the nitrogen from the tube into the gas receiver by means of the carbonic-acid gas evolved. As soon as all the gas bubbles are completely absorbed by the potassium solution the delivery tube may be removed. The nitrogen collected in the apparatus is now transferred to the measuring tube by means of a tube having the form shown in Fig. 58, and which, immersed in the mercury, is fitted into the tubulure of the gas vessel by means of a perforated cork. The entrance of air with the cork is best prevented by moistening the cork with a solution of mercuric chloride. Now pour mercury into the tube so that its level will be considerably higher than that in the gas vessel, and let the whole stand for two hours, so that all the carbonic-acid gas may be absorbed. In the meantime fill the gas-measuring tube with mercury, after first introducing a drop of water, and then invert in the trough. Now bring the end of the tube connected with the gas appara- tus under the measuring tube, untie the cord from around'the glass * The heating may be effected, of course, in a gas furnace instead of a charcoal furnace. 185. NITROGEN DETERMINATION. rod, and pour mercury into the perpendicular tube as shown in Fig. 60. FIG. 60. When the gas has thus almost entirely been driven over, the mercury must be added by drops, until the potassa solution be- comes just visible in. the gas-delivery tube. By this procedure just exactly as much nitrogen is kept out of the tube as air had first entered (from the delivery tube). When pouring hi the mercury care must be taken that it carries along with it no air. The upright tube should hence be kept quite full from the begin- ning and the glass rod inserted in the rubber tube should be of such a dimension as to oppose considerable resistance to the passage of the gas. After taking barometric and thermometric readings, measure the moist gas and calculate its weight. The results obtained by SIMPSON in analyses of alkaloids, saltpeter, and am- monium chloride are very satisfactory. It is advisable before proceeding to calculate the nitrogen, to test it for oxygen and nitric oxide. 74 ORGANIC ANALYSIS. [ 185. cc. W. GIBBS' Method. Subsequent to the publication by E. FRANKLAND and H. E. ARMSTRONG * of their method of estimating carbon and nitrogen in the organic matter of potable water (which method also included the determination of nitrogen), depending on exhausting the air from the combustion tube, both before and after combustion, with a SPRENGEL air-pump, W. GIBBS f also published a method in which the SPRENGEL air-pump is used. This method, which is a combination of both the FRANKLAND-ARMSTRONG and the SIMP- SON methods, differs nevertheless from these in a number of par- ticulars. In the determination of the nitrogen in asparagin and allantoin it gave excellent results. Regarding the construction of the meroury air-pump used by GIBBS, and which is less fragile than that described by FRANKLAND and ARMSTRONG, I refer to the original paper. The operation is carried out as follows: Into a rather short combustion tube introduce first a few grammes of magnesium carbonate, then the substance mixed with plumbic chromate and 5 or 6 grm. of mercurous chromate. Then fill the fore part of the tube with freshly reduced, finely divided metallic copper. Now connect the tube with the mercury air-pump by means of a perforated rubber stopper bearing a glass tube, one end of which is connected with the iron T-piece of the pump. Next test the tightness of the entire apparatus by operating the pump for a few minutes and then allowing the whole to stand, and ob- serving whether the height of the mercurial column remains un- changed. Now completely exhaust the combustion tube, which requires 5 to 10 minutes, and cautiously heat the magnesium carbonate until the entire apparatus is filled with carbonic-acid gas and the pressure within the tube is equal to that without. The combustion is then effected in the ordinary manner. When completed, set the pump again in operation until a complete vacuum is obtained. SIMPSON'S receiver, Fig. 58, simply filled *Journ. Chem. Soc., 1868, xxi, 77; Zeitschr. /. analyt. Chem., vin, 489. t Amer. Journ. of Sciences and Arts, XLVIII; Zeitschr. /. analyt. Chem., XI, 206. 185.] NITROGEN DETERMINATION. 75 with mercury, serves to collect the gas. When the operation is at an end, absorb the carbonic-acid gas with 50 c.c. of potassa solution, of 1 -2 sp. gr., transfer the nitrogen to the measuring tube and proceed as in 66. Another method embodying the exhaustion of the combustion tube with an air-pump, and measurement of nitrogen in SCHIFF'S azotometer, is described* as follows: REAGENTS. Cupric Oxide. "Copper scale," which may contain cuprous oxide, coal dust, oil, etc., is mixed in an iron pot with 10 per cent, of potassium chlorate and enough water to make a thin paste. The mass is heated and stirred till dry; the heat is then raised to the point of ignition and until the mass does not glow nor sparkle when stirred. The potassium chloride is washed out by decantation and the cupric oxide is dried and moderately ignited. Metallic Copper. Granular copper oxide, or fine copper gauze, is suitable for its preparation. The granular copper is most con- venient; copper gauze must be made into rolls adapted to the combustion tube. The copper is reduced and cooled as usual in a stream of hydrogen. Potassium Chlorate. Commercial potassium chlorate is fused in porcelain and pulverized. Sodium Bicarbonate. It must contain no organic matter. Solution of Caustic Potash. Dissolve commercial "stick pot- ash" in less than its weight of water, making a solution so concen- trated that, on cooling, it deposits crystals of potassium hydroxide. The same clear solution may be used for a number of combus- tions or until the absorption of carbonic-acid gas is not quite prompt. APPARATUS. The Combustion Tube should be of the best hard Bohemian glass, about 2 feet 4 inches long. The rear end is bent and sealed as in Fig. 63. * By JOHNSON and JENKINS, American Chemical Journal, n, 27. 76 ORGANIC ANALYSIS. [ 185. It is best to protect the horizontal part with thin copper foil. The tube is connected with the pump by a close-fitting rubber- cork smeared with glycerin. Azotometer. This is a modification of the apparatus invented and described by SCHIFF, Fres. Zeitsckrift, Bd. 7, p. 430. It is rep- resented in Fig. 61. The gas is measured in an accurately calibrated cylinder (bu- rette), A, of 120 c.c. capacity, graduated to fifths of cubic centimetres, and closed at the upper end by a glass stop-cock. The lower end is connected, by means of a per- forated rubber stopper about 1J inches long and 1J inches diameter, with another tube having two arms, one, D, to receive the delivery tube from the pump, the other connected by a rubber tube with a bulb of 200 c.c. capacity, F, through which potassa solution is supplied. The gradu- ated tube is enclosed in a water-jacket with an external diameter of about 1} inches. Its lower end is closed by the caoutchouc stopper that connects the two parts of the azotometer described above. The upper end of the jacket is closed by a thin rubber disc slit radially and hav- ing four perforations: one in the centre, through which the neck of the graduated tube passes, and three others near the circumference. Through one of the latter a glass tube, L, bent as in the figure, reaches to the bottom of the jacket, another short tube just passes through the disc, and the third hole is for supporting a thermom- eter. The azotometer is held upright and firm on a stand by rings fitting around the jacket and by cork wedges. The bulb for potassa solution rests in a slotted, sliding ring. The Air-pump used is the SPRENGEL mercury pump, modified merely so as to be easily constructed and durable. Its essential 61. f 185.] NITROGEN DETERMINATION. 77 4 LC parts are sketched in Fig. 62. Some of them are exaggerated in order to show their construction more plainly. Through a rubber stopper wired into the nozzle of the mercury reser- voir, A, passes a glass tube, B, 4 inches long; this connects by a caoutchouc tube with the straight tube D, 3 feet long. The rubber tube E, 6 inches long, connects D with a straight glass tube F of .about the same length as D. G is a piece of combustion tube 1^ inches long, closed below by a doubly perforated soft-rubber stopper admitting the tubes F and H, and above by a singly perforated rubber stopper into which a tube / is fitted. The tube H has a length of 45 inches. At the bottom it is connected by rubber with a straight tube of 3 inches, and this again with a tube K of 7 inches. The tubes H K should have an internal diameter of T V inch, F may be T \ inch, and D still larger. We have used for H and F slender Bohemian glass tubes of ^ inch exterior diameter. Their elasticity compensates for their slenderness. If heavy barometer tubes be used, the stoppers and {JT must be of correspondingly larger dimensions. The joints at G must be made with the greatest care. It is best to insert the lower stopper for half its length into G, having the dimensions of the parts so related that it requires considerable effort to force the slightly greased tubes F and H to their places just through the stopper. The tube 7 must be of stout glass a decimetre in diameter. It is drawn out at either end to a long taper, and bent as in the figure, in order to bring its free extremity to the level of the combustion furnace. The hole in the upper rubber stopper has a diameter of 5 mm., just sufficient to admit the narrowed end of the tube, which, after greasing or moistening with glycerin, is "screwed down" into the stopper. FIG. 62. 78 ORGANIC ANALYSIS. [ 185. These three joints are the only ones belonging to the pump which have to resist diminished pressure, and require extreme care in making. If not entirely secure they are to be trapped with glycerin. For this purpose it is needful to pass F and H through a stopper of half an inch greater diameter than G and correspondingly per- forated before entering the latter. Then, previous to inserting /, a tube 4 inches long is slipped over G upon this wider stopper. When / has been inserted and the tubes have been secured to their support, the space between G and the outer tube is filled with the most concentrated glycerin, which is prevented from absorbing moisture by corking above. The two rubber tubes are both provided with stout screw clamps, to admit of exactly regulating the flow of mercury. The tubes, D, F, H, and I are secured to a vertical plank framed below into a heavy horizontal wooden foot on which rests the mercury trough, and having above a horizontal shelf through an aperture of which passes the neck of A. The tubes D, F, H, and I are secured to the plank at several points by wooden or cork clamps clasping the tubes and fastened by screws or wires. These fastenings are made elastic by the intervention of a thick rubber tube between the glass and wood. The connections C and E should be made of stout vulcanized rubber; those at the base of HK of fine black rubber. The latter should be soaked in melted tallow previous to use, all excess being carefully removed from the interior. The joints should be wound with waxed silk. A glass funnel is placed within A to prevent spattering of the mercury when it is filled. OPERATION. From 3 to 4 grammes of potassium chlorate, according to the amount of carbon to be burned, are put into the tail of the com- bustion tube, Fig. 63, followed by an asbestos plug just at the bend. The substance to be analyzed (0 6-0 8 gramme) is well mixed in 185.] NITROGEN DETERMINATION. 79 a mortar with enough cupric oxide that has been freshly ignited and allowed to cool to make a layer 11 or 12 inches long in the tube. The mixture is introduced through a funnel and rinsed with enough cupric oxide to make a layer of 3 inches, a second asbestos plug, and upon it a layer of reduced copper of 4 or 5 MIXTURE JmNSINGs] Cu. jCuOico" I ASBESTOS j ]8cm. i 30cm. i 8cm. ! 12 cm. :8cmJ3cml 10cm. ! FIG. 63. inches long are put in, then a third asbestos plug, then 2 inches of cupric oxide, a fourth asbestos plug, then 0-8 to 1-0 gramme of sodium bicarbonate. The remaining space in the tube is loosely filled with asbestos to absorb the water which is formed during combustion and prevent it from flowing back upon the heated glass. The anterior part of the tube containing the cupric oxide and re- duced copper is wound with copper foil, leaving, however, a little of the copper (Cu in Fig. 63) visible at its rear. The combustion tube is placed in the furnace at the bend of the tube 7 and connected with the latter by a close-fitting rubber stopper smeared with glycerin. Care must be taken to make the joint perfectly tight. The combustion tube has its conical rubber stopper partly inserted, and is then forced and rotated upon the tapering and stout end of the tube 7, the latter being supported by one hand applied at the lower bend. PREPARATION OP THE AZOTOMETER. Fill the bottom of the azotometer with mercury to about the level indicated by the dotted line G. Close the arm D securely with a rubber stopper. Grease the stop-cock H and insert the plug, leaving the cock open. Pour potassa solution into F till A is nearly full, and there is still some solution in the bulb F. Raise the bulb cautiously with one hand, holding the stop-cock H in the other hand. When the solution in A has risen very nearly to the glass cock, close the latter, 80 ORGANIC ANALYSIS. [ 185. avoiding contact of the alkali with the ground-glass bearings. Replace the bulb in the ring and lower it as far, as may be. If the level of the solution in the azotometer does not fall in 15 or 20 minutes it is tight. Place the delivery tube of the pump K in a mercury trough. Supply the vessel A with at least 500 c.c. of mercury. Cau- tiously open the clamps C and E. If the mercury does not start at once pinch the rubber at E repeatedly. The mercury should flow nearly as fast as it can be discharged at K, without filling the cylinder G. Five to ten minutes' working of the pump will gen- erally suffice to make a complete exhaustion of the combustion tube. If most of the mercury runs out before exhaustion is complete, close the clamp C, return the mercury to A, and repeat the opera- tion. When there is a complete exhaustion, the mercury falls with a rattling or clicking sound. After it has been distinctly heard for half a minute, close the clamp C. If the mercury column in H remains stationary for some minutes, the connections are proved to be tight. ADJUSTING THE AZOTOMETER. Remove the mercury trough, placing K in a capsule. Heat the part of the tube containing sodium bicarbonate. Water vapor and carbon dioxide are evolved, which fill the vacuum in H and expel the mercury. While this is being done place the azotometer near by, remove the bulb F from the ring and support it in a box near the level of D, so that the stopper may be removed from D without greatly changing the level of the mercury G, and so that the azotometer can be moved freely without disturbing it. When the cork in D has been removed fill D half full or more with water. As soon as the mercury has fully escaped from K insert the latter in D. Let a few bubbles escape through the water and theti pass the tube K down so that the escaping gas enters the azotome- ter. It will much facilitate the delivery of gas if the extremity of the tube K just touches the inside of the azotometer tube, and is kept, as near as possible, to the surface of the mercury. 185.] NITROGEN DETERMINATION. 81 The carbon dioxide is absorbed in passing through the caustic- potassa solution. In spite of all precautions very minute bubbles of permanent gas will occasionally ascend, but, as will be seen on observing the amount of potassa solution thus displaced, the error thereby occasioned is extremely small. THE COMBUSTION. First heat the anterior cupric oxide to full redness, and after- wards the copper. The fine gauze or pulverulent copper com- pletely reduces any oxides of nitrogen which might be produced in the combustion, and also retains any excess of oxygen which is evolved at the close of the process. The anterior cupric oxide burns the traces of hydrogen which may be held by the reduced copper, even when the tube is ex- hausted, and also destroys the carbon monoxide which is usually formed when steam and carbon dioxide pass together over reduced copper, if iron or carbon be present. Go on with the combustion as usual, bringing the heat up to a fair redness. The flow of gas may be made quite rapid, say one bubble a second or a little faster. When the horizontal part of the tube has all been heated, and the evolution of gas has nearly ceased, heat the potassium chlorate so that it boils vigorously from evolution of oxygen. The reoxidiza- tion of the reduced copper oxide and of any unburned carbon proceeds rapidly. When the oxygen, whose flow admits of easy regulation, begins to attack the anterior layer of reduced copper, stop its evolution and lower the flames all along the tube, keeping the reduced cop- per still faint red. After a few minutes start the pump, slowly at first, ha^ng some vessel under the tube D of the azotomer to receive the mercury. A few minutes pumping suffices to clear the tube. Remove the azotometer, close the tube D with its rubber stopper, and then raise the bulb into its ring to such a height that the potassa solution in it will be at about the same level as that in the graduated tube. Connect L at its upper end with a water supply, insert a 82 ORGANIC ANALYSIS. [ 186. thermometer in the top of the water-jacket and let the water run until the temperature and the volume of gas are constant. Read off the volume of gas and temperature, after having accu- rately adjusted the level of the solution in the bulb to that in the azotometer. Read the barometer and make the calculations in the usual way. When 50-per cent, potassa solution is used, no correction need be made for tension of aqueous vapor, as SCHIFF has shown. The calculation is somewhat shortened by the use of the table in Journ. of Chem. Soc., Vol. XVIII (1865), p. 212. Very fair results are got by employing, with suitable precau- tion, a stream of carbon dioxide to displace the air of the com- bustion tube, but the process is very tedious, the sources of error are more numerous, and the results are apt to be higher and not so concordant as when the mercury pump is used to evacuate the tube. The pump above described has been in use for eighteen months without any repairs, and by its help two or even three analyses may be performed in a day. /?. Determination of Nitrogen by Conversion into Ammonia. VARRENTRAPP and WILL'S Method. 186. This method is based upon the same principle as the method of examining organic bodies for nitrogen ( 172, 1, a), viz., upon the circumstance that, when nitrogenous bodies are ignited with an alkali hydroxide, the latter is decomposed, yielding water, the oxygen of which combines with carbon to CO 2 , which remains in combination with the alkali as carbonate, whilst the hydrogen at the moment of its liberation combines with the whole of the nitrogen present to form ammonia. In the case of substances very rich in nitrogen, such as uric acid, mellon, etc., the whole of the nitrogen is not at once con- verted into ammonia in this process; a portion of it combining with part of the carbon of the organic matter to cyanogen, which 186.] NITROGEN DETERMINATION. 83 then combines either in that form with the alkali metal or in the form of cyanic acid with the alkali. Direct experiments have proved, however, that even in such cases the whole of the nitrogen is ultimately obtained as ammonia, if the alkali hydroxide is pres- ent in excess, and the heat applied is sufficiently intense. As in all organic nitrogenous compounds the carbon prepon- derates over the nitrogen, and the oxidation of the former, at the expense of the water, will invariably liberate a quantity of hydro- gen more than sufficient to convert the whole of the nitrogen pres- ent into ammonia; for instance, CN+ 2H 2 = CO 2 + NH 3 + H. The excess of the liberated hydrogen escapes either in the free state or in combination with the not yet oxidized carbon, accord- ing to the relative proportions of the two elements and the tem- perature, as marsh gas, olefiant gas, or vapor of readily condensible hydrocarbons, which gases serve in a certain measure to dilute the ammonia. As a certain dilution of that product is necessary for the success of the operation, I will here state that substances rich in nitrogen should be mixed with more or less of some non- nitrogenous body sugar recrystallized from alcohol, for instance so that there may be no deficiency of diluent gas. It was formerly supposed that this method was applicable for all nitrogenous substances that did not contain the nitrogen in the form of nitric acid, hyponitric acid, etc. This supposition, however, is no longer tenable, as more searching investigations have shown. Even though many of the assertions regarding the inapplicability of the VARRENTRAPP-WILL method are ascribable to incorrect procedures and the use of impure soda-lime, particu- larly a soda-lime containing sodium nitrate, the results obtained in other cases cannot be ascribed to such causes. Thus STRECKER found the results too low with guanidin, and KONINCK and MAR- QUART also obtained too low results with bryonicin. RITTHAUSEN and KREUSLER * similarly found the results far too low with leucin, * Zeitschr. /. analyt. Chem., x, 350. 84 ORGANIC ANALYSIS. [ 186. and obtained correct results only when the substance was burned with an admixture of sugar. The applicability of the method to albuminoids and allied substances has given rise to an animated discussion. Thus NOWACK and SEEGEN state that it is not appli- cable,* while KREUSLER on the contrary firmly declares that it is,f and considers the results of the former to be due to tho use of soda-lime containing sodium nitrate; again, ABESSER and MARCKER,J in the estimation of nitrogen in gluten, horse flesh, and blood albumin, obtained results which were 0-22, 0-23 and 0-33 below the volumetric determinations. On the other hand, E. SCHULZE found that the VARRENTRAPP- WILL method, contrary to the previously held supposition, is applicable also in the case of plant substances (beets, tobacco) containing nitrates, when the quantity of nitric acid does not exceed a certain proportion; thus with from 2 to 3 per cent, of nitric acid the results were quite accurate, whereas with from 6 to 7 per cent, the nitrogen was 0-2 per cent, too low. The determination of the ammonia formed in the combustion with soda-lime is 'effected by receiving the NH 3 in diluted hydro- chloric acid, converting the ammonium chloride into ammonium platinum chloride, and either weighing this or igniting it and cal- culating the ammonia or nitrogen from the residual metal. Certain nitrogenous organic compounds afford no ammonia on ignition with soda-lime, but yield other oxygen-free, nitrogenous, volatile bases. For instance, indigo-blue yields aniline; and narcotine, morphine, quinine, and cinchonine yield new volatile bases. All these volatile bases have the property, just like am- monia, of forming double salts with hydrochloric acid and plati- num chloride. Were we to weigh these double salts and, assuming them to be ammonium platinum chloride, calculate the nitrogen from the weight, we would naturally commit a grave error. If we ignite them, however, and calculate the nitrogen from the * Zeitschr. f. analyt. Chem., xi, 324; xii, 316; xin, 460. f Ibid., xii, 354. I Ibid., xii, 447. Ibid., vi, 384. 186.] NITROGEN DETERMINATION. 85 weight of the residual metal, all error is avoided, because these bases, just like ammonia, contain 2 eq. of nitrogen to each equiva- lent of platinum (LIEBIG). No theoretical explanation is necessary in order to understand the other part of the process (collection and determination of the ammonia). The process and requisites arc as follows: aa. Requisites. 1. THE SUBSTANCE. This must be in the form of finest pow- der, a condition not always easily attainable, as, for instance, with albuminoid substances, but which is, nevertheless, indispensable for the attainment of accurate results with many substances. H. RITTHAUSEN * who has called particular attention to this point, gives methods of reducing albuminoid substances to a finely pulverulent condition. After drying, the substance is transferred to the drying tubes, in which it is weighed; if the mixing with soda-lime is to be effected in a mortar, such a tube as shown in Fig. 2 will serve, but if the mixing is to be accomplished by means of the mixing wire, a longer and narrower tube is used (compare 175). 2. A COMBUSTION TUBE of the kind described 174, 3; length about 40 cm., width about 12 mm. The combustion is effected in one of the combustion furnaces described in 174, 16. 3. SODA-LIME f (66, 4). The analyst himself should make the caustic soda from the crystallized sodium carbonate for the preparation of the soda-lime, as the commercial carbonate almost invariably contains sodium nitrate, and the latter is the source of many errors, as already pointed out. The soda-lime is best tested as to its freedom from nitrogenous matters by burning it with chemically pure sugar. The soda-lime should in this case not fuse, but simply cake, and on evaporating with hydrochloric acid and platinum chloride and treating the residue with alcohol, no ammo- * Journ. f. prakt. Chem., N. F., vni, 10; Zeitschr. /. analyt. Chern., xin, 240. f S. W. JOHNSON (Zeitschr. f. analyt. Chem., xn, 222, and 446) recom- mends as a substitute for soda-lime a mixture of 1 vol. dry sodium carbonate or sulphate with 1 vol. dry calcium hydrate. 86 ORGANIC ANALYSIS. [ 186. nium platinic chloride should remain. It is advisable to gently heat in a platinum or porcelain dish a quantity of the sandy or granular soda-lime sufficient to fill the combustion tube, so as to have it perfectly dry for the process of combustion. In the analysis of non-volatile substances, the best way is to use the soda-lime while still warm. 4. ASBESTOS. A small portion of this substance is ignited in a platinum crucible previous to use. 5. A VARRENTRAPP AND WILL'S BULB APPARATUS. This may be obtained from the shops. Fig. 64 shows its form. It is filled FIG. 64. to the extent indicated in the drawing with hydrochloric acid of about 1-07 sp. gr. The acid is introduced either by dipping the point into the acid and applying suction to d, or by means of a burette. In order to guard against the receding of the acid into the combustion tube, ARENDT and KNOP have sug- gested the form indicated in Fig. 65. PELIGOT'S U-formed bulb-tube also affords good service (see 187). 6. A soft well-perforated CORK or rubber FIG. 65. stopper which fits the combustion tube air-tight, and in which the tube d of the bulb apparatus fits closely. E. MULDER * recommends to wrap the cork with tin-foil in order to prevent its absorbing ammonia. 7. A SUCTION TUBE filled with potassa and closed at the anterior end by a perforated cork, in which the point of the bulb apparatus passes; or, an aspirator. * Chem. CentralbL, 1861, 44; Zeitschr. f. analyt. Chem., i, 98. 186.] NITROGEN DETERMINATION. 87 8. A MIXING MORTAR ( 174, 8). 9. A sheet of GLAZED PAPER. The reagents required in the after treatment of the liquid ob- tained from the combustion will not be detailed here, as it is un- necessary to have them ready at the beginning of the operation. bb. The Process. The combustion tube is half filled with soda-lime, which is then gradually transferred to the perfectly dry, and, if the nature of the substance permits, rather warm mortar, where it is most intimately mixed with the weighed substance (compare 174), forcible pres- sure being carefully avoided; a layer of sandy soda-lime occupying about 3 cm. is now introduced into the posterior part of the com- bustion tube and the mixture filled in after; the latter, which will occupy about 18 cm., is followed by a layer of about 5 cm. of soda- lime which has been used to rinse the mortar, and this again by a layer of 10 cm. of pure, preferably granulated, soda-lime, leaving thus about 4 cm. of the tube clear. The tube is then closed with a loose plug of asbestos and a free passage for the evolved gases formed by a few gentle taps; it is then connected with the bulb apparatus by means of the perforated cork or stopper and finally placed in the combustion furnace (see Fig. 64). To ascertain whether the apparatus closes air-tight, some air is expelled by holding a piece of red-hot charcoal to the bulb a, and the apparatus observed, to see whether the liquid will, upon cooling, permanently assume a higher position in a than in the other limb. The tube is then gradually surrounded with ignited charcoal, com- mencing at the anterior part and progressing slowly towards the tail, the operation being conducted exactly as in an ordinary com- bustion (174). Care must be taken to keep the anterior part of the tube tolerably hot throughout the process, since this will almost entirely prevent the passage of liquid hydrocarbons, the presence of which in the standard acid would be inconvenient; on the other hand, if the heat is too high, the ammonia may be decomposed into nitrogen and hydrogen. The stopper should be kept sufficiently hot to guard against its retaining water and, with this, ammonia. The combustion should be conducted so as to 88 ORGANIC ANALYSIS. [ 186. maintain a steady and uninterrupted evolution of gas; there is no fear of any ammonia escaping unabsorbed, even if the evolu- tion is rather brisk; but the operator must constantly be on his guard against the receding of the acid, which takes place the mo- ment the evolution of gas ceases, and this, in some instances, with such impetuosity as to force the acid into the combustion tube, which, of course, spoils the whole analysis. With compounds very rich in nitrogen, even the greatest care during combustion will be of no avail, because of the powerful affinity of the hydro- chloric acid for the ammonia gas which almost completely fills the tube. This difficulty may be readily met, however, by mixing with the substance an equal quantity of chemically pure sugar (white rock candy * recrystallized from alcohol), which will give rise to the evolution of more permanent gases diluting the am- monia. When the tube is ignited in its whole length, and the evolu- tion of gas has just ceased,f the point of the combustion tube is broken off, and air to the extent of several times the volume of the gas in the tube is sucked through the apparatus, to force all the rest of the ammonia into the acid. In order to guard against inhaling the acid fumes, use a suction tube filled with potassa, or else use a small aspirator. { If the substance to be analyzed con- tains ammoniacal salts, a loss of ammonia on triturating the sub- stance with the soda-lime is unavoidable. In this case the mixing must be effected in the tube with the mixing wire (175). Some chemists even prefer this method in ordinary cases as well. Liquid nitrogenous compounds are weighed in small sealed glass bulbs, and the process is conducted as directed in 180, with this difference, that soda-lime is substituted for oxide of copper. * Regarding the nitrogen content of commercial sugars, see KREUSLER, Zeitschr. f. analyt. Chem., xn, 362. White rock candy contains about 0-012 per cent, of nitrogen; fine white refined sugar, 0-055; and beet sugar, 0-039 per cent. f This is indicated by the white color which the mixture reassurr.es when all the carbon deposited on the surface is oxidized. J The suction may be altogether avoided by placing in the hinder end of the tube a layer of calcium oxalate dried at 110. as proposed by Bouis. RITTHAUSEN, Zeitschr. f. analyt. Chew.. X T TT, 240. 186.] NITROGEN DETERMINATION. 89 It is advisable to employ tubes of greater length for the combus- tion of liquids than are required for solid bodies. The best method of conducting the operation is to heat first about one-third of the tube at the anterior end, and then to force the liquid from the bulbs into the tube by heating the hinder end of the latter; the expelled liquid will thus become diffused in the central part of the tube without being decomposed. By a progressive application of heat, proceeding slowly from the anterior to the posterior end, a steady and uniform evolution of gas may be easily maintained. When the combustion is terminated, the bulb apparatus is emptied, through the opening at the point, into a beaker, and rinsed with water until the rinsings cease to manifest acid reaction. If liquid hydrocarbons have formed, pass the liquid through a moistened filter in order to separate them, then evaporate the acid liquid containing the ammonium chloride to a small volume, add pure * platinic-chloride solution in excess, evaporate to dryness on the water-bath, and pour over the residue a mixture of 2 vol. strong alcohol and 1 vol. ether. If the liquid acquires a bright- yellow color, it is an evidence that sufficient platinic chloride was added; if it does not, more must be added (best in the form of an alcoholic solution). f Collect the undissolved platinum ammo- nium chloride in a weighed filter dried at 125, wash it with the above-mentioned mixture of alcohol and ether, dry, and weigh it (compare 99, 2). The dried filter should be weighed between two closely fitting watch-glasses held together by a clamp. The platinum ammonium chloride so obtained is not always of a fine * If the platinic chloride contains potassium or ammonium chloride, the results for nitrogen will be too high; if it contains nitric acid, chlorine is formed during evaporation and a portion of the ammonia will be destroyed, and the results for nitrogen will hence be too low. One should therefore never neglect to test the platinic chloride most carefully as to its eligibility for use. f As the platinum double salts of some volatile bases resulting from the decomposition of certain organic substances (see above) are more soluble in alcohol than the platinum ammonium chloride, it is better to employ ether mixed with only a few drops of alcohol for the washing, instead of the alcohol-ether ordinarily employed, if such double salts are suspected as being present (A. W. HOFMANN). 90 ORGANIC ANALYSIS. [ 186. yellow color, but is at times darker and brownish-yellow. This is particularly the case with difficultly combustible substances rich in carbon, because with such substances the formation of liquid hydrocarbons, which bliwjken the hydrochloric acid during the evaporation, is more difficult to avoid. Direct experiments have shown, however, that this darkening of the precipitate has no perceptible influence on the result. The platinum ammonium chloride may be purified, particularly if the quantity is not too large, by dissolving it on the filter with boiling water, collecting the filtrate in a weighed platinum dish or porcelain crucible, and evaporating it together with the washings. After drying at 125, the increase in weight of the dish or crucible gives the quantity of the pure platinum ammonium chloride. To test whether the platinum ammonium chloride is pure, convert it into platinum, according to 99, 2. If volatile nitrogenous bases have formed with the ammonia, the nitrogen content of the substance can be calculated only from the metallic platinum obtained (compare II, p. 84). In the analysis of such nitrogenous substances for which the method is particularly adapted (see II, pp. 82-84 *), and when pure soda-lime is used, the results are quite accurate, being as a rule slightly too low rather than too high, about in the ratio of 100 : 99 5. This may be owing to the fact that traces of the ammonium-chloride vapor escape condensation in the absorption apparatus, and are carried off with the permanent gases ;f or because the combustion is not complete, i.e., nitrogenous decomposition products are evolved which are not preciptated by platinic chloride; or, finally, because a small quantity of the ammonia is decomposed into hydrogen and nitrogen. It will be seen that if in order to avoid the second source of error a longer layer of granulated soda- lime be employed, as recommended by E. MULDER, there is danger * LIEBERMANN (Annol. d. Chem., CLXXXT, 103) in estimating the nitrogen content of milk according to the VARRENTRAPP-WILL method invariably obtained lower results than with the DUMAS method. f E. MULDER on this account replaces the bulbs containing the hydro- chloric acid by a U-tube filled with broken fragments of glass moistened with hydrochloric acid. 187.] NITROGEN DETERMINATION. 91 of increasing the error from the last source mentioned (W. KNOP *). If the results obtained are too high, the cause is often due to the use of impure platinic chloride. Errors from this cause, or from the presence of ammonia in the hydrochloric acid, are best guarded against by taking such quantities of hydrochloric acid and platinic chloride as are used in the analysis, and treating exactly in the same manner; the small quantity of platinum ammonium chloride so obtained, if any, is deducted from the results obtained in the analysis. If soda-lime is used containing sodium nitrate or nitrite, not only may the results obtained be too high, but also too low, be- cause of the combustion of the ammonia by the nitrate or nitrite (KREUSLER f). f. Peligot's Modification of the VARRENTRAPP-WILL Process. 187. This modification consists in receiving the ammonia generated on igniting the substance with soda-lime in a measured quantity of standard sulphuric or oxalic acid, and then titrating the still uncombined acid with standard sodium hydroxide (or baryta water); the quantity of acid neutralized by the ammonia, and hence the ammonia itself, may thus be determined (compare 99, 3). Normal sulphuric- or oxalic-acid solution is most conveniently used (215). 10 c.c. of the standard acid, containing respectively 0-49043 grm. monohydrated sulphuric acid and 0-63024 grm. crys- tallized oxalic acid, and which hence correspond to 0-1404 grm. nitrogen or 0-17064 grm. ammonia, are, as a rule, sufficient in the analysis of 0-5 grm.. a substance containing 10 to 20 per cent, nitrogen. The acid may be placed in the bulbs shown in either Fig. 64 or 65. In this case place the accurately measured acid in a beaker, suck up as much as possible into the bulbs, and rinse off the point. After the combustion empty the bulbs into the * Chem. Centralbl., 1860, 44. t Zeitschr. /. analyt. Chem., xn, 363. 92 ORGANIC ANALYSIS. [ 187. same beaker again, carefully rinse out the bulbs, and then titrate the liquid. The receiver shown in Fig. 66 is more suitable for this method. The tube a, previously provided with a perforated rubber stopper, b, is first connected by the aid of a good cork with the combustion tube, and then the U-tube c, having been charged with the proper quantity of acid from a MOHR burette, is added. At the termination of the combustion, when air has been drawn through the apparatus, the tube a is rinsed into the apparatus c, some tincture of litmus added, and the standard alkali FIG. 66. run into the tube from a second burette until the acid is almost blue. Now pour the contents into a beaker, rinse with water, and complete the tit ration. With this receiver neither receding nor spirting is possible. By not pouring out the fluid until the point of saturation is nearly attained, less water is required for rinsing out the tube. Of course the form of the receiver may be varied; thus in the modification of the VARRENTRAPP-WILL apparatus, recommended by J. VOLHARD,* the anterior bulb and point are replaced by a 150-c.c. to 200-c.c. ERLENMEYER flask. The standard sodium-hydroxide solution used must be per- fectly free from carbonic acid. I prefer to dilute it so that 3 c.c. will neutralize 1 c.c. of the acid. Some chemists prefer dilute baryta water. In highly colored liquids a sensitive litmus paper is better than litmus tincture for recognizing the neutrality point. PELIGOT'S modification is particularly suitable for technical and agricultural investigations. In the hands of an experienced operator, and using correct standard fluids and measures, this method is scarcely inferior in accuracy to that described in 186. The results obtained by many chemists are, nevertheless, even in this respect, not in accord. MXRCKER,t for instance, states that titration gives lower results with substances containing carbon and nitrogen^^gluten) than does the platinum method, because * Annal. Chem., CLXXVI, 282; Zeitschr. f. analyt. Chem., xiv, 332. t Zeitschr. f. analyt. Chem., xn, 221. 187.] NITROGEN DETERMINATION. 93 aniline-like products form and escape being titrated. On the other hand, KREUSLER,* in analyses of meat, residues of meat extracts, and conglutin, obtained results that were almost identical with both methods, and which agreed, moreover, with those afforded by DUMAS' method. [From the results of a critical investigation of this method by JOHNSON and JENKINS,! the following facts may be here added : 1. The efficiency of the ''soda-lime" mixture described 66, 5, is fully confirmed. It is easier to prepare than the mixture of caustic lime and soda ( 66, 4) formerly used for this purpose, and does not, like the latter, attract moisture readily from the air, and is not liable to swell and choke the tube during combustion. 2. Neither the highest heat possible to obtain in an ERLEN- MEYER gas combustion furnace, nor a long layer of strongly heated soda-lime, nor these two conditions united, occasion any appreciable dissociation of the ammonia formed in combustion. 3. A suitable length of the anterior layer of soda-lime must be secured in order to get a good result. With 0-5 grm. of substances, such as are encountered in agricultural chemistry, containing less than 8 per cent, of nitrogen, a glass tube of 12 to 14 inches is long enough. As the content of nitrogen increases to 10 per cent, or over, the tubes should be made several inches longer. In the combustion of dried blood or egg-albumin a tube 20-25 inches long is preferred, and the mixture of soda-lime and substance should occupy rather less than half the tube, a layer of pure soda- lime of 12 or more inches long being essential for perfectly destroy- ing the volatile organic matters. 4. The long anterior layer of pure soda-lime must be brought to a full red heat before heating the mixture, and must be so kept throughout the combustion. 5. No fumes or tarry matters, indicative of incomplete com- bustion, should appear in bulb-tube or receiver. 6. When the combustion proper is begun under the conditions * Zeitschr. f. analyt. Chem.. xn, 357. t Report of Connecticut Agr. Exp. Station, 1878, p. 111. 94 ORGANIC ANALYSIS. [ 187. above described, it can be carried on quite rapidly until completed. The contents of the tubes then show no sign of unburned carbon. 7. Equally good results are obtained whether the mixture is made intimately in a mortar or more roughly by stirring with a spatula in a metallic capsule or scoop, or by mixing in the tube with a wire.] In using the DUMAS method in the factory, as, for instance, in a manure works, it is advantageous to replace the glass combustion tubes by iron ones. In order to show how this may be done, the process devised by THIBAULT * is here given. He recommends the employment of a wrought-iron tube of 20 mm. bore and 90 cm. length. It extends 15 cm. from the furnace at each end. Both orifices are closed by corks bearing narrow glass tubes. A 35-cm. layer of granular soda-lime is introduced in the fore part of the tube and is kept in place by iron-wire plugs. The substance to be analyzed is mixed with pulverulent soda-lime, and is placed in a sheet-iron boat about 20 cm. long, which is inserted into the tube from behind. The apparatus used to hold the acid is that ordi- narily employed. The operation is conducted as follows: First heat the empty combustion tube to redness in order to purify it, and pass a current of pure hydrogen gas through it. After the tube has cooled, charge the fore part with granular soda-lime, insert the boat containing pulverulent soda-lime into the hinder end, and heat the tube to redness while passing a current of hydrogen gas through it. Now allow the hinder end to cool, withdraw the boat by means of a suitable wire, remove some of the soda-lime from the boat, mix the weighed substance to be analyzed with the re- mainder, and then cover the mixture with the soda-lime first removed. Now replace the boat in the tube and gradually heat the mixture to redness while a slow current of hydrogen is passed through the tube. When the operation is at an end, remove the acid bulbs and the boat, and heat the tube more strongly while a more rapid current of hydrogen is passed through it in order to free the layer of soda-lime from any hydrocarbons that may have condensed on it. The tube is then ready for another opera- * J. Pharm. Chim., [4], xxu, 39; Journ. Chem. Soc., CLIX, 433. 188.] SULPHUR IN ORGANIC COMPOUNDS. 95 tion, and by using a number of boats, a whole series of analyses may be uninterruptedly made. C. ANALYSIS OF ORGANIC COMPOUNDS CONTAINING SULPHUR.* 188. The usual method of determining the carbon in organic bodies viz., by combustion with cupric oxide or lead chromate would give results too high in the analysis of compounds containing sulphur, since more especially if cupfic oxide is used a portion of the sulphur would be converted in the process into sulphurous acid, which would be absorbed with the carbonic acid in the potash bulbs. In order to avoid this error, LIEBIG and WOHLER interpose between the calcium-chloride tube and potash bulbs a tube 10 to 20 cm. long and filled with perfectly dry lead dioxide. According to CARIUS' t experiments, however, this means does not suffice to retain all the sulphurous acid yielded by substances rich in sulphur, while at the same time it impairs the accuracy of the carbon determina- tion, because lead dioxide has the power to take up quite a con- siderble quantity of carbonic acid (BUNSEN). CARIUS recommends to burn substances containing sulphur in a tube 60-80 cm. long with lead chromate, care being taken that the anterior 10-20 cm., which contains pure lead chromate, are never heated above low redness. The lead chromate may be used again three or four times without refusion; and, finally, if treated by VOHL'S method (Vol. I, p. 152 J), it is just as fit for use as if it had not been employed for the combustion of a substance containing sulphur. For the process employed by CLOEZ with substances containing sulphur, compare 192. * The method of qualitatively determining sulphur in organic substances by heating with sodium, and ascribed to SCHONN, was first recommended by VOHL (Zeitschr. f. analyt. Chem., n, 442). [WARREN'S method of deter- mining carbon hydrogen, and sulphur in one operation is described in Am. Journ. Sci., XLI, 2d ser., p. 40.] f Annal. d. Chem. u. Pharm., cxvi, 28. J This is as follows : Wash first, if necessary, then fuse and powder. After having been used twice, powder it, moisten with nitric acid, dry, and fuse. VOHL states (Annal. d. Chem. u. Pharm., cvi, 127) that lead chromate thus treated may be used over and over again indefinitely. 96 ORGANIC ANALYSIS. [ 188. The presence of sulphur demands no modification in the process described in 185, 186, and 187 for the determination of nitrogen. In substances containing oxygen in presence of sulphur, the oxygen is estimated from the loss. As regards the estimation of the sulphur in organic compounds, that element is invariably weighed in the form of barium sulphate, into which it may be converted either in the dry or in the wet way. Both processes may be carried out in various ways; and as one or another of the methods may be found more easy of application, or more rapid, according to circumstances, I feel it incumbent to describe a number of them. I. METHODS IN THE DRY WAY.* 1. Method suitable, more particularly, to determine the sulphur in non-volatile Substances poor in Sulphur, e.g., in the so-called Protein Compounds (v. LIEBIG). Put some lumps of pqtassa free from sulphuric acid ( 66, 6, c) into a capacious silver dish, add J of pure potassium nitrate, and fuse the mixture, with addition of a few drops of water. When the mass is cold, add to it a weighed quantity of the finely pul- verized substance, fuse over the lamp, stir with a silver spatula, and increase the heat, continuing the operation until the color of the mass shows that the carbon separated at first has been com- pletely consumed. Should this occupy too much time, you may accelerate it by the addition of potassium nitrate in small portions. Let the mass cool, then dissolve in water, supersaturate the solu- tion with hydrochloric acid in a capacious beaker covered with a glass dish, and precipitate with barium chloride. Wash the pre- cipitate well with boiling water, first by decantation, then on the filter. Dry and ignite. Treat the ignited barium sulphate as directed in 132, 1 ; if this latter operation is omitted, the result is almost always too high. * Besides the methods here given, many others have been recommended, but are here only referred to. e.g., HEINTZ (POGGEND. Annal., LXXXV, 424); Annal. d. Chem. u. Pharm., cxxxvi, 225; R. OTTO (Zeitschr. f. analyt. Chem., vii, 117); W. F. GINTL (ibid., vn, 302); MULDER (ibid., ix, 271), etc. AL. MITSCHERLICH'S method will be given under 192. 188.] SULPHUR IN ORGAXIC COMPOUNDS. 97 A suitable alcohol lamp is preferable to a gas flame, since the latter may communicate sulphur to the fused mass, and hence be the cause of error. As it is by no means easy to obtain the required reagents perfectly free from sulphur, it is well to try a parallel experiment, using the same quantities of each that is used for the analysis, and if an appreciable amount of barium sulphate is ob- tained, make the necessary correction in the analysis. 2. Method adapted more particularly for the Analysis of non- volatile or difficultly volatile Substances containing more than 5 per cent, of Sulphur (KOLBE *). Introduce into the posterior part of a straight combustion tube f 40-54 cm. long, a layer 7-8 cm. long of an intimate mixture of 8 parts of pure anhydrous sodium carbonate and 1 part of pure potassium chlorate; % after this introduce the weighed substance, then another layer, 7 or 8 cm. long, of the same mixture; mix the organic compound intimately with the sodium carbonate and potas- sium chlorate by means of the mixing wire (Fig. 32, p. 33, this vol.) ; fill up the still vacant part of the tube with anhydrous sodium carbonate or potassium carbonate mixed with a little potassium chlorate. Clear a wide passage from end to end by a few gentle taps, place the tube in a combustion furnace, heat the anterior part to redness, and then, progressing slowly toward the posterior part, proceed to surround with red-hot charcoal the part occupied by the mixture. In the analysis of substances abounding in carbon, it is advisable to introduce into the posterior part of the tube a few lumps of pure potassium chlorate, to insure complete combustion of the carbon and perfect conversion into sulphates of the com- pounds of potassa with the lower oxides of sulphur that may have formed. The sulphuric acid in the contents of the tube is deter- mined as in 1; but the silica taken up from the glass must be separated by first evaporating to dryness the liquid acidulated with hydrochloric acid. * Supplemente zum Handworterbuch der Chem., 1. edit., p. 205. f Sealed and rounded at the end like a test-tube. t Instead of the mixture of potassium chlorate and sodium carbonate, HOBSON (Annal. d. Chem. u. Pharm., en, 77) employs a mixture of potassium chlorate and magnesium carbonate. 98 ORGANIC ANALYSIS. [ 188. 3. Method adapted for the Analysis both of non-volatile and volatile Substances, but more especially the latter (DEBUS *). Dissolve 1 eq. (294-42 parts) of potassium dichromate purified by recrystallization and 2 eq. (212-2 parts) anhydrous sodium carbonate in water, evaporate the solution to dryness, reduce the lemon-colored saline mass (K 2 CrO 4 +Na2CrO 4 +Na 2 CO 3 ) to powder, heat to intense redness in a Hessian crucible, and transfer still hot to a flask, Fig. 29, 175. f When the powder is cold, introduce a layer of it, 7-10 cm. long, into a common combustion tube; then introduce the substance, and after this another layer, 7-10 cm. long, of the powder. Mix intimately by means of the mixing wire, then fill the still unoccupied part of the tube with the saline mixture, and apply heat as in an ordinary ultimate analysis. When the entire mass is heated to redness, conduct a slow stream of dry oxygen gas over it for J- 1 hour. When cold, wipe the ash off the tube, cut the latter into several pieces over a sheet of paper, and treat them in a beaker with a sufficient quantity of water to dis- solve the saline mass. Add hydrochloric acid (absolutely free from sulphuric acid) in tolerable excess, then some alcohol, and apply a gentle heat until the solution shows a beautiful green color; filter off the chromic oxide produced by the combustion (this con- tains sulphuric acid); wash first with water containing hydro- chloric acid, then with alcohol, dry, and transfer to a platinum crucible; add the filter-ash, mix with 1 part of potassium chlorate and 2 parts of potassium (or sodium) carbonate, and ignite until the chromic oxide is completely converted into potassium chromate. Dissolve the fused mass in dilute hydrochloric acid and reduce by heating with alcohol; add the solution to the fluid filtered from the chromic oxide, heat the mixture to boiling, and precipitate the sulphuric acid with barium chloride ( 132, 1). DEBUS'S test analyses were very satisfactory; thus he obtained 99-76 and 99-50 * Annal. d. Chem. u. Pharm., LXXVI, 90. ] The saline mass must always first be tested for sulphur. For this purpose a small portion of it is reduced with hydrochloric acid and alcohol, barium chloride added, and the mixture allowed to stand 12 hours at rest. No trace of a precipitate should be discernible. 188-] SULPHUR IX ORGAXIC COMPOUXDS. 99 of sulphur for 100; again 30-2 of sulphur in xanthogenamide for 30-4, etc. 4. Method equally adapted for the Analysis of Solid and Liquid Volatile Compounds (W. J. RUSSELL; * suggested by BUNSEN). Introduce into a combustion tube, 40 cm. long, sealed at the posterior end, first 2-3 grm. pure mercuric oxide, then a mixture of equal parts of mercuric oxide and pure anhydrous sodium car- bonate, mixed with the substance, and fill up the tube with sodium carbonate mixed with a little mercuric oxide. Connect the open end of the tube with a gas delivery tube dipping under water, to effect the condensation of the mercurial fumes. Place a screen in front of the part of the tube occupied by the substance, then heat the anterior part to bright redness, and maintain this temperature during the entire process. At the same time, heat another portion of the tube, nearer to the end, but not to the same degree of inten- sity, so that there may be alternate parts in the tube in which the mercuric oxide is left undecomposed. When the part before the screen is at bright redness, remove the screen, heat the mixture containing the substance, regulating the application of heat so as to insure complete decomposition in the course of 10-15 minutes, and heat at the same time the still unheated parts of the tube, and lastly also the pure oxide of mercury at the extreme end. The gas must be tested from time to time, to ascertain whether it con- tains free oxygen. Xext dissolve the contents of the tube in a little water, add some mercuric chloride, to decompose the sodium sulphide which may have formed, acidify with hydrochloric acid, oxidize with potassium chlorate the mercuric sulphide which may have formed, and finally precipitate the sulphuric acid with barium chloride ( 132, 1). W. J. RUSSELL obtained by this method very satisfactory results in the analysis of pure sulphur, potassium sulphocyanate, and carbon disulphide. * Journ. f. prakt. Chem., LXIV, 230. 100 ORGANIC ANALYSIS. [ 188. 5. Methods based upon the Combustion of the Sulphur-containing Substance in Oxygen Gas. Such methods have been proposed by C. M. WARREN,* W. G. MIXTER,! A. SAUER,t and G. BRUGELMANN. These methods are advantageous in that they yield the sulphur as sulphuric acid in a fluid containing little other matter, give uniformly good re- sults, and are adapted for all kinds of organic substances containing sulphur. I would further state here that WARREN'S method also permits the carbon, hydrogen, and chlorine to be determined, while BRUGELMANN'S method allows of the determination of the sulphur, chlorine, and phosphorus in the one portion of the substance. a. WARREN burns the substance in a combustion tube open at both ends, but the hinder third of which is bent upwards at an obtuse angle. The substance is contained in this bent part, and is heated by a special gas lamp. The mixture of the excess of oxygen gas with the combustion products passes first through a long layer of asbestos, then an unfilled space of about 6 cm., then a dense asbestos plug, next a layer of pure asbestos mixed with lead dioxide (which is heated only just sufficiently to prevent any condensation of aqueous vapors in it), and finally another asbestos plug. After the combustion the sulphur is found in the lead-dioxide layer in the form of lead sulphate. Hence the mixture of the latter with the lead dioxide and asbestos is digested with a strong solution of sodium bicarbonate for twenty-four hours, whereby the lead sul- phate is decomposed, and the sulphuric acid is finally titrated in the filtrate according to 132, 1. b. MIXTER'S method depends upon the use of oxygen gas mixed with bromine vapors, and contained in a flask having a capacity of 4-10 liters. The combustion tube used is like that of WARREN'S. The apparatus is a closed one, so that the oxygen-bromine mixture continuously circulates through it. The circulation is effected by heating the bent-up portion of the tube containing the substance. By rinsing out the various parts of the apparatus a solution is finally obtained which contains all the sulphur as sulphuric acid, * Zeitschr. /. analyt. Chem., v, 169. t Ibid., xn, 32, and xn, 178. f Ibid., xii, 212. Ibid., xv, 1, and xv, 175. 188.] SULPHUR IN ORGANIC COMPOUNDS. 101 besides hydrobromic acid and some free bromine; the sulphuric acid is determined as in 132 ; 1. Both MIXTER'S and SAUER'S methods possess the advantage FIG. 67. that the sulphur is obtained as free sulphuric acid in a solution containing no fixed matter, and consequently in a condition to be easily and accurately determined. MIXTER'S method is described * as follows : The apparatus (Fig. 67) is designed to effect the combustion in a confined volume of gas, a device resorted to on account of the difficulty of completely condensing by liquid absorbents in U-tubes the dense white fumes of sulphuric acid produced by combustion. The bottle (a) has a capacity of from 4 to 10 litres, according to * American Journ. Sci. and Arts, iv, 90. 102 ORGANIC ANALYSIS. [ 188. the amount of oxygen required. The neck should be large enough for a stopper 35 to 40 mm. in diameter. /The condenser 6 is made of rather thin tubing 14 mm. in diameter; at the upper end it is expanded to a bulb in order to admit some motion to the tube c d. Below the bulb it is surrounded by a water-jacket 22 cm. high; from the point where it enters the stopper of the bottle it is nar- rowed somewhat for convenience of fitting. The combustion tube c d is made of hard glass of 12-15 mm. internal diameter; the portion c is 18 cm. from curve to curve, and is protected by a sheet-iron trough lined with asbestos; the part d is from 35 to 45 cm. in length. The wire attached at / is to sustain c in case d breaks; c is joined to b by a collar of black rubber. The U-tube e is connected with d by a rubber collar drawn over the latter at k; this U-tube is slightly inclined, that no liquid may run against the rubber connectors. The tube / connects a with e; it is narrowed at both ends to 10 mm. diameter. Near the upper end it is jointed by a piece of black-rubber tubing in order that the apparatus may be easily disconnected at k. The ends of / extend 2 cm. or more beyond the stoppers. Through the rubber stopper i a small glass tube passes beyond the end of /, where it is narrowed to an open- ing of 1 mm. The double bulb tube j is to accommodate varia- tions of pressure, and to admit air as the original volume of gas diminishes during the combustion. The tubes 6, c, d, and / should at no point have an internal diameter less than 8 mm. (10 mm. is preferable) and the narrowed ends should be cut obliquely that drops of water may not obstruct the circulation. The rubber stop- pers and connections should be freed from adhering sulphur by heating in a solution of soda. The joints of the apparatus are suffi- ciently tight when water will stand in one limb of the safety tube. The bottle a is filled over water with oxygen, and, if necessary, rinsed with distilled water; a few drops of bromine are poured in, the tubes adjusted, and a slow stream of water made to flow through the water-jacket. The assay, if not volatile, is introduced into the tube d in a platinum tray,* which should not fill more than half * A platinum tray which answers well may be made 10 to 20 cm. long, 10 mm. wide, and 7 to 10 mm. deep by bending thin foil over a glass tube. The ends may be roughly bent together or left open. 188.] SULPHUR IN ORGANIC COMPOUNDS. 103 the bore of d, leaving space enough for the free circulation of the oxygen. The part c is gradually heated and kept hot during the combustion. This hot inclined tube acts as a chimney; the heated gases rise in it, pass into the cold tube b and fall, thus causing a constant steam of gas to pass over the assay. It is important to ignite the assay without distilling off any considerable portion. To do this a small splinter of wood may be placed in contact with that part of the substance nearest I, or that end of the tray may hold a thin layer of the assay, which is heated as rapidly as safety allows by a lamp held in the hand. To insure a full supply of gas in the tube d at the commencement of the combustion, oxygen is passed from a gasometer through the tube i till the white fume which appears in the condenser b passes into a. The products of combustion being denser falHo the bottom of the bottle, and for a while displace the oxygen, thus increasing the circulation. After the substance is ignited, the fire passes to the other end of the tray. The part of the tube about the tray is heated by a lamp as required to keep up the combustion. At the end of the operation the heat is increased. If drops of liquid collect in c, and are liable to run down to the hotter parts of the tube, they should be driven off by heat. If carbonic acid be the principle product of the com- bustion, there is little change in the volume of gases in the appa- ratus; but if water and sulphuric acid are formed in much quantity, the volume is diminished and air enters through the safety tube. Most solid substances heated alone in the open tray yield vola- tile products too rapidly for entire combustion, but if mixed with sand in suitable proportion they burn slowly and completely. Liquids should be enclosed in narrow tubes sealed at one end and drawn out at the other to a capillary bore for two or three inches of length. Upon the point of the tube a bit of platinum sponge is fixed to assist the oxidation. The liquid should not fill more than two- thirds of the wider part of the tube. Before introducing very volatile substances, the 10 cm. of the combustion tube I d should be heated to dull redness. Oxygen is passed in at i, the tubes are disjointed at k, and the tube holding the assay is then pushed in till the platinum just reaches the heated 104 ORGANIC ANALYSIS. [ 188. zone. The apparatus being connected at k, slow volatilization of the liquid is effected by cautiously applying a flame under the empty portion of the tube containing the substance, so as to main- tain the platinum sponge in a steady glow. As soon as a cloud of combustion products appears in the vessel a, oxygen is shut off from i. When all the liquid has distilled from the interior tube, the tube c d is cooled slowly and the apparatus is left for two hours or until the fume has entirely subsided. If no odor of bromine be perceptible when the apparatus is disconnected at k to remove the tray or tube, a few drops of it should be poured through a funnel tube put in the place of /, and the whole allowed to stand some time to ensure complete oxidation of the sulphur compounds and deposition of the sulphuric acid. The tubes d and e are then rinsed into a beaker, this water is poured into 6, which is then thoroughly washed by the aid of the wash-bottle; the large rubber stopper is lifted from the bottle and the lower part of b rinsed; without removing the tube / from the stopper, it is rinsed into a beaker, and finally the bottle is care- fully washed. The solution obtained, which need not exceed 500 c.c., is evaporated to a small volume, filtered if necessary, and the sulphuric acid is determined by precipitation with barium chloride, observing all precautions mentioned in 132, 1. In case the sub- stance leaves an ash or residue in the tray, this must be dissolved in aqua regia, the nitric acid removed by evaporation with strong hydrochloric acid, and any sulphuric acid it may contain separated in the usual manner. In the use of this apparatus there is no danger from explosions if care be taken to have the combustion tube hot enough to ignite combustible vapor. Before attempting to burn a substance in the apparatus, it is best to try it in a large inclined tube open at both ends, or with oxygen supplied at the lower end. Such a preliminary trial will usually indicate the pre- cautions necessary in burning the substance in the apparatus. For the determination of sulphur in substances rich in sulphur, 0-5 to 0-75 grm., requiring about 4 litres of oxygen may be used. When but little sulphur is present, a combustion of 2 grms. may be effected with 9 litres of oxygen. External heat is best applied 188.] SULPHUR IN ORGANIC COMPOUNDS.. 105 to the part of the tube containing the substance by a BUNSEN burner held in the hand. The length of time required for the actual com- bustion seldom exceeds 20 minutes. This method gives very accurate results. c. SAUER'S apparatus is comparatively simple, and will hence be described. The substance is burned in a current of oxygen and the sulphurous acid formed is collected in hydrochloric acid con- taining some bromine; after the greater part of the hydrochloric acid and free bromine is evaporated off, the sulphuric acid is esti- mated as in 132, 1. a. FOR SUBSTANCES WHICH YIELD BUT LITTLE VAPOR AND PARTICULARLY No SULPHUR ON HEATING, e.fa COKE, the method is very simple. The apparatus used is shown in Fig. 68. FIG. 68. The substance is contained in a porcelain boat which is placed at b in a combustion tube about 60 to 80 cm. long. The brominated hydrochloric acid is contained in the receiver c. A current of purified oxygen gas is passed through the tube, which is then heated to redness at the point where the boat is placed. The escaping bromine is absorbed by calcium hydrate or dilute hydrochloric acid, in order to prevent any interference from it. After the combustion, any liquid that may have condensed is driven into the absorption apparatus c, and the gaseous contents of the com- bustion tube finally displaced by a current of oxygen or air. As at times small quantities of sulphuric anhydride remain in the fore part of the combustion tube even after the passage of 106 ORGANIC ANALYSIS. [ 188. oxygen or air, it is advisable to rinse the tube with water and to add the washings to the liquid in the receiver (F. MUCK *). The ash remaining in the boat may be first weighed and then treated with hydrochloric acid for the determination of the sul- phate contained in it, provided not too much ferric oxide is present; otherwise it must be fused with potassium and sodium carbonates (132, II). SAUER'S method, modified by MIXTER,! is as follows: A combustion tube 30 to 40 cm. in length is drawn out quite narrow at one end, and the drawn-out narrow part is bent down- ward at a right angle and fitted by means of a perforated stopper into the U-tube A, Fig. 69, containing aqueous solution of bro- FIG. 69. mine and also a large drop of undissolved bromine. The globule of bromine is made to rest at the point / by giving the apparatus a suitable inclination. The combustion tube is laid in a combus- tion furnace, and the substance contained in a tray is pushed into * Zeitschr. /. analyt. Chem., xiv, 16. t Am. Journ. Chem., n, 396. 188.] SULPHUR IN ORGANIC COMPOUNDS. 107 the open end about 15 cm. This end is then closed with a stop- per, through which passes a glass tube. Pure oxygen gas is then conducted into the combustion tube, and the part containing the tray is heated to redness. If during the process the bromine in solution becomes nearly exhausted by the action of sulphurous acid, a portion of the undissolved globule is shaken over into the narrow part e of the U-tube, where it is rapidly dissolved by the agitation caused by the passing gas-bubbles. In order to complete the condensation of fumes of sulphuric acid which may pass through the U-tube, they are conducted by means of the tube g to the bottom of the bottle B, which has a capacity of about 8 litres. The bottom of the bottle should be barely covered with water. During the process of combustion a cloud of fumes may be observed in the lower part of the bottle, while the air in the upper part remains perfectly clear. After combustion is com- pleted, the tube g is removed and the bottle with its mouth closed is allowed to stand until the visible fumes are absorbed. The com- bustion tube is rinsed to remove sulphuric acid which may have condensed in the part near the U-tube. The rinsings are added to the united solutions obtained in A and B. The solution contain- ing the sulphuric acid is now heated to remove free bromine, and concentrated if the volume appears too great. The sulphuric acid in it is determined as in the similar solution obtained by the process described above in 1. If the operator cannot procure a U-tube of the form represented by A, the more common form shown by Fig. 6& may be used. In that case it is best to use a saturated solution of bromine in hydro- chloric acid, of which the U-tube should contain 12 to 15 c.c. when filled to extent indicated in Fig. 66. On account of the small volume of liquid which can be used in such tube, an aqueous solu- tion would hardly suffice. The free hydrochloric acid should be nearly all removed by evaporation from the final solution of sul- phuric acid before proceeding to precipitate the latter with barium chloride. If inorganic matter remains in the tray after completing the combustion, it is to be treated as directed in c, 1. 108 ORGANIC ANALYSIS. [ 188. (I. FOR SUBSTANCES WHICH VOLATILIZE WITH OR WITHOUT DECOMPOSITION, the apparatus used is somewhat more complicated; it is shown in Fig. 70. r FIG. 70. A combustion tube about 85 cm. long is narrowed at b to a width of 5 mm. The substance, which is here assumed not to be volatile unless heated, is contained in a porcelain boat d; the com- bustion tube is placed in the furnace; the oxygen is delivered through the tube x x, which is fixed to the outside of the furnace in order to keep it cool, and which is somewhat widened at' 6. The rubber tube z may, according to circumstances, be connected with an apparatus delivering dry carbonic-acid gas, pure oxygen, or purified air. The receiver y contains brominated hydrochloric acid, and is connected with an apparatus containing calcium hydrate or dilute hydrochloric acid for arresting the escaping bromine. According to SAUER'S directions, the space in the com- bustion tube between the boat and b should remain unfilled. I believe, however, that it might be advisable to at least partially fill it with ignited asbestos, as recommended by WARREN * as well as by me f in similar operations. After the apparatus has been set up, the part b is heated to bright redness, a current of oxygen slowly passed through the tube x x, while a slow current of air is allowed to enter the rubber tube z, { * Zeitschr. f. analyt. Chem., in, 272. f Ibid., m, 339. j SAUER does not direct this to be done, but I consider it very advisable because otherwise products of the dry distillation may readily penetrate as far as the stopper a. 188.] SULPHUR IN ORGANIC COMPOUNDS. 109 and the substance then heated gradually. The evolved vapors meeting the oxygen at the strongly ignited part 6 are burned; as soon as this occurs an excess of oxygen must be supplied. When no more gases are evolved and the tube has been heated to redness progressively from a to b, the air current is somewhat increased until no more combustion is observed at b and oxygen instead of air is then passed through the tube z, to burn the residue in the boat as well as any unburned matter adhering to the tube. Care must be taken to so cautiously heat the substance that no unburned tarry matters may collect in the tube between b and c. Should any such have formed, however, they may with proper caution be finally burned in the current of oxygen. It must always be remembered that a part of the sulphur may remain in the boat in the form of sulphates, and occasionally as sulphides; thus, in the analysis of vulcanized caoutchouc, zinc sulphide is frequently found in the residue. The residue in the boat should hence be dissolved in brominated hydrochloric acid and the sulphuric acid determined in it alone, or along with that in the receiver. [With substances which give off volatile matter at a high tem- perature, a combustion tube about 85 cm. long, narrowed at the point indicated by c in Fig. 71, is employed. Having introduced the substance in a tray (or if volatile at the ordinary temperature in a bulb tube with capillary orifice), the narrow part of the combus- tion tube and also a portion beyond extending to within 10 or 15 cm. of the end entering the U-tube is heated to dull redness in a combustion furnace. Oxygen gas is now conducted by means of the hard-glass tube a to the point c beyond the tray. At the same time a very slow current of carbon dioxide is made to enter through FIG. 71. the tube b in order to prevent vapors from receding. Now, by a cautious application of heat the volatile matter in the tray is first 110 ORGANIC ANALYSIS. [ 188. distilled off and burned by the constantly supplied current of oxy- gen. Next the combustion of any fixed residue remaining in the tray is effected by transferring the supply of oxygen from a to b, and that of carbon dioxide from b to a. The only use of carbon dioxide at this stage is to prevent products of combustion from entering the tube a. The combustion tube during the process is connected with the same absorbing apparatus as used in MIXTEK'S modification of SAUER'S method (page 106, this vol.). The re- maining part of the process is also conducted as in the latter method. MIXTER * obtained quite satisfactory results with this process. When very volatile substances, e.g., carbon disulphide, are to be burned, it is necessary to apply heat very cautiously to the part of the tube containing the substance, so that the flame produced by the meeting of the combustible vapor with oxygen shall be a few millimetres back of the end of the tube delivering the oxygen.] 7-. SULPHUR IN COAL GAS may also be determined as in /?. The apparatus is first filled with carbon dioxide, then the meas- ured volume of the coal gas is passed through the tube and burned at the constricted part b with oxygen. Finally, carbon dioxide is again passed through the apparatus until the coal gas is all expelled and burned. d. WHEN DETERMINING SULPHUR IN READILY VOLATILE FLUIDS, e.g., carbon disulphide, weigh the substance in a small glass tube 5 to 6 rnm. wide and bent into the form shown in Fig. 72. First, however, weigh the tube while empty and open, then fill it, seal both ends, and weigh again. Pack the hinder FlG * 72> part of the combustion tube with small pieces of porcelain, then fill the apparatus with carbon dioxide, and insert one limb of the U-shaped tube (which may be drawn out thin) air-tight into the perforation of the stopper. When the constricted part of the tube is red-hot, conduct oxygen through xx, push the U-shaped tube further in so that the point is broken * Am. Journ. Chem., n, 396. 188.] SULPHUR IN ORGANIC COMPOUNDS. Ill by the pieces of porcelain and gently warm the fluid so that the vapors reach the red-hot part of the combustion tube but slowly. I consider it doubly necessary to place a layer of asbestos both in this as well as in the previously mentioned process between d and 6. When the whole of the fluid has been volatilized and expelled from the tube, insert the outer limb of the latter into the rubber tube connected with the carbon-dioxide apparatus, break off the point within the rubber tube, and pass a slow current of carbon dioxide through the apparatus until combustion at b is no longer observed. d. G. BRUGELMANN also burns the substance in a tube open at both ends, but absorbs the combustion products hi a short layer of granular caustic lime or granulated, pure soda-lime * (4 parts pure lime and 1 part pure sodium hydroxide) . Much depends upon the quality of the lime. At times the ordinary caustic lime from marble may be employed, particularly if the small quantity of sulphur is first determined and taken into account. In most cases, however, it is preferable for the chemist to prepare the lime himself. For this purpose slack some lime from marble and add nitric acid until but a small quantity of the lime remains undissolved, and the reaction therefore remains alkaline. Evaporate without filtering over a naked flame until the boiling-point reaches 140. The boiling solution will then exhibit a pellicle of calcium nitrate. Mix the solution thoroughly in a beaker with two volumes of a mixture of two volumes absolute alcohol and one volume ether, and let the whole stand in a closed flask for twelve hours to deposit. The ether and alcohol are now expelled by carefully heating the pure calcium-nitrate solution in a porcelain dish, after which evaporate to dryness with stirring. The calcium nitrate so obtained must be preserved in a well-closed bottle. Heat a portion of it to redness in an unglazed porcelain flask in a suitable furnace. As soon as the calcium nitrate is decomposed and the evolution of gas has ceased, introduce a fresh quantity of the nitrate into the flask, and continue thus until the flask is filled with caustic lime. Now break the flask, separate the * Zeitschr. f. analyt. Chem., xv, 175, and xvi, 1. 112 ORGANIC ANALYSIS. [ 188. lime from the fragments of the flask, break it into very small pieces in a porcelain mortar until the largest pieces have a diameter of 5 mm. Finally pass the fine powder through a sieve of 1 mm. mesh. Commercial lime from marble which is used without further treair- ment is granulated similarly. The details of the method vary somewhat according to the nature of the substance. a. SOLID SUBSTANCES OF ALL KINDS, AS WELL AS NON-VOLA- TILE COMPOUNDS. The combustion tube should be about 50 cm. long and 12 mm. in diameter. In the end farthest from the oxygen gasometer introduce a closely fitting roll of platinum foil, leaving an unfilled space of about 2 cm. ; then introduce a 10-cm. layer of granulated caustic lime or soda-lime, tap the tube so that the layer of lime settles well, clean the tube from adhering lime, and keep the lime layer well in place by inserting a second roll of platinum foil, or, when the substances contain phosphorus, by a layer of broken glass 5 cm. long. In the case of substances which are likely to yield explosive gases, introduce next a layer of ignited asbestos 15 to 20 cm. long, and then the substance, either in pieces (e.g., parts of plants) or in a boat. The last 15 cm. of the tube should remain unfilled. Place the prepared tube in the furnace so that 3 cm. of the end to be connected with the oxygen gasometer projects, and take care that the sheet-iron trough in which the tube rests underlies only that part of the tube containing the lime, platinum rolls (or pieces of glass), and 1 cm. of the asbestos layer. If the substance has to be used in large pieces (e.g., parts of plants) and for which, therefore, a boat will not suffice, connect the tube with the oxygen apparatus, the delivery tube of which should have an aperture 0-5 mm. wide, and regulate the current of oxygen so as to always ensure an excess of the gas, otherwise all the sulphur will not be converted into calcium sulphate and obtained as such. As a rule, 100 c.c. of oxygen is about the proper quantity to pass through in one minute. Now heat to redness 5 cm. of the anterior layer of lime, then gradually also the other 5 cm., and finally the substance, cautiously, as directed below. If the substance is to be burned in a boat, first heat to redness the entire layer of lime, 188.] SULPHUR IN ORGANIC COMPOUNDS. 113 the glass or platinum foil, and 1 cm. of the asbestos, then begin to pass in the oxygen, remove the hinder plug, insert the boat, and rapidly close the tube. The combustion of the substance is begun by cautiously heat- ing it, taking care that oxygen is always present in excess; this may be recognized by applying a glowing match from time to time to the exit end of the tube.* Care must also be taken throughout the entire combustion that the lime remains quite white, and should the substance begin to glow (burning with a flame is to be avoided) , turn off the heat from below the substance until the glow ceases. Slight irregularities of combustion may be controlled by diminishing the oxygen current. Finally, slowly heat to redness the rest of the tube, proceeding from the hinder to the anterior end. As soon as this is effected, the carbon all burned, and oxygen plainly to be detected at the exit end of the tube, the operation is finished. If an asbestos layer and glass or platinum foil have been interposed between the substance and the lime, crack the hot tube with a few drops of cold water at the point where the glass or plati- num foil adjoins the asbestos; if asbestos has not been used, the whole tube is treated as detailed below. First clean the entire tube or the piece of tube externally, withdraw the platinum foil from the end of the tube, and empty the first 2 cm. of lime into a small beaker, dissolve it in hydro- chloric acid, and test it for sulphuric acid. If this is found, reject the analysis. If absent, empty all the contents of the tube, or the piece of tube (excepting the platinum foil and boat, which may be rinsed in the tube) into a beaker, treat" it with water and hydrochloric acid (if necessary, with the addition of some bromine) , filter, and in the solution determine the sulphuric acid according to 132, 1. /?. VOLATILE LIQUIDS are weighed in a small thin-walled glass * In the case of substances the decomposition products of which may give rise to explosions, first heat in a current of air so that the decomposi- tion products may be driven into the asbestos layer and then replace the air current by one of oxygen (Zeitschr. f. analyt. Chem., xvi, 1). 114 ORGANIC ANALYSIS. [ 188. bulb with a long, narrow neck ( 180), and having a total length of 8 cm. After the introduction of the substance seal the point. The combustion tube is charged as in a. The asbestos layer should be 20 cm. long, and when it has been introduced, constrict the tube immediately behind it by heating in the lamp. When the layer of lime, the platinum foil or glass fragments, and 1 cm. of the asbestos layer are red hot, introduce the sealed bulb with its point towards the constricted part of the tube. Now close the hinder end of the tube with a rubber stopper in the well-greased perforation of which is inserted the delivery tube of the oxygen apparatus. The delivery tube should be of stout glass, the end rounded by fusion, and the opening constricted to 0-5 mm. diameter. Now start the current of oxygen, and push in the oxygen delivery tube so as to break off the point of the bulb. Push the bulb forward so that it will be within 4 cm. of the constricted part of the tube; the oxygen delivery tube, however, draw back to its original posi- tion, so that its point will extend only a few mm. from the inner end of the stopper. The bulb must be heated very cautiously and gradually, and in proportion to the volatility of the substance. As soon as all the liquid has been expelled from the bulb, crush the latter by pushing in the oxygen delivery tube, draw back the latter again to its proper position, and finally heat the entire tube to redness, proceeding gradually from the hinder to the fore part, concluding the analysis as detailed under a. f. DETERMINATION OF SULPHUR IN ILLUMINATING GAS. The combustion tube is charged as in a. The asbestos layer should be 20 cm. long. The hinder end of the combustion tube is closed by a rubber stopper carrying two glass tubes with narrow exits; the tubes should project but a short distance beyond the inner end of the stopper. When the fore part of the tube is hot, let the oxygen enter by one of the tubes (say about 110 to 120 c.c. per minute), then also the illuminating gas which had been collected in a glass globe of known capacity, or the volume of which is deter- mined by a gas meter. Long flexible tubes should be avoided for conducting the illuminating gas; the relative currents of the two gases must be so regulated that the oxygen will be always in excess. 188.] SULPHUR IN ORGANIC COMPOUNDS. 115 Should a small flame appear at the exit end of the combustion tube, the current of illuminating gas must be reduced at once. The combustion takes place at the beginning of the heated part of the tube, and only when the operation is carried on too rapidly does it extend into the asbestos layer. About 10 litres of gas should be burned, and this may be done very well in an hour and a half to two hours. Finally, heat to redness the entire asbestos layer, and conclude the operation as soon as oxygen can be dis- tinctly detected at the exit. The further treatment is as described under a. The original paper gives all the details as to the manner of measuring the gas, etc. 6. Method of Determining Sulphur in Coal and Coke. ESCHKA * recommends the following comparatively simple method: Intimately mix about 1 grm. of the substance in the finest possible powder with 1 grm. of calcined magnesia and 0-5 grm. of anhydrous sodium carbonate in a platinum crucible by stirring with a glass rod. Heat the uncovered, obliquely placed crucible in an alcohol flame in such a manner that only the lower half becomes red-hot. In order to promote the combustion which according to the nature of the substance requires from three- quarters to one hour, frequently stir the mixture with a platinum wire. After the coal is burned and the gray color has given place to a yellowish or brownish, intimately mix with the mixture in the crucible 0-5 to 1 grm. of finely powdered anhydrous ammo- nium nitrate, cover the crucible and ignite once more for 5 to 10 minutes. By this treatment the conversion into sulphates of sul- phites which may have formed at first is insured. Now transfer the mixture, which will have retained its pulveru- lent form, into a beaker, rinse the crucible with water into the beaker, warm the whole (which may have a volume of 150 c c.\ filter, acidulate with hydrochloric acid, and precipitate the sul- phuric acid with barium chloride (132, 1). If the calcined mag- nesia or the sodium carbonate contains slight traces of sulphates, it is necessary to determine these and deduct their weight from * Zeitschr. /. analyt. Chem., xni, 344. ORGANIC ANALYSIS. [ 188. the total found. The ignition with ammonium nitrate may be replaced by dissolving the product of the first ignition at once in brominated hydrochloric acid. In this process as well as in all those previously given, the total sulphur of the coal (even that present as calcium sulphate) is obtained as barium sulphate. If only the sulphur exclusive of the calcium sulphate is desired, the finely powdered substance must be continuously boiled for twenty-four hours with an equal weight of sodium carbonate dissolved in water. By this treat- ment the calcium sulphate is decomposed, while the iron sul- phide is not attacked. Filter off, wash with boiling water, and use the residue for the sulphur determination. The sulphuric acid in the calcium sulphate so removed may be determined in the filtrate (FR. GRACE CALVERT *). II. METHODS IN THE WET WAY. 1. According to BEUDANT, DAGUIN, and RivoTf the sulphur in organic compounds may be readily determined by heating with pure solution of potassa, adding 2 volumes of water and conducting chlorine into the fluid. When the oxidation is effected, the solu- tion is acidified and freed from the excess of chlorine by applica- tion of heat, then filtered, and the filtrate precipitated by barium chloride. C. J. MERZ, in my laboratory, has employed both this method and also LIEBIG'S (I, 1) in the analysis of fine horn shav- ings. This process appears convenient and exact. J 2. CARIUS'S Method. .This chemist has made the determination of sulphur (phosphorus, chlorine, bromine, iodine, arsenic, and other metals) the subject of repeated, most careful, and compre- hensive investigation. We owe to him the following method which in expert hands is not at all difficult, and which depends * Chem. News, xxiv, 76; Zeitschr. f. anah/t. Chem., xn, 331. t Compt. rend., 1853, 835; Journ. f. prakt. Chem., LXI, 135. t Two experiments were made with each method, on horn dried at 100. The percentages obtained were as follows : By v. LIEBIG'S method, 3 ' 37 and 3'345; by the present method, 3 '31 and 3 '33. 188.J SULPHUR IN ORGANIC COMPOUNDS. 11? upon the oxidation of the substance in a sealed glass tube by a volatile acid liquid. The very numerous test analyses leave nothing to be desired so far as accuracy is concerned. When CARIUS first published his method,* he recommended as an oxidizer 25- to 60-per cent, nitric acid. As, however, many sulphur compounds, particularly the sulphonic acids, are not com- pletely or are only difficultly oxidized by it, he neutralized the nitric-acid solution first with sodium carbonate and then fused with an excess of sodium carbonate; subsequently f he recommended for the oxidization of such difficultly oxidizable sulphur compounds po- tassium dichromate and nitric acid of sp. gr. 1 -4, finally J returning to nitric acid, but of sp. gr. 1-5, to the use of which he adhered, and which completely oxidizes all substances at temperatures of from 200 to 320. At this temperature the acid itself already undergoes decomposition to considerable extent into oxygen, water, and nitrous anhydride. In order to effect complete oxidiza- tion of a substance, it suffices to employ one and a half to twice the quantity of nitric acid as is theoretically required; any greater excess is disadvantageous and should be avoided. Thus, for 0-24 grm. of methyl mercaptan, one of the substances requiring the largest quantity of oxygen, 3-3 to at most 4-4 grm. of nitric acid are hence to be taken. The ease with which various organic substances are oxidized by nitric acid varies greatly; thus with some substances heating for one hour to 150 to at most 200 suffices; others, e.g., those of the aromatic series, require heating for one to two hours at 250 to 260; difficultly oxidizable sulphonic acids and their derivatives again require heating for several hours at a temperature of 250 to 260, but are soon and completely oxidized at 300. In carrying out the process certain rules must be carefully observed. * \nnal. d. Chem. u. Pharm., cxvi, 11. f Ibid., cxxxvi, 129; Zeitschr f. analyt. Chem., rv, 451. t Ber. d. deutsch. chem. Geselkch., m, 697; Zeitschr. f. analyt. Chem., x, 103. 118 ORGANIC ANALYSIS. [ 188. The experimental tube is made of ordinary combustion tubing 45 to 50 cm. long, with an inner diameter of 13 mm. and walls 1-5 to 2 mm. thick. To avoid any risk of an explosion the proportion of 4 grm. of nitric acid to a tube capacity of 50 c.c. should under no circumstances be exceeded. The substance is weighed in a tube shown full size in Fig. 73. The proper quantity of nitric acid, according to the observations made above, is weighed out and in- troduced into the experimental tube already containing the small tube with the substance inclosed; the experi- mental tube is now sealed and drawn out to a thick- walled capillary tube. The intensity and duration of the heating depend upon the nature of the substance. One hour and a half is usually sufficient as a rule, if the first half hour, which is required to raise the tube to the proper tem- perature, is not counted. The heating of the tubes is effected in the sheet- iron air-bath shown in Fig. 74, the glass tubes being inserted into the iron tubes. The latter are loosely stoppered in front, and the ends directed towards the wall of the laboratory; or better yet, cover the whole with a wooden box, so that no damage may be caused should an explosion take place. When the heating is over and the tube is cold, cautiously warm the drawn-out point in order to expel any liquid in it, and then heat it to redness so that it may blow out and allow the imprisoned gases to escape. If any doubt exists as to the completeness of the oxidization, seal the point again after the gases have escaped and heat once more. This operation is recommended also when it is desired to heat difficulty oxidizable substances to 300, and when there exists a doubt as to the ability of the tube to with- stand the pressure of the gases if the heating is carried out all in one operation. Finally rinse the acid liquid out of the tube, dilute, and de- 188.] SULPHUR IN ORGANIC COMPOUNDS. 119 termine the sulphuric acid according to 132, 1. KULZ* recom- mends (when determining sulphur in bile) repeatedly evaporat- ing the contents of the tube with concentrated hydrochloric acid in order to decompose and remove the nitric acid, then to treat FIG. 74. with water, filter, and precipitate the sulphuric acid in the fil- trate with barium chloride. 3. PEARSON'S Method. t Treat the weighed substance with pure nitric acid of 39 Be. (sp. gr. 1-36) in a porcelain dish, add potassium chlorate, and warm gently, first, however, covering the dish with an inverted and well-fitting funnel, the stem of which is bent into a right angle. From time to time add fresh quantities of potassium chlorate and continue the heat until oxidization is complete. The quantity of potassium chlorate required and the time required depend upon the nature of the substance. For the complete oxidation of 1 grm. potassium sulphocyanate 5 to 10 minutes suffice, while 1 grm. of sulphur requires three-quarters of an hour to one hour. The sulphuric acid in the solution is finally determined according to 132, 1. The method is, of course, not applicable to volatile substances. Substances which contain sulphur and leave an ash on com- bustion may contain part of the sulphur present in the form of * Zeitschr. /. analyt. Chem., xi, 353. f Ibid., ix, 271. 120 ORGANIC ANALYSIS. [ 189. sulphates. The sulphur in these must be determined in a separate sample of the substance and deducted from the total quantity. The method of doing this in the case of coal has been given above (pages 115, 116). In other cases the object is as a rule accom- plished by boiling the substance with hydrochloric acid, whereby the sulphates are dissolved, and then determining the sulphuric acid in the solution according to 132, 1. D. DETERMINATION OF PHOSPHORUS IN ORGANIC COMPOUNDS. 189. The phosphorus in organic compounds is determined by methods similar to those employed for determining sulphur in organic com- pounds, i.e., the organic substance is oxidized either in the wet or dry way, and a solution is obtained in which the phosphoric acid formed by oxidization is determined. For oxidation the methods given in 188, 1, 1, 2, 4, and 5 d, as well as II, 2, are suitable. From the solution obtained phosphoric acid is precipitated, either directly with ammonium chloride, magnesium chloride, and ammonia mixture, or with molybdic-acid solution, after remov- ing hydrochloric acid by repeated evaporation with nitric acid (134, 6, a, and /?). The phosphorus cannot be determined by incineration of the substance and examination of the ash. Vitellin, which when treated with nitric acid gives 3 per cent, of phosphoric acid, yields barely 0-3 per cent, of ash (V. BAUMHAUER). If a substance contains phosphorus both in an unoxidized state and in the form of phosphates, boil a separate portion with hydro- chloric acid, filter if necessary, and determine the phosphoric acid in the solution. The quantity thus found is deducted from the total phosphoric acid found in the portion submitted to oxidation in order to find the amout which existed in the compound in an unoxidized state. 190.] HALOGENS IN ORGANIC SUBSTANCES. 121 E. ANALYSIS OF ORGANIC SUBSTANCES CONTAINING CHLORINE, BROMINE, OR IODINE. 190. The combustion of organic substances containing chlorine with cupric oxide gives rise to the formation of cuprous chloride, which, were the process conducted in the usual manner, would condense in the calcium-chloride tube, and would thus vitiate the deter- mination of the hydrogen. This and every other error may be prevented by the employment of lead chromate ( 176). The chlorine is, in that case, converted into lead chloride, and retained in that form in the combustion tube. If the combustion is effected with cupric oxide in a current of oxygen, the cuprous chloride is decomposed by the oxygen, cupric oxide and free chlorine being formed; the latter is retained partly in the calcium-chloride tube, partly in the potash bulbs. To remedy this defect, STAEDELER * proposes to fill the anterior part of the tube with clean copper turnings; these must be kept red-hot during the combustion, and the current of oxygen must be arrested the moment they begin to oxidize. KEKULE recommends placing a few pieces of fused lead chromate in the anterior part of the tube. K. KRAUT f observes with reference to this process that it is well to place a roll of silver foil about 15 cm. long in front of the layer of metallic copper. In the absence of the silver the transmission of oxygen has to be conducted with caution, in order that no chlorine may be expelled from the cuprous chloride first formed, but by adopting KRAUT'S recommendation we may continue passing the gas without fear till it escapes free from the potash tube. The process so modified is suitable also for substances containing bro- mine and iodine. [In the case of substances containing iodine, it is needless to employ metallic copper as well as silver foil.] The silver may be used over and over again, but at last requires ignition * Annal. d. Chem. u. Pharm., LXIX, 335. f Zeitschr. /. analyt. Chem., n, 242. 122 ORGANIC ANALYSIS. [ 190. in a stream of hydrogen. According to A. VOLCKER,* the evolu- tion of chlorine may be prevented by mixing the oxide of copper with \ lead oxide. In the analysis of bodies containing bromine the above methods do not always answer, v. GORUP-BESANEZ f satisfied himself of this by analyzing dibromotyrosin. Whether this body was burnt with lead chromate, with a mixture of lead chromate and potassium chromate, - with cupric oxide and oxygen and an anterior layer of lead chromate, with an anterior layer of copper turnings, whether mixed or in the platinum boat, in whichever way the analysis was performed the carbonic acid always came out several per cents, too low, because metallic bromide was formed, which fused and inclosed carbon, thereby preventing its oxidization. The follow- ing process, on the contrary, yielded good results : Into a combus- tion tube drawn out to a long point, introduce first a layer about 9 cm. long of cupric oxide, then a plug of asbestos, then a mixture of the substance (finely powdered) with about an equal weight of well-dried lead oxide in a porcelain boat; again a plug of asbestos, then granulated cupric oxide, then lead chromate or copper turn- ings. First heat the anterior and then the posterior layers to igni- tion, and warm the part where the boat is very cautiously and gradually; everything combustible distils over, arrives at the cupric oxide in the form of vapor, and is there burnt. In the boat noth- ing remains but a mixture of lead bromide and oxide. Complete the combustion with oxygen, taking care not to heat the point where the boat is too strongly, nor continue the transmission of oxygen longer than necessary. If silver foil is placed in the very front part of the tube the hydrogen will also be correct. Observe also that no copper bromide sublimes into the calcium-chloride tube. The halogens themselves are, as a rule, determined according to one of the following methods: * Chem. Gaz., 1849, CCXLV, 29. f Zeitschr. f. analyt. Chem., i, 438. 190.1 HALOGENS IN ORGANIC SUBSTANCES. 123 I. METHODS IN THE DRY WAY. 1. Ignition with lime or soda-lime. As chlorine-free lime is easily obtainable (by burning marble), this body is usually preferred to effect the decomposition of or- ganic substances containing chlorine, bromine, or iodine. It must always be tested for chlorine previous to use, and if traces are found, the quantity is determined in a weighed sample. The analysis is made with a weighed quantity of lime, and the chlorine in it is de- ducted from the total found.* Introduce into a combustion tube about 40 cm. long, the pos- terior end of which is sealed and rounded like a test tube, a layer of lime 6 cm. long, then the substance, after this another layer of lime 6 cm. long, and mix with the wire; fill the tube almost to the mouth with lime, clear a free passage for the evolved gases by a few gentle taps, and apply heat in the usual way. Volatile fluids are introduced into the tube in small glass bulbs. When the de- composition is terminated, dissolve in dilute nitric acid and pre- cipitate with solution of silver nitrate ( 141). KOLBE recom- mends the following process to obtain the contents of the com- bustion tube: When the decomposition is completed, remove the charcoal, insert a cork into the open end of the tube, remove every particle of ash, and immerse the tube, still hot, with the sealed end downwards, into a beaker filled two-thirds with distilled water; the tube breaks into many pieces and the contents are then more readily acted upon. Now add nitric acid until the lime is dissolved, filter off from the separated carbon, and precipitate with silver nitrate. As in this method the ignition of compounds abounding in nitrogen may be attended with formation of calcium cyanide,! the separation of the chlorine, bromine, or * Special methods for preparing pure lime free from calcium chloride and sulphide have been given by F. SESTINI (Zeitschr. f. analyt. Chem., iv, 51), and BRUGELMANN (ibid., xv, 5). f The formation of cyanides may be prevented by using, instead of lime, a mixture of lime and soda, obtained by slaking 3 parts quicklime in a solu- tion of 1 part sodium hydroxide (free from chlorine) and heating the mix- ture to dryness in a silver dish. ROSE, Hand, der Anal. Chem., 6. Aufl. von FINKENER, n, 735. 124 ORGANIC ANALYSIS. [ 190, iodine, if required, is to be effected by the process given in 169, ft (NEUBAUER and KERNER *). If the lime contains calcium sulphide (F. SESTINI f) the silver chloride, bromide, or iodide must be sep- arated from the silver sulphide. It is advantageous to ust, soda- lime (free from chlorine or of known chlorine content) instead of lime, as then all the carbon is oxidized to carbonic acid and no cyanides form. J In determining iodine by this method, a little iodine set free by action of nitric acid must be converted into hydriodic acid by adding a little sulphurous acid before precipitating with silver nitrate. CLASSEN prefers, in the case of substances con- taining iodine, to pass moist carbonic acid over the mass for several hours after ignition with lime, then to warm with water, filter off, cautiously neutralize with nitric acid, and precipitate the iodine as silver iodide. In the analysis of acid organic com- pounds containing chlorine (e.g., chlorospiroylic acid), the chlorine may often be determined in a simpler manner, viz., by dissolving the substance under examination in an excess of dilute solution of potassa, evaporating to dryness, and igniting the residue, by which means the whole of the chlorine, bromine, or iodine present is converted into a soluble haloid salt (Lowio). In more readily decomposable compounds, e.g., in the sub- stitution products of acids, the halogen may also be determined by decomposing the substance by contact during several hours with water and sodium amalgam, acidifying the fluid with nitric acid, and precipitating with silver solution (KEKULE ||). 2. Ignition with ferric oxide and iron (E. KOPP ]f). The combustion tube used is about 60 cm. long and 5 to 6 mm. wide, and is sealed at one end. To more readily control the decom- position, the organic substance is intimately mixed with pure ferric * Annal. d. Chem. u. Pharm., ci, 324, 344. f Zeitschr. f. analyt. Chem., iv, 51. % Handb. der. analyt. Chem. von H. ROSE, 6 Aufl. von R. FINKENER, n, 735. Zeitschr. f. analyt. Chem., iv, 202. j| Jahresb. v. KOPP u. WILL, 1861, 832. f Zeitschr f. analyt. Chem., xv, 107. 190-] HALOGENS IN ORGANIC SUBSTANCES. 125 oxide, prepared by igniting pure ferrous sulphate in the air, and the mixture introduced first into the tube. The layer should be loose and from 12 to 18 cm. long. After adding the rinsings, in- troduce several closely wound spirals of rather fine iron wire; this layer is to have a length of from 20 to 25 cm. Fill the rest of the space in the tube with porous crusts of pure anhydrous sodium carbonate, obtained by moderately heating the crystalline salt in a platinum dish. Now heat to redness first that part of the tube containing the iron-wire spirals, and then heat the part containing the mixture, beginning at the fore part and proceeding to the closed end. The organic substance is thus completely decomposed. The halogens are obtained as ferrous compounds; any small quantity of these that may volatilize is decomposed and retained by the sodium carbonate. After the tube is cold, clean it, cut it into pieces, and boil the whole for some time with water. The iron-halogen com- pounds are thus decomposed by the sodium carbonate. Filter, wash, acidulate cautiously with nitric acid, and precipitate with silver nitrate. 3. Combustion in a current of oxygen. a. C. M. WARREN'S* process for determining sulphur (188, I, 5, a), and to which we shall again refer in 192 ; p. 145, is also employed for the determination of chlorine in organic substances. The chlorine evolved by the combustion of the substance in oxygen is absorbed by brown copper oxide (obtained by precipitating a solution of a copper salt with potassa and igniting over a gas lamp) placed in the anterior part of the tube between two layers of as- bestos. If the carbon and hydrogen are to be also estimated with the chlorine in the same portion of substance, the fore part of the tube containing the cupric oxide must be so heated that, while no carbonic acid or water is retained, no chlorine is allowed to escape. WARREN effects this by surrounding this part with an air-bath heated by a gas flame, and the temperature of which is easily regulated. * Zeitschr. /. analyt. Chem., v, 174. 126 ORGANIC ANALYSIS. [ 190. Difficultly combustible substances, like chloroform, require different treatment, otherwise a difficultly volatile fluid condenses in the unfilled space between the hinder asbestos layer and the layer of cupric oxide and asbestos. In such cases mix with the asbestos in the hinder end of the tube some zinc oxide (about 3 grm.), and place in the fore part of the tube a mixture of zinc oxide (about 1 grm.) and asbestos. The temperature of the air-bath should not be allowed to exceed 160. After the combustion the chloride with the excess of oxide is extracted from the asbestos with dilute nitric acid and the solu- tion precipitated by adding silver nitrate. The test analyses given by WARREN are entirely satisfactory. Whether the method is also applicable for bromides remains to be determined, although WARREN considers it probable. /?. G. BRUGELMANN'S process for determining sulphur and phosphorus in organic substances, which was detailed in 188 I, 5, d, is well adapted for the determination of chlorine (if chlorine- free lime be used); it is also applicable for bromine and iodine if the lime be replaced by soda-lime. After the combustion is ended and the first 2 cm. of the layer of lime or soda-lime have been tested as to their freedom from chlorine, dissolve the main portion of the lime in very dilute nitric acid which had previously been used to rinse out the tube with, digest with the dilute acid for a long time also the part of the tube attacked by the fused calcium chloride, filter, and precipitate the solution with silver nitrate. The test analyses given BRUGELMANN are very satisfactory. Since the decomposition of the substance is effected in a current of oxygen, just as in WARREN'S method, it follows that in the analysis of difficultly combustible chlorine compounds, like chloro- form, a modification will be necessary, similar to that detailed under a. II. METHODS IN THE WET WAY. 1. Carius' Method* Just as in the method of determining isulphur, CARIUS has gradually improved that for determining * Zeitschr. /. analyt. Chem., i, 240; iv, 451; x, 103. 190.] HALOGENS IN ORGANIC SUBSTANCES. 127 chlorine, bromine, and iodine in organic substances, the method depending also upon the oxidation of the substance with nitric acid in a sealed glass tube. The most improved method is based upon the use of nitric acid of sp. gr. 1 5, just as in the determina- tion of sulphur, described under 188, 11, 2. The additional use of potassium dichromate, which CARIUS formerly recommended, is hence unnecessary. The operation is exactly the same as in the sulphur determinations, with the single exception that a small ex- cess of silver nitrate is placed with the weighed substance and 4 grm. of nitric acid in the tube. All the chlorine, bromine, or iodine in the substance is separated as a silver salt. Neither bromic nor iodic acid can form, because these would be reduced by the nitrous acid also formed. The decomposition of organic substances is effected with extraordinary ease in the presence of silver nitrate; with most substances in fact already partially in the cold. In the case of the compounds of the aromatic series the complete separa- tion of the halogens is more difficult, but even then heating to 250 to 260 always suffices for complete decomposition. The precipitate of silver chloride, bromide, or iodide is filtered off and weighed. Before filtering off, CARIUS recommends neutralizing the greater portion of the free nitric acid present with pure sodium carbonate. With substances containing iodine it must be par- ticularly noted that silver iodide fuses in the hot tube with the ex- cess of silver nitrate, and forms a yellow compound which, on cool- ing, solidifies to an opaque, yellow mass. This must be heated for one to two hours with the dilute liquid in order to remove all the silver nitrate. The silver iodide then obtained is perfectly pure. According to LINNEMANN * the determination of iodine is less satisfactory than that of chlorine or bromine. He observed losses which he ascribed to the fact that silver iodide is somewhat soluble in the liquid containing the silver nitrate and nitric acid. It is hence recommended to avoid too large an excess of silver nitrate, i.e., to employ only 1 equivalent. Zeitschr. /. analyt. Chem., xi, 325. 128 ORGANIC ANALYSIS. [ 190. 2. In the case of readily decomposable compounds of chlorine, bromine, or iodine, such as the substitution derivatives of acids, the halogens may also be determined by treating the substance for several hours with water and sodium-amalgam, and (in the case of chlorine and bromine compounds) acidulating with nitric acid and precipitating with silver nitrate. With iodine compounds, first add to the still alkaline solution some silver nitrate and then add nitric acid to dissolve the precipitated silver iodide (KEKULE *). 3. For determining the iodine in ethyltropine hydriodide, K. KRAUT f employed a very simple method which is advantageous besides, in that the substance is not lost. The process was also employed by RICH. MALY J for determining the extra-radical bro- mine in a substance obtained by the action of bromine on thio- sinamine. Dissolve an accurately weighed quantity of pure silver in nitric acid, dilute the solution, precipitate with hydrochloric acid, de- cant through a weighed filter to retain the slight quantity of silver chloride in suspension, and wash the filter. Now add the weighed substance to the washed silver chloride. After a few minutes' standing and warming, all the iodine will have combined with the silver, while the base will have united with the hydrochloric acid. Now collect the silver iodo-chloride on the weighed filter first used, and from the difference between the weight of the precipitate and that of the silver nitrate equivalent to the silver taken calculate the iodine. This method yields only the iodine or bromine which is capable of replacing chlorine in ammonium chloride (MALY, loc, cit.). 4. In compounds of organic bases with hydrochloric, hydro- bromic, or hydriodic acid, the halogen may be very easily de- termined by precipitating the aqueous solution with silver nitrate. * Jahresber. von KOPP und WILL, 1861, 832. t Zeitschr. /. analyt. Chem., iv, 167. t Ibid., v, 68. 191. J COMPOUNDS CONTAINING INORGANIC BODIES. 129 F. ANALYSIS OF ORGANIC COMPOUNDS CONTAINING INORGANIC BODIES. 191. In the analysis of organic compounds containing inorganic bodies, it is, of course, necessary first to ascertain the quantity of the latter before proceeding to the determination of the carbon, etc., as otherwise the amount of the organic body whose constitu- ents have furnished the carbonic acid, water, etc., not being known, it would be impossible to estimate the oxygen from the loss. If the substances in question are salts or similar compounds, their basic radicals are determined by the methods given in the Fourth Section; but in cases where the inorganic bodies are of a nature to be regarded more or less as impurities (e.g., the ash in coal), they may usually be determined with sufficient accuracy by the combustion of a weighed portion of the substance in an obliquely placed platinum crucible, or in a platinum dish with the aid of a cylinder, to promote a draught (see "Analysis of Ashes"). If the ash still contains carbon, ignite repeatedly with mercuric oxide until the weight is constant. In the analysis of substances containing fusible salts, even long-continued ignition will often fail to effect complete combustion, as the carbon is protected by the fused salt from the action of the oxygen. In such cases the best way to effect the purpose is to carbonize the substance, treat the mass with water, and incinerate the undissolved residue; the aqueous solution is, of course, likewise evaporated to dryness and the weight of the residue added to that of the ash. The determination of inorganic substances in organic substances is not always as simple as might appear at first sight, for the ash often does not simply contain the sum of the inorganic substances present; for instance, bases may have taken up acids which were formed during the combustion, or chlorides may have been vola- tilized during incineration (BEHAGHEL v. ADLERSKRON *), etc The details will be given under "Analysis of Ashes." * Zeitschr. f. analyt. Chem., xii, 390. 130 ORGANIC ANALYSIS. [ 191. If organic compounds whose ash contains potassium, sodium, barium, strontium, or calcium are burnt with cupric oxide, part of the carbonic acid evolved remains as carbonate of these metals. As in many cases the amount of carbonic acid thus retained is not constant, and the results are, moreover, more accurate if the whole amount of the carbon is expelled and weighed as carbonic acid, certain bodies are added to the substance before mixing this with the cupric oxide, which will decompose the carbonates at a high temperature, e.g., antimony oxide, cupric phosphate, boric acid (FREMY), etc., or the combustion is effected with lead chromate, with addition of T V of potassium dichromate, according to the di- rections given in 176. Accurate experiments have shown that in this case not a trace of carbonic acid remains with the bases. If the substance is weighed in a porcelain or platinum boat, and the combustion is effected according to 178, a, the ash, carbon, and hydrogen may be determined in one portion. The amount of carbonic acid contained in the ash is added to that found by the process of combustion; if the carbonic acid in the ash cannot be calculated, as in the case of alkali carbonates, it may be deter- mined by means of fused borax, fusing with potassium dichromate, by PERSOZ'S method, or by some other means ( 139). In burning substances containing mercury, the arrival of any of the metal at the calcium-chloride tube may be prevented by having a layer of metallic copper (copper turnings, a roll of foil, or wire spiral) in the anterior part of the combustion tube, and by not al- lowing the foremost portion to get too hot. Substances with radicals containing metals, or such as contain volatile metals, may be analyzed with the greatest ease by CARIUS'S method (page 117). The metals are determined in the nitric- acid solution obtained by means of the usual methods. If the substances also contain sulphur, the metals may be precipitated by sodium carbonate (should they be precipitable by this), and the sulphuric acid determined in the nitrate. In the case of substances which contain chlorine, bromine, and iodine, the silver in the nitrate from the precipitated silver chloride, bromide, or iodide must first be precipitated by hydrochloric acid, 192.] DIRECT DETERMINATION OF OXYGEN, ETC. 131 and the metal in the organic substance then determined in the nitrate. If the substances contain mercury, this may be determined together with the carbon and hydrogen by a modification of the usual combustion process (FRANKLAND and DUPPA*). Substances containing arsenic may also be analyzed by BRUGELMANN'S phos- phorus method, pages 112 and 120. f SUPPLEMENT TO 174 TO 191. 192. In this supplement there are detailed under A those methods whereby oxygen is directly determined, whether by itself alone or conjointly with other elements; under B, however, are given several methods of ultimate organic analyses in which the princi- ples upon which they are based or the apparatus used differ ma- terially from the methods ordinarily followed. A. METHODS FOR THE DIRECT DETERMINATION OF OXYGEN. As already mentioned, the oxygen is determined, in the ordinary methods of organic analysis, from the loss. Formerly no methods were known for its direct determination ; such are now known, but they are only exceptionally used because they are as a rule incon- venient, and afford accurate results only when the greatest care is exercised. It is remarkable, too, that of all the methods here detailed scarcely any have been tested except by their authors. a. v. BAUMHAUER was the first to propose a method for the direct determination of oxygen.! It consists in employing a pre- viously measured volume of oxygen in the process usually followed in determining the carbon and hydrogen, in order that the copper may be reoxidized. The difference between the oxygen taken up by the copper and that present in the carbonic acid and water formed gives the oxygen in the substance analyzed. As in this method the total cubic capacity of the apparatus must be known in order to make the necessary correction for * Annal. d. Chem. u. Pharm., cxxx, 107; Zeitschr. f. analyt. Chem., iv, 138. t Zeitschr. f. analyt. Chem., xvi, 1. t Annal. d. Chem. u. Pharm., xc 228. 132 ORGANIC ANALYSIS. [ 192. temperature and pressure, and as this requirement cannot be easily and accurately met, v. BAUMHAUER now recommends * using a weighed quantity of a substance which, on ignition, will yield a given quantity of oxygen; e.g., dry silver iodate, which answers the purpose admirably. The process is thus adapted not only for the determination of carbon, hydrogen, and oxygen, but, with a modification to be described further on, also of nitrogen, and in one and the same portion of substance. The combustion tube used is from 70 to 80 cm. long and open at both ends. It is charged as follows, beginning at the fore part (which is connected with the weighed absorption apparatus) : 20 cm. copper turnings, 20 cm. fragments of porcelain (previously washed with hydrochloric acid and ignited), 25 cm. strongly ig- nited, coarsely granular cupric oxide free from powder and held between asbestos plugs, then an unfilled space of 5 cm., then the weighed substance (contained in a boat if solid, or in a small glass bulb if liquid) which, if difficultly combustible, may be mixed with cupric oxide; then another unfilled space of 6 to 7 cm., and lastly a second boat containing a known weight (a few grammes) of pure silver iodate dried at about 140. f A constant hydrogen-gas ap- paratus and a gasometer filled with pure nitrogen are also required. Both gases are passed through the same purifying apparatus con- nected with the hinder end of the combustion tube. The purify- ing apparatus consists of a tube filled with copper turnings and maintained at a red heat during the whole operation, and two U-tubes, one of which is filled with fragments of pumice-stone saturated with sulphuric acid; the other U-tube is half filled with soda-lime, the other half, which is next the combustion tube, being filled with calcium chloride. Before attaching the apparatus for absorbing the water and carbonic acid, heat the fore part of the tube for a short distance beyond the copper turnings, and pass a slow current of hydrogen through the tube, in order to make sure that the copper is free from cupric or cuprous oxide. Now displace the hydrogen by * Zeitschr. /. analyt. Chem., v, 141. f For its preparation, see loc. tit., p. 143. 192.] DIRECT DETERMINATION OF OXYGEN, ETC. 133 nitrogen, and, while still maintaining a gentle current of the gas, heat the part of the tube containing the fragments of porcelain and the cupric oxide. Then attach the calcium-chloride tube and the potash bulbs with their potassium-hydroxide tube to the combustion tube. After the nitrogen gas has been passed through the apparatus long enough to completely fill it, and even to saturate the potassa solution, weigh the cooled absorption apparatus and place it again in position. Now heat with great caution the sub- stance to be analyzed, while constantly maintaining a slow current of nitrogen. As soon as the substance has been burned, or at least completely carbonized, very gradually heat the silver iodate. The oxygen evolved burns the carbon and oxidizes the copper resulting from the reduction of the cupric oxide. The excess of oxygen is taken up by the copper turnings. After complete de- composition of the silver iodate, continue to pass for some tune a gentle current of nitrogen through the apparatus and then re- move the absorption apparatus to weigh it. Now close the gas cocks one by one until only those that heat the copper turnings remain lit. Without stopping the current of nitrogen, wait until the cupric oxide has become perfectly cold and then attach a fresh, weighed calcium-chloride tube. Now replace the current of nitro- gen by one of hydrogen in order to reduce the cupric and cuprous oxides which have formed on the surface of the copper turnings- The oxygen contained in these oxides unites with the hydrogen to form water; the quantity is equivalent to the increase in weight of the calcium-chloride tube. After the boat has been withdrawn by means of a wire from the combustion tube, the latter is ready for a fresh analysis. The calculation is as follows: Add together the oxygen in the carbonic acid and the water (collected in both calcium-chloride tubes) , and from this sum deduct the oxygen in the weighed silver iodate used (100 parts of the salt dried at about 140 yielded v. BAUMHAUER 16-92 parts of oxygen*). The difference is the oxygen contained in the substance. * With the atomic weights used in this translation the theoretical quantity is 16 97 parts TRANSLATOR. 134 ORGANIC ANALYSIS. [ 192. The test analyses of oxalic acid and of uric acid, supplied by v. BAUMHAUER, gave very satisfactory results.* If the nitrogen is to be determined in the same portion of sub- stance, prepare the apparatus as before, but place a screw pinch- cock on the rubber tube which connects the hinder end of the com- bustion tube with the U-tubes. Proceed just as before up to the point where the combustion of the substance is to be commenced. While the nitrogen is still passing slowly through the apparatus, connect the potash bulbs with a system of tubes, which serves to measure the volume of gas in the whole apparatus before and after combustion of the substance. The system consists of two vertical tubes the lower ends of which are connected by a long, very stout rubber tube. One tube is fixed and graduated; the other is sus- pended by a cord, and may be raised or lowered. The system is filled with sufficient mercury to completely fill the rubber tube and about half fill the vertical tubes. Before connecting the graduated tube with the potash bulbs, it must be completely filled with mercury by raising the movable tube. As soon as the mercury reaches the level at which the gradua- tions on the tube begin, close the screw pinch-cock behind the combustion tube, allow to cool, and determine the volume of gas in the apparatus by taking two readings at different pressures, the first at diminished pressure of 20 mm., the second with the mercury at the same height in both tubes. Now burn the sub- stance as before, but without using a current of nitrogen, and with- out heating the silver iodate. After the combustion is over, and the apparatus has been allowed to cool for several hours, take two readings again at different pressures, in order to ascertain the volume of gas in the entire apparatus. The difference gives the volume, and from this the weight, of the nitrogen in the substance. *ALEX. MITSCHERLICH (Elementar analyse vermittelst Quecksilberoxyds, Berlin, MITTLER u. SOHN, 1875; Zeitschr. f. analyt. Chem., xv, 371) con- cludes, from observations made by him, that it is very difficult to completely reconvert reduced copper into cupric oxide by heating in oxygen, as a kernel of cuprous oxide will remain if the grains are of any size, and particularly if the substances are rich in carbon and hydrogen ; v. BAUMHAUER'S method hence presents a source of error very difficult to obviate. 192.] DIRECT DETERMINATION OF OXYGEN, ETC. 135 Now disconnect the tube system from the potash bulbs, remove the screw pinch-cock from behind the combustion tube, and com- plete the combustion by heating the silver iodate, etc., as already described. The method of simultaneously determining nitrogen, although very well conceived, is nevertheless imperfect, so that, even as v. BAUMHAUER admits, it may be only rarely employed. As a rule it is preferable to determine the nitrogen in a separate portion of the substance. 6. STROMEYER'S method* is based on the determination of the metallic copper or cuprous oxide formed in the combustion. The residue is taken up with a solution of ferric chloride and hydro- chloric acid, or better, ferric sulphate and sulphuric acid, and the ferrous salt titrated with permanganate (Cu+Fe 2 Cl 6 = CuCl 2 + 2FeCl 2 ; or,Cu 2 O+Fe 2 Cl 6 +2HCl = 2CuCl 2 +2FeCl 2 +H 2 0). It is thus evident that, no matter whether cupric oxide is reduced to copper or to cuprous oxide, for each equivalent of oxygen given up 2FeCl 2 or 2FeO are obtained. On adding together the oxygen contained hi the carbonic acid and water, and deducting from this sum 1 eq. of oxygen for every 2 eq. of FeO obtained, the oxy- gen in the substance is found. As the cupric oxide to be used must be free from cuprous oxide, it should be prepared from basic cupric carbonic by heating in a glass flask (not in a crucible). The oxide prepared thus is not so well adapted for determinations -of carbon and hydrogen, because with it the carbonic acid and water are very rapidly evolved. STROMEYER hence recommends not to determine the oxygen simultaneously with the carbon and hydrogen, but to use for this a separate portion of the substance. As the cupric oxide above mentioned is very reducible, much less of it need be employed than of the coarse oxide. Organic substances containing sufficient oxygen to form water with the hydrogen require about three times as much oxide as would be required theoretically, and those which contain an excess of hydrogen will require four times as much. For the sake of certainty, however, * Annal. d. Chem. u. Pharm., cxvii, 247. 136 ORGANIC ANALYSIS. [ 192. more than this is taken. The cupric oxide is mixed with half its weight of dry sodium carbonate. This mixture sinters on being ignited, so that the last particles of carbon are thereby burned. The sulphur in organic substances burns with this mixture to sodium sulphate, and chlorine yields sodium chloride; and here it must not be forgotten that the oxygen of the sodium carbonate is expelled and is utilized to form carbonic acid and water. For nitrogenous substances, the method is not so well adapted, as nitro-compounds yield too much reduced copper, because nitrogen oxides escape; with other nitrogenous compounds, however, the results are almost correct. Mix the substance with the mixture of oxide and sodium car- bonate in a smooth dish, using a spoon, introduce into the tube through a small funnel, and then add an equal quantity of cupric oxide. The latter is granulated like gunpowder by adding to it one-tenth its weight of sodium carbonate, moistening the mixture with water and passing it through a sieve made from a metallic plate with holes one-twelfth of an inch in diameter, then drying, and sifting it free from dust. The glass tube is connected by means of a cork or rubber tube with a glass tube drawn out to a fine point. Now give the tube a few taps and then heat as usual, proceeding slowly from the fore part to the rear. When the entire tube is red-hot fuse the opening of the small glass tube and allow the combustion tube to cool. Then transfer the contents of the tube (with the pieces of the glass tube, if it cannot be done other- wise) to a flask, and digest with a solution of ferric sulphate con- taining 8 per cent, of ferric oxide and free from ferrous oxide and nitric acid. Use double the quantity of solution theoretically required, and which, based upon the determination as usual of oxygen from the loss (which should be here controlled), is known, and add somewhat more dilute sulphuric acid (prepared from the distilled acid) than is required to neutralize the sodium carbonate and dissolve the cupric oxide. Provide the flask with a MOHR caoutchouc valve (if it is not preferred to pass in a stream of car- bonic acid), and carefully heat until all the copper is dissolved. If a few red specks remain adhering to the glass, in consequence 192.] DIRECT DETERMINATION OF OXYGEN, ETC. 137 of the application of too high a heat, pour the sulphuric-acid solu- tion, when cold, into a litre flask, heat the fragments of the glass tube with a small quantity of ferric chloride and hydrochloric acid, add this solution to the other, and dilute with water. Should the solution so obtained not possess a color like that of copper sul- phate, but be yellowish green, it indicates a deficiency of sul- phuric acid, hence some of this must be added. Finally fill with water up to the mark, mix, and take 250 c.c. of the solution for titration, first mixing it with about 250 c.c. of water. In order to correct the error which is introduced by reason of a fluid con- taining both ferric sulphate and cupric sulphate requiring more permanganate to color it than does water, dissolve one-fourth of the cupric oxide employed (the fine and the granulated) in dilute sulphuric acid, add one-fourth of the above-mentioned ferric-sul- phate solution, dilute to 500 c.c., and add permanganate solution (diluted for this purpose tenfold, however) to redness. The test analyses given by the author of the process are satisfactory * enough, but as detailed even in the experiment, there is always less oxygen used than theory requires, hence the oxygen content of the sub- stance is always too high. The main cause of this error is most probably the atmospheric air in the tube, and STROMEYER hence suggests that in order to obtain more accurate results it would be advisable to remove the air by alternately exhausting and filling with carbonic acid. c. AL. MITSCHERLICH has for years been at work trying to find a method by which all the elements of an organic substance * For the sake of greater clearness, the details of one analysis are here given : 0- 202 grm. of cane-sugar mixed with 3 grm. CuO and 1 5 grm. Na 2 CO 3 and 3 grm. granulated cupric oxide, placed in front. Dissolved in 50 c.c. solution of ferric sulphate containing 8 per cent, of Fe 2 O 3 and 8 c.c. distilled sulphuric acid and diluted to 1 litre. 250 c.c. of this solution diluted to 500 c.c. required in two experiments 48-6 c.c. permanganate solution, of which 17 -3 c.c.= l grm. ferrous-ammonium sulphate or 0-020408 oxygen. A solution of 0- 75 grm. fine and 0- 75 grm. granulated CuO in dilute sulphuric acid mixed with 12-5 c.c. ferric oxide in solution, and water to make half a litre, required 0-9 c.c. of the permanganate solution. This 0-9 c.c. deducted from the 48-6 c.c. gives 47-7 c.c., which multiplied by 4 gives 190- 8= 0- 225078 oxygen. For 1 eq. of cane-sugar, C 12 H 22 O U , this makes 190-5 O instead of 192 (12 at.), which are actually required. 138 ORGANIC ANALYSIS. [ 192. may be determined in one and the same analysis. For this pur- pose he first decomposed the organic substances by heating in a current of chlorine,* whereby the hydrogen was obtained in the form of hydrochloric acid, the oxygen in the form of carbonic acid and carbonic oxide, and all thus determined (the numerous test analyses give the hydrogen and oxygen very satisfactorily). Later onf he used potassium-platinic chloride instead of chlorine, in order to be able to determine the carbon also, as well as the oxy- gen and hydrogen, by one combustion, and further, still more im- proved this method by burning the substance with a mixture of potassium-platinic chloride and potassium chloride. As, how- ever, in these methods a portion of the carbon is obtained as car- bon tetrachloride, whereby the carbon determination is rendered more difficult, he endeavored to attain the desired effect by other methods, and finally succeeded in devising a process whereby the carbon, hydrogen, and especially oxygen, as well as nitrogen, chlo- rine, bromine, iodine, sulphur, phosphorus, and any inorganic sub- stances that might be present, could be accurately determined in one singl" analysis.^ The process consists in effecting the combustion of the sub- stance with mercuric oxide. At the temperature at which mer- curic oxide itself is decomposed, there form, at the expense of the oxygen of a portion of the mercuric oxide, water, carbonic acid, and mercury. On weighing the carbonic acid and water the car- bon and hydrogen are found; on weighing the mercury reduced the oxygen used up in the combustion is found; and on deducting this latter from the oxygen present in the combustion products, that present in the organic substance is found. In the case of nitrogenous substances, the nitrogen is obtained partly as such and partly as nitric oxide. Chlorine, bromine, and iodine, if pres- ent, combine with the mercury reduced. Sulphur and phosphorus are obtained as mercury sulphate and mercury metaphosphate respectively. These salts as well as almost all the inorganic sub- * Zeitschr. /. analyt. Chem., vi, 136. f Ibid -> VII > 272 - J Ibid., xm, 74; xv, 371; also in the brochure, Elementaranal. vermitt. Queckiilberoxyd, Berlin, MITTLER u. SOHN, 1875. 192.] DIRECT DETERMINATION OF OXYGEN, ETC. 139 stances usually present remain with the mercuric oxide and must later be separated therefrom and determined. AL. MITSCHERLICH has analyzed a large number of various substances according to his method, and generally with very satis- factory results^ Reports of other chemists regarding the method are not at hand. The method and the special apparatus required for it have been most minutely described by MITSCHERLICH. As, however, serviceable results cannot be had without careful attention to all details, it would be useless to give a brief description of the method, hence I refer to the original source. d. A. LADENBURG * oxidizes the substance to be analyzed in a sealed tube with silver iodate and sulphuric acid. The substance is weighed in a small glass bulb and introduced with sulphuric acid and a known weight of silver iodate into a tube, which is then drawn out and sealed. After the small glass bulb has been shat- tered by striking the tube on the hand, heat the tube. When the reaction is over and the tube has cooled, weigh the latter, fuse the point so as to allow the gas to blow out and escape, expel the carbonic acid absorbed by the sulphuric acid by heating and exhausting, weigh, and repeat the operations until the weight is constant. The loss of weight is equal to the carbonic acid formed, from which the carbon content of the substance may be calculated. Now cut the tube in two, rinse out its contents, add potassium iodide, and determine the liberated iodine as under 146. The iodine found gives the undecomposed (as well as the decomposed) silver iodate, from the quantity of which the oxygen necessary for the oxidation of the substance may be calculated. The test analyses supplied by LADENBURG are on the whole quite satisfactory. e. J. MAUMEN^ f effects the combustion of the substance with litharge to which, in order to prevent fusion, one-fourth its weight of calcium phosphate is added. Carbonic acid and water are ob- tained, as in the ordinary process, but also metallic lead. In order * Annal. d. Chem. u. Pharm., cxxxv, 1; Zeitschr. f. analyt. Chem., iv, 192. t Compt. rend., LV, 432; Zeitschr. f. analyt. Chem., i, 487. 140 ORGANIC ANALYSIS. [ 192. to obtain this as a button, mix the contents of the tube, after the combustion, with about double their quantity of pure litharge, trans- fer the mass to a crucible, cover with a layer of pure litharge, and heat to fusion. The button obtained is finally cleaned and weighed. The oxygen in the substance is found by adding together the oxygen in the carbonic acid and water and subtracting from the sum that corresponding to the lead obtained. MAUMENE does not state how the error occasioned by the atmospheric oxygen inclosed in the tube is avoided. /. CRETIER * conducts the products of the dry distillation of the substance over a known weight of magnesium heated in a weighed combustion tube, reduces thereby the water and the greater part also of the carbon oxides, weighs the tube again, sub- jects to special analysis the gaseous mixture which escapes from the tube and which consists of hydrogen, methyl hydride, and perhaps carbonic oxide. From the data so obtained, the carbon,, hydrogen, and oxygen in the substance are calculated. The results are inaccurate, however, and leave much to be desired. B. METHODS OF ORGANIC ANALYSIS WHICH DIFFER MATERIALLY FROM THE ORDINARY METHODS IN PRINCIPLE OR APPA- RATUS USED, AND WHICH DO NOT EFFECT A DIRECT DETER- MINATION OF THE OXYGEN. a. CLOEZ f has described a process for determining the car- bon and hydrogen (and nitrogen also) in organic substances, and which is adapted for solid or liquid, non-volatile or volatile bodies, whether they consist only of carbon, hydrogen, and oxygen, or whether they contain also nitrogen, sulphur, chlorine, bromine, iodine, or inorganic substances. In order to be able to present the method in a connected form, it has been preferably given in this supplement. The characteristic feature of the process, which in general is modeled after that described in 178, is that the glass * Zeitschr. /. analyt. Chem., xm, 1. t Annal. de chim. et de Phys., Ser. [Ill] LXVIII, 394. 192.J VARIOUS METHODS OF ANALYSIS. 141 combustion tube is replaced by a tube of wrought iron, and that instead of oxygen, purified air only is used. In con- sequence of the first change the apparatus remains in a condition to be used over and over again, and is hence especially adapted for extensive series of scientific or technical experiments. The accuracy of the process has been fully proved by numerous test analyses of the most varied kind. The majority of the results obtained are thoroughly satisfactory. The com- bustion tube, Fig. 75, is of wrought iron 20 to 22 mm. diameter and 115 cm. long. Each end projects 20 cm. from the furnace. The first thing done is to oxidize the inner surface by heating the tube to redness and passing steam through it.* As soon as this is fully accomplished, . fill the part between E and F with a layer of strongly ignited coarse cupric oxide, keeping it well in place by means of superficially oxidized copper-foil spirals. The unfilled portions of the tube, FB and AE, are destined jj to contain the long, semi-cylindrical boats of stout sheet iron, which may be removed by means of an iron wire ^ attached to one end of each. The boat inserted in the fore part of the tube at D is 20 cm. long; in the case of substances composed only of carbon, hydrogen, and oxygen, it is filled with coarse cupric oxide, or, if the sub- stance is readily combustible, it is omitted altogether. If the substance contains nitrogen, the boat is filled with freshly reduced copper turnings; when the substance contains sulphur or chlorine, the boat is filled with minium or lead chromate. The boat inserted into the hinder end of the tube from C to E is 30 cm. long. In the analysis of substances which consist only of carbon, hydrogen, and oxygen, the boat is filled with moderately ignited cupric oxide; in the analysis of such as contain sulphur, chlorine, or bromine, it is filled with fused and * This procedure is of great importance, since it appears to destroy the very notable permeability of red-hot iron observed by SAIXT-CLAIRE DE- 142 ORGANIC ANALYSIS. [192 powdered lead chromate. To collect the water produced by the combustion, CLOEZ uses a U-tube filled with pumice-stone saturated with sulphuric acid, then the potash bulbs, and finally a U-tube filled with fragments of potassium hydroxide. The air to be passed through the tube is first passed through a small flask containing dilute potassa solution into which the air-delivery tube just dips, then through an upright cylinder contracted at its lower end and filled with pumice- stone saturated with sulphuric acid (Fig. 83, Vol. I, p. 290), then through two long, horizontal tubes with turned-up ends, the first being filled with porous calcium chloride, the second with frag- ments of potassium hydroxide.* If a solid substance composed only of carbon, hydrogen, and oxygen is to be burned, fill both boats with cupric oxide, as already stated, heat the tube along its entire length within the furnace, and for 10 to 15 minutes conduct a slow current of air through it, while the fore end is left open. Allow part of the tube containing the boat C E to cool, seize the tube with a pair of tongs, Fig. 76, remove the stopper A, and with- draw the boat, leaving it to cool in a closed iron tube kept for this purpose, unless it is preferred to allow it to cool in the combustion tube. As soon as the boat is sufficiently cool, so that volatilization FIG. 76. FIG. 77. FIG. 77a. or decomposition of the substance is no longer to be feared, with- draw it with the tongs, place it on the sheet of copper foil, and by means of a polished iron hook, Fig. 77, transfer a portion of the VILLB and TROOST (Compt. rend., LVII, 965, and Zeitschr. f. analyt. Chem., in, 351), and CAILLETET (Compt. rend., LVIII, 327 and 1057; Zeitschr. f m analyt. Chem., in, 353). * This arrangement of the drying apparatus is not correct. It allows the entrance of air dried by calcium chloride, whereas air dried by sulphuric acid leaves the water-absorbing U-tube. This explains why CLOEZ always found a few tenths per cent, too much hydrogen. The construction of the drying apparatus should hence be so changed that the air, freed from car- bonic acid, should pass last through the sulphuric-acid tube before entering the combustion tube. 192.] VARIOUS METHODS OF ANALYSIS. 143 cupric oxide to the small brass shovel, Fig. 77 a. Now quickly dis- tribute the substance to be burned over the cupric oxide remain- ing in the boat, cover rapidly with the cupric oxide in the shovel, reinsert the boat at once in the combustion tube, which has previ- ously been connected with the absorption apparatus, close the hinder end of the tube with its stopper, and pass air slowly through the apparatus. The combustion is then effected, i.e., the sub- stance is heated beginning at the fore end and proceeding gradu- ally to the hinder end, while the middle and fore parts of the tube are maintained at a red heat. The progress of the combustion as well as the end may be known by comparing the air-bubbles passing through the potassa solution of the air-purifying apparatus on the one side and those passing through the weighed potash bulbs on the other. When the operation is at an end, remove the weighed absorption apparatus and continue heating the tube while a stronger current of air is passed through it in order to re- oxidize the reduced copper; the tube is then ready for the next analysis. Fluid non-volatile substances are treated similarly, being placed on the cupric-oxide layer in the boat C E by means of a drawn-out tube, and their weight determined by reweighing the tube. Volatile hydrocarbons (amylene, benzin, etc.) are weighed in a small, stoppered tube with drawn-out end. After removing the stopper place the tube on the layer of cupric oxide in boat C E, and near the end insert this into the combustion tube, and pass a slow current of air through the tube, the foremost half of which is kept red-hot. If the current of air is insufficient to con- vey the fluid at ordinary temperature to the cupric oxide, heat that part of the tube containing the fluid, proceeding from the fore part to the hinder. In the combustion of nitrogeneous substances the boat D, filled with cupric oxide, is replaced by a copper boat filled with copper turnings the surface of which has been first oxidized, and then reduced by ignition in a current of hydrogen. In this case the current of air must be particularly slow, and may be more rapid only towards the end, in order that the fore part of the tube 144 ORGANIC ANALYSIS. [ 192. may remain metallic, and hence be capable of reducing the nitro- gen oxides. In the analysis of compounds containing sulphur, chlorine, bromine, or iodine, fill the boat CE with lead chromate, and the boat D with perfectly dry minium or lead chromate, and heat the foremost boat to incipient redness only, so that its contents do not fuse. In the combustion of organic substances containing inorganic compounds, the substances are put in a porcelain boat which is placed on a sheet of platinum foil with turned-up ends, and by means of a wire attached to one end of the platinum foil, pushed up to the permanent layer of cupric oxide in the middle of the tube. After the products of the dry distillation have been burned, finally burn the residual carbon at the expense of the oxygen of the cur- rent of air. In the case of difficultly combustible substances, e.g., graphitic carbon deposited in gas-resorts, the operation requires somewhat more time than when oxygen is used, but, according to CLOEZ, the results are equally accurate. The apparatus above described is equally applicable for the de- termination of nitrogen by volume, on DUMAS' principle ( 185, ad). The foremost boat in this case is filled with copper turnings which have first been oxidized and then reduced; the hinder boat is filled with cupric oxide and the substance. Into the hinder end of the tube pass pure carbonic-acid gas (through a tube provided with a stopcock) until all the air has been expelled, then close the stopcock, bring the point of the gas-delivery tube attached to the fore part of the tube under the cylinder filled with mercury and potassa solution, and heat the hinder end of the tube, the middle and fore parts of which have previously been heated to redness; finally raise the cylinder as high as practicable, in order to diminish the mercurial pressure as much as possible, open the stopcock again, and pass carbon dioxide through the tube until all the nitrogen has been transferred to the cylinder. The details of the process will be found in 185, aa. In the construction of the carbon dioxide apparatus care must be taken that the gas may be given the necessary tension to overcome the mercurial pressure. 192.] DETERMINING EQUIVALENTS. 145 b. C. M. WARREN, whose methods of determining sulphur and chlorine in organic substances were detailed in 188, 5, a, and 190, 3, also determines carbon and hydrogen by burning the substance altogether (or nearly so) at the expense of oxygen. The hinder part of the combustion tube used by him is bent upwards at an obtuse angle. The substance is contained in the bent-up part, into which air or oxygen is passed, according to requirements, and which is heated by a special gas-lamp in the case of volatile substances a copper rod is interposed. The horizontal part of the tube is very uniformly packed, next to the bend, with a layer of asbestos 30 to 36 cm. long, then with 6 to 9 cm. of strongly ignited, coarse cupric oxide, and finally another asbestos plug. The cupric oxide serves as an indicator to show whether any unconsumed gases reach it, and it also completes their combustion. c. Regarding WHEELER'S* method, in which carbon, hydro- gen, and nitrogen are determined in one analysis; and FRANZ ScHULZE'st method, which is based on gas-measuring, and permits the determination of the nitrogen as well; and also TH. SCHLO- SING'S{ method, which too serves for the determination of carbon, hydrogen, and oxygen in one operation, I must refer to the original sources. d. BRUNNER effects the oxidation of the substance in the wet way by treatment with potassium dichromate and sulphuric acid. The process, modified by ULLGREN, i.e., using chromic and sulphuric acids, is employed in determining carbon in iron, and is given in detail under "Analysis of Cast Iron" in the Special Part. III. DETERMINATION OF THE EQUIVALENT OF ORGANIC COMPOUNDS. The methods of determining the equivalent of organic com- pounds differ materially according to the properties of the various compounds. There are three general methods in use which afford the desired purpose. * Journ. f. prakt. Chem., xcvi, 239; Zeitschr. f. analyt. Chem., v, 217. f Zeitschr. f. analyt. Chem., v, 269. I Compt. rend., LXV, 957 ; Zeitschr. f. analyt. Chem., vn, 270. Poggend. Annal, xcv, 379. Jahresber. v. LIEBIG u. KOPP, 1855, 773. 146 ORGANIC ANALYSIS. [ 193. 193. 1. A determination is made of the quantity of a Substance of known Equivalent, which combines with the substance the Equivalent of which is to be determined, to form a well-characterized Compound. In this manner is determined the equivalent of organic acids, organic bases, and many indifferent substances which possess the property, of combining with bases or acids. How the equivalent is calculated from the results obtained will be found under "The Calculation of Analyses"; only the methods will be given here. a. The equivalent of organic acids is preferably determined from the silver salt, because of the almost positive certainty that no basic or hydrated compound is produced, and because the analysis is exceedingly simple. Other salts, however, are also frequently used, e.g., compounds of lead, barium, and calcium. (In the case of lead compounds especial care must be exercised not to mistake basic salts for neutral; again, in the case of barium or calcium salts, hydrated must not be considered as anhydrous salts.) The method of carrying out the determination is fully detailed in Section 4 (Vol. I). 6. The equivalent of organic bases which yield well-crystallized salts with sulphuric, hydrochloric, or other easily determined acid, may be readily ascertained by determining the quantity of acid in a weighed portion of the salt, by the usual methods. If the salts do not crystallize, a small weighed quantity of the dried alkaloid is introduced, according to LIEBIG, into a drying- tube, Fig. 78, which is then weighed; then a stream of well-dried hydrochloric-acid gas passed slowly and for a long time through the tube ; finally the tube is heated to 100 (see 29, Fig. 34) while a current of air is passed through it. The weight of the FIG. 78. hydrochloric acid taken up is determined from the increase in weight. To control the results the hydro- chloride may be dissolved in water and the chlorine precipitated with silver nitrate. The equivalent of the alkaloids may also be 1 I 194.] DETERMINING EQUIVALENTS. 147 determined from the insoluble double salts obtained by precipitat- ing the hydrochlorides with platinic chloride. The compounds are cautiously ignited ( 124) and the residual platinum weighed. c. In the case of indifferent substances there is frequently no other choice than to determine the equivalent from the lead com- pound, because many of these substances either form no other than lead compounds, or else form such as cannot be obtained in a state of purity. Although the value of the equivalent is thus left in doubt, because lead oxide often combines with such substances in varying proportions, the analysis of such compounds is still of interest, as it shows whether the substance combines as such with the lead oxide or with elimination of water. At times organic substances yielcf solid and crystallizable salts also with water, from the analysis of which then the equivalent may be determined. 194. 2. The Vapor Density of the Compound is determined. Of the many methods which have been proposed for effecting this object, I will describe in detail only those two which are most easily applied and are most frequently used in the laboratory. In all vapor-density determinations it is necessary that the temperature at which they are made should be sufficiently raised above the boiling-point of the substances, so that the vapors may have the coefficient of expansion of a gas. The extreme importance of this rule is evident from the fact that at temperatures only slightly above the boiling-point the vapor densities are too high, and decrease with increasing temperature, becoming constant only at a certain point. A. DUMAS' PROCESS. The outlines of this method are as follows: A glass globe, filled with dry air, and the capacity of which may be afterwards ascertained, is weighed; the weight of the air for the temperature and pressure prevailing during the weighing is then determined and the weight subtracted from the weight of the globe plus the air; the difference gives the weight of the globe when empty. The 148 ORGANIC ANALYSIS. [ 194. substance, the vapor density of which is to be determined, is now introduced in excess into the globe, which is then uniformly heated to a temperature sufficiently above the boiling-point of the sub- stance, and until the latter is completely converted into vapor, when the excess, together with the atmospheric air originally present, is then expelled. The globe is now sealed air-tight and weighed, and the weight of the empty globe deducted from this. The difference gives the weight of the volume of vapor, and this affords the data necessary for determining the vapor density. It need scarcely be mentioned that the result can be accurate only when the volume of the air and the vapor are first reduced to the same temperature and normal barometric pressure, and that consequently the state of the barometer and thermometer must be taken at the first weighing and at the time of sealing the globe with vapor. This method is of course only applicable in the case of substances which volatilize without decomposition, and will afford accurate results only when the substance is absolutely pure. Only the practical manipulation of the process is here described, while the necessary corrections and calculations, as well as the conclusions they afford regarding the composition of the substances, will be given in "The Calculation of Analyses/' 204. a. APPARATUS AND REQUISITES. 1. THE SUBSTANCE. About 8 grammes are required. Its boiling-point must be fairly accurately known. 2. A GLASS GLOBE WITH DRAWN-OUT NECK. Select an ordinary glass globe of pure glass free from air-bubbles, and of a capacity of 250 to 500 c.c.; rinse it clean with water, dry it perfectly, exhaust it, allow dry air to enter, and repeat the operation, using the apparatus illustrated in Fig. 24, 174. The neck of the globe is then softened near the body and drawn out to the shape shown in Fig. 79. Cut off the extreme tip and slightly round the edges by fusion. (As this point must be later on rapidly sealed by fusion, it is advis- able to ascertain the fusibility of the glass by trying to seal the 194.] DETERMINING EQUIVALENTS. 149 point on the originally drawn-out neck. If this is not easily effected, the globe is unserviceable.) 3. A SMALL IRON OR COPPER VESSEL for the reception of the liquid, and in which the globe is to be heated (see Fig. 80). The liquid to be used for the bath must admit of being heated at least 30 to 40 above the boiling-point of the substance. Almost all determinations may be effected by the use of water, paraffin, or oil. A calcium-chloride bath is more convenient, however, than a paraffin- or oil-bath, if the temperature afforded by it (which may be raised to 180 with a perfectly saturated solution) is sufficiently high for the purpose, as it permits the globe to be more easily cleaned. 4. AN APPARATUS FOR HOLDING THE GLOBE. This may be easily made from a rod and some iron wire. During the operation it is attached to a retort stand (see Fig. 80). FIG. 80. 5. MERCURY, in more than sufficient quantity to fill the globe. 6. A MEASURING TUBE, accurately graduated, of about 100 c.c. capacity. 7. A GAS OR ALCOHOL LAMP and a BLOWPIPE. 8. An accurate BAROMETER. 9. An accurate THERMOMETER, with a sufficiently long scale. 6. THE PROCESS. a. Weigh the globe, placing a thermometer within the balance- case, and leaving the globe on the balance for ten minutes to ascer- 150 ORGANIC ANALYSIS. [ 194. tain whether its weight remains constant. As soon as it is so, note the temperature, and the height of the barometer. /?. Gently heat the globe and dip the point into about 8 grammes of the fluid substance; if solid, liquefy by gently heating. (If the substance has a high melting-point, the neck and point as well as the body of the globe must be heated, in order that solidification does not take place within the neck.) As soon as the globe cools (which may be accelerated by dropping ether on it, in the case of very volatile substances), the fluid enters and spreads out within it. Not more than from 5 to 7 grammes should be allowed to enter. f. Heat the bath (a, 3) to between 40 and 60, and in it then fasten the globe with a thermometer, as shown in Fig. 80. Raise the temperature of the bath 30 to 40 above the boiling-point of the substance, and (if a calcium-chloride, paraffin-, or oil-bath is used) maintain this temperature as uniformly as possible, by regulating the heat. As soon as the temperature of the flask rises somewhat above the boiling-point of the substance, the vapor of the latter streams out through the point. The volume of the current increases as the temperature of the bath rises; gradually, however, it diminishes, and finally (after about 15 minutes) ceases altogether. Should any vapor have condensed in the point in droplets, a glowing piece of charcoal is passed be- neath the point to and fro, whereby they are quickly volatilized. As soon as perfect equilibrium is established at the desired tem- perature, rapidly fuse and seal the point with the blowpipe, and immediately take note of the temperature. The certainty that the point is perfectly sealed is ascertained by directing a current of air on to the projecting point with the blowpipe, and thus cooling it; a small quantity of the vapor will condense and form a column of liquid which will be held in the point by capillary attraction. If the point is not hermetically sealed, this does not take place. A barometric reading is then again taken, and a note made of it should it have changed since the first reading. d. Now remove the sealed globe from the bath, clean it very carefully after cooling, completely dry, weigh it as above, and thus ascertain the weight of the inclosed substance. 194.] DETERMINING EQUIVALENTS. 151 e. Immerse the point of the globe for its entire length in mer- cury, make a scratch with the file near the end, and break off the point. The mercury at once rushes into the globe because of the vacuum caused by the condensation of the vapor. (The globe should be held in the hollow of the hand, while this rests upon the edge of the trough.) If the globe contained no more air at the moment it was sealed, it will become completely filled with mercury ; otherwise a small air-bubble will remain in it. In either case measure the mercury in the globe by transferring it to a graduated tube (a, 6) ; if a bubble of air remained in the globe, fill the latter with water, and measure this also. The difference between the volumes of mercury and that of the w r ater gives the volume of the air-bubble. The results are very accurate if the process has been carefully carried out; for the calculation see "Calculation of Analyses" 204. B. PROCESS BASED ox GAY-LUSSAC'S PRINCIPLE. In the Dumas process the substance, the vapor of which has filled a known volume under determined conditions, is subsequently weighed, whereas in GAY-LUSSAC'S method the volume which the vapor of a previously weighed portion of the substance occupies under determined conditions, is determined. The latter process is best carried out according to the method recommended by A. W. HOFMANN.* For this there is required a calibrated tube, closed at one end and about 1 metre long and 15 to 20 mm. wide. This tube is carefully filled with mercury and inverted into a small mercurial trough, so that a vacuum of from 20 to 30 cm. forms in the upper part of the tube. Almost the entire length of the tube is inclosed in another glass tube 80 to 90 cm. long and 30 to 40 mm. wide, narrowed at its upper end over the sealed end of the calibrated tube to a moderately wide delivery tube which is bent at a right angle. The lower opening of the tube is closed by a stopper through * Ber. der deutsch. chem. Gesellsch., i, 198; Zeitschr. /. analyt. Chem., vin, 83 152 ORGANIC ANALYSIS. [ 194. the central wide perforation of which the calibrated tube passes, while a narrow exit tube is fitted in a second perforation. The external tube serves for raising the calibrated tube to a definite high temperature and maintaining it at the point required. The heating is effected by passing the vapor of a liquid having a con- stant and suitable boiling-point (water, aniline, etc.) into the upper tube, bent at right angles. When water is employed the vapors are permitted to ecape freely through the exit tube; if aniline or other liquid is used, however, this tube is connected with a suitable condenser. HOFMANN has satisfied himself by direct ex- periment that with a sufficiently rapid evolution of vapor, the space between the external tube and the calibrated tube, as well as the latter itself, will be constantly maintained at the temperature of the boiling-point of the liquid used, and will render it unnecessary to take the temperature during the experiment. In carrying out the process, the liquid, the vapor density of which is to be determined, is weighed in a very small flask, made from a piece of thin glass tubing, and closed with a ground-glass stopper. The size of the flask must depend upon the nature of the liquid; the capacity of the smallest may be 0-01 grm.,that of the largest 0-1 grm., of water. The weighed flask is now allowed to rise in the calibrated tube filled with mercury. The stopper frequently springs out as soon as the flask acquires the Torricellian vacuum. No matter whether this takes place or not, the heating is next begun by conducting into the right-angled tube the vapors of water, aniline, or other liquid of constant boiling-point, and generated by boiling the liquid in a glass or copper vessel. After a short time the stopper of the small flask will spring out if it has been properly adjusted, the liquid will run out and be converted into vapor, and the mercurial column will sink. When the vapor has circulated long enough in the space between the two tubes to insure a uniform temperature, and the height of the mercurial column no longer changes, read off the height of the barometer, and that of the mercury within and without the calibrated tube. The reading-off of the latter is rendered more convenient by having the barometer tube graduated in millimetres as well as cubic 194.] DETERMINING EQUIVALENTS. 153 centimetres. The temperature of the vapor and of the mercury is, as above noted, that of the boiling-point of the liquid, the vapor of which has served for heating at the observed barometric pressure. In making the calculations, which are explained in 204, the tension of the mercurial vapor and the temperature of the mercury must both be taken into account, if a high temperature has been used. So far as the temperature of the mercury is con- cerned a slight error is unavoidable, as the mean temperature of the mercury at the point where the heated mercury within the tube and that unheated below the tube join cannot be ascertained. This slight error has no appreciable influence on the results, however. The advantages afforded by HOFMANN'S process are quite important, since the GAY-LUSSAC principle may be applied for the determination of vapor densities at high temperatures without the operator being subjected in any way to the poisonous fumes of mercury; further, the atmosphere of vapor enables a constancy of temperature to be maintained which it would be difficult to secure otherwise, and the vapor volume may be read off with great accuracy. The greatest advantage, however, is that at so low a pressure, which may be reduced to 20 and even 10 cm., the work may be done at a comparatively low temperature. For many substances which boil at 120 and even 150 (according to A. SCHRODER even 182), the vapor of water suffices under these circumstances; and the vapor of aniline (boiling at 185) is hot enough to enable its own vapor density to be accurately deter- mined, as well as that of toluidine boiling at 198, naphtalin boiling at 218, and according to A. SCHRODER also of cumarin, boiling at 270.* H. WICHELHAUS t recommends a somewhat modified form of HOFMAXX'S apparatus, shown in Fig. 81. a is a ground-glass cup fitted to the barometer tube, and which is put on in the mercurial trough after the substance has been intro- * Regarding the clever manner in which A. SCHRODER employs HOF- MAXX'S apparatus for determining the water of crystallization in salts, etc., see Ber. d&r deutsch. chem. Gesellsch., iv, 471 ; Zeitschr. f. analyt. Chem., Xi, 98. t Ber. der deutsch. chem. Gesellsch., 1870, 166; Zeitschr. f. analyt. Chem., IK, 496. 154 ORGANIC ANALYSIS. [ 194. duced. The cup remains filled with mercury and attached to the tube, thus forming a siphon, and permitting the entire tube to be FIG. 81. surrounded by vapor, and dispensing entirely with the mercurial trough. The consideration regarding the difference in tempera- 194.] DETERMINING EQUIVALENTS. 155 ture between different parts of the mercurial column is thus en- tirely obviated. The mercury displaced by the heat flows out of the narrow opening of the cup and passes with the vapors through the tube e into the condenser and receiver, b denotes the zero-point on the tube, which is graduated in cubic centimetres and millimetres, and from which the height of the mercurial column is always read off. The outer tube, d, has the form of a cylinder, widened below, it is of such dimensions as to require as little vapor to fill the space be- tween the two tubes as possible. The whole rests upon a large cork, c, carrying also the tube e, which passes above the surface of the table. The inner tube is secured near its sealed end within the outer tube by means of a notched cork; this is done because were the tube allowed to rest directly upon the glass cup, the latter might be easily broken by the weight. Other methods also based on GAY-LUSSAC'S principle have been proposed by HUGO SCHIFF,* W. M. WATTS,! and others. C. GRABOWSKI % and LANDOLT have also proposed methods founded on principles slightly different from that of GAY-LUSSAC. In GRABOWSKI'S method two similar tubes, at first filled with mer- cury, are heated together to the same temperature in an air-bath. One of these tubes receives the bulb or tube containing the weighed substance. As soon as the vapor of the liquid has reached the proper temperature, dry air is passed into the other tube until the volumes of air and vapor are alike. This equality of volume must be maintained, unless dissociation occurs, with increasing temperature, as well as on cooling to the temperature which is the lower limit of the normal vapor density of the substance. After completely cooling, the volume of air used is measured in the usual manner, and from this the vapor density of the substance is very simply calculated. While in GRABOWSKI'S method the quantity of normal sub- * Zeitschr. f. analyt. Chem., i, 321. f Ibid., vii, 82. t Ibid., v, 338. Ibid., xi, 322. 156 ORGANIC ANALYSIS. . . . [ 194. stance (air) is adapted to that of the substance to be examined, LANDOLT, on the contrary, adapts the weight of the substance to be examined to that of the quantity of normal substance (water or chloroform). The direct comparison of volumes under the same pressure and temperature is common to both methods. L. PFAUNDLER * has studied both methods, and has recommended a modification of GRABOWSKI'S apparatus, in which steam is used instead of an air-bath, and the air is differently introduced. Re- garding the details I refer to the original paper. D. BUNSEN'S method f is based upon the well-known principle that the specific gravity of gases and vapors is known when the weight of equal volumes under the same conditions is known. The application of the principle is, however, quite original. There are required three, sometimes two, glass tubes having similar ca- pacities (to within 0-01 c.c. of each other), and equal in weight to within a fraction of a milligramme. BUNSEN employs an air-tight stopper of so simple a construction that it is possible to use the tubes, the weight of which has been determined once and for all, as often as desired for determining the specific gravity of gases or vapors. For heating BUNSEN employs a peculiarly constructed large air-bath which permits an almost constant temperature to be maintained for a long time. The method (the details of which are minutely given loc. cit.) is remarkable in that the density of gases and vapors is obtained by always using the same tubes and simply determining two dif- ferent weights, without its being necessary to know the volume, pressure, or temperature of the vapors or gases. The accuracy of the results obtained by BUNSEN is so high that in the case of car- bonic acid, as well as ether vapor, the figures are identical to the third decimal, but the method requires a high degree of skill in the construction of glass apparatus, as well as great dexterity. E. The determination of the vapor densities of substances having high boiling-points is effected by DEVILLE and TROOST'S * Ber. der deutsch. diem. Gesellsch., v, 575; Zeitschr. f. analyt. Chem., xu, 100. f Zeitschr. f. analyt. Chem., vi, 1. 195.J DETERMINING EQUIVALENTS. 157 method,* for a description of which I must refer to -the original paper. 195. 3. A great many indifferent substances unfortunately either do not combine with bases or acids, or form compounds from which the equivalent cannot well be determined. In such cases the equivalent is determined by subjecting the compounds to the ac- tion of acids, bases, halogens, etc., and thus preparing substitution or decomposition products the equivalents of which are either known or may be determined, or which may be inferred from the mode of formation of the compound in question. In these cases that equivalent is considered as the correct one which affords the simplest explanation of the processes of formation and decompo- sition. This method of determining equivalents is ultimately connected with the higher branches of organic chemistry and will not be here further considered, since methods which are applicable in general cannot be given. * Annal. d. Chem. u. Pharm., cxni, 42. DIVISION II. CALCULATION OF ANALYSES. THE calculation of the results obtained by an analysis presupposes, as an indispensable preliminary, a knowledge of the general laws of the combining proportions of bodies, on one hand, and of the more simple rules of arith- metic on the other. It is a great error to suppose that the ability to make chemical calculations involves an extensive acquaintance with mathematics, a knowledge of decimal fractions and simple equations being for the most part sufficient. These remarks are not intended to dissuade students of chemistry from pursuing the highly important study of mathematics, but merely to encourage those who have had no opportunity of entering more deeply into this science, and who, as experience has shown me, are often afraid to venture upon chemical calculations. For this reason I have made the whole of the calculations given in the following paragraphs in the most in- telligible manner possible, and without logarithms. I. CALCULATION OF THE CONSTITUENTS SOUGHT FROM THE COMPOUND OBTAINED IN THE ANALYTICAL PROCESS, AND EXHIBITION OF THE RESULT IN PER-CENTS, 196. The bodies the weight of which it is intended to determine are separated, as we have seen in Division I, treating of the " Execution of Analysis," either in the free state or and this most frequently in combinations of known composition. The results are usually calculated upon 100 parts of the exam- ined substance, since this gives a clearer and more intelligible view of the composition. In cases where the several constituents have been separated in the free state the calculation may be made at once; but if the constituents have been separated in combination with other substances, they must first be calculated from the compounds obtained. 1. Calculation of the Results into Per-cents by Weight, in Cases where the Substance sought has been separated in the Free State. a. Solid Bodies, Liquids, and Gases, which have been determined by Weight. 197. The calculation here is exceedingly simple. Suppose you have analyzed mercurous chloride, and separated the mer- cury in the metallic state ( 118, 1) 2-945 grm. mercurous chloride have given say 2 -499 grm. metallic mercury. 2-945 : 2-499 :: 100 :x z=84-85 158 198.] CALCULATION OF ANALYSES. 159 which means that your analysis shows 100 parts of mercurous chloride to contain 84-85 of mercury, and consequently 15-15 of chlorine. Now as mercurous chloride is known to consist of 2 at. mercury and 2 at. chlorine, and as the atomic weights of both of these elements are also known, the true percentage composition of the body may be readily calculated from these data. When analyzing substances of known composition for practice, the results theoretically calculated and those obtained by the analysis are usually placed in juxtaposition, as this enables the student at once to perceive the degree of accuracy with which the analysis has been performed. Thus for instance Found. Calculated (compare 84, 6). Mercury 84-85 84-94 Chlorine 15-15 15-06 100-00 100-00 b. Gases which have been determined by Measure. 198. If a gas has been determined by measure, it is, of course, necessary first to ascertain the weight corresponding to the volume found before the percent- age by weight can be calculated. But as the exact weights of a definite volume of the various gases have been severally determined by accurate experiments, this calculation also is a simple rule-of-three question, if the gas may be measured under the same circumstances to which the known relation of weight to volume refers. The circumstances to be taken into consideration here are : Temperature and Atmospheric Pressure. Besides these the Tension of the Aqueous Vapor may also claim consideration in cases where water is used as the confining fluid, or generally where the gas has been measured in the moist state. The respective weights assigned in Table V* to 1 litre of the gases there enumerated refer to a temperature of and an atmospheric pressure of 76 metre of mercury. We have, therefore, in the first place, to consider the man- ner in which volumes of gas measured at another temperature and another height of the barometer are to be reduced toO and 0-76 of the barometer. a. Reduction of a Volume of Gas of any given Temperature to 0, or any other Temperature between and 100. The following propositions regarding the expansion of gases were formerly universally adopted : 1 . All gases expand alike for an equal increase of temperature. 2. The expansion of one and the same gas for each degree of the ther- mometer is independent of its original density. * See Tables at the end of the volume. 160 ORGANIC ANALYSIS. [ 198. Although the correctness of these propositions has not been fully conr firmed by the minute investigations of MAGNUS and REGNAULT, yet they may be safely followed in reductions of the temperature of those gases which a,re most frequently measured in the course of anah'tical processes, as the coefficients of expansion of these gases scarcely differ from each other, and as there is never any very considerable difference in the atmospheric pressure under which the gases are severally measured. The investigations just alluded to have given 0-3665 as the coefficient of the expansion of gases which comes nearest to the truth; in other words, as the extent to which gases expand when heated from the freezing- to the boiling-point of water. They expand, therefore, for every degree of the centigrade thermometer, ^0.003665. ,: If we wish to ascertain how much space 1 c.c. of gas at will occupy at 10, we find 1X[1 + (10X0- 003665)]= 1-03665. If we wish to ascertain how much space 100 c.c. at will occupy at 10, we find 100X[1 + (10X0- 003665)] = 100 X 1 03665= 103 665. If we wish to know how much space 1 c.c. at 10 will occupy at 0, we find 1 + (10X0- 003665) = How much space do 103-665 c.c. at 10 occupy at 0? 103-665 1 + (10X0 -003665) = 100. The general rule of these calculations may be expressed as follows: To calculate the volume of a gas from a lower to a higher temperature, we have in the first place to find the expansion for the volume unit, which is done by adding to 1 the product of the multiplication of the thermometrical differ- ence by 003665, and then to multiply this by the number of volume units found in the analytical process. On the other hand, to reduce the volume of a gas from a higher to a lower temperature, we have to divide the number of volume units found in the analytical process by 1 -I- the product of the multi- plication of the thermometrical difference by 0-003665. In the case of carbonic acid the coefficient of expansion differs somewhat from that of air and other permanent gases. According to MAGNUS it is 0-00369 for 1, and not 0-003665; according to REGNAULT it is 0-00371. 198.] CALCULATION OF ANALYSES. 161 /?. Reduction of the Volume of a Gas of a certain given Density to 0-76 Metre Barometric Pressure, or any other given pressure. According to the law of MARIOTTE, the volume of a gas is inversely as the pressure to which it is exposed; in accordance with this a gas occupies the greater space the less the pressure upon it, and the less space the greater the pressure upon it. Thus, supposing a gas to occupy a space of 10 c.c. at a pressure of 1 atmosphere, it will occupy 1 c.c. at a pressure of 10 atmospheres, and 100 .c. at a pressure of ^ atmosphere. Nothing, therefore, can be more easy than the reduction of a gas of a certain given tension to 760 mm. bar. pressure, or any other given pressure, e.g., 1000 mm., which is frequently used in the analysis of gases. Supposing a gas to occupy 100 c.c. at 780 mm. bar., how much space will it occupy at 760 mm.? 760 : 780 :: 100 : x\ z=102-63. How much space will 100 c.c. at 750 mm. bar. occupy at 760 mm.? 760:750 :: 100 : x\ z=98-68. How much space will 150 c.c. at 760 mm. bar. occupy at 1000 mm.? 1000 : 760 :: 150 : x\ z=114. Condensible gases do not accurately follow MARIOTTE 's law, and those most readily condensible deviate most. Of the condensible gases carbonic- acid gas is the one most frequently met with in analyses, but no attention need be paid to the error caused by the slight differences in pressure, except in those cases where the highest degree of accuracy is required. In the case of greater differences of pressure the deviation from MARIOTTE 's law become more marked ; e.g., in order to condense carbonic-acid gas to half its volume at the same temperature, a pressure of 1-98292 (according to REGNAFLT), instead of two atmospheres, will be required. 7. Reduction of the. Volume of a Gas saturated with Aqueous Vapor to its actual Volume in the Dry State. It is a well-known fact that water has a tendency, at all temperatures, to assume the gaseous state. The degree of this tendency (the tension of the aqueous vapor) which is dependent solely and exclusively upon the tempera- ture, and not upon the circumstance of the water being in vacua or in any gaseous atmosphere is usually expressed by the height of a column of mer- cury counterbalancing it. The following table indicates the amount of tension for the various temperatures at which analyses are likely to be made.* Therefore if gas is confined over water, its volume is, cceteris paribus, always greater than if it were confined over mercury; since a quantity of aque- ous vapor proportional to the temperature of the water mixes with the gas, and the tension of this partly counterbalances the column of air that presses * Compare MAGNUS, Pogg. Annal. LXI, 247. 162 ORGANIC ANALYSIS. [ 198. upon the gas, and to that extent neutralizes the pressure. To ascertain the- actual pressure upon the gas, we must therefore subtract from the apparent pressure so much as is neutralized by the tension of the aqueous vapor. TABLE. Temperature (in degrees C.). Tension of the aqueous vapor expressed in millimetres. Temperature (in degrees C.). Tension c.f the aqueous vapor expressed in millimetres. 4-525 21 18-505 1 4-867 22 19-675 2 5-231 23 20-909 3 5-619 24 22-211 4 6.032 25 23-582 5 6-471 26 25-026 6 6-939 27 26-547 7 7-436 28 28-148 8 7-964 29 29-832 9 8-525 30 31-602 10 9-126 31 33-464 11 9-751 32 35-419 12 10-421 33 37-473 13 11-130 34 39-630 14 11-882 35 41-893 15 12-677 36 44-2G8 16 13-519 37 46-758 17 14-409 38 49-368 18 15-351 39 52-103 19 16-345 40 54-969 20 17-396 Suppose we had found a gas to measure 100 c.c. at 759 mm. bar., the tem- perature of the confining water being 15; how much space would this volume of gas occupy in the dry state and at 760 mm. of the barometer? Our table gives the tension of aqueous vapor at 15= 12 -677; the gas is consequently not under the apparent pressure of 759 mm., but under the actual pressure of 759-12-677=746-323 mm. The calculation is now very simple; it proceeds in the manner shown in p; we say 760 : 746-323 :: 100 : x s-98-20. When the volume of a gas has thus been adjusted by the calculations in a and ,5, or 7% to the thermometrical and barometrical conditions to which the data of Table V refer, the percentage by weight may now be readily calculated by substituting the weight for the volume and proceeding by simple rule-of- three. What is the percentage by weight of nitrogen in an analyzed substance of which 0-5 grm. has yielded 30 c.c. of dry nitrogen gas at 0, and 760 mm* bar.? 198.] CALCULATION OF ANALYSES. 163 In Table V we find that 1 litre (1000 c.c.) of nitrogen gas at 0, and 760 mm. bar., weighs 1-25617 gnu.* We say accordingly 1000 : 1-25617 :: 30 : x x= 0-0377. And then 0-5 : 0-0377 :: 100 : x z=7-54. The analyzed substance contains consequently 7-54 per cent, by weight of nitrogen. DR. GIBBS' method of finding at once the total correction for temperature, press- ure, and moisture in absolute determinations of nitrogen, or other gases: f ' ' I take a graduated tube, which I fill with mercury, then displace about two-thirds of the mercury with air, and invert the tube into a cistern of mer- cury. Then I make four or five determinations of the volume of the included (moist) air in the usual manner and find the volume of the air at and 760 mm. as a mean of all the determinations. This tube I call the companion tube, and it always hangs in the little room I use for gas analyses. Suppose the volume of (dry) air at and 760 mm. is 132-35 c.c. " Now, in making an absolute nitrogen determination I collect the nitrogen moist over mercury in a graduated tube, and then suspend the measuring tube by the side of the companion tube. I then by a cord and pulley bring the level of the mercury in the two tubes to correspond exactly, and then read off the volume of air in the companion tube and the volume of nitrogen in the measur- ing tube. I ought to have stated that the two tubes hang in the same cistern of mercury. Suppose the volume of air in the companion tube to be 143 c.c. ; then the total correction for temperature, pressure, and moisture will be 143 - 132 35= 10 65 c.c. The correction for the nitrogen will then be found by rule-of -three. As the observed volume of air in the companion tube is to the observed volume of nitrogen, so is (in this case) 10-65 to the required cor- rection. In this way, when the volume of air in the companion tube is once * Taking MORLEY'S value, 0-089873, as the most probable weight in grammes of a litre of hydrogen at 0, 760 mm. bar., and at 45 latitude, then 1 litre of nitrogen, using the atomic weights employed in this work, would weigh 0- 089873 X 13 93 (if H 1, then N = 13 93) = 1 25193 grm. Using this value instead of that of the author, the proportion would then be as follows: 1000 : 1-25193 :: 30 : x, and x = 0-03756, and 0.5:0-03756:: 100: x, whence x = 7 -51, the percentage weight of the nitrogen in the analyzed substance. The value 1 25193 grm. for 1 litre of nitrogen also agrees more closely with the value obtained for nitrogen which was prepared chemically, and which was found to be 1 -2507 (see RAYLEIGH, Chem. New8, Lxvn, 183. 198, and 211); while that used by the author, 1-25617, is most probably based on the value obtained for atmospheric nitrogen, which contained argon. In fact it was the difference between the observed values of chemically prepared and atmospheric nitrogen (the latter was found by RAYLFIGH to be 1-257) that led to the discovery of argon (Proc. Roy.Soc., Iv, 340 [1894J; Zeitschr. f. phys. Chem., xvi, 344 [1895]). TRANS- LATOR. t Private communication. 164 ORGANIC ANALYSIS. [ 199. found, no further observations of temperature, pressure, or height of mercury above the mercury in the cistern are necessary. The companion tube lasts for an indefinite time. I have even used it filled with water, without any appreciable change in some weeks, but I prefer mercury. As the two tubes hang side by side, there is never an appreciable difference of temperature. My results are most satisfactory. Williamson & Russell have, as you know, used a companion tube for equating pressures, but not for finding the total value of the tem- perature and pressure correction at once; and I believe that my process is wholly new. Certainly it is wonderfully convenient, and saves all tables and labor of computation." 2. Calculation of the results into Per-cents by Weight, in Cases where the Body sought has been separated in Combination, or where a Compound has to be determined from one of its Constituents. 199. If the body to be determined has not been weighed or measured in its own form, but in some other form, e.g., carbonic acid as calcium carbonate, sulphur .as barium sulphate, ammonia as nitrogen, chlorine by a standard solution of iodine, etc., its quantity must first be reckoned from that of the compound found before the calculation described in 1 can be made. This may be accomplished either by rule-of-three or by some abridged method. Suppose we have weighed hydrogen in the form of water, and have found 1 grm. of water; how much hydrogen does this contain? A molecule of water consists of Hydrogen ................... 2 at.= 2-016 pts. Oxygen .................... 1 at. = 16-000 " 18-016 We say accordingly 18-016:2- 016::l:rc Or, expressed in general terms, Water X 1 1 19 = Hydrogen. EXAMPLE. 517 of water; how much hydrogen? 517X0-1119=57-8523. The following equation results also from the above proportion: 18-016^ 1 2-016 x 2-016 18-016 = 199.] CALCULATION OF ANALYSES. 165 Or, expressed in general terms, Water divided by 8 -9365= Hydrogen. EXAMPLE. 517 of water, how much hydrogen? 517 8-9365 = 57-8523. In this manner we may find for every compound constant numbers by which to multiply or divide the weight of the compound, in order to find the weight of the constituent sought (comp. Table III*). Thus, for instance, the nitrogen contained in ammonium platinic chloride may be obtained by multiplying the weight of the latter by 0-06328; thus the carbon may be calculated from carbonic acid by multiplying the weight of the latter by 0-2727, or dividing it by 3-6667. These numbers are by no means simple, convenient, and easy to remember. It is therefore advisable, in the case of carbonic acid, for instance, to fix upon, another general expression, viz., Carbonic, acid X 3 ~ , = Carbon; in carbonic acid being carbon, as may be seen from tne C 12 2O 32 44 12 parts in 44 (= composition The object in view may also be attained in a very simple manner, by refer- ence to Table IV,* which gives the amount of the constituent sought for every number of the compound found, from 1 to 9; the operator need, therefore,, simply add the several values together. As regards hydrogen, for instance, we find: TABLE. Found, water Sought, hydrogen 1 0-1119 2 0-2238 3 0-3357 4 0-4476 5 0-5595 6 0-6714 7 0-7833 8 0-8952 9 1-0071 From this table it is seen that 1 part of water contains () 1119 of hydrogen, that 5 parts of water contain 0-5595 of hydrogen; 9 parts, 1-0071, etc. Now, if we wish to know, for instance, how much hydrogen 5s contained in 5-17 parts of water, we find this by adding the values for 5 parts, for f ff part, and for jfo parts, thus: 0-5595 0-01119 0-007833 0-578523 * See Tables at the end of the volume. 166 ORGANIC ANALYSIS. [ 200. Why the numbers are to be placed in this manner, and not as follows: 0-5595 0-1119 0-7833 1-4547 is self-evident, since arranging them in the latter way would be adding the value for 5, for 1, and for 7 (5 + 1+7= 13), and not for 5-17. This reflection shows also that, to find the amount of hydrogen contained in 517 parts of water, the points must be transposed as follows: 55-95' 1-119 0-7833 57-8523 3. Calculation of the Results of Indirect Analyses into Per-cents by Weight. 200. The import of the term "indirect analysis," as denned in 151, p. 596, shows sufficiently that 110 universally applicable rules can be laid down for the calculations which have to be made in indirect analyses. The selection of the right way must be left in every special case to the intelligence of the analyst. I will here give the mode of calculating the results in the more important indirect separations described in Section V. They may serve as examples for other similar calculations. a. Indirect Determination of Sodium and Potassium. This is effected by determining the sum total of the chlorides and the chlo- rine contained in them. The calculation may be made as follows : Suppose we have found 3 grm. of sodium and potassium chlorides, and in these 3 grm. 1-6877 of chlorine. At. Chlorine. Mol. KC1. Chlorine found. 35-45 : 74-56 :: 1-6877 : x x = 3-5525 If all the chlorine present were combined with potassium, the weight of the chloride would amount to 3-5525. As the chloride weighs less, sodium chloride is present, and this in a quantity proportional to the difference (i.e., 3-5525 3=0-5525), which is calculated as follows: The difference between the mol. weight of KC1 arid that of NaCl (16-06) is to the mol. weight of NaCl (58-50) as the difference found is to the sodium chloride present: 16-06 : 58-50 :: 0-5525 : x z=2NaCl and 3-2=lKCl. 200.] CALCULATION OF ANALYSES. 167 From this the following short rule is derived : Multiply the quantity of chlorine in the mixture by 2 10324, deduct from the product the sum of the chlorides, and multiply the remainder by 3 6426 ; the product expresses the quantity of sodium chloride contained in the mixed chloride. The following formula* may also be used: 50n=C (sum of the chlorides). -45rc=c (sum of the chlorine). K denotes the number of equivalents (expressed in grammes) of potassium chloride contained in the potassium-chloride mixture, and therefore also the number of equivalents of potassium in the potassium present, or the chlorine equivalent of the chlorine combined with the potassium; n is the equivalent -for sodium corresponding to K. .'. 74-5QK= potassium chloride present. 58-50n = sodium 35-45K= chlorine combined with potassium. 35-45n = " " " sodium. Using C and c, we have C-74-56# C-35-45X and /. K= 58-50 35-45 C-l-6502c 16-06 The quantity of potassium chloride required is therefore KCl=74-56K=4-6349C-7-647r. 4 b. Indirect Determination of Strontium and Calcium. This may be effected by determining the sum total of the carbonates and the carbonic acid contained in them ( 154, 8). Suppose we have found 2 grm. of mixed carbonate, and in these 2 grm. 0-7383 of carbonic acid, Mol. CO, Mol. SrCOs CO, found 44 : 147-60 :: 0-7383 : x x = 2-47666. If, therefore, the whole of the carbonic acid were combined with strontia, the weight of the carbonate would amount to 2-47666 grm. The deficiency, = 0-47666, is proportional to the calcium carbonate present, which is calcu- lated as follows: The difference between the molecule of SrCO 3 and the molecule of CaC0 3 fJ.7-50) is to the molecule of CaCO 3 (100-1) as the difference found is to the calcium carbonate contained in the mixed salt: .'. 47-5 : 100-1 :: 0-47666 : x 91. * KRETSCHY, Zeitschr. f. analyt. Chem., xv, 44. A clerical error in this paper has been here corrected. 168 ORGANIC ANALYSIS. [ 201, The mixture, therefore, consists of 1 grm. calcium carbonate and 1 grm. strontium carbonate. 'From this the following short rule is derived: Multiply the carbonic acid found by 3-3545, deduct from the product the sum of the carbonates, and multiply the difference by 2 10737 ; the product expresses the quantity of the calcium carbonate. c. Indirect Determination of Chlorine and Bromine ( 169, 1). Let us suppose the mixture of silver chloride and bromide to have weighed 2 grm., and the diminution of weight consequent upon the transmission of chlorine to have amounted to 1 grm. How much chlorine is there in the mixed salt, and how much bromine? The decrease of weight here is simply the difference between the weight of the silver bromide originally present and that of the silver chloride which has replaced it; if this is borne in mind, it is easy to understand the calculation which follows: The difference between the molecules of silver bromide and silver chloride is to the molecule of silver bromide as the ascertained decrease of weight is to x, i.e., to the silver bromide originally present in the mixture: /. 44-50 : 187-87 :: 0-1 : x x= 0-42218. The 2 grm. of the mixture therefore contained 42218 grm. silver bromide, and consequently 2-0-42218 = 1-57782 grm. silver chloride. It results from the above that we need simply multiply the ascertained decrease of weight by 4-2218 to find the amount of silver bromide originally present in the analyzed mixture. And if we know this, we also know, of course, the amount of the silver chloride; and from these data we next calculate the quantities of chlorine and bromine as directed in 199, and the percentages as directed in 196. SUPPLEMENT TO I. REMARKS ON LOSS AND EXCESS IN ANALYSES, AND ON TAKING THE AVERAGE. 201. If, in the analysis of a substance, one of the constituents is estimated from the loss, or, in other words, by subtracting from the original weight of the analyzed substance the ascertained united weight of the other constituents, it is evident that in the subsequent percentage calculation the sum total must invariably be 100. Every loss suffered or excess obtained in the determination of the several constituents will, of course, fall exclusively upon the one con- stituent which is estimated from the loss. Hence estimations of this kind cannot be considered accurate, unless the other constituents have been de- termined by good methods and with the greatest care. The accuracy of the results will, of course, be the greater the less the number of constituents determined in the direct way. 201.] CALCULATION OF ANALYSES. 169 If, on the other hand, every constituent of the analyzed compound has been determined separately, it is obvious that, were the results absolutely accurate, the united weight of the several constituents must be exactly equal to the original weight of the analyzed substance. Since, however, as we have seen in 96, certain inaccuracies attach to every analysis without exception, the sum total of the results in the percentage calculation will sometimes exceed, and sometimes fall short of, 100. In all cases of this description, the only proper way is to give the results as actually found. Thus, for instance, PELOUZE found, in his analysis of potassium chloro- chromate, Potassium 21-88 Chlorine 19-41 Chromic acid 58-21 99-50 BERZELIUS, in his analysis of potassium uranate, Potassa 12-8 Uranic oxide 86-8 99-6 PLATTNER, in his analysis of pyrrhotite, Of Fahlun. Of Brasil. Iron 59-72 59-64 Sulphur 40-22 40-43 99-94 100-07 It is altogether inadmissable to distribute any chance deficiency or excess proportionately among the several constituents of the analyzed compound, as such deficiency or excess of course never arises from the several estimations hi the same measure; moreover, such "doctoring " of the analysis deprives other chemists of the power of judging of its accuracy. No one need be ashamed to confess having obtained somewhat too little or somewhat too much hi an analysis, provided, of course, the deficiency or excess be confined within cer- tain limits, which differ in different analyses, and which the experienced chem- ist always knows how to fix properly. In cases where an analysis has been made twice, or several times, it is usual to take the mean as the most correct result. It is obvious that an aver- age of the kind deserves the greater confidence the less the results of the several analyses differ. The results of the several analyses must, however, also be given, or, at all events, the maximum and minimum. Since the accuracy of an analysis is not dependent upon the quantity of substance employed (provided always this quantity be not altogether too small), the average of the results of several analyses is to be taken quite inde- pendently of the quantities used ; in other words, you must not add together the quantities used, on the one hand, and the weights obtained in the several analyses, on the other, and deduce from these data the percentage amount; 170 ORGANIC ANALYSIS. [ 202. but you must calculate the latter from the results of each analysis separately, and then take the mean of the numbers so obtained. Suppose a substance, which we call AB, contains fifty per cent, of A, and suppose two analyses of this substance have given the following results: (1) 2 grm. AB gave 0-99 grm. of A. (2) 50 " " " 24-00 " " " From 1, it results that AB contains 49-50 per cent, of A. H o lt " ft tl (t 48 . 00 " " " Total ..................... 97-50 Mean ..................... 48-75 It would be quite erroneous to say 2 + 50=52 of AB gave 0-99 + 24-00=24-99 of A, therefore 100 of AB contain 48-06 of A; for it will be readily seen that this way of calculating destroys nearly alto- gether the influence of the more accurate analysis (1) upon the average, on account of the proportionally small amount of substance used. II. DEDUCTION OF EMPIRICAL FORMULAS. 202. When the percentage composition of a substance is known, a so-called empirical formula may be found for it, i.e., the relative proportion of the several constituents may be expressed in a formula which, upon calculation in percentages, will give figures corresponding exactly, or nearly so, with those obtained on analysis. We are confined to the use of such empirical formulas in the case of all substances the equivalent of which cannot be de- termined, such as wood fibre, mixed substances, etc. The very simple method of deducting the empirical formulas will be readily understood from the following considerations : How should we proceed to find the relative number of equivalents in carbonic acid? We should say : The equivalent of the oxygen is to the quantity of oxygen in the equivalent of carbonic acid as 1 is to x, i.e. 16 : 32 :: 1 : *; z=2. In a similar manner one should find the number of carbon equivalents by the following equation : 12 : 12 :: 1 : x; x=l. (eq. of carbon) (carbon in 1 eq. of carbonic acid) 202.]' CALCULATION OF ANALYSES. 171 Now let us suppose we did not know the carbonic-acid equivalent, but only the percentage composition, thus: C 27-273 O 72-727 100-000 carbon dioxide. The relative proportion of the equivalents would still be ascertained even though any other given number, e.g., 100, were selected. Supposing we adopted 100 as the number, we should then have the following-- 16 : 72-727 :: 1 : z; z=4-5454. (eq. of oxygen) (oxygen in the as- sumed eq. 100) further, 12 : 27-273 :: 1 : x\ x=2>ZI27. (eq. of carbon) (carbon in the as- sumed eq. 100) We see that, though the numbers expressing the relative proportions of oxygen and carbon have changed, yet the relative proportion has not; since 2-2727 : 4-5454 :: 1 : 2. The process may hence be expressed as follows : Assume any number, most conveniently 1 00, as the equivalent of the com- pound, and ascertain how many times the equivalent of each constituent of the compound is contained in the quantity of the same constituent present in 100 parts. When the numbers expressing the relative proportions have been thus found, the empirical formula has, in fact, been found. It is usual, however, to reduce the number found to the simplest expression possible. Suppose we take a more complicated case, for example, the calculation of the empirical formula of mannite. The percentage composition of mannite is C 39-536 H 7-749 O 52-715 100-000 We obtain hence the following proportions : 12 : 39-536 :: 1 : x; z=3-295, 1-008 : 7-749 :: 1 : x; z=7-6S8, 16 : 52-715 :: 1 : x: z=3-295. We have now the empirical formula for mannite, thus: C 3-295, H 7-688, O 3-295. We see at a glance that the numbers of the equivalents of carbon and oxygen are identical ; and the question arises whether the relative proportion 172 ORGANIC ANALYSIS. [ 202. found may not be expressed by smaller numbers. A simple calculation en- ables this question to be answered, as follows: 3-295 : 7-688 :: 60 : x; x=UQ. (Any other number might be substituted for 60 as the third term of the pro- portion, but the number chosen is very suitable because it is divisible without remainder by most numbers.) We have now the simple formula O 60 = C 6 H 14 O 6 . The percentage composition of mannite, as given above, being that calcu- lated from the formula, no doubt, of course, remains as to the correctness of the latter. Let us now take the results of an actual analysis of mannite. By the combustion of 1 593 grm. of mannite with cupric oxide, OPPER- MAN obtained 2-296 CO 2 and 1-106 water. In per-cents this gives C 39-31 H 7-77 O 52-92 100-00 This, calculated as above, would give ^3-270 H 7 . 708 O 3 . 308 as the first expression of the empirical formula, and by the proportion 3-276 : 7-708 :: 6 : 14-11. A glance at these numbers will show that 14 may be readily taken for the 14-11, and that the difference between 3-276 and 3-308 is so small that both may be expressed by one number. From these considerations we again come to the formula C 6 H 14 6 . The proof as to whether the formula is correct or not is obtained by recal- culation in per-cents. The smaller the difference between the per-cents calcu- lated and those found, the more reason is there to consider the formula as correct. If the difference is greater than can be accounted for by the defects incidental to the methods, there is ground to consider the formula as incorrect, and to establish another ; it will be evident that in the case of substances the equivalent of which is not known, different formulas may be calculated from the same analysis, or from a number that closely agree, while the numbers found are never absolutely correct, but are always only approximately so. For instance in the case of mannite: Calculated Found forC 6 39-536 f or C 8 39-65 39-31 H 14 7-749 H 18 7-49 7-77 O. 52-715 O 3 52-86 52-92 100-000 100-00 100-00 203.] CALCULATION OF ANALYSES. 173 III. DEDUCTION OP RATIONAL FORMULAS. 203. If in addition to the percentage composition the equivalent of a substance is also known, it is easy to deduce its rational formula, i.e., a formula expressing not only the relative proportion of the equivalents, but also their absolute number in one equivalent of the substance. The following examples will serve for illustration: 1. Determining the rational Formula of Hyposulphuric (Dithionic) Add. By analysis we find first the percentage composition of hyposulphuric acid, secondly that of potassium hyposulphate, thus : Sulphur 44-50 Potassa (K 2 O) 39-528 Oxygen 55-50 Hyposulphuric acid 60-472 100-00 100-000 (equivalent of K 2 O= 94 - 22) From the equation 39-528 : 60-472 :: 94-22 : x\ z=144-14 it follows that 144-14 is the sum of the equivalents of the constituents of hypo- sulphuric acid, i.e., the equivalent of hyposulphuric acid. We need no longer assume any hypothetical equivalent for our calculation, as we did in 202 for mannite, since we know now the correct one, but can at once proceed to state the following: 100 : 44-50 :: 144-14 : x; rr=64-14; i.e., the sum of the sulphuric equivalents; and further, 100 : 55-50 :: 144-14 : z; x=80, i.e., the sum of the ogygen equivalents. Now the equivalent of sulphur, 32 07, is contained twice in 64-14; and the equivalent of oxygen, 16, is contained 5 times in 80, hence the rational formula for hyposulphuric acid is SjO 6 . 2. Determining the rational Formula of Benzoic Acid. STENHOUSE obtained 0-9575 CO 2 and 0-1698 water from 0-3807 hydrated benzoic acid dried at 100. 0-4287 silver benzoate dried at 100 gave 0-202 silver. From these num- bers the following percentage compositions are calculated: C 68-58 Silver oxide 54-13 H 4-99 Benzoic acid 45-87 O.. .26-43 Silver benzoate. ... Benzoic acid 100-00 100-00 (equivalent of silver oxide, 123-92) 64-13 : 45-87 :: 123-92 : x; x= 105-01; 174 ORGANIC ANALYSIS. [ 203^ i.e., the equivalent of the anhydrous benzole acid would be 105-01; hence- that of the hydrated acid would be 105.01+18-016= 123-026. We now say 100 : 68-58 :: 123-026 : or; =84-371, 100 : 4-99 :: 123-026 : x\ x= 6-140, 100 : 26-43 :: 123-026 : x\ z=32.516. 12 is contained in 84-371 7-03 times. 1-008 " " " 6-140 6.09 " 16 " " " 32-516 2-03 " It will be seen at a glance that these quotients may be exchanged for whole numbers, 7, 6, and 2 respectively. The rational formula for the benzoic acid would hence be C 7 H O 2 . This gives By calculation. Found. . ..// C 68-82 68-58 H 4-96 4-99 O 26-22 26-43 3. Deduction of the Rational Formula of Theine. STENHOUSE obtained the following figures on an analysis of theine freed from its water of crystallization: 1. 0-285 grm. of substance gave 0-5125 carbonic acid and 0-132 grm. of water. 2. On combustion with cupric oxide a mixture of gas was obtained consist- ing of CO 2 and N in the proportions of 4 r 1. 3. 0-5828 grm. of the double salt of platinum and theine (caffeine) hydro- chlorate gave 0-142 grm. platinum. From these data the following percent- age composition is deduced: v C 49-05 H 5-18 N 28-65 O 17-12 and as the equivalent of theine, 195-15, since there is every reason to believe that the formula for the platinum-theine hydrochlorate is 2 (theine + HCl)+PtCl 4 . The equivalent of the double salt is found from the equation 0-142 : 0-5828 :: 194-9 (eq. of Pt) : x; x- 799 -91; and consequently the equivalent of theine is obtained by subtracting from 799-98 the sum of 1 eq. of platinum tetrachloride (336-7) and 2 eq. of hydro- chloric acid (72-916), and dividing by 2, thus: 799-91 -(336-7 + 72-916) = 390-30; and 390-30 + 2= 195 -15 203.] CALCULATION pF ANALYSES. 175 This now gives the following equations: 100 : 49-05 :: 195-15 z; *=95-721, 100 : 5-18 :: 195-15 : x; z=10-108, 100 : 28-65 :: 195-15 : x; x=55-911, 100 : 17-12 :: 195-15 : x; z=33-409. In the numbers found 12 is contained in 95-720 7-98 times, 1-008 " " " 10-108 10-02 " 14-04 " " " 55-911 3-98 " 16 " " " 33-409 2-09 " for which numbers we may substitute 8, 10, 4, and 2, respectively, when we get the following formula: This gives By calculation. Found. 49-42 49-05 5-19 5-18 28-91 28-65 16-48 17-12 100-00 100-00 The platinum-theine hydrochlorate yields in 100 parts, Calculated. Found. 24-42 24-36 4. Special Method of deducing the Formulas of Oxygen Salts, a. In substances containing no Isomorphous Substances. The rational formulas of oxygen salts may also be deduced by an entirely different method, based upon ascertaining the ratio which the different quan- tities of oxygen bear to each other. This method is exceedingly simple. In the analysis of crystallized sodium-ammonium sulphate the author found Soda (Xa 2 O) 17-93 Ammonium oxide ([NHJjO). . '. 15-23 Sulphuric anhydride (SO 3 >. 46-00 Water 20-84 100-00 1 eq. of Na 2 O =62-10, contain 16 O; hence 17-93 contain 4-62O. 1" " (XH 4 ) 2 O=52-144, " 16 O; " 15-23 " 4-670. 1 " " SO 3 =80-07, " 48 O; " 46-00 " 27-58 O. 1" " H 2 O =18-016, " 16 O; " 20-84 " 18-51 O. The proportions obtained are then 4-62 : 4-67 : 27-58 : 18-51 = 1 : 1-01 :: 5-97 : 4-01, 176 ORGANIC ANALYSIS. [ 203. and these may be properly replaced by 1, 1, 6, and 4, respectively, which would lead to the formula Na^O (NH 4 ) : O 2SO 3 4H 2 O, or Na 2 SO 4 + (NH 4 ) 2 SO 4 +4H 2 O. b. In substances containing Isomorphous (or mutually-replacing) Constituents. Isomorphous constituents may replace each other in all proportions, as is well known, hence to establish a formula for compounds containing isomor- phous constituents, the latter are taken collectively, i.e., they are expressed in the formula as one and the same substance. This occurs very frequently in the calculation of the formulas of minerals in particular. A. ERDMANN found in monradite Silicic acid 56-17 29-759 Magnesia 31-63 12-558 Ferrous oxide 8-56 1-905 f Water. . 4-04 3-588 100-00 3-588 : 14-463 : 29-759=1 : 4-03 : 8-3, for which 1, 4, and 8 may be prop- erly taken. If now we designate 1 eq. of metal by R, we obtain from these numbers the formula 4(RO.Si0 2 ) + H 2 0, or Not only may isomorphous substances replace each other in compounds, but all bodies generally of analogous compounds do so as well. We find thus that Na^O, K 2 O, CaO, MgO, etc., replace each other. These substances must then likewise be expressed collectively in the formula. ABICH found in andesine Silicic acid (SiO 2 ) 59-60 31-58 Alumina (A1 2 O 3 ) 24-28 H-40) Ferric oxide (Fe 2 O 3 ) 1-58 0-48 J Lime (CaO) 5-77 Magnesia (MgO) 1-08 Soda (Na,O) 6-58 Potassa (K 2 6) 1-08 99-97 3-91 : 11-88 : 31-58=1:3-04 : 8-07; and these numbers may be properly replaced by the numbers 1, 3, and 8, respectively. Designating 1 eq. of metal by R, we obtain from the numbers the formula RO,R 2 O s +4SiO 2 , or we can write it Ca K 2 J 204.] CALCULATION OF ANALYSES. 177 From this it may be seen that this mineral has a composition similar to that of leucite (K 2 O-SiO 2 + Al 2 O 3 -3SiO 2 ). The potassa in the leucite is, in the case of andesine, replaced to a great extent by lime, soda, and magnesia; and a part of the ferric oxide is replaced by alumina. It need scarcely be stated that what has here been said regarding the deduction of formulas of the oxygen salts applies equally as well to the metallic sulphides. IV. CALCULATION OF THE VAPOR DENSITY OF VOLATILE SUBSTANCES, AND APPLICATION OF THE RESULTS AS A MEANS OF CONTROL OF ANALYSES AND OF DETERMINATION OF THE EQUIVALENTS. 204. It is well known that the specific gravity of a complex gas is equal to the sum of specific gravities of the individual constituents in one volume. For instance, 2 volumes of hydrogen gas and 1 volume of oxygen gas give 2 volumes of aqueous vapor. If they gave but 1 volume of aqueous vapor, the specific gravity of the latter would be equal to the sum of the specific gravities of the oxygen and double the specific gravity of the hydrogen, thus: 2X0-06959=0-13918 + 1-10509 1 24427 As, however, the gases yield 2 volumes, the specific gravity of 1 volume would be half of 1-24427, or 0-62214. It will be readily seen that the knowledge of the vapor density of a com- pound substance affords an excellent means of control as to the correctness of the relative proportions of the equivalents found, provided, however, that the vapor density has been properly determined, and at a temperature at least 30 to 40 above the boiling-point of the substance, because only under these conditions is the vapor density constant and to be considered as a true one. For instance, the ultimate analysis of camphor gives to the latter the em- pirical formula C 10 H 10 0. . DUMAS found the vapor density of camphor to be 5-3136. How may we ascertain whether the formula found is correct with regard to the relative proportion of the equivalents? Specific gravity of carbon vapor 82882 " " hydrogen gas 0-06959 " " " oxygen gas 1 10509 10 eq. C =10 vol. =10X0-82882= 8-28820 16 " H -16 " =16x0-06959= 1-11344 1 " Q = 1 " = 1x1-10509= 1-10509 10-50673 178 ORGANIC ANALYSIS. [ 204. It will be seen that this figure is almost exactly twice as large as that found for the vapor density by direct experiment, a proof that the relative proportions of the equivalent of the empirical formula are correct. Whether the formula is also correct, however, in regard to the absolute number of equivalents cannot be determined with certainty from the vapor-density, because it cannot be known how many volumes of camphor vapor correspond to 1 equivalent of camphor. Thus LIEBIG assumed 1 eq. of camphor to correspond to 2 volumes of vapor, and assigned it the formula C 10 H 16 O, while DUMAS assumed 1 eq. to correspond to 4 volumes of vapor, and accordingly gave it the formula C 20 H 32 O 2 . The knowledge of the vapor density hence affords simply a means of control as to the correctness of the analysis, but not as to that of the rational formula, and though notwithstanding it is used for the latter purpose, this can be done only in the case of such substances for which, by analogy, we may infer a certain ratio of condensation. For instance, experience proves that in the case of the hydrates of the volatile organic acids, alcohol, etc., 1 equivalent corresponds to 2 volumes. We found above the rational formula of benzoic acid to be C 7 H 6 O 2 ; DUMAS and MITSCHERLICH found the vapor density to be 4-26. A number very nearly approximating this, however, is obtained by divid- ing by 2 the sum of the vapor densities of the constituents in 1 eq. of benzoic acid; e.g., 7 volumes C =5-8017 6 " H =0-4175 2 " O=2-2102 8-4295 and 8-4302-2=4-2147. HERMANN KOPP * has called attention to the fact that if the equivalent of a substance referred to H=l, and the vapor density of the same substance referred to atmospheric air= 1, the division of the equivalent by the vapor density will give the quotients 28-944, 14-472, and 7-236, according as the equivalent corresponds to 4, 2, or 1 volume of vapor respec- tively. 28-944 corresponds to a condensation to 4 volumes. 14472 " " ft tl lt 2 " 7-236 " " " " " 1 " KOPP terms these numbers normal quotients. If the vapor density has not been accurately obtained, but only approximately (by experiment), numbers differing from these will be found, but which should nevertheless closely ap- proximate them. We may, hence, with the greatest ease ascertain whether a vapor-density determination has been obtained approximately correct or not, if the equiva- alent of the substance be known. *Compt. rend., XLIV, 1347. 204.] CALCULATION OF ANALYSES. 179 GAY-LUSSAC found the vapor density of alcohol to be 1-6133; DALTON found it to be 2-1.* Which number is correct? The equivalent of alcohol is C 2 H 6 O=46-048. 3 We see thus that GAY-LUSSAC'S number is the one more nearly approximate, as the quotient afforded by it most nearly approaches the normal quotient 28-944. Further, it is very easy to calculate the theoretical vapor density of a substance, provided its equivalent is known as well as the number of volumes of vapor corresponding to 1 equivalent. For instance, the equivalent of ben- zoic acid is 122-048. Dividing this number by 28-944 gives 4-216, i.e., the number which we obtained above as the vapor density of benzoic acid. Finally, by the aid of these quotients, the equivalent of a substance may be approximately ascertained, provided we know its vapor density approxi- mately (by experiment), as well as the ratio of condensation. For instance, the vapor density of acetic ether was found by BOULLAY and DUMAS to be 3-06. On multiplying this number by 28-944 we obtain as the equivalent of acetic ether the number 88 56, whereas the actual equiva- alent is 88-064. Having now found how the knowledge of the vapor density of a substance may be applied as a control in elementary analysis, we will proceed to show how the vapor density may be calculated from the data given in 194, A and B. A. Let us take as an example DUMAS' determination of the vapor density of camphor. The results of the experiment were as follows : Temperature of the air ............................. 13-5 Barometer ....................................... 742 mm. Temperature of the bath when sealing the globe. .' ...... 244 Increase of weight of globe . . ........................ 708 grm. Volume of mercury entering the globe ................ 295 c. c. Residual air. . . . ................................... To find the vapor density we must answer three questions: 1. What is the weight of the air held by the globe? (This weight must be known before the second question is answered.) 2. What is the weight of the camphor vapor held by the globe? 3. To what volume at and 760 mm. does the camphor vapor correspond? The answers to these questions are quite simple; and if the calculations appear to be rather complicated it is only because certain reductions and cor- rections are necessary. 1. The weight of the air in the globe. The globe holds 295 c.c., as we have seen from the mercury required to fill it. Now what will be the volume of 295 c.c. of air measured at 13-5 and 742 -mm. when measured at and 760 mm.? * Gmelin, Handbuch der Chem., 4. Aufl., 550. 180 ORGANIC ANALYSIS. [ 204. This question is answered according to 198, as follows: 760 : 742 :: 295 : x; x = 288 c.c. (at 13-5 and 760 mm.); Again : 288 288 _. 274 c.c. 1 + (13 -5X0- 00366) 1-04941 (at and 760 mm.) As, however, 1 c.c. of air at and 760 mm. weighs 0-0012932 gm., 274 c.c. will weigh - 0012932 X 274 = - 35434 grm. 2. The weight of the vapor. On beginning the experiment we first tared the globe + the air within it. On afterwards weighing we ascertained the weight of the globe + the vapor (but not the air). To find the actual weight of the vapor, therefore, it is not enough to subtract the tare from the weight of the globe + the vapor, because (globe + vapor) (globe + air) does not give the weight of the vapor ; we must either subtract the weight of the air from the tare or add it to the in- crease in weight of the globe. We shall do the latter : Weight of air in globe 0-35434 grm. Increase of weight of globe 70800 grm. Weight of vapor, hence 1 06234 grm. 3. The volume to which this 1-06234 grm. of vapor corresponds at and 760 mm. From the above data we know that this weight corresponds to 295 c.c. at 244 and 742 mm. Before we can proceed to the reductions as given under 198, it is necessary to first make the following corrections: a. 244 of the mercurial thermometer correspond, according to MAGNUS' experiments, to 239 of the air- thermometer (see Table VI). b. According to DU!,ONG and PETIT glass expands, beginning at 0, T g vv of its volume for every degree Centigrade. The volume of the globe, at the moment of sealing, must hence accordingly have been 295X239 295+ -35000- ==297C ' C - If we now make the reductions for temperature and barometric pressure, we obtain by the proportion 760 : 742 :: 297 : x; x (i.e., the c.c. of vapor at 290 760 mm. and 2390) = 290; and by the equation 1 + (239xQ . 00366) = *; x (i.e., the c.c. of vapor at 760 mm. and 0) = 154-6. 154-6 c.c. of camphor vapor at and 760 mm. hence weigh 1-06234, and consequently 1 litre (1000 c.c.) will weigh 6-87218 grm., since 154-6 : 1-06234 :: 1000 : 6-87154. Now, 1 litre of air at and 760 mm. .weighs 1-2932 grm., consequently the vapor density of camphor is 5-31245, since 1-2932 : 6-87154 :: 1 : 5-31359. 204.] CALCULATION OF ANALYSES. 181 B. Determination of the vapor density of ether by the method of A, W. H OFMANN-WlCHELHAUS. Weight of ether .................................. 0-0724 grm. Heated to ....................................... 100 Volume read off ................................. 49-201 c.c. Barometer ...................................... 754 mm. Temperature of air ............................... 20 Murcurial column after heating to 100 ............. 300 mm. Mercurial tension at 100 ......................... 0-746 mm. The volume read off at 100 corresponds to a somewhat larger volume, because of the expansion of the globe. For every degree Centigrade glass expands STS^ of its volume, hence the 49-201 c.c. read off after correction gave actually This volume must now be reduced from 100 to 0. According to 198, 49-342 c.c. at 100 become = 36-108c.c.atO, 1+0-003665X100 and at the pressure at which the volume was read off. This pressure, however, is equal to the height of the barometer minus the height of the mercurial column at 100 and the mercurial tension at 100. As we have read off the barometer at 20, however, we must reduce this to 0. The coefficient of expansion of mercury is 0-00018, therefore the barometric pressure of 754 mm. at 20 becomes = 751-295 mm. at 0. 1+0-00018X20 The mercurial column of 300 mm. at 100 becomes reduced to 0: 300 1 + 0-00018X100 = 294 -695 mm. The tension of the mercurial vapor at 100 = 0-746 mm. Accordingly, the pressure = 751 295 - (294 695+ 746) = 455 - 854 mm. The 36-108 c.c. at 455-854 mm. must now be reduced to 760 mm. pres- sure, as follows: 760 : 455-854 :: 36-108 : x; s= 21 -6579. 1000 c.c. of air at and 760 mm. weigh 1-2936 grm., therefore 21-6579 grm. of air will weigh 0-028 grm. The 21-6579 c.c. of ether is, however, 0-0724 grm., hence the vapor density of the ether is 0-0724 PART II. SPECIAL PART. 1. ANALYSIS OF WATER. A. ANALYSIS OF FRESH WATER (SPRING -WATER, RIVER -WATER, ETC.).* 205. The analysis of the several kinds of fresh water is usually re- stricted to the quantitative estimation of the following substances : a. DISSOLVED SUBSTANCES. a. Inorganic. Basic metals: Sodium, calcium, magnesium. Acids: Sulphric acid, nitric acid, silicic acid, carbonic acid, chlorine. /?. Organic. Acids of humus and other organic substances. 6. MECHANICALLY SUSPENDED MATTERS. Clay, etc. We confine ourselves, therefore, here to the estimation of these bodies. If the examination is to include other constituents also, the methods described under 206-213 must be resorted to. I. THE WATER IS CLEAR. 1. Determination of the Chlorine. This may be effected either, a, in the gravimetric or, b, in the volumetric way. a. Gravimetrically. Take 500-1000 grm. or c.c.f Acidify with nitric acid and precipitate with silver nitrate. Filter when the precipitate has * Compare Qualitative Analysis, p. 320 et seq. See a paper read before the Chemical Society by DR. MILLER the Society's Journal (II), in, 117 et seq.; also FRANKLAND, idem (II) iv, 239, and vi, 77; and WANKLYN, CHAP- MAN, and SMITH, idem, vi. 152. f As the specific gravity of fresh water differs but little from that of pure water, the several quantities of water may safely be measured instead of weighed The calculation is facilitated by taking a round number of c.c. 185 186 ANALYSIS OF WATER. [ 205. completely subsided ( 141 , I, a). If the quantity of the chlorine is so inconsiderable that the solution of silver nitrate produces only a slight turbidity, evaporate a larger portion of the water to 4> i; i> etc., of its bulk, filter, wash the precipitate, and treat the filtrate as directed. b. Volumetrically. Evaporate 1000 grin, or c.c. to a small bulk, and determine the chlorine in the residual fluid, without previous filtration, by solution of silver nitrate, with addition of potassium chromate (141,1, 6, a). 2. Determination of the Sulphuric Add. Take 1000 grm. or c.c. Acidify with hydrochloric acid and mix with barium chloride. Filter after the precipitate has com- pletely subsided ( 132, I, 1). If the quantity of the sulphuric acid is very inconsiderable, evaporate the acidified water, to J, J, J, etc., of the bulk, before adding the barium chloride. The filtrate may serve for the direct determination of the sodium ( 205, 7). 3. Determination of Nitric Acid. A. For the exact determination of nitric acid in natural waters only those methods are, as a rule, suitable which give good results also in the presence of organic matter, and which are described in 149. Of these, the methods based upon the decomposition of nitric acid by ferrous chloride, and described by SCHLOSING ( 149, II, d, r) and F. SCHULZE (Vol. I, p. 581), and also 149, II, /, are of more particular service. F. SCHULZE'S method as described by H. WULFERT * (Vol. I, p. 581), in which the nitric oxide is collected and measured over mercury, requires a deep trough holding a comparatively large quantity of mercury and a special tube provided with a glass cock at its upper end. The accuracy of the results obtainable by this method is perfectly satisfactory. TIEMANN,! without in any way diminishing the precision, has greatly simplified the method * Zeitschr. f. analyt. Chem., ix, 400. f Anleitung zur Untersuchung von Wasser, von W. KUBEL, 2. Auflage von F. TIEMANN, Braunschweig bei FR. VIEWEG u. SOHN, 1874, p. 55. 205.] ANALYSIS OF FRESH WATER. 187 by replacing the mercury by well-boiled soda-lye. The process so modified is excellently adapted for accurately determining the nitric acid in water; it requires the apparatus shown in Fig. 82. In this A is a flask holding about 150 c.c. The tube c b a is drawn out at a, but not too finely, and projects about 2 cm. from FIG. 82. the lower surface of the rubber stopper. The orifice of tube e f g, on the other hand, is flush with the lower surface of the stopper. A piece of rubber tubing is slipped over the lower end of the tube g h in order to protect it from breakage. The trough B and also the tube C are filled with well-boiled 10-per cent, soda-lye. The tube C should be as narrow as convenient and be graduated in 0-lc.c. 100 to 300 c.c. (or more, if necessary) of the water to be ex- amined are evaporated to about 50 c.c. in a dish and then trans- ferred to the flask A, the dish being repeatedly rinsed with small quantities of water. It is immaterial whether any portion or all of the precipitate, should such have formed during evaporation, 188 ANALYSIS OF WATER. [ 205. is transferred to A. The tubes are left open and the water is boiled down further; toward the end of the operation the lower end of the tube e f g h is immersed in the soda-lye so that the vapors may pass through the latter. After a few minutes compress the rubber tube between the fingers at g. . If all the air has been ex- pelled by the steam, the soda-lye will rise suddenly in the tube and a slight shock will be felt by the finger; when this occurs, put on a pinch-cock at g and let the steam pass off through d. The evaporation is continued until only about 10 c.c. of fluid remain in A. Then remove the heat, close c by means of a pinch-cock, and fill the tube dc with water from a wash-bottle. If an air- bubble remains in c it should be removed by pressing between the fingers. ._ Now place the measuring tube C over the Orifice; of the tube efgh so that about 2 to 3 cm. of the latter project into C. As soon as the rubber tubes collapse at c and g, owing to the external pressure, pour a nearly saturated solution of ferrous chloride acid- ulated with hydrochloric acid into a small beaker on the upper part of which two scratches have been made, the space between them indicating a volume o'f 20 c.c.; fill a second beaker with con- centrated hydrochloric acid. Now dip the tube d into the ferrous- chloride solution, open the pinch^cock at c long enough -to let 15 to 20 c.c. of the solution flow into A, then dip d into the hydro- chloric acid, and let this follow the iron solution, repeating the introduction of the acid in small quantities to completely wash all the iron solution from the tube deb a. A small bubble of hydro- chloric-acid gas frequently forms at b, but this disappears com- pletely, or nearly so, as soon as the pressure in A increases. Now warm A, at first gently, until the rubber tubes swell slightly at c and g, then substitute the pressure of the fingers for that of the pinch-cock at g, and, as soon as the pressure of the gas becomes stronger, allow the nitric oxide evolved to pass into C. Finally heat more strongly, until the volume of gas in C ceases to increase, and remove the delivery tube from the soda-lye. The operation must not be hurried too much near the end, in order that the hydrochloric-acid gas may be completely absorbed. Ab- I 205.] ANALYSIS OF FRESH WATER. 189 solutely tight india-rubber joints are necessary in order to assure success; they can be obtained only by binding them with wire. (F. HESS.*) Now close the tube C with the thumb, shake it well, and trans- fer it to a large glass cylinder filled with water at 15 to 18, im- merse it, and finally read off the volume as usual ( 15), noting also the temperature of the water and the barometric pressure. After reducing the volume found to and 760 mm., allowing for the tension of aqueous vapor ( 198), the nitric acid (as N 2 O 5 ) in the water is found by multiplying the c.c. of dry nitric oxide by 2-413 and expressing the result in milligrammes. If the water contains also nitrous acid, this will be included in the results obtained; the correction necessary for this is made by subtracting from the results 1-421 parts for every 1 part of nitrous acid (as N 2 O 3 ) present, assuming that this is present in sufficient quantity to estimate. B. For approximately determining nitric acid in waters, MARX'S f method, with certain modifications, is usually used. This method, like the older one of BOUSSINGAULT,! is based upon the decolori- zation of indigo by nitric acid. In BOUSSINGAULT'S method the reaction is effected in hydrochloric-acid solution with the aid of heat, whereas MARX employs the hot liquid resulting from the addition of a large quantity concentrated sulphuric acid to water. The process has the advantage of being very rapid. It has further been studied by H. TROMMSDORFF, F. GOPPELSRODER,|| H. STRUVE,! VAN BEMMELEN,** R. WARRiNGTON,ft KUBEL and TIE- MANN,;!; t SUTTON, and others. Before describing the modifications of the process which has * Zeitschr. f. analyt. Chem., xiii, 260. t Ibid., vii, 412. J Agronomic, Chimie agricole et Physiologic, n, 244 (1862). Zeitschr. f. analyt. Chem., vin, 364, and ix, 171. || Ibid., ix, 3, and x, 266. f Ibid., xi, 25. ** Ibid., xi, 136. ft Chem. News, Feb. 2 and 9, 1877. 1J Anl. zur Uritersuchung von Wasser, 2. Aufl., 65. Volumetric Analysis. 190 ANALYSIS OF WATER. [ 205. given the best results in my laboratory, some important observa- tions made in the memoirs cited will be given here. These are to the effect that the results obtainable by titration with indigo solution are serviceable only under very definite conditions, and can lay no claim to perfect accuracy. a. The quantity of the indigo which is oxidized by the nitric acid is constant only when the conditions under which the reac- tion takes place (dilution, temperature, quantity of sulphuric acid, etc.) are identical. b. Even when the conditions are identical, varying quantities of indigo are oxidized, according as the indigo solution is added gradually to the water mixed with the sulphuric acid, or added in proper quantity before the sulphuric acid is added. In the former case far less indigo is oxidized (VAN BEMMELEN). c. Like conditions must be observed in standardizing the indigo solution against nitric acid, particularly under such whereby the largest quantity of indigo is oxidized. d. As the reaction products resulting from the action of nitric acid upon indigo are not colorless, but yellow, the liquid is colored brownish by incipient excess of indigo, in the absence of chlorides, and acquires a greenish color only with a somewhat large excess; of course varying shades are obtained according to the quantity of nitric acid present, i.e., according to the quantity of the yellow decomposition-product formed. The quantity of sulphuric acid and the presence of chlorides also have an influence on the color of the solution at the moment the indigo begins to be in excess. The end of the reaction is hence not readily recognized, and must be learned by experience. e. The variation in the results is further increased when readily oxidizable substances are present, because then the liberated nitric acid acts on these as well as on the indigo. If a large quantity of organic matter is present, approximately correct results will be obtained only when the organic matter is oxidized first, and before the nitric-acid estimation. If only a small quantity is present, however, as is usually the case in spring-water, the error caused by it is so slight that it may be disregarded. 205.] ANALYSIS OF FRESH WATER. 191 /. Nitrous acid, if present in water, also oxidizes indigo; if present in considerable quantity, therefore, a correction becomes necessary. Accurate experiments showing the exact relative action of nitric and nitrous acids on indigo are wanting. KUBEL. and TIEMANN (loc. cit., p. 81) deduct 0-473 parts of nitric acid for every 1 part of nitrous acid. g. Chlorides, when present only in the small quantities ubually found in spring-water, have no appreciable action on the end reaction. EXECUTION OF THE METHOD. Requisites. a. A solution of pure potassium nitrate in distilled water, 1 litre to contain 1-8718 grm. Each c.c. will then contain 1 mgrm. NA- 6. A solution of best indigo-carmine in water. Its effective value is approximately ascertained with the potassium-nitrate solution a by the process described below; it is then diluted so that 6 to 8 c.c. will be the equivalent of 1 mgrm. nitric acid. c. Chemically pure, concentrated sulphuric acid, sp. gr. 1 842, perfectly free from sulphurous and arsenous acids and nitrogen oxides. d. Several thin flasks of about 200 c.c. capacity. e. A small cylinder holding 50 c.c., and graduated in c.c. /. A pinch-cock burette, graduated in 0-1 c.c. g. A 25-c.c. pipette, or another pinch-cock burette. h. A 5-c.c. pipette graduated in c.c. or 0-5 c.c. i. A measuring flask holding 250 c.c. aa. Preliminary Test. Measure off 25 c.c. of the water to be examined, transfer it to one of the flasks: fill the small cylinder with concentrated sul- phuric acid, and the burette with the indigo solution. Pour the sulphuric acid all at once into the water, agitate for a moment, and without delay, and as rapidly as possible, run in the indigo solution until the liquid just acquires a permanent greenish tint. If not 192 ANALYSIS OF WATER. [ 205. more than 20 c.c. of the indigo solution have been required for this, the water may be titrated directly; otherwise the water must be diluted suitably, and the preliminary test applied again. bb. The Titration. a. Measure off 25 c.c. of the original water (or that properly diluted), introduce it into one of the flasks, add as much indigo solution to it as had been used in the preliminary test, measure off a volume of concentrated sulphuric acid equal to that of the liquid in the flask and add it all at once, and then rapidly run in from the burette sufficient indigo solution until the liquid just becomes permanently green. /?. Repeat the test, but add to the water at first 5 c.c. less indigo solution than the total quantity used in a; then proceed as in a. The volume of indigo solution so found is to be taken as correct, and used in the final calculations. 7-. From the approximately known effective value of the indigo solution, calculate the quantity of potassium-nitrate solution corresponding with the indigo solution used in /?, multiply the result in c.c. by 10, transfer this quantity to a 250-c.c. measuring flask, fill with distilled water up to the mark, and then titrate 25 c.c. of fluid with indigo solution (as in /?). If the quantity of indigo solution does not quite correspond with that used in /?, another potassium-nitrate solution must be made up in the 250-c.c. flask, either more concentrated or dilute, to more nearly approxi- mate the water, and the titration repeated. The effective value of the indigo solution so found is used in the final calculations. d. If the water contains a rather large quantity of organic matter, this is first oxidized by potassium permanganate (p. 204). In this case the determination of the organic matter and the nitric acid may be conveniently combined. 4. Determination of Nitrous Acid. Nitrous acid is never found in good potable waters. It, how- ever, frequently occurs in inferior potable waters and in natural waters. As a rule the quantity present is very minute, but a 205.] ANALYSIS OF FRESH WATER. 193 knowledge of the quantity is of great value in forming an opinion as to the quality of the water. Two methods are in use for determining the nitrous acid in water: a colorimetric, based on the formation of starch iodide, ^,nd devised by H. TROMMSDORFF,* and the other based on the oxidation of nitrous to nitric acid by potassium permanganate, and first described by JEAN DE SAINT-GILLES,! and later critically tested by S. FELDHAUS, J and finally improved and specially adapted to water analysis by W. KUBEL. The two methods complement each other; the former is excellently adapted for such waters as contain but very small quantities of nitrous acid, while the latter is preferable in cases where the water contains more than 1 mgrm. per 100 c.c. (TIEMANN-KUBEL, loc. cit., p. 79). a. Starch-iodide Method. This method is based upon the fact that a water perfectly free from nitrous acid affords no starch-iodide reaction on treating it with pure, dilute sulphuric acid and zinc-iodide-starch solution,! and setting it aside in a dark place, ^ whereas if the water contains nitrous acid it acquires a blue color either at once or after a while, -the intensity depending on the quantity of nitrous acid present. For this method there are required perfectly pure water, free particularly from nitrous acid,** pure dilute sulphuric acid, zinc- * Zeitschr. /. analyt. Chem., vm, 358. f Compt. rend., 1858, XLVI, 624; Journ. f. prakt. Chem., LXXIII, 473. J Zeitschr. /. analyt. Chem., i, 426. Journ. /. prakt. Chem., en, 229. || To prepare the solution boil 5 grm. starch, 20 grm. zinc chloride, and 100 grm. distilled water for several hours (replacing the water as it evaporates) or until the starch envelopes are completely dissolved, then add 2 grm. dry- zinc iodide, dilute to measure 1 litre, and filter. The filtration is slow, but a clear liquid is obtained which, after several months, deposits a few flocks, but which, preserved in a dark place in well-stoppered bottles, remains color- less (RICHTER, Zeitschr. f. analyt. Chem., viu, 358). *" By the action of direct sunlight a water to which sulphuric acid and zinc- iodide-starch solution have been added, but which is free from nitrous acid, is colored in about 10 minutes, but in diffused daylight only after several hours or days. ** If a water free from nitrous acid is not at hand, such may be prepared t>y adding a few drops dilute sulphuric acid to a pure spring water and dis- 194 ANALYSIS OF WATEll. [ 205. iodide-starch solution, a solution of potassium nitrite 1 c.c. of which should represent 0-01 mgrm. of N 2 3 ,* and four test cylinders of equal width, and which will hold 50 c.c. at a mark scratched 15 to 16 cm. from the bottom. a. Preliminary Test. Add 1 c.c. of dilute sulphuric acid and 1 c.c. of zinc-iodide-starch solution to 25 c.c. of the water to be examined. If a blue color develops at once, or after a few minutes, the water contains too much nitrous acid, and requires dilution. In this case introduce 25, 10, or 5 c.c. of the water into the test cylinder, fill with water up to the mark, and repeat the test with sulphuric acid and zinc-iodide- starch solution. If no coloration is observed until at least two minutes have elapsed the color being best observed by looking down through the column of liquid placed on a white surface the water is adapted for further examination. /?. The Actual Test. Introduce into one of the test cylinders 50 c.c. of the water either as on hand, or diluted as under a ; into a second, third, and fourth respectively introduce 0-1, 0-2, and 0-3 c.c. of the potas- sium-nitrite solution, and fill them up to the mark with pure water. Now add to each of the four cylinders 1 c.c. of dilute sulphuric acid followed by 1 c.c. of zinc-iodide-starch solution, and mix. If the reaction in the first cylinder occurs simultaneously with that of one of the other cylinders, and if it proceeds similarly, the two liquids contain like quantities of nitrous acid. If this is not the tilling. Collect the distillate in four fractions in separate receivers, and test each with zinc-iodide-starch and sulphuric acid, and use those fractions which are found to be pure. *This is prepared by dissolving about 2-5 grm. fused potassium nitrite in 100 c.c. water, diluting 10 c.c. of this solution to 1 litre, testing the solu- tion with a solution of potassium permanganate (0-3162 : 1000) as on p. 195, and then diluting so that 1 litre will contain 0-1 grm. N 2 O 3 (1 c.c. hence should equal 0-0001 grm. N 2 O 3 ). 10 c.c. of the solution diluted with pure water to 100 c.c. will be the solution required, and of which 1 c.c. will con- tain 0-00001 grm. N 2 O 3 . As the potassium-nitrite solution does not remain unaltered on keeping, it must be tested each time before using, and, if neces- sary, prepared freshly. 205.] ANALYSIS OF FRESH WATER. 195 case repeat the tests with liquids of known nitrous-acid content until like results are obtained. The tints are at first compared by looking down through the column of liquid in the cylinder placed on a sheet 01 wnite paper; later on, when the colors become more intense, the two cylinders are held side by side in an inclined position, and the observations made through sections of similar thickness and against the white paper background. If so little nitrous acid is present that the color first begins to develop in 10 to 20 minutes, it is unnecessary to note the increase in intensity of color, but merely to observe the moment when the color appears in both cylinders. In calculating it suffices to remember that the nitrous acid is present in like quantity in the two cylinders in which the reactions were seen to be alike. b. Permanganate Method. In the case of dilute fluids, and usually containing organic matter, such as natural waters, the oxidation, the method based on the oxidation of nitrous acid to nitric acid by potas- sium permanganate cannot be applied as is usually done ( 131, 5), i.e., the permanganate solution cannot be added directly to the acidulated water until the pale-red color persists, as the time required for the appearance of the end-reaction is so long that the permanganate would act on the organic matter, and hence render the nitrous-acid determination inaccurate. In the following modification of KUBEL/S process the object is attained much more rapidly, so that the influence of such small quantities of organic matter as is usual in spring water does not appreciably affect the accuracy of the results. There are required for the process a solution of pure ferrous- ammonium sulphate containing 3-92 grm. of the pure, crystallized, dry salt in the litre (the salt is dissolved in a litre flask, by the aid of a little dilute sulphuric acid, using water which has been freshly boiled and cooled); also a corresponding solution of potassium permanganate, i.e., one of which 10 c.c. suffice to oxidize 10 c.c. of the iron solution, leaving it faintly red. 196 ANALYSIS OF WATER. [ 205. In performing the analysis an excess of potassium permanganate solution (5, 10, or 20 c.c., according to circumstances) is added to 100 c.c. of the water to be tested; 6 to 8 c.c. of pure dilute sulphuric acid (1:5) are now added, followed immediately by sufficient of the ferrous-ammonium-sulphate solution to effect decolorization ; then add again permanganate solution until the liquid is pale red, even if only transiently. In making the calculation, deduct the entire number of c.c. of Iron solution taken from the total c.c. of permanganate solution used; the remainder is the permanganate solution used up in oxidizing the nitrous acid present in the water. Each c.c. =0 1902 mgrm. N 2 3 . By this method of operating, any organic matter that may be present will not appreciably affect the results, as may be seen by refer- ence to the experiments made by TIEMANN-KUBEL (loc. cit., p. 79). 5. Determination of the Silicic Acid, Calcium, and Magnesium. Evaporate 1000 grm. or c.c. to dryness after addition of some hydrochloric acid preferably in a platinum dish, treat the residue with hydrochloric acid and water, filter off the separated silicic acid, and treat the latter as directed 140, II, a. Determine calcium and magnesium in the filtrate as directed 154, 6, a (36). 6. Determination of the total Residue and of the Sodium. a. Evaporate 1000 grm. or c.c. of the water, with proper care, to dryness in a weighed platinum dish, first over a lamp, finally on the water-bath. Expose the residue, in the air-bath, to a temperature of about 180, until no further diminution of weight takes place. This gives the total amount of the salts (together with the organic matter). 6. Treat the residue with water, and add, cautiously, pure dilute sulphuric acid in moderate excess; cover the vessel during this operation with a dish, to avoid loss from spirting; then place on the water-bath, without removing the cover. After ten minutes, rinse the cover by means of a washing bottle, evaporate the con- tents of the dish to dryness, expel the free sulphuric acid, ignite the residue, in the last stage with addition of some ammonium car- 205.] ANALYSIS OF FRESH WATER. 197 bonate (97, 1), and weigh. The residue consists of sodium sul- phate, calcium sulphate, magnesium sulphate, and some separated silica. It must not redden moist litmus paper. The quantity of the sodium sulphate in the residue is now found by subtracting from the weight of the latter the known weight of the silica and the weight of the calcium and magnesium sulphates calculated from the quantities of these earths found in 5. 7. Direct Determination of the Sodium. If it is desired to estimate the sodium directly, the filtrate from the sulphuric-acid determination ( 205, 2) may be employed, proceeding as in 209. The sodium may also be determined in the direct way, with comparative expedition, by the following method: Evaporate 1250 grm. or c.c. of the water, in a dish, to about and then add 2 to 3 c.c. of thin pure milk-of-lime, so as to impart a strongly alkaline reaction to the fluid ; heat for some time longer, then wash the contents of the dish into a quarter-litre flask. (It is not necessary to rinse every particle of the precipitate into the flask; but the whole of the fluid must be transferred to it, and the particles of the precipitate adhering to the dish well washed, and the washings also added to the flask.) Allow the contents to cool, dilute to the mark, shake, allow to deposit, filter through a dry filter, measure off 200 c.c. of the filtrate, corresponding to 1000 grm. of the water, transfer to a quarter-litre flask, mix with ammonium car- bonate and some ammonium oxalate, add water up to the mark, shake, allow to deposit, filter through a dry filter, measure off 200 c.c., corresponding to 800 grm. of the water, add some ammonium chloride,* evaporate, ignite, and weigh the residual sodium chloride as directed 98, 2.f Or the following method may be employed: * To convert the still remaining sodium sulphate, on ignition, into sodium chloride. f This process, which entirely dispenses with washing, presents one source of error viz., the space occupied by the precipitates is not taken into account. The error resulting from this is, however, so trifling that it may safely be disregarded, as the excess of weight amounts to 5^5 at the most. 198 ANALYSIS OF WATER. [ 205. Evaporate the filtrate from the barium sulphate obtained in 2 to dryness in a platinum dish (or if nitrates are present in porcelain) to remove free hydrochloric acid and separate silica. Digest the residue with a few c.c. water, and precipitate magnesium without previous nitration by addition of solution of barium hydroxide, avoiding a large excess. Enough has been added if a pellicle of barium carbonate forms upon the surface of the liquid on exposure a short time to the air. Filter and wash the usually slight precipi- tate. Heat the filtrate, and add ammonium carbonate to precipitate the barium introduced and the calcium originally present, filter from the precipitated carbonates, evaporate the filtrate to dryness, and remove the ammonium chloride completely by heating. Dissolve the sodium chloride in the residue with 4 or 5 c.c. water, warm, and add a few drops of ammonium carbonate and ammonia to separate possible remaining traces of barium and calcium, filter again into a weighed platinum dish, evaporate to dryness, heat nearly to fusion, and weigh the sodium chloride. The sodium chloride obtained by either process will contain the potassium (as chloride) if any is present in the water. If enough alkali chloride is obtained it may, after weighing, be examined for potassium according to 152, I,. a. 8. Calculate the numbers found in 1-7 to 1000 parts of water, and determine from the data obtained the amount of carbonic acid in combination, as follows: Add together the quantities of SO 3 corresponding to the basic oxides found, and subtract from the sum, first, the amount of sul- phuric acid as SO 3 precipitated from the water by barium chloride (2), secondly, the amount equivalent to the nitric acid found, and thirdly, the amount equivalent to the chlorine found; the remain- der is equivalent to the carbonic acid combined with the bases in the form of normal carbonates. 80 07 parts of SO 3 remaining after subtracting the quantities just stated, correspond accordingly to 44 parts of CO 2 . If, by way of control, you wish to determine the combined car- bonic acid in the direct way, evaporate 1000 grm. or c.c. of the water in a flask to a small bulk; add tincture of cochineal, then standard nitric acid, and proceed as directed in Vol. I, p. 483, bb. 205.] ANALYSIS OF FRESH WATER. 199 9. Control If the quantities of the Na 2 O, CaO, MgO, SO 3 , N 2 O 5 , SiO 2 , CO 2 , and Cl are added together, and an amount of oxygen equivalent to the chlorine (since this latter is combined with metal and not with oxide) is subtracted from the sum, the remainder must nearly correspond to the total amount of the salts found in 6, a. Perfect correspondence cannot be expected, since, 1, upon the evaporation of the water magnesium chloride is partially decomposed and con- verted into a. basic salt; 2, the silicic acid expels some carbonic acid; and 3, it being difficult to free magnesium carbonate from water without incurring loss of carbonic acid, the residue remain- ing upon the evaporation of the water contains the magnesium carbonate as a basic salt, whereas, in our calculation, we have assumed the quantity of carbonic acid corresponding to the normal salt. Nor do we take into account the organic matter present (and the actual quantity of which can scarcely be determined), as well as the slight traces of nitrites, and the influence of any ammonium salts present on the weight of the total residue. 10. Determination of the free Carbonic Acid. In the case of well-water this may be conveniently executed by the process described 139, 7- (p. 484). We here obtain the carbonic acid which is contained in the water over and above the quantity corresponding to the normal carbonates, or in other words, the carbonic acid which is free and which is combined with the carbonates to bicarbonates. 11. Determination of the Organic Matter. Many fresh waters contain so much organic matter as to be quite yellow, others contain traces, and many again may be said to be free from such substances. The exact estimation of organic matter is by no means an easy task, and the method usually adopted viz., ignition of the residue of the water dried at 180, treatment with ammonium carbonate, gentle ignition again, and calculation of the organic matter from the loss of weight yields merely an approximate result, since we can never be sure as to the condition 200 ANALYSIS OF WATER. [ 205* of the magnesium carbonate in the residue dried at 180 and in the same after ignition, and since the silicic acid expels some car* bonic acid, which is not taken up again on treatment with am- monium carbonate, etc. As it is important, however, to know the quantity of organic matter present in a water in order to judge of the quality of the latter, many chemists have sought to solve the problem, without complete success, however, so far. FRANKLAND and ARMSTRONG* boil a measured quantity (1 litre) of water with 30 c.c. of a saturated aqueous solution of sulphurous acid, 0-2 grm. sodium sulphite, and a few drops of a solution of ferrous or ferric chloride for two to three minutes. (If the water contains much organic matter, the flask or retort is connected with a reflux condenser.) The liquid is then evaporated to dryness. in a glass dish while protecting it from all dust. Mix the residue (which will now be free from carbonic, nitric, and nitrous acids) with perfectly pure lead chromate, introduce the mixture into a, combustion tube which is then charged with cupric oxide and copper turnings, exhaust the tube by means of a SPRENGEL mercury air-pump, and effect the combustion in the usual way, at first very slowly. By the aid of the pump collect the combustion products in a glass tube filled with and standing in mercury, and determine in the mixture the carbonic acid, nitric oxide, and nitrogen by the usual methods; from the results then calculate the carbon and nitrogen in the organic matter. M. DITTMAR and H. ROBINSON! have modified the FRANKLAND- ARMSTRONG method, estimating the carbon and nitrogen of the organic matter in two separate portions of the water to one of which is added sulphurous acid, and to the other sulphurous acid with a little ferrous or ferric chloride. Both are evaporated first partially in a flask held in an inclined position, and finally to dry- ness in a dish, at times a little potassium sulphate being added in order to increase the bulk of the residue. The carbon and nitro- gen are then determined in the residues by combustion. For estimating the carbon there is used a combustion tube charged *Journ. Chem. Soc., vi, 77; Zeitschr. f. analyt. Chem., viu, 488. t Chem. News, xx, July, 1877. 205.] ANALYSIS OF FRESH WATER. 201 with a spiral of silver foil and then granulated cupric oxide. The water and sulphurous acid are absorbed by an apparatus consist- ing of two tubes, one containing concentrated sulphuric acid and a little chromic acid, the other being filled with calcium chloride. The silver spiral and cupric oxide are first heated in a current of air until the escaping air no longer renders baryta water turbid; then the boat containing the residue from the evaporated water is inserted and the combustion effected in a current of oxygen. The carbonic acid may be absorbed by a soda-lime tube (Fig. 48). The nitrogen is determined according to VARRENTRAPP-WILL'S method ( 186). The ammonia is determined colorimetrically by means of NESSLER'S reagent (p. 208). F. SCHULZE,* F. BELLAMY,! and others had previously rec- ommended the determination of the carbon in the evaporation residues. Various objections have been made against these methods,^ and more particularly that during the evaporation some organic matter may be lost through volatilization and decomposi- tion. The data afforded by these determinations may nevertheless be useful in forming an opinion on waters, particularly if the latter be rather rich in organic matter. Since these methods are rather inconvenient while they do not completely attain the object sought, it is usually considered suf- ficient to determine how much permanganate is reduced by the organic matter held in solution in the water, i.e., to determine the quantity of oxygen required to oxidize this matter. Comparative experiments of this kind are of value, although they do not express numerically the quantity of organic matter present, because different substances reduce differing quantities of permanganate; still less do they permit any conclusion to be drawn regarding the harmlessness or otherwise of the organic matter present; further, there can be no doubt that putrefying * Landwirthschaftliche Versuchsstationen, x, 516; Zeitschr. f. analyt. Chem., viii, 494. f Zeitschr. f. analyt. Chem., vm, 495. J Comp. J. A. WANKLYN, E. T. CHAPMAN, and M. H. SMITH (Jmirn. Chem. Soc., [II], vi, 152; and Zeitschr. f. analyt. Chem., vm, 492; also KUBEL-TIE- MANN (loc. cit., p. 98). 202 ANALYSIS OF WATER. [ 205. nitrogenous matter has a more pernicious influence on health than have humus substances. In order to differentiate between such organic substances as are more easily or more difficultly oxidized, FLECK* employs an alkaline silver solution instead of potassium permanganate. Neither in this case does the quantity of reduced silver afford any conclu- sion regarding the quantity of organic matter f present, but like potassium permanganate it affords comparative values which may serve to characterize the water. The same, but no more, may be said of the method proposed by WANKLYN, CHAPMAN and SMITH,! in which, after the ammonia present as such is re- moved by boiling, the ammonia formed by further boiling with potassium permanganate and potassium hydroxide affords an indication of the quantity of certain (albuminoid) organic matter present. A quantitative determination of the nitrogen in this is not obtained in this way, because by the treatment described the nitrogen of only certain nitrogenous substances is completely converted into ammonia, while in other cases more or less of the nitrogen is con- verted into other nitrogenous decomposition products. Which of these methods will be of most service in examining water as to its fitness for drinking purposes must still be consid- ered an open question; it is most advisable hence to describe these methods in detail. A. METHODS BASED ON THE REDUCTION OF POTASSIUM PERMANGANATE . Potassium permanganate was used almost thirty years ago by FORCHHAMMER for testing water for organic matter; later it was employed by EM. MONNIER.|| Both chemists added the per- manganate to the heated water (the latter acidulating the liquid, the former not) until permanent redness. The method employed * Journ. /. prakt. Chem., N. F., iv, 364. f 1 grin, grape sugar precipitates 9 grm. silver; 1 grm. uric acid, 1 285, and 1 grm. gallic acid, 3-812 grm. silver. J Journ. Chem. Soc., N. S., v, 591. Institut, 1849, 383; Jahresber., Y. LIEBIQ u. KOPP, 1849, 603. || Compt. rend., L, 1084; Dingier* 's Polyt. Journ., CLVII, 132. 205.] ANALYSIS OF FRESH WATER. 203 at present is different; the permanganate is first added in excess, then sulphuric acid is adde'd, then standard oxalic acid to decolori- zation, and finally again permanganate to incipient reddening. H. TROMMSDORFF,* who improved SCHULZE'S earlier method, allows the permanganate to act first in alkaline solution, then in acid solution, whereas KUBEL f effects oxidation only in acid solu- tion. As the action is more energetic in alkaline than in acid solution, slightly more permanganate is required in the SCHULZE- TROMMSDORF method, under similar conditions, than in the KUBEL method, but the differences are, as a rule, small (KUBEL-TIEMANN, loc. cit., p. 109). The following is the description of the SCHULZE-TROMMSDORFF method, which is to be preferred on the grounds above stated: a. REQUISITES. a. Distilled Water, which should have no (or scarcely any) reducing action on permanganate. It may be obtained by adding some crystallized permanganate and pure sodium hydroxide to the water, distilling, and rejecting the first quarter of the distillate; the remainder collected may be used. No organic matter (luting, caoutchouc, etc.) should be used at the joints of the apparatus. TROMMSDORFF states that water is serviceable when 100 c.c. will decolorize not more than 1 c.c. of the permanganate solution, e. b. Solution Sodium Hydroxide. This is prepared by dissolv- ing 1 part of pure caustic soda prepared from sodium, and freshly fused in a silver crucible, in 2 parts of distilled water, a. c. Dilute Sulphuric Acid. Mix 3 volumes of distilled water with 1 volume pure concentrated sulphuric acid. d. Centinormal Oxalic-acid Solution. Purify oxalic acid by rapidly cooling a hot concentrated solution of the acid, and of the thin needles so obtained and dried at the ordinary tempera- ture on filter paper dissolve 0-63024 grm. in sufficient distilled water to measure 1 litre; or dilute 10 c.c. of normal oxalic-acid solu- * Zeitschr. /. analyt. Chem., vin, 344. f Ard. zur Untersuchung von Wasser, von KUBEL und TIEMANN, 2. Aufl., p. 104. 204 ANALYSIS OF WATER. [ 205. tion to measure one litre. The 63024 grm. oxalic acid is capable of reducing 0-31622 grm. potassium permanganate. The oxalic- acid solution should be preserved in glass-stoppered bottles in a dark place. e. Solution Potassium Permanganate. Dissolve about 0-32 grm. crystallized potassium permanganate in 1 litre distilled water. To standardize it, warm 20 c.c. of the oxalic-acid solution d, after the addition of 2 c.c. of pure dilute sulphuric acid, to 60, and then run in the permanganate solution until a pale-reddish per- manent coloration persists (Vol. I, p. 316, cc); according to the re- sults so obtained, dilute the solution so that 20 c.c. will exactly decompose 20 c.c. of the oxalic-acid solution. 1000 c.c. of the diluted solution will then contain exactly 0-31622 grm. perman- ganate. The solution should be preserved in glass-stoppered bottles in a dark place. For measuring it use either a GAY-LUSSAC burette, or a burette provided with a glass cock. ^. THE ANALYSIS. Introduce 100 c.c. of the water to be examined in a flask of about 300 c.c. capacity, add 0-5 c.c. sodium-hydroxide solution and 10 c.c. of the permanganate solution, boil for ten minutes, allow to cool to 50 to 60, and add 5 c.c. of the dilute sulphuric acid and 10 c.c. of the centinormal oxalic-acid solution. As soon as the liquid has become perfectly colorless cautiously add drop by drop permanganate solution, while constantly agitating, until the liquid acquires a faint permanent redness. The permanganate solution required to effect this is the quantity required for the decomposition of the organic matter in the 100 c.c. of water.* * This result is accurate, however, only when the water contains no nitrous acid, which also exerts a reducing action on the permanganate. If such is present, 1 6626 parts of solid potassium permanganate must be deducted for every 1 part of N 2 O 3 found, e.g., 4 eq. of KMnO 4 for every 5 eq. of N 2 O 5 ; or 1 344 parts of permanganate must be deducted for every part of HNO 2 , e.g., 2 eq. of KMnO 4 for every 5 eq. of HNO 2 . If the water contains decided traces of ammonia, this too occasions an error. In this case boil off one-third of the water, remove the ammonia, then make up the volume again with dis- tilled water, and then proceed to add permanganate. Of course, small quan- tities of volatile organic matter may be lost in this process. 205.] ANALYSIS OF FRESH WATER. 205 The results so obtained are expressed in terms of pure per- manganate, or of the oxygen contained in it and used up in oxi- dizing the organic matter in 1000 c.c. of water. 1 c.c. of the above-named solution contains 0-00031622 grm. permanganate, or 0-00008 grm. of available oxygen. If 100 c.c. of water require more than 4 c.c. permanganate solution for the oxidation of organic matter, a second experiment must be made using more permanganate solution and a corre- spondingly larger quantity of sodium-hydroxide solution, as the undecomposed permanganate remaining after boiling must be at least twice as great as the quantity decomposed. Good spring- waters never require a larger addition than 10 c.c. of permanganate solution, as 100 c.c. of such a water never decolorize more than 1 to 2 c.c. of the solution. B. METHOD BASED ON THE REDUCTION OF SILVER. H. FLECK,* who first proposed using an alkaline solution of silver nitrate for the comparative estimation of organic matter in spring- waters, etc., claims this method to be preferable to the per- manganate method, because the latter reduces all organic matter alike, whereas the alkaline silver solution reduces only those or- ganic substances which may be expected to have an injurious effect. For instance, it is not reduced by the fatty acids and their salts, or the salts of the lactic and succinic-acid series, whereas it is re- duced by biliary pigments, and generally by animal and vegetable coloring matters, taurin, mucus, uric acid, tannin, gallic acid, dis- solved proteids, grape sugar, and particularly by all volatile de- composition products. It will be seen that among the substances mentioned many are harmful, while others again are quite in- nocuous. a. REQUISITES. a. Alkaline Silver Solution. Dissolve 17 grm. silver nitrate in about 50 c.c. water and pour the solution into a litre flask con- taining an aqueous solution of 48 grm. sodium hydroxide and 50 gnu. crystallized sodium thiosulphate. Shake, fill to the mark, * Jowrn. /. prakt. Chem., N. F., iv, 364. 206 ANALYSIS OF WATER. [ 205. shake again, pour the mixture into a larger flask, and boil for 15 minutes continuously. A little silver is thus precipitated, caused by reduction due to organic matter present. After twenty-four hours decant from the sediment and preserve in the dark in dark- colored bottles. In using it, a GAY-LUSSAC or GEISSLER burette is employed, or one with a glass cock. b. Potassium-iodide Solution. Dissolve 8-298 grm. (^g- eq.) of chemically pure potassium iodide (dried at 180) in water to make 1 litre. The solution thus made will precipitate exactly 5-396 grm. (sV eq.) of silver from a solution of silver nitrate.* c. A small quantity of freshly prepared mixture of equal vol- umes of potassium-dichromate solutions, pure hydrochloric acid, and starch paste, all of ordinary strength. /?. THE ANALYSIS. In employing the silver solution three operations are required to ascertain how much silver is precipitated from the alkaline silver solution by the organic matter present in 1 litre of water: a, determination of the silver in the silver solution; b, treatment of the water with a known volume of silver solution; and c, determination of the silver remaining in solution after b (this will give hence the precipitated silver also). a. Introduce 10 c.c. of the silver solution into a beaker, add 100 c.c. of distilled water, afid then run in from a burette the potassium-iodide solution until a trace of potassium iodide is in excess. This point is found by testing as soon as the silver pre- cipitation begins to decrease a drop of the fluid now and then on a porcelain dish, with a drop of the chromic-starch mixture, the excess of potassium iodide being indicated by the develop- ment of a blue color. The slightest excess may be thus recog- nized, as silver iodide is decomposed only after very long contact of the two drops. If too much potassium iodide has been added, add a little more silver solution and approach the end reaction more cautiously. 6. Introduce 100 c.c. of the water to be examined into a beaker, * Fleck determined the potassium iodide in solution by precipitating the iodine as silver iodide according to 145, I, a, a. 205.] ANALYSIS OF FRESH WATER. 207 add 10 c.c. of the silver solution,* and heat to boiling, when a white precipitate, consisting of calcium and magnesium salts, usually forms; the precipitate gradually becomes gray or black if organic substances are present. The boiling should be continued for about ten minutes, until the precipitate settles rapidly on re- moving the heat. The water lost by evaporation is then replaced by distilled water and the whole allowed to cool. c. In the cold solution determine the dissolved silver as in a, and without removing the precipitate. The difference in c.c. between the potassium-iodide solution used in a and c corresponds to the precipitated silver; every c.c. represents 0-005396 grm. of silver, and by multiplying the silver found by 10 gives the silver reduced by 1 litre of water. C. METHOD BASED ON THE CONVERSION OF ALBUMINOID NITROGEN INTO AMMONIA. This method, which was introduced by WANKLYN, CHAPMAN, and SMITH f is based, as already stated, on the expulsion of any ammonia as such from the water by boiling with or without the addition of an alkali, and then decomposing the albuminoid sub- stanc.e by boiling with potassium permanganate and potassium hydroxide, distilling off and determining the ammonia: formed. This method gives two results the ammonia present as such and that formed from the albuminoid substances. a. REQUISITES. a. Nessler's Reagent. This is prepared as follows: Boil to- gether 35 grm. potassium iodide and 13 grm. mercuric chloride with 800 c.c. water. When a clear solution results, add drop by drop a cold saturated solution of mercuric chloride until the precipitate just begins to be permanent. Now add 160 grm. potassium hydroxide (or 120 grm. sodium hydroxide), make up * Should a precipitate immediately form, it may be either silver sulphide or metallic silver ; the former would indicate the presence of hydrogen sulphide or dissolved sulphides, the latter ferrous (or possibly stannous) salts. t Jowrn. Chem. Soc., N. S., v, 591; also "Water Analysis," by J. A. WANKLYN and ERN. TH. CHAPMAN, 3d edit., London, TRUBNER & Co., 1874. 208 ANALYSIS OF WATER. [ 205. the volume to 1 litre with water, add a little more mercuric-chlo- ride solution, and set the liquid aside to deposit. The clear solu- tion has a very pale-yellowish color. 2 c.c. added to 50 c.c. of water containing 0-05 mgrm. ammonia should give an immediate yellowish-brown coloration. The solution must be preserved in well-stoppered bottles. In using it, some is poured from the stock bottle into a small bottle. b. Standard Ammonium-chloride Solutions. The stronger so- lution contains 0-001 grm. NH 3 in every c.c., and is prepared by dissolving 3-137 ammonium chloride in sufficient distilled water to measure 1 litre; the weaker contains in every c.c. 0-01 mgrm. NH 3 , and is prepared by mixing 10 c.c.' of the stronger solution with sufficient distilled water to measure 1 litre. c. Alkaline Potassium-permanganate Solution. Dissolve 100 grm. potassium hydroxide and 4 grm. crystallized potassium permanganate in 500 c.c. water, boil for fifteen minutes, introduce into a 500-c.c. flask, and after cooling, fill up to the mark. d. Freshly-ignited Sodium Carbonate, or a solution of the salt freed from all traces of ammonia by boiling. e. Ammonia-free Distilled Water. If the distilled water at hand is at all colored when 50 c.c. of it are treated with 2 c.c. of NESSLER'S solution, some must be especially prepared by adding a trace of sulphuric acid to the water and redistilling. /. A tubulated Retort (with glass stopper) having a capacity of somewhat more than one litre when quite filled. This is to be clamped in a strong retort-holder, and heated directly by a large gas-burner, preferably a MASTE burner, Fig. 47, p. 82, Vol. I. g. A large LIEBIG Condenser. The condenser tube should be 90 cm. long and 3 cm. wide. The neck of the retort is bound with a strip of writing paper, and inserted directly into the condenser tube. h. Six Cylinders of white glass, about 17 cm. high and about 4 cm. diameter. In use they are placed on a white porcelain tile, or on a sheet of white paper. i. Measuring Vessels. A half-litre flask for measuring the water; a 50-c.c. measuring cylinder for the alkaline permanganate 205-] ANALYSIS OF FRESH WATER. 209 solution; a burette for the ammonium-chloride solution; and a 2-c.c. pipette for the NESSLER'S reagent. As all the vessels kept in the laboratory usually have traces of ammonia salts on their surfaces, care must always be taken to rinse them with pure distilled water just before using; further- more the most scrupulous cleanliness must be observed through the entire process. ft. THE ANALYSIS. a. Introduce 500 c.c. of the water to be examined into the well-washed retort properly supported and connected with the condenser, and heat with the naked flame.* The flame is moved at first to and fro beneath the retort, and the drops of water which condense on its surface wiped off with a cloth. The water soon boils. The distillate is collected in a cylinder. As soon as 50 c.c. have been collected, replace the first cylinder (^4.) by a second, and continue the distillation until 150 c.c. more have been collected. In the retort there will hence be left 500-200 = 300 c.c. Now stop the distillation for a moment, and introduce 50 c.c. of the alkaline permanganate solution into the retort through the tubulure, by means of a wide-necked funnel, then close the retort again, and continue the distillation. Should the liquid show signs of bumping, gently shake the contents of the retort ; this will prevent it. When 50 c.c. of the distillate have been collected replace the cylinder ( B 1 ) by another and continue until two further portions of 50 c.c. each have been collected in cylinders marked respectively B2 and 53, then stop the distillation. b. The small quantities of ammonia in the four cylinders are now determined colorimetrically by means of the NESSLER'S reagent. t For this purpose add 2 c.c. of the NESSLER'S reagent by means * If the water is acid add to it, before applying heat, some freshly-ignited sodium carbonate, in order to liberate the ammonia. In the case of waters containing, as they usually do, carbonates of the alkali earths, this addition is unnecessary. f This method of estimating ammonia was first employed by W. A. MILLER (Zeitschr. /. analyt. Chem., iv, 459). 210 ANALYSIS OF WATER. [ 205, of the 2-c.c. pipette into the fluid in the cylinder A. If the fluid contains ammonia, it acquires on being stirred a reddish-brown- color which is the deeper the greater the quantity of ammonia present. This color has now to be duplicated by adding a meas- ured quantity of ammonium-chloride solution of known strength to water in another cylinder, and adding to this NESSLER'S reagent.. To effect this a measured quantity of the weaker ammonium- chloride solution is introduced into a clean cylinder, ammonia- free water added to the mark, and then 2 c.c. of the NESSLER'S reagent added. After thoroughly shaking, the cylinder is placed beside that marked A on a white surface (a porcelain tile or sheet of white paper), and after a few minutes, the colors of the two liquids compared, looking down through the liquid in the tubes. If the colors in both tubes are alike, the object is attained, as it will then be known that the cylinder A contains just as much ammonia as the other cylinder the ammonia content of which is known;: if the colors are not alike, a new trial must be made, using more or less of the ammonium-chloride solution until the colors in both cylinders are alike in depth. The ammonium-chloride solution should never be added after the NESSLER'S reagent, as this causes turbidity, and turbid solutions cannot be compared with success. It must be further remarked that the conclusion that liquids exhibiting similar colors contain like quantities of ammonia is true only when the fluids have the same mean temperature * ; and that the colorimetric comparisons according to the process just detailed are successful only when the quantity of ammonia in 50 c.c. of the liquid lies between 0-0025 and 0-05 mgrm. The ammonia found in the cylinder A was present in the water as such, i.e., in the form of an ammonia salt. As the result of numerous experiments by Messrs. CHAPMAN, WANKLYN, and SMITH, the authors find that it is only necessary to add one-third to the ammonia found in the cylinder A in order to obtain all the ammonia present as such in the 500 c.c. of water. In this * NESSLER, Zeitschr. /. analyt. Ghent., vn, 415. 205.] ANALYSIS OF FRESH WATER. 211 manner the trouble of Nesslerizing the first 150 c.c. of distillate is saved. The contents of cylinders B\,B2, and B 3 are separately treated like that of cylinder A ; the quantities of ammonia found are added together, and this represents the ammonia formed by the action of the alkaline permanganate on the nitrogenous albuminoid matter. The authors designate the ammonia found in the cylinder A as free ammonia; that found in cylinders B 1, 2, and 3, albu- minoid ammonia. 12. Determination of Ammonia. Great importance is justly placed on the determination of ammoniacal compounds in natural waters, since the presence of any considerable quantity of ammoniacal compounds generally in- dicates that the water has been contaminated by the decomposition- products of nitrogeneous substances, and that it has not been sufficiently purified by the action of the air on it, and by filtration through earth. Various methods may be employed for determining the am- monia in waters ; the more important will be here given. a. Expulsion of the Ammonia by Distillation, and Conversion into Ammonium-platinic Chloride. This method is frequently employed in the analysis of mineral waters, and is described in 209. 6. Expulsion of the Ammonia by Distillation, and Colorimetric Determination by NESSLER'S Reagent. This method has been already described in detail on pages 207-211. It is particularly suitable for determining very small quantities of ammonia. c. Direct Nesslerizing, after Precipitation of the Calcium, etc. This method, which is exceedingly simple, and suffices for most cases, must be considered as a decided improvement on the original CHAPMAN method.* It was devised by FRANKLAND and STRONG^ and improved by HUGO TROMMSDORFF.}: * Zeitschr. /. analyt. Chem., vn, 478. f Ibid., vn, 479. j Ibid., vin, 356. 212 ANALYSIS OF WATER. [ 205. Place 300 c.c. of the water to be examined into a cylinder, add 2 c.c. of a solution of sodium carbonate (1 part of the salt to 2 of distilled water), and 1 c.c. of a sodium-hydroxide solution (1 part NaOH to 2 of distilled water), stopper the cylinder, shake, and allow to settle. As a rule the liquid settles sufficiently to permit 100 c.c. of clear liquid to be poured off; if this is not the case, how- ever, 100 c.c. must be passed through a washed filter. To the 100 c.c., contained in a cylinder or test-tube bearing a scratch, add 1 c.c. of NESSLER'S reagent (p.' 207). If more than a yellow color develops, add 1 c.c. more. Into a second cylinder or test- tube exactly like the first, introduce 90 c.c. of pure, ammonia- free distilled water (p. 208), 0-6 c.c. of the sodium-carbonate so- lution, and 0-3 c.c. of the sodium-hydroxide solution, fill to the mark, and from a 1-c.c. pipette graduated in 0-01 c.c. run in a suitable quantity of the dilute ammonium-chloride solution (p. 208), add 1 or 2 c.c. of NESSLER'S reagent according to circumstances, and after a few minutes compare the colors of both cylinders or test-tubes as detailed on p. 210. The general rules there given apply here naturally also. Hence, should the NESSLER'S reagent develop too dark a color, a fresh portion of the clarified water must be taken, diluted with a suitable quantity of distilled water to 100 c.c., and the experiment repeated. d. Precipitation of the Ammonia by means of Potassium-mer- curic Iodide, and determination of the Mercury in the Precipitate. This method, devised by FLECK,* is especially adapted in cases where the water contains a relatively large quantity of ammonia. It hence supplements the methods b and c, which are especially suitable for waters containing very little ammonia. The method is based upon the precipitation of ammonia by NESSLER'S reagent as insoluble ammonium iodohydrargyrate (NHg 2 I.H 2 0), a com- pound of constant composition. In order to be able to filter this off well, care must be taken to precipitate it in conjunction with calcium carbonate or magnesium hydroxide; and to be certain that the precipitation is effectual, a little of a solution of magnesium sulphate is added to the water. * Journ. /. prakt. Chem., N. F., v, 263. 205.] ANALYSIS OF FRESH WATER. 213 The determination of the mercury is effected by dissolving the ammonium iodohydrargyrate in a solution of sodium thiosulphate and titrating with a solution of potassium- or sodium-sulphide. 2 eq. of mercury found correspond to 1 eq. of ammonia. The following reagents are required for the process: Nessler's reagent (p. 207). Magnesium-sulphate solution (1:8). Sodium-thiosulphate solution (1:8). Standard potassium-sulphide solution. Lead-acetate paper, made by immersing filtering-paper in a 1 : 10-solution of lead acetate, and drying. The paper should be preserved in well-stoppered bottles. The sulphide solution is prepared by heating 10 grm. sodium- potassium carbonate and 4 grm. sulphur in a covered porcelain crucible to calm, fusion, dissolving the sulphide when cold in water, adding 10 grm. sodium hydroxide, and making up the whole to 1 litre. The solution may be preserved unchanged for weeks in a well-stoppered flask. It is titrated with a standard mercuric- chloride solution 100 c.c. of which contain 1 grm. mercuric chloride. Ammonium carbonate is added to 10 c.c. of the solution, the white precipitate dissolved in a few drops of the sodium-thiosulphate solution, and the sulphide solution run in from a burette until the liquid, in which a black precipitate of mercury sulphide forms, floc- culent at first, but granular later, begins to become clear, and until a drop placed on a strip of the dry lead-acetate paper de- velops a faint brown ring. Should the sulphide solution be too concentrated, it must be diluted. Its titre is correct when 100 c.c. of the solution precipi- tates 0-5 grm. mercury. When everything is in readiness, add to 200 c.c. of the water to be examined in a cylinder 0-5 c.c. of the magnesium-sulphate solution, and 4 c.c. of NESSLER'S reagent, close the cylinder, shake, and allow to settle. Should the result- ing precipitate have a yellow instead of a red color, because so little ammonia is present, employ a larger quantity of water, say 500 c.c. at least. The quantities of the magesium-sulphate solu- tion and NESSLER'S reagent are to be increased proportionately. 214 ANALYSIS OF WATER. [ 205. When the precipitate has thoroughly settled, decant the clear liquid so far as possible, collect the precipitate on a small filter, and wash it with cold water until the filtrate is no longer alkaline. The filtering and washing must, of course, be done in an atmos- phere free from hydrogen sulphide and ammonia. The filter containing the washed precipitate is now filled com- pletely with the solution of sodium thiosulphate, whereby the ammonium iodohydrargyrate is dissolved, after which it is washed with cold water, and the mercury determined in the solution (which may measure 100 to 150 c.c.) by means of the sulphide solution as above. In calculating, 2 eq. of mercury (400) = 1 eq. of am- monia (NH 3 =17-064). On testing the methods b, c, and d, KUBEL and TIEMANN (loc. dt.y p. 97) obtained on the whole satisfactorily accurate and fairly concordant results. II. THE WATER IS NOT CLEAR. 1. Fill with the water a large bottle of known capacity, close it with a glass stopper, allow to settle in the cold, siphon off the clear liquid so far as possible, collect the deposit on a filter, weigh it, then dry and ignite. The clear water is treated as directed in I. 2. Fill a second glass-stoppered bottle with the water and allow to settle in the dark. As soon as it is clear, very carefully siphon off the water without disturbing the deposit. Shake up the latter with the remainder of the water and pour it into a small beaker, which is then covered and set aside for the deposit to settle again. The clear water is again poured off as closely as possible and some of the deposit drawn up in a tube the end of which is drawn out to a capillary point. A drop is now placed on an object- glass, covered with a cover-glass, and microscopically examined for organized bodies (bacteria, infusoria, etc.). Regarding the calculation of the analysis I refer to 213; and it may be observed that usually the principles here laid down are followed in stating the results (a certain latitude being, of course, allowed) : Chlorine is first combined with sodium; if any remains (which 205.] ANALYSIS OF FRESH WATER. 215 seldom occurs) it is combined with calcium. Sulphuric acid is next combined with calcium; the nitric acid then with ammonia, any residual acid being combined with sodium if such has not been entirely neutralized by chlorine, otherwise with magnesium. Silicic acid is stated as such, and the remainder of the calcium and mag- nesium as carbonates, usually as monocarbonates. It must be remembered, of course, that at times the results of the qualitative analysis may cause another arrangement of the calculation to be adopted. For instance, should the evaporated water be strongly alkaline, sodium carbonate is present, usually with sodium sulphate, sodium chloride, and at times also sodium nitrate. In this case the calcium and magnesium are then to be entirely combined with carbonic acid. In the report the quantities are most convienently stated in parts per 1000 by weight or (in the case of spring-waters the specific gravity of which differs but little from that of distilled water) in grammes per litre. I prefer this form of statement to that of KUBEL-TIEMANN (who recommended reporting the results in parts per 100,000), because the. litre is now adopted generally, and by moving the point three decimal places, the results may at once be expressed in milligrammes. APPENDIX. ESTIMATION OF THE HARDNESS. FOR technical purposes it is at times sufficient to determine the so-called hardness of water. By this term is understood the quality imparted to the water by the presence of a larger or smaller quantity of calcium and magnesium salts. A hard water is one rich in these salts; a soft water, one containing but very little of them. By total hardness is understood the hardness exhibited "by unboiled water; the permanent hardness is that retained after water is boiled and made up to its original volume with distilled water; the temporary hardness is the difference between the total and permanent hardness. 216 ANALYSIS OF WATER. [ 205* The total hardness, both permanent and temporary, may be obviously calculated from the results of the analysis. Since an analysis of water usually requires not inconsiderable time, a more rapid method has been sought for, and was first proposed by CLARK.* His method has been variously modified, but the reagent which he employed, soap solution, is still always used. The soap decom- poses all the calcium and magnesium salts present in the water, and a slight excess of the soap is very readily recognized by the permanent lather it gives on. shaking the water. As this test,, however, does not differentiate between the calcium or magnesium salts, the results afforded by it are quite different from those obtained by actual analysis, and require some agreement regarding the form of expressing the relationship of the soap used to the results obtained. Unfortunately such an agreement does not exist between the various countries, the various degrees of hardness having different meanings in Germany, France, and England, as follows: Value of Degree of Hardness. In Germany: 1 part CaO in 100,000 parts water, or 0-001 grm. CaO in 100 c.c.f In France: 1 part CaCO 3 t in 100,000 parts water. In England: 1 part CaC0 3 in 70,000 parts water or 1 grain CaC0 3 in an imperial gallon. The various degrees of hardness, therefore, compare as follows: German, 0-56; French, 1; English, 0-7. To convert the German standard into French, multiply by 1-7857; into English, by 1-25. To convert the English standard into French multiply by 1-4286; into German by 0-8. According to various experiments made by KUBEL-TIEMANN, the best general method is that of CLARK modified by A. FAISZT and * Jahresber. /. Chem., 1850, 608. f Magnesium salts, if present, are calculated in equivalent quantities of lime. | Or an equivalent quantity of a magnesium salt. 205.J ANALYSIS OF FRESH WATER. 217 C. KNAUSZ.* It must be stated, however, that' the methods of BOUTRON and BOUDET,! and of WILSON,:}: have also certain ad- vantages. Only the first method will be here described. a. REQUISITES. a. Standard Barium-chloride Solution. Dissolve 0-5226 grm. of pure, dry, crystallized barium chloride (BaCl 2 +2H 2 0), i.e., the equivalent of 0-12 grm. calcium oxide (CaO) in sufficient distilled water to measure 1 litre. 100 c.c. will then contain barium chloride equivalent to 12 milligrammes of calcium oxide (CaO) and the solution will be of 12 hardness (German). 6. A Glass-stoppered Bottle, of about 200 c.c. capacity, with a mark at 100 c.c. c. Standard Soap Solution. To prepare this heat 150 parts of lead plaster on a water-bath, add 40 parts of pure potassium carbonate, and rub down to a homogeneous mass. Treat this with strong alcohol, allow to deposit, filter, distil off the alcohol, and dry the residual soap on a water-bath (Huoo TROMMSDORFF). Dissolve 20 parts of the soap so made in 1000 parts of dilute alcohol (sp. gr. 0-9213); introduce 100 c.c. of the barium-chloride solution into the stoppered bottle, b, and from a burette run in the soap solution until, on shaking, there forms a thick white foam which remains for at least fifteen minutes on the surface of the liquid. The soap solution is added at first in larger quantities, but towards the last drop by drop, shaking after each addition. The bottle should be held upright, and shaken up and down. If the soap solution has been prepared as above, 100 c.c. of the barium-chloride solution will require less than 45 c.c. of soap solu- tion. After the experiment is repeated, in order to make sure of the result, dilute the soap solution with dilute alcohol (sp. gr. 0-9213) * Gewerbeblatt aus Wurtemberg, 1852, 193; also Chemisch-PharmaceuL CentralbL, 1852, 513. f Chem. CentralbL, 1855, 343. J Annal. d. Chem. und Pharm., cxix, 318; Zettschr. f. analyt. Chem., 1, 106. Zeitschr. f. analyt. Chem., vm, 333. 218 ANALYSIS OF WATER. [ 205. so that 45 c.c. will exactly suffice to produce the foam in 100 c.c. of the barium-chloride solution. d. The following table was compiled by FAISZT and KNATJSZ from direct experiments; c.c. soap solution used. Degree of hardness. = to 1 c.c. soap solution. 3-4 0-5 :: ::::::::::::::: 1:2 > 9-4 2-0 11-3 2-51 13-2 3-0 15-1 3-5 17-0 4-0 18-9 4-5 20-8 5-OJ 22-6 5-5^ 24-4 6-0 26-2 6-5 I n 28-0 7-0 f * m 29-8 7-5 I 31-6 8-Oj 33-3 8-51 35-0 :.. 9-0 36-7 9.5! 38-4 : 10- Of 02W 40-1 10.5 I 41-8 11. Oj 43-4 11.5) 45-0 12- Of C It will be seen from this table that the degrees of hardness are not proportional to the c.c. of soap solution used. The necessity for this table is therefore evident for obtaining accurate results. [The soap solution may be more conveniently made by dis- solving 10 grammes of Castile (Syria)-soap shavings, from a fresh piece of soap, in 1 litre of dilute alcohol (2 parts alcohol and 1 part water). Filter, if necessary. The solution may be standardized against the barium-chloride solution, or, as is more commonly done, against a solution prepared by dissolving 1 gramme of pure calcium carbonate in a little hydrochloric acid, neutralizing with a 205.] ANALYSIS OF FRESH WATER. 219 slight excess of ammonia water, and diluting to 1 litre. Each c.c. of this solution will contain a quantity of calcium salt equivalent to 0-001 gramme of CaCO 3 . In standardizing, 10 c.c. of this solution are diluted with pure water to 100 c.c., introduced into a stoppered flask, and the soap solution run in from a burette little by little, and shaking after each addition, until a foam, persisting for 10 minutes, forms. It is well not to add more than 0-5 c.c. of soap solution at a time. The experiment is now repeated with 100 c.c. of pure water alone; the difference in the soap solution used will give the soap solution required for the calcium salt alone (quite an appreciable quantity may have been used for the pure water). The proper value of 1 c.c. of the soap solution in terms of CaCO 3 is thus ascertained, and should be noted. TRANSLATOR.] ft. THE DETERMINATION. aa. Determining the total hardness. Introduce 20 c.c. of the water into a test-tube, add about 6 c.c. of the soap solution, shake, and note whether the water becomes simply opalescent, or whether a more or less pronounced cloudi- ness develops, or a notable precipitate forms. According to the result obtained, the proper quantity of water to be tested is judged, i.e., if the water is very soft, 100 c.c. are introduced into a stop- pered flask; if moderately soft, 50 c.c. are mixed with 50 c.c. of distilled water; in the case of moderately hard waters, 20 c.c. are taken and mixed with 80 c.c. of distilled water; of hard waters, 10 c.c. are mixed with 90 c.c. of distilled water. If, on shaking the test-tube in the preliminary test, a frothy pellicle forms on the surface of the liquid, it indicates the presence of magnesium salts in considerable quantity; the water in this case must be largely diluted. The soap solution is now run from a burette into the stoppered flask, shaking after each addition, until the characteristic per- manent froth forms. At the first test the soap solution is added in larger quantities at first, and towards the end in quantities of only 1 c.c. each, in order to expedite matters; in the second ex- 220 ANALYSIS OF WATER. [ 205. periment, nearly the entire quantity of soap solution, as ascer- tained by the first test, is run in at once, and then the solution added drop by drop, the end of the experiment being thus rapidly reached. The concentration of the water may, as a rule, be con- sidered correct when from 20 to 45 c.c. soap solution have been used. Not more than 45 c.c. should ever be required. After the c.c. of soap solution have been read off, the degree of hardness is found from the table, as follows: If the c.c. of soap solution is a number found in the table, e.g., 22-6, the degree of hardness is given directly, and in the given case would be 5-5 (assuming that 100 c.c. of the water to be ex- amined had been taken). If another number of c.c. of soap solu- tion has been used, the degree of hardness is found by first noting the nearest lower number in the table, and noting its correspond- ing degree of hardness; the difference between the nearest lower number and the c.c. of soap solution used is now multiplied by the proper correction number in the third column of the table, and the product added to the degree of hardness already noted. An example will make this clear. Let us suppose we have used for 100 c.c. of water 43-6 c.c. of soap solution. The water will in this case have a degree of hardness of 11-562, thus: 43-4 c.c 11 -5 hardness + (43-6-43-4)XO-31 = Q.Q62 11-562 If the water has been used diluted, the degree found must be increased in the proper proportion. bb. Determination of permanent hardness. Boil 500 c.c. of the water in a flask of about 1 litre capacity for one-half to one hour, replacing the water as it evaporates by dis- tilled water. After cooling, pour the water into a 500-c.c. flask, rinsing out the larger flask with small quantities of distilled water, then fill up to the mark, shake, allow to settle, filter into a dry flask, and determine the hardness as above in 100, 50, or 25 c.c. 206.] ANALYSIS OF MINERAL WATERS. 221 B. ANALYSIS OF MINERAL WATERS.* 206. In mineral waters a much larger number of substances are to be determined by analysis than are present in sweet waters. The substances which may require our attention are as follows: a. Bases: Ammonia, oxides of potassium, sodium, lithium, csesium, rubidium, calcium, barium, strontium, magnesium, aluminium, iron (ous), manganese (ous), (zinc, nickel [ous], cobalt [ous], copper [ic], lead [ic], thallium [ous], and sometimes also the oxides of the heavy metals). b. Acids, etc.: Sulphuric, phosphoric, silicic, carbonic, boric, nitric, nitrous, and thiosulphuric acids; chlorine, bromine, iodine, fluorine, hydrogen sulphide; crenic, apocrenic, formic, and pro- pionic acids, etc. (arsenous, arsenic, and titanic acids). c. Uncombined Elements and Indifferent Gases: Oxygen, nitrogen, and light hydrogen carbide. d. Indifferent Organic Matter. Many of these substances are found in quite considerable quantity in most springs; more partic- ularly soda, lime, and magnesia, and at times ferrous iron, besides sulphuric, carbonic, and silicic acids, chlorine, and sometimes hydrogen sulphide. The others are nearly always found in only small, frequently very minute quantities. The substances above enumerated inclosed in parenthesis are usually detected only in the evaporation residues of large quantities of water, or in the muddy ochreous deposits or solid sinter-deposits which form in most mineral springs in those places where the air acts on the water which runs out of or is stored in reservoirs.f The analysis of these waters quite naturally falls under two heads: 1. The analytical process; 2. The calculation, control, and arrangement of results. * Compare Qualitative Analysis, 211. f As already mentioned in the Qualitative Analysis, if any oxides of lead, copper, or tin are found, the water must be carefully investigated in order to ascertain whether these oxides are really present in the water itself, or are derived from any metallic pipes, cocks, etc. 222 ANALYSIS OF WATER. [ 207. I. THE ANALYTICAL PROCESS. The performance of the analytical process is divided into two parts: 1. Operations at the well; 2. Operations in the laboratory. A. OPERATIONS AT THE WELL. I. Apparatus and Requisites. 207. 1. A common plunging-siphon of from 200 to 250 c.c. capacity. 2. Four flasks of about 300 c.c. capacity each. Each contains about 3 grammes of calcium hydrate perfectly free from car- bonate, or containing a known quantity of carbonate (Vol. I, p. 480) ; and, if the mineral water contains sodium carbonate, about 1-5 grm. dry calcium chloride. Each flask is weighed with its calcium hydrate, stopper, etc., and the weight stated on a label gummed on the flask. The orifices of the flasks must be nearly of the same size so that a single stopper bearing its glass tubes, as shown in Fig. 92, Vol. I, will fit all the flasks; this stopper should be pre- pared beforehand. 3. An accurate thermometer with very distinct scale. 4. About eight white bottles with well-fitting glass stoppers, and of about 2 to 3 litres capacity. 5. Four white bottles with well-fitting glass stoppers, and of about 6 to 7 litres capacity. 6. A perfectly clean sulphuric-acid carboy in a basket, pro- vided with a rubber stopper, and rinsed out with distilled water. 7. A litre- and half-litre flask. 8. One medium-large and two large funnels. 9. Swedish filtering-paper. 10. Flasks, beakers, alcohol-lamp, blast-lamp, blowpipe, glass rods, glass tubes, rubber tubing, files, scissors, knife, rubber and cork stoppers, twine, etc. 11. Reagents, more especially the following: ammonia, hydro- chloric and acetic acids, silver nitrate, barium chloride, ammonium oxalate, tannic and gallic acids (or infusion of galls), freshly-pre- pared litmus tincture, and test papers. 207.] ANALYSIS OF MINERAL WATERS. 223 Besides these, the following are also required at times: a. When the water contains hydrogen sulphide or an alkaline sulphide. 12. A standard solution of iodine in potassium-iodide solution. This must be very dilute, so that 1 c.c. will contain, say, about 0-001 grm. iodine. It may be prepared by diluting one volume of BUNSEN'S iodine solution ( 146, b, /) with four volumes of water. 13. Powdered starch. 14. A pinch-cock burette and a few pipettes. 15. A solution of arsenous acid in hydrochloric acid, or of sodium arsenite, or of cupric acetate; also all the reagents and apparatus detailed on pp. 230, 231 of this volume. b. When the water contains much ferrous oxide, and this is to- be determined directly (volumetrically) at the well. 16. A solution of potassium permanganate. For waters con- taining much iron, this solution is to be diluted so that 100 c.c. of it will oxidize about 1 grm. of iron from the ferrous to the ferric state. For waters containing but little iron, the solution must be still weaker. If the solution is to be standardized on the spot, there will be required also weighed pieces of piano wire or a standard oxalic-acid solution (Vol. I, p. 316), and burettes and pipettes. c. When the total dissolved gases in the water are to be determined. According as the water is poor or rich in carbonic-acid gas, the methods detailed under 208, a or 6, are employed. 17. The apparatus there described is then required. d. When the free gases evolved at the spring are to be determined* 18. The apparatus described under 208, 11, is then required. e. If the well is deep, and specimens from various depths are to be examined. 19. The apparatus figured and described on pp. 225, 226 is then required. /. // the specific gravity of highly aerated water is to be deter- mined. 20. There will be required one or, better, several bottles, like that figured and described in 208, 13. 224 ANALYSIS OF WATER. [ 208. II. Analytical Processes. 208. 1. The appearance (color, clearness, etc.) of the water is noted. It must be observed, here, that water will frequently appear to be clear at the first glance, while on closer inspection in a large white bottle a few, or even many, colorless or colored flocks, etc., may be observed. In this case the bottle is set aside in a cool dark place, the clear water then carefully siphoned off, and the de- posited matters then microscopically examined. Infusoria, plants of the lowest order, etc., may thus be often found.* 2. Observe whether any gases are evolved from the well, and whether small bubbles of gas form on the sides of a dry bottle when the latter is filled with water, or whether any gas is disengaged on shaking a bottle half filled with the water. 3. Note the taste and odor of the water. To detect very minute quantities of odorous matters half -fill a water-bottle with the water, close with the hand, shake vigorously, and then observe whether any odor is perceptible. 4. Test the reaction of the water with the various test-papers, as well as with blue and also very slightly reddened litmus tincture, and note whether the colors imparted to blue litmus and curcuma papers change when the latter are dried in the air. 5. Ascertain the temperature of the water. If practicable, the best and simplest method of ascertaining this is to sink the thermometer into the well, and to take the reading while it is immersed; or suspend a thermometer in a large bottle and im- merse this in the well, allowing it to remain for some time after it has been filled, then withdraw the bottle from the well and accurately read off the temperature from the thermometer in the bottle. If the water flows from a pipe, allow it to run into a large glass funnel the neck of which is so constricted as to let about as much water flow out as runs in above. The thermometer is then fixed in the middle of the water in the funnel and the tem- perature taken after some time. * Compare SCHULZ, Jahrb. des Vereins /. Naturkunde im Herzogthume Nassau, vin, 49. 208.] ANALYSIS OF MINERAL WATERS. 225 Besides the temperature, note must be taken of a. The date. b. The temperature of the air. c. The circumstance whether the temperature of the water varies at different periods of the year; this may usually be ascer- tained at the spot. 6. Fill the bottles and carboy specified in 207, 4, 5, and 6, with water. In doing this the greatest care must be taken to prevent the water from becoming turbid, which may readily happen when, on immersing the bottles in the well, the bottle grazes the bottom or sides. If the water cannot be obtained perfectly clear, it must be filtered into 4 of the 8 smaller bottles and into the larger bottles. For this purpose use large funnels with folded filters of pure, good FIG. 83. filtering paper, so that the filtration may be very rapid. The necessity for filtration may often be obviated by filling the 6 or 7 litre flasks and setting them aside for an hour or two in the shade, and then, after the flocks have completely subsided, siphoning off the clear water into other bottles, which must be securely stop- pered and marked. As impurities occasionally float on the surface of water in springs And wells, it is always advisable to completely immerse the bottles, and to a sufficient depth. Where it its important to avoid any 226 ANALYSIS OF WATER. [ 208. agitation of the water, the bottle or flask should be provided with the contrivance shown in Fig. 83. As soon as the thumb is raised, the water flows in, while air escapes through the tube extending above the surface of the water. If the surface of the water is deep down and out of reach, tie the flask or bottle to a rod, or tie a weight to it and lower it with a string. To keep the bottle or flask upright, use may be made of a net, through a hole in the middle of which the neck of the flask is thrust; the net is then tied together below the bottom of the flask and a weight attached to it, while the whole is suspended by a strong string tied around the neck of the flask. If the well is very deep, and it is desired to collect samples from various depths, the apparatus shown in Fig. 84 may be advan- tageously used. The strong flask, a, is provided with brass cap, 6, cemented air-tight on it and bearing two brass tubes, c and d. To the tube c is joined a glass tube, e, which constitutes the lower continuation of c, and extends down nearly to the bottom of the flask. The tube d, on the other hand, ends flush at the interior surface of the cap, and surrounds the glass tube, as shown in Fig. 85. The brass tubes are pro- vided with cocks, / and u, which when open afford a perfectly free passage for water, and which are connected with the arms, g and h, whereby they may be opened and shut with ease. If the cocks are to operate simul- taneously, as is ususally the case, the ends of the arms are joined by the rods i and k. In the position shown by the illustra- tion, both cocks are closed ; when PIG. 84. FIG. 85. i is raised, both are opened. In order to prevent any mistake 208.] ANALYSIS OF MINERAL WATERS. 227 occurring as to whether the cocks are open or shut, the ends of the arms g and h should be suitably marked. The tubes e f and m fit air-tight on to the taps and are fastened in place by the screws n and o. The flask is enmeshed by a white silk net to which are fastened a weight, p, below, and a knotted cord, q, above. This cord allows the flask to be immersed, and also serves to measure the depth by the knots. The cord r is connected with the arm k, while another cord, s, is connected with i\ the upper ends of these cords are fastened to wooden rollers which are marked to avoid confusion. To use the apparatus, which must be empty and clean, close the cocks and sink it in the well to the required depth. While the immersion is being effected by the operator, whom we may designate as Q, an assistant, S, holds the cord s, while a second assistant, R, holds the cord r, loosely, but taking care that the flask does not rotate on its axis and twist the cords. After the apparatus has been immersed for some time and the water has become perfectly still again, S pulls upon the cord s while R loosens his hold on r. The cocks are thus opened, and the water enters through e' e, while the air escapes from the flask through the cres- cent-shaped opening and m, and ascends through the water in the form of large bubbles; when these cease to appear, the flask is full. R now pulls on r, while S loosens his hold on s. The cocks are thus closed, and the apparatus is then drawn up by q, while r and s are held loosely. If the flask has been properly constructed it will be found to be completely full, and will show no bubbles on being inverted. To empty it, invert the apparatus, place a bottle under m, and open the cocks.* 7. To determine the total carbonic acidfi fill each of the weighed flasks ( 207, 2) containing calcium hydroxide, or calcium hydrox- * The apparatus used by me has the f ollowing dimensions : Capacity of the flask, 600 c.c.; internal diameter of the brass tubes, 7 mm.; bore of the cocks, 5 mm. ; length of the arms, 90 mm. ; length of the rods connecting the arms, 105 mm.; weight of the sinker, 2-5 kilos. f Regarding other methods of determining carbonic acid compare 139, i, b, /?. The method here described is exceedingly simple, and is superior to all others in point of exactness. (Zeitschr. f. analyt. Chem., n, 56.) 228 ANALYSIS OF WATER. [ 208. FIG ide with calcium chloride, almost up to the neck, while gently shaking round with water just taken from the well. If the flask can be immersed in the well, provide it with a stopper carrying two glass tubes (Fig. 86) and submerge it in such a manner that the water enters through a 6, while the air escapes through c d. If the spring issues from a narrow bore - hole, however, a siphon is first rinsed out with some of the mineral water, and then gradually inserted, so that it may slowly fill; on withdrawing it, rapidly dry its surface, and empty into one of the weighed flasks. If the mineral water issues from a tube, the weighed flask (with the calcium hydroxide, etc.) is simply held under the stream. but not so close that carbonic acid, which often (without being absorbed by the water) flows out, can get into the flask. When the flasks have been filled as described, it is tightly stoppered with rubber stoppers, which are then tied down with parchment paper. If the carbonic acid is to be determined in water obtained as described by aid of the apparatus, Fig. 84, from the bottom of a well, and which may hence be supersaturated with carbonic acid, it is safest to use the whole quantity of the water contained in the flask a. In this case proceed as follows: Introduce an excess of carbonate-free calcium hydroxide (or a weighed quantity of calcium hydroxide of known carbonate content), and also, if neces- sary, a quantity of calcium chloride more than sufficient to decom- pose any sodium carbonate present, into a flask holding half again as much as the flask a. After the filled flask a has been with- drawn from the well, unscrew the connectors i and k (so that the cocks may be operated separately), and also the tube-joints ra and e t and remove the small quantities of water that remain above the -cocks. Now invert the flask and hold it obliquely so that the cock 208.J ANALYSIS OF MINERAL WATERS. 229 u is lowermost; next open the cock u and allow the water to flow through it into a flask, by carefully opening the cock / for the ad- mission of air. As soon as about one-fourth of the contents has run out, close the cocks, close the flask with its rubber stopper, shake it gently to distribute the calcium hydroxide through the water and to effect the absorption of any carbonic acid that may have been disengaged from the water in pouring it in and thus have entered the flask. Now empty the remainder of the water into the flask as described above. In order not to lose any car- bonic acid that may have remained behind in a, introduce into this 50 c.c. of lime-water or very dilute milk-of-lime, shake for some time, and then empty into the lime flask, into which also-- empty the water with which a is to be rinsed; the flask is then, stoppered, and the stopper tied down. The capacity of a, and consequently the quantity of water employed in this experiment should be accurately determined by- measuring. As the quantity of free carbonic acid dissolved by water varies with the pressure, it is hence necessary to note the height of the barometer. 8. // the water contains hydrogen sulphide, determine it by means of standard iodine solution ( 207, 12) according to the directions- given in 148, I, a. If the water contains an alkali thiosulphate r it will, of course, be necessary to deduct the quantity of iodine solution equivalent to the thiosulphuric acid present (and which is separately determined), from the total iodine solution used, in order to ascertain how much has been used up by the hydrogen sulphide. If a gravimetric control is considered desirable, use the method employing copper solution or arsenous-acid solution, and described in 148, I, c. Since in the analysis of alkaline waters the question frequently arises as to how much of the sulphur compound should be calcu- lated as hydrogen sulphide, metallic sulphide, or hydrosulphide respectively, it is important to know whether the whole or a part of the sulphur will be removed from the water on passing through it a current of some indifferent gas for some time. To ascertain. 230 ANALYSIS OF WATER. [ 208- ' this, pass a current of hydrogen gas which has been passed first through a concentrated alkaline solution of potassium permanga- nate, and then through potassa solution, through a measured volume of the mineral water contained in a flask provided with a doubly perforated cork, in one opening of which is inserted a tube reaching to the bottom of the flask for admitting the gas; the other aperture is fitted with a tube bent at right angles and ending flush with the lower surface of the stopper. As soon as the gas Issuing no longer contains the least trace of sulphur, and hence no longer decolorizes a small quantity of very weak starch-iodide solution (and which occurs only after the gas has been passing for some hours) , break off the current of hydrogen, and again determine the sulphur remaining in the mineral water thus treated, using as before a solution of iodine, copper, or arsenous acid. A cool and shady place should be selected in which to conduct the opera- tion of passing the hydrogen gas through the mineral water. By the simultaneous use of an air-pump, the removal of the absorbed hydrogen sulphide is greatly facilitated. The sulphur compound remaining in the water after the above- described treatment is, in the case of mineral waters containing also free hydrogen sulphide, metallic hydrosulphide. Although this method of deciding the question (as above stated), and which is also recommended by W. B. and E. ROGERS,* is adapted for use in the case of waters containing hydrogen sulphide alone or almost exclusively so, but no thiosulphate,f it is nevertheless unserviceable for sulphur waters containing chiefly soluble metallic sulphide or hydrosulphides, and besides these, as may frequently be the case, thiosulphates. In such waters determine the sulphur combined with the hydrogen or metal, first jointly, best by means of a cadmium solution, which is at least as sensitive as any other metal solution (Expt. No. 85), and is not affected by sodium thiosulphate. The cadmium sulphide precipitated must not be weighed directly, * Journ. /. prakt. Chem., LXIV, 123. f Comp. FRESENIUS'S Analysis of Weilbach Mineral Water, Journ. /. prakt. Chem., LXX, 8; also of the Gnndbrunnen at Frankfort a. M., Jahresber. des physikal. Vereins zu Frankfurt f. 1873 bis 1874, S. 74. 208.] ANALYSIS OF MINERAL WATERS. 231 as it is apt to contain cadmium chloride (Expt. No. 86), hence the sulphur in it must be determined according to 148, II, A, 1 or 2. From a fresh quantity of water the free hydrogen sulphide is now expelled, and then that combined with the metal as hydrosulphide, both being determined by passing the gas expelled through am- moniacal silver-nitrate solution; the sulphur combined with metal as a monosulphide is then determined from the difference (if no disulphide is present). For this purpose the following method employed by SIMMLER * in his exceedingly careful analysis of the Stachelberg mineral water may be used : First expel the free hydrogen sulphide from the water by means of a current of pure hydrogen, with the aid -of an air-pump, then pour into the water through a funnel-tube a solution of manganous sulphate, and remove the liberated hydro- gen sulphide, which was present as a sulpho-a^id combined with a metallic sulphide. Filter off the manganese sulphide, and add to the warm filtrate a solution of neutral silver nitrate if a thiosulphate is present, a precipitate of silver sulphide, containing generally also silver chloride, forms. Collect the precipitate on a filter, remove the silver chloride with ammonia, dissolve the washed silver sulphide in nitric acid, and determine the silver in the solution as a chloride, and from this calculate the thiosulphuric acid (comp. 168). Of course the silver in the silver sulphide need not be determined at the well. The precipitate of manganese sulphide filtered off contains the sulphur which was present in the water as a monosulphide. If however, the water contains a disulphide (in which case it will have a yellowish color in large volumes), the manganous sulphide is added to the sulphur which was combined with the monosulphide to disulphide; on treating the precipitate with hydrochloric acid, the free sulphur remains undissolved. For the details of the process and description of the apparatus employed by SIMMLER for expelling the hydrogen sulphide, I refer to the author's original memoir (loc. cit.). * Journ. /. prakt. Chem., LXXI, 27. 232 ANALYSIS OF WATER. [ 208, 9. // the water contains a rather large quantity of jerrous carbonate, which is indicated by a fairly dark-violet color on adding gallic or tannic acid, an attempt should be made to volumetrically determine the ferrous salt by means of the dilute potassium- permanganate solution (207, 16 comp. also Vol. I, p. 317). For this purpose 500 c.c. of the water are used, and the experiment performed in a white bottle standing on a sheet of white paper. Some dilute sulphuric acid should first be added to the water. A number of experiments should be made until sufficiently constant results are obtained.* If the water smells of hydrogen sulphide, or if it contains any notable quantity of organic matter, this method cannot be employ ed.f In the case of waters rich in chlorides the results will be too high, and for the reasons stated in Vol. I, p. 319, unless the precautions there given are observed.^ 10. To determine the total gases held in solution by the water, proceed as follows, according to a or b, as the water is poor or rich in carbonic acid: a. For water poor in carbonic acid. Fill a globe, Fig. 87, with the mineral water, and sink it, thus filled, by means of a rod * This rapid method is of particularly great value, as by means of it the chemist is enabled to quickly ascertain the quantity of ferrous salt which the spring loses in its passage first to the reservoir and then to the baths, or how much is lost when kept for a shorter or longer time in crocks. The iron determination which I made by this process in a preliminary examination of the Schwalbach springs corresponded almost exactly with the results obtained by gravimetric analysis. This method is also serviceable in prospecting the water of chalybeate springs, as by means of it every small contributory spring may be examined at the spot at once with sufficient accuracy. f If only hydrogen sulphide is present with the ferrous salt, the following modification, which I have not tried, however, might be adopted : Determine first the relation between solutions of iodine and also potassium perman- ganate with respect to their action on a very dilute pure hydrogen-sulphide water; then test 500 c.c. of the mineral water with iodine solution, and another 500 c.c. with the permanganate solution; the former process gives the hydrogen sulphide present, and the latter gives the iron contact after deducting from the c.c. of permanganate solution used a quantity correspond- ing in its action upon the hydrogen sulphide to the iodine solution used. % The characteristic odor usually perceived when testing acidulated saline waters with permanganate is frequently due to bromine or chlorine. The odor of bromine was most distinctly observed by me during an examination of the Elisabethenquelle at Homburg v. d. H. 208.] ANALYSIS OF MINERAL WATERS. 233 or attached weights, into the well; then empty it by applying suction to a gutta-percha tube, a, reaching to the bottom of the globe until the mineral water in this has been completely replaced by fresh water from the spring. In order to prevent the return of any water in the tube on discontinuing suction, a cock, b, or a small piece of rubber tubing, which may be closed by pressing between the fingers, is made use of. Over the mouth of the globe is tied a piece of sheet rubber, the elasticity of which permits the tube to be inserted laterally, while yet completely closing the mouth of the globe when the tube is withdrawn. The globe just filled in the well is then pulled up out of the water, after the suction tube has been FIG. 87. FIG. 88. withdrawn, and immediately connected with the flask of a so-called rubber stop-cock, a, Fig. 88,* which is filled with well-boiled water, and tightly stoppered (R. BuNSEx).f * Such a stop-cock has already been described on page 71, this vol. f Gasometrische Methoden, 2. Aufl., 18. 234 ANALYSIS OF WATER. [ 208. If the water flows from a pipe, connect this with a rubber tube, conduct the water to the bottom of the flask and let it run in for some time, and finally close the flask with the rubber stop- cock as already described. Now connect the other end of the cock a with the tube b, and the latter again, after pouring some water into it, with the graduated tube c by means of another rubber stop-cock, d. The capacity of c must be at least half as much again as the volume of the gas held in solution by the water, and measured in the cold and at the ordinary pressure. (Were this process to be used for waters rich in carbonic acid, either the tube c would have to be greatly increased in size, or else the volume of water taken would have to be so small that it would render it imprac- ticable to determine the other gases dissolved in the water.) Incline the apparatus so that some of the water enters the bulb 6, close the cock a, open d, and boil until all the atmos- pheric acid has been expelled and is replaced by aqueous vapor ; then close the tube e by means of a ligature or compression cock. When the apparatus is cold, open the cock a; the water in the globe immediately begins to boil, while the gas held by it in solution escapes into the vacuum. Now warm for about an hour and a half at a temperature not exceeding 90 C.; this will keep the water boiling and will completely expel all the gases from it. Heat the globe somewhat more strongly until, from the greater expansion of the vapor, the boiled water just reaches the ligature d. The instant this occurs, tie the ligature, remove the tube c from 6, and open it under mercury by loosening the ligature e; now note the state of the barometer and thermome- ter, the height of the mercury column in the tube, and the volume of the gas obtained (R. BUNSEN *). If a graduated tube, c, is not at hand, one not graduated, but of known capacity, may be used. As soon as the mercury within and without the tube, after re- moving the ligature, stands at the same level, the ligature is again applied and the mercury within the tube transferred to a graduated cylinder, where it is measured and its volume deducted from that * Gasometrische Methoden, 2. Aufl., 18. 208.J ANALYSIS OF MINERAL WATERS. 235 of the known capacity of the tube; the difference will give the volume of the gas expelled from the water. As it may be inconvenient to transport to the well the entire apparatus necessary for the actual analysis of the expelled gases, it is better to take the latter to the laboratory in sealed tubes. For this purpose replace the tubes c by tubes not graduated, but of similar form and drawn out at each end near the thicker part so that they may be readily sealed. The process is carried out as detailed above, and after the gases have been expelled from the water by boiling, and the ligature at d has been closed, seal the tubes at the drawn-out parts by means of a blowpipe, as in Fig. 89,* or with an eolipile. It is ad- visable to fill two or three such tubes with the gas in this manner. As the total volume of gas in a definite quantity of water has already been ascertained by the first experiment ; it is immaterial whether the tubes used for transporting the gas to the laboratory contain all the gas ex- pelled from the water, or whether a small part of it remains in the globe. Instead of BUNSEN'S method other ones may be used. LOTHAR MEYER recommends LUDWIG'S apparatus based on the principle of the Toricellian vacuum,f and as described by NAW- ROCKI.J He employed this apparatus in an analysis of the Landeck thermal springs. HERBERT McLEOD | heats the water in the vacuum obtained by the aid of a SPRENGEL mercury-pump. * a is a small lamp holding about 3 grm. of oil, and connected with the blowpipe by a somewhat flexible wire, b, through a loop in which the blowpipe tip is passed. The flame may be readily adjusted by bending the wire. The <;ork c serves as a mouthpiece, so that the whole contrivance may be held and managed with the teeth alone. f SETSCHENOW, Wiener Sitz.-Ber., xxxvi, 293; SCHOFFER, ibid., XLI, 589. t Zeitschr. f. analyt. Chem., n, 120. Ibid., n, 236. | Journ. Chem. Soc., xxn, 307; Zeitschr. f. analyt. Chem., ix, 364. 236 ANALYSIS OF WATER. [ 208. These methods yield very good results, but require complicated apparatus which are described and figured in the Zeitschrift fur analytische Chemie (loc. cit.). b. For waters rich in carbonic acid. For such waters the meth- ods detailed under a are not suitable, as already mentioned. The escape of the other dissolved gases is in this case facilitated by the large volume of carbonic-acid gas evolved, hence the vacuum may therefore be dispensed with. In the examination of such waters I use the following method : Fill a flask of about 500 c.c. capacity with the mineral water in the manner already described, then close it with a perforated rubber stopper which has been well kneaded under the surface of the mineral water; into the perforation, which should be filled with water, insert the end of a delivery tube which has been entirely filled with the water. This tube is bent first at a right angle, then at an obtuse; the end of the long downward limb is turned upwards. By using the methods detailed, it is an easy matter to obtain the flask and tube com- pletely filled with water. Now place the flask on a wire gauze with the turned-up end of the tube in a dish containing a well-boiled solution of potassa, sp. gr. 1 27, and with the tube also filled with the same potassa solution inverted over the orifice of the tube. The part a, Fig. 90, holds about 5 c.c. ; on the part b is gummed before use a strip of paper with a scale marked on it showing the capacity of the tube in c.c. at that part. (The scale may be easily and rapidly made by allowing water to run from a burette into the tube, held inverted until it has just reached the shoulder, then let 1 c.c. run in, and make a mark; run in a second c.c. and make another mark, etc.) When the mouth of the tube filled with the potassa solution has been brought over the orifice of the delivery tube, slowly FIG. 90. nea "k the flask. The carbonic acid is absorbed by the potassa solution, while the unabsorbed gas collects in a. Heat gradually to boiling, and continue until the volume of gas 208.] ANALYSIS OF MINERAL WATERS. 237 no longer increases. Then remove the tube, allow to cool, read off the volume of gas on the scale, having due regard to the prevailing temperature and barometric pressure, and fuse off the part of the tube a by means of the blowpipe, Fig. 89, or an eolipile, for removal to the laboratory where the gas may be further examined. Should the gas not reach as far as the scale at one operation, that obtained from a second quantity of water is emptied into the same tube. It is advisable to fill two tubes in this manner. The error incident to this method is due to two facts: First the volume of water from which the gas is ob- tained is not accurately known (since on warming the water a portion of it is driven into the tube before its gas has been expelled, and although strongly heated afterwards affords no certainty that all its gas has been expelled); second, the tension of the water contained in the potassa cannot be accurately calculated. This error is, however, far smaller than when small quantities of highly aerated water are treated as in method a, and scarcely measurable quantities of unabsorbable gas obtained. 11. If it is desired to accurately ascertain the nature of the gases spontaneously evolved from the spring, collect them in test-tubes of from 40 to 60 c.c. capacity, connected by means of a cork or rub- ber stopper with a funnel, as shown in Fig. 91. At a the tubes are to be narrowed to the thickness of a thin straw. For col- lecting larger quantities of gas, use is made of bottles with drawn- out necks as shown in Fig. 92. After the tubes or bottles have been filled with the mineral water and connected air-tight with the funnel by means- of the cork or rubber stopper, submerge the whole, with the mouth of the funnel upwards, in the mineral water, and by means of a narrow tube reaching to the bottom of the tube or bottle, suck out the water of the first filling (and which had been in contact with the air), until certain that it has been replaced by a fresh quantity which has not been ex- posed to air. Now invert the apparatus in the water and allow the gas spontaneously disengaged to ascend in the funnel. If the gas bubbles are restrained from rising in the neck of the funnel, or at the constricted part of the tube, they may be 238 ANALYSIS OF WATER. [ 208. readily dislodged by tapping the rim of the funnel against a hard body. Enough gas is allowed to enter to fill the tube and the neck of the funnel, then a dish is slipped beneath the funnel and the apparatus lifted out of the wate r ; the constricted part of the tube FIG. 91. FIG. 92. is then gently heated to remove moisture and then sealed. As the column of water in the funnel above the level of that in the dish diminished the pressure of the gas against that of the atmos- phere, there need be no fear that the glass will blow out in sealing (R. BUNSEN*). The warming and fusing are effected by means of an eolipile or blowpipe (Fig. 89). It is necessary to fill several tubes or bottles in this manner. If the nature of the spring renders it impossible to fill the tubes in the manner described, use is made of a funnel weighted by a leaden ring, c, Fig. 93, and which is suspended by a stout string and lowered into the well (R. BUNSEN f). The funnel tube is con- nected by a rubber tube with a tin tube, a 6, and this in turn with the glass tubes c c c. After the funnel is filled with water by suc- * Gasometrische Methoden, 2. Aufl., 3. f Ibid., 2. Aufl., 5. 208.] ANALYSIS OF MINERAL WATERS. 239 tion up to the cock 6, allow the gas to ascend in the funnel until it is under a pressure greater than that of the atmosphere. Then open the cock b and allow the gas to pass through c c c until cer- tain that all the air has been expelled and replaced. The tubes c c c are of from 40 to 60 c.c. capacity, and those parts near the ends where they are to be sealed are somewhat thickened and constricted; they are connected by short pieces of rubber tubing. FIG. 93. After being filled with gas from the spring, they are warmed, and the two outside rubber connectors are closed air-tight by pressure between the fingers or by a clamp; finally, as soon as the tem- perature has fallen so that the external pressure is somewhat greater than that within the tube, they are fused off in succession. Very often in the case of acidulous waters the carbonic acid predominates to such an extent in the spontaneously evolved gas, that a large number of tubes must be filled in order that after absorption of the carbonic acid by potassa, a sufficient quantity of the other gases (nitrogen, marsh gas, oxygen) may be obtained for analysis. In the case of such wells I prefer to determine at the well the proportion between the gases absorbable and non- absorbable by potassa, and to collect only the latter for further investigation. To effect the former, fill a graduated cylinder. 20 to 30 mm. wide and of about 200 to 300 c.c. capacity, with the mineral water by sucking out with a glass tube the water first entering, and then invert it in the basin or spring, or in a porcelain dish filled with 240 ANALYSIS OF WATER. [ 208. the mineral water. It must be filled entirely with the gas; in the first case directly so, and in the second by aid of the above-described weighted funnel which, in this case, is provided with a rubber tube and gas-evolution tube instead of the collecting tubes. Now remove the cylinder from the well with the aid of a porcelain dish, draw off almost all the confining water in the dish by means of a pipette, and replace it by well-boiled potassa solution; then agitate the cylinder to favor the absorption of the carbonic acid. When this has been done, read off the volume of unabsorbed gas, paying due regard to the prevailing temperature and pressure. With many wells the measurement of the unabsorbed gases is only possible, even when large cylinders are used, when the upper part of these is constricted as shown in Fig. 94. To collect the unabsorbable gases alone, I make use of a large tin funnel (weighted with a leaden ring), the narrow stem of which is connected by means of a rubber tube with a narrow gas-delivery tube. This tube dips into a well-boiled potassa solution contained in a dish in which is inverted a tube having the form shown in Fig. 95. The rubber tube should be provided with a screw pinch-cock, which should at first be open. When certain that all the gas FlG 94 rising from the funnel is perfectly free from atmospheric air, bring the end of the gas-delivery p IG . 95. tube ' under the inverted tube, Fig. 95, and by properly ad- justing the pinch-cock, allow the gas to rise regularly in small bubbles. As these will be almost entirely absorbed, it will naturally take some time until the tube is filled to about the point a, where it is to be sealed off as soon as this has taken place. 12. If hydrogen sulphide is evolved, it is determined by filling a large flask, with neck somewhat elongated, with the mineral water, and slipping over the neck a wide rubber tube cleaned with soda-lye and provided with a strong pinch-cock. In the other end 208.] ANALYSIS OF MINERAL WATERS. 241 'of the tube insert a funnel, fill it also with the water, invert the whole under the surface of the water, and collect the gases. As soon as the flask is filled, close the pinch-cock, hi vert the flask in a beaker containing a solution of cupric chloride with ammonia in excess, open the pinch-cock, allow a sufficient quantity of the solution to enter the flask, shake, let stand for some time, and finally deter- mine the sulphur in the copper sulphide filtered off (from which the volume of hydrogen sulphide may be calculated), as directed in 148, II, A, 2, a. On deducting the volume of hydrogen sul- phide so found from the gases absorbed by potassa solution (as detailed in 11) the volume of carbonic acid is found. 13. For determining the specific gravity of highly aerated mineral waters, a bottle as shown in Fig. 96 may be used with advantage. Its capacity may be from 200 to 300 c.c., and its neck, as shown in the illustration, should have a narrowed part about 50 mm. long and of as uniform a bore as possible, its internal diameter to be from 5 to 6 mm.; on this constricted part should be scratched or etched a millimetre scale. The mouth of the bottle must be perfectly round, so that it may be closed air-tight by a rubber stopper. In order to fill the bottle, it is submerged in the liquid, first inserting a narrow tube in order to allow the air to escape; the bottle is thus filled without difficulty. When nearly full, the glass tube, which has meanwhile been withdrawn in proportion as the bottle filled, is entirely removed. As soon as the water level stands at about the middle of the elongated neck, close the mouth under water with the thumb, remove the bottle, and immediately insert and tie down the stopper. Thus prepared, the bottle is ready to be transported. It is well to fill three or four such bottles. Each should be separately packed in cardboard in order to prevent breakage during transportation. In default of such bottles, several ordinary narrow-necked and ungraduated prescription bottles should be filled. FIG. 96. 242 ANALYSIS OF WATEB. [ 209- 14. Attention should be paid to every particular connected with the spring, and every circumstance that may have a bearing on the investigation; for instance, as to how much water and free gas the spring yields; whether these quantities remain constant at different seasons and at the varying water-levels in neighboring streams; whether the level in the spring is constant; whether a muddy deposit or solid sinter forms in the delivery tubes or reser- voir (in which case a fairly large quantity should be taken for examination); to what geological formation the mountain belongs on which the spring rises; the depth of the spring; the character of the basin; the predominant action of the water, etc. B. OPERATIONS IN THE LABORATORY. I. Qualitative Analysis. This is carried out in the manner detailed in the "Qualitative Analysis," 211.* IL Quantitative Analysis. 209. The course to pursue in the quantitative analysis of mineral waters varies according to the absence or presence of alkali car- bonates. As the analysis is simpler in the case of alkaline waters (as those containing alkali bicarbonates are termed), we will first con- sider the methods employed for these, starting with the assump- tion that there are present all the substances which are usually found in alkaline waters. Thereafter will be detailed the modi- fications required in mramifiing saline waters and sulphur waters. DETERiaxiXG THE SPECIFIC GRAVITY. a. Water Poor in Gas. In such a case, bring a bottle of the mineral water and a bottle of distilled water to the same temperature and note this. Then * Mineral waters which have been kept for a long time in jugs frequently have an odor of hydrogen sulphide, even though perfectly free from this odor when fresh. This is due to the contact of the moist cork or other organic mat- ters with the sulphates, whereby a part of these is reduced to sulphides, and from which the free carbonic acid then liberates the hydrogen sulphide. 209.J ANALYSIS OF MINERAL WATERS. 243 fill an accurately tared bottle of at least 100 grammes capacity, and provided with a tightly-fitting ground-glass stopper, first with distilled water, and weigh; then weigh again filled with the min- eral water. The quotient obtained by dividing the weight of the mineral water by that of the distilled water gives the specific gravity of the former. It is preferable to use a pyknometer, Fig. 97 a bottle with a long, perforated, tightly" fitting ground stopper. Great care must be taken that no gas bubbles adhere to the sides of the filled bottles, and also that the bottle be not warmed by the hand when drying it. The great- est certainty against any inequality of tempera- ture hi the liquids to be weighed is afforded by the use of a pyknometer with a thermometer p IG g 7 ground in. b. Highly Aerated Water. With such waters the method just described is inapplicable, unless a part of the carbonic acid has first been expelled from the water. It is evident, however, that in this case the true specific gravity of the mineral water as yielded by the spring will not be obtained, and that analysts will obtain varying results. The specific gravity of such a water is determined by the aid of the flask de- scribed hi 208, 13, and filled as there directed. The flask is placed on a horizontal support in a room of fairly constant temperature; by the side of the bottle place a somewhat larger bottle filled with distilled water and closed by a perforated cork bearing a thermometer which dips into the water. After twelve hours the contents of both bottles will certainly have the same temperature. Now read off the thermometer, and also note the height of the mineral water on the scale, which is best done by means of a telescope placed horizontally, 6 to 8 feet distant and movable up or down on a vertical rod. Now weigh the bottle with its stopper on a sufficiently delicate balance, remove the stopper without wetting it, empty the bottle, 244 ANALYSIS OF WATER. [ 209. rinse it out, fill with distilled water to slightly above the mark at which the mineral water had stood, dry the flask thoroughly, and place it for a sufficient length of tune beside the other bottle con- taming the thermometer, and then lower the level in the neck un- til it is at exactly the same height as when filled with the mineral water. After making certain that the temperature has remained the same, insert the stopper, and weigh. On deducting the weight of the empty dry bottle and its stopper (which must be now ascer- tained if this was not done before) from both of the two weights obtained, the data necessary for accurately calculating the analysis of the mineral water are obtained. If, for lack of bottles of the above description, the determina- tion is to be made with narrow-necked prescription bottles, mark three fine points on three narrow strips of paper, and gum these on the neck of the bottle, to take the place of the scale. The pro- cess is then carried out in the manner described. The several quantities of the mineral waters required for the estimations here described may be determined directly by weight, or by measure, in which case multiplying the number of c.c. by the sp. gr. of the water will give the w r eight. I prefer to weigh the quantities, as then they are quite independent of the tempera- ture, and furthermore, in cases where it is important the entire contents of a bottle can be used, or quantities of water can be taken weighing a round number of grammes. 1. DETERMINING THE TOTAL QUANTITY OF FIXED CONSTITUENTS. For this purpose carefully evaporate the contents of a small or large bottle (say from 200 to 2000 grm. according to the con- centration of the mineral water) in a weighed platinum dish at a temperature below the boiling-point of the liquid, and adding the water from time to time as it evaporates. If the water con- tains much gas, cover it with a large watch-glass when beginning the evaporation, and also after adding each fresh portion. The evaporation is most safely effected on a water-bath, nevertheless it may be accomplished also over the small naked flame of a lamp 209.] ANALYSIS OF MINERAL WATERS. 245 if care be taken. It is nevertheless completed on a water-bath, and the residue dried over an air- or oil-bath at 180 until the weight is constant; this is then noted. Now fill the dish half full with distilled water, add from time to tune a drop of hydrochloric acid, keeping the dish meanwhile well covered with a large watch- glass, and when all carbonates have been decomposed, warm care- fully to expel the liberated carbonic acid, rinse out the cover into the platinum dish, and add diluted sulphuric acid sufficient to convert all the bases into sulphates, avoiding, however, too large an excess. Now evaporate to dryness, and ignite gently for some time, while every now and then adding ammonium carbonate to convert the acid sulphates into neutral sulphates ( 97, 1), and until the weight becomes constant ; this then note. If there remained in the bottle a small quantity of precipitate which could not be rinsed out, dissolve it in a little nitric acid, evaporate the solution to dryness, and ignite and treat the residue as will be presently detailed. The weight so obtained must be added to that of the principal residue. In highly ferruginous waters it is preferable to determine the fixed residue in such bottles in which, from prolonged action of the air on the iron, this has been completely precipitated as ferric hydroxide. Filter off the precipitate, wash it, and treat the filtrate as detailed above. Dissolve the precipitate in nitric acid; if any silicic acid remains undissolved, this is to be determined and its weight added. Evaporate the nitric-acid solution, ignite the residue, treat it with water and ammonium carbonate to convert any small quantities of caustic lime that may be present into cal- cium carbonate, heat moderately so as not to decompose the cal- cium carbonate formed, weigh, and add the weight so found to that of the contents of the platinum dish dried at 180. This mode of procedure avoids the difficulty arising when, on treating the residue with sulphuric acid and igniting, some magnesium sulphate is prone to be decomposed if the heat is too strong; while if insufficiently heated, on the other hand, some sul- phuric acid remains behind combined with the iron. How the evaporation-residue and the sulphates into which. 246 ANALYSIS OF WATER. [ 209. it is converted, etc., are used to control the analysis will be de- scribed further on. 2. DETERMINING THE CHLORINE, BROMINE, AND IODINE. 200 to 2000 grm. of the water are taken, according to the chlo- rine content. If the water contains relatively much chlorine, acidulate it with nitric acid, precipitate with silver nitrate, and determine the precipitate according to 141, 1, a, as silver chloride containing some iodide, or convert it into metallic silver by ignition in a current of hydrogen ( 115, 4, a). Waters which contain but little chlorine should be evaporated down to about one-fourth before adding the nitric acid. It is then filtered, washed, and the filtrate treated as described. 3. DETERMINATION OF THE SILICIC ACID, IRON, MANGANESE, ALU- MINIUM, CALCIUM (TOGETHER WITH BARIUM AND STRONTIUM) AND MAGNESIUM. Use the contents of one or more bottles for this purpose say 2000 to 7000 grm. The determinations, especially of the iron, can, of course, be correct only when the water is clear and free from ochreous flocks (comp. 208, 6). After the bottle or bottles have been weighed smear on the lip a very thin layer of tallow, then carefully pour out a portion of the contents into a beaker, avoid- ing the loss of even a drop, and then carefully add hydrochloric acid in slight excess to the contents of both the bottle and the beaker. Now evaporate to dryness the whole of the water in one or more large platinum dishes, finishing on a water-bath * (140, II, a), moisten the residue with hydrochloric acid, add a little water after some time, warm, filter off the undissolved silicic acid, and wash and weigh it. After the weighing treat it with pure ammonium fluoride or pure hydrofluoric acid and sulphuric acid. Any non-volatile residue (small quantities of barium sulphate or titanic acid)f must be taken into account. Now precipitate the fil- * If porcelain dishes are used for the evaporation the silicic-acid determi- nation will be less reliable, while that of the alumina will be totally valueless. j- In order to further test a residue of this kind, fuse it with a little potas- I 209.] ANALYSIS OF MINERAL WATERS. 247 trate from the silicic acid with ammonia (best in a large platinum dish), warm the whole, and collect the precipitate and wash it. Dissolve the greater part of the ferric hydroxide, of which the pre- cipitate consists, in hydrochloric acid, then neutralize with a dilute ammonium-carbonate solution almost to the point of turbidity, boil, and filter off from the precipitate, now free from manganese and alkaline earths. If ammonia produces traces of a precipitate in the filtrate, collect this separately on a filter, dissolve in a very little hydrochloric acid, reprecipitate with ammonia, and collect again by filtration. Add the filtrate to that first obtained. Now dissolve the larger precipitate of basic ferric salt, as well as that subsequently obtained with ammonia, in hydrochloric acid, add to the solution a little chemically pure potassium bitartrate (the bitartrate frequently contains alumina), then some ammonia, and precipitate the iron from the clear solution by means of am- monium sulphide in a flask, which must be nearly filled and kept closed, and thus separated from alumina and phosphoric acid. Dissolve the sulphide in hydrochloric acid, oxidize the solution with nitric acid, precipitate with ammonia, and ignite and weigh the ferric oxide so obtained. After weighing dissolve the oxide in fuming hydrochloric acid to ascertain if there is any residue left other than that due to the filter ash. In case there is (silicic acid), its weight must be deducted from that of the ferric oxide. Evaporate to dryness the filtrate from the iron sulphide in a platinum dish with the addition of some solution of sodium car- bonate perfectly free from alumina (and obtained by saturating with carbonic acid and filtering after standing for a long time); heat the residue with a little pure potassium nitrate, soften with water, transfer to a beaker, dissolve in hydrochloric acid, filter, and precipitate with ammonia; there are usually obtained a few flocks of aluminium phosphate; and that this is the case is shown by the fact that ammonium molybdate gives a further precipitate with the phosphoric acid in the filtrate, as usually happens. If shim bisulphate, treat the melt with cold water, and filter. Titanic acid goes into solution, and precipitates out on prolonged boiling; barium sulphate remains undissolved. 248 ANALYSIS OF WATER. [ 209- this is not the case, the phosphoric acid must be determined in. the weighed alumina precipitate. Slightly acidulate the filtrate (containing the manganese, cal- cium, and magnesium) with hydrochloric acid, concentrate, and precipitate the manganese with ammonium sulphide. Allow the nearly filled and stoppered flask to remain at rest for twenty-four hours in a moderately warm place, then filter off the precipitate, wash it, dissolve again in hydrochloric acid, and reprecipitate as before with ammonium sulphide. Finally, mix the manganese sul- phide with sulphur, ignite in a current of hydrogen, and weigh as such; it must be tested as to its purity ( 109, 2). Heat the filtrate with hydrochloric acid, evaporate, filter off from the sulphur, and precipitate the calcium (together with the strontium) with ammonia and ammonium oxalate. After the precipitate has subsided collect it, wash, dry, ignite, dissolve the residue in hydrochloric acid, reprecipitate with ammonia and am- monium oxalate, allow to deposit, collect again, and for the pur- pose of weighing finally convert the calcium oxalate into either calcium carbonate, calcium oxide, or calcium sulphate ( 103. 2, b and 154, 6). As a rule it contains strontium, which, after it has been determined (as carbonate, oxide, or sulphate, as in 6) must be deducted from the weight of the calcium compound in order to ascertain the true weight of the calcium salt. Evaporate the united filtrates to dryness, drive off the am- monia salts by igniting the residue in a platinum dish, moisten with hydrochloric acid, evaporate to dryness on a water-bath, take up with hydrochloric acid and water, and after ascertaining by testing a small portion of the liquid that lime is absent (with ammonia and ammonium oxalate), return the small quantity of liquid used in making the test and precipitate the magnesium with sodium-ammonium phosphate and ammonia, and weigh it finally as magnesium pyrophosphate ( 104, 2). If the mineral water is so rich in calcium and magnesium that 2000 to 7000 grm. would yield too large a precipitate, the filtrate freed from the manganese and also the sulphur from the excess of ammonium sulphide, is heated, evaporated, and made up to 209.] ANALYSIS OF MINERAL WATERS. 249 1 litre, of which then an aliquot part, one-half or one-quarter, is used for the determination of the calcium and magnesium. 4. DETERMINATION OF THE SULPHURIC ACID, SODIUM, AND POTASSIUM. Acidulate with hydrochlroic acid 2000 to 4000 grm., or the contents of one or two bottles, of the water, evaporate, and sep- arate the silicic acid as in 3. The filtrate, which must not con- tain a large excess of hydrochloric acid, is then precipitated hot by cautiously adding barium chloride. The precipitate of barium sulphate is first weighed as it is, then warmed with hydrochloric acid and washed. Add a few drops of barium-chloride solution to the acid washings, evaporate almost to dryness, add some water, filter, collect the slight quantity of barium sulphate so obtained, and add it to the main bulk, and again weigh (132, 1). The weight so obtained is to be considered as correct, and from it the sulphuric add should be calculated. If a weighable quantity of barium sul- phate is found with the silicic acid it must be added to the main bulk. Evaporate the filtrate from the barium sulphate to dryness on a water-bath, take up the residue with water, and boil the solu- tion with a slight excess of milk-of-lime ( 153, 4, a, /?). Filter , precipitate the filtrate with ammonium carbonate and ammonia, and finally add a little ammonium oxalate. Evaporate to dryness the filtrate from the precipitate so obtained, drive off the am- monia salts by ignition in a platinum dish, and repeat the opera- tion to effect the separation of the magnesium (which is still pres- ent in slight quantities), using, however, carefully measured quan- tities of the reagents. After expelling the ammonia salts by gen- tly igniting, the alkali chlorides are finally weighed in a covered platinum dish. In order to separate the potassium chloride from the sodium chloride and the small quantity of lithium chloride present, con- vert them all into double platinum salts by adding platinic chlo- ride, treat with 80-per cent, alcohol, filter, wash with alcohol ( 152, 1, a), and dry on the filter. Transfer the potassium-platinum chloride to a small weighed platinum dish; dissolve the remainder 250 ANALYSIS OF WATER. [ 209. on the filter with boiling water, evaporate the whole to dryness, dry at 130, and weigh as potassium-platinum chloride. In order to ascertain if this is pure, treat it repeatedly with small quantities of cold water, pour the solution into a porcelain dish, add some platinic chloride, evaporate almost to dryness on a water-bath, treat with alcohol, filter, dissolve the small quantity of residual potassium-platinum chloride on the filter in some boiling water (after first washing it with alcohol and drying the filter), and evap- orate together with the main quantity of potassium-platinum chloride, dry at 130, and weigh. If the weight is not the same as that at first obtained, it shows that the potassium-platinum chloride first obtained contained some lithium- or sodium-platinum chloride. The last weighing is taken as the correct one, and the potassium calculated from it. The quantity of sodium chloride, and consequently that of the sodium, is found by subtracting the weight of the potassium chloride from the total weights of the alkali chloride after deducting that of the lithium chloride (the method of estimating which will be given further on). In order to be quite certain that the alkali chlorides contain no traces of alkaline earths, evaporate the solution of the sodium- lithium-platinum chloride to dryness, heat the residue in a cur- rent of hydrogen, treat with hydrochloric acid and water, filter off the liquid from the metallic platinum, and test it first witn sulphuric acid for barium, then with ammonium and ammonium oxalate for calcium, and finally with sodium-ammonium phos- phate for magnesium. If traces of the alkaline earths are still found, they are to be determined and their weight m the form of chlorides deducted from that of the total alkali chlorides. The amount of the alkalies combined with carbonic acid is de- termined indirectly with perfect accuracy by calculation of the results of the analysis, provided, of course, that this has been care- fully made. Of the direct methods which may be advantageously used in a preliminary examination of alkaline waters, I recom- mend the following: Boil 600 to 800 grm. of the water for a long time, filter, and wash the precipitate with hot water. Divide the filtrate mixed 209.] ANALYSIS OF MINERAL WATERS. 251 with the washings into two equal portions (or at least into aliquot parts), concentrate one portion, and in it volumetrically determine the alkali carbonate (together with the trace of calcium and the small quantity of magnesium present in it) according to 220; the other portion is used to determine the calcium and magnesium, in order to correct the result obtained with the first portion, as calcium carbonate and magnesium carbonate neutralize acids in the same way as the equivalent quantity of sodium carbonate. 5. DETERMINATION OF THE TOTAL CARBONIC ACID.* The flasks previously prepared at the spring ( 208, 7) serve for this purpose. Weigh them, and, if but a short time has elapsed between the filling and the analysis, heat them for some time in a water-bath ( 139, I, 6, a); if, however, they have already stood for a long time filled, the heating is unnecessary. Filter as much as possible of the clear liquid through a small folded filter t with- out disturbing the precipitate, and, without washing the filter, introduce it into the flask containing the precipitate and the re- mainder of the liquid; then determine the carbonic acid according to 139, II, e. In the case of waters rich in carbonic acid, and particularly if many determinations have to be made, the carbonic acid may be collected hi weighed GEISSLER'S potash bulbs (Fig. 46), with a soda-lime tube placed behind them. The frequent filling of the soda-lime tubes is avoided by renewing the potassa solution after every second operation. The results obtained leave nothing to be desired (Expl. No. 87). If the water from which the calcium-containing precipitate is obtained has been measured, multiply the number of c.c. taken by the specific gravity to obtain the weight in grammes of the water corresponding to the carbonic acid found. If the carbonic acid is to be determined hi mineral waters contained in bottles or jugs, a loss of carbonic acid will be una- * See also the exhaustive paper on The Estimation of Carbonic Acid in Water, by Jos. W. ELLMS and JAY C. BENEKER, Jour. Amer. Chem. Soc., xxiii. No. 6. Translator. f The liquid must be strongly alkaline, and must remain clear on adding calcium chloride. 252 ANALYSIS OF WATER. [ 209. voidable on drawing the corks, and particularly if the water i& highly charged with the gas. In such cases it is first necessary to determine the carbonic acid which escapes on drawing the cork, and then to determine that remaining dissolved in the water. Of the many methods of boring the stopper without loss of gas, that of FR. ROCHLEDER* is the simplest (Fig. 98). a is a cork-borer with a hole, b, in the side; the upper aperture of the borer is closed by a stopper in which is inserted, air-tight, a tube c. On introducing the borer into the cork, a short section projects below the lower side of the cork without allow- ing any gas to escape. Now connect the tube c with an apparatus for drying and collecting carbonic acid (described in Vol. I., p. 493, e), by means of a short rubber tube provided with a screw pinch-cock, then slowly turn the borer downwards. As soon as the opening, b, passes the cork, the gas begins to issue from the bottle, the stream being regulated by the pinch-cock. When no more gas issues, remove the bottle or jug, and draw air, freed from carbonic acid, through the tubes. The increase in weight of the absorption apparatus gives, together with the weight of the gas in the upper part of the bottle, the carbonic acid lost by the water on removal of the pressure. Immediately after disconnecting the bottle from the apparatus, siphon off the water from it, and determine the carbonic acid in the water according to 139, I, 6, a. 6. DETERMINATION OF THE IODINE, BROMINE, LITHIUM, BARIUM, AND STRONTIUM.! Evaporate the contents of a carboy (about 60 litres) in a tinned copper or polished iron vessel to about 4 or 5 litres, filter off the * Zeitschr. f. analyt. Chem., i, 20. f If the quantities of manganese or aluminium present are so small that they could not be determined in the water used in 3, they must be determined in this larger quantity; and so must also bases and acids (oxides of cassium,. 209.] ANALYSIS OF MINERAL WATERS. 253 alkaline liquid, and wash the residue with boiling water until the washings cease to have an alkaline reaction. For the sake of safety, the residue is examined spectroscopically to see that it no longer gives the lithium lines. The solution A serves for the determination of the iodine, bro- mine, and lithium; the residue B for the determination of the aluminium, manganese, barium, and strontium. A. The Aqueous Solution. Evaporate it until only a moist saLne mass remains, and while triturating with a pestle, add a considerable quantity 96-per cent, alcohol. Filter, and boil the residue thrice with alcohol of the same strength. Add two drops of strong potassa solution to the alcoholic solution and distil off the alcohol. Dissolve the residue so obtained in a little water, evaporate again until only a moist saline mass is obtained, and repeat the treatment with 96-per cent, alcohol as above. Again distil off the alcohol, and repeat the treatment of the residue once more as before. By this treatment there is finally obtained an alcoholic solution containing all the iodine and bromine and but a smah 1 quantity of alkali chlorides. Add to the solution two drops of potassa solu- tion, evaporate to dryness in a platinum dish, gently ignite the residue,* and completely extract with boiling water. If the solu- tion still has a brownish color, again add two drops of potassa solution and a very small quantity of potassium nitrate, evaporate, and again gently ignite the residue. On now extracting, a clear, colorless solution will be obtained. To this solution add carbon disulphide, acidulate with diluted sulphuric acid, cautiously add a small quantity of a sulphuric- rubidium, zinc, nickel, cobalt, copper, lead, thallium, and antimony, and boric, arsenous, arsenic, and titanic acids), if such are present in quantity sufficient to render their determination possible, and if sufficiently large supplies of water are not available. * If the residue is very strongly ignited, considerable iodine may be lost in consequence of the decomposing action of the chlorides on potassium iodide (UBALDINI, Compt. rend., XLIX, 306; Journ. f. prakt. Chem., LXXXIV, 191), whereas by gentty igniting in the presence of potassium hydroxide there is no loss of iodine. Compare FRESENIUS, Zeitschr. /. analyt. Chem., v, 318. 254 ANALYSIS OF WATER. [ 209. acid solution of nitrous acid, and shake; the carbon disulphide will take up the iodine and become violet-colored. It is separated from the aqueous liquid, washed, and the iodine determined in it by means of a very dilute sodium-thiosulphate solution of known strength ( 145, I, b, /?). From the liquid separated from carbon disulphide precipitate the bromine and chlorine as silver salts, and determine the bromine from the loss in weight on heating a weighed portion of the mixed silver bromide and chloride in a cur- rent of chlorine ( 169, I, a). Precipitate the excess of silver in the filtrate from the mixed silver bromide and chloride by means of hydrochloric acid, and reserve the filtrate. To determine the lithium (and some other substances present in small quantities in the aqueous solution A) there are used: a, the three saline residues insoluble in alcohol; /?, both filters (these must be incinerated) through which the solutions freed from organic matter and containing the iodides, bromides, and chlorides had been filtered; and f, the solution from which the excess of silver had been precipitated by hydrochloric acid. These are all mixed, some water added, then hydrochloric acid in slight excess, filtered (if necessary) into a flask of one or two litres capacity, filled up to the mark and shaken (the silicic acid filtered off may contain some titanic acid). To determine the lithium, an aliquot part of the solution is used; the quantity taken depends upon the quantity of lithium present, this being approximately ascertained by evaporating a small quantity of the original water and examining spectro- scopically. As a rule one-fourth of the solution is sufficient, corresponding to about 15 litres of water. In this portion the caesium, rubidium, and thallium may also be tested for. The remainder of the liquid is reserved for the detection or estima- tion of boric acid, and also for the detection of arsenic. a. Evaporate almost to dryness the measured portion of the solution for determining the lithium. Triturate the residue with a sufficient quantity of strong alcohol, filter, and repeatedly boil the residue with small quantities of strong alcohol until neither 209.] ANALYSIS OF MINERAL WATERS. 255 the residue of sodium chloride nor the residue from the last alco- holic extract gives the lithium spectrum. Distil off the alcohol from the alcoholic solution, add two drops of hydrochloric acid to the residue, dissolve it in water, and evaporate to a moist saline mass; repeat the treatment with strong alcohol, distil off again, and treat this residue exactly like the original one. The last time add to the alcohol half its volume of ether. The residue should always be examined spectroscopically to see that it is free from lithium. If any is still found, the treatment with boiling alcohol must be continued. Distil off the ether-alcoholic solution, moisten the residue with a little water, add a little hydrochloric acid, evaporate to dryness in a porcelain dish on a water-bath, take up with water, and, hi order to remove any phosphoric acid that may have been taken up by the water, add two drops ferric-chloride solution, then milk- of-lime in slight excess, boil, filter off the precipitate (consisting chiefly of magnesium hydroxide), and wash it with boiling water until it no longer gives a lithium reaction. To the filtrate add ammonium oxalate, wash and ignite the precipitate, dissolve it in hydrochloric acid, evaporate, and test a small portion of the resi- due spectroscopically for lithium. If this is still found to be pres- ent, dissolve the residue hi water, and again precipitate with am- monia and ammonium oxalate. Evaporate to dryness the filtrate (or both filtrates) from the calcium oxalate, drive off the ammonia salts, moisten the residue with hydrochloric acid, add a little water, evaporate to dryness on a water-bath, and repeat the treatment with milk-of-lime, etc., using small, very carefully measured quantities of reagents, and frequently testing the precipitates for lithium. After repeatedly driving off the ammonia salts, moistening with hydrochloric acid, and evaporating on the water-bath, precipitate the lithium finally as lithium phosphate ( 100), weigh it, and test it to see if it dis- solves in hydrochloric acid without leaving a residue, and whether the solution, somewhat diluted, yields a slight precipitate on supersaturating with ammonia in the cold. If a precipitate forms, dissolve it in hydrochloric acid, precipitate again with ammonia, 256 ANALYSIS OF WATER. [ 209. collect the precipitate, weigh, and deduct its weight, together with that of the small residue insoluble in hydrochloric acid, from the weight of the lithium phosphate. Of course the precipitates must be previously tested spectroscopicaUy to see that they are free from lithium. The filtrate from the lithium phosphate may serve for testing for ccesium, rubidium, and thallium, and even for their determina- tion, when the evaporation residues of larger quantities of the water are not available. For this purpose, heat the liquid to drive off any ammonia that may be present, add some ferric chloride to precipitate any phosphoric acid present, then cautiously neu- tralize with ammonia. Filter off the precipitate, which must be yellowish brown and not white, evaporate to dryness the filtrate, drive off the ammonia salts by gently igniting, dissolve the residue in a little hot water, precipitate with concentrated platinic-chloride solution, and boil the precipitate repeatedly with small quantities of water to free it from the greater part of the potassium-platinum chloride; reduce in a current of hydrogen at a low red heat, ex haust with boiling alcohol, and test the residue left on evaporating the alcoholic solution spectroscopically for caesium and rubidium; the undissolved part test for thallium.* In 60 litres of a mineral water there will scarcely ever be suffi- cient of these metals present to separate them and determine them quantitatively. Should this, however, happen, the mixture of potassium, rubidium, and caesium chloride, obtained by decom- posing the precipitate yielded by platinic chloride may be best separated by adding stannic-chloride solution to the concentrated hot solution to which quite a considerable quantity of hydrochloric acid has been added. The caesium is thus thrown down as csesium- * R. BOTTGER in this manner found thallium in the saline residue obtained on evaporating the Nauheim mother liquors. If insufficient platinic chloride is used to precipitate the extract of the saline mass made with 80-per-cent. alcohol, the potassium-platinum chloride obtained contains caesium and rubidium; an aqueous extract treated similarly yields potassium-platinum chloride containing thallium (Begluckwunschungsschrift des Frankf. physik. Vereins zur Jubelfeier des hundertjahrigen Bestehens der Senkenberg' schen Stiftung, 1863). : "* 209.] ANALYSIS OF MINERAL WATERS. 257 stannic chloride, in the form of a crystalline precipitate (STOLBA*), whereas potassium and rubidium remain in solution. The tin may be thrown down from the solution by means of hydrogen sulphide, and the potassium and rubidium in the filtrate converted into chlorides, and these metals indirectly determined by esti- mating the chlorine in the weighed mixture of chlorides ( 200). 6. The remainder of the solution, in an aliquot part of which the lithium was determined, may be used for testing for arsenic, and for determining the boric acid. Treat the solution, warmed to 70, with hydrogen sulphide for some time, and if any precipitate forms, test it for arsenic (and also antimony). Free the filtrate from hydrogen sulphide by a prolonged gentle heat (not boiling, however), add a slight excess of potassium carbonate, evaporate to dryness, extract the residue with alcohol and a little hydrochloric acid (the insoluble residue may contain titanic acid), make the filtrate strongly alkaline with potassa solution, distil off the alcohol, heat the residue wifh water and a little potassium carbonate (to precipitate the last trace of calcium), boil, filter, acidulate the nitrate with hydrochloric acid, separate the phosphoric and boric acids according to 166, 3, c (231), and determine the latter according to 136, I, 1, d (Vol. I, p. 466). B. The Residue Insoluble in Water. Cover the residue with water in a large porcelain dish, add hydrochloric acid in considerable excess, and also five drops diluted sulphuric acid. If any residue remains adhering to the vessel, remove it by means of a little diluted acetic acid, add the solution to the main bulk of the liquid, and evaporate to dryness. Treat the residue with hydrochloric acid and water, filter off the silicic acid, etc., boil the precipitate with a solution of sodium carbonate until the silicic acid appears to be dissolved, filter the solution (using a hot-water funnel), and wash the residue. (The silicic acid may be precipitated from the solution and tested for titanic acid.) Incinerate the filter with the residue, fuse with sodium * Zeitschr. f. analyt. Chem., xn, 440. 258 ANALYSIS OF WATER, [ 209. carbonate, boil the melt with water, and filter off the small residue of barium carbonate, etc. (Here, too, the silicic acid may be pre- cipitated from the solution and tested for titanic acid.) Wash the precipitate, dissolve in diluted hydrochloric acid, remove any traces of lead with hydrogen sulphide, evaporate the fluid (filtered off from the lead sulphide, if necessary) on the water-bath, take up the residue with water and several drops hydrochloric acid, and precipitate by adding a few drops diluted sulphuric acid. After allowing to settle for some time, filter, and mix the filtrate with three volumes of alcohol. If a precipitate forms, it is barium sulphate, or possibly calcium sulphate, and it must be kept. We will designate it as x. After collecting and washing the barium sulphate, allow it to remain in contact with a concentrated solution of ammonium carbonate for twelve hours in a funnel the stem of which has been closed by a stopper, or in a separatory funnel. Then remove the stopper, allow the liquid to run off, wash the precipitate, treat it with very dilute nitric acid (to remove any strontium that may be present now as carbonate), wash with water, dry, ignite, and weigh the now pure barium sulphate. The solution, containing nitric acid, and possibly also strontium, is kept. We will designate it as y. Largely dilute the filtrate from the silicic acid, treat it warm with hydrogen sulphide in order to precipitate any metals of the fifth and sixth groups that may be present,* filter, boil the filtrate with nitric acid, precipitate ferric oxide ( 160, B, 3, a), and slightly supersaturate the filtrate with ammonia. If a further small quantity of precipitate is thus obtained, free it from manganese by repeatedly dissolving in hydrochloric acid and precipitating with ammonia. Precipitate the manganese from the concentrated filtrate with ammonium sulphide as usual f (see 3, p. 248); and pre- * If a precipitate occurs, and if any of the metals of the fifth or sixth group are found, care must be taken to ascertain whether they may not have been derived from the vessel in which the water was evaporated. t If the ammonium-sulphide precipitate is dark-colored, it may contain nickel or cobalt, and even zinc also; the separation may be effected according to 160, B, 6. 209.] ANALYSIS OF MINEKAL WATERS. 259 cipitate the calcium, etc., in the filtrate with ammonium carbonate and ammonia. If the aluminium in 3 has not yet been determined, unite the larger precipitate obtained by basic precipitation with the smaller precipitate obtained by ammonia (and consisting chiefly of ferric hydroxide, but which contains the aluminium, and the residual silicic acid as well as titanic acid, if present), dissolve them, and in the solution determine the aluminium ac- cording to 3, p. 247. Collect the precipitate, consisting chiefly of calcium carbonate, wash, dissolve in nitric acid, add to the solution the above-men- tioned solution y, which may contain strontium, and evaporate to dryness, this operation being finally accomplished in a flask heated on a sand-bath and freed from its moist air by means of a water air-pump. Then treat the residue with ether-alcohol, in not too large a quantity, however, to dissolve the calcium nitrate. Dissolve the residue insoluble in ether-alcohol in water (any residual matter should be incinerated and examined spectroscopic- ally), evaporate to a small bulk, add a concentrated (1:4) solution of ammonium sulphate in excess, and set aside for twelve hours. Next collect the above-mentioned precipitate x, if any, on a small filter; then collect that produced by the ammonium sulphate, in doing which it is advisable to at first close the funnel at the bottom, so that the ammonium-sulphate solution may dissolve any calcium sulphate there may be in x. After the precipitate has been washed with ammonium-sulphate solution until the filtrate is no longer rendered cloudy by ammonium oxalate, dry and ignite the strontium sulphate. After being weighed, it must be examined spectroscopically. 7. DETERMINATION OF THE PHOSPHORIC ACID. The determination of the phosphoric acid may be combined with that of the ferric oxide, alumina, etc., in 3, and, if necessary, in the portion 6; it is far better, however, and safer to use for the determination the contents of a separate bottle (about 6 litres). Add hydrochloric acid, evaporate, separate the silicic acid, evap- orate the filtrate repeatedly with nitric acid almost to dryness, 260 ANALYSIS OF WATER. [ 209. dissolve the residue in nitric acid and water, precipitate with a solution of ammonium molybdate in nitric acid, and finally de- termine the phosphoric add as magnesium pyrophosphate ( 134, I, 6, -ft- 8. DETERMINATION OF THE AMMONIA. For determining the ammonia I, as a rule, use the following method: Add a small measured quantity of diluted hydrochloric acid to about 2000 grammes of the water, and evaporate with the greatest care to a small bulk in a tubulated retort. Now add through a funnel a sufficient quantity of a freshly prepared sodium- hydroxide solution,* the neck of the resort being inclined upwards, and prolong the boiling until the liquid has almost entirely evap- orated. Conduct the whole of the vapors passing off through a LJEBIG condenser and collect the distillate in a tubulated receiver containing a small quantity of water acidulated with hydrochloric acid, the tubulure being connected with a U-tube containing some water. Convert the ammonium chloride in the water in the receivers into ammonium-platinic chloride by evaporation with a measured quantity of platinic-chloride solution (99, 2). Make a control test, using like quantities of hydrochloric acid, platinic chloride, and alcohol, and deduct the platinic-chloride salt so ob- tained from that found in the first experiment; the difference gives that afforded by the water, and with great exactness. Instead of this method the simpler one proposed by BOUSSIN- GAULT f may also be satisfactorily used. It is carried out as follows : Heat about 10 litres of the water in a retort until about two- fifths have distilled off (in the case of saline waters a little soda solution or milk-of-lime must be added in order to insure all the ammonia passing over in the distillate). Now transfer this dis- tillate to a flask connected with a LIEBIG condenser, and distil off one-fifth; in this distillate determine the ammonia by adding * Should the water contain any notable quantity of organic matter, it is advisable to replace the sodium hydroxide by freshly ignited magnesia sus- pended in water, for the expulsion of the ammonia. f Compt. rend., xxxvi, 814; Pharm. Centralbl, 1853, 369. 209.] ANALYSIS OF MINERAL WATERS. 261 5 to 10 c.c. of very dilute sulphuric acid, and neutralizing the excess with soda-lye of which 5 c.c. should neutralize 1 c.c. of the sulphuric acid (comp. 99, 3). Now distil off another one-fifth, and in this determine the ammonia (if any) similarly. As a rule the first portion will contain all the ammonia. Regarding the determination of ammonia with NESSLER'S reagent see 205, 12 (p. 211). 9. DETERMINING THE NITRIC ACID. The determination of nitric acid in mineral waters is effected in precisely the same way as hi spring waters, comp. 205, 3 (p. 1 86). 10. DETECTION AND DETERMINATION OF THE CRENIC AND APOCRENIC ACIDS. Boil a fairly large quantity of the precipitate obtained on evaporating the water, for about one hour with potassa-lye, filter, acidulate the filtrate with acetic acid, and add ammonia; after twelve hours collect the precipitate of silica and alumina, which as a rule forms, again acidulate with acetic acid, and then add neutral cupric acetate. If a brownish precipitate forms, it is cupric apocrenate (which, according to MULDER, contains variable quantities of ammonia, and which, dried at 140, gave 42-8 per cent, cupric oxide). Filter, and to the filtrate add ammonium carbonate until the greenish color has changed to blue, and then warm gently. If a bluish-green precipitate forms, it is mercuric crenate, which, dried at 140, gave MULDER* 74-12 per cent, cupric oxide. 11. DETECTION AND DETERMINATION OF VOLATILE ORGANIC ACIDS. ScHERERf in his analysis of the Briickenau (Bavaria) mineral spring found also butyric, propionic, acetic, and formic acids * Further details regarding crenic and apocrenic acids are afforded by BERZELIUS (Lehrbuch der Chem., 4 Aufl., vin, 393 and 405), and also MULDEB (Journ. f. pract. Chem., xxxn, 321). t Annal. d. Chem. u. Pharm., xcix, 257. 262 ANALYSIS OF WATER. [ 209. substances which had not been observed before in mineral waters. Soon thereafter I found these acids, although present in traces, in the Weilbach sulphur water.* If a mineral water is to be tested for the presence of these acids, it must be used quite fresh, otherwise these acids may result from decomposition subsequent to collection of the water. The process employed by SCHERER for their de- termination was as follows: Evaporate a rather large quantity of the water (if no bicar- bonate is present, add first some sodium carbonate to alkaline reaction), and filter off the liquid from the precipitate. Cautiously acidulate the concentrated mother-liquor with sulphuric acid, and precipitate the chlorine with silver sulphate, taking care to leave a trace of chlorine present rather than an excess of silver. Distil the filtrate so long as the distillate has an acid reaction, saturate the distillate with baryta water, remove any excess of baryta with carbonic acid, boil, concentrate, filter, evaporate in a weighed dish to dryness, dry at 100, and weigh the barium salts of the volatile acids. Now extract the residue with warm alcohol; barium formate remains undissolved, and after it has been dried and weighed test it with silver solution and mercuric chloride. f Evaporate the alcoholic solution of the other barium compounds at a gentle heat, take up the greater part of the residue with a large quantity of water, and cautiously precipitate the barium with silver sulphate. Filter, and allow the filtrate to evaporate in the desiccator. As soon as a sufficient quantity of the silver salt has crystallized out, remove it from the liquid, dry it over sulphuric acid, and employ it for the determination of the equivalent. Fin- ally, allow the remainder of the silver solution to evaporate over sulphuric acid, press between blotting-paper, dry over sulphuric acid, and analyze. As a control test determine with sulphuric acid the barium in another portion of the barium salts yielded by the alcoholic solution. In this experiment the characteristic odor of the volatile fatty acid * Journ. f. prakt. Chem., LXX, 15. t Attention is called to the fact that the barium formate may contain barium nitrate. 209.] ANALYSIS OF MINERAL WATERS. 263 (propionic acid, butyric acid, etc.) may be recognized; and if the liquid has been sufficiently concentrated, and allowed to remain at rest for some time, the microscope will occasionally distinctly show minute fatty drops on the surface of the liquid. If only very small traces of the volatile acids are present, while the quantity of chlorides present is large, the precipitation of the chlorine with silver sulphate, as in SCHERER'S method, cannot be carried out at all, or is effected only with great difficulty. This occurred to me hi an examination of the Grindbrunnen, Frankfurt. A modification of SCHERER'S method was hence employed,* and this I would recommend for similar cases. Evaporate a rather large quantity of water (if necessary adding some sodium carbon- ate) to a small bulk, filter the strongly alkaline fluid, gradually add diluted sulphuric acid first to neutrality, and then until the liquid is slightly acid. Now distil the acidulous liquid until only a small quantity remains in the retort. Neutralize the slightly acid dis- tillate with baryta water, evaporate to dryness, and heat the resi- due with absolute alcohol. Evaporate the solution, and repeat the treatment with the hot absolute alcohol. On the evaporation of the alcohol, there are obtained the barium compounds of pro- pionic, butyric, etc., acids, which are readily soluble in alcohol, while the barium formate, difficultly soluble in alcohol, can be extracted from the residue with water, f 12. DETERMINATION OF OTHER ORGANIC MATTERS (RESINS, EXTRACTIVES). Besides the substances mentioned in 10 and 11, mineral waters may contain other organic matters. Those which may be ex- tracted by alcohol from the evaporation-residue of a mineral water are, as a rule, of a resinous nature, and are so put down ; others are insoluble in alcohol, but are dissolved out from the residue by water, and these are usually designated as extractive matters, * Zeitschr. f. analyL Chem., xiv, 323. - f 100 grammes of boiling absolute alcohol dissolve 0-0055 grm. barium formate; 0-0284 grm. barium acetate; 0-261 grm. barium propionate, and 1 1717 grm. barium butyrate (E. LUCK, Zeitschr. /. analyt. Chem., x, 185). 264 ANALYSIS OF WATER. [ 209. for lack of more accurate knowledge regarding their nature. Some- times also small quantities of organic matters remain in the residue after extraction with water and with alcohol; these are decom- position products which have formed during evaporation. To accurately detect or determine any resinous or extractive matter it is absolutely necessary that the water, during trans- portation, does not come into contact with the cork or rubber stopper; that during evaporation all contamination from dust be prevented; and that there be used perfectly pure alcohol, which, on evaporation, should not leave the slightest residue. // these pre- cautions are not observed resinous or extractive matters may be found which may not owe their origin to the mineral water. For the determination of these organic matters in the Grind- brunnen waters at Frankfurt the following method * was em- ployed, and it is recommended in similar cases : Evaporate to dryness a large volume of the water (10 to 20 litres) with the most scrupulous regard to cleanliness, the final stage being conducted with the greatest care, and then extract the residue, reduced to powder, with perfectly pure alcohol. There are thus obtained a solution, a, and a residue, b. Distil off the solution a, treat the resulting residue with water (in which the greater part dissolves), and pass through a small asbestos filter. If this retains a trace of resin, wash it with water, dry, dissolve in absolute alcohol, evaporate the solvent in a weighed platinum dish, weigh the residue, heat, and note the odor; weigh any in- combustible residue, and enter the difference in weight between the two as resin. Add the aqueous liquid filtered off from the resin to the residue b, exhaust the whole with water, acidulate the solution with diluted sulphuric acid, and gently heat for some time to drive out all the carbonic acid. Now add some freshly ignited lead oxide perfectly free from carbonate, evaporate to dry- ness, then add an excess of lead chromate to the residue, and sub- ject it to analysis by combustion ( 176). The humus-like sub- stance may be calculated from the carbon with approximate ac- * Zeitschr. /. analyt. Chem., xiv, 323. 210.] ANALYSIS OF MINERAL WATERS. 265 curacy by taking the figures given by FR. SCHULZE * for 100 parts of humus-like substance, viz. : 58 parts- carbon. Treat the residue, insoluble in alcohol and water, with diluted hydrochloric acid, Should the residue left contain organic matter, collect it on an asbestos filter, wash, ignite it with lead chromate ( 176), and calculate the insoluble humus-like substance from the carbon. 13. EXAMINATION OF THE GASES. 210. To examine the gases collected at the spring and transported to the laboratory in sealed tubes, whether expelled from the water by boiling ( 208, 10, a or b) or whether spontaneously disengaged at the spring ( 208, 11), proceed as follows: Fill with mercury f a graduated tube of the kind described in Vol. I, p. 29, Fig. 4, after first moistening the inside with a drop of water, then im- merse tne tube containing the gas hi the mercurial trough, break off the point, and by properly inclining the tube allow the gas to ascend into the graduated tube. After the volume of the gas has been carefully read off, the temperature and barometric pressure being duly noted, push up into the tube a ball of potassium hydrox- ide fused on the end of a platinum wire and moistened with water. J The potassium hydroxide must contain water of crys- tallization in addition to its water of hydration; and care must be also taken that the end of the wire does not project above the surface of the mercury, otherwise diffusion of the combined gas with the air will take place along the wire not in contact with the mercury. When the volume of gas no longer diminishes replace the moist ball of potassium hydroxide by another, and when ab- sorption finally ceases replace it again by a dry one, and remove * Jcmrn. f. prakt. Chem., XLVII, 241. t See footnote page 59. t Such balls are made by pouring fused crystallized potassium hydroxide into a bullet mold of about 6 mm. inner diameter, while the end of a platinum wire is inserted to about the middle. After cooling, the potassium hydroxide adheres fast to the wire. The neck which forms on the wire may be removed with a knife. 266 ANALYSIS OF WATER. [ 210. this after an hour, and read off the volume of gas. The gas ab- sorbed is carbonic acid; and in cases where it is present hydrogen sulphide also (which has already been determined, or may be de- termined from the potassium sulphide in the potassa ball, accord- ing to Vol. I, p. 569, B, a). The residual gas consists, as a rule, only of oxygen and nitrogen, and may be examined exactly as directed in the chapter on the Analysis of Atmospheric Air. If the presence of marsh gas is sus- pected the oxygen is removed. This is best effected by means of a ball of papier-mache fixed on a platinum wire and impregnated with a concentrated alkaline solution of potassium pyrogallate; if necessary the ball may be replaced after some time by a second one. After this operation also dry the gas by means of a potassium-hydroxide ball (BUNSEN). Now ascertain the composition of the residual gas,* which consists generally of either nitrogen alone, or of a mixture of nitrogen and marsh gas, by transferring it, wholly or in part, to a eudiometer (Vol. I, p. 29, Fig. 3), mixing it with 8 to 12 volumes of air and 2 volumes of oxygen (to guard against the formation of nitric acid), and trying to explode the mixture. If the attempt is unsuc- cessful add detonating gas, electrolytically prepared from water, to the mixture until this becomes explosive ; finally absorb the car- bonic acid generated, calculate from it the marsh gas, and deter- mine the nitrogen from the difference. The details of the process will not be here given, as they are minutely described in BUNSEN'S "Gasometry," which should be in the possession of every one en- gaged in gas analysis. To determine whether any carburetted hydrogen is present in the residual gas left after the carbonic acid has been absorbed, and to estimate its quantity, I have frequently made use of the following * Should the gas have contained but little oxygen there need be no fear that any appreciable trace of carbonic may be formed by the action of the oxygen on the potassium pyrogallate; if, however, considerable oxygen has been found, it is necessary, in order to avoid any error, to test for hydrocar- bons another portion of the original gas, from which the carbonic acid, but not the oxygen, has been removed (BOUSSINGAULT, CALVERT, CLOEZ, POLECK, Zeitschr. /. analyt. Chem., in, 347, and vin, 451. 210.] ANALYSIS OF MINERAL WATERS. 267 method with good results: Bend a narrow glass tube to an angle of 45, and introduce one limb into the cylinder containing the re- sidual gas confined over water; to the other limb fasten a rubber tube provided with a pinch-cock. An apparatus is now arranged as follows: Introduce a little potassa solution into a small U-tube, the outer limb of which carries a small tube bent at right angles and closed by a bit of rubber tubing provided with a screw pinch-cock. The other limb of the U-tube connect with a small U-tube filled with soda-lime; to this is now connected a thin piece of combustion tubing about 2 decimeters long, the middle part of which is filled with fine copper turnings strongly oxidized by ignition in oxygen, and rather tightly packed in a layer about 8 cm. long. Connect the tube in turn with a somewhat larger U-tube containing baryta water, and this again connect with a potassium-hydroxide tube, and finally with an aspirator. After the cock of the latter has been opened, to ascertain whether the joints are all air-tight, heat the copper turnings to redness with two gas-lamps, cautiously open the screw pinch-cock, and allow a current of air to pass slowly for five minutes through the apparatus. The baryta water must not be rendered turbid in the slightest degree by this operation; if this should happen, renew the baryta water after the first ignition, and repeat the experiment. When the baryta water remains clear connect the rubber tube, which is closed by a plain pinch-cock, with the small glass tube provided with the screw pinch-cock. As the former, which closes the U-tube leading to the cylinder, remains closed, no more air-bubbles can pass through the apparatus. Now slightly open the pinch-cock, and allow the gas to very slowly enter the cylinder. The quantity of gas is usually so small that it remains entirely in the first U-tube. After the gas has been entirely drawn in allow also some water to enter, and finally close the pinch-cock when the water just makes its appear- ance in the little tube behind it. Now close the screw pinch-cock, remove the rubber tube with the plain pinch-cock, then slightly open the screw pinch-cock, and allow a very slow current of pure air (taken from the open and filtered through cotton) to pass for a sufficient length of time over the red-hot cupric oxide. The 268 ANALYSIS OF WATER. [ 211. current of air carries with it the gas which has previously entered. If the latter contains carburetted hydrogen the baryta water is rendered turbid from the formation of barium carbonate. If the turbidity is sufficiently marked, the barium carbonate may be determined, and from this the quantity of marsh gas may be calculated. If the carbonic acid formed is to be collected in a weighed soda-lime tube, the apparatus described by me in the Zeitschr. f. analyt. Chem., Ill, 340, should be used. MODIFICATIONS REQUIRED WITH SALINE WATERS, I.E., WITH SUCH AS CONTAIN NO ALKALI BICARBONATE. 211. 1. DETERMINATION OF THE TOTAL FIXED CONSTITUENTS. If the total quantity of the fixed constituents is determined by the method detailed in 209, 1, there is a slight loss of magnesium chloride, as a small portion is decomposed by the water during evaporation, hydrochloric acid being evolved, and magnesia remaining. The error is, however, as a rule, scarcely appreciable, and may hence be usually disregarded, especially as the total salts found by direct evaporation never agrees accurately with the total constituents determined directly, and from causes already stated in 205, I, 9. To avoid the source of error noted we may adopt FR. MOHR'S suggestion to evaporate the water with the addition of a weighed quantity of ignited sodium carbonate, or, according to TILLMANN'S * method, to add a known quantity of potassium sulphate before evaporation. In the latter case the MgCl 2 and 2K 2 S0 4 form the double salt MgSO 4 -K 2 SO 4 , and also 2KC1. 2. DETERMINATION OF THE CALCIUM AND MAGNESIUM. If a mineral water contains alkali carbonate no soluble cal- cium or magnesium salt can be present, but all the calcium and magnesium found must be considered as carbonates dissolved by * Annal der Chem. u. Pharm., LXXXI, 369. 211.] MODIFICATIONS REQUIRED WITH SALINE WATERS. 269 carbonic acid, even though only a part of the calcium, and still less of the magnesium is precipitated on boiling the water. With saline waters, however, the case is different. These contain almost always calcium and magnesium carbonates, together with soluble calcium and magnesium salts. In order to determine in saline waters just in what proportions both bases are combined with car- bonic acid and other acids, it is necessary, in addition to the de- termination of the total calcium according to 209, 3, to separately determine the calcium remaining in solution on boiling the water; the portions of magnesium combined with carbonic and other acids may then be calculated (see 213).* Tare or weigh a flask of about 1500 c.c., introduce into it 1000 grm. of the mineral water, and boil for an hour, replacing the evaporated water from time to time by distilled water. When perfectly cold weight the flask and its contents, deduct the weight of the empty flask, and thus ascertain the weight of the boiled liquid. Now~ pass through a dry filter, without washing the pre- * The earlier method of determining the calcium precipitated and remain- ing dissolved or boiling, and which consisted in filtering the boiled water, thoroughly washing the precipitate with water, and determining the calcium in the precipitate and filtrate, I have discarded and replaced by the process above described. It will be readily understood that in both processes the calcium in the solution must be too high, while that in the precipitate must be too low, because the small quantity of ammonium chloride usually present in saline waters reacts with calcium carbonate on boiling, and also because calcium carbonate is not absolutely insoluble in water. The error caused by the latter becomes naturally the greater when the precipitated calcium car- bonate is washed. Under these circumstances the correction given in the method described may be neglected, as the water, after boiling, contains some calcium carbonate in suspension, so that its influence on the result is scarcely appreciable, it being so small, in fact, as to lie well within the limits of un- avoidable error. The determination of what portions of the magnesium are combined with carbonic acid, hydrochloric acid, sulphuric acid, etc., cannot be accurately effected by boiling the water and determining the magnesium in the precipitate and filtrate ; moreover, it is unnecessary, because the desired result is obtained on the calculation of the analysis. With waters containing calcium sulphate, however, this is not the case with certainty, because, as E. BOHLIG (Pharm. Centralb., xvm, 430) has shown, magnesium bicarbonate and calcium sulphate are decomposed on boiling into magnesium sulphate, calcium carbonate, and carbonic acid. According to my investigations, how- ever, this decomposition does not occur in waters rich in magnesium sulphate. 270 ANALYSIS OF WATER. [ 211. cipitate, weigh the filtrate, and in it determine the calcium by precipitation with ammonium oxalate as in 209, 3, and calculate the quantity remaining dissolved in 1000 grm. from the following consideration : Knowing the weight of calcium given by the weighed quantity of filtrate filtered off from the precipitate, how much calcium will the 1000 grm. of water retain in solution after boiling? If this determination is performed twice, perfectly concordant results will be obtained. That thcee are too high, because of the solubility of the calcium carbonate in water, is an error that cannot be well avoided. A correction can be made for this it is true, as we know that 1 part of calcium carbonate is soluble in 28,500 parts of water (Vol. I, p. 174), and I would recommend such a correction to be made, though it can make no claim to great ac- curacy, as the various soluble salts present in the mineral have an appreciable influence on the solubility of the calcium carbonate, but which it is difficult to estimate. 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 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 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 84701 12. Lime retained in solution after boiling Sum of the lime and strontia retained in solution, ex- pressed as carbonates 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 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 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 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 00692 To form calcium sulphate 0-01680 d. Magnesium bromide Bromine present (2) 0-002486 Combines with magnesium 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) 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 34627 h. Lithium chloride 00764 Lithia present (15) 00356 Corresponds with lithium 0-01807 Which combines with lithium 0-02163 i. Ammonium chloride Ammonium oxide present (19) 0-01065 Corresponds with ammonium . 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 . 54457 Which combines with magnesium 0-18429 To form magnesium chloride 0-72886 m. Calcium phosphate Phosphoric acid present (14). . . 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 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 00152 r. Silicic acid Silicic acid present (6) 0-02635 s. Free carbonic acid Total carbonic acid (5) 3-32925 Of this is combined to form neutral salts With lime (n) 0-66511 With magnesia (o) 0-01485 With ferrous oxide (p) 0-00879 With manganous oxide (q) 0-00058 0-68933 Remainder 2-63992 Of this is combined with monocarbonates forming bicarbonates 0-68933 Remainder, free carbonic acid 1-95059 280 ANALYSIS OF WATER. [ 213. 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 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 001266, calculated as strontium sulphate 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 . . 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,SO 4 ) and Anhydride (SO 3 ) corresponding to various specific gravities of aqueous Sulphuric Acid by BINEAU; calculated for 15 by OTTO. Specific ' gravity. Percentage of H^SO 4 . Percentage of SO 3 . Specific gravity. Percentage of H2S0 4 . Percentage of S0 3 . 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 to 66, with the corresponding specific gravities at 15, by J. KOLB.* Degree BAUME, Sp.gr. 80s. H2S0 4 . Degree BAUME. Sp.gr. S0 4 . HaSO,. 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 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 C. at 15 C. at C. at 15 C. 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 N 2 3 at at 15 HNO 3 N^Os at 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 P 2 O S . Sp. gr. at 15-5 C. Percentage of P 2 6 . Sp. gr. at 15-5 C. Percentage of P 2 6 . 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. 0-9992 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 Na 2 O, 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. We refill both burettes up to the zero-point. ft. Weigh off two portions of the pure, anhydrous sodium carbonate, weighing from 1 to 1-5 grammes each, introduce them into flasks of about 300 c.c. capacity each, and dissolve them in 100 to 150 c.c. of water each. f. Heat one of the solutions of sodium carbonate, color it * For a complete treatise on indicators, see " Indicators and Test Papers," by ALFRED I. COHN. JOHN WILEY & SONS, New York, 2d edition, 1902. 296 DETERMINATION OF COMMERCIAL VALUES. [ 215. faintly blue with litmus tincture, and run in from the burette acid in small portions at a time with constant agitation, until the liquid has become reddish violet. Now heat and maintain at a gentle boil for some time. The liquid becomes blue again, as the carbonic acid is expelled. Now run in more acid until the color becomes distinctly yellowish-red, boil for a few minutes, and then cautiously add from the burette soda solution until the liquid just appears blue. If this point has not been accurately hit, add some more acid and then soda solution until the right point is reached. After a few minutes, read off the height in both burettes and from the quantities of alkali solution used calculate, according to the proportion found in 2, a, the excess of the dilute acid em- ployed above that necessary to neutralize the sodium carbonate; deduct this excess from the total acid used, and thus obtain the acid required to saturate the weighed quantity of sodium car- bonate, and consequently the exact quantity of absolute acid con- tained in the dilute acid, since 1 mol. of sodium carbonate, or 106-1 grm., corresponds with 98-086 grm. sulphuric acid (H 2 S0 4 ), or 80-07 grm. sulphuric anhydride (SO 3 ), 72-916 grm. (2 mol.) hydrochloric acid (HC1), or 126-096 grm. (2 mol.) nitric acid (HNO 3 ), or 108-08 grm. nitric anhydride (N 2 5 ). An example will illustrate this: weight of sodium carbonate, 1-2 grm.; total hydrochloric acid used, 22 c.c.; total soda solution used, 1-2; hence 20 c.c. of the dilute acid corresponds to 19-5 c.c. soda solution. Since 19 5 c.c. of soda solution corresponds to 20 c.c. of the dilute hydrochloric acid, 1-2 c.c. soda solution will correspond to 1-23 c.c. of dilute acid. Therefore the quantity of acid required to saturate the sodium carbonate was 22 1 23 = 20 77 c.c. ; and this contains the hydrochloric acid equivalent to 1-2 grm. sodium carbonate, according to the proportion 106-1 : 72-916 :: 1-2 : x; z = 0-8247 grm. hydrochloric acid. But as 20-77 c.c. of the dilute acid con- tains 0-8247 grm. hydrochloric acid, 1000 c.c. will contain 39-71 grammes. .!' The second portion of sodium carbonate is treated in exactly the same way, and a comparison made as to whether the results 215.] ACIDIMETRY. 297 obtained are just or nearly like those obtained with the first portion. The comparison is best made by calculating the results of both experiments to 1 grm. sodium carbonate. A closer agreement than 0-1 grm. of acid content in 1000 c.c. cannot be expected, as under the conditions of the experiment, this corresponds to only 0-05 c.c. of the acid employed. For instance, if the first experi- ment gave 39-71 grm. and the second gave 39-8 grm. of hydro- chloric acid in 1000 c.c., there would be no cause for making a third experiment. If the difference, however, is considerably greater, i.e., if much more than 0-05 c.c. of the dilute acid per 1 grm. of sodium carbonate has been required, the experiment must be repeated with a fresh weighed portion of sodium carbonate. 3. Dilution of the Acid to Normal Strength. When the quantity of anhydrous acid in the dilute acid has been determined according to 2, the liquid must be dilute so that 1000 c.c. at 17-5 will contain the equivalent of the acid (H = 1-008) in grammes, and thus becomes a normal acid. Let us suppose that we found the 1000 c.c. to contain 39-71 grammes of hydrochloric acid in our first experiment and 39-8 grammes in our second, or a mean of 39 76 grammes. According to the equation 36 458 : 1000 ::39-76 : x; z= 1090 -57, we should have to dilute each 1000 c.c. of the hydrochloric acid with distilled water to measure 1090-57 c.c. This is simply and accurately done by filling a one-litre flask to the mark with the acid at a temperature of 17-5, carefully emptying it into a larger, dry flask in which the acid is to be preserved later, then measuring 66-3 c.c. of distilled water from a burette or pipette into the litre flask, shaking well, and pouring into the larger flask; after again shaking well, pour back half of the liquid into the litre flask, shake once more, and again pour back into the larger flask, and preserve for use after finally shaking again. Each time before use the flask should be shaken, because water evaporates in the half-filled flask and condenses in the upper part, mixing with the liquid when this is poured out, whereby this is rendered weaker in acid, while that remaining in the flask becomes so much the stronger. 298 DETERMINATION OF COMMERCIAL VALUES. [ 215. 4. Diluting the Soda Solution to Normal Strength. By normal soda solution is understood a solution of sodium hydroxide of which one volume suffices to neutralize one volume of normal acid, so that on mixing the two the last drop of the soda solution will render blue the normal acid reddened by litmus. 1000 c.c. of such a soda solution, measured at 17-5, will saturate 1 equivalent of a monobasic acid, expressed in grammes. Though the proportion in which the soda solution must be diluted may be readily determined from the relation already de- termined (2, a) between the original acid solution (2, 7-, the strength of which has now been accurately determined) and the soda solu- tion, the proportion may be more simply found by directly ascer- taining the relation between the soda solution and the recently prepared normal acid; i.e., to find out how much soda solution must be added to render distinctly blue 20 or 30 c.c. of the normal acid diluted with 100 c.c. water and faintly reddened with litmus tincture. Suppose we found that 27-4 c.c. of soda solution were required for 30 c.c. of normal acid; we should have to add to each 27-4 c.c. of soda solution 30-27-4=2-6 c.c. , and to each 1000 c.c. hence 94-9 c.c., distilled water. The addition of the water is made in exactly the same manner as described in preparing the normal acid (in 3). The bottle in which the normal soda solution is to be preserved should be closed, as recommended by MOHR, with a cork bearing a small bulb-tube of the form of a calcium-chloride tube. This tube is to be filled with soda-lime, and is provided with a narrow open tube (Fig. 99). Besides the normal soda solution, FIG. 99. other solutions five or ten times as dilute may also be prepared if desired. These solutions are 215.] ACIDIMETRY. 299 best prepared by introducing 50 c.c. of the normal solution (for example in the case of the more dilute solution) into a 500-c.c. measuring flask, and filling up to the mark with distilled water, shaking well occasionally. b. SPECIAL METHODS FOR PREPARING NORMAL ACID AND ALKALI SOLUTIONS. 1. Preparing Normal Sulphuric Add. To prepare this there is used a dilute sulphuric acid of specific gravity 1-032 to 1-033. Measure off accurately two portions of 20 c.c. each (best by means of a pinch-cock burette) of the acid, and determine the sulphuric acid hi both with barium chloride (132 I, 1). If the results of the two determinations are quite concordant, take the mean, and then dilute the sulphuric acid so that each 1000 c.c. will contain exactly 40-035 grm. anhydrous sulphuric acid (SO 3 ). Suppose we found that 20 c.c. of our liquid contained 0-840 sulphuric acid; then 1000 c.c. will contain 42 grammes. According to the proportion 40-035 : 1000 ::42:x; x= 1049-1, each 1000 c.c. of the acid must hence be diluted with dis- tilled water to measure 1049-1 c.c. The best method of diluting has already been described (p. 297). 2. Preparation of Normal Hydrochloric Add. To prepare this there is used a hydrochloric acid of specific gravity 1-018 to 1-019 (and which must leave no residue on evap- oration in a platinum or porcelain dish). Measure off accurately two portions of 20 c.c. each, and determine the hydrochloric acid in each by acidulating with nitric acid, precipitating with silver nitrate, and weighing the silver chloride precipitated ( 141, I, a). If the results of both experiments are quite concordant, take the mean, and calculate how much water to add to reduce the acid to normal strength. Supposing we had found 0-78 grm. hydro- chloric acid in the 20 c.c., then 1000 grm. would contain 39 grm.; hence, according to the equation 36-458:1000 :: 39: x; x =1069 -7, each 1000 c.c. would have to be diluted with distilled water to 300 DETERMINATION OF COMMERCIAL VALUES. [ 215. measure 1069-7 c.c. The method of diluting and preserving the solution has already been detailed (p. 297). 3. Preparation of Normal Oxalic Acid. An essential requirement for the preparation of this solution is perfectly pure oxalic acid free from potassium binoxalate, cal- cium oxalate, sulphuric acid, sulphates, etc. The method of pre- paring such an acid, as recommended by MOHR, is detailed in Vol. I, p. 144). REISCHAUER,* who, using MOHR'S method, did not obtain a perfectly pure oxalic acid, but one containing somewhat less potassium, recommends the analyst to prepare the oxalic acid himself by the action of nitric acid on starch. HABEDANKf dissolves commercial oxalic acid in the smallest possible quantity of hot absolute alcohol. After several hours the crystals which form in the liquid filtered off from the residual calcium oxalate and potassium binoxalate (the mother liquor may be used for dissolving a fresh quantity of oxalic acid) are collected, drained well, and recrystallized from boiling distilled water. F. STOLBA dissolves commercial oxalic acid in a 10- to 15-per cent, boiling hydrochloric acid, filters, cools the liquid rapidly under constant stirring, siphons off the mother liquor from the crystalline powder, and washes the latter with small quantities of cold water until the washings contain only very slight traces of hydrochloric acid; the oxalic acid is then recrystallized from boiling water. The method by which the oxalic acid is tested as to its purity and properly dried in order to give it the formula H 2 C 2 O 4 + 2H 2 O, and hence the equivalent 126-048, is detailed in 65, 1. It is to be noted that the solution must be tested for free sulphuric acid and sulphates (by observing whether the acid remains clear on adding hydrochloric acid and barium chloride ). As a rule the crystalline oxalic acid is used, i.e., H 2 C 2 O 4 + 2H 2 O. According to 0. L. ERDMANN'S recommendation, however, the * DINGLER'S polyt. Joum., CLXVII, 47; Zeitschr. f. analyt. Chem., 11, 426. f Zeitschr. f. analyt. Chem., xi, 282. % Ibid., XIIT, 50. Comp. O. BINDER, Ibid., xvi, 334. 215.J ACIDIMETRY. 301 acid may be dried to constant weight at 100, and freed from its water of crystallization, and thus converted into the anhydrous salt, H 2 C 2 O 4 . When the hydrated acid is used 63 024 grammes, or when the anhydrous salt is used, 45-008 grammes, are accurately weighed off, transferred to a litre flask and dissolved hi water by shaking, then diluted to the mark at 17-5, shaken again, and preserved where it is not exposed to direct sunlight.* The flask should be shaken each time before using, and for the reasons already stated. It must be remarked that only concentrated, hence also normal, oxalic-acid solutions can be preserved in the manner stated with- out suffering decomposition. More dilute solutions, e.g., deci- normal solutions, undergo a change, the oxalic acid being gradually decomposed (G. Biziof). According to NEUBAUER| the decom- position is accompanied by a moldy growth; this, however, can be entirely prevented by heating the decinormal solution in se- curely closed vessels for half an hour on a water-bath at 60 to 70. 4. Preparation of Normal Alkali. To use the normal acid solution prepared according to 6, we must have also a normal alkali solution. This is made from a carbonic-acid-free sodium-hydroxide solution of specific gravity 1-046 to 1-048. Its relation to the normal acid, and its dilution, to correspond accurately with this, are described on p. 298. II. VERIFICATION OF THE STANDARD ACID AND ALKALI. Although the standard solutions prepared as above must of course be correct, if the operations have been carefully performed, there is a greater sense of certainty if we ascertain their accuracy before using them. This is done by beginning a fresh experiment the object of which is to show whether equal volumes when mixed perfectly neutralize each other; we proceed thus: Weigh off two portions of 1 to 1 5 grammes each of chemically pure sodium carbonate perfectly dehydrated by gentle ignition * WITTSTEIX, Zeitschr. f. analyt. Chem., i, 496. f Ibid., ix, 392. J Ibid., ix, 392. 302 DETERMINATION OF COMMERCIAL VALUES. [ 215. and proceed as detailed on p. 295, f. The sodium carbonate theo- retically corresponding with the acid used is then calculated thus: 1000 : 106-08 (eq. of Na 2 CO 3 ) : : the c.c. of acid used : x. The result should correspond with the known weight of the sodium carbonate taken. Differences of from 0-001 to 0-003 grammes may be neglected, as they are within the limits of experi- mental error. It is usually advisable to repeat the experiment once more. Instead of using sodium carbonate for testing the normal hydro- chloric (or nitric) acid, pure Iceland spar may also be used. Pow- der the spar, dry it at 100, and weigh off two portions of 1 or 1 5 grammes each. Introduce one of the portions into a flask, and from a burette filled with hydrochloric acid to the zero-point, allow sufficient acid to gradually run in to dissolve the spar. Solution may be facilitated by gently heating, but a strong heat should be avoided as yet, as the liquid may contain more than a slight trace of hydrochloric acid, and in such a case some hydrochloric acid may be lost if a strong heat is applied. After solution is effected, add sufficient litmus tincture to just color the liquid faintly red, and from a burette filled to the zero-point run in soda solution until the liquid contains but a trace of free acid. Now expel the carbonic acid by gently boiling the liquid for several minutes, and finally add soda solution until the liquid just becomes blue. After deducting the soda used from the acid, proceed to calculate as above detailed. III. DETERMINATION OF FREE ACIDS. a. ORDINARY METHOD. As 1000 c.c. of normal soda solution correspond with the equiva- lent number of each monobasic acid expressed in grammes; 1000 c.c. of the one-fifth normal solution with one-fifth gramme-equiva- lent; 1000 c.c. of decinormal solution with one-tenth gramme-equiva- lent: there remains but little to be said regarding the process, as it is evident that according to the quantity of free acid to be neu- tralized one or other of the three alkali solutions is chosen, the se- lection being so made as to require about 15 to 30 c.c. of the soda 215.] ACIDIMETRY. 303 solution, the last portions of which must be very cautiously added until the liquid faintly reddened by litmus tincture is just rendered blue. In scientific investigations I recommend the weighing off of indeterminate quantities of the acids, as this can be far more easily done on a chemical balance, and the trifling calculation gives but little or no trouble. For instance, suppose we had weighed off 4-5 grammes of a dilute acetic acid, and 25 c.c. of normal soda solution had been required to neutralize this; the equation 1000 : 60 - 032 (eq. of C 2 H 4 O 2 ) : : 25 : x\ x=l- 5008 shows that the 4 . 5 grammes of dilute acetic acid weighed off con- tained 1-5008 grammes of hydrated acetic acid; and the further equation 4-5 : 1-5008 :: 100 : z; z = 33-35 gives the percentage of hydrated acetic acid in the liquid used. Or the calculations may also be made as follows: 4-5 grammes of acetic acid having required 25 c.c. normal alkali solution, for neutralization how much would be required had we weighed off 6-0032 grammes (one-tenth the gramme-equivalent of hydrated acetic acid) ? 4-5 : 6-0032 :: 25 :x; z = 33.55. It will be seen that in this case the number of c.c. found as x ex- presses at once the percentage of hydrated acetic acid, since 100 c.c. of normal alkali solution corresponds with one-tenth gramme- equivalent of pure hydrated acid, i.e., acetic acid of 100 per cent, strength. In technical analysis it is mare convenient if the number of c.c. or half c.c. of the normal soda solution used directly expresses, and without need of any further calculation, the percentage of the acid being tested. In order to accomplish this, the one-tenth or one- twentieth equivalent in grammes of the hydrated or anhydrous acid is weighed out, according as the number of c.c. or half c.c. of normal alkali used is to express the percentage of hydrated or anhydrous acid in the liquid examined. 304 DETERMINATION OF COMMERCIAL VALUES. [ 215. The following are the quantities for the more common acids: T*j5 eq. number 5^ eq. number of grammes. of grammes. Sulphuric anhydride (SO 8 ) 4 0035 2-0018 Sulphuric acid (H 2 SO 4 ) 4-9043 2-4521 Nitric anhydride (N 2 O 5 ) 5-404 2-702 Nitric acid (HNO 3 ) 6-3048 3-1524 Hydrochloric acid (HC1) 3-6458 1 8229 Oxalic acid, anhydrous (H 2 C 2 O 4 ) 4 - 5008 2-2504 Oxalic acid, crystallized (H 2 C 2 O 4 -2H 2 O). . 6-3024 3-1512 Acetic anhydride (C 4 H 6 O 3 ) 5-1024 2-5512 Acetic acid (C 2 H 4 O 2 ) 6-0032 3-0016 Tartaric acid (C 4 H 6 O 6 ) 7-5024 3-7512 As the weighing of small definite quantities, however, is far less accurate, it is better to weigh the half -equivalent in grammes (e.g., 20-018 grammes of sulphuric anhydride, or 24-521 grammec of the monohydrated sulphuric; 18-229 hydrochloric acid, etc.) in a 500-c.c. flask, to dilute with water (in the case of sulphuric acid the acid should be cautiously poured into half the water already contained in the flask), allowed to cool, if necessary, then accu- rately filled with water to the mark, shaken, and then 100 c.c. or 50 c.c. withdrawn with a pipette according as one-tenth or one- twentieth gramme-equivalent of acid is to be used. b. DEVIATIONS FROM THE PRECEDING METHOD. 1. At times it is preferred to use a soda solution of approxi- mately correct strength, rather than to prepare & normal soda solution, in which case its effective strength is ascertained by means of accurately measured quantities of normal acid. Of course a short rule-of-three calculation then becomes necessary. Suppose 18-5 c.c. of soda solution had been found to correspond to 10 c.c. normal sulphuric acid (i.e., y^-g- gramme-equivalent, or 0-40035 gramme of sulphuric anhydride), they will correspond equally with Y-J--0- gramme-equivalent of all other acids, and consequently with 0-60032 gramme acetic acid. For instance, had 12 e.c. of the soda solution been required to neutralize 10 grammes of vin- egar, the acetic acid contained in this would be found as follows: 18-5: 0-60032:: 12: x; z=0-3894; 215.] ACIDIMETRY. 305 and expressed in per cent. : 10:0-3894 : : 100 : x; z=3-894. 2. At times it is preferable to have the soda solution of such a strength that the number of c.c. or half-c.c. used to neutralize a definite quantity of acid should directly express the percentage of acid present. For instance, if we add 20 c.c. of water to 1000 c.c. of normal alkali solution, these 1020 c.c. will neutralize 51-024 grammes of anhydrous acetic acid, 1000 grammes will consequently neutralize 50 grammes of acetic anhydride. If, hence, we add to 10 grammes of vinegar (10 c.c. will do as well, as the sp. gr. of vinegar scarcely differs from that of water) sufficient of the soda solution diluted as just described, i.e., until the liquid colored with litmus tincture is just rendered blue, the c.c. of soda solution used, divided by 2, will express directly the percentage of acetic an- hydride in the vinegar tested.* 3. If the color of a liquid prevents the distinct recognition of the color change afforded by the litmus tincture added, red litmus paper or turmeric paper is used to indicate the neutrality point; i.e., the soda solution is added until a strip of the paper im- mersed in the liquid gives a faint alkaline reaction. As, however, in this process somewhat more alkali is used than when litmus tincture is employed, it is necessary, when making exact deter- mination, to make a correction for the excess. This is done by very cautiously adding to a volume of distilled water equal to that used in the experiment, just sufficient soda solution to give an alkaline reaction equal in intensity to that afforded in the experiment. The quantity of soda solution required to effect this is then deducted from that used hi the first experiment. This method is used in testing crude argol for its content of potassium bitartrate. If one-tenth equivalent-grammes, or 18-815 grammes, are weighed out, the c.c. of soda-lye used will directly express in per-cents. the potassium bitartrate present; as this quantity is too large, however, one-fourth of it may be taken, i.e., 4-7038 grammes, and the number of c.c. of soda solution used * Zeitschr. f. analyt Chem., i, 253. 306 DETERMINATION OF COMMERCIAL VALUES. [ 215. then multiplied by 4. In the analysis of crude tartar, it must be remembered that, on account of its high equivalent, a small dif- ference in the quantity of soda solution used will have a serious effect on the result. For instance, suppose 21 6 c.c. of soda solution were used in one case for 4-7038 grammes of tartar, while in a second 21-7 c.c. were used; the former would give a percentage of 21-6x4=86-4, while the latter would give 21-7x4 = 86-8. The argol should be in very fine powder; it should be heated with the water under constant stirring, and the soda solution added under constant heating until a drop of the liquid just gives a brownish spot on turmeric paper, or a blue one on red litmus paper. In a second experiment, almost the entire quantity of soda solution may be added at once, and then, after heating for a sufficiently long time, adding the soda solution drop by drop until the end reaction is reached. According to my investigations it is not proper to add an excess of soda solution, heat, add normal acid, and again add alkali until neutral, as this method gives, after subtracting the normal acid from the soda solution, too high a number for the soda solution, and consequently too high a result because the coloring matter combines with the soda. In accurate analyses the correction made as above described must not be omitted. That this method of analyzing tartar is suitable only when no other substances which afford an acid reaction (except potassium bitartrate) are present is of course readily understood.* 4. The titration of free (tribasic) phosphoric acid with normal alkali is not successful, because the so-called neutral salt, Na 2 HP0 4 , which has an alkaline reaction, and the acid salt, NaH 2 P0 4 , which has an acid reaction, do not neutralize each other, so that the acid reaction of one is observed along with the alkaline re- action of the other. When phosphoric acid is saturated with soda solution, it will be found that at a certain stage the liquid turns red litmus paper blue or blue litmus paper red. This point, which was observed already long ago in many urines, was termed by BAMBERGERf amphoter. Milk, too, shows a similar reaction * Comp. A. SCHEURER-KESTNER, Compt. rend., LXXXVI, 1024; Chem. Centralbl, 1878, 423. f Wurzburger medicin. Zeitschr., 1861, 93. 215-j ACIDIMETRY. 307 (SOXHLET*). Hence, if it is desired to titrate free phosphoric acid, or to determine how much base is still required to form the basic salt, NagPO 4 , the formation of a soluble alkaline phosphate must be prevented; i.e., the phosphoric acid must be removed from the liquid, and in the form of a compound of known composition. MALY| has based on this principle an acidimetric method of determining phosphoric acid, whether free or combined, and which gives satisfactory results. The phosphoric acid is precipi- tated as barium phosphate, Ba 3 (PO 4 ) 2 . The process is as follows: Measure the not too concentrated solution of the free phos- phoric acid, or of the neutral or acid alkali phosphate, into a flask, run in a measured quantity of semi- or one-fourth normal soda solution, more than sufficient to convert all the phosphoric acid into basic phosphate, then color with the indicator, add a suf- ficient quantity of barium chloride, heat, and titrate with semi- or one-fourth normal acid to just acid reaction. The liquid must be kept hot during the experiment. The barium phosphate floating in the liquid does not interfere with the tit-ration. Corallin (see below, 6, cc) is particularly recom- mended as the indicator to be used; one drop of a moderately concentrated solution suffices to color the liquid, and the precipitate also, a deep rose-red. Add the acid until the whole is milk-white, boil, and dissipate the pink .color, which again appears, by adding a drop or two of acid. The neutrality point is reached when, after boiling for a few- minutes, the mixture remains milk-white or has at most a yellowish tint. Deduct the c.c. of acid used from the c.c. of soda solution; the difference represents the quantity of alkali which was required by the phosphoric acid or phosphate to form the basic salt, Na s PO 4 . 5. For all ordinary analyses by saturation, litmus tincture prepared from good litmus (Vol. I, p. 145) answers perfectly. For especially accurate investigations, a litmus tincture prepared from purified litmus, or made in a different manner, is recommended * Journ. f. prakt. Chem., N. F., vi, 16. f Zeitschr. f. analyt. Chem., xv, 417. 308 DETERMINATION OF COMMERCIAL VALUES. [ 215. by different persons. BERTHELOT and A. DE FLEURIEU * add pure diluted sulphuric acid to concentrated, aqueous litmus tincture to acidity, expel the carbonic acid by boiling, add baryta water to alkalinity, pass in a little carbonic acid, boil once more, filter, and add to the filtrate one-tenth its volume of alcohol. WARTHA,| who pointed out that litmus frequently contains indigo, recom- mends the following process for preparing litmus tincture : Shake the commercial litmus with ordinary alcohol, and reject the cloudy, bluish-violet liquid. Then treat the residual litmus with distilled water for twenty-four to forty-eight hours, pour off the deeply colored liquid and evaporate it on the water-bath; treat the residue repeatedly with absolute alcohol acidulated with acetic acid, and evaporate this also. By this treatment, the residue becomes dehydrated and brittle. Powder it, exhaust the brown powder with absolute alcohol acidulated with acetic acid, and by this treatment remove a scarlet-red coloring matter which gives a purple-red, not blue, color with alkalies. Dissolve the brown coloring matter, insoluble in absolute alcohol, in water; filter the solution, evaporate to dryness on a water-bath, and repeatedly moisten with alcohol, and evaporate to drive off all the acetic acid. The residue dissolved in water affords a very sensitive litmus tincture. FR. MOHR| exhausts the litmus with hot dis- tilled water, evaporates the filtered solution, supersaturates with acetic acid (which causes evolution of carbonic acid), evaporates further to the consistency of a thick extract, introduces the mass into a flask, and treats it with a large quantity of 90-per-cent. alcohol. The blue coloring matter is thus precipitated, while a red coloring matter and potassium acetate dissolve. Filter, wash the precipitate with alcohol, dissolve the residual coloring matter in warm water, and filter. 6. Instead of litmus tincture, various other coloring matters may be used to detect the first excess of alkali when neutralizing * Zeitschr. /. analyt. Chem., v, 100. f Ber. der deutsch. chem. Gesellsch., ix, 217; Zeitschr. /. analyt. Chem. xv, 322. t Lehrbuch der Titrirmethode, 5. Aufl., 724. 215.] ACIDIMETRY. 309 an acid. As a whole, I prefer litmus tincture to all other indicators, although in certain cases other indicators possess advantages over it. In selecting these, it must be remembered that the power of distinguishing colors varies in different individuals, and that some eyes are better adapted for recognizing one tint, some another. Furthermore, the illumination has some influence, and indicators which cannot be advantageously used by daylight, may be well adapted for use by gaslight. When we further consider that every discoverer of a new indicator has his own particular liking for it, and that habituation to its use has a great influence, it may be readily understood how the literature of indicators may gradually become very extensive. In the following only the most essential of the indicators proposed are described.* aa. Cochineal Tincture.^ This was recommended by C. LucKowJ for acidimetric and alkalimetric purposes. It has a deep ruby- red color, which, on gradually diluting the tincture with the purest distilled water, becomes orange, then yellowish orange. By gaslight the color appears almost colorless. On adding the slightest trace of caustic alkali or alkali carbonate, or caustic alka- line earth, or of dissolved alkaline-earth carbonate, the liquid ac- quires a violet-carmine color. Cochineal tincture may be ad- vantageously used whenever, in the determination of free acid, free carbonic acid is naturally present or evolved during the de- termination. While carbonic acid interferes with the detection of the first trace of alkali when litmus tincture is used, and thus renders it necessary to expel the carbonic acid by heating the liquid, this is not the case to the same extent with cochineal tinc- ture, as the coloring matter of this is an acid carminic acid. Car- bonic acid is not, however, altogether without influence, as the * For a complete treatise on indicators, see "Indicators and Test Papers ", by ALFRED I. COHN. JOHN WILEY & SONS, New York. f The tincture is prepared as follows : Digest about 3 grammes of good cochineal in powder with 250 c.c. of a mixture of 3 to 4 volumes of distilled water and 1 volume alcohol at the ordinary temperature, and with frequent shaking, and then filter through Swedish filter paper. The tincture may be preserved well in closed bottles. J Journ, f. prakt. Chem., LXXXIV, 424; Zeitschr. f. analyt. Chem., i, 386. 310 DETERMINATION OF COMMERCIAL VALUES. [ 215. first drop of normal alkali imparts a violet color to distilled water to which some cochineal tincture has been added; but this is not the case if carbonic-acid water is first added. Salts of ammonia have no prejudicial influence on the results. If acetates are pres- ent, or salts of iron or aluminium, cochineal tincture cannot be used. In alkaline solution the carminic acid is decomposed by the atmospheric oxygen, so that an alkaline solution colored violet by cochineal becomes first discolored, then colorless. bb. Extract and Tincture of Logwood. These were recom- mended by POHL* and WILDENSTEIN.! The former used the commercial liquid extract of about 1-036 sp. gr. The latter prepares the tincture by splitting a sound piece of logwood free from splits or cracks, removes from the inner surfaces fine shavings by means of a plane, boils the shavings with distilled water, and mixes one volume of the concentrated decoction with one or two volumes of alcohol. The tincture must be protected from the action of light. The commercial ground logwood (Hcematoxylum campechianum) cannot be employed for the preparation of the tincture, as the desired red color is already imparted to it during the grinding by moistening with cal- careous spring-water. On adding extract or tincture of logwood to neutral liquids, these acquire a yellow color which, on adding an acid, remains yellow or becomes only slightly paler. On now neutralizing with an alkali, the slightest trace in excess of the latter causes a hand- some deep-red to purple-violet color to develop. The transition is very characteristic, and is very sharply observed even by lamp- light. POHL recommends extract of logwood particularly for the determination of free acid in wine (even in red wine, if sufficiently diluted) and in must. The logwood tincture cannot be used if even the slightest traces of oxides of the heavy metals (iron, copper, lead, tin, antimony, etc.) are present. It should be especially remarked that the coloring matter is * Journ. f. jyrakt. Chem., LXXXI, 59. f Zeitschr. /. analyt. Chem., n, 9. 115.] ACIDIMETRY. 311 very rapidly oxidized in alkaline solution under the influence of atmospheric oxygen. cc. Rosolic Add (Corallin). This is prepared by heating a mix- ture of 1 part of crystallized oxalic acid, 1J parts crystallized color- less phenol, and 2 parts concentrated sulphuric acid (all by weight) for five to six hours in a flask provided with an upright reflux condenser, and on an oil-bath heated to 140 to 150. The re- sulting dark, semi-fluid mass is poured into a large volume of water, when the rosolic acid separates in the form of a resinous mass, which is then boiled with water until free from the odor of phenol, and washed thoroughly with cold w T ater. The product so ob- tained, although not perfectly pure rosolic acid, is nevertheless perfectly well adapted for use as an indicator. It is dissolved in alcohol and the solution filtered. The deep-reddish-violet fluid colors water a reddish yellow; with a drop of normal acid the liquid becomes colorless, or very pale yellow, and with the slightest excess of alkali, a handsome reddish violet. A liquid so colored becomes pale yellow on the addition of also carbonic-acid water. Corallin is very well adapted for use as an indicator when free acids are to be neutralized by caustic alkalies. Carbonic acid, however, exerts a disturbing action if present. Neutral ammo- nium salts do not interfere with the reaction. dd. Phenolphtalein. This coloring matter, discovered by BAEYER,* was recommended by E. LUCK f as an indicator in vol- umetric analysis. It is prepared by heating a mixture of 10 parts phenol, 5 parts phtalic anhydride, and 4 parts concentrated sul- phuric acid for several hours at 120 to 130. The reddish mass so obtained is first boiled with water, and the resinous residue then boiled with benzene, whereby it is converted into a yellowish- white powder. The indicator is prepared by dissolving 1 part of phenolphtalein in 30 parts of 90-per-cent. alcohol. 1, or at most 2, drops of this solution are added to 80 to 100 c.c. of the liquid to be titrated. If the liquid is acid, it becomes at first opalescent, but becomes perfectly clear on stirring. Water or a dilute acid is not * Ber. d.deutsch. chem. Ges. zu Berlin, iv, 658 (1871). f Zeitschr. f. analyt. Chem., xvi, 332. 312 DETERMINATION OF COMMERCIAL VALUES. [ 215. colored by the indicator, but if an alkali is added, the slightest trace in excess develops an intensely purple-red color. On adding a drop of acid, the liquid again becomes colorless. The liquid reddened by an alkali is decolorized by carbonic acid; hence the presence of carbonic acid must be avoided, as it disturbs the re- action. The indicator cannot be used if ammonia salts are present. ee. Tropceolin. Under this name various dyes, discovered by Dr. O. WITT (Star Works, Brentford, near London), are found on the market. Two of them, bearing the numbers 00 and OOO, have been recommended as indicators by W. v. MILLER.* A 05- per-cent. aqueous solution, or a cold saturated alcoholic solution of the tropseolin OO is prepared; if 2 c.c. of the aqueous or several drops of the alcoholic solution are added to 50 c.c. water, a bright- yellow solution is obtained which is unchanged by free carbonic acid or bicarbonates, but which, on the addition of a dilute min- eral acid (as well as certain organic acids, particularly oxalic acid), becomes colored yellowish red, and with a large excess of acid, red. On adding an alkali the red color again changes to yellow. MILLER recommends this indicator especially because carbonic acid has no influence on the color change, and because with tropseolin solu- tion (best the alcoholic) free acid may be recognized and deter- mined in the presence of metallic salts. Ammonia salts have no disturbing effect on the reaction when tropseolin OO is used. Tropseolin OOO may be used just like tropseolin OO for the detection of free alkalies. One drop of a cold saturated aqueous solution of tropseolin 000 is added to the acid solution to be titrated; this develops a scarcely noticeable yellow color which, on adding an alkali, becomes red as soon as the alkali is present in excess. The color change is distinct and sharp. Ammonia salts have no disturbing effect on the reaction. If carbonic acid is present, tropseolin OOO cannot be used. The fact that the methods of preparing these two tropjeolins are not yet known is likely to stand in the way of the more general employment of these two indicators. * Ber. d. deutsch. chem. Gesellsch., xi, 460; Zeitschr. f. analyt. Chem., xvn, 474. 215.] . ACIDIMETRY. 313 IV. APPLICATION OF THE ACIDIMETRIC PRINCIPLE TO THE DETER- MINATION OF COMBINED ACIDS. a. The acidimetric principle may be frequently employed also for the determination of combined acids, particularly when the base is completely precipitated, and in a state of purity, by soda solution (or also sodium carbonate). For instance, acetic acid in iron mordant, or in verdigris, may be thus estimated: Precipitate the solution with a measured excess of normal soda solution (a solution of sodium carbonate of known strength), boil, filter, wash, concentrate the filtrate, add normal acid just to acidity, boil to expel the carbonic acid taken up by the soda during evaporation, and then titrate the liquid with soda solution, using litmus as the indicator, until a blue color develops. On deducting the acid used from the total soda solution used, the difference gives the soda solution neutralized by the acid contained in the substance (both combined and free). Of course trustworthy results can be ex- pected only when no basic salt is precipitated by the soda solution 6. If the salt contains a base precipitable by hydrogen sulphide, and a non-volatile acid having no action on hydrogen sulphide, conduct into the boiling solution hydrogen sulphide (according to WALCOTT GIBBS*) until decomposition is complete, filter, wash with hot water, allow to cool, dilute to a litre or half litre, and in an aliquot portion determine the free acid. If the acid is nitric or hydrochloric acid, add some sodium-potassium tartrate; this prevents the decomposing action of the nitric acid on the hy- drogen sulphide, and the volatilization of the acid. Salts of the alkalies and alkaline earths are without influence, if present; iron or aluminium salts must, however, be absent. This method can, of course, give accurate results only when the precipitated metallic sulphides are pure, i.e., free from any of the acids present. c. If the sulphuric acid in alum is to be titrimetrically deter- mined, it cannot be done by the direct addition of normal soda solution to saturation, because then basic aluminium sulphate is * Sillim. American Journ. [n], XLIV, 207; Zeitschr. f. analyt. Chem., vii, 94. 314 DETERMINATION OF COMMERCIAL VALUES. [ 215. precipitated, and the soda solution used up does not correspond to the sulphuric acid present. If, however, before adding the soda solution, an excess of barium chloride is added, as recommended by E. ERLENMEYER and LEWINSTEIN, this difficulty is avoided, as then pure aluminium hydrate is prepitated from the aluminium- chloride solution thus formed. If the aluminium salt as is the case with pure alum is a neutral salt, and if no free acid is present, the quantity of acid found gives also the quantity of alumina present, by calculating 1 equivalent of alumina for every 3 equivalents of acid. The easiest method of ascertaining whether an aluminium salt contains free acid, is, according to W. STEIN* by means of ultramarine paperf which is decolorized by free acid. Reliable results are also afforded by the use of freshly precipitated, carefully washed ammonium- magnesium phosphate, which was recommended for a similar pur- pose by ERLENMEYER and LEWINSTEIN. On adding an excess of the phosphate this is decomposed by neutral aluminium salts in such a manner as to afford a neutral liquid. The most convenient method, however, is to test with an alcoholic solution of tropseolin OO (see p. 312). d. The method in which, in many cases, a slight excess of a particular acid can be determined acidimetrically in conjunction with the gravimetric method, will be later on detailed under the analysis of calcium and lead acetates. * Zeitschr. f. analyt. Chem., v, 289. f STEIN (Zeitschr. f. analyt. Chem., vm, 450) prepares this paper by stir- ring ultramarine of suitable quality with carragheen (Iceland moss) jelly (1 part of the moss boiled with 30 to 40 parts of water), and spreading it evenly on unsized paper with a broad brush. It is advisable to prepare both a light- colored and dark-colored paper. The ultramarine may be considered to be suitable when the paper prepared from it is readily decolorized by diluted sulphuric acid, but is not affected by a neutral solution of alum which has been prepared by repeated precipitation with alcohol. 216.] ACIDIMETRY. 315 C. DETERMINATION BY SATURATING THE FREE ACID WITH AN ALKALINE LIQUID WITHOUT USING A COLORING MATTER AS AN INDICATOR. 216. Instead of titrating free acid with soda solution of known strength and determining the neutrality-point with litmus tincture, an ammoniacal copper solution may be used for this purpose, as recommended byKiEFER*; the neutrality-point is hi this case known by the turbidity which occurs the moment all the free acid is neutralized. The copper solution used for this purpose is pre- pared by adding ammonia to an aqueous cupric-sulphate solution until the precipitate of basic salt just redissolves. After the effective value of this solution has been determined by means of normal sulphuric or hydrochloric (not oxalic) acid, the copper solution can be used for the determination of all the stronger acids (excepting oxalic acid), provided the fluids are clear. As the precipitate of basic salt which characterizes the end reaction is not insoluble in the ammonia salt formed, but can hence form only when the solution is saturated with it, and as its solubility depends upon the degree of concentration and upon the presence of other salts, particularly ammonia salts (CAREY LEA f), the method lacks scientific accuracy. As the variations occasioned by the causes mentioned are inconsiderable,! the method still remains applicable for technical purposes, for which, in fact, it was originally proposed. KIEFER'S method is of particular use in cases in which free acid is to be determined in the presence of a neutral mineral salt with acid reaction, e.g., free sulphuric in the mother liquors of cupric sulphate, zinc sulphate, etc. It is advisable to determine the effective value of the ammoniacal copper solution before every fresh series of experiments. * Annal. d. Chem. u. Pharm., xcm, 386. t Chem. Neics, 1861, 195. J Compare my experiments on the subject in the Zeitschr. /. analyt. Chem., i, 108. 316 DETERMINATION OF COMMERCIAL VALUES. [ 217. D. DETERMINATION BY WEIGHING THE CARBONIC ACID EXPELLED FROM SODIUM BICARBONATE. 217. Weigh a portion of the acid to be tested in the flask A (Fig. 100), and if too concentrated, add sufficient water to have the liquid occupy about one-third the space in the flask. Next fill a small glass tube with sodium (or potassium) bicarbonate, and suspend it by a thread in the flask A, by pressing the thread between the stopper and the neck of the flask, the apparatus being arranged exactly as described in 139, d, Vol. I, p. 488. (The sodium or potassium bicarbonate used may contain sodium chloride, sulphate, etc., but must be free from carbonate, and the quantity used must be more than sufficient to saturate the acid in the flask.) Tare the flask on the balance, then raise the stopper slightly, allow the tube together with the thread to fall into the flask, and immediately reinsert the stopper air-tight. When this has been done, place the flask A in hot water (50 to 55) ; as soon as the renewed evolution of carbonic acid thus produced has again ceased, slightly open the wax stopper b on the tube a, re- move the flask from the water-bath, and apply suction to d by means of a rubber tube, until all the carbonic acid still in the apparatus is replaced by air. Suction is best applied by means of an aspirator or hydraulic air-pump. After cooling, again place the apparatus on the balance and restore the equilibrium with the proper weights. The sum of these gives the quantity of carbonic acid expelled. For every equivalent of acid used, one equivalent of carbon dioxide is obtained, thus: FIG. 100. 217-1 ACIDIMETRY. 317 NaHC0 3 +HN0 3 =NaN0 3 +C0 2 +H 2 O. The results are sat- isfactory.* If possible, the quantity of acid taken should be so adjusted as to yield 1 to 2 grms. carbon dioxide. This method is preferable to that described under B only when the liquid is so colored that the litmus reaction cannot be distinctly observed. Instead of determining the carbonic acid from the loss of weight, the method described in Vol. I, p. 493, may be used. E. METHODS USED FOR PARTICULAR ACIDS. Determining the Strength of Acetic Acid from its Solidifying point. FR. RUDORFF f recommends the determination of the solidifying- point for the valuation of highly concentrated acetic acid. The following table, based on his results, shows the relation of the temperature of solidification to the quantity of hydrated acetic acid: 100 parts of hydrated acetic acid are mixed with 100 parts of the mixture contain Solidifying temperature. 0-0 water 0-0 water + 16-70 0-5 " 0-497 " 15-65 1-0 " 0-990 " 14-80 1-5 " 1-477 " 14-00 2-0 " 1-961 " 13-25 3-0 " 2-912 " 11-95 4-0 " 3-846 " 10-50 5-0 " 4-761 " 9-40 6-0 " 5-660 " 8-20 7-0 " 6-542 ' 7-10 8-0 " 7-407 ' 6-25 9-0 " 8-257 ' 5-30 10-0 ' 9-090 ' 4-30 11-0 ' 9-910 ' 3-60 12-0 ' 10-774 ' 2-70 15-0 ' 13-043 ' -0-20 18-0 ' 15-324 ' 2-60 21-0 ' 17-355 ' 5-10 24.0 19.354 ' 7.40 * Compare "New Methods of Testing Potash and Soda, and of Determin- ing the Commercial Value of Acids and Manganese, ' ' by Drs. R. FRESENIUS and WILL. Edited by J. L. BULLOCK. TAYLOR & WALTON, 1843. f Bericht d. deutsch. chem. Gesellsch., in, 390; Zeitschr. /. analyt. Chem., X, 106. 318 DETERMINATION OF COMMERCIAL VALUES. [ 217. Table showing the percentages of Acetic Acid (HC 2 H 3 O 2 ) corresponding to vari* ous specific gravities of aqueous solutions of Acetic Acid, by MOHR. Specific gravity. Percentage of acetic acid (HC 2 H 3 2 ). Specific gravity. Percentage of acetic acid (HC 2 H 3 O 2 ). Specific gravity. Percentage of acetic acid (HC 2 H 3 2 ). Specific gravity. Percentage of acetic acid (HC 2 H 3 2 ). Specific gravity. Percentage of acetic acid (HC 2 H 3 2 ). 0635 100 1-0735 80 1-067 60 1-051 40 1-027 20 0555 99 1-0735 79 1-066 59 1-050 39 1-026 19 0670 98 1-0732 78 1-066 58 1-049 38 1-025 18 0680 97 1-0732 77 1-065 57 1-048 37 1-024 17 0690 96 1-0730 76 1-064 56 047 36 023 16 0700 95 0720 75 1-064 55 046 35 022 15 0706 94 , -0720 74 1-063 54 045 34 020 14 0708 93 -0720 73 1-063 53 044 33 018 13 0716 92 -0710 72 1-062 52 042 32 017 12. 0721 91 0710 71 1-061 51 041 31 016 11 0730 90 0700 70 1-060 50 1-040 30 015 10 0730 89 0700 69 1-059 49 1-039 29 013 9 0730 88 0700 68 1-058 48 1-038 28 1-012 8 0730 87 0690 67 1-056 47 1-036 27 1-010 7 -0730 86 0690 66 1-055 46 1-035 26 1-008 6 0730 85 0680 65 1-055 45 1-034 25 1-007 5 1-0730 84 0680 64 1-054 44 1-033 24 1-005 4 1-0730 83 0680 63 1-053 43 1-032 23 1-004 3 1-0730 82 0670 62 1-052 42- 1-031 22 1-002 2 1-0732 81 0670 61 1-051 41 1-029 21 1-001 1 In determining the solidifying-point it is necessary to take care that only a little of the acid separates. This is accomplished with the most certainty by cooling the fluid to about 1 below the approximately determined solidifying-point, and then throwing in -a small fragment of solid hydrated acetic acid and stirring, and thus causing the separation of the hydrated acetic acid. The temperature is thus caused to rise to the solidifying-point of the mixture. Small quantities of solid acetic acid are readily pro- cured by introducing a small quantity of glacial acetic acid into a small test-tube, and with it stirring a mixture of cold water with ammonium chloride, ammonium nitrate, or potassium sulpho- cyanide. 218.] ALKALIMETRY. 319 2. DETERMINATION OF CAUSTIC ALKALI AND ALKALI CARBONATE (ALKALIMETRY.) A. ESTIMATION OF POTASSA, SODA, POTASSIUM AND SODIUM CAR- BONATES, OR AMMONIA, FROM THE SPECIFIC GRAVITY OF THEIR SOLUTIONS. 218. In pure or nearly pure solutions of hydrated soda or potassa, or of ammonia, the percentage of alkali may be estimated from the specific gravity of the solution. TABLE I. Potassa and Potassium Hydroxide in Potassa Solution at various specific gravities, by SCHIFF and TUNNERMANN, calculated by GERLACH.* Amount in 100 parts by weight of solution. Potassa, (K 2 0), sp. gr. at 15. Potassium hydrate, (KOH) sp. gr. at 15. Amount in 100 parts by weight of solution. Potassa (K 2 0), sp. gr. at 15. Potassium hydrate, (KOH), sp. gr. at 15. 1 010 009 36 1-455 1-361 2 020 017 37 1-460 1-374 3 030 025 38 1-475 1-387 4 039 033 39 1-490 400 5 048 041 40 1-504 -411 6 058 049 41 1-522 425 7 068 058 42 1-539 438 8 078 065 43 1-564 450 9 089 074 44 1-570 462 10 1-099 083 45 1-584 475 11 1-110 092 46 1-600 488 12 1-121 110 47 1-615 499 13 1-132 111 48 1-630 511 14 1-143 119 49 1-645 527 15 1-154 128 50 1-660 -539 . 16 1-166 137 51 1-676 552 17 178 146 52 1-690 565 18 1-190 155 53 1-705 578 19 1-202 166 54 1-720 1-590 20 1-215 177 55 1-733 1-604 21 1-230 188 56 1-746 1-618 22 1-242 198 57 1-762 1-630 23 1-256 209 58 1-780 1-641 24 1-270 220 59 1-795 1-655 25 1-285 1-230 60 1-810 1-667 26 1-300 1-241 61 1-682 27 1-312 1-252 62 1-695 28 326 1-264 63 1-705 29 340 1-278 64 718 30 355 1-288 65 729 31 370 1-300 66 740 32 385 1-311 67 751 33 403 1-324 68 .768 34 418 1-336 69 70 35 431 1-319 70 1-790 Zcitachr. f. analyt. Chem., vm, 279. 320 DETERMINATION OF COMMERCIAL VALUES. [ 218. TABLE Ha. Soda, (Na 2 O), and Sodium Hydroxide, (NaOH), in soda solutions at various specific gravities, by SCHIFF. Calculated by GERLACH.* Quantity in 100 parts by weight of solution. Soda, (Na 2 0), sp. gr. at 15. Sodium hydroxide, (NaOH), sp. gr. at 15. Quantity in 100 parts by weight of solution. Soda, (Na 2 0), sp. gr. at 15. Sodium hydroxide, (NaOH), sp. gr. at 15. 1 1-015 1-012 36 1-500 -395 2 1-020 1-023 37 1-515 -405 3 043 1-035 38 1-530 -415 4 058 1-046 39 1-543 426 5 074 1-059 40 1-558 437 6 089 1-070 41 1-570 447 7 104 1-081 42 1-583 456 8 119 1-092 43 1-597 -468 9 132 103 44 1-610 478 10 145 115 45 1-623 488 11 160 126 46 1-637 1-499 12 175 137 47 650 1-508 13 1-190 148 48 663 1-519 14 1-203 159 49 -678 1-529 15 1-219 170 50 -690 1-540 16 1-233 1-181 51 -705 1-550 17 1-245 1-192 52 1-719 1-560 18 1-258 1-202 53 1-731 1-570 19 1-270 1-213 54 1-745 1-580 20 1-285 1-225 55 1-760 1-591 21 1-300 1-236 56 1-770 1-601 22 1-315 1-247 57 1-785 1-611 23 1-329 1-258 58 1-800 1-622 24 1-341 1-269 59 1-815 1-633 25 1-355 1-279 60 1-830 1-643 26 1-369 1-290 61 1-654 27 1-381 1-300 62 1-664 28 1-395 1-310 63 674 29 1-410 1-321 64 684 30 1-422 1-332 65 695 31 1-438 1-343 66 705 32 1-450 1-351 67 715 33 1-462 1-363 68 726 34 1-475 1-374 69 1-737 35 1-488 1-384 70 1-748 * Zeitschr. f. analyt. Chem., viu, 279. I 218.] ALKALIMETRY. 321 TABLE 116. Percentages of Anhydrous Potassa, (K 2 O), corresponding to different specific gravities of solution of potassa. DALTON. TUNNERMANN (at 15). Specific gravity. Percentage of anhydrous potassa. Specific gravity. Percentage of anhydrous potassa. Specific gravity. Percentage of anhydrous potassa. 1-60 46-7 1-3300 28-290 1 1437 14-145 1-52 42-9 1-3131 27-158 1 1308 13-013 1.47 39-6 1-2966 26-027 1-1182 11-882 1-44 36-8 1-2803 24-895 1 1059 10-750 1-42 34-4 1-2648 23-764 1-0938 9-619 1-39 32-4 1-2493 22-632 1-0819 8-487 1-36 29-4 1-2342 21-500 1-0703 7-355 1-33 26-3 1-2268 20-935 0589 6-224 1-28 23-4 1-2122 19-803 0478 5-002 1-23 19-5 1 1979 18-671 0369 3-961 1-19 16-2 1 1839 17-540 0260 2-829 1-15 13-0 1-1702 16-408 0153 1-697 1-11 9-5 1-1568 15-277 0050 0-5658 1-06 4-7 TABLE He. Percentages of Anhydrous Soda, (Na^jO), corresponding to different specific grav- ities of solution of soda. DALTON. TUNNERMANN (at 15). Specific gravity. Percent- age of anhydrous soda. Specific gravity. Percent- age of anhydrous soda. Specific gravity. Percent- age of anhydrous soda. Specific gravity. Percent- age of anhydrous soda. 1-56 41-2 1-4285 30-220 -2982 20-550 1-1528 10-275 1-50 36-8 1-4193 29-616 -2912 19-945 1-1428 9-670 1-47 34-0 1-4101 29-011 -2843 19-341 1-1330 9-066 1-44 31-0 1-4011 28-407 2775 18-730 1-1233 8-462 1-40 29-0 1-3923 27-802 2708 18-132 1-1137 7-857 1-36 26-0 1-3836 27-200 2642 17-528 1-1042 7-253 1-32 23-0 1-3751 26-594 2578 16-923 1-0948 6-648 1-29 19-0 1-3668 25-989 2515 16-319 1-0855 6-044 1-23 16-0 1-3586 25-385 1-2453 15-714 0764 5-440 1-18 13-0 1-3505 24-780 1-2392 15-110 0675 4-835 1-12 9-0 1-3426 24-176 1-2280 14-506 0587 4-231 1-06 4-7 3349 23-572 1-2178 13-901 -0500 3-626 3273 22-967 1-2058 13-297 0414 3-022 3198 22-363 1 - 1948 12-692 0330 2-418 3143 21-894 1-1841 12-088 0246 1-813 3125 21-758 1-1734 11-484 1-0163 1-209 3053 21-154 1 1630 10-879 1-0081 0-604 322 DETERMINATION OF COMMERCIAL VALUES. [ 2l8~ TABLE III. Anhydrous Potassium and Sodium Carbonates in aqueous solutions at various? specific gravities, by GERLACH.* Amount in 100 parts by weight of the solution. Potassium carbonate, sp. gr. at 15. Sodium carbonate, sp. gr. at 15. Amount in 100 parts by weight of the solution. Potassium carbonate, sp. gr. at 15. Sodium carbonate, sp. gr. at 15.. 1 1-00914 01050 27 1-26787 2 1-01829 02101 28 1-27893 3 1-02743 03151 29 1-28999 4 1-03658 04201 30 1-30105 5 1-04572 -05255 31 1-31261 6 1-05513 1-06309 32 1-32417 7 1-06454 1-07369 33 1-33573 8 1-07396 1-08430 34 1-34729 9 1-08337 1-09500 35 1-35885 10 1-09278 1-10571 36 1-37082 * 11 1 10258 1-11655 37 1-38279 12 1-11238 1 - 12740 38 1-39476 13 1-12219 1 - 13845 39 1-40673 14 1-13199 1 - 14950 40 1-41870 15 1-14179 41 1-43104 16 1-15200 42 1-44338 17 1 16222 43 1-44573 18 17243 44 1-46807 19 1 - 18265 45 1-48041 20 1 - 19286 46 1-49314 21 20344 47 1-50588 22 1-21402 48 1-51861 23 22459 49 1-53135 24 1-23517 50 1-54408 25 1-24575 51 1-55728 26 1-25681 52 1-57048 TABLE IVa. Ammonia, (NH 3 ), in Solutions of Ammonia of various specific gravities, by CARIUS, calculated by GERLACH.* Amount Amount Amount Amount in 100 parts by weight of solu- Ammonia, sp. gr. at 16. in 100 parts by weight of solu- Ammonia, sp. gr. at 16. in 100 parts by weight of solu- Ammonia, sp. gr. at 16. in 100 parts by weight of solu- Ammonia* sp.gr. at tion. tion. tion. tion. 1 0-9959 10 0-9593 19 0-9283 28 0-9026 2 0-9915 11 1-9556 20 0-9251 29 0-9001 3 0-9873 12 0-9520 21 0-9221 30 0-8976 4 0-9831 13 0-9484 22 0-9191 31 0-8953 5 0-9790 14 0-9449 23 0-9162 32 0-8929 6 0-9749 15 0-9414 24 0-9133 33 0-8907 7 0-9709 16 0-9380 25 0-9106 34 0-8885 8 0-9570 17 0-9347 26 0-9078 35 0-8864 9 0-9631 18 0-9314 27 0-9052 36 0-8844 * Zeitschr ./. analyt. Chem , vin, 279. 219.] ALKALIMETRY. TABLE IVb. 323 Percentages of Ammonia, (NH 3 ), corresponding to different specific gravities of solution of ammonia at 16 (J. OTTO). Specific gravity. Percentage of ammonia. Specific gravity. Percentage of ammonia. Specific gravity. Percentage of ammonia. 0-9517 12-000 0-9607 9-625 0-9697 7-250 0-9521 11-875 0-9612 9-500 0-9702 7-125 0-9526 11-750 0-9616 9-375 0-9707 7-000 0-9531 11-625 0-9621 9-250 0-9711 6-875 0-9536 11-500 0-9626 9-125 0-9716 6-750 0-9540 11-375 0-9631 9-000 0-9721 6-625 0-9545 11-250 0-9636 8-875 0-9726 6-500 0-9550 11-125 0-9641 8-750 0-9730 6-375 0-9555 11-000 0-9645 8-625 0-9735 6-250 0-9556 10-950 0-9650 8-500 0-9740 6-125 0-9559 10-875 0-9654 8-375 0-9745 6-000 0-9564 10-750 0-9659 8-250 0-9749 5-875 0-9569 10-625 0-9664 8-125 0-9754 5-750 0-9574 10-500 0-9669 8-000 0-9759 5-625 0-9578 10-375 0-9673 7-875 0-9764 5-500 0-9583 10-250 0-9678 7-750 0-9768 5-375 0-9588 10-125 0-9683 7-625 0-9773 5-250 0-9593 10-000 0-9688 7-500 0-9778 5-125 0-9597 9-875 0-9692 7-375 0-9783 5-000 0-9602 9-750 B. DETERMINATION OP THE TOTAL CAUSTIC ALKALI AND ALKALI CARBONATE IN A SUBSTANCE. I. VOLUMETRIC METHODS. a. Method of DESCROIZILLES and GAY-LUSSAC, slightly nidified. 219. The principle of this method is the converse of that on which the acidimetrie method described 215 is based, i.e., if we know the quantity of an acid of known strength required to saturate an unknown quantity of caustic potassa or soda, or of potassium car- bonate or sodium carbonate, we may readily calculate from this the amount of alkali present. This method requires but one solution of known strength- standard sulphuric acid. This is now almost generally made of such a strength that 50 c.c. of it will saturate 5 grm. of pure, anhy- drous sodium carbonate. 324 DETERMINATION OF COMMERCIAL VALUES. [ 219. The method of preparing and using it is as follows: a. Mix about 60 grm. of concentrated sulphuric acid with 500 c.c. of water, or 120 grm. with 1000 c.c. water, and allow to cool. b. Accurately weigh off 5 grm. of pure, anhydrous sodium car- bonate, introduce it into a flask, dissolve it in about 200 c.c. of water, and color the solution distinctly blue with a measured quantity (about 1 c.c.) of violet litmus tincture* (see p. 295, d). N.B. This method is intended for the use of those who are not accustomed to weigh on fine analytical balances. Where chemical balances are used, as is generally the case in chemical laboratories, it is far better to gently ignite 4-5 to 5 grm. of the sodium carbonate in a platinum crucible, then to dry under an exsiccator, and to finally weigh the crucible accurately. The contents of the crucible are now introduced into the flask, the crucible weighed once more, and the quantity of sodium car- bonate transferred to the flask accurately ascertained from the difference in the two weighings. This process is far more easily performed by the skilled chemist than the other, and yields much more trustworthy results, since the weighing is effected with covered crucibles. If several portions are to be consecutively weighed, the ignited salt is transferred while still hot to a test- tube provided with a stopper, weighed, a suitable quantity shaken out, the tube weighed again, etc. The potash or soda to be subsequently examined is to be treated in the same man- ner as the pure sodium carbonate. c. Fill a burette (preferably one holding 50 c.c.) .to the zero- point with the cooled acid, and allow enough of it to flow into the soda solution until saturation is complete (see below). This' experiment it is better to repeat. If less than exactly 5 grm. of sodium carbonate were taken, it is necessary to calculate from the results obtained just how much acid would have been required for 5 grm. of sodium carbonate. * Regarding the use of other indicators, see page 309 ; also " Indicators and Test Papers ", by ALFRED I. COHN. JOHN WILEY & SONS, New York. 219.] ALKALIMETRY. 325 d. Dilute the remainder of the acid with water so that 50 c.c. of it will exactly neutralize 5 grm. of sodium carbonate. Had 45 c.c. of the acid, for instance, been required to saturate 5 grm. of sodium carbonate, then 5 volumes water would have to be added for every 45 volumes of the acid. The dilution is effected in the manner described on p. 297. I urgently recommend that the acid, after dilution, be once more tested in the manner described above. e. The standard acid thus prepared should be preserved in well-stoppered vessels, and should be well shaken before every fresh series of experiments (p. 297). It serves for the examination of soda, potash, and caustic alkalies; the number of half-c.c. used gives directly the percentage of alkali carbonate or caustic alkali provided the experiment be made with a weighed quantity of the substance equivalent to 5 grm. of sodium carbonate. The following table gives the equivalent quantities: 50 c.c. of the standard acid saturates 5 grm. Na^CO, " " " " " " " 2-926 " NajO " " " " " " " 6-515 " K 2 CO 3 " " " " " " " 4-441 " K 2 O Accordingly, if 6*515 grm. potassium carbonate mixed with potassium salts having a neutral reaction be taken, the number of half-c.c. used gives directly the percentage of alkali expressed as potassium carbonate; if 4'441 grm. be taken, the number of half-c.c. of the standard acid gives the percentage of alkali ex- pressed as anhydrous caustic potassa, K 2 O, etc. When examining substances poor in caustic alkali or alkali carbonate, a multiple, i.e., twice, thrice, ten times, etc., of the quantities above stated should be taken, and the number of half-cc. of acid used divided by the corresponding number. /. Regarding the determination of the saturation -point, this is easily done in the case of caustic alkalies; but with alkali car- bonates the carbonic acid liberated changes the color of the liquid to a wine-red and causes some difficulty. This may be overcome in two ways. a. When sufficient of the standard acid has been added to im part a wine-red color to the cold, or even previously heated solu- 326 DETERMINATION OF COMMERCIAL VALUES. [ 219. tion of alkali carbonate contained in a flask, heat the liquid to boiling, with frequent shaking, when the color will change again to blue as the carbonic acid escapes. Now add more of the stand- ard acid to the almost boiling liquid, heating occasionally; the point of saturation, or more properly incipient supersaturation, is thus very easily and accurately observed by the color of the liquid becoming red with a yellowish tint. ft. The saturation point may also be ascertained without heat- ing the liquid, but not with equal accuracy. The flask in this case must not be too small. After every addition of the acid, the flask must be carefully but vigorously shaken, the acid being con- stantly added so long as the red color of the liquid continues to have a violet tint. When the saturation-point is nearly reached, the acid is added two drops at a time, and after every fresh ad- dition, a glass rod is dipped into the solution, and one, or better, two spots made with it on a strip of good blue litmus paper, the volume read off each time, and the reading marked down between the spots. This procedure is continued until the spots appear decidedly red. The litmus paper is now allowed to dry, and the lowest reading taken as correct where the spots between which it is marked just remain red. It must be remembered as a rule that the standard acid must be tested by the same method which is to be used in the actual analysis. On this account a normal sulphuric, hydrochloric or oxalic acid, prepared according to 215, cannot be employed for the direct and immediate titration of alkalies. For the analysis we may also conveniently weigh off such a quantity of the substance that the number of c.c. of normal acid required to neutralize it shall directly express its percentage of the alkali or carbonate sought. Since 100 c.c. of the normal solution contain ^ of 98*086 grm. H 2 SO 4 , the proper quantities of the sodium and potassium com- pounds to employ are ^ of the weight of the compound required to neutralize 98*086 grm. H 2 S0 4 , viz. : 219.] ALKALIMETRY. 327 Potassa, K 2 O 4-711 grm. Potassium hydroxide, KOH 5-612 " Potassium carbonate, K 2 CO 3 6-911 " Hydrogen potassium Carbonate, KHCO 3 10-012 " Soda, Na/) 3-105 " Sodium hydroxide, NaOH 4-006 " Sodium carbonate (dry), NaaCOj 5-305 " Sodium carbonate crystallized, Na 2 CO 3 -10H 2 14-313 " Hydrogen sodium carbonate, NaHCO 3 8-406 " With regard to the examination of pearlash by this method, the following points deserve attention: The various sorts of potash of commerce contain, besides potas- sium carbonate (and caustic potassa): a. Normal salts (e.g., potassium sulphate, potassium chloride). b. Salts with alkaline reaction (e.g., potassium silicate, potas- sium phosphate). c. Admixtures insoluble in water, more especially calcium car- bonate, phosphate, and silicate. The salts named in a exercise no influence upon the results, but not so those named in b and c. Those in c may be removed by filtration; but the admixture of the salts named in b constitutes an irremediable though slight source of error; that is to say, if it is desired to confine the determination to the caustic and carbon- ated alkali. But as regards the estimation of the value of pearl- ash for many purposes, the term error cannot be applied; as, for instance, in the preparation of caustic potassa, by boiling the solu- tion with lime, the alkali combined with silicic acid and with phos- phoric acid is converted, like the carbonate, into the caustic state. If you are not satisfied with finding the percentage of available alkali, but desire also to know whether the remainder consists simply of foreign salts, or whether water is also present, the de- termination of the latter substance must precede the alkalimetric examination. The same remark applies also to soda. With regard to the examination of soda by this method, the fol- lowing points deserve attention: The soda of commerce, prepared by LEBLANC'S method, con- tains, besides sodium carbonate, always, or at least generally, 328 DETERMINATION OF COMMERCIAL VALUES. [ 219. sodium hydroxide, sodium sulphate, sodium chloride, sodium silicate and aluminate, and not seldom also sodium sulphide, sodium thiosulphate and sulphite.* The three last-named substances impede the process, and inter- fere more or less with the accuracy of the results. Their presence is ascertained in the following way: a. Mix with sulphuric acid; a smell of hydrogen sulphide re- veals the presence of sodium sulphide, with which sodium thio- sulphate is also invariably associated. 6. Color dilute sulphuric acid with a drop of solution of potas- sium permanganate or chromate, and add some of the soda under examination, but not sufficient to neutralize the acid. If the solu- tion retains its color, this proves the absence of both sodium sul- phite and thiosulphate; but if the fluid loses its color, or turns green, as the case may be, one of these salts is present. c. Whether the reaction described in b proceeds from sodium sulphite or thiosulphate is ascertained by supersaturating a clear solution of the sample under examination with hydrochloric acid. If the solution, after the lapse of some time, becomes turbid, owing to the separation of sulphur (emitting at the same time the odor of sulphurous acid), this may be regarded as a proof of the presence of sodium thiosulphate; however, the solution may, besides the thiosulphate, also contain sodium sulphite. With respect to the detection of sodium sulphite in the presence of thiosulphate, comp. "Qual. Anal.," p. 204. The defects arising from the presence of the three compounds in question may be remedied in a measure by igniting the weighed sample of the soda with potassium chlorate before proceeding to saturate it. This operation converts the sodium sulphide, thiosul- phate, and sulphite into sodium sulphate. But if sodium thiosul- phate is present, the process serves to introduce another source of error, as that salt, upon its conversion into sulphate, decomposes a molecule of sodium carbonate and expels the carbonic acid of the latter. [Na 2 S 2 O 3 +40 (from the potassium chlorate) + Na 2 CO 3 = 2(Na 2 S0 4 )+C0 2 .] * * Traces of sodium cyanide are also occasionally found. 220.] ALKALIMETRY. 329 The presence of sodium silicate and of sodium aluminate may be generally recognized by the separation of a precipitate as soon as the solution is saturated with acid. If you intend the result to express the quantity of carbonated and caustic alkali only, the presence of these two bodies becomes a slight source of error; but if you wish to estimate the value of the soda for many purposes, no error will be caused. b. Method of FR. MOHR, modified. 220. Instead of estimating the alkalies in the direct way by means of an acid of known strength, we may estimate them also, as pro- posed first by FR. MOHR,* by supersaturating with standard acid, expelling the carbonic acid by boiling, and finally by determining by standard alkali solution the excess of standard acid added. This process gives very good results, and is therefore particu- larly suited for scientific investigations. It requires the standard fluids mentioned in 215, viz., a standard acid and standard solu- tion of potassium or sodium hydroxide. Each of these fluids is filled into a MOHR burette. The process is as follows: Dissolve the alkali carbonate or caustic alkali hi water, and color a pale blue with a measured quantity of litmus tincture ;f run hi now as much of the standard acid as will suffice to impart a violet tint to the fluid; then boil, run in more acid until the color is decidedly yellowish red, then a further quantity to the next c.c. mark. The alkali will now be decidedly supersaturated; then remove the last traces of carbonic acid by boiling, shaking, blowing into the flask, and finally sucking out the air. Now add standard solution of potassa, drop by drop, until the color just appears light blue. This point is easily determined if the liquid is free from carbonic acid, and only slightly colored by litmus; if, however, the reverse is the case, the end-point cannot * Annal. d. Chem. u. Pharm., LXXXVI, 129. t For other indicators see page 309. 330 DETERMINATION OF COMMERCIAL VALUES. [ 220. be accurately determined, as the blue color imparted to the liquid continues to change to a violet for some time. If the standard solutions of soda and acid are of correspond- ing strength, the number of c.c. of the soda solution used is simply deducted from the number of c.c. of the acid used. The remainder expresses the volume of the acid solution neutralized by the alkali in the examined sample. If the two standard fluids are not of corresponding strength, the excess of acid added, and sub- sequently neutralized by the soda solution, is calculated from the known relation the one bears to the other. If one-tenth equivalent number (H = 1-008) in grammes of the alkali to be tested had been weighed out, e.g., anhydrous sodium carbonate 5-305 grm., or potassium carbonate (pearlash) 6-911 grm., the number of c.c. of normal acid used expresses directly the percentage of anhydrous sodium carbonate or of potassium carbonate in the samples examined, since 100 c.c. of normal acid containing one-tenth gramme equivalent of acid will just suffice to neutralize one-tenth gramme-equivalent of pure sodium or potassium carbonate. If any other suitable quantity of alkali has been weighed out, a simple calculation will give the proper result. To make this simple calculation quite clear, a most complicated one is selected, assuming that the soda solution and the normal acid do not correspond in strength, but that 1-1 c.c. of the soda solution neutralize 1 c.c. of the normal acid; and also that instead of one-tenth gramme-equivalent, 2 12 grm. of impure potassium carbonate had been weighed out. The quantity of normal acid added was 26 c.c.; the excess required 2-1 c.c. of soda solution for neutralization. The equation 1-1 :1 ::2-l :x; z=l-91 shows that an excess of 1-91 c.c. of acid was present. 26 1 -91 = 24-09 c.c. of the acid were accordingly neutralized by the potas- sium carbonate. The equation 2-1 : 24-09 :: 6-911( T V eq. K 2 CO 3 ):x; z = 79-28 I 221.] ALKALIMETRY. 331 shows that the impure potassium carbonate contains 79-28 per cent, of pure carbonate. II. GRAVIMETRIC METHOD OP FRESENIUS AND WlLL.* 221. In this method the quantity of alkali carbonate is calculated from the quantity of carbonic acid disengaged by it. It is accord- ingly necessary that all the alkali to be determined is present in the form of a neutral carbonate, and also that the substance should contain no other carbonate. If these conditions are not fulfilled, it is necessary to treat the substance in order to bring them about. If the substance to be tested contains alkali bicarbonate (yielding carbonic acid on ignition), it must be first ignited before proceeding to the carbonic-acid determination; if, on the other hand, it con- tains caustic alkali (which gives an alkaline filtrate after adding an excess of barium chloride), heat the quantity weighed off with about its own weight of quartz sand, about one-third its weight of powdered ammonium carbonate, and as much water as the mixture will absorb until all the water has been driven off; then proceed to determine the carbonic acid in the residue thus abtained. The determination of the carbonic acid is effected in the manner described in Vol. I, p. 488, da. Other methods may, however, be also employed ; for instance that detailed in Vol. I, p. 493, e. The former method is more suitable for technical purposes; the latter for scientific investigations. If 6 2827 grm. of a substance containing potassium carbonate, or 4-822 grm. of one containing sodium carbonate, are weighed out, it is only necessary to divide the number of centigrammes of carbonic acid found by 2, in order to obtain without further calculation the percentage content of anhydrous potassium- or sodium carbonate in the substance examined. It is of course evident that neither this nor the volumetric method will enable a determination to be made of potassium car- bonate in the presence of sodium carbonate; the results are accurate * Compare the pamphlet mentioned in the foot-note, p. 317. 332 DETERMINATION OF COMMERCIAL VALUES. [ 222. only when either potassium or sodium carbonate alone is present (besides other neutral salts). The special points to be noted in the analysis of pearlash or soda-ash will be detailed later on (224 and 229). C. DETERMINATION OF CAUSTIC ALKALI PRESENT WITH ALKALI CARBONATE. 222. a. When it is desired to determine both the caustic alkali and alkali carbonate in mixtures of sodium carbonate and sodium hydroxide, the methods described in 219 or 220 may be com- bined with that detailed in 221, i.e., the total caustic alkali and carbonate expressed in per-cents. of sodium- or potassium carbon- ate may be estimated by one of the former methods, while by the latter of course without previous treatment with ammonium car- bonate the quantity of carbonic acid, and hence that of the alkali carbonate present, is determined. The difference between both determinations gives the quantity of alkali carbonate correspond- ing with the caustic alkali present. To calculate anhydrous sodium carbonate into anhydrous caustic soda (Na 2 O), multiply it by 0-5853; to calculate it into sodium hydroxide (NaOH), multiply it by 0-7551. To calculate potassium carbonate into anhydrous caustic potassa (K 2 0), multiply by 0-68167; to calculate it into potassium hydroxide (KOH), multiply it by 0-812. b. It will be readily seen that the object may also be attained by the method described in 221, by directly determining the carbonic acid in one weighed sample, while in another it is deter- mined after previous treatment with ammonium carbonate. c. The purpose may also be accomplished by purely volumetric methods, and by the aid of the same principle which has already been made use of when testing alkali carbonate for caustic alkali. Weigh out three-tenths gramme-equivalents of the carbon- ate to be tested for caustic alkali, i.e., 20-733 grammes of potas- sium carbonate, or 15-915 grammes of sodium carbonate, dissolve it in water in a 300-c.c. flask, fill to the mark, shake, allow the liquid 222.] ALKALIMETRY. 333 to settle out of contact with the air, and then remove two por- tions of 100 c.c. each for analysis. In one portion determine the total caustic alkali and carbonate according to 220; the number of c.c. of normal acid used up will give the caustic alkali and alkali carbonate expressed in per cents, of the latter. Introduce the other portion into a 500-c.c. flask, add 200 c.c. of water, then barium- chloride solution until no further precipitate is given by it, fill up with water to the mark, shake, allow to settle out of contact with the air,* measure off 250 c.c. of the clear, supernatant liquid (containing now caustic baryta equivalent to the caustic alkali present in the sample), add litmus tincture, and then normal hydrochloric acid to acid reaction. Now titrate the excess of acid with normal soda solution, and thus ascertain from the num- ber of c.c. of normal acid used the equivalent quantity of caustic baryta. On now multiplying by 2 (since only one-half of the sec- ond portion had been taken in the experiment), the result will give the percentage of caustic alkali expressed as anhydrous sodium- or potassium carbonate. On deducting this number from that obtained in the first experiment the difference will give the potassium- or sodium carbonate present as such. In order to calculate the caustic alkali into the anhydrous or hydrated forms, it is only necessary to multiply by the numbers stated in a. D. ESTIMATION OF SODIUM CARBONATE IN THE PRESENCE OF POTASSIUM CARBONATE. Soda, being much cheaper than potash, is occasionally used to adulterate the latter. The common alkalimetric methods not only fail to detect this adulteration, but they give the admixed sodium carbonate as potassium carbonate. Many processes f have been proposed for estimating in a simple way the soda con- tained in potash, but not one of them can be said to satisfy the requirements of the case. * By filtering through a dry filter, somewhat too low a yield of caustic alkali is obtained, as the paper retains caustic baryta (A. MULLER, Journ. f. prakt. Chem., LXXXIII, 384; Zeitschr. /. analyt. Chem., i, 84). f Comp. Handworterbuch der Chemie, 2 Aufl., i, 443. 334 DETERMINATION OF COMMERCIAL VALUES. [ 223. The following tolerably expeditious process, however, gives accurate results: Dissolve 6-25 grm. of the gently-ignited pearlash in water, filter the solution into a quarter-litre flask, add acetic acid in slight excess, apply a gentle heat until the carbonic acid is expelled, then add to the fluid, while still hot, lead acetate, drop by drop, until the formation of a precipitate of lead sulphate just ceases; allow the mixture to cool, add water up to the mark, shake, allow to deposit, filter through a dry filter, and transfer 200 c.c. of the filtrate, corresponding to 5 grm. of pearlash, to a J-litre flask. Add hydrogen-sulphide water up to the mark, and shake. If the lead acetate has been carefully added, the fluid will now smell of hydrogen sulphide, and no longer contain lead; in the con- trary case, hydrogen-sulphide gas must be conducted into it. After the lead sulphide has subsided filter through a dry filter. Evaporate 50 c.c. of the filtrate (corresponding to 1 grm. of pearl- ash) with addition of 10 c.c. hydrochloric acid, of 1-10 sp. gr., in a weighed platinum dish, to dry ness, then cover the dish, heat, and weigh; the weight found expresses the total quantity of potassium and sodium chlorides given by 1 grm. of the pearlash. Estimate the potassium and sodium now severally in the indirect way, by determining the chlorine volumetrically ( 141, I, 6). 3. ESTIMATION OF ALKALI-EARTH METALS BY THE ALKALIMETRIC METHOD. 223. The alkali-earth metals, when in the form of oxides, hydrox- ides, or carbonates, may also be determined volumetrically by means of standard acid and alkali solutions. Standard sulphuric acid may be used for magnesium; standard hydrochloric or nitric acid for barium, strontium, and calcium. The only advantage which these acids possess over hydrochloric is that there is less liability of loss on heating solutions containing them in the free state, which is necessary when carbonic is present. Hydrochloric acid can, however, be used with safety if precaution be taken to avoid the presence of an unnecessary quantity when the solution is heated. 223.] ALKALIMETRY. 335 If an oxide or hydroxide free from carbonic acid is to be exam- ined, add some water to a weighed quantity, and allow the stand- ard hydrochloric or nitric acid to flow in from a burette until solu- tion is effected and the solution colored with litmus gives an acid reaction. Then determine the excess of acid used by means of the standard soda solution. Deduct the soda solution used from the acid, and calculate the result from the equation as follows: 1000 c.c. : number of c.c. acid used : : 76-7 (i eq.) BaO, or 51-8 (i eq.) SrO, or 28-05 (i eq.) CaO, or 20-15 ( eq.) of MgO : x ( = grammes of BaO, SrO, CaO, or MgO). Should the exact neutrality point not have been hit the first time, add another c.c. of acid, and then again soda solution to neutrality. In case of a carbonate, dissolve a weighed quantity in a flask by heating with water, then add standard hydrochloric or nitric acid from a burette in small successive portions, until solution is complete and a slight excess of acid is present; next add the indi- cator (litmus or cochineal) and allow the standard alkali solution to run in from a burette until the free acid is nearly neutralized and only 0-5 or 1 c.c. of acid is in excess. Now remove the car- bonic acid by boiling a few minutes and shaking, and complete the neutralization with the standard alkali. 1000 c.c. of normal acid correspond to 98-7 grm. BaCO 3 , 73-8 grm. SrCO 3 , 50-05 grm. CaCO 3 , or 42-15 grm. MgCO 3 . If it is desired to avoid all calculation whatever, ^ or -^ gramme- equivalent of the pure caustic alkaline earth, or carbonate of the alkaline earth, may be weighed off; in the former case the number of c.c., in the latter half the number of c.c. of the normal acid used expresses the percentage. To determine the alkaline earths in soluble neutral salts of the latter, precipitate the barium, strontium, or calcium solution with ammonia and ammonium carbonate, warm, filter, wash with pure water, and then treat the precipitate as above described. Mag- nesium salts may be precipitated with potassa or soda-lye, and the washed magnesium hydrate treated similarly, but the de- termination made thus is apt to give too low a result because of the solubility of magnesium hydrate. 336 DETERMINATION OF COMMERCIAL VALUES. [ 224. 4. THE TECHNICALLY MOST IMPORTANT POTASSIUM COMPOUNDS. A. POTASH (PEARLASH). 224. Potash, which was formerly almost exclusively obtained from wood ashes or the ashes of other portions of plants, is now manu- factured in large quantities in the same manner as sodium car- bonate by the LEBLANC process, which consists in fusing potassium sulphate with carbon (coal) and calcium carbonate. Potash is also obtained from the residues of beet-root molasses by evaporat- ing, calcining, lixiviating, and concentrating the lye. In con- sequence of this the substances which potashes may contain besides potassium carbonate, may be exceedingly various. Those soluble in water may be specially noted as follows: Potassium sulphate, potassium chloride (present in potash from plant-ashes in only small quantity usually, but present in considerable quantity in potash made by the LEBLANC process or from beet-root molasses). In smaller quantity there are or may be found caustic alkalies, silicates, phosphoric acid, alkali manganates-, alkali sulphides (and from the action of the air on these also alkali thiosulphates), besides alkali cyanides and sulphocyanates, and under certain circumstances also alkali iodides and bromides and organic matter. Of the constituents insoluble in water, the following may be especially noted: Silicic acid, calcium silicate, carbonate and phosphate, magnesium phosphate and carbonate, ferric oxide, manganese oxides, cupric oxide, alumina, sand, and carbon (coal). Besides these, potashes as a rule contain also water. The substances insoluble in water may, of course, be removed by treatment with water and filtration; the frequent occurrence of sodium carbonate in the potashes, now often found in commerce, however, renders it very difficult to analyze and determine the constituents soluble in water, as the sodium carbonate interferes with the analysis which is directed to the determination of the 224.] POTASSIUM COMPOUNDS. 337 content of potassium carbonate (and caustic potassa). It is therefore necessary, before beginning an analysis of a potash, to first ascertain whether it contains an appreciable quantity of sodium carbonate. As potash attracts water very rapidly, correct and, on repeating the analysis, concordant results are only possible when all the determinations of potash are based upon or referred to the original water content. Before opening the bottle containing the potash to be examined, the operator should provide himself with two or three perfectly dry test-tubes with well-fitting stoppers; these tubes are to be rapidly filled after the bottle is opened, then stop- pered, and kept in the desiccator. I. Determination of Moisture. Weigh off about 2 grm. of potash from one of the test-tubes into a platinum crucible, heat to dull redness, and determine the Joss of weight. This is considered as water. The determination is not quite accurate if the potash contains free silicic acid, because this, on heating, expels carbonic acid from the potassium carbonate. If in such a case the water is to be accurately determined, proceed according to 36. If the potash contains potassium hydroxide, the water of hydration of the latter is not driven off by ignition. II. Determination of all other Constituents. a. Weigh off about 10 grm. of the potash from one of the test- tubes and treat with water in a beaker, at a gentle heat, until all the soluble portion is dissolved, then filter through a small filter paper and wash the insoluble portion with hot water until the washings are no longer alkaline. Collect the filtrate and washings in a 500-c.c. measuring flask and fill with water to the mark. Dry the filter with the insoluble residue, incinerate, treat with a little ammonium carbonate, evaporate, gently ignite, and weigh. In almost 'all cases it suffices to enter the weight as "portion insoluble in water" b. Treat 100 c.c. of the solution according to 220 or 219. The acid required for neutralization corresponds with the potas- 338 DETERMINATION OF COMMERCIAL VALUES. [ 224. slum carbonate, and also the potassium hydroxide, sodium car- bonate, and sodium hydroxide, if these are present. First calculate the acid as used up for potassium carbonate. If an alkali s.licate is present in any appreciable quantity, a correction must be made for it. Alkali phosphates, sulphides, and cyanides also use up a small quantity of acid; the quantity of these present is as a rule so small, however, that no correction need be made for them. c. Carefully supersaturate 50 c.c. with hydrochloric acid in a flask or covered beaker, heat to drive off all the carbonic acid,, evaporate in a porcelain or platinum dish to dryness, moisten the residue with hydrochloric acid, take up with water, filter off the silicic acid, and determine this according to 140, II, a. Heat the filtrate to boiling, and very cautiously add barium-chloride solution until a precipitate no longer forms. From the weight of the barium sulphate filtered off that of the sulphuric acid present may be calculated (132, 1). d. If the potash contains a determinable quantity of sodium carbonate, the solution filtered off from the barium sulphate in c- may be used for the preparation of pure alkali chlorides, and for the determination of the potassium chloride contained in them. In this case evaporate to dryness, take up the residue with water, precipitate the excess of barium salt which had been added with ammonium carbonate (101, 2), evaporate the filtrate to dryness, expel the ammonium salt by gently igniting, take up with water,, remove the last traces of dissolved barium by a little ammonia and ammonium carbonate, filter, evaporate in a weighed platinum dish, weigh the alkali chlorides, and determine the potassium chloride present as potassium-platinic chloride (p. 345); the difference gives the sodium chloride, and from this the sodium present hi the potash is obtained. Of course the quantity of potassium chloride and sodium chloride in the weighed alkali chlorides may also be indirectly determined (152, 3), but this method is to be recommended only when the quantity of sodium salt present is not too small. e. In 50 c.c. of the solution determine the chlorine according to 141, I, a or 6. 224.] POTASSIUM COMPOUNDS. 339 /. If the potash contains caustic alkali (i.e., if its solution affords a filtrate of alkaline reaction on being treated with an excess of barium chloride), add an excess of barium-chloride solution to 200 c.c. of the solution contained in a 500-c.c. flask, nil with water to the mark, stopper, shake, allow to settle, and in 250 c.c. of the clear fluid determine the alkalinity with normal acid ( 222). The acid used corresponds to the caustic alkali contained in 100 c.c. of the potash solution. g. Finally smaller quantities of the potash solution are em- ployed for qualitative tests for phosphoric acid, etc. If a large quantity of phosphoric acid is found to be present, as now and then happens, it must, of course, be determined; and since in that case the potassium-carbonate content cannot be accurately de- duced from the determination of the alkalinity (according to II, 6), a determination of the carbonic acid in the potash solution be- omes necessary. For this purpose the last 50 c.c. of the solution, may be used, and the determination made according to 139, II* d or e. Calculation and Statement of Results. Although a potash neither loses nor gains in value if the bases and acids contained in it are combined in one way or another to form salts, still it is very desirable that certain principles should be agreed upon regarding the arrangement in stating the results, otherwise different chemists, using exactly the same analytical results, would calculate very different constituents of the potash. I consider it best to combine any soda present if caustic potassa is present first with water to form sodium hydroxide, then with silicic acid as sodium silicate, then with carbonic acid as sodium carbonate. Potassa, on the other hand, is first combined with sulphuric acid, then (as potassium) with chlorine, then with car- bonic acid, silicic acid, and finally with water as potassium hy- droxide. In order to arrive at the correct quantity of potassium carbonate in the absence of determinable quantities of phosphoric acid 340 DETERMINATION OP COMMERCIAL VALUES. [ 224. the following are to be deduced, according to circumstances, from the number found in II, 6, for potassium carbonate: 1 eq. potassium carbonate for 2 eq. sodium or potassium hy- droxide. 1 eq. potassium carbonate for 1 eq. sodium or potassium silicate (Na 2 SiO 3 or K 2 SiO 3 ). 1 eq. potassium carbonate for 1 eq. sodium carbonate. If determinable quantities of phosphoric acid are present, the content of alkali carbonates must be calculated from the carbonic acid found. III. Determination of the Potash Alone. Under " potash content " is properly understood the quantity litre flask, and thoroughly wash the small residue which generally remains. Finally, fill the flask with water up to the mark, and shake the fluid. If small white grains of calcium sulphate are left on dissolving the salt, reduce them to powder in a mortar, add water, let the 372 DETERMINATION OF COMMERCIAL VALUES. [ 230. mixture digest for some time, decant the clear supernatant fluid on to a filter, triturate the undissolved deposit again, add water, etc., and repeat the operation until complete solution is effected. b. Ignite and weigh the dried insoluble residue of a, and sub- ject it to a qualitative examination, more especially with a view to ascertain whether it is perfectly free from calcium sulphate. c. Of the solution a measure off successively the following quantities : For d. 50 c.c. corresponding to 1 grm. of common salt. " e. 150 c.c. " " 3 " " " " " f. 150 c.c. " " 3 " " " " " g. 50 c.c. " " 1 " " " " d. Determine, in the 50 c.c. measured off, the chlorine as directed in 141, I, a or 6. e. Determine, in the 150 c.c. measured off,, sulphuric acid as directed in 132, I, 1. /. Determine, in the 150 c.c. measured off, the calcium and magnesium as directed in 154, B, 6, [36]. g. Mix the 50 c.c. measured off in a platinum dish with about 0-5 c.c. of pure concentrated sulphuric acid, and proceed as di- rected in 98, 1. The neutral residue contains the sulphates of sodium, calcium, and magnesium. Deduct from this the quantity of the two latter substances resulting from /; the remainder is sodium sulphate. h. Determine, in another weighed portion of the salt, the water as directed in 35, a, a (at the end). i. Bromine, potassium, and other bodies, of which only very minute traces are found in common salt, are determined by the methods described in the analysis of mineral waters. Calculation. The sulphuric acid is first combined with the calcium, then with the magnesium. If there is any remainder of sulphuric acid, it is combined with potassium, if this has been determined, and then with sodium. If, on the other hand, there is a balance 231.J SODIUM COMPOUNDS. 373 of magnesium, it is calculated as magnesium chloride. This mode of arrangement is in agreement with that adopted in the case of potassium chloride (p. 343), and is based upon the fact that when magnesium chloride and sodium sulphate are dis- solved in water and the solution is evaporated, sodium chloride separates out. I would mention, however, that in the published analyses of salt there is an entire lack of agreement as to the manner in which the various bases and acids have been com- bined. C. SODIUM SULPHATE (SALT-CAKE). 231. The impure sodium sulphate which formed in the salt-cake furnaces by the action of sulphuric acid on common salt is found in the market under the name of "salt-cake." It is used not only for the manufacture of soda, but is sent into the market as such, and in large quantities, as it is used particularly in the manufacture of glass. Smaller quantities serve for the prepara- tion of crystallized GLAUBER'S salt. Salt-cake contains as a rule the following constituents in weighable quantities : Neutral sodium sulphate, frequently also some sodium bisul- phate, ferric sulphate, aluminium sulphate, calcium sulphate, magnesium sulphate, sodium chloride, and a residue insoluble in water. The sampling is done as in the case of potash (p. 337). 1. Determination of Moisture. If the sample yields acid vapors when heated in a glass tube, the quantity of water cannot be ascertained from the loss in weight on ignition, but if must be determined as described in 225, I. 2. Treat about 10 grm. of the sample with 100 c.c. of cold water until the greater part is dissolved, then filter into a 500-c.c. flask, and thoroughly wash the residue with cold water. Should the filtrate be cloudy, add first a little hydrochloric acid, then fill up with water to the mark, and mix. 374 DETERMINATION OF COMMERCIAL VALUES. [ 231. 3. Ignite the undissolved residue, weigh, and examine further according to circumstances. 4. In 50 c.c. of the solution determine the sulphuric acid ac- cording to 132, I, 1, or 2, e. 5. Add some ammonium chloride to 100 c.c. of the liquid, heat with addition of ammonia, and determine the ferric oxide alumina, calcium, and magnesium according to 229, 1, 2, b (p. 364) . 6. Add two drops of pure concentrated sulphuric acid to 50 c.e, of the solution in a weighed platinum dish, evaporate to dryness, ignite (finally in an atmosphere of ammonium carbonate, 97, 1), and weigh. After deducting the calcium and magnesium (cal- culated as sulphates), and iron and aluminium (as oxides), the residue gives the caust c soda from the weight of -the sodium sul- phate. (This determination is not absolutely necessary if the determination given in 8 is adopted, because the caustic-soda content may be calculated from the chlorine and sulphuric acid; it furnishes, however, a good control). 7. Determine the chlorine in 100 c.c. of the liquid ( 141, I, a or 6, a), provided hydrochloric acid has not been added in 2. If this has been done, the chlorine must be determined by treating a fresh quantity of the substance with water and adding nitric acid to the filtrate instead of hydrochloric acid. 8. Although the sodium bisulphate present is already given by the calculation presupposing the determination of the caustic soda it is nevertheless advisable to make a direct determina- tion. For this purpose dissolve about 5 grm. of the salt-cake in the least possible quantity of cold water, and without filtering add about 9 grm. crystallized barium chloride, then a little litmus tincture, .and finally from a burette, decinormal soda solution just to incipient alkalinity. On deducting from the soda solu- tion used up the equivalent quantity of sulphuric acid, corre- sponding; with the ferric .and aluminium sulphates (FeSO 4 and AUS0 4 ] 3 ), the acid which is combined as hydrate with neutral sodium sulnhate to form sodium bisulnhate (Na-jSCX + NaHSOj, is obtained. Regarding the addition of barium chloride, see p. 313, c. 232.] BARIUM COMPOUNDS. 375 6. BARIUM COMPOUNDS. HEAVY SPAR. 232. Heavy spar is employed partly as an adulterant of white lead, etc., and partly for the preparation of barium chloride and other barium compounds. If it is not perfectly pure white when ground, it is useless for the former purpose, and its purity must be unquestioned, if it is to be used for the latter purpose. Heavy spar must, therefore, frequently be examined analytic- ally. As a rule, it contains, besides barium sulphate, the folow- ing constituents in weighable quantities: Calcium sulphate, strontium sulphate, ferric oxide, alumina, silica, and moisture 1. The moisture is determined most simply by gently igniting a sample of about 2 grm. in a platinum crucible. 2. Mix the ignition-residue from 1 with four times its quan- tity of potassium and sodium carbonates, fuse, and treat the melt with water ( 132, II, 6, a). 3. Cautiously neutralize the solution obtained in 2 with hy- drochloric acid, heat to drive off the carbon dioxide, evaporate to dryness, separate the silica ( 140, II, a), and in the filtrate determine the sulphuric acid ( 132). 4. Dissolve the residue remaining in 2 in diluted hydrochloric acid, evaporate to dryness, treat the residue with hydrochloric acid, separate the remainder of the silica ( 140. II, a), and in the nitrate precipitate the ferric oxide and alumina by adding ammonia ( 161, 4). After moderately washing, dissolve the residue again in hydrochloric acid, heat, again precipitate with ammonia, filter, dry, ignite, and determine the ferric oxide and alumina according to 160, B, 12. 5. Neutralize with hydrochloric ' acid the filtrate obtained in 4, and containing the alkaline earths, heat, and add diluted hydrochloric acid in slight excess. After the precipitate has settled completely, pour the supernatant liquid through a filter 376 DETERMINATION OF COMMERCIAL VALUES. [ 233. (Filtrate I). As soon as this has been done, treat the bulk of the precipitate which has remained in the beaker as well as that which has gone on the filter, and without previously washing, with am- monium carbonate ( 154, B, 3). To effect this, close the stem of the funnel containing the filter. After twelve hours remove the stopper, allow the liquid to run off, and transfer the contents of the beaker (Filtrate II) together with the precipitate to the filter, wash the precipitate, and treat it with very dilute hy- drochloric acid. The liquid which passes through now mix with Filtrates I and II ; dry the precipitate, however, which is now pure barium sulphate, weigh, and calculate the barium. 6. Concentrate the united filtrates from 5, taking care that the liquid is just acid, add 4 volumes of alcohol, allow to stand for 12 hours, filter, wash with alcohol, and finally separate the calcium and strontium in the precipitate by ammonium sulphate ( 154, B, 5). 7. CALCIUM COMPOUNDS. A. CALCIUM PHOSPHATE (PHOSPHORITE, ETC.). (See V. Analysis of Manures.) B. CHLORINATED LIME. 233. The "chloride of lime," or "bleaching powder" of commerce, contains calcium hypochlorite, calcium chloride, and calcium hydroxide. The two latter ingredients are for the most part combined with one another as calcium oxy chloride. In freshly prepared and perfectly normal chlorinated lime, the quantities of calcium hypochlorite and calcium chloride present stand to each other in the proportion of their mol. weights. When such chlo- rinated lime is brought into contact with dilute sulphuric acid, the whole of the chlorine it contains is liberated in the elemen- tary form, in accordance with the following equation: (CaCl 2 2 + CaCl 2 ) + 2H 2 SO 4 = 2CaSO 4 + 2H 2 + 4C1. On keeping chlorinated lime, however, the proportion between calcium hypochlorite and calcium chloride gradually changes 233.J CALCIUM COMPOUNDS. 377 the former decreases, the latter increases. Hence, from this cause alone, to say nothing of original difference, the commercial article is not of uniform quality, and on treatment with acid gives some- times more and sometimes less chlorine. As the value of this article depends entirely upon the amount of chlorine set free on treatment with acid, chemists have devised various simple methods of determining the available quantity of chlorine in any given sample. These methods have collectively received the name of Chlorimetry. The number of chlorimetric methods proposed is so great that I cannot give them all here, hence only those will be described which are characterized either by the ease with which they may be carried out or by the accuracy of the results afforded by them. GAY-LUSSAC'S method, which depends upon the conversion of arsenous acid into arsenic acid in hydrochloric-acid solution, and in which indigo solution is used as an indicator, was dropped from the Sixth Edition because it is surpassed by PENOT'S method both in convenience and in accuracy. Before proceeding to a description of the method, I would point out that the results obtained in testing chlorinated lime are expressed in various ways. While it is usual scientifically to characterize a chlorinated lime according to its percentage content of available chlorine, in practice it is usual to quote and sell it by chlorimetric degrees. This mode of expression, origi- nating with GAY-LUSSAC, denotes how many litres of chlorine gas at and 760 mm. pressure are contained in 1000 grm. of chlorinated lime. Both modes of expression may be easily compared with each other, since we know that 1 litre of chlorine at and 760 mm. weighs 3-16636 grm. For instance, a chlorinated lime of 90 contains 3-16636X90 = 284-97 grm. chlorine in 1000 grm., hence 28-5 per cent.; and a chlorinated lime containing 34-2 per cent, of chlorine is 108-01; for, since 100 grm. contain 34-2 chlorine, 342 1000 grm. will contain 342. These, however, = 3 <16636 ; ** = 108-01 litres. 378 DETERMINATION OF COMMERCIAL VALUES. [ 233. Preparation of the Solution of Chlorinated Lime. The solution is prepared alike for all methods, and best in the following manner: Weigh off 10 grm., triturate finely with a little water, add gradually more water, pour the liquid into a litre flask, triturate the residue again with water, and rinse the contents of the mortar carefully into the flask; fill the latter to the mark, shake the milky fluid, and examine it at once in that state, i.e., without allowing it to deposit; and every time, before measuring off a fresh portion, shake again. The results obtained with this turbid solution are much more constant and correct than when, as is 1 usually recommended, the fluid is allowed to deposit, and the experiment is made with the supernatant clear portion alone. The truth of this may readily be proved by making two separate experiments, one with the decanted clear fluid and the other with the residuary turbid mixture. Thus, for instance, in an experiment made in my own laboratory, the decanted clear fluid gave 22-6 of chlorine, the residuary mixture 25-0, the uniformly mixed turbid solution 24-5. One c.c. of the solution of chlorinated lime so prepared corre- sponds to 0-01 grm. chlorinated lime. RUD. WAGNER* recommends preparing the chlorinated-lime solution by shaking. He shakes together 10 grm. of the chlori- nated lime with coarsely powdered glass (pieces of broken-up glass rods about 5 to 10 mm. long) and water in a strong flask, until the chlorinated lime is completely divided. The volume occupied by the pieces of glass must be previously determined in a glass measuring cylinder by pouring over them a measured quantity of water. The milky liquid, together with the glass, is rinsed into a litre flask and diluted to measure 1 litre at 17-5; a volume of water equal to that occupied by the glass is then added and the whole shaken. One c.c. of this solution, there- fore, corresponds also with 0-01 grm. chlorinated lime. * Zeitschr. /. analyt. Chem., iv, 223. 233.] CALCIUM COMPOUNDS. 379 A. PENOT'S METHOD.* This method, like that of the older one of GAY-LUSSAC, is based upon the conversion of arsenous acid into arsenic acid, or, more strictly, an arsenite into an arsenate, since the conversion is effected in an alkaline solution. Potassium iodide-starch paper is employed to ascertain the exact point when the reaction is completed. a. Preparation of the Potassium Iodide-Starch Paper. The following method is preferable to the original one given by PENOT: Stir 3 grm. of potato starch in 250 c.c. of cold water, boij with stirring, add a solution of 1 grm. potassium iodide and 1 grm. crystallized sodium carbonate, and dilute to 500 c.c. Moisten strips of fine white unsized paper with this fluid and dry. Keep in a closed bottle. b. Preparation of the Solution of Arsenous Add. Dissolve 4-4213 grm. of pure arsenous oxide, (A^O,,), and 13 grm. pure crystallized sodium carbonate in 600-700 c.c. water, with the aid of heat, let the solution cool, and then dilute to 1 litre. Each c.c. of this solution contains an amount of sodium arsenite equivalent to 0-0044213 grm. arsenous oxide, (As 2 Og), which corresponds to 1 c.c. chlorine gas of and 760 mm. at- mospheric pressure.f * Bulletin de la Sodete Industriette de Mulhcwse, 1852, No. 118. DINO LER'S Polytech. Journal, cxxvn, 134. f PENOT gives the quantity of arsenous oxide as 4 44 ; but this number has been corrected to 4-4213, in accordance with the atomic weights of the substances used in this book and specific gravity of chlorine gas after the following proportion: 141-8 (4 at. Cl): 198 (1 mol. AsA):: 3-16636 (weight of 1 litre of chlorine gas) : x ; x= 4 - 4213, i.e. , the quantity of arsenous oxide which 1 litre of chlorine gas converts into arsenic acid. This solution is arranged to suit the foreign method of designating the strength of chlorinated lime, viz., in chlorimetrical degrees (each degree represents 1 litre of chlorine gas at and 760 mm. pressure in a kilogramme 380 DETERMINATION OF COMMERCIAL VALUES. [ 233. As sodium arsenite in alkaline solution is liable, when exposed to access of air, to be gradually converted into sodium arsenate, PENOT'S solution should be kept in small bottles with glass stoppers, filled to the top, and a fresh bottle used for every new series of experiments. According to FR. MOHR * the solution keeps un- changed if the arsenous oxide and the sodium carbonate are both absolutely free from oxidizable matters (arsenous sulphide, sodium sulphide, and sodium sulphite). c. The Process. Measure off with a pipette 50 c.c. of the solution of chlo- rinated lime prepared according to the directions in 233, transfer to a beaker, and from a 50-c.c. burette add slowly, and at last drop by drop, the solution of arsenous acid, with constant stirring, until a drop of the mixture produces no longer a blue-colored spot on the iodized paper; it is very easy to hit the point exactly, as the gradually increasing faintness of the blue spots made on the paper by the fluid dropped on it indicates the approaching termination of the reaction, and warns the operator to confine the further addition of the solution of arsenous acid to a single drop at a time.. The number of J c.c. used indicates directly the number of chlorimetrical degrees (see note), as the following calculation shows: If you have used 40 c.c. of solu- tion of arsenous acid, then the quantity of chlorinated lime used in the experiment contains 40 c.c. of chlorine gas. Now the 50 c.c. of solution employed correspond to 0-5 grm. of chlo- rinated lime; therefore 0-5 grm. of chlorinated lime contain of the substance). This method was proposed by GAY-LUSSAC. The de- grees may readily be converted into per cents., and vice versa, thus: A sample of chlorinated lime of 90 contains 90X3-16636=284-97 grm. chlorine in 1000 grm. or 28 50 in 100 ; and a sample containing 34 2 per cent, chlorine is of 108-01, for 100 grm. of the substance contain 34-2 grm. chlorine; . . 1000 grm. of the substance contain 342 grm. chlorine, but 342 grm. chlorine 342 = ;r - litres =108 -01 litres; .'. 1000 grm. of the substance contain 3-16636 108-01 litres chlorine. * Lehrbuch der Titrirmethode, 5. Aufl., S. 325. 233.] CALCIUM COMPOUNDS. 381 40 c.c. chlorine gas, therefore 1000 grm. contain 80,000 c.c. = 80 litres. This method gives very constant and accurate results, and appears to be particularly well suited for use in manufacturing establishments where there is no objection on the score of dan- ger in the employment of arsenous acid. B. MOHR'S MODIFICATION OF PENOl's METHOD.* The principle of this modification is as follows: Measure off a definite quantity of the chlorinated-lime solution, add a meas- ured quantity of a standardized solution of potassium arsenite in excess, and then determine the excess of potassium arsenite with iodine ( 127, 5). MOHR employs a decinormal potassium-arsenite solution, and a corresponding decinormal iodine solution. The former is pre- pared by digesting 4-95 grm. (one-fourth of the one-tenth equiv- alent, because 1 eq. of As 2 O 3 is converted into As-jOg by 4 eq. of iodine) of pure powdered arsenous acid in about 200 c.c. of water and 5 to 10 grm. of potassium bicarbonate and shaking until the greater part of the arsenous acid is dissolved. Then pour off the liquid into a litre flask and dissolve the residual arsenous acid in water with the addition of a small quantity of potassium bicarbonate, add 20 to 25 grm. more of potassium bicarbonate, and make up the whole to measure 1 litre and shake. One c.c. corresponds to 0-003545 grm. chlorine, i.e., the arsenous acid contained in 1 c.c. will be converted into arsenic acid by 0.003545 grm. chlorine. The iodine solution is prepared by dissolving 6-4 grm. of iodine by means of about 9 grm. of potassium iodide in sufficient water to measure 500 c.c. ; the solution is then standardized against the arsenous-acid solution ( 127, 5), and diluted to agree with it. In the valuation of chlorinated lime it is convenient to use 50 c.c. of the chlorinated-lime solution prepared as above. To this add potassium-arsenite solution until a drop of the liquid no longer causes a blue spot on potassium iodide-starch paper, * Lehrbuch der Titrirmethode, 5th edit., p. 321. 382 DETERMINATION OF COMMERCIAL VALUES. [ 233. then dilute with 150 to 200 c.c. water, add some ammonium- bicarbonate solution prepared in the cold, then some starch solu- tion, and lastly some iodine solution until the blue color of starch iodide develops, and remains even on adding a small quantity of ammonium carbonate. Deduct the c.c. of iodine solution used from those of the potassium-arsenite solution, and thus ascertain how many c.c. of the latter solution have been oxidized by the chlorinated lime. These c.c. multiplied by 0-003545 give the chlorine content of 0-5 grm. of the chlorinated lime. This method gives good results, but certainly will not super- sede PENOT'S method, which is simpler and equally as accurate. C. IODOMETRIC METHODS. In his treatise on "A Volumetric Method of Very General Applicability,* BUNSEN remarked that hypochlorites, and par- ticularly chlorinated lime, could very well be analyzed by adding an excess of potassium-iodide solution to the solution of the salt, then adding hydrochloric acid to slightly acid reaction, and then determining the iodine volumetrically. For this purpose BUN- SEN employed, as is well known, an aqueous solution of sulphurous acid. Later on most chemists preferred to use sodium thiosulphate, as first proposed by H. ScHWARZ,f instead of the aqueous solu- tion of sulphurous acid for the iodine determination; and it is thus that the iodometric method described in 146 originated. This "combined method" of iodine determination, which is de- scribed elsewhere, has also been specially recommended for chlo- rinated-lime determinations by R. WAGNER. J FR. MOHR de- clared WAGNER'S method to be inaccurate, but CL. WINKLER || * Annal. d. Chem. u. Pharm., LXXXVI, 277. f Anleiten zu Maasanalysen, Supplement, Brunswig, FR. VIEWEG & SOHN, 1853, p. 21. t DINGL. polyt. Journ., CLTV, p. 146, and CLXXVI, p. 131. Lehrbuch der Titrirmethode, 2. Aufl. i, 254; also Z&itschr. /. analyt. Chem., vui, 311 !! DINGL. volyt. Journ., CXLIII, 198. 233.] CALCIUM COMPOUNDS. 383 pointed out why MOHR had obtained varying results, and proved, as WAGNER had already done, that when the iodometric method is correctly carried out, it also gives exceedingly good results when sodium thiosulphate is used. This opinion I must con- firm and would advise the following procedure: To 10 c.c. of the chlorinated-lime solution containing 0-1 grm. chlorinated lime prepared as above and contained in a beaker, add first about 100 c.c. of water, then about 6 c.c. of potassium- iodide solution (containing 0-6 grm. KI and prepared accord- ing to Vol. I, p. 544, 7-) acidulated with hydrochloric acid, and determine the liberated iodine according to 146. Since 1 eq. of iodine corresponds to 1 eq. of chlorine, the calculation is quite easy. R. WAGNER recommends using 2 5 grm. of potassium iodide to 1 grm. chlorinated lime dissolved in 100 c.c. of water, and to add hydrochloric acid only to faintly acid reaction. Although an unnecessarily large excess of acid is not to be recommended, yet there is no need to be so very careful in acidulating. WINKLER (loc. cit.) obtained equally good results whether he added 1, 5, 10, or 20 c.c. of hydrochloric acid to 10 c.c. of the chlorinated-lime solution. D. OTTO'S METHOD. The principle of this method is as follows: Two molecules of ferrous sulphate when brought into contact with chlorine in presence of water and free sulphuric acid give 1 mol. ferric sulphate and 2 mol. HC1, the process consuming 2 at. chlorine: Fe 2 (S0 4 ) 3 +2HCl. One mol. crystallized ferrous sulphate, (FeSO 4 -7H 2 O)=278-082, corresponds to 35-45 of chlorine, or, in other terms, 0-7844 gnu. crystallized ferrous sulphate corresponds to 0-1 grm. chlorine. The ferrous sulphate required for these experiments is best prepared as follows: 384 DETERMINATION OF COMMERCIAL VALUES. [ .233 Take iron nails free from rust and dissolve in dilute sulphuric acid, applying heat in the last stage of the operation; filter the solution, still hot, into about twice its volume of common alcohol. The precipitate consists of FeSO 4 + 7H 2 O. Collect upon a filter, wash with common alcohol, spread upon a sheet of blotting-paper, and dry in the air. When the mass smells no longer of alcohol, transfer to a bottle and keep this well corked. Instead of ferrous sulphate, ammonium ferrous sulphate, FeS0 4 (NH 4 ) 2 SO 4 + 6H 2 O, may be used. 1 grm. of chlorine reacts with 1-1066 grm. of this double sulphate. The Process. Dissolve 3-1376 grm. (4x0-7844 grm.) of the precipitated ferrous sulphate, or 4-4264 grm. (4x1-1066 grm.) of ammonium ferrous sulphate, with addition of a few drops of dilute sulphuric acid, in water, to 200 c.c. ; take out with a pipette 50 c.c., corresponding to 0-7844 grm. ferrous sulphate, or 1-1066 grm. ammonium ferrous sulphate, dilute with 150-200 c.c. water, add a sufficiency of pure hydrochloric acid, and run in from a 50-c.c. burette the freshly shaken solution of chlorinated lime, prepared according to 225, until the ferrous sulphate is completely con- verted into ferric sulphate. To know the exact point when the reaction is completed, place a number of drops of a solution of potassium ferricyanide on a plate, and when the operation is drawing to an end apply some of the mixture with a stirring-rod to one of the drops on the plate, and observe whether it produces a blue precipitate; repeat the experiment after every fresh addi- tion of two drops of the solution of chlorinated lime. When the mixture no longer produces a blue precipitate in the solution of potassium ferricyanide on the plate, read off the number of volumes used of the solution of chlorinated lime. The quantity of solution of chlorinated lime used contained 1 grm. of chlorine. Suppose 40 c.c. have been used; as every c.c. corresponds to 0-1 grm. of chlorinated lime, the percentage by weight of available chlorine in the chlorinated lime is found by the following proportion: 0-40:0-1 ::100 :x; x = 25; 233.] CALCIUM COMPOUNDS. 385 or by dividing 1000 by the number of c.c. used of the solution of chlorinated lime. This method also gives very satisfactory results, provided always that the ferrous salt is perfectly dry and free from ferric salt. Modifications of the preceding Method. 1. Instead of the solution of ferrous sulphate, a solution of ferrous chloride, prepared by dissolving pianoforte wire in hy- drochloric acid (according to Vol. I, p. 318, /?), may be used with the best results. If 0-6307 of pure metallic iron, i.e., 0-6326 of fine pianoforte wire (which may be assumed to contain 99-7 per cent, of iron), are dissolved to 200 c.c., the solution so prepared contains exactly the same amount of iron as the solution of fer- rous sulphate above mentioned that is to say, 50 c.c. of it corre- sponds to 0- 1 grm. chlorine. But as it is inconvenient to weigh off a definite quantity of iron wire, the following course may be pur- sued in preference: Weigh off about 0-15 grm., dissolve, dilute the solution to about 200 c.c., convert the ferrous into ferric chloride with the solution of chlorinated lime, prepared according to the directions of 225, and calculate the chlorine by the proportion 55-9 : 35-45 :: the quantity of iron used : x; the x found corresponds to the chlorine contained in the volume of the solution of chlorinated lime used. This calculation may be dispensed with by the application of the following formula, in which the carbon in the pianoforte wire is taken into account: Multiply the weight of the pianoforte wire by 6307, and divide the product by the number of c.c. of the solution of chlorinated lime used; the result expresses the percentage of chlorine by weight. This method gives very good results. I have described it here principally because it dispenses altogether with the use of standard fluids. It is therefore particularly well adapted for occasional examinations of samples of chlorinated lime, and also by way of control. 2. Instead of directly oxidizing ferrous oxide or chloride by 386 DETERMINATION OF COMMERCIAL VALUES. [ 233. the chlorinated lime, the following may also be employed with good results: Weigh off accurately 0-3 grm. of fine iron wire, dissolve it to ferrous chloride in a current of carbon dioxide, dilute the still acid solution with water to 200 or 300 c.c., and from a burette run in 50 c.c. of the chlorinated-lime solution (prepared as above) slowly and while stirring; then determine the quantity of ircn remaining still unoxidized (or raised from ferrous to ferric chloride) by means of a solution of potassium dichromate (Vol. I, p. 319, 6). If permanganate solution is used instead of dichromate, the re- marks in Vol. I, p. 318, j, must be borne in mind, as the solution contains hydrochloric acid. By this means the quantity of iron oxidized by the chlorinated lime is ascertained, and from this the chlorine content, according to the proportion stated above in 1. These by no means exhaust the number of excellent chlo- rometric methods. For instance, a standard solution of potassium ferrocyanide may be used with good results instead of the ferrous salt, as recommended by E. DAVY.* After adding an excess of solution of potassium ferrocyanide to the chlorinated-lime solu- tion, acidulate with hydrochloric acid and determine the residual ferrocyanide by means of potassium dichromate. The end of the reaction is reached when a drop taken out and brought into con- tact with dilute ferric-chloride solution on a porcelain plate no longer affords a blue or green color. The determination of the residual potassium ferrocyanide may be just as accurately and more conveniently ac omplished by means of potassium-per- manganate solution, Vol. I, p. 554, g. Again, an acid ferrous- chloride solution may be added in excess to the chlorinated-lime solution, and the ferric chloride formed titrated with stannous chloride (Vol. I, p. 327, 6, a). Each equivalent of ferric chloride, Fe 2 Cl , corresponds with 2 eq. of CL, (2FeCl 2 + 2Cl = Fe 2 Cl e ). The solution of iron employed must, of course, be free from ferric chloride; or if it contains any, the quantity must be determined (Vol. I, p. 578). * Phil. Mag. (4), xxi, 214. 234.] CALCIUM COMPOUNDS. 387 C. CALCIUM ACETATE. 234. The calcium acetates which are obtained by neutralizing rectified or crude wood vinegar with calcium hydroxide and evap- orating the solution, and which, as is well known, are intermediate products between wood vinegar and pure acetic acid or pure acetates, come into the market in bulk; as their composition is variable, they must be tested as to their acetic-acid content in order to determine their value. The products consist of calcium acetate containing small quantities of calcium propionate and butyrate, etc., empyreu- matic substances which remain undissolved on treatment with water, and usually a little calcium carbonate, alumina, etc. They also contain varying quantities of water. In testing calcium acetate, the small quantities of propionic and butyric acids, etc., are determined with the acetic acid, and calculated as such. Should it be particularly desired to deter- mine the quantities of these acids, the method proposed by E. LUCK may be used.* Of the methods which are here described, the first is suitable for every kind of calcium acetate; the other two only for the purer sorts. I. DISTILLATION METHOD .f a. Introduce a weighed average sample (about 5 grm.) of the calcium acetate into a small tubulated retort, add 50 c.c. of water and 50 c.c. of ordinary phosphoric acid (free from nitric acid) of about 1-2 sp. gr., and place the retort on a small sand- bath with the neck inclined slightly upwards; connect the retort with a condenser by means of a glass tube bent into an obtuse angle, and distill off the contents at a gentle heat almost to dryness, taking care that all the distillate is collected without loss. A * Zeitschr. f. analyt. Chem., x, 184. f R. FUESENIUS, Ibid., v, 315. 388 DETERMINATION OF COMMERCIAL VALUES. [ 234. 250-c.c. flask serves as the receiver. It is advisable to surround the upwardly inclined neck of the retort with a paper covering. After cooling, dilute the contents of the retort with 50 c.c. of water, distill again almost to dryness, and repeat the operation a third time. Now dilute the distillate to 250 c.c., shake, and in 50 or 100 c.c. determine the free acid by means of normal soda solution (215). Before calculating the quantity of acetic acid from the soda solution used, test a small portion of the distillate with silver nitrate. If only a faint opalescence develops, which is as a rule the case, the above calculation may be proceeded with, i.e., after calculating the relation of the portion taken to the whole: 6-0032 grm. of acetic acid, (C 2 H 4 2 ), or 7-9074 grm. of calcium acetate, (Ca[C 2 H 3 O 2 ] 2 ), correspond with every 100 c.c. of normal soda solution used. If, however, silver nitrate causes any con- siderable precipitate insoluble in diluted nitric acid, the hydro- chloric acid in the distillate must be determined in an aliquot portion and allowed for in the calculation. 6. If there is frequent necessity for testing calcium acetates by the distillation method, it is advisable to employ the steam- distillation method * proposed by me. The small tubulated retort is arranged as detailed under a, but the condenser had better be larger. A 500-c.c. flask is used as a receiver. Into the tubu- lure of the retort there is inserted a glass tube, bent at an obtuse angle and its end slightly drawn out inside the retort; the other end of the tube bears a piece of rubber tubing provided with a screw pinch-cock. Through this tube steam is passed in as re- quired. For the supply of an easily regulated current of steam, a small iron or copper steam-boiler with a safety-valve is most suitable; if this is not available, a flask fitted with a doubly perforated rubber stopper will answer. In one perforation insert a tube bent at right angles and connected with the steam-inlet tube of the retort by means of a piece of rubber tubing; in the other aperture fit a tube bent twice at right angles, and the outer limb * Zeitschr. /. analyt. Chem., xiv., 172. 234.] CALCIUM COMPOUNDS. 389 of which, about 25 cm. long, dips into a strong test-tube about 6 cm. high and filled with mercury. This test-tube, securely fixed in a large cork, stands in a beaker of cold water. It will be seen that this contrivance serves to supply steam at a certain tension, and at the same time acts as a safety-valve, and allows the current of steam to be regulated as desired. Distillation is carried on with the screw pinch-cock closed until only a very small quantity of rather thick liquid remains, taking care, by cautiously heating, that the liquid, inclined to froth, does not come over. As soon as the contents of the retort again begin to froth, lower the heat applied to the sand-bath, and by cautiously opening the screw pinch-cock admit steam, which, of course, must already have the required tension. The distilla- tion is proceeded with in this manner until the last drops of dis- tillate cease to have an acid reaction. By more or less strongly heating the sand-bath, and by opening the pinch-cock more or less, the operation may be regulated at will, and completed in a shorter time than is possible when no steam is used. c. The distillation carried out according to a may also be ac- celerated by using an air-current. In this case there are used a distilling flask and a receiver of strong glass. The latter is fitted airtight to the condenser, and through its tubulure air is pumped out most conveniently with a water air-pump until the pres- sure on the liquid is only about one-half an atmosphere. The distillation flask may be heated in a water-bath filled with a satu- rated solution of common salt; the air pumped out is passed through a U-tube containing a little water (comp. L. WEIGERT, "On the Determination of Acetic Acid in Wine" *). II. ALKALIMETRIC METHOD. Boil 5 grm. of the calcium acetate to be examined with water, filter into a 500-c.c. flask, wash, make up the filtrate when cold to 250 c.c., and shake; measure off 100 c.c. and evaporate in a platinum dish, ignite the residue with access of air until the car- * Zeitschr. f. analyt. Chem., xviu, 207. 390 DETERMINATION OF COMMERCIAL VALUES. [ 234. bon is consumed, and in the residue determine the calcium alkali- metrically ( 223), calculating 2 eq. of acetic acid for every equiv- alent of calcium found. In the case of a salt considerably contaminated with empy- reumatic substances, this simple method, as already mentioned above, gives an incorrect (too high) result, because the compounds of the empyreumatic substances with calcium dissolve in water in appreciable quantities, and on evaporation and ignition also yield calcium carbonate or caustic lime. III. COMBINED ACIDIMETRIC METHOD. This method published by me * a few years ago is based on the following reaction : If an excess of oxalic acid is added to the solution of all the soluble substances dissolved out from cal- cium acetate by water, all the calcium will be obtained in the precipitate as an oxalate, together with a portion of the empy- reumatic substances, and also alumina, silica, sand, etc., while the solution will contain the acid substances, i.e., acetic acid together with small quantities of its homologues and the excess of oxalic acid (that portion not neutralized by the calcium); in addition to these, there are also present in the solution empyreu- matic substances which have no acid reaction, and which impart a more or less yellow to brown color to the solution. If in the solution, on the one hand, we determine the acidity, i.e., the sum of the acetic acid (together with propionic and butyric acids) and oxalic acid by means of normal alkali, and on the other hand the quantity of oxalic acid, we have but to subtract the normal alkali solution corresponding with the latter from the total quantity employed, in order to be able to calculate from the difference the acetic acid (together with propionic and butyric acids, etc.) present. This conclusion is, of course, correct only if the solution con- tains no other neutral acetates the bases of which are incompletely or not at all precipitated by oxalic acid, e.g. magnesium acetate. * Zeitschr. f. analyt. Chem., xiu, 153. 234.] CALCIUM COMPOUNDS. 391 As, however, every manufacturer of calcium acetate knows that the employment of lime for the saturation of wood vinegar is disadvantageous, calcium acetates strongly contaminated with magnesium are but seldom met with in commerce; and the pos- sible error caused by the presence of magnesium in the calcium acetate is rarely of any importance, and is due to subtraction of too large a quantity of oxalic acid, i.e., the sum of the free and of the combined oxalic acid remaining in the solution, from the total free acids found, thus causing the quantity of acetic acid found to be too low. The Process: Accurately weigh off 5 grm. of the calcium acetate to be examined, introduce it into a 250-c.c. flask (which has also a mark at which it holds 252-1 c.c.), and dissolve in 150 c.c. of water; then add, without filtering, 70 c.c. of normal oxalic-acid solution, fill to the 252-1-c.c. mark,* close the flask with a rubber stopper, shake well, allow to settle, and filter off at least 200 c.c. of liquid through a dry, plaited filter, using a covered funnel, into a dry flask. 1. To 100 c.c. of the clear, frequently yellow filtrate add a little litmus tincture, and then normal soda solution until per- fectly neutral. As the color of the liquid renders it difficult to observe the change from red to blue, litmus and turmeric papers must be also employed to ascertain the neutrality point; it is also advisable to determine it several times by adding, after one experiment is finished, a small quantity of normal hydrochloric acid, and then again normal soda solution to neutralization. The titration may be considered as completed only when concordant results are thus obtained. By multiplying the number of c.c. of soda solution used by 2-5, the quantity corresponding with 250 c.c. of solution, i.e., with the 5 grm. of substance taken, is found. 2. To another 100 c.c of the solution add a solution of pure * The 2-1 c.c. (i.e., the difference between 250 and 252-1 c.c.) represent, as nearly as possible without accurately knowing the composition of the calcium acetate, the volume which the precipitated calcium oxalate (sp. gr. 2-2202) occupies. 392 DETERMINATION OF COMMERCIAL VALUES. [ 234. calcium acetate, allow to settle in a moderately warm place, filter off the calcium oxalate, wash it, and convert it as usual (by gently igniting and treating the residue with ammonium carbonate, etc.) into calcium carbonate; multiply the number obtained by 49-95 (see below), and thus find the number of c.c. of normal soda solu- tion which the free oxalic acid (as H 2 C 2 O 4 ) in the solution required for saturation. Deduct this number from the number of c.c. of soda solution found in 1, and from the remainder calculate the acetic acid (together with the small quantities of propionic and butyric acids, etc.) contained in the 5 grm. of substance taken.* If it is desired to avoid weighing the calcium carbonate ob- tained by gently igniting the calcium oxalate, the calcium oxa- late obtained by precipitating 100 c.c. of the acid liquid with calcium acetate may be strongly ignited, and the calcium in the residue, whether as calcium oxide or carbonate, titrated with normal, hydrochloric acid, the excess of hydrochloric acid being titrated back with normal soda solution ( 223). The calculation is then simply effected by subtracting the c.c. of normal hydro- chloric acid required for neutralizing the calcium obtained from the calcium oxalate, from the c.c. of normal soda solution required for neutralizing the free acid in 100 c.c. of the filtrate. The re- mainder, multiplied by 2-5, directly gives the quantity of soda solution corresponding to the acetic acid (together with the pro- pionic and butyric acids, etc. in the 250 c.c. of filtrate, and hence in the 5 grm. of substance weighed out. *The abbreviation of the calculation as detailed here, i.e., the fact that it is only necessary to multiply by 49-95 the calcium carbonate obtained by gently igniting the calcium oxalate obtained from 100 c.c. of the nitrate, in order to find the number of c.c. of soda solution corresponding with the free oxalic acid (as H 2 2 O 4 =90-016) present in the 250 c.c., is based on the following proportions, from which the free oxalic acid contained in the 250 c.c. is calculated from the calcium carbonate (=y) obtained from the calcium oxalate precipitated from 100 c.c. : 100 :250 ::y:x. The calcium carbonate = 100-1 (=y f ) thus found for the 250 c.c. is calculated into oxalic acid thus: 100-1 : 90 -01 6 ::?/, \x, and the oxalic acid thus found is calculated into nor- , 2000 , ., 2-5X90-016X2000 mal soda solution by multiplying by ^Q^\ but y X iOQ.ix90-016 ' = y X 49-95. 235.] CALCIUM COMPOUNDS. 393 The results obtained by me when using this method corre- sponded very satisfactorily with those afforded by the distillation method in the case of calcium acetate prepared from rectified wood vinegar. D. ANALYSIS OF LIMESTONES, DOLOMITES, MARLS, CEMENTS, ETC. 235. As the minerals containing calcium and magnesium carbonates play a very important part in manufactures and agriculture, the chemist, is often called upon to analyze them. The analytical process varies according to the object in view. For technical purposes, it is sufficient to determine the principal constituents; the geologist takes an interest also in the substances present in smaller proportions, whilst the agricultural chemist seeks a knowledge not only of the constituen s but also of the state of solubility, in different menstrua, in which they are severally present. I will give, in the first place, a process for effecting a complete and accurate analysis ; in the second place, the volumetric methods by which the calcium and magnesium carbonates may be deter- mined; and lastly, the analysis of the products formed by heating these minerals, i.e., quicklime and cements. An accurate qual- itative examination should always precede the quantitative an- alysis. I. METHOD OF EFFECTING THE COMPLETE ANALYSTS. a. Reduce a large piece of the mineral to powder, mix this uniformly, and preserve in a well-stoppered bottle. b. Weigh off about 2 grm. of the powdered mineral between two watch-glasses, and dry to constant weight at 100 (the loss in weight gives the moisture); then introduce the powder into a beaker, add water, warm, cover the beaker with a large watch- glass, and gradually add hydrochloric acid until all the carbonates are just dissolved. Too large an excess of hydrochloric acid and too strong a heat must be avoided, in order that any clay present may be decomposed as little as possible. After gently warming 394 DETERMINATION OF COMMERCIAL VALUES. [ 235. for quite some time, collect the residue on a filter paper previously dried at 100, wash it, and weigh. It generally consists of sep- arated silica, day, and sand; but it often contains also humus-like matter. Opportunity will be afforded in g for examining this residue. c. Mix the hydrochloric-acid solution with chlorine water (or aqueous solution of bromine), then with ammonia in slight excess, and let the mixture stand at rest for some time, in a covered vessel, at a gentle heat. Filter off the precipitate, which contains be- sides the hydrate of sesquioxide of manganese, ferric and aluminium hydroxides the phosphoric acid which the analyzed compound may contain, the silicic acid which may have gone into solution, and, moreover, invariably traces of calcium and magnesium; wash slightly, and redissolve in hydrochlo ic acid; heat the solu- tion, add chlorine (or bromine) water, and then precipitate again with ammonia; filter off the precipitate, wash, dry, ignite, and weigh. If a pure white precipitate of magnesium hydrate is obtained on adding the ammonia, in the case of dolomites, instead of a small quantity of a yellowish one, it is an evidence that the solu- tion does not contain sufficient ammonium chloride. In this case dissolve the precipitate, without filtering, by means of hy- drochloric acid, add chlorine water, and then precipitate with ammonia. For the estimation of the several components of the precipitate, viz., Von, manganess, aluminium, and phosphoric acid, opportunity will be afforded in g. d. Unite the fluids filtered from the first and second precipi- tates produced by ammonia, and determine the calcium and mag- nesium as directed in 154, 6 [36]. e. As a rule the minerals here considered contain, besides moisture, a small quantity of water which is not driven off at 100. To determine this heat a fresh sample of the undried mineral (or even if it has been dried at 100) in a small boat, inserted into a glass tube about 25 cm. long, while passing a current of dry air, and collect the water in a weighed calcium-chloride tube 235.J CALCIUM COMPOUNDS. 395 (36). As certain minerals give off dust when thus treated, the glass tube is constricted in front of the boat, and a loose as- bestos plug is placed there to retain the powder. Before inserting the boat with the powdered mineral, the tube, asbestos plug, and corks must be thoroughly dried by heating in a current of air. If the substance dried at 100 has been used, the increase in weight of the calcium-chloride tube gives directly the combined water. When an undried mineral is used, the moisture determined in a must be subtracted from the total water contained in it, in order to find the combined water. /. If the mineral contains no volatile substances other than water and carbon dioxide, the latter may be determined by igni- tion with vitreous borax (Vol. I, p. 487, c). If the mineral has been dried at 100, the water found in e is subtracted from the loss of weight it undergoes, in order to find the carbonic acid from the difference; if, however, the undried mineral has been taken, both the combined water, e, and the moisture must be subtracted. If it is not desired to use this method, or if it is inapplicable, the carbon dioxide may be determined according to Vol. I, p. 490, 66; or, more accurately, Vol. I, p. 493. g. To effect the estimation of the constituents present in smaller proportion, as well as the analysis of the residue insoluble in hydrochloric acid, and of the precipitate produced by ammonia, dissolve 10 to 50 grm. of the undried mineral in diluted hydrochloric acid in the manner described in 6. As the evaporation to dryness of large quantities of fluid is always a tedious operation, gently heat the solution for some time, to expel the carbonic acid; then filter through a weighed filter into a litre flask, wash the residue, dry it at 100, and weigh it. (The weight will not quite agree with that of the residue in 6, as the latter contains also that part of the silicic acid which here still remains in solution.) a. Analysis of the Insoluble Residue. aa. Treat a portion with boiling solution of pure sodium car- bonate ( 235, 6), and separate the silicic acid from the solution ( 140, II, a); this process gives the quantity of that portion of 396 DETERMINATION OF COMMERCIAL VALUES. [ 235. the silicic acid contained in the residue, which is soluble in alkalies. bb. Ignite a portion with access of air; the loss of weight cor- responds with the content of water together with organic matter. In the ignition residue determine the silicic acid and the bases ( 140, II, 6). On deducting the silicic acid found in aa from the quantity found here, the silicic acid present in the form of sand and clay is ascertained. If it is required, as in the determination of hydraulic limes, to estimate each separately, a separate portion of the residue must be heated with sulphuric or phosphoric acid (comp. Analysis of Clay). cc. If the residue contains organic matter (humus), determine, in a portion, the carbon by the method of ultimate analysis ( 178, a). PETZHOLDT,* who determined the coloring organic matter of sev- eral dolomites by this method, assumes that 58 parts of carbon correspond to 100 parts of organic substance (humic acid). Of the hydrogen found, 4-5 parts for every 58 of carbon must be calculated as belonging to organic matter, the remainder being calculated as derived from the water contained in the residue. dd. If the residue contains pyrites,^ fuse another portion of it with sodium carbonate and potassium nitrate; macerate in water, add hydrochloric acid, evaporate to dryness, moisten with hydro- chloric acid, gently heat with water, filter, determine the sulphuric acid in the filtrate, and calculate from the result the amount of pyrites present. % /?. Analysis of the Hydrochloric- Acid Solution. Make the solution up to 1 litre. aa. For the determination of the silicic acid that has passed into solution, and of the barium, strontium, aluminium, manga- * Journ. f. prakt. Chem., LXIII, 194. f Compare PETZHOLDT, loc. cit.; EBELMEN (Compt. rend., 33, 681); DEVTLLE (Compt. rend., xxxvn, 1001; Journ. /. prakt. Chem., LXII, 81); ROTH (Journ. f. prakt. Chem., LVIII, 84). J If the residue contains barium or strontium sulphate, these compounds are formed again upon evaporating the soaked mass with hydrochloric acid; they remain accordingly on the filter, while the sulphuric acid formed by the sulphur of the pyrites passes into the filtrate. 235.] CALCIUM COMPOUNDS. 397 nese, iron, phosphoric acid, as well as traces of cupric oxide and other metals precipitable by hydrogen sulphide in acid solution, evaporate 500 c.c., and proceed as on p. 257, B, this vol. bb. Determine the phosphoric acid in 250 c.c. of the hydro- chloric-acid solution, according to p. 259, this vol. cc. The remaining quarter of the dilute hydrochloric-acid solu- tion is used for the estimation of the alkalies* Mix with chlo- rine water, then with ammonia and ammonium carbonate; after allowing the mixture to stand for some time, filter off the precipi- tate, evaporate the filtrate to dryness, ignite the residue in a platinum dish to remove the ammonium salts, and finally separate the magnesium from the alkalies as directed (Vol. I, p. 610, ft [16]). The reagents must be most carefully tested for fixed alkalies, and the use of glass and porcelain vessels avoided so far as practicable in order to obtain trustworthy results. Should the limestone contain a sulphate soluble in hydrochloric acid, precipitate the sulphuric acid by adding a small excess of barium chloride, allow to settle, and filter off the barium sulphate (which is to be determined in the usual manner) before proceed- ing as above to the estimation of the alkalies. h. The iron found in g may be present in the mineral as ferric or ferrous oxide, or as compounds of both oxides. To decide this question, dissolve about 10 grm. of the undried mineral in a 250-c.c. flask by warming with diluted hydrochloric acid (Fig. 84, Vol. I). When cold, dilute the solution to 250 c.c., shake, allow to settle; draw off 100 c.c. of the liquid with a pipette, and in it determine the ferrous oxide according to PENNY'S method (Vol. I, p. 319). Any ferric oxide is finally determined from the difference. * The simplest way of ascertaining whether and what alkalies are present in a limestone is the process given by ENGELBACH (Annal. d. Chem. u. Pharm., cxxm, 260) viz., ignite a portion of the triturated mineral strongly in a platinum crucible over the blast, boil with a little water, filter, neutralize with hydrocholoric acid, precipitate with ammonia and ammonium car- bonate, filter, evaporate the filtrate to dryness and examine with the spec- t-o^oone. The ammonium-carbonate precipitate may be evaporated with hydrochloric acid to dryness, and examined in like manner for barium and strontium. 398 DETERMINATION OF COMMERCIAL VALUES. [ 235. i. As calcite and aragonite may contain -fluorides (JENZSCH*), the possible presence of fluorine must not be disregarded in accu- rate analyses of limestones. Treat, therefore, a larger sample of the mineral with acetic acid until the calcium and magnesium car- bonates are decomposed; evaporate to dryness until the excess of acetic acid is completely expelled, and extract the residue with water ( 138, I). We have the fluorine in the residue. If it can be distinctly detected in a portion of the latter, f the determination may be attempted as in 166, 4, b. k. If the limestone under examination contains chlorides, treat a large sample with water and nitric acid, at a very gentle heat; filter, and precipitate the chlorine from the filtrate by solution of silver nitrate. /. It is often interesting for agriculturists to know the degree of solubility of a sample of limestone or marl in the weaker solv- ents. This may be ascertained by treating the sample first with water, then with acetic acid, finally with hydrochloric acid, and examining each solution and the residue. The analysis of marls made by C. STRUCKMANN J were done in this manner. m. To effect the separation of the caustic or carbonated lime, in hydraulic limes, from, the silicates, DEVILLE proposed to boil with solution of ammonium nitrate, which he stated would dissolve the caustic lime and carbonate of lime, without exercising a decom- posing action on the silicates. GUNNING || found, however, that by this process the double silicates of aluminium and calcium are more or less decomposed, with separation of silicic acid. As yet no method is known by which the object here stated can be accom- plished with absolute accuracy. Even though at times treatment with diluted acetic acid gives good results , yet as a general rule, careful treatment with diluted hydrochloric acid gives best results. C. KNAUSZ If also recommends hydrochloric acid. * Pogg. AnnaL, xcvi, 145. f See Qual Anal, 146, 6. j AnnaL d. Chem u. Pharm.., LXXIV, 170. Compt. rend., xxxvn, 1001; Journ. /. prakt. Chem., LXII, 81. || Journ. f. prakt. Chem., LXII, 318. IT Gewerbeblatt aus Wurtemberg, 1855, Nr. 4; Chem. Centralbl, 1855, 244. 235.] CALCIUM COMPOUNDS. 399 II. VOLUMETRIC DETERMINATION OF CALCIUM CARBONATE AND MAGNESIUM CARBONATE (FOR TECHNICAL PURPOSES). a. If a mineral contains only calcium carbonate, the amount of the latter may be estimated from the quantity of acid required to effect its decomposition, the method described in 223 being employed for the purpose.* Or the carbonic acid in the mineral may be determined, say by the method detailed in Vol. I, p. 490, 66, and 1 mol. calcium carbonate = 100 1 calculated for each mol. carbon dioxide = 44. 6. But if the mineral contains, besides calcium carbonate, also magnesium carbonate, the results obtained by either process give the quantity of calcium carbonate + magnesium carbonate, the latter being expressed by its equivalent quantity of calcium car- bonate (i.e., 100-1 of calcium carbonate for 84-3 of magnesium carbonate). If, therefore, you desire to know the actual amount of each, you must, in addition to the above determination, de- termine one of the alkali-earth metals separately. For this pur- pose one of the two following methods may be employed: 1. Mix the dilute solution of 2 to 5 grm. of the mineral with ammonia and ammonium oxalate in excess, allow to stand for twelve hours and then filter. Ignite the precipitate of calcium oxalate, together with the filter, and treat the calcium carbonate produced as directed 223. This process gives the amount of calcium contained in the analyzed mineral the difference between- this and the former result gives the calcium carbonate which is equivalent to the amount of magnesium carbonate present. To obtain perfectly accurate results by this method, repeated precip- itation is indispensable (see 154, 6, a). 2. Dissolve 2 to 5 grm. of the mineral in the least possible excess of hydrochloric acid, and add a solution of lime in sugar water so long as a precipitate forms. By this operation the mag- nesia only is precipitated. Filter, wash, and treat the precipitate as directed in 223 ; the result represents the quantity of the mag- nesium. Deduct the quantity of calcium carbonate equivalent * This method, somewhat modified, was first proposed by BINEAU. 400 DETERMINATION OF COMMERCIAL VALUES. [ 235. thereto from the result of the total determination; the remainder is the amount of calcium carbonate present. The method 2 is only suitable when the proportion of magne- sium is small. III. ANALYSIS OF QUICK-LIME AND CEMENTS. Ordinary limestones when properly ignited yield quick-lime, which is used in the preparation of mortar, and for many other pur- poses; limestones which contain 25 per cent, of clay, or ex- pressed in general terms silicates which are decomposable on ignition with lime, yield cements on suitably igniting. Such cements are also obtained, as is well known, when, instead of limestones containing clay in their natural condition, an artifi- cially prepared mixture of clay with lime or calcium carbonate is heated. The changes which occur on ' ' burning " the ordinary lime- stone, as well as that containing clay, are as follows: Water and carbon dioxide are expelled, ferrous carbonate and manganous carbonate are converted into ferric and manganic oxides respectively, and organic matters are burnt or at least decom- posed, leaving a small residue of carbon ; but above all, any silicates present are decomposed so that their bases become soluble in hydrochloric acid, while their silicic acid is partially dissolved on treatment with hydrochloric acid, and partly separates as a hydrate. Any admixed quartz, on the other hand, scarcely undergoes change by heating. If the burned limestones or cements are exposed to the action of the air, they gradually absorb water and carbon dioxide. Of course no mention is here made of technical tests, by which the suitability of the burned limes and cements for building pur- poses is determined;* regarding the most suitable methods for their analysis, however, the following remarks may be made : 1. Ignite several grm. in a platinum crucible over the * Excellent advice on this point is given by Dr. W. MICHAELIS in his work "Zur Beurtheilung des Cementes," Berlin, polytechnische Buchhandlung (A. SEIDEL), 1876. ^ 235.] CALCIUM COMPOUNDS. 401 gas blowpipe. The loss in weight gives the water and carbon dioxide. 2. In a larger sample (about 10 grm. determine the carbon dioxide according to Vol. I, p. 493. The water is found from the difference, or it may be directly determined according to 235, I, e. 3. Treat about 5 grm. with an excess of diluted hydrochloric acid, evaporate to dryness in a platinum or porcelain dish, moisten the residue with hydrochloric acid, warm, add water, filter, and wash the undissolved portion ( 140, II. a). 4. Wash the contents of the filter in 3 into a dish without damaging the filter, boil with successive quantities of a concen- trated solution of sodium carbonate, pass through the same filter placed in a hot- water funnel, until all the hydrated silica is dis- solved (i.e., until a few drops remain clear when heated with ammonium-chloride solution), and wash the residue. From the alkaline solution separate the silicic odd according to 140, II, a, ab. The residue insoluble in sodium carbonate consists of quartz sand and residual undecomposed silicate. Wash this into a platinum dish, add the filter ash to it, evaporate w'th water to a small bulk, when cold add sulphuric acid, and then heat for some time. The bases are dissolved by this treatment, and the silica separated from them may now be separated from the quartz sand by treating the insoluble washed residue with sodium-car- bonate solution. In the sulphuric acid solution any alumina, ferric oxide, etc., are determined. Should the treatment with sulphuric acid in open vessels not be successful, heat with sul- phuric acid in sealed tubes (Vol. I. p. 521). 5. Make up the hydrochloric-acid solution obtained in 3 to 500 c.c., and in 250 c.c. determine the sulphuric add, * potassium, and sodium ( 209, 4) ; in the other 250 c.c. separate the ferric oxide (manganic oxide} and alumina by repeatedly precipitating with ammonia ( 235, I, c). Make up the filtrate to 500 c.c., and in 250 c.c. of it determine the calcium and magnesium. * Cements generally contain this. See Dr. W. MICHAELIS, Die hydrau- lischen Mortel, insbesondere der Portland-Cement," Leipzig, QUANDT u. HANDEL, 1869, p. 89. 402 DETERMINATION OF COMMERCIAL VALUES. [ 235. [6. It is often desirable in cement analysis to estimate only CaO. The usual method of procedure is to disolve the cement in dilute HC1, add excess of ammonia to precipitate silica, A1 2 3 , and Fe 2 O 3 , precipitate the calcium as oxalate, and ignite to CaO. According to R. F. YOUNG and B. F. BAKER,* this method gives an entirely erroneous result, which may be as much as 1.5 per cent too high or too low, and the reason of which is that when cement is dissolved in dilute hydrochloric acid, part of the calcium silicate is not decomposed, but merely dissolves and is precipitated on neutralizing the acid with ammonia. This causes a low result; but, on the other hand, the ignited CaO will invariably contain very appreciable quantities of SiO 2 , A1 2 O 3 , and Fe 2 O 3 , which will cause a high result. The two following methods have been found to give very satis- factory results: 1. One grm. of the cement is treated in a conical beaker with a small quantity of concentrated hydrochloric acid. A little nitric acid is added, and the contents evaporated to dryness on a sand-bath, and heated till the contents are distinctly red; then treated with dilute hydrochloric acid, and excess of ammonia added. The SiO 2 , A1 2 (OH) 6 , and Fe 2 (OH) 6 are filtered off, and the calcium precipitated as oxalate and ignited to CaO in the usual way. 2. One grm. of cement is dissolved in dilute hydrochloric acid, ammonia added, and the precipitate of iron, alumina, and silica filtered off. This precipitate is re-dissolved in concentrated hydro- chloric acid and re-precipitated by ammonia. The two filtrates and washings are collected, and the calcium estimated as above. In accurate estimations, it is advisable in both methods to dissolve the ignited CaO after weighing in hydrochloric acid, and estimate the Si0 2 , A1 2 O,, and Fe 2 3 it may contain. The volumetric estimation of calcium by titrating the excess of a known quantity of standard oxalic acid left after precipitating in ammoniacal solution, was found to invariably give low results. * Chem. News, LXXXVI, p. 146. 236.] ALUMINIUM COMPOUNDS. 403 This seems to point to the fact that all the calcium is not precipi- tated as oxalate. TRANSLATOR.] 8. ALUMINIUM COMPOUNDS. A. CLAYS. (See Silicon Compounds, 238.) B. ALUMINIUM SULPHATE. 236. Of the aluminium compounds, aluminium sulphate will be first considered. It is manufactured on a large scale according to various methods (more recently by treating with sulphuric acid the aluminium hydroxide obtained from cryolite or bauxite), and occurs in the market usually in the form of crystalline cakes containing variable quantities of water; it exhibits varying de- grees of purity and is hence frequently the subject of chemical analysis. 1. The quantity of water, which amounts to from 40 to 50 per cent., cannot be accurately ascertained by direct heating, because the water driven off has an acid reaction. To determine it from the loss of weight, therefore, ignite about 0-5 grm. of the aluminium sulphate with pure lead oxide 35, /?). The water may be de- termined directly by igniting the aluminium sulphate with anhy- drous sodium carbonate ( 225. I). It must be observed that both of these methods of water determination give, besides the water of crystallization, also the water in any acid alkali sulphate or sul hate that may be present 2. Dissolv^ about 12 grm. in water. If an insoluble residue remains, collect it on a filter, ignite, and weigh. Make up the solution to 500 c.c. 3. Dilute 150 c.c. of the solution, add a little hydrochloric acid, and precipitate hot with barium chloride, but in slight excess only ( 132, 1). The total sulphuric acid is determined from the barium sulphate so obtained. 4. Precipitate the aluminium and the excess of barium from 404 DETERMINATION OF COMMERCIAL VALUES. [ 236. the filtrate, obtained in 3 by adding ammonia and ammonium carbonate; from the filtrate separate the alkali chlorides ( 225, II, e), and in these finally determine the potassium. As a rule the preparations found in the market contain cnly sodium. 5. To 100 c.c. of the solution obtained in 2 add ammonium chloride, precipitate with ammonia ( 105, a), wash the pre- cipitate moderately and dissolve it in hot hydrochloric acid, and reprecipitate the diluted solution with ammonia. The weight of the thoroughly washed and ignited precipitate gives the quan- tity of alumina together with any ferric oxide that may be present. 6. Gradually add 200 c.c. of the solution obtained in 3 to a hot, moderately concentrated potassa or soda solution, finally .adding a larger quantity, so as to redissolve the alumina pre- cipitated. After prolonged heating, there still remains, as a rule, .a small quantity of residue undissolved. Dilute, filter, wash, dissolve the precipitate in hot hydrochloric acid, heat, precipitate with ammonia, heat again until the fluid is but just faintly alkaline, filter, and in the filtrate determine the small quantities of calcium and magnesium, should these be present. In the precipitate, which usually contains a little alumina, determine the ferric oxide according to 160, A, 2. 7. If all the bases are calculated as neutral sulphates, (A1 2 [SO 4 ] 3 ; Fe? [SO 4 ] 3 ; Na 2 SO 4 , etc.), and the sulphuric acid contained in them is subtracted from that found in 3, there is generally obtained a small remainder which, so far as the quantity of alkaline sulphates is concerned, is considered to be combined with a corresponding quantity of these to form alkali disulphates; in the other case the excess of sulphuric anhydride would be expressed as hydrated sulphuric acid. If it is desired to determine the sulphuric acid which will neutralize alkali (such as that combined with aluminium and iron, as well as that combined with neutral alkali sulphate to form disulphate, or present in the free state) as an acidimetric control, the method detailed on p. 314, c, this vol., must be used. 237.] SILICON COMPOUNDS. 405 9. SILICON COMPOUNDS. A. ANALYSIS OF NATIVE, AND MORE PARTICULARLY OF MIXED, SILICATES.* 237. As the analysis of silicates completely decomposable by acids has been described in 140 / II, a; and that of silicates not de- composable by acids in 140, II, b, there but remains to add here a few remarks particularly regarding the examination of mixed silicates, i.e., such as are composed of silicates of both classes (phonolites, clay slates, basalts, etc.). 1. Prepare a homogeneous, air-dried, finely powdered sample and in it determine the moisture by drying 1 or 2 grm. at 120 to constant weight. 2. It is customary to treat a second portion of the air-dried substance with moderately concentrated hydrochloric acid for a long time at a gentle heat, evaporate to dryness on a water-bath, moisten the residue with hydrochloric acid, add water, and then filter; it is often preferable, however, to digest the powder with diluted hydrochloric acid (of about 15 per cent.) for several days at a gentle heat, and then to at once filter. Which of the two methods is to be resorted to, or whether the method here described, and which was first employed by CHR. GMELIN in the analysis of phonolites, is at all eligible for use, depends upon the nature of the mixed minerals. The more easily decomposable one of the constituents of the mixture is, and the more undecomposable the remainder, the more constant will be the proportion between the undissolved and the dissolved portions in different experiments ; and the less the undissolved part is attacked by further treatment with hydrochloric acid the more safely may this method of de- composition be employed. * Comp. Qual. Anal., 205 to 208. It is absolutely essential to make a minute and comprehensive qualitative analysis before proceeding to the quantitative analysis. 406 DETERMINATION OF COMMERCIAL VALUES. [ 237. This process gives: a. A hydrochloric-acid solution, containing, besides more or less quantities of silicic acid according to circumstances, the bases of the decomposed silicate in the form of metallic chlorides; these, after the removal of the silicic acid ( 140, II, a), are separated and determined according to the methods detailed in the fifth section. b. An insoluble residue, which contains, besides the unde- composed silicate, the silica separated from the decomposed silicate. After the latter has been thoroughly washed with water to which a few drops of hydrochloric acid have been added, it is transferred, while still moist, and in small portions at a time, to a boiling solution of silica-free sodium carbonate contained in a platinum dish; maintain the boiling for some time, and filter each time, while very hot (most conveniently by the aid of a hot- water funnel), through a weighed filter. Finally, rinse the last portions of the residue adhering to the filter completely into the dish. If this cannot be successfully done, incinerate the dried filter, transfer the ash to the platinum dish, and again boil with sodium-carbonate solution until a few drops of the liquid finally passing through remains clear on being warmed with an excess of ammonium-chloride solution. Wash the undissolved residue first with hot water, then in order to insure the removal of every trace of adhering sodium carbonate with water faintly acidu- lated with hydrochloric acid, and finally again with pure, water. Acidulate the alkaline fluid with hydrochloric acid and in it determine the silicic acid which resulted from the silicate de- composed by the acid, according to 140, II, a. Dry the undis- solved silicate at 120 and weigh. Deduct its weight together with that of the moisture from the weight of the substance origi- nally taken; the difference gives the quantity of the dissolved silicate in the dry state. Treat the undissolved silicate exactly as directed in 140, IT, b. 3. Water. Silicates dried at 120 occasionally contain water. This is determined by taking a weighed portion dried at 120 (see 1) and igniting in a platinum crucible, or in presence of 237.] SILICON COMPOUNDS. 407 carbon, carbonates, or ferrous iron in a tube, through which a stream of dry air is drawn, the moisture expelled from the sub- stance being retained by a weighed calcium-chloride tube. To ascertain whether the water expelled proceeds from the silicate decomposable by hydrochloric acid, or from that not decomposable, ignite in a similar manner a sample of the silicate dried at 120. For instance, suppose the mixed silicate consisted of 50 per cent, decomposable and 50 per cent, undecomposable silicate; and that the latter contains 47 parts of anhydrous substance and 3 parts water; the water determination would give for the mixed silicate 3 per cent., and for the undecomposable portion 6 per cent. Now as 3:6 as the undecomposed silicate (50 per cent.): the mixed silicates (100 per cent.), it is evident that the decomposable sili- cate gives no water on ignition. If the escaping aqueous vapors manifest an acid reaction, owing to the disengagement of hydrofluoric acid or silicon fluoride, mix the finely powdered substance with anhydrous sodium car- bonate, ignite in a current of dry air, and collect the water in a weighed calcium-chloride tube ( 36). The best method of con- ducting this water determination in silicates has been thoroughly studied by E. LUDWIG * and L. Sipocz.f The former ignites the mixture in an expanded platinum tube; the latter in a platinum boat. SIPOCZ recommends the following method: Ignite 4 parts sodium carbonate in a platinum crucible till water is completely expelled, allow to cool to 50 or 60, mix in- timately with a platinum wire with 1 part of the pulverized dried silicate, and introduce the mixture into a capacious platinum boat, rinsing out the last adhering portions with sodium carbonate. The boat, provided with a cover, is now placed in the middle of a porcelain tube (glazed inside) 40 cm. long and 17 mm. inner diameter, and heated in an air-bath for an hour to 120 or 130. During this time every trace of moisture should be removed from * Untersuchungen vber die chemisette Zusammensetzung des Pyrosmaliths, mineralog. Mittheilungen von G. TSCHERMAK, 1875, 211 (Zeitschr. J. analyt. Chem. xvii, 206). t Zeitschr. f. analyt. Chem., xvii, 207. 408 DETERMINATION OF COMMERCIAL VALUES. [ 237. the mixture by passing dried air through the tube by means of a gasometer. The end of the tube through which the current of air makes its exit is provided with a calcium-chloride tube, which at the end of the drying process is replaced by a weighed U-tube containing glass beads moistened with pure strong sulphuric acid. The other end, connected with the gasometer, is provided with intermediate soda-lime and sulphuric-acid tubes. The substance is now gradually brought to a red heat in a combustion furnace, and a regulated current of air (dried by sulphuric acid) is passed over it for about half an hour to carry the expelled water vapor into the absorbing apparatus. (It is obvious that this method can be used in any case instead of ignition with lead oxide.) According to SAINTE-CLAIRE DEVILLE and FOUQUE * the water in silicates containing fluorine compounds may as a rule be expelled free from the latter by properly igniting, since the fluorine compounds require far higher temperatures for their expulsion than does water. After the water has been driven off the fluorine is expelled, if the substance is ignited, either as an alkali fluoride or silicofluoride. 4. Occasionally the portion of silicates undecomposable by hydrochloric acid contains carbonaceous organic matter. In this case it is safest to treat an aliquot part in a current of oxygen, and to weigh the resulting carbon dioxide ( 178). According to DELESSE traces of nitrogen are always, or nearly always present in the organic matter contained in silicates. 5. Silicates quite frequently contain admixtures of other minerals (magnetite, pyrites, apatite, calcium carbonate, etc.) which may sometimes be detected with the naked eye or with the aid of a magnifying-glass. It is scarcely possible to devise a process which would be applicable to all such cases; it may be noted, however, that it is occasionally advantageous to first treat the substance with acetic acid before acting on it with hydro- chloric acid. In this way the separation of the carbonates of the alkaline earths in particular is effected without difficulty. * Compt. rend., xxxviu, 317; Journ. f. prakt. Chem., LXII, 78. 237.] SILICON COMPOUNDS. 409 The analyses by DOLLFUSS and NEUBAUER,* which were carried out in our laboratory, may be adduced as examples of complete examinations of this kind. 6. If the silicates contain sulphides, determine the sulphur content according to one of the methods described in 148, 11,^4, by the dry way; or, which is as a rule preferable, in the wet way, or according to CARIUS' method ( 190, p. 126). When operating in the wet way, it must be remembered that if barium, strontium, or lead is present, a part of the resulting sulphuric acid is found in the insoluble residue: this, however, is not the case if the min- eral is fused with an alkali carbonate and nitrate. If a sulphate is present besides sulphide, determine the sulphuric acid by boiling a separate portion of the silicate with a potassium- or sodium- carbonate solution for a long time, filtering, and precipitating the acidulated filtrate with barium chloride. The quantity of sul- phuric acid thus found is subtracted from that obtained by treat- ment with oxidizers; the difference gives the sulphur in the sul- phide. In many cases it is preferable to extract the substance with hydrochloric acid rather than to boil with sodium carbonate, in order to determine the sul huric acid in sulphates. 7. The iron, which is almost always found in silicates, may be present in either the ferric or ferrous state, or in both. As the knowledge as to whether ferric or ferrous iron is present (or both) is of great importance in forming a judgment regarding a min- eral, and the accurate determination of the ferrous iron is beset with many difficulties, the subject is one that has been the object of frequent and much research. The following methods are of importance : a. HERMANN'S method: Decomposition of the mineral by fusing with borax in a current of carbon dioxide; this gives too high a ferrous-oxide content, and is to be rejected (RAMMELSBERG ; f b. In many cases the object may be effected by heating a * Journ. f. prakt. Chem., LXV, 199. f Zeitschr. der deutsch. geologischen Gesellsch., 1872, 69. t Zeitschr. f. analyt. Chem., xvn, 212, 410 DETERMINATION OF COMMERCIAL VALUES. [ 237. portion of the substance with hydrochloric or sulphuric acid in a sealed glass tube (Vol. I, p. 521, e) and determining the ferrous iron in the solution so obtained by means of potassium chromate or permanganate, or the ferric iron volumetrically with stannous chloride. c. In those cases where 6 does not give the desired results, and in all cases generally, a solution in which the ferrous or ferric iron may be titrated can be obtained by decomposing the sub- stance with hydrofluoric and sulphuric acids, or hydrofluoric and hydrochloric acids. Quite frequently it suffices to carry out the treatment in open vessels with exclusion of air (comp. Vol. I, p. 310*). If the hydrofluoric acid contains reducing substances (arsenous acid [C. JEHN f], hydrogen sulphide, sulphurous acid, etc.), it must be distilled with potassium permanganate from a platinum retort (E. LUDWIG). In order to avoid this operation DOLTER (loc. tit.) recommends evaporating the solution obtained by decomposing the substance with hydrofluoric and sulphuric acids, in an atmosphere of carbon dioxide, in order to expel the excess of the hydrofluoric acid and with it the reducing sulphur compounds contained in it, before titrating. This does not, however, exclude those errors which arise from the reduction of the ferric iron during solution by the reducing substances present in the hydrofluoric acid. In the case of silicates which are decomposed with great diffi- culty, heat the very finely powdered substance with pure hydro- fluoric acid and moderately dilute sulphuric acid in sealed tubes of Bohemian potash glass. In order to obtain perfectly accurate results SUIDA J recommends treating in precisely the same manner like quantities of the same hydrofluoric and sulphuric acids in a piece of the same glass tubing by the side of that containing the substance to be decomposed, and subtracting the quantity * Regarding other apparatus used for this purpose, see COOKE, Zeitschr. f. analyt. Chem., vii, 98. WILBUR and WHITTLESEY, ibid., x, 98. A. R. LEEDS, ibid., xvi, 323. DOLTER, ibid., xviu, 53. f Zeitschr. f. analyt. Chem., xni, 176 I Ibid., xvn, 213. 237.] SILICON COMPOUNDS. 411 of potassium permanganate required to color the liquid from that used for the decomposed substance. 8. If the silicates contain a small quantity of titanic acid, which is frequently the case, special care must be exercised not to over- look it. When the silicic acid has been separated by evaporation with hydrochloric acid, whether the decomposition of the silicate has been effected by hydrochloric acid or whether the silicate has been previously submitted to the action of alkali carbonate, the titanic acid is as a rule found partly with the silicic acid, partly in the hydrochloric-acid solution. In order to ascertain whether the silicic acid separated contains titanic acid, treat it in a platinum dish with hydrofluoric acid and a little sulphuric acid, evaporate, fuse any residue with potas- sium disulphate, dissolve in cold water, filter if necessary, and separate the titanic acid from the sulphuric-acid solution according to the method detailed in 107, 2. The greater portion of the titanic acid is frequently found in the hydrochloric-acid solution filtered off from the silicic acid. It is precipitated with ferric oxide and alumina on the addition of ammonia ( 161, 4), and is determined in the precipitate either by igniting this in a current of hydrogen, extracting the reduced iron by digestion with diluted nitric acid (Vol. I, p. 652, 7, a), fusing the residue with potassium disulphate, taking up the melt with cold water, and precipitating the titanic acid by boiling ( 107) ; or by at once fusing the precipitate (consisting of ferric oxide, alumina, and titanic acid) with potassium disulphate, dis- solving the melt in cold water, neutralizing the solution as nearly as possible with sodium carbonate, and diluting with water so that 50 c.c. of the liquid will contain not more than 0-1 grm. of the oxides. Now add to the cold solution a slight excess of sodium thiosulphate, wait until the liquid, at first violet, has be- come colorless, and the ferric iron has consequently been reduced to a ferrous state, heat, and maintain boiling until no more sul- phurous acid is evolved; then filter, wash the precipitate with boiling water, dry, and gently ignite in a covered porcelain cruci- ble to expel the sulphur, then remove the lid, and ignite strongly 412 DETERMINATION OF COMMERCIAL VALUES. [237. with access of air. In this manner the alumina (CHANCEL*) and the titanic acid (A. STROMEYER f) are obtained free from iron, and may be separated by the method given above. When separating the titanic acid by boiling the sulphuric-acid solution, the operation must be conducted very carefully (comp. 107), otherwise the titanic acid will not be completely precipitated (see RILEY I). In order to with certainty precipitate pure titanic acid by boiling from solutions containing iron, G. STREIT and B. FRANZ recommended adding about an equal volume of acetic acid. 9. If the silicates contain boric acid, the method proposed by A. DITTE || may be employed instead of that described in Vol. I, p. 738, 6; the method is based upon the separation of boric acid in the form of calcium borate, which is allowed to crystallize from a fused mixture of calcium, sodium, and potassium chlorides. See Appendix. 10. The determination of chlorine, fluorine, and phosphoric acid in silicates has already been minutely described in 166 and 167. 11. Among the most complicated analyses of silicates is that of meteorites, in which, besides the silicates, there are found present also uncombined metals, sulphides, phosphides, and carbides, as well as chrome iron ore. Regarding the examination of meteor- ites, which occurs but seldom, I would refer to the treatise on the analysis of Zsadanyer meteorites by W. PILLITZ,^[ in which the method considered most advantageous is accurately detailed. 12. The analysis of ultramarines also presents unusual dif- ficulties. Regarding the most suitable methods for their analysis I refer to REINHOLD HOFFMANN'S comprehensive work on ultra- marine.** * Compt. rend., XLVI, 987; Ann. d. Chem. u. Pharm., cvm, 237. \Annal. d. Chem. u. Pharm., xcui, 127. \Journ. Chem. Soc., xv, 311; Zeitschr. f. analyt. Chem., u, 70. Journ. f. prakt. Chem., cvin, 65; Zeitschr. /. analyt. Chem., ix, 388. \\Annal. Chim. Phys. (5 ser.), iv, 549; Zeitschr. f. analyt. Chem., xiv, 360. ^Zeitschr. f. analyt. Chem., xvm, 58. ** " Ueber Ultramarin," 1873. Frankfort, R. BAIST. WAGNER'S Jahres- ber., 1873, 378 et seg. 238.] SILICON COMPOUNDS. 413 13. If a silicate undecomposable by acids contains #n ad- mixture of quartz, and if the quantity of this is to be separately determined, proceed according to one of the methods described in 238, II, /. The analysis of clay, about to be described, may be effected according to processes differing slightly from those employed in the analysis of silicates. B. ANALYSIS OF CLAYS. 238. The various clays, resulting from the disintegration, i.e., mechan- ical reduction and chemical decomposition, of rocks containing aluminium silicates (such as felspar and clay shale), consist com- monly of a mixture of true clay with quartz-sand or felspar-sand, etc., and frequently contain also separated silicic acid, which may be extracted by means of a boiling solution of sodium car- bonate. If the clays are no longer in the locality where they were found, they are usually less pure, and contain admixtures of various minerals and, as a rule, also organic matter. As it is important to know not only the chemical composition, but also the constituents into which it may be mechanically sep- arated, in order to judge of the fitness of the clays for technical purposes, it is best to make a mechanical analysis before pro- ceeding to the chemical analysis.* I. MECHANICAL ANALYSTS. By the aid of mechanical analysis the quantities of coarse and very fine sand, and of the finest portions removable by elutriation (clay) which form the constituent parts of the natural clays are ascertained. The mechanical analysis of clays has of late been repeatedly the object of investigation. The elutriation apparatus with which the analysis is effected, have been improved, and the me- * Compare FRESENIUS' " Untersuchung d?r vnchtigsten Nassauischen Thone," Journ. fur prakt. Chem., LVII, 65. 414 DETERMINATION OF COMMERCIAL VALUES. [ 238. chanioally separable constituents of the clay more sharply de- fined. The best apparatus for elutriating is that of SCHONE,* which has been slightly modified by W. SCHUTZE f for washing clay; the component parts of the clay mechanically separable have also been more accurately defined by SEGER J as follows: Coarse sand all the grains of which are over 0-2 mm. large; medium sand all the grains of which are from 0-04 to 0-02 mm. in size; fine sand all the grains of which are from 0-02 to 0-04 mm. in size; marly clay all the grains of which are from 0-01 to 0-02 mm. in size; clay everything smaller. In spite of these improvements the mechanical analysis of clays is still incomplete. For instance the fine sand obtained by SEGER with the SCHONE washing machine from the SEFTEN- BERG clay still contained 9-3 per cent, alumina; and that ob- tained similarly from the ARDENNES clay contained as much as 25-32 per cent. I would therefore refer those who are specially engaged in the mechanical analysis of clay to the treatises above quoted, and particularly to Dr. CARL BISCHOF'S comprehensive and excellent work " Die feuerfesten Thone, etc./' Leipzig, QUANDT u. HANDEL, 1876, in which pages 74 to 86 treat of the analysis of clay by elu- triation. For the ordinary valuation of a clay, the simple elutriation of the clay as effected by the author in the case of the Nassau clay above quoted, and as will be described below, is, as a rule, sufficient. For this purpose there is used the elutriating apparatus recom- mended by FR. SCHULZE || for the mechanical analysis of soils, and which, while not perfect, is n vertheless very convenient, and particularly simple. The more complete, but at the same time more complicated elutriation apparatus devised by SCHONE, * Zeitschr. /. analyt. Chem. r vn, 29. t Notizblatt f. Fabrikation von Ziegeln u. s. w. % 1872, 188 % Ibid., 1873,. 109. Zeitschr. /. analyt. Chem., ix, 397. . /. prakt. Chem., XLVII, 241. 238.] SILICON COMPOUNDS. 415 and above alluded to, will be described when treating of the analysis of soils. For the analysis by elutriation FR. SCHULZE employs: a A glass of the form of a large champagne glass, on the rim of which is cemented a brass ring 15 mm. wide, and with an exit tube directed slightly downward proceeding from its side. The body of the glass is 20 cm. deep, and the diameter at the mouth 7 cm. 6. A funnel-tube, the funnel of which is 5 cm. and the tube 40 cm. long and about 7 m.m. in diameter. The tube is drawn out at the point so that the aperture is only 1-5 mm. wide. c. A vessel of at least 10-litres capacity filled with water, provided at the top with an aperture for filling, and at the side near the bottom with a stop-cock. The vessel is best made of sheet zinc, and should be placed upon a support which may be raised or lowered. The funnel-tube is suspended from the stop-cock by a small cord; and the aperture of the stop-cock should be within or directly above the funnel. d. A dish or large beaker to receive the liquid running from the discharge tube. For the elutriation, crush 30 grm. of the air-dried clay and boil the substance for an hour in a porcelain dish with twice or thrice its volume of water, gently stirring with a pestle, in order to effect as complete a separation as possible of the component parts. After cooling, wash the contents of the dish completely into the elutriating glass, open the stop-cock of the water reser- voir slightly, and insert the funnel-tube, while the water is flowing from it, into the elutriating glass. Care must be taken to have the point of the funnel-tube a few millimetres above the deepest part of the elutriating glass, and this may be accomplished by lowering the water reservoir, or raising the elutriating glass. The stop-cock must be so regulated that the funnel should always be about half filled with water. Under these conditions the pressure of water (i.e., the difference in levels in the elutriating glass and the funnel-tube) will be about 20 cm. By the force of the stream of water the particles of clay are 416 DETERMINATION OF COMMERCIAL VALUES. [ 238. violently stirred up, but only the finer and finest are thrown up sufficiently high to be carried off with the stream of water flowing through the side-tube, while the coarser sand remains in the elu- triating glass. When the water flows off almost clear, close the stop-cock, remove the elutriating glass, and rapidly decant the slightly turbid liquid from the coarse sand in the dish; then wash the residual sand into a small dish by the aid of a wash-bottle with upwardly directed jet, and dry, ignite, and weigh it. Allow the dish or beaker containing the turbid liquid to settle for at least six hours, and decant the clear or slightly turbid super- natant liquid from the deposit; the deposit, however, which is now sure to contain all the fine sand, wash into an elutriating glass, and repeat the operation of elutriation, with the difference that the flow of water is restricted only to a mere dropping on to the side of the funnel, and so that the level of water in the funnel-tube is only about 3 cm. higher than that in the elutriat- ing glass. This operation is repeated until the water runs off clear, which usually is the case in from three to four hours. The residual fine sand is then treated in the same manner as the coarse sand was treated above. The water . content is now determined by igniting a separate weighed portion of the air-dried clay, and the quantity of the finest particles (the clay proper) separable by elutriation ascer- tained from the difference. The following analysis of the poor clay of Hillscheid and the far fatter clay from Ebernhahn, made by me, gave the following results: Hillscheid Clay. Ebernhahn Clay. Coarse sand 24-68 6-66 Finesand 11-29 9-66 Ciay 57-82 74-82 Water., 6-21 8-86 100-00 100-00 II. CHEMICAL ANALYSIS. The quantitative analysis should be preceded by a qualitative examination which should be sufficiently extended to show what 238.J SILICON COMPOUNDS, 417 substances are dissolved on prolonged boiling of the clay with water and allowing to stand for some time to settle (sodium and ammonium chlorides, calcium sulphate, ferrous sulphate, or- ganic substances, etc.); and also what substances are dissolved by treatment with very dilute hydrochloric acid at a gentle heat (calcium and magnesium carbonates, ferric oxide, phosphoric acid, etc.). The clay is quantitatively examined either as it is, or, according to circumstances, after previous treatment with weak acids (acetic or very dilute hydrochloric acid) to free it from ad- mixed alkaline-earth carbonates; or, after the coarser sand has been separated by elutriation. First Method. a. Triturate the air-dried clay as fine as possible, and transfer it to a stoppered test-tube. 6. Dry about 2 grm. in a platinum crucible or dish at 120 to constant weight. The loss of weight gives the moisture. Then ignite, at first gently, then strongly, and for quite some time; the loss in weight represents the combined water (together with the organic and volatile constituents of the clay, if such are present). c. Decompose 1 or 2 grm. of the air-dried clay with potassium and sodium carbonates, proceeding exactly as detailed in 140, II, b. The silicic acid obtained is weighed, and then volatilized by treatment with ammonium fluoride and sulphuric acid. If any non- volatile residue remains, its weight must be subtracted from that of the impure silicic acid. Fuse this residue with potas^- sium disulphate, and in the solution determine any titanic acid that may be present ( 237, 8), and also the small quantity of alumina that is sometimes present. d. Evaporate the hydrochloric-acid solution separated from the silicic acid, with the addition of a few drops of nitric acid, until the greater part, of the free acid has been driven off, then dilute with water, add an excess of pure barium carbonate, and digest in the cold for twenty-four hours with frequent stirring; filter off the precipitate of aluminium hydroxide containing a little ferric hydroxide and barium carbonate, then wash, first 418 DETERMINATION OF COMMERCIAL VALUES. [ 238. by decantation, then on the filter. Now dissolve the precipitate in hydrochloric acid, precipitate the barium with sulphuric acid, collect the precipitate, wash, add the washings to the filtrate, and divide the latter into two equal portions, a and /?, either by measur- ing or weighing: a. Precipitate with ammonia, decant, and filter after standing some time in a warm place; wash thoroughly, dry, ignite (finally with a gas blast-lamp), weigh, multiply by 2, and thus ascertain the alumina and ferric oxide.* /?. Concentrate, and determine the iron present with stannous chloride (Vol. I, p. 328), or add potassium tartrate, ammonia, and ammonium sulphide, and determine the iron as ferric oxide (Vol. I, p. 642 [77]). Multiply the ferric oxide obtained by 2. The alumina = the result of a minus the result of ft, and minus the small quantities of titanic and silicic acids (if these have been found) obtained in a, and which, of course, must be first multiplied by 2. To the filtrate from the precipitate caused by the barium car- bonate, and without previous concentration, carefully add sulphuric acid ( 132, 1), filter off the barium sulphate and wash it until the washings no longer react for sulphuric acid; collect and unite the washings and filtrate, concentrate somewhat (yet not sufficiently to precipitate calcium sulphate), and separate the calcium and magnesium according to 154, 6 [36]. e. Add a little sulphuric acid to 2 grm. of the air-dried clay with strong aqueous hydrofluoric acid (Vol. I, p. 513), gaseous hydro- fluoric acid (Vol. I, p. 515), or ammonium fluoride (Vol. I, p. 516). Treat the sulphates obtained by any one of these methods with hydrochloric acid. If there is any residue, allow it to settle, decant the liquid so far as possible, and treat the residue again with hy- * In this precipitate is usually found the greater part of any titanic acid that may be present, if the precipitate is treated according to the method described in the preceding paragraphs, p. 411. If an insoluble residue remains on fusing with potassium disulphate and treating the melt with water, it consists of silicic acid. This must be flocculent in appearance, otherwise the residue must be fused again with potassium disulphate, or decomposed with sodium carbonate ( 140, II, 6). 238.] SILICON COMPOUNDS. 419 drofluoric acid or ammonium fluoride. To the diluted hydro- chloric-acid solution cautiously add barium chloride so long as a precipitate forms; then, without i.ltering, add ammonium carbon- ate and some ammonia. Allow to settle in the cold, filter, wash, evaporate the solution, and ignite the residue to drive off the ammonium salts ; take up the residue with water, boil with a little pure milk-of-lime to remove magnesium, filter, and in the filtrate precipitate any calcium and barium present by adding ammonium carbonate and ammonia, etc.; determine the alkalies present according to p. 249 this volume. The general composition of the clay is ascertained by these methods. If, however, it is desired to ascertain also (A) how much of the silicic acid found is chemically combined with the bases of the clay; (B) how much as hydrated acid; (C) and how much as quartzr-sand. or as silicate present in the form of sand (e. g. felspar sand), the following additional processes are required: /. Heat a third portion of the air-dried clay (1 to 2 grms.) with an excess of pure sulphuric acid to which a little water has been added, for ten to twelve hours, until near the end the excess of acid has been nearly but not altogether driven off. Allow to cool, add a considerable quantity of water, wash the undissolved residue A + 5-hsand), and while still moist, transfer it to a plati- num or porcelain dish, and treat it with a boiling solution of so- dium carbonate, as detailed in 237, 2, b. By determining the silicic acid dissolved by the alkaline solution we ascertain A+B. The sand is washed, ignited, and weighed. If the weight of the sand + A +B is equal to the total weight of the silicic acid found in c, the sand is pure quartz sand; if, on the contrary, it is higher, the sand is not pure quartz sand, but is the more or less sandy powder of a silicate, e.g., felspar sand; in this case C is then found by subtracting A + B from the total silicic acid found in c. If the composition of the sand is to be more minutely ascertained, the separated sand must be subjected to a special analysis. The quartz sand may be separated from the admixed silicates by heating with a little dilute sulphuric acid in sealed glass tubes 420 DETERMINATION OF COMMERCIAL VALUES. [ 238. (Vol. I, p. 521, e), or, by cautiously heating with phosphoric acid which, on gradually raising the temperature, decomposes first the silicates with the separation of gelatinous silicic acid, and then attacks the quartz (AL. MULLER*). The heat must be very .cautiously regulated and maintained at from 190 to 200. A. MULLER has devised a suitable furnace for this purpose.f E. LAUFER'S communication J shows this, and also to what extent f quartz sand is attacked by heating with phosphoric acid. g. To ascertain the quantity of silicic acid which will be dissolved out from clay by a boiling solution of sodium carbonate (B), and which may be assumed to be present as hydrated silicic acid, repeatedly boil a somewhat larger portion of the air-dried clay -with the sodium-carbonate solution, and in the filtrate determine the silicic acid by evaporating with hydrochloric acid. Finally 4 = (A + B) -B. h. If clays contain weighable quantities of organic substances or sulphides, determine the former according to 237, 4; and the latter according to 237, 6. Second Method. If the clays to be analyzed are composed of quartz sand, the clayey part of which is readily decomposed by sulphuric acid, the analysis may be greatly simplified by employing the following process: a. Preparation for analysis, drying, and determination of water, just as in the first method. b. Decompose about 2 grm. of the clay with sulphuric acid as In / in the first method, remove the greater portion of the sulphuric acid by evaporating, dilute with water, filter off the silicic acid and sand, separate these by boiling with a solution of sodium carbonate, and determine both as in 237, 1, b. c. To the filtrate from 6 cautiously add a solution of lead nitrate, taking care to avoid any considerable excess, filter off the * Zeitschr. /. analyt. Chem., v, 431. f Ibid., vii, 465. I Ibid, xvn, 368. 239.] CHROMIUM COMPOUNDS. 421 lead sulphate after several hours, wash, add the washings to the filtrate, and from the united liquids remove the last trace of lead with hydrogen sulphide; then filter, evaporate the filtrate (finally in a small dish), and treat the residue according to 161, 5 [118]. As clay rarely contains weighable traces of manganese, this method is reduced to a very simple form. 10. CHROMIUM COMPOUNDS. ANALYSIS OF CHROME IRON ORE. 239. Chrome iron ore is essentially a compound of chromic oxide and ferrous oxide; occasionally a part of the chromic oxide is replaced by ferric oxide and alumina, while a part of the ferrous OAide is replaced by magnesia. The mineral frequently contains, in addition, silicic acid or silicates, small quantities of calcium,, manganese oxides, titanic acid, etc. On account of its very vary- ing chromium content, the mineral is frequently the object of chemical analysis. As chrome iron ore is not as easily decomposed as most other minerals, many chemists have made investigations with a view to finding the best methods of decomposing it. As a knowledge of these is instructive, I give in the foot-note * a list of the most important papers that have been published lately, and give a detailed description only of the best and simplest *P. HART (Journ. f. prakt. Chem., LXVII, 320). CALVERT (Dingl. polyL Journ., cxxv, 466.) CH. O'NEILL (Chem. News, 1862, No. 123, 199; Zeitschr. /. analyt. Chem., i, 497). OUDESLUYS (Chem. News, 1862, No. 127, 254; Zeitschr. f. analyt. Chem., i. 498). T. S. HUNT (Sill. Am. Journ. [2], v, 418). F. A. GENTH (Chem. News, 1862, No. 137, 32; Zeitschr. f. analyt. Chem., L 49 8 )._G IBBS and P. C. DUBOIS (Zeitschr. f. analyt. Chem., in, 401). F. W. CLARKE (Zeitschr. f. analyt. Chem., vn, 463). J. BLODGET BRITTON (Chem, News, xxi, 266; Zeitschr. f. analyt. Chem., ix, 487). FR. C. PHILLIPS (Zeit- schr. f. analyt, Chem., xn, 189). F. H. STORER (Zeitschr. f. analyt. Chem., ix, 71, and comp. F. E. STODDART, ibid , xm, 86). R. KAYSER (Zeitschr. /. analyt. Chem. xv, 187). H. HAGER (Untersuchungen, i, 163). A. CHRIS- TOMANOS (Zeitschr. f. analyt. Chem., xvii, 249). E. F. SMITH (ibid., 514). W. DITTMAR (ibid., xvm, 126). F. FELS (ibid., xvm, 498). W. J. SELL (Jaurn. Chem. Soc., 1879, 293). 422 DETERMINATION OF COMMERCIAL VALUES. [ 239. methods. These include both the determination of the chromium and the accurate determination of all the substances present. In all the methods it is required that the chrome iron ore be reduced to the form of very finest, impalpable powder. This oper- ation must be patiently and conscientiously performed, as upon it depends the success of the analysis. CHRISTOMANOS recommends to strongly ignite the coarse powder on a platinum cover for a short time, in order to facilitate the subsequent trituration in the agate mortar. The powder must finally be separated from the coarser portions by sifting, and these again powdered and mixed in. Elutriation is inadmissible, as this renders the sample uneven. If CHRISTOMANOS' method of powdering is adopted, the sifted powder is heated again before weighing. The analysis is then performed on the anhydrous substance. I. METHOD OF DECOMPOSITION. a. J. BLODGET BRITTON'S Method. Mix as intimately as possible 0-5 grm. of the very finely powdered mineral with 4 grm. of a mixture of 1 part potassium chlorate and 3 parts soda-lime, and heat for at least an hour and a half to bright redness in a covered platinum crucible. The unfused mass may be readily removed from the crucible and powdered. The decomposition is complete. If the temperature be raised by employing a gas blast-lamp, the total decomposition may be effected in 20 minutes (FELS). The melt contains all the chromium as alkali chromate. The operation, a modification of CALVERT'S process (in which potassium nitrate is used instead of potassium chlorate), is simple, certain, and, as it may be performed in a platinum crucible, is strongly to be recommended. b. KAYSER'S Method. Mix 1 part (about 0-5 grm.) of the very finely powdered chrome iron ore with 2 parts of anhydrous sodium carbonate and 3 parts of calcium hydroxide, and maintain the mixture at a bright-red heat for about an hour with the aid of a gas blast-lamp, in an open platinum crucible, and with fre- quent stirring. The result is a sintered mass, from which the 239.] CHROMIUM COMPOUNDS. 423 sodium chromate formed may be easily extracted with hot water. If the operation has been properly conducted, the residue will contain no chromium. c. DITTMAR'S Method. Fuse 2 parts of borax glass with 3 parts of sodium-potassium carbonate, and preserve the flux in closed vessels. For the decomposition, fuse 0-5 grm. of the very finely powdered ore with 5 to 6 grm. of the flux in a platinum crucible, over a BUXSEX burner. At first heat to redness for about five minutes with the crucible covered, then remove the cover, place it obliquely over the flame, heat as strongly as possible, and stir the mixture with a platinum wire until the ore is completely dissolved, maintaining the mixture at fusion for about three- quarters of an hour with access of air. All the chromium in the melt may be extracted from the mass, and in the form of alkali chromate, by means of hot water. Should the BUNSEN burner be insufficient to heat the mixture to bright redness, the gas blow- pipe must be employed if the decomposition is to be effected with certainty (FELS). d. CHRTSTOMANOS' Method. Where chromite is to be com- pletely analyzed, CHR-STOMAXOS recommends the method of PE- LIGOT and CLOUET, somewhat modified. Mix 0-3 to 0-5 grm. of the very finely powdered chrome iron ore intimately with 3 to 3-5 grm. of pure, anhydrous sodium carbonate, and heat the mixture in a platinum dish, provided with a cover, for two hours by means of a gas blowpipe, so that it is kept in a fused state. 'By adding about 0-5 grm. saltpetre, the decomposition may be greatly hastened, but then the dish will be strongly attacked. Hence it is inadvisable to add any saltpetre). The decomposi- tion is complete, but the continued heating for two hours is rather inconvenient. The melt contains all the chromium as alkali chro - mate. e. To just simply determine the quantity of chromium present, CHRISTOMAXOS intimately mixes 0-3 to 0-5 grm. of the chrome iron ore with 4 grm. of thoroughly dried and still warm caustic soda and 1-7 to 2 grm. calcined magnesia in a mortar, and heats the mixture in a platinum (or, better, gold) crucible for an hour 424 DETERMINATION OF COMMERCIAL VALUES. [ 239. by means of an ordinary BUNSEN burner, frequently stirring the mixture with a platinum wire. On boiling the sintered mass with water, all the chromium is readily obtained in solution in the form of sodium chromate. /. Method of T. S. HUNT and F. A. GENTH. Fuse about 0-5 grm. of the powdered ore in a capacious platinum crucible with 6 grm. of potassium disulphate for fifteen minutes at a tempera- ture but slightly above the melting-point of the latter, then in- crease the heat somewhat so that the bottom of the crucible ap- pears just red-hot, and maintain at this temperature for from fifteen to twenty minutes. The melt must never more than half fill the crucible. During this period the mass begins to flow quietly, and vapors of sulphuric acid are copiously evolved. After twenty minutes, increase the heat so that the second equivalent of sul- phuric acid is driven off, and even the iron and chromium sul- phates are partially decomposed. To the fused mass now add 3 grm. pure sodium carbonate, heat to fusion, and gradually add 3 grm. saltpetre during the course of an hour while maintaining the whole at a gentle red heat; then heat for fifteen minutes to bright redness. The melt contains the chromium as alkali chro- mate. The operation is rather inconvenient, and the platinum crucible is attacked, but the results obtained are good. II. ANALYTICAL METHODS. a. Determination of all the Constituents. If all the constituents of the chrome iron ore are to be de- termined, it is best to employ one of the methods in which only salts of the alkalies are used, preferably in order to avoid the presence also of boric acid the method d 01 /. Treat the cooled melt with boiling water, filter hot, and wash the undissolved por- tion with boiling water. Digest the residue with warm hydro- chloric acid. If any ore remains undecomposed, this must not be weighed and deducted, but subjected to the decomposition process until decomposed. In the alkaline filtrate, containing all the chromium as alkali chromate, are occasionally found small 239.] CHROMIUM COMPOUNDS. 425 quantities cf manganic and silicic acids, alumina, and more rarely titanic acid. To separate these evaporate the solution with an excess of ammonium nitrate on the water-bath almost to dryness, and until all the ammonia liberated is expelled. After adding water, there remain undissolved silicic and titanic acids, alumina, and manganic oxide. Filter, add an excess of sulphurous acid to the filtrate to reduce the chromic acid to chromic oxide, cautiously heat to boiling, and add pure ammonia free from silicic acid in slight excess, best in a platinum dish; a porcelain dish may be used if this is not at hand, but a glass dish must not be used. Boil for several minutes, and wash the separated chromium hydroxide by repeatedly boiling and decanting on a filter until the washings are free from sulphuric acid. Afte the precipitate has been dried and ignited, it will contain alkali chromate, in consequence of the presence of a small quantity of alkali not re- moved by the washing. Before weighing the precipitate, hence boil it with a little water, add first a few drops sulphurous acid, then ammonia, filter again, wash, dry, ignite, and weigh the now perfectly pure chromic oxide (F. A. GENTH *). The constituents of the hydrochloric-acid solution, as well as those separated by evaporation with ammonium nitrate, sepa- rate by the methods detailed in the General Part. CHRISTOMANOS f has also thoroughly investigated the com- plete analysis of chrome iron ore. He advises the following method: Prepare the melt according to I, d. Just before it has become cold, place the crucible with its contents and cover in a deep porcelain dish containing 300 to 400 c.c. boiling water. The melt rapidly disintegrates. After about five minutes remove the crucible and cover, rub off the adhering particles, and carefully wash with hot water. Then introduce, a small quantity of hydro- chloric acid into the crucible and set the latter aside for a time. Now boil the contents of the porcelain dish for five or ten minutes until the color of the liquid, which is at first rusty brown, green, or bluish-green from the presence of sodium manganate and ferrate, has changed to a pure deep yellow. As soon as this * Zeitschr. /. analyt. Chem., i, 498. t *&*& XVII > 249 - 426 DETERMINATION OF COMMERCIAL VALUES. [ 239. occurs, filter the liquid by means of a vacuum filter, thoroughly wash the precipitate with hot water, and dry it by drawing through it a rather strong current of air, so that it may be readily removed from the filter. Then treat it, together with the filter ash, with hydrochloric acid, add the hydrochloric acid from the crucible which was set aside, and evaporate on the water-bath to dryness with the addition of a few drops nitric acid, moisten the residue with hydrochloric acid, and once more evaporate to dry- ness; treat with hydrochloric acid r then with water remove the silicic acid, and then separate the iron, calcium, and magnesium according to the methods detailed in Vol. I. Should the silicic acid removed not completely dissolve in a boiling solution of sodium carbonate, the residue of undecomposed chrome iron ore must again be treated and decomposed. In the yellow solution obtained by boiling the molt with water, all the aluminium is found as sodium aluminate, and the chromium as sodium chromate; the solution may also contain a little sodium silicate, and in certain cases a little titanic acid. These are sep- arated by the methods already described. [The silica in chrome ore, as well as the silicon in ferro-chromium, may also be determined according to GEO. TATE * as follows: One to two grm. of ferro-chromium or of ore are fused with about five times their weight of sodium peroxide in a nickel crucible. The crucible and contents, after cooling, are brought into water contained in a capacious nickel dish. The alkaline liquid so obtained, containing chromate and silicate, together with oxides of iron and nickel in suspension, is treated with hydrochloric acid in quantity insufficient to neutralize the alkali, and then evaporated to dryness in a nickel dish. The residue is scraped, so far as is practicable, from the sides to the bottom of the dish, and 40 c.c. of strong pure sulphuric acid rapidly poured on. Fumes of hydro- chloric and chlorochromic acids are evolved, and completely ex- pelled by applying heat. The temperature is raised until the sulphuric acid begins to fume, thereby ensuring the dehydration * Chem. News, LXXX, p. 235 239.] CHROMIUM COMPOUNDS. 427 of the silicic acid. After removal of the flame and cooling for a few minutes, water is cautiously added. To prevent undue corrosion of the nickel vessel, the turbid liquid is transferred to a porcelain dish, and, after making the bulk about 250 c.c., boiled for fifteen to thirty minutes, or until the sulphates have completely dissolved The silica is filtered off, washed thoroughly, ignited in a platinum crucible, and weighed. The silica so obtained should be white, but, as a few mgrm. of metallic oxides usually accompany it, the real weight of SiO 2 (from which the silicon is reduced) is obtained by determining the loss in weight occasioned by evaporation with hydrofluoric acid and one drop of sulphuric acid, followed by strong ignition. It is advisable to test the purity of the reagents by conducting a blank test. The results are very concordant and apparently exact. Ex- periments have shown that 90 to 95 per cent, of the chromium can be volatilized by the action of the sulphuric acid ; the removal of the chromium prevents the contamination of the silica by basic salts of that metal. Test experiments, wherein known weights of silica were fused with bichromate of sodium peroxide, and the products submitted to the above treatment, have shown that the process brings prac- tically the whole of the silicon into a weighable form. TRANSLATOR.] In the calculation and arrangement of the results, the chro- mium is to be put down as chromic oxide; with iron, however, the question is mo*re difficult. As a rule, it is all present as fer- rous iron, but in certain chromites ferric oxide replaces part of the chromic oxide. In this case the information desired can only be gained from the loss of weight which the anhydrous mineral sustains on prolonged ignition in a current of hydrogen. Chro- mites containing ferric oxide in the admixed gangue give it up on prolonged heating of the finely powdered mineral with hydro- chloric acid. If calcium is present (usually as carbonate), a carbon-dioxide determination is as a rule required. The chromite to be used for this determination must, of course, not be ignited. 428 DETERMINATION OF COMMERCIAL VALUES. [ 24Q. b. Simple Chromium Determination in Chrome Iron Ore. As the value of chrome iron ore depends only upon the chromium content, it is frequently sufficient to simply determine the chromium only. For this purpose a volumetric method is as a rule chosen, one of the following being; adopted: a. Thoroughly extract the melt (best prepared according to I, a, b, or e) by boiling with water, warm with an excess of sul- phuric acid to redissolve the precipitated aluminium hydroxide, cool the solution, and in it, or in an aliquot portion of it, determine the chromic acid according to 130, I, e, a. If the solution con- tains no chloride (melt I, b or e), determine the excess of ferrous sulphate with (most conveniently) potassium permanganate ( 112 ; 2, a) ; if, however, a chloride is present (melt I,- a), PENNY'S method is preferable ( 112, 2, b). /?. Heat melt I a with a small quantity (about 20 c.c.) of water, and after cooling, add 15 c.c. of hydrochloric acid, sp. gr. 1-12. Everything but the separated silica should go into solution. Now add (according to 130, I, 'e, a) a known quantity of ferrous sulphate in excess and determine the excess (J. BLODGET BRITTON). The determination of the excess of ferrous sulphate by means of potassium permanganate as recommended by BRITTON, is inad- missible (comp.Vol. I, p. 319, f) ; for this purpose PENNY'S method ( 112, 2, 6, p. 319) must be employed. Melts prepared with the addition of an alkali nitrate cannot be examined by these methods, as alkali nitrates are present, the acid of which would partially reduce the chromic acid on acidulat- ing the aqueous solution of the melt. 11. ZINC COMPOUNDS. A. CALAMINE; B. ELECTRIC CALAMINE. 240. Calamine consists of zinc carbonate with more or less admixed ferrous, manganous, lead, cadmium, calcium, and magnesium oxides, and silicic acid, and sometimes also cupric oxide. Electric 240.] ZINC COMPOUNDS. 429 calamine consists of a hydrated basic zinc silicate, frequently con- taining admixed zinc carbonate, and which besides usually contains ferric and ferrous oxides, and occasionally also manganous, lead, aluminium, calcium, and magnesium oxides. The minerals are finely powdered, and analyzed in an air- dried condition, or after drying at 100. In the former case, the moisture is determined by drying a sample at 100. If the degree of oxidation of the iron is to be accurately determined, the analysis should be carried out with the air-dried powder. Determination of all the Constituents. a. Treat a sample according to 140, II, a; i.e., separate the silicic acid in the usual manner. As the acid generally contains sand or undecomposed gangue, it must be separated from these by boiling with a solution of sodium carbonate ( 237, 2, 6). When treating the residue with hydrochloric acid and water, care must be taken to use about 100 parts of water for every 4 parts of hydro- chloric acid of sp. gr. 1-1 ( 162, A, /?). b. Precipitate the solution so obtained with hydrogen sulphide, and separate any metals of the fifth and sixth groups that may be thrown down, according to the methods described in Section V. A too long-continued passing-in of hydrogen sulphide should be avoided, otherwise zinc sulphide may also be precipitated. In any case it is advisable to dissolve the precipitated sulphides in hot hydrochloric acid with the addition of a little brominized hydro- chloric acid, and after driving off the excess of bromine, to repeat the precipitation with hydrogen sulphide. In this second pre- cipitation, too, care must be taken to add 4 parts of hydrochloric acid to every 100 parts of water ( 162, A, /?*). c. Neutralize the filtrate or filtrates with ammonia, precipitate * According to GERH. LARSEN (Zeitschr. f. analyt. Chem., xvii, 312) the double precipitation may be avoided if during the first prec : p ; tation with hydrogen sulphide 30 c.c. of hydrochloric acid of sp. gr. 1-1 are present in 250 c.c. of the solution (a proportion of acid which is suitable for the separation of zinc from copoer, but not from cadmium), and the precipitate H f rst washed with hydrochloric acid of sp. gr. 1-05 saturated with hydrogen sulphide, and then with aqueous solution of hydrogen sulphide. 430 DETERMINATION OF COMMERCIAL VALUES. [ 241. with ammonium sulphide, treat the precipitate exactly as described in 108, b, boil the ignited zinc oxide (containing ferric and man- ganic oxides and some silicic acid) with water, weigh, then volu- metrically determine the manganese present (Vol. I, p. 665 [109]); filter the solution from the un dissolved silicic acid which is then to be determined, and finally determine in the hydrochloric-acid solution obtained the ferric oxide by means of stannous-chloride solution (Vol. I, p. 327). The quantity of zinc oxide is ascertained from the difference. Of course any other of the methods described in 160 may be employed for the separation or determination of the zinc, manganese, and iron in ammonium-sulphide precipi- tates, but in none other are accuracy and rapidity so equally com- bined as in the one described. If, however, too large a ferric- or ferrous-oxide content is present, it is preferable to make a direct determination of the zinc by the second method given in 241. d. Acidulate the filtrate from the zinc sulphide with hydro- chloric acid, boil for some time, filter off the separated sulphur, and determine the calcium and magnesium according to 154, 6 [36]. e. Ignite a separate sample in a bulb-tube of the apparatus described in Vol. I, p. 76. The loss of weight of the bulb-tube gives the water + the carbon dioxide the increase of weight of the calcium-chloride tube gives the water alone; the difference gives the carbon dioxide. In cases where the presence of a considerable proportion of ferrous oxide or lime impairs the accuracy of the indirect determination of the carbon dioxide, or if the carbon dioxide is present in but very small quantity, one of the methods described in 139, II, e } should be employed. /. If the ore contains ferrous and ferric oxides, determine them by means of potassium chromate in a hydrochloric-acid solution prepared in a current of carbon dioxide (Vol. I, p. 319, b). C. ZINC BLENDE. 241. Zinc blende consists of zinc sulphide, frequently containing other admixed sulphides, more especially those of lead, cadmium, 241.] ZINC COMPOUNDS. 431 copper, iron, and manganese. Occasionally there are also found in blende small quantities of arsenic, antimony, nickel, and cobalt. Besides these, due regard must be had in the analysis to admixed gangue. The blende must be very finely powdered, and dried at 100. DETERMINATION OF ALL THE CONSTITUENTS. First Method. a. Determine the sulphur in one portion, best according to the process detailed in Vol. I, p. 562, 1, a; it must be remembered that blende frequently contains lead. b. The metals are determined in a fresh portion. For this purpose heat 1 or 2 grm. of the ore with fuming hydrochloric acid until no more hydrogen sulphide is evolved, then add a little nitric acid and about 5 to 6 c.c. pure sulphuric acid previously diluted with a little water, and evaporate until the hydrochloric and nitric acids have been driven off. Then dilute with 20 to 30 c.c. water, and filter off the residue from the solution. If the residue con- tains (as it frequently does) lead sulphate, wash it first with water acidulated with sulphuric acid, then with alcohol (the alcoholic washings must be collected separately). Boil the washed residue repeatedly with a solution of ammonium acetate until all the lead sulphate is dissolved, and ignite and weigh the small quantity of residual gangue. Precipitate the lead in the ammonium-acetate solution with hydrogen sulphide and determine it as lead sulphide H6 ? 3). To the sulphuric-acid solution add hydrochloric acid of sp. gr. 1 1 in the proportion of 4 parts of acid to 100 parts of solution, and proceed according to 240, b. In the case of blende rich in iron, it is better to proceed according to the second or third method, or to separate the zinc as a sulphide in the presence of ammonium sulphocyanate, according to a method recently proposed by ZIM- MERMANN.* For this purpose evaporate on the water-bath, almost to dry- * Ann. der Chem., cxcix, 1. 432 DETERMINATION OF COMMERCIAL VALUES. [ 241. ness, the filtrate from the precipitate caused by hydrogen sulphide, dilute, and cautiously add sodium carbonate (towards the last in dilute solution) until a permanent, slight turbidity ensues, and the solution is as nearly neutral as possible; this is an essential condition for the success of ZIMMERMAN'S method. Now add an excess of a not too dilute ammonium-sulphocyanate solution, rinse down the walls of the vessel (best by means of an ERLENMEYER flask) with water, warm to 60 or 70, and pass a very moderate current of hydrogen sulphide through the liquid several times, but for not too long a time, until the odor of the gas no longer disappears on exposing the solution to the air. The liquid at first acquires a nearly milk-white turbidity, but later on the zinc sulphide sepa- rates completely, while the iron and manganese (also nickel and cobalt) remain dissolved. Allow to deposit in a moderately warm place, filter, wash the perfectly white precipitate with water con- taining hydrogen sulphide and ammonium sulphocyanate, dry, and ignite the zinc sulphide according to Vol. I, p. 289, 2). Instead of this jnethod of determination, the method proposed by VOLHARD * may be employed. This method consists in dissolving the zinc sulphide in hydrochloric acid, evaporating the solution to dryness in a weighed platinum dish, adding an excess of pure, alkali- free mercuric oxide suspended in water, again evaporating, and igniting ; 'the zinc oxide thus obtained is then weighed. In the liquid filtered off from the zinc sulphide the sulpho- cyanates are next decomposed by cautiously heating with nitric acid added gradually in small quantities, conducting the opera- tion in a capacious flask; then, if necessary, after filtering, pre- cipitate the iron as a basic ferric salt (Vol. I, p. 644, 3, a), and in the filtrate precipitate the manganese with ammonium sulphide. Second Method (HAMPE'S f). a. Boil about 1 grm. of the finely powdered ore dried at 100 with nitric acid in a long-necked flask. After all the nitrous acid has been expelled, and the liquid has been highly concen- * Loc. cit., p. 6. f Zeitschr. /. analyt. Chem., xvn, 362. 241.] ZINC COMPOUNDS. 433 trated, add 30 c.c. nitric acid of sp, gr. 1-2, and about 200 c.c. water. b. Precipitate the solution, without previous filtration, with hydrogen sulphide and without warming, filter off the precipitate (when this is completely deposited) together with the undissolved gangue, wash, and treat the precipitate on the filter with hot but not too concentrated nitric acid; then perforate the point of the filter, wash all the undissolved substance into a flask, wash the filter, concentrate the liquid by evaporation, add about 200 c.c. water and 30 c.c. nitric acid of sp. gr. 1-2, again precipitate with hydrogen sulphide, and add the filtrate to that first obtained. c. Concentrate the filtrate almost to dryness by boiling in a long-necked flask, supersaturate with ammonia the solution now free from hydrogen sulphide but containing all the iron as a ferric salt, filter, wash, dissolve the precipitate on the filter with hot, moderately strong nitric acid, and when cold precipitate again with an excess of ammonia; filter through the same filter, and repeat the operation of dissolving with nitric acid and precipitating with ammonia once or twice more. The precipitate consists chiefly of ferric oxide, but it may also contain alumina and man- ganese sesquioxide, hence effect the separation according to 161. d. Acidulate with acetic acid the ammoniacal liquids obtained in c, dilute to at least two litres, and pass in hydrogen sulphide, Allow to stand for at least twelve (better twenty-four) hours, pour off the clear fluid through the filter, and then transfer also the perfectly white zinc sulphide to the filter. On account of the extreme dilution, and because in the analysis neither hydro- chloric acid nor other non-volatile substances have been added, it suffices to wash but for a short time with hydrogen-sulphide water to which a small quantity of ammonium acetate has been added. Fuse the dried zinc sulphide in a ROSE crucible together with the filter ash and a little pure sulphur, and then proceed ac- cording to 108, 2. e. To the fluid separated from the zinc sulphide, and con- tained in a large flask, add ammonia to alkaline reaction, then add ammonium sulphide, and allow to stand for at least twenty- 434 DETERMINATION OF COMMERCIAL VALUES. [ 241. four hours in a warm place. If a precipitate deposits, examine it to see if it contains anv zinc ; if the operation has been properly performed it will contain none. As a rule the precipitate thus formed is manganese sulphide. /. The filter-contents obtained in b treat with hydrochloric acid containing a little bromine; the gangue remains undissolved, and is to be dried and weighed. As a precaution, heat it with ammonium-acetate solution to see whether it yields up to this solution any lead sulphate. g. Heat with ammonia the brominized hydrochloric acid obtained in /, in order to remove the excess of bromine, and in the solution then determine the metals present (lead, copper, cadmium, arsenic, and antimony) according to the methods de- tailed in 163 and 164. h. Determine the sulphur by the first method. Third Method (CLASSEN'S*). Heat the blende with concentrated hydrochloric acid, add towards the end a little nitric acid, evaporate the excess of the acids, take up the residue with hydrochloric acid and water, filter off the gangue, and precipitate the metals of the fifth and sixth groups with hydrogen sulphide (comp. 240, a and 6). Con- centrate the filtrate and washings by evaporation, adding towards the end some nitric acid or bromine water in order to insure all the iron being present as ferric 'oxide or chloride. Expel the excess of acids by evaporating on the water-bath, and after cooling add 10 c.c. bromine water and digest for some time on the water- bath. Now add a 1 : 3 potassium-oxalate solution equal to about seven times the quantity of the oxides present, warm for about fifteen minutes on the water-bath, and dissolve any slight residue of basic ferric salt by adding acetic acid drop by drop. Tf suf- ficient potassium oxalate has been employed, there is obtained a perfectly clear more or less green solution; if, however, insufficient * has been used to form potassio-ferric oxalate and potassio-zinc *Zeitschr. f. analyt. Chem., xvi, 471; xvin, 190, 381, 397. 242.] ZINC COMPOUNDS. 435 oxalate, the liquid will be turbid from the presence of zinc oxalate ; if the latter is the case potassium oxalate must be added until the liquid is clear. Now heat the solution to boiling, and add concentrated (80-per cent.) acetic acid, with constant stirring. The quantity of acetic acid added must be at least equal in volume to that of the liquid to be precipitated. By this treatment all the zinc is precipitated as heavy, crystalline zinc oxalate, while the iron remains in solution. Heat the well-covered beaker for about six hours at about 50, filter while hot, thoroughly wash with a mixture of equal volumes of concentrated acetic acid, alcohol, and water, and dry the precipitate; burn the filter first on a platinum wire, then heat the precipitate in a covered crucible, at first gently, then with increased heat, finally igniting with access of air, and then weigh. Now heat the ignition-residue with a little water and test its reaction; if alkaline, remove the potas- sium carbonate still present by washing with water, and weigh again. If the ore contains manganese, the zinc oxide may contain the whole of it as manganese oxide. If the quantity is weighable, determine the manganese according to Vol. I, p. 665, d. The quan- tity of zinc oxide is then ascertained from the difference. The iron in the liquid filtered off from the zinc oxalate may be precipitated by ammonia. The sulphur is determined as in the first method. The test analyses communicated by CLASSEN are very sat- isfactory. I am not personally, sufficiently familiar with the method, however, to give a decided opinion regarding it. D. Zixc ORES GENERALLY. I. VOLUMETRIC ZINC DETERMINATION. 242. As the gravimetric methods of determining zinc take much time, volumetric methods are almost exclusively employed in zinc work, as the results afforded are sufficiently accurate for most purposes, and may be much more rapidly obtained. 436 DETERMINATION OF COMMERCIAL VALUES. [ 242. a. Sodium-Sulphide Method. This method, first proposed by SCHAFFNER,* has been modified in many ways, in the course of time. These are described in the foot-note here given, f The following methods have been found to be the best: a. Method with SCHAFFNER'S Modified End Reaction. REQUISITES. Sodium-Sulphide Solution. Prepare this either by dissolving crystallized sodium sulphide in water (about 100 grm. to 1000 or 1200 c.c. water), or by supersaturating a carbonate-free caus- tic-soda solution with hydrogen sulphide and then heating the solution in a flask to expel the excess of hydrogen sulphide. Then dilute the solution, prepared by either process, so that 1 c.c. will precipitate about 0-01 grm. of zinc (see below). Zinc Solution. To prepare a solution of accurately known zinc content, dissolve 10 grm. of chemically pure zinc, or 12-4465 grm. of pure zinc oxide, in hydrochloric acid, or 43-973 dry, crys- tallized zinc sulphate (ZnSO 4 -7H 2 O) or 62-358 grm. of dry, crys- tallized zinc and potassium sulphate (ZnK 2 [SO 4 ] 2 -4H 2 O) in water, and dilute the solution with water to measure 1 litre. Each c.c. will then contain 0-01 grm. zinc. Ferric Hydroxide. Dissolve 3 grm. of iron wire in hydrochloric acid with the aid of heat, add a little nitric acid, and boil to con- vert the ferrous into ferric chloride, and dilute the solution to 100 c.c. Just before using, add 1 or 2 drops (always taking the same number of drops) to 1 c.c. of undiluted aqueous ammonia / each drop producing a ring of ferric hydroxide, which requires but a few moments to impart the desired opacity to the liquid. * Journ. f. prakt. Chem., LXXIII, 410. f C. KITNZEL (Jour. f. prakt. Chem., LXXXVIII, 486). C. GROLL (Zeitschr. f. analyt. Chem., i, 21). STABLER (ibid., iv, 213 and 468). DEUS (ibid., ix, 465). SCHOTT (ibid., x, 209). LAUR (Berg- und Hiittenmann. Ztg., xxxv, 148, 173). THUM (ibid., xxxv, 225). TOBLER (ibid., xxxv, 304, Zeitschr. f. analyt. Chem., xvn, 357). W. HAMPE und FRAATZ (Ibid., xvn; 359). 242.] ZINC COMPOUNDS. 437 In about one minute the ferric hydroxide suspended in the liquid is ready for use (THUM). The Method. SOLUTION OF THE ORE AND PREPARATION OF THE AMMONIACAL ZINC SOLUTIONS. Introduce into a small flask about 1 gnn. of rich ore, or 2 grm. of poor ore,* finely powdered and either air-dried or dried at 100, dissolve with the aid of heat in hydrochloric acid with a little nitric acid added, and expel the excess of acid by evaporation. If lead is present, separate it by evaporating with sulphuric acid, take up the residue with water, and filter. If other metals of the fifth and sixth groups are present, precipitate these with hy- drogen sulphide (comp. 240, a and 6), Boil the solution, free from or no longer containing metals of the fifth or sixth groups, with nitric acid if necessary in order to convert all the iron into ferric oxide or chloride, add (if manganese is present) brominized hydrochloric acid, and dilute with water; then add to the cold liquid an excess of ammonia, and filter off the precipitate consisting chiefly of ferric hydroxide. If the quantity of the precipitate is small, wash it with luke-warm water and aqueous ammonia until the washings no longer give a white turbidity (zinc sulphide) with ammonium- or sodium sulphide; for in this case the quantity of zinc which is contained in, and cannot be washed out from, the ferric hydroxide (which, according to HAMPE and FRAATZ is approximately one-fifth of the weight of the iron present) , may, as a rule, be disregarded. If, however, the quantity of ferric hydroxide precipitated is considerable, wash it moderately, dissolve it in hydrochloric acid, and precipitate the iron again as a basic ferric salt, best according to 160, 3, a, or by method 4. The solution filtered off from it concentrate by evap- oration, then add an excess of ammonia, filter if necessary, add to the principal solution, and make up to 1 litre. If the zinc ore contains an appreciable quantity of manganese, add brominized * If the ore contains organic matter, destroy this by gentle ignition. 438 DETERMINATION OF COMMERCIAL VALUES. [ 242. hydrochloric acid to the filtrate separated from the basic ferric salt and concentrated by evaporation, before adding the excess of ammonia; then, after standing for quite some time, filter off from the precipitated hydrated manganese peroxide,* and make up the liquid to 1 litre. TITRATION OF THE SOLUTION. To 500 c.c. of the ammoniacal zinc solution add ferric hydroxide suspended in ammonia (see above), and then from a burette run in sodium-sulphide solution until the greater part of the ferric hydroxide collected on the sides and bottom of the beaker just acquires a brown or black tint (it is necessary to select one of these tints once and for all), and read off. Now measure off a quantity of zinc solution of known strength approximately cor- responding to the sodium-sulphide solution used, add excess of ammonia, dilute with water so that the volume will be as nearly equal as possible to that of the solution first titrated, add an equal quantity of ferric hydroxide suspended in ammonia water, and then run in sodium-sulphide solution until the ferric hydroxide, after an equal interval of time, exhibits the same shade of brown or black as was obtained in the first titration. If it is believed that the end point of the reaction has not been sharply hit, the other half litre may be used with which to repeat the experiment. The relation of the sodium-sulphide solution to the zinc solu- tion of known content is thus accurately ascertained, as was pre- viously done with that of unknown strength, hence the zinc con- tained in the solution of the ore may be readily calculated. It is unnecessary to make any correction for the quantity of sodium sulphide required to blacken the ferric hydroxide, because the titration is effected under similar conditions in both cases, and with solutions containing almost identical quantities of zinc (THUM; HAMPE). But even when all these precautions are taken, this method is accurate only up to within 0-5 per cent. (HAMPE). *A11 these precipitates of hydrated manganese peroxide, or those ob- tained in a similar manner, retain a little zinc. 242.] ZINC COMPOUNDS. 439 BARRESWIL,* instead of using flocks of ferric hydroxide, em- ploys small fragments of ignited porcelain saturated with ferric- chloride solution and then thrown into an ammoniacal zinc solu- tion. ft. The KUNZEL-GROLL End Reaction. There are required solutions of sodium sulphide and of zinc of known strength, as in a, and also a pure, dilute nickelous- chloride solution. The Method. The ore is dissolved, and the zinc is made up to one litre of ammoniacal solution free from any of the other heavy metals, as detailed in a. To 500 c.c. of this solution now run in from a burette sodium- sulphide solution so long as a distinct precipitate still forms, then stir thoroughly, transfer a few drops of the liquid with a glass rod to a porcelain plate, spread them on the plate, and in the centre place 1 drop of pure dilute nickelous-chloride solution. If all the zinc is not yet precipitated by the sodium-sulphide solution, the margin of the drop of nickelous-chloride solution remains colored blue or green; in this case continue to add sodium sulphide, and until, on testing, the margin of the nickelous-chloride solution exhibits a grayish-black color; the reaction is then complete, all the. zinc having been precipitated, and a little sodium sulphide being present in excess. The depth of the color exhibited by the drop of nickelous-chloride solution must be carefully noted, as it must serve as a standard in the succeeding experiments. To make certain that all the zinc has been precipitated, a few tenths of a c.c. of sodium-sulphide solution may be added, when the color of the drop of nickelous-chloride solution must become darker. Note the number of c.c. of sodium-sulphide solution used, and repeat the experiment with the remaining 500 c.c. of solution, adding at once all but a few c.c. of the sodium-sulphide solution, and then *Journ de pharm., 1857, 431; Polytechn. Centralbl, 1858, 285. 440 DETERMINATION OF COMMERCIAL VALUES. [ 242. adding only 0-2 c.c. at a time until the end reaction is reached. This experiment is considered as giving the correct result. Now measure off as much of the zinc solution of known strength as will correspond with the sodium-sulphide solution used in the last experiment, add an excess of ammonia, and then add water until the volume is about equal to that of the solution first titrated ; then run in sodium-sulphide solution until the end reaction is reached. In this manner the relation of the sodium sulphide solution to the zinc solution of unknown strength is once more determined; and from this the zinc content of the ore may be easily calculated. According to C. KUNZEL, the error, when carefully operating with this method, does not exceed 0-5 per cent. [J. E. CLENNELL * describes a method in which the zinc is pre- cipitated by means of a solution of sodium sulphide of known strength, added in slight excess, the excess in sulphide being then determined by making use of the reaction Na 2 S +2KAgCy 2 = Ag 2 S +2NaCy +2KCy. Requisites. The solutions required are: Sodium Sulphide. A convenient strength being about 0.2 per cent. Na 2 S. Silver Double Cyanide. Prepared by adding silver nitrate to a solution of potassium cyanide (say 2 or 3 per cent. KCy) till a slight permanent precipitate of AgCy is produced, allowing to stand, and filtering. Silver Nitrate. Any dilute solution of known strength. A convenient standard is one containing 5.165 grms. AgNO 3 per litre, 1 c.c. being equivalent to 0.001 grm. zinc. Potassium Iodide. 1-per cent, solution. It is perhaps advisable also to have a standard zinc solution prepared from pure metallic zinc or re-crystallized zinc sulphate, and containing (say) 5 per cent, to 1 per cent. Zn. * Chem. Neivs, LXXXVII, 121. 242.] ZINC COMPOUNDS. 441 Method. The zinc in ores or similar substances is brought into solution in the ordinary way, and the liquid made strongly alkaline with caustic soda or ammonia, boiled, diluted, and filtered if necessary. In cyanide solutions, the sulphide may in general be applied direct; in some cases, however, it may be necessary to remove the cyano- gen by a preliminary operation. The liquid to be tested is mixed with a measured volume of sodium sulphide, slightly in excess of that required to precipitate the whole of the zinc. The liquid is well shaken in a stoppered flask; a little lime may be added to promote settling. The whole, or an aliquot part, is then filtered, and an excess of the double silver cyanide added. The precipitate of Ag 2 S generally settles rapidly, and is easily filtered and washed (occasionally it may be necessary to add a little more lime). About 5 c.c. of the 1 per cent. KI solution are added to the filtrate, and the liquid titrated with AgNO 3 till a slight yellowish turbidity remains per- manent. 1 grm. KCy=0-3 grm. Na^O-25 grm. 7n. In the presence .of ferrocyanide and thiocyanate, it appears to be necessary to make the solution strongly alkaline to ensure com- plete precipitation of the zinc sulphide. TRANSLATOR.] Regarding other reactions by means of which small quantities of sodium sulphides may be detected in the precipitated zinc solution, the following may be briefly noted: DEUS, in his criticism of the end reactions, arrives at the con- clusion that the most certain indicator is afforded by filter-paper impregnated with cobaltous-chloride solution (0-27 grm. cobalt in 100 c.c. of the solution) and dried. On being moistened with a drop of the liquid containing zinc sulphide in suspension, the paper exhibits a white ring with a pale-blue margin. As soon as the slightest excess of sodium sulphide is present, however, a sharply defined dark color develops in the centre of the white ring. The formation of lead sulphide is also frequently utilized to indicate the end reaction; and the following process, which I 442 DETERMINATION OF COMMERCIAL VALUES. [ 242. proposed long ago, is preferred by me to all others : * Moisten a strip of white filter-paper with lead-acetate solution, place it on a layer of blotting-paper, drop onto it a little ammonium car- bonate so that a thin coating of lead carbonate may form on the moderately moist paper, allow the excess of moisture to be ab- sorbed by the blotting-paper, and then spread the lead paper on a porcelain plate. As soon as the zinc seems to be all precipitated, place a small piece of filter-paper on the lead paper, and on the former place a drop of the liquid with the blunt end of a glass rod, and with moderate pressure. So long as the sodium sul- phide is not present in excess no brown spot forms on the lead paper, but the moment a slight excess is present, the color de- velops. ScHOTT employs sized paper covered with a coating of lead carbonate; this paper is known as "Polka Paper," and is em- ployed for visiting-cards. If a few drops of the liquid containing the suspended zinc sulphide are taken out with a glass tube and allowed to run back over a strip of polka paper into the beaker, the paper remains uncolored ; as soon, however, as the liquid contains any sodium sulphide, a brown ring forms where the liquid has flowed ' between the end of the tube and the paper. b. Potassium-Ferrocyanide Method. GALLETTI f was the first to employ potassium ferrocyanide as a precipitant of zinc in the volumetric determination of the latter. The precipitation is effected in an acetic-acid solution at 40; and the milky appearance which the liquid assumes when the potassium ferrocyanide is present in excess serves to indicate the end of the reaction. GALLETTI dissolves 32-311 grm. crystallized potassium ferrocyanide (K 4 Fe[CN] 6 + 3H 2 O) in water to make one litre, and assumes that 100 c.c. of the solution will precipitate 1 grm. of zinc. As, however, the precipitate is not pure zinc ferro- cyanide, as he supposed, but zinc-potassium ferrocyanide, J his * Quant. Chem. Anal, 5th German edit., 814. t Zeitschr. /. analyt. Chem., iv, 213. J REINDEL, Zeitschr. /. analyt. Chem., vin, 460; Neues Handworterbuch der Chemie, in, 244. 242.] ZINC COMPOUNDS. 443 assumption is incorrect. In a more recent communication * GAL- LETTI modified the original method as regards the separation of the iron. RENARDf has altered the method, in that he adds an excess of potassium-ferrocyanide solution of known strength to the ammoniacal zinc solution, makes up the whole to a definite volume, niters off an aliquot portion, adds considerable hydro- chloric acid (30 c.c. to 100 c.c. of the fluid), and determines the excess of potassium ferrocyanide with potassium permanganate (comp. Vol. I, p. 554, g). Thus is ascertained the quantity of potas- sium ferrocyanide required to precipitate the zinc, and from which the latter may hence be calculated. C. FAHLBERG,| however, has devised the simplest form of the ferrocyanide method. He employs a potassium-ferrocyanide solution 1 c.c. of which precipitates 0-01 gnu. of zinc. The zinc solution of known strength is prepared by dissolving 10 grm. pure zinc in hydrochloric acid, adding 50 grm. ammonium chloride, and diluting to measure 1 litre. The addition of the ammonium chloride has been found advantageous, as, when it is present, the precipitate caused by the ferrocyanide is very fine and flocculent, and incloses no potassium ferrocyanide. To determine the value of the potassium-ferrocyanide solution, prepared by dissolving 46 to 48 grm. of the crystallized salt in water to make 1000 c.c., fill one burette with the zinc solution, and a second one with the ferrocyanide solution; introduce 50 c.c. of the zinc solution into a beaker, add 10 to 15 c.c. hydrochloric acid (sp. gr. 1 12) and 450 c.c. water, and while diligently stirring, run in the ferrocyanide solution in quantities of 1 to 2 c.c., until a drop of the liquid brought into contact with a drop of uranium- nitrate solution on a porcelain plate gives a permanent brownish- red spot. Now very cautiously run in zinc solution until the reaction again disappears, and finally add the ferrocyanide solution, two drops at a time, until it is again manifested. If, for example, there had been used 4 to 8 c.c. of the potassium-ferrocyanide solution * Zeitschr. f. analyt. Chem., vni, 135, and xiv, 190. t Ibid., viii, 459. 1 Ibid., xin, 379. 444 DETERMINATION OF COMMERCIAL VALUES. [ 242. for 51 c.c. of zinc solution, the former must be diluted by adding 3 c.c. of water to every 48 c.c. The solution of the ore is prepared as already described above. After removing the metals of the fifth and sixth groups and the iron, neutralize 500 c.c. of the ammoniacal solution with hydro- chloric acid, add a further quantity of 10 to 15 c.c. of hydrochloric acid (sp. gr. 1-12), and then titrate with ferrocyanide solution, taking no heed as to whether manganese is present or not. The fact that the titrations are effected in liquids containing consider- able hydrochloric acid, in which manganese ferrocyanide is soluble, thus rendering it unnecessary to remove manganese, makes FAHL- BERG'S the most convenient of all the modifications of the ferro- cyanide methods. As regards accuracy, the differences never ex- ceed 5 per cent. c. C. MANN'S Method* This method, although more inconvenient and troublesome than those already mentioned, yet affords more accurate results; it is based upon the fact that hydra ted zinc sulphide and moist silver chloride readily and completely react, yielding silver sulphide and neutral zinc chloride. If, hence, the chlorine in the solution is determined, the quantity of the zinc is also readily ascertained. The requisites are: Well-washed, moist silver chloride. This must be protected from the action of light, and must be preserved under water. Silver-nitrate solution, 1 c.c. of which contains 0-033 grm. silver, corresponding to 0-01 grm. zinc. It is prepared by dissolv- ing 33 grm. of pure silver in nitric acid, boiling off the nitrous acid, and diluting the solution to measure 1 litre. Ammonium-sulphocyanate solution, of which 3 c.c. will just precipitate 1 c.c. of the silver solution. A cold saturated solution of ammonio- ferric alum. The Method. Dissolve 0-5 to 1 grm. of the ore in nitric acid, remove the metals of the fifth group with hydrogen sulphide, and iron and * Zeitschr. /. analyt. Chem., xvm, 162. 242.J ZINC COMPOUNDS. 445 aluminium by double precipitation with ammonia. Acidulate the united filtrates with acetic acid, pass in hydrogen sulphide until the zinc is completely precipitated, and remove the excess of hydrogen sulphide by tumultuous boiling until a drop of the liquid no longer colors lead paper; then let the liquid settle, decant while hot, filter, transfer the filter (without washing) together with the zinc sulphide to a small beaker, add 30 to 50 c.c. of hot water, stir, and add an excess of silver chloride ; now boil until the super- natant liquid has become clear, and to the boiling liquid finally add 5 to 6 drops of dilute sulphuric acid (1:6). A few minutes suffice to effect the complete conversion of the zinc sulphide into zinc chloride. Filter off the precipitate of silver sulphide and chloride, wash, and in the solution determine the chlorine according to VOLHARD'S method.* For this purpose add to the zinc-chloride solution (which may measure 200 to 300 c.c.) 5 c.c. of the ammonio-ferric-alum solution and sufficient nitric acid to cause the disappearance of the color of the iron salt; then add a measured quantity of silver solution, and in fact somewhat more than is necessary to pre- cipitate all the chlorine. Now run in ammonium-sulphocyanate solution from a second burette, drop by drop, without previously filtering off the silver chloride or causing it to aggregate by shaking or boiling. The liquid must be constantly shaken about while the sulphocyanate solution is being added, so that the drops as they fall may be immediately mixed with the liquid. As soon as the latter has acquired a pale brownish-yellow color, which persists for ten minutes on allowing the liquid to stand quietly, the pre- cipitation of the silver is complete. Now deduct the c.c. of silver solution corresponding to the ammonium-sulphocyanate solution from the total silver solution, and for every c.c. found in the dif- ference (and corresponding to the chlorine of the zinc chloride) calculate 0-01 grm. of zinc. The test analyses given by MANN are in the highest degree * Zeitschr. /. analyt. Chem., xvm, 272. 446 DETERMINATION OF COMMERCIAL VALUES. [242. satisfactory / and in my laboratory also excellent results have been obtained. J. B. SCHOBER'S* method of determining zinc is also based on the VOLHARD method of determining silver. SCHOBER precipi- tates the zinc with sodium-sulphide solution, decomposes the excess of the latter with silver solution, and finally determines the excess of this with ammonium sulphocyanate. The method is too incon- venient, and is not likely to be generally used. [The following method by HANDY f is a modification of Stolba's. This process may be much more easily used for the determination of zinc than for magnesium, and it is carried out as follows : To the zinc solution, which should contain ammonium chloride, a large ex- cess of ammonia is added, then a large excess of sodium phosphate. The solution remains clear ; but if the excess of ammonia is cautiously neutralized, a white cloud is formed as each drop of acid falls into the strong ammoniacal liquid. On stirring, this cloud dissolves Until nearly all the ammonia is neutralized, when the whole solu- tion becomes milky. It should now be heated to about 75 and stirred constantly, at the same time continuing the addition of dilute acid, drop by drop. In a very few minutes the precipitate becomes crystalline, and with care the liquid may be almost per- fectly neutralized. It is a good plan to add a small piece of litmus- paper to the liquid; this should not turn red, but should remain blue or violet, while the hot liquid should have no odor, or only a very faint odor of ammonia. When the precipitation is made as above, the zinc ammonium phosphate is easily filtered, which may be safely done after five minutes' standing. The precipitate should be washed with cold water until the washings show only a faint trace of chlorides, then the paper with the precipitate returned to the beaker in which the precipitation was made, an excess of standard acid added, a few drops of methyl orange, and the exact point of neutrality determined with standard alkali. * Zeitschr. f. analyt. Chem., xvm, 467. \Journ. Amer. Chem. Soc., xxn, 31; ibid., xxm, No. 7. 242.] ZINC COMPOUNDS. 447 According to the equation ZnNH 4 PO 4 + H 2 SO 4 = ZnSO 4 + NH 4 H 2 PQ 4 , we see that 1 c.c. of normal acid corresponds to 32-7 mgrm. zinc. Since the zinc ammonium phosphate is not precipitated in presence of a large excess of ammonia, the process may be used in the presence of magnesium, which is precipitated in the strongly alkaline liquid, and the filtrate from the precipitate neutralized to precipitate the zinc. The process gives fairly good results in the presence of iron, calcium, and magnesium. Manganese, however, must be pre- viously separated, best by the nitric -acid and potassium-chlorate method. A. C. LANGMUIR* describes the following method: From 0-5 to 1 grm. of the zinc ore is dissolved, and the metals of the hydro- gen sulphide group are separated as usual. After expulsion of H 2 S by boiling, the solution is peroxidized with bromine water, and iron and manganese are separated by ammonia, the precipitate being redissolved and reprecipitated two or three times. If the ore be free from lime and magnesia, the filtrate may at once be boiled down with excess of nitric acid to destroy chlorides and ammonium salts; when the chlorine is expelled, the solution is transferred to a platinum dish, evaporated to dryness, and ignited, and the zinc is weighed as oxide. Otherwise the warm ammoniacal solution is acidulated with hydrochloric acid, the bromine thus set free is absorbed by the addition of a few drops of sulphurous acid, and three or four drops of methyl-orange solution are added. The solution is now carefully neutralized with ammonia, and ammo- nium sulphide is added, little by little, until a drop of the liquid gives a dark coloration with a drop of ferric chloride on a porcelain plate; the mixture is warmed on the water-bath until the precipi- tate has subsided, when it is filtered through a double-ribbed filter. Washing should be avoided, otherwise the filtrate will be turbid. The precipitate is therefore at qnce dissolved in hot nitric acid (1:3), or in dilute hydrochloric acid, if cobalt or nickel is present, *Journ. Amer. Chem. Soc., 1899, xxi, 115-118. 448 DETERMINATION OF COMMERCIAL VALUES. [ 243. and correction is subsequently made for lime or magnesia, if any be present. The solution is evaporated in a porcelain dish, with the addition of nitric acid to expel chlorine; when almost dry it is transferred to a tared platinum dish, dried, and ignited, at first over a BUNSEN burner, and finally, intensely, over the blowpipe, so as to decompose any zinc sulphate present. Ammonium car- bonate may be added, but it tends to cause loss. After weighing, the oxide is redissolved in hydrochloric acid; the trace of iron present is thrown down with ammonia, filtered, and weighed, and the amount deducted from the weight of ZnO. The filtrate is acidified with hydrochloric acid, and tested for sulphate with barium chloride. If necessary, the barium sulphate is collected and weighed and the SO 3 determined ; but if the ignition has been prop- erly performed, there should not be more than a trace of precipi- tated BaS0 4 . If lime or. magnesia be present, the filtrate from the precipitate of iron contained in the ZnO should be divided into two parts, one to be tested for sulphates, the other to be used for the determination of the earths. TRANSLATOR.] II. ELECTROLYTIC DETERMINATION OF ZINC IN ZINC ORES. 243. Quite a number of processes have already been proposed for the electrolytic precipitation of zinc.* From these it may be seen that the electrolytic precipitation can be effected without difficulty. The different experimenters differ, however, regard- ing the best method. PARODI and MASCAzziNif first proposed the precipitation in a solution of the sulphate to which an excess of ammonium acetate had been added, but subsequently J they gave the following method the preference: Dissolve the zinc (0-1 to 0-25 grm.) as a sulphate, add 4 c.c. of an ammonium-acetate solution (naturally a rather concentrated solution) and 2 c.c. of a (also concentrated) citric- *See Zeitschr. /. analyt. Chem., vm, 24; xv, 303; xvi, 469; xvn, 216; xvin, 587; and xvm, 588. f Ibid., xvi, 469. $ Ibid.; xvm, 587. 243.] ZINC COMPOUNDS. 449 acid solution, dilute to 200 c.c., introduce the electrodes* so that they are separated only a few millimetres, and close the circuit; the platinum cone must be the negative electrode. Cover the beaker with a glass plate properly arranged. The current fur- nished by the CLAMOND thermopile should be strong enough to produce 250 to 300 c.c. of oxy-hydrogen mixture per hour. When a sample of the liquid is no longer rendered turbid by potassium ferrocyanide. the separation of zinc may be considered as complete. Then draw off the liquid with a siphon, wash the cone with water, and break the current. Finally wash the cone with the adhering zinc twice with absolute alcohol, dry at 40 to 50 with access of air, and weigh. If the ore contains lead, cadmium, iron, etc., these metals must first be removed by one of the methods detailed in 242. ALF. RICHE f first removes all other metals from the sulphuric- acid or nitric-acid solution of the zinc ore, then supersaturates with ammonia until the precipitate of hydrated zinc oxide first formed redissolves, then adds an excess of acetic acid, and sub- mits the solution to electrolysis. The deposited zinc adheres firmly to the (negative) platinum cone. F. BEILSTEIN and L. JAWEIN J add caustic soda to the sul- phuric-acid solution (or otherwise suitably prepared solution) of the zinc ore until a precipitate develops, and potassium cyanide until the precipitate redissolves and a clear solution results. The current is obtained from four BUXSEN elements. If the liquid becomes warm, the beaker is placed in cold water. When the precipitation is considered to be complete, remove the electrodes from the liquid, wash the cone successively with water, alcohol, and ether, dry in an exsiccator first, then at 100, weigh, and dissolve the zinc in hydrochloric or nitric acid. Then wash and weigh the cone, place the electrodes again in the liquid, and note whether a further deposit of zinc takes place. * As the electrolytic method is particularly important in the precipitation of copper, the details will be described under the analysis of the copper compounds. t Zeitschr. /. analyt. Chem., xvii, 216. J Ibid., xviii, 588. 450 DETERMINATION OF COMMERCIAL VALUES. [ 244. [For further processes and details of electrolytic methods see "Quantitative Chemical Analysis by Electrolysis," by ALEX. CLASSEN, translated by B. B. BOLTWOOD. JOHN WILEY & SONS, New York, 1903. Also "Electro-chemical Analysis," by EDGAR F. SMITH. P. BLAKISTON'S SON & Co., Philadelphia, 1902. TRANS- LATOR.] E. METALLIC ZINC. 244. Metallic zinc as obtained by metallurgical processes contains various impurities. These have been investigated by many chem- ists, and particularly by C. W. ELIOT and FR. H. STORER,* who have most carefully examined ten kinds of zinc (German, English, French, Belgian, and American). The following are the most important results of their investigations: Almost all zincs (nine out of the ten kinds) contain lead, in quan- tities varying from 0-079 to 1-66 per cent. All contain small quantities of cadmium] the quantity of cadmium oxide, which in some zincs contains also small quantities of stannic oxide varies from 0-0035 to 0-4471 per 100 parts of zinc All zincs contain iron, in quantities varying from 0-0549 to 0-2088 per cent. Copper was found in only one sample. Arsenic does not occur so generally as is usually believed; quite a number of zincs are free from it, and others contain traces, while some contain notable quantities. Of the other metals, nickel, cobalt, man- ganese, and antimony are only exceptionally found, and then but in very minute quantities. Carbon and silicon are not, as a rule, found in zinc, but sometimes traces are. Sulphur is always present but only in slight traces. Phosphorus, of which also traces may be found in zinc, was not included in the investigations of ELIOT and STORER. .For ordinary cases it suffices to quantitatively determine the lead, iron, and cadmium; regarding the other impurities it suf- fices, as a rule, to test for them qualitatively. * Memoirs of the American Academy of Arts and Sciences, New Series* Vol. vni, p. 57-94. 244.] ZINC COMPOUNDS. 451 The analysis is conducted as follows: 1. Treat about 30 grm. of the zinc (either granulated or cut into small pieces if sheet-zinc) with diluted sulphuric acid (1 part concentrated acid to 4 parts water) with moderate heat. When the zinc is almost completely dissolved, decant or filter off the zinc solution from the undissolved, black residue; wash the latter, dissolve in a little nitric acid (any residue should be tested for tin), add a little diluted sulphuric acid, and evaporate until all the nitric acid has been expelled. Treat the residue again with the same diluted sulphuric acid, etc., and determine the separated lead sulphate according to 116, 3, a, /?. 2. Dilute the filtrate from the lead sulphate with water, and add to every 100 c.c. 4 c.c. of hydrochloric acid (sp. gr. 1-12); then pass in hydrogen sulphide for fifteen minutes to precipitate any cadmium and any traces of tin or perhaps copper that may be present. As a part of the cadmium, etc., may also have passed into the main zinc solution, treat this tco, after suitably diluting and adding 4 c.c. of hydrochloric acid to every 100 c.c. of solution, with hydrogen sulphide for fifteen minutes. If a precipitate forms, collect this in the small filter in which the first precipitate of cadmium sulphide was collected. After washing, dissolve the con- tents of the filter in 2 c.c. brominized hydrochloric acid, add 2 c.c. hydrochloric acid, dilute with 100 c.c. water, expel the bromine by heating, and precipitate with hydrogen sulphide as before. Col- lect, wash, and dry the precipitate; dry the filter, impregnate it with a concentrated ammonium-nitrate solution, dry again, in- cinerate, heat the residue with a little sulphuric acid, evaporate off the acid, and weigh the sulphate obtained ( 121, 3). If the residue affords with water and a slight excess of ammonia a clear, colorless solution which gives a yellow precipitate with ammo- nium sulphide, the weighed sulphate may be at once calculated as .cadmium sulphate; if, on the other hand, the ammoniacal solution is blue, the separation of the cadmium and copper salts must first be effected ( 163). If an insoluble residue remains on treating the sulphate with water and ammonia, it should be tested for tin. 452 DETERMINATION OF COMMERCIAL VALUES. [ 245. 3. To determine the iron, it is best to dissolve a fresh quantity of at least 10 grm. of the zinc in pure, diluted sulphuric acid (in the apparatus Fig. 84, Vol. I); pour the cooled solution into a beaker, repeatedly wash the separated spongy lead, and deter- mine in the solution the iron as ferrous sulphate, by means of a suitably diluted potassium-permanganate solution, according to Vol. I, p. 318, /?. The qualitative detection of arsenic is best accomplished by means of MARSH'S method as modified by OTTO (see Qualit. Anal. , 14 ed., [Germ.], 188), using absolutely pure sulphuric acid. Any sulphur present is most easily detected by dissolving the zinc in hydrochloric acid and testing whether the gas evolved blackens an alkaline lead solution or lead paper. The greatest care must be exercised in selecting the acid, for if it contains traces of sul- phurous acid, the lead preparations will be blackened even if the zinc contains no sulphur, while on the other hand, if it con- tains chlorine, the blackening will not occur even though the zinc contains sulphur. ELIOT and STORER (loc. cit., p. 72) found these conditions so difficult to fulfill with the hydrochloric acid ordinarily obtainable, that they prepared the acid themselves by decomposing a solution of pure calcium chloride with pure oxalic acid. Phosphorus in zinc is best detected by the color of the flame of the hydrogen evolved on treating zinc with pure sulphuric acid (see Qual. Anal, 14 ed.,[Germ.], p. 396). F. ZINC-DUST. 245. Commercial zinc-dust, consisting of more or less pure finely divided zinc intimately mixed with zinc oxide, is valued, not according to its total zinc content, but according to the quantity of zinc it contains in the metallic state, as the zinc-dust is used almost exclusively as a reducer. For determining the value of zinc-dust, the two following methods are employed in my laboratory: 245.] ZINC COMPOUNDS. 453 First Method* This method is based upon the solution of the zinc-dust in diluted sulphuric or hydrochloric acid, burning the evolved hydrogen, and \\eighing the water thus formed, 1 eq. of zinc being calculated for 1 eq. of water. The apparatus used for this purpose is as follows: The flask in which the zinc is to be dissolved should have a capacity of about 100 c.c. , and be provided with a safety-tube for the introduction of the acid; also a screw pinch-cock, as shown in Fig. 103, p. 365. The hydrogen evolved is passed through a small cooling apparatus (see the figure) to remove the water. The gas is then passed into the U-tube a, Fig. 104, two-thirds filled with small fragments of FIG. 104. glass, and containing besides 12 c.c. of pure, concentrated sulphuric acid. b c is a combustion-tube 34 cm. long. Near the end b it contains, between two copper-gauze plugs, a 12-cm. long layer of asbestos which has been ignited first in moist, then in dry, air; the rest of the tube is filled with well-ignited, granular cupric oxide, retained in place at c by a plug of copper-wire gauze, or asbestos. d is a U-tube half-filled with glass fragments, and containing besides 6 c.c. pure concentrated sulphuric acid;f e is a guard-tube containing calcium chloride, and / is an aspirator. * " Ueberdie Werthbestimmung des Zinkstaubes," R. FRESENIUS, Zeitschr. f. analyt. Chem., xvn, 465. f Instead of this tube a SCHROTTER sulphuric-acid tube may, of course, be employed, as described on page 52, Fig. 44. 454 DETERMINATION OF COMMERCIAL VALUES. [ 245. The apparatus is put together as shown in the illustration, but the tube b c is connected directly (i.e. without interposing d and e) with the aspirator. Then slightly open the screw pinch-cock on the safety-tube of the gas-evolution flask, open the pinch-cock g, draw a current of air through the apparatus, and heat the whole length of the tube 6 c to a redness, finally al owing to cool in a current of dry air. In the meantime introduce the weighed quantity of zinc-dust (about 3 grm.) into the gas-evolution tube, add a little water, weigh the tube d, close g, assemble the apparatus as shown in the illustration, close the pinch-cock on the safety- tube, open g again, and thus make certain that the apparatus is tight. Now heat the tube b c to redness at the place where it contains the cupric oxide, open the pinch-cock of the safety-tube slightly, pour diluted sulphuric acid, to which a drop of platinic-chloride solution has been added, into the funnel ra, and allow it to run into the gas-evolution tube. The screw pinch-cock on the safety- tube should be opened so far that single air-bubbles may slowly pass through the acid, closing the lower end of the safety-tube. The evolution of hydrogen goes on quietly; from time to time more acid, but without platinic chloride, is added, and until all the zinc is dissolved. The operation requires about one hour; it may be hastened, however, by a gentle heat. The mixture of hydrogen with the excess of air is completely dried in a, then burned in b c to water, without the cupric oxide being permanently reduced ; and the water formed is collected and retained in d. Toward the end of the operation heat the evolution flask moderately in order to com- pletely expel the slight quantity of hydrogen still held in solution by the liquid. After cooling, ascertain the increase in weight of the tube d, and calculate 65-4 parts of metallic zinc for every 18-016 parts of water found. The apparatus is then ready for a fresh determination; the sulphuric acid in a and d should first be renewed, however. 245.] ZINC COMPOUNDS. 455 Second Method (DREWSEN*). This method is based on the following principle: Zinc-dust hi contact with a sufficient quantity of potassium dichromate and diluted sulphuric acid evolves no hydrogen, but the chromic acid liberated by the sulphuric acid is reduced to chromic oxide, as follows: 2CrO 3 + 6H = Cr 2 O 3 + 3H 2 O. The requisites are: a. A potassium-dichromate solution of known strength. This is prepared by dissolving 40 grm. of the pure fused salt in water to make 1 litre. b. A ferrous-sulphate solution, containing about 200 grm. of the salt in the litre. The solution must be strongly acidulated with sulphuric acid to prevent oxidation. The relation between the two solutions is first ascertained, as follows: Measure off 20 c.c. of the ferrous-sulphate solution into a beaker, add some sulphuric acid and about 50 c.c. water, and from a burette run in the potassium-dichromate solution until a drop of the iron solution is no longer rendered blue by potassium ferricyanide (see Vol. I, p. 319, 6). Now place the weighed zinc-dust (about 0-05 grm.) in a beaker, add 55 c.c. of the potassium-dichromate solution, then add 5 c.c. diluted sulphuric acid, stir thoroughly, add a further 5 c.c. of diluted acid, and allow to stand for 15 minutes with frequent agi- tation. When certain that all is dissolved but a slight residue, which always remains, add an excess of sulphuric acid, 100 c.c. water, and 25 c.c. ferrous-sulphate solution, in order to reduce the greater part of the excess of potassium dichromate; then continue to add the ferrous-sulphate solution in portions of about 1 c.c. each until a drop of the liquid gives a distinct blue color with potassium ferricyanide, and finally titrate back with the potassium dichro- mate until the reaction just ceases to take place. * Zeitschr. /. analyt. Chem., xix, 50. 456 DETERMINATION OF COMMERCIAL VALUES. [ 246 From the total cubic centimetres of the potassium-dichromate solution used deduct the quantity corresponding to the ferrous- sulphate solution employed. On multiplying the difference by 0-66639 the metallic zinc in the zinc-dust is ascertained. 12. MANGANESE COMPOUNDS. A. BLACK OXIDE OF MANGANESE. 246. The native black oxide of manganese (as also the regenerated artificial product) is a mixture of manganese dioxide with lower oxides of that metal, and with ferric oxide, clay, etc.; it also invariably contains moisture and frequently chemically combined water. The commercial value of the article depends entirely upon the amount of dioxide (or, more correctly expressed, of available oxygen) which it contains, hence it is of the greatest interest for the manufacturer who uses the substance as a source of chlorine to ascertain this. By " available oxygen' 7 we understand the excess of oxygen contained in a manganese over the 1 at. com- bined with the metal to monoxide; upon treating the ore with hydrochloric acid, an amount of chlorine is obtained equivalent to this excess of oxygen. This available oxygen is always ex- pressed in the form of manganese dioxide. 1 at. corresponds to 1 mol. manganese dioxide, since MnO 2 = MnO+O. DE VRY* had already called attention to the importance not only of the drying of the sample to be analyzed, but also to the method by which the drying should be effected; and I, too, have paid special attention to the subject of drying, as it may give rise to many differences.! I therefore give a detailed account of the methods of drying the manganese dioxide before describing the methods of analysis. * Ann. d. Chem. u. Pharm., LXI, 249. f DINGL. polyt. Journ., cxxxv, 277. 246.] MANGANESE COMPOUNDS. 457 I. DRYING THE SAMPLE. All analyses of manganese proceed, of course, upon the sup- position that the sample operated upon is a fair average specimen of the ore. A portion of a tolerably finely powdered average sample is generally sent for analysis to the chemist; in the case of new lodes, however, a number of samples, taken from different parts of the mine, are also occasionally sent. If, in the latter case, the average composition of the ore is to be ascertained, and not simply that of several samples, the following course must be resorted to : Crush the several samples of the ore to coarse powder in an iron mortar, and pass the whole through a rather coarse sieve. Mix uniformly, then remove a sufficiently large por- tion of the coarse powder with a spoon, and reduce it to powder in a steel mortar, passing the whole powder through a fine sieve. Mix the powder obtained by this second process of pulverization most intimately; take about 8 to 10 grm. of it and triturate, in small portions at a time, in an agate mortar, to an impalpable pow- der. Average samples are generally sufficiently fine to require only the last operation. As regards the temperature at which the powder is to be dried, if you desire to expel the whole of the moisture without disturbing any of the water of hydration, the temperature adopted must be 120 (this is the result of my own experiments; see Expt. No. 89). In this case it is best to use the drying-disk described in 31, Fig. 42, the finely powdered substance being placed in one of the pans and heated to the temperature indicated for an hour and a half. But as there a pears to be at present an almost universal under- standing in the manganese trade to limit the drying temperature to 100, the fine powder is exposed for 6 hours in a shallow copper or brass pan to the temperature of boiling water, in a water-bath ( 28, Fig. 31). Where it becomes frequently necessary to dry a number of samples at the same time, it is best to employ copper water-baths of the form of rather shallow square boxes, with 4, 6, 12, or more small drying-closets fixed into the side so that 458 DETERMINATION OF COMMERCIAL VALUES. [ 247. they are surrounded by boiling water or steam on all sides except the front. When the samples have been dried, they are introduced, still hot, into glass tubes 12 to 14 cm. long and 8 to 10 mm. wide, sealed at one end; these tubes are then corked and allowed to cool. In laboratories where whole series of analyses of different ores are of frequent occurrence, it is advisable to number the drying- pans and glass tubes, and to transfer the samples always from the pan to the tube of the corresponding number. II. DETERMINATION OF THE MANGANESE DIOXIDE. 247. Of the many methods that have been proposed for the valua- tion of manganese ores, I select three as the most expeditious and accurate. The first is more particularly adapted for technical purposes, and is employed almost everywhere for the purposes of valuation. a. FRESENIUS and WILL'S Method* The principle upon which this method is based has been already applied by BERTHIER and THOMSON; the following will explain : 1. If oxalic acid (or an oxalate) is brought into contact with manganese dioxide in the presence of water and an excess of sulphuric acid, manganous sulphate is formed and carbon dioxide evolved, while the oxygen, which we may assume to exist in the manganese dioxide in combination with the monoxide, combines with the elements of the oxalic acid and thus converts the latter into carbon dioxide: Mn0 2 + H 2 S0 4 + H 2 C 2 4 = MnSO 4 + 2H 2 O + 2C0 2 . Each atom of available oxygen, or, what amounts to the same, * Comp. the papers mentioned in the foot-note on p. 317, this vol. 247.] MANGANESE COMPOUNDS. 459 each mol. of manganese dioxide = 87, gives 2 mol. carbon dioxide = 88. 2. If this process is performed in a weighed apparatus from which nothing except the evolved carbonic acid can escape, and which, at the same time, permits the complete expulsion of that acid, the diminution of weight will at once show the amount of carbonic acid which has escaped, and consequently, by a very sim- ple calculation, the quantity of dioxide contained in the analyzed manganese ore. As 88 parts, by weight, of carbon dioxide corre- spond to 87 of manganese dioxide, the carbon dioxide found need simply be multiplied by 87 and the product divided by 88, or the carbon dioxide may be multiplied by 87 1 = 0-9887 to find the corresponding amount of manganese dioxide. 3. But even this calculation may be avoided by simply using in the operation the exact weight of ore which, if the latter con- sisted of pure dioxide, would give 100 parts of carbon dioxide. The number of parts of carbon dioxide evolved directly ex- presses, in that case, the number of parts of dioxide contained in 100 parts of the analyzed ore. It results from 2, that 98-87 is the number required. Suppose the experiment is made with 0-9887 grm. of the ore, the number of centigrammes of carbon dioxide evolved in the process expresses directly the percentage of dioxide contained in the analyzed manganese ore. Now, as the amount of carbon dioxide evolved from 0-9887 grm. of man- ganese would be rather small for accurate weighing, it is advis- able to take a multiple of this weight, and to divide afterwards the number of centigrammes of carbon dioxide evolved from this multiple weight by the same number by which the unit has been multiplied. The multiple which answers the purpose best for superior ores is the triple, = 2 966 ; for inferior ores I recom- mend the quadruple, = 3 955, or the quintuple, = 4 9435. 4. The analytical process is performed in the apparatus illus- trated in Fig. 105. 460 DETERMINATION OF COMMERCIAL VALUES. [ 247. The flask A should hold, up to the neck, about 120 c.c.; B about 100 c.c. The latter is half filled with concentrated sulphuric acid free from nitric and nitrous acids; the tube a is closed at b with a little wax ball, or a very small piece of caoutchouc tubing, with a short piece of glass rod inserted in the other end. Place 2-966 or 3-955 or 4-9435 grm. according to the quality of the ore in a watch-glass, and tare the latter most accurately on a delicate balance; then remove the weights from the watch-glass and very cautiously replace them by manganese from the tube with the aid of a gentle tap of the finger, until the equilibrium is exactly restored. Transfer the weighed sample, with the aid of a card, to the flask A, add 5 to 6 grm. normal sodium oxalate, or about 7-5 grm. normal potassium oxalate, in powder, and as much water as will fill the flask to about one- third. Insert the cork into A, and tare the apparatus on a strong but delicate balance by means of shot, and lastly, tin-foil, not placed directly on the scale, but in an appropriate vessel. The tare is kept under a glass bell. Test whether the apparatus is airtight (Vol. I, pp. 488, 489) . Then make some sulphuric acid flow from B into A by applying suction to d, by means of a caoutchouc tube. The evolution of carbon dioxide com- mences immediately and proceeds in a steady and uniform manner. When it begins to slacken, cause a fresh portion of sulphuric acid to pass into A } and repeat this until the manganese ore is com- pletely decomposed, which, if the sample has been very finely pulverized, requires at the most about five minutes. A too rapid evolution of gas must be avoided, or else the sulphuric acid will not remove all the water from the carbon dioxide. The complete decomposition of the analyzed ore is indicated, on the one hand, by the cessation of the disengagement of carbon dioxide, and its non-renewal upon the influx of a fresh portion of sulphuric into A ; 247. J MANGANESE COMPOUNDS. 461 and, on the other hand, by the total disappearance of every trace of black powder from the bottom of A* Now cause some more sulphuric acid to pass from B into A, to quite strongly heat the fluid in the latter, but not above 70, and expel the last traces of carbon dioxide therein dissolved. The apparatus must not be exposeed to direct sunlight during the analysis, otherwise the ferric oxalate may be decomposed with evolution of carbon dioxide vLucKf). Now remove the wax stopper or india-rubber tube from b and apply gentle suc- tion to d until the air drawn out tastes no longer of carbon dioxide. Let the apparatus cool completely in the air, and place it on the balance, with the tare on the other scale, and restore equilib- rium. The weight in centigrammes added, divided by 3, 4, or 5, according to the multiple of 0-9887 grm. used, expresses the percentage of dioxide contained in the analyzed ore. 5. In experiments made with definite quantities of the ore, weighing in an open watch-glass cannot well be avoided, and the dried manganese is thus exposed to the chance of a reabsorption of water from the air, which of course tends to interfere to a trifling extent however with the accuracy of the results. In very pre- cise experiments, therefore, the best way is to analyze an indeter- minate quantity of the ore, and to calculate the percentage as shown above. For this purpose one of the little corked tubes filled with the dry pulverized ore is accurately weighed and about 3 to 5 grm. (according to the quality of the ore) are trans- ferred to the flask A. By now reweighing the tube, the exact quantity of ore in the flask is ascertained. To facilitate this opera- tion it is advisable to scratch marks on the tube with a file indi- cating approximately the various quantities which may be required for the analysis, according to the quality of the ore. 6. If the manganese ore is more than usually difficult to de- compose, the temperature developed on mixing the concentrated sulphuric acid and water is at times insufficient to effect com- * If the maganese ore has been pulverized in an iron mortar, a few black spots (particles of iron from the mortar) will often remain perceptible, f Zeitschr. /. analyt. Chem.,- x, 322. 462 DETERMINATION OF COMMERCIAL VALUES. [ 247. plete decomposition. In this case place the flask A of the ap- paratus on an iron plate, and the flask B on a board, and heat the iron plate. The temperature must never be allowed to ex- ceed 70, otherwise the oxalic acid may also be decomposed by the ferric sulphate (LucK, loc. cit.). 7. With proper skill and patience on the part of the operator, a good balance ; and correct weights, this method gives most accurate and corresponding results, differing in two analyses of the same ore barely to the extent of 0-2 per cent. I have never observed a greater difference than this. If the results of two assays differed by more than 0-2, or at most 0-3, per cent., a third experiment should be made. In labo- ratories where analyses of manganese ores are matters of fre- quent occurrence, it will be found convenient to use an aspirator for sucking out the carbon dioxide. In the case of very moist air, the error which proceeds from the fact that the water in the air drawn through the apparatus is retained, and which is usually quite inconsiderable, may now be increased to an important ex- tent. Under such circumstances, connect the end of the tube b with a calcium-chloride tube during the suction. It is needless to remark that the drying and powdering be properly effected, and that the alkali oxalate must be tested as to its purity. Very accurate determinations may also be made by weighing the evolved carbon dioxide. For this purpose the apparatus described on page 498, Fig. 99, Vol. I, is well adapted. From 0-5 to 1 grm. ore should be used for a determination. Introduce the ore and oxalic acid or oxalate into the decomposing flask, fill the flask about one-third with water, connect the several parts of the apparatus as for the determination of carbonic acid, de- compose the ore by admitting gradually strong sulphuric acid, and remove the evolved C0 2 completely from the unweighed por- tion of the apparatus into the potash bulbs as described for the determination of CO 2 . 8. Some ores of manganese contain carbonates of the alkali- earth metals, which of course necessitates a modification of the foregoing process. To ascertain whether carbonates of the alkali- 247.] MANGANESE COMPOUNDS, 463 earth metals are present, boil a sample of the pulverized ore with water and add nitric acid. If any effervescence takes place, the process is modified as follows (ROHR*): After the weighed portion of ore has been introduced into the flask A, treat it with water, so that the flask may be about one- quarter full, add a few drops of dilute sulphuric acid (1 part, by weight, sulphuric acid, to 5 parts water), and warm with agitation, preferably in a water-bath. After some time dip a *od in and test whether the fluid possesses a strongly acid reaction. If it does not, add more sulphuric acid. As soon as the whole of the car- bonates are decomposed by continued heating of the acidified fluid completely neutralize the excess of acid with soda solution free from carbonic acid, allow to cool, add the usual quantity of sodium oxalate, and proceed as above. ' , If you have no soda solution free from carbonic acid at hand, you may place the sodium oxalate or oxalic acid (about 3 grm.) in a small tube and suspend this in the flask A by means of a thread fastened by the cork. When the apparatus is tared, and you have satisfied yourself that it is airtight, release the thread and proceed as above. 9. If the manganese ore contains magnetic iron oxide f (or any ferrous compound), the determination of its value in terms of manganese dioxide, i.e., the quantity of chlorine it is capable of evolving, will be inaccurate if the methods described are fol- lowed without modification; the results obtained will be too high because in carrying out the method only the greater part of the ferrous compound, but not all of it, is oxidized,! while on treating the manganese ore with hydrochloric acid, chlorine is not evolved until all the ferrous iron present has been converted into ferric chloride. * Zeitschr. f. analyt. Chem., I, 48. f The presence of any magnetic iron oxide may be detected by the action on an astatic magnetic needle. See MOHR, Zeitschr. f. analyt. Chem. , vm, 314. t Compare TESCHEMACHER and SMITH, Zeitschr. f. analyt. Chem., vm, 509. SHERER and RUMPF, ibid., ix, 46. PATTINSON, ibid, ix, 509. LUCK, ibid., x, 310. 464 DETERMINATION OF COMMERCIAL VALUES. [ 247. The portion of the ferrous compound remaining unoxidized, and hence the quantity of ferric oxide found in excess by the methods already described, is due to the rapidity with which the reaction proceeds, and is therefore the larger the more rapid the operation. By slightly modifying the process, however, perfectly satis- factory results may be obtained even with ores containing ferrous compounds, the results agreeing well with those obtained by other methods. LUCK * has shown that the ferrous compound is al- most completely oxidized if some sodium acetate is introduced into the decomposition flask. In the case of manganese ores containing ferrous iron, there- fore, it suffices, according to LUCK, to introduce as a rule about 6 c.c. of a 1:9 sodium-acetate solution into the decomposition flask, and to then conduct the process as usual. It is preferable to allow the decomposition to proceed somewhat slowly. Instead of determining the carbon dioxide from the loss in weight of the apparatus, it may be estimated by collecting it in a weighed absorption apparatus, as first recommended by KOLBE. Ths modification is preferred by those chemists who are not provided with a sufficiently large yet very sensitive balance, and by those who prefer weighing on one balance rather than on two. The most convenient method to use is the one described in Vol. I, p. 493, e; a simple form of the apparatus may be used. The decomposition flask should hold from 100 to 120 c.c. up to the neck. The carbon dioxide evolved in it is passed first through two U-tubes the limbs of which are 170 mm. long and 18 mm. wide; the first is empty, but the second is filled with calcium chloride (pp. 15, 16). The carbon dioxide issuing from the latter passes through two smaller U-tubes the limbs of which are 110 to 120 mm. long and 15 mm. wide. These are filled with granular soda- lime, and at the exit end with coarsely granular calcium chloride; both tubes are weighed before and also after the experiment. After these tubes there follows a small safety-tube the lower part * Zeitschr. /. analyt. Chem., x, 317. 247.] MANGANESE COMPOUNDS. 465 of which is filled with soda-lime, the remaining space being filled with calcium chloride; then a small U-tube follows, the lower part of which contains some water in order that the progress of the operation may be observed; and lastly there is an aspirator. Introduce the manganese ore into the decomposition-flask with the sodium oxalate (if the ore contains magnetic iron oxide, add also some sodium acetate, as stated above), and through a funnel-tube let run in diluted sulphuric acid (1 vol. concentrated acid to 2 vol. water). Care must be taken to avoid exposing the apparatus to direct sunlight, and that the temperature of the decomposition-flask (heated on an iron plate) does not rise above 70. If the manganese ores contain carbonates of the alkaline earths, the carbon dioxide in these may be first conveniently determined, by means of this method, by adding a slight excess of diluted sulphuric acid, moderately heating, drawing a current of purified and dried air through the apparatus, and then, after previously neutralizing the free acid, determining the CO 2 evolved from the sodium oxalate by the action of sulphuric acid and manganese ore. It is almost unnecessary to state that for the absorption of larger quantities of carbon dioxide, the soda-lime tubes may be replaced by a potash apparatus, after which is placed a U-tube half filled with soda-lime, half with calcium chloride. b. BUNSEN'S Method* Reduce the ore to the very finest powder, weigh off about 4 grm., introduce this together with a few compact fragments of magnesite into the small flask d, Fig. 89, Vol. I, p. 425, and pour pure fuming hydrochloric acid over it; conduct the process exactly as in the analysis of chroma tes. Boil until the ore is completely * Closely allied to BUNSEN'S method is that of GAY-LUSSAC, very widely used in France, and in which the evolved chlorine is passed into milk-of- lime and the chlorinated-lime solution formed determined chlonmetrically ( 233). SHERER and RUMPF (Zeitschr. f. analyt. Chem., ix, 48 and 51) in a critical investigation of this method obtained no satisfactory results whatever, and in a comparative test with PERREY'S method (Chem. Cen- tralbi, 1878, 15), GAY-LUSSAC'S method gave the lower results. 466 DETERMINATION OF COMMERCIAL VALUES. [ 247. dissolved and all the chlorine expelled, which is effected in a few minutes. 2 at. of iodine separated correspond to 2 at. chlorine evolved, and accordingly to 1 mol. of manganese dioxide. For the estimation of the separated iodine, the method 146 may be employed. Results most accurate, but only in skilful hands. For dissolving the manganese ore, and absorbing the evolved chlorine by potassium-iodide solution, I would recommend the apparatus illustrated by Fig. 103, Vol. I, p. 530. There must be no delay in determining the separated iodine immediately after the decomposition is complete, otherwise the quantity will be in- creased by the decomposition of the hydriodic acid liberated, and consequently too high a result will be obtained. c. Determination by means of Iron. On heating manganese ore with hydrochloric acid and a known excess of ferrous chloride, the latter is converted into ferric chloride by the evolved chlorine corresponding to the available oxygen of the manganese ore. As the quantity of ferric chloride formed may be determined by estimating the unaltered ferrous chloride according to PENNY'S method (Vol. I, p. 319, 6), the effective value of the manganese ore, expressed in terms of manganese dioxide, may be readily calculated. This method, which was described in the 5th (German) edition, was critically examined in my laboratory by SHERER and RUMPF,* but the results ob- tained were unsatisfactory, being somewhat too low and not sufficiently concordant, because small quantities of chlorine es- cape without acting on the ferrous chloride. PATTINSON f therefore modified the method by employing sulphuric acid instead of hydrochloric acid, and thereby obtained good results. He recommends the following process: Introduce into a 600-c.c. flask (arranged as shown in Fig. 84, Vol. I, p. 314) 2 grm. fine iron wire, ignited and accurately weighed; dissolve by the aid of heat in 90 c.c. of diluted pure sulphuric acid (1 part by weight concentrated acid and 3 of water), then ad 2 grm. of * Zeitschr. /. analyt. Chem., ix, 46. f Ibid., ix, 510. 247.] MANGANESE COMPOUNDS. 467 the finely powdered manganese ore, accurately weighed, and boil gently until all is dissolved (soft specimens dissolve very quickly, but hard ones require about fifteen minutes for solution). When solution is complete, allow the water distilled over, together with some additional water, to run back, dilute to about 250 to 300 c.c., and after cooling, determine the excess of ferrous chloride with potassium dichromate (Vol. I, p. 319, b). The difference expresses the quantity of iron converted by the oxygen of the manganese ore from ferrous to ferric chloride.* This dif- 43- 5 f erence multiplied by ^-^ or 7782, gives the quantity of man- ganese dioxide in the analyzed ore. It must be noted that if manganese ore contains more than 78 per cent, of dioxide, either more iron wire or less manganese ore must be employed. [ The permanganate method of estimating manganese, although a rapid and simple method, is very generally ignored, and in some cases is held in bad repute. The cause for this, perhaps, is to be found in the fact that under certain conditions inconsistent results can be easily obtained. The sources of error when working on ferro and spiegel are chiefly due to three causes: first, non- elimination of the organic matter present; secondly, reckless addition of zinc oxide in large excess and in hot solutions; and thirdly, standardizing the permanganate with iron instead .of manganese. To eliminate these errors, F. W. DAW f adopted the following method, which he finds gives very concordant results: 0-5 grm. of ferro or spiegel is weighed out and introduced into a wide-mouth 16-oz. PHILLIPS beaker, and in the case of ferro 0-4 grm. of pure iron wire is added, to render the precipitation by zinc oxide easier. The ferro or spiegel is dissolved in 30 c.c. hydrochloric acid, and the iron oxidized with a few c.c. nitric acid; 15 c.c. of 50 per cent, sulphuric acid are then added, and the whole evaporated on the * In very precise experiments, the weight of the iron must be multiplied by 0-996, since pianoforte wire may always be assumed to contain about 0-004 impurities. PATTINSON takes it at 99-9 per cent. t Chem. News, LXXIX, p. 25. 468 DETERMINATION OF COMMERCIAL VALUES. [ 248. hot plate till fumes of sulphuric acid are copiously evolved. When cool, water is added, the sulphates dissolved, and the solution washed out into a 1000 c.c. conical flask. Cold water is added to make up to about 500 c.c., the acid partially neutralized with sodium car- bonate and zinc oxide gradually added till the iron is all precipi- tated, but a large excess of zinc is to be avoided. The solution containing the precipitate is, without filtering, brought to a boil, and standard permanganate run in till within a few c.c. of the ex- pected amount; the flask is well shaken, and the permanganate run in, a few drops at a time, till a pink color appears above the precipitate. This is easily observed by holding the flask on one side, covering the mouth of the flask with a cloth, and waiting a few seconds till the precipitate is partially settled, when a pink color is easily seen near the neck. The standard permanganate solution is made up by dissolving 10 grm. KMn0 4 to a litre of water, and standardizing it by means of ferro-manganese of known composition. If iron is used to standardize the solution, a figure is obtained which gives low results when working on manganese. BREARLEY * considers this due to a small amount of carbon in the iron wire used, but the same result is found if pure ferrous ammonium sul- phate is used containing no carbon. TRANSLATOR.] III. ESTIMATION OF MOISTURE IN MANGANESE. 248. In the purchase and sale of manganese a certain proportion of moisture is usually assumed to be present, and often a percentage is fixed within which the moisture must be confined. In estimat- ing the moisture the same temperature should as a rule be em- ployed as that at which the drying for the purpose of determining the dioxide is effected ( 246, I). As the amount of moisture in an ore may be altered by the operations of crushing and pulverizing, the experiment should be made with a sample of the mineral which has not yet been sub- * Chem. News, Ixxv., 15. 249.] MANGANESE COMPOUNDS. 469 jected to these processes. In taking this it is best to use a round glass vessel 80 to 100 mm. in diameter and 30 mm. high, with a flat bottom, and closed by a ground-glass plate of equal diameter, or an equally large tin box provided with a well-fitting cover. The vessel is first weighed empty, then filled with the manganese ore and covered. After removing the glass plate or lid, place it, without its cover, in a water-, oil-, or air-bath, and continue the drying until the weight remains constant. The vessel must be covered before weighing. If the moisture in a manganese ore is not to be estimated on the spot, but in the laboratory, a fair average sample of the ore should be forwarded to the chemist in a strong, perfectly dry, and well-corked bottle. IV. ESTIMATION OF THE AMOUNT OF HYDROCHLORIC ACID REQUIRED FOR THE COMPLETE DECOMPOSITION OF A MANGANESE. 249. Different manganese ores containing the same amount of avail- able oxygen, or, as it is usually expressed, of manganese dioxide, may require very different quantities of hydrochloric acid to effect their decomposition and solution, so as to give an amount of chlorine corresponding to the available oxygen in them. Thus an ore consisting of 60 per cent, of manganese dioxide and 40 per cent, of sand and clay requires 4 mol. hydrochloric acid to 1 at. of available oxygen; whereas an equally rich ore containing lower oxides of manganese," ferric oxide, or calcium carbonate requires a much larger proportion of hydrochloric acid. The quantity of hydrochloric acid in question may be deter- mined by the following process: Determine volumetrically the strength of a moderately strong hydrochloric acid (of, say, 1 10 sp. gr.) by means of an ammoniacal solution of copper sulphate ( 216). Warm 10 c.c. of the acid with a weighed quantity (about 1 grm.) of the manganese ore in a small, long-necked flask fitted with a reflux condenser. As soon as the manganese is decomposed, apply a somewhat stronger 470 DETEEMINATION OF COMMERCIAL VALUES. [ 250. heat for a short time, to expel the chlorine which still remains in solution, but carefully avoid continuing the application of heat longer than is absolutely necessary, as it is of importance to guard against the slightest loss of hydrochloric acid. Let the flask cool, dilute the contents with water, and determine the free hydrochloric acid remaining with ammoniacal copper-sulphate solution. Deduct the quantity found from that originally added; the difference expresses the amount of hydrochloric acid required to effect the decomposition of the manganese ore. As is well known, in the manufacture of chlorinated lime by the WELDON method treating manganous chloride with calcium hydroxide and air there is obtained a preparation termed ' ' WEL- DON mud," which is used over again as a sour e of chlorine. The effective oxygen value of WELDON mud (the composition of which is usually CaO-2MnO 2 ) is best determined by BUNSEN'S method. The methods described under a and c are less suitable because of the large quantity of calcium chloride it contains. The de- termination of the hydrochloric acid which the WELDON mud requires for decomposition is effected according to the method detailed in 249. B. MANGANESE ORES GENERALLY. DETERMINATION OF THEIR METALLIC MANGANESE CONTENT. 250. Manganese ores were formerly used almost exclusively for the preparation of chlorine, or as oxidizers in the manufacture of glass, but since they are also now used for the manufacture of manganese iron, the quantity of metallic manganese they contain has become of great importance. For the determination of this, hence quite a large number of new methods have been proposed in addition to those already known. These methods, mostly volumetric, are, however, also 250.] MANGANESE COMPOUNDS. 471 considered in connection with the analysis of iron, hence they will not be described here, but in 255. I will detail the mothod here which for many years has been used in my laboratory. It is true it is rather more inconvenient than is desirable, but as regards accuracy it leaves nothing to be desired, while at the same time it allows of the determination of the other constituents of the ore. Dissolve in hydrochloric acid about 1 grm. of the mineral dried at 100, evaporate the solution to dryness, warm the residue with hydrochloric acid, add water, filter and dilute the solution to about 500 c.c. The entire absence of manganese from the residue may be ascertained by fusing a small sample with sodium carbonate with access of air. If any manganese is found, the whole of the residue must be decomposed by fusion with sodium carbonate, the silicic acid separated by hydrochloric acid, and the filtrate from the silicic acid added to the main solution. // the solution is poor in iron, add ammonia to it to slight alka- linity, filter at once into a flask containing a little acetic acid, dissolve the precipitate (after washing) in hot hydrochloric acid, heat, allow to cool, add 10 c.c. (but not more) ammonium-chloride solution, and precipitate the iron as a basic salt according to the method detailed in Vol. I, p. 644, 3, a [82]. If, on the other hand, the solution contains much iron, add 20 c.c. ammonium-chloride solution, precipitate the iron at once as a basic salt according to the method given, dissolve the precipitate after moderately washing it in hydrochloric acid, add 10 c.c. ammonium-chloride solution, and repeat the precipitation of the basic salt. After washing it, fuse a small portion of the basic iron salt with sodium carbonate with access of air in order to make certain that no manganese is present. Unite the filtrate with the washings, add a little acetic acid, concentrate by evaporation to 300 c.c., allow to cool, make very weakly alkaline with ammonia (in order to precipitate any traces of aluminium), and at once filter off from the precipitate which as a rule is formed. After washing somewhat, dissolve the pre- cipitate in hot hydrochloric acid, repeat the precipitation with 472 DETERMINATION OF COMMERCIAL VALUES. [ 250. ammonia as before, and again filter. The appearance of the pre- cipitate white or brownish will denote whether a reprecipitation will be necessary. Unite the washings and the filtrate, acidulate weakly with acetic acid, add ammonium acetate, and treat with hydrogen sulphide. As a rule a black precipitate (cobalt sulphide, etc.) forms. Filter this off, concentrate the filtrate if necessary, and precipitate and determine the manganese as manganese sul- phide according to 109, 2. ELECTROLYTIC DETERMINATION. The electrolytic determination of manganese has been worked out by LUCKOW * and ALF. RicHE.f As, however, it is necessary that the iron be first removed and the liquid then concentrated to a very small volume (the manganese separates at the positive pole as dioxide), while the separation occurs only in a sulphuric-acid or nitric-acid solution, this method offers no special advantages. [ CLASSEN J could not confirm the assumption that manganese dioxide dried at 68 has the composition MnO 2 -H 2 O. On attempt- ing to convert the hydrated dioxide into anhydrous dioxide by prolonged drying at a, higher temperature, a strongly hygro- scopic substance results which rapidly increases in weight during the process of weighing. It is therefore necessary to convert the dried dioxide into mangano-manganic oxide by ignition, an oper- ation conducted with ease and safety. After determining the necessary conditions for the separation of large quantities of lead dioxide, the author found that strong inorganic acids interfere with complete precipitation, and even make it impossible. Of the organic acids, acetic acid alone is suitable, although the precipi- tation of large quantities, even when roughened dishes are used, cannot be successfully carried out, since it is impossible to obtain firmly adhering precipitates. If a salt other than acetate is at hand, it is best to precipitate the manganese as dioxide with ammoniacal hydrogen peroxide. The * Zeitschr. f. analyt. Chem., vm, 24. f Ibid., xvn, 216. J " Quantitative Chemical Analysis by Electrolysis." by ALEX. CLASSEN, translated by B. B. BOLTWOOD. JOHN WILEY & SONS, New York, 1903. 250.] MANGANESE COMPOUNDS. 473 precipitate is washed thoroughly and dissolved in 5 c.c. acetic acid, 5 c.c. hydrogen dioxide (4- to 5-per cent.), and 25 c.c. water. This is especially necessary when the manganese is present as chloride or when the solution contains other chlorides. Permanganic acid is first reduced to a manganous salt. In acetic-acid solutions, even when roughened dishes are used, the maximum quantity of manganese which can be satisfactorily determined as dioxide is only about 0-08 grm. A rapid and complete separation was secured by ENGELS in CLASSEN'S laboratory. The method is as follows: 1 to 2 grm. of the manganese salt are dissolved in about 125 c.c. of water, and 10 grm. ammonium acetate and 1-5 to 2 grm. chrome alum are also added. The clear solution is then electrolyzed. Chlorides must not be present, since the solution of chlorine interferes with the separation of the manganese. If they are present, the man- ganese is converted into acetate as described above. In the determination of manganese in the salts of permanganic acid, the solution of the latter is decomposed, according to ENGELS, with 5 c.c. acetic acid and enough hydrogen dioxide to completely decolorize it. Since the presence of even small quantities of hydro- gen dioxide prevent the separation and the firm adherence of the precipitate, the excess of hydrogen dioxide must be removed. This may be most easily accomplished by the addition of small quantities of chromic acid, until further addition no longer causes the evolution of gas ; generally 3 to 5 grm. is sufficient. F. KAEPPEL * has devised a method enabling him to precipitate the manganese in the state of dioxide as a coherent powder, and at the same time to prevent the transformation of this dioxide into saline oxide by calcination in a platinum crucible. It is, of course, known that the platinum is strongly attacked in this operation. The following is the method; The manganese salt (containing manganese equivalent to about 0- 15 to 1 -6 grm. MnO 2 ) is dissolved in 150 c.c. of water, and acetone is added. The solution is kept at a temperature of 50 to 55, *Zeitschr. f. anorg. Chem., xvi, 268; Chem. News, LXXX, 195. 474 DETERMINATION OF COMMERCIAL VALUES. [ 251. and electroly zed with a current of 4 to 4-25 volts, and 0-7 to 1-2 amperes; care must be taken to add water to replace that which is gradually lost by evaporation. At the end of from two to five and a half hours, according to the proportion of acetone present (1-5 to 10 grm.), the operation is terminated; the manganese dioxide is washed by means of a siphon without interrupting the current; the electrode is dried at 150 to 180 and weighed. In this method the acetone is converted into acetic acid, and this in its nascent state is believed by KAEPPEL to have a better action on the deposition than if added directly to the electrolyte. TRANSLATOR.] 13. NICKEL COMPOUNDS * A. NICKEL ORES, NICKELSTEIN, AND OTHER INTERMEDIATE PRODUCTS OF NICKEL MANUFACTURE. 251. In the analysis of copper-nickel, antimony-nickel, nickelstibine, and nickel glance, it becomes necessary as a rule to separate also nickel cobalt, iron, arsenic, antimony, and sulphur, and some- times also lead; in white nickel pyrites there are also present copper and bismuth, while nickel pyrites contain determinable quantities of nickel, cobalt, iron, copper, and sulphur. In the analysis of nickeliferous copper and iron pyrites also., only the last-mentioned elements, as a rule, have to be considered, apart from silicic acid and alkaline earths, which may be present. The kupfer-nickelstein, obtained as an intermediate product in obtaining copper-nickel or nickel from nickeliferous ores, contains chiefly cop- per, iron, nickel, with a little cobalt and sulphur, but it frequently contains also arsenic, antimony, and sometimes lead. Ores and *The cobalt compounds are examined in exactly the same way as the nickel compounds, and in fact the three methods described in 251 may be used for the former. Regarding the testing of nickel and cobalt ores by the dry way by PLATTNER'S method (conversion of the nickel and cobalt into arsenides) see MUSPRATT'S Chemistry, 3d Ed., by KERL and STOHMANN, in, 1914. 251.] NICKEL COMPOUNDS. 475 metallurgical products contain very variable quantities of nickel, and are frequently the objects of quantitative analysis since the manufacture of nickel has become of very great industrial value. As a rule it is sufficient to determine the content of nickel plus cobalt, or of nickel and of cobalt, or of nickel, cobalt, and copper. I shall here confine myself to giving the details of the determina- tions of these metals only, reference having already been made in the first part of this work to the further examination of the pre- cipitates, etc., obtained during the operations. First Method. Treat a portion of the finely powdered mineral or metallurgical product, containing about 0-5 to 1 grm. nickel, with hydrochloric acid and a little nitric acid until all the soluble portion is dissolved, evaporate repeatedly almost to dryness with hydrochloric acid to expel the excess of nitric acid, take up the residue with hydrochlo- ric acid and water, and then filter. If any sulphur remains, ignite the residue in the air and treat again with hydrochloric acid and a little nitric acid as before. If now too a residue remains which is not perfectly white, fuse it with potassium disulphate and treat the melt with hydrochloric acid and water, or fuse it with sodium carbonate, treat the melt with water and hydrochloric acid, and separate the silicic acid and treat it with hydrochloric acid. The solution obtained by either of these methods is added to the main solution, which is then treated as follows: Add sufficient hydrochloric acid to the solution (400 c.c. of which should contain about 40 c.c. of hydrochloric acid, sp. gr. 1-12), and pass in hydrogen sulphide to precipitate all the metals precipi table by it; it is advantageous to pass in the gas first at about 70, and then in the cold. Filter and then heat the filtrate gradually, adding nitric acid, so that all ferrous iron is converted into ferric iron. After the liquid has cooled somewhat add ammonia 'in excess, filter off the impure ferric hydroxide, wash it, dissolve in hydrochloric acid, dilute the solution largely, add 30 c.c. ammonium-chloride solution, and then add, in the cold, a dilute ammonium-carbonate solution until the liquid becomes 476 DETERMINATION OF COMMERCIAL VALUES. [ 251. slightly turbid, but does not yield a precipitate. The liquid should not become clear on standing, but the turbidity should rather increase. The liquid at this period has still a distinctly acid reaction. Now heat to boiling, wash the precipitated basic ferric salt, first by decantation, then on the filter, with boiling water containing some ammonium chloride, and then test a portion of the ferric salt by dissolving it in hydrochloric acid, reprecipitat- ing, and testing the filtrate with ammonium sulphide for nickel. Should a small quantity of this be still found present, the entire precipitate must be dissolved in hydrochloric acid and the iron once more reprecipitated as a basic ferric salt. Mix the two or three filtrates containing the nickel and cobalt, acidulate with acetic acid, then make weakly alkaline with ammonia, and con- centrate by evaporation. If a small quantity of a precipitate (ferric hydroxide or aluminium hydroxide) forms, filter it off, dis- solve in hydrochloric acid, precipitate with an excess of ammonia, and repeat the entire operation once more. To the filtrate, suit- ably concentrated and containing all the nickel and cobalt in solution, now add acetic acid until distinctly acid, and then add to the clear liquid 30 to 50 c.c. of a 1 : 10 ammonium-acetate solu- tion, warm to about 70, and pass in hydrogen sulphide until the liquid smells strongly of the gas. After precipitation is complete, filter off the precipitate of nickel and cobalt sulphides, wash, rinse into a beaker, and incinerate the filter. Concentrate the filtrate by evaporation, add first ammonium hydrosulphide and then acetic acid, whereby very frequently a still further slight quantity of nickel and cobalt sulphides is obtained. As a matter of precau- tion, test the filtrate again in like manner in order to be certain that all the nickel and cobalt have been converted into sulphides. Treat the nickel and cobalt sulphides which were washed into the beaker, and also the filter ash, with hydrochloric acid and a little nitric acid added until completely decomposed and the metals are dissolved; then evaporate with hydrochloric acid in order to drive off the nitric acid, dilute with water, filter, incinerate the filter, add the hydrochloric-acid solution of the filter ash to the main solution, and precipitate (best in a large platinum dish) 251.] NICKEL COMPOUNDS. 477 with pure potassa solution, by pouring the nickel solution into an excess of the heated potassa solution. Wash the precipitate very thoroughly, first by decantation, then on the filter, with boiling water,* and after partially or even completely drying, heat gently in a ROSE crucible, first with the cover on and then with access of air. Now increase the heat until the filter has been completely incinerated, conducting the heating finally in a current of pure hydrogen until the weight remains constant. Next treat the metallic nickel and cobalt in the crucible with boiling water; should this acquire an alkaline reaction, or con- tain chlorine or sulphuric acid, or leave a residue on evaporation on platinum foil, the metals must be exhausted with boiling water and again ignited in a current of hydrogen and once more weighed. Now dissolve the metals in nitric acid, .whereby, as a rule, a small quantity of silicic acid remains undissolved. Collect this on a small filter and determine its weight. Nearly neutralize the nitric-acid solution w r ith ammonia, add an excess of ammonium carbonate, warm gently for a long time, filter off the small quan- tity of precipitated ferric hydroxide or aluminium hydroxide usually obtained, dissolve it in nitric acid, reprecipitate once more with ammonium carbonate, ignite the small quantity of precipitate first in the open air, then in hydrogen, and deduct its weight, together with that of the silicic acid, from the weight of the metals. It is easy to see that in most cases it is more convenient and rapid to incinerate the small filter with the silicic acid and that containing the iron and aluminium hydroxides, in the same crucible, and then, after igniting in hydrogen, to weigh both impurities together. Should the silicic acid or the alumina, etc., exhibit a bluish color from the presence of cobalt, the one or the other must be fused with a little alkali carbonate, and the silicic acid * The statements of FINKENER (Handbuch d. analyt. Chem., von H. ROSE, 6. Aufl. von FINKEXER, n, 136), and of BUSSE (Zeitschr. f. analyt. Chem., XYII, 60), that nickel hydroxide is somewhat soluble in water, I can con- firm, but the traces which dissolve in water are so minute that they can have no appreciable influence on the result. Comp. Analyt. Note, No. 90. 478 DETERMINATION OF COMMERCIAL VALUES. [ 251. or alumina, etc., separated in the pure state and weighed. As the metallic nickel may at times contain also slight quantities of magnesia, it is necessary to add a little ammonium phosphate to the blue ammoniacal solution obtained when separating the impurities, and to allow the whole to stand for a time in order to see if any ammonium-magnesium phosphate separates; if this occurs, the precipitate is converted into and weighed as mag- nesium pyrophosphate, and calculated as magnesia. If much Cobalt is present, ammonium-cobaltous phosphate is precipitated with the ammonium-magnesium phosphate. In this case, in order to obtain the magnesium salt in a state of purity, wash the precipitate with water containing a little ammonia, dissolve in acetic acid, add ammonium acetate, precipitate the cobalt with hydrogen sulphide (as above), concentrate the filtrate, and then add ammonia and some ammonium phosphate to precipitate the magnesia. There remains now but to speak of the sulphuric-acid or hy- drochloric-acid solution occasionally obtained by decomposing the portion of residue of ore, etc., insoluble in hydrochloric and nitric acids, and containing still a small quantity of the heavy metals (see above). The simplest method would seem to be to add the solution so obtained to the main solution before precipitating with hydrogen sulphide. This method, however, has the dis- advantage of unnecessarily introducing a comparatively large quantity of alumina into the solution, which is very inconvenient. It is hence best to treat the small quantity of solution by itself; first pass in hydrogen sulphide in order to separate any metals of the fifth and sixth groups that may be present, then heat the filtrate with nitric acid, precipitate with ammonia, Wash, dissolve the precipitate in hydrochloric acid, and precipitate once more with ammonia. Unite the filtrates and separate the small quantity of nickel with hydrogen sulphide as in the case of the main solution. Then dissolve this small quantity of nickel sulphide with the larger quantity in nitric acid (see above). If the nickel and cobalt are to be determined separately, effect the separation (if comparatively much nickel and little 251.] NICKEL COMPOUNDS. 479 cobalt are present) according to 160, 9, by means of potassium nitrite. If, however, little nickel but much cobalt are present, it is better to. operate according to 160, 10, using potassium cyanide and chlorine or bromine. The most convenient method is to make up to 250 c.c. the solution obtained by treating the nickel and cobalt sulphides with nitric acid, and to determine in 100 c.c. the nickel and cobalt as above detailed, while in a second 100 c.c. (or in the remaining 150 c.c.) either the nickel or the cobalt is determined, according to circumstances. After weighing the metals treat them exactly as above described for nickel and cobalt, in order to remove any adhering impurities. If the cobalt has been precipitated by potassa solution from the hydrochloric-acid solution of potassium-cobalt nitrite,* the filtrate together with the washings must be treated with ammonium sulphide. If this yields a slight precipitate of cobalt sulphide^ determine the cobalt in it separated as cobaltous sulphate ( 111, 2, b). In order to avoid this double determina- tion it is usually more convenient to supersaturate with am- monia the hydrochloric-acid solution of the potassium-cobalt nitrite, precipitate- the cobalt with ammonium sulphide as cobalt sulphide, then to dissolve this in nitric acid, evaporate the solu- tion with sulphuric acid, and weigh the cobaltous sulphate ( 111, 2, &). In case it is deemed inadvisable to divide the nickel-cobalt solution, acidulate with acetic acid the ammoniacal solution ob- tained in purifying the weighed nickel and cobalt, reprecipitate both metals as sulphides, dissolve these in nitric acid, and in the solution determine the nickel or cobalt as already described; the metal not determined may be estimated in either case by dif- ference. If very little cobalt is present together with much nickel, all the cobalt may be precipitated with some nickel, and the separa- tion of the two metals then undertaken. For this purpose dis- solve both metals in hydrochloric acid, neutralize the solution * For another method of determining cobalt in potassium-cobalt nitrite see BRAUNER, Zeitschr. /. analyt. Chem., xvi, 195. 480 DETERMINATION OF COMMERCIAL VALUES. [ 251. as nearly as possible with sodium carbonate, heat the liquid, and then cautiously add a weakly alkaline solution of sodium hypochlorite, thus precipitating the cobalt completely and the nickel partially. If the operation is conducted so that at least two parts of nickel are present for one part of cobalt, the precipitate will certainly contain all the cobalt present. Whether the proper proportion has been hit or not may be observed from the color of the hydrochloric-acid solution of the brownish-black hydroxide; if almost colorless, or with but a greenish or reddish tinge, all the cobalt has been precipitated, but if the solution is deep red, a further partial separation is necessary (FLEITMANN *). The separation is then effected in the hydrochloric-acid solution by means of potassium nitrate, as above described. If copper also is to be determined in the ores or furnace products, treat the hydrogen-sulphide precipitate first obtained according to 261. Second Method. According to CLASSEN,! nickel, like zinc, can be separated as an oxalate from iron. I am not in a position to offer an opinion regarding this method, as yet. The test analyses cited by CLASSEN show very satisfactory results. In order to apply the method to nickel ores, etc., effect the solution as in Method 1, and re- move the precipitable metals with hydrogen sulphide from the acid solution in a similar manner. Drive off the hydrogen sul- phide, oxidize the ferrous salt by boiling with nitric acid, and evaporate to dryness on the water-bath. Treat the residue with about seven times its quantity of a 1 : 3 solution of neutral potas- sium oxalate, warm on the water-bath for fifteen minutes, and effect solution of any slight undissolved residue of ferric oxide by adding acetic acid drop by drop. If sufficient potassium oxalate has been added there is obtained a clear, greenish solution. Heat the solution to boiling, and add at least an equal volume of 80 per-cent. acetic acid while stirring, whereby nickelous and * Zeitschr. f. analyt. Chem., xiv, 76. f Ibid., xvi, 471; xvm,' 189; xvm, 386. 251. J NICKEL COMPOUNDS. 481 cobaltous oxalates are precipitated. The nickelous oxalate has a more or less crystalline character only when the quantity of nickel present is small. CLASSEN therefore operated only upon quantities of from 0-1 to 0-2 grm. Now heaffor six hours at 50, filter hot, and thoroughly wash with a mixture of equal volumes of con- centrated acetic acid, alcohol, and water. After drying the nickel- ous oxalate and burning the filter-paper on a platinum wire, heat the two in a covered platinum crucible, at first gently, then grad- ually more strongly, and finally very strongly with access of air for a sufficiently long time, and weigh the nickelous oxide ob- tained. If the nickelous oxalate has been insufficiently washed, the nickelous oxide resulting will be contaminated with potassium carbonate. This may be known on warming the residue with water; if the solution so obtained gives an alkaline reaction, the nickelous oxide must be thoroughly washed with hot water, and once more weighed. If any cobalt is present, reduce the ignition residue, first washed if necessary, by heating in a current of hy- drogen, and weigh as metal. Regarding the separation of nickel and cobalt see the first method. Third Method. ELECTROLYTIC SEPARATION OF NICKEL, OR OF NICKEL AND COBALT. The electrolytic determination of nickel, to which W. GIBBS * called attention already in 1864, has been further extended by the labors of C. LucKOW,f the MANSFELD OBER-BERG- UND HUTTEN- DIRECTION, t HERPIN, F. WRIGHTSON,|| TH. SCHWEDER,^ and W. OHL.** These labors have shown that nickel and cobalt are not precipitated by the electric current from solutions containing free acids, but that they are precipitated from ammoniacal solu- tions, or from solutions of their cyanides in potassium-cyanide solu- * Zeitschr. f. analyt. Chem., in, 334. f DINGLER'S polyt. Journ., CLXXVII, 235. J Zeitschr. f. analyt. Chem., xi, 10, and xiv, 350. Ibid., xv, 335. || Ibid., xv, 300. 1 Ibid., xvi, 344. ** Ibid., xvm, 523. 482 DETERMINATION OF COMMERCIAL VALUES. [ 251. tion, as well as from solutions of their neutral sulphates to which an alkali acetate, tartrate, or citrate has been added (LucKOw). More recently H. FRESENIUS and F. BERGMANN* have most care- fully studied the conditions which appear to be most favorable for the quantitative determinations by this method. Ammoniacal solutions should be employed, and they must contain a sufficient excess of free ammonia to remain strongly ammoniacal through- out. The presence of ammonium sulphate or of sodium phosphate (M. S. CHENEY and E. S. RICHARDS f) favor the separation, while ammonium chloride hinders or prevents it; ammonium nitrate also acts disadvantageously. The most favorable conditions for the separation of nickel and also cobalt are as follows: The strength of the current of the CLAMOND pile (comp. 261) should be such as to liberate 300 c.c. oxyhydrogen gas per hour. The nickel or cobalt should be present as neutral sulphate in the proportion of 0-1 to 0-15 grm. per 200 c.c. of aqueous solution containing 2-5 to 4 grm. ammonia and 6 to 9 grm. ammonium sulphate (both calculated as being in the anhydrous state. The dis- tance of the lower edge of the weighed platinum cone forming the negative pole from the annular foot of the platinum spiral form- ing the positive pole (see 261) should be from 3 to 5 rnm. The beaker containing the solution should be covered with a large watch- glass provided with suitable openings for the passage of the bat- tery wires. The solution loses color in proportion as the nickel deposits. As soon as it appears perfectly colorless test a few drops with potassium sulphocarbonate ; if only a scarcely notice- able rose-red color develops, the precipitation may be considered as complete. Cobalt solutions at first become darker from the absorption of oxygen, but they gradually become lighter in color, and finally colorless; the sulphocarbonate test should be applied in this case also, discontinuing the operation when only a scarcely perceptible wine-yellow color develops. As soon as the deposition is complete draw off the liquid by * Zeitschr. f. analyt. Chem., xix, 314. ., xvn, 215. 252.] NICKEL COMPOUNDS. 483 means of a water-pump or aspirator into a flask provided with a doubly-perforated stopper, employing the same simple apparatus for removing the washings and for final rinsings with the wash-bottle. The wires must not be disconnected until the washing has been terminated; then suspend the cone over a hot iron plate until perfectly dry, allow it to become cold, and weigh. The nickel deposited on the platinum cone presents a handsome polished surface; cobalt is less lustrous. The manner of employing the electrolytic method to nickel ores, nickelstein, etc., depends upon the kind and quantity of the metals present with the nickel and cobalt. The metals can always be removed according to Method 1, the nickel and cobalt sulphides being then dissolved in nitric acid with some hydrochloric acid added, the solution evaporated with a definite quantity of sul- phuric acid, and supersaturating with ammonia; if required, more ammonium sulphate may be added in order to obtain the favorable conditions above noted. The separation of the foreign metals may also at times be effected by electrolysis (comp. 264). B. COMMERCIAL METALLIC NICKEL (NICKEL CUBES AND GRANULAR NICKEL). 252. Commercial nickel contains about 97 to 98 per cent, nickel, besides some cobalt, copper, iron, and at times traces of arsenic and antimony; generally some calcium, magnesium, aluminium, and silicic acid are present, and occasionally traces of alkalies; and frequently small quantities of carbon and sulphur. The analysis is frequently intended to give the average composition of a large shipment, in which case the analyst receives a smaller or greater number of cubes, each taken from a different box. As in this case the individual cubes cannot be divided, the only course to pursue is to dissolve them all in nitric acid after weighing them. As a rule there remains a small quantity of insoluble residue, which may contain carbon, sulphur, slag, and silicic acid. Collect the residue on a filter dried at 100, and collect the filtrate and washings in an accurately weighed flask having a capacity of J, 1, 484 DETERMINATION OF COMMERCIAL VALUES. [ 252. or 2 litres, according to circumstances. Dry the washed precipi- tate at 100. and weigh. Dilute the filtrate and washings up to the mark, weigh accurately and mix. I. EXAMINATION OF THE SOLUTION. a. Measure off so much of the solution as will contain about 0-5 to 1 grm. nickel into a light, tared glass vessel and weigh accurately. The measuring serves merely to approximately fix upon the correct quantity, while the weighing affords the exact quantity, since the total weight of the liquid is also known. Evaporate to dryness with hydrochloric acid, treat the residue with hydrochloric acid, separate the silicic acid, and treat the nitric-acid free liquid (100 c.c. of which must contain about 10 c.c. of hydrochloric acid) with hydrogen sulphide at 70; collect the precipitate, wash, and determine in it qualitatively the metals present. Concentrate the united filtrate and washings by evapora- tion, and after driving off the hydrogen sulphide, boil with a little nitric acid, add an excess of ammonia, filter, wash, dissolve the precipitate in hydrochloric acid, and then precipitate the iron as a basic salt by nearly neutralizing with ammonium carbonate and then boiling. Mix the filtrate with the first main ammoniacal filtrate, acidulate with acetic acid, precipitate with hydrogen sulphide in the heat, and in this precipitate along with any blackish precipitate which may be obtained from the filtrate by adding ammonia, ammonium sulphide, and acetic acid, determine the nickel together with the small quantity of cobalt according to the first method detailed under 251, wherein all the details are minutely given. Of course, the second or third method described in 251 may also be used for determining the nickel together with the small quantity of cobalt. 6. Measure off and weigh a larger volume of the solution, con- taining about 4 to 5 grm. nickel, and separate the silicic acid and the metals of the fifth and sixth groups, as in a; wash the precipi- tate containing the latter, and in it determine the copper, and also the other metals that may be present. Treat the filtrate as de- tailed in a, but determine in this portion any iron and aluminium 252.] NICKEL COMPOUNDS. 485 that may be present. As, in consequence of the excess of am- monia, aluminium may be found in the ammoniacal nickel solu- tion, and as in the precipitation of the basic ferric salt all of the alumina is not completely thrown down, unite the solutions con- taining the nickel, acidulate with acetic acid, cautiously add ammonia in very slight excess, and allow to stand for some time at a gentle heat. If any flocks of alumina separate, filter them off and add them to the basic precipitate before beginning the separa- tion and determination of the iron and aluminium. Acidulate the solution remaining clear or filtered from the flocks of alumina with acetic acid, precipitate with hydrogen sulphide with heat, and filter off the precipitate. To the nitrate first add ammonia, then ammonium sulphide, and then acetic acid until the solution is acid. If a slight blackish precipitate forms, collect it after pro- longed warming, add it to the main precipitate thrown dowTi by hydrogen sulphide in the acetic-acid solution, and then determine in this the cobalt, which will usually be found present in this larger quantity in w r eighable amount. On deducting the cobalt from the nickel plus cobalt found in 1, the quantity of nickel is found. Evaporate to dryness in a large platinum dish the nitrate freed from the last traces of nickel, drive off the ammonium salts, and in the residue determine the calcium, magnesium, and alkalies ( 154, 6, and 153, 4, 6). c. Lastly, measure off another portion of the solution repre- senting about 10 grm. nickel, drive off the free nitric acid so far as possible by evaporating, dilute with water, make nearly neutral with ammonia, then add barium chloride to the still distinctly acid solution, and allow to stand for a long time. If a small pre- cipitate of barium sulphate forms, determine it; it corresponds to the sulphur which was converted into sulphuric acid when effecting solution of the nickel. II. EXAMINATION OF THE INSOLUBLE RESIDUE. Triturate to a uniform powder the residue dried at 100 and weighed, and in an aliquot portion determine the sulphur by fusing with potassium carbonate and nitrate, etc. (Vol. I, p. 562, 1, a). 486 DETERMINATION OF COMMERCIAL VALUES. [ 253. Fuse the residue with sodium carbonate with the addition of a small quantity of potassium nitrate, and in the melt determine the silicic acid, the alumina, and any other substances that may be present. The carbon content is determined from the difference. If the insoluble residue is very small, it is generally sufficient in reporting the analysis to note it simply as "residue insoluble in nitric acid.". 14. IRON COMPOUNDS. A. IRON ORES. The iron ores which occur most frequently, and which are hence most often examined, are as follows: Hematite, limonite, bog iron ore, magnetite, and spathic iron ore. In some cases a complete analysis is required; in others a determination only of individual constituents (iron, phosphoric acid, sulphuric acid, etc.); in others again, the determination of only the iron. I. METHODS FOR COMPLETE ANALYSIS. 253. a. HEMATITE. If the hematite contains only ferric oxide, moisture, and gangue insoluble in acids, the first method here given should be employed in its analysis; if, however, it contains also phosphoric acid, al- kaline-earth carbonates, manganous oxide, etc., I would recom- mend the second method. First Method. Reduce the ore to an impalpable powder, and dry at 100. a. Weigh off a portion into a platinum or porcelain boat, insert this into a porcelain tube,* pass a current of dry air through the tube, and heat the mineral until all the water is expelled. * Glass tubes, even when of very difficultly fusible glass, are less ad- visable to use, as during the prolonged heating required the boat is frequently fused to the glass. 253-] IRON COMPOUNDS. 487 Allow to cool in a current of air, and weigh. The loss of weight corresponds with the water. b. Insert the boat again into the porcelain tube and heat in a gas- or charcoal-furnace (pp. 18 to 22) for several hours in a current of pure, dry hydrogen, until no more water is formed; towards the end heat as strongly as possible. Allow to cool in the current of hydrogen, and weigh. The loss of w r eight corresponds with the oxygen combined with the iron to form ferric oxide, hence from it the quantity of the oxide may be calculated. c. Fasten a platinum wire to the handle of the boat containing the reduced iron, and introduce the boat in a 250-c.c. flask, add first some water, then diluted sulphuric acid, and stopper the flask, but not airtight, the stopper pinching and holding the platinum wire in place in the neck of the flask. The finely divided iron dissolves with the evolution of hydrogen; gentle warming accelerates the process. As soon as this is complete, raise the boat, rinse it off, heat the liquid to gentle boiling in order to ex- pel the hydrogen, and allow to cool; then fill to the mark, shake, allow to settle, take out 100 c.c. of the fluid, and in it determine the iron with potassium permanganate or dichromate (Vol. I, p. 313 and p. 319). The result must correspond with that obtained in b. If the results do not agree sufficiently, the cause may be due to the ferrous solution having become slightly oxidized. In this case another 100 c.c. must be boiled with a little zinc (best in a current of carbon dioxide) and the titration with perman- ganate repeated. d. Collect the residue (which has settled on the bottom of the bottle) in a filter, wash, dry, ignite, and weigh. As a rule it con- sists of silicic acid, but it may also contain alumina and titanic acid, and occasionally also some iron. Fuse it with potassium disulphate, and treat the melt with cold water; the silicic acid remains undissolved. In the solution precipitate (if iron is present, first pass in hydrogen sulphide) any titanic acid by prolonged boiling ( 107); and in the filtrate the alumina, or the alumina and any ferric oxide still present, by adding ammonia. The separation of these may be effected according to 160, A, 2. 488 DETERMINATION OF COMMERCIAL VALUES. [ 253. Second Method. This is the same as that employed in the analysis of brown iron ore (limonite) ( see 6). If the hematite is very finely powdered and digested with sufficient fuming hydrochloric acid at an elevated temperature below the boiling-point, the decomposition and solu- tion may be effected in a few hours. The separated silicic acid should be tested for titanic acid according to p. 411; if this is found, some of it will have also passed into solution. If the quantity appears to be weighable, the titanic acid is best de- termined by treating a separate portion of the hematite accord- ing to the first method. 6. BROWN IRON ORE (LIMONITE). Limonite contains, besides ferric hydroxide, occasionally also small quantities of ferrous oxide, besides oxides of manganese and alumina, and at times small quantities of oxides of copper, zinc, nickel, and cobalt, and frequently small quantities of lime and magnesia, silicic acid (combined with bases), carbonic, phosphoric, and sulphuric acids, and larger or smaller quantities of quartz-sand or gangue insoluble in hydrochloric acid. Sometimes the limonite contains also organic matter.* 1. Begin the analysis by first finely powdering the ore and then drying it, according to circumstances, either in a desiccator or at 100. Introduce the powder thus prepared into a glass tube and stopper tightly. The quantity must be sufficient for the entire analysis. 2. To determine the water it is frequently sufficient to ignite a sample of the powder in a platinum crucible. The water is thus determined from the loss of weight. If the iron stone, how- * Besides these substances, which are usually found, traces of other substances are frequently detected in very accurate analyses. Thus A. MiiLLER (Ann. d. Chem. u. Pharm., LXXXVI, 127) found in a bean-ore, smelted at Carlshiitte, near Alfeld, also weighable traces of potassa, arsenic acid, and vanadic acid, and un weighable traces of chromium, copper, and molybdenum. Titanic acid is also found occasionally. Regarding an iron ore very rich in vanadium, see H. DEVILLE (Compt. rend., XLIX, 210; Journ. f. prakt Chem., LXXXIV, 255). 253.] IKON COMPOUNDS. 489 ever, contains carbonates of the alkaline earths, ferrous oxide, or weighable quantities of organic matter, this method is inap- plicable. The water must in this case be determined by direct weighing (comp. 36 and 235, I, e). 3. Weigh off about 3 grm. of the powder, ignite gently in a platinum dish, and in such a manner as to insure the complete destruction of any organic matter, that may be present, then trans- fer to a flask and digest with fuming hydrochloric acid at a gentle heat until completely decomposed. Now add a little potassium chlorate, heat for some time, transfer to a porcelain dish, add 5 to 10 grm. pure sodium chloride, and evaporate to dryhess on the water-bath.* Now moisten with hydrochloric acid, warm, dilute with water, filter into a 500-c.c. flask, and wash the residue. After drying this ignite and weigh it; to the solution, however, add water up to the mark, and shake. 4. The residue consists of quartz-sand or gangue and separated silicic acid. This last may be separated and determined by treat- ing an aliquot portion with a boiling solution of sodium carbonate ( 237, 2, 6). If it is desired to determine more precisely the nature of the gangue, which frequently contains also a small quan- tity of iron, treat the thoroughly washed precipitate insoluble in sodium carbonate, or else another aliquot portion of the original residue insoluble in hydrochloric acid, according to the method described for decomposing silicates, 140, II, b. If the residue has a reddish appearance, a further examination is absolutely necessary. 5. Dilute 250 c.c. of the solution obtained in 3 quite freely (to about 1 litre), add 25 c.c. ammonium-chloride solution, nearly neutralize with ammonia, then add a dilute solution of ammonium carbonate until the liquid is permanently slightly turbid, boil, and thus separate the ferric oxide and a part of the alumina (comp. 160, 3, and this volume, p. 471). If the iron solution is not colorless after boiling, add a few c.c. of a neutral solution of am- * If a weighable quantity of arsenic is present, the evaporation of the hydrochloric-acid solution must be omitted. Of course, hi this case, it is also unnecessary to add sodium chloride. 490 DETERMINATION OF COMMERCIAL VALUES. [ 253. monium acetate and boil once more. Any phosphoric acid, etc., is precipitated with the ferric oxide (see 6). Decant while hot, filter, and wash with hot water containing a little ammonium chloride. The precipitate is meanwhile kept moist. If the iron ore is rich in manganese, it is necessary to repeat the precipita- tion of the iron as a basic salt (comp. p. 471). 6. To the nitrate or filtrates obtained in 5, and mixed with the washings, add a little acetic acid, concentrate by evaporation, allow to cool, add ammonia until just alkaline, and filter off the precipitated aluminium hydroxide. Collect the nitrate in a flask containing a small quantity of acetic acid. After briefly washing, dissolve the precipitate in hydrochloric acid, again precipitate with ammonia, filter into the first filtrate, wash, and treat the precipitate, together with that obtained in 5, according to 7. The precipitates contain the ferric oxide, the alumina, and silicic acid which were dissolved, as well as the phosphoric acid (and arsenic acid). If necessary, the solution containing a slight ex- cess of acetic acid and filtered off from the aluminium hydroxide is slightly concentrated by evaporation. 7. Dissolve the precipitates mentioned in 6 in hot hydro- chloric acid and make up the solution to 250 c.c. If any silicic acid remains, filter it off and weigh it. a. Precipitate 50 c.c. of the solution with ammonia (Vol. I, p. 278, a) ; the weight of the precipitate expresses the sum of the following substances present in the solution : Ferric oxide, alumina, silicic acid, and phosphoric acid (also arsenic acid). Separate the silicic acid by prolonged digestion with fuming hydrochloric acid, and finally by fusion with potassium disulphate; lastly, weigh. b. In 50 c.c. determine the ferric oxide with stannous chloride (Vol. I, p. 327). If a gravimetric method is preferred, that given in Vol. I, p. 642, 2, is recommended. c. On deducting from the weighed precipitate obtained in 7, a the silicic acid, ferric oxide, and the phosphoric acid determined in 10 (and also any arsenic acid present), the weight of the alu- mina is obtained. 253.] IRON COMPOUNDS. 491 8. To the solution from 6, containing free acetic acid, add ammonia until weakly alkaline, then again acetic acid until dis- tinctly acid; next add ammonium acetate, and while gently warm- ing pass in hydrogen sulphide. If a slight, usually black, pre- cipitate forms, filter it off; then precipitate the manganese in the filtrate as manganese sulphide, and determine it as such ( 109, 2). The precipitate, however, dissolve in a little brominized hydro- chloric acid, heat to expel the free bromine, precipitate any copper present with hydrogen sulphide, and in the filtrate determine the nickel, cobalt, and zinc present, according to 160, 6, 6. 9. Acidulate the filtrate from the manganese sulphide with hydrochloric acid, evaporate, drive off the ammonium salts, and in the residue determine the lime and magnesia ( 154, 6). 10. The remaining 250 c.c. of the solution obtained in 3 is employed for the determination of the phosphoric acid, or both phosphoric and arsenic acids, as well as the copper. If only phos- phoric acid is to be determined, and it is present in not too small a quantity, evaporate to dryness on a water-bath with repeated addition of nitric acid, take up the residue with nitric acid, pre- cipitate with molybdenum solution, and determine the phosphoric acid according to 134, 6, /9. If, however, copper or arsenic acid is present in determinable quantity, or if the quantity of phos- phoric acid present is very small, subject the liquid to prolonged treatment at 70 with hydrogen sulphide, filter, and determine in the precipitate the copper, or arsenic, or both ( 164) ; in the filtrate determine the phosphoric acid according to 135, h, f (Vol. I, pp. 460 and 461). The phosphoric acid, which separates with a small quantity of ferric oxide, is then determined according to 134, 6, p. 11. To determine any sulphuric acid present, fuse 3 to 5 gnn. of the dried ore with one part by weight each of sodium carbonate, and of potassium nitrate (F. MUCK* in a platinum crucible over a BERZELIUS alcohol-lamp); treat the melt with boiling water, filter, and in the filtrate determine the sulphuric acid (Vol. I, p. 562, 1, a). * Zeitschr. /. analyt. Chem., vn. 416. 492 DETERMINATION OF COMMERCIAL VALUES. [ 253. 12. If the ore contains ferrous oxide, digest a suitable quantity in a 250-c.c. flask with strong, chlorine-free hydrochloric acid and best in a current of carbon dioxide, until the decomposi- tion is complete; then fill the flask to the mark, mix, and in an aliquot part determine the ferrous chloride according to 112, 2, 6. If the iron ore can be decomposed by prolonged heating with diluted, sulphuric acid, this mode of decomposition is preferable; the ferrous oxide is then determined according to 112, 2, a. If manganic oxide is present, it must be remembered in calculating the ferrous oxide that the oxygen liberated from the manganic oxide during solution has oxidized a corresponding quantity of fer- rous oxide to ferric oxide. On deducting the ferric oxide corre- sponding to the ferrous oxide from the quantity found in 7, the ferric-oxide content of the mineral is ascertained. 13. If carbonic acid is present, it is best determined according to the method detailed in Vol. I, p. 493. 14. In testing for titanic acid it is best to ignite a separate portion of the mineral in a current of hydrogen until the ferric oxide is completely reduced, and to then treat the residue accord- ing to the process described on page 487, d, this volume.* 15. If the brown iron ore contains vanadium and chromium, as in the case of the bean-ore from Haverloh in the Harz, mix the finely powdered ore with one-third of its weight of potassium nitrate, expose to a low red heat for an hour, crush the mass, and boil it with not too large a quantity of water. To the solution, which will have a yellow color if chromium is present, add very cautiously, and with constant stirring, diluted nitric acid until it is only just slightly alkaline. (The liquid must never be allowed to become acid, otherwise the liberated nitrous acid will reduce the chromic and vanadic acids.) Filter off the precipitate formed (silicic acid and aluminium hydroxide), and precipitate with [* For the determination of titanic acid in iron ores see also JAS. BRAKES (Journ. Soc. Chem. Indust., xvm, No. 12); also CHARLES BASKERVILLE (Ibid., 1900, p. 419). The latter gives a method of analysis of titaniferous ores which has been used successfully by him for a number of years in a large number of analyses. TRANSLATOR.] 253.] IRON COMPOUNDS. 493 barium chloride, with the addition of ammonia; collect the pre- cipitate of barium chromate and vanadate, wash, and boil it with a not too large excess of diluted sulphuric acid. Neutralize with ammonia the reddish-yellow filtrate from the barium sulphate, con- centrate strongly by evaporating, and place a piece of ammonium chloride in the liquid. In proportion as the latter becomes satu- rated with this salt, ammonium vanadate separates as a white or yellow crystalline powder. After the separation is complete, filter, wash with a saturated solution of ammonium chloride, dry, heat gradually with full access of air, and thus obtain the vanadium as dark-red, almost black vanadic acid, melting to a red liquid on being strongly heated, and solidifying to a crystalline mass on cooling (F. WOHLER*). In the filtrate from the ammonium vanadate the chromium may be precipitated as a hydroxide by adding sulphurous acid. Re- garding another method of detecting minute traces of chromium in iron ores see A. TERREIL (Zeitschr. /. Analyt. Chem., iv, 440). c. BOG IRON ORE. The bog iron ores consist essentially of sedimentary ferric hydroxide resulting from the oxidation of ferrous compounds in waters, the oxidation being usually assisted by organic action. These ores are characterized by the invariable presence of phos- phoric acid, occasionally in quantities up to 4 per cent., as well as by the presence of humic acids. In addition, they always contain silicic acid (in combination and as quartz-sand); at times sul- phuric and arsenic acids are present; manganic oxide is always present, and ferrous oxide, alumina, lime, and magnesia, often. After the ore has been powdered and dried, ignite a portion in an open platinum crucible, at first very gently, in order to burn off the organic acids; then heat gradually more strongly, and main- tain this for some time with the crucible placed obliquely. The loss of weight corresponds to the water and the organic matter. Treat a second weighed portion, which has been very gently *" Die Mineralanalyse in Beispielen," 2d Ed, p. 150. 494 DETERMINATION OF COMMERCIAL VALUES. [ 253. ignited, so as to destroy the organic matter, according to the method described under brown iron ore, b. If the organic acids are to be detected and determined boil a larger quantity of the finely powdered ore with pure potassa solu- tion until it has become converted into a flocculent mass. Then filter, and treat the filtrate according to 209, 10 to 12. d. MAGNETIC IRON ORE. Magnetic iron ores contain the iron as ferroso-ferric oxide. In analyzing them the possible presence of titanic acid, magnesia, and gangue must not be overlooked; in the earthy magnetic ores there is also found considerable manganous oxide, and occasion- ally a small quantity of cupric oxide. Phosphoric acid is but seldom found in magnetic iron ore, and then only in small quantity. The magnetic iron ore is analyzed in the same way as hematite, and afterwards a portion is separately weighed off, dissolved in hydrochloric acid in a current of carbon dioxide, and the ferrous iron in the solution determined volumetrically with potassium dichromate (Vol. I, p. 319, b), or the ferric iron with stannous- chloride solution (Vol. I, p. 327). e. SPATHIC IRON ORE. Spathic iron ore contains ferrous carbonate, usually associated with manganous carbonate and carbonates of the alkaline earths, and frequently mixed with clay and gangue. Occasionally a part of the ferrous carbonate is found already converted into ferric hydroxide. The powdered mineral is dried either in the air or at 100. a. The water content is determined according to 36. b. The carbonic acid is best determined as in Vol. I, p. 493. c. Dissolve a third portion, about 8 to 10 grm., in hydrochloric acid, add a little potassium chlorate in order to convert all the ferrous into ferric chloride, boil until the liquid no longer smells of chlorine, and then proceed as directed under brown iron ore, b. d. In a fourth portion, dissolved in hydrochloric acid in a current of carbon dioxide, determine the iron volumetrically 254.] IRON COMPOUNDS. 495 either as ferric iron with stannous-chloride solution (Vol. I, p. 327), or as ferrous iron, with potassium dichromate (Vol. I, p. 319, 6). II. DETERMINING THE IRON IN IRON ORES. 254. 1. Volumetric Methods. Many volumetric methods have been proposed for determining the iron in iron ores, and adopted, some again falling into disuse. The method long considered as the most convenient and best, and based on the employment of potassium permanganate, sus- tained a severe set-back when LOWENTHAL and LENSSEN showed that correct results could be obtained in hydrochloric-acid solu- tions only when the conditions of testing, the effective value of the permanganate solution, the quantity of hydrochloric acid present, the degree of dilution, and the temperature, were identical (see Vol. I, p. 319). Of the methods here described the first is especially recom- mended because of its simplicity and accuracy. First Method. Gently ignite about 5 grm. of the very finely powdered ore dried either in the air or at 100, until all the organic matter pres- ent has been destroyed, then heat in a flask with hydrochloric acid at a temperature below the boiling-point of the acid. With hematite fuming hydrochloric acid is absolutely necessary; and it is advisable also with brown iron ore. After decomposition and solution are effected as completely as possible, add, if the ore contains ferrous oxide, some potassium chlorate, heat for a long time, then transfer the contents of the flask to a porcelain dish, rinse out the flask into the dish, and evaporate almost to dryness on the water-bath. The operator may then be certain that the potas- sium chlorate added has been completely decomposed, and all the free chlorine expelled. Now add to the residue a little hydro- chloric acid, then water, filter into a 500-c.c. flask, and wash the residue. 496 DETERMINATION OF COMMERCIAL VALUES. [ 254. // the iron stone contains no ferrous oxide, dilute the contents of the flask with water, filter into a 500-c.c. flask, and wash the residue. In either case now fill up to the mark, mix, and, as a precaution, test a small quantity of the liquid with potassium ferricyanide to be sure that no ferrous chloride is present. Then in two separate portions of 100 c.c. each of the solution deter- mine the iron volumetrically with stannous chloride (Vol. I, p. 327). instead of the apparatus shown in Vol. I, p. 330, Fig. 86, the apparatus here shown, Fig. 106, may be used for preserving the FIG. 106. stannous-chloride solution, and particularly if the solution is used only occasionally. In this apparatus it may be preserved unchanged for a long time. The solution is drawn from the bottle a by means of a siphon, e. The air which enters passes first through the U-tubes b and c, then through the bottle d, all containing pumice-stone saturated with a strongly alkaline solution of potas- sium pyrollagate. This solution is prepared in the tubes and bottle by pouring together concentrated solutions of potassa and pyrogallic acid some time before the apparatus is required for use; I 254.] IRON COMPOUNDS. 497 as potassium pyrogallate rapidly absorbs the oxygen of the air, the vessels in a short time contain only pure nitrogen. Every- thing being in readiness, insert a glass tube into the rubber tube /, fill the siphon by suction, and then close the pinch-cock. To fill a pipette or pinch-cock burette, insert the point into the rubber tube after the burette pinch-cock has been pushed back over the delivery tube, then open pinch-cock /, and allow the fluid to as- cend from below. Then close the pinch-cock /, and remove the burette. Ascertain the iron content of the hydrochloric-acid solution of the iron ore in the manner detailed. At times small quantities of iron are still contained in the residue insoluble in hydrochloric .acid. This is particularly the case when the residue either before or after ignition has a red color or appears reddish. In order to determine any iron present in the residue decompose it by fusion with sodium carbonate, separate the silicic acid (Vol. I, p. 511, b), and in the hydrochloric-acid solution determine the ferric chloride with stannous chloride. If this solution is added to the main solution, however, the necessity for a special titration is avoided. Second Method. For the preparation of the hydrochloric-acid solution of the iron ore, containing the iron as ferric chloride, and perfectly free from nitric acid and chlorine, proceed as in the first method; the determination of the iron, however, is made in aliquot por- tions of the solution with potassium iodide, as described hi Vol. I, p. 331, p. If the residue insoluble in hydrochloric acid still contains any iron compound, treat it as in the first method, and in the solution determine the ferric chloride similarly with potassium iodide. According to my investigations the first method yields more trustworthy results in the analysis of iron-stone than the second, the latter being better adapted for determining smaller quantities of iron. 498 DETERMINATION OF COMMERCIAL VALUES. [ 254., Third Method. Prepare a hydrochloric-acid solution as in the first method, dilute, reduce with zinc * in a current of carbon dioxide (Vol. I,, p. 325, 3, a), and determine the ferrous chloride by PENNY'S method (Vol. I, p. 319, 6), or by means of a standard potassium-perman- ganate solution, observing the special precautions recommended for ferrous solutions containing hydrochloric acid, Vol. I, 319, f. If the residue, insoluble in hydrochloric acid, still contains some iron, decompose it as in the first method. Fourth Method. Fuse about 0-5 grm. of the very finely powdered iron ore with 3 to 4 grm. potassium or sodium disulphate, at first gently, but gradually more strongly; maintain the heat for a long period, but yet not so long as to drive off the second equivalent of sul- phuric acid. Dissolve the residue in diluted sulphuric acid, re- duce the solution by boiling with zinc * in a current of carbon dioxide (Vol. I, p. 325, 3, a) and finally determine the ferrous iron by means of a standard solution of potassium permanganate, according to Vol. I, p. 312, 2, a. The difficulty in carrying out. this process lies in the fact that the decolorization of the solution is no criterion of the completion of the reaction. Hence, when it appears to be completed, it is necessary to bring a drop of the solution into contact with a drop of potassium-sulphocyanate solution on a porcelain plate. If a distinct redness supervenes, the reduction is still incomplete. The reaction between the sul- phocyanate and the ferric iron is so delicate that no notice need be taken of a very faint reddening. The results are naturally correct only when complete decomposition and solution of the iron has been effected. * Zinc crushed in a mortar heated to 210, and sifted so as to yield a uniform, rather coarsely granular powder, is far better adapted for this pur- pose than granulated zinc or sheet-tin (J. M. BROWN, Zeitschr. /. analyt. Chem., xvin, 98). 254.] IRON COMPOUNDS. 499 2. Gravimetric Methods. Of these, I describe only FUCHS'S method,* as the unfavor- able statements regarding it made by other chemists were refuted by J. LOWE f and R. KONIG,{ in 1857. I would remark, how- ever, that the method has been almost entirely supplanted by the volumetric methods. a. The Ordinary Method (as described by LOWE, loc. cit.). Heat 1 to 1 5 grm. of the ore, if of a superior grade, or 2 to 3 grm. if of an inferior quality, in the form of finest powder, in an obliquely held, long-necked 500-c.c. flask with strong hydrochloric acid, and when all the iron is dissolved add a little potassium chlorate in small portions, and best in the form of fused fragments, until the liquid has a decided odor of chlorine; then continue the heat until the odor of chlorine is no longer perceptible. Dilute with water until the flask is half filled, stopper with a sound cork bearing a tightly fitting glass tube about 10 inches long, open at both ends, and not too narrow; support the flask in an oblique position and maintain at least fifteen minutes at a moderate boil, in order to make certain that every trace of chlorine and air has been expelled rom the flask and the water. While the solution is continuously boiling remove the cork and slowly lower into the solution a strip of clean, pure copper foil fastened to a thin platinum wire. In doing this, first suspend the copper foil within the flask, pinching the wire between the cork and the glass, and until the copper foil has become warm; other- wise the liquid is very apt to spirt if the cold foil is lowered into it. Then remove the cork again, allow the foil to sink down horizontally and become completely immersed in the liquid, stopper tightly, and secure the flask obliquely again, taking care through all these operations to maintain the iron solution in con- stant ebullition. The boiling must be slow and not too violent, *Joum. /. prakt, Chem., xvn, 160. t Ibid., LXXII, 28. J Ibid., LXXII, 36. 500 DETERMINATION OF COMMERCIAL VALUES. [ 254. and must be continued until the iron solution has been completely reduced and is therefore either entirely colorless or at least so very slightly greenish that it is difficult to determine its color with certainty. As a rule the reduction is complete in two hours, but the boiling may be continued for three or even four hours without any effect whatever on the accuracy of the result. The copper foil must always be kept completely covered by the solu- tion during the boiling. As the addition of water during the operation is quite impracticable, care must be taken that suf- ficient water be added at the beginning. The strip of copper should weigh about 6 grm. It may be made from copper precipitated by galvanic action, and of such a width and length as to conveniently pass into the flask and lie horizontally on the bottom. It should be scoured brightly with sandpaper, then weighed, and attached to the platinum wire. When the reduction of the ferric chloride is complete, remove the cork, quickly withdraw the copper strip from the still boiling solution by means of the platinum wire and immerse it in a beaker filled with distilled water, rinse it off with distilled water after removing it from the beaker, dry it thoroughly between blotting- paper, disconnect it from the platinum wire, and weigh ; for every equivalent of copper dissolved calculate one equivalent of iron, according to the equation: Fe 2 Cl 6 +2Cu = 2FeCl 2 +Cu 2 Cl 2 . The copper loses its original lustre during the operation, and appears* dull, but not blackish, as it usually does if the ordinary sheet copper is used. In four analyses of chemically pure ferric oxide, J. LOWE found by this method 99-7, 99-6, 99-6, and 99-6 per cent, ferric oxide respectively. KONIG'S process (loc. cit.) is quite similar. He recommends to dry the copper strip, after removing it from the boiling liquid, by keeping it immersed for some time in hot water in order that every portion of the solution that may have penetrated into the pores may be washed out, then displacing the water by immersion in alcohol, and finally displacing the alcohol with ether. He also recommends winding platinum wire around the strip, as this not only prevents loss of small particles of copper from the bump- 255.] IRON COMPOUNDS. 501 ing of the metal against the glass during ebullition, but also acceler- ates the reduction. KONIG obtained results in a series of ex- periments with this process, varying between 99-5 and 100-5 per cent. The solubility of copper hi boiling dilute hydrochloric acid is so slight that the effect on the accuracy of the results is quite within the limits of experimental error (J. LOWE *). b. Modified Method. If iron ores contain any considerable quantity of titanic acid, the process a, according to FUCHS, can be employed only with certain modifications. As such cases are comparatively rare, however, I refer to the original paper,! where the modifications are described. If the iron ore contains arsenic acid the method is similarly inapplicable, because then the copper becomes covered with black scales of copper arsenide. In this case the arsenic acid may be removed by fusing the powdered ore with sodium carbonate and exhausting the melt with water, then dissolving the residue in hydrochloric acid, and treating this solution as in a. B. ANALYSIS OP VARIOUS KINDS OF IRON. I. CAST IRON. 255. Cast iron, one of the most important metallurgical products, contains a whole series of elements, either admixed in greater or less quantity, or in combination with it. Although the effect that the various admixed substances has on the character of the cast iron is not yet accurately known, yet it is undoubtedly a fact that the substances have a considerable influence on the quality of the iron. The analysis of cast iron is one of the more difficult problems * Zeitschr. f. analyt Chem., TV., 361. f Journ. f. prakt. Chem., xvm, 495; see also KONIG, Journ. f. prakk Chem., LXXII, 38. 502 DETERMINATION OF COMMERCIAL VALUES. [ 255. of analytical chemistry. The following substances are those to which special attention must be directed: Iron, carbon (combined with iron } and also in the form of graphite), nitrogen, silicon } phosphorus, sulphur, potassium, sodium, lithium, calcium, magnesium, aluminium, chromium, titanium, zinc, man- ganese, cobalt, nickel, vanadium, copper, tin, arsenic, antimony, and tungsten. As a rule only those elements indicated by italics .are quantitatively determined. 1. CARBON DETERMINATION. A. Total Carbon. Of the various methods proposed in former as well as in more recent times for determining carbon in cast iron, only those afford invariably accurate results in which the carbon is converted into carbonic acid and weighed as such; on the other hand, all those methods must be considered as less reliable in which the carbonaceous residue left on treating the substance by some solvent process is weighed, its incombustible portion determined, and the carbon found from the difference. The reason why the latter methods are unreliable is because the combustible portion of the residue is not as a rule pure carbon. The methods here given are, hence, almost all of the former kind, and they differ from one another partly in that the combustion of the carbon is performed either on the residue (containing all the carbon) left on suitably dissolving the iron, or upon mechanically divided iron; or, the oxidation of the carbon is effected in the dry or in the wet way. Under a I detail the methods of obtaining from cast iron a residue containing all the carbon; under /? the determina- tion of the carbon therein; and under ?-, the determination of the carbon by direct combustion of the iron. a. METHODS OF OBTAINING A RESIDUE CONTAINING ALL THE CARBON OF CAST IRON. aa. BERZELIUS'* Method and its Modifications. As on dissolving cast iron in hydrochloric or sulphuric acid the combined carbon is evolved in the form of hydrocarbons, * BERZELIUS' Lehrbuch der Chemie, WOHLER'S translation, x, 118. 255.] IRON COMPOUNDS. 503 BERZELIUS employed as solvents of iron solutions of neutral metal- lic salts, especially a solution of cupric chloride * free from excess of hydrochloric acid, or a solution of equal equivalents of cupric sulphate and sodium chloride. He recommends to allow the action to take place in the cold until the color of the liquid shows that the copper has been almost completely precipitated, and then to either renew the cupric-chloride solution, or to add some crystallized cupric chloride to it. When copper is no longer precipitated, either in the cold or on gently warming, allow to stand for twenty-four hours to make certain. Then add hydro- chloric acid, and if necessary, cupric chloride, until all the pre- cipitated copper has redissolved, collect the carbonaceous residue in a filtering-tube containing spongy platinum, and wash it first with water, then with hydrochloric acid, and finally again with water. In the course of time this method has been modified, and it has been found especially advantageous to use, instead of cupric chloride, ammonio-cupric chloride (PEARSE;! CREATH J), as this greatly accelerates the solution of the iron; asbestos filters also are now usually used for collecting the carbon. The solution of ammonio-cupric chloride is prepared by dis- * According to H. HAHN (Zeitschr. f. analyt. Chem., rv, 210), when dis- solving iron in cupric-chloride solution, a little hydrogen, containing hy- drocarbons, is evolved, as a result of the galvanic action induced by the contact of the iron with the copper deposited, which causes a slight loss of carbon. According to MAX BUCHNER, however (ibid., iv, 211), when the cupric chloride used is perfectly free from acid the quantity of gas evolved is so small that the carbon passing off in it is unweighable. j- Eng. and Min. Jvurn., New York, xxi, 151; also Zeitschr. /. analyt. Chem., xvi, 504. \Eng. and Min. Jmtrn., New York, xxin, 168; also Zeitschr. f. analyt. Chem., xvi, 504. An asbestos filter may be most conveniently made by placing in an ordinary glass funnel a little glass wool and pouring on this asbestos made into a pulp with water, and then washing until no more fibres of asbestos are washed away. There is thus formed a good filtering layer of asbestos on the glass wool (compare SATTER, Zeitschr. f. analyt. Chem., xrv, 312). The asbestos employed must be ignited in a current of moist air in order to free it from chlorine (compare KRAUT, Zeitschr. f. analyt. Chem., in, 34). 504 DETERMINATION OF COMMERCIAL VALUES. [ 255. solving 340 grm. crystallized cupric chloride and 214 grm. am- monium chloride in 1850 c.c. water. The cast iron should be in a very finely divided state, in the form of turnings, borings, or very small pieces. If any oil from the borer, etc., adheres to the iron, it must first be removed by washing with ether. If the comminuted iron contains any other admixed organic matter, separate it by the aid of a magnet. Treat 2 to 5 grm. of the suitably purified, finely divided iron with solu- tion of ammonio-cupric chloride, using about 20 to 25 c.c. of the solution to every gramme of iron, and when all is dissolved, treat the residue by one of the following methods, according as to whether the carbon is to be determined by means of chromic acid or by combustion. aa. Collect the separated carbon together with the metallic copper in an ordinary funnel in which a plug of asbestos has been loosely placed, and preferably by the aid of a pump; wash (to re- move the precipitated cuprous chloride) first with concentrated hydrochloric acid, and then with water or alcohol * until every trace of hydrochloric acid has been removed. If the residue contains any chlorine compound, this, on treatment with chromic acid and sulphuric acid, gives rise to chlorochromic acid, and the results are then too high. When alcohol has been used for the washing, the contents of the funnel must be thoroughly dried. /?/?. To the contents of the vessel add hydrochloric acid, and, if necessary, a further quantity of solution of ammonio-cupric chloride until all the metallic copper has dissolved, then collect the residual carbon on an asbestos filter,t and wash it, first with a little hydrochloric acid, and then with water or alcohol, until every trace of hydrochloric acid has been washed out. Then thoroughly dry the contents of the funnel at about 100 to 110. * L. KLEIN (Zeitschr. f. analyt. Chem., xvui, p. 76) gives the preference to alcohol, because by use of it the carbon is more readily washed from the margin of the funnel, and, after drying, more easily removable from the funnel. t See foot-note, p. 603. 255.] IRON COMPOUNDS. 505 66. 0. ULLGREN'S Method* Instead of using cupric chloride or aminonio-cupric chloride, ULLGREN treats the finely divided iron with a solution of 1 part cupric sulphate in 5 parts of water at a gentle heat ; ELLIOT f uses the same method. The solvent is easily prepared, but is far slower in action than aminonio-cupric chloride. If the pre- cipitated copper is to be dissolved, the residue, in this method also, must be heated with cupric chloride and hydrochloric acid. cc. BOUSSINGAULT'S Method. I Triturate the finely divided iron for half an hour in an agate or glass mortar with fifteen times its weight of mercuric chloride and some water to make a thin paste. After adding water, trans- fer the whole to a beaker and heat for an hour at 80 to 100. Filter through an asbestos filter, wash the residue with hot water, dry thoroughly in an air-bath, then heat in a platinum boat in a current of dry hydrogen, raising the heat gradually to redness, and in this manner drive off the admixed mercurous chloride. In order to obtain the hydrogen perfectly free from oxygen, con- duct it through a long layer of spongy platinum, and then through sulphuric acid. Regarding the further treatment, see ft below (Third Method). dd. W. WEYL'S Method.^ This excellent method possesses the great advantage that it. is unnecessary to comminute the iron, during which operation, as is well known, it is very apt to become contaminated. The solu- tion is effected by means of a weak galvanic current, employing a BUNSEN element, using the iron fragment to be analyzed, and immersed in diluted sulphuric acid, as the positive electrode. The iron dissolves as ferrous chloride without the evolution of any gas from its surface, and leaves the carbon behind, while hydrogen * Ann. d. Chem. u. Phar., cxxiv, 59; Zeitschr. /. analyt. Chem., n, 430. f Journ. Chem. Soc., vn, 182. ICompt. rend., LXVI, 873; Zeitschr. /. analyt. Chem., vni, 506. Poggend. Annul., cxiv, 507; Zeitschr. /. analyt. Chem., i, 112 and 250. 506 DETERMINATION OF COMMERCIAL VALUES. [ 255. is evolved at the negative electrode. If a strong current is used the purpose desired will not be effected, because then the iron would readily become passive; in this case there would be liber- ated from its surface chlorine, which would oxidize the carbon already separated, and would directly form with it a compound which would be decomposed by the galvanic current in a manner analogous to hydrochloric acid, carbon as well as hydrogen separat- ing at the negative pole. It is obvious that in both cases there is a loss of carbon, as carbonic oxide or carbon dioxide in the former case, and in the latter as hydrogen carbide, which may be formed from the hydrogen and carbon simultaneously sep- arated at the negative electrode. Select a piece of iron about 10 to 15 grm. in weight, clamp it in a pair of pincers provided with platinum points, and suspend it in diluted hydrochloric acid so that the points of contact between the iron and the pincers are not touched by the acid (otherwise the carbon separated at these points rapidly impedes the process of solution). Connect the pincers with the wire from the positive pole; immerse also the platinum foil fastened to the negative wire in the acid, and regulate the strength of the current by increasing the distance between the electrodes, so that ferrous chloride alone is formed, but no ferric chloride. The formation of the latter is immediately recognized by the yellowish color of the streams of concentrated iron solution which descend from the iron. The piece of iron changes but little in external appearance during the process of solution, as the carbon remaining retains the original form of the piece of iron. As soon as the immersed portion of the iron has dissolved (which takes about twelve hours) interrupt the operation, separate the undissolved, compact piece of iron from the adhering carbon, dry, weigh, and thus ascertain the quantity of iron dissolved. Collect the carbon on an asbestos filter. When this method is employed for those kinds of iron which do not deposit the carbon in a coherent mass, as is the case in " spiege- leisen," but only in a finely divided state, the negative platinum electrode becomes colored black from the carbon deposited upon 255.] IRON COMPOUNDS. 507 it. RINMANN * made this observation first when treating Bessemer steel according to WEYL'S method. According to WEYI/)- the method must be slightly modified when used with these kinds of iron, the apparatus shown in Fig. 107 being then employed. This consists of a beaker half filled with diluted hydrochloric acid, and containing a glass cylinder (held in place by a suitable disc), closed at the bottom by a bladder of parchment paper, and filled with the diluted hydrochloric up to the level of the surrounding acid. The cylinder contains the positive electrode, i.e., the piece FIG. 107. of iron, the negative electrode of platinum foil occupying the space between the cylinder and the beaker. Otherwise the process is similar to the one described above. In this apparatus, too, the platinum foil is blackened after several hours' use, but the black deposit dissolves in hydrochloric acid, and is iron, not carbon. *Zeitschr. /. analyt. Chem., in, 336. f Ibid., iv, 157. 508 DETERMINATION OF COMMERCIAL VALUES. [ 255 ee. WOHLER'S Method.* WOHLER'S method is based upon the fact that upon heating cast iron in a current of chlorine, the whole of the iron is volatilized as ferric chloride, while all the carbon remains. The method is comparatively rapid, and affords very good results, for which reasons many chemists prefer it to all other methods. f Weigh off the iron (1 to 2 grm.) into a porcelain boat, insert this into a tube of difficultly fusible glass, and heat it to faint redness in a current of chlorine gas dried by previously passing it over pumice stone saturated with concentrated sulphuric acid. The treat- ment is continued until no more ferric chloride is formed. All the carbon remains in the boat. Great care must be exercised in drying the chlorine, for if it contains even small quantities of moisture, a loss of carbon may occur from the formation of hydro- carbons. //. Other Methods. Besides the methods described from aa to ee, several others have been proposed, especially those in which bromine is employed,]; and WEYL'S process, in which dilute chromic acid is used. Some are but little to be recommended, while others have been less care- fully studied than those above described; a detailed description of them is hence omitted. /?. DETERMINING THE CARBON IN THE RESIDUE FROM a. The determination of the carbon in the residue obtained from a is usually effected by converting the carbon into carbonic acid, and weighing this; the usual processes are by combustion in oxygen (First Method), or by oxidation with chromic acid (Second * Zeitschr. f. analyt. Chem., vin, 401. f Compare MAX BUCHNER, Berg- und Huttenmdnn. Zeitung, Jahrg. xxiv, 84; Zeitschr. /. analyt. Chem., iv, 211. B. KERL, ibid. E. G. TOSH, Chem. News, 1867, No. 401, p. 67, and No. 403, p. 94; Zeitschr. f. analyt. Chem., vii, 498, and vm, 401. t Compare WERTHER, Journ. f. prakt. Chem., xci, 250; Zeitschr. f. analyt. Chem., iv, 211. Zeitschr. /. analyt. Chem., iv., 158. 255.] IRON COMPOUNDS. 509 Method). Lastly, BOUSSINGAULT determines the carbon from the loss of weight on combustion (Third Method). aa. First Method (Combustion of the Carbon and Weighing the Carbonic Add). If a residue containing all the carbon but free from copper has been obtained according to cc or ee, this will already be in a boat; if, however, it has been collected on an asbestos filter, according to aa, /?/?, or dd, or bb, transfer it, together with the asbestos, to a porcelain or platinum boat, remove any particles of carbon adher- ing to the funnel by means of a moist pledget of asbestos which is also put into the boat, and, if necessary, thoroughly dry the con- tents of the latter. Now insert the boat into a tube, the hinder end of which is empty, but the fore part filled with granular cupric oxide (p. 41 this volume), and proceed exactly as detailed on pp. 39 to 43 this volume. The absorption apparatus is best arranged thus : The end of the combustion tube is directly connected with the end, 6, of a tube as shown in Figs. 13, 14, or 15, p. 16 this volume; both limbs of the tube contain calcium chloride, but the bend is filled with lead peroxide held between cotton plugs. The tube so arranged is capable of retaining not only the water, but also sul- phurous acid, which may be evolved during combustion should the residue contain any sulphides. Before use, conduct through the tube, first, dry carbon dioxide, then dry air continuously until every trace of carbon dioxide has been expelled. The outlet end g connect with two weighed U-tubes, filled with soda-lime and a little calcium chloride (p. 54 this volume); connect the second tube with a similar but unweighed safety-tube, the exit limb of which is filled with soda-lime, the other with calcium chloride. This safety-tube bears a glass tube bent at right angles, and dipping for a distance of a few centimetres into water; this enables the prog- ress of the operation to be properly watched. With regard to the heating, it must be remarked that the carbon which was chemi- cally combined with the iron burns readily, whereas for the com- bustion of graphite there is required a more prolonged heating and at a higher temperature, in a current of oxygen. But as 510 DETERMINATION OF COMMERCIAL VALUES. [ 255. even this does not always afford complete combustion, the residue in the boat must always be carefully examined to make certain that it is quite free from graphite. All things considered, there- fore, it is preferable to employ chromic acid for effecting the oxi- dation of residues rich in graphite. If the combustion method is employed in the place of residues consisting of carbon and copper, and obtained by dissolving iron in cupric-sulphate solution, mix the residue from 1 grm. of the iron with 50 grm. of cupric oxide, and conduct the combustion as described on p. 43, b, this volume. I cannot, however, recom- mend this method for residues containing graphite, because it is impossible to be certain of the complete combustion of the graphite. Respecting a modified method of gasometric determination of the carbon, compare PARRY (Zeitschr. f. analyt. Chem., xn, 225). [Regarding the determination of carbon in steel by combustion see p. 550 this volume. TRANSLATOR.] bb. Second Method (Oxidation with Chromic Acid). The method first recommended by the ROGERS brothers, and later on by BRUNNER,* and which consists in oxidizing the carbon with potassium dichromate and sulphuric acid (hence in the wet way) to carbonic acid, was first employed by ULLGREN in a modi- fied form (using chromic acid instead of potassium dichromate) for the determination of carbon in carbonaceous iron residues. This method, even with residues rich in graphite, insures complete oxidation of the carbon, and is hence particularly to be recom- mended in the case of residues from gray cast iron. I shall first describe the method recommended by ULLGREN,! and, because of its suitableness, shall repeat the description of the process for effecting the solution (compare p. 505 this volume) ; then the modifications will be described. Treat about 2 grm. of the cast iron in the form of borings if it is gray, or in coarse powder if it is white, in a small beaker with a solution of 10 grm. of cupric sulphate in 50 grm. water, at a gentle * Pogg. Annal, xcv, 379. Jahresber. von LIEBIG und KOPP, 1855, 773. \Annal. d. Chem. u. Pharm., cxxiv, 59. Zeitschr. f. analyt. Chem., n, 430. 255.] IRON COMPOUNDS. 511 heat and with stirring. As soon as the iron has dissolved, allow to settle, and decant the clear solution from the deposited carbon; then transfer the residue, both liquid and solid, to the flask a, Fig. 108, by means of a wash-bottle, taking care, however, that FIG. 108. the volume of the liquid does not exceed 25 c.c. Now add to the contents of the flask 40 c.c. of concentrated sulphuric acid (or proportionally more if more wash- water had been required). When the mixture has become cold, add 8 grm. chromic acid,* * ULLGREN chose chromic acid, sulphuric acid, and water instead of the mixture of potassium dichromate and excess of sulphuric acid recom- mended by the ROGERS brothers and by BRUNNER, on the ground that it avoids the formation of anhydrous chromium-potassium sulphate, which not only interferes with but operates to conceal the completion of the oxida- tion, the salt being deposited as a green, muddy powder almost insoluble in water, acids, and alkalies, when concentrated sulphuric acid is employed. 512 DETERMINATION OF COMMERCIAL VALUES. [ 255. and connect the flask with the apparatus for absorbing the carbon dioxide. The carbon dioxide resulting from the oxidation of the carbon by the chromic acid, corresponds with the total quantity of the carbon. The apparatus is arranged as shown in Fig. 108. The flask a has a capacity of 150 c.c., and stands in a wire basket, 6; during the operation c is closed by a glass rod, which, when air is drawn through the apparatus, is replaced by a potash-tube; e is connected with the bulb-tube, d, fused to the side of the flask, and serves to condense the greater part of the vapors; its bulb should have a capacity of from 70 to 80 c.c. The cylinder / holds about 250 c.c., and contains pumice-stone which has been satu- rated with sulphuric acid and then heated until all the hydrochloric and hydrofluoric acids (arising from the presence of chlorides and fluorides in the pumice) have been expelled. The tube g leading into the cylinder ends just at the lower surface of the stopper; the exit-tube, on the contrary, extends nearly to the bottom; h con- tains calcium chloride, and is 0-6 metre long; i i is a weighed absorption tube filled mostly with potassa-pumice,* but contain- ing calcium chloride at the end. During the operation it is con- nected with a small guard- tube, k } filled with potassa. When all is in readiness, gradually heat the flask until the evolu- tion of gas is so violent that the mass threatens to boil over. Main- tain the temperature at this point so long as the gas is uniformly freely evolved, but as soon as it decreases, increase the heat, so that white vapors begin to rise into the bulb e. Conduct the action by regulating the heat suitably, and until the evolution of gas is but very feeble. Now connect k with an aspirator, and slightly open the cock of the latter before connecting c with the potash tube (c be- ing previously pressed down until its end dips into the liquid). Then * Potassa-pumice is prepared thus : Dissolve 1 part potassium hydroxide in 3 to 4 parts water, warm the solution in an iron vessel, and continuously heat at a temperature somewhat above 100, while coarsely granular pumice- stone is added under constant stirring, until the mixture forms a nearly dry mass. While still hot, transfer the mass to a glass-stoppered bottle, and shake until the mass has become so cool that the grains no longer adhere to each other. Potassa-pumice very rapidly and completely absorbs carbon dioxide (according to ULLGREN, more rapidly than soda-lime). 5 255.] IRON COMPOUNDS. 513 'open the cock of the aspirator still further. After 5 or 6 litres of water have run out, and at such a rate that about two bubbles of air per second pass through the liquid in a, the whole of the carbon dioxide will have been driven into the absorption tube. After this has cooled, weigh it, but, to make certain, connect it again with the apparatus, draw air once more through the ap- paratus, and ascertain by weighing whether it has gained weight. Instead of introducing into the flask a the residue of carbon mixed with precipitated copper obtained by ULLGREN'S method of solution, the residues obtained according to a, aa to ee may be similarly treated. In the case of those free from copper, some- what less chromic acid may be taken, 3 grm. chromic acid suf- ficing for the residue from 1 grm. iron. A mixture of 2 parts pure concentrated sulphuric acid and 1 part water is recommended as the decomposing fluid. Instead of the apparatus recommended by ULLGREX, others may, of course, also be employed. CLASSEN * recommends for the purpose the apparatus .devised by him for determining carbon dioxide, and with which KLEIN f obtained very good results. This apparatus is shown in Fig. 109. Its chief peculiarity is its condenser, which effects its purpose admirably. It consists of a tube, b, 27 to 30 mm. wide, at the upper end of which is fused a tube 15 mm. wide, while to its lower end one of 6 to 7 mm. width is fused. This tube is placed within a wider tube, which may be the chimney of an ARGAXD burner 23 cm. long and 45 mm. wide, and through which is passed a current of cold water. The condenser so completely condenses the vapors ascending from the 200-c.c. flask, /, that the U-tube c perfectly suffices to dry the carbon dioxide. This tube contains glass beads over which sufficient pure concentrated sulphuric acid has been poured to close the bend of the tube, thus allowing the progress of the reaction to be observed, d and e are the soda-lime tubes for weighing (p. 54 this volume). The sulphuric acid in c re- quires to be renewed only after a series of experiments. After the residue containing the carbon, the requisite quan- tity of chromic acid, and about 50 c.c. of the above-mentioned * Zeitschr. f. analyt. Chem., xv, 288. t Ibid., xvm, 76. 514 DETERMINATION OF COMMERCIAL VALUES. [ 255. mixture of sulphuric acid and water have been introduced into the flask / ; connect g with a soda-lime tube and h with an aspirator, and draw a slow, perfectly regular current of air through the ap- paratus in order to prevent the stopping up of the funnel tube. FIG. 109. Then apply heat, which increase very gradually, finally boiling the contents of the flask for about fifteen minutes, and weigh- ing d and e when these have become perfectly cold. Instead of CLASSEN'S apparatus, the apparatus figured on p. 365 this volume, may also be used with best results, but naturally omitting the tubes i and k. This apparatus is, in fact, more 255.] IRON COMPOUNDS. 515 rationally constructed than either ULLGREN'S or CLASSEN'S, as in it the air entering and leaving the soda-lime tubes is dried by calcium chloride, while in the others the air entering is dried by sulphuric acid, but on leaving is dried by calcium chloride. cc. Third Method (Determination of Carbon by loss of Weight on Combustion). BOUSSINGAULT employed this method for determining the carbon in residues obtained according to a, cc (p. 505 this volume). Free the boat from mercurous chloride and cool it in a current of hy- drogen, then weigh it, burn the carbon in it, weigh the residue after igniting and cooling in hydrogen, and calculate the loss in weight into carbon dioxide. If the carbon is from white pig iron (or bar iron or steel) it is black, voluminous, easily ignitible, and burns like tinder; if, however, it is from gray iron, and hence contains graphite, it requires prolonged heating in oxygen, and the residue must, moreover, be carefully examined to see that it is perfectly free from graphite. The fact that the combustible portion of the residue is not absolutely pure carbon, but contains hydrogen as well, causes the results of the carbon determination made thus to fall out too high. According to BOUSSINGAULT'S * investigations, however, the error is quite small. ;-. REGNAULT'S METHOD OF DETERMINING CARBON BY DIRECT COMBUSTION OF THE IRON. In order to directly burn the carbon in cast iron, the latter must be reduced to the finest powder. This is effected in the case of the harder irons, by breaking on an anvil, crushing in a steel mortar (Vol. I, p. 52, Fig. 25), and sifting through a tinned- iron sieve with very fine holes ; softer irons are filed with a hard file. For irons which cannot be reduced by either of these means, the method ?- here described is inappli cable. REGNAULT, who was the first to employ the method of direct combustion of carbonaceous iron, and BROMEIS f also, use a * Zeitschr. f. analyt. Chem., x, 114. t Annal d. Chem. u. Pharm., XLIH, 242. 516 DETERMINATION OF COMMERCIAL VALUES. [ 255 mixture of lead chromate with potassium chlorate; KUDERNATSCH,* who observed a slight evolution of chlorine to occur with this mixture, prefers pure cupric oxide. H. ROSE recommends mixing with cupric oxide and igniting in a current of oxygen (p. 43, 6, this volume). WOHLER employs the method described on p. 39, a, this volume (combustion of the iron in a boat in a current of oxy- gen). MEYER recommends the mixture of potassium dichromate with lead chromate ( 176). Although the water is not deter- mined in this method, nevertheless place a calcium-chloride tube between the combustion tube and the potash apparatus to collect any moisture that may be present. This method is but little used, and is apt to give results which are too low. See TOSH f and PARRY. J B. Determination of the Graphite. a. Treat another portion of the cast iron with mqderately con- centrated hydrochloric acid at a gentle heat until gas is no longer evolved; then filter the solution through asbestos which has been previously ignited in a current of moist air, wash the undissolved resi- due first with boiling water, then with potassa lye, next with alcohol, and finally with ether (MAX BUCHNER ) ; dry, and then convert the graphite into carbon dioxide, best by oxidation with chromic acid (p. 510). Direct weighing is not advisable because the graphite is usually impure. /?. In order to determine the graphite together with the chemi- cally combined carbon, BOUSSINGAULT || heats the residue obtained as on p. 505, by treating iron with mercuric chloride in the air at a temperature just below a dark redness. The chemically combined carbon present is thereby burned, leaving the graphite unchanged ; the latter is then burned in a current of oxygen. As BOUSSINGAULT determined the chemically combined carbon and the graphite * Journ. f. prakt. Chem., XL, 499. f Zeitschr. f. analyt. Chem., vn, 498. I Ibid., xii, 225. Journ. f. prakt. Chem., LXXII, 364. || Annal. de Chim. et de Phys. [IV], xix, 78, and xx, 243; also Zeitschr. f. analyt. Chem., x, 112. 255.] IRON COMPOUNDS. 517 from the loss in weight, the residue, consisting chiefly of silicic acid, must be heated, after every combustion, in a current of pure hydro- gen, in order to convert any iron present into the same condition in which it was in the weighed carbonaceous mixture. The re- sults of the graphite determination by this method may easily fall out somewhat too low, and those of the combined carbon some- what too high, because finely divided graphite is not altogether incombustible when gently ignited in air. C. Determination of the Chemically Combined Carbon. a. On deducting the graphite obtained in B, a, from the weighed total carbon obtained in A, the combined carbon is ascertained. 1. BOUSSINGAULT'S method for determining the combined carbon is described under B, /?. 7-. If the iron contains so little chemically combined carbon that the determination by difference (a) gives insufficiently ac- curate results, the chemically combined carbon must be deter- mined directly. The process devised by me * for this purpose consists in dissolving the iron in diluted sulphuric acid with the aid of heat, passing the mixture of hydrogen and hydrocarbons with air over red-hot cupric oxide, collecting the carbon dioxide, after drying, in a soda-lime tube, and calculating the carbon from the increase in weight of the tube. Introduce the iron to be dissolved (1 to 5 grm.) into the flask a shown on p. 365 this volume. Connect the small glass tube proceeding from the condenser b by means of a rubber tube with a descending glass tube bent at right angles, the connection being made in such a manner that the ground ends of the two tubes lie close together. Then connect the horizontal portion of the right- angled tube with the hinder end of a combustion-tube by means of a cork or rubber stopper. The combustion-tube rests in a suitable furnace, and is about 30 cm. long. Fill about 15 cm. of that portion next the generating flask with asbestos ignited first in moist, then in dry, air, and so as to leave no visible empty * Zeitschr. f. analyt. Chem., iv, 73. 518 DETERMINATION OF COMMERCIAL VALUES. [ 255. spaces; then follow coarsely granular cupric oxide and a short asbestos plug. The end of the tube farthest from the generating flask connect with a sufficiently large calcium-chloride tube, and this in turn connect with a small, light, accurately weighed U- tube filled with granular soda-lime, the exit end being filled with calcium chloride. To this tube attach a safety U-tube the limb of which nearest the soda-lime tube is filled with calcium chloride while the other limb is filled with soda-lime; this tube is lastly connected with an aspirator. After the combustion-tube has been heated to redness in a current of carbon dioxide, the ap- paratus tested and found to be tight, and it has been ascertained that the soda-lime tube does not increase in weight on igniting the combustion-tube in a current of air free from carbon dioxide, replace v (Fig. 103, p. 365 this volume), which was first connected by means of the rubber tube with s, by the small funnel tube, and by suitably aspirating, draw into the evolution flask a a suf- ficient quantity of diluted sulphuric acid (1:5) to effect solution, pouring the diluted acid gradually into the funnel-tube. Then replace the funnel-tube by v, suitably open the stop-cock s, and also the aspirator stop-cock, and thereby draw through the ap- paratus a slow current of air which must be maintained through the whole process. The part of the combustion-tube containing the cupric oxide is meanwhile kept at a gentle redness which must be maintained during the whole process. Now heat the evolution flask on an iron plate so that solution may be easily effected. The operation proceeds quietly, and is completed in from one and one- half to two hours; towards the end of the operation heat the contents of the flask to boiling. In the case of iron poor in graphite it is advantageous to add a very small quantity of spongy plat- inum in order to facilitate solution. As soon as hydrogen is no longer evolved, heat also that portion of the combustion-tube containing the asbestos in order to burn up any condensed hydro- carbons that may have collected there. Lastly, allow the ap- paratus to cool in a slow current of air, determine the increase of weight of the soda-lime tube, and from it calculate the quantity of carbon evolved in the form of hydrocarbons. 255.] IRON COMPOUNDS. 519 Of course this operation can serve for the determination of chemically combined carbon only when one is certain that this has completely volatilized in the form of hydrocarbons. This is the case with many kinds of iron, but with others, hydrocarbons remain behind with the graphite.* Whether this is the case is readily ascertained on observing if the residue remaining in the evolution flask yields, after thorough washing with boiling water, any carbon compounds to potassa lye, alcohol, or ether, i.e., whether the solvents become colored, and whether the alcohol and ether, the lye having previously been displaced by water, afford an or- ganic residue on evaporation or not. d. For practical purposes, an exact determination of the chem- ically combined carbon is frequently not attempted, it being re- placed by a colorimetric determination. This method, devised by EoGERTZ,t depends upon the fact that cast iron dissolves in nitric acid, yielding a solution the color of which is deeper brown the more combined carbon there is present. Regarding this method compare GRUNER,| BRITTON, HERMANN,|| CREATH,!" and MORRELL.** 2. DETERMINATION OF THE SULPHUR. a. Method in which the greater part of the Sulphur is converted into Hydrogen Sulphide. This method, which was devised by me and first described by LipPERT,ft later on improved by me,Jt and finally simplified by my assistant, Mr. J. MOFFAT JOHNSTON, is best carried out by the aid of the apparatus shown in Fig. 110. * Compare MAX BUCHNER, Journ. f. prakt. Chem., LXXII, 365. j- Chem. News, 1863, No. 182, p. 254; Zeitschr. f. analyt. Chem., n, 434. % Berg- und Huttenmdnn. Zeit., 1869, 52; Zeitschr. f. analyt. Chem., x, 245. Chem. News, xxn, 101 ; Zeitschr. f. analyt. Chem., x, 245. \\Journ. Chem. Soc. [II], vin, 375; Zeitschr. f. analyt. Chem., x, 246. H Eng. and Min. Journ., New York, xxm, 168; Zeitschr. f. analyt. Chem., xvi, 504. ** Amer. Chemist, v, 365; Zeitschr. f. analyt. Chemist, xvi, 505. ft Zeitschr. f. analyt. Chem., n, 46. tJ Ibid., xin, 37. 520 DETERMINATION OF COMMERCIAL VALUES. [ 255~ a is a flask holding from 300 to 400 c.c., in which the irorn is dissolved; b is a smaller flask, containing the requisite quantity of hydrochloric acid used for effecting solution ; c leads to a small, upwardly inclined glass condenser having a not too narrow tube. The exit tube of the condenser is provided with a U-shaped bulb- tube, and this latter is connected in turn with an ordinary U-tube FIG. 110. (see Fig. 103, p. 530, Vol. I) from which a rubber tube and glass lead into the open air, or into a flask containing caustic soda solution. The rubber tube d is connected with a hydrogen ap- paratus. The hydrogen is purified by passing it first through potassa solution, then through potassium-permanganate solution, and finally through a solution of lead oxide in potassa solution. The bend of the U-tubes is filled with brominized hydrochloric acid. After introducing about 10 grm. of the finely divided iron into a and adding a little water, pass hydrogen through the apparatus until the latter is filled with it, force down the greased tube e (which up to now had not dipped into the liquid in 6) through the rubber stopper until it dips into the hydrochloric acid. The pressure of the hydrogen now forces a certain quantity of the 255.] IRON COMPOUNDS, 521 hydrochloric acid into a, and solution of the iron then begins. Now close the pinch-cock / and assist the action of the acid by gently heating. As soon as the evolution of the gas slackens, force a fresh portion of the hydrochloric acid from b into a, as before. When the iron has dissolved, draw up e a little way in its stopper, and pass hydrogen through the liquid in a, heated almost to boiling, in order to expel all the hydrogen sulphide from a. If care has been taken to have sufficient bromine present, no sulphur will separate in the U-tubes, but the oxidation of the sul- phur will be complete. When the operation is at an end, evaporate the brominized hydrochloric acid in a water-bath until almost all the hydrochloric acid has been expelled, dilute the residue with water, and precipitate the sulphuric acid present with barium chloride. As the insoluble residue left on dissolving iron may still con- tain sulphur compounds, collect it on a filter, wash, dry, and fuse it with sodium carbonate and potassium nitrate over an alcohol lamp; take up with water, filter, acidulate the aqueous solution with hydrochloric acid, evaporate on a water-bath, add a few drops hydrochloric acid and water, filter, and add to the solution some barium chloride. If a precipitate forms, collect it on the filter together with the other barium sulphate obtained, dry, ignite, and weigh. It is an essential condition in this determination that the reagents brominized hydrochloric acid, sodium carbonate, potas- sium nitrate, and hydrochloric acid contain no sulphuric acid. If there is any doubt, certain weighed and measured quantities must be tested, and allowance made for any small quantity of sulphuric acid found. Instead of passing the hydrogen containing hydrogen sulphide through brominized hydrochloric acid, the gas may be passed through a solution of lead oxide in potassa solution. In this case collect the separated lead sulphide, dry, oxidize it with fum- ing nitric acid, and evaporate the excess of the acid; the residue, together with that insoluble in the hydrochloric acid, fuse with sodium carbonate and potassium nitrate, moisten with water, 522 DETERMINATION OF COMMERCIAL VALUES. [ 255. and pass in carbon dioxide to precipitate any traces of dissolved lead; then filter, acidulate the nitrate with hydrochloric acid, evaporate on a water-bath, take up the residue with water and a few drops of hydrochloric acid, filter, and precipitate with barium chloride. Of course it will be readily understood that the hydrogen sulphide may be converted into sulphuric acid by other means also. For instance, HAMILTON * employs potassa solution and chlorine, while DROWN f uses a potassium-permanganate solution, the sulphur being in both cases ultimately converted into barium sulphate. ELLIOT J uses caustic-soda solution, and iodometrically determines the sulphide formed ( 148). M. KOPPMAYER pro- poses a solution of iodine in potassium-iodide solution, and determines the residual iodine. HIBSCH || has shown, however, that this last method gives inaccurate results because the hydro- carbons also act on iodine; and the same objection can be made against ELLIOT'S method. b. Methods in which the Iron is Dissolved in such a Manner that all the Sulphur Remains in the Insoluble Residue. a. GINTL'S T method. Introduce about 5 to 10 grm. of the moderately fine iron in a capacious glass flask, and digest it for eight to ten hours at a gentle heat (25 to 30) with about 20 times the quantity of a moderately concentrated solution of ferric chloride as free as possible from excess of acid, the flask being fixed obliquely during the operation. The greater part of the iron is dissolved as ferrous chloride, with a gentle evolution of hydrogen. Dilute, and collect the residue, which contains, besides small quantities of iron, also carbon, graphite, all the sulphur, phosphorus, and nearly all the silicon. * Chem. News, xxi, 147; Zeitschr. /. analyt. Chem., ix, 508. ^Zeitschr. f. analyt. Chem., xm, 343. j Chem. News, xxui, 61; Zeitschr. /. analyt. Chem., xi, 105. DINGL. pol. Journ., ccx, 184. || Ibid., ccxxv, 611; Zeitschr. f. analyt. Chem., xvin, 625. H Zeitschr. f. analyt. Chem., vn, 428. 255.] IRON COMPOUNDS. 523 Wash the residue rapidly, dry, transfer it together with the filter to a porcelain crucible, the bottom of which has been covered with a layer of a mixture of 3 parts potassium nitrate and 1 part caustic potassa (of course both must be free from sulphuric acid), and cover it with a layer of the same mixture. Heat the crucible over an alcohol lamp, at first moderately, then gradually more strongly. After oxidation is complete, lixiviate the cooled fused mass with water, filter, acidulate with hydrochloric acid, and precipitate the sulphuric acid with barium chloride, etc. The results shown by test analyses given by GIXTL do not differ greatly from those obtained by the first method (a). E. RICHTERS* and J. E. HIBSCH f also obtained quite concordant results with both methods. /?. MEINECKE I employs a process very similar to that of GINTL, but, in order to avoid the inconvenient separation of the basic ferric salt, he replaces the ferric-chloride solution by an acid solution of cupric chloride, the action of which may be assisted by gently warming. The separated copper is finally dissolved by adding a solution of sodium chloride in cupric-chloride solution. Then filter, and in the residue, washed first with hot sodium-chloride solution, then with water, determine the sulphur. MEINECKE oxidizes this in the wet way, with nitric acid and potassium chlorate (Vol. I, p. 568); of course this can also be effected by fusing the residue with sodium carbonate and potassium nitrate (Vol. I, p. 562). c. Methods in which the iron and Sulphur are Dissolved by Oxi- dizing Agents, and the Sulphuric Acid precipitated from the Solution by Barium Chloride. None of these methods, whether the iron is dissolved by nitro- hydrochloric acid or bromine, or is converted into ferric chloride by chlorine in the dry way (HIBSCH, loc. cit.) are to be recom- mended, because on precipitating the sulphuric acid from the * DINGL. pol Jaurn., cxcvn, 168; Zeitschr. f. analyt. Chem., x, 370. f DINGL. pol. Journ., ccxxv, 61; Zeitschr. f. analyt. Chem., xvm, 625. i Zeitschr. f. analyt. Chem., x, 280. 524 DETERMINATION OF COMMERCIAL VALUES. [ 255- solutions containing ferric chloride or ferric bromide a little barium sulphate remains dissolved, while on the other hand the barium sulphate obtained contains iron.* 3. DETERMINATION OF THE NITROGEN. Nitrogen, apart from that occluded in the gaseous state (Fr. C. G. MULLER|) occurs in cast iron (steel and wrought iron) in two conditions, according to the researches of Bouis, BOUSSIN- GAULT, FREMY, and ULLGREN.J. In dissolving iron in hydro- chloric acid a portion of the nitrogen is converted into ammonia by the nascent hydrogen, while another part remains in the insol- uble carbonaceous residue. The methods detailed below for determining the nitrogen in each condition are taken from ULL- GREN'S papers, the most recent published on this subject, and in which attention is called to several important points which were formerly overlooked. a. Determination of the Nitrogen which forms Ammonia on Dissolving the Iron in Hydrochloric Acid. a. Dissolve the iron in hydrochloric acid in a flask or tubulated retort, taking care to pass the evolved hydrogen, which carries off a little ammonia, through a U-tube containing a little dilute hydro- chloric acid. When the solution of the iron is complete add the contents of the U-tube to those of the flask, and distill the whole with an excess of calcium hydroxide until about half the liquid has passed over, and then determine the evolved ammonia accord- ing to 99, 3, a. P. Treat about 2 grm. of the finely divided iron in a tubulated retort with a solution of 10 grm. crystallized cupric sulphate and 6 grm. fused sodium chloride. When the iron has dissolved add milk-of-lime and proceed as in a. *Zeitschr. f. analyt. Chem., n, 46 and 439; vn, 429; and xix, 53, f Ber. d. deutsch. Chem. Gesellsch. , xiv, 6. j Zeitschr. f. analyt. Chem. , n, 435. Annal. d. Chem. u. Pharm., cxxiv, 70, and cxxv, 40; Zeitschr. f. analyt Chem., n, 435. 255.] IKON COMPOUNDS. 525 ULLGREN gives preference to the latter method. If there is any neglect as was formerly the case to take note of the ammonia carried off by the hydrogen in the process a, some one-fifth to one- sixth of the whole is lost. b. Determination of the Nitrogen remaining in the Carbonaceous Residue on Dissolving the Iron. If the carbonaceous residue left on dissolving iron in hydro- chloric acid is burned with soda-lime ( 186), as recommended by BOUSSINGATJLT, unsatisfactory results are obtained according to ULLGREN, because graphite requires for its oxidation at the FIG. 111. expense of the water in sodium hydroxide a temperature much higher than that at which ammonia remains undecomposed. On this account it is necessary to separate the nitrogen in the gaseous form. ULLGREN employs for the Combustion mercuric sulphate, and makes use of the apparatus shown in Fig. 111. A is an ordinary combustion tube 30 cm. long, filled up to g with about 12 grm. magnesite or sodium bicarbonate * ; at g an asbestos plug is placed, while the space from g to / is filled with a mixture of about 0-1 * As since the manufacture of ammonia-soda commercial sodium bi- carbonate containing ammonia is frequently met with, it is necessary to carefully test the salt for ammonia before using it. 526 DETERMINATION OF COMMERCIAL VALUES. [ 255. grm. of the carbonaceous residue dried at 130, with about 3 -5 to 4 grm. mercuric oxide as free as possible from mercurous salt, and also the small quantity of the mercuric salt used for rinsing out the agate mortar. Then follow an asbestos plug, and a two-inch layer of coarsely powdered pumice-stone (/ to h) which has been previously mixed with mecuric sulphate and a little water and again dried; lastly a plug of asbestos is inserted. The fore part of the tube is filled with pieces of pumice-stone which have been boiled with a concentrated solution of potassium dichromate and allowed to cool therein. After draining, the pieces are introduced, still moist, into the tube; they serve to absorb sulphurous acid, which they do easily and rapidly. The combustion-tube A is con- nected with the gas-tube a, which dips into a mercurial trough (not shown in the illustration) in which the absorption- and measur- ing-tube B is inverted. The narrower part, d, of the latter is gradu- ated to hold 20 c.c., and must permit reading off to 0-1 c.c. The bulb c holds about 40 c.c., and the lower part of the tube b from 20 c.c. to 30 c.c. The tube is at first filled completely with mer- cury, then sufficient of a solution of 1 part potassium hydroxide in 2 parts water is sent up the tube so that the bulb c is filled to within about 10 c.c. of its capacity, and lastly, 15 c.c. of a clear, saturated tannic-acid solution. The level of the mercury will then be at about e. When the apparatus is in readiness, and that portion of the combustion-tube to be heated has been surrounded with a thin sheet of tinned iron, expel the air from the tube in the usual manner by heating one-half of the sodium bicarbonate in the hinder end, then insert the upturned end of a under B, warm the part g f of the tube, gently at first to expel any moisture deposited, then heat the part / h, containing the pumice-stone impregnated with mercuric sulphate,* and when this is red-hot heat the mixture rapidly to a bright redness, continuing the heat until the evolution of gas ceases and the level of the column of liquid in the measuring- tube ceases to fall; then heat the remainder of the bicarbonate. As soon as the tubes are filled with pure carbon dioxide the height * By employing this layer of pumice-stone the otherwise possible evolu- tion of carbonic oxide is prevented. 255.] IRON COMPOUNDS. 527 of the column of liquid in B remains constant. Now transfer B to a pneumatic trough, allow the mercury and potassa solution to run out and be replaced by water, measure the nitrogen with due regard to barometric and thermometric conditions, and from the volume calculate its weight. 4. DETERMINATION OF THE PHOSPHORUS, OR OF THE PHOSPHORUS, ARSENIC, AND COPPER. In determining the phosphorus the iron must not be dissolved in nitrohydrochloric acid, as was frequently done formerly, because as C. STOCKMANN * has shown, a phosphorus compound volatilizes,f and because the precipitation of phosphoric acid (as ammonium phosphomolybdate) from solutions containing organic matter is not quite complete, and the results are, hence, too low. This makes necessary a considerable alteration in the method of deter- mining phosphorus as described in the fifth (German) edition. Of the methods here described I decidedly prefer the first. First Method. This method (a slight modification of C. STOCKMANN'S loc. tit.) also permits the determination of the arsenic and copper present. Treat about 5 grm. of the comminuted cast iron, in a litre flask in the neck of which a funnel is placed, with 60 c.c. of pure nitric acid (sp. gr. 1-2). Add the acid gradually, and when the frothing ceases, gently heat to boiling until all the iron is dissolved. Now gradually evaporate the contents of the flask, together with the water used in rinsing it out, in a porcelain dish of from 160 c.c. to 200 c.c. capacity, and add about 5 grm. ammonium nitrate toward the end; then transfer the dish to a sand-bath; evaporate to dryness with constant stirring, and strongly heat the contents of the dish over the naked flame so that all the nitrates and organic matter are destroyed. This is greatly facilitated by the addition * Zeitschr. /. analyt. Chem., xvi, 174. f According to the investigations made in my laboratory the quantity of the phosphorus so lost is exceedingly small 528 DETERMINATION OF COMMERCIAL VALUES. [ 255. of the ammonium nitrate, which modification was introduced by me some time ago. Now digest the residue with fuming hydro- chloric acid, employing heat, until all the ferric oxide is dissolved, then dilute, filter, and repeatedly evaporate the solution with nitric acid until the hydrochloric acid is expelled.* Then add ammonium molybdate, and proceed as described in Vol. I, p. 446, /?. As, however, ammonium-magnesium arsenate may be pre- cipitated with the ammonium-magnesium phosphate, dissolve the precipitate, after first washing it with water containing ammo- nia, in a little hydrochloric acid, precipitate with hydrogen sul- phide at 70, filter off the precipitate of arsenic sulphide and some molybdenum sulphide, concentrate the filtrate and washings, and precipitate with ammonia and some magnesia mixture; then add a little more ammonia, and convert the now perfectly pure ammonium- magnesium phosphate into magnesium pyrophos- phate (Vol. I, p. 445). If the arsenic and copper are also to be determined, or if the quan- tity of phosphorus present is very small, modify the process as fol- lows : Largely dilute the solution obtained by digesting the ignited evaporation-residue with hydrochloric acid and filtering; through the solution (to which is also to be added the hydrochloric-acid solution of the substance obtained by fusing with sodium ca bonate the residue insoluble in hydrochloric acid) pass hydrogen sulphide at 70, filter and heat the filtrate until all the hydrogen sulphide has been expelled; then precipitate all the phosphoric acid, to- gether with a small part of the ferric oxide, according to the method given in Vol. I, p. 461, 7- (best with calcium carbonate), dissolve the precipitate in nitric acid, heat to boiling, and then prec'pitate with molybdic-acid solution, etc. Vol. I, p. 446, /?. In the precipitate caused by the hydrogen sulphide, and con- sisting chiefly of sulphur, separate the copper and arsenic accord- * Should the residue not be white it necessitates the precaution to de- compose it by fusion with sodium carbonate, dissolving the melt in nitric acid, separating the silicic acid, and testing the filtrate with ammonium molybdate to ascertain if there is any phosphoric acid present. 255.] IRON COMPOUNDS. 529 ing to 164, after first removing the greater part of the sulphur by means of carbon disulphide. Second Method (by ANDREW A. BLAIR *). First treat about 5 grm. of the iron with nitric acid as in the first method, evaporate the solution to dryness, add 35 c.c. hydro- chloric acid, cover, and heat until the iron is dissolved; then evaporate again to dryness and heat to 120 to 130 until the odor of hydrochloric acid is no longer noticeable; when cold, dissolve in 35 c.c. hydrochloric acid, add 50 c.c. water, and boil for half an hour in order to convert any pyrophosphate that may have formed into orthophosphate ; then evaporate the excess of acid, and filter off the silicic acid and wash it first with diluted hydrochloric acid and then with hot water. Dilute the filtrate to about 400 c.c., add ammonium bisulphite in sufficient quantity to convert the ferric chloride into ferrous chloride, heat to boiling, and nearly neutralize with ammonia (the reduction is not complete in too strongly acid liquids). Now add to the colorless solution 50 c.c. concentrated hydrochloric acid, boil until all the sulphurous acid has been expelled, cool rapidly, and when perfectly cold add ammonia, until on shaking a slight green precipitate forms. Dissolve this in a few drops acetic acid, add 1 or 2 c.c. of a concentrated ammonium-acetate solution and 3 to 5 c.c. diluted acetic acid. Now dilute with hot ater to 750 c.c., and, if the precipitate formed is white, add drop by drop very dilute ferric-chloride solution (about 7 grm. iron in 1000 c.c. liquid) until the precipitate acquires a dull-red color; then heat to boiling, rapidly filter the hot solution, and wash the precipitate with boiling water; now dissolve it in hydrochloric acid, evaporate almost to dryness, add sufficient citric acid to keep all the iron in solution (about 2 to 3 grm.), then add ammonia just to alkalinity, ammonium-magnesium chloride solution, and lastly more ammonia. The quantity of the liquid must not exceed * Zeitschr. /. analyt. Chem., xvm, 122. This method is employed in the experimental station established in the United States for the examination of iron, steel, etc. 530 DETERMINATION OF COMMERCIAL VALUES. [ 255. 20 c.c. to 30 c.c. After 12 hours collect the precipitate by filtration, wash with water containing ammonia, dry, and ignite; then dis- solve the residue in equal parts of hydrochloric acid and water in a platinum crucible, and boil for half an hour in order to con- vert the pyrophosphate into orthophosphate.* Now filter, con- centrate to 20 c.c. or 30 c.c., then add 2 to 3 drops magnesia mix- ture, a little citric acid, and some ammonia, and determine the now pure precipitate ammonium-magnesium phosphate as pyro- phosphate. If the precipitate of ammonium-magnesium phos- phate first obtained is very small, Blair recommends to weigh it after ignition, and then to determine the silicic acid in it and deduct its weight, f Third Method (by F. KESSLER];). Dissolve 5-59 grm. of the sufficiently comminuted iron in a covered porcelain dish in 60 c.c. nitric acid (sp. gr. 1-2), evaporate, finally with stirring over the direct flame, and ignite; transfer so far as possible to a platinum crucible and heat until all the carbon is consumed. Now retransfer the contents of the crucible to the dish and treat with 35 c.c. hydrochloric acid (sp. gr. 1-19). By this treatment the ferric oxide is dissolved while the silicic acid remains. If the latter is not to be determined it need not be fil- tered off, but introduce the ferric-chloride solution with the silicic acid into a flask, add 200 c.c. water, and reduce the iron completely by passing in hydrogen sulphide; then add 200 c.c. of a solution of potassium ferrocyanide (210 grm. of the crystallized salt per litre) and make up the volume to 518 c.c. (The 18 c.c. repre- sent the volume which the voluminous, bright-blue precipitate of potassium ferri- ferrocyanide occupies.) After mixing, filter through a folded filter in a covered funnel; collect the first por- tions passing through, and which are usually turbid, separately, but the clear filtrate collect in a 250-c.c. flask and add 20 c.c. mag- * The conversion js, however, incomplete; compare 74, c. j- According to the investigations made in my laboratory, this method gives results which are too low. $Zeitschr. /. analyt. Chem., xi, 106. 255.] IRON COMPOUNDS. 531 nesia mixture (Vol. I, p. 445). After 12 hours collect the precipi- tate, wash it with ammoniacal water, dissolve in nitric acid of sp. gr. 1-035, filter off the slight insoluble residue of blue ferrocy- anogen compound, precipitate again with ammonia and a little magnesia mixture, and proceed as described hi Vol. I, p. 445, According to the investigations made in my laboratory, this method gives results with iron rich in phosphorus which quite fairly agree with those obtained by the first method; the method, in my opinion, is not so well adapted, however, for irons containing but little phosphorus. Fourth Method (by GINTL*). In this method the phosphorus is determined together with the sulphur (p. 522 this volume). For this purpose treat the fil- trate from the barium sulpha e with sulphuric acid in order to remove any excess of barium, supersaturate the filtrate with am- monia, remove any manganese present with ammonium sulphide, and in the filtrate precipitate the phosphoric acid with magnesia mixture (Vol. I, p. 445). E. RiCHTERsf thus obtained results which agreed to some extent with those obtained by the first method, but yet not sat- isfactorily. I would advise, above all, to test the ferric-chloride solution for phosphoric acid, and would also recommend to dissolve in nitric acid the residue left on treating the fused mass with water, and to test the solution with molybdic solution, as the ferric oxide may retain phosphoric acid. It need scarcely be remarked that the phosphoric acid in the filtrate from the barium sulphate may also be precipitated by molybdic solution (Vol. I, p. 446). * Zeitschr. f. analyt. Chem., vn, 428. t Ibid., x, 370. 532 DETERMINATION OF COMMERCIAL VALUES. [ 255. 5. DETERMINING THE TOTAL AMOUNT OF SILICON, IRON, MANGA- NESE, ZINC, COBALT, NICKEL, CHROMIUM, ALUMINIUM, TITANIUM, AND ALSO THE METALS OF THE ALKALINE EARTHS AND ALKALIES.* a. General Methods. Dissolve 5 to 10 grm. of the cast iron in a covered beaker in moderately dilute hydrochloric acid, rinse the solution into a porcelain dish,t and evaporate to dryness on the water-bath until the mass no longer has an odor of hydrochloric acid; then moisten with hydrochloric acid, warm, add water, and collect the precipi- tate, wash and dry; this we will call a. Divide the solution into two parts, each of which put into a large flask, heat with nitric acid, dilute largely, and precipitate the ferric oxide by nearly saturating with ammonium carbonate and boiling, according to Vol. I, p. 644, 3, a; collect the precipitate, wash somewhat, dis- solve again in hydrochloric acid, and repeat the precipitation as before. Wash the precipitate so obtained with water con- taining ammonium nitrate, and dry; we will call it b. Concentrate the nitrate from b, add ammonia in slight excess, filter after standing a short time, dissolve the precipitate in hydro- chloric acid, and reprecipitate once more in the same way. Then collect the precipitate, wash, and dry; we will call this c. Acidulate the filtrate from c with acetic acid, concentrate it, make alkaline with ammonia, then again add acetic acid until just distinctly acid ; now add ammonium acetate and pass in hydro- gen sulphide at 70. As soon as the precipitate, d, has settled, collect it. Transfer the filtrate from d to a flask, which it should almost fill, make it alkaline with ammonia, add ammonium sulphide, * Comp. LIPPERT, Beitrdge zur Analyse des Roheisens, Zeitschr. /. analyt. Chem., n, 39. f If it is desired to determine the silicon and aluminium as accurately as possible, the solution of the iron and the evaporation must be effected in a platinum dish ; but in this case the solution may readily take up some plat- inum, whereby the separation and determination of the other metals is rendered considerably more difficult. 255.] IRON COMPOUNDS. 533 stopper loosely, and allow to stand for twenty-four hours in a warm place. The precipitate (manganese sulphide) is e. Evaporate the liquid separated from the manganese sulphide to dryness in a platinum dish, drive off the ammonia salts, take up the residue with water and hydrochloric acid, filter, and pre- cipitate any calcium present with ammonium oxalate; then precipitate any magnesium with ammonium phosphate, and lastly, after the phosphoric acid has been removed, determine any potassium or sodium should these be present (compare 154, 6, and 153, 4, &*). We now proceed to the further examination of the precipitates a to e. The residue a contains the whole of the substances insoluble or difficultly soluble in hydrochloric acid. Besides carbon, silicic acid and leukon, there may be present also iron phosphide, chro- mium iron, vanadium iron, iron arsenide, iron carbide, silicon (?),t molybdenum, etc., and also the slag in a more or less altered con- dition. Titanic acid also may be found in the residue. Fuse the latter with sodium-potassium carbonate and a little potassium nitrate, separate the silicic acid as usual by evaporating with hydrochloric acid, weigh and test it as to its purity (comp. Vol. I, p. 511), and specially for titanic acid. The silicic acid may have been formed partly from the silicon, or have been present partly as such in the slag. In the filtrate from the silicic acid separate by double precipitation any matter precipitable by ammonia and collect the precipitate cf ; acidulate the filtrate weakly with acetic acid, add ammonium acetate, and pass in hydrogen sulphide at 70 to obtain the precipitate d' ', which is then collected; in the filtrate from this throw down the precipitate e* by ammonium sulphide, and lastly test the filtrate for alkaline earths; any small * It is obvious that the determination of the alkalies is of value only when care has been taken to ascertain if the ammonia and ammonia cal salts used are free from fixed alkalies, and when all the operations have been carried out in platinum dishes. See my paper in Zettschr. /. analyt. Chem., iv, 69. f Compare TOSH, Zeitschr. /. analyt. Chem., v, 430. 534 DETERMINATION OF COMMERCIAL VALUES. [ 255. quantities of these that may be present can be weighed together with the somewhat larger quantity obtained above. The precipitates b, c, and c 1 contain all the ferric oxide and alumina and those portions of the silicic and titanic acids that have passed into solution. Transfer the mixed, ignited precipi- tates to several porcelain boats, insert these in a porcelain tube, and subject them to prolonged ignition in a current of pure hydro- gen until no more aqueous vapor forms. Treat the boats con- taining the reduced iron with very dilute nitric acid to dissolve the iron (Vol. I, p. 652 [91]), make up the volume of the solution to 1000 c.c., and in a measured portion determine the iron by add- ing first tartaric acid and then ammonia and ammonium sulphide, and finally converting the ferrous sulphide into ferric oxide ( 113, 1, b *). The residue insoluble in very dilute nitric acid fuse with potassium disulphate, take up with cold water, filter off any in- soluble residual silicic acid (which is to be added to that found above) and pass in hydrogen sulphide, precipitate any titanic acid present by boiling while passing in a current of carbon dioxide ( 107), filter, boil the filtrate, or the solution if that has remained clear, with nitric acid, and precipitate the alumina by adding ammonia, and separate it from any slight admixed ferric oxide by the method described on p. 247 this volume. Here too, as before, regard must be paid to any phosphoric acid, for if this is present in the alumina the weight of the latter would of course be too high. Were any chromium present, its oxide too would have to be separated in this precipitate and determined. The precipitates d and d' contain, or may contain, the sul- phides of copper, cobalt, nickel, and zinc. Dissolve the precipi- tates in brominized hydrochloric acid, heat until the excess of bromine has been expelled, precipitate the copper with hydro- gen sulphide, and in the filtrate separate and determine the co- balt, nickel, and zinc according to 160. The precipitates e and e' consist of manganese sulphide. Treat * It is advisable to determine the iron in a separately weighed smaller quantity only when the iron to be examined is perfectly homogeneous. 255.] IRON COMPOUNDS. 535 them according to 109, 2, and finally test the weighed man- ganese sulphide as to its purity. 6. Special Methods. a. For Determining the Total Silicon. aa. If the phosphoric acid is determined according to 4 (first or third method), the residue insoluble in hydrochloric acid con- tains all the silicon as silicic acid. The latter can be determined by fusing it with sodium carbonate and a little potassium nitrate and proceeding according to the usual methods. bb. THOMAS M. DROWN and PORTER W. SHIMER * recommend, for the determination of the total silicon, to treat the cast iron with nitric acid until everything soluble has dissolved, then to evaporate with sulphuric acid until the nitric acid has been ah 1 or very nearly all driven off. Then dilute, collect the residue consisting of silicic acid and carbon, wash it with water first, then with hy- drochloric acid, and finally with hot water, dry, ignite with access of air, and weigh the residual silicic acid. So obtained, it is free from titanic acid. In another very rapid method recommended by the same authors f it is recommended to fuse the iron with twenty-five times its quantity of potassium disulphate in a very capacious platinum crucible, treat the melt with water, and to treat the insoluble residue of silicic acid with hydrochloric acid and water. This method gives with many kinds of iron very serviceable re- sults, but with others it gives results that are too low, hence it is suitable only for approximate determinations when these have to be very rapidly made. /?. Determining Titanium. To determine titanium, TH. M. DROWN and PORTER W. SHIMER J heat the iron in a porcelain boat in a glass tube in a current of pure, dry chlorine. The glass tube must be sufficiently long to receive all * Transactions of the American Institute of Mining Engineers, vii, 346. f Ibid., vin. t Ibid., vin. 536 DETERMINATION OF COMMERCIAL VALUES. [ 255. the volatilized ferric chloride, and its exit end must be connected with three U-tubes containing water. These tubes retain the volatilized silicon and titanium chlorides. When the operation is at an end, transfer the contents of the tubes to a porcelain dish, acidulate strongly with hydrochloric acid, add 15 c.c. sulphuric acid of sp. gr. 1-23, and evaporate until all the hydrochloric acid has been driven off. Now collect the separated silicic acid, and in the filtrate, diluted with water, precipitate the titanic acid by boiling ( 107). The silicon determinations made under these conditions usually afforded results that were too low. f. Determining the Iron. The iron content of cast iron may, of course, be also deter- mined volumetrically, best by dissolving about 10 grm. in the manner described on p. 527, 4, this volume (First Method). The solution then contains all the iron as ferric chloride. Should it contain free chlorine, remove this by evaporating the solution, then make up to 1 litre, and in 50 c.c. of this determine the iron with stannous chloride according to Vol. I, p. 327. A variation of this latter method has been recommended by KESSLER.* In this stannous chloride is first added until all the ferric chloride has been converted into ferrous chloride, then an excess of mercuric chloride to convert the excess of stannous chloride into stannic chloride, then standard potassium-dichromate solution until a drop test with potassium ferricyanide no longer gives the ferrocy- anide reaction, and lastly a subsidiary ferrous-chloride solution until the ferro-ferricyanide reaction is just observable. On de- ducting the quantity of dichromate corresponding to the ferrous chloride used from the total dichromate, we find the quantity rquired to convert the ferrous chloride yielded by the cast iron into ferric chloride, and from this the quantity of iron can then be calculated (Vol. I, p. 319, 6). If the cast iron contains notable quantities of arsenic or copper, the volumetric methods above mentioned do not afford very * Zeitschr. /. analyt. Chem., xi, 249. 255.] IRON COMPOUNDS. 537 accurate results. In such cases KESSLER advises the following method : Precipitate the hydrochloric-acid solution with hydrogen sulphide at 70, filter, and boil the filtrate while passing in carbon dioxide in order to expel the greater part of the hydrogen sul- phide; remove the last portions of the gas as mercury chloro- sulphide by adding an excess of mercuric chloride, and then titrate direct with potassium dichromate without filtering off the pre- cipitate. d. Determining the Manganese. As a relatively rapid method of determining manganese in cast iron is of importance in iron manufacture, a number of methods have been recommended for effecting this object volumetrically. The most important of these are the following : aa. F. KESSLER'S Method* This is based (a) upon the precipitation of the iron as basic ferric sulphate, which is thus separated from manganese; and (6) upon the fact that on adding bromine water to a manganous- chloride solution to which zinc chloride and sodium acetate have been added, and then heating, all the manganese is precipitated as peroxide, together with zinc oxide. The requisites for the method are: A saturated aqueous solution of bromine; a solution of 100 grin, crystallized sodium carbonate in sufficient water to make 1 litre; a. solution of 100 grm. crystallized sodium sulphate in water to make 1 litre; a solution of sodium acetate containing 500 grm. crystallized salt per litre; a dilute solution of sodium acetate (20 c.c. of the preceding solution diluted to 1 litre) ; a solution of zinc chloride (200 grm. zinc, but no free hydrochloric acid, per litre); a solution of antimony chloride (15 grm. anti- monic oxide and 300 c.c. hydrochloric acid of sp. gr. 1-19 dissolved in water to make 1 litre); and a solution of 3-3 grm. potassium permanganate in water to make 1 litre. Dissolve a suitable quantity of the iron in the manner described * Zeitschr. f. analyt. Chem., xvm, 1. 538 DETERMINATION OF COMMERCIAL VALUES. [ 255. on p. 530 this volume (Third Method) ; the liquid will then be free from organic substances, and will contain all the iron as ferric chloride, and all the manganese as manganous chloride. Dilute the solution to about 100 c.c. in a flask, and while being kept rapidly rotating, run in from a burette the sodium-carbonate solution until the precipitate formed ceases to redissolve. The stream of liquid run in must not be directed against the sides of the vessel, but on the peripheral part of the solution. Then run in from another burette, cautiously, and drop by drop, hydro- chloric acid of sp. gr. 1-01 until the liquid becomes just, but com- pletely, clear, and this in not too short a time and after frequent stirring. Now dilute, add 15 c.c. of the sodium-sulphate solution for every 1 grm. of iron, fill up to the mark, mix, and filter through a folded dry filter into a dry flask, keeping the funnel covered. Now measure off a volume of the filtrate containing at most 0-11 grm. manganese, concentrate it if necessary to 100 c.c., and add this to a mixture of 100 c.c. bromine water, 50 c.c. of the zinc-chloride solution, and 20 c.c. of the sodium-acetate solution contained in a flask. The addition should be made in five equal portions, and at intervals of fifteen minutes each. Next add a further 20 c.c. of sodium-acetate solution, and heat to boiling until the odor of bromine has entirely disappeared and the liquid containing the precipitate in suspension has become perfectly colorless. Collect the precipitate, wash it with the dilute sodium-acetate solution, and finally replace it, together with the filter, in the pre- cipitation vessel. Now add antimony-chloride solution in quan- tities of 5 c.c. to the precipitate until, after sufficiently stirring in the cold, the residue of the precipitate is no longer black, but brown or light-brown, then add 25 c.c. hydrochloric acid, wash the solution into a beaker as soon as the precipitate is completely dissolved, and run in from a burette potassium permanganate until a reddish color supervenes and persists for at least six seconds. On now titrating an equal quantity of antimony chloride under similar conditions with potassium permanganate, the difference will give the potassium permanganate equivalent in oxidizing 255.] IRON COMPOUNDS. 539 effect to the manganese dioxide present in the precipitate (2 eq. KlLnO 4 = 5MnO 2 ). The quantity of manganese that was present may thus be easily calculated. If the potassium-permanganate Solution has been standardized against iron (Vol. I, p. 313), 10 eq. of iron (559) will be the equivalent of 2 eq. of potassium per- manganate (KMnO 4 = 316-22) or 5 eq. of manganese dioxide (435) containing 5 eq. of manganese (275). TYESSLER, however, prefers to standardize the permanganate solution exactly as above de- scribed, by aid of a manganese solution of known strength and prepared by dissolving a weighed quantity of manganous pyro- phosphate * in hydrochloric acid. The test analyses cited by KESSLER are very satisfactory. bb. VOLHARD'S Method.^ This is based upon the separation of ferric oxide from manga- nous oxide by zinc oxide, and upon the volumetric determination of the manganous oxide in the filtrate with potassium perman- ganate. Regarding the latter method of determination (comp. Vol. 1, p. 300, 6), VOLHARD has shown that the precipitate thrown down by potassium permanganate in a hot, dilute solution of manganous sulphate or chloride is never pure hydrated manga- nese dioxide, but that it always contains some manganous oxide. If, however, a salt of zinc, calcium, or magnesium is added to the solution, the precipitate will contain all the manganese as dioxide along with zinc oxide, lime, or magnesia. The following equation shows the reaction: 3MnS0 4 + 2KMnO 4 + 7H 2 O = 5MnO 2 H 2 O + KjSO, + 2H 2 SO 4 . * To prepare the manganous pyrophosphate mix a solution of 40 gnn. crystallized manganous sulphate with one of 60 grm. crystallized sodium phosphate, add hydrochloric acid until the precipitate has dissolved, and then add ammonia to alkalinity. Add hydrochloric acid again to clarify the liquid, filter if necessary, dilute to about 1 litre, precipitate with ammo- nia, wash the precipitate by decantation until the washings no longer react for chlorides; then dissolve in dilute nitric acid with the addition of a little sulphurous acid, supersaturate with ammonia, clear the liquid again with nitric acid, reprecipitate with ammonia, wash the precipitate repeatedly by decantation, dry, and ignite. f Annal. d, Chem., cxcvm, 318 to 354. 540 DETERMINATION OF COMMERCIAL VALUES. [ 255. Dissolve a suitable quantity of cast iron, containing say 0-3 to 0-5 grm. manganese, in nitric acid in a flask, evaporate to dryness in a porcelain dish, adding toward the end a little ammo- nium nitrate, heat finally over the naked flame until all the nitrate has been decomposed and the carbon consumed, and digest with hydrochloric acid; now add cautiously a sufficient quantity of concentrated sulphuric acid, and evaporate, first on the water- bath, then on a gas-stove, until the sulphuric acid begins to pass off in fumes. Next rinse into a litre flask, neutralize the free acid with sodium carbonate or caustic soda free from manganese, and then add sufficient zinc oxide suspended in water* until all the iron is precipitated, i.e., until the gradually darkening brown-red solution suddenly coagulates and the supernatant liquid becomes milky. Now fill with water up to the mark, mix, allow to settle for a while, and filter through a dry, folded filter into a dry flask. Of the filtrate acidulate 200 c.c. in a flask with 2 to 4 drops nitric acid, and heat to boiling; then remove the source of heat and run in potassium-permanganate solution (containing about 3-8 grm. per litre) until the liquid becomes just permanently reddened. The titration should be repeated with another 200 c.c. of the filtrate. If the permanganate solution has been standardized against iron, as in Vol. I, p. 313, it must be noted that 1 eq. of permanganic anhydride, (Mn 2 O 7 ), converts 10 eq. of iron from a ferrous to a ferric state, while 3 eq. of manganous manganese is converted into 5 eq. of manganic manganese, thus: Mn 2 O 7 +10 FeO = 5Fe 2 O 3 + 2MnO ; and Mn 2 7 + 3 MnO = 5MnO 2 . *VOLHARD employs commercial zinc white. This is strongly heated for some time in a Hessian crucible, with stirring, and then elutriated with water. A test must be made of a small sample from near the lowermost part of the deposit to make certain that it contains no small particles of metallic zinc. The test is made by dissolving in diluted sulphuric acid colored by a drop of potassium-permanganate solution. The color must not disappear even on warming. The zinc oxide is kept mixed with water ready for use. 255.] IRON COMPOUNDS. 541 Hence 559 of ferrous iron correspond to 165 of manganous manganese. The manganese standard is therefore obtained from the iron standard by multiplying by Jf| = 0-29517. Of course the standard of the potassium-permanganate solution may also be established by means of a manganese solution of known strength, or, as VOLHARD prefers, iodometrically (see loc. cit., p. 333) . The test analyses given by VOLHARD are very satisfactory. cc. JOHN PATTTNSON'S Method* This is based upon the following fact: On adding chlorinated- lime solution or bromine water to a manganous-chloride solution containing a sufficient quantity of ferric chloride, heating to from 60 to 70, and then adding an excess of calcium carbonate, all the manganese is thrown down as dioxide in the precipitate. It is sufficient if the solution contains half as much iron as manganese, but equal quantities are preferable ; an excess of iron is not pre ju- dicial. The dioxide is determined by treating the precipitate with an excess of an acid solution of ferrous sulphate and then deter- mining the excess of the latter. The following equation shows the reaction: MnO 2 + 2FeSO 4 + 2H 2 SO 4 = Fe^SO^ + MnS0 4 + 2H 2 O. For carrying out the process there are required: Chlorinated- lime solution (15 grm. good chlorinated lime per litre), the clear liquid obtained by subsidence being used; calcium carbonate (ob- tained by precipitating calcium- chloride solution with sodium carbonate at 80) ; acid ferrous-sulphate solution, containing about 10 grm. iron per litre (dissolve 53 grm. ferrous sulphate in a mixture of one part sulphuric acid and 3 parts water to make one litre); a solution of potassium dichromate (see Vol. I, p. 319, b) containing exactly 14-721 grm. per litre. 1000 c.c. of this solu- tion have the same oxidizing action on ferrous iron as 26-1 grm. manganese dioxide, and correspond with 16-5 grm. manganese. * Journ. Chem. Soc., 1879, p. 365; Zetischr. /. analyt. Chem., xix, 346. 542 DETERMINATION OF COMMERCIAL VALUES. [ 255. Dissolve a quantity of cast iron containing about 0-1 to 0-15 gnn. of manganese in hydrochloric acid free from organic matter (comp. p. 539, bb, this volume), add calcium carbonate until the liquid acquires a deep-red color, then acidulate again with a few drops hydrochloric acid, add about 60 c.c. of the chlorinated- lime solution, then hot water until the temperature is about 60 to 70, and lastly about 1-5 gnn. calcium carbonate. Now stir until carbon dioxide is no longer evolved, and then allow to settle. If the liquid above the dark-brown precipitate (which soon settles) exhibits a reddish color from the presence of permanganic acid, add a few drops alcohol until decolorization is effected. Collect the precipitate on a filter and wash \vith warm-water until the washings cease to react for chlorine when tested with potassium- iodide-starch paper (p. 379 this volume). Now replace the pre- cipitate with the filter in the beaker in which the precipitation was effected f and* to the sides of which some of the precipitate usually still adheres) and in which an accurately measured volume of the acid ferrous-sulphate solution (say 50 c.c. to 60 c.c.) has been poured. The precipitate rapidly dissolves. Dilute with cold water if necessary, and titrate the excess of ferrous sulphate with potassium-dichromate solution (Vol. I, p. 319). In order to accurately ascertain the relation of the ferrous-sulphate solu- tion to the potassium-dichromate solution a quantity equal to that employed must be titrated with the dichromate solution, first placing in the liquid a filter * identical with the one used. Lead, copper, nickel, or cobalt must be absent from the liquid being titrated , or may be present at most in traces only. The calculation is most simply made as follows: Deduct from the number of c.c. of dichromate solution corresponding with the ferrous-sulphate solution added, the number of c.c. corresponding to the residual ferrous oxide. The difference indicates the quantity of dichn> mate solution equivalent in oxidizing action to the manganese * PATTINSON considers this precaution necessary, as, according to his investigations, certain filter-papers exert a slightly reducing action, which is thus eliminated. 255.] IRON COMPOUNDS. 543 dioxide present, and the quantity of manganese is hence given (see above) by the equation: 1000 : 16-5 :: the difference in question : x. The test analyses given by PATTINSON are very satisfactory.* e. Determining the Chromium and Aluminium, a. ANDREW A. BLAIR'S Method^ (greatly modified). Over 5 grm. iron in a 500-c.c. flask pour 20 c.c. of strong hydro- chloric acid diluted with 3 to 4 times its volume of water, and close the flask with a rubber stopper provided with a valve opening outwards.J When the iron is all dissolved, replace the valved stopper by another, allow to cool, add water until the flask is three-fourths filled, and then introduce pure barium carbonate until it is present in excess, occasionally lifting the stopper. After twelve hours coll ct the precipitate, which will now surely con- tain all the chromium and aluminium, and wash with cold water. Now fuse it with sodium carbonate and potassium nitrate, treat the melt with water and hydrochloric acid, separate the silicic acid, precipitate the hydrochloric acid with ammonia, filter off the precipitate, consisting of iron, aluminium, and chromium oxides, and in it determine the chromium and aluminium according to Vol. I, p. 642, 2 [77]- b. Determining Chromium according to ROD. SCHOFFEL. If the iron (or chrome-iron alloy) contains not more than eight per cent, of chromium, dissolve it in ammonio-cupric chloride solution (p. 502, a, aa, this volume), filter, and fuse with sodium carbonate and potassium nitrate the residue which contains all the * Other methods of determining manganese in cast iron have been given by THOM. M. CHATARD (Zeitschr. /. analyt. Chem., xi, 308); CLASSEN (Ibid., xviii, 175); C. ROSSLER (Ibid., xix, 75); F. BEILSTEIN and L. JA\YEIN (Ibid., xix, 77); and others. ^'Amer. Journ. of Science and Arts, cxin, 421; Zeitschr. /. analyt. Chem., xx, 138. + The solution may also be effected in a*, atmosphere of carbon dioxide, of course. Ber. d. deutsch. chem. Gesellsch., xn, 1863. 544 DETERMINATION OF COMMERCIAL VALUES. [ 255. chromium. Digest the melt with water until the residue appears to be pulverulent, whereby any manganic acid formed will be de- composed, and then filter. If the solution contains but very little silicic acid, it may be very carefully and accurately neutralized with nitric acid, and the chromic acid precipitated as mercurous chromate (Vol. I, p. 423, a, /?) ; if, however, much silicic acid is pres- ent, evaporate the solution with hydrochloric acid with the addition of a little alcohol, separate the silicic acid, and in the filtrate pre- cipitate the chromium as chromic hydroxide (Vol. I, p. 281, 1, a). After weighing, test the chromic oxide as to its freedom from alu- mina; if this is present determine it and make the proper allow- ance. If the chrome-iron alloy contains more than eight per cent, chromium, the iron will not be sufficiently dissolved by treatment with ammonio-cupric chloride. In such cases dissolve in hydro- chloric acid, filter, fuse the residue with sodium carbonate and potassium nitrate, dissolve the melt in water and hydrochloric acid, and unite the solutions. Neutralize them nearly, and add to the still distinctly acid liquid sodium acetate in sufficient excess to insure the presence only of free acetic acid ; no precipitate should be formed. Now add an excess of bromine, allow to stand in a stop- pered flask for several hours with frequent shaking, then boil until the excess of bromine has been driven off, add sodium carbonate until all the ferric oxide is precipitated, and filter. All the chromium is now in the filtrate as alkali chromate, and is then determined as described above. 6. DETERMINING THE METALS OF THE FIFTH AND SIXTH GROUPS. As will have been seen above, the determination of the copper and arsenic may be made conjointly with that of the phosphorus (comp. p. 527 this volume;. If, however, there are other metals of the fifth and sixth groups present also, or if the quantity of the arsenic or copper is so small that it cannot be readily determined in 5 grm. iron, a separate and larger portion of cast iron (about 20 grm.) must be employed for the determination of the metals of 255.] IRON COMPOUNDS. 545 the fifth and sixth groups. Dissolve the iron in nitric acid, add 32 c.c. pure sulphuric acid, evaporate until all the nitric acid has been driven off, dilute, and filter. Fuse the insoluble residue with some sodium carbonate and potassium nitrate, take up the melt with water, add sulphuric acid, evaporate until all the nitric acid has been expelled, dilute, filter, unite both sulphuric-acid solu- tions, boil with ammonium bisulphite until the greater part of the ferric oxide is reduced, and precipitate with hydrogen sul- phide at 70; if necessary, free the precipitate from sulphur by treatment with carbon disulphide, and in the insoluble residue determine the copper, arsenic, and any other metals of the fifth and sixth groups that may be present, according to 164 and 165. 7. DETERMINING TUNGSTEN. As tungsten, if present, cannot be determined in the manner detailed above in 6, a separate portion of iron must be taken. HUD. SCHOFFEL* recommends one of the following methods: a. Treat .the very finely divided iron, or tungsten-iron alloy, with ammonio-cupric chloride (p. 502, a, aa, this vol.), filter, fuse the residue with sodium carbonate, dissolve in water, filter, nearly neutralize with nitric acid, precipitate with mefcurous nitrate, filter, dry, ignite, and weigh the residual tungstic acid containing silicic acid; fuse this residue with potassium disulphate, treat the melt with water, determine the residual silica, and deduct this from the weight first obtained. If chromium is also present the tungstic acid contains chromic oxide also, and the two must there- fore be separated. 6. Treat the iron or alloy in very finely divided form with nitrohydrochloric acid until all reaction ceases, dilute, and let stand for a day or two. All the tungsten, including that originally dis- solved, will now be found in the insoluble residue. Collect this, dry, ignite first with access of air, then fuse with sodium carbon- ate, and proceed further as in a. *Berichtts der deutschen chem. GeseUschaft, xii, 1866. 546 DETERMINATION OF COMMERCIAL VALUES. [ 255. 8. DETERMINING VANADIUM. Should an iron contain vanadium, as may perchance happen, the determination of this is effected by treating a large quantity of the iron with diluted sulphuric acid until all reaction ceases; then filter, dry the residue, fuse it with 1 part sodium carbonate and 2 parts potassium nitrate, extract with water, and in the melt determine the vanadium according to p. 492, 15, this volume. 9. DETERMINATION OF THE SLAG CONTAINED IN IRON; OR THE SILICON, ALUMINIUM, AND THE METALS OF THE ALKALINE EARTHS COMBINED AS SUCH WITH THE IRON. Cast iron not infrequently contains a small quantity of slag. The determination of this, as well as of its constituents, is not without value, as only after a knowledge of these is acquired, can it be decided what part of the silicon, aluminium, calcium, mag- nesium, potassium, etc., is present in the metallic iron. The methods above detailed give the total amount of the elements, but the analysis of the adhering slag gives the proportions present in oxidized condition; and the difference gives the quantities present combined with the metallic iron. For the determination of the slag and its constituents the following methods are employed : a. Heating the Iron in a current of Chlorine* Heat a weighed quantity (about 5 grm.) of the powdered iron in a porcelain boat inserted in a glass tube, in a current of per- fectly dry chlorine free from air and hydrochloric acid. This is effected by first driving out the air from the apparatus by means of carbon dioxide before beginning the operation, and then passing through chlorine gas which has been first passed through a U-tube filled with fragments of manganese dioxide, and then through a sulphuric-acid apparatus. The heating is continued until no more ferric chloride, or chlorides of silicon, sulphur, phosphorus, etc., volatilize. To prevent any stoppage of the apparatus and any in- * See my memoir "Beitrage zur Analyse des Roheisens," Zeitschr. analyt. Chem., iv, 72. 255.] IRON COMPOUNDS. 547 convenience from the excess of chlorine, the glass tube used should be sufficiently long to contain all the ferric chloride, and its exit end should be connected by means of a rubber tube and glass tube with a carboy containing calcium hydroxide. When cold, treat the contents of the boat with water to remove all the soluble matter (manganous chloride, calcium chloride, etc.), dry the resi- due, and ignite in a* current of oxygen to consume all the graphite present. Now ignite again, for the sake of greater certainty, first in a current of hydrogen, then again in chlorine, extract again with water, heat, if necessary, once more in oxygen, weigh the residual slag, and then determine its constituents. If the slag obtained with the cast iron is available, it is preferable to analyze this, de- termining the silicic acid in the residual slag from the iron, and from this, by comparison with the slag analysis, determining the other slag constituents. The reason why this method is to be prefered is because the slag may be attacked to some extent by pure, dry, chlorine, so that in fact water will extract appreciable quantities of calcium chloride, etc. The slag residue then no longer contains all the lime, etc., that was in the slag, but all the silicic acid is left. b. Treating the Iron with Solvents. It may be readily seen that the solvents must be so chosen that the iron will be dissolved, but that the slag, will be not at- tacked at all, or only as little as possible. The following solvents may be employed: Very dilute hydrochloric acid aided by a galvanic current*; iodine or bromine in the presence of water f ; or, mercuric-chloride solution, t The residue left after the iron is dissolved contains, or may contain, the combined carbon, graphite, silicic acid, leukon, slag, etc. It is now necessary, if the first mentioned solvent has been used, to burn off the combined carbon and graphite first, but by this procedure silicic acid may be introduced into the slag * LIPPERT, Zeitschr. f. analyt. Chem., n, 48. t V. EGGERTZ, Ibid., vn, 500. J H. ROSE, Handb. d. analyt. Chem., 6th ed., by R. FINKENER, n, 757. 548 DETERMINATION OF COMMERCIAL VALUES. [ 255. (EGGERTZ, loc. tit., p. 501). It is hence preferable to first remove the silicic acid and the leukon by heating the residue with a satu- rated solution of pure sodium- carbonate. Then wash the residue, and burn off the carbon. In order now to remove the last traces of ferric oxide it is only necessary to ignite first in a current of hydrogen, and then in chlorine. Extract the residue with water, then heat again with a solution of sodium carbonate, wash again with water, and weigh. If mercuric-chloride solution was used as the solvent, the residue must be washed, and then treated with chlorine water free from hydrochloric acid, or with bromine water, to remove the mercurous chloride formed. It therefore follows that the methods described under b are in nowise simpler, while in fact less accurate, than the methods detailed under a, hence the latter are to be preferred. II. STEEL AND WROUGHT IRON. Steel and also wrought iron contain essentially the same con- stituents as cast iron, but, as a rule, far smaller quantities of those elements which are combined with the iron. Thus the total carbon in steel varies between 2 and 0-65 per cent., and in wrought iron between 0-6 and 0-016 per cent.; the maximum of silicon in steel as well as in wrought iron is about 0-6 per cent., etc. The following are the elements usually quantitatively determined in both: Carbon (chemically combined, and also mechanically admixed, if this is present), silicon, sulphur, phosphorus, man- ganese, and copper. If a large quantity of wrought iron or steel is operated upon, other elements also present, as nickel, cobalt, arsenic, tungsten, etc., may be quantitatively determined. Although the methods are, on the whole, identical with those used in cast iron, it is desirable to add a few supplementary re- marks. 1. DETERMINING THE CARBON. a. If unhardened steel is dissolved slowly and without warm- ing, in diluted hydrochloric or sulphuric acid, a carbonaceous resi- 255.] IRON COMPOUNDS. 549 due remains (CARON,* RINMANN f), whereas the same unhardened steel gives no carbonaceous residue when dissolved with heat in hydrochloric acid of sp. gr. 1 12, and, the solution when com- plete boiled for half an hour longer. When hardened, the same steel yields no residue when dissolved in cold diluted acid; the carbon in the carbonaceous residue mentioned cannot, hence, be graphite. RINMANN terms it "cementkohle" (cement car- bon). DEBRUNNER J arrived at the same conclusion, i.e. that in steel, and in various kinds of iron generally, the carbon may be present in a third form, differing from combined carbon or graphite. He found, namely, that on dissolving cast steel (crucible or Bes- semer steel) in nitric acid of sp. gr. 1 2, there forms in the liquid a brown, flocculent precipitate which disappears on heating. On similarly treating welding-steel (puddle-steel or cementation-steel) however, a black velvety powder separates, which, while re- sembling graphite in appearance, completely dissolves on heat- ing. The carbon thus obtained from welding-steel DEBRUNNER terms semi-combined carbon, and he utilizes the different be- havior of steels on solution in nitric acid as a means of differenti- ating them. I call attention to these later investigations in order to point out that it must not be assumed, without further inquiry, that the carbon which remains on dissolving steel or wrought iron in cold dilute hydrochloric (or even nitric) acid, is graphite. A carbon may rather be considered to be graphite only when on rapidly dissolving an iron in hot hydrochloric acid the carbon separates, and cannot be dissolved by continued boiling, or by subsequent treatment with alkali and with alcohol. Whether the quantity of the so-called "cement carbon" (semi-combined carbon) may be accurately determined by dissolving the steel or wrought iron in cold dilute hydrochloric acid, whereby it is left undissolved with the graphite, requires further comprehensive investigation. * Compt. rend., 1863. f Zeitschr. f. analyt. Chem., iv, 159, and vn, 499. t Iron, xii, 775; DINGL. polyt. Jvurn., ccxxxi, 475; Zeitschr. f. analyt. Chem., xvm, 624. 550 DETERMINATION OF COMMERCIAL VALUES. [ 255. b. To determine the total carbon in steel and wrought iron the method most frequently employed is to treat with copper salts (pp. 502 to 505, this volume), and convert the separated carbon into carbon dioxide by combustion in a current of oxygen or by means of chromic acid (pp. 510 to 515, this volume). As the car- bon content is considerably smaller than in the case of cast iron, 5 to 10 grm. should be operated upon. c. If WEYL'S method (pp. 505 to 507, this volume) is used for dissolving the steel or wrought iron, the modification described on p. 507, and the apparatus shown in Fig. 107, must be employed, otherwise the results obtained will be too low, because of the reasons given on p. 506. Compare RINMANN,* SCHNITZLER,! and WEYL.J d. EGGERTZ' colorimetric method (p. 519, d, this volume) of approximately determining the combined carbon is excellently adapted for use in steel works where similar raw materials are constantly being worked, and the steel obtained varies practically only in the amount of carbon it contains. The method has been variously modified; compare GRUNER, J. B. BRITTON,|| and MORRELL^ [e. Carbon may also be determined in steel by direct combus- tion in oxygen. Although this simple method was formerly decried as uncertain and yielding too low results, it has been recently shown that it is reliable if the necessary conditions are adhered to. LAWRENCE DUFTY ** states that if the drillings used be sufficiently thin, the process gives perfectly accurate results, and a carbon determination can be made in the remarkably short time of forty minutes or less from time of receipt of sample. Thin curly drillings may be simply placed in a boat and burnt in oxygen without any reagent. As a general rule, however, especially if * Zeitschr. f. analyt. Chem., in, 336. t IUd., iv, 78. t Ibid., iv, 157. Berg- und Huttenmdnn Ztg., 1869, 52. || Chem. News, xxn, 101; Zeitschr. f. analyt. Chem., x, 245. IF Amer. Chemist, v, 365; Zeitschr. f. analyt. Chem., xvr, 305. ** Chem. News, LXXXVII, 289. 255.] IRON COMPOUNDS. 551 the drillings are very small or inclined to be powdery, it is necessary to mix with some material which will separate the particles and, if possible, assist hi the oxidation of the sample without fusing to a liquid mass, as is the case when using the oxides of lead or bismuth, as recommended by BREARLEY* and LEFFLER-)-. ROZYETTI used AljOg, RHEAD and SEXTON ("Assaying and Metallurgical Analysis") suggest MgO, whilst BREARLEY and IBBOTSON ("Analysis of Steel Works Materials") find ZnO satis- factory for certain alloys; other oxides suggested are SiO 2 , CaO, SnO 2 , Mn 3 O 4 , etc. The method adopted by DUFTY was as follows: 2 727 grm. of drillings (not exceeding 5 mm. in thickness for hard, and 0-25 mm. for mild steels), or 1-3636 grm. of pig iron (gray pig is powdered until it all passes through a sieve 40 meshes to the inch), are mixed with 0-5 grm. of freshly ignited MgO by shaking in a weighing bottle, and then transferring to a boat con- taining a layer of MgO a further portion of the oxide being spread over the top to cover any drillings exposed. (If the mag- nesia gives any "blank," a definite quantity must always be used and the blank deducted.) Having placed the boat in the red-hot tube, the aspirator is set working, and at the end of a few minutes sufficient time being given for the boat to attain a red heat the oxygen is turned on, and, as soon as the steel begins to burn, is allowed to enter at a decidedly rapid rate. At this stage very little gas passes through the KOH absorption bulb, practically all the oxygen combining with the steel. When the gas bubbles through the absorption bulb at about the same rate as that at which it enters the furnace, the oxygea is turned off (the combustion of the sample being complete), and about a litre of air is passed through, the absorption bulb being then detached and weighed. The increase in weight, minus the blank, multiplied by 10 or 20, according to the weight taken, converts the CO 2 to carbon per cent. By the process given above, special steels and alloys, when hi the form of drillings, give up the whole of their carbon almost * Chem. News, LXXXIV, 23. f Ibid., LXXXV, 121. 552 DETERMINATION OF COMMERCIAL VALUES. [ 255. as readily as ordinary steels. It is essential, however, when chromium is present to any appreciable extent, that the drillings do not exceed 0-25 mm. in thickness. Alloys which will not drill after careful annealing, if powdered and ground to a fine state of division in the agate mortar, and then well shaken with MgO or CaO, will in the majority of cases burn completely in oxygen. Some ferro-chromes, even, will oxidize if thoroughly " floured" in the mortar and ignited for a sufficient length of time.* From what has been stated it will be apparent that the direct combustion process is not only an alternative to the usual solution method, strongly appealing to the steel- works chemist on account of its reliability, simplicity, and speed, but, as shown, such a direct method is absolutely essential in the case of most special steels and some alloys, if an accurate determination of the carbon is to be made. A few notes on the process, and details of the apparatus used, may be of service. When a combustion is finished, the boat is withdrawn, its contents turned out by means of a piece of wire or the tang of an old file, and then re-charged with the next sample. The oxi- dized drillings should always fit together in the form of a long cake, which is very easily extracted owing to the boat being protected by the unfused magnesia. If the steel should not have been completely burnt, the drillings will be detached from each other no fritting whatever having taken place. In this case either thinner drillings are required or more heat should be applied. Both MgO and CaO require igniting at a high temperature in the muffle to completely drive off CO 2 , and, in the case of lime that has been prepared from marble, it is advisable to do a blank of each batch after ignition. As these oxides, however, absorb CO 2 from the air, their use has lately been discarded in favor of A1 2 O 3 , which, after ignition in the muffle, gives no blank, nor does * For these very refractory alloys, however, the use of Bi,O 3 or Pb 3 O 4 , as recommended by BREARLEY (Chem. News, LXXXIV, 23), is to be preferred as being quicker and more certain of giving the full carbon contents. 256.] IRON COMPOUNDS. 553 it absorb C0 2 ; on this account it is preferable to either of the other two, and is now regularly used by the author as a standard reagent. The combustion tube (porcelain, 26"XlJ") is covered with asbestos cloth or mill-board. It is packed as usual with a few inches of copper oxide, and the cooler exit portion with granular fused lead chromate to absorb sulphur compounds the CuO and PbCrO 4 being separated by a large asbestos plug. The test analyses by the author are very satisfactory. Regarding methods of determining carbon in cast iron by combustion in oxygen, see pp. 515 and 216 this volume. TRANS- LATOR.] 2. DETERMINING THE OTHER CONSTITUENTS. In regard to these I need but add to what has already been stated in 255, that because of the small quantities of these present as compared with the other elements, the quantity of iron to be taken for the analysis must be proportionately increased. C. PYRITES. 256. Pyrites, which is now almost exclusively used for the prepara- tion of sulphuric acid, is in consequence very frequently the subject of chemical analyses, more particularly since the small percentage of copper and small quantities of silver and gold present may be advantageously extracted from the roasted pyrites. In the analyses of pyrites the following constituents, as a rule, have to be con- sidered: Sulphur, selenium, sulphuric acid, iron as sulphide (mostly as FeS 2 ), and at times also as ferric or ferrous oxide copper, zinc, lead, bismuth, thallium, cobalt, nickel, arsenic, anti- mony, calcium, magnesium, carbon dioxide, the portion insoluble, in acids (gangue) containing occasionally barium sulphate and carbon, and the chemically combined water. In certain pyrites particularly the Spanish, there are present also traces of gold and silver. As a rule, even in complete analyses, only those constitu- ents printed in italics are quantitatively determined. 554 DETERMINATION OF COMMERCIAL VALUES. [ 256. I. COMPLETE ANALYSIS. Dry the very finely powdered mineral at 100. 1. Determining the Sulphur, Sulphuric Acid, and Arsenic; and testing for Antimony. Very intimately mix in a capacious platinum crucible about 1 grm. of the powdered pyrites with 10 grm. of an intimate mixture of 2 parts pure potassium carbonate and 1 part pure potassium nitrate; cover the whole with a layer of the last-named mixture, heat gradually over a BERZELIUS alcohol-lamp,* to fusion, and maintain therein for some time; then allow to cool, introduce the crucible with its contents into a beaker, add water, and heat until all soluble matters are dissolved. If the pyrites contain lead, pass in carbon dioxide to precipitate the small quantity of lead held in solution by the caustic potassa; then filter the solution into a 500-c.c. flask, boil the residue with a solution, of pure potassium carbonate, filter, wash with boiling water to which a little potassium carbonate has been added, and until the washings cease to react for sulphuric acid. Now allow to cool, fill up to the mark, and mix by agitation. a. To 250 c.c. of the alkaline liquid in a large flask add 30 c.c. pure concentrated hydrochloric acid of sp. gr. 1 15, warm the strongly acid solution until all the carbon dioxide has been ex- pelled, evaporate to dryness in a porcelain dish, add 5 c.c. concentrated hydrochloric acid, evaporate again, and in this manner free it from all nitric acid. Moisten the residue with two drops concentrated hydrochloric acid, add some water, heat, filter, and precipitate the hot solution with a moderate excess of hot barium-chloride solution. After settling, collect the precipitate, wash it very thoroughly with boiling water, incinerate the filter, add the precipitate to the ash, ignite, and weigh. Moisten the residue in the platinum crucible now with hydrochloric acid, add * If illuminating gas containing sulphur is employed, the quantity of sulphuric acid in the melt may be hereby increased, and give rise to erro- neous results (PRICE, Zeitschr. /. analyt. Chem., in, 483). 256.] IRON COMPOUNDS. 555 water, heat, pass through a small filter, repeating this operation thrice; then evaporate the filtrate (with a few drops of barium- chloride solution added) almost to dryness on a water-bath, take up with water, filter through the small filter, wash, incinerate the filter in a platinum spiral over the platinum crucible containing the bulk of the barium sulphate which has hi the meantime been dried, and then ignite and weigh. The weight thus obtained differs, as a rule, only by a few mgm. from that first obtained, and is to be regarded as the correct one. If the mixture of the potassium nitrate and carbonate, the potassium-carbonate solution, or the hydrochloric acid, is not per- fectly free from sulphuric acid, the small quantity of the acid present must be determined in the reagent, and the operations car- ried out with weighed or measured quantities. Before calculating the sulphur deduct the small quantity of barium sulphate cor- responding with the sulphuric acid in the reagent from the total barium sulphate. This method of determination of course gives the total sulphur in the pyrites. In order to determine the sulphur combined with the heavy metals, the sulphur existing as sulphates, if such are present in the pyrites, must be deducted from the total sulphur. If only barium sulphate is present, the quantity of this may be ascertained from the barium content of the ignition residue, the determination being made by dissolving in hydrochloric acid the portion of the residue insoluble in water, neutralizing any too great excess of acid with ammonia, and precipitating the barium from the now mod- erately acid solution with sulphuric acid (Vol. I, p. 263). The barium sulphate so obtained contains a little iron; if the quantity of this is large it must, in order to obtain accurate results, be fused with sodium carbonate, and the melt treated with boiling water. "The operator may now choose between determining the iron in the residue, or the sulphuric acid in the solution. If other sulphates (of calcium, ferrous iron, etc.) are present, determine their sulphuric-acid content by repeatedly boiling a larger sample of the pyrites with dilute hydrochloric acid in a current of carbon dioxide, and after neutralizing the greater part 556 DETERMINATION OF COMMERCIAL VALUES. [ 256. of the excess of acid with ammonia, precipitating with barium chloride (Vol. I, p. 434). b. Evaporate the remaining 250 c.c. with pure sulphuric acid on the water-bath until all the nitric acid has been driven off, take up the residue with water acidulated with hydrochloric acid, and pass a large excess of hydrogen sulphide for a long time into the solution maintained first at 70, and then after the liquid has cooled. If a precipitate forms, allow it to settle in a moderately warm place, then collect it on a small filter dried at 110 and weighed, wash (best with the aid of the water-pump) by filling up the filter eight times with alcohol, four times with carbon disulphide, and lastly thrice with alcohol. After drying at 110, weigh, and calculate the precipitate as arsenic pentasulphide (BUNSEN*). After weighing, it may be tested for antimony, which, as a rule, is not present at all, or is so in unweighable quantity. If it is nevertheless to be determined, the method recommended by BUNSEN (loc. cit.) may be employed. Dissolve the still moist sulphide on the filter, and before the treatment with alcohol and carbon disulphide, in an excess of a solution of pure potassium hy- droxide (purified by alcohol) ; into the solution, mixed with the concentrated washings, pass in chlorine until all the alkali is de- composed. Now heat in the water-bath, gradually add a large excess of concentrated hydrochloric acid, carefully avoiding any loss from spirting, evaporate the fluid to one-half, replace the evaporated portion by an equal volume of concentrated hydro- chloric acid, and again evaporate to one-half or one-third, in order to expel all free chlorine. Now mix with very dilute hydro- chloric acid, add freshly prepared, saturated hydrogen-sulphide water (100 c.c. for each 0-1 grm. or less of the expected antimonic acid), wait a short time until the precipitate of antimony penta- sulphide has entirely settled, and then blow through the liquid a strong current of air, filtered through cotton and propelled by the blowpipe bellows, in order to remove the excess of hydrogen sulphide, keeping the beaker covered meanwhile with a perforated * Annal. d. Chem., cxcu, 305; Zeitschr. /. analyt. Chem., xvni, 266. 256.] IRON COMPOUNDS. 557 watch-glass. After fifteen or twenty minutes transfer the pre- cipitate to a weighed filter, wash with alcohol and carbon disulphide as above detailed for arsenic sulphide, dry at 110, and weigh the antimony pentasulphide. Heat the arsenical filtrate on the water-bath after adding a few drops chlorine water, and in it deter- mine the arsenic as above described. If an absolutely complete separation of the metals is to be effected, dissolve the antimony sulphide, before washing with alcohol and carbon disulphide, in potassa solution, and repeat the separation in the manner detailed. If the arsenic alone is to be determined, the alkaline solution of the fused mass may be treated as follows, according to F. MUCK: * Acidulate the solution, and add sufficient ferric-chloride solution to yield with ammonia a reddish-brown precipitate, i.e. one con- taining an excess of ferric oxide, but avoid any too great an excess by adding ammonia. Now heat until the precipitate has settled, filter, wash, dissolve in hydrochloric acid, reduce the sulphurous acid, and boil off the excess of the latter; then precipitate with hydrogen sulphide, oxidize the arsenic sulphide with fuming nitric acid, concentrate strongly, and precipitate the arsenic acid with magnesia mixture, etc. (Vol. I, p. 412). 2. Determining the Iron, Copper, Lead, Zinc, etc., as well as the Residue insoluble in Acid. Digest 2 or 3 grm. of the very finely powdered pyrites with nitro-hydrochloric acid until completely decomposed and all the sulphur is dissolved, then repeatedly evaporate with hydrochloric acid to remove the nitric acid, add water, and pass through a filter dried at 100 and weighed; now wash the insoluble residue by fil- tration and decantation, exhaust it, if it contains lead sulphate, by repeated boiling with a solution of ammonium acetate, and wash. Now dry the filter with its contents at 100, weigh, incin- erate the filter, and weigh again. The difference in weight between the dried and ignited residue gives the water in combination in the residue, and, if the latter is blackish, also the carbon content. * Zeitschr. f. analyt. Chem., v, 312. 558 DETERMINATION OF COMMERCIAL VALUES. [ 256. If barium sulphate has been found in 1, deduct its weight from that of the ignited residue, and calculate the difference as gangue, if there is no special reason to subject the residue to further analy- sis. If the residue contains lead, precipitate this from the am- monium-acetate solution with hydrogen sulphide, dissolve the lead sulphide obtained, after washing, in nitric acid, and deter- mine the lead as sulphate (Vol. I, p. 355). The hydrochloric-acid solution treat with hydrogen sulphide at 70, filter, exhaust the precipitate with warm sodium-sulphide solution, then dissolve in nitric acid, and separate any lead that may be present by evapo- rating with sulphuric acid; then add first ammonia until nearly neutral, next a sufficient excess of ammonium carbonate, warm, filter if necessary (a precipitate may contain bismuth), acidulate, precipitate with hydrogen sulphide, and determine the copper as sulphide (Vol. I, p. 375). Concentrate the filtrate from the hydrogen-sulphide precipitate, oxidize by heating with nitric acid, and separate the iron as on pp. 475 and 476 this volume. The filtrate acidulate with acetic acid, and add ammonia in slight excess. If a slight precipitate of ferric hydroxide is formed thereby, and perhaps also of aluminium hydroxide, filter this off, dissolve it in hydrochloric acid, repre- cipitate with ammonia, acidulate the ammoniacal liquid with acetic acid, add ammonium acetate, and precipitate with hydrogen sulphide at 70. Any precipitate formed is zinc sulphide, fre- quently with some cobalt and nickel sulphides. The precipitate is best weighed in this state (Vol. I, p. 289, 2) ; determine the small quantities of cobalt and nickel sulphides in the not quite pure zinc, which may in this case be done with sufficient accuracy by treat- ing with dilute hydrochloric acid and determining the small quan- tity of insoluble residue. In the filtrate from the zinc sulphide separate the manganese by means of ammonia and ammonium sulphide. Evaporate the fil- trate finally to dryness, ignite, and determine in any residue the calcium and magnesium, if these are present. The precipitate containing the ferric oxide, or the united pre- cipitates in which alumina may also be present, dissolve in hydro- 256.] IRON COMPOUNDS. 559 chloric acid, make up the solution to 500 c.c., and in 100 c.c. deter- mine the iron and alumina by precipitation with ammonia, and in another 100 c.c. or 200 c.c. determine the iron volumetrically with stannous chloride (Vol. I, p. 327), or gravimetrically accord- ing to Vol. I, p. 642, 2. 3. Determination of any Carbon Dioxide Present. This is effected by heating a suitable quantity of the finely com- minuted pyrites with very dilute hydrochloric acid, passing the evolved gas first through calcium-chloride tubes, then through tubes containing pumice-copper sulphate, and finally through weighed soda-lime tubes. The increase in weight of the latter gives the quantity of carbon dioxide evolved. Regarding the procedure, see p. 365, d, this volume. 4. Determination of any Oxygen Compounds of Iron that may be Present. If the pyrites yields any ferrous sulphate to water, or ferric or ferrous oxide to cold, dilute hydrochloric acid, without hydrogen sulphide being simultaneously evolved, the oxygen compounds of iron may be directly determined in the solution obtained (Vol. I, pp. 311 and 322) ; if this is not the case, however, the direct deter- mination of the oxygen compounds of iron must be abandoned, and their determination made by calculation. 5. Testing for Gold and Silver. Roast a large quantity (say about 500 grm.) of the pyrites, best in a muffle, but lacking this, in an inclined, open, Hessian cru- cible, until sulphurous acid is no longer evolved; heat toward the last to bright redness, powder the residue, exhaust next with hot water, and test the aqueous extract, by adding a few drops hydro- chloric acid, whether it contains any silver. Collect any slight pre- cipitate of silver chloride that may have settled after some time (Precipitate No. I). The residue left after exhausting with water 560 DETERMINATION OF COMMERCIAL VALUES. [ 256. digest with bromine water* for a long time in the dark, filter with exclusion of sunlight, add a few drops hydrochloric acid, and evaporate until all free bromine has been expelled and the fluid measures about 200 c.c. To the liquid, frequently green from the presence of copper salts, add a clear sulution of ferrous sul- phate, warm, and into the warm liquid pass hydrogen sulphide, and allow to stand for at least' 24 hours to settle. Collect the precipitate on a filter, wash, and dry (Precipitate II). The residue extracted with bromine water heat on a water-bath for a long time with a concentrated ammonium-chloride solution in order to dissolve any silver bromide present. Filter hot into a flask, wash with hot ammonium-chloride solution, add first a few drops mer- curic-chloride solution,! then some ammonia until the liquid is distinctly alkaline, and lastly ammonium sulphide in excess. Stopper the flask loosely, set aside in a warm place until the pre- cipitate has completely settled, then collect it on a filter, wash, and dry (Precipitate III). Heat the precipitates I, II, III under a good draught until the filters are consumed and the mercuric sulphide has volatilized. Then triturate the residue, which contains the whole of the gold and silver that was present in the roasted pyrites, with some anhy- drous borax, transfer the whole to a scorifier, add the necessary quantity of pure lead, and proceed as described on p. 579 this vol- ume. After weighing the gold and silver button obtained by cupellation, determine the gold according to Vol. I, p. 703 [169]. The silver present is found from the difference. 6. Testing for Thallium. Any thallium in pyrites may be often detected by placing some of the powdered mineral on the moistened end of a platinum wire and holding it in the flame of the spectroscope. The charac- * The application of bromine water or tincture of iodine for the extrac- tion of gold, instead of the chlorine water formerly employed, was first re- commended by SKEY (Chem. News, xxn, 245; Zeitschr. f. analyt. Chem., x, 221). f The addition of the mercuric chloride is made for the purpose of facili- tating the deposition of the usually very slight precipitate of silver sulphide. 256.] IRON COMPOUNDS. 561 teristic, intensely green thallium line coincident with Ba d flashes out transiently. On heating finely powdered pyrites containing thallium to bright redness in a tube with as complete exclusion of air as possible, thalh'um sulphide sublimes along with the sul- phur; if the sublimate is burned away in the loop of a platinum wire, and the residue then spectroscopically examined, the green line appears very distinctly. Thallium may be detected in the wet way with the greatest delicacy, according to CROOKES and BOTTGER. Dissolve the powdered pyrites in hydrochloric acid with the addition of the least possible necessary quantity of nitric acid boil with sodium sulphite until the ferric oxide is reduced, and to the filtrate add one or two drops potassium-iodide solution. If thallium is present, a light-yellow precipitate of thallium iodide forms. I would advise to test this spectroscopically for the sake of certainty. I!. DETERMINATION OF SULPHUR ONLY. 1. The Dry Method, in which the Sulphur is weigfied as Barium Sulphate. Although this method has already been minutely and completely described in A, 1, reference is again made to it here in order to remark that in determining the sulphur alone, it is best to mix about 0-5 grm. of the pyrites, dried at 100, with 10 parts of a mixture of 2 parts dry sodium carbonate* and 1 part potassium nitrate, cover the whole with a layer of the latter mixture, and to make use of a solution of pure sodium carbonate with which to boil the residue insoluble in water in order to extract it. In other respects, the method is conducted exactly as above detailed; the operator must never neglect, however, to test his reagents for the presence of sulphuric acid, and to deduct the sulphur present in the pyrites in the form of sulphates from the total sulphur ob- tained, when it is intended to ascertain the quantity of sulphur combined with the heavy metals. * Sodium carbonate may be used here instead of potassium carbonate because antimony need not be considered. 562 DETERMINATION OF COMMERCIAL VALUES. [ 256 Instead of the mixture of potassium nitrate and sodium car- bonate, B. DEUTECOM* recommends a mixture containing potas- sium chlorate. He heats 1 grm. of the pyrites with 8 grm. of a mixture of equal parts potassium chlorate, sodium carbonate, and sodium chloride, in a large, covered, porcelain crucible, at first slowly until perfectly dried, and then strongly until homo- geneously fused. When cold the mass is treated with boiling water, then transferred together with the precipitate into a flask, allowed to settle, and the sulphuric acid determined in an aliquot. part of the clear solution. FR. BocKMANNf recommends some- what different proportions, namely, .0-5 grm. pyrites (or 2 grm. roasted pyrites) and 25 grm. of a mixture of 6 parts sodium car- bonate and 1 part potassium chlorate. 2. Wet Methods, in which the Sulphur is weighed as Barium Sulphate. These methods consist in treating the powdered pyrites with nitrohydrochloric acid, or with hydrochloric or nitric acid with the addition of potassium chlorate, or with similar oxidizing solvents, so that all the sulphur combined with metal is converted into sulphuric acid, which is then precipitated with barium chlo- ride from the solution containing the iron as ferric chloride or other ferric salt. In the Zeitschr. f. analyt. Chem., xix, 53, I published an exhaustive critique regarding these methods, and showed that they contain two sources of error, yielding on the one hand more or less red barium sulphate containing ferric oxide; while on the other hand the barium sulphate is not completely precipitated, because some of it remains dissolved in the acid liquid containing ferric chloride. These two sources of error counterbalance each other, however, to some extent, and more or less completely. In general, the following may be stated regarding this: An increased proportion of free hydrochloric acid and rapid filtration increase the quantity of barium sulphate remaining in solution * Zeitschr. f. analyt. Chem., xix, 313. t Ibid., xxi, Heft 2. 256.] IRON COMPOUNDS. 563 and lessen its iron content, whereas a much smaller proportion of free acid and filtering after standing for some time, lessen the quantity of barium sulphate remaining in solution but increase the iron content. A suitable and equal dilution of the liquid to be precipitated is here presupposed. As a rule the results obtained in this way are too low. In consequence of my critique, LUNGE * has somewhat modi- fied the procedure of the method in the wet way previously rec- ommended by him,t and according to him the best method of determining the sulphur in the wet way now is as follows: a. When Economy of Time is of More Importance than Absolute Accuracy. Place about 0-5 grm. of the very finely powdered and bolted mineral in an ERLENMEYER flask or in a capacious beaker, the former being covered with a funnel, the latter with a watch-glass, and pour over it 50 parts of nitrohydro chloric acid (prepared from 1 part fuming hydrochloric acid and 3 to 4 parts nitric acid of sp. gr. 1-36 to 1-40). If the reaction does not set in at once, gently warm on the water-bath under a good draught, until a brisk reac- tion sets in, when the vessel should at once be removed from the water-bath. When the reaction becomes very feeble, replace the vessel on the water-bath. As a rule, the decomposition is effected in at most ten minutes; should it, however, be incomplete even after long-continued warming, add a little more nitrohydro- chloric acid and warm anew. If the object is even then not fully accomplished, or if any sulphur has separated, repeat the decom- position, using a fresh quantity of substance which has been more finely powdered. Now evaporate the whole to dryness with an excess of hydro- chloric acid, most safely on the water-bath, whereby the nitric acid is expelled and any silicic acid that had become soluble is again rendered insoluble ; treat the residue once more with some hydrochloric acid, warm, and observe whether any vapors of * Zeitschr. f. analyt. Chem., xix, 421. f LUNGE, Handbvch der Sodaindustrie, i, 92. 564 DETERMINATION OF COMMERCIAL VALUES. [ 256. nitrohydrochloric acid are evolved. If this is the case, repeat the evaporation with more hydrochloric acid until the object is attained. When the hydrochloric acid has been almost com- pletely expelled by evaporation, add 3 to 4 drops concentrated hydrochloric acid, warm, add 100 c.c. water, filter, heat to boiling, precipitate with a slight excess of a boiling solution of barium chloride of known strength (1:10); then remove the heat, let the precipitate settle for 20 to 30 minutes, decant the supernatant liquid into a filter, and wash the precipitate four times in suc- cession by decantation with boiling water, using 100 c.c. each time, moistening the precipitate in the precipitation glass with 2 c.c. normal hydrochloric acid each time before adding the water (p. 293 this volume). Transfer the precipitate to the filter, wash out thoroughly, and proceed according to p. 554, a, this volume. The precipitate remains more or less reddish even after purification. i b. When a High Degree of Accuracy is of More Importance than Economy of Time. Effect the decomposition and evaporation with hydrochloric acid as in a, treat the residue with a little hydrochloric acid, add water, then add to the moderately warm liquid ammonia in not too great excess, filter after about ten minutes, thoroughly wash the ferric hydroxide with boiling water until the washings cease to give a turbidity with barium chloride, even after standing a short time. Very weakly acidulate the filtrate and washings with hydrochloric acid, heat to boiling, add hot solution of barium chloride in slight excess, wash the precipitate first by decantation several times, then on the filter, and ignite. As, under these circumstances, no salts of the fixed alkalies are present, the puri- fication by treatment with hydrochloric acid, etc., may be more readily effected. The results obtained with Method b, according to LUNGE'S experiments, gave 0-18 per cent, more sulphur than when Method a was used. Of course the methods in the wet way require also that the reagents used, particularly the acids, be free from sulphuric acid. 'The testing can be accurately carried out only by completely 256.] IRON COMPOUNDS. 565 evaporating the acids, lastly on the water-bath, then putting a little water in the dish, and testing the solution with barium chlo- ride. It must be remarked that in the methods by the wet way any barium sulphate that may be present is practically completely excluded from the sulphur; calcium sulphate, on the other hand, goes partly, and if the quantity present is not too large, entirely into solution. The sulphur of the galena is reckoned in only to the very smallest extent, because the greater part of the lead sulphate formed remains undissolved. 3. Technical Methods for indirectly (Alkalimetrically) determining the Sulphur in the Wet Way. a. PELOUZE'S Method* Mix 1 grm. of the very finely powdered pyrites with 5 grm. (exactly weighed) perfectly pure anhydrous sodium carbonate,t add 7 grm. (approximately weighed) potassium chlorate, and 5 grm.t (approximately weighed) fused, or at least anhydrous sodium chloride, mix thoroughly, and gradually heat the mixture for eight to ten minutes to low redness in a wrought-iron spoon. When cold treat it five or six times with hot water, and transfer the solution to a filter by means of a pipette. Lastly boil the residue with water, and thoroughly wash it on the filter with boiling water. Then test the filtrate and washings as to their alkalinity according to 219 or 220. The calculation of the sulphur content of the pyrites is based upon the following considerations: To neutralize the quantity of the sodium carbonate originally added, a certain quantity of normal acid would have been required, and to neutralize the liquid * Compt. rend., Lin, 685; Zeitschr. f. analyt. Chem., i, 249. f Should this not be at hand, the experiment may be made with sodium carbonate which is not quite pure; but in this case a special test must be made to determine how much normal acid corresponds to 5 grm. t The quantity of sodium chloride may be varied according to the nature of the pyrites, and may be increased until oxidation takes place without deflagration. 566 DETERMINATION OF COMMERCIAL VALUES. [ 256. extracted from the fused mass with hot water less is naturally required, the quantity being in fact smaller in proportion as the quantity of sulphur oxidized to sulphuric acid is greater. Hence the difference between the quantity of acid corresponding with the quantity of sodium carbonate employed, and that required for neutralizing the liquid extracted from the fused mass, represents the sulphur in the pyrites, calculating 1 eq. of sulphur for 1 eq. of acid; 1000 c.c. of the standard acid prepared according to 219 correspond with 30-224 grm. sulphur, while 1000 c.c. of the normal acid prepared according to 215 correspond with 16-035 grm. sulphur. As a precaution, finally test a sample of the insoluble residue left on treating the fused mass with water, by treating with hydro- chloric acid, etc., to make sure it contains no sulphur. The process requires from 30 to 40 minutes for its execution, and gives results which, according to PELOUZE, vary not more than 1 to 1 5 per cent, from the truth. Any loss of sodium car- bonate causes the sulphur content to be too high. When employing the method on roasted pyrites, the sodium chloride need not be added. In this case 5 grm. of the roasted pyrites, 5 grm. pure anhydrous sodium carbonate, and 5 grm. potassium chlorate are taken. The sulphur present in the form of sulphates is determined just as if it were combined with metals. The fact that this method, which is still used in not a few works, yields results that are not very reliable has been demonstrated by BARRESWIL, BOTTOMLEY, BOCHEROFF, LUNGE, and with par- ticular exhaustiveness by J. KOLB,* and the latter has critically made clear the causes of the inaccuracy. The facts that, in this process, chlorine is evolved, that sulphuric acid may be evolved from any ferric sulphate which has been formed and not yet de- composed again, that sulphur chloride may be evolved, and also that the fused mass may at times contain sodium sulphide, may easily allow the alkalimetric titre of the fused mass to appear too * Journ. de Pharm. et de Chim. [iv], x, 401; Zeitschr. /. analyt. Chem., IX, 407. 257.] URANIUM COMPOUNDS. 567 high, and the sulphur content, consequently, too low, while, on the other hand, arsenic, which is converted into sodium arsenate, and silicic acid, which gives rise to' the formation of insoluble double silicates containing sodium at the high temperature employed, makes the sulphur content too high. These errors, which become so much the greater the less sul- phur the pyrites or burnt pyrites contains, may be altogether, or at least very largely, avoided, according to KOLB, by adopting the following method: b. J. KOLB'S Method (loc. tit.). Mix about 1 grm. of the pyrites or 5 to 10 grm. roasted pyrites in finely powdered form with 50 grm. cupric oxide, also finely pow- dered, and 5 grm. sodium carbonate, and heat. The conversion of the sulphur into sodium sulphate takes place, according to KOLB, without fusion or disturbance of the mixture, and at a sufficiently low temperature, so that a decomposition of the re- fractory sulphates, or the action of the silicic acid on sodium carbonate, need not be feared. The calculation is made just as in PELOUZE'S method. I would point out, however, that in this method arsenic is deter- mined as its equivalent of sulphur, and that easily decomposable sulphates, e.g., gypsum, give rise to the same error as in PELOUZE'S method. 15. URANIUM COMPOUNDS. 257. For the rapid determination of uranium in uranium ores, the following method, proposed by A. PATERA,* is recommended: Dissolve the weighed quantity of ore in nitric acid, avoiding so far as possible an excess of acid. Dilute the acid solution with water, supersaturate with sodium carbonate, heat to boiling in order to completely dissolve the uranic oxide and to decom- pose any calcium bicarbonate, ferrous oxide, etc., that may have formed, collect the precipitate, and wash with hot water. The * DINGLER'S polyt. Journ., CLXXX, 242; Zeitschr. f. analyt. Chem., v, 228. 568 DETERMINATION OF COMMERCIAL VALUES. [ 258. filtrate which, besides uranium, may also contain traces of foreign metals, precipitate with soda lye, and slightly wash and dry the orange-colored precipitate of acid sodium uranate. Detach the dry precipitate from the filter, ignite in a platinum crucible, and add to this the ash of the separately incinerated filter. Now transfer the contents of the crucible to a small filter, wash it, dry, and ignite. It consists now of Na2U 2 7 , 100 parts of which ac- cording to PATERA are equivalent to 88-58 parts uranosouranic oxide, U 3 O 8 . The results afforded by this method are so satis- factory that it is used in Joachimsthal as the recognized test in the purchase of uranium ores. CL. WINKLER,* who has frequently had occasion to test this method, also reports that it is good, and that the results afforded by it agree so closely with those obtained by other methods of analysis, that it is undoubtedly sufficiently accurate for technical purposes. With ores rich in copper, WINKLER obtained results that were somewhat too high. In this case a small quantity of the copper dissolves in the alkaline solution, and, on the sub- sequent addition of caustic soda, is precipitated with the sodium uranate. 16. SILVER COMPOUNDS. 258. The silver compounds which are most frequently examined in chemical laboratories are either ores containing silver, or silver alloys. A. SILVER ORES. Silver ores may be analyzed both in the dry and the wet way. If only the silver content to is be determined, particularly in the case of small quantities of silver, the dry methods are usually the more direct and certain; if, however, all the constituents are to be determined, the wet method must be chosen, under all cir- cumstances. An exact qualitative analysis is first made, and then the individual metals are separated according to the methods * Zeitschr. /. analyt. Chem., vm, 387. 258.] SILVER COMPOUNDS. 569 detailed in the fifth section of the first part. If the ore, on treat- ment with nitric acid, yields a solution containing all the silver, begin with this mode of treatment; in other cases, particularly in analyses of ores containing antimony and arsenic (antimonial silver, brittle silver ore, ruby silver ore, miargyrite, polybasite, fahl- erz, etc.), it is preferable to heat the powdered ore in a current of chlorine, and to thus separate the volatile metallic chlorides from the non-volatile. See Vol. I, p. 695 [160] (where also the apparatus to be used is illustrated and described), Vol. I, p. 709 [180], and 261. The examination of the silver ores by the dry way is more accurately accomplished by subjecting the ore along with pure lead to a roasting process, whereby the elements accompany- ing the silver in the ore are either volatilized as oxides and acids, or run into a slag together with the lead oxide. When the oxida- tion has proceeded sufficiently far, it is interrupted, and the un- oxidized lead containing all the silver separated from the slag and driven off in a cupel. Regarding the details of the process I refer to 259 (Determination of Silver in Galena), where the details are given. B. SILVER ALLOYS. Of the silver alloys those of silver and copper have, by far, the most frequently to be examined. That these may be analyzed by the dry or the wet way follows from Vol. I, p. 341 et seq., and p. 698, 11 [164]. This is here again referred to for the purpose of adding VOLHARD'S volumetric method,* which is distinguished for its simplicity and also accuracy, as well as by the fact, in contradistinction to GAY-LUSSAC'S method, that it does not pre- suppose an approximate knowledge of the silver content of the alloy. This method was not known at the time the particular section in the first volume was written. The method is based upon the precipitation of the silver as silver sulphocyanate from its nitric-acid solution, the moment * Journ. f. prakt. Ghent. [N. F.], ix, 217; Annal. d. Chem., cxc, 1; Zeitschr. /. analyt. Chem., xiu, 171, and xvii, 482. 570 DETERMINATION OF COMMERCIAL VALUES. [ 258. the ammonium or potassium sulphocyanate is in excess being ascertained by the iron-sulphocyanate reaction. To prepare the titrating solution VOLHARD employs ammonium sulphocyanate, while others, as B. LINDEMANN,* prefer potassium sulphocyanate. Both salts are equally stable in dilute solution. The presence of a small quantity of chlorine in the sulphocyanate is not prejudicial in the determination of silver, but a large quan- tity is very decidedly so, and VOLHARD prefers the ammonium sulphocyanate on the ground that it is much more readily ob- tained free from chlorine than is the potassium salt.| Dissolve 7-5 to 8 grm. ammonium sulphocyanate (approxi- mately weighed) in water to make one litre, and then ascertain its effective value by standardizing it against a silver solution of accurately known strength. For this purpose weigh off accurately 10 grm. chemically pure silver, dissolve in 160 to 200 c.c. pure nitric acid of sp. gr. 1 2, expel all the nitrous acid, when solution is complete, by prolonged heating, allow to become cold, dilute to one litre, and pipette off 50 c.c. (containing 0-5 grm. silver). Dilute these 50 c.c. with about 150 c.c. water, and add 5 c.c. of a cold saturated solution of ammonio-ferric alum; if the color of the ferric salt is observable, add a little nitric acid until the color disappears. Now run in the sulphocyanate solution from a burette. At first only a white precipitate forms and remains suspended in the liquid, and imparts to it a milky appearance. On the further addition of the ammonium sulphocyanate, the drops, as they fall into the liquid, produce a blood-red cloud which rapidly disappears on shaking. When the point of complete precipitation of the silver is approached, the precipitated silver sulphocyanate collects in flocks, and the liquid begins to become clear without, however, becoming perfectly so, so long as a trace of silver still remains in the solution. As soon, however, as all * Zeitschr. /. analyt. Chem., xvi, 352. f As the ammonium sulphocyanate is prepared from materials which are nearly or altogether free from chlorine, it, as a rule, contains no chlorine compounds, or only minute quantities, from which it may be easily freed by a single recrystallization from boiling water. The commercial potassium sulphocyanate always contains more chlorine than the ammonium salt (VOLHARD, loc. cit.\ 258.] SILVER COMPOUNDS. 571 the silver is precipitated, the flocculent precipitate subsides; con- tinue to add the sulphocyanate solution at last drop by drop, until the liquid becomes clear, and acquires a very pale, brownish tint which does not disappear even on frequent shaking. The color is best observed if the liquid is held, not against the light, but away from the window and against a white wall. Repeat the experiment, and, if the results correspond, dilute the am- monium-sulphocyanate solution on the basis of the results ob- tained, so that 50 c.c. of it accurately correspond with 50 c.c. of the silver solution, when 1 c.c. of the sulphocyanate solution will correspond to 0-01 grm. silver. To determine the silver in alloys, proceed exactly as just de- scribed in titrating. If exactly 1 grm. of the alloy is taken, then every 0-1 c.c. of the sulphocyanate solution will indicate 1 per 1000 of silver. In using this method the following points must be observed: 1. Nitrous acid must never be present, either in the solution or in the nitric acid which is subsequently added. If, therefore, the nitric acid contains nitrous acid, remove this by boiling, and protect the purified acid from exposure to bright light. 2. The action of the sulphocyanate solution must take place in the cold, as, when warm, sulphocyanic acid is decomposed by nitric acid, and the color of the iron sulphocyanate is destroyed. 3. The solution of the ammonio-ferric alum must always be employed in large excess, and in approximately the same pro- portion to the total quantity of liquid. 4. It makes no difference on the result whether the quantity of free nitric acid present is greater or less. 5. Copper, if present, has no disturbing influence on the result, so long as the alloy does not contain more than 70 per cent, of copper. In the case of alloys containing more than this, weigh off a suitable quantity of silver and add it to the sample, taking care that the copper content of sample weighed (1 grm.) does not exceed 0-7 grm. 6. Mercury must not be present. If an alloy contains mer- cury, this must be first expelled by ignition. 572 DETERMINATION OF COMMERCIAL VALUES. [ 258. 7. Palladium makes the titration of silver inexact, as it is indi- cated as silver. 8. If nickel or cobalt is present, the recognition of the end of the reaction requires practice; otherwise a few drops too much of sulphocyanate may be easily added. On carefully titrating back with silver solution, the pure color of the nickel or cobalt solution appears so suddenly and sharply that the end-point of the reaction is easily observed on again titrating back, when the color of the solution has become yellowish brown from the admixture of the ferric sulphocyanate. [PisANi's method* is adapted for the determination of very small quantities of silver. The method is based upon the fact that on adding iodine to a dilute neutral solution of silver nitrate there are formed silver iodide and silver hypoiodite or iodate, as follows r 2AgN0 3 + 21+ H 2 = Agl+ AgIO+ 2HNO 3 . 6AgNO 3 + 61+ 3H 2 O = 5AgI+ AgIO 3 + 6HNO 3 . If a solution of starch iodide is used instead of iodine solution, the blue color of the solution will continue to disappear until all the silver has combined with the iodine, the quantity of iodine used up being proportional to the quantity of silver present. The effective value of the iodine solution is determined directly by means of a solution of known silver content. The starch-iodide solution is prepared by triturating 2 grm. iodine with 15 grm. starch and 6 to 8 drops of water, heating the mixture in a closed vessel on a water-bath for about one hour, and then dissolving in water. To standardize this solution, add to 10 c.c. of a neutral silver-nitrate solution (1 grm. Ag per litre) sufficient pure, precipitated calcium carbonate to neutralize the nitric acid liberated, and run in the blue iodide solution until the mixture assumes a bluish-green color. Dilute the starch-iodide solution so that 50 to 60 c.c. of it will correspond to 10 c.c. of the silver solution. Very dilute silver solution, however, should be concentrated so that from 50 to 100 c.c. of the iodide solution may * Annal. des Mines, 1856, 83; Jahresber. von LIEBIG und KOPP, 1856, 749. 258.] SILVER COMPOUNDS. 573 be used up. There must be no substances present which will decompose starch iodide, e.g., reducers, mercuric and mercurous salts, stannous and antimonic salts, arsenites, ferrous and man- ganous salts, gold chloride, etc. Lead and copper salts have no disturbing influence on the reaction. ELECTROLYTIC DETERMINATION OF SILVER. CLASSEN * states that silver can be obtained as a white, strongly adhering deposit on roughened dishes by electrolyzing a solution containing 1 to 2 c.c. of nitric acid (sp. gr. 1-4) and 5 c.c. of alcohol at 55 to 60, if the potential-difference between the electrodes is carefully regulated so as to be within the limits 1 35-1 38 volts. The time required for precipitation is from 6 to 8 hours, and depends but little on the amount of silver contained in the solu- tion. A quantity of from 0-1 to 0-5 grm. of silver is convenient, but may be as great as 2 grm. The chief factor of importance is the potential-difference, which must be kept within the limits specified, since an increase to even 1-4 volts causes the silver to separate in a spongy state, which is useless for quantitative deter- mination. For other electrolytic methods of determination, as well as separation of silver from other metals, see u Electro-chemical Analysis," by EDGAR F. SMITH. P. BLAKISTON'S SON & Co., Philadelphia, 1902; CLASSEN'S "Quantitative Chemical Analysis by Electrolysis," B. B. BOLTWOOD. JOHN WILEY & SONS, New York, 1903; and also "Electrolytic Determinations and Separa- tions," LILY G. KOLLOCK (Journ. Amer. Chem. Soc., xxi, No. 10). TRANSLATOR.] * "Ausgewahlte Methoden," p. 3. CLASSEN'S "Quantitative Chemical Analysis by Electrolysis," p. 199. B. B. BOLTWOOD. JOHN WILEY & SONS, N T ew York, 1903. 574 DETERMINATION OF COMMERCIAL VALUES. [ 259 17. LEAD COMPOUNDS. 259. A. GALENA. Galena, the most widely distributed and most important of all the lead ores, contains, besides lead and sulphur, frequently, or occasionally, smaller or larger quantities of zinc, copper, anti- mony, arsenic, iron, silver, traces of gold, and usually more or less gangue insoluble in acids. In the following are described (1) the determination of all the constituents of the galena; (2) the determination of the lead alone; and (3) the dete mination of the silver in galena, by the dry way, and (4 in the wet way. 1. DETERMINATION OF ALL THE CONSTITUENTS OF GALENA. a. Oxidize a weighed quantity (1 or 2 grm.) with very concen- trated, red, fuming nitric acid free from chlorine and sulphuric acid (Vol. I, p. 567, a). For this purpose make use of a capacious flask, which is to be kept covered with a watch-glass during the operation; the small tube in which the galena has been weighed must not be put into the flask. If the acid is sufficiently strong all the sulphur will be oxidized. After warming gently for some time, rinse the contents of the flask into a porcelain dish, add 3 to 4 c.c. pure, concentrated sulphuric acid which has been pre- viously diluted wi h a little water, and heat on the water-bath until all the nitric acid has been evaporated off. Now dilute with 50 to 60 c.c. water, filter, wash the residue with water acidulated with sulphuric acid, and displace the latter by alcohol. Collect the alcoholic washings separately. a. When the residue is dry ignite it and weigh (Vol. I, p. 355, 3). It consists of lead sulphate, gangue undecomposed by the acid, silicic acid, etc. Heat the residue, or an aliquot portion, to boiling with hydrochloric acid and filter after some time, but in such a manner that the precipitate does not come on the filter; treat the precipitate with a fresh portion of hydrochloric acid, boil again, 259.] LEAD COMPOUNDS. 575 and repeat the operations until all the lead sulphate has been dissolved; finally transfer everything to the filter, wash with boiling water until every trace of lead chloride has been removed, and then dry, ignite, and weigh the residue. Deduct the weight found from that of the original residue; the difference expresses the quantity of lead sulphate the latter contained. Instead of using hydrochloric acid, the lead sulphate may be dissolved by heating with an aqueous solution of ammonium tartrate or acetate to which some ammonia has been added, or with sodium acetate; or it may be converted into lead carbonate by digestion with a solution of sodium carbonate, then washed and dissolved in di- luted nitric acid. One of the methods just mentioned must be employed for separating the lead sulphate from the gangue if there is any fear that the latter may be attacked by hydrochloric acid. /?. The sulphuric-acid solution will contain no weighable trace of lead, if the operation has been properly carried out, but in it will be found the metals which were present in the ore with the lead. Add first some hydrochloric acid, to test for silver. If a cloudiness or precipitate forms, set the liquid aside in a warm place for some time until the silver chloride has settled, then collect it on a small filter, and determine it according to Vol. I, p. 338, In the case of very small quantities, I prefer to proceed as follows: Incinerate the filter with the silver chloride in a porcelain crucible, ignite the residue for a short time in a current of hydrogen, dis- solve the trace of metallic silver in nitric acid, evaporate the solu- tion in a crucible to dryness, take up the residue with water, and in the solution determine the silver by PISANI'S method (Vol. I, p. 349). As a rule, however, galena contains so little silver that an accurate determination of the quantity in 1 or 2 grm. of the ore is impossible, hence for silver determinations a larger quantity must be operated upon, according to 259, 3 or 4. The clear liquor, or that filtered off from the silver chloride, precipitate with hydrogen sulphide; the precipitate contains usually a little copper sulphide and antimony sulphide, and at times also other sulphides. Separate these, as well as the metals in the 576 DETERMINATION OF COMMERCIAL VALUES. [ 259. solution precipitable by ammonium sulphide (iron, zinc, etc.), according to the methods described in Section V of the First Part. Regarding the separation of antimony from arsenic see also pp. 556 and 557 this volume. b. To determine the sulphur take a fresh portion of the finely powdered galena and proceed exactly as described in Vol. I, p. 562, 1, b. Do not neglect, as there pointed out, to treat the solu- tion of the fused mass with carbon dioxide before filtering. If a wet method is preferred, that detailed in Vol. I, p. 568, b } is to be recommended. 2. DETERMINATION OF LEAD ALONE IN GALENA. The method of analyzing lead salts given by F. STOLBA *, i.e., separation of the lead by zinc in the wet way, has also been recom- mended by STORER f and MASCAZZINI J for the determination of lead in galena. Both weigh the separated lead as such, the former after drying in a current of illuminating-gas, the latter after fusing with a reducing flux. The former brings the powdered galena directly together with hydrochloric acid and zinc, while the latter first converts the galena into lead sulphate by ignition with ammo- nium sulphate before acting on it with zinc and hydrochloric acid. These methods do not, however, appear to deserve com- mendation, at least G. C. WITTSTEIN and A. B. CLARK, JR. ; when testing STORER' s method, obtained very unsatisfactory results, and FR. MOHR || in his investigations also obtained unsatisfactory results on weighing the separated lead after drying, or after fusing with reducing fluxes. FR. MOHR (loc. cit.) has, however, based the following method for determining lead in galena, on the decomposition of the latter by zinc : Weigh off about 2 grm. of the finely powdered ore, intro- duce into a small porcelain dish or casserole, treat it with ordinary * Journ. f. prakt. Chem., ci, 150; Zeitschr. /. analyt, Chem., vn, 102. f Chem. News., xxi, 137; Zeitschr. /. analyt. Chem., ix, 514. j Zeitschr. f. analyt. Chem., x, 491. Ibid., xi, 460. D Ibid., xii, 143. S 259.] LEAD COMPOUNDS. 577 hydrochloric acid of sp. gr. 1 12, cover with a convex glass, and heat, finally to boiling. Hydrogen sulphide is evolved, and lead chloride separates. When the acid ceases to act because the unde- composed galena becomes covered with a layer of lead chloride, and the hydrochloric acid becomes saturated with lead chloride, drop in a small ball of zinc. Hydrogen is at once briskly evolved, and lead is precipitated on the zinc. On gently warming, fresh portions of the lead chloride dissolve and become decomposed until finally no more hydrogen sulphide is evolved, and the liquid appears clear and colorless. Decant the liquid then, and thor- oughly wash the lead with water; * this may be easily done by simple decantation. Dissolve the separated lead in dilute nitric .acid, filter the solution from the undissolved gangue, concentrate ; by evaporation with sulphuric acid, and proceed with the deter- mination of lead according to Vol. I, p. 355, a, /?. 3. DETERMINATION OF THE SILVER IN GALENA, AND TESTING FOR GOLD IN THE DRY WAY. As already mentioned, the method described in 259, 1, does not suffice to detect and determine very small quantities of silver f and the very small traces of gold which, according to PERCY and SMITH I are frequently found in galena. To effect this, it is, as a rule, advisable to first obtain a button which will contain all or a part of the lead of the galena, but surely all the gold and silver, and to then treat the button in the dry way. PREPARATION OF THE BUTTON. a. Methods suitable for poor Argentiferous Galenas, a. Mix 20 grm. of the finely, powdered galena, 60 grm. anhy- drous sodium carbonate, and 6 grm. potassium nitrate, introduce * According to STOLBA (Zeitschr. f. analyt. Chem., vii, 103) distilled water is unsuitable for washing the spongy lead, because, even when pre- viously boiled and cooled with exclusion of air, it dissolves a little lead. He therefore recommends spring-water for the washing. f Argentiferous galenas usually contain from 0-03 to 0-18 per cent, of silver, and rarely above 0-5 per cent.; very many galenas, however, contain less silver than the minimum mentioned. J Phil. Mag., vn, 126; Journ. f. prakt. Chem., LXI, 435. 578 DETERMINATION OF COMMERCIAL VALUES. [ 259. the mixture into a Hessian crucible, cover it with an 8-mm. deep layer of decrepitated sodium chloride, and fuse, finally at a bright- red heat, so that the slag flows well. After slowly cooling, break the crucible, flatten the button, which must be clean and compact, on an anvil, and cleanse it by boiling with water. According to BERTHIER (and my own investigations) there is thus obtained from 75 to 78 per cent, of lead from pure galena, instead of the 86 6 per cent, which it contains, but all the silver is found in the lead. In order to understand the process, it must be remembered that, on fusing galena with sodium carbonate out of contact with air, there are obtained lead, and a slag consisting of lead and sodium sulphide and sodium sulphate, thus: 4Na 2 CO ;j +7PbS = 4Pb + 3(PbS.Na 2 S)+Na 2 SO 4 + 4CO 2 . The addition of the potassium nitrate serves to decompose the sulpho-salt, the lead being sepa- rated, and the sodium and sulphur oxidized. /?. Mix 20 grm. of the powdered galena, 40 grm. black flux,* and 5 or 6 grm. very small iron nails, and fuse the mixture in a Hessian crucible at a bright redness. If a refractory gangue is present, add 2 to 3 grm. borax glass. The galena is first decom- posed by the carbonate and the carbon with the separation of lead and the formation of lead and potassium sulphide, the latter being then desulphurized by the iron at a higher temperature, when the fused lead separates. After cooling, break the crucible, and pro- ceed as in a. Care must be taken that the lead incloses no nails. According to BERTHIER this method yields 72 to 79 per cent, lead; from pure galena, however, 85-5 per cent, may be obtained if the temperature is not too high.f b. Method more particularly suitable for rich Argentiferous Galenas (Scorification j) . For this process there are required scorifiers of baked clay, * Prepared by deflagrating 1 part potassium nitrate with 2 parts potas- sium bitartrate. f " Probirkunst," by KERL, Leipzig, A. FELIX, 1866, p. 155. J Compare the excellent work by BODEMANN, A nleitung zur Probirkunst, edited by KERL, 2d ed., CLAUSTHAL, 1857, p. 287; also M etallurgische Probirkunst, by KERL. Leipzig, A. FELIX, 18fi6, p. 241; and Probirkunst, by C. A. M. BALLING, Braunschweig, FR. VIEWEG u. SOHN, 1879, p. 299. 259.] LEAD COMPOUNDS. 579 Fig. 112, and a properly constructed muffle furnace with good draught.* Mix 4 grm. of the finely powdered ore with 16 grm. of silver- free leadf in a scorifier, and cover the mixture uniformly with 16 grm. more of the lead. According to the nature of the im- purities present, there must be added borax, quartz, or glass. Borax is added when the galena contains much calcium, mag- nesium, zinc, etc., the quantity to be added varying according to the quantities of the foreign bases, and amounting at times up to 2 5 grm. No borax is added to ores that contain quartz or silicates, or only a little not more than 0-5 grm. To ores which contain little or no silicic acid, whether free or combined, add a very small quantity of glass or quartz. FIG O 112. FIG. 115. FIG. 116. FIG. 113. FIG. 114. The above proportions between ore and lead may be considered as normal; if the ore, however, contains a considerable quantity of zinc blende or pyrites, 48 grm. or even 64 grm. of lead are used instead of 32 grm., and if copper or tin compounds are present, even more must be taken. * The construction such a furnace should have is not detailed here, but it is accurately described in the above-named works. j- This may be prepared in the laboratory most conveniently by pre- cipitating lead-acetate solution with zinc. 580 DETERMINATION OF COMMERCIAL VALUES. [ 259. The scorifiers, charged as above, are placed into the muffle, Fig. 116, previously heated to bright redness, and the mouth of the muffle is closed with live coal in order to rapidly effect the fusion of the lead. The lead melts while the lighter ore floats on its surface and is roasted. The character of the vapors evolved during the roasting varies according to the nature of the prod- ucts evolved; the fumes of sulphur are light-gray, those of zinc are dense- white, those o arsenic grayish- white, and those of -antimony bluish. After 15 to 20 minutes a fluid slag forms, which completely surrounds the fused metal at the edges, and from which dense fumes of lead arise. Refractory samples require 35 minutes or more until this point is reached and the surface of the fused metal has become smooth. Now remove the live coal from the mouth of the muffle, close the damper of the furnace, and .allow the lead to be oxidized by the access of air until the scoriae completely or nearly cover the metal, then heat again very strongly for five minutes in order to render the slag very fluid. The process of scorification requires, as a rule, half an hour, or at most one hour. Now remove the samples from the muffles with suitable tongs about three feet long, Fig. 113, and pour the metal and slag into a mould, which may be made of sheet-iron or sheet-copper with hemispherical depressions 3 to 6 cm. in diameter; the mould should be warmed, and the depressions rubbed with reddle or chalk. The lead alloy obtained must form a single button, which must readily separate from the slag. Now hammer down the button so that it may easily be held with the three-foot tongs shown in Fig. 114, and subsequently placed on the cupel without projecting over the edge. In the operation here described, the ore is first roasted and litharge produced, the latter decomposing the metallic sulphides the sulphur being oxidized to sulphurous acid and the metals separating; the lead oxide formed in addition dissolves the earths and foreign oxides present and removes them as slag. 259.] LEAD COMPOUNDS. 581 Determining the Silver in the Argentiferous Lead Button. The silver in the lead button may be determined either in the wet -or the dry way. In laboratories where suitable muffle fur- naces are not at hand, the determination is frequently made hi the wet way ( 259, 4, a), whereas in metallurgical laboratories the dry way (cupellation) is invariably used.* For this operation there are required small cups or cupels of compressed bone-ash, Fig. 115, which are generally obtainable. Although 1 part of the porous cupel mass can absorb the oxide from 2 parts of lead, it is usual to calculate that it takes up the oxide from only 1 part of lead ; hence the button must not be much heavier than the cupel. As soon as half of the bottom of the muffle, Fig. 116, is at a white heat, it is ready for the cupellation. Introduce the empty cupels, and gradually push them toward the back until they are at a bright-red heat; for it is necessary that the lead-silver alloy now to be introduced should rapidly melt, otherwise small particles of lead are prone to adhere to the upper edge of the cupel. If the furnace is very hot, the separation soon begins; if not, place live coal in the mouth of the muffle in order to more rapidly effect the separation. As soon as the surface of the lead is in motion, close the damper of the furnace and leave only one small coal at the mouth of the muffle. It must now be the object to properly effect complete separation at the lowest possible temperature, for at too high a heat the cupel will absorb some of the silver with the litharge. Too low a temperature must equally be avoided, as in this case the lead will be chilled, and even though the heat is subsequently raised to the proper point, the results are not reliable. If the cupellation is properly conducted, the lead fumes slowly rise in curls to the middle of the muffle, and at the margin of the cupel, now at a reddish-brown heat, there forms a ring of imperfect crystals of lead. If the lead fumes disappear just above the cupels while these are at a bright-red heat, and if no crystals form at the * The description of this interesting and important operation is taken from BODEMANN-KERL'S work already mentioned. 582 DETERMINATION OF COMMERCIAL VALUES. [ 259. edges, the heat is too strong. If the lead fumes, on the other hand, rise to the vault of the muffle, and if the edges of the cupels appear dark brown, the heat is insufficient, and the sample is very apt to solidify. Toward the end of the cupellation the heat must again be raised, as the bead becomes less fusible as the proportion of silver in it increases, and the last portions of lead are entirely converted into litharge and absorbed by the cupels only at a higher tem- perature. The heat must not, however, be raised too soon, and then only gradually, nor must it be so high as to remelt the ring of lead crystals. At the end of the process, the residual net-like film of litharge disappears from the surface of the metal, the irri- descence ceases at the same time, and the globule of silver is sud- denly visible in all its purity the assay flashes. Allow to cool slowly in order to avoid the spitting of the silver, and which is caused by the violent escape of the oxygen absorbed by the fused silver. The surface of the silver globule must be silvery white and perfectly lustrous, and hemispherical or round, and readily detach- able from the cupel by aid of a small pair of pincers; and the surface which was in contact with the cupel must be clean and silvery white, though not lustrous, after brushing. Beads having projections of any kind on the lower surface, due to fissures or depressions in the cupel, must be rejected, as these projections always contain lead. After cleaning, the silver bead is weighed. If the lead added was not absolutely free from silver a correction must be made, the silver in the lead being first determined, and the quantity allowed for. After weighing, the silver bead may be tested for the presence of gold, and the quantity of this determined if possible according to Vol. I, p. 703 [169]. A small quantity of silver is invariably lost in cupellation. From investigations made by BURBIDGE HAMBLY * it appears that the loss increases with the proportion of the lead to the silver; thus with 1 part silver to 1 part lead the loss of silver was 5-5 * Chem. Gazette, p. 1856, 185; Chem. Centralblatt, 1857, p. 509. 259.] LEAD COMPOUNDS. 583 per 100 parts of silver; with 1 part silver to 15 parts lead the loss was 16-2; and with 1 part silver to 35 parts lead it was 18-8 parts silver. 4. DETERMINING THE SILVER IN GALENA IN THE WET WAY. a. Prepare a lead button containing the whole of the silver, according to 259, 3, a, a or 3, purify it so far as possible, dissolve in chlorine-free, moderately diluted nitric acid, dilute the solution largely, and add a little very dilute hydrochloric acid or solution of lead chloride. Set aside the turbid liquid in a warm place until the silver chloride has settled, then collect it, wash thoroughly with boiling water, and finally determine it as metallic silver (p. 575, /?, this volume). This method afforded me very satisfac- tory results in cases where the quantity of silver present was not too small (Analytical Supplement, 91), but with exceedingly small quantities this method is inapplicable because very small traces of silver chloride remain dissolved in the liquid containing much lead nitrate (HAMPE*). Regarding the concentration of silver in lead, see p. 589 this volume. 6. Treat the nitric-acid solution of the regulus according to PISANI'S method, p. 349. Take care that the sulphuric acid used for precipitating the lead, and the calcium carbonate used for neutralizing the acid, are both perfectly free from chlorine com- pounds. I have had no experience with this method. c. C. A. M. BALLING f recommends the following method, which dispenses with the preparation of a regulus: Mix 2 to 5 grm. of the finely powdered galena with 3 to 4 times its weight of a mix- ture of equal parts of sodium carbonate and potassium nitrate, introduce the whole into a porcelain crucible of suitable size, cover, heat the contents to fusion, and stir well with a hot glass rod. When cold place the crucible in a porcelain dish, soften the mass with water, and empty the contents of the crucible into the porcelain dish; then warm, filter, and wash the residue, trans- fer again to the dish, dissolve the lead oxide containing silver in diluted pure nitric acid, and evaporate to dry ness ; now take up * Zeitschr. f. analyt. Chem., xi, 221. f Chem. CentralbL, 1879, p. 490. 584 DETERMINATION OF COMMERCIAL VALUES. [ 259- the residue with water acidulated with a little nitric acid, warm,, filter the solution into a flask, wash with hot water, allow to cool, add ammonio-ferric alum solution, and titrate the silver accord- ing to VOLHARD'S method with ammonium-sulphocyanate solu- tion (compare p. 570, this volume). The ammonium-sulpho- cyanate solution should be diluted so that 1 c.c. should be equiva- lent to 1 c.c. of a solution containing 1 grm. metallic silver per litre. 1 c.c. of the sulphocyanate solution will thus represent 1 mgm. silver. I have had no personal experience with this method. B. VARIETIES OF METALLIC LEAD. The purity of the metallic lead which has to be examined varies greatly. In the following paragraphs are detailed the- analyses of refined lead (soft lead), crude lead, and hard lead. a. ANALYSIS OF REFINED LEAD (SOFT LEAD). This contains from 99-96 to 99-99 per cent, metallic lead, hence only very minute quantities of other metals, such as silver, copper, bismuth, cadmium, antimony, arsenic, iron, nickel, cobalt, zinc, and manganese. First Method* 1. Cut up the lead to be analyzed into large pieces, and scrape the surfaces of each with a bright knife until they are perfectly clean and bright; then warm them with dilute hydrochloric acid, wash with hot water, and dry them rapidly. If this cleaning process is omitted, there is danger that the mechanically adhering impurities may appreciably affect the accuracy of the results. 2. Weigh off exactly 200 grm. of lead cleaned as in 1, and dis- solve (in a flask of 1000 to 1500 c.c. capacity) in pure diluted nitric acid, of which about 500 c.c. acid of sp. gr. 1-2 are required, with the addition of enough water (about 500 c.c.) to prevent the separa- tion of any lead nitrate. Solution is assisted by suitably warming; * R. FRESENIUS, "On the Analysis of Soft or Refined Lead," Zeitschr. /. analyt. Ghent., vm, 148. 259.] LEAD COMPOUNDS. 585 an unnecessary excess of nitric acid must be avoided. Allow the solution to stand for from 12 to 24 hours. As 200 grm. of lead yield practically 320 grm. lead nitrate, (Fb[NOJ 2 ), and as the latter requires about two parts of water for solution, no lead nitrate will crystallize out if the solution be diluted to 1 litre. Should this nevertheless be the case, it is the result of using too large an excess of nitric acid, as it is well known that lead nitrate is far more insoluble in dilute nitric acid than in water. 3. As a rule (i.e., in the case of all pure soft leads) the solutions are and remain clear. It is only in the case of leads which are rather rich in antimony that there forms a more or less decided quantity of a white precipitate, either immediately or on standing. These less usual cases are treated as under 15; we here presuppose that the solution has remained clear. 4. Transfer the solution completely to a 2-litre flask, add 115 grm. (about 62 to 63 c.c.) of perfectly pure, concentrated sulphuric acid (approximately measured or weighed), allow to cool, fill up to the mark, mix thoroughly by shaking, and allow to settle. The quantity of sulphuric acid added should be so adjusted that there will remain an excess of from about 10 to 12 grm. After the precipitated lead sulphate has subsided, siphon off the clear, or nearly clear, supernatant fluid by means of a siphon previously filled with a small quantity of the liquid. In this manner over 1750 c.c. of the liquid may be easily siphoned off. Of course the siphoning may be replaced by filtration through a dry filter, but the method of siphoning deserves the preference, as it excludes any impurities. Measure off exactly 1750 c.c. of the clear or nearly clear liquid, and evaporate it under a perfectly clean draught hood, and without covering the dish with paper, until sulphuric- acid vapors are freely evolved a sign that the nitric acid has been driven off. Allow to cool, add about 60 c.c. water, collect the slight quantity of separated lead sulphate on a small filter previously thoroughly washed with hydrochloric acid and water, and then wash the precipitate with water. 5. The small quantity of lead sulphate so obtained frequently 586 DETERMINATION OF COMMERCIAL VALUES. [ 259. contains slight quantities of antimony. Dissolve it in hydro- chloric acid, dilute with at least ten times as much hydrogen- sulphide water as the hydrochloric acid employed for solution, heat, and treat with hydrogen sulphide. After subsidence, collect the precipitate, wash, spread out the filter in a dish, and treat the precipitate for a short time at near the boiling-point with a solu- tion of pure potassium sulphide or ammonium sulphide, with the addition of a small quantity of pure sulphur. Filter off, wash, acidulate the filtrate with hydrochloric acid, and allow the precipi- tate to subside at a gentle heat. 6. Into the sulphuric-acid solution obtained in 4, and which, if necessary, is diluted with water to 200 c.c., pass hydrogen sul- phide until the precipitate subsides, keeping the temperature at about 70; then allow to stand in a warm place for 12 hours, pass through a small filter, and wash the precipitate. Treat the filtrate and washings according to 9, but the precipitate heat with potas- sium-sulphide solution with the addition of a trace of sulphur as in 5. Acidulate the filtrate containing potassium sulphide with hydrochloric acid, and allow the precipitate to subside at a gentle heat. 7. The small quantity of precipitate insoluble in potassium sulphide, and containing the metals of the fifth group, treat, after spreading out the filter in a small dish, with diluted nitric acid (about 1 part nitric acid of sp. gr. 1-2 and 2 parts water) at near the boiling-point. When the precipitate has dissolved, filter, wash the filter, dry it, and incinerate; add the ashes to the nitric-acid solution, and evaporate this after adding 2 c.c. diluted sulphuric acid, until all the nitric acid has been driven off; then add a little water, filter off the trace of lead sulphate which will have separated, nearly neutralize with pure potassa lye, then add sodium carbonate and a little potassium cyanide free from potassium sulphide, and gently heat. If a precipitate forms, dissolve it, after washing, in dilute nitric acid, and in the solution determine the bismuth by precipitating with ammonium carbonate and weighing as oxide. To the solution filtered from the bismuth, or which has remained clear after adding potassium cyanide, add first a further 259.] LEAD COMPOUNDS. 587 quantity of potassium cyanide, and then a few drops potassium- sulphide solution. If a precipitate forms it may contain cadmium sulphide or silver sulphide. Collect it, dissolve in hot dilute nitric acid, precipitate any silver present by adding a few drops hydro- chloric acid, evaporate the filtrate almost to dryness, and test with sodium carbonate to see if any cadmium is precipitated. If this is the case, determine the cadmium* as oxide, the best method being to dissolve the well-washed precipitate in nitric acid, evapo- rate, ignite, and weigh the residue. To the liquid filtered from the silver and cadmium sulphides, or which has remained clear on adding potassium sulphide, add a little sulphuric and nitric acids and a few drops hydrochloric acid, and evaporate until the odor of hydrocyanic acid has altogether disappeared; then precipitate the clear, or, if necessary, filtered, solution with hydrogen sulphide, and determine the copper as sulphide (Vol. I, p. 375). If the quantity of copper is very small, control the determination by a volumetric analysis, by again dissolving the copper sulphide in nitric acid, evaporating the solution to dryness with sulphuric acid, and decomposing the cupric sulphate with potassium iodide {Vol. I, p. 377, a). If no cadmium is present, the separation of bismuth from copper by means of ammonia and ammonium carbonate is simpler; if, however, it is present, which cannot, as a rule, be known, the analysis is thereby rendered more difficult, because the cadmium may be partly thrown down with the bismuth precipitate, and partly retained in solution with the copper. It must never be forgotten to test the acid copper solution for silver by adding hydrochloric acid before the final precipitation with hydrogen sulphide, as otherwise the copper sulphide may be contaminated with silver sulphide 8. The precipitates obtained in 5 and 6 by acidulating the potassium-sulphide solutions with hydrochloric acid collect on a small filter, dissolve in an excess of potassa lye while still moist, treat with chlorine, and separate and determine the antimony and arsenic according to BUNSEN'S method (pp. 556 and 557 this volume). The antimony sulphide may be advantageously col- 588 DETERMINATION OF COMMERCIAL VALUES. [ 259. lected in an asbestos filter-tube according to Vol. -I, p. 397, and Weighed as black antimony trisulphide. 9. Unite the filtrate from 6 with the washings, and if they exceed 500 c.c. concentrate by evaporation, then transfer to a flask, make alkaline with ammonia, and add ammonium sulphide. Fill up the flask to the neck, stopper, and set aside for at least twenty-four hours. In any case, filter only when the slight precipitate has completely subsided. Add acetic acid to the filtrate just to acidity, then add ammonium acetate, and evaporate at a gentle heat so that if a trace of nickel sulphide is still retained in solution by the ammonium sulphide, it may be precipitated together with the sulphur. After subsidence, collect this sulphur on a filter. 10. Treat the precipitate afforded by ammonium sulphide in 9, just after collecting, and on the filter, with a mixture of about 6 parts hydrogen-sulphide water and 1 part hydrochloric acid of sp. gr. 1 12, and pour the filtrate repeatedly back onto the filter. By this treatment the iron and zinc sulphides are dissolved, while the nickel and cobalt sulphides remain. This filter, and that obtained in 9. the sulphur of which may contain nickel, incinerate together, treat with a little nitrohydrochloric acid, evaporate to a small bulk, make just alkaline with ammonia add a little ammonium carbo- nate, filter, and heat the ammoniacal liquid with a slight excess of pure potassa lye in a platinum dish until ammonia is no longer evolved. If weighable flocks separate, collect them, wash dry, incinerate, ignite, weigh, and test with the blowpipe whether the nickelous oxide contains any cobaltous oxide. 11. The filtrate obtained in 10 by treating the ammonium- sulphide precipitate with very dilute hydrochloric acid, concen- trate by evaporation, and finally with the addition of a little nitric acid ; then precipitate with ammonia, warm, and collect the flocks of ferric hydroxide; redissolve this in hydrochloric acid, again precipitate with ammonia, wash, dry, incinerate, and weigh the ferric oxide. As a control the oxide may be fused with potassium disulphate, reduced with zinc, and the ferrous oxide determined volumetrically with potassium permanganate. 12. To the filtrate from the ferric hydroxide add a little ammo- 259.] LEAD COMPOUNDS. 589 nium sulphide, and allow to stand for at least twenty-four hours at a gentle heat. If weighable flocks separate, collect them, wash, and treat at once upon the filter with diluted acetic acid in order to dissolve out any admixed manganese sulphide. If a trace of zinc sulphide remains on the filter, it is best weighed by converting the sulphide into oxide by VOLHARD'S method (see p. 432 this volume). Evaporate the acetic-acid solution, however, to a small volume, and test with caustic potassa for any manganese that may be present. 13. In calculating the constituents found thus far, it must not be forgotten that the quantities obtained correspond with 179 grm. of lead, and not 200 grm. These figures result from the fact that the 2-litre flask, when filled to the neck, contains 45 c.c. lead sulphate and 1955 c.c. solution, and that of the latter only 1750 c.c. have been used ; hence 1955 c.c. : 200 grm. : : 1750 c.c. : 179 03, or in round numbers, 179 grm. 14. The silver * is best determined by cupellation (pp. 581 and 582 this volume), because exceedingly slight traces of silver cannot be precipitated by hydrochloric acid from the nitric-acid solution of lead (p. 583, 4, a, this volume). As many soft leads, e.g., the Oberharz refined lead (HAMPE), contain only 0-0005 per cent, silver, 200 grm. of the lead must be cupelled in order to obtain 1 mgm. of silver. If the operator lacks the facilities for the cupellation of so large a quantity of metal, the volume of the metal may be reduced, according to MERRicK,f by fusing the lead in a rather capacious Hessian crucible and adding half its weight of potassium nitrate. Then increase the heat until the crucible is white-hot up to its margin, stir the contents with a pointed iron rod, remove from the heat before the lead oxide has eaten through * The cause of the difference in the silver in lead bars is often due to the unequal distribution of the silver in the bars. The silver collects to a greater extent in the portions which solidify first than in those that remain fluid longer, hence the outer and upper portions are richer in silver than the middle and lower portions. SCHWEITZER (Zeitschr. f. analyt. Chem., xvi, 504) found from this cause, in a bar of lead, differences between 79-83 oz. (middle portion) and 104-54 oz. (upper length) per ton of lead. t Zeitschr. f. analyt. Chem., x, 494. 590 DETERMINATION OF COMMERCIAL VALUES. [ 259. the crucible, allow to cool, and break the latter. In this manner the silver in lead may be concentrated so that its determination is rendered possible by the wet way. 15. Lastly, there remain to be considered those cases in which the leads contain rather more antimony. In these there is formed. even during the solution, or on its standing, a white precipitate of antimony oxide and antimonic antimonate, which may, however, also contain arsenic and traces of other metals. Collect the pre- cipitate, wash, dissolve in hydrochloric acid, dilute exactly to 100 c.c. with water acidulated with tartaric acid, and of the solu- tion take a quantity in the proportion of 1955 : 1750 (see above, 13), i.e., 89-5 c.c., and precipitate this with hydrogen sulphide; mix the precipitate formed with that obtained in 6 by precipitation with hydrogen sulphide and treat both together as already de- scribed. 16. If other metals besides those already noted above are present in soft leads, the processes must, of course, be correspondingly modified. 17. The quantity of lead is found from the difference. It is useless to make a direct determination of lead because it would in no way control the accuracy of the determinations of the foreign metals present. Second Method (by W. HAMPE *). 1. Beat out the carefully cleaned metal on a steel anvil with a polished steel hammer, into thin sheets, and cut these into small strips with a pair of scissors. To determine the foreign metals, excepting silver, present in the lead, 400 grm. are used. 200 grm. each are dissolved in large covered beakers, in a mixture of 500 c.c. nitric acid of sp. gr. 1-2, and 500 cc. water, and to the still hot, clear solutions add 70 c.c. of pure concentrated sulphuric acid mixed with a little water to precipitate the lead. Decant the clear liquids from both beakers, so far as possible, into a porce- lain dish, and wash the united precipitates with water acidulated * Zeitschr. /. das Berg-, Hutten-, und Salinenwesen in dem preussischen Staate, xviu, 195; Zeitschr. /. analyt. Chem., xi, 215. 259.] LEAD COMPOUNDS. 591 with sulphuric acid, either by decantation 8 to 10 times or on a vacuum filter, the platinum cone of which is fitted with a very small filter. Concentrate the washings by evaporation, add to the decanted liquid, and lastly evaporate the whole, continuing the heat until the greater part of the sulphuric acid is driven off. 2. When the residue obtained hi 1 is cold, mix it with water, whereby a still further small quantity of lead is precipitated; then boil the strongly acid liquid for some time so that no basic bismuth sulphate will remain with the lead sulphate, add a drop of hydrochloric acid in order to precipitate the silver, filter, and wash with diluted sulphuric acid. 3. The precipitate obtained in 2, and containing some admixed lead antimonate, boil with potassium-sulphide solution, and filter. The solution we will term A. 4. The solution filtered off from the lead sulphate and silver chloride in 2, treat as in the First Method (6 and 7) hi order to precipitate the metals of the fifth and sixth groups. There are thus obtained a filtrate containing the metals of the fourth group, and a precipitate. On treating the latter with potassium-sulphide solution, however, there is obtained an insoluble residue, and a potassium-sulphide solution containing the remainder of the anti- mony and arsenic (B). 5. Treat the solutions A and B obtained in 3 and 4 with diluted sulphuric acid to precipitate the metallic sulphides, remove the hydrogen sulphide by evaporation, filter, and wash with water to which has been added a little ammonium nitrate and a few drops nitric acid (because on washing antimony sulphide with pure water the washings may easily pass through the filter turbid). Remove any excess of sulphur from the precipitate by treatment with carbon disulphide, dissolve the residue in freshly prepared, strong ammonium-sulphide solution, evaporate the solution on a water-bath, treat the residue with hydrochloric acid and potas- sium chlorate at a moderate heat, and separate the arsenic and antimony according to Vol. I, p. 720 [204]. The antimony sulphide precipitated by hydrogen sulphide in the filtrate from the am- monium-magnesium arsenate, dissolve, after washing in warm 592 DETERMINATION OF COMMERCIAL VALUES. [ 259. freshly prepared ammonium sulphide, evaporate the solution in a weighed porcelain crucible, at first only at a moderate heat on a water-bath, then oxidize the evaporation-residue with fuming nitric acid, ignite, and weigh the antimony antimonate obtained. 6. The separation of the metals of the fifth group, the sulphides of which constitute the residue insoluble in potassium-sulphide solution obtained in 4 ; is effected as in the First Method (7) ; but HAMPE prefers to dissolve the carbonates of bismuth and cadmium in hot nitric acid, evaporate the solutions in small weighed porcelain crucibles, ignite the residues, and weigh the oxides thus obtained. 7. Evaporate the filtrate obtained in 4, add ammonia to alka- line reaction, and precipitate the metals of the fourth group with ammonium sulphide; if the solution is brown from the presence of dissolved nickel sulphide, boil until the brown color has dis- appeared, filter, wash first with water, then with alcohol, remove any admixed sulphur by treatment with carbon disulphide, and separate nickel, cobalt, iron, manganese, and zinc as in the First Method (9 to 12). Lastly separate the cobalt and nickel by means of potassium nitrite. 8. The silver is determined by cupellation. b. ANALYSIS OF CRUDE LEAD AND HARD LEAD. Crude lead contains from 95 to 99 per cent, lead, 0-01 to 0-18 silver, and somewhat larger quantities than this of the other metals that have been considered in the analysis of soft lead. Hard lead differs from the other varieties of lead chiefly in its containing a relatively large quantity of antimony, which ranges from about 2 to 6 per cent. In the analysis of crude lead quan- tities of from 50 to 200 grm. are taken, according to the degree of purity; in the case of hard lead, from 5 to 10 grm. are sufficient. Treat either of the leads with a warm mixture of equal parts of nitric acid of sp. gr. 1-2 and water until all soluble matter is dis- solved, dilute with water, allow to settle, and filter off the white precipitate which nearly always remains, and which consists chiefly of oxygen compounds of antimony and of lead antimonate. After washing, separate the precipitate from the filter, without 259.] LEAD COMPOUNDS. 593 destroying the latter, by careful washing, or by drying and rubbing; in the former case evaporate the water in the precipitate in a porcelain crucible, and fuse the residue with 3 to 4 parts sulphurated potassa in the covered crucible. Dissolve the melt in hot water, pass through the filter first used, ahd then treat this, together with the precipitate thrown down from the sulpho-salt solution by diluted sulphuric acid, and also the precipitate insoluble in the sulphurated-potassa solution, and consisting, according to HAMPE, of lead, silver, and bismuth sulphides, together with the analogous precipitates to be obtained from the sulphuric- acid solution. Precipitate the lead from the nitric-acid solution by adding a moderate excess of sulphuric acid, allow the precipitate to sub- side, decant the solution, wash the precipitate by decantation or on a vacuum filter (see a, Second Method, 1, p. 481), and evaporate until the greater part of the excess of sulphuric acid has been ex- pelled. The residue is then best treated, according to HAMPE, as follows: Add a little water and hydrochloric acid, boil, then allow to cool, add alcohol, filter after twelve hours, and wash with alcohol acidulated with hydrochloric acid. In this manner all the arsenic, antimony, copper, bismuth, cadmium, iron, etc., besides small quantities of lead, are obtained in solution. Evap- orate off all the alcohol, precipitate with hydrogen sulphide, sep- arate the metals of the fifth and sixth groups by fusing with potas- sium sulphide, and then determine the individual metals accord- ing to the methods employed for soft lead. If BUNSEN'S method is used for the separation of arsenic from antimony, it is advisable, as the quantity of antimony present is large, to again dissolve in potassa lye the antimony sulphide first precipitated, and to repeat the separation, in order to obtain the antimony sulphide per- fectly free from arsenic. The determination of the iron, zinc, and silver is effected as in a, this section. 594 DETERMINATION OF COMMERCIAL VALUES. [ 259. [C. ELECTROLYTIC SEPARATION AND DETERMINATION OF LEAD. According to A. HOLLARD * the estimation of lead by elec- trolysis in the state of dioxide is of incomparable exactness and simplicity, provided that a certain number of precautions are ob- served very closely, such as density of current, composition of the electrolyte, temperature of desiccation of the deposit of lead dioxide, etc. The author has also laid down the conditions under which the method may be applied to the most widely divergent alloys. It is only after experiments carried out under the most varying conditions and methods of control, during the course of several years, that the author publishes this method, believing that it will be found to be of great service. The deposits of lead dioxide which occur exclusively on the anode are very adherent, and correspond exactly to the formula PbO 2 ; further, no trace of metallic lead is deposited on the cathode. The quantity of lead submitted to estimation need not be more than 0-2 grm. ; with a larger quantity, in fact, there is a danger of the deposit not being sufficiently adherent. Electrolytic Apparatus. The electrodes consist of a truncated cone of platinum which serves as anode, and on which the lead dioxide is deposited; the cathode is a spiral of platinum wire fixed on a stand. They are, in fact, LUCKOW'S apparatus modified as to construction and dimensions; the truncated cone is made of a sheet of pure platinum; its upper diameter is 18 mm. and its lower diameter 45 mm., its generatrix 63 mm. A hard platinum wire is gold-soldered to the trunk of the cone. Each electrode weighs about 20 grm. The vessels containing the electrolytes are of ordinary cylin- drical Bohemian glass, about 6-5 cm. diameter, holding about 370 to 400 c.c. The solution of the alloy, as well as the electrolysis of the lead, is conducted in the same beaker; the whole operation does not require, as will be seen, either decantation or filtration. During the a' tack with acid the beaker must be covered with a * Bull. Soc. Chim. [3], xiv, No. 22.Chem. News, LXXX, 123. 259.] LEAD COMPOUNDS. 595 unnel, the edge of which should rest just inside the edge of the beaker, forming a little gutter in which a few drops of water will make a perfect hydraulic joint; all loss by projection is thus avoided. The distance from the lower edge of the cone to the foot of the spiral should be about 6 mm. For better receiving the electrolytic deposit of lead the cone should not be polished, but dull, so that the deposit will adhere to it more easily. This can be effected by immersing the platinum hi aqua regia for a few hours. Estimation of Pure Lead. The lead is dissolved in dilute nitric acid. The solution, diluted to about 350 c.c., should contain 80 c.c. of ordinary pure nitric acid in the free state. With a less quantity of acid there is a lia- bility to deposit part of the lead on the cathode. The electrolysis is effected at the ordinary temperature with a current of 0-15 ampere. The voltage cannot be denned; it depends on the quan- tity of lead hi the electrolyte, and, hi the case of alloys, on the nature and proportion of foreign metals present.* The cone should be plunged completely into the bath, and the foot of the spiral should be as near as possible to the bottom of the beaker. The electrolysis goes on at the ordinary temperature. At the end of twenty-four hours the precipitation is complete and the deposit very adherent. The cone is then plunged successively into two beakers filled with distilled water, and then placed in an oven and heated gradually to 200, which temperature should be maintained for a quarter of an hour. This temperature is abso- lutely necessary to obtain a deposit corresponding exactly with the formula PbO 2 . In CH. MARIE'S f method the lead in the form of sulphate or chloride is placed in the beaker in which it is to be electrolyzed, and attacked with nitric acid to which crystals of ammonium nitrate are gradually added. To hasten the solution it is heated on a water-bath. When all the sulphate is dissolved the solution * For 0-2 grm. of pure lead under the conditions described above the electromotive force should be from 2-'6 to 2-7 volts. t Bull. Soc. Chim. [3], xxiu, No. 12. Chemical News, LXXXI, p. 51. 596 DETERMINATION OF COMMERCIAL VALUES. [ 259- is diluted with warm water, and the electrolysis is proceeded with in the ordinary manner, keeping the temperature up to 60 70 The quantities of the reagents necessary are as follows: For 0-3 grm. of sulphate it is necessary to have 5 grm. of ammonium nitrate; as for the nitric acid, its quantity is determined by this condition, viz., that after dilution the liquid ought to contain 10 per cent, of free acid. As the sulphate dissolves more easily in acid which has been slightly diluted than in concentrated acid, it is as well, before adding the latter, to pour a little water over the sulphate. In three hours, with an unpolished platinum electrode having a surface of 90 square cm., and with a current of 0-3 ampere intensity, 0-4 grm. of lead dioxide can easily be deposited. This method allows of the application of electrolysis to the analy- sis of lead glass. It is sufficient to attack the finely powdered glass with hydrofluoric acid containing the necessary quantity of sulphuric acid to transform the bases into sulphates. Too great an excess of sulphuric acid will prevent the solution of the sulphate of lead, which should be carried out as described above. After the electrolysis we can proceed immediately to the estimation of the alkaline metals, if the material under examination contains no metal of the iron group, or of the alkaline-earthy group. The chromates of lead dissolve still more easily than the sul- phates in the mixture of nitric acid and nitrate of ammonia. For 0-5 grm. of chromate 2 grm. of nitrate suffice; as for the nitric acid, it is sufficient for the final solution to contain 10 per cent. The electrolysis is conducted as in the case of the sulphate; the chromic acid, during the operation, is completely brought into the state of chromium sesquioxide directly precipitable by am- monia. From the simplicity of the analytical method and the exact- ness of the results furnished, this method will be very useful for the analysis of such important commercial products as the silicates and chromates of lead. TRANSLATOR.] 259.] LEAD COMPOUNDS. 597 C. LEAD OXIDES AND SALTS. The lead oxides and salts met with in commerce, e.g. mas- sicot, litharge, white lead, and lead sulphate, present no difficulties in analysis. The analysis of minium and of the more impure varieties of lead acetate, however, require a brief mention. a. MINIUM. Minium is frequently the subject of analysis in technical labora- tories, and it is by no means a question of simply detecting the impurities and adulterations, but the determination in particular of also the relation between the lead peroxide and the lead oxide. The impurities insoluble in acids remain behind on dissolving the minium in diluted nitric acid to which is added some alcohol, sugar, or oxalic acid. If the nitric-acid solution is made up to a definite volume, an aliquot portion may be qualitatively tested for any dissolved foreign metals, while another portion may be used for the quantitative determination of the lead according to Vol. I, p. 355, 3. Any carbonic acid present may be determined by the method in Vol. I, p. 493, employing a larger quantity of minium, and using nitric acid for the expulsion of the carbon dioxide. The lead-peroxide content can be determined in the same manner as the manganese dioxide is determined in manganese ores, and in fact by means of oxalic and sulphuric acids according to p. 458, and pp. 462 and 463 this volume, and also iodometrically, according to p. 465, 6, this volume. FR. Lux,* finally has devised the following process for rapidly determining the value of minium, with sufficient accuracy for commercial purposes; the process is also based on the action of oxalic acid on lead peroxide, thus: PbO 2 + C 2 H 2 O 4 = PbO + 2C0 2 + H 2 0. If the quantity of oxalic acid originally added is known, and a determination made of the acid remaining after the reaction is complete, which may be easily done with a solution of potassium permanganate after dissolving the lead oxalate formed in nitric * Zeitschr. f. analyt. Chem., xrx, 153. 598 DETERMINATION OF COMMERCIAL VALUES. [ 259. acid, the difference will give the quantity of oxalic acid decom- posed, and from this the lead dioxide present may be calculated, since 1 eq. of C 2 H 2 O 4 corresponds to 1 eq. of lead dioxide. It is convenient to employ a one-fifth normal oxalic-acid solu- tion, hence containing 12-605 grm. crystallized oxalic acid (H 2 C 2 O 4 + 2H 2 O) per litre, and an equivalent solution of potassium per- manganate, of which 1 c.c. corresponds with 1 c.c. of the oxalic- acid solution (Vol. I, pp. 316 and 317). Place 2-069 grm. of the minium (the one-hundredth part of the lead equivalent expressed in grammes) to be tested in a porcelain dish of about 300 c.c. capacity, pour over it 20 to 30 c.c. diluted nitric acid (of sp. gr. 1-2) and stir while warming gently. In a few minutes the minium will have been decomposed into lead monoxide, which dissolves, and dioxide, which remains undissolved. Now add 50 c.c. of the oxalic-acid solution, and heat to boiling; the lead dioxide is im- mediately decomposed and dissolved, while any insoluble im- purities (barytes, lead sulphate, clay, sand, ferric oxide, larger quantities of gypsum) remain. Maintain the solution at the boiling- point, and, without removing any insoluble residue, add at once 5 to 10 c.c. of the potassium-permanganate solution. As soon as this is decolorized add fresh portions, until all the oxalic acid present has been decomposed. The titration may be considered at an end when the pink color afforded by two drops of the perman- ganate solution does not completely disappear within half a minute. (If the permanganate solution is added at first only in drops, the decomposition of the oxalic acid takes place but very slowly.) On deducting the number of c.c. of permanganate solution used from 50, the difference will give the quantity of lead dioxide present expressed in per cents. After the liquid has been decolorized by a few drops oxalic- acid solution, add first ammonia almost to neutrality, and then ammonium or sodium acetate in sufficient quantity, and determine the lead volumetrically with potassium chromate solution ac- cording to Vol. I, p. 360, 6. On deducting the lead dioxide from the total lead we find the lead present in the minium as lead mon- oxide. The determination of the lead dioxide is not interfered 259.] LEAD COMPOUNDS. 599 with by any of the impurities or adulterants present in the min- ium; that of the lead, however, can only be properly made in the manner described when barium carbonate is absent (and this should scarcely ever be present in minium). 6. LEAD ACETATE (SUGAR OF LEAD). Besides the crystallized, almost pure lead acetate, the properties and composition of which may be decided usually without a quan- titative analysis, other varieties of lead acetate occur in com- merce regarding which this cannot be said, and which, according to their method of preparation, contain more or less lead and acetic acid. To these belong the so-called amorphous white lead acetate as well as the yellow and brown acetates (which are obtained by dissolving litharge in impure acetic acid made from wood vinegar, or in rectified or crude pyroligneous acid). All kinds of lead acetates may now be simply analyzed by a process devised by me,* and which is a suitable combination of gravimetric with volumetric analysis. The principle of the method is as follows: On dissolving the lead acetate to be examined in water in a flask, and adding normal sulphuric acid in slight excess, all the lead will be obtained in the precipitate as lead sulphate, and all the acetic acid together with the excess of sulphuric acid in the solution. On now filling the flask to the mark, and adding a volume of water equal to that displaced by the lead sulphate (and which can be ascertained with sufficient accuracy as the lead content of lead acetate varies only between certain 'limits) , the above-named acids are obtained in a known volume of liquid. If now the excess of sulphuric acid is determined in a measured quantity of the clear liquid by means of barium chloride, the entire quantity of lead present may be readily calculated; for since the total quantity of sulphuric acid is known, and that re- maining is determined, the difference will give that which has com- bined with the lead, and thus, calculating 1 eq. of the sulphuric acid for 1 eq. of lead, also the quantity of the latter. * Zeitschr. f. analyt. Chem., xin, 30. 600 DETERMINATION OF COMMERCIAL VALUES. [_ 259. In an equally simple manner the quantity of acetic acid (together with the small quantities of propionic and butyric acids, etc.) may be ascertained, for, on determining the number of c.c. of normal soda solution required to neutralize a measured quantity of the liquid containing the acetic, etc., acids, and the excess of sulphuric acid, and deducting from this the quantity of soda solution required to neutralize the already known excess of sul- phuric acid, the difference will correspond to the acetic acid, etc., from which the quantity of the latter may hence be easily calcu- lated. The following simple method is recommended in practice: Weigh off 10 grm. of the lead acetate to be examined, dissolve it in water in a 500-c.c. flask, add 60 c.c. normal sulphuric acid, fill the flask, which has also a mark at 501-3 c.c., to the latter mark, close with a rubber stopper, shake thoroughly, and allow to settle. 1. In 100 c.c. of the clear solution determine the sulphuric acid with barium chloride, calculate the quantity for the 500 c.c., deduct the result from the sulphuric acid contained in the 60 c.c. of normal solution (i.e. 2-943 grm. H 2 SO 4 , or 2-402 grm. SO 3 ), and from the difference calculate the equivalent lead. As this refers to 10 grm. the percentage will be obtained by multiplying the result by 10. 2. To another 100 c.c. of the clear solution add a few drops litmus tincture, then add normal soda solution to neutrality, cal- culate the number of c.c. used to the 500 c.c., and deduct from this nUmber of c.c. of soda solution corresponding with the sul- phuric acid found in 1 and contained in the 500 c.c. of liquid; from the difference the acetic acid contained in the 10 grm. of lead acetate is then calculated. [M. LIEBIG * recommends the following method for the deter- mination of the proportion of lead dioxide in minium. This method is very convenient, and can be generally recommended on account of the sharpness of the end of the reaction: 0-5 gramme of finely powdered minium is placed in a small * Zeitschr. f. angew. Chem., 1901, p. 528. Chem. News, LXXXV, 229. 260.] MERCURY COMPOUNDS. 601 Lrlenmeyer flask, with a little distilled water. By means of a burette 25 c.c. of a decinormal solution of sodium thiosulphate are added, then 10 c.c. of about 30-per cent, acetic acid. On well shaking, the mass goes into solution. Then add 10 c.c. of a 10-per cent, potassium-iodide solution, and 2 or 3 c.c. of a solu- tion of zinc iodide and starch, and titrate the excess of thio- sulphate with a decinormal solution of iodine. By multiplying the number of c.c. of iodine used by 238-92 (the molecular weight of lead dioxide), we obtain the proportion of dioxide present in the minium. The end of the reaction is recognized by the change of color caused by the lead iodide formed from citron-yellow, as it is at first, to a deep dirty yellow. As above stated, the reaction is very sharp and rapid, and it is not necessary to have a very practised eye to perform the opera- tion. TRANSLATOR.] 18. MERCURY COMPOUNDS. 260. A. MERCURY ORES. The analysis of mercury ores scarcely requires special mention, as all that is necessary has been detailed in 118, 162, 163, and 164. As a rule the method described in 118, 1, a, is the best and most rapid for the determination of mercury. Mention may, however, here be made of A. ESCHKA'S method * for determining mercury in ores, and which is fairly rapid, while giving sufficiently accurate results for technical purposes, particularly in testing poor ores. For this method a porcelain crucible is required, with an even rim, ground if necessary, and provided with a tightly fitting, very highly concave bevel-edged cover of gold plate. Introduce the powdered ore into the crucible, taking about 5 grm. if the ore con- tains from 1 to 10 per cent., 2 grm. if it contains from 10 to 30 per * Oesterr. Zeitschr. /. Berg- u. Hiittenwesen, 1872, No. 9; DINGLER'S polyt. Journ., cciv, 47; Zeitschr. f. analyt. Chem., xi, 344. 602 DETERMINATION OF COMMERCIAL VALUES. [ 260. cent., or 1 grm. if it contains above 30 per cent., of mercury. Mix the powdered ore with half its weight of clean iron filings, perfectly free particularly from oil, with the aid of a glass rod, cover the mixture with a uniform layer of iron filings 0-5 to 1 cm. in thick- ness, and place the previously weighed gold cover in position; fill the concavity of the gold cover with distilled water to keep it cool, and then heat the crucible for ten minutes with a flame the tip of which plays around the bottom. Heating for this length of time suffices to volatilize all the mercury from the ore and to cause it to collect on the gold cover. Now remove the cover, pour out the water from it, wash the mercury mirror on the convex sur- face with alcohol, dry at 100, and weigh after it has become per- fectly cold in the desiccator. The increase in weight of the cover represents the weight of the mercury contained in the ore exam- ined. The gold cover is weighed by placing it on a porcelain crucible as a support, and weighing this each time with it. When the test has been completed, heat the cover under a good draught, at first very gently, but finally to bright redness, in order to free it from mercury and prepare it for the next assay. The weight of the cover changes but very little with repeated use, provided the necessary care is exercised in heating it. If larger quantities of mercury have been volatilized during the examination, a mobile amalgam is obtained which flows about on inclining the cover. Should this occur, the alcohol used in washing must be collected, of course, in order not to lose any mercury. From the test analyses given by ESCHKA it appears that this method gives results that are always too low. The loss, for in- stance, amounted : to 0-002 grm. mercury in 0-083 grm. cinnabar, and to 0-005 grm. mercury in 0-2855 cinnabar. B. METALLIC MERCURY. The analysis of commercial mercury offers certain difficulties because quite considerable quantities must be taken to be oper- ated upon in order to detect and determine the frequently very small quantities of admixed foreign metals. According to my investi- gations * the object may be best attained by the following method: * Zeitschr. /. analyt. Chem., n, 343. 260.] MERCURY COMPOUNDS. 603 1. Dissolve 100 grm. of the mercury to be tested in a flask in an excess of pure, moderately strong nitric acid, and heat for a long time to boiling in order to convert the mercurous salt first formed entirely into a mercuric. If any insoluble residue remains, collect it by filtration, wash, dry, fuse it with potassium sulphide, treat the melt with water, filter off any lead sulphate, etc., and acidulate the solution with hydrochloric acid. After settling, filter through an asbestos filter tube, wash, dry, and heat in a current of chlorine (Vol. J, p. 716 [196]). Treat the metallic chlorides in the receiver with hydrogen sulphide, and preserve the precipitate for a while ; the contents of the filter-tube, however, treat with nitrohydrochloric acid, and test the solution for gold (Vol. I, p. 392, b, 0). 2. Add to the solution of mercuric nitrate 56 grm. pure, con- centrated sulphuric acid mixed with 120 grm. water, evaporate to dryness in a porcelain dish, and continue the heat until all the nitric acid has been expelled. Dilute the residue now with water, and wash the whole into a stoppered flask of 3 or 4 litres capacity. We now have all the mercury in the flask, partly dissolved as mercuric sulphate, partly undissolved as basic sulphate; and with these are present all the foreign metals as sulphates, either dissolved or undissolved. 3. Add ammonia to the contents of the flask to alkalinity, then add ammonium sulphide until it strongly predominates, and digest for 24 hours a a gentle heat with frequent stirring. The liquid above the dense, black precipitate must be yellow in color, and smell strongly of ammonium sulphide. If this is not the case, a little more ammonium sulphide must be added, and the digestion prolonged. Pass the ammonium-sulphide solution, containing the metals of the sixth group (antimony, tin, arsenic, etc.), through a large, smooth filter, and wash the dense black precipitate of mercuric sulphide with water to which some ammo- nium sulphide has been added. 4. Acidulate with hydrochloric acid the liquid containing the ammonium sulphide, add the precipitate (reserved from 1) ob- tained from the solution of the metallic chlorides volatilized in 604 DETERMINATION OF COMMERCIAL VALUES. [ 260. the current of chlorine, allow to stand 2 or 3 days, siphon off the clear, supernatant liquid from the precipitate, and collect the latter consisting chiefly of sulphur, on a filter. After washing this first with water and then with alcohol, treat it with carbon disulphide. The residue which usually remains treat once more with warm ammonium sulphide, in order to remove any possible traces of mercury and copper, and then determine in the filtrate any tin, antimony, and arsenic, if such are present, by one of the methods detailed in 165. Regarding a convenient method of separating arsenic and antimony, see p. 556, b, this volume. 5. If the presence of alkalies and alkaline earths is suspected, these are to be tested for in the filtrate from the precipitated sulphur and metallic sulphides obtained in 4. 6. Rinse into a flask the precipitate of mercuric sulphide ob- tained in 3, together with any traces of lead, copper, and mercuric sulphides obtained in 1 and 4 If much water has been required for this purpose, allow to settle, pass the supernatant liquid through a small filter, and rinse the small quantity collected into the main precipitate. Now add 50 c.c. of pure nitric acid of sp. gr. 1-2 and about 1 grm. ammonium nitrate to the 500 c.c. or so of liquid in the flask, and keep the whole boiling gently for an hour. Allow the liquid to become clear, filter, wash, evaporate the nitric-acid solution to a small bulk, dilute, and precipitate any silver present by adding a few drops diluted hydrochloric acid. To the clear liquid, or the filtrate from any silver chloride deposited on long standing, add pure sulphuric acid in excess, evaporate until all the nitric acid has been expelled, then dilute, heat, filter off the precipitated lead sulphate, wash it first with water acidulated with sulphuric acid, then with alcohol, and determine the lead according to Vol. I, p. 355, a, ft. Add a little hydrochloric acid to the filtrate from the lead sulphate, precipitate with hydro- gen sulphide, and in the precipitate determine the bismuth, copper, and cadmium, should these be present, as detailed on p. 586, 7, this volume. 7. To the filtrate from the precipitate obtained by hydrogen sulphate in 6, and contained in a flask which it must nearly fill, 261.] COPPER COMPOUNDS. 605 add ammonia, ammonium chloride, and ammonium sulphide, allow to stand 24 hours, and in the precipitate formed determine the metals of the fourth group, particularly zinc. The iron which is found here can be considered as originating in the mercury only when all the reagents and filters are absolutely free from iron. 8. Lastly, exhaust a sample of the mercuric sulphide with boil- ing diluted nitric acid, dry, and ignite under a good draught in a porcelain crucible. If the operation has been properly conducted, no residue should remain. 9. If, on shaking with diluted hydrochloric acid, mercury yields a solution containing mercuric chloride, the mercury contains mercuric oxide. The quantity of this may be ascertained from the mercury contained in the hydrochloric-acid solution. [Regarding the electrolytic determination of mercury, as well as separations from other metals, see CLASSEN'S "Quantitative Chemical Analysis by Electrolysis," B. B. BOLTWOOD (JOHN WILEY & SONS, New York, 1903); "Electro-Chemical Analysis," EDGAR F. SMITH (P. BLAKISTON'S SON & Co., 1902); and "Electrolytic Determinations and Separations," by LILY G. KOLLOCK (Jour. Amer. Chem. Soc., xxi, No. 10). TRANSLATOR.] 19. COPPER COMPOUNDS. A. COPPER ORES. 261. Of the copper ores those that contain metallic copper, cuprous oxide, cupric oxide, or copper salts require no special considera- tion; but detailed accounts are necessary of the complicated analyses of the sulphuretted copper ores (copper pyrites, purple copper ore, copper-glance, etc.), as well as of those containing large quantities of antimony and arsenic (fahlerz). I. METHODS OF COMPLETE ANALYSIS. A Sulphuretted Copper Ores. The sulphuretted copper ores, of which copper pyrites is the most frequently subjected to analysis, always or nearly always 606 DETERMINATION OF COMMERCIAL VALUES. [ 261. contain copper, iron, sulphur, and gangue. Whether any other metals (nickel, cobalt, zinc, manganese, arsenic, antimony, sil- ver, etc.) are also present must be ascertained by qualitative analysis. Dry the very finely powdered mineral at 100. 1. The sulphur content is best determined according to the method detailed for pyrites (p. 554, 1 ; and 561, 1). 2. To determine the copper, iron, and gangue, treat about 1 grm. of the ore with concentrated nitric acid in an inclined, long- necked flask, add some strong hydrochloric acid after a while, digest until entirely decomposed, and evaporate nearly to dryness at a gentle heat. If the hydrochloric acid added does not suffice to remove all the nitric acid, .add a further small quantity and evaporate again as described. Add hydrochloric acid to the residue, warm, dilute with water, filter, and dry, ignite, and weigh the residual gangue. If the ore contains any admixed galena, the residue may con- tain lead sulphate. In such a case this must be removed by digestion with ammonium acetate or tartrate before the drying and ignition. Dilute the hydrochloric-acid solution, precipitate hot with hydrogen sulphide, filter after settling, wash the copper sulphide with water containing hydrogen sulphide, spread out the filter in a dish, and warm with sodium-sulphide solution; dilute, filter, wash, dissolve the copper sulphide in nitrohydrochloric acid, dilute, and filter; incinerate the washed filter paper, treat the ash also with a little nitrohydrochloric acid, strongly concentrate the solutions containing the copper, add ammonia until the free acid is neutralized, then add ammonium carbonate, allow to stand for a long time at a gentle heat, filter, acidulate with hydrochloric acid, precipitate hot with hydrogen sulphide, and determine the copper according to Vol. I p. 375, 3, a. The filtrate from the still impure copper sulphide first precipi- tated by hydrogen sulphide concentrate by evaporation, oxidize with nitric acid, precipitate the iron according to Vol. I, p. 644 [82], and determine it in the hydrochloric-acid solution of the precipi- 261.] COPPER COMPOUNDS. 607 tate either according to Vol. I, p. 642 [77], or volumetrically accord- ing to p. 327, a. 3. To determine the constituents present in small quantity, treat about 10 grm. of the finely powdered ore with fuming nitric acid, evaporate with a slight excess of sulphuric acid in order to remove the nitric acid, and until vapors of sulphuric acid begin to be evolved, then allow to cool, add water, warm, filter into a weighed flask of about one litre capacity, and wash the residue with water acidulated with sulphuric acid. Any lead that may have been present is now found in the residue as lead sulphate. Extract the residue with a hot solution of ammonium acetate to which has been added some ammonia, and in the solution deter- mine the lead by precipitating with hydrogen sulphide and converting the lead sulphide into lead sulphate. Exhaust the residue with ammonium acetate, heat with hydrochloric acid, dilute, filter, add the filtrate to the sulphuric-acid solution first obtained, and, whether clear or rendered turbid by the separation of a small quantity of silver chloride, precipitate hot with hydrogen sulphide, add water until the flask is almost filled, mix, let stand for a long time to settle, and weigh the whole. The weight of the empty flask and that of the copper sulphide from 2 being known, the difference gives the weight of the solution in the flask. Siphon off as much of the dear liquid from the flask as possible, and again weigh the flask with the residue. Filter the liquid, the weight of which is now known; and should it not be absolutely clear, boil an aliquot portion of the solution so obtained w th some nitric acid, then precipitate with an excess of ammonia, dis olve the slightly washed precipitate in hydrochloric acid, and again precipitate the ron as a basic salt according to Vol. I, p. 644 [82]; test the filtrate by adding ammonia to it to see if a further precipitate of alumina forms, filter from this should it occur, acidulate the solution with acetic acid, and in the liquid determine nickel, cobalt, zinc, and manganese, should such be present, according to Vol. II, p. 491, 8. In the precipitates afforded by ammonium carbonate, and sub- sequently perhaps by ammonia, determine any alumina according to Vol. I, p. 642 [78]. As the weights of the alumina, nickel, cobalt, 608 DETERMINATION OF COMMERCIAL VALUES. [ 261. etc., are obtained from only a part of the solution, it must not be forgotten to calculate them for the total solution. To the residue containing copper sulphide, and remaining in the flask, add first potassa or soda lye to alkaline reaction, then potassium- or sodium-sulphide, and warm for a long time. Dilute with water until the flask is nearly filled, mix, allow to cool, and weigh. On deducting from this weight that of the flask, of the cop- per sulphide, and of the iron sulphide here present, the weight of the alkaline solution containing the metals of the sixth group is ascertained. Siphon off as much of the clear liquid as possible, determine the weight of the liquid siphoned off by weighing the flask with the residue, filter the solution if necessary, precipitate with hydrochloric acid, and allow the precipitate to subside; then collect it, wash, digest with brominized hydrochloric acid, filter, remove the excess of bromine by cautiously adding sulphurous acid, precipitate with hydrogen sulphide at 70, and separate and determine the arsenic and antimony according to pp. 556 and 557 this volume ; calculate the values so obtained from the part to the whole. If the ore contains any mercury, this would pass, in the form of mercuric sulphide, into the solution containing sodium or potassium sulphide, and would be obtained together with the antimony and arsenic sulphides, hence it would have to be separ- ated from these by ammonium sulphide. 4. Should any other metals of the fifth group be present besides copper, lead, and mercury, the copper must ultimately be washed, dissolved in nitric acid, and this solution employed for the deter- mination of the other metals of the fifth group. Compare 263. Any small quantity of silver present may be best determined by cupellation (pp. 579 and 580 this volume). 5. In regard to the testing for thallium, see p. 560, 6, this volume. b. Ores containing Antimony and Arsenic (Fahlerz). In the analysis of fahlerz (gray copper ore) the determination of copper, silver, mercury, iron, zinc, antimony, arsenic, lead, sulphur, and gangue, must be kept in mind, even though certain kinds of fahlerz do not contain all the metals mentioned. The 261.] COPPER COMPOUNDS. 609 analysis is best conducted by heating about 1 grm. of the finely powdered ore in a slow current of chlorine.* For this purpose the apparatus shown on p. 695, Vol. I, is used, but modified to the extent only that the bulb-tube D is replaced by a similar one with two bulbs. Introduce the powdered ore into the bulb connected with the chlorine-evolution apparatus, and after almost completely expelling all the air from the evolution flask and drying apparatus, connect the bulb-tube, which is fixed slightly inclined downwards, with C. Charge the tubes E and F with a solution of tartaric acid to which a little hydrochloric acid has been added. The decomposition of the fahlerz begins at once, the bulb becoming heated thereby, and the volatile chlorides are carried partly as far as the at first empty second bulb of the bulb-tube, partly as far as E and F. When the bulb containing the ore has become almost cold, heat it very gently with a small flame while passing a slow current of chlorine through it in order to drive all the volatile chlorides into the second bulb. It is inadvisable to continue the heating until all the ferric chloride has passed into the second bulb, but rather to stop when the vapor of ferric chloride alone begins to come over. As soon as the piece of tubing between the two bulbs has become clean, and the apparatus has become cold, cut the tube between the two bulbs by means of a file mark and a piece 'of ignited charcoal, and close that portion attached to the bulb containing the sublimate with a short glass tube sealed at one end and moistened internally with water. Allow the apparatus to stand for twenty-four hours in order that the sublimate may absorb moisture and thus be rendered soluble in water without disengagement of heat. Then treat the contents of the bulb with a dilute solution of tartaric acid to which some hydrochloric acid is added. Should the liquid be turbid from the separation of oxygen compounds of antimony, warm it until they dissolve; if sulphur has separated, filter the liquid. The analysis now resolves itself into an examination of the * Compare H. ROSE, Handbuch der analyt. Chemie, 6th edit., by R. FIXKENER, n, 479. F. WOHLER, Die Mineralanalyse in Beispielen, 2d edit., p. 73. 610 DETERMINATION OF COMMERCIAL VALUES. [ 261. residue remaining in the first bulb of the solution of the volatile chlorides, and lastly into the separate determination of the sul- phur. 1. The residue contains or may contain the chlorides of silver, lead, and copper, a portion of the ferric chloride, all or nearly all the zinc chloride, and gangue. Digest it with diluted hydro- chloric acid for a long time, dilute with much water, allow to stand for quite a while, and filter off the silver chloride; wash this with boiling water until all the lead chloride has been removed, if neces- sary separate the silver chloride from the gangue by means of ammonia, precipitate the silver chlor de in the ammoniacal solu- tion by means of nitric acid, and determine the silver in the pre- cipitate according to p. 342, Vol. I. Precipitate the filtrate with hydrogen sulphide (Vol. I p. 677), and in the precipitate then separate the lead and copper according to Vol. I, p. 689, 2 [146]. Preserve the filtrate for a while however. 2. The solution, which contains the mercury, antimony, arsenic, and a portion of the iron, precipitate with hydrogen sulphide at 70, filter, and wash. In the precipitate separate the mercuric sulphide from antimony and arsenic sulphides by means of ammo- nium sulphide (Vol. I, p. 701, 2 [167]), and determine the mercury as sulphide (Vol. I, p. 366, 3). Arsenic and antimony, however, are best separated according to BUNSEN'S method (pp. 556 and 557 this volume). Boil the mercuric sulphide obtained with di- luted nitric acid, and in the filtrate determine any slight quantity of lead that may be present. The liquid filtered off from the precipitate thrown down by hydrogen sulphide, add to the similar solution obtained from the residue in 1, and determine therein the iron and zinc (pp. 557 to 559 this volume), and also any alkaline earths, should these be present. 3. The sulphur is best determined by fusing a fresh sample of the ore with sodium carbonate and potassium nitrate, as in the case of pyrites (p. 561, 1, this volume). 261.] COPPER COMPOUNDS. 611 II. DETERMINATION OF THE COPPER CONTENT OF COPPER ORES. 1. By Ordinary Gravimetric Analysis. The process is conducted exactly as in 261, I, a f weighing the copper as sulphide, and omitting the determination of the other metals, etc. 2. Determination of the Copper by Electrolysis. When it is a question of making a number of copper deter- minations daily in ores of a simliar character the electrolytic method is preferable to all others. This was first described by WOLCOTT GIBBS,* and by LucKOW,f and introduced into general use by the MAXSFELD Ober-Berg- und Hiittendirection in Eisleben, for ores containing no antimony, arsenic, or bismuth.]; The method is unsuitable for ores contain- ing these metals, because they are precipitated on the copper and blacken it. Further references to the electrolytic determination of copper are given in the foot-note. a. Production of the Current. For the production of the current MEIDINGER'S element was first made use of in the laboratories of the MANSFELD Ober-Berg- und Hiittendirection, and later on PINKUS' modified MEIDINGER'S element, but now the MURE and CLAMOND || thermopile as im- proved by CLAMOND. *[ HERPIN who also operated with the BUNSEN battery, a fmall GRAMME machine, and the CLAMOND thermopile, * Zeitschr. /. analyt. Chem., in, 334. j- DINGL. polyt. Journ., CLXXVII, 296; also, Zeitschr. f. analyt. Chem., xix, 1. | Zeitschr. f. analyt. Chem., vin, 23; xi, 1 ; and xiv, 350. MERRICK, Americ. Chem., n, 136. WRIGHTSON, Zeitschr. f. analyt. Chem., xv, 299. HERPIN, "'bid., xv, 335. OHL, ibid., xvni, 523. A. CLASSEN and M. A. v. REIS, Berichte der deutsch. chem. Gesellsch., 1881, No. 13> p. 1627. A. RICHE, Zeitschr. f. analyt. Chem., xvn, 216, and xxi, 116. . 11 DINGL. polyt. Journ., ccvii, 125. Tf Ibid., ccxv, 427; Zeitschr. f. analyt. Chem., xiv, 350. 612 DETERMINATION OF COMMERCIAL VALUES. [ 261. 4 FIG. 117. FIG. 118. 261.] COPPER COMPOUNDS. 613 recommends the use of the last by preference. For use in the chemical laboratory the CLAMOND thermopile is undoubtedly the most convenient apparatus for the production of a suitable cur- rent. I would therefore refer to the reports. of the MANSFELD Ober-Berg- und Hiittendirection * for particulars regarding the MEIDINGER-PINKUS element and its working, and will here confine myself to a description of the CLAMOND thermopile f only. This apparatus is illustrated by Figs. 117, 118, and 119. Fig. 117 is a perspective view; Fig. 118 a vertical section, showing also the armatures; and 119, a cross-section of the bars and the armatures in position. The elements are composed of iron, and an alloy of zinc and antimony. In order to impart greater durability to the latter the bars must be cast in molds heated to a temperature slightly below the melting-point of the alloy; nor should the alloy itself be strongly overheated. The elements are arranged, as shown in Fig. 119, radially around a centre, several such superimposed rings constituting one pile. In Fig. 119 B denotes the bars of zinc-antimony alloy, while L denotes the tinned-iron plate; the latter serve as conductors from one element to another, hence they are laid on the upper surfaces of the bars B. As the bars B expand much more than the iron, the contact increases on heating. The individual ele- ments are insulated by layers of asbestos (r, Fig. 118), and so are also the different superimposed rings of elements B. The whole forms a cylinder, all the junctions being directed toward the inner side; the junctions are protected from the direct action of the gas-flame by lining the inner cylinder with asbestos. The heating is effected by means of gas, and for this purpose a porcelain tube, A, perforated with holes, Figs. 118 * Zeitschr. f. analyt. Chem., xi, 4. f Ibid., xv, 334. 614 DETERMINATION OF COMMERCIAL VALUES. [ 261. and 119, is placed within the cylinder. The gas passes first through a GIKOUD regulator, C (Fig. 118), in order to secure a uniform flame under varying pressures, and thus obtain a constant cur- rent; it then passes through the tube T, into which air flows through various apertures, and reaches A, at the perforations of which the mixture of gas and air burns, any further quantity of air necessary for perfect combustion entering from below by the annular space D between the tube A and the inner walls of the FIG. 120. FIG. 121. cylinder (Fig. 118). The burner is lighted from above, the cover being first removed. The individual elements of a ring are connected in series, but the rings themselves can be made up variously, according to the external resistance. For this purpose the poles of each ring terminate in binding-screws arranged on two vertical metallic strips as shown in Fig. 117. In the illustration the elements are shown combined in series, while in the sketch plan to Fig. 118 the rings are made up in compound circuit. 261.] COPPER COMPOUNDS. 615 6. Form of the Electrodes. Regarding the form of the electrodes used in electrolytic deter- minations, LUCKOW at first employed a cylinder of platinum foil as the negative electrode, and a spiral of stout platinum wire as the positive electrode. Repeated experiments in the laboratory of the MANSFELD Ober-Berg- und Hiittendirection at Eisleben FIG. 122. have resulted in the adoption of the electrodes having the form shown in Figs. 120 and 121. The hollow truncated cone weighs 20 grin, and is 75 mm. high, 9 mm. in diameter at the top, and 58 mm. in diameter at the base. The platinum cone is provided with several openings in the sides in order to allow the escape to the outer surface of the cone of the oxygen liberated when electro- lyzing solutions containing much iron ; this is indispensable in order to prevent the partial reduction with a current of sufficient strength 616 DETERMINATION OF COMMERCIAL VALUES. [ 261. of ferric to ferrous salts, and of free nitric acid to nitric oxide, and to thereby avoid the black-brown coloration which the liquid would otherwise acquire. The platinum spiral weighs 16 grm. In the laboratory of CHRISTOFLE & Co., of Paris, where, in the analysis of copper-nickel alloys and German silver, it is necessary to operate with concentrated solutions, another form of electrode is used; this is described by HERPIN (loc. cit.), and is shown in Figs. 122 and 123. The apparatus consists of a platinum dish, A, supported on a tripod, B, and connected with negative pole of the thermopile; the positive electrode is formed by the platinum spiral, C. The whole is covered with the glass funnel, D, in order to prevent any loss of sub- stance by reason of the escape of the gas evolved. FIG. 123. A. CLASSEN and M. A. VON REIS * also employ as negative electrode a rather deep platinum dish covered with a watch-glass; and for the positive electrode they use a disc of platinum foil about 4-5 cm. in diameter, and fastened to a rather stout platinum wire by means of a plati- num screw. RICHE t employs in the electrolysis of small quantities of fluid a platinum crucible which at the same time acts as the positive electrode. The negative electrode is a platinum cone, Fig. 124, open at both ends, and corresponding as nearly as possible to the form of the crucible. Elongated openings are cut in the sides of the cone so that the concentration may be maintained as uni- form as possible. The distance between the cone and the crucible may be from 2 to 4 mm. Fig. 125 shows the entire arrangement and requires no further description, except that the rod A is made of some non-conducting material, like glass. If the current is * Ber. d. deutsch. chem. Gesellsch., 1881, No. 13, p. 1623; also, Quanti- tative Analyse auf electrolytischem Wege, by AL. CLASSEN, Aachen, J. A. MAYER, 1882. f Ann. de chim. et de Phys. [5 s6r.] xm, 508; Zeitschr. /. analyt. Chem., xxi, 116. 261.] COPPER COMPOUNDS. 617 to act in a warm liquid, the crucible is set in a basin of water which is then heated. If the deposition must be effected in larger quan- tities of liquid in a beaker, RICHE employs as a negative electrode FIG. 124. FIG. 125. a platinum cylinder, and as a positive a piece of platinum gauze bent into a cylindrical form; and the rapidity of action is in- creased by employing, besides the platinum gauze outside the platinum cylinder, a supplementary positive electrode in the form of a platinum spiral placed within the cylinder. [F. A. GOOCH and H. E. MEDWAY * employ as a cathode an or- dinary 20-c.c. platinum crucible rotating at a speed of from 600 to 800 revolutions a minute. The crucible is driven by a small inexpensive electric motor fastened so that its shaft is vertical. Upon this shaft the crucible is fixed by pressing it over a rubber stopper bored centrally and fitted tightly on the end of the shaft (Fig. 125a). To secure electrical connection between crucible and shaft, a narrow strip of sheet platinum is soldered to the shaft and then bent upward along the sides of the stopper, thus putting the shaft in contact with the inside of the crucible when the latter * Amer. Journ. of Science, xv, 320. 618 DETERMINATION OF COMMERCIAL VALUES. [ 261. is pressed over the stopper. The shaft is made in two parts as a matter of convenience in removing the crucible, and is joined, with care to make a good contact between the two pieces of shaft- ing, by a rubber connector of sufficient thickness to prevent the crucible from wobbling when rotated. The solution to be electrolysed is placed in a beaker upon a small adjustable stand, so that the crucible may be dipped into the liquid to any desired depth. A platinum plate is employed as an FIG. 125 a. anode, and this is connected with the positive pole of a series of four storage batteries, while the negative pole of this series is connected with the bearing in which the shaft rotates, thus allowing the current to go from the platinum plate through the solution to the crucible ; up the shaft of the motor and back to the batteries. The pow r er to run the motor is taken from the incandescent light circuit of the street. From results obtained in a number of experiments, it has been found that nickel also, like copper and silver, may be deposited with rapidity and completeness. The metallic deposits of these metals obtained by means of the 261.] COPPER COMPOUNDS. 619 revolving cathode are sufficiently coherent and compact to permit accurate manipulation and weighing, even when the current den- sity on the cathode is very considerable, and variable within wide limits. Other metals have been found to behave similarly. The advantages claimed for this rotating cathode in analytical operation are: The process as described is rapid, exact, and very simple; the apparatus required, moreover, is inexpensive, and, if it is required to make many determinations simultaneously, a single motor may be made to drive a running belt over any reason- able number of rotating shafts. TRANSLATOR.] c. Dissolving the Ore (or Lode) and Preparing the Solutions for Electrolysis* a. If the Ores contain no Silver. The electrolysis is always effected in nitric-acid solution; small quantities of free sulphuric acid, such as occur when a nitric- acid solution of neutral copper sulphate is electrolyzed, are not prejudicial, but hydrochloric acid must never be present in the solution, otherwise the copper will not be deposited on the nega- tive electrode the platinum cylinder with its usual handsome color, but will be blackish. If the ores contain bitumen, they are roasted before proceeding to dissolve them. If nitric acid suffices to effect solution, employ only this acid, evaporate the excess, and dissolve the residue by the aid of 20 c.c. nitric acid of sp. gr. 1-2 and water to make 200 c.c. of liquid. This volume of liquid, and also the proportion of acid to water, must be adhered to in all electrolytic determinations of copper. If nitric acid alone does not suffice, nitric acid, or, better, nitro- hydrochloric acid, with the addition of sulphuric acid, is em- ployed. * The directions given under c are taken from the above cited reports of the MANSFELD Ober-Eerg- und Hiittendirection, in the laboratory of which the electrolytic determination of copper has been practiced for about twelve years. On p. 623, /, are described various modifications recommended by others. 620 DETERMINATION OF COMMERCIAL VALUES. [ 261. In the case of ores or lodes rich in copper, take about 2 grm., effecting solution in a hemispherical porcelain dish 14 cm. in diameter and 6 cm. deep, and using 40 c.c. nitric or nitrohydro- chloric acid, and 4 c.c. concentrated sulphuric acid, which is previously diluted with an equal volume of water. Cover the dish with a glass cover while effecting the solution, this being assisted by heating on a sand-bath. After rinsing off the glass cover into the porcelain dish, cautiously evaporate the con- tents of the latter to dryness, drive off the excess of sulphuric acid, and, if any sulphur has separated, burn it off. Dissolve the residue in 20 c.c. nitric acid of sp. gr. 1-2, dilute with water, and filter into a beaker 8 cm. inside diameter and 12 cm. high; the beaker should bear a mark to show where it will hold 200 c.c., and it should also be provided with an opening 11 mm. wide and 9-5 cm. from the bottom, through which the acid liquid may be removed when the electrolysis is complete. After washing the undissolved residue, dilute the solution to the mark. If, after separating the copper, the liquid is to be used for the deter- mination of other substances present, such beakers must be selected as are provided with a glass tube bent at right angles and inserted at a distance of 20 mm. from the upper edge. /?. For Ores containing Silver. If the ores contain silver, the latter, when chlorine-free nitric and sulphuric acids are employed as the solvents, will pass com- pletely into solution with the copper, and will be thrown down and weighed with it. The silver must hence be determined in a separate quantity of ore and its weight deducted. If this is not desired, the silver may be separated from solutions prepared with pure nitric acid by adding an accurately known quantity of very dilute hydrochloric acid, 1 c.c. of which will be the equiv- alent of 0-001 grm. silver. If nitric acid alone does not suffice to effect the solution, use nitrohydrochloric acid, but in this case evaporate to dryness, treat the residue with nitric acid, dilute with water, and filter. The solution, now free from silver, evapo- rate to dryness with the addition of sulphuric acid and proceed as in a. 261.] COPPER COMPOUNDS. 621 d. Electrolytic Precipitation of Copper. After the solution has been well stirred, introduce first the platinum spiral (positive electrode), then the platinum cylinder (negative electrode). The distance of the latter from the base of the spiral should be barely 5 mm. in the case of strongly ferru- ginous liquids; in solutions very rich in copper the distance may be 10 mm. Before connecting the electrodes with the thermopile, it must be ascertained whether the current is of the right strength. In this connection it must be noted that for samples containing small quan- tities of copper, the current should be of such strength as to yield from 16 to 25 c.c. of oxyhydrogen gas in thirty minutes on decom- posing water acidulated with sulphuric acid. If, however, larger quantities of copper are to be deposited, the strength of the current in case of solutions poor in iron must be such as to yield from 75 to 100 c.c., and with those rich in iron, from 100 to 120 c.c., of the oxyhydrogen gas in thirty minutes. The strength of the current may, of course, be measured by the tangent galvanometer instead of by a voltmeter. The copper begins to deposit on the platinum cylinder soon after the electrodes are connected with the thermopile. If the deposit is pure, it exhibits the fine light color of copper, and if the current strength is correct, the deposit is bright and adherent. The time required for the deposition varies according to the copper content. Solutions very rich in copper require more than twelve hours for complete deposition, hence hi such cases the current must be allowed to act for about eighteen hours. When the deposition appears to be complete, raise the level of the water in the beaker by adding water. If the clean portion of the platinum cylinder which was previously above the liquid, but which is now submerged, exhibits no reddish deposit after the lapse of half an hour, the precipitation is complete. Further assurance of this is obtained by pipetting off a small quantity of the liquid and testing with hydrogen-sulphide water. Now, while the current is still acting, introduce a current of 622 DETERMINATION OF COMMERCIAL VALUES. [ 201. water at the bottom of the beaker so as to completely expel the acid liquid. As soon as the water running off no longer has an acid reaction, loosen the binding screws, remove the platinum cylinder, wash it with alcohol, dry at 90 to 95, and weigh when cold. The increase in weight gives the quantity of copper deposited. e. Procedure when the Deposited Copper is Blackish. If the copper solutions contain arsenic, antimony, selenium, or bismuth, the copper becomes covered with a brown to blackish deposit, and the accuracy of the results is interfered with. A grayish-black or occasionally peacock-like color may also occur if the solution contains traces of hydrochloric acid. If the elements causing the black deposit are present in very small quantity only, and if they rnay be volatilized by heating to redness with access of air, as in the case with arsenic, antimony, or selenium, then wash the platinum electrode on which the black deposit has formed with alcohol, dry, and heat to redness in a gas- or alcohol-flame, or in a muffle. Arsenic and antimony vola- tilize, but the copper is converted, without any loss whatever, into cupric and cuprous oxides. Now place the platinum electrode, thus treated, in a beaker, suspend over it a similar but larger and weighed platinum electrode, connect the latter with the nega- tive and the former with the positive pole of the battery, and pour a sufficient quantity of diluted nitric acid (1 part of acid to 6 parts of water) into the beaker. The copper oxides dissolve, and the pure copper is deposited on the outer platinum electrode; it is then determined in the usual way. If the elements causing the black color are present in larger quantities, the moment when they begin to be deposited must be watched for; the acid liquid is then at once expelled, and the platinum electrode bearing the only slightly blackened deposit treated as described above. If the copper solution contains lead, the latter is not deposited with the copper at the negative pole, but separates at the positive pole as lead dioxide, and may, if the quantity is not too large, be determined by the increase in weight of the spiral dried at 100. If larger quantities of lead are present, only a part of the lead 261.] COPPER COMPOUNDS. 623 dioxide adheres to the platinum spiral, while the rest separates in the form of thin flakes. /. Methods differing from those adopted by the MANSFELD Works. Under this heading I call attention to several modifications of the process described above. a. WRIGHTSON* effects the deposition in ordinary beakers, and while the current is acting, siphons off the acid liquid while pure water is being constantly added; he does not dry the copper spiral with alcohol, but simply dries it at 100 to 120. /?. AL. CLASSEN and M. A. VON REIS f deposit the copper from solutions containing it in the form of ammonio-cupric oxalate with a considerable excess of ammonium oxalate. For the deter- mination of large quantities of copper, a current is employed capable of evolving 330 c.c. of oxyhydrogen gas per hour, and which will hence deposit 0-15 grm. copper in about twenty-five minutes. For separating copper from zinc, AL. CLASSEN J prefers to deposit from acid sulphuric-acid solutions rather than from acid nitric- acid solutions. Compare also p. 630, e, this volume. f. RICHE employs a BUNSEN element for the deposition of copper. The sulphuric-acid or nitric-acid solution is evaporated almost to dryness, the residue taken up with water, and ths liquid electrolyzed at 60 to 90. The copper rapidly deposits as a handsome, red, adherent coating. When the deposition is com- plete, the cone is removed from the crucible without interrupting the current (comp. p. 616 this volume), and immediately sub- merged in distilled water; it is then dried at 50 to 60, and weighed. RICHE in this manner effects the deposition of 1 grm. copper in three and one half hours. If iron is present, the decomposition must be conducted at a temperature not exceeding 70. * Zeitschr. f. analyt. Chem., xv, 299. t Berichte der deutsch. chem. Gesellsch., xrv, No. 13, 1627. t Quantitative Analyse auf elektrolytischem Wege, by Dr. AL. CLASSEN, Aachen, J. A. MATER, 1882, p. 12. A*in. de chim. tt de phys. [5 sr.], xni, 508; Zeitschr. f analyt. Chem., xxi, ) 8. 624 DETERMINATION OF COMMERCIAL VALUES. [ 261. d. LECOQ DE BOISBAUDRAN * employs the following process for determining copper in solutions containing much ferrous sulphate: For the production of the current he uses three BUNSEN elements, weakly charged, and for the negative electrode a platinum crucible, a semicylindrical piece of platinum foil serving as the positive electrode. In order to prevent the ferric salt separated at the positive pole from corroding the copper, which may easily happen in acid solutions, he rapidly siphons off the iron solution when the deposition is complete, while the positive electrode is mean- while lowered very close to the bottom of the crucible, so that the current continues to pass while the liquid is being removed. The copper is then, without interrupting the current, repeatedly washed first with diluted sulphuric acid and then with boiling hot water. [Regarding the commercial analysis of copper see A. HoLLARD'sf paper on this subject. The electrolytic determination of copper and its separation from other metals electrolytically is al o fully treated of by EDGAR F. SMITH, "Electro-Chemical Analysis," and CLASSEN'S "Quantitative Analysis by Electrolysis," translated by B. B. BOLT- WOOD. JOHN WILEY & SONS, New York, 1903. TRANSLATOR.] 3. OTHER METHODS OF DETERMINING COPPER. a. FR. MOHR J recommends the following methods of determin- ing copper in ores: a. For Oxidized Ores (Cupric and Cuprous Oxides, Malachite, and Cupric Phosphate). Treat 5 grm. of a rich, or 10 grm. of a poor, ore, in fine powder, with some sulphuric acid, water, and nitric acid in a porcelain dish of 10 cm. diameter, and after covering the dish with a large watch glass, heat to boiling. As soon as the mass is nearly dry, and has ceased to spirt, remove the watch-glass and increase the flame. Sulphuric acid and sulphuric anhydride * Bull. mens. de la soc. chim. de Paris, 1869, p. 35; Zeitschr. f. analyt. Chem., ix, 102. t "Commercial Analysis of Copper" (Bull. Soc. Chim., [3], xxiu, No. 8; Chem. News, LXXXI, 258). | Zeitschr. f. analyt. Chem., i, 143. 261.] COPPER COMPOUNDS. 625 are evolved from the ferric sulphate only at a high temperature; the heat must be increased to a point until no more fumes are given off; then allow to cool, add distilled water, heat to boiling, filter into a small platinum dish, wash with hot water, transfer the evaporated and concentrated washings to the platinum dish, and lastly, after making certain that the residue insoluble in water yields no copper to acids, precipitate the copper by means of zinc according to Vol. I, p. 373. The bright-red color of the copper indicates that this is pure. It is seen that the object of this method is to remove, so 'far as possible, the metals precipi- table by zinc (lead, antimony, and tin). /?. For Sulphuretted Ores, Mixed Metallurgical Products, and Ore-furnace Regulus,. The substance must be powdered with special care; it is then treated as in a, taking 5 grm. of the ore, and heating as before with sulphuric acid, water, and a larger quantity of nitric acid. The action must be allowed to go on at a gentle heat in a covered porcelain dish, during which considerable spirting, and condensation of liquid from the watch-glass will take place. A large quantity of sulphur separates, which collects and incloses some of the pow- dered ore. It is therefore necessary to evaporate the liquid to dryness with a stronger heat, remove, increase the heat until the sulphur is burned off, and volatilize the free acid. When cold, add a fresh quantity of nitric acid and a very little sulphuric acid; the evolution of red fumes points to the presence of ore still un- decomposed. Evaporate to dryness as before, allow to cool, moisten once more with nitric acid, and burn off the sulphur a second time. If the ore is very rich in copper, it is necessary to repeat the entire operation once more. The extraction of the residue and the copper determination are made as detailed under a. b. STOKER * and PEARSON f in order to obtain a solution free from separated sulphur, heat the finely powdered ore, pre- viously mixed with potassium chlorate, with strong nitric acid * Zeitschr. f. analyt. Chem., ix, 71. f Ibid -t IX l01 - 626 DETERMINATION OF COMMERCIAL VALUES. [ 261. on the water-bath, and, at short intervals, add more chlorate and acid, until no more separated sulphur is visible. When cold, strong hydrochloric acid is added in sufficient excess, the whole evaporated to dryness on the water-bath, and the residue treated with hydrochloric acid and water, and filtered. PEARSON precipitates the copper with iron / and, in order to obtain the solution perfectly free from nitric acid, washes the evaporation residue with water into a beaker, heats almost to boiling, adds about 25 c.c. of a concentrated ferrous-sulphate solution weakly acidulated with sulphuric acid, and heats for about five minutes nearly to boiling. If any ferrous salt still remains at the end of this time, and which may be ascertained by testing a drop with potassium ferricyanide, the object is at- tained; if otherwise, the heating must be continued with the ad- dition of more ferrous sulphate. The metallic copper is finally precipitated in the filtered solution by the introduction of a piece of sheet iron, and is then ignited in a current of hydrogen in a porcelain crucible, and weighed. c. Solutions containing all the copper may be prepared by various fusion methods. Thus FLEISCHER,* for decomposing sulphuretted ores, recommends fusing the finely powdered ore with a mixture of exactly 5 parts potassium chlorate, 4 parts sodium carbonate, and 3 parts sodium chloride, until the mass flows quietly, and then dissolving the melt in water. W. GIBBS, f on the other hand, recommends mixing the finely powdered ore in a porcelain crucible with three or four times its Weight of a mixture of equal parts of potassium disulphate and potassium nitrate, and gradually heating to a low red heat, preferably in a muffle, by which procedure oxidation is effected without frothing. Sufficient sulphuric acid is then added to the cooled mass to con- vert all the potassium sulphate into disulphate, and the whole is again carefully heated until the contents of the crucible have fused to a clear mass which, after cooling, is dissolved in water. d. When all the copper has been brought into solution in one * Zeitschr. f. analyt. Chem., ix, 258. f Ibid., vii, 257. 261.] COPPER COMPOUNDS. 627 way or another (according to p. 606, 2, this volume), or according to 3, a, b, or c, it may also be determined volumetrically. The older volumetric methods have already been described in Vol. I, pp. 377 to 382; of the new or improved methods I would mention the following : a. FR. WEIL * supplements his method described in Vol. I, p. 380, by the following special instructions: Dissolve 5 grm. of the mineral in hydrochloric or sulphuric acid free from nitric acid, and dilute to 250 c.c. Dissolve 4-5 to 5 grm. crystallized stannous chloride in about 100 c.c. water with the addition of about 30 c.c. hydrochloric acid, and dilute the solution to 500 c.c. with a mixture of about 40 c.c. hydrochloric acid and 100 c.c. water. Prepare also a normal copper solution, each 10 c.c. of which contains 1 grm. copper. To determine the effective value of the stannous-chloride solution, allow this to act, in a flat-bot- tomed flask, upon 10 c.c. of the normal copper solution to which 25 c.c. of hydrochloric acid have been added, and the whole heated to boiling. In a simila* manner allow the stannous-chloride solution to act upon 10 c.c. of the copper-ore solution also mixed with 25 c.c. hydrochloric acid and heated to boiling. If it has been necessary to employ nitric or nitrohydrochloric acid to effect solution, evaporate to dryness, dissolve the residue in hydro- chloric acid, dilute to 250 c.c., pipette off 10 c.c., evaporate to dryness with 5 to 10 c.c. hydrochloric acid, dissolve the residue, which is now certainly free from nitric acid, in 25 c.c. hydrochloric acid, and proceed as above. During the titration at the boiling temperature the flask is full of hydrochloric-acid vapors, and this circumstance prevents oxidation by the atmosphere. The procedure to follow when the copper solution contains ferric chloride or sulphate, was described in Vol. I, p. 381. If the ore contains antimony, effect solution with hydro- chloric acid or a mixture of much hydrochloric acid with a little nitric acid, add potassium permanganate until a red tint persists, and boil until the redness has disappeared and the vapors evolved * Zeitschr. f. analyt. Chem., xvn, 438; Precedes FR. WEIL pour le dosage vol du cuivre, du fer, et de Vantimoine. 628 DETERMINATION OF COMMERCIAL VALUES. [ 261. DO longer render potassium-iodide starch paper blue. Then dilute the liquid to 250 c.c. with an aqueous solution of tartaric acid containing 5 to 10 per cent, of the acid, or with water to which the necessary quantity of hydrochloric acid has been added. The solution contains the copper as cupric chloride, and the antimony as antimonic acid. On now mixing 10 c.c. of the solution with 25 c.c. of hydrochloric acid and boiling, and then titrating with the standardized stannous-chloride solution, the cupric chloride will be reduced to cuprous chloride, and the antimony penta- chloride to trichloride, and the volume of stannous-chloride solu- tion used up will therefore show the quantity of copper and anti- mony present, according to the following equations: SbCl 5 +SnCl 2 = SbCl 3 +SnCl 4 ; and 2CuCl 2 +SnCl 2 = Cu 2 Cl 2 +SnCl 4 . Under the conditions stated, the reducing effect of the stannous chloride is the same for 2 eq. of copper (2X63-6=127-2) as for 1 eq. of antimony (120-4). In order to now ascertain the quantity of copper alone, allow the reduced liquid to stand in a shallow porce- lain dish for twelve hours exposed to the air; by this treatment all the cuprous chloride will have been reconverted into cupric chloride. On now titrating again with stannous-chloride solution, the copper alone will be found, from the difference between the volume of stannous-chloride solution employed and that corre- sponding to the antimony, and from this the latter also is found. Arsenic acid, according to WEIL, is not reduced during the short time required for titration. ft. VOLHARD * determines the copper volumetrically by precipitating it as sulphocyanate and determining the residual excess of ammonium-sulphocyanate solution (see the method of silver determination based on the same principle, pp. 569 to 571 this volume). He employs decinormal solutions, hence a silver-nitrate solution containing 10-792 grm. per litre, and a solution of ammonium sulphocyanate so standardized against the silver solution that on mixing equal volumes of the two solutions ferric sulphate will, if present, afford only a barely perceptible * Zeitschr. f. analyt. Chem., xvm, 285. 261.] COPPER COMPOUNDS. 629 color; 1 c.c. of the ammonium-sulphocyanate solution will hence correspond with 0-00636 grm. copper. Dissolve the copper in sulphuric or nitric acid, and drive off the excess of acid by evaporation. If the excess is not very large, it may be neutralized with sodium carbonate until a permanent cloudiness forms. Place the liquid to be titrated in a 300-c.c. flask, add aqueous solution of sulphurous acid until the liquid smells strongly of it, whereby any precipitate of basic cupric car- bonate which may have been produced is dissolved, heat to boil- ing, and run in from a burette sulphocyanate solution until a further addition develops no more change of color ; then for the sake of safety, add 3 or 4 c.c. more, and note the total quantity taken. Allow the liquid containing the precipitated, almost white, copper sulphocyanate to cooi, fill with water up to the mark, mix, and filter through a dry filter into a dry flask; pipette off 100 c.c., add to this 10 c.c. cold, saturated solution of ammonio-ferric alum and a little nitric acid, titrate with silver solution until the liquid has become colorless, and then cautiously run in from a pipette or burette graduated in -fa c.c. ammonium- sulphocyanate solution until a just permanent reddish color de- velops. The number of c.c. of silver solution used, after deducting the sulphocyanate solution used in retitration, is multiplied by 3, and deducted from the sulphocyanate solution originally added; the difference gives the number of c.c. of sulphocyanate solution required for precipitation of the copper. In the presence of iron the point of complete precipitation of the copper cannot be recognized by the absence of any color change. Ferric oxide, even when all the copper is precipitated, affords a dark coloration at the point where the sulphocyanate solution falls into the liquid, but, on shaking, it disappears through the action of the sulphurous acid. Hence, in order to ascertain when the precipitation of the copper is complete, it is necessary to transfer some of the fairly clear liquid above the precipitate to a test-tube, and while warming, to allow a drop of sulphocj^anate solution to fall in from a burette. If the tur- bidity does not increase, all the copper has been precipitated. 630 DETERMINATION OF COMMERCIAL VALUES. [ 261. Then return the sample to the main bulk of the solution, and proceed as above detailed. In the presence of halogens, silver, and mercury the method is inapplicable. e. CLASSEN * employs the oxalic-acid method already described for zinc (p. 434 this volume) and nickel (p. 480 this volume), for determining copper in solutions which, as in the case of copper- ore solutions, contain ferric chloride, antimonous chloride, ar- senous chloride, etc. If but little antimony is present, evaporate to dryness the nitric-acid solution, add a concentrated solution of potassium oxalate in excess, filter hot, and wash the residue with water to which potassium oxalate has been added. Con- centrate the filtrate to about 50 c.c., whereby almost the entire quantity of copper crystallizes out as potassio-cupric oxalate in the form of blue needles, add 2 volumes of 80-per cent, (about) acetic acid, and allow to stand for some time. Then filter, wash the precipitate with a mixture of equal parts of acetic acid, al- cohol, and water, dry, and ignite gently in a platinum crucible; dissolve the residue in sulphuric acid, and in this solution precip- itate the copper electrolytically, whereby it is obtained free from zinc, nickel, magnesium, etc. If considerable quantities of antimony are present beside arsenic, mix the finely powdered substance, or the evaporation- residue of the solution with about four times its quantity of am- monium chloride, and heat very gently in a covered crucible. By this treatment nearly all the arsenic and antimony, as well as considerable ferric chloride, are votalilized. The copper can be determined in the residue in the manner above described. [ /. Copper is also determined colorimetrically by the so-called "Heine's method/' in poor copper ores and slags. It consists in bringing the copper into ammoniacal solution, and comparing the color of the solution so obtained with that of a copper solution of known strength. Although the method appears simple, it is, nevertheless important to observe the precautions detailed by HEATH f as the result of many years' experience with this method. * Zeitschr. f. analyt. Chem., xvm, 390 and 391. t Journ. Amer. Chem. Soc., xix, 24, 1897. 261.] COPPER COMPOUNDS. 631 In the first place it is necessary to so prepare and preserve the standard solution that it will remain unchanged for at least one year; secondly, the solution to be compared must be prepared in a manner to easily permit of the separation of the notable quan- tities of silica, ferric oxide, alumina, and lime present with the small quantity of copper. The first requisite is accomplished by using copper sulphate instead of nitrate, adding a sufficient quan- tity of ammonia to the solution to obtain a clear, blue solution, and then preserving the latter so stoppered as to prevent any loss whatever of ammonia. To prepare the standard solution, dissolve about 0.3 grm. pure copper hi 5 c.c. nitric acid of sp. gr. 1-4, with the addition of 5 c.c. concentrated sulphuric acid of sp. gr. 1-84, and evaporate the solution until vapors of sulphuric acid begin to be evolved. When cold, add 25 c.c. of water, and then sufficient strong ammonia to yield a clear solution. The latter is then diluted with ammonia water (1 vol. stronger ammonia and 6 vols. water) so that 1 c.c. of the resulting liquid will accurately represent 0025 grm. copper. This copper solution, which we will term A, serves for the prepa- ration of a scale of colors representing from 0-1 to 1-3 per cent, of copper. As 2 5 grm. of the substance to be examined is always taken, and made up into 200 c.c. of solution, the latter will contain exactly 0-0025 grm. copper, assuming the substance to contain 1 per cent, of copper. The standard copper solution correspond- ing with this strength is prepared by diluting 1 c.c. of the solution A with sufficient of the diluted ammonia (1 + 6) to measure 200 c.c. Similarly a standard solution of 2 c.c. solution A in 200 c.c. corre- sponds to a copper content of 0-2 per cent., always assuming, of course, at 2-5 grm. of the substance to be examined be taken. Standard solutions prepared in like manner, and corresponding to from 0-1 to 1-3 per cent, copper, are filled into cylindrical flasks of thin, colorless glass, and most carefully closed with ground- glass stoppers to prevent any and all escape of ammonia. HEATH gives as the most suitable dimensions, a length of about 180 mm. to the neck, and a diameter of about 44 mm. ; and the flasks should 632 DETERMINATION OF COMMERCIAL VALUES. [ 261. bear a scratch at the 200-c.c. point. The dimensions and the thickness of the glass must be uniform throughout; and the flasks must be preserved in a rather cool place, and protected from ex- posure to direct sunlight. The determination is made as follows: Powder the substance Very finely, weigh, and sift. If any pieces remain in the sieve, and which are usually of a metallic nature, determine their weight, and analyze them separately. Moisten 2-5 grrn. of the powder (if this contains over 1 2 per cent, copper, only 1 25 grm. is taken) with water in a porcelain dish, add 15 c.c. nitric acid of sp. gr. 1-42, and heat gently with occasional stirring until completely decomposed. Then add 5 c.c. concentrated sulphuric acid, and heat until the mass acquires a doughy consistency, whereby the silica is dehydrated, and the copper is converted into sulphate. Now dissolve in 70 c.c. water, add an excess of ammonia all at once (as a rule 30 c.c. suffice), filter, wash twice with 10 c.c. diluted ammonia (1:10), and wash the precipitate back again into the dish as completely as possible with the aid of 50 c.c. water. After the ferric oxide and alumina have been brought into solution by the addition of sulphuric acid, drop by drop, repeat the precipita- tion with 20 to 25 c.c. of ammonia of sp. gr. 0-9, filter, and wash with diluted ammonia. Now pour the solution into one of the flasks, make up to 200 c.c. with the 1 :6 ammonia water, and com- pare the color with those of the standard solutions, the comparison being made, however, with only one standard solution at a time. HEATH recommends not to compare three flasks together, as in such a case the color of the middle flask appears too light. The determination permits of an accuracy up to 03 per cent. If the ammoniacal copper solution has a greenish tint, this may be due to the presence of organic matter, which impairs the complete precipitation of ferric oxide by the ammonia. In mak- ing comparisons with a greenish liquid, too high a copper content is, as a rule, found, nevertheless the difference is usually within the limits of experimental error. Should the green tint be too pronounced, it is better to ignite the weighed sample for a short 262.] COPPER COMPOUNDS. 633 time in a porcelain crucible before proceeding to dissolve it. TRANSLATOR.] B. VARIETIES OF COPPER. I. CEMENT COPPER. 262. Since Spanish pyrites containing copper is being so largely used, particularly in the manufacture of sulphuric acid, and as cement copper is prepared from the waste, this cement copper comes into the market in large quantities; and as it exhibits great variations as regards both its copper and moisture contents, it is frequently the subject of analysis. The commercial varieties are, as a rule, fine, homogeneous, and either red with a content of from 5 to 15 per cent, of moisture, or, if precipitated by cast iron instead of wrought iron, or if de- prived of its water by heating at a high temperature, it is black; in the latter case it is almost anhydrous. At times, however, cement copper is met with consisting partly of fine, partly of me- dium fine, powder and larger lumps of copper. The homogeneous and irregular kinds must be treated differently if the results of the analysis are to correctly express their average composition. 1. Fine Homogeneous, Red or Black Cement Copper, a. Determination of Water. Dry about 75 grm. of the uniformly mixed cement copper at 100 to constant weight. I employ for this purpose a semicylindri- cal tin box, like that shown in Fig. 126, 16 cm. long, 40 nun. wide, FIG. 126 and 22 mm. deep, and provided with a sliding cover.* The box, without the cover, is inserted in a slightly larger copper tube * I use this box not only for the determination of water in cement copper, but also for the determination of moisture in minerals and other substances of which it is necessary to take large quantities in order to obtain a correct average of the quantity of moisture contained. 634 DETERMINATION OF COMMERCIAL VALUES. [ 262. which is fixed crosswise and slightly inclined in a box-shaped copper water-bath in such a manner as to be completely surrounded by boiling water or steam at 100. After several hours remove the box from the tube, slide the lid in place, allow to cool in a desiccator, and weigh; then remove the cover, insert the box again in the tube, and ascertain if the weight remains constant after heating for an hour; when this is the case, the determination is completed. b. Copper Determination. Treat about 60 grm. of the copper dried at 100, or, if the water determination and the solution are to be made in one operation, of the undried copper, with hydrochloric acid of sp. gr. 1-12, to which nitric acid is gradually added, and apply heat until all reaction ceases; then dilute and filter into a weighed, two-litre- flask. Wash the residue, which is mostly carbonaceous, and ignite with access of air until all the combustible matter is consumed, then treat with hydrochloric acid at a gentle heat with the addition of nitric acid, dilute, filter this solution into the main solution, allow to cool, fill to the mark, mix thoroughly, and weigh. In an aliquot part of the liquid now determine the copper. The method to be described next allows all the foreign metals that may be present to be separated, and hence gives thoroughly re- liable results under all circumstances. It will of course be under- stood that the copper determination may be effected by one of the simpler methods described in 261, II, but it must always be remembered that cement copper may contain impurities (lead, antimony, iron, etc.) which affect the accuracy of the determina- tion. a. Measure off 30 c.c. of the solution with a pipette into a light, glass-stoppered flask (which is to be weighed with its stopper) and weigh. The weight of the solution alone is here the desider- atum, the measuring of the solution being merely for the purpose of enabling the operator to take a suitable quantity for the analysis. ft. Rinse the contents of the weighing-flask into a 400- or 500- c.c. flask, add 20 c.c. hydrochloric acid of sp. gr. 1 12, precipitate 262.] COPPER COMPOUNDS. 635 hot with hydrogen sulphide, collect the precipitate ; and wash it with water to which a little hydrogen-sulphide water and some acetic acid are added. The washing is to be considered completed when the washings cease to afford a precipitate or color on adding ammonia and ammonium sulphide. f. Transfer the precipitated copper sulphide, together with the filter, to a beaker, and add 10 or 20 c.c. sodium-sulphide solution and about 50 c.c. water; heat about five minutes, dilute with about 100 c.c. water, filter, and wash with water to which some sodium-sulphide solution has been added. Acidulate the filtrate and washings with hydrochloric acid in order to make certain that the sulphur precipitated contains no copper sulphide, and which is recognized by the color of the precipitate. d. Transfer the copper sulphide and the filter back again to the beaker in which the treatment with sodium sulphide was effected, add 20 c.c. nitric acid of sp. gr. 1-2, and 20 to 30 c.c. water, warm until the copper sulphide is dissolved, dilute, filter into a flask, and wash the filter. Then cautiously incinerate the dried filter in a porcelain crucible, warm the residue with a little hydrochloric and nitric acids, dilute, and filter into the other solution. Should this be turbid in consequence of the separa- tion of a slight quantity of silver chloride, it must be given suf- ficient time to settle; then filter. As a rule, however, this is unnecessary. Now add ammonia to the clear or filtered liquid until weakly alkaline, then add ammonium carbonate, allow to stand for twelve hours at a moderately warm temperature, filter, acidulate the filtrate with acetic acid, precipitate hot with hydrogen sulphide, and determine the copper as cuprous sulphide according to Vol. I, p. 375. . Should the cement copper contain a relatively large quan- tity of lead, it is preferable to separate this by adding an excess of diluted sulphuric acid to the nitric-acid solution first obtained from the evaporated, weighed quantity. 2. Non-homogeneous Cement Copper. If the cement copper consists of portions of very unequal character, i.e., fine and moderately fine powder, and coarser lumps, 636 DETERMINATION OF COMMERCIAL VALUES. [ 263. an average sample cannot be properly obtained by mere mixture.* In such a case, after the moisture in the entire sample has been determined, the unequal portions must be separated by sifting, each grade again dried at 100, and then an aliquot part of each, say one-tenth, accurately weighed, and these portions used for preparing the solution. In the case of the cement copper referred to in the foot-note, a sample weighing 4358-7 grm. consisted of 3197-5 grm. fine powder, 747 grm. moderately fine powder, and 414-2 grm. in lumps. One-tenth of each was weighed off and the 435-87 grm. of sample thus obtained dissolved in nitric acid; the solution weighed 7845-3 grm., and the copper was determined in aliquot, weighed portions. ii. COARSE COPPER; REFINED COPPER. 263. Although in the analysis of cement copper the determination of the copper content is, as a rule, sufficient, in the case of coarse copper a determination of all the constitutents must be made. The carrying out of such an analysis becomes the more difficult the greater the number of foreign elements to be determined, and which are usually present in very small quantities, and in order to form an opinion regarding the copper it does not suffice to simply ascertain what these are and their quantities, but the forms, in which they exist in combination in the copper must also be ascertained; this was first accomplished by the exhaustive in- vestigation carried out with the most extreme care by W. HAMPE.f The foreign elements that usually occur, or may occur, are silver, gold, arsenic, antimony, tin, bismuth, lead, iron, cobalt, nickel, zinc, sulphur, phosphorus, and oxygen. In the following I shall first describe two methods which are suitable for the quantitative determination of these elements, which usually altogether amount only to 0-5 to 1-0 per cent.; * Compare my communication regarding this in Zeitschr f. analyt. Chem., xv, 63. t " Beitrage zur Metallurgie des Kupfers," Zeitschr. /. Berg-, Hutten- und Salinenwesen, xxvii, 205; 'Zeitschr. f. analyt. Chem., xui, 176. 263.] COPPER COMPOUNDS. 637 then will follow methods for determining the forms in which the combinations of the foreign elements are present. a. First Method, in which the Copper is not Precipitated Electrolytically. 1. Treat 100 grm. of the carefully cleaned copper with a suf- ficient quantity of perfectly pure nitric acid of sp. gr. 12 (in the case of copper turnings with addition of water), to effect solution until even when warmed there is no longer any reaction; then dilute with water, filter, and wash the undissolyed residue. Col- lect the filtrate in a tared two-litre flask, fill this up to the mark, and mix. 2. Rinse the residue into a porcelain dish, add to it the filter ash, evaporate to dryness, transfer to a porcelain crucible, re- move any adhering particles by rubbing with a little sodium car- bonate, introduce this also into the crucible, add sulphurated potassa, and fuse with exclusion of air; after cooling, treat with water, filter the yellow solution from the black residue, and wash the latter. 3. Heat the black residue obtained in 2, together with the filter, with moderately dilute nitric acid, filter, wash, incinerate the filter, heat the filter ash with nitric acid, dilute, and filter; add the filtrate to the solution first obtained, incinerate the filter, and preserve the filter ash, which may contain a portion of the gold present. To the solution, however, add a small quantity of hydrochloric acid ; if a precipitate of silver chloride forms, allow it to settle, then filter, and convert the silver chloride into silver for the purpose of weighing, finally testing its purity. Evapo- rate the clear or filtered solution with some sulphuric acid to separate the lead, and precipitate the copper and bismuth if these are present; precipitate the solution with hydrogen sulphide, and in the filtrate from this separate any metals of the fourth group by adding ammonium sulphide. 4. Precipitate the sulphurated-potassa solution from 2 with hydrochloric acid, filter, treat the precipitate, which contains much admixed sulphur, together with the filter, with bro- 638 DETERMINATION OF COMMERCIAL VALUES. [ 263. minized hydrochloric acid until everything soluble is dissolved; then filter, wash, remove the free bromine present with ammonia, acidulate with hydrochloric acid, and precipitate with hydrogen sulphide at 70; collect the precipitated sulphides, dissolve in weak yellow ammonium sulphide, filter, evaporate the solution to dryness in a porcelain crucible, cautiously oxidize the residue with fuming nitric acid, evaporate to dryness, add caustic soda and a small quantity of sodium nitrate, fuse, and effect the sepa- ration of antimony, tin, and arsenic, if these are present, according to ROSE'S method, Vol. I, p. 718 [201]. After washing, incinerate the filter through which the ammonium-sulphide solution of the sulphides and the sodium antimonate dissolved by the hydro- chloric and tartaric acids have been filtered, add to it the filter ash of the filter preserved, and treat with nitrohydrochloric acid. Dilute, filter, evaporate with hydrochloric acid in order to drive off the nitric acid, and after evaporating the solution to a small bulk, precipitate the gold by adding ferrous chloride. If tin is not present, remove the free bromine from the bromin- ized hydrochloric-acid solution, and in the liquid then separate the antimony and arsenic most conveniently by BUNSEN'S method (see pp. 556 and 557 this volume). The weighed metallic sulphides must, however, be tested for gold. 5. In about 20 grm. of the solution obtained in 1 determine the copper by the method described for cement copper, p. 633 this volume. 6. Add four drops hydrochloric acid to one litre of the liquid obtained in 1, and representing 50 grm. copper. If a turbidity or precipitate forms, due to silver chloride, allow it to subside in a warm place, add a few more drops of hydrochloric acid, and observe whether all the silver has been precipitated. If a further turbidity develops, a couple of drops more acid must be added; any con- siderable excess of acid must, however, be avoided. Convert the silver chloride most conveniently into metallic silver for the pur- pose of weighing. The quantity found and multiplied by 2, and added to that found in 3, gives the percentage of silver. 7. The liquid from 6, which remained clear on adding the hydro- 263.] COPPER COMPOUNDS. 639 chloric acid, or that filtered off from the silver chloride, transfer to a porcelain dish, cautiously add 85 grm. pure, concentrated sulphuric acid which has previously been diluted with water, and evaporate until all the nitric acid has been expelled; then add water, warm until all the cupric sulphate has dissolved, filter the liquid into a two-litre flask, wash the undissolved residual lead sulphate first with water acidulated with sulphuric acid and then with alcohol (which must be collected and preserved apart), weigh (Vol. I, p. 355), and test its purity by boiling with a solution of ammonium acetate containing a small quantity of free ammonia; if an insoluble residue remains even after repeated boiling, it must be deducted from the lead sulphate and tested further. 8. Make up to two litres the liquid filtered off from the lead sulphate in 7, mix, and transfer 500 c.c. to each of four flasks of about 1500 c.c. capacity.* Dilute the contents of each flask with about 500 c.c. water, add 50 c.c. hydrochloric acid of sp. gr. 1-12 to each, warm to about 70, and precipitate with hydrogen sul- phide. When cold, transfer the contents of the four flasrs to a weighed flask of about six litres capacity and provided with a glass stopper, repeatedly rinse the flasks with hydrogen-sulphide water so that the whole of their contents are brought into the large flask, then mix well and weigh the flask. The weight of the solution in the flask is ascertained by deducting from the total weight the tare of the flask together with the weight of the cupric sulphide, the quantity of which can be calculated from the weight of the copper. After settling, siphon off the supernatant liquid from the precipitate so far as possible, weigh the flask with the precipi- tate and the remainder of the solution, and thus ascertain the weight of 'the liquid siphoned off. Filter the latter, evaporate in a porce- lain dish until by far the greater part of the sulphuric acid has been expelled, heat finally with a little nitric acid, add ammonia, and filter; dissolve the precipitate in hydrochloric acid, repre- cipitate with ammonia, and in the precipitate determine any iron * The reason for recommending the measuring of the contents of each flask is that in case of accident to one of them the whole labor may not be lost. 640 DETERMINATION OF COMMERCIAL VALUES. [ 263. present according to Vol. I, p. 642 [77]. Add to the filtrate ammonium acetate, acidulate with acetic acid, and then precipi- tate nickel, cobalt, and zinc, which separate and determine ac- cording to the methods described on pp. 431, 476 and 477, and 478 and 479 this volume. Finally, the quantities of iron, nickel, cobalt, and zinc obtained must be calculated from the part to the whole, since they are obtained from only a part of the solution drawn off from the cupric sulphide. 9. To the precipitate, together with the remainder of the solu- tion left in the large flask, add first caustic-potassa or soda solu- tion until the liquid is strongly alkaline, then a solution of potas- sium or sodium sulphide containing some disulphide, and in suffi- cient quantity to make certain of dissolving all the antimony and arsenic sulphides, and warm gently for some time. Then dilute copiously with water, mix, weigh, siphon off the liquid so far as possible, weigh the flask with the precipitate and the remainder of the solution, and thus ascertain the weight of the liquid siphoned off. Filter the latter, acidulate with hydrochloric acid, and allow to settle. From the explanation given in 8, it follows that the copper content of the sulphides of the sixth group precipitated from the alkali-sulphide solution can be readily calculated. As these sulphides contain considerable sulphur admixed, collect it after it has settled, wash, treat it while still moist with brominized hydrochloric acid, dilute, filter, add ammonia until the solution has become colorless, then gently heat for a long time, and finally add hydrochloric acid. In the clear liquid now precipitate the metals of the sixth group with hydrogen sulphide, and separate them as detailed in 4. The weights obtained must be calculated from the part to the whole. 10. The precipitated cupric sulphide separated from the main bulk of the liquid in 9 containing the alkali sulphide, now bring onto the filter through which the liquid has been filtered, wash it with water containing some potassium or sodium sulphide, then dissolve in hydrochloric acid with the addition of nitric acid, filter, and evaporate the solution, with the addition of hydro- chloric acid in excess, to dryness on a water-bath; take up the 263.] COPPER COMPOUNDS. 641 saline mass with water and filter after long settling. Dissolve the insoluble residue, containing all the bismuth as basic bismuth chloride, in hydrochloric acid, add caustic-potassa solution until the liquid is alkaline, and then add an excess of potassium cyanide and potassium sulphide. The bismuth is thus separated as bismuth sulphide, while the copper present with it remains in solution. As the bismuth sulphide may contain some nickel sulphide, dissolve it in nitric acid, precipitate the solution, after dilution, with hy- drogen sulphide, and now determine the pure bismuth sulphide either as such (Vol. I, p. 385, 3) or after conversion into bismuth oxide. 11. To 400 c.c. of the solution obtained in 1, and corresponding to 20 grm. copper, add ammonia until the greater part of the free nitric acid present has been neutralized, then add a few drops of a solution of barium nitrate and allow to stand for a long time in a warm place. If the copper contains any considerable traces of sulphurous acid (any sulphur present in coarse copper is in this state HAMPE*), a slight precipitate of barium sulphate forms, and is to be collected and determined. Very slight quantities of sulphurous acid cannot, however, be detected in this manner, as barium sulphate is not altogether insoluble in the solution of copper nitrate. For the detection of very small quantities, there- fore, the copper (about 30 to 40 grm.) must be treated, accord- ing to HAMPE f, in a current of pure, dry chlorine, and the sulphuric acid determined in the volatile products. For this purpose the copper is placed in a tube of refractory Bohemian glass which is bent at its exit end at first downwards and then upwards. The tube is fixed in a slightly inclined position, with the exit end lowermost, and connected with a PELIGOT bulb-tube, which in turn is connected with another. Vulcanized india- rubber must be altogether avoided in setting up this apparatus. The PELIGOT tubes are partly filled with water which is saturated with chlorine gas before beginning the operation. In order that the gas may be pure and free from moisture it must be well washed *Zeitschr. /. analyt. Chem., xm, 222. f *&*& XIII 223 - 642 DETERMINATION OF COMMERCIAL VALUES. [ 263. and dried by passing over calcium chloride. When the apparatus is set up, warm the copper for a short time; it then becomes red- hot as it combines with the chlorine to form cuprous chloride, which flows down the bent-down portion of the tube. As soon as only a little copper remains unattacked, warm the tube again, and at the same time moderate the current of gas. After the experiment is at an end, unite the contents of the receivers, heat until all the chlorine has been expelled, and determine the sulphuric acid with barium chloride. For other methods of determining the sulphurous acid present in refined copper, see 13. 12. Evaporate 400 c.c. of the solution obtained in 1 repeatedly with hydrochloric acid to remove the nitric acid, dilute with about 1200 c.c. water, precipitate with hydrogen sulphide at 70, bring the whole into a weighed flask of about two litres capacity, rinse, mix, and weigh; allow to settle, siphon off as much as possible of the supernatant liquid, weigh the flask with the precipitate and the remainder of the solution, and thus ascertain the quantity of copper corresponding to the liquid siphoned off (compare 8). Filter the latter, evaporate to a small bulk with repeated addition of nitric acid, and determine any phosphoric acid arising from the presence of phosphorus in the copper, according to Vol. I, p. 446/2. 13. To determine any oxygen present in coarse copper, and which, as HAMPE (loc cit.) has shown, is combined partly with copper as cuprous oxide, partly with other metals as oxides and acids, and partly with sulphur as sulphuric acid, the following method, described by HAMPE,* yields very accurate results if all the precautions given are observed, but not otherwise : Reduce the perfectly bright copper to filings by means of a not too coarse file, sift through a hair sieve, extract any particles of iron that may be present by means of a magnet, and boil the comminuted copper with caustic-potassa solution, whereby any traces of fat are dissolved, and paper fibres are washed away. Then wash the purified copper thoroughly and dry rapidly. The oxygen is determined by ascertaining the loss in weight * Zeitschr. /. analyt. Chem., xm, 202. 263.] COPPER COMPOUNDS. 643 the powdered copper sustains on being ignited in a current of hydro- gen. The reduction is effected in a Bohemian glass bulb-tube drawn out at both ends. Heat the tube in a current of dry air, allow to cool in it, and immediately close both ends with small rubber tubes closed by small glass rods; then weigh, introduce the dried powdered copper (about 30 grm.) into the bulb, and weigh again. Now pass perfectly pure, dry carbon dioxide through the tube, the gas being evolved from marble * by hydrochloric acid in a constant-delivery apparatus. The evolution apparatus is set in operation about two hours before it is required for use; and to purify and dry the gas, conduct it first through a solution of sodium bi- carbonate, then through a tube containing lumps of the salt, a wash- bottle containing a solution of silver nitrate, a tube filled with pieces of pumice-stone impregnated with the same solution, a flask containing concentrated sulphuric acid, and lastly through a tube containing porous calcium chloride. After the carbon dioxide has passed for five minutes through the bulb-tube containing the copper, heat the latter very moderately in order to remove every trace of moisture. Empyreumatic products should not in this case be evolved. Too strong heating of the copper must be avoided, as otherwise, if the copper contains arsenates, a sublimate of arsenous acid may form. After cooling in the current of carbon dioxide, displace the latter by dry air, stopper the tube, and weigh it. The difference between this weight and that obtained before will be but a few milligrammes. Now pass a very slow current of pure hydrogen over the copper and heat at first gently, and later until the whole of the copper is red-hot, maintaining this temperature for about fifteen minutes. During the heating water forms, and in the case of impure copper, there forms in the upper part of the bulb and close behind it a black sublimate of arsenic, antimony, and lead. On this account the end of the tube must be sufficiently long, and the current of hydrogen so slow that in no case may any of the sublimate leave the tube. * The air contained in marble may be easily removed, according to A. BERNTHSEN (Zeitschr. /. analyt. Chem., xxi, 63). 644 DETERMINATION OF COMMERCIAL VALUES. [ 263. In the case of copper containing sulphurous acid, some hydrogen sulphide is evolved with the water vapor. As it is necessary to ascertain its quantity, conduct the evolved gas through an alkaline lead solution, or through brominized hydrochloric acid, and deter- mine it as detailed on pp. 520 and 521 this volume.* After the copper has become perfectly cold in a current of hydrogen, and this gas has been displaced by dry air, close the tube and weigh it. The loss in weight minus that of the sulphur evolved as hydrogen sulphide gives the quantity of oxygen. b. Second Method, in which the Copper is Electrolytically Deposited. (According to HAMPE.f) 1. For the main analysis, the copper is used in the form of clean, chiselled pieces, two portions of 25 grm. each being weighed off. Treat each portion in a beaker with a mixture of 175 to 180 c.c. nitric acid of sp. gr. 1-2, and 200 c.c. water at a gentle heat, until everything soluble has dissolved; then, without previously filtering off any insoluble residue, evaporate each liquid to dryness on a water-bath after adding 25 c.c. pure concentrated sulphuric acid which has been previously diluted with water; then heat more strongly until all the free sulphuric acid is volatilized. Now cover each perfectly cold dish with a glass cover, and cau- tiously and gradually add 20 c.c. nitric acid of sp. gr. 1 -2, and 350 c.c. of water. When all the cupric sulphate is dissolved add an accurately measured quantity of standard hydrochloric acid (1 c.c. = 0-001 grm. silver) sufficient to exactly precipitate the silver present, and the quantity of which has been previously ascer- tained by scorification and cupellation (pp. 579 and 580 this vol- ume). Allow to stand for twenty-four hours, and collect the precipitate, consisting of lead sulphate, silver chloride, and anti- monic acid or antimonates, on a small filter, and thoroughly wash the dishes and filter. These precipitates we will designate I, a and b. Rinse out the dishes with hot concentrated hydrochloric acid in * The quantities of sulphur obtained agreed very well in the results published by HAMPE (Zeitschr. /. analyt. Chem., xm, 226) with those ob- tained by heating the copper in a current of chlorine. \ Zeitschr. /. analyt. Chem., xin, 180. 263.] COPPER COMPOUNDS. 645 order to remove any adhering particles of antimonic acid, unite both solutions, dilute with water, precipitate with hydrogen sul* phide, and for the present set aside the liquid and the precipitate of antimony sulphide, etc., which we will designate as II. 2. The two copper solutions from 1, and the washings, each amounting to from 400 to 450 c.c., place in separate glass vessels 9-2 cm. wide and 15 cm. high, and precipitate the copper electrolyt- ically (p. 621 this volume). The current employed must be of a strength sufficient to yield 130 c.c. of oxyhydrogen gas in thirty minutes from diluted sulphuric acid (1 :22) ; and it is important to maintain the current approximately at this strength. The pre- cipitation of the copper from the solution requires about seventy- two hours. When the liquid has become colorless or nearly so, and deposits but a trace of copper on a freshly immersed portion of the platinum electrode on continuing the current, run off the liquid, while still maintaining the current, into a large flask of about four litres capacity, wash out until the evolution of gas at the positive pole ceases, and the liquid is therefore no longer acid. Now interrupt the current, and wash the cone bearing the deposited copper first with water, then with alcohol, dry rapidly (best by sus- pension in a current of hot air ascending from a large platinum or silver dish heated from below), and weigh the copper. The two copper determinations carried out in this manner check each other. If the copper has a bright, pure color it is a certain indication that no antimony or arsenic has yet been deposited upon it, as would be the case if the current were allowed to pass after complete precipitation of the copper. As the copper must be tested for bismuth (see p. 648, 8, this volume), it must be preserved for a while. 3. Rinse the siphon and platinum spirals used in 2 with water into the large flask, dissolve the slight quantities of lead dioxide adhering to the platinum spiral in hot hydrochloric acid over one and the same porcelain dish, evaporate to dry ness with sulphuric acid the solution containing also a small quantity of platinic chloride, ignite the residue, dissolve the lead sulphate in hot hydrochloric acid, add ammonia to alkalinity, then nitric acid until just acid, 646 DETERMINATION OF COMMERCIAL VALUES. [ 263. precipitate with hydrogen sulphide, and reserve for the present the liquid with the precipitate, which we will designate as III. 4. The liquid in the large flask, and obtained in 2, boil, and then evaporate in a porcelain dish, at first on the water-bath; finally heat more strongly, until the free sulphuric acid is almost completely expelled, and but a few drops remain in the dish. When cold, add concentrated hydrochloric acid, warm, dilute, filter off from the small quantity of silicic acid derived from the vessels, saturate with hydrogen sulphide, and allow to stand for twenty- four hours at 75; repeat the saturation with the gas, and expel the excess by applying a gentle heat, in order to effect complete precipitation of the arsenic. Now filter through a suitable filter: a, the precipitate of lead sulphide, III (see 3); 6, the pre- cipitate of antimony sulphide, etc., II (see 1); and c (after previously removing the filtrates from III and II), the precipitate caused by hydrogen sulphide in the electrolyzed liquid. Wash the precipitate well, but do not dry it (term it IV) ; the filtrate, however, evaporate until all hydrogen sulphide is expelled, boil with a little nitric acid, and add ammonia in excess. If a pre- cipitate of ferric hydroxide forms, redissolve it in hydrochloric acid, reprecipitate with ammonia, weigh as ferric oxide, and con- trol the gravimetric determination of the iron by a volumetric determination. Precipitate the nickel and cobalt electrolytically from the ammoniacal solution (p. 481 this volume), and then separate them by means of potassium nitrite (Vol. I, p. 655, 9). 5. Now remove the precipitates I, a and b (see 1), and which are to be united, as completely as possible from the filters, treat with fuming nitric acid in a porcelain crucible, evaporate to dry- ness, add a little ammonium nitrate to completely destroy the organic matter present, and heat cautiously; when cold, transfer the precipitates removed from the filters to the crucible, and fuse the whole with three times its quantity of a mixture of sodium carbonate and sulphur, with exclusion of air as much as possible. Allow the melt to disintegrate in water as completely as possible, filter the hot yellow solution through the filter containing the still moist precipitate IV (see 4), and wash, first with dilute 263.] COPPER COMPOUNDS. 647 potassium-sulphide solution, and then with hydrogen-sulphide water. The filtrate contains all the arsenic, antimony, and tin (also any traces of gold that may be present) in the form of sulpho-salts, while the precipitate (V) contains all the lead and silver and the portions of bismuth and copper here present. 6. Precipitate the solution of the sulpho-salts obtained in 5 with diluted sulphuric acid, filter, dissolve the precipitate in freshly prepared ammonium sulphide, and evaporate the solution to dryness. If, now, only antimony and arsenic are present, heat the residue with hydrochloric acid and potassium chlorate, add tartaric acid, then ammonia, filter, and precipitate the arsenic acid with mag- nesia mixture; after long standing dissolve the precipitate in hydrochloric acid, again precipitate with ammonia, and weigh either as ammonium-magnesium ar senate (Vol. I, p. 412, 2), or dissolve in hydrochloric acid, precipitate the arsenic with hydrogen sulphide, determine the magnesium as pyrophosphate in the filtrate after con- centration (Vol. I, p. 275, 2), and from the quantity found calcu- late the arsenic acid. HAMPE recommends the latter method par- ticularly when rather large quantities of arsenic are present. Acid- ulate the filtrate from the magnesium arsenate, precipitate the antimony with hydrogen sulphide, and determine small quantities as antimony tetroxide (Sb 2 O 4 ) (Vol. I, p. 398, 2), but larger quan- tities determine as anhydrous antimony sulphide (Vol. I, p. 397). If zinc is present (a case of which HAMPE takes no special note), the residue obtained by evaporating the ammonium-sulphide solution containing all three sulphides must be reoxidized with fuming nitric acid, and the antimony, tin, and arsenic separated according to Vol. I, p. 718, a [201]. 7. Dissolve the precipitate V from 5 in a covered funnel in warm, moderately dilute nitric acid by repeatedly pouring it back, then wash, dry, and incinerate the filter, transfer the ash to the nitric-acid solution, boil, filter, and if but little bismuth is present, precipitate the silver with hydrochloric acid; determine the lead by evaporating with sulphuric acid, and lastly separate the copper and bismuth in the filtrate by ammonium carbonate. In the 648 DETERMINATION OF COMMERCIAL VALUES. [ 263. case of larger quantities of bismuth neutralize the nitric-acid solution with sodium carbonate, add potassium cyanide in excess, filter off the precipitate containing the lead and bismuth oxides, precipitate the silver in the nitrate as silver cyanide by cautiously acidulating with nitric acid (Vol. I, p. 341, 3), evaporate the filtrate to dryness with sulphuric acid in order to decompose the cyanogen compounds, and in the hydrochloric-acid solution of the copper precipitate the latter as cupric sulphide. The mixture of lead and bismuth oxides, however, dissolve in hot hydrochloric acid, evaporate to a small bulk, and pour into a large volume of water. After twenty-four hours collect the precipitate containing all the bismuth as basic chloride, dissolve it in nitric acid, precipi- tate the bismuth with ammonium carbonate, boil, filter after twenty-four hours, and determine the bismuth as oxide (Vol. I, p. 383, 1, a). In the filtrate, however, precipitate the lead with ammonium sulphide, and convert the lead sulphide into lead sulphate. 8. The bismuth determined in 7 was that left in the residue on dissolving the copper in nitric acid ; the bismuth that had passed into the nitric-acid solution, on the other hand, is precipitated with the electrolytically deposited copper, and must be determined in this. Hence dissolve this in nitric acid (using about 350 c.c. nitric acid of sp. gr. 1-2 for every 50 grm. copper), and boil the solution in a large flask with a large excess of hydrochloric acid, and until all the nitric acid has been expelled. Evaporate to dryness on a water-bath until the excess of hydrochloric acid has been driven off and the residue has acquired a brown color, and then pour into a large volume of boiling water. All the bismuth is thereby separated as basic chloride, mixed with a little basic copper salt. Filter after twenty-four hours, and separate the two metals either directly, or after reprecipitating the hydrochloric- acid solution with ammonium carbonate. 9. The methods recommended by HAMPE for determining the sulphur and the total oxygen I have already described above (pp. 640 to 643). HAMPE has not touched upon the determina- tion of phosphorus in his paper. 263.] COPPER COMPOUNDS. 649 c. Ascertaining the Forms of Combination in which the Foreign Metals occur in Coarse Copper, etc. (HAMPE *). It was formerly assumed that the foreign metals in coarse copper were present in the metallic form; it is now known, how- ever, that they are present partially in the form of oxides and acids. This fact was first pointed out by FLEITMANN f on the basis of a research carried out by REISCHAUER,! but HAMPE, after making a comprehensive investigation, elaborated the methods detailed below, which render it possible to determine in what form the foreign metals are present in coarse copper, etc. The examina- tion requires two sets of experiments, i.e. the quantitative analysis of the residues remaining on : 1. Treating the copper with nitric acid; and 2. Treating the copper with silver nitrate. In addition to this, the quantity of the oxygen must be known or else ascertained, i.e. the total quantity, and that combined with copper as cuprous oxide in the rough copper, etc. As regards the basis of the analytical method I refer to HAMPE'S original paper, as here the process only will be described. 1. Treat 300 grm. of bright filed pieces of copper in a ten-litre flask with a mixture of 4 litres water and 2-5 litres nitric acid of sp. gr. 1-2, at a moderate heat. When all the copper has dis- appeared allow to settle, and pour off the perfectly clear liquid into another vessel; the precipitate, however, rinse into a beaker, and wash it by decantation, but pass the liquid through a small filter in order to prevent any loss. After washing the contents of the filter into the undissolved residue, boil repeatedly with concentrated nitric acid, whereby a little more copper is dissolved ; then remove the gold in the residue with chlorine water, and any slight quantity of silver chloride by repeated extraction with ammonia water. As the residue may contain, in addition to antimonates, also hydra ted antimonic acid, the latter derived from * Zeitschr. f. analyt. Chem., xin, 188. f DINGL. polyt. Journ., CLXXV, 32. J Ibid., CLXXIII, 195; Journ. f. prakt. Chem., xcii, 508. Zeitschr. /. analyt. Chem., xm, 188. 650 DETERMINATION OF COMMERCIAL VALUES. [ 263. the metallic antimony contained in the rough copper, treat it, in order to remove the hydrated antimonic acid, with hot, rather strong, hydrochloric acid containing some tartaric acid, and until the nitrate no longer gives a reaction for antimony on testing with hydrogen sulphide. Finally, collect the residue thus treated and thoroughly washed, on a filter dried at 100, and weigh. Lastly, shake it so far as possible into a porcelain crucible, weigh the filter with the particles still adhering, and thus ascertain the quantity remaining for further analysis. Fuse this with three times its quantity of a mixture of equal parts sodium carbonate and sulphur, extract the melt with water, and in the solution determine the antimony and any arsenic and tin that may be present, according to the method detailed in 263, b. The residue, however, dis- solve in nitric acid, separate the silicic acid by evaporation, and treat the residue with nitric acid; then precipitate the solution with hydrogen sulphide, filter, dissolve the precipitate in nitric acid, evaporate the solution with hydrochloric acid almost to dryness, and dilute with much water. Dissolve the separated basic bismuth chloride in nitric acid, precipitate with ammonium carbonate, and determine the bismuth as oxide. The lead, copper, nickel, cobalt, and iron are determined according to the methods detailed in 263, b. In HAMPE'S analysis of toughened copper and dry copper from Oker, the residue insoluble in nitric acid consisted of about 75 per cent, bismuth antimonate, Bi(SbO 3 ) 3 , the remainder being lead, cuprous, ferric, nickelous, and cobaltous antimonates. The small quantity of silicic acid found appeared to have been derived from the glass vessels. That the antimonates existed ready formed in the copper, and were not formed from the latter by treatment with nitric acid, was shown by HAMPE in the varieties 1 of copper examined by him in that he treated 50 grm. of each to fusion in a current of hydrogen, and dissolved the residual copper in nitric acid; it dissolved completely, with the exception of only a trace of gold. This test must be carried out in the same way with all varieties of copper, if it is desired to know with certainty the state of combination of the foreign metals. 263.J COPPER COMPOUNDS. 651 2. For many metals, particularly arsenic, lead, and iron, the method detailed under 1 does not suffice to determine whether they are present in the copper in the metallic form, or in the form of oxides or salts. The examination in 1 may therefore be supple- mented as follows: Cover 8 to 10 grm. of the copper, in the form of thin, rolled sheet, or less preferably as filings (these must be freed from mechan- ically admixed iron by means of a magnet, and from any adherent grease by boiling with diluted potassa solution), with 100 to 150 times its weight of distilled water containing rather more than sufficient pure silver nitrate hi solution to completely displace the copper; stir for a long time, until no more particles of copper are visible, and repeat the stirring from time to time during the next twenty-four hours. Then collect on a filter, wash thoroughly by aid of the pump, dry, remove from the filter, add the filter ash, treat with nitric acid, filter off from any slight residual pow- der, and precipitate the silver with hydrochloric acid, avoiding any considerable excess. Dilute, decant, filter, evaporate the filtrate to a small volume, dilute, and precipitate warm with hy- drogen sulphide. In the precipitate determine the arsenic, anti- mony, lead, bismuth, and copper according to the methods de- tailed in 263, b, bearing in mind, however, that the precipitate may still contain a little silver sulphide. Regarding the antimony here found, it must be noted that if the whole of the antimony is not found in the copper in the form of insoluble antimonates, some antimony from the antimony com- pounds in the silver precipitate passes into the nitric-acid solu- tion; as regards the copper here found, it must be noted that it is derived from the cuprous oxide of the rough copper, and serves for the quantitative determination of the former (see 4, below). In the filtrate from the hydrogen-sulphide precipitate finally determine the iron which was contained in the copper as ferric oxide or as a salt. The examination of the filtrate from the silver precipitate, and containing the excess of silver nitrate, and cupric nitrate, together with the nickel, cobalt, and arsenic, which were present 652 DETERMINATION OF COMMERCIAL VALUES. [ 263. in the copper in metallic form, is superfluous. It may, however. be carried out for the purposes of control. 3 The determination of the total oxygen is effected according to the method detailed on p. 642 this volume. 4. To determine the oxygen present in the form of cuprous oxide, and hence also the quantity of the latter,* it is necessary to know the reaction which occurs when cuprous-oxide acts upon a neutral solution of silver nitrate. H. ROSE has already studied this subject, and shown that cuprous oxide, in this connection, behaves exactly as a mixture of equal equivalents of copper and cupric oxide would, i.e., that a mixture of metallic silver and a basic cupric salt is precipitated. HAMPE, who carefully studied this reaction, found that the basic cupric salt formed possesses a definite composition (4CuO-N 2 O 5 + 3H 2 O), and expresses the reac- tion in the cold by the following equation: 3Cu 2 + 4AgN0 3 + zH 2 O = (4CuO - N 2 O 5 + 3H 2 O) + 2CuNO 3 + 4Ag + (x-3) H 2 0. In accordance with this the copper existing as cuprous oxide is found by multiplying by 1 5 the copper in the precipitate from 2. Again, this copper multiplied by 1 6886, gives the weight of cuprous oxide ; or by 1887, the quantity of oxygen in the latter. 5. The sulphur found in rough copper containing oxygen compounds is not in the form of copper sulphide, as this would react with the cuprous chloride in molten copper, nor would it give rise to the evolution of hydrogen sulphide, which has been ob- served by HAMPE, and also previously by ABEL f and DICK J; when heating rosette copper in a current of hydrogen (see p. 643 this volume). 6. In order to show how the true constitution of the rough * HAMPE (Zeitschr. /. analyt. Chem., xni, 215) criticises the method given by AUBEL V^BERGGEIST, xn, 279; Zeitschr. f. analyt. Chem., vi, 456) for determining the cuprous oxide in refined copper, and gives an account of the not generally applicable method of determining cuprous oxide volu- metrically (ibid., 221). t Polyt. Centralbl, 1864, 904. J Berg- und Huttenmdnnische Zeit., 1856, 329. 263.] COPPER COMPOUNDS. 653 O i O tf 8 a i^ S O w s'-S si il 1-4 s CD ii ^ CJ ~03 O Ii POSITION .mounts of e Leference to 8 of the stopper falling out, it is fastened to the constriction of the funnel with fine copper wire ; and to render it air-tight, it is smeared with a little petrolatum, but in 271.] NITROGEN COMPOUNDS. 713 such a manner that none enters the holes of the stopper, b is a strong glass tube of approximately the same diameter and capacity as a. Both tubes are connected by a thick-walled rubber tube. The rest of the details may be gathered from the illustration. In operating with the apparatus, place the tube b so that its lower end is somewhat higher than the stop-cock on a, and, the cock being open, pour mercury into b until it ascends into a. Then close the stop-cock, allow the excess of mercury to run out through the side opening in the cock, and lower b; then, by means of a very fine pipette, introduce a measured quantity of the nitrose (2 to 5 c.c. in the case of weaker nitroses, or only 0-5 c.c. if very strong) into the funnel, allow it to flow into a by cautiously opening the stop-cock, and so that no air may be carried along with it, and rinse the funnel twice with concentrated, pure sulphuric acid in a similar manner, using 2 to 3 c.c. the first time, and 1 to 2 c.c. the second. It is not advisable to have, altogether, more than 8 to 10 c.c. of acid in the apparatus, and it is better to operate with less. The volume of nitric oxide must in no case exceed 50 c.c., and the vacant space in the tube a below the graduation must be great enough to prevent any acid entering the rubber tube, even when 50 c.c. of nitric oxide are evolved. In any case, for the reaction to be successful, an excess of strong sulphuric acid must be present, and, when the acid being analyzed is rich in nitrogen acids, quite a large quantity, about 5 c.c., of concentrated sulphuric acid must be used for rinsing, as otherwise the . unavoidable, but usually harmless, separation of mercurous sulphate soils the measuring-tube too much. Now remove the tube a from the spring clamp, and shake it thoroughly. The evolution of gas begins at once, the acid acquiring a violet color. (In the case of sulphuric acid containing nitric acid instead of nitrous acid as in the case of nitrose, the evolution of gas begins only after shaking a few times.) The evolution is facilitated by inclining the tube several times to a nearly horizontal position, and then quickly raising it to a vertical position so that the mercury falls through the acid. As soon as some gas has collected, the shaking becomes easy. In from one to two minutes 714 DETERMINATION OF COMMERCIAL VALUES. [ 271. (five minutes are seldom necessary) the reaction is complete. When the acid has become clear and cool, and the froth has disappeared, which as a rule does not take long, raise the tube b so that the level of mercury in it will be so much higher than in a as will correspond with the sulphuric acid (1 mm. height of mercury is equivalent to 7 mm. of sulphuric acid), read off the volume of nitric oxide, reduce it to and 760 mm. pressure, and from this ascertain the content of nitrous acid (or, in the case of liquids containing nitric acid, the latter), calculating 1-699 mgrm. N 2 O 3 (or 2-413 mgrm. N 2 O 5 ) for each c.c. of nitric oxide at and 760 mm.* When the reading off is finished, check the accuracy of the compensation of the acid layer by the column of mercury, by opening the stop-cock. If the level of the acid rises, the pressure has been too great, and hence a larger volume of gas should have been read off; if the level falls, the pressure was too low, and the volume read off consequently too large. If, for exam- ple, 15-3 c.c. have been read off, and the acid rises to 15-2 c.c. when the stop-cock is opened, it follows that the correct volume is 15-3 + 0-1 = 15-4. Now raise the tube b so as to drive into the funnel first the nitric oxide, and then the acid rendered turbid by the mercurous oxide. When the mercury just enters the funnel, close the stop-cock, allow the acid to run off through the side-open- ing in the stopper into a vessel placed to receive it, remove the last traces with blotting paper, and turn the cock so as to shut off the funnel both from a and the side opening; the apparatus is now ready for a fresh analysis. The accuracy of the result is not affected by any arsenous acid, organic acid, etc., present in the acid to be analyzed. If notable quantities of sulphurous acid are present, add to the acid in the funnel of the nitrometer a little powdered | potassium permanganate. * LUNGE has calculated special tables for use with the nitrometer, both for reducing the gas volume to normal temperature and pressure, as also for calculating the nitric oxide so reduced, into oxygen compounds of nitro- gen. See DINGLER'S Polyt. Journ., ccxxxi, 522, and LUNGE'S Handb. der Sodaindustrie, n, 922-932. 271.] NITROGEN COMPOUNDS. 715 B. CHAMBER ACID, ETC. Under this heading are discussed the products containing nitrous and nitric acids resulting from the manufacture of sulphuric acid, as is the case, for example, with chamber acid. Liquids containing nitrogen tetroxide, N 2 4 , may also be regarded as if consisting of 1 eq. of nitrous anhydride and 1 eq. of nitric anhydride (N 2 O 3 + N 2 5 = 2NA). The determination of the nitrogen acids in nitrous acid in sul- phuric acid containing nitrous and nitric acids, always requires two separate analyses, one for determining the nitrous-acid content, the other for determining the sum of both acids, expressed either as nitrous acid or as nitric acid. 1. Determination of the Nitrous Acid. The method employed is simply that described in 271, A, 1. If the acid contains other substances which reduce potassium per- manganate (e.g., arsenous acid, sulphurous acid, etc.), the deter- mination will of course be exact only when these are separately determined and the corresponding corrections made. This cir- cumstance must be considered, of course, not only when determin- ing nitrous acid with permanganate, but also to an equal extent in all methods based upon the conversion of nitrous acid into nitric acid (chromic-acid method, chlorinated-lime method).* 2. Determination of the Nitrous and Nitric Acids. This is most simply accomplished according to the method detailed in 271, A, 2, using the LUNGE nitrometer. It may also be effected in nearly all the ways recommended in 149, and par- ticularly according to 149, d, a, or /? (Vol. I, pp. 575 and 577), or 149, e (Vol. I, p. 584). In using PELOUZE'S method, 149, d, a, LUNGE f employs ferrous sulphate instead of the ferrous chloride, and in the following manner: An iron solution is used containing 100 grm. of pure ferrous sulphate and 50 grm. of pure, concentrated sulphuric acid per * See LUNGE, Handbuch der Soda-industrie, i, 58 and 59. t Ibid., FR. VIEWEG und SOHN, i, pp. 49-51. 716 DETERMINATION OF COMMERCIAL VALUES. [ 271. litre; and for titrating, a solution of potassium permanganate containing 15-811 grin, per litre, the strength of which is to be checked as in Vol.- 1, p. 313, a, a. The first step is to ascertain how much of the permanganate solution is required to oxidize 25 c.c. of the ferrous-sulphate solution. Then intro- duce 25 c.c. of the latter solution into a flask (Fig. 130) provided with a glass tube and a BUN SEN rubber valve,* and add the solution obtained from the de- termination of the nitrous acid in 271, B, 1 (and now containing all the nitrogen combined with oxygen in the form of nitric acid), together with FIG. 130. a f ur ther and not too small quantity of pure sulphuric acid; now add 1 to 2 grm. sodium bicar- bonate in order to drive out the air by the carbon dioxide evolved. After quickly inserting the stopper carrying the rubber valve, heat to boiling, which continue for some time (often for an hour), until all the nitric oxide has been expelled, and the liquid has in consequence become lighter in color. Now cool, dilute, and titrate again with the permanganate solution. From the difference between the quantity used up now and that required in the previous titration, calculate the quantity of nitric acid (1 c.c. of the permanganate of the above strength corresponds to 0.009 grm. N 2 O 5 ). So far as the calculation is concerned, the following must be considered: If both the nitrogen acids have been determined as nitric acid, as in LUNGE'S modification of PELOUZE'S method, just described, or in any of the other methods in which the nitrogen of the nitrogen acids is converted into ammonia or nitric oxide, * This may be simply made from a piece of thick rubber tubing closed at the top by a small piece of glass rod, and with a long slit in the side. The cut is made by bending the tube over the index finger of the left hand, and making an incision 10 to 15 mm. long with a sharp razor moistened with water. See also KRONIG (Zeitschr. /. analyt. Chem., iv, 95). 272.] . CARBON COMPOUNDS. 717 from which in turn the nitric acid is calculated, then the quantity of nitrous acid found as in 1 is increased in the proportion of 76-08: 108:08 (or 9-51: 13-51), i.e., it is calculated into nitric acid; the weight of this deducted from the total nitric acid found gives, as a difference, the nitric acid originally present as such ; if, however, one of the methods has been employed based upon the oxidation of iron with a separate sample of the unaltered acid, then the cal- culation is most simply made by considering the oxidation as if effected by nitrous acid, i.e., for every 111-8 parts of iron (2 at.) converted from ferrous into ferric iron, calculate 76-08 parts of N 2 O 3 (1 mol.), and deduct from the nitrous acid so found the quantity found in 1 ; and, in order to ascertain the content of nitric acid, reduce the difference in the proportion of 228 24 : 108 08, i.e., in the proportion of 3 eq. of N 2 O 3 to 1 eq. of N 2 O 5 , since 3 eq. of N 2 3 yield as much oxidizing oxygen as 1 eq. of N 2 O 5 . 27. CARBON COMPOUNDS. 272. Under this heading the analysis of graphite, coal, and coke is detailed. A. GRAPHITE. Natural graphite, which is used for many purposes, particu- larly for the manufacture of graphite crucibles and pencils, is found in very different grades of purity, and is hence not infre- quently the subject of chemical analysis. This alone does. not, however, give the value of the various sorts of graphites, as the carbon present is, according to its degree of fineness, more or less adapted for the manufacture of lead pencils, and also exhibits very great differences in degree of combustibility, which is of im- portance in the manufacture of crucibles. It is hence necessary to supplement the chemical analysis by a practical examination based upon the purposes for which the graphite is to be used. I. METHOD FOR COMPLETE AND ACCURATE ANALYSES. 1. To determine the moisture dry a sample at about 150. If the drying is effected in a bulb-tube (Vol. I, p. 64), the same 718 DETERMINATION OF COMMERCIAL VALUES. [ 272. portion of substance can also be used for determining the water chemically combined (and partly present in the clay). For this purpose heat the contents of the bulb-tube in a current of dry air to low redness, and collect the water in a calcium-chloride tube (Vol. I, p. 76). 2. The carbon in the graphite may be most surely (as the method may be used for all kinds of graphite) oxidized to carbon dioxide by means of chromic acid and sulphuric acid, and the CO 2 col- lected in weighed soda-lime tubes. The operation is carried out in one of the forms of apparatus shown on pp. 510 to 514 this volume, and by the method given on p. 513, i.e., using a sulphuric acid obtained by mixing 2 parts by weight concentrated sulphuric acid and 1 part by weight of water, and an excess of chromic acid (about 5 to 10 grm. chromic acid to about 0-25 grm. to 0-5 grm. graphite). In many kinds of graphite the carbon may also be determined by heating in a current of oxygen, as in the ordinary combustion (p. 39 et seq., this volume). Before this method can be adopted with safety, however, a preliminary test must be made in order to make certain whether the carbon in the graphite in question will be completely consumed under the conditions prevailing in ordinary combustion. If the graphite contains carbonates, e.g., calcium carbonate, the carbonic acid must be determined and deducted from the total obtained by the oxidation with chromic and sul- phuric acids, or by combustion, before calculating the carbon of the graphite from the carbon dioxide obtained. 3. The total mineral constituents of a graphite is indirectly found by deducting from 100 the carbon, moisture, and chemically combined water, expressed in per cents. If a direct determination is required, it suffices, for many kinds of graphite, to place a small quantity (about 0-5 grm.) of the finely powdered substance in a platinum crucible, and expose it, with free access of air, to the long-continued and strong heat of a BUNSEN or MASTE gas burner (see Vol. I, p. 116, Fig. 77). F. STOLBA* recommends a platinum * DINGLER'S polyt. Journ., cxcvni, 213; Zeitschr. /. analyt. Chem., x, 369. 272.] CARBON COMPOUNDS. 719 crucible provided with a projecting perforated lid, the round hole in which is 5 mm. in diameter. The crucible is fixed in an inclined position, and the cover is so placed on that about one-quarter of the opening is left uncovered. The combustion of the carbon is facilitated by exposing a fresh surface of the graphite by turning the crucible round occasionally, or stirring the contents with a platinum wire. As the operation requires from 3 to 4 hours for its completion, and as the weight of the platinum crucible may be affected by so prolonged a heating, the crucible must be weighed again. If a muffle is available, the combustion of the carbon may also be accomplished in a platinum dish placed in the muffle heated to redness. This method, which permits of the incineration of large quantities of graphite, is particularly to be recommended when the ash is to be further analyzed. If the graphite contains calcium carbonate, the carbonic acid is naturally expelled during the ignition; in order to replace it, the ash must be repeatedly moistened with a concentrated solu- tion of ammonium carbonate, dried, and gently ignited. A com- plete agreement between the quantity of the mineral constituents directly determined and that directly found can not always be expected even after the treatment with ammonium carbonate, e.g., when the graphite contains iron sulphide or ferric hydroxide. J. STIXGL* has called attention to this circumstance, and has given examples. STOLE A (loc. cit.) failed to obtain favorable results in his attempts to burn graphite in a current of oxygen, because some of the min- eral constituents were carried off by the current of gas, and during the fusion there were also formed small globules which enveloped particles of graphite. As a check to make certain that the graphite ash no longer contains carbon, a weighed portion of the finely powdered ash may be mixed with pure mercuric oxide and ignited under a good draught hood, and again weighed; carbon-free ash should suffer no loss of weight. The most certain test, however, that the ash is free from carbon, consists in treating a sample of the * Berichte der deutsch. chem. Gesellsch. zu Berlin, vi, 391 ; Zeitschr. /. analyt. Chem., xiv, 397. 720 DETERMINATION OF COMMERCIAL VALUES. [ 272. ash with chromic and sulphuric acids according to 2, and observing whether carbon dioxide is obtained or not. 4. To determine the individual mineral constituents, so far as the silicic acid, aluminium, iron, etc., are concerned, the ash obtained in 3 may be employed, and treated according to the method de- tailed for silica (Vol. I, p. 511, b), or the graphite itself may be decomposed by some method. WITTSTEIN * recommends for this purpose the following method: Mix about 1 grm. of the finely powdered graphite with about 3 grm. sodium-potassium carbonate in a platinum crucible, place upon the surface of the mixture about 1 grm. potassium hydroxide, and slowly heat to redness. From time to time break the crust formed during the fusion with a stout platinum wire. After half an hour's fusion, allow to cool, macerate the mass with water, heat for fifteen minutes to boiling, filter, and wash the residue. Treat the contents of the filter together with the filter ash with hydrochloric acid of sp. gr. 1 12, and after digest- ing for half an hour, add water, filter off from the insoluble residue of carbon, unite the hydrochloric-acid solution so obtained with the alkaline liquid first obtained, and add hydrochloric acid in excess; then evaporate to dryness on a water-bath, separate the silicic acid, and in the hydrochloric-acid filtrate determine the bases (Vol. I, pp. 509 and 510). In order to make certain that the carbon filtered off contains no mineral constituents, it is burnt. It is of no use to weigh this carbon, as it does not represent the entire quantity of carbon present, but only about four-fifths. 5. If the graphite contains carbonates, determine the carbonic acid in a separate, somewhat larger, sample, according to Vol. I, p. 493. 6. If metallic sulphides (iron or copper pyrites) are present, determine the sulphur in a sample according to pp. 561, 1, or 562, 2, this volume. It must not be considered strange if, when using the first method, the carbon of the graphite remains partly or wholly unoxidized, since many kinds of graphite are not at- tacked by fused potassium nitrate (RAMMELSBERG f) . * DINGLER'S polyt. Journ., ccxvi, 45; Zeitschr. /. analyt. Chem., xiv, 395. t His Handbuch der Miner 'alchemic, 2 ed., Leipzig, W. ENGELMANN, n, 2. 272.] CARBON COMPOUNDS. 721 II. METHODS OF DETERMINING THE CARBON ONLY. Of the methods proposed for the rapid determination of carbon in graphite, that of GINTL * alone will be here described. In this process there is required a stout tube of refractory glass, 10 to 12 cm. long, about 1 cm. wide, and sealed at one end, and which may be advantageously blown out to a moderately sized bulb. Into this introduce 0-05 to 0-1 grm. of the graphite dried at 150 to 180, add 1 5 to 3 grm. of pure, powdered lead oxide, previously ignited, weigh, and carefully mix the lead oxide with the graphite by means of a mixing-wire; then heat that part of the tube containing the mixture, at first over a BUNSEN burner, and finally with a blowpipe- lamp until the contents are completely fused and froth is no longer visible. According to GINTL the operation is complete in ten min- utes. Allow to cool, weigh, and from the loss in weight (the carbon dioxide expelled) calculate the carbon. Of course the results ob- tained by this method are serviceable only when the graphite con- tains neither water chemically combined or capable of expulsion at 150 to 180, nor carbonates, and when all the carbon is oxidized by fusion with the lead oxide. GINTL' s method is a modification of that devised by SCHWARZ,! in which the lead which separates on fusing graphite with an excess of litharge is weighed (also of BERTHIER'S method of determining the calorific value of combustibles applied to graphite). GINTL (loc. cit., p. 423) did not obtain satisfactory results with this method. Regarding the pyrometric determination of pure graphite, as well as of that containing clay and silicic acid, consult BISCHOF'S}: paper. B. COAL AND COKE. Coal, being one of the most important industrial factors, is fre- quently the subject of chemical analysis, both in its unchanged * Zeitschr. /. analyt. Chem., vn, 425. f Breslauer Gewerbeblatt, 1863, No. 18; Zeitschr. /. analyt. Chem., in, 215. J DINGLER'S polyt. Journ., cciv, 139. 722 DETERMINATION OF COMMERCIAL VALUES. [ 272. state and as coke, as it varies greatly in character, and its value and applicability for various uses cannot be sufficiently determined by its external characteristics. If, however, such an examination is to be of any value, it is absolutely necessary to obtain samples which will truly represent the average composition of the coal or coke. This requires that a relatively large quantity must be coarsely ground and uniformly mixed. By further comminuting a portion of this mixture, samples consisting of fragments about the size of a bean (or for coke, of a hazel nut) are obtained, and these are to be preserved in glass-stoppered bottles. 1. DETERMINATION OF WATER. Coal, when heated to a high temperature, first yields water, and later other volatile constituents; many kinds are also prone to absorb oxygen at higher temperatures. As, however, dried coal is besides prone to abstract moisture from the atmosphere, an accurate determination of the water content is not at all easy. As a rule it is considered sufficient to determine the water from the loss in drying, although BRITTON * has pointed out that the results afforded by this method are doubtful, not only because of the reasons above mentioned, but also because the water present in the coal is more or less combined and firmly retained. To determine the water in coal from the loss in weight, the tin boxes described on p. 633, Fig. 126, this volume, are adapted, a few of these being half-filled with the coal reduced to the size of a bean. The boxes are then weighed together and dried at 100 in the water-bath as described on p. 633 this volume, and weighed hourly until they cease to lose weight. 100 is the temperature recommended as most suitable by MucK,t whereas LUNGE J recommends 105 and HINRICHS 115. * Engineering and Mining Journal, xxn, No. 7; Zeitschr. f. analyt. Chem., xvi, 501. f POST'S Chem.-Techn. Analyse, Brunswick, FR. VIEWEG u. SOHN, 1881 , p. 16. J His Taschenbuch fur die Soda-, etc.; -Fabrikation, Berlin, J. SPRINGER, p. 82. Zeitschr. f. analyt. Chem., vin, 133. 272.J CARBON COMPOUNDS. 723 To directly determine the water in coal, a current of dry air must be passed over the coal heated in a glass tube in an air-bath, and then passed through a weighed calcium-chloride tube; the water-content is then ascertained from the increase in weight of the latter. In this method the temperature may be raised con- siderably above 100, but it should never be allowed to reach a point at which other permanently gaseous decomposition products are evolved. The water-content of coke may with certainty be determined from the loss in weight on drying. MUCK (loc. tit.) recommends drying at a temperature which may approach 200, while LUNGE, (loc. cit.) advises 110. In the case of coke there is of course no danger of volatile decomposition products being formed and passing off with the water during drying. 2. DETERMINATION OF THE ASH. The determination of the mineral constituents of coal and coke is an operation which is very frequently performed. Before des- cribing the best methods of incineration, attention must be called to the fact that the yield of ash in one and the same powdered coal may vary greatly, since the mineral constituents present may be left in varying states of combination according to the tem- perature, duration of the heating, and admission of air. This may be especially the case with coal rich in sulphur, in which the calcium carbonate is converted into calcium sulphate, the iron sulphide more or less completely into ferric oxide, etc. According to MUCK,* however, the differences arising from this cause do not exceed 0-1 to 0-2 per cent. When incinerating, the caking of the coal must above all be prevented, as the caking renders complete combustion of the carbon much more difficult. When the incineration is effected over the gas lamp, therefore, place from 1 grm. to 3 grm. of the very finely powdered coal dried at 100 in a covered platinum crucible, or in a covered platinum dish, and subject it at first to a gentle heat for a long time, whereby not only decrepitation, with * Zeitschr. f. analyt. Chem., xix, 137. 724 DETEKMINATION OF COMMERCIAL VALUES. [ 272. its possible attendant slight loss, but also the subsequent caking of the coal, are avoided; then heat to low redness with access of air for a prolonged period, until all the carbon appears to be con- sumed. In order to shorten this otherwise tedious operation, LUNGE * recommends placing the platinum crucible in the round opening of an inclined clay tile or asbestos disk, and to heat that part of the crucible projecting below. The air required for oxida- tion does not then mix with the gases from the flame, and hence acts more energetically. Now add to the apparently pure ash a little alcohol, when the unconsumed particles of carbon will be readily recognized by their color as well as by their buoyancy in the liquid (MucK, loc. cit., p. 133). After burning off the alcohol, ignite again, and until the object is fully attained, and finally check the weight of the platinum vessel. If a muffle is at hand, a number of samples may be incinerated at the same time. They are placed in the cold muffle in shallow platinum or porcelain dishes, but most conveniently in square platinum trays, and then slowly warmed, gradually raising the temperature to and maintaining it at redness. Coke requires a much higher heat for the complete combustion of its carbon. For its incineration, therefore, it is best to use the muffle; the object may, however, also be attained by heating the sample in a boat in a current of oxygen. 3. DETERMINATION OF THE SULPHUR. Coal may contain sulphur in three different forms of com- bination; namely, as metallic sulphides, as sulphates, and in the organic matter of the coal. The method of determining sulphur must hence be differentiated into such as give the total sulphur present, and such as give the sulphur present only in certain forms of combination. a. Determination of the Total Sulphur. For this purpose ESCHKA'S method, described on p. 115 this volume, is especially well adapted. MucKf recommends to ignite with magnesia and * His Taschenbuch fur Soda-, etc., Fabrikation, p. 83. t POST'S Chem.-Techn. Analyse, Brunswick, FR. VIEWEG u. SOHN, 1881, p. 21. 272.] CARBON COMPOUNDS. 725 sodium carbonate, then to treat the mass with hot water, and to add bromine water until the liquid has a faint yellowish color. Then boil, decant through a niter, wash with hot water, acidulate the filtrate with hydrochloric acid, boil until the liquid is decolor- ized, and finally precipitate the sulphuric acid (and corresponding to the total sulphur in the coal) with barium chloride. If the reagents employed are not quite free from sulphuric acid, their acid-content must be ascertained and deducted from the result. 6. Determination of the Sulphur Combined with Metals and that Contained in Organic Combination. These quantities of sulphur may be determined either indirectly, by deducting that found as sulphates in c from the total sulphur found in a; or directly , according to one of the methods described on p. 100, 5, this volume. According to TSCHIRIKOW,* it is advisable, when employing SAUER'S method, to insert plugs of platinum gauze both hi the fore part of the combustion tube, as well as behind the platinum boat, particularly when determining sulphur in coal rich in volatile substances. This ensures complete combustion, and hence pre- vents the passing over of organic decomposition products into the receiver. c. Determination of the Sulphur Present as Sulphates (and Particularly as Gypsum). For this purpose the GRACE CALVERT method is employed (see p. 116 this volume). d. Determination of the Total Sulphur Present as Sulphides and Sulphates. In order to effect this determination, and to thus obtain also the organically combined sulphur by difference, the following method may, according to TH. M. DROWN,! be employed (but of which I have had no personal knowledge): There is required for it a saturated solution of bromine in soda lye of 1-25 sp. gr., and to which sodium hydroxide is then added until it no longer gives off free bromine. Moisten about 1 grm. of the very finely powdered coal with about 10 c.c. of this liquid, heat, and add hydrochloric acid just to acidity. At intervals of ten * Pharm. Zeit. fur Russland, xix, 333; Zeitschr. /. analyt. Ghent., xx, 304. f Ghent. News, XLIII, 89; Zeitschr. f. analyt. Chem., xxi, 440. 726 DETERMINATION OF COMMERCIAL VALUES. [ 272. minutes, and while the liquid is kept hot, add two portions of 20 c.c. each of the bromine solution, acidulating after each addi- tion. Now evaporate to dryness, heat to from 110 to 115 to separate the silicic acid, heat with hydrochloric acid, dilute, and precipitate the sulphuric acid with barium chloride. By this mode of treatment the organically combined sulphur is not attacked. I would point out, however, that should the barium sulphate have a reddish tint, i.e., contain iron, it must be purified accord- ing to Vol. I, p. 435, by fusing with sodium carbonate, etc. 4. DETERMINATION OF THE PHOSPHORUS. This is best effected in the ash. Hence incinerate a suitable quantity of coal, digest the ash for a considerable time with strong hydrochloric acid on the water-bath, and evaporate to dry- ness; then add first hydrochloric acid, then some water, warm, filter, evaporate with repeated additions of nitric acid almost to dryness, take up with water with a little nitric acid added, pre- cipitate with molybdenum solution, and determine the phosphorus according to 134, 6, /?. 5. DETERMINATION OF THE NITROGEN. This is effected according to one of the methods detailed on pp. 82 to 94 this volume, using coal dried at 100. 6. DETERMINATION OF THE CARBON, HYDROGEN, AND OXYGEN. For this purpose the coal dried at 100 may be burned with lead chromate (p. 95 this volume) or in boats, using a current of oxygen (p. 39 this volume). If the latter method is adopted, introduce into the fore part of the combustion tube a 10-cm. layer of lead chromate (or, according to MUCK, of pea-sized pieces of pumice- stone which have been thoroughly mixed with powdered lead chromate, and which are of course perfectly free from water), so that the combustion products first pass .over the glowing granu- lated cupric oxide, then over the lead chromate, which is to be maintained at a low red heat. This suffices as a rule to retain all the sulphurous acid ; otherwise, in the case of coal very rich in sul- 722.] CARBON COMPOUNDS. 727 phur, a lead-dioxide tube would also have to be used (p. 95 this volume). Before the carbon and hydrogen can be calculated from the carbon dioxide and water obtained by the ultimate analysis, it must be ascertained whether the coal or coke contains any car- bonates, and whether the coal dried at 100 contains any water. In such a case the quantities of carbon dioxide and water found in the sample on combustion (and which must be determined in sepa- rate portions) must be deducted from those obtained in the ultimate analysis. The oxygen is obtained by difference; as the values for ash, sul- phur, nitrogen, hydrogen, and carbon, as well as the possible con- tent of water, in the coal dried at 100, have an influence on this, it may be readily seen that the determination of the oxygen by differ- ence cannot be exact. Regarding the direct determination of the oxygen, compare 192. 7. DETERMINATION OF THE YIELD OP COKE. By this is understood the determination of the non-gasifiable residue left on heating the coal in a loosely covered crucible until the evolution of combustible gases ceases. Experience shows that the results obtained by this means may vary considerably, according as the operation is conducted with larger or smaller quantities of coal, the kind of crucible employed, and the mode of heating. MUCK,* who has thoroughly studied this question, gives the following rules, which must be followed in order to obtain constant results: Never use more than 1 grm. of coal, and if the coal cakes strongly, take even less; select a platinum crucible with a closely fitting lid of large surface, and which, for coal which swells up greatly, must be over 3 cm. in height; place this crucible on a plati- num triangle, so that the bottom is 3 cm. from the top of the tube of a BUNSEN burner fitted with a chimney, and heat it with a flame not less than 18 cm. high, until any flame issuing from between the crucible and lid-edge has almost completely disappeared. By * Chemische Beitrage zur Kentnisse der Steinkohlen, Bonn, MAX COHEN u. SOHN, 1876, p. 14. 728 DETERMINATION OF COMMERCIAL VALUES. [ 273. observing these rules the variations in the yield of coke are gener- ally far below 1 per cent. Stronger heating over the blowpipe lowers the yield of coke but very slightly. In order to obtain comparative results, the yield of coke must be calculated to coal free from ash. Regarding the influence of mineral constituents on the extent of the yield of coke, see MUCK, loc. tit., p. 15. I have omitted the method of gravimetric analysis of gases con- taining carbon dioxide and hydrocarbons, devised by me, and which it had been my intention to insert in this place (see Vol. I, p. 480) in view of the appearance of CL. WINKLER'S excellent treatise . "Anleitung zur chemischen Untersuchung der Industriegase," in which a full description of the method is given ; see the second part of the aboVe-named work, p. 192. 28. HYDROGEN COMPOUNDS. 273. HYDROGEN DIOXIDE. As hydrogen dioxide has of late come into use as a bleaching; agent, and is also used in surgery and medicine, and consequently is manufactured on a large scale, its aqueous solutions, which are found in the market in varying strengths, are frequently the subject of chemical analysis. Before proceeding to describe the methods of determination, it must be stated that solutions of hydro- gen dioxide are not as unstable as was formerly believed, but if kept in a dark place and at a temperature below 30, they lose but a very small porportion of their hydrogen-dioxide content.* Of all the methods of determining hydrogen dioxide in liquids containing no organic matter, the simplest and most accurate has been found to be that based upon the decomposition of the dioxide by potassium permanganate in acid solution. The reaction takes * See P. EBELL, "Das Wasserstoff-hyperoxid und seine Verwendung in der Technik, Chirugie und Medicin," a paper read before the Hanover Section of the Societ}' of German Engineers, Dec. 9, 1881; Zeitschr. des Vereins deutsch. Ingenieure, xxvi. 273.] HYDROGEN COMPOUNDS. 729 place according to the following equation: 2KMn0 4 +5H 2 O 2 + 3H 2 SO 4 =K 2 S0 4 +2MnSO 4 +8H 2 O+10 0; it was first observed by BRODIE, and used by SCHONBEIN for the approximate, and by ASCHOFF for the accurate, determination of hydrogen dioxide. Among many other chemists, E. SCHONE * in particular deserves credit for critically testing this method, as well as all others pro- posed for the determination of hydrogen dioxide. This method requires a solution of potassium permanganate the strength of which must be proportional to that of the hydro- gen-dioxide solution. For testing the ordinary commercial solu- tions, one containing about 3 grm. of potassium permanganate per litre is suitable. The effective value of the permanganate solution is ascertained by means of metallic iron (Vol. I, p. 313). In the cal- culation it must be noted that 100 c.c. of a permanganate solution capable of converting 559 grm. of iron from a ferrous to a ferric state corresponds to 0-18016 grm. H 2 O 2 . The operation is very simple. By means of a pipette introduce a suitable quantity of the hydrogen-dioxide solution (about 2 to 10 c.c.) into a beaker containing about 300 c.c. of water stongly acidulated with sulphuric acid, and then, while stirring, run in the permanganate solution until the liquid acquires a just permanent reddish tint. Occasionally, according to SCHONE,! and partic- ularly if the solution has been exposed to sunlight, the first por- tions of permanganate added are not immediately decolorized (this is also observed when titrating with oxalic acid, Vol. I, p. 316) ; when the reaction has once begun, however, the fresh additions of permanganate are decolorized immediately. BRODIE, who was the first to make this observation, J believed this to be due to the dilution of the solution, but SCHONE observed it also in relatively strong solutions. The method of determination with permanganate is adapted, not only for concentrated, but also for very dilute solutions of hydro- gen dioxide; and SCHONE obtained good results with solutions containing but a few grammes per litre (loc. tit., p. 142). * Zeitschr. f. analyt. Chem., xvin, 133. t Ibid., xvin, 140. J POGGEND. AnnaL, cxx, 318. 730 DETERMINATION OF COMMERCIAL VALUES. [ 273. Besides this method, there are others that may be employed; e.g., the hydrogen-dioxide solution may be brought into con- tact with potassium iodide in an acid solution, and the liberated iodine determined with sodium thiosulphate; or it may be decom- posed by platinum-black, and the oxygen evolved measured (in SCHEIBLER'S apparatus, Fig. 101, Vol. I, p. 501); these methods, however, are neither simpler nor more accurate than titration with permanganate. If, however, the hydrogen dioxide is to be determined in liquids containing organic matter, then the platinum-black deserves the preference. Regarding this method, it may be remarked that according to EBELL'S investigations (see foot-note, p. 728) platinum- black that has not been ignited decomposes hydrogen dioxide very rapidly, whereas when ignited, its action is slower, but otherwise equally as complete. If the hydrogen dioxide is to be determined in atmospheric deposits, in which it occurs in exceedingly minute quantities, the methods above described are inapplicable. SCHONE,* who has occupied himself with the solution of this problem, makes use of a colorimetric method based upon the separation of iodine from neutral potassium iodide by hydrogen dioxide, without the addition of ferrous sulphate or any other similar excitant. Re- garding the details I refer to the original treatise. SUPPLEMENT TO SECTION II. I. DETERMINATION OF GRAPE-SUGAR (DEXTROSE), FRUIT-SUGAR (LEVULOSE), INVERT-SUGAR, MALTOSE, MILK-SUGAR, CANE- SUGAR (SACCHAROSE), STARCH, AND DEXTRIN. As the determination of these substances is frequently required in the analysis of agricultural and technical products, and also pharmaceutical preparations; and as it is also of some importance in the examination of diabetic urine, a few of the best methods for the purpose are here given. * Berichte der deutsch. chem. Gesellsch., vn, 1693; Zeitschr. f. analyt. Chem., xiv, 90, and 91 and above all xvin, 154. 273.] DETERMINATION OF GRAPE-SUGAR, ETC. 731 Apart from the purely physical processes, which are based either upon the specific gravity of the saccharine solutions,* or upon their behavior toward polarized light,f the following methods serve for the determination of the various kinds of sugars : A. Methods based upon the reduction of cupric oxide to cuprous oxide. B. Methods based upon the reduction of mercury compounds. C. Methods based upon the decomposition of sugar by alcoholic fermentation. These methods are detailed in the f olio wing sections : * For the determination of cane-sugar from the specific gravity of the solution, the BALLING or BALLING-BRIX tables are most generally used. These tables are found in many works, e.g., in the Handworterbuch der reinen und angewandten Chemie, by LIEBIG, POGGENDORFF, and WOHLER (Brunswick, FR. VIEWEG und SOHN, 1859, vii, 4) ; OTTO'S Lehrbuch der rationetten Praxis der landwirthschaftlichen Gewerbe, 5th ed., 1860-1862, i, 233; STAMMER'S Lehrbuch der Zuckerfabrikation, 1874, 38; MUSPRATT'S Chemie, 3d ed., by KERL und STOHMANN (Brunswick, SCHWETSCHKE und SOHN, 1874, i, 194, and vii, 694) ; BOLLEY'S Handbuch der techn. chem. Untersuchungen, 4th ed., by E. KOPP (Leipzig, FELIX, 1874, p. 679) ; FRUHLING and SCHULZ, Anleitung zur Untersuchung der fur die Zuckerindustrie in Betracht kommenden Rohma- terialien, etc. (Brunswick, FR. VIEWEG und SOHN, 1876, p. 16); POST'S chem. techn. Analyse, 1881, p. 694. The BALLING-BRIX tables, although compiled only for cane-sugar, are also frequently employed for grape-sugar, because the difference in density between sugar solutions and grape-sugar solutions of equal strength is but slight see GRAHAM, HOFMANN and RED- WOOD, Jahresber. der Chem., 1852, 803; POHL, Ber. der Wien. Akad., 1854, xi, 664; HOPPE-SEYLER, Zeitschr. f. analyt. Chem., xiv, 305. A compara- tive table, by which the difference in densities may be seen, may also be found in BOLLEY'S Handbuch (see above), p. 681. A special table for the determination of grape-sugar from the specific gravity of its aqueous solutions was prepared by SALOMON (Ber. d. deutsch. chem. Gesellsch., xiv, 2711), and a corresponding one for invert-sugar by CHANCEL (LIPPMANN, Die Zuckerarten, etc.. Brunswick, FR. VIEWEG und SOHN 1882, p. 73). f The determination of sugar by the polariscope will also be found de- scribed in the above-named works, but the most complete description is given in LANDOLT'S work, Das optische Drehungsvermogen organischer Sub- -stanzen, etc., Brunswick, FR. VIEWEG und SOHN, 1879. 732 DETERMINATION OF COMMERCIAL VALUES. [274. A. METHODS BASED UPON THE REDUCTION OF CUPRIC OXIDE. 274. I. GENERAL PRINCIPLES. The fact that a solution of cupric sulphate to which potassium- or sodium tartrate, and caustic potassa or soda have been added (and which, if these are added in proper proportion, remains un- altered when boiled) is decomposed by grape-sugar at the boiling temperature, with separation of cuprous oxide, was first utilized by BARRESWIL* for the determination of sugar. Subsequently the method was thoroughly investigated, particularly by FEHLING,! who also greatly improved upon BARRESWIL' s formula for the prep- aration of the alkaline copper solution,! and established the rule, later on confirmed by NEUBAUER and others, that 1 equivalent of grape-sugar, C 6 H 12 O 6 = 180-096 reduces 5 equivalents of cupric oxide, 5CuO = 398. This important method has in course of time been widely investigated, and variously modified. More recently SOXHLET,|| in particular has subjected the method to a most thorough investigation; and amongst others who have done * Arch, d'anatomie, 1846, p. 50; Journ. de Pharm., vi, 361; BERZELIUS' Jahresber., xxv, 556. f Annal d. Chem. u. Pharm., LXXII, 106, and cvi, 75. JThe original formula for FEHLING'S solution is as follows: Dissolve 40 grm. pure, crystallized copper sulphate free of adhering moisture, in about 600 c.c. water; further, dissolve in a separate vessel 160 grm. neutral potassium tartrate in a little water, add 600 to 700 grm. of a solution of pure caustic lye of sp. gr. 1-12; gradually pour the first solution into the latter, and dilute the deep-blue solution until it measures exactly 1154-4 c.c. at 15. Calculated down to 1000 c.c. and sodium hydroxide, and moreover, substi- tuting for the equivalent of copper sulphate formerly used (124-75) that based upon the atomic weights used in this book (CuSO 4 -5H 2 O=249-75), we obtain the quantities 34-669 grm. cupric sulphate, 138-6 grm. potassium tartrate, and 54-58 to 63-67 sodium hydroxide. Archiv der Pharm. [2], LXXII, 278. II Chem. Centralbl [3], ix, 218, and 236; Journ. f. prakt. Chem., N. S., xxi, 227; Zeitschr. f. analyt. Chem., xvm, 348, and xx, 425. 274.] DETERMINATION OF GRAPE-SUGAR, ETC. 733 important work on this subject are GRATAMA,* ULBRicHT,f MARCKER, BEHREND and MORGEN,J RODEWALD and TOLLENS, ALLIHN,|| DEGENER,^]" and MEISSL.** As the fruit of all these exhaustive investigations the laws laid down by SOXHLET are here given : 1. The assumption that 1 equivalent of grape-sugar (180-096) reduces 5 equivalents of cupric oxide and that therefore 10 c.c. of the FEHLING'S solution correspond with 0-05 grm. of anhydrous grape-sugar, is only correct, or more accurately, nearly correct at the degree of dilution prescribed by FEHLING (10 c.c. copper solution + 40 c.c. water), and when a 0-5- to 1-per cent, solution of sugar is used. SOXHLET found that when using a 1-per cent, sugar solution, the proportion is 1 equiv. : 5 055 instead of 1:5. Hence 10 c.c. of FEHLING'S solution under these circumstances do not correspond with 0-05 grm. grape-sugar, but only with 0-0495 grm. 2. On altering the degree of concentration, the reducing action of the solution is also changed; thus SOXHLET found that on em- ploying undiluted FEHLING'S solution and a 1-per cent, grape- sugar solution, the proportion was 1 equiv. : 5 26 equiv. 3. The quantity of the sugar solution acting upon the copper solution also influences the reducing action. Hence, on allowing the sugar solution to run into the boiling copper solution, the first portions, coming into contact with a large excess of copper, will reduce more than the succeeding portions. The proportion in which the reduction takes place is hence, under these circum- stances, not constant but gradually diminishes. 4. Grape-sugar, fruit-sugar, invert-sugar, and maltose, have not * Zeitschr. f. analyt. Chem., xvii, 155. f Chem. Centralbl. [3], ix, 392; Landwirthschaftl. Versuchsstat., xxvii, 81. t Ibid. [3], ix, 584. Zeitschr. f. analyt. Chem., xvni, 605. || Neue Zeitschr. f. Rubenzuckerindustrie, in, 230, and Zeitschrift des Vereins fur Rubenzuckerindustrie, xix, 865; Zeitschr. f. analyt. Chem., xx, 434, and xxii, 448. ^f Zeitschrift des Vereins fur Rubenzuckerindustrie, xvin, 349 ; Zeitschr. f. analyt. Chem., xxn, 444. ** Zeitschr. des Vereins f. Rubenzuckerindustrie, 1879, 1034. 734 DETERMINATION OF COMMERCIAL VALUES. [ 274. identical, but different reducing effects. Thus, using the propor- tions stated in 1, i.e., a FEHLING'S solution diluted with four vol- umes of water and a 1-per cent, sugar solution, 10 c.c. FEHLING'S solution = 0-0495 grm. grape-sugar, C 6 H 12 6 . " " " " =0-0515 " invert-sugar, C 6 H 12 6 . " " " " =0-0740 " maltose, C 12 H 22 O n . That the reducing action of milk-sugar differs considerably from that of grape-sugar was already known long ago, but opinions dif- fered as to the extent of the difference. SOXHLET found that 10 c.c. of FEHLING'S solution corresponded with 0-0676 grm. of milk- sugar, C 12 H 22 11 -H 2 0, and further, that with milk-sugar the dilu- tion of the copper and sugar solutions had no effect, or only an inappreciable one, on the results. 5. On allowing 1-per cent, solutions of the different sugar solu- tions to act on undiluted FEHLING'S solution, the following results were obtained by SOXHLET: 50 c.c. FEHLING'S solution= 0-2375 grm. grape-sugar, C 6 H 12 O 6 . " " " " =0-2470 " invert-sugar, C 6 H 12 O 6 . " " " " =0-2572 " levulose, C 6 H 13 O 6 . " " " " =0-3890 " maltose, C 12 H 22 O n . 11 " " " =0-3380 " milk-sugar, C 12 H 22 O n H 2 O. 6. The reducing action of the different sugars on FEHLING'S solution at the boiling temperature varies greatly, thus: Grape-sugar required boiling for 2 minutes. Invert-sugar " il il 2 " Levulose " " " 2 " Maltose " " " 3 to 4 " Milk-sugar " " " 6 to 7 " Bearing these newly-ascertained facts in mind, SOXHLET has so modified FEHLING'S method of volumetric analysis, that the results, so far as accuracy is concerned, leave nothing to be desired, while MARCKER in conjunction with BEHREND and MORGEN have shown, SOXHLET recognized, and ALLIHN as well as MEISSL, more accurately demonstrated, that accurate determinations may also be obtained by gravimetric methods. 274.] DETERMINATION OF GRAPE-SUGAR, ETC. 735 II. METHODS OF DETERMINING SUGAR. There will be here described: 1. FEHLING'S volumetric method of determining grape-sugar, in its original or but slightly modified form, as this method is still adapted for the approximate determination of grape-sugar in must, diabetic urine, etc. 2. SOXHLET'S modification of FEHLING'S method, for the more accurate determination of the various sugars. 3. Gravimetric methods of determining sugar. 1. FEHLING'S Method. Instead of the copper solution originally employed by FEHLING, the preparation of which was described in the foot-note on p. 732, and the stability of which leaves much to be desired, it is advan- tageous to employ two solutions: a. An aqueous cupric-sulphate solution containing 34-669 * grm. of pure, crystallized cupric sul- phate per liter; and 6. A solution prepared by dissolving 153 grm. crystallized potassium and sodium tartrate in water in a litre flask, adding 572 grm. of soda lye of sp. gr. 1-12 (containing 60 grm. sodium hydroxide), and filling up to the mark; or, which is as a rule preferable in the case of 6 (which does not remain long unchanged), by dissolving 43-3 grm. potassium and sodium tar- trate in water in a 250-c.c. flask, adding 143 c.c. soda lye of sp. gr. 1 12, or 15 grm. sodium hydroxide, and making up to 250 c.c. It will be seen that similar proportions of mixture and dilution are obtained in both cases, e.g., in i, 10 c.c. of the original FEHLIXG'S solution (see foot-note, p. 732) diluted with 40 c.c. of water, or n, mixing 10 c.c. of the alkaline solution of potassium and sodium tartrate b described, with 10 c.c. of the pure aqueous cupric- sulphate solution a, and diluting with 30 c.c. of water. Either of the two liquids therefore corresponds, under given conditions (see 274, i, 1), almost exactly to 0-05 grm. grape-sugar. * The figure given by the author is 34 639, but recalculated on the basis of the atomic weights used in this book, c is as given in the text. TRANS- LATOR. 736 DETERMINATION OF COMMERCIAL VALUES. [ 274. Now dilute the sugar solution to be tested so that it will contain between 0-5 and 1 per cent, of sugar; this can generally be done by determining the specific gravity. In order to afford the necessary data for this purpose for use in ordinary cases, I give the following abstract from SALOMON'S table: GRAMMES OF ANHYDROUS GRAPE-SUGAR IN 100 C.C. OF AN AQUEOUS SOLUTION AT 17-5. Grammes Grape-sugar. Sp. Gr. Grammes Grape-sugar. Sp. Gr. Grammes Grape-sugar. Sp. Gr. 1 00375 10 1-0381 19 1-0725 2 0075 11 1-0420 20 1-0762 3 0115 12 1-0457 21 1-0800 4 0153 13 1-0495 22 1-0838 5 0192 14 1-0533 23 1-0876 6 1-0230 15 1-0571 24 1-0910 7 1-0267 16 1-0610 25 1-0946 8 1-0305 17 1-0649 26 1-0985 9 1-0342 18 1-0687 Heat to gentle boiling a quantity of the above-mentioned diluted copper solution, i or n, corresponding with 0-05 grm. grape- sugar, in a small flask, and from a burette calibrated in 0-1 c.c. run in the sugar solution slowly and in small portions at a time. After the addition of the first few drops the liquid appears greenish- brown, owing to the cuprous hydroxide and cuprous oxide sus- pended in the blue liquid; in proportion as more sugar solution is added, the more voluminous and redder does the precipitate become, and the more rapidly does it settle. As -soon as the pre- cipitate appears deep-red, remove the source of heat, allow the pre- cipitate to settle somewhat, and place the flask on a sheet of white paper, or hold it up between the eye and the window, in order to observe the liquid by transmitted light; the slightest bluish-green color may thus be easily detected. In order to make absolutely certain, however, pour a small portion of the supernatant clear liquid into a test-tube, add a few drops sugar solution, and heat ; if the slightest trace of undecomposed salt copper is still present, there will form at first a flocculent, yellowish-red precipitate. If this forms, return the contents of the test-tube to the flask, and add more sugar solution until the reduction is complete. The vol- $ 274.] DETERMINATION OF GRAPE-SUGAR, ETC. 737 ume of sugar solution used up will have contained 0-05 grm. grape-sugar. When the experiment is finished, test the liquid to ascertain whether the precise point at which reduction is complete has been struck, i.e., whether the solution contains any copper, sugar > or a brown decomposition product of the latter. For this purpose rapidly filter off a sample of the still hot liquid. If the exact point has been hit, the filtrate must be colorless or only very faint- ly yellowish, and not brownish; and samples of the liquid must remain unchanged when heated either with a drop of the copper solution or with some of the sugar solution; or on acidulating with hydrochloric acid and treating with hydrogen sulphide; or on acidulating with acetic acid and adding potassium ferrocyanide. If it is found that there is a notable excess of copper or of sugar present, the experiment must be repeated. As a rule, the first determination will give only approximately correct results. In the second experiment it is best to add to the cold copper solution all but a little of the entire quantity of sugar solution as ascer- tained in the first test, then to heat, maintain boiling for two minutes, and then to continue, cautiously adding two drops at a time until the operation is complete. The results are quite concordant, and are approximately correct. That the sugar solution was of the proper degree of dilution will be evidenced by the fact that from 5 to 10 c.c. of it will have been required for the determination. Care must be taken that the copper solution is always strongly alkaline. If the sugar solution is acid, it must be rendered feebly alkaline before diluting to the requisite volume. If this method is employed for diabetic urine, it must be remem- bered that on boiling the urine with caustic soda, ammonia is liberated, and that this will retain cuprous oxide in solution. As such a solution turns blue on exposure to air, this must be pre- vented so far as possible, and the hot liquid must hence be allowed to stand, for the determination of its color, only so long as is un- avoidably necessary to see through the liquid free from' cuprous oxide. For the same reason it is inadvisable to filter the liquid 738 DETERMINATION OF COMMERCIAL VALUES. [ 274, when determining sugar in urine ; nor is it of any use to test the nitrate with hydrogen sulphide or potassium ferrocyanide, as copper (dissolved in the ammonia as cuprous oxide) may be, and often is, present in it, even when all the cupric oxide has been reduced by the sugar. 2. SOXHLET' s Modification of FEHLING'S Method. - a. Dissolve 34-669* grm. cupric sulphate f in sufficient water to make 500 c.c. b. Dissolve 173 c.c. grm. of crystallized potassium and sodium tartrate in 400 c.c. water, and add 100 c.c. caustic-soda solution containing 500 grm. sodium hydroxide in the litre. It will be evident that if such a caustic-soda solution is not at hand, the solution may be also more simply prepared by dissolving 173 grm. of the potassium and sodium tartrate in about 400 c.c. of water, adding 50 grm. of sodium hydroxide, and when perfectly cold, filling up to the mark and mixing. J c. Mix 25 c.c. of the copper-sulphate solution a, and 25 c.c. of the alkaline Rochelle-salt solution b, in a deep porcelain dish,| * The author's figures are 34-639, but when recalculated according to the values adopted in this work (Cu=63-6; 8=32-07; H= 1-008; O=16) the figures are as stated in the text, since grape-sugar, C 6 H 12 O 6 = 180-096, and 5CuSO 4 -5H 2 O= 1248-75, from which it follows that 5 grm. grape-sugar are the equivalent of 34-669 grm. cupric sulphate. TRANSLATOR. f SOXHLET advises to recrystallize the commercial so-called chemically pure cupric sulphate by stirring the hot, saturated, and filtered solution until it cools ; the crystalline powder dried between filter-paper, and exposed for 24 hours in a thin layer in a dry place, will then have the proper water content. J SOXHLET prepares the alkaline solution of potassium and sodium tar- trate fresh every time, and states that "the use of Rochelle-salt solution which has been kept for some time should be avoided just as much as the employment of ready-made FEHLING'S solution which has been kept on hand for some time, even though the container has been kept ever so well stoppered." It will be evident that the 50 c.c. of liquid contained in the dish will contain exactly as much cupric sulphate and Rochelle salt in solution as 50 c.c. of the solution prepared by FEHLING'S original formula. 274.] DETERMINATION OF GRAPE-SUGAR, ETC. 739 heat to boiling, and add the sugar solution in small portions until the liquid, after sufficient boiling, the duration of which must depend upon the kind of sugar ( 274, i, 6), no longer appears blue. From this preliminary test calculate, according to 274, i, 5, the approximate quantity of the sugar corresponding with 50 c.c. of FEHLING'S solution, and then dilute the solution so as to contain about 1 per cent, of sugar. d. Now heat a fresh mixture of 25 c.c. of copper-sulphate solution a, and 25 c.c. Rochelle-salt solution 6, without diluting it with water, but with a quantity of the approximately 1 per cent, sugar solution corresponding with the preliminary test (i.e., about 23 c.c. grape-sugar, 24 c.c. invert-sugar, 25 c.c. levulose-, 38 c.c. maltose-, or 33 c.c. milk-sugar solution) so long as is necessary for the particular kind of sugar ( 274, i, 6), and then pour the whole through a sufficiently large folded filter. If the filtrate is green or appreciably greenish, it is of course unnecessary to test further for copper; if, however, it is yellow, some copper may still be present. In order to ascertain this, acidulate about one- third of the filtrate with acetic acid, and add potassium ferro- cyanide. A dark-red color indicates the presence of large quan- tities of copper, while a pale pink indicates traces; if there is no change in color all the copper has been precipitated. If copper was found in the solution, make a fresh test in exactly the same way as before, but use a larger quantity of sugar solution, propor- tional to the intensity of the copper reaction observed; if, on the other hand, no copper was found, take about 1 c.c. less sugar solu- tion for the second test. These trials are repeated until two, differing in the quantity of sugar used only by 0-1 c.c., yield filtrates one of which contains copper while the other is free from it. The mean between the two is regarded as the exact quantity of sugar solution required to decompose 50 c.c. FEHLING'S solution. As a rule 5 or 6 such tests will suffice to attain the object. The calculation is then made on the basis of the comparative figures given in 274, i, 5. For instance, were 24 cc. of grape-sugar solution used, these would 740 DETERMINATION OF COMMERCIAL VALUES. [ 274. contain 0-2375 grm. grape-sugar; if 40 c.c. maltose solution have been employed, these contained 389 grm. maltose. In colored liquids it is more difficult to detect any copper in the filtrate by means of potassium ferrocyanide, and the hydrogen sulphide gives even still more uncertain results. In such cases SOXHLET advises to boil the liquid in the beaker with a few drops of sugar solution for about one minute, and to then allow to stand quietly for 3 to 4 minutes. On now pouring the liquid from the beaker, and wiping the bottom of the latter with a piece of white blotting-paper wrapped around a glass rod, the paper will be colored red by any adherent cuprous oxide. Larger quantities of copper in the filtrate may be easily detected by the red deposit on the sides and bottom of the glass vessel. e. SOXHLET' s modification of FEHLING'S method is also gen- erally applicable to diabetic urine; the operator must, however, be content with boiling two minutes, and allowing to settle for a very short time, to determine whether the supernatant liquid is green or not, as the testing for copper in the filtrate is impracti- cable (see above, FEHLING'S method). /. As in SOXHLET' s modification the period of boiling is defi- nitely fixed, and must not be prolonged longer than is necessary it can yield serviceable results only when reducing sugars are present with substances which reduce FEHLING'S solution only after prolonged action. Hence grape-sugar or invert-sugar may be determined by this method in solutions containing also cane- sugar (compare 277, I). 3. Gravimetric Methods of Sugar Determination. a. Determination of Grape-sugar. This is based upon the fact, ascertained by MARCKER, that when grape-sugar acts upon FEHLING'S solution at the boiling tem- perature, there is no proportional relation between the quantity of grape-sugar and the cuprous oxide precipitated, but that a definite relation exists when in all cases equal quantities of copper solution act under like conditions. The method rests, therefore, 274.] DETERMINATION OF GRAPE-SUGAR, ETC. 741 upon a purely empirical basis. MARCKER based the formula for the calculation on three determinations only, and with different quantities of sugar. ALLIHN placed the method on a more secure foundation by making eleven determinations; he also greatly facilitated the performance of the method by calculating a table based upon his determinations, from which the relations between the copper thrown down as cuprous oxide and the grape-sugar may be directly ascertained. In order that the table may apply, the details of ALLIHN' s method must be strictly adhered to, as it rests upon a purely empirical basis. The reagents required are: a, a copper sulphate solution, prepared by dissolving 34-6 grnu crystallized copper sulphate in sufficient water to measure 500 c.c.; b, a Rochelle-salt solution, prepared by dissolving 173 grm. Ro- chelle salt and 125 grm. potassium hydroxide in water to make 500 c.c. The solutions are kept separate. Now mix 30 c.c. of the alkaline Rochelle-salt solution 6, and 30 c.c. of the copper-sulphate solution a, in a 300-c.c. beaker, and heat to boiling over the naked flame or on a sand-bath. For each test, run into the boiling liquid from a burette 25 c.c. of the sugar solution (which must not contain more than 1 per cent, of sugar) > boil the mixture up once more, and immediately filter off the- precipitated cuprous oxide. SOXHLET directs an asbestos filter- tube to be used for filtering. ALLIHN recommends to prepare it from a piece of combustion tubing 10 cm. long, drawn out to about one-half the width at one end, and the wider part one-fourth filled with freshly ignited, long-fibred, soft asbestos. Under the asbestos layer, in the conical part of the filter-tube (shown in Fig. 131, a), place a small plug of glass wool, so that no particles of asbestos can be carried away during filtration. The asbestos must be packed neither too loosely nor too tightly, as in the former case some cuprous oxide might easily run through with the liquid, while in the second place the filtration would be too slow. It is well to place a loose plug of asbestos upon the rather tightly packed asbestos mass. The cuprous oxide in this case dis- tributes itself in the former, instead of forming, as it otherwise does, a compact layer, which hinders filtration. 742 DETERMINATION OF COMMERCIAL VALUES. [ 274 The prepared filter-tube is now carefully heated with the lamp while a current of dry air is drawn through it in order to remove all moisture; after cooling in the exsiccator it is weighed. When in use, a small funnel is fitted into the filter-tube by means of a perforated cork, and, in order to facilitate filtration, the flask for receiving the nitrate is connected with a pump. After repeated decantation, bring the cuprous oxide on to the filter, wash with cold water, and finally rinse with alcohol and ether to facilitate the drying. The traces of cuprous oxide adhering to the beaker remove with a glass rod over the end of which a short piece of rubber tubing has been slipped. The drying is best effected by heating in an air-bath; it requires scarcely 15 minutes. Now proceed to reduce the cuprous oxide, as the metallic copper resulting has to be weighed. For this purpose fix the filter-tube in an inclined po- sition and pass a current of pure, dry hydrogen FIG. 131. through it while gently heating. The reduction is effected even at a moderate heat (according to SOXHLET'S investi- gations already at 130 to 135). It is hence unnecessary for the flame to touch the glass tube, and special care must be taken not to directly heat that part of the tube wherein the glass wool is placed, in order that the lead oxide it contains may not be reduced. As soon as the precipitate exhibits the characteristic color of copper, and droplets of water cease to form at the cold end of the tube (which usually is the case in a few minutes), the object is attained. Now allow to cool in the current of hydrogen, then pass a current of dry air through the tube for a short time, and weigh. The quantity of copper found (in milligrammes) is now sought in the following table, and the corresponding quantity of grape-sugar read off in the adjacent column: 1274.] DETERMINATION OF GRAPE-SUGAR, ETC. 743 TABLE FOR CALCULATING THE GRAPE-SUGAR FROM THE QUANTITY OF COPPER DETERMINED BY GRAVIMETRIC ANALYSIS. Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. 10 6-1 59 30-3 108 55-0 157 80-1 11 6-6 60 30-8 109 55-5 158 80-7 12 7-1 61 31-3 110 56-0 159 81-2 13 7-6 62 31-8 111 56-5 160 81-7 14 8-1 63 32-3 112 57-0 161 82-2 15 8-6 64 32-8 113 57-5 162 82-7 16 9-0 65 33-3 114 58-0 163 83-3 17 9-5 66 33-8 115 58-6 164 83-8 18 10-0 67 34-3 116 59-1 165 84-3 19 10-5 68 34-8 117 59-6 166 84-8 20 11-0 69 35-3 118 60-1 167 85-3 21 11-6 70 35-8 119 60-6 168 85-9 22 12-0 71 36-3 120 61-1 169 86-4 23 12-5 72 36-8 121 61-6 170 86-9 24 13-0 73 37-3 122 62-1 171 87-4 25 13-5 74 37-8 123 62-6 172 87-9 26 14-0 75 38-3 124 63-1 173 88-5 27 14-5 76 38-8 125 63-7 174 89-0 28 15-0 77 39-3 126 64-2 175 89-5 29 15-5 78 39-8 127 64-7 176 90-0 30 16-0 79 40-3 128 65-2 177 90-5 31 16-5 80 40-8 129 65-7 178 91-1 32 17-0 81 41-3 130 66-2 179 91-6 33 17-5 82 41-8 131 66-7 180 92-1 34 18-0 83 42-3 132 67-2 181 92-6 35 18-5 84 42-8 133 67-7 182 93-1 36 18-9 85 43-4 134 68-2 183 93-7 37 19-4 86 43-9 135 68-8 184 94-2 38 19-9 87 44-4 136 69-3 185 94-7 39 20-4 88 44-9 137 69-8 186 95-2 40 20-9 89 45-4 138 70-3 187 95-7 41 21-4 90 45-9 139 70-8 188 96-3 42 21-9 91 46-4 140 71-3 189 96-8 43 22-4 92 46-9 141 71-8 190 97-3 44 22-9 93 47-4 142 72-3 191 97-8 45 23-4 94 47-9 143 72-9 192 98-4 46 23-9 95 48-4 144 73-4 193 98-9 47 24-4 96 48-9 145 73-9 194 99-4 48 24-9 97 49-4 146 74-4 195 100-0 49 25-4 98 49-9 147 74-9 196 100-5 50 25-9 99 50-4 148 75-5 197 101-0 51 26-4 100 50-9 149 76-0 198 101-5 52 26-9 101 51-4 150 76-5 199 102-0 53 27-4 102 51-9 151 77-0 200 102-6 54 27-9 103 52-4 152 77-5 201 103-1 55 28-4 104 52-9 153 78-1 202 103-7 56 28-8 105 53-5 154 78-6 203 104-2 57 29-3 106 54-0 155 79-1 204 104-7 58 29-8 107 54-5 156 79-6 205 105-3 744 DETERMINATION OF COMMERCIAL VALUES. [ 274. TABLE FOR CALCULATING THE GRAPE-SUGAR FROM THE QUANTITY OF COPPER DETERMINED BY GRAVIMETRIC ANALYSIS. (Continued.) Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. 206 105-8 255 131-9 304 158-7 353 186-0 207 106-3 256 132-4 305 159-3 354 186-6 208 106-8 257 133-0 306 159-8 355 187-2 209 107-4 258 133-5 307 160-4 356 187-7 210 107-9 259 134-1 308 160-9 357 188-3 211 108-4 260 134-6 309 161-5 358 188-9 212 109-0 261 135-1 310 162-0 359 189-4 213 109-5 262 135-7 311 162-6 360 190-0 214 110-0 263 136-2 312 163-1 361 190-6 215 110-6 264 136-8 313 163-7 362 191-1 216 111-1 265 137-3 314 164-2 363 191-7 217 111-6 266 137-8 315 164-8 364 192-3 218 112-1 267 138-4 316 165-3 365 192-9 219 112-7 268 138-9 317 165-9 366 193-4 220 113-2 269 139-5 318 166-4 367 194-0 221 113-7 270 140-0 319 167-0 368 194-6 222 114-3 271 140-6 320 167-5 369 195-1 223 114-8 272 141-1 321 168-1 370 195-7 224 115-3 273 141-7 322 168-6 371 196-3 225 115-9 274 142-2 323 169-2 372 196-8 226 116-4 275 142-8 324 169-7 373 197-4 227 116-9 276 143-3 325 170-3 374 198-0 228 117-4 277 143-9 326 170-9 375 198-6 229 118-0 278 144-4 327 171-4 376 199-1 230 118-5 279 145-0 328 172-0 377 199-7 231 119-0 280 145-5 329 172-5 378 200-3 232 119-6 281 146-1 330 173-1 379 200-8 233 120-1 282 146-6 331 173-7 380 201-4 234 120-7 283 147-2 332 174-2 381 202-0 235 121-2 284 147-7 333 174-8 382 202-5 236 121-7 285 148-3 334 175-3 383 203-1 237 122-3 286 148-8 335 175-9 384 203-7 238 122-8 287 149-4 336 176-5 385 204-3 239 123-4 288 149-9 337 177-0 386 204-8 240 123-9 289 150-5 338 177-6 387 205-4 241 124-4 290 151-0 339 178-1 388 206-0 242 125-0 291 151-6 340 178-7 389 206-5 243 125-5 292 152-1 341 179-3 390 207-1 244 126-0 293 152-7 342 179-8 391 207-7 245 126-6 294 153-2 343 180-4 392 208-3 246 127-1 295 153-8 344 180-9 393 208-8 247 127-6 296 154-3 345 181-5 394 209-4 248 128-1 297 154-9 346 182-1 395 210-0 249 128-7 298 155-4 347 182-6 396 210-6 250 129-2 299 156-0 348 183-2 397 211-2 251 129-7 300 156-5 349 183-7 398 211-7 252 130-3 301 157-1 350 184-3 399 212-3 253 130-8 302 157-6 351 184-9 400 212-9 254 131-4 303 158-2 352 185-4 401 213-5 274.] DETERMINATION OF GRAPE-SUGAR, ETC. 745 TABLE FOR CALCULATING THE GRAPE-SUGAR FROM THE QUANTITY OF COPPER DETERMINED BY GRAVIMETRIC ANALYSIS. (Concluded.) Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. Copper. Mg. Grape- sugar. Mg. ' 402 214-1 418 223-3 434 232-8 450 242-2 403 214-6 419 223-9 435 233-4 451 242-8 404 215-2 420 224-5 436 233-9 452 243-4 405 215-8 421 225-1 437 234-5 453 244-0 406 216-4 422 225-7 438 235-1 454 244-6 407 217-0 423 226-3 439 235-7 455 245-2 408 217-5 424 226-9 440 236-3 456 245-7 409 218-1 425 227-5 441 236-9 457 246-3 410 218-7 426 228-0 442 237-5 458 246-9 411 219-3 427 228-6 443 238-1 459 247-5 412 219-9 '428 229-2 444 238-7 460 248-1 413 220-4 429 229-8 445 239-3 461 248-7 414 221-0 430 230-4 446 239-8 462 249-3 415 221-6 431 231-0 447 240-4 463 249-9 416 222-2 432 231-6 448 241-0 417 222-8 433 232-2 449 241-6 b. Determination of Invert-sugar. Although invert-sugar behaves in other respects just like grape- sugar towards alkaline copper-sulphate solution containing an alkali tartrate, its reducing effect, however, as SOXHLET has shown, is different from that of grape-sugar; hence ALLIHN'S tables for grape-sugar cannot be used for invert-sugar, and a new set of empirical tables must necessarily be constructed. For such a one we are indebted to MEISSL.* In the gravimetric process of determining invert-sugar, proceed exactly in the manner detailed for grape-sugar, using, however, the table on p. 746 for ascertaining the quantity of invert-sugar from the copper obtained. Examples in the Use of this Table. The weight of the copper = 0-175 grm. According to the table 0-1705 Cu = 0-09 grm. invert-sugar; hence 0-175-0-1705= 0-045 Cu, = 1 *| T invert-sugar =0-0025 grm. invert-sugar. Hence 0-175 grm. Cu= 0-09 + 0- 0025 =0-0925 grm. invert-sugar. * Zeitschrift des Vereins fur Rubenzuckerindustrie, 1879, 1034. 746 DETERMINATION OF COMMERCIAL VALUES. [ 274. TABLE FOR SOLUTIONS OP PURE INVERT-SUGAR. Mgrms. Invert-sugar. Mgrms. Reduced Copper. 1 Mgrm. Invert-sugar corresponds with Mgrm. Reduced Cu. Mgrms. Invert-sugar. Mgrms. Reduced Copper. 1 Mgrm. Invert-sugar corresponds with Mgrm. Reduced Cu. 50 96-0 140 259-4 ) 55 105-4 145 268-1 [ 1-744 60 114-8 1C7A 150 276-8 ) 65 124-2 - o/O 155 285-2 1 70 133-5 160 293-6 75 142-9 165 302-1 y 1-684 80 152-1 1 170 310-5 85 161-3 175 318-9 J 90 170-5 V 1-840 180 327-2 1 95 179-7 185 335-5 100 188-9 I 190 343-7 \ 1-656 105 197-8 1 195 352-0 110 206-6 200 360-3 J 115 215-5 Se 1-772 205 368-2 1 120 224-4 210 376-2 125 233-2 J 215 384-2 I 1-592 130 135 241-9 \ 250-6 J 1-744 220 225 392-4 400-1 J c. Determination of Milk-sugar. In the case of milk-sugar, the degree of dilution, according to SOXHLET'S experiments, has no effect on the reducing action, but the quantity of copper solution, whether smaller or larger, has. The latter fact has also been confirmed by RODEWALD and TOLLENS, hence the gravimetric determination of milk-sugar must also be based upon proportions empirically ascertained. The following table has been prepared by SOXHLET, and presupposes the carrying out of the following directions: Mix 25 c.c. of the copper solution a, p. 738, and 25 c.c. of the alkaline Rochelle-salt solution, 6, p. 738, with 20 to 60 c.c. of an approximately 0-5-per cent, milk-sugar solution, and make up the volume to 150 c.c. with water. Then heat to boiling for 6 minutes, collect the cuprous oxide in an asbestos filter- tube, and weigh the reduced copper, just as in the case of grape-sugar. The quantity of milk-sugar is then ascertained from the weight of the copper, by completing SOXHLET'S table by interpolating: 274.] DETERMINATION OF GRAPE-SUGAR, ETC. 747 Weight of Copper in Mgrms. Sugar in Mgrms> 392-7 ........ co ............................ 300 363-6, ..................................... 275 333-0 ...................................... 250 300-8 ........ o.o .......................... 225 269-6 ......... o ........................... 200 237-5 ...... o .............................. 175 204-0 ...... . .............................. 150 171-4... ............. , .................... 125 138-3 ................ o .................... 100 If the milk-sugar in milk is to be determined, first precipitate the albumin (and fat) by means of cuprous sulphate and caustic- potassa solution in the manner described by RITTHAUSEN.* For this purpose dilute 25 c.c. milk with 400 c.c. water, add 10 c.c. of the cuprous-sulphate solution described on p. 738 (and containing 34-669 grm. in 500 c.c.). then add 6-5 to 7-5 c.c. of a potassa lye of such strength that one volume will exactly precipitate the copper from one volume of copper solution. The liquid must still have an acid reaction after the alkali has been added, and may contain some dissolved copper. Now make up the liquid to 500 c.c. and filter through a dry, folded filter. Mix 100 c.c. of the approx- imately 0-25-per cent, milk-sugar solution with 25 c.c. of the alkaline Rochelle-salt solution and 25 c.c. of the cuprous-sulphate solution (p. 738) in a beaker, cover the latter, place on a double- wire gauze, and heat to boiling. After boiling for six minutes, filter, and proceed as described above. Assuming with SOXHLET that 0-294 grm. copper is obtained, this would correspond with 0-2236 grm. milk-sugar. d. Determination of Maltose. As, according to SOXHLET' s investigations, an excess of undiluted PEHLING'S solution (but only when undiluted) does not, as hi the * Journ. /. prakt. Chem., N. S., xv, 332. 748 DETERMINATION OF COMMERCIAL VALUES. [ 274. case of other sugars, increase the reducing action of maltose, and as hence a definite quantity of maltose reduces the same quantity of cupric oxide, irrespective of the quantity of the copper excess present^ the gravimetric determination of maltose is simpler than that of the other sugars, because, when an approximately 1-per cent, maltose solution is used, only one relation has to be considered, namely, that determined by SOXHLET, i.e., 113 of copper =100 of anhydrous maltose, C u H tt O n . In carrying out the determination, the oper- ator need only observe that the mixture of equal volumes of the cupric-sulphate solution a and of alkaline Rochelle-salt solution 6, p. 738, be used undiluted, and in excess. The liquids are mixed cold, then boiled for four minutes, and filtered (see Grape-sugar). A passing glance at the literature on the subject suffices to show that, besides the above-named investigators, many others have worked with modifications of FEHLING'S test. The variations are confined in part to the preparation of the copper solution, and in part to the manner of determining the precipitated cuprous oxide. Regarding the former point, I would mention the work by J. LOWE,* who recommends a glycerinic cupric-soda solution; those of LA- GRANGE t and of DEGENER,J who give preference to solutions of cupric tartrate in caustic-soda solutions, and prepared in different ways; and that of PAVY, who employs a FEHLING'S solution to which ammonia is added. Regarding the latter point, however, I would mention the work of FR. MOHR ; || who collects the cuprous oxide and dissolves it in a solution of acid ferric sulphate, and determines the ferrous sulphate formed with potassium perman- ganate; that of W. PILLITZ,!" who replaces the ferric sulphate by a solution of sodium chloride in diluted sulphuric acid, and oxidizes * Zeitschr. f. analyt. Chem,, ix, 20, and x, 452. f Compt. rend., 1874, 1005; Zeitschr. f. analyt. Chem., xv, 111. J Zeitschrift des Vereins fur Rubenzuckerindustrie, xviu, 349, and xix, 736; Zeitschr. f. analyt. Chem., xxu, 444. Chem. News, xxxix, 77; Zeitschr. f. analyt. Chem., xix, 98. II Zeitschr. f. analyt. Chem., xn, 296. IT Ibid., xvi. 48. 275.] DETERMINATION OF GRAPE-SUGAR, ETC. 749 the cuprous oxide directly with permanganate ; of FR. WEIL,* who titrates the residual excess of cupric oxide in the solution with stannous-chloride solution (see Vol. I, p. 380, d) and thus finds the cuprous oxide from the difference; that of HOLDEFLEISS f and of GRATAMA,{ who convert the cuprous oxide collected into cupric oxide by means of nitric acid; and that of ARNOLD, who dissolves the cuprous oxide in nitric acid and determines it by VOLHARD'S method (p. 628 this volume). These modifications, however, offer no advantages, and all those that require filtration of the excess of FEHLING'S solution through paper have the disadvantage besides, that the filter-paper retains some copper, the quantity of which varies according to the con- centration and copper content of the solution. B. METHODS BASED UPON THE REDUCTION OF MERCURY COMPOUNDS. 275. On this basis three methods are founded: 1. KNAPP'S;|| 2, SACHSSE'S ; 1" and 3, H ACER'S,** of which the first two have been repeatedly and critically studied, particularly .by SoxHLET.ft 1. KNAPP'S Method. This was employed by KNAPP, at the suggestion of LIEBIG, for the quantitative determination of grape-sugar. The mercury solution required is obtained by dissolving 10 grm. pure, dry mer- curic cyanide in water, adding 100 c.c. of caustic-soda solution * Zeitschr. f. analyt. Chem., xi, 284. f Landwirthschaftl. Jahrbiicher, 1877, Suppl. Heft. j Zeitschr. f. analyt. Chem., xvii, 155. Ibid., xx, 231. H Annal. d. Chem. u. Pharm., CLIV, 252; Zeitschr. f. analyt. Chem. t ix, 395. f Pharmaceut. Zeitschr. f. Russland, 1876, 549 ; Zeitschr. f. analyt. Chem., xvi, 121. ** Pharm. Centralhalle, xvm, 313; Zeitschr. f. analyt. Chem., xvn, 380. tf Journ. f. prakt. Chem. [2], xxi, 300; Zeitschr. f. analyt. Chem., xx, 447. 750 DETERMINATION OF COMMERCIAL VALUES. [ 275^ of 1 145 sp. gr., and diluting to measure 1000 c.c. The sugar solution employed should have a strength of about 5-per cent. As, according to BRUMME'S * observation, confirmed by SOXH- LET, the reducing effect of sugar is greater when the sugar solu- tion is added all at once, and less when added in separate portions, KNAPP'S method in its original form, in which the sugar solution is gradually added to the boiling mercury solution until all the mercury has been precipitated, does not give satisfactory results according to SOXHLET. Concordant and accurate results may be obtained, however, according to him, by proceeding in a manner analogous to that employed in his modification of FEHLING'S method, i.e., when the whole of the sugar solution (whether in 5- or 1-per cent, solution is quite immaterial) is added all at once to the mercury solution most conveniently to 100 c.c. the liquid boiled for two or three minutes, then tested as to whether it still contains any mercury, and then making other tests with fresh portions of the mercury solution and larger or smaller quantities of sugar solution, until two experiments are made in which the quan- tities of sugar contained differ but very little, -one of which con- tains, however, a slight quantity of mercury, the other being free from it. To determine the quantity of dissolved mercury the reaction introduced by SACHSSE is to be usually recommended. It consists in removing a few drops, or towards the end, about 5 c.c. of the liquid above the precipitated mercury, and mixing it in a small porcelain dish with an alkaline stannous-oxide solution. If fairly large quantities of mercury are present, a black precipitate forms; if very small quantities, a brown color only develops. The alka- line stannous-oxide solution is made simply by supersaturating a stannous-chloride solution with caustic-soda solution. HAAS f recommends to filter the solution to be tested for mercury through a triple filter. By operating in this manner, the following relations, according to SOXHLET, are to be recognized as existing between KNAPP'S * Zeitschr. f. analyt. Chem., xvi, 12 l e f Ibid., xxn, 216. 275.] DETERMINATION OF GRAPE-SUGAR, ETC. 751 solution and the various sugars, and should be used in calculating. 100 c.c. KNAPP'S solution are reduced by the following quantities of sugar when a 0-5-per cent, sugar solution is employed: Grape-sugar, CeH^Oe 202 mgnn. Invert-sugar, C^Oe 200 " Levulose, C^Oe 198 " Maltose, C^H^ 308 " Milk-sugar, C^H^On H 2 O 311 " Accurate results may, however, also be obtained by adding 0-5- to 1-per cent, sugar solutions gradually, according to WORM MULLER and J. HAGEN,* and more recently confirmed by further investigations by WORM MULLER f and J. G. OTTO.t They advise the following procedure: For a 1-per cent, sugar solution take 100 c.c., or for a 0-5-per cent, take 50 c.c., of KNAPP'S solution, dilute it with three to four volumes of water, heat to boiling, add the sugar solution, the larger bulk in portions of about 2 c.c. each,, and boil for one-half to one minute between each addition. W. MULLER employs the end reaction used by PILLITZ, but OTTO employs that recommended by LENSSEX.|| Operating in the manner stated, the above-named chemists confirmed the relation of reducing power stated by KNAPP, in which 100 c.c. of KNAPP'S solution correspond to 0-25 grm. grape- sugar, while on the other hand SOXHLET'S results were also con- firmed when operating according to his method. 2. R. SACHSSE'S Method. An alkaline solution of mercuric iodide serves as the mercury solution in this method. It is prepared by dissolving on the one * PFLUGER'S Archiv fur die gesammte PhysioL, xvi, 569 and 590, and xxin, 220. f Journ. f. prakt. Chem. [2], xxvi, 78. t Ibid., xxvi, 87. Zeitschr. f. analyt. Chem., x, 459. PILLITZ places a drop of the solution on a piece of Swedish filtering-paper and exposes the spot first to the vapors of hydrochloric acid, and then to hydrogen sulphide. H Zeitschr. f. analyt. Chem., ix, 455. LENSSEN acidulates a filtered sample with acetic acid and tests for mercury with hydrogen sulphide. 752 DETERMINATION OF COMMERCIAL VALUES. [ 275. hand 18 grm. of pure, dried mercuric iodide with 25 grm. potas- sium iodide in water, and on the other dissolving 80 grm. caustic potassa in water. The latter solution is added to the former, and the whole diluted to 1000 c.c. According to SACHSSE the sugar solution should be added in portions to the boiling mercury solu- tion until all the mercury is precipitated. As, however, SOXHLET found that titrations made by adding the sugar solution gradually and in portions give results which differ from those obtained when all the sugar solution is added at once, it is necessary, in order to obtain exact results, to proceed in the same manner when using SACHSSE'S mercury solution as prescribed by SOXHLET for KNAPP'S solution. It is noteworthy that the action of sugar solution when added gradually or all at once is quite different in KNAPP'S and SACHSSE'S methods. In the former, when the sugar solution is added gradu- ally, more sugar is required to effect reduction, and in the latter, less. This must, of course, be taken into consideration when determining, from the preliminary, the quantity of sugar solution with which it is advisable to begin the actual experiment. In carrying out SACHSSE'S method it must be further borne in mind that the reducing action of sugar differs according as a 1-per cent, or 0-5-per cent, solution is used. Hence a concen- tration of 0-5-per cent, must not be appreciably departed from. In operating, it is convenient to employ 100 c.c. of SACHSSE'S solution ; the boiling should be continued for two or three minutes, and the test for any mercury present in the solution made with alkaline stannous-oxide solution. Under the conditions determined by SOXHLET the relation between SACHSSE'S solution and the different sugars is as below. 100 c.c. of SACHSSE'S solution are reduced by the following quantities of sugar when in 0'5-per cent, solution: Grape-sugar, C fl H 12 O 6 325 mgrm. Invert-sugar, C 6 H 12 O fl 269 " Levulose, C 6 H 12 O fl 213 " Maltose, C^H^Ou 491 " Milk-sugar, C 12 H 22 O n I^O 387 " 275.] DETERMINATION OF GRAPE-SUGAR, ETC. 753 With reference to both of the methods based upon the precipi- tation, it must be remarked that the values obtained by SOXHLET hold good, of course, for sugars in a perfectly pure state. With such, uniform results will be obtained by using the empirically found values under the given conditions, whether FEHLING'S, KNAPP'S, or SACHSSE'S method, as modified by SOXHLET, is em- ployed. The case is different, however, if the various methods are employed with sugar solutions which as for example com- mercial grape-sugar contain products intermediate between dextrin and grape-sugar, or as wine extract which contains glycerin, as both the latter as well as the intermediate products reduce mercury solutions (at least HAAS found this to be the case in SACHSSE'S method), but not FEHLING'S copper solution.* When SACHSSE'S method is hence employed with such impure sugar solutions (and this is probably true with KNAPP'S method), the results obtained are too high. It is therefore decidedly pref- erable to make use of SOXHLET'S modification of FEHLING'S method for determining the sugar in such cases. 3. H. H ACER'S Gravimetric Method. Up to the present time this method has been proposed only for determining grape-sugar, and, so far as I am aware, has not yet been tested for other sugars. A solution made as follows serves as the reagent: Triturate 30 grm. mercuric oxide with 30 grm. sodium acetate, transfer to a flask, add 25 grm. concentrated acetic acid (or 100 c.c. diluted acetic acid of 1-04 sp. gr.), then add 50 grm. sodium chloride and sufficient warm water to make up to 1000 c.c. Solution is facili- tated by shaking and gently warming. When cold, filter the liquid and preserve it in a cool place protected from light. To determine the sugar, introduce the sugar solution together with an excess of the mercury solution (about 200 c.c. of the mer- cury solution should be used for every gramme of grape-sugar) into a glass flask provided with a perforated cork carrying a glass tube * HAAS states that 2-1618 grm. glycerin reduces 20 c.c. of SACHSSE'S mercury solution. 754 DETERMINATION OF COMMERCIAL VALUES. [ 276. about 15 cm. long, and heat the flask either in a water-bath or over the naked flame for from one to two hours, taking care that the liquid always remains acid. In proportion as the sugar acts mercurous chloride precipitates. The reaction is complete when a small portion of the clear liquid, because of the presence of some mercuric acetate, is rendered turbid by ammonia, while the filtrate remains clear on further boiling. Collect the precipitated mer- curous chloride on a filter dried at 100 and weighed, wash it. first with 5-per cent, hydrochloric acid, then with water, and finally with alcohol, then dry on the water-bath and weigh. As, according to HAGER, 2 equivalents of grape-sugar (2X180-096 = 360-192) decompose 9 equivalents of mercuric oxide (9X216 = 1944), yielding 4J equivalents of mercuous chloride (4^Hg 2 Cl 2 = 4^X470-90=2119-05), it follows that 1 grm. of grape-sugar, C c H 12 O ti , is represented by 5-883 grm. of mercurous chloride, Hg 2 Cl, The acid solution of mercuric acetate containing sodium chloride does not act upon cane-sugar, glycerin, gum arabic, dextrin, or uric acid, but it does act upon other constituents of urine, hence the method is not applicable for the determination of sugar in diabetic urine. C. METHOD BASED UPON THE DECOMPOSITION OF SUGAR BY ALCOHOLIC FERMENTATION.* 276. 1. When a liquid containing grape-sugar and some ferment or yeast is exposed to a suitable temperature it undergoes alcoholic fermentation. It was formerly believed that 1 equivalent of the anhydrous grape-sugar yielded 2 equivalents of alcohol and 2 equivalents of carbon dioxide, thus: C 6 H 12 O 6 = 2(C 2 H 6 O) + 2CO 2 . According to this assumption 48-86 parts of carbon dioxide would correspond with 100 parts of anhydrous grape-sugar. PAS- TEUR^ however, has shown that this assumption is incorrect, as * Compare KROCKER, "Ueber die Bestimmung des Starkemehlgehaltes in vegetabilishchen Nahraingsmitteln," Annal. d. Ghent, u. Pharm., LVIII, 212. f Compt. rend., XLVIII, 1149; Journ. /. prakt. Chem., LXXXV, 465. 276.] DETERMINATION OF GRAPE-SUGAR, ETC. 755 during the alcoholic fermentation a number of other products are formed from the elements of sugar, namely, glycerin, succinic acid, cellulose, and fats, and also very small quantities of other sub- stances, the formation of which was already known, e.g., amyl alcohol, butyl alcohol, etc. If, therefore, the quantity of carbon dioxide evolved during the alcoholic fermentation is to serve for the determination of the sugar decomposed, the determination cannot be made by calculation, but must be made from the practical results obtained by experiments. As, however, the quantity of the individual decomposition products is by no means a constant one, it may be easily seen that the method of determining sugar from the carbon dioxide evolved during alco- holic fermentation can make no claim to absolute accuracy. According to PASTEUR'S experiments (loc. tit.), of 100 parts of grape- sugar 95 parts are decomposed, as in the above equation, into alco- hol and carbon dioxide; the balance of the sugar decomposes into 2-5 to 3-6 glycerin, 0-4 to 0-7 succinic acid, 0-6 to 0-7 carbon dioxide, and 1-2 to 1-5 cellulose, fat, and other still undetermined substances. Consequently we shall not depart very far from the truth if we assume every 47 parts of carbon dioxide obtained by alcoholic fermentation to represent 100 parts of anhydrous grape- sugar. 2. To determine the carbon dioxide evolved during the fer- mentation, the apparatus shown on p. 494, Fig. 97, Vol. I, may be employed, omitting the copper-sulphate pumice tube, I, and taking care that the tubes n and o contain a sufficient quantity of soda- lime to surely retain all the carbon dioxide evolved. If it is desired to determine the carbon dioxide from the loss in weight of the appa- ratus, employ a flask arranged as shown in A, Fig. 93, p. 489, Vol. I. In order to prevent the liquid from returning backwards, replace the flask B by a U-tube filled with pumice-stone saturated with sulphuric acid. The quantity of sulphuric acid must be so adjusted that the bend of the U-tube may be just closed by the liquid. The outer limb of the U-tube is connected with a calcium-chloride tube (not weighed with the apparatus), so that the sulphuric acid hi the U-tube may not absorb moisture from the atmosphere. 756 DETERMINATION OF COMMERCIAL VALUES. [ 276. 3. Take of the saccharine liquid a quantity which will contain about 2 to 3 grm. anhydrous sugar. If much more is taken, the fermentation takes too long, while if much less is taken, the deter- mination, will be inaccurate at least if the carbon dioxide is deter- mined from the loss in weight because then the volume of the evolved carbon dioxide will be too small. 4. As regards the concentration of the liquid, the solution should contain about 4 or 5 parts of water to 1 part of sugar ; when solutions are more dilute, they should therefore be concentrated by evaporation on the water-bath. 5. Introduce the sugar solution into the flask, add a few drops of tartaric-acid solution, and a comparatively large, weighed por- tion of washed yeast, say 20 grm. fresh, or a corresponding quantity of pressed yeast. As yeast itself also generally evolves some carbon dioxide, a parallel experiment may be made at the same time with a larger, weighed quantity of the yeast in a similar apparatus, in order to determine the carbon dioxide it evolves, and to be thus able to allow for that evolved by the 20 grm. of yeast. 6. When the apparatus has been arranged and the weight taken, place it, or the flask containing the sugar solution and yeast, in a place where a fairly constant temperature of 25 is maintained. Fermentation soon sets in, and is rapid at first, but slackens later on, becoming slower and slower. When bubbles of gas are no longer formed, which is the case in four or five days, the process is complete. Then heat the flask to 100, exhaust the carbon dioxide still remaining in the flask, allow to cool, and weigh. The increase of weight of the carbonic-acid apparatus, or the loss in weight of the fermentation apparatus and drying tube, corresponds to the carbon dioxide evolved. For every 47 parts of carbon dioxide found cal- culate, as above stated, 100 parts of anhydrous grape-sugar. 277.] DETERMINATION OF GRAPE-SUGAR, ETC. 757 D. DETERMINATION OF CANE-SUGAR, DEXTRIN, AND STARCH.* 277. 1. CANE-SUGAR. Cane-sugar is usually determined optically or araeometrically- (see p. 731 this volume). f Of the other methods the inversion- method particularly, and hi many cases also the fermentation, method, is well adapted. a. The inversion is as a rule most simply effected by heating the- cane-sugar with very dilute hydrochloric acid. The most favorable^ proportions were ascertained by NICOL,{ and hi the main confirmed. by SOXHLET. NICOL recommends to dissolve 1-25 grm. of sugar in 200 c.c.. water hi a 250-c.c. flask, add 10 drops of hydrochloric acid of 1- 11 sp.gr., and to heat on a water-bath for half an hour at 100. Then neutralize the liquid with sodium carbonate, fill the flask to the mark with water, and thoroughly mix the liquid. If the heating is continued for a longer period, a part, although only a very small one, of the in vert-sugar is decomposed; and this will hence lower the reducing action of the solution somewhat. According to SOXH- LET, for example, on heating for an hour and a half the propor- tion will be 100: 99-3.|| The latter recommends for the purpose of conversion the following proportions which, if pure, dry sugar is: used, are adapted for yielding a solution of invert-sugar 100 c.c. of which contain exactly 1 grm. or 0-5 grm. of invert-sugar: Dissolve * See also Appendix I, Section III. f Regarding the optical determination of cane-sugar in the presence of other sugars or the ordinary carbohydrates, see CLERGET (Annales de chim. et de Phys. [3], xxvi, 175); H. REICHARDT and C. BITTMANN (Zeitschr. des Vereins f. d. Rubenzuckerindustrie, 1882, 764) ; S. CASAMAJOR (Chem. News, XLV, 150); K. ZULKOWSKY (Ber. der osterr. Gesellsch. zur Forderung der chem. Industrie, n, 1883) ; J. KJELDAHL (Meddelelser fra CARLSBERG Laboratoriet Part. 3, Copenhagen, H. HAGERUP); also Zeitschr. /. analyt. Chem., xxii, 588, Part 4. t Zeitschr. f. analyt. Chem., xiv, 177. Journ. f. prakt. Chem. [2], xxi, 228. II Ibid. [2], xxi, 235. 758 DETERMINATION OF COMMERCIAL VALUES. [ 277. 9-5 grm. cane-sugar in 700 c.c. of hot water, add 100 c.c. one-fifth- normal hydrochloric acid (containing 0-729 HC1), heat for 30 min- utes on a water-bath at 100, accurately neutralize with standard caustic-soda solution, and make up the volume to either 1000 c.c. or 2000 c.c. In either of the solutions thus obtained then determine the invert-sugar volumetrically according to SOXHLET'S method, or gravimetrically according to MEISSL'S method, pp. 738 and 745 this volume, and for every 100 parts of invert-sugar, C 6 H 12 6 , calculate 95 parts of cane-sugar, C^H^On. If the method is to be employed for determining the sugar in beet-juice, in the aqueous extract of the residue left after extraction, etc., add first some lead acetate to the weighed or measured quan- tity of the liquid until a precipitate no longer forms, then filter, remove the excess of lead by means of sodium sulphate, and then invert the sugar by heating with hydrochloric acid. If it is feared that other substances present besides sugar may be converted, by heating with hydrochloric acid, into products which also reduce FEHLING'S solution, e.g., dextrin into grape- sugar, effect the conversion by J. K ELDAHL'S method* with invertin (the inverting ferment of yeast). The invertin is em- ployed in the form either of an aqueous extract of the previously well- washed yeast, or as a mixture of the well-washed yeast with a little of an alcoholic solution of thymol, the addition of which completely checks the fermentative power of the yeast, while it is entirely without influence on the invertin. Invertin easily and completely changes cane-sugar into invert^ sugar without acting on most of the other carbohydrates, f The most favorable temperature is between 52 and 56. The presence of salts of the alkalies hinders the action of invertin, while smol 1 quantities of acid increase it. If cane-sugar is to be determined in the presence of grape-sugar, the latter is determined in a separate portion of the solution by * Meddelelser fra CARLSBERG Laboratoriet, Copenhagen, H. HAGERUP, 1881, 339, and 189; Zeitschr. f. analyt. Chem., xxn, 588. j- With the exception of a few sugars which but rarely occur, synanthrose is the only one which is changed by invertin. 277.] DETERMINATION OF GRAPE-SUGAR, ETC. 759 SOXHLET'S volumetric method (p. 738 this volume). An equal quantity of the solution is then inverted in the manner above detailed by heating with hydrochloric acid or by means of in- vertin. In this solution there will then be found all the invert- sugar from the cane-sugar, together with the unchanged grape- sugar. The quantity of FEHLING'S copper solution reduced by the solution is now ascertained by SOXHLET'S method, and the quantity corresponding to that required for the grape-sugar de- ducted from the total; the difference gives the quantity corre- sponding to the invert-sugar. Finally calculate 95 parts of cane- sugar for every 100 parts of invert-sugar found. In a similar manner cane-sugar may be determined in ike presence of invert-sugar. KJELDAHL. (loc. cit.}, employing inversion with invertin, determined in this manner cane-sugar not only in the presence of grape-sugar and invert-sugar, but also in the presence of maltose, dextrin, and inulin. This method presupposes that cane-sugar when present is without effect on the reducing action of grape- or invert-sugar, an -assumption which SOXHLET admitted in view of the short time the boiling is continued in his process of determining sugar; but according to MEISSL'S experiments this assumption is not abso- lutely correct. At all events it holds good only for SOXHLET'S method, but in no way for the gravimetric processes for deter- mining invert-sugar (and also grape-sugar). Nevertheless in order to render possible a gravimetric determination of invert- sugar in the presence of cane-sugar, MEISSL * has prepared a special table in which allowance is made for the influence of cane- sugar. This table was subsequently still further extended by ZuLKOWSKY.f 6. Fermentation Method. The method detailed on p. 754 this volume, for determining sugar from the carbon dioxide evolved during alcoholic fermentation, may also be employed for cane- sugar. The fermentation of the latter is more difficult to effect * Zeitschr. des Vereins f. Riibenzuckerindustrie, 1879, 1034. j- Bericht der osterreich. Gesettsch. zur Forderung der chemisch. Industr., n, 1883. 760 DETERMINATION OF COMMERCIAL VALUES. [ 277. than that of grape-sugar, hence a larger quantity of yeast must be taken. This acts by the ferment in it, invertin, first inverting the cane- sugar; then the dextrose ferments, and later the levulose. The products of the fermentation of cane-sugar are the same as in the case of grape-sugar. For 49 parts of carbon dioxide calculate 100 parts of cane-sugar. The number 49 is the average of the values 48-889 and 49-20, directly determined by BALLING and PASTEUR. 2. DEXTRIN AND STARCH. Of the various methods which may be used for determining dextrin and starch only those based upon the conversion of these into grape-sugar will be here described. The conversion was formerly effected by the aid of sulphuric acid in pressure-flasks on a salt-bath (MuscuLus), or in sealed tubes (PILLITZ*). The object may, however, be effected more simply and completely by heating with hydrochloric acid. R. SACHSSE f recommends for this purpose the following method : Heat 2 5 to 3 grm. of starch in a flask with 200 c.c. of water and 20 c.c. of hydrochloric acid of 1 125 sp. gr., on a water-bath maintained briskly boiling for three hours, under a reflux condenser. According to SACHSSE the con- version is then complete, i.e., no change in the proportions, whether of water, acid, time, or heat, will produce more dextrose from a given weight of starch than will be afforded by adhering to the above rules. When through heating, filter, almost completely neutralize with caustic-soda solution (alkalinity must be avoided), dilute to 500 c.c., and in a portion then determine the grape-sugar formed, either volumetrically or gravimetrically, and for every 1080 parts of grape-sugar found calculate 990 parts of starch, i.e., for every 100 parts of grape-sugar 91-67 parts of starch. This * Zeitschr. f. analyt. Chem., xi, 57. See also the extended investigations of ALLIHN (Journ. /. prakt. Chem. [2], xxn, 84 et seq.) ; according to him, under the most favorable conditions (0-5-per cent, sulphuric acid at 108), only 94-5-per cent, of starch are converted into sugar in 14 hours. f Chem. Centralbl, 1877, 732; Zeitschr. f. analyt. Chem., xvii, 231. 277.] DETERMINATION OF GRAPE-SUGAR, ETC. 761 proportion, which was obtained by SACHSSE in his experiments with potato-starch, does not correspond with the formula usually assigned to starch, C 6 H 10 O 5 , but with the formula C sa H 82 O 81 , assigned to it by W. NAGELI. If the calculation is based upon the usual formula for starch, then 90 parts of starch must be calculated for every 100 parts of grape-sugar, i.e., the same pro- portion as is used in calculating dextrin from the grape-sugar found. SALOMON * found, when using SACHSSE'S method of inversion on potato-starch dried at 120, and determining the grape-sugar formed according to ALLIHN, that the quantity of grape-sugar obtained (100 parts equivalent to 90 parts starch) corresponded with the formula generally accepted for starch, C 6 H 10 O 5 , and ascribed the difference in SACHSSE'S results partly to insufficient dehydra- tion of the starch (drying only at 100 to 110), and partly to the mode of determining the sugar. While it was formerly assumed that starch from different plants exhibited a like behavior on being heated with acids, and that equal weights of starch, from any source, afforded equal weights of grape-sugar, it must now be accepted, if the labors of SACHSSE and SALOMON f are to be considered as conclusive and comparative, that this is not the case, or at least not with the commercial starches. SACHSSE and SALOMON found, namely, that on treating rice- and wheat-starches less grape-sugar was formed than from an equal quantity of potato-starch. The question whether the starches of different plants exhibit differences in behavior, is not hereby decided, because the differ- ences in behavior of the commercial starches may also be ascrib- able to their manner of preparation. On the basis of his experi- ments, SALOMON assumes that the differences noted are due to the fact that while certain starches, e.g., rice-starch, on heating with diluted acids, are completely dissolved, it is true, a part of * Repertor. d. analyt. Chem., i, 274, and Journ. f. prakt. Chem. [a], xxv, 348; Zeitschr. f. analyt. Chem., xxii, 111. \Journ. f. prakt. Chem. [a], xxvi, 324; Zeitschr. f. analyt. Chem., xxn, 594. 762 DETERMINATION OF COMMERCIAL VALUES. [ 277. the starch, however, is not converted into grape-sugar, but into other substances which do not reduce FEHLING'S solution. The proportional figures found by SALOMON for rice-starch are as fol- lows: 100 parts of grape-sugar formed correspond with 93-5 parts rice-starch. In the case of wheat-starch, L. SCHULZE* found the relation recently to be 100 of grape-sugar =90 starch. I therefore do not consider the question as settled for rice-starch. On employing the above-described method of determining starch in grain, the results obtained are, according to G. FRANCKE,| too high, because cellulose also is converted into sugar on heating with hydrochloric acid. The treatment of starch with malt infusion (diastase) at temperatures up to 65, readily effects com- plete solution of the starch, it is true, but either does not effect a complete conversion into maltose or does so but very slowly. The solution always contains, besides maltose, also dextrin, or, more accurately, various dextrins, and in fact in proportion varying with the temperature at which the diastase acts (O'SuLLiVAN J). If it is desired to make a direct determination of starch on this basis, therefore, one of the following methods more recently pro- posed may be adopted: a. FAULENBACH makes use of the following solution of diastase : Crush 3 5 kilos of fresh, green malt, treat with a mixture of two litres water and 4 litres glycerin, and allow to stand for eight days with occasional stirring; then express and filter. Five drops of the liquid so obtained dissolve 1 grm. starch, and 15 drops con- tain a quantity of carbohydrates corresponding with 1 mgrm. grape-sugar. The solution is very stable. In testing the nutrient, which may contain about 2 grm. starch, gelatinize the starch first, and then effect solution by adding 15 drops of the diastase solution, and digesting at about 63; then filter off the undissolved * Journ. f. prakt. Chem. [2], xxvin, 311. f Zeitschr. f. Spiritusindustr., 1882, 306; Berichte der deutsch. chem. Gesellsch., xvi, 976. J Journ. Chem. Soc. [2], x, 579 ; [3], I, 478, and n, 125. Zeitschr. f. physiol Chem., vn, 510; Chem. CentralbL, 1883, p. 632. 278.] DETERMINATION OF ALCOHOL. 763 cellulose, etc., heat the solution with 20 c.c. hydrochloric acid on a water-bath for three hours, just neutralize with caustic-soda solution, determine the grape-sugar, deduct 1 mgrm., and then calculate the starch from the sugar. b. O'SuLLiVAN * employs pure diastase,f and in determining starch in cereal, treats 5 grm. of the finely ground substance suc- cessively with ether, with alcohol at 35 to 40, and with water (at the same temperature) so as to remove the fat, sugar, soluble albuminates, and soluble carbohydrates. The residue is then boiled for a few minutes at 62 to 63 to gelatinize the starch, and then allowed to cool; 0-025 to 0-035 grm. of the diastase dissolved in a little water is now added, and the whole maintained for an hour at a temperature of 62 to 63. Then heat to boiling, filter, wash with hot water, make up the filtrate when cool to 100 c.c. and in it determine on the one hand the maltose ( 274), and on the other hand the dextrin by polarization, deducting from the total polarization that due to the action of the maltose. Both maltose and dextrin are then calculated into starch and the results added. II. DETERMINATION OF ALCOHOL. J 278. The determination of alcohol (ethyl alcohol) in mixtures of alcohol and water is almost exclusively accomplished arseomet- rically, either by the aid of an alcoholometer, from which the per- centage by weight or volume may be directly read off, or by using an ordinary araeometer and ascertaining the alcohol content from the specific gravity, for which purpose numerous tables have been *J&urn. Chem. Soc., 1884, p. 1. t This is prepared as follows : Pour sufficient water over 2 or 3 kilos of finely crushed pale barley malt to just cover it. After 3 or 4 hours, express, filter the solution, and add alcohol of 83 sp. gr. until the liquid above the flocculent precipitate becomes opalescent or milky. Collect the precipitate, wash it first with alcohol of 0-86 to 0-88 sp. gr., then with absolute alcohol, then press it between linen, and finally dry it completely in a vacuum over sulphuric acid. I See also Appendix I, Section V. 764 DETERMINATION OF COMMERCIAL VALUES. [ 278. compiled for facilitating the object in view. The tables compiled by O. HEHNER,* and based upon FOWNE'S tables (which only give the percentage in whole numbers) are very convenient, as they afford complete readings of percentages by both weight and volume. This simple method of determining the alcohol needs no more extended discussion here, nor is it necessary to dilate upon the use of the vaporimeter, the utility of the results of which depends entirely on the proper adjustment of the instrument. f In the following I will describe only those methods of determining alcohol which are used in the analysis of wines and other liquids obtained by alcoholic fermentation. It will be readily seen that the method described, and which has been in use in my laboratory for a long time, is quite independent of the accuracy of special apparatus. The principle of the method is well known. The alcoholic liquid is distilled until all the alcohol has passed over into the distillate, taking care that the latter contains no notable quantities of other volatile substances; the absolute weight and specific gravity are then taken, and from these data, using the alcohol tables, the quantity of alcohol in the distillate, and hence which was originally present in the liquid, is calculated. The distillation may, of course, be carried out in various forms of apparatus; the form shown in Fig. 132, which scarcely requires further explanation, may be recommended, because it takes up but little space and requires no renewal of the condensing water.J If a large quantity of the alcoholic liquid to be examined, and containing presumably not more than 20 per cent, of alcohol by volume, is available, introduce 150 c.c. or grm. into the flask, * Zeitschr. /. analyt. Chem., xix, 485. The tables are published separately by C. W. KREIDEL, Wiesbaden, 1881, and in English by J. and A. CHURCHILL, London, 1880. t Compare A. KRAFT, Zeitschr. f. analyt. Chem., xn, 50; and A. SALOMON, Annal. d. Oenologie, I, 374. t An apparatus that admits of the simultaneous distillation of several samples of wine has been described by B. LANDMANN, Zeitschr. /. analyt. Chem., xxn, 394. 278.] DETERMINATION OF ALCOHOL. 765 a, and to prevent frothing in wines, etc., add a little tannin, then distil and collect the distillate in a weighed or tared flask, b, having a capacity of 200 c.c. to the mark on the neck (i.e., about two-thirds of the liquid taken). As soon as the distillate reaches the mark, it may be safely assumed that it will contain all the FIG. 132. alcohol. Now weigh the flask, 6, together with its contents, and thus ascertain the absolute weight of the latter. To ascertain the specific gravity of the distillate, which must, of course be done only after thoroughly mixing, a pyknometer, shown at c in Fig. 132, and having a capacity of 25 to 60 c.c., may be employed. The neck of the flask should have a diameter of 5 to 6 mm. Its weight,* and the number of grammes of distilled water it holds at 15-5, must be previously ascertained by re- peated experiments. Fill the pyknometer to a little above the mark with the distillate by aid of a small funnel with very narrow * In order to dry such a pyknometer, heat it, and exhaust the moist air by means of a narrow glass tube. The neck may be finally dried with filter- paper. 766 DETERMINATION OF COMMERCIAL VALUES. [ 278. stem, and place it in water of 15-5 (see Fig. 132, d). As soon as certain that the contents of the pyknometer have the same temperature as the surrounding water, remove the excess of dis- tillate, by the aid of a strip of filtering paper, until the pyknometer is filled exactly to the mark; then dry and weigh. On dividing the weight of the distillate in the flask by the known weight of the distilled water contained at 15-5, the specific gravity of the distillate is ascertained, and from this the alcohol content may be found by the aid of HEHNER'S tables above mentioned.* If only a limited quantity of the liquid to be tested is at com- mand, distill only 50 c.c. or grm. The mark on the receiver, 6, must then be at a height where the flask will hold about 35 c.c. It is, of course, evident that in this case the pyknometer used must have a capacity of 25 to 30 c.c., or a suitable quantity of water must be added to the distillate, before weighing, in order to fill a larger pyknometer. An example will make this clear: 150 c.c. of wine yielded 102 grm. distillate having a specific quantity of 0-9809 at 15-5. Hence, according to HEHNER'S tables, 100 grm. distillate contained 12-46 grm. absolute alcohol. If 100 grm. contained 12-46 grm., then 102 grm. will contain 12 709 grm. As all the alcohol passed over into the distillate, the latter quantity represents the quantity present in the 150 c.c. of wine. But, if 150 c.c. contain 12-709 grm., 100 c.c. contain 8-47 grm. alcohol. If it is also desired to ascertain how many grammes of alcohol are present in 100 grm. of wine, the specific gravity of the wine must be ascertained in order to find the weight of 100 c.c. of wine. When it is a question of determining the alcohol content of liq- uids containing comparatively small quantities of alcohol, collect the distillate in an un weighed flask. When all the alcohol has passed over, redistil the distillate, and then determine the absolute weight and specific gravity as above in the last obtained distillate. When liquids are so viscid that direct distillation is difficult, it is advisable to accomplish the first distillation by steam (see p. 388, * See also the alcohol tables in Appendix I, Section V. 279.] DETERMINING TANNIN. 767 6, this volume). The distillate so obtained is then again distilled, as above detailed. E. BORGMANN * employed this method with best results in the determination of small quantities of alcohol in American malt extracts. If the liquids to be distilled contain much free carbon dioxide, as, for instance, in the case with new or sparkling wines, or beer, first remove the greater part of the carbon dioxide by shaking in a half-filled flask, then add a little milk-of-lime until the liquid is just alkaline, and then distil. The last-named addition is also made when the liquid to be examined contains any notable quan- tity of acetic acid or other volatile acid. In distilling with milk- of-lime, however, care must be taken that the distillate contains no ammonia which will, of course, be present when the liquid being distilled contains ammonium salts. Should the distillate contain any ammonia, add to it an aqueous solution of tartaric acid until the liquid is acid, and then rectify the distillate. III. DETERMINING TANNIN.! 279. The determination of tannin in oak-barks and other tanning materials, in extracts containing tannin, and also in commercial tannins, is of such frequent occurrence in chemical laboratories that a description of the methods most useful for the purpose may properly find a place here. Of the great number proposed I select only those which are at present considered as most reliable. A. LOWENTHAL'S Method^ This method is based upon the oxidation of the tannin in sul- phuric-acid solution by potassium permanganate (formerly chlor- inated lime was used) in the presence of a large quantity indigo- carmine. If care is taken that the liquid is properly diluted, the oxidations are normal, and if the indigo solution has been added * Zeitschr. /. analyt. Chem., xxn, 534. f See also Appendix I, Section VIII. t This method in its earliest form is described in the Journ. f. prakt. Chem., 1860, m, 150. Compare FR. GAUHE, Zeitschr. f. analyt. Chem., in, p. 123. 768 DETERMINATION OF COMMERCIAL VALUES. [ 279. in such quantity as to require about twice as much of the oxidizing agent as is required for the tannin, the operator may be certain that the last portion of the tannin will be oxidized with the last portion of indigo. At first it was assumed,* with LOWENTHAL, that of the sub- stances contained in tannin extracts, only the tannin was oxidized, but it was soon proved that certain other substances passing into solution, and which for brevity we will designate as non-tannins, use up a determinable quantity of potassium permanganate.! NEUBAUER { hence so modified the method that, on the one hand both the tannin and the non-tannins were determined, while on the other, he determined the non-tannins, after first precipitating the tannin with animal charcoal, and from the difference calculated the tannin. LOWENTHAL, after further investigating the method, retained the principle of NEUBAUER'S method, but for the animal charcoal used in precipitating the tannin, he substituted a solution of glue containing much sodium chloride, or the animal hide pre- pared for tanning and reduced to powder (see Method B) first used by HAMMER the so-called "Blosse." As he gave preference to the glue, the improved LOWENTHAL method was almost exclusively carried out with glue or gelatin. After SIEMAND,!) however, had found that the improved LOW- ENTHAL method afforded concordant results with uniform con- centrations while with varying concentrations the results also varied widely, due to a slight solubility of the glue (or gelatin) tannate, he showed that the method could be further improved by determining the quantity of potassium permanganate used up by the dissolved glue (gelatin) tannate, and deducting this from the total required for the combined tannin and non-tannins. As, however, this correction, the value of which must be deter- mined by experiment each time for different dilutions, makes the *Journ. f. prakt. Chem., 1860, 150; Zeitschr. f. analyt. Chem., in, 122. t Compare FR. GAUHE, Zeitschr. f. analyt. Chem., in, 125. t Zeitschr. f. analyt. Chem., x, 1. Ibid., xvi, 33 and 201 ; also xx, 91. H DINGLER'S polyt. Journ., CCXLIV, 390; Zeitschr. /. analyt. Chem., xxn, 595. $ 279.] DETERMINING TANNIN. 769 method inconvenient, SIEMAND finally reverted to HAMMER'S principle, already applied by LOWENTHAL, of removing the tannin by means of a solid substance capable of combining with it. In the experiments which were made to ascertain the substance most suitable for this purpose, he finally found that the glue-yielding tissue of bones, horn cartilage (the so-called "Hornschlauche"), is preferable to the " blosse" proposed by HAMMER and employed by LOWENTHAL, as the former is easier to obtain, gives up less soluble matter to water on digestion,* and effects the precipitation of the tannic acid more rapidly. LOWENTHAL' s method, in consequence of these improvements, has gained greatly in reliability over its earlier form, and I will hence confine myself to a description of its latest and best form. I. REQUISITES. The method requires the following: 1. A Potassium-Permanganate Solution. Dissolve 1 grm. of the pure salt in sufficient water to make 1 litre. 2. Indigo-carmine Solution. Dissolve 40 grm. of purest indigo- carmine paste in water, add 60 c.c. sulphuric acid, dilute with water to 1 litre, and filter. 3. Glue-yielding tissue of Bones or Horn Cartilage. a. The former is prepared according to SIEMAND, as follows: Hollow bones, from which the ends have been cut and the marrow removed, are broken into large pieces and digested for two days with a 5-per cent, sodium-carbonate solution, then brushed, and washed repeatedly with water with which they are left in contact each time for several hours. Then break the bones hi to pieces the size of a nut, and treat with diluted hydrochloric acid, 8 litres of which contain 1 litre of commercial hydrochloric acid, until they * SIEMAND, on treating each 10 grm. of the substance for forty-eight hours with 200 c.c. of water and evaporating 100 c.c. of the filtrate, obtained the following residues: From blosse, 0*25; from extracted bones, 0-008; and from "hornschlauche " (horn cartilage) 0-004 grm. The aqueous solutions of all three substances, however, contained no substances appre- ciably oxidizable by potassium permanganate. 770 DETERMINATION OF COMMERCIAL VALUES. [ 279. become soft. Then wash them with water until nearly free from acid, and grind them while moist in a small mill.* In order to remove the last traces of calcium salts and also ferric oxide, digest the comminuted mass repeatedly with diluted (1:20) hydrochloric acid, then thoroughly wash first with rain- or spring-water until no longer acid, and then with distilled water, then press, and dry. It is convenient to sort the preparation by sifting, and using each size separately. b. Horn Cartilage (the bony, vascular nucleus of cattle horn). This is freed from calcium salts in the same manner as the bone- preparation. When softened by water, the preparation appears cartilaginous. Instead of these substances, hide prepared for tanning may, as already remarked, also be employed, but the former are pref- erable. The prepared hide is best obtained from a tannery; for its further preparation, see below, Method B. II. PROCEDURE. 1. Prepare an aqueous solution of the tanning material suitable for tannin determination, taking care to take sufficient of the sub- stance, the tanning principle of which is to be brought into solu- tion, to afford a solution containing about 0-5 to 1 grm. of the tanning principle per litre. For this purpose, the following quantities of the substances mentioned should be weighed off: Pine bark from about 10 to 15 grm. Oak bark " " 8 to 10 " Spanish chestnut wood " " 6 to 8 " Valonia " " 3 to 4 " Sumach " " 6 to 8 " Extract the vegetable substance by boiling at least four times with water, and then make up the liquid to one litre. In the case of wood, as, for example, Spanish chestnut, care must be taken * According to experiments made in my laboratory the object is better attained by grinding the dry preparation. 279.] DETERMINING TANNIN. 771 that the boiling is continued each time for at least 15 minutes, because woods are more difficult to extract. In the case of extracts, the tanning-matter content of which is, as a rule, approximately known, it is quite easy to determine the quantity to be dissolved in one litre of water in order to yield a liquid of the concentration named. If the liquid extracts are clear, or if they become clear on standing, they may be used at once for the determination; if otherwise, a sufficient quantity must be passed through a dry filter. If the turbid extract is used, somewhat higher results are obtained, and these I consider inaccurate because the suspended organic matters also use up some potassium permanganate.* If the liquid extracts also contain pectinous substances, these must first be separated if correct results are to be obtained, because, as JULIUS LOWE f first showed, these are also precipitated by the preparations which precipitate tannin (particularly hide powder, and also prepared bone and horn cartilage). To effect this pur- pose, hence, according to LOWE, evaporate the liquid extract, e.g., of the oak bark, w T hich always contains pectinous substances, with the addition of a drop of acetic acid, to dryness on a water- bath, extract the residue with strong alcohol (which dissolves the tannin but leaves the pectinous substances), evaporate the alcoholic solution on the water-bath until all the alcohol has been completely driven off, and then take up the residue with water. 2. Determine the effective value of the potassium-perman- ganate solution by means of iron or oxalic acid (see pp. 313 and 316, Vol. I). 3. Measure off 20 c.c. of the indigo solution, add 1 litre of water, place the beaker containing the liquid in a white porcelain dish, and then run in (best from a burette provided with a glass cock) the permanganate solution drop by drop in a period of about four * In experiments carried out in my laboratory, the following results, as examples, were obtained: With an oak-bark extract, using a filtered solu- tion, 26-04, as against 27-52 per cent, with an unfiltered solution of oak tannin. With an extract containing tannin, the filtered solution gave 12-53 while the unfiltered solution gave 13-66 per cent, tannin. f Zeitschr. /. analyt. Chem., iv, 368. 772 DETERMINATION OF COMMERCIAL VALUES. [ 279. minutes, and with constant stirring. The deep-blue solution gradually changes to dark-green, then light-green, and then yellow- ish-green, the last greenish tint disappearing with the addition of the next drop of permanganate solution. In order to sharply recognize the end reaction, it is advisable to add the permanganate solution towards the end very slowly in single drops. If the change from the yellowish-green color is not sharp, the indigo-carmine was not sufficiently pure, and especially not free from indigo-red. In suqh a case the solution cannot be used for accurate determina- tions. The concentration of the indigo solution is correct if 20 c.c. of it require about an equal quantity of permanganate solution; if much more or less is required, the indigo solution must be corre- spondingly diluted, or strengthened by the addition of more indigo- carmine, and then again standardized against the permanganate solution. The solution that has become yellow is reserved for comparison. 4. To 1 litre of water add 20 c.c. of the indigo solution and 10 c.c. of the tannin extract, and then run in permanganate solu- tion, timing the addition so that about four minutes are required to run in the total quantity, and until the liquid exhibits a pure yellow color exactly like that obtained by standardizing the indigo solution against permanganate solution in 3. If in this experiment considerably more than 30 c.c. permanganate solution have been used, the quantity of tannin extract taken was too large. In this case repeat the experiment with a correspondingly smaller quantity, and ascertain the quantity of permanganate solution corresponding with the total tannin and non-tannin, by deducting from the total the permanganate solution required for the indigo. 5. Introduce 5 grm. of the extracted bone, or horn cartilage, into a flask, and moisten the substance with exactly 50 c.c. water, then add 50 c.c. of the liquid containing the tannin, stopper, and allow to stand for twenty-four hours, frequently shaking; then filter off a little of the liquid in order to make certain that all the tannin has been precipitated. This is effected by concentrating the filtered liquid by evaporation, and adding a clear solution of glue or gelatin saturated with sodium chloride; if a precipitate forms, 279.] DETERMINING TANNIN. 773 add to the contents of the flask a further quantity of extracted bone or horn cartilage, and continue the digestion until the object is attained. When all the tannin is precipitated, filter, measure off 40 c.c., corresponding with 20 c.c. of the liquid containing tannin, add 20 c.c. of the indigo solution and 1 litre water, and then permanganate solution as above, until the liquid has a pure, yellow color. In this manner ascertain the quantity of perman- ganate used up by the non-tannins in 20 c.c., and by halving that required for 10 c.c. of the extract; and from the difference ascertain the permanganate corresponding with the tannin. An example will make this clear 10 grm. chestnut wood gave 1000 c.c. extract. 100 c.c. permanganate solution corresponded with 0-1819 crystallized oxalic acid. 20 c.c. indigo solution required 21 c.c. permanganate solution. 20 c.c. indigo solution plus 10 c.c. chestnut-wood extract re- quired 32 c.c. permanganate solution. On deducting from this the 21 c.c. corresponding with the indigo solution, there remained 11 c.c. for the tannin and non-tannins. 5 grm. extracted bones plus 50 c.c. water plus 50 c.c. chestnut- wood extract yielded a filtrate free from tannin; and 40 c.c. of the filtrate ( = 20 c.c. of the extract) plus 20 c.c. indigo solution required 22-6 c.c. permanganate solution, hence the quantity of perman- ganate used up by the non-tannins in 20 c.c. of the extract is 22-621 = 1-6 c.c., and consequently that in 10 c.c. would be 0-8 c.c. On now deducting this 0-8 c.c. from the 11 c.c. obtained above, there remains 10-2 c.c. permanganate solution for the tannin in 10 c.c. of the extract. III. CALCULATION. NEUBAUER'S experiments have shown that 63-024 grm. crys- tallized oxalic acid (hence, also 55-9 grm. ferrous iron), and 41-57 grm. tannin decompose equal quantities of permanganate solution, and are, hence, equivalent in this respect.* If the sub- * I must mention here that the proportion here stated has been 774 DETERMINATION OF COMMERCIAL VALUES. [ 279. stances contained the same kind of tanning matter as nut galls, i.e., gallotannic acid, the tannin may be readily calculated and expressed in per cents, from the figures obtained in n, i.e., from the quantity of permanganate solution required to oxidize the tanning matter. As, however, the various tanning matters do not as a rule contain gallotannic acid, but other tannins, which are practically still unknown in a pure state, and of which it is not known in what proportions they decompose potassium per- manganate, it is therefore by a sort of tacit understanding that notwithstanding this, the tannin content of certain tanning sub- stances is calculated from the above proportion by the perman- ganate used. For instance, according to this practice, 12-24 per cent, of tannin is found in the chestnut wood in the example cited in n, according to the following calculation: 100 c.c. permanganate solution correspond to 0-1819 grin, oxalic acid, and hence, according to the proportion 63 024 : 41 57, also 0- 12 grm. tannin. 1 c.c. corresponds therefore to 0-0012 grm. tannin. To oxidize the tannin in 10 c.c. of the chestnut-wood extract there would thus be required 10-2 c.c. permanganate solu- tion, which hence corresponds with 10-2X0-0012 grm. = 0-01224 grm. tannin. But, if 10 c.c. of chestnut-wood extract contain 0-01224 grm. tannin, then 1000 c.c. would contain 1-224 grm.; and this quantity being obtained from 10 grm. chestnut wood, 100 grm. would of course contain 12-24 grm. tannin. I must repeat that this, and every analogous calculation, has no scientific basis, and that the result based on it and expressing the confirmed by ULBRICHT (Annalen der Oenologie, in, 63), and by OSER (Sitz- ungsber. der mathem.-naturwissenschaftl. Classe der k. Akademie in Wien, LXXII, 186); but on the other hand, COTTNCLER and SCHRODER (Ber. d. deutsch. chem. Gesettsch. zu Berlin, xv, 1373; Zeitschr. /. analyt. Chem., 274) have called it in question; they found the proportion to be 63-024 : 34-25. [This discrepancy has been shown by SCHRODER to be due to the different manner in which the permanganate was added in titration, NEU- BAUER employing the "drop method," while COUNCLER and SCHRODER added the solution in successive quantities of 1 c.c. with a short interval between each addition. This modification seriously affects the volume of the standard solution consumed (ALLEN, Commercial Organ. Anal., in, part 1, p. 76, P. BLAKISTON'S SON & Co., 1900).] 280.] DETERMINING TANNIN. 775 tannin present in per cents, means in fact no more than that the tannin in 100 grm. of the chestnut wood in question reduces as much permanganate as do 12-24 grm. tannin, presupposing that the calculation is based on the proportion of 63-024 of oxalic acid to 41-57 of tannin. As NEUBAUER and others have done for gallotannic acid, so has OSER * sought to determine in what proportion quercitannic acid is equivalent to oxalic acid as compared with permanganate. He found that 63 024 crystallized oxalic acid and 62 32 querci- tannic acid decolorize equal quantities of permanganate, but he does not consider the last figure to be in any way reliable. SIMAND, as the result of preliminary experiments, obtained the proportion 63-024:60-11. No comparisons are necessary to show what differences must arise when, on determining the tannin in a tanning substance, e.g., chestnut wood, NEUBAUER'S ratio, 63-024:41-57, or that of COUNCLER and SCHRODER, 63-024:34-25, or those obtained for quercitannic acid, 63 024 : 62 32 or 63 024 : 60 11, are taken as basis for the calculation; it is therefore necessary not only to state the result, but also the proportion between oxalic acid and tannin used in the calculation. B. K HAMMER'S Method.-\ 280. This method, worked out in my laboratory in 1860, affords at least with tannin solutions, and with careful manipulation, per- fectly reliable and accurate results; it is simple to perform, and adapted for both scientific and technical purposes. Compare also FR. GAUHE,J W. HALLWACHS, TH. SALZER,|| FR. KATHREINER,*[ and PROCTER and HEWITT.** NEUBAUER ft used this method for * Sitzungsber. der mathemat.-naturwissenschaftl. Classe der k. Akademie in Wien, LXXII, 186. f Journ. f. prakt. Chem., LXXXI, 159. J Zeitschr. f. analyt. Chem., in, 128. Ibid., v, 231. 1 Ibid., vii, 70. ^ Ibid., xvm, 113. ** Ibid., xvm, 115. ff Ibid., x, 2. 776 DETERMINATION OF COMMERCIAL VALUES. [ 280. determining the tannin in the solution by the aid of which he ascer- tained the equivalent proportion existing between oxalic acid and tannin with reference to permanganate solution. In the case of solutions of other tanning substances, the objec- tion against the method may be made that it is not known whether the relations between the content and the specific gravity of solu- tions of other tanning substances correspond with those found for tannin solution an objection which in all probability is not of great weight, but which can be completely met only by experimen- tally determining these relationships for solutions of other tanning substances. In solutions of tanning substances containing also pectinous matters, HAMMER'S original method must, as JUL. LOWE * showed, be modified in order to show correct results, as will be shown below. a. Principle. On determining the specific gravity of a tannin solution containing also other dissolved substances, and then removing the tannin alone, but in such a manner that the solution is not thereby diluted or otherwise changed, and on finally deter- mining the specific gravity again, the decrease in the specific gravity must be proportional to the quantity of tannin that was. present. There is hence needed but an exact table giving the re- lationships between the content and the specific gravities of tannin solutions of varying degrees of concentration, in order to be able immediately to ascertain the tannin content of the solution from the difference found. b. Requisites. To determine the specific gravity there is re- quired either a pyknometer (p. 765 this volume), or a fine hydrom- eter indicating either the specific gravities from 1-0000 to 1-0201, or the percentages of tannin corresponding with these specific gravities for pure aqueous solutions of tannin (see table below) . To remove the tannin from its solutions, HAMMER recommended finely comminuted hide powder, the so-called "blosse," made from hide prepared for tanning. The prepared hide is first exhausted by washing with water, then stretched on a board, dried at a gentle heat, and reduced by means of a rough file to a coarse powder, * Zeitschr. f. analyt. Chem., iv, 368. 280.] DETERMINING TANNIN. 777 which is then preserved in well-stoppered flasks. Instead of the hide powder, the preparations described on pp. 769 and 770 this volume can be used and in fact with better results i.e., the glue-yielding tissue of the bones, or the horn cartilage, as these give up less soluble matter to water than hide powder does (compare foot-note, p. 769). 4 parts of hide powder, prepared bone, or horn cartilage suffice to remove 1 part of tannin from a fluid. In using it, a weighed quantity of the preparation is soaked in water and then expressed in order that the adhering water may not noticeably dilute the solution with which the preparation is to be brought into contact. If it is desired to entirely eliminate the slight source of error occasioned by this water, the expressed preparation may be again weighed in order to ascertain the quantity of water taken up, and which may be subsequently taken into account.* The relations between the tannin content and specific gravity are shown in the table on p. 778, which, as heretofore, must serve also for solutions of other tanning matters until tables for these are specially prepared. c. Procedure. Care must be taken that the tannin to be deter- mined is obtained in a clear and not too dilute solution. Hence first boil barks or the like, in comminuted form-, with water, and then completely exhaust them in a percolator ; triturate inspissated vegetable juices with water in a mortar, filter through linen, and thoroughly wash the residue. From 1 part of the substance pre- pare about 10 parts of solution. If, after complete exhaustion of the substance, the solution is too dilute, it must be concentrated by evaporation. Care must be taken to obtain from about 200 to 500 c.c. of solution of a suitable degree of concentration. If the extract contains pectinous substances, these must first be removed; * TH. SALZER (Zeitschr. f. analyt. Chem., vii, 71) obtained results that did not appreciably vary on treating the same tannin solution once with hide powder dried at 100, and again with the hide powder moistened and gently pressed. By employing hide powder dried at 100, and carefully washing it after it had taken up the tannin, collecting on a double filter, drying at 100, and again weighing, he obtained from the increase in weight a (satisfactorily concordant) means of controlling the value obtained by taking the specific gravity. 778 DETERMINATION OF COMMERCIAL VALUES. [ 280. for this purpose use JUL. LOWE'S method, described on p. 771 this volume. Percentage of Tannin. Specific Gravity at 15. Percentage of Tannin. Specific Gravity at 15. Percentage of Tannin. Specific Gravity at 15. 0-0 1-0000 1-7 1-0068 3-4 1-0136 0-1 1-0004 1-8 1-0072 3-5 1-0140 0-2 1-0008 1-9 1-0076 3-6 1-0144 0-3 1-0012 2-0 0080 3-7 1-0148 0-4 1-0016 2-1 -0084 3-8 1-0152 0-5 1-0020 2-2 0088 3-9 1-0156 0-6 1-0024 2-3 0092 4-0 1-0160 0-7 1-0028 2-4 0096 4-1 1-0164 0-8 1-0032 2-5 -0100 4-2 1-0168 0-9 1-0036 2-6 0104 4-3 1-0172 1-0 0040 2-7 0108 4-4 1-0176 1-1 -0044 2-8 0112 4-5 1-0180 1-2 -0048 2-9 0116 4-6 1-0184 1-3 -0052 3-0 0120 4-7 1-0188 1-4 0056 3-1 0124 4-8 1-0192 1-5 -0060 3-2 -0128 4-9 1-0196 1-6 0064 3-3 -0132 5-0 1-0201 Now weigh the prepared tannin solution. To simplify the cal- culation, it is convenient to make up the weight of the liquid to a round number of grammes by adding water; then mix uniformly and determine the specific gravity by a pyknometer or hydrom- eter. If the latter is used, care must be taken that the cylinder is either dry or has been rinsed off with a small quantity of the liquid to be tested ; further, that no air-bubbles adhere to the float ; and that when reading off the eye is brought to the level with the lower border of the meniscus of the liquid. Now weigh off in a dry flask, or in one rinsed out with the tannin-containing liquid, somewhat more of the tannin solution than is required to fill the pyknometer or the cylinder used with the hydrometer, and add 4 times the quantity of hide powder, pre- pared bone, or horn cartilage required for the tannin found as present from the specific gravity of the liquid, cork the flask, vig- orously shake for some time, and then set aside for 24 hours, with occasional shaking.* The weighing of the precipitant and the * According to HAMMER the precipitation of the tannin is already com- plete after shaking a short time ; the experience gained in using the modified 280.] DETERMINING TANNIN. 779 liquid to be precipitated need but be approximately made. Now filter the liquid, freed from its tannin, through a cloth into the cylinder of the hydrometer, or the pyknometer, and again deter- mine the specific gravity. If the hydrometer was graduated to show tannin per cents., the difference between the two readings will give directly the tannin content of the solution examined; if, on the other hand, the hy- drometer gives but the specific gravity, or if this has been ascer- tained by means of the pyknometer, add 1 to the difference between the two specific gravities, and from the number so obtained find the corresponding tannin percentage from the table. This being known, the weight of the tannin in the entire quantity of the solu- tion, i.e., in the quantity of the substance examined, may be found by a simple calculation. d. Example. 500 grm. solution were obtained from 40 grm. oak bark. At 15 the hydrometer showed the liquid to contain apparently 1 7 per cent, of tannin, with a specific gravity of 1 0068. 200 grm. of the liquid were now weighed off, this quantity appar- ently- containing 3 4 grm. tannin (1 7 per cent.) ; to it 4 times its quantity or 13 6 grm. of hide powder were added after having been soaked and then expressed. After filtration, the hydrometer showed the specific gravity of the liquid to be 1 0032, correspond- ing to a tannin content of 0-8 per cent. The difference between the two determinations, 1-7 and 0-8, is 0-9, hence the solution contains exactly 0-9 per cent, tannin. But if 100 grm. contained 0-9 grm., then the 500 grm. contained 4-5 grm. tannin; and as this was obtained from 40 grm. oak bark, it follows that the latter con- tained 11-25 per cent. Like results are of course obtained when the calculations are based upon the difference between the specific gravities. This difference amounted to 1-0068- 1-0032 = 0-0036; on adding 1, we get 1-0036, and this, from the table, which see, corresponds to 9 per cent. LOWENTHAL method, however, makes a more prolonged action appear advisable. 780 DETERMINATION OF COMMERCIAL VALUES. [ 28L C. Gravimetric Modification of HAMMER'S Method. 281. As may be readily seen, tannin may be also gravimetrically determined by using HAMMER'S principle. This modification was first proposed by A. MUNTZ and RAMSPACHER,* and more recently by SiMAND.f The latter employed it as a means of controlling or verifying the relations which tannin and quercitannic acid, and oxalic acid or ferrous iron in solution, respectively bore to potas- sium permanganate. To carry out the method, first prepare the extracts as in HAM- MER'S method; and they must also, like those of the latter, be free from pectinous substances. Evaporate a suitable quantity (SIMANI> employs 100 c.c.) in a weighed platinum dish, dry the residue at 100 to constant weight, weigh, incinerate, deduct the mineral constituents from the residue, and thus ascertain the total quan- tity of dissolved organic substances. Further, add to a like quantity of the tannin-containing extract the required quantity of horn cartilage (vide supra), and allow to act for 24 hours in order to precipitate all the tannin. At the end of this time, filter, wash thoroughly, evaporate the filtrate as above, dry at 100, incinerate, deduct the mineral constituents from the total weight of the residue, ' and thus ascertain the weight of the substances not removed by the horn cartilage (non-tannins). Lastly, on deducting the latter from the total tannin and non- tannins first obtained, the difference will give the weight of the tannin. D. Other Methods of Determining Tannin. As it is not the purpose of this work to detail all the numerous methods proposed or employed formerly, as well as in recent times, I would refer regarding them to the Zeitschrift fur analytische Chemie, I, 103, 104; n, 137, 287, 419; in, 484; v, 1, 455, 456; x, * Compt. rend., LXXIX, 380; Zeitschr. f. analyt. Chem., xiu, 462. j* DINGLER'S polyt. Journ., CCXLVI, 41; Zeitschr. f. analyt. Chem., xxn, 598. 281.] DETERMINING TANNIN. 781 1; xin, 243; xiv, 204; xv, 112; xvi, 123; xvin, 112; and xxi, 415, 552. Critical, or at least partly critical, investigations of the methods of determining tannin have been made, and the results published, by FR. GAUHE (Zeitschr. f. ancdyt. Chem., in, 122); HALLWACHS (ibiti., v, 231); TH. SALZER (ibid., vn, 70); C. O. CECH (ibid., vii, 130); PH. BUCHNER (ibid., vn, 139); NEUBAUER (ibid., x, 1); GUNTHER (ibid., x, 354); KATHREINER (ibid., xvni, 113); and others. [At a meeting of the American Association of Official Agricul- tural Chemists, held hi Washington, U. S. A., on November 16, 1900, a paper was read by the referee of the Association, Mr. OMA CARR, giving the following particulars of experiments which had been carried out with a view to the improvement of the official method of the association for the analysis of tanning materials.* Soluble Solids. The conclusions drawn from experiments as to the best method of determining the soluble solids are (1) that if the filtration is performed without the addition of an "assistant," the insoluble matters are not entirely removed; (2) that the absorption of the tannin by the filter-paper is largely dependent upon the length of time the solution is hi contact with the paper; (3) that acetic acid modifies the basic nature of the filter-paper; (4) that it is possible to secure concordant results by the addition of lead acetate and acetic acid, afterwards filtering through paper; (5) that as the method stands it gives low figures for oak wood, and high for quebracho, and this will hold good hi comparison with any materials so differing. Hide Powder. The Vienna powder generally used because of its close adherence to the limits of insolubility and absorption adopted by the association, has recently shown such a wide depar- ture from these limits as to fall wholly without the range of allow- able variation; it has also been noticed that many of the samples of Vienna hide powder recently received contained small quantities of acid. * Journ. Soc. Chem. Ind., 1901, p. 286; Leather Manufacturer, Dec. 1900, 241-248. 782 DETERMINATION OF COMMERCIAL VALUES. [ 281. It will be seen that inasmuch as the moisture content of the wet pressed hide is variable with the physical condition thereof, a definite statement of the dry hide present in the wet cake must be made; the results are concordant for any definite quantity of powder, but the fineness of some powders permits great loss in squeezing, and the actual dry powder present in the solution is thereby variable. Volume of Solutions for Drying. Owing to the sensitiveness of tanning materials to heat and oxidation whilst drying, it is believed that the use of volumes yielding 4 to 5 grm. of residue would give more concordant results. The experience of the referee is that residues of 0-4 grm. may be dried to nearly constant weight on the steam-bath in five hours, afterwards drying in an air- or water-oven for half an hour; it is therefore to be recommended to substitute 50 c.c. wherever 100 c.c. are stipulated in the official method. Fairly concordant results were obtained by eight different members of the association making analyses of the same samples of oak-wood and quebracho extract, the analyses being done by the official method of the association. The quebracho is a severe trial on the accuracy of the method owing to the large amount of tanning matter present and the extreme fineness of the insoluble matter; variations in the amount of non-tanning matters may be largely attributed to variations in the character of the hide powder used. It was eventually resolved that the following be the amended method of the association: 1. Preparation of Sample. Barks, woods, leaves, dry extracts, and similar tanning materials should be ground to such a degree of fineness that they can be thoroughly extracted. Fluid extracts must be heated to a temperature of 50 C., well shaken and allowed to cool to room temperature. 2. Quantity of Material. In the case of barks and similar materials, use such quantity as will give about 0-8 grm. of total solids per 100 c.c. of the solution, and extract in SOXHLET or similar apparatus at steam heat for non-starchy materials. For canaigre 281.] DETERMINING TANNIN. 783 and substances containing like amounts of starch, use a tempera- ture of 50 to 55 C., until near completion, finishing the extraction at steam heat. In the case of extracts, weigh such quantity as will leave a residue of 0-8 grm. on evaporation of 100 c.c. of the solution, dissolve in 800 c.c. of water at a temperature of 80 C., allow to stand 12 hours and make up the quantity to 1 litre. 3. Moisture. Place 2 grm., if it be an extract, in a flat-bot- tomed dish not less than 6 cm. hi diameter, add 25 c.c. of water, warm slowly until dissolved and continue the evaporation until dry. Ah 1 evaporations called for after evaporation to dryness on the water-bath, shall be done by one of the following three methods, the soluble solids and non-tanning residues being dried under as nearly identical conditions as possible. (a) For 24 hours at a temperature of 100 C. (6) For 8 hours at 100 to 110 C. in air-oven. (c) To constant weight in vacuo at 70 C. 4. Total Solids. Shake the solution, and without filtering immediately remove 50 c.c. with a pipette, evaporate in a weighed dish, and dry ; the dishes should be flat-bottomed and not less than 6 cm. in diameter. 5. Soluble Solids. Filtration shall take place through double- pleated filter-paper, the first 150 c.c. passing through shall be re- jected, and the 50 c.c. next passing through shall be collected, evaporated, and dried. When a clear filtrate may not otherwise be obtained, the use of 10 grm. of barytes previously washed in a portion of the solution is permissible. Evaporation during filtra- tion must be guarded 'against. 5a. Optional Method. (a) To 100 c.c. of the solution add 10 c.c. of a solution of lead acetate, 4 grm. per litre, adding the reagent drop by drop from a burette and stirring meanwhile. Now add 10 c.c. of a solution of acetic acid, 36 grm. of glacial acid per litre, stirring. Throw on double-pleated filter, until clear reject, and evaporate and dry 50 c.c. (b) On another portion of 100 c.c. repeat the foregoing, except that 20 c.c. of lead-acetate solution shall be used. 784 DETERMINATION OF COMMERCIAL VALUES. [ 281. Residue from (a) shall be multiplied by 1-2, and from (6) by 1-3, to bring back to the original 100 c.c. Add to the corrected weight of the residue from (a) the difference between (a) and (b), and calculate the found residue to soluble solids. This corrects for dilution and removal by lead. 6. Non-tanning Matters. Prepare 20 grm. of hide powder by washing in a No. 7 beaker with from 800 to 1,000 c.c. of water, stir well and let stand one hour, filter the magma through linen, squeeze thoroughly by hand, remove as much moisture as possible by means of a press, weigh the pressed hide, and take approximately one-fourth for moisture determination. Weigh this portion care- fully and dry to constant weight. Weigh the remaining three- quarters, which must contain between 12 and 13 grm. of dry hide, add to 200 c.c. of the solution and shake 10 minutes. Throw on a funnel with cotton plug in stem, return until clear, evaporate 50 c.c. and dry. The weight of this residue must be corrected for the moisture contained in the wet pressed hide. The shaking must be done in some form of mechanical shaker. The machine used by druggists, and known as the milk-shake, is recommended. 7. Tanning Matters. The amount of these is shown by the difference between the soluble solids and the non-tannins. 8. Testing the Hide Powder. (a) Shake 10 grm. of powder with 250 c.c. of water for five minutes, strain through linen, and squeeze the magma thoroughly by hand; repeat this operation three times, pass the last filtrate through paper until clear, evapo- rate 50 c.c. and dry; if this residue amounts to more than 5 mgrm., the powder must be rejected. (6) Prepare a solution of pure gallotannic acid by dissolving 5 grm. in 1,000 c.c. of water. Determine the total solids by evapo- rating and drying 50 c.c. of this solution. Treat 200 c.c. of this solution with hide powder, exactly as in paragraph 6. The powder must absorb at least 95 per cent, of the total solids. The gallotannic acid used must be completely soluble in water, acetone, alcohol, and acetic ether, and shall not contain more than 1 per cent, of substances not removed by digesting with yellow mercuric oxide on the steam-bath for two hours. 282.] DETERMINATION OF ANTHRACENE. 785 (c) Any analysis made with a powder which does not fulfil the conditions of the preceding paragraphs shall not be reported as by this method. 9. Testing the Non-tanning Filtrate. (a) For tannin. Test a small portion of the clear non-tanning filtrate with a few drops of a 1-per cent, solution of NELSON'S gelatin, A cloudiness indicates the presence of tannin, in which case repeat 6, using 25 instead of 20 grm. of powder. (6) For soluble hide. To a small portion of the clear non- tannin filtrate add a few drops of the filtered tanning solution. A cloudiness indicates the presence of soluble hide, hi which case repeat 6, giving the powder a more thorough washing. 10. Temperature of Solutions. The temperature of solutions shall be between 16 and 20 C. when measured and filtered. All dryings shall be in flat-bottomed dishes not less than 6 cm. in diameter. SCHLEICHER and SCHULL'S filters No. 590, 15 cm., shall be used for all nitrations. TRANSLATOR.] IV. DETERMINATION OF ANTHRACENE. 282. Since the production of alizarin from anthracene has now become an exceedingly large industry, the determination of anthra- cene in crude anthracene has become a frequently occurring prob- lem in chemical laboratories. The method first worked out by E. LUCK * in the laboratory of MEISTER, Lucius, and BRUNING, of Hochst, and published by him in 1873, and based upon the con- version of anthracene into anthraquinone, has gradually devel- oped into that published by MEISTER, Lucius, and BRUNING in 1876,f and now generally employed. I consider it proper to here describe the method, and to supplement the description with such details as to modifications as the experience gained in my laboratory has shown to be of value. * Zeitschr. f. analyt. Chem., xii, 347; and xin, 251. f Ibid., xvi, 61. 786 DETERMINATION OF COMMERCIAL VALUES. [ 282. 1. Above all it is of most importance that the sample be homo- geneous, and that care be taken in preparing the sample that this suffers no change by the evaporation of adhering volatile hydro- carbons. To effect this, empty the crude anthracene into a dish, mix it quickly, using a spatula or piece of cardboard, and crushing any large lumps, and then transfer it to a glass-stoppered flask. The sample to be analyzed must be weighed in a closed tube, which must be reweighed after the anthracene has been emptied out. About 1 grm. (0-97 1-03 grm.) is required for each analysis. 2. Introduce the weighed anthracene into a flask of about 500 c.c. capacity, and cover it with 45 c.c. glacial acetic acid. The flask should be provided with a twice-perforated stopper, one hole bear- ing a funnel tube fitted with a glass cock and terminating below in a narrow opening, while the other aperture is fitted with a glass tube bent at an obtuse angle and connected with a reflux con- denser. Now heat the contents of the flask to boiling, and keep it boiling while introducing through the funnel tube a solution of 15 grm. chromic acid * in 10 c.c. glacial acetic acid and 10 c.c. water, allowing the solution to drop in slowly so that the operation will require two hours for completion. When all the chromic acid has been added, keep the contents of the flask boiling for another two hours. 3. Allow the flask to stand for 12 hours, then add 400 c.c. cold water to its contents, and allow to stand for 3 hours longer. Now collect the precipitated anthraquinone on a filter, wash it first with cold water until the washings are no longer acid, then with about 200 c.c. boiling diluted 1-per cent, caustic-potassa solution, and finally with pure, hot water until the washings are no longer alkaline. 4. Now rinse the anthraquinone by means of a fine but strong stream of water into a platinum dish the weight of which is approx- imately known, spreading open the filter on a glass plate in order to enable the anthraquinone to be more readily removed; then evaporate on a water-bath, dry at 100, weigh the still impure anthraquinone approximately, cover it with ten times its weight * This must be prepared according to FRITZSCHE'S method, using pure sulphuric acid. 283.] INORGANIC CONSTITUENTS OF PLANTS. 787 of fuming sulphuric acid of 68 Be". = 1-86 sp. gr., and heat for 10 minutes in the water-oven (p. 58, Fig. 31, Vol. I), the water in which must be maintained briskly boiling. 5. Pour the anthraquinone solution into a shallow porcelain dish, and allow it, and also the platinum dish in which small por- tions of the solution have been retained, to stand in a humid place for 12 hours in order to attract moisture. At the end of this time rinse out the platinum dish with 200 c.c. cold water into the porcelain dish, filter off the anthraquinone, wash it first with cold water until the washings are no longer acid, then with about 200 c.c . boiling 1-per cent, caustic-pot assa solution, and lastly with hot, water until the washings are no longer alkaline. 6. Now rinse the washed anthraquinone into a platinum dish, evaporate on a water-bath, and dry the residue at 100 to constant weight; then carefully heat the dish so that the anthraquinone completely volatilizes, but without taking fire, and again weigh the dish with the residual ash and carbon. The difference between the weighings gives the weight of the anthraquinone, and this multiplied by 0-856 gives the anthracene. [Anthracene, C 14 H lt = 178 08 ; anthraquinone, C 14 H 8 O 2 = 208 064.] III. DETERMINATION OF THE INORGANIC CONSTIT- UENTS OF PLANTS * 283. Since the researches in agricultural chemistry have established the fact that every plant requires for its development certain * As the determination of the inorganic constituents of animal substances is less frequently undertaken than the determination of those of plants, since they are required almost entirely for scientific rather than technical purposes, 1 have omitted a detailed description in the text. I would merely point out, howeveJ, that, in general, the same methods of procedure may be adopted as given in ihe text. According to H. ROSE, the substances which fuse are first heated, in order to incinerate them, in a platinum dish, with stirring, until they have lost their fluidity, and the greater part of the organic matter is decomposed. The almost completely carbonized residue is next transferred to a platinum crucible (at this stage even a clay crucible may be employed without disadvantage) which is well covered, and then heated 788 INORGANIC CONSTITUENTS OF PLANTS. [ 283. inorganic constituents, a strong desire has arisen to learn what inorganic constituents are required for the individual plants, more particularly for cultivated plants and weeds, as these enable con- clusions to be formed regarding the constituents of the soil. This object it was first sought to reach by analyzing the ash obtained by incinerating the entire plant or particular parts of it, e.g., the seeds. As it has been found, however, that the object is not fully accomplished by this means, because during the incineration of the plant several of the inorganic constituents must be lost, while others may be lost, the ash analysis, in order to fully answer the question, must be supplemented by separate determinations of the individual elements, as the methods otherwise employed have so far not sufficed to accomplish the object.* to dull redness. Burn the charcoal so obtained with the aid of spongy platinum. STRECKER'S method (described in the text) of incinerating with the addition of baryta, is also very well adapted for animal substances. The incineration may be particularly well effected according to SLATER (Chem. Gaz., 1855, 53) by mixing the substance with pure, dry, finely pow- dered barium dioxide and igniting. STRECKER calls attention in his paper (Annal. d. Chem. u. Pharm., LXXIII, 370) to the fact that the ashes of animal substances frequently contain considerable quantities of cyanates. These are most simply decomposed by moistening the ash with water and then gradually heating to redness. As a rule, only a single moistening is necessary in order to convert the cyanates into carbonates. In order to determine the chlorine, incinerate the animal substance with sodium carbonate, using 1-5 to 2-5 grm. for every 50 grm. of the organic substance (BEHAGHEL VON ADLERSKRON, Zeitschr. f. analyt. Chem., XH, 405). Finally, I would point out that in order to accurately determine the total phosphorus and sulphur, those methods must be employed which are adapted for the determination of phosphorus and sulphur in organic substances, and which are de- scribed in 188 and 189. Special details regarding the analysis of animal substances are given by F. VERDEIL in his paper on the analysis of the ash of blood of man and many animals (Annal. d. Chem. u. Pharm^, LXIX, 89; Pharm. Centralbl., 1849, 198; LIEBIG and KOPP, Jahresber., 1849, 598); and also in that of FR. KELLER on the ash of meat bouillon and meat (Annal. d. Chem. u. Pharm., LXX, 91; Pharm. Centralbl. f 1849, 581; LIEBIG and KOPP, Jahresber., 1849, 599). * CAILLAT states that on treating herbaceous plants (clover, lucern, sanfoin) with diluted nitric acid, he has succeeded in extracting the in- organic constituents so completely that the easily combustible residual mass from 10 grm. of vegetable matter yielded but 18 to 22 mgrms. of ash consisting of silica and ferric oxide. This treatment, he states further, yields a larger 283.] ASH ANALYSES. 789 In the following chapter the Ash Analysis will be given under A, while under B will be detailed the Supplementary Determina- tions, and under C the Arrangement of the Results. A. ASH ANALYSES. As, according to the researches heretofore made, the ashes of plants contain but a limited number of acids and bases, methods which are generally applicable may be devised for their analysis; as these offer many peculiarities, and are frequently employed, only those will be here described which appear to me to be the simplest and best. A comprehensive critique of the numerous widely differing methods proposed cannot be given here, as it is beyond the scope of this work. The substances which are generally found in larger quantities in plant ashes are as follows : Bases: Potassium, sodium, calcium, magnesium, iron (as Fe 2 O 3 ), and manganese (as Mn 3 O 4 ). Adds, or Substances Capable of Replacing Them: Silicic acid, phosphoric acid, sulphuric acid, carbon dioxide, and chlorine. Besides these there are sometimes found oxides of lithium, rubidium, strontium, barium, and copper; fluorine; occasionally alumina (e.g., in the ashes of the Lycopodiacece, in comparatively large quantities); iodine, bromine, cyanides, and cyanates (only in the ash of highly nitrogenous substances); boric acid, sulphides, and also traces of zinc oxide or of other oxides of the heavy metals. Of the substances here mentioned, most are unquestionably original constituents of the plants; many again may have been present as such, or they may have been formed during incineration ; lastly quantity o( inorganic constituents, more particularly sulphuric acid, than can be obtained by incinerating the plant (Compt. rend., xxxix, 137; Jahresber. von LIEBIG und KOPP, 1849, 601). RIVOT, BEUDANT, and DAGUIN (Compt. rend., 1853, 835; Journ. f. prakt. Chem., LXI, 135) prefer destroying the organic matter by treatment with potassa lye and passing in chlorine. W. KXOP'S experiments may also be mentioned here; he sought to ascer- tain the mineral substances required for the plant nutrition by allowing plants to grow in solutions containing known quantities of inorganic sub- stances and subsequently determining the quantities left in solution. 790 INORGANIC CONSTITUENTS OF PLANTS. [ 284. some certainly owe their origin to that destructive process. Thus the sulphates, and by exception even the carbonates, found in the ash may have been original constituents of the plants, but they may also have been formed by the destruction of salts of organic acids and by the combustion of the unoxidized sulphur present in every plant ; thus the metallic sulphides are formed by the action of the carbon on sulphates with an insufficient air supply, the cyanides of the metals result from heating nitrogenous carbon with alkali carbonates, while the cyanates result from the oxidation of the cyanides, etc. The variety of these constituents, and the fact that some of them are as a rule present only in very small quantities, make it a by no means easy task to devise methods that will be generally applicable, the more so as the method sought must unite accuracy with some degree of despatch. I will first treat of the preparation of the ash for the purpose of analysis, and then of the analysis itself. I. PREPARATION OF THE ASH. 284. In preparing the ash the following conditions must be fulfilled : 1. The plants or parts of plants to be incinerated must be dry, suitably comminuted if necessary, and free from all adhering im- purities. 2. The ash must be as free from unconsumed particles as possible. 3. During the process of incineration, loss of essential constit- uents must be avoided so far as possible. To fulfil the first condition, the plants or parts of the plants must therefore be carefully selected, cleaned, and, if necessary, cut up and dried. It is not always possible to remove adhering sand or clay by simple rubbing or brushing, more particularly from small seeds. For cleaning the latter, H. ROSE gives the follow- ing directions: Treat the seeds in a beaker with not too large a quantity of water, stir well for a moment with a glass rod, and then transfer to a coarse sieve in order to allow the fine sand to 284.] INORGANIC CONSTITUENTS OF PLANTS. 791 pass through while retaining the seeds. Repeat this operation several times, taking care, however, never to leave the seeds long in contact with water, otherwise soluble salts may be extracted from them. Then transfer the seeds to a linen cloth, and rub them between its folds, whereby the adhering fine sand is removed. Seeds cleaned in this manner are almost entirely free from foreign admixtures. Then dry them so as to be ready for incineration. The jumping of the seeds during heating may be prevented by first crushing them. When cutting plants, it is of course necessary to employ a perfectly clean knife or pair of scissors; and when drying, care must be taken to protect the plant parts from dust and from loss of any sap. To fulfil the second and third conditions, the main thing to be borne in mind is that the incineration must be effected at the lowest possible temperature (at a dull red heat) ; and with neither too plentiful nor too little a supply of air. With too strong a current of air particles of the ash may be readily carried away, while if insufficient, the incineration takes too long, and reductions take place more easily. If the ignition is too strong, not only do all the chlorides, carbonates, and phosphates of the alkalies fuse and greatly impede the combustion by enveloping the carbon, but the alkali chlorides and carbonates * may be easily volatilized by the heat; and even phosphoric acid may be lost because, as ERD- MANN first showed, acid phosphates of the alkalies when ignited with carbon, are converted into neutral salts, with reduction and volatilization of a part of the phosphorus. A loss of chlorine, too, cannot be avoided by careful incineration, as the acid products of the dry distillation of the organic substances expel hydrochloric acid compare H. RosE,f R. WEBER,! and BEHAGHEL VON AD- LERSKRON. Although loss of chlorine and phosphoric acid may * Comp. LANDOLT, Zeitschr. f. analyt. Chem., vn, 20; A. VOGEL, iUd. 9 vii, 149. f POGGENDORFF'S Annal., LXXX, 113. J Ibid., LXXXI, 407. Zeitschr. /. analyt. Chem., xn, 405. 792 PREPARATION OF THE ASH. [ 284. be perfectly prevented by proper methods of incineration, and if necessary, by an admixture of carbonate of sodium, barium or calcium to the substance to be incinerated, this is not the case with carbon dioxide. The determination of carbon dioxide in the ash will therefore never afford any certain conclusions regarding the constituents of the vegetable, as it is incorrect to suppose that the presence of carbonates in the ash of a plant, which itself con- tains no carbonates, may be regarded as pointing to the presence of salts of organic acids in the plant, since alkali carbonates are readily formed by the action of nitrates on carbon, or by the action of the acid products of the dry distillation of organic substances on alkali chlorides and subsequent decomposition of the alkali compound so formed; furthermore, as STEECKER has shown, alkali carbonates are formed when orthophosphoric acid is ignited with a large excess of sugar or sugar-charcoal, while at the same time alkali pyrophosphates are formed. Considering not only this fact, but that further the reverse action takes place, i.e., alkali pyro- phosphates, when strongly ignited with carbonates, are converted into orthophosphates, it follows that the presence of orthophos- phates or pyrophosphates in an ash may also depend upon the manner in which the latter has been prepared. The conclusions which may be drawn from the presence of sulphuric acid in an ash are also very inaccurate, even when the incineration is effected with the addition of an alkaline earth, as plants contain, in the first place, sulphuric acid in the form of sulphates, and, secondly, as sulphur organically combined, par- ticularly in the proteids. If the incineration is properly performed, the whole of the sulphates originally present may, it is true, be obtained, but certainly in many cases, the quantity will be increased by such other sulphates as were formed during the incineration. The sulphuric-acid content of an ash can, therefore, never serve to afford a conclusion even as to the approximate quantity of sulphur present in the plant.* I now proceed to a description of the methods which may be chosen for effecting the incineration. * Compare MAYER, Annal. d. Chem. u. Pharm., ci, 136 and 154. 284.] PREPARATION OF THE ASH. 793 1. Incineration in a Muffle or Crucible. Incineration in a muffle, which was first recommended by ERDMANN,* and later by STRECKER,! has almost entirely super- seded the older method, in which the substance was burned in obliquely fixed Hessian crucibles. The muffles employed are made of the same material as Hessian crucibles, and are about 25 cm. long, 17 cm. wide, and 12 cm. high; these are inside measurements. The muffles are placed in furnaces; they have no draught chimney, and the openings are loosely closed with perforated covers. The air circulation so obtained suffices for the complete combustion of the carbonized substance. a. First dry about 100 grm. of the substance to be incinerated, at 100 or 110. Succulent roots or fleshy fruits should be cut up and laid on glass plates for this purpose. Weigh the dried substance, then place it in a shallow platinum or porcelain dish (better still in a shallow platinum or porcelain capsule just fitting into the muffle), insert it in the muffle, and heat the latter gradually. As soon as pyroligneous products are no longer evolved, slightly increase the heat, but not beyond a very faint red heat not visible by daylight. At this temperature, which is insufficient to fuse either sodium chloride or sodium pyrophosphate, the carbon burns off with feeble incandescence, and twelve hours suffice to obtain sufficient carbon-free ash for analysis. Substances which are not adapted for this mode of incineration should first be car- bonized in a large, covered platinum or even Hessian crucible, at a low red heat, and the carbonized mass then burned in the muffle. As a rule, it is inadvisable to stir the mass during incinera- tion, because this reduces the porosity of the mass. This method, according to STRECKER, occasions no loss of sodium chloride by volatilization. When the combustion is completed, reconvert any alkalies or alkaline earths formed from the carbonates by loss of carbon * Annul, d. Chem. u. Pharm., LIV, 353. f Ibid., LXXIII, 366. 794 INORGANIC CONSTITUENTS OF PLANTS. [ 284. dioxide, so far as possible, into neutral, anhydrous carbonates, weigh the ash obtained, triturate it, mix, and then transfer it to a well-closed flask. The conversion of the alkalies or alkaline earths into carbonates may be effected: (a) by moistening the ash, placing under a tubulated bell-jar, passing carbon dioxide through the tubulure, and allowing to stand for some time, repeating the operation if necessary, after stirring the ash; or (/9) by repeatedly evaporating the ash on the water-bath, with carbonic-acid water or a solution of ammonium carbonate. Finally dry, and heat moderately until all the water has been expelled. In this manner alkalies and lime (also baryta, in the case of an ash prepared with barium hydroxide as in 4, see below), are converted into neutral carbonates; mag- nesia, however, is not, as when it is present as such in the ash, it will also be obtained as such, or at least partly as such, in the ash treated with carbon dioxide. 6. If the incineration is to be carried out on the small scale, an obliquely fixed platinum crucible heated by a gas- or alcohol-lamp is used. The crucible should be fitted with a slightly arched cover of burned clay, or a disk of asbestos cardboard, fitting as closely as possible at three fourths of the height into the circular opening of the crucible. A suitably inclined position may be given the apparatus by using a tripod with one short leg. If the crucible is then heated from below the entrance of air is not interfered with by the burning gases, and the incineration proceeds just as in a muffle (J. LOWE,* G. LUNGE f). As regards the further treat- ment of the ash, compare a. c. In the case of vegetables the ash of which is rich in alkali salts, particularly chlorides, and which is hence readily fusible, it is, as a rule, preferable to first carbonize the substance in a crucible by prolonged heating at the lowest temperature possible, then to treat with water to extract all the soluble salts, dry the residue, and then to incinerate in a muffle, platinum dish, or platinum * Zeitschr. f. analyt. Chem., xx, 223. f Taschenbuch fur die Soda-, etc., Fabrikation, Berlin, F. SPRINGER, 1883, p. 83. 284.] PREPARATION OF THE ASH. 795 crucible. After treating the ash of the insoluble portion with carbonic-acid water or ammonium carbonate, and weighing (see. above, a), dilute the solution so as to obtain as many tenth-, half-, or whole-cubic centimetres as there are milligrammes of ash of the insoluble portion, and later, in the analysis, add a corresponding number of cubic centimetres of the solution to the weighed quanti- ties of the ash. I have frequently employed this method with de- cided success, and first in the analysis of the ash of the ox-eye daisy.* The total quantity of ash is ascertained by evaporating to dryness a measured quantity of the solution with the addition of carbonic- acid water or a solution of ammonium carbonate, and weighing the moderately heated, dry residue. Then calculate this part to the whole, and add the result (representing the weight of the residue afforded by the entire solution) to the weight of the ash of the insoluble portion. 2. Incineration in a Dish, with the Aid of an Artificial Air-current (F. SCHULZE).! a. The organic substance, dried at 100 and weighed, carbonize in a crucible at a low red heat, transfer the carbon to a shallow platinum dish, lay on the latter a triangle of platinum wire, and on the triangle place an ordinary lamp chimney or Argand lamp chimney (or even a sufficiently wide retort neck) ; the chimney may also be clamped in a retort stand and thus held over the dish. The increased air-current caused by the chimney, and which may be regulated by employing a longer or shorter chimney, and placing it lower or higher, suffices to effect the incineration, even of cereal grains at an astonishingly low temperature. J When the incinera- tion is complete, weigh the ash, and proceed as in 1. 6. For incinerating vegetables rich in alkali salts, the method described in 1, c, is recommended. * Journ. f. prakt, Chem., LXX, 85. f Communicated to the author by letter J F. SCHULZE employs this method also for incinerating filters, placing the crucible containing the filter into the dish. 796 INORGANIC CONSTITUENTS OF PLANTS. [ 284. 3. Incineration with the Aid of an Artificial Air-current (HLASIWETZ) .* This method requires a silver, platinum, or porcelain tube shaped like a tobacco pipe. For difficultly combustible carbon it should be cylindrical, 21 cm. long, 4-5 cm. wide, and tapering to a point at the lower end. A small platinum plate provided with 6 to 8 perforations prevents any carbon or ash from falling out. For readily combustible carbons, the tube is given a conical or crucible- like form. The pipe is fitted air-tight into one tubulure of a two- ne3ked WOULFF bottle which is connected in the usual manner with a second and a third, and the latter with a very large aspirator (a capacious barrel) or a water-pump. On allowing water to flow from the barrel, or on effecting suction with the pump, the air enters through the pipe and passes through the water with which the second and third bottles are not quite half filled. To conduct the process, carbonize the suitably comminuted organic substance in a covered porcelain crucible; as soon as the gases cease to burn, transfer the feebly glowing carbon to the pipe by means of a funnel, and immediately allow the water to run from the barrel, or employ moderate suction. The aspiration must be so regulated that the combustion proceeds regularly, but at not too high a temperature. From time to time gather the mass together by means of a plati- num wire ; finally heat the ash for a short time in a platinum dish in order to consume the last particles of carbon. In the water of the WOULFF bottles will be found traces of fixed salts, particularly chlorides; also carbon dioxide and ammonia. If the salts are weighable, determine them. 4. Incineration in a Muffle with the Addition of Baryta (STRECKER).| Dry the organic substance at 100, and slightly carbonize it in a platinum or porcelain dish over the lamp. Moisten the carbon with a concentrated solution of pure barium hydroxide, employing * Annal. d. Chem. u. Pharm., xcvn, 244 f Ibid., LXXIII, 366. 284.] PREPARATION OF THE ASH. 797 such a quantity that the ash left on incineration may contain about half its weight of baryta. Dry the moistened carbon again, and burn it in the muffle at the lowest temperature possible. By this treatment the ash does not fuse, but remains voluminous and loose, thus allowing complete combustion of the carbon. The residue must still contain a considerable excess of baryta. If this is not the case, a loss of phosphorus may be apprehended, at least in some incinerations; it is advisable in such cases, therefore, to in- cinerate a fresh portion with a large excess of baryta. The residue is then finely powdered and intimately mixed. As E. VON RAUMER,* on incinerating maize grains according to the method just described, observed that the ash contained pyrophosphates, he recommended, in order to avoid this happen- ing when incinerating cereals, to soak these with baryta water, then to dry and incinerate. The ash of maize so treated contained only orthophosphates . If the quantity of ash is to be determined in the baryta-contain- ing ash, measured quantities of baryta water of known strength must be added, and the ash treated as in 1, a, so as to convert into carbonates the alkalies and alkaline earths resulting from the loss of carbon dioxide. Finally it must be noted that baryta-contain- ing ash, as a rule (i.e., when a very large excess of baryta has not been added), no longer contains all the chlorine originally present in the substance incinerated. The quantities of ash obtained will hence usually be too low, and therefore an accurate determination of the chlorine in the organic substance should be made in a sepa- rate portion (see below, p. 810, BUNGED BEHAGHEL VON ADLERS- KRON) 4 5. Incineration with the Aid of Spongy Platinum (H. ROSE). Carbonize about 100 grm. of the substance dried at 100, in a platinum or clay crucible at a dark-red heat, finely triturate the carbonized mass in a porcelain mortar, mix it intimately with 20 * Zeitschr. f. analyt. Chem., xx, 375. f Zeitschr. f. Biologie, ix, part 1. j Zeitschr. f. analyt. Chem., xii, 405. 798 INORGANIC CONSTITUENTS OF PLANTS. [ 285. to 30 grm. spongy platinum, transfer the mixture in portions to a shallow, thin, platinum dish, and heat over a lamp with double draught. After a short time, and before the contents begin to ignite, every particle of carbon begins to glimmer, and the surface of the black mixture becomes covered with a gray layer. By dili- gent, careful stirring with a small platinum spatula, renew the sur- face and promote the combustion. So long as the mass still con- tains unconsumed carbon, the glimmering continues; as soon, however, as all the carbon is completely burned, all visible in- candescence ceases, even though the mass is still more strongly heated. When all the successive portions added are incinerated, mix uniformly, convert any oxides that may have formed into carbonates (see above, 1, a, p. 793), and weigh. On deducting the weight of the spongy platinum added, the weight of the ash is obtained. A loss of chlorine occurs also in this method of incineration (compare p. 791). 6. Other Methods of Incineration, The processes described under 1 to 5 do not by any means exhaust all the methods of incineration proposed or employed. Thus GRAGER* and AL. MuLLERf add ferric oxide when incin- erating, while BECHAMP,t for the incineration of difficultly combus- tible vegetable or animal substances, e.g., beer yeast, recommends the addition of bismuth nitrate. I consider it sufficient to here confine myself to a mere mention of these particular methods of incineration. H. ANALYSIS OF THE ASH. 285. After having described the most advantageous methods of preparing the plant-ash, I would now point out that in by far the majority of cases the methods 1 and 2, if properly carried out, par- ticularly 1 c or 2 b in suitable cases, are perfectly satisfactory. * Jahresberich von KOPP und WILL, 1859, 693. j- Journ. /. prakt. Chem., LXXX, 118. J Compt. rend., LXXIII, 337; Zeitschr. f. analyt. Chem., xi, 332. 285.] ANALYSIS OF THE ASH. 799 I make this statement in order to explain why, in the following, reference is made exclusively to the analysis of pure ash (free from barium and platinum). In such cases where methods 4 or 5 are used, the modifications required and which are described below, are but slight, and readily suggest themselves. According to their main constituents, the ashes may be classi- fied as follows : a. Ashes in which carbonates of the alkalies and alkaline earths predominate. Such ashes are afforded by woods, herbaceous plants, etc. ft. Ashes in which phosphates of the alkalies and alkaline earths predominate. To this class belong the ashes of almost all seeds. 7-. Ashes in which silica predominates. These are yielded by the stalks of the Graminece, Equisetacece, etc. Although it is clear that this classification cannot be quite strict, and that numerous lapses from one group to another occur, it must nevertheless be retained if the analytical methods about to be described are to be used, since the general mode of procedure must be modified according as the ash belongs to the first, second, or third class. a. Qualitative Analysis. As the constituents which usually occur in ashes are in general known, it would be superfluous to make a complete qualitative analysis of every ash. It is only necessary to make a few pre- liminary tests to ascertain the presence or absence of more rarely occurring constituents, and also to which of the above-mentioned classes the ash belongs. These tests are as follows: 1. Test the reaction of the ash. 2. Test whether the ash is completely decomposed on warming with concentrated hydrochloric acid. If the ash effervesces on treatment with the strong acid, it may be regarded as a proof that the ash can be decomposed. As a rule it is only the ashes of the stalks of the Graminece, etc., rich hi silica, which cannot be com- pletely decomposed. 3. On adding an alkali acetate to the hydrochloric-acid solution 800 INORGANIC CONSTITUENTS OF PLANTS. [ 286. of an ash, after separating the silica and removing the greater part of the free acid, or on neutralizing the solution with ammonia and then adding free acetate acid, a yellowish-white, gelatinous precipitate of ferric phosphate separates in the case of almost all ashes. It is now necessary to ascertain whether, in addition to the phosphoric acid found in this precipitate, there is a further quan- tity left in the ash. To decide this question, filter off the precipitate thus obtained, and add an excess of ammonia to the filtrate. If no precipitate forms, or if a brownish-red precipitate (of ferric hydroxide) forms, the ash contains no more phosphoric acid; if, however, a white precipitate (calcium phosphate and ammonium- magnesium phosphate) forms, it is certain that the ash contains more phosphoric acid than the ferric oxide present in it can com- bine with, and the ash must consequently be placed in the second class. 4. Test the ash for manganese, by mixing a small quantity with sodium carbonate and exposing on platinum foil to the outer flame of the blowpipe (see "Qualitative Analysis," 14th Germ, ed., p. 140). 5. Test whether hydrogen sulphide is evolved on treating the ash with hydrochloric acid. 6. Test for lithium, rubidium, strontium, barium, copper, aluminium, iodine, bromine, fluorine, and the other substances mentioned as occasionally occurring in very minute quantities, if it is considered of interest to ascertain if traces of these are present (see " Qualitative Analysis," 14th Germ, ed., p. 398). b. Quantitative Analysis. (v. Ashes in which Carbonates of the Alkalies or Alkaline Earths Predominate, and in which All the Phosphoric Acid may be Assumed to be Combined with Ferric Oxide. 286. The constituents are determined in two separate portions of the ash, which we will designate as AA and BB. 286.] DETERMINATION OF VARIOUS CONSTITUENTS. 801 In BB the carbon dioxide * and chlorine are determined. In AA all the other constituents are determined. If the ash, however, contains sulphides, three separate portions must be taken, one for carbon dioxide and hydrogen sulphide, the second for chlorine, and the third for the remaining constit- uents. AA. 1 DETERMINATION OF SILICA, CARBON, AND SAND. Cover 4 or 5 grm. of the ash with some water in a porcelain dish, and gradually add hydrochloric acid. If the ash is rich in carbonates, cover the dish with an inverted funnel in the stem of which is inserted a small funnel through which the acid is added. In this manner all loss from spirting may be avoided. Now heat gently, and as soon as all the carbon dioxide has been driven off, rinse off the funnels into the dish. When no more undecomposed ash is visible besides the readily distinguishable carbonaceous particles (and which are almost always present), evaporate to dryness in a water-bath, frequently stirring towards the end, and crushing all the lumps, any sand present being easily recog- nized by the grating sound. When cold, moisten the dry mass with concentrated hydro- chloric acid, and after half an hour, heat with a moderate quantity of water on the water-bath; then dilute further, filter the acid liquid through a stout filter dried at 110 and weighed. On the filter will be found the silica, mixed with carbon and sand if these are present. If the residue consists only of silica and carbon, wash it well,f dry at 110, weigh, incinerate, and thus determine the silica, the difference being carbon. Whether the silica is pure or not may be ascertained by heating it with hydrofluoric and sulphuric acids. If the residue, however, consists of silica, carbon, and sand, transfer it, after washing and drying, * The determination of this, although it is of no great significance (see p. 792 this volume), is yet necessary, in order to complete the analysis and thus afford a certain control of its accuracy. j* As any considerable quantity of carbon can be washed only with diffi- culty, ashes rich in carbon are not adapted for accurate analyses. 802 INORGANIC CONSTITUENTS OF PLANTS. [ 286. to a platinum dish, without, however, injuring the filter. (If the powder is perfectly dry, this may be readily accomplished, only a few particles of carbon adhering to the paper, usually just sufficient to color this slightly.) Now boil the powder for half an hour with: pure (silica-free), diluted caustic-soda solution (or with a concen-' trated sodium-carbonate solution), whereby the silica is gradually/ dissolved without any of the sand or carbon present being attacked. Now filter through the original filter-paper, wash the undissolved residue thoroughly, and dry it with the filter at 110 until it ceases to lose weight. On deducting the weight of the filter, the remainder is calculated as carbon and sand. The filtrate supersaturated with hydrochloric acid gives, accord- ing to 140, II, a, the quantity of silica. 2. DETERMINATION OF ALL THE REMAINING CONSTITUENTS EXCEPTING CHLORINE AND CARBON DIOXIDE. Mix the hydrochloric-acid solution filtered off from the silica, carbon, and sand with the washings, and divide the whole, either by weight or measure, into three, or more conveniently, four parts, in order that should a determination miscarry, the last por- tion may be utilized for a new determination. The division is most simply effected by filtering the liquid into a 200-c.c. flask or cylinder, adding first the washings, then sufficient pure water to fill up to the mark, shaking and then pipetting off three portions of 50 c.c. each. These three portions we will designate as aa, bb, and cc. In aa we determine the ferric phosphate, any free ferric oxide and manganous oxide, the alkaline earths, and also alumina should this happen to be present. In bb the sulphuric acid is determined, and in cc. the alkalies. aa. Determination of the Ferric Phosphate, etc., and the : , Alkaline Earths. Cautiously add ammonia to the liquid until the resulting precip- itate just no longer redissolves, then add ammonium acetate and sufficient acetic acid to decided acidity. The persistent yellowish- white precipitate, which separates best on gently warming, consists , 286.] DETERMINATION OF VARIOUS CONSTITUENTS. 803 of ferric phosphate; it should be filtered off without loss of time. If the quantity of the precipitate is small, and the ash contains no determinable quantities of manganese and alumina, and if the filtrate is not red, wash the precipitate with hot water containing some ammonium nitrate, ignite, weigh, and calculate the residue as Fe2(PO 4 ) 2 (comp. Vol. I, p. 227). If, however, under conditions similar to those noted, the precipitate is larger, wash it three or four times, then dissolve in the smallest quantity of hydrochloric acid possible, add ammonia until a permanent precipitate just begins to form, then add ammonium acetate and a little acetic acid. After gently warming, filter, wash as above, dry, ignite, and calculate this residue also as Fe 2 (PO 4 ) 2 . If any of the above conditions do not exist, the precipitate (whether that collected directly or whether first collected, washed, dissolved in hydrochloric acid, and reprecipitated by ammonium acetate) cannot be weighed directly and calculated as Fe 2 (PO 4 ) 2 , as in this case it may contain manganous oxide and alumina, or, if the filtrate was red, basic ferric phosphate. If only the latter is present, ignite and weigh the precipitate, dissolve in hydrochloric acid, determine the iron in the solution according to Vol. I, p. 460, g, /?, and from the difference ascertain the phosphoric acid that was combined with it. If, however, the precipitate contains also manganese, and per- haps alumina too, dissolve it in hydrochloric acid, separate the iron and manganese according to Vol. I, p. 460, g, ft (separating these according to Vol. I, p. 644 [82]), evaporate the filtrate hi a platinum dish with an excess of pure sodium carbonate until ammonia is no longer evolved, then add some potassium nitrate, evaporate to dryness and heat until the mass melts ; then soften the melt with water, transfer it to a small beaker, add hydrochloric acid, warm, filter, and add ammonia until alkaline. If no precipitate forms, alumina is absent. In this case evaporate repeatedly with nitric acid on the water-bath, and determine the phosphoric acid by the molybdenum method (Vol. I, p. 446, /?). If, on the other hand, the ammonia throws down a precipitate, add nitric acid until it is dis- solved, evaporate repeatedly with nitric acid, determine the phos- 804 INORGANIC CONSTITUENTS OF PLANTS. [ 286. phoric acid by the molybdenum method, precipitate the molybde- num from the nitrate by means of hydrogen sulphide, filter, and in the filtrate determine the alumina according to Vol. I, p. 278, a. If the hydrochloric-acid solution of the fused mass gives a pre- cipitate with ammonia, it contains aluminium ; and if it is desired to avoid the inconvenient molybdenum separation, determine the aluminium in the hydrochloric-acid solution of the melt as alumin- um phosphate by adding to the solution some sodium phosphate, then ammonia, and finally acetic acid in excess. Collect the pre- cipitate thus obtained, wash, dry, ignite, and weigh as A1 2 (P0 4 ) 2 . To determine the phosphoric acid use the last 50 c.c. of the solution filtered off from the silica, etc., and proceed according to p. 807, a, this volume. In the filtrate from the ferric phosphate, and rendered acid by acetic acid, determine the calcium and magnesium, and also the rest of the iron and manganese* if these are present. For this pur- pose precipitate the iron, if necessary, with ammonia, or the iron and manganese (which are to be separated as in Vol. I, p. 644 [82]) with ammonia and ammonium sulphide, and determine the cal- cium and magnesium according to Vol. I, p. 619 [36], after decom- posing the excess of ammonium sulphide in the filtrate by evapo- rating with hydrochloric acid and filtering. bb. Determining the Sulphuric Acid. Precipitate the liquid, bb, with barium chloride, and determine the precipitate according to Vol. I, p. 434, 1. If the solution con- tains a large excess of hydrochloric acid, partially neutralize this first with ammonia. cc. Determining the Alkalies. Add as much barium chloride to the liquid bb as will just suffice to precipitate the sulphuric acid, then evaporate off on the water- bath the greater part of the free acid, dilute, add a few drops ferric- * I have made no reference in the text to the very rare event of this liquid still containing aluminium. Should this be present, precipitate it by means of ammonia or ammonium sulphide, and then separate the alu- minium from the iron or manganese according to 160. 286.] DETERMINATION OF VARIOUS CONSTITUENTS. 805 chloride solution, then pure milk-of-lime in slight excess, heat for some time on the water-bath, and filter. In this manner all the sulphuric acid, phosphoric acid, iron, manganese, and magnesium are removed. Wash the precipitate until the last washings cease to give a turbidity with silver-nitrate solution acidulated with nitric acid ; then precipitate the excess of calcium in the filtrate by adding ammonium carbonate mixed with ammonia, allow to settle, filter, evaporate to dryness in a platinum dish and ignite ; dissolve reprecipitate with ammonium carbonate and ammonia, if necessary repeating the precipitation a third time (in fact until the solution of the gently ignited residue is no longer rendered turbid by am- monium carbonate and ammonia) ; then evaporate, ignite gently, weigh the residual alkali chlorides, and separate potassium and sodium, if both are present, according to Vol. I, p. 599 [i]. N.B. If the quantity of ash is small, the filtrate from the silica may be divided into two parts, and the sulphuric acid and alkalies determined in one, first precipitating the sulphuric acid with barium chloride, avoiding any appreciable excess, however, then filtering and proceeding as in cc. BB. DETERMINATION OF THE CARBONIC ACID, CHLORINE, AND ANY SUL- PHUR THAT MAY BE PRESENT AS METALLIC SULPHIDES. 1. When the qualitative tests have shown metallic sulphides to be absent from the ash. Treat a second portion of the ash according to Vol. I, p. 490, bb, or p. 493, in order to determine the carbonic acid. Filter the contents of the small flask in which the solution is effected by means of diluted nitric acid, and precipitate the chlorine with silver solution according to Vol. I, p. 521, a. 2. When the qualitative tests have shown metallic sulphides to be present in the ash. Treat a second portion of the ash with hydro- chloric acid in order to determine the hydrogen sulphide (and thus the sulphur present in combination with metals) and the carbon dioxide evolved, according to p. 365, d, this volume. In order that the hydrogen-sulphide determination may be accurate it is advis- 806 INORGANIC CONSTITUENTS OF PLANTS. [ 287. able to conduct the operation in an atmosphere of hydrogen (p. 519, a, this volume). To determine the chlorine, boil a third portion of the ash with water, filter, and mix the filtrate with a solution of silver nitrate in excess; treat the portion of the ash insoluble in water with cold, diluted nitric acid, filter, and use this filtrate for acidulating the aqueous filtrate which was precipitated with silver nitrate. Allow the whole to settle in a place secluded from light, filter off the precipitate consisting of silver chloride and silver sulphide, wash it, treat with ammonia to dissolve the silver chloride, filter, then acidulate the filtrate with nitric acid, and determine the now pure silver chloride according to Vol. I, p. 521, a. N.B. Should the quantity of ash be very small, all the con- stituents, if no sulphides are present, may be determined in one por- tion. In this case ascertain first the carbon dioxide as in BB, 1, then filter through a weighed filter, determine the chlorine in the filtrate, and precipitate the excess of silver with hydrochloric acid; spread the first filter on a glass plate, and rinse off its contents into the second filtrate, and then proceed as in AA. Carbon, sand, and silica are subsequently again collected on the filter which mean- while has been rinsed off and dried. /?. Ashes Decomposable by Hydrochloric Acid, and in which a Further Quantity of Phosphoric Acid is Present Above that Combined with Iron. 287. Take two portions of ash,* a larger one, AA and a smaller, BB. In BB determine the carbon dioxide and chlorine as in 286. In A A determine the other constituents. If the quantity of ash at hand is very small, determine all the constituents in one portion (see286,BB,"N.B."). Treat AA with hydrochloric acid and separate silica, carbon, and sand, as in 286. Make up the hydrochloric-acid solution to * Should such ashes contain metallic sulphides, by exception, three por- tions would be required, and the analysis, with reference to the determina- tion of the chlorine, carbon dioxide, and hydrogen sulphide, carried out according to the methods described on p. 805, 2, this volume. 287.J DETERMINATION OF VARIOUS CONSTITUENTS. 807 300 c.c., and divide it into two portions, one, aa, of 100 c.c., and the other, bb, of 200 c.c. In aa first determine the sulphuric acid by adding barium chloride in the least possible excess and filtering. Then add ferric-chloride solution until the liquid appears yellow, expel almost all the free acid hi the solution by evaporating on the water-bath, dilute, and add pure milk-of-lime until the liquid is strongly alkaline; heat almost to boiling, filter, wash until the washings cease to react for chlorine, remove the calcium and barium from the filtrate with ammonium carbonate, and proceed to determine the alkalies according to 286. To bb add first ammonia in slight excess, then immediately acetic acid until the alkaline-earth phosphates as first precipitated are redissolved. The precipitate, which usually consists chiefly of ferric phosphate, but which may also contain manganous oxide, in rare cases alumina, too, and if the quantity is considerable, also small quantities of alkaline-earth phosphates, treat as detailed on p. 802, aa, this volume. Divide the filtrate into two portions, a and {3; in a determine the phosphoric acid, and in [3 the calcium and magnesium. a. To determine the phosphoric acid, evaporate the liquid repeatedly with nitric acid on the water-bath, almost to dryness, take up the residue with nitric acid, and determine the phosphoric acid by the molybdenum method (Vol. I, p. 446, /?). I would remark here that after dissolving the ammonium phosphomolyb- date in ammonia and neutralizing the greater part of the ammonia with hydrochloric acid, it is advisable to add a definite quantity of ammonia (4 to 6 c.c.), then to add the magnesia mixture, drop by drop, and lastly to add a still further quantity of ammonia until the latter forms one-fourth of the whole. By this mode of deter- mining the phosphoric acid, accurate results are obtained with certainty, whether the ash contains ortho- or pyrophosphates. /?. To determine the calcium and magnesium in /? proceed according to Vol. I, p. 621 [37]. If the ash contains a determinable quantity of manganese, this must be removed from the portion fi in which the calcium and magnesium are to be determined, other- 808 INORGANIC CONSTITUENTS OF PLANTS. [ 288. wise it would be thrown down partly with one, partly with the other. Hence treat /?, acidulated with acetic acid, and still .con- taining alkali acetate, first with chlorine or bromine, at a tem- perature of 50 to 60, collect the hydrated manganese dioxide, wash it, dissolve in hydrochloric acid, and precipitate and deter- mine the manganese as sulphide; evaporate the filtrate which still contains portions of the alkaline earths (Vol. I, p. 635, a) with hydrochloric acid, filter, add the filtrate to the filtrate from the hydrated manganese dioxide, and in the united filtrates determine the calcium and magnesium as above detailed. Of the great variety of methods which may be chosen for /?, if this contains no manganese, I will only mention the following: After separating the ferric phosphate, precipitate first the calcium from the acetic-acid solution by means of ammonium oxalate (Vol. I, p. 621 [37]). Divide the filtrate into two equal parts, and in one determine the magnesia by adding ammonia and sodium- ammonium phosphate; in the other determine the phosphoric acid by evaporating with the addition of nitric acid, and then adding ammonia and solution of magnesium chloride containing some ammonium chloride. 7*. Ashes not Decomposed by Hydrochloric Acid. 288. Carbonic acid is seldom found in such ashes; when it is, how- ever, determine it as in 286. This is also true of chlorine. So far as the determination of the other constituents is concerned, the ash must first be decomposed. The decomposition may be effected in various ways. 1. It may be effected, as WILL and I first proposed, by evapo- rating the ash to dryness with pure soda lye in a platinum or silver dish. (Experiments have shown that by this treatment the sili- cates in the ash are completely decomposed, while any admixed sand is not affected, or at least, but very slightly. The heat must not be raised towards the end of the process to a point sufficient to fuse the mass.) Cover the residue then with diluted hydrochloric 288.] DETERMINATION OF VARIOUS CONSTITUENTS. 809 acid, evaporate, treat again with hydrochloric acid, and proceed with the insoluble residue (of silica, carbon, and sand), as above, 286, AA, 1; the solution, however, treat as in 286, AA, 2, or in 287, AA. It is, of course, evident that the alkalies cannot be determined in the latter, but must be determined in a separate portion of the ash after this has been decomposed by fusion with barium hydroxide or treatment with hydrofluoric acid. 2. WAY and OGSTON * mix the (sand-free) ash with an equal weight barium nitrate, and introduce the mixture in small portions into a large platinum crucible. By this treatment the ash is rendered readily decomposable by hydrochloric acid, and, should it have contained carbon, also perfectly white. Separate the silica as in 286, AA, 1, and also determine and allow for any barium sulphate that may be present. In a portion of the hydrochloric- acid solution determine the alkalies (according to 286, AA, 2, cc); the balance is precipitated with a slight excess of sulphuric acid. (The quantity of barium nitrate used being known, the quantity of any calcium sulphate present is calculated from the excess over the weight of the barium sulphate obtained.) The nitrate is divided into two portions, the ferric phosphate, calcium, and magnesium being determined in one ( 287), and the phos- phoric acid in the other, as in 134, d, a. Regarding other methods of analysis of plant ashes or other ashes, I would refer to the works of E. REICHARDT,! R. W. BuNSEN,J J. KONIG, and R. ULBRICHT, (Analysis of the Ash of Must and Wine ||). * Journ. of the Royal Agricult. Soc. of England, vin, Part I; Jahresber. von LIEBIG und KOPP, 1849, 600. f Archiv. der Pharm [2], cxxxn, 88; Jahresber. von H. WILL, 1867, 831. % AnnaL d. Onologie, i, 3; Zeitschr. f. analyt. Chem., ix, 283. Landwirthschaftl. Versuchsstationen, x, 396; Zeitschr. /. analyt. Chem., ix, 288. || Landwrthschaftlichl. Versuchsstationen, xxv, 399. 810 INORGANIC CONSTITUENTS OF PLANTS. [ 289. B. SUPPLEMENTARY DETERMINATIONS OF CERTAIN OTHER INORGANIC SUBSTANCES IN PLANTS. 289. From what has been stated in 284, it follows that, although by the analysis of the plant ash or portion of a plant, the composition of the ash, which in itself is interesting to know, may be ascer- tained, yet the analysis affords no knowledge of the quantities of those elements which are lost to a greater or less extent during incineration, e.g., chlorine, sulphur, and in many cases, phosphorus. If therefore the quantities of these elements present in the plant or plant portions are also to be ascertained, the following supplementary determinations must also be made: 1. DETERMINATION OF THE CHLORINE. This is effected thus: Moisten about 10 grm. of the commi- nuted plant or plant portion with a solution of about 1 grm. sodium carbonate and dry. Then incinerate in a platinum dish at a moderate, long-continued heat, whereby if the incipient red heat is not exceeded, no loss of alkali chloride will occur. As soon as the particles of carbon cease to glimmer, moisten the ash (still containing carbon) with water, triturate, exhaust with boiling water, filter, wash the filter, and add it to the remainder of the ash in the platinum dish ; now dry, incinerate, completely Ureat the ash with cold, diluted nitric acid, filter into the aqueous solution, add a further quantity of nitric acid, if necessary, until present in excess, and then determine in the solution the chlorine as silver chloride, according to Vol. I, p. 521, a (BEHAGHEL VON ADLERS- KRON *). Another method of determining chlorine is described below under 3. 2. DETERMINATION OF THE SULPHUR. This may, if desired, be combined with that of phosphorus. * Zeitschr. /. analyt. Chem., xu, 395. 289.] SUPPLEMENTARY DETERMINATIONS. 811 a. W. KNOP and R. ARENDT'S Method.* Cover the comminuted plant portion (about 4 to 5 gnu.) with very concentrated nitric acid, evaporate to dryness on the water- bath, moisten again with nitric acid, evaporate once more but not quite to dryness, add first some water, then 2 or 3 grm. pure anhydrous sodium carbonate (which must suffice, however, to neutralize all the free acid), and dry, finally, with stirring. Now moisten with water, whereby the mass readily separates from the dish, add first a further quantity of water so that the whole acquires a thin, mushy consistency, then 20 to 25 grm. of ground, anhydrous,, sodium carbonate, mix intimately, dry completely, triturate to a fine powder, and clean out the dish, which has become damp from the steam, with sodium carbonate. Next heat the powder, in portions, if necessary, in a silver or platinum crucible over an alcohol lamp, until the mass, which must not be allowed to melt, has become perfectly white. If this cannot be accomplished, triturate the substance once more, mix with a few centigrammes of potassium nitrate, and heat anew. Finally treat the mass with water, supersaturate with hydrochloric acid, separate the silica, precipitate the sulphuric acid in the moderately acid liquid by adding barium chloride, and from the impure barium sulphate (which is to be purified as in Vol. I, p. 434) calculate the sulphur. If the phosphoric acid is to be determined in the filtrate, this is effected, according to KNOP, by means of the uranium method (Vol. I, p. 451) after reduction of the small quantity of ferric chloride present with uranous chloride. 6. Any of the methods suitable for determining sulphur and phosphorus in organic substances, and detailed in 188 and 189, may be employed, and preferably LIEBIG'S ( 188, 1). Take up the melt with water, supersaturate the solution with hydro- chloric acid, separate the silica, and in the filtrate precipitate the sulphuric acid with barium chloride. If the phosphoric acid * Compare R. ARENDT, "Das Wachsthum der Faserpflanzen " (personal communication from D. G. BRUGELMANN). 812 INORGANIC CONSTITUENTS OF PLANTS. [ 289. is also to be determined, this may be done not only as described in a, but also by nearly neutralizing with sodium carbonate the nitrate from the barium sulphate, then adding first some ferric chloride, and then a slight excess of barium carbonate. Filter after settling, wash the precipitate containing all the phos- phoric acid, dissolve it in nitric acid, and determine the phos- phoric acid by the molybdenum method (Vol. I, p. 446, /?). 3. DETERMINATION OF THE SULPHURIC ACID, AND IF DESIRED, ALSO THE CHLORINE, IN PLANTS. If the question has also to be decided as to what portion of the sulphur found in 2 is present in the plant as sulphuric acid, exhaust the plant with cold water acidulated with nitric acid, as already recommended by CAILLAT (comp. p. 788, foot-note, this vol- ume). E. WOLFF * recommends for this purpose the employment of a glass tube about 60 cm. long and 1-5 to 2 cm. diameter, drawn out at one end. Connect the drawn-out, open end with a glass tube by means of a small rubber tube provided with a pinchcock. Introduce a plug of cotton wool boiled in very dilute nitric acid into the narrow part of the tube, and over it place about 10 grm. of the finely divided vegetable substance. Close the pinchcock, and fill the apparatus with a mixture of 20 parts water and 1 part nitric acid of 1-2 sp. gr.; after several hours, allow some of the liquid to run off, so that a new stratum of the acid may come into contact with the substance to be extracted, fill the tube again, and repeat the operation until a sample of the liquid drawn off gives but a faint opalescence with silver solution. If only the sulphuric acid is to be determined in the liquid, evaporate this, best on a water-bath, to a small bulk, dilute it with water, pre- cipitate with barium chloride, and purify the barium sulphate according to Vol. I, p. 434. If, however, the chlorine is also to be determined, precipitate first with silver nitrate, filter off the silver chloride (containing organic matter), remove the excess of silver * His "Anleitung zur chem. Untersuch. landwirthschaftlich wichtiger Stoffe," 3d edit- 167 290.] ARRANGEMENT OF THE RESULTS. 813 from the filtrate with hydrochloric acid, evaporate the filtrate until nearly all the free acid has been expelled, then dilute, and determine the sulphuric acid as above. Wash the silver chloride containing the organic matter, dissolve in ammonia, add sodium carbonate, evaporate the solution, and heat the residue just to incipient fusion; then treat with water, acidulate the solution with nitric acid, precipitate the silver solution, and determine the now pure silver chloride according to Vol. I, p. 521, a. The determina- tion of the sulphuric acid and chlorine made as just detailed do not, however, usually give satisfactory results, because the plant tissues can only with difficulty be completely exhausted with cold water acidulated with nitric acid. C. ARRANGEMENT OF THE RESULTS. 290. If it is but a question of presenting the results of ash analyses, it is usually advisable to state the percentages of the bases and acids separately, as the manner in which the bases and acids are combined cannot always be accurately deduced. In the case of chlorine, an equivalent quantity of oxygen must be deducted. It is usually preferred to put down chlorine as sodium (or potas- sium) chloride, calculating the alkali in the chloride into oxide, and deducting this from the total soda or potassa. Any man- ganese contained in ashes containing carbonates of the alkaline earths, is present as manganic oxide, Mn 2 O 3 (see Vol. I, p. 636), or as mangano-manganic oxide (Mn 3 O 4 ). If the results are given in this way, i.e., as they are directly obtained, they cannot be compared with those of other analyses, as among the constituents put down there are, or may be, some which are immaterial, e.g., carbon and sand. In order to obtain comparable results, therefore, the influence of these immaterial constituents must be eliminated. This is effected by crossing out the carbon and sand, and calculating the essential constituents into parts per 100. The carbon dioxide, on the other hand, although not derived from the inorganic constituents of 814 INORGANIC CONSTITUENTS OF PLANTS. [ 290. the plant, must be put down if the ash is to be characterized as such (e.g., wood-ash, which is employed as a manure, or as a source of potash). In order to decide the question as to what inorganic substances a plant withdraws from the soil, a mere statement of the ash constituents does not suffice, as has already been shown (p. 788 this volume); the results of the supplementary determinations must, rather, be also included, and the whole calculated into parts per 100 of the dried plant. The supplementary determinations give the quantity of chlorine, sulphur, and also the phosphorus ; the other constituents, however, are ascertained from the ash analysis. In this state- ment of results the carbon dioxide is omitted. In order to calculate the ash constituents into percentages of plant substance, it was customary formerly to calculate the total weight of ash from that afforded by a portion of the carefully dried and cautiously incinerated vegetable substance, and then to incinerate a larger, unweighed, and less carefully dried quantity, and to analyze the ash so obtained. From this a very simple calculation afforded the percentages of the several constituents in the plant. For instance, wheat yielded 3 per cent, of ash, and this was found to contain 50 per cent, phosphoric acid; hence 100 parts of wheat contained 1 5 per cent, phosphoric acid. It will be seen at a glance that this method is very convenient; but it must be noted that it does not give sufficiently exact results in all cases, as the total quantity of the ash, for the reasons stated in 284, is not constant, but is variable within certain limits, dependent upon the duration, intensity, and mode of heating. As the operator can never, therefore, be certain that the small portion obtained in the determination of the total ash accurately corre- sponds in quantity and composition with the larger portion which is to serve for the analysis, it is at all events preferable to determine on the one hand the total quantity of the substance to be incin- erated, and on the other the total quantity of the ash obtained and intended for analysis, as already above recommended. If this is not desired, the object in view may also be effected with 291.] ANALYSIS OF SOILS. 815 accuracy by first incinerating a large, unweighed quantity of the vegetable substance, analyzing the ash, and thus determining the relative proportions of the constituents. On now incinerating a smaller weighed quantity of the vegetable dried at 100, and deter- mining in the ash one of the constituents the quantity of which can suffer no change because of the mode of incineration (e.g., lime), we may then, knowing the relative quantity of it present in the plant, as well as the proportions in which it and the other constituents are present, readily calculate the percentages in which the other constituents are present in the plant. IV. ANALYSIS OF SOILS. 291. The fertility of a soil depends, apart from climatic conditions, upon its chemical as well as physical nature. The chemical nature is dependent not only upon the character and relative proportions of the constituents, but also upon the solubility and forms of com- bination of the constituents. Hence if an analysis is to afford a conclusion as to the fertility, of a soil, it must take into account all the above points, so far as possible. I say so far as possible advisedly, as it is impossible, in a laboratory, to secure the action of solvents in the same manner in which they operate in nature ; and so, too, the chemico-physical examination scarcely affords sufficient conclusions regarding the various ways in which the constituents are combined in the soil. These variations may be seen, for instance, from the fact that a still perfectly uncultivated soil, although containing all the sub- stances necessary to support a particular plant, is still unable to support it while capable of supporting other plants requiring an equal or even greater supply of material. The combination of the substances is, therefore, the resistance the soil offers against yield- ing certain constituents to plants, a resistance which is overcome by some plants, but not by others; and which experiments have shown to decrease with cultivation of the soil.* * Comp. v. LIEBIG, Die Chemie in ihrer Anwendung auf Agricultur und Physiologic, n, p. 65 et seq. 816 COLLECTING THE SAMPLE. [ 292. In the following, bearing in mind the scope of this work, I will fully describe the mechanical and chemical analysis, but as regards the investigation of the most important physical properties of soils, I shall have to' refer to works on agricultural chemistry and to the many papers devoted to this subject.* A. COLLECTING THE SAMPLE. 292. The surface soil may be considered to be the upper layer which is turned up by the plough to the depth of 30 cm. ; the subsoil is the layer some 60 cm. deep next below the surface soil. If surface soil or subsoil is to be taken from any particular spot, dig a hole about 30 to 50 cm. square and with perpendicular sides and as nearly level bottom as possible, and cut from one of the side walls a vertical slice of uniform thickness, as a sample. The sample of the subsoil should be taken in like manner. If the earth to be exam- ined is to represent the average composition of a field, take samples * More or less comprehensive information regarding the investigation of the physical characteristics of soils is given by the older writers, SCHUBLER (Grundsdtze der Agriculturchemie, u) and FR. SCHULZE (Journ. f. prakt. Chem., XLVII, 241); and from among later writers, Dr. EMIL WOLFF'S paper on soil analysis, reported by the members of the commission (Dr. BRETSCHNEI- DER, Dr. GROUVEN, Dr. KNOP, Dr. PETERS, Dr. STOHMANN, and Dr. ZOLLER) appointed at the meeting of the German Agricultural Chemists, in May, 1863 (Landwirthschaftl. Versuchsstationen, 1864, vi; Zeitschr. f. analyt. Chem,, in, 85); also E. WOLFF'S Anleitung zur chemischen Untersuchung land- wirthschaftl. wichtiger Stoffe, 3d ed. (Berlin, WIEGAND, HEMPEL, and PAREY, 1875) ; also E. HEIDEN, Denkschrift zur Feier des 25 jahrigen Bestehens der agriculturchemischen Versuchsstation Pommritz (Hannover, PH. COHEN, 1883, p. 152 et seq.). Special reference regarding the absorption power of soils, and the methods of determining it, is given in the papers by v. LIEBIG (Annal. d. Chem. u. Pharm., cv, 113); A. SALOMON (Landw. Versuchsstat., ix, 351); R. BIEDERMANN (ibid., xi, 1); CL. TREUTLER (ibid., xiv, 301); W. KNOP (Zeitschr. f. analyt. Chem., xm, 101; xiv, 241; xv, 171); W. PILLITZ (ibid., xiv, 55 and 282); A. LISSAUER (Landwirth. Versuchsstat., xix, 11); VAN BEMMELEN (ibid., xxi, 135; and xxm, 265); KONIG (ibid., xxvi, 400); and concerning the retention of water by the soil, in the papers of F. SEEL- HEIM (Zeitschr. f. analyt. Chem., xix, 387); H. FLECK (DiNGL. polytech. Journ., ccxxxvm, 93); ARMSBY (Landwirthsch. Versuchsstat., xxi, 397); and HEIDEN (ibid., xxvi, 407). 293.] MECHANICAL ANALYSIS. 817 in like manner from several places and mix uniformly. Allow the samples to become thoroughly air dry. In summer this is attained by exposing the earth in a shallow box in a dry room ; in winter by drying the earth slowly in a drying closet at a temperature of 30 to 50. About 5 kilos are required for a complete analysis. B. MECHANICAL ANALYSIS. 293. 1. Weigh the entire quantity of air-dried earth, then pick out the stones and brush and weigh them. 2. Now place the earth in a tin sieve with holes 3 mm. in diam- eter, and sift out everything that will pass through. Break up any residual lumps in a mortar, with moderate pressure, and preferably with a wooden pestle; then sift again and preserve the sifted earth. Now place the sieve in a dish, add sufficient water * to cover the contents, allow to stand for a considerable time, and then wash, either with the hand or with a brush, until all the clay has been removed from the stones. Lastly, rinse off the latter with a little water, transfer to a dish, dry at 125, and weigh. The weighed matter is gravel. On igniting the dried gravel hi air, the loss hi weight will represent the organic matter incident to the gravel, provided this consists of such stones and fragments of rocks as lose no water, carbon dioxide, or volatile constituents. The contents of the dish, containing all the earth washed from the gravel, are allowed to dry slowly, towards the end at 30 to 50; then mix the residue uniformly with the dry, sifted earth, spread out in as thin a layer as possible, and allow to stand for several days in a vapor- and dust-free place at a moderate temperature; the air-dried fine earth (thus designated by E. WOLFF) is then preserved in well-stop- pered flasks. I must here remark that a definition as to what constitutes "fine earth," and which, of course, cannot be determined scien- * Distilled water must be used in all these operations; see note, p. 820 this volume. 818 ANALYSIS OF SOILS. [ 293. tifically, but only by agreement, has so far not been agreed upon. While, for instance, according to E. WOLFF'S suggestion, which has been adopted by many other agricultural chemists, the term ''fine earth" is given to that portion passing through a sieve with holes 3 mm. in diameter, others select 2 mm., and not a few even still finer sieves, in order to obtain "fine earth"; thus HEIDEN (Denk- schrift, p. 119) and GRANDEAU * take 1 mm.; E. DIETRICH,! 0-66 mm.; A. MULLERJ and also KNOP, 0-2 to 0-3 mm. As may be readily seen, a comparison of analyses of "fine earth" which is not further characterized, may lead to quite erroneous conclusions, as analyses are comparable only when made with "fine earth" prepared in a uniform manner. In the following the term " fine earth " will be applied to the preparation conforming to E. WOLFF'S definition, but the methods of analysis are, of course, applicable to all other kinds of "fine earth." 3. Many very different methods have been proposed and em- ployed for the further mechanical separation of air-dried fine -arth. Many agricultural chemists recommend elutriation and subse- quent separation of the residual sand into portions of different degrees of fineness by passing through sieves of various sizes. Others sift first and elutriate only the finest sifted portion. For sifting, however, sieves of varying fineness are recommended, and for elutriation some prefer so-called flushing apparatus, and others sedimentation apparatus. It may, hence, be readily seen that the results obtained by different methods cannot exactly concur. Although the comparison of results is thus already made difficult, it is rendered still more so by the fact that the names given to the sand of different degrees of fineness vary, e.g., "fine gravel," "coarser sand," "finer sand," "argillaceous sand," * His Handb. f. agriculturchem. Analysen, German edit., by HENNEBERG (Berlin, WIEGAND, HEMPEL, and PAREY, 1879, p. 103). f Zeitschr. /. analyt. Chem., v, 298. J Ibid., v, 443. According to A. MAYER the largest particles of KNOP'S "fine earth" are 0-3 mm. in diameter (BOCKMANN'S, chem. techn. Untersuchung., Berlin J. SPRINGER, 1884, n, 664). 294.] MECHANICAL ANALYSIS. 819 or "finer gravel/' "pearl sand/' "coarse sand," "fine sand/' or "coarse gravel/ 7 "medium gravel," "fine gravel," "coarse sand/1 "fine sand," etc. But even the causes here enumerated as affording non-con- cordant results in the mechanical separation of the constituents of a " fine earth," and whereby the clay found is too high, and fre- quently much too high, are by no means exhausted. The most common source of error in the usual methods is rather that, in all the elutriations made in the ordinary manner, the clay contained in the soil is not obtained pure, but mixed with fine sand, and under certain circumstances with finely divided calcium carbonate (SCHLOSING,* GRANDEAU,f F. SESTINI,J and N. PELLEGRINI ). It is not my purpose to here detail all the methods proposed for the mechanical analysis; it will suffice to describe the following: a. One of the best purely mechanical methods, that by E. WOLFF || and somewhat modified by W. KNOP. 6. SCHLOSING'S method, which combines mechanical separa- tion with chemical treatment, and which, so far as my experience goes, is the only one that correctly gives the quantity of clay present in the soil. a. Purely Mechanical Method. 294. Of the many methods, I give here only E. WOLFF'S modifica- tion of KNOP'S process because, with very simple apparatus, it gives as good results as can be expected from a purely mechanical analysis. Regarding the other methods, I must refer to the original treatises and books mentioned in the foot-note.l" * Compt. rend., LXXVIII, 1276. t His Handbuch., p. 104. J Landwirthschajil. Versuchsstat., xxv, 47. Ibid., xxv, 48. || His Anleitung zur chem. Untersuchung landwirthschaftlich wichtiger Stoffe, 3d edit., p. 9. IF Of the apparatus for elutriation belonging to the flushing apparatus, those of SCHULZE and SCHONE have already been mentioned on pp. 414 and 415 this volume. Others belonging to this category are described by NOBEL (comp. E. WOLFF'S treatise in Zeitschr. f. analyt. Chem., in, 90, and in Land- irirthschaftl. Versuchsstat., vin, 408); E. DIETRICH (Zeitschr. f. analyt. Chem., v, 295); and AL. MULLER (ibid., xvi, 83). Slight modifications of 820 ANALYSIS OF SOILS. [ 294. Boil 50 grm. of the air-dried fine earth with distilled water for a long time, transfer to a brass sieve perforated with holes 1 mm. in diameter, and set in a basin of water so that the contents of the sieve are covered with water; then operate as above de- tailed, in order to separate the portion of more than 1 mm. in diameter from the smaller. In the same manner proceed with the latter portion, using successively sieves with holes 0-5 mm. and 0-25 mm. in diameter. The residues remaining in the sieves are treated as above described for gravel. If many analyses of earths are to be made, it is advisable to use an apparatus consisting of sieves of various degrees of fineness fitted into each other so as to form one system, which is suspended in a wide, deep glass cylinder filled with water. The sieves, the contents of which are kept in motion by revolving brushes, then work simultaneously, and the operation is considerably facilitated. The further separation of the portion passing through the finest sieve into fine sand and finest elutriable portions (called " dust " by E. WOLFF) is effected by an elutriation flask holding fully a litre, and about 20 cm. high ; in the neck of the flask there is fitted a perforated stopper bearing a siphon, the short end of which reaches to the bottom of the flask, and is bent upwards at the lower end. Introduce the portion that has passed through the finest sieve into the flask, fill this to a height of about 18 cm. with distilled water,* shake thoroughly, and allow to stand for a definite time; now insert the siphon and draw off the turbid fluid from the sediment, fill again with water and repeat the operations. WOLFF recommends that, after the first shaking, the flask should SCHONE'S apparatus are recommended by E. HEIDEN (Denkschrift, p. 121), and by C. HOLTHOF (Zeitschr. /. analyt. Chem., xxv, 34). Furthermore, sedimentation apparatus have been constructed by KNOP (see his Bonitirung der Ackererde, 2d edit., p. 50 et seq.} ; J. KUHN (BOCKMANN'S chem. techn. Untersuchungen, Berlin, J. SPRINGER, u, 665); and R. DEETZ (Zeitschr. /. analyt. Chem., xv, 428). * Elutriation cannot be carried out with spring-water, because the slightest traces of lime, magnesia, and alkali salts coagulate the clay to a certain extent, and precipitate it with the sand (SCHLOSING; GRANDEAU, loc. cit., p. 105). 294.] MECHANICAL ANALYSIS. 821 be allowed to stand for one hour ; then for half an hour, one-quarter of an hour, and finally only five minutes, repeating the operation thrice for each settling. Lastly, rinse the fine sand into a dish and treat it like the other sands. To obtain and determine the finest elutriated portions warm the united, turbid washings in large dishes until they have be- come perfectly clear, then siphon off the clear liquid above sediment so far as possible, rinse into a porcelain dish and dry, after which transfer the residue to a platinum or porcelain crucible, dry at 125, weigh, ignite in air, and then weigh again. In order to facilitate the deposition of the finest elutriable portions, A. MULLER* recommends adding ammonia soap, while FR. SCHULZE recommends ammonium carbonate. According to E. LAUFER,| however, neither affords satisfactory results, although he finds that the warming greatly hastens deposition. Compare, however, A. MULLER' s J criticism of this. On adding together the component portions of the air-dried fine earth, and calculating them into percentages, they do not give 100, but less ; the difference is equivalent to the moisture con- tained in the fine earth. The results found can be controlled or checked by the direct method of determining moisture given in 296, 1. If the direct determination of the finest elutriable por- tion has been omitted, while the direct determination of the moisture has been carried out at 125, the quantity of the former in per cents is ascertained by deducting the sum of the sand dried at 125 and the moisture from 100. As the moisture content of different fine earths may vary greatly, it is advisable, for the purpose of comparison, to refer the figures obtained to the substance dried at 125. The results of the purely mechanical analysis may be thus conveniently stated as follows: 100 parts of the fine earth dried at 125 contain (for example) * Zeitschr. f. analyt. Chem., v, 243. ) Landwirthschajil. Versuchsstat., xvm, 61 ; Zeitschr. f. analyt. Chem. % xiv, 398. I Landwirthschaftl Versuchsstat., xxiv, 65. 822 ANALYSIS OF SOILS. [ 294. Non-com- Combustible bustible or volatile matter. matter. 7'51 -i Sand of 1 to 3 mm. diameter ............... 6-91 ( Organic substances, etc., belonging thereto ........ 0-60 30-96 J Sand 9 f * 5 to 1<0 mm - diameter ........... 30-05 ( Organic substances, etc., belonging thereto. ....... 0-01 Sand of 0-15= 0-5 mm. diameter ....... _____ 31-61 1-10 00.71 i Sand of 0-15= 0-5 mm. diameter ....... I Organic substances, etc., belonging thereto .. _ j Sand of less than 25 mm. diameter ......... 16-77 '1 Organic substances, etc., belonging thereto ........ 0-87 11 19 ! Finest particles ........................... 10-36 ( Organic substances, etc., belonging thereto ........ 0-82 100-00 95-70 4-30 7-16 Gravel associated with 100 parts of the fine earth dried at 125. 2- 10 Stones " " " " " " " " " " " 5 -03 Moisture belonging to " " " " " " " " " (in air-dried condition). The loss in weight which the soil, dried at 125, undergoes on ignition in air, cannot be considered merely as caused by the com- bustion of organic matter, since the clay, dried at 125, gives up water on ignition, calcareous sand loses carbonic acid, etc. The carbonic acid evolved may in great part be restored to the residue by moistening this with a solution of ammonium carbonate, dry- ing, repeating this treatment several times, and lastly very gently igniting. Compare 296, 2. The figures so obatined for organic matter are, however, only of approximate value, being very near the truth with many soils, but in others widely divergent, as may be seen from many analyses of soils, e.g., those by G. LOGES.* [ F. POQUILLON | gives a method whereby an estimation of clay in soils may be made in two or three days at the most. It is based on the fact that if, instead of mixing the earth with distilled water, a dilute solution of ammonium chloride is used, the clay is held in suspension while it is at the same time coagulated, thus enabling the sand to deposit almost immediately. Ten grm. of the soil are placed in a small porcelain crucible and rubbed round the sides with the first finger while adding water drop by drop, until about 25 c.c. have been added. This mixture is transferred to a beaker of 150 c.c. capacity, and about 100 to * Landwirthschaftl Versuchsstat., xxvm, 238. f Chem. News, LXXXI, 219. 294.] MECHANICAL ANALYSIS. 823 120 c.c. of a solution of ammonium chloride, 1 grm. per litre, are added. After well stirring with a glass rod, it is allowed to settle for five minutes, and the liquid decanted into a litre beaker. On this residue 100 to 125 c.c. more of the ammonium-chloride solution are poured; stir well again, allow to stand for five minutes, and decant into the litre beaker. This operation is repeated until the wash-waters are quite clear; this will require six or eight washings for the most argillaceous soils. The residue is treated with hydrochloric acid diluted with water, washed with distilled water,, and dried; its weight gives the total sand. The thick liquid remaining in the litre beaker is treated with a few drops of hydrochloric acid, to decompose the calcareous matter and complete the coagulation of the clay. It is then allowed to stand until the supernatant liquid is clear; this requires two or three hours. The clay which deposits is collected on a weighed filter, washed with distilled water, dried, and weighed. POQUILLOX claims for this method the following advantages over the older ones: 1. Instead of making two washings on the filter, one to remove the lime and chalky matter and the other to free the clay from the ammonium chloride, a single washing enables us to get rid of both the lime and chloride at the same time. .2. Instead of obtaining the clay in suspension in 4 or 5 litres of water, it is now found in 750 to 1,000 c.c.; this is in one-fifth or in one-sixth of the volume. 3. Instead of getting the clay on the filter after five or six days, this stage is reached after about three hours. 4. The clay obtained by this process is washed more rapidly than that obtained by the old method. (The author states that he has never taken more than a day and a half to effect the same amount of washing that used to require three or four days by the old method.) TRANSLATOR.] 824 ANALYSIS OF SOILS. [ 295. b. SCHLOSING'S Method* 295. This method has for its object the determination of the fol- lowing constituents of fine earth: 1. Sand insoluble in acids. 2. Clay. 3. Humus substances. 4. Calcium carbonate. 5. Moisture. Stir 10 grm. of air-dried fine earth in a porcelain dish to a stiff paste by spirting in a small quantity of distilled water; then add more water, and knead between the fingers so as to uniformly and thoroughly mix the soil. Now add more distilled water, and then pour the turbid liquid into a beaker of about 250 to 300 c.c. capacity, and until the whole mass of soil has been separated and elutriated. The quantity of water taken should be so ad- justed that not more than 200 to 250 c.c. of fluid are obtained. Now add hydrochloric acid by drops, until the calcium carbonate is completely dissolved, whereby the calcium humate is at the same time decomposed; in the ase of soils rich in calcium assist the action by gently warming. When the liquid has become clear, separate the solution from the precipitate by decantation and filtration, and lastly thoroughly wash the residue collected on the filter. The calcium may be directly determined in the liquid, if desired, according to the method described below ( 298, a). Now wash back the contents of the filter into the beaker pre- viously used, by the aid of small quantities of water, add 0-5 grm. caustic potassa or 2 to 3 c.c. ammonia, and allow to act for four to five hours with frequent stirring, thereby effecting the solu- tion of the humus substances adhering to the clay. Next nearly fill the beaker with distilled water, stir thoroughly, allow to stand twenty-four hours, f siphon off the liquid above the sandy sediment * Compt. rend., LXXVIII, 1276; GRANDEAU'S Handbuch, p. 105. f According to SESTINI (Landwirthschaftl. Versuchsstat., xxv, 47), twelve hours suffice. 296.] ANALYSIS OF SOILS. 825 into a flask of about 1 5 litres capacity, replace the water siphoned off by distilled water, stir again, and once more allow to stand twenty-four hours, repeating this operation six times,* until the supernatant liquid appears perfectly clear. The 1-5-litre flask now contains the total clay and humus substances, the latter in alkaline solution, while the beaker contains the sand, which may be separated into various fractions as in 294. To the liquid containing the clay add 5 to 10 grm. potassium chloride, in order to facilitate the deposition of the clay, allow the liquid to be ome perfectly clear, siphon off so far as possible, and decant through a filter ; finally bring the total clay onto the filter, wash it with distilled water until the last quantity added no longer runs through the filter, which is the case when the clay no longer contains potassium chloride. Now siphon off the clear water from the clay, which adheres strongly to the filter-paper, spread the latter on blotting-paper until the clay may be removed, then introduce the latter into a weighed platinum dish, dry it at 150, and weigh. Should any particles still adhere to the filter-paper, incinerate this and add the residue to the main bulk of the clay. To the colored liquid separated from the clay add acetic acid to distinct acidity, boil until the carbon dioxide has been ex- pelled, precipitate with lead acetate until the supernatant liquid appears colorless, allow to settle, then decant, filter, wash, dry somewhat, remove the precipitate from the filter-paper, dry at 100, and weigh. Now cautiously heat it in air, oxidize any reduced lead with ammonium nitrate, weigh the residue, deduct its weight from that of the lead humate, and calculate the difference as humus substances. Finally, to determine the moisture, dry a separate sample of the air-dried fine earth at 150 to constant weight. C. CHEMICAL ANALYSIS. 296. If the soil were treated as a whole, the object of the analysis being merely to determine the quantities of potassium, calcium, * SESTINI considers twelve repetitions to be necessary. 826 CHEMICAL ANALYSIS. [ 296. phosphoric acid, silica, alumina, etc., present in it, the results could be rapidly obtained, but they would afford no conclusions regarding the solubilities of which the individual constituents were capable. If, on the other hand, we treat a soil successively with various solvents, e.g., first water, then with water containing carbon dioxide and ammonium salts, then with a cold hydrochloric acid, then boiling hydrochloric acid, and lastly with concentrated sulphuric acid, certain conclusions are afforded regarding the relative solubilities of the soil constituents, but the analysis in this case becomes extremely complicated and requires the expen- diture of an extraordinary amount of time and labor. When, moreover, it must be remembired in addition that the power of the soil to retain some substances more firmly than others, hinders the complete extraction of the substances soluble in a given weak solvent, there must necessarily exist some uncertainty regarding the manner in which the chemical analysis of a soil may be best effected. It is quite certain that analyses of soils cannot be compared when they are carried out with quite different solvents, and that chemists must agree to employ certain definite solvents if the analyses are to have any value. Unfortunately, however, our knowledge does not yet suffice to enable us to decide with certainty the question as to what analytical treatment will afford the most practical statement of results, i.e., the form which, viewed in connection with the agricultural experiments made upon the same soil, will lead to the clearest and most certain conclusions; and it is hence evident that the views of chemists differ regard- ing the choice of the solvents to be employed. As none of the many methods proposed for treating soils with solvents have been generally adopted, or can be considered as having been generally agreed upon, I will detail the method of analysis described in the first edition of this work, and which appeared to me then most suitable; and this method, though naturally improved by reason of the experience gained since then, still appears to be the best adapted for practical purposes. If, for some special purpose, the investigation is to be still 297.] ANALYSIS OF SOILS. 827 further extended, and the behavior of the soil towards the solvents (e.g., water containing carbonic acid or ammonium salts) ascer- tained, this may be done without further directions, as the prepa- ration of such extracts, and the determination of the dissolved constituents in them, is in general carried out in the manner described for the aqueous extract. 1. DETERMINATION OF THE MOISTURE. Weigh off about 3 to 5 grm. of the air-dried fine earth in a platinum crucible or dish, dry at 125 to constant weight, and determine the loss of weight. 2. DETERMINATION OF THE CHEMICALLY-COMBINED WATER. Ignite the soil (dried at 125) with access of air, first over a lamp, finally with the blow-pipe, to constant weight. A loss of weight results from the expulsion of the chemically-combined water, carbon dioxide, nitric acid, ammonium c mpounds, and combustible organic matter, humus-like and otherwise; on the other hand, an increase in weight may occur under certain cir- cumstances, from the absorption of oxygen by ferrous and manganous compounds or metallic sul hides. The water of com- bination, therefore, can be ascertained from the loss in weight on ignition in air only when all the other substances present which may effect an increase or loss in weight, have been determined. Even then, the quantity found can be only approximate, because many of the factors which influence the resul cannot be deter- mined accurately. 3. DETERMINATION OF THE SUBSTANCES SOLUBLE IN WATER.* 297. For the separation of the aqueous extract, one of the following methods may be chosen : a. Weigh off as much fine soil as will be equivalent to 1000 grm. soil dried at 125, introduce it into a flask of about 6 litres capacity, * Compare the note in my Anleitung zur qualitativen chemischen Analyse 15th edit., p. 435. 828 CHEMICAL ANALYSIS. [ 297. add sufficient distilled water * to make 5000 c.c., including that contained in the weighed soil and removable at 125, and mark the level of the water in the flask by a strip of gummed paper or the like.f Allow the water to remain in contact with the soil for three days, frequently shaking or rolling the flask, then allow to settle, and siphon off the clear liquid into another flask; allow to stand again for two days, siphon off, and filter if necessary. 1000 c.c. of the liquid thus obtained contain the soluble constituents of 200 grm. soil dried at 125, and amounting, on an average, to 0- 1 to 0: 15 grm. /?. FR. SCHULZE'S method. For this method of extraction there is required a three-necked WOULFF'S flask of about 2 litres capacity, and with a tubulure fitted in one side near the bottom. Into the middle neck there is fitted air-tight a wide glass cylinder, open above, and narrowed below. After placing a loose plug of sponge in the narrowed part of the tube, covering this with sifted, clean gravel, and this in turn with sufficient washed, fine sand so that a small part of the wider tube may be filled with it, fill the cylinder with as much air-dried fine earth as will represent 1000 grm. of the earth after being dried at 125. One of the other two necks is connected with the tube of an air- pump; the other, as well as the tubulure at the side, is closed. Moisten the earth with water, add more from time to time, and allow to stand for 24 hours ; then exhaust the air in the flask, thus causing the water laden with the soluble portions of the earth to run off rapidly. When the flask is nearly filled, open the third tubulure, and allow the liquid to run off through the lower tubu- * E. WOLFF recommends to saturate one-fourth of the water with car- bon dioxide. j- This mark is required only when, after emptying out the first extract, it is desired to make a second, third, etc., with an equal volume of water, in order to determine their constituents also, and which some agricultural chemists consider of value (compare E. WOLFF'S Anleitung zur chemischen Untersuchung landwirthschaftlich wichtiger Stoffe, 3d edit., p. 25). Complete exhaustion of a soil cannot be effected even by repeated extraction with water, partly on account of its power of absorbing many substances, and partly because of the slow but continuous decomposition of the organic substances contained in it (compare A. COSSA, Zeitschr. /. analyt. Chem., v, 166). 297.] ANALYSIS OF SOILS. 829 lure.* The aqueous extract so obtained is perfectly clear. As a rule it is sufficient to continue the extraction until 5 litres of extract are obtained. By proceeding thus, the extract obtained in /? has the same degree of concentration as that obtained in a. The aqueous extract usually contains the following substances, which may be determined, if necessary, and if the quantities present are not too small: Potassium, sodium, ammonium, calcium, mag- nesium, ferric and perhaps also ferrous iron, sulphuric acid, phos- phoric acid, nitric acid, chlorine, silica, at times carbon dioxide, and humus substances. To determine these it is best to proceed as follows : a. Evaporate 2000 c.c. of the solution in a platinum dish, dry the residue at 125, and weigh. Note the weight as total con- stituents soluble in water. Then gently ignite the residue for a long time with access of air, moisten with a concentrated solution of ammonium carbonate, evaporate, gently ignite, ,and weigh. The loss of weight arises from the combustion of the organic sub- stances and the expulsion of the nitric acid and ammonium com- pounds; on deducting the weight of the two latter from the total loss in weight, the difference gives the humus substances. Treat the residue with water and some hydrochloric acid in a porcelain dish, add some nitric acid, evaporate to dryness, take up again with hydrochloric acid and water, and filter. Silica remains in the filter, sometimes mixed with a little carbon, which may be burned off by igniting .f Thy hydrochloric-acid solution divide into two parts, a and /?. a. To this first add ammonia until alkaline, then acetic acid in slight excess, then a few drops diluted ferric-chloride solution to color the solution red, heat to boiling, and filter. Dissolve the precipitate, after washing, in hydrochloric acid, evaporate the solu- tion with nitric acid, and determine the phosphoric add by the molybdenum method (p. 807 this volume). In the filtrate from * If the lower tubulure is lacking, empty the flask by means of a siphon. t If the aqueous extract was not quite clear, the silica thus obtained contains admixed clay, and must be separated from the latter by boiling with a solution of sodium carbonate (compare p. 406, 6, this volume). 830 DETERMINATION OF COMMERCIAL VALUES. [ 297. the basic ferric phosphate precipitate the calcium with ammonium oxalate, and in the filtrate from this precipitate the magnesium with ammonium phosphate (Vol. I, p. 621 [37]). /?, To this also add first ammonia until alkaline, then acetic acid in slight excess, heat to boiling if the liquid appears reddish, and filter. The precipitate contains all the iron. To determine this, wash, dissolve in hydrochloric acid, add tartaric acid, ammo- nia, and ammonium sulphide, allow to settle, filter, convert the ferric sulphide into ferric oxide, and weigh as such (Vol. I, p. 323, 6). (Should the iron precipitate also contain alumina, it must be treated as detailed on p. 803 this volume.) In the filtrate from the ferric phosphate precipitate the sul- phuric acid by a little barium chloride, evaporate the filtrate to dryness, remove the ammonium salts by igniting, add water, pre- cipitate the magnesia by adding a very small quantity of milk-of- lime, and proceed to determine the potassium and sodium accord- ing to p. 249 this volume. Should the composition of the portion soluble in water give rise to the fear that sulphuric acid may be driven off or reduced on igniting the residue, the sulphuric acid must be determined in a separate portion of the aqueous solution according to 205, 2. 6. Evaporate 1000 c.c. of the solution to dryness in not too large a dish, and determine any carbonates, and hence combined car- bonic acid that may be present, by means of decinormal nitric acid and decinormal soda lye (which must be free from metallic chlo- rides), according to p. 334, 3, this volume, using an indicator free from chlorine compounds (e.g., a little phenolphtalein p. 311 this volume). Then add a little pure sodium carbonate, evaporate to dryness, gently ignite, treat the residue with water, filter, acidu- late with nitric acid, and determine the chlorine by precipitation with silver nitrate (Vol. I, p. 521, a). c. Nitric acid (and also any nitrous acid present), and ammonia, if this is present in determinable quantity in the aqueous solution, are determined in other portions of the solution by the methods used in the analysis of natural waters (pp. 186 and 211 this vol- ume). The nitric acid may of course be determined by any of the 298.] ANALYSIS OF SOILS. 831 methods described in 149, especially those which may be carried out in the presence of organic substances, and which yield suffi- ciently accurate results even when determining very small quan- tities of nitric acid. Other methods of determining nitric acid will be found described under the Analysis of Manures. 4. DETERMINATION OF THE SUBSTANCES SOLUBLE IN HYDROCHLORIC ACID.* 298. Weigh off as much air-dried fine earth as will be equivalent to 100 grm. of soil dried at 125, cover it with 50 c.c. water in a 400- to 500-c.c. flask, mix uniformly, heat on the water-bath, and then add hydrochloric acid, sp. gr. 1 149, corresponding with 30- per cent. HC1, hi portions of 2 c.c. each, gradually and with shak- ing, until the last addition ceases to cause foaming from the evolu- tion of escaping carbon dioxide.f To the solution so obtained (water and hydrochloric acid), add an equal volume of hydrochloric acid of the strength mentioned above, heat on a water-bath for five hours with frequent shaking, then transfer the contents to a weighed porcelain dish, and rinse out with water, add 10 c.c. nitric acid, sp. gr. 1-2, and evaporate to dryness on the water-bath. Then add 50 c.c. hydrochloric acid of sp. gr. 1 1, corresponding to 20- per cent. HC1, allow to stand for one hour, then heat for one hour on the water-bath, add about 200 c.c. water, and separate the solution from the insoluble portion by decanting through a filter and thoroughly washing the residue. Collect the solution in a marked litre flask. If it is seen that the filtrate together with the washings measure more than 1 litre, collect the last washings separately, concentrate them by evaporating, and then transfer them to the litre flask, the contents of which, after the whole is made up to the mark, are uniformly mixed by shaking. * The following inorganic substances pass into solution in hydrochloric acid : Oxides and hydroxides ; bases of the carbonates ; phosphates, sulphates, bases of the silicates decomposable by hydrochloric acid, and a small quantity of the silicic acid from these. f Should the mass froth so that a running-over is feared, a few drops of alcohol will settle the foam. 832 DETERMINATION OF COMMERCIAL VALUES. [ 298. Spread the filter out on a glass plate, wash its contents into the dish containing the bulk of the insoluble matter, evaporate to dryness on the water-bath, weigh the dish together with its con- tents, and thus ascertain the relative weights of the undissolved residue and the fine earth originally weighed out. Then mix it thoroughly by triturating, transfer the uniformly mixed powder to a glass-stoppered bottle, and proceed with it as in 5; the hydro- chloric-acid solution, made up to 1 litre, however, treat as fol- lows : * a. 300 c.c., corresponding to 30 grm. of the fine earth dried at 125, are used for the determination of the ferric iron,f alumina, manganese, calcium, and magnesium, proceeding according to one of the methods detailed in 161, usually that described in 161, 2. As the presence of phosphoric and silicic acids renders necessary a few slight modifications, and as, moreover, a few additions must be made in view of the manganese determination, I will again give here a short sketch of the process. Remove the too great an excess of acid by evaporation, nearly neutralize with sodium carbonate, and precipitate with sodium acetate, as in Vol. I, p. 647 [85]. Dissolve the washed precipitate in hydro- chloric acid, filter, and determine any residual undissolved silica. Divide the filtrate into two parts, after it has been united with the hydrochloric-acid solution from the secondary alumina pre- cipitation, and which will be presently treated of; in one of these parts determine the iron either gravimetrically (Vol. I, p. 642, [77]), or volumetrically (Vol. I, p. 327, 6, a), and in the other part the ferric oxide and alumina, together with the phosphoric acid and some silica, by precipitating with ammonia, igniting, and weighing the precipitate. Fuse the latter with potassium di- * Regarding an essentially different method of treating the hydrochloric- acid solution, see P. LATSCHINOW, Zeitschr. /. analyt. Chem, vu, 211. f If the earth contains also ferrous iron, a separate portion of the soil must be extracted with diluted hydrochloric acid in a current of carbon dioxide with the aid of heat, and the ferrous iron determined in the solution according to Vol. I, p. 319, b. On deducting the ferrous iron found from the total iron obtained above, after calculating to equal quantities of soil, the difference will give the ferric iron present in the soil. 298.] ANALYSIS OF SOILS. 833 sulphate, treat with hydrochloric acid and water, and thus ascer- tain the small quantity of silica present. On deducting this, also the phosphoric acid found in 6, and also the ferric oxide, from the weight of the precipitate thrown down by the ammonia, the alumina is obtained. Acidulate with hydrochloric acid the nitrate from the pre- cipitate thrown down by sodium acetate, and add ammonia until just alkaline, thereby usually obtaining a further slight precipitate of alumina, which collect, wash, and dissolve in hydrochloric acid (if it had still contained manganese it would have been necessary to once more precipitate, avoiding any appreciable excess of ammonia). Add the hydrochloric-acid solution of the alumina to the hydrochloric-acid solution of the precipitate thrown down by uie sodium acetate, as detailed above. From the solution which remained clear on the addition of ammonia, or which was filtered from the alumina precipitate, precipitate the manganese with ammonium sulphide (Vol. I, p. 295, a), or by adding bromine and ammonia, the latter method being preferable in the case of small quantities of manganese. To -effect this, add brominized hydrochloric acid to the liquid until it appears yellow, then add ammonia until alkaline, and heat to boiling. The resulting brown precipitate of hydrated manganese dioxide cannot be directly ignited and weighed, as it contains alka- line earths. It should, after being collected and washed, be dissolved in a little hot hydrochloric acid, the solution diluted, then pre- cipitated in a small flask with ammonia and ammonium sulphide, and the precipitated manganous sulphide weighed. The liquid filtered from the latter, and acidulated with hydrochloric acid, mix with the filtrate from the hydrated manganese dioxide, and evapo- rate the whole to dryness; then remove the ammonium salts by igniting, and in the residue determine the calcium and magnesium according to Vol. I, p. 619. If the manganese has been previously precipitated as manganous sulphide, treat the filtrate from this, and acidulate with hydrochloric acid, in the same way. 6. 300 c.c. of the solution, corresponding to 30 grm. of the fine earth dried at 125, are used for the determination of the 834 DETERMINATION OF COMMERCIAL VALUES. [ 298. phosphoric acid* proceeding as detailed on p. 491, 10, this volume. c. 300 c.c. of the liquid corresponding to 30 gnn. of the fine earth dried at 125, serve for the determination of the sulphuric acid and alkalies. For this purpose remove the greater part of the free acid by evaporating, dilute, and precipitate the sulphuric acid by adding a slight excess of barium-chloride solution to the hot liquid; allow to stand for some time, filter, ignite, and weigh the barium sulphate. Should this appear reddish from admixed ferric oxide, it must, in order to obtain accurate results, be fused with sodium carbonate and the sulphuric acid in the aqueous solution of the melt determined as in Vol. I, p. 441, 6, a. Precipitate the filtrate from the barium sulphate with am- monia and ammonium carbonate, filter, evaporate to dryness, and remove the ammonium salts by gently igniting; heat the residue with water, boil with a little milk-of-lime, filter, precipitate with ammonia and ammonium carbonate, filter, evaporate, and heat gently; add a little water, precipitate once more with a little ammonia and ammonium carbonate, evaporate, heat, weigh the now pure alkali chlorides, and separate the potassium and sodium by means of platinum chloride (Vol. I, p. 599, 1, a). In the case of soils very rich in humus, this method does not answer, as the large quantity of organic matter present in the solution, and which has beon but incompletely decomposed by evaporating with nitrohydrochloric acid, interferes with the pre- cipitation of the hydrates and also of the ferric phosphate and alu- mina. The organic matter may, of course, be removed by evapo- rating and igniting, but in this case the iron and aluminium are converted into the very inconvenient condition of difficultly soluble basic salts. In such a case it is best to proceed as follows: 1. 300 c.c. of the hydrochloric-acid solution serve for the determination of the sulphuric acid and alkalies; any notable deviation from the method described above in c is unnecessary. * Regarding other methods of determining phosphoric acid, see TH. SCHLOSING (Zeitschr.f. analyt. Chem., vu, 473, and viu, 500) ; and W. ScntiTZE (ibid., ix, 413). 299.] ANALYSIS OF SOILS. 835 2. Evaporate 600 c.c. almost to dryness in a platinum dish, then add pure potassa lye until strongly alkaline. Evaporate the whole to dryness with the addition of a little sodium carbonate and potassium nitrate, and ignite to destroy the organic matter; soften with water, and decant the solution into a flask ; transfer the insoluble residue to a glass or porcelain dish, and warm it with hydrochloric acid until dissolved, unite the two solutions, and make up to 600 c.c., and in 300 c.c. determine the constituents mentioned in a, and in the other 300 c.c. determine the phosphoric acid according to the method above detailed. 5. EXAMINATION OF THE PORTION OF SOIL INSOLUBLE IN HYDROCHLORIC ACID.* 299. Dry that portion of the fine earth insoluble in hydrochloric acid on the water-bath, weigh, triturate, and uniformly mix, then trans- fer to a dish, mix rapidly once more, and weigh immediately without delay portions of 5, 10, and 15 grm. each. The portions are best taken from the mass by means of a teaspoon. It must always be remembered that a powder like the one in question is very prone to lose in uniformity, as the coarser particles tend to sink to the bottom, leaving the finer portion at the surface. a. Ignite the 5-grm. portion with access of air, and weigh the residue. After calculating from the part to the whole, the total quantity of anhydrous mineral constituents of the soil insoluble in hydrochloric add, is ascertained. 6. Extract the 10-grm. portion several times by boiling with a concentrated solution of sodium carbonate, and proceed to deter- mine the silica thus dissolved, according to p. 406, 6, this volume. The silica found here may be either that separated in the hydrated condition from the decomposable silicates on treating the earth * Of inorganic substances, this contains in particular the silica from the silicates decomposable by hydrochloric acid, the silicates not decomposable by hydrochloric acid, and at times fragments of rock; at other times clay, together with the hydrated silica often admixed with it, and quartz sand. 836 DETERMINATION OF COMMERCIAL VALUES. [ 300. with hydrochloric acid, or that mixed with the clay of the soil as hydrate (p. 420, g, this volume). c. Heat the 15-grm. portion with about 40 c.c. concentrated, pure sulphuric acid to which a little water has been added, for 10 to 12 hours in a platinum dish, and so that the excess of acid is nearly but not quite driven off. When cold, moisten with concen- trated hydrochloric acid, allow this to act for some time in the warm, add water, heat, pass through a filter, and repeat the opera- tion until the insoluble residue has been completely and thoroughly washed. Spread out the filter on a glass plate, wash the adhering portion of the residue into the dish containing the main bulk, evap- orate the whole, dry at 100, weigh, and thus ascertain the relation in weight to that portion of the soil insoluble in hydrochloric acid, and thereby also to the weighed fine earth; then mix uniformly. Mix the filtrate from the residue with the washings in a 500-c.c. flask, and in 250 c.c. determine any silica that may have passed into solution, together with the alumina, iron, calcium, and mag- nesium, as in 4, a; in the remaining 250 c.c. determine the potas- sium and sodium as in 4, c. It must here be noted that the copious precipitate of barium sulphate obtained on precipitating the sul- phuric acid with barium chloride, must be ignited after being washed and dried, then extracted by boiling with diluted hydro- chloric acid, and lastly exhausted with water, in order not to lose the alkali salts carried down with it. The solution so obtained is united with the filtrate from the barium sulphate. 6. EXAMINATION OF THE RESIDUE INSOLUBLE IN SULPHURIC ACID. 300. a. Boil 3 or 4 grm. of the residue repeatedly with a solution of sodium carbonate, and determine in the solution the dissolved silica (p. 420, g, this volume). On deducting from the quantity * By treatment with sulphuric acid, the clay is 4 e composed, the bases ccntained therein going into solution. The residue thus contains: The silica from the silicates decomposed by hydrochloric acid, that admixed as hydrate with the clay, and that which was combined with bases in the clay, as well as the silicates not decomposable by hydrochloric or sulphuric -acid (fragments of rock), and also quartz sand. 301.] ANALYSIS OF SOILS. 837 found that obtained in 5, 6, the remainder will give that belonging to the clay in the soil; it is the principal constituent of the clayey portion of the soil, which resists the solvent action of hydrochloric acid, but is decomposed by sulphuric acid. The residue remaining after extraction by boiling with sodium carbonate, wash, dry, ignite, and weigh. After calculating from the part to the whole, the result will give the soil constituents insoluble in hydrochloric acid and decomposable by sulphuric acid. 6. Triturate 4 to 6 grm. of the residue insoluble in sulphuric acid to an exceedingly fine powder in an agate mortar, and uniformly mix the powder. Decompose about 3 grm. of this with hydro- fluoric acid (Vol. I, pp. 513 to 516), and then determine the bases present. If the silica is to be determined not only by difference, but also directly, treat 0-5 grm. of the fine powder as in Vol. I, p. 511, b, a. On deducting the total silica thus obtained from that found in 6, a, the silica of the silicates not decomposable by sul- phuric acid, and present as quartz sand, is ascertained. c. As by b only the total silica present in the form of quartz and that combined with bases is obtained, it is necessary, in order to find the latter, to directly determine that present as quartz. For this purpose use the remainder of the fine powder prepared as in 6, b. The methods suitable for isolating the quartz (heating with phosphoric acid, or with sulphuric acid in sealed glass tubes *) have already been detailed under the analysis of clay (p. 419 this volume). 7. DETERMINATION OF THE CARBON CONTAINED IN THE ORGANIC COMPOUNDS. 301. Carbon is present in the soil not only as carbonic acid, but also in organic substances, and in fact, chiefly in those which, through mouldering and decay, have become converted into humus (ulmin, humin, ulmic acid, humic acid, geic acid, etc.). It may suffice to determine the total carbon present in the organic matter, or to * Regarding this method, compare J. HAZARD (Zeitschr. f. analyt. Chem., xxui, 158), who has shown that by this treatment a great deal, but by no means all, of the silicates is decomposed. 838 DETERMINATION OF COMMERCIAL VALUES. [ 301. make supplementary determinations also regarding the portion soluble in a solution of sodium carbonate (humus acids), of the portion soluble on boiling with potassa solution (ulmin, humin), and lastly of the waxy and resinous substances occasionally present. a. Determination of the total Organically Combined Carbon, a. By ultimate analysis in the dry way. aa. If the analysis of the fine earth dried at 125 is conducted as detailed on p. 129, this volume, 191, then, from the carbonic acid obtained, that present in the form of carbonates must be deducted ( 303, a). As the quantity of carbon in the organic matter is thus ascertained from the difference between the two determinations, the accuracy of the result is impaired. bb. R. WARINGTON and W. A. PEAKE * recommend to first decompose the carbonates present, and for this purpose cover about 10 grm. of the finely powdered soil with a concentrated solu- tion of sulphurous acid, and then evaporate the whole to dryness. The residue is then transferred to a platinum boat, and the organic matter burnt in a combustion tube with the aid of a current of oxygen in the presence of cupric oxide (compare p. 39, this vol- ume). For the absorption of the nitrogen oxides and aqueous vapors, WARINGTON and PEAKE employ a wash-bottle containing concentrated sulphuric acid, and a U-tube filled with pieces of pumice stone moistened with sulphuric acid, collecting the carbon dioxide in two U-tubes filled with caustic soda (or soda-lime) . cc. G. LOGES f recommends to weigh off the earth to be ex- amined in a very thin glass dish (a HOFFMEISTER dish), then to add to it diluted phosphoric acid (in the case of sandy soil too large an excess of acid must not be employed) , and then to evaporate the whole to dryness on the water-bath. The dish and its con- tents are then ground, mixed with powdered cupric oxide, and introduced into a combustion tube about 60 cm. long, open at both ends, and in the fore part of which is placed a layer of granu- * Berichte der deutsch. chem. Gesellsch., xm, 2096. t Landwirthschaftl. Versuchsstationen, xxvin, 229 and 241 ; Zeitschr. /. analyt. Chem., xxn, 619. $ 301.] ANALYSIS OF SOILS. 839 lar cupric oxide 20 cm. long between asbestos plugs. The hinder end of the combustion tube is connected with two wash-bottles, the first containing potassa solution, and the second baryta water; the fore part of the tube is connected first with a drying cylinder the upper half of which is filled with cotton, then with an absorp- tion tube for retaining baryta water, next with a wash-bottle containing baryta water, and lastly with an aspirator. The drying cylinder containing the cotton is for the purpose of retaining any water and oxygen compound of nitrogen; it may be replaced t>y a copper spiral inserted in the fore part of the tube. The flask of baryta water interposed between the absorption tube and the aspirator enables the operator to ascertain whether all the carbon dioxide has been retained by the former, a condition which must prevail in order to obtain successful results. The operation is begun by heating the granular cupric oxide to bright redness, while a current of air is drawn through the apparatus; 100 to 150 c.c. of baryta water (titrated by the aid of -an oxalic-acid solution containing 10 grm. per litre) are then intro- duced into the absorption tube. Next, slowly heat the combustion tube, proceeding from the fore to the hinder part of the tube, while a quite rapid current of air from a MARIOTTE flask is con- stantly drawn through the apparatus. Lastly determine the residual barium hydroxide in 25 or 50 c.c. of the clear baryta water after settling, by the aid of oxalic acid, using potassium rosolate as an indicator; this gives the barium precipitated by the carbonic acid, and consequently the carbon dioxide and the carbon.* P. By oxidation in the wet way, with chromic and sulphuric acids, in the manner described on p. 510, bb, this volume. This method, which was formerly much used, I call attention to here simply in order to point out that it is useless in soil analysis. According to WARINGTON and PEAKE (loc. cit.) only 80 to 90 per cent., and according to G. LOGES (loc. cit.) only 64 to 96 per cent., of the carbon present is thus determined; and in fact, accord- * Compare the determination of carbonic acid in the atmosphere ( 336 to 340). 840 DETERMINATION OF COMMERCIAL VALUES. [ 301. ing to the latter's investigations, because many of the organic substances in soils, on oxidation, yield acetic acid, which resists further oxidation by chromic acid.* According to FR. SCHULZE, 58 parts of carbon represent on an average 100 parts of organic matter in soil; and every 60 parts represent 100 parts of humus. b. Determination of Humus. The brown or black substances formed as a result of the action of moisture and air on the residual plant matter in the soil, and which are of great influence on the character and fertility of the soil, (although opinions have been, and still are, held regarding their mode of action), are termed humus substances. Attempts have been made to isolate a number of these, and to characterize them as individual chemical compounds, with various names, e.g., ulmic acid, humic acid, ulmin. humin, etc. As numerous, however, as these investigations f have been, the subject cannot be considered as at all exhausted, or as having led to any definite conclusion, and this is easily understood from the fact that the various constituents of humus very closely resemble each other in properties, and that neither they nor their compounds are obtainable in a crystalline form. Certain facts, however, have been established, and, being of importance in judg- ing of the character of soils, they must be here considered. Among these is the fact that many of the humus constituents (humus acids) dissolve in boiling solutions of alkali carbonates whether due to the humus acids being present in the free state, or whether because their saline compounds are decomposed by alkali carbonates while other humus constituents are not dissolved although they do dissolve in caustic alkalies, being of course con- verted into humus acids thereby. * Compare CROSS and BEVAN, Zeitschr. /. analyt. Chem., xxvi, Part I. f See the collection of the many old investigations in L. GMELIN'S Hand- buck der chemie, 4th edit., by K. KRAUT, vn, 1855; OTTO, in SPRENGEL'S Bodenkunde, p. 430; FR. SCHULZE, Journ. f. prakt. Chem., XLVII, 241; W. DETMER, Landwirthschaftl Versuchsstat., xiv, 248; GRANDEAU'S Handbuch, pp. 108 and 112; O. PITSCH, Landwirthschaftl. Versuchsstat., xxvi, 1. 301.] ANALYSIS OF SOILS. 841 a. Determination oj the humus constituents (humus adds soluble in alkali carbonates). Digest from 10 to 100 grm. of the air-dried fine earth (accord- ing as to whether the qualitative analysis has shown much or little humus acid to be present) with a solution of sodium car- bonate (1 part anhydrous salt to 10 parts water) on the water- bath for about four hours, then filter, and wash with boiling water. In order to determine the dissolved humus substances, treat the more or less brown filtrate either according to the method described on p. 825 this volume (acidulating with acetic acid, boiling, pre- cipitating with lead oxide, etc.), or, acidulate with hydrochloric acid, collect the brown flocks on a filter dried at 100 and weighed, wash with cold water until the washings no longer have an acid reaction, dry at 100, weigh, incinerate, and deduct the weight of the ash from the weight first obtained, calculating the difference as humus acids. As in the latter method the filtrate is always colored, the first method is to be preferred in the case of light-brown solutions. /?. Determination of the humus constituents (humin, etc.) insoluble in alkali carbonates. Digest the residue from a in a porcelain dish with a solution of 1 part potassium hydroxide in 10 parts water on the water-bath for several hours, replacing the water as it evaporates; then dilute, decant through a filter, treat the residue anew with caustic potassa just as before, dilute, filter, wash, and in the filtrate deter- mine the humus acids formed from the humin, etc., as in a.* * FR. SCHULZE has proposed to determine the humus substances ex- tractable by alkaline solutions, with potassium permanganate, i.e., in the same way organic matter in water is determined (see p. 203 this volume). SCHULZE, to effect this supplementary determination, boils 5 grm. of fine earth with 100 c.c. of a 0-1- to 1-per cent, potassa solution (E. WOLFF uses a 0-5-per cent, solution), according to the quantity of humus in the soil; he then pours the mixture on a filter (instead of using paper, the lower part of the funnel is filled with well-ignited finely granular sand), washes, makes up the filtrate to 150 or 200 c.c., and employs a few c.c. of this solution for the above-named determination, which, naturally, cannot give a very accu- rate result. 842 DETERMINATION OF COMMERCIAL VALUES. [ 302. c. Determining the Waxy and Resinous Substances. If it is desired to more closely determine these substances, which occur in appreciable quantities in some kind of soil (meadow, marsh, etc.), dry on the water-bath a quantity of air-dried earth corresponding to 100 grm. fine earth dried at 125, then boil it repeatedly with strong alcohol, transfer the filtrates to a flask, and distil cff half the alcohol; then allow to c.c. magnesium-chloride mixture, allow to stand covered for two hours, and then proceed as in aa. cc. Second modification by P. Wagner f ; this depends upon the fact ascertained by GILBERT J and E. RICHTERS that in the pres- ence of 15 per cent, ammonium nitrate, about half the usual quantity of molybdenum solution suffices to precipitate all the phosphoric acid. To 25 or 50 c.c. of the phosphate solution contained in a beaker, and containing perhaps 1 to 2 grm. phosphoric acid, add so much of a concentrated ammonium-nitrate solution | and 5 5- or 6 1-per cent, molybdenum solution (see foot-note, p. 856) that the total liquid will contain 15 per cent, ammonium nitrate, and at least 50 c.c. molybdenum solution for every 0-1 grm. phosphoric acid present. Heat the contents of the beaker in a water-bath to 80 or 90, and * Zeitschr. /. analyt. Chem., xix, 444. t Ibid., xxi, 289. J Correspondenzblatt d. Vereins analytischer Chem., i, Nov. J 78. DINGLER'S polyt. Jour., cxcix, 183; Zeitschr. f. analyt. Chem., x, 469 II 750 grm. ammonium nitrate dissolved in sufficient water to measure 1 litre. 860 DETERMINATION OF COMMERCIAL VALUES. [ 310. then set aside for about an hour. Then filter, and wash the precipi- tate with a diluted, acidulated solution of ammonium nitrate.* Next dissolve the precipitate as in bb with 2^-per cent, ammonia, add a further quantity of the latter so that the volume of the liquid will be about 75 c.c., and then while stirring, drop in 10 c.c. mag- nesium-chloride mixture for every 1 grm. phosphoric acid present,, and proceed further as in bb. /?. C. GLASER'S Method. 310. I have no personal knowledge of this method, which was first proposed by C. GLASER.f As, however, according to GLASER, it has constantly given good results, I give a description of it here. The method is based upon the fact that phosphoric acid in the presence of calcium salts, etc., and ammonium citrate, is at once and completely precipitated by magnesia mixture, if sufficient sul- phuric acid is present to convert all the calcium salts into sulphates, and provided no more ammonium citrate is used than is necessary to keep the calcium salts dissolved in alkaline solution. The method is carried out as follows : Add ammonia to the acid liquid containing the calcium phosphate until a turbidity just forms, then cautiously add, best by means of a dropping-tube or small pipette, as much of a 50-per cent, citric- acid solution as will suffice to clear the liquid again. If the solution is now alkaline, it is ready for precipitation. Should it, however, still have an alkaline reaction, add ammonia and citric acid by turns until the desired point is reached, i.e., until after the addition of the last drop of citric acid, the perfectly clear liquid is still dis- tinctly alkaline. The point may be easily hit, after some practice, with 3 or at most 4 c.c. of citric-acid solution. To the cooled liquid now add, drop by drop, and with constant stirring, the requisite * 150 grm. ammonium nitrate, 10 c.c. nitric acid, and sufficient water to measure 1 litre. t Zeitschr. /. analyt. Chem., xxiv, 178. 310.] ANALYSIS OF MANURES. 861 quantity of magnesia mixture,* and then a large excess of ammonia. After 6 to 8, or, better, 12 hours, filter, wash with 4-per cent, am- monia, dissolve the precipitate on the filter in diluted (about 15-per cent.) sulphuric acid, and reprecipitate with ammonia and a little magnesia mixture. After settling, which is usually complete in one hour, collect on asbestos contained in a GOOCH platinum cru- cible, with the aid of the pump, wash with ammoniacal water, then ignite, and weigh the magnesium pyrophosphate.t If it is desired to determine the phosphoric acid in any of the phosphates enumerated in I volumetrically (by the uranium method) , more particularly in the case of phosphates poor in ferric oxide, solution is effected as in 308 ; but hydrochloric may be used instead of nitric acid. In this case remove the free acid so far as possible by evaporation, finally neutralize with potassa or soda lye, and then proceed according to 313, ftp. Should the phosphoric acid soluble in ammonium citrate be de- termined in one of the phosphates mentioned in I, proceed accord- ing to 315, and then determine that still remaining in the insoluble residue. On deducting this quantity from the total phosphoric acid, that soluble in the ammonium citrate is ascertained. * C. GLASER gives the following directions for preparing this : Dissolve 140 gnn. magnesium sulphate, 150 grm. ammonium sulphate, and 30 grm. ammonium chloride, in 360 c.c. 16-per cent, ammonia and 1650 c.c. water, and after standing for several days, filter. f The three test analyses detailed by C. GLASER appear to be perfectly satisfactory; in my opinion, however, there remains to be ascertained whether in these cases two errors have not compensated each other. According to observations hitherto made, ammonium citrate may hold some ammonium- magnesium phosphate in solution (as is known of tartaric acid, see Vol. I, p. 459, e, ), while, on the other hand, the precipitate will contain an ad- mixture of magnesium sulphate (compare ROSE'S Handbuch der analyt. Chem., 6th ed., by FINKENER, u, 513). 862 DETERMINATION OF COMMERCIAL VALUES. [ 311. II. MANURES CONTAINING PHOSPHORIC ACID PARTLY IN THE FORM OF WATER-SOLUBLE COMPOUNDS. 311. Under this heading are comprised the products obtained on treating the phosphates mentioned in I with sulphuric acid, i.e., superphosphates. These contain in the first place, besides large quantities of cal- cium sulphate and smaller quantities of undecomposed basic cal- cium phosphate, large quantities of acid calcium phosphate, and, under some circumstances, also free phosphoric acid. The phos- phoric acid in the two last forms is soluble in water; that in the other forms is insoluble. The superphosphates are not, however, unchangeable, as when stored. The acid calcium phosphate, CaH 4 (PO 4 ) 2 , or the phosphoric acid, H 3 (PO 4 ) acts upon the basic calcium phosphate, Ca 3 (PO 4 ) 2 , with the production of neutral cal- cium phosphate, Ca 2 H 2 (PO 4 ) 2 . As this is insoluble in water, the portion of the phosphate soluble in water decreases, while the por- tion insoluble in water increases. This change is termed "rever- sion of the superphosphate." While this may occur in super- phosphates prepared by the action of sulphuric acid upon almost pure basic calcium phosphate, it occurs to a much greater extent in such obtained from crude phosphates rich in ferric oxide or aluminium silicate, and particularly when these contain also cal- cium fluoride, as the latter evolves hydrofluoric acid by the action of the sulphuric acid upon it, whereby the admixed silicates are decom- posed. The reversion is then due not alone to the reactions already mentioned, but also to the formation of insoluble ferric and alu- minium phosphates. Phosphoric acid hence has a different agricultural value accord- ing to the condition in which it is present, whether it is soluble in water, reverted, or undecomposed (already insoluble); hence in a complete analysis of superphosphates, the phosphoric acid present in each of these forms must be separately determined. As, how- ever, such analyses require much time and labor, attempts have been made to determine the agricultural value more simply. To 312.] ANALYSIS OF MANURES. 863 these attempts are due the terms "soluble phosphoric acid," and "citrate-soluble phosphoric acid." In the following all these methods of determination will b considered, beginning however, with the determination of the moisture. 1. Determination of the Moisture. This is effected as in I, 1, (p. 854, this volume), and as a rule at ^ 00. As, however, the large quantity of calcium sulphate present yields all of its water but very slowly at 100, a constant weight is obtained only after prolonged heating. . 2. Determination of the Phosphoric Acid, a. In the three forms in which it may occur in Superphosphates. a. Determination of the water-soluble phosphoric acid. 312. aa. Preparation of the Solution. act. By washing on the filter* Triturate the superphosphate with a little water in such a manner as to completely break down the lumps, but not to reduce the coarser, hard pieces to fine powder, then rinse onto a filter, and wash, best with the aid of the water- pump, with cold water, until the washings cease to have an acid reaction. If the first filtrate becomes turbid on mixing with the washings, dissipate the turbidity by adding a little nitric acid; then make up to a definite volume, and mix. In the case of finely powdered, homogeneous superphosphates, prepare 250 c.c. of solu- tion from about 5 grm. of the substance; with less uniform prepa- rations, use 10 or 20 grm., and make 500 or 1000 c.c. of solution. Pfi. By digestion with Water. Although the method described in aa must be considered as giving the most accurate results,! yet, because it requires more time, it is not employed in the German agricultural experimental stations; these have agreed upon the following method:! * Compare Zeitschr. /. analyt. Chem., vn, 304, and XH, 276. t Ibid., XH, 275. J Ibid., xxi, 288. 864 DETERMINATION OF COMMERCIAL VALUES. [ 313. Mix 20 grm. of the superphosphate with water in a mortar, lightly crush with the pestle without finely triturating, and rinse into a litre flask. Then immediately fill to the mark, allow to stand for two hours,* with frequent shaking at the temperature of the room, and then pass through a dry filter. The volume of the undissolved residue must be taken into account in the subsequent calculation. bb. Determining the Contents of the Solution. 313. aa. Gravimetric Method. Take a measured volume of the solu- tion prepared according to 312 aa or /?/?, and containing 1 to 0-2 grm. phosphoric acid and determine the latter according to 309. pp. Volumetric Uranium Method.^ As different quantities of uranium solution may be used for precipitating one and the same quantity of phosphoric acid, according as the solution of the latter contains or is free from a calcium salt, and according to whether an ammonium salt is present or not, it must be considered an essential rule that the phosphoric-acid solution which is to serve for stand- ardizing the uranium solution, must be as nearly as possible like the one to be tested. Upon this basis is founded the following method agreed upon by the German agricultural experimental stations, which, however, is considered as suitable only for those superphosphates that contain less than 1 per cent, of phosphoric acid in combination with iron or aluminium. J In the case of superphosphates containing not appreciably more than 20 per cent, of water-soluble phosphoric acid, add 50 c.c. of * The duration of the digestion, in the case of certain superphosphates, exerts a not inappreciable effect on the result, hence the period of digestion agreed upon must not be arbitrarily altered; compare ABESSER, JANI, and MARCKER, Zeitschr. f. analyt. Chem., xn, 275. f As the uranium method, which was already described in Vol. 1, p. 453, g, has in the meantime been greatly improved (compare particularly ABESSER, JANI, and MARCKER, Zeitschr. /. analyt. Chem., xn, 254), I must make here further additions to what has been said before. t Zeitschr. f. analyt. Chem., xxi, 288. 313.] ANALYSIS OF MANURES. 865 an acidulated solution of ammonium acetate * to 200 c.c. of the solution prepared according to 312, /?/?. As soon as the resulting white precipitate of ferric phosphate and aluminium phosphate has settled, pass through a dry filter, remove th nitrate, and wash the precipitate thrice with hot water, then ignite and weigh ; calculate one-half its weight as phosphoric acid combined with iron and aluminium. When superphosphates contain appreciably more than 20 per cent, of water-soluble phosphoric acid, employ only 100 c.c. of the solution, and add 100 c.c. of water and 50 c.c. of the acidulated ammonium-acetate solution. The uranium solution employed is made from uranium nitrate t the titration being effected by using 50 c.c. of the filtrate from the ferric and aluminium phosphates (but not diluted with the wash- ings), and consisting of 40 c.c. of the original solution and 10 c.c. cf ammonium-acetate solution (see Vol. I, p. 455). The end reaction is ascertained, after briskly boiling over a naked flame or heating in a boiling water-bath, each time, by adding finely powdered potassium f errocyanide, or a freshly made solution of it, to the solu- tion on a white porcelain plate. In order to prevent any separation of calcium phosphate from the solution, it is advisable to add the approximately necessary quantity of uranium solution in the cold, and to then heat. The effective value of the uranium solution is ascertained by the i id of an iron-free solution of a superphosphate containing about 16 per cent, of phosphoric acid, or a solution of approximately equal phosphoric-acid strength prepared by treating pure basic calcium phosphate with a corresponding quantity of sulphuric acid. When standardizing the uranium solution the same proportion must be maintained between the phosphoric-acid solution and that of the ammonium acetate, as in the analysis of the superphosphate. * 100 grm. pure ammonium acetate and 100 c.c. acetic acid of sp. gr. 1 039 to 1 040, with sufficient water to measure 1 litre. f Dissolve 100 grm. uranium nitrate in 2820 c.c. water, and neutralize the usually small quantity of free nitric acid present by adding 10 grm. ammonium acetate; 1 c.c. of the solution corresponds to about 0-005 phos- phoric acid. 866 DETEEMINATION OF COMMERCIAL VALUES. [ 314. The phosphoric-acid content of the titrating solution is determined by the molybdenum method. ff. Acidimetric Methods. 314. The acidimetric methods of superphosphate analysis are based upon the determination of the acidity by a standard alkaline solu- tion. Even though the aqueous solution of the superphosphate contains as a rule only acid calcium phosphate together with cal- cium sulphate, it must nevertheless be remembered that the solu- tion may also contain free phosphoric acid, and in faultily prepared substances, free sulphuric acid too. As, in such cases, on direct titration with soda-lye correct results cannot be obtained, the acidimetric method of determining the value of superphosphates must be founded on another basis. The first method proposed for this purpose is that of A. MOLLENDA ; * it is based upon the precipi- tation of the calcium in the solution by sodium or ammonium oxalate at the boiling temperature, and subsequent titration of the solution now containing acid alkali phosphate, by normal, or, better yet, semi-normal, soda-lye, with phenolphtalein as indicator. The end reaction (a violet coloration) appears as soon as the acid alkali phosphate (e.g., monosodium phosphate) has become converted into the so-called neutral salt (disodium phosphate). 1 equivalent of sodium corresponds to 1 equivalent of phosphoric acid. If the superphosphate contains free acid, add lime water or sodium car- bonate to the solution until a slight turbidity forms and persists even on stirring, whereby the free sulphuric acid is converted into neutral sulphate. Then precipitate with the alkali oxalate and proceed as described. It is better to ascertain the quantity of lime water or sodium carbonate required for this purpose by a sepa- rate experiment, and according to the results obtained to add to the solution to be titrated only so much of the neutralizing sub- stance that the solution will just remain clear. It is unnecessary to filter off the calcium oxalate. The liquid to which the excess of * Zeitschr. /. analyt. Chem., xxn, 155. 314.] ANALYSIS OF MANURES. 867 ammonium oxalate has been added may be directly titrated with normal soda solution, using phenolphtalein or phenacetolin as indicator. The test analyses given by MOLLENDA are satisfactory. See also R. T. THOMSON.* The process devised by A. EMMERLING! has also been thor- oughly worked out and adapted as well for ferruginous super- phosphates. The method is based upon the two following experi- mentally established facts: 1. Phosphoric acid is almost completely precipitated as basic calcium phosphate on adding soda lye to a solution of superphos- phate to which an excess of calcium chloride has been added; the precipitation is perfectly complete, however, only when the mix- ture of the superphosphate solution and calcium chloride is allowed to run into the soda-lye, because in that case the liquid is alkaline during precipitation. On adding phenolphtalein to the solution, the end reaction appears when 2 equivalents of Na-jO have been used for 1 equivalent of phosphoric anhydride. 2. On adding caustic soda to a solution of free phosphoric acid colored with methyl orange, the color changes from violet-red to yellow or orange-yellow when all the phosphoric acid has been con- verted into acid sodium phosphate (monosodium phosphate). For carrying out the method the following are required : 1. A solution of caustic soda, 1 c.c. of which corresponds with about 0-005 grm. phosphoric anhydride (P 2 O 5 ), calculated on the proportion of 2NaOH : P 2 O 5 . When standardizing this solution by means of one-fifth- or one-tenth-normal hydrochloric acid, the same quantity of phenolphtalein (2 c.c.) should be added as is used when titrating the phosphoric acid. 2. A calcium-chloride solution, prepared by dissolving 200 grm. of pure, dry calcium chloride in one litre water. The alkaline solution must be most carefully neutralized. The quantity of normal hydrochloric acid required to neutralize 100 c.c. of the solution is ascertained by titration, and the remaining 900 c.c. are then correspondingly neutralized. * Zeitschr. /. analyt. Chem., xxiv, 232. f Landwirihschaftl. Versuchsstationen, 1886, 429. 868 DETERMINATION OF COMMERCIAL VALUES. [ 314. 3. A solution of 1 grm. phenolphtalein in 100 grm. alcohol. 4. A solution of methyl orange prepared by adding small quan- tities of methyl orange to water until the solution has a deep orange-yellow color, and then filtering. The analysis is carried out as follows: Mix 200 c.c. of the super- phosphate solution (prepared as in 312) with 50 c.c. of the cal- cium-chlor-de solution and allow the mixture to run from a burette into a beaker containing a measured quantity of the soda-lye (which has been slightly diluted with water, and to which 2 c.c. of the phenolphtalein solution have been added), until the red color en- tirely disappears. In the case of superphosphates of mj.h per- centage measure off 20 c.c.; with superphosphates containing 10 to 15 per cent. P 2 O 5 take 10 c.c.; and with poorer superphos- phates take 5 c.c. The addition of the mixture of superphosphates with calcium chloride is made rapidly at first until the color begins to be weak, but towards the end, drop by drop only. The end reaction is reached when every trace of the reddish tint has van- ished, and a whitish, yellowish, or faintly brownish color has devel- oped. When stirring the liquid while the mixture is being dropped in, the formation of foam should be avoided as much as possible, as this renders difficult the recognition of the color change. The experiment must be repeated. In this manner there is found the quantity of soda required to neutralize any sulphuric acid present, or that required to convert free phosphoric acid into acid sodium phosphate. Now measure off the same number of c.c. of the superphosphate- calcium-chloride solution as were required for the last test, or the mean of the two tests, then dilute with a little water, add four to six drops methyl-orange solution (i.e., a sufficient quantity to afford a distinct but not too deep violet-red with the free acid present), and then run in from a burette caustic-soda lye until every trace of a reddish tint has disappeared and the liquid has acquired a yellow or orange-yellow color. This test also must be repeated. On deducting from the soda solution used in the titration with phenolphtalein the quantity required in the methyl-orange test, we ascertain the number of c.c. of soda solution required to pre- 315.] ANALYSIS OF MANURES. cipitate the phosphoric acid as basic calcium phosphate (tricalcium phosphate) ; on now multiplying this difference by the quantity of phosphoric acid corresponding with 1 c.c., we find the quantity of phosphoric acid in the number of c.c. of superphosphate-calcium- chloride mixture, and from this the quantity in the superphos- phate solution according to the proportion 250 : 200. The many test analyses given by EMMERLING are very satis- factory, also with ferruginous superphosphates; the differences, compared with those afforded by the uranium method, do not ex- ceed 0-3 per cent. The results are apt to fall out too high, rather than too low; about 0-16 per cent, according to EMMERLING. /?. Determination of the "Reverted" and Unattached Phosphoric Acid* 315 The "reverted" phosphoric acid may be determined both directly and indirectly. Both methods are based upon the fact that the phosphoric-acid compounds formed by "reversion" are soluble in a solution of neutral ammonium citrate, whereas the unattacked phosphates, particularly those of mineral origin, are practically insoluble. The direct method is inconvenient, hence I will only refer to the treatise mentioned in the foot-note. The indirect method, which is here described, is far more convenient; it at the same time gives also the quantity of the unattacked phosphates. Weigh off two portions of 2 grm. each of the superphosphate, and extract them by the method described under "Washing on the Filter" ( 312). In the residue from the one (a) determine the total unattacked and " reverted" phosphoric acid by dissolving it according to 308, and determining the phosphoric acid accord- ing to 309. Spread the filter containing the second residue (6) on a glass plate, and rinse the residue completely into a porcelain mortar provided with a lip, using for the purpose a solution of * Compare FRESENIUS, NEUBAUER, and LUCK, Zeitschr. f. analyl. Chem., x, 156. 870 DETERMINATION OF COMMERCIAL VALUES. [ 316- neutral ammonium citrate, sp. gr. 1-09, 100 c.c. of which have been put into a small wash-bottle. Allow to settle, decant the cloudy supernatant liquid into a small flask, triturate the residue in the mortar to a very smooth paste, and wash this with the balance of the ammonium-citrate solution into the small flask. Allow to stand for half an hour at a temperature of 30 to 40, with very frequent shaking, and then filter. Wash the residue in the filter twice or thrice with a mixture of equal parts water and the ammonium-citrate solution above mentioned, then with water alone, then dissolve the residue according to 308, and in the solution determine the unattacked phosphoric acid according to 309. On deducting the quantity found from that found in the residue a, the reverted phosphoric acid is ascertained. 6. Shortened Methods of Determining the Values of Superphosphates. a. Determination of "Soluble" Phosphoric Acid. 316. The term " soluble phosphoric acid," employed to denote the value of superphosphates (and which must not be confounded with the term er cent, magnesium sulphate, 12 to 15 per cent, magnesium chloride, 37 to 42 per cent, sodium chloride, about 2 per cent, calcium sulphate, 1 to 2 per cent, insoluble residue, and about 5 to 8 per cent, water. Furthermore, the preparations poor in chlorine, and obtained by calcining crude kainite, should be mentioned; these come into the market as " prepared kainite," "crude potassium-magnesium sulphate," or " potassium-mag- nesium sulphate manures"; and finally the "pure, crystallized potassium-magnesium sulphate" obtained from kainite by treat- ment with water, and containing 38 to 40 per cent, potassium sulphate. As the analysis of potassium salts has already been thoroughly treated of in 225 (this volume, p. 341) both with reference to the simple determination of potassium as well as to the complete analy- sis, I will only refer to the section mentioned. For the potassium determination I would advise taking of the aqueous solution of the salt a volume that will yield about 8 to 1 2 grm. potassium-platinic chloride. By multiplying the weight of the potassium-platinic chloride dried at 130, by 3056, the potas- sium chloride is obtained. This number corresponds, according to WATT'S* calculation, with BERZELIUS' equivalent of platinum. On multiplying the weight of the double platinum salt dried at 130, by 30697, the number given by SEUBERT'S f equivalent, the result * Zeitschr. f. analyt. Chem., ix, 156. f Annal. d. Chem., ccvn, 31. 320.] ANALYSIS OF MANURES. 875 will be somewhat too high; or if multiplied by 0-3051, the num- ber obtained when using ANDRE ws' * equivalent for platinum, the result will be too low for potassium chloride, as shown by investi- gations made by me. f [When the calculations are based upon the atomic weights used in this translation, i.e., Pt= 194- 9; K=39-ll; 01=35-45, then the factor for multiplying the potassium-platinic chloride, (KCl) 2 PtCl 4 , in order to obtain the potassium chloride, is 0-30695. TRANS- LATOR.] E. ANALYSIS OF MANURES THE VALUE OF WHICH DEPENDS SOLELY OR NEARLY ALTOGETHER UPON THE NITROGEN THEY CONTAIN. In this class belong the nitrates, foremost among which are Chili saltpetre, ammonium salts, and such nitrogenous manures of organic origin as contain so little of other manurial substances (potassium, phosphoric acid), that the value of the latter is scarcely or not at all, taken into account, e.g., dried blood, horn meal, etc. As the methods of determining nitrogen vary according to the form of combination in which it occurs, they must be described separately. I. CHILI SALTPETRE. J 320. Although pure sodium nitrate contains 63-51 per cent, of N 2 O 5 , or 16 5 per cent, of nitrogen, Chili saltpetre, as it contains also some sodium chloride, sodium sulphate, insoluble residue, water, etc., can be guaranteed by the dealer to contain only from 15 to 15-5 per cent, nitrogen. Of the methods detailed in 149 (Vol. I, p. 571) for determining nitric acid in Chili saltpetre, the one best adapted for the purpose is that of REICH, described in Vol. I, p. 572, i.e., ignition with quartz * Annal. d. Chem. u. Pharm., LXXXV, 255. f Zeitschr. f. analyt. Chem., xxi, 234. J In this section will be described those newer methods of nitric-acid determination which, though not necessary for determining the value of Chili saltpetre, are nevertheless to be borne in mind as of use in mixed ma- nures. 876 DETERMINATION OF COMMERCIAL VALUES. [ 320. sand, as it is rapid, simple and yields good results. It may also be carried out in the manner described by MARCKER and ABESSER,* a modification of REICH'S original method (loc. cit.). Mix care- fully the weighed quantity of the triturated Chili saltpetre (about 1 to 1 5 grm.) with about seven times its quantity of quartz sand that has been previously extracted with hydrochloric acid, washed, and ignited, and then heat the mixture in a crucible for four hours, but in such a manner that only about one-third of the crucible is red-hot. After weighing, make certain that no further loss of weight follows ignition for another half-hour. From the total loss (nitric acid + water) found, the water in the Chili saltpetre must be deducted in order to ascertain the nitric-acid content; this may, as a rule, be accomplished by drying sharply (at about 130), but under certain circumstances, e.g., when adulterated with kainite, by heating even to fusion. Of course, other methods of determining the nitric acid in Chili saltpetre may be employed. Many of these have already been described in 149 (Vol. I, p. 571t), and others are of more recent date. Although REICH'S method, already mentioned, so far as simplicity and accuracy are concerned, suffices for deter- mining the value of Chili saltpetre, attention must be called to other methods which are largely used for the same purpose, as well as to a few new ones for use in the analysis of mixed manures. Instead of REICH'S method, that of PERSOZ (Vol. I, p. 572) is frequently employed for determining the value of Chili saltpetre; it consists in heating the anhydrous nitrate with anhydrous potassium dichromate, and determining the nitric acid from the loss of weight. E. PFEIFFER J recommends the use of 3 to 4 parts of potassium dichromate for every part of Chili saltpetre, as the expulsion of the nitric acid is thereby facilitated, and also advises placing a triangle of thin platinum wire between the platinum crucible and its lid, in order * Zeitschr. f. analyt. Chem., xn, 281. f J. M. EDER (Zeitschr. /. analyt. Chem., xvi, 267), has supplied a most praiseworthy critique of most of the methods there mentioned. % Arch. Pharm. [3], xui, 539; Zeitschr. /. analyt. Chem., xvui, 597. 320.] ANALYSIS OF MANURES. 877 to allow space for the vapors to escape. The temperature must not be allowed to exceed a dark red heat; and the operation is over when the mass is in a state of quiet fusion. If green particles of chromic oxide are observed on the cooled melt, or on the por- tions spirted onto the lid, the experiment must be rejected. Instead of potassium dichromate, some recommend using a mixture of equal parts of chromate and dichromate of potassium.* A. WAGNER f recommends a method based upon a new principle; it consists in fusing together the nitrate with sodium carbonate and chromic oxide in a glass tube filled with carbon dioxide, lixiviating the melt, and determining in the filtrate the chromic acid formed, from which then the nitric acid may then be calculated. This method also gives good results,! but is far more inconvenient than the method of REICH or PERSOZ. The nitric oxide evolved may be collected for the purposes of control, and measured; or, as in SCHLOSING'S method (Vol. I, p. 579), converted into nitric acid. All the methods more recently recommended for determining the nitric acid are but modifications of those described in 149, or of that originally devised by WALTER CRUM (p. 711 this volume). Most of them are based upon the conversion of nitric acid into nitric oxide, i.e., upon the same principle as that described in Vol. I, p. 575, d, and many are but modifications of SCHLOSING'S method (Vol. I, p. 579), which had also previously been modified in various ways (Vol. I, p. 581, and this volume, p. 65). Above all, SCHLOSING himself has considerably altered his method, and has imparted to it a high degree of simplicity, both in regard to manipulation and calculation, by collecting and measuring over water the nitric oxide obtained, on the one hand, by the action of a known volume of nitrate on ferrous chloride, and on the other hand from the unknown quantity of nitric acid in the substance examined under identical circumstances. As the first experiment gives the quantity of nitric acid, or the nitrogen * P. WAGNER, Chemiker-Ztg., 1883, p. 1710. t DINGLER'S Polyt. Journ., cc, 120, and cci, 420; Zeitschr. f, analyt. Chem., xi, 91 and 314. t Compare also EDER, loc. cit., p. 287. GRANDEAU'S Handb. d. agriculturchem. Analysen, German edit., p. 31. 878 DETERMINATION OF COMMERCIAL VALUES. [ 320. contained therein, corresponding with 1 c.c. of nitric oxide under existing conditions, so in the second experiment the quantity of the unknown nitric acid or nitrogen may be ascertained from the volume of nitric oxide obtained, as the pressure, degree of mois- ture, and temperature of the volume of gas in both cases are, of course, alike. Even the other usual sources of error inherent in the measurement of nitric oxide over water (the slight solubility of nitric oxide in water, influence of the oxygen in the air dissolved in the water) are hereby excluded, and in fact the more completely the greater the care taken that the volumes of nitric oxide obtained from the known and unknown quantities of nitric acid are approxi- mately equal, or that they do not differ to any great extent. SCHLOSING has devised, and recommends, a special apparatus for use with his method, and especially a peculiarly arranged pneu- matic trough, which answers every requirement, and which is illus- trated in GRANDEAU'S Handbuch, p. 34. I consider it, however, more useful to here describe a slightly modified form of the appa- ratus devised by P. WAGNER,* and shown in Fig. 136, as this may be readily put together from vessels ordinarily used in the labora- tory. The method to be followed in determining Chili saltpetre is as follows : Introduce 40 c.c. of a ferrous-chloride solution (containing about 200 grm. iron per litre) into the flask a, having a capacity of from 250 to 300 c.c., then add 40 c.c. hydrochloric acid of 1 1 sp. gr. Then pour a few c.c. of the same hydrochloric acid into the funnel-tube b (provided with a glass cock) the finely drawn out tip of which reaches down into the body of the flask, but does not dip into the liquid. Now open the glass cock in order to displace the air in the tube by the acid, but promptly close before the last of the acid has run through. The gas-delivery tube, c, dips into the water contained in a glass trough about 24 cm. wide and 20 cm. deep, and into which cold water may be conducted through the opening at e, in order to expel the water, warmed and contami- nated by hydrochloric acid through the glass tube inserted at /. * Chemiker-Ztg., 1884, 651 ; Zeitschr. /. analyt. Chem., xxni, 559. 320.] ANALYSIS OF MANURES. 879 In the trough are supported four or more measuring cylinders graduated in 0- 5 or 1 c.c., and filled with water; they are suspended from a wire holder having rings at the tops, and half -rings at the middle, as shown. None of these graduated cylinders should be FIG. 136. placed over the upturned end of the gas-delivery tube, c, at the beginning. Now heat the contents of the flask a to boiling, and keep it boiling until all the air has been expelled, which may be readily ascertained by placing a test-tube filled with water over the end of the delivery-tube c. Then support one of the measuring tubes over the delivery-tube, pour 10 c.c. of normal nitrate solution con- taining exactly 33 grm. pure sodium nitrate per litre, into the 8*80 DETERMINATION OF COMMERCIAL VALUES. [ 320. funnel-tube b, and arrange the stop-cock so that the normal solution will slowly drop into the iron solution, which must be kept con- stantly boiling. When all but a very small residue has passed fill the funnel twice with hydrochloric acid of 1- 1 sp. gr., and allow this also to drop in until only sufficient acid remains to fill the tube. When this is accomplished, the first operation is com- pleted. Now, still keeping the contents of a boiling, move the graduated tube to one side for the time being, and replace it by an- other. Pour 10 c.c. of the Chili-saltpetre solution to be examined and which, too, must contain 33 grm. per litre, into the funnel 6, and proceed with the process just as before, also washing out the funnel twice with hydrochloric acid. In this manner, and without exhausting the ferrous-chloride solution, six or seven more deter- minations may be made and also a final control determination with the normal nitrate solution, as well. When this, too, is com- pleted, open the glass cock in order to allow air to enter into a, and then remove the heat. The graduated tube c ntaining the nitric oxide has in the mean- time been sunk into a glass cylinder about 44 cm. high and 15 cm. wide in which it is held fast by brass clips fastened to the edge of the cylinder. The water displaced on sinking the tube into the cylinder runs off through a side tube. When certain that the tem- perature of all the tubes and their contents is identical, read off the volume of gas. If the process has been carried out as above described, the percentage of sodium nitrate in Chili saltpetre may be calculated from the following proportion: The nitric-oxide gas evolved from 33 grm. pure NaNO 3 : the nitric-oxide gas evolved from 33 grm. of the Chili saltpetre :: 100 : x. If, however, unlike quantities of pure sodium nitrate and of the substance to be examined have been taken, it is simplest to calculate the quantity of nitric acid or nitric oxide corresponding to 1 c.c. of the nitric oxide obtained from the former, and to then multiply the value thus found by the number of c.c. of nitric oxide yielded by the unknown quan- tity of nitric acid. None of the other modifications of SCHLOS- ING'S original method are as rapid as that just described. I will 320.] ANALYSIS OF MANURES. 881 therefore confine myself here to just pointing out the principles upon which they are based. C. BOHMER * recommends to gravimetrically determine the nitric-oxide gas collected in a LIEBIG'S potash bulb filled with con- centrated chromic-acid solution. E. WILDT and A. SCHEIBE | re- convert the nitric oxide into nitric acid, and determine this by titration, using for the purpose an apparatus that excludes the use of a mercurial trough. They consider their method preferable to measuring the volume of nitric-oxide gas, more particularly when it is feared that the nitric-oxide gas may contain an admixture of other and indifferent gases, as may happen when investigat- ing the sap of plants. WARINGTON J removes the air from the flask, as SCHLOSING had already also proposed, by means of a current of carbon dioxide passed through a small flask containing a little water and placed in a calcium-chloride bath heated to 140; the nitric oxide is collected over mercury, treated with potassa lye, and finally absorbed by a saturated ferrous-chloride solution. He recommends his method particularly for the accurate deter- mination of small quantities of nitric acid. WILFARTH converts the nitric oxide into nitric acid by treatment with an alkaline solu- tion of hydrogen dioxide of known strength, and then determines the nitric acid by titration. Various other methods proposed have also been based up n the principle mentioned in 149, e, (Vol. I, p. 571), e.g., conversion of the nitric acid into ammonia, and will be but briefly mentioned here. Such are : The method proposed by E. PUGH, and modified by O. v. DUMREICHER,|| in which a hydrochloric-acid solution of stannous chloride is used; and those of J. WEST-KNIGHTS!" and B. KINXEAR,** in which zinc and sulphuric acid are employed. WALTER CRUM'S method of determining nitric acid, and the * Zeitschr. f. analyt. Chem., xxii, 20. f Ibid., xxiii, 151. % Ibid., xxiii, 547. Ibid., xxm, 587. || Ibid., xx, 290. f Ibid., xxu, 572. ** Ibid., xxv, 224. 882 DETERMINATION OF COMMERCIAL VALUES. [ 320. nitrometer devised by LUNGE for carrying out the method, have already been minutely described in 271, 2 (p. 711 this volume). According to WARINGTON'S * investigations, the method is particu- larly well adapted for the determination of small quantities of nitric acid, but gives too low results if large quantities of organic substances are present; this opinion, however, is not in accord with LUNGE'S f experience. SHEPHERD J has recently recommended using the nitrometer for determining the nitric acid in manures. As reference will have to be made to these paragraphs when treat- ing of the analysis of mixed manures, the method will be given here in detail. In the case of manures containing about 5 per cent, nitric acid, take not more than 2 grm. of the substance ; if they contain less than 1 per cent., take from 2 to 3 grm. The extracts are prepared with hot water, evaporated to a small volume, and introduced into the nitrometer. It is unnecessary to remove the chlorine by treat- ment with silver sulphate. The volume of the liquid should be so small that, including the washings, it should not exceed 5 c.c. Into the perfectly cooled liquid in the nitrometer allow double its volume of pure, concentrated sulphuric acid to cautiously flow, mix the acid with the aqueous liquid by gently shaking, allow any carbon dioxide evolved to escape by momentarily opening the glass cock, if necessary, and then shake vigorously in order to evolve the nitric oxide. The reaction is completed in a few minutes. Then allow to cool, and read off the volume of the gas. If comparative parallel experiments are made under similar conditions with nitre solutions of known strength, corrections for temperature and pressure may be disregarded, the calculation being then made as in SCHLOSING'S new method. The question as to what influence organic substances exercise upon the result requires further investigation. * Zeitschr. f. analyt. Chem., xix, 85. f Ibid., xix, 208. ., xxv, 270. 321.] ANALYSIS OF MANURES. 883 II. AMMONIUM SALTS. The determination of ammonia in ammonium salts is as a rule effected either by distillation with the addition of calcined magnesia, or by the separation and measurement of the nitrogen, according to the method to which KNOP has given the name "azotometry." a. Distillation Method. 321. This method has already been described hi 99, 3 (Vol. I, p. 253), and in regard to its employment for the determination of the am- monia in soils, in 302, b. I will but point out that not only with mixed manures, but also with the ammonium salts prepared on the large scale, and frequently containing ammonium sulpho- cyanate, the distillation must always be carried out with the addition of calcined magnesia, and never with potassium or sodium hydroxide, because by the action of these alkalies the nitrogen of the sulphocyanogen is also converted into ammonia; * the dis- tillation with magnesia, besides, yields accurate results also when phosphates are present,! and any explosive ebullition of the ammo- niacal liquid may be entirely avoided by passing steam through the liquid instead of heating the latter directly (RuDORFF)4 With regard to the receivers for holding the titrated acid, it is of course unnecessary to adhere strictly to the form described in 99, 3, but care must be taken that the ammoniacal distillate does not come into contact with cork or rubber, as both of these retain a little of it. KNUBLAUCH highly recommends the appa- ratus shown in Fig. 137 as being very practical. a is the distillation flask, having a capacity of from 200 to 250 c.c., and fitted with a tube, 6, connected with the absorption apparatus, e, the latter having the form of a flask without a bottom, 40 mm. wide below, and with several lips formed on the rim in * Comp. ESILMAN, Zeitschr. f. analyt. Chem., xiv, 94. t Comp. MARCKER, Ibid., x, 277. i Ibid,, xii, 440. Ibid., xxi, 161. 884 DETERMINATION OF COMMERCIAL VALUES. [ 321. order to better distribute the bubbles of gas evolved. The vessel e is suspended in the glass cylinder c, by means of a cork slab, d, fitted around the neck, and in such a manner that e is a few milli- metres above the bottom. In c is placed the measured quantity FIG. 137. of titrated acid, together with sufficient water to cover the edge of e to a height of 1 cm. Finally, the cylinder c is placed in an outer vessel g, filled with water for the purpose of cooling and condensing. After the contents of a have been reduced to one- half or one-third by distillation, and all the ammonia has thus been driven off, remove the stopper from e, remove c from the cooler, and when quite cold, titrate the excess of acid, without removing e. When examining ammonium sulphate, it is convenient to dissolve 20 grm. to make 500 c.c. of solution, and to take 25 c.c., corresponding to 1 grm., for the distillation. For rinsing the walls of a about 10 c.c. of water are required. If 20 c.c. of normal sulphuric acid have been taken, then about 6 c.c. of normal soda will be required to neutralize the excess. In order to expel the ammonia, KNUBLAUCH uses a little solid caustic potassa, which is wrapped in filter-paper and introduced into the contents of a; the paper floating on the surface of the liquid facilitates a more quiet boiling. From what has been said above, however, it is 322.] ANALYSIS OF MANURES. 885 evident that caustic potassa can be used only when sulphocyan- ogen and other nitrogenous organic substances are absent. According to THOMSON'S * investigations the best indicators for ammonia titrations are litmus (or the preparation of litmus mentioned on p. 845 this volume), methyl orange, or phenacetolin; rosolic acid is not so well adapted, while phenolphtalein is unsuit- able. 6. Azotimetric Method. 322. The azotimetric method, to which reference has already been made on p. 845, this volume, is based upon the reaction which takes place when an excess of an alkali hypobromite acts upon ammonia: 3NaBrO+2NH 3 = 3NaBr+2N+3H 2 O. All the nitro- gen of the ammonia is liberated, and can be measured. I here describe the method in its most complete form as given by W. KXOP (who originated it) in one of his most recent publications.! The apparatus required for the method is shown in Fig. 13S.J a, the decomposition flask in which the sodium-hypobromite solution is allowed to act upon the ammonium salt, is from 10 to 11 cm. high, 5 cm. diameter, and is closed by a hollow glass stopper which is prolonged to form a stout glass tube, 6, 8 to 9 cm. long and 2 cm. wide; this may be closed above by means of a glass cock, the latter being connected above with a strong tapering glass tube sealed on to the upper external part of the cock. The wide tube is tightly packed with coarse glass beads which are prevented from falling into a by a loose ball of fine platinum wire. The vessel a is suspended in the glass cylinder d d by means of a stout metal rod c, the ower end of which has soldered to it at right angles a metal plate for a to rest upon, and provided with a metallic spring clamp * Zeitschr. f. analyt. Chem., xxiv, 225. t Ibid., xxv, 301. \ Regarding other apparatus the construction of which differs more or less from the one shown, see P. WAGNER, Zeitschr. f. analyt. Chem., xiu, 383, and xv, 250: SOXHLET, ibid., xvi, 81; GAWALOWSKI, ibid., xvm, 244, and xxiv, 61; C. MOHR, ibid., xxm, 26; and MOSSALKI, Bull, de la Soc. chim. de Paris, XL, 18. DETERMINATION OF COMMERCIAL VALUES. [ 322. higher up; the cylinder d d is 50 cm. high and 18 cm. in diameter, and is filled with cold water for cooling purposes. The metal rod may be raised or lowered to any convenient height, and secured in place by a screw, as shown. If this is removed, the support for FIG. 138. the decomposition flask still hangs from the metal ring on the edge of d d on two stout, steel pins, from which it may readily be removed and on which it may as easily be replaced. To the metal ring on d d is also attached by means of a screw the metal clamp for holding the U-tube e, one limb of which is graduated. After removing the screw, and taking off the stop- cock /, from g, as well as removing the short rubber tube connected with the ungraduated limb of the U-tube, in order to allow the 322.] ANALYSIS OF MANURES. 887 water to run off, the U-tube itself can be taken out for cleaning or if necessary, for renewing the rubber tube. The graduated, as well as the plain, and somewhat longer limb of the U-tube (which should extend a few cm. above the surface of the water in d d, so that the U-tube may be filled with distilled water), are connected together below by means of a rubber tube, as shown in the illustra- tion. The U-tube may, however, also be made in one piece, in order to simplify the repairs that are occasionally necessary. In order to connect the short tube projecting from the side of the lower end of the non-graduated limb, with the glass cock /, slip over the former the end of a rubber tube 20 cm. long, place the U-tube in d d, draw the free end of the rubber tube by means of a hook through the tubulure g, and slip over the end of the glass cock which has first been inserted into a perforated cork impreg- nated with melted paraffin ; then insert the cork into the tubulure, g. The rubber tube h, connecting the graduated limb of the U-tube with the vessel a, must be of thick, soft material, with an internal diameter of about the thickness of a stout knitting-needle. It must be so long, that a may be removed from the water in the cooler and placed on the table beside d d without stretching the tube at all. With a tube of such length no change in its volume need be feared, and the shaking and reversing of a outside of d d may be conve- niently effected. The process is carried out as follows : 1. Dissolve 15-2484* grm. of pure, anhydrous ammonium chloride in water to measure 1000 c.c. 10 c.c. of this solution will contain 0-04 grm. nitrogen. 2. Dissolve 20 grm. of the ammonium salt to be examined if ammonium sulphate, or 16 grm. if ammonium chloride, in suffi- cient water to measure 1000 c.c. 3. After loosening the screw on c, lift out the flask a together with its support, place a alongside the azotometer on the table, remove the stopper, invert it, and into the funnel-shaped opening of the stopper, the glass cock being open, pour as much brominized * The figures in the German text are 15-2422; recalculated according to the values used in the translation they are 15-2484. TRANSLATOR. 888 DETERMINATION OF COMMERCIAL VALUES. [ 322. soda solution* from a measured quantity of 50 c.c. as will suffice to thoroughly wet the glass beads, then pour the remainder of the 50 c.c. of brominized lye into a, and after having greased the stopper with tallow, insert it in a and allow to stand until no more lye drips from the beads ; then, by means of a pair of forceps, place into the lye a glass tube of suitable width and length, closed at one end, and containing 10 c.c. of the ammonium-chloride solution of known strength, f again insert the stopper, and connect a, the cock of b being open, with the graduated limb of the U-tube by means of the rubber tube ; then immerse a and the tube in the cold water in d d by suspending the support on the two metal pins already mentioned, and allow to stand for 20 minutes, taking care that the level of the water is at the same height in both limbs, and noting the height. A small, movable plate painted one-half white, one- half black, serves to better observe the level. The temperature of the water in c(d should not differ appreciably from that of the sur- rounding air. Now allow about 30 c.c. of water to run out of /, remove a from the water, and incline it slightly so that a little of the am- monium-salt solution may run out, and the evolution of gas slowly proceeds. The small quantities of gaseous ammonia carried off is absorbed and decomposed by the lye adhering to the glass beads. The further mixture of the two liquids is effected in the same way. When the evolution of gas finally slackens, close the cock on b and shake and repeatedly invert a. Then open the cock on b again, replace a and the tube in- the cold water, and move both the latter up and down to mix the water; next fix its lowest possible position, allow to stand for 20 minutes, allow enough water to run off through until the water-level in both limbs of the U-tube is at the same height, and then read off the number of c.c. of nitrogen gas evolved. This number, * To prepare this dissolve 100 grm. caustic soda in 1250 c.c. water, cool strongly, add 25 c.c. bromine, and mix. The solution must be protected from the action of light. t P. WAGNER recommends to fuse the tube containing the ammonium- salt solution to the bottom of the decomposition flask (Zeitschr. f. analyt. Chem., xv, 250). 322.] ANALYSIS OF MANURES. 889 about 32 c.c., corresponds to 0-04 grm. nitrogen at the prevailing pressure, and the temperature of the water used for cooling. 4. In exactly a similar manner carry out the experiment with solution No. 2, and, basing the calculation upon the proportion between the volume and weight of nitrogen found in 3, determine the nitrogen content of the ammonium salt in solution No. 2. For instance, if in 3, we had obtained 33 c.c., whereas in No. 4 we obtained 30 c.c., of nitrogen, it follows that in the 10 c.c. of the solution No. 2 the weight of the nitrogen is 33 c.c. : 0-04 grm. N:: 30 c.c.: z; and z=0. 03636 grm. Should experiment 4 have yielded a volume of nitrogen differing considerably from that obtained in 3, repeat the experiment, using a correspondingly larger quantity of solution No. 2. 5. When a long series of such tests are made consecutively, it is advisable to check the relation of volume to weight of nitrogen found in 3 by making another determination, using 10 c.c. of solution No. 1. 6. Instead of making the calculation as in 4, and which is based simply upon the comparison of the nitrogen to be deter- mined with a known volume obtained under identical conditions, the volume of the gas may, of course, be measured, and its weight calculated from the volume. In this case, however, it is evident that regard must be paid to pressure, temperature, and hygro- scopicity, as well as to the circumstance that a small quantity of nitrogen remains dissolved in the decomposing fluid, this quan- tity being dependent upon the temperature. These calculations may be avoided by making use of the following tables calculated by E. DIETRICH,* and given on pp. 890 to 892. 7. KNOP uses as normal liquid an aqueous ammonium-chloride solution containing 10 grm. of pure, dry ammonium chloride in 2089-4 c.c. Every c.c. of this solution corresponds to 1 c.c. of dry nitrogen at and 760 mm. pressure. When using this solution, the experiment will also give the relation between moist nitrogen at the temperature of the cooling water and prevailing barometric pressure, and dry nitrogen measured at and 760 mm. pressure. * Zeitschr. f. analyt. Chem., v, 38 to 40. 890 DETERMINATION OF COMMERCIAL VALUES. [ 322. I. Table of the weight in milligrams of one cubic centimetre of Nitrogen under pressures of 720 to 770 mm. mercury and at temperatures between 10 and 25. mm. 720 722 724 726 728 730 732 H 10 1-13380 1 - 13699 1-14018 1 14337 1 14656 1-14975 1 15294 4 11 1 - 12881 1-13199 1-13517 1 13835 1-14153 1-14471 1 14789 & 12 1 12376 1 - 12693 1 - 13010 1 13326 1 13643 1 - 13960 - 14277 H 13 1-11875 12191 1 - 12506 1 12822 1-13138 1 13454 -13769 9 14 1-11369 11684 1-11999 1-12313 1-12628 1 12942 - 13257 K 15 1 - 10859 -11172 1-11486 1-11789 1-12113 1 - 12426 - 12739 2 16 1 - 10346 10658 1-10971 1-11283 1-11596 1- 11908 12220 * 17 1-09828 -10139 1 10450 1-10761 1-11073 1-11384 11695 5 18 1-09304 1-09614 1-09924 1 10234 1 10544 1 - 10854 11165 K 19 1-08774 1-09083 1-09392 1-09702 -10011 10320 10629 E 20 1-08246 1-08554 1-08862 1-09170 09478 09786 10094 21 1-07708 1-08015 1-08322 1-08629 08936 1-09243 09550 o 22 1-07166 1-07472 1-07778 1-08084 08390 08696 09002 fc 23 1-06616 1-06921 1-07226 1-07531 07836 08141 08446 S3 24 1-06061 1-06365 1-06669 1-06973 07277 07581 07885 H 25 1-05499 1-05801 1-06104 1-06407 06710 -07013 -07316 mm. 734 736 738 740 742 744 B 10 1-15613 1-15932 1 16251 1 - 16570 1-16889 1-17208 4 H 1-15107 1-15424 1-15742 1 - 16060 1-16378 1 - 16696 & 12 1 - 14593 1 - 14910 1-15227 1-15543 1-15860 1-16177 13 1 - 14085 1-14401 1-14716 1-15032 1-15348 1 - 15663 14 1 13572 1 13886 1-14201 1-14515 1-14830 1-15145 a 15 1 - 13053 1-13366 1-13680 1 13993 1 14306 1 14620 16 1 12533 1 - 12845 1 - 13158 1-13470 1 13782 1 14095 fc 17 1 12006 1-12317 1-12629 1 - 12940 1 13251 1 - 13562 18 1-11475 1-11785 1-12095 1 - 12405 1-12715 1 - 13025 19 1-10938 1-11248 1-11557 1-11866 1-12175 1 - 12484 20 1 10402 1-10710 1-11018 1-11327 1-11635 1-11943 21 1-09857 1-10165 1 10472 1 10779 1-11086 1-11393 o 22 1-09308 1-09614 1-09921 1 10227 1-10533 1 - 10839 6 23 1-08751 1-09056 1-09361 1-09666 1-09971 1-10276 S 24 1-08189 1-08493 1-08796 1-09100 1-09404 1-09708 fi 25 1-07619 1-07922 1-08225 1-08528 1-08831 1-09134 322.] ANALYSIS OF MANURES. 891 I. Table of the weight in milligrams of one cubic centimetre of Nitrogen under pressures of 720 to 770 mm. mercury and at temperatures between 10 and 25. mm. 746 748 750 752 754 756 758 K 10 1 17527 1-17846 1-18165 -18484 1-18803 19122 19441 < 11 1-17014 1-17332 1-17650 17168 1 18286 18603 18921 12 1 16493 1-16810 1-17127 17444 17760 18077 18394 H 13 1 15979 1-16295 1-16611 16926 17242 -17558 17873 9 14 15459 1-15774 1-16088 16403 16718 17032 17347 5 15 14933 1-15247 1-15560 15873 16187 16500 16814 g 16 14407 1-14720 1 15032 15344 15657 15969 16282 S 17 13873 1-14185 1 14496 14807 -15118 15429 - 15741 a i8 13335 1-13645 1 13955 14266 -14576 14886 15196 H 19 12794 1-13103 1-13412 1-13721 14030 -14340 14649 20 12251 1-12559 1-12867 1-13175 13483 1 13791 -14099 ^ 21 11700 1-12007 1-12314 1 - 12621 12928 1 - 13236 13543 1 22 11145 1-11451 1-11757 1 12063 123G9 1-12675 12982 fa 23 10581 1 - 10886 1-11191 1-11496 11801 1-12106 12411 S 24 10012 1-10316 1 - 10620 1 - 10924 11228 1-11532 11835 H 25 09437 1-09740 1 10043 1 - 10346 10649 1-10952 -11255 mm. 760 762 764 766 768 770 w 10 1-19760 20079 1-20398 1-20717 21036 1-21355 11 1 - 19239 - 19557 1 19875 1-20193 20511 1-20829 & 12 1-18710 -19027 1 - 19344 1 19660 19977 1-20294 13 1 - 18189 -18505 1-18820 1 19136 19452 1 19768 14 1-17661 17976 1 18291 1-18605 18920 1 19234 15 1-17127 17440 1-17754 1-18067 18381 1 - 18694 16 1 - 16594 16906 1-17219 17531 17844 1-18156 fc 17 1 - 16052 16363 1 16674 16985 17297 1-17608 Q 18 1 15506 15816 1 - 16026 16436 16746 1-17056 19 1 14958 15267 1-15576 - 15886 16195 1 16504 20 1 - 14408 14716 1-15024 - 15332 -15640 1 15948 21 1 - 13850 14157 1 14464 14771 -15078 1 15385 o 22 1 13288 13594 1-13900 14206 -14512 1 14818 fa 23 1-12716 13021 1 13326 13631 - 13936 1 14241 24 1-12139 12443 1-12747 1 13051 1-13355 1 13659 S 25 1-11558 1-11861 1-12164 1 12467 1-12770 1-13073 892 DETERMINATION OF COMMERCIAL VALUES. [ 322. II. Table of Absorption of Nitrogen in 60 c.c. of the decomposing fluid (50 c.c. of brominized lye and 10 c.c. water), the lye having a sp. gr. of 1-1, and such strength that 50 c.c. corresponds with 0-2 grm. nitrogen, in the evo- lution of from 1 to 100 c.c. of gas. 1 1 Absorbed. Evolved. Absorbed. Evolved. 1 < 1 1 1 Absorbed. 1 0-06 21 0-56 41 1-06 61 1-56 81 2-06 2 0-08 22 0-58 42 1-08 62 1-58 82 2-08 3 0-11 23 0-61 43 11 63 1-61 83 2-11 4 0-13 24 0-63 44 13 64 1-63 84 2-13 5 0-16 25 0-66 45 16 65 1-66 85 2-16 6 0-18 26 0-68 46 18 66 1-68 86 2-18 7 0-21 27 0-71 47 21 67 1-71 87 2-21 8 0-23 28 0-73 48 23 68 1-73 88 2-23 9 0-26 29 0-76 49 26 69 1-76 89 2-26 10 0-28 30 0-78 50 28 70 1-78 90 2-28 11 0-31 31 0-81 51 31 71 1-81 91 2-31 12 0-33 32 0-83 52 33 72 1-83 92 2-33 13 0-36 33 0-86 53 36 73 1-86 93 2-36 14 0-38 34 0-88 54 38 74 1-88 94 2-38 15 0-41 35 0-91 55 41 75 1-91 95 2-41 16 0-43 36 0-93 56 43 76 1-93 96 2-43 17 0-46 37 0-96 57 46 77 1-96 97 2-46 18 0-48 38 0-98 58 48 78 1-98 98 2-48 19 0-51 39 1-01 59 51 79 2-01 99 2-51 20 0-53 40 1-03 60 53 80 2-03 100 2-53 In 302, f, the description of the azotimetric method for de- termining the ammonia in soils is referred to azotimetry in manure analysis. It is hence necessary to here add the special details required when employing the methol in the analysis of soils. They are as follows: 1. Instead of the vessel with lead cover * originally used by him, KNOP now uses f as the decomposing vessel a wide-necked flask, divided internally by a vertical glass partition into two unequal chambers. This replaces the vessel a in Fig. 138 (p. 886 this volume), but is provided with the same form of stopper and glass cock. 2. As the one chamber must be large enough to hold 100 grm. of soil and also 125 c.c. of liquid, the vessel will be so large that it cannot be immersed with the U-tube in the same cooling cylinder. * Chem. CentralbL, 1860, 251. t Zeitschr. /. analyt. Chem., xxv, 304. 322.] ANALYSIS OF MANURES. 893 It must hence be cooled in a separate vessel, taking care that the temperature at the beginning and end remains the same. 3. Place in the larger chamber a quantity of fine earth repre- senting 100 grm. of soil dried at 125, mix with it 125 c.c. of a sat- urated, clear borax solution,* place 25 c.c. of the brominized lye in the smaller chamber of the decomposition vessel, insert the stopper lightly, connect the latter with the U-tube, and sur- round both it and the decomposition vessel with water in the cooling vessels; allow to stand for 20 minutes, taking care to adjust the water-levels in the U-tube, and gradually bring the brominized lye in contact with the soil by moderately shaking, the cock at b being at first open, and then closed. This suffices for the complete decomposition of the ammonia. After the decomposition flask has regained its original temperature, measure the evolved nitrogen. As the quantity of liquid in the decom- position flask is not very small, the quantity of nitrogen absorbed must, in accurate experiments, not be neglected. DIETRICH,! however, has pointed out the difficulty of determining this factor with accuracy. 4. According to A. BAUMANN J the results obtained when treat- ing the soil according to 3, are incorrect. He proposes, as DIETRICH (loc. tit. had already done, to submit, not the soil itself, but its hydrochloric-acid extract, to the azotimetric test. According to W. KNOP the incorrect results obtained by othess in the direct azotimetric determination of soils are due to the employment of too strongly alkaline brominized lye. To avoid the error caused by this, he recommends in his above-mentioned latest treatise to prepare the decompo ing liquid by simply pouring on to the soil mixed with borax solution a solution of calcium hypobromite (200 c.c water, calcium hydroxid in excess, and 15 c.c. bromine), or at most to add a small quantity of sodium hydroxide. || * The object of the borax solution is to avoid the errors due to the con- traction usually observed when strongly alkaline liquids are shaken with soils. t Zeitschr. f. analyt. Chem., v, 44. \ Landwirthschaftl. Versuchsstationen, 1886, 247. Zeitschr. f. analyi. Chcm., xxvi, Part I. 1| As the treatises of A. BAUMANN and W. KNOP came into my hands only 894 DETERMINATION OF COMMERCIAL VALUES. [ 323. III. SUBSTANCES CONTAINING ORGANICALLY COMBINED NITROGEN. The nitrogen in organic combinations can be determined accord- ing to the methods detailed in 183 to 188 (pp. 56 to 95 this volume).* It was customary until lately to use almost exclu- sively PELIGOT'S modification of VARRENTRAPP-WILL'S method ( 187). In 1883, however, J. KJELDAHL published a method of determining nitrogen, based upon an entirely new principle, and this method has rapidly gained such wide recognition as to make it appear as though it would gradually replace the VARRENTRAPP- WILL'S method, at least in the analysis of manures.! Before proceeding to describe the KJELDAHL method, I wish to add here a few supplementary points to the description given on p. 94 this volume, regarding the mode of carrying out PELIGOT'S modification of the VARRENTRAPP-WILL process on the manu- facturing scale. a. Modified VARRENTRAPP-WILL Method. 323. 1. P. WAGNER, J as well as THIBAULT, recommend igniting with soda-lime in a current of hydrogen in a wrought-iron tube open at both ends (Fig. 139). This tube is 95 cm. long, and 17 cm. wide; it extends 17 cm. beyond the fore part of the combustion-furnace, when correcting the proofs of this section, I could only detail the more im- portant features in the text; I would therefore strongly advise all who are occupied with the determination of ammonia in soils by the azotimetric method, to thoroughly study both treatises. * Since 185 was written a whole series of papers has appeared regarding the DUMAS method of determining nitrogen, for which consult Zeitschr. f. analyt. Chem., KREUSLER (Landwirthschaftl. Versuchsstationen, xxxi, 207; Zeitschr. f. analyt. Chem., xxiv, 438) has published a treatise giving all the details of the method, as well as a modified form of the process which gives the most reliable results. j- See MARCKER, or HEFFTER, HOLLRUNG, and MORGEN (Chemiker-Ztg., vm, 432; Zeitschr. f. analyt. Chem., xxin, 553); E. SCHULZE or BOSSHARDT (Zeitschr. f. analyt. Chem., xxiv, 199); and TH. PFEIFFER and F. LEHMAN (ibid., xxiv, 388). | Chemiker-Ztg. , vm, 650; Zeitschr. f. analyt. Chem., xxm, 557. 323.] ANALYSIS OF MANURES. 895 and 25 cm. beyond the hinder end, and it rests in a sheet-iron trough. The ends are closed by rubber stoppers. At a distance of about 15 cm. from the fore end of the tube is placed a 12-cm. long layer of soda-lime, granulated, but net caked, and retained in place between an asbestos plug in front and a roll of iron wire be- hind: this will suffice for about 100 combustions. To fill the tube, mix the substance with powdered soda-lime in a mortar, and, by aid of a sheet-copper scoop, h, transfer the mixture to a tinned- iron trough, i, 31 cm. long, provided with a turned-down piece of FIG. 139. tinned iron at the back. In order to collect any portions which may have been spilled, place the tinned-iron trough in a sheet- copper trough, k, 3i cm. wide. After covering the contents in i with the soda-lime which has been used for rinsing out the mortar, insert the trough into the combustion-tube, and push the latter into place with the wire, e, which is left in with it; now close the tube with rubber stoppers, attach the receiver, and pass a slow cur- rent of hydrogen* (which must be maintained throughout the process) through the apparatus. Then heat first the soda-lime to redness, and next the mixture of the organic substance and soda- lime, gradually proceeding from the fore to the hinder end. The * Instead of hydrogen, G. LOGES (Chemiker-Ztg., vin, 1741 ; Zeitschr. /. analyt. Chem., xxiv, 449) recommends using a current of illuminating gas freed from ammonia by passing it through a vertical tube filled with glass beads moistened with diluted sulphuric acid (1 part concentrated sulphuric acid and 3 parts water). DETERMINATION OF COMMERCIAL VALUES. [ 323. termination of the combustion may be recognized on shutting off the supply of hydrogen, and observing whether the height of the acid in the receiver suffers any change. If it does not, and if no more gas bubbles are evolved, extinguish the burners, change the receiver, and as soon as the trough and wire are no longer red-hot, withdraw them by means of the hooked wire, n, insert a freshly charged trough in the still hot tube, and proceed with a new com- bustion. P. WAGNER recommends the apparatus g f as a receiver. The acid is introduced at /, which is partly filled with glass-wool. The escaping hydrogen is thus compelled to pass through the glass-wool moistened with the sulphuric acid, and hence gives up to the acid the last trace of ammonia. P. WAGNER titrates back by adding a little rosolic acid to the contents of g, then adding titrated soda- lye until a red color develops, then transferring the liquid to a porcelain dish, pouring back again into the receiver through /, thence back again into the porcelain dish, and finally completing the titration. The receiver is rinsed out a second and a third time with the titrated liquid, finally adding, if necessary, more soda-lye until the end-reaction persists. Should the end-reaction not be sufficiently sharp because of the coloration of the acid by empyreumatic products, add to. the titrated liquid a few drops acid, evaporate to dryness on the water- bath, rinse the residue with the aid of 10 c.c. water into the azo- tometer, and determine the nitrogen (p. 885 this volume). P. WAGNER points out that when employing this method, the acid very seldom exhibits a color, and that the method will give trust- worthy results even with such substances as blood meal or leather meal;* the results, however, can be obtained by combustion in a glass tube without the current of hydrogen, but only with greater difficulty. 2. If it is impossible to effect the comminution of the organic * Compare KREUSLER'S investigations (Landwirthschaftl. Versuchsstationen, xxxi, 248 ; Zeitschr. /. analyt. Chem., xxiv, 446) which in general confirm those of WAGNER. Since 186 and 187 were written, numerous other treatises have been written regarding combustions with soda-lime, and may be found in the Zeitschrift fur analytische Chemie. 324-] ANALYSIS OF MANURES. 897 substance required in the VARRENTRAPP-WILL method, or at least if it requires a long time to effect it, treat the weighed substance, e.g., horn shavings, wool, or the like, with concentrated sulphuric acid, with the aid of heat, if necessary, until a clear, thickish liquid results. After sufficient action, neutralize the excess of acid carefully with finely powdered calcium carbonate, and then mix the dry powder so obtained with soda-lime (GRAXDEAU,* KRAUCH |). CRETE, J who essentially recommended the same treatment, neu- tralizes the sulphuric acid with soda-lime. I would point out that, by the action of sulphuric acid on nitrogenous organic substances on heating, ammonium sulphate may be formed (compare KJEL- DAHL'S method below), hence in such cases care must be taken that on adding the soda-lime no loss of ammonia occurs. If it is advisable to use a large quantity of the substance under examina- tion in order to obtain a correct average sample, weigh the dry powder obtained after the treatment with sulphuric acid and calcium carbonate, and take an aliquot part for the combustion with the soda-lime. 6. KJELDAHL'S Method. 324. KJELDAHL'S method is based upon the fact, previously unknown, that the nitrogen of nitrogenous organic substances is converted into ammonia on heating the substances for some time with a large quantity of sulphuric acid at a temperature approaching the boiling-point of the acid, and then oxidizing with potassium permanganate the solution so obtained. After supersaturating with soda- or potassa-lye, the ammonia formed can be distilled off and determined by the usual methods. * His Handbuch /. agriculturchem. Analysen, German edit., p. 18. t Chemiker-Ztg., v, 703. J Zeitschr. /. analyt. Chem., xvm, 486. Ibid., xxn, 366. As this method is of great importance for the de- termination of nitrogen, not only in manures, but also in inorganic sub- stances generally, and could not be described earlier in this work, I give it here in full detail. 898 DETERMINATION OF COMMERCIAL VALUES. [ 324. The reactions occurring in this interesting process were first investigated by DAFERT,* and are stated by him to be as follows : 1. The sulphuric acid abstracts from the organic substance the elements of water, with the formation of the latter. 2. The sulphurous acid produced by heating the sulphuric acid with the resulting carbonized mass, exerts a reducing action on the nitrogenous organic matter. 3. The powerful oxidizing action of the potassium perman- ganate converts any stable nitrogenous decomposition products into ammoniacal compounds. The reaction described under 2 is the general and principal one; that mentioned under 3 can be considered only as completing it under certain circumstances. 'According to ASBOTH,! hydrogen is also evolved by the action of sulphuric acid on organic substances containing hydrogen, and this latter effects the conversion of the nitrogen into ammonia. He bases this opinion upon the fact that the whole of the nitrogen is obtained as ammonia only when there is no lack of substances containing hydrogen present. KJELDAHL'S method was very soon and repeatedly tested, after being made public, and, as already above mentioned, has gained general recognition both in its original form and in its various modifications, because of the ease and rapidity with which it may be carried out. from its extended applicability, on account of the reliability of its results, as well as on account of its inexpensiveness. The method, as may be seen from what has already been stated, comprises two operations, namely: a. Decomposition of the or- ganic substance and conversion of the nitrogen into ammonia ; and 6. Determination of the ammonia in the solution obtained in a. In the following I will first describe the method in its original form, and will then describe the modifications proposed and adopted. * Zeitschr. f. analyt. Chem., xxiv, 455. f Chem. CentralbL, 1886, 165; Zeitschr. f. analyt. Chem., xxv, 575. 325.] ANALYSIS OF MANUKES. a. KJELDAHL'S Original Method. 325. If the substance contains from 1 to 2 per cent, nitrogen weigh off about 7 grm. ; if it contains about 5 per cent, weigh off 25 grm.* The substance need be comminuted only to such an extent as to enable a true average sample to be obtained, and the weighing may be effected in the small flask in which solution is to be effected. The flask should have a capacity of about 100 c.c., and be of good, refractory glass ; its neck should be rather long and narrow. If the substance is a liquid, take a quantity of it containing the proper quantity of dry matter, and evaporate the solvent f (if no loss of ammonia is feared thereby) in a drying-closet, or on the water-bath in a current of air freed from ammonia. Now introduce into the flask 10 c.c. of sulphuric acid to which, to compensate for the water it contains, a little fuming sulphuric acid, or preferably phosphoric anhydride,| is added; then fix the flask in a slanting position dur- ing the reaction, and heat on a wire gauze with a small flame. As during the course of the operation copious fumes of sulphuric and sulphurous acids are evolved, the heating should be done under a good draught. As a rule, the contents of the flask at first become black and tarry. On continued heating to near the boiling-point of the acid, when the liquid lightly " bumps" from time to time, a brisk reaction sets in with evolution of gas, during which the sub- stance is completely dissolved. When the evolution of gas slackens, * When the substance is still richer in nitrogen, KJELDAHL recommends instead of taking a smaller quantity, to weigh off about four times the neces- sary quantity, and to make up the acid solution to 100 c.c., taking then 25 c.c. for the determination of the ammonia. t Urine should not be evaporated, PFLUGER and BORLAND (Zeitschr. /. analyt. Chem., xxiv, 636). | The sulphuric acid or mixture of acids must be free from ammonia and carefully guarded from contamination with it. For the sake of certainty treat 0-5 grm. pure sugar with 10 c.c. acid exactly as detailed in the text, oxidizing with potassium permanganate, and then distil with soda or potassa lye. If any ammonia is hereby obtained, the quantity must be deducted from the result obtained in determination (see the calculation of the analysis). 900 DETERMINATION OF COMMERCIAL VALUES. [ 325. the condensed vapors of sulphuric acid wash the sides of the flask clean again, and carry back into the liquid the carbonaceous par- ticles that have been spirted up. After heating for about two hours continuously, the solution appears clear, and is pale-brown. It is unnecessary, however, in the case of many substances (e.g., albu- minous substances and their derivatives), to prolong the action for so long a time, as the object is effected by heating for an hour or two, and even though the mixture is still black. In the case of substances, however, that offer greater resistance to the conversion of their nitrogen into ammonia, it is best to prolong the heating until incipient decolorization, which is most easily effected with the aid of phosphoric anhydride. As a rule, on treatment with sulphuric acid or a mixture of this with phosphoric anhydride, the greater part of the nitrogen, and with many substances, e.g.. uric acid, gluten-proteids, etc., even the whole, is converted into ammonia ; but with other albuminoid substances and most bodies belonging to the fatty series only 90 to 95 per cent, is converted into ammonia, and in the case of certain alkaloid (quinine, morphine) only 25 to 40 per cent, of nitrogen is thus converted. When the action of the acid is at an end, remove the flame, and add to the liquid powdered potassium permanganate in small por- tions, which may be added in rapid succession, and best in the form of a continuous shower of dust.* The reaction is very brisk, and is accompanied by the evolution of greenish vapors and strong detonations; frequently small flashes of flame are also seen. No loss of ammonia occurs during the operation. The at first usually dark liquid rapidly becomes paler by the action of the permanganate, then colorless, and on further addition, dark-green, or, if phosphoric anhydride has also been used, bluish- green from the formation of manganic salts. When these colors appear the oxidation is complete; then allow the liquid to cool. * For producing this KJELDAHL recommends a wide glass tube with narrow mouth-piece, e.g., the upper, broken-off part of a condenser tube, within the lower part of which a small, sufficiently fine piece of wire gauze is fixed: on gently tapping the tube filled with dry, quite finely powdered potassium permanganate, this falls through the gauze. 325.] ANALYSIS OF MANURES. 901 Next dilute the cooled acid solution by pouring it into the dis- tilling flask containing water, and rinsing out well with water. On adding the water the green color of the liquid passes into brown. The distilling flask should have a capacity of about 750 c.c., and the exit tube with which it is provided, is bent obliquely upwards, and is connected with a condenser. KJELDAHL prefers for this a spiral tube the exit end of which is connected with an absorption apparatus. The latter may be a 250-c.c. ERLENMEYER flask fitted with a two-holed rubber stopper; the straight lower part of the condenser passes through one hole to about the centre of the flask, without dipping into the acid, while in the other hole is fitted a glass tube bent at a right angle and open to the air. Introduce into the absorption flask 30 c.c. semi-decinormal sulphuric acid, remove the stopper of the distilling flask, introduce a few zinc turnings in order to prevent ''bumping during boiling, then immediately run in 40 c.c. soda-lye of 1-3 sp. gr., replace the stopper without delay, and heat the now alkaline liquid until all the ammonia has gone over, which is, as a rule, the case when about one-half of the liquid has been distilled off. * The ammonia in the receiver can now be determined by any suitable method. KJELDAHL prefers one of the older volumetric methods now but little used, and which is based upon the fact that, on adding an acid to a mixture of potassium iodate and potassium iodide, a quantity of iodine is liberated equivalent to that of the acid, and may be titrated by means of sodium thiosulphate. To carry out this process, dissolve a few crystals of potassium iodide in the still acid liquid in the absorption flask, then add a not too small quantity of well-made, thin starch paste, followed by a few drops of a 4-per-cent., potassium-iodate solution, and lastly a titrated solution of sodium thiosulphate (about equal to the semi- decinormal acid) until decolorization. As such a dilute solution of sodium thiosulphate possesses but little stability, its titre must be newly determined for every series of tests, and this may be done by means of iodine, as in 146, or as above, by aid of a titrated acid. KJELDAHL checks his results, as above mentioned, by treating 0-5 grm. pure sugar exactly in the manner detailed, employing 902 DETERMINATION OF COMMERCIAL VALUES. [ 326. like quantities of acids and other reagents in order to eliminate any errors due to the presence of nitrogen in the reagents. If 30 c.c. of sodium-thiosulphate solution are required for 30 c.c. of semi- decinormal sulphuric acid, but only 29-8 c.c. have been used in the control experiment, then this latter figure must be used in calcu- lating the analysis. The calculation is very simple. The number of c.c. of semi- decinormal sodium-thiosulphate solution corresponding with the neutralized acid is multiplied by 7 02 (half the equivalent of nitro- gen). The number so obtained, divided by the number of centi- grammes of substance taken, gives the percentage content of nitro- gen. As an example, KJELDAHL gives a determination of nitrogen in barley. 0-645 grm. of barley was treated as above described, and 30 c.c. of semi-decinormal sulphuric acid were taken. The relation found between this and the semi-decinormal sodium-thiosulphate solu- tion in the control test was found to be 30 : 29-8. Titrating back required 14-5 c.c. of the thiosulphate solution: IK Q v 7 02 29.8-14.5=15-3; - l^-^! = 1 . 66 per cent, nitrogen. o4 o /?. Modifications of KJELDAHL'S Method. 326. As may be seen from what has been said in 325, KJELDAHL'S method was first introduced in a form worked out with the greatest care, and the test analyses given by KJELDAHL also leave scarcely anything to be desired so far as accuracy is concerned. Notwith- standing this, nearly all chemists who have busied themselves with the testing and employment of this method and their number is large, as may be seen by reference to the foot-note * have em- ployed and recommended modifications : * HEFFTER, HOLLRUNG, and MORGEN (Chemiker-Ztg., vni, 432; Zeitschr. j. analyt. Chem., xxin, 553) ; PETRI and TH LEHMANN (Zeitschr. /. physiolog. Chem., vin, 200; Zeitschr. f. analyt. Chem., xxin, 596) ; E. BOSSHARD (Zeitschr. /. analyt. Chem., xxiv, 199); E. PFLUGER and K. BORLAND (Archiv. /. d. 326.] ANALYSIS OF MANUEES. 903 Of this number, many are but slight modifications. WILFARTH'S modification, however, is of more importance, as are also those of v. ASBOTH and JODLBAUER, with reference to the determination of nitrogen in nitrates. I will first touch upon the slighter modifications, then upon WILFARTH'S, and lastly upon the modifications by v. ASBOTH and JODLBAUER. As nearly all of the chemists cited in the foot-note titrate the excess of acid in the ammonia determination by the usual acidi- metric method with baryta water or soda-lye, using litmus or another indicator, and without commenting upon the KJELDAHL method of separating iodine and determining this, they use larger quantities of substance (1 to 1-5 grm.), larger flasks for heating (150 to 250 c.c. capacity), and 20 c.c. of the acid mixture instead of 10 c.c. Regarding this last, many discard the fuming sulphuric acid (which often contains nitric acid) and as an acid mixture employ a solution of 200 grm. phosphoric anhydride in 1 litre of pure concentrated sulphuric acid, while others employ a mixture of equal volume of concentrated and fuming sulphuric acid, others again preferring either this mixture or one of 4 volumes of concentrated and 1 volume of fuming sulphuric acid with the addi- tion of 100 grm. of phosphoric anhydride per litre of mixture. BRUNNEMANN and SEYFERT mix the substance with 2 grm. phosphoric anhydride, then heat with 5 c.c. of a mixture of 4 volumes concentrated and 1 volume of fuming sulphuric acid gesammte Physiolog., xxxv, 454, and xxxvi, 102; Zeitschr. /. analyt, Chem., Kxrv, 299 and 635); TH. PFEIFFER and F. LEHMANN (Zeitschr. f. analyt. Chem., xxiv, 388); KREUSLER (ibid., xxiv, 393 and 453; Landwirthschaftl. Versuchsstationen, xxxi, 269) ; C. ARNOLD (Archiv. der Pharm. [3], xxin, 177; Zeitschr. f. analyt. Chem., xxiv, 454; Chem. Centralbl, 1886, p. 337).; F. W. DAFERT (Zeitschr. f. analyt. Chem., xxrv, 454); H. WILFARTH (Chem. Cen- tralbl. [3], xvi, 17 and 113; Zeitschr. f. analyt. Chem., xxiv, 455); BALCKE (Wochenschr. f. Brauerei, I, No. 11); P. KULISCH (Zeitschr. /. analyt. Chem,, xxv, 149) ; RINDELL and HANNIN (ibid., xxv, 155) ; CZECZETKA (Monats- hefte f. Chem., vi, 63: Zeitschr. f. analyt. Chem., xxv, 252); A. v. ASBOTH (Chem. Centralbl., 1886, p. 161) ; ULSCH (ibid., 375) ; M. JODLBAUER (ibid., 433) ; BRUNNEMANN and SEYFERT (Chemiker-Ztg., vm, 1820) ; R. WARINGTON (Chem. News, LII, 162: Zeitechr. f. analyt. Chem., xxv, 427). 904 DETERMINATION OF COMMERCIAL VALUES. [ 326. until the brisk evolution of gas slackens, and then continue the heating after a further quantity of 15 c.c. of the acid mixture has been added. Other changes are such as are concerned with the manner, intensity, and duration of heating; all agree, however, that it is safest to prolong the action until the solution acquires the color of Rhine wine, or appears reddish or colorless. HEFFTER, HOLL- RUNG and MORGEN, and also KREUSSLER, have described special stoves for heating a number of flasks at the same time. KREUSSLER places on the flask a cylindrical glass vessel open above and below, in order to lessen the evolution of acid vapors. ULSCH employs glass bulbs with stems. CZECZETKA employs for oxidizing purposes a solution of potas- sium permanganate in concentrated sulphuric acid instead of the powdered salt. A 500- to 750-c.c. flask is sufficient for the distillation, even when larger quantities of the substance and 20 c.c. of the acid mixture are used. The quantity of liquid to be distilled should be from 200 to 250 c.c., according to the quantity of water used for dilution. The alkali solution (preferably potassa solution, which is less likely than soda to cause bumping during boiling) is added to the cold, diluted liquid, and it is best to add it first in quantity sufficient to nearly neutralize the acid, then to cool the liquid, and then to add a further quantity of the alkali solution in sufficient, but not too great, excess. When employing zinc turnings, it is especially necessary to avoid too large an excess of alkali, because if the evolution of hydrogen becomes too violent, it is difficult to prevent drops of alkali solution from being carried over, even when employing safety apparatus, of which many have been pro- posed. If the lye contains nitric acid, the nitrogen of this is con- verted into ammonia on using zinc. In order to prevent bumping, it has been recommended to pass in a gentle current of steam or air. The form of the distilling-flask and receiver may of course be variously modified. It is always advisable to have several bulbs, which are to be partly filled with fragments of glass, blown on the tube connecting the distillation-flask with the condenser 326.] ANALYSIS OF MANURES. 905 tube. The apparatus shown in Fig. 81, and described in Vol. I, p. 254, is excellently adapted for the purpose, and so also is the one, so far as the receiver is concerned, described on p. 884 this volume, Fig. 137. If, as recommended by most of the chemists above cited, a larger quantity of substance is taken, a stronger acid than the semi-decinormal recommended by KJELDAHL must be employed, in fact normal, seminormal, or decinormal acid. When titrating according to the iodine method proposed by KJELDAHL, both PFLUGER and BORLAND, who have retained and recommended the method, point out that the last small quantities of free acid require some time to decompose the mixture of potas- sium iodide and iodate, particularly in the case of very dilute solu- tions. Twenty-four hours are required for complete decomposition, but at the end of one or two hours the error amounts only to at most 0-1 to 0-2 c.c. of decinormal sodium-thiosulphate solution. When titrating the excess of acid by the usual acidimetric methods, many prefer baryta water to potassa- or soda-lye. The indicators to be specially recommended are SCHLOSING'S prepara- tion of litmus,* p. 845 this volume, methyl orange, and phenacet- olin (THOMSON f). WILFARTH'S modification is based upon the fact that the addi- tion of metallic oxides facilitates the action of the acid mixture on the organic mixture; the most suitable have been found to be cupric oxide, and particularly mercuric oxide prepared by the wet way (when prepared by the dry way the mercuric oxide is apt to contain nitric oxide). WILFARTH'S modification, which has proved satisfactory in every respect, is carried out as follows : Mix 1 grm. of the nitrogenous substance (if poor in nitrogen 2 to 3 grm. may be taken) with 20 c.c. of an acid mixture consisting of 3 volumes of pure, concentrated sulphuric acid and 2 volumes of fuming sul- phuric acid and with the addition of 7 grm. of the mercuric oxide prepared by the wet way (or an equivalent quantity of mercuric * Compare RINDELL and HANNIN, Zeitschr. f. analyt. Chem., xxv, 155. t Ibid., xxiv, 225. 906 DETERMINATION OF COMMERCIAL VALUES. [ 326. sulphate or metallic mercury), and heat in a flask, which should be of good potash glass, on a wire gauze over a naked flame, gently at first, then somewhat more strongly, and finally to gentle boiling. On continuing the heat until the liquid has become colorless, the oxidization with potassium permanganate will be unnecessary; if it is desired, however, to save time, heat only until the liquid has acquired the color of light Rhine wine, and then oxidize with potas- sium permanganate. After it has been diluted, and made alkaline with potassa-lye, as above described, add a quantity of solution of sulphurated potassa (40 g-m. sulphurated potassa per litre) more than corresponding to the mercury used, and whereby the mercury is precipitated as sulphide. In order to ascertain the approximate quantity of sulphurated-potassa solution required, dissolve 5 grm. mercuric oxide in diluted sulphuric acid and then find out how much of the sulphurated potassa solution is required to completely precipitate it. It is advisable to employ a con- siderable excess of the sulphurated-potassa solution, in order to be certain of the complete decomposition of the mercuro-ammo- nium compounds. It is only after twice or thrice the requisite quantity has been added that the odor of hydrogen sulphide be- comes perceptible, but this does not affect the accuracy of the results. No bumping occurs when the liquid holds mercuric sul- phide in suspension, at least not when potassa-lye is used; of course, a little zinc may also be added. WILFARTH'S method has also been modified; thus KULISCH recommends an acid mixture of equal volumes of concentrated and fuming sulphuric acids containing 100 grm. phosphoric anhy- dride per litre. He obtained absolutely accurate results with the substances (wine yeast and must extract) only when the heating was prolonged until the liquid became colorless, and then sub- sequently oxidized with potassium permanganate. KULISCH also recommends adding a small quantity of metallic mercury. ARNOLD uses 5 grm. cupric sulphate and 1 grm. metallic mercury, while ULSCH employs 05 grm. cupric oxide and 5 drops (but no more) of a platinic-chloride solution 1 c.c. of which contains 0-04 grm. platinum. 326.] ANALYSIS OF MANURES. 907 If the nitrogen is present in the form of nitric acid, neither the original KJELDAHL method nor the WILFARTH modification will yield good results. The object, may, however, be effected by making certain additions; \hus according to v. ASBUTH (.oc. dt.) fairly good results are obtained by adding benzoic acid. He recom- mends using 1 75 benzoic acid to 5 grm. potassium nitrate, finally decomposing the difficultly decomposab.e benzoate with po.assium permanganate and subsequent prolonged heating. If the nitrogen is present as oxide, or in he form of cyanogen, v. ASBOTH adds 1 grm. sugar; as the metallic addition, he employs 0-5 grm. cupric sulphate. The distillation is effected after the addition of a solu- tion of Rochelle salt in soda-lye (350 grm sodium pota shim tar- trate and 300 grm. sodium hydroxide dissolved in 1 litre water), in order to keep the cupric and manganous oxides in solution. According to JODLBAUER (loc. a';.) the addition of benzoic acid when nitrates are present does not with certainty yield sufficiently satisfactory results, but they are satisfactory on treating 0-2 to 0-5 grm. potassium nitrate (or a corresponding quantity of another nitrate) with 20 c.c. concentrated sulphuric acid and 2 5 c.c. phenol- sulphuric acid (obtained by dis olving 50 grm. phenol in concen- trated sulphuric acid to make 100 c.c.), with the addition of from 2 to 3 grm. zinc dust and 5 drops of a platinic-chloride solution, 1 c.c. of which contains 0-04 grm. platinum. After heating for about four hours, the liquid is colorless, and is then ready for further treatment and distillation. When a mixture of sulphuric acid and phosphoric anhydride is employed, heating for two hours already suffices, but then the decomposing flask is strongly attacked, and in a short time becomes unserviceable. F. ANALYSIS OF MANURES CONTAINING TWO OR MORE MANURIAL SUBSTANCES. In order to afford some data for a choice of methods suitable for all cases, I give here a general process first, applicable not only to stable manure, but also to nearly all kinds of manures, and will then proceed to detail the methods which are specially adapted for commercial manures. 908 DETERMINATION OF COMMERCIAL VALUES. [ 327. I. GENERAL PROCESS. 327. The manure is uniformly mixed by chopping and grinding, and the several portions required for the various determinations are then successively weighed out.* 1. DETERMINATION OF WATER. Dry 10 grm. at 110, and determine the loss of weight ( 29). (It will be but seldom necessary to make a correction for the ammo- nium carbonate that escapes with the water, f) 2. TOTAL FIXED CONSTITUENTS. Incinerate a weighed portion of the residue obtained in 1, in a platinum dish or large, obliquely placed platinum crucible, at a gentle heat (pp. 794 and 795, this volume), moisten the ash with a solution of ammonium carbonate, allow to dry, gently ignite, and then weigh. 3. CONSTITUENTS BOTH SOLUBLE AND INSOLUBLE IN WATER. Digest 10 grm. of the fresh manure with about 300 c.c. water, collect the residue on a weighed filter ( 50), wash, dry at 110, and weigh. The total weight of insoluble constituents is thus obtained, and the difference after deducting the water as found in 1 will give the weight of those soluble in water. Now incinerate the insoluble residue, treat with ammonium carbonate as in 2, weigh, and thus ascertain the total weight of the fixed constituents con- tained in the insoluble portion, and from the difference, the total quantity of those contained in the soluble part. 4. FIXED CONSTITUENTS SINGLY. Dry a larger portion of the manure, and treat it exactly as in one of the methods given for the preparation and analysis of plant ashes. * Accurate directions for obtaining a correct average sample of stable manure are given in E. WOLFF'S Anleitung zur chem. Untersuchung land- wirthschaftl. wichtiger Stoffe (Berlin: WIEGAND, HEMPEL, and PAREY, 3d edit., p. 115). f Should this happen, proceed as in the determination of water in guano ( 331, 1). 328.] ANALYSIS OF MANURES. 909 5. TOTAL CARBON. Subject a portion of the residue obtained in 1 to elementary analysis; as manures may contain chlorine and sulphur com- pounds, it is best to make the combustion with lead chromate V 176). On account of the nitrogen content, and also of inor- ganic substances present, what has been said in 183 and 191, respectively, must be borne in mind. If the dried manure con- tains carbonates, the carbonic acid must be determined in a separate portion. On deducting this from the quantity found in the ele- mentary analysis, the difference will give the quantity derived from the carbon of the organic matter. The method given on p. 510 this volume (oxidation of the organic matter with chromic acid with the addition of sulphuric acid) may also occasionally be employed with good results, particularly if no chlorine compounds are present.* When carbonates are present, the properly diluted sulphuric acid is first allowed to act alone, until all carbon dioxide has been evolved, before adding the chromic acid and connecting the decomposing-flask with the ab orption apparatus. 6. SULPHUR COMPOUNDS. If the manures contain unoxidized sulphur (as, for instance, is usually the case with manures taken from the sewers of towns), determine the total sulphur in a sample by the method detailed for soil analysis ( 303, 6) ; then heat a second portion with diluted hydrochloric acid, repeatedly if necessary, filter, determine in the filtrate the sulphuric acid which is present as such, and from the difference ascertain the unoxidized sulphur that was present. 7. TOTAL NITROGEN. 328. If the manure, as is frequently the case, contains the nitrogen in the form of nitric acid, ammonia, and in organic combination, then DUMAS' method (185) is unquestionably best adapted for obtaining the total nitrogen at one operation. KJELDAHL'S method ( 324 to 326) and that of VARREXTRAPP-WILL ( 186 * Compare, however, in this connection p. 839, /3, this volume. 910 DETERMINATION OF COMMERCIAL VALUES. [ 328. and 187), on the other hand, cannot be used in their original form if any notable quantity nitric acid is present, but the modifications detailed below must be employed. a. Preparatory Treatment. If the manure is damp and not homogeneous, and gives off ammonia on drying, moisten a weighed quantity (about 10 grm.) with a dilute solution of oxalic acid so that the whole mass is neutral or only slightly acid, dry at about 50, weigh, mix uni- formly, and employ portions of the dry substance so obtained for the nitrogen determination. If the manure is of a similar character, but does not give off ammonia on drying, treat it in like manner, but without adding oxalic acid. If the manure, on the other hand, is dry, uniform, and in fine powder, it is, of course, fit for examination without further preparation. 6. The Process. a. DUMAS' Method. The only objection that may be made against this method (which was minutely detailed in 185, and which was also alluded to on p. 894 this volume), is, that it is too complicated for the examination of manures. The employment of it cannot, however, be avoided when it is a question of checking the results of other analyses. Instead of, as in this method, driving the nitrogen into the measuring-cylinder by carbon dioxide, the SPRENGEL mercury pump is now being frequently employed with the test results. Compare with this the work of FRANKLAND and ARMSTRONG,* 'GiBBS,f PFLUGER,J JOHNSOHN and JENKINS, DABNEY, Jr., and VON HERFF.|| ft. JODLBAUER'S Modification of KJELDAHL'S Method (p. 907, this volume). This method, as already mentioned, also gives accurate results when the nitrogen is present in the form of nitric acid. * Zeitschr. f. analyt. Chem., vm, 489. f Ibid., xi, 206. J Ibid., xvin, 296. Ibid., xxi, 274. || Ibid., xxv, 425. 328.] ANALYSIS OF MANURES. 911 f. VARRENTRAPP-WILL'S Method and its Modifications. If the quantity of nitrates is rather small, while that of the organic matter is sufficiently large, then the VARRENTRAPP-WILL method in its original form, or PELIGOT'S modification of it ( 187, see also p. 84, this volume) is satisfactory. If, however, the quantity of nitric acid is somewhat larger, then such modifications must be chosen whereby the acid will be fully and completely reduced. Such methods have been repeatedly proposed, and as I had no occasion to describe them before this, I will detail them here, although the modified methods no longer possess the same im- portance they first had, because of the introduction of the modified KJELDAHL method, which accomplished the object more easily and surely. The first modification of the VARRENTRAPP-WILL method to be mentioned is that of E. A. CRETE;* he employed a mixture of soda-lime and xanthogenates for converting the nitric acid into ammonia. Later on RUFFLE f recommended a mixture of 2 equivalents sodium hydroxide, 1 equivalent lime, and 1 equivalent of crystallized sodium thiosulphate. He used an iron combustion tube, closed at the hinder end, and charged as follows : 5 grm. of the above mixture were placed in the hinder end, followed by about 30 grm. of the mixture triturated with from 1 to 1 5 grm. of the substance to be analyzed, the latter having previously been uni- formly incorporated with 1 grm. of a mixture of equal parts of sublimed sulphur and powdered charcoal; after this follows more soda-lime mixture, then about 18 grm. pure soda-lime, and lastly an asbestos plug which is so placed as to still leave about 20 cm. of the tube empty. The test-analyses given by RUFFLE are satisfac- tory. In the analysis of artificial manures it is at times necessary to effect the intimate mixture of the substance with sodium thio- sulphate by evaporating it with a solution of the thiosulphate. A. GUYARD (H. TAMM J) proposed to heat to redness a mixture * Ber. der deutsch. Chem. Gesellsch. zu Berlin, xi, 1557; Zeitschr. f. analyt. Chem., xvin, 106. t Joum. Chem. Soc., 1881, p. 87; Zeitschr. f. analyt. Chem., xxi, 412. \ Chem. News, XLV, 159; Zeitschr. f. analyt. Chem., xxi, 584. 912 DETERMINATION OF COMMERCIAL VALUES. [ 328. of the substance with soda-lime and dried sodium acetate. A. GOLDBERG * recommends a mixture of 100 parts soda-lime, 100 parts stannous sulphide, and 20 parts sulphur; and with this he obtained approximate (about 0-3 to 1 per cent, too low) results with potassium nitrate. Most of these modifications were critically tested by various experimenters, and with very varying results. First, as concerns RUFFLE'S method, CRISPO,! PELLET,J and also DABNEY, Jr., and VON HERFF obtained good results with it; FASSBENDER,|| and also ARNOLD, ^[ however, who effected the combustion in glass tubes and consequently employed anhydrous sodium thiosulphate, obtained much less satisfactory results. SHEPHERD** obtained approximately accurate results with guanos containing only small quantities of nitre, but with potassium nitrate the results were too low. J. KONIG ft reported that the method gives correct results with natural Peruvian guanos, and even when they contain nitrates, but the results were too low in the case of artificial mix- tures of guano with saltpetre ; RUBE JJ also obtained good results with manures, particularly guano, and ascribes the unfavorable results recorded by others to their not having adhered strictly to RUFFLE'S original method, but to having made changes in it. P. WAGNER also obtained serviceable results with guanos containing potassium nitrate, by employing the following slightly modified method, in which mixtures having the composition here given are used: 1. 100 parts by weight powdered soda-lime and 10 parts by weight oxalic acid. 2. 100 grm. calcined gypsum mixed with 6 c.c. concentrated, pure sulphuric acid (preserved in * Zeitschr. f. analyt. Chem., xxm, 244. f Neue Zeitschr. f. Rubenzuckerindustrie, ix, 162; Zeitschr. f. analyt. Chem., xxn, 434. | Rev. d. ind. chim. ebagr., vi, 605; Zeitschr. f. analyt. Chem., xxn, 434. Amer. Chem. Journ., vi, 234: Zeitschr. f. analyt. Chem., xxv, 425. || Repert. d. analyt. Chem., n, 225; Zeitschr. f. analyt. Chem., xxn, 434. If Arch. d. Pharm. [3], xx, 92; Zeitschr. f. analyt. Chem., xxn, 435. ** Chem. News, XLVII, 75; Zeitschr. f. analyt. Chem., xxn, 435. ft Rep. d. analyt. Chem., in, 1 ; Zeitschr. f. analyt. Chem., xxn, 436. jt Zeitschr. /. analyt. Chem., xxm, 43. Chemiker-Ztg., vni, 651; Zeitschr. /. analyt. Chem., xxm, 559. 328.] ANALYSIS OF MANURES. 913 well-stoppered bottles). 3. 100 parts by weight of sodium thiosulphate dried at 100, and intimately mixed in a warmed mortar with 100 parts powdered and well-dried soda-lime, 8 parts finely powdered charcoal, and 8 parts sublimed sulphur, all by weight (to be preserved in a long-necked bottle closed by a rubber stopper). The glass tube used for the determination is 40 cm. long, 8 mm. wide, and with one end sealed and rounded; it is charged by first introducing a 5-cm. long layer of the mixture No. 1 ; then 1 5 grm. of an intimate mixture of equal parts by weight of the guano to be examined and of mixture No. 2, is mixed with about 20 grm. of mixture No. 3, and introduced without de!ay into the tube, after which the latter is- filled with granulated soda-lime, and stoppered with an asbestos plug. By making blank com- bustions any correction that may be necessary to make is ascer- tained. GRETE'S method afforded J. KONIG (loc. cit.) results like those of RUFFLE; TAMM'S method, on the other hand, found no de- fender, although C. ARNOLD* and subsequently HouzEAuf also sought to combine the methods of RUFFLE and TAMM, and with success. In his most recent publication C. ARNOLD J recommends igniting 0-5 grm. of the substan e (or cnly 0-3 grm., if the sub- stance contains more than 20 per cent, nitrogen) with a mixture of 2 parts anhydrous sodium thiosulphate with 1 part each of soda- lime and sodium formate (to which a little sugar is added when analyzing nitrates of the heavy metals). The glass tube contains at the hinder end 5 cm. of the mixture just described, then the mixture containing the substance (12 to 15 cm.), next a layer 15 to 20 cm. long of the finely powdered mixture, and lastly 5 to 10 cm. of soda-lime. The heat must not be raised during combustion to such a point as to allow the mass to sinter and form a large channel, but must nevertheless be sufficient for the complete combustion of the substance. If the latter is not the case, and the acid in the receiver appears dark or cloudy, the results are unreliable. The * Rep. der analyt. Chem., n, 331 ; Zeitschr. f. analyt. Chem., xxn, 437. t Compt. rend., c, 1445; Zeitschr. f. analyt. Chem., xxv, 424. Rep. der analyt. Chem., v, 41 ; Zeitschr. /. analyt. Chem., xxrv, 451. 914 DETERMINATION OF COMMERCIAL VALUES. [ 329. results obtained by ARNOLD by this method, in the analysis of nitrates and nitro-compcunds are entirely satisfactory. Lastly, I would point out that the total nitrogen may also be ascertained by adding together that existing as nitric acid (see below under 8, /?), and the sum of the quantities present as ammonia and in the organic matter (see below, 8, 7-, bb or cc). 8. NITROGEN IN ITS DIFFERENT FORMS OF COMBINATION. 329. a. In Ammoniacal Compounds. The ammonia is most conveniently determined by distilling a weighed sample of the substance with water and calcined magnesia (p. 253, a, Vol. I, and p. 883 this volume). If any organic matter is present, the nitrogen of which may be thereby partly converted into ammonia, it is preferable to employ SCHLOSING'S method, based upon the action of milk-of-lime in the cold (Vol. I, p. 255, 6, and p. 843 this volume). If it is desired to determine the ammo- nia azotimetrically, this is best effected in the hydrochloric-acid extract of the manure (compare 322, azotimetric determination of ammonia in soils) . /?. In the Form of Nitric Acid. Thoroughly extract a sample of the manure with hot water, con- centrate the solution (first neutralizing if it is acid) by evaporation, make up to a definite volume, and in a measured portion determine the nitric acid, and hence the nitrogen in it, most conveniently by P. WAGNER'S slight modification of SCHLOSING'S method (p. 877 this volume). The nitrometric method (p. 713 this volume), may also be em- ployed with good results, and is preferred and recommended by many analysts.* In this case evaporate almost to dryness the measured quantity of the aqueous solution, neutralized if neces- sary, add a little sulphuric acid in order to decompose any carbon- * See SHEPHERD (Chem. News, XLVII, 76; Zeitschr. /. analyt. Chem., xxv, 270). YARDLEY (Chem. News, XLVII, 92; Zeitschr. f. analyt. Chem., xxv, 448). 329.] ANALYSIS OF MANURES. 915 V ates that may be present, expel the carbonic acid by gently warming, and introduce the liquid (which should measure not more than 2 or 3 c.c.) into the nitrometer, rinsing the funnel of the latter twice with concentrated sulphuric acid. SHEPHERD (loc. cit.) introduces the liquid, which, together with the washings should not exceed 5 c.c., at once into the nitrometer, adds to the cold liquid twice its volume of concentrated sulphuric acid, mixes the latter with the aqueous liquid by gently shaking, opens the cock momentarily to allow any carbon dioxide evolved \o escape, and then shakes vigorously to dis- engage the nitric oxide. In case of manures which have an acid reaction, all direct evaporation of the aqueous extract must, of course, as already mentioned, be avoided, as otherwise there may be a loss of nitric acid. To directly determine this nitrometrically, extract a weighed, not too small, sample of the manure with warm water in such a manner that while the residue is exhausted, the solution is as con- centrated as possible, then make the latter up to a definite volume, and use 5 c.c. for the nitrometric determination. (YARDLEY, loc. cit.) Y. In Organic Combination. aa. Deduct from the total nitrogen found in 328 the nitrogen of the ammonia compounds (a) and that present as nitric acid (/?), and thus ascertain from the difference the nitrogen present in or- ganic combination. bb. According to O. REITMAIR,* if the manure contains nitrates pour 3 c.c. of 50-per-cent. sulphuric acid f over about 1 grm. of the finely powdered sample in a shallow tin-foil dish about 60 mm. in diameter and 20 mm. deep, stir with a very short, glass rod, and heat in a drying closet for 3 to 4 hours at 60 to 80, then for 1 hour at 120 to 130. The dish will now contain a moist mass from which all the nitric acid (but no other nitrogen) has been expelled. The * Rep. dcr analyt. Chem., v, 262; Zeitschr. f. analyt. Chem., xxv, 583. t The employment of concentrated sulphuric acid as used by DREYFUS (Bull, de la Societe Chim. de Paris, XL, 267; Zeitschr. f. analyt. Chem., xxiri, 246), is not to be recommended, because if organic matter is present, a part of the nitrogen of the nitric acid may be converted into ammonia. 916 DETERMINATION OF COMMERCIAL VALUES. [ 330. nitrogen in this mass may then be determined either by the KJEL- DAHL or the VARRENTRAPP-WILL method. If the former method is used transfer the dish together with its contents into the decom- posing-flask ; if the latter method is employed, add to the con- tents of the dish a pulverulent mixture of gypsum and marble, stir well together, remove the mass from the dish, and mix it with soda-lime in the usual manner. The tin-foil dish, sprinkled with soda-lime, and bent together, is also introduced, together with the glass rod, into the combustion tubes. . On deducting the nitrogen of the ammonia (8, a) from the total nitrogen determined in the residue obtained by one or other of the above methods, after the expulsion of the nitric acid, the difference gives the nitrogen present in the form of organic matter. cc. Heat the weighed substance, if it contains nitrates, with a suitable quantity of ferrous sulphate and concentrated hydrochloric acid, thus freeing it completely from nitric acid, then dry the residue, and determine in the latter the total nitrogen present in the form of ammonia and organic compounds, by KJELDAHL'S method (R. WARINGTON).* The calculation is made as in 7-, bb. II. ANALYSIS OF COMMERCIAL MANURES. 1. BONE PREPARATIONS. 330. The bones of vertebrate animals in the dry state contain about 70 per cent, of inorganic and 30 per cent, of organic matter. The former consists of basic calcium phosphate and small quantities of calcium carbonate, calcium fluoride, and magnesium phosphate; the latter consists chiefly of cartilaginous substances and fat. The average nitrogen content of the dry bones is from 4 to 5 per cent. ; the phosphoric-acid content from 27 to 30 per cent.; and the fat about 10 per cent. On boiling with water, as also on exposure to air, the content of nitrogen and fat decreases, while that of the phosphoric acid increases. The manurial value of bones depends upon the degree of comminution of the latter and their content of * Chem. News, LII, 162; Zeitschr. f. analyt. Chem , xxv, 427. 330.] ANALYSIS OF COMMERCIAL MANURES. 917 nitrogen and phosphoric acid. The presence of fat is rather preju- dicial than otherwise. In commerce the following bone prepara- tions are met with : a. Bone-meal. Bone-meal comes into commerce in three forms namely as crude, steamed, and fermented. It is customary to guarantee the crude to contain from 2-5 to 4-5 per cent, nitrogen and 18 to 21 per cent, phosphoric acid; the steamed, from 3 to 4-5 per cent, nitrogen and 20 to 21 per cent, phosphoric acid; and the fermented, 4 per cent, nitrogen and 20 per cent, phosphoric acid. The analy- sis is usually confined only to the determinations a, /?, 7-, and occa- sionally also d. a. Moisture. Dry about 5 grm. of the substance at 110 in a light, wide-mouthed flask (Fig. 135i, p. 854 this volume) and determine the loss of weight. /?. Ash, Sand, and Phosphoric Add. Heat about 5 grm., gently at first, but gradually more strongly, with access of air, until the ash has become white, then moisten the latter with ammo- nium carbonate, dry, gently ignite, and weigh the ash. Then gently boil this for some time with 15 to 20 c.c. nitric acid, slightly diluted with water, and until all the soluble matter has dissolved, then dilute, and filter into a 500-c.c. flask ; wash the insoluble residue, dry, ignite, weigh, and calculate it as sand. When cold, dilute the contents of the flask to the mark, mix, and in 50 c.c. of the mixture, containing about 0-1 grm. phosphoric acid, determine the acid according to 309, or 313, /?/?. If it is desired to determine in the ash the other substances usually present (calcium, magnesium, iron, etc.), treat a further measured portion of the nitric-acid solu- tion according to 287. f. Nitrogen. As the nitrogen in bone-meal is present only in the form of organic matter, it is sufficient to determine it in about 1 grm. of the substance by combustion with soda-lime ( 187 and 323), or according to KJELDAHL ( 325 and 326). With either method 20 c.c. of seminormal sulphuric acid are required. d. As. in determining the manurial value of bone-meal, the 918 DETERMINATION OF COMMERCIAL VALUES. [ 330. degree of comminution must be taken into account, determine this by dividing 100 grm. into four grades of fineness by the aid of three sieves. STOHMANN* has proposed for this purpose the following sieves: No. I has 11 meshes to the square millimetre; No. II has 5; and No. Ill has 2 5. What remains on sieve No. Ill is residue IV. e. If the fat also is to be determined, exhaust the residue from a (powdering more finely, if necessary) with carbon disulphide or ether in one of the forms of extraction apparatus adapted for this purpose,f evaporate the solvent in a light, wide-mouthed flask, heat the residue for some time at 100, and weigh the fat. . The carbonic acid may be determined by one of the methods described in 139, II. b. Bone-black (Animal Charcoal). Bone-black is extensively employed in the manufacture of sugar for decolorizing and removing lime. Recently prepared, it con- sists of a mixture of bone earth with 7- 5 to 10-5 per cent, of carbon, but during use it takes up lime, coloring matter, pectinous matter, etc., from which it is freed during the process of revivifying by treatment with acids, fermentation, washing, and ignition. When it is finally " spent," it is taken by the manure manufacturers, and is then usually employed in the manufacture of superphosphate. As the bone-black is greatly altered and in many ways contami- nated, the quality of that met with in the market varies greatly, and can only be determined by analysis. Although this is one reason why bone-black is so frequently analyzed, yet there is another, as it is necessary to have analyses made of the bone-black which is to be revivified and used in the sugar manufacture. In order to ascertain how much hydrochloric acid it is necessary to employ for revivifying the bone-black, the quantity of calcium which is present not in combination with phosphoric acid (and * P. WAGNER'S Lehrbuch der Dungerfabnkation. Brunswick, FR. VIEWEG und SOHN, 187. f Compare Zeitschr. /. analyt. Chem., xn, 179; xiv, 82; xvn, 174 and 320; xvm, 441; xxi, 98; xxn, 528; xxiv, 48; xxv, 396; Rep. der analyt. Chem., 1886, p. 390. 330.] ANALYSIS OF COMMERCIAL MANURES. 919 usually present as calcium carbonate) must be determined in each individual case. In the following paragraphs I give a complete analysis of bone- black, but would point out that it is, as a rule, sufficient to deter- mine the phosphoric-acid content in order to ascertain its manurial value. 1. Dry about 5 grm. of the substance at 110, and from the loss of weight determine the moisture. 2. Dissolve about 5 grm. in the flask a, shown on p. 365, Fig. 103 this volume, and determine the carbonic acid according to the method there described. If only the phosphoric acid is to be determined in the filtrate by the molybdenum method, use diluted nitric acid as the solvent, but otherwise employ diluted hydro- chloric acid. To make certain that everything soluble passes into solution, the acid must be allowed to act for 15 to 20 minutes at a temperature near the boiling-point. 3. Filter the solution obtained in 2, through a filter dried and weighed at 100; wash the residue, dry at 110, and thus ascertain the sum of the carbon, any insoluble inorganic substance that may be present, and the mineral impurities (sand and clay) insoluble in the nitric or hydrochloric acid. Then ignite the dried filter with access of air, and thus obtain the sand and clay as a residue, the carbon and any insoluble organic matter being ascertained from the difference. 4. The filtrate from 3 make up to 500 c.c., and in 50 c.c. deter- mine the phosphoric acid as in 330, a. In other portions deter- mine the other constituents (iron, calcium, magnesium, alkalies, and sulphuric acid) according to 287. 5. Dissolve another weighed portion of the substance in diluted nitric acid, dilute, and in the filtrate determine any hydrochloric acid that may be present. 6. To determine the calcium sulphide, which is usually present in quantities too small to permit of its exact determination with the carbonic acid (see 2) . it is best to heat about 10 grm. of the bone- black with diluted hydrochloric acid in a current of hydrogen, pass the gas containing hydrogen sulphide through brominized 920 DETERMINATION OF COMMERCIAL VALUES. [ 330. hydrochloric acid, determine the sulphuric acid formed, and from this calculate the calcium sulphide (see p. 519 this volume). 7. To determine the calcium carbonate, or the carbonate and the free lime, SCHEIBLER'S method, described on p. 500, g, a, Vol. I,, is usually employed in the factories. The bone-black is first dried, and reduced to as fine a powder as possible. The quantity taken should be so chosen as not to contain too small a quantity of car- bonic acid ; about 3 grm. of the dried bone-black may be considered as about the proper quantity. SCHEIBLER has given his apparatus a no mal weight, and in his treatise * gives tables for facilitating calculation. If a bone-black contains calcium hydroxide, moisten the weighed portion with 10 to 20 drops of an ammonium-carbonate solution in a porcelain dish, evaporate to dryness, heat the residue somewhat more strongly (but nowhere near redness), and trans- fer the contents of the dish without loss to the decomposing flask. If the work is carefully done, the results are very concordant and accurate; and many analyses can be made in a short time. c. Bone-ash; and d. Precipitated Calcium Phosphate from Bones. These owe their value solely to their phosphoric-acid content, which may be determined according to 307 to 310, or also 313, /9/?. e. Superphosphates prepared from Bone. If these are prepared from bone-black or bone-ash, only the phosphoric acid in its various conditions of solubility need be considered in determining their value; if, however, they are pre- pared from bone-meal, then the nitrogen also must be determined. Regarding the determination of the phosphoric acid see 311 to 318; the nitrogen is determined as in the case of bone-meal (330,a, r ). * Anleitung zum Gebrauch des Apparates zur Bestimmung der Kohlensauren Kalkerde in der Knochenkohle, etc., by C. SCHEIBLER, printed as MS., 6th edit., Berlin, 1874. 331.] ANALYSIS OF COMMERCIAL MANURES. 921 2. GUANO (PERUVIAN GUANO). 331. a. Crude Guano. Guano, the more or less modified excrement of sea-birds, occur- ring on the islands and coasts whence it is obtained, is of exceed- ingly irregular composition, due to the various influences to which it has been exposed in the course of time, hence its value, which depends upon its content of nitrogen and phosphoric acid, can be ascertained only by chemical analysis. The good guano beds of the Chinchas Islands, which for a long time supplied all the de- mands, and yielded a guano containing on an average 12 per cent, nitrogen and 12 3 per cent, phosphoric acid, are now almost com- pletely denuded, and the guano beds now being worked, afford a preparation poorer in nitrogen, but richer in phosphoric acid.* In the following I will first give an introduction to the analysis of guano, such as is usually sufficient, and will then detail the methods which are to be employed when making a complete analy- sis of guano. 1. Determination of Moisture. As guano, on heating, not only gives up water, but may also lose ammonia, the latter evolved during the determination may be estimated along with the moisture. FRUHLIXG and SCHULZ | recommend the following method and apparatus (Fig. 140; for this purpose: Weigh off about 2 grm. of the guano in a porcelain boat, insert this into the glass tube m n placed in a water-bath, connect it with the bulb-tube c containing 10 c.c. seminormal sulphuric acid, and by means of a water-pump or aspirator connected at d draw a slow current of air through the apparatus, the air being dried and freed * Regarding the occurrence of guano ii various parts of the world, see E. HEIDEN, " Lehrbuch der Diingerlehre," 2d edit. Hanover, PHIL. COHEN, 1884, u, part 2, p. 340. f See his Anleitung zur Untersuchung der fur die Zueker-Industrie in Betracht Kommenden Rohmaterialien, etc. Brunswick, F. VIEAVEG und SOHN, 1876. 922 DETERMINATION OF COMMERCIAL VALUES. [ 331. from ammonia by means of the tube b filled with pieces of pumice stone moistened with concentrated sulphuric acid.* When the water in the water-bath has been maintained boiling for about an hour, the drying is complete. The loss of weight of the boat with the guano gives the moisture together with the ammonia evolved; and the quantity of the latter can be determined by titrating the contents of c with soda lye or baryta water, the difference then giving the moisture. FIG. 140. 2. Determination of the Nitrogen. Guano contains the nitrogen for the most part in the form of ammonia salts, and in less quantity in the form of uric acid and other organic compounds, and in smallest quantity in the form of nitric acid, if any of this last is present. Determine the total nitro- gen, and also the quantities present in the various forms of combina- tion according to 328 and 329. 0-5 to 1 grm. of the substance suffices for the determination of the total nitrogen. When KJEL- DAHL'S or VARRENTRAPP-WILL'S method is employed, it is advis- able to introduce 20 c.c. of seminormal sulphuric acid. If the combustion is made with soda-lime, the guano is best mixed with the soda-lime in the combustion tube itself by means of a wire, because on triturating together guano with soda-lime in a mortar, an appreciable quantity of ammonia is evolved (see p. 88 this volume). * Compare the foot-note, p. 930 this volume. 331.] ANALYSIS OF COMMERCIAL MANURES. 923 3. Determination of the Phosphoric Add. a. Total Phosphoric Acid. Heat about 2 5 grm. guano with from two to four times its weight of a mixture of 2 parts anhydrous sodium carbonate and 1 part potassium nitrate, gently at first, but gradually increasing the heat, until the contents of the crucible have become white. When cold, soften the mass by warming with water, rinse into the beaker, add about 30 c.c. nitric acid of 1-25 sp. gr., by the aid of which any portions adhering to the crucible are also to be removed; then warm until all the soluble portion has dissolved, evaporate to dryness to remove silica, take up the resi- due with nitric acid and water, filter, make up the solution to 250 c.c., and in 50 c.c. determine "the phosphoric acid according to 309, or 313, /?/?. Instead of a mixture of sodium carbonate and potassium nitrate, G. GILBERT* employs a mixture of 2 parts anhydrous sodium carbonate and 1 part potassium chlorate. When the mass has become white, the contents of the crucible are further heated for 15 minutes at a bright red heat; when cold, the fused mass is treated as above. 6. Phosphoric Acid "Soluble in Water," or "Soluble" as defined in 316. If the phosphoric acid soluble in water, and that soluble in an ammonium-citrate solution containing free citric acid ( 316) are to be determined, treat 5 grm. of the guano with the solvent according to 312 or 316 respectively, wash the undissolved residue, and determine the phosphoric acid in it as in a, using how- ever, 100 c.c. of the solution which was made up to 250 c.c., the "water-soluble" or " soluble" phosphoric acid being found from the difference. 4. Total Fixed Constituents. Incinerate about 5 grm. of the guano in an obliquely fixed platinum or porcelain crucible, and weigh the ash. If the analysis of a guano is to be complete, the following additional determina- tions must be made: * Zeitschr. /. analyt. Chem., xn, 1. 924 DETERMINATION OF COMMERCIAL VALUES. [ 331. 5. Fixed Constituents Singly. These are determined in the manner described in 287 and 289. 6. Total Carbon. Determine this according to 327, 5. 7. Carbonic Acid. Determine this by one of the methods described in 139, II; the most accurate results, however, are obtained by the method described in Vol. I, p. 493. Genuine guano contains but a very small quantity of carbonates, hence if a guano effervesces strongly when treated with diluted hydrochloric acid, this may be consid- ered conclusive proof that it has been adulterated with calcium carbonate. 8. Uric Acid. If it is desired to ascertain the quantity of uric acid in a guano * containing it, digest a not too small, weighed quantity of the guano with water containing a little soda-lye, for several hours at a gentle heat, then filter, wash, concentrate the washings by evap- oration, add this to the nitrate, and acidulate with hydrochloric acid; allow to stand 48 hours at the lowest available temperature, and collect the precipitated uric acid on a small filter dried at 100 and weighed; then wash with the smallest possible quantity of ice- cold water until the last washings no longer react for hydrochloric acid, then dry at 100, and weigh. 9. Oxalic Acid. To determine the oxalic acid in guano containing ammonium oxalate, boil 5 grm. of the guano with 20 grm. sodium carbonate and about 200 c.c. water, make up the fluid, when cold, to 500 c.c., mix, and pass through a dry filter. Acidulate 50 or 100 c.c. of the filtrate with acetic acid if necessary, and determine the oxalic acid according to 137, a. * To qualitatively test for uric acid, pour a little diluted nitric acid over some guano, and carefully evaporate to dryness; if uric acid is present, the residue will have a yellow or yellowish-red color, changed to a beautiful purple-red by a trace of ammonia (the murexid reaction). 331.] ANALYSIS OF COMMERCIAL MANURES. 925 10. Constituents Soluble and Insoluble in Water. Warm 10 grm. guano with about 200 c.c. water, and filter with- out delay through a weighed filter; wash the residue with hot water until the washings no longer have a yellowish tinge and leave no appreciable residue when evaporated on platinum foil, then dry, and weigh. On deducting the sum of the water and the insoluble residue from the weight of the guano, the difference will give the quantity of the soluble constituents. Incinerate the insoluble portion, weigh the ash, and deduct its weight from the value ascer- tained in 4 the difference will give the sum of the fixed, soluble salts. With very good grades of guano the residue insoluble in water amounts to from 50 to 55 per cent., but in the inferior grades, it amounts to from 80 to 90 per cent. The brown, aqueous solu- tion of good, genuine guano evolves ammonia on evaporation, has a urinous odor, and leaves a brown saline mass consisting chiefly of sodium and potassium sulphates, ammonium chloride, and oxalate, urate, and phosphate of ammonium.* b. Decomposed Guano. The nitrogen, and also the phosphoric acid, are determined in this just as in crude guano. The moisture, and the phosphoric * Although the determination of the portions soluble and insoluble in water is not without value in judging of the value of a guano, it must never- theless be pointed out, that the quality and quantity of the water-soluble constituents are by no means constant, or characteristic of a guano. VON LIEBIG (Annal. d. Chem. u. Pharm., cxix, 13), has, in fact, shown that the kind of salts passing into solution varies according to whether the solution is filtered immediately, or only after some time. In the former case, the solution will contain much oxalate and little phosphate together with some ammonium sulphate; in the latter case, the ammonium oxalate is more or less completely replaced by ammonium phosphate, the oxalic acid on the other hand remaining behind in the residue, combined with calcium. The cause of this interesting behavior is that though calcium phosphate in contact with ammonium oxalate and water scarcely undergoes any change, yet it is very soon converted into calcium oxalate, with formation of ammo- nium phosphate, if ammonium sulphate (or ammonium chloride) is present also, as this renders the calcium phosphate more soluble. The dissolved por- tion is immediately precipitated by oxalic acid, and the ammonium sulphate is thus enabled to act on a fresh portion of calcium phosphate. 926 DETERMINATION OF COMMERCIAL VALUES. [ 332. acid in its various conditions of solubility, however, are deter- mined in the manner detailed for superphosphates ( 311 to 317 inclusive). 3. FISH GUANO, "GRANAT" GUANO, HORN-MEAL, TENDON- MEAL, AND FLESH-MEAL MANURE. 332. The manures mentioned above owe their mamirial value to their organically combined nitrogen, and also, although to a much less degree, to their phosphoric acid. Their potassa content is usually so small as to require little or no consideration. The average content* of fish guano is from 7 to 9 per cent, nitrogen and 10 to 13-5 per cent, phosphoric acid; of "granat" guano, 8 per cent, nitrogen and 3 per cent, phosphoric acid; of horn-meal, 10 per cent, nitrogen and 5 to 6 per cent, phosphoric acid; of tendon-meal, 9-7 per cent, nitrogen and 6-3 per cent, phosphoric acid. In the case of flesh-meal manure the nitrogen and phos- phoric-acid contents vary between rather wide limits. Determine the phosphoric acid and also the nitrogen by the method described- for guano, using for the nitrogen determination 0-7 to 1 grm. of substance, and 20 c.c. of the seminormal sulphuric acid in the receiver. Determine the moisture, ash, and sand, as described for bone-meal. 4. MIXED MANURES. 333. As it is of great importance in agriculture to employ manures of which the quantity and character of the manurial constituents are accurately known, manure manufacturers prepare mixed man- ures of most varied kind, and guarantee the quantity, form of combination, and solubility of the important constituents, i.e., nitrogen, phosphoric acid, and potassium. * See Mittlere Zusammensetzung der Dilngemittel, by E. WOLFF (M.ENZEL and v. LENGERKE'S landwirthschaftliche Kalender, 1875). 333.] ANALYSIS OF COMMERCIAL MANURES. 927 These mixed manures may be divided into those having a neu- tral or alkaline reaction, and those having an acid reaction. To the former belong especially those guanos made up to a definite com- position by admixtures of ammonium sulphate, Chili saltpetre, blood-meal, etc.; the latter comprises mixtures of superphosphates with ammonium sulphate, Chili saltpetre, potassium salts, etc. The former are analyzed by the methods detailed for guano ( 331), or, if they contain Chill saltpetre, the nitrogen is deter- mined by the methods detailed in 328 and 329. The superphosphates containing nitrogen and potassium are analyzed, so far as the moisture and the total phosphoric acid as well as that present in its various forms of solubility, are con- cerned, according to 311 to 318 inclusive; the nitrogen, how- ever, both total and in its various forms of combination, is deter- mined accord'ng to 328 and 329. The potassium is determined as follows: Heat about 20 grm. of the substance with about 200 c.c. water to boiling, allow to settle, decant the liquid into a litre flask, and boil the residue again with about 200 c.c. water, and then rinse the whole into the litre flask; allow to become cold, fill up to the mark with water, shake, and pass through a dry filter. If the manure is rich in potassium salts, employ 50 c.c. of the filtrate for the potas- sium determination, but i ? poor in potassium salts, make the determination in 100 c.c. of filtrate. Add 100 to 200 c.c. of water, boil, and carefully add barium-chloride solution, avoiding too large an excess, so long as a precipitate forms, then allow to settle, and filter. In the filtrate then determine the alkalies, particularly the potassium, according to 287. If only the potassium is to be determined, ascertain the approximate weight of the alkali chlorides in order to obtain an idea as to the quantity of platinic-chloride solution required. In cases where extreme accuracy is required, the collected barium sulphate must be gently ignited and boiled with diluted hydrochloric acid, the filtrate then evaporated to dryness, the residue taken up with water, and this liquid added to the main solution. 928 DETERMINATION OF COMMERCIAL VALUES. [ 333. VI. ANALYSIS OF ATMOSPHERIC AIR. In the analysis of atmospheric air we usually confine our atten- tion to the following constituents: Oxygen, nitrogen, carbonic acid, and aqueous vapor. It is only in exceptional cases that the exceedingly minute quantities of ammonia and other gases many of which may be assumed to be always present in infinitesimal traces are also determined. It does not come within the scope of the present work to de- scribe all the methods which have been employed by BRUNNER, BUNSEN, DUMAS and BOUSSINGAULT, REGNAULT and REISET, FRANKLAND and WARD, MORLEY, VON JOLLY, KREUSLER, HEMPEL, and others, in their comprehensive investigations made to estab- lish the relative proportions of oxygen and nitrogen in atmospheric air. I have nothing to add to them, and there is therefore little object in giving here abstracts of the original papers. A com- pilation of all these, and especially the methods employed for deter- mining the oxygen in the air, has been published by KREUSLER,* who has also given all the references in his admirable work, so that in this connection his original papers may be consulted. I must add, however, that in the interim, HEMPEL has published a second paper,! in which the consensus of all reliable investigations, namely, that the proportion of oxygen in atmospheric air varies but between narrow limits, is also confirmed. I will therefore here confine myself to those methods which may be best employed in testing atmospheric air for its chief con- stituent i for hygienic or technical purposes, and will omit the description of the methods for the physical examination of air, and the determination of its content of ozone, ammonia, and other gases occurring in very minute quantities.! * Landwirthschaftliche Jahrbucher, by Dr. H. THIEL, 1885, p. 305 et seq. t fierichte der deutschen chem. Gesellschaft, xvm, 1800. J C. FLUGGE'S Lehrbuch der hygienischen Untersuchungs-Methoden (Leipzig, VEIT & Co., 1881) gives a comprehensive statement of the relative methods. A special introduction to the bacterial examination of air is given by F. HUEPPE, in Die Methoden der Bakterienforschung, 3d edit., Wiesbaden, C. W. KREIDEL, 1886. 5 334.] ANALYSIS OF ATMOSPHERIC AIR. 929 A. DETERMINATION OF THE WATER AND CARBONIC ACID. I. BRUNNER'S Method. 334. In this method, a measured volume of air is slowly drawn, by means of an aspirator, through an accurately weighed apparatus filled with substances having the property of retaining the aqueous vapor and the carbonic acid, and estimating these two constituents from the increased weight of the apparatus. * Fig. 141 represents the arrangement recommended by REG- ;NAULT. FIG. 141. The vessel V is made of galvanized iron, or of sheet zinc; it holds from 50 to 100 litres, and stands upon a strong tripod in a trough large enough to hold the whole of the water that V con- tains. At a a brass tube, c, with stop-cock, is firmly fixed in with cement. Into the aperture b, which serves also to fill the appara- tus, a thermometer reaching down to the midddle of V is fixed air- tight by means of a perforated cork impregnated with wax. * There are, however, more accurate and far more rapid methods for determining the carbonic acid. 930 DETERMINING WATER AND CARBONIC ACID. [ 334. The efflux tube, r, which is provided with a cock, is bent slightly upward, to guard against the least chance of air entering the vessel from below. The capacity of the vessel is ascertained by filling it completely with water, and then accurately measuring the contents in graduated vessels. The end of the tube c is connected air-tight with F, by means of a caoutchouc tube; * the tubes A to F are similarly connected with one another. A, B, E, and F are filled with small pieces of pumice stone f moistened with pure concen- trated sulphuric acid; C and D with moist, slaked lime.J Finally A is connected with a long tube leading to the place from which the air intended for analysis is to be taken. The corks of the tubes are coated with sealing wax. The tubes A and B are intended to withdraw the moisture from the air; they are weighed together. C, D, and E are also weighed joint ly. C and D absorb the car- *As the walls of caoutchouc tubes are to a certain extent permeable by moist air (LASPEYRES, DIBBITS), and absorb carbon dioxide (MUNTZ and AUBIN, SPRING and ROLAND), care must be taken that the ends of the glass tubes connected by the rubber tubing are ground to fit closely, and are pressed tightly together. f In order to completely free the pumice from chlorides, moisten it with concentrated sulphuric acid, and heat it to redness in a Hessian crucible. J I have again adopted the method of filling the tubes, so far as con- cerning the lime, as in BRUNNER'S original plan, instead of filling with potassa lye tubes containing pumice stone, because, as HLASIWETZ (Chem. Centralbl., 1856, p. 517) has shown, potassa lye absorbs not only carbonic acid, but also oxygen, a fact which had already been previously pointed out by H. ROSE. The object may also be attained by the use of soda-lime. Calcium chloride is to be rejected for absorbing the water, as it fails to thorough^ dry the air, and because, as HLASIWETZ (loc. cit., p. 517) has shown, traces of chlorine corresponding with the ozone content of the air are carried off. Nor can concentrated sulphuric acid be recommended in very accurate investigations, because it retains carbonic acid, although but a very small quantity (W. B. and R. E. ROGERS, HLASIWETZ, SPRING and ROLAND). In such cases it is usually best to use phosphoric anhydride, which dries the air somewhat more thoroughly than sulphuric acid; it cannot, however, be employed in U-tubes, but in straight tubes inclined upw r ards, and of the form shown in Fig. 12, p. 15, this volume (DIBBITS, Zeitschr. f. analyt. Chem., xv, 156; compare also A. MITSCHERLICH, p. 51 this volume, and W. E. MORLEY, Zeitschr. f. analyt. Chem., xxiv, 533). When weighing the tubes, care must be taken to allow them to attain, while closed, the temperature of the weighing-room. They are then, if necessary, again wiped off, and, after being stoppered (best with ground- 334.] ANALYSIS OF ATMOSPHERIC AIR. 931 bonic acid ; E the aqueous vapor which may have been withdrawn from the hydrate of lime by the dry air. F need not be weighed; it simply serves to protect E against the entrance of aqueous vapor from V. The aspirator is completely filled with water; c is then con- nected with F, and thus with the entire system of tubes; the cock r is opened a little, just sufficiently to cause a slow efflux of water. As the height of the column of water in F is continually dimin- ishing, the cock must from time to time be opened a little wider,, to maintain as nearly as possible a uniform flow of water. When V is completely emptied, the height of the thermometer and that of the barometer are noted, and the tubes A and B, and C, D, and E weighed again. As the increase of weight of A and B gives the amount of water, that of C, D, and E the amount of carbonic acid, and the capacity of V * the volume of the air (freed from water and car- bonic acid) which has passed through the tubes, the calculation is in itself very simple ; but it involves, at least in very accurate analy- ses, the following corrections: .- a. Reduction of the air in V, which is saturated with aqueous vapor, to dry air; since the air which penetrates through c is dry (see 198, r ). P. Reduction of the volume of dry air so found to 0, and 760 mm. ( 198, a and ,9). When these calculations have been made, the weight of the air which has penetrated into V is readily found (1000 c.c. of dry air at and 760 mm. weigh 1-2932 grm.), and as the carbonic acid and water have also been weighed, the respective quantities of these constituents of the air may now be expressed in per cents, by glass stoppers), or left open, hung on the balance beam, and weighed after ten minutes. It is not advisable to close the tubes with rubber stoppers (DIBBITS, loc. cit., p. 160). The balance-case must be kept as dry as possible by keeping in it large quantities of calcium chloride. * Or from the quantity of water which has flown from V, as the experi- ment may be altered in this way, that a portion only of the water is allowed to run out, and received in a measuring-vessel. 932 DETERMINING WATER AND CARBONIC ACID. [ 335. weight, or, calculating the weights into volumes, in per cents, by measure. Considering the great weight and size of the absorption appara- tus, in comparison with the increase of weight by the process, at least 25,000 c.c. of air must be passed through; the air inside the balance-case must be kept as dry as possible by means of a sufficient quantity of calcium chloride, and the apparatus left for some time in the balance-case before proceeding to weigh. Neglect of these measures would lead to considerable errors, more particularly as regards the carbonic acid, the quantity of which in atmospheric air is, on an average, about one-eighth that of the aqueous vapor (comp. HLASIWETZ, loc. cit.). II. PETTERSSON'S Method. 335. Water and carbonic acid in small quantities of air can be deter- mined far more rapidly, and yet very accurately, by the recently published method of O. PETTERSSON * which is carried out by the aid of the apparatus illustrated in Fig. 144. A is a 100-c.c. pipette, the lower portion of which is graduated in millimetres (Fig. 142). For this a table is calculated showing the amount in parts of a cubic centimetre corresponding with the divisions marked on the tube. The upper part of the pipette communicates on the right with the reservoir B, filled with glass-wool and phosphoric anhydride; and on the left with the reservoir C, filled with glass-wool, and thoroughly dried, and still hot soda-lime, the whole being con- nected by a system of narrow, but yet not capillary tubes .f The whole system of three reservoirs is immersed in a vessel filled with water, in which a uniform, but of course not constant, temperature is maintained by means of a stirrer, the handles of which, r r, are seen at the top of Fig. 144, the plate being shown in Fig. 143. The analysis is effected by meas- IG ' 142 ' * Zeitschr. /. analyt. Chem., xxv, 467. t The tubes in the illustration, Fig. 143, are, for the sake of clearness, 335.] ANALYSIS OF ATMOSPHERIC AIR. FIG. 143. 933 FIG. 144. 934 DETERMINING WATER AND CARBONIC ACID. [ 335. uring the sample of air in the pipette A, and passing it first into the drying vessel B, and then, after the air has been dried, bringing it back to A, and then measuring by means of the graduated tube the diminution in volume caused by drying; the carbonic acid in the air to be examined is then absorbed in the same manner, and the . diminution again measured in A. The carrying out of the operation hence involves two distinct operations: 1. The transfer and retransfer of the air from one vessel to another; and 2. The leveling of the mercury in the graduated tube, and the measuring of the volume of air inclosed in A. In carrying out the analysis, first fill both B and A with the air to be examined; that in B being first dried, while that in A is left unchanged. For this purpose completely fill A with mercury, by means of a mercury reservoir connected with the cock X by a rubber tube wound* with thin, flexible copper wire, the reservoir being suspended by a cord whereby it may be raised or lowered at con- venience; then empty A again by sinking the mercury reservoir, while the cocks 7-, d, and /? are closed, and the lower end of the tube p containing phosphoric anhydride is in connection by means of a suitable glass tube with the space containing the air to be analyzed. The dried air then enters through p and the cock n into B, entering through a short, pointed tube over the end of which a small bell- jar is inverted. The air previously contained in B is hereby expelled, and after repeating the operation a number of times by suitably opening and closing the cocks e, and f, is completely re- placed by the air to be examined. When B has been filled in this manner, close //, and proceed to fill A with the air to be examined. For this purpose, open the cock r, while d and e are closed, fill A with mercury, and, if the air to be tested is other than that of the room in which the apparatus is contained, connect the upper outlet of A with the glass tube leading to the space occupied by the air to be examined, the tube drawn wider than they should be, but the other parts of the apparatus are correctly proportioned, so far as possible. The inner diameter of the tubes and cocks should, nevertheless, not be narrower than 1 mm. 335.] ANALYSIS OF ATMOSPHERIC AIR. 935 having previously been filled with this air by suction, and then allow the mercury to run out to about the zero point on the scale. Then close the cock A and regulate the height of the mercury by the screw / which is made to compress by means of a brass plate the rubber tube connecting the graduated tube with the cock X, until the mercury stands exactly at zero, which may be ascertained by means of a lens. As the rubber tube compressed by the screw / must at tunes resist considerable pressure, one should be selected having stout walls, and, after it has been fixed in position it should be covered with a strong piece of silk, stitched on. A being thus filled with the air to be examined, open d, e, ct, and ft, so that the pressure will be equal throughout the apparatus,and set the stirrer in motion so that all parts of the apparatus will acquire the same temperature. The small drop constituting the liquid seal x in the differential manometer, and which occupies only about 3 to 4 mm. of the manometer tube, and consisting preferably of concentrated sulphuric acid colored with indigo blue,* auto- matically comes to rest at one of the marks on the small scale. This must be accurately observed by means of a lens, and noted, as in each of the succeeding operations the drop must be brought back to exactly the same point before reading off the volume. The horizontal part of the manometer tube is slightly depressed at the centre so that the drop naturally assumes a central position. After all the differences of temperature and pressure have been adjusted, close 7-, , and /?, but leave e open. Now open A, raise the mercury reservoir so that A will be gradually filled and the air in it driven into B. As the dry air already in B cannot escape, the pressure in it of course increases considerably, hence the mercury reservoir must be raised to a height of about 130 cm. in order to bring the level of the mercury from the zero mark on the scale tube up to the T-shaped branch of the narrow connecting tube above the pipette A, and so completely drive the contents of A into B. After about 10 to 20 minutes, the last traces of moisture origin- ally in A, and now compressed in B, are absorbed. Then allow the *An index still more sensitive than the sulphuric acid is a petroleum of high boiling-point. 936 DETERMINING WATER AND CARBONIC ACID. [ 335- air to return again from B to A by gradually lowering the mercury^ reservoir, so that the air in A is at about its original pressure, set the stirrer in motion in order to make the temperature uniform throughout the apparatus, then very cautiously open /?, whereupon the small index moves either to the right or left, according as the mercury in the graduated tube has been placed too high or too low; now close A, turn the screw / until x has about resumed its original position, open a cautiously, and bring the index to its old position by turning the screw /; now wait a few minutes to see that the index remains stationary, and as soon as this is the case, read off the height of the mercury in the graduated tube. The difference found corresponds with the moisture that the air in A had contained. If there is any doubt as to whether the absorption of the moisture was complete in B, the air may be driven once more from A into B, and the reading repeated. When the determination of the moisture is finished, drive the air in a similar manner from A into C, in order to allow the carbon dioxide to be absorbed. For this purpose the cocks 7-, s and a must be closed, while d is open. The absorption of the carbon dioxide is, as a rule, complete in ten minutes, so that on repeating the operation, no further decrease in volume is observed in the graduated tube. If, as directed, C has been filled with sharply dried and still hot soda-lime, the air freed from the carbonic acid will be (at least in cases where the air contains the usual propor- tion of carbonic acid) so dry that the diminution in volume may be read off at once. Should there be any fear that the air in C has again taken up moisture, it must be dried again in B, and the diminution in volume then read off. As is evident, variations in the pressure of the external air cannot affect the measurements, because the cocks 7- and // are closed during the process of absorption. The temperature through- out the apparatus, although uniformly maintained, nevertheless is not constant, hence the internal pressure naturally varies. As, however, the alteration in volume of the glass vessels A, B, and C, as well as of the air contained in them, is proportional, the effects of the variations of temperature are automatically neu- 335.] ANALYSIS OF ATMOSPHERIC AIR. 937 tralized, and the determinations, on reference to the calibrating tables, give the percentage by volume of water and carbonic acid, and sufficiently accurate at least for ordinary analyses. When it becomes a question of the highest degree of accuracy, care must be taken that the temperature within the system does not vary at all, or does so only by not more than 1 ; * for, if the varia- tion amounts to a whole degree, it will be found that, in conse- quence of the unequal expansion of the phosphoric anhydride in B and the soda-lime in C, the compensation is only approximate, and never complete. If, as described, first the moisture and then the carbonic acid is determined hi one and the same volume of air, then, as the mercury- level at the close of the moisture determination will usually be in the wider part of the graduated tube, the diminution in volume corresponding with the carbonic acid will always be read off in this part. If it is desired to read off in the narrow part, so as to insure greater accuracy, open the cock /z, after determining the moisture, and admit so much dry air through p and B to that already in A that the mercury-level again stands at the zero-mark of the graduated tube, then open for a couple of seconds the cocks f t s, a, and /?, so that the air in C is also reduced to the atmospheric pressure, next close 7-, a, and e, and //, drive the dry air in A into C, and in ten minutes or so, when the carbonic acid has been absorbed, read off the diminution hi volume thus caused in the narrower part of the graduated tube. The method described is, according to PETTERSSOX'S experi- ments, accurate to about 002 per cent. If an accuracy of about 0-05 per cent, suffices, as in hygienic examinations of the air hi rooms for carbonic acid, and the hygrometric determinations of atmospheric moisture, PETTERSSON recommends a much smaller ap- paratus, readily transportable in a wooden case, and the pipette A of which holds only 18 c.c. When using this instrument, the water absorption is effected in an ORSAT tube filled with concen- * This must be accomplished by keeping the temperature of the room approximately constant, but not by raising or lowering the temperature of the water reservoir by adding hot or cold water. 938 DETERMINATION OF CARBONIC ACID. [ 336. trated sulphuric acid; the carbonic acid, however, is absorbed by means of dry soda-lime. The graduated tube, in the small apparatus, also has a wider and a narrower part, but the wider part is below, and serves for the determination of the moisture, while the carbonic acid is deter- mined in the narrower, upper part of the tube. The PETTERSSON apparatus must naturally be very carefully operated. Those used by PETTERSSON in his investigations were made by FRANZ MULLER, of Bonn. B. DETERMINATION OF THE CARBONIC ACID ALONE. I. PETTENKOFER'S Original Method* 336. a. Principle and Requisites. In PETTENKOFER'S method a known volume of air is made to act upon a definite quantity of standard baryta water (standardized by oxalic-acid solution), in such manner that the carbonic acid is completely combined with the baryta. The baryta water is then poured out into a cylinder and allowed to deposit with exclusion of air, an aliquot part of the clear fluid is then removed, and the baryta remaining in solution is determined. Calculating from the part to the whole, the differ- ence between the oxalic acid required for a certain quantity of baryta water before and after the action of the air represents the barium carbonate formed, and consequently the carbonic acid present. Two kinds of baryta water are used: one contains 21 grm. and the other 7 grm. crystallized barium hydroxide f in the litre; * Abhandl. der naturwissensch. u. techn. Commission der k. bayer. Akad. der Wiss., n, 1; Annal. der Chem. u. Pharm., n, Supplementband, p. 1. f The barium hydroxide must be entirely free from caustic potassa, and soda, the smallest quantities of which render the volumetric estimation in the presence of barium carbonate impossible, since the normal alkali oxalates decompose the alkali-earth carbonates. When a trace even of barium car- bonate is suspended in the fluid and this is always the case when a baryta water which has been used for the absorption of carbonic acid is not filtered the reaction continues alkaline if the smallest trace of potassa or soda is present, because the alkali oxalate formed immediately enters into reaction 336.] ANALYSIS OP ATMOSPHERIC AIR. 939 these serve for the determination of larger and smaller quantities of carbonic acid respectively. 1 c.c. of the stronger corresponds to about 3 mgrm. carbonic acid, of the weaker 1 c.c. corresponds to about 1 mgrm. The baryta solutions should be kept in the bottles described and figured on p. 496 this volume. The tubes b and c contain pumice stone impregnated with potassa lye; the bottle d may be omitted. The oxalic-acid solution which serves for standardizing the baryta water contains 2-8647 grm. per litre of cryst. oxalic acid, which must be neither effloresced nor moist;* 1 c.c. corresponds to 1 mgrm. CO 2 . The baryta water is standardized as follows: Transfer 30 c.c. of it to a flask, and then run in the oxalic acid from a MOHR'S burette with an ERDMAXX float; shake the fluid from time to time, closing the mouth of the flask with the thumb. The vanishing point of the alkaline reaction is ascertained with delicate turmeric-paper .f As soon as a drop of the acid solution placed on the paper does not give a brown ring, the end is attained. If you were obliged, in the first experiment, to take out too many drops for testing with turmeric-paper, consider the result as only approximate, and make a second experiment, adding at once the whole quantity of oxalic acid to within 1 or 0-5 c.c. and then be- ginning to test wdth paper. A third experiment would be found to agree with the second to 0-1 c.c. The reaction is so sensitive with the barium carbonate. A fresh addition of oxalic acid converts the alkali carbonate again into oxalate, and the fluid is for a moment neutral, till, on shaking with air, the carbonic acid escapes, and any barium carbonate still present converts the alkali oxalate again into car- bonate. To test a baryta water for caustic alkali, determine the alkalinity of a perfectly clear portion, and then of a portion that has been mixed with a little pure precipitated barium carbonate. If you use more oxalic acid in the second than in the first experiment, caustic alkali is present, and some barium chloride must be added to the baryta water before it can be used. * It may be obtained perfectly pure by decomposing lead oxalate with diluted sulphuric acid. Other methods for preparing it are given on p. 300 this volume. As regards the drying, see Vol. I, p. 144. f Prepared with lime-free Swedish filter-paper and tincture of turmeric. The alcohol used in making the latter must be free from acid. Dry the paper in a dark room, and keep it protected from the light. It should have a lemon-yellow color. 940 DETERMINATION OF CARBONIC ACID. [ 336 that all foreign alkaline matter, particles of ash, tobacco smoke r etc., must be carefully guarded against. b. The Actual Analysis. This may be effected in two different ways. a. Take a perfectly dry bottle, of about 6 litres capacity, with well-fitting ground-glass stopper, and accurately determine the capacity; fill the bottle, by means of a pair of bellows, with the air to be analyzed; add 45 c.c. of the dilute standard baryta water, and cause the baryta water to spread over the inner surface of the bottle by turning the latter about, but without much shaking. In the course of about half an hour the whole of the carbonic acid is absorbed. Pour the turbid baryta water into a cylinder, close securely, and allow to deposit; then take out, by means of a pipette, 30 c.c. of the clear supernatant fluid, run in standard oxalic acid, multiply the volume used by 1-5 (as only 30 c.c. of the original 45 are employed in this experiment), and deduct the product from the c.c. of oxalic acid used for 45 c.c. of the fresh baryta water; the difference represents the quantity of baryta converted into carbonate, and . consequently the amount of the carbonic acid. If the air is unusually rich in carbonic acid, the concentrated baryta water is employed. /?. Pass the air through a tube or through two tubes contain- ing measured quantities of standard baryta water and finish the experiment as in a. For passing a definite quantity of air we should generally employ an aspirator (p. 929 this volume) ; PETTEN- KOFER in his experiments with the aspiration apparatus forced the air by means of small mercurial pumps first through the tubes, and then through an apparatus for measuring the gas. The form and arrangement of the tubes is illustrated by Fig. 145. Two such tubes were used; the first was 1 metre, the second 0-3 metres long; they were filled with baryta water the former with the stronger solution, the latter with the weaker. The tubes are held in a brass holder lined with rubber and cork, and, by means of pointers, levels, and leveling screws, can be fixed at any desired inclination. The inclination should be such that the single bubbles of air which enter through the short limbs of the tubes, and are carried beyond the 337.] ANALYSIS OF ATMOSPHERIC AIR. 941 bend of the tube by a narrow, flexible tube, move on with the necessary rapidity without uniting. The motion of the gas bubbles keeps up a constant mixing of the baryta water. On exhausting the air with an aspirator, a water manometer will be necessary Fig. 14& to ascertain the true volume of air. The pressure, reduced to mercurial pressure, must be deducted from the prevailing baro- metric pressure. II. Modifications of PETTENKOFER'S Method. 1. Such as refer to Method a. 337. As in the filling of a 6-litre flask by means of a bellows, the object can be accomplished with certainty only after prolonged blowing, and as the unavoidable noise is sometimes (in churches, schools, theatres, etc.) very disturbing, KL. SONDEN * recommends the following apparatus for filling the flask with the air to be examined; the apparatus, however, can be used only in com- paratively large spaces, as in small ones the carbonic acid result- ing from the combustion of the photogen exerts an appreciable influence : b, in Fig. 146, is a tin cylinder inclosing a photogen lamp a, the lamp-glass, c, of which extends for a distance of 75 cm. into the chimney. At e the tin cylinder 6 sets in a foot-plate, by which it is closed below. The tin side-tube d carries a rubber ring at its upper end, the opening of which corresponds with that in the * Arbeiten frdn Stockholms Helsovdrdsndmds Laboratorium. Stock- holm, pub. by K. L. BECKMANN, 1886, p. 14. 942 DETERMINATION OF CARBONIC ACID. [ 338. bottom of the flask g, and prevents the admission of the air from the side. On lighting the lamp, there is set up a current of air in the direction shown by the arrows, by which a 6-litre flask may be filled with fresh air in less than a minute and a half. On allow- ing the lamp to burn for five minutes, the object is accomplished TIG. 146. with still greater certainty. The neck of the flask g and the open- ing in its bottom are then closed with rubber stoppers. 2. Modifications of the Method described in /3. 338. W. SPRING and L. ROLAND, who have made exhaustive inves- tigations regarding the determinations of carbonic acid in air* * Recherches sur ks proportions d'acide carbonigue contenues dans I'air. Brussels: F. HAYEZ, 1885. 338.1 ANALYSIS OF ATMOSPHERIC AIR. 943 have modified PETTENKOFER'S absorption tubes, in the manner shown in Fig. 147. FIG. 147. As will be seen, the tubes R and r can be closed by glass cocks. They are 1 1 metres long, 14 mm. internal diameter, and are fixed at a slight inclination, so that it takes from 12 to 15 seconds for an air bubble entering at B or b' to pass through one of the tubes filled with baryta water. E and E r are graduations giving the capacity of the tubes in cubic centimetres; the graduations serve for the purpose of indicating the degree of evaporation which the baryta water undergoes from the passage of the air through it. It may be remarked here that the lower tube only serves at first as a check for ascertaining whether all the carbonic acid has been absorbed in the upper tube. According to the investigations of SPRING and ROLAND it is found that when operating according to the directions given, and only about 1000 litres of air are passed through the tubes, no turbidity occurs in the second tube; but when about 30,000 litres of air have passed through, a decided precipitate of barium carbonate is observed also in the second tube. The tube T leads to the space the air of which is to be investigated;* S, * If it is desired to introduce the air in a dried condition into the tubes, 944 DETERMINATION OF CARBONIC ACID. [ 338. however, leads to an aspirator having a capacity of about 115 litres, and the general arrangement of which is about like that described on p. 929 this volume. The exit tube is of glass, and dips into a water tank provided with an overflow spout. The height of the water in the tube affords an indication as to the degree of rarefaction of the air in the apparatus at the end of the opera- tion. The water manometer, M, serves as a control; and a ther- mometer inserted into the aspirator shows the temperature of the .air in it. The tubes are filled with baryta water saturated at a compara- tively low temperature, so that during the experiment its tempera- ture is increased rather than diminished, a separation of barium- hydroxide crystals being thereby with certainty avoided. The baryta water is prepared by dissolving crystals of baryta in water by the aid of heat, and allowing the unfiltered solution to become old. As the baryta crystals always contain a little barium carbonate, the operator is certain also of obtaining a baryta water saturated with barium carbonate. To start with, the tubes are first rinsed out with hydrochloric acid, then with water, and lastly several times with some of the baryta water to be employed. Then, with the cocks all closed, they are allowed to drain thoroughly, being fixed vertically for this purpose with the cocks at the top. Now introduce into each tube by means of a pipette 125 c.c. of the titrated baryta water, fix the tubes perpendicularly with the cocks below, read off the height of the liquids on the graduations E and E', and then fix the tubes in the positions shown in Fig. 147; assemble the apparatus, open the cocks R and r, and then also the exit cock of the aspirator, and in such a manner that it will take 12 to 15 seconds for every air-bubble to pass through one tube; at this speed, it will require from 10 to 12 hours to empty the aspirator. Now measure the height of the water in the exit-tube of the aspirator and also that in the manometer, M, and divide the number of millimetres by concentrated sulphuric acid cannot be recommended for drying purposes (SPRING and ROLAND, loc. cit., p. 64) ; a tube filled with phosphoric anhydride is best adapted for the purpose; see foot-note, p. 930 this volume. 339.] ANALYSIS OF ATMOSPHERIC AIR. 945 13-5 in order to calculate the water-pressure into mercuria pres- sure, read off the barometric pressure, and the temperature of the air within the aspirator, and using these figures, calculate the volume of the air drawn through the tubes, reduced to and 760 mm. pressure and hi the dry condition (compare 198). From this volume the weight of the air can be ascertained by multiplying the number of litres by 1 2932. Before proceeding to determine the caustic baryta remaining in the tubes B B' , or in both tubes, place the tubes again vertically, with the cocks below, and if necessary, open the latter cautiously in order to remove any slight quantity of ah- remaining hi t, and then read off the height of the liquid on the graduations E and E r , in this manner ascertaining the loss in volume sustained by the 125 c.c. of baryta water by evaporation; this loss must be taken into account in making the calculations. The contents of the tubes may be treated either hi the manner directed by PETTENKOFER, i.e., by allowing the baryta water rendered turbid by suspended barium carbonate to settle hi a closed flask, or the barium carbonate may be filtered off. If the latter method be chosen, the fact observed by A. MULLER (Vol. I, p. 486), that filter-paper retains barium hydroxide, must be taken into consideration. The papers employed must, therefore, always be alike, and the quantity of baryta retained on passing through them 125 c.c. baryta water of the same strength as that used in the experiment, must be determined, and the proper correction made. SPRING and ROLAND preferred the latter method. 3. Modifications in the Manner of Titrating the Baryta Water. 339. Whereas PETTENKOFER recommends oxalic acid, with curcuma- paper as indicator, for titrating baryta water, SPRING and ROLAND (loc. cit., p. 51) prefer to use hydrochloric acid, using litmus tincture as the indicator; they also point out (loc. cit., p. 71 et seq.) that glass vessels, if not previously rinsed out with baryta water, con- vert determinable quantities of baryta into an insoluble com- pound, wherefore they first rinse out with baryta water both the 946 DETERMINATION OF CARBONIC ACID. [ 340, absorption tubes and the measuring pipette, and let them drain before using them. REISET gives sulphuric acid the preference. KL. SONDEN also uses the latter, diluted so that 1 c.c. corresponds with 1 mgrm. of carbonic acid. In order to exclude so far as possible the influence of atmospheric carbonic acid on the baryta water, he recommends * to take up the 50 c.c. to be titrated with a pipette provided with a protecting soda-lime tube. The con- tents are emptied into a flask, some phenolphtalein added, and then sulphuric acid until they are colorless (see p. 311 this volume). Now measure off into another flask a quantity of acid exactly equal to that just employed, add phenolphtalein, and then add 50 c.c. of the baryta water in such a way that the point of the pipette is below the surface of the acid. To the liquid, which is now red, very cautiously add sulphuric acid until the color just vanishes, the acid used being then considered as the correct quantity. It will be seen that by this mode of operating the atmospheric air remains in contact but a few moments with the liquid still slightly alkaline from baryta. Employing this method, SONDEN obtained the figures published by him in the Zeitschr. f. analyt. Chem., xxv, 478, and which were compared with those obtained by PETTERSSON'S method. III. Method proposed by FR. MOHR, and tested by HLASIWETZ and H.V.GlLM.t 340. This, like PETTENKOFER'S method, consists in drawing a large quantity of air, at least 60 litres, through a long, slightly inclined tube containing pieces of glass and clear baryta water, collecting the barium carbonate formed with exclusion of air, and washing the tubes, as well as the precipitate on the filter, first with distilled water saturated with barium carbonate, and then with pure, boiled water. Lastly, the barium carbonate still in the tube, and also that remaining on the filter, is dissolved by diluted hydro- chloric acid, the solution evaporated to dryness, the residue gently * Personal communication. f Chem. CentralbL, 1857, 760. 340.] ANALYSIS OF ATMOSPHERIC AIR. 947 ignited, and the chlorine in the barium chloride formed deter- mined as in 141, 6, a, calculating 1 equivalent of carbonic acid for 2 equivalents of chlorine. As may be readily seen, the barium content of the hydrochloric-acid solution may also be determined by precipitating with sulphuric acid. For filtering the barium carbonate, v. GILM employed a double funnel (Fig. 148) ; the inner cork has, besides the perforation through which the neck of the funnel passes, a lateral slit, which establishes a communication between the air in the outer fun- nel and the air in the bottle. As, with the absorption apparatus arranged as described, the air has to force its way through a column of fluid, the manometer is required to determine the actual volume of the air; the height indicated by this instrument being de- ducted from the barometric pressure observed during the process. FR. MOHR* now recommends as the absorb- FIG. 148. ent fluid a solution of barium hydroxide in pot- ash. This is prepared by dissolving crystals of barium hydroxide in weak solution of potassa with the aid of heat, and filtering off the barium carbonate, which invariably forms in small quantity. The clear filtrate is accordingly saturated with barium carbonate. MOHR now leaves out the fragments of glass. This method afforded v. GILM very concordant results. Nev- ertheless, it involves one source of error apart from the unavoidable effect of the action of the atmospheric air during filtration. If clear baryta water is passed through paper with the most careful possible exclusion of air, and the filter is washed till the washings are free from baryta, and dilute hydrochloric acid is then poured upon the filter, and the filtrate thus obtained is evaporated, a small quantity of barium chloride will be left, showing that a little baryta was kept back by the paper. AL. MuLLERf has already called attention to the capacity of filter-paper for retaining baryta; and * Lehrbuch der Titrirmethode, 5th ed., F. VIEWEG und SOHN, p. 526. f Journ. /. prakt. Chem., LXXXIII, 384. 948 DETERMINING OXYGEN AND NITROGEN. [ 341. the proper correction must also be made for the baryta rendered insoluble by the surface of the glass vessel (see 339) . C. DETERMINATION OF THE OXYGEN AND NITROGEN. 341. As already mentioned, the methods for the exact determination of the oxygen, and also of the nitrogen, in atmosphere, to which reference has been made on p. 928 this volume, will not be treated of here. Those who desire* to investigate this subject, must not only become familiar with the original treatises, but must also have become experienced in gas analysis, for which the works of R. BUNSEN,* W. HEMPEL,f and CL. WINKLER,} especially, will be found to be of great assistance. n f w 6* FIG. 149. The method I shall give is that proposed by v. LIEBIG; it is useful when it is required to determine the quantity of oxygen in air in a more or less confined space, within 1 or 2 per cent, of * Gasometrische Methoden, by ROB. BUNSEN, 2d edit., F. VIEWEG und SOHN, Brunswick, 1877. f WALTHER HEMPEL, Neue Methoden zur Analyse der Gase, F. VIEWEG und SOHN, Brunswick, 1880. J CLEMENS WINKLER, Lehrbuch der technischen Gasanalyse, J. G. ENGEL- , Freiberg, 1885. Annal. d. Chem. u. Pharm., LXXVII, 107. 341 .J ANALYSIS OF ATMOSPHERIC AIR. 949 the volume, in a short time and without the aid of complicated apparatus. LIEBIG'S method is based upon the observation made by CHEVREUL and DOBEREINER, that pyrogallic acid, in alkaline solutions, has a powerful tendency to absorb oxygen. 1. A strong measuring tube, holding 30 c.c. and divided into- 0-2 or 0-1 c.c., is filled to J with the air intended for analysis. The remaining part of the tube is filled with mercury, and the tube is inverted over that fluid in a tall cylinder, widened at the top (Fig. 149). 2. The volume of air confined is measured ( 12). If it is intended to determine the carbonic acid which can be done with; sufficient accuracy only if the quantity of the acid amounts to* several per cents. the air is dried by the introduction of a ball of cal- cium chloride ( 16) before measuring. If it is not intended to determine the carbonic acid this operation is omitted. A quantity of solution of potassa of 1-4 sp. gr. (1 part of dry potas- sium hydroxide to 2 parts of water),* amounting to from ^ to -g^j- of the volume of the air, is then introduced into the measuring tube by means of a pipette with the point bent upwards (Fig. 150), and spread over the entire inner surface of the tube by shaking the latter (see p. 61 this volume) ; when no further diminution of volume takes FIG. 150. place, the decrease is read off. If the air has been dried previously with calcium chloride, the diminution of the volume expresses exactly the amount of carbonic acid contained in the air; but if it has not been dried with calcium chloride, the diminution in the volume cannot afford correct information as to the amount of the carbonic acid, since the strong solution of potassa absorbs aqueous vapor. 3. When the carbonic acid has been removed, a solution of pyrogallic acid, containing 1 grm. of the acid in 5 or 6 c.c. of water, is introduced into the same measuring tube by means of another pipette, similar to the one used in 2 (Fig. 150) ; the quan- tity of pyrogallic acid employed should be half the volume of the * These are the quantities and the concentrations of potassa and pvro- gallic-acid solutions recommended by LIEBIG; they may, of course, be also varied somewhat ; see 6. 950 DETERMINING OXYGEN AND NITROGEN. [ 341. solution of potassa used in 2. The mixed fluid (the pyrogallic acid and solution of potassa) is spread over the inner surface of the tube by shaking the latter, and, when no further diminution of volume is observed, the residuary nitrogen is measured. 4. The solution of pyrogallic acid mixing with the solution of potassa of course dilutes it, causing thus an error from the diminu- tion of its tension; but this error is so trifling that it has no appreciable influence upon the results ; it may, besides, be readily corrected, by introducing into the tube, after the absorption of the oxygen, a small piece of hydrate of potassa corresponding to the amount of water in the solution of the pyrogallic acid. 5. There is another source of error in this method: viz., on account of a portion of the fluid always adhering to the inner sur- face of the tube, the volume of the gas cannot be read off with absolute accuracy. In comparative analyses, the influence of this defect upon the results may be almost entirely neutralized, by taking nearly equal volumes of air in the several analyses.* 6. The volume of nitrogen will finally, under certain circum- stances, be found to be a little too high, because, as CALVERT, CLOEZ, and BOUSSINGAULT have shown, a little carbon monoxide may be formed by the action of the potassa lye on the pyrogallic acid, and remain unabsorbed together with the nitrogen. I have pur- posely said may be formed, as, according to W. HEMPEL,! this does not occur, for example, on mixing one volume of a 25-per cent, pyrogallic-acid solution with six volumes of about 60-per cent, potassa solution. 7. Notwithstanding these sources of error, the results obtained by this method are very accurate and constant. In eleven analyses which v. LIEBIG reports, the greatest difference in the amount of oxygen found was between 20-75 and 21-03. The numbers given express the actual and uncorrected results. *As already stated on p. 266 this volume, BUNSEN (Gasometrischen Methoden, 2d edit., p. 94) employs for the absorption of oxygen a papier- mch6 ball saturated with a concentrated alkaline solution of potassium pyrogallate, which he introduces into the gaseous mixture attached to a platinum wire. By adopting this proceeding the source of error mentioned in 5 is avoided. See also RUSSELL, Journ. Chem. Soc., 1868, pp. 130, 131. f Berichte der deulsch. chem. Gescllsch., xvm, 278. PART III. EXERCISES FOR PRACTICE. EXEECISES FOE PRACTICE. IN the following pages I have given 60 exercises which appear to me to be specially well adapted for teaching the theory and practice of quantitative chemical analysis. They are almost identical with those that, for many years, have been given in my laboratory, hence I can with confidence state that they can all be easily carried out, and that the order in which they are arranged has been found practical. A glance through this section will show that a few volumetric methods have been inserted among the gravimetric methods. By this change the monotony of the gravi- metric operations has been varied in a useful manner, while the hurried manner of working into which beginners are easily led by continuous operations in volumetric methods, is effectively ob- viated, while at the same time the knowledge is properly awakened to the fact that hi the realm of analysis very different me'aecte lead to the same result, and the mind is stimulated to make comparisons of the various methods and to critically judge them. The principal point kept in view in the selection of these exer- cises has been that most of them, and more particularly the first, should permit an exact control of the results. This is of the utmost importance for students, since a well-grounded self- reliance is among the most indispensable requisites for a successful pursuit of quantitative investigations, and this is only to be attained by ascertaining for one's seif how near the results found approach the truth. Now a rigorously accurate control is practicable only in the analysis of pure salts of known composition, or of mixtures com- posed of definite proportions of pure bodies. When the student has acquired, in the analysis of such substances, the necessary self- 953 954 EXERCISES FOR PRACTICE. reliance, he may proceed to the analysis of minerals or products of industry in which such rigorous control is unattainable. The second point kept in view in the selection of these exer- cises has been to make them comprise both the more important analytical methods and the most important bodies, so as to afford the student the opportunity of acquiring a thorough knowledge of every branch of quantitative analysis. Bearing this in mind, it will be naturally found that I have not always employed the simplest methods. Organic analysis offers less variety than the analysis of inor- ganic substances; the exercises relating to the former branch are therefore less numerous than those relating to the latter. I would advise the student to analyze the same substance repeatedly, until the results are quite satisfactory. [It is a good habit always to carry on together duplicate analyses. It requires but little more time to make two analyses than to make one, and the operator's experience is thus very economically doubled.] It is by no means necessary for the student to go through the whole of these examples ; the time which he may require to attain proficiency in analysis depends, of course, upon his own abilities. One may be a good analyst without having tried every method or determined every body. A few substances well analyzed yield more profit than can be obtained from going over many processes in a superficial manner. Finally, the student is warned against prematurely attempting to discover new methods; he should wait until he has attained a good degree of proficiency in general chemistry, and more particu- larly in practical analysis. IRON. 955 EXERCISES. A. SIMPLE DETERMINATIONS IN THE GRAVIMETRIC WAY, INTENDED TO PERFECT THE STUDENT IN THE PRACTICE OF THE MORE COMMON ANALYTICAL OPERATIONS. 1. IRON. Procure 10 to 15 grm. of fine bright pianoforte wire, cut it into lengths of about 0-3 grm. and keep it free from rust in a dry bottle. Weigh, on a watch-glass, for each estimation, about 0-3 grm. of wire, and dissolve in hydrochloric acid, with addition of nitric acid. The acids are diluted with a little water. The solution is effected by heating in a moderate-sized beaker covered with a watch-glass. When complete solution has ensued, and the color of the fluid shows that all the iron is dissolved as ferric chloride (if this is not the case some more nitric acid must be added), rinse the watch-glass, dilute the fluid to about 200 or 300 c.c., heat to incipient ebullition, add ammonia in moderate excess, and filter through a filter exhausted with hydrochloric acid, etc. (Comp. 113, 1, a). As the ferric oxide generally contains a small quantity of silica partially arising from the silicon in the wire, partially taken up from the glass vessels, after it is weighed, digest with fuming hydrochloric acid, with the addition of a few drops stannous chloride, dilute, collect the silica on a small filter, ignite and weigh. The weight is the silica + the ashes of both filters. The residue should be white; if it is red, it indicates that some of the ferric oxide has remained undissolved. The best method of writing down the records of an analysis is here given, once and for all; and a rather complicated example is here selected as being all the better for the purpose. Watch-glass + iron 10-3192 " empty , 9-9750 Iron 0-3442 956 EXERCISES FOR PRACTICE. Crucible + ferric oxide + silica + filter ash 17 0703 " empty 16-5761 0-4942 Ash of large filter.^. 0-0008 Ferric oxide+silica 4934 Crucible + silica + ashes of both filters 16 5809 " empty 16-5761 0-QQ48 Ashes of the filters . 0014 Silica 0-0034 0-4934-0-0034=0-4900 ferric oxide = 0-343 iron which gives 99 65 per cent. 2. LEAD ACETATE. Determination of Lead. Triturate the dry and non-effloresced crystals* in a porcelain mortar, and press the powder between sheets of blotting paper until fresh sheets are no longer moistened by it. a. Weigh about 1 grm., dissolve in 100 c.c. of water, with addi- tion of a few drops of acetic acid, and proceed exactly as directed 116, 1, a. b. Weigh about 1 grm., dissolve in 50 c.c. of water with the addition of a few drops acetic acid and proceed exactly as directed 116, 3, a, a. PbO 222-92 58-82 (C 2 H 3 O) 2 102-048 26-92 3H 2 O 54-048 14-26 379-016 100-00 * Obtained by dissolving the pulverized commercial salt in hot water nearly to saturation, filtering, adding a drop or two of acetic acid to the solution, and slowly evaporating to crystallization. ARSENOUS OXIDE. 957 3. ARSENOUS OXIDE. Dissolve about 0-2 grm. pure arsenous oxide in small lumps in a flask of about 500 c.c. capacity, in some solution of soda ; by digesting on the water-bath ; dilute with a little water, add hydro- chloric acid in excess, and then nearly fill the flask with clear water. Pass in hydrogen sulphide without access of air and without warm- ing, until present in excess; then proceed in all other respects ex- actly as directed 127, 4, a. A pair of watch-glasses should be used in drying the filter. Asa 150 75-76 O 3 48 24-24 198 100-00 4. POTASH ALUM. Determination of Aluminium. Press pure triturated potash alum between sheets of blotting-paper; weigh off about 2 grm., dissolve in water, and determine aluminium as directed in 105, a. K 2 94-22 9-93 A1 2 O 3 102-2 10-77 4SO 3 320-28 33-74 24H 2 432-384 4556 949-084 100-00 5. POTASSIUM BICHROMATE. Determination of the Chromic Acid a. Fuse pure, potassium dichromate at a gentle heat, weigh off about 0-4 to' 0-6 grm., dis- solve in water in a porcelain dish, and reduce with hydrochloric acid and alcohol; expel the latter by heating on the water-bath, dilute the residue with about 200 c.c. water and proceed to deter- mine the chromic acid exactly as detailed in 130, 1, a, a. b. Weigh off again about 0-2 grm., dissolve in water, and precipitate the solution (the volume of which should be about 100 c.c.) with mercurous nitrate ( 130, I, a, /?). The precipita- 958 EXERCISES FOR PRACTICE. tion is best effected at the boiling temperature, and the washing with hot water to which a little mercurous nitrate has been added K 2 94-22 32-01 2Cr(X. , . 200-20 67-99 294-42 100-00 6. SODIUM CHLORIDE. Preparation. Sodium chloride is far less soluble in hydro- chloric acid than in water. On account of this property the crude produce common salt may be purified from the magnesium chloride and calcium sulphate which it contains as follows: To 100 c.c. of a saturated solution add very gradually an equal vol- ume of pure concentrated hydrochloric acid Drain the mass of fine crystals which separates on a funnel, the throat of which is loosely closed with filter-paper. Wash with a small volume of pure dilute hydrochloric acid, and at last, in order to test the purity of the product, allow 5 or 6 c.c. of distilled water to pass through. Collect the water that runs through in a test-tube separately, and add to it barium chloride. If no turbidity results, the sodium chloride is free from sulphates and may be assumed to be pure enough for analysis. Remove it from the funnel and dry it in a porcelain dish. If not free from sulphates, the product may be subjected to a repetition of the process. This, however, will rarely be neces- sary.* A portion f of the salt thus obtained is heated in a covered cru- cible until it ceases to decrepitate, but not to fusion, and preserved in a weighing-tube (like a small test-tube, but not flared at the mouth) which is to be closed with a soft, well-fitting, and smooth cork. * When large quantities of pure sodium chloride are required, it is more economical to prepare it from a solution of common salt by saturating the solution with HC1 gas. f Pure sodium chloride is needed in other analyses, and the chief part of what is thus prepared should be carefully bottled and reserved for future ESTIMATION OF CHLORINE. 959 6 a. ESTIMATION OF CHLORINE. Heat pure sodium chloride in a platinum crucible until anhy- drous (compare p. 522, Vol. I), dissolve about 4 grm. of it in about 150 c.c. of water, and determine the chlorine according to 141,1, a . Na 23-05 39-40 Cl 35-45 60-60 58-50 100-00 The procedure next detailed may also be profitably followed: 1. Weighing out ihe substanc The tube containing the pre- pared salt is wiped, if need be, free from dust. The cork is taken out, and by means of a bit of thin paper, or a clean linen handkerchief, any particles of salt adhering to the cork, and to the inside of the tube as far as the cork reaches, are removed. The cork is replaced and the whole is weighed (see 9 and 10), the weight being imme- diately recorded in the note-book A clean beaker or assay-flask, of about 200 c.c. capacity, being ready, the weighing-tube is held over it and the cork carefully removed. A portion of substance is allowed to fall in the vessel, and, the cork being replaced, the tube is again counterpoised. If two to three decigrammes have been emptied, the operator is ready to proceed. If less, more should be transferred from the tube to the vessel If more, or much more, it is 'better to begin anew, by weighing off another portion into another beaker or flask. In this manner weigh off two portions in separate vessels, so as to carry together duplicate analyses. Now affix a piece of gummed paper to each vessel, and label them to correspond with their designation in the note-book. 2. Solution and precipitation. Dissolve the weighed portions, each in about 100 c.c. of cold distilled water, add a few drops of pure nitric acid, and, lastly, clear solution of silver nitrate * until further addition no longer produces a precipitate. Agitate the mixture well, but with care to avoid loss. This can be done by shaking, if a flask is used, or by stirring with a glass rod, if a beaker be employed. * Solution of a silver coin in nitric acid answers for this purpose as well as pure nitrate, provided it be clear and contain but little free acid. 960 EXERCISES FOR PRACTICE. Set the vessel aside in a dark place, covered with paper or a watch-glass to exclude dust, and let stand for about 12 hours, or until the precipitate has subsided and the liquid above it is perfectly clear, then add a drop of silver nitrate to make sure that the pre- cipitation is complete (if not complete, add more solution of silver, and let stand again for some hours) . 3. Filtration. A filter is placed in a funnel at least \ inch deeper than itself, and moistened with water, at the stme time being carefully pressed down so that its edges touch the glass at all points. The funnel being supported on a stand, a clean beaker or flask is put beneath it, and the operator proceeds to pour the liquid on whose surface some particles of silver chloride usually float into the filter, leaving the bulk of the precipitate undisturbed. To do this without loss the following precautions may be regarded: a. Touch the edge or lip of the vessel with a very slight coat of tallow (a small bit of which is kept at hand under the edge of the work- table, and is applied with the finger). 6. Pour lowly over the greased place, along a glass rod* held nearly vertical, so directing the stream that it shall strike against the ide, not into the vertex of the filter, c. When the filter is filled to within \ inch of the top discontinue the pouring, bringing the rod into the vessel con- taining the precipitate, after it has drained so that nothing will fall from it. The vessel containing the precipitate, as well as that which receives the filtrate, and likewise the funnel, should be kept covered as much as possible in all cases when nicety is required, to prevent access of dust, insects, etc.f The filtration of silver chloride should be conducted without exposing it to strong light, whereby it is blackened, with loss of chlorine. * The pouring-rod may be simply straight, and an inch longer than the diagonal of the vessel, or when it is desirable not to disturb a precipitate, it may be 3 to 4 inches long and bent siphon fashion so as to hang on the edge of a beaker or flask. In either case its end should be rounded by fusion, and those portions along which the liquid flows must not be handled. f The most convenient covers are large watch-glasses, but square plates of glass, or even cards, will generally answer. ESTIMATION OF CHLORINE. 961 4. When all, or nearly all, the liquid has passed the filter, there remains to wash and to transfer the precipitate. These operations may be carried on as follows: pour about 100 .c. of cold distilled water upon the precipitate, which mostly remains in the vessel where it was formed, and agitate vigorously, in order to break up and divide the lumpy silver chloride, and bring every part of it perfectly in contact with the water.* The water and precipitate are now poured together upon the filter, with the precautions before detailed. The last portions of the precipitate are removed from the beaker or flask by repeated rins- ings, in which a wash-bottle (Figs. 58 to 61, p. 99, Vol. I) may be conveniently employed. Any portions of precipitate that adhere to the sides of the ves- sel too strongly to be removed by a stream from the wash-bottle must be rubbed off. For this purpose a feather is employed.! The dish being wiped clean, externally, a little water is put in it, -and, it being held up to the light, its whole interior surface is gently rubbed with the feather, then rinsed, rubbed again and rinsed, so long as . careful inspection discovers any portions of adhering pre- cipitate; finally, the feather is rinsed in a stream of water, the rinsings in each case being poured upon the filter. The washing is now continued by help of the wash-bottle. A jet of cold water is directed, first, upon the interior of the funnel, just above the filter, then upon the edge of the filter itself. If thrown immediately" against the paper, this is liable to be perfo- rated. The stream of water is carried around the edge of the filter until the latter is nearly full, and the liquid is then allowed to dram off. This process is repeated until a portion of the wash-water, collected to the depth of an inch in a test-tube containing a drop * When in a beaker, the agitation must be made with great caution, by means of a glass stirring-rod: when in a narrow-mouthed flanged flask, this may be tightly closed by a perfectly smooth cork (softened for the purpose by squeezing) and then shaken violently. f It is made from a goose-quill, by cutting off the extreme tip for an inch or so, and smoothly trimming away the beard, except a portion of one-half inch in length on the inside of the curve. The tubular part may be removed or not, to suit the depth of the dish which is to be washed. 962 EXERCISES FOR PRACTICE. of hydrochloric acid, gives no turbidity of silver chloride. When this is accomplished, the precipitate is washed down into the ver- tex of the filter. The funnel is then closely covered with paper, labelled, allowed to drain thoroughly, and set away in a warm place for drying. 5. Drying the filter. In public laboratories a heated closet is usually provided for drying filters. Its temperature should not exceed 100 C. In default of such special arrangement, the dry- ing may be effected over the register of a hot-air furnace, or over a common stove or kitchen range. The funnel may also be supported on a retort-stand over a sheet of iron, which is heated beneath by a lamp, or may be placed at once in the water-bath. See 50. 6. When the precipitate is perfectly dry we proceed to ignite it for weighing. A small porcelain crucible (platinum must not be used) is cleaned, gently ignited, and when cool (after 15 to 28 minutes) weighed. The work-table being clean, two small sheets of fine and smooth writing or glazed paper are opened and laid down side by side. The filter is removed from the funnel and carefully inverted upon one of the papers. The precipitate is loosened from the filter by squeezing and rubbing gently between the fingers, and when it has mostly separated the filter is lifted, reversed, and any portions of silver chloride still adhering are loosened by rubbing its sides together. What is thus detached is poured or shaken out on the paper. . The filter is now spread out as a half -circle upon the other sheet of paper, and, beginning with the straight edge, is folded up into a narrow flattened roll, the two ends of which are then brought together. In this way those central portions of the filter to which particles of precipitate adhere are thoroughly enveloped by the exterior parts, so that in the subsequent burning nothing can easily escape. The crucible being placed on the glazed paper, the filter is taken by the two free ends in a clean pincers or tongs, put to the ESTIMATION OF CHLORINE. 963 flame of a lamp to set it on fire, and then held over the crucible until it is completely charred. It is then dropped into the crucible and moistened with two or three drops of nitric acid. The cruci- ble is covered and placed over a low flame until its contents are dry ; it is then heated somewhat more strongly, whereby the carbon is nearly or entirely consumed. The crucible being allowed to cool, one more drop of nitric acid, and afterwards a drop of hydrochloric acid, is added to the residue, and it is heated cautiously, without the cover, until fumes cease to escape. This treatment with nitric acid serves to Destroy carbon and convert any reduced silver to nitrate, which the hydro- chloric acid in turn transforms into chloride. When the crucible is cool, it is placed again on the paper, and the precipitate is poured into it from the other sheet, the last particle being detached by cautious tapping with the fingers underneath, or by the use of a clean camel's-hair pencil. The crucible is now put over a low flame and heated cautiously until the silver chloride begins to fuse on the edges. It is then covered and let cool. When cold it is weighed Read 115 1, and the references there made 7. Record and ca culati n o " results. The amount of silver chloride is learned by subtracting from the total the joint weight of the crucible and filter-ash. The quantity of chlorine is obtained by multiplying the amount of silver chloride by the decimal 0-2473. In order to compare results they are reduced to per cent, statements by the following proportion: Substance : chlorine in substance :: 100 : chlorine in 100; i.e., per cent. The record may be made as follows: It is well to work out the calcula- tions in full in the weight-book, as in case of mistake the data are at hand for revision. No. 1. No. 2. NaCl and tube 6*615 6-180 substance 6-180 5-765 Substance 0-435 0-415, 964 EXERCISES FOR PRACTICE. Crucible, AgCl, and ash 15 3630 14 3270 Cr- 14-298 ) 149QQ - 13-309 > Ash.. 0-0015 f 14 ' 2 " 5 0-0015 f 13 ' 3105 AgCl 1-0635 1-0165 0-2473 0-2473 31905 30495 74445 71155 42540 40660 21270 20330 a ." =0-26300355 0-25138045 0-435)26-300355(60-46 0-415)25-138045(60-57 2610 2490 2003 2380 1740 2075 2635 3054 2610 2905 Found. Calculated. No. 1. No. 2. Chlorine 60-46 60-57 60-62 [We have here employed the simplest arithmetical calculation. It is well to duplicate the calculation with help of the tables given in the Appendix. The first determination given above is not only fair for this method, but answers all ordinary purposes. The second is very good, though with care still closer accordance with theory can be easily attained.] B. COMPLETE ANALYSIS OF SALTS IN THE GRAVIMETRIC WAY- CALCULATION OF THE FORMULA FROM THE RESULTS OBTAINED ( 202, 203). 7. CALCIUM CARBONATE.* Heat pure calcium carbonate in powder (no matter whether Iceland spar or the artificially prepared substance), gently in a platinum crucible. a. Determination of Calcium. Dissolve in a covered beaker about 1 grm. in dilute hydrochloric acid with the addition of some water, heat gently until the carbonic acid is completely expelled, dilute if necessary to about 300 c.c., and determine calcium as directed ( 103, 2, b, a). To control, convert the calcium carbonate into calcium sul- *CaCO. CUPRIC SULPHATE. 965 phate, and weigh it as such. For this purpose transfer it to a weighed platinum dish, dissolve it in very dilute hydrochloric acid while keeping the dish covered with a watch-glass, which is after- wards rinsed, and then proceed as in 103, 1, b. b. Determination of Carbonic Add. Determine in about 0-8 grm. the carbonic acid as in 139, II, c. CaO 56-1 56-04 CO 2 . . 44-0 43-96 100-1 100-00 8. CUPRIC Sui PHATE.* A complete analysis of this should be made. Triturate the pure crystals f in a porcelain mortar > and press between blotting-paper. a. Weigh an empty bulb-tube, then half fill the bulb with the copper sulphate, J weigh again, place it in an air-bath having openings in its sides (Vol. I, p. 64, Fig. 38), and proceed as directed in 29, employing a current of dry air. When no more water escapes at 120 to 140, and repeated weighing of the bulb-tube gives constant results, the loss in weight gives the quantity of water of crystallization present in the salt. Instead of the bulb-tube an ordinary wide tube may also be employed, the copper sulphate being placed in a boat and the latter inserted into the tube and heated as described. In order to guard against the reabsorption of water by the dehydrated copper sulphate during the weighing, insert the boat in a small tube closed by a glass or even a cork stopper, which is weighed along "with it both before and after the heating, a wire being twisted around the tube near the stopper and *CuSO 3 +2H 2 O. 970 EXERCISES FOR PRACTICE. thus may be at once ignited, and weighed as mangano-manganic oxide. 14. VOLUMETRIC DETERMINATION OF IRON BY SOLUTION OF POTASSIUM PERMANGANATE. a. Standardizing the Solution of Potassium Permanganate. By metallic iron (fine piano wire), 1 grm. of which should be dissolved in dilute sulphuric acid ( 112, 2, a, Vol. I, p. 312). I would point out that it is better to allow only boiled distilled water to reascend into the flask a, and not the water used as a seal, which often contains hydrocarbons. b. Determining the Percentage Content of Oxalic Acid. Weigh off 1 or 2 grm. of pure oxalic acid, press between blotting-paper, dis- solve in water, dilute to 250 c.c., and titrate 50 c.c. according to 112, 2, a, a, cc. (Vol. I, p. 316). c. Determination of Ferrous Iron in Ammonium Ferrous Sul- phate. Dissolve 12 grm. of the pressed salt in water with the addi- tion of a little diluted sulphuric acid, dilute to 500 c.c., and in por- tions of 50 c.c. determine the iron: a. In the solution of the salt acidulated with sulphuric acid (Vol. I, p. 318,/?). /?. In the solution acidulated with hydrochloric acid, i.e., after the addition of about 30 c.c. hydrochloric acid of sp. gr. 1 12 (Vol. I, p.3i9,r). 7-. In the solution acidulated with hydrochloric acid as in /?, with the addition of 20 c.c. of a solution of manganous sulphate containing 200 grm. per litre. By this addition the disturbing influence of the hydrochloric acid is counteracted (F. KESSLER; CL. ZIMMERMANN) . d. In the solution acidulated with hydrochloric acid as in /?, with the addition of 10 to 20 c.c. of a cold, saturated solution of lead chloride (N. W. THOMAS). FeO 71-900 18-33 (NH 4 ) 2 52-144 13-29 2SO 3 160-140 40-82 6H 2 108-096 27-56 392-280 100-00 DETERMINATION OF IRON WITH STANNOUS CHLORIDE. 971 15. VOLUMETRIC DETERMINATION OF IRON WITH STANNOUS CHLORIDE. Warm about 5 grm. of the finely powdered brown hematite (dried at 100 and moderately ignited) with strong hydrochloric acid until the ferric oxide has completely dissolved, add, if neces- sary, a little potassium chlorate, then heat until all the free chlorine has been expelled, dilute, filter, make up the solution to 250 c.c. or 500 c.c., and mix by shaking. In 50 or 100 c.c. of the solution determine the iron by means of stannous chloride according to 113, 3, 6, a (Vol. I, p. 327). 16. DETERMINATION OF NITRIC ACID IN POTASSIUM NITRATE. Heat pure potassium nitrate, but not to fusion, and transfer it to a dry, well-stoppered tube. Determine the nitric acid in 0-2 to 0-3 grm. as hi 149, II, d, ft (Vol. I, p. 577). K,O 94-24 46-57 N 2 O 5 108-08 53-43 202-30 100-00 17. SEPARATION OF MAGNESIUM FROM SODIUM. Dissolve about 0-2 grm. pure recently ignited magnesia (which is easily obtained by igniting pure magnesium oxalate, but which, for the sake of safety, should be washed with boiling water and after drying, again ignited) and about 0-3 grm. pure well-dried sodium chloride in dilute hydrochloric acid (avoiding a large excess), and separate by ammonium-phosphate methods described in 153, /?, 4 (Vol. I, p. 612). As it is important that the ammonium phosphate should be added only in slight excess, a solution of known strength should be employed, and the quantity added calculated. From the filtrate remove the phosphoric acid by means of ferric chloride (Vol. I, p. 612, 6, a). 972 EXERCISES FOR PRACTICE. 18. SEPARATION OF POTASSIUM FROM SODIUM. Triturate crystallized sodium-potassium tartrate (Rochelle salt), press between blotting-paper, weigh off about 1-5 grm., heat in a platinum crucible, gently at first, then for some time to gentle ignition. The carbonaceous residue is completely extracted with water, and the residue, after being collected and washed, is care- fully ignited, and again extracted with water. The united alka- line filtrates are then acidulated with hydrochloric acid, the acid fluid is evaporated in a weighed platinum dish, and the chlorides are weighed together ( 97, 3). Then separate them by platinic chloride ( 152, a, and this volume, pp. 345 and 874) ; then weigh the potassium-platinic chloride, and calculate the sodium from the difference. K 2 94-22 Na 2 62-10 C 8 H 8 O 10 264-064 8H 2 O.' 144-128 564-512 100-00 19. VOLUMETRIC DETERMINATION OF CHLORINE IN CHLORIDES, AND THE INDIRECT DETERMINATION OF THE POTASSA AND SODA IN ROCHELLE SALT. a. Preparation and examination of the solution of silver nitrate (141, 1, 6, a, Vol. I, p. 522). b. Indirect determination of the sodium and potassium in Rochelle salt, by volumetric estimation of the chlorine in the alkali chlorides prepared as in No. 18. For calculation see 200, a f this volume, p. 166. 20. ACIDIMETRY. a. Preparation of normal hydrochloric acid and soda-lye ( 215, I, p. 293, this volume). b. Testing the correctness of the normal hydrochloric acid with pure sodium carbonate, and with Iceland spar ( 215, II, p. 301, this volume). ACIDIMETRY. 973 c. Preparation of normal sulphuric acid by means of normal soda solution, known to be correct. d. Determination of the strength of a diluted sulphuric acid by its specific gravity: a, By means of the pyknometer ( 209, a, p. 242, or 278, p. 765, this volume; or 6, By the araeometer ; or c, By MOHR'S balance (Zeitschr. f. analyt. Chem., ix, 233). For the calculation see 214, I, a, p. 285 this volume. e. Determination of the strength of the same diluted sulphuric acid by normal soda solution ( 215, III, a, p. 302, this volume), using various indicators ( 215, 6, pp. 309 to 312, this volume). Compare also THOMSON (Zeitsch. f. analyt. Chem., xxiv, 222). /. Determination of the strength of a vinegar ( 215, III, a and 6, 3, pp. 302 and 303, this vol.). In the case of colorless or only slightly colored vinegar, phenolphtalein is to be particularly recommended. g. Determination of the total tartaric acid in potassium bitar- trate, according to the method of GOLDENBERG, GEROMONT & Co. (Zeitschr. f. analyt. Chem., xxn, 270). Heat to boiling exactly 3 grm. of the finely powdered substance with 30 to 40 c.c. water and 2 to 2-5 grm. potassium carbonate for 10 to 20 minutes, with frequent stirring; when somewhat cooled, transfer the liquid (which now contains all the tartaric acid in the form of neutral potassium tartratg) to a 100-c.c. flask or cylinder, allow to become perfectly cold, fill up the flask or cylinder to the mark, and shake ; after standing a while, filter through a dry filter- paper into a dry flask. Then evaporate 50 c.c. of the filtrate down to 10 c.c., add 2 c.c. glacial acetic acid to convert all the neutral tartrate into potassium bitartrate, add 100 to 120 c.c. of 95-per cent, (at least) alcohol, stir vigorously, and after allowing to stand for a while, filter. Wash the residue with 95-per cent, alcohol until the washings, when diluted with water, no longer have an acid re- action. Now retransfer the still moist precipitate with the filter to the porcelain dish, and heat to boiling with water, under con- stant stirring. Titrate this liquid with normal soda solution, using litmus tincture or phenolphtalein as indicator. The number of c.c. used, when multiplied by 10, gives at once the percentage of 974 EXERCISES FOR PRACTICE. tartaric acid in the substance examined, as it relates to 1.5 grm v i.e., the quantity corresponding to yf^- equivalent of tartaric acid, which, in the form of potassium bitartrate, requires 10 c.c. of nor- mal soda solution. If the tartar is so impure that the precipitated potassium bitartrate is not white, the titration must be effected by the aid of a sensitive, pale-red litmus-paper (p. 305, 3, this volume). Further, when this is the case, it is necessary, in order to obtain perfectly accurate results, to standardize the soda solution also against chemically pure potassium bitartrate dried at 100, using the same litmus-paper, because the standard thus obtained differs somewhat from that obtained by normal acid, or even potassium bitartrate, when litmus tincture is employed. h. Determination of the potassium bitartrate in crude tartar. The following method may be used instead of or in addition to the method detailed in g, i.e., the determination of pure potassium bitartrate in crude tartar or in beer-yeast may be effected by F. KLEIN'S * method. First determine the approximate acidity of the triturated, uniformly mixed substance (p. 305, 3, this volume), and from this ascertain the approximate quantity of the potassium bitartrate. Then weigh off so much as will contain about 1 8 to 2 2 grin, potas- sium bitartrate, boil repeatedly (about five times) with water, decanting each time through a filter; finally bring the residue on to the filter and wash it with boiling water until the washings cease to redden litmus-paper in the least degree. Now evaporate the mixed washings to 40 c.c., add 5 grm. potassium c loride, and stir vigorously for 15 minutes with a gla s rod. To separate the now completely deposited potassium bitartrate from the liquid there is required a solution made by dissolving 5 grm. finely pow- dered, pure potassium bitartrate in 200 c.c. distilled water in a 250-c.c. flask, and, after shaking, adding 25 grm. potassium chloride, filling the flask up to the mark, setting aside for several hours, with frequent shaking, and then filtering. A filter is now moistened with this solution and the potassium- * Zeitschr. f. analyt. Chem., xxiv, 383. ALKALIMETRY. 975 bitartrate precipitate brought onto it. After it has completely drained, wash it by dropping onto it the solution just described, using altogether about 15 c.c., then allow to again drain thoroughly, retransfer the precipitate together with the filter to the dish, heat with water, and titrate the potassium bitartrate with seminormal soda solution.* KLEIN recommends phenolphtalein as indicator. If the impure nature of the precipitated potassium bitartrate necessitates the use of litmus paper for titrating, then the semi- normal soda solution must be standardized by the aid of the same paper against pure, potassium bitartrate dried at 100 (see at end of g). 21. ALKALIMETRY. a. Preparation of the normal acid after DESCROIZILLES and GAY-LUSSAC ( 219). b. Valuation of commercial potash afte expulsion o the water by gentle ignition ( 224, III, 1, p. 340 this volume). a. After MOHR ( 220). /?. After DESCROIZILLES and GAY-LUSSAC ( 220). 22. DETERMINATION OF AMMONIUM. Treat about 0-8 grm. pure (unsublimed), and dried ammonium chloride as directed ( 99, 3, a, Vol. I, p. 253). NH 4 18-072 33-77 NH 3 17-064 30-59 Cl. . .35-45 66-23 HC1.. ..36-458 69-41 53-522 100-00 53-522 100-00 23. SEPARATION OP IODINE FROM CHLORINE. Dissolve about 0-8 grm. pure potassium iodide dried at 180 ( 65. 6), and about 2 to 3 grm. pure, anhydrous sodium chloride, in water to make 250 c.c., and determine the iodine and chlorine: a. In 50 c.c. according to 169, 2, b [263], For calculation, see 200, c. 6. In 10 c.c. according to 169, 2, c [264]. * As the 40 c.e. of filtrate contain a small quantity of tartar, a correction must be made; in fact, according to my experience, 0-2 c.c. of seminormal alkali should be allowed for 40 c.c. of the filtrate. 976 EXERCISES FOR PRACTICE D. ANALYSIS OF ALLOYS, MINERALS, INDUSTRIAL PRODUCTS, ETC., IN THE GRAVIMETRIC AND VOLUMETRIC WAY. 24. ANALYSIS OF BRASS. Brass consists of from 25 to 35 per cent, of zinc and from 75 to 65 per cent, of copper. It also contains usually small quantities of tin and lead, and occasionally traces of iron. The analysis is car- ried out as follows: a. According to 264, first method (p. 655 this volume). 6. Partly by electrolysis. a. As a preliminary test ; dissolve about 2 grm. pure, pressed copper sulphate in wat r to make 250 c.c., and in 50 c.c. determine the copper by electrolysis. For this purpose add 20 c.c. nitric acid of 1-2 sp. gr. and 130 c.c. water (p. 620 this volume), and precipi- tate the copper by the lectric current (p. 621 this volume). ft. Dissolve about 1 5 grm. brass in nitric acid, separate any tin and lead as in a, make up the solutio i freed from these to 250 c.c., and in 50 c.c. after the addition of 20 c.c. nitric acid of 1-2 sp. gr., and 130 c.c. water, precipitat the copper as on p. 502 this volume. Without interrupting the current, draw off first the solution, then the washings, into a flask, by means of a suitable aspirator,* con- centrate the whole by evaporating down to about 100 c.c., and precipitate the zinc as in a. 25. DETERMINATION OF SILVER IN SILVER COIN. Dissolve a silver coin (say a dime) in 16 to 20 c.c. nitric acid of 1 2 sp. gr. with the addition of a little water, heat until all nitrous acid is expelled, dilute to 100 c.c., and in 50 c.c. determine the silver volumetrically by VOLHARD'S method (p. 570 this volume). 26. ANALYSIS OF SOFT SOLDER (TiN AND LEAD). According to 267, C, II, first method (p. 683 this vol.). * Compare, for example, H. FRESENIUS and F. BERGMANN, Zeitschr. j. analyt. Chem., xix, 316. See 235. ANALYSIS OF FELSPAR. 977 27. ANALYSIS OF A DOLOMITE. 28. ANALYSIS OF FELSPAR. a. Decomposition by sodium carbonate ( 140, II, b, a) ; re- moval of the silicic acid which is weighed and then volatilized by hydrofluoric acid (Vol. I, p. 5 11, second paragraph) in order to ascertain whether the silica contains any alumina; precipitation of the aluminium with the small quantity of iron as hydroxides by ammonia (hi platinum or Berlin porcelain, not hi glass vessels) as in 161, 4 [i 15] ; separation of barium, if present, from the filtrate with dilute sulphuric acid, and then of calcium with ammonium oxalate, as in 154 6 [36]. Finally, solution of the weighed alu- mina in concentrated hydrochloric acid, separation and weighing of traces of silica if present; evaporation with sulphuric acid and volumetric determination of iron, generally present in small quan- tities as in 160, 2 [97]. 6. Decompose with hydrofluoric acid, preferably by AL. MITSCHERLICH'S method (Vol. I, pp. 514 and 515). Evaporate with the addition of a little sulphuric acid until no more hydrochloric acid is evolved, then gradually heat more strongly until the greater part of the free sulphuric acid is also expelled shake up the res- idue with water, heat, add barium chloride cautiously so long as a precipitate forms, and when cold, but without previous filtration, add ammonium carbonate and ammonia. Allow to settle in the cold, filter, evaporate the filtrate to dryness, ignite the residue in order to expel the ammonium salts, dissolve in water, remove any magnesium and any small quantities of barium and calcium that may be present, according to p. 418, e, this vol., and lastly determine the potassium according to 97, 3. If sodium is also present, the alkalies should be separated as in 152 [i]. If ex- ceedingly great accuracy is desired, the small quantity of potas- sium salt precipitated with the barium sulphate must also be taken into account, see p. 927 this volume. c. Decomposition by SMITH'S method (Vol. I, p. 519). 978 EXERCISES FOR PRACTICE. 29. ANALYSIS OF ZINC BLENDE. a. Complete Analysis. Proceed to determine the sulphur, as well as to dissolve and separate any lead and other metals of the fifth or sixth groups that may be present, according to 241, first method (p. 431 this vol.), after which proceed as follows: Heat the filtrate in order to expel the hydrogen sulphide, add nitric acid, and continue the heat in order to convert the ferrous into ferric iron, allow to cool, and add an excess of ammonia. Then filter, wash, dissolve the precipitate in hydrochloric acid, and precipitate the ferric oxide and any aluminium present, as basic salt, as in 160, 3, a [82]. Concentrate by evaporation the filtrate thus obtained, add a slight excess of ammonia in order to precipitate any slight residual alu- minium and iron, filter if necessary, and if the quantity of precipi- tate is considerable, repeat the solution and reprecipitation of the latter with hydrochloric acid and ammonia. Dissolve the precipi- tate in hydrochloric acid, add the solution to the hydrochloric-acid solution of the main precipitate of ferric oxide, precipitate the mixed solution with ammonia, wash the precipitate, then dry and weigh it. Then dissolve it in concentrated hydrochloric acid, deter- mine any residual silica, and deduct this from the weight found. If the solution thus obtained contains also aluminium, separate the ferric oxide and alumina as in 160, 2 [77]. Acidulate with acetic acid the united ammoniacal filtrates con- taining the whole of the zinc, add ammonium acetate, and pre- cipitate with hydrogen sulphide with the aid of heat; then thor- oughly wash the zinc sulphide first by decantation, and then on the filter, with hot water containing a little ammonium nitrate, and determine it according to 108, 2. The filtrate from the zinc sulphide concentrate down to a small volume, add bromine, then ammonia, and heat. If a precipitate of hydrated manganese di- oxide forms, filter this off, wash it dry, ignite, and weigh as mangano- manganic oxide. As at times the zinc sulphide carries down with it small quantities of manganese sulphide, it is necessary, as a pre- caution, to dissolve the weighed zinc sulphide in hydrochloric acid,. ANALYSIS OF GALENA. 979 with the addition of some nitric acid, then to add bromine followed by ammonia to the solution, and to then ascertain whether, on digestion at a gentle heat, any flocks of hydrated manganese dioxide separate; if this occurs, the manganese so precipitated should be determined as above, and the quantity taken into account in the calculation. 6. Volumetric Determination of the Zinc according to 242. 30. ANALYSIS OF GALENA. a. Determination of the sulphur, lead, iron, etc., according to 259, A, 1 (p. 574 this volume). 6. Determination of the silver in galena, according to 259, A, 3, b (p. 578 this volume). 31. VALUATION OF CHLORINATED LIME. According to 233, p. 376 this volume. a. By PENOT'S method (p. 379 this volume). b. lodometrically (p. 382 this volume) . The preparation of the solutions required for this, and the method of determining the liberated iodine, are described in 146. In order to obtain concordant results with both methods, all the preparations must first be properly made, so that the exam- ination of the same " chlorinated-lime milk" can be carried out in the shortest tune by the methods a and b. 32. VALUATION OF MANGANESE ( 247). a. After FRESENIUS and WILL (p. 458 this volume). b. After BUNSEN (p. 465 this volume). c. By means of iron (p. 466 this volume). 33. DETERMINATION OF SULPHUR IN PYRITES. a. Determination hi the dry way ( 256, II, 1, p. 561 this volume) . b. Determination in the wet way ( 256, II, 2, 6, p. 564 this volume). 980 EXERCISES FOR PRACTICE. 34. DETERMINATION OF ARSENIC IN AN IRON OCHRE OR IN AN OCHREOUS SEDIMENT FROM A FERRUGINOUS WATER. Digest about 10 to 20 grm. with about 50 to 100 c.c. pure fum- ing hydrochloric acid, and treat the solution according to 268, p. 691 this volume. If the receive; is connected with the con- denser so as to be air-tight, as shown in Fig. 81, Vol. I, p. 254, a little water placed in the receiver, and in the P ELI GOT tube connected with it, the hydrochloric-acid solution mixed with the excess of ferrous-chloride solution may be distilled at once, i.e., without previously diluting it with water, thus attaining the pur- pose much more rapidly. 35. ANALYSIS OF GUNPOWDER. According to 227. 36. DETERMINATION OF CHROMIUM IN CHROME IRON ORE. According to 239, I, a, b or c and II b, /?. When titrating the excess of ferrous oxide with potassium permanganate, care must be taken to add manganese sulphate (see Exercise 14, c). 37. DETERMINATION OF MANGANESE IN A MANGANESE ORE. According to 250. 38. ANALYSIS OF A CLAY OR A SOIL. a. Mechanical analysis, according to 238, I, or 293, re- spectively. b. Chemical analysis, according to 238, II, or 296, respec- tively. 39. DETERMINATION OF NICKEL AND COBALT IN AN ORE. According to 251, first method. 40. DETERMINATION IN PIG IRON OF CHEMICALLY-COMBINED CARBON, GRAPHITE, SULPHUR, PHOSPHORUS, SILICON, AND ANY OTHER CONSTITUENTS WHICH MAY BE PRESENT. According to 255. ANALYSIS OF SPRING- OR MINERAL WATER. 981 41. ANALYSIS OF A SPRING WATER OR A MINERAL WATER. According to 205 or 206, et seq., respectively. 42. ANALYSIS OF A PLANT ASH. According to 283 to 290. 43. DETERMINATION OF THE SUGAR IN FRUIT, HONEY, MILK, OR THE LIKE. According to 274 to 277. 44. DETERMINATION OF ANTHRACENE IN A CRUDE ANTHRACENE. According to 282. 45. DETERMINATION OF ALCOHOL IN WINE OR OTHER LIQUID CONTAINING ALCOHOL. According to 278. 46. DETERMINATION OF TANNIC ACID IN TANNING MATERIALS.. According to 279. E. DETERMINATION OF THE SOLUBILITY OF SALTS. 47. DETERMINATION OF THE DEGREE OF SOLUBILITY OF COMMON SALT. a. At boiling heat. Dissolve perfectly pure pulverized sodium chloride in distilled water, in a flask, heat to boiling, and keep in ebullition until part of the dissolved salt separates. Filter the fluid now with the greatest expedition, through a funnel surrounded with boiling water and covered with a glass plate, into an accurately tared capacious measuring flask. As soon as about 100 c.c. of fluid have passed into the flask, insert the cork, allow to cool, and weigh. Fill the flask now up to the mark with water, and deter- mine the salt in an aliquot portion of the fluid, by evaporating in a platinum dish (best with addition of some ammonium chloride, which will, in some measure, prevent decrepitation) ; or by deter- mining the chlorine ( 141). b. At 14. Allow the boiling saturated solution to cool down 982 EXERCISES FOR PRACTICE. to this temperature with frequent shaking, and then proceed as in a. 100 parts of water dissolve at 109-7. . . .40-35 of sodium chloride. 100 " " " " " 14 35-87 " * 48. DETERMINATION OF THE DEGREE OF SOLUBILITY OF CALCIUM SULPHATE. a. At 100. 6. At 12. Digest pure pulverized calcium sulphate for some time with water, in the last stage of the process at 40 to 50 (at which tempera- ture sulphate of lime is most soluble) ; shake the mixture frequently during the process. Decant the clear solution, together with a little of the precipitate, into two flasks, and boil the fluid in one of them for some time; allow that in the other to cool down to 12, with frequent skaking, and let it stand for some time at that tem- perature. Then filter both solutions, weigh the filtrates, and deter- mine the amount of calcium sulphate respectively contained in them, by evaporating and igniting the residues. 100 parts of water dissolve at 100 0-217 of anhydrous calcium sulphate 100 " " " " " 12 0-233 " " " " Compare MARIGNAC, Zeitschr. /. analyt. Chem., xm, 57. F. DETERMINATION OF THE SOLUBILITY OF GASES IN LIQUIDS; AND ANALYSIS OF GASEOUS MIXTURES. 49. DETERMINATION OF THE ABSORPTION-COEFFICIENT OF SULPHUROUS ACID. See Ann. d. Chem. u. Pharm.. xcv, 1; also 131, 2. 50. ANALYSIS OF ATMOSPHERIC AIR. Determination of the carbonic acid ( 336 to 339), and oxygen tt 341). ANALYSIS OF TARTARIC ACID. 983 G. ORGANIC ANALYSIS, AND DETERMINATIONS OF THE EQUIVALENTS OF ORGANIC COMPOUNDS; ALSO ANALYSES IN WHICH ORGANIC ANALYSIS HAS TO BE EMPLOYED. 51. ANALYSIS OF TARTARIC ACID. Select clean and white crystals. Powder and dry at 100. a. Burn with cupric oxide, by LIEBIG'S method ( 174). b. Burn with cupric oxide, by BUN SEN'S method ( 175). c. Burn in oxygen ( 178). C 4 48-000 31-99 H 6-048 4-03 0. . 96-000 63-98 150-048 100-00 -52. DETERMINATION OF THE NITROGEN IN CRYSTALLIZED POTAS- SIUM FERROCYANIDE. Triturate the perfectly pure crystals, press hi blotting-paper, if necessary, and preserve in a closed tube Determine the nitro- gen: a. By VARRENTRAPP- WILL'S method ( 186). b. By PELIGOT'S modification of VARRENTRAPP-WILL'S method ( 187). c. By WILFARTH'S modification of KJELDAHL'S process ( 326). 4>3. ANALYSIS OF URIC ACID (or any other pure organic compound of carbon, hydrogen oxygen, and nitrogen). Dry pure uric acid at 100 a. Determine the carbon and hydrogen according to 183. b. Determine the nitrogen : a. According to 187. t 8. By KJELDAHL'S process, WILFARTH'S modification ( 326). f. By DUMAS' method ( 185). C 5 60-00 N 4 56-16 H 4 4-032 O 8 48-00 168-192 100-00 984 EXERCISES FOR PRACTICE. 54. ANALYSIS OF ETHER. The portion employed must have been recently rectified and rendered anhydrous by digestion with fused calcium chloride. Process 180. C 4 48-00 64-79 H lo 10-08 13-61 O. . 16-00 21-60 74-08 100-00 55. ANALYSIS OF A HARD COAL. According to 272, B, p. 721 this volume. The determination is best effected by WILFARTH'S modification of KJELDAHL'S method ( 326). 56. ANALYSIS OF A BONE MEAL. According to 330, a. 57. ANALYSIS OF A MANURE MIXTURE IN WHICH THE NITROGEN IS PRESENT IN THE FORM OF AMMONIA, NlTRIC ACID, AND IN ORGANIC COMBINATION, AND THE PHOSPHORIC ACID IS PRESENT IN DIFFERENT DEGREES OF SOLUBILITY. According to 333. 58. ANALYSIS OF BENZOIC ACID, AND DETERMINATION OF ITS EQUIVALENT. a. The silver in silver benzoate is determined as directed in 115, 1 or 4. b. The carbon and hydrogen in benzoic acid dried at 100, are determined by any suitable method. Calculation, 203, 2. 59. ANALYSIS OF AN ORGANIC BASE, AND DETERMINATION OF ITS EQUIVALENT. Analysis of the base and its platinum double salt. Calculation, 203, 3. 60. DETERMINATION OF THE DENSITY OF CAMPHOR VAPOR. Method described in 194. Calculation, 204. ANALYTICAL EXPERIMENTS. 985 ANALYTICAL EXPERIMENTS. 1. ACTION OF WATER UPON GLASS AND PORCELAIN VESSELS, IN THE PROCESS OF EVAPORATION (to 41). A large bottle was filled with water cautiously distilled from a copper boiler with a tin condensing tube. All the experiments hi 1 were made with this water. a. 300 c.c., cautiously evaporated in a platinum dish, left a residue weigh- ing, after ignition, 0-0005 grai. =0-0017 per 1000. 6. 600 c.c. were evaporated, boiling, nearly to dryness, in a wide flask of Bohemian glass; the residue was transferred to a platinum dish, and the flask rinsed with 100 c.c. distilled water, which was added to the residue in the dish ; the fluid in the latter was then evaporated to dryness, and the residue ignited. The residue weighed 0-0104 grm. Deducting from this the quantity of fixed matter origi- nally contained in the distilled water, viz 0-0012 " There remains substance taken up from the glass 0-0092 " =0-0153 per 1000. In three other experiments, made hi the same manner, 300 c.c. left, in two 0049 grm., in the third 0037 grm. ; which, calculated, for 600 c.c., gives an average of 0-0090 grm. And after a deduction of 0-0012 " 0-0078 " =0-013 per 1000. We may therefore assume that 1 litre of water dissolves, when boiled down to a small bulk in glass vessels, about 14 milligrammes of the constituents of the glass. c. 600 c.c. were evaporated nearly to dryness in a dish of Berlin porcelain and in all other respects treated as in 6. The residue weighed 0015 grm. Deducting from this the quantity of fixed matter con- tamed in the distilled water, viz 0-0012 " There remains substance taken up from the porcelain. . . 0-0003 " =0-0005 per 1000. 2. ACTION OF HYDROCHLORIC ACID UPON GLASS AND PORCELAIN VESSELS, IN THE PROCESS OF EVAPORATION (to 41). The distilled water used in 1 was mixed with -fa of pure hydrochloric acid. a. 300 grm., evaporated in a platinum dish, left 0-002 grm. residue. &. 300 grm., evaporated first in Bohemian glass nearly to dryness, then in a platinum dish, left 0019 residue ; the dilute hydrochloric acid, therefore, had not attacked the glass. EXERCISES FOR PRACTICE. c. 300 grm.. evaporated in Berlin porcelain, etc., left 0-0036 grm., accord- ingly after deducting 0-002, 0-0016 = 0-0053 per 1000. d. In a second experiment made in the same manner as in c., the residue amounted to 0-0034, accordingly after deducting 0-002, 0-0014=0-0047 per 1000. Hydrochloric acid, therefore, attacks glass much less than water, whilst porcelain is about equally affected by water and dilute hydrochloric acid. This shows that the action of water upon glass consists in the formation of soluble basic silicates. Porcelain is attacked much more by water containing hydro- chloric acid than by pure water. 3. ACTION OF SOLUTION OF AMMONIUM CHLORIDE UPON GLASS AND PORCELAIN VESSELS, IN THE PROCESS OF EVAPORATION (to 41). In the distilled water from 1, T ^ of ammonium chloride was dissolved, and the solution filtered. a. 300 c.c., evaporated in a platinum dish, left 0-006 grm. fixed residue. 6. 300 c.c., evaporated first nearly to dryness in ^Bohemian glass, then to dryness in a platinum dish, left 0-0179 grm. ; deducting from this 006 grm., there remains substance taken up from the glass, 0-0119 =0-0397 per 1000. c. 300 c.c., treated in the same manner in Berlin porcelain, left 0-0178, deducting from this 0-006, there remains 0-0118=0-0393 per 1000. Solution of ammonium chloride, therefore, strongly attacks both glass and porcelain in the process of evaporation. 4. ACTION OF SOLUTION OF SODIUM CARBONATE UPON GLASS AND PORCELAIN VESSELS (to 41). In the distilled water from 1, T V of pure crystallized sodium carbonate was dissolved. a. 300 c.c., supersaturated with hydrochloric acid and evaporated to dry- ness in a platinum dish, etc., gave 0-0026 grm. silica =0-0087 per 1000. 6. 300 c.c. were gently boiled for three hours in a glass vessel, the evaporat- ing water being replaced from time to time ; the tolerably concentrated liquid was then treated as in a; it left a residue weighing 0-1376 grm.; deducting from this the 0026 grm. left in a, there remains 0-135 grm. =0 450 per 1000. c. 300 c.c., treated in the same manner as in b, in a porcelain vessel, left 0-0099; deducting from this 0-0026 grm., there remains 0-0073=0-0243 per 1000. Which shows that boiling solution of sodium carbonate attack^ glass very strongly, and porcelain also in a very marked manner. 5. WATER DISTILLED FROM GLASS VESSELS (to 56, 1). 42-41 grm. of water distilled with extreme caution from a tall flask with a LIEBIG'S condenser, left upon evaporation in a platinum dish, a residue weigh- ing, after ignition, 0-0018 grm., consequently ^kw ANALYTICAL EXPERIMENTS. 987 6. POTASSIUM SULPHATE AND ALCOHOL (to 68, a). a. Ignited pure potassium sulphate was digested cold with absolute alco- hol, for several days, with frequent shaking; the fluid was filtered off, the filtrate diluted with water, and then mixed with barium chloride. It re- mained perfectly clear upon the addition of this reagent, but after the lapse of a considerable time it began to exhibit slight opalescence. Upon evapora- tion to dryness, there remained a very trifling residue, which gave, how- ever, distinct indications of the presence of sulphuric acid. 6. The same salt treated in the same manner, with addition of some pure concentrated sulphuric acid, gave a filtrate which, upon evaporation in a plati- num dish, left a clearly perceptible fixed residue of potassium sulphate. 7. DEPORTMENT OF POTASSIUM CHLORIDE IN THE AIR AND AT A HIGH TEMPERATURE (to 68, c). 0-9727 grm. of pure, ignited (not fused) pure potassium chloride, heated for 10 minutes to dull redness in an open platinum dish, lost 0-0007 grm. ; the salt was then kept for 10 minutes longer at the same temperature, when no further diminution of weight was observed. Heated to bright redness and semi-fusion, the salt suffered a further loss of weight to the extent of 0-0009 grm. Ignited intensely and to perfect fusion, it lost 0-0034 grm. more. Eighteen hours' exposure to the air produced not the slightest increase of weight. 8. SOLUBILITY OF POTASSIUM PLATINIC CHLORIDE IN ALCOHOL (to 68, d). a. In absence of free Hydrochloric Acid. a. An excess of perfectly pure, recently precipitated potassium platinic chloride was digested for 6 days at 15 to 20, with alcohol of 97 5 per cent., in a stoppered bottle, with frequent shaking. 72 5 grm. of the perfectly colorless filtrate left upon evaporation in a platinum dish a residue which, dried at 100, weighed 006 grm. ; 1 part of the salt requires therefore 12083 parts of alcohol of 97 5 per cent, for solution. {3. The same experiment was made with alcohol of 76 per cent. The fil- trate might be said to be colorless ; upon evaporation, slight blackening ensued, on which account the residue was determined as platinum. 75 5 grm. yielded 008 grm. platinum, corresponding to 02 grm. of the salt. One part of the salt dissolves accordingly in 3775 parts of alcohol of 76 per cent. f. The same experiment was made with alcohol of 55 per cent. The fil- trate was distinctly yellowish. 63-2 grm. left 0-0241 grm. platinum, cor- responding to 06 grm. of the salt. One part of the salt dissolves accordingly in 1053 parts of alcohol of 55 per cent. b. In presence of free Hydrochloric Acid. Recently precipitated potassium platinic chloride was digested cold with alcohol of 76 per cent., to which some hydrochloric acid had been added. The solution was yellowish; 67 grm. left 0-0146 grm. platinum, which corresponds to 0-0365 grm. of the salt. One part of the salt dissolves accordingly in 3185 parts of alcohol mixed with hydrochloric acid. EXERCISES FOR PRACTICE. 9. SODIUM SULPHATE AND ALCOHOL (to 69, a). Experiments made with pure anhydrous sodium sulphate, in the manner described in 6, showed that this salt comports itself both with pure alcohol, and with alcohol containing sulphuric acid, exactly like potassium sulphate. 10. DEPORTMENT OF IGNITED SODIUM SULPHATE IN THE AIR (to 69, a). 2 5169 grm. anhydrous sodium sulphate were exposed, in a watch-glass, to the open air on a hot summer day. The first few minutes passed without any increase of weight, but after the lapse of 5 hours there was an increase of 0-0061 grm. 11. EXPERIMENTS WITH SODIUM NITRATE (to 69, 6). a. 4*5479 grm. of pure fused sodium nitrate on being exposed to the air (in April, in fine weather) for 24 hours, increased in weight 0006 grm. 6. 4 5479 grm. of pure sodium nitrate were dissolved in water, in a plati- num dish, and pure nitric acid added to the solution; the mixture was then evaporated to dryness on the water-bath, and the residue cautiously heated until the mass at the, bottom of the dish began to fuse. The contents of the dish when cooled weighed 4-5503 grm., and after being heated again to com- plete fusion, 4 5474 grm. 12. DEPORTMENT OF SODIUM CHLORIDE IN THE AIR (to 69, c). 4-3281 grm. of chemically pure, moderately ignited (not fused) sodium chloride, which had been cooled under a bell-glass over sulphuric acid, ac- quired during 45 minutes' exposure to the (somewhat moist) air an increase of weight of 0-0009 grm. 13. DEPORTMENT OF SODIUM CHLORIDE UPON IGNITION BY ITSELF AND WITH AMMONIUM CHLORIDE (to 69, c). 4.3281 grm. chemically pure, ignited sodium chloride were dissolved in water, in a moderate-sized platinum dish, and pure ammonium chloride was added to the solution, which was then evaporated and the residue gently heated until the evolution of ammonium chloride fumes had apparently ceased. The residue weighed 4 3334 grm. It was then very gently ignited for about 2 minutes, and after this re-weighed, when the weight was found to be 4-3314 grm. A few minutes' ignition at red heat reduced the weight to 4-3275 grm., and 2 minutes' further ignition at a bright red heat (upon which occasion white fumes were seen to escape), to 4 3249 grm. 14. DEPORTMENT OP SODIUM CARBONATE IN THE AIR AND ON IGNITION (to 69, d). 2-1061 grm. of moderately ignited chemically pure soduim carbonate were exposed to the air in an open platinum dish in July in bad weather; after 10 minutes the weight was 2 1078, after 1 hour, 2-1113, after 5 hours, 2 1257. 1-4212 grm. of moderately ignited chemically pure sodium carbonate were ignited for 5 minutes in a covered platinum crucible, but so that no fusion took place, and the weight was unaltered. Heated more strongly for 5 ANALYTICAL EXPERIMENTS. 989 minutes it partially fused, and then weighed 1-4202. After being kept fusing for 5 minutes, it weighed 1 4135. 15. DEPORTMENT OF AMMONIUM CHLORIDE UPON EVAPORATION AND DRYING (to 70, a). 0-5625 grm. pure and perfectly dry ammonium chloride was dissolved in water in a platinum dish, evaporated to dryness in the water-bath, and com- pletely dried ; the weight was now found to be 5622 grm. (ratio 100 : 99 94). It was again heated for 15 minutes in the water-bath, and afterwards re- weighed, when the weight was found to be 0-5612 grm. (ratio 100:99-77). Exposed once more for 15 minutes to the same temperature, the residue weighed 0-5608 grm. (ratio 100 : 99-69). 16. SOLUBILITY OF AMMONIUM PLATINIC CHLORIDE IN ALCOHOL (to 70, 6). a. In absence of free Hydrochloric Acid. a. An excess of perfectly pure, recently precipitated ammonium platinic chloride was digested for 6 days, at 15 to 20, with alcohol of 97 5 per cent., in a stoppered bottle, with frequent agitation. 74-3 grm. of the perfectly colorless filtrate left, upon evaporation and ignition in a platinum dish, 0-0012 grm. platinum, corresponding to 0-0028 of the salt. One part of the salt requires accordingly 26535 parts of alcohol of 97 5 per cent. /?. The same experiment was made with alcohol of 76 per cent. The filtrate was distinctly yellowish. 81.75 grm. left. 0-0257 platinum, which corresponds to 0-0584 grm. of the salt, One part of the salt dissolves accordingly in 1406 parts of alcohol of 76 per cent. f. The same experiment was made with alcohol of 55 per cent. The nitrate was distinctly yellow. Slight blackening ensued upon evaporation, and 56-5 grm. left 0-0364 platinum, which corresponds to 0-08272 grm. of the salt. Consequently, 1 part of the salt dissolves in 665 parts of alcohol of 55 per cent. 6. In presence of Hydrochloric Acid. The experiment described in /? was repeated with this modification, that some hydrochloric acid was added to the alcohol. 76 5 grm. left 0501 grm. of platinum, which corresponds to 0-1139 grm. of the salt. 672 parts of the acidified alcohol had therefore dissolved 1 part of the salt. 17. SOLUBILITY OF BARIUM CARBONATE IN WATER (to 71, b). a. In Cold Water. Perfectly pure, recently precipitated BaCO 3 was di- gested for 5 days with water of 16 to 20, with frequent shaking. The mix- ture was filtered, and a portion of the filtrate tested with sulphuric acid, another portion with ammonia ; the former reagent immediately produced turbidity in the fluid, the latter only after the lapse of a considerable time. 84-82 grm. of the solution left, upon evaporation, 0-006 BaCO 3 . One part of that salt dissolves consequently in 14137 parts of cold water. 990 EXERCISES FOR PRACTICE. 6. In Hot Water. The same barium carbonate being boiled for 10 minutes with pure distilled water, gave a filtrate manifesting the same reactions as that prepared with cold water, and remaining pertectly clear upon cooling. 84-82 grm. of the hot solution leit, upon evaporation, 0-0055 grm. of barium carbonate. One part of that salt dissolves therefore in 15421 parts of boiling water. 18. SOLUBILITY OF BARIUM CARBONATE IN WATER CONTAINING AMMONIA AND AMMONIUM CARBONATE (to 71, 6). A solution of chemically pure barium chloride was mixed with ammonia and ammonium carbonate in excess, gently heated and allowed to stand at rest for 12 hours; the fluid was then filtered off; the filtrate remained per- fectly clear upon addition of sulphuric acid; but alter a lapse of a very con- siderable time, a hardly perceptible precipitate separated. 84-82 grm. of the filtrate left, upon evaporation in a small platinum dish, and subsequent gentle ignition, 0006 grm. One part of the salt had consequently dissolved in 141000 parts of the fluid. 19. SOLUBILITY OF BARIUM SILICO-FLUORIDE IN WATER (to 71, c). a. Recently precipitated, thoroughly washed barium silico-fluoride was digested for 4 days in cold water, with frequent shaking; the fluid was then filtered off, and a portion of the filtrate tested with dilute sulphuric acid,* another portion with solution of calcium sulphate; both reagents produced turbidity the former immediately, the latter after one or two seconds pre- cipitates separated from both portions after the lapse of some time. 84-82 grm. of the filtrate left a residue which, after being thoroughly dried, weighed 0-0223 grm. One part of the salt had consequently required 3802 parts of cold water for its solution. 6. A portion of another sample of recently precipitated barium silico-fluo- ride was heated with water to boiling, and the solution allowed to cool (upon which a portion of the dissolved salt separated). The cold fluid was left for a considerable time longer in contact with the undissolved salt, and was then filtered off. The filtrate showed the same deportment with solution of sul- phate of lime as that of a. 84 82 grm. of it left 025 grm. One part of the salt had accordingly dissolved in 3392 parts of water. 20. SOLUBILITY OF BARIUM SILICO-FLUORIDE IN WATER ACIDIFIED WITH HYDROCHLORIC ACID (to 71, c). a. Recently precipitated pure barium silico-fluoride was digested with fre- quent agitation for 3 weeks with cold water acidified with hydrochloric acid. The filtrate gave with sulphuric acid a rather copious precipitate. 84 82 grm. left 0-1155 grm. of thoroughly dried residue, which, calculated as barium silico-fluoride, gives 733 parts of fluid to 1 part of that of salt. 6. Recently precipitated pure barium silico-fluoride was mixed with water very slightly acidified with hydrochloric acid, and the mixture heated to boil- ing. Cooled to 12, 84-82 grm. of the filtrate left a residue of 0-1322 grm., Which gives 640 parts of fluid to 1 part of the salt. ANALYTICAL EXPERIMENTS. 991 N.B. The solution of barium silico-fluoride in hydrochloric acid is not effected without decomposition; at least, the residue contained, even after ignition, a rather large proportion of barium chloride. 21. SOLUBILITY OF STRONTIUM SULPHATE IN WATER (to 72. a), a. In Water of 14. 84-82 grm. of a solution prepared by 4 days' d/gestion of recently pre- cipitated strontium sulphate with water at the common temperature, left 0-0123 grm. of strontium sulphate. One part of strontium sulphate dissolves consequently in 6895 parts of water. b. In Water of 100. 84 82 grm. of a solution prepared by boiling recently precipitated strontium sulphate several hours with water, left 0-0088 grm. Consequently 1 part of strontium sulphate dissolves hi 9638 parts of boiling water. 22. SOLUBILITY OF STRONTIUM SULPHATE IN WATER CONTAINING HYDROCHLORIC ACID AND SULPHURIC ACID (to 72, a). a. 84-82 grm. of a solution prepared by 3 days' digestion, left 0-0077 grm. SrS0 4 . b. 42 41 grm. of a solution prepared by 4 days' digestion, left 0036 grm. c. Pure strontium carbonate was dissolved in an excess of hydrochloric acid, and the solution precipitated with an excess of sulphuric acid and then allowed to stand in the cold for a fortnight. 84 82 grm. of the filtrate left 0-0066 grm. In a. 1 part of SrSO 4 required 11016 parts. b. 1 " " " " 11780 " c. 1 " " " " 12791 " Mean 11862 parts. 23. SOLUBILITY OF STRONTIUM SULPHATE IN DILUTE NITRIC Acn>, HYDROCHLORIC ACID, AND ACETIC ACID (to 72, a). a. Recently precipitated pure strontium sulphate was digested for 2 days in the cold with nitric acid of 4 8 per cent. 1 50 grm. of the filtrate left 3451 grm. One part of the salt required accordingly 435 parts of the dilute acid for its solution; in another experiment 1 part of the salt was found to require 429 parts of the dilute acid. Mean, 432 parts. b. The same salt was digested for 2 days in the cold with hydrochloric acid of 8 5 per cent. 100 grm. left 21 1 5, and in another experiment, 0-2104 grm. One part of the salt requires, accoicdngly, in the mean, 474 parts of hydrochloric acid of 8 5 per cent, for its solution. c. The same salt was digested for 2 days in the cold with acetic acid of 15-6 per cent. C 2 H 4 O.,. 100 grm. left 0-0126, and in another experiment, 0-0129 grm. One part of the salt requires, accordingly, in the mean, 7843 parts of acetic acid of 15-6 per cent. 992 EXERCISES FOR PRACTICE. 24. SOLUBILITY OF STRONTIUM CARBONATE IN COLD WATER (to 72, 6). Recently precipitated, thoroughly washed strontium carbonate was digest- ed several days with cold distilled water, with frequent shaking. 84 82 grm. of the nitrate left, upon evaporation, a residue weighing, after ignition, 0047 grm. One part of strontium carbonate requires therefore 18045 parts of water for its solution. 25. SOLUBILITY OF STRONTIUM CARBONATE IN WATER CONTAINING AMMONIA AND AMMONIUM CARBONATE (to 72, 6). Recently precipitated, thoroughly washed strontium carbonate was di- gested for 4 weeks with cold water containing ammonia and ammonium car- bonate, with frequent shaking. 84.82 grm. of the filtrate left 0-0015 grm. SrCO 3 . Consequently, 1 part of the salt requires 56545 parts of this fluid for its solution. If solution of strontium chloride is precipitated with ammonium carbonate and ammonia as directed 102, 2, a, sulphuric acid produces no turbidity in the filtrate, after addition of alcohol. 26. SOLUBILITY OF CaCO 3 IN WATER CONTAINING AMMONIA AND AMMONIUM CARBONATE (to 73, 6). Pure dilute solution of calcium chloride was precipitated with ammonium carbonate and ammonia, allowed to stand 24 hours, and then filtered. 84 82 grm. left 0-0013 grm. CaCO 3 . One part requires consequently 65246 parts. 26, a. SOLUBILITY OF CALCIUM CARBONATE IN COLD AND IN BOILING WATER (to 73, 6). a. A solution prepared by boiling as in 26, 6, was digested in the cold for 4 weeks, with frequent agitation, with the undissolved precipitate. 84 82 grm. left 0-0080 CaCO 3 . One part therefore required 10601 parts. 6. Recently precipitated calcium carbonate was boiled for some time with distilled water. 42-41 grm. of the filtrate left, upon evaporation and gentle ignition of the residue, 0048 CaCO 3 . One part requires consequently 8834 parts of boiling water. 27. DEPORTMENT OF CALCIUM CARBONATE UPON IGNITION IN A PLATINUM CRUCIBLE (to 73, 6). 7955 grm. of perfectly dry calcium carbonate was-exposed, in a small and thin platinum crucible, to the gradually increased and finally most intense heat of a good BERZELIUS' lamp. The crucible was open and placed obliquely. After the first 15 minutes the mass weighed 6482 ; after half an hour 6256 ; after one hour 0-5927, which latter weight remained unaltered after 15 minutes' additional heating. This corresponds to 74-5 per cent., whilst the proportion of CaO in the carbonate is calculated at 56 per cent. ; there re- mained therefore evidently still a considerable amount of the carbonic acid. 28. COMPOSITION OF CALCIUM OXALATE DRIED AT 100 (to 73, c). 0-8510 grm. of thoroughly dry pure calcium carbonate was dissolved in hydrochloric acid ; the solution was precipitated with ammonium oxalate and ANALYTICAL EXPERIMENTS. 993 ammonia, and the precipitate collected upon a weighed filter and dried at 100, until the weight remained constant. The calcium oxalate so produced weighed 1-2461 grm. Calculating this as CaC 2 O 4 -f- H 2 O, the amount found contained 0-4772 CaO, which corresponds to 56-07 per cent, in the calcium carbonate ; the calculated proportion of CaO in the latter is 56 per cent. 29. DEPORTMENT OF FRESHLY IGNITED CAUSTIC LIME ON EXPOSURE TO AIR (to 73, d). 0-5599 grm. of caustic lime, obtained by igniting calcium oxalate in a covered platinum crucible over the blow-pipe, after standing in the scale pan 1 minute weighed 0-5599 grm.; after 2 minutes, 0-5605; after 6 minutes, 0-5609; after 17 minutes, 0-5625. The platinum crucible containing the caustic lime, was left for 15 minutes in the desiccator before making the first weighing. 30. DEPORTMENT OF MAGNESIUM SULPHATE IN THE AIR AND UPON IGNITION (to 74, a). 0-8135 grm. of perfectly pure anhydrous MgSO 4 in a covered platinum crucible acquired, on a fine and warm day in June, in half an hour, an increase of weight of 004 grm., and in the course of 12 hours, of 067 grm. The salt could not be accurately weighed in the open crucible, owing to continual increase of weight. 0-8135 grm., exposed for some time to a very moderate red heat, suffered no diminution of weight ; but after 5 minutes' exposure to an intense red heat, the substance was found to have lost 0-0075 grm., and the residue gave no longer a clear solution with water. About 2 grm. of pure magnesium sul- phate exposed in a small platinum crucible, for 15 to 20 minutes, to the heat of a powerful blast gas lamp, gave, with dilute hydrochloric acid, a solution in which barium chloride failed to produce the least turbidity. 31. SOLUBILITY OF AMMONIUM MAGNESIUM PHOSPHATE IN PURE WATER (to 74, 6). a. Recently precipitated ammonium magnesium phosphate was thoroughly washed with water, then digested for 24 hours with water of about 15, with frequent shaking. 84-42 grm. of the filtrate left 0-0047 grm. of magnesium pyrophosphate. b. The same precipitate was digested in the same manner for 72 hours. 84-42 grm. of the filtrate left 0-0043 " Mean 0-0045 " which corresponds to 00552 grm. of the anhydrous double salt. One part of that salt dissolves therefore in 15293 parts of pure water. The cold saturated solution gave, with ammonia, after the lapse of a short time, a distinctly perceptible crystalline precipitate; on the addition of sodium phosphate, it remianed perfectly clear, and even after the lapse of 994 EXERCISES FOR PRACTICE. 2 days no precipitate had formed; ammonium sodium phosphate produced a precipitate as large as that caused by ammonia. 31, a. SOLUBILITY OF AMMONIUM MAGNESIUM PHOSPHATE IN WATER CONTAINING AMMONIA (to 74, 6). a. Pure ammonium magnesium phosphate was dissolved in the least pos- sible amount of nitric acid; a large quantity of water was added to the solu- tion, then ammonia in excess. The mixture was allowed to stand at rest for 24 hours, then filtered; its temperature was 14. 84-42 grm. left 0-0015 magnesium pyrophosphate, which corresponds to 0-00184 of the anhydrous double salt. Consequently 1 part of the latter requires 45880 parts of ammo- niated water for its solution. 6. Pure ammonium magnesium phosphate was digested for 4 weeks with ammoniacal water, with frequent shaking; the fluid (temperature 14) was then filtered off; 126-63 grm. left 0-0024 magnesium pyrophosphate, which corresponds to 0-00296 of the double salt. One part of it therefore dissolves in 42780 parts of ammoniacal water. Taking the mean of a and 6, 1 part of the double salt requires 44330 parts of ammoniacal water for its solution. 31, 6. ANOTHER EXPERIMENT ON THE SAME SUBJECT (to 74, 6). Recently precipitated ammonium magnesium phosphate, most carefully washed with water containing ammonia, was dissolved in water acidified with hydrochloric acid, ammonia added in excess, and allowed to stand in the cold for 24 hours. 169-64 grm. of the filtrate left 0-0031 magnesium pyrophos- phate, corresponding to 0-0038 of anhydrous ammonium magnesium phos- phate. One part of the double salt required therefore 44600 parts of the fluid. 31, c. SOLUBILITY OF AMMONIUM MAGNESIUM PHOSPHATE IN WATER CONTAINING AMMONIUM CHLORIDE (to 74, 6). Recently precipitated, thoroughly washed ammonium magnesium phos- phate was digested in the cold with a solution of 1 part of ammonium chloride in 5 parts of water. 18-4945 grm. of the filtrate left 0-002 magnesium pyro- phosphate, which corresponds to 0-00245 of the double salt. One part of the salt dissolves therefore in 7548 parts of the fluid. 31, d. SOLUBILITY OF AMMONIUM MAGNESIUM PHOSPHATE IN WATER CONTAINING AMMONIA AND AMMONIUM CHLORIDE (to 74, 6). Recently precipitated, thoroughly washed ammonium magnesium phos- phate was digested in the cold with a solution of 1 part of ammonium chloride in 7 parts of ammoniacal water. 23-1283 grm. of the filtrate left 0-0012 magnesium pyrophosphate, which corresponds to 0-00148 of the double salt. One part of the double salt requires consequently 15627 parts of the fluid for its solution. 32. DEPORTMENT OF ACID SOLUTIONS OF MAGNESIUM PYROPHOSPHATE WITH AMMONIA (to 74, c). 0-3985 grm. magnesium pyrophosphate was treated for several hours, at a high temperature, with concentrated sulphuric acid. This exercised no ANALYTICAL EXPERIMENTS. 995 perceptible action. It was only after the addition of some water that the salt dissolved. The fluid, heated for some time, gave, upon addition of ammo- nia in excess, a crystalline precipitate, which was filtered off after 18 hours; the quantity of magnesium pyrophosphate obtained was 0-3805 grm., that is, 95-48 per cent. Sodium phosphate produced in the filtrate a trifling precipitate, which gave 0-0150 grm. of magnesium pyrophosphate, that is, 3-76 per cent. 0-3565 grm. magnesium pyrophosphate was dissolved in 3 grm. nitric acid, of 1-2 sp. gr. ; the solution was heated, diluted, and precipitated with ammonia: the quantity of magnesium pyrophosphate obtained amounted to 0-3485 grm., that is, 98-42 per cent.; 0-4975 grm. was treated in the same manner with 7 6 grm. of the same nitric acid : the quantity re-obtained was 4935 grm., that is, 99 19 per cent. 0-786 grm., treated in the same manner with 16-2 grm. of nitric acid, gave 0-7765 grm., that is, 98-79 per cent. The result of these experiments may be tabulated thus : Retained. Loss. 1:9 98-42 percent. 1-58 1:15 99-19 " 0-81 1:20 98-79 " 1-21 33. SOLUBILITY OF PURE MAGNESIA IN WATER (to 74, d). a. In Cold Water. Perfectly pure well-crystallized magnesium sulphate was dissolved in water, and the solution precipitated with ammonium carbonate and caustic ammonia; the precipitate was thoroughly washed in spite of which it still retained a perceptible trace of sulphuric acid then dissolved in pure nitric acid, an excess of acid being carefully avoided. The solution was then re- precipitated with ammonium carbonate and caustic ammonia, and the pre- cipitate thoroughly washed. The so-prepared perfectly pure magnesium carbonate was ignited in a platinum crucible until the weight remained con- stant. The residuary pure magnesia was then digested in the cold for 24 hours with distilled water, with frequent shaking. The distilled water used was perfectly free from chlorine, and left no fixed residue upon evaporation. a. 84-82 grm. of the filtrate, cautiously evaporated in a platinum dish, left a residue weighing, after ignition, 0-0015 grm. One part of the pure magnesia dissolved therefore in 56546 parts of cold water. The digestion was continued for 48 hours longer, when 0. 84 82 grm. left 0-0016 grm. One part required there- fore 53012 f. 84-82 grm. left 0-0015 grm. One part required 56546 Average 55368 The solution of magnesia prepared in the cold way has a feeble yet distinct alkaline reaction, which is most easily perceived upon the addition of very 996 EXERCISES FOR PRACTICE. faintly reddened tincture of litmus; the alkaline reaction of the solution is perfectly manifest also with slightly reddened litmus paper, or with turmeric- or dahlia-paper, if these test-papers are left for some time in contact with the solution. Alkali carbonates fail to render the solution turbid, even upon boiling. Sodium phosphate also fails to impair the clearness of the solution, but if the fluid is mixed with a little ammonia and shaken, it speedily becomes tur- bid, and deposits after some time a perceptible precipitate of ammonium magnesium phosphate. b. In Hot Water. Upon boiling pure magnesia with water, a solution is obtained which con- ports itself in every respect like the cold-prepared solution of magnesia. A hot-prepared solution of magnesia does not become turbid upon cooling, nor does a cold-prepared solution upon boiling. 84 82 grm. of hot-prepared solu- tion of magnesia left 0-0016 grm. MgO. 34. SOLUBILITY OF PURE MAGNESIA IN SOLUTIONS OF POATSSIUM CHLORIDE AND SODIUM CHLORIDE (to 74, d). Three flasks of equal size were charged as follows: 1. With 1 grm. pure potassium chloride, 200 c.c. water and some perfectly pure magnesia. 2. With 1 grm. pure sodium chloride, 200 c.c. water and some pure mag- nesia. 3. With 200 c.c. water and some pure magnesia. The contents of the three flasks were kept boiling for forty minutes, then filtered, and the clear filtrates mixed with equal quantities of a mixture of sodium phosphate, ammonium chloride and ammonia. After twelve hours a very slight precipitation was visible in 3, and a considerably larger precipi- tation had taken place in 1 and 2. 35. PRECIPITATION OF ALUMINIUM BY AMMONIA, ETC. (to 75, a). a. Ammonia produces in neutral solutions of aluminium salts or of alum, as is well known, a gelatinous precipitate of aluminum hydroxide. Upon fur- ther addition of ammonia in considerable excess, the precipitate redissolves gradually, but not completely. 6. If a drop of a dilute solution of alum is added to a large quantity of ammonia, and the mixture shaken, the solution appears almost perfectly clear; however, after standing at rest for some time, slight flakes separate. c. If a solution of alumina, mixed with a large amount of ammonia, is filtered, and a. The filtrate boiled for a considerable time, flocks of aluminium hydrox- ide separate gradually in proportion as the excess of ammonia escapes. /?. The filtrate mixed with solution of ammonium chloride, a very percep- tible flocculent precipitate of aluminium hydroxide separates immediately; the whole of the aluminium present in the solution will thus separate if the ammonium chloride be added in sufficient quantity. ANALYTICAL EXPERIMENTS. 997 7-. The filtrate mixed with ammonium sesquicarbonate, the same reaction takes place as in /?. o. The filtrate mixed with solution of sodium chloride or of potassium chloride, no precipitate separates, but, after several days' standing, slight flakes of aluminium hydroxide subside, owing to the loss of ammonia by evaporation. d. If a neutral solution of alumina is precipitated with ammonium car- bonate, or if a solution strongly acidified with hydrochloric or nitric acid is precipitated with pure ammonia, or if to a neutral solution a sufficient amount of ammonium chloride is added besides the ammonia; even a considerable excess of the precipitants will fail to redissolve the precipitated aluminium hydroxide, as appears from the continued perfect clearness of the filtrates upon protracted boiling and evaporation. 36. PRECIPITATION OF ALUMINIUM BY AMMONIUM SULPHIDE (to 75, a). (Experiments made by J. FUCHS, formerly Assistant in my Laboratory.} a. 50 c.c. of a solution of pure ammonium-alum, which contained 0-3939 A1 2 O 3 were mixed with 50 c.c. water and 10 c.c. solution of ammonium sul- phide, and filtered after ten minutes. The ignited precipitate weighed 3825 grm. b. The same experiment was repeated with 100 c.c. water; the precipitate weighed 0-3759 grm. c. The same experiment was repeated with 200 c.c. water; the precipitate weighed 0-3642 grm. 37. PRECIPITATION OF CHROMIUM BY AMMONIA (to 76, a). Solutions of chromic chloride and of chrome-alum (concentrated and dilute, neutral and acidified with hydrochloric acid) were mixed with ammo- nia in excess. All the filtrates drawn off immediately after precipitation appeared red, but when filtered after ebullition, they all appeared colorless, if the ebullition had been sufficiently protracted. 38. SOLUBILITY OF THE BASIC ZINC CARBONATE IN WATER (to 77, a). Perfectly pure, recently (hot) precipitated basic zinc carbonate was gently heated with distilled water, and subsequently digested cold for many weeks, with frequent shaking. The clear solution gave no precipitate with ammo- nium sulphide, not even after long standing. 84-82 grm. left 0-0014 grm. zinc oxide, which corresponds to 0-0019 basic zinc carbonate (74 per cent, of ZnO being assumed in this salt). One part of the basic carbonate requires therefore 44642 parts of water for solution. 39. DEPORTMENT OF ZINC SULPHIDE ON WASHING (to 77, c). In these experiments, as also in 40 and 41, the sulphide of the metal was precipitated from a solution of the neutral salt, containing ammonium chlo- ride, by adding to it yellow ammonium sulphide and allowing it to remain in a closed vessel for twenty-four hours; first the clear liquid and then the precipitate was poured on to 6 filters of equal size, so that the quantity of 998 EXERCISES FOR PRACTICE. the metallic sulphide on each filter was about the same. The washing was at once commenced and continued, without interruption, the following liquids being used: I. Pure water; II. Water containing sulphuretted hydrogen; III. Water containing sulphide of ammonium; IV. Water con- taining chloride of ammonium, afterwards pure water; V. Water con- taining sulphuretted hydrogen and chloride of ammonium, afterwards water containing sulphuretted hydrogen; and VI. Water containing sulphide of ammonium and chloride of ammonium, afterwards water containing sul- phide of ammonium. The nitrates were at first colorless and clear. On washing, the first three filtrates ran through turbid, the turbidity was strongest in II, and weakest in III ; the last three remained quite clear. On adding ammonium sulphide no change took place; the turbidity of the first three was not increased, the clearness of the last three was not impaired. Ammonium chloride there- fore decidedly exercises a favorable action, and the water containing it may be displaced by water containing ammonium sulphide. 40. DEPORTMENT OF MANGANESE SULPHIDE ON WASHING (to 78, e). The filtrates, as in 39, \rere at first clear and colorless. But after the washing had been continued some time, I appeared colorless, slightly opales- cent; II, whitish and turbid; III, yellowish and turbid; IV, colorless, slightly turbid; V, slightly yellowish, nearly clear; VI, clear, yellowish. To obtain a filtrate that remains clear, therefore, the wash- water must at first contain ammonium cliloride. Addition of ammonium sulphide also cannot be dispensed with, as all the filtrates obtained without this addition gave distinct precipitates of manganese sulphide when the reagent was subse- quently added to them. 41. DEPORTMENT OF NICKEL SULPHIDE (ALSO OF COBALT SULPHIDE AND FERROUS SULPHIDE) ON WASHING (to 79, e). In the experiments with nickel sulphide the clear filtrates were put aside/ and then the washing was proceeded with. The washings of the first three ran through turbid, of the last three clear. When the washing was finished, I was colorless and clear; II, blackish and clear; III, dirty yellow and clear; IV, colorless and clear; V, slightly opalescent; VI, slightly brownish and opalescent. On addition of ammonium sulphide, I became brown; II re- mained unaltered; III remained unaltered; IV became black and opaque; V became brown and clear; VI became pure yellow and clear. Cobalt sulphide and ferrous sulphide behaved in an exactly similar manner. It is plain that these sulphides oxidize more rapidly when the wash-water contains ammonium chloride, unless ammonium sulphide is also present. Hence it is necessary to wash with a fluid containing ammonium sulphide; and the addition of ammonium chloride at first is much to be recommended, as this diminishes the likelihood of our obtaining a muddy filtrate. ANALYTICAL EXPERIMENTS. 999 41, a. DEPORTMENT OF COBALTOUS HYDROXIDE PRECIPITATED BY ALKALIES (to 80, a). A solution of cobaltous chloride was precipitated boiling with solution of soda, and the precipitate washed with boiling water until the filtrate gave no longer the least indication of presence of chlorine. The dried and ignited residue, heated with water, manifested no alkaline reaction. It was reduced by ignition in hydrogen gas, and the metallic cobalt digested hot with water. The decanted water manifested no alkaline reaction, even after considerable concentration; but the metallic cobalt, brought into contact, moist, with turmeric-paper, imparted to the latter a strong brown color. 42. SOLUBILITY OF LEAD CARBONATE (to 83, a). a. In pure Water. Recently precipitated and thoroughly washed pure lead carbonate was digested for eight days with water at the common temperature, with frequent shaking. 84-42 grm. of the filtrate were evaporated, with addition of some pure sulphuric acid; the residuary lead sulphate weighed 0-0019 grm., which corresponds to 0-00167 lead carbonate. One part of the latter salt dissolves therefore in 50551 parts of water. The solution, mixed with hydrogen sulphide water, remaining perfectly colorless, not the least tint being de- tected in it, even upon looking through it from the top of the test-cylinder. b. In Water containing a little Ammonium Acetate and also Ammonium Carbonate and Ammonia. X highly dilute solution of pure lead acetate was mixed with ammonium carbonate and ammonia in excess, and the mixture gently heated and then allowed to stand at rest for several days. 84-42 grm. of the filtrate left, upon evaporation with a little sulphuric acid, 0-0041 grm. lead sulphate, which corresponds to 0-0036 of the carbonate. One part of the latter salt requires accordingly 23450 parts of the above fluid for solution. The solu- tion was mixed with hydrogen sulphide water; when looking through the fluid from the top of the test-cylinder, a distinct coloration was visible; but when looking through the cylinder laterally, this coloration was hardly perceptible. Traces of lead sulphide separated after the lapse of some tune. c. In Water containing a large proportion of Ammonium Nitrate, together with Ammonium Carbonate and Caustic Ammonia. A highly dilute solution of lead acetate was mixed with nitric acid, then with ammonium carbonate and ammonia in excess; the mixture was gently heated, and allowed to stand at rest for eight days. The filtrate, mixed with hydrogen sulphide, exhibited a very distinct brownish color upon looking through it from the top of the cylinder; but this color appeared very slight only when looking through the cylinder laterally. The amount of lead dissolved was unquestionably more considerable than in b 1000 EXERCISES FOR PRACTICE. 43. SOLUBILITY OF LEAD OXALATE (to 83, 6). A dilute solution of lead acetate was precipitated with ammonium oxalate and ammonia, the mixture allowed to stand at rest for some time, and then filtered. The filtrate, mixed with hydrogen sulphide, comported itself exactly like the nitrate of No. 42 f b, i.e., the liquid appeared faintly brown on looking through it from the top of the cylinder, while, when viewed later- ally, the color was scarcely perceptible. The same deportment was observed in another similar experiment, in which ammonium nitrate had been added to the solution. 44. SOLUBILITY OF LEAD SULPHATE IN PURE WATER (to 83, d). Thoroughlyjwashed and still moist lead sulphate was digested for five days with water, at 10 to 15, with frequent shaking. 84-42 firm, of the filtrate (filtered off at 11) left 0-0037 grm. lead sulphate. Consequently 1 part of this salt requires 22816 parts of pure water at 11 for solution. The solution, mixed with hydrogen sulphide, exhibited a distinct brown color when viewed from the top of the cylinder, but this color appeared very slight upon looking through the cylinder laterally. 45. SOLUBILITY OF LEAD SULPHATE IN WATER CONTAINING SULPHURIC ACID (to 83, rf). A highly dilute solution of lead acetate was mixed with an excess of dilute pure sulphuric acid ; the mixture was very gently heated, and the precipitate allowed several days to subside. 80-31 grm. of the filtrate left 0-0022 grm. lead sulphate. One part of this salt dissolves therefore in 36504 parts of water containing sulphuric acid. The solution, mixed with hydrogen sul- phide appeared colorless to the eye looking through the cylinder laterally, and very little darker when viewed from the top of the cylinder. 46. SOLUBILITY OF LEAD SULPHATE IN WATER CONTAINING AMMONIUM SALTS AND FREE SULPHURIC ACID (to 83, d}. A highly dilute solution of lead acetate was mixed with a tolerably large amount of ammonium nitrate, and sulphuric acid in excess added. After several days' standing, the mixture was filtered. The filtrate was nearly indifferent to hydrogen-sulphide water; viewed from the top of the cylinder, it looked hardly perceptibly darker than pure water. 47. DEPORTMENT OF LEAD SULPHATE UPON IGNITION (to 83, d). Speaking of the determination of the atomic weight of sulphur, ERDMANN and MARCHAND * state that lead sulphate loses some sulphuric acid upon ignition. In order to inform myself of the extent of this loss, and to ascertain how far it might impair the accuracy of the method of determining lead as a sulphate, I heated 2-2151 grm. of absolutely pure PbSO 4 to the most intense redness, over a spirit-lamp with double draught. I could not perceive the * Journ. fur Prakt. Chem., xxxi, 385. ANALYTICAL EXPERIMENTS. 1001 slightest decrease of weight; at all events, the loss did not amount to 0-0001 grm. 48. DEPORTMENT OP LEAD SULPHIDE ON DRYING AT 100 (to 83, /). Lead sulphide was precipitated from a solution of pure lead acetate with hydrogen sulphide, and when dry, kept for a considerable time at 100 and weighed occasionally. The following numbers represent the results of the several weighings: L 0-8154. II. 0-8164. III. 0-8313. IV. 0-8460. V. 0-864. 49. DEPORTMENT OF METALLIC MERCURY AT THE COMMON TEMPERATURE AND UPON EBULLITION WITH WATER (to 84, a). To ascertain in what manner loss of metallic mercury occurs upon drying, and likewise upon boiling with water, and to determine which is the best method of drying, I made the following experiments : I treated 6-4418 grm. of perfectly pure mercury in a watch-glass, with distilled water, removed the water again as far as practicable (by decanta- tion and finally by means of blotting-paper), and weighed. I now had 6-4412 grm. After several hours' exposure to the air, the mercury was reduced to 6 441 1. I placed these 6 441 1 grm. under a bell-jar over sulphuric acid, the temperature being about 17. After the lapse of twenty-four hours the weight had not altered in the least. I introduced the 6-4411 grm. mer- cury into a flask, treated it with a copious quantity of distilled water, and boiled for fifteen minutes violently. I then placed the mercury again upon the watch-glass, dried it most carefully with blotting-paper, and weighed. The weight was now 6 4402 grm. Finding that a trace of mercury had adhered to the paper, I repeated the same experiment with the 6 4402 grm. After fifteen minutes' boiling with water, the mercury had again lost 0004 grm. The remaining 6-4398 grm. were exposed to the air for six days (in summer, during very hot weather), after which they were found to have lost only 0-0005 grm. 49. a. DEPORTMENT OF MERCURIC SULPHIDE WITH SOLUTION OF POTASSA, AMMONIUM SULPHIDE, ETC. (to 84, c). a. If recently precipitated pure mercuric sulphide is boiled with pure solution of potassa, not a trace of it dissolves in that fluid; hydrochloric acid produces no precipitate, nor even the least coloration, in the filtrate. 6. If mercuric sulphide is boiled with solution of potassa, with addition of some hydrogen-sulphide water, ammonium sulphide, or sulphur, com- plete solution is effected. c. If freshly precipitated mercuric sulphide is digested in the cold with yellowish or very yellow ammonium sulphide, slight but distinctly per- ceptible traces are dissolved, while in the case of hot digestion scarcely any traces of mercury can be detected in the solution.* d. Thoroughly washed mercuric sulphide, moistened with water, suffers * Comp. my experiments in the Zeitschrift f. Anal. Chem., m, 140. 1002 EXERCISES FOR PRACTICE. no alteration upon exposure to the air; at least, the fluid which I obtained by washing mercuric sulphide which had been thus exposed for twenty-four hours, did not manifest acid reaction, nor did it contain mercury or sulphuric acid. 50. DEPORTMENT OF CUPRIC OXIDE UPON IGNITION (to 85, 6). Pure cupric oxide (prepared from cupric nitrate) was ignited in a platinum crucible, then cooled under a bell-jar over sulphuric acid, and finally weighed. The weight was 3 542 grm. The oxide was then most intensely ignited for five minutes over a BERZELIUS' lamp, and weighed as before, when the weight was found unaltered ; the oxide was then once more ignited for five minutes, but with the same result. 51. DEPORTMENT OF THE CUPRIC OXIDE IN AIR (to 85, 6). A platinum crucible containing 4 3921 grm. of gently ignited cupric oxide (prepared from the nitrate) stood for ten minutes, covered with the lid, in a warm room (in winter) ; the weight of the oxide was found to have increased to 4 3939 grm. The oxide was then intensely ignited over a spirit-lamp; after ten min- utes standing in the covered crucible, the weight had not perceptibly in- creased ; after twenty-four hours' it had increased by 0036 grm. 52. DEPORTMENT OF BISMUTH SULPHIDE UPON DRYING AT 100 (to 86, g). 4558 grm. of bismuth sulphide prepared in the wet way were placed in the desiccator on a watch-glass, and allowed to stand at the common tem- perature. After three hours the weight was 4270, after six hours 4258, after two days the same. 0-3602 grm. of the bismuth sulphide so dried was put into a water-bath, in fifteen minutes it weighed 3596, half an hour afterwards 3599, in half an hour more 0-3603, in two hours 0-3626. In a second experiment the drying was kept up for four days, and a continual increase of weight was observed. 5081 grm. of bismuth sulphide dried in the desiccator was heated in a boat in a stream of carbonic acid. After gentle ignition the weight was 0-5002, after repeated heating 0-4992. The bismuth sulphide was visibly volatilized on ignition in the current of carbonic acid. 53. DEPORTMENT OF CADMIUM SULPHIDE WITH AMMONIA, ETC. (to 87, c). Recently precipitated pure cadmium sulphide was diffused through water, and the following experiments were made with the mixture: a. A portion was digested cold with ammonia in excess, and filtered. The filtrate remained perfectly clear upon addition of hydrochloric acid. b. Another portion was digested hot with excess of ammonia, and filtered. This filtrate likewise remained perfectly clear upon addition of hydrochloric aeid. c. Another portion was digested for some time with solution of potassium ANALYTICAL EXPERIMENTS. 1003 cyanide, and filtered. This filtrate also remained perfectly clear upon addi- tion of hydrochloric acid. d. Another portion was digested with ammonium hydrosulphide, and filtered. The turbidity which hydrochloric acid imparted to this filtrate was pure white. (A remark made by WACKENRODER, in BUCHNER'S Repertor. d. Pharm., XL vi, 226, induced me to make these experiments.) 54. DEPORTMENT OF PRECIPITATED ANTIMONOUS SULPHIDE ON DRYING (to 90, a). 0-4457 grm. of the substance dried at 100 lost, when heated to blacken- ing in a stream of carbonic acid, 0-0011 water. 2899 grm. of pure precipitated antimonous sulphide dried in the desic- cator lost, when dried at 100, 0-0007. 0- 1932 grm. of the substance dried at 100 gave up 0-0012, when heated to blackening in a stream of carbonic acid, and after stronger heating, during which fumes of antimony sulphide began to escape, the total loss amounted to 0022 grm. 0-1670 grm. of the substance dried at 100 lost 0-0005 grm. on being heated to blackening in a stream of carbonic acid. 55. DETERMINATION OF AMMONIA, as in 99, 3. The accuracy of this method of estimating ammonia is now so well estab- lished that any observations on the subject are rendered unnecessary. 55, a. AMOUNT OF WATER IN HYDRATED SILICA (to 93, 9). (Experiments made by my assistant, Mr, LIPPERT.) A dilute solution of soluble glass was slowly dropped into hydrochloric acid, so long as the precipitate continued to dissolve rapidly, then the clear fluid was heated in the water-bath, till it set to a transparent jelly. This jelly was dried so far as possible with blotting-paper, diffused in water, and washed by decantation till the fluid altogether ceased to give the chlorine reaction. It was then transferred to a filter, and the latter spread on blotting- paper and exposed till a crumbly mass was left from the spontaneous evapo- ration of water. One half (I) was dried for eight weeks in the desiccator over sulphuric acid, with occasional trituration, the other half (II) was dried under similar circumstances, but in a vacuum. Both were transferred to closed tubes and these were kept in the desiccator. The weighing of the substance dried at 100 was effected between watch- glasses. For the purpose of igniting the residue, it was allowed to satiate itself with aqueous vapor by exposure to the air, otherwise a considerable quantity of the substance would have been lost, then water was dropped upon it in the watch-glass, then it was rinsed into a platinum crucible, dried in a water-bath, and ignited, at first cautiously, towards the end intensely. 1004 EXERCISES FOR PRACTICE. The substance I contained Expt. 1. Expt. 2. Water, escaping at or below 100 4 19 ) 2 above 100 4-76 J Silica.. 91-05 90-72 100-00 100-00 Consequently the hydrate dried at 100 consists of 4 97 water and 95 03 silica. In the substance dried in the desiccator the oxygen of the total water : the oxygen of the silica (SiO 2 ), according to the first experiment : : 1 : 6-1, accord- ing to the second experiment : : 1 : 5 86. And in the substance dried at 100 the oxygen of the water : the oxygen of the silica : : 1 : 11 5. The substance II contained Expt. 1. Expt. 2. Expt. 3. Water, escaping at or below 100. . 4-75 4-71) at above 100. ... 5-26 5 21 ) Silica.. 89-99 90-08 90-05 100-00 100-00 100-00 Consequently the hydrate dried at 100 consists on the average of 5-49 water and 94 51 silica. In the substance dried in a vacuum over sulphuric acid the oxygen of the total water : the oxygen of the silica on an average:: 1 : 5-41. And in the substance dried at 100 the oxygen of the water : the oxygen of the silica:: 1:10-43. 56. DETERMINATION OF BARIUM BY PRECIPITATION WITH AMMONIUM CARBONATE (to 101, 2, a). 0-7553 grm. pure ignited barium chloride precipitated after 101, 2, a, gave 7142 BaCO 3 , which corresponds to 554719 BaO = 73-44 per cent. (100 parts of BaCl 2 ought to have given 73 59 parts). The result accordingly was 99-79 instead of 100. 57. DETERMINATION OF BARIUM IN ORGANIC SALTS (to 101, 2, 6). 0-686 grm. barium racemate (Ba 2 C 8 H 8 O 12 +5Aq.) treated according to 101, 2, b, gave 0-408 barium carbonate = 0-3169 BaO = 46 -20 per cent, (calculated 46-38 per cent.); i.e., 99-61 instead of 100. 58. DETERMINATION OF STRONTIUM AS STRONTIUM SULPHATE (to 102, 1, a). a. An aqueous solution of 1 2398 grm. SrCl 2 was precipitated with sul- phuric acid in excess, and the precipitated strontium sulphate washed with water. It weighed 1-4113, which corresponds to 0-795408 SrO=64-15 per cent, (calculated 65-38 per cent.) ; i.e., 98-12 instead of 100. b. 1 1510 grm. SrCo 3 was dissolved in excess of hydrochloric acid, the solu- tion diluted, and then precipitated with sulphuric acid ; the precipitated SrSO 4 was washed with water; it weighed 1-4024 = 0-79039 SrO = 68-68 per cent, (calculated 70-07 per cent.) ; i.e., 98-02 instead of 100. ANALYTICAL EXPERIMENTS 1005 59. DETERMINATION OF STRONTIUM AS SULPHATE, WITH CORRECTION (to 102, 1, a). The filtrate obtained in No. 58, b, weighed 190-84 grm. According to experiment No. 22, 11862 parts of water containing sulphuric acid dissolve 1 part of strontium sulphate; therefore, 190-84 grm. dissolve 0-0161. The washings weighed 63-61 grm. According to experiment No. 21, 6895 parts of water dissolve 1 part of SrSO 4 ; therefore, 63-61 grm. dissolve 0.0161 grm. Adding 0-0161 and 0-0092 to the 1-4024 actually obtained, we find the total amount = 1 4277 grm., which corresponds to 0-80465 SrO = 69 91 per cent, in SrCO 3 (calculated 70-07 per cent.) ; i.e., 99-77 instead of 100. 60. DETERMINATION OF STRONTIUM AS STRONTIUM CARBONATE (to 102, 2). 1-3104 grm. strontium chloride, precipitated according to 102, 2, gave 1 - 2204 SrCO 3 , containing 8551831 SrO =65-26 per cent, (calculated 65 38) ; i.e., 99-82 instead of 100. 61. DETERMINATION OF CALCIUM AS CALCIUM SULPHATE BY PRECIPITATION (to 103, 1, a). In the four following experiments, Nos. 61 to 64, pure air-dried calcium carbonate was used, in a portion of which the amount of anhydrous car- bonate had been determined by very cautious heating. 0-7647 grm. left 0-7581 grm., which weight remained unaltered upon further (extremely gentle) ignition; the air-dried carbonate contained accordingly 55-516 per cent, of lime. 1-186 gnn. of "the air-dried calcium carbonate" was dissolved in hydro- chloric acid, and the solution precipitated with sulphuric acid and alcohol, after 103, 1, a. Obtained 1 5949 grm. CaSO 4 , containing 65598 CaO, i.e., 55-31 per cent, (calculated 55-51), which gives 99-64 instead of 100. 62. DETERMINATION OF CALCIUM AS CaCO,,, BY PRECIPITATION WITH AMMONIUM CARBONATE AND WASHING WITH PURE WATER (to 103, 2, a). A hydrochloric acid solution of 1-1437 grm. of "the air-dried calcium car- bonate" gave upon precipitation as directed, 1 1243 grm. anhydrous calcium carbonate, corresponding to 629608 CaO = 55-05 per cent, (calculated 55 51 per cent), which gives 99-17 instead of 100. 63 DETERMINATION OF CALCIUM AS CaCO 3 , BY PRECIPITATION WITH AMMONIUM OXALATE FROM ALKALINE SOLUTION (to 103, 2, 6, a). 1 1734 grm. of "the air-dried calcium carbonate" dissolved in hydrochloric acid, and treated as directed 103, 2, 6, a, gave 1 1632 grm. CaCO 3 (reaction not alkaline), containing 651392 of CaO = 55 513 per cent, calculated 55 516 per cent.), which gives 99-99 instead of 100. 1006 EXERCISES FOR PRACTICE. 63, a. DETERMINATION OF CALCIUM AS OXALATE (to 103, 2, 6, d). 0-857 grm. of "the air-dried calcium carbonate" were dissolved in hydro- chloric acid; the solution was precipitated with ammonium oxalate and ammonia, the precipitate washed, and then dried at 100, until the weight remained constant. The precipitate (CaC 2 O 4 +H 2 O) weighed 1-2461 grm. containing 0-477879 CaO = 55-76 per cent, (calculated 55-516 per cent), which gives 100-45 instead of 100. 64. DETERMINATION OF CALCIUM AS CaCO 3 BY PRECIPITATION AS CALCIUM OXALATE FROM ACID SOLUTION (to 103, 2, 6, /?). 0-857 grm. of "the air-dried calcium carbonate" dissolved in hydrochloric acid and precipitated from this solution according to the directions of 103, 2, 6, /?, gave 0-8476 calcium carbonate (which did not manifest alkaline reaction, and the weight of which did not vary in the least upon evaporation with ammonium carbonate), containing 0-474656 CaO = 55-39 per cent, (calculated 55-51), which gives 99-78 instead of 100. 64, a. DETERMINATION OF MAGNESIUM AS Mg 2 P 2 O 7 (to 104, 2). a. A solution of 1 - 0587 grm. pure anhydrous magnesium sulphate in water, precipitated according to 104, 2, gave 0-9834 magnesium pyro- phosphate, containing 0-35438 MgO = 33-476 per cent, (calculated 33-33 per cent.), which gives lO'0-43 instead of 100. 6. 0-9672 MgSO 4 gave 0-8974 Mg 2 P 2 O 7 = 33-43 per cent, of MgO (calcu- lated 33-33), which gives 100-30 instead of 100. 65. VOLUMETRIC DETERMINATION OF CALCIUM PRECIPITATED AS OXALATE (to 103, 3, a and 6). Six portions, of 10 c.c. e,ach, were taken of a solution of pure calcium chloride, in 2 portions the calcium was determined in the gravimetric way (by precipitation with ammonium oxalate, and weighing as CaCO 3 ) ; in two by the alkalimetric method ( 103, 3, a), and in two by precipitation with ammonium oxalate, and estimation of the oxalic acid in the precipitate by solution of potassium permanganate. The following were the results ob- tained : a. In the gravimetric 6. By the alkalimetric c. By solution of potas- way. method. sium permanganate. 0-5617CaCO 3 0-5614 0-5613 0-5620 " 0-5620 0-5620 66. PRECIPITATION OF ZINC ACETATE BY HYDROGEN SULPHIDE (to 108, 6). a. A solution of pure zinc acetate was treated with the gas in excess, allowed to stand at rest for some time, and then filtered. The filtrate was mixed with ammonia. It remained perfectly clear at first, and even after long standing a few hardly visible flocks only had separated. 6. A solution of zinc acetate to which a tolerably large amount of acetic ANALYTICAL EXPERIMENTS. 1007 acid had been added previously to the precipitation with hydrogen sulphide, showed exactly the same deportment. 67. DETERMINATION OF IRON AS SULPHIDE (to 113, 2). 10 c.c. of a pure solution of ferric chloride was precipitated with ammonia; obtained 1453 Fe,O 3 = - 10171 Fe. 10 c.c. was precipitated with ammonia and ammonium sulphide, and treated after 113, 2, obtained 0-1596 FeS = 0-10157 Fe. 10 c.c. again yielded 0-1605 FeS = 0-1021 Fe. 68. DETERMINATION OF LEAD AS CHROMATE (to 116, 4). 1-0083 grm. pure lead nitrate were treated according to 116, 4. The precipitate was collected on a weighed filter, and dried at 100, obtained 0-9871 grm. =0-67833 PbO. This gives 67-3 per cent. Calculation 67-4. 0-9814 lead nitrate again yielded 0-9625 chromate = 67 - 4 per cent. 68, a. DETERMINATION OF MERCURY IN THE METALLIC STATE, IN THE WET WAY, BY MEANS OF STANNOUS CHLORIDE (to 118, 1, 6). 2-01 grm. mercuric chloride ^gave 1-465 grm. metallic mercury = 72-88 per cent, (calculated 73-83 per cent.), which gives 98-71 instead of 100 (SCHAFFNER). The loss is not inherent in the method, i.e., it does not arise from mercury evaporating during the ebullition and desiccation, but its origin lies in the fact that one usually does not allow sufficient time for the mercury to settle quite completely, and in general is not careful enough in decanting, and drying with paper, etc. 69. DETERMINATION OF COPPER BY PRECIPITATION WITH ZINC IN A PLATINUM DISH (to 119, 2, a). 30-882 grm. pure cupric sulphate were dissolved in water to 250 c.c.; 10 c.c. of the solution contained accordingly 0-31387 grm. metallic copper. a. 10 c.c. precipitated with zinc in a platinum dish, gave 0-3140 = 100-06 per cent. 6. In a second experiment 10 c.c. gave 0-3138 = 100 per cent. 70. DEPORTMENT OF COPPER PRECIPITATED BY ZINC, WHEN IGNITED IN HYDROGEN (Vol. I, p. 374, foot-note). A dilute solution of copper sulphate, acidified with hydrochloric acid, was precipitated with zinc in a platinum crucible, and the precipitate washed with water, then with alcohol, and dried at 100; 0-7961 grm. of this was ignited for a quarter of an hour in hydrogen. It then weighed 7952 grm. 71. DETERMINATION OF COPPER AS CUPROUS SULPHOCYANATE (to 119, 3, 6). 0-5965 grm. of pure cupric sulphate was dissolved in a little water, and after addition of an excess of sulphurous acid, precipitated with potassium sulphocyanate. The well-washed precipitate, dried at 100, weighed 0-2893, 1008 EXERCISES FOR PRACTICE. corresponding to 0-1892 CuO = 31-72 per cent. As cupric sulphate contains 31-83 per cent., this gives 99-66 instead of 100. 72. DETERMINATION OF COPPER BY DE HAEN'S METHOD (to 119, 4, a). Four 10 c.c.'s of a solution of cupric sulphate, each 10 c.c. containing 0-0254 grm. Cu, were severally mixed with potassium iodide, then with 50 c.c. of a solution of sulphurous acid (50 c.c. corresponding to 12-94 c.c. iodine solution). After addition of starch paste, iodine solution was added until the fluid appeared blue. This required, In a, 4-09 6,3-95 c, 4-06 d, 3-95 As 100 c.c. of iodine solution contained 0-58043 grm. iodine, this gives For a, 0-0256 Cu instead of 0-0254 " 6,0-0260 " " " " c, 0-0257 " " " " " d, 0-0260 " " " " Another experiment, made with 100 c.c. of the same solution of cupric sulphate, gave 0-2606 instead of 0-254 of copper. Ammonium nitrate having been added to 10 c.c. of the solution of cupric sulphate, then some dilute hydrochloric acid, 3-4 and 3-5 c.c. of iodine solution were required instead of 4 c.c. a proof that considerably more iodine had separated than corresponded to the copper. 73. ACTION OF POTASSIUM-CYANIDE SOLUTION ON AMMONIACAL SOLUTION OF CUPRIC OXIDE (to 119, 4, 6). a. Each of three 10 c.c. solutions of copper sulphate, containing 0-1 grm. of copper sulphate, was mixed with increasing quantities of solution of ammonia, and sufficient water to equalize the degree of concentration in the three portions; solution of potassium cyanide was then added, drop by drop, until the blue color had disappeared. This required the following quantities : Copper-sulphate Solution. Ammonia. Water. Potassium-cyanide Solution. 10 c.c. 4 c.c. 12 c.c. 6-7 c.c. 10 c.c. 8 c.c. 8 c.c. 6-85 c.c. 10 c.c. 16 c.c. c.c. 7-1 c.c. Neutral ammonium salts also exert some influence, as shown by the fol- lowing experiments, which were made the next day with the same solutions : Copper-sulphate Ammonia Wafoi Potassium-cyanide Solution. Solution. 6-7 c.c. 0) 7-4 c.c. 7-0 c.c. 7-3 c.c. 10 c.c. 2 c.c. 14 c.c. 10 c.c. 2 c.c. 14 c.c. Solution NH 4 C1 ( 10 c.c. 6 c.c. ( 10 c.c. H 2 O 1 4 c.c. HSO< (1 : 5) 10 c.c. 2 c.c ( 8 c.c. NHF. Per Cent. Alco- hol by Vol. Per Cent. Alco- hol &. Specific Gravity atirr. Per Cent. Alco- hol by Vol. Per Cent. Alco- hol ,&. 0.95185 40-0033-35 0.94786 42-50 35-58 0.94364 45-00 37-84 0.93916 47-50 40-13 177 i .05 .39 778 .55 .6? 355 .05 .89 906 .18 169 .10 .44 770 .60 .67 346 .10 .93 898 leo .22 161 .15 .48 761 .65 .72 338 .15 .98 888 .65 .27 154 .20 .53 753 .70 .76 329 .20 38.02 879 .70 .32 146 . 25 .57 745 .75 .81 320 .25 .07 870 .75 .37 138 .30 .61 737 .80 .85 311 .30 .12 861 .80 .41 130 .35 .66 ! 729 .85 .90 302 .35 .16 852 .85 .46 122 .40 .70 720 .90 .94 294 .40 .21 842 .90 .51 114 .45 .75 712 .95 .99 285 .45 .25 833 .95 .55 .95107 40-5033-79 099 .55 .84 94704 696 43-00 .05 36 :81 '"IT 6 45 -M 38 :1 .93824 815 48 :8i 40.60 .65 09i; .60 .88 687 .10 .12 258 .60 .39 805 .10 .69 083 i .65 .93 679 .15 .17 250 .65 .44 796 .15 .74 075 .70 .97 670 .20 .21 241 .70 .48 786 .20 .78 067 .7534.021 662 .25 .23 232 .75 .53 777 .25 .83 059 .80 .06 654 .30 .30 223 .80 .57 768 .30 .88 052 .85 .11 645 .35 .35 214 .85 .62 758 .35 .92 044 .90 .15 637 .40 .39 206 .90 .66 749 .40 .97 036 .95 .20 628 .45 .44 197 .95 .71 739 .45 41.01 .95028 020 41 :8i 34-24 .94620 43-50 .55 : ! 46.00 .05 38 :ia .9373 2 48 :!E 41.0, 012 .10 .33 603 .60 .57 170 .10 .84 711 .60 .15 004 .15 .37 595 .65 .62 161 .15 .89 702 .65 .20 .94996 .20 .42 586 .70 .66 152 .20 .93 692 .70 .24 988 .25 .46 578 .75 .71 143 .25 .98 683 .75 .29 980 .30 .50 570 .80 .75 134 .30 39.03 679 .80 .34 972 .35 .55 561 .85 .80 125 .35 .07 664 .85 .38 964 .40 .59 553 .90 .84 116 .40 .12 655 .90 .43 956 .45 .64 544 .95 .89 107 .45 .16 645 .95 .47 .94948 940 41 :ii 3t :tt .94536 U :!S 36.9| .94098 089 46 :i? 39 -i 3636 49 :8i 41 % 932 .60 .77 519 .10 37.02 080 .60 .30 617 .10 .61 924 .65 .82 510 .15 .07 071 .65 .35 607 .15 .66 916 .70 .86 502 .20 .11 062 .70 .39 598 .20 .71 908 .75 .91 493 .25 .16 053 .75 .44 588 .25 .76 900 .80 .95 484 .30 .21 044 .80 .49 578 .30 .80 892 .8535.00 476 .35 .25 035 .85 .53 569 .35 .85 884 .90 .04 467 .40 .30 026 .90 .58 559 .40 .90 876 .95 .09 459 .45 .34 017 .95 .62 550 .45 .94 -94868 860 *:S 35 :il 94450 441 44 - 50 .55 37.35 94008 . 93999 47 :8 39-67 -93540 530 49-50 41-99 .55 42.04 852 .10 .22 433 .60 At 990 .10 '.76 521 .60 .08 843 .15 .27 424 .65 .53 980 .15 .81 511 .65 .13 835 .20 .31 416 .70 .57 971 20 .85 502 .70 .18 827 .25 .36 407 .75 .62 962 .25 .90 492 .75 .23 819 .30 .40 398 .80 .66 953 .30 .95 482 .80 .27 811 .35 .45 390 .85 .71 944 .35 .99 473 .85 .32 802 .40 .49 381 .90 .76 934 .40 40.04 463 .90 .37 794 .45 .54 373 .95 .80 925 .45 .08 454 .95 .41 1078 APPENDIX I. 3. DETERMINATION OF EXTRACT. (a) IN DISTILLED LIQUORS, DRY WINES, BEERS, ALES, ETC. (1) Direct Method. Fifty c.c. of the sample are weighed in a flat platinum dish about 85 mm. in diameter and capable of holding about 75 c.c. and evaporated on the water-bath to a sirupy consistence. The residue is heated for two and a half hours in a drying oven at the temperature of boiling water and weighed. (6) IN SWEET WINES. Ten c.c. of the liquor are weighed and diluted to 100 c.c. with water. Fifty c.c. of this solution are evaporated as described under (1). 4. DETERMINATION OF TOTAL ACIDITY. Expel any carbon dioxide that is present by continued shaking. Trans- fer 10 c.c. of the sample to a beaker and, in the case of white wines, add about 10 drops of a neutral litmus solution. Add decinormal sodium-hydroxide solution until the red color changes to violet. Continue adding a few drops at a time until a drop of the mixture, placed on delicate red litmus paper, shows an alkaline reaction. The result is expressed in terms of tartaric acid. One c.c. of decinormal sodium-hydroxide solution = 0075 grm. tartaric acid. 5. DETERMINATION OF VOLATILE ACIDS. Fifty c.c. of wine, to which a little tannin has been added to prevent foaming, are distilled in a current of steam. The flask is heated until the liquid boils, when the lamp under it is turned down, and the steam passed through until 200 c.c. have been collected in the receiver. The distillate is titrated with decinormal sodium-hydroxide solution and the result ex- pressed as acetic acid. One c.c. of decinormal sodium-hydroxide solution = 006 grm. acetic acid. 6. DETERMINATION OF GLYCERIN. (a) IN DRY WINES. One hundred c.c. of wine are evaporated in a porcelain dish to about 10 c.c., a little quartz sand and milk-of-lime added, and the evaporation carried almost to dryness. The residue is mixed with 50 c.c. of 90-per cent, alcohol, using a glass pestle or spatula to break up any solid particles, heated to boiling on the water-bath, allowed to settle, and the liquid filtered into a small flask. The residue is repeatedly extracted in a similar manner with small portions of boiling alcohol until the filtrate in the flask amounts to about 150 c.c. A little quartz sand is then added to it, the flask connected \\ith a condenser, and the alcohol slowly distilled until about 10 c.c. remain. The evaporation is then continued in the water-bath until the residue becomes simpy. It is cooled and dissolved in 10 c.c. of absolute alcohol. The solution mav be facilitated by gentle heating on the water-bath. Fifteen c.c. of anhvdrous ether are added and the flasks stoppered and allowed to stand until the precipitate has collected on the sides and bottom of the flask. OFFICIAL METHODS OF ANALYSIS. 1079 The clear liquid is decanted into a tared weighing bottle, the precipitate repeatedly washed with a few cubic centimeters of a mixture of 1 part abso- lute alcohol and 1 5 parts anhydrous ether and the washings added to the solution. The ether-alcohol is evaporated on the water-bath and the residue dried one hour in a water-oven, weighed, the amount of ash determined, and its weight deducted from that of the weighed residue. (6) IN SWEET WIXES. One hundred c.c. of wine are evaporated on the water-bath to a sirupy .on.-sistence, a little quartz sand being added to render subsequent extraction easier. The residue is repeatedly extracted with absolute alcohol until the united extracts amount to from 100 to 150 c.c. The extract is collected in a flask, and for every part of alcohol 1-5 parts of ether are added, the liquor well shaken, and allowed to stand until it becomes clear. The supernatant liquid is decanted into a beaker, and the precipitate washed with a few cubic centimeters of a mixture of 1 part alcohol and 1 5 parts ether. The united liquids are distilled, the evaporation being finished on the water-bath, the residue is dissolved in water, transferred to a porcelain dish, and treated as under (a). It is necessary to test the glycerin from sweet wines for sugar, and if any be present, it must be estimated by methods already described and its weight subtracted from that of the glycerin. 7. DETERMINATION OF REDUCING SUGARS. The reducing sugars are estimated as dextrose, and may be determined by any of the methods given for the estimation of dextrose. S. POLARIZATION. All results are to be stated as the polarization of the undiluted wine. The VEXTZKB scale saccharimeter is to be used, and the results expressed in terms of the sugar scale of this instrument. If any other instrument be used, or if it be desirable to convert to angular rotation, the folio wing factors may be employed: 1 VENTZKE = 3468 angular rotation D. 1 angular rotation D. =2-8835 VENTZKE. 1 VENTZKE = 2 - 6048 Wild (sugar scale) . 1 Wild (sugar scale) = 3840 VENTZKE. 1 Wild (sugar scale) =0- 1331 angular rotation D. 1 angular rotation D. =0-7511 Wild (sugar scale). 1 LAURENT (sugar scale) =0-2167 angular rotation D. 1 angular rotation D. =4-6154 LAURENT (sugar scale). (a) IN WHITE WINES. Sixty c.c. of wine are clarified with 3 c.c. of lead-subacetate solution and filtered after adding 3 c.c. of water. Thirty-three c.c. of the filtrate are treated with 3 c.c. of a half-saturated solution of sodium carbonate, filtered and polarized. This gives a dilution of 10 to 11, which must be considered hi 1080 APPENDIX I. the calculation, and the polariscope reading must accordingly be increased one-fifth. (6) IN RED WINES. Sixty c.c. of wine are clarified with 6 c.c. of lead-subacetate solution and filtered. To 33 c.c. of the filtrate 3 c.c. of a saturated solution of sodium carbonate are added, filtered, and the filtrate polarized. The dilution in this case is 5 to 6, and the polariscope reading must accordingly be increased one-fifth. (c) IN SWEET WINES. (1) Before Inversion. One hundred c.c. are clarified with 2 c.c. of lead-subacetate solution, and filtered after the addition of 8 c.c. of water. One-half c.c. of a saturated solution of sodium carbonate and 4-5 c.c. of water are added to 55 c.c. of the filtrate, and the liquid mixed, filtered, and polarized. The polariscope reading is multiplied by 1-2. (2) After Inversion. Thirty-three c.c of the filtrate from the lead subacetate in (1) are placed in a flask with 3 c.c. strong hydrochloric acid. After mixing well, the flask is placed in water and heated until a thermometer, placed in the flask with the bulb as near the center of the liquid as possible, marks 68, consuming about fifteen minutes in the heating It is then removed, cooled quickly to room temperature, filtered, and polarized, the temperature being noted. The polariscope reading is multiplied by 1-2. (3) After Fermentation. Fifty c.c. of wine, which have been dealcoholized and made up to the original volume with water, are mixed in a small flask with well-washed beer yeast and kept at 30 until fermentation has ceased, which requires from two to three days. The liquid is then washed into a 100 c.c. flask, a few droDS of a solution of acid mercuric nitrate and then lead-subacetate solution, followed by sodium carbonate, added. The flask is filled to the mark with water, shaken, and the solution filtered and polarized (d) APPLICATION OF ANALYTICAL METHODS, (1) The Wine shows no Rotation. This may be due to the absence of any rotatory body, to the simulta- neous presence of the dextrorotatory non-fermentable constituents of com- mercial dextrose and levorotatory sugar, or to the simultaneous presence of dextrorotatory cane-sugar and levorotatory invert-sugar. (a) THE WINE is INVERTED. A levorotation shows that the sample contains cane-sugar. (6) THE WINE is FERMENTED. A dextrorotation shows that botli levo- rotatory sugar and the unfermentable constituents of commercial dextrose are present. OFFICIAL METHODS OF ANALYSIS. 1081 If no change take place in either (a) or (6) in the rotation, it proves the absence of unfermented cane sugar, the unfermen table constituents of com- mercial dextrose, and of levorotatory sugar. (2) The Wine Rotates to the Right. This may be caused by unfermented cane sugar, the unfennentable con- stituents of commercial dextrose, or both, (a) THE WINE is INVERTED. (a t ) It rotates to the left after inversion. Unfermented cane sugar is present. (a 2 ) It rotates more than 2-30 to the right. The unfennentable constituents of commercial dextrose are present (a 3 ) It rotates less than 2 30 and more than 9 to the right. It is in this case treated as follows : Two hundred and ten c.c. of the wine are evaporated in a porce- lain dish to a thin sirup with a few drops of a 20-per cent, solution of potassium acetate. To the residue 200 c.c. of 90-per cent, alcohol are added with constant stirring. The alcoholic solution is filtered into a flask, and the alcohol removed by distillation until about 5 c.c. remain. The residue is mixed with washed bone black, filtered into a gradu- ated cylinder, and washed until the filtrate amounts to 30 c.c. When the filtrate shows a dextrorotation of more than 1-5, it indicates the presence of the unfennentable constituents of commercial dextrose (3) The Wine Rotates to the Left. It contains unfermented levorotatory sugar, derived either from the must or from the inversion of added cane sugar. It may, however, also con- tain unfermented cane sugar and the unfennentable constituents of com- mercial dextrose. (a) The wine is fermented according to 8 (c), (3). (aj It polarizes 3 after fermentation. It contains only levo- rotatory sugar. M It rotates to the right. It contains both levorotatory sugar and the unfennentable constituents of commercial dextrose. (b) The wine is inverted according to 8 (c), (3). (6,> It is more strongly levorotatory after inversion. It contains both levorotatory sugar and unfermented cane sugar. 9. DETERMINATION OF TANNIN AND COLORING MATTER. (a) PREPARATION OF REAGENTS. DeTinarmal Solution of Oxalic Acid. 10 c.c. =0-04157 grm. tannin. Potassium --permanganate Solution. I 333 grm. of potassium perman- ganate are dissolved in 1 litre of water and the solution standardized by means of the decinormal oxalic-acid solution. Tndiqo Solution. 6 grm. of sodium sulphindigotate are dissolved in 500 c.c. of water with the aid of heat, cooled. 50 c.c. of concentrated sulphuric acid added, and the solution made up to 1 litre and filtered. 1082 APPENDIX I. Purified Bone-black. Finely pulverized bone-black is extracted with hydrochloric acid and washed with distilled water until the acid is entirely removed. The bone black is kept covered with water. (6) LETERMINATION. (1) One hundred c.c. of wine are dealcoholized by evaporation, and the original volume restored with water. Ten c.c. are measured into a porce- lain casserole having a capacity of about a litre, and 750 c.c. of water and 20 c.c. of the indigo solution added, the latter being measured from a burette. The potassium -permanganate solution is added, a cubic centimeter at a time, until the blue color changes to green , then a few drops at a time until the liquid becomes golden yellow. Designate by a the number of cubic centimeters of permanganate solution used. (2) Ten c.c. of the dealcoholized wine, obtained as in (1), are treated with bone-black for fifteen minutes, filtered, and the bone-black washed carefully. The filtrate is diluted with 750 c.c. of water, 20 c.c. of indigo solution added, and the titration carried out as in (1). Designate burette reading by b. Then a 6=c=the number of cubic centimeters of the potassium per- manganate solution required for the oxidation of the tannin and coloring matter in 10 c.c. of wine. 10. DETERMINATION OF POTASSIUM BITARTRATE. The determination of potassium bitartrate is necessary when an esti- mation of the tartaric acid is desired. Fifty c.c. of wine are placed in a porcelain dish and evaporated to a sirupy consistence, a little quartz sand being added to render subsequent extrac- tion easier. After cooling, 70 c.c. of 96-per cent, alcohol are added with constant stirring. After standing for twelve hours at as low a tempera- ture as practicable, the solution is filtered and the precipitate washed with alcohol until the filtrate is no longer acid. The alcoholic filtrate is preserved for the estimation of the tartaric acid. The filter and precipitate are returned to the porcelain dish and repeatedly treated with hot water, each extraction being filtered into a flask or beaker until the washings are neutral. The combined aqueous filtrates and washings are titrated with decinormal sodium- hydroxide solution. One c.c. decinormal sodium -hydroxide solution =0-0188 grm. potassium bitartrate. 11. DETERMINATION OF TARTARIC ACID. (a) IN THE ALCOHOLIC FILTRATE FROM THE POTASSIUM BITARTRATE. The filtrate is made up to a definite volume with water and divided into two equal portions. One portion is exactly neutralized with decinormal sodium-hydroxide solution, the other portion added, the alcohol evaporated, the residue washed into a porcelain dish, and treated as under 10. One c.c. decinormal sodium -hydroxide solution =0-0075 grm. tartaric acid. OFFICIAL METHODS OF ANALYSIS. 1083 As, however, only half of the free tartaric acid is determined by this method One c.c. decinormal sodium hydroxide =0-015 gnn. of tartaric acid, (6) MODIFIED BERTHELOT-FLEURY METHOD. Ten c.c. of wine are neutralized with potassium-hydroxide solution and mixed in a graduated cylinder with 40 c.c. of the same sample. To one- fifth of the volume, corresponding to 10 c.c. of wine, 50 c.c. of a mixture of equal parts of alcohol and ether are added and allowed to stand twenty-four hours. The precipitated potassium bitartrate is separated by filtration, dissolved in water and titrated. The excess of potassium bitartrate over the amount of that constituent present in the wine corresponds to the free tartaric acid. 12. DETERMINATION OF TARTARIC, MALIC, AND SUCCINIC ACIDS. [SCHMIDT and HIEPE'S method.] Two hundred c.c. of wine are evaporated one-half, cooled, and lead-eub- acetate solution added until the reaction is alkaline. The precipitate is separated by filtration and washed with cold water until the filtrate shows only a slight reaction for lead. The precipitate is washed from the filter into a beaker by means of hot water, and treated hot with hydrogen sulphide until all the lead is converted into sulphide. It is then filtered hot and the lead sulphide washed with hot water until the washings are no longer acid. The filtrate and washings are evaporated to 50 c.c. and accurately neutralized with potassium hydroxide. An excess of a saturated solution of calcium acetate is added and the liquid allowed to stand from four to six hours with frequent stirring. It is then filtered and the precipitate washed until the filtrate amounts to exactly 100 c.c. The precipitate of calcium tartrate is converted into calcium oxide by igniting in a platinum crucible. After cooling, from 10 to 15 c.c. of normal hydrochloric acid are added, the solution washed into a beaker, and accurately titrated with normal potassium- hydroxide solution. Every cubic centimeter of normal acid saturated by the calcium oxide is equivalent to 0-075 grm. tartaric acid. To the amount so obtained 0-0286 grm. must be added, representing the tartaric acid held in solution in the filtrate as calcium tartrate. The sum represents the total tartaric acid in the wine. The filtrate from the calcium tartrate is evaporated to about 25 c.c., cooled, and mixed with three times its volume of 96-per cent, alcohol. After standing several hours the precipitate is collected on a weighed filter, dried at 100, and weighed. It represents the calcium salts of malic, succinic, and sul- phuric acids and of the tartaric acid which remained in solution. This pre- cipitate is dissolved in a minimum quantity of hydrochloric acid, filtered, and the filter washed with hot water. Potassium-carbonate solution is added to the hot filtrate and the precipitated calcium carbonate separated by filtra- tion and washed. This filtrate contains the potassium salts of the above- named acids. It is neutralized with acetic acid, evaporated to a small volume, and precipitated hot with barium chloride. The precipitate of barium 1084 APPENDIX I. succinate and sulphate is separated by filtration, washed with hot water, and treated on the filter with dilute hydrochloric acid. The barium sulphate remaining is washed, dried, ignited, and weighed. In the filtrate which con- tains the barium succinate, the barium is precipitated hot with sulphuric acid, washed, dried, ignited, and weighed. Two hundred and twenty-three parts barium sulphate equal 118 parts succinic acid. The succinic and sulphuric acids, as well as the tartaric acid remaining in solution which is equal to 0286, are to be calculated as calcium salts and the result deducted from the total weight of the calcium precipitate. The remainder is the calcium ma- late, of which 172 parts equal 134 parts malic acid. 13. DETECTION OF COLORING MATTER, (a) CAZENEUVE REACTION. Add 0-2 grm. of precipitated mercuric oxide to 10 c.c. of wine, shake for one minute, and filter. Pure wines give filtrates which are colorless or light yellow, while the presence of a more or less red coloration indicates that an aniline color has .been added to the wine. (6) METHOD OP SOSTEGNI AND CARPENTIERI. Evaporate the alcohol from 200 c.c. of wine, add from 2 to 4 c.c. of a 10- per cent, solution of hydrochloric acid, immerse some threads of fat-free wool, and boil for five minutes. Remove the threads, wash them with cold water acidified with hydrochloric acid, then with hot water acidified with hydro- chloric acid, then with pure water, and dissolve the color in a boiling mixture of 50 c.c. of water and 2 c.c. of concentrated ammonia. Replace the threads by new ones, acidify with hydrochloric acid, and boil again for five minutes. In the presence of aniline colors to the amount of 2 mgrm.per litre, the threads are dyed as follows Safranin light rose-red. Vinolin rose-red to violet. Bordeaux red rose-red to violet. Ponceau red rose-red. Fuchsin dirty white. Tropa?olin 00 straw-yellow. Tropseolin 000 light orange. Corallin dirty white. This method is not suitable for the detection of fuchsin or corallin. (c) DETECTION OF FUCHSIN AND ORSEILLE. To 20 c.c. of wine add 10 c.c. of lead-subacetate solution, heat slightly, and mix by shaking. Filter into a test-tube, add 2 c.c. of amyl alcohol, and shake. If the amyl alcohol be colored red, separate it and divide it into two portions. To one portion add hydrochloric acid, to the other ammonia. When the color is due to fuchsin, the amyl alcohol will in both cases be de- colorized; when due to orseille, the ammonia will change the color of the amyl alcohol to purple-violet. OFFICIAL METHODS OF ANALYSIS. 1085 14. DETERMINATION OF ASH. The residue from the direct extract determination is ineinerated at as low a heat as possible. Repeated moistening, drying, and heating to redness is advisable to get rid of all organic substances. 15. DETERMINATION OF POTASH. (a) KAYSER'S METHOD. Dissolve 0.7 grm. of pure sodium hydroxide and 2 grm. of tartaric acid in 100 c.c. of wine, add 150c. c. of 92- to 94-per cent, alcohol, and allow the liquid to stand twenty-four hours. The precipitated potassium bitartrate is col- lected on a small filter and washed with 50-per cent, alcohol until the filtrate amounts to 260 c.c. The precipitate and filter are transferred to the beaker in which the precipitation was made, the precipitate dissolved in hot water, the volume made up to 200 c.c. and 50 c.c. titrated with decinormal sodium- hydroxide solution ; 004 grm. must be added to the final result, this represent- ing the potash which remains in solution as bitartrate. (6) PLATINUM CHLORIDE METHOD. Evaporate 100 c.c. of wine to dryness, incinerate the residue, and de- termine potash as given under methods for ash. 16. DETERMINATION OF SULPHUROUS ACID. One hundred c.c. of wine are distilled in a current of carbon dioxide after the addition of phosphoric acid until about 50 c.c. have passed over. The distillate is collected in accurately standardized iodine solution. When the distillation is finished, the excess of iodine is determined with standard- ized sodium-thiosulphate solution. 17. DETECTION OF SALICYLIC ACID. (a) SPICA'S METHOD. Acidify 100 c.c. of the liquor with sulphuric acid and extract with ether. Evaporate the extract to dry-ness, warm the residue carefully with 1 drop of concentrated nitric acid, and add 2 or 3 drops of ammonia. The presence of salicylic acid in the liquor is indicated by the formation of the yellow color of ammonium picrate, and may be confirmed by dyeing a thread of fat-free wool. (5) BIGELOW'S METHOD. Place 100 c.c. of the wine in a separatory funnel, add 5 c.c. of sulphuric acid (1-3), and extract with a sufficient quantity of a mixture of eight or nine parts of ether to one part of petroleum ether. Throw away the aqueous portion, wash the other once with water, then shake thoroughly with about 50 c.c. of water, to which from 6 to 8 drops of 0-5 per cent, solution of ferric chloride have been added. Discard the aqueous portion, which contains the greater part of the tannin in combination with iron, wash again with water, transfer the ethereal solution to a porcelain dish, and allow to evapo- rate spontaneously. Heat the dish on the steam-bath, take up the residue 1086 APPENDIX I. with 1 or 2 c.c, of cold water, transfer quickly to a test-tube without stirring, and add 1 or 2 drops of 0-5 per cent, solution of ferric chloride. The pres- ence of salicylic acid is indicated by the appearance of a violet-red colora- tion. In the case of red wines a second extraction of the residue with ether mixture is sometimes necessary. This is indicated by the amount of residue left in the dish on the evaporation of the ether. This method cannot be used in the examination of beers and ales. (c) GIRARD'S METHOD. Extract a portion of the acidified liquor with ether as in the preceding methods, evaporate the extract to dryness, and extract the residue with petroleum ether. The residue from the petroleum-ether extract is dissolved in water and treated with a few drops of a very dilute solution of ferric chloride. The presence of salicylic acid is indicated by the appearance of a violet-red coloration. 18. DETECTION OF GUM AND DEXTRIN. Four c.c. of wine are mixed with 10 c.c. of 96-per cent, alcohol. When gum arable or dextrin is present, a lumpy, thick, and stringy precipitate is produced, whereas pure wine becomes at first opalescent and then gives a flocculent precipitate. 19. DETERMINATION OF FUSEL OIL. The apparatus recommended for this determination is BROMWELL'S modification of ROESE'S fusel-oil apparatus. This apparatus consists of a pear-shaped bulb holding about 200 c.c., stoppered at the upper end and sealed at the lower to a graduated stem about 4 mm. in internal diameter. To the lower end of this graduated stem is a sealed bulb of 20 c.c. capacity, the lower end of which bears a stop-cock tube. The apparatus is graduated to 0-02 c.c., from 20 c.c. to 22-5 c.c. The reagents required are fusel-free alcohol that has been prepared by fractional distillation over caustic potash, and diluted to exactly 30 per cent, by volume (specific gravity, 0-96541); chloroform freed from water and redistilled; and sulphuric acid (specific gravity, 1-2857 at 15-6). Distill slowly 200 c.c. of the sample under examination till about 175 c.c. have passed over, allow the distilling flask to cool, add 25 c.c. of water, and distill again till the total distillate measures 200 c.c. Dilute the distillate to exactly 30 per cent, by volume (specific gravity, 0-96541 at 15-6). The following is an accurate method for diluting any given alcohol solu- tion to a weaker solution of definite percentage: Designate the volume per- centage of the stronger alcohol by V and that of the weaker alcohol by v. Mix v volumes of the stronger alcohol with water to make V volumes of the product. Allow the mixture to stand till full contraction has taken place, and till it has reached the temperature of the original alcohol and water and make up any deficiency in the V volumes with water. Example. It is desired to dilute a distillate containing 50 per cent, of alcohol by volume until it contains 30 per cent. To 30 volumes of the 50 OFFICIAL METHODS OF ANALYSIS. 1087 per cent, alcohol add enough water to make 50 volumes or place 150 c.c. of the distillate in a 250 c.c. flask, fill to the mark with water, mix, cool, and ml to tne mark again. Prepare a water-bath, the contents of which are kept at exactly 15, and place in it the apparatus (covering the end of the tube with a rubber cap to prevent wetting the inside of the tube) and ffasks containing the 30-per cent, fusel-free alcohol, chloroform, sulphuric acid, and the distillate diluted to 30 per cent, by volume. When the solutions have all attained the tem- perature of 15, fill the apparatus to the 20 c.c. mark with the chloroform, drawing it through the lower tube by means of suction, add 100 c.c. of the 30-per cent, fusel-free alcohol and 1 c.c. of the sulphuiic acid, invert the apparatus, and shake vigorously for two or three minutes, interrupting once or twice to open the stop-cock for the purpose of equalizing pressure. Allow the apparatus to stand ten or fifteen minutes in water that is kept at the temperature of 15, turning occasionally to hasten the separation of the reagents, and note the volume of the chloroform. After thoroughly cleansing and drying the apparatus, repeat this operation, using the diluted distillate from the sample under examination in place of the fusel-free alcohol. The increase in the chloroform volume with the sample under examination over that with the fusel-free alcohol is due to fusel oil, and this difference (expressed hi cubic centimeters), multiplied by the factor 0-63, gives the volume of fusel oil in 100 c.c., which is equal to the percentage of fusel oil by volume in the 30-per cent, distillate. This must be calculated to the percentage of fusel oil by volume in the original liquor. Example. A sample of liquor contains 50 per cent, of alcohol by volume. The increase in the chloroform volume with the 30-per cent, fusel-free alcohol, is 1-42 c.c. ; the increase in the chloroform volume with the distillate from the liquor under examination, diluted to 30 per cent., is 1-62 c.c.; differ- ence, 20 c.c. The volume of fusel oil in 100 c.c. of the 30-per cent, distillate then is 0-20x0-663=0-1326 c.c., and by the proportion 30 : 50 :: 0-1326 : 0- 221, we obtain the percentage of fusel oil by volume in the original liquor. 20. DETERMINATION OF ALDEHYDES. (a) Preparation of Reagents. Eighty c.c. of a saturated solution of sodium disulphite are mixed with a solution of 0- 12 grm. of fuchsin in about * of water, 12 c.c. of sulphuric acid added, the solution thoroughly mixed, and diluted with water to 1 l : tre. (V) Determination. A portion of the sample is diluted with water, or strengthened with aldehyde-free alcohol until it contains 50 per cent, of ; hy volume, and 25 c.c. of this solution are treated with 10 c.c. of the reager ?nd allowed to stand twenty minutes. At the same time 25 c.c. of a s< tion of 0-05 grm. of acetic aldehyde in 1000 c.c. of 50- per cent, alcohol i treated in the same manner and allowed to stand the same length of t The relative intensity of the colors of the two solutions is then determined bv means of a colorimeter, and from the figure thus obtained the weight of aldehvde is estimated as acetic aldehyde, and calculated to percentage of the original liquor. 1088 APPENDIX I. 21. DETERMINATION OF ETHEREAL SALTS. After the determination of the volatile acids, the neutralized distillate is transferred to a flask connected with a reflux condenser, treated with 25 c.c. of tenth-normal sodium hydroxide, and boiled one-half hour. The flask and contents are then cooled, 25 c.c. of tenth-normal hydrochloric acid added, and the excess of acid titrated with sodium hydroxide, using phenolphtalein as indicator. The number of cubic centimeters of tenth-normal alkali used in this titration. multiplied by 0088, is equal to the weight in grm. of ethereal salts (calculated as ethyl acetate) in the volume of liquor taken for the deter- mination. VI. METHODS FOR THE ANALYSIS OF SOILS. 1. PREPARATION OF SAMPLE. Surface accumulations of decaying leaves, etc., should be removed and a slice of uniform thickness from the surface to the desired depth should be secured. To eliminate the effects of accidental variations in the soil, select specimens from five or six places in the field and remove several pounds of the soil, to the depth of 6 inches, or to the change between the surface soil and the subsoil, in case such change occurs between the depth of 6 and 12 inches. In no case is the sample to be taken to a greater depth than 12 inches. If the surface soil extends to a greater depth, a separate sample below the depth of 12 inches is to be obtained. If the surface soil extends to a depth of less than 6 inches, and the difference between it and the subsoil is unusually great, a separate sample of the surface soil should be secured, besides the one to the depth of 6 inches. The depth to which the sample of subsoil should be taken will depend on circumstances. It is always necessary to know what constitutes the foundation of a soil, to the depth of 3 feet at least, since the question of drain- age, resistance to drought, etc., will depend essentially upon the nature of the substratum. But in ordinary cases 10 or 12 inches of subsoil will be suffi- cient for the purpose of examination in the laboratory. The specimen should be obtained in other respects precisely like that of the surface soil, while that of the material underlying this subsoil may be taken with less exact- ness, perhaps at some ditch or other easily accessible point, and should not be broken up, but left, as nearly as possible, in its original state. Mix these soils intimately, remove any stones, shake out all roots and foreign matters, expose in thin layers in a warm room till thoroughly air-dry, or dry it in an air-bath at a temperature of 40. The soil is rapidly driect to arrest nitrification. It is not heated above 40 lest there be dissipation of ammonium compounds, or a change in the solubility of the soil. The normal limit to which the soil may be heated in place by the sun's rays should not be exceeded in preparing a soil for an agricultural chemical analysis. Five hundred grm. or more of the air-dried soil, which may be either the original soil or that which has been passed through a sieve of coarser mesh. OFFICIAL METHODS OF ANALYSIS. 1089 are sifted through a sieve with circular openings one-half mm. in diameter, rubbing, if necessary, with a rubber pestle in a mortar until the fine earth has been separated as completely as possible from the particles that are too coarse to pass the sieve. The fine earth is thoroughly mixed and preserved in a tightly stoppered bottle, from which the portions for analysis are weighed. The coarse part is weighed and examined microscopically or with THOU- LET'S solution.* It may sometimes be necessary to wash the soil through the one-half- mm. sieve with water; but this is to be avoided whenever possible. 2. DETERMINATION OF MOISTURE. Heat from 2 to 5 grm. of the air-dried soil in a flat-bottomed, tared plati- num dish for five hours in a water-oven kept briskly boiling ; cover the dish, cool in a desiccator and weigh. Repeat the heating, cooling, and weighing at intervals of two hours till nearly constant weight is found, and estimate the moisture by the loss of weight. Weigh rapidly, to avoid absorption of moisture from the air. 3. DETERMINATION OF VOLATILE MATTER. Heat the dish and dry soil from the above determination to full redness, until all organic matter is burned away. If the soil contains appreciable quantities of carbonates, the contents of the dish, after cooling, are moistened with a few drops of a saturated solution of ammonium carbonate, dried, and heated to dull redness to expel salts of ammonium, cooled in the desiccator, and weighed. The loss in weight represents the organic matter, water of combination, salts of ammonium, etc. 4. DETERMINATION OF ACID-SOLUBLE MATERIALS. In the following scheme for soil analysis it is intended to use the air-dried soil from the sample bottle for each separate investigation. The determina- tion of moisture, made once for all on a separate portion of air-dried soil, will afford the datum for calculating the results of analysis upon the soil dried at the temperature of boiling water. It is not desirable to ignite the soil before analysis, or to heat it so as to change its chemical properties. The acid digestion is jib be performed in a flask so arranged that the evap- oration of acid shall be reduced to a minimum, but under atmospheric pres- sure and at the temperature ot boiling water. The digestion is easily accom- plished in a flat-bottomed conical flask of hard glass, earning a stopper and hard-glass condensing tube at least 18 inches long. Where sulphuric acid is to be determined, a rubber stopper cannot be used. A flask with ground- glass stopper, carrying a condensing tube, is useful in such cases. The flask must be immersed in the water-bath up to the neck, or at least to the level of the acid, and the water must be kept boiling continuously during the digestion. In the following scheme 10 grm. of soil are used, this being a convenient quantity of most soils, in which the insoluble matter is about 80 per cent. * Principles and Practice of Agricultural Analysis, i, p.p. 268, 269. 1090 APPENDIX I. If desired, a larger quantity of such soil may be used, with a proportionately larger quantity of acid, and making up the soil solution to a proportionately larger volume. In very sandy soils, where the proportion of insoluble matter is 90 per cent, or more, 20 grm. of soil are to be digested with 100 c.c. of acid and the solution made up to 500 c.c. ; or a larger quantity may be used, preserving the same proportions. It is very important that the analyst assure himself of the purity of all the reagents to be used in the analysis of soils before beginning the work. (a) ACID DIGESTION OF THE SOIL. Place 10 grm. of the air-dried soil in an ERLENMEYER glass flask of from 150 to 200 c.c. capacity, add 100 c.c. of pure hydrochloric acid of specific gravity 1:115, insert the stopper with condensing- tube, place in a water- or steam-bath, and digest for ten hours continuously at the tempera- ture of boiling water, shaking once each hour. Pour the clear liquid from the flask into a small beaker and wash the residue out of the flask with dis- tilled water on a filter, adding the washings to the contents of the beaker. The residue, after washing until free from acid, is dried and ignited, as directed below. Oxidize the organic matter present in the filtrate with nitric acid and evaporate to dryness on the water-bath, finishing on a sand- or air-bath to complete dryness; take up with hot wa,er and a few cubic centimeters of hydrochloric acid and again evaporate to complete dryness. Take up as before, filter, and wash thoroughly with cold water, or with hot water slightly acidified at first with hydrochloric acid. Cool and make up to 500 c.c. This is solution A. The residue is to be added to the main residue and the whole ignited and weighed, giving the " insoluble matter." (See 5, p. 1094.) (6) DETERMINATION OF FERRIC OXIDE, ALUMINA, AND PHOSPHORIC ACID, COLLECTIVELY. To 100 or 200 c.c. of solution A, according to the probable amount of iron and alumina present, add ammonium hydroxide to slightly alkaline reaction to precipitate ferric and aluminic hydrates and phosphates. Expel the excess of ammonia by boiling, allow to settle, and decant the clear solution through a filter; add to the flask 50 c.c. of hot distilled wditer, boil, settle, and de- cant as before. After pouring off all the clear solution possible, dissolve the residue with a few drops of hydrochloric acid and precipitate again with ammonium hydroxide exactly as before; transfer all the precipitate to the filter and wash with hot distilled water till the washings become free from chlorides. Save the filtrates and washings which form solution B. Dry the filtrate and precipitate, transfer the precipitate to a tared platinum crucible, burn the filter, and add the ash to the precipitate ; ignite to bright redness, cool in a desiccator, and weigh. The increase of weight, minus the ash of filter and the phosphoric acid (found in a separate process), repre- sents the weight of the Fe 2 O 3 and A1 2 O 3 . (c) DETERMINATION OF MANGANESE. Concentrate the filtrates and washings (solution B) to 100 c.c: or less; add ammonium hydroxide to alkalinity; add bromine water and heat to OFFICIAL METHODS OF ANALYSIS. 1091 boiling, keeping the beaker covered with a watch crystal; as the bromine escapes the beaker is allowed to cool somewhat, more ammonia and bromine water being added and heated as before. This process is continued until the manganese is completely precipitated, which requires from fifteen to thirty minutes. The solution is then to be slightly acidified with a few drops of acetic acid and filtered while still boiling hot, the precipitate washed with hot water, dried, ignited, and weighed as Mn 3 O 4 . (d) DETERMINATION OF CALCIUM. If no manganese be precipitated, evaporate solution B or the filtrates and washings from (c) to about 50 c.c., make slightly alkaline with ammonia, and add, while still hot, ammonium-oxalate solution so long as any precipi- tate is produced, adding a few cubic centimeters in excess to convert the mag- nesium also into oxalate. Heat to boiling, allow the precipitate to settle, decant the clear solution on a filter, pour from 15 to 20 c.c. of hot distilled water on the precipitate, and again decant the clear solution on the filter. Dissolve the precipitate in the beaker with a few drops of hydrochloric acid, add a little water, and reprecipitate, boiling hot, by adding ammonium hydroxide to slight alkalinity and a little ammonium-oxalate solution ; filter through the same filter, transfer the precipitate to the filter, and wash it free from chlorides; dry, ignite the precipitate over the blast lamp until it ceases to lose weight, weigh, and estimate as CaO. 0) DETERMINATION OF MAGNESIUM. Slightly acidify the filtrate and washings from (d) with hydrochloric acid and concentrate to about 50 c.c., place in a small ERLENMEYER flask or beaker, make slightly alkaline with" ammonium hydroxide, and add sufficient acid-sodium-phosphate solution to precipitate the magnesium; then add gradually 10 c.c. strong ammonium hydroxide, cover closely to prevent escape of ammonia, and let stand in the cold. Filter after twelve hours, wash the precipitate free from chlorides, dry, burn at first at a moderate heat, finally igniting intensely, and weigh as Mg 2 P 2 O 7 . (/) DETERMINATION OF FERRIC OXIDE. Evaporate 100 c.c. of solution A, with the addition of about 10 c.c. of sul- phuric acid, until all hydrochloric acid is expelled; dilute with water, reduce with zinc, and estimate ferric oxide by a standard solution of potassium permanganate. To prepare potassium-permanganate solution, dissolve 3-156 grm. of the pure salt in 2000 c.c. of distilled water, and preserve in a glass-stoppered bottle, shielded from the light. Standardize this solution, after it has stood twenty-four hours with pure ammonio-ferrous sulphate, oxalic acid, or metallic iron. Instead of using another portion of the solution, the weighed precipi- tate from (6) may be dissolved by digestion on the water-bath in a covered beaker or flask with from 10 to 20 c.c. of a mixture of one part H^O, with four parts of water. Deduct the per cent, of ferric oxide obtained from the per cent, of ferric 1092 APPENDIX I. oxide and alumina (6), and make corrections for filter ash and phosphoric acid, to obtain the per cent, of alumina. (0) DETERMINATION OF PHOSPHORIC ACID. Evaporate 100 or 200 c.c. of solution A to about 25 or 30 c.c. ; nearly neutralize with ammonium hydroxide, add about 10 grm. pure crystallized ammonium nitrate, and gradually add about 20 c.c. molybdic solution ((1) (6), p. 1018) and set in water-bath at a temperature of 40. When the precipitate has settled sufficiently, draw out with a pipette about 5 c.c. of the clear liquid, and test it by allowing it to run into 5 c.c. of warm molybdic solu- tion. If any precipitate be produced, the test liquid is returned to the main portion and more molybdic solution is added and the operation repeated until all the phosphoric acid is precipitated. After standing from eight to twelve hours at a temperature not above 40, the ammonium phospho- molybdate is filtered off and the phosphoric acid determined as magnesium pyrophosphate, as directed under total phosphoric acid in fertilizers (page 1018). It is recommended to redissolve the magnesium-ammonium phosphate precipitate in acetic acid, after it has been washed once or twice, and re- precipitate with ammonia and a fresh quantity of magnesia mixture, giving the usual time for the separation of the precipitate. If there be any residue of phosphates remaining on dissolving the phosphomolybdate in ammonia, or the magnesium-ammonium phosphate in acetic acid, this residue is dis- solved in a little hydrochloric acid, neutralized with ammonium hydroxide, and precipitated with molybdic solution, and the phosphomolybdate ob- tained added to the main quantity. (/l) PROVISIONAL METHOD FOR DETERMINING AVAILABLE PHOSPHORIC ACID. Ten grm. of the air-dried soil, passed through a sieve of one-millimetre mesh, are placed in a small KJELDAHL flask marked at 250 c.c. From 20 to 30 c.c. concentrated sulphuric acid and approximately 0-7 grm. yellow oxide of mercury are added, the contents of the flask well mixed by shaking, and oxidized over the open flame, as in the determination of nitrogen, for an hour. After cooling, about 100 c.c. of water, 5 c.c. of concentrated hydro- chloric acid and 2 c.c. of concentrated nitric acid are added, and the mixture reboiled to oxidize the iron, cooled, the volume completed to the mark with water, and the contents of the flask filtered through a dry, folded filter-paper. One hundred cubic centimetres of the filtrate are placed in a flask of about 450 c.c. capacity, strong ammonia added until a permanent precipitate is formed, which is dissolved by the addition of about 7 c.c. of nitric acid, and the mixture boiled until clear. The flask is removed from the flame and cooled at room temperature for exactly two minutes, 75 c.c. molybdate solution added, and the flask placed in a water-bath kept at 80 for 15 minutes, shaking vigorously four or five times meanwhile. After removing from the bath, the flask is allowed to stand for ten minutes until the precipitate has settled, and the supernatant liquid is poured onto the filter-paper under pres- sure, the precipitate being partially brought upon the paper. The flask and precipitate are thoroughly washed with ammonium-nitrate solution, OFFICIAL METHODS OF ANALYSIS. 1093 the precipitate either by decantation or on the filter-paper. The flask is placed under the funnel, the precipitate is dissolved in ammonia, and the phosphoric acid estimated by the usual processes. Details of the manipula- tion are given in Bulletin No. 43 of the Division of Chemistry, pp. 58-60. (l) PROVISIONAL METHOD FOR THE DETERMINATION OF THE MORE ACTIVE FORMS OF THE PHOSPHORIC ACID IN SOILS. (a) Prepare a large stock solution of normal HC1 by titrating against a standard KOH solution containing little or no carbonate, using phenol- phtalein as the indicator. (6) Digest 10 grm. of air-dried soil, in a stoppered flask, with 100 c.c. of N/5 HC1, for exactly five hours in a water-bath kept at a temperature of 40. Filter the solution through a dry paper, cool to the room tempera- ture, and titrate 20 c.c. of the filtrate with standard carbonate-free KOH solution, using phenolphtalein as the indicator. From the data thus se- cured, calculate the exact number of cubic centimeters of normal acid of the stock solution and of water to make exactly one or two litres of acid of N/5 strength after allowing for the amount neutralized by the amount of soil to be used in (c). (c) Place 200 grm. of the air-dried soil in a large, dry. glass-stoppered bottle and add exactly 2000 c.c. of X/5 HC1 corrected for neutralization as in (6). In the case of soils known to be rich in available phosphoric acid 100 grm. of soil and 1000 c.c. of acid will be sufficient. Place the bottle in a large water-bath and keep at a temperature of 40 for exactly five hours, shaking thoroughly each half hour. At the end of the digestion shake con- tents of bottle well and pour quickly upon a large, dry, ribbed filter of two thicknesses of paper and of sufficient size to receive the entire contents of the bottle. The filtrate is to be received in a dry vessel and the solution poured back through the paper until entirely clear. Evaporate 1000 c.c. of the filtrate if 200 grm. of soil be used, or 500 c.c. if 100 grm. be employed, to dryness in a porcelain dish, after adding a few c.c. of nitric acid to oxidize organic matter, etc., moisten the residue with HC1, take up with water, and filter into a flask of about 500 c.c. capacity. Add 15 grm. of ammonium nitrate in solution, add strong ammonia until a permanent precipitate forms, and then concentrated nitric acid until the precipitate dissolves. Dilute the solution to about 100 c.c., if not already of that volume, place a ther- mometer in the flask, and heat to exactly 85. Add 75 c.c. of recently pre- pared molybdate solution, digest in a water-bath at 80 for fifteen minutes, with occasional shaking, remove from the bath and allow to stand at least 10 minutes before filtering. Continue the determination in the usual way. (/) DETERMINATION OF SULPHURIC ACID. Evaporate 100 or 200 c.c. of solution A nearly to dryness on a water- bath to expel the excess of acid; then add 50 c.c. of distilled water; heat to boiling and add from 2 to 3 c.c. of a solution of barium chloride, and con- tinue the boiling for five minutes. When the precipitate has settled pour the liquid on a tared Gooch, treat the precipitate with from 15 to 20 c.c. of 1094 APPENDIX I. boiling water, and transfer to the filter and wash 'with boiling water, at first slightly acidified with a few drops of hydrochloric acid, finally with pure water, till the filtrate is free from chloride. Dry the filter, ignite, and weigh as barium sulphate, which multiplied by 0-34331 equals SO 3 . (K) DETERMINATION OF POTASH AND SODA. Treat the filtrate from (/) with ammonium hydroxide exactly as in (6). Evaporate the filtrate and washings to dryness, heat below redness, until ammonium salts are expelled, dissolve in about 25 c.c. of hot water, add 5 c.c. of baryta water, and heat to boiling; let settle a few minutes, and test a little of the clear liquid with more baryta water to be sure that enough has been added. When no further precipitate is produced, filter and wash thor- oughly with hot water. Add ammonia and ammonium carbonate to com- plete the precipitation of the barium, let stand a short time on the water- bath, filter and wash the precipitate thoroughly with hot water, evaporate nitrate and washings to dryness in a porcelain dish, expel ammonium salts by heat below redness, take up with a little hot water, add a few drops of ammonium hydroxide and a drop or two of ammonium carbonate, let stand a few minutes on the water-bath, filter into a tared platinum dish, evaporate to dryness on the water-bath and heat to dull redness, until all ammonium salts are expelled and the residue is nearly or quite white. The heat must not be sufficient to fuse the residue. The weight of the residue represents potassium and sodium chlorides. Determine the potassium present with platinum chloride in the usual manner. The sodium chloride is obtained by subtracting potassium chloride thus found from the total weight of the two chlorides. Instead of this, a fresh aliquot portion of solution A may be evaporated to dryness, redissolved in water and treated directly with milk-of-lime as in ash analysis, but without previous addition of barium chloride. 5. DETERMINATION OF ACID-INSOLUBLE MATERIALS. The residue from 4 (a) may be analyzed by the usual methods for sili- cates. If it be desired to determine the silica soluble in alkalies, the residue must be dried at 100 and an aliquot portion removed before ignition, for treatment with sodium-carbonate solution, as described under ash analysis, page 1097. Another aliquot portion, or the rest of the residue, is ignited and weighed. 6. DETERMINATION OF TOTAL ALKALIES. Determine in a separate portion of the soil by J. LAWRENCE SMITH'S method, given in CROOKES'S Select Methods, second edition, pp. 28-40, and Principles and Practice of Agricultural Analysis, Vol. I, pp. 378-381; or, preferably, determine by this method the alkalies in the insoluble residue from 4 (a) and add the amount obtained from the hydrochloric-acid solution. OFFICIAL METHODS OF ANALYSIS. 1095 7. IDENTIFICATION OF LITHIUM, CESIUM, AND RUBIDIUM. The salts of these elements are occasionally ioimd in very small amounts in soils. Their agricultural uses are still in question, and their amount is too small to admit of quantitative estimation. A qualitative examination may be made by the spectroscope with the water-soluble materials evapor- ated to dryness and dissolved with two or three drops of hydrochloric acid or with the alkaline chlorides separated as in 4 (i) or 6. 8. DETERMINATION OF TOTAL NITROGEN. From 7 to 14 grm. of the soil are placed in a small KJELDAHL digesting flask, about 250 c.c. capacity, with 30 c.c. of strong sulphuric acid, or more, if necessary, and 0-7 grm. yellow oxide of mercury, and boiled for an hour. The residue is oxidized with potassium permanganate in the usual way. After cooling, the flask is half filled with water, vigorously shaken, the heavy matters allowed to subside, and the supernatant liquid poured into a flask of from 1000 to 1200 c.c. capacity. This operation is repeated until the ammonium sulphate is practically all removed and the digestion flask is a little more than half full, and the ammonia distilled hi the usual manner. If a sample be known to contain a considerable amount of nitrate, use method p. 1024 (c). 9. DETERMINATION OF CARBON DIOXIDE. Determine as in ash analysis, page 1098, using from 5 to 10 grm. of the sample. 10. DETERMINATION OF HUMUS. Ten grm. of the sample are placed in a Gooch, extracted with 1-per cent, hydrochloric acid until the filtrate gives no reaction with ammonia and ammonium oxalate, and the acid removed by washing with water. The contents of the crucible (including the asbestos filter) are then washed into a glass-stoppered cylinder with 500 c.c. of 4-per cent, ammonia and allowed to remain, with occasional shaking, for twenty-four hours. During this time the cylinder is inclined as much as possible without bringing the con- tents in contact with the stopper, thus allowing the soil to settle on the side of the cylinder, and exposing a very large surface to the action of the ammonia. The cylinder is then placed in a vertical position and left for twelve hours, to allow the sediment to settle to the bottom. The supernatant liquid is filtered and an aliquot portion evaporated, dried at 100, and weighed. The residue is then ignited and again weighed. The humus is calculated from the difference in weights between the dried and the ignited residues. 11. DETERMINATION OF HUMUS NITROGEN. Digest the soil with 2 per cent, hydrochloric acid and wash as nearly free of acid as possible with distilled water. Extract the humus with a 3-per cent, solution of sodium hydrate and determine nitrogen in the extract in the usual wav. 1096 APPENDIX I. 12. STATEMENT OF RESULTS. All results of soil analysis are to be calculated as per cent, of the soil dried to constant weight in the water-oven (see determination of moisture, p. 1089), and are to be stated in the following order : Insoluble matter ) Soluble silica ) Potash (K 2 O) Soda (Na 2 O) Lime (CaO) Magnesia (MgO) Manganese oxide (MnO) Ferric oxide (Fe 2 O 3 ) Alumina (A1 2 O 3 ) Phosphorus pentoxide (P 2 O 6 ) Sulphur trioxide (SO 3 ) Carbon dioxide (CO 2 ) Water and organic matter Total Humus Ash Phosphorus pentoxide. Silica Nitrogen (organic) Hygroscopic moisture Moisture absorbed at t. . VII. METHODS FOR THE ANALYSIS OF ASHES. 1. PREPARATION OF THE ASH. Before combustion the material must be thoroughly cleaned from all foreign matter, especially from adhering soil. The combustion should be carried on at a comparatively low temperature, never reaching a full red heat, because of the danger of volatilizing alkaline chlorides, etc., and of fusing the ash ; nor in a strong draft of air, lest the lighter part of the ash be carried away. Combustion is best carried on in a flat platinum dish in a muffle. With substances rich in silica and alkalies it is better to first char the sub- stance, wash with distilled water to remove soluble salts, then dry and incinerate the residue. Evaporate the aqueous extract and add this to the rest of the ash. With substances rich in phosphates, e.g., seeds and animal substances, char the material, remove salts by acetic acid, decant the acetic solution, wash with distilled water, and then complete the combustion. Add the acetic solution and washings to the final ash, evaporate to dryness, and gently ignite the whole to decompose the acetates. In whatever way obtained, the whole of the ash should be pulverized and intimately mixed while still warm, and preserved in a tight, dry bottle for analysis. If after incineration the ash has absorbed moisture, dry thoroughly at low redness before bottling. OFFICIAL METHODS OF ANALYSIS. 1097 It is intended that the preliminary preparation of the ash shall bring it to a perfectly dry condition, rendering a moisture determination unnecessary, and that the portions for analysis shall be weighed from the prepared sample in this condition. As it is sometimes difficult or impossible to prepare an ash for analysis in large quantity, the following method has been arranged so that a small amount of ash may be used. Where the ash is to be had in abun- dance larger quantities and more portions may be used, but the proportion of acid to substance taken is to be preserved. Much latitude must be left to individual judgment in adapting the method to particular cases. 2. SOLUTION AND DETERMINATION OF CARBON, SAND, AND SILICA. Five grm. of ash are treated hi a beaker, covered with a watch-glass, with 50 c.c. of hydrochloric acid of specific gravity 1-115, and digested on the water-bath until ah 1 effervescence has ceased. The watch-glass is then re- moved to allow the liquid to evaporate, any adhering substance washed back into the beaker, and the residue is thoroughly dried and pulverized to render silica insoluble. The dry residue is moistened with from 5 to 10 c.c. of hydro- chloric acid, taken up with about 50 c.c. of water, allowed to stand on the water- bath a few minutes, filtered through a parchment-paper filter (S. and S. "hardened" filters), and thoroughly washed. The solution and washings are to be made up to 250 c.c. or other convenient volume and preserved for analysis. (a) The residue is washed from the filter (which may be used again) into a platinum dish and boiled about five minutes with about 20 c.c. of a satu- rated solution of pure sodium carbonate, a few drops of pure sodium- hydroxide solution are added, the solids are allowed to settle, and the liquor decanted through a tared Gooch. The residue in the dish is to be boiled with sodium-carbonate solution and decanted as before, and the process repeated a third time, after which the residue is brought upon the filter and thoroughly washed, first with hot water, then with a little dilute hydrochloric acid, and finally with hot water until free from chlorides. The Gooch and contents are dried to constant weight at 110, and the combined weight of carbon and sand determined. After incineration the loss in weight gives the carbon. It is advisable to examine the residue under the microscope to ascertain if it be really sand. The alkaline filtrates and washings are to be united, acidified with hydrochloric acid, evaporated to dryness, and the silica separated and determined in the usual way. (6) Instead of determining directly the silica dissolved by the sodium- carbonate solution, as described above, another portion of the ash may be treated as in (2), and the residue of silica, sand, and carbon filtered on an ordinary filter, washed, burned, and weighed, giving the combined weight of silica and sand, from which the weight of sand found in (a) is to be deducted to obtain the silica. It is inadmissible to separate the soluble silica from the residue after ignition. 3. DETERMINATION OF MANGANESE, CALCIUM, AND MAGNESIUM. To an aliquot portion of the solution of the ash prepared as in (2), corres- ponding to 5 to 2 grm., add a quantity of pure ferric-chloride solution, more 1098 APPENDIX I. than equivalent to the phosphoric acid which may be present, neutralize with ammonia, add one or two grm. of sodium acetate and boil one or two minutes, filter and wash with boiling water. Evaporate the filtrate and washings to about 50 c.c., and determine manganese, calcium, and magnesium as in the analysis of soils (pp. 1090 and 1091, c, d, and e). 4. DETERMINATION OF PHOSPHORIC ACID. An aliquot portion of the hydrochloric-acid solution (see 2) correspond- ing to 2 to 1 grm. is to be used for the determination by any of the methods described for total phosphoric acid in fertilizers. 5. DETERMINATION OF SULPHURIC ACID AND ALKALIES. An aliquot part of the hydrochloric-acid solution (see 2) corresponding to 5 to 1 grm. of ash is heated to boiling, and barium-chloride solution added in small quantities until no further precipitation is produced. Let stand on the water-bath until clear, filter on a tared Gooch, wash thoroughly with hot water, at first slightly acidified with hydrochloric acid, finally with pure water until free from chlorides, dry, burn, and weigh the barium sulphate. Evaporate the filtrate and washings from the barium sulphate to dryness, redissolve the residue in about 50 c.c. of water, and add milk-of-lime or barium- hydroxide solution, which must be perfectly free from alkalies, until no further precipitation is produced and it is certain that there is an excess of calcium or barium hydroxide present; boil for two or three minutes, filter hot, wash thoroughly with boiling water, precipitate the lime and baryta from the solution with ammonia and ammonium carbonate, filter after standing at least one-half hour on the water-bath, evaporate filtrate and washings to dryness, and drive off the ammonium salts by careful heating below red- ness. When cold, redissolve the residue in about 10 c.c. of water, add a few drops of ammonia and ammonium-carbonate solution, let stand a few minutes on the water-bath, filter into a tared platinum dish, evaporate to dryness, expel the ammonium salts by heating to just perceptible dull redness and weigh the chlorides of potassium and sodium. If on dissolving the chlorides in a little water any residue be left the precipitation with ammonia and am- monium carbonate may be repeated before the final weighing, or the residue may be collected on a small ashless filter, burnt, and weighed back with the dish. 6. DETERMINATION OF CARBON DIOXIDE. Use from 1 to 5 grm. of ash in any of the usual forms of apparatus, de- termining the carbon dioxide evolved either by increase of weight of potash bulbs or loss of weight of the apparatus. 7. DETERMINATION OF CHLORINE. Determine as silver chloride, either gravimetrically or by one of the standard volumetric processes, in a nitric-acid or aqueous solution of the ash. Nitric acid may be used in (e) and the solution employed for this pur- pose. OFFICIAL METHODS OF ANALYSIS. 1099 VIII. METHODS FOR THE ANALYSIS OF TANNING MATERIALS. I. PREPARATION OF SAMPLE. Barks, woods, leaves, dry extracts, and similar tanning materials should be ground to such a degree of fineness that they can be thoroughly extracted. Fluid extracts must be heated to 50 C., well shaken, and allowed to cool to room temperature. II. QUANTITY OF MATERIAL. In the case of bark and similar material use such quantity as will give about 0-8 grm. solids per 100 c.c. of solution, extract in SOXHLET or similar apparatus at steam heat for non-starchy materials. For canaigre and substances containing like amounts of starch use temperature of 50 to 55 C. until near complete extraction, finishing the operation at steam heat. In the case of extract weigh such quantity as will give 0-8 grm. solids per 100 c.c. of solution, dissolve in 900 c.c. of water at 80, let stand twelve hours, and make up to 1000 c.c. III. MOISTURE. (a) Place 2 grm., if it be an extract, into a flat-bottomed dish not less than 6 cm. in diameter, add 25 c.c. of water, warm slowly till dissolved, continue evaporation, and dry. (6) All dryings called for, after evaporation to dryness on water-bath or others, shall be done by one of the following methods, the soluble solids and non-tannins being dried under similar, and, so far as possible, identical conditions : 1. For twenty-four hours at the temperature of boiling water hi a steam- bath. 2. For eight hours at 100 to 103 in an air-bath. 3. To constant weight in vacuo at 70. IV. TOTAL SOLIDS. Shake the solution, and without filtering immediately measure out 100 c.c. with a pipette, evaporate in a weighed dish, and dry to constant weight, at the temperature of boiling water. Dishes should be flat-bottomed and not less than 6 cm. in diameter. V. SOLUBLE SOLIDS. Filtration shall take place through a double-folded filter (S. and S. No. 590), the first 150 c.c. passing through shall be rejected, 100 c.c. next passing through shall be evaporated and dried. When a clear filtrate cannot be otherwise obtained the use of 10 grm. of kaolin previously washed in a portion of the tanning solution is permissible. Evaporation during filtration must be guarded against. VI. NON-TANNINS. Propare 20 grm. of hide-powder by washing in a No. 7 beaker with from 800 to 1000 c.c. of water, stir well and let stand one hour, filter the magma 1100 APPENDIX I. through linen, squeeze thoroughly by hand, and remove as much water as possible by means of a press, weigh the pressed hide, and take approximately one-fourth of it for moisture determination. Weigh this fourth carefully and dry to constant weight. Weigh the remaining three-fourths carefully and add them to 200 c.c. of the original solution; shake ten minutes, and squeeze the tanned hide through linen. Collect this nitrate, add 5 gnu. of kaolin, free from soluble salts, stir well and filter through folded filter (S. and 5. No. 590, 15 cm.), returning the first 25 c.c. Evaporate 100 c.c. of the clear filtrate. The weight of this residue must be corrected for the dilution caused by the water contained in the pressed hide-powder. The shaking must be done in some form of mechanical shaker. The simple machine used by druggists, and known as the milk-shake, is recommended. VII. TANNINS. The amounts of these is shown by the difference between the soluble solids and the corrected non-tannins. VIII. TESTING HIDE-POWDER. (a) Shake 10 grm. of hide-powder with 250 c.c. of water for five minutes, strain through linen, squeeze the magma thoroughly by hand ; repeat this operation three times, pass the last filtrate through paper (S. and S. No. 590, 15 cm.) till clear, evaporate 100 c.c., and dry. If this residue amounts to more than 10 mg. the hide must be rejected. (fe) Prepare a solution of pure gallo-tannin by dissolving 5 grm. in 1000 c.c. of water. Determine the total solids by evaporating 100 c.c. of this solution and drying to constant weight. Treat 200 c.c. of the solution with hi Je -powder exactly as described in paragraph 6. The hide-powder must absorb at least 95 per cent, of the total solids present. The gallo- tannin used must be completely soluble in water, alcohol, acetone, and acetic ether, and should not contain more than 1 per cent, of substances not re- moved by digesting with excess of yellow mercuric oxide on steam-bath for two hours. IX. TESTING NON-TANNIN FILTRATE. (a) For Tannin. Test a small portion of the clear non-tannin filtrate with a few drops of a 1-per cent, solution of NELSON'S gelatin. A cloudiness indicates the presence of tannin, in which case repeat the process described under 6, using 25 instead of 20 grm. of hide powder. (6) For Soluble Hide. To a small portion of the clear non-tannin filtrate add a few drops of the filtered tannin solution. A cloudiness indicates the presence of soluble hide, in which case repeat the process described under 6, giving the hide-powder a more thorough washing. The temperature of solutions shall be between 16 and 20 when measured or filtered. All dryings should be made in flat-bottomed dishes of at least 6 cm. diameter. S. and S. No. 590, 15 cm. filter-paper should be used on all filtrations. APPENDIX II. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. (Bulletin of the United States Geological Survey, No. 176, 1900.) BY WILLIAM FRANCIS HILLEBRAND. TART I. INTRODUCTION. I. IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES. The composition of the ultimate ingredients of the earth's crust the different mineral species which are there found and of many of which its rocks are made up was the favorite theme of the great workers in chemistry of the earlier half of this century, and for the painstaking care and accuracy of BERZELIUS, WOHLER, and others the mineralogists and geologists of to-day have need to be thankful. Considering the limited facilities at their dis- posal in the way of laboratory equipment and quality of reagents, the general excellence of their work is little short of marvelous. As an outgrowth of and closely associated with the analysis of minerals came that of the more or less complex mixtures of them the rocks to aid whose study by the petrographer and geologist a host of chemists have for many decades annually turned out hundreds of analyses of all grades of quality and completeness. With the growth and extraordinary development of the so-called organic chemistry, inorganic chemistry gradually fell into a sort of disfavor. In many, even the best, European laboratories, the course in mineral analysis, while maintained as a part of the curriculum of study, became but a sub- ordinate prelude to the ever-expanding study of the carbon compounds, whose rapid multiplication, offering an easy and convenient field for original research and possible profit, proved a more tempting opening to young chemists than the often-worked-over and apparently exhausted inorganic pasture. For one student devoting his time to higher research on inorganic lines were perhaps fifty engaged in erecting the present enormous structure of carbon chemistry. The instruction afforded the student in mineral analysis was confined to the ordinary separations of the commoner ingredients occurring in appreciable quantities, with little regard to supposed traces and with still less attempt to find out if the tabulated list really comprised all that the mineral or rock contained. With the introduction of improved methods of examination by the petrog- rapher, especially as applied to thin rock sections, and the use of heavy 1101 1102 APPENDIX II. solutions, whereby, on the one hand, the qualitative mineral composition of a rock could be preliminarily ascertained with considerable certainty, and on the other, chemical examination of the more or less perfectly separated ingredients was rendered possible, a great help and incentive was afforded to t>he few chemists engaged in rock analysis. The microscope often obviated in part the necessity for tedious and time-wasting qualitative tests, and the heavy solutions, by permitting the concentration and separation of certain components, facilitated the detection of elements whose existence had long been overlooked. Meanwhile in the progress of chemistry new methods and reagents for qualitative detection and quantitative separation and estimation were gradu- ally being discovered and devised. The supposed adequacy of some well- established methods was shown to be unwarranted; some had to be dis- carded altogether; others were still utilizable after modification. In the light thus shed it became possible to explain many hitherto incomprehensible variations in the composition of some rock species or types, as shown in earlier analyses, and in not a few cases it appeared that the failure to report the presence of one or more elements had obscured relations and differences which more thorough examination showed to exist- (see pp. 1103 and 1104). Consequently there arose a feeling of distrust of much of the older work in the minds of those chemists and petrographers best fitted to judge of its probable qualities. This, and the incompleteness of nearly ah 1 the earlier work (and much of that of to-day, unfortunately), as shown by the largely increased list of those elements now known to enter into the normal composition of rocks, is rendering the old material less and less available to meet the increas- ing demands of the petrographer. And yet these demands on his part are, with few exceptions, by no means so exacting as they should be. Often the analysis is intrusted to the hands of a student without other experience than that gained by the analysis of two or three artificial salts and as many comparatively simple natural minerals, and with a laboratory instructor as adviser whose experience in rock analysis may be little superior to his own. In other words, one of the most difficult tasks in practical analysis is expected to be solved by a tyro, and his results are complacently accepted and published broadcast without question. Even to those thoroughly familiar with the subject rock analysis is a complex and often trying problem. Although long practice may have enabled one to do certain parts of it almost mechanically, one is still from time to time con- fronted with perplexing questions which require trained judgment to properly meet and answer, and there is still room for important work in some of the supposedly simplest quantitative determinations. If the results are to have any decided value for purposes of scientific interpretation and comparison, they should be the product of one competent to find his way through the intricacies of an analysis in which from fifteen to twenty-five different com- ponents are to be separated and estimated with close approach to accuracy, and this a beginner cannot hope to do in the majority of cases. The con- scientious chemist should have a live interest in this matter. He should work with a two-fold purpose in view that of lightening the labors of those SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1103 who come after him by enabling them to use his work with less supple- mentary examination, and of thereby enhancing his own reputation by merit- ing encomiums on work that has stood the test of time. The petrographer, again, should seek to have his analyses made as com- plete as possible, and not, as is so often the case, be content with determina- tions of silica, alumina, the oxides of iron, lime, magnesia, the alkalies, and water. The latter, it is true, are entirely justifiable at times, and may serve the immediate purpose for which they were intended, but their incomplete- ness may, on the other hand, not only conceal points fruitful of suggestion to the attentive mind, but, what is of still greater importance, they may be actually misleading. Enough instances of totally inaccurate conclusions to be drawn from them have fallen under my own observation to fully justify this plea in favor of greater completeness in rock and mineral analyses made for purely scientific purposes. The importance of the points indicated in the foregoing paragraph is shown by the difference between the analyses given in the following tables. The specimens were taken and analyzed at widely separated times and by different persons, it is true, but they were unquestionably from the same rock mass, in which, however much the relative proportions of the different mineral constituents might vary within certain limits, there can be no reason to doubt the general distribution of all the elements shown by the second analysis. Earlier Analysis. Later Analysis.* Earlier Analysis. Later Analysis. SiO 2 . . 54-42 53-70 Li 2 O. . Trace Trace TiO 2 1-92 H 2 O below 110C 80 AljO 3 13-37 11-16 H 2 O above 1 10 C J2-76 2-61 O 2 O 3 . . . 04 CO 2 . 1-82 FeX>, . t -61 3-10 P 9 O V 1-75 Feo 3 : : 13-52 1-21 s6 3 . . 06 MnO 04 F..V. 44 CaO 4-38 3-46 Cl 03 SrO . . . 19 BaO -62 99-58 100 40 MgO 6-37 6-44 Less O for F. .... 19 K,O 10-73 11-16 Na^O 1-60 1-67 100-21 * A still more recent analysis of another of the series of rocks of which this is an ex- ample has shown that this "later analysis" is itself probably incomplete and incorrect in part incomplete because of the probable presence of 0'2 per cent, or more of ZrO 2 , incorrect because of the error in A1 2 O 3 resulting from having counted ZrO 2 as A1 2 O 3 , and from the fact that titanium is not fully precipitable in presence of zirconium by GOOCH'S method (the one employed). The latter error involves both the TiOo and the Al^Oj. (See pp. 1153 and 1154.) t From the fact that repeated determinations of the iron oxides in this and related rocks from the same region show always a great preponderance of ferric oxide, it is not improbable that the figures given for the two oxides in the first analysis were accidentally transposed. t In the published analysis it does not appear whether this is total water or, as seems probable, only that remaining above 100 C. 1104 APPENDIX II. Another instance of similar kind is given below. Here, again, certain differences -are explainable by natural variations in the proportions of the constituent minerals, but it can hardly be doubted that TiO 2 , BaO, SrO, P 2 O 5 , and SO 3 were present in both specimens in approximately the same amounts. In the earlier analysis determinations of some supposed unim- portant constituents were purposely omitted, or made only qualitatively, with results that cannot be otherwise than fatal to a full comprehension of the mineralogical nature of the rock. Earlier Analysis. Later Analysis. Earlier Analysis. Later Analysis. SiO, 44-31 44-65 Na 2 O. . 4-45 5-67 TiO 2 Not est 95 Li 2 O Trace. A1 2 O 3 17-20 13-87 H 2 O below 1 10 C. 77 -95 Fe,Oo 4-64 6-06 H 2 O above 1 10 C 2-10 FeO I 3-73 2-94 H 2 O by ignition. . . 3-30 MnO 10 17 CO 2 11 CaO 10-40 9-57 P,O,. . 1-50 SrO *-37 d... Trace. BaO 76 so, 61 Mo-O fi. ^7 K.I pj K 2 O 3-64 4-49 99-11 99-92 * Not entirely free from CaO. Prof. F. W. CLARKE has shown that the combined percentages of titanic and phosphoric oxides in rock of the earth's crust, averaged from hundreds of analyses, is 0-8 per cent. When the determination of these is neglected the error falls upon the alumina. If the latter is then used as a basis for calculating the feldspars, it is easy to see that a very large average error in the latter may result, amounting to several per cent, of the rock. In order to more strongly emphasize the importance of completeness in analysis, a few facts brought out by the hundreds of rock analyses made in this laboratory may be cited. It has been demonstrated most conclu- sively that barium and strontium are almost never-failing constituents of the igneous rocks of the United States and of many of their derivatives. These amounts are usually below 0-1 per cent, for each of the oxides of those metals, but higher amounts are by no means uncommon. Furthermore, the weight of barium is almost without exception in excess of that of strontium. But a still more important point is that the igneous rocks of the Rocky Mountain region, so far as examined, show far higher average percentages of both metals than the rocks from the eastern and the more western portions of the United States. The following examples serve to illustrate certain types of Rocky Mountain igneous rocks: Of seven rocks forming a Colorado series, six held from 0-13 to 0-18 per cent, of BaO, while in the seventh the percentage was 0-43. The SrO ranged from 0-07 to 0-13 per cent, for six, and was 0-28 for that one highest in BaO. Of thirteen geo- logically related rocks from Montana, embracing basic as well as acid and intermediate types, the range of BaO was from 0-19 to 0-37 per cent., with SOME PKINCIPLES AND METHODS OF ROCK ANALYSIS. 1105 an average of 0-30 per cent. Three others of the same series contained 0-10 per cent, or less, while the seventeenth carried 0-76 per cent. BaO. The SrO ranged from 0-37 per cent, in the last instance to an average of 0-06 for the other sixteen. Certain peculiar rocks from Wyoming carry from 62 to 1 25 per cent. BaO, and from 02 to 33 per cent. SrO. Surely this concentration of certain chemical elements in certain geographic zones has a significance which future geologists will be able to interpret, if those of to-day are not. Again, vanadium is an element which few chemists have ever thought of looking for in igneous rocks, though it has long been known to occur in mag- netites and other iron ores. HAYES, in 1875, reported its occurrence in a great variety of rocks and ores. Quoting from THORPE'S Dictionary of Chem- istry: "It is said to be diffused with titanium through all primitive granite rocks (DIEULAFAIT), and has been found by DEVILLE in bauxite, rutile, and many other minerals, and by BECHI and others in the ashes of plants and in argillaceous limestones, schists, and sands." It is further reported to com- prise, as the pentoxide, up to 1 per cent, of many French and Australian clays, 02-0 03 per cent, of some basalts, 24 per cent, of a coal of unknown origin, and 45 per cent, of one from Peru. Still later examinations in this laboratory of about 100 rocks, chiefly igneous, covering the whole territory of the United States, show not only its general qualitative and qualitative distribution, but that it predominates in the less siliceous igneous rocks and is absent, or nearly so, in those high in silica. In some of the more basic rocks it occurs in sufficient amount to seriously affect the figures for the oxides of iron unless separately estimated and allowed for (see p. 1175) a matter of considerable importance, since the petrographer lays great stress on accuracy in their determinations. This same investigation has also thrown some light on the distribution of molybdenum, which seems to be confined to the more siliceous rocks and to occur in quantities far below those commonly found for vanadium. Finally, had it not been the writer's practice of late years to look for sulphur in rocks, even when no sulphides were visible to the eye, its almost invariable presence in the form of sulphide, and consequent connection with the long mystifying lack of agreement between results for ferrous iron ob- tained by the MITSCHERLICH and the hydrofluoric -acid methods, might not have been suspected. (See p. 1169.) While strongly upholding the necessity for more thorough work, necessar- ily somewhat at the expense of quantity, it is far from the writer's intention to demand that an amount of time, although disproportionate to the im- mediate objects to be sought, should be expended on every analysis. But it is maintained that in general the constituents which are likely to be present in sufficient amount to admit of determination in the weight of sample usually taken for analysis say 1 grm. for SiO 2 , A1 2 O 3 , etc., to 2 grm. for certain other constituents should be sought for, qualitatively at least, in the ordi- nary course of quantitative work, and their presence or absence noted among the results. If present in little more than traces, that knowledge alone may suffice, for it is often more important to know whether or not an ele- 1106 APPENDIX II. ment is present than to be able to say that it is there in amount of exactly 0-02 or 0-06 per cent. In the tabulation of analyses a special note should be made in case of intentional or accidental neglect to look for substances which it is known are likely to be present. Failure to do this may subject the analyst to unfavorable criticism, when at some future time his work is reviewed and the omissions are discovered by new analyses. Finally, whenever possible, a thorough microscopical examination of the rocks in thin section should precede the chemical analysis. This may be of the greatest aid to the chemist in indicating the. presence of unusual constituents, or of more than customary amounts of certain constituents, whereby, possibly, necessary modifications in the analytical procedure may be employed without waste of time or labor.* II. OBJECT AND SCOPE OF THE PRESENT TREATISE. The literature relating to analysis of silicates is extensive but scattered, and in no single article is there to be found a satisfactory exposition of the methods to be followed or the precautions to be observed, especially in the search for some of the rarer constituents or those which, without being rare, have been of late years recognized as occurring persistently in small amounts. It is not intended to make this little volume a treatise on mineral analysis, but it is believed that the experience gained by the chemists of this Survey during the twenty years since the establishment of its first chemical labora- tory in Denver may be useful to most chemists interested in mineral and especially rock analysis. The original publication of these data in Bulletin No. 148 was primarily intended to show the principles and methods according to which the major part of the very many hundreds of analyses therein brought together had been executed, and thus to furnish a partial measure of the trustworthi- ness of those analyses, rather than to serve as a practical manual of rock analysis. But the use which has been made by mineral chemists of that bulletin has seemed to render it advisable to amplify somewhat in detail and to add, besides a few new methods, a number of alternative ones which are known or believed to be good, in order that those who may wish to use this treatise as a practical guide shall have a choice from which to select in case the rather expensive apparatus or complicated arrangements sometimes preferred are not available. Where silicate analyses are very frequently made, however, it is a saving of time and of money in the end to set up per- manent arrangements for convenience in estimating water, carbon dioxide, ferrous iron, making reductions in hydrogen, etc. Stress will be laid on those points meriting particular attention, and now * The foregoing tables and accompanying remarks, including several sentences pre- ceding the tables, have been largely taken from the writer's papers entitled "A Plea fcr Greater Completeness in Chemical Rock Analysis," published in the Journal of the Ameri- can Chemical Society, xvi, pp. 90-93. 1894; also in the Chemical News, LXIX, p. 163, 1894. See also "Distribution and Quantitative Occurrence of Vanadium and Molybdenum in Rocks of the United States," in the American Journal of Science, 4th Series, vi. p. 209, 1898, and Chemical News, LXXVIII, p. 216. 1898. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1107 and then a brief discussion or criticism of methods elsewhere in vogue may be entered into. In the earlier years of the existence of the Washington laboratory oppor- tunity was afforded for the testing of novel methods and the devising of new ones, with most excellent results, as shown especially by the methods for separation of titanium, of lithium, and of boron, due to Prof. F. A. GOOCE, to whose inventive skill chemists owe likewise the perforated filtering crucible and the tubulated platinum crucible arrangement for the estimation of water. Of late years the press of routine work has been such as to more fully fill up the time of the much-reduced chemical force, and as a consequence it has been found impossible to subject to critical trial several separation methods of recent origin, some of which seem to be full of promise, or to follow out certain lines of investigation which have been suggested by the observations made in this laboratory. This, then, must be offered in explanation if, in the following discussion, it may seem to some that any of the methods followed are too conservative. In general the discussion will be confined strictly to such separations as may be required in the analysis of an igneous, metamor- phic, or sedimentary silicate rock of complex mineralogical composition, in which the majority and possibly all of the ingredients in the list given below may occur hi weighable or readily discoverable quantities : SiO.,, TiO 2 , ZrO 2 , A1A, Fe 2 O 3 , Cr 2 O 3 , V 2 O 3 , FeO, MnO, NiO, CoO, MgO, CaO, SrO, BaO, ZnO, CuO, K 2 O, Na 2 O, Li 2 O, H 2 O, P 2 O 5 , S,* SO 3 C,f CO 9 Fl, Cl, N. The special problems often arising in the analysis of rocks of extra- terrestrial origin the more or less stony meteorites will not be considered^ An analysis of that kind should never be intrusted to the novice, but only to the chemist who has a knowledge of the composition and properties of the peculiar mineral constituents of those bodies and a judgment fit to cope with the oftentimes difficult problems presented by them. Thorium, cerium, and other rare earths are seldom encountered in quan- tities sufficient to warrant the expenditure of the time necessary for their isolation. A search for them qualitatively, even, is at present rarefy justi- fiable unless there is microscopic or other evidence of the presence of min- erals likely to contain them. Tantalum, columbium, boron, and glucinum have never been certainly met with in the writer's experience, and yet they must be present in certain rocks, and doubtless traces have been overlooked at times. There is no reason to suppose that other elements may not be tound by careful search, possibly all in the known category, and, indeed, SAXDBERGER'S icsearches have shown to what an extent this is true of a large number of those elements contributing to the filling of metalliferous veins. But those in the above list may usually be estimated with ease in weights of from one-half to 2 grm. If the point be raised that many of the published analyses emanating from the Survey laboratories, even the earlier ones of the writer, are not in * Usually as pyrite not infrequently as pyrrhotite. t As graphite or coaly matter. 1108 APPENDIX II. accord with the advocacy of completeness contained in the foregoing pages, it may be remarked that these ideas have been to a considerable degree evolved during a personal experience of twenty years in this line of work, and that frequently the exigencies were such as to compel restriction in the examination. Where the latter has been the case subsequent developments have in some cases shown it to be bad policy in every respect. It is better, both for the geologist and the chemist, to turn out a limited amount of thor- ough work than a great deal of what may prove to be of more than doubtful utility in the end. III. STATEMENT OF ANALYSES. Until recently it has been the practice in this laboratory to tabulate the constituents of a rock somewhat in the order of their determination, begin- ning with SiO 2 as the chief constituent and grouping together all chemically related oxides, as shown, for instance, on pages 1103 and 1104. From a strictly scientific point of view a chemical classification founded on a separation into basic and acidic atoms or radicals would be more satis- factory, but until we learn to find out what silicic radicals are present and in what relative amounts, also how much free silica there may be, it is useless to think of employing the arrangement so valuable in stating water analyses. Of late petrographers have begun to demand, with considerable reason, an arrangement ''which shall bring the essential chemical features both the percentage figures and the molecular ratios prominently and compactly before the eye, so that the general chemical character and the relations of the various constituents may be seen at a glance." * In accordance with this demand it is now our practice to follow pretty closely the arrangement proposed by PIRSSON and very recently strongly advocated by WASHINGTON (loc. cit.}, namely: SiO 2 , A1 2 O 3 , Fe 2 O 3 , FeO, MgO, CaO, Na 2 O, K 2 O, H 2 O (above 105-110 C.), H 2 O (below 105-110 C.), CO 2 , TiO 2 , ZrO 2 , P 2 O 5 , SO 3 , Cl, Fl, S (FeS 2 ), Cr 2 O 8 , V 2 O 3 > NiO, CoO, CuO, MnO, SrO, BaO, Li 2 O, C, NH 3 . By this arrangement the nine constituents which in the great majority of cases determine the character of the rock are placed at the head of the list, thus greatly facilitating the comparison of different analyses similarly ar- ranged, especially when, as WASHINGTON recommends, the molecular ratios are calculated for these leading constituents and placed immediately after the corresponding oxides. The order of the remaining members is determined somewhat by the following considerations: CO 2 is placed next after H.,0, since these two are generally a measure of the alteration the rock may have undergone. TiO 2 and ZrO 2 naturally follow CO 2 on chemical grounds, and SO 3 and Cl, being common constituents of the sodalite group, are conveniently placed together. * H. S. WASHINGTON " The Statement of Rock Analysis," Am.Journ. Sci., 4th Series, , p. 61, 1900. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1109 IV. TIME NEEDED FOR MAKING AN ANALYSIS. The question has often been put, ' ' How long does it take to complete an analysis of this kind?" This will depend, of course, on the mineral com- plexity of the sample and on the personal factor of the individual worker. If there is a competent assistant to do the grinding, and specific-gravity determinations are not required, it is quite possible after long experience for a quick worker to learn to so economize every moment of time in a working day of seven hours, with an abundance of platinum utensils and continuous use of air- and Crater-baths through the night, as to finish every three days, after the completion of the first analysis, barring accidents and delays, one of a series of rocks of generally similar character, each containing from eight- een quantitatively determinable constituents, excluding, for instance, fluorine, carbon as such, nitrogen, metals of the hydrogen-sulphide group, and cobalt. On one occasion a series of fourteen rocks, of comparatively simple composition, was completed in one month, with the help of an assist- ant who made the phosphorus and ferrous iron determinations. But such an output of work is more than exceptional and implies an unusual freedom from those occasional setbacks to which every chemist is exposed. It should here be remarked that the Survey laboratory is most excep- tionally well supplied with all kinds of platinum vessels and utensils, so that it is rare indeed for delay to arise through lack of dishes of even the largest sizes. V. TWO USEFUL AIDS IN CHEMICAL MANIPULATION. In connection with the foregoing remarks it is in place to mention two aids to the chemist which are in constant use in this laboratory and have come to be well-nigh indispensable. Neither is novel in principle and both are in use elsewhere, but they are not so commonly known as they deserve to be, hence this allusion to them. Fig. 1 represents a form of platinum-tipped crucible tongs devised by Dr. A. A. BLAIR many years ago. With them a crucible can be securely grasped and brought into any desired position while still hot. To the con- tents, if in fusion over the blast flame, can be imparted the rotatory motion so often desirable. Above all, the cover need not be in the slightest degree displaced, as when using the common form of platinum-tipped tongs. Fig. 2 represents a very useful adjunct to the work-table and especially to the draught cupboard, whereby the liquid contents of crucibles can be speedily evaporated at almost any desired temperature and the dehydration of many solids effected much more safely than on an iron plate or sand-bath. I do not recall who originated this form of air-bath, but it has been in use here for over fifteen years and is identical in principle with the later Xickel- becher of JANNASCH. Nickel undoubtedly has a certain advantage in not rusting as does iron, but the form depicted in R of Fig. 2 can easily be made anywhere of sheet iron riveted at the joint, the bottom (not shown in the 1110 APPENDIX II. figure) being securely held by a flange at the extremity of the truncated cone. A crucible placed on the platinum triangle becomes uniformly heated FIG. 1. FIG. 2. FIG. ! Platinum-tipped crucible tongs. The parts AB, also of heavy platinum, are hollow, to serve as sockets for the cheaper metal of the handles. FlQ- 2. Radiator for rapid and safe evaporation. R is of sheet iron, also nickel (JAN- NASCH). Various sizes. A convenient height is 7 cm., width at top 7 cm., and at bottom 5 cm. by hot air, and large quantities of liquid, even sulphuric acid, can be thus volatilized in a short time without ebullition or spattering. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1111 VI. LIMITS OF ALLOWABLE ERROR IN SUMMATION OF ANALYTICAL RESULTS. As is well known, a complete silicate rock analysis which foots up less than 100 per cent, is generally less satisfactory than one which shows a summation somewhat in excess of 100. This is due to several causes. Nearly all reagents, however carefully purified, still contain, or extract from the vessels used, traces of impurities, which are eventually weighed in part with the constituents of the rock. The dust entering an analysis from first to last is very considerable, washings of precipitates may be incomplete, and if large filters are used for small precipitates the former may easily be insufficiently washed. Given the purest obtainable reagents, an ample supply of platinum, facilities for working, and a reasonably clean laboratory, there is no excuse for failure on the part of a competent chemist to reach a summation within the limits 99-75 and 100-50. Failure to attain 100 per cent, in several of a series of analyses of similar nature should be the strongest evidence that something has been overlooked. Excess above 100-5 per cent, should be good ground for repeating portions of the analysis in order to ascertain where the error lies, for it is not proper to assume that the excess is distributed over all determined constituents. It is quite as likely, in fact more than likely to affect a single determination and one which may be of importance in a critical study of the rock from the petrographic side. VII. QUALITY OF REAGENTS. It is due to say that all analyses performed in the Survey laboratories have been made with the purest reagents obtainable, either by purchase in the open market or by special preparation on the part of manufacturers or in the laboratory. The best acids made in this country are of a high grade and need no redistillation except for special experiments. Ammonia has always been redistilled at short intervals; and no sodium carbonate which exceeds 2* mg. of total impurity (see p. 1134) in 20 grm. (0-012 per cent.) is used for the main portions, in which silica, alumina, etc., are to be estimated. For other portions, as phosphoric acid, fluorine, sulphur, a poorer grade is entirely allowable, provided it is free from the elements to be determined, and from any other which might interfere with its estimation. Hydrofluoric acid was always freshly distilled with potassium permanga. nate imtil the introduction of ceresine bottles afforded an article sufficiently pure for all but the most exacting work. Care must be exercised even yet ? however, that no particles of paraffin or ceresine are floating on the acid, and that the latter is free from traces of chlorine whenever it is to be used for attacking silicates with a view to estimating chlorine (p. 1182). Potassium bisulphate has usually been prepared in the laboratory from sulphuric acid and potassium sulphate, since it is not always to be bought of satisfactory quality. Even then the normal sulphate had first to be 1112 APPENDIX II. examined, for it has been found to contain, on different occasions, notable amounts of lead, calcium, and silica. The phosphorus salt used for precipitating magnesium has been found to contain iron, and calcium is almost always a constituent of ammonium oxalate. The latter has therefore to be purified or specially prepared, as also oxalic acid, ammonium chloride (in which latter manganese has been observed), and occasionally other reagents. Some hydrogen peroxide con- tains fluorine, which renders it unfit for use as a chemical reagent. A "C. P." label is no guaranty whatever of the purity of a reagent; hence no chemicals should be taken on trust because of bearing such a label. Every new purchase should be examined, if it is one in which purity is a desidera- tum. In general all so-called "C. P." chemicals should at least stand the tests laid down by KRAUCH.* Of late years the appearance upon the market of so-called guaranteed reagents promised to meet a long-felt want. But experience has shown that with the pioneer in this line at least the guaranty amounts to nothing, the reagents being sometimes worse than the "C. P." articles emanating from sources which make no claim to special purity for their goods, and redress being unobtainable. The "guaranteed reagent" needs checking as much as any other. VIII. PRELIMINARY QUALITATIVE ANALYSIS. A complete qualitative analysis of a rock, preceding the quantitative examination, is in most cases a sheer waste of time. A few constituents may now and then be specially looked for, but in general time is saved by assuming the presence of most of them and proceeding on that assumption in the quantitative analysis. PART II. METHODS. I. INTRODUCTORY REMARKS. The order hereinafter followed in describing the various chemical sepa- rations has little relation to the affinities of the constituents of the rock, but those are grouped together which can be conveniently determined in the same portion of rock powder. Thus, in the main portion are usually de- termined SiO 2 , TiO 2 , MnO, NiO, CaO, SrO, MgO, total iron, and the com- bined weight of all the following: A1 2 O 3 , TiO 2 , P 2 O 5 , ZrO 2 , all iron as Fe 2 3 , and nearly if not quite all vanadium as V 2 O 5 , also perhaps rare earths if present. In a separate portion is estimated FeO; and also the total iron, as well as BaO, if these last are desired as checks. The alkalies need a por- tion for themselves. In another, ZrO 2 , BaO, and total sulphur are very con- veniently determined. For V 2 O 3 and Cr 2 O 3 still another and usually much larger portion is to be used. Determinations of CO 2 , C, H 2 O, Fl, Cl, are all best made in separate portions of substance, though various combinations are possible, as CO 2 and H 2 O, C and H 2 O, or H 2 O, Fl, and Cl. In fact, by a * Die Prufung der chemischen Reagentien, 3d ed., Berlin, JULIUS SPRINGER, 1896. S^e also the English translation of RRAUCH'S work by J. A. WILLIAMSON and L. W. DUPRE. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1113 judicious selection and combination of methods a very satisfactory analysis can sometimes be made on 4 grm. of material without omission of anything of importance, though the time consumed will be greater than if ample material is available. As an illustration of the advantage to be gained by a little judgment in the combination of methods, the case of sulphur, barium, and zirconium may serve. Many chemists never look for the second and third of these, but by following the procedure given on pages 1155 to 1157 very little more labor is expended in confirming their presence or absence than that of sulphur alone. With only occasional exceptions, nearly all the constituents mentioned on page 1108 can be estimated if present in portions of powder not exceed- ing 1 grm. each in weight. This is a convenient weight to take for the main portion in which silica, alumina, etc., the alkaline earths, and magnesia are to be sought; but it should, in general, be a maximum, because if larger, the precipitate of alumina, etc., is apt to be unwieldy. Its weight cannot often be much reduced with safety if satisfactory determinations of manganese, nickel, and strontium are to be expected. For the alkali portion one-half grm. is a very convenient weight. In general, it may be made a rule not to use more than 2 grm. for any portion which has to be fused with an alkali carbonate, as for sulphur, fluorine, and chlorine. For carbon dioxide the weight may rise to 5 grm., or even more, if the amount of this constituent is very small, without expen- diture of any more time than is required by 1 grm., and with correspondingly greater approach to correctness in the result. For vanadium also a larger weight than 2 grm. is usually demanded. II. SPECIFIC GRAVITY. BY SUSPENSION IN WATER. Ordinary Method. This determination, when required, is best made upon one or several fragments weighing up to 20 grm. They are held together by a fine platinum wire ready for suspension from the balance, and thus held are placed in a small beaker to soak over night in distilled water under the exhausted receiver of an air-pump, side by side with a similar beaker of water. Boiling is, of course, a much less effective means of removing air than the air-pump, and the boiling water may exert an undesirable solvent and abrading effect. In the morning the wire is attached to the balance-arm, the rock fragm'ents remaining immersed in the water; a thermometer is placed in the companion beaker of water, now likewise in the balance case, and the weight is at once taken. Both vessels of water having precisely the same temperature, it is quite unnecessary to wait for the water to assume that of the balance should it not already possess it. The fragments are now lifted out, without touching the vessel, and carefully transferred to a tared crucible or dish; the wire is removed and at once reweighed with the precaution that it dips just as far into the water now as when weighed. Hereby a special weighing of the wire out of water is avoided. The sample may now 1114 APPENDIX II. be dried on the water-bath and then at 110 C. for some hours to certainly expel all absorbed water, and weighed after prolonged cooling in the desic- cator. It is better to ascertain the weight of the dry rock after soaking in water than before, in order to avoid the error due to possible breaking off a few grains between the two weighings. Should the density of the rock in air-dry condition be required, it may be left exposed to the air for a long period after drying and before weighing;* but the difference will only in exceptional cases affect the second decimal by more than a single unit. For instance, an undried rock of 2-775 specific gravity containing in the un- crushed sta.te the high percentage of 0-3 hygroscopic moisture will have a density of 2-79 when dry ; a rock of 2 982 specific gravity, undried, will have a density of 3-00 after removal of 0-3 per cent, of moisture. The difference becomes greater as the density of the rock increases. This method of ascertaining the specific gravity of rocks is certainly more convenient than, and for compact rocks is believed to be decidedly preferable to, that of the pycnometer, in which the fragments must be re- duced to small size with consequent formation of more or less powder, which is subject to slight loss in the various manipulations. To exclude this powder and employ only small fragments would introduce a possible source of error, since it is likely to consist largely of the most easily abraded minerals and consequently not to have the average composition of the mass. By following the instructions given above, loss of material is absolutely avoided, a decided saving in time is effected, and considerable weights can be easily employed with consequent lower probable error in the results. To vesicular rocks, however, notably certain lavas, the above procedure is, of course, inapplicable, unless the datum is desired for certain considerations in which the relative density of large rock masses as they occur in nature is sought, as for the comparison of building-stones or the calculation of large known or acsumed areas of particular rocks. PENFIELD'S Method for Mineral Fragments. PENFIELD f recommends the following modification of the suspension method as more convenient than that by the pycnometer in many cases for small fragments of minerals. After boiling in water, the substance is transferred with water to a small glass tube about 8 mm. by 35 mm., provided with a fine platinum wire for suspension. This is weighed full of water in another vessel of water, and again after the removal of the mineral, the weight of which is found after drying. This method is, of course, more applicable to homogeneous minerals than to rock fragments, and will therefore be applied in rock analysis chiefly * In view of the uncertainty as to what constitutes hygroscopic water (see p. 1117 et seq.), this course is perhaps more to be commended than the former, and seems imperative for certain zeolitic rocks. In such cases it is best to weigh the fragments before putting to soak, and afterwards to collect on a GOOCH crucible the grains which may have fallen off in the water. Should no crucible of this kind be available, a paoer filter may un- hesitatincrlv be used and incinerated with the powder, owing to the small amount of which the error due to loss of even all its water during ignition is quite negligible, t Am. Journ. Sci., 3d Series, L, p. 448, 1895. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1115 to the determination of the specific gravity of the mineral grains separated by heavy solutions or acids. PYCNOMETER METHOD. If the pycnometer has to be used, as is generally the case when the den- sity of any one of the mineral ingredients of a rock is desired after separation by one of the approved methods, it being then in a more or less finely divided state, the most accurate procedure is that adopted in this laboratory by Mr. L. G. EAKINS a number of years ago. The pycnometer used is one with a capil- lary stopper, provided with a millimeter scale etched in the glass, the divisions being numbered both ways from the centre and calibrated by mercury so that the value of each one in weight of water is known. The capacity of the flask filled with water to the zero division is then calculated for every half degree of temperature from C. to 30 C., by making a series of careful weighings, in which the capacity of the stem being known, it is quite imma- terial at what level the water stands provided it is within the limits of the scale. The exact temperature is obtained by an accurate thermometer placed in a companion vessel of similar shape to the pycnometer and con- taining a like amount of water, both being left in the balance-case till its temperature has been nearly or quite assumed, as shown by a second ther- mometer. The weighing must of course be made before the thread of water has sunk beneath the lowest division, which it will do after a time, even though at first filling the bore to the top of the stopper; and the corrected weight when full of water to the zero mark is found by adding or subtracting the needed amount, as shown by the height of the thread on the scale. For each pycnometer in use, and these are of different sizes, is prepared a table showing its weight, the value of each scale division in grm. of water, and the capacity of the flask at different temperatures, as indicated above. The preparation of such a series of flasks is time saved in the end, for the weighing of the flask full of water each time a density determination is made is rendered superfluous. All that is necessary is to look up in the table the weight corresponding to the temperature. The density of the previously weighed substance in this case is now de- termined in much the same way, after the unstoppered pycnometer con- taining it and nearly filled with water has stood with its companion vessel of water under the air-pump the necessary length of time. The water needed to fill the flask is taken from its companion. All who have used the pycnometer method for fine substances know the difficulty experienced in preventing a portion from being held at the surface, despite all attempts at making it sink. Hence it often happens that a very small portion runs out around the sides of the stopper on inserting it. If the flask rests in a small tared dish the grains thus forced out may be washed down into it and weighed after evaporation in order to get the correct weight of that in the flask ; or, after weighing, the contents of the flask may be emptied into a tared dish and the water slowly evaporated off in order to get the weight of the mineral Usually this way is less to be recommended than the other. 1116 APPENDIX II. HEAVY SOLUTIONS NOT SUITABLE FOR ROCKS. Because of their roughness, porosity, and complex mineral composition the density of rock fragments cannot be accurately determined by that of heavy solutions in which they may remain suspended. III. PREPARATION OF SAMPLE FOR ANALYSIS. QUANTITY OF ROCK TO BE CRUSHED. In the great majority of cases a few chips from a hand specimen will well represent the average of the mass, but with rocks in which a porphyritic structure is strongly developed the case is different. Here a large sample should be provided, gauged according to the size of the crystals, and the whole of this should be crushed and quartered down for the final sample, Unless this is done, it is manifest that the analysis may represent anything but the true average composition of the rock. . CRUSHING. Mechanical appliances for reducing samples to fine powder are much in use in technical laboratories, where they answer their purpose more or less satisfactorily, and something similar is needed in those scientific labora- tories where rock analysis is of daily occurrence and many samples must be reduced to fine powder in a short space of time. For accurate analyses the use of steel crushers and mortars is out of the question, because of the danger of contamination by particles of metal and the impossibility of cleansing the roughened surfaces after they have been in use a short time. Extraction by the aid of a magnet of steel particles thus introduced into the powder is quite inadmissible, since the rocks themselves, almost without exception, contain magnetic minerals. The method of rough crushing on a small scale found to be most satisfactory in practice is to place each fragment as received on a hard steel plate about 4 cm. thick and 10 cm. square, on which is like- wise placed a steel ring 2 cm. high and of about 6 cm. inner diameter, to prevent undue flying of fragments when broken by a hardened hammer. In this way a considerable sample can soon be sufficiently reduced for transfer to the agate grinding mortar with a minimum of metallic contamination. For breaking large pieces of rock to small sizes a thick iron plate with specially hardened surface and a similarly hardened pounder, such as street- pavers use, will probably render the best service, but the hardening must be done with extreme care. GRINDING. Of the various grinding arrangements on the market purporting to fulfill their purpose few, if any, observed have met the conditions required by the work in hand. Either the mechanical arrangement is complicated or cum- bersome, requiring more power or space than is usually at disposal or csusirg too much noise, or thorough cleansing is difficult and troublesome, or there is likelihood of contamination from oil or grease or lack of facility for the SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1117 removal of all powder from the mortar. These last defects are especially prominent in those forms in which the mortar is fixed in its setting. All rock samples have therefore been reduced to powder by hand, involv- ing a great expenditure of time and labor. Ordinarily an extremely fine state of division is unnecessary, except in the case of those portions in which alkalies and ferrous iron are to be estimated or where soluble constituents are to be removed by acids, etc., and in such cases the final grinding can be doae at the balance-table on a small portion slightly in excess of the quantity to be weighed off. The process of sifting through fine cloth, the German ' ' Beuteln," is not one always to be commended, because of the time required and, more especially, because of the certainly of contamination by cloth fiber, which in the ferrous- iron portion might affect the result. Still less should metal sieves be used. WEIGHT OF GROUND SAMPLE. The sample when ground should weigh not less than 10 grm., and prefer- ably 20 in case it should be necessary to repeat or advisable to employ un- usually large portions for certain determinations, notably carbonic acid. Rock analysis has in this respect an advantage over mineral analysis, since material is almost always available in ample quantity and any desired num- ber of separate portions may be used, whereas with a mineral the analyst is frequently compelled to determine many or all constituents in a single, often very small, portion of the powder. This course often involves delay and the employment of more complicated methods of separation than are usually necessary in rock analysis. IV. WATER HYGROSCOPIC, ZEOLITIC, CRYSTAL. Importance of Employing Air-dry Powder for Analysis. The time- honored custom of drying a powdered specimen before bottling and weighing has long seemed to the writer one that has no sound basis in reason. Its object is of course plain, namely, that of securing a uniform hygroscopic condition as a basis for convenient comparison of analytical results, since some rocks contain more hygroscopic moisture than others. Nothing, however, is more certain than that by the time the substance is weighed it has reabsorbed a certain amount of moisture, small, indeed, in most cases, but very appre- ciable in others; and further, with every opening of the tube, moisture-laden air enters and is inclosed with the remainder of the dry powder. It therefore may very well happen that a powder at first dry will, after several openings of the tube, especially at considerable intervals, be nearly as moist as when first inclosed. It is preferable to weigh the air-dry powder and to make a special deter- mination of moisture. If all the portions necessary for an analysis are weighed out one after another, or even at different times on the same day, the error due to difference of hygroscopicity in dry and moist weather, which for most of the separate portions is an entirely negligible quantity, is eliminated. Onlv 1118 APPENDIX II. in the main portion, in which silica and the majority of the bases are to be estimated, can it ever be an appreciable factor. Temperature of Drying. As to the temperature to be adopted for drying in order to determine so-called hygroscopic moisture, the practice has varied at different times and with different workers, ranging from 100 to 110 C. For the great majority of rock specimens it is quite immaterial which of these temperatures is adopted, since no greater loss is experienced at the higher than at the lower temperature, given a sufficient time for the latter. It is the present practice in this laboratory to employ a toluene-bath giving a tem- perature of about 105 C. Should the results show a very unusually high loss, the powder is reheated at, say, 125, in order to leaiai if the loss is progressive with increased temperature In the affirmative case it may be well to repeat the drying at 100, for a portion of the loss at 105 was probably due to com- bined water from a mineral or minerals in the rock; but in that case even the loss at 100 may sometimes very well include combined water, in which case drying over sulphuric acid alone may be desirable, or over dry sand. Cautionary Hints. In this latter connection it is proper to point out cer- tain pitfalls in the path of the unwary, which, however, are far more likely to be encountered in the analysis of minerals, where their influence may be of far-reaching consequence A mineral which loses a great deal of water over sulphuric acid "2 or 3 per cent, for instance may need an exposure of several days or even weeks for its complete extraction. If the weighings are made from day to day, the apparent limit may be reached long before all water really removable has been taken up by the acid. Whenever the crucible, after weighing, is re- placed in the desiccator it is no longer in a dry but a more of less moist atmos- phere, and its contents, even when covered, sometimes absorb a part of this moisture and retain it so persistently that the acid is unable to bring the powder beyond its previous state of dryness in the next twenty-four hours. In fact, it may be unable even to reach it unless greater time is allowed. An experiment on 1 grm. of tyrolite, made and published some years ago, seems to illustrate this point in part? Hours Exposed. Loss. Hours Exposed. Loss. 18 26 23 24 23 24 25 Grm. 0.0231 0083 0029 0012 0008 0001 0003 24 24 48 24 Grm. 0-0002 0003 0006 0002 283 0380 The experiment might reasonably have been considered ended after the one hundred and fifty-eighth hour, when a loss of but 1 mgrm. was shown during twenty-four hours; but nevertheless a nearly steady loss of 0-3 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1119 mgrm. per day took place for six days more, and might have been longer ob- served but for the interruption of the experiment. Again, it is a common practice to determine the water given off by hydrous minerals in an air-bath at temperatures far above 100 C. To insure accuracy this experiment should not be made in crucibles or dishes which must be cooled in a desiccator. One instance will suffice : A gramme of a mineral mix- ture containing about 17 per cent, of water, of which about 3 per cent, was driven off at 100 and 8 or 9 per cent, at 280, was, after several hours' heat- ing at the latter temperature, placed in a desiccator over sulphuric acid and weighed as soon as cold, then replaced and again weighed the next day. It had regained 1 per cent, of its original weight, although the desiccator was tightly closed and the crucible covered, showing apparently a drying power superior to that of the acid. A specimen of tyrolite was found on one occasion to lose 10 34 per cent, at 280 C., and on another occasion 14-33 per cent. In the latter case the drying and heating at progressive temperatures had continued during a period of 528 hours, the weighings being made usually from day to dayj whereas in the former the duration of the experiment was much shorter and the intervals between weighings were but a few hours each. Procedure in Special Cases. For experiments of the kind just indicated the powder should be heated in a weighed tube, through which a current of dry air can be passed, and allowed to cool therein, or else the water given off should be collected and directly weighed in suitable absorption tubes, even though the long time often required is an objection to this latter method, since the absorption tube may gain weight, other than that of the water from the mineral, sufficient to introduce an appreciable error. The recent important research of FRIEDEL * well shows what errors are possible in the determination of this easily removable water, since he found that certain zeolites which had been largely dehydrated but not heated to the point of rupture of the molecular net, could then absorb, instead of water, various dry gases in which they might be placed, as carbon dioxide, ammonia, carbon disulphide, and others, even air in large quantities, and certain liquids. In the light of this observation the cause of the great increase of 1J per cent, in weight of the partially dehydrated mineral mentioned above may very possibly be attributed to air from the desiccator instead of moisture, as was at the time supposed. At any rate, as FRIEDEL says, the danger of accepting a loss in weight as an index of the amount of water lost is clearly shown, and thus that method of determining water is for many cases fully discredited. Just what method to adopt must be largely left to the judgment of the oper- ator, who will often be guided by the mineral composition of the rock as revealed by the unaided eye or the microscope, FRIEDEL (loc. cit}. indicates a means for determining the true weight of water lost by minerals behaving like the zeolites, even without collecting the water lost, namely, by driving out of the dehydrated and weighed mineral, under proper precautions, any air it may have absorbed in the process of * Bull. Soc. Min., xix, pp. 14, 94, 1896; Couples rendus, cxxn, p. 1006, 1896. 1120 APPENDIX II. drying and cooling, and collecting and measuring this air and thus finding its weight, which, added to the apparent loss, gives the true contents in water. Argument in Favor of Including Hygroscopic Water in Summation. The question has been asked : '' If the so-called hygroscopic water is not always such, but not infrequently includes combined water, why is not its deter- mination and separate entry in the analysis entirely unnecessary? Why make a distinction, which, after all, may not be a true one?" The question involves the further consideration of the advisability of including in the analysis at all the loss at 100 or 110 C. Many petrographers desire to have all analyses referred to a moisture-free basis, in order that they shall be strictly comparable, and therefore would omit the "hygroscopic" water from the list of constituents. This would be eminently proper were it always possible to be sure that the loss at 100 truly represents mechanically held water. Since it very often represents more, and the determination as to whether or not it does in each case is not always possible, and would add to the time required for the analysis, it seems necessary to include this water. What errors may arise from its exclusion the following rather extreme case well illustrates: Certain rocks of Wyoming in powder form lost from 1 to 2 per cent, of moisture at 110. That not even an appreciable fraction of this was truly hygroscopic the fact of the uncrushed rocks losing the same amount fully demonstrates; yet the rule followed by many chemists and petrographers would have involved the removal of all this water as a preliminary to begin- ning the analysis, and not only would a most important characteristic have passed unnoticed, but the analyst would have reported an incorrect analysis, inviting to false conclusions and possibly serious confusion. Separate Entry of Hygroscopic and Combined Water. To revert now to the primary question, it may be said that the estimation of the loss at 100 or 110 C. and its separate entry in the analysis is advisable as not infrequently affording at once to the lithologist an indication of the mineral character of one or more of the rock constituents, thus perhaps confirming the micro- scopical evidence or suggesting further examination in that line. An un- usually high loss at 100 would be regarded as probable evidence of the pres- ence of zeolites or other minerals carrying loosely combined water. It has been objected that the true hygroscopic moisture varies with the degree of com- minution of the sample and with the condition of the air at the time of weigh- ing, and that it is therefore improper to incorporate it in the analysis; but this variation is ordinarily not at all great. Perhaps the time may come when it will be the rule to ascertain by additional heating at a higher tem- perature whether the water lost at 100 is to be regarded as purely hygro- scopic. In such case it would be proper to omit it, and a distinct advance would undoubtedly be scored. Is all True Hygroscopic Water Expelled at 100? It has been tacitly assumed in the foregoing that true hygroscopic water can all be expelled at 100, which perhaps is not to be accepted as universally true. Eminent authority holds that it is impossible, in the cases of certain foliaceous minerals, notably the micas, to thus entirely remove it, but that a part is only driven off at SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1121 higher temperatures. If this is true a further uncertainty is introduced in its determination, which not only strengthens the argument hi favor of enter- ing all water in the tabulation, but also serves to emphasize the difficulties of the situation. APPARATUS FOR THE DIRECT DETERMINATION OF WATER AT DIFFERENT TEMPERATURES. A form of drying -oven devised by Dr. T. M. CHATARD * is in use in this laboratory for determining water at different temperatures up to 350 C., and gives entire satisfaction. It is an asbestos-covered copper box B, shown in different aspects and parts in the accompanying Fig. 3. The box is so con- n FIG. 3. CHATARD'S form of drying oven for water determinations. B, copper box 18 cm. long, 1(H cm. high, 9 cm. wide, open in front, its sides and top covered with asbestos board; S, two slides of different sizes to close the openings O, after the tube is in position; F, asbestos-board front stiffened by an interlaid sheet of copper; R, metal rod to hold front in place; A, calcium-chloride absorption tube. structed that the tube with its contents can be removed without detaching from either the drying or collecting tubes, which is a great advantage if it is desired to afterwards apply the direct heat of a lamp in order to expel the water retained at 300 to 350. To facilitate this removal the stand is on rollers, so that after clamping the projecting end of the tube and removing the front of the box F and the little side pieces S closing the horizontal slits, the oven can be rolled bodily backward, leaving the tube and its attachments * Am. Chem. Journ.. xm, p. 110. 1891; Bull. U. S. Geol. Survey, No. 78, p. 84. 1122 APPENDIX II. in their original position, ready for further heating over a burner or blast. The removable front F of the oven is made of two pieces of sheet asbastos board stiffened by an interlaid piece of sheet copper. The inner piece of asbestos board fits snugly into the box, while the outer one, being slightly larger, by its projecting edges hinders the door from falling in and helps to prevent air currents. This door is held in place by the metal rod R. The little slides S are made in a somewhat similar manner, and are intended to slip in from the front and close the two openings after the tube is in place, but before closing the front. For other forms of tubes adapted to similar determinations, see pages 1124 and 1130. V. WATER TOTAL OR COMBINED. ARGUMENTS AGAINST "LOSS ON IGNITION" METHOD. In a few cases the simple loss on ignition of a rock will give the total water with accuracy, but in the great majority there are so many possible sources of error that this old-time method can rarely be used with safety. Only when the rock is free from fluorine, chlorine, sulphur, carbon, carbon dioxide, and fixed oxidizable constituents can the loss be accepted as the true index of the amount of water present, and it is rarely that a rock is met with fulfilling these conditions, especially as to the absence of ferrous iron. Blast ignition in presence of carbon dioxide alone of the above list may give a correct result, after separate estimation of the carbon dioxide, provided this emanates from carbonates of the earths and not from those of iron or manganese. The long-maintained and still upheld idea that in presence of ferrous iron a sufficiently correct result is obtainable by adding to the observed loss an amount needed for oxidizing all ferrous iron is not justifiable. There can be no certainty that the oxidation has been complete, especially in the case of readily fusible rocks, and at the high temperature of the blast a par- tial reduction ot higher oxides is not only possible, but sometimes certain. The inability to insure complete oxidation by simple ignition is illustrated in the case of precipitated ferric hydroxide which has been ignited in contact with its filter-paper. If the quantity was in any degree large it is sometimes decidedly magnetic, presumably from presence of magnetic oxide, which no amount of heating wholly oxidizes, especially in the larger grains. Neither is evaporation with nitric acid and reignition sufficient to destroy the mag- netic property of the oxide, as has been claimed. Direct weighing of the water evolved is then imperative in most cases, and of the numerous methods advocated, or in general use, several will now be considered. DIRECT WEIGHING OF THE WATER WITHOUT THE USE OF ABSORPTION TUBES PENFIELD'S METHODS. For Minerals Easily Deprived of their Water. If no other volatile constitu- ents than water are present, the beautifully simple method first used by SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1123 Prof. G. J. BRUSH and extended by Prof. S. L. PENFIELD * leaves nothing to be desired for accuracy. It consists simply in heating the powder in a nar- row tube of hard glass, enlarged at the closed end and provided with one or two further enlargements in the middle to hold the water and prevent its running back and cracking the hot glass. A capillary glass stopper fitted in with rubber tubing prevents loss of water by circulating air currents. The tube being held horizontally, the bulb is heated to any required degree by the BUNSEN or blast flame. Moistened filter-paper or cloth wound about the cooler parts of the tube insures condensation of all water. The heated end being finally pulled off, the tube is weighed after cooling and external cleansing, and again after the water has been removed by aspiration. For most rocks, as they contain little water, central enlargements of the tube are hardly needed. Various forms of tubes used by PENFIELD are shown in Fig. 4. Before using, even if apparently dry, "these tubes must be thoroughly dried inside, w r hich is best accomplished by heating and aspirating a current of air through them by means of a glass tube reaching to the bottom." How this simple tube is made to afford entirely satisfactory results with C f FIG. 4 PENFIELD'S tubes for water determination in minerals, a, b, c, different forms of tubes; d, thistle tube for introducing the powder; e, capillary-tipped stopper. minerals, even when carbonates are present, is fully set forth in the paper cited. Few rocks, comparatively, are altogether free from other volatile con- stituents. Hence, for refined work the application of this apparatus in the simple manner above set torth is limited. It may, however, be used with the addition of a retainer for fluorine, sulphur, etc., in the shape of calcium, lead, or bismuth oxides. Far Minerals not Easily Deprived o/ their Water. When minerals are pres- ent which do not give up their water wholly, even over the blast, as talc, * Am. Journ. Sci., 3d Senes, XLVIII, p. 31, 1894; Zetfsch. fur anorg. Chemie, vii, p. 22 1894. 1124 APPENDIX II. topaz, chondrodite, staurolite, etc., PENFIELD'S simple combination of fire- brick and charcoal oven, depicted in Fig. 5, must be used, either with or without a retainer for fluorine, as circumstances demand. The part of the tube in the fire is to be protected by a cylinder of platinum foil tightly sprung about its end, and the part outside by asbestos board, as well as by wet cloth or paper. A piece of charcoal is likewise laid on the tube, as well as beneath and behind, and the blast flame is given a horizontal direction, so as to play upon the side of the apparatus. In this way a most intense temperature can be reached. In 'whichever way the apparatus may be used, the water found is the FIG. 5. PENFIELD'S fire-brick and charcoal oven for use in determining water, total water, from which that found separately at 105 may be deducted if desired. DIRECT WEIGHING OF THE WATER IN ABSORPTION TUBES. Penfield's Procedure. The simplest of these methods as to apparatus, and one permitting, by the use of auxiliary arrangements such as are shown and described on page 1121, the determination of the hygroscopic as well as any other fraction of the water, is the following glass-tube arrangement (Fig. 6) of Dr. PENFIELD'S,* whereby the brick and charcoal oven already referred to (Fig. 5) comes again into play, but without the half-brick shown in that figure. u 16 C.Mr A 11 C.M.- + 16C.M.-- Fio. 6 Tube for water determination according to PENFIELD. A outer protecting covering of platinum foil. A second similar foil on the inside prevents the glass from collapsing when heated to softness. 6, cross-section of platinum boat. The tube is of about 15 mm. internal diameter, and is fitted with two platinum cylinders at A, one inside, the other outside, where the heat expo- sure is to be most intense. These cylinders are made from pieces of platinum foil, about 0-07 mm. in thickness and 8 by 11 cm. in diameter, which have been previously bent around glass tubes of such a size that when applied to the combustion tubing the * Am. Journ. Sci., 3d Series, XLVIII, p. 37. 1894; Zeitsch. fur anorg. Chemie, vx, p. 2? SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1125 spring of the metal will hold them in place. A large platinum boat, 7 to 8 cm. long and 11 to 12 mm. in diameter, with a cross-section like 6, should be used, since this will readily hold a gramme of mineral mixed with 5 grm. of sodium carbonate. The tube is placed in the angle formed by the char- coal lining, some pieces of charcoal are placed at the sides in front, leaving an opening through which the flame may be directed, and an additional piece is laid on top. The tube can readily be brought to a full white heat, and by forcing a slow current of dry air through the apparatus the carbon dioxide resulting from the decomposition can be removed and the water carried over into the weighed absorption tube. The glass fuses between the plati- num casings, and in a number of experiments that have been tried there has not been a single instance where the glass tube has broken or shown any indication of breaking. After heating the tube will not crack if it is left to cool slowly on the charcoal, but it cannot be used a second time. At the high temperature to which the glass is subjected it of course becomes very soft and the ends must be properly supported; also the rubber connec- tions and absorption apparatus must be carefully screened by asbestos board. By constructing a cover for the boat no material need be lost by spattering, and after making the water determination the contents may be used for the remainder of the analysis. The inner cylinder of platinum serves to prevent the glass from collapsing as it softens, whereby distortion of the boat would result and its withdrawal for further examination of its contents would be impossible. Gooch's Apparatus. Of more elaborate apparatus, designed to be used with fluxes, the tubulated platinum crucible invented by Dr. GOOCH * is capable of affording most excellent service, and it is the one by which far the larger number of water determinations in this laboratory have been made. Fig. 7, which hardly needs detailed description, shows it in a modified form, which differs from the original forms of GOOCH in that the tubes for connecting with both the drying and absorption vessels are constructed wholly of platinum instead of lead glass, the vertical one being bent hori- zontally at right angles for convenient attachment to the drying towers, and the side one also bent at right angles, but downward, and having its end slightlv drawn in at E (Fig. 7) so as to admit of easy insertion in the rubber stopper of a U-shaped calcium-chloride tube as shown in Fig. 9 (page 1128). With tubes of the lengths shown in the figure there is absolutely no danger of their ends becoming hot enough by conduction to scorch or soften the rubber stopper or other connection. The extra first cost of the platinum extension to these tubes over the lead- jrlass ends of GOOCH'S original and modified forms need hardly enter as a factor into the question of emplovment of this apparatus The glass ends often break, and onlv a rich lead glass, not easily obtainable, can be used, since it alone will not crack at the joint with the platinum after cooling. In its present form the whole apparatus weighs aDproximately 88 grammes. As an adjunct to its convenient use there is needed an ordinary upright * Am. Chem. Jour., n, p. 247, 1880; Chemical News, XLH, p. 326. 1880. 1126 APPENDIX II. iron ring-stand, with two small sliding rings, and a sliding ring-burner pro- vided with entering ducts for gas and air blast. Across the uppermost ring FIG. 7. Modified form of the GOOCH tubulated platinum crucible for the determination of water, about one-half natural size. Weight about 88 grm. there is an arrangement of stout platinum wire (S, Fig. 8), forming at the center of the ring a secure seat for the upturned flange of the crucible proper. Both rings and burner can be clamped firmly at any height. The rock powder, having been placed in the cylindrical crucible (C, Fig. 7), is there mixed with not more than 3 or 4 grammes of fully dehydrated sodium carbonate,* or more of lead chromate if carbon is to be likewise determined. The crucible is sunk in its seat S (Fig. 8) in the upper ring R' and the tubu- lated cap T (Fig. 7) is fitted on and attached to the calcium-chloride drying towers preceded by one containing potassium hydroxide if carbon is like- wise to be estimated on the one side, and to a sulphuric-acid bulb tube B (Fig. 9) on the other. Powdered sodium tungstate free from arsenic, which would soon ruin the crucible lips is now poured into the flanged lip L fFig. 7) in which the cap rests, and a metal vessel of cold water having been * This has been heated for a length of time to near its fusing-point over a free flame or in an air-bath, to decompose the bicarbonate it usually contains, and then placed in a desiccator. Thus heated it is not very hygroscopic. PENFIELD found that 2-5 grm. of it, spread out on a watch-glass, gained only .0002 grm. in 15 minutes. Potassium carbonate and potassium-sodium carbonate are too hygroscopic by far to be available. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1127 raised up by the lower ring R" (Figs. 8 and 9) until the platinum crucible is sufficiently immersed, the flame of an ordinary blast-lamp is turned on to melt the tungstate. As soon as this is fused the flame is removed and the salt solidifies and makes an air-tight joint, the test of which is the perma- FIG. 8. Details of the GOOCH crucible for determining water. S, seat of stout platinum wire resting on ring R' , and serving as a support for the crucible; R'", blast -fed ring burner; R" , support for air- or toluene-bath O. nence of the column of sulphuric acid in the bulb tubes caused by the contrac- tion of the air in the platinum apparatus as it cools. After drying by a current of air at 105 for two hours, more or less (see below, page 1129), by means of an air- or toluene-bath as shown in Fig. 8, the absorption tube A (Fig. 9) is interposed between the sulphuric-acid bulbs and the apparatus, being fitted to the latter by its stopper, which is at other 1128 APPENDIX II. times closed b}' a glass plug, and while a slow current of air continues to pass the gradual heating and subsequent fusion of the flux is brought about by the blast-fed sliding ring-burner R'" (Figs. 8 and 9). The sodium-tungstate joint is shielded from the flame by small pieces of asbestos board P (Fig. 9), cut out so as to fit the crucible. When fusion is complete, as shown in the case of sodium-carbonate flux by the decided slackening of the gas current through the safety bulbs attached to the drying tube, the flame is extin- guished and a current of air is allowed to continue until the apparatus is cold. This apparatus suffers from the drawback of being slightly permeable to combustion gases at high temperature. The defect can be overcome by Fio. 9. Arrangement during fusion of GOOCH apparatus for determining water. R'" blast -fed ring burner; P, protective asbestos-board shield resting on ring R" ; FF, board forming end of frame and covered with asbestos board to prevent being set on fire by the heat of the blast. This serves at the same time as an efficient shield for the absorption tube A. In it there is bored a round hole at hh, through which passes the outlet tube from the crucible. B, sulphuric-acid bulbs serving to show the rate of gas currrent through the absorption tube and at the same time to prevent back entry of moisture from the air into A. > causing the flame to play upon an outer ordinary platinum crucible, kept permanently filled with sodium-potassium carbonate. This protective cm- ciblp, However, is soon ruined for other purposes, being distorted by the alternate expansion and contraction of the carbonate. It has been found that if the operation is carried out expeditiously and the final full heat applied for but a few minutes, the error due to penetrating SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1129 water gases is inappreciable. This hastening may be rendered safer by using rather finely powdered calcium chloride in the central section of the U-shaped absorption tube to avoid large air channels. Through this, or any apparatus based on similar principles, the air current should always be forced, not drawn. A warm blast directed upon the exit tube near its entrance into the absorption tube greatly shortens the time required and is to be recom- mended. In this apparatus only the water expelled above 100 to 1 10 should as a rule be determined, and to effect drying of the mixed mineral powder and sodium carbonate, after luting the tubulated cap on the cylindrical crucible with sodium tungstate, the tube is sunk through a round hole in the cover into a small cylindrical air-bath (Fig. 8), which can be heated from beneath by the same ring-burner which is subsequently to fuse the flux. A slow cur- rent of air is then forced through and the drying satisfactorily accomplished. The reason why it is unsafe to attempt estimation of 'hygroscopic" mois- ture in this apparatus is, that the luting of the two parts must be done by direct application of a flame to the tungstate, and considerable water-vapor may enter the apparatus and be in part retained by the dried sodium car- bonate. CHATARD'S A pparatus. The platinum apparatus devised by Dr. CHATARD* overcomes the permeability of the metal to gases and affords sharp results, moreover permitting of determining by direct absorption not only the hygro- scopic water, but that which may be driven off at any desired temperature, either with or without fluxes. It is, however, perhaps even more costly than the GOOCH apparatus, and the supposed non-liability to injury by warping, because of the protective layer of borax and asbestos, can hardly be considered as proved. Merits of the above Three Forms of A pparatus. All of these apparatus, except the glass tube of the modified BRUSH method, permit of the estimation of other constituents besides water in the same portion if necessary, and by the use of lead chromate or potassium chromate, instead of sodium carbonate, graphite, or the carbon of organic matter, can be simultaneously determined with the water. To one accustomed to its use, and with a drying and suspension attach- ment permanently set up, the GOOCH apparatus, considering its limitations above set forth, offers perhaps the most handy and convenient means for the determination of water in rocks. Its high first cost, in comparison with the glass tube, is fully made up in time by its durability. JANNASCH'S Methods. This zealous deviser of methods for mineral analysis has published in the Zeitschrift fur anorganische Chemie and the Berichte der deutschen chtmischen Gesettschaft several papers dealing with the problem of water determination in minerals, and in his text-book f these are collected in more or less modified form. For the majority of silicates he finds dehydrated borax powder a most * Am. Chem. Journ., xm, p. 110, 1891; Bull. U. S. Geol. Survey, No. 78, p. 84, 1891. *t Praktischer Leitfaden der Gewichtsanalyse, Leipzig, vov VEIT & Co., 1897. 1130 APPENDIX II. efficacious flux, usually at a very moderate temperature. The fusion is accomplished either in a platinum boat within a glass tube or in a tube of the form and dimensions shown in the accompanying Fig. 10. For rocks or minerals containing not much fluorine a retaining layer of granular lead chromate, or of previously fused and powdered lead oxide, is used as shown at a. Plugs of glass wool are used at c, c. Whether or not FIG. 10. Glass tube for determination of water (JANNASCH). 6, mixture of mineral powder with borax; c. c, plugs of glass wool; a, layer of lead chromate or lead oxide. Total length of the tube, 33 cm. ; inside diameter, 12-14 mm. the boat is employed the borax is first introduced and, together with the re- tainer, is thoroughly dried out in an asbestos oven by a hot-air current. Then, after cooling, the mineral powder is added and thoroughly mixed with the borax. Heat is applied by a flat flame to the mixture, which soon melts and forms a clear fusion, when the action is complete. The blast may be used in extreme cases. The layer of retainer must be kept warm by an auxiliary flame, and the absorption tube must be removed before the flame under the fused mass is extinguished, for the glass breaks as soon as this is A A Fio. 11. Glass tube for determination of water in special cases (JANNASCH). Length from a to e, 26 cm.; inside diameter somewhat over 1 cm. ; volume of bulb 6,25 c.c.; c, d, retaining layer of lead oxide between plugs of glass wool; /, calcium-chloride absorption tube; g, protective tube. done. Carbon dioxide can simultaneously be determined by attaching a soda-lime tube to the calcium-chloride tube. For one-half to 1 grm. of silicate JANNASCH uses 1 to 2 grm. of borax. Regarding the borax method, its inventor insists upon the following points as essential to success, especially when the blast cannot be applied: Most thorough mixing of flux and mineral powder and a most impalpable fine- ness of the latter. The borax itself is prepared by heating pure crystallized borax in a plati- num dish till a small portion has melted. That remaining unfused is pow- dered and again heated in the dish to dull redness for fifteen minutes, with constant stirring. The powder is placed in a tube with tightly fitting glass stopper, and kept over sulphuric acid. It must not be kept long without reheating, because of being hygroscopic. Another form of tube used by JANNASCH for special purposes is shown in Fig. 11. Minerals, such as topaz, which is not fully decomposed by the borax method and ^hich contains a large amount of fluorine, are fused at SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 3131 b with about six times their weight of lead oxide. A layer of lead oxide between c d serves to retain any fluorine escaping from the fusion, VL SILICA, SEPARATION FROM ALUMINA, ETC. ALTERNATIVE METHODS OF DECOMPOSITION. PRELIMINARY REMARKS. The practice of separating alumina, etc., by the usual method, after first attacking the rock powder with hydrofluoric and sulphuric acids silica being estimated in a separate portion while attractive . in principle, was aban- doned by the writer after fair trial, owing to the disturbance sometimes occasioned by incomplete expulsion of fluorine and to a less degree by the presence of sulphates instead of chlorides. With exception of the compar- atively few analyses made thus, the sodium-carbonate method has always been employed. In the case of rocks rich in fluorine strict accuracy would require the separation of silica to be made as in the BERZELIAN method for fluorine estimation (see toot-note, page 1133), but in practice it is not often necessary to resort to this tedious procedure, since the amount of fluorine is usually small and it can by no possibility cause a loss of much more than three-fourths its own weight of silica by volatilization as silicon fluoride when the sodium-carbonate fusion is evaporated directly with hydrochloric acid. Probably the loss is less, since some fluorine perhaps escapes as hydrofluoric acid. However this may be, the error is of comparatively slight importance, since it attaches to the constituent always present in greatest amount. Various fluxes other than alkali carbonates have been recommended for breaking up silicates insoluble in ordinary acids, such as lead and bismuth oxides, lead carbonate, borax, and boric oxide. Professor JANNASCH and his pupils have been especially active of recent years in this line of work, as evidenced by their numerous published papers. One of the advantages these fluxes possess over the alkali carbonates is their removability after serving their purpose, thus allowing the various separations to be made more perfectly and without the annoying interference of several grammes of foreign fixed salts, w r hich are most troublesome in that part of the analysis devoted to the separation of silica, alumina, iron, lime, and magnesia. Another of their advantages is that with some of them it is possible to estimate in one portion the alkalies, in addition to those constituents usually determined in the silica portion. Where the material is limited, as it so often is in mineral analysis, this is a most important advantage, sufficient to out- weigh all possible objections; but in rock analysis, where the supply of ma- terial is usually ample, it is rarely worth considering. A still further point in their favor is that it is probably more easy to obtain them entirely free from fixed impurities than an alkali carbonate. There are, however, objections to their use. With some of them an ex- traordinary amount of time must be devoted to grinding the mineral to an impalpable powder, and the flux itself may need considerable hand pulveri- zation. Once introduced, they must be removed before the analysis can be 1132 APPENDIX II. proceeded with, and this removal takes much time and is always a possible source of error. In mineral analysis these objections are entitled to far less weight than in rock analysis, since the object sought usually the deduction of a formula warrants the expenditure of much time and painstaking care. Finally, it has been found that one or more of these fluxes are not available for altogether general use, since certain minerals do not fully succumb to their attack under simple conditions, as andalusite with boric oxide and others with lead oxide (JANNASCH). Therefore, however well adapted one or the other of these methods may be for the analysis of homogeneous minerals, it is very im- probable that the vivid anticipations of Professor JANNASCH, to the effect that the boric-oxide method will soon supersede the alkali-carbonate-fusion method in rock as well as in mineral analysis, will be speedily realized. Never- theless, the boric-oxide-fusion method, owing to its evident merit, will be described in detail after brief reference to a means of bringing refractory silicates into solution without employing any solid reagent. DECOMPOSITION OF REFRACTORY SILICATES BY HYDROCHLORIC ACID UNDER PRESSURE. JANNASCH * pours upon the finely ground rock powder contained in a platinum tube of about 26 c.c. capacity a somewhat diluted hydrochloric acid (4 acid to 1 water), places over the open end a cap which does not her- metically close the tube, inserts the latter in a larger one of potash glass like- wise partially filled with the diluted acid, seals the glass tube, and places it hi turn in an inclined position in a steel MANNESMANN tube containing ether or benzene to equalize the pressure, and heats to any desired temperature up to 400 C. The chief drawback seems to be a somewhat incomplete decomposition doubtless due to the necessarily inclined position of the tube, which causes the powder to collect at the lower end, and thus renders decomposition less complete than if the material were spread evenly throughout the length of the tube. Further, the acid strongly attacks the platinum unless the air in both the platinum and the glass tubes is replaced by carbon dioxide. Even when this is done, several milligrammes of platinum are found in the silicate solution. Nevertheless, to those possessing the necessary platinum and steel tubes the method can render efficient service in special cases when economy of material is imperative. THE BORIC OXIDE METHOD OF JANNASCH AND HEIDENREICH.f Preparation of the Boric Oxide. This demands, if the alkalies are to be estimated in the same proportion as silica, etc., an absolutely alkali-free boric acid, which can be prepared by two or three recrystallizations of a good commercial article. The purified crystals are dehydrated and fused in a * Ber. deutsch. chem. Gesell., xxiv, p. 273. 1891, and Zeitschr. fur anorg. Chem. VI, p. 72, 1894. t Zeitschr. fur anorg. Chem., xn, p. 208, 1896. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1133 large platinum crucible. This is then suddenly cooled to cause the anhydride to crack into pieces of a size convenient for powdering, which are to be kept in a tight glass and powdered as needed, since the anhydrous oxide is hygro- scopic. Treatment of Easily Decomposable Silicates. To this flux JANNASCH and HEIDEXREICH find that nearly all silicates readily succumb over the ordinary blast-lamp. The fusion is made in a large crucible holding 40-65 c.c., and the proportion of flux to be used is gauged according to the nature of the silicate, ranging from 3 to 8 and more parts to 1 of mineral. This last must be finely powdered, especially the most resistant, the authors recommend- ing the expenditure of one-half to one hour's time for the grinding of one- half to 1 grm. of powder. A low-burner heat is applied for five to ten minutes till water is expelled, which is then gradually increased till the gas is fully turned on. Bubbling and rising in the crucible is prevented so far as pos- sible by using a short platinum rod which does not reach above the edge of the crucible. When the mass has been in quiet fusion for a time in the covered crucible the blast-flame is applied. The average duration of the entire operation is twenty to thirty minutes, but depends much on the char- acter of the mineral. Treatment of Refractory Silicates. For those minerals which, like anda- lusite, cyanite, and topaz, are not fully decomposable by the heat of the ordi- nary blast-flame, JANNASCH and WEBER * use a flame fed by oxygen instead of air. The blast-lamp, of 2 mm. opening, is supplied with gas from at least five or six ordinary gas cocks, and the flame is made broad and free from luminosity. The mineral having been first heated as above described but with a much larger proportion of flux as high as 30 to 1 a few grm. additional of boric oxide are added and the oxygen blast is applied till, in ten or fifteen minutes, the fusion is as transparent as glass, f Further Treatment After Fusion. From this point the further treatment is the same in both cases, and as modified by JANNASCH and WEBER (loc. cit.) is as follows: The hot crucible is cooled in cold water and the contents are turned into a very large porcelain or platinum dish, to which, after covering with a glass, a saturated solution of hydrochloric-acid gas in methyl alcohol is added. J The cover being then removed, the liquid is heated to boiling over asbestos board by an inch-high flame, stirring constantly, or it is left without atten- tion over a lower flame or on a water-bath heated short of boiling. The crucible is cleansed in a similar manner, and its contents are added to the dish. In ten to fifteen minutes, with occasional addition of the methyl chloride, solution is complete and the liquid is then boiled down to a small * Her. deutsch. chem. Geaell., xxxn, p. 1670. 1899. t An interesting and important observation reported by JANNASCH and WEBER is that when the oxygen blast has been used fo- ; hcates carrying fluorine or mixed with H'londes. the fluorine seems to be wholly expelled as boric fluoride, without loss of silica. If this should prove to be generally true, an easy way is at last afforded for estimating silica in such cases, where even its detection, when present in small amount, has hereto- fore been difficult. t Made by passing dry HC1 into cooled CH 4 O for from one to two hours. 1134 APPENDIX II. volume and evaporated to dryness on the bath. The residue is then digested on a bath at' 80 to 85 three or four times in succession, with the ether solution, in order to remove the last traces of boron as boric ether. Care should be taken to wash down from the sides of the dish, with methyl-chloride solution, the boric acid formed and deposited thereon during the evaporation. Possible Objections to the Boric-oxide Method. Very much is claimed by JANNASCH for this method, but with all its undoubted merit there are two points which may militate against it in time. The boric ether, driven off in such enormous quantities, at once decomposes in contact with mois- ture, and boric acid settles over all objects with which it comes in contact. The hood must become thickly coated. Hence a special hood for these evaporations alone seems to be called for, otherwise boric acid may at any time fall into other dishes and cause untold trouble. The second objection attaches to the use of the oxygen flame when alkalies are to be estimated in the fusion, and the ability to so determine them is one of JANNASCH'S chief claims in favor of the method, for it cannot be doubted that at the high temperature of this flame alkalies are volatilized in part. Borax can be slowly but wholly volatilized over the ordinary blast, hence there is great reason to fear sufficient loss at this much higher temperature to give rise to serious error at times. THE SODIUM-CARBONATE METHOD. Purity of the Sodium Carbonate used as a Flux. Notwithstanding the most earnest efforts for years, it has been impossible to procure, either in the open market or by special arrangement with manufacturers, an article of sodium carbonate which can be called chemically pure. With special precautions small lots can be prepared in the laboratory that will contain less than 1 mgrai. total impurity in 10 grm. ; but such an article cannot be purchased in the market, and rarely will the so-called chemically pure dry sodium carbonate contain as little as 1 mgrm. in 10 grm. The invariable contam- inating substances, aside from sand and straw, which have sometimes been found in large amount, are silica, alumina, iron, lime, and magnesia, all of these going into aqueous solution with the carbonate. The chief of these impurities are usually silica, alumina, and lime. An article of the above degree of purity is satisfactory in almost all imaginable cases, since the use of the usually extravagant amount of 10 grm. for a fusion would introduce an error of but 0-1 per cent, in the analysis, supposing 1 grm. of mineral to be operated on, and it would, moreover, be distributed over several con- stituents. This error is undoubtedly fully equalled by the introduction of dust from the air in the various long evaporations. Precautions in Fusing. Special directions with regard to the fusion and its first treatment are unnecessary, except to say that ordinarily from 4 to 6 parts of flux should be used to 1 of rock and that the flame should not be , directed vertically against the bottom of t.he crucible, but at an angle against the side and bottom, nor should the flame be allowed to envelop the whole crucible. These precautions apply in all ignitions of reducible substances, and yet they are rarely observed. In neither case, if neglected, will there be SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1135 the necessary oxidizing atmosphere within the crucible; on the contrary, reduction may occur fraught with serious consequences. This is especially true if the rock contains more than traces of pyrite or other sulphide, when, after cleansing and igniting the crucible, there may appear on its interior a darkening due to oxidation of reduced iron which had alloyed with the platinum. This may in exceptional cases amount to several milligrammes in weight, and can be removed only by repeated ignitions, followed each time by scouring or treatment with hydrochloric acid or acid potassium sulphate. In order to avoid the use of nitre in case of pyritiferous rocks, it is well to first roast the weighed powder in the crucible in which the fusion is to be made. Treatment after Fusion. When fusion is complete, the crucible is seized with the tongs (Fig. 1, p. 1110) and the contents are caused to solidify in a thin sheet over the sides and bottom by imparting an appropriate rotating motion with the arm during the cooling process. This is far preferable to allowing the melt to form a thick cake at the bottom, since much less time is required for disintegration, and separation from the crucible is usually much easier. It sometimes happens that the cooled flux, and even its solution, will indicate absence of manganese when it is really present in quantity to give normally a strong coloration. Two fusions made side by side or successively, under apparently similar conditions, may in one case show little or no man- ganese, in the other considerable. This observation has been frequently made, and therefore the absence of a bluish-green color in the fusion is not to be taken as proof of the absence of manganese. This difference of behav- ior I can ascribe to no other cause than that of a reducing atmosphere in one of the crucibles and an oxidizing one in the other, even though the con- ditions were apparently alike. The contents of the crucible are placed in a rather tall covered beaker with some water, and hydrochloric acid of 1-1 specific gravity is added in excess. The depth of the pink color usually produced on addition of the acid allows of judging approximately as to the amount of manganese present. The beaker is placed on the water-bath, and when disintegration is complete, having been assisted by gentle pressure with a blunt glass rod, the contents are transferred to a large platinum dish and evaporated on the bath. SUBSEQUENT TREATMENT. From this point the treatment will ordinarily be the same whether the boric-oxide or the sodium-carbonate method of decomposition has been employed. Drying and Testing of Silica. As to the best way of rendering silica insolu- ble by evaporation, the writer's predilection is for a double evaporation instead of a single one on the water-bath. By fusing with sodium carbonate in the forenoon the silica is ready for the first filtration in the afternoon. It is quite unnecessary to carry the evaporation beyond approximate dryness. The filtrate is again evaporated, always in platinum, and is ready for final filtration the following morning when approximately 1 per cent, of silica is recovered and added to the main portion. The writer's experience is that 1136 APPENDIX II. a better separation of silica is effected hereby, and in no more time than bv a single long evaporation. That which is subsequently recovered from the precipitate of alumina, etc. (p. 1139), rarely exceeds a half or, at the most, 1 mgrm. Drying in an air-bath at 110 or higher, or on a hot plate or sand-bath, or over a free flame, in order to render silica insoluble, offers no advantage unless much magnesium is present, and then the most favorable tempera- ture, according to GILBERT,* is 120. The presence of much calcium chloride seems to facilitate dehydration of the silica, while magnesium chlo- ride above 120, on the other hand, by decomposing, forms a silicate which dissolves in hydrochloric acid and increases the amount of silica carried into the filtrate. It does not appear from GILBERT'S paper that the blast- furnace slags, on which he experimented, contained titanium, phosphorus, or iron in appreciable amounts. Basic magnesian rocks usually do, and in such cases it is probable that the employment of a drying temperature of 120 would materially add to the large impurity always to be expected with the silica. In other cases he confirms the earlier belief that drying tempera- tures higher than that of the water-bath increase the amount of insoluble impurity, chiefly alumina, in the s'lica, and that this amount cannot be reduced by long digestion with hydrochloric acid. Further, he confirms LINDO'S statement that evaporation with sulphuric acid till the appearance of white fumes gives a higher result in silica than with hydrochloric acid. But for general rock analysis the use of sulphuric acid at this stage must be rejected utterly. Blasting for twenty to thirty minutes f is necessary to expel all moisture from the silica, and it is then not hygroscopic. Its weight should always be corrected for impurities, which are never absent, by evaporating with hydrofluoric and sulphuric acids and again blasting. If toward the end of evaporation with these acids, when the hydrofluoric acid has been driven off and the sulphates begin to appear in solid form, the residue has a pecu- Jiar milky or enamel-like appearance, it may be taken as evidence of much phosphorus and titanium. This appearance is possibly due to zirconium with the phosphorus and titanium,:}: and is so unusual and striking that it is worth while calling attention to it. With basic rocks very rich in titanium and phosphorus the residue may amount to 2 or even 3 per cent, of the rock. The subsequent precipitate of alumina, etc., is usually ignited in the crucible containing the residue from the silica. It might be supposed that this residue would contain most of the barium of those rocks carrying that element, together with sulphur or sulphates, * Technology Quarterly, in,. p. 61, 1890. Abstract in FRESENIUS'S Zeitschr. fur anal. Chemie, xxix, p. 688, 1890. t It must be borne well in mind that some platinum crucibles lose weight steadily and very appreciably on long blasting, not only when new but even after long use. When a crucible suffers from this defect the rate of loss should be ascertained from time to time and allowance made accordingly, or else the weight of the crucible should be taken after and not before ignition of the precipitate. (See on this subject HALL, Journ, Am. Chem. Soc., xxn, p. 494, 1900.) J See second foot-note, p. 1133. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1137 but the reverse is true as a rule. Only when there is a considerable excess of SO 3 over the BaO will much of the latter be found there, and in the vast majority of cases there is none at all. Should some be present, its removal and estimation at this stage is not necessary, as it can be more conveniently recovered later, together with the silica accompanying the alumina, etc., precipitate (p. 1139). The separation of silica in rocks containing fluorine has been touched upon in commenting on the boric-oxide and sodium-carbonate methods of fusion,* and will be considered further under the head of Fluorine (p. 1182). Platinum in Filtrates. The filtrates from the silica always contain nota- ble amounts of platinum. This arises in very small degree from the crucible fusion, in a larger one indirectly from the action of hydrochloric acid on manganate, vanadate, and sometimes chromate of sodium, and, if much iron is present, in no small degree from the reduction of ferric chloride to ferrous by the platinum of the dish. This last reaction is little known, apparently, but is mentioned in GMELIN-KRAUT,| and can be readily de- monstrated by evaporation of ferric chloride in platinum. The removal of this platinum before precipitating alumina and iron is not necessary (but see first foot-note, p. 1140), and to do so involves the reoxidation of all iron and subsequent boiling to remove or destroy the excess of oxidizing agent, together with the expenditure of much valuable time. The iron is already oxidized by the fusion, and needs no further help in that direction. Nevertheless, if time is not a prime object, its removal by hydrogen sulphide is to be recommended. In the following descriptions, however, it is assumed that the platinum has not been gotten rid of at this stage. VII. METALS PRECIPITABLE BY HYDROGEN SULPHIDE. The presence in appreciable amounts of metals precipitable by hydro- gen sulphide, except perhaps copper, is of such infrequent occurrence in most rocks that discussion is unnecessary in their connection. In case it is necessary to precipitate them at this stage, however, it is always well to bear in mind that a little titanium may be thrown down along with them. Separations of the silica should be made in porcelain, to eliminate platinum, or, better still, the quantitative estimation of these metals should be made in a separate portion of the rock broken up by the action of hydrofluoric and sulphuric acids. VIII. ALUMINIUM. TOTAL IRON. INDIRECT METHOD FOR ALUMINIUM. The common practice in this laboratory is to find alumina by difference, after deducting from the precipitate produced by ammonia or sodium ace- tate the sum of all other oxides this precipitate may contain. Of these, only ferric oxide, titanic oxide, and the trace of silica are determined in this * See p. 1131, and foot-note, p. 1133. t Anorg. Chem., in, p. 359. Sixth revised edition. 1138 APPENDIX II. portion (see also first foot-note, p. 1140), those of phosphorus, vanadium, chromium, and zirconium being looked for in other portions of the rock powder. This throws upon the alumina all errors involved in their separate determinations: but these may balance, and in any case the probable error can hardly be as high as that involved in the direct weighing of the alumina itself, considering the difficulty of effecting a satisfactory separation of it from all the other admixtures, an operation which would, moreover, immod- erately extend the time required for each analysis. PRECIPITATION OF ALUMINIUM, IRON, ETC. Precipitation by Ammonia. Two precipitations by ammonia at boiling heat are usually quite sufficient to separate iron, aluminium, phosphorus, vana- dium, chromium, titanium, and zirconium, if all these are present, from nickel, manganese, the alkaline-earth metals, and magnesium, provided ammoniacal salts are present in sufficient quantity. This last point is of special importance as regards magnesium, and failure to observe it is doubtless the reason why many old analyses, and sometimes modern ones, show utterly improbable percentages of alumina, especially as chemists were formerly often satisfied with a single precipitation. The necessary ammonium chloride is better obtained by the use of purified ammonia water and hydrochloric acid than by the addition of the solid salt, which is seldom pure. Precipitation by the Basic Acetate Method. But it will occasionally happen that the separation from even very small amounts of manganese is alto- gether incomplete, and the uncertainty of insuring this separation has led the writer of late to employ the basic acetate method for the first precipitation in all cases where manganese is present and the exceptions are few even though the precipitation of alumina is sometimes less complete than by ammonia, and in spite of other admitted defects, as, for instance, a tendency of the precipitate to run through the filter on washing.* Not more than 2, or at most 3, grm. of sodium acetate need be used. After slight washing and sucking dry at the pump, the precipitate is redissolved in a large excess of hydrochloric acid and reprecipitated by ammonia in slight excess. The complete boiling off of this excess is unnecessary, as pointed out by GENTH and PENFIELD, since it is apparently the washing with pure water and not the free ammonia which carries small amounts of alumina into the filtrate. PENFIELD and HARPER f recommend washing with a dilute solution of ammo- nium nitrate (20 c.c. nitric acid, neutralized by ammonia, to the liter), and also the solution of the first precipitate in nitric instead of hydrochloric acid, in order to shorten the washing, there being no chloride to remove. The filtrates are strongly concentrated separately J in platinum, a drop * The fact must not be overlooked that certain of the rare earths may pass completely into the nitrate if the basic acetate method is followed. If then, later, on rendering the combined filtrates ammoniacal, an unexpectedly large precipitate appears, this should b# carefully examined as to its nature. In an analysis, of piedmontite from Maryland cover 2 per cent", of rare earths, including cerium and others not identified, were quanti- tatively separated in, this way from iron, alumina, etc. t Am. Journ. Sci., 3d Series, xxxn, p. 112, 1886. t If. instead of sodium acetate, ammonia alone has been used to precipitate alumina etc., it has sometimes happened in the experience of others than the writer that on con- SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1139 or two of ammonia being added toward the end to the second one, and fil- tered successively through the same small filter into a flask of 150 to 200 c.c. capacity, tte ammoniacal filtrate serving as wash water for the first dish and containing: enough ammoniacal salt to prevent precipitation of magnesium in the first filtrate when mixed with it. If manganese has been deposited upon the surface of the dish it is removed by hydrochloric and a drop or two of sulphurous acids, which mixture is then passed hot through the filter. A reprecipitation by ammonia is then made, and the precipitate collected again on the filter and added to the main one, the filtrate passing into the flask containing the previous one. If much manganese is present, of course a second precipitation by ammonia of the small precipitate may be required. In these cases there is no difficulty in getting all the manganese into the filtrate. IGNITION OF THE PRECIPITATE. The combined precipitates of alumina, etc., are ignited moist, in the paper, unless considerable iron is present, when the main one is dried, removed so far as possible from the paper, and the latter ignited separately to prevent partial reduction of a portion of the iron, which cannot then be wholly reoxi- dized by heating or by treatment with nitric acid (see p. 1122). Alumina in the quantities ordinarily found cannot be fully dehydrated by the full heat of the BUNSEN burner. It must be blasted for five or ten minutes. If iron is present in large amount this last operation must be conducted so as to insure free access of air to the crucible (p. 1134). RECOVERY OF SILICA AND POSSIBLE BARIUM IN THE ALUMINA PRECIPITATE. The precipitate is dissolved by fusion with acid potassium sulphate, an operation which is accomplished without trouble in from two to four hours if the temperature is kept low and the acid salt has been properly made free from water and excess of acid. The melt is taken up with hot water and considerable dilute sulphuric acid, the residue collected, weighed, and corrected by hydrofluoric and sulphuric acids for silica, which, as said before, rarely amounts to 1 mgrm. in weight, and further examined for barium (see p. 1136) by dissolving any remaining residue in hot, strong sul- phuric acid and diluting with cold water.* oentration of the first filtrate a pale straw-colored precipitate appeared, which remained on the filter with the traces of alumina that may also separate, although it is slowly solu- ble in hot water. This is said to be some compound of platinum, and attention is called to it here for the guidance of others who may notice it and be unaware of its character. * Some years ago, in a series of analyses of rocks from the Leucite Hills, in Wyoming, there was obtained at this stage, when it was customary to dissolve the melt in cold water preliminary to precipitation of titanium by boiling the neutralized sulphuric solution in presence of sulphur dioxide, a white, more or less flocculent residue amounting to 1 to 3 per cent, of the rock, which was at first taken to be a mixture of tantalic and Columbia acids. Eventually it was found to consist apparently of nothing but TiO2 and P-2Os, with perhaps a little ZrO 2 . By repeated fusion with acid potassium sulphate and leach- ing with cold water it could be gradually brought into solution. It was these rocks which furnished the most striking instance of the peculiar, milky, sulphate residues men- tioned on p. 1136, as derived from the ignited silica. KXOP (Zeitschr. fur Kryst., x, p. 73, 1885) seems to have obtained a similar mixture in analyzing minerals from the Kaiserstuhl in Baden, but its nature was not ascertained, though suspected to be. if not silica, columbiferous titanic acid. 1140 APPENDIX II. ESTIMATION OF IRON IN THE PRECIPITATE OF ALUMINA, ETC. Without Regard to the Presence of Vanadium. The filtrate obtained in the preceding paragraph is reduced, hot, by hydrogen sulphide, boiled to collect sulphur and the platinum sulphide * resulting from the bisulphate fusion, the hydrogen sulphide being allowed to pass for a short time after boiling. It is then filtered f hot into a flask attached to a carbonic-acid apparatus and brought to boiling to expel hydrogen sulphide. When this is fully effected the flask is cooled in water while the carbon dioxide still passes, and the solution is then titrated by potassium permanganate. The results are strictly accurate, with the limitations set forth in the paragraph below, when care is taken with the reduction by hydrogen sulphide. The method is altogether superior to that involving the use of zinc, since no foreign impurity affecting the result is introduced and the ever-present titanium is not affected, nor is vanadium reduced below the condition of V 2 O 4 , whereas nascent hydrogen converts it, in part at least, to V 2 O 3 . Tita- nium can be conveniently estimated by adding hydrogen peroxide to the titrated iron solution (see p. 1149). Having Regard to the Presence of Vanadium. If vanadium is present the value found for iron will be in error by the amount of permanganate required to oxidize V 2 O 4 to V 2 O 5 . The amount of the correction will differ according as titration of the iron is made after reduction by hydrogen sul- phide or by nascent hydrogen. If the former is used, as should always be the case, because of the ever-present titanium, the vanadium is reduced by it to V 2 O 4 , which in its action on permanganate is equivalent to two molecules of FeO, while the reduction goes further with hydrogen. After the first transitory pink blush throughout the liquid, the slower-acting vanadium may require the addition of a drop or two more of permanganate before a comparatively permanent coloration appears. * It may be mentioned that the precipitation of platinum from a hot sulphate solution is far quicker and cleaner than from hydrochloric acid. Further, this platinum sulphide, when ignited in the crucible in which the bisulphate fusion was made, should weigh together with the crucible itself what the latter weighed before the main silica precipitate was ignited in it; in other words, the weight of the platinum recovered by hydrogen sulphide should equal the loss in weight of the crucible due to attack by the bisulphate. In some- what rare instances this will not be so, but the weight will be greater, showing again in platinum which may amount to a milligramme. Tests have shown that this is not due to retention of platinum by the main A^Oa, etc. , precipitate ; hence it must come from platinum mechanically loosened from the dish during the drying and powdering of the silica pre- paratory to its collection on the filter, or to some insoluble compound of platinum formed during evaporation and drying of the silica. It may also be in part or wholly due to contamination from reduction of platinum during evaporation of the filtrate from the basic acetate separation. It will be remembered that from this filtrate a small amount of iron and alumina is recovered and added to the main precipitate. Hence it is always well in fine work to collect the sulphide and weigh the platinum in the original crucible, deducting any excess from the alumina, or else to get rid of the platinum by hydrogen sulphide before proceeding to the precipitation of alumina, etc. (see p. 1137). t Filtration is not necessary if only precipitated sulphur and no sulphides are in sus- pension, since this is without reducing action on cold permanganate solution, as WELLS tiid MITCHELL, and others before them, have pointed out. The above authors used this method of reducing ferric iron in titanic iron ores. (Journ. Am. Chem. Soc., xvii, p. 78, 1895; also Chemical News, LXXIII, p. 123, 1896.) SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1141 When the amount of vanadium in the rock is known, a correction can be applied on the assumption that practically all the vanadium is here col- lected, a p:>int that needs further investigation. Various authors assert its precipitability with alumina and iron by ammonia and ammonium acetate, though CARNOT * states that repeated precipitation by ammonia, ammonium carbonate, or ammonium sulphydrate, separates it from iron. The writer'? experience with ores very rich in vanadium shows that precipi- tation along with iron and aluminium is only partial. RIDSDALE f has deter- mined its precipitability with various metals and gives numerous figures which show an approximation to 90 per cent, thus thrown down under the conditions prevailing in analysis of iron slags, the remainder passing into the filtrates and appearing in small part" with the lime and to a greater extent with the magnesium phosphate. For all practical purposes it is probably safe to assume that the small amounts of vanadium met with in rocks are wholly in the alumina precipitate. If the amount of vanadium in the rock is not known, and great accuracy is necessary, caution requires the determination of the total iron to be made either in a separate portion or after reprecipitation from the above solution, as follows: Fuse with sodium carbonate, extract with water, bring the insolu- ble residue into sulphuric solution, reduce and titrate as above directed. But unless a certain precaution is here observed an error greater than that which it is designed to avoid will be committed. Contrary to general belief, the aqueous extract from the sodium-carbonate fusion carries a small but appre- ciable fraction of a per cent, of iron, as the writer has repeatedly found by actual test. This iron is thrown out with the alumina (and silica, if present) by the usual methods of neutralizing the alkaline solution, and can be brought to light when the precipitate thus formed is treated with a fixed caustic- alkali, or again fused with sodium carbonate and leached with water, when it remains wholly or in part undissolved. Hence it is necessary to collect this iron and add it to the main portion before titration. DETERMINATION OF THE TRUE VALUE FOR FERRIC IRON. Having in one way or another found the total iron in the rock, it remains to deduct an amount equivalent to the ferrous oxide the rock contains, and a further amount corresponding to the sulphides often present, in order to get what may pass for the true value for ferric iron. That this is often only an approximation appears from the difficulties due to the presence of vana- dium and the generally indeterminable effect of sulphides on the ferrous- oxide determination. (See pp. 1173 to 1175.) METHODS AIMING AT THE MORE OR LESS DIRECT ESTIMATION OF ALUMINIUM AFTER FIRST REMOVING IRON AS SULPHIDE. Should it be defeirable for any reason to effect an actual separation of aluminium, this may best be done, up to a certain point, after the bisulphate * Comptea rendus, crv, p. 1803, 1887 ; Zeitschr. fur anal. Chem., xxxii, p. 223, 1893. t Journ. Soc. Chem. Industry, vn, p. 73, 1888. 1142 APPENDIX II. fusion (p. 1139), by removal of the iron* by ammonium sulphide in ammo- nium- tartrate solution, evaporation of the filtrate, ignition of the residue with sodium carbonate and nitrate, and extraction with water, whereby titanium and zirconium are left on the filter as sodium salts, while chromium and vana- dium are carried into the filtrate as chromate and vanadate along with aluminium and phosphorus. The further separation of the two last from the chromium and vanadium is outlined under Phosphorus, p. 1160. This is as far as the separation can well be carried, and the A1 2 O 3 must still be found by subtracting the P 2 O 5 from the combined weights of the A1 2 O 3 and P 2 O 5 . The possibility of loss of some P 2 O 5 by volatilization f during the bisulphate fusion must be borne in mind here, for if it takes place the final weight of A1 2 O 3 +P 2 O 5 will not contain all the P 2 O 5 . Some writers recommend dissolving the ignited alumina, iron oxide, etc., in hydrochloric acid, but when the precipitate has been heated over the blast, as it should be, this is very ineffective. BY EXTRACTION WITH A FIXED CAUSTIC ALKALI. A favorite practice in some countries of Europe is to fuse the ignited precipitate containing A1 2 O 3 , Fe 2 O 3 , TiO 2 , P 2 O 5 , etc. or that of the A1 2 O 3 TiO 2 , P 2 O 5 , etc., after separation of iron by ammonium sulphide in tartrate solution with sodium hydroxide in a silver crucible, or to boil the freshly precipitated mixture with a solution of the alkali, on the assumption that the titanium oxide is hereby rendered wholly insoluble and thus separated from the alumina. This, however, is in part an error long since pointed out by GoocH,J who showed that pure titanic oxide is markedly soluble under both conditions of treatment. Experiments very recently made by the writer to test the extent of this error brought out the following interesting results: When 0-045 grm. of titanic oxide was fused by itself with sodium hy- droxide, the clear aqueous extract of the fusion held 0-0031 TiO 2 , or about 7 per cent., determined colorimetrically. When freshly precipitated and boiled with the alkali the solubility was less. When fused with sodium, carbonate but an infinitesimal trace was dissolved, which required strong concentration for its detection. When mixed with a large excess of alumina and fused with the caustic alkali, the solubility was still very marked, though less than when alumina was absent. With a large excess of ferric oxide, with or without alumina, no titanium could be detected in the unconcen- trated filtrate. It thus appears that fusion with caustic alkali after first removing iron involves an error in the gravimetric determination of both aluminium and titanium which does not appear if the iron has not been removed. * This being first reduced to the ferrous condition by hydrogen sulphide in acid solu- tion in order to obviate the possibility of precipitating some titanium, which otherwise is likely to happen. (CiTHREiN, Zeitschr. fur Kryst., vi, p. 246, 1882, and vn, p. 250, 1883.) t H. ROSE speaks of such loss when volatilizing sulphuric acid in presence of phos- phoric acid. (Handb. f. quant. Anal., FINKENER edition, n, p. 575, and elsewhere.) J Proc. Am. Acad, Arts and Sci., xn, p. 436, 1885; Bull. U. S. Geol. Survey, No. 27, pp. 16 and 17. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1143 DIRECT PRECIPITATION OF ALUMINA. A recent and promising method for the "direct determination of alumina presence of iron, manganese, calcium, and magnesium " is that of HESS and CAMPBELL,* but, as with the methods just considered, it involves finally weighing aluminum and phosphorus together, and the behavior of titanium has not been investigated. For this latter reason the details of the method will not be given. Suffice it to say that precipitation of the aluminium and phosphorus is made by phenylhydrazine, after first neutralizing the (prefer- ably chloride) solution by ammonia and reducing iron by a saturated solution of ammonium bisulphite. Phenylhydrazine "precipitates aluminium from its solutions quantitatively as the hydroxide without a trace of the precipi- tate being redissolved in excess of the precipitant." IX. MANGANESE/NICKEL, COBALT, COPPER, ZINC. Ammonia is added to the flask containing manganese, the earths, etc. (p. 1139), and hydrogen-sulphide gas is introduced, whereby manganese, nickel, cobalt, copper, zinc, and a small part of the platinum from the dish are precipitated. The flask is set aside, corked, for at least twelve hours, and preferably twenty-four, or even longer; the precipitate, collected and washed on a small filter with water containing ammonium chloride and sul- phide, is extracted by hydrogen-sulphide water acidified with one-fifth its volume of hydrochloric acid (sp. gr. l-ll), manganese and zinc, if present, going into solution. MANGANESE AND ZINC. The filtrate is evaporated to dryness, ammonium salts are destroyed by evaporation with a few drops of sodnjm-carbonate solution, hydrochloric and a drop of sulphurous acids are added to decompose excess of carbonate and to dissolve precipitated manganese, and the latter is reprecipitated at boiling heat by sodium carbonate after evaporation of the hydrochloric acid. If zinc is present, it can be separated from the manganese after weigh- ing. For the small quantities of manganese usually found the sodium-car- bonate method of precipitation is to be preferred to that by bromine or sodium phosphate, as equally accurate and a great time saver. The precipitation of manganese in alkaline solution by hydrogen per- oxide, as proposed by JANNASCH and CLOEDT,* a method which appeared to be simple and accurate, besides affording a separation from zinc, has been shown by FRIEDHEIM and BRUHL } to be valueless, as also other separation methods of JANNASCH based on the use of hydrogen peroxide. The employment of ammonium sulphide instead of bromine for the sep- aration of manganese from the alkaline earths and magnesia has the advan- tage that, by a single operation, nickel, copper, and zinc are likewise removed * Journ. Am. Chem. Soc., xxi, p, 776, 1899; Chemical News, LXXXI, p. 158, 1900. * Zeitschr. fur anorg. Chemie, x, p. 405, 1895. t Zeitschr. fur anal. Chemie, xxxvm, p. 681, 1899. 1144 APPENDIX II. if present. There need be no fear of overlooking nickel or copper, for under the conditions of the precipitation they are not held in solution. Now and then a trace of alumina may be found in the precipitate, and magnesia, too, would contaminate it if ammonium salts were not present in sufficient quan- tity. Regard must therefore be had to these possibilities, and also to the rather remote possibility of the presence of rare earths which were not thrown out by the basic acetate precipitation (see foot-note, p. 1138). NICKEL, COBALT, COPPER. The paper containing these is incinerated in porcelain, dissolved in a few drops of aqua regia, evaporated with hydrochloric acid, the copper and platinum thrown out warm by hydrogen sulphide, and nickel and cobalt thrown down from the ammoniacal filtrate by hydrogen sulphide. This is then rendered faintly acid by acetic acid and allowed to stand. The sul- phide of nickel is simply burned and weighed as oxide, its weight being always very small, and is then tested for cobalt in the borax bead. It is somewhat unsafe to consider traces of copper found at this stage to belong to the rock if the evaporations have been conducted, as is usually the case, on a copper water-bath, or if water has been used which has been boiled in a copper kettle, even if tinned inside. Therefore, and because of its contamination by a little platinum, it is better to determine copper in a separate portion if its presence is indicated with certainty. (See p. 1137). X. CALCIUM AND STRONTIUM (BARIUM). SEPARATION FROM MAGNESIUM. Precipitation and Ignition of the Oxalates Together. The platinum derived from the dish in the silica evaporation, except for the small portion precipi- tated with the manganese sulphide, is now wholly in the nitrate from the latter. Its separation at this or any other stage is quite unnecessary, nor is the removal of ammonium chloride usually demanded, since there is no undue amount present in most cases, the first precipitation of alumina, etc., having been by sodium acetate.* Therefore, without lestroying ammo- nium sulphide the calcium and strontium are thrown out by ammonium oxalate at boiling heat, the precipitate, often darkened by deposited platinum sulphide, is ignited and redissolved in hydrochloric acid, boiled with ammo- nia to throw out traces of alumina sometimes present and reprecipitated as before, but in a small bulk of solution. It is weighed as oxide, trans- ferred to a small flask of 20 c.c. capacity, dissolved in nitric acid, evapor- ated to dryness at 150 to 160, and the separation of strontium from cal- cium effected by ether-alcohol f as described below. * If two or three precipitations by ammonia alone are depended on, the second and third filtrates are evaporated rapidly to dryness and the ammonium salts removed by ignition. t See FRESENITTS, Zeitschr. fur anal. Chemie, xxxn, pp. 189, 312, 1893, for the latest improvements in this method. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1145 The weight of strontia found deducted from that of the two oxides gives that of the lime. Necessity for Two Precipitations by Ammonium Oxalate. It may be said with regard to the separation of calcium from magnesium that two precipi- tations by ammonium oxalate are essential to the attainment of correct results, not only for the complete removal of magnesium but of sodium as well, the retention of compounds of the latter element by calcium oxalate being now generally known. For the treatment of the filtrates, see Mag- nesium, p. 1146. SEPARATION OP STRONTIUM (BARIUM) FROM CALCIUM BY ETHER- ALCOHOL. The thoroughly dried nitrates are treated with as little (rarely over 2 c.c., of a mixture in equal parts of absolute alcohol and ether as may be needed to dissolve the calcium salt, solution being hastened by occasional gentle agitation. After standing over night in a corked flask the insoluble matter is collected on the smallest possible filter and washed with more of the above mixture of alcohol and ether. After drying, a few cubic centimetres of hot water are passed through the filter, on which may remain a few tenths of a milligramme of residue which does not usually contain any lime or other alka- line earth and whose weight is therefore to be deducted from that of the lime, unless it can be shown that it is derived from the glass of the little flask in which the nitrates of calcium and strontium were evaporated. To the solu- tion of strontium nitrate in a small beaker sulphuric acid and then alcohol is added, whereby the strontium is precipitated as sulphate, in which form it is weighed and then tested spectroscopically as to freedom from calcium and barium. Because of the slight solubility of strontium nitrate in amyl alcohol, the method of BROWNING * does not appear to be adapted for the separation from calcium of the small amounts of strontium met with in rocks, though with barium the case is different, since its nitrate according to BROWNING is insolu- ble in absolute amyl alcohol. BEHAVIOR OF BARIUM. Barium will, after two ammonium-oxalate precipitations, never be found with the ignited calcium and strontium in more than spectroscopic traces, unless originally present in excess of 3 or 4 mgrm., and very often only when in considerable ex cess, f If present with them, however, it will be separated with the strontium by ether-alcohol or amyl alcohol, and these two must then be treated by the ammonium-chromate method, given below, in order to arrive at the strontium. The barium is best estimated hi a separate por- tion. (See Barium, p. 1155.) * Am. Journ. Sci., 3d Series, XLIII, pp. 50, 314, 1892. t W. F. HILLEBRAND, Journ. Am. Chem. Soc., xvi. p. 83, 1894; Chemical News, LXIX, p. 147, 1894. 1146 - APPENDIX II. SEPARATION OF BARIUM FROM STRONTIUM. FRESENIUS has shown * in what manner only a correct separation of barium and strontium can be made by the ammonium-cnromaie metnod, involving double precipitation when tne amounts are at all large, ims procedure is here given for the amounts used by him, but a single precipi- tation will suffice for the small amounts met with in rock analysis, ine volumes of solutions used should be largely reduced and the operations other- wise shortened. The chlorides corresponding to 0-2774 grm. BaO and 0-4864 grm. SrO were dissolved in 300 c.c. of water with addition of 6 drops of acetic acid (1-065 sp. gr.). To the hot solution was added an excess (10 c.c.) of ammo- nium-chromate solution (1 c.c. =0-1 grm. neutrarchrohiate). After settling and cooling for an hour the precipitate was washed, mainly by decantation, with water holding ammonium chromate till the nitrate gave no precipitate with ammonia and ammonium carbonate (100 c.c. used). The washing was continued with warm water till silver nitrate gave but a very slight red- dish coloration (110 c.c.). The precipitate was then washed into the pre- cipitating dish, the filter rinsed with warm dilute nitric acid (1 2 sp. gr.) and more nitric acid (2 c.c. in all) added to the dish. The solution having been diluted to 200 c.c. and heated, 5 c.c. of ammonium- acetate solution (1 c.c. =0-31 grm. ammonium acetate) were very gradually added, and then ammonium chromate till the odor of acetic acid had wholly disappeared (10 c.c.). After one hour the supernatant liquid was passed through the filter and the precipitate digested with hot water, which was then cooled; thereupon the precipitate itself was brought on the filter and washed with cold water till silver nitrate gave a scarcely perceptible reaction. The strontium was thrown down from the filtrate by ammonia and ammonium carbonate, after concentration in presence of a little nitric acid, and weighed as carbonate; or the carbonate can be redissolved, precipitated by sulphuric acid and alcohol, and weighed as sulphate. The barium is weighed as chro- mate after ignition, the filter being burned separately. XI. MAGNESIUM. PRECIPITATION. The first precipitation of magnesium is made without special precau- tions in the filtrate from the first calcium-oxalate separation (p. 1144) by sodium-ammonium-hydrogen phosphate (microcosmic saltf) in indefinite decided excess and without the great excess of ammonia usually prescribed. It is not necessary to first remove ammoniacal salts unless very little mag- nesium is present, and then only in order to hasten precipitation. NEU- BAUER | has shown that precipitation is complete even in presence of large * Zeitachr. fur anal. Chemie, xxix, p. 428, 1890. t The objection that has been made by one writer to the use of this salt instead of disodium-hydrogen phosphate is, so far as our experience teaches, entirely groundless. J Zeitschr. fur angew. Chemie, 1896, p. 435. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1147 quantities of salts of ammonium, including the oxalate. He has, however, also shown that the composition of the precipitate is largely affected by ammonium salts, and also by the way in whicn the precipitation is made. These points are only of importance when a single precipitation is to be made or in the final of two or more, as will be discussed later. Hatinum sulphide usually strongly contaminates the separated phos- phate, but this matters not, as it remains on the filter when the' phosphate id redissolved in hydrochloric acid, of which not more than the amount really needed should be used. The solution thus obtained is united with that of tne residue from evaporation and ignition of the second filtrate from calcium oxalate, and is diluted if necessary. A few drops of sodium-ammonium- phosphate solution are now added, and ammonia in slight excess, with con- stant stirring till the crystalline precipitate has well formed. 'The laree excess of ammonia of 0-96 specific gravity (one-third the original volume) usually prescribed has been shown by GOOCH and AUSTIN * to be quite unnec- essary, in fact, disadvantageous. XEUBAUER hi the above-cited paper has shown, and GOOCH and AUSTIN (toe. cit.} have confirmed his statements, that it is only by working under these conditions absence of any large excess of precipitant, of ammoniacal salts, and of ammonia that a precipitate'of normal composition is obtain- ble. It usually differs from the normal in containing relatively more ammo- nium and less magnesium for instance, an admixture of such a molecule as Mg(XH 4 ) 4 (PO 4 ) 2 the result being that when ignited in the ordinary way too much magnesium is found, because of formation of some metaphosphate. To obviate this error NEUBAUER considers it absolutely necessary to blast the precipitate for half an hour, and then to repeat the blasting for a second half hour to see if a constant weight has been reached. The phosphate is then entirely pyrophosphate, which is quite unaffected by further blasting. The intense heat has caused a decomposition of the metaphosphate with volatilization of P 2 O 6 , as follows: 2Mg(PO,) 2 = Mg 2 P,O 7 + P 2 O 5 . NEUBAUER worked with the usual excess of ammonia, and it remains to be seen whether by precipitating and working according to GOOCH and AUSTIN the com- position of the precipitate is always close enough to the ideal MgXH 4 PO 4 to obviate the necessity for blasting. From the labors of XEUBAUER and of GOOCH and AUSTIN it is clear that the common way of adding the phosphate precipitant to the ammoniacal solution of the magnesium salt is not calculated to produce a precipitate of normal composition. The precipitant should be added to the acid solution of the magnesium, and ammonia should then be added in slight excess. GOOCH and AUSTIN call attention to a modification proposed some years ago by WOLCOTT GIBBS,* whereby the phosphorus and magnesium salts ate first boiled together in neutral solution for a few minutes and to the cooled solution ammonia is added. The results are said to be remarkably exact. * Am. Journ. Sci.. 4th Series, vii, p. 187, 1899; Chemical News, LXXIX, pp. 233, 244, 555, 1899; Zeitschr. fur anorg. Chemie, xx, p. 121, 1899. t Am. Journ. Sci., 3d Series, v, p. 114, 1873. 1148 APPENDIX II. METHODS OF COLLECTING AND IGNITING THE PRECIPITATE. If the blast has not to be employed, the weight of the pyrophosphate can doubtless be most accurately arrived at by collecting and igniting the pre- cipitate in a GCOCH crucible, provided the asbestos felt is well constructed and not of the serpentine variety so largely on the market. NEUBAUER ignites slowly in platinum after drying, without removing from the paper, applying the blast only when the carbon has been wholly burned off.* Almost as exact are the two modifications of the method in use for phos- phate analyses at the agricultural experiment stations at Danzig and Lisbon, described by SCHMOEGER f and MASTBAUM. J According to the former the precipitate after drying is detached from the paper and placed in a platinum crucible, followed by the folded filter. To the covered crucible the full flame of a burner is applied, and after a short time the burning off of the carbon is accomplished with the crucible open. A short blasting follows. In a num- ber of experiments on quantities ranging from 0-06 to 0-28 grm. of pyro- phosphate the results were, with a few exceptions, naturally lower than those obtained on duplicates by the ordinary method of igniting, but only by 0-0013 grm. in maximum. MASTBAUM, to shorten time, applies the full flame to the moist precipi- tate wrapped in its filter. Later, when most of the carbon is burned off, he moistens the residue with two or three drops of strong nitric acid, evaporates this carefully, heats with full burner for a few minutes, then blasts for half a minute. He describes the results as irreproachable. In this laboratory only the MASTBAUM modification has been tried, and it certainly seems to be satisfactory when the extreme of accuracy is not required. At one time the procedure first recommended by ULBRICHT, later by BROOCKMANN, and also by L. L. DE KONINCK, was used. It consists in dis- solving the ammonium-magnesium phosphate off the filter with nitric acid, collecting the filtrate in a weighed crucible, evaporating the contents to dry- ness, and subsequently igniting, the product being presumably pyrophos- phate. But it was soon observed that the ignited salt, especially when large in amount, does not always dissolve completely in hydrochloric acid, but that sometimes a white residue is left in light lumps which appears to be quite insoluble in acids. This residue contains no silica, but only the con- stituents of a magnesian phosphate, and it may be a peculiar metaphosphate. Whether its appearance is due to an abnormal composition of the original magnesian precipitate or to conceivable change during evaporation in the . crucible with nitric acid remains to be determined. Until this is done the employment of this method of igniting is not to be recommended. * Zeitschr. fur anal. Chentie, xxxin, p. 362, 1894. t Ibid., xxxvn, p. 308, 1898. t Ibid., p. 581, 1898. A pink color of varying intensity almost invariably becomes apparen' as the mass approaches dryness, a most delicate test for the traces of manganese which always escape precipitation by ammonium sulphide or bromine. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1149 CONTAMINATION BY AND REMOVAL OF BARIUM AND CALCIUM. Barium phosphate will not contaminate the second magnesian precipi- tate unless there are notable amounts of barium in the rock, in which case it must be removed by sulphuric acid prior to the final precipitation of the magnesium Calcium, however, is probably never absent, and has to be estimated and allowed for as follows : To the ignited pyrophosphate, dissolved in but slight excess of hydro- chloric acid, ammonia is added to alkalinity, and then acetic acid, drop by drop, till the solution, which should not be hot, clears. It now and then happens that a little flocculent matter fails to dissolve. This is to be re- moved, ignited, and subtracted from the original weight. It is likely to consist, in great part or wholly, of phosphates of iron or manganese, or both, and shows often a reddish color on ignition. If an excess of acetic acid has been used, this is cautiously removed by ammonia. Then a drop or two of solution of ammonium oxalate is added, and the small beaker is set aside for twelve hours if necessary. Almost invariably a small precipitate soon shows itself, which if fine-grained and non-adherent to the glass may be regarded as pure calcium oxalate ; otherwise it contains, or may largely con- sist of, magnesium oxalate. It is in that case to be collected, ignited, redissolved, and reprecipitated. Its final weight, averaging perhaps one- half milligramme, is to be added to that of the lime already found, and subtracted as tricalcium phosphate from that of the magnesium pyrophos- phate in order to arrive at the true figure for magnesia. This separation, to be satisfactory, requires great care. XII. TITANIUM. COLORIMETRIC ESTIMATION WITH HYDROGEN PEROXIDE (WfiLLER'S METHOD).* The method consists in comparing the color of a known bulk of solution to be tested with that of a standard solution of titanium sulphate, both having been fully oxidized by hydrogen peroxide. The strength of the per- oxide should be approximately measured by titration with permanganate on opening a fresh bottle, and again after a few weeks, otherwise very serious error may arise through its deterioration. Mere traces of hydrofluoric acid, either in the peroxide or the titanium solution, render this method inexact ,f hence care should be exercised as to the character of the peroxide, which, as sold in the market, often contains fluorine. DUNNINGTONJ has pointed out the necessity for the presence of at least 5 per cent, of sulphuric acid in solutions which are to be thus tested for tita- nium, in order, as he concludes, to prevent partial reversion to metatitanic * Ber. deutsch. chem. Gesell.. xv, p. 2593, 1882. t HILLEBRAXD, Journ. Am. Chem. Soc., xvn, p. 718, 1895; Chemical News, LXXH, p. 158- 1895: Butt. U. S. Geol. Survey, No. 167, p. 56. J Journ. Am. Chem. Soc., xin, p. 210, 1891. 1150 APPENDIX II. acid, which does not give a color with hydrogen peroxide. The standard solution of titanium sulphate, holding conveniently about 1 centigramme TiO 2 in 10 c.c., equivalent to 1 per cent, of TiO 2 in 1 grm. of rock, contains, there- fore, 5 per cent, or more of sulphuric acid. Of this, 10 c.c. are mixed with a sufficiency of hydrogen peroxide (2 c.c. of most commercial brands is ample) and diluted to 100 c.c. in a measuring flask. Titanium can be estimated, as a rule, most conveniently in the solution which has served for the tit-ration of total iron (p. 1140). This, having been evaporated, if necessary, to less than 100 c.c. is to be fully oxidized with hydrogen peroxide, and if the color is less intense than that of the standard, is made up to 100 c.c. with dilute sulphuric acid in a measuring flask and mixed; otherwise, in a flask of sufficient size to insure that its color shall be less intense. One of the rectangular 'glasses described below being filled with the solution to be tested, 10 c.c. of the diluted standard are run into the other from a burette, and water is added from a second burette until there is no distinction as to color. A second and a third portion of the stand- ard can be run in and diluted and the mean of several determinations struck, when a simple calculation gives the percentage of TiO 2 in the rock. If the convenient but expensive SOLEIL-DUBOSCQ colorimeter is used, or the simple NESSLER tubes, it is of course unnecessary to dilute the rock solution to the extent above required, should it be stronger than the standard. Ex- perience has shown, however, that differences cannot be sharply estimated in strongly colored solutions, and that the results are much more satisfactory when the color intensity is not much, if any, greater than that given by a standard of the above concentration. For the percentages of titanium found in rocks, clays, and soils, usually under 1 per cent., but rising to 2 or even 3 per cent, or more occasionally, the colorimeter method gives results which are fully equal to those of the best gravimetric method, besides being a great time -saver. The error introduced by iron, in consequence of the yellowish color of its sulphate solution, is practically negligible unless its percentage is very high; then either the iron must be removed prior to making the color test, or correction should be applied for known amounts of ferric sulphate in solutions of the requisite dilution. The exact correction to be applied in such cases is difficult of determina- tion because of the impossibility of matching the colors of titanium- peroxide solutions with those of ferric sulphate; but tests made go to show that the coloring effect of 0-1 grm. of Fe 2 O 3 in 100 c.c. 5 per cent, sulphuric-acid solution is about equal to 0-2 mgrm. of TiO 2 in 100 c.c. when oxidized by hydrogen peroxide. This amounts to a correction of only 02 per cent, on 1 grm. of rock containing the unusual amounts of 10 per cent. Fe 2 O 3 . It will be more satisfactory, when much iron is present, to remove this as de- scribed on page 1153 and to colorimetrically estimate the uranium thus froed from iron! ALTERNATIVE MODE OF PREPARING THE TEST SOLUTION. As said above, and on p. 1140, the solution that has been used for volu- metric estimation of total iron can most conveniently be used for the colori- SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1151 metric determination of titanium, but if desired this can, of course, be made on some other portion of rock powder. At one time it was the practice in this laboratory to combine it with the determination of barium, as described in Bulletin 148 of the United States Geological Survey, by decomposing th*: powder by sulphuric and hydrofluoric acids,* expelling the latter by repeated evaporations with sulphuric acid, taking up with dilute sulphuric acid,f fil- tering from barium sulphate, etc., and estimating the titanium colorimetric- ally in the filtrate. The expulsion of fluorine must be thorough, or else the titanium result will be low, as already stated (p. 1149), and it is not always easy to effect this complete removal, though the time required to do so seems to be in no slight degree dependent on the nature of the fluorides to be decom- posed. Long after every trace of fluorine seems to be gone, the formation of a crust on the evaporating solution sometimes allows an accumulation of enough hydrofluoric-acid gas to become plainly manifest to the smell on breaking the crust. THE COLORIMETRIC APPARATUS AND ITS USE. The glasses G (Fig. 12) may be of square or rectangular section, 8 to 12 cm. high and 3 to 3 cm. inside measurement between those sides through which the liquid is to, be observed. i These sides should, of course, be exactly parallel; the others need not be, but should be blackened externally. In order to further exclude the effect of side light in this and other similar methods (chromium, for instance, p. 1161), it is very convenient to have a simple, light box (B, Fig. 12) that can be easily held in one hand, about 35 cm. long and 12 cm. square, stained black inside and out, and with one 'end closed by a piece of ground glass W, the other open. For a space equal to the width of the glasses the cover is removed at the top next the glass end to permit of the insertion of the glasses side by side in such a way that no light shall penetrate around their sides or between them. Immediately back of the * It is to be borne in mind that evaporation with hydrofluoric acid alone results in loss of titanium by volatilization, but that there is no loss if excess of sulphuric acid is also present. t With acid rocks solution is very complete, and it can be made nearly so with the most basic by transference to a small beaker and gentle boiling. The residue thus ob- tained may contain, besides barium sulphate, a little calcium sulphate, zircon, andalu- site. topaz, and possibly a trace of titanium in some form. It is therefore to be thor- oughly fused with sodium carbonate, leached with water, fused with potassium bisul- phate, dissolved in dilute sulphuric acid, filtered, and the filtrate added to the main one. The insoluble matter will now be chiefly barium sulphate, for the furthei treatment of which, see p. 1155. J The allowable error in distance between the corresponding pairs of sides of the two glasses should not in any case exceed 1 per cent. Unfortunately there seems to be a disinclination or inability on the part of dealers in this country to furnish glasses fulfilling this requirement, and held together by a durable cement which shall be proof acain?t dilute sulphuric acid. Cadada balsam answers well for a time, but sooner or later it cracks, leaks then appear, and the sides soon drop off. It is, however, but a simple matter to cement them on again. A pair of entirely satisfactory glasbes can be made from a couple of square or rectan- gular 3 to 4 ounce bottles by cutting off one pair of sides from each and grinding down till the calipers show that agreement is perfect. The tops are then to be sawed off and pieces of plate glass cemented on the sides. 1152 APPENDIX II. glasses is a partition P, with openings of appropriate size cut in it. A stiffly sliding black cardboard shutter S is movable up and down immediately back of the partition, so that all light can be cut off except that which comes through the liquid. Precautions of this kind are necessary if accurate results are to be counted on. Except for mere traces, this combination of glasses and darkened box insures greater accuracy and rapidity of work than NESSLER tubes, and is preferable likewise, so far as the writer's experience goes, to expensive instru- FIG. 12. Apparatus for colorimetric determinations, in different aspects. G, one of two glasses of square or rectangular section, 8 to 12 cm. high and 3 to 3 cm. inside measurement between those sides through which the liquid is to be observed. The other sides are blackened on the outside. B, rectangular box about 35 cm. long and 12 cm. square, stained black inside and out, one end closed by a ground-glass window, W, the other open, and a portion of the top removed. P, blackened parti- tion, with openings corresponding to the interior dimensions of the glasses when in position. S, blackened cardboard shutter sliding stiffly up and down between parti- tion and glasses, so as to shut off all light above the lowest surface of the liquid in the glasses. ments like the colorimeter of SOLEIL-DUBOSCQ, etc. In making the color comparisons the box is best held close to a window, so as to get a full, strong light. Daylight is far preferable to artificial light. GOOCH'S GRAVIMETRIC METHOD. When titanium is present in excess of 4 to 5 per cent, and whenever for any reason it is desired to employ a gravimetric method, among the few that have been thoroughly tested that of Dr. GOOCH * is unequaled. With * Proc. Am. Acad. Arts and Sci., n. s., xn, p. 435; Bull. U. S. Geol. Survey, No. 27. p. 16, 1886; Chemical News, LII, pp. 55 and 68, 1885. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1153 one or two minor modifications introduced by Dr. T. M. CHATARD,* it is as follows : . Any solution of the rock freed from silica can be used, and the first step is to remove the iron. This is best done, after adding tartaric acid and re- ducing the iron by means of hydrogen sulphide to the ferrous condition, by rendering the solution ammoniacal and introducing more hydrogen sulphide. If the iron is not thus reduced before precipitation, titanium will be in part thrown down also.f The amount of tartaric acid is to be gauged according to the combined weights of the oxides to be held by it in solution, and three times this weight is ample. After removing the iron sulphide by filtration little washing suffices, because of the relatively small amount of titanium commonly present the tartaric acid is destroyed as follows: Potassium permanganate to the extent of two and one-half tunes the weight of the tartaric acid used is made into a strong solution, and to the ammoniacal filtrate from the iron sulphide enough sulphuric acid is intro- duced to leave some excess after all the permanganate has been reduced. After expulsion of hydrogen sulphide by boiling, the permanganate is added gradually to the hot solution contained in a large beaker or flask. A vigor- ous reaction ensues. When a permanent brown precipitate of manganic hydrate appears the tartaric acid has been fully broken up, and the precipi- tated manganese is to be redissolved by a few drops of ammonium-bisulphite or of sulphurous-acid solution. . Ammonia is then added in slight excess, followed at once by acetic acid in considerable excess, and the boiling is continued for a few minutes. Thereby the titanium is freed from most of the alumina, and from lime and magnesia if they had not been earlier removed, also from most of the manga- nese introduced. The precipitate is filtered and washed with water con- taining acetic and sulphurous acids, then ignited, fused thoroughly with sodium carbonate, and leached with water to remove phosphoric acid and most of the remaining alumina. The residue is again ignited and fused with sodium carbonate. To the cooled melt in the crucible strong sulphuric acid is to be added, wherein it dissolves readily by aid of gentle heat. This solution is to be poured into a small volume of cold water and the platinum it contains precipitated by hydrogen sulphide at or near boiling tempera- ture. After filtering and cooling, ammonia is added till the titanium is just precipitated, and a measured volume, containing a known weight of absolute sulphuric acid, is then added just enough to redissolve the precipitate. The solution is then made up with acetic acid in such amount that the final bulk shall contain from 7 to 11 per cent, of absolute acid, and then enough solid sodium acetate is stirred in to more than take up the sulphuric acid introduced. Upon rapidly bringing the liquid to ebullition the titanium is precipitated in flocculent and easily filterable condition, and the precipi- tation is complete after a minute's boiling, provided all the prescribed con- ditions have been followed and zirconium is absent. * Am. Chem. Journ., xra, p. 106, 1891; Butt. U. S. Geol. Survey, No. 78, Pr.87;_ col News, Lxm, p. 267, 1891. t CATHREIN, Zeitschr. fur Kryst., vi, p. 243, 1882; vii, p. 250, 1883. 1154 APPENDIX II. The precipitate is washed first with acetic acid of 7 per cent, strength and then with hot water. After 15 to 20 minutes' ignition over a good burner it is in condition for weighing, and will lose no more weight over the blast- lamp. For large amounts of titanium a repetition of the sodium-carbon- ate fusion, etc., should be made. The actual carrying out of all these oper- ations, when once the method is understood, requires much less time than the detailed description would indicate. GOOCH'S METHOD NOT DIRECTLY APPLICABLE TO ROCKS CONTAINING ZIRCONIUM. Prior to the adoption of the colorimetric method, Dr. GOOCH'S was invari- ably used in this laboratory. Occasional inability to secure clean and com- plete precipitation by it was experienced, especially with a certain series of rocks rather poor in titanium. Long research showed the difficulty to be due to the presence of zirconium, which acts as a marked preventive of the precipitation of titanium by boiling in an acetic-acid solution under the conditions of the GOOCH method. The above rocks were found to contain up to 0-2 per cent, of ZrO 2 , and this amount was able to prevent precipitation of 0-3 per cent, of TiO 2 . The titanium which came down in excess of this amount did not settle out in flocculent condition, as happens when zirconium is not present, and it was difficult to filter. After the removal of the zirconium in the manner to be hereafter described (p. 1156), however, no difficulty was experienced in pre- cipitating all the titanium with the usual ease. SUPERIORITY OF THE COLORIMETRIC AND GOOCH METHODS OVER THE OLDER ONES. In view of the good results obtainable by the colorimeter method in all cases and by the GOOCH method in the absence of zirconium, it is incom- prehensible that the old method of precipitation by many hours' boiling in a nearly neutral sulphate solution in presence of sulphurous acid should still find adherents in any part of the world. Attention has been directed (p. 1142) to the error resulting from attempt- ing to separate aluminium from titanium by either fused or dissolved sodium hydroxide. BASKERVILLE'S METHOD. BASKERVILLE * has proposed the separation of titanium from iron and aluminium by boiling the neutralized solution of the chlorides for a few min- utes in presence of sulphurous acid. The test separations as given by him are sharp, and a single precipitation is said to suffice, the titanium being free from iron and easily filterable. This last statement and the ready precipi- tability are fully confirmed by the experiments of the writer on titaniferous iron ores, but, although the titanium is completely thrown out, it carries with it a little iron, for instance, about 0-25 per cent. Fe 2 O 3 with 8 to 10 per * Journ. Am. Chem. Soc., xvi, p. 427, 1894. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1155 cent. TiO-j. Zirconium would probably be likewise precipitated (see p. 1158) and phosphorus perhaps also, but this last point has not been investigated, neither has the applicability of the method to aluminous rocks been tested. XIII. BARIUM (ZIRCONIUM, TOTAL SULPHUR). Reasons for Estimating Barium in a Separate Portion of Rock Powder. It has been said above (p. 1 145) that only in very exceptional cases will barium be found with the calcium and strontium after two, or possibly three, precipi- tations of the latter as oxalate, since it passes into the filtrates with the mag- nesium, whence it may be obtained as sulphate after removal of ammoniacal salts. Addition of some alcohol insures also the recovery of traces of stron- tium if the rocks are very rich in it. But it is unsafe to regard the amount thus separated from the magnesium as representing the total amount of barium in the rock. It will almost always be found lower than the truth, probably for the reason that there are opportunities during the analysis for slight losses. It is best to estimate it in a separate 2-grm. portion, which may also serve with advantage for the estimation of zirconium and total sulphur. Modes of Attack and Subsequent Treatment. If zirconium and sulphur are not to be looked for, the simplest procedure is to decompose the powder by sulphuric and hydrofluoric acids (see p. 1151, under Titanium), and to com- plete the purification of the barium sulphate thus obtained in the manner described in the third paragraph below. If zirconium and sulphur are both to be likewise determined, decomposi- tion is effected by fusing over the BUNSEN flame and then over the blast with sulphur-free sodium carbonate and insufficient nitre to injure the cruci- ble, first fitting the latter snugly into a hole in asbestos board (LUNGE) to prevent access of sulphur from the gas-flame. In case sulphur is not to be regarded, the nitre and asbestos board are omitted. After thorough disin- tegration of the melt in water, to which a drop or two of methyl- or ethyl- alcohol has been added for the purpose of reducing manganese, the solution is filtered and the residue washed with a very dilute solution of sodium car- bonate free from bicarbonate. This is to prevent turbid washings. A yel- low colof in the filtrate indicates chromium. For the further treatment of the filtrate see Sulphur, p. 1184, and Chro- mium (colorimetric method), p. 1161. The residue is dissolved in quite dilute warm sulphuric acid (stronger acid may be used if barium only is sought) and filtered through the original filter. This, with its contents, is ignited, evaporated with hydrofluoric and sulphuric acids, and taken up with hot dilute sulphuric acid. The filtrate, added to the former one, now contains all the zirconium (see pp. 1156 and 1157 for its further treatment). The residue contains all the barium, besides some of the strontium, and perhaps a good deal of calcium. It is fused with sodium carbonate, leached with water, the residue dissolved off the filter by a few drops of hydrochloric acid, from which solution the barium is thrown out by a large excess of sulphuric acid. A single solution of the barium sul- 1156 APPENDIX II. phate in concentrated sulphuric acid and reprecipitation by water suffices to remove traces of calcium which might contaminate it if the rock was one rich in calcium, and even strontium is seldom retained by it in quantity sufficient to give concern. Should this be the case, however, which will occur when the SrO and BaO are together in the rock in, roughly speaking, 0-2 and 0-4 per cent., respectively, ftie only satisfactory way is to convert the sulphates into chlorides and to apply to the mixture the ammonium- chromate method of separation (p. 1146). Barium and srontium sulphates can be brought into a condition for testing spectroscopically by reducing for a very few moments the whole or part of the precipitate on a platinum wire in the luminous tip of a BUNSEN burner, and then moistening with hydrochloric acid. This should be known to every one, but probably is not. The procedure outlined in the foregoing paragraphs for the estimation of calcium, stronium, and barium in silicate rocks is the one which long expe- rience has shown to be best adapted for securing the most satisfactory results with a minimum expenditure of time.* Even where no attempt is made to separate contaminating traces of SrO and BaO one from the other, the error is usually of no great consequence, for an absolute error of 25 per cent., even, in a substance constituting only one or two tenths per cent, of a rock, is ordinarily of small moment compared with the ability to certify to its presence with approximate correctness. With such small amounts of barium as are usually found in rocks it is doubtful if MAR'S f method for the separation of barium from calcium and magnesium, by the solvent action of concentrated hydrochloric acid mixed with 10 per cent, of ether on the chlorides, could be conveniently applied here, although for larger amounts the method would seem to be accurate and easily executed. Moreover, it would probably not entirely remove contaminating strontium, and hence offers no advantage. XIV. ZIRCONIUM. This element is rarely looked for by chemists, though shown by the micro- scope to be one of the most constant rock constituents, usually in the form of zircon, in which occurrence its amount can be approximately judged of and a chemical test rendered almost unnecessary; but sometimes it occurs in other minerals, and is then unrecognizable under the microscope. It may rarely be present up to a few tenths of 1 per cent, of the rock. AUTHOR'S METHOD. For its detection and estimation in such cases, or whenever a search for it seems called for, the following procedure, based on a method by G. H. BAILEY,J has been devised, which serves, when carried out with care, to * For details consult W. F. HILLEBRAND, Journ. Am. Chem. Soc., xn, p. 83, 1894; Chemical News, i,xix, p. 147, 1894. t Am. Journ. Sci.. 3d Series, XLIII, p. 521, 1892. t Journ. Chem. Soc., XLIX, pp. 149, 481, 1886. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1157 detect with certainty the merest trace 0-02 per cent., for instance in 1 grm. The preliminary treatment of the rock power has been fully given under Barium (p. 1155), where the separation from barium has been described and also the concentration of the zirconia in a small amount of very dilute sul- phuric solution. This should probably not contain much above 1 per cent, of sulphuric acid, though the actually permissible limit has not been estab- lished. To the solution, which should be in a small flask, is now added hydrogen peroxide to oxidize the titanium, and then a few drops of a soluble orthophosphate solution. The flask is set aside in the cold for twenty-four to forty-eight hours. If the color bleaches after a time, more hydrogen peroxide should be added. Under these circumstances the zirconium is thrown out as phosphate and collects as a flocculent precipitate, which at this stage is not always pure. No matter how small or insignificant, it is collected on a filter, ignited, fused with sodium carbonate, leached with water, the filter again ignited, fused with very little acid potassium sulphate, brought into solution in hot water with a few drops of dilute sulphuric acid, poured into a flask of about 20 c.c. capacity, a few drops of hydrogen per- oxide and of sodium phosphate added, and the flask skt aside. Titanium is now almost never present, and the zirconium appears after a time as a white flocculent precipitate, which can be collected and weighed as phosphate. For the small amounts usually met with it is safe to assume that it contains 50 per cent, of ZrO f (51-8 by theory). If the amount is rather large, it may be fused with sodium carbonate, leached, ignited, fused with acid potassium sulphate, reprecipitated by ammonia, and weighed as ZrOj. Certainty as to its identity can be had by again bringing it into solution, precipitating by ammonia, dissolving in hydrochloric acid, evaporating to a drop or two, and testing with turmeric paper or by a microchemical reaction. With the very smallest amounts no color can be obtained by this turmeric-paper test,, which, however, responds readily to as little as 1 mgrm. of dioxide, and with proper care for as small an amount as 0-3 mgrm. (Dr. H. N. STOKES). No element other than thorium is ever likely to contaminate the zirconium thus precipitated. In BAILEY'S experiments the precipitation was not made by addition of a phosphate, but is said to be due solely to the hydrogen peroxide, the pre- cipitate being a hydrated peroxide, Zr 2 O 5 , or ZrO 2 .* My own efforts to secure a precipitate in acid solutions of zirconium sulphate by hydrogen peroxide alone were unsuccessful, perhaps for lack of a sufficiently strong peroxide. The ability to obtain the zirconium free from phosphoric acid would certainly be a great improvement on the method described above. Were it not for the necessity of working in a weakly acid solution, the separation of zirconium could be made in the same portion in which the tita- nium is colorimetrically determined. * BAILEY, Chemical News, LX. p. 6. 1889. 1158 APPENDIX II. OTHER METHODS OF SEPARATING ZIRCONIUM. STREIT and FRANZ * claim to secure complete separation of titanium from iron and zirconium by boiling the neutralized solutions of the sulphates with a large excess (50 per cent.) of acetic acid. The method has been from time to time recommended, but without any data showing its value. The single separation made by STREIT and FRANZ was far from perfect. DAVIS f separated zirconium sharply from aluminium, but not from iron, by precipitation as an oxyiodate in a boiling neutralized solution of chlorides, but the method is hardly applicable for rock analysis. BASKERVILLE J has proposed a method for the separation of zirconium from iron and aluminium similar to his method for the separation of titanium from those elements (p. 1154). It is based on the precipitability of ZrO 2 by boiling the neutralized chloride solution for two minutes in presence of sul- phurous acid, and seems to be excellent. As titanium is always present and is presumably quantitatively thrown down also, the two would have to be separated by hydrogen peroxide. No tests as to the availability of the method for separating the small amounts met with in rock analysis have been made. XV. RARE EARTHS OTHER THAN ZIRCONIA. For the few cases in which it may be necessary to look for rare earths other than zirconia, the following procedure is suggested as likely to prove satisfactory : The rock powder is thoroughly decomposed by several partial evapora- tions with hydrofluoric acid, the fluorides of all earth metals except zirconium are collected on a platinum cone, washed with water acidulated by hydro- fluoric acid, and the precipitate washed back into the dish or crucible and evaporated with enough sulphuric acid to expel all fluorine. The filter is burned and added, By careful heating the excess of sulphuric acid is re- moved and the sulphates are taken up by dilute hydrochloric acid. The rare earths, with perhaps some alumina, are then separated by ammonia, washed, redissolved in hydrochloric acid, and evaporated to dryness, then taken up with water and a drop of hydrochloric acid, and only enough ammo- nium acetate to neutralize the latter added, followed by oxalic acid (not ammonium oxalate, which would fail to precipitate thorium) . In 'this way as little as 0-03 per cent, of rare earths have been found when working on not more than 2 grm. of materials. This method eliminates at once most of the aluminium, all the iron, phos- phorus, titanium, and zirconium, and has the further advantage of collecting with the earthy fluorides, as UF 4 , any uranous uranium that the rock might have held. An alternative method would be to fuse with sodium carbonate, leach with water to get rid of phosphorus so far as possible, dissolve the residue in * Journ. fur prakt. Chemie, cvui, p. 65, 1869. t Am. Chem. Journ., xi, p. 27 1889. t Journ. Am. Chem. Soc.. xvi, p. 475 1894; Chemical News, LXX, p. 57 ,'1894. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1159 hydrochloric acid, separate silica as usual, precipitate alumina, etc., by ammonia, dissolve the precipitate again in hydrochloric acid, evaporate, and proceed as by the former method, which in most cases would undoubtedly give better results than this one. XVI. PHOSPHORUS. It is sometimes possible to extract all phosphorus from a rock by simple digestion with nitric acid, but quite as often, if not oftener, this fails; hence the necessity for resorting to one of the longer methods of extraction detailed below. PROCEDURE WHEN MATERIAL is AMPLE. When material is ample it is best to use one portion for phosphorus only and to proceed as follows: Fuse with sodium carbonate, separate silica by a single evaporation with nitric acid, treat the ignited silica with hydrofluoric and a drop or two of sulphuric acids, evaporate to expel hydrofluoric acid, bring the small residue into solution by boiling with nitric acid and add it to the main portion, hi which, after addition of considerable ammonium nitrate, precipitate the phosphorus by molybdate solution. The turbidity often observed on dissolving the precipitated and washed phospho-molybdate in ammonia is due to a compound of phosphorus. If the addition of a small fragment of a crystal of citric or tartaric acid fails to dissolve it, this should always be re-fused with sodium carbonate, extracted with water and the filtrate otherwise treated as above, in order to secure the phosphorus in it. According to GOOCH and AUSTIN,* in order to secure a magnesium- ammonium phosphate of normal composition, the procedure at this point should be as follows: To the phosphate solution, containing not more than 5 to 10 per cent, of ammonium chloride and a slight excess of magnesia mix- ture, a little ammonia is added, and the precipitate is washed in due time with weak ammonia water. In general, however, as these conditions can seldom be fulfilled, they recommend to decant the supernatant liquid through the filter which is later to receive the precipitate, to dissolve this in as little hydrochloric acid as possible, to reprecipitate by dilute ammonia without further addition of magnesia mixture, and to wash finally with weakly ammo- niacal water. Excess of ammonia, of ammonium salts, and of precipitant are all objectionable. In rock analysis the second precipitation will seldom be necessary. For ignition, etc., of the precipitate, see this subject under Magnesium (p. 1148). PROCEDURE WHEN MATERIAL is SCANTY. The following procedure admits of determining in the same portion, be- sides phosphorus, barium, iron, vanadium, chromium, and titanium, the last * Am, Journ. Sci., 4th Series, vrr, p. 187, 1899; Zeitschr. fur anorg. Chemie xx, p. 121 1 1899; Chemical News, LXXIX, pp. 233, 244, 255, 1899. 1160 APPENDIX II. two either colorimetrically or gravimetrically, and is in large part extracted from a paper by Dr. T. M. CHATARD.* Silica is removed by hydrofluoric and sulphuric acids, excess of fluorine expelled, the residue brought into solution so far as possible with sulphuric or hydrochloric acid and hot water, filtered, the residue ignited, fused with sodium carbonate, dissolved in hydrochloric acid, and the solution, after precipitation of barium, added to the main one, which is now precipitated by ammonia to get rid of the magnesium salts usually present and thus insure a cleaner subsequent fusion with sodium carbonate. The precipitated A1 2 O 3 , P 2 O 5 , Cr 2 O 3 , Fe 2 O 3 , and TiO 2 is dissolved in hot hydrochloric acid and filtered into a large platinum crucible, the filter burned and added, the solution evaporated to pastiness, a little water added to dissolve the salts, and dry sodium carbonate added in portions and stirred in thor- oughly to prevent lumpiness in the fusion to follow, which is continued for half an hour. Addition of sodium nitrate is not necessary. The fused mass is boiled out with water and washed with very dilute sodium-carbonate solution. In the residue iron and titanium can be deter- mined by the methods already described. In the filtrate chromium can be determined colorimetrically if present in sufficient amount to give a pro- nounced color (see p. 1161). Afterwards, or immediately if the chromium is not to be thus estimated, enough ammonium nitrate is added to react with all the carbonate, and the solution is digested on the bath till most of the ammonium carbonate is gone. Nearly if not quite all alumina is thus thrown out, carrying with it all phosphorus. The precipitate is washed with dilute ammonium-nitrate solution till the yellow color wholly disappears, after which it is dissolved in nitric acid and the phosphorus thrown out by molyb- date solution. The filtrate, containing chromium and vanadium, can be treated as detailed in the next following sections. XVII. CHROMIUM. If vanadium is absent, or nearly so, as is apt to be the case in those highly magnesian rocks (peridotites) usually carrying a good deal of chromium, the following separation and gravimetric method for chromium gives good and concordant results, but in presence of vanadium, and it is best generally to assume its presence, the colorimetric method should always be adopted. GRAVIMETRIC METHOD. Having obtained chromium in solution as chromate and free from all else but a little alumina, as at the conclusion of the preceding section on phosphorus, proceed as follows : Concentrate if necessary and add fresh ammonium sulphide, or intro- duce hydrogen sulphide. The chromium is reduced and appears as a pre- cipitate of sesquioxide mixed with the rest of the alumina. This precipi- * Am. Chem. Joum., xm, p. 106, 1891 ; Bull. U. S. Geol. Survey, No. 78, p. 87 ; Chemi- cal News, ucxin, p. 267, 1891. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1161 tate is now treated according to BAUBIGNY * by dissolving in nitric acid, evaporating to near dryness, and heating with strong nitric acid and potas- sium chlorate, finally evaporating to dryness to get rid of the acid. Oxida- tion is complete and very speedy. On dilution with cold water, acid sodium carbonate is added in slight excess, and after two or three hours the pre- cipitated alumina is filtered off. From the filtrate the chromium is then thrown out by fresh ammonium sulphide, redissolved and reprecipitated to free from alkali, and weighed. The separation of aluminium from chromium by hydrogen peroxide in ammoniacal solution, as recommended by JANNASCH and CLOEDT,-}- has been shown by FRIEDHEIM and BRUHL,! together with most of the other separa- tions of JANNASCH based on the use of hydrogen peroxide and from which so much was hoped, to be valueless. COLORIMETRIC METHOD. For this very accurate and by far the quickest method for determin- ing chromium in rocks and ores where the amount does not exceed a few per cent., there is needed the aqueous extract of a sodium-carbonate fusion of the rock (as obtained, for instance, under Phosphorus, p. 1160) in order to compare its color with that of a standard solution. Preparation and Strength of Standard Solution. This standard solution is made by dissolving 25525 grm. or double that amount of pure potassium monochromate in one liter of water made alkaline by a little sodium carbonate- Each cubic centimeter then corresponds to one-tenth mgrm. or two-tenths mgrm. of chromic oxide (Cr 2 O 3 ), in which condition chromium is usually reported in rocks and ores. It is probably 'inadmissible to increase the strength of the standard much above the figure given. Preparation of the Test Solution. Before filtering the aqueous extract of the sodium-carbonate fusion a few drops of alcohol (ethyl or methyl) are added to destroy the color of sodium manganate. If the yellow color of the filtrate is very faint, concentration by evaporation will strengthen it, and less than 2 mgrm. of chromic oxide in 1 grm. of rock can then be exactly measured. For smaller amounts it is best to employ from 3 to 5 grm. of powder, and then to concentrate the chromium by precipitation by mer- curous nitrate, as detailed in the nexts ection under VANADIUM (p. 1163); otherwise it may be difficult or impossible, because of the large amount of alkali carbonate present, to obtain a filtrate of sufficiently small bulk to show a decided color. If nitre has been used in the fusion, and the crucible has been at all attacked by it, a yellow coloration of the filtrate may be due to dissolved platinum, * Bull. Soc. Chimique (n. s.), XLII, p. 291, 1884; Chemical News, L, p. 18, 1885. + Zeitschr. fur anarg. Chemie, x, p. 402, 1895. t Zeitschr. fur anal. Chemie, xxxvni, p. 681, 1899. W. F. HII.I.EBRAND, Journ. Am. Chem. Soc., xx, p. 454, 1898; Chemical Newt, LXXVTII, pp. 227, 239, 1898; Bull. U. S. Geol. Survey, No. 167, p. 37. First applied by L. DE KOXIXGH (Nederl. Tyds. voor Pharm. Chem. and Tox.. 1889) for the estimation of chromium in foodstuffs. 1162 APPENDIX II. but neither the proportion of nitre nor the temperature of the blast should ever be high enough to permit the crucible to be attacked. Comparison of Colors. The final solution is transferred to a graduated flask of such size that its color shall be weaker than that of the standard chromium solution. Definite amounts of the latter are then diluted with water from a burette until of the same strength as the test solution, exactly as described on page 1150 for the colorimetric estimation of titanium. For very minute amounts it is necessary to use NESSLER tubes, as in ammonia estimations, instead of the glasses and apparatus described and depicted under Titanium (p. 1152). As with colorimetric methods in general, this one gives better results with small than with large percentages of chromium, yet it can be applied in the latter cases with satisfactory results by making a larger number of consecutive comparisons with the same solution. A FEW COMPARATIVE DATA. A few comparisons between colorimetric and gravimetric determina- tions of chromium are here given to show the order of agreement, the former having been made several months and even years after the latter. Gravimetric Colorimetric Gravimetric Colorimetric per cent. Cr^Gg. per cent. C^Oa. per cent. Cr 2 O 3 . per cent. Cr 2 O 3 . Trace. 0-018 Trace. 013 0-05 051 None. 0086 14 12 None. 0067 08 083 The outcome was somewhat surprising, for it was hardly to be expected that the long and laborious quantitative separations should have resulted so well as they are shown to have done. It should be mentioned that for the gravimetric tests but 1 or 2 grm. at most were used, which accounts for the reported absence of chromium in two instances, this report being based on the lack of color in the aqueous extract of the alkali fusion after removal of manganese. XVIII. VANADIUM (CHROMIUM) AND MOLYBDENUM. DISTRIBUTION OF VANADIUM AND MOLYBDENUM. The wide distribution of vanadium throughout the earth's crust has in recent years been clearly established (see ante, p. 1105), not only in ores and in coals, but in clays, limestones, sandstones, and igneous rocks.* The writer has shown (loc. cit.) that vanadium occurs in quite appreciable amounts * W. F. HILLEBRAND, "Distribution and Quantitative Occurrence of Vanadium and Molybdenum in Rocks of the United States," Am. Journ.Sci.,4ih Series, vi, p. 209, 1898; Chemical News, LXXVIII, p. 216, 1898: Bull. U. S. Geol. Survey, No. 167, p. 49. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1163 in the more basic igneous and metamorphic rocks up to 0-08 per cent, or more of V 2 O 3 , but that it seems to be absent, or nearly so, from the highly siliceous ones. Some of their ferric aluminous silicate constituents carry still higher percentages up to 0-13 per cent. V 2 O 3 in a biotite separated from a pyroxenic gneiss. Molybdenum, on the other hand, appears to be confined in quantities susceptible of detection to the more siliceous rocks, and, except perhaps in rare instances, is not present hi them in quantitatively determinable amount when operating on 5 grm. of material. Hence the quantitative search for vanadium will usually be limited to rocks with less than 60 per cent, of silica. The search for it even then will perhaps not often warrant the necessary expenditure of time, but in this connection it is to be remembered that neglect to estimate it introduces an error in the figures for both ferrous and ferric oxides, which in extreme cases met with may be of considerable moment. (See p. 1140, and also pp. 1174 and 1175.) DESCRIPTION OF METHOD. In the following method there is nothing absolutely novel except that chromium and vanadium, when together, need not be separated, but are determined, the former colorimetrically, as already described (p. 1161), the latter volumetrically, in the same solution.* Five grm. of the rock are thoroughly fused over the blast with 20 grm. of sodium carbonate and 3 grm. of sodium nitrate. After extracting with water and reducing manganese with alcohol it is probably quite unnecessary, if the fusion has been thorough, to remelt the residue as above, though for some magnetites and other ores containing larger amounts of vanadium than the generality of rocks, this may be necessary, as EDO CLAASSEN has shown.f The aqueous extract is next nearly neutralized by nitric acid, the amount to be used having been conveniently ascertained by a blank test with exactly 20 grm. of sodium carbonate, etc., and the solution is evaporated to approximate dry- ness. Care should be taken to avoid overrunning neutrality, because of the reducing action of the nitrous acid set free from the nitrite produced during fusion, but when chromium is present it has been my experience that some of this will invariably be returned by the precipitated silica and alumina, though only in one case have I observed a retention of vanadium, it being then large. The use of ammonium nitrate instead of nitric acid for con- verting the sodium carbonate into nitrate does not seem to lessen the amount of chromium retained by the silica and alumina. As a precautionary measure, therefore, and always when chromium is to be estimated also, the silica and alumina precipitate should be evaporated with hydrofluoric and sulphuric acids, the residue fused with a little sodium carbonate and the aqueous extract again nearly neutralized with nitric acid and boiled for a few moments, the filtrate being added to the main one. Mercurous nitrate is now added to the cold alkaline solution in some *W. F. HILLEBRAND, Journ. Am. Soc., xx, p. 461, 1898; Chemical News, LXXVIII, p. 295, 1898; Bull. U. S. Geol. Survey, No. 167, p. 44. t Am. Chem. Journ., vm, p. 437, 1886. 1164 APPENDIX II. quantity, so as to obtain a precipitate of considerable bulk, containing, besides mercurous carbonate, chromium, vanadium, molybdenum, tung- sten, phosphorus, and arsenic, should all happen to be in the rock. The mercurous carbonate serves to counteract any acidity resulting from the decomposition of the mercurous nitrate. Precipitating in a slightly alkaline instead of a neutral solution, renders the addition of precipitated mercuric oxide unnecessary for correcting this acidity. If the alkalinity, as shown by the formation of an unduly large precipitate, should have been too great, it may be reduced by careful addition of nitric acid until an added drop of mercurous nitrate no longer produces a cloud. After heating and filtering, the precipitate is ignited in a platinum cru- cible, after drying and removing from the paper to obviate any chance of loss of molybdenum and of injury to the crucible by reduction of arsenic. The residue is fused with a very little sodium carbonate, leached with water and the solution, if colored yellow, filtered into a graduated flask of 25 or more cubic centimeters capacity. The chromium is then estimated accurately in a few minutes by comparing with a standard alkaline solution of potassium monochromate (p. 1161). Then, or earlier in absence of chromium, sulphuric acid is added in slight excess and molybdenum and arsenic, together with occasional traces of platinum, are precipitated by hydrogen sulphide, prefera- bly in a small pressure bottle.* If the color of the precipitate indicates absence of arsenic the filter, with its contents, is carefully ignited in porcelain, and the delicate sulphuric-acid test for molybdenum is applied as follows: The molybdenum compound is heated in porcelain with a single drop of strong sulphuric acid till the acid is nearly volatilized. On cooling a beau- tiful blue color is proof of the presence of molybdenum. The filtrate, in bulk from 25 c.c. to 100 c.c. is boiled to expel hydro- gen sulphide, and titrated at a temperature of 70 to 80 with a very dilute solution of permanganate representing about 1 mgrm. V 2 O 5 per cubic centimeter as calculated from the iron strength of the permanganate, one molecule of V 2 O 5 being indicated for each one of Fe 2 O 3 . One or two checks are always to be made by reducing again by means of a current of sulphur dioxide gas, boiling this out again,f and repeating the titration. The latter results are apt to be a very little lower than the first, and are to be taken as the correct ones. In case the volume of permanganate used is so small as to make doubtful * From a sulphuric solution the separation of platinum and molybdenum by hydro- gen sulphide is much more rapid and satisfactory than from a hydrochloric solution. t The direct use of a solution of sulphur dioxide or of an alkali sulphite is inadmissible unless these have been freshly prepared since after a lapse of time they contain other oxidizable bodies than sulphurous acid or a sulphite. The sulphur dioxide is best ob- tained as wanted by heating a flask containing a solution of sulphur dioxide, or of a sul- phite to which sulphuric acid has been added. The expulsion of the last traces of sulphur dioxide is said to be more effectively ac- complished by boiling with simultaneous passage of a rapid current of carbon dioxide for a few minutes at the last than by boiling alone. Because of the small amount of air carried with it, long passage of the gas is said to result in slight oxidation of the vana- dium (MANASSE, Ann. Chem. u. Pharm., CCXL, p. 23, 1887; Zeitschr. fur anal. Chemie* xxxii, p. 225, 1893.) SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1165 the presence of vanadium, it is necessary to apply a qualitative test, which is best made as follows: The solution is evaporated arid heated to expel excess of sulphuric acid, the residue is taken up with two or three cubic centimetres of water and a few drops of dilute nitric acid, and a couple of drops of hydro- gen peroxide are added. A characteristic brownish tint indicates vanadium. Unless the greater part of the free sulphuric acid has been removed, the ap- pearance of this color is sometimes not immediate and pronounced, hence the above precaution. It is also necessary that the nitric acid shall be hi con- siderable excess, since in a neutral or only faintly acid solution the color does not appear strongly. The above is a surer test to apply than the following: Reduce the bulk to about 10 c.c., add ammonia in excess and introduce hydrogen sulphide to saturation. The beautiful cherry-red color of vanadium in ammonium- sulphide solution is much more intense than that caused by hydrogen per- oxide in acid solution, but the action of ammonia is to precipitate part or all of the vanadium with the chromium or aluminium that may be present or with the manganese used in titrating, and ammonium sulphide is unable to extract the vanadium wholly from these combinations. Usually, however, the solution will show some coloration, and addition of an acid preciptiates brown vanadium sulphide, which can be collected, ignited, and further tested if desired. APPLICATION OF THE METHOD IN PRESENCE OF RELATIVELY MUCH CHROMIUM. The application of the method in its foregoing simplest form is subject to one limitation the chromium must not be present above a certain mod- erate amount. This limitation is due to the considerable amount of per- manganate then required to produce a clear transition tint when titrating in a hot solution, as is advisable with vanadium. In a cold solution of chromic sulphate much less permanganate is needed to produce the peculiar blackish tint without a shade of green, which affords a sure indication of excess of permanganate, but in a hot and especially a boiling solution, the oxidation of the chromium itself takes place so rapidly that a very large excess of the reagent may be added before a pronounced end reaction is obtained. Never- theless, quite satisfactory determinations of as little as 1 or 2 mgrm. of vana- dium pentoxide can be made in presence of as much as 30 mgrm. of chromic oxide. To accomplish this it is only necessary to apply a simple correction obtained by adding permanganate to a like bulk of equally hot chromic-sul- phate solution containing approximately the same amount of chromium. RIDSDALE* titrated the cold solution to avoid oxidation of chromium, and obtained accurate results, but in the writer's experience the end reaction is then uncertain. The following tables contain the results of a considerable number of tests, those in Table II being tabulated separately in order to show the degree of accuracy attainable with a large excess of chromium by applying the correction above mentioned and also the amount of this correction : * Journ. Chem. Soc., vn, p. 73, 1888. 1166 APPENDIX II. TABLE I. TESTS FOR VANADIUM IN THE PRESENCE OF CHROMIUM. No. Chromic Oxide. Vanadium Pentoxide. Vanadium Pentoxide Found. Error. Milligrams. Milligrams. Milligrams. Milligram. 1 1 9-87 9-22 -0-15 2 1 94 1-04 + -10 -98 + -04 3 1-5 5-25 5-49 + -24 5-43 + -19 4 2 5-62 5-5 - -12 5-5 - -12 5 3 4-68 4-78 + -10 4-78 + -10 4-83 + -15 6 3 5-62 5-58 - -04 5-58 - -04 7 3-5 18-74 18-89 + -15 18-97 + -23 8 6 5-6 6-1 + -50 9 6 4-68 4-78 + -10 10 6 5-62 5-58 - -04 11 10 5-62 5-58 - -04 12 10 23-52 23-81 + -29 23-71 + -19 13 10 46-85 46-98 + -13 47-20 + -35 14 25 23-52 23-65 + -13 23-75 + -23 15 87-5 23-52 23-71 + -19 TABLE II. SHOWING APPLICATION OF CORRECTION FOR LARGER AMOUNTS OF CHROMIUM, OBTAINED BY ADDING POTASSIUM PERMANGANATE TO AN EQUAL BULK OF SOLUTION CONTAINING A LIKE AMOUNT OF CHROMIC SULPHATE. No. Chromic Oxide. Vanadium Pentoxide. Vanadium Pentoxide Found. Vanadium Pentoxide Found. Error. Volume of Solution. Milligrams. Milligrams. Uncorrected. Corrected. Milligram. 16 20 0-94 1-59 0-99 + 0-05 50-100 c.c. 17 20 1-87 2-69 2-09 + -22 50-100 c.c. 2-39 1-79 - -08 2-59 1-99 + -12 18 20 18-74 19-4 18-73 - -01 50-100 c.c. 19-3 18-63 - -11 19-3 18-63 - .11 19 30 1-87 2-99 2-14 + -27 About 100 c.c. 2-79 1-94 + -07 2-79 1-94 + -07 2-69 1-84 - -03 2-69 1-84 - -03 20 30 1-87 2-69 1-79 - -08 200 c.c. 2-89 2-09 + -22 2-89 2-09 + -22 2-79 1-99 + -12 21 62 46-85 48-60 47-60 + -75 200 c.c. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1167 In spite of the fact that the correction in most of the trials of this last table represents a large proportion of the permanganate used, the results must be considered satisfactory in view of the small amount of vanadium present, and they show that the method in competent hands after a little experience affords trustworthy figures. The method of T. FISCHER* digestion of the precipitated lead salts with a strong solution of potassium carbonate appears to offer the long- needed satisfactory quantitative separation of arsenic, phosphorus, chro- mium, tungsten, and molybdenum from vanadium, the normal lead meta- vanadate remaining quite unattacked, according to the author, while the other lead salts are wholly decomposed, but the applicability of this method to the separation of the minute amounts often found in rocks and ores has not been tested. The object has been in the present case to reach satis- factory results with the greatest expedition, and when chromium is not present in considerable amount this is accomplished. Fortunately, chromium is almost never a prominent constituent of clays, coals, iron ores, and those rocks in which vanadium has thus far been re- ported, for although it is usually certain of the most basic of the silicate rocks that are highest in chromium as the peridotites yet in these, so far as present experience teaches, vanadium is lacking, a fact doubtless connected with the simultaneous absence from them of ferric-aluminous silicates. CONDITION OF VANADIUM IN ROCKS. The above and elsewhere mentioned connection of vanadium with the ferric-aluminous silicates of rocks, taken in connection with the existence of the mineral roscoelite, classed as a vanadium mica, indicates a condi- tion of the vanadium corresponding to aluminium and ferric iron, and that it is to be regarded as replacing one or both of these elements. Hence it should be reported as V 2 O 3 and not as V 2 O 5 . What its condition may be in matter of secondary origin, like clays, limestones, sandstones, coals, and ores of iron, is yet open to discussion. It was the writer's opinion until recently, that it should then be regarded as in the pentavalent state (V 2 O 5 ), but his work upon certain remarkable vanadiferous sandstones f of Western Colorado, in which it unquestionably occurs as trivalent vanadium, (V 2 O 3 ), has led to a decided unsettling of this view. It is but proper to recall that CZUDNOWICZ,! because of the extreme difficulty in completely extracting it from iron ores by an alkali-carbonate fusion and because of the easy reducibility of vanadic acid by ierrous salts, under the conditions in which brown iron ores are supposed to form, con- sidered the vanadium in such ores to be in a lower condition of oxidation, (V 2 O 3 ). LINDEMANN'S contrary conclusion with regard to certain iron ores, because the vanadium was extracted as V 2 O 5 by sodium-carbonate * Inaugural Dissertation, ROSTOCK, 1894. t HILLEBRAND and RANSOME, Am. Journ. Sci., 4th Series, x, p. 120, 1900. 1 POGG. Ann., cxx, p. 20, 1863. Dissertation, Jena, 1878, through Zeitschr. fur anal. Chemie, xvin, p. 99, 1879. 1168 APPENDIX II. fusion without niter, is not valid, since this would probably be the case even if it existed in the ore as V 2 O 3 . XIX. FERROUS IRON. COMPARISON OF SEALED-TUBE AND HYDROFLUORIC-ACID METHODS COM- PARATIVE WORTHLESSNESS OF THE FORMER IN ROCK ANALYSIS. No point in rock analysis has been the cause of greater solicitude to the chemist, and especially to the mineralogist and petrographer, than the determination of iron in ferrous condition. The sealed-tube or MITSCHER- LICH method with sulphuric acid, for a long time the only available one. is in theory perfect, since complete exclusion of oxygen is easily attainable, Its chief hitherto recognized defect lies in the inability to always secure complete decomposition of the iron-bearing minerals, and even to ascertain oftentimes, whether or not the decomposition has been complete. The addition of hydrofluoric acid to the sulphuric in the tube, in order to insure this breaking up, is to be regarded as of very doubtful utility in most cases, since the glass may be so strongly attacked as to add an appreciable amount of iron to the solution, and the hydrofluoric acid may have exhausted itself in attacking the glass before the more refractory minerals succumb. Never- theless, if decomposition can be effected by sulphuric acid alone the results obtained are sharp and concordant, and what has seemed especially re- markable, and up to almost the present moment without a satisfactory explanation, they are in rock analysis usually higher than when made by any of the modifications of the hydrofluoric-acid method now so extensively practiced. This difference is not very marked with rocks containing but 1 or 2 per cent, of ferrous iron, but it increases with rising percentage to such an extent that where the sealed-tube method will show 12 per cent. FeO the other may indicate no more than 10 per cent. This is a fact of which the writer has long been cognizant, but it does not seem to be known to chemists or petrographers at large, though WULFING * has noticed this difference in certain analyses without appreciating its significance. Experiments with soluble iron salts of known composition, like ferrous sulphate and ferrous-ammonium sulphate, throw no light on the subject, for both methods give with them the same sharp and accurate results. In spite of several attempts to find a solution to the problem, none pre- sented itself until very recently, when, as a result of observations made in this laboratory by Dr. H. N. STOKES in a pending investigation on the action of ferric salts on pyrite and other sulphides, the clue was given. Dr. STOKES found that ferric salts exercise a most marked oxidizing effect on pyrite and probably other sulphides.f The reaction is not new (see J. H. L. VOGT in Zeitschr. fur prakt. Geol., 1899, pp. 250, 251), but the ease with which the * Ber. deutach. chem. Gesell., xxxn, p. 2217, foot-note, 1899. tThis effect had, however, been already pointed out by Prof. L L. de KONINCK in a communication (Ann. soc. geolog. Belg. x [1882-83] 101), which, from lack of publicity, was overlooked. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1169 change takes place and the completeness of the oxidation of the pyrite, not only of its iron but of the greater part of the sulphur as well, were entirely unexpected. Pure pyrite itself is attacked with extreme slowness by boiling dilute sulphuric and hydrofluoric acids, either alone or mixed, but the moment a ferric salt is introduced the case is altogether differant. However, experiment has shown (p. 1174) that with the amounts of sul- phides usually found in igneous rocks their effect upon the estimation of ferrous iron by the hydrofluoric-acid method at atmospheric pressure and boiling heat is negligible, though by increasing the amount of sulphide the effect becomes more and more apparent, because of the greater surface of pyrite exposed to the action of the ferric iron of the rock. Under the conditions of the MITSCHERLICH method, on the other hand a temperature of 150 to 200 C., and even higher, high pressure, much longer time of action, and impossibility of escape of any hydrogen sulphide that may be formed the sulphur of the sulphides becomes nearly, if not fully, oxidized to sulphuric acid at the expense of the ferric iron in the rock, with the production of an equivalent amount of ferrous iron in addition to that resulting from the sulphide itself. Now, rocks with hardly an exception, and many minerals, carry pyrite or pyrrhotite, or both, often in consider- able amount, often in traces only. My own experience has been that sul- phur can almost always be detected in 2 grm. of rock powder. Let us now see what the effect of these traces when fully oxidized amounts to. One atom of sulphur (32) requires for its complete conversion to tri- oxide the oxygen of three molecules of ferric oxide (480), which then becomes six molecules of ferrous oxide (432). In other words 0-01 per cent, of sul- phur may cause the ferrous oxide to appear too high by 0- 135 per cent, and 0-10 per cent, of sulphur may bring about an error of 1 35 per cent, in ferrous oxide. The case is still worse if the sulphur is set free as hydrogen sulphide from a soluble sulphide, for then the above percentages of sulphur produce errors of 0-18 and 1-8 per cent., respectively, in the ferrous oxide deter- mination. The error caused by sulphides tends to become greater the more there is present of either or both sulphide and ferric salt. Now, the highly fer- ruginous rocks usually carry more ferric iron than the less ferruginous ones, and they are often relatively high in pyrite and pyrrhotite ; hence the increas- ing discrepancy between the results by the two methods as the iron con- tents of the rocks rise is fully in accord with the above explanation.* Notwithstanding that the MITSCHERLICH method has thus been dis- credited in its general applicability to rocks and minerals, it is still capable of affording valuable assistance with those which are totally free from sul- phides. Hence the conditions under which success can best be achieved by it are set f ort-h in the following paragraphs : * For details of experiments showing the worthlessness of the MITSCHERLICH method for rocks and minerals which contain even a trace of free sulphur or sulphides, see HILLE- BRAND and STOKES, in and as yet unpublished paper in Journ. Am. Chem. Soc., xxn, and Zeiischr. fur anorg. Chem., xxv, 1900, entitled. "Relative Value of the MITSCHERLICH and hydrofluoric-acid methods for ferrous iron deteminations. 1170 APPENDIX II. THE MODIFIED MITSCHERLICH METHOD. Strength of Acid. The method in its original and usual application calls for a mixture of three parts of sulphuric acid and one of water by weight, or about three to two by volume, though a still stronger acid is sometimes used. In some cases, however, perhaps in most, much better decomposi- tion of the silicates is effected by reversing the proportions of water and acid, or at any rate by diluting considerably beyond the above proportion. Hereby the separation of salts difficultly soluble in the stronger acid is avoided and the actual solvent effect on the minerals seems to be in nowise diminished. Filling, Sealing, and Heating of the Tube. The very finely powdered mineral having been introduced into a tube of resistant glass free from fer- rous iron, the open end is drawn out, so as to leave a funnel for the intro- duction of the acid. A very little water is then introduced and carefully heated to boiling for a moment to expel all air from the powder. The diluted acid which has just been boiled down from a state of greater dilution in order to have it free from air is then poured in until the tube is about three- fourths filled. Carbon dioxide is then introduced from a generator which has been in active operation for some time, through a narrow glass tube drawn out of the same kind of glass as that of which the decomposing tube consists. In a few moments the air is expelled, and the small tube is then sealed into the large one over the blast-lamp without interrupting the gas- current until the very last instant, when to prolong it would perhaps cause a blowing out of the softened glass. The interruption of the current at the proper moment is easily effected by the pressure of the thumb and finger holding the small tube at the point where it enters the rubber tube leading from the gas-generator. No breakage in the oven ever occurs as a conse- quence of thus fusing one tube into the other. The heating is done in a bomb oven at any desired temperature up to, say, 200 and continued at intervals until examination by aid of a low- power lens shows that decomposition is complete or has progressed as far as can be hoped for. By inclosing the glass in an outer tube of strong steel, properly capped * and containing a little ether or benzin to equalize the pressure on both sides of the glass, the temperature can be elevated far be- yond what is otherwise permissible, and the decomposition will then doubt- less be more complete with refractory silicates. Reason for Introducing Gas and Sealing as Above Directed. The usual practice in employing the above method has been to expel air before sealing by introducing a few crystals or lumps of an alkali carbonate or bicarbonate, the gas set free on their contact with the acid being supposed to effectively expel all air. That this is not accomplished the following series of compara- tive results long since published elsewhere f fully show. The material used was the oxide of uranium, U 3 O 8 , requiring by theory 32-07 per cent, of UO 2 . * ULLMANN, Zeitschr. fiir angew. Chemie, 1893. p. 274; Zeit. fur. anal. Chemie, xxxni p. 582. 1894. t Bull. U. S. Geol. Survey, No. 78, p. 50; Chemical News, LXIV, p. 232, 1891. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1171 Operating as just above described on from 0-3 to 0-5 gnn., the results were 31-06, 31-07, 29-72, 29-33, 29-89, 30-69, whereas after filling the tube with gas from a generator there was found 32-11, 31-90, 32-15, 32-12, 32-06, 32-17, 32-28, the average error of the former series being 1 78 per cent. The percentage error would, of course, be reduced by increasing the weight of mineral operated on. An average error equal to the above when employing 1 grm. of ferrous minerals would make the percentage for FeO about 0-3 per cent, too low. While the absolute error might be the same in all cases, the relative error would increase with minerals low in ferrous iron. THE HYDROFLUORIC-ACID METHOD. This method is the one which has been almost exclusively used since the earliest years of the Survey's existence. The specially ground powder, in a capacious crucible, is placed, after stirring up with dilute sulphuric acid, on a small water-bath of a single open- ing (Fig. 13) and covered with a glass funnel, the stem of which has been cut off near the flare, resting in a depression of the specially made cover, into which water constantly drops from a tubulated bottle, thus securing a per- fect water joint and serving to keep the bath full. Through a small metal pipe carbonic-acid gas flows into the bath above the surface of the water, and rising through orifices in the cover fills the funnel and crucible.* The lamp under the bath is lighted and hydrofluoric acid is poured into the cru- cible through a platinurn funnel, which is left in place to serve as an occa- sional starrer, for which a rod or wire may be substituted. After boiling commences the rapid gas current can be safely interrupted, to be restored when the lamp is extinguished after one-half to one or more hours. A full stream of cold water is then caused to flow from the tubulated bottle into the bath, the overflow from the outlet tube being caught in a receiver. As soon as cool the contents of the crucible are emptied into a platinum dish containing cold water and titrated till the first permanent color appears, which usually will last for only a few seconds. Duplicate determinations are to be advised whenever possible, since even with the utmost care the results will occasionally differ more than is allowable. In absence of a suitable water-bath an ordinary one can be used covered with a beaker, through a hole in the bottom of which a strong current of carbon dioxide is introduced, or the crucible may be set in a sand-bath and covered in the same way with a broken beaker (DOELTER). The cause of the rapid disappearance of the first pink blush when titrating in hydrofluoric-sulphuric solution appears to be the ready oxidizability of manganous fluoride by permanganate. The latter can be added by the cubic * J. P. COOKE, Am. Journ. Sci., 2d Series, xuv, p. 347. 1867. 1172 APPENDIX II. centimeter to solutions already containing manganous sulphate in presence of hydrofluoric acid without producing a more than passing pink blush. The solution, however, takes on in ever-increasing intensity the red-brown color Fio. 13. COOKE'S apparatus for the determination of ferrous iron. characteristic of manganic salts. The decolorization due to this cause is hence much more pronounced in the case of rocks high in ferrous iron than of those low in this constituent, because of the greater amount of manganous SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1173 salt resulting from reduction of a correspondingly larger amount of perman- ganate. When pyrite is present the bleaching is hi part due to its action on any permanganate added in excess of the requirements of the ferrous oxide. But this action is not so immediate as to affect the ferrous oxide determination if the end point hi the latter has been properly observed. PRATT'S MODIFICATION OF THE HYDROFLUORIC-ACID METHOD. J. H. PRATT * has shown that very satisfactory ferrous-iron determinations can be secured by simple boiling of the rock powder with hydrofluoric and sulphuric acids hi a large crucible fitted with a cover and platinum tube for introduction of carbon dioxide. His test experiments on ferrous sulphate show that there need be practically no oxidation, even if the heating lasts several hours. The directions given on page 150 of his paper, with reference to the treatment of very refractory minerals which are not fully decomposed by this treatment, must be understood as referring only to homogeneous minerals and not to rocks, where the relations of ferrous and ferric iron in the undecomposed portion are certainly different from those in the part dissolved. INFLUENCE OF SULPHIDES, VANADIUM, AND CARBONACEOUS MATTER ON THE DETERMINATION OF FERROUS IRON BY THE HYDROFLUORIC-ACID METHOD. A dark color of the undissolved residue may be due to pyrite, graphite, or carbonaceous matter. The first of these affects the result but little, the second probably not at all, and they can be distinguished by their behavior toward nitric acid. Organic matter of course renders impossible the esti- mation of ferrous iron. Sulphides. Pyrite, in the quantities usually met with in igneous rocks, is probably without serious effect on the ferrous-iron determination by any of the hydrofluoric-acid methods. This sulphide is very resistant toward attack in the absence of oxygen, as is shown by the fact that if present in any quan- tity it can be readily recognized in the residue after titration. In any case it is impossible to allow for an error introduced by its possible decomposition, and the result of titration must count as ferrous iron. In the case of soluble sulphides two sources of error are introduced that of reduction of ferric iron by hydrogen sulphide evolved, and that due to the ferrous iron which the sul- phides themselves may contain, especially if pyrrhotite is present. The first of these is perhaps negligible, since most of the hydrogen sulphide would probably be expelled without reducing iron. The second is approximately measurable if it is known that pyrrhotite is the only soluble sulphide present and its amount has been ascertained by determining the hydrogen sulphide sot free on boiling; with hydrochloric acid in a current of carbon dioxide. In this case a correction is to be applied to the result of titration for total ferrous iron. (See also page 1184, under Sulphur.) In order to obtain quantitative data regarding the effect of pyrite on the ferrous-iron estimation by the hydrofluoric-acid method the following tests * Am. Journ. Sci., 3d Series, XLVIII, p. 149, 1894. 1174 APPENDIX II. were recently made: Part of a fine crystal of pyrite was rather finely pow- dered and boiled with dilute sulphuric acid, which extracted considerable ferrous iron, derived presumably from admixed or intergrown pyrrhotite, since a second boiling with fresh acid gave a negative test for ferrous iron. After washing by decantation with water, followed by alcohol and ether, the powder was dried and further pulverized. A quarter of a gramme, of it when treated with hydrofluoric and sulphuric acids in a large crucible by the COOKE method for ferrous iron, then rapidly filtered through a very large perforated platinum cone fitted with filter-paper, required but 2 drops of a permanganate solution representing only 0032 grm. FeO to the cubic centi- meter. Since, however, Dr. H. N. STOKES has found in a pending investigation that the oxidizing effect of ferric salts on pyrite and other sulphides is vastly greater than seems to have been suspected (see page 1168), the following tests were made in order to ascertain the probable error due to this action under the conditions prevailing in rock analysis : Successive portions of 1 grm. each of a hornblende-schist, free from sulphur and carrying 10-09 per cent. FeO as the mean of several determinations and 4-00 percent. Fe 2 O 3 , were mixed in a large (50 c.c.) platinum crucible with 0-02, 0-025, and 0-10 grm., respectively, of the above purified pyrite powder, and treated with hydro- fluoric and sulphuric acids by the COOKE method, the water-bath being at boiling heat for one hour. The cooled contents of the crucible were poured into a platinum dish containing water and titrated rapidly nearly to an end. Then, in order to get rid of the pyrite, which would obscure the end reaction by its reducing effect on the permanganate, the solution was filtered as above and in the clear filtrate the titration was carried to completion. The results were 10 02, 10 16, and 10 70. Inasmuch as the smallest of these three charges of pyrite was several times greater than what may be considered an unusually high amount for an igneous rock, it is very evident that for all practical pur- poses the influence of pyrite on the ferrous estimation by the COOKE method is negligible. At the same time it is to be borne in mind that with increased content in ferric iron an increased amount of pyrite will be attacked, and that the extent of this attack is undoubtedly influenced by the degree of fineness of the pyrite powder. Vanadium. If vanadium, when present, exists in the trivalent condition, it necessarily affects with an error varying with its amount the result of titra- tion for ferrous iron. Knowing the amount of vanadium a correction can be applied as follows: One molecule of V 2 O 3 (150-8) in oxidizing to V 2 O 5 requires as much oxygen as four molecules of FeO (288) when oxidized to Fe 2 O. The proportion, 150-8 : 288 : : V 2 O 3 present : x, therefore gives the figure to be deducted from the unconnected value for FeO. That this correction is very needful with many of the basic rocks becomes at once evident from the fol- lowing perhaps extreme example : Found 2-50 per cent, apparent FeO in a rock containing 0-13 per cent. V 2 3 . Deduct 25 per cent. FeO equivalent in its action on KMnO 4 to 13 V 2 O 3 . Leaving 2 25 per cent. FeO corrected. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1175 Found 5 00 per cent, apparent total iron as Fe 2 O 3 in the same rock. Deduct 14 per cent. Fe 2 O 3 corresponding to 0-13 per cent. V 2 O 3 . Leaving 4 86 per cent, corrected total iron as Fe 2 O 3 . Deduct 2 50 per cent. Fe 2 O 3 equivalent to 2 25 per cent. FeO. Leaving 2 36 per cent. Fe 2 O 3 in the rock. Failure to correct for the vanadium in both cases would have made the figures for FeO and Fe 2 O 3 , respectively, 2-50 and 2-22 instead of 2-25 and 2 36 as shown above. Carbonaceous Matter. As said before (page 1173), matter of organic origin other than graphic carbon lenders the results from the ferrous iron determi- nation altogether unreliable. UNCERTAINTIES OF THE FERROUS IRON DETERMINATION. From the foregoing it is apparent that, despite the utmost care in prac- tical manipulation, the exact estimation of ferrous iron in rocks is one fraught with extraordinary difficulties and uncertainties. Only in absence of de- composable sulphides, and when the amount and condition of vanadium are known, can the result be regarded as above suspicion. XX. ALKALIES. THE LAWRENCE SMITH METHOD. The various methods for getting at the alkalies in insoluble silicates differ more in the mode of attack of the mineral powder and in the immediately subsequent treatment than in the final stages. With very few exceptions, since the early days of the Survey's existence, all alkali determinations have been made by the method of J. LAWRENCE SMITH,* which is far more conven- ient than and fully as accurate as those in which decomposition is effected by hydrofluoric and sulphuric acids, or by bismuth, lead, or boric oxides. One of its chief advantages is the entire elimination of magnesia at the start. Decomposition of the powder is effected by heating it with its own weight of ammonium chloride and eight times as much precipitated calcium car- bonate. The ammonium chloride used must be purified, preferably by sublima- tion, or made by neutralizing pure ammonia by pure hydrochloric acid, and the calcium carbonate is best obtained from pure calcite by solution and reprecipitation. However obtained, this last is rarely free from alkalies, which must be estimated once for all in a blank test in order to apply a cor- rection. Eight grm. of the carbonate will contain usually from 0-0012 to 0-0016 grm. of alkali chlorides, almost entirely the sodium salt, but the amount has been brought down to half the above by very long washing. This correction may be admitted at once to be a defect of the method, but it is one easily applied with safety. 41 The ignition may be made in a covered crucible of ordinary shape and * Am. Journ. Sci., 2d Series, L, p. 269, 1871; Am. Chemist, x, 1871; Annalen Chem. vnd Pharm., CLIX, p. 82, 1871. 1176 APPENDIX II. of about 20 to 30 c.c. capacity, heated to dull redness for not more than two-fifths of its height, but the heat has to be kept so low in this case to avoid loss by volatilization that perfect decomposition is not always assured. Hence, to avoid waste of time, in very fine grinding, the form of crucible with cap originally advocated by SMITH is very much to be preferred, since it permits, when set at an angle through an opening in the side of a fire-clay cylinder, of the application of the full heat of two burners, and perfect decomposi- tion invariably results without the need of extraordinary care in grinding. The crucible used in this laboratory (Fig. 14) for one-half grm. of rock pow- der and 4 grm. calcium carbonate is 8 cm. long, 1 8 cm. wide at the mouth, FIG. 14. The J. LAWRENCE SMITH crucible for alkali determinations, dimensions see text. For and 1*5 at the bottom. For double the amounts or more the dimensions are 8 cm., 2-5 cm., and 2-2 cm. The weights are 25 and 40 grm. Treatment of the Mineral Powder. Perfectly satisfactory results are to be obtained with but a half gramme of rock powder. This is weighed out, ground down somewhat finer in a large agate mortar, mixed with its own weight of sublimed ammonium chloride, and the two thoroughly ground together. Then nearly all of 4 grm. of calcium carbonate is added and the grinding continued till a thorough mixing has resulted. The contents of the mortar are transferred to the long crucible, the rest of the carbonate being used for rinsing off mortar and pestle. The crucible is then capped and placed in a clay cylinder (Fig. 14), or through a hole in a piece of stout asbestos board clamped in a vertical position, and heated for about ten minutes by a low, flat flame placed at considerable distance beneath. As soon as the odor of ammonia is no longer perceptible, the nearly full flame of two BUNSEN burners is applied, and continued for forty to fifty minuses. The sintered cake * detaches readily from the crucible as a rule ; if not, it is * To avoid the formation of a melted cake with silicates very high in iron it is advisable to increase the proportion of calcium carbonate. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1177 softened up in a few minutes by hot water and digested in a dish until thor- oughly disintegrated. It is first washed by decantation, and any lumps are broken up by a pestle, then thrown on the filter and well washed with hot water. The residue should dissolve completely in hydrochloric acid without showing the least trace of unattacked mineral, not even of quartz. Separation of Calcium and Sulphuric Acid. All but a trifling amount of the calcium is separated at boiling heat in a large platinum dish by double precipitation by ammonia and ammonium carbonate. The combined filtrates are evaporated to dryness and the ammonium salts are carefully driven off. From the aqueous solution of the residue but a few cubic centimetres in bulk the rest of the calcium is thrown out by ammonia and ammonium oxalate, this last being more effective than the carbonate. The filtrate, caught in an untared platinum crucible or small dish, is evapo- rated to dryness and gently ignited; the residue is moistened with hydro- chloric acid to decompose any alkali carbonate that may have been formed, again evaporated, ignited, and weighed. On solution in water a few tenths of a milligramme of fixed residue is invariably left, which should be collected, ignited, and weighed in the same crucible or dish in order to arrive at the weight of the chlorides. If the rock contains sulphur this will be in part found with the chlorides as sulphate. Therefore, if the sulphur is at all considerable in amount it must be removed by a drop of barium chloride before the final precipitation of the calcium. The excess of barium is removed by ammonium carbonate and the last of the calcium by ammonium oxalate, as above. If the sul- phur is not thus removed there is danger, if not certainty, of the potassium- platinic chloride carrying sodium sulphate. A faint reaction for sulphate can usually be obtained, anyway, if the evaporations have been made on a water-bath heated by gas. Precipitation of Potassium. To the solution of the chlorides in a small porcelain * dish an excess of platinic-chloride solution is added. The dilu- tion should be such that when heated on the water-bath any precipitate that may form wholly redissolves. Evaporation is then carried on till the residue solidifies on cooling. It is then drenched with absolute alcohol f or with that of 80-per cent, strength, filtered by decantation through a very small filter and washed by decantation with alcohol of the same strength, The precipitate is not brought onto the filter more than can be avoided. Dish and filter are then dried for a few minutes to remove adhering alcohol; the contents of the former are transferred to a weighed platinum crucible or very small dish, and what still adheres to the porcelain is washed through the filter with hot water into the weighed receptacle. This is now placed * Preferred to platinum because of the possibility, under certain rare and ill-under- stood conditions, of the formation of an insoluble subchloride of platinum, probably by reaction between the platinum of the dish and that of the salt. (See also BOHX, Zeitschr. fiir anal. Chemie, xxxvm, p. 349, 1899.) t PRECHT (Zeitschr. fiir anal. Chemie, xvin, p. 513, 1879) claims that this is to be preferred to 80-per cent, alcohol, especially if evaporation has been carried to dehydra- tion of the sodium salt. ATTERBERG disputes this final statement and says that 80-per cent, alcohol gives better results. 1178 APPENDIX II. on the water-bath and afterwards heated to 135 in an air-bath. The factor used for reduction of K 2 PtCl 6 to 2KC1 is 0-307 of 2KC1 to K 2 O, 0-632. LITHIUM. After separation of the potassium-platinic chloride, the alcoholic filtrate is evaporated and tested spectroscopically for lithium. This element is al- most invariably present, but almost never in amount to warrant quantita- tive estimation. Should it be so, however, the very excellent GOOCH method (summarized below) of separation by amyl alcohol is to be followed, after removal of the platinum by hydrogen gas.* In rock analysis there need be no fear of enough lithium falling with the potassium to cause any concern. If ammonium carbonate alone has been relied on to separate all calcium (ante, page 1177) the few tenths of a milligramme of calcium chloride that escaped precipitation can now be found with the sodium. GOOCH'S METHOD f FOR SEPARATING LITHIUM. To the concentrated solution of the chlorides amyl alcohol is added and heat is applied, gently at first, to avoid danger of bumping, until, the water disappearing from solution and the point of ebullition rising and becoming constant for some minutes at a temperature which is approximately that at which the alcohol boils by itself, the chlorides of sodium and potassium are deposited and lithium chloride is dehydrated and taken into solution. At this stage in the operation the liquid is cooled and a drop or two of strong hydrochloric acid added to reconvert traces of lithium hydrate in the deposit, and the boiling continued until the alcohol is again free from water. If the amount of lithium chloride present is small, it will now be found in solution and the chlorides of sodium and potassium will be in the residue, excepting the traces for which correction will be made subsequently. If, however, the weight of lithium chloride present exceeds 10 or 20 mgrm., it is advisable at this point, though not absolutely essential to the attainment of fairly correct results, to decant the liquid from the residue, wash the latter a little with anhydrous amyl alcohol, dissolve in a few drops of water, and repeat the separation by boiling again in amyl alcohol. For washing, amyl alcohol previously dehydrated by boiling is to be used, and the filtrates are to be measured apart from the washings. In filtering it is best to make use of the perforated crucible and asbestos felt, and apply gentle pressure. The cruci- ble and residue are ready for the balance after drying for a few minutes * When haste is not an object, this way of BUNSEN'S for removing platinum from the chlorides of the alkalies is by far the neatest and most satisfactory. The small flask containing the solution is placed in a water-bath and attached to a hydrogen generator. After expelling all air the flask is closed, without breaking connection with the generator, and left to itself, except for occasional light shaking up, till reduction is accomplished. A more expeditious and very satisfactory reduction is effected by evaporating the solu- tion to dryness with metallic mercury, then heating-to expulsion of the excess of mercury and of its chloride (SONSTADT, Journ. Chem. Soc., LXVTI, p. 984, 1895), who thus reduces potassium-platinic chloride in order to weigh its platinum. t Proc. Am. Acad. Arts and Sci., p. 177, 1886; Bull. U. S. Geol. Survey, No. 42, p. 73, 1887; Chemical News, LV, pp. 18, 29, 40, 56, 78, 1887; Am. Chem. Journ., ix, p. 33, 1887. - SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1179 directly over a flame turned low. The weight of insoluble chlorides actually obtained in this manner is to be corrected by the addition of 0-00041 grm. for every 10 c.c. of amyl alcohol in the filtrate, exclusive of washings, if the insoluble salt is entirely sodium chloride, 0-00051 grm. for every 10 c.c. if potassium chloride constitutes the residue, and if both sodium and potassium chlorides are present, 0-00092 grm.; but the entire correction may in any case be kept within very narrow limits if due care be given to the re- duction of the volume of residual alcohol before filtration. The filtrate and washings are evaporated to dryness, treated with sulphuric acid, the excess of the latter driven off, and the residue ignited to fusion and weighed. From the weight thus found the subtraction of 0005 grm. is to be made if sodium chloride constitutes the precipitate, 0-00059 grm. if potassium chloride alone is present in the residue, and 0-00109 grm. if both these chlorides are present, for every 10 c.c. of filtrate, exclusive of washings. Amyl alcohol is not costly, the manipulations of the process are easy, and the only objectionable feature the development of the fumes of amyl alcohol is one which is insignificant when good ventilation is available. The process has been used for some months frequently and successfully, by others as well as by myself, for the estimation of lithium hi waters and minerals. SEPARATION OF ALKALIES BY OTHER METHODS. When, as may happen in rare instances, it is necessary to estimate alka- lies in the main portion after elimination of silica, alumina, lime, etc., in one of the usual ways, the question of a suitable method for separating mag- nesium becomes important. The Mercuric-oxide Method. The old barium-hydroxide method is not to be recommended. The mercuric- oxide method of ZIMMERMANX, whereby the magnesia is precipitated from solution of the chlorides by moist, freshly precipitated, and alkali-free mercuric oxide, can give satisfactory results. The oxide is added in excess to the solution in a platinum crucible and evapo- rated to dryness. Then the mercuric chloride and most or all of the excess of oxide are expelled by cautious heating. On leaching with water the mag- nesia remains on the filter. With more than 1 per cent, of magnesia the operation must be repeated (DITTRICH). The Ammonium-Carbonate Method. Lately the once-favored method of precipitating the magnesium by neutral ammonium carbonate in con- centrated solution has been again recommended.* The magnesium solu- tion must be as strongly concentrated as possible, and a great excess of ammo- nium-carbonate solution must be used. A voluminous precipitate forms, which dissolves on vigorous stirring if enough of the precipitant was used. After a time a crystalline precipitate falls a double carbonate of magnesium and ammonium which is insoluble in a concentrated solution of ammonium carbonate. Allow to stand for six to twenty-four hours. Wash with the * WtLFixo, d . Ber. deutsch. Chem. Gesell., xxxn, p. 2214, 1899. The neutral carbonate is prepared by dissolving 230 grm. of ammonium carbonate in 180 c.c. of ammonia of - 92 specific gravity and enough water to make 1 litre. 1180 APPENDIX II. concentrated ammonium-carbonate solution. It is probably no exercise of undue caution to redissolve and reprecipitate to make sure of getting all alkali in the filtrate. The Amyl-olcohol Method. Under certain circumstances, notably ab- sence of lithium, the method of GOOCH developed by RIGGS * may be satis- factory. It is similar to that of GOOCH for separating lithium from sodium and potassium chlorides by amyl alcohol, and involves the same solubility corrections for the alkali chlorides above noted (p. 1179) in the description of GOOCH'S method. RIGGS'S summary is as follows: Evaporate the solution nearly or quite to dryness. Dissolve the residue in as little water as possible and add a few drops of hydrochloric acid. Then add 30 to 40 c.c. of amyl alcohol and expel the water by bringing the alcohol to boiling. Continue the boiling until the volume of the solution is reduced to 10 c.c., or even considerably less. In filtering, it is of great advantage to use a perforated crucible and an asbestos felt and to filter under pressure. In case the total chlorides exceed 0-2 grm. it may be advisable to decant the liquid, wash the residue, redissolve, and repeat the precipitation. If this be not done, the precipitate should be redissolved with the least possible quantity of water, a few drops of hydrochloric acid added, and the pre- cipitation repeated in the original solution. The filtrate is transferred to a weighed platinum dish and evaporated. Water is added before the alcohol has been expelled and the evaporation continued. The residue is dis- solved in water. Sulphuric acid is added in slight excess. This solution is evaporated to dryness, the residue ignited and weighed, and the treatment with sulphuric acid is repeated. The residue of insoluble chlorides may be transferred to the weighed perforated crucible and dried at a tempera- ture below their melting-points, or it may be dissolved and the solution transferred to a weighed platinum dish, evaporated, and the residue dried as above and weighed. As with the GOOCH method for lithium, the numerous test results are good. XXI. CARBON DIOXIDE, CARBON. For this estimation an apparatus (Fig. 15) permanently set up is used, of which several forms have been described by different writers. The rock powder is boiled with dilute hydrochloric acid in a small ERLENMEYER flask attached to an upward-inclined condenser, whence, after passing through a compact arrangement of drying-tubes first, one of calcium chloride, then one of anhydrous copper sulphate to retain hydrogen sulphide from decomposable sulphides and any hydrochloric acid that may pass over, and finally a second calcium-chloride tube the carbon dioxide is retained by absorption tubes filled with soda-lime followed by calcium chloride. Of course, arrangement is made for a current of CO,-free air with which to sweep out the apparatus before and after the experiment, and for a slow * Am. Journ. Sci., 3d Series, XLIV, p. 103, 1892. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1181 current during its continuance. The results are very accurate and the deter- mination can be quickly carried out. In the preliminary qualitative test for carbon dioxide, it must be re- membered that while calcite gives off its carbon dioxide on treatment with FIG. 15. Compact form of apparatus for estimation of carbon dioxide. cold acid, dolomite and siderite do not, and hence warming should not be omitted; otherwise, a few tenths per cent, of carbon dioxide can very well be overlooked. Moreover, the powder should first be stirred up with a little hot water, to remove all entangled air which might otherwise be mistaken for carbon dioxide. It has been already shown under water (p. 1129) how, in case of need, 1182 APPENDIX II. the determination of carbon dioxide can be combined with that of water by fusion with lead chromate or potassium chromate. This latter method must always be resorted to when the carbon of graphite or carbonaceous matter has to be estimated. If carbonates are present at the same time the result of the test includes the carbon from both sources, and a separate deter- mination by the wet way of that of the carbonates is necessary. XXII. CHLORINE. To make sure of getting all the chlorine, it is best to fuse with chlorine- free sodium-potassium carbonate, or even sodium carbonate alone, first over the full burner, then for a moment or two over the blast, leach with water, acidify with nitric acid, and precipitate by silver nitrate without preliminary separation of silica. If 1 grm. of material has been used no precipitation of silica need be feared on acidifying or on standing. In many cases it is quite sufficient to attack the powder by chlorine- free hydrofluoric acid and a little nitric acid, with occasional stirring, and after filtering through paper fitted into a large platinum cone or rubber funnel, to throw down the chlorine by silver nitrate. The presence of nitric acid is necessary, since otherwise ferrous fluoride reduces silver nitrate with deposition of crystallized silver. When coagulated by heating and stirring, the precipitate is collected on the filter, washed, dissolved by a little ammonia, and reprecipitated by nitric acid, when it can be collected in a GOOCH crucible and weighed, or, if very small in quantity, on a small filter- paper, which is then dried, wound up in a tared platinum wire, and care- fully ignited. The increased weight of the wire is due to the metallic silver of the chloride which has alloyed with it. XXIII. FLUORINE. Fluorine can only be estimated by the method of ROSE, care being taken to use sodium -potassium carbonate as a flux, and to avoid use of the blast if possible. For minerals rich in fluorine and low in silica it may be neces- sary to add pure silica before the fusion in order to effect complete decom- position of the fluoride just as with the alkaline-earth phosphates. To the hot aqueous extract several grammes of ammonium carbonate are added, and more on cooling. After twelve hours the solution is filtered, ammonium carbonate is expelled, and an ammoniacal solution of zinc oxide added, whereupon evaporation is carried on till the odor of ammonia is entirely gone. After filtering, add nitric acid in insufficient quantity to fully neutralize. The use of ammonium nitrate or chloride, instead of carbonate, for throwing out the silica and alumina is not to be recommended, because of loss of fluorine on evaporation (ROSE). If the rocks are very basic it may happen that the amount of silica in the alkaline solution is so small that ammonium carbonate may be dispensed with and the ammoniacal zinc- oxide solution added at once. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1183 By whatever modification of the method the silica and alumina may have been separated, the alkali carbonate must be converted into nitrate and not chloride if phosphorus or chromium, or both, are present. To remove the chromium and the last of the phosphorus, silver nitrate in excess is added to the solution containing still enough alkali carbonate to cause a copious precipitate of silver carbonate, which shall take up the acid set free and thus insure a neutral solution and consequent complete precipita- tion of phosphorus and chromium. After heating and filtering, the excess of silver is to be removed by sodium or potassium chloride, and sodium carbonate is to be added, in order to furnish by addition of calcium chloride in excess to the hot solution a sufficient admixture of calcium carbonate with the fluoride. At this stage there must be no ammoniacal salts in solu- tion, otherwise calcium fluoride may be held up. The next operation is perhaps best conducted as recommended by PEN- FIELD and MINOR.* To the gently ignited precipitate of carbonate and fluoride of calcium, at most 1 to 2 c.c. of acetic acid are added in the crucible, which is then placed for a time on the water-bath and afterwards its con- tents are evaporated to dryness. They are then taken up with hot water, the solution is decanted through a small filter, likewise the washings. The filter is burned in the same crucible, more acetic acid is added, and the various operations are repeated until all calcium oxide and carbonate have been extracted. The above authors find that if a great excess of acetic acid is used at the start, the results are low. While their experiments related to the determination of fluorine in a mineral rich in that element topaz their precautions are probably not needless with the small amounts of fluorine met with in rocks. The well-washed and gently ignited calcium fluoride finally obtained in the course of this method should be converted into sulphate as a check upon its purity, and at the same time as a qualitative test to ascertain if it really is calcium fluoride by the characteristic odor of the gas given off. Should fluorine be found, and the weight of sulphate not correspond to that of the fluoride, the former should be dissolved in hot nitric acid and tested for phosphorus by ammonium-molybdate solution. If phosphate is absent the impurity may have been silica or calcium silicate which of these it would be difficult to decide. In the former case the fluorine might be safely deduced from that of the sulphate, but not in the latter. If the rock were rich in sulphur it might happen that calcium sulphate would be thrown down with the fluoride, but this should be removed by thorough washing. If not, and it were certainly the only impurity present, the fluorine could be calculated, after conversion of the fluoride into sulphate, by the formula : CaSO 4 CaF 2 : 2F : : Diff. between impure CaSO 4 and CaF 2 : x. It is an exceptional case when there is exact agreement between the weight of fluoride and sulphate, and with the small amounts usually met in * Am. Journ. Sci., 3d Series, XLVII, p. 389, 1894. 1184 APPENDIX II. rocks the error may be an appreciable one in percentage of fluorine, though of no great significance otherwise. There is no qualitative test which will reveal with certainty the presence of fluorine in rocks. Heating the powder before the blow-pipe with sodium metaphosphate on a piece of curved platinum foil inserted into one end of a glass tube, or in a bulb tube, is not to be relied on in all cases. While as little as one-tenth of 1 per cent, of fluorine can sometimes be thus detected with ease, much larger amounts in another class of rocks may fail to show. XXIV. SULPHUR. Before proceeding to the estimation of sulphur, its condition, if present, should be ascertained. Evolution of hydrogen sulphide on boiling with hydrochloric acid is evidence of a soluble sulphide, usually pyrrhotite, but possibly lazurite. Extraction of magnetic particles reacting for sulphur shows pyrrhotite to have been, in part at least, the source of the hydrogen sulphide. A reaction for sulphuric acid in the filtered solution indicates a soluble sulphate, usually noselite or hauynite. If the residue, when well washed and treated with aqua regia or hydrochloric acid and bromine, gives more sulphuric acid, the probable presence of pyrite is shown. Should this solution likewise show arsenic, the sulphide may be arsenopyrite, which, however, is of very rare occurrence in igneous rocks, if, indeed, it is ever found there. For the quantitative extraction of the sulphur of soluble sulphates, simple boiling with hydrochloric acid suffices, which should be done in an atmos- phere of carbonic acid if pyrites or other oxidizable sulphides are present, and should be finished as quickly as possible in order to minimize the error resulting from oxidation to sulphuric acid of the sulphur of sulphides, if present, by any ferric salts that may have been dissolved. The sulphur of sulphides may sometimes be correctly determined by extraction with aqua regia or some other powerful oxidizer, but not always, so that it is better by far to fuse with sulphur-free sodium carbonate and a little nitre over the BUNSEN burner, and for a few moments over the blast, fitting the crucible into a hole in asbestos board (LUNGE) to prevent access of sulphur from the flame. After thorough disintegration of the fusion in water, to which a d/op or two of alcohol has been added for the purpose of reducing manganese, the solution is filtered and the residue washed with a dilute solution of sodium carbonate. In the filtrate (100-250 c.c. in bulk) the sulphur is precipitated at boiling heat by barium chloride in excess after slightly acidifying by hydrochloric acid. Evaporation to dryness first with acid, in order to eliminate silica, is needless, for in the above bulk of solution there will almost never be the least separation of silica with the barium sulphate. It is well that this is so, for evaporation on the water- bath heated by gas to remove silica would in many cases involve an error fully equal to the sulphur present by contamination from the sulphur of the gas burned. Owing to the small amount of sulphur in rocks, special purification ol SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1185 the barium sulphate obtained is hardly ever needful, especially as it has been precipitated in absence of iron. Should there be fear of a trace of silica being present, it can be removed by a drop of hydrofluoric and sulphuric acids before weighing the barium sulphate. This, of course, gives the total sulphur in the rock. If soluble sulphates and sulphides as well as insoluble sulphates and sulphides are present together, the sulphur of the first is found in solution after extraction by hydrochloric acid in a carbon-dioxide atmosphere, and that of the decomposable sulphides by collecting the hydrogen sulphide evolved.* In the residue the sulphur of the insoluble sulphides can be estimated, or from the total sulphur found in another portion its amount can be calculated. The error involved in the above estimation of the sulphur of soluble sulphides, due to the possible reducing effect of hydrogen sulphide on ferric salts, is probably negligible. Most of the hydrogen sulphide would be expelled before any such action could take place, and probably before the ferric salts were largely attacked, but of course the small proportion of sulphur set free as such from pyrrhotite would escape estimation and introduce further uncertainty. In general, it would be safe enough to assume the composition FejSg for pyrrhotite. How- ever carefully all these separate determinations may be carried out, the final figures for ferrous and ferric oxides can hardly be regarded as more than approximations when much sulphide is present. (See pp. 1173 and 1174.) XXV. BORON. To the best of the writer's belief, it has never been found necessary in this laboratory to estimate boron in a silicate rock. Should the determina- tion be required, since most silico-borates are insoluble minerals, it would probably be necessary to fuse with sodium carbonate, extract with water, faintly acidify with nitric or acetic acid, expel the boron by distillation with methyl alcohol, and collect the boric ether in a suitable manner. For simple borates, artificial or native, this method,* first devised by ROSENBLADT and GOOCH independently, gives entire satisfaction when all needful precautions are carefully observed, but its application to boro-silicates yet needs investi- gation, in view of the as yet unexplained very discordant results obtained * With pyrrhotite a small fraction of its sulphur one-eighth if the formula Fe 7 S 8 is adopted is liberated as free sulphur and not as hydrogen sulphide. * ROSENBLADT (Zeitschr. fur anal. Chemie, xxiv, p. 217. 188) used magnesia for bind ing the boron, while GOOCH (Proc. Am. Acad. Arts and Sci., p. 167, 1887; Bull. U. S. Geol. Survey, No. 42, p. 64; Chemical News, LV, p. 7, 1887) preferred lime, as more active and reliable. GOOCH and JONES have later (Am. Journ. Sci., 4th Series, vn, p. 34, 1899; Chemical News, LXXIX, pp. 99, 111, 1899) upheld the use of lime, and proposed, as a con- venient though perhaps not quite so perfect substitute, sodium tungstate containing an excess of tungstic oxide. In this article they likewise indicate the precautions now used to insure complete collection and retention of the boron. For a useful modification in the way of collecting the boric ether in ammonia before bringing in contact with the lime, see PENFIELD and SPERRT (Am. Journ. Sci., 3d Series, xxxiv, p. 222, 1887); also MOISSAN (Comptes rendus, cxvi, p. 1087, 1893, and Bull. Soc. Chim., xii, p. 955, 1894), who modifies the GOOCH distilling apparatus in certain respects 1186 APPENDIX II. some years ago by J. E. WHITFIELD in this laboratory on the mineral war- wickite, a boro-titanate of magnesium and iron. It is nlso quite possible that the accurate estimation of but a few milli- grammes or even less of boric oxide by the use of a large excess of lime as a retainer would not be feasible. Fluorine would have to be first removed by calcium nitrate or acetate before freeing the boron. XXVI. NITROGEN. Nitrogen has been found in igneous rocks or the minerals occurring in them by several observers. Thus, H. ROSE * says that pitchstone gives off ammoniacal water on heating; SILVESTRI| mentions a nitride of iron in lavas from Etna; SANDBERGER finds ammonium carbonate to be given off from certain rocks of Pribram; the writer has shown nitrogen to exist in uraninite; RAMSAY and others have noted it in traces with or without helium, etc., in numerous minerals; and later ERDMANN! found it to be given off as ammonia on treating various minerals of "ancient igneous rocks" with a caustic alkali. LUEDEKING also found ammonium sulphate in a barite from Missouri, the presence of which the writer was able to confirm. It has been noted in this laboratory on three separate occasions, when series of ores, roofing slates, and eruptive rocks were analyzed, that ammonia, either in the form of chloride or sulphate, or even as free ammonia, was given off on heating. Its appearance was not limited to one or a few speci- mens of a series, but seemed to be characteristic cf all, and to be afforded by the unbroken rock as well as by the powdered sample. The precise condi- tions under which the specimens were collected not being known, it is impossi- ble to affirm positively that the ammonia may not have been due to recent organic contamination of some sort, especially in the case of the slates, but it is believed that a more critical collection of material w r ill not alter the gen- eral result. Its amount was sometimes readily determinable by Nessleriza- tion being as high as 0-04 per cent, in some slates. Carbonaceous organic matter was absent from most of these, but doubtless existed in them in their early history. In their case the ammonia was, in part at least, evolved as such, imparting a strong alkaline reaction to the water in the upper part of the tube. The presence of sulphides, fluorides, or chlorides in the rock might cause the ammonia to appear as a sublimate of sulphate, fluoride, or chloride. Speculation on this matter would be altogether premature, but attention is called to it in the hope that other observers may be led to look for and investigate similar appearances. It should be borne in mind that the nitrogen present would not necessarily appear as ammonia or ammonium salts, since it might be given off in the elemental condition, as with the gases obtained from uraninite. * Quantitative Analyse, p. 673. FINKENER edition, t Gazz. Chim. ital., v, p. 303, 1875. J Ber. d. deutsch. chem. Gesell., xxix, p. 1710, 1896. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1187 XXVII. SPECIAL OPERATIONS. The problem often presents itself of ascertaining the composition of that portion of a rock powder which is soluble in special reagents or hi a reagent of a particular concentration. No precise directions can be for- mulated to meet such cases. The procedure must vary with the character of the constituents of the rock and with the object which it is sought to attain, and only in exceptional cases can a separation of this kind be sharp. Much depends on the degree of fineness of the powder and on the length of time it is exposed to the action of the reagent. DETECTION OF NEPHELINE IN PRESENCE OF OLTVTNE. For confirmation of the microscopic diagnosis. Prof. L. V. PIRSSON* has indicated a means of detecting nepheline in presence of olivine, as in nepheline basalts, based on the very ready solubility of nepheline, as com- pared with olivine, when boiled for but one minute with a sufficiency of very dilute nitric acid (1 : 40). Gelatinization of the filtrate on evaporation is taken as evidence of the presence of nepheline. If olivine is present hi quantity, however, this test must not be accepted at once as final, for some, if not all, olivines are much more soluble in nitric acid of the above strength than Professor PIRSSON was led to believe from his original tests. If, there- fore, on evaporation of the filtrate, much iron is indicated, the gelatiniza- tion may well be due to olivine alone or in part, and then the quantitative relation of silica to iron plus magnesium should be ascertained. It must also be borne in mind that any other very soluble silicates present will be more or less affected, and that apatite is largely or wholly dissolved. It is possible that still more dilute nitric, or perhaps some other, acid may exert a slighter solvent action on olivine without being appreciably less effective in dissolving nepheline, etc. In combination with a quantitative analysis of the extract the method is perhaps susceptible of a wider application than the particular case for which it was first used. It is well worth further study. ESTIMATION OF SOLUBLE SILICA. Very often hi treatment by acids silica is separated hi gelatinous or granular form mixed with the unattacked minerals, and it becomes neces- sary to remove or estimate this silica, or else to discriminate between soluble and insoluble silica already existing together. Usually a boiling solution of sodium carbonate has been employed for this purpose, though the caustic alkalies have found advocates. LUNGE and MiLLBERof have lately conclusively shown that quartz is not nearly so insoluble in solutions of the caustic alkalies as has been sup- posed, but that given a sufficient degree of subdivision it can be brought wholly into solution-, that it is impossible to secure correct separation of * Am. Jvum. Sci. 4th Series n p. 142. 18%. t Zeitschr. fur angewandte Chemie, 1897. pp. 393, 425. 1188 APPENDIX II. quartz and opaline silica by the use of either caustic or carbonated alkalies, and that digestion on the water-bath for 15 minutes with 5-per cent, solu- tion of sodium carbonate is the only way to secure exact separation of un- ignited precipitated silica from quartz, and then only when the finest flour has been removed by levigation. The authors say : " If, however, no more of such flour is present than is produced in the ordinary operations of powdering and sifting through cloth of the finest mesh, the error arising from the above mentioned treatment is so slight that it can generally be neglected; it reaches 0- 1 to at the most 0-2 per cent of the total silica, by which amount the quartz will appear too low, the amorphous silica too high." The above authors also show, however, that the solvent action of the caustic alkalies on quartz becomes very apparent only when the material has been reduced to such an utterly impalpable degree of fineness as is prac- tically never reached in the preparation of samples for rock analysis. For this reason I have no hesitation hi recommending the employment of a dilute solution of sodium hydroxide when the silica separated by acid from one of several mineral constituents of a rock is to be estimated. Even when dilution is considerable, solution is almost immediate, and as soon as this is accomplished the point being known by the change in appear- ance of the residue the solution should be diluted with cold water and filtered at once. The difficulty met with in filtration may often be over- come by faintly acidifying, which has the added advantage of at once arrest- ing any further action of the alkali. If the dilution is sufficient no separa- tion of silica results from so doing. Very dilute acid should also be used for washing. LUNGE, when using sodium carbonate, washes with hot car- bonate solution to which alcohol has been added, thus obtaining clear fil- trates. XXVIII. ESTIMATION OF MINUTE TRACES OF CERTAIN CONSTITUENTS If, as sometimes may happen, the problem is presented of examining rocks for traces of gold, silver, and other elements which are not ordinarily looked for, as in SANDBERGER'S investigations bearing on the origin of the metalliferous contents of veins, large weights of material must be taken, up to 50 grm. or more. This involves the use also of large quantities of reagents, the purity of which must then be looked to with the utmost care. Special directions to meet such cases cannot now be given, nor even a com- plete reference list of the scanty and scattered literature on this subject. SANDBERGER'S own writings deal but little with its analytical side, and from its inaccessibility in the Washington libraries the writer is as yet unacquainted with the report by VON FOULLON, "Ueber den Gang und die Ausfuhrung der chemischen Untersuchung,"* following SANDBERGER'S own paper in the general report, " Untersuchungen der Nebengesteine der Pribramer * Jahrbuch der Bergakademie, Leoben u. Pribram, 1887, p. 363. SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. 1189 Gange."* The present writer has published a few data as to gold, silver, lead, zinc, etc.,f in Mr. S. F. EMMON'S report on "The Geology and Mining Industry of Leadville"; and Mr. J. S. CURTIS,^ in his report on "The Silver- Lead Deposits of Eureka, Nevada," has given his method of assaying rocks for traces of gold and silver. * From SANDBERGER'S report it appears that the rocks were treated successively with water, acetic acid, boiling dilute hydrochloric acid for two days, and finally hydrofluoric acid, the several extracts and final residue of fluorides (and pyrite) being separately ex- amined for heavy metals. The products of distillation were also examined. A striking fact observed in all cases was the complete insolubility of the pyrite. even after the severe treatment mentioned. This speaks strongly in favor of the correctness of ferrous-iron estimations in silicates by the hydrofluoric and sulphuric acid method when pyrite is present unaccompanied by other sulphides. (See p. 1173.) t Man. U. S. Geol. Survey, xn, Appendix B. pp. 592-596, 1886. t Man. U. 8. Geol. Survey, vn, pp. 12O-138, 1884. TABLES FOR THE CALCULATION OF ANALYSIS. TABLE I. ATOMIC WEIGHTS OF THE ELEMENTS CONSIDERED IN THE PRESENT WORK.* Name. Sym- bol. Atomic Weight. Name. Sym bol. Atomic Weight. O = 16. H = l. O = 16. H = l. Aluminium Antimony Al St. As Ba Bi B Br Cd Cs Ca C Ce Cl Cr Co Cb Cu Er Fl Ga Ge Gl Au H In I Ir Fe La Pb Li Mg Mn ss 27.1 120.4 75.0 137.40 208 . 1 11.0 79.95 112.4 132.9 40.1 12.0 139.0 35.45 52.1 59.00 93.7 63.6 166.0 19.05 157.0 70.0 72.5 9.1 197.2 1.008 114.0 126.85 193 . 1 55.9 138.6 206.92 7.03 24.3 55 . 200.0 96.0 26.9 119.5 74.45 136.4 206.5 10.9 79.34 111.55 131.9 39.8 11.9 138.0 35.18 51.7 58.55 93.0 63.1 164.7 18.9 155.8 69.5 71.9 9.0 195.7 1.00 113.1 125.89 101 .7 55.5 137.6 205.36 6.97 24.1 54.6 198.50 95.3 Neodymium. . . . Nickel Nitrogen 'Ni" N Oa O Pd P Pt K 'Rh Rb Ru Sm Sc Se Si Ag Na Sr S Ta Te Tb Tl Th Tu Sn Ti W U V Yb Yt Zn Zr 143.6 58.70 14.04 191.0 16.00 107.0 31.0 194.9 39.11 140.5 103.0 85.4 101.7 150.3 44.1 79.2 28.4 107 .92 23.05 87.60 32.07 182.8 127.52 160.00 204.15 232.6 170.7 119.0 48.15 184.00 239.6 51.4 173.2 89.0 65.4 90.4 142 . 5 58.25 13.93 189.6 15.88 106.2 30.75 193.4 38.82 139.4 102.2 84.75 100.9 149.2 43.8 78.6 28.2 107.11 22.88 86.95 31.83 181.5 126.5 15S.8 202.61 230.8 169.4 118.1 47.8 182.5 237.8 51.0 171.9 88.3 64.9 89 7 Osmium Oxygen. . . Bismuth Boron Bromine Palladium Phosphorus. . . . Platinum Potassium Praseodymium . Rhodium . . Cadmium Csesium Calcium Carbon Cerium Chlorine Rubidium. . Ruthenium Cobalt Columbium Selenium Copper Erbium Silver Fluorine Gadolinium. . . . Sodium Strontium Sulphur Tantalum Tellurium Terbium Thallium Thorium TTiiiliiim Gallium. Germanium. . . . Glucinum Gold Hydrogen Indium Iodine Iridium Iron Tin Titanium Tungsten Lanthanum Lead Lithium Magnesium Manganese Mercury. . . Uranium. . . . Vanadium Ytterbium Yttrium Zinc Molybdenum Zirconium * Journal of the American Chemical Society, March, 1902. 1190 TABLE II. 1191 TABLE II. COMPOSITION OF THE BASIC AND ACID OXIDES. GROUP I. a. BASIC OXIDES. sesia. Cs^ 265-80 94-32 O. . . 16-00.. 5-68 Cs 2 O 281-80 100.00 Rubidia Rb 2 170-80 91-43 O .. . 16-00.. 8-57 Rb 2 O 186-80 100-00 Potassa K, 78-22 83-02 O .. . 16-00.. . 16-98 94-22 ........ 100-00 Soda ....................... Na,.. .............. 46-10 ........ 74-24 O .. . 16-00.. . 25-76 Na.,0 62-10 100-00 Lithia Li 14-06 46-77 O .. . 16-00.. . 53-23 L Li 2 30-06.... 100-00 Ammonium oxide (NH 4 ) 2 36-144 69-32 O .. . 16-00.. . 30-68 (NH 4 ) a O 52-144 100-00 GROUP IL Baryta Ba 137-40 89-57 O .. . 16-00.. . 10-43 BaO 153-40 100-00 Strontia. . . . :Sr 87-60 84-56 O .. . 16-00.. . 15-44 SrO. ;; 103-60 100-00 Lime Ca 40-10 71-48 O .. . 16-00.. . 28-52 CaO 56-10 100-00 Magnesia. Mg 24-30 60-30 O .. . 16-00.. . 39-70 MgO 40-30 100-00 1192 TABLES FOR THE CALCULATION OF ANALYSIS. TABLE II. Continued. GROUP III. Alumina A1 2 54-20 53-03 O 3 48-00 46-97 A1 2 O 3 102-20. ..... . .100-00 Chromic oxide O 2 104-20 68-46 O 3 48-00 31-54 Cr 2 O 3 152-20 100-00 GROUP IV. Zinc oxide. Zn 65-40 80-34 O 16-00 19-66 ZnO 81-40 100-00 Manganous oxide .Mn 55-00 77-46 O 16-00.. . 22-54 MnO 71-00 100-00 Manganic oxide Mn 2 110-00 69-62 O 3 48-00 30-38 Mn 2 O 3 158-00 100-00 Nickelous oxide Ni 58-70. ... 78-58 O .; . 16-00.. . 21-42 NiO 74-70 100-00 Cobaltous oxide Co 59-00 78-67 O ,, . 16-00.. . 21-33 CoO 75-00 100-00 Cobaltic oxide Co 2 118-00 71-08 3 .. . 48-00.. . 28-92 Co 2 O 3 166-00 100-00 Ferrous oxide Fe 55-90 77-75 O .. . 16-00.. . 22-25 FeO . 71-90.. ..100-00 Ferric oxide ,.,.,Fe 2 ., 111-80 69-96 O 3 48-00 30-04 Fe a 3 159-80 100-00 TABLE II. 1193 TABLE II. Continued. GROUP V. Ag 215-84. 93-10 O 16-00. 6-90 Lead oxide Ag 2 0.... ...Pb O 231-84. 206-92. 16-00. 100-00 92-82 7-18 Mercurous oxide PbO.... 222-92. 400-00. 100-00 96-15 O 16-00. 3-85 Mercuric oxide Hg 2 0... ...Hg O 416-00. 200-00. 16-00. 100-00 92-59 7-41 Cuprous oxide HgO . . . ...Cu 2 O 216-00. 127-20. 16-00. 100-00 88-83 11-17 Cupric oxide 0X1,0.... ...Cu O 143-20. 63-60. 16-00 100-00 79-90 20-10 Bismuth trioxide CuO.... 79-60. 416-20. 100-00 89-66 2 48-00. 10-34 Cadmium oxide Bi 2 3 ... ...Cd. .... 464-20. 112-40. 100-00 87-54 O 16-00. 12-46 \uric oxide. CdO. . . . GROUP . Au . . 128-40. VL 394-40 100-00 89-15 3 48-00. 10-85 Au,O, . 442-40 100-00 Platinic oxide ...Pt 2 194-90. 32-00. 85-90 14-10 Antimonous oxide PtO 2 . . . ...Sb 2 3 226-90. 240-80. 48-00. 100-00 83-38 16-62 .288-80. 100-00 1194 TABLES FOR THE CALCULATION OF ANALYSIS. TABLE II. Continued. GROUP VI. Continued. Stannous oxide Sn 119-00 88-15 O 16-00.. . 11-85 SnO 135-00 100-00 Stannic oxide Sn 119-00 78-81 O 2 32-00 21-19 SnO 2 151-00 100-00 Arsenous oxide As 2 150-00 75-76 O 3 48-00.. . 24-24 > 3 198-00 100-00 Arsenic oxide As 2 150-00 65-22 O 6 80-00. . . 34-78 As 2 O 5 230-00 100-00 6. ACID OXIDES (ANHYDRIDES). Chromic anhydride ..Cr. .. 3 ... Cr0 3 . 52-10... 48-00... 52-05 47-95 100-10... 100-00 Sulphuric anhydride ..S. .. 3 ... SO 3 . 32-07... 48-00... 40-05 ..... 59-95 100-00 80-07... Phosphoric anhydride " 00 CO 1C CO ~ ~ II til S. d H -H t^ -^ - II 43 C3 f! CO (M CO - -i O O CO 'O CO l-H CO o -2 . ,-H . I-H 7 ^^^ II 'I O fS O ^ TJH ^2 H-T -2 "5 - - S .. GQ Alum A1 2 O 3 = fflllf|HwPl 5 4 4-1^1 ^ -3 1198 TABLE IV. o i> tliflr- ^ 10 ^ * TO aoeog -Lg - = 1 CO rH O OS 00 CO CO 00 S TABLE IV. CO t^ 00 O CO 00 t>- (M 1199 8 3 00 CO CM CO (M $ rH O 8 S CO (N g s i i S . CO rH O O 00 CO O 3 o OS CO O O CO t^ O rH CO ^O t^ t^* t^* OS iO t>. -^ 00 O t^- iO CO O o o OS 1> CO rH 10 os t^ co 00 3 i || 5 II S II II PQ ^WOPQOPQO rn 03*3303 cq 7 7 ^ . OS gt- o II && - 8 PQ la *- PQ 2 1 Cadmium oxide CdO=128.4 admium sulphat CdSO 4 =208.47 1200 TABLE IV. CO l> CO rH GO OS % s $ rt | 1> O CO CO to i I OS l> C iO O to p oo CO rjn t^ (N CO OS CO O (N CO oo s CO "H^ H^ CO C^l rH (N CO (N OS rH OS CO l> 00 rH rH os co o OS O Tfl 00 t>. OS o d (N to t^ OS OS iO ^ CO 00 OS O O rt< CO to odd N CO d d 'SO ss ti s ilili! ^ 6 6 6 8 'C to'C to o g o co o COTS co 3 II 3 II II TABLE IV. 1201 CO CO 00 *O rH 00 N. >0 CO rH (N CO S 3 t^ rH rH rH rH 5 CO CO co o o to rH 00 l>- OS ol CO rH DC 'M cc O to OS tO to Tt< rH OS OS t>. 1C Tj< rH f"* CO 00 l> CO CO to CQ 00 CO ^f C^ C*^ O OS rH CO t^ tO rH CO O O s to to oo ^ Os ^2 OS Os CO CO rH 00 CO CO CO t^ 8 CO OS 10 TF -s -s 666 O^ Ot^ 66 66 -6-3 s Il a II 24 ^^3 SM-5 SW ico -*^ '"/^ cfi i >i ^ N + SO" of- 1.9 loo a|^ 16 1202 TABLE IV. 8 rH 05 O iO O5 00 TH O CO 00 TH IO IO CO t> C<1 CO l> O5 - 0:0^ t> iO IO CM CO (M i co oo ^ TH CO CM 1> 00 g CO 1> CM O CO ^H C5 O5 CO CN S3 l- ^ 8 co co co odd - - ^ I II 13 a be -^t- co 8 s 'ilSla M I *"H II ^^ I' IIP. 1204 TABLE IV. CO CD s CO os 5 So (N r-i GO O OS I-H O r-i -* CO g So - GO O ^ ^H 1-5 I i-i (N CO CO * . GO CO odd t>. CO CO O5 CO t> d d o o d i-I 1-4 i- 00 CO l> (M to d d t^ O t> QO d d ^ co 1 I d d O * CO to % s d o_ i i i i CO O (N GC (N O CO i-i i i !>. CO CO CO i- to i> c^ i-t l> 30 o o s >0 CO GO * CO to X Tt< to i-l i-l O5 lO ^\ ^7 ^7 ^ ii S ii ^7 >^7 >^7 50 rn eo'1 u -S 1 'I a f N ^ 2 rf.8 S O 3' g I | S ' tao S TABLE IV. 1207 CO CO O 1-1 i-H CO 1-1 t> O 1-H *H f-* CQ 25 S i- O (N CO ,-i 1C t^ It} c to O ^H O TH l> CO CO 00 II >> II > II > II > II > II > II > Ss-IM- a|*-8 s - ^^s s^^ IT s? Ss lasisla -gsil |7lal? ''^Uiliiild^TU 5 3 O ** d g 1208 TABLE IV. C co 10 1 8 ^ CO l> l> TH 1 Si s ^ *O CO "5nr~S 8 8 CO TH TH TH Tt* ^ OS 05 TH t^ l> ^ CO CO CO CO 00 TH CO CO O oj B g II TH 00 OS HH TH 1C - "t O t$ . co p co t^ to cd g s CO CO to b- CO CO OO i-H O CO o oo -^ I-H ^ CO ^ o co -H 00 tO (N t^ (N b- I-H CO 00 OS OS co O 00 OS Ct b- (N 00 -H tO CO Tf (N to t C^ CO O^ ^O -* ^ O I> O CQ O oo t^* os ^2 co co o ^f ^ to co co co os oo Tf to CO CO tO d d o o d CO CO ^^ tO O OS oc to i> d o o -Ji ifi (O S^.2? co .25 co* loBO I I s n z ii 1^1% - (M c i c (M CO 01 CO tO t^ CO CO o oo >o a 2 00 O Tt< tO O (M CO iO 8 2 i (N CO CO CO (N O $ 3 S . o A O5 O 00 O5 O os ^3 1 a.: If f: cc T^ Tin Sn=119 nnous oxi SnO=135 ^ * " ^i^ 4 Ba Ba Stannic ox SnO 2 = 15 Stannic ox SnO 2 =15 N TABLE V. 1211 TABLE V. INTERNATIONAL ATOMIC WEIGHTS, 1903. O = in. H = l. O = 16. H = l. Aluminium. . . Antimony. . . . Argon. Al Sb A 27-1 120-2 39-9 26-9 119-3 39-6 Molybdenum. . Neodymium. . Neon Mo Nd Ne 96-0 143-6 20-0 95-3 142-5 19-9 Arsenic As 75-0 74-4 Nickel Ni 58-7 58-3 Barium . . . Bi 137-4 136-4 Nitrogen. . . N 14-04 13-93 Bismuth. Bi 203-5 206-9 Osmium. . . Os 191-0 189-6 Boron. . B 11-0 10-9 Oxygen. . o 16-00 15-88 Bromine. Br 79-96 79-36 Palladium Pd 106-5 105-7 Cadmium. . Td 112-4 111-6 Phosphorus . p 31-0 30-77 Caesium. . . Cs 133 -O 132-0 Platinum Pt 194-8 193-3 Calcium Carbon. . . Ca c 40-1 12-00 39-8 11-91 Potassium. . . . Praseodymium K Pr 39-15 140-5 38-86 139-4 Cerium Ce 140-0 139-0 Radium . . R^ 225-0 223-3 Chlorine. . . . Cl 35-45 35-18 Rhodium Rh 103-0 102-2 Chromium. . . . Cobalt. . . Cr Co 52-1 59-0 51-7 58-56 Rubidium. . . . Ruthenium Rb Ru 85-4 101-7 84-8 100-9 Columbium (Niobium). . Copper Cb Cii 94-0 63-6 93-3 63-1 Samarium. . . . Scandium. . . . Selenium Sm Sc Se 150-0 44-1 79-2 148-9 43-8 78-6 Erbium F, 166-0 164-8 Silicon Si 28-4 28-2 Fluorine. . . . F 19-0 18-9 Silver Ag 107-93 107-12 Gadolinium. . . Gd 156-0 155-0 Sodium Na 23-05 22-88 Gallium. Ga 70-0 69-5 Strontium Sr 87-6 86-94 Germanium. . . Glucinum (Beryllium). Gold Ge Gl Au 72-5 9-1 197-2 71-9 9-03 195-7 Sulphur Tantalum. . . . Tellurium. .' . . Terbium S Ta Te Tb 32-06 183-0 127-6 160-0 31-83 181-6 126-6 158-8 Helium HP 4-0 4-0 Thallium. Tl 204-1 202-6 Hydrogen. . . . Indium H In 1-008 114-0 1-000 113-1 Thorium. .... Thulium. . Th Tm 232-5 171-0 230-8 169-7 T 126-85 125-90 Tin Sn 119-0 118-1 Iridium Tr 193-0 191-5 Titanium Ti 48-1 47-7 Iron Fe 55-9 55-5 Tungsten W 184-0 182-6 Krypton Kr 81 ; 8 81-2 Uranium. . u 238-5 236-7 Lanthanum. . . Lead . La Pb 138-9 206-9 137-9 205-35 Vanadium. . . . Xenon. . V x 51-2 128-0 50-8 127-0 Lithium . . . T,i 7-03 6-98 Ytterbium. . . . Yb 173-0 171-7 Magnesium Mff 24-36 24-18 Yttrium Yt 89-0 88-3 Manganese Mn 55-0 54-6 Zinc Zn 65-4 64-9 Hr 200-0 198-5 Zirconium. . . . 7,T 90-6 89-9 1212 TABLE VI. TABLE VI. SPECIFIC AND ABSOLUTE WEIGHTS OF SOME GASES. Calculated on the Values used in this Work. Values used in the German Edition. Specific Weight, AirI. 1000 c.c. of Gas at and 760 mm. Pressure Weighs in Grammes. Specific Weight, Air I. Specific Weight, Air=l. 1000 c.c. Gas at and 760 mm. Pressure Weighs in Grammes. Atmospheric air 1.00000 1 . 10526 1 . 2930 1.4291* 1.2930 1.4291* 1.00000 1 . 10563 (Renault) 1.00000 1 . 10563 1.293635* 1.430282 O=16. O = 16. H-l. Cal- culated.! Deter- mined .1 Hydrogen . 0.069651 0.622256 0.828937 1.519718 0.967093 0.553730 0.968199 4.282842 2.215335 1 . 177298 8.762557 5.522794 2.448819 0.969857 1.037553 0.589374 1.796031 0.08988* 0.80458 1.07183 1.96502 1 . 25047 0.71598 1.25189 5 . 53778 2.85824 1.52227 11.33012 7.14105 3.16636 1.25403f 1.34157 0.76207 2.32587 0.08988* 0.80353 1.06957 1.96208 1.24843 0.71455 1.24933 5.52762 2.86088 1.52032 11.31499 7.13108 3.16198 1.25203f 1 . 33966 0.76083 2.32160 0.06910 0.62191 0.82922 1.52024 0.96742 0.55281 0.96742 4.28432 2.2112611 1 . 17473 8.76557 5.52470 2.45035 0.97019 1.03791 0.58875 1.79941 0.06927 1 . 52908 0.97136 0.089610 1 . 978071 1 . 256585 Water vapor Carbon vapor. Carbonic acid Carbonic oxide Marsh-gas (methane) . . Ethylene Phosphorus Vapor Sulphur vapor Hydrogen sulphide. . . . Iodine vapor. . . Bromine vapor Chlorine. . . Nitrogen . Nitric oxide. Ammonia, NHs Cyanogen * These are the most probable values for oxygen and hydrogen, according to RAYLEIGH, and are in close agreement with the values obtained by others (REGNAULT, JOLLY, MORLEY, etc.); they are calculated for 0, 760 mm., and lat. 45. t RAYLEIGH gives 1.2507 as the most probable value for nitrogen, and this figure is in close concordance with that obtained by other investigators (MORLEY. JOLLY, etc.). J For Berlin, calculated by W. Lasch (Chem. Pharm. Centralbl., 1852. p. 148. The specific weights here given are calculated from the equivalents used in the German edition and are based on the specific weight of oxygen, 1 . 10563, as determined by REGNAULT. II Sulphur vapor has not this specific weight below 800 to 1000; at 450 to 500 it is 6.6. 1 The values of hydrogen, carbonic acid, and nitrogen as determined by REGNAULT are given for comparison with the calculated values. From these the weights of a litre of the different gases at Berlin are reckoned, taking the weight of a litre of atmospheric air in Berlin as the standard. TABLE VII. 1213 TABLE VIT. COMPARISON OF DEGREES OF THE MERCURIAL THERMOMETER WITH THOSE OF THE AIR- OR HYDROGEN-THERMOMETER. (According to CRAFTS.*) Degrees of the Degrees of the Mercurial Thermometer. Air-thermometer. 110 110-02 120 120-04 130 130-09 140 140-16 150 150-25 1 60 160-33 170 170-35 180 180-34 190 190-32 200 200-27 210 210-18 220 .- 220-08 230 229-98 ?40 239-86 250 249-74 260 259-61 270 269-50 280 279 37 290 289 1 2 300 298-79 310 308-40 320 317-97 330 327-52 * Comptes rendus, xcv, 836 and 910: Zeitschr. f. analyt. Chem., xxin, 526. The figures are the mean of experiments with fifteen thermometers. They hold good for lead glass containing 18 per cent, of lead oxide, as well as for German soda-glass. CRAFTS found no important difference between the two kinds of glass; the differences between his values and those arrived at by REGNAITLT and others are accounted for by him from the circumstances that the composition of the glass of which thermometers were formerly made was very different from that of the glass now employed for this purpose. INDEX. PAGE Abbe refractometer ii, 1062 Absorption bulbs for carbonic acid ii, 53 for water ii, 51 Acid apocrenic, determining in mineral waters ii, 261 boric, determination. . i. 465 as potassium borofluoride i, 466 separation from basic radicals i, 468 arsenic, separation from alkalies, alkali earths, zinc etc ....... i. 711 arsenous acid i, 716. 721, 729 barium, strontium calcium, and lead . . i f 713 copper, cadmium iron (ic) : manganese, etc i, 712 manganese, iron, zinc, copper, nickel, and cobalt i, 710 tin and antimony i, 721 metals of groups i and n i, 713 of groups i-iv . i. 712 arsenous, determination gravimetrically, indirectly i. 419 by Rose's method , i. 419 by Vohl's method . i. 419 separation from arsenic acid i. 716, 721, 729 carbonic, apparatus for absorbing ii, 53 determination by Dietrich's method v 504 by Kolbe's method i. 493 by measuring the gas i. 500 by Pettenkofer s method i. 484 by Rose's method i, 496 by Scheibler's method. , i. 500 by weighing ii, 31 6 in carbonates i t 487 in gases , i. 479 in mineral waters ii 227, 232, 236, 251 in water ii, 199 gravimetrically i, 482 1215 1216 INDEX. PAGES Acid carbonic, determination volumetrically i, 483 with barium chloride or calcium chloride and ammonia i, 481 with calcium hydroxide i, 480 Geissler's apparatus for determining i, 491 separation from all other acids i, 733 from basic radicals i, 487 table of absorption of i, 508 of weight of 1 c.c. at various temperatures and pres- sures i, 506 Well's apparatus for determining i, 499 chloric, determination i, 593 in chlorates i, 593 separation from bases i, 593 from other acids i, 757 chromic, determination as barium chromate i, 423 as lead chromate ! i, 423 as oxide i, 422 by Bunsen's method i, 424 by oxalic acid i, 423 by Schwarz's method i, 424 by Vohl's method i, 423 volumetrically i, 424 separation from aluminium i, 427 from basic radicals i, 426 from chromium i, 427 crenic, determining in mineral waters ii, 261 determination acidimetrically ii, 295 hydrochloric i, 129 normal ii, 299 hydrofluoric i, 130 determination as calcium fluoride i, 472 separation from other acids i, 735 hydrofluosilicic, determination of i, 442 by Stolba's method i, 443 iodic, determination of i, 432 molybdic, determination as dioxide, lead molybdate, or disulphide, i, 420 by Pisani's method i, 421 nitric i, 128 determination. i, 571 as ammonia i, 584 as ammonia by Harcourt's method i, 585 as ammonia by Siewert's method i, 587 as nitrogen i, 592 by distillation i, 573 by decomposition with alkalies i, 574 INDEX 1217 Acid nitric, determination by decomposition with ferrous chloride by Pelouze's method i, 575 by Schlosing's method. i, 579 by Tiemann-Schulze's method i, 532 from loss of hydrogen, by Schulze's method, i, 588 in mineral waters ii, 261 in water ii, 186 separation from basic radicals. . i, 572 from other acids i, 757 nitrous, determination i, 433 in water ii, 192 in water by permanganate method ii, 195 in water by starch-iodide method ii, 193 normal, for acidimetry ii, 293, 297 oxalic, crystallized, pure i, 144 determination as calcium carbonate i, 470 as carbonic acid i, 471 with gold, by Rose's method i, 470 with permanganate i, 470 normal ii, 300 separation from basic radicals i. 471 phosphoric, determination as ferric phosphate i, 452 as lead phosphate i, 445 as magnesium phosphate by Schulze's method i, 453 as magnesium pyrophosphate i, 445 as uranyl pyrophosphate i, 451 by Chancel's method i, 450 by Girard's method i, 449 by Neubauer's method i, 454 by Reissig's method i, 448 by Rose's method i, 448 by Sonnenschein's method i, 446 by Weeren's method i, 452 in manures ii, 854, 856 in mineral waters ii, 259 in superphosphates ii, 863 volumetrically i, 453 separation from alkalies, barium, calcium, lead, and strontium i, 457 from all bases i, 464 from aluminium, and magnesium i, 458 from basic metals i, 462 from chromium i, 460 from metals of the second, third, and fourth groups i, 460 1218 INDEX. Acid phosphoric, separation from metals of fifth and sixth groups i, 462 rosolic ii, 311 salicylic, determination in wines. ii, 1085 selenous, determination ii, 429 silicic *t 233 determination i, 505 by fusion with alkali carbonates i, 511 by Mitscherlich's method i, 521 by Smith's method i, 519 in compounds decomposable by HC1 or HNO 3 , i, 509 in mineral waters ii, 246 in water ii, 196 with ammonium fluoride i, 516 with barium hydroxide or carbonate i, 517 with calcium carbonate and ammonium chloride . i, 518 with hydrofluoric acid i, 513 with hydrogen potassium fluoride i, 516 separation from all other acids i, 737 from basic radicals i, 509 sulphuric, determination i, 434 by Bohlig's method i, 436 by Clemm's method i, 436 by Mo.hr's method i, 435 by Wildenstein's method i, 437 in mineral waters ii, 249 in presence of sulphates i, 442 in sulphur water ii, 272 in water ii, 186 fuming, analysis of ii, 706 normal ii, 299 separation from all other acids i, 731 from barium, calcium, lead, and strontium, i, 441 from mercury in mercurous sulphate i, 442 sulphurous i, 149 determination i, 431 tartaric, determination in wines ii, 1082 thiosulphuric, determination of i, 432 Acidimetry ii, 284 Acids arsenous and arsenic, separation from all other acids i, 730 combined, determining acidimetrically ii, 313 free, determination acidimetrically ii, 301 organic, volatile, determination in mineral waters ii, 261 in saline waters ii, 272 separation of i, 739 volatile, determination in butter ii, 1055 INDEX. 1219 PAGE Air, atmospheric, analysis of ii, 928 Air-baths i, 63 Albuminoid nitrogen in water, determination as ammonia ii, 207 Alcohol, determination in liquors ii, 1072 in mixtures ii, 763 Aldehydes, determination in liquors ii, 1037 Alkali, caustic with carbonate, determining ii, 323, 332 normal ii, 293 Alkali-earths, determination alkalimetrically ii, 334 Alkalies, determination alkalimetrically by Descroizilles-Gay-Lussac's method ii, 323 by Mohr's method ii, 329 hi carbonates by Fresenius-WilPs method. ... ii, 331 in ferrocyanides i, 554 in minerals ii, 1 175 Alkalimetry ii, 319 Allihn's method of determining grape-sugar ii, 741 solution (modified Fehling's) ii, 741 table for determining dextrose ii, 1046 Alumina i, 180 cream for sucrose determination ii, 1049 Aluminium, determination as oxide i, 278 in cast iron ii, 543 in minerals ii, 1137 in mineral waters ii, 246 hydroxide i, 179 oxide i, 180- separation from alkali-earth metals i, 623 from ammonium i, 622 from barium and strontium : . . i, 627 from calcium . i, 627 from chromium i, 630 from iron (ic) i, 646 from iron (ic and ous), cobalt, and nickel i, 643 from magnesium and calcium i, 628 from potassium and sodium i, 622 from radicals of the fourth group i, 640 from uranyl i, 674 from zinc, cobalt, and nickel i, 656 sulphate ii, 403 Ammonia, determination by the zinc-iron method ii, 1030 in mineral waters ii, 260 hi saline waters ii, 272 in water ii, 207, 211 colorimetrically ii, 207 with potassium-mercuric iodide. . . ii, 212 1220 INDEX. PAGE Ammonia-iron alum i, 147 Ammonium, arseno-molybdate i, 224 carbonate i, 142 chloride i, 143, 167 determination as ammonia i, 253 as ammonium-platinic chloride i, 252 as chloride i, 252 as nitrogen i, 256 -ferrous sulphate i, 146 -hydrogen fluoride ii, 142 -magnesium arsenate i, 222 phosphate i, 177 -manganese phosphate i, 188 molybdate i, 136 nitrate i, 142 phosphate . r i, 135 phospho-molybdate .- i, 230 -platinic chloride i, 167 salts, determination in manures ii, 883 separation from metals of the fourth group i, 631 from potassium and sodium i, 604 from sodium i, 603 succinate. ......... i, 135 Analyses, calculation of ii, 158 Analysis, volumetric i, 122 Analytical experiments ii, 985 Animal charcoal, analysis of ii, 918 Anthracene, determination in crude anthracene ii, 785 Antimony i, 218 alloys, analysis of ii, 674 determination as sulphide (ous) i, 396 as tetroxide '. . . i, 398 by decomposing the sulphide i, 403 by Kessler's method i, 400 by Mohr's method i, 400 by Schneider's method i, 403 electrolytically ii, 673 volumetrically i, 400 with dichromate i, 401 with permanganate i 402 -nickel, analysis of ii, 474 ores, analysis of ii. 669 separation from antimonic acid i. 729 from arsenic i, 720 from lead i. 714 from mercury. i, 708 INDEX. 1221 Antimony, separation from metals of groups iv and v in alloys i. 707 from tin i 716 from tin and arsenic . . . i, 718 sulphide i, 217 tetroxide i, 21 3 Apparatus for absorbing carbonic acid ii. 53 water ii, 5 Argentan. analysis of ii, 6G' Arsenic, see also acid arsenous. compounds, analysis of ii, 690 determination as ammonium-magnesium arsenate. i, 412 as arsenate i, 41 1 as sulphide (ous) i, 414 as uranyl pyroarsenate i, 413 by Bunsen's method i. 41V by Kessler's method i. 417 by Mohr's method i, 416 by Werther's method i, 413 in iron ii, 527 in organic matter ii, 693 in pigments ii. 691 in tin i, 726 volumetrically i, 416 separation from antimony i. 720 from antimony and tin i, 722 from antimony in alloys i, 718 from copper i, 714 from metals of groups n, iv, and v I 708 from tin i, 717, 728 sulphide, determination in antimony sulphide i, 720 Arsenous acid, see acid arsenous. oxide i, 149 sulphide i, 221 Asbestos filters i, 120; ii, 503 (foot-note) Ash analysis , ii, 789, 798, 1096 Aspirator, Bunsen's i, 103 Azotometer. SchifFs ii. 76 Azotimetric method of determining ammonia in manures ii, 885 in soils ii, 845 Babcock asbestos method of determining fat in milk ii, 1069 water in milk ii, 1069 Balance, testing, etc i, 12 Barium acetate i, 137 carbonate i. 138, 170 chloride. . i, 137 1222 INDEX. Barium chromate i, 226 compounds, analysis of ii, 375 determination as carbonate ii, 264 as sulphate i, 263 in minerals . ii, 1144, 1155 in mineral waters ii, 246, 252 in saline waters ii, 271 separation from calcium i, 617 from potassium and sodium i, 607, 608 from strontium and calcium i, 616, 617 silicofluoride i, 171 sulphate i, 168 Baskerville's method of separating titanium from iron and aluminium in mineral analysis ii, 11 54 Bearing metal, white, analysis of ii, 686 Beet-juice, determining sugar in ii, 758 Beilstein-Jawein's method of determining zinc electrolytically ii, 449 Bell metal, analysis of ii, 680 Belohoubeck's method of determining uranium i, 336 Berthelot-Fleury's modified method of determining tartaric acid in wines ii, 1083 Berzelius' method of determining carbon in cast iron ii, 502 of separating phosphoric acid from aluminium i, 459 -Rose's method of determining sulphur i, 564 Bigelow's method of determining salicylic acid in wines ii, 1085 Bismuth i, 212 alloys, analysis of ii, 665 and copper, separation from lead and cadmium i, 692 carbonate i, 212 chloride, basic i, 212 chromate i, 212 determination as arsenate i, 387 as carbonate i, 383 as chromate i, 385 as metal i, 386 as trioxide i, 383 as trisulphide i, 383, 384 by Lowe's method i, 385 ores, analysis of ii, 661 salts, analysis of ii, 666 separation from all other metals i, 684, 690 from cadmium i, 694 from copper . i, 692 from copper, cadmium, and mercury (ic) i, 692 from lead and cadmium i, 692 from silver, lead, and copper. i, 696 INDEX. 1223 PAGE Bismuth trioxide i, 211 trisulphide i, 213 -white, determination of bismuth in ii, 668 Black ash, analysis of ii, 361 Blair's method of determining phosphorus in iron ii, 529 Bog-iron ore, analysis of ii, 493 Bohlig's method of determining chlorine i, 526 ferrocyanides i, 557 sulphuric acid i, 436 Bohmer's method of analysis of Chili saltpetre ii, 881 Boisbaudran's method of determining copper electrolytically ii, 624 Bone-black, analysis of ii, 917 manures, analysis of ii, 916 -meal, analysis of ii, 917 Boussingault's method of determining ammonia in mineral waters ii, 260 carbon in cast iron ii, 505, 515 Borax i, 140 Boric acid, see acid boric. anhydride, determination of ii, 465 Boron, determination in minerals ii, 1185 Brass, analysis of ii, 655 Britannia metal, analysis of ii, 685 Britton's method of analysis of chromium ores ii, 422 Bromine containing chlorine, analysis of i, 754 determination as silver bromide i, 532 colorimetrically by Heine's method i, 534 gravimetrically and volumetrically i, 532 in free state i, 536 in mineral waters ii, 252 in organic compounds ii, 121 in saline waters ii, 271 with chlorine water and chloroform by Rei- mann's method i, 532 with chlorine water and heat by Figuier's method i, 533 In organic bodies, testing for ii, 7 separation from chlorine i, 744 from chlorine and iodine i, 750 from metals i, 535 Brominized soda solution for nitrogen determinations ii, 888 Bronze, antique, analysis of ii, 680 coin, analysis of ii, 680 medal, analysis of. . . ii, 680 patent, analysis of ii, 680 Brugelmann's method of determining chlorine in organic compounds. . ii, 126 sulphur in organic compounds. . ii, 111 1224 INDEX. PAGB El-miner's method of determining water and carbonic acid in air ii, 929 Buisson-Ferray's method of determining bismuth in bismuth- white . . . . ii, 668 Bunsen's aspirator i, 103 method of determining arsenic i, 417 chlorine volumetrically i, 530 chromic acid i, 424 manganese dioxide ii, 465 sulphur i, 566 vapor densities ii, 156 modification of Liebig's combustion method. ii, 30 Burette, Gay-Lussac's i, 48 Geissler's i, 49 Mohr's i, 42 Burettes i, 42 Butter, analysis of ii, 1054 determination of casein, ash, and chlorine in ii, 1054 of salt in ii, 1054 of soluble and insoluble acids in ii, 1059 of volatile acids in ii, 1055 Cadmium carbonate i, 214 determination as oxide. . i, 388 as sulphate i, 389 as sulphide i, 388 oxide i, 213 separation trom copper i, 693 from zinc i, 684 sulphide i, 214 Calamine, analysis of. ii, 428 electric, analysis of ii, 428 Calcium i, 132 acetate, analysis of ii, 387 carbonate. i, 173 chloride i, 155 tubes ii, 14 determination as carbonate i, 269 as oxide i, 269 as sulphate. . . , i, 269 by volumetric methods i, 273 in minerals ii, 1144 in mineral waters ii, 246 in saline waters ii, 268 in water ii, 196 fluoride i, 232 oxalate i, 175 separation from aluminium. . i, 627 INDEX. 1225 PACK Calcium, separation from magnesium i, 618, 619 from nickel and cobalt i, 633, 638 from potassium and sodium i, 607, 609 from strontium i, 619 sulphate i, 173 Calculation of analyses ii, 158 Cane-sugar, determination of ii, 730 by fermentation ii, 759 by inversion ii, 751 Carbohydrates, determination by Soxhlet's method ii, 1042, 1043 in agricultural products. ii, 1037 in grains and cattle foods ii, 1034 Carbon and hydrogen, determination in nitrogenous substances ii, 56 in organic substances by CloeV method ii, 14Q in organic substances by War- ren's method ii, 145 determination in minerals ii, 1180 dioxide, see also acid carbonic. determination in minerals ii, 118fr disulphide i, 128 in cast iron ii, 502, 517 determining as carbonic acid ". ii, 509 by Berzelius' method ii, 502 by Boussingault's method ii, 505 by oxidation with chromic acid ii, 510 by Ullgren's method ii, 505 by Weyl's method ii, 505 by Wohler's method ii, 508 hi steel, determining ii, 548 colorimetrically by Eggertz' method ii, 550 Carbonic acid, see acid carbonic. Cairus' method of determining chlorine, bromine, and iodine in organic compounds ii, 124 sulphur in organic compounds ii, lid Casein, ash, and chlorine hi butter ii, 1054 Cast iron, analysis of ii, 501 determining iron in ii, 536 Caustic lime, method of preparing ii, 111 Cazeneuve's reaction for coloring-matter in wine ii, 1084 Cement copper, analysis of ii, 633 Cements, analysis of ii, 393, 400 Chancel's method of determining phosphoric acid i, 450 Chamber acid, analysis of ii, 715 Charcoal, animal, analysis of ii, 918 Chatard's apparatus for determining water in minerals ii, 1129- 1226 INDEX. PAGE Chatard's drying-oven for determining moisture ii, 1121 Cheese analysis ii, 1070 determination of fat in ii, 1071 of nitrogen in ii, 1071 of water in ii, 1071 Chili saltpetre, analysis of ii, 875 Chlorates, see acid chloric. Chloric acid, see acid chloric. "Chloride of lime," analysis of ii, 376 Chlorides, determining, in presence of fluorides i, 741 Chlorinated lime, analysis of ii, 376 Chlorine i, 143 determining, alkalimetrically by Bohlig's method i, 526 as chloride i, 521 by silver nitrate (volumetrically) i, 522 gravimetrically. . . ! i, 531 in free state i, 529 in minerals ii, 1182 in organic compounds ii, 121 in silicates i, 740 in water ii, 185 volumetrically with potassium iodide by Bun- sen's method i, 530 with mercuric nitrate, by Liebig's method i, 525 with silver nitrate and starch iodide, by Pisani's method i, 524 in organic bodies, testing for ii, 7 separation from bromine i, 744 from iodine i, 748 from iodine and bromine i, 750 from metals i, 527 Christomanos' method of analyzing chromite ii, 423, 425 Chrome-iron ore ii, 421 Chromic acid, see acid chromic. Chromite, analysis by Christomanos' method ii, 423, 425 Chromium, see also acid chromic. determination as oxide i, 281 in cast iron ii, 543 in minerals ii, 1160, 1162 hydroxide i, 181 separation from alkali-earth metals i, 628 from aluminium i, 630 from ammonium i, 622 from barium, strontium, and calcium i, 629 from metals of fourth group i, 653 from potassium and sodium ... i, 622 INDEX. 1227 Chromium, separation from radicals of the fourth group i, 640 Citrate-soluble phosphoric acid, determination in superphosphates. . . . ii, 871 Clamond thermopile ii, 613 Classen-Reis' method of determining copper electrolytically ii , 623 Classen's method of analysis of zinc blende ii, 434 of determining manganese electrolytically ii, 472 silver electrolytically ii, 573 tin in fine solder electrolytically ii, 684 tin alloys electrolytically ii, 683 of nickel analysis ii, 480 Clays, analysis of ii, 413 Clemm's method of determining sulphuric acid i, 436 Clennell's method of zinc determination ii, 440 Clerget's method of determining sucrose ii, 1050 Clips i, 43, 44 Cloez' method of determining carbon and hydrogen in organic sub- stances ii, 140 Coal, analysis of ii, 721 determination of sulphur in ii, 115 Cobalt i, 192 and nickel, separation from barium and strontium. . . . i, 633, 634, 638 from manganese i, 651 frotffmanganese and iron i, 651 from manganese and zinc i, 659 from zinc i, 659 determination as hydroxide i, 306 as metal i, 306 in minerals ii, 1 144 hydroxide (ous) i, 191 separation from alkalies i, 632 from nickel i, 654, 656, 665 from nickel, manganese, and zinc i, 655 from zinc i, 657 sulphate (ous) i, 193 sulphide i, 192 -tripotassium nitrite i, 193 Cochineal tincture ii, 309 Coin bronze, analysis of ii, 680 Coke, analysis of ii, 721 determination of sulphur in ii, 115 method of combustion for ii, 105 Colorimetric determination of copper ii, 630 Coloring matter, determination of, in wines ii, 1081 hi wines, Cazeneuves reaction for ii, 1084 Combustion by Cloez' method ii, 140 furnaces ii ; 18-22 1228 INDEX. PAGE Combustion of difficultly combustible non-volatile matters ii, 33 of extractive matters ii, 33 of hygroscopic substances ii, 44 of liquids ii, 46 of oils ii, 49 of resinous matters ii, 33 of substances yielding little vapor and no sulphur on heat- ing ii, 105 of volatile substances ii, 108 tube ii, 13 with cupric oxide and oxygen ii, 37 and potassium chlorate or perchlorate. . . ii, 36 by Liebig's method ii, 12 with lead chromate, or with lead chromate and potassium dichromate, or with potassium chromate and cupric oxide ii, 33 Oooke's apparatus for determining ferrous iron ii, 1172 Copper i, 133, 154, 203 alloys, analysis of ii, 655 coarse, analysis of ii, 636 determination as metal i, 373 as oxide (ic) i, 371 as sulphide i, 375, 379 as sulpho-cyanate i, 376, 382; ii, 628 by De Haen's method i, 377 by Fleck's modification of Parkes' method i, 378 by Fleischer's method i, 382 by Fleitmann's method i, 382 by Parkes' method i, 378 by reduction with stannous chloride i, 380 by Rivot's method i, 376 by Schwarz's method i, 381, 382 by Weil's method i, 380 colorimetrically ii, 630 electrolytically i, 375; ii, 611 in cuprous oxide in sugar determination ii, 1048 in iron ' ii, 527 in minerals ii, 1144 in ores ii, 624 volumetrically i, 377 electrolytic separation of ii, 621 -nickel, analysis of ii, 474 ores, analysis of ii, 605 oxide (ic) i, 151, 208 preparing for combustions ii, 17 oxides, determination of copper in ii, 624 INDEX. 1229 PAGE Copper phosphate (ic), determining copper in ii, 624 pyrites, analysis of ii, 605 refined ii, 636 separation from arsenic i, 714 from arsenic and antimony i, 714 from bismuth i, 692 from cadmium i, 693, 694 from iron i, 683 from mercury (ic) and cadmium i, 691 from nickel i, 683 from other metals i, 680 from zinc i, 683 (ic) from (ous) i, 697 (ous) from (ic) i, 697, 698 sulphide (ic) i, 210 sulphide (ous) i, 211 sulphocyanate (ous) i, 210 Corallin . ii, 311 Cretier's method of determining constituents of organic substances. . . . ii, 140 Creydts' method of determining raffinose and sucrose ii, 1050 Crucible tongs ii, 1109 Crude lead, analysis of ii, 592 Crum's method of analysis of nitrose ii, 711 Crushing rocks for analysis ii, 1116 Cupellation of lead buttons ii, 581 Cupric-oxide method of determining nitrogen in fertilizers ii, 1025 Cyanides, see also cyanogen. Cyanogen, determining by Liebig's volumetric method i, 549 in mercuric cyanide by Rose-Finkener's method i, 552 separation from chlorine, bromine, or iodine i, 755 from the metals i, 551 volumetric determination by Fordos-Gelis's method i, 550 Dairy products ii, 1054 Daw's method of determining manganese dioxide ii, 467 Debu's method of determining sulphur in organic compounds ii, 98 Decantation i, 93 De Haen's method of determining copper i, 377 ferro- and ferricyanides i, 554 Descroizilles-Gay-Lussac's method of determining caustic alkali and carbonate alkalimetrically ii, 323 Desiccation i, 54 Desiccators i, 56 Dextrin, determination of ii, 730, 760 Dextrose, determination of ii, 730 Diastase, preparation of for determining starch ii, 763 1230 INDEX. PAGtt Dietrich's method of determining carbonic acid i, 504 Distilled liquors, analysis of ii, 1072 Dittmar's method of analysis of chromium ores ii, 423 Dittmar-Robinson's method of determining organic matter in water . . . ii, 200- Dolomite, analysis of ii, 393 Drewsen's method of zinc-dust analysis ii, 455 Drying i, 54 Drying-disk i, 67 Dufty's method of determining carbon in steel. ii, 550 Duflos' method of determining iodine i, 540 Dumas' method of determining nitrogen from the volume ii, 66 vapor densities ii, 147 Dupasquier's method of determining hydrogen sulphide i, 558 Eggertz' method of determining carbon in steel colorimetrically ii, 550 Electrode, revolving, Gooch-Medway ii, 617 Electrodes for electrolytic determinations ii, 615 Electrolytic determination of zinc ii, 448 Elements in organic bodies, determination of . . ii, 9 Elutriation i, 53 Engel's method of determining manganese electrolytically ii, 473 Equivalent of organic compounds, determining ii, 145 Erdmann's float i, 47 Eschka's method of determining mercury in ores ii, 601 sulphur in coal and coke ii, 115 Eudiometer i, 28 Evaporation i, 81 Exercises for practice ii, 953 Extract logwood indicator ii, 310 Extractive matters, combustion of ii, 33 determination in mineral waters ii, 263 Fahlberg's method of determining zinc volumetrically ii, 443 Fahlerz, analysis of ii, 608 Faulenbach's diastase solution for determining starch ii, 762 Feldhau's method (modified by Lunge) of analysis of nitrose ii, 711 Fehling's solution ii, 732, 735 Fermentation method of determining sugar ii, 754 Fermented liquors, analysis of ii, 1072 Ferricyanides, determination by Lenssen's method i, 556 by Bohlig's method i, 557 by Rheineck's method i, 557 Ferrocyanogen, separation from hydrochloric acid i, 756 volumetric determination by De Haen's method. . : i, 554 Fertilizers, analysis of ii, 1017 determination by absolute or cupric-oxide method ii, 1025 INDEX. 1231 PAGE Fertilizers, determination of phosphoric acid hi ii, 1017 Fiber, crude, determination of ii. 1036 Figuier's method of determining bromine i, 533 Filter, Gooch i, 120 Filtering i, 94 Filters, asbestos i, 120 Fine solder, analysis of ii, 683 Fish guano, analysis of ii. 926 Fixed constituents of mineral waters, determining ii, 244 Fleck's method of determining organic matter in water ii, 205 modification of Parkes' method of determining copper i, 378 Fleischer's method of decomposing sulphuretted ores ii, 626 of detennining copper i, 382 Fleitmann's method of determining copper i. 382 Flesh-meal guano, analysis of ii. 926 Float, Erdmann's i. 47 Fluid bodies, combustion of i. 46 Fluids, measuring i. 36 Fluorides, determination by decomposition with alkali carbonates. i. 474 with sulphuric acid i, 474 from silicon fluoride evolved i, 475 Fluorine, determination in minerals ii. 1182 separation from metals i, 473 Foods, analysis of ii, 1032 determination of albuminoid nitrogen in, by Stutzer's method, ii, 1033 of carbohydrates in ii, 1034 of crude fibre hi ii, 1034 of crude protein in ii, 1033 Fordos-Gelis's method of determining cyanogen volumetrically i, 550 Frankland- Armstrong's method of determining organic matter in water ii, 200 Fresenius- Will's method of determining alkalies in carbonates ii. 331 manganese-dioxide ii, 458 Fruit-sugar, determination of ii, 730 Fuch's method of determining ferric iron i. 334 Fuchsin. detection in wine ii, 1084 Fusel oil, determination in liquors ii, 1087 Galactan, determination of ii, 1036 Galena, analysis of ii, 574 determining lead in ii, 576 silver in ii, 577 Galletti's method of determining zinc volumetrically ii, 442 Gas, illuminating, determination of sulphur in ii, 114 -lamp i, 82 Gases in mineral waters, examination of ii, 265 1232 INDEX. Gases, measuring.. i, 27 reading-off i. 30 total, determining in mineral waters ii. 232 Gautier's method (Johnson-Chittenden's modification) of determining arsenic in organic matter ii, 693 Gay-Lussac's burette. i . 48 method of chlorimetric analysis ii. 377 of determining silver. . i. 342 vapor densities. . . , ii. 151 Geissler's apparatus for determining carbonic acid i, 491 burette ii, 49 German silver, analysis of. . ii, 660 Gibbs' method of determining nitrogen in organic matter ii, 74 Gintl's method of combustion. ii, 35 of determining phosphorus and sulphur in iron ii, 531 sulphur in iron ii, 522 Girard's method of determining phosphoric acid i, 449 salicylic acid in wines ii, 1086 Glaser's magnesia mixture ii, 861 method of determining phosphoric acid in manures ii, 860 Glycerin, determination in liquors ii. 1078 Gold i: 215 determination as metal. i 391 as sulphide (ic) i 393 in platinum ore i. 727 separation from lead and bismuth i, 715 from metals of group i i , 705 from metals of groups iv and v in alloys i. 703 from platinum i. 716. 727 from silver j 713 from tin i. 727 sulphide i 215 Gooch apparatus for determining water in minerals ii, 1 125 filters i. 120 -Medway revolving electrode , ii, 617 method of determining titanium in minerals ii, 1152 of separating lithium from alkalies in rock analysis. . . ii 1178 Goppelsroder-Trechsel's method of analysis of stannous chloride ii. 689 Grabowski's method of determining vapor densities ii 155 Granat guano, analysis of ii, 926 Grape-sugar, determination of ii, 730, 735, 740 Graphite, analysis of , ii. 717 determination in cast iron ii, 516 Grinding rocks for analysis ii, 1116 Guano, analysis of ii 921 Gunning method of determining nitrogen. . . ii, 1024 INDEX. 1233 PAGE Gunpowder, analysis of ii 349 residues, examination of by Werthers method i, 742 Hager's method of determining sugar ii, 753 solution for determining mercury ii , 753 Hammer's method of determining tannin ii, 775 Hampe's method of analysis of soft or refined lead ii. 590 of zinc blende ii, 432 of determining copper in coarse and refined copper., .ii, 649 refined copper electrolytically ii, 644 Handy' s method of determining zinc volumetrically ii, 446 Harcourt's method of determining nitric acid as ammonia i 5S5 Hard lead, analysis of ii. 592 Hardness of water, determining . ii 215 Heat radiator for evaporations ii. 1110 Heavy spar, analysis of ii, 375 Heine's method of determining bromine colorimetrically i, 534 copper colorimetrically . ii, 630 Hematite, analysis of ii. 486 Hertzfeld's table for determining invert-sugar ii, 1044 Hide-powder, preparation of ii 776 testing ii, 1100 Hillebrand's method of determining zirconium in minerals ii 1156 Hlasiwetz' method of incinerating plant tissues ii, 796 Hofmann's method of determining vapor densities ii, 151 Hollard's method of determining lead electrolytically. ii, 594 Horn cartilage ii, 769 770 Horn-meal guano, analysis of ii 926 Hornschlaiiche ii, 769 Hunt-Genth's method of analysis of chrome-iron ore ii, 424 Hydrofluoric acid, see acid hydrofluoric. Hydrofluosilicic acid, see acid hydrofluosilicic. Hydrogen i, 143 -ammonium fluoride i, 142 dioxide, analysis of ii, 728 peroxide, see hydrogen dioxide. -potassium fluoride i, 141 sulphide, determination by Motif's method i 560 in mineral waters ii, 229, 240 with iodine by Dupasquier's method, i, 558 Hygroscopic substances, combustion of ii, 44 Hypobromite solution ii. 888 Inorganic constituents of plants, determination of ii. 787 substances, determination n organic substances ii, 129 in organic bodies, testing for ii^ 8 1234 INDEX. PAGE Invertin, for determining sugar by inversion ii, 758 Invert-sugar, determination of ii, 730, 745 lodic acid, see acid iodic. Iodine i, 148 absorption number ii, 1063 containing chlorine, analysis of i, 753 determination as palladious iodide by Lassaigne's method i, 536 as silver iodide i, 536 colorimetrically by Struve's method i, 541 in free state by Schwarz's method i, 542, 543 in mineral waters ii, 252 in organic compounds ii, 121 in saline waters ii, 271 with ferric chloride by Duflos' method . i, 540 with nitrous acid and carbon disulphide i, 537 with palladious chloride by Kersting's method. .. i, 540 with permanganate by Reinige's method i, 538 with silver solution and starch iodide by Pisani's method i, 539 volumetrically i, 537 in organic bodies, testing for ii, 7 separation from chlorine i, 748 from chlorine and bromine i, 750 from metals i, 541 lodometric methods in chlorimetry ii, 382 Iron acetate, basic (ic) i, 197 -alum i, 147 -ammonium sulphate (ous) i, 146 arsenate (ic) i, 224 carbonate, ferrous, determining in mineral waters ii, 232 cast, analysis of ii, 501 determining iron in ii, 536 converting ferrous into ferric i, 31 1 determination gravimetrically ii, 499 in iron ores, volumetrically ii, 495 in minerals ii, 1137 in mineral waters ii, 246 ferric, determination as oxide or hydroxide i, 323 as sulphide i, 323, 325 by Oudeman's method i, 332 by reduction with hydrogen sulphide i, 326 by reduction with stannous chloride i, 327 by reduction with zinc i, 325 volumetrically i, 325 with thiosulphate i, 331 with thiosulphate and copper sulphate i, 332 INDEX. 1235 PAGE Iron, ferric, Fuch's method of determining i, 334 separation from aluminium i, 646, 652, 650 from aluminium and chromium i, 652 from barium and strontium i, 633, 634 from calcium and magnesium i, 633, 634 from ferrous iron i, 664, 666 from ferrous iron, zinc, and nickel i, 661 from manganese, nickel, cobalt, and zinc . . i, 644, 649 from manganese, zinc, cobalt, nickel, and fer- rous iron i, 647 from potassium and sodium i, 632 from radicals of the fourth group i, 640 from uranium i, 675 ferrous, determination i, 31 1 as metal i, 313 by Penny's method i, 319 in minerals ii, 1168 volumetrically i, 312 with ammonium-ferrous sulphate i, 315 with oxalic acid i, 316 with permanganate i, 313 separation from ferric iron i, 645 formate, basic (ic) i, 197 hydroxide (ic) i, 194 ore, chrome ii, 421 magnetic, analysis of ii, 494 spathic, analysis of ii, 494 ores, analysis of ii, 486 oxide (ic) i, 195 phosphate (ic) i, 227 separation from copper i, 683 succinate, basic (ic) i, 196 sulphide (ous) i, 195 Jannasch's methods of determining water in minerals ii, 1129 Jannasch-Heidenreich's method of decomposing silicates ii, 1132 Johnson-Chittenden's simplified Gautier's method of determining arsenic in organic matter ii, 693 Kaeppel's method of determining manganese electrolytically ii, 473 Kayser's method of analysis of chromium ores ii, 422 of determining potash in wines ii, 1085 Kersting's method of determining iodine i, 540 Kessler's method of determining antimony i, 400 arsenic i, 417 manganese in iron ii, 537 phosphorus in iron ii, 530 1236 INDEX. PAGH Kjeldahl method of determining nitrogen ii, 879, 899, 1021 modifications of ii, 902 Knapp's method of sugar determination ii, 749 mercury solution for sugar determination ii, 749 Knop's method and apparatus for azotimetrically determining ammo- nia in manures ii, 885 Knop-Arendt's method of determining sulphur in plants ii, 811 Knublauch's apparatus for determining ammonia in manures ii, 883 Koettstorfer number, determination of ii, 1060 Kolbe's method of determining carbonic acid , i, 493 sulphur in organic compounds ii, 97 Kolb's method of determining sulphur in pyrites ii, 567 Konig's method of determining iron ii, 500 Kopp's method of determining chlorine, bromine, and iodine in organic compounds ii, 124 Kiinzel-GrolTs method of zinc determination ii, 439 Lactose, determination ii, 1051 by Soxhlet's method ii, 1052 in milk ii, 1051 Ladenburg's method of determining constituents of organic compounds, ii, 139 Lamp, Haste's i, 82 Langmuir's method of determining zinc volumetrically ii, 447 Lassaigne's method of determining iodine i, 536 Lead acetate, analysis of ii, 599 -acetate paper ii, 213 arsenate i, 221 carbonate, normal i, 201 chloride. i, 203 chromate i, 152, 225 crude, analysis of ii, 592 determination as chloride i, 357 as chromate i, 356 as metal .' i, 358 as oxide i, 353 as oxide + lead i, 357 as sulphate i, 355 as sulphide i, 354 by Schwarz's method i, 360 electrolytically ii, 594 in galena ii, 576 volumetrically i, 359 hard, analysis of ii, 592 ores, analysis of ii, 574 oxalate i, 202 oxide i, 134, 202 INDEX. 1237 PAGE Lead oxides, analysis of ii, 597 phosphate i, 227 refined, analysis of ii, 534 salts, analysis of r ii, 597 separation from antimony i, 714 from bismuth i, 697 from other metals i, 689, 690 from silver i, 693 soft, analysis of ii, 584 -subacetate solution for sucrose determination ii, 1049 sulphate i, 202 sulphide i, 203 Leffmann-Beam method of saponification ii, 1057 Lenssen's method of determining ferricyanides i, 556 tin i, 403 Levigation i, 52 Levulose, determination of ii, 730 Liebig's method of combustion, modified by Bunsen ii, 30 with cupric oxide ii, 12 of determining chlorine i, 525 cyanogen volumetrically i, 549 lead dioxide in minium ii, 600 nitrogen from the volume ii, 59 oxygen in air ii, 948 sulphur hi organic compounds ii, 96 potash bulbs ii, 53 Lime i, 132 caustic, method of preparing ii, 111 chlorinated ("chloride"), analysis of *. ii, 376 Limestone, analysis of ii, 392 Limonite, analysis of ii, 488 Lindo-Gladding method of determining potash in fertilizers ii, 1030 Link's method of analysis of gunpowder ii, 353 Liquids, reading-off . i, 46 Liquors, analysis of ii, 1072 determination of alcohol in ii, 1072 of aldehydes in ii, 1087 of ethereal salts in ii, 1088 of fusel-oil in ii, 1037 of glycerin in ii, 1078 of volatile acids in ii, 1078 Lithium, determination of i, 253 in mineral waters ii, 252 separation from other alkalies i, 605 Litmus, tincture i, 145; ii, 307 Loge's method of determining organic carbon in soils ii, 838 1238 INDEX. PAGE Logwood, extract and tincture ii, 310 Lowe's method of determining bismuth i, 385 iron ii, 499 Lowenthal's method of determining tannin ii, 767 Luck-Fresenius' method of analysis of red phosphorus ii, 700 Lunge's modification of Feldhaus' method of nitrose analysis ii, 711 nitrometer ii, 712 Magnesia mixture for determining phosphoric acid in manures ii, 1018 Glaser's ii, 861 Magnesium-ammonium arsenate i, 222 phosphate ii, 177 chloride ii, 138 mixture for determining phosphoric acid ii, 858 determination as oxide i, 276 as pyrophosphate i, 275 as sulphate i, 275 in minerals ii, 1146 in mineral waters ii, 246 in saline waters ii, 268 in water ii, 196 oxide i, 179 phosphate - i, 227 pyroarsenate i, 223 pyrophosphate. i, 178 separation from barium and strontium i, 617 from calcium i, 619 from potassium and sodium i, 610 from uranium i, 674 sulphate i, 176 Magnetic iron ore, analysis of ii, 494 Malachite, determining copper in ii, 624 Maltose, determination of ii, 730, 747 Maly's method of determining bromine and iodine ii, 128 Manganese-ammonium phosphate i, 188 carbonate i, 185 determination as carbonate i, 293 as dioxide i, 294 as hydroxide i, 294 as protosesquioxide i, 293 as pyrophosphate i, 297 as sulphate i, 297 as sulphide i, 295 electrolytically ii, 472 of hydrochloric acid required for decomposi- tion of. . , ii, 469 INDEX. 1239 PAGE Manganese, determination of moisture in. . . . ii, 468 in iron ii, 537 in minerals ii, 1143 in mineral waters ii, 246 volumetrically i, 298 with potassium ferricyandide i, 298 permanganate i, 300 dioxide i, 186 determination of ii, 458 hydroxide (ous) i, 186 ores, analysis of ii, 470 oxide, black, analysis of ii, 456 protosesquioxide i, 186 pyrophosphate i, 189 (ous) preparing ii, 539 separation from alkalies i, 632 from aluminium and iron i, 665 from barium and strontium i, 633, 634, 635, 636 from cobalt and nickel i, 651 from lead, bismuth, cadmium, and copper i, 685 from nickel and cobalt i, 633, 638 from nickel and zinc i, 644 from zinc i, 665 sulphate, anhydrous (ous) i, 188 sulphide i, 187 Mann's method of determining zinc volumetrically ii, 444 Manures, analysis of ii, 850 Marcker's method of determining grape-sugar ii, 740 Marguerite's method of ferrous determination i, 312 Marie's method of determining lead electrolytically ii, 595 Marl, analysis of ii, 393 Marx's method of determining nitric acid in water ii, 189 Maste's lamp ii, 82 Maumen^'s method of determining oxygen in organic compounds ii, 139 Measuring i, 26 Mechanical division i, 51 Medal bronze, analysis ii, 680 Meinecke's method of determining sulphur in iron ii, 522 Meissl-Hiller's factors for determining invert-sugar ii, 1045 Melting-point of fat, determination by Wiley's method ii, 1066 Mercury i, 205 analysis of ii, 602 chloride (ous) i, 205 chromate (ous) i, 226 mercuric, determination as chloride (ous) i, 366 determination as metal i, 364 1240 INDEX. PAGE Mercury, mercuric determination as oxide i, 367 as sulphide i, 366 by Scherer's method i, 369 volumetric i, 367 ores, analysis of ii, 601 separation from mercury (ous), copper, cadmium, and lead. . . i, 688 mercurous, determination as chloride i, 361 determination volumetrically i, 362 separation from mercury (ic), copper, cadmium, bismuth, and lead i, 688 oxide (ic) V. . .. r . i, 134, 207 phosphate (ous) i, 230 separation from antimony , i, 708 from arsenic and antimony oxides i, 713 from gold and silver i, 710 from metals i, 679 from silver, bismuth, copper, cadmium, and lead. . . i, 694 sulphide (ic) i, 206 Metals in cyanides, determination of i, 553 Meteorites, analysis of ii, 412 Milk, analysis of ii, 1068 determination of fat in ii, 1069 of fat in by the paper-coil method ii, 1069 of lactose in ii, 1051 of water in ii, 1068 -sugar, determination of ii, 730, 746 Mineral waters, analysis of ii, 221 calculation, control, and arrangement of results of anal- yses of ii, 274 taking samples of ii, 225, 226 Minium, analysis of ii, 597 Mitscherlich's absorption bulbs ii, 53 method of determining all the constituents in organic compounds ii, 137 of determining silicic acid i, 521 (modified) of determining ferrous iron in minerals ii, 1 170 Mixter's method of determining sulphur in organic substances ii, 100 modification of Sauer's combustion method ii, 106 Mohr's burette i, 42 method of determining alkalies alkalimetrically ii, 329 antimony i, 400 arsenic i, 416 carbonic acid in air ii, 946 copper in ores ii, 624 hydrogen sulphide i, 560 INDEX. 1241 PACK. Mohr's method of determining lead in galena ii, 576 sulphuric acid i, 435 modified Penot's method of chlorimetric analysis ii, 331 Moisture, determining in rocks by Chatard's drying oven ii, 1121 influence of upon gases, in reading-off i, 34 Molasses, determination of ii, 1050 Molybdenum, determining in minerals ii, 1 162 method of determining phosphoric acid in manures .... ii, 856 solution for determining phosphoric acid in manures ... ii, 856- Molybdic acid, see acid molybdic. Mortreux's method of determining sulphur in free state i, 570 Miiller's modified Schulze's method of determining phosphoric acid as ferric phosphate i, 452 Muntz-Ramspacher's modified Hammer's method of determining tannin ii, 780 Nepheline, determination in presence of olivine ii, 1187 Neubauer's method of determining phosphoric acid i, 454 Nessler's reagent ii, 207 Neutralization, methods of ii, 294 Nickel i, 190 and cobalt, determining electrolytically ii, 481 separation from barium and strontium. . . . i, 633, 634, 638 -coinage metal, analysis of ii, 659 cubes, analysis of ii, 483 determination as metal i, 304 as nickel tripotassium nitrate i, 307 as oxide and hydroxide i, 302 as sulphate i, 304, 308 as sulphide i, 303, 307 electrolytically ii, 481 in minerals ii, 1144 volumetrically i, 305, 308 granular, analysis of ii, 483 hydroxide (ous) i, 189 metallic, analysis of ii, 483 ores, analysis of ii, 474 oxide (ous) i, 189 separation from alkalies i, 632 from copper i, 683 from zinc i, 653 sulphide, hydrated (ous) i, 190 Nickelstein, analysis of ii, 474 Nickelstibine, analysis of ii, 474 Nicol's method of determining sugar by inversion . . ii, 757 Nitrates, determining in manures ii, 914 1242 INDEX. Nitrates, see also acid nitric. Nitrogen i, 168 albuminoid, in water, determination as ammonia ii, 207 determination by absolute or cupric-oxide method ii, 1025 by conversion into ammonia by Varrentrapp- Will's method r ii, 82 by Gunning's method ii, 1024 by Kjeldahl's method ii, 1021 by magnesium-oxide method ii, 1029 by Ruffle's method ii, 1027 by soda-lime method ii, 102S by Stutzer's method ii, 1033 by Ulsch's method, modified by Street ii, 1029 in air ii, 948 in cheese ii, 1071 in iron ii, 524 in manures ii, 909 in milk ii, 1069 in minerals ii, 1 186 in organic compounds ii, 58 by Dumas' method ii, 66 by Gibbs' method ii, 74 by Liebig's method ... . ii, 59 by Simpson's method. . . ii, 69 by Thibault's method . . ii, 94 testing for, in organic bodies ii , 4 table of absorption i, 259 table of weight of 1 c.c. at different temperatures and pressures, i, 260 Nitric acid, see acid nitric. "Nitrose," analysis of ii, 710 Nitrous acid, see acid nitrous. Non-tannins, determination of ii, 1099 Official methods of analysis adopted by the Ass'n of Official Agric. Chemists ii, 1017 Oil-baths i, 66 Oils, combustion of ii, 49 Operations i, 11 Organic acids, volatile, determining in mineral waters ii, 261 analysis ii, 1 compounds containing sulphur, analysis of ii, 95 determination of all constituents in ii, 137 of inorganic substances in i, 129 qualitative examination of ii, 4 matter, determination in water ii, 199 by permanganate method. ... ii, 202 INDEX. 1243 PAGE Organic matter, determination in water with alkaline silver solution . . ii, 205 Ore-furnace regulus, determination of copper in ii, 625 Orseille, detection in wine ii, 1034 O'Sullivan's method of preparing pure diastase for determining starch, ii, 763 Otto's chlorimetric method ii, 3?3 method of separating phosphoric acid from aluminium i, 459 Oudeman's method of determining ferric iron i, 332 Oxalic acid, see acid oxalic. Oxgyen i, 153 determination in air ii, 948 hi organic substances ii, 131 Palladium, determination as chloride (ic) i, 390 as metal i, 390 iodide (ous) i, 237 Parodi-Mascazziiii's method of determining zinc electrolytically ii, 448 Patera's method of analysis of uranium ores ii, 567 Pattinson's method of determining manganese dioxide . . . ii, 466 in cast iron ii, 541 Pearlash, determination of ii, 336 Pearson's method of determining sulphur hi organic compounds ii, 119 Peligot's modification of Varrentrapp- Will's method ii, 91, 894 Pelouze's method of determining nitric acid with ferrous chloride i, 573 sulphur in pyrites ii, 565 Penfield's method of determining silicon fluorides evolved from fluorides, i, 478 specific gravities of rock fragments, ii, 1114 water in minerals ii, 1123 oven for determining water in minerals ii, 1124 tubes for determining water in minerals ii, 1123 Penny's method of ferrous-iron determination i, 319 Penot's method of chlorimetric analysis ii, 379 Pentosans, determination by phloroglucin ii, 1035 Permanganate method of determining nitrous acid in water ii, 195 organic matter in water ii, 202 Pettenkofer's method of determining carbonic acid i, 484 in air ii, 938 modifications of, for determining carbonic acid in air ii, 941 Pettersson's method of determining water and carbonic acid in ah-. . . ii, 932 Pewter, analysis of ii, 685 Phenolphtalein ii, 311 Phosphates, see also acid phosphoric Phosphor-bronze, analysis of ii, 680 Phosphoric acid, see acid phosphoric. Phosphorus, determination in iron ii, 527 in minerals ii, 1 159 1244 INDEX. PAGB Phosphorus, determination in organic compounds.... ii, 120 hi organic bodies, testing for ii, 7 red, analysis of ii, 700 Pigments, determination of arsenic in ii, 691 Pinch-cocks i, 43, 44 Pipettes i, 39 Pisani's method of determining chlorine i, 524 iodine i, 539 molybdic acid i, 421 silver i, 349 Vogel's modification of i, 351 Plants, determination of inorganic constituents of ii, 787 Platinum i, 216 determination as metal i, 393 as potassium-platinic chloride i, 394 as sulphide (ic) i, 395 separation from gold i, 716, 727 from metals of groups iv and v in alloys i, 705 sulphide (ic) i, 216 and gold, separation from tin, antimony, and arsenic i, 716 Polarization of wines ii, 1079 Poquillon's method of determining clay in soils ii, 822 Potash bulbs ii, 14 Liebig's ii, 53 determination ii, 336 in fertilizers by Lindo-Gladding's method ii, 1030 in wino ii, 1035 Potassa i, 131 fused ii, 155 solution i, 155 Potassium bitartrate, analysis of ii, 357 determination in wines ii, 1032 borofluoride i, 232 chloride i, 162 analysis of ii, 341 cyanide i, 136 determination as chloride i, 245 as nitrate i, 244 as potassium-platinic chloride i, 245 as silicofluoride i, 248 as sulphate i, 243 in manures ii, 873 in mineral waters ii, 249 dichromate i, 156 disulphate i, 141 -ferrocyanide method of determining zinc ii, 442 INDEX. 1246 PAGE Potassium hydroxide i, 131 -hydrogen fluoride i, 141 iodide i, 148 -starch paper ii, 379 nitrate i, 162 analysis of ii, 346 permanganate i, 145 -platinic chloride i, 163 separation from sodium i, 599, 604 silicofluoride i, 164 sulphate i, 161 analysis of ii, 341 Pratt' s modified hydrofluoric-acid method of determining ferrous iron, ii, 1173 Precipitates, drying i, 110 igniting i, 112 washing i, 98 Precipitation, effecting i, 91 Pressure, influence of, upon gases in reading-off i, 33 Pycnometer method of determining specific gravities of rock fragments, ii, 1115 Pyrites, analysis of ii, 553 Qualitative examination of organic bodies ii, 4 Quicklime, analysis of ii, 400 Radicals, determination of i, 239 Raffinose and sucrose, determination by Creydt's method ii, 1050 Rare earths, determination hi minerals ii, 1158 Reagents i, 127 Red phosphorus, analysis of ii, 700 Reducing action of different sugars on Fehling's solution ii, 734 Refined lead, analysis of . . ' ii, 584 Refractometers ii, 1061 Regnault's method of determining carbon in cast iron ii, 515 Reimann's method of determining bromine i, 532 Reinige's method of determining iodine i, 538 Reitmair's method of determining nitrates in manures ii, 915 Reissig's method of determining phosphoric acid i, 448 Resinous matters, combustion of ii, 33 Reverted phosphoric acid, determination in superphosphates ii, 869 Rheineck's method of determining ferrocyanides ii, 557 Riche's method of determining copper electrolytically ii, 623 zinc electrolytically ii, 449 Rivot's method of determining copper i, 376 Rivot-Beudant-Daguin'c method of determining sulphur i, 568 Rock analysis ii, 1101 Rocks, crushing and grinding ii, 1116 determining water hi ii, 1117, 1122 1246 INDEX. PAGE Rose's method of determining arsenous acid i, 419 carbonic acid i, 496 oxalic acid i, 470 phosphoric acid i, 448 of incinerating plant tissues ii, 797 Rose-Finkener's method of determining cyanogen in mercuric cyanide, i, 552 Rosolic acid ii, 311 Ruffle's method of determining nitrogen in fertilizers. . . .1 ii, 1027 Russel's method of determining sulphur in organic compounds ii, 99 Saccharose, determination of ii, 730 Sachsse's mercury solution for determining sugar ii, 751 method of determining dextrin and starch ii, 760 sugar ii, 751 Saline waters, examination of ii, 268 Salt cake, analysis of ii, 373 Saltpetre, Chili, analysis of ii, 875 Samples, selection of i, 50 Saponification ii, 1056 equivalent, determination of ii, 1060 Leffmann-Beam method of ii, 1057 Sauer's method of combustion, modified by Mixter ii, 106 Schaffner's method of determining zinc volumetrically ii, 436 Scheibler's method of determining carbonic acid i, 500 Scherer's method of determining mercury (ic). . ; i, 369 Schiff's azotometer ii, 76 Schlosing's method of analysis of soils ii, 824 of determining ammonia in soils ii, 843 nitric acid i, 579 Schmidt-Hiepe's method of determining tartaric, malic, and succinic acids in wine ii, 1083 Schneider's method of determining antimony i, 403 Schober's method of determining zinc ii, 446 Schoffel's method of determining chromium in cast iron ii, 543 tungsten in cast iron ii, 545 Schulze's method of determining nitric acid i, 582 from loss of hydrogen. . . . i, 588 in water ii, 186 phosphoric acid as magnesium phos- phate i, 453 of incinerating plant tissues ii, 795 Schulze-Trommsdorff's method of determining organic matter in water, ii, 203 Schwarz's method of determining chromic acid i, 424 copper i, 381, 382 free iodine i, 542^ 543 lead i,'360 INDEX. 1247 PAGE Scorification of galena ii, 578 Selenium, determination ii, 429 Selenous acid, see acid selenous. Sifting i, 53 Silica (see also acid silicic) i, 233 separation from alumina in rock analysis ii, 1131 soluble, determination in minerals ii, 1187 Silicates, analysis ii, 405 boric-oxide method of decomposing in rock analysis ii, 1132 decomposition by sodium carbonate in rock analysis ii, 1134 method of decomposing in rock analysis ii, 1132 Silicic acid, see acid silicic. Silicon determination in iron ; ii, 535 Siewert's method of determining nitric acid as ammonia i, 587 Silver i, 150, 198 alloys, analysis of ii, 569 bromide i, 236 chloride i, 198 cyanide i, 201 determination as chloride i, 338 as cyanide i, 341 as metal i, 341 as sulphide i, 340 by cupellation ii, 581 by Gay-Lussac's method i, 342 by Pisani's method i, 349 electrolytically ii, 573 in galena ii, 577, 583 volumetrically i, 342 iodide i, 236 method of determining organic matter hi water ii, 205 ores, analysis of ii, 568 phosphate, normal i, 230 separation by cupellation i, 698 from copper, cadmium, bismuth, mercury, and lead. . . i, 686 from gold i, 713 from lead .- i, 693 from mercury (ic), copper, and cadmium i, 690 from metals i, 679 sulphide i, 200 Simpson's method of determining nitrogen in organic substances ii, 69 Smith's crucible for alkali determinations hi minerals ii, 1176 method of determining alkalies in minerals ii, 1175 silicic acid i, 519 Soap solution for determining hardness of water ii, 217, 218 Soda i,131 1248 INDEX. PAGE Soda, analysis of ii, 360 commercial, analysis of ii, 368 -lime i, 153, 154 method of determining nitrogen in fertilizers ii, 1028 preparation of ii, 85 solution, normal ii, 293 iSodium carbonate i, 135 anhydrous i, 166 analysis of ii, 360 as standard for acidimetry ii, 294 determining in presence of potassium carbonate. . . ii, 333 method of decomposing silicates in rock analysis, ii, 1134 chloride i, 150, 165 analysis of ii, 371 determination as carbonate i, 250 as chloride ii, 250 as nitrate i, 249 as sulphate i, 249 in mineral waters ii, 249 in water ^ ii, 196 disulphate i, 141 hydroxide i, 131 nitrate i, 165 -platinic chloride i, 166 separation from ammonium i, 603 from potassium : i, 599, 604 silicofluoride i, 167 sulphate, analysis of . ii, 373 anhydrous. i, 164 thiosulphate i, 135 Soft lead, analysis of ii, 584 Soils, analysis of ii, 1088 chemical analysis of ii, 825 mechanical analysis of ii, 815 Solder, fine, analysis of ii, 683 "Soluble" phosphoric acid, determination in superphosphates ii, 870 Solution, Allihn's modification of Fehling's ii, 741 ammonium citrate for determining phosphoric acid in fer- tilizers ii, 1017 arsenous acid for chlorimetric analysis ii, 379 barium chloride for determining hardness of water ii, 217 chlorinated lime for chlorimetry ii, 378 citric acid for dissolving " soluble phosphoric acid" in super- phosphates ii, 871 Faulenbach's diastase for determining starch ii, 762 Fehling's ii, 732 INDEX. 1249 PAGE Solution, hypobromite ii, 888 Knapp's, for sugar determination ii, 749 lead subacetate for sucrose determination ii, 1049 magnesium nitrate for determining phosphoric acid in fertil- izers ii, 1018 mercury, Hager's, for determining sugar ii, 753 iodide, alkaline, for determining sugar ii, 751 molybdic for phosphoric-acid determination hi fertilizers. . . ii, 1018 of substances i, 79 potassa i, 155 potassium arsenite for chlorimetric analysis ii, 381 permanganate for determining organic matter in water ii, 204 silver nitrate, alkaline, for determining organic matter in water ii, 205 soap, for determining hardness of water ii, 217, 218 soda, brominized, for nitrogen determinations ii, 888 for acidimetry ii, 293, 294, 298 sodium sulphide, for Schaffner's method of zinc determina- tion ii, 436 thiosulphate for determining the iodine absorption number ii, 1036 Soxhlet's modification of Fehling's ii, 738, 1042 stannous chloride for ferric iron determination i, 329 uranium for determining phosphoric acid in superphosphates, ii, 865 zinc, for Schaffner's method of determination ii, 436 zinc iodide-starch ii, 193 Sonnenschein's method of determining phosphoric acid i, 446 Sostegni-Carpentieri's method of detecting coloring-matter in wine. . . ii, 1084 Soxhlet's method of determining carbohydrates. . ii, 1043 lactose ii, 1052 sugar ii, 738 modified Fehling's solution t ii, 738 solution ii, 1042 Spathic-iron ore, analysis of ii, 494 Specific gravity, determining in rock analysis ii, 1113 of mineral waters ii, 242 Speculum metal ii, 680 Spica's method of determining salicylic acid in wines ii, 10S5 Spring-Roland's method of determining carbonic acid in air ii, 942, 945 Starch, determination ii, 760 by the diastase method ii, 1034 in commercial starches and potatoes ii, 1034 iodide i, 349 method of determining nitrous acid in water ii, 193 Stein's method of combustion of hygroscopic or volatile substances .... ii, 44 1250 INDEX. PAGE Stockmann's method of determining phosphorus in iron ii, 527 Stolba' method of determining hydrofluosilicic acid i, 443 Storer-Pearson's method of determining copper ii, 625 Strecker's method of incinerating "plant tissues ii, 796 Stromeyer's method of determining oxygen in organic compounds. ... ii, 135 Strontium carbonate i, 172 determination as carbonate i, 267 as sulphate i, 266 in minerals ii, 1144 in mineral waters ii, 246, 252 in saline waters ii, 271 separation from calcium i, 619, 621 from potassium and sodium i, 607, 609 sulphate i, 171 Struve's method of determining iodine colorimetrically i, 541 Stutzer's method of determining albuminoid nitrogen ii, 1033 Substances, converting into weighable forms i, 81 Sucrose, determination ii, 1034, 1049 by Clerget's method. ii, 1050 Sugar, determination by fermentation ii, 754 of lead, analysis of ii, 599 Sugars, different reducing effect on Fehling's solution ii, 734 reducing, determination ii, 1042 Sulphates, see acid sulphuric. Sulphides, determining in presence of carbonates i, 742 in silicates i, 742 Sulphur, commercial, analysis of ". ii, 703 determination as hydrogen sulphide i, 558, 562, 569 by Berzelius-Rose's method i, 564 by Bunsen's method i, 566 by Rivot-Beudant-Daguin's method i. 568 in cast iron ii, 519 in coal and coke ii, 115 in free state by Mortreux's method i, 570 in illuminating gas ii, 114 in minerals ii, 1155, 1184 in organic compounds ii, 95 in pyrites ii, 561 in sulphides i, 562, 569 in sulphur "water ii, 272 in organic bodies, testing for ii, 5 in sulphides, separation from chlorine. , i, 756 water, examination of ii, 272 Sulphuretted copper ores, analysis of ii, 605 ores, determination of copper in ii, 625 Sulphuric acid, see acid sulphuric. INDEX. 1251 PAGE Sulphurous acid, see acid sulphurous i, 431 Superphosphates, analysis of ii, 862 Table for calculating grape-sugar from copper determined gravimetri- cally ii, 743 for determining dextrose, Allihn's ii, 1046 invert-sugar, Hertzfeld's ii, 1044 for comparison of specific gravities, degrees Brix, and degrees Baume ii, 1039 for correction of readings of the Brix spindle ii, 1040 for determination of lactose ii, 1053 of absorption of carbonic acid i, 508 of absorption of nitrogen by brominized lye ii, 892 of butyro-refractometer readings ii, 1062 of International atomic weights, 1903 ii, 1211 of weight of 1 c.c. of carbonic acid at various temperatures and pressures i, 506 of weight in mgrms. of 1 c.c. nitrogen at various pressures, etc. . . ii, 890 showing amount of the constituent sought for every number of the compound found ii, 1197 comparison of degrees of mercurial thermometer with those of the air- or hydrogen-thermometer ii, 1213 percentage of alcohol by weight and volume ii. 1073 of ammonia at different specific gravities. . ii, 323 of anhydrous acetic acid at various specific gravities ii, 318 of anhydrous phosphoric acid at various specific gravities ii, 290 of free sulphuric acid and sulphuric anhy- dride at various specific gravities ii, 285 of hydrated acetic acid at various specific gravities ii, 291 of hydrochloric acid at various specific gravities ii , 287 of nitric acid at various specific gravities ... ii 289 of potassa in potassa solution at different specific gravities ii, 321 of soda in soda solutions at different specific gravities ii, 321 of tartaric and citric acids in solutions of various specific gravities ii, 292 the quantity of ammonia hi solutions of various specific gravities' ii, 322 of anhydrous potassium and sodium car- bonates hi solutions at various specific gravities ii, 322 1252 INDEX. PAGE Table showing the quantity of hydrochloric acid at various degrees Baume ii, 288 of potassa and potassium hydroxide at various specific gravities ii, 319 of soda and sodium hydroxide at various specific gravities ii, 320 of sulphuric acid and sulphuric anhydride in mixtures with water ii, 286 specific and absolute weights of some gases ii, 1212 Tamm's method of determining antimony in ores ii, 672 Tannin determination ii, 767, 1099 by methods, decided upon by the Amer. Assn. Off. Agric. Chemists, 1900 ii, 781 hi wines ii, 1081 Tartar, analysis of ii, 357 Tate's method of analysis of chrome-iron ore ii, 426 Temperature, influence of on gases, in reading-off i, 33 Tendon-meal guano, analysis of ii, 926 Thermopile, Clamond ii, 613 Thibault's method of determining nitrogen ii, 94 Thiosulphuric acid, see acid thiosulphuric. Tiemann-Schulze's method of determining nitric acid i, 582 Tin alloys, analysis of. ... ii, 6SO chloride (ous), analysis of ii, 689 determination as oxide (ic) i, 405 as stannic (or metastannic) acid i, 405 as sulphide (ous or ic) i, 406 by alkaline iodine solution i, 408 by Lenssen's method i, 408 in fine solder ii, 683 with ferric chloride i, 408 volumetrically i, 407 ores, analysis of ii, 675 oxide (ic) i, 219 phosphate (ic) i ; 230 preparations, analysis of ii, 689 pyrites, analysis of ii, 676 separation from antimony i, 716, 725 from antimony and arsenic i. 723, 726, 728 from arsenic i, 717, 728 from gold i, 727 from metals of groups i, IT, and in i, 707 from metals of groups iv and v i, 706 from stannic tin i, 730 sulphide, hydrated (ous) i, 220 INDEX. 1253 Tin sulphide, hydrated (ic) i, 220 varieties, analysis of ii, 677 Tincture cochineal ii, 309 litmus ii, 307 logwood ii, 310 Tinstone, analysis of ii, 675 Titanium, colorimetric determination in minerals ii, 1151 determination i, 284 in iron ii, 535 in minerals ii, 1149 Tripotassium cobaltic nitrite i, 193 Trommsdorff s method of determining nitrous acid in water ii, 193 Tropseolin OO and OOO ii, 312 Tungsten in cast iron, determining ii, 545 Ulsch method modified by Street, of determining nitrogen ii, 1029 Ullgren's method of determining carbon in cast iron ii, 505 nitrogen in iron ii, 525 Uranium acetate i, 139 determination ii, 335 by Belohoubeck's method i, 336 method of determining phosphoric acid in superphosphates ii, 864 ores, analysis of ii, 567 separation from aluminium i, 674 from barium, calcium, and strontium i, 673 from chromium i, 674 from cobalt, nickel, and zinc i, 675 from iron (ic) i, 675 from magnesium i, 674 from other metals of groups i-rv i, 672 Uranyl pyroarsenate i, 223 pyrophosphate i, 229 Vanadium determination in cast iron ii, 546 in minerals ii, 1 162 Vapor density of compounds, determining ii, 147 Varrentrapp- Will's method of determining nitrogen ii, 82 modifications of, for determining nitrogen, ii, 911 Peligot's modification of ii, 91, 894 Vogel's modification of Pisani's method i, 351 Vohl's method of determining arsenous acid i, 419 chromic acid i, 423 von Baumhauer's method of determining oxygen in organic substances ii, 131 Volhard's method of determining copper as sulphocyanate ii, 623 manganese in iron ii, 539 1254 INDEX. PACE Wackenroder-Fresenius' method of separating phosphoric acid from aluminium i, 459 Wagner's method of analysis of Chili saltpetre ii, 878 of determining phosphoric acid in manures ii, 859 Wanklyn-Chapman-Smith's method of determining albuminoid nitro- gen as ammonia ii, 207 Warren's method of determining carbon and hydrogen in organic sub- stances ii, 145 chlorine in organic compounds ii, 125 Water, analysis of ii, 185 apparatus for absorbing ii, 51 -bath i, 58 determining hardness of ii, 217 distilled i, 127 estimating i, 72 sulphur, examination of ii, 272 Waters, mineral analysis of, ii, 221 calculation, control, and arrangement of results of analyses of, ii, 274 saline, examination of ii, 268 taking samples of '. ii, 225, 226 Weeren's method of determining phosphoric acid by Miiller's modified Schulze's method i, 452 Weighing, process of i, 21, 70 Weights, testing, etc i, 19 Weil's method of decomposing sulphuretted ores ii, 627 of determining antimony in ores ii, 672 copper i, 380 Weldon mud, determination of effective oxygen value of ii, 470 Well's apparatus for determining carbonic acid i, 499 Werther's method of determining arsenic as uranyl pyroarsenate i, 413 of examining gunpowder residues i, 742 Weyl's method of determining carbon in cast iron ii, 505 White-bearing metal, analysis of ii, 686 Wichelhaus' apparatus for determining vapor densities ii, 154 Wildenstein's method of determining sulphuric acid i, 437, 438 Wiley's method of determining melting-point of fats ii, 1066 Wines, detecting coloring matter in ii, 1084 detection of fuchsin and orseille in ii, 1084 determination of dextrin in ii, 1086 of gum in ii, 1086 of coloring matters in ii, 1081 glycerin, etc., in ii, 1079 of potash in ii, 1085 of potassium bitartrate in ii, 1082 of salicylic acid in . ii, 10S5 INDEX. 1255 PAGE Wines, determination of sulphurous acid in ii, 1085 of tannin in ii, 1081 of tartaric acid in ii, 1082 of tartaric, malic, and succinic acids in, by Schmidt-Hiepe's method ii, 1 083 Winkler's method of determining tin in alloys ii, 685 Wohler's method of determining carbon hi cast iron ii, 508 silicon fluoride, evolved from fluorides i, 478 Wolff's method of determining sulphuric acid and chlorine in plants. . . ii, 812 modified Knapp's method of mechanical analysis of soils ii, 819 Wood's metal, analysis of ii, 665 W T rightson's method of determining copper electrolytically ii, 623 Zeiss' butyro-refractometer ii, 1061 Zimmermann's method of analysis of zinc blende ii, 431 Zinc i, 132 blende, analysis of ii, 430 carbonate, basic i, 182 determination as carbonate i, 287 as oxide i, 287 as sulphide i, 288, 289 electrolytically ii, 448 in minerals ii, 1143 volumetrically ii, 435 -dust, analysis of ii, 452 -iodide-starch solution ii, 193 metallic, analysis of ii, 450 ores, analysis of ii, 435 oxide i, 183 separation from aluminium and manganese i, 649 from barium and strontium i, 633, ii, 634 from cadmium i, 684 from calcium i, 633, 634 from copper i, 683 from iron in alloys i, 660 from nickel, cobalt, and manganese i, 650 from potassium and sodium i , 632 sulphide i, 184 Zirconium, determination hi minerals ii, 1155, 1156 R A UN: UNIVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped below. DEC 22 1947 1953 REC'D LD 21-100m-9,'47(A5702sl6)476 ro 8 4 THE ORNIA LIBRARY