UNIVERSITY OF CALIFORNIA MEDICAL CENTER LIBRARY SAN FRANCISCO SYSTEM OF INSTRUCTION QUALITATIVE CHEMICAL ANALYSIS. Tig.1 Fig SYSTEM OF INSTRUCTION QUALITATIVE CHEMICAL ANALYSIS. BY DR. C. REMIGIUS/TRESENIUS, PRIVT A.CLIC COUN8ELLOR O{,MMKZ OF NASSAU ; DIRECTOR Or THE CHEMICAL LABORATORY AT WIESBADEXJ PROFESSOR OF CHEMISTRY, NATURAL PHILOSOPHY, AND TECHNOLOGY AT THI W1ESBADBM AGRICULTURAL IM8TITUTK. EDITED BY J. LLOYD BULLOCK, F.C.S. LONDON: JOHN CHURCHILL & SONS, NEW BURLINGTON STREET. Q U 8 I MDCCCLXIV. F88 1 - A 0. EDITOR'S PREFACE TO THE SIXTH EDITION. A STEADY and ever-increasing demand for this work in Germany has led to the issue of successive editions until an eleventh has been reached. In every new edition the Author has introduced whatever improve- ment in the processes described, or in the distribution of his material, the progress of the science has suggested. The present is characterized by two important additions : 1st. The original plan of the work excluded all the rarer elements and their compounds ; but, inasmuch as many of these have recently acquired importance, as chemical reagents or in the arts, it has been deemed advisable to embrace the whole. Now, therefore, all the known elements are treated of, and processes given for their preparation and detection j but in order to avoid increasing too much the size of the volume, or to embarrass the beginner in the study of analysis, many of these are printed in smaller type. 2nd. The other addition is that of SPECTRUM ANALYSIS, the most interesting, beautiful, and important acquisition which Analytical Chemistry has ever received. This is treated of fully, as its intrinsic importance and the requirements of students of such a work as this demanded. The reader will also observe that the new process known ae Dialysis has not been overlooked.' J. LLOYD BULLOCK. 3, HANOVER-STREBT, Dec., 1863. CONTENTS. PAET I. INTRODUCTORY PART. PAGE PRELIMINARY REMARKS. Definition, general principles, objects, utility, and importance of qualitative chemical analysis. Conditions and requirements for a successful study of that science 1 SECTION I. OPERATION, 1 . . . .3 1. Solution, 2 . 3 2. Crystallization, 3 . 5 3. Precipitation, 4 6 4. Filtration, 5 . . .7 5. Decantation, 6 . . 8 6. Evaporation, 7 9 7. Distillation, 8 . .10 8. Ignition, 9 . . .10 9. Sublimation, 10 . .11 10. Fusion and Fluxing, 11 . . 11 11. Deflagration, 12 . .12 12. The use of the blowpipe, 13 . 13 13. The use of lamps, particularly of gas lamps, 14 . . .17 14. Observation of the coloration of flame by certain bodies, and spectral analysis, 15 . .21 Appendix to the First Section. Apparatus and utensils, 16 , .25 SECTION II. Reagents 111 .... 27 A. REAGENTS IN THE HUMID WAY. I. SIMPLE SOLVENTS . . . .29 1. Water, 18 . . . .29 2. Alcohol, 19 . . . .30 3. Ether, ) 4. Chloroform, > 20 . .30 5. Sulphide of carbon, J II. ACIDS AND HALOGENS, 21 . .31 a. Oxygen acids. 1. Sulphuric acid, 22 . . .31 2. Nitric Acid, 23 . . .33 3. Acetic acid, 24 . . .33 4. Tartaric-acid, 25 . . .34 PAGE &. Hydrogen acids and halogens. 1. Hydrochloric acid, 26 . .34 2. Chlorine and chlorine water, 27 35 3. Nitrohydrochloric acid, 28 . 36 4. Hydrofluosilicic acid, 29 . .37 c. Sulphwr acids. 1. HydrosulpLuric acid, 30 . .37 III. BASES AND MEIALS, 31 . 42 a. Oxygen bases. a. Alkalies. 1. Potassa and soda, 32 . .42 2. Ammonia, 33 . . ,44 ft. A Ikaline earths. 1. Baryta, 34 . . . .45 2. Lime, 35 .... 46 7. Heavy metals and their oxides. 1. Zinc, 36 .... 46 2. Iron, 37 . . . .47 3. Copper, 38 . . . .47 4. Hydr-ate of teroxide of bismuth, 39 47 I. Sulphur loses. 1. Sulphide of ammonium, 40 . 48 2. Sulphide of sodium, 41 . .49 IV. SALTS. a. Salts of the alkalies. 1. Sulphate of potassa, 42 . .50 2. Phosphate of soda, 43 . .50 3. Oxalate of ammonia, 44 . .50 4. Acetate of soda, 45 . .51 5. Carbonate of soda, 46 . .51 6. Carbonate of ammonia, 47 .52 7. Bisulphite of soda, 48 .52 8. Nitrite of potassa, 49 . . 5$ 9. Bichromate of potassa, 50 .53 10. Granular antimonate of potassa, 51 . . . . . 54 11. Molybdate of ammonia, dissolved in nitric acid, 52 . . .54 12. Chloride of ammonium, 53 . 55 13. Cyanide of potassium, 54 . .55 14. Ferroeyanide of potassium, 55 ^ 56 Vlll CONTENTS. PAGE 15. Ferricyanide of potassium, 56 . 57 16. Sulphocyanide of potassium, 57 57 b. Salts of the alkaline earths. 1. Chloride of barium, 58 58 2. Nitrate of baryta, 59 58 3. Carbonate of baryta, 60 59 4. Sulphate of lime, 61 59 5. Chloride of calcium, 62 59 6. Sulphate of magnesia, 63 60 c. Salts of the oxides of the heavy metals. 1. Sulphate of protoxide of iron, 64 60 2. Sesquichloride of iron, 65 .61 3. Nitrate of silver, 66 . .62 4. Acetate of lead, 67 . . 62 5. Nitrate of suboxide of mercury, 68 62 6. Chloride of mercury, 69 . .63 7. Sulphate of copper, 70 . . 63 8. Protochloride of tin, 71 . .64 9. Bichloride of plantinum, 72 .64 10. Sodio-protochloride of palladium, 73 65 11. Terchloride of gold, 74 . .65 V. COLORING MATTERS AND INDIFFERENT VEGETABLE SUBSTANCES, 75 .65 1. Test papers. a. Blue litmus-paper . .65 /3. Reddened litmus- paper . 66 7. Georgina paper . .66 8. Turmeric-paper . . 66 2. Indigo solution, 76 . .67 B. REAGENTS IN THE DRY WAY. I. Fluxes and decomposing agents. 1. Mixture of carbonate of soda and carbonate of potassa, 77 .67 2. Hydrate of baryta, 78 . .68 3. Fluoride of calcium, 79 . .69 4. Nitrate of soda, 80 . . .69 II. Blowpipe reagents. 1. Carbenate of soda, 81 . .69 2. Cyanide of potassium, 82 .70 3. Biborate of soda, 83 . .71 4. Phosphate of soda and ammonia, 84 71 5. Nitrate of protoxide of cobalt, 85 72 SECTION III. REACTIONS, OR DEPORTMENT OF BODIES WITH REAGENTS, 86 . .73 A. REACTIONS, OR DEPORTMENT AND PROPERTIES OF THE METALLIC OXIDES AND OF THEIR RADICALS, 87 74 FIRST GROUP. Potassa, soda, ammonia; oxide of cesium, oxide of rubidium, lithia, PAGE Special reactions of the more common oxides of the first group. a. Potassa, 89 . . .75 b. Soda, 90 . . . .76 c. Ammonia, 91 . . .78 Recapitulation and remarks, 92 . 79 Special reactions of the rarer oxides of the first group. 1. Oxide of cesium . . .80 2. Oxide of rubidium 93 . .80 3. Lithia . . ... 80 SECOND GROUP. JBaryta, strontia, lime, magnesia, 94 81 Special reactions. a. Baryta, 95 . . .82 b. Strontia, 96 . . . .83 c. Lime, 97 . . . .85 d. Magnesia, 98 . . . .86 Recapitulation and remarks, 99 . 88 THIRD GROUP. More common oxides of the third group : alumina, sesquioxide of chromium. Rarer oxides of the third group : berylla, thoria, zirconia, yttria, oxide of terbium, oxide of erbium, oxide of cerium, oxide of lan- thanium, oxide of titanic acid, tantalic acid, poniobic acid, 100 . . ".90 Special reactions of the more common oxides of the third group. a. Alumina, 101 . . .90 b. Sesquioxide of chromium, 102 . 92 Recapitulation and remarks, 103 . 93 Special reactions of the rarer oxides of the third group, 104 . .94 1. Berylla 94 2. Thoria 94 3. Zirconia 94 4. Yttria 95 5. Oxide of terbium 95 6. Oxide of erbium 7. Oxides of cerium 8. Oxide of lanthanium 9. Oxide of didymium 10. Titanic acid 11. Tail tali c acid 12. Hy poniobic acid 95 95 96 96 97 98 98 FOURTH GROUP. More common oxides of the fourth group : oxide of zinc, protoxide of manganese, protoxide of nickel, protoxide of cobalt, protoxide of iron, sesquioxide of iron. Rarer oxides of the fourth group : sesqui- oxides of uranium, oxides of vanadium, oxides of thallium, 105 99 Special reactions. a. Oxide of zinc, 106 . . . 99 b. Protoxide of manganese, 107 . 101 CONTENTS. IX PAGE c. Protoxide of nickel, 108 . .102 d. Protoxide of cobalt, 109 . . 104 e. Protoxide of iron, 110 . .105 /. Sesquioxide of iron, 111 . . 107 Recapitulation and remarks, 112 . 108 Special reactions of the rarer oxides of the fourth group, 113 . . 110 a. Oxides of uranium . . .110 6. Oxides of vanadium . . .110 c. Oxides of thallium . . . Ill FIFTH GROUP. More common oxides of the fifth group : oxide of silver, suboxide of mercury, oxide of mercury, oxide of lead, teroxide of bismuth, oxide of copper, oxide of cad- mium. Rarer oxides of the fifth group: oxides of palladium, rhodium, osmium, ruthenium, 114 Ill Special reactions of the more common oxides of the fifth group. First division of the fifth group : oxides which are precipitated by hydro- chloric acid. a. Oxide of silver, 115 . ,112 b. Suboxide of mercury, 116 . 113 c. Oxide of lead, 117 . . .114 Recapitulation and remarks, 118 . 116 Second division of the fifth group : oxides which are not precipitated, by hydrochloric acid. Special reactions. a. Oxide of mercury, 119 . . 116 5. Oxide of copper, 120 . . 117 c. Teroxide of bismuth, 121 . 119 d. Oxide of cadmium, 122 . . 121 Recapitulation and remarks, 123 . 121 Special reactions of the rarer oxides of the fifth group, 124 . .123 a. Protoxide of palladium . . 123 b. Sesquioxide of rhodium . . 123 c. Oxides of osmium . . . 123 d. Oxides of ruthenium . .124 SIXTH GROUP. More common oxides of the sixth group; teroxide of gold, bin- oxide of platinum, protoxide of tin, binoxide of tin, teroxide of antimony, arsenious acid and arsenic acid. Rarer oxides of the sixth group : oxides of iridium, molybdenum, tungsten, tellurium, selenium, 125 . . . 125 125 126 127 Special reactions. a. Teroxide of gold, 126 b. Binoxide of platinum, 127 Recapitulation and remarks, 12S Second division of the sixth group. Special reactions. a. Protoxide of tin, 129 . 128 b. Binoxide of tin, 130 . . 129 c. Teroxltie of antimony, 131 . 131 d. Arsenious acid, 132 . . 134 e. Arsenic acid, 133 . . . 143 Recapitulation and remarks, 134 . 144 Special reactions of the rarer oxides of the sixth group, 135 . .147 a. Oxide of iridium . . .147 b. Oxides of molybdenum . .148 c. Oxides of wolframium or tungsten 148 d. Oxides of tellurium . . 149 e. Oxide of selenium . . .149 B. REACTIONS OR DEPORTMENT OF THE ACIDS AND THEIR RADICALS WITH REAGENTS, 136 . . . 150 Classification of acids in groups, 136 151 I. INORGANIC ACIDS. FIRST GROUP. Acids which are precipitated from neu- tral solutions by chloride of ba- rium : chromic acid (sulphurous acid, hyposulphurous acid, iodic acid), sulphuric add (hydrofiuosi- licic acid), phosphoric acid (bi- basic, monobasic phosphoric acid), boracic acid, oxalic acid, hydro- fluoric acid (phosphorous acid), carbonic acid, silicic acid, 137 151 First division of the first group of the inorganic acids, 138 . . 152 Chromic acid Remarks 152 153 Rarer acids of the first division of the first group, 139 . . .154 a. Sulphurous acid . . .154 6. Hyposulphurous acid . .154 c. Iodic acid . . . .154 Second division of the first group of the inorganic acids. Sulphuric acid, 140 . . . 155 Remarks . . .. . .156 Hydrofluosilicic acid, 141 . . 156 Third division of the first group of the inorganic acids. a. Phosphoric acid, 142 . .156 a. Bibasic phosphoric acid, ) /3. Monobasic phosphoric > 143 160 acid, . . ) b. Boracic acid, 144 . . .160 c. Oxalic acid, 145 . . . 162 d. Hydrofluoric acid, 146 . . 163 Recapitulation and remarks, 147 . 166 Phosphorous acid, 148 . . . 167 CONTENTS. Fourth division of the first group of the inorganic adds. a. Carbonic acid, 149 . . 167 6. Silicic acid, 150 . . . 169 Recapitulation and remarks, 151 . 170 SECOND GROUP OP INORGANIC ACIDS. Acids which are precipitated by nitrate of silver, but not by chloride of ba- rium: hydrochloric acid, hydro- bromic acid, hydriodic add, hydrocyanic acid (hydroferro and hydroferricyanic acid}, hydro- sulphuric acid (nitrous acid, hypo- chlorous acid, chlorous acid, Jiypophosphorous acid). a. Hydrochloric acid, 152 . .171 b. Hydrobromic acid, 153 . . 172 c. Hydriodic acid, 154 . .174 d. Hydrocyanic acid, 155 . . 176 Appendix. a. Hydroferrocyanic acid . .178 b. Hydroferricyanic acid . . 178 e. Hydrosulphuric acid, 156 . 178 Recapitulation and remarks, 157 . 180 Rarer acids of the second group 1. Nitrous acid 2. Hypochlorous acid 3. Chlorous acid . 4. Hypophosphorous acid 158 181 . 181 . 182 . 182 , 182 THIRD GROUP OP THE INORGANIC ACIDS. Acids which are not precipitated by salts of baryta nor by salts of silver: nitric acid, chloric acid (perchloric acid). a. Nitric acid, 159 . . .183 6. Chloric acid, 160 . . . 184 Recapitulation and remarks, 161 . 185 Perchloric acid, 162 . . .186 PAGE II. ORGANIC ACIDS. FIRST GROUP. A dds which are invariably predpitated by chloride of calcium: oxalic add, tartaric acid (paratartaric or racemic add), citric add, malic add. a. Oxalic acid, 163 . 186 b. Tartaric acid, 163 . . 186 c. Citric acid, 164 . . 187 d. Malic acid, 165 . . 188 Recapitulation and remarks, 166 189 Kacemic or paratartaric acid, 167 190 SECOND GROUP OF THE ORGANIC ACIDS. Adds which chloride of caldum fails to predpitate under any drcum- stances, but which are predpitated from neutral solutions by sesqui- chloride of iron : sucdnic add, benzoic add. a. Succinic acid, 168 . .191 b. Benzoic acid, 169 . . .192 Recapitulation and remarks, 170 . 192 THIRD GROUP OF THE ORGANIC ACIDS. Adds which are not precipitated by chloride of caldum nor by sesqui- chloride of iron: acetic add, formic add (lactic add, propi- onic acid, butyric add). a. Acetic acid, 171 . . .193 6. Formic acid, 172 . . . 194 Recapitulation and remarks, 173 . 195 Rarer adds of the third group of organic adds, 174 . .196 1. Lactic acid . . . .196 2. Propionic acid and butyric acid . 196 PART II. SYSTEMATIC COURSE OP QUALITATIVE CHEMICAL ANALYSIS. Preliminary remarks on the course of qualitative analysis in general, and on the plan of this part of the pre- sent work in particular . . 201 SECTION I. PRACTICAL PROCESS FOR THE ANALYSIS OP COMPOUNDS AND MIXTURES IN GENERAL. I. Preliminary examination, 175 . 203 A. The body under examination is solid. I. It is neither a pure metal nor an alloy, 176 . . . .204 II. The substance is a metal or an alloy, 177 . . . . 209 PAGE B. The substance under examination is a fluid, 178 . . . . 209 II. Solution of bodies, or classifica- tion of substances according to their deportment with certain solvents, 179 . . . 210 A. The substance under examination is neither a metal nor an alloy, 180 211 B. The substance under examination is a metal or an alloy, 181 . . 213 III. Actual examination. SIMPLE COMPOUNDS. A. Substances soluble in water. Detection of the base, 182 . 214 Detection of the aeid, 183 . 219 CONTENTS. XI I. Detection of inorganic acids, 183 219 II. Detection of organic acids, 184 221 B. Substances insoluble or sparingly soluble in water, but soluble in hydrochloric acid, nitric acid, or nitrohydrochloric acid. Detection of the base, 185 . 223 Detection of the acid, 185 . 225 I. Detection of inorganic acids, 186 225 II. Detection of organic acids, 187 226 C. Substances insoluble or sparingly soluble in water, hydrochloric acid, nitric acid, or nitrohydrO' chloric acid. Detection of the base and the acid, 188 226 COMPLEX COMPOUNDS. A. Substances soluble in water, and also such as are insoluble in water, but dissolve in hydrochloric acid, nitric acid, or nitrohydrochloric acid. Detection of the bases . . . 228 Treatment with hydrochloric acid : detection of silver, suboxide of mercury (lead), 189 . .228 Treatment with hydrosulphuric acid, precipitation of the metallic oxides of Group V., 2nd division, and of Group VI., 190 . . . 231 Treatment of the precipitate produced by hydrosulphuric acid with sul- phide of ammonium ; separation of the 2nd division of Group V. from Group VI., 191 . . . 232 Detection of the metals of Group VI. Arsenic, antimony, tin, gold, pla- tinum, 192 . . . .233 Detection of the metallic oxides of Group V., 2nd division. Oxide of lead, teroxide of bismuth, oxide of copper, oxide of cadmium, oxide of mercury, 193 . . . 236 Precipitation with sulphide of ammo- nium, detection and separation of the oxides of Groups III. and IV. Alumina, sesquioxide of chromium, oxide of zinc, protoxide of manga- nese, protoxide of nickel, protoxide of cobalt, proto- and sesquioxide of iron, and also of those salts of the alkaline earths which are preci- pitated by ammonia from their solution in hydrochloric acid : phos- phates, borates, oxalates, silicates, and fluorides, 194 . . . 238 Separation and detection of the oxides of Group II., which are precipitated by carbonate of ammonia in pre- sence of chloride of ammonium, viz., baryta, strontia, lime, 195 244 Examination for magnesia, 196 . 245 PAGE Examination for potassa and soda, 197 246 Examination for ammonia, 198 . 246 DETECTION OP THE ACIDS. 1. Substances soluble in water. I. In the absence of organic acids, 199 . . . 247 II. In presence of organic acids, 200 . . < . . .249 2. Substances insoluble in water, but soluble in hydrochloric acid, nitric acid, or nitrohydrochloric acid. I. In the absence of organic acids, 201 251 II. In presence of organic acids, 202 252 B. Substances insoluble or sparingly soluble both in water and in hy- drochloric acid, nitric add, or nitrohydrochloric acid. Detection of the bases, acids, and non- metallic elements, 203 . 252 SECTION II. PRACTICAL COURSE IN PARTICULAR CASES. I. Special method of effecting the ana- lysis of cyanides, ferrocyanides, &c., insoluble in water, and also of insoluble mixed substances containing such compounds, 204 256 II. Analysis of silicates, 205 . 258 A. Silicates decomposable by acids, 206 258 B. Silicates which are not decom- posed by acids, 207 . . 260. C. Silicates which are partially de- composed by acids, 208 . 262, III. Analysis of natural waters, 209 262 A. Analysis of the fresh waters (spring- water, well- water, brook- water, river-water, &c.), 210 263 B. Analysis of mineral waters, 211 266 1. Examination of the water, 212 266 a. Operations at the spring, 212 266 b. Operations in the laboratory, 213 . . . . . 267 2. Examination of the sinter-deposit, 214 271 IV. Analysis of soils, 215 . . 273 1. Preparation and examination of the aqueous extract, 216 . 274 2. Preparation . and examination of the acid extract, 217 . ^ . 276 3. Examination of the inorganic con- stituents insoluble in water and acids, 218 . .^ . 277 4. Examination of the organic con- stituents of the soil, 219 . 277 a. Examination of the organic sub- stances soluble in water . . 277 Xll CONTENTS. b. Treatment with an alkaline car- bonate 277 c. Treatment with caustic alkali 278 V. Detection of inorganic substances in presence of organic substances, 220 278 1. General rules for the detection of inorganic substances in presence of organic matters, which by their color, consistence, &c., im- pede the application of the re- agents, or obscure the reactions produced, 221 . . . 278 2. Detection of inorganic poisons in articles of food, in dead bodies, &c., in chemico-legal cases, 222 279 I. Method for the detection of arsenic, 223 280 A. Method for the detection of undis- solved arsenious acid . . 281 B. Method of detecting soluble arse- nical and other metallic com- pounds, by means of Dialysis, 224 281 C. Method for the detection of arsenic iu whatever form of combination it may exist, which allows also a quantitative determination of that poison, and permits at the same time the .detection of other me- tallic poisons which may be pre- sent, 225 . . . . 283 1. Decoloration and solution . 283 2. Treatment of the solution with hydrosulphuric acid . .284 3. Purification of the precipitate produced by hydrosulphuric acid 284 4. Preliminary examination for ar- senic and other metallic poisons of the fifth and sixth groups . 285 5. Treatment of the purified preci- pitate produced by hydrosulphu- ric acid in cases where arsenic alone is assumed to be present . 286 6. Treatment of the purified pre- cipitate produced by hydrosul- phuric acid in cases where there is reason to suppose that another metal is present, perhaps with arsenic . . . .286 7. Reduction of the sulphide of arsenic ... . 287 8. Examination of the reserved re- sidues for other metals of the fifth and sixth groups . . 288 a. Residue I. . . .288 I. Residue II. . . .289 c. Residue III. . . .289 d. Residue IV. . . 289 9. Examination of the reserved fil- trate for metals of the third and fourth groups . . .289 II. Method for the detection of hydro- cyanic acid, 226 . . . 290 III. Method for the detection of phos- phorus, 227 ... 292 A. Detection of unoxidized phos- phorus . . . .292 B. Detection of phosphorous acid . 296 3. Examination of the inorganic con- stituents of plants, animals, or parts of the same, of manures, &c. (analysis of ashes). . . 297 A. Preparation of the ash, 228 . 297 B. Examination of the ash . . 297 a. Examination of the part so- luble in water . . . 297 6. Examination of the part so- luble in hydrochloric acid . 298 c. Examination of the residue insoluble in hydrochloric acid 299 . SECTION III. EXPLANATORY NOTES AND ADDITIONS TO THE SYSTEMATIC COURSE OF ANALYSIS. I. Additional remarks to the prelimi- nary examination, To 175 178 300 II. Additional remarks to the solution of substances, &c., To 179 181 301 III. Additional remarks to the actual examination, To 182204 . 302 A. General review and explanation of the analytical course . . 302 a. Detection of the bases . . 302 6. Detection of the acids . . 305 B. Special remarks and additions to the systematic course of analysis. To 189 308 190 and 191 . . .309 192 310 193 310 194 311 195198 . . .312 203 312 204 313 APPENDIX. I. Deportment of the most important medicinal alkaloids with re- agents, and systematic method of effecting the detection of these substances, 229 . . . 315 I. Volatile alkaloids. 1. Nicotina, 230 . . . 316 2. Conia, 231 . . . . 317 II. Non-volatile alkaloids. FIRST GROUP. Non-volatile alkaloids which are pre- cipitated by potassa or soda, from the solution of their salts, and redissolve readily in an ex- cess of the precipitant . .318 Morphia, 232 . . . . 318 SECOND GROUP* Non-volatile alkaloids which are CONTENTS. Xlll PAGE precipitated by potassa from the solutions of their salts, but do not redissolve to a perceptible extent in an excess of the pre- cipitant, and are precipitated by bicarbonate of soda even from acid solutions . . .320 a. Narcotina, 223 . . 320 &. Quina, 234 . . . 321 c. Cinchonia, 235 . . . 322 Recapitulation and remarks, 236 323 THIRD GROUP. Non-volatile alkaloids which are pre- cipitated by potassa from the solutions of their salts, and do not redissolve to a perceptible extent in an excess of precipi- tant, but are not precipitated from acid solutions by the bicar- bonates of the fixed alkalies . 324 a. Strychnia, 237 . . . 324 b. Brucia, 238 . . . 326 c. Veratria, 239 . . . 327 Recapitulation and remarks, 240 328 Salicine, 241 ... 329 Systematic course for the detection of the alkaloids treated of in the preceding paragraphs, and of salicine .... 329 I. Detection of the alkaloids, and of salicine, in solutions supposed to contain only one of these sub- stances, 242 . . . 329 II. Detection of the alkaloids, and of salicine, in solutions supposed to contain several or all of these substances, 243 . . . 331 Detection of the alkaloids, in presence PAGE of coloring and extractive vege- table or animal matters, 244 332 1. Stas's method of detecting poi- sonous alkaloids . . . 333 2. Otto's modifications of Stas's me- thod 335 3. Uslar and Erdmann's method . 335 4. Method of detecting strychnia, based upon the use of chloroform 337 a. Rodgers and Gird wood's method 337 6. Prollin's method . . 337 5. Method of effecting the detection of strychnia in beer, by Graham and Hofmann . . .337 6. Separation by dyalisis . . 338 II. General plan of the order and suc- cession in which substances should be analyzed for practice, 245 .... 338 III. Arrangement of the results of the analysis performed for practice, 246 339 IV. Table of the more frequently occur- ring forms and combinations of the substances treated of in the present work ; arranged with special regard to the ciass to which they respectively belong, according to their solubility in water, in hydrochloric acid, ni- tric acid, or nitrohydrochloric acid 342 Preliminary remarks, 247 . . 342 Table . . . . . 344 Notes .: ... 344 V. Table of weights and measures . 347 INDEX 349 PART I. INTRODUCTORY. PRELIMINARY REMARKS. DEFINITION, GENERAL PRINCIPLES, OBJECTS, UTILITY, AND IMPORTANCE OF QUALITATIVE CHEMICAL ANALYSIS CONDITIONS AND REQUIREMENTS FOR A SUCCESSFUL STUDY OF THAT SCIENCE. CHEMISTRY is the science which treats of the various materials entering into the structure of the earth, their composition and decomposition, their mutual relations and their deportment in general. A special branch of this science is designated Analytical Chemistry, inasmuch as it pursues a distinct and definite object viz. the analysis of compound bodies, and the determination of their component elements. Analytical chemistry, again, is subdivided into two branches viz. qualitative analysis, which simply studies the nature and properties of the com- ponent parts of bodies ; and quantitative analysis, which ascertains the quantity of every individual constituent present. The office of qualitative analysis, therefore, is to exhibit the constituent parts of a substance of unknown composition in forms of known composition, from which the constitution of the body examined and the presence of its several com- ponent elements may be positively inferred. The efficiency of its method depends upon two conditions viz., 1st, it must attain the object in view with unerring certainty, and 2nd, it must attain it in the most expeditious manner. The object of quantitative analysis, on the other hand, is to exhibit the elements revealed by the qualitative investiga- tion in forms which will permit the most accurate estimate of their weight, or to effect by other means the determination of their quantity. These different ends are, of course, attained respectively by very different ways and means. The study of qualitative analysis must, therefore, be pursued separately from that of quantitative analysis, and must naturally precede it. Having thus generally denned the meaning and scope of qualitative analysis, we have now still to consider, in the first place, the preliminary information required to o/ualify students for a successful cultivation of this branch of science, the rank which it holds in the domain of chemistry, the bodies that fall within the sphere of its operations, and its utility and importance ; and, in the second place, the principal parts into which its study is divided. It is, above all, absolutely indispensable for a successful pursuit of qua- I. B 2 PRELIMINARY REMARKS. litative investigations that the student should possess some knowledge of the chemical elements, and of their most important combinations, as well as of the principles of chemistry in general j and that he should combine with this knowledge some readiness in the apprehension of chemical processes. The practical part of this science demands more- over strict order, great cleanness and neatness, and a certain skill in manipulation. If the student joins to these qualifications the habit of invariably ascribing the failures with which he may happen to meet to some error or defect in his operations, or, in other words, to the absence of some condition or other indispensable to the success of the experiment and a firm reliance on the immutability of the laws of nature cannot fail to create this habit he possesses every requisite to render his study of analytical chemistry successful. Now, although chemical analysis is based on general chemistry, and cannot be cultivated without some previous knowledge of the latter, yet, on the other hand, we have to look upon it also as one of the main pillars upon which the entire structure of the science rests, since it is of almost equal importance for all branches of theoretical as well as of practical chemistry ; and I need not expatiate here on the advantages which the physician, the pharmaceutist, the mineralogist, the rational farmer, the manufacturer, the artisan, and many others derive from it. This consideration would surely in itself be sufficient reason to re- commend a thorough and diligent study of this branch of science, even, if its cultivation lacked those attractions which yet it unquestionably possesses for every one who devotes himself zealously and ardently to it. The human mind is constantly striving for the attainment of truth j it delights in the solution of problems ; and where do we meet with a greater variety of them, more or less difficult of solution, than in the province of chemistry ? But as a problem to which, after long pondering, we fail to discover the key, wearies and discourages the mind ; so, in like manner, do chemical investigations, if the object in view is not attained if the results do not bear the stamp of truth, of unerring certainty. A half-knowledge is therefore, as indeed in every department of science, but more especially here, to be considered worse than no know- ledge at all ; and a mere superficial cultivation of chemical analysis is consequently to be particularly guarded against. A qualitative investigation may be made with a twofold view viz., either, 1st, to prove that a certain body is or is not contained in a sub- stance, e.g., lime in spring-water ; or, 2nd, to ascertain all the constituents of a chemical compound or mixture. Any substance may of course be- come the object of a chemical analysis. But all elements are not equally important for the purposes of practical chemistry, a certain number of them only being found more widely disseminated in nature, and more generally employed in phar- macy, in the arts and manufactures, and in agriculture, whilst the others are met with only as constituents of rarely occurring minerals ; the elements of the former class alone, therefore, and the more important of their compounds, will be considered more fully in the present work, whilst those of the latter class will be discussed more briefly and in a manner to enable the learner to separate, without difficulty, the study of the former from that of the latter. This arrangement will serve to render the study of the science more easy to beginners, and to lighten the labors of practical chemists. OPERATIONS. 3 The study of qualitative analysis is most properly divided into four principal parts viz., 1. CHEMICAL OPERATIONS. 2. REAGENTS AND THEIR USES. 3. REACTIONS, OR DEPORTMENT OF THE VARIOUS BODIES WITH REAGENTS. 4. SYSTEMATIC COURSE OF QUALITATIVE ANALYSTS. It will now be readily understood that the pursuit of chemical analysis requires practical skill and ability as well as theoretical knowledge ; and that, consequently, a mere speculative study of that science can be as little expected to lead to success as purely empirical experiments. To attain the desired end, theory and practice must be combined. SECTION I. OPERATIONS. I- THE operations of analytical chemistry are essentially the same as those of synthetical chemistry, though modified to a certain extent to adapt them to the different object in view, and to the small quantities operated upon in analytical investigations. The following are the principal operations in qualitative analysis. 2. 1. SOLUTION. The term " solution" in its widest sense, denotes the perfect union of a body, no matter whether gaseous, liquid, or solid, with a fluid, resulting in a homogeneous liquid. However, where the substance dissolved is gaseous, the term "absorption" is more properly made use of; and the solution of one fluid in another is more generally called a mixture. The application of the term solution, in its usual and more restricted sense, is confined to the perfect union of a solid body with a fluid. A solution is the more readily effected the more minutely the body to be dissolved is divided. The fluid by means of which the solution is effected, is called the solvent. We call the solution chemical, where the solvent enters into chemical combination with the substance dissolved ; simple, where no definite combination takes place. In a simple solution the dissolved body exists in the free state, and retains all its original properties, except those dependent on its form and cohesion ; it separates unaltered when the solvent is withdrawn. Com- mon salt dissolved in water is a familiar instance of a simple solution. The salt in this case imparts its peculiar taste to the fluid. On evapo- rating the water, the salt is left behind in its original form. A simple solution is called saturated if the solvent has received as much as it can retain of the dissolved substance. But as fluids dissolve generally larger quantities of a substance the higher their temperature, the term saturated, as applied to simple solutions, is only relative, and refers invariably to a certain temperature. It may be laid down as a general rule that eleva- tion of temperature facilitates and accelerates simple solution. B 2 4 -SOLUTION. A chemical solution contains the dissolved substance not in the same state nor possessed of the same properties as before ; the dissolved body is no longer free, but intimately combined with the solvent, which latter also has lost its original properties ; a new substance has thus been pro- duced, and the solution manifests therefore now the properties of this new substance. A chemical solution also may be accelerated by elevation of temperature j and this is indeed usually the case, since heat generally promotes the action of bodies upon each other. But the quantity of the dissolved body remains always the same in proportion to a given quantity of the solvent, whatever may be the difference of temperature the combining proportions of substances being invariable and altogether independent of the gradations of temperature. The reason of this is, that in a chemical solution the solvent and the body upon which it acts have invariably opposite properties, which they strive mutually to neutralize. Further solution ceases as soon as this tendency of mutual neutralization is satisfied. The solution is in this case also said to be saturated or, more properly, neutralized, and the point which denotes it to be so is termed the point of saturation or neu- tralization. The substances which produce chemical solutions are, in most cases, either acids or alkalies. With few exceptions, they have first to be converted to the fluid state by means of a simple solvent. When the opposite properties of acid and base are mutually neutralized, and the new compound is formed, the actual transition to the fluid state will ensue only if the new compound possesses the property of forming a simple solution with the liquid present ; e.g., if solution of acetic acid in water is brought into contact with oxide of lead, there ensues, first, a chemical combination of the acid with the oxide, and then a simple solu- tion of the new-formed acetate of lead in the water of the menstruum. In pharmacy solutions are often made in a porcelain mortar, by triturating the body to be dissolved with the solvent added gradually in small quantities at a time ; in chemical laboratories solutions are rarely made in this manner, but generally by digesting or heating the substance to be dissolved with the fluid in beaker- glasses, flasks, test-tubes, or dishes. In the preparation of chemical solutions the best way generally is to mix the body to be dissolved in the first place with water (or with whatever other indifferent fluid may happen to be used), and then gradually add the chemical agent. By this course of proceeding a large excess of the latter is avoided, an over- energetic action guarded against, the process greatly facilitated, and complete solution ensured, which is a matter of some importance, as it will not seldom happen in chemical combinations that the product formed refuses to dissolve if an excess of the chemical solvent is present ; in which case the molecules first formed of the new salt, being insoluble in the menstruum present, gather round and enclose the particles still unacted on, weakening thereby or prevent- ing altogether further chemical action upon them. Thus, for instance, Witherite (carbonate of baryta) dissolves readily if water is poured upon the pulverised mineral and hydrochloric acid gradually added ; but it dissolves with difficulty and imperfectly if it is projected into a concen- trated solution of hydrochloric acid in water ; since chloride of barium will indeed dissolve in water, but not in hydrochloric acid. CRYSTALLIZATION and PRECIPITATION are the reverse of solution, since they have for their object the conversion of a fluid or dissolved substance CRYSTALLIZATION. 5 to the solid state. As both generally depend on the same cause, viz., on the absence of a solvent, it is impossible to assign exact limits to either ; in many cases they merge into one another. We must, however, con- sider them separately here, as they differ essentially in their extreme forms, and as the special objects which we purpose to attain by their application are generally very different. 3. 2. CRYSTALLIZATION. We understand by the term crystallization, in a more general sense, every operation or process whereby bodies are made to pass from the fluid to the solid state, and to assume certain fixed, mathematically definable, regular forms. But as these forms, which we call crystals, are the more regular, and consequently the more perfect, the more slowly the operation is carried on, we always connect with the term " crystal- lization" the accessory idea of & slow separation of & gradual conversion to the solid state. The formation of crystals depends on the regular arrangement of the ultimate constituent particles of bodies (molecules or atoms) it can only take place, therefore, if these atoms possess perfect freedom of motion, and thus in general only when a substance passes from the fluid or gaseous to the solid state. Those instances in which the mere ignition, or the softening or moistening of a solid body, suffices to make the tendency of the molecules to a regular arrangement (crystal- lization) prevail over the diminished force of cohesion such as, for instance, the turning white and opaque of moistened barley-sugar are to be regarded as exceptional cases. To induce crystallization, the causes of the fluid or gaseous form of a substance must be removed. These causes are either lieat alone, e.g., in the case of fused metals ; or solvents alone, as in the case of an aqueous solution of common salt ; or both combined, as in the case of a hot satu- rated solution of nitrate of potassa in water. In the first case we accord- ingly obtain crystals by cooling the fused mass ; in the second by evapo- rating the menstruum ; and in the third by either of these means. The most frequently occurring case is that of crystallization by cooling hot saturated solutions. The liquors which remain after the separation of the crystals are called mother-waters or mother-liquors. The term, amor- phous is applied to such solid bodies as have no crystalline form. We have recourse to crystallization mostly either to obtain the crystal- lized substance in a solid form, or to separate it from other substances dissolved in the same menstruum. In many cases also the form of the crystals or their deportment in the air, viz., whether they remain unal- tered or effloresce or deliquesce upon exposure to the air, will afford an excellent means of distinguishing between bodies otherwise resembling each other ; for instance, between sulphate of soda and sulphate of potassa. The process of crystallization is usually effected in evaporating dishes or, for very small quantities, in watch-glasses. In cases where the quantity of fluid to be operated upon is only small, the surest way of getting well-formed crystals is to let the fluid evaporate in the air or, better still, under a bell-glass, under which is also placed an open vessel half-filled with concentrated sulphuric acid. Minute crystals are examined best with a lens or under the microscope. O PRECIPITATION. * 3. PRECIPITATION. This operation differs from the preceding in this, that the dissolved body is converted to the solid state, not slowly and gradually, but suddenly, no matter whether the substance separating is crystalline or amorphous, whether it sinks to the bottom of the vessel or ascends or remains suspended in the liquid. Precipitation is either caused by a modification of the solvent thus sulphate of lime (gypsum) separates immediately from its solution in water upon the addition of alcohol ; or it ensues in consequence of the separation of an educt insoluble in the menstruum thus metallic copper precipitates if a solution of chloride of copper is brought into contact with zinc, as this separates the copper from the chlorine, and the eliminated metal is insoluble in the water of the menstruum. Precipitation, lastly, takes place also where, by the action of simple or double chemical affinity, new compounds are formed which are insoluble in the menstruum ; thus oxalate of lime precipitates upon addition of oxalic acid to a solution of acetate of lime ; chrornate of lead if chromate of potassa in solution is mixed with solution of nitrate of lead. In decompositions of this kind, induced by simple or double affinity, one of the new compounds remains generally in solution, and the same is sometimes the case also with the educt ; thus in the instances just mentioned the chloride of zinc, the acetic acid, and the nitrate of potassa remain in solution. It may, however, happen also that both the product and the educt, or two products, precipitate, and that nothing remains in solution ; this is the case, for instance, when a solution of sulphate of magnesia is mixed with water of baryta, or when a solution of sulphate of silver is precipitated with chloride of barium. Precipitation is resorted to for the same purposes as crystallization, viz., either to obtain a substance in the solid form, or to separate it from other substances dissolved in the same menstruum. But in qualitative analysis we have recourse to this operation more particularly for the purpose of detecting and distinguishing substances by the color, pro- perties, and general deportment which they exhibit when precipitated either in an isolated state or in combination with other substances. The solid body separated by this process is called the precipitate, and the sub- stance which acts as the immediate cause of the separation is termed the precipitant. Various terms are applied to precipitates by way of particu- larizing them according to their different nature ; thus we distinguish crystalline, pulverulent, flocculent, curdy, gelatinous precipitates, &c. The terms turbid and turbidity, or cloudy and cloudiness, are made use of to designate the state of a fluid which contains a precipitate so finely divided and so inconsiderable in amount, that the suspended particles, although impairing the transparency of the fluid, yet cannot be clearly distinguished. The separation of flocculent precipitates may generally be promoted by a vigorous shake of the vessel ; that of crystalline preci- pitates, by stirring the fluid and rubbing the inside of the vessel with a glass rod ; lastly, elevation of temperature is also an effective means of promoting the separation of most precipitates. The process is therefore conducted, according to circumstances, either in test-tubes, flasks, or beakers. FILTHATION. The two operations described respectively in 5 and 6, viz. filtration and decantation, serve to effect the mechanical separation of fluids from matter suspended therein. 5. 4. FILTRATION. This operation consists simply in passing the fluid from which we wish to remove the solid particles mechanically suspended therein through a filtering apparatus, formed usually by a properly folded piece of unsized paper placed in a funnel. An apparatus of this description allows the fluid to trickle through with ease, whilst it completely retains the solid particles. We employ smooth filters and plaited filters ; the former in cases where the separated solid substance is to be made use of, the latter in cases where it is simply intended to clear the solution. Smooth filters are prepared by double-folding a circular piece of paper, with the folds at right angles ; they must in every part fit close to the funnel. The preparation of plaited filters is more properly a matter for ocular demonstration than for description. In cases where the contents of the filter require washing, the paper must not project over the rim of the funnel. It is in most cases advisable to moisten the filter previously to passing the fluid through it ; since this not only tends to accelerate the process, but also to prevent the solid particles being carried through the pores of the filter. The paper selected for filters must be as free as possible from inorganic substances, especially such as are dissolved by acids, as sesquioxide of iron, lime, s proposed, /ittu- 8en*8, as shown in its simplest, form in Figs. 14 and 15, is tho most convenient. (i l> is :i toot, of cast iron measuring 7 cen- timetres in diameter. In the centre of this is fixed a square brass box, c millimetres high and 1C millimetres wide; it has a cylindrie cavity of \'l millimet res deep and 10 mil- limetres in diameter. Kach side of the box has, 4 millimetres from tho upper rim, a circular aperture of S millimetres diameter, leading to tlie inner ca\ity. One of tho sides has fitted into it, 1 milli- metre below the circular aperture, a tube over which is drawn vulcanized india- rubber which serves to convey the gas to tho apparatus. This tube is turned in tho shape shown in Fig. 14; it has a bore of 4 millimetres diameter. The gas conveyed into it through the india- rubber re- issues from a tube placed in the centre of the cavity of the box. This tube, which is -1 millimetres thick at the top, thicker at the lower end, projects 3 millimetre above the rim of the box; the gas issues from a narrow opening which appears formed of 3 radii of a circle, inclined to each other at an angle of 1-0'. The length of each radius is 1 milli- metre ; the opening of the slit is J millimetre wide ; e /is a brass tube 90 millimetres long, open at both ends, and having an inner diameter of 9 millimetres; the screw at the lower end of this tube tits into a nut in the tipper part- of the cavity of the box. With this tube screwed in, the lamp is completed. On opening the stop-cock the gas rushes from the tritid slit into the tube e f, where it mixes with tho air coming in through the circular apertures (c). When this mixture is kindled at/, it burns with a straight, upright, bluish flame, entirely tree from soot, which may be regulated at will by opening the stop cock more or less; a partial opening of the cock suffices to give a flame fully answering the purpose of the common simple spirit-lamp ; whilst with the full stream of gas turned on, the flame, which will now rise up to 2 decimetres in height, burning with a roaring noise, affords a most excellent. substitute for the Berzelius lamp. If the flame is made to burn very low, it will often occur that it recedes; in other words, that instead of the mixture of gas and air burning at the mouth of the tube a f, the gas takes fire on issuing from the slit, and burns Fig. 14. TIIK USK 01' I, A Mrs. 19 below in the tube. This delect may bo j>erfectly obviated by covering tho tube < f at the j..p uitha linl,. w irc cap. Flasks, \ eal.le ring on the same pillar serves to support the objects to be operated upon. The I) radii round the tube of (he lamp serve to support an iron-plate chimney (see Fig. 1C), or a porcelain plate used in quan- titative analyses. To heat crucibles to the brightest red heat, or to a white heat, the gas-blast ia resorted to. But even without this the action of the gas- lamp may be considerably heightened by ] i rating the crucible within a small clay fur- nace, as recommended by O. L. ERDMANN. Fi>f. 1C shows tho simple contrivance by which this is effected. The furnaces are 115 millimetres high, and measure 70 milli- metres diameter in the clear. The thickness of material is 8 millimetres. ttn-n,Mn* has devised also a somewhat im- proved form of his lamp, to fit it for processes of reduction, oxidation, fusion, and volatiliza- tion, and also to serve as a substitute for the blowpipe-blast. ' Fig. 15. Fig. 16. (See The illustration shows the part a, which is fitted for screwing on and off; also the conical iron-plate chimney, 6, which is 30 millimetres * Ann. d. Chem. u. Pharm., iii. 257. c 2 THE USE OF LAMPS. Fig. 17. wide at the top, and 55 millimetres at the bottom, and rests on the supporters c ccc in such a manner that the burner-tube d is placed in the axis of the chimney and ends 45 millimetres below the upper mouth of the lat- ter. As this construction, on the one hand, permits an easy regulation of the access of air, the chimney, on the other hand, ensures a tall, steady, and evenly-burning flame of the shape shown in the illustration. Looking atten- tively at the flame in the illustration, we distinguish in it an inner part and two mantles surrounding it. The inner part corresponds to the dark nucleus of the common candle, oil or gas flame, and contains the mixture of gas and air issuing from the burner. If the gas- cock is so adjusted that the apex of the inner part of the flame is on an exact level with the upper mouth of the chimney, a flame is obtained of perfectly constant dimensions, which remains quite steady, and is sharply defined in its parts, and may also, at all times, be reproduced in exactly the same condition. The mantle imme- diately surrounding the inner part contains still some unconsumed carbide of hydrogen ; the outer mantle, which looks bluer and less lumi- nous, consists of the last products of combustion. The hottest part of the flame has, according to Bunsen's calculation, a temperature of 2300 centigrade (4172 Fahrenheit.) This hottest part lies in the mantles surrounding the inner part of the flame, in a zone extending a few millimetres upwards and downwards from the transverse section of the flame across the apex of the inner part. We will term this region the zone effusion. BUNSEN calls it the " Schinelzrauin? It serves to try the deportment of bodies at a temperature of about 2300 centigraue (4172 Fahrenheit.) The outer margin of this zone of fusion acts as oxidizing flame, the inner part of it as reducing flame. The spot where the reducing action is the most powerful and energetic lies immediately above the apex of the inner part of the flame. The flame of this lamp is most admirably suited to bring out the coloration which many sub- stances impart to flames, and by which the attentive observer is enabled to detect many bodies, even though present in such exceedingly minute traces that all other known means of detection fail to discover them. The subject of the coloration of flames will be discussed more fully in the next paragraph. Here we will simply state, in addition, that the substitution of the gas-flame in lieu of the blowpipe affords the great advantage that the samples for examination may be placed, by means of a holder, in any desired part of the flame, and kept there quite fixed and immoveable. A holder of the kind required is shown in Fig. 18. The arm a is easily moved along the pillar c by means of the spring slide b. The glass tube d, which bears, fused into its sealed end, a platinum wire about 0.145 millimet. thick, with the outer end twisted into a small loop, is pushed over the horizontal arm a. If this loop is moistened, and then dipped into the powder of the substance to be examined, a portion OBSERVATION OF THE COLORATION OF FLAME. 21 of the powder adheres to it. If this loop is now held near the flame, the powder agglutinates or fuses, and sticks fast to the loop, which is then thrust into the desired part of the flame. Decrepitating substances must previously be ig- nited in a covered platinum crucible. If fluids are to be examined, with a view to ascertain whether they hold flame-coloring substances in solution, the round loop of the platinum wire is flattened by a few blows with the hammer into the shape of a platinum ring. If this is dipped into the fluid to be examined, and taken out again, there remains adhering to the inner circle a drop of the liquid. This is evaporated by holding the loop near the flame, taking care, however, to keep the liquid from boiling, and the residue is then examined by thrusting the loop into the zone of fusion. (BUNSEN). Fig. 18. 14. OBSERVATION OP THE COLORATION OF FLAME BY CERTAIN BODIES AND SPECTRUM ANALYSIS. Many substances have the property of coloring a colorless flame in a very remarkable manner. As most of these substances impart each of them a different and distinct, and accordingly characteristic, tint to the flame, the observation of this colorization of flame affords an excellent, easy, and safe means of detecting many of these bodies. Thus, for instance, salts of soda impart to flame a yellow, salts of potassa a violet, salts of lithia a carmine tint, and may thus be easily distinguished from each other. The flame of BUNSEN'S gas-lamp, with chimney, described in 14, and shown in Fig. 17, is more particularly suited for observations of the kind. The substances to be examined are put on the small loop of a fine platinum wire, and thus, by means of the holder shown in Fig. 18, placed within the zone of fusion of the gas-flame. A particularly striking coloration is imparted to the flame by the salts of the alkalies and alkaline earths. If different salts of one and the same base are com- pared in this way, it is found that every one of them, if at all volatile at high temperatures, or permitting at least the volatilization of the base, imparts the same color to the flame, only with different degrees of intensity, the most volatile of the salts producing also the most intense colorization ; thus, for instance, chloride of potassium gives a more intense coloration than carbonate of potassa, and this latter again a OBSERVATION OF THE COLORATION OF FLAME more intense one than silicate of potassa. In the case of difficultly volatile compounds, the coloration of the flame may often be brought about, or made more apparent, by adding some other body which has the power of decomposing the compound under examination. Thus, for instance, in silicates containing only a few per cents of potassa, the latter body cannot be directly detected by coloration of flame ; but this detec- tion may be accomplished by adding to the silicate a little pure gypsum, as this will cause formation of silicate of lime and of sufficiently volatile sulphate of potassa. But however decisive a test the mere coloration of flame affords for the detection of certain metallic compounds, when present unmixed with others, this test becomes apparently quite useless in the case of mixtures of compounds of several nietals. Thus, for instance, mixtures of salts of potassa and soda show only the soda flame, mixtures of salts of baryta and strontia only the baryta flame, &c. This defect may be remedied, however, in two ways, with the most surprising success. Both ways have only quite recently been discovered. The one way, started first by CARTMELL,* and perfected afterwards by BuNSENf and by MERZ, J consists in looking at the colored flame through some colored medium (colored glasses, indigo solution, &c.). Such colored media, in effacing the flame coloration of the one metal, bring out that of the other metal mixed with it. For instance, if a mixture of a salt of potassa and a salt of soda is exposed to the flame, the latter will only show the yellow soda coloration ; but if the flame be now looked at through a deep-blue-tinted cobalt glass, or through solution of indigo, the yellow soda coloration will disappear and will be replaced by the violet potassa tint. A simple apparatus suffices for all observations and experiments of the kind ; all that'is required for the purpose being, 1. A hollow prism (see Fig. 19) composed of mirror plates, the chief section of which forms a triangle with two sides of 150 millimetres, and one side of 35 millimetres length. Fig. 19. The indigo solution required to fill this prism is prepared by dissolving 1 part of indigo in 8 parts of fuming sulphuric acid, adding to the solution 1800-2000 parts of water, and filtering the fluid. When using this apparatus, the prism is moved in a horizontal direction close before the eyes in such a way that the rays of the flame are made to penetrate suc- cessively thicker and thicker layers of the effacing medium. 2. A blue, a violet, a red, and a green glass. The blue glass is tinted with protoxide of cobalt ; the violet glass with sesquioxide of man- ganese ; the red glass (partly colored, partly uncolored) with suboxide of copper ; and the green glass with sesquioxide of iron and protoxide of * Phil. Mag., xvi. 328. f Annal. d. Chem. u. Pharm., iii. 257. J Journ. f. prakt. Chem., 80, 487. BY CERTAIN BODIES. 23 copper. The common colored glasses sold in the shops for ornament- ing windows, will generally be found to answer the purpose. As regards the tints imparted to the flame by the different bodies, when viewed through the aforesaid media, and their combinations, by which these bodies are severally identified, the information required will be found in Section III., in the paragraphs treating of the several bases and acids. The other method, which is called Spectrum Analysis, was discovered by KIRCHHOFF and BUNSEN. It consists in letting the rays of the colored flame pass first through a narrow slit, then through a prism, and ob- serving the so refracted rays through a telescope. A distinct spectrum is thus obtained for every flame-coloring metal : this spectrum consists either, as in the case of baryta, of a number of colored lines lying side by side ; or, as in the case of lithia, of two separate, differently-colored lines ; or, as in the case of soda, of a single yellow line. These spectra are charac- teristic in a double sense viz., the spectrum lines have a distinct color, and they occupy also a fixed position. It is this latter circumstance which enables us to identify without difficulty, in the spectrum observation of mixtures of flame-coloring metals, every individual metal. Thus, for instance, a flame in which a mixture of potassa, soda, and lithia salts is evaporated, will give, side by side, the spectra of the several metals in the most perfect purity. KIRCHHOFF and BUNSEN have constructed two kinds of apparatus, which are both of them suited for spectrum observation, and enable the operator to determine by measure the spots in which the spectrum lines make their appearance. Both are constructed upon the same principle. A description, with illustration, of the larger of the two, which is also the most perfect one, has been published in Poggendorjffs " Annalen," 113, 374, and in the "Zeitschrift fur Analytische Chemie," 1862, 49. Fig. 20 a. The smaller, more simple, and accordingly cheaper apparatus, which 24) OBSERVATION OF THE COLORATION OP FLAME. suffices for all common purposes, and will probably be used most in chemical laboratories, we will describe here. It is shown in Fig. 20 a. A is an iron disk, in the centre of which a prism, with circular re- fracting faces of about 25 millimetres diameter, is fastened by a bow, which presses upon the upper face of the prism, and is secured below to the iron plate by a screw. The same disk has also firmly fastened to it the three tubes B, C, and D. Each of these tubes is soldered to a metal block, of which Fig. 20 b gives an enlarged representation. This block contains the nuts for two screws, which pass through wider openings in the iron plate, and are firmly secured beneath when the tube has been adjusted in the proper position. B is the observation telescope ; it has a magnifying power of about 6, with an object-glass of 20 millimetres diameter. The tube C is closed at one end by a tin-foil disk, into which the perpendicular slit is cut through which the light is admitted. The tube D carries a photographic copy of a millimetre- scale, produced in the camera obscura on a glass plate of about one- fifteenth the original dimensions. This scale is covered with tin- foil, with the exception of the narrow strip upon which the divisional lines and the numbers are engraved. It is lighted by the flame of a taper or candle placed close behind it. The axes of the tubes B and D are directed, at the same inclination, to the centre of one face of the prism, whilst the axis of the tube C is directed to the centre of the other face of the prism. This arrangement makes the spectra produced by the refraction of the colored light passing through C, and the image of the scale in D produced by total reflection appear in one and the same spot, so that the positions occupied by the spectrum lines may be read off on the scale. The prism is placed in about that position in which there is a minimum divergence of the rays of the sodium line ; and the telescope is set in that direction in which the red and the violet potassium lines are about equidistant from the middle of the field of view. The colorless flame into which the flame-coloring bodies are to be introduced, is placed 10 centimetres from the slit. BUNSEN'S lamp de- scribed page 19, and shown in Fig. 17, gives the best flame. The lamp is adjusted so as to place the upper border of the chimney about 20 mil- limetres below the lower end of the slit. When this lamp has been lighted, and a bead of substance say of sulphate of potassa, for instance introduced into the zone of fusion by means of the holder described page 20, and shown in Fig. 18, the iron disk of the spectrum apparatus, which, with all it carries, is moveable round its vertical axis, is turned until the point is reached where the luminosity of the spectrum is the most intense. To cut off foreign light in all spectrum observations, a black cloth, with three circular openings in it for the three tubes, is thrown over the prism and the tubes. The spectra produced by the alkalies and the alkaline earths are shown in Table I., Fig. 1. The solar spectrum has been added simply as a guide to the position and bearings of the lines. The spectra are represented as they appear in the apparatus furnished with an astronomic telescope. In the third section, in the chapters treating of the several bodies, attention will be called to the lines which are most characteristic for each metal. Here 1 will simply state the manner in which the highest degree of certainty is imparted to spectrum analysis. This is done by exposing the beads of the pure and unmixed APPARATUS AND UTENSILS. 25 metallic compounds to the flame, and marking on copied scales the posi- tion which the most striking spectrum lines occupy on the scale of the apparatus, in the manner shown, by way of illustration, in Table I., Fig. 2, with regard to the strontium spectrum. It is self-evident that the spectrum of an unknown substance can only pass for the strontium spectrum, if the characteristic lines not only agree with those of the latter in point of color, but appear also in exactly the same position where they are marked on the strontium scale. The drawings of such scales every operator must, of course, make for his own apparatus ; and they become useless for the intended purpose if any alteration is made in the position of the prism or the scale. It is therefore always advisable to set the apparatus so , that it can be easily readjusted to its original position, which is most readily done by making the left border of the sodium line coincide with the number 50 of the scale. With the introduction of spectrum analysis a new era has, in many respects, begun for chemical analysis, as by means of this discovery we can detect such minute quantities of bodies as by no other method. Spectrum analysis is marked moreover by a certainty above all doubt, and gives results in a few seconds, which could formerly be obtained only, if at all, in hours or days. APPENDIX TO SECTION I. 16. APPARATUS AND UTENSILS. As many students of chemical analysis might find some difficulty in the selection of the proper apparatus, &c., I append here a list of the articles which are required for the performance of simple experiments and investigations, together with instructions to guide the student in the purchase or making of them. 1. A BERZELIUS SPIRIT LAMP ( 14, Fig. 11). 2. A GLASS SPIRIT LAMP ( 14, Fig. 13). Or, instead of these two, where coal-gas is procurable, a Bunseris Gas-lamp, best one with chaplet and chimney ( 14, Figs. 14, 15, and 17). 3. A BLOWPIPE (see 13). 4. A PLATINUM CRUCIBLE. Select a crucible which will contain about a quarter of an ounce of water, with a cover shaped like a shallow dish j it must not be too deep in proportion to its breadth. 5. PLATINUM FOIL, as smooth and clean as possible, and not very thin : length about 40 millimetres ; width about 25 millimetres. 6. PLATINUM WIRE (see 13 and 14, Figs. 10 and 18). Three stronger wires and three finer wires are amply sufficient. They are kept most conveniently in a glass filled with water, most of the beads being dissolved by that fluid when left in contact with it for some time j the wires may thus be kept always clean. 26 APPARATUS AND UTENSILS. Fig. 21. 7. A STAND WITH TWELVE TEST TUBES 1 6 to 1 8 centimetres is about the proper length of the tubes, from 1 to 2 centimetres the proper width. The tubes must be made of thin white glass, and so well annealed that they do not crack even though boiling water be poured into them. The rim must be quite round, and slightly turned over ; it ought not to have a lip, as this is useless and simply prevents the tube being closely stopped with the finger, and also shaking the contents. The stand shown in Fig. 21 will be found most suitable. The pegs on the upper shelf serve for the clean tubes, which may thus be always kept dry and ready for use. 8. SEVERAL BEAKER GLASSES AND SMALL RETORTS of thin, well annealed glass. 9. SEVERAL PORCELAIN EVAPORATING DISHES, AND A VARIETY OF SMALL PORCELAIN CRUCIBLES. Those of the royal manufacture of Berlin are unexceptionable, both in shape and durability. Meissen porcelain will also answer the purpose. 10. SEVERAL GLASS FUNNELS of various sizes. They must be inclined at an angle of 60, and merge into the neck at a definite angle. 11. A WASHING BOTTLE of a capacity of from 300 to 400 cubic centi- metres (see 6). 12. SEVERAL GLASS RODS AND GLASS TUBES. The latter are bent, drawn out, &c., over a Berzelius spirit-lamp ; the former are rounded at the ends by fusion. 1 3. A selection of WATCH-GLASSES. 14. A small AGATE MORTAR. 15. A pair of small STEEL or BRASS PINCERS, about four or five inches long. 1 6. A WOODEN FILTERING STAND (see 5). 17. A TRIPOD of thin iron, to support the dishes, &c., which is in- tended to heat over the small spirit or gas lamp: 18. The Colored Glasses described in 15, especially blue and green. REAGENTS. 27 SECTION II. REAGENTS. 17. A VARIETY of phenomena may manifest themselves upon the decom- position or combination of bodies. In some cases liquids change their color, in others precipitates are formed; sometimes effervescence takes place, and sometimes deflagration, a test for lead. * The evaporation is attended with copious evolution of sulphurous acid. 54 GRANULAR ANTIMONATE OF POTASSA. 51. 10. GRANULAR ANTIMONATE OF POTASSA (KO,Sb0 5 + 7aq.). Preparation. Project a mixture of equal parts of pulverized tartar- emetic and nitrate of potassa in small portions at a time into a red- hot crucible. After the mass is deflagrated, keep it at a moderate red heat for a quarter of an hour longer, which will make it froth at first, but after some time it will be seen in a state of calm fusion. Remove the crucible now from the fire, let the mass get sufficiently cold, and then extract it with warm water. Transfer to a suitable vessel, which is easily done by rinsing, and decant the supernatant clear fluid from the heavy white powder deposit. Concentrate the decanted fluid by evaporation. After 1 or 2 days a doughy mass will separate. Treat this mass with three times its volume of cold water, working it at the same time with a spatula. This operation will serve to convert it into a fine granular powder, to which add the powder from which the fluid was decanted, wash slightly, and dry on blotting paper. 100 parts of tartar-emetic give about 36 parts of antimonate of potassa (BRUNNER). Tests and Uses. Granular antimonate of potassa is very sparingly soluble in water, requiring 90 parts of boiling and 250 parts of cold water for solution. The solution had always best be prepared imme- diately before required for use, by repeatedly shaking the salt with cold water, and filtering off the fluid from the undissolved portion. The solution must be clear and of neutral reaction ; it must give no precipi- tate with solution of chloride of potassium, nor with solution of chloride of ammonium ; but solution of chloride of sodium must produce a crystalline precipitate in it. Antimonate of potassa is a valuable reagent for soda, but only under certain conditions, for which see 90. 52. 11. MOLYBDATE OF AMMONIA (NH 4 0, MoO g ), DISSOLVED IN NlTRIC ACID. Preparation. Triturate sulphide of molybdenum with about an equal bulk of coarse quartz sand washed with hydrochloric acid, until the mass is reduced to a moderately fine powder ; heat the powder to faint red- ness, with repeated stirring, until the mass has acquired a lemon -yellow color (which after cooling turns whitish). With small quantities this operation may be conducted in a flat platinum dish, with large quantities in a muffle. Extract the residuary mass with solution of ammonia, filter, evaporate the filtrate, heat the residue to faint redness until the mass appear yellow or white, and then digest this residuary mass for several days with nitric acid in the water bath, in order to convert the phosphoric acid which is almost invariably present in the ore to the tribasic state. When the nitric acid is evaporated dissolve the residue in 4 parts of solution of ammonia, filter rapidly, and pour the filtrate into 15 parts by weight of nitric acid of 1*20 specific gravity. Keep the mixture standing several days in a moderately warm place, which will cause the separation of any remaining traces of phosphoric acid or phos- pho-molybdate of ammonia. Decant the colorless fluid from the precipi- CHLORIDE OF AMMONIUM. 55 tate, and keep it for use. Heated to 104 Fahrenheit no white precipi- tate (molybdic acid or a molybdate) will separate ; but if the temperature is raised beyond that point this will at once take place unless more nitric or hydrochloric acid be added (EGGERTZ). Uses. Phosphoric acid and arsenic acid form with molybdic acid and ammonia peculiar yellow compounds which are almost absolutely in- soluble in the nitric acid solution of molybdate of ammonia. Molybdate of ammonia affords therefore an excellent means to detect these acids, and more especially very minute quantities of phosphoric acid in acid solutions containing sesquioxide of iron, alumina, and alkaline earths. 53. 12. CHLORIDE OF AMMONIUM (NH 4 ,C1). Preparation. Select sublimed white sal ammoniac of commerce. If it contains iron it must be purified. For that purpose add some sulphide of ammonium to the solution, let the precipitate which forms subside, and filter ; add hydrochloric acid to the filtrate until the latter manifests a feebly acid reaction ; boil the mixture some time, saturate with ammonia, filter if necessary, and crystallize. Dissolve 1 part of the salt in 8 parts of water for use. Tests. Solution of chloride of ammonium must upon evaporation on a platinum knife leave a residue which volatilizes completely upon con- tinued application of heat. Sulphide of ammonium must leave it un- altered. Its reaction must be perfectly neutral. Uses. Chloride of ammonium serves principally to retain in solution certain oxides (e.g. protoxide of manganese, magnesia) or salts (e.g. tartrate of lime) upon the precipitation of other oxides or salts by ammonia or some other reagent. This application of chloride of ammonium is based upon the tendency of the ammonia salts to form double compounds with other salts. Chloride of ammonium serves also to distinguish between precipitates possessed of similar properties ; for instance, to distinguish the basic phosphate of magnesia and ammonia, which is insoluble in chloride of ammonium, from other precipitates of magnesia. It is used also to precipitate from their solutions in potassa various substances which are soluble in that alkali, but insoluble in ammonia j e.g. alumina, sesquioxide of chromium, &c. In this process the elements of the chlo- ride of ammonium transpose with those of the potassa, and chloride of potassium, water, and ammonia are formed. Chloride of ammonium is applied also as a special reagent to effect the precipitation of platinum as aminonio-bichloride of platinum. 54. 13. CYANIDE OF POTASSIUM (KCy). Preparation. Heat ferrocyanide of potassium of commerce (perfectly free from sulphate of potassa) gently, with stirring, until the crystalli- zation water is completely expelled ; triturate the anhydrous mass, and mix 8 parts of the dry powder with 3 parts of perfectly dry carbonate of potassa ; fuse the mixture in a covered Hessian or, better still, in a covered iron crucible, until the mass is in a faint glow, appears clear, and a sample of it, taken out with a heated glass or small iron rod, looks 56 FERROCYANIDE OP POTASSIUM. perfectly white. Remove the crucible now from the fire, tap it gently, and let it cool a little until the evolution of gaa has ceased ; pour the fused cyanide of potassium into a heated tall, crucible-shaped vessel of clean scoured iron or silver, or into a moderately hot Hessian crucible, with proper care, to prevent the running out of any of the minute par- ticles of iron which have separated in the process of fusion and have sub- sided to the bottom of the crucible. Let the mass now slowly cool in a somewhat warm place. The cyanide of potassium so prepared is exceed- ingly well adapted for analytical purposes, although it contains carbonate and cyanate of potassa ; which latter is upon solution in water trans- formed into carbonate of ammonia and carbonate of potassa (K O, C 2 NO + 4 HO - KO, CO a + NH 4 0, CO 2 ). Keep it in the solid form in a well-stoppered bottle, and dissolve 1 part of it in 4 parts of water, without application of heat, when required for use. Tests. Cyanide of potassium must be of a milk-white color and quite free from particles of iron or charcoal. It must completely dis- solve in water to a clear fluid. It must contain neither silicic acid nor sulphide of potassium ; the precipitate which salts of lead produce in its solution must accordingly be of a white color, and the residue which its solution leaves upon evaporation, after previous supersaturation with hydrochloric acid,* must completely dissolve in water to a clear fluid. Uses. Cyanide of potassium prepared in the manner described pro- duces in the solutions of most of the salts with metallic oxides precipi- tates of cyanides of metals or of oxides or carbonates which are insoluble in water. The precipitated cyanides are soluble in cyanide of potassium, and may therefore by further addition of the reagent be separated from the oxides or carbonates which are insoluble in cyanide of potassium. Some of the metallic cyanides redissolve invariably in the cyanide of potassium as double cyanides, even in presence of free hydrocyanic acid and upon boiling ; whilst others combine with cyanogen to new radicals, which remain in solution in combination with the potassium. The most common compounds of this nature are cobalticyanide of potassium and ferro- and ferricyanide of potassium. These differ from the double cyanides of the other kind particularly in this, that dilute acids fail to precipitate the metallic cyanides which they contain. Cyanide of potas- sium may accordingly serve also to separate the metals which form com- pounds of the latter description from others the cyanides of which are precipitated by acids from their solution in cyanide of potassium. In the course of analysis this reagent is of great importance, as it serves to effect the separation of cobalt from nickel ; also that of copper, the sulphide of which metal is soluble in it, from cadmium, the sulphide of which is insoluble in this reagent. 55. 14. FERROCYANIDE OF POTASSIUM (2 K,C 6 N Fe + 3 aq. = 2 K, Cfy + 3aq.). Preparation. The ferrocyanide of potassium is found in commerce sufficiently pure for the purposes of chemical analysis. 1 part of the salt is dissolved in 12 parts of water for use. * This supersaturation with hydrochloric acid is attended with disengagement of hydrocyanic acid. FERRICYANIDE OT 1 POTASSIUM. 57 Uses. Ferrocyanogen forms with most metals compounds insoluble in water, which frequently exhibit highly characteristic colors. These ferrocyanides are formed when ferrocyanide of potassium is brought into contact with soluble salts of metallic oxides, with chlorides, &c., the potassium changing places with the metals. Ferrocyanide of copper and ferrosesquicyanide of iron exhibit the most characteristic colors of all ; ferrocyanide of potassium serves therefore particularly as a test for oxide of copper and sesquioxide of iron. 56. 15. FERRICYANIDE OP POTASSIUM (3K,C 12 N 6 Fe 2 = 3 KCfdy). Preparation. Conduct chlorine gas slowly into a solution of 1 part of ferrocyanide of potassium in 1 parts of water, with frequent stirring, until the solution exhibits a fine deep red color by transmitted light (the light of a candle answers best), and a portion of the fluid produces no longer a blue precipitate in a solution of sesquichloride of iron, but imparts a brownish tint to it. Evaporate the fluid now in a dish to J of its weight, and let crystallize. The mother liquor will upon further evaporation yield a second crop of crystals equally fit for use as the first. Dissolve the whole of the crystals obtained in 3 parts of water, filter if necessary; evaporate the solution briskly to half its volume, and let crystallize again. Whenever required for use, dissolve a few of the crystals, which are of a splendid red color, in a little water. The solu- tion, as already remarked, must produce neither a blue precipitate nor a blue color in a solution of sesquichloride of iron. Uses. Ferricyanide of potassium decomposes with solutions of me- tallic oxides in the same manner as ferrocyanide of potassium. Of the metallic ferricyanides the ferriprotocyanide of iron is more particularly characterized by its color, and we apply ferricyanide of potassium there- fore principally as a test for protoxide of iron. 57. 16. SULPHOCYANIDE OF POTASSIUM (K,C 3 NS 2 or K, Cy S a ). Preparation. Mix together 46 parts of anhydrous ferrocyanide of potassium, 17 parts of carbonate of potassa, and 32 parts of sulphur; introduce the mixture into an iron pan provided with a lid, and fuse over a gentle fire ; maintain the same temperature until the swelling of the mass which ensues at first has completely subsided and given place to a state of tranquil and clear fusion ; increase the temperature now, towards the end of the operation, to faint redness, in order to decompose the hyposulphite of potassa which has been formed in the process. Re- move the half refrigerated and still soft mass from the pan, crush it, and boil repeatedly with alcohol of from 80 to 90 per cent. Upon cooling, part of the sulphocyanide of potassium will separate in colorless crystals ; to obtain the remainder, distil the alcohol from the mother liquor. Dissolve 1 part of the salt in 10 parts of water for use. Tests. Solution of sulphocyanide of potassium must remain perfectly colorless when mixed with perfectly pure dilute hydrochloric acid. 58 CHLORIDE OF BARIUM. Uses. Sulphocyanide of potassium serves for the detection of sesqui- oxide of iron, for which substance it is at once the most characteristic and the most delicate test. 5. SALTS OF THE ALKALINE EARTHS. 58. 1. CHLORIDE OF BARIUM (BaCl + 2 aq.). Preparation. a. From heavy spar. Mix together 8 parts of pulverized sulphate of baryta, 2 parts of charcoal in powder, and 1 part of common resin. Put the mixture in a crucible, and expose it in a wind furnace to a long-continued red heat ; or put the mixture in an earthen pot, lute the lid on with clay, and expose to the heat of a brick-kiln (compare 34). Triturate the crude sulphide of barium obtained, boil about -f$ of the powder with 4 times its quantity of water, and add hydrochloric acid until all effervescence of sulphuretted hydrogen has ceased, and the fluid manifests a slight acid reaction. Add now the remaining J^ part of the sulphide of barium, boil some time longer, then filter, and let the alkaline fluid crystallize. Dry the crystals, redissolve them in water, and crystallize again, b. From Witherite. Pour 10 parts of water upon 1 part of pulverized Witherite, and gradually add crude hydrochloric acid until the Witherite is almost completely dissolved. Add now a little more finely pulverized Witherite, and heat, with frequent stirring, until the fluid has entirely or very nearly lost its acid reaction ; add solution of sulphide of barium as long as a precipitate forms; then filter, evaporate the filtrate to crystallization, and purify them by crystallizing again. For use dis- solve 1 part of the chloride of barium in 10 parts of water. Tests. Pure chloride of barium must not alter vegetable colors ; its solution must not be colored or precipitated by hydrosulphuric acid, nor by sulphide of ammonium. Pure sulphuric acid must precipitate every fixed particle from it, so that the fluid filtered from the precipitate formed upon the addition of that reagent leaves not the slightest residue when evaporated on platinum foil. Uses. Baryta forms with many acids soluble, with others insoluble compounds. This property of baryta affords us therefore a means of distinguishing the former acids, which are not precipitated by chloride of barium, from the latter, in the solution of the salts of which this reagent produces a precipitate. The precipitated salts of baryta severally show with other bodies (acids) a different deportment. By subjecting these salts to the action of such bodies we are therefore enabled to subdivide the group of precipitable acids and even to detect certain individual acids. This makes chloride of barium one of our most important re- agents to distinguish between certain groups of acids, and more especially also to effect the detection of sulphuric acid. 59. 2. NITRATE OF BARYTA (BaO,N0 6 ). Preparation. Treat carbonate of baryta, no matter whether Witherite or precipitated by carbonate of soda from solution of sulphide of barium, CARBONATE OF BARYTA. 59 with dilute nitric acid free from chlorine, and proceed exactly as directed in the preparation of chloride of barium from Witherite. For use dis- solve 1 part of the salt in 15 parts of water. Tests. Solution of nitrate of baryta must not be made turbid by solution of nitrate of silver. Other tests the same as for chloride of barium. Uses. Nitrate of baryta is used instead of chloride of barium in cases where it is desirable to avoid the presence of a metallic chloride in the fluid. 60. 3. CARBONATE OP BARYTA (BaO,C0 2 ). Preparation. Dissolve crystallized chloride of barium in water, heat to boiling, and add a solution of carbonate of ammonia mixed with some caustic ammonia, or of pure carbonate of soda, as long as a precipitate forms ; let the precipitation subside, decant five or six times, transfer the precipitate to a filter, and wash until the washing water is no longer rendered turbid by solution of nitrate of silver. Stir the pre- cipitate with water to the consistence of thick milk, and keep this mix- ture in a stoppered bottle. It must of course be shaken every time it is required for use. Tests. Pure sulphuric acid must precipitate every fixed particle from a solution of carbonate of baryta in hydrochloric acid (compare 34, caustic baryta). Uses. Carbonate of baryta completely decomposes the solutions of many metallic oxides, e.g. sesquioxide of iron, alumina ; precipitating from them the whole of the oxide as hydrate and basic salt, whilst some other metallic salts are not precipitated by it. It serves therefore to separate the former from the latter, and affords an excellent means of effecting the separation of sesquioxide of iron and alumina from prot- oxide of manganese, oxide of zinc, lime, magnesia, &c. It must be borne in mind, however, that the salts must not be sulphates, as carbonate of baryta equally precipitates the latter bases from these compounds. 61. 4. SULPHATE OF LIME (CaO,SO 8 , crystallized Ca 0,80,4-2 aq.). Preparation. Digest and shake powdered crystallized gypsum for some time with water ; let the undissolved portion subside, decant, and keep the clear fluid for use. Uses. Sulphate of lime, being a difficultly soluble salt, is a convenient agent in cases where it is wished to apply a solution of a lime salt or of a sulphate of a definite degree of dilution. As dilute solution of a lime salt it is used for the detection of oxalic acid ; whilst as dilute solution of a sulphate it affords an excellent means of distinguishing between baryta, strontia, and lime. 62. 5. CHLORIDE OF CALCIUM (CaCl, crystallized CaCl + 6aq.). Preparation. Dilute 1 part of crude hydrochloric acid with 6 parts of water, and add to the fluid marble or chalk until the last portion 60 SULPHATE OF MAGNESIA. added remains undissolved ; add now some hydrate of lime, then sul- phuretted hydrogen water until a filtered portion of the mixture is no longer altered by sulphide of ammonium. Then let the mixture stand 12 hours in a gentle heat ; filter, exactly neutralize the filtrate, concentrate by evaporation, and crystallize. Let the crystals drain, and dissolve 1 part of the salt in 5 parts of water for use. Tests. Solution of chloride of calcium must be perfectly neutral, and neither be colored nor precipitated by sulphide of ammonium ; nor ought it to evolve ammonia when mixed with hydrate of potassa or hydrate of lime. 27,9es. Chloride of calcium is in its action and application analogous to chloride of barium. For as the latter reagent is used to separate the inorganic acids into groups, so chloride of calcium serves in the same manner to effect the separation of the organic acids into groups, since it precipitates some of them, whilst it forms soluble compounds with others. And, as is the case with the baryta precipitates, the different conditions under which the various insoluble lime salts are thrown down enable us to subdivide the group of precipitable acids, and even to detect certain individual acids. 63. 6. SULPHATE OF MAGNESIA (MgO,S0 3 , crystallized MgO,S0 8 , H0 + 6aq.). Preparation. Dissolve 1 part of sulphate of magnesia of commerce in 10 parts of water; if the salt is not perfectly pure, subject it to re- crystallization. Tests. Sulphate of magnesia must have a neutral reaction. Its solu- tion, when mixed with a sufficient quantity of chloride of ammonium, must, after the lapse of half an hour, not appear clouded or tinged by pure ammonia, or by carbonate or oxalate of ammonia, or by sulphide of ammonium. Uses. Sulphate of magnesia serves almost exclusively for the detec- tion of phosphoric acid and arsenic acid, which it precipitates from aqueous solutions of phosphates and arsenates, in presence of ammonia and chloride of ammonium, in the form of almost absolutely insoluble highly characteristic double salts (basic phosphate or basic arsenate of magnesia and ammonia). Sulphate of magnesia is also employed to test the purity of sulphide of ammonium (see 40). c. SALTS OF THE OXIDES OF THE HEAVY METALS. 64. 1. SULPHATE OP PROTOXIDE OF IRON (FeO,SO a , crystallized FeO, Preparation. Heat an excess of iron nails free from rust, or of clean iron wire, with dilute sulphuric acid until the evolution of hydrogen ceases ; filter the sufficiently concentrated solution, add a few drops of dilute sulphuric acid to the filtrate, and allow it to cool. Wash the crystals with water very slightly acidulated with sulphuric acid, dry, and keep for use. The sulphate of protoxide of iron may also be prepared SESQUICHLOEIDE OF IRON. 61 from the solution of sulphide of iron in dilute sulphuric acid which is obtained in the process of evolving hydrosulphuric acid. Tests. The crystals of sulphate of protoxide of iron must have a fine pale green color. Crystals that have been more or less oxidized by the action of the air, and give a brownish-yellow solution when treated with water, leaving undissolved basic sulphate of sesquioxide of iron behind, must be altogether rejected. Hydrosulphuric acid must not precipitate solution of sulphate of protoxide of iron after addition of some hydro- chloric acid, nor even impart a blackish tint to it. Uses. Sulphate of protoxide of iron has a great disposition to absorb oxygen, and to be converted into the sulphate of the sesquioxide. It acts therefore as a powerful reducing agent. We employ it principally for the reduction of nitric acid, from which it separates nitric oxide by withdrawing three atoms of oxygen from it. The decomposition of the nitric acid being attended in this case with the formation of a very peculiar brownish-black compound of nitric oxide with an undecom- posed portion of the salt of the protoxide of iron, this reaction affords a particularly characteristic and delicate test for the detection of nitric acid. Sulphate of protoxide of iron serves also for the detection of hydroferricyanic acid, with which it produces a kind of Prussian blue, and also to effect the precipitation of metallic gold from solutions of the salts of that metal. 65. 2. SESQUICHLORIDE OF IRON (Fe a C1 8 ). Preparation. Heat in a flask a mixture of 10 parts of water and 1 part of pure hydrochloric acid with small iron nails until no further evolution of hydrogen is observed, even after adding the nails in excess ; filter the solution into another flask, and conduct into it chlorine gas, with frequent shaking, until the fluid no longer produces a blue precipi- tate in solution of ferricyanide of potassium. Heat until the excess of chlorine is expelled. Dilute until the fluid is twenty times the weight of the iron dissolved, and keep the dilute fluid for use. Tests. Solution of sesquichloride of iron must not contain an excess of acid \ this may be readily ascertained by stirring a sample of it with a glass rod dipped in ammonia, when the absence of any excess of acid will be proved by the formation of a precipitate whicli shaking the vessel or agitating the fluid fails to redissolve. Ferricyanide of potassium must not impart a blue color to it. Uses. Sesquichloride of iron serves to subdivide the group of organic acids which chloride of calcium fails to precipitate, as it produces pre- cipitates in solutions of benzoates and succinates, but not in solutions of acetates and formates. The aqueous solutions of the neutral acetate and formate of sesquioxide of iron exhibit an intensely red color ; ses- quichloride of iron is therefore a useful agent for detecting acetic acid and formic acid. Sesquichloride of iron is exceedingly well adapted to effect the decomposition of phosphates of the alkaline earths (see 142). It serves also for the detection of hydroferrocyanic acid, with which it produces Prussian blue. 62 NITKATE OF SILVER. 66. 3. NITRATE OP SILVER (AgO,N0 5 ). Preparation. Dissolve pure silver in pure nitric acid, evaporate the solution to dryness, and dissolve 1 part of the salt in 20 parts of water. Tests. Dilute hydrochloric acid must completely precipitate all fixed particles from solution of nitrate of silver, which should have a neutral reaction ; the fluid filtered from the precipitated chloride of silver must accordingly leave no residue when evaporated on a watch-glass, and must be neither precipitated nor colored by hydrosulphuric acid. Uses. Oxide of silver forms with many acids soluble, with others in- soluble compounds. Nitrate of silver may therefore serve, like chloride of barium, to effect the separation and arrangement of acids into groups. Most of the insoluble compounds of silver dissolve in dilute nitric acid ; chloride, bromide, iodide, and cyanide, ferrocyanide, ferricyanide, and sulphide of silver are insoluble in that menstruum. Nitrate of silver is therefore a most excellent agent to distinguish and separate from all other acids the hydracids corresponding to the last enumerated compounds of silver. Many of the insoluble salts of silver exhibit a peculiar color (chromate of silver, arsenate of silver), or manifest a cha- racteristic deportment with other reagents or upon the application of heat (formate of silver) ; nitrate of silver is therefore an important agent for the positive detection of certain acids. 67. 4. ACETATE OF LEAD (Pb 0, A, crystallized Pb 0,^4 3 aq.). The best acetate of lead of commerce is sufficiently pure for the purpose of chemical analysis ; for use dissolve 1 part of the salt in 10 parts of water. Tests. Sugar of lead must completely dissolve in water acidified with one or two drops of acetic acid ; the solution must be quite clear and colorless ; hydrosulphuric acid must throw down all fixed particles from it. On mixing the solution of sugar of lead with carbonate of ammonia in excess, and filtering the mixture, the nitrate must not show a bluish tint (copper). Uses. Oxide of lead forms with a great many acids compounds in- soluble in water, which are marked either by peculiarity of color or characteristic deportment. The acetate of lead therefore produces pre- cipitates in the solutions of these acids or of their salts, and essentially contributes to the detection of several of them. Thus chromate of lead, for instance, is characterized by its yellow color, phosphate of lead by its peculiar deportment before the blowpipe, and malate of lead by its ready fusibility. 68. 5. NITRATE OF SUBOXIDE OF MERCURY (Hg 2 0,N0 6 , crystallized Hg 2 0,NO B + 2aq.). Preparation. Pour 1 part of pure nitric acid of 1'2 spec. gr. on 1 part of mercury in a porcelain dish, and let the vessel stand twenty-four CHLORIDE OF MERCURY. G3 hours in a cool place ; separate the crystals formed from the undissolved mercury and the mother liquor, and dissolve them in water mixed with one-sixteenth part of nitric acid, by trituration in a mortar. Filter the solution, and keep the filtrate in a bottle with some metallic mercury covering the bottom of the vessel. Tests. The solution of nitrate of suboxide of mercury must give with dilute hydrochloric acid a copious white precipitate of subchloride of mer- cury; hydrosulphuric acid must produce no precipitate in the fluid filtered from this, or at all events only a trifling black precipitate (sulphide of mercury). Uses. Nitrate of suboxide of mercury acts in an analogous manner to the corresponding salt of silver. In the first place, it precipitates many acids, especially the hydracids ; and, in the second place, it serves for the detection of several readily oxidizable bodies, e.g. of formic acid, as the oxidation of such bodies, which takes place at the expense of the oxygen of the suboxide of mercury, is attended with the highly characteristic separation of metallic mercury. 69. 6. CHLORIDE OF MERCURY (HgCl). The chloride of mercury of commerce is sufficiently pure for the pur- poses of chemical analysis. For use dissolve 1 part of the salt in 1 6 parts of water. Uses. Chloride of mercury gives with several acids, e.g. with hydri- odic acid, peculiarly colored precipitates, and may accordingly be used for the detection of these acids. It is an important agent for the detec- tion of tin where that metal is in solution in the state of protochloride ; if only the smallest quantity of that compound is present the addition of chloride of mercury in excess to the solution is followed by separation of subchloride of mercury insoluble in water. In a similar manner chlo- ride of mercury serves also for the detection of formic acid. 70. 7. SULPHATE OF COPPER (CuO,S0 8 , crystallized CuO,S0 8 ,HO + 4aq.). Preparation. This reagent may be obtained in a state of great purity from the residue remaining in the retort in the process of preparing bisulphite of soda ( 48), by treating that residue with water, applying heat, filtering, letting the filtrate crystallize, and purifying the salt by recrystallization. For use dissolve 1 part of the pure crystals in 10 parts of water. Tests. Pure sulphate of copper must be completely precipitated from its solutions by hydrosulphuric acid ; ammonia and sulphide of ammo- nium must accordingly leave the filtrate unaltered. Uses. Sulphate of copper is employed in qualitative analysis to effect the precipitation of hydriodic acid in the form of subiodide of copper For this purpose it is necessary to mix the solution of 1 part of sulphate of copper with 2 J parts of sulphate of protoxide of iron, otherwise half of the iodine will separate in the free state. The protoxide of iron changes in this process to sesquioxide, at the expense of the oxygen of the oxide 64 PROTOCHLORIDE OF TIN. of copper, which latter is thus reduced to the state of suboxide. Sulphate of copper is used also for the detection of arsemous and arsenic acids ; it serves likewise as a test for the soluble ferrocyanides. 71. 8. PROTOCHLORIDE OF TIN (SnCl, crystallized Sn Cl + 2 aq.). Preparation. Reduce English tin to powder by means of a file, or by fusing it in a small porcelain dish, removing from the fire, and triturating the fused liquid mass with a pestle until it has passed again to the solid state. Boil the powder for some time with concentrated hydrochloric acid in a flask (taking care always to have an excess of tin in the vessel) until no more hydrogen gas is evolved j dilute the solution with 4 times the quantity of water slightly acidulated with hydrochloric acid, and filter. Keep the filtrate for use in a well-stoppered bottle containing small pieces of metallic tin, or some pure tin-foil. If these precautions are neglected the protochloride will soon change to bichloride, with sepa- tion of white oxychloride, which will of course render the reagent totally unfit for the purpose for which it is intended. Tests. Solution of protochloride of tin must, when added to a solution of chloride of mercury, immediately produce a white precipitate of sub- chloride of mercury ; when treated with hydrosulphuric acid it must give a dark brown precipitate ; it must not be precipitated nor rendered turbid by sulphuric acid. Uses. The great tendency of protochloride of tin to absorb oxygen, and thus to form binoxide, or rather bichloride as the binoxide in the moment of its formation decomposes with the free hydrochloric acid pre- sent makes this substance one of our most powerful reducing agents. It is more particularly suited to withdraw part or the whole of the chlo- rine from chlorides. We employ it in the course of analysis as a test for mercury ; also to effect the detection of gold. 72. 9. BICHLOEIDE OF PLATINUM (Pt C1 2 , crystallized Pt Cl a + 10 aq.). Preparation. Treat platinum filings, purified by boiling with nitric acid, with concentrated hydrochloric acid and some nitric acid in a narrow-necked flask, and apply a very gentle heat, adding occasionally fresh portions of nitric acid, until the platinum is completely dissolved. Evaporate the solution on the water-bath, with addition of hydrochloric acid, and dissolve the semifluid residue in 10 parts of water for use. Tests. Bichloride of platinum must, upon evaporation to dryness in the water-bath, leave a residue which dissolves completely in spirit of wine. Uses. Bichloride of platinum forms very sparingly soluble double salts with chloride of potassium and chloride of ammonium, but not so with chloride of sodium ; it serves therefore to detect ammonia and potassa, and may, indeed, be looked upon as our most delicate reagent for the latter substance. SODIO-PROTOCHLORIDE OF PALLADIUM. 65 73. 10. SODIO-PROTOCHLORIDE OF PALLADIUM (NaCl,PdCl). Dissolve 5 parts of palladium in nitrohydrochloric acid (comp. 72), add 6 parts of pure chloride of sodium, evaporate in the wafer bath to dryness, and dissolve 1 part of the residuary double salt in 12 parts of water for use. The brownish solution affords an excellent means for de- tecting and separating iodine. 74. 11. TERCHLORIDE OF GOLD (AuCl,). Preparation. Take fine shreds of gold, which may be alloyed with silver or copper, treat them in a flask with nitrohydrochloric acid in excess, and apply a gentle heat until no more of the metal dissolves. If the gold was alloyed with copper which is known by the brownish-red precipitate produced by ferrocyanide of potassium in a portion of the solution diluted with water mix it with solution of sulphate of protoxide of iron in excess. This will reduce the terchloride to metallic gold, which will separate in the form of a fine brownish-black powder ; wash the powder in a small flask, and redissolve it in nitrohydrochloric acid ; evaporate the . lotion to dryness on the water-bath, and dissolve the residue in 30 parts ol water. If the gold was alloyed with silver, the latter metal remains as chloride upon treating the alloy with nitrcfoydro- chloric acid. In that case evaporate the solution at once to dryness, and dissolve the residue in water for use. Uses. Terchloride of gold has a great tendency to yield up its chlo- rine ; it therefore readily converts protochlorides into higher chlorides, protoxides, with the co-operation of water, into higher oxides. These- peroxidations are usually indicated by the precipitation of pure metallic gold in the form of a brownish- black powder. In the course of analysis this reagent is used only for the detection of protoxide of tin, in the solutions of which it produces a purple color or a purple precipitate. V. COLORING MATTERS AND INDIFFERENT VEGETABLE SUBSTANCES. 75. 1. TEST PAPERS. a. BLUE LITMUS PAPER. Preparation. Digest 1 part of litmus of commerce with 6 parts of water, and filter the solution ; divide the intensely blue filtrate into 2 equal parts ; saturate the free alkali in the one half by repeatedly stirring with a glass rod dipped in very dilute sulphuric acid, until the color of the fluid just appears red ; add now the other half of the blue filtrate, pour the whole fluid into a dish, and draw slips of fine unsized paper through it ; suspend these slips over threads, and leave them to dry. The color of litmus paper must be perfectly uniform and neither too light nor too dark. The paper must be readily wetted by aqueous fluids. , Uses. Litmus paper serves to detect the presence of free acid in fluids, as acids change its blue color to red. It must be borne in mind, I, T 66 REDDENED LITMUS PAPER. however, that the soluble neutral salts of most of the heavy metallic oxides produce the same effect. /3. REDDENED LITMUS PAPER. "Preparation. Stir blue solution of litmus with a glass rod dipped in dilute sulphuric acid, and repeat this process until the fluid has just turned distinctly red. Steep slips of paper in the solution, and dry them as in a. The dried slips must look distinctly red. Uses. Pure alkalies and alkaline earths, and also the sulphides of their metals, restore the blue color of reddened litmus paper ; carbonates of the alkalies and the soluble salts of several other weak acids, especially of boracic acid, possess the same property. This reagent serves therefore for the detection of these bodies in general.* y. GEORGINA PAPER (Dahlia Paper). Preparation. Boil the violet colored petals of Georgina purpurea (purple dahlia) in water, or digest them with spirit of wine, and steep slips of paper in the tincture obtained. The latter should be neither more nor less concentrated than is necessary to make the paper when dry again appear of a fine and light violet blue color. Should the color too much incline to red this may be remedied by adding a very little am- monia to the tincture. Uses. Georgina paper is reddened by acids, whilst alkalies impart a beautiful green tint to it. 'It is therefore an extremely convenient sub- stitute both for the blue and the reddened litmus paper. This reagent, if properly prepared, is a most delicate test both for acids and alkalies. Concentrated solutions of caustic alkalies turn Georgina paper yellow by destroying the coloring matter. 5. TURMERIC PAPER. Preparation. Digest and heat 1 part of bruised turmeric root with 6 parts of weak spirit of wine, filter the tincture obtained, and steep slips of fine paper in the filtrate. The dried slips must exhibit a fine yellow tint ; they must be readily wetted by aqueous fluids. Uses. Turmeric paper serves the same as reddened litmus paper and dahlia paper for the detection of free alkalies, &c., as they change its yellow color to brown. It is not quite so delicate a test as the other reagent papers; but the change of color which it produces is highly characteristic, and is very distinctly perceptible in many colored fluids ; we therefore cannot well dispense with this paper. When testing with turmeric paper it is to be borne in mind that, besides the substances enumerated in (3, several other bodies (boracic acid, for instance) possess the property of turning its yellow color to brown-red, more especially on drying. It affords an excellent means for the detection of boracic acid. All test papers are cut into slips, which are kept in small well-closed boxes, or in bottles covered with black paper, as continued action of light destroys the color. * Mr. A. S. Taylor has suggested that a very delicate test paper for detecting alkalies ijaay be prepared by steeping slips of paper in an acid infusion of rose petals. SOLUTION OF INDIGO. 67 76. 2. SOLUTION OP INDIGO. Preparation. Take from 4 to 6 parts of faming sulphuric acid, add slowly and in small portions at a time 1 part of finely pulverized indigo, taking care to keep the mixture well stirred. The acid has at first imparted to it a brownish tint by the matter which the indigo con- tains in admixture, but it subsequently turns deep blue. Elevation of temperature to any considerable extent must be avoided, as part of the indigo blue is thereby destroyed ; it is therefore advisable when dissolv- ing larger quantities of the substance to place the vessel in cold water. When the whole of the indigo has been added to the acid, cover the vessel, let it stand forty-eight hours, then pour its contents into 20 times the quantity of water, mix, filter, and keep the filtrate for use. Uses. Indigo is decomposed by boiling with nitric acid, yellow- colored oxidation products being formed. It serves therefore for the detection of nitric acid. Solution of indigo is also well adapted to effect the detection of chloric acid and of free chlorine. B. REAGENTS IN THE DRY WAY. L FLUXES AND DECOMPOSING AGENTS, 77. 1. MIXTURE OF CARBONATE OF SODA AND CARBONATE OF POTASSA. (NaO,CO a + 1^0,00,). Preparation. Digest 10 parts of purified bitartrate of potassa in powder with 10 parts of water and 1 part of hydrochloric acid for several hours on the water-bath, with frequent stirring ; put the mass into a funnel with a small filter inserted into the pointed end ; let it drain ; cover with a disc of rather difficultly permeable filtering paper with upturned edges, and wash by repeatedly pouring upon this small quantities of cold water ; continue this washing process until the fluid running off is no longer rendered turbid by solution of nitrate of silver, after addition of nitric acid. Dry the bitartrate of potassa freed in this manner from lime (and phosphoric acid). It is now necessary to prepare pure nitrate of potassa. To effect this, dissolve nitrate of potassa of commerce in half its weight of boiling water, filter the solution into a porcelain or stoneware dish, using a hot funnel, and stir it well with a clean wooden or porcelain spatula until cold. Transfer the crystalline powder to a funnel loosely stopped with cotton, let it drain, press down tight, make even at the top, cover with a double disc of difficultly per- meable filtering paper with upturned edges, and pour upon this at proper intervals small portions of water until the washings are no longer made turbid by solution of nitrate of silver. Empty now the contents of the funnel into a porcelain dish, dry in this vessel, and reduce the mass to a fine powder by trituration. Mix now 2 parts of the pure bitartrate of potassa with 1 part of the pure nitrate of potassa ; project the perfectly dry mixture in small portions at a time into a clean-scoured cast-iron pot heated to gentle redness ; when the mixture has deflagrated heat strongly until a sample taken from the edges gives with water a perfectly colorless solution. Triturate the charred mass with water, filter, wash slightly, and evapo- F2 68 HYDRATE OF BARYTA. rate the filtrate in a porcelain or, better still, in a silver dish, until the fluid is covered with a persistent pellicle. Let the mixture now cool, with constant stirring ; put the crystals of carbonate of potassa on a funnel, let them well drain, wash slightly, dry thoroughly in a silver or porcelain dish, and keep the crystals in a well-stoppered bottle. The mother liquor leaves upon evaporation a salt which, though containing traces of alumina and silicic acid, may still be turned to account for many purposes. Mix 13 parts of the pure carbonate of potassa prepared in the manner just now described with 10 parts of pure anhydrous carbonate of soda, and keep the mixture in a well-stoppered bottle. The mixture of car- bonate of potassa and carbonate of soda may also be prepared by defla- grating 20 parts of pure bitartrate of potassa with 9 parts of pure nitrate of soda, treating with water, and evaporating the solution to dry- ness. Or by igniting pure tartrate of potassa and soda, extracting the car- bonaceous mass with water, and evaporating the clear solution to dryness. Tests. The purity of the mixed salt is tested as directed 46 (car- donate of soda). To detect any trace of cyanide of potassium that may happen to be present, add to the solution of the salt a little of a solution of proto-sesquioxide of iron, then hydrochloric acid in excess, when the bluish-green coloration of the fluid and the formation of a blue preci- pitate after a time will indicate the presence of cyanide of potassium. Uses. If silicic acid or a silicate is fused with about 4 parts (con- sequently with an excess) of carbonate of potassa or soda, carbonic acid escapes with effervescence, and a basic alkaline silicate is formed, which, being soluble in water, may be readily separated from such metallic oxides as it may contain in admixture ; from this basic alkaline silicate hydrochloric acid separates the silicic acid as hydrate. If a fixed alkaline carbonate is fused together with sulphate of baryta, strontia, or lime, there are formed carbonates of the alkaline earths and sulphate of the alkali, in which new compounds both the base and the acid of the originally insoluble salt may now be readily detected. However, we do not use either carbonate of potassa or carbonate of soda separately to effect the decomposition of the insoluble silicates and sulphates ; but we apply for this purpose the above-described mixture of both, because this mixture requires a far lower degree of heat for fusion than either of its two components, and thus enables us to conduct the operation over a Berzelius lamp, or over a simple gas-lamp. The fusion with alkaline carbonates is invariably effected in a platinum crucible, provided no reducible metallic oxides be present 78. 2. HYDRATE OF BARYTA (BaO,HO). Preparation. The crystals of baryta prepared in the manner directed 34 are heated gently in a silver or platinum dish, until the water of crystallization is completely expelled. The residuary white mass is pulverized, and kept for use in a well- closed bottle. Uses. Hydrate of baryta fuses at a gentle red heat without losing its water. Upon fusing silicates which resist decomposition by acids together with about 4 times their weight of hydrate of baryta, basic silicates are formed which acids will decompose. If, therefore, the fused mass is treated with water and hydrochloric acid, the solution evaporated FLU011IDE OF CALCIUM. 69 to dryness, and the residue digested with dilute hydrochloric acid, the silicic acid is left behind, and the oxides are obtained in solution in the form of chlorides. We use hydrate of baryta as a flux when we wish to test silicates for alkalies. This reagent is preferable as a flux to the car- bonate or nitrate of baryta, since it does not require a very high tempe- rature for its fusion, as is tlie case with the carbonate, nor does it cause any spirting in the fusing mass, arising from disengagement of gas, as is the case with the nitrate. The operation of fluxing with hydrate of baryta is conducted in silver or platinum crucibles. 79. 3. FLUORIDE OF CALCIUM (Ca Fl). Take fluor-spar as pure as can be procured and, more particularly, free from alkalies, reduce to fine powder, and keep this for use. Uses. Fluoride of calcium applied in conjunction with sulphuric acid serves to effect the decomposition of silicates insoluble in acids, and more especially to detect the alkalies which they contain. Compare Section III. Silicic acid, 150. 80. 4. NITRATE OF SODA (NaO, N0 6 ). Preparation. Neutralize pure nitric acid with pure carbonate of soda exactly, and evaporate to crystallization. Dry the crystals thoroughly, triturate, and keep the powder for use. Tests. A solution of nitrate of soda must not be made turbid by solution of nitrate of silver or nitrate of baryta, nor precipitated by carbonate of soda. Uses. Nitrate of soda serves as a very powerful oxidizing agent, by yielding oxygen to combustible substances when heated with them. We use this reagent principally to convert several metallic sulphides, and more particularly the sulphides of tin, antimony, and arsenic, into oxides and acids ; also to effect the rapid and complete combustion of organic substances ; for the latter purpose, however, nitrate of ammonia is in many cases preferable ; which latter reagent is prepared by saturating nitric acid with carbonate of ammonia. II. BLOWPIPE REAGENTS. 81. 1. CARBONATE OF SODA (NaO, C0 2 ). Preparation. See 46. Uses. Carbonate of soda serves, in the first place, to promote the reduction of oxidized substances in the inner flame of the blowpipe. In fusing it brings the oxides into the most intimate contact with the char- coal support, and enables the flame to embrace every part of the substance under examination. It co-operates in this process also chemically by the transposition of its constituents (according to R. Wagner, in consequence of the formation of cyanide of sodium). Where the quantity operated upon was very minute the reduced metal is often found in the pores of the charcoal. In such cases the parts surrounding the little cavity which contained the sample are dug out with a knife, and triturated in a small mortar ; the charcoal is then washed off" from the metallic particles, 70 CYANIDE OF POTASSIUM. which now become visible either in the form of powder or as small flat spangles, according to the nature of the particular metal or metals present. Carbonate of soda serves, in the second place, as a solvent. Platinum wire is the most convenient support for testing the solubility of substances in fusing carbonate of soda. A few only of the bases dissolve in fusing carbonate of soda, but acids dissolve in it with facility. Carbonate of soda is also applied as a decomposing agent and flux, and more particu- larly to effect the decomposition of the insoluble sulphates, with which it exchanges acids, the newly formed sulphate of soda being reduced at the same time to sulphide of sodium ; and to effect the decomposition of sulphide of arsenic, with which it forms a double sulphide of arsenic and sodium, and arsenite or arsenate of soda, thus converting it to a state which permits its subsequent reduction by hydrogen. Carbonate of soda also is the most sensitive reagent in the dry way for the detection of manganese, as it produces when fused in the outer flame of the blowpipe together with a substance containing manganese a green opaque bead, owing to the formation of manganate of soda. 82. 2. CYANIDE OF POTASSIUM (KCy). Preparation. See 54. Uses. Cyanide of potassium is an exceedingly powerful reducing agent in the dry way ; indeed it excels in its action almost all other reagents of the same cla*s, and separates the metals not only from most oxygen compounds, but also from many sulphur compounds. This reduction is attended in the former case with formation of cyanate of potassa, by the absorption of oxygen, and in the latter case with formation of sulpho- cyanide of potassium, by the taking up of sulphur. By means of this reagent we may effect the reduction of metals from their compounds with the greatest possible facility ; thus we may, for instance, produce metallic antimony from antiinonious acid or from sulphide of antimony, metallic iron from, sesquioxide of iron, &c. The readiness with which cyanide of potassium enters into fusion facilitates the reduction of the metals greatly ; the process may usually be conducted even in a porcelain crucible over a spirit lamp. Cyanide of potassium is a most valuable and important agent to effect the reduction of binoxide of tin, antimonic acid, and more particularly of tersulphide of arsenic (see 132). Cyanide of potassium is equally important as a blowpipe reagent. Its action .is exceedingly energetic ; substances like binoxide of tin, the reduction of which by means of carbonate of soda requires a tolerably strong flame, are reduced by cyanide of potassium with the greatest facility. In blow- pipe experiments we invariably use a mixture of equal parts of carbonate of soda and cyanide of potassium ; the admixture of carbonate of soda is intended here to cheek in some measure the excessive fusibility of the cyanide of potassium. This mixture of cyanide of potassium with car- bonate of soda, besides being a far more powerful reducing agent than the simple carbonate of soda, has moreover this great advantage over the latter, that it is absorbed by the pores of the charcoal with extreme facility, and thus permits the production of the metallic globules in a state of the greatest purity. BIBORATE OF SODA. 71 83. 3. BIBORATE OF SODA (Borax) (NaO,2BO,, crystallized + 10 aq.). The purity of commercial borax may be tested by adding to its solu- tion carbonate of soda or, after previous addition of nitric acid, solution of nitrate of baryta or of nitrate of silver. The borax may be consi- dered pure if these reagents fail to produce any alteration in the solu- tion ; but if either of them causes the formation of a precipitate, or renders the fluid turbid, recrystallization is necessary. The pure crys- tallized borax is exposed to a gentle heat, in a platinum crucible, until it ceases to swell ; it is then left to cool, and afterwards pulverized and kept for use. Uses. Boracic acid manifests a great affinity for oxides -when brought into contact with them in a state of fusion. This affinity enables it, in the first place, to combine directly with oxides; secondly, to expel weaker acids from their salts ; and, thirdly, to predispose metals, sul- phides, and haloid compounds to oxidize in the outer flame of the blow- pipe, that it may combine with the oxides. Most of the thus produced borates fuse readily, even without the aid of a flux, but far more so in conjunction with borate of soda; the latter salt acts in this operation either as a mere flux, or by the formation of double salts. Now in the biborate of soda we have both free boracic acid and borate of soda ; the union of these two substances renders it one of our most important blowpipe reagents. In the process of fluxing with borax we usually select platinum wire for a support ; the loop of the wire is moistened or heated to redness, then dipped into the powder, and exposed to the outer flame ; a colorless bead of fused borax is thus produced. A small por- tion of the substance under examination is then attached to the bead, by bringing the latter into contact with it whilst still hot or having previ- ously moistened it. The bead with the sample of the substance in- tended for analysis adhering to it is now exposed to the blowpipe flame, and the reactions to the manifestation of which this process gives rise are carefully observed and examined. The following points ought to be more particularly watched : (1) Whether or not the sample under exa- mination dissolves to a transparent bead, and whether or not the bead retains its transparency on cooling; (2) whether the bead exhibits a distinct color, which in many cases at once clearly indicates the indi- vidual metal which the analysed compound contains ; as is the case, for instance, with cobalt ; and (3) whether the bead manifests the same or a different deportment in the outer and in the inner flame. Reactions of the latter kind arise from the ensuing reduction of higher to lower oxides, or even to the metallic state, and are for some substances parti- cularly characteristic. 84. 4. PHOSPHATE OF SODA AND AMMONIA (Microcosmic Salt) (NaO,NH 4 0,HO,P0 6 , crystallized + 8 aq.). Preparation. a. Heat to boiling 6 parts of phosphate of soda and 1 part of pure chloride of ammonium with 2 parts of water, and let the solution cool. Free the crystals produced of the double phosphate of soda and ammonia from the chloride of sodium which adheres to them 72 NITRATE OF PROTOXIDE OF COBALT. by recry stall! zation, with addition of some solution of ammonia. Dry the purified crystals, pulverize, and keep for use. b. Take 2 equal parts of pure tribasic phosphoric acid, and add solu- tion of soda to the one, solution of ammonia to the other, until both fluids have a distinct alkaline reaction ; mix the two together, and let the mixture crystallize. Tests. Phosphate of soda and ammonia dissolves in water to a fluid with feebly alkaline reaction. The yellow precipitate produced in this fluid by nitrate of silver must completely dissolve in nitric acid. Upon fusion on a platinum wire, microcosmic salt must give a clear and color- less bead. Uses. On heating phosphate of soda and ammonia the ammonia escapes with the water of crystallization, leaving acid pyrophosphate of soda (NaO,HO,PO fi ) ; upon heating more strongly the last equiva- lent of water escapes likewise, and readily fusible metaphosphate of soda (NaO,PO 6 ) is left behind. The action of microcosmic salt is quite analogous to that of biborate of soda. We prefer it, however, in some cases to borax as a solvent or flux, the beads which it forms with many substances being more beautifully and distinctly colored than those of borax. Platinum wire is also used for a support in the process of flux- ing with microcosmic salt ; the loop must be made small and narrow, otherwise the bead will not adhere to it. The operation is conducted as directed in the preceding paragraph. 85. 5. NITRATE OF PROTOXIDE OF COBALT (CoO,NO 6 , crystallized + 5 aq.). Preparation. Fuse in a Hessian crucible 3 parts of bisulphate of potassa, and add to the fused mass, in small portions at a time, 1 part of well- roasted cobalt ore (the purest zaffre you can procure) reduced to fine powder. The mass thickens, and acquires a pasty consistence. Heat now more strongly until it has become more fluid again, and con- tinue to apply heat until the excess of sulphuric acid is completely ex- pelled, and the mass accordingly no longer emits white fumes. Remove the fused mass now from the crucible with an iron spoon or spatula, let it cool, and reduce it to powder ; boil this with water until the undis- solved portion presents a soft mass ; then filter the rose-red solution, which is free from arsenic and nickel, and mostly also from iron. Add to the filtrate a small quantity of carbonate of soda, so as to throw down a little carbonate of protoxide of cobalt, boil, and filter. Preci- pitate the solution, which is now free from iron, boiling with carbonate of soda, wash the precipitate well, and treat it still moist with oxalic acid in excess. Wash the rose-red oxalate of protoxide of cobalt thoroughly, dry, and heat to redness in a glass tube, in a current of hydrogen gas. This decomposes the oxalate into carbonic acid, which escapes, and metallic cobalt, which is left behind. Wash the metal, first with water containing acetic acid, then with pure water, dissolve in dilute nitric acid, treat if necessary with hydrosulphuric acid, filter the fluid from the sulphide of copper, &c., which may precipitate, eva- porate the solution in the water- bath to dry ness, and dissolve 1 part of the residue in 10 parts of water for use. Tests. Solution of nitrate of protoxide of cobalt must be free from other metals, and especially also from salts of the alkalies ; when, preci- REACTIONS. 73 pitated with sulphide of ammonium, and filtered, the filtrate must upon evaporation on platinum leave no fixed residue. Uses. Protoxide of cobalt forms upon ignition with certain infusible bodies peculiarly colored compounds, and may accordingly serve for the detection of these bodies (oxide of zinc, alumina, and magnesia ; see Section III.V SECTION III. REACTIONS, OR DEPORTMENT OF BODIES WITH REAGENTS. 86. I STATED in ray introductory remarks that the operations and experi- ments of qualitative analysis have for their object the conversion of the unknown constituents of any given compound into forms of which we know the deportment, relations, and properties, and which will accord- ingly permit us to draw correct inferences regarding the several consti- tuents of which the analysed compound consists. The greater or less value of such analytical experiments, like that of all other inquiries and investigations, depends upon the greater or less degree of certainty with which they lead to definite results, no matter whether of a positive or negative nature. But as a question does not render us any the wiser if we do not know the language in which the answer is returned, so in like manner will analytical investigations prove unavailing if we do not understand the mode of expression in which the desired information is conveyed to us ; in other words, if we do not know how to interpret the phenomena produced by the action of our reagents upon the sub- stance examined. Before we can therefore proceed to enter upon the practical investiga- tions of analytical chemistry, it is indispensable that we should really possess the most perfect knowledge of the deportment, relations, and properties of the new forms into which we intend to convert the sub- stances we wish to analyse. Now this perfect knowledge consists, in the first place, in a clear conception and comprehension of the conditions necessary for the formation of the new compounds and the manifestation of the various reactions ; and, in the second place, in a distinct impres- sion of the color, form, and physical properties which characterize the new compound. This section of the work demands therefore not only the most careful and attentive study, but requires moreover that the student should examine and verify by actual experiment every fact asserted in it. The method usually adopted in elementary works on chemistry is to treat of the various substances and their deportment with reagents in- dividually and separately, and to point out their characteristic reactions. I have, however, in the present work deemed it more judicious and better adapted to its elementary character, to arrange those substances which are in many respects analogous into groups, and thus, by com- paring their analogies with their differences, to place the latter in the clearest possible light. 74 METALLIC OXIDES AND THEIR RADICALS. A. REACTIONS, OR DEPORTMENT AND PROPERTIES OF THE METALLIC OXIDES AND OF THEIR RADICALS. 87. Before proceeding to the special study of the several metallic oxides, I give here a general view of the whole of them classified in groups showing which oxides belong to each group. The grounds upon which the classification has been arranged will appear from the special consi- deration of the several groups. First group Potassa, soda, ammonia (oxide of caesium, oxide of rubidium, lithia). Second group Baryta, strontia, lime, magnesia. Third group Alumina, sesquioxide of chromium (berylla, thoria, zirconia, yttria earths ; oxide of terbium, oxide of erbium ; oxides of cerium, lanthanium, didymium, titanium, tantaliurn, niobium). Fourth group Oxides of zinc, manganese, nickel, cobalt, iron (uranium, vanadium, thallium). Fifth group Oxides of silver, mercury, lead, bismuth, copper, cadmium (palladium, rhodium, osmium, ruthenium). Sixth group Oxides and acids of gold, platinum, tin, antimony, arsenic (iridium, molybdenum, tellurium, tungsten, selenium). Of these metallic oxides only those printed in italics are found distri- buted extensively and iu large quantities in that portion of the earth's crust which is accessible to our investigations ; these are therefore most important to chemistry, arts and manufactures, agriculture, pharmacy, The best method of applying this reagent is to evaporate the aqueous solution of the potassa salt with bichloride of platinum nearly to dryness on the water-bath, and to pour a little water over the residue (or, better still, some spirit of wine, provided no substances insoluble in that menstruum be present), when the potassio-bichloride of platinum will be left undis- solved. Care must be taken not to confound this double salt with ammonio-bichloride of platinum, which greatly resembles it (see 91, 4.) 4. Tartaric acid produces in neutral or alkaline* solutions of salts of potassa a white, quickly subsiding, granular crystalline precipitate of ACID TAHTRATE OF POTASSA (K O, H O C g H 4 O 10 ). In concentrated solutions this precipitate separates immediately ; in dilute solutions often only after the lapse of some time. Vigorous shaking or stirring of the fluid greatly promotes its formation. Very dilute solutions are not pre- cipitated by this reagent. Free alkalies and free mineral acids dissolve the precipitate ; it is sparingly soluble in cold, but pretty readily soluble in hot water. In acid solutions the free acid must, if practicable, first be expelled by evaporation and ignition, or the solution must be neutral- ized with soda or carbonate of soda, before they can be tested for potassa with tartaric acid. Acid tartrate of soda answers still better as a test for potassa than free tartaric acid. The reaction is the same in kind, but different in degree, being much more delicate with the salt than with the free acid, since where the former is used the soda salt of the acid combined with the potassa is formed, whereas where free tartaric acid is the test ap- * To alkaline solutions the reagent must be added until the fluid shows a strongly acid reaction. 76 SODA. plied the hydrate of the acid combined with the potassa is formed, which tends to increase the dissolving action of the water of the men- struum upon the acid tartrate of potassa, and thus to check the separa- tion of the latter (K 0, N 6 + Na 0, H 0, C 8 H 4 O 10 = K O, H O,C 8 H 4 O 10 + NaO,N0 6 ). 5. If a potassa salt which is volatile at an intense red heat is held on the loop of a platinum wire in the fusion zone of the flame of Bunsens gas-lamp ( 14, fig. 17), the salt volatilises, and imparts a blue violet tint to the part of the flame above the sample. Chloride of potassium and nitrate of potassa volatilize rapidly, the carbonate and sulphate less rapidly, and the phosphate still more slowly ; but they all of them dis- tinctly show the reaction, though decreasing in degree. If it is wished to obtain a more uniform manifestation of the reaction, i. e. a manifesta- tion independent of the nature of the acid that may chance to be com- bined with the potassa, the sample need simply be moistened with sulphuric acid, dried at the border of the flame, and then introduced into the fusion zone. With silicates, and other compounds of potassa of difficult volatility, the reaction may be ensured by fluxing the sample first with pure gypsum, as this serves to form silicate of lime and sul- phate of potassa, which latter salt then readily colors the flame. Decrepitating salts are ignited in a platinum spoon before they are attached to the loop. The sample of the potassa salt under examination may also be held before the apex of the inner blowpipe flame produced with a spirit-lamp. Presence of a salt of soda completely obscures the potassa coloration of the flame. The spectrum of the potassa flame produced by the spectrum apparatus ( 15, fig. 20) is shown on Table I. It contains two characteristic lines, the red line a and the indigo blue line /3. If the potassa flame is ob- served through the indigo prism ( 15, fig. 19) the coloration appears sky-blue, violet, and at last intensely crimson, even through the thickest layers of the solution. Admixtures of lime-, soda-, and lithia-com pounds do not alter this reaction, as the yellow rays cannot penetrate the indigo solution, and the rays of the lithia flame also are only able to pass through the thinner layers of that solution, but not through the thicker layers ; the exact spot where the penetrating power of the rays of the lithia flame ceases has to be marked by the operator on his indigo prism. But organic substances which impart luminosity to the flame might lead to mistakes, and must therefore, if present, first be removed by combustion. Instead of the indigo prism a blue glass may be used ; if lithia is present the glass must be sufficiently thick to keep out the red lithia rays. 6. If a salt of potassa (chloride of potassium answers best) is heated with a small quantity of water, alcohol (burning with colorless flame) added, heated, and then kindled, the flame appears VIOLET. The pre- sence of soda obscures this reaction, which is altogether much less delicate than the one described in 5. 90. b. SODA (Na 0). 1. SODA and its HYDRATE and SALTS present in general the same pro- perties and reactions as potassa and its corresponding compounds. The SODA. 77 oily fluid which soda forms by deliquescing in the air resolidifies speedily by absorption of carbonic acid. Carbonate of soda crystallizes readily ; the crystals (Na O, CO 2 + 10 aq.) effloresce rapidly when exposed to the air. The same applies to the crystals of sulphate of soda (Na, O, S0 3 + 10 aq.). 2. If a sufficiently concentrated solution of a soda salt with neutral or alkaline reaction is mixed, for greater convenience, in a watch-glass, with a solution of granular antimonate of potassa prepared according to the directions of 51, the mixture remains clear at first, or appears only slightly colored ; but upon rubbing the part of the glass wetted by the fluid with a glass rod, a crystalline precipitate of ANTIMONATE OF SODA (NaO,SbO 4 + 7 aq.) speedily separates, which makes its appearance first along the lines rubbed with the rod, and subsides from the fluid as a heavy sandy precipitate. From dilute solutions of soda salts the precipitate separates only after some time, occasionally as much as twelve hours. From very dilute solutions it does not separate at all. The precipitated antimonate of soda is invariably crystalline. Where it has separated slowly it occasionally consists of well-formed microscopic cubic octahedrons, but more frequently of four-sided columns tapering pyramid fashion ; where it has separated promptly, it appears in the form of small boat-shaped crystals. Presence of larger quantities of salts of potassa interferes very considerably with the reaction. Acid solutions cannot be tested with antimonate of potassa, as free acids will separate from the latter substance hydrated antimonic acid or acid antimonate of potassa. It is indispensable therefore, before adding the reagent, to remove, if possible, the free acid by evaporation or ignition, or where this is not practicable, by neutralizing the acid solution with a little carbonate of potassa until the reaction is feebly alkaline. It should also be borne in mind that only such solutions can be tested with antimonate of potassa which contain no other bases besides soda and potassa. 3. If salts of soda are held in the fusion zone of Bunserfs gas-lamp, or in the inner spirit-blowpipe, flame, they show, with regard to their rela- tive volatility and the action of decomposing agents upon them, a similar deportment to the salts of potassa ; the soda salts are, however, a little less volatile than the corresponding potassa salts. But the most charac- teristic sign of the presence of soda salts is the intense yellow coloration which they impart to the flame. This reaction will effect the detection of even the minutest quantities of soda, and is not obscured even by the presence of larger quantities of potassa. The soda spectrum (Table I.) shows only a single yellow line, a. The re- action is so exceedingly delicate that the chloride of sodium contained in at- mospheric dust generally suffices to give a soda spectrum, although afaintone. It is characteristic of the soda flame that a crystal of bichromate of potassa appears colorless in its light, and that a slip of paper coated with iodide of mercury appears white with a faint shade of yellow (BUNSEN) ; also that it looks orange yellow when observed through a green glass (MERZ). These reactions are not obscured by presence of salts of potassa, lithia, and lime. 4. If salts of soda (chloride of sodium answers best) are treated as stated in the preceding paragraph on potassa, sub. 6, the alcohol flame is colored intensely YELLOW. The presence of a potassa salt does not impair the distinctness of this reaction. 78 AMMONIA. 5. Bichloride of platinum produces no precipitate in solutions of soda salts. Sodio-bichloride of platinum dissolves readily both in water and in spirit of wine ; it crystallizes in rosy prisms. 6. Tartaric acid and acid tartrate of soda fail to precipitate even con- centrated neutral solutions of soda salts. 91. c. AMMONIA (NH 4 0). 1. Anhydrous AMMONIA (N H 3 ) is gaseous at the common temperature ; but we have most frequently to deal with it in its aqueous solution, in which it betrays its presence at once by its penetrating odor. It is expelled from this solution by the application of heat. It may be assumed that the solution contains it as oxide of ammonium (NH O) (see 33). 2. All the SALTS OF AMMONIA are volatile at a high temperature, either with or without decomposition. Most of them are readily soluble in water. The solutions are colorless. The neutral compounds of ammonia with strong acids do not alter vegetable colors. 3. If salts of ammonia are triturated together with hydrate of lime, best with the addition of a few drops of water, or are, either in the solid state or in solution, heated with solution of potassa or of soda, the ammonia is liberated in the gaseous state, and betrays its presence I, by its characteristic ODOR ; 2, by its REACTION on moistened TEST-PAPERS ; and 3, by giving rise to the formation of WHITE FUMES when any object (e.g. a glass rod) moistened with hydrochloric acid, nitric acid, acetic acid, or any of the volatile acids, is brought in contact with it. These fumes arise from the formation of solid ammoniacal salts produced by the con- tact of the gases in the air. Hydrochloric acid is the most delicate test in this respect ; acetic acid, however, admits less readily of a mistake. If the expulsion of the ammonia is effected in a small beaker, best with hydrate of lime, with addition of a very little water, and the beaker is covered with a watch-glass having a slip of moistened turmeric or red- dened litmus-paper attached to the centre of the convex side, the reaction will show the presence of even very minute quantities of ammonia; only it is not immediate in such cases, but requires some time for its mani- festation. It is promoted and accelerated by application of a gentle heat. 4. BicJdoride of platinum shows the same deportment with salts of ammonia as with salts of potassa ; the yellow precipitate of BICHLORIDE OF PLATINUM AND CHLORIDE OF AMMONIUM (N H 4 Cl,PtCl 2 ) is, however, of a somewhat lighter color than potassio-bichloride of platinum. It consists, like the corresponding potassium compound, of octahedrons dis- cernible under the microscope. 5. Tartaric acid throws down from most highly concentrated ammonia salt solutions with neutral reaction part of the ammonia as acid tartrate of ammonia (N H 4 O, HO, C 8 H 4 O 10 ). Less concentrated solutions are not precipitated. Acid tartrate of soda precipitates concentrated solu- tions more completely, and produces a precipitate even in more dilute solutions. The precipitated acid tartrate of ammonia is white and crystal- line. Its separation may be promoted by shaking the glass, or rubbing it inside with a glass rod. By solvents it is acted upon the same as the corresponding potassa salt, only that it is a little more readily soluble in water and in acids. RECAPITULATION AND REMARKS. 79 92. Recapitulation and remarks. The salts of potassa and soda are not volatile at a moderate red heat, whilst the salts of ammonia volatilize readily ; the latter may therefore be easily separated from the former by ignition. The expulsion of ammonia from its compounds by hydrate of lime affords the surest means of ascertaining the presence of this sub- stance. Salts of potassa can be detected in the humid way positively only after the removal of the ammoniacal salts which may be present, since both classes of salts manifest the same or a similar deportment with bichloride of platinum and tartaric acid. After the removal of the am- monia the potassa is clearly and positively characterized by either of these two reagents. Let it be borne in mind always that the reactions will only show in concentrated fluids, and that dilute solutions must therefore first be concentrated. A single drop of a concentrated solution will give a positive result, which cannot be obtained with a large quan- tity of a dilute fluid. The most simple way of detecting the potassa in the two sparingly soluble compounds that have come under our consider- ation here viz., the potassio-bichloride of platinum and the acid tartrate of potassa is to decompose these salts by ignition ; the former thereupon yields the potassa in the form of chloride of potassium, the latter in the form of carbonate of potassa. As regards soda, this alkali may be de- tected with positive certainty in the humid way by antimonate of potassa, provided the reagent be properly prepared and freshly dissolved, and the soda salt solution be concentrated, neutral, or feebly alkaline, and free from other bases, and that it be borne in mind that antimouate of soda invariably separates in the crystalline form, and not in a flocculent state. To detect in this way very minute quantities of soda in presence of a large proportion of potassa, precipitate the latter alkali first with bichloride of platinum, filter, remove the platinum from the filtrate by hydrosulphuric acid ( 127), filter, evaporate the filtrate to dryness, ignite gently, dissolve the residue in a very little water, and then test the solution finally with antimonate of potassa. Potassa and soda may be detected much more readily and speedily than in the humid way, and also with far greater delicacy, by the flame colo- ration. We have seen, indeed, that the soda coloration completely obscures the potassa coloration, even though the potassa salt contains only a trifling admixture of soda salt. But with the aid of the spectrum apparatus the spectra of the two are obtained so distinct and beautiful that a mistake is altogether impossible. And even without a spectrum apparatus the potassa coloration can always be distinctly recognised through the in- digo prism, or through a blue glass, even in a flame colored strongly yellow by soda ; and the soda coloration again may be placed beyond doubt, if necessary, with the aid of iodide of mercury paper, or green glass, in the manner already described. Exceedingly minute traces of ammonia may be detected by the follow- ing test, which was first recommended by J. NESSLER. Dissolve 2 grammes of iodide of potassium in 5 cubic centimetres of water, heat the solution, and add iodide of mercury until the portion last added remains undissolved. Let this mixture cool, then dilute with 20 cubic centi- metres of water. Let the fluid stand some time, filter, and mix 20 cubic centimetres of the filtrate with 30 cubic centimetres of a concentrated solution of potassa. Should the fluid turn turbid, filter it once more. 80 OXIDE OF (LESIUM. Upon adding to this solution a little of a fluid containing ammonia, or an ammonia salt, a reddish-brown precipitate is formed if the am- monia is present in some quantity ; but there is, at any rate, always a yellow coloration produced, even if only most minute traces of ammonia are present. The precipitate consists of tetrahydrargyro-iodide of ammonium (NH g J,2HO): 4 (Hgl,KI) + 3 KO + NH 8 = (NHg 4 I + 2HO) + 7KI + HO. Application of heat promotes the ^separation of the precipitate. Presence of chlorides of the alkali metals, or of salts of the alkalies with oxygen acid, does not interfere with the reaction ; but presence of cyanide of potassium, and of sulphide of potassium, will prevent it. 93. Special Reactions of the rarer Oxides of the first group. 1. OXIDE OF CAESIUM (CsO), and 2. OXIDE or RUBIDIUM (RbO). The caesium and rubidium compounds are, it would appear, found pretty widely disseminated in nature, but always in very minute quantities only. They have hitherto been found chiefly in the mother liquors of mineral waters, and in a few minerals (lepidolite, for instance). The caesium and rubidium compounds bear in general great resemblance to the potassium compounds, more particularly in this, that their concen- trated aqueous solutions are precipitated by tartaric acid and by bichloride of plati- num, and also that those of them that are volatile at a red heat jtinge the jlame violet. The most notable characteristic differences, on the other hand are that the precipitates produced by bichloride of platinum are far more insoluble in water than the potassio- bichloride of platinum ; 100 grammes of water will, at 50 Fahrenheit, dis- solve 900 milligrammes of potassio- bichloride of platinum, but only 154 milligrammes of the rubidio- bichloride of platinum, and as little as 50 milligrammes of the caesio- bichloride of platinum and, above all, that the flames colored by caesium and rubidium compounds give spectra quite different from the potassium spectrum (see Table I). The caesium spectrum is especially characterized by the two blue lines a and /3, which are remarkable for their wonderful intensity and sharp outline ; also by the line y, which, however, is less strongly marked. Amongst the lines in the rubidium spectrum, the splendid indigo-blue lines marked a and /3 strike the eye by their extreme bril- liancy. Less brilliant, but still very characteristic, are the lines 5 and*7. Lastly, we have still to mention that carbonate of oxide of caesium is soluble in absolute alcohol, whilst carbonate of oxide of rubidium is insoluble in that menstruum. Still, a separa- tion of the two oxides is effected only with difficulty by this means, as they seem to form a double salt which is not absolutely insoluble in alcohol. 3. LITHIA (Li 0). Lithia is also found pretty widely disseminated in nature, but in minute quantities only. It is often met with in the analysis of mineral waters and ashes of plants, less frequently in the analysis of minerals, and only rarely in that of technical and phar- maceutical products. Lithia forms the transition from the first to the second group. It dissolves with difficulty in water; it does not attract moisture from the air. Most of its salts are soluble in water ; some of them are deliquescent (chloride of lithium). Carbonate of lithia is difficultly soluble, particularly in cold wacer. Phos- phate of soda produces in not over dilute solutions of salts of lithia upon boiling, a white crystalline precipitate of tribasic phosphate of lithia (3 LiO, P0 g ), which quickly subsides to the bottom of the precipitating vessel. This reaction, which is characteristic of lithia, is rendered much more delicate by adding with the phosphate of soda a little solution of soda, just sufficient to leave the reaction alkaline, evapo- rating the mixture to dryness, treating the residue with water, and adding an equal volume of liquid ammonia. By this course of proceeding even very minute quantities of lithia will be separated as 3 LiO, PO S . The precipitate fuses before the blowpipe, and gives upon fusion with carbonate of soda a clear bead ; when fused upon char- coal it is absorbed by the pores of the latter body. It dissolves in hydrochloric acid to a fluid which, supersaturated with ammonia, remains clear in the cold, but upon boiling gives a heavy crystalline precipitate of 3 LiO, PO S . (Reactions by which the phosphates of lithia differ from the phosphates of the alkaline earths). Tartaric acid and bichloride of platinum fail to precipitate even concentrated solutions of salts of lithia. If salts of lithia are exposed to the gas or blow pipe flame, in the manner BARYTA, STKONTIA, LIME, MAGNESIA. 81 described in the chapter on the potassa reactions ( 89, 5), they tinge the flames car- mine-red. Silicates containing lithia demand addition of gypsum to produce this reaction. Phosphate of lithia will tinge the flame carmine-red if the fused bead is moistened with hydrochloric acid. The soda coloration conceals the lithia coloration ; in presence of soda, therefore, the lithia tint must be viewed through a blue glass, or through a thin layer of indigo solution. Presence of a small proportion of potassa will not conceal the lithia coloration. In presence of a large proportion of potassa, the lithia may be identified by placing the bead in the point of fusion, viewing the colored flame through the indigo prism ( 15), and comparing it with a pure potassa flame produced in the opposite fusion mantle. Viewed through thin layers, the lithia-colored flame appears now redder than the pure potassa flame ; viewed through somewhat thicker layers, the flames appear at last equally red, if the proportion of the lithia to the potassa is only trifling ; but when lithia predominates in the examined sample the intensity of the red coloration imparted by lithia decreases perceptibly when viewed through thicker layers, whilst the pure potassa- flame is scarcely impaired thereby. By this means lithia may still be detected in potassa salts, even though present only ill the proportion of one part in several thousand parts of the latter. Soda, unless present in over-large quantities, interferes but little with these reactions (CAETMELL, BUNSEX). The lithium spectrum (Table I.) is most brilliantly characterized by the splendid carmine-red line a, and the orange-yellow very faint line /3. If alcohol be poured over chloride of lithium, and then ignited, the flame shows also a carmine-red tint. Pre- sence of salts of soda will mask this reaction. To detect small quantities of csesium, rubidium, and lithium in presence of very large quantities of soda or potassa, extract the dry chlorides, with addition of a few drops of hydrochloric acid, with alcohol of 90 per cent., which leaves behind the far larger portion of the chloride of sodium and chloride of potassium. Evaporate the solution to dryness, dissolve the residue in a little water, and precipitate with bichloride of platinum. Filter the fluid off, wash the precipitate repeatedly with boiling water, to remove the potassio- bichloride of platinum present, and examine in the course of this process repeatedly by the spectroscope. The potassa spectrum will now be found to grow fainter and fainter, whilst the spectra of rubidium and caesium will become visible, if these metals are present. Evaporate the fluid filtered off from the platinum preci- pitate to dryness, heat the residue to slight redness in the hydrogen current, to decompose the sodio-bichloride of platinum and the excess of bichloride of platinum, moisten with hydrochloric acid, drive off the acid again, and extract the chloride of lithium finally with a mixture of absolute alcohol and ether. The evaporation of the solution obtained leaves the chloride of lithium behind in a state of almost perfect purity ; it may then be further examined and tested. Before drawing from the simple coloration of the flame the conclusion that lithia is present, it is advisable, in order to guard against the chance of error, to test a portion of the residue, dissolved in water, with carbonate of ammonia, to make quite sure that strontia or lime is not present. The addition of hydrochloric acid, which is repeatedly prescribed in the above process to precede the extraction of the chloride of lithium with alcohol, is necessary for this reason, that chloride of lithium is, even at a moderate red heat, converted by the action of aqueous vapor into caustic lithia, which then attracts car- bonic acid, forming carbonate of lithia, which is insoluble in alcohol. 94. SECOND GROUP. BARYTA, STRONTIA, LIME, MAGNESIA. Properties of the group. The alkaline earths are soluble in water in the pure (caustic) state. Magnesia, however, dissolves but very sparingly in water. The solutions manifest alkaline reaction ; the alkaline reaction of magnesia is most clearly apparent when that earth is laid upon moistened test-paper. The neutral carbonates and phosphates of the alkaline earths are insoluble in water. The solutions of the salts of the alkaline earths are therefore precipitated by carbonates and phosphates of J. G 82 BARYTA. the alkalies. This reaction distinguishes the oxides of the second group from those of the first. From the oxides of the other groups they are distinguished by the solutions being neither precipitated by hydrosul- phuric acid, nor by sulphide of ammonium. The alkaline earths and their salts are not volatile at a moderate red heat ; they are colorless. The solutions of their nitrates and chlorides are not precipitated by car- bonate of baryta. Special Reactions. 95. a. BARYTA (BaO). 1. CAUSTIC BARYTA is pretty readily soluble in hot water, but rather sparingly so in cold water ; it dissolves freely in dilute hydrochloric or nitric acid. Hydrate of baryta fuses at a red heat, without losing its water. 2. Most of the SALTS OF BARYTA are insoluble in water. The soluble salts do not affect vegetable colors, and are decomposed upon ignition, with the exception of chloride of barium. The insoluble salts dissolve in dilute hydrochloric acid, except the sulphate of baryta and the silico- fluoride of barium. Nitrate of baryta and chloride of barium are inso- luble in alcohol, and do not deliquesce in the air. Concentrated solu- tions of baryta are precipitated by hydrochloric or nitric acid added in large proportions, as chloride of barium and nitrate of baryta are not soluble in the aqueous solutions of the said acids. 3. Ammonia produces no precipitate in the aqueous solutions of salts of baryta ; potassa or soda (free from carbonic acid) only in highly con- centrated solutions. Water redissolves the bulky precipitate of CRYS- TALS OF BARYTA (Ba 0, H O + 8 aq.) produced by potassa or soda. With acid fluids the application of heat is required to effect complete precipi- tation. 4. Carbonates of the alkalies throw down from solutions of baryta CAR- BONATE OF BARYTA (Ba O, C ) in the form of a white precipitate. When carbonate of ammonia is used as the precipitant, or if the solution was previously acid, complete precipitation takes place only upon heating the fluid. Tn chloride of ammonium the precipitate is soluble to a trifling yet clearly perceptible extent ; carbonate of ammonia therefore produces no precipitate in very dilute solutions of baryta containing much chloride of ammonium. 5. /Sulphuric acid and all the soluble sulphates, more particularly also solution of sulphate of lime, produce even in very dilute solutions of baryta, a heavy, finely pulverulent, white precipitate of SULPHATE OF BARYTA (Ba O, S O 3 ), which is insoluble in alkalies, nearly so in dilute acids, but perceptibly soluble in boiling concentrated hydrochloric and nitric acids, as well as in -concentrated solutions of ammonia salts ; how- ever, in these latter only if there is no excess of sulphuric acid present. This precipitate is generally formed immediately upon the addition of the reagent ; from highly dilute solutions, however, especially when strongly acid, it separates only after some time. 6. Hydrofluosilicic acid throws down from solutions of baryta SILICO- FLUORIDE OF BARIUM (Ba Fl, Si F1 2 ) in the form of a colorless crystalline quickly subsiding precipitate. In dilute solutions this precipitate is STRONTIA. 83 formed only after the lapse of some time ; it is perceptibly soluble in hydrochloric and nitric acids. Addition of an equal volume of alcohol hastens the precipitation and makes it so complete that the filtrate re- mains clear upon addition of sulphuric acid. 7. Phosphate of soda produces in neutral or alkaline solutions of baryta a white precipitate of PHOSPHATE OF BARYTA (2 BaO, HO, PO.), which is soluble in free acids. Addition of ammonia only slightly in- creases the quantity of this precipitate, a portion of which is in this process converted into basic phosphate of baryta (3 BaO, P0 6 ). Chlo- ride of ammonium dissolves the precipitate to a clearly perceptible extent. 8. Oxalate of ammonia produces in moderately dilute solutions of baryta a white pulverulent precipitate of OXALATE OF BARYTA (2 BaO, C 4 O 6 + 2 aq.), which is soluble in hydrochloric and nitric acids. When recently thrown down, this precipitate dissolves also in oxalic and acetic acids; but the solutions speedily deposit binoxalate of baryta (BaO, JSO, C 4 O 6 + 2 aq.) in the form of a crystalline powder. 9. If soluble salts of baryta in powder are heated with dilute spirit of wine, they impart to the flame a GREENISH- YELLOW color, which, however, is not very characteristic. 10. If salts of baryta are held on the loop of a platinum wire in the hottest part of Bunseris gas flame, the part of the flame above the sample is colored YELLOWISH-GREEN \ or, if the baryta salts are held in the inner spirit-blowpipe Jlame, the same coloration is imparted to the part of the flame before the sample. With the soluble baryta salts, and also with the carbonate and sulphate of baryta, the reaction is immediate or very soon ] but the phosphate demands previous moistening of the sample with sulphuric acid or hydrochloric acid, by which means the baryta may be detected by the flame coloration also in silicates decom- posable by acids. Silicates which hydrochloric acid fails to decompose must be fluxed with carbonate of soda, when the carbonate of baryta produced will show the reaction. It is characteristic of the yellowish- green baryta coloration of the flame that it appears bluish-green when viewed through the green glass. If the sulphates are selected for the experiment, presence of lime and strontia will not interfere with the reaction. The baryta spectrum, is shown in Table I. The green lines, a and /3, are the most intense ; y is lesser marked, but still characteristic. 11. Cold solutions of bicarbonates of the alkalies or of carbonate of ammonia fail to decompose sulphate of baryta, or, to speak more cor- rectly, they decompose that salt only to a scarcely perceptible extent ; the same applies to a boiling solution of 1 part of carbonate and 3 parts of sulphate of potassa. Repeated action of boiling solutions of simple or monocarbonates of the alkalies upon sulphate of baryta succeeds in the end completely in decomposing that salt. It is readily decomposed also by fusion in conjunction with carbonates of the alkalies, which results in the formation of a sulphate of the fluxing alkali, which is soluble in water, and of carbonate of baryta, which is insoluble in that menstruum 96. b. STRONTIA (SrO). 1. STRONTIA and its HYDRATE and SALTS have nearly the same general properties and reactions as baryta and its corresponding compounds. G2 84 ASTRONTI. Hydrate of strontia is more sparingly soluble in water than hydrate of baryta. Chloride of strontium dissolves in absolute alcohol and deli- quesces in moist air. Nitrate of strontia is insoluble in absolute alcohol and does not deliquesce in the air. 2. The salts of strontia show with ammonia, potassa, and soda, and also with the carbonates of the alkalies and with phospJiate of soda, nearly the same reactions as the salts of baryta. Carbonate of strontia dissolves somewhat more difficultly in chloride of ammonium than is the case with carbonate of baryta. 3. Sulphuric acid and sulphates precipitate from, solutions of strontia SULPHATE OF STRONTIA (SrO, SO 3 ) in the form of a white powder. Sulphate of stroutia is insoluble in spirit of wine ; addition of alcohol will therefore promote the separation of the precipitate. Application of heat greatly promotes the precipitation. Sulphate of strontia is far more soluble in water than sulphate of baryta ; owing to this readier solu- bility, the precipitated sulphate of strontia separates from rather dilute solutions in general only after the lapse of some time ; and this is inva- riably the case (even in concentrated solutions) if solution of sulphate of lime is used as precipitant. In hydrochloric acid and in nitric acid sul- phate of strontia dissolves perceptibly. Presence of larger quantities of these acids will accordingly most seriously impair the delicacy of the re- action. Solution of sulphate of strontia in hydrochloric acid is, after dilution with water, rendered turbid by chloride of barium. 4. Hydrofluosilicic acid fails to produce a precipitate even in concen- trated solutions of strontia ; even upon addition of an equal volume of alcohol no precipitation takes place, except in very highly concentrated solutions. 5. Oxalate of ammonia precipitates even from rather dilute solutions OXALATE OF STRONTIA (2 S 2 0,0 + 5 aq.) in the form of a white powder, which dissolves readily in hydrochloric and nitric acid, and perceptibly in salts of ammonia, but is only sparingly soluble in oxalic and acetic acid. 6. If salts of strontia soluble in water or alcohol are heated with dilute spirit of wine, and the spirit is kindled, the flame appears of a very intense CARMINE color, more particularly upon stirring the alcoholic mixture. 7. If a strontia salt is held in the fusion zone of Eunsens gas flame, or in the inner spirit-blowpipe flame, an INTENSELY RED color is imparted to the flame. With chloride of strontium the reaction is the most distinct, less clear with strontia and carbonate of strontia, fainter still with sulphate of strontia, and scarcely at all with strontia compounds with fixed acids. The sample is therefore, after its first exposure to the flame, moistened with hydrochloric acid, and then again exposed to the flame. If sulphate of strontia is likely to be present, the sample is first exposed a short time to the reducing flame (to produce sulphide of strontium), before it is moistened with hydrochloric acid. Viewed through the Hue glass, the strontia flame appears purple or rose (diffe- rence between strontia and lime, which latter body shows a fainfc greenish-gray color when treated in this manner) ; this reaction is the most clearly apparent if the sample moistened with hydrochloric acid is let spirt up in the flame. In presence of baryta the strontia reaction shows only upon the first introduction of the sample moistened with hydrochloric acid into the flame. The strontia spectrum is shown in Table I. It contains a number of characteristic lines, more especially LIME. 85 the orange line a, the red lines /3 and y, and the blue line 5, which latter is more particularly suited for the detection of strontia in presence of lime. 8. Sulphate of strontia is completely decomposed by continued diges- tion with solutions of carbonate of ammonia or of bicarbonates of the alkalies, but much more rapidly by boiling with a solution of 1 part of carbonate of potassa and 3 parts of sulphate of potassa (essential dif- ference between sulphate of strontia and sulphate of baryta). 97. c. LIME (CaO). 1. LIME and its HYDRATE and SALTS present in their general properties and reactions, a great similarity to baryta and stroutia and their cor- responding compounds. Hydrate of lime is far more difficultly soluble in water than the hydrates of baryta and strontia ', it dissolves also more sparingly in hot than in cold water. Hydrate of lime loses its water upon ignition. Chloride of calcium and nitrate of lime are soluble in absolute alcohol and deliquesce in the air. 2. Ammonia, potassa, carbonates of the alkalies, and phospJtate of soda show nearly the same reactions with salts of lime as with salts of baryta. Kecently precipitated CARBONATE OF LIME (CaO, C0 2 ) is bulky and amorphous after a time, and immediately upon application of heat, it falls down and assumes a crystalline form. Recently precipitated car- bonate of lime dissolves pretty readily in solution of chloride of ammo- nium ; but the solution speedily becomes turbid, and deposits the greater part of the dissolved salt in form of crystals. 3. Sulphuric acid and sulphate of soda produce immediately in highly concentrated solutions of lime white precipitates of SULPHATE OF LIME (CaO, S0 8 , HO + aq.), which redissolve completely in a large proportion of water, and are still far more soluble in acids. In less concentrated solutions the precipitates are formed only after the lapse of some time ; and no precipitation whatever takes place in dilute solutions. Solution of sulphate of lime of course cannot produce a precipitate in salts of lime ; but eveu a cold saturated solution of sulphate of potassa, mixed with 3 parts of water, produces a precipitate only after standing from twelve to twenty-four hours. In solutions of lime which are so very dilute that sulphuric acid has no apparent action on them, a precipitate will immediately form upon addition of alcohol. 4. Hydrojluosilicic acid does riot precipitate salts of lime. 5. Oxalate of ammonia produces in solutions of lime a white pulverulent precipitate of OXALATE OF LIME. If the fluids are in any degree con- centrated or hot, the precipitate (2 CaO, C 4 O 6 + 2 aq.) forms at once ; but if they are very dilute and cold, it forms only after some time, in which latter case it is more distinctly crystalline and consists of a mixture of the above salt with 2 CaO, C 4 O 6 + 6 aq. Oxalate of lime dissolves readily in hydrochloric and nitric acids ; but acetic and oxalic acids fail to dissolve it to any perceptible extent. 6. Soluble salts of lime when heated with dilute spirit of wine impart to the flame of the latter a YELLOWISH-RED color, which is liable to be confounded with that communicated to the flame of alcohol by salts of strontia. 86 MAGNESIA. 7. If salts of lime are held in the hottest part of Bunseris gas flame, or in the inner spirit-blow-pipe flame, they impart to the flame a YEL- LOWISH-RED color. This reaction is the most distinct with chloride of calcium ; sulphate of lime shows it only after its incipient conversion into basic salt, and carbonate of lime also most distinctly after the escape of the carbonic acid. Compounds of lime with fixed acids do not color flame ; those of them which are decomposed by hydrochloric acid will, however, show the reaction after moistening with that acid. The reaction is in such cases promoted by flattening the loop of the platinum wire, placing a small portion of the lime compound upon it, letting it frit, adding a drop of hydrochloric acid, which remains hanging to the loop, and then holding the latter in the hottest part of the flame. The reaction shows now the most distinct light immediately upon the dis- appearance of the drop, which in this process, as in LEIDENFROST'S phe- nomenon, evaporates without boiling (BUNSEN). Viewed through the green glass, the lime coloration of the flame appeal's finch-green colored on letting the sample moistened with hydrochloric acid spirt in the flame (difference between lime and strontia, which latter substance under similar circumstances shows a very faint yellow) (MERZ). In presence of baryta the lime reaction shows only upon the first introduction of the sample into the flame. The lime spectrum is shown in Table I. The intensely green line j3 is more particularly characteristic, also the intensely orange line a. It requires a very good apparatus to show the indigo-blue line to the right of Gr in the solar spectrum, as this is much less luminous than the other lines. 8. With monocarbonates and bicarbonates of the alkalies, sulphate of lime shows the same reactions as sulphate of strontia. 98- d. MAGNESIA (MgO). 1. MAGNESIA and its HYDRATE are white powders of far greater bulk than the other alkaline earths and their hydrates. Magnesia and hydrate of magnesia are nearly insoluble both in cold and hot water. Hydrate of magnesia loses its water upon ignition. 2. Some of the SALTS OP MAGNESIA are soluble in water, others are insoluble in that fluid. The soluble salts of magnesia have a nauseous bitter taste ; in the neutral state they do not alter vegetable colors j with the exception of sulphate of magnesia, they undergo decomposition when gently ignited, and the greater part of them even upon simple evaporation of their solutions. Nearly all the salts of magnesia which are insoluble in water dissolve readily in hydrochloric acid. 3. Ammonia throws down from the solutions of neutral salts of mag- nesia part of the magnesia as HYDRATE (MgO, HO) in the form of a white bulky precipitate. The rest of the magnesia remains in solution as a double salt, viz., in combination with the ammonia salt which forms upon the decomposition of the salt of magnesia ; these double salts are not decomposed by ammonia. It is owing to this tendency of salts of magnesia to form such double salts with ammoniacal compounds that ammonia fails to precipitate them in presence of a sufficient proportion of an ammonia salt with neutral reaction ; or, what comes to the same, that ammonia produces no precipitate in solutions of magnesia contain- MAGNESIA.. 87 ing a sufficient quantity of free acid, and that precipitates produced by ammonia in neutral solutions of magnesia are redissolved upon the addition of chloride of ammonium. 4. Potassa, soda, caustic baryta, and caustic lime, throw down from solutions of magnesia HYDRATE OF MAGNESIA. The separation of this precipitate is greatly promoted by boiling the mixture. Chloride of ammonium and other similar salts of ammonia redissolve the washed precipitated hydrate of magnesia. If the salts of ammonia are added in sufficient quantity to the solution of magnesia before the addi- tion of the precipitant, small quantities of the latter fail altogether to produce a precipitate. However, upon boiling the solution afterwards with an excess of potassa, the precipitate will of course make its appear- ance, since this process causes the decomposition of the ammonia salt, removing thus the agent which retains the hydrate of magnesia in solution. 5. Carbonate of potassa and carbonate of soda produce in neutral solu- tions of magnesia a white precipitate of BASIC CARBONATE OF MAGNESIA 4 (Mg 0, C 2 ) + Mg O, H + 10 aq. One-fifth of the carbonic acid of the decomposed alkaline carbonate is liberated in the process, and combines with a portion of the carbonate of magnesia to bicarbonate, which remains in solution. This carbonic acid is expelled by boiling, and an additional precipitate formed (Mg 0, CO 2 + 3 aq.) Application of heat therefore promotes the separation and increases the quantity of the precipitate. Chloride of ammonium and other similar salts of ammonia prevent this precipitation also, and redissolve the precipitates already formed. 6. If solutions of magnesia are mixed with carbonate of ammonia, the fluid always remains clear at first ; but after standing some time, it deposits, more or less quickly or slowly according to the greater or less concentration or dilution of the solution, a crystalline precipitate of CARBONATE OF MAGNESIA AND AMMONIA (NH 4 O, CO 2 + MgO, C O 2 + 4 aq.) In rather highly dilute solutions this precipitate will not form. Addition of ammonia promotes its separation. Chloride of ammonium counteracts it, but it cannot prevent the formation of the precipitate in rather highly concentrated solutions. 7. Phosphate of soda precipitates from solutions of magnesia, if they are not too dilute, PHOSPHATE OF MAGNESIA (2 Mg O, HO, PO 5 , + 14 aq.) as a white powder. Upon boiling, basic phosphate of magnesia (3 Mg O, P0 5 + 7aq.) separates, even from rather dilute solutions. But if the addition of the precipitant is preceded by that of chloride of ammonium and ammonia, a white crystalline precipitate of BASIC PHOSPHATE OF MAGNESIA AND AMMONIA (2 Mg 0, N H 4 O, P0 6 +12aq.) will separate even from very dilute solutions of magnesia; its separation may be greatly promoted and accelerated by stirring with a glass rod; even should the solution be so extremely dilute as to forbid the formation of a precipitate, yet the lines of direction in which the glass rod has moved along the side of the vessel will after the lapse of some time appear distinctly as white streaks. Water and solutions of salts of ammonia dissolve the precipitate but very slightly ; but it is readily soluble in acids, even in acetic acid. In water containing ammonia it may be considered insoluble. 8. Oxalate of ammonia produces no precipitate in highly dilute solu- tions of magnesia ; in less dilute solutions no precipitate is formed at 88 RECAPITULATION AND REMARKS. first, but after standing some time crystalline crusts of various oxalates of ammonia and magnesia make their appearance. In highly concentrated solutions oxalate of ammonia very speedily produces precipitates of oxalate of magnesia (2MgO, C 4 6 + 4aq.), which contain small quanti- ties of the above-named double salts. Chloride of ammonium, especially in presence of free ammonia, interferes with the formation of these pre- cipitates, but will not in general absolutely prevent it. 9. Sulphuric acid and hydrofluosilicic acid do not precipitate salts of magnesia. 10. Salts of magnesia do not color flame. 99. Recapitulation and remarks. The difficult solubility of the hydrate of magnesia, the ready solubility of the sulphate, and the disposition of salts of magnesia to form double salts with ammonia compounds, are the three principal points in which magnesia differs from the other alkaline earths. To detect magnesia in solutions containing all the alkaline earths, we always first remove the baryta, strontia, and lime. This is effected most conveniently by means of carbonate of ammonia, with addition of some ammonia and of chloride of ammonium, and application of heat ; since by this process the baryta, strontia, and lime are obtained in a form of combination suited for further examination. If the solutions are some- what dilute, and the precipitated fluid is quickly filtered, the carbonate of baryta, strontia, and lime is obtained on the filter, whilst the whole of the magnesia is found in the filtrate. But as chloride of ammonium dissolves a little carbonate of baryta, and also a little carbonate of lime, though much less of the latter than of the former, trifling quantities of these bases are found in the filtrate ; nay, where only traces of them are present, they may altogether remain in solution. In accurate experi- ments, therefore, the separation is effected in the following way : Divide the filtrate into three portions, test one portion with dilute sulphuric acid for the trace of baryta which it may contain in solution, and another portion with oxalate of ammonium for the minute trace of lime which may have remained in solution. If the two reagents produce no turbidity even after some time, test the third portion with phosphate of soda for magnesia. But if one of the reagents causes turbidity, filter the fluid from the gradually subsiding precipitate, and test the filtrate for mag- nesia. Should both reagents produce precipitates, mix the two first por- tions together, filter after some time, and then test the filtrate to make sure that the precipitate thrown down by oxalate of ammonia is actually oxalate of lime, and not, as it may be, oxalate of magnesia and ammonia, dissolve it in some hydrochloric acid, and add dilute sulphuric acid, and then spirit of wine. To show the presence of the baryta, strontia, and lime in the precipi- tate produced by carbonate of ammonia, dissolve the precipitate in somft dilute hydrochloric acid ; add solution of gypsum to a small portion of this solution, when the immediate formation of a precipitate will prove the presence of baryta. Evaporate the remainder of the hydrochloric acid solution to dryness, and treat the residue with absolute alcohol, which will dissolve the chloride of strontium and the chloride of calcium, leaving the greater part of the chloride of barium uudissolved. Mix the alcoholic solution with an equal volume of water and a few drops of RECAPITULATION AND REMARKS. 89 hydrofluosilicic acid, and let the mixture stand several hours, when the last traces of the baryta present will be found precipitated as silicoflu- oride of barium. Filter, and add sulphuric acid to the alcoholic filtrate. This will throw down the strontia and the lime. Filter the fluid from the precipitate, wash with weak spirit of wine, and convert the sulphates into carbonates by boiling with solution of carbonate of soda. Wash the carbonates, dissolve them in a small quantity of hydrochloric acid, evapo- rate the solution to dryness, dissolve the residue in a very little water, and divide the solution into two portions, after previous filtration if necessary. Mix the one portion with solution of gypsum. The formation of a precipitate after some time, often only after a considerable time, shows the presence of STRONTIA. To remove the latterearth from the otherportion, mix this with a solution of sulphate of potassa, boil, filter, and test the filtrate with oxalate of ammonia for LIME. If much lime is present, a portion of it may fall down with the sulphate of strontia precipitate pro- duced by sulphate of potassa ; but there always remains sufficient of it in solution to permit its positive detection in the filtrate without diffi- culty. The best and most convenient way of effecting the detection of the alkaline earths in their phosphates, is to decompose these latter by means of sesquichloride of iron, with addition of acetate of soda ( 142). The oxalates of the alkaline earths are converted into carbonates by ignition, preparatory to the detection of the several earths which they may contain. The following method will serve to analyse mixtures of the sulphates of the alkaline earths. Extract the mixture under exami- nation with small portions of boiling water. The solution contains the whole of the sulphate of magnesia, besides a trifling quantity of sulphate of lime. Digest the residue, according to H. ROSE'S direction, in the cold for 12 hours, with a solution of carbonate of ammonia, or boil it 10 minutes with a solution of 1 part of carbonate and 3 parts of sulphate of potassa, filter, wash, then treat with dilute hydrochloric acid, which will dissolve the carbonates of strontia and lime formed, but always also a minute trace of baryta (FRESENIUS), leaving behind the undecomposed sulphate of baryta. The latter may then be decomposed by fusion with carbonates of the alkalies. The solutions obtained are to be examined further according to the above directions. The detection of baryta, strontia, and lime in the moist way is very instructive, but also rather laborious and tedious. By means of the spectral apparatus these alkaline earths are much more readily detected, even when present all three together. According to the nature of the acid, the sample is either introduced at once into the flame, or after pre- vious ignition and moistening with hydrochloric acid. To detect very minute quantities of baryta and strontia in presence of large quantities of lime, ignite a few grammes of the mixed carbonates a few minutes in a platinum crucible strongly over the blast,* extract the ignited mass by boiling with a little distilled water, evaporate with hydrochloric acid to dryness, and examine the residue by spectrum analysis (ENGELBACH). But even without a spectrum apparatus the three alkaline earths may be detected in mixtures containing all three of them by the different colora- tion which they severally impart to flame. To this end the sample under examination is repeatedly moistened with sulphuric acid, then cautiously * The carbonates of baryta and strontia are much more readily reduced to the caustic state in this process than would be the case in the absence of carbonate of lime. 90 ALUMINA. dried, and introduced into the fusion zone of the gas flame. After the evaporation of the alkalies that may chance to be present, the baryta coloration ( 95, 1 0) will make its appearance alone. After this colora- tion has completely disappeared, and the sample moistened with hydro- chloric acid gives on spirting no longer a flame coloration of a bluish- green tint when viewed through the green glass, the sample is moistened again with hydrochloric acid, and tested for lime by viewing it through the green glass when spirting ( 97, 7), for strontia by viewing it under the same circumstances through the blue glass ( 96, 7) (MERZ). 100. THIRD GROUP. More common oxides of the third group : ALUMINA, SESQUIOXIDE OF CHROMIUM. Rarer oxides of the third group : BERYLLA, THORIA, ZIRCONIA, YTTRIA, OXIDE OF TERBIUM and OSIDE OF ERBIUM, OXIDES OF CERIUM, OXIDE OF LANTHANIUM, OXIDE OF DIDYMIUM, TITANIC ACID, TANTALIC ACID, HY- PONIOBIC ACID. Properties of the group. The oxides of the third group are insoluble in water, both in the pure state and as hydrates. Their sulphides cannot be produced in the moist way. Hydrosulphuric acid therefore fails to precipitate the solutions of their salts. Sulphide of ammonium throws down, from the solutions of the salts in which the oxides of the third group constitute the base,* in the same way as ammonia, the hydrated oxides. This reaction with sulphide of ammonium distin- guishes the oxides of the third from those of the two preceding groups. Special Reactions oj the more common Oxides of the third group. 101. a. ALUMINA (A1 2 3 ). 1. ALUMINIUM metal is nearly white. It is not oxidized by the action of the air, in compact masses not even upon ignition. It may be filed, and is very ductile ; its specific gravity is only 2'56. It is fusible at a bright red heat. In the pulverulent form it slowly decomposes water at a boiling heat \ the compact metal does not show this reaction. Aluminium dissolves readily in hydrochloric acid, as well as in hot solution of potassa, with evolution of hydrogen. Nitric acid dissolves it only slowly, even with the aid of heat. 2. ALUMINA is non-volatile and colorless ; the hydrate is also color- less. Alumina dissolves in dilute acids slowly and with very great difficulty, but more readily in concentrated hot hydrochloric acid. In * The oxides of the third group may nearly all of them combine to saline com- pounds with acids as well as with bases ; alumina, for instance, combines with potassa to aluminate of potassa, with sulphuric acid to sulphate of alumina. The oxides of the third group stand, accordingly, partly on the verge between bases and acids. Those which incline more to the latter, as is the case with the three last members of the group, are therefore also called acids. ALUMINA. 91 fusing bisulphate of potassa, it dissolves readily to a mass soluble in water. The hydrate in the amorphous condition is readily soluble in acids ; in the crystalline state it dissolves in them with very great difficulty. After previous ignition with alkalies, the alumina, or, more correctly speaking, the alkaline aluminate formed, is readily dissolved by acids. 3. The SALTS OF ALUMINA are colorless and non-volatile; some of them are soluble, others insoluble. The soluble salts have a sweetish astringent taste, redden litmus-paper, and lose their acid upon ignition. The insoluble salts are dissolved by hydrochloric acid, with the excep- tion of certain native compounds of alumina ; the compounds of alumina which are insoluble in hydrochloric acid are decomposed and made soluble by ignition with carbonate of soda and potassa, or bisulphide of potassa. This decomposition and solution may, however, be effected also by heating them, reduced to a fine powder, with hydrochloric acid of 25 per cent., or with a mixture of 3 parts by weight of hydrated sulphuric acid, and 1 part by weight of water, in sealed glass tubes, to 392 410 Fahrenheit, continuing the operation for two hours (A. MITSCHERLICH). 4. Potassa and soda throw down from solutions of alumina salts a bulky precipitate of HYDRATE OF ALUMINA (A1 2 O 3 , 3 HO), which contains alkali and generally also an admixture of basic salt ; this precipitate redissolves readily and completely in an excess of the precipitant, but from this solution it is reprecipitated by addition of chloride of ammo- nium, even in the cold, but more completely upon application of heat (compare 53). The presence of salts of ammonia does not prevent the precipitation by potassa or soda. 5. Ammonia also produces in solutions of alumina a precipitate of HYDRATE OF ALUMINA, which contains ammonia and an admixture of basic salt ; this precipitate also redissolves in a very considerable excess of the precipitant, but with difficulty only, which is the greater the larger the quantity of salts of ammonia contained in the solution. It is this deportment which accounts for the complete precipitation of hydrate of alumina from solution in potassa by an excess of chloride of ammonium. 6. Carbonates of t/ie alkalies precipitate BASIC CARBONATE OF ALUMINA, which is insoluble or barely soluble in an excess of the precipitant. 7. If the solution of a salt of alumina is digested with finely pulverized carbonate of baryta, the greater part of the acid of the alumina salt com- bines with the baryta, the liberated carbonic acid escapes, and the alumina precipitates completely as HYDKATE mixed with BASIC SALT OF ALUMINA ; even digestion in the cold suffices to produce this reaction. 8. If alumina or one of its compounds is ignited upon charcoal before the blowpipe, and afterwards moistened with a solution of nitrate of protoxide of cobalt, and then again strongly ignited, an unfused mass of a deep SKY-BLUE color is produced, which consists of a compound of the two oxides. The blue color becomes distinct only upon cooling. By candlelight it appears violet. This reaction is decisive only in the case of infusible or difficultly fusible compounds of alumina pretty free from other oxides, as solution of cobalt will often impart a blue tint to readily fusible salts, even though no alumina be present. 92 SESQUIOXIDE OF CHROMIUM. 102. b. SESQUIOXIDE OF CHROMIUM (Cr 2 8 ). 1. SESQUIOXIDE OF CHROMIUM is a green, its HYDRATE a bluish gray- green powder. The hydrate dissolves readily in acids ; the non-ignited sesquioxide dissolves more difficultly, and the ignited sesquioxide is almost altogether insoluble. 2. The SALTS OF SESQUIOXIDE OF CHROMIUM have a green or violet color. Many of them are soluble in water. Most of them dissolve in hydro- chloric acid. The solutions usually exhibit a fine green or a dark violet color, which latter, however, changes to green upon heating. The salts of sesquioxide of chromium with volatile acids are decomposed upon ignition, the acids being expelled. The salts of sesquioxide of chromium which are soluble in water redden litmus. Anhydrous sesquichloride of chromium is crystalline, violet-colored, insoluble in water and in acids, and volatilizes with difficulty. 3. Potassa and soda produce in the green as well as in the violet solutions of salts of sesquioxide of chromium a bluish-green precipitate of HYDRATE OF SESQUIOXIDE OF CHROMIUM, which dissolves readily and completely in an excess of the precipitant, imparting to the fluid an emerald-green tint. Upon long-continued ebullition of this solution, the whole of the hydrated sesquioxide separates again, and the supernatant fluid appears perfectly colorless. The same reprecipitation takes place if chloride of ammonium is added to the alkaline solution. Application of heat promotes the separation of the precipitate. 4. Ammonia produces in green solutions of salts of sesquioxide of chromium a grayish-green, in violet solutions a grayish-blue precipitate of HYDRATE OF SESQUIOXIDE OF CHROMIUM. The former precipitate dissolves in acids to a green fluid, the latter to a violet fluid. Other circumstances (concentration, way of adding the ammonia, &c.) exercise also some influence upon the composition and color of these hydrates. A small portion of the hydrates redissolves in an excess of the precipitant in the cold, imparting to the fluid a peach-blossom red tint ; but if after the addition of ammonia in excess heat is applied to the mixture the pre- cipitation is complete. 5. Carbonates of the alkalies precipitate BASIC CARBONATE OF SESQUI- OXIDE OF CHROMIUM, which redissolves in a large excess of the precipitant. 6. Carbonate of baryta precipitates from solutions of sesquioxide of chromium the whole of the sesquioxide as a GREENISH HYDRATE mixed with BASIC SALT. The precipitation takes place in the cold, but is com- plete only after long-continued digestion. 7. If a solution of sesquioxide of chromium in solution of potassa or soda is mixed with some brown peroxide of lead in excess, and the mixture is boiled a short time, the sesquioxide of chromium is oxidized to chromic acid. A yellow fluid is therefore obtained on filtering, which consists of a solution of CHROMATE OF OXIDE OF LEAD in solution of potassa or soda. Upon acidifying this fluid with acetic acid, the chromate of lead separates as a yellow precipitate (CHANCEL). Very minute traces of chromic acid may be detected in this fluid with still greater certainty by acidifying with hydrochloric acid, and bringing it in contact with peroxide of hydrogen and ether. Compare chromic acid ( 138). 8. The fusion of sesquioxide of chromium or of any of its compounds RECAPITULATION AND EEMAEKS. 93 with nitrate of soda and carbonate of soda gives rise to the formation of yellow CHROMATE OF SODA, part of the oxygen of the nitric acid sepa- rating from the nitrate of soda and converting the sesquioxide of chro- mium into chromic acid, which then combines with the soda. Chromate of soda dissolves in water to an intensely yellow fluid. For the reactions of chromic acid see 138. 9. Phosphate of soda and ammonia dissolves sesquioxide of chromium and its salts, both in the oxidizing and reducing flame of the blowpipe, to clear beads of a faint YELLOWISH-GREEN tint, which upon cooling changes to EMERALD- GREEN. The sesquioxide of chromium and its salts show a similar reaction with biborate of soda. Bunseris gas flame ( 14) is used for the experiment, or the blowpipe flame. 103. Recapitulation and remarks. The solubility of hydrate of alumina in solutions of potassa and soda, and its reprecipitation from the alkaline solutions by chloride of ammonium, afford a safe means of detecting alumina in the absence of sesquioxide of chromium. But if the latter substance is present, which is seen either by the color of the solution, or by the reaction with phosphate of soda and ammonia, it must be removed before alumina can be tested for. The 'separation of sesquioxide of chro- mium from alumina is effected the most completely by fusing 1 part of the mixed oxides together with 2 parts of carbonate and 2 parts of nitrate of soda, which may be done in a platinum crucible. The yellow mass obtained is boiled with water ; by this process the whole of the chromium is dissolved as chromate of soda, and part of the alumina as aluininate of soda, the rest of the alumina remaining undissolved. If the solution is acidified with nitric acid, it acquires a reddish-yellow tint ; if ammonia is then added to feebly alkaline reaction, the dissolved portion of the alumina separates. The precipitation of sesquioxide of chromium effected by boiling its solution in solution of potassa or soda is also sufficiently reliable if the ebullition is continued long enough ; still it is often liable to mislead in cases where only little sesqnioxide of chromium is present, or where the solution contains organic matter, even though in small proportion only. I have to call attention here to the fact that the solubility of hydrated sesquioxide of chromium in an excess of cold solution of potassa or soda is considerably impaired by the presence of other oxides (protoxides of manganese, nickel, cobalt, and more particularly sesquioxide of iron). If these oxides happen to be present in preponderating proportion, these may even altogether prevent the solution of the hydrated sesqui- oxide of chromium in potassa or soda solution. This circumstance should never be lost sight of in the analysis of compounds containing sesquioxide of chromium. Lastly, it must be borne in mind also that alkalies pro- duce no precipitates in the solutions of alumina if non-volatile organic substances are present, such as sugar, tartaric acid, &c. The precipitation of sesquioxide of chromium by alkalies is more especially impeded and counteracted by the presence of organic acids (oxalic acid, tartaric acid, acetic acid), owing to the formation of double salts which the alkalies fail to decompose. If organic substances are present therefore, ignite, fuse the residue with carbonate and nitrate of soda, and proceed as directed before. 94 BERYLLA. Special Reactions of the rarer Oxides of the third group. 104. 1. BERYLLA (Be 2 8 ). Berylla is a rare earth found in the form of a silicate in phenacite, and, with other silicates, in beryl, euclase, and some other rare minerals. It is a white tasteless powder insoluble in water. The ignited earth dissolves slowly but completely in acids ; it is readily soluble after fusion with bisulphate of potassa. The hydrate dissolves readily in acids. The compounds of berylla very much resemble the alumina com- pounds. The soluble berylla salts have a sweet astringent taste ; their reaction is alka- line. The native silicates of berylla are completely decomposed by fluxing with 4 parts of carbonate of soda and potassa. Potassa, soda, ammonia, and sulphide of ammonium throw down from solution of berylla salts a white flocculent hydrate, which is insoluble in ammonia, but dissolves readily in solution of potassa or soda, from which solution it is precipitated again by chloride of ammonium ; the concentrated alkaline solutions remain clear on boiling, but from more dilute alkaline solutions the whole of the berylla separates upon continued ebullition (difference between berylla and alumina). Upon continued ebullition with chloride of ammonium, the freshly precipitated hydrate dissolves as chloride of beryllium, with expulsion of ammonia (difference between berylla and alumina). Carbonates of the alkalies precipitate white carbonate of berylla, which redissolves in a great excess of the carbonates of the fixed alkalies, and in a much less considerable excess of carbonate of ammonia (most charac- teristic difference between berylla and alumina). Upon boiling these solutions basic carbonate of berylla separates, readily and completely from the solution in carbonate of ammonia, but only upon dilution and imperfectly from the solutions in carbonates of the fixed alkalies. Carbonate of baryta precipitates berylla incompletely upon cold digestion, completely upon boiling. Oxalic acid and oxalates do not precipitate berylla. Moistened with solution of nitrate of protoxide of cobalt, the berylla compounds give gray masses upon ignition. 2. TflOBlA(ThO). Thoria is a very rare earth found in thorite and monacite. It is white. The ignited earth is soluble only upon heating with a mixture of 1 part of concentrated sulphuric acid and 1 part of water ; but it is not soluble in other acids, not even after fusion with alkalies. The moist hydrate dissolves readily in acids, the dried hydrate only with difficulty. Thorite (silicate of thoria) is decomposed by concentrated hydrochloric acid. Potassa, ammonia, and sulphide of ammonium precipitate from solutions of thoria salts white hydrate, which is insoluble in an excess of the precipitant, even of potassa (difference between thoria and berylla). Carbonate of potassa and carbonate of ammonia precipitate basic carbonate of thoria, which readily dissolves in an excess of the precipitant in concentrated solutions, with difficulty in dilute solutions (dif- ference between thoria and alumina). From the solution in carbonate of ammonia basic salt separates again even at 122 Fahrenheit. Oxalic acid produces a white precipitate (difference between thoria and berylla and alumina) ; the precipitate does not dissolve in oxalic acid, and barely in other acids. A concentrated solution of sulphate of potassa precipitates thoria solutions, slowly but completely (difference between thoria and alumina and berylla). The precipitate, which is sulphate of thoria and potassa, is insoluble in a concentrated solution of sulphate of potassa ; it dissolves slowly in cold water, readily in hot water. The solution deposits basic salt upon con- tinued boiling. 3. ZIRCONIA (Zr 2 3 ). Found in zircon and some other rare minerals. A white powder insoluble in hydro- chloric acid, soluble upon addition of water, after continued heating with a mixture of 2 parts of hydrated sulphuric acid and 1 part of water. The hydrate resembles hydrate of alumina. It dissolves readily in hydrochloric acid when precipitated cold, and still rnoist, but with difficulty only when precipitated hot, or after drying. The zirconia salts soluble in water redden litmus. The native silicates of zirconia may be decomposed by fusion with carbonate of soda. The finely elutriated silicate is fused at a high temperature, together with 4 parts of carbonate of soda. The fused mass gives to water silicate of soda, a sandy zirconate of soda being left behind, which is washed, and dissolves in hydrochloric acid. Potassa, soda, ammonia, and sulphide of ammonium precipitate from solutions of zirconia salts a flocculent hydrate, which is insoluble in an excess of the precipitant, even of soda and potassa (difference between zirconia and alumina and berylla), and is not dissolved even by boiling solution of YTTBIA. 95 chloride of ammonium (difference between zirconia and berylla). Carbonates of potassa, soda, and ammonia, throw down carbonate of zirconia as a flocculent precipitate, which redissolves in a large excess of carbonate of potassa, more readily in bicarbonate of potassa, and most readily in carbonate of ammonia (difference between zirconia and alumina), from which solution it precipitates again on boiling. Oxalic acid produces a bulky precipitate of oxalate of zirconia (difference between zirconia and alumina and berylla), which is insoluble in oxalic acid, difficultly soluble in hydrochloric acid. A concentrated solution of sulphate of potassa speedily produces a white precipitate of sulphate of zirconia and potassa (difference between zirconia and alumina and berylla), which if precipitated cold dissolves readily in a large proportion of hydrochloric acid, but is almost absolutely insoluble in water and in hydrochloric acid if precipi- tated hot (difference between zirconia and thoria). Carbonate of baryta fails to effect complete precipitation in solutions of zirconia salts, even upon boiling. Turmeric paper dipped into solutions of zirconia salts slightly acidified with hydrochloric or sulphuric acid, acquires a reddish-brown color after drying (difference between zirconia and thoria). 4. YTTRIA (YO). Yttria is a rare earth found in gadolinite, orthite, yttro-tantalite. The ignited earth dissolves readily in hydrochloric acid (difference between yttria and zirconia and alumina). In the pure state it is white ; presence of oxides of erbium and terbium imparts a brownish- yellow tiut to it. The hydrate is white ; it attracts carbonic acid ; if freshly precipitated, it dissolves in boiling solution of chloride of ammonium (difference between yttria and alumina and zirconia). The salts are white, with a slight shade of amethyst red. Anhydrous chloride of yttrium is not volatile (difference between yttria and alumina, berylla, thoria, and zirconia). Potassa precipitates white hydrate, which is insoluble in an excess of the precipitant (difference between yttria and alumina and berylla). Ammonia and sulphide of ammonium produce the same reaction. Presence of a small quantity of chloride of ammonium will not prevent the precipitation by sul- phide of ammonium ; but in presence of a large excess of chloride of ammonium sul- phide of ammonium fails to precipitate solutions of salts of yttria. Carbonates of the alkalies produce a white precipitate, which dissolves with difficulty in carbonate of potassa, but more readily in bicarbonate of potassa and in carbonate of ammonia, though by no means so readily as the corresponding berylla precipitate. The solution of the pure hydrate in carbonate of ammonia deposits on boiling the whole of the yttria ; if chloride of ammonium is present at the same time, this is decomposed upon continued heating, with separation of ammonia, and the precipitated yttria redissolves as chloride of yttrium. Saturated solutions of carbonate of yttria in carbonate of ammonia have a tendency to deposit carbonate of yttria and ammonia, which should be borne in mind. Oxalic acid produces a white precipitate (difference between yttria and alumina and berylla). The precipitate does not dissolve in oxalic acid, but it dissolves in hydrochloric acid. Sulphate of potassa precipitates sulphate of yttria and potassa. The precipi- tate, even if thrown down hot, dissolves, though slowly, in a large proportion of water (difference between yttria and zirconia) ; it dissolves a little more readily in solution of sulphate of potassa (difference between yttria and thoria), and still more readily in solu- tion of ammonia salt. Carbonate of baryta produces no precipitate ; not even on boiling. Turmeric paper is not altered by acidified solutions of salt of yttria (difference between yttria and zirconia). Tarfaric acid does not interfere with the precipitation of yttria by alkalies (characteristic difference between yttria and alumina, berylla, thoria, and zirconia). The precipitate is tartrate of yttria. The precipitation ensues only after some time, but it is complete. 5. OXIDE OF TERBIUM (TrO), and 6. OXIDE or ERBIUM (EO). These oxides are generally found associated with yttria. Upon gradual addition of ammonia to a solution containing these three bases, the oxide of erbium precipitates first, the oxide of terbium next, and the yttria last. Ignited oxide of erbium varies from yellow to orange-yellow. Oxide of terbium, which is not yet known in the pure state, appears to be white. We know as yet of no other reactions by which to separate these bases from yttria, or to distinguish between them and that earth. 7. OXIDES OF CERIUM. Cerium is a rare metal ; it is found in the form of protoxide in cerite, orthite, &c. It forms two oxides, the protoxide (CO) and the sesquioxide (C g 3 ). The hydrate of the protoxide is white, but turns yellow upon exposure to the air, by absorption of oxvgen. By ignition in the air it is converted into orange-red or red sesquioxide (difference between it and the preceding earths). Hydrate of protoxide of cerium dis- yb OXIDE OF LANTHANIUM. solves readily in acidg. Ignited sesquioxide of cerium containing oxide of lanthanium and didymium dissolves readily in hydrochloric acid, with evolution of chlorine ; in the pure state it dissolves very slightly in boiling hydrochloric acid, except upon addition of some alcohol (difference between oxide of cerium and thoria and zirconia) ; the solution con- tains protochloride. The salts of protoxide of cerium are colorless, occasionally with a slight shade of amethyst red ; the soluble protoxide salts redden litmus. Protochloride of cerium is not volatile (difference from alumina, berylla, thoria, and zirconia). Cerite (hydrated silicate of protoxide of cerium [CO, LaO, DiO] 2, SiO 8 + 2aq.) does not dissolve in aqua regia ; but is decomposed by fusion with carbonate of soda, and also by concentrated sulphuric acid. Potassa precipitates white hydrate, which turns yellow in the air, and does not dissolve in an excess of the precipitant (difference from alumina and berylla). Ammonia precipitates basic salt, which is insoluble in an excess of the precipitant. Carbonates of the alkalies produce a white precipitate, which dissolves sparingly in an excess of carbonate of potassa, somewhat more readily in carbonate of ammonia. Oxalic acid produces a white precipitate ; the precipitation is complete even in moderately acid solutions (difference from alumina and berylla). The precipitate is not dissolved by oxalic acid ; but it dissolves in a large proportion of hydrochloric acid. A saturated solution of sulphate of potassa precipitates, even from somewhat acid solutions, white sulphate of potassa and protoxide of cerium (difference from alumina and berylla), which is very difficultly soluble in water and altogether insoluble in a saturated solution of sulphate of potassa (difference from yttria). The precipitate may be dissolved by boiling with 'a large quantity of water, to which some hydrochloric acid has been added. Carbonate of baryta precipitates solutions of cerium salts slowly, but completely upon long-continued action. Tartaric acid prevents pre- cipitation by ammonia (difference from yttria), but not by potassa. Borax and phos- phate of soda and ammonia dissolve cerium compound in the outer flame to red beads (difference from the preceding earths) ; the coloration gets fainter on cooling, and often disappears altogether. In the inner flame colorless beads are obtained. 8. OXIDE OF LANTHANIUM. This oxide is generally found associated with protoxide of cerium. It is white and remains unaltered by ignition in the air (difference from protoxide of cerium). In contact with cold water it is slowly converted into a milk-white hydrate ; with hot water the conversion is rapid. The oxide and its hydrate change the color of reddened litmus-paper to blue ; they dissolve in boiling solution of chloride of ammonium, also in dilute acids. Oxide of lanthanium in this resembles magnesia. The salts of oxide of lanthanium are colorless ; the saturated solution of sulphate of oxide of lanthanium in cold water deposits a portion of the salt already at 86 Fahrenheit (difference from protoxide of cerium). Sulphate of potassa, oxalic acid, and carbonate of baryta give the same reactions as with protoxide of cerium. Potassa precipitates hydrate, which is insoluble in an excess of the precipitant, and does not turn brown in the air. Ammonia precipitates basic salts, which pass milky through the filter on washing. The precipitate produced by carbonate of ammonia is insoluble in an excess of the precipitant (difference from protoxide of cerium). If a cold saturated solution of acetate of oxide of lanthanium is supersaturated with ammonia, the slimy precipitate repeatedly washed with cold water, and a little iodine in powder added, a blue coloration makes its appearance, which gradually pervades the entire mixture (characteristic difference between oxide of lanthanium and the other earths). 9. OXIDE OF DIDYMIUM. This oxide, like the oxide of lanthanium and in conjunction with it, is found associated with the protoxide of cerium. After intense ignition it appears white, moistened with nitric acid and feebly ignited dark brown, after intense ignition again white. In contact with water it is slowly converted into hydrate ; it rapidly attracts carbonic acid ; its reaction is not alkaline ; it dissolves readily in acids. The concentrated solutions have a reddish or a faint violet color. The saturated solution of the sulphate deposits salt, not at 86 Fahrenheit, but upon boiling. Potassa precipitates hydrate, which is insoluble in an excess of the precipitant, and does not alter in the air. Am- monia precipitates basic salt, which is insoluble in ammonia, but slightly soluble in chloride of ammonium. Carbonates of the alkalies produce a copious precipitate, which is insoluble in an excess of the precipitant, even in an excess of carbonate of ammonia (difference from protoxide of cerium), but dissolves slightly in concentrated solution of chloride of ammonium. Oxalic acid precipitates solutions of salt of oxide of didymium almost completely ; the precipitate is difficultly soluble in cold hydrochloric acid, but dis- solves in that menstruum upon application of heat. Carbonate of baryta precipitates TITANIC ACID. 97 oxide of didymium from its solutions slowly (more slowly than protoxide of cerium and oxide of lanthanium), and never completely. A concentrated solution of sulphate of po- tassa precipitates didymium solutions more slowly and less completely than protoxide of cerium solutions. Th precipitate is insoluble in cold, difficultly soluble in hot hydro- chloric acid. Phosphate of soda and ammonia dissolves didymium compounds in the reducing flame to amethyst-red beads, shading off to violet. With soda a grayish white mass is obtained in the outer flame (difference from manganese). Perfectly satisfactory methods for effecting the separation of cerium, lanthanium, and didymium are not known. The oxide of cerium may be obtained in a state of approximate purity by treating the mixed oxides, after ignition, first with dilute, then with concentrated nitric acid, which will leave, undissolved, the greater part of the oxide of cerium. If the solution is evaporated and the residue ignited and then again treated with nitric acid, the remainder of the oxide of cerium, which had been dissolved, together with the other oxides, is now also left undissolved. The oxides of lanthanium and didymium are precipitated from the solution by an alkali ; the precipitate is dissolved in sulphuric acid, water saturated with the dry saline mixture at 41 to 42-8 Fahrenheit, and the solution heated to 86 Fahrenheit. Sulphate of oxide of lanthanium separates, sulphate of oxide of didymium remains in solution. 10. TITANIC ACID. Titanium forms two oxides, sesquioxide of titanium (Ti 3 3 ) and titanic acid (Ti0 2 ). The latter is somewhat more frequently met with in analysis. It is found in the free state in rutile and anatase, in combination with bases in titanite, titaniferous iron, &c. It is found in small proportions in many iron ores, and consequently often in blast-furnace slags. The small copper-colored cubes which are occasionally found in such slags con- sist of a combination of cyanide of titatinum with nitride of titanium. Feebly ignited titanic acid is white ; it transiently acquires a lemon tint when heated ; very intense ignition gives a yellowish or brownish tint to it. It is infusible, insoluble in water, and its specific gravity is 3'9 to 4 '25. a. Deportment with acids and reactions of acid solutions of titanic acid. Ignited titanic acid is insoluble in acids, except in hydrofluoric acid and in concentrated sul- phuric acid. With bisulphate of potassa it gives upon sufficiently long-continued fusion a clear mass, which dissolves in a large proportion of cold water to a clear fluid. Hydrate of titanic acid dissolves, both moist and when dried without the aid of heat, in dilute acids, especially in hydrochloric and sulphuric acids. All the solutions of titanic acid in hydrochloric or sulphuric acid, but more particularly the latter, when subjected in a highly dilute state to long-continued boiling, deposit titanic acid as a white powder, insoluble in dilute acids. Presence of much free acid retards the sepa- ration and diminishes the quantity of the precipitate. The precipitate which separates from the hydrochloric acid solution may, indeed, be filtered, but it will pass milky through the filter upon washing, except an acid or chloride of ammonia be added to the washing water. Solution of potassa throws down from solutions of titanic acid in hydrochloric or sulphuric acid hydrate of titanic acid as a bulky white precipitate, which is insoluble in an excess of the precipitant ; ammonia, sulphide of ammonium, carbonate of the alkalies, and carbonate of baryta act in the same way. The precipi- tate, thrown down cold and washed with cold water, is soluble in hydrochloric acid and in dilute sulphuric acid ; presence of tartaric acid prevents its formation. Ferro- cyanide of potassium produces in acid solutions of titanic acid a dark-brown precipi- tate ; infusion of galls a brownish precipitate, which speedily turns orange-red. Me- tallic zinc produces, in consequence of the ensuing reduction of titanic acid to sesqui- oxide of titanium, at first a blue coloration of the solution, afterwards a blue precipi- tate of hydrate of sesquioxide of titanium. b. Reactions with alkalies. Eecently precipitated hydrate of titanic acid is almost absolutely insoluble in solution of potaesa. If titanic acid is fused together with hydrate of potassa, and the fused mass treated with water, the solution contains a little more titanic acid. By fusion with carbonates of the alkalies neutral titanates of the alkalies are formed, with expulsion of carbonic acid. Water extracts from the fused mass free alkali and alkaline carbonate, leaving behind acid titanate of alkali which dissolves in hydrochloric acid. Titanic acid mixed with charcoal gives upon ignition in a stream of chlorine bichloride of titanium as a volatile liquid, which emits copious fumes in the air. Phosphate of soda and ammonia readily dissolves titanic acid in the outer flame to a clear bead of a yellowish color whilst hot, but colorless when cold. Upon long-continued exposure to a strong reducing flame this bead acquires a yellow tint, which turns to red when the bead is half cold, and to violet when quite cold. I. H 98 TANTALIC ACID. Addition of a little tin promotes the reduction. If a small quantity of sulphate of prot- oxide of iron is added, the bead obtained in the reducing flame looks blood red. 11. TANTALIC ACID. Tantalum forms two oxides, Ta0 2 and Ta 3 . The latter, which is called tantalic acid, is found in tantalite, yttro-tantalite, and some other rare minerals. Tantalic acid is white, and remains so upon ignition (difference between tantalic acid and titanic acid). Ignited tantalic acid has a specific gravity of from 7 to 8. Tantalic acid com- bines with acids and with bases. a. Reactions with acids. The ignited acid is insoluble in hydrochloric acid and in concentrated sulphuric acid. It fuses with sulphate of potassa to a mass which on extraction with water leaves behind tantalic acid in combination with sulphuric acid (difference between tantalic acid and titanic acid ; but which affords only an imperfect means of separating the two acids from each other). Ignition in an atmosphere of ammonia converts this compound of sulphuric acid with tantalic acid into pure tantalic acid. If a solution of tantalate of an alkali is mixed with hydrochloric acid in excess, the precipitate which forms at first redissolves to an opalescent fluid. Ammonia and sul- phide of ammonium throw down from it hydrated or acid tantalate of ammonia ; pre- sence of tartaric acids prevents precipitation. Sulphuric acid throws down from the opalescent solution sulphate of tantalic acid. If tantalates of the alkalies be strongly acidified with hydrochloric acid, v and then brought into contact with zinc, even addition of sulphuric acid will fail to produce a blue coloration of the fluid, or at all events the coloration will only be slight ; but if solid chloride of tantalum be dissolved in concen- trated sulphuric acid, and water and zinc added to the solution, the fluid will turn blue, not changing to brown by standing, b. Reactions with alkalies. By continued fusion with hydrate of potossa tantalate of potassa is formed ; the fused mass dissolves in water. By fusion with hydrate of soda a turbid mass is obtained ; a little water poured on this mass will dissolve out the excess of soda, leaving the whole of the tantalate of soda undissolved, as this latter salt is insoluble in solution of soda ; but the tantalate of soda will dissolve in water after the removal of the excess of soda. Solution of soda throws down from this solution the tantalate of soda ; if the preci- pitant be added slowly, the form of the precipitate is crystalline. Carbonic acid throws down from solutions of tantalates of the alkalies acid salts, which are not dissolved by boiling with solution of carbonate of soda. Sulphuric acid throws down even from dilute solutions of tantalates of the alkalies sulphate of tantalic acid ; ferrocyanide of potassium and infusion of galls produce precipitates only in acidified solutions ; the pre- cipitate produced by the former is yellow, by the latter light brown. By ignition with charcoal in pure dry chlorine gas white yellow chloride of tantalum is formed, which sublimes in crystals ; if the tantalic acid contains titanic acid, this reaction is at- tended moreover by the formation of bichloride of titanium, which emits copious fumes in the air. Phosphate of soda and ammonia dissolves tantalic acid to a colorless bead, which remains colorless even in the inner flame, and does not acquire a blood-red tint by addition of sulphate of protoxide of iron (difference between tantalic acid and titanic acid). 12. HYPONIOBIO ACID. Niobium forms two oxides, viz., hyponiobic acid (Nb z 3 ) and niobic acid (Nb 2 ). Hyponiobic acid is a rare substance ; it is found in columbite, samarskite, &c. It is white, but turns transiently yellow when ignited (difference between hyponiobic acid and tantalic acid). Specific gravity varies from 4 '6 to 6' 5 at the most (difference from tantalic acid). Hyponiobic acid combines with acids and with bases, a. Acid solutions of hyponiobic acid. Concentrated sulphuric acid dissolves hyponiobic acid upon heating ; by addition of a large proportion of cold water a clear solution is obtained, from which the hyponiobic acid separates in combination with sulphuric acid, slowly and gradually in the cold, rapidly upon boiling. By washing the precipitate with car- bonate of ammonia, then with highly dilute hydrochloric acid, the hydrate is obtained by ignition in an atmosphere of carbonate of ammonia we obtain the acid. Ammonia and sulphide of ammonium precipitate acid hyponiobate of ammonia. Hyponiobic acid is readily dissolved by fusion with bisulphate of potassa ; on treating the fused mass with hot water sulphate of hyponiobic acid is left behind undissolved. b. Alkaline solutions. Hyponiobic acid fuses with hydrate of potassa to a clear mass, which is soluble in water ; with hydrate of soda it fuses to a turbid mass ; water dissolves the excess of soda out of this mass ; after the removal of the solution of soda, the hypo- niobate of soda dissolves in water. Fusion with carbonate of soda gives rise to similar reactions as fusion with hydrate of soda. Solution of soda slowly added to the aqueous solution separates from it crystallized hyponiobate of so.da. The solutions of OXIDE OF ZINC. S9 the hyponiobates of the alkalies are not rendered turbid by boiling ; sulphuric acid precipitates from them the whole of the hyponiobic acid upon boiling ; the precipita- tion by chloride of ammonium is less complete ; hydrochloric acid produces a precipi- tate which does not re-dissolve in an excess of the precipitant (difference between hyponiobic acid and titanic and tantalic acids). If zinc is added after the hydrochloric acid, the precipitated hypouiobic acid acquires a blue tint, which gradually changes to brown (difference from tantalic acid). Carbonic acid throws down acid hyponiobate of alkali, which is soluble in boiling dilute solution of carbonate of soda (means of separating hyponiobic acid from tantalic acid). Ferrocyanide of potassium produces no precipitate, except in acidified solutions, which it precipitates dark brown. Infusion of galls produces no precipitate, except in acidified solutions, which it precipitates deep orange-red. By ignition of hyponiobic acid, mixed with charcoal, in a stream of chlorine gas, white solid sesquichloride of niobium, and yellow solid somewhat more volatile bichlo- ride of niobium are obtained. Phosphate of soda and ammonia dissolves hyponiobic acid copiously ; the bead produced in the inner flame shows a violet, blue, or brown color, according to the mode of preparation of the hyponiobic acid, and the quantity used of it ; addition of sulphate or protoxide of iron imparts a blood- red tint to the bead. For the best methods and processes of detecting many, possibly even all the oxides of the third group in presence of each other, the reader is referred to Part II., Section III. 105. FOURTH GROUP. More common oxides of the fourth group: OXIDE OP ZINC, PROTOXIDE OF MANGANESE, PROTOXIDE OF NICKEL, PROTOXIDE OF COBALT, PROT- OXIDE OF IRON, SESQUIOXIDE OF IRON. Rarer oxides of the fourth group : SESQUIOXIDE OF URANIUM, OXIDES OF VANADIUM, OXIDES OF THALLIUM. Properties of the group. The solutions of the oxides of the fourth group, if containing a stronger free acid, are not precipitated by hydro- sulphuric acid ; nor are neutral solutions, at least not completely. But alkaline solutions are completely precipitated by hydrosulphuric acid ; and so are other solutions if a sulphide of an alkali metal is used as the precipitant, instead of hydrosulphuric acid. The precipitated metallic sulphides corresponding to the several oxides are insoluble in water ; some of them are readily soluble in dilute acids; others (sulphide of nickel and sulphide of cobalt) dissolve only with very great difficulty in these menstrua. Some of them are insoluble in sulphides of the alkali metals, others (nickel) are sparingly soluble in them, under certain circum- stances, whilst others again (vanadium) are completely soluble. The oxides of the fourth group differ accordingly from those of the first and second groups in this, that their solutions are precipitated by sulphide of ammonium, and from those of the third group inasmuch that the precipi- tates produced by sulphide of ammonium are sulphides, and not hydrated oxides, as is the case with alumina, sesquioxide of chromium, &c. Special Reactions of the more common Oxides of the fourth group. 106. a. OXIDE OF ZINC (ZnO). 1. METALLIC ZINC is bluish-white and very bright; when exposed to the air, a thin coating of basic carbonate of zinc forms on its surface. 100 OXIDE OF ZINC. It is of medium hardness, ductile at a temperature of between 212 and 302 Fah., but otherwise more or less brittle ; it fuses readily on char- coal before the blowpipe, boils afterwards, and burns with a bluish-green flame, giving off white fumes, and coating the charcoal support with oxide. Zinc dissolves in hydrochloric and sulphuric acids, with evolu- tion of hydrogen gas ; in dilute nitric acid, with evolution of nitrous oxide ; in more concentrated nitric acid, with evolution of nitric oxide. 2. The OXIDE OF ZINC and its HYDEATE are white powders, which are insoluble in water, but dissolve readily in hydrochloric, nitric, and sulphuric acids. The oxide of zinc acquires a lemon-yellow tint when heated, but it reassumes its original white color upon cooling. When ignited before the blowpipe, it shines with considerable brilliancy. 3. The salts of OXIDE OF ZINC are colorless ; part of them are soluble in water, the rest in acids. The neutral salts of zinc which are soluble in water redden litmus-paper, and are readily decomposed by heat, with the exception of sulphate of zinc, which can bear a dull red heat without undergoing decomposition. Chloride of zinc is volatile at a red heat. 4. Hydrosulphuric acid precipitates from neutral solutions of salts of zinc a portion of the metal as white hydrated SULPHIDE of ZINC (Zn S). In acid solutions this reagent fails altogether to produce a precipitate if the free acid present is one of the stronger acids ; but from a solution of oxide of zinc in acetic acid it throws down the whole of the zinc, even if the acid is present in excess. 5. Sulphide of ammonium throws down from neutral, and hydrosul- phuric acid from alkaline solutions of salts of zinc, the whole of the metal as hydrated SULPHIDE OF ZINC, in the form of a white precipitate. Chloride of ammonium greatly promotes the separation of the precipitate. From very dilute solutions the precipitate separates only after long standing. This precipitate is not redissolved by an excess of sulphide of ammonium, nor by potassa or ammonia ; but it dissolves readily in hydrochloric acid, nitric acid, and dilute sulphuric acid. It is insoluble in acetic acid. 6. Potassa and soda throw down from solutions of salts of zinc HYDRATED OXIDE OF ZINC (Zn O, H 0), in the form of a white gela- tinous precipitate, which is readily and completely redissolved by an excess of the precipitant. Upon boiling these alkaline solutions they remain, if concentrated, unaltered ; but from dilute solutions nearly the whole of the oxide of zinc separates as a white precipitate. Chloride of ammonium does not precipitate alkaline solutions of oxide of zinc. 7. Ammonia also produces in solutions of oxide of zinc, if they do not contain a large excess of free acid, a precipitate of HYDRATED OXIDE OF ZINC, which readily dissolves in an excess of the precipitant. The concentrated solution turns turbid when mixed with water. On boiling the concentrated solution part of the oxide of zinc separates imme- diately ; on boiling the dilute solution all the oxide of zinc precipitates. 8. Carbonate of soda produces in solutions of salts of zinc a precipi- tate of BASIC CARBONATE OF ZINC (3 [ZnO, HO] + 2 [Zn 0, CO 2 ] + 4 aq.), which is insoluble in an excess of the precipitant. Presence of salts of ammonia in great excess prevents the formation of this pre- cipitate. 9. Carbonate of ammonia' also produces in solutions of salts of zinc the same precipitate of BASIC CARBONATE OF ZINC as carbonate of soda ; PROTOXIDE OP MANGANESE. 101 but this precipitate redissolves upon further addition of the precipi- tant. On boiling the dilute solution oxide of zinc precipitates. 10. Carbonate of baryta fails to precipitate solutions of salts of zinc in the cold, with the exception of the sulphate. 11. If a mixture of oxide of zinc or one of its salts with carbonate of soda is exposed to the reducing flame of the blowpipe, the charcoal support becomes covered with a slight coating of OXIDE OF ZINC, which presents a yellow color whilst hot, and turns white upon cooling. This coating is produced by the reduced metallic zinc volatilizing at the moment of its reduction, and being reoxidized in passing through the outer flame. 12. If oxide of zinc or one of the salts of zinc is moistened with solution of nitrate of protoxide of cobalt, and then heated before the blowpipe, an unfused mass is obtained of a beautiful GREEN color : this mass is a compound of oxide of zinc with protoxide of cobalt. If there- fore in the experiment described in 11 the charcoal is moistened around the little cavity with solution of nitrate of protoxide of cobalt, the coating appears green when cold. 107. b. PROTOXIDE OF MANGANESE (MnO). 1. METALLIC MANGANESE is whitish-gray, brittle, extremely hard, and fuses with very great difficulty. It takes a high polish, which it rather speedily loses again upon exposure to the air. At first it blues, like steel when heated, but after a time it becomes covered with a layer of brown oxide. It oxidizes only slowly in water at the common tem- perature, but more rapidly in boiling water. It dissolves readily in acids, the solutions contain protoxide. 2. PROTOXIDE OF MANGANESE is grayish-green; the hydrated prot- oxide is white. Both the protoxide and its hydrate absorb oxygen from the air, and are converted into the brown proto-sesquioxide. They are readily soluble in hydrochloric, nitric, and sulphuric acids. All the higher oxides of manganese without exception dissolve to protochloride, with evolution of chlorine, when heated with hydrochloric acid ; to sulphate of protoxide, with evolution of oxygen, when heated with concentrated sulphuric acids. 3. The SALTS OF PROTOXIDE OF MANGANESE are colorless or pale red ; part of them are soluble in water, the rest in acids. The salts soluble in water are readily decomposed by a red heat, with the exception of the sulphate. The solutions do not alter vegetable colors. 4. Hydrosulphuric acid does not precipitate acid solutions of salts of protoxide of manganese ; neutral solutions also it fails to precipitate, or precipitates them only very imperfectly. 5. Sulphide of ammonium throws down from neutral, and hydrosul- phuric acid from alkaline solutions of salts of protoxide of manganese, the whole of the metal as hydrated SULPHIDE OF MANGANESE (MnS), in form of a light flesh-colored* precipitate, which acquires a dark-brown color in the air ; this precipitate is insoluble in sulphide of ammonium and in alkalies, but readily soluble in hydrochloric, nitric, and acetic acids. The separation of the precipitate is materially promoted by * If the quantity of the precipitate is only trifling, the color appears yellowish-white. 102 PROTOXIDE OP NICKEL. addition of chloride of ammonium. Erom very dilute solutions the precipitate separates only after standing some time in a warm place. Solutions containing much free ammonia must first be neutralized with hydrochloric acid. 6. Potassa, soda, and ammonia produce whitish precipitates of HY- DRATE OF PROTOXIDE OF MANGANESE (MnO, H O), which upon exposure to the air speedily acquire a brownish and finally a deep blackish-brown color, owing to the conversion of the hydrated protoxide into hydrated proto-sesquioxide by the absorption of oxygen from the air. Ammonia and carbonate of ammonia do not redissolve this precipitate ; but presence of chloride of ammonium prevents the precipitation by am- monia altogether, and that by potassa partly. Of already formed pre- cipitates solution of chloride of ammonium redissolves only those parts which have not yet undergone peroxidation. The solution of the hydrated protoxide of manganese in chloride of ammonium is owing to the disposition of the salts of protoxide of manganese to form double salts with salts of ammonia. The ammoniacal solutions of the double salts turn brown in the air, and deposit dark-brown hydrate of proto- sesquioxide of manganese. 7. Tf a few drops of a fluid containing protoxide of manganese, and free from chlorine, are sprinkled on binoxide of lead or red-lead, and nitric acid free from chlorine is added, the mixture boiled and allowed to settle, the NITRATE OF SESQUIOXIDE OF MANGANESE formed imparts a purple-red color to the fluid. 8. Carbonate of baryta does not precipitate protoxide of manganese from aqueous solutions of its salts upon digestion in the cold, with the exception of sulphate of protoxide of manganese. 9. If any compound of manganese, in a state of minute division, is fused with carbonate of soda on a platinum wire, or on a small strip of platinum foil (heated by directing the flame upon the lower surface), in the outer flame of the blowpipe, MANGANATE OF SODA (NaO, Mn0 3 ) is formed, which makes the fused mass appear GREEN while hot, and of a BLUISH-GREEN tint after cooling, the bead at the same time becoming turbid. This reaction enables us to detect the smallest traces of manganese. 10. Borax and phosphate of soda and ammonia dissolve manganese compounds in the outer gas or blowpipe flame to clear VIOLET-RED beads, which upon cooling acquire an AMETHYST-RED tint : they lose their color in the inner flame, owing to a reduction of the sesquioxide to protoxide. The bead which borax forms with manganese compounds appears black when containing a considerable portion of sesquioxide of manganese, but that formed by phosphate of soda and ammonia never loses its transparency. The latter loses its color in the inner flame of the blowpipe far more readily than the former. 108. c. PROTOXIDE OF NICKEL (NiO). 1. METALLIC NICKEL in the fused state is silvery white, inclining to gray ; it is bright, hard, malleable, ductile, difficultly fusible ; it does not oxidize in the air at the common temperature, but it oxidizes slowly upon ignition ; it is attracted by the magnet and may itself become magnetic. It slowly dissolves in hydrochloric acid and dilute sulphuric PROTOXIDE OF NICKEL. 103 acid upon the application of heat, the solution being attended with evolution of hydrogen gas. It dissolves readily in nitric acid. The solutions contain protoxide of nickel. 2. HYDRATE OP PROTOXIDE OF NICKEL is green ; and remains un- altered in the air, but is converted by ignition into grayish-green PROTOXIDE OF NICKEL. Both the protoxide and its hydrate are readily soluble in hydrochloric, nitric, and sulphuric acids. But the protoxide which crystallizes in octahedrons is insoluble in acids ; it dissolves how- ever in fusing bisulphate of potassa. SESQUIOXIDE OF NICKEL is black ; it dissolves in hydrochloric acid to protochloride. 3. Most of the SALTS OF PROTOXIDE OF NICKEL are yellow in the anhydrous, green in the hydrated state ; their solutions are of a light green color. The soluble neutral salts slightly redden litmus-paper, and are decomposed at a red heat. 4. H ydrosulplmric acid does not precipitate solutions of salts of prot- oxide of nickel with strong acids in presence of free acids ; in the absence of free acid a small portion of the nickel gradually separates as black SULPHIDE OF NICKEL (Ni S). Acetate of protoxide of nickel is not precipitated, or scarcely at all, in presence of free acetic acid. But in the absence of free acid the greater part of the nickel is thrown down by long-continued action of hydrosulphuric acid upon the fluid. 5. Sulphide of ammonium produces in neutral, and hydrosulphuric acid in alkaline solutions of salts of protoxide of nickel, a black precipitate of hydrated SULPHIDE OF NICKEL (Ni S), which is not altogether insoluble in sulphide of ammonium, especially if containing free ammonia ; the fluid from whicli the precipitate has been thrown down exhibits there- fore usually a brownish color. Sulphide of nickel dissolves scarcely at all in acetic acid, with great difficulty in hydrochloric acid, but readily in nitro-hydrochloric acid upon application of heat. 6. Potassa and soda produce a light green precipitate of HYDRATE OP PROTOXIDE OF NICKEL (NiO, HO), which is insoluble in an excess of the precipitants, and unalterable in the air. Carbonate of ammonia dis- solves this precipitate, when filtered and washed, to a greenish-blue fluid, from which potassa or soda reprecipitates the nickel as an apple-green hydrate of protoxide of nickel. 7. Ammonia added in small quantity to solutions of protoxide of nickel produces in them a trifling greenish turbidity ; upon further addition of the reagent this redissolves readily to a blue fluid containing a compound of PROTOXIDE OF NICKEL AND AMMONIA. Potassa and soda precipitate from this solution hydrate of protoxide of nickel. Solutions con- taining salts of ammonia or free acid are not rendered turbid by ammonia. 8. Cyanide of Potassium produces a yellowish-green precipitate of CYANIDE OF NICKEL (NiCy), which redissolves readily in an excess of the precipitant as a double cyanide of nickel and potassium (NiCy + !K Cy) ; the solution is brownish-yellow. If sulphuric acid or hydro- chloric acid is added to this solution, the cyanide of potassium is decom- posed, and the cyanide of nickel reprecipitated. .From more highly dilute solutions the cyanide of nickel separates only after some time ; it is very difficultly soluble in an excess of the precipitating acids in the cold, but more readily upon boiling. 9. Carbonate of baryta does not precipitate protoxide of nickel from aqueous solutions of its salts, upon digestion in the cold, with the excep- tion of sulphate of protoxide of nickel. 104} PROTOXIDE OP COBALT. 10. Nitrite of potassa, used in conjunction with acetic acid, fails to precipitate even concentrated solutions of nickel. 11. Borax and phospliate of soda and ammonia dissolve compounds of protoxide of nickel in the outer flame of the blowpipe to clear beads ; the bead produced with borax is violet whilst hot, reddish-brown when cold ; the bead produced with the phosphate of soda and ammonia is reddish, inclining to brown whilst hot, but turns yellow or reddish- yellow upon cooling. The bead which phosphate of soda and ammonia forms with saltp of protoxide of nickel remains unaltered in the inner flame of the blowpipe, but that formed with borax turns gray and turbid from reduced metallic nickel. Upon continued exposure to the blowpipe flame the particles of nickel unite, but without fusing to a bead, and the glass becomes colorless. 109. d. PROTOXIDE OF COBALT (Co 0). 1. METALLIC COBALT in the fused state is steel-gray, pretty hard, slightly malleable, ductile, difficultly fusible, and magnetic ; susceptible of polish ; it oxidizes very slowly in the air at the common temperature, more rapidly at a red heat ; with acids it presents the same reactions as nickel. The solutions contain protoxide of cobalt. 2. PROTOXIDE OP COBALT is an olive-green, its hydrate a pale red powder. Both dissolve readily in hydrochloric, nitric, and sulphuric acids. SESQUIOXIDE OF COBALT (Co O 8 ) is black ; it dissolves in hydro- chloric acid to protochloride, with evolution of chlorine. 3. The SALTS OF PROTOXIDE OF COBALT containing water of crystalliza- tion are red, the anhydrous salts mostly blue. The moderately concen- trated solutions appear of a light red color, which they retain even though considerably diluted. The soluble neutral salts redden litmus-paper slightly, and are decomposed at a red heat ; sulphate of protoxide of cobalt alone can bear a moderate red heat without suffering decomposi- tion. When a solution of chloride of cobalt is evaporated, the light red color changes towards the end of the operation to blue ; addition of water restores the red color. 4. Hydrosulphuric acid does not precipitate solutions of salts of prot- oxide of cobalt with strong acids, if they contain free acid ; from neutral solutions it gradually precipitates part of the cobalt as black sulphide of cobalt (CoS). Acetate of protoxide of cobalt is not precipitated, or to a very slight extent, in presence of free acetic acid. But in the absence of free acid it is completely precipitated, or almost completely. 5. Sulphide of ammonium precipitates from neutral, and hydrosulphuric acid from alkaline solutions of salts of protoxide of cobalt, the whole of the metal as black hydrated SULPHIDE OF COBALT (Co S). Chloride of ammonium promotes the precipitation most materially. Sulphide of cobalt is insoluble in alkalies and sulphide of ammonium, scarcely soluble in acetic acid, very difficultly soluble in hydrochloric acid, but readily so in nitrohydrochloric acid, upon application of heat. 6. Potassa and soda produce in solutions of cobalt BLUE precipitates of BASIC SALTS OF COBALT, which turn GREEN upon exposure to the air, owing to the absorption of oxygen ; upon boiling they are converted into pale red HYDRATE OF PROTOXIDE OF COBALT, which contains alkali, and generally appears rather discolored from an admixture of sesquioxide PROTOXIDE OF IRON. 105 formed in the process. These precipitates are insoluble in solutions of potassa and soda ; but neutral carbonate of ammonia dissolves the washed precipitates completely to intensely violet-red fluids, in which a somewhat larger proportion of potassa or soda produces a blue precipitate, the fluid still retaining its violet color. 7. Ammonia produces the same precipitate as potassa, but this redis- solves in an excess of the ammonia to a reddish-brown fluid, from which solution of potassa or soda throws down part of the cobalt as a blue basic salt. Ammonia fails to precipitate solutions of protoxide of cobalt con- taining salts of ammonia or free acid. 8. Addition of cyanide of potassium to a solution of cobalt gives rise to the formation of a brownish-white precipitate of PROTOCYANIDE OP COBALT (Co Cy), which dissolves readily as a double cyanide of cobalt and potassium in an excess of solution of cyanide of potassium. Acids precipitate from this solution cyanide of cobalt. But if the solution is boiled with cyanide of potassium in excess, in presence of free hydrocyanic acid (liberated by addition of one or two drops of hydrochloric acid), a double compound of sesquicyanide of cobalt and cyanide of potassium (K 3 , Co 2 Cy 6 = K 3 Ckdy) is formed, in the solution of which acids produce no precipitate (essential difference between cobalt and nickel). 9. Carbonate of baryta acts upon solutions of salts of protoxide of cobalt the same as upon solutions of salts of protoxide of nickel. 10. If nitrite of potassa is added in not too small proportion to a solution of protoxide of cobalt, then acetic acid to strongly acid reaction, and the mixture put in a moderately warm place, all the cobalt separates, from concentrated solutions immediately or very soon, from dilute solu- tions after some time, as NITRITE OF SESQUIOXIDE OF COBALT AND POTASSA (Co 2 O 3 , 3 K 0, 5 N 3 , 2 H O), in the form of a crystalline precipitate of a beautiful yellow color. The mode in which this precipitate forms may be seen from the following equation: 2 (CoO, S0 3 ) + 6 (KO, N0 3 ) + A - K 0, A + 2 K 0, S 3 + Co t O 8 , 3 K 0, 5 N O 3 + N O 2 . The precipitate is very perceptibly soluble in pure water, but altogether insoluble in more concentrated solutions of salts of potassa and in alcohol. When boiled with water it dissolves, though not copiously, to a red fluid, which remains clear upon cooling, and from which alkalies throw down hydrate of protoxide of cobalt (Fischer, Aug. Stromeyer). This excellent reaction enables us to distinguish and separate nickel from cobalt. 11. Borax dissolves compounds of cobalt both in the inner and outer flame of the blowpipe, giving clear beads of a magnificent BLUE color, which appear violet by candlelight, and almost black if the cobalt is present in considerable proportion. This test is as delicate as it is cha- racteristic. Phosphate of soda and ammonia manifests with salts of cobalt before the blowpipe an analogous but less delicate reaction. 110. e. PROTOXIDE OF IRON (FeO). 1. METALLIC IRON in the pure state has a light whitish gray color (iron containing carbon is more or less gray) ; the metal is hard, lustrous, malleable, ductile, exceedingly difficult to fuse, and is attracted by the magnet. In contact with air and moisture a coating of rust (hydrate of sesquioxide of iron) forms on its surface : upon ignition in the air a coat- 106 PROTOXIDE OF IRON. ing of black protosesquioxide. Hydrochloric acid and dilute sulphuric acid dissolve iron, with evolution of hydrogen gas ; if the iron contains carbon, the hydrogen is mixed with carbide of hydrogen. The solutions contain protoxide. Dilute nitric acid dissolves iron in the cold to nitrate of protoxide, with evolution of nitrous oxide j at a high temperature to nitrate of sesquioxide, with evolution of nitric oxide ; if the iron contains carbon, some carbonic acid is also evolved, and there is left undissolved a brown substance resembling humus, which is soluble in alkalies ; under certain circumstances graphite is also left behind. 2. PROTOXIDE OF IRON is a black powder; its hydrate is a white powder, which in the moist state absorbs oxygen and speedily acquires a grayish-green, and ultimately a brownish-red color. Both the protoxide and its hydrate are readily dissolved by hydrochloric, sulphuric, and nitric acids. 3. The SALTS or PROTOXIDE OF IRON have in the anhydrous state a white, in the hydrated state a greenish color ; their solutions only look greenish when concentrated. The latter absorb oxygen when exposed to the air, and are converted into salts of the protosesquioxide, with precipita- tion of basic salts of sesquioxide. Chlorine or nitric acid converts them by boiling into salts of sesquioxide. The soluble neutral salts redden litmus-paper, and are decomposed at a red heat. 4. Solutions of salts of protoxide of iron made acid by strong acids are not precipitated by hydrosulpliuric acid ; nor are neutral solutions of salts of protoxide of iron acidified with weak acids precipitated by this reagent, or at the most but very incompletely ; the precipitates are in that case of a black color. 5. Sulphide of ammonium precipitates from neutral, and hydrosulpliuric acid from alkaline solutions of salts of protoxide of iron, the whole of the metal as black hydrated PROTOSULPHIDE OF IRON (Fe S), which is insoluble in alkalies and sulphides of the alkali metals, but dissolves readily in hydrochloric and nitric acids : this black precipitate turns reddish-brown in the air by oxidation. To highly dilute solutions of protoxide of iron addition of sulphide of ammonium imparts a green color, and it is only after some time that the protosulphide of iron separates as a black pre- cipitate. Chloride of ammonium promotes the precipitation most materially. 6. Potassa and ammonia produce a precipitate of HYDRATE OF PROT- OXIDE OF IRON (FeO, HO), which in the first moment looks almost white, but acquires after a very short time a dirty green, and ultimately a reddish-brown color, owing to absorption of oxygen from the air. Pre- sence of salts of ammonia prevents the precipitation by potassa partly, and that by ammonia altogether. If alkaline solutions of protoxide of iron thus obtained by the agency of salts of ammonia are exposed to the air, hydrate of protosesquioxide of iron and hydrate of sesquioxide of iron precipitate. 7. Ferrocyanide of potassium produces in solutions of protoxide of iron a bluish- white precipitate of FERROCYANIDE 6r POTASSIUM AND IRON (K, Fe a , Cfy 2 ), which, by absorption of oxygen from the air, speedily acquires a blue color. Nitric acid or chlorine converts it immediately into Prussian blue, 3 (K, Fe 8 , Cfy 2 ) + 4 Cl = 3 KC1 + FeCl + 2 (Fe 4 CfyJ. 8. Ferricyanide of potassium produces a magnificently blue precipitate of FERRICYANIDE OF IRON (Fe a Cfdy). This precipitate does not differ in color from Prussian blue. It is insoluble in hydrochloric acid, but is SESQUIOXIDE OF IROX. 107 readily decomposed by potassa. In highly dilute solutions of salts of protoxide of iron the reagent produces simply a deep blue-green coloration. 9. Sulphocyanide of potassium does not alter solutions of protoxide of iron free from sesquioxide. 10. Carbonate of baryta does not precipitate solutions of protoxide of iron in the cold, with the exception of the sulphate of protoxide of iron. 11. Borax dissolves protoxide of iron compounds in the oxidizing flame, giving beads varying in color from yellow to dark red ; when cold the beads vary from colorless to dark yellow. In the inner flame the beads change to bottle-green, owing to the reduction of the newly-formed sesquioxide to protosesquioxide. Phosphate of soda and ammonia show a similar reaction with the salts of protoxide of iron ; the beads produced with this reagent lose their color upon cooling still more completely than is the case with those produced with borax ; the signs of the ensuing reduction in the reducing flame are also less marked. HI. /. SESQUIOXIDE OF IRON (Fe a 8 ). 1. The native crystallized SESQUIOXIDE OP IRON is steel-gray ; the native as well as the artificially prepared sesquioxide of iron gives upon trituration a brownish-red powder ; the color of hydrate of sesquioxide of iron is more inclined to reddish-brown. Both the sesquioxide and its hydrate, dissolve in hydrochloric, nitric, and sulphuric acids; the hydrate dissolves readily in these acids, but the anhydrous sesquioxide dissolves with greater difficulty, and completely only after long exposure to heat. PROTOSESQUIOXIDE OF IRON (Fe O, Fe 2 O 3 ) is black; it dissolves in hydrochloric acid to protochloride and sesquichloride, in aqua regia to sesquichloride. 2. The neutral anhydrous SALTS OF SESQUIOXIDE OF IRON are nearly white; the basic salts are yellow or reddish-brown. The color of the solutions is brownish-yellow, and becomes reddish-yellow upon the appli- cation of heat. The soluble neutral salts redden litmus-paper, and are decomposed by heat. 3. Uydrosulpliuric acid produces in solutions made acid by stronger acids a milky white turbidity, proceeding from separated SULPHUR ; the salt of the sesquioxide being at the same time converted into salt of the protoxide : Fe 2 3 , 3 S0 3 + HS = 2 (Fe O S0 3 ) + HO, S0 8 + S. If solution of hydrosulphuric acid is rapidly added to neutral solutions, the reaction is marked by a transient blackening of the fluid, besides the separation of sulphur. From solution of neutral acetate of sesqui- oxide of iron hydrosulphuric acid throws down the greater part of the iron ; but in presence of a sufficient quantity of free acetic acid sulphur alone separates. 4. Sulphide of ammonium precipitates from neutral, and hydrosul- phuric acid from alkaline solutions of salts of sesquioxide of iron, the whole of the metal as black hydrated PROTOSULPHIDE OF IRON (Fe S) : Fe a Cl g + 3 NH 4 S - 3 NH 4 Cl + 2 Fe S + S. In very dilute solutions the reagent produces only a blackish-green coloration. The minutely divided protosulphide of iron subsides in such cases only after long standing. Chloride of ammonium most materially promotes the preci- pitation. Protosulphide of iron, as already stated ( 110, 5), is inso- 108 RECAPITULATION AND REMARKS. luble in alkalies and alkaline sulphides, but dissolves readily in hydro- chloric and nitric acids. 5. Potassa and ammonia produce bulky reddish-brown precipitates of HYDRATE OF SESQUioxiDE OF IRON (F a O 8 , HO), which are insoluble in an excess of the precipitant as well as in salts of ammonia. 6. Ferrocyanide of potassium produces even in highly dilute solutions a magnificently blue precipitate of FERROCYANIDE OF IRON, or Prussian blue (Fe 4 Cfy,) : 2 (Fe 2 C1 3 ) + 3 (Cfy, 2 K) - 6 K 01 + Fe 4 Cfy 3 . This precipitate is insoluble in hydrochloric acid, but is decomposed by potassa, with separation of hydrate of sesquioxide of iron. 7. Ferricyanide of potassium deepens the color of solutions of salts of sesquioxide of iron to reddish-brown ; but it fails to produce a precipitate. 8. Sulphocyanide of potassium imparts to acid solutions of salts of sesquioxide of iron a most intense blood-red color, arising from the for- mation of a soluble SULPHOCYANIDE OF IRON. Addition of acetate of soda destroys this color, hydrochloric acid restores it again. This test is the most delicate of all ; it will indicate the presence of sesquioxide of iron even in fluids which are so highly dilute that every other reagent fails to produce the slightest visible alteration. The red coloration may in such cases be detected most distinctly by resting the test-tube upon a sheet of white paper, and looking through it from the top. 9. Carbonate of baryta precipitates even in the cold all the iron as HYDRATE OF SESQUIOXIDE MIXED WITH A BASIC SALT. 10. The reactions before the blowpipe are the same as with the prot- oxide. H2. Recapitulation and remarks. On observing the reactions of the several oxides of the fourth group with solution of potassa, it would appear that the separation of the oxide of zinc, which is soluble in an excess of this reagent, might be readily effected by its means ; but in the actual expe- riment we find that rather notable quantities of oxide of zinc are thrown down with the sesquioxide of iron, protoxide of cobalt, &c. To such an extent indeed that it is often impossible to demonstrate the presence of oxide of zinc in the alkaline filtrate. Again, the reactions of the different oxides with chloride of ammonium and an excess of ammonia would lead to the conclusion that the sepa- ration of sesquioxide of iron from the protoxides of cobalt, nickel, and manganese, and from oxide of zinc, might be readily effected by these agents. But this method also if applied to the mixed oxides is inaccu- rate, since greater or smaller portions of the other oxides will always precipitate along with the sesquioxide of iron ; and it may therefore happen that small quantities of cobalt, manganese, &c., altogether escape detection in this process. It is far safer therefore to separate the other oxides of the fourth group from sesquioxide of iron by carbonate of baryta, as in that case the iron is precipitated free from oxide of zinc and protoxide of manganese, and, if chloride of ammonium is added previously to the addition of the carbonate of baryta, almost entirely free also from protoxide of nickel and protoxide of cobalt. Protoxide of manganese may conveniently be separated from the protoxides of cobalt and nickel, as well as from oxide of zinc, by treating the washed precipitated sulphides with moderately dilute acetic acid, RECAPITULATION AND REMARKS. 109 which dissolves the sulphide of manganese, leaving the other sulphides undissolved. If the acetic acid solution is now mixed with solution of potassa, the least trace of a precipitate will be sufficient to recoguise the manganese before the blowpipe with carbonate of soda. If the sulphides left undissolved by acetic acid are now treated, after washing, with very dilute hydrochloric acid, the sulphide of zinc dis- solves, leaving almost the whole of the sulphides of cobalt and nickel behind. If the fluid is then boiled, and strongly concentrated to expel the hydrosulphuric acid, and afterwards treated with solution of potassa or soda in excess, the zinc is sure to be detected in the filtrate by hydro- sulphuric acid. Cobalt may mostly be readily and safely detected in presence of nickel by the reaction with borax in the inner flame of the blowpipe ; to which end the filter with the mixed sulphides of nickel and cobalt upon it is burnt in a small porcelain dish, and a portion of the residue tested with borax in the inner flame. The detection of nickel in presence of cobalt is a less easy task. The best way of effecting it is to mix the concen- trated solution containing the two metals with a sufficient quantity of nitrite of potassa, then add acetic acid to strongly acid reaction, and let the mixture stand at least twelve hours in a moderately warm place ; when the cobalt will separate as nitrite of sesquioxide of cobalt and potassa ; the nickel may then be readily precipitated from the filtrate by soda, and tested before the blowpipe, to make quite sure of its nature. la practical analysis we generally separate the whole of the oxides of the fourth group as sulphides by precipitation with sulphide of ammo- nium. It is therefore in most cases still more convenient to separate nickel and cobalt, or at least the far larger portion of these two metals at the outset. To this end the moist precipitate of the sulphides is treated with water and some hydrochloric acid, with active stirring, but with- out application of heat. Nearly the whole of the sulphide of nickel and sulphide of cobalt is left behind undissolved, whilst all the other sulphides are dissolved. The undissolved residue of sulphide of cobalt and sulphide of nickel is filtered and washed, and treated as directed above. By boiling the filtrate with nitric acid the iron is converted from the state of protoxide, as it existed in the solution of the sulphide, into that of sesquioxide. After the free acid has been nearly neutralized by carbonate of soda, the iron may be thrown down as basic salt either by carbonate of baryta in the cold, or by acetate of soda and boiling. Manganese and zinc alone remain in the filtrate ; these metals are then also precipitated with sulphide of ammonium and some chloride of ammonium, the precipitate is filtered and washed, and the two metals are finally separated from each other by acetic acid as directed above, or, after removal of the baryta by sulphuric acid and great concentration, by solution of potassa or soda. The trifling quantities of cobalt and nickel, dissolved on the first treatment of the sulphide precipitate with dilute hydrochloric acid, remain with the sulphide of zinc in the separa- tion of the latter from the sulphide of manganese by acetic acid or with the protoxide of manganese if the separation of the oxide is effected by solution of potassa or soda. The sulphide of zinc may be extracted from the blackish precipitate by dilute hydrochloric acid, and the detection of the manganese in presence of the cobalt and nickel may be readily effected by means of soda in the outer flame. 110 OXIDES OF URANIUM. Protoxide and sesquioxide of iron may be detected in presence of each other by testing for the former with ferricyanide of potassium, for the latter with ferrocyanide of potassium or, better still, with sulphocyanide of potassium. In conclusion it is necessary to mention that alkalies fail to preci- pitate the oxides of the fourth group in presence of n on- volatile organic substances (such as sugar, tartaric acid, &c.). We have already seen that the same remark applies to alumina. As regards sesquioxide of iron, even carbonate of baryta fails to precipitate this in presence of non- volatile organic substances. Special Reactions of the rarer Oxides of the fourth group. 113. a. OXIDES OF URANIUM. This metal is found in a few minerals, as pitchblende, uran-ochre, &c. The sesqui- oxide of the metal is used to stain glass yellowish-green. Uranium forms two oxides, viz., the protoxide (UO), and the sesquioxide (U a 3 ). The protoxide is brown; it dissolves in nitric acid to nitrate of sesquioxide. The hydrate of the sesquioxide is yellow ; at about 572 Fahrenheit it loses its water and turns red ; it is converted by ignition into the dark blackish-green protosesquioxide. The solutions of sesquioxide of uranium in acids are yellow. Hydrosulphuric add does not alter them ; sulphide of ammonium throws down from them, after neutralization of the free acid, a slowly subsiding precipitate, varying in color from dirty yellow to reddish- brown, and nearly blood-red, according to the presence and quantity of chloride of ammonium, ammonia, and sulphide of ammonium. Chloride of ammonium materially promotes the precipi- tation. The precipitate is readily soluble in acids, even in acetic acid, but insoluble in sulphide of ammonium. It does not consist of pure sulphide of uranium, but con- tains, besides uranium and sulphur, also ammonium, oxygen, and water. Ammonia, potassa, and soda produce yellow precipitates of sesquioxide of uranium and alkali, which are insoluble in an excess of the precipitants. Carbonate of ammonia and bi- carbonate of potassa or soda produce yellow precipitates of carbonate of sesquioxide of uranium and alkali, which readily redissolve in an excess of the precipitants. Potassa and soda throw down from such solutions th*e whole of the sesquioxide of uranium. Carbonate of baryta completely precipitates solutions of sesquioxide of uranium, even in the cold. Ferrocyanide of potassium produces a reddish-brown precipitate (a most delicate test for uranium). Borax and phosphate of soda and ammonia give with uranium compounds in the inner flame of the blowpipe green beads, in the outer flame yellow beads, which acquire a yellowish-green tint on cooling. 6. OXIDES OF VANADIUM. Vanadium is a rare metal, found in vanadate of lead, and occasionally in small quantity in iron and copper ores, and in the slags left by them. Vanadium forms three' oxides, viz., Protoxide (VO), binoxide (V0 g ), and vanadic acid (V0 8 ). The lower oxides are converted into the acid by heating with nitric acid or aqua regia, or by fusion with nitrate of potassa. Vanadic acid is yellowish-red ; it melts at an in- cipient red heat, and solidifies in crystals on cooling ; it is not volatile. It dissolves very sparingly im -water, but the solution acts powerfully upon moist litmus-paper, im- . parting a decided.red tint to it. Vanadic acid combines with acids and with bases. a. Add solutions. The stronger acids dissolve vanadic acid to yellow or red fluids. The solutions are often decolorized by boiling. Sulphurous acid, many metals, organic substances, &c., reduce vanadic acid and color the fluid blue by the formation of binoxide of vanadium. Hydrosulphuric acid does not precipitate acidified solutions, but imparts a blue tint to them, sulphur separating at the same time. Sulphide of am- monium imparts a brown tint to solutions of vauadic acid ; on acidifying the solution with hydrochloric acid, or, better still, with sulphuric acid, brown tersulphide of vana- dium separates, which dissolves in an excess of sulphide of ammonium to a reddish- brown fluid. Ferrocyanide of potassium produces a green precipitate, infusion of galls, after some time, a bluish-black precipitate, b. Vanadates. Most of the neutral salts are yellow, those of the alkalies and some others are by heating with water con- verted into a colorless modification. The acid salts are yellowish-red. The salts can bear a red heat j most of them are soluble in water, all of them in nitric acid. The OXIDES OF THALLIUM. Ill vanadate of the alkalies dissolve the more sparingly in water the more free alkali or alkaline salt is present. If the solution of a vanadate of an alkali is saturated with chloride of ammonium, the whole of the vanadic acid separates as white vanadate of ammonia, insoluble in solution of chloride of ammonium (most characteristic reaction). The precipitate gives by ignition vanadate of binoxide of vanadium. If an acidified solution of vanadate of alkali is shaken together with peroxide of hydrogen, the fluid acquires a red tint ; if ether is then added, and the mixture shaken, the solution re- tains its color, the ether remaining colorless (most delicate reaction) (WERTHER). Borax dissolves vanadic acid in the inner and outer flame to a clear bead ; the bead produced in the outer flame is colorless, with large quantities of vanadic acid, yellow ; the bead produced in the inner flame has a beautiful green color ; with larger quantities of vanadic acid it looks brownish whilst hot, and only turns green on cooling. c. Oxides of Thallium. Thallium is the last discovered of the known elements. It is found chiefly in iron pyrites, also in copper pyrites, and some other sulphuretted ores, and in native sulphur. It is found accumulated in the dust of the flues leading to the sulphuric acid chambers where the furnaces are fed with such ores. Thallium is a lead-like metal. It is soft, melts readily, and is volatile at a white heat. When bent or twisted it emits the same peculiar crackling sound as tin. It does not decompose pure water, but decom- poses it after addition of aoid. It forms a basic oxide, a sesquioxide, and a peroxide. Protoxide of thallium dissolves in water forming an alkaline fluid. The solutions of its salts are not precipitated by alkalies nor by alkaline carbonates. The sulphate, nitrate, and carbonate of protoxide of thallium are white, soluble in water, and readily crystallizable. The phosphate is a crystalline precipitate almost insoluble in water and alkaline solutions, but readily soluble in mineral acids. Ghromate of potassa produces a pale yellow, and bichromate of potassa a deep orange precipitate almost insoluble in water and acids. Hydrochloric acid, or soluble chlorides, precipitate white chloride of thallium, which is nearly insoluble in water, hydrochloric acid or ammonia ; it is soluble in boiling water and crystallizes out on cooling ; hot nitric acid dissolves it permanently. Iodide of potassium precipitates it yellow, and bromide of potassium white. Hydro- sulphuric acid does not precipitate acid solutions, and only very imperfectly when neutral. Sulphide of ammonium throws down brownish black sulphide of thallium which readily collects in lumps ; it is insoluble in ammonia, in alkaline sulphides and in cyanide of potassium : it dissolves sparingly in hydrochloric acid, readily in sulphuric acid and nitric acid ; when moist it oxidizes rapidly in the air, being converted into sulphate. Sulphide of thallium is more fusible than the metal. Zinc precipitates from thallium solutions the metal in small crystalline leaflets or scales. Colorless flames are colored intensely green by thallium compounds. The spectrum of thallium consists of a single most characteristic line of a magnificent emerald-green color, which nearly coincides with Ba, 8 (See Table I.) With minute quantities of thallium the spectral reaction is but of very short duration. Spectrum analysis affords by far the best means for the detection of thallium. Thalliferous pyrites give the green line mostly at once. In native sulphur thallium is detected the most readily by first removing the principal part of the sulphur by means of sulphide of carbon, and then examining the residue. 1U. FIFTH GROUP. More common oxides of the fifth group : OXIDE OF SILVER, SUBOXIDE OF MERCURY, OXIDE OF MERCURY, OXIDE OF LEAD, TEROXIDE OF BISMUTH, OXIDE OF COPPER, OXIDE OF CADMIUM. Rarer oxides of the fifth group ; OXIDES OF PALLADIUM, RHODIUM, OSMIUM, RUTHENIUM. Properties of the group. The sulphides corresponding to the oxides of this group are insoluble both in dilute acids and in alkaline sulphides.* The solutions of these oxides are therefore completely precipitated by * Consult however the paragraphs on oxide of copper and suboxide and oxide of mercury, as the latter remark applies only partially to them. OXIDE OF SILVEE. hydrosulphuric acid, no matter whether they be neutral, or contain free acid or free alkali. The fact that the solutions of the oxides of the fifth group are precipitated by hydrosulphuric acid in presence of a free stronger acid, distinguishes them from the oxides of the fourth group and from the oxides of all the preceding groups. For the sake of greater clearness and simplicity, we divide the oxides of this group into two classes, and distinguish, 1. OXIDES PRECIPITABLE BY HYDROCHLORIC ACID, viz., oxide of silver, suboxide of mercury, oxide of lead. 2. OXIDES NOT PRECIPITABLE BY HYDROCHLORIC ACID, viz., oxide of mercury, oxide of copper, teroxide of bismuth, oxide of cadmium. Lead must be considered in both classes, since the sparing solubility of its chloride might lead to confounding its oxide with suboxide of mercury and oxide of silver, without affording us on the other hand any means of effecting its perfect separation from the oxides of the second division. Special Reactions of the 'more common Oxides of the fifth group. FIRST DIVISION OF THE FIFTH GROUP ; OXIDES WHICH ARE PRECIPITATED BY HYDROCHLORIC ACID. H5. a. OXIDE OF SILVER (Ag 0.) 1. METALLIC SILVER is white, very lustrous, moderately hard, highly malleable, ductile, rather difficultly fusible. It is scarcely oxidized by fusion in the air. Nitric acid dissolves silver readily ; the metal is in- soluble in dilute sulphuric acid and in hydrochloric acid. 2. OXIDE OF SILVER is a grayish-brown powder ; it is not altogether insoluble in water, and dissolves readily in dilute nitric acid. It forms no hydrate. It is decomposed by heat into metallic silver and oxygen gas. The black suboxide of silver (Ag 2 0) and the binoxide (Ag0 2 ) are likewise decomposed by heat into metallic silver and oxygen. 3. The SALTS OF OXIDE OF SILVER are non- volatile and colorless ; many of them acquire a black tint upon exposure to light. The soluble neutral salts do not alter vegetable colors, and are decomposed at a red heat. 4. Hydrosulphuric acid and sulphide of ammonium precipitate from solutions of salts of silver black. SULPHIDE OF SILVER (AgS) which is insoluble in dilute acids, alkalies, alkaline sulphides, and cyanide of potassium. Boiling nitric acid decomposes and dissolves this precipitate readily, with separation of sulphur. 5. Potassa and soda precipitate from solutions of salts of silver OXIDE OF SILVER in the form of a grayish-brown powder, which is insoluble in an excess of the precipitants, but dissolves readily in ammonia. 6. Ammonia, if added in very small quantity to neutral solutions of oxide of silver, throws down the oxide as a brown precipitate, which readily redissolves in an excess of ammonia. Acid solutions of silver are not precipitated. 7. Hydrochloric acid and soluble metallic chlorides produce in solutions of salts of silver a white curdy precipitate of CHLORIDE OF SILVER (AgCl). In very dilute solutions these reagents impart at first simply a bluish- white opalescent appearance to the fiuid j but after long SUBOXIDE OF MERCURY. standing in a warm place the chloride of silver collects at the bottom of the vessel. By the action of light the white chloride of silver first acquires a violet tint, and ultimately turns black ; it is insoluble in nitric acid, but dissolves readily in ammonia as ammonio-chloride of silver, from which double compound the chloride of silver is again sepa- rated by acids. Concentrated hydrochloric acid and concentrated solu- tions of chlorides of the alkali metals dissolve chloride of silver to a very perceptible amount, more particularly upon application of heat ; but the dissolved chloride separates again upon dilution. Upon exposure to heat chloride of silver fuses without decomposition, giving upon cooling a transparent horny mass. 8. If compounds of silver mixed with carbonate of soda are exposed on a charcoal support to the inner flame of the blowpipe, white brilliant ductile metallic globules are obtained, with or without a slight dark red incrustation of the charcoal. 116. b. SUBOXIDE OF MERCURY (Hg 2 0). 1. METALLIC MERCURY is grayish-white, lustrous, fluid at the common temperature ; it solidifies at 40, and boils at 680 Fah. It is insoluble in hydrochloric acid ; in dilute cold nitric acid it dissolves to nitrate of suboxide, in more concentrated hot nitric acid to nitrate of oxide of mercury. 2. SUBOXIDE OF MERCURY is a black powder, readily soluble in nitric acid. It is decomposed by the action of heat, the mercury volatilizing in the metallic state. It forms no hydrate. 3. The SALTS OF SUBOXIDE OF MERCURY volatilize upon ignition ; most of them suffer decomposition in this process. Subchloride and sub- bromide of mercury volatilize unaltered. Most of the salts of suboxide of mercury are colorless. The soluble salts in the neutral state redden litmus-paper. Nitrate of suboxide of mercury is decomposed by addi- tion of much water into a light yellow insoluble basic and a soluble acid salt. 4. Hydrosulphuric acid and sulphide of ammonium produce black pre- cipitates of SUBSULPHIDE OF MERCURY (Hg 2 S), which are insoluble in dilute acids, sulphide of ammonium, and cyanide of potassium. Mono- sulphide of sodium, in presence of some caustic soda, dissolves this sub- sulphide, with separation of metallic mercury. Bisulphide of sodium dissolves the subsulphide without separation of metallic mercury. The solutions contain sulphide of mercury (HgS). Subsulphide of mercury is readily decomposed and dissolved by nitrohydrochloric acid, but not by boiling concentrated nitric acid. 5. Potassa, soda, and ammonia produce in solutions of salts of sub- oxide of mercury black precipitates, which are insoluble in an excess of the precipitants. The precipitates produced by the fixed alkalies con- sist of SUBOXIDE OF MERCURY ; whilst those produced by ammonia consist of BASIC COMPOUNDS OF MERCURY WITH AMMONIA OR AMIDOGEN. 6. Hydrochloric acid and soluble metallic chlorides precipitate from solutions of salts of suboxide of mercury SUBCHLORIDE OF MERCURY (Hg 2 Cl) as a fine powder of dazzling whiteness. Cold hydrochloric acid and cold nitric acid fail to dissolve this precipitate ; it dissolves however, although very difficultly and slowly, upon long-continued boiling with these acids, being resolved by hydrochloric acid into chloride 114 OXIDE OF LEAD. of mercury and metallic mercury, which separates ; and converted by nitric acid into chloride of mercury and nitrate of oxide of mercury. Nitrohydrochloric acid and chlorine water dissolve the subchloride of mercury readily, converting it into chloride. Ammonia and potassa decompose the subchloride of mercury, separating from it, the former a compound of protamide of mercury with protochloride of mercury (Hg 2 NH 2 , Hg 2 Cl), the latter suboxide of mercury. 7. If a drop of a neutral or slightly acid solution of suboxide of mer- cury is put ou a clean and smooth surface of copper, and washed off after some time, the spot will afterwards, on being gently rubbed with cloth, paper, &c., appear white and lustrous like silver. The application of a gentle heat to the copper causes the metallic mercury precipitated on its surface to volatilize, and thus removes the silvering. 8. Protochloride of tin produces in solutions of suboxide of mercury a gray precipitate of METALLIC MERCURY, which may be united into glo- bules by boiling the metallic deposit, after decanting the fluid, with hydrochloric acid, to which a little protochloride of tin may also be added. 9. If an intimate mixture of an anhydrous compound of mercury with anhydrous carbonate of soda is introduced into a sealed glass tube, and covered with a layer of carbonate of soda, arid the tube is then strongly heated, the mercurial compound invariably undergoes decom- position, and METALLIC MERCURY separates, forming a coat of gray sub- limate above the heated part of the tube. The minute particles of mercury may be united into larger globules by rubbing this coating with a glass rod. 117. c. OXIDE OF LEAD (Pb 0). 1. METALLIC LEAD is bluish-gray ; its surface recently cut exhibits a metallic lustre ; it is soft, malleable, readily fusible. It evaporates at a white heat. Fused upon charcoal before the blowpipe it forms a coating of yellow oxide on the support. Hydrochloric acid and moderately concentrated sulphuric acid act upon it but little, even with the aid of heat ; but dilute nitric acid dissolves it readily, more particularly on heating. 2. OXIDE OP LEAD is a yellow or reddish-yellow powder, looking brownish-red whilst hot, and fusible at a red heat. Hydrated oxide of lead is white. Both the oxide and its hydrate dissolve readily in nitric and acetic acids. SUBOXEDE OF LEAD (Pb 2 0) is black, MINIUM (2 PbO, Pb O 2 ) red, BINOXIDE (Pb 2 ) brown. They are all of them converted into the oxide by ignition in the air. The binoxide is not dissolved by heating with nitric acid, but it dissolves readily in that menstruum on addition of some spirit of wine. The solution contains nitrate of oxide of lead. 3. The SALTS OF OXIDE OF LEAD are non-volatile ; most of them are colorless ; the neutral soluble salts redden litmus-paper, and are decom- posed at a red heat. If chloride of lead is ignited in the air, part of it volatilizes, and leaves behind a mixture of oxide of lead and chloride of lead. 4. Hydrosulphuric acid and sulphide of ammonium produce in solu- tions of salts of lead black precipitates of SULPHIDE OF LEAD (Pb S), which are insoluble in cold dilute acids, in alkalies, alkaline sulphides, and OXIDE OF LEAD. 115 cyanide of potassium. Sulphide of lead is decomposed by hot nitric acid. If the acid was dilute, the whole of the lead is obtained in solution as nitrate of oxide of lead, and sulphur separates if the acid was fuming, the sulplmr is also completely oxidized, and insoluble sulphate of lead alone is obtained ; if the acid was of medium concentration, both processes take place, a portion of the lead being obtained in solution as nitrate of lead, whilst the remainder separates as sulphate of lead, together with the unoxidized sulphur. In solutions of salts of lead con- taining a large excess of a concentrated mineral acid, hydrosulphuric acid produces a precipitate only after the addition of water or after neutralization of the free acid by an alkali. If a solution of lead is pre- cipitated by hydrosulphuric acid in presence of a large quantity of free hydrochloric acid, a red precipitate is formed, consisting of chloride and sulphide of lead, which is however converted by an excess of hydrosul- phuric acid into black sulphide of lead. 5. Potassa, soda, and ammonia throw down BASIC SALTS OF LEAD in the form uf white precipitates, which are insoluble in ammonia and diffi- cultly soluble in potassa and soda. In solutions of acetate of lead am- monia (free from carbonic acid) does not immediately produce a pre- cipitate, owing to the formation of a soluble triacetate of lead. 6. Carbonate of soda throws down from solutions of salts of lead a white precipitate of BASIC CARBONATE OF LEAD [e.g., 6 (Pb 0, C O 2 ) + Pb 0, H 0], which is insoluble in an excess of the precipitant and also in cyanide of potassium. 7. Hydrochloric acid and soluble chlorides produce in concentrated solutions of salts of lead heavy white precipitates of CHLORIDE OF LEAD (Pb Cl), which are soluble in a large amount of water, especially upon application of heat. This chloride of lead is converted by ammonia into basic chloride of lead (Pb Cl, 3 Pb O + H O), which is also a white powder, but almost absolutely insoluble in water. In dilute nitric and hydrochloric acids chloride of lead is more difficultly soluble than in water. 8. Sulphuric acid and sulphates produce in solutions of salts of lead white precipitates of SULPHATE OF LEAD (Pb O, S 0,), which are nearly insoluble in water and dilute acids. From dilute solutions, especially from such as contain much free acid, the sulphate of lead precipitates only after some time, frequently only after a long time. It is advisable to add a considerable excess of dilute sulphuric acid, as this tends to increase the delicacy of the reaction, sulphate of lead being more insoluble in dilute sulphuric acid than in water. The separation of small quan- tities of sulphate of lead is best effected by evaporating, after the addi- tion of the sulphuric acid, as far as practicable on the water-bath, and then treating the residue with water. Sulphate of lead is slightly soluble in concentrated nitric acid ; it dissolves with difficulty in boiling concentrated hydrochloric acid, but more readily in solution of potassa. It dissolves also pretty readily in the solutions of some of the salts of ammonia, particularly in solution of acetate of ammonia; dilute sulphuric acid precipitates it again from these solutions. 9. Chromate of potassa produces in solutions of salt of lead a yellow precipitate of CHROMATE OF LEAD (PbO, Cr0 3 ), which is readily soluble in potassa, but difficultly so in dilute nitric acid. 10. If a mixture of a compound of lead with carbonate of soda is ex- posed on a charcoal support to the reducing flame of the blowpipe, soft i 2 116 OXIDE OF MEKCUEY. malleable METALLIC GLOBULES OP LEAD are readily produced, the charcoal becoming covered at the same time with a slight yellow incrustation of OXIDE OF LEAD. H8. Recapitulation and remarks. The metallic oxides of the first division of the fifth group are most distinctly characterized in their corresponding chlorides ; since the different reactions of these chlorides with water and ammonia afford us a simple means both of detecting them and of effecting their separation from one another. For if the precipitate con- taining the three metallic chlorides is boiled with a somewhat large quantity of water, or boiling water is repeatedly poured over it on the filter, the chloride of lead dissolves, whilst the chloride of silver and the subchloride of mercury remain undissolved. If these two chlorides are then treated with ammonia, the subchloride of mercury is converted into the black basic salt, insoluble in an excess of the ammonia, described in 116, 5, whilst the chloride of silver dissolves readily in the am- monia, and precipitates from this solution again upon addition of nitric acid. When operating upon small quantities it is advisable first to expel the greater part of the ammonia by heat. In the aqueous solution of chloride of lead the metal may be readily detected by sulphuric acid. SECOND DIVISION OF THE MORE COMMON OXIDES OF THE FIFTH GROUP : OXIDES WHICH ARE NOT PRECIPITATED BY HYDROCHLORIC ACID. Special Reactions. 119. a. OXIDE OF MERCURY (HgO). 1. OXIDE OF MERCURY is generally crystalline, and has a bright red color, which upon reduction to powder changes to a pale yellowish-red ; the oxide precipitated from solutions of the nitrate or from solutions of the chloride forms a yellow powder. Upon exposure to heat it tran- siently acquires a deeper tint ; at a dull red heat it is resolved into me- tallic mercury and oxygen. Both the crystalline and non-crystalline oxide dissolve readily in hydrochloric acid and in nitric acid. 2. The SALTS OF OXIDE OF MERCURY volatilize upon ignition ; they suffer decomposition in this process ; chloride, bromide, and iodide of mercury volatilize unaltered. Most of the salts of oxide of mercury are colorless. The soluble neutral salts redden litmus-paper. The nitrate and sulphate of oxide of mercury are decomposed by a large quantity of water into soluble acid and insoluble basic salts. 3. Addition of a very small quantity of hydrosulpkuric acid or sul- phide of ammonium produces in solutions of oxide of mercury, after shaking, a perfectly white precipitate. Addition of a somewhat larger quantity of these reagents causes the precipitate to acquire a yellow, orange, or brownish-red color, according to the less or greater proportion added ; an excess of the precipitant produces a black precipitate of SUL- PHIDE OF MERCURY (HgS). This progressive variation of color from white to black, which depends on the proportion of the hydrosulphuric acid or sulphide of ammonium added, distinguishes the oxide of mercury from all other bodies. The white precipitate which forms at first con- OXIDE OF COPPER. 117 sists of a double compound of sulphide of mercury with the still unde- composed portion of the salt of oxide of mercury (in a solution of chlo- ride of mercury, for instance, HgCl + 2 HgS) ; the gradually increasing admixture of black sulphide causes the precipitate to pass through the several gradations of color above mentioned. Sulphide of mercury is not dissolved by sulphide of ammonium, nor by potassa or cyanide of po- tassium ; it is altogether insoluble in hydrochloric acid and in nitric acid, even upon boiling. It dissolves completely in sulphide of potassium and sulphide of sodium, in presence of some caustic soda or potassa; it is readily decomposed and dissolved by nitrohydrochloric acid. In solu- tions of oxide of mercury containing a large excess of concentrated mineral acid, hydrosulphuric acid produces a precipitate only after addi- tion of water. 4. Potassa added in small quantity produces in neutral or slightly acid solutions of oxide of mercury a reddish-brown precipitate, which ac- quires a yellow tint if the reagent is added in excess. The reddish- brown precipitate is a BASIC SALT; the yellow precipitate consists of OXIDE OF MERCURY. An excess of the precipitant does not redissolve these precipitates. In very acid solutions this reaction does not take place at all, or at least the precipitation is very incomplete. In presence of salts of ammonia potassa produces in solutions of salts of oxide of mercury, instead of reddish-brown or yellow, white precipitates. The precipitate thrown down by potassa from a solution of chloride of mer- cury containing an excess of chloride of ammonium is of analogous composition to the precipitate produced by ammonia (see 5). 5. Ammonia produces in solutions of salts of oxide of mercury white precipitates quite analogous to those produced by potassa in presence of chloride of ammonium ; thus, for instance, ammonia precipitates from solutions of chloride of mercury a DOUBLE COMPOUND OF CHLORIDE OF MERCURY AND AMIDE OF MERCURY (HgCl + Hg N H 2 ). 6. ProtocJdoride of tin added in small quantity to solution of chloride of mercury, or to solutions of salts of oxide of mercury in presence of hydrochloric acid, throws down SUBCHLORIDE OF MERCURY (2 HgCl-f Sn Cl = Hg 2 Cl + Sn C1 2 ). By addition of a larger quantity of the reagent the pure precipitated subchloride is reduced to METAL (Hg a Cl + SnCl = Hg 2 + !SnCl 2 ). The precipitate, which was white at first, acquires therefore now a gray tint, and may, after it has subsided, be readily united into globules of metallic mercury by boiling with hydrochloric acid. 7. The salts of oxide of mercury show the same reaction as the salts of the suboxide with metallic copper and when heated together with carbonate of soda in a glass tube. 120. b. OXIDE OF COPPER (CuO). 1. METALLIC COPPER has a peculiar red color, and a strong lustre; it is moderately hard, malleable, ductile, rather difficultly fusible ; in con- tact with water and air it becomes covered with a green crust of basic carbonate of oxide of copper ; upon ignition in the air it becomes coated over with black oxide. In hydrochloric acid and dilute sulphuric acid it is insoluble or nearly so, even upon boiling. Nitric acid dissolves the metal readily. Concentrated sulphuric acid converts ib into sulphate of oxide of copper, with evolution of sulphurous acid. 118 OXIDE OF COPPER. 2. SUBOXTDE OP COPPER is red, its hydrate yellow ; both change to oxide upon ignition in the air. On treating the suboxide with dilute sulphuric acid metallic copper separates, whilst sulphate of oxide of copper dissolves ; on treating suboxide of copper with hydrochloric acid white subchloride of copper is formed, which dissolves in an excess of the acid, but is re precipitated from this solution by water. 3. OXIDE OF COPPER is a black fixed powder; its hydrate (CuO, HO) is of a light blue color. Both the oxide of copper and its hydrate dissolve readily in hydrochloric, sulphuric, and nitric acids. 4. Most of the neutral SALTS OF OXIDE OF COPPER are soluble in water ; the soluble salts redden litmus, and suffer decomposition when heated to gentle redness, with the exception of the sulphate, which can bear a somewhat higher temperature. They are usually white in the anhydrous state ; the hydrated salts are usually of a blue or green color, which their solutions continue to exhibit even when much diluted. 5. Hydrosulphuric acid and sulphide of ammonium produce in alka- line, neutral, and acid solutions of salts of oxide of copper, brownish- black precipitates of SULPHIDE OF COPPER (CuS). This sulphide is insoluble in dilute acids and caustic alkalies. Hot solutions of sulphide of potassium and sulphide of sodium fail also to dissolve it or dissolve it only to a very trifling extent ; but it is a little more soluble in sulphide of ammonium. The latter reagent is therefore not well adapted to effect the perfect separation of sulphide of copper from other metallic sulphides. Sulphide of copper is readily decomposed and dissolved by boiling nitric acid, but it remains altogether unaffected by boiling dilute sulphuric acid. It dissolves completely in solution of cyanide of potassium. In solutions of salts of copper which contain an excess of a concentrated mineral acid hydrosulphuric acid produces a precipitate only after the addition of water. 6. Potassa or soda produces in solutions of salts of oxide of copper a light blue bulky precipitate of HYDRATE OF OXIDE OF COPPER (OuO, HO). If the solution is highly concentrated, and the precipitant is added in excess, the precipitate turns black after the lapse of some time, and loses its bulkiness, even in the cold ; but the change takes place immediately if the precipitate is boiled with the fluid in which it is suspended (and which must, if necessary, be diluted for the purpose). In this process the (CuO, HO) hydrated oxide is converted into the (3 CuO, HO) hydrated oxide. 7. Carbonate of soda produces in solutions of salts of oxide of copper a greenish-blue precipitate of HYDRATED BASIC CARBONATE OF COPPER (CuO, CO 2 + CuO, HO), which upon boiling changes to brownish-black hydrate of oxide of copper, and dissolves in ammonia to an azure-blue, and in cyanide of potassium to a brownish fluid. 8. Ammonia added in small quantity to solutions of neutral salts of oxide of copper produces a greenish-blue precipitate, consisting of a BASIC SALT OF COPPER. This precipitate redissolves readily upon further addition of ammonia to a perfectly clear fluid of a magnificent azure- blue, which owes its color to the formation of a BASIC DOUBLE SALT OF AMMONIO-OXIDE OF COPPER. Thus, for instance, in a solution of .sulphate of oxide of copper ammonia produces a precipitate of N H 3 , Cu O + N H 4 O, S0 8 . In solutions containing a certain amount of free acid ammonia produces no precipitate, but this azure-blue coloration makes its appear- ance at once the instant the ammonia predominates. The blue color TEROXIDE OF BISMUTH. 119 ceases to be perceptible only in very dilute solutions. Potassa produces in such blue solutions in the cold, after the lapse of some time, a preci- pitate of blue hydrate of oxide of copper ; but upon boiling the fluid this reagent precipitates the whole of the copper as black hydrated oxide. Carbonate of ammonia shows the same reactions with salts of copper as pure ammonia. 9. Ferrocyanide of potassium produces in moderately dilute solutions a reddish-brown precipitate of FERROCYANIDE OF COPPER (Cu 2 , Cfy), which is insoluble in dilute acids, but suffers decomposition when acted upon by potassa. In very highly dilute solutions the reagent produces only a reddish coloration of the fluid. 10. Metallic iron when brought into contact with concentrated solu- tions of salts of copper is almost immediately covered with a coppery- red coating of METALLIC COPPER ; very dilute solutions produce this coating only after some time. Presence of a little free acid accelerates the reaction. If a fluid containing copper and a little free hydrochloric acid is poured into a small platinum dish (the lid of a platinum crucible), and a small piece of zinc is introduced, the bright platinum surface speedily becomes covered with a COATING OF COPPER j even with very dilute solu- tions this coating is clearly discernible. 11. If a mixture of a compound of copper with carbonate of soda is exposed on a charcoal support to the inner flame, of the blowpipe, METALLIC COPPKR is obtained, without incrustation of the charcoal. The best method of freeing this copper from the particles of charcoal is to triturate the fused mass in a small mortar with water, and to wash off the charcoal powder, when the coppery-red metallic particles will be left behind. 12. If copper, or some alloy containing copper, or a trace of a salt of copper, or even simply the loop of a platinum wire dipped in a highly dilute copper solution, is introduced into the fusion zone of the gas flame, or exposed to the inner blowpipe flame, the upper or outer portion of the flame shows a magnificent emerald-green tint. Addition of hydrochloric acid to the sample considerably heightens the beauty and delicacy of this reaction. 13. Jjorajs and phospliate of soda and ammonia readily dissolve oxide of copper in the outer gas- or blowpipe-flame. The beads are green while hot, blue when cold. In the inner flame the bead produced with borax appears colorless, that produced with phosphate of soda and ammouia turns dark green; both acquire a brownish-red tint upon cooJiug. 121. c. TEROXIDE OF BISMUTH (Bi0 3 ). 1. BISMUTH has a reddish tin-white color and moderate metallic lustre ; it is of medium hardness, brittle, readily fusible j fused upon a charcoal support it forms a coating of yellow teroxide on the surface of the charcoal. It dissolves readily in nitric acid, but is nearly insoluble in hydrochloric acid and altogether so in dilute sulphuric acid. Concen- trated sulphuric acid converts it into sulphate of teroxide of bismuth, with evolution of sulphurous acid. 2. The TEROXIDE OF BISMUTH is a yellow powder, which transiently acquires a deeper tint when heated. It fuses at a red heat. Hydrate 120 TEROXIDE OF BISMUTH. of teroxide of bismuth is white. Both the teroxide and its hydrate dissolve readily in hydrochloric, sulphuric, and nitric acids. The grayish- black binoxide of bismuth (Bi0 2 ) and the red bismuthic acid (BiO 6 ) are converted into teroxide by ignition in the air. By heating with nitric acid they are converted into nitrate of teroxide of bismuth. 3. The SALTS OF TEROXIDE OF BISMUTH are non-volatile; most of them are decomposed at a red heat. Terchloride of bismuth is volatile. The salts of teroxide of bismuth are colorless or white ; some of them, are soluble in water, others insoluble. The soluble salts in the neutral state redden litmus paper ; they are decomposed by a large quantity of water into insoluble basic salts, which separate, whilst the greater portion of the acid remains in solution together with some teroxide of bismuth. 4. Hydrosulphuric acid and sulphide of ammonium produce in neutral and acid solutions black precipitates of TERSULPHIDE OF BISMUTH (BiS 3 ), which are insoluble in dilute acids, alkalies, alkaline sulphides, and cyanide of potassium, but are readily decomposed and dissolved by boiling nitric acid. In solutions of salts of bismuth which contain a considerable excess of hydrochloric or nitric acid hydrosulphuric acid produces a precipitate only after the addition of water. 5. Potassa and ammonia throw down from solutions of salts of bis- muth HYDRATE OF TEROXIDE OF BISMUTH as a white precipitate, which is insoluble in an excess of the precipitant. 6. Carbonate of soda throws down from solutions of salts of bismuth BASIC CARBONATE OF TEROXIDE OF BISMUTH (BiO g , COJ, as a white bulky precipitate, which is insoluble in an excess of the precipitant, and equally so in cyanide of potassium. 7. Chromate of potassa precipitates from solutions of salts of bismuth CHROMATE OF TEROXIDE OF BISMUTH (Bi O g , 2 CrO 3 ) as a yellow powder. This substance differs from chromate of lead in being readily soluble in dilute nitric acid and insoluble in potassa. 8. Dilute sulphuric acid fails to precipitate even only moderately dilute solutions of nitrate of teroxide of bismuth. On evaporating with an excess of sulphuric acid on the water-bath to dryness, a white saline mass is left, which always dissolves readily and to a clear fluid in water acidified with sulphuric acid (characteristic difference between teroxide of bismuth and oxide of lead). After long standing (several days occasionally) basic sulphate of teroxide of bismuth (BiO 8 , SO 3 , + 2 aq.) separates from this solution in white microscopic needle-shaped cr} ^tals, which dissolve in nitric acid. 9. The reaction which characterizes the teroxide of bismuth more particularly is the decomposition of its neutral salts by water, which is attended with separation of insoluble basic salts. The addition of a large amount of water to solutions of salts of bismuth causes the imme- diate formation of a dazzling white precipitate, provided there be not too much free acid present. This reaction is the most sensitive with terchloride of bismuth, as the BASIC CHLORIDE OF BISMUTH (BiCl 3 , 2 BiO 3 ) is almost absolutely insoluble in water. Where water tails to precipitate nitric acid solutions of bismuth, owing to the presence of too much free acid, a precipitate will almost invariably make its appearance immediately upon addition of solution of chloride of sodium. Presence of tartaric acid does not interfere with the precipitation of bismuth solutions by water. 10. If a mixture of a compound of bismuth with carbonate of soda OXIDE OF CADMIUM. 121 is exposed on a charcoal support to the reducing flame, brittle GLOBULES OF BISMUTH are obtained, which fly into pieces under the stroke of a hammer. The charcoal becomes covered at the same time with a slight incrustation of TEROXIDE OF BISMUTH, which is orange-colored whilst hot, yellow when cold. 122. d. OXIDE OF CADMIUM (Cd 0.) 1. METALLIC CADMIUM has a tin-white color ; it is lustrous, not very hard, malleable, ductile ; it fuses at a temperature below red heat, and volatilizes at a temperature somewhat above the boiling point of mercury, and may accordingly easily be sublimed in a glass tube. Heated on charcoal before the blowpipe it takes fire and burns, emitting brown fumes of oxide of cadmium, which form a coating on the charcoal. Hydrochloric acid and dilute sulphuric acid dissolve it, with evolution of hydrogen ; but nitric acid dissolves it most readily. 2. OXIDE OF CADMIUM is a yellowish- brown, fixed powder \ its hydrate is white. Both the oxide and its hydrate dissolve readily in hydrochloric, nitric, and sulphuric acids. 3. The SALTS OF OXIDE OF CADMIUM are colorless or white ; some of them are soluble in water. The soluble salts in the neutral state redden litmus-paper, and are decomposed at a red heat. 4. Hydrosulphuric acid and sulphide of ammonium produce in alkaline, neutral, and acid solutions of salts of cadmium, bright yellow precipitates of SULPHIDE OF CADMIUM (Cd S), which are insoluble in dilute acids, alkalies, alkaline sulphides, and cyanide of potassium (difference from copper). They are readily decomposed and dissolved by boiling nitric acid, as well as by boiling hydrochloric acid and by boiling dilute sul- phuric acid (difference between cadmium and copper). In solutions of salts of cadmium containing a large excess of acid, hydrosulphuric acid produces a precipitate only after dilution with water. 5. Potassa and soda produce in solutions of salts of cadmium white precipitates of HYDRATE OF OXIDE OF CADMIUM (CdO, HO), which are insoluble in an excess of the precipitants. 6. Ammonia likewise precipitates from solutions of salts of cadmium, white HYDRATE OF OXIDE OF CADMIUM, which however redissolves readily and completely to a colorless fluid in an excess of the precipitant. 7. Carbonate of soda and carbonate of ammonia produce white pre- cipitates of CARBONATE OF CADMIUM (CdO, C 2 ), which are insoluble in an excess of the precipitants. The presence of salts of ammonia does not prevent the formation of these precipitates. The precipitated car- bonate of cadmium dissolves readily in solution of cyanide of potassium. From dilute solutions the precipitate separates only after some time. 8. If a mixture of a compound of cadmium with carbonate of soda is exposed on a charcoal support to the reducing flame, the charcoal becomes covered with a reddish-brown coating of OXIDE OF CADMIUM, owing to the instant volatilization of the reduced metal and its subsequent re- oxidation in passing through the oxidizing flame. The coating is seen, most distinctly after cooling. 123. Recapitidation and remarks. The perfect separation of the metallic oxides of the second division of the fifth group from suboxide of mercury 122 RECAPITULATION AND REMARKS. and oxide of silver may, as already stated, be effected by means of hydro- chloric acid ; but this agent fails to separate them completely from oxide of lead. Traces of salt of oxide of mercury, which are at first retained by the precipitated chloride of silver by surface attraction, are dissolved out completely by washing (G. J. MULDER). The oxide of mercury is distinguished from the other oxides of this division by the insolubility of the corresponding sulphide in boiling nitric acid. This property affords a convenient means for its separation. Only care must always be taken to free the sulphides completely by washing from all traces of hydro- chloric acid or a chloride that may happen to be present, before pro- ceeding to boil them with nitric acid. Moreover, the reactions with protochloride of tin or with metallic copper, as well as those in the dry way, will, after the previous removal of the suboxide, always readily indi- cate the presence of oxide of mercury. When the moist way is chosen, the sulphide of mercury is dissolved most conveniently by heatihg it with hydrochloric acid and a few crystals of chlorate of potassa. From the still remaining oxides the oxide of lead is separated by addi- tion of sulphuric acid. The separation is the most complete if the fluid, after addition of dilute sulphuric acid in excess, is evaporated on the water-bath, the residue diluted with water, slightly acidified with sul- phuric acid, and the undissolved sulphate of lead filtered oft' immediately. The sulphate of lead may be further examined in the dry way by the reaction described in 117, 10, or also as follows : Pour over a small portion of the sulphate of lead a little of a solution of chromate of potassa, and apply heat, which will convert the white precipitate into yellow chromate of lead. Wash this, add a little solution of potassa or soda, and heat ; the precipitate will now dissolve to a clear fluid ; by acidifying this fluid with acetic acid, a yellow precipitate of chromate of lead will again be produced. After the removal of the oxides of mercury and lead, the teroxide of bismuth may be separated from oxide of copper and oxide of cadmium by addition of ammonia in excess, as the latter two oxides are soluble in an excess of this agent. If the filtered precipitate is dissolved in one or two drops of hydrochloric acid on a watchglass, and water added, the appearance of a milky turbidity is a confirmation of the presence of teroxide of bismuth. The presence of a notable quantity of oxide of copper is revealed by the blue color of the ammoniacal solution ; smaller quantities are detected by evaporating the ammoniacal solution nearly to dryness, adding a little acetic acid, and then f'errocyanide of potassium. The separation of oxide of copper from oxide of cadmium may be effected by acting on the sulphides with cyanide of potassium or with boiling dilute sulphuric acid (5 parts of water to 1 part of concen- trated sulphuric acid). The solution obtained of the two sulphides is then precipitated by hydrosulphuric acid, and the precipitate separated from the fluid by decantation or filtration. On treating the precipitate now with some water and a small lump of cyanide of potassium, the sulphide of copper will dissolve, leaving the yellow sulphide of cadmium undissolved in the residue. By boiling the precipitate of the mixed sul- phides, on the other hand, with dilute sulphuric acid, the sulphide of copper remains undissolved, whilst the sulphide of cadmium is obtained in solution. Hydrosulphuric acid will therefore now throw down from the filtrate yellow sulphide of cadmium (A. W. HOFMANN). PROTOXIDE OF PALLADIUM. 123 Special Reactions of the rarer Oxides of the fifth group. 124. a. PROTOXIDE OF PALLADIUM (PdO). PALLADIUM is a rare metal. It is found in the metallic state, occasionally alloyed with gold and silver, but more particularly in platinum ores. It greatly resembles platinum, but is somewhat darker in color. It fuses with great difficulty. Heated in the air to dull redness it becomes covered with a blue film : but it recovers its light color and metallic lustre upon more intense ignition. It is sparingly soluble in pure nitric acid, but dissolves somewhat more readily in nitric acid containing nitrous acid ; it dissolves very sparingly in boiling concentrated sulphuric acid, but readily in nitro- bydrochloric acid. It combines with 1 and 2 eq. of oxygen to protoxide and binoxide. PROTOXIDE OF PALLADIUM is black, its hydrate dark-brown ; both are by intense igni- tion resolved into oxygen and metallic palladium. BIXOXIDE OF PALLADIUM (Pd 2 ) is black ; by heating with dilute hydrochloric acid it is dissolved to protochloride, with evolution of chlorine. The SALTS OF PROTOXIDE OF PALLADIUM are mostly soluble in water ; they are brown or reddish-brown ; their concentrated solutions are reddish- brown, their dilute solutions yellow. Water precipitates from a solution of nitrate of protoxide of palladium containing a slight excess of acid a brown-colored basic salt. The oxygen salts, as well as the protochloride, are decomposed by ignition, leaving metallic palladium behind. Hydrosulphuric acid and sulphide of ammonium throw down from acid or neutral solutions of salts of protoxide of palladium black proto- sulphide of palladium, which dissolves neither in sulphide of ammonium nor in boiling hydrochloric acid, and with difficulty in boiling nitric acid, but readily in nitrohydro- chloric acid. From the solution of the protochloride potassa precipitates a brown basic salt, soluble in an excess of the precipitant ; ammonia flesh-colored ammonio- protochloride of palladium (Pd Cl, N H 8 ) ; cyanide of mercury yellowish- white gela- tinous protocyanide of palladium, soluble in hydrochloric acid and in ammonia (this reaction is particularly characteristic). Protochloride of tin produces, in absence of free hydrochloric acid, a brownish- black precipitate; in presence of free hydrochloric acid, a red-colored solution, which speedily turns brown and ultimately green, and upon addition of water brownish-red. Sulphate of protoxide of iron produces a deposit of palladium on the sides of the glass. Iodide of potassium precipitates black prot- iodide of palladium (this reaction also is very characteristic). Chloride of potassium precipitates from highly concentrated solutions of protoxide of palladium potassio- protocbloride of palladium (KCI, PdCl), in the form of golden-yellow needles, which dissolve readily in water to a dark-red fluid, but are insoluble in absolute alcohol. &. SESQUIOXIDE OF KHODIUM (R 2 8 ). RHODIUM is found in small quantity in platinum ores. It is a steel-gray hard and brittle metal. It occurs also as a gray powder. In this latter state it is converted by ignition in the air into protoxide (R 0), then into protosesquioxide ; but upon more intense ignition it again loses the absorbed oxygen. None of the acids dissolve rhodium ; even in aqua regia this metal is soluble only when alloyed with platinum, copper, &c., but not when alloyed with gold or silver. Fusing hydrate of phosphoric acid and fusing bisulphate of potassa dissolve it to salt of sesquioxide. SESQUIOXIDE OF RHODIUM is black, its hydrate greenish-gray or brown ; it is insoluble in acids, but dissolves in fusing hydrate of phosphoric acid and in fusing bisulphate of potassa. The solutions are rose -red. Hydrosulphuric acid and sulphide of ammonium precipitate on long-continued action, more particularly with the aid of heat, brown sulphide of rh i- dium, which is insoluble in sulphide of ammonium, but dissolves in boiling hydrochloric and nitric acids. Hydrate of potassa precipitates brown hydrate only on boiling. If some alcohol is added to the solution made alkaline by potassa, rhodium shortly preci- pitates as a black powder ; in presence of a larger excess of potassa the rhodium takes a longer time to separate. Ammonia produces after some time a yellow precipitate, soluble in hydrochloric acid. Zinc precipitates black metallic rhodium. All solid rhodium compounds give by ignition in hydrogen rhodium in the metallic state, which is well characterized by its insolubility in aqua regia, its solubility in fusing bisulphate of potassa, and the reaction of this solution with potassa and alcohol. c. OXIDES OF OSMIUM. OSMIUM is a rare metal ; it is found in platinum ores as a native alloy of osmium and iridiuin. It is generally obtained as a black powder, or gray and with metallic lustre ; it is infusible. The metal, the PROTOXIDE (Os 0), and the BINOXIDE (Os Og) burn. 124 OXIDES OF RUTHENIUM. readily when heated to redness in the air, and give OSMIC ACID (Os 4 ), which volatilizes and makes its presence speedily known by its peculiar exceedingly irritating and offensive smell, resembling that of chlorine and iodine (highly characteristic). If a little osmium on a strip of platinum plate is held in the outer mantle of a gas or alcohol flame, at half height, the flame becomes most strikingly luminous. Even minute traces of. osmium may by this reaction be detected in alloys of iridium and osmium ; but the reaction is in that case only momentary ; it may however be reproduced by holding the sample first in the reducing flame, then again in the outer mantle. Nitric acid, more particularly red fuming nitric acid, and aqua regia dissolve osmium to osmic acid. Application of heat promotes the solution, which is however attended in that case with volatilization of osmic acid. Very intensely ignited osmium is in- soluble in acids. It is fused with nitrate of potassa, and the fused mass distilled with nitric acid ; the osmic acid is found in the distillate. By heating osmium in chlorine gas volatile green protochloride of osmium and still more volatile red bichloride of osmium are formed. BICHLORIDE OF OSMIUM in solution is rapidly decomposed, if no alkaline chloride is present, into hydrochloric acid, osmic acid, and osmium metal. All osmium compounds give osmium metal by ignition in a current of hydrogen gas. An- hydrous OSMIC ACID is white, crystalline, fusible by gentle heat ; it boils at about 212 Fahrenheit ; the fumes have a most irritating action upon the nose and eyes. Heated with water osmic acid fuses, and dissolves only slowly. The solution has scarcely acid reaction; it has a strong irritating and offensive smell. Alkalies color the solution yellow and remove the smell, which however is immediately restored by heating with nitric acid or hydrochloric acid ; by heating in a distilling apparatus the osmic acid is obtained in the distillate (most characteristic). In the evaporation of a solution of osmate of alkali, OSMOUS ACID (Os O a ) is formed, more particularly in presence of an excess of alkali. Addition of alcohol promotes the reduction. Hydrosulphuric acid precipitates brown tetrasulphide of osmium, which separates only in presence of a stronger free acid ; the precipitate does not dissolve in sulphide of ammonium. Nitrite of soda imparts to osmium solutions a deep blue-violet tint, and the fluid gra- dually deposits black osmium. Sulphate of protoxide of iron throws down black osmium ; formic acid produces the same precipitate ; zinc also and many other metals in presence of a stronger free acid. POTASSIO-BICHLOEIDE OF OSMIUM dissolves v* ry sparingly in cold, a little more readily in hot water ; it is insoluble in spirit of wine ; the solution in water acquires a deep blue tint by heating with tannic acid (charac- teristic) ; formate of soda precipitates black osmium upon application of heat. d. OXIDES OF KUTHENIUM. BUTHENIUM is found in small quantity in platinum ores. It is a grayish-white brittle and very difficultly fusible metal. It is barely acted upon by aqua regia ; fusing bisulphate of potassa fails altogether to affect it. By ignition in the air it is converted into bluish-black sesquioxide of ruthenium (Ru 2 8 ), insoluble in acids ; by ignition with chloride of potassium in a current of chlorine gas into potassio-sesqui- chloride of ruthenium ; by fusion with nitrate of potassa, with hydrate of potassa, or with chlorate of potassa, into rhutenate of potassa (KO, Ru0 8 ). The fused mass obtained in the latter case is greenish- black, and dissolves to an orange-colored fluid, which tinges the skin black, from causing reduction and separation of black oxide. Acids throw down from the solution black OXIDE, which dissolves in hydrochloric acid to an orange-yellow fluid. This solution is resolved by heat into hydrochloric acid and brownish- black oxide. In a concentrated state it gives with chloride of potassium and chloride of ammonium crystalline glossy-violet precipitates, which on boiling with water deposit black oxyprotochloride. Potassa precipitates black hydrate of sesqui- oxide of ruthenium, which is insoluble in alkalies, but dissolves in acids. Hydrosul- phuric acid gas causes at first no alteration ; but after some time the fluid acquires an azure-blue tint, and deposits brown sulphide of ruthenium (very characteristic). Sulphide of ammonium produces brownish-black precipitates, barely soluble in an excess of the precipitant. Sulphocyanide of potassium produces in the absence of other metals of the platinum ores after some time a red coloration, which gradually changes to purple-red, and upon heating to a fine violet tint (very characteristic). Zinc produces at first an azure- blue coloration, which subsequently disappears, ruthe- nium being deposited at the same time in the metallic state. TEROXIDE OF GOLD. 125 125. SIXTH GROUP. More common oxides of the sixth group : TEROXIDE OF GOLD, BIXOXIDE OF PLATINUM, PROTOXIDE OF TIN, BINOXIDE OF TIN, TEROXIDE OF ANTIMONY, ARSENIOUS ACID AND ARSENIC ACID. Rarer oxides of the sixth group : Oxides of IRIDIUM, MOLYBDENUM, TUNGSTEN, TELLURIUM, SELENIUM. The higher oxides of the elements belonging to the sixth group are all of them more or less strongly pronounced acids. But we class them, here with the bases, as they cannot well be separated from the lower degrees of oxidation of the same elements, to which they are very closely allied in their reactions with hydrosulphuric acid. Properties of the group. The sulphides corresponding to the oxides of the sixth group are insoluble in dilute acids. These combine with alka- line sulphides to soluble sulphur salts, in which they perform the part of the acid. Hydrosulphuric acid precipitates these oxides therefore, like those of the fifth group, completely from acidified solutions. The preci- pitated sulphides differ however from those of the fifth group in this, that they dissolve in sulphide of ammonium, sulphide of potassium, &c., and are reprecipitated from these solutions by addition of acids. We divide the more common oxides of this group into two classes, and distinguish, 1. OXIDES WHOSE CORRESPONDING SULPHIDES ARE INSOLUBLE IN HYDRO- CHLORIC ACID AND IN NITRIC ACID, and are reduced to the metallic state upon fusion in conjunction with nitrate and carbonate of soda : viz., TEROXIDE OF GOLD and BINOXIDE OF PLATINUM. 2. OXIDES WHOSE CORRESPONDING SULPHIDES ARE SOLUBLE IN BOILING HYDROCHLORIC ACID OR NITRIC ACID, and are upon fusion with nitrate and carbonate of soda converted into oxides or acids, which then combine with the soda : viz., TEROXIDE OF ANTIMONY, PROTOXIDE and BINOXIDE OP TIN, ARSENIOUS and ARSENIC ACIDS. FIRST DIVISION. Special Reactions. 126. a. TEROXIDE OF GOLD (Au0 3 ). 1. METALLIC GOLD has a reddish-yellow color and a high metallic lustre : it is rather soft, exceedingly malleable and ductile, difficultly fusible ; it does not oxidize upon ignition in the air, and is insoluble in hydrochloric, nitric, and sulphuric acids ; but it dissolves in fluids con- taining or evolving chlorine, e.g., in nitrohydrochloric acid. The solu- tion contains terchloride of gold. 2. TEROXIDE OF GOLD is a blackish-brown, its HYDRATE a chestnut- brown powder. Both are reduced by light and heat, and dissolve readily in hydrochloric acid, but not in dilute oxygen acids. Concen- trated nitric and sulphuric acids dissolve a little TEROXIDE OF GOLD ; water reprecipitates it from these solutions. PROTOXIDE OF GOLD (AuO) is violet-black ; it is decomposed by heat into gold and oxygen. 3. SALTS OF GOLD with oxygen acids are nearly unknown. The 126 BINOXIDE OF PLATINUM. HALOID SALTS of gold are yellow, and their solutions continue to exhibit this color up to a high degree of dilution. The whole of them are readily decomposed by ignition. Neutral solution of terchloride of gold reddens litmus-paper. 4. Hydrosulphuric acid precipitates from neutral or acid solutions of gold the whole of the metal, from cold solutions as black TERSULPHIDE OF GOLD (AuS 8 ), from boiling solutions as PROTOSULPHIDE OF GOLD (AuS). The precipitates are insoluble in hydrochloric acid and in nitric acid, but soluble in nitrohydrochloric acid. They are insoluble in color- less sulphide of ammonium, but soluble in yellow sulphide of ammo- nium, and more readily still in yellow sulphide of sodium or sulphide of potassium. 5. tiidphide of ammonium precipitates brownish -black TERSULPHIDE OF GOLD (AuS 3 ), which redissolves in an excess of the precipitant only if the latter contains an excess of sulphur. 6. Ammonia produces, though only in concentrated solutions of gold, reddish-yellow precipitates of AURATE OF AMMONIA (fulminating gold). The more acid the solution and the greater the excess of ammonia added the more gold remains in solution. 7. Protockloride of tin containing an admixture of bichloride (which may be easily prepared by mixing solution of protochloride of tin with a little chlorine-water), produces even in extremely dilute solutions of gold, a purple-red precipitate (or coloration at least), which sometimes inclines rather to violet or to brownish-red. This precipitate, which has received the name of PURPLE OF CASSIUS, is insoluble in hydrochloric acid. It is assumed to be a hydrated compound of binoxide of tin and protoxide of gold with protoxide and binoxide of tin ( Au 0, Sn 2 + Sn O, 8. Salts of protoxide of iron reduce the teroxide of gold in its solu- tions, and precipitate METALLIC GOLD in form of a most minutely divided brown powder. The fluid in which the precipitate is suspended appears of a blackish-blue color by transmitted light. The dried precipitate shows metallic lustre when pressed with the blade of a knife. 9. Potassa or soda added in excess to a solution of terchloride of gold leaves the fluid clear ; upon addition of tannic acid a deep black preci- pitate of protoxide of gold (AuO) separates, which subsides completely after some time. 127. b. BINOXIDE OF PLATINUM (Pt0 2 ). 1. METALLIC PLATINUM has a light steel-gray color ; it is very lus- trous, moderately hard, very difficultly fusible ; it does not oxidize upon ignition in the air, and is insoluble in hydrochloric, nitric, and sulphuric acids. It dissolves in nitrohydrochloric acid, especially upon heating. The solution contains bichloride of platinum (PtCl 2 ). 2. BINOXIDE OF PLATINUM is a blackish-brown, its hydrate a reddish- brown powder. Both are reduced by heat ; they are both readily soluble in hydrochloric acid, and difficultly soluble in oxygen acids. The HYDRATE OF PROTOXIDE OF PLATINUM (PtO) is black ; it is by igni- tion reduced to the metallic state. 3. The SALTS OF BINOXIDE OF PLATINUM are decomposed at a red heat. They are yellow. BICHLORIDE OF PLATINUM is reddish-brown, its solu- tion reddish -yellow, which tint it retains up to a high degree of dilu- RECAPITULATION AND REMARKS. 127 tion. The solution reddens litmus-paper. Exposure to a very low red heat converts bichloride of platinum to protochloride (PtCl) ; applica- tion of a stronger red heat reduces it to the metallic state. Solution of bichloride of platinum containing protochloride has a deep dark brown color. 4. Hydrosulphuric acid throws down from acid and neutral solutions, but always only after the lapse of some time, a blackish-brown precipitate of BISULPHIDE OF PLATINUM (PtSJ. If the solution is heated after the ad- dition of the hydrosulphuric acid the precipitate forms immediately. It dissolves in a great excess of alkaline sulphides, more particularly of the higher degrees of sulplmration. Bisulphide of platinum is insoluble in hydrochloric acid and in nitric acid ; but it dissolves in nitrohydrochloric acid. 5. Sulphide of ammonium produces the same precipitate ; this redis- solves completely, though slowly and with difficulty, in a large excess of the precipitant if the latter contains an excess of sulphur. Acids re- precipitate the bisulphide of platinum unaltered from the reddish-brown solution. 6. Chloride of potassium and chloride of ammonium (and accordingly of course also potassa and ammonia in presence of hydrochloric acid) pro- duce in not too highly dilute solutions of bichloride of platinum yellow crystalline precipitates of POTASSIO and AMMONIO-BICHLORIDE OF PLA- TINUM, which are as insoluble in acids as in water, but are dissolved by heating with solution of potassa. From dilute solutions these precipi- tates are obtained by evaporating the fluid mixed with the precipitants on the water-bath to dryness, and treating the residue with a little water or with dilute spirit of wine. Upon ignition ammonio-bichloride of platinum leaves spongy platinum behind. Potassio-bichloride leaves platinum and chloride of potassium. The decomposition of the latter compound is complete only if the ignition is effected in a current of hydrogen gas or with addition of some oxalic acid. 7. Protochloride of tin imparts to solutions of bichloride of platinum containing much free hydrochloric acid an intensely dark brownish-red color, owing to a reduction of the bichloride of platinum to simple chloride. But the reagent produces no precipitate in such solutions. 8. Sulphate of protoxide of iron does not precipitate solution of bi- chloride of platinum, except upon very long-continued boiling, in which case the platinum ultimately suffers reduction. 128. Recapitulation and remarks. The reactions of gold and platinum enable us, at least partially, to detect these two metals in the presence of many other oxides, and more particularly where platinum and gold are present in the same solution. In the latter case the solution is most conveniently evaporated to dryness at a gentle heat with chloride of ammonium, and the residue treated with spirit of wine, in order to ob- tain the gold in solution and the platinum in the residue. The precipi- tate will thus give platinum by ignition, and the gold may be precipi- tated from the solution by sulphate of protoxide of iron, after removing the spirit of wine by evaporation. 128 PROTOXIDE OF TIN. SECOND DIVISION OF THE SIXTH GKOUP. Special Reactions. 129. a. PKOTOXIDE OF TIN (Sn 0). 1. TIN has a light grayish-white color and a high metallic lustre; it is soft and malleable ; when bent it produces a crackling sound. Heated in the air it absorbs oxygen and is converted into grayish-white binoxide ; heated on charcoal before the blowpipe it forms a white coating on the support. Concentrated hydrochloric acid dissolves tin to protochloride, with evolution of hydrogen gas ; nitrohydrochloric acid dissolves it, according to circumstances, to bichloride or to a mixture of proto- and bichloride. Tin dissolves with difficulty in dilute sulphuric acid ; con- centrated sulphuric acid converts it, with the aid of heat, into sulphate of binoxide ; moderately concentrated nitric acid oxidizes it readily, particularly with the aid of heat ; the white binoxide formed (hydrate of metastannic acid, Sn O 2 2 HO) does not redissolve in an excess of the acid. 2. PROTOXIDE OF TIN is a black or grayish-black powder ; its hydrate is white. Protoxide of tin is reduced by fusion with cyanide of potas- sium. It is readily soluble in hydrochloric acid. Nitric acid converts it into hydrate of metastannic acid which is insoluble in an excess of the acid. 3. The SALTS OF PROTOXIDE OF TIN are colorless ; they are decom- posed by heat. The soluble salts, in the neutral state, redden litmus- paper. The salts of protoxide of tin rapidly absorb oxygen from the air, and are partially or entirely converted into salts of binoxide. Proto- chloride of tin, no matter whether in crystals or in solution, also absorbs oxygen from the air, which leads to the formation of insoluble oxy-pro- tochloride of tin and bichloride of tin. Hence a solution of protochloride of tin becomes speedily turbid if the bottle is often opened and there is only little free acid present ; it is therefore only quite recently prepared protochloride of tin which will completely dissolve in water free from air, whilst crystals of protochloride of tin that have been kept for any time will dissolve to a clear fluid only in water containing hydrochloric acid. 4. Hydrosulphuric acid throws down from neutral and acid solutions of salts of protoxide of tin a dark brown precipitate of hydrated PROTO- SULPHIDE OF TIN (Sn S), which is insoluble, or nearly so, in protosul- phide of ammonium, but dissolves readily in the higher yellow sulphide. Acids precipitate from this solution yellow bisulphide of tin, mixed with sulphur. Protosulphide of tin dissolves also in solution of soda or potassa. Acids precipitate from these solutions brown protosulphide. Boiling hydrochloric acid dissolves it, with evolution of hydrogen ; boil- ing nitric acid converts it into insoluble hydrate of metastannic acid. Alkaline solutions of protosalts of tin are not, or at least only imper- fectly, precipitated by hydrosulphuric acid. Presence of a very large quantity of free hydrochloric acid may also prevent precipitation of solutions of salts of protoxide of tin by hydrosulphuric acid. 5. Sulphide of ammonium produces the same precipitate of hydrated PROTOSULPHIDE OF TIN. BINOXIDE OF TIN. 129 6. Potassa, soda, ammonia, and carbonates of the alkalies, produce in solutions of salts of protoxide of tin a white bulky precipitate of HYDRATE OF PROTOXIDE OF TIN (Sn 0, H 0), which redissolves readily in an excess of potassa or soda, but is insoluble in an excess of the other precipitants. Tf the solution of hydrate of protoxide of tin in potassa is briskly evapo- rated a compound of binoxide of tin and potassa is formed, which remains in solution, whilst metallic tin precipitates ; but upon evaporating slowly crystalline anhydrous protoxide of tin separates. 7. Terchloride of gold produces in solutions of protochloride of tin and in solutions of salts of protoxide of tin mixed with hydro- chloric acid, upon addition of some nitric acid (without application of heat), a precipitate or coloration of PURPLE OF CASSIUS. (Compare 126, 7.) 8. Solution of chloride of mercury, added in excess, produces in solu- tions of protochloride or protoxide of tin a white precipitate of SUB- CHLORIDE OF MERCURY, owing to the protosalt of tin withdrawing from the chloride of mercury half of its chlorine. 9. If a fluid containing protoxide or protochloride of tin is added to a mixture offerricyanide of potassium and sesquichloride of iron a preci- pitate of Prussian blue separates immediately, owing to the reduction of the ferricyanide (Fe 2 Cfdy) to ferrocyanide (Fe 4 Cfy s ). (Fe 4 Cfy 4 *) + 2 HC1 + 2 Sn 01 = Fe 4 Cfy 8 + H 2 Cfy + 2*SnCl 2 ). This reaction is ex- tremely delicate, but it can be held to be decisive only in cases where no other reducing agent is present. 10. If compounds of protoxide of tin, mixed with carbonate of soda and some borax, or, better still, with a mixture of equal parts of car- bonate of soda and cyanide of potassium, are exposed on a charcoal support to the inner blowpipe flame malleable grains of METALLIC TIN are obtained. The best way of making quite sure of the real nature of these grains is to triturate them and the surrounding parts of charcoal with water in a small mortar, pressing heavily upon the mass j then to wash the charcoal off from the metallic particles. Upon strongly heating the grains of metallic tin on a charcoal support the latter becomes covered with a coating of white binoxide. 130. b. BINOXIDE OF TIN (Sn0 2 ). 1. BINOXIDE OF TIN is a powder varying in color from white to straw- yellow, and which upon heating transiently assumes a brown tint. It forms two different series of compounds with acids, bases, and water. The hydrate precipitated by alkalies from solution of bichloride of tin dissolves readily in hydrochloric acid ; whilst that formed by the action of nitric acid upon tin hydrate of metastannic acid remains undis- solved. But if it is boiled for some time with hydrochloric acid it takes up acid ; if the excess of the acid is then poured off, and water added, a clear solution is obtained. The aqueous solution of the common bichlo- ride of tin is not precipitated by concentrated hydrochloric acid, whilst that acid produces in the aqueous solution of the metastannic chloride a white precipitate of the latter compound. The solution of the common, bichloride of tin is not colored yellow by addition of protochloride of tin, as is the case in a remarkable degree if the solution contains nieta- * 2 (Fe 2 Cfdy) = Fe 4 Cfy 4 ; for Cfdy = C 19 N 6 Fe 2 = 2 Cfy. I. K 180 PROTOXIDE OF TIN. stannic chloride (LOWENTHAL). The dilute solutions of both chlorides of tin give upon boiling precipitates of the hydrates corresponding to the chlorides. 2. The SALTS OF BINOXIDE OP TIN are colorless. The soluble salts are decomposed at a red heat \ in the neutral state they redden litmus paper. Bichloride of tin is a volatile liquid, strongly fuming in the air. 3. Hydrosulphuric acid throws down from all acid and neutral solu- tions of salts of binoxide of tin, particularly upon heating, a white floc- culent precipitate if the solution of the binoxide is in excess ; & faintly yellow precipitate if the hydrosulphuric acid is in excess. The former (the white precipitate) may safely be assumed, in the case of a solution of bichloride of tin, to consist of a mixture of bichloride and bisulphide of tin (it has not however as yet been analysed) ; the latter (the yellow precipitate) consists of hydrated BISULPHIDE OF TIN (Sn S 2 ). Alkaline solutions are not precipitated by hydrosulphuric acid ; presence of a very large quantity of hydrochloric acid can also prevent precipitation. The bisulphide of tin dissolves readily in potassa or soda, alkaline sul- phides, and concentrated boiling hydrochloric acid, as also in aqua regia. It dissolves with some difficulty in pure ammonia, and is nearly inso- luble in carbonate of ammonia. Concentrated nitric acid converts it into insoluble hydrate of nietastannic acid. Upon deflagrating bisul- phide of tin with nitrate and carbonate of soda sulphate of soda and binoxide of tin are obtained. If a solution of bisulphide of tin in potassa is boiled with teroxide of bismuth tersulphide of bismuth and binoxide of tin are formed, which latter substance remains dissolved in the potassa solution. 4. Sulphide of ammonium produces the same precipitate of hydrated BISULPHIDE OF TIN j the precipitate redissolves readily in an excess of the precipitant. From this solution acids reprecipitate the bisulphide of tin unaltered. 5. Potassa, soda, and ammonia, carbonate of soda and carbonate of ammonia produce in solutions of salts of binoxide of tin white precipi- tates which, according to the nature of the solutions, consist of hydrate of binoxide of tin, or of hydrate of metastannic acid. Both dissolve readily in an excess of solution of potassa or soda. 6. Sulphate of soda or nitrate of ammonia (in fact, most neutral salts of the alkalies), when added in excess, throw down from solutions of both modifications of binoxide of tin, provided they are not too acid, the whole of the tin as HYDRATED BINOXIDE or HYDKATED METASTANNIC ACID. Heating promotes the precipitation : Sn C1 2 + 4 NaO, S0 3 + 4 HO = Sn O 2 , 2 HO + 2 Na 01 + 2 (Na O, HO, 2 SO 8 ). 7. Metallic zinc precipitates from solutions of bichloride of tin, in the absence of free acid, first some metallic tin, then oxychloride ; but in presence of a sufficient quantity of free hydrochloric acid METALLIC TIN in the shape of small gray scales, or as a spongy mass. If the operation is conducted in a platinum dish, no blackening of the latter is observed (difference between tin and antimony). 8. The compounds of the binoxide of tin show the same reactions before the blowpipe as those of the protoxide. Binoxide of tin is also readily reduced when fused with cyanide of potassium in a glass tube or in a crucible. TEROXIDE OF ANTIMONY. 131 131. c. TEROXIDE OP ANTIMONY (Sb0 3 ). 1. METALLIC ANTIMONY has a bluish tin- white color and is very lustrous ; it is hard, brittle, readily fusible. When heated on charcoal before the blowpipe it emits thick white fumes of teroxide of antimony, which form a coating on the charcoal ; this combustion continues for some time even after the removal of the metal from the flame ; it is the most distinctly visible if a current of air is directed with the blowpipe directly upon the sample on the charcoal. But if the sample on the support is kept steady, that the fumes may ascend straight, the metallic grain becomes surrounded with a net of brilliant acicular crystals of teroxide of antimony. Nitric acid oxidizes antimony readily : the dilute acid converting it almost entirely into teroxide, boiling concentrated acid into antimonic acid ; neither of the two is altogether insoluble in nitric acid j traces of anti- mony are therefore always found in the acid fluid filtered from the pre- cipitate. Hydrochloric acid, even boiling, does not attack antimony. In nitrohydrochloric acid the metal dissolves readily. The solution contains terchloride of antimony (SbCl s ), or pentachloride of antimony (SbCl 5 ), according to the degree of concentration of the acid and the duration of the action. 2. According to the different modes of its preparation, TEROXIDE OF ANTIMONY occurs either in the form of white and brilliant crystalline needles, or as a grayish-white powder. It fuses at a moderate red heat ; when exposed to a higher temperature it volatilizes without decomposi- tion. It is almost insoluble in nitric acid, but dissolves readily in hydro- chloric and tartaric acids. No separation of iodine takes place on boiling it with hydrochloric acid (free from chlorine) and iodide of potassium (free from iodic acid) BUNSEN. Teroxide of antimony is easily reduced to the metallic state by fusion with cyanide of potassium. 3. ANTIMONIC ACID (Sb O 6 ) is pale yellow ; its hydrates are white. Both the acid and its hydrates redden moist litmus-paper ; they are only very sparingly soluble in water, and insoluble in nitric acid, but dissolve pretty readily in hot concentrated hydrochloric acid : the solution con- tains pentachloride of antimony (Sb Cl s ), and turns turbid upon addition of water. On boiling antimonic acid with hydrochloric acid and iodide of potassium iodine separates, which dissolves in the hydriodic acid pre- sent to a brown fluid (BUNSEN). Upon ignition antimonic acid loses oxygen, and is converted into antimonate of teroxide of antimony (SbO 8 , SbO 5 ). Of the antimonates the potassa and ammonia salts are almost the only ones soluble in water : acids precipitate hydrate of antimonic acid from the solutions, chloride of sodium throws down from them antimonate of soda ( 90, 2). 4. The greater part of the SALTS OF TEROXIDE OF ANTIMONY are de- composed upon ignition ; the haloid salts volatilize readily and unaltered. The soluble neutral salts of antimony redden litmus-paper. With a large quantity of water they give insoluble basic salts and acid solutions con- taining teroxide of antimony. Thus, for instance, water throws down from solutions of terchloride of antimony in hydrochloric acid a white bulky precipitate of BASIC TERCHLORIDE OF ANTIMONY (powder of Al- garoth), SbCl 3 , 5SbO 3 , which after some time becomes heavy and crys- talline. Tartaric acid dissolves this precipitate readily, and therefore K 2 132 TEROXIDE OF ANTIMONY. prevents its formation if mixed with, the solution previously to the addi- tion of the water. It is by this property that the basic terchloride of antimony is distinguished from the basic salts of bismuth formed under similar circumstances. 5. Hydrosulphuric acid precipitates from acid solutions of teroxide of antimony (if the quantity of free mineral acid present is not too large), the whole of the metal as orange-red amorphoses TERSULPHIDE OP ANTIMONY (Sb S 8 ). In alkaline solutions this reagent fails to produce a precipitate or, at least, it precipitates them only imperfectly ; neutral solutions also are only imperfectly thrown down by it. The tersulphide of antimony produced is readily dissolved by potassa and by alkaline sulphides, especially if the latter contain an excess of sulphur ; it is but sparingly soluble in ammonia, and, if free from pentasulphide of anti- mony, almost insoluble in bicarbonate of ammonia. It is insoluble in dilute acids, as also in acid sulphite of potassa. Concentrated boiling hydrochloric acid dissolves it, with evolution of hydrosulphuric acid gas. By heating in the air it is converted into a mixture of antimonate of teroxide of antimony with tersulphide of antimony. By deflagration with nitrate of soda it gives sulphate and antimonate of soda. If a potassa solution of tersulphide of antimony is boiled with teroxide of bismuth tersulphide of bismuth precipitates, and teroxide of antimony dissolved in potassa remains in the solution. On fusing tersulphide of antimony with cyanide of potassium metallic antimony and sulphocyanide of potassium are produced. If the operation is conducted in a small tube expanded into a bulb at the lower end, or in a stream of carbonic acid gas (see 132, 12), no sublimate of antimony is produced. But if a mixture of tersulphide of antimony with, carbonate of soda or with cyanide of potassium and carbonate of soda is heated in a glass tube in a stream of hydrogen gas (compare 132, 4), a mirror of antimony is deposited on the inner surface of the tube, immediately behind the spot occupied by the mixture. From a solution of antimonic acid in hydrochloric acid sulphuretted hydrogen throws down pentasulphide of antimony (SbS 5 ), which dissolves readily when heated with solution of soda or ammonia, and equally so in concentrated boiling hydrochloric acid, with evolution of hydrosulphuric acid gas and separation of sulphur, but dissolves only very sparingly in cold bicarbonate of ammonia. 6. Sulphide of ammonium produces in solutions of teroxide of anti- mony an orange-red precipitate of TERSULPHIDE OF ANTIMONY, which readily redissolves in an excess of the precipitant if the latter contains an excess of sulphur. Acids throw down from this solution pentasulphide of antimony (SbS 6 ). However, the orange color appears in that case usually of a lighter tint, owing to an admixture of free sulphur. 7. Potassa, soda, ammonia, carbonate of soda and carbonate of am- monia throw down from solutions of terchloride of antimony, and also of simple salts of teroxide of antimony but far less completely, and mostly only after some time, from solutions of tartar emetic or analogous com- pounds a white bulky precipitate of TEROXIDE OF ANTIMONY, which redissolves pretty readily in an excess of potassa or soda, but requires the application of heat for its re-solution in carbonate of potassa, and is altogether insoluble in ammonia. 8. Metallic zinc precipitates from all solutions of teroxide of anti- mony, if they contain no free nitric acid, METALLIC ANTIMONY as a black TEROXIDE OF ANTIMONY. 133 powder. If a few drops of a solution of antimony, containing some free hydrochloric acid, are put into a platinum dish (the lid of a platinum crucible), and a fragment of zinc is introduced, hydrogen is evolved and antimony separates, staining the part of the platinum covered by the liquid brown or black, even in the case of very dilute solutions : this new reaction I can therefore recommend as being equally delicate and characteristic. Cold hydrochloric acid fails to remove the stain, heating with nitric acid removes it immediately. 9. If a solution of teroxide of antimony in solution of potassa or soda is mixed with solution of nitrate of silver, a deep black precipitate of SUBOXIDE OF SILVER forms along with the grayish-brown precipitate of oxide of silver. Upon now adding ammonia in excess the oxide is redissolved, whilst the suboxide is left undissolved (H. Rose). The formation of the suboxide of silver in this process is explained as follows : K O, Sb0 3 + 4 Ag = KO, Sb0 5 -f- 2 Ag 2 0. This exceedingly delicate reaction affords more especially also an excellent means of detecting teroxide of antimony in presence of antimonic acid. 10. If a solution of teroxide of antimony is introduced into a flask in which hydrogen gas is being evolved from pure zinc and dilute sul- phuric acid the zinc oxidizes not only at the expense of the oxygen of the water, but also at the expense of that of the teroxide of antimony, and antimony separates accordingly in the metallic state ; but a portion of the metal combines in the moment of its separation with the libe- rated hydrogen of the water, forming ANTIMONETTED HYDROGEN GAS (SbH 3 ). If this operation is conducted in a gas evolution flask, con- nected by means of a perforated cork with the limb of a bent tube of which the other limb ends in a finely drawn-out point, pinched off at the top,* and the hydrogen passing through the fine aperture of the tube is ignited after the atmospheric air is completely expelled, the flame appears of a bluish-green tint, which is imparted to it by the antimony separating in a state of intense ignition upon the decomposition of the antimonetted hydrogen ; white fumes of teroxide of antimony rise from the flame, which condense readily upon cold substances, and are not dissolved by water. But if a cold body, such as a porcelain dish (which answers the purpose best), is now depressed upon the flame, METALLIC ANTIMONY is deposited upon the surface in a state of the most minute division, forming a deep black and almost lustreless spot. If the middle part of the tube through which the gas is passing is heated to redness the bluish-green tint of the flame decreases in intensity, and a metallic mirror of antimony of silvery lustre is formed within the tube on both sides of the heated part. As the acids of arsenic give under the same circumstances similar stains of metallic arsenic, it is always necessary to carefully examine the spots produced, in order to ascertain whether they really consist of antimony or contain any of that metal. With stains deposited on a porcelain dish the object in view is most readily attained by treating them with a solution of chloride of soda (a compound of hypochlorite of soda with chloride of sodium, prepared by mixing a solution of chlo- ride of lime with carbonate of soda in excess, and filtering) ; which will immediately dissolve arsenical stains, leaving those proceeding from antimony untouched, or, at least, removing them only after a very pro- * In accurate expez-iments it is advisable to use Marsh's apparatus ( 132, 10). 1-34 AKSENIOUS ACID. tracted action. A mirror within the glass tube, on the other hand, may be tested by heating it whilst the current of hydrogen gas still continues to pass through the tube : if the mirror volatilizes only at a higher temperature, and the hydrogen gas then issuing from the tubes does not smell of garlic ; if it is only with a strong current that the ignited gas deposits spots on porcelain, and the mirror before volatilizing fuses to small lustrous globules distinctly discernible through a magnifying glass, the presence of antimony may be considered certain. Or the metals may be identified by conducting through the tube a very slow stream of dry hydrosulphuric acid gas, and heating the mirror, by means of a spirit-lamp, proceeding from the outer to the inner border, and accord- ingly in an opposite direction to that of the gaseous current. The antimonial mirror is by this means converted into tersulphide of anti- mony, which appears of a more or less reddish-yellow color, and almost black when in thick layers. If a feeble stream of dry hydrochloric acid gas is now transmitted through the glass tube, the tersulphide of antimony, if present in thin layers only, disappears immediately ; if the incrustation is somewhat thicker it takes a short time to dissipate it. The reason for this is, that the tersulphide of antimony decomposes readily with hydrochloric acid, and the terchloride of antimony formed is exceedingly volatile in a stream of hydrochloric acid gas. If the gaseous current is now conducted into some water the presence of anti- mony in the latter fluid may readily be proved by means of hydrosul- phuric acid. By this combination of reactions antimony may be distinguished with positive certainty from all other metals. The reac- tion which hydrogen gas containing antimonetted hydrogen shows with solution of nitrate of silver will be found in 134, 6. 11. If a mixture of a compound of antimony with carbonate of soda and cyanide of potassium is exposed on a charcoal support to the reducing flame, of the Uowpipe, brittle globules of METALLIC ANTIMONY are pro- duced, which may be readily recognised by the peculiar reactions that mark their oxidation (compare 131, 1). 132. d. ARSENIOUS ACID (As0 8 ). 1. METALLIC ARSENIC has a blackish-gray color and high metallic lustre, which it retains in dry air, but loses in moist air, becoming covered with suboxide ; the metallic arsenic of commerce looks there- fore rather dull, with a dim bronze lustre on the planes of crystallization. Arsenic is not very hard, but very brittle : at a dull red heat it volatilizes without fusion. The fumes have a most characteristic odor of garlic, which proceeds from the suboxide of arsenic formed. Heated with free access of air arsenic burns at an intense heat with a bluish flame emitting white fumes of arsenious acid, which condense on cold bodies. If arsenic is heated in a glass tube sealed at the lower end the greater part of it volatilizes unoxidized, and recondenses above the heated spot as a lustrous black sublimate (arsenical mirror) ; a very thin coating of the sublimate appears of a brownish-black color. In contact with air and water arsenic oxidizes slowly to arsenious acid. Weak nitric acid converts it, with the aid of heat, into arsenious acid, which dissolves only sparingly in an excess of the acid ; strong nitric acid converts it par- tially into arsenic acid. It is insoluble in hydrochloric acid and dilute ARSENIOUS ACID. 135 sulphuric acid ; concentrated boiling sulphuric acid oxidizes it to arsenious acid, with evolution of sulphurous acid. 2. ARSENIOUS ACID generally presents the appearance either of a trans- parent vitreous or of a white porcelain-like mass. By trituration it gives a heavy, white, gritty powder. When heated it volatilizes in white inodorous fumes. If the operation is conducted, in a glass tube a subli- mate is obtained consisting of small brilliant octahedrons and tetrahe- drons. Arsenious acid is only difficultly moistened by water ; it com- ports itself in this respect like a fatty substance. It is sparingly soluble in cold, but more readily in hot water. It is copiously dissolved by hydrochloric acid, as well as by solution of soda and potassa. "Upon boiling with nitrohydrochloric acid it dissolves to arsenic acid. It is highly poisonous. 3. The ARSENITES are mostly decomposed upon ignition either into arsenates and metallic arsenic, which volatilizes, or into arsenious acid and the base with which it was combined. Of the arsenites those only with alkaline bases are soluble in water. The insoluble arsenites are dissolved, or at least decomposed, by hydrochloric acid. Anhydrous terchloride of arsenic (AsCl 3 ) is a colorless volatile liquid, fuming in the air, which will bear the addition of a little water, but is decomposed by a larger amount into arsenious acid, which partly separates, and hydro- chloric acid, which retains the rest of the arsenious acid in solution. If a solution of arsenious acid in hydrochloric acid is evaporated by heat, chloride of arsenic escapes along with the hydrochloric acid. 4. Hydrosulphuric acid colors aqueous solutions of arsenious acid yellow, but produces no precipitate in them j it fails equally to precipi- tate aqueous solutions of neutral arsenites of the alkalies ; but upon addition of a stronger acid a bright yellow precipitate of TERSULPHIDE OP ARSENIC (As!S 3 ) forms at once. The same precipitate forms in like manner in the hydrochloric acid solution of arsenites insoluble in water. Even a large excess of hydrochloric acid does not prevent complete pre- cipitation. Alkaline solutions are not precipitated. The precipitate is readily and completely dissolved by pure alkalies, alkaline carbonates and bicarbonates, and also by alkaline sulphides ; but it is nearly inso- luble in hydrochloric acid, even though concentrated and boiling. Boiling nitric acid decomposes and dissolves the precipitate readily. If recently precipitated tersulphide of arsenic is digested with sul- phurous acid and acid sulphite of potassa the precipitate is dissolved j upon heating the solution to boiling the fluid turns turbid, owing to the separation of sulphur, which upon continued boiling is for the greater part redissolved. The fluid contains, after expulsion of the sulphurous acid, arsenite and hyposulphite of potassa: 2 AsS 3 + 8 (K0 a , SO 2 ) = 2 (KO, AsO 3 ) + 6 (KO, S 2 2 ) + S 8 + 7 S0 2 (BUNSEN). The deflagration of tersulphide of arsenic with carbonate of soda and nitrate of soda gives rise to the formation of arsenate and sulphate of soda. If a solution of tersulphide of arsenic in potassa is boiled with hydrated carbonate or basic nitrate of teroxide of bismuth tersulphide of bismuth and arsenite of potassa are produced. If a mixture of tersulphide of arsenic with from 3 to 4 parts of car- bonate of soda, made into a paste with some water, is spread over small glass splinters, and these, after being well dried, are rapidly heated to redness in a glass tube through which dry hydrogen gas is transmitted, a large portion of the arsenic present is reduced to the metallic state and 136 AUSENIOUS ACID. expelled if the temperature applied is sufficiently high. Part of the reduced arsenic forms a metallic mirror on the inner surface of the tube, the remainder is carried away suspended in the hydrogen gas ; the minute particles of arsenic impart a bluish tint to the flame when the gas is kindled, and form stains of arsenic upon the surface of a porcelain dish depressed upon the flame. The fusion of the mixture of tersulphide of arsenic with carbonate of soda first gives rise to the formation of a double tersulphide of arsenic and sulphide of sodium, and of arsenite of soda (2 AsS 3 + 4NaO, CO 2 = 3 NaS, AsS 8 + NaO, AsO 8 + 4 C0 2 ). Upon heating these products the arsenite of soda is resolved into arsenic and arsenate of soda (5 AsO 3 2 As 4- 3 As0 6 ), and the tersulphide of arsenic and sulphide of sodium into arsenic and pentasulphide of arsenic and sulphide of sodium (5 AsS 8 = 2 As + 3 AsS 5 ) ; and by the action of the hydrogen the arsenate of soda is also converted into hydrate of soda, arsenic, and water. The whole of the arsenic is accordingly expelled, except that portion of the metal which constitutes a component part of the double pentasulphide of arsenic and sulphide of sodium formed in the process, a sulphur salt which is not decomposed by hydrogen (H. KOSE). This method of reduction gives indeed very accurate results, but it does not enable us to distinguish arsenic from antimony with a sufficient degree of certainty, nor to detect the one in presence of the other. (Compare 131, 5.) The operation is conducted in the apparatus illustrated by 26. a is the evolution flask, 6 a tube containing chloride of calcium, c the tube in which, at the point d, the glass splinter with the mixture of tersulphide of arsenic and carbonate of soda is placed ; this tube is made of difficultly fusible glass free from lead. When the apparatus is com- pletely filled with pure hydrogen gas d is exposed to a very gentle heat at first, in order to expel all the moisture which may still be present, and then suddenly to a very intense heat,* to prevent the sublimation of undecomposed tersulphide of arsenic. The metallic mirror is deposited near the point e. Another method of effecting the reduction of ter- sulphide of arsenic to the metallic state, which combines with the very highest degree of delicacy the advantage of precluding the possibility of * The flame of the gas- lamp with chimney, or of the blowpipe, answers the purpose best. ARSENIOUS ACID. 137 confounding arsenic with antimony, will be found described in number 12 of this . 5. Sulphide of ammonium also causes the formation of TERSULPHIDE OF ARSENIC. In neutral and alkaline solutions, however, the tersulphide formed does not precipitate, but remains dissolved as a double sulphide of arsenic and ammonium (tersulphide of arsenic and sulphide of ammo- nium). From this solution it precipitates immediately upon the addition of a free acid. 6. Nitrate of silver leaves aqueous solutions of arsenious acid perfectly clear, or at least produces only a trifling yellowish-white turbidity in them ; but if a little ammonia is added a yellow precipitate of ARSENITE OF SILVER (3 AgO, AsOJ separates. The same precipitate forms of course immediately upon the addition of nitrate of silver to the solution of a neutral arsenite. The precipitate dissolves readily in nitric acid as well as in ammonia, and is not insoluble in nitrate of ammonia ; if there- fore a small quantity of the precipitate is dissolved in a large amount of nitric acid, and the latter is afterwards neutralized with ammonia, the precipitate does not make its appearance again, as it remains dissolved in the nitrate of ammonia formed. 7. Sulphate of copper produces under the same circumstances as the nitrate of silver a yellowish-green precipitate of ARSENITE OF COPPER. 8. If to a solution of arsenious acid in an excess of concentrated solu- tion of soda or potassa, or to a solution of an alkaline arsenite mixed with caustic potassa or soda, a few drops of a dilute solution of sulphate of copper are added, a clear blue fluid is obtained, which upon boiling de- posits a red precipitate of SUBOXIDE OF COPPER, leaving arsenate of potassa in solution. This reaction is exceedingly delicate, provided not too much of the solution of sulphate of copper be used. Even should the red pre- cipitate of suboxide of copper be so exceedingly minute as to escape detection by transmitted light, yet it will always be discernible with great distinctness upon looking in at the top of the test-tube. Of course this reaction, although really of great importance in certain instances as a confirmatory proof of the presence of arsenious acid, and more particu- larly also as a means of distinguishing that acid from arsenic acid, is yet entirely inapplicable for the direct detection of arsenic, since grape sugar and other organic substances also produce suboxide of copper from salts of oxide of copper in the same manner. 9. If a solution of arsenious acid mixed with hydrochloric acid is heated with a perfectly clean slip of copper or copper wire, an IRON- GRAY film of metallic arsenic is deposited on the copper, even in highly dilute solutions ; when this film increases in thickness it peels off in black scales. If the coated copper, after washing off the free acid, is heated with solution of ammonia the film peels off from the copper, and separates in form of minute spangles (KEINSCH). Let it be borne in mind that these are not pure arsenic, but consist of an ARSENIDE OF COPPER (Cu 5 As). If the substance, either simply dried or oxidized by ignition in a current of air (which is attended with escape of some arse- nious acid), is heated, there escapes relatively but little arsenic, alloys richer in copper being left behind (FRESENIUS, LIPPERT). It is only after the presence of arsenic in the alloys has been fully demonstrated that this reaction can be considered a decisive proof of the presence of that metal, as antimony and other metals will under the same circumstances also precipitate in a similar manner upon copper. 138 ARSENIOUS ACID. 10. If an acid or neutral solution of arsenious acid or any of its com- pounds is mixed with zinc, water, and dilute sulphuric acid ARSENETTED HYDROGEN (AsH 8 ) is formed, in the same manner as compounds of antimony give under analogous circumstances antimonetted hydrogen. (Compare 131, 10.) This reaction affords us a most delicate test for the detection of even the most minute quantities of arsenic. The operation is conducted in the apparatus illustrated by Fig. 27, or in one of similar construction.* a is the evolution flask, b a bulb in- tended to receive the water carried along with the gaseous current, c a tube filled with cotton and small lumps of chloride of calcium for drying the gas. This tube is connected with b and d by india-rubber tubes which have been boiled in solution of soda ; d should have an inner diameter of 7 millimetres (see Fig. 28), and must be made of difficultly fusible glass Fig. 27. free from lead. In experiments requiring great accuracy the tube should be drawn out as shown in Fig. 27. The operation is now commenced by evolving in a a moderate and uniform current of hydro- gen gas, from pure granulated zinc and pure sulphuric acid diluted with 3 parts of water. Addition of a few drops of bichloride of platinum will be found useful. When the evolu- tion of hydrogen has proceeded for some time, so that it may safely be concluded the air has been completely expelled from the apparatus, the gas is kindled at the open end of the tube d. It is advisable to wrap a piece of cloth round the flask before kindling the gas, to guard against accidents in case of an explosion. It is now absolutely necessary first to ascertain whether the zinc and the sulphuric acid are quite free from any admixture of arsenic. This is * I use the very convenient form of Marsh's apparatus recommended by Otto in his excellent Manual of Chemistry. Fig. 28. ARSENIOTJS ACID. 139 done by depressing a porcelain dish horizontally upon the flame to make it spread over the surface : if the hydrogen contains arsenetted hydrogen brownish or brownish-black stains of arsenic will appear on the porce- lain ; the non-appearance of such stains may be considered as a proof of the freedom of the zinc and sulphuric acid from arsenic. In very accu- rate experiments, however, additional evidence is required to ensure the positive certainty of the purity of the reagents employed ; for this purpose the part of the tube d shown in Fig. 27 over the flame is heated to red- ness with a Berzelius or gas-lamp, and kept some time in a state of ignition : if no arsenical coating makes its appearance in the narrowed part of the tube the agents employed may be pronounced free from arsenic, and the operation proceeded with, by pouring the fluid to be tested for arsenic through the funnel tube into the flask, and afterwards some water to rinse the tube. Only a very little of the fluid ought to be poured in at first, as in cases where the quantity of arsenic present is considerable, and a somewhat large supply of the fluid is poured into the flask, the evolution of gas often proceeds with such violence as to stop the further progress of the experiment. Now if the fluid contains an oxygen compound of arsenic or arsenic in combination with a salt radical, there is immediately evolved, along with the hydrogen, arsenetted hydrogen, which at once imparts a bluish tint to the flame of the kindled gas, owing to the combustion of the particles of arsenic separating from the arsenetted hydrogen in pass- ing through the flame. At the same time white fumes of arsenious acid arise, which condense upon cold objects. If a porcelain plate is now depressed upon the flame the separated and not yet reoxidized arsenic condenses upon the plate in black stains, in a very similar manner to antimony. (See 131, 10.) The stains formed by arsenic incline how- ever more to a blackish- brown tint, and show a bright metallic lustre ; whilst the antiraonial stains are of a deep black color and but feebly lustrous. The arsenical stains may be distinguished moreover from the antimonial stains by solution of chloride of soda hypochlorite of soda with chloride of sodium (compare 131, 10), which will at once dissolve arsenical stains, leaving antimonial stains unaffected, or removing them only after a considerable time. If the heat of a Berzelius or gas-lamp is now applied to the part of the tube d shown in Fig. 27 over the flame, a brilliant arsenical mirror makes its appearance in the narrowed portion of the tube behind the heated part ; this mirror is of a darker and less silvery-white hue than that produced by antimony under similar circumstances ; from which it is moreover distinguished by the facility with which it may be dissipated in a current of hydrogen gas without previous fusion, and by the charac- teristic odor of garlic emitted by the escaping (unkindled) gas. If the gas is kindled whilst the mirror in the tube is being heated the flame will, even with a very slight current of gas, deposit arsenical stains on a porcelain plate. The reactions and properties just described are amply sufficient to enable us to distinguish between arsenical and antimonial stains and mirrors ; but they will often fail to detect arsenic with positive certainty in presence of antimony. In cases of this kind the following process will serve to set at rest all possible doubt as to the presence or absence of arsenic : Heat the long tube through which the arsenetted hydrogen passes to 140 ARSENIOUS ACID. redness in several parts, to produce distinct metallic mirrors ; then transmit through the tube a very weak stream of dry hydrosulphuiic acid gas, and heat the metallic mirrors with a common spirit-lamp, proceeding from the outer towards the inner border. If arsenic alone is present yellow tersulphide of arsenic is formed inside the tube ; if antimony alone is present an orange-red or black tersulphide of anti- mony is produced ; and if the mirror consisted of both metals the two sulphides appear side by side, the sulphide of arsenic as the more volatile lying invariably before the sulphide of antimony. If you now transmit through the tube containing the sulphide of arsenic or the sulphide of antimony, or both sulphides together, dry hydrochloric gas, without applying heat, no alteration will take place if sulphide of arsenic alone is present, even though the gas be transmitted through the tube for a con- siderable time. If sulphide of antimony alone is present this will entirely disappear, as already stated, 131, 10, and if both sulphides are present the sulphide of antimony will immediately volatilize, whilst the yellow sulphide of arsenic will remain. If a small quantity of am- monia is now drawn into the tube the sulphide of arsenic is dissolved, and may thus be readily distinguished from sulphur which may have separated. My personal experience has convinced me of the infallibility of these combined tests for the detection of arsenic. The reaction of hydrogen containing arsenetted hydrogen with solu- tion of nitrate of silver will be found in 134, 6. Marsh was the first who suggested the method of detecting arsenic by the production of arsenetted hydrogen. 11. If a small lump of arsenious acid (a) be introduced into the pointed end of a drawn-out glass tube (Fig. 29), a fragment of quite recently burnt charcoal (6) pushed down the tube to within a short distance of the arsenious acid, and first the charcoal then the arsenious acid heated to redness by the flame of a spirit-lamp, a MIRROR OF METALLIC ARSENIC will form at c, owing to the reduction of the arsenious acid vapor by the red-hot charcoal. If the tube be now cut between b and c and then heated in an inclined position, with the cut end c turned upwards, the metallic mirror will volatilize, emitting the characteristic odor of garlic. This is both the simplest and safest way of detecting pure arsenious acid. Fig. 29. 12. If arsenites, or arsenious acid, or tersulphide of arsenic are fused together with a mixture of equal parts of dry carbonate of soda and cyanide of potassium the whole of the arsenic is reduced to the metallic ARSENIOUS ACID. 141 state, and so is the base also, if easily reducible ; the eliminated oxygen converts part of the cyanide of potassium into cyanate of potassa. In the reduction of tersulphide of arsenic sulphocyanide of potassium is formed. The operation is conducted as follows : introduce the perfectly dry arsenical compound into the bulb of a small bulb- tube (Fig. 30), and cover it with six times the quantity of a perfectly dry mixture of equal parts of carbonate of soda and of cyanide of potassium. The whole quan- tity must not much more than half-fill the bulb, otherwise the fusing cyanide of potassium is likely to ascend into the tube. Heat the bulb now gently with a gas or spirit-lamp ; should some water still escape upon gently heating the mixture wipe the inside of the tube perfectly dry with a twisted slip of paper. It is of the highest importance for the success of the experiment to bestow great care upon expelling the water, drying the mixture, and wiping the tube clean and dry. Apply now a strong heat to the bulb, to effect the reduction of the arsenical compound, and continue this for some time, as the arsenic often requires Fig. 30. some time for its complete sublimation. The mirror which is deposited at b is of exceeding purity. It is obtained from all arsenites whose bases remain either altogether imaffected, or are reduced to such metallic arsenides as lose their arsenic partly or totally upon the simple applica- tion of heat. This method deserves to be particularly recommended on account of its simplicity and neatness, as well as for the accuracy of the results attainable by it, even in cases where only very minute quantities of arsenic are present. It is more especially adapted for the direct production of arsenic from tersulphide of arsenic, and is in this respect superior in simplicity and accuracy to all other methods hitherto suggested. The delicacy of the reaction may be very much heightened by heating the mixture in a stream of dry carbonic acid gas. A series of experiments made by Dr. V. Babo and myself has shown that the most accurate and satisfactory results are obtained in the following manner : Figs. 31 and 32 show the apparatus in which the process is con- ducted. A is a capacious flask intended for the evolution of carbonic acid ; it is half-filled with water and lumps of solid limestone or marble (not chalk, as this would not give a constant stream of gas). B is a smaller flask containing concentrated sulphuric acid. The flask A is closed with a double-perforated cork, into one aperture of which is inserted a funnel-tube (a), which reaches nearly to the bottom of the flask j into the other perforation is fitted a tube (b), which serves to conduct the evolved gas into the sulphuric acid in , where it is thoroughly freed from moisture. The tube c conducts the dried gas into the reduction- tube 6 y , of which Fig. 32 gives a representation, on the scale 142 AESENIOUS ACID. of one-third of the actual length. The tubes which I employ for the purpose in iny own experiments have an inner diameter of eight millimetres. Fig. 81. When the apparatus is fully prepared for use triturate the perfectly dry sulphide of arsenic or arsenite in a slightly heated mortar with about twelve parts of a well-dried mixture consisting of three parts of carbonate of soda and one part of cyanide of potassium. Put the powder upon a narrow slip of card-paper bent into the shape of a gutter, and push this into the reduction-tube down to e ; turn the tube now half-way round its axis, which will cause the mixture to drop into the tube between e and d, every other part remaining perfectly clean. Connect the tube now with the gas-evolution apparatus, and evolve a moderate stream of carbonic acid, by pouring some hydrochloric acid into the flask A. Heat the tube G in its whole length very gently with a spirit-lamp until the mixture in it is quite dry ; when every trace of water is expelled, and the gas stream has become so slow that the single bubbles pass through the sulphuric acid in B at intervals of one second, heat the reduction-tube C, to redness at c (Fig. 32), by means of a spirit or gas lamp ; when c is red-hot, apply the flame of a gas or a larger spirit lamp to the mixture, proceeding from d to e, until the whole of the arsenic is expelled. The far greater portion of the volatilized arsenic recondenses at h, whilst a small portion only escapes through i, imparting to the surrounding air the peculiar odor of garlic. Advance the flame of the second lamp slowly and gradually up to c, by which means the whole of the arsenic which may have condensed in the wide part of the tube is driven to h. When you have effected this, close the tube at the point i by fusion, and apply heat, proceeding from i towards h, by which ARSENIC ACID. 143 means the extent of the mirror is narrowed, whilst its beauty and lustre are correspondingly increased. In this manner perfectly distinct mirrors of arsenic may be produced from as little as the ^-J-^th part of a grain of tersulphide of arsenic. No mirrors are obtained by this process from tersulphide of antimony, nor from any other compound of antimony. 13. If arsenious acid or one of its compounds is exposed on a charcoal support to the reducing flame of the blowpipe a highly charac- teristic garlic odor is emitted, more especially if some carbonate of soda is added to the examined sample. This odor has its origin in the reduction and re-oxidation of the arsenic, and enables us to detect very minute quantities. This test, however, like all others that are based upon the mere indications of the sense of smell, cannot be impli- citly relied on. 133. e. ARSENIC ACID (As0 5 ). 1. ARSENIC ACID is a transparent or white mass, which gradually deliquesces in the air, and dissolves slowly but copiously in water. It fuses at a gentle red heat without suffering decomposition j but at a higher temperature it is resolved into oxygen and arsenious acid, which volatilizes. It is highly poisonous. 2. Most of the ARSENATES are insoluble in water. Of the so-called neutral arsenates those with alkaline bases alone are soluble in water. Most of the neutral and basic arsenates can bear a strong red heat without suffering decomposition. The acid arsenates lose their excess of acid upon ignition, the free acid being resolved into arsenious acid and oxygen. 3. Hydrosulphuric acid fails to precipitate alkaline and neutral solu- tions of arsenates ; but in acidified solutions it causes first reduction of the arsenic acid to arsenious acid, with separation of sulphur, then preci- pitation of tersulphide of arsenic. This process continues until the whole of the arsenic is thrown down as AsS 3 , mixed with 2 S (WAC- KENRODER, LUDWIG, H. ROSE). The action never takes place imme- diately, and in dilute solutions frequently only after the lapse of a considerable time (twelve to twenty-four hours, for instance). Heating (to about 158 F.) greatly accelerates the action. If a solution of arsenic acid, or of an arsenate, is mixed with sulphurous acid, or with sulphite of soda and some hydrochloric acid, the sulphurous acid is converted into sulphuric acid, and the arsenic acid reduced to arsenious acid ; applica- tion of heat promotes the change. If hydrosulphuric acid is now added the whole of the arsenic is immediately thrown down as tersulphide. 4. Sulphide of ammonium converts the arsenic acid in neutral and alkaline solutions of arsenates into pentasulphide of arsenic, which remains in solution as ammonio-pentasulphide of arsenic (pentasulphide of arsenic and sulphide of ammonium). Upon the addition of an acid to the solution this double sulphide is decomposed, and pentasulphide of arsenic precipitates. The separation of this precipitate proceeds more rapidly than is the case when acid solutions of arsenates are precipitated with hydrosulphuric acid. It is promoted by heat. The precipitate formed is AsS 6 , instead of consisting of a mixture of AsS 3 with S a , as in precipitation with hydrosulphuric acid. 5. Nitrate of silver produces under the circumstances stated 132, 6, 144 RECAPITULATION AND REMARKS. a highly characteristic reddish-brown precipitate of ARSENATE OF SILVER (3 AgO, AsO 5 ), which is readily soluble in dilute nitric acid and in ammonia, and dissolves also slightly in nitrate of ammonia. Accord- ingly, if a little of the precipitate is dissolved in a large proportion of nitric acid, neutralization with ammonia often fails to reproduce the precipitate. 6. Sulphate of copper produces under the circumstances stated 132, 7, a greenish-blue precipitate of ARSENATE OF COPPER (2 Cu 0, H O, As0 6 ). 7. If a solution of arsenic acid mixed with some hydrochloric acid is heated with a clean slip of copper the metal remains perfectly clean (WERTHER, REINSCH) ; but if to one volume of the solution two volumes of concentrated hydrochloric acid are added, a gray film is deposited on the copper, the same as with arsenious acid. The reaction is under these circumstances equally delicate with arsenic acid as with arsenious acid (REINSCH). . 8. With zinc in presence of sulphuric acid, with cyanide of potassium, and before the blowpipe, the compounds of arsenic acid comport them- selves in the same way as those of arsenious acid. If the reduction of arsenic acid by zinc is effected in a platinum dish the platinum does not turn black, as is the case in the reduction of antimony by zinc ( 131, 8). 9. If a solution of arsenic acid, or of an arsenate soluble in water, is added to a clear mixture of sulphate of magnesia, chloride of ammo- nium, and a sufficient quantity of ammonia, a crystalline precipitate of ARSENATE OF AMMONIA AND MAGNESIA (2 MgO, NH 4 , O, As O fi 4- 12 aq) separates ; from concentrated solutions immediately, from dilute solu- tions after some time. If a small portion of the precipitate is dissolved on a watch-glass in a drop of nitric acid, a little nitrate of silver added, and the solution touched with a glass rod dipped in ammonia, brownish- red arsenate of silver is formed (difference between arsenate and phosphate of magnesia and ammonia). 134. Recapitulation and remarks. I will here describe first the different ways best adapted to effect the detection or separation of tin, antimony, and arsenic, when present together in the same compound or mixture, and afterwards the most reliable means of distinguishing between the several oxides of each of the three metals. 1. If you have a mixture of sulphide of tin, sulphide of antimony, and sulphide of arsenic, triturate 1 part of it, together with 1 part of dry carbonate of soda and 1 part of nitrate of soda, and transfer the mixed powder gradually to a small porcelain crucible containing 2 parts of nitrate of soda kept in a state of fusion at a not over-strong heat ; oxidation of the sulphides ensues, attended with slight deflagration. The fused mass contains binoxide of tin, arsenate and antimonate of soda, with sulphate, carbonate, nitrate, and nitrite of soda. You must take care not to raise the heat to such a degree, nor continue the fusion so long, as to lead to a reduction of the nitrite of soda to the caustic state, that there may not be formed stannate of soda soluble in water. Upon treating the mass with a little cold water binoxide of tin and antimonate of soda remain undissolved, whilst arsenate of soda and the other salts are dissolved. If the filtrate is acidified with nitric acid, and RECAPITULATION AND REMARKS. 145 heat is applied to remove carbonic acid and nitrous acid, the arsenic acid may be detected and separated, either with nitrate of silver, according to 133, 5, or with a mixture of sulphate of magnesia, chloride of am- monium, and ammonia, according to 133, 9. If the undissolved residue, consisting of binoxide of tin and antimo- nate of soda, is, after being washed once with cold water and three times with dilute spirits of wine, treated with some hydrochloric acid in the lid of a platinum crucible, and a gentle heat applied, the mass is either completely dissolved or, if the tin is present in a large proportion, a white residue is left undissolved. If, regardless of the presence of this latter, a fragment of zinc is added, the compounds are reduced to the metallic state, when the antimony will at once reveal its presence by blackening the platinum. If, after the evolution of hydrogen has nearly stopped, the remainder of the zinc is taken away, and the contents of the lid are heated with some hydrochloric acid, the tin dissolves the protochloride, whilst the antimony is left undissolved in the form of black flakes. The tin may then be more distinctly tested in the solution, with chloride of mercury, or with a mixture of sesqui- chloride of iron and ferricyanide of potassium, and the antimony, after solution in a little aqua regia, with hydrosulphuric acid. As this method of detecting arsenic, tin, and antimony in presence of each other, forms one of the processes in the systematic course of analysis, I have here simply explained the principle upon which it is based, and refer for the details of the process to the first section of Part II. 2. If the mixed sulphides, after being freed from the greater part of the adhering water, by laying the filter containing them on blotting paper, are treated with fuming hydrochloric acid, with applica- tion of a gentle heat, the sulphides of antimony and tin dissolve, whilst the sulphide of arsenic is left almost completely undissolved. By treating this with ammonia, and evaporating the solution obtained, with addition of a small quantity of carbonate of soda, an arsenical mirror may easily be produced from the residue, by means of cyanide of potas- sium and carbonate of soda in a stream of carbonic acid gas ( 132, 12). The solution, which contains the tin and the antimony, may be treated as stated in 1. If a great excess of antimony is present the solution may also be mixed with sesquicarbonate of ammonia in excess, and the mixture boiled ; when a large proportion of the antimony will dissolve, leaving binoxide of tin behind, mixed with but little teroxide of antimony; in which undissolved residue the tin may now be the more readily detected by the method described in 1 (BLOXAM). 3. If the mixed sulphides are digested at a gentle heat with some common solid carbonate of ammonia and water sulphide of arsenic dis- solves, whilst the sulphides of antimony and tin remain undissolved. But even this separation is not quite absolute, as traces of sulphide of antimony are apt to pass into the solution, whilst some sulphide of arsenic remains in the residue. The sulphide of arsenic precipitating from the alkaline solution upon acidifying this latter with hydrochloric acid must therefore, especially if consisting only of a few flakes, after washing, be treated with ammonia, the solution evaporated, with addition of a small quantity of carbonate of soda, and the residue fused with cyanide of potassium in a stream of carbonic acid, to make quite sure by the pro- I. L 146 RECAPITULATION AND REMARKS. duction of an ar?enical mirror. The residue, insoluble in carbonate of ammonia, should be treated as directed in 2. 4. If sulphide of antimony, sulphide of tin, and sulphide of arsenic are dissolved in sulphide of potassium, a large excess of a concentrated solu- tion of sulphurous acid added, the mixture digested for some time on the water-bath, boiled until all sulphurous acid is expelled, then filtered, the filtrate contains all the arsenic as arsenious acid (which may be precipitated from it by hydrosulphuric acid), whilst tersulphide of antimony and bisulphide of tin are left behind undissolved (BUNSEN). These latter may then be treated as directed in 2. 5. In the analysis of alloys, biuoxide of tin, teroxide of antimony, and arsenic acid are often obtained together as a residue insoluble in nitric acid. The best way is to fuse this residue with hydrate of soda in a silver crucible, to treat the mass with water, and add one-third (by volume) of spirit of wine ; then to filter the fluid off from the antimonate of soda, which remains undissolved, and wash the latter with spirit of wine mixed with a few drops of solution of carbonate of soda. The filtrate is acidified with hydrochloric acid, and the tin and arsenic are then precipitated as sulphides, with the aid of heat. On heating the precipitated sulphides in a stream of hydrosulphuric acid gas the whole of the tin is left as sulphide, whilst the sulphide of arsenic volatilizes, and may be received in solution of ammonia (H. HOSE). 6. For the most accurate way of separating antimony and arsenic, and distinguishing between the two metals, viz., by treating with hydro- sulphuric acid the mirror produced by MARSH'S method, and separating the resulting sulphides by means of hydrochloric acid gas, I refer to 132, 10. Antimony and arsenic may, however, when mixed together in form of hydrogen compounds, be separated also in the following way : Conduct the gases mixed with an excess of hydrogen, first through a tube contain- ing glass splinters moistened with solution of acetate of lead, to retain the hydrochloric and hydrosulphuric gas, then in a slow stream into a solu- tion of nitrate of silver. All the antimony in the gas falls down as black autimonide of silver (Ag 3 Sb), whilst the arsenic passes into the solution as arsenious acid, with reduction of the silver, and may be de- tected in the fluid as arsenite of silver, by cautious addition of ammonia, or after precipitating the excess of silver by hydrochloric acid by means of hydrosulphuric acid. In the precipitated antirnonide of silver, which is often mixed with much silver, the antimony may be most readily detected, by heating the precipitate thoroughly freed from arsenious acid by boiling with water with tartaric acid and water to boiling. This will dissolve the antimony alone, which may then be readily detected by means of hydrosulphuric acid in the solution acidified with hydro- chloric acid (A. W. HOFMANN). 7. Protoxide and binoxide of tin may be detected and identified in presence of each other, by testing one portion of the solution containing both oxides, for the protoxide with chloride of mercury, terchloride of gold or a mixture of ferricyanjde of potassium and sesquichloride of iron, and another portion for the binoxide, by pouring it into a concentrated hot solution of sulphate of soda. 8. Teroxide of antimony in presence of antimonic acid may be identified by the reaction described in 131, 9. Antimonic acid in presence of teroxide of antimony, by heating the teroxide suspected to contain an admixture of the acid, but without any other ad- OXIDE OF IKIDIUM. 147 mixture, with hydrochloric acid and iodide of potassium ( 131, 2 and 3). 9. Arsenious acid and arsenic acid in the same solution may he distin- guished by means of nitrate of silver. If the precipitate contains little arsenate and much arsenide of silver it is necessary, in order to identify the former, to add cautiously and drop by drop most highly dilute nitric acid, which dissolves the yellow arsenite of silver first. A still safer way to detect small quantities of arsenic acid in presence of arsenious acid is to precipitate the solution which contains the two acids, with a mixture of sulphate of magnesia, chloride of ammonium, and ammonia ( 133, 9), by which means an actual separation of the two acids is also effected. The immediate precipitation of arsenic acid from an acidified solution by hydrosulphuric acid unaided by the application of heat affords also a ready means of distinguishing between the two acids, as this reaction differs considerably in the case of arsenious acid. Arsenious acid in presence of arsenic acid may also be identib'ed by the reduction of oxide of copper effected by its agency in alkaline solutions. To ascertain the degree of sulphuration of a sulphide of arsenic in a sulphur salt, boil the alkaline solution of the salt under examination with hydrate of teroxide of bismuth, filter off from the tersulphide of bismuth formed, and test the filtrate for arseuious and arsenic acids. To distin- guish between the ter- and pentasulphide of arsenic, extract first the sulphur which may be present by means of sulphide of carbon, then dis- solve the residue in ammonia, add nitrate of silver in excess, filter off the sulphide of silver, and observe whether arsenite or arsenate of silver is formed upon addition of ammonia. Special Reactions of the rarer Oxides of the Sixth Group. 135. a. OXIDE or IRIDIDM (Ir0 2 ). IRIDIUM is found in combination with platinum and other metals in platinum ores, also, and more especially, as a native alloy of osmium and iridium. Alloyed with platinum, it has of late been employed for crucibles, c. Iridium resembles pla-. tinum, but is brittle ; it fuses with extreme difficulty. In the compact state, or reduced at a red heat by hydrogen, it dissolves in no acid, not even in aqua regia (difference between iridium and gold and platinum) ; reduced in the moist way, say by formic acid, or largely alloyed with platinum, it dissolves in aqua regia to bichloride (Ir C1 2 ). Acid sulphate of potoxsa in a state of fusion will oxidize, but not dissolve it (difference between iridium and rhodium). It oxidizes by fusion with hydrate of soda, with access of air, or by fusion with nitrate of soda. The compound of sesquioxide of iridium (Ir 2 O 3 ) with soda, which is formed in this process, dissolves partially in water : by heating with aqua regia it gives a deep-black solution of bichloride of iridium and chloride of sodium. If iridium in powder is mixed with chloride of sodium, the mixture heated to insi- pient redness, and treated with chlorine gas, sodio-bichloride of iridium is formed, which dissolves in water to a deep reddish-brown fluid. Potassa, ad led in exce.ss, decolorizes the solution, alittle brownish-black potassio-bichloride of iridium precipi- tating at the same time. If the solution is heated, and exposed some time to the air, it acquires at first a reddish tint, which changes afterwards to azure blue (characteristic difference between iridium and platinum) ; if the solution is now evaporated todryness, and the residue treated with water, a colorless fluid is obtained, with a blue deposit left undissolved. Hydrosulphuric acid in the first place decolorizes solutions of bi- chloride of iridium, protochloride is formed, with separation of sulphur, and finally brown sulphide of iridium precipitates. Sulphide of ammonium produces the same preci- pitate, which redissolves readily in an excess of the precipitant. Chloride ofammo.-iii', precipitates from more concentrated solutions ammonio-bichloride of iridium in form of a blackish- red powder consisting of microscopic octahedrons. Protockloridc of tin L 2 148 OXIDES OF MOLYBDENUM. produces a light-brown precipitate. Sulphate of protoxide of iron decolorizes, but fails to precipitate solutions of bichloride of iridiura ; zinc precipitates black irictium. &. OXIDES OF MOLYBDENUM. MOLYBDENUM is not largely disseminated in nature, and is found only in moderate quantities, more especially as sulphide of molybdenum and as molybdate of lead (yellow lead ore). Since the use of molybdate of ammonia as a means of detecting and deter- mining phosphoric acid, molybdenum has acquired greater importance for practical chemistry. MOLYBDENUM is silvery white ; it fuses with very great difficulty. The PROTOXIDE of the metal (Mo 0) is* black, the BINOXIDE (Mo O a ) dark brown. By heating in the air, or treating with nitric acid, the metal and the two oxides are con- verted into MOLYBDIC ACID (Mo O K ). Molybdic acid is a white porous mass, which in water separates as fine scales ; it fuses at a red-heat ; in close vessels it volatilizes only at a very high temperature, in the air easily at a red-heat, subliming to transparent laminae and needles. The non-ignited acid dissolves in acids. The solu- tions are colorless ; in contact with zinc or tin they first turn blue, then green, and ultimately black, with separation of protoxide of molybdenum ; by digestion with copper the sulphuric acid solution acquires a blue, the hydrochloric acid solution a brown tint. The reaction often takes place only after some time. Ferrocyanide of potassium produces a reddish-brown precipitate, infusion of galls a green precipitate. Hydrosul- phuric acid, added in small proportion, imparts a blue tint to solutions of molybdic acid ; added in larger proportion it produces a brownish-black precipitate ; the fluid over the latter at first appears green. But after being allowed to stand for some time, and heated, additional quantities of hydrosulphuric acid being repeatedly conducted into it, the whole of the molybdenum present will ultimately though slowly separate as black tersulphide of molybdenum (Mo S 8 ). The precipitated tersulphide of molyb- denum dissolves in sulphides of the alkali metals ; acids reprecipitate from the sulphur salts the sulphur acid (Mo S 5 ). Application of heat promotes the separation. By heating to redness in the air, or by heating with nitric acid, sulphide of molybdenum is converted into molybdic acid. Molybdic acid dissolves readily in solutions of pure alkalies and carbonates of the alkalies; from concentrated solutions nitric acid or hydrochloric acid throws down molybdic acid, which redissolves upon further addition of the precipitant. The solutions of molybdates of the alkalies are colored yellow by hydrosulphuric acid, and give afterwards, upon addition of acids, a brownish-black precipitate. For the deport- ment of molybdic acid with phosphoric acid and ammonia, see 142, 10. If a fragment of zinc is put into a hydrochloric acid solution of molybdic acid, and a few drops of solution of sulphocyanide of potassium are added, and as much hydrochloric or sulphuric acid as will suffice to bring on a slight evolution of hydrogen, the fluid acquires a carmine-red tint, which, however, is not very persistent (C. D. BRAUN). Molybdic acid volatilizes when heated on charcoal in the oxidizing flame, coating the charcoal with a yellow, often crystalline, powder, which turns white on cooling. In the reducing flame the acid suffers reduction to the metallic state, the molybdenum is obtained as a gray powder by washing the charcoal support. Sulphide of molyb- denum gives in the oxidizing flame sulphurous acid and an incrustation of molybdic acid on the charcoal support. c. OXIDES OF WOLFRAMIUM OB TUNGSTEN. WoLFRAMiUMor tungsten metal is not widely disseminated in nature, and is found only in very moderate quantity. It occurs most frequently as tungstate of lime and in the mineral wolfram, which is a double tungstate of protoxide of iron and protoxide of manganese. TUNGSTEN, or WOLFRAMIUM, obtained by ihe reduction of tungstic acid in a stream of hydrogen gas at an intense red heat, is an iron-gray powder, which fuses with extreme difficulty, and is converted by ignition in the air into tungstic acid (W0 3 ), by ignition in a stream of chlorine gas into a sublimate of red bichloride of tungsten (WC1 2 ). The latter in contact with water gives first hydrochloric acid and binoxide of tungsten (W O a ), which, however, oxidizes subsequently in the air to blue oxide (W0 2 WO 8 ). Tungsten is insoluble in acids, even in aqua regia, and also in solutions of potassa ; it dissolves, however, in solution of potassa mixed with hypochlorite of alkali. BlNOXiDE OF TUNGSTEN is black ; by intense ignition with free access of air it is converted into tungstic acid. TUNGSTIC ACID is lemon -yellow, fixed, insoluble in water and in acids. By fusing tungstic acid with acid sulphate of potassa, and treating the fused mass with water, an acid solution is obtained, which contains no tuno-stic acid. After the removal of this solution, the residue, consisting of tungstate of potassa, dissolves. Tungstates of the alkalies, soluble in water, are formed readily by fusion, with carbonated alkalies, with difficulty by boiling with solutions of OXIDES OF TELLURIUM. 149 alkalies. Hydrochloric acid, nitric acid, and sulphuric acid produce in the solution of these tungstates white precipitates, which are insoluble in an excess of the acids (difference from molybdic acid), but soluble in ammonia. Upon evaporating with an excess of hydrochloric acid to dryness, and treating the residue with water, the tung- stic acid is left uudissolved. Chloride of barium, chloride of calcium, nitrate of silver, nitrate of suboxide of mercury produce white precipitates. Ferrocyanide of potassium, with addition of some acid, colors the fluid deep brownish-red, and after some time produces a precipitate of the same color. Tincture of galls, with a little acid added, produces a brown precipitate. Hydrosulphuric acid barely precipitates acid solutions. Sulphide of ammonium fails to precipitate solutions of tungstates of alkalies ; upon acidifying the mixture light-brown tersulphide of tungsten (W S 3 ) pre- cipitates, which is slightly soluble in pure water, but insoluble in water containing salts. Protochloride of tin produces a yellow precipitate ; on acidifying with hydro- chloric acid, and applying heat, this precipitate acquires a beautiful blue color (highly delicate and characteristic reaction). If solutions of tungstates of alkalies are mixed with hydrochloric acid, or, better still, with an excess of phosphoric acid, and zinc is added, the fluid acquires a beautiful blue color. Phosphate of soda and ammonia dissolves tungstic acid. The bead, exposed to the oxidizing flame, appears clear, varying from colorless to yellowish ; in the reducing flame it acquires a pure blue color, and upon addition of sulphate of protoxide of iron a blood-red color. By mixing with a little carbonate of soda, and exposing in the cavity of the charcoal support to the reducing flame, tungsten in powder is obtained, which may be washed off the charcoal. The tungstates which are insoluble in water may, most of them, be decom- posed by digestion with acids. The mineral Wolfram, which strongly resists the action of acid, is fused with carbonated alkali, when water will dissolve out of the fused mass the tungstate of alkali formed. d. OXIDES OF TELLURIUM. TELLURIUM is not widely disseminated, and is found in small quantities only in the native state, or alloyed with other metals, or as tellurous acid. It is a white brittle, but readily fusible metal, which may be sublimed in a glass tube. Heated in the air it burns with a greenish-blue flame, emitting thick white fumes of tellurous acid. Tellurium is insoluble in hydrochloric acid, but dissolves readily in nitric acid to tellurous acid (Te0 2 ). Tellurium in powder dissolves in cold concentrated sulphuric acid to a purple-colored fluid, from which it separates again upon addition of water. TELLUROUS ACID is white ; at a gentle red heat it fuses to a yellow fluid ; it is vola- tilized by strong ignition in the air, forming no crystalline sublimate. The anhydrous acid dissolves readily in hydrochloric acid, sparingly in nitric acid, freely in solution of potassa, slowly in ammonia, barely in water. The hydrate of tellurous acid is white ; it is perceptibly soluble in cold water, and dissolves in hydrochloric acid and in nitric acid. By addition of water white hydrate is thrown down from the solution, and from the nitric acid solution nearly the whole of the tellurous acid separates after some time as a crystalline precipitate, even without addition of water. Pure alkalies and car- bonates of the alkalies throw down from the hydrochloric acid solution white hydrate, which is soluble in an excess of the precipitant. Hydrosulphuric acid produces in acid solutions a brown precipitate (Te S t ) (in color like protosulphide of tin), which dissolves very freely in sulphide of ammonium. Sulphite of soda, protochloride of tin, and zinc precipitate black metallic tellurium. TELLURIC ACID (Te O 8 ) is formed by fusing tellurium or tellurites with nitrates and carbonates of the alkalies. The fused mass is soluble in water. The solution remains clear upon acidifying with hydrochloric acid in the cold ; but upon boiling chlorine is disengaged, and tellurous acid formed, and the solution is therefore now precipitated by water if the excess of acid is not too great. If tellurium, its sulphide, or an oxygen compound of the metal is fused with cyanide of potassium in a stream of hydrogen, a double cyanide of tellurium and potas- sium is formed. The fused mass dissolves in water, but a current of air throws down from the solution the whole of the tellurium (difference and means of separating tellu- rium from selenium). By fusion of tellurous or telluric acid with carbonate of potassa, and charcoal, telluride of potassium is formed, which with acids evolves stinking tellu- retted hydrogen gas. Upon exposing tellurium compounds mixed with carbonate of soda to the inner blowpipe flame, reduction, volatilization, and reoxidaiion take place, and the charcoal support becomes accordingly covered with white tellurous acid. e. OXIDES or SELENIUM. SELENIUM is a rare substance ; it occurs in nature in the form of selenides of inetals, It is found occasionally in_ the dust of roasting- furnaces, and also in the Nord- 150 GENERAL REAGENTS. Imisen oil of vitriol. It resembles sulphur in some respects, tellurium in others, and stands thus on the border between the metals and the non- metallic elements. Fused selenium is grayi.-h-black ; it volatilizes at a higher temperature, and may be sublimed. Heated in the air it burns to selenious acid (Se O 2 ), exhaling a characteristic smell of decaying horse-radish. Concentrated sulphuric acid dissolves selenium without oxi- dizing it ; upon diluting the solution the selenium falls down in red flakes. Nitric acid and aqua regia dissolve selenium to SELENIOUS ACID. Sublimed anhydrous selenious add appears in form of white four- sided needles, its hydrate in form of crystals resembling those of nitrate of potassa. Both the acid and its hydrate dis- solve readily in water to a strongly acid fluid. Of the neutral salts only those with the alkalies are soluble in water ; the solutions Lave alkaline reactions. All selenites dissolve readily in nitric acid, with the exception of the selenites of lead and silver, which dissolve with difficulty. Hydrosulphuric acid produces in solu- tions of selenious acid or of selenites (in presence of free hydrochloric acid) a yellow precipitate of SULPHIDE OP SKLENIUM (?) which, upon heating, turns reddish- yellow, and is soluble in sulphide of ammonium. Chloride of barium produces (afcer neutralization of the free acid, should any be present) a white precipitate of selenite of baryta, which is soluble in hydrochloric acid and in nitric acid. Protochlorlde of tin or sulphurous acid, with addition of hydrochloric acid, produces n red precipitate of SELKMIUM, which turns gray at a high temperature. SELENIC ACID is formed by heating selenium or its compounds with carbonates and nitrates of the alkalies. The fused mass dissolves in water ; the solution remains clear upon acidifying with hydrochloric acid ; when concentrated by boiling, it evolves chlorine, whilst the selenic acid is reduced to selenious acid. By fusing selenium or its compounds with cyanide of potassium in a stream of hydrogen gas, a double cyanide of selenium and potassium is obtained, from which the selenium is not eliminated by the action of the air (as is the case with tellurium); it separates, however, upon long- continued boiling, after addition of hydrochloric acid. When exposed on a charcoal support to the reducing Jfame, the selenites evolve selenium, exhaling at the same time a most characteristic odor of decaying horse-radish, which unmistakeably betrays their presence. B. REACTIONS OR DEPORTMENT OF THE ACIDS AND THEIR RADICALS WITH REAGENTS. 136. The reagents which serve for the detection of the acids are divided, like those used for the detection of the bases, into GENERAL REAGKNTS, i.e., such as indicate the GROUP to which the acid under examination belongs ; and SPECIAL REAGENTS, i.e., such as serve to effect the detection and identification of the INDIVIDUAL ACIDS. The groups into which we classify the various acids can scarcely be defined and limited with the same degree of precision as those into which the bases are divided. The two principal groups into which acids are divided are those of INORGANIC and ORGANIC ACIDS. We base this division upon those cha- racteristics by which, irrespectively of theoretical considerations, the ends of analysis are most easily attained. We select therefore here, as the characteristic mark to guide us in the classification into organic and inorganic acids, the deportment which the various acids manifest at a high temperature, and call organic those acids of which the salts (par- ticularly those which have an alkali or an alkaline earth for base) are decomposed upon ignition, the decomposition being attended with sepa- ration of carbon. By selecting this deportment at a high temperature as the distinctive characteristic of organic acids, we are enabled to determine at once by a most simple preliminary experiment the class to which an acid belongs. The salts of organic acids with alkalies or alkaline earths are converted into carbonates when heated to redness. Before proceeding to the special study of the several acids considered INORGANIC ACIDS. 151 in this work, I give here, the same as I have done with the bases, a general view of the whole of them classified in groups. CLASSIFICATION OF ACIDS IN GROUPS. I. INORGANIC ACIDS. FIRST GROUP : Division a. Chromic acid (sulphurous and hyposulphurous acids, iodic acid). Division b. Sulphuric acid (hydrofluosilicic acid). Division c. Phosphoric acid, boracic acid, oxalic acid, hydrofluoric acid (phosphorous acid). Division d. Carbonic acid, silicic acid. SECOND GROUP : Chlorine and hydrochloric acid ; bromine and hydrobromic acid ; iodine and hydriodic acid : cyanogen, and hydrocyanic acid, together with hydroferro- and hydroferricyanic acids; sulphur and hydrosulphuric acid (nitrous acid, hypochlo- rous acid, chlorous acid, hypophosphorous acid). THIRD GROUP : Nitric acid, chloric acid (perchloric acid). II. ORGANIC ACIDS. FIRST GROUP : Oxalic acid, tartaric acid, citric acid, malic acid (racemic acid). SECOND GROUP : Succinic acid, benzoic acid. THIKD GROUP : Acetic acid, formic acid (propionic acid, butyric acid, lactic acid). The acids printed in italics are more frequently met with in the exami- nation of minerals, waters, ashes of plants, industrial products, medi- cines, &c. ; the others are more rarely met with. I. INORGANIC ACIDS. 137. First Group. ACIDS WHICH ARE PRECIPITATED FROM NEUTRAL SOLUTIONS BY CHLORIDE OF BARIUM. This group is again subdivided into four divisions, viz. : 1. Acids which are decomposed in acid solution by hydrosulphuric acid, and to which attention has therefore been directed already in the testing for bases, viz., CHROMIC ACID (sulphurous acid and hyposul- phurous acid, the latter because it is decomposed and detected by the mere addition of hydrochloric acid to the solution of one of its salts ; and also iodic acid).* * To this first division of the first group of inorganic acids belong properly also all the oxygen compounds of a distinctly pronounced acid character, which have been discussed already with the Sixth Group of the metallic oxides (acids of arsenic, antimony, selenium, &c.). But as the reaction of these compounds with hydrosulphuric acid tends to lead to confounding them rather with other metallic oxides than with other acids, it appeared the safer course to class these compounds, which may be said to stand between the bases and the acids, with the metallic oxides. 152 CHROMIC ACID. 2. Acids which are not decomposed in acid solution by hydrosulphnric acid, and the baryta compounds of which are insoluble in hydrochloric acid : SULPHURIC ACID (hydrofluosilicic acid). 3. Acids which are not decomposed in acid solution by hydrosulphuric acid, and the baryta compounds of which dissolve in hydrochloric acid, apparently WITHOUT DECOMPOSITION, inasmuch as the acids cannot be completely separated from the hydrochloric acid solution by heating or evaporation ; these are PHOSPHORIC ACID, BORACIC ACID, OXALIC ACID, HYDROFLUORIC ACID (phosphorous acid). (Oxalic acid belongs more properly to the organic group. We consider it, however, here with the acids of the inorganic class, as the property of its salts to be decomposed upon ignition without actual carbonization may lead to its being overlooked as an organic acid.) 4. Acids which are not decomposed in acid solution by hydrosulphuric acid, and the baryta salts of which are soluble in hydrochloric acid WITH DECOMPOSITION (separation of the acid) : CARBONIC ACID, SILICIC ACID. First Division of the First Group of the Inorganic Acids. 138. CHROMIC ACID (Cr0 8 ). 1. CHROMIC ACID appears as a scarlet-red crystalline mass, or in the form of distinct acicular crystals. Upon ignition it is resolved into sesquioxide of chromium and oxygen. It deliquesces rapidly upon ex- posure to the air. It dissolves in water, imparting to the fluid a deep reddish-brown tint, which remains still visible in very dilute solutions. 2. The CHROMATES are all red or yellow, and for the most part insoluble in water. Part of them are decomposed upon ignition ; those with alkaline bases are fixed, and are soluble in water ; the solutions of the neutral alkaline chromates are yellow, those of the alkaline bichro- mates are reddish-brown. These tints are still visible in highly dilute solutions. The yellow color of the solution of a neutral salt changes to reddish-brown on the addition of a mineral acid, owing to the formation of an acid chromate. 3. Hydrosulphuric acid acting upon the acidified solution of a chro- inate produces first a brownish coloration of the fluid, then a green coloration, arising from the salt of sesquioxide of chromium formed ; this change of color is attended with separation of sulphur, which imparts a milky appearance to the fluid (KG, 2 Cr 8 + 4 S 8 + 3 H S KO, S0 3 + Cr 2 8 , 3 S0 8 + 3 HO + 3 S). Heat promotes this reaction, part of the sulphur being in that case converted into sulphuric acid. 4. Chromic acid may also be reduced to sesquioxide of chromium by means of many other substances, and more particularly by sulphurous acid, or by heating with hydrochloric acid, especially upon the addition of alcohol (in which case chloride of ethyle and aldehyde are evolved) ; also by metallic zinc, or by heating with tartaric acid, oxalic acid, &c. All these reactions are clearly characterized by the change of the red or yellow color of the solution to the green tint of the salt of sesquioxide of chromium. 5. Chloride of "barium produces in aqueous solutions of chromates a yellowish- white precipitate of CHROMATE OF BARYTA (BaO, CrOJ, which is soluble in dilute hydrochloric acid and nitric acid. CHROMIC ACID. 153 6. Nitrate of silver produces in aqueous solutions of chromates a dark purple-red precipitate of CHROMATE OF SILVER (AgO, CrO 3 ), which is soluble in nitric acid and in ammonia ; in slightly acid solutions it produces a precipitate of BICHROMATE OF SILVER (AgO, 2 Cr0 3 ). 7. Acetate of lead produces in an aqueous or acetic acid solution of a chromate a yellow precipitate of CHROMATE OF LEAD (PbO, CrO 3 ), which is soluble in potassa, but only sparingly soluble in dilute nitric acid. Upon heating with alkalies the yellow neutral salt is converted into basic red chromate of lead (2 PbO, Cr.O 3 ). 8. If a very dilute acid solution of peroxide of hydrogen* (about 6 or 8 cubic centimetres) is covered with a layer of ether (about half a centimetre thick), and a fluid containing chromic acid is added, the solu- tion of peroxide of hydrogen acquires a fine blue color. By inverting the test-tube, closed with the thumb, repeatedly, without much shaking, the solution becomes colorless, whilst the ether acquires a blue color. The latter reaction is particularly characteristic. One part of chromate of potassa in 40,000 parts of water suflices to produce it distinctly (STORER) ; presence ^cf vanadic acid materially impairs the delicacy of the test (WERTHER) compare 113, b. The blue coloration is in all probability caused, not by perchromic acid (the existence of which is altogether doubtful), but by a combination of chromic acid with peroxide of hydrogen. After some time reduction of the chromic acid to sesqui- oxide of chromium takes place, and at the same time decoloration of the ether. 9. If insoluble chromates are fused together with carbonate of soda and nitrate of soda, and the fused mass is treated with water, the fluid obtained appears YELLOW from the alkaline chromate which it holds in solution ; upon the addition of an acid the yellow colour changes to reddish-brown. The oxides are left either in the pure state or as carbonates, unless they are soluble in the caustic soda formed from the nitrate. 10. The compounds of chromic acid show the same reactions with phospJiate of soda and ammonia and with borax in the blowpipe flame, as the compounds of sesquioxide of chromium. 11. Very minute quantities of chromic acid may be detected by mixing with the fluid, slightly acidified with sulphuric acid, a little tincture of guaiacum (1 part of the resin to 100 parts of alcohol of 60 per cent.), when an intense blue coloration of the fluid will at once make its appearance, speedily vanishing again, however, where mere traces of chromic acid are present (H. SCHIFF). Chromic acid being reduced by hydrosulphuric acid to sesquioxide of chromium, this acid is in the course of analysis always found already in the examination for bases. The intense color of the solutions containing chromic acid, the excellent reaction with peroxide of hydrogen, and the characteristic precipitates produced by solutions of salts of lead and salts of silver, afford moreover ready means for its detection. * Solution of peroxide of hydrogen may be easily prepared by triturating a frag- ment of peroxide of barium (about the size of a pea) with some water, and adding it with stirring to a mixture of about 30 cubic centimetres of hydrochloric acid, and 120 cubic centimetres of water. The solution keeps a long time without suffering decomposition. In default of peroxide of barium, impure peroxide of sodium may be used instead, which is obtained by heating a fragment of sodium iu a small porcelain dish until it takes fire, and letting it burn. 154; SULPHUROUS ACID. Rarer A cids of the First Division of the First Group. 139. a. SULPHUROUS ACID (S0 2 ) SULPHUROUS ACID is a colorless, uninflammable gas, which exhales the stifling odor of burning sulphur. It dissolves copiously in water. The solution has the odor of the gas, reddens litmus-paper, and bleaches Brazil-wood paper. It absorbs oxygen from the air, and is thereby converted into sulphuric acid. The salts of sulphurous acid are colorless. Of the neutral sulphites those with alkaline base only are readily soluble in water ; many of the sulphites insoluble or sparingly soluble in water dissolve in an aqueous solution of sulphurous acid, but fall down again upon boiling. All the sulphides evolve sulphurous acid when treated with sulphuric acid or hydro- chloric acid. Chlorine water dissolves most sulphites to sulphates. Chloride of barium precipitates neutral sulphites, but not free sulphurous acid. The precipitate dissolves in hydrochloric acid. Hydrosulphuric acid decomposes free sulphurous acid, water and pentathionic acid being formed and free sulphur eliminated, which latter separates from the fluid. If a trace of sulphurous acid or of a sulphite is introduced into a flask in which hydrogen is be'n^ evolved from zinc and hydrochloric acid, hydro- sulphuric acid is immediately evolved along with the hydrogen, and the gas now produces a black coloration or a black precipitate in a solution of acetate of lead to which has been added a sufficient quantity of solution of soda to redissolve the preci- pitate which forms at first. Sulphurous acid is a powerful reducing agent ; it reduces chromic acid, permanganic acid, chloride of mercury (to subchloride), decolorizes iodide of starch, produces a blue precipitate in a mixture of ferricyanide of potassium and sesqu (chloride of iron, &c. With a hydrochloric acid solution of protochloride of tin a brown precipitate of PROTOSULPHIDE OP TIN is formed after some time. If an aqueous solution of an alkaline sulphite is mixed with acetic acid just to give it an incipient acid reaction, and is then added to a relatively large amount of solution of sulphate of zinc, mixed with a very small quantity of nitroprusside of sodium, the fluid acquires a red color if the quantity of the sulphite present is not too inconsider- able, but when the quantity of the sulphite is very minute the coloration makes its appearance only after addition of some solution of ierrocyanide of potassium. It tha quantities are not altogether too minute, a purple-red precipitate will form at once upon the addition of the ferrocyanide of potassium (BoDEKEh). Hyposulphites of the alkalies do not show this reaction. 1. HTPOSULPHUROUS ACID (S.,0 2 ). This acid does not exist in the free state. Most of its salts are soluble in water. The solutions of most hyposulphites may be boiled without suffering decomposition ; hyposulphite of lime is resolved upon boiling into sulphite of lime and sulphur. If hydrochloric acid or sulphuric acid is added to the solution of a hyposulphite, the fluid remains at first clear and inodorous, but after a short time the shorter the more concentrated the solution it becomes more and more turbid, owing to the separation of sulphur, and exhales the odor of sulphurous acid. Application of heat promotes this decomposition. Nitrate of silver produces a white precipitate of HYPOSULPHITE OF SILVER, which is soluble in an excess of the hyposulphite ; after a little while (upon heating almost immediately) this precipitate turns black, being decomposed into sulphide of silver and sulphuric acid. Hyposulphite of soda dissolves chloride of silver ; upon the addition of an acid the solution remains clear at first, but after some time, and immediately upon boiling, sulphide of silver separates. Chloride of barium produces a white precipitate, which is soluble in much water, more especially hot water, and is decomposed by hydrochloric acid. Where it is required to find sulphites and hyposulphites of the alkalies in presence of alkaline sulphides, as is often the case, solution of sulphate of zinc is first added to the fluid until the sulphide is decomposed ; the sulphide of zinc is then filtered off, and one part of the filtrate is tested for hyposulphurous acid by addition of acid, another portion for sulphurous acid with nitroprusside of potassium, &c. c. IODIC ACID (IO 5 ). IODIC ACID crystallizes in white, six-sided tables ; at a moderate heat it is resolved into iodine vapor and oxygen ; it is readily soluble in water. The salts are decom- posed upon ignition, being resolved either into oxygen and a metallic iodide, or into iodine, oxygen, and metallic oxide ; the iodates with an alkaline base alone dissolve SULPHURIC ACID. 155 readily in water. Chloride of barium throws down from solution of iodates of the alkalies a white precipitate of IODATE OP BARYTA, which is soluble in nitric acid ; nitrate of silver a white granular- crystalline precipitate of IODATE OF SILVEK, which dissolves readily in ammonia, but only sparingly in nitric acid. Hydrosulphuric acid throws down from solutions of iodic acid IODINE, which then dissolves in hydriodic acid ; the precipitation is attended with separation of sulphur. If an excess of hydro- sulphuric acid is added, the fluid loses its color, and a further separation of sulphur takes place, the iodine being converted into hydriodic acid. Iodic acid combined with bases is also decomposed by hydrosulphuric acid. Sulphurous acid throws down IODINE, which upon addition of an excels of the acid is converted into hydriodic acid. Second Division of the First Group of the Inorganic Acids. 140. SULPHURIC ACID (S 3 ). 1. Anhydrous sulphuric acid is a white feathery-crystalline mass, which emits strong fumes upon exposure to the air ; hydrated sulphuric acid forms an oily liquid, colorless and transparent like water. Both the anhydrous and hydrated acid char organic substances, and combine with water in all proportions, the process of combination being attended with considerable elevation of temperature, and in the case of the anhydrous acid with a hissing noise. 2. The neutral sulphates are readily soluble in water with the exception of the sulphates of baryta, strontia, lime, and lead. The basic sulphates of the oxides of the heavy metals which are insoluble in water dissolve in hydrochloric acid or in nitric acid. Most of the sulphates are colorless or white. The sulphates of the alkalies are not decomposed by ignition. The other sulphates are acted upon in different ways by a red heat, some of them being readily decomposed, others with difficulty, and some resisting decomposition altogether. 3. Chloride of barium produces even in exceedingly dilute solutions of sulphuric acid and of the sulphates a finely-pulverulent, heavy, white precipitate of SULPHATE OF BARYTA (Ba 0, S O s ), which is insoluble in dilute hydrochloric acid and nitric acid. From very dilute solutions the precipitate separates only after standing some time. Concentrated acids and concentrated solutions of many salts impair the delicacy of the reaction. 4. Acetate of lead produces a heavy white precipitate of SULPHATE OF LEAD (Pb 0, S 8 ) which is sparingly soluble in dilute nitric acid, but dissolves completely in hot concentrated hydrochloric acid. 5. The salts of sulphuric acid with the alkaline earths which are inso- luble in water and acids are converted into CARBONATES, by fusion with alkaline carbonates. Bub the sulphate of lead is reduced to the state of PURE OXIDE when treated in this manner. Both the conversion of the former into carbonates and the reduction of the latter to the state of oxide are attended with the formation of an alkaline sulphate. The sulphates of the alkaline earths and sulphate of lead are also resolved into insoluble carbonates and soluble alkaline sulphate by digestion or boiling with concentrated solutions of carbonates of the alkalies (comp. 95, 96, 97). _ 6. Upon fusing siilphates with carbonate of soda on charcoal in the inner flame of the blowpipe the sulphuric acid is reduced, and sulphide of sodium formed, which may be readily recognised by the odor of hydro- 156 HYDROSULPHUKIC ACID. sulphuric acid emitted upon moistening the sample and the part of the charcoal into which the fused mass has penetrated, and adding some acid. If the fused mass is transferred to a clean silver plate, or a polished silver coin, and then moistened with water and some acid, a black stain of sulphide of silver is immediately formed. Remarks. The characteristic and exceedingly delicate reaction of sul- phuric acid with salts of baryta renders the detection of this acid an easier task than that of almost any other. It is simply necessary to take care not to confound with sulphate of baryta precipitates of chloride of barium, and particularly of nitrate of baryta, which are formed upon mixing aqueous solutions of these salts with fluids containing a large proportion of free hydrochloric acid or free nitric acid. It is very easy to distinguish these precipitates from sulphate of baryta, since they re- dissolve immediately upon diluting the acid fluid with water. It is a rule that should never be departed from, in testing for sul- phuric acid with chloride of barium, to dilute the fluid largely ; a little hydrochloric acid should also be added, which counteracts the adverse influence of many salts, as, for instance, citrates of the alkalies. Where very minute quantities of sulphuric acid are to be detected the fluid should be allowed to stand several hours at a gentle heat, the trace of sulphate of baryta formed will in that case be found deposited at the bottom of the vessel. When the least uncertainty exists about the nature of the precipitate produced by chloride of barium in presence of hydro- chloric acid, the reaction sub 6 will at once set all doubt at rest. To detect free sulphuric acid in presence of a sulphate the fluid under examination is mixed with a very little cane-sugar, and the mixture evaporated to dry ness in a porcelain dish at 212 Fah. If free sulphuric acid was present a black residue remains, or, in the case of most minute quantities, a blackish-green residue. Other free acids do not decompose cane-sugar in this way. 141. HYDROFLOOSILICIC ACID (H F, Si F g ). Hydrofluosilicic acid is a very acid fluid ; upon evaporation on platinum it volatilizes completely as fluoride of silicon and hydrofluoric acid. When evaporated on glass it etches the latter. With bases it forms water and silico-fluorides of the metals, which are most of them soluble in water, redden litmus-paper, and are resolved upon ignition into metallic fluorides and fluoride of silicon. Chloride of barium forms a crystalline precipitate with hydrofluosilicic acid ( 95, 6). Chloride of strontium and acetate of lead form no precipitates with this acid ; salts of potassa precipitate transparent GELATINOUS SILICO- FLUORIDE OF POTASSIUM ; am- monia in excess precipitates HYDRATED SILICIC ACID, with formation of fluoride of ammonium. By heating metallic silico-fluorides with concentrated sulphuric acid dense fumes are emitted in the air, arising from the evolution of hydrofluoric and silicofluoric gas. If the experiment is conducted in a platinum vessel covered with glass the fumes ETCH the glass ( 146, 5) ; the residue contains the sulphates formed. Third Division of the First Group oftlie Inorganic Acids. 142. a. PHOSPHORIC ACID (PO 5 ). 1. Phosphorus is a colorless, transparent, solid body, of 2-089 specific gravity ; it has a waxy appearance. Taken internally it acts as a virulent poison. It fuses at 113, and boils at 554 Fah. By the influence of light phosphorus kept under water turns first yellow, then red, and is PHOSPHORIC ACID. 157 finally covered with a white crust. If phosphorus is exposed to the air at the common temperature, it exhales a highly characteristic and most disagreeable odor, and is gradually entirely oxidized to phosphorous acid ; this process is attended with the formation of dense fumes of nitrite of ammonia, and in the dark with strong phosphorescence. Phos- phorus very readily takes fire spontaneously, and burns with a luminous flame, being converted into phosphoric acid, which is dissipated for the most part in white fumes through the surrounding air. Nitric acid and nitrohydrochloric acid dissolve phosphorus pretty readily upon heating. The solutions contain at first, besides phosphoric acid, also phosphorous acid. Hydrochloric acid does not dissolve phosphorus. If phosphorus is boiled with solution of soda or potassa, or with milk of lime, hypo- phosphites and phosphates are formed, whilst spontaneously inflammable phosphuretted hydrogen gas escapes. If a substance containing unoxi- dized phosphorus is placed at the bottom of a flask, and a slip of paper moistened with solution of nitrate of silver is by means of a cork loosely inserted into the mouth, suspended inside the flask, and a gentle heat applied (from 86 to 104 Fah.), the paper slip will turn black in consequence of the reducing action of the phosphorus fumes, even though only a most minute quantity of phosphorus should be present. If after the termination of the reaction the blackened part of the paper is boiled with water, the undecomposed portion of the silver salt precipitated with hydrochloric acid, the fluid filtered, and the filtrate evaporated as far as practicable on the water-bath, the presence of phosphoric acid in the residue may be shown by means of the reactions described in 2, &c. (J. SCHERER). It must be borne in mind that the silver salt is blackened also by hydrosulphuric acid, formic acid, volatile products of putrefac- tion, &c. j and also that the detection of phosphoric acid in the slip of paper can be of value only where the latter and the filtering paper were perfectly free from phosphorus. As regards the deportment of phos- phorus upon boiling with dilute sulphuric acid, and in a hydrogen gas evolution apparatus supplied with zinc and dilute sulphuric acid, see Part II. Section II., V., III. 2. Anhydrous PHOSPHORIC ACID is a white, snowlike mass, which rapidly deliquesces in the air, and dissolves in water with a hissing uoise. It forms with water and bases three different series of com- pounds : viz., with three equivalents of water or base hydrate of tribasic phosphoric acid or common phosphates ; with two equivalents of water or base hydrate of pyrophosphoric acid or pyrophosphates ; with one equivalent of water or base hydrate of metaphosphoric acid or metaphosphates. The phosphates which we generally meet with in nature and in ana- lytical investigations belong, as a rule, to the tribasic series ; we therefore make them alone the object of a fuller study in this place, devoting a supplemental paragraph to a briefer consideration of monobasic and bibasic phosphoric acids and their salts. 3. The HYDRATE of TRIBASIC PHOSPHORIC ACID (3HO, P0 g ) forms colorless and pellucid crystals, which deliquesce rapidly in the air to a syrupy non-caustic liquid. The action of heat changes it into hydrated pyro- or metaphosphoric acid, according as either one or two equivalents of water are expelled. Heated in an open platinum dish the hydrate of common phosphoric acid, if pure, volatilizes completely, though with difficulty, in white fumes. 158 PHOSPHOKTC ACID. 4. The action of heat fails to decompose the TRTBASIC PHOSPHATES with fixed bases, but converts them into pyrophosphates if they contain one equivalent of basic water or ammonia, and into metaphosphates if they contain two equivalents. Of the tribasic phosphates those with alkaline base alone are soluble in water, in the neutral state. The solutions manifest alkaline reaction. If pyro- or metaphosphates are fused with carbonate of soda the fused mass contains the phosphoric acid invariably in the tribasic state; 5. Chloride of barium produces in aqueous solutions of the neutral or basic phosphates of the alkalies, but not in solutions of the hydrate, a white precipitate of PHOSPHATE OF BARYTA [2 BaO, HO, P0 5 ; or 3 BaO, P0 6 ],* which is soluble in hydrochloric acid and in nitric acid, but sparingly soluble in chloride of ammonium. 6. /Solution of sulphate of lime produces in neutral or alkaline solutions of phosphates, but not in solutions of the hydrate, a white precipitate of PHOSPHATE OF LIME (2 CaO, HO, PO g or 3CaO, P0 5 ), which dissolves readily in acids, even in acetic acid, aud is soluble also in chloride of ammonium. 7. Sulphate of magnesia produces in concentrated neutral solutions of phosphates of the alkalies a white precipitate of PHOSPHATE OF MAGNESIA (2 MgO, HO, PO 6 4- 14 aq.), which often separates only after some time j upon boiling, a precipitate of basic salt (3 MgO, P0 6 + 5 aq.) is thrown down immediately. The latter precipitate forms also upon addition of sulphate of magnesia to the solution of a basic alkaline phosphate. But if sulphate of magnesia, mixed with a sufficient quantity of chloride of ammonium to leave the solution clear upon addition of ammonia, is added to a solution of free phosphoric acid or of an alkaline phosphate, and ammonia in excess is then added, a white, crystalline, and quickly subsiding precipitate of BASIC PHOSPHATE OF MAGNESIA AND AMMONIA (2 MgO, NH 4 0, PO 6 + 12aq.) is formed, even in highly dilute solutions. This precipitate is insoluble in ammonia and most sparingly soluble in chloride of ammonium, but dissolves readily in acids, even in acetic acid. It makes its appearance often only after the lapse of some time ; stirring promotes its separation ( 98, 7). The reaction can be considered decisive only if no arsenic is present ( 133, 9). 8. Nitrate of silver throws down from solutions of neutral and basic alkaline phosphates a light-yellow precipitate of PHOSPHATE OF SILVER (3 AgO, PO 5 ), which is readily soluble in nitric acid and in ammonia. If the solution contained a basic phosphate the fluid in which the preci- pitate is suspended manifests a neutral reaction ; whilst the reaction is acid if the solution contained a neutral phosphate. The acid reaction in the latter case arises from the circumstance that the nitric acid receives, for the 3 equivalents of oxide of silver which it yields to the phosphoric acid, only 2 eq. of alkali and 1 eq. of water ; and as the latter does not neutralize the acid properties of the nitric acid, the solu- tion becomes acid. 9. If to a solution containing phosphoric acid and the least possible excess of hydrochloric or nitric acid a tolerably large amount of acetate of soda is added, and then a drop of sesquichloride of iron, a yellowish- * Precipitates of the former composition are produced in solutions containing an alkaline phosphate with two equivalents of a fixed base or ammonia ; whilst precipi- tates of the latter composition are formed in solutions which contain an alkaline phos- phate with three equivalents of a fixed base or ammonia. PHOSPHORIC ACID. 159 white, flocculent-prelatinous precipitate of PHOSPHATE OP SESQUIOXIDE OP IRON (Fe 2 O 3 , PO 5 + 4 aq.) is formed. An excess of sesquichloride of iron must be avoided, as acetate of sesquioxide of iron (of red color) would thereby be formed, in which the precipitate is not insoluble. This re- action is of importance, as it enables us to detect the phosphoric acid in phosphates of the alkaline earths ; but it can be held to be decisive only if no arsenic is present, as this shows the same reaction. To effect the complete separation of the phosphoric acid from the alkaline earths, a sufficient quantity of sesquichloride of iron is added to impart a reddish color to the solution, which is then boiled (whereby the whole of the sesquioxide of iron is thrown down, partly as phosphate, partly as basic acetate), and filtered hot. The filtrate contains the alkaline earths as chlorides. If you wish to detect, by means of this reaction, phosphoric acid in presence of a large proportion of sesquioxide of iron, boil the hydrochloric acid solution with sulphite of soda until the sesquichloride is reduced to protochloride, which reduction is indicated by the decolor- ation of the solution ; add carbonate of soda until the fluid is nearly neutral, then acetate of soda, and finally one drop of sesquichloride of iron. The reason for this proceeding is, that acetate of protoxide of iron does not dissolve phosphate of sesquioxide of iron. 10. If a few cubic centimetres of the solution of molybdate of ammonia in nitric acid ( 5'2) are poured into a test-tube, and a little of a fluid is added containing phosphoric acid in neutral or acid solution, a light- yellow finely-pulverulent precipitate forms at once or after a very short time, even in the cold, if the quantity of phosphoric acid is not too incon- siderable ; this precipitate speedily subsides to the bottom of the tube, or is deposited on the sides. With exceedingly minute quantities of phosphorus, as e.g. 0-00002 grin. = about O'OOOS grain, a few hours must be allowed for the manifestation of the reaction, which should be aided also by applying a gentle heat, but not higher than 104 F. If no other coloring substances are present, the fluid above the precipitate appears colorless. The fluid to be tested for phosphoric acid should not be added in larger proportion than an equal volume to that of the molyb- date of ammonia solution ; a mere yellow coloration of the fluid should never be considered to prove the presence of phosphoric acid. The yellow precipitate contains MOLYBDIO ACID, AMMONIA, WATER, and a little PHOSPHORIC ACID (about 3 per cent.). As it is insoluble in dilute acids only in presence of an excess of molybdic acid, addition of phos- phoric auid in excess will necessarily altogether prevent its formation, which should be borne in mind. Presence of certain organic substances, e.g. tartaric acid, will also prevent the precipitation. The precipitate, after subsiding, may be readily recognised even in dark-colored fluids. By washing it with the solution of molybdate of ammonia with which the precipitation has been effected, dissolving in ammonia, and adding a mixture of sulphate of magnesia, chloride of ammonium, and ammonia, phosphate of magnesia and ammonia is produced. By conducting the operation in the manner above stated, phosphoric acid cannot well be confounded with any other acid ; since arsenic acid gives in the cold no precipitate with solution of molybdate of ammonia in nitric acid, though it gives one upon application of heat, and more especially upon boiling (the fluid above this precipitate appears yellow) ; and silicic acid shows no reaction with it in the cold, and gives only a yellow coloration on heating, but no precipitate. 160 BORACIC ACID. 11. If a finely-powdered substance containing phosphoric acid (or a metallic phosphide) is intimately mixed with 5 parts of a flux consisting of 3 parts of carbonate of soda, 1 part of nitrate of potassa, and 1 part of silicic acid, the mixture fused in a platinum spoon or crucible, the fused mass boiled with water, the solution obtained decanted, carbonate of ammonia added to it, the fluid boiled again, and the silicic acid which is thereby precipitated filtered oif, the filtrate now holds in solution alkaline phosphate, and may accordingly be tested for phosphoric acid as directed in 7, 8, 9, or 10. 12. White of egg is not precipitated by solution of hydrate of tribasic phosphoric acid, nor by solutions of tribasic phosphates mixed with acetic acid. 143. &. Bibasic phosphoric acid. The solution of the hydrate 2 HO, P0 8 is converted by boiling into solution of the hydrate 3 HO, P0 6 The solutions of the salts bear heating without suffering decomposition ; but upon boiling with a strong acid the phosphoric acid is converted into the tribasic state. If the salts are fused with car- bonate of soda in excess tribasic phosphates are produced. Of the neutral pyrophos- phates only those with alkaline bases are soluble in water ; the acid salts (e.g., NaO, HO, P0 5 ) are by ignition converted into metaphosphates (NaO, P0 5 ). Chloride of larium fails to precipitate the free acid ; from solutions of the salts it precipitates PYROPHOSPHATE OF BARYTA (2 BaO, P 6 ). Nitrate of silver throws down from a solution of the hydrate, especially upon addition of an alkali, a white, earthy -looking precipitate of PYROPHOSPHATE OF SILVER (2 AgO, P O s ), which is soluble in nitric acid and in ammonia. Sulphate of magnesia precipitates PYROPHOSPHATE OF MAGNESIA (2 Mg 0, P O s ). The precipitate dissolves in an excess of the pyrophosphate, as well as in an excess of the sulphate of magnesia. Ammonia fails to pi'ecipitate it from these solutions. Upon boiling the solution it separates again. White of egg is not pre- cipitated by solution of the hydrate nor by solutions of the salts mixed with acetic acid. Molybdate of ammonia, with addition of hydrochloric acid, fails to produce a precipitate. p. Monobasic phosphoric acid. Five sorts of monobasic phosphates are known, and the hydrates also of most of these have been produced. The several reactions by which to distinguish between these I will not enter upon here, and confine myself to the simple observation that the monobasic phosphoric acids differ from the bibasic and tribasic phosphoric acids in this, that the solutions of the hydrates of the monobasic acids precipitate white of egg at once, and the solutions of their salts after addition of acetic acid. Those hydrates and salts which are precipitated by nitrate of silver pro- duce with that reagent a white precipitate. A mixture of sulphate of magnesia, chloride of ammonium, and ammonia fails to precipitate the monobasic phosphoric acids and their salts, or produces precipitates soluble in chloride of ammonium. All monobasic phosphates yield upon fusion with carbonate of soda tribasic phosphate of soda. U4. 6. BORACIC ACID (B0 3 ). 1. Boracic acid, in the anhydrous state, is a colorless, fixed glass, fusible at a red heat ; hydrate of boracic acid (3 H O, B O g ) is a porous, white mass ; in the crystalline state (HO, BO 3 + 2 aq.), it presents small scaly lamina. It is soluble in water and in spirit of wine ; upon eva- porating the solutions a large proportion of boracic acid volatilizes along with the aqueous and alcoholic vapors. The solutions redden litmus- paper, and impart to turmeric-paper a faint brown-red tint, which acquires intensity upon drying. The borates are not decomposed upon ignition ; those with alkaline bases alone are readily soluble in water. The solutions of borates of the alkalies are colorless, and all of them, even those of the acid salts, manifest alkaline reaction. 2. Chloride of barium produces in solutions of borates, if not too BORACIC ACID. 161 highly dilute, a white precipitate of BORATE OF BARYTA, which is soluble in acids and ammoniacal salts. The formula of this precipitate, when thrown down from solutions of neutral borates, is BaO, BO 3 + aq. ; when thrown down from solutions of acid borates, 3 BaO, 5 B0 3 + 6 aq. (H. ROSE). 3. Nitrate of silver produces in concentrated solutions of neutral borates of the alkalies a white precipitate, inclining slightly to yellow from admixture of free oxide of silver (AgO, BO 3 + HO) ; in concen- trated solutions of acid borates a white precipitate of 3 AgO, 4 BO 3 . Dilute solutions of borates give with nitrate of silver a grayish-brown precipitate of oxide of silver (H. ROSE). All these precipitates dissolve in nitric acid and in ammonia. 4. If dilute sulphuric add or hydrochloric add is added to highly concentrated, hot prepared solutions of alkaline borates, the BORACIC ACID separates upon cooling, in the form of shining crystalline scales. 5. If alcohol is poured over free boracic acid or a borate with addi- tion, in the latter case, of a sufficient quantity of concentrated sulphuric acid to liberate the boracic acid and the alcohol is kindled, the flame appears of a very distinct YELLOWISH-GREEN color, especially upon stirring the mixture ; this tint is imparted to the flame by the ignited boracic acid which volatilizes with the alcohol. The delicacy of this reaction may be considerably heightened by heating the dish which contains the alcoholic mixture, kindling the alcohol, allowing it to burn for a short time, then extinguishing the flame, and afterwards rekindling it. At the first flickering of the flame its borders will now appear green, even though the quantity of the boracic acid be so minute that it fails to produce a perceptible coloring of the flame when treated in the usual manner. As salts of copper also impart a green tint to the flame of alcohol, the copper which might be present must first be removed by means of hydrosulphuric acid. Presence of metallic chlorides also may lead to mistakes, as the chloride of ethyle formed in that case colors the borders of the flame greenish. 6. If a solution of boracic acid, or of a borate with an alkali or an alkaline earth for base, is mixed with hydrochloric acid to slight, but distinct, acid reaction, and a slip of turmeric paper is half dipped into it, and then dried on a watch-glass at 212 Fah., the dipped half shows a peculiar RED tint (H. ROSE). This reaction is very delicate ; care must be taken not to confound the characteristic red coloration with the blackish-brown color which turmeric-paper acquires when moistened with rather concentrated hydro- chloric acid, and then dried ; nor with the brownish-red coloration which sesquichloride of iron, or a hydrochloric acid solution of molybdate of ammonia, gives to turmeric paper, more particularly upon drying. By moistening turmeric-paper reddened by boracic acid with a solution of an alkali or an alkaline carbonate, the color is changed to bluish-black or greenish-black ; but a little hydrochloric acid will at once restore the brownish-red color (A. YOGEL, H. LUDWIG). 7. If a substance containing boracic acid is reduced to a fine powder, this, with addition of a drop of water, mixed with 3 parts of a flux com- posed of 4 J parts of bisulphate of potassa and 1 part of finely pulverized fluoride of calcium, free from boracic acid, and the paste exposed on the loop of a platinum wire in the outer mantle of Bunsens gas flame, or at the apex of the inner flame of the blowpipe, fluoride of boron escapes, I. M 162 OXALIC ACID. which imparts to the flame though only for a few instants a green tint. With readily decomposed compounds the reaction may be ob- tained by simply moistening the sample with hydrofluosilicic acid, and holding it in the flame. 8. Boracic acid or borates, fused together with carbonate of soda, give, when placed in the flame of the spectrum apparatus, a spectrum of four strong green and blue lines of equal width, and placed at equal dis- tances. BOa is yellowish-green, and coincides with Ba y; BO/3 is light green, and coincides withBa/3; B y is faint bluish -green, and almost coincides with the blue barium line. B O S is very faint blue, and does not quite reach Sr 3. Presence of alkali and alkaline earths does not prevent the reaction. 145. c. OXALIC ACID (C 4 6 ^O). 1. The HYDRATE OF OXALIC ACID (2 HO, C 4 g ) is a white powder; the crystallized acid (2 HO, C 4 O 6 + 2 aq.) forms colorless rhombic prisms. Both dissolve readily in water and in spirit of wine. By heating rapidly in open vessels part of the hydrated acid undergoes decomposition, whilst another portion volatilizes unaltered. The fumes of the vola- tilizing acid are very irritating and provoke coughing. If the hydrate is heated in a test-tube the greater part of it sublimes unaltered. 2. The whole of the OXALATES undergo decomposition at a red heat, the oxalic acid being converted into carbonic acid and carbonic oxide. Those with an alkali or an alkaline earth for base are in this process converted into carbonates (if pure, almost without separation of char- coal). Oxalate of magnesia is converted into pure magnesia even by a very gentle red heat. The oxalates with metallic bases leave either the pure metal or the oxide behind, according to the greater or less degree of reducibility of the metallic oxide. The alkaline oxalates, and also some of the oxalates with metallic bases, are soluble in water. 3. CJdoride of barium produces in neutral solutions of oxalates a white precipitate of OXALATE OF BARYTA (2 BaO, C 4 O 6 + 2 aq.), which dissolves very sparingly in water, more readily in water containing chloride of ammonium, acetic acid, or oxalic acid, freely in nitric acid and in hydro- chloric acid; ammonia reprecipitates it from the latter solutions un- altered. 4. Nitrate of Silver produces in neutral solutions of oxalic acid and of alkaline oxalates a white precipitate of OXALATE OF SILVER (2 AgO, C 4 6 ), which is readily soluble in concentrated hot nitric acid and also in ammonia, but dissolves with difficulty in dilute nitric acid, and is most sparingly soluble in water. 5. Lime-water and all the soluble salts of lime, and consequently also solution of sulphate of lime, produce in even highly dilute solutions of free oxalic acid or of oxalates of the alkalies, white finely pulverulent precipitates of OXALATE OF LIME (2 CaO, C 4 O 6 + 2 aq., and occasionally 2 CaO, C 4 O 6 + 6aq.), which dissolve readily in hydrochloric acid and in nitric acid, but are nearly insoluble in oxalic acid and in acetic acid, and almost absolutely insoluble in water. The presence of salts of ammonia does not interfere with the formation of these precipitates. Addition of ammonia considerably promotes the precipitation of the free oxalic acid by salts of lime. In highly dilute solutions the precipitate is only formed after some time. HYDROFLUORIC ACID. 163 6. If hydrated oxalic acid (or an oxalate), in the dry state, is heated with an excess of concentrated sulphuric acid, the latter withdraws from the oxalic acid its constitutional water, and thus causes its decomposition into CARBONIC ACID and CARBONIC OXIDE (0 4 O 6 = 2 CO + 2 CO 2 ), the two gases escaping with effervescence. If the quantity operated upon is not too minute the escaping carbonic oxide gas may be kindled ; it burns with a blue flame. Should the sulphuric acid acquire a dark color in this reaction, this is a proof that the oxalic acid contained some organic substance in admixture. 7. If oxalic acid or an oxalate is mixed with some finely pulverized binoxide of manganese (which must be free from carbonates), a little water added and a few drops of sulphuric acid, a lively effervescence ensues, caused by the escaping CARBONIC ACID [2 Mn O 2 + C 4 O 6 + 2 S 3 = 2 (MnO,SO s ) + 4COJ. 8. If oxalates of alkaline earths are boiled with a concentrated solu- tion of carbonate of soda, and the fluid filtered, the oxalic acid is obtained in the filtrate in combination with soda, whilst the precipi- tate contains the base as carbonate. With oxalates containing for their base oxides of heavy metals, this operation is not always sure to attain the desired object, as many of these oxalates, e.g. oxalate of prot- oxide of nickel, will partially dissolve in the alkaline fluid, with forma- tion of a double salt. Metals of this kind should therefore be separated as sulphides. 146. d. HYDROFLUORIC ACID (HF). 1. Anhydrous HYDROFLUORIC ACID is a colorless corrosive gas, which fumes in the air, and is freely absorbed by water. Liquid hydrofluoric acid is distinguished from all other acids by the exclusive property it possesses of dissolving crystallized silicic acid, and also the silicates which are insoluble in hydrochloric acid. Fluoride of silicon and water are formed in the process of solution (SiO ? + 2 HF = SiF 2 + 2 HO). Hy- drofluoric acid decomposes with metallic oxides in the same manner, metallic fluorides and water being formed. 2. The FLUORIDES of the alkali metals are soluble in water ; the solu- tions have an alkaline reaction. The fluorides of the metals of the alkaline earths are either altogether insoluble in water, or they dissolve in that menstruum only with very great difficulty. Fluoride of alu- minium is readily soluble. Most of the fluorides corresponding to the oxides of the heavy metals are very sparingly soluble in water, as, for instance, the fluorides of copper, lead, and zinc ; many other of the fluorides of the heavy metals dissolve in water without difficulty, as, for instance, the sesquifluoride of iron, protofluoride of tin, fluoride of mercury, &c. Many of the fluorides insoluble or difficultly soluble in water dissolve in free hydrofluoric acid ; others do not. Most of the fluorides bear ignition in a crucible without suffering decomposition. 3. Chloride of barium precipitates aqueous solutions of free hydro- fluoric acid, but much more completely solutions of fluoride of the alkalies. The bulky white precipitate of FLUORIDE OF BARIUM (BaF) is almost absolutely insoluble in water, but dissolves in large quantities of hydrochloric acid or nitric acid, from which solutions ammonia fails to precipitate it, or throws it down only very incompletely, owing to the dissolving action of the neutral ammonia salts. M2 164 HYDROFLUORIC ACID. 4. Chloride of calcium produces in aqueous solutions of hydrofluoric acid or of fluorides a gelatinous precipitate of FLUORIDE OP CALCIUM (Ca F), which is so transparent as at first to induce the belief that the fluid has remained perfectly clear. Addition of ammonia promotes the complete separation of the precipitate. The precipitated fluoride of calcium is almost absolutely insoluble in water, and only very slightly soluble in hydrochloric acid and nitric acid in the cold ; it dissolves somewhat more largely upon boiling with hydrochloric acid. Ammonia produces no precipitate in the solution, or only a very trifling one, as the salt of ammonia formed retains it in solution. Fluoride of calcium is scarcely more soluble in free hydrofluoric acid than in water. It is insoluble in alkaline fluids. 5. If a finely pulverized fluoride, no matter whether soluble or in- soluble, is treated in a platinum crucible with just enough concentrated sulphuric acid to make it into a thin paste, the crucible covered with the convex face of a watch-glass of hard glass coated with bees-wax, which has been removed again in some places by tracing lines in it with a pointed piece of wood, the hollow of the glass filled with water, and the crucible gently heated for the space of half an hour or an hour, the exposed lines will, upon the removal of the wax, be found more or less deeply ETCHED into the glass.* If the quantity of hydrofluoric acid disengaged by the sulphuric acid was very minute, the etching is often invisible upon the removal of the wax ; it will, however, in such cases reappear when the plate is breathed upon. This reappearance of the etched lines is owing to the unequal capacity of condensing water which the etched and the untouched parts of the plate respectively possess. The impressions which thus appear upon breathing on the glass may, however, owe their origin to other causes ; therefore, though their non- appearance may be held as a proof of the absence of fluorine, their ap- pearance is not a positive proof of the presence of that element. At all events, they ought only to be considered of value where they can be developed again after the glass has been properly washed with water, dried, and wiped. t This reaction (o) fails if there is too much silicic acid present, or if the body under examination is not decomposed by sulphuric acid. In such cases the one or the other of the two following methods is resorted to, according to circumstances. 6. If we have to deal with a fluoride decomposable l>y sulphuric acid, but mixed with a large proportion of silicic acid, the fluorine in it may be detected by heating the mixture in a test-tube with concentrated sulphuric acid, as FLUOSILICIC GAS is evolved in this process, which forms dense white fumes in moist air. Tf the gas is conducted into water through a bent tube moistened inside, the latter has its transparency more or less impaired, owing to the separation of silicic acid. If the * The coating with wax may be readily effected by heating the glass cautiously, putting a small piece of wax upon the convex face, and spreading the fused mass equally over it. The removal of the w;ix coating is effected by heating the glass gently, and wiping the wax off with a cloth. f J. NICKLES states that etchings on glass may be obtained with all kinds of sulphuric acid, and, in fact, with all acids suited to effect evolution of hydrofluoric acid. I have tried watch-glasses of Bohemian glass with sulphuric and other acids, but could get no etchings in confirmation of this statement. Still, proper caution demands that before using the sulphuric acid, it should first be positively ascertained that its fumes will not etch HYDROFLUORIC ACID. 165 quantity operated upon is rather considerable, hydrate of silicic acid sepa- rates in the water, and the fluid is rendered acid by hydrofluosilicic acid. The following process answers best for the detection of smaller quan- tities of fluorine. Heat the substance with concentrated sulphuric acid in a flask closed with a cork with double perforation, bearing two tubes, of which one reaches down to the bottom of the flask, whilst the other terminates immediately under the cork. Conduct through the longer tube a slow stream of dry air into the flask, and conduct this, upon its re-issuing through the other tube, into a U-shaped tube containing a little ammonia, and connected at the other end with an aspirator. The silicon* uoric gas, which escapes along with the air, decomposes with the ammonia, mere particularly upon the application of a gentle heat towards the end of the process, fluoride of ammonium and hydrated silicic acid being formed. Filter, evaporate in a platinum crucible to dryness, and examine the residue by the method described in 5. For more difficultly decomposable substances bisulphate ot potassa is used instead of sulphuric acid, and the mixture, to which some marble is added (to ensure a con- tinuous slight evolution of gas), heated to fusion, and kept in that state for some time. 7. Compounds not decomposable by sulphuric acid must first be fused with four parts of carbonate of soda and potassa. The fused mass is treated with water, the solution filtered, the filtrate concentrated by evapo- ration, allowed to cool, transferred to a platinum or silver vessel, hydro- chloric acid added to feebly acid reaction, and the fluid allowed to stand until the carbonic acid has escaped. It is then supersaturated with am- monia, heated, filtered into a bottle, chloride of calcium added to the still hot fluid, the bottle closed, and allowed to stand at rest. If a precipitate separates after some time it is collected on a filter, dried, and examined by the method described in 5 (H. HOSE). 8. Minute quantities' of metallic fluorides in minerals, slags, &c., may also be readily detected by means of the blowpipe. To this end bend a piece of platinum foil in gutter-shape, insert it in a glass tube as shown in Fig. 33, introduce the finely tritu- rated substance mixed with powdered phosphate of soda and ammonia fused on charcoal, and let the blowpipe flame Fig. 33. play upon it in a manner to make the products of combustion pass into the tube. If fluorides of metals are present hydrofluoric acid gas is evolved, which betrays its presence by its pungent odor, the dimming of the glass tube (which becomes percep- tible only after cleaning and drying), and the yellow tint which the acid air issuing from the tube imparts to a moist slip of Brazil-wood paper* (BERZELIUS, SMITHSON). When silicates containing metallic fluorides are treated in this manner gaseous fluoride of silicon is formed, which also colors yellow a moist slip of Brazil-wood paper inserted in the tube, and leads to silicic acid being deposited within the tube. After washing and drying the tube, it appears here and there dimmed. In the case of minerals containing water the presence of even a small proportion of metallic fluorides will usually suffice upon heating, even without addi- tion of phosphate of soda and ammonia, to color yellow a moistened slip of Brazil-wood paper inserted in the tube (BERZELIUS). * Prepared by moistening slips of fine printing-paper with decoction of Brazil- wood. 166 RECAPITULATION AND REMARKS. 147. Recapitulation and remarks. The baryta compounds of the acids of the third division are dissolved by hydrochloric acid, apparently without undergoing decomposition ; alkalies therefore reprecipitate them unaltered, by neutralizing the hydrochloric acid. The baryta compounds of the acids of the first division of the first group show, however, the same deport- ment ; these acids must, therefore, if present, be removed before any con- clusion regarding the presence of phosphoric acid, boracicacid, oxalic acid, or hydrofluoric acid, can be drawn from the reprecipitation of a salt of baryta by alkalies. But even leaving this point altogether out of the question no great value is to be placed on this reaction, not even so far as the simple detection of these acids is concerned, and far less still as regards their separation from other acids, since ammonia fails to repreci- pitate from hydrochloric acid solutions the salts of baryta in question, and more particularly the borate of baryta and the fluoride of barium, if the solution contains any considerable proportion of free acid or of an arn- moniacal salt. Boracic acid is well characterized by the coloration which it imparts to the flame of alcohol, and also by its action on turmeric- paper. The latter reaction is more particularly suited for the detection of very minute traces of boracic acid. Oxides of the heavy metals, if present, are most conveniently removed first by hydrosulphuric acid or sulphide of ammonium. Before proceeding to concentrate dilute solu- tions of boracic acid the acid must be combined with an alkali, otherwise a large portion of it will volatilize along with the aqueous vapors. The detection of phospJioric acid in compounds soluble in water is not difficult ; the reaction with sulphate of magnesia is the best adapted for the purpose. The detection of phosphoric acid in insoluble com- pounds cannot be effected by means of magnesia solution. Sesquichloride of iron ( 142, 9) is well suited for the detection of phosphoric acid in its salts with the alkaline earths, and more particularly for the separation of the acid from the alkaline earths ; the nitric acid solution of molyb- date of ammonia is more especially adapted to effect the detection of phosphoric acid in presence of alumina and sesquioxide of iron. I must repeat again that both these reactions demand the strictest attention to the directions given in 142, 9 and 10. If present in combination with metallic oxides of the fourth, fifth, or sixth group, it may be isolated, either by the method given in 142, 11, or simply by removing the bases by precipitating them with hydrosulphuric acid or sulphide of ammonium. Oxalic acid may always be easily detected in aqueous solutions of oxalates of the alkalies, by solution of sulphate of lime. The formation of a finely pulverulent precipitate, insoluble in acetic acid, leaves hardly a doubt on the point, as racemic acid alone, which occurs so very rarely, gives the same reaction. In case of doubt the oxalate of lime may be readily distinguished from the paratartrate, or racemate, by simple ignition, with exclusion of air, as the decomposed paratartrate leaves a considerable proportion of charcoal behind ; the paratartrate dissolves moreover in cold solution of potassa or soda, in which oxalate of lime is insoluble. The deportment of the oxalates with sulphuric acid, or with binoxide of manganese and sulphuric acid, affords also sufficient means to confirm the results of other tests. In insoluble salts the oxalic acid is detected most safely by decomposing the insoluble PHOSPHOROUS ACID. 167 compound by boiling with solution of carbonate of soda, or in oxalates with oxides of the heavy metals, by hydrosulphuric acid or sulphide of ammonium ( 145, 8). I must finally also call attention here to the fact that there are certain soluble oxalates which are not precipitated by salts of lime ; these are more particularly oxalate of sesquioxide of chromium, and oxalate of sesquioxide of iron. Their non-precipitation is owing to the circumstance that these salts form soluble double salts with oxalate of lime. In salts decomposable by sulphuric acid, the hydrofluoric acid is readily detected ; only it must be borne in mind that an over large proportion of sulphuric acid impedes the free evolu- tion of hydrofluoric gas, and thus impairs the delicacy of the reaction ; also that the glass cannot be distinctly etched if, instead of hydrofluoric gas, fluosilicic gas alone is evolved ; and therefore, in the case of com- pounds abounding in silica, the safer way is to try, besides the reaction given 146, 5, also the one given in 146, 6. x ln silicates which are not decomposed by sulphuric acid the presence of fluorine is often over- looked, because the analyst omits to examine the compound carefully by the method given 146, 7. 148. PHOSPHOROUS Acm (P0 3 ). Anhydrous phosphorous acid is a white powder, which admits of sublimation, and burns when heated in the air. It forms with a small proportion of water a thickish fluid, which crystallizes by long standing. Heat decomposes it into hydrated phos- phoric acid and phosphuretted hydrogen gas, which does not spontaneously take fire. It freely dissolves in water. Of the salts those with alkaline base are readily soluble in water. All the others sparingly soluble ; the latter dissolve in dilute acids. All the salts are decomposed by ignition into phosphates, which are left behind, and hydrogen gas, or a mixture of hydrogen and phosphuretted hydrogen, which escapes. With nitrate of silver separation of metallic silver takes place, more especially upon addition of ammonia and application of heat ; with nitrate of suboxide of mercury, under the same circumstances, separation of metallic mercury. From chloride of mercury in excess phosphorous acid throws down subchloride of mercury after some time, more apidly upon heating. Chloride of barium and chloride of calcium produce in not over-dilute solutions of phosphorous acid, upon addition of ammonia, white precipitates, which are soluble in acetic acid. A mixture of sulphate of magnesia, chloride of am- monium, and ammonia will precipitate only somewhat more concentrated solutions. Acetate of lead throws down white phosphite of lead, insoluble in acetic acid. By heating to boiling with sulphurous acid in excess phosphoric acid is formed, attended by separation of sulphur. In contact with zinc and dilute sulphuric acid phosphorous acid gives a mixture of hydrogen gas with phosphuretted hydrogen, which accordingly fumes in the air, burns with an emerald-green color, and precipitates phosphide of silver from solution of nitrate of silver. Fourth Division oftlie First Group of the Inorganic Acids. 149. a. CARBONIC ACID (C0 2 ). 1. CARBON is a solid tasteless and inodorous body. The very highest de- grees of heat alone can effect its fusion and volatilization (DESPRETZ). All carbon is combustible, and yields carbonic acid when burnt with a sufficient supply of oxygen or atmospheric air. In the diamond the carbon is crystallized, transparent, pellucid, exceedingly hard, difficultly combus- tible j in the form of graphite it is opaque, blackish-gray, soft, greasy to the touch, difficultly combustible, and stains the fingers; as charcoal 168 CARBONIC ACID. produced by the decomposition (destructive distillation) of organic matters it is black, opaque, noncrystalline occasionally dense, shining, and difficultly combustible, and occasionally porous, dull, and readily combustible. 2. CARBONIC ACID, at the common temperature and common atmo- spheric pressure, is a colorless gas of far higher specific gravity than atmospheric air, so that it may be poured from one vessel into another. It is almost inodorous, has a sourish taste, and reddens moist litmus-paper ; but the red tint disappears again upon drying. Carbonic acid is readily absorbed by solution of potassa ; it dissolves pretty copiously in water. 3. The AQUEOUS SOLUTION OF CARBONIC ACID has a feebly acid and pungent taste j it transiently imparts a red tint to litmus-paper, and colors solution of litmus wine-red ; it loses its carbonic acid when shaken with air in a half-filled bottle, and more completely still upon appli- cation of heat. Some of the CARBONATES lose their carbonic acid by ignition ; those with colorless oxides are white or colorless. Of the neutral carbonates only those with alkaline bases are soluble in water. The solutions manifest a very strong alkaline reaction. Besides the car- bonates with alkaline bases, those also with an alkaline earth for base, and some of those with a metallic base, dissolve as acid or bicarbonates. 4. The carbonates are decomposed by all free, acids soluble in water, with the exception of hydrocyanic acid and hydrosulphuric acid. The decomposition of the carbonates by acids is attended with EFFERVESCENCE, the carbonic acid being disengaged as a colorless and almost inodorous gas, which transiently imparts a reddish tint to litmus-paper. It is necessary to apply the decomposing acid in excess, especially when operating upon carbonates with alkaline bases, since the formation of bicarbonates will frequently prevent effervescence if too little of the decomposing acid be added. Substances which it is intended to test for carbonic acid by this method should first be heated with a little water, to prevent any mistake which might arise from the escape of air-bubbles upon treating the dry substances with the acid. Where there is reason to apprehend the escape of carbonic acid upon boiling with water, lime water should be used instead of pure water. If it is wished to determine by a direct experiment whether the disengaged gas is really carbonic acid or not, this may be readily accomplished by dipping the end of a glass rod in baryta water, and inserting the rod into the test-tube, bringing the moistened end near the surface of the fluid in the tube, when ensuing turbidity of the baryta water on the glass rod will prove that the evolved gas is really carbonic acid, since 5. Lime-water and baryta-water, brought into contact with carbonic acid or with soluble carbonates, produce white precipitates of neutral CARBONATE OF LIME (CaO, C 2 ), or neutral CARBONATE OF BARYTA (BaO, C O 2 ). In testing for free carbonic acid the reagents ought always to be added in excess, as the acid carbonates of the alkaline earths are soluble in water. The precipitated carbonates of lime and baryta dissolve in acids, with effervescence, and are not reprecipitated from such solutions by ammonia, after the complete expulsion of the carbonic acid by ebul- lition. As lime-water dissolves very minute quantities of carbonate of lime, the detection of exceedingly minute traces of carbonic acid requires the use of a lime-water saturated with carbonate of lime by long digestion with the latter salt (WELTER, BERTHOLLET). 6. Qldoride of calcium and chloride of barium immediately produce in SILICIC ACID. 169 solutions of neutral alkaline carbonates, precipitates of CARBONATE OP LIME or of CARBONATE OF BARYTA ; in dilute solutions of bicarbonates these precipitates are formed only upon ebullition ; with free carbonic acid these reagents give no precipitate. 150. b. SILICIC ACID (Si O a ). 1. SILICIC ACir is colorless or white, even in the hottest blowpipe flame unalterable and infusible. It fuses in the flame of the oxy hydrogen blowpipe. It is met with in two modifications (more correctly speaking, in the crystalline and in the amorphous state). It is insoluble in water and acids, with the exception of hydrofluoric acid j whilst its hydrate is soluble in acids, but only at the moment of its separation. The amor- phous silicic acid and the hydrate dissolve in hot aqueous solutions of caustic alkalies and of fixed alkaline carbonates ; but the crystallized acid is insoluble or nearly so in these fluids. If either of the two is fused with pure alkalies or alkaline carbonates a basic silicate of the alkali is obtained, which is soluble in water, and from which acids again separate hydrated silicic acid. The SILICATES with alkaline bases alone are soluble in water. 2. The solutions of the alkaline silicates are decomposed by all acids. If a large proportion of hydrochloric acid is added at once to even con- centrated solutions of alkaline silicates the separated silicic acid remains in solution ; but if the hydrochloric acid is added gradually drop by drop, whilst stirring the fluid, the greater part of the silicic acid sepa- rates as gelatinous hydrate. The more dilute the fluid, the more silicic acid remains in solution, and in highly dilute solutions no precipitate is formed. But if the solution of an alkaline silicate, mixed with hydro- chloric or nitric acid in excess, is evaporated to dryness silicic acid separates in proportion as the acid escapes ; upon treating the residue with hydrochloric acid and water the silicic acid remains in the free state (or, if the temperature in the process of drying was restricted to 212, as hydrate, HO, 4 SiO 2 ), as an insoluble white powder. Chloride of ammonium produces in not over-dilute solutions of alkaline silicates precipitates of hydrate of silicic acid (containing alkali). Heating pro- motes the separation. 3. Some of the silicates insoluble in water are decomposed by hydro- chloric acid or nitric acid, others are not affected by these acids, not even upon boiling. In the decomposition of the former the greater portion of the silicic acid separates usually as gelatinous, more rarely as pulverulent hydrate. To effect the complete separation of the silicic acid, the hydro- chloric acid solution, with the precipitated hydrate of silicic acid suspended in it, is evaporated to dryness, the residue heated with stirring, at a uniform temperature above the boiling point of water until no more acid funies escape, then moistened with hydrochloric acid, heated with water, and the fluid containing the bases filtered from the residuary in- soluble silicic acid. 4. Of the silicates not decomposed by hydrochloric acid many, e.g., kaolin, are completely decomposed by heating with a mixture of 8 parts of hydrated sulphuric acid and 3 parts of water, the decomposition being attended with separation of silicic acid in the pulverulent form ; many others are acted upon to some extent by this reagent. 170 RECAPITULATION AND REMARKS. 5. If a silicate, reduced to a fine powder, is fused with 4 parts of car- bonate ofpotassa and soda until the evolution of carbonic acid has ceased, and the fused mass is then boiled with water, the greater part of the silicic acid dissolves as alkaline silicate, whilst the alkaline earths, the earths proper (with the exception of alumina and baryta, which pass more or less completely into the solution), and the heavy metallic oxides are left undissolved. If the fused mass is treated with water, then, without previous filtration, hydrochloric or nitric acid added to strongly acid reaction, and the fluid treated as directed in 3, the silicic acid is left undissolved, whilst the bases are dissolved. If the powdered silicate is fused with 4 parts of hydrate of baryta, the fused mass digested with water, with addition of hydrochloric or nitric acid, and the acid solution treated as directed in 3, the silicic acid separates, and the bases, especially also the alkalies, are found in the filtrate. 6. If hydrofluoric acid, in concentrated aqueous solution or in the gaseous state, is made to act upon silicic acid, fluosilic gas escapes (SiO + 2 HF = Si F 2 + 2 HO) ; dilute acid dissolves silica to hydrofluo- silicic acid (Si O 2 + 3 H F = Si F 2 , H F + 2 H 0). Hydrofluoric acid acting upon silicates gives rise to the formation of silicofluorides (CaO, Si0 2 4- 3HF=SiF 2 , CaF + 3HO), which by heating with hydrated sulphuric acid are changed to sulphates, with evolution of hydrofluoric and flue- silicic gas. If the powdered silicate is mixed with 5 parts of fluoride of calcium in powder, the mixture made into a paste with hydrated sul- phuric acid, and heat applied (best in the open air) until no more fumes escape, the whole of the silicic acid present volatilizes as fluosilicic gas. The bases present are found in the residue as sulphates, mixed with sulphate of lime. 7. If silicic acid or a silicate is fused with carbonate of soda on the loop of a platinum wire FROTHING is observed in the fusing bead, owing to the disengagement of carbonic acid. If the proper proportion of car- bonate of soda is not exceeded the bead of silicate of soda formed in the process will remain transparent on cooling. 8. PhospJiate of soda and ammonia, in a state of fusion, fails nearly altogether to dissolve silicic acid. If therefore silicic acid or a silicate is fused, in small fragments, with phosphate of soda and ammonia on a platinum wire the bases are dissolved, whilst the silicic acid separates and floats about in the clear bead as a more or less transparent mass, exhibiting the shape of the fragment used in the experiment. 151. Recapitulation and remarks. Free carbonic acid is readily known by its reaction with lime-water ; the carbonates are easily detected by the evolution of a nearly inodorous gas, which takes place when they are treated with acids. When operating upon compounds which evolve other gases besides carbonic acid, the disengaged gas is to be tested with lime-water or baryta-water. Silicic acid, both in the free state and in silicates, may usually be readily detected by the reaction with phosphate of soda and ammonia. It differs moreover from all other bodies in the form in which it is always obtained in analyses, by its insolubility in acids (except hydrofluoric acid), and its solubility in boiling solutions of pure alkalies and alkaline carbonates, and from many bodies by com- pletely volatilizing upon repeated evaporation in a platinum dish, with hydrofluoric acid or fluoride of ammonium and sulphuric acid. HYDROCHLORIC ACID. 171 SECOND GROUP OF THE INORGANIC ACIDS. ACIDS WHICH ARE PRECIPITATED BY NlTRATE OF SlLVER, BUT NOT BY CHLORIDE OF BARIUM : Hydrochloric Acid, Hydrobromic Acid, Hy- driodic Acid, Hydrocyanic Acid, Hydroferro- and Hydroferricyanic Acid, Hydrosulphuric Acid (Nitrous Acid, Hypochlorous Acid, Chlo- rous Acid, Hypophosphorous Acid). The silver compounds corresponding to the acids of this group are in- soluble in dilute nitric acid. The acids of this group decompose with metallic oxides, the metals combining with the chlorine, bromine, cyanogen, iodine, or sulphur, whilst the oxygen of the metallic oxide forms water with the hydrogen of the hydracid. 152. a. HYDROCHLORIC ACID (HC1). 1. CHLORINE is a heavy yellowish-green gas of a disagreeable and suffocating odor, which has a most injurious action upon the respiratory organs ; it destroys vegetable colors (litmus, indigo-blue, since this is a proof that lead, bismuth, copper, cadmium, oxide of mercury, gold, platinum, tin, antimony, arsenic, and sesquioxide of iron are not present. b. A PRECIPITATE IS FORMED. a. THIS PRECIPITATE is WHITE ; it consists in that case of 51 separated sulphur, and is indicative of the presence of SES- QUIOXIDE OF IRON ( 111, 3). However, as the separation of sulphur may also be caused by other substances, it is indis- pensable that you should satisfy yourself whether the substance present is really sesquioxide of iron or not. For this purpose test this solution with ammonia, and with ferrocyanide of potassium ( 111, 5 and 6). (3. THE PRECIPITATE is YELLOW ; in this case it may con- 52 sist either of sulphide of cadmium, sulphide of arsenic, or bisulphide of tin ; it indicates accordingly the presence of either cadmium, arsenic, or binoxide of tin. To distinguish between them, mix a portion of the fluid wherein the precipitate is suspended with ammonia in excess, add some sulphide of am- monium, and heat. aa. The precipitate does not dissolve ; it consists of CADMIUM ; for sulphide of cadmium is insoluble in ammonia and sulphide of ammonium. The blowpipe is resorted to as a confirmatory test ( 122, 8). bb. The precipitate dissolves : BINOXIDE OF TIN or ARSENIC : add ammonia to a small portion of the original solution. aa. A white precipitate is formed. BINOXIDE OF TIN is the substance present. Positive conviction is obtained by reducing the precipitate before the blowpipe, with cyanide of potassium and carbonate of soda ( 130, 8). /3/3. No precipitate is formed. This indicates the presence of ARSENIC. Positive conviction may be arrived at by the production of an arsenical mirror, which is effected by reducing the original substance or the precipitated sulphide of arsenic, either with cya'nide of potassium and carbonate of soda, or in some other way ; and moreover by exposing the original substance in conjunction with carbonate of soda to the inner flame of the blowpipe ( 132, 12 and 13). If the solution (50) contained arsenious acid, the yellow preci- pitate (52) formed immediately upon the addition of the hydrosulphuric acid ; if arsenic acid, it formed only upon the application of heat, or after long standing. For further information respecting the means of distinguishing between the two acids see 134, 9. y. THE PRECIPITATE is ORANGE-COLORED ; it that case it 53 consists of tersulphide of antimony, and indicates the pre- sence of TEROXIDE OF ANTIMONY. For confirmation the original solution is tested with zinc in a small platinum dish ( 131, 8). & THE PRECIPITATE is DARK-BROWN. It consists of pro- 54 tosulphide of tin, and indicates the presence of PROTOXIDE OF TIN. To remove all doubt, test a portion of the original solution with solution of chloride of mercury ( 129, 8). 216 ACTUAL EXAMINATION. . THE PRECIPITATE IS BROWNISH-BLACK OR BLACK. It may in that case consist of sulphide of lead, sulphide of 55 copper, tersulphide of bismuth, tersulphide of gold, bisul- phide of platinum, or sulphide of mercury. To distinguish between these different sulphides, the following experiments are resorted to. aa. Add dilute sulphuric acid to a portion of the original solution ; if a white precipitate is formed, this indicates LEAD. To dispel all doubt, test with chromate of potassa ( 117). bb. Add solution of soda to a portion of the original solu- tion ; if a yellow precipitate is formed, this indicates OXIDE OF MERCURY. The reactions with protochloride of tin and me- tallic copper afford positive certainty on the point ( 119). The presence of oxide of mercury is usually sufficiently indicated by the several changes of color through which the precipitate produced by the solution of hydrosulphuric acid in the fluid under examination is observed to pass ; this precipi- tate is white at first, but changes upon the addition of an excess of the precipitant to yellow, then to orange, and finally to black (119, 3). cc. Add ammonia in excess to a portion of the original solu- tion ; if a bluish precipitate is formed which redissolves in an excess of the precipitant, imparting an azure color to the fluid, or even if the ammonia simply colors the solution azure-blue, without producing a precipitate, this indicates COPPER. To remove all doubt, test with ferrocyanide of potassium ( 120). dd. If the precipitate produced by ammonia was white, and excess of ammonia has failed to redissolve it, filter the fluid off, wash the precipitate, dissolve it on a watch-glass in 1 or 2 drops of hydrochloric acid, with addition of 2 drops of water, and then add more water. If the solution turns turbid and milky, this is caused by basic terchloride of bismuth : the reaction consequently indicates BISMUTH. The blowpipe is resorted to as a conclusive test ( 121). ee. Add solution of sulphate of protoxide of iron to a portion of the original solution. The formation of a fine black preci- pitate is indicative of the presence of GOLD, To remove all doubt as to the nature of the precipitate, expose it to the flame of the blowpipe, or test the original solution with protochloride of tin ( 126). ff. Add chloride of potassium and alcohol to a portion of the original solution ; the formation of a yellow crystalline precipitate is indicative of the presence of PLATINUM. To remove all doubt, heat the precipitate to redness ( 127). 3. Mix a small portion of the original solution with chloride of 56 ammonium,* add ammonia to alkaline reaction, and then, no matter whether the latter reagent has produced a precipitate or not, a little sulphide of ammonium, and apply heat, if a precipitate fails to separate in the cold. a. No PRECIPITATE is FORMED j pass on to (62) j for iron, cobalt, * The chloride of ammonium is used for the purpose of preventing the precipitation by ammonia of any magnesia which might be present. ACTUAL EXAMINATION. 217 nickel, manganese, zinc, chromium, alumina, and silicic acid, are not present. b. A PRECIPITATE IS FORMED. a. The precipitate is black : protoxide of iron, nickel, or 57 cobalt. Mix a portion of the original solution with some solution of potassa or soda. aa. A dirty greenish-white precipitate is formed, which soon changes to reddish-brown upon exposure to the air : PROT- OXIDE OP IRON. To remove all doubt, test with ferricyanide of potassium ( 110). bb. A precipitate of a light greenish tint is produced, which does not change color : NICKEL. The reaction with ammonia, and the precipitation of the ammoniacal solution by potassa or soda, will afford positive certainty on the point ( 108). cc. A sky-blue precipitate is formed, which turns to a light- red upon boiling, or is discolored and acquires a dark tint : COBALT. The blowpipe is resorted to as a conclusive test (109). /3, The precipitate is not black. 58 aa. If the precipitate is distinctly flesh-colored, it con- sists of sulphide of manganese, and is consequently indica- tive of the presence of PROTOXIDE OF MANGANESE. To remove all doubt, add soda to the original solution, or try before the blowpipe ( 107). bb. If the precipitate is bluish-green, it consists of hydrated sesquioxide of chromium, and is consequently indicative of the presence of SESQUIOXIDE OF CHROMIUM. To dispel all doubt, test the original solution with soda, and apply the blow- pipe tests ( 102). cc. If the precipitate is white, it may consist of hydrate 59 of alumina, or hydrate of silicic acid, or sulphide of zinc, and may accordingly point to the presence of either alu- mina or oxide of zinc or silicic acid ; the latter, in that case, is generally contained in the original solution as an alkaline silicate. To distinguish between these three bodies, add to a portion of the original solution a drop of solution of soda, and wait to see whether this produces a precipitate ; then add some more solution of soda until the precipitate formed is re- dissolved. aa. If solution of soda fails to produce a precipitate, 60 there is reason to test for SILICIC ACID. For that purpose evaporate a portion of the original solution with hydrochloric acid to dryness, and treat the residue with hydrochloric acid and water ( 150, 2), when the silicic acid will be left undissolved. Determine the nature of the alkali which has been dissolved, as directed (66)- i8/3. If solution of soda produces a precipitate, which re- dissolves in an excess of the precipitant, add to a portion of this alkaline fluid a solution of hydrosulphuric acid ; the for- mation of a white precipitate indicates the .presence of ZINC. The reaction with solution of nitrate of protoxide of cobalt before the blowpipe will afford conclusive proof (106). If hydrosulphuric acid fails to produce a precipitate, add to 218 ACTUAL EXAMINATION. the remaining portion of the alkaline fluid chloride of ammo- nium, and apply heat. The formation of a white precipitate indicates the presence of ALUMINA. The reaction with solution of nitrate of protoxide of cobalt before the blowpipe will afford conclusive proof ( 101). Note to (58) and (59). As very slight contaminations may impair the distinctness of the tints exhibited by the precipitates considered in (58) and (59), it is advis- able, in all cases where the least impurity is suspected, to adopt the following method for the detection of manganese, chromium, zinc, alumina, and silicic acid. Add solution of soda to a portion of the original solution, first 61 in small quantity, then in excess. aa. No precipitate is formed: SILICIC ACID may be assumed to be present ; proceed as directed (60)- bb. A whitish precipitate is formed, which does not redissolve in an excess of the precipitant, and speedily turns blackish-brown upon exposure to the air : MANGANESE. The blowpipe is re- sorted to as a conclusive test ( 107). cc. A precipitate is formed, which redissolves in an excess of the precipitant : SESQUIOXIDE OF CHROMIUM, ALUMINA, OXIDE OF ZINC. aa. Add hydrosulphuric acid water to a portion of the alkaline solution. The formation of a white precipitate indi- cates the presence of ZINC. /3/3. If the original or the alkaline solution is green, and if the precipitate produced by soda and redissolved by an excess of the precipitant was of a bluish color, SESQUIOXIDE OF CHROMIUM is present. To remove all doubt, heat the alkaline solution to boil- ing, or try the reaction before the blowpipe ( 102). yy. Add chloride of ammonium to the alkaline solution. The formation of awhite precipitate indicates the presence of ALUMINA. The reaction with solution of nitrate of protoxide of cobalt before the blowpipe will afford conclusive proof ( 101). 4. Add to a portion of the original solution chloride of ammonium 62 and carbonate of ammonia, mixed with some caustic ammonia, and heat gently. a. No PRECIPITATE is FORMED : absence of baryta, strontia, and lime. Pass on to (64)- b. A PRECIPITATE is FORMED : presence of baryta, strontia, 63 or lime. Add solution of sulphate of lime in sufficient quantity to a portion of the original solution. a. The solution does not become turbid, not even after the lapse of from five to ten minutes : LIME. To remove all doubt, test with oxalate of ammonia (97). /3. The solution becomes turbid, but only after the lapse of some time : STRONTIA. It is only in neutral or, at least, but slightly acid solutions that the reaction is sure to make its appearance. The flame-coloration is resorted to as a conclusive test ( 96, 6 or 7). ACTUAL EXAMINATION. 219 y. A precipitate is immediately formed : BARYTA. To re- move all doubt, test with hydrofluosilicic acid ( 95). 5. Mix that portion of the solution of 4 in which carbonate of 64 ammonia has, after previous addition of chloride of ammonium, failed to produce a precipitate (62)> with phosphate of soda, add some more ammonia, and rub the sides of the vessel with a glass rod. a. No PRECIPITATE is FORMED : absence of magnesia. Pass on to (65). b. A CRYSTALLINE PRECIPITATE IS FORMED : MAGNESIA. 6. Evaporate a drop of the original solution on perfectly clean 65 platinum-foil as slowly as possible, and gently ignite the residue. a. THERE is NO FIXED RESIDUE LEFT. Test for AMMONIA, by adding to the original solution hydrate of lime, and observing the odor and reaction of the escaping gas, and the fumes which it forms with acetic acid ( 91). b. THERE is A FIXED RESIDUE LEFT : potassa or soda. Add 66 bichloride of platinum to a portion of the original solution, having first concentrated it by evaporation if dilute, and shake the mixture. a. J\o precipitate is formed, not even after the lapse of ten or fifteen minutes : SODA. The flame coloration is selected as a con- clusive test, or the reaction with antimonate of potassa is resorted to for the purpose ( 90). /3. A yellow crystalline precipitate is formed : POTASSA. The reaction with tartaric acid or the flame coloration is selected as a conclusive test (89). Simple Compounds. A. SUBSTANCES SOLUBLE IN WATER. DETECTION OF THE ACID. I. Detection of Inorganic Acids. 183. Reflect in the first place which of the inorganic acids form soluble com- pounds with the detected base (compare Appendix IV.), and bear this in mind in your subsequent operations, giving due regard also to the result of the preliminary examination. 1. ARSENIOUS ACID and ARSENIC ACID have already been consi- 67 dered in the preceding paragraph (detection of the base). These two acids are distinguished from each other by their respective reaction with nitrate of silver, or with potassa and sulphate of copper (see 134, 9). 2. The presence of CARBONIC ACID, HYDROSULPHURIC ACID, and 68 CHROMIC ACID, is also indicated already in the course of the process pursued for the detection of the bases. The two former betray their presence by effervescing upon the addition of hydrochloric acid ; they may be distinguished from one another by the smell. Should additional proof be required, the presence of carbonic acid may be ascertained beyond a doubt by the reaction with lime-water (see 149), and that of hydrosul- phuric acid by the reaction with solution of acetate of lead ( 156). The presence of chromic acid is invariably indicated by the yellow or red tint of the solution, as well as by the transition of the red or yellow color to 220 ACTUAL EXAMINATION. green, accompanied by the separation of sulphur, upon the addition of hydrosulphuric acid water. To remove all doubt, try the reactions with solutions of acetate of lead and of nitrate of silver ( 138). 3. Acidify a portion of the solution with hydrochloric acid, or 69 if oxide of silver or suboxide of mercury has been found with nitric acid, and add chloride of barium or where nitric acid has been the acidifying agent used nitrate of baryta, a. THE FLUID REMAINS CLEAR. Absence of sulphuric acid. Pass on to (70). b. A PRECIPITATE IS PRODUCED, IN FORM OF A FINE WHITE POWDER : SULPHURIC ACID. The precipitate must remain undissolved even after further addition of hydrochloric or nitric acid. 4. Add solution of sulphate of lime to another portion of the 70 solution (which, if it has an acid reaction, must first be neutralized, or made slightly alkaline, by means of ammonia). a. No PRECIPITATE is FORMED : absence of phosphoric acid, silicic acid, oxalic acid, and fluorine. Pass on to (73)* b. A PRECIPITATE is FORMED. Add acetic acid in excess. 71 a. TJie precipitate redissolves readily : PHOSPHORIC ACID or SILICIC ACID. Evaporate a portion of the original solution, after acidifying with hydrochloric acid, to dryness, and treat the residue with some hydrochloric acid and water. If an insoluble residue is left, mix a sample of the original solution with chloride of ammonium, sulphate of magnesia, and ammonia. A crystal- line precipitate shows the presence of PHOSPHORIC ACID. ( 142). (3. TJie precipitate remains undissolved or dissolves with 72 difficulty : OXALIC ACID or FLUORINE. Oxalate of lime is pulverulent, fluoride of calcium flocculent and gelatinous. The reaction with binoxide of manganese and sulphuric acid ( 145) will afford conclusive proof of the presence of oxalic acid ; the reaction on glass (etching) of the presence of fluorine ( 146). 5. Acidify a fresh portion of the original solution with nitric acid, 73 and add solution of nitrate of silver. a. THE FLUID REMAINS CLEAR. This is a proof of the absence of chlorine, bromine, iodine, ferrocyanogen, and ferricyanogen ; the absence of cyanogen (in simple cyanides) is also probable. Of the soluble metallic cyanides, cyanide of mercury is not precipitated by nitrate of silver ; if, therefore, in the analytical process for the de- tection of the bases, mercury has been found, cyanide of mercury may be present. For the manner of detecting the cyanogen in the latter see 155, 8. Pass on to (76). b. A PRECIPITATE IS FORMED. a. TJie precipitate is orange : FERRICYANOGEN. The reaction 74 with sulphate of protoxide of iron is resorted to as a con- firmatory test ( 155, Supplement). /3. The precipitate is white or yellowish-white. Treat the pre- cipitate with ammonia in excess immediately, if the base was an alkali or an alkaline earth after filtering and washing, if the base was an earth proper or the oxide of a heavy metal. aa. The precipitate is not dissolved : IODINE or FERRO- CYANOGEN. In the former case the precipitate is pale yellow, in the latter white and gelatinous. The reaction with starch ACTUAL EXAMINATION. 221, and hyponitric acid ( 154) will afford conclusive proof of the presence of iodine, the reaction with sesquichloride of iron of the presence of ferrocyanogen ( 155, Supplement). )3/3. The precipitate is dissolved : CHLORINE, BROMINE, or 75 CYANOGEN. If the original substance smells of hydrocyanic acid, and the silver precipitate dissolves with some diffi- culty in the ammonia, the precipitate may be assumed to con- sist of cyanide of silver, and, consequently, to indicate the presence of CYANOGEN. To remove all doubt on the point, add to the original solution sulphate of protoxide of iron, solution of soda, and hydrochloric acid ( 155). If addition of chlorine- water imparts a yellow tint to the original solution, the preci- pitate may be held to consist of bromide of silver, and conse- quently indicates the presence of BROMINE ; if the bromine is present only in very small proportion, chloroform or bisulphide of carbon must be used in conjunction with chlorine- water to make the reaction distinctly apparent ( 153). In the proved absence of both bromine and cyanogen the precipitate consists of chloride of silver, and consequently shows the presence Of CHLORINE. 6. Add to a small portion of the aqueous solution hydrochloric 76 acid, drop by drop, until a distinct acid reaction is just imparted to the fluid, then dip in a slip of turmeric-paper, take it out, and dry- it at 212 F. If the dipped portion looks brownish-red, BORACIC ACID is present. To settle all doubt on the point, add sulphuric acid and alcohol, and set fire to the latter ( 144). 7. With regard to NITRIC ACID and CHLORIC ACID, these are 77 usually discovered already in the course of the preliminary exami- nation (6). The reaction with sulphate of protoxide of iron and sulphuric acid ( 159) will afford conclusive evidence of the presence of the former, treatment of the solid salt with concentrated sulphuric acid, of the presence of the latter acid ( 1GO). Simple Compounds. A. SUBSTANCES SOLUBLE IN WATER. DETECTION OF THE ACID. II. Detection of Organic Acids. 184. Consider, in the first place, which of the organic acids form soluble compounds with the detected base (Compare Appendix IV.), and bear this in mind in your subsequent operations, giving due regard also to the results of the preliminary examination. The following course of proceeding presupposes the organic acid to be present in the free state, or in combination with an alkali or an alkaline earth. If the detected base belongs to another group, therefore, it must first be removed. Where the base belongs to group V. or group VI. the removal is effected by means of hydrosulphuric acid, where it belongs to group IV., by means of sulphide of ammonium. After filtering off the sulphides, and removing the excess of sulphide of ammonium by acidifying with hydrochloric acid, heating, and filtering off the eliminated sulphur, proceed to (78) Where the basis is alumina or sesquioxide of 222 ACTUAL EXAMINATION. chromium, try first to precipitate these substances by boiling with car- bonate of soda ; should this fail, as it will where the acid is non- volatile, precipitate the latter with neutral acetate of lead, wash the precipitate, diffuse it through water, conduct hydrosulphuric acid into the water in which the precipitate is suspended, filter off the sulphide of lead formed, and treat the filtrate as directed below. Alumina may also be precipi- tated from its compounds with non-volatile organic acids by solution of soluble glass, as silicate of alumina. 1. Add ammonia to a portion of the aqueous solution of the 78 compound under examination to slight alkaline reaction, then chlo- ride of calcium. If the solution was neutral, or only slightly acid, add chloride of ammonium before adding the chloride of calcium. a. No PRECIPITATE IS FORMED, NOT EVEN AFTER SHAKING THE FLUID NOR AFTER THE LAPSE OF A FEW MINUTES : absence of oxalic acid and tartaric acid. Pass on to (80)- b. A PRECIPITATE is FORMED. Add lime-water in excess 79 to a fresh portion of the original solution, and add solution of chloride of ammonium to the precipitate formed. a. Tlie precipitate redissolves : TARTARIC ACID. The reaction with acetate of potassa may be resorted to as a confirmatory test ; but a still more positive proof will be afforded by the deportment which the precipitate produced by the chloride of calcium, and properly washed, exhibits with solution of soda or with ammonia and nitrate of silver ( 1 63). /3. The precipitate does not redissolve : OXALIC ACID. To remove all doubt, try the reaction with concentrated sul- phuric acid ( 145). 2. Heat the fluid of 1, a, to boiling, keep at that temperature for 80 some time, and add some more ammonia to the boiling fluid. a. IT REMAINS CLEAR i absence of citric acid. Pass on to (81). b. IT BECOMES TURBID, AND DEPOSITS A PRECIPITATE : CITRIC ACID. To remove all doubt as to the nature of the acid, add solution of acetate of lead in excess, wash the precipitate formed, and see whether it dissolves readily in ammonia ( 164). 3. Mix the fluid of '2, a, with alcohol. 81 a. IT REMAINS CLEAR : absence of malic acid. Pass on to (82). b. A PRECIPITATE is FORMED : MALIC ACID. To remove all doubt, it is invariably necessary to try the reaction with acetate of lead, to see whether the precipitate produced by that reagent dissolves with difficulty in ammonia, and to examine its deportment when the fluid in which it is suspended is heated to boiling ( 1'65). m 4. Neutralize a portion of the original solution completely (if not 82 already absolutely neutral) with ammonia or with hydrochloric acid, and add solution of sesquichloride of iron. a. A BULKY PRECIPITATE FORMS, OF A CINNAMON BROWN, OR DIRTY YELLOW COLOR. Wash the precipitate, heat it with ammonia, filter, strongly concentrate the filtrate by evaporation, divide into two parts, and add to the one some hydrochloric acid, to the other alcohol and chloride of barium. The formation of a precipitate in the first portion indicates the presence of BENZOIC ACID, a precipi- ACTUAL EXAMINATION. 223 tate in the second denotes the presence of SUCCINIC ACID. Compare 168 aud 169. b. THE LIQUID ACQUIRES A RATHER INTENSE DEEP RED TINT, 83 AND, UPON PROTRACTED BOILING, A LIGHT REDDISH- BROWN PRECIPITATE SEPARATES i acetic acid or formic acid. Heat a portion of the solid salt under examination or, if the substance is in the fluid state, of the residue left upon evaporating the fluid (which, if acid, you must neutralize first with soda), with sulphuric acid and alcohol ( 171). The characteristic odor of acetic ether indicates the presence of ACETIC ACID. If you do not detect acetic acid in the fluid, you may conclude that the substance under examination contains FORMIC ACID : to remove all doubt, try the reactions with nitrate of silver and chlo- ride of mercury ( 172). Simple Compounds. B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR NITRO-HYDRO- CHLORIC ACID. Detection of the Base* 185. Dilute a portion of the solution in hydrochloric acid, nitric acid, 84 or nitro-hydrochloric acid with water,t and proceed as directed 182, beginning at (46)> in cases where the substance is dissolved in nitric acid, and at 2, (50)> if the solution already contains hydrochloric acid. This course will answer for bases of the second, fifth, and sixth groups, but in testing for bases of the third and fourth groups, with sulphide of ammonium, according to (56)> the usual course of proceeding is under the circumstances departed from. Particular regard must be had in this to the following observations : we have seen (59) that if in cases where we have A SUBSTANCE SOLUBLE IN WATER we obtain, in the course of the examination, a white precipitate upon adding chloride of ammo- nium, ammonia, and sulphide of ammonium, this precipitate can consist Only Of SULPHIDE OF ZINC, Or ALUMINA, Or HYDRATE OF SILICIC ACID. But the case is different if the body is INSOLUBLE IN WATER, but dissolves in hydrochloric acid ; for in that case a white precipitate produced by ammonia, in presence of chloride of ammonium, may consist also of PHOSPHATES, BORATES, OXALATES, SILICATES OF THE ALKALINE EARTHS, or of FLUORIDES OF THEIR METALS, since all these bodies are insoluble in water, but dissolve in hydrochloric acid, and (being only very sparingly soluble also in solution of chloride of ammonium) accordingly separate again upon neutralization of that acid. If, therefore, a white precipi- tate is produced upon testing an acid solution, under the circumstances stated, and in pursuing the course laid down in 182, (56)> pro- ceed as follows : 1. If the results of the preliminary examination have given you 85 * Regard is also had here to certain salts of the alkaline earths, as this course of examination leads directly to their detection. i If upon the addition of water the liquid becomes white and turbid or deposits a white precipitate, this indicates the presence of antimony or bismuth, possibly also of tin. Compare 121, 9, and 131, 4. Heat with hydrochloric acid until the fluid has_become clear again, then pass on to (50)- 224 ACTUAL EXAMINATION. reason to suspect the presence of SILICIC ACID (20)> evaporate a portion of the hydrochloric acid solution to dryness, moisten the residue with hydrochloric acid and add water. If silicic acid is present, it will remain undissolved. Determine the base in the solution as directed (56) or (62), as the case may be. 2. Add to a portion of the original hydrochloric acid solution 86 some tartaric acid, and after this ammonia in excess. a. No PERMANENT PRECIPITATE is FORMED : absence of the above enumerated salts of the alkaline earths. Mix another portion of the original solution with solution of soda in excess, and add to the one half of the clear fluid chloride of ammonium, to the other half solution of hydrosulphuric acid. The formation of a preci- pitate in the former indicates the presence of ALUMINA j in the latter, the presence of ZINC. b. A PERMANENT PRECIPITATE is FORMED : presence of a salt of an alkaline earth. a. Bring a sample of the original substance, on a watch- 87 glass, in contact with a little binoxide of manganese, a few drops of water, and some concentrated sulphuric acid. If evolution of carbonic acid gas takes place instantly, the salt is an OXALATE. To find the base, ignite a fresh sample, dissolve the residue in dilute hydrochloric acid, and examine the solution as directed (62). /3. Add to a portion of the hydrochloric acid solution 88 ammonia until a precipitate forms ; then acetic acid until this is redissolved ; lastly, acetate of soda and a drop of solution of sesquichloride of iron : the formation of a white flocculent precipitate indicates the presence of PHOSPHORIC ACID. Add now some more sesquichloride of iron until the fluid has acquired a distinct red color, boil, filter boiling, and test the filtrate, which is now free from phosphoric acid, for the alkaline earth with which the phosphoric acid was combined, as directed (62), after having previously removed, by precipitation with ammonia, the iron which may possibly have been dissolved. ' y. Test for FLUORINE, by heating a portion of the original 89 substance, or of the precipitate produced in the hydrochloric acid solution by ammonia, with sulphuric acid ( 146). After removal of the fluorine, ascertain the nature of the alkaline earth which you have now in the residue, in combination with sulphuric acid ( 188). I. BORACIC ACID is detected in the hydrochloric acid solution by means of turmeric-paper ( 144). and the base combined with it, by boiling a portion of the original substance with water and carbonate of soda, filtering, washing, dissolving the carbonate formed in the least possible amount of dilute hydrochloric acid, and examining the solution as directed (62)- DETECTION OF INORGANIC ACIDS. 225 | Simple Compounds. B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR NITRO-HYDRO- CHLORIC ACID. DETECTION OF THE ACID. I. Detection of Inorganic Acids. 186. 1. CHLORIC ACID cannot be present, since all chlorates are 90 soluble in water ; NITRIC ACID, which may be present in form of a basic salt, must have been revealed already by the ignition of the body in a glass tube, and so must CYANOGEN (8). -For the analysis of the insoluble metallic CYANIDES insoluble in water see 204. The results of the test with phosphate of soda and ammonia will have directed attention to the presence of SILICIC ACID. Evaporation of the hydrochloric acid solution to dryness, and treatment of the residue with hydrochloric acid and water, will remove all doubt on this point. 2. The course of examination laid down for the detection of 91 the bases leads likewise to that of ARSENIOUS and ARSENIC ACIDS, CARBONIC ACID, HYDROSULPHURIC ACID, and CHROMIC ACID. With regard to the latter acid, I repeat that its presence is indicated by the yellow or red color of the compound, the evolution of chlorine which ensues upoa boiling with hydrochloric acid, and the subsequent presence of sesquioxide of chromium, in the solution. Fusion of the compound under examination with carbonate of soda is, however, the most conclusive test for chromic acid ( 138). 3. Boil a portion of the substance with nitric acid. 92 a. If nitric oxide gas is evolved, and sulphur separates, this is confirmative of the presence of a metallic sulphide. b. If violet vapors escape, the compound is a metallic IODIDE. c. If reddish-brown fumes of a chlorine-like smell are evolved, the compound is a metallic BROMIDE, in which case the fumes will color starch yellow ( 153). 4. Dilute a small portion of the nitric acid solution or of the 95 filtrate of this solution, should the nitric acid have left an undis- solved residue with water, and add solution of nitrate of silver to the fluid. The formation of a white precipitate, which, after wash- ing, is soluble in ammonia, and fuses without decomposition when heated, indicates the presence of CHLORINE. 5. Boil a portion of the substance with hydrochloric acid, filter if 94 necessary, dilute with water, and add chloride of barium. The for- mation of a white precipitate, which does not redissolve even upon addition of a large quantity of water, indicates the presence of SUL- PHURIC ACID. 6. Test for BORACIC ACID as directed 144, 6. 7. If none of the acids enumerated from 1 to 6 are present, there 95 is reason to suspect the presence of PHOSPHORIC ACID, OXALIC ACID, or FLUORINE, or the total absence of acids. To the presence of oxalic acid your attention will have been called already in the course of the preliminary examination (8). If the acids named had been combined Q 226 DETECTION OF THE BASE AND THE ACID. with an alkaline earth, they would already have been detected in the course of the examination for these bases (87) to (89) ; they need there- fore here be tested for only where the examination has revealed the presence of some other base. To that end precipitate the base, if belong- ing to Group V. or VI., with hydrosulphuric acid, or if belonging to Group IV., with sulphide of ammonium, and filter. If you have preci- pitated with sulphide of ammonium, add to the filtrate hydrochloric acid to acid reaction, expel in either case the hydrosulphuric acid by boiling, and filter if necessary. Test a portion of this solution for phosphoric acid, oxalic acid, and fluorine, as directed (70). If the basis was alumina or sesquioxide of chromium, test for phosphoric acid with solution of molybdate of ammonia in nitric acid ( 14:2, 10) ; for oxalic acid with binoxide of manganese and sulphuric acid ( 145) ; for fluorine with sul- phuric acid ( 146). Simple Compounds. B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT SOLUBLE IN ACIDS. DETECTION OF THE ACID. II. Detection of Organic Acids. 187. 1. FORMIC ACID cannot be present, as all the formates are soluble 96 in water. 2. ACETIC ACID has been revealed already in the course of the preliminary examination, by the evolution of acetone. The re- action with sulphuric acid and alcohol ( 171) will afford conclusive proof. 3. Boil a portion of the substance for some time with solution of 97 carbonate of soda in excess, and filter hot. You have now, in most cases, the organic acid in solution in combination with soda. Aci- dulate the solution slightly with hydrochloric acid, expel the carbonic acid by heat, and test as directed 184. With bases of the fourth group and also in presence of oxide of lead, this mode of separation is not com- pletely successful. In exceptional cases of the kind add to the filtrate, after boiling with carbonate of soda, sulphide of ammonium until the whole of the metallic oxide is thrown down. Simple Compounds. C. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, HYDRO- CHLORIC ACID, NITRIC ACID, AND NITRO-HYDROCHLORIC ACID. DETECTION OP THE BASE AND THE ACID. 188. Under this head we have to consider here SULPHATE OF BARYTA, 98 SULPHATE OF STRONTIA, SULPHATE OF LIME, FLUORIDE OF CALCIUM, SILICA, SULPHATE OF LEAD, Compounds of LEAD With CHLORINE and BROMINE ; compounds of SILVER with CHLORINE, BROMINE, IODINE, and CYANOGEN ; and lastly SULPHUR and CHARCOAL, as the only bodies belong- ing to this class which are more frequently met with. For the simple DETECTION OF THE BASE AND THE ACID. 227 silicates I refer to 205, for the ferro- and ferricyanides, to 204. The preliminary examination will have informed you whether you need pay any regard to the possible presence of these compounds. Sulphate of lime and chloride of lead are not altogether insoluble in water, and sulphate of lead may be dissolved in hydrochloric acid. However, as these compounds are so sparingly soluble that complete solution of them is seldom effected, they are included here also among the class of insoluble substances, to insure their detection, should they have been overlooked in the course of the examination of the aqueous or acid solution of the body to be analyzed. 1. Free SULPHUR must have been detected already in the course of the preliminary examination. 2. CHARCOAL is generally black ; it is insoluble in aqua regia ; put on platinum foil, with the blowpipe name playing upon the under side of the foil, it is always consumed ; by deflagration with nitrate of potassa it yields carbonate of potassa. 3. Pour sulphide of ammonium over a very small quantity of the 99 substance under examination. a. It TURNS BLACK j this indicates the presence of lead or a salt of silver. a. The body fused in the glass tube without decomposition (3) : chloride of lead, bromide of lead ; chloride of silver, bromide of silver, iodide of silver. Fuse one part of the compound with 4: parts of carbonate of soda and potassa in a small porcelain crucible, let cool, boil the residue with water, and test the nitrate for CHLORINE, BROMINE, and IODINE, as directed (73)- Dissolve the residue, which consists either of metallic SILVER or OXIDE OF LEAD, in nitric acid, and test the solution as directed (46)- /3. The body evolved cyanogen by ignition in the glass tube, and left metallic silver behind : CYANIDE OF SILVER. y. The body remained unaltered by ignition in the glass tube : SULPHATE OF LEAD. Boil a sample of it with solution of carbo- nate of soda, filter, acidulate the filtrate with hydrochloric acid, and test with chloride of barium for SULPHURIC ACID ; dissolve the washed residue in nitric acid, and test the solution with hydrosuljihuric acid and with sulphuric acid for LEAD. b. IT REMAINS WHITE : absence of an oxide of a heavy metal. 100 Triturate a small sample together with quartz sand, moisten the mixture on a watch-glass with a few drops of concentrated sulphuric acid, and heat gently. a. White fames are evolved, which redden litmus paper. This indicates the presence of BXUORIDE OF CALCIUM. Reduce a portion of the substance to a fine powder, decompose this in a platinum crucible with sulphuric acid, and try the reaction on glass ( 146), to prove the presence of FLUORINE ; boil the residue with hydro- chloric acid, filter, neutralize the filtrate with ammonia, and test for LIME with oxalate of ammonia. /3. No fumes reddening litmus paper are evolved. Mix a portion of the very finely pulverized substance with 4 times the quantity of pure carbonate of soda and potassa, and fuse the mixture in a platinum crucible, or on platinum foil. Boil the fused mass with water, filter should a residue be left, and wash the latter. Acidulate a portion of the filtrate with hydrochloric acid, and Q 2 228 COMPLEX COMPOUNDS DETECTION OF BASES. test with chloride of barium for SULPHURIC ACID ; and in case you do not find that acid, test another portion of the filtrate for SILICIC ACID, by evaporating the fluid acidified with hydro- chloric acid ( 150, 2). If the SILICIC ACID was present in the pure state, the mass resulting from the fusion of the substance with carbonate of soda and potassa must have dissolved in water to a clear fluid ; but if silicates also happened to be present, the bases of them are left behind undissolved, and may be further examined. If, on the other hand, sulphuric acid has been found, the alkaline earth which was combined with it is found on the filter as a carbonate. Wash this, then dissolve in dilute hydrochloric acid, and test the solution for BARYTA, STRONTIA, and LIME, as directed (62)- Complex Compounds* A. SUBSTANCES SOLUBLE IN WATER, AND ALSO SUCH AS ARE INSOLUBLE IN WATER, BUT DISSOLVE IN HYDROCHLORIC ACID, NITRIC ACID, OB NlTRO-HYDROCHLORIC ACID. Detection of the Basest 189.$ (Treatment with Hydrochloric Acid : Detection of Silver, Suboxide of Mercury [Lead].) The systematic course for the detection of the bases is essentially 101 the same for bodies soluble in water, as for those which are soluble only in acids. Where, from the different nature of the original solution, a departure from the ordinary course is rendered neces- sary, the fact will be distinctly stated. I. SOLUTION IN WATER. MlX THE PORTION INTENDED FOR THE DETECTION OF THE BASES WITH SOME HYDROCHLORIC ACID. 1. THE SOLUTION HAD AN ACID OR NEUTRAL REACTION PREVIOUSLY 102 TO THE ADDITION OF THE HYDROCHLORIC ACID. a. No PRECIPITATE is FORMED; this indicates the absence of silver and suboxide of mercury. Pass 011 to 190. b. A PRECIPITATE is FORMED. Add more hydrochloric acid, drop by drop, until the precipitate ceases to increase ; then add about six or eight drops more of hydrochloric acid, shake the mixture, and filter. The precipitate produced by hydrochloric acid may consist of chloride of silver, subchloride of mercury, chloride of lead, a basic * I use this term here and hereafter in the present work to designate compounds in which all the move frequently occurring bases, acids, metals, and metalloids are sup- posed to be present. f Consult the explanations in the Third Section, with the contents of which you should make yourself thoroughly acquainted first, before proceeding further. Regard is here had also to the presence of the acids of arsenic, and of those salts of the alkaline earths which dissolve in hydrochloric acid, and separate again from that solution un- altered upon neutralization of the acid by ammonia. Consult the remarks in the Third Section. DETECTION OF BASES. 229 salt of antimony, basic chloride of bismuth, possibly also of benzoic acid. The basic salt of antimony and the basic chloride of bismuth, however, redissolve in the excess of hydrochloric acid ; consequently, if the instructions given have been strictly followed, the precipitate collected upon the filter can consist only of chloride of silver, sub- chloride of mercury, or chloride of lead (possibly also of benzoic acid, which, however, is altogether disregarded here). Wash the precipitate collected upon the filter twice with cold water, add the washings to the filtrate, and examine the solution as directed 190, even though the addition of the washingvS to the acid filtrate should produce turbidity in the fluid (which indicates the presence of compounds of antimony or bismuth). Treat the twice-washed precipitate on the filter as follows : 103 a. Pour hot water over it upon the filter, and test the fluid running off with sulphuric acid for LEAD. The non- formation of a precipitate upon the addition of the sulphuric acid simply proves that the precipitate produced by hydrochloric acid contains no lead, and does not by any means establish the total absence of this metal, as hydrochloric acid fails to precipitate lead from dilute solutions. /3. Pour over the now thrice-washed precipitate upon the filter solution of ammonia. If this changes its color to black or gray, it is a proof of the presence of SUBOXIDE OF MERCUKY. y. Add to the ammoniacal fluid running off in /3 nitric acid to strongly acid reaction. The formation of a white, curdy pre- cipitate indicates the presence of SILVER.* (If the precipitate did contain lead, the ammoniacal solution generally appears turbid, owing to the separation of a basic salt of lead. This, however, does not interfere with the testing for silver, since the basic salt of lead redissolves upon the addition of nitric acid.) 2. THE OKIGINAL AQUEOUS SOLUTION HAD AN ALKALINE RE- ACTION. 104 a. THE ADDITION OF HYDROCHLORIC ACID TO STRONGLY ACID REACTION FAILS TO PRODUCE EVOLUTION OF GAS OR A PRE- CIPITATE, OR THE PRECIPITATE WHICH FORMS AT FIRST REDIS- SOLVES UPON FURTHER ADDITION OF HYDROCHLORIC ACID : paSS on to 190. b. THE ADDITION OF HYDROCHLORIC ACID TO THE ORIGINAL SOLUTION PRODUCES A PRECIPITATE WHICH DOES NOT REDIS- SOLVE IN AN EXCESS OF THE PRECIPITANT, NOT EVEN UPON BOILING. a. The formation of the precipitate is attended neither with 105 evolution of hydrosulphuric acid nor of hydrocyanic acid. Filter, and treat the filtrate as directed 190. aa. THE PRECIPITATE is WHITE. It may, in that case, con- sist of a salt of lead or silver, insoluble in water and hydro- chloric acid (CHLORIDE OF LEAD, SULPHATE OF LEAD, CHLORIDE OF SILVER, &c.), or it may be HYDRATE OF SILICIC ACID. Test for the bases and acids of these compounds as directed 203, bearing in mind that the chloride of lead or chloride of silver * If the quantity of silver is only very small, its presence is indicated by opalescence of the fl uid. 230 DETECTION OF BASES. which may be present, may possibly only have been formed in the process. bb. THE PRECIPITATE is YELLOW on ORANGE. In that case it may consist of SULPHIDE OF ARSENIC (and if the fluid from which it has separated was not boiled long, or only with very dilute hydrochloric acid, also of SULPHIDE OF ANTIMONY or BISULPHIDE OF TIN), which substances were originally dis- solved in solution of ammonia, potassa, soda, phosphate of soda, or some other alkaline fluid, with the exception of solu- tions of alkaline sulphides and cyanides. Examine the preci- pitate, which may also contain HYDRATE OF SILICIC ACID, as directed (40)- (3. The formation of the precipitate is attended with evolu- 106 tion of hydrosulphuric acid gas, but not of hydrocyanic acid* aa. THE PRECIPITATE is OF A PURE WHITE COLOR, AND CONSISTS OF SEPARATED SULPHUR. In that Case a SULPHURETTED ALKALINE SULPHIDE is present. Boil, filter, and treat the nitrate as directed 194, the precipitate as directed 203. bb. THE PRECIPITATE is COLORED. In that case you may conclude that a METALLIC SULPHUR SALT is present, i.e., a com- bination of an alkaline sulphur base with a metallic sulphur acid. The precipitate may accordingly consist of TERSULPHIDE OF GOLD, BISULPHIDE OF PLATINUM, BISULPHIDE OF TIN, SULPHIDE OF ARSENIC, or SULPHIDE OF ANTIMONY. It might, however, consist also of SULPHIDE OF MERCURY or of SULPHIDE OF COPPER or SULPHIDE OF NICKEL, or contain these substances, as the former will dissolve in sulphide of potassium, and the latter are slightly soluble in sulphide of ammonium. Filter, and treat the nitrate as directed 194, the precipitate as directed (40). y. The formation of the precipiiate is attended with evolu- 107 tion of hydrocyanic acid, with or without simultaneous dis- engagement of hydrosulphuric acid. This indicates the pre- sence of an ALKALINE CYANIDE, and, if the evolution of the hydrocyanic acid is attended with that of hydrosulphuric acid, also of an alkaline SULPHIDE. In that case the precipitate may, besides the compounds enumerated in a and , contain many other substances (e.g., cyanide of nickel, cyanide of silver, &c.). Boil, with further addition of hydrochloric acid, or of nitric acid, until the whole of the hydrocyanic acid is expelled, and treat the solution, or, if an un dissolved residue has been left, the nitrate, as directed 190; arid the residue (if any) according to 203. C. THE ADDITION OF HYDROCHLORIC ACID FAILS TO PRODUCE 1Q8 A PERMANENT PRECIPITATE, BUT CAUSES EVOLUTION OF GAS. a. The escaping gas smells of hydrosulphuric acid ; this indicates the presence of a SIMPLE ALKALINE SULPHIDE. Proceed as directed 194. /3. The escaping gas is inodorous ; in that case it is CARBONIC ACID which was combined with an alkali. Pass on to 190. * Should the odor of the evolved gas leave any doubt regarding the actual presence or absence of hydrocyanic acid, add some chromate of potassa to a portion of the fluid, previously to the addition of the hydrochloric acid. ACTUAL EXAMINATION COMPLEX COMPOUNDS. 231 y. The escaping gas smells of hydrocyanic acid (no matter whether hydrosulphuric acid or carbonic acid is evolved at the same time or not). This indicates the presence of an ALKALINE CYANIDE. Boil until the whole of the hydrocyanic acid is ex- pelled, then pass on to 190. II. SOLUTION IN HYDROCHLORIC ACID OR IN NITROHYDROCHLORIC ACID. Proceed as directed 190. III. SOLUTION IN NITRIC ACID. Dilute a small sample of it with water ; should this produce 109 turbidity or a precipitate (indicative of the presence of bismuth), add nitric acid until the fluid is clear again, then hydrochloric acid. 1. No PRECIPITATE is FORMED. Absence of silver and suboxide of mercury. Treat the principal solution as directed 190. 2. A PRECIPITATE is FORMED. Treat a larger portion of the nitric acid solution the same way as the sample, filter, and examine the pre- cipitate as directed (103), the nitrate as directed 190. 190.* (Treatment with Hydrosulphuric Acid, Precipitation of the Metallic Oxides of Group V., 2nd Division, and of Group VI.) ADD TO A small PORTION OF THE CLEAR ACID SOLUTION HYDROSUL- PHURIC ACID WATER, UNTIL THE ODOR OF HYDROSULPHURIC ACID IS DISTINCTLY PERCEPTIBLE AFTER SHAKING THE MIXTURE, AND WARM GENTLY. 1. No PRECIPITATE is FORMED, even after the lapse of some HO time. Pass on to 194, for lead, bismuth, cadmium, copper, mercury, gold, platinum, antimony, tin, and arsenic, t are not present the absence of sesquioxide of iron and of chromic acid is also indicated by this negative reaction. 2. A PRECIPITATE IS FORMED. a. The precipitate is of a pure white color, light, and HI finely pulverulent, and does not redissolve on addition of hydrochloric acid. It consists of separated sulphur, and indicates the presence of SESQUIOXIDE OF IRON. None of the * Consult the remarks in the Third Section. t Where the preliminary examination has led you to suspect the presence of arsenic acid, you must endeavor to obtain the most conclusive evidence of the absence of this acid ; this may be done by allowing the fluid to stand for some time at a gentle heat (about 158 F.), or by heating it with sulphurous acid previous to the addition of the hydrosulphuric acid. (Compare 133, 3.) In solutions containing much free acid the precipitates are frequently formed only after dilution with water. Sulphur will precipitate also if sulphurous acid, or iodic acid, or bromic acid is pre- sent (which substances are not included in our analytical course), and also if chromic acid, or chloric acid, or free chlorine is present. In presence of chromic acid the sepa- ration of the sulphur is attended with reduction of the acid to sesquioxide of chromium, in consequence of which the reddish-yellow color of the solution changes to green. (Compare 138.) The white sulphur suspended in the green solution looks at first like a green precipitate, which frequently tends to mislead beginners. 232 ACTUAL EXAMINATION COMPLEX COMPOUNDS. other metals enumerated in (110) can be present. Treat the principal solution as directed 194. b. The precipitate is colored. Add to the larger proportion of the acid or acidified 112 solution, best in a small flask, hydrosulphuric acid water in excess, i.e., until the fluid smells distinctly of it, and the precipitate ceases to increase upon continued addition of the reagent ; apply a gentle heat, shake vigorously for some time, filter, keep the filtrate (which contains the oxides present of Groups I. IV.), for further examination according to the instruc- tions of 194, and thoroughly wash* the precipitate, which con- tains the sulphides of the metals present of Groups Y. and VI. Jn many cases, and more particularly where there is any reason to suspect the presence of arsenic, it will be found more convenient to transmit hydrosulphuric acid gas through the solution DILUTED WITH WATER, instead of adding hydro- sulphuric acid water. If the precipitate is yellow, it consists principally of sul- 113 phide of arsenic, bisulphide of tin, or sulphide of cadmium ; if orange -colored, this indicates sulphide of antimony ; if brown or black, one at least of the following oxides is present : oxide of lead, teroxide of bismuth, oxide of copper, oxide of mercury, teroxide of gold, binoxide of platinum, protoxide of tin. However, as a yellow precipitate may contain small particles of an orange-colored, a brown, or even a black precipitate, and yet its color not be very perceptibly altered thereby, it will always prove the safest way to assume the presence of all the metals named in (110) in any precipitate produced by hydrosulphuric acid, and to proceed accordingly as the next paragraph ( 191) directs. 191. (Treatment of the Precipitate produced by Hydrosulpliur'iG Acid with Sulphide of Ammonium; Separation of the '2nd Division of Group V. from Group VI.) INTRODUCE A SMALL PORTION OF THE PRECIPITATE PRODUCED 114 BY HYDROSULPHURIC ACID IN THE ACIDIFIED SOLUTION INTO A TEST-TUBE,t ADD A LITTLE WATER, AND FROM TEN TO TWENTY DROPS OF YELLOWISH SULPHIDE OF AMMONIUM, AND EXPOSE THE MIXTURE FOB A SHORT TIME TO A GENTLE HEAT, if * Compare 6. t If there is a somewhat large precipitate, this may be readily effected by means of a small spatula of platinum or horn ; but if you have only a very trifling precipitate, make a hole in the bottom of the filter, insert the perforated point into the mouth of the test- tube, rinse the precipitate into the latter by means of the washing-bottle, wait until the precipitate has subsided, and then decant the water. J If the solution contains copper, which is generally revealed by the color of the fluid, and may be ascertained positively by testing with a clean iron rod (see 120, 10), use solution of sulphide of sodium instead of sulphide of ammonium (in which sulphide of copper is not absolutely insoluble, see 120, 5), and boil the mixture. But if the fluid, besides copper, contains also oxide of mercury (the presence of which is generally suffi- ciently indicated by the several changes of color exhibited by the precipitate forming upon the addition of the hydrosulphuric acid [ 119, 3], and which, in doubtful cases, may be detected with positive certainty by testing a portion of the original solution acidified with hydrochloric acid with protochloride of tin), sulphide of ammonium must be used, although the separation of the sulphides of the antimony group from the DETECTION OF BASES. 233 1. THE PRECIPITATE DISSOLVES COMPLETELY IX SULPHIDE OF H5 AMMONIUM (or SULPHIDE OF SODIUM, as the case may be) : absence of the metals of Group Y. cadmium, lead, bismuth, copper, mercury. Treat the remainder of the precipitate (of which you have digested a portion with sulphide of ammonium) as directed 192. If the precipitate produced by hydrosulphuric acid was so trifling that you have used the whole of it in treating with sulphide of ammonium, pre- cipitate the solution obtained in that process by addition of hydro- chloric acid, filter, wash the precipitate, and treat it as directed 192. 2. THE PRECIPITATE IS NOT REDISSOLVED, OR AT LEAST NOT H6 COMPLETELY i presence of metals of Group V. Dilute with 4 or 5 parts of water, filter, and mix the filtrate with hydrochloric acid in slight excess. a. Tke fluid simply turns milky, owing to the separation of sulphur. Absence of the metals of Group VI. gold, platinum, tin, anti- mony, and arsenic.* Treat the rest of the precipitate (of which you have digested a portion with sulphide of ammonium) according to the directions of 193. b. A colored precipitate is formed : presence of metals of 117 Group VI. by the side of those of Group V. Treat the entire precipitate produced by hydrosulphuric acid the same as you have treated a portion of it, i.e., digest it with yellow sulphide of ammonium or, as the case may be, sulphide of sodium, let subside, pour the supernatant liquid on a filter, digest the residue in the tube once more with yellow sulphide of ammonium (or sulphide of sodium), and filter. Wash the residuet (con- taining the sulphides of Group V.), and treat it afterwards as directed 193. Dilute the filtrate which contains the metals of Group VI. in the form of sulphur salts with water, add hydro- chloric acid to distinctly acid reaction, heat gently, filter the pre- cipitate formed which contains the sulphides of the metals of Group VI. mixed with sulphur wash thoroughly, and proceed as directed next paragraph ( 192.) 192. (Detection of the Metals of Group VI. : Arsenic, Antimony, Tin, Gold, Platinum.) If the precipitate consisting of the sulphides of Group VI. has a 118 PURE YELLOW COLOR, this indicates principally arsenic and tin ; if sulphide of copper is not fully effected in such cases ; since, were sulphide of sodium used, the sulphide of mercury would dissolve in this reagent, which would impede the ulterior examination of the sulphides of the antimony group. * That this inference becomes uncertain if the precipitate produced by hydrosulphuric acid, instead of being digested with a small quantity of sulphide of ammonium, has been treated with a larger quantity of that reagent, is self-evident ; for the large quantity of sulphur which separates in that case will of course completely conceal any slight traces of sulphide of arsenic or bisulphide of tin which may have been thrown down. t If the residue suspended in the fluid containing sulphide of ammonium, and inso- luble.therein, subsides readily, it is not transferred to the filter, but washed in the tube by decantation. But if its subsidence proceeds slowly and with difficulty, it is transferred to the filter, and washed there ; a hole is then made in the bottom of the filter, and the residue rinsed into a small porcelain basin by means of a washing-bottle ; the application of a gentle heat will now materially aid the subsidence of the residue, and the super- natant water may then be decanted. The sulphides are occasionally suspended in the fluid in a state of such minute division that the fluid cannot be filtered off clear. In cases of the kind some chloride of ammonium should be added to the fluid. 234 ACTUAL EXAMINATION COMPLEX COMPOUNDS. it is distinctly CHANGE-YELLOW, antimony is sure to be present ; if it is BROWN or BLACK, this denotes the presence of platinum or gold. Beyond these general indications the color of the precipitate affords no safe guidance. It is therefore always advisable to test a yellow pre- cipitate also for antimony, gold, and platinum, since minute quantities of the sulphides of these metals are completely hid by a large quantity of bisulphide of tin or sulphide of arsenic. Proceed accordingly as follows : Heat a little of the precipitate on the lid of a porcelain crucible, or on a piece of porcelain or glass.* 1. Complete volatilization ensues : probable presence of 119 ARSENIC, absence of tbe other metals of Group VI. Re- duction of a portion of the precipitate with cyanide of potassium and carbonate of soda ( 132, 12)t will afford positive proof of the presence or absence of arsenic. Whether that metal was present in the form of arsenious acid or in that of arsenic acid, may be ascertained by the methods described 134, 9. 2. A fixed residue is left. In that case all the metals of 120 Group VI. must be sought for. Dry the remainder of the precipitate thoroughly upon the filter, triturate it together with about 1 part of anhydrous carbonate of soda and 1 part of nitrate of soda, and transfer the mixture in small portions at a time to a little porcelain crucible, in which you have previously heated 2 parts of nitrate of soda to fusion. J As soon as complete oxidation is effected, pour the mass out on a piece of porcelain. After cooling soak the fused mass (the portion still sticking to the inside of the crucible as well as the portion poured out on the porcelain) in cold water, filter from the insoluble residue which will remain if the mass contained antimony, tin, gold, or platinum and wash thoroughly with a mixture of about equal parts of water and alcohol. (The alcohol is added to prevent the solution of the anti- monate of soda. The washings are not added to the filtrate.) The filtrate and the residue are now examined as follows : a. EXAMINATION OF THE FILTRATE FOR ARSENIC (which 121 must be present in it in the form of arsenate of soda). Add nitric acid to the fluid to distinct acid reaction, * That this preliminary examination may be omitted if the precipitate has any other color than yellow, and that it can give a decisive result only if the sulphur precipitate submitted to the test has been thoroughly washed, is self-evident. f* In cases where tlie precipitate contains much free sulphur, dissolve the sulphide of arsenic which may be present, by digestion in the ammonia, filter, evaporate the solution, with addition of a small quantity of carbonate of soda, to dryness, and heat the residue with cyanide of potassium and carbonate of soda. Should the amount of the precipitate be so minute that this operation cannot be conveniently performed, cut the filter, with the dried precipitate adhering to it, into small pieces, triturate these together with some carbonate of soda and nitrate of soda, and pro- ject both the powder and the paper into the fusing nitrate of soda. It is preferable, however, in such cases, to procure at once, if practicable, a sufficiently large amount of the precipitate, as otherwise there will be but little hope of effecting the positive detec- tion of all the metals of Group VI. Supposing all the metallic sulphides of the sixth group to have been present, the fused mass would consist of antimonate and arsenate of soda, binoxide of tin, metallic gold and platinum, sulphate, carbonate, nitrate, and some nitrite of soda. Compare also 134, 1. In some cases where a somewhat larger proportion of carbonate of soda has been used, or a very strong heat applied, a trifling precipitate (hydrated binoxide of tin) may separate upon the acidification of the filtrate with nitric acid. This may be filtered off, and then treated in the same manner as the undissolved residue. DETECTION OF BASES. 235 heat, to expel carbonic acid and nitrous acid, then divide the fluid into two portions. Add to the one portion some nitrate of silver (not too little), filter (in case chloride of silver* or nitrite of silver should have separated), pour upon the filtrate, along the side of the tube held slanting, a layer of dilute solution of ammonia 2 parts of water to 1 part of solution of ammonia and let the mixture stand for some time without shaking. The formation of a reddish-brown precipitate, which appears hovering cloud-like between the two layers (and may be seen far more readily aad distinctly by reflected than by transmitted light), denotes the presence of ARSENIC. If the arsenic is present in some quantity, and the free nitric acid of the solution is exactly saturated with ammonia, the fluid being stirred during this process, the precipitate of arsenate of silver which forms imparts a brownish-red tint to the entire fluid. Add to the other portion of the acidified solution, first 122 ammonia, then a mixture of sulphate of magnesia and chloride of ammonium, and rub the sides of the vessel with a glass rod. A crystalline precipitate of arsenate of magnesia and ammonia, which often forms only after long standing, and deposits the crystalline particles more particularly on the side of the vessel, shows the presence of arsenic. By way of confirmation, the arsenic compound may be reduced to the metallic state (compare 132 and 133). Whether the arsenic was present in the form of arsenious acid or in that of ar- senic acid, may be ascertained by the methods described 134, 9. b. EXAMINATION OF THE RESIDUE FOR ANTIMONY, TIN, 123 GOLD, PLATINUM. (As the antimony, if present in the residue, must exist as white pulverulent antimonate of soda, the tin as white flocculent biuoxide, the gold and platinum in the metallic state, the appearance of the residue is in itself in- dicative of its nature.) Transfer the precipitate to the inverted lid of a platinum crucible, or to a small platinum dish, heat with hydrochloric acid, add a little water, and throw in a small com- pact lump of pure zinc (more particularly, free from lead), no matter whether the precipitate has completely dissolved or not in the hydrochloric acid. This operation leaves the gold and platinum in the same state in which the fused mass contained them, viz., in the metallic state, to which the tin and antimony are now likewise reduced by the action of the zinc. The antimony reveals its presence at once, or after a short time, by blackening the platinum. As soon as the disengagement of hydrogen has pretty nigh stopped, take out the lump of zinc, remove the solu- tion of chloride of zinc by cautious decantatiou, treat the metals with hydrochloric acid, and test the solution which, if tin is present, must contain protochloride of tin with chloride of mercury ( 129,8). After removing the tin by repeated boiling with hydro- 124: * Chloride of silver will separate if the reagents were not perfectly pure, or the precipitate has not been thoroughly washed. 233 ACTUAL EXAMINATION COMPLEX COMPOUNDS. chloric acid, and all the hydrochloric acid by thoroughly washing with water, examine the insoluble residue (if one is left) as follows : Heat it in the platinum dish with some water, with addition of a few grains of tartaric acid, then add some nitric acid, and heat gently. If the residue dissolves com- pletely, no gold or platinum is present ; if a residue is left un- dissolved, you must test it for these metals. For this purpose remove the acid solution (which may be tested again for ANTI- MONY with hydrosulphuric acid) by decantation and washing, heat the residue, transferred to a porcelain dish, with a little aqua regia, evaporate the solution until but little of it is left, and test this small remainder for GOLD and PLATINUM as directed 128. 193. (Detection~of tJie Metallic Oxides of Group V., 2nd Division : Oxide of Lead, Teroxide of Bismuth, Oxide of Copper, Oxide of Cadmium, Oxide of Mercury!) THOROUGHLY WASH THE PRECIPITATE WHICH HAS NOT BEEN DIS- 125 SOLVED BY SULPHIDE OF AMMONIUM, AND BOIL WITH NITRIC ACID. This operation is performed best in a small porcelain dish : the boiling mass must be constantly stirred with a glass rod during the process. A great excess of acid must be avoided. 1. THE PRECIPITATE DISSOLVES, AND THERE REMAINS FLOATING IN 126 THE FLUID ONLY THE SEPARATED LIGHT FLOCCULENT AND YELLOW SULPHUR ; this indicates the absence of mercury. CADMIUM, COPPER, LEAD, and BISMUTH may be present. Filter the fluid from the separated sulphur, and treat the filtrate as follows (should there be too much nitric acid present, the greater part of this must first be driven off by evaporation) : add to a portion of the filtrate dilute sulphuric acid in moderate quantity, heat gently, and let the fluid stand some time. a. No PRECIPITATE FORMS ; absence of lead. Mix the re- 127 mainder of the filtrate with ammonia in excess, and gently heat. a. No precipitate is formed; absence of BISMUTH. If the 128 liquid is blue, COPPER is present ; very minute traces of copper, however, might be overlooked if the color of the ammoniated fluid alone were consulted. To be quite safe, and also to test for cadmium, evaporate the ammoniated solution nearly to dryness, add a little acetic acid, and, if necessary, some water, and aa. Test a small portion of the fluid for copper with 129 ferrocyanide of potassium. The formation of a reddish- brown precipitate, or a light brownish-red turbidity, in- dicates the presence of COPPER (in the latter case only to a very trifling amount). bb. Mix the remainder of the fluid with solution of 130 hydrosulphuric acid in excess. The formation of a yellow precipitate denotes CADMIUM. If, on account of the pre- sence of copper, the sulphide of cadmium cannot be distinctly recognised, allow the precipitate produced by the hydrosulphuric acid to subside, decant the supernatant fluid, and add to the precipitate solution of cyanide of potassium until the sulphide DETECTION OF BASES. 237 of copper is dissolved. If a yellow residue is left undis- solvecl, CADMIUM is present ; in the contrary case, not. j3. A precipitate is formed. BISMUTH is present. Filter 131 the fluid, and test the nitrate for copper and cadmium as directed in (128)- To test the washed precipitate more fully for bismuth, slightly dry the filter containing it between blotting-paper, remove the still moist precipitate with a platinum spatula, dissolve on a watch-glass in the least possible quantity of hydrochloric acid, and then add a proper quantity of water. The appearance of a milky turbidity confirms the presence of bismuth. b. A PRECIPITATE is FORMED. Presence of LEAD. Mix 132 the whole of the nitric acid solution in a porcelain dish with a sufficient quantity of dilute sulphuric acid, evaporate on the water-bath until the nitric acid is expelled, dilute the residue with some water containing sulphuric acid, filter off at once the sulphate of lead left undissolved, and test the filtrate for bismuth, copper, and cadmium, as directed in (127)-* Test the precipi- tate, after washing, by one of the methods described in 123. 2. THE PRECIPITATE OP THE METALLIC SULPHIDES DOES NOT 133 COMPLETELY DISSOLVE IN THE BOILING NITRIC ACID, BUT LEAVES A RESIDUE, BESIDES THE LIGHT FLAKES OF SULPHUR THAT FLOAT IN THE FLUID. Probable presence of OXIDE OF MERCURY (which may be pronounced almost certain if the precipitate is heavy and black). Allow the precipitate to subside, filter off the fluid, which is still to be tested for CADMIUM, COPPER, LEAD, and BISMVTH ; mix a small portion of the filtrate with a large amount of solution of hydrosulphuric acid, and should a precipitate form or a coloration become visible, treat the re- mainder of the filtrate according to the directions of (126)- Wash the residue (which may, besides sulphide of mercury, also con- tain sulphate of lead, formed by the action of nitric acid upon sulphide of lead, and also binoxide of tin, and possibly sulphide of gold arid sul- phide of platinum, as the separation of the sulphides of tin, gold, and platinum from the sulphides of the metals of the fifth group is often incomplete), and examine one half of it for mercury,t by dissolving it in some hydrochloric acid, with addition of a very small proportion of chlorate of potassa, and testing the solution with copper or protochloride of tin ( 119) ; fuse the other half with cyanide of potassium and carbonate of soda, and treat the fused mass with water. If metallic grains remain, or if a metallic powder is left undissolved, wash this residue, heat with nitric acid, and test the solution obtained with sulphuric acid for lead. Wash the residue which the nitric acid may leave undissolved, and extract from it any hydrate of metastanuic acid which it may contain, according to the directions of 130, 1, as metastannic chloride. Should a metallic powder be left undissolved in the process, heat it with aqua regia, and test the solution for gold and platinum as directed 128. * For another method of distinguishing cadmium, copper, lead, and bismuth from each other, I refer to the Third Section (additions and remarks to 193). f If you have an aqueous solution, or a solution in very dilute hydrochloric acid, the oxide of mercury formed was present in the original substance in that form ; but if the solution has been prepared by boiling with concentrated hydrochloric acid, or by heating with nitric acid, the mercury may most likely have been originally present in the form of suboxide, and may have been converted into oxide in the process. 238 ACTUAL EXAMINATION COMPLEX COMPOUNDS. 1^4. (Precipitation with Sulphide of Ammonium, Separation and Detection of the Oxides of Groups ill. an d IV : Alumina, Sesquioxide of Chromium ; Oxide of Zinc, Protoxide of Manganese, Protoxide of Nickel, Prot- oxide of Cobalt, Proto- and Sesquioxide of Iron ; and also of those Salts of the Alkaline Earths which are precipitated by Ammonia from their Solution in Hydrochloric Acid : Pliospliates, Borates, Oxalates, Silicates, and Fluorides.) PUT A small portion OF THE FLUID IN WHICH SOLUTION OF HYDRO- 134 SULPHURIC ACID HAS FAILED TO PRODUCE A PRECIPITATE (HQ), OR OF THE FLUID WHICH HAS BEEN FILTERED FROM THE PRECI- PITATE FORMED (112), in & test-tube, observe whether it is colored or not,* boil to expel the hydrosulphuric acid which may be present, add a few drops of nitric acid, boil, and observe again the color of the fluid ', then cautiously add ammonia to alkaline reaction, observe whether this produces a precipitate, then add some sulphide of ammonium, on matter whether ammonia has produced a precipitate or not. a. NEITHER AMMONIA NOR SULPHIDE OF AMMONIUM PRO- 135 DUCES A PRECIPITATE. Pass on to 195, for iron, nickel, cobalt, zinc, manganese, sesquioxide of chromium, alumina, are not present, nor are phosphates, borates,t silicates, and oxalates J of the alkaline earths; nor fluorides of the metals of the alkaline earths, nor silicic acid originally in combination with alkalies. * b. SULPHIDE OF AMMONIUM PRODUCES A PRECIPITATE, AMMO- 136 NIA HAVING FAILED TO DO so; absence of phosphates, borates,t silicates, and oxalatesj of the alkaline earths ; of the fluorides of the metals of the alkaline earths ; of silicic acid originally in combination with alkalies ; and also, if no organic matters are present, of iron, sesquioxide of chromium, and alumina. Pass on to (138). c. AMMONIA PRODUCES A PRECIPITATE before the addition 137 of sulphide of ammonium. The course of proceeding to be pursued now depends upon whether, (a) the original solution is simply aqueous, and has a neutral reaction, or (/3) the original solution is acid or alkaline. In the former case pass on to (138)> since phosphates, borates, oxalates, and silicates of the alkaline earths cannot be present ; nor can fluorides of the metals of the alkaline earths, nor, lastly, silicic acid in combination with alkalies. * If the fluid is colorless, it contains no chromium. If colored, the tint will to some extent act as a guide to the nature of the substance present ; thus a green tint, or a violet lint turning green upon boiling, points to the presence of chromium ; a light green tint to that of nickel ; a reddish color to that of cobalt ; the turning yellow of the uid upon boiling with nitric acid to that of iron. It must, however, be always borne in mind that these tints are perceptible only if the metallic oxides are present in larger quantity, and also that complementary colors, such as, for in=tance, the green of the nickel solution and the red of the cobalt solution will destroy each other, and that, accordingly, a solu- tion may contain both metals arid yet appear colorless. *t* Presence of much chloride of ammonium has a great tendency to prevent the pre- cipitation of borates of the alkaline earths. J Oxalate of magnesia is thrown down from hydrochloric acid solution by ammonia after some time only, and never completely ; dilute solutions are not precipitated by ammonia. DETECTION OF BASES. 239 In the latter case regard must be had to the possible presence of all the bodies enumerated in (135) ' P as s on to (150) 1. DETECTION OF THE BASES OF GROUPS III. AND IV. IF PHOS- 138 PHATES, &C., OF THE ALKALINE EARTHS ARE NOT PRESENT.* Mix the fluid mentioned at the beginning of the paragraph (134)> a portion of which you have submitted to a preliminary exami- nation, with some chloride of ammonium, then with ammonia, just to alkaline reaction, lastly with sulphide of ammonium until the fluid, after being shaken, smells distinctly of that reagent ; shake the mixture until the precipitate begins to separate in flakes, heat gently for some time, and filter. Keep the FILTRATED which contains, or may contain, the bases of Groups II. and I., for subsequent examination according to the directions of 195. Wash the PRECIPITATE with water to which a very little sulphide of ammonium has been added, then proceed with it as follows : a. IT HAS A PURE WHITE COLOR ; absence of iron, cobalt, 139 nickel. You must test for all the other bases of Groups III. and IV., as the faint tints of sesquioxide of chromium and sul- phide of manganese are imperceptible in a large quantity of a white precipitate. Dissolve the precipitate by heating it in a small dish with the least possible amount of hydrochloric acid ; boil should hydrosulphuric acid be evolved until this is completely expelled, concentrate by evaporation to a small residue, add concentrated solution of soda in excess, heat to boiling, and keep the mixture for some time in a state of ebullition. a. T/ie precipitate formed at first dissolves 'completely in 140 the excess of solution of soda. Absence of manganese and chromium, presence of alumina or oxide of zinc. Testa portion of the alkaline solution with solution of hydrosulphuric acid for ZINC ; acidify the remainder with hydrochloric acid, add ammonia slightly in excess, and apply heat. The formation of a white flocculent precipitate shows the presence of ALUMINA. /3. The precipitate formed does not dissolve, or dissolves 141 only partially, in the excess of solution of soda. Filter and test the FILTRATE, as in (140)j for ZINC and ALUMINA. With the undissolved PRECIPITATE, which, if containing manganese, looks brown or brownish, proceed as follows : aa. If the color of the solution gives you no reason to suspect the presence of chromium, test the precipitate for manganese, by means of the reaction with carbonate of soda in the outer blowpipe flame. bb. But where the color of the solution indicates 142 chromium, the examination of the residue insoluble in solution of soda is more complicated, since it may in that case contain also oxide of zinc, possibly even the whole * This simpler method will fully answer the purpose in most cases ; for very accu- rate analysis the method beginning at (150) is preferable, as this will permit also the detection of minute quantities of alkaline earths, which may have been thrown down together with the alumina and sesquioxide of chromium. f If the filtrate has a brownish color, this points to the presence of nickel, sulphide of nickel, as is well known, being, under certain circumstances, slightly soluble in. sulphide of ammonium; this, however, involves no modification of the analytical course. 240 ACTUAL EXAMINATION COMPLEX COMPOUNDS. quantity present of this metal (11 2). Dissolve the preci- pitate therefore in hydrochloric acid, evaporate the solution to a small residue, dilute, nearly neutralize the free acid with car- bonate of soda, add carbonate of baryta in slight excess, let the fluid digest in the cold until it has become colorless, filter, and test the precipitate for CHROMIUM, by fusion with carbonate of soda and nitrate of soda ( 102, 8). Remove the baryta from the filtrate, by precipitating with some sulphuric acid, filter, evaporate to a small residue, add concentrated solution of potassa or soda in excess, and test the filtrate for ZINC with hydrosulphuric acid, the precipitate, if any, for MANGANESE as in aa. b. IT is NOT WHITE ; this points to the presence of 143 chromium, manganese, iron, cobalt, or nickel. If it is black, or inclines to black, one of the three metals last-mentioned is present. Under any circumstances all the oxides of Groups III. and IV. must be looked for. .Remove the washed precipitate from the filter with a spatula, or by rinsing it with the aid of a washing-bottle, through a hole made in the bottom of the filter, into a test-tube, and pour over it rather dilute cold hydrochloric acid in moderate excess. a. It dissolves completely (except perhaps a little sulphur, 144 which may separate) ; absence of cobalt and nickel, at least of notable quantities of these two metals. Boil until the hydrosulphuric acid is completely expelled, filter if particles of sulphur are suspended in the fluid, concentrate by evaporation 'to a small residue, add concentrated solution of potassa or soda in excess, boil, filter the fluid from the insoluble precipitate which is sure to remain, wash the latter, and proceed first to examine the filtrate, then the precipitate. aa. Test a small portion of the filtrate with hydro- 145 sulphuric acid for zinc; acidify the remainder with hydrochloric acid, then test with ammonia for ALUMINA. Compare (140). bb. Dissolve a small portion of the precipitate in hydro- 146 chloric acid, and test the solution with sulphocyanide of potassium for IRON. Test another portion for CHROMIUM, by fusing together with carbonate and nitrate of soda ( 102, 8). If no chromium has been found, examine the remainder for MANGANESE, by the reaction of carbonate of soda in the oxidizing flame. If chromium is present, on the other hand, test the remainder of the precipitate for manganese and zinc (of which latter metal the precipitate may in that case possibly contain the entire quantity originally present in the com- pound under examination ['11 2] ) as directed (142)- ]3. The precipitate is not completely dissolved, a black re- 147 sidue being left ; this indicates the presence of cobalt and nickel. Filter, wash the undissolved precipitate, and test the filtrate as directed (144) j proceed with the residuary precipitate as follows : aa. Test a small portion of it with borax, first in the 148 outer, then in the inner blowpipe-flame. If the bead in the oxidizing flame is violet whilst hot, and of a pale DETECTION OF BASES. reddish-brown when cold, and turns in the reducing flame gray and turbid, NICKEL is present ; but if the color of the bead is and remains blue in both flames, and whether hot or cold, COBALT is present. As in the latter case the pre- ' sence of nickel cannot be distinctly recognised, examine bb. The remainder of the precipitate by incinerating 149 it together with the filter in a coil of platinum wire, heating the ash with some hydrochloric acid, filtering the solution, then evaporating nearly to dryness, and adding nitrite of potassa and, lastly, acetic acid ( 109, 10). If a yellow precipitate forms, after standing for some time at a gentle heat, this confirms the presence of COBALT. Filter after about twelve hours, and test the filtrate with solution of soda for nickel. 2. DETECTION OF THE BASES OF GROUPS III. AND IV. IN CASES 150 WHERE PHOSPHATES, BORATES, OXALATES, OR SILICATES OF THE AL- KALINE EARTHS, OR FLUORIDES OF THE METALS OF THE ALKALINE EARTHS, OR HYDRATE OF SILICIC ACID, MAY POSSIBLY HAVE BEEN THROWN DOWN ALONG WITH THESE BASES, i.e., in cases where the original solution was acid or alkaline, and a precipitate was produced by ammonia in the preliminary examination. See (134). Mix the fluid mentioned in (134) with some chloride of ammonium, then with ammonia just to alkaline reaction, lastly with sulphide of ammonium until the fluid, after being shaken, smells distinctly of the reagent ; shake the mixture until the precipitate begins to separate in flakes, heat gently for some time, and filter. Keep the FILTRATE, which contains, or may contain, the bases of Groups II. and I., for subsequent examination according to the directions of 195. Wash the precipitate with water to which a very little sulphide of ammonium has been added, then proceed with it as directed in (152)- To give a clear notion of the obstacles to be overcome in this analytical process, I must remind you that it is necessary to examine the precipitate for the following bodies : Iron, nickel, cobalt (these show their presence to a certain extent by the black or blackish coloration of the precipitate), manganese, zinc, sesquioxide of chromium (the latter generally reveals its presence by the color of the solution), alumina; baryta, strontia, lime, magnesia, which latter substances may have fallen down in combination with phos- phoric acid, boracic acid, oxalic acid, silicic acid, or in form of fluorides. Besides these bodies, free silicic acid may also be contained in the precipitate as hydrate. As the original substance must, under all circumstances, be 151 afterwards examined for all acids that might possibly be present, it is not indispensable to test for the above enumerated acids at this stage of the analytical process ; still, as it is often interesting to know these acids at once, more especially in cases where a somewhat large proportion of some alkaline earth has been found in the precipitate produced by sulphide of ammonium, a method for the detection of th^ acids in question will be found appended by way of supplement to the method for the detection of the bases. Remove the precipitate from the filter with a small spatula, or 152 by rinsing it off" with the washing-bottle, and pour over it cold dilute hydrochloric acid in moderate excess. a. A RESIDUE REMAINS, filter, and treat the filtrate as 153 I. K 242 ACTUAL EXAMINATION COMPLEX COMPOUNDS. directed in (154)- The residue, if it is black, may contain sulphide of nickel and sulphide of cobalt and, besides these, sulphur and silicic acid. Wash, and examine a sample of it in conjunction with phosphate of soda and ammonia before the blowpipe, in the outer flame. If a silica skeleton remains undissolved ( 150, 8), this proves the presence of silicic acid. If the color of the bead is blue, COBALT is present ; if reddish, turning yellow on cooling, NICKEL. Should the color leave you in doubt, incinerate the filter containing the remainder of the residue, and test for cobalt and nickel by means of nitrite of potassa, as directed (149)- I. No RESIDUE is LEFT (except perhaps a little sulphur, 154 which may separate) : absence of nickel and cobalt, at least in any notable proportion. Boil the solution until the sulphuretted hydrogen is ex- pelled, filter if necessary, and then proceed as follows : a. Mix a small portion of the solution with dilute 155 sulphuric acid. If a precipitate forms, this may consist of sulphates of BARYTA and STRONTIA, possibly also of sulphate of lime. Filter, wash the precipitate, and examine it either by the coloration of flame (see 99, at the end), or decompose it by boiling or fusion with carbonated alkali, wash the carbonates pro- duced, dissolve them in hydrochloric acid, and test the solution as directed 195. Mix the fluid which has not been precipitated by dilute sulphuric acid, or the fluid filtered from the precipitate produced, with 3 volumes of spirit of wine. If a precipitate forms, this consists of sulphate of LIME. Filter, dissolve in water, and add oxalate of ammonia to the solution, as a confirmatory proof of the presence of lime. /3. Heat a somewhat larger sample with some nitric 156 acid, and test a small portion of the fluid with sulpho- cyanide of potassium for IRON ;* mix the remainder with sesquichloride of iron in sufficient quantity to make a drop of fluid give a yellowish precipitate t when mixed on a watch-glass with a drop of ammonia ; evaporate the fluid now until there is only a small quantity left ; add to this some water, then a few- drops of solution of carbonate of soda, just sufficient to nearly neutralize the free acid, and lastly carbonate of baryta in slight excess ; stir the mixture, and let it stand in the cold until the fluid above the precipitate has become colorless. Filter now the precipitate (aa) from the solution (i6), and wash. aa. Boil the precipitate for some time with solution of 157 soda, filter, and test the filtrate for ALUMINA, J by heating * Whether the iron was present as sesquioxide or as protoxide, must be ascertained by testing the original solution in hydrochloric acid with ferricyanide of potassium and sulphocyanide of potassium. f The addition of sesquichloride of iron is necessary, to effect the separation of phos- phoric acid and silicic acid which may be present. J If the solution contains silicic acid, the precipitate" taken for alumina may also eon- tain silicic acid. A simple trial with phosphate of soda and ammonia, on a platinum wire, in the blowpipe flame, will show whether the precipitate really contains silicic acid.' Should this be the case, ignite the remainder of the supposed alumina precipi- tate on the lid of a platinum crucible, add some acid sulphate of potassa,, fuse the mixture, and treat the fused mass with hydrochloric acid, which will dissolve the alumina, leaving the silicic acid undissolved ; precipitate the alumina from the solu- tion by ammonia. DETECTION OF BASES. 213 with chloride of ammonium in excess. The part of the precipitate insoluble in solution of soda is examined for CHRO- MIUM, by fusion with nitrate of potassa and carbonate of soda ( 102, 8). bb. Mix the solution first with a few drops of hydrochloric acid, boil to expel the whole of the carbonic acid, then add some ammonia and sulphide of ammonium. aa. No precipitate- forms : absence of manganese 158 and zinc. Mix the solution containing chloride of barium with dilute sulphuric acid in slight excess, boil, filter, supersaturate with ammonia, and mix with oxalate of ammonia. If a precipitate of oxalate of LIME forms, filter, and test the filtrate with phosphate of soda for magnesia. (3{3. A precipitate forms. Filter, and proceed with 159 the filtrate according to the directions of (158)- The precipitate may consist of sulphide of manganese and sulphide of zinc, and may contain traces also of sulphide of cobalt and sulphide of nickel. Wash it with water containing some sulphide of ammonium, then treat with acetic acid, which will dissolve the sulphide of MANGANESE, if any is present, leaving the other sulphides undissolved. Filter, boil the filtrate with solution of soda, and test the precipitate, which may form, with carbonate of soda in the outer blowpipe flame for MANGANESE. Free the residuary part of the precipitate which acetic acid has failed to dissolve, by washing, from the acetic acid solution still adhering to it, and then treat it with dilute hydrochloric acid, which will dissolve the zinc, if any is present. Filter, add some nitric acid to the filtrate, and concentrate the mixture considerably by boiling ; then add to it concentrated solution of soda in excess, boil, filter if necessary, and test the filtrate with sulphide of ammonium for ZINC. Should a precipitate insoluble in solution of soda remain in the last operation, or should the dilute hydrochloric acid have left a black residue, test this precipitate and residue for COBALT and NICKEL, if you have not already previously detected the presence of these bodies ; compare (148 and 149)- y. If you have found alkaline earths in a and /3, and 160 wish to know the acids in combination with which they have passed into the precipitate produced by sulphide of ammonium, this may be ascertained by making the following experiments with the remainder of the hydrochloric acid solution. aa. Evaporate a small portion in a small dish or on a 161 watch-glass on the water-bath, dry the residue thoroughly, then treat with hydrochloric acid. If there was any SILICIC ACID in the solution, this will be left undissolved. Test the solution now for PHOSPHORIC ACID, by means of molybdic acid( 142, 10). bb. Mix another portion with carbonate of soda in excess, boil for some time, filter, and test one-half of the Bltrate for OXALIC ACID, by acidifying with acetic acid and adding solution R2 244 ACTUAL EXAMINATION COMPLEX COMPOUNDS. of sulphate of lime ; the other half for BORACIC ACID, by slightly acidifying with hydrochloric acid, and testing with turmeric-paper ( 144 and 145.) cc. Precipitate the remainder with ammonia, filter, 162 wash and dry the precipitate, and examine it for FLUORINE according to 146, 5. 195. (Separation and Detection of the Oxides of Group II. which are precipi- tated by Carbonate of Ammonia in Presence of Chloride of Ammonium, viz., Baryta, Strontia, Lime). TO A SMALL PORTION OF THE FLUID IN WHICH AMMONIA AND SUL- PHIDE OF AMMONIUM HAVE FAILED TO PRODUCE A PRECIPITATE (135), OR OF THE FLUID FILTERED FROM THE PRECIPITATE FORMED, ADD CHLO- RIDE OF AMMONIUM, IF THE SOLUTION CONTAINS NO AMMONIACAL SALT, THEN CARBONATE OF AMMONIA AND SOME CAUSTIC AMMONIA, AND HEAT FOR SOME TIME VERY GENTLY (not to boiling). 1. No PRECIPITATE FORMS i absence of any notable quantity of 163 baryta, strontia, and lime. Traces of these alkaline earths may, however, be present : to detect them, add to another portion of the fluid some sulphate of ammonia (prepared by supersaturating dilute sulphuric acid with ammonia) : if the fluid becomes turbid, it contains traces of BARYTA ; add to a third portion some oxalate of ammonia ; if the fluid turns turbid which reaction may perhaps require sometime to manifest itself traces of lime are present. Treat the remainder of the fluid as directed 196, after having previously removed the traces of lime and baryta which may have been found, by means of the reagents that have served to effect their detection. 2. A PRECIPITATE is FORMED. Presence of LIME, BARYTA, or 164 STRONTIA. Treat the whole fluid of which a portion has been tested with ammonia, and carbonate of ammonia, the same as the sample, filter off the precipitate formed, after gently heating, as directed above, and test portions of the filtrate with sulphate and oxalate of ammonia for traces of lime and baryta, which it may possibly still con- tain ; remove such traces, should they be found, by means of the said reagents, and examine the fluid, thus perfectly freed from baryta, strontia, and lime, for magnesia according to the directions of 196. Wash the precipitate produced by carbonate of ammonia, dissolve it in the least possible amount of dilute hydrochloric acid, and add to a small portion of the fluid a sufficient quantity of solution of sulphate of lime. a. No precipitate is formed, NOT EVEN AFTER THE LAPSE OF SOME TIME. Absence of baryta and strontia ; presence of LIME. To remove all doubt, mix another sample with oxalate of ammonia. b. A precipitate is formed by solution of sulphate of lime. a. It is formed immediately; this indicates BARYTA. 165 Besides this, strontia and lime may also be present. Evaporate the remainder of the hydrochloric acid solu- [ tion of the precipitate produced by carbonate of ammonia to dry ness, digest the residue with strong alcohol, decant the fluid from the uridissolved chloride of barium, dilute with an equal volume of water, mix with a few drops of hydrofluosilicic acid DETECTION OP OXIDES. which will throw down the small portion of baryta that had dis- solved in form of chloride of barium allow the mixture to stand for some time ; filter, and mix the filtrate with dilute sulphuric acid. The formation of a precipitate indicates the presence of strontia or lime, or of both. Filter after some time, wash the precipitate with weak spirit of wine, boil with solution of car- bonate of soda, to convert the sulphates into carbonates, filter these off, wash, dissolve in hydrochloric acid, evaporate the solution to dryness, dissolve the residue in water, and test a portion of the solution with dilute solution of sulphate of potassa ( 96, 3). If a precipitate forms immediately, or in the course of half an hour, the presence of STRONTIA is demonstrated. In that case let the fluid with the precipitate in it stand at rest for some time, then filter, and add ammonia and oxalate of am- monia to the filtrate. The formation of a white precipitate indicates LIME. If sulphate of potassa has failed to produce a, precipitate, the remainder of the solution of the residue left upon evaporation is tested at once with ammonia and oxalate of ammonia for lime. /3. It is formed only after some time. Absence of baryta, 166 presence of STRONTIA. Mix the remainder of the hydro- chloric acid solution with sulphate of potassa, let the mixture stand for some time, then filter, and test the filtrate with ammonia and oxalate of ammonia for LIME. 196. (Examination for Magnesia.) To A PORTION OF THE FLUID IN WHICH CARBONATE, SULPHATE, AND OXALATE OF AMMONIA HAVE FAILED TO PRODUCE A PRECIPITATE (163) OR OF THE FLUID FILTERED FROM THE PRECIPITATES FORMED (164), ADD AMMONIA, THEN SOME PHOSPHATE OF SODA, AND, SHOULD A PRECIPITATE NOT AT ONCE FORM, RUB THE INNER SIDES OF THE GLASS-TUBE WITH A GLASS ROD, AND LET THE MIXTURE STAND FOR SOME TIME. 1. No PRECIPITATE is FORMED ; absence of magnesia. Evapo- 167 rate another portion of the fluid to dryness,* and ignite gently. If a residue remains, treat the remainder of the fluid the same as the sample, and examine the residue, which by the moderate ignition to which it has been subjected has been freed from ammonia, for potassa and soda, according to the directions of 197. If no residue is left t this is a proof of the absence of the fixed alkalies ; pass on at once to 198. 2. A PRECIPITATE is FORMED : presence of MAGNESIA. As testing 168 for alkalies can proceed with certainty only after the removal of magnesia, evaporate the remainder of the fluid to dryness, and ignite until all ammoniacal salts are removed. Warm the residue with some water, add baryta-water (prepared from the crystals) as long as a precipitate continues to form, boil, filter, add to the filtrate a mixture of carbonate of ammonia with some caustic ammonia in slight excess, heat for some time gently, niter, evaporate the filtrate to dry u ess, * The most convenient way is to conduct the evaporation on the lid of a platinum crucible. EXAMINATION FOR POTASSA AND SODA. adding some chloride of ammonium during the process (to convert into chlorides the caustic alkalies or alkaline carbonates that may happen to form), ignite the residue gently, then dissolve in a little water, precipi- tate if necessary once more with ammonia and carbonate of ammonia, evaporate again, and if a residue remains, ignite this gently, and examine it according to the directions of 197. (Examination for Polassa and Soda.) YOU HAVE NOW TO EXAMINE FOR POTASSA AND SODA THE GENTLY IGNITED RESIDUE, FREE FROM SALTS OF AMMONIA AND ALKALINE EARTHS, WHICH HAS BEEN OBTAINED IN (167)> O R IN (168)- Dissolve it in a little water, filter if necessary, evaporate until there is only a small quantity of fluid left, and transfer one-half of this to a watch-glass, leaving the other half in the porcelain dish. 1. To the one-half in the porcelain dish add, after cooling, a few 169 drops of solution of bichloride of platinum. If a yellow crystal- line precipitate forms immediately, or after some time, POTASSA is present. S hould no precipitate form evaporate to dryness at a gentle heat, and t eat the residue with a very small quantity of water, or, if chlorides alone are present, with a mixture of water and alcohol, when the presence of minute traces of potassa will be revealed by a small quantity of a heavy yellow powder being left undissolved ( 89, 3). 2. To the other half of the fluid (on the watch-glass) add some 170 antimonate ofpotassa. If this produces at once or after some time a crystalline precipitate, SODA is present. If the quantity of soda present is only very trifling, it often takes twelve hours before minute crystals of antimonate of soda will separate; you must therefore always 'wait full that time for the possible manifestation of the reaction, before deciding from its non-appearance that no soda is present. As regards the form of the crystals, consult 90, 2. 198. (Examination for Ammonia.) THERE REMAINS STILL THE EXAMINATION FOR AMMONIA. Tritu- 171 rate some of the body under examination or, if a fluid, a portion of the latter, together with an excess of hydrate of lime, and, if necessary, a little water. If the escaping gas smells of ammonia, if it restores the blue color of reddened litmus-paper, and forms white fumes with hydrochloric acid vapors, brought into contact with it by means of a glass rod, AMMONIA is present. The reaction is the most sensitive if the trituration is made in a small beaker, and the latter covered with a glass plate with a slip of moistened turmeric or moist reddened litmus- .paper adhering to the under side. DETECTION OF ACIDS. 247 Complex Compounds. A, 1. SUBSTANCES SOLUBLE IN WATER. DETECTION OF ACIDS.* I. In the Absence of Organic Acids. 199. Consider, in the first place, which are the acids that form with the bases found compounds soluble in water, and let this guide you in the examination. To students the table given in Appendix IV. will prove of considerable assistance. 1. The ACIDS of ARSENIC, as well as CARBONIC ACID, HYDROSUL- 172 PHURIC ACID, CHROMIC ACID, and SILICIC ACID, have generally been detected already in the course of testing for the bases ; see (67) and (68). 2. Add to a portion of the solution chloride of barium or, if lead, silver, or suboxide of mercury are present, nitrate of baryta, and, should the reaction of the fluid be acid, add ammonia to neutral or slightly alkaline reaction. a. No PRECIPITATE is FORMED : absence of sulphuric acid, 173 phosphoric acid, chromic acid, silicic acid, oxalic acid, arse- nious and arsenic acids, as well as of notable quantities of boracic acid and hydrofluoric acid.t Pass on to (175)- b. A PRECIPITATE is FORMED. Dilute the fluid, and add 174 hydrochloric acid or, as the case may be, nitric acid ; if the precipitate does not redissolve, or at least not completely, SULPHURIC ACID is present. 3. Add nitrate of silver to a portion of the solution. If this 175 fails to produce a precipitate, test the reaction, and if acid, add to the fluid some dilute ammonia, taking care to add the reagent so gently and cautiously that the two fluids do not intermix ; if the re- action is alkaline, on the other hand, add with the same care some dilute nitric acid, instead of ammonia, and watch attentively whether a precipitate or a cloud will form in the layer between the two fluids. a. No PRECIPITATE IS FORMED IN THE LAYER BETWEEN THE 176 TWO FLUIDS, NEITHER IMMEDIATELY NOR AFTER SOME TIME, Pass on to (181) j there is neither chlorine, bromine, iodine, cyanogen, J ferro- and ferricyanogen present, nor sulphur; nor phosphoric acid, arsenic acid, arsenious acid, chromic acid, silicic acid, oxalic acid j nor boracic acid, if the solution was not too dilute. b. A PRECIPITATE is FORMED. Observe the color of it, 177 then add nitric acid, and shake the mixture. * Consult also the explanations in Section III. f If the solution contains an ammoniacal salt in somewhat considerable proportion, the non- formation of a precipitate cannot be considered a conclusive proof of the absence of these acids, since the baryta salts of most of them (not the sulphate) are in pre- sence of ammoniacal salts more or less soluble in water. That the cyanogen in cyanide of mercury is not indicated by nitrate of silver has been mentioned (73)- Chloride, bromide, cyanide, and ferrocyanide ot silver, and oxalate, silicate, and boz-ate of silver are white ; iodide of silver, tribasic phosphate, and arsenite of silver are yellow ; arsenate of silver and ferricyanide of silver are brownish-red ; chromate of silver is purple-red ; sulphide of silver black. 248 DETECTION OF ACIDS. a. The precipitate redissolves completely : absence of chlorine, bromine, iodine, cyanogen, ferro- and ferricyanogen, and also of sulphur. Pass on to (181). /3. A residue is left : chlorine, bromine, iodine, cyanogen, 178 ferro- or ferricyanogen may be present ; and if the residue is black or blackish, HYDROSULPHURIC ACID or a soluble METALLIC SULPHIDE. The presence of sulphur may, if necessary, be readily established beyond doubt, by mixing another portion of the solution with some solution of sulphate of copper. aa. Test another portion of the fluid for IODINE, and sub- sequently for BROMINE, by the methods described in 157. bb. -Test a small portion of the fluid with sesqui- 179 chloride of iron for FERROCYANOGEN; and, if the color of the silver precipitate leads you to suspect the presence of FERRICYANOGEN, test another portion for this latter substance with sulphate of iron. If the original solution has an alkaline reaction, some hydrochloric acid must be added before the ad- dition of the sesquichloride of iron, or the sulphate of iron. cc. CYANOGEN, if present in form of a simple cyanide of an alkali metal soluble in water, may usually be readily recognised by the smell of hydrocyanic acid which the body imder examina- tion emits, and which is rendered more strongly perceptible by- addition of a little dilute sulphuric acid. If no ferrocyanogen or ferricyanogen is present, the presence of cyanogen may be ascertained by the method given in 155, 6. dd. Should bromine, iodine, cyanogen, ferrocyanogen, 180 ferricyanogen, and sulphur not be present, the precipi- tate which nitric acid has failed to dissolve consists of CHLORIDE of silver. But where the analytical process has revealed the presence of any of the other bodies, a special examination for chlorine may become necessary, viz.. in cases where the quantity of the pre- cipitate will not enable the operator to pronounce with positive certainty on the presence or absence of the latter element.* In such cases, which are of rare occurrence however, the methods given in 157 are resorted to. 4. Test another portion for NITRIC ACID, by means of sulphate 181 of iron and sulphuric acid ( J59). 5. To ascertain whether CHLORIC ACID is present, pour a little concentrated sulphuric acid over a small sample of the solid substance on a watch-glass : ensuing yellow coloration of the acid resolves the question in the aflirmative ( 160). You have still to test for phosphoric acid, boracic acid, silicic acid, oxalic acid, and chromic acid, as well as for hydrofluoric acid. For the first five acids test only in cases where both chloride of barium and nitrate of silver have produced precipitates in neutral solutions. Compare also foot note to (173)- 6. Test for PHOSPHORIC ACID, by adding to a portion of the fluid * Supposing, for instance, the solution of nitrate of silver to have produced a copious precipitate insoluble in nitric acid, and the subsequent examination to have shown mere traces of iodine and bromine, the presence of chlorine may be held to be demou- titrated, without requiring additional proof. DETECTION OE ACIDS* 249 ammonia in excess, then chloride of ammonium and sulphate of 182 magnesia ( 142, 7). Very minute quantities of phosphoric acid are detected most readily by means of molybdic acid ( 142, 10). 7. To effect the detection of OXALIC ACID and HYDROFLUORIC ACID, add chloride of calcium to a fresh portion of the solution. If the reaction of the fluid is acid, add ammonia to alkaline reaction. If the chloride of calcium produces a precipitate which is not redissolved by addition of acetic acid, one or both bodies are present. Examine therefore now a sample of the original substance for fluorine according to the directions of 146, 5, another sample for oxalic acid by the method given in 145,7. 8. Acidulate a portion of the fluid slightly with hydrochloric 183 acid, then test for BORACIC ACID, by means of turmeric-paper ( 144, 6). 9. Should SILICIC ACID not yet have been found in the course of testing for the bases, acidulate a portion of the fluid with hydrochloric acid, evaporate to dryness, and treat the residue with hydrochloric acid ( 150, 3). 10. CHROMIC ACID is readily recognised by the yellow or red color of the solution, and by the purple-red color of the precipitate produced by nitrate of silver. If there remains the least doubt on the point, test for chromic acid with acetate of lead and acetic acid ( 138, 7). Complex Compounds. A, 1. SUBSTANCES SOLUBLE IN WATER. DETECTION OF ACIDS. II. In Presence of Organic Adds. 200. 1. The examination for the inorganic acids, inclusive of oxalic 184 acid, is made in. the manner described in 199. As the tartrates and citrates of baryta and oxide of silver are insoluble in water, tartaric acid and citric acid can be present only in cases where both chloride of barium and nitrate of silver have produced precipitates in the neutral fluid ; still, in drawing a conclusion, you must bear in mind that the said salts are slightly soluble in solutions of salts of ammonia. The proper testing for the organic acids requires in the first place the removal of those bases the presence of which might prove an obstacle, i.e., all the bases of groups III., I V., V., and VI. Their removal is effected by the methods described in 184, at the beginning; and the ex- amination for the organic acids is then conducted as follows : 2. Make a portion of the fluid feebly alkaline by addition of 185 ammonia, add some chloride of ammonium, then chloride of cal- cium, shake vigorously, and let the mixture stand at rest from ten to twenty minutes. . No PRECIPITATE IS FORMED, NOT EVEN AFTER THE LAPSE OF SOME TIME. Absence of tartaric acid ; pass on to (186)- 6. A PRECIPITATE IS FORMED IMMEDIATELY, OR AFTER SOME TIME. Filter, wash, and keep the filtrate for further examination according to tiie directions of (186)- 250 DETECTION OF ACIDS. Digest and shake the precipitate with solution of soda, without applying heat, then dilute with a little water, filter, and boil the filtrate some time. If a precipitate separates, TARTARIC ACID may be assumed to be present. Filter hot, and subject the precipitate to the ammonia and nitrate of silver test described in 163, 8. 3. Mix the fluid in which chloride of calcium has failed to pro- 186 duce a precipitate, or that which has been filtered from the preci- pitate formed in which latter case some more chloride of calcium is to be added with alcohol. a. No PRECIPITATE is FORMED. Absence of citric acid and 187 malic acid. Pass on to (190)- b. A PRECIPITATE is FORMED. Filter and treat the filtrate 188 as directed in (190)- As regards the precipitate, treat this as follows : After washing with some alcohol, dissolve on the filter in a little dilute hydrochloric acid, add ammonia to the filtrate to alkaline reaction, and boil for some time. a. THE FILTRATE REMAINS CLEAR. Absence of citric acid. Probable presence of MALIC ACID. Add alcohol again to the fluid, and test the lime precipitate in the manner directed 166, to make sure whether malic acid is really present or not. /3. A HEAVY WHITE PRECIPITATE is FORMED. Presence 189 of CITRIC ACID. Filter boiling, and test the filtrate for malic acid in the same manner as in a. To remove all doubt as to whether the precipitate is citrate of lime or not, it is advisable to dissolve once more in some hydrochloric acid, to supersaturate again with ammonia, and to boil; if the precipitate really consisted of citrate of lime, it will now be thrown down again. (Compare 164, 3.) 4. Heat the filtrate of (188) (or the fluid in which addition of 190 alcohol has failed to produce a precipitate (187)> to expel the alcohol, neutralize exactly with hydrochloric acid, and add sesqui- chloride of iron. If this fails to produce a light brown flocculent preci- pitate, neither succinic nor benzoic acid is present. If a precipitate of the kind is formed, filter, digest, and heat the washed precipitate with ammonia in excess ; filter, evaporate the filtrate nearly to dryness, and test a portion for SUCCINIC ACID with chloride of barium and alcohol ( 168) ; the remainder for BENZOIC ACID with hydrochloric acid ( 169). Benzoic acid may generally be readily detected also in the original sub- stance, by pouring some dilute hydrochloric acid over a small portion of the latter, which will leave the benzoic acid undissolved ; it is then filtered and heated on platinum foil ( 169, 1). 5. Evaporate a portion of the solution to dryness if acid, after 191 previous saturation with soda introduce the residue or a portion of the original dry substance into a small tube, pour some alcohol over it, add about an equal volume of concentrated sulphuric acid, and heat to boiling. Evolution of the odor of acetic ether demonstrates the presence of ACETIC ACID. This odor is rendered more distinctly peiceptible by shaking the cooling or cold mixture. 6. To effect the detection of FORMIC ACID, add to a portion of 192 the solution a sufficient quantity of nitrate of silver, then soda DETECTION OF ACIDS. 251 until the fluid is exactly neutralized, and boil. If formic acid is present, reduction of the silver to the metallic state ensues ( 172, 4). The reac- tion with nitrate of suboxide of mercury may be had recourse to as a conclusive test ( 172, 5)* Complex Compounds. A, 2. SUBSTANCES INSOLUBLE IN WATER, BUT SOLUBLE IN HYDRO- CHLORIC ACID, NITRIC ACID, OR NITROHYDROCHLORIC ACID. DETECTION OF THE ACIDS. In the Absence of Organic Acids. 201. In the examination of these compounds attention must be directed to all acids, with the exception of chloric acid. Cyanogen compounds and silicates are not examined by this method. (Compare 204 and 205.) 1. CARBONIC ACID, SULPHUR (in form of metallic sulphides), 193 ARSEXIOUS ACID, ARSENIC ACID, and CHROMIC ACID, if present, have been found already in the course of the examination for bases ; NITRIC ACID, if present, has been detected in the course of the preliminary examination,' by the ignition of the powdered sub- stance in a glass tube (8). 2. Mix a sample of the substance with 4 parts of pure carbonate 194: of soda and potassa, and, should a metallic sulphide be present, add some nitrate of soda ; fuse the mixture in a platinum crucible if there are no reducible metallic oxides present, in a porcelain crucible if such oxides are present ; boil the fused mass with water, and add a little nitric acid, leaving the reaction of the fluid, however, still alkaline; heat again, filter, and proceed with the filtrate according to the directions of 199, to effect the detection of all the acids which were com- bined with the bases. t 3. As the phosphates of the alkaline earths are only incom- 195 pletely decomposed by fusion in conjunction with carbonate of soda and potassa, it is always advisable in cases where alkaline earths are present, and phosphoric acid has not yet been detected, to dissolve a fresh sample of the body under examination in hydrochloric acid or nitric acid, and test the solution for PHOSPHORIC ACID with solu- tion of molybdic acid, after removal of the arsenic acid and silicic acid, should these be present. ( 142, 10.) 4. If in the course of the examination for bases alkaline earths have * In presence of chromic acid the reduction of oxide of silver and of suboxide of mer- cury is not a positive proof of the presence of formic acid. In cases where the two acids are present the following method must be resorted to : Mix the original solution with some nitric acid, add oxide of lead in excess, shake the mixture, filter, add to the filtrate dilute sulphuric acid in excess, and distil. Test the distillate as directed 173. In presence of tartaric acid also it is the safest way to distil the formic acid first, with addition of dilute sulphuric acid. f If the body examined has been found to contain a metallic sulphide, a separate por- .tiou of it must be examined for sulphuric acid, by heating it with hydrochloric acid, filtering, adding water to the filtrate, and then testing the fruid with chloride of barium. 252 DETECTION OF BASES, ACIDS, ETC. been found, it is also advisable to test a separate portion of the body under examination for FLUORINE, by the method described in 146, 5. 5. That portion of the substance under examination which has 196 been treated as directed in (194), can be tested for SILICIC ACID only in cases where the fusion has been effected in a platinum crucible ; in cases where a porcelain crucible has been used it is neces- sary to examine a separate portion of the body for silicic acid, by evapo- rating the hydrochloric or nitric acid solution ( 150, 3). 6. Examine a separate sample of the body for OXALIC ACID as directed in (198). Complex Compounds. A, 2. SUBSTANCES INSOLUBLE IN WATER, BUT SOLUBLE IN HYDRO- CHLORIC ACID, NITRIC ACID, OR NITRO-HYDROCHLORIC ACID. DETECTION OP THE ACIDS. II. In Presence of Organic Acids. 202. 1. Conduct the examination for inorganic acids according to the 197 directions of 201. 2. Test for ACETIC ACID as directed 171, 7i 3. Dissolve a portion of the compound under examination in 198 the least possible amount of hydrochloric acid, filter if necessary, and test the uridissolved residue which may be left for BENZOIC ACID, by application of heat ; add to the filtrate solution of carbonate of soda in considerable excess, and, besides this, also a little solid carbonate of soda, boil the mixture for a few minutes, then filter the fluid from the precipitate. In the filtrate you have now all the organic acids in solu- tion, combined with soda. Acidify the filtrate with hydrochloric acid, heat, and proceed according to the direction of (185). Complex Compounds. B, SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE BOTH IN WATER AND IN HYDROCHLORIC ACID, NITRIC ACID, OR NITRO-HYDRO- CHLORIC ACID. DETECTION OF THE BASES, ACIDS, AND NON-METALLIC ELEMENTS. 203. To this class belong the following bodies and compounds. 199 SULPHATE OF BARYTA, SULPHATE OF STRONTIA, and SULPHATE OF LIME.* SULPHATE OF LEADT and CHLORIDE OF LEAD.J * Sulphate of lime passes partially into the solution effected by water, and often completely into that effected by acids. t Sulphate of lead may pass completely into the solution effected by acids. + Chloride of lead can here only be found if the precipitate insoluble in acids has not been thoroughly washed with hot water. DETECTION OF BASES, ACIDS, ETC. 253 CHLORIDE OF SILVER, bromide of silver, iodide of silver, cyanide of silver,* ferro- and ferricyanide of silver, t SILICIC ACID and many SILICATES. Native alumina, or alumina which has passed through a process of intense ignition, and many aluminates. Ignited sesquioxide of chromium and CHROME-IRONSTONE (a compound of sesquioxide of chromium and protoxide of iron). Ignited and native binoxide of tin (tin- stone). Some metaphosphates and some arsenates. FLUORIDE OF CALCIUM and a few other compounds of fluorine. SULPHUR. CARBONACEOUS MATTER. Of these compounds those printed in small capitals are more frequently met with. As the silicates perform a highly important part in mineral analysis, a special chapter ( 205 208) is devoted to them. The substance under examination which is insoluble in water and in acids is in the first place subjected to the preliminary experiments here described in a e, if the quantity at the disposal of the operator is not absolutely too small to admit of this proceeding ; in cases where the quantity proves insufficient for the purpose, the operator must omit this preliminary examination, and at once pass on to (205?) bearing in mind, however, that the body may contain all the aforesaid substances and compounds. a. Examine attentively and carefully the physical state and con- 200 dition of the residue, to ascertain whether you have to deal with a homogeneous mass or with a mass composed of dissimilar particles \ whether the body is sandy or pulverulent, whether it has the same color throughout, or is made up of variously-colored particles, &c. The micro- scope, or even a simple magnifying glass, will be found very useful at this stage of the examination. b. Heat a small sample in a glass tube sealed at one end. If 201 brown fumes arise, and SULPHUR sublimes, this is of course a proof of the presence of that substance. c. If the substance is black, this indicates, in most cases, the 202 presence of carbonaceous matter. Heat a small sample on plati- num-foil over the blowpipe flame ; if the substance which blackens the fingers is consumed, this may be held to be a positive proof of the presence of CARBON in some shape or other. Graphite, which may be readily recognised by its property of communicating its blackish-gray color to the fingers, to paper, &c., requires the aid of oxygen for its ready combustion. d. Heat a small sample, together with a small lump of cyanide 203 of potassium and some water, for some time, filter, and test the filtrate with sulphide of ammonium. The formation of a brownish- black precipitate shows that the residue under examination con- tains a compoiind of SILVER. e. If an uudissolved residue has been left in d, wash this tho- 204 * Bromide, iodide, and cyanide of silver are decomposed by boiling with nitro-hydro- chloric acid, and converted into chloride of silver ; they can accordingly be found here only in cases where the operator has to deal with a substance which as nitrohydro- chloric acid has failed to effect its solution is examined directly by the method described in this paragraph ( 203). t With regard to the examination of these compounds, compare also 20 4. 25 i DETECTION OF BASES, ACIDS, ETC. roughly with water, and if white, sprinkle a few drops of sulphide of ammonium over it ; if it turns black, salts of LEAD are present. If, however, the residue left in d is black, heat it with some acetate of ammonia, adding a few drops of acetic acid, filter, and test the filtrate for LEAD, by means of sulphuric acid and hydrosulphuric acid.* The results obtained by these preliminary experiments serve to guide the operator now in his further course of proceeding. 1, a. SALTS OF LEAD ARE NOT PRESENT. Pass on to (206). 205 b. SALTS OF LEAD ARE PRESENT. Heat the substance re- peatedly with a concentrated solution of acetate of ammonia until the salt of lead is completely dissolved out. Test a portion of the filtrate for CHLORINE, another for SULPHURIC ACID, and the remainder for LEAD, by addition of sulphuric acid in excess, and by hydrosulphuric acid. If acetate of ammonia has left a residue, wash this, and treat it as directed in (206). 2, a. SALTS OF SILVER ARE NOT PRESENT. Pass on to (207)- 206 b. SALTS OF SILVER ARE PRESENT. Digest the substance free from lead, or which has been freed from that metal by acetate of ammonia, repeatedly with cyanide of potassium arid water, at a gentle heat (in presence of sulphur, in the cold), until all the salt of silver is removed. If an un dissolved residue is left, wash this, and proceed with it according to the directions of (207)- Of the filtrate, which contains cyanide of potassium, mix the larger portion with sulphide of ammonium, to precipitate the silver. Wash the precipitated sulphide of silver, then dissolve in nitric acid, dilute the solution, and add hydrochloric acid, to ascertain whether the precipitate really consisted of sulphide of silver. Test another small portion of the filtrate for SULPHURIC ACiD.f 3, a. SULPHUR is NOT PRESENT. Pass on to (208). 207 b. SULPHUR is PRESENT. Heat the substance free from silver and lead in a covered porcelain crucible until all the sulphur is expelled, and if a residue is left, treat this accord- ing to the directions of (208)- 4, Mix the substance free from silver, lead, and sulphur with 208 2 parts of carbonate of soda, 2 parts of carbonate of potassa, and 1 part of nitrate of potassa,J heat the mixture in a platinum crucible until the mass is in a state of calm fusion, place the red-hot crucible on a thick cold iron plate, and let it cool. By this means you will generally succeed in removing the fused mass from the crucible in an unbroken lump. Soak the mass now in water, boil, filter, and wash the residue until chloride of barium no longer produces a precipi- tate in the washings. (Add only the first washings to the filtrate.) a. The solution so obtained contains the acids which were 209 * The presence of lead in silicates, e.g. in glass containing lead, cannot be detected by this method. f As the carbonate of potassa contained in the cyanide of potassium may have pro- duced a total or partial decomposition of any sulphates of the alkaline earths which happened to be present. Addition of nitrate of potassa is useful even in the case of white powders, as it counteracts the injurious action of silicate of lead, should any be present, upon the p'atinuin crucible. In the case of black powders the proportion of nitrate of potassa must be correspondingly increased, in order that carbon, if present, may be consumed as completely as possible, and that any ;hrome-ironstone present in the compound may be more thoroughly decomposed. DETECTION OF BASES, ACIDS, ETC. 255 present in the substance decomposed by fluxing. But it may, besides these acids, contain also such bases as are soluble in caustic alkalies. Proceed as follows : a. Test a small portion of the solution for SULPHURIC ACID. /3. Test another portion with molybdic acid for PHOSPHORIC ACID and ARSENIC ACID. If a yellow precipitate forms, remove the arsenic acid which may be present with hydrosulphuric acid, and then test once more for phosphoric acid, after having removed also any silicic acid that may be present. y. Test another portion for FLOURINE ( 146, 7). 5. If the solution is yellow, CHROMIC ACID is present. To remove all doubt on the point, acidify a portion of the solu- tion with acetic acid, and test with acetate of lead. f. Acidify the remainder of the solution with hydrochloric 210 acid, evaporate to dryness, and treat the residue with hydro- chloric acid and water. If a residue is left which refuses to dissolve even in boiling water, this consists of SILICIC ACID. Test the hydrochloric acid solution now in the usual way for those bases which, being soluble in caustic alkalies, may be present. b. Dissolve the residue left in (208) in hydrochloric acid 211 (effervescence indicates the presence of alkaline earths), and test the solution for the bases as directed in 190. (If much silicic acid has been found in e (210)? it is advisable to evaporate the solution of the residue to dryness, and to treat the residuary mass with hydrochloric acid and water, in order that the silicic acid remaining may also be removed as completely as possible.) 5. If you have found in 4 that the residue insoluble in acids 212 contains a silicate, treat a separate portion of it according to the directions of (228)> to ascertain whether this silicate contains alkalies. 6. If a residue is still left undissolved upon treating the 213 residue left in (208) with hydrochloric acid (211)> this may con- sist either of silicic acid, which has separated, or of an undecom- posed portion of sulphate of baryta ; it may, however, also be fluoride of calcium, and if it is dark-colored, chrome-ironstone, as the last-named two compounds are only with difficulty decomposed by the method given in (208)- I would therefore remind the student that fluoride of calcium may be readily decomposed by means of sulphuric acid ; and, as regards the decomposition of chrome- ironstone, I can recommend the following method, first proposed by Hart : Project the fine powder into 8 times the quantity of fused borax, stir the mixture frequently, and keep the crucible lor half-an-hour at a bright red heat. Add now to the fusing mass carbonate of soda so long as effervescence continues, and finally add 3 times the weight of the chrome-ironstone of a mixture of equal parts of carbonate of soda and nitrate of potassa, whilst actively stirring the mixture with a platinum wire. Let the mass cool, and, when cold, boil it with water. 7. If the residue insoluble in acids contained silver, you have 214 still to ascertain whether that metal was present in the original substance as chloride, bromide, iodide, &c., of silver, or whether it has been converted into the form of chloride of silver by the treatment employed to effect the solution of the original substance. For that 256 ANALYSIS OF INSOLUBLE CYANIDES, FERROCYANIDES, ETC. purpose treat a portion of the original substance with boiling water until the soluble part is completely removed ; then treat the residuary portion in the same way with dilute nitric acid, wash the un- dissolved residue with water, and test a small sample of it for silver ac- cording to the directions of (203)- If silver is present, proceed to ascer- tain the salt-radical with which the metal is combined ; this may easily be effected by boiling the remainder of the residue in the first place with rather dilute solution of soda, filtering, and testing the filtrate, after acidifying it, for ferro- and ferricyanogen. Digest the washed residue now with finely granulated zinc and water, with addition of some sul- phuric acid, and filter after the lapse of ten minutes. You may now at once test the filtrate for chlorine, bromine, iodine, and cyanogen ; or you may first throw down the zinc with carbonate of soda, in order to obtain the salt-radicals in combination with sodium. SECTION II. PRACTICAL COURSE IN PARTICULAR CASES. I. SPECIAL METHOD OF EFFECTING THE ANALYSIS OF CYANIDES, FERROCYANIDES, ETC., INSOLUBLE IN WATER, AND ALSO OF INSO- LUBLE MIXED SUBSTANCES CONTAINING SUCH COMPOUNDS.* 204. THE analysis of ferrocyanides, ferricyanides, &c., by the common 215 method is often attended by the manifestation of such anomalous reactions as easily to mislead the analyst. Moreover, acids often fail to effect the complete solution of these compounds. For these reasons it is advisable to analyze them, and mixtures containing them, by the following special method : Treat the substance with water until the soluble parts are entirely removed, and boil the residue with strong solution of potassa or soda ; after a few minutes' ebullition add some carbonate of soda, and boil again for some time ; filter, should a residue remain, and wash the latter. 1. The residue, if any has be.n left, is now free from cya- 216 nogen, unless the substance under examination contains cya- nide of silver, in which case the residue would of course still contain cyanogen. Examine the residue now by the common method, beginning at (35). 2. The solution or filtrate, which, if combinations of com- 217 pound cyanogen radicals (Ferrocyanogen, Cobalticyanogen, &c.), were originally present, contains these combined with alkali metals, may also contain other acids, which have been separated from their bases by the process of boiling with car- * Before entering upon this course of analysis, consult the special remarks to tbe paragraph ( 204) in the Third Section. ANALYSIS OF INSOLUBLE CYANIDES, FERROCYANIDES, ETC. 257 bonate of soda, and lastly also, such oxides as are soluble in caustic alkalies. Treat the solution as follows : a. Mix the alkaline fluid with a sufficient quantity of hy- 218 drosulphuric acid, to test for metals of the fourth and fifth groups.* a. No permanent precipitate is formed. Absence of zinc and lead. Pass on to (219). ft. A permanent precipitate is formed. Add to the fluid a little yellow sulphide of sodium, drop by drop, until the metals of the fourth and fifth groups present in the alkaline solution are just thrown down, heat moderately, filter, wash the precipi- tate, and treat the filtrate as directed in (219). Dissolve the washed precipitate in nitric acid, which may leave sulphide of mercury behind, and examine the solution for copper and lead, as well as for zinc and other metals of the fourth group, which may, in the same way as copper, have passed into the alkaline solution, by the agency of organic matters. b. To test the alkaline fluid, which now also contains some 219 sulphide of an alkali metal, for mercury, which may be pre- sent, as its sulphide is soluble in sulphide of potassium, and for the metals of the sixth group, mix with a sufficient quantity of water, then with dilute nitric acid to acid reaction, and if the fluid does not smell strongly of hydrosulphuric acid, add some more of the latter reagent. a. No precipitate is formed. Absence of mercury and of the oxides of the sixth group. Pass on to (220). /3. A precipitate is formed. Filter, wash the precipitate, then examine it for mercury and the metals of the sixth group according to the directions of 191. c. The fluid, acidified with nitric acid, and therefore abun- 220 dantly supplied with nitrates of alkalies, may still contain those metals which in combination with cyanogen form com- pound radicals (iron, cobalt, manganese, chromium), and, besides these, also alumina. You have to test it also for cyanogen, respec- tively ferrocyanogen, cobalticyanogen, &c., and for other acids. Divide it, therefore, into two portions, a and ft. Examine a for the acids according to the directions of 199, or, as the case may be, 200. (Cobalticyanogen may be recognised as such by its giving with salts of nickel greenish, with salts of manganese and zinc white precipitates, in which the presence of cobalt is revealed by fusing with borax.) Evaporate ft to dryness, and heat the residue to fusion. Pour the fused mass upon a piece of porcelain, boil with water, filter, and examine the residue for IRON, MANGANESE, COBALT, and ALUMINA. Test a portion of the filtrate (if yellow) for CHROMIC ACID, the remainder for ALUMINA (which may have passed partially or com- * The analyst must, of course, avoid adding solution of hydrosulphuric acid, or con- ducting: hydrosulphuric acid gas into the fluid, until the mixture smells of the reagent (accordingly, until all the alkali present has been converted into hydrosulphate of sulphide of alkali metal), since this inujht lead to the precipitation also of the alumina which may be present in the alkaline solution, and even of sulphides of metals of the sixth grjup a precipitation which is not. intended here. I. S 258 ANALYSIS OF SILICATES. pletely into the solution, through the agency of the caustic alkalies formed in the process of fusion from the nitrates of the alkalies present.) II. ANALYSIS OF SILICATES. 205. Whether the body to be analyzed is a silicate or contains one, is 221 ascertained by the preliminary examination with phosphate of soda and ammonia before the blowpipe ; since in the process of fusion the metallic oxides dissolve, whilst the separated silicic acid floats about in the liquid bead as a transparent swollen mass ( 150, 8). The analysis of the silicates differs, strictly speaking, from the common course only in so far as the preliminary treatment is concerned, which is required to effect the separation of the silicic acid from the bases, and to obtain the latter in solution. The silicates and double silicates are divided into two distinct classes, which require respectively a different method of analysis; viz., (1) sili- cates readily decomposable by acids (hydrochloric acid, nitric acid, sul- phuric acid), and (2) silicates which are not, or only with difficulty, decomposed by acids. Many minerals consist of mixtures of the two classes of silicates. To ascertain to which of these two classes a silicate belongs, reduce it to a very fine powder, and digest a portion with hydrochloric acid at a temperature near the boiling-point. If this fails to decompose it, try another portion by long-continued heating with a mixture of three parts of concentrated sulphuric acid and 1 part of water. If this also fails, after some time, to produce the desired effect, the silicate belongs to the second class. Whether decomposition has been effected by the acid or not, may generally be learned from external indications, as a colored solution forms almost invariably, and the separated gelatinous, flocculent, or finely-pulverulent hydrate of silicic acid takes the place of the original heavy powder which grated under the glass rod with which it was stirred. But whether the decomposition is complete, or extends only to one of the components of this mineral, may be ascertained by boiling the separated hydrate of silicic acid in a solution of carbonate of soda. If perfect solution ensues, complete decomposition has been effected ; if not, the decomposition is only partial. The result of these prelimi- nary tests will show whether the silicate should be examined according to 206, or to 207, or to 208. Before proceeding further, examine a portion of the pulverized compound also for water, by heating it in a perfectly dry glass tube. If the sub- stance contains hygroscopic moisture, it must first be dried by protracted exposure to a temperature of 212 F. Apply a gentle heat at first, but ultimately an intense heat, by means of the blowpipe ; you may al.-o conveniently combine with this a preliminary examination for fluorine ( U6, 8). A. SILICATES DECOMPOSABLE BY ACIDS. 206. a. Silicates decomposable by hydrochloric acid or by nitric acid* 1. Digest the finely pulverized silicate with hydrochloric acid at * Nitric acid is preferable to hydrochloric acid in cases where compounds of silver or lead are present. ANALYSIS OF SILICATES. 259 a temperature near the boiling-point, until complete decompo- 222 sition is effected, filter off a small portion of the fluid, evaporate the remainder, together with the silicic acid suspended therein, to dryness, and expose the residue to a temperature somewhat exceeding 212 F., with constant stirring, until no more, or very few, hydrochloric acid fumes escape ; allow it to cool, moisten the residue with hydro- caloric acid or, as the case may be, with nitric acid, afterwards add a little water, and heat gently for some time. This operation effects the separation of the silicic acid, and the solu- tion of the bases in the form of chlorides, or, as the case may be, nitrates. Filter, wash the residue thoroughly, and examine the solution by the common method, beginning at 189, II. or III.* To be quite safe, the residuary silicic acid may be digested with ammonia, filtered, and the filtrate tested for silver, by supersaturation with nitric acid. 2. As in silicates, and more particularly in those decomposed 223 by hydrochloric acid, there are often found other acids, as well as metalloids, the following observations and instructions must be attended to, that none of these substances may be overlooked : a. SULPHIDES of METALS and CARBONATES are detected in the process of treating with hydrochloric acid. /3. If the separated silicic acid is black, and turns subsequently white upon ignitiou in the air, this indicates the presence of CARBON or of ORGANIC SUBSTANCES. In presence of the latter, the silicates emit an empyreumatic odor upon being heated in a glass tube. y. Test the portion of the hydrochloric acid solution filtered off before evaporating for SULPHURIC ACID, PHOSPHORIC ACID, and ARSENIC ACID for sulphuric acid with chloride of barium, after diluting with water; for arsenic acid by heating the solution to 158 Fah., conducting sulphuretted hydrogen into it, and examining the precipitate formed ; for phosphoric acid with solution of molyb- date of ammonia in nitric acid. Where arsenic is found, the fluid filtered off the sulphide of arsenic is tested for the phosphoric acid, after the removal of the hydrosulphuric acid. & BORACIC ACID is best detected by fusing a portion of the 224 substance in a platinum spoon with carbonate of soda and * Minute traces of titanic acid are occasionally met with in silicates. If the sepa- ration of the silicic acid has been effected on the water- bath, the greater part of the titanic acid passes into the hydrochloric acid solution, whilst a small portion separates along with the silicic acid. The titanic acid is found in the following way : a. Heat the silicic acid repeatedly in a platinum dish with hydrofluoric acid and sulphuric? acid until the silica is completely removed as fluoride of silicon, then evaporate to dryness. 6. Precipitate the solution with ammonia, filter, wash the precipitate (which contains alumina, sesquioxide of iron, &c., and the rest of the titanic acid), add to it the residue left in a, and fuse the whole with a quantity of acid sulphate of potassa suffi- cient to effect solution ; continue heating until the greater part of the excess of sulphuric acid is removed. Let the fused mass cool, dissolve in cold water (which, if the operation has been successful, and no more silicic acid remains, will effect complete solution to a clear fluid) ; filter if necessary, dilute freely, transmit sulphuretted hydrogen gas through the fluid until the whole of the sesquioxide of iron present is reduced to protoxide, arid keep the fluid boiling half an hour, with constant trans- mission of carbonic acid through it (without previously filtering off the sulphur). The titanic acid will gradually separate, the bases remaining in solution (Tn. SCHEEREK). filter, wash, ignite, and examine the residue finally as directed in 104, 10. 260 ANALYSIS OF SILICATES. potassa, boiling the fused mass with water, and examining the solu- tion for boracic acid by the method given in 144, 6. c. With many silicates, boiling with water is sufficient to dissolve the metallic CHLORIDES present, which may then be readily detected in the nitrate by means of solution of nitrate of silver ; the safest way, however, is to dissolve the mineral in dilute nitric acid, and test the solution with nitrate of silver. . Metallic FLUORIDES, which often occur in silicates in greater or smaller proportion, are detected by the method described 146, 6. &. Silicates which resist the action of hydrochloric acid, but are decomposed by concentrated sulphuric acid. Heat the finely pulverized mineral with a mixture of 3 parts of 225 concentrated pure sulphuric acid and 1 part of water (best in a plati- num dish), finally drive off the greater portion of the sulphuric acid, boil the residue with hydrochloric acid, dilute, filter, and treat the filtrate as directed 190 ; and the residue, which, besides the separated silicic acid, may contain also sulphates of the alkaline earths, &c., according to the directions of 203. If you wish to examine silicates of this class for acids and salt radicals, treat a separate portion of the substance according to the directions of 207. B. SILICATES WHICH ARE NOT DECOMPOSED BY ACIDS.* 207. As the silicates of this class are most conveniently decomposed 226 by fusion with carbonate of soda and potassa, the portion so treated cannot, of course, be examined for alkalies. The analytical process is therefore properly divided into two principal parts, viz., a portion of the mineral is examined for the silicic acid and the bases, with the ex- ception of the alkalies, whilst another portion is specially examined for the latter. Besides these, there are some other experiments required, to obtain information as to the presence or absence of other acids. 1. Detection of the silicic acid and the bases, with the exception of tlie alkalies. Reduce the mineral to a very fine powder, mix this with 4 227 parts of carbonate of soda and potassa, and heat the mixture in a platinum crucible over a gas or Berzelius spirit-lamp until the mass is in a state of calm fusion. Place the red-hot crucible on a thick cold iron plate, and let it cool there ; this will generally enable you to remove the fused cake from the crucible, in which case break the mass to pieces, and keep a portion for subsequent examination for acids. Put the remainder, or, if the mass still adheres to the crucible, the latter, with its contents, into a porcelain dish, pour water over it, add hydrochloric acid, and heat gently until the mass is dissolved, with the exception of the silicic acid, which separates in flakes. Remove the crucible from * It will be understood, from what has been stated 205, that these are not decomposed by heating with hydrochloric acid and sulphuric acid in open vessels ; but by heating them, reduced to a fine powder, in a sealed glass tube, with a mixture of 3 parts of concentrated sulphuric acid and 1 part of water, or with hydrochloric acid, to 392 or 410 Fah., most of them are decomposed, and may accordingly be analyzed also in this manner (AL. MITSCHERLICH). ANALYSIS OF SILICATES. 2G1 the dish if necessary, evaporate the contents of the latter to dryness, and treat the residue as directed (222)- 2. Detection of the alkalies. To effect this, the silicates under examination must be decom- 228 posed by means of a substance free from alkalies. Hydrofluoric acid or a metallic fluoride answers this purpose best ; but fusion with hydrate of baryta will also accomplish the end in view. a. DECOMPOSITION BY MEANS OF A METALLIC FLUORIDE. Mix 1 part of the very finely pulverized mineral with 5 parts of fluoride of barium, or pure, finely pulverized fluoride of calcium, stir the mixture in a platinum crucible with concentrated sulphuric acid to a thickish paste, and heat gently for some time in a place affording a free escape to the vapors ; finally heat a little more strongly, until the excess of sulphuric acid is completely expelled. Boil the residue now with water, add chloride of barium cautiously as long: as a precipitate continues to form, then baryta-water to alkaline reaction, boil, filter, mix with carbonate of ammonia and some ammonia as long as a precipitate forms, and proceed exactly as directed (168)- b'. DECOMPOSITION BY MEANS OF HYDRATE OF BARYTA. Mix 229 1 part of the very finely pulverized substance with 4 parts of hydrate of baryta, expose the mixture for half an hour in a platinum crucible to the strongest possible heat of a good Berzelius or gas-lamp, and treat the fused or agglutinated mass with hydro- chloric acid and water until it is dissolved ; precipitate the solution with ammonia and carbonate of ammonia, filter, evaporate to dry- ness, ignite, dissolve the residue in water, precipitate again with ammonia and carbonate of ammonia, filter, evaporate, ignite, and test the residue for potassa and soda as directed 197. If the residue still contains magnesia, this may be readily removed, by adding to the aqueous solution of the residue a little pure oxalic acid, evaporating to dryness, igniting the dry mass, then treating it with water, which will leave the magnesia iindissolved. Filter, acidify the filtrate with hydrochloric acid, evaporate to dryness, and examine the residue for potassa and soda. 3. Examination for fluorine, chlorine, boracie acid, phosphoric acid, arsenic acid, and sulphuric acid. Use for this purpose the portion of the fused mass reserved in 230 (227)> or > if necessary, fuse a separate portion of the finely pulve- rized substance with 4 parts of pure carbonate of soda and potassa until the mass flows calmly ; boil the fused mass with water, filter the solution, which contains all the fluorine as fluoride of sodium, all the chlorine as chloride of sodium, all the boracie acid as borate, all the sulphuric acid as sulphate, all the arsenic acid as arsenate, and at least part of the phosphoric acid as phosphate of soda, and treat the filtrate as follows : a. Acidify a small portion of it with nitric acid, and test for CHLORINE with nitrate of silver. b. Test another portion for BORACIC ACID as directed 144, 6. c. To effect the detection of the FLUORINE, treat a third portion of the filtrate as directed 146, 7. d. Acidify the remainder with hydrochloric acid and test a small portion with chloride of barium for SULPHUBIC ACID ; heat the 262 ANALYSIS OF SILICATES. remainder to 158 Fah., and test with hydrosulphuric acid for ARSENIC ACID. If no precipitate forms, evaporate the fluid, if a precipitate forms, the filtrate, to dryuess, test the residue with hydro- chloric acid and water, and examine the solution for PHOSPHORIC ACID with sulphate of magnesia, or with solution of naolybdate of ammonia in nitric acid ( 142). C. SILICATES WHICH ARE PARTIALLY DECOMPOSED BY ACIDS. 208. Most of the native rocks and minerals are mixtures of several 231 silicates, of which some are often decomposable by acids, others not. If such minerals were analyzed by the same method as the absolutely insoluble silicates, the analyst would indeed detect all the elements present, but the analysis would afford no satisfactory insight into the actual composition of the mineral. It is therefore advisable to examine separately those parts of the mineral which show a different deportment with acids. For this purpose digest the very finely pulverized mineral for some time with hydrochloric acid at a gentle heat, filter off a small portion of the solution, evaporate the remainder to dryness, and expose to a temperature somewhat exceeding 212 Fah., with stirring, until no more, or very little hydrochloric acid vapor is evolved ; let the residue cool, moisten it when cold with hydrochloric acid, heat gently with water, and filter. The filtrate contains the bases of that part of the mixed mineral which has been decomposed by the hydrochloric acid ; examine this as directed (222)- Examine the portion first filtered off as directed in (223? y) Test portions of the original substance for other acids as directed (224)- Boil the residue which, besides the silicic acid separated from the decomposed portion of the silicate, contains that part of the mixed mineral which has resisted the action of the hydrochloric acid with an excess of solution of carbonate of soda, filter hot, and wash, first with hot solution of carbonate of soda, finally with boiling water. Treat the residuary undecomposed part of the mineral, thus freed from the admixed separated silicic acid, according to the instructions given in 207. In cases where it is of no consequence or interest to effect the separation of the silicic acid of the part decomposed by acids, you may omit the troublesome operation with carbonate of soda, and may proceed at once to the decomposition of the residue. III. ANALYSIS OF NATURAL WATERS. 209. In the examination of natural waters the analytical process is 232 simplified by the circumstance that we know from experience the elements and compounds which are usually found in them. Now, although a quantitative analysis alone can properly inform us of the true nature and character of a water, since the differences between the various waters are principally caused by the different proportions in which the several constituents are respectively present, a qualitative analysis may yet render very good service, especially if the analyst notes with proper care whether a reagent produces a faint or a distinctly ANALYSTS OF FRESH WATERS. 263 marked turbidity, a slight or a copious precipitate ; since these circum- stances will enable him to make an approximate estimation of the relative proportions in which the several constituents are present. I separate here the analysis of the common fresh waters (spring-water, well-water, brook-water, river-water, &c.) from that of the mineral waters, in which latter we may also include sea-water ; for, although no well- defined limit can be drawn between the two classes, still the analytical examination of the former is necessarily far more simple than that of the latter, as the number of substances to be looked for is much more limited than in the case of mineral waters. A. ANALYSIS OF FRESH WATERS (SPRING-WATER, WELL-WATER, BROOK-WATER, RIVER-WATER, &c.). 210. We know from experience that the substances to be had regard 233 to in the analysis of such waters are the following : a. BASES : Potassa, soda, ammonia, lime, magnesia, protoxide of iron. b. ACIDS, &c. : Sulphuric acid, phosphoric acid, silicic acid, carbonic acid, nitric acid, nitrous acid, chlorine. c. ORGANIC MATTERS. d. MECHANICALLY SUSPENDED SUBSTANCES : Clay, . t. xxvii. p. 418) found iodine in all fresh- water plants, but not in land plants, a proof that the water of rivers, brooks, ponds, &c., contains traces, even though extremely minute, of metallic iodi if the latter contained organic matter. If you have reason to ft-ar that such has been the case, and you have not already found nitric acid in (249)' examine a larger portion of non-ignited residue for that acid, according to the directions of (257)- ANALYSIS OF MINERAL WATERS. 271 add a little sesquichloride of iron, then ammonia in slight excess, and a small quantity of oxalate of ammonia ; let the mixture stand for some time, then filter off the fluid, which is now entirely free from phosphoric acid and lime ; evaporate the nitrate to dry ness, and gently ignite the residue until the salts of ammonia are expelled ; treat the residue with some chlorine water (to remove the iodine and bromine) and a few drops of hydrochloric acid, and evaporate to dry ness ; add a little water and (to remove the magnesia) some finely divided oxide of mercury, evaporate to dryness, and gently ignite the residue until the chloride of mer- cury is just driven off; treat the residue now with a mixture of absolute alcohol and anhydrous ether, filter the solution obtained, concentrate the filtrate by evaporation, and set fire to the alcohol. If it burns with a carmine flame, LITHIA is present. By way of confirmation convert the lithia found into phosphate of LITHIA ( 93, 3). 3. EXAMINATION FOB THOSE CONSTITUENTS OF THE WATER WHICH ARE PRESENT IN MOST MINUTE QUANTITIES ONLY. 1. Evaporate 200 or 300 Ibs. of the water in a large perfectly 259 clean iron vessel until the salts soluble in water begin to separate. If the mineral water contains no carbonate of soda, add sufficient of that substance to impart a perceptibly alkaline reaction to the fluid. After evaporation filter the solution off, wash the precipitate, without adding the washings to the first filtrate, arid a Examine the precipitate by the method given in 214 for sinter deposits ; b. Mix the solution with hydrochloric acid to acid reaction, heat, just precipitate the sulphuric acid which may be present with chloride of barium, filter, evaporate the filtrate to dryness, digest the residue with alcohol of 90 per cent., and examine the solution for CAESIUM arid RUBIDIUM according to the direc- tions of 93, last paragraph. 2. Test a portion of the original water for NITROUS ACID accord- 260 ing to the directions of (241)' If the water contains hydrosul- phuric acid, this is removed first by very cautious addition of some sulphate of silver (under no circumstances must silver salt be allowed to remain in solution). II. EXAMINATION OF THE SINTER-DEPOSIT. 214. 1. Free the ochreous or sinter-deposit from impurities, by picking, 261 sifting, elutriation, &c., and from the soluble salts adhering to it, by washing with water ; digest a large quantity (about 200 grammes) of the residue with water and hydrochloric acid (effervescence : CAR- BONIC ACID) until the soluble part is completely dissolved ; dilute, let cool, filter, and wash the residue. a. Examination of the filtrate. a. Heat the larger portion of the filtrate nearly to boiling, 262 and add gradually a solution of pure hyposulphite of soda until the whole of the sesquichloride of iron is converted to 272 ANALYSTS OF MINERAL WATERS. protochloride ; heat and conduct carbonic acid into the fluid until the mixture smells no longer, or only very faintly, of sulphurous acid. Then conduct hydrosulphuric acid into the unfiltered fluid, which, if necessary, should previously be diluted. Let the fluid, now stand in a moderately warm place until it retains only a faint smell of sulphuretted hydrogen, then filter and wash. Displace the washing water by strong alcohol, and 263 remove the greater part of the free sulphur by digestion and washing with sulphide of carbon ; then warm the precipitate gently with some yellowish sulphide of ammonium, filter, wash with water containing sulphide of ammonium, and evaporate the filtrate and washings in a small porcelain dish to dryness. Pour pure red fuming nitric acid over the residue, warm until the greater part of the nitric acid is driven off, add carbonate of soda in slight excess, then a little nitrate of soda, heat to fusion, treat the fused mass with cold water, filter, wash with a mixture of spirit of wine and water, and test the aqueous solution for ARSENIC ACID (121) and (122), the residue for ANTIMONY, TIN, and COPPER, by dissolving in dilute hydrochloric acid, and testing one half of the solution in the platinum dish with zinc for antimony and tin (123)> the other half with ferrocyanide of potas- sium for copper. If a residue has been left upon treating the precipitate 264 produced by hydrosulphuric acid with sulphide of ammo- nium, wash, and remove from the filter by means of the washing bottle ; boil with a little dilute nitric acid, filter, wash, and pour solution of hydrosulphuric acid over the contents of the filter that any sulphate of lead present may not be overlooked then test for BARYTA and STRONTIA as in (254)' Mix the filtrate (the nitric acid solution) with some pure sulphuric acid, evapo- rate on the water-bath to dryness, and treat the residue with water. If this leaves an undissolved residue, the latter consists of sulphate of LEAD. To make quite sure, filter, wash the residue, treat it with hydrosulphuric acid water, and observe whether that reagent imparts a black color to it. Test the fluid filtered from the sulphate of lead which may have separated, a with ammonia, b with ferrocyanide of potassium, for COPPER. Evaporate a portion of the fluid filtered from the preci- 265 pitate produced by hydrosulphuric acid to dryness, treat the residue with hydrochloric acid and water, filter, and test the filtrate for PHOSPHORIC ACID with solution of molyb- date of ammonia in nitric acid. Mix the remainder in a flask with chloride of ammonium, ammonia, and yellowish sulphide of ammonium, close the flask, filled up to the neck, and let it stand in a moderately warm place until the fluid above the pre- cipitate looks no longer greenish, but yellow ; filter, and wash the precipitate with water to which some sulphide of ammonium has been added. Dissolve the washed precipitate in hydrochloric acid, and examine for COBALT, NICKEL, IRON, MANGANESE, ZINC, ALUMINA, and SILICIC ACID, according to the directions of (152) to (160)- Examine now the fluid filtered from the precipitate produced by sulphide of ammonium for LIME and MAGNESIA in the usual way. ANALYSIS OF SOILS. 273 . Mix a portion of the hydrochloric acid solution, considerably diluted, with chloride of barium, and let the mixture stand 12 hours in a warm place. The formation of a white precipitate in- dicates the presence of SULPHURIC ACID. b. Examination of the residue. This consists usually of silicic acid, clay, and organic mat- 266 ters, but it may also contain sulphate of baryta and sulphate of strontia. Boil in the first place with solution of soda or potassa, to dissolve the SILICIC ACID ; then fuse the residue with carbonate of soda and potassa, and a little nitrate of potassa. Boil the mass with water, wash the residue thoroughly, and dissolve it in some hydrochloric acid ; the silicic acid still present then sepa- rates, add ammonia to thefiltrate, filter again from the ALUMINA, for IRON, MANGANESE, ALUMINA, and, if necessary, also for lime and magnesia, which may have been thrown down by the sulphide of ammonium, in combination with phos- phoric acid. 5. The separated SILICIC ACID obtained in 4 is usually colored by organic matter. It must, therefore, be ignited to obtain it pure. * Complete lixiviation is generally impracticable. ANALYSIS OF SOILS. 277 6. If it is a matter of interest to ascertain whether the hydro- chloric acid extract contains ARSENIC ACID, OXIDE OF COPPER, to guard against overlooking even the minutest traces of arsenic, &c. b. A precipitate is formed, of a pure yellow color like that 295 of tersulphide of arsenic. Take a small portion of the fluid, together with the precipitate suspended therein, add some ammonia, and shake the mixture for some time, without appli- cation of heat. If the precipitate dissolves readily and, with the exception of a trace of sulphur, completely, and if, in the preliminary examination (293), carbonate of ammonia has failed to produce a precipitate, arsenic alone is present, and no other metal (at all events, no quantity worth mentioning tin or antimony). Mix the solution of the small sample in, ammonia with hydrochloric acid to acid reaction, return the acidu- lated sample to the fluid from which it was taken, and which con- tains the yellow precipitate produced by the hydrosulphuric acid, and proceed as directed in (297)- If> n the other hand, the addition of ammonia to the sample completely or partially fails to redissolve the precipitate, or if, in the preliminary examination (293) car- bonate of ammonia has produced a precipitate, there is reason to suppose that another metal is present, perhaps with arsenic. In this latter case also, add to the sample in the test-tube hydrochloric acid to acid reaction, return the acidulated sample to the fluid from which it was taken, and which contains the yellow precipi- tate produced by the hydrossulphuric acid, and proceed as directed in (298). 286 DETECTION OF ARSENIC. c. A precipitate is formed of another color. In that case you have to assume that other metals are present, perhaps with 296 arsenic. Proceed as directed in (298)- 5. Treatment of the Yellow Precipitate produced by Hydrosulphuric 297 Acid, in Cases where the Results of the Examination in (295) lead to the Assumption that Arsenic alone is present. Determina- tion of the Weight of the Arsenic. As soon as the fluid precipitated according to the directions of (293) has nearly lost the smell of sulphuretted hydrogen, transfer the yellow precipitate to a small filter, wash thoroughly, pour upon the still moist precipitate solution of ammonia, and wash the filter on which, in this case, nothing must remain undissolved, except some sulphur thoroughly with dilute ammonia j evaporate the ammonical fluid in a small ac- curately tared porcelain dish, on the water-bath, dry the residue at 212 Fah. until its weight suffers no further diminution, and weigh. If it is found, upon reduction, that the residue consisted of perfectly pure tersulphide of arsenic, calculate for every part of it 0*8049 of arsenious acid, or 0'6098 of arsenic. Treat the residue in the dish according to the instructions given in (300)- 6. Treatment of the Yellow Precipitate produced by Hydrosulphuric Acid, in Cases wJiere t/ie Results of the Examination in (295)> or in (296) feud to the Assumption that another Metal is present 298 perhaps with Arsenic. Separation of the Metals from each other. Determination of the Weight of the Arsenic. If you have reason to suppose that the fluid precipitate by hydrosul- phuric acid (293) contains other metals, perhaps with arsenic, proceed as follows : As soon as the precipitation is thoroughly accomplished, and the smell of sulphuretted hydrogen has nearly gone off, transfer the precipitate to a small filter, wash thoroughly, perforate the point of the filter, and rinse the contents with the washing-bottle into a small flask, using the least possible quantity of water for the purpose ; add to the fluid in which the precipitate is now suspended, first ammonia, then some yellowish sulphide of ammonium, and let the mixture digest for some time at a gentle heat. Should part of the precipitate remain undis- solved, filter this off, wash, perforate the filter, rinse off the residuary precipitate, mark it III., and reserve for further examination according to the instructions given in (305)- Evaporate the filtrate, together with the washings, in a small porcelain dish, to dryness. Treat the residue with some pure fuming nitric acid (free from chlorine), nearly drive off the acid by evaporation, then add, as C. Meyer was the first to recommend, gradually and in small portions at a time, a solution of pure carbonate of soda until it predominates. Add now a mixture of 1 part of carbonate and 2 parts of nitrate of soda in sufficient, yet not excessive quantity, evaporate to dryness, and heat the residue very gradu- ally to fusion. Let the fused mass cool, and, when cold, extract it with cold water. If a residue remains undissolved, filter, wash with 299 a mixture of equal parts of spirit of wine and water, mark it IV., and reserve for further examination, according to the directions of (306)- Mix the solution, which must contain all the arsenic as arsenate of soda, with the washings, previously freed from alcohol by evaporation, add gradually and cautiously pure dilute sulphuric acid to strongly acid DETECTION OP ARSENIC. 287 reaction, evaporate in a small porcelain dish, and, when the fluid is strongly concentrated, add again sulphuric acid, to see whether the quantity first added has been sufficient to expel all nitric acid and nitrous acid ; heat now very cautiously until heavy fumes of hydrated sulphuric acid begin to escape \ then let the liquid cool, and, when cold, add water, transfer the solution to a small flask, heat to 158 F., and conduct into it, for at least 6 hours, a slow stream of washed hydro- sulphuric acid gas. Let the mixture finally cool, continuing the transmis- sion of the gas all the while. If arsenic is present, a yellow precipitate will form. When the precipitate has completely subsided, and the fluid has nearly lost the smell of sulphuretted hydrogen, filter, wash the precipi- tate, dissolve it in ammonia, and proceed with the solution as directed in (297)> to determine the weight of the arsenic. 7. Reduction of the Sulphide of Arsenic. The production of metallic arsenic from the sulphide, which may 300 be regarded as the keystone of the whole process, demands the greatest care and attention. The method recommended in 132, 12, viz., to fuse the arsenical compound, mixed with cyanide of potassium and carbonate of soda, in a slow stream of carbonic acid gas, is the best and safest, affording, besides the advantage of great accuracy, also a positive guarantee against the chance of confounding the arsenic with any other body, more particularly antimony ; on which account it is more especially adopted for medico-legal investigations. Take care to have the whole appa- ratus filled with carbonic acid, and to give the proper degree of force to the gaseous stream, before applying heat. It is advisable to substitute for the evolution flask in Fig. 31 ( 132, 12), a flask which will allow the operator to regulate the current of gas. The arrangement shown in Fig. 35, which is a matter of easy contrivance, will fully answer the purpose. Caoutchouc stoppers should be used ; the compression stopcock is furnished with an adjusting screw. As regards the process of reduc- tion, either proceed at once with the sulphide of arsenic, or previously convert the latter into arsenic acid (see 301). In the former case take care, if possible, not to use the whole of the residue in the dish, obtained by the evaporation of the ammoniacal solution, but use only a portion of it, so that the process may be repeated several times if necessary. Should the residue be too trifling to admit of being divided into several portions, dissolve it in a few drops of ammonia, add a little carbonate of soda, and evaporate on the water- Fig. 35. 288 DETECTION OF ACIDS. bath to dry ness, taking care to stir the mixture during the process ; divide the dry mass into several portions, and proceed to re- duction. Otto* recommends to convert the sulphide first into arsenic acid, 301 then to reduce the latter with cyanide of potassium. The follow- ing is the process given by him to effect the conversion : Pour concentrated nitric acid over the sulphide of arsenic in the dish, evaporate, and repeat the same operation several times if necessary, then remove every trace of nitric acid by repeatedly moistening the residue with water, and drying again; when the nitric acid is completely expelled, treat the residue with a few drops of water, add carbonate of soda in powder, to form an alkaline mass, and thoroughly dry this in the dish, with frequent stirring, taking care to collect the mass within the least possible space in the middle of the dish. The dry mass thus obtained is admirably adapted for reduc- tion. I can, from the results of my own experience, fully confirm this statement of Otto ; but I must once more repeat that it is indis- pensable for the success of the operation that the residue should be per- fectly free from every trace of nitric acid or nitrate, since otherwise de- flagration is sure to take place during the process of fusion with cyanide of potassium, and, of course, the experiment will fail. When the operation is finished, cut off the reduction -tube at c 302 (see Fig. 36), set aside the fore part, which contains the arsenical mirror, put the other part of the tube into a cylinder, pour water over it, and let it stand some time ; then filter the solution obtained, add Fig. 36. to the filtrate hydrochloric acid to acid reaction ; then conduct some hydrosulphuric acid into it, and observe whether this produces a preci- pitate. In cases where the reduction of the sulphide of arsenic has been effected in the direct way, without previous conversion to arsenic acid, a trifling yellow precipitate will usually form ; had traces of antimony been present, the precipitate would be orange-colored and insoluble in car- bonate of ammonia. After all the soluble salts of the fused mass have been dissolved out, examine the metallic residue which may be left, for traces of tin and antimony ; these being the only metals that can possibly be present if the instructions here given have been strictly followed. Should appreciable traces of these metals, or either of them, be found, proper allowance must be made for this in calculating the weight of the arsenic. 8. Examination of the reserved Residues, marked severally I., II., III., and IV"., for other Metals of the Fifth and Sixth Groups. a. Residue I. Compare (290)- 303 This may contain more particularly chloride of silver and sulphate of lead, possibly also binoxide of tin. Incinerate the * " Anleitung zur Ausmittelung der Gifte," von Dr. Fr. Jul. Otto, p. 36. DETECTION OF ARSENIC. 289 residue (I.) in a porcelain dish, burn the carbon with the aid of some nitrate of ammonia, extract the residue with water, dry the part left undissolved, then fuse it with cyanide of potassium in a porcelain crucible. When the fused mass is cold, treat it with water until all that is soluble in it is completely removed ; warm the residue with nitric acid, and proceed as directed in 181. b. Residue II. Compare (292)- 304 The carbonaceous residue which is obtained in the purifica- tion of the crude sulphide by means of nitric acid and sul- phuric acid, may more particularly contain lead, mercury, and tin ; antimony and bismuth may also be present. Heat the residue for some time with nitrohydrochloric acid, and filter the solution ; wash the undissolved residue with water, at first mixed with some hydrochloric acid, add the washings to the filtrate, and treat the dilute fluid thus obtained with hydrosulphuric acid. Should a precipitate form, examine this according to the instructions given in 191. Incinerate the residue insoluble in nitrohydro- chloric acid, fuse the ash in conjunction with cyanide of potas- sium, and proceed with the fused mass as directed in (303)' c. Residue III. Compare (298). 305 Examine the precipitate insoluble in sulphide of ammonium for the metals of the fifth group according to the instructions given in 193. d. Residue IV. Compare (299). 306 This may contain tin and antimony, perhaps also copper. Proceed as directed (123). If the color of the residue was black (oxide of copper), treat the reduced metals according to the instructions given in 181. 9. Examination of tlie filtrate reserved in (291)>./*07* Metals of the Fourth and Third Groups, especially for Zinc and Chromium. a. As we have seen in (291)) the fluid filtered from the precipi- 307 tate produced by hydrosulphuric acid, and temporarily re- served for further examination, has already been mixed with sulphide of ammonium. The addition of this reagent to the filtrate is usually attended with the formation of a precipitate consisting of sulphide of iron and phosphate of lime, but which may possibly also contain sulphide of zinc. Filter the fluid from this precipitate, and treat the filtrate as directed in (3g8) ; wash the precipitate with water mixed with some sulphide of ammonium, dissolve by warming with hydrochloric acid, and boil the solution with nitric acid, to convert the protoxide of iron into sesquioxide ; add, if necessary sufficient sesquichloride of iron for carbonate of soda to produce a brownish-yellow precipitate in a sample of the fluid ; neutralize almost completely with carbonate of soda, precipitate with carbonate of baryta, and filter ; the precipitate contains all the sesquioxide of iron and all the phosphoric acid. Concentrate the filtrate, precipitate the baryta with dilute sulphuric acid, filter, add to the filtrate am- monia to alkaline reaction, and precipitate with sulphide of ammo- nium the zinc which may be present. For the further examination of the precipitate see 106. i. u 290 DETECTION OF ARSENTC. b. The fluid filtered from the precipitate produced by sulphide of ammonium (307) will usually contain all the chromium 308 that may be present, as sulphide of ammonium fails to preci- pitate sesquioxide of chromium from solutions containing or- ganic matters. If you wish to ascertain whether chromium is really present, evaporate the filtrate to dryness, ignite, mix the fixed residue with 3 parts of nitrate of potassa and 1 part of carbonate of soda, and project the mixture into a crucible heated to moderate red- ness, Allow the fused mass to cool, and, when cold, boil with water : yellow coloration of the fluid shows the presence of alkaline chromate, and accordingly of chromium. For confirmatory tests see 138. II. METHOD FOR THE DETECTION OF HYDROCYANIC ACID. 226. In cases of actual or suspected poisoning with hydrocyanic acid, 309 where it is required to separate that acid from articles of food or from the contents of the stomach, and thus to prove its presence, it is highly necessary to act with the greatest expedition, as the hydro- cyanic acid speedily undergoes decomposition. Still this decomposition is not quite so rapid as is generally supposed, and indeed it requires some time before the complete decomposition of the whole of the acid present is effected.* Although hydrocyanic acid betrays its presence, even in minute quan- tities, by its peculiar odor, still this sign must never be looked upon as conclusive. On the contrary, to adduce positive proof of the presence of the acid, it is always indispensable to separate it, and to convert it into certain known compounds. The method of accomplishing this, which I am about to describe, is based upon distillation of the acidified mass, and examination of the dis- tillate for hydrocyanic acid. Now, as the non-poisonous salts, ferro- and ferricyanide of potassium give by distillation likewise a product contain- ing hydrocyanic acid, it is, of course, indispensable as Otto very properly observes first to ascertain whether one of these salts may not be present. To this end, stir a small portion of the mass to be examined with water, filter, acidify the filtrate with hydrochloric acid, and test a portion of it with sesquichloride of iron, another with sulphate of protoxide of iron. If no blue precipitate or coloration forms in either, soluble ferro- and ferricyanides are not present, and you may safely proceed as follows : Test, in the first place, the reaction of the mass under examina- 310 tion ; if necessary, after mixing and stirring it with water. If it is *not already strongly acid, add solution of tartaric acid until the fluid strongly reddens litmus-paper ; introduce the mixture into a retort, aijd place the body of the retort, with the neck pointing upwards, in an iron or copper vessel, but so that it does not touch the bottom, which * Thus I succeeded in separating a notable quantity of hydrocyanic acid from the stomach of a man who had poisoned himself with that acid in very hot weather, and whose intestines were handed to me full 36 hours after death. A dog was poisoned with hydrocyanic acid, r-nd the contents of the stomach, mixed with the blood, were left for 24 hours exposed to an intense summer heat, and then examined : the acid was still detected. DETECTION OF ACIDS. 291 should, moreover, by way of precaution, be covered with a cloth ; fill the vessel with a solution of chloride of calcium, and apply heat, so as to cause gentle ebullition of the contents of the retort. Conduct the vapors passing over, with the aid of a tight-fitting tube, bent at a very obtuse angle, through a Liebig's condensing apparatus, and receive the distillate in a small weighed flask. When about half-an-ounce of distillate has passed over, remove the receiver, and replace it by a somewhat larger flask, also previously tared. Weigh the contents of the first receiver now, and proceed as follows : a. Mix one-fourth of the distillate with solution of potassa 311 or soda to strongly alkaline reaction, then add a small quantity of solution of sulphate of protoxide of iron, mixed with a little sesquichloride of iron ; digest a few minutes at a very gentle heat, and supersaturate finally with hydrochloric acid. If a blue precipitate forms, this shows the distillate to contain a relatively large, if a blue-greenish fluid is obtained, from which blue flakes separate after long standing, a relatively small, quantity of hydrocyanic acid. 6. Treat another fourth as directed 155, 7, to convert the 312 hydrocyanic acid into sulphocyanide of iron. As the distillate might, however, contain acetic acid, do not neglect to add towards the end of the process a little more hydrochloric acid, in order to neutralize the adverse influence of the acetate of ammonia. c. If the experiments a and b have demonstrated the pre- 313 sence of hydrocyanic acid, and you wish now also to approxi- mately determine its quantity, continue the distillation until the fluid passing over contains no longer the least trace of hydro- cyanic acid ; add one-half of the contents of the second receiver to the remaining half of the contents of the first, mix the fluid with nitrate of silver, then with ammonia until it predominates, and finally with nitric acid to strongly acid reaction. Allow the pre- cipitate which forms to subside, filter on a tared filter, dried at 212 Fah., wash the precipitate, dry it thoroughly at 212 Fah., and weigh. Ignite the weighed precipitate in a small porcelain crucible, to destroy the cyanide of silver, fuse the residue with car- bonate of soda and potassa to effect the decomposition of the chloride of silver which it may contain boil the mass with water, filter, acidify the filtrate with nitric acid, and precipitate with nitrate of silver ; determine the weight of the chloride of silver which may precipitate, and deduct the amount found from the total weight of the chloride and cyanide of silver : the difference gives the quantity of the latter ; by multiplying the quantity found of the cyanide of silver by 0*2017, you find the corresponding amount of anhydrous hydrocyanic acid ; and by multiplying this again by .2 as only one-half of the distillate has been used you find the total quantity of hydrocyanic acid which was present in the ex- amined mass. Instead of decomposing the fused silver precipitate by fusion with carbonate of soda and potassa, it may be reduced also by means of zinc, with addition of dilute sulphuric acid, and the chlorine determined in the filtrate. Instead of pursuing this indirect method, you may also 314 determine the quantity of the hydrocyanic acid by the fol- lowing direct method : introduce half of the distillate into a u2 292 DETECTION OF PHOSPHORUS. retort, together with powdered borax ; distil to a small residue, and determine the hydrocyanic acid in the distillate as cyanide of silver. Hydrochloric acid can no longer be present in this distillate, as the soda of the borax retains it in the retort ( Wackenroder.) III. METHOD FOB THE DETECTION OP PHOSPHORUS. 227. Since phosphorus paste has been employed to poison mice, &c., 315 and the poisonous action of lucifer matches has become more ex- tensively known, phosphorus has not unfrequently been resorted to as an agent for committing murder. The chemist is therefore occa- sionally called upon to examine some article of food, or the contents of a stomach, for this substance. It is obvious that, in cases of the kind, his whole attention must be directed to the separation of the phosphorus in the free state, or to the production of such reactions as will enable him to infer the presence of free phosphorus ; since the mere finding of phosphorus in form of phosphates would prove nothing, as phosphates invariably form constituents of animal and vegetable bodies. A. Detection of Unoxidized Phosphorus. \. Ascertain in the first place whether the substance under ex- 316 animation does not betray the presence of phosphorus to the sense of smell, by the peculiar odor of that element, or to the sense of sight, by luminosity in the dark. To this end take care to increase the contact of the phosphorus in the substance with the air, by rub- bing, stirring, and shaking. 2. Put a little of the substance into a flask, fasten to the loosely 317 inserted cork a strip of filtering-paper moistened with neutral solution of nitrate of silver, and heat to from 86 to 104 Fah. If the paper does not turn black, not even after some time, no unoxidized phosphorus is present, and there is consequently no need to try 3 and 4, but the operator may at once pass on to B (324). If, on the other hand, the paper strip turns black, this is no positive proof of the presence of unoxidized phosphorus, as hydrosulphuric acid, formic acid, putrifying matters, (sulphide of copper) will demonstrate the presence of copper. Where there is reason to suppose that the precipitate containing the sulphides of the fifth group (of copper, bismuth, &c.), contains also the sulphides of palladium, rhodium osmium, and ruthenium, proceed as follows : Fuse the precipitate with hydrate of potassa and chlorate of potassa, heat, ultimately to redness, let cool, then treat the fused mass with water. The solution contains osmate and ruthenate of potassa, which latter imparts a deep yellow color to it. If the fluid is cautiously neutralized with nitric acid, black sesquioxide of ruthenium separates ; if more citric acid is added to the filtrate, and the fluid then distilled, osmic acid passes over. If the residue left upon the extraction of the fused mass with water is gently ignited in hydrogen gas,* then cautiously treated with dilute nitric acid, the copper, lead, &c., are dissolved, whilst the rhodium and palladium are left undissolved. The palladium, may then be dissolved out of the residue by means of aqua regia, leaving the rhodium undissolved. For the further examination of the isolated metals, I refer to 124. A separate portion of the precipitate of the sulphides must be examined for mercury, in tho event of the above process being adopted. To 194. Assuming all elements not yet precipitated to be present in the fluid filtered from the precipitate produced in an acid solution by hydrosulphuric acid, the precipitate produced by addition of chloride of ammonium to this filtrate, neutralization with ammonia, and addition of sulphide of ammonium in excess, will contain the following elements : a. In the form of sulphides : cobalt, nickel, manganese, iron, zinc, uranium ; b. In the form of oxides : aluminium, beryllium, thorium, zirconium, yttrium, terbium, erbium, cerium, lanthanium, didymium, chromium, titanium, tantalum, niobium, f Where there is reason to suspect the presence of some of the rarer elements in the precipitate, the following method may be recommended as the most suitable in many cases : Dry the washed precipitate, ignite in a porcelain crucible, then fuse perseveringly in a platinum crucible with acid sulphate of potassa ; let the fused mass cool, soak in cold water, and digest for some time, without application of heat. Filter the solution from the residue. The RESIDUE, which contains the acids of tantalum and niobium, and may contain also silicic acid and a little undissolved sesquioxide of iron and sesquioxide of chro- mium, gives, on fusion with hydrate of soda and some nitrate of soda, a mass out of which dilute solution of soda will dissolve chromate and silicate of potasa, leaving undissolved, with the sesquioxide of iron, tantalate and hyponiobate of soda (being insoluble in solution of soda). After removing the excess of soda, treat repeatedly with a very dilute solution of carbonate of soda, in which the HTPONIOBATE of soda dissolves much more readily than the TANTALATE. For further examination compare 104, 31 and 12. Treat the SOLUTION, which contains all the other bases, &c., of the third and fuurch groups, with hydrosulphuric acid, to reduce the sesquioxide of iron, dilute considerably, heat to boiling, and keep boiling for some time, whilst conducting carbonic acid into * Cadmium may escape in this operation. + Of hyponiobic acid only the trifling traces redissolved on the precipitation by hydrochloric acid can be present here. 312 SPECIAL KEMARKS AND ADDITIONS. the fluid. If a precipitate is formed, examine this for TITANIC ACID ; it may possibly contain also a little ZIRCONIA. Concentrate the filtrate by evaporation, with addition of some nitric acid, precipi- tate with ammonia, filter, and wash ; redissolve the washed precipitate in hydrochloric acid, and precipitate again with ammonia. This will give almost the whole of the ZINC, MANGANESE, NICKEL, and COBALT in solution, whilst the earths are left undis- solved with the sesquioxides of iron, uranium, and chromium. Redissolve the preci- pitate in hydrochloric acid, and add to the solution concentrated solution of potassa, without applying heat. This will leave in solution the sesquioxide of chromium, the alumina, and the berylla whilst precipitating the other earths with the sesquioxides of iron and uranium. Dilute the alkaline solution, and boil some time ; this will throw down the berylla and the sesquioxide of chromium, leaving the ALUMINA in solution. The latter earth may then be precipitated by chloride of ammonium. Fuse the precipitate of berylla and sesquioxide of chromium with carbonate of soda and nitrate of potassa, and separate the BERILLA from the CHROMIC ACID in the same way in which the separation of alumina from chromic acid is efiected ( 103). The precipitate, which contains the sesquioxides of iron and uranium and the earths insoluble in potassa, may under circumstances, e.g., in presence of yttria and sesqui- oxide of cerium, also contain alumina and berylla. Dissolve it in hydrochloric acid, remove an over-large excess of the acid by evaporation, dilute, add carbonate of baryta, and let the mixture stand from four to six hours in the cold. The precipitate produced contains the SKSQUIOXIDE OF IRON, the SESQUIOXIDE OP URANIUM, and the ALUMINA which may still be present. Redissolve in hydrochloric acid, and separate the sesquioxide of uranium from the alumina and the sesquioxide of iron, by means of carbonate of ammonia added in excess. From the fluid filtered off the precipitate produced by carbonate of baryta, remove the baryta by sulphuric acid, concentrate strongly by evaporation, neutralize exactly with potassa (leaving the re- action rather acid than alkaline), add neutral sulphate of potassa in crystals, boil, and let the fluid stand twelve hours. Then filter, and wash with a solution of neutral sulphate of potassa. The filtrate contains that portion of the berylla which may have escaped solution by potassa, also yttria (together with oxide of erbium and oxide of terbium). These substances are precipitated by ammonia, and may then easily be separated by treating with a concentrated warm solution of oxalic acid, in which the BERYLLA is soluble, whilst the oxalates of YTTRIA and of OXIDE OF ERBIUM and OXIDE OF TERBIUM are left undissolved. Now boil the precipitate of the double sulphates of zirconia, &c. and potassa repeatedly in water, with addition of some hydrochloric acid, which will dissolve the THOKIA and the OXIDES OF CERIUM, leaving the sulphate of ZIRCONIA and potassa undissolved. The thoria and the oxides of cerium may then be precipitated from the solution by ammonia, and tested by the reactions described in 104. To 195198. The fluid filtered from the precipitate produced by sulphide of ammonium may not only contain the alkaline earths and the alkalies, but some nickel, and also vanadic acid and that portion of the tungstic acid which has been left unprecipitated by hydro- chloric acid. The nickel, the vanadic acid, and the tungstic acid, are present as sul- phides dissolved in the excess of sulphide of ammonium ; they are thrown down in that form by just acidifying the fluid with hydrochloric acid. Filter the precipitate, wash, dry, fuse with carbonate of soda and nitrate of potassa, and treat the fused mass with water ; this will dissolve the vanadate and tungstate of potassa, leaving the protoxide of nickel undissolved. From this solution the vanadic acid may be separated by means of solid chloride of ammonium, the tungstic acid by evaporating with hydrochloric acid and treating the residue with water. The two acids may then be examined as directed 113, 6, and 135, c. For the detection of lithium, caesium, and rubidium, I refer to the analysis of mineral waters (258) and (259)- To 203. If the rarer elements are taken into account, the number of bodies which are left undissolved by treating a substance under examination with water, hydrochloric acid, nitric acid, and aqua regia, is much enlarged. The following bodies, more especially, are either altogether, or in the ignited state, or in certain combinations, insoluble or slowly and sparingly soluble in acids : Berylla, thoria, and zirconia ; the oxides of cerium ; titanic acid and tantalic acid ; hyponiobic acid and niobic acid ; molybdic acid and tungstic acid ; rhodium, iridmm, osmio-iridium, ruthenium. When you have, in the systematic course of analysis, arrived at (2G8)> fuse the SPECIAL REMARKS AND ADDITIONS. 313 substance, free from silver, lead, and sulphur, with carbonate of soda and some nitrate of potassa, extract the fused mass repeatedly with hot water, and, if a residue is left, fuse this some time, in a silver crucible, with hydrate of potassa and nitrate of potassa, and again treat the fused mass repeatedly with water. The alkaline solutions, which may be examined separately or together, may contain berylla, a portion of the titanic acid, the tantalic acid, the niobic acid, the molybdic acid, the tungstic acid, the osmic and ruthenic acids, and a portion of the iridiuni present. If the residue left undissolved by the preceding operation is fused with acid sulphate of potassa, and the fused mass treated with water, the thoria and zirconia, the oxides of cerium, the remainder of the titanic acid, and the rhodium may dissolve. A residue left by this operation may consist of platinum ore metals that have escaped decompo- sition by fluxing, and had best be mixed with chloride of sodium, and ignited in a stream of chlorine. With respect to the separation and individual detection of the several elements that have passed into the different solutions, the requisite directions and instructions have been given in the third section of Part I., and in the additional remarks to 189-198. To 204. The analysis of cyanogen compounds is not very easy in certain cases, and it is sometimes a difficult task even to ascertain whether we have really a cyanide before us or not. However, if the reactions of the sub- stance under examination upon ignition (8) be carefully observed, and also whether upon boiling with hydrochloric acid any odor of hydro- cyanic acid is emitted (35)> the presence or absence of a cyanide will generally not long remain a matter of doubt. It must above all be borne in mind that the insoluble cyanogen com- pounds occurring in pharmacy, &c., belong to two distinct classes. Viz., they are either SIMPLE CYANIDES, or COMPOUNDS OF METALS WITH FERRO- CYANOGEN or some other analogous compound radical. All the simple cyanides are decomposed by boiling with concentrated hydrochloric acid into metallic chlorides and hydrocyanic acid. Their analysis is therefore never difficult. But the ferrocyanides, &c., to which indeed the method described 204 more exclusively refers, suffer by acids such complicated decompositions that their analysis by means of acids is a task not so easily accomplished. Their decomposition by potassa or soda is far more simple. The alkali yields its oxygen to the metal combined with the ferrocyanogen, o O 02 342 APPENDIX. IV. TABLE OF THE MORE FREQUENTLY OCCURRING FORMS AND COMBINATIONS OF THE SUBSTANCES TREATED OF IN THE PRESENT WORK, ABBANGED WITH ESPECIAL REGARD TO THE CLASS TO WHICH THEY RESPECTIVELY BELONG ACCORDING TO THEIR SOLUBILITY IN WATER, IN HYDROCHLORIC ACID, IN NITRIC ACID, OR IN NITROHYDROCHLORIC ACID. 247. PRELIMINARY REMARKS. The class to which the several compounds respectively belong accord- ing to their solubility in water or acids (see 179), is expressed by figures. Thus 1 or I means a substance soluble in water ; 2 or II a substance insoluble in water, but soluble in hydrochloric acid, nitric acid, or nitrohydrochloric acid ; 3 or III a substance insoluble in water, in hydrochloric acid, and in nitric acid. For those substances which stand as it were on the limits between the various classes, the figures of the classes in question are jointly expressed : thus 1 2 signifies a substance sparingly soluble in water, but soluble in hydrochloric acid or nitric acid ; 1 3 a body sparingly soluble in water, and of which the solubility is not notably increased by the addition of acids ; and 2 3 a substance insoluble in water, and sparingly soluble in acids. Wherever the deport- ment of a substance with hydrochloric acid differs materially from that which it exhibits with nitric acid, this is stated in the notes. The Roman figures denote officinal and more commonly occurring compounds. The haloid salts and sulphur compounds are placed in the columns of the corresponding oxides. The salts given are, as a general rule, the neutral salts ; the basic, acid, and double salts, if officinal, are mentioned APPENDIX. 343 in the notes ; the small figures placed near the corresponding neutral or simple salts refer to these. Cyanogen, chloric acid, citric acid, malic acid, benzoic acid, succinic acid, and formic acid, are of more common occurrence in combination with a few bases only, and have therefore been omitted from the table. The most frequently occurring compounds of these substances are : cyanide of potassium I, ferrocyanide of potassium I, ferricyanide of potassium I, sesqui-ferricyanide of iron (Prussian blue) III, ferrocyanide of zinc and potassium II III, chlorate of potassa I, the citrates of the alkalies I, the malates of the alkalies I, malate of sesquioxide of iron I, the benzoates of the alkalies I, the succinates of the alkalies I, and the formates of the alkalies I. 344 APPENDIX. INDEX OF THE SOLUBILITY 01 KO NaO NH 4 BaO SrO CaO MgO A1 2 8 MnO FeO Fe 2 0, CoO NiO ZnO I I I I 1 I-II II II 2 2 II II II II s I I I I 1 MI 2 II II 2 2,. 2 I6 2,r Cl I I I, 2 I I I 1 1 I I In I I 1 I I 1 1 1 1 1 1 1 I 1 1 SOg It I 1,8 III III I-III I I|M. I I I I I I N0 5 I I I I I 1 1 1 1 1 1 I 1 1 PO S 1 I,o l,o 2 2 n u 2 2 2 2 II 2 2 2 C0 3 I 2 I,i I II II ii II II II II 2 II I. 1 I 2 2 ii 2 2 2 1-2 1-2 2 2 2 B0 8 1* I* 1 2 2 2 2 2 2 2 2 2 2 2 A I I I I 1 I 1 1 1 1 I 1 1 I T~ !.. IT 1. 2 2 II 1-2 1 1-2 1-2 I 8 1 2 2 As0 6 I I 1 2 2 2 2 2 2 2 2 2 2 2 As0 8 I 1 1 2 2 2 2 2 2 2 2 Cr0 3 I 1 1 2 2 2 1 2 1 1 2 1 NOTES. 1. SULPHATE of potassa and alumina I. 2. Bicarbonate of potassa I. 3. Binoxalate of potassa I. 4. Tartarized borax (bitartrate of potassa and borate of soda) I. 5. Bitartrate of potassa I-II. 6. Tartrate of potassa and ammonia I. 7. Tartrate of potassa and soda I. 8. Tartrate of potassa and sesquioxide of iron I. 9. Tartrate of antimony and potassa I. 10. Phosphate of soda and ammonia I. 11. Bicarbonate of soda I. 12. Sesquichloride of iron and chloride of ammonium I. 13. Sulphate of alumina and ammonia I. 14. Basic phosphate of lime II. 15. Sulphide of cobalt is pretty readily decomposed by nitric acid, bu very difficultly by hydrochloric acid. This substance is no officinal. APPENDIX. 345 SUBSTANCES IN WATER OR ACIDS. CdO PbO SnO Sn0 2 Bi0 3 CuO Hg 2 HgO AgO PtO a Au0 8 SbO a Cr s O, 2 n 18 2 2&3 2 II 22 II II 2 2 H 3 5 II & III s 2 ii 2 20 2 20 2 2 28 II II 2 8 o 2 3 i II 36 CI 1 i-m I I I I* II-III I 28 III I 32 ,,3 ! I 8 7 i&m I 1 i-n 1 1 II II 3 S0 3 I ii-in 1 1 I 25 1-2 1. I-II 1 2 MI N0 5 1 i 1 I 21 I I I I 1 i PO S 2 2 2 2 2 2 2 2 C0 2 2 II 2 II 2 2 2 2 2 2 1 2 2 2 2 2 1-2 1 BO S 1-2 2 2 2 2 1 2 -J 1 T i 1 7 X 19 X T 1-2 2 1-2 2 1 1-2 2 2 I 38 1 As0 5 2 2- 2 2 2 2 2 2 AsO, 2 II 2 2 2 2 Cr0 8 II-III 2 2 1 2 1-2 2 2 2 1 6. The same applies to sulphide of nickel. 17. Sulphide of zinc is readily soluble in nitric acid, somewhat more sparingly soluble in hydrochloric acid. 18. Minium is converted by hydrochloric acid into chloride of lead; by nitric acid into oxide, which redissolves in an excess of the acid, and into brown binoxide of lead, which is insoluble in nitric acid. 19. Trisacetate of lead I. 20. Proto- and bisulphide of tin are decomposed and dissolved by hydrochloric acid ; by nitric acid they are converted into binoxide, which is insoluble in an excess of the acid. Sub- limed bisulphide of tin dissolves only in nitrohydrochloric acid. 21. Basic nitrate of teroxide of bismuth II. 22. Ammoniated oxide of copper 1. 23. Sulphide of copper is difficultly decomposed by hydrochloric acid, but with facility by nitric acid. 24. Chloride of copper and ammonium I. 25. Sulphate of copper and ammonia I. 346 APPENDIX. 26. Basic acetate of copper, partially soluble in water, and completely in acids. 27. Basic nitrate of suboxide of mercury and ammonia II. 28. Ammonio-chloride of mercury II. 29. Basic sulphate of oxide of mercury II. 30. Sulphide of silver soluble only in nitric acid. 31. Bisulphide of platinum is not affected by hydrochloric acid, and but little by boiling nitric acid ; it dissolves in hot nitrohydrochloric acid. 32. Bichloride of platinum and chloride of potassium 1 3. 33. Bichloride of platinum and chloride of ammonium 1 3. 34. Terchloride of gold and chloride of sodium I. 35. Teroxide of antimony is soluble in hydrochloric acid, but not in nitric acid. 36. Tersulphide of antimony and sulphide of calcium I IL 37. Basic terchloride of antimony II. 38. Tartrate of teroxide of antimony and potassa I. NOTE TO PAGE 111. For a full account of THALLIUM, the Editor refers to the original papers of its discoverer, Mr. CROOKES, published in the Chemical News, Philo- sophical Transactions, and Proceedings during the years 1861, 2, and 3. APPENDIX. 347 Y. TABLE OF WEIGHTS AND MEASURES. GRAMMES. 1 2 3 4 5 6 7 8 CENTIGRAMMES. 1 2 3 4 5 6 7 8 9 METRES. 1 2 3 4 5 6 7 8 9 CENTIMETRES. 1 2 3 4 5 6 7 8 9 GRAINS. DECIGRAMMES. 15-4323 1 = 30-8646 2 46-2969 3 61-7292 4 77-1615 5 92-5938 6 108-0261 7 123-4584 8 138-8907 9 GRAINS. MILLIGRAMMES. 1543 1 3086 2 4630 3 6173 4 7717 5 9260 6 1-0804 7 1-2347 8 1-3891 9 INCHES. DECIMETRES. 39-37 1 = 78-74 2 118-11 3 157-48 4 196-85 5 236-22 6 275-59 7 314-96 8 354-33 9 INCHES. MILLIMETRES. 3937 1 = 7874 2 1-1811 3 1-5748 4 1-9685 5 2-3622 6 2-7559 7 3-1496 8 3-5433 9 GRAINS. 1-5432 3-0864 4-6296 6-1728 7-7160 9-2592 10-8024 12-3456 13-8888 GRAINS. 0154 0308 0463 0617 0771 0926 1080 1234 1389 INCHES. 3-937 7-874 11-811 15-748 19-685 23-622 27-559 31-496 35-433 INCHES. 03937 07874 11811 15748 19685 23622 27559 31496 35433 One kilogramme One cubic centimetre One litre 15432 grains. 0-0610 cubic inch. 61-0270 cubic inches. ALPHABETICAL INDEX. A. PAGE Acetic acid (as reagent) ... 33 deportment with reagents 193 detection of, in simple com- pounds . . . 223 in complex com- pounds 250, 252 Acids, as reagents .... 30 Actual examination . . . .214 Alcohol (as reagent) . . . .30 Alkaloids, detection of . . ^ . 329 in presence of coloring and extractive vege- table or animal matter 332 Alkaline solutions, examination of . 229 Alloys, examination of . . 209, 213 Alumina, deportment with reagents . 90 detection of, in soluble simple compounds . 218, 224 in soluble complex compounds 239, 240, 242 in insoluble complex compounds . . 253 phosphate (see phosphate of alumina). Ammonia (as reagent) ... 44 deportment with reagents . 78 detection of, in simple com- pounds . . .219 in complex com- pounds 1 246 in soils . .276 in fresh waters 265 in mineral waters 267 carbonate of (as reagent) . 52 molybdate of (as reagent) . 54 oxalate of (as reagent) . 50 Antimonic acid, detection of . . 309 Antimony, detection of, in alloys . 213 properties of . . .131 teroxide of, detection of, in simple compounds . 215 in complex compounds 235 in sinter deposits . 272 in food, &c. . . 289 PAGE Antimony, teroxide of, deportment with reagents . . . .131 Apocrenic acid, detection of, in soils . 277 in mineral waters 273 Apparatus and utensils ... 25 Arsenic, properties of . . .134 acid, deportment with reagents 143 produced from arsenious acid . 140 the tersulphide 140 Arsenious acid, deportment with re- agents 134 Arsenious and arsenic acids, detection of, in simple compounds . 215 in complex compounds 234,255 in mineral waters . 266 in food, &c. . .285 in sinter deposits . .272 Arsenious from arsenic acid, how to distinguish . . . .147 Ashes of plants, animals, manures, &c., examination of ... 297 B. Baryta, deportment of, with reagents . detection of, in soluble simple compounds in insoluble simple compounds in soluble complex compounds in insoluble com- plex compounds in mineral waters in sinter deposits . carbonate of (as reagent) hydrate of (as reagent) nitrate of (as reagent) water (as reagent) Bases (as reagents) . Benzoic acid, detection of, in simple compounds . in complex com- pounds . . deportment with reagents 82 219 228 244 252 269 273 59 68 58 45 42 26 222 252 192 350 ALPHABETICAL INDEX. PAGE Berylla, deportment with reagents . 74 detection of . . 311, 312 Bismuth, detection of, in alloys . 209 in articles of food, &c. . 289 properties of . 119 teroxide, deportment of, with reagents . .119 detection of, in simple compounds . 216 in complex com- pounds . 236, 237 hydrated (as reagent) 47 Blowpipe 13 flame ... 14, 15 Boracic acid, deportment with re- agents . . . 160 detection of, in simple compounds 221, 224, 225 in complex com- pounds 244, 249 in silicates 259, 261 in mineral wa- ters . . 270 Borax (as reagent) . . . .71 Bromicacid, detection of . . .310 Bromine, properties and deportment with reagents . .172 detection of 221, 225, 227, 248 in mineral wa- ters . . 270 Brucia, deportment with reagents . 326 detection of, in simple com- pounds 329, 330, 331 in complex com- pounds . . 332 Butyric acid, deportment with reagents 196 C. Cadmium, properties of . . . 121 oxide, detection of, in simple compounds 215 in complex compounds 236, 237 deportment with re- agents . . . 121 Caesium, oxide, deportment with re- agents . . 80 detection of . . 271 Carbon, detection of, in compound bodies 227, 253 in silicates . 259 properties of . . .167 Carbonic acid, deportment with reagents 167 detection of, in simple compounds 219 in complex compounds 230 in soils 275, 276 in well and mineral waters 264, 265, 266 Cerium, oxides, deportment with re- agents . . 95 detection of . .312 Charcoal for blowpipe experiments . 15 PAGE Chloric acid, detection of . . 221, 248 deportment with reagents 184 Chloride of ammonium (as reagent) 55 of baT'ium (as reagent) 58 of calcium (as reagent) 59 of mercury (as reagent) 63 Chlorine (as reagent) . . 35 properties and deportment with reagents 171 detection of, in soluble simple compounds 221, 225 in insoluble sim- ple compounds 227 in soluble com- plex compounds 248 in insoluble com- plex compounds 254 in soils . .275 in fresh and mi- neral waters . 264 in silicates 260, 261 Chloroform (as reagent) . . .30 Chlorous acid, deportment with reagents 182 detection of . .310 Chrome-ironstone, analysis of .255 Chromic acid, deportment with reagents 1 52 detection of, in simple compounds . .219 in complex compounds 249 in insoluble com- pounds . . 255 Chromium, sesquioxide, deportment with reagents . . 92 detection of, in soluble simple com- pounds 217, 218 in complex com- pounds 240, 243 Cinchonia, deportment with reagents . 322 detection of, in simple com- pounds . 330 in complex com- pounds . 332 Citric acid, deportment with reagents 187 detection of, in simple com- pounds . 222 in complex com- pounds . 250 Cobalt, properties of . . .104 protoxide, deportment with re- agents . 1 04 detection of, in sim- ple compounds . 217 in complex com- pounds 24], 242 nitrate (as reagent) . .72 Coloration of flame . . . .21 Conia, deportment with reagents . 317 Copper (as reagent) . . . .47 properties of . . .117 oxide, deportment with reagents 117 detection of, in simple com- pounds . 216 in complex com- pounds 236, 237 ALPHABETICAL INDEX. 351 PAGE Copper, oxide, detection of, in sinter deposits . 272 sulphate (as reagent) . . 63 Crenic acid, detection of, in soils . 277 in mineral waters 273 Crystallization 5 Cyanide of potassium (as reagent) . 55 in the moist way 55 in the dry way . 70 Cyanides, insoluble in water, analysis of 256 Cyanogen, detection of, in simple com- pounds 220, 227 in complex com- pounds 231, 248 properties of ... 176 D. Decantation .... Deflagration .... Dialysis ..... Didymium, oxide, deportment with re detection of Distillation . Distilling apparatus E. 8 12 282 96 311 10 10 Edulcoration 8 Erbium, oxide, deportment with re- agents . 9 5 detection of. . . 311, 312 Ether (as reagent) .... 30 Evaporation ..... 9 F. 57 220 F?rricyanide of potassium (as reagent) Ferricyanogen, detection of, in simple compounds . in complex com- pounds 248, 256, 257 Ferrocyanide of potassium (as reagent) 56 Ferrocyanogen, detection of, in simple compounds . 220 in complex compounds 248, 256, 257 Filtering paper . 7 stands . 7 Filtration . . 7 Flame, coloration of 21 parts of 13 Fluoride of calcium (as reagent) 69 Fluorine, detection of, in simple com pounds 220, 224, 225, 227 in complex com- pounds 244, 252 in insoluble com- pounds . 255 in mineral waters 268 in sinter deposits 273 in silicates 260, 261 Fluxing 11 Formic acid, deportment with reagents 194 PAGE Formic acid, detection of, in simple com- pounds . 223 in complex compounds 250 Funnels 7, 26 Fusion . . , . .11 G. Gas-lamp 18, 25 Geic acid, detection of, in soils 277 Georgina paper ... 66 Gold, properties of . . . 125 detection of, in alloys . 213 terchloride of (as.reagent) . 65 teroxide, deportment with re agents . . .125 detection of, in simple compounds 216 in complex compounds 235 H. Halogens (as reagents) . . .31 Humic acid, detection of, in soils . 277 Hydriodic acid, deportment with re- agents ..... 174 Hydrobromic acid, deportment with re- agents . . 172 Hydrochloric acid (as reagent) . . 34 deportment with re- agents . . 171 Hydrocyanic acid, deportment with re- agents . . 176 in organic mat- ters . . 290 Hydroferricyanic acid, deportment with reagents 178 Hydroferrocyanicacid, deportment with reagents 178 Hydrofluoric acid, properties and de- portment with reagents . .163 detection of . .249 Hydrofluosilicic acid (as reagent) . 37 deportment with reagents . 156 Hydrogen acids (as reagents) . . 34 Hydrosulphuric acid (as reagent) . 37 deportment with reagents . 178 detection of, in sim- ple compounds 219 in complex com- pounds - 248 in mineral waters 267 Hypochlorous acid, deportment with re- agents 182 detection of . . .310 Hyponiobic acid, deportment with re- agents 98 detection of . . .309 Hypophosphorous acid, deportment with reagents . . . .182 Hyposulphurous acid, deportment with reagents 154 detection of . . 309, 310 852 ALPHABETICAL INDEX. I. PAGE Ignition . .... 10 Indigo solution (as reagent) . . 67 Inorganic bodies, detection of, in pre- sence of organic bodies . . 278 lodic acid, deportment with reagents 154 detection of . . . 310 Iodine, detection of, in simple com- ^ pounds 220, 225, 227 in complex com- pounds . 248 in mineral waters 277 properties of . . . .174 Iron (as reagent) . . , .47 properties of . . .105 protoxide, deportment with reagents 105 detection of, in simple compounds . 217 in complex com- pounds . 242 in well and mi- neral waters 264, 267, 268 sulphate of protoxide (as reagent) 60 sesquichloride (as reagent) . . 61 sesquioxide, deportment with re- agents . _ . . .107 detection of, in simple compounds . 215 in complex com- pounds 231, 242 in soils . . 276 in well and mine- ral waters 264, 268 Iridium, oxide, deportment with re- agents . . .147 detection . 310, 312 Lactic acid, deportment with reagents . 196 Lamps, use of 17 Lanthanium, oxide, deportment with reagents . 96 detection of .311 Lead, properties of, and deportment of oxide with reagents . . 114 oxide, detection of, in soluble simple compounds 214, 216 in insoluble simple compounds . 227 in soluble complex compounds 229, 237 in insoluble complex compounds . 254 in organic matters 289 in sinter deposits 272 acetate (as reagent) . . 62 Lime, deportment with reagents . 85 detection of, in soluble simple compounds . 218 in soluble complex compounds 242, 243, 2*5 PAGE Lime, detection of, in insoluble simple compounds 227, 228 in insoluble complex compounds in soils inwelland minera waters . sulphate (as reagent) water (as reagent) . Lithia, deportment with reagents detection of, in mineral waters 252 276 264 59 46 80 270 Litmus-paper 65 M. 86 Magnesia, deportment with reagents . detection of, in simple com- pounds in complex com- pounds in soils . in well and mi- neral waters 264, 265 sulphate of (as reagent) . 60 Malic acid, detection of, in simple compounds in complex compounds deportment with reagents . Manganese, properties of . protoxide, detection of, in simple compounds in complex compounds 240,243 in soils . . 275, 276 in mineral waters . 269 protoxide, deportment with reagents Marsh's apparatus .... Mercury, detection of, in articles of food, &c. properties of ... chloride (as reagent) . oxide, deportment with re- 219 245 276 222 250 188 101 217 101 138 289 113 detection of, in soluble simple com- pounds . oxide, detection of, in soluble complex compounds suboxide, deportment with reagents .... detection of, in sim- ple com- pounds in complex compounds nitrate of, (as re- agent) Metallic poisons, detection of, in ar tides of food, &c. Metals (as reagents) . Mineral waters, analysis of Molybdenum, deportment of oxide of with reagents 116 216 237 113 detection of 24 229 62 279 12 266 148 309, 312 ALPHABETICAL ISDEX. 353 PAGE Morphia, deportment with reagents . 318 detection of, in simple com- pounds 329, 330 in complex com- pounds . 331 N. Narcotina, deportment with reagents . 320 detection of, in simple com- pounds 329, 330 in complex com- pounds . 332 Nickel, properties of . . . .102 protoxide, deportment with re- agents . .102 detection of, in simple compounds . 217 in complex compounds, 241, 242 Nicotina, deportment with reagents . 316 Niobicacid, detection . . .312 Nitric acid (as reagent) ... 33 deportment with reagents . 183 detection of, in simple com- pounds . 221 in complex com- pounds . 248 in soils . . 275 in well and mi- neral waters, 264, 270 Nitrohydrochloric acid (as reagent) . 36 Nitrous acid, deportment with reagents 181 detection of . . .310 in fresh waters 265 in mineral waters 271 0. Osmium, oxides, deportment with re- agents . . .123 detection of 310, 311, 312 Oxalic acid, properties of . . .162 deportment with reagents . 162 detection of, in simple com- pounds 220, 224, 225 in complex com- pounds 243, 249, 252 Oxidizing flame . . . .14 Oxygen acids (as reagents) . . 31 bases (as reagents) ... 42 P. Palladium, properties of . . .123 protoxide of, deportment with reagents . .123 detection of . . .310 sodio-chloride as reagent . 65 Paratartaric acid, deportment with re- agents 190 Perchloric acid, deportment with re- agents 186 Phosphate of soda and ammonia (as reagent) 71 Phosphates of alkaline earths, detec- tion of, in simple compounds . 224 PAGE Phosphates in complex compounds . 241 Phosphoric acid, deportment with re- agents . .156 monobasic . .160 bibasic . . .160 detection of, in simple compounds, 220, 224, 225 in complex compounds, 243, 248, 251, 255 in soils 275, 276 in mineral waters, 264, 268 in silicates, 259, 261, 262 in articles of food, &c. . 292 Phosphorous acid, deportment with re- agents .... 167 Phosphorus, properties of . 156 Pincers 26 Platinum, detection of, in alloys 213 properties of . 126 bichloride of (as reagent) 64 binoxide of, deportment with reagents . 126 detection of in sim- ple compounds 216 in complex compounds 235 crucibles and their use 11, 25 foil and wire . 16, 25 Porcelain dishes and crucibles . 26 Potassa (as reagent) . .42 antimonate (as reagent) . 54 bichromate (as reagent) . 53 nitrite (as reagent) . 53 sulphate (as reagent) . 50 deportment with reagents . 75 detection of, in simple com- pounds . .219 in complex com- pounds . 246 in well and mi- neral waters . 265 in silicates . 261 in soils . . 276 Potassium, ferricyanide of (as reagent) 57 ferrocyanide of (as reagent) 56 sulphocyanide of (as reagent) 57 Precipitation 6 Preliminary examination of solid bodies 204 of fluids . 209 Propionic acid, deportment with re- agents 196 Q. Quina, detection of, in simple compounds 331 Quina, detection of, in complex com- pounds .... 332 deportment with reagents . 321 R. Racemic acid, deportment with reagents 190 A A LONDON : SAVILL AND EDWARDS, PRINTERS, CHANDOS STREET, COVENT GARDEN. London, New Burlington Street, June, 1867. MESSRS. CHURCHILL & SONS' IN MEDICINE AND THE VAKIOUS BRANCHES OF NATUEAL SCIENCE. " It would be unjust to conclude this notice without saying a few words in favour of Mr. Churchill, from whom the profession is receiving, it may be truly said, the most beautiful series of Illustrated Medical Works which has ever been published." Lancet. "All the publications of Mr. Churchill are prepared with so much taste and neatness, that it is superfluous to speak of them in terms of commendation." Edinburgh Medical and Surgical Journal. " No one is more distinguished for the elegance and recherche' style of his publica- tions than Mr. Churchill." Provincial Medical Journal. 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