[0hvt gjjtttjj ®Itttt;i5it0tt ^ mn u 1303 /f./^^73^ Cornell University Library olin,anx 3 1924 031 246 1 Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031246139 8vo, 3s. &d. sewed, THE GEOUND BENEATH US; ITS GEOLOGICAL PHASES AND CHANGES: Being Three Lecttires on the Geology of Clapham and the Neighbourhood of London generally. By Joseph Prestwich, F.E.S., F.G.S., &e. " A popular exposition of the geology of the London neighbourhood, or, to state it more generally, of the Tertiary Series, exceedingly well done. Seldom or never have we met with any geological statement, intended for an ungeological audience, which is at once so lucid, consecutive, and complete. No one can rise from a careful perusal of these Lectures without a thorough comprehension of what is meant by the succession of the Tertiary strata, a good general idea of the nature of their probable formation, and of the con- temporaneous aspect of the world around, and, what is perhaps yet more valuable, a clear notion of the amount and degree of evidence on which these reconstructive theories rest. Nothing tends more to the sound advance of popular, as well as scientific geology, than careful local monographs of this kind." — The Guardian, August 4, 1858. THE AQXJAEIAN NATUEALIST. A MANTTAL FOE THE SEA-SIDE. By Professor T. Eymeb Jones, F.E.S. Post 8vo, with numerous Coloured Figures on eight Plates. Price 18s. " The hoUday-maker who intends to seek edification among the sea-cucum- bers, and to cultivate acquaintance among the oldest inhabitants of the shore of his watering place, whether Crabs or Jelly-fishes, Qasteropod MoUuscs or compound Ascidians, will receive from none of the many pleasant books upon salt-water life, written for his especial use, so much help as from this volume by Professor T. Eymer Jones. Of all popular books upon the natural history of our shores, it is the most complete and the most scientific, while of scientific books it is the most popular. His former writings have shown how well Professor Eymer Jones is able to think with the few and to speak with the many. A nice criticism would be dissatisfied occasionally with his flowers of speech and his quotations from the poets, but the general reader is more than content when he receives exact science from a foremost naturalist who is desperately resolved not to be dull, and who is not duU, but whose only fault is, that he does not trust sufiiciently to his own power of making the details of science themselves entertaining. This power Mr. Eymer Jones habitually exercises by his freedom from pedantry, his clear- ness of expression, and that pleasant way of apprehending facts in nature which is a part of the constitution of his own mind, and which gives life to his discussions over living creatures." — Examiner, August 21, 1858. JOHN VAN VOOEST, 1 PATEENOSTEE EOW. A MANUAL QUALITATIVE CHEMICAL ANALYSIS. A. BEAUCHAMP NOETHCOTE, E.C.S., DEMONSTEATOR TO THE PKOPeTsoE OF CHEMISTRY AT OXFORD ; LATE SENIOR ASSISTANT IN THE ROYAL COLLEGE OP CHEMISTRY, LONDON ; AlfD ^ AETHUE H.'^CHUECH, E.C.S., or LINCOLN COLLEGE, OXFORD ; LA^'E ASSISTANT TO PROFESSOR BRODIE. LONDON: JOHN VAN VOORST, 1 PATERNOSTER ROW. 1858. ^jg-^-^a^ PBINTBD BY TATLOB AND PBANCIS, EED LION CODKT, FLEET STREET. PREFACE. It has been the intention of the Authors, in writing the present work, to prepare a complete Manual of Qualitative Chemical Analysis for the use of Laboratory Students, while it is hoped that more advanced experimenters also wiU find in it ample in- formation concerning the rarer subjects of research. In attempt- ing to accomplish this double purpose, care has been taken to avoid perplexing the beginner with the descriptions of the less common substances ; with this intention, such descriptions are printed in small type. The present volume is not an account of general chemistry, nor does it contain descriptions of the apparatus employed, or of technical processes ; for information on these points, reference must be made to special treatises* : but it aims to be a complete and systematic Guide to Qualitative Analysis, and to represent the present condition of this department of che- mical science. To the following features of the present work the Authors would request the attention of Chemists, and of aU those engaged in instructing pupils in Chemical Analysis : — 1. In the First Part of the volume, at the end of each group * Mr. C. GrreviUe WilliamB's admirable work will afford the student every information concerning apparatus and manipulation, wliile Dr. Odling's forthcoming Manual will convey, on all points connected with theoretical and descriptive chemistry, the most exact and trustworthy information, and also an able explanation of the grounds upon which the system of notation and equivalents adopted in the present work is based. VI PREFACE. of elements or salts, concise Tables are given, which show at a glance the most striking properties of the more common sub- stances, as well as their most characteristic reactions. 2. The student is gradually accustomed to the use of chemical language, symbols, and formulae, while, on the first mention of any new reaction, the equation representing it is clearly expressed, and the rationale of the process given. 3. In describing the salts and reactions of the various acid and basic radicals, the same order is invariably preserved. The mono- basic salts come first, then the bibasic, and lastly the tribasie, — the basic elements commencing with those most decidedly positive. 4. If, ill treating of any basic or acid-radical, a salt of charac- teristic properties is described, the correspondinrj salt of all basic or acid-radicals subsequently spoken of is invariably noticed. 5. The most characteristic compounds of each radical are printed in a conspicuous type. 6. Facilities are afforded for the progress of the student, in the simple analytical schemes appended to each group. 7. In the Second Part of the work, " The Method of Analysis " is described, ample directions and Tables being given, — while something is still left to the judgment of the pupH, who may frame tables for his own use from a study of the reactions, &e. detailed in Part I. 8. Whole the best methods of procedure in separations and testings are given, endeavour is made to impress on the student the necessity of an exact acquaintance with the nature of the processes concerned. By such means as those which they have just indicated, the Authors trust that they have attained to some degree of unity and simplicity, as well as of completeness, in the present treatise. The atomic weights employed in the present volume are those of Gerhardt, — the atomic weights of Oxygen, Sulphur, Selenium, Tellimmn, and Carbon being doubled, alid the atomic weights of all the other elements remaining the same as those usually adopted. These alterations have long been made by Continental chemists; in England they have been strongly advocated by Professors Brodie and "Williamson and Dr. Odling ; and they have quite recently received the sanction of a large portion of the eminent British chemists. May the Authors hope that their work will be found to supply, in some degree, that want of a suitable handbook of analysis which must be caused by these changes ? EEEATA, Page 24, line 13 from bottom, for " anhydrous chloric acid, or chloric anhydride," read " the chloric radical." 52, „ 23, for " HjCjH^O,," read " H^CjE^Oj." 61 , „ 12, for " to dissolTed," read " to be dissolved. 65, „ 20, for " Ha C^ H^ 0,," read " H^ C^H, O^." 66, „ 3, halve the equation. 96, „ 15, for " soda," read " sodium." CONTENTS. Part I.— CHEMICAL REACTIONS. Chapter I. Page Nickel . . . . 9 Introductory. Page Zinc 9 The Elements . . 1 Tabular view 9 Their characteristics . . 1 Subdivision IV. . 10 Their classification .... o Cadmium 10 Copper . . 10 Chapter II. Silver . . . 11 The Basic Elements. Mercury 11 Their classification . 3 Lead 11 Subdivision I 4 Bismuth . . . . 11 Potassium . 4 Palladium . 12 Sodium 5 Tin ... 12 Lithium 5 Antimony 12 Tabular Tiew 5 Arsenic . . . 12 Subdivision II. 6 Platinum ... 13 Barium . 6 Bhodium, Ruthenium, Iri Strontium 6 dium, and Osmium 13 Calcium ... 6 Gold 13 Magnesium Tabular view . . . 6 Tungsten, Molybdenum 6 and Vanadium . 13 Subdivision III 7 Tabular view .... 13 Yttrium, Erbium, Terbium Subdivision V. ... 14 Cerium, Tianthanium Hydrogen . . 14-17 Didymium, Thorinum Chapter III. Zirconium, G-lucinum and TTranium 7 The Acid Elements. Aluminium 7 Their classification . . 17 Chromium . 7 Subdivision I. . . . 18 Manganese . 8 Chlorine . . . 18 Iron . 8 Bromine . . 20 Cobalt . 8 Iodine . . 21 CONTENTS. Page Page Fluorine ... 22 Sublimation, crystallization, Tabular Tiew 23 precipitation, and distil- Subdivision II 23 lation 49 Osygen 23 List of reagents employed . . 51 Sulphur 25 Basic elements .... 53 Selenium and TeUurimn . 27 Salts of potassium . . . 53 Tabular view . . . . 27 sodium 55 Subdivision III. . . 27 ammonium 66 Carbon ... 28 barium . . 58 Boron 29 calcium 59 Silicon ... ... 30 magnesium . 59 Tantalum, Niobium, Pelo- iron, cobalt, copper. pium, and Titanium . . 30 and silver .... 60 Tabular view 30 lead, mercury, and bis- Subdivision IV 31 muth .... 61 Nitrogen . . . . 31 palladium, platinum. Phosphorus 32 gold, and ethyle . . 62 Arsenic . . . . 34 hydrogen . . 63 Antimony . . ... 35 Acid elements ... 66 Tabular view . 36 Test papers ... . . 66 Chapter IV. Organic bodies . . . 67 The Laws of Chenuca] Craptee VI. Combination. Detection of the Basic Radi- Definite proportions . . 37 cals in their Compounds Equivalents . . . . Atomic volumes and weights Biatomic and triatomic ele- 37 37 Means of detection . . Analytical classification . 68 69 ments 38 Subdivision I. . . . 70 Condensation in combining 39 Section 1. Salts 39 Salts of potassium . 72 Basic, neutral, and acid salts 40 sodium . . . 7o Various series of salts . 41 lithium 77 Compound acid-radicals . . . 42 Section 2. Compound basic radicals 42 Double decompositions . . Acids 43 45 ammonium . Table of reactions 78 SO Monobasic, bibasic, and tri- Scheme for the analysis of basic acids . . . 46 Subdivision I. 81 Solvents . . ... 48 Subdivision II. . Section I. 81 Chapter V. Salts of barium 83 Of Reagents. strontium 8(i Purification of reagents 49 calcium . . 89 com Page ENIS. XI Page Section 2. arsenic . . . 209 magnesium . . . . 92 platinum . . . 219 Table of reactions . . . 96 rhodium, ruthenium Scheme for the analysis of iridium, and osmium 223 Subdivision II. . . 97 gold 232 JBDIVISIOK III 97 tungsten, molybdenum. and vanadium 236 Section 1. Scheme for the analysis o; Salts of yttrium, thoriuum the 2nd Section of Subdi- cerium, lanthanium vision IV 245 didymium, zirco Table of reactions . . 246 nium, and glucinum 99 aluminium . . 108 Chaptee VII. chromium . . . Ill Detection of the Acid-Radi- uranium .... 116 cals in tlieir Compotmds. iron . ... 119 • Means of detection . . . 248 Section 2. Classification .... 251 manganese . . . 127 Subdivision I. . . 252 cobalt . ... . 132 nickel . 135 Section 1. zinc . ... . 139 Chlorides 253 morphine, quinine, and Bromides . . 256 strychnine . . 142 Iodides 260 Table of reactions . 14^ -149 Fluorides . . 263 Scheme for the analysis of Section 2. Subdivision III. . 150-151 Hypochlorites . 267 UBDIVISION IV. . . 152 Chlorates . 26« Perchlorates . . . 270 Section 1. Bromates . . . 271 Salts of cadmium 154 lodates 273 copper . . . 157 silver 163 Section 3. mercury . . 163 Chlorocadmiates, chloro- lead . . 177 platinates, &c. 276 bismuth . . . 181 Table of reactions . . . 276 paUeidium . 185 Scheme for the analysis of Table of reactions . . 188 Subdivision I 278 Scheme for the analysis o: Subdivision II. . . . 279 the 1st Section of Subdi- Section 1. vision IV. • . 190 Oxides and hydrates . . 281 Section 2. Sulphides .... 283 Salts of tin . . . 191 Selenides . . . 286 antimony . 199 TeUurides 287 CONTENTS. Section 2, Hyposulphites .... 289 Sulphites 290 Hyposulphates .... 293 Trithionates, tetrathion- ates, and pentathionates 294 Sulphates 294 Selenites 298 Seleniates 299 Tellurites 301 TeUuiiates 302 Section 3. Aluminates and chromites 304 Chromates 304 Perohromates, ferrates, manganates, permanga- nates, bismuthates, and stannates 307 Tungstates 308 Molybdates 310 Vanadiates 311 Table of Reactions . . . 313 Scheme for the Analysis of Subdivision II. ... 314 Subdivision III. . . . 315 Cyanides Section 3. . . .336 ... 340 Sulphocyanides .... 341 Ferrocyanides . ... 344 Ferricyanides 346 Cobalticyanides .... 347 Acetates . . . 348 Benzoates . .... 351 Lactates . . . 352 Succinates . ... 353 Tartrates 354 Citrates ... . . 356 Gallates 357 Tannates . . . 358 Urates ... .359 Table of Reactions . . . 361 Scheme for the Analysis of Subdivision III. . . .362 Subdivision IV. . . 363 Section 1. Nitrides, phosphides, arse- nides, and antimonides . 369 Section 2. Section 1. Carbides, borides, siUcides, Nitrites 370 &o 316 Nitrates . . . 371 Phosphites 375 Section 2. Phosphates . 376 Silicofluorides . 317 Arsenites 380 Carbonates . . . . 318 Arseniates . .381 Oxalates 323 Antimoniates, sulpharseui- Borates ... . . 326 ates, &c. ... 382 Silicates .... 329 Table of Reactions . 383 Tantalates and titanates 3.32 Scheme for the Analysis of Sulphocarbonates . . 334 Subdivision IV. . . 3S4 CONTENTS. Pakt II.— the method op ANALYSIS. Chapteb I. Introductory. Page The Object of Chemical Analysis .... . 385 The use of group and spe- cial tests . ... 387 CH.iPTEE, II. Qualitative Analysis of a ' Sii^le Salt. Section 1. Preliminary examination for the basic constituent 391 Preparation of the solution 392 Actual analysis . . 392 General Table for the ana- lysis of a single salt . . 397 Table for Group I. . . . 398 II. . . . 399 III. . . 400 Ilia. . 401 IV. . . . 401 V. . 402 Section 2. Page Preliminary examination for the acid constituent . 404 Special tests .... 405 Preparation of the solution 406 Actual analysis . . . 410 General Table for the de- tection of the acid-radical 413 Table for Group I. . 413 „ 11. . . 414 „ III. . 414 Chapieb III. Analysis of Mixed Salts. General Table for the de- tection of basic radicals . Table for Group I. . „ 11. „ III. . . „ IV. „ V. . . . Table for Appendix to Group II. . . Mixtures for analysis 416 416 418 420 422 422 423 424 EXAMPLES OF FOEMUL^. Notation and nomenclature ClCl HCl KCl MnCl^ HNO3 AgNO, CNCN EE=Cu. The metal copper does not decompose water at the ordinary temperature, and but very slowly when raised to a high degree of heat. On exposure to moist air it tarnishes and when heated iu the air it absorbs oxygen and yields two oxides THE BASIC ELEMENTS. 11 (Cu^O and Cu^O); these, however, do not yield up their oxygen when further heated. Hydrochloric acid acts upon this metal with great diflleulty. Copper has a well known red colour ; it is malleable ; at about 788° C. it melts, and volatilizes sensibly at a very elevated tempera- ture. Its density after fusion is 8-86, and after hammering 8-95. III. SiivEE=Ag. The metal silver does not decompose water, or withdraw oxygen from dry or moist air; if, however, it is heated in contact with air, at an elevated temperature it absorbs, or more properly, dissolves oxygen, but yields it up again on a further increase of heat. It is acted upon by hydrochloric acid with the greatest diflS.culty. The peculiar lustre of silver is perhaps more beautiful than that of any other metal. It is very malleable. At about 1000° C. it melts, and volatUizes slowly at a very high degree of temperature. Its density is 10-47 after fusion, and 10'51 after hammering. IV. MEECinRT=IIg. The metal mercury does not decompose water at any temperature, nor does it combine with oxygen when exposed to dry or moist air ; if heated in the air it combines with oxygen, forming the oxide (Hg^O), which is again resolved into its constituents at a higher degree of heat. Hydrochloric acid is not decomposed by this metal. The great peculiarity of mercury is its liquidity at common temperatures; at — 40° C, however, it becomes soUd, and at 360° C. it boils, and is converted into a colourless vapour. In lustre and colour it resembles silver, yet has a tinge of the blue-grey hue of lead. Its density is 13-59 at 4° C. V. LEAD=Pb. The metal lead does not decompose perfectly pure water ; it tarnishes slightly in moist air ; if heated in the air it rapidly absorbs oxygen, and the oxide thus formed (Pb^O) is not decomposed by heat alone into metal and oxygen. Hydro- chloric acid acts upon this metal with great difficulty. Lead is a metal of a bluish- white lustre, very malleable, melting at 334°C.,and volatilizing to a considerable extent at high tempera- tures. Its density is 11-445, and increases slightly by hammering. VI. BisMirTH=Bi. The metal bismuth appears not to decom- 12 CHEMICAL EEACTIONS. pose water if the latter is quite free from air ; it tarnislies slightly in damp air ; and if heated ia the air is converted into its oxide (BijOj), which is not decomposed by heat. Hydrochloric acid acts upon it very slowly. ' Bismuth is of a reddish-white coloiu-, rather brittle ; it melts at 247° C, and can be distilled at a very high temperature. Its density is 9-82, and is slightly dimiaished by compression. VII. PALLADiUM=Pd. The metal palladium does not decom- pose water ; it does not tarnish in the air unless heated, when a blue film of oxide appears on the surface which vanishes upon further heating : cold hydrochloric acid does not attack it. Palladium is a metal of a greyish-white colour ; it does not melt at the temperature of the blast-furnace. Its density is 11'3 after fusion, and 11-8 after hammering. VIII. TiN=Sn. The metal tin does not decompose water, nor does it absorb oxygen from the air ; heated in the air it forms an oxide which an accession of temperature does not decompose ; it is but slowly attacked by hydrochloric acid in the cold. Its brilliant white colour is well known ; it is malleable, and melts at a temperature of 228° C. Its density is 7-291 after fusion, and 7'299 after rolling. IX. ANiiMONr=Sb. The metal antimony does not decompose water or attract oxygen from the air at ordinary temperatures ; heated in the air it oxidizes, and the oxide produced is not de- composed at an increased heat : cold hydrochloric acid acts upon it ^^^.th extreme slowness. It has a bluish-white colour, is very brittle, melts at 430° C, and has a density of 6 '71. X. Absenic=As. The so-called metal arsenic does not de- compose water freed from air, nor does it absorb oxygen from dry air. It becomes oxidized by exposure to air and water, or to moist air only. When heated in the air it burns into an oxide not easily decomposable by heat. Hydrochloric acid is readily decomposed by this body. The metal has a steel-grey colour, is very brittle, and volatilizes without molting at 300° C. Its density is 5-7.5. THE BASIC ELEMENTS. 13 XI. PLATiNTrM^Pt. The metal platinum does not decompose water except at a most elevated temperature ; it does not absorb oxygen from the air at any temperature, nor does hydrochloric acid exert any action upon it. Its colour is white with a tinge of grey. It is malleable, and possesses the property of welding at a white heat. It melts only at the temperature of the oxyhydrogen blowpipe. Its density is 21-16 after fusion, and 21'45 after hammering. XII. The metals rhodium, iridium, ruthenium, and osmium are Tery rare, and are not likely to come in the way of the student. XIII. GoLD=Au. The metal gold does not decompose water, nor does it tarnish in. the air or absorb oxygen from it at any temperature : it is whoUy unattaeked by hydrochloric acid. Its rich yellow colour is well known. It melts at about 1200° C. ; its ductility is very considerable. Its density is 19-2 after fusion, and 19-3 or 19-4 after hammering. XTV. The metals tungsten, molybdenum, and vanadium are not likely to pass through the hands of the student. Metals, the majoritij of which do not expel Hydrogen from Hydro- chloric Acid, even at the boiling temperature. Name. Symbol. Equi- valent. Colour. Specific gravity (after tusion). Melting point. Cadmium . Cd 56- bluish white 8-604 ' below a red heat 788° Copper . . Cu 32- red 8-85 Silver ... Ag 108- brilliant white 10-47 1000° Mercmy . . Hg 100- bluish white 13-59 -40° 1 Lead Pb 103-5 bluish white 11-44 334° ; Bismuth . . Bi 208- red 9-82 247^ Palladium. Pd 63-3 greyish white 11-3 / oxyhyd. 1 blowpipe 228° Tin Sn 58- brilliant white 7-291 Antimony . . Sb 120-3 bluish white 6-7 430° Arsenic As 75- steel grey 5-75 9 Platinum . Pt 98-7 greyish white 21-16 f oxyhyd. \ blowpipe Gold . . . Au 197- deep yellow 19-2 1200° 14 CHEMICAL EEACTIONS. SUBDIVISION V. HYDROGEN. The only member of this suhdivision is the gas hydrogen, which, from the numerous chemical antilogies which it bears to the metals, is expected, if ever condensed, to appear in the me- taUic form; its gaseous state at ordinary temperatures is no argument against this view, since it must be remembered that many of the metals, as mercury, zinc and sodium, are known as transparent gases at an elevated temperature; it has not yet, however, been condensed, and so the features which its liquid or solid forms may present are merely a matter of conjecture. Hydrogen is an exceedingly abundant element, occui-ring in combination with oxygen as water ; its aifinity for this body and for chlorine is very great, as exemplified by the facts stated above, which show that only a few of the metals have, by reason of their superior affinity, the power of directly expelling hydrogen from these combinations. Since hydrogen is a substance frequently employed in chemical operations, and as it differs in many material points from the elements of the same class which have been described, it is im- portant that the student should prepare it and examine its pro- perties. It occurs in nature, as many of the metals do, combined with oxygen, and in this form of combination (H^O) it constitutes a large part of terrestrial matter ; it also occurs ia commerce com- bined with various other elementary and compound bodies, form- ing a large class of substances to which the name of acids has been assigned, such as hydrochloric (HCl), sulphuric (H, SO ), and nitric acid (H NO J; fi-om any one of these compounds hydro- gen may be set free by employing a suitable process, or in other words, by presenting to the hydrogen compound some substance which has a greater tendency to combine with that body with which the hydrogen is united than the hydi-ogen itself possesses. Thus, if potassium be added to water, hydi-ogen (H) and the substance called potash, or hydrate of potassium (K HO), are ob- THE BASIC EIEIIENTS. 15 tained ; for, as the result of all the forces brought into play, the potassium acts just as if it had a greater tendency to unite with the oxygen than the hydrogen has, with which the oxygen is previously combined. And if, again, ziac is added to hydro- chloric or to sulphuric acid, hydrogen is likewise, and for the same reasons, liberated, with the simultaneous production of chloride or sulphate of zinc, as the case may be. By one of these latter methods the student invariably isolates this element, using the apparatus shown in the accompanying diagram. Fig. 1. The hydrochloric acid and zinc are placed in the generator (A), and some water in the wash-bottle (B) for the puri- fication of the gas ; the delivery-tube (C) dips beneath the surface of some water in a basin, while the bubbles of hydrogen are caught as they issue in test-tubes previously filled with water, and inverted, vrith their mouths just below the level of the water in the basin. The following observations and experiments should be made with this substance : — Hydrogen is a transparent colourless gas, scarcely soluble in water, 1 volume of water dissolving only -015 of a volume of hydrogen. When pure it is inodorous, but, as commonly pre- pared, it has a peculiar odour which is easily recognized. It does not combine with oxygen at common temperatures, but if a small portion only of the gas be highly heated by the appKcation of a burning body, that part then combines with the atmospheric oxygen present, and the heat evolved by this chemical union is sufficient to raise another portion of the gas to the temperature at which this combination takes place ; this is repeated imtil the whole of the hydrogen is converted into its oxide water (H^O). Thus if a light be applied to the gas in a tube or other vessel having its mouth open to the air, a blue flame is seen to move slowly down till it reaches the bottom, marking, in fact, in its passage the surface of the unconsumed hydrogen. 16 CHEMICAL EEACTIONS. The foregoing experiment may be so modified as to bum all the hydrogen at once ; for this purpose it is only necessary to mix the gas thoroughly with half its bulk of oxygen and apply intense heat to any portion of the mixture, as by the application of a burning body ; oxygen is then ready at every point to combine with the hydrogen; and so great is the heat evolved that the vapour of the water formed is expanded suddenly and immensely, and the result is an explosion. A less violent result is obtained by mixing air instead of oxygen with the gas ; and by lighting either mixture in an open test-tube all unpleasant effects are obviated. The density of this element, hydrogen, is less than that of any other known body. The density of gaseous bodies is, however, generally referred to that of air as a standard, and air being taken as 1-000, hydrogen is -0692. This low density is well exem- plified by taking two tubes which have been filled with the gas, uncovering their mouths, and holding one in its ordinary, and the other in an inverted position ; from the former the gas may be shown to have escaped almost immediately, for on the application of a lighted taper a few seconds only after the uncovering, no ig-nition will take jslace ; the second vessel will, however, retain its contents for a considerable length of time, for it will be fomid that the gas in it wiU. take fire after the lapse of some minutes, on the approach of the lighted taper. A peculiarity with regard to this gas is, that if burnt at a jet (formed conveniently of an upright tube with a fine point and small aperture, inserted in the cork of the washing-bottle figured above, instead of the ordinary delivery-tube), and a tube of about i-inch internal diameter be placed cautiously over the flame so as not to extinguish it, a variety of peculiar notes are produced, some of which are remarkably clear and musical. All chemical reactions, or changes which take place when bodies act chemically upon each other, are rendered most di- stinctly intelligible by being placed in the form of an equation, and the student should familiarize himself ■«'itli the method of so expressing them. Thus in the changes above alluded to as taking place in the production of hydi-ogen, the decompo- THE ACID ELEMENTS. 17 sition of water by potassium is clearly sho-wn in the following manner ; — H,0+K=KHO + H Hydrate of potassium. In tlie same way the decomposition of hydrochloric or sulphuric acid by zinc may be exhibited : — HCl+Zn=ZnCl+H Chloride of zinc. H, S0,+2Zn=Zn, S0,+2H Sulphate of zinc. CHAPTER III. THE ACID ELEMENTS. Undbe this title are comprehended the remainder of the ele- mentary bodies. The acid elements are also sometimes termed " non-metaUic elements" and " salt radicals." Although for the most part possessed of properties powerfully antagonistic to those of the basic elements, they do not all bear to each other the strong resemblance exhibited in the case of the latter class of bodies ; they may, however, be arranged in subdivisions, each containing a few members which present among themselves many points of accordance. The state of physical aggregation in which these substances exist, is as varied as that which the basic ele- ments present ; the majority of them occur in the solid form, one, bromine, in the liquid, and several in the gaseous condition. The class of acid elements may for convenience sake be thus subdivided : — 1. Bodies which, in combining with hydrogen, lose nothing of their acid character : — Chlorine=Cl. Bromine=Br. Iodine=I. Fluorine=F. 18 CHEMICAL EEACIIONS. 2. Bodies, tte acid character of whicli is masked by combina- tion with hydrogen : — Oxygen=0. Snlphur=S. Selenium=Se. TeUurium=Te. 3. Bodies which lose their acid character completely by com- bining with hydrogen : — Carbon=C. Boron=Bo. Silicon=Si. Tantalum=Ta. Wio- bium=Nh. Pelopium=Pe. Titanium=Ti. 4. Bodies which acquire a basic character by combining with hydrogen : — Nitrogen=N. Phosphonis=P. Arsenic=As. SUBDIVISION I. CHLOEINE, BROMINE, IODINE, FLUORINE. The three former of these substances are known, the fourth has never yet been isolated ; they are possessed of the most ener- getic tendency to combine with the basic elements, and it is this obstacle which has always hitherto prevented the isolation of the last member of the group, fluoriue. The intensity of their che- mical attraction for the bodies most opposed in chemical character is well exhibited by the fact that many metals, upon simply being brought into contact with these substances, ignite, burning in the act of combination ; and as may be readily supposed, the com- pounds thus formed are as difficult of decomposition as they are easy of production. The first member, chlorine, is a gas ; the second, bromine, a liquid ; and the third, iodine, a solid : fluorine is behoved to be a gas. As will be seen hereafter, the three first members of this group exhibit a most singular family resemblance both in their chemical and physical properties, and it is generally thought that some far more intimate connexion subsists between them than any of which we are at present aware. I. CHL0Enfii=Cl. The non-metaUic element, or salt-radical chlorine, is a gas at all ordinary temperatures and pressures, but under a considerably increased pressure it liquefies ; no combi- nation of cold and pressure has, however, yet proved capable of effecting its soUdification. THE ACID ELEMENTS. 19 Chlorine occurs in nature in combination with many of the metals, but its most abundant source is common salt, NaCl, which exists so largely in the sea and in extensive deposits in different parts of the earth. Prom common salt, chlorine is frequently prepared by a me- thod which consists essentially of two processes joined into one : — the mode of proceeding is to add sulphuric acid (H^ SO J to a mixture of black oxide of manganese (Mn^ 0^) and common salt (NaCl), and to apply heat, when chlorine is given off, and may be collected either over hot water or by displacement. For the better understanding of this process, the action may be supposed to be divided into two parts ; the first consisting of the addition of sulphuric acid (H^ SO J to chloride of sodium (NaCl) : here a simple interchange between the basic and acid elements occurs, the result being the production of sulphate of soda (Na^SO^) and hydrochloric acid (HCl), thus — H, SO, + 2]SraCl= Na, SO, + 2HC1 ; and the second action being that of the black oxide of manga- nese, Mn^ O2' upon the hydrochloric acid, the final result being represented thus — Mn,0,+4HCl=2MnCl4-2H,0-t-2Cl. A very usual way of preparing chlorine is by performing the latter only of the processes given above, that is, to commence with Mn^Oj and HCl, hydrochloric acid being a cheap article of commerce. The student wiU do well to prepare chlorine by both methods, and to observe the following properties of the gas, collecting it both by displacement and over warm water : — (a) It has a peculiar yeUowish-green colour, whence its name ; it has also a peculiar unmistakeable odour : both of these cha- racters it imparts to water when dissolved in that liquid. (/3) It has the property of bleaching almost all animal and vegetable colours ; the presence, however, of a trace at least of water is necessary before submitting the coloured substances under examination to the action of the gas. (7) It exerts a very singular action on some bodies contain- ing carbon and hydrogen, by reason of its tendency to combine 20 CHEMICAL EEACTIONS. with their hydrogen, formiag hydrochloric acid, their carhon being consequently set free as soot : this is weU shown by the introduction of paper dipped in turpentine, or of a lighted taper, into a jar of chlorine. (8) It imparts no colour to starch-paste. The specific gravity of chlorine gas is 2-44 ; being thus much heavier than atmospheric air, it may be collected ia vessels filled with that fluid, by allowing it to issue from a delivery- tube at the bottom of the jar to be filled ; in virtue of its superior density it im- mediatelyocoupies the floor of the jar or bottle, and, gradually rising, buoys up the air upon its surface, until it finally expels it wholly. Chlorine gas is soluble in cold water ; its maximum solubility is in water at 8° C, 1 volume of water at that temperature dis- solving 3-04 volumes of the gas ; at 50° C, 1 volume dissolves only 1-09 volume; and at 100° C, the temperature of boiling Avater, it dissolves nothing. In collecting cMorine over water, then, the temperatm-e of the latter is an important point. As a chemical agent, chlorine is among the most powerful with which we are acquainted, its affinity for the basic elements being so great, that many metals when introduced into the gas in the form of leaf or fine powder, burst into flame from the great energy of their chemical combination : the basic element hydi'ogen also, when mixed with this gas and exposed to the bright light of the sun or of the voltaic arc, explodes from the same cause. By reason of these powerful afiinities it is a very dangerous gas to breathe, since the fine structure of the lungs is very liable to injury from exposure to energetic chemical agents. II. BiiOMiNE=Br. The non-metallic element, or salt-radical bromine, is a reddish-brown liquid, boiling at 63° C, and be- coming solid at — 22° C. Bromine is an element of somewhat rare occiu-rence in nature ; it is chiefly found in combination with sodixrm (Na), magnesium (Mg), and calcium (Ca), in sea-water and some mineral springs, and more rarely as the mineral, bromide of silver (AgBr). The method for its isolation is the same as that adopted in the case of chlorine ; hydrobromic acid being at first set free, is imme- THE ACID ELEJIENTS. 21 diately decomposed by black oxide of manganese, Mn.^O^, which oxidizes its hydrogen, liberating the bromine, which condenses in the liquid form : by this process the student should prepare a small quantity of bromine and observe — (a) Its physical characters, such as its colour, odour, great volatility, and its solubility ia water. (/S) Its bleaching power, somewhat inferior to that of chlorine. (y) Its far less powerful action on hydrocarbons. (S) That, when brought into contact with starch-paste (made by boiling starch in water), it produces a beautiful series of colours, varying from pale yellow to the richest orange, accord- ing to the amount of bromine present. In the liquid state bromine has a density of 2-966, in the gaseous, of 5-39. One part of water at 15° C. dissolves 'OSOOS of liquid bromine. The bromine escapes from its aqueous solution on heating, just as chlorine does. Bromine is a substance which, in its chemical relations, bears a striking resemblance to chlorine, forming compounds with the various metals possessed of chemical and physical properties almost identical with those of the chlorides. What we, for con- venience sake, call the power of chemical attraction, is, however, less between the bromine and the basic element than that ma- nifested by chlorine, which latter element consequently, in many circumstances, removes bromine from its combinations, taking its place. Bromine vapour, although not so injurious to the human organism as chlorine, nevertheless, if breathed in any quantity, acts very detrimentally ; and the liquid bromine, if left in contact with the skin, produces a wound very difficult to heal. III. Iodine =1. The non-metaUic element, or salt-radical iodine, is a solid at ordinary temperatures, of a metallic grey colour, and somewhat resembhng ia appearance the substance known as plumbago or black-lead. Iodine crystallizes in rhom- boidal plates, and also in rhombic octahedra, which belong to the same system. lodiae occurs in nature associated with bromine and chlorine, 22 CHEMICAL EEACTIONS. in the waters of the sea and of various mineral springs, being chemically combined with sodium (Na), calcium (Ca), and mag- nesium (Mg): it is also sometimes met with combined with silver (Ag). Its great source, however, is the ash obtained by burning sea- weeds : these plants extract the very minute quantity of iodine contained in sea-water, and by continually storing it up in their organisms, succeed in accumulating, comparatively speaking, so large a quantity of iodine as to repay the cost of extraction. It is prepared in precisely the same manner as the two former elements, hydriodic acid being in the first place pro- duced and immediately submitted to the action of black oxide of manganese (Mn^ O^). The student should prepare a small quantity of iodine by acting with sulphuric acid (Hj, SO^) and Mn^O^ upon some iodide of potassium, and observe — (a) Its physical characters both in the solid and gaseous con- dition, its colour and odour, the crystallization of the solid iodine from the vapour on cooling, and its solubility in water. (ft) Its bleaching power, far feebler than that of chlorine or bromine. (y) Its comparatively feeble action on hydrocarbons. (8) The very fitne and characteristic blue colour which is pro- duced when iodine and starch-paste are mixed. Iodine melts at the temperature of 107° C, and boils at 180° C, but it passes into the gaseous state long before it reaches its boiling-point, appearing as a violet vapour of exquisite colour. Its density in the solid state at 17° C. is 4'948, and in the gaseous condition 8-716. Iodine is less soluble in water than bromine, one part of water dissolving -007 of its weight of iodine. This element bears a strong general likeness to the two pre- ceding elements in its chemical characters; it also resembles them in odour, &c. Its chemical affinities are, however weaker than those of bromine, and it is displaced from its combinations by that element, just as bromine itself is expelled by chlorine. lY. rnjOEiNE=E. The non-metaUic element, or salt-radical fluorine, has not yet been isolated. THE ACID ELEMENTS. 23 Bodies which in combining with Hydrogen lose nothing of their acid character. Name. Symbol. Equi- valent. Colour. Specific gravity. Melting- point. Boiling- point. Chlorine . . Bromine . . Iodine . . . . CI Br I 35-5 80- 126- f v.* green- ish yellow [ L. yellow rV.red \ L. red-brown rV. violet \ S. blue-blaok V. 2-44 L. 1-33 V. 5-39 1 L. 2-966. V. 8-716-1 S. 4-948/ -22° C. 107° 63° 180° SUBDIVISION II. OXYGEN, SULPHUR, SELENIUM, TELLURIUM. All these substances are known, and can be easily isolated ; the two former in fact occur in great abundance, and nearly pure in nature. They are very slightly inferior to the former group in their power of uniting -with the basic elements, and when thus combined, they form compounds which are difficult of decompo- sition. The first member of this subdivision, oxygen, is a gas ; the other three are solids, at common temperatures. As a family, they bear almost as strong a resemblance to each other as do the members of the first subdivision. One remarkable feature, how- ever, must be noticed with regard to oxygen and sulphur, the two most abundant elements of this group, — ^bodies whose pro- perties have been very thoroughly investigated. These elements enjoy the power of combining, not only with basic elements, but also with nearly all bodies of their own class : oxygen, e. g., forms chemical compounds with every known simple substance except fluorine, and when it combines with an acid element, the resulting compound, as might naturally be expected, possesses in a marked degree the characteristic acid properties of its two constituents. I. OxTGEN=0. The non-metallic element, or salt-radical oxygen, is a gas at all known temperatures and pressures. * V.=vapour; L.=liquid; S.=8olid. 24 CHEMICAL EEACIIONS. The great reservoir of this gas is the atmosphere, of the total volume of which it constitutes one-fifth ; and by reason of its power of combining with every other known element, fluorine only excepted, it is also an abundant constituent of the earth's crust. It is the presence of this substance which fits the air for the support of animal life : the pure gas inhaled into the lungs does not prove poisonous. The simplest method of isolating this element is by heating some compound in which it exists not very closely combined, for the action of heat is often one of decomposition ; and thus if we select a combination of mercury (Hg) with oxygen (0), oxide of mercury (Hg^O) in fact ; or of silver (Ag) with oxygen (0), oxide of silver (Ag^O) ; we shall find that these bodies wiU split into metal on the one hand, and into oxygen gas on the other, by the simple elevation of temperature. If we employ a still higher degree of heat, other oxides, such as that of manganese (iln^O,), wiU be foimd to part with a portion of their oxygen. But the most usual method is to heat the substance known as chlorate of potassium (KCl O,), which is a compoimd containing the basic element potassium (K), united to an acid body called a compound salt-radical, and composed of two acid elements, namely, chlorine (CI) and oxygen (0), in the proportion of three equivalents of oxygen to one equivalent of chlorine. This compound is called anhydrous chloric acid, or chloric anhydride. ^Tien chlorate of potassium (KCl 0,) is heated, the 30 are expelled, and the com- pound called chloride of potassium (KCl) remains, according to the foUo'U'ing equation — KC103=KCl-|-30. This is the method which the student should employ in the preparation of this element. The following properties of oxygen gas are to be noticed : — - (a) It is without coloiu' and odour, and does not perceptibly dissolve in Avater. (/3) It does not exert a bleaching power like chlorine. (y) A taper or match just blown out, but with the wick still glowing, is immediately rekindled when plunged into this gas, THE ACID ELEMENTS. 25 and bums with much increased brilliancy and rapidity ; tbis is the most common test for the presence of oxygen. (^) A piece of sulphur (S), ignited ia the air, bums with much increased brilliancy when placed ia this gas. The same effect is observed, though in a still more marked degree, in the case of phosphorus (P). Carbon (C), too, bums with great energy, and so also does the metal iron (Fe), when plunged while red-hot into a jar of oxygen. The specifi-C gravity of oxygen gas is 1-1057. It is slightly soluble ia water, 1 volume dissolviag -035 of a volume of the gas ; this very trifling solubUity does not iaterfere with its being col- lected over water, which is by far the most convenient method of storing gases. In the free state it is not so energetic a chemical agent as chlorine and its congeners, at least at common tempera- tures, a few rare cases excepted ; but when its temperature is raised, it combines with both basic and acid elements with perhaps greater energy than ehloriae itself, and forms compounds of similar or nearly equal stability. These compoimds are readily produced by heatiag the substance whose combination with oxygen we are desirous of obtainiag, before their iatroduction into that gas ; a union immediately begias, the temperature of the heated body is very much augmented, and a brilliant light is frequently kept up until the supply either of the oxygen or of the substance intro- duced is exhausted. Very striking effects are obtaiaed by the combustion of heated iron, sulphur, carbon and phosphorus in this manner. II. Si7iPHUE=S. The non-metallic element, or salt-radical sulphur, is a solid at ordinary temperatures. This element is met with, unoombiaed, in extensive deposits which abound iu volcanic districts ; its great European source is Sicily. It is also largely diffused through the earth's crast in combiaation with various metals, and occurs ia almost all waters in the form of sulphates, and ia some springs as sulphuretted hydrogen (H^ S). The great abundance of sulphur ia the im- combiaed state renders it almost whoUy unnecessary to extract it from any of its compounds ; it is, however, sometimes ob- 26 CHEMICAL REACTIONS . tained as a kind of bye-product in the manufacture of other substances. Native sulphur is purified by simple distillation, and then sent into commerce. The student should observe with this substance : («) Its physical properties, colour, fusibility, and volatility. (/3) Its power of combining, when heated, with the atmospheric oxygen. (y) Its power of combining with metals (such as copper [Cu]) when they are plunged into its vapoiir. The specific gravity of sulphur in its ordinary solid form is 2-087; it melts at 120° C, and boils at 440°, becoming at that temperature a transparent gas of an orange colour, with a specific gravity of 6-654. Between, however, the temperatures of melt- ing and ebullition, sulphur undergoes very peculiar changes of consistence, becoming up to the temperature of 260° C. more viscous, instead of more filuid, with each augmentation of heat. If sulphur thus heated be suddenly cooled, it presents none of the original features of the substance before fusion, as seen in the foUowing comparison. Ordinary sulphur is yellow, this is brown : ordinary sulphur crystaEi^es well either in acute rhombic oetahedra or in long rhombic prisms, while this presents no trace of crystalline structure : ordinary sulphur is extremely brittle, this is as elastic as india-rubber. The present instance is the first which has been hitherto brought under the student's notice of an element existing in two forms or distinct states, but some of the elements shortly to be considered exhibit this pecu- liarity even more distinctly. To this phenomenon the term allotropy has been assigned. There are several other allotropic modifications of sulphur in addition to those just described. As a chemical agent sulphur is less energetic than oxygen, but it must not be forgotten that the solid form in which it usuallv exists is an obstacle to powerful chemical action ; this is shown by the fact that sulphur in the gaseous condition combines ener- getically with many metals, which become red-hot in the act of combination ; it can be considered therefore only slightly inferior to oxygen in chemical energy. THE ACTB ELEMENTS. 27 III, Selenium =Se. The non-metaUic element, or salt-radical selenium, is of comparatively rare occurrence; in most of its physical and chemical properties it strongly resembles sulphur. Its ordinary form is that of a reddish-bro-wn solid, -with a some- -what metallic lustre. It fuses at 100° C, and if heated beyond this point and suddenly cooled, yields a viscous aUotropic modi- fication similar to that of sulphur. Selenium boUs at a lo-w red heat, and is converted into a yello-w vapour. In its chemical properties it resembles sulphur stiU more closely, if possible, than in its physical characteristics. IV. TELLTmiUM=Te. The non-metallic element, or salt-radical tellurium, is even rarer than selenium ; it occurs in nature com- bined -with certain metals. In its physical properties it assimi- lates closely to the basic elements, but in its chemical tendencies it is allied to sulphur and selenium. It is -white -with a metallic lustre, crystaUine, brittle, and has a density of 6-2. It is rather more fusible than antimony, and volatilizes at a red heat. Bodies, the add character of which is masked hy combination with Hydrogen. Name. Symbol. Equi- valent. Colour. Specific gravity. Melting- point. Boiling- point. Oxygen ... 16- (colourless) V. 1-1057 Sulphur ... s 32- S.J yellow rv. 6-654 is. 2-087 jl20°C. 440" Selenium .. Se 79- / V. yellow \ S. red-brown j S. 4-3 100° 1 low red heat Tellurium. Te 128-4 dull white 6-26 ' low red heat red heat SUBDIVISION III. CAKBON, BORON, SILICON, tantalum, niobilw, pelopium, TITANIUM. The first three bodies are all kno-wn in the isolated state; they are comparatively destitute of affinity for the basic elements ; c2 28 CHEMICAL EEACTIOirS. carbon, however, is an exception, as it tas a very powerful ten- dency to unite with hydrogen, a union which takes place in many proportions ; it also combines with the metals. They all combiae with oxygen, Kke the members of the two preceding classes, to form compound salt-radicals or acid bodies. In many of their characters these three elements bear a strong family resem- blance to one another. They are all solids. The remaining four elements of this group are of very rare occurrence. I. CAEBOir=C. The non-metaUic element, or salt-radical carbon, is a solid at ordinary temperatures. There is no element which enters into so large a number of compound bodies as carbon. It forms a great part of the organic world, the animal and vegetable kingdoms ; and organic chemistry includes the history not only of aU the compounds of carbon occurring in nature, but also of a countless host of such com- pounds produced from time to time by artificial aid. Carbonic acid (COj), a combination of carbon and oxygen, is the great reservoir of this element ; and just as marine plants withdraw iodine (I), as we have seen, from sea- water, so does terrestrial vegetation remove carbonic acid (00^) from its reservoir the at- mosphere (in which, however, it exists in small proportion), de- composes it, and accumulates the carbon in various forms of com- bination with hydrogen, nitrogen, and oxygen. Since many animals live on plants, and carnivorous animals prey on the her- bivorous, the whole organized world is thus supplied with the necessary carbon. The carbon is restored to the atmosphere by various processes of civilized life, but especially by the respiratory process going on in the animal organism. The great deposits of coal which occur in many parts of the earth's crust are chiefly combinations of carbon with hydrogen, but they also contain some nitrogen, oxygen, and small quantities of other bodies ; they result from the gradual decomposition of vegetable matters out of con- tact with air. Carbon, as it usually occurs, is infusible, inodorous, and cannot be distilled. It exhibits allotropy in a more marked degree even than sulphur or selenium, occurring in three very distinct modi- THE ACID ELEMENTS. 29 fications. The first form, kno-vm as diamond, is transparent — the hardest of all bodies — and magnificently crystalline, the crystals, which are octahedra, having a density of 3-35 : ia the second condition carbon presents itself in the form of hexagonal plates, of bluish-black metallic lustre, soft and unctuous to the touch, with a specific gravity of 1-9 to 2-3 ; this second form is known as plumbago, black-lead, and graphite ; while the third variety is densely black, without lustre or any trace of crystalline struc- ture; it occurs in numerous varieties of anthracite, charcoal, jet, and gas-coke, and in soot, lamp-black, &c. In this thu-d form carbon has a specific gravity varying greatly in different cases. The first variety, or diamond, is termed a-carbon ; the second, /3-earbon ; and the third, y-carbon. The peculiar characteristics of the different Mnds of carbon mentioned above are weU known : the great brilliancy of the diamond, — ^the imctuous feel of graphite, — the rich black and con- siderable hardness of jet, anthracite, or cannel coal, — the dense, heavy and compact structure of the coke from gas-retorts, — the very light spongy texture of wood-charcoal, and the pulverulent lamp-black, are familiar to every one. There is, however, one property which the student should observe with regard to wood- charcoal especially, viz. its power of absorbing and retaiaing gases; one volume of this substance absorbing of ammonia, for instance, 90 volumes ; of carbonic acid, 35 ; and of oxygen, 9 volumes. As a chemical agent carbon has little power, possessing as it does, but a slight tendency to combine with other elementary bodies, oxygen and sulphur excepted. The chemist has therefore little influence in efifecting artificial combinations between carbon and other bodies directly. Nevertheless there is no element which plays a more active or universal part in the chemistry of nature than carbon. II. BoKON=Bo. Of the non-metallic element, or salt-radical boron, but little was known until recently. It resembles carbon in beiag tasteless and odourless, and in being, if at aU volatile, but doubtfully so. Boron differs from carbon by being soluble to a slight extent in water, and by not forming compounds with 30 CHEMICAl REACTIONS. hydrogen, hydrogen and oxygen, or hydrogen, oxygen, and nitro- gen (N), in the same way as carbon. It occurs in nature com- bined with oxygen. Boron, like carbon, may be obtained in three distinct forms. The first variety, or diamond of boron (a-Bo), is a brilliant and extremely hard substance, crystal 1i zing in acute octahedra; the second resembles graphite or plumbago most closely in its appearance, and is termed graphitoidal boron, or (/3-Bo), while the third variety has no trace of crystalline struc- ture, but is a soft brown powder (y-Bo). III. Silicon = Si. The non-metallic element, or salt-radical silicon, has been recently investigated. In most of its properties it resembles boron, and like that element, occurs in three allotropic forms, the octahedral, the graphitoidal, and the amorphous. rV. The other four bodies which are placed in this group, on account of a certain resemblance which they bear to silicon in some physical and chemical characters, are of very rare occurrence ; titanium is met with more frequently than the others. They stand, together with vana- dium, molybdenum, timgsten and arsenic, on the neutral ground between the basic and acid elements. Bodies which lose their acid character completely hy combination with Hydrogen. Carbon Boron. Silicon Symbol. Bo Si Equi- valent. 12 11 22 Colour. D.* (colourless) Q-. metallic blue. black A. black D. (colourless) G-. metallic blue- black A. black rC (coloui-less) G-. metaUio blue- black A. brown Specific gravity. D. 3-3 to 3-5 G-. 1-9 to 2-3 A. ? D. ? a. ? A. ? D. ? G. 2-49 A. ? * D. refers to the diamond form of the element ; G-. to the graphitoidal A. to the amorphous. THE ACID ELEMENTS. 31 SUBDIVISION IV. NITROGEN, PHOSPHORUS, ARSENIC, ANTIMONY. These four bodies form a very peculiar group, the members of which are linked together by close chemical similarities, although differing greatly in their physical character : nitrogen, for in- stance, is a gas which has never been condensed ; phosphorus is a solid occurring in two aUotropic forms ; and arsenic is a sub- stance frequently classed among the metals. For the true metallic elements these substances have little afimity, although they do combine with some of them, especially with the more energetically basic ; but for hydrogen they have a greater chemical attraction, uniting with three equivalents of that substance to form gases which partake in a greater or less degree of the basic character of the hydrogen. Perhaps the most striking compounds they yield are those with oxygen, with which element these radicals unite in several proportions ; the combinations which contain three or four equivalents of oxygen being most energetic compound acid-radicals. I. NiTE0GEN=N'. The non-metallic element, or salt-radical nitrogen, is a gas at aU known temperatures and pressures. It forms four-fifths of our atmosphere, in which it is com- monly said only to subserve the end of diluting the oxygen, and preventing it thus from exerting too violent an action on the animal respiratory organs, and the processes of combustion which are continually taking place upon the earth's surface ; but it is probable that it plays another very important part in nature's economy, and that the vegetable world has the power of with- drawing it in some manner from the atmosphere, and consoli- dating it in the various organisms in which it occurs combined with carbon, hydrogen, and oxygen. This element is prepared directly from the air, in which it exists merely mechanically mixed, not chemically combined, with oxygen, by removing the latter ; this is done by the introduction of a substance capable of combining with the oxygen, leaving meanwhile the nitrogen unabsorbed; there is no difficulty in 32 CHEMICAL EEACTIONS. Kg. 2. finding sucli an agent. If the metal copper (Cu), e.g., be heated in a tube and atmospheric air passed over it, the copper with- draws the oxygen, so that the gas collected at the delivery-tube is pure nitrogen. Or, again, Lf a portion of air be confined in a jar over water and a piece of sulphur (8) or phosphorus (P), contained in a cup floating on the liquid, be ignited by a red-hot wire, the sulphur or phosphorus in burning combines with the oxygen, leaving the nitrogen free : the oxygen compound of sulphur (or phosphorus) formed is absorbed and dissolved by the water. By this second method the student had better pre- pare some nitrogen, and notice — That any substance which bums m the atmosphere is imme- diately extinguished upon being plunged into this gas, simply because it is no longer in contact with an element with which it can combine. The gas nitrogen has a specific gravity of -972; it is less soluble in water even than oxygen, water dissolving only -016 of its volume. Its chemical actions in the free state are so feeble, that nitrogen is commonly chosen as the type of chemical indif- ference ; the elements for which it seems to have considerable affinity are potassium (K), sodium (Na), &c., hydrogen (H), carbon (C), and oxygen (0) ; but unlike most of the other ele- ments which have passed under review, nitrogen is not known to combine with any other element directly ; the only exceptions to this behaviour are in the cases of titanium (Ti), and perhaps of boron (Bo). Titanium combines with nitrogen with the utmost avidity, precisely in the same way as the metals with oxygen or chlorine, &c. II. Phosphorus = P. The non-metaUic element, or salt-radical phosphorus, is a solid at the ordinary temperature. Phosphorus, oxidized as phosphoric acid, is very widely dis- THE ACID ELEMENTS. 33 tributed tkroughout nature, although, it occurs in small quantities. It is found in most rocks and soUs ; from thence it passes into the various vegetable organisms, these ia their turn supplying it to animals, to whom it is strictly essential for the formation of their skeleton. The bones of animals, which contain, after calcination and removal of the organic constituents, 77 per cent, of phosphate of calcium, constitute the great source whence phosphorus is ob- tained. They are digested with sulphuric acid (H^ SO^), which removes the greater part of their calcium as sulphate of calciimi (Ca^ SOj), leaving an acid phosphate of calcium (CaH^ PO^). This, when thoroughly dried and then ignited, is intimately mixed with one-fourth its weight of wood- charcoal, the mixture being afterwards placed in an earthen retort and strongly heated. Part of the oxygen of the phosphate of calcium is removed by the carbon, and phosphorus distils over. The annexed equation ex- presses this decomposition symbolically : — 4(CaP03)-|-5C=5C0-|-Ca, P,0,+2P. Air is of course carefully excluded in this experiment. The student should examine the foUovdng properties of phos- phorus ; — (a) Its "phosphorescence," the lambent greenish-blue light which it exhibits when exposed to the air in a dark place. (/3) Its ready fusibility : for this purpose a small piece should be placed in a flask, then be covered with water, and afterwards heated gently. (y) Its ready inflammability when heated Ln the air. {I) Its inflammability even under water, if melted and sup- plied with sufficient oxygen. For this experiment a few small pieces of phosphorus are to be placed at the bottom of a beaker in contact with some crystals of chlorate of potassium (KCl O3) (a salt which was mentioned when treating of oxygen). The frag- ments are then to be covered an inch or two deep with water, and afterwards sulphuric acid (H^SO^) poured upon them by means of a funnel-tube, so as to reach the chlorate before dilu- tion with the water. The chloric acid thus set free (HCIO3) c5 34 CHEMICAL EEACTIONS. being a body which parts readily with its oxygen, is at once de- composed by the phosphorus, which bums vividly with formation of phosphoric acid. Phosphorus, as it usually occurs, is a solid having the density of 1-83 ; it melts at 44° C, and boils at 290°, forming a vapour the density of which has been found to be 4-355. Phosphorus is insoluble in water, but excessively soluble in bisulphide of carbon (CSJ. Its affinity for oxygen is so very great, that if exposed to this gas it gradually combines with it, becoming converted into oxide ; and if the temperature be but slightly raised, this affinity increases so greatly that the phosphorus enters into combustion. This element presents the peculiarity which has been stated to belong to sulphur, carbon, boron, and silicon, namely, that of allotropy, and which oxygen also probably presents, since ozone seems to be only a modification of that element. If the ordinary phosphorus is exposed to a heat of 215° — 250° C. out of contact with the air, it becomes converted into the second variety (/3-P), which, by further heating to the temperature of 260° C, may be reconverted into the original form. The differences between these two forms of the element are these : — ordinary phosphorus (a-P) is a wax-like solid, translucent and nearly colourless ; its specific gravity is 1'83, and it combuies with oxygen at 76° C. with in- flammation, and is phosphorescent at ordinary temperatures; while the second variety (/3-P) is a red uncrystaUizable solid with an almost metallic lustre on the fractured surface, with a specific gravity of 2-089, and admitting of exposure to atmospheric air without combining with its oxygen, unless heated to 260°, the poiat at which the ordinary modification is regenerated ; it is not in the least degree phosphorescent. A third variety of phos- phorus (y-P) has been obtained by heating ordiaary phosphoms considerably higher than its melting-point, and then suddenly cooling it. In this state it is black, but will recover its former translucence, &c. when fused and slowly cooled. III. Aesenic=As. The non-metallic element, or salt-radical arsenic (for so we may venture to call it, although since it has some claims to be considered a basic element we have already, in Chap. THE ACID ELEMENTS, 35 II., mentioned it among those bodies), is a solid at the ordinary temperature. Arsenic is sometimes found in a pure state in nature, but more frequently associated with metals, such as iron (Fe), copper (Cu), nickel (Ni), cobalt (Co), &c. ; it is obtained in the form of an oxide by heating these compounds in a current of air, and from this the arsenic is separated by the action of carbon. The student should observe — (a) The volatUity of this substance, and its peculiar physical characteristics, and particularly its garlic odour. (/S) Its ready conversion into a white crystalline sublimate (ASjOg), when heated in a current of air. Arsenic has a metallic appearance, with a steel-grey lustre. It crystallizes in tetrahedra, and is very brittle. Its density is 5-75 in the solid form, 10-39 in the gaseous. It volatilizes at 300° C. It is tasteless, insoluble in water, but soluble in hydro- chloric acid (HCl), When powdered arsenic is thrown into a jar of chlorine gas, it combines with that gas, forming chloride of arsenic (ASCI3). Arsenic combines very readily with hydrogen to form arseniuretted hydrogen (AsHj), but does not seem capable, like nitrogen, of forming a stable compound containing another equivalent of hydrogen, together with one equivalent of some such acid radical as chlorine, in which compound the group *YH^ plays the part of a powerful basic radical. Some arsenic compounds have indeed been obtained formed on this type, but they are in general very unstable. IV. AfrTiMOiirT:=Sb. This substance, which has already been noticed among the basic elements, may also be regarded as a body possessed of acid characters. In its combinations it closely re- sembles arsenic, and forms with hydrogen an analogous compound, antimoniuretted hydrogen (SbHj). Antimony is the link between this class of salt radicals and the basic elements, of which latter the metal bismuth is generally considered to present the greatest resemblance to antimony. * y represents nitrogen, phosphorus, &o. 36 CHEMICAL REACTIONS. Bodies which acquire a basic character hy combinincf with Hydrogen. Name. Symbol. Equi- valent. Colour. Specific gravity. Melting- point. Boiling- point. Nitrogen Phosphorus .. Arsenic Antimony' . . . N P As Sb 14- 31' 7.5- 120-3 (colourless) C a. white i. /3. red [ y. black steel-grey white -972 V. „ fa. 1-83 ''• t /3. 2-089 rV. 10-391 IS. 5-75 j 6-71 a. 44-2 1 ;8.250- ; 4-30 290° 300° /white theat CHAPTER IV. THE LAWS OF CHEJIICAL COMBINATION. The two great classes of elements -with. -(vHch the student has now become acquainted have the most powerful attraction for each other ; they combine together, and in so doing are said to exercise mutual chemical affinity. When hydrogen (or any other basic element) unites -with oxygen (or any other acid element), the properties which these elements possessed pre-vious to their combination are nullified, and in the compound produced we no longer recognize the characters of its components. The extent of this neutralization varies with the nature of the combining bodies, and is more or less perfect as the elements concerned occupy more or less completely corresponding positions in theu- respective scales. Thus when potassium combines with chlorine, or sodium with bromine, or barium -vsdth iodine, or calcium -vsith fluorine, or iron with sulphur, or hydrogen -with oxygen, substances are pro- duced which are said to be perfectly neutral, since in them no indication of the specific properties of the basic or acid constituent can be observed ; but if a body at the summit of the basic scale be united with one low in the opposite Hst, or vice versd, then the THE LAWS OF CHEMICAL COMBINATION. 37 properties of the more energetic element are found to predominate over those of the weaker, and the resulting compound exhibits either basic or acid properties : the two classes of such com- pounds, which are particularly abundant, are by an unfortunate nomenclature termed hoses and acids, on account of their ex- hibiting, for the reason above given, either basic or acid proper- ties ; they are the combinations which oxygen produces with the metals, and hydrogen with the salt-radicals. The doctrine of definite peopoetions lies at the very founda- tion of the science of chemistry, and when any two elements are said to combine, it must be understood that they unite in well- defined ratios of weight and volume, which, to produce the same substance, are under aU possible circumstances accurately the same. It matters not, for instance, whether hydrochloric acid (HCl) is produced by the simple union of its components, hydro- gen and chlorine, or by any more complex mode of formation ; 1 part by weight of hydrogen will always unite with 35-5 parts by weight of chlorine, while the gaseous bulks of these two quantities of matter will be equal. Again, those quantities and volumes of the other elements which are capable of replacing the hydrogen or the chlorine respectively in the typical compound hy- drochloric acid (HCl) which we have chosen, are equally constant, and when once accurately determined, serve for ever as indubi- table facts upon which to build the superstructure of chemical reasoning : the annexed list shows this clearly : — Formula. Hydrochloric acid HCl Chloride of sodium NaCl Hydrobromio acid HBr Bromide of sodium If aBr Proportion by Weight. H = 1 CI =35-5 Na=23 CI =35-5 H = 1 Br=80 Na=23 Br=80 Proportion by Volume. H =1 Cl = l Na=l Cl = l H =1 Br=l Na=l Br=l. The term eqttivalent, or combining proportion, is applied to the quantities which thus enter into these most simple combina- tions ; and in compounds more complex than these, the law of definite proportions still holds good ; for if the elements exist in larger quantity, that amount is invariably found to be some 38 CHEMICAL REACTIONS. multiple of the original combining proportional, or to bear some simple relation to it. But it must be observed that certain acid elements combine ■with 2, others again mth 3 equivalents of basic element : such are the elements oxygen, sulphur, selenium and tellurium, which combine in the proportion of 1 volume or 1 equivalent with 2 volumes or 2 equivalents of hydrogen, sodium, &c., and are consequently sometimes called hiatomic, from their being thus equal to two combining proportions of chlorine or its con- geners ; while the members of a third class of acid elements, as nitrogen, phosphorus and arsenic, unite in the proportion of 1 volume or 1 equivalent with 3 volumes or 3 equivalents of basic element, and are said to be triatomic, that is, equal to 3 equivalents of chlorine, bromine, &c. The nature of the com- binations which the second or biatomic class of acid elements forms, is exempUiied in the following Table : — Formula. Proportion by Weight. Proportion by Volume. Water, or oxide of hy H, H, = 2 0=16 H, =2 = 1 drogen Oxide of cadmium . . . .. Cd^O Cd2=112 0=16 Cd2=2 = 1 Hydrosulphuric acid .. H^ S H^ = 2 S=32 H, =2 S =1 Sulphide of mercury .. Hg,S Hg,=2{)0 S=32 Hg,=2 S=l. "When these combinations take place, if the body produced re- mains a gas, it is found to be condensed to -frds the volume of its gaseous constituents, i. e. the 3 volumes of which it was composed occupy, after combination, the space of only 2. The combinations formed by the members of the third class of acid-radicals, those to which the name " triatomic" has been assigned, are shown below ; thus — Formula, Ammonia Hj N Phosphide of copper Cuj P Arsenide of nickel . . . Ni, As Proportion by Weight. H3 = 3 N =14 Cu3=96 P =31 Ni, =88-5 As=7o Proportion by Volume. Hj =3 N =1 Cu3=3 P =1 Ni3=3 As = l. When it is possible to examine this third class of compound sub- stances in the gaseous state, its members also are found to have suffered condensation, and that to one-half the gaseous bulk of THE LAWS OF CHEMICAL COMIilNATION, 39 their components : thus the 2 volumes of the condensed com- pound contain the 4 volumes of vrhich it is composed. In this manner we find three series of bodies remarkable in their relations of weight and volume. 1st series : suifers no condensation in combination, — 2 vols. remam 2 vols. H CI H CI 2nd series : suffers a condensation to two-thirds,- 3 vols. become 2 vols. H HO H, 1 3rd series : suffers a condensation to one-half, — 4 vols. become 2 vols. H H H N H3 N The different saturating power possessed by the three classes of these acid elements, and shown by the formulae given above (HCl, H,0, HjN", &c.), is not confined to them alone, but is manifested, as will be seen presently, in numerous compound molecules, which present analogous features, and are capable of replacing the simple bodies just aUuded to. The term "salt" is generally applied to those of the above combinations in which the properties of the constituents are com- pletely, or nearly completely masked and merged in those of the new substance, which is thus in every way dissimilar from its components ; thus the combination of potassium and chlorine, or sodium and iodine, gives rise to substances in which no property of the component elements is retained ; the metal in each case has lost its metallic character, and has no longer any tendency to combine with a further quantity of the acid element, while the salt-radical has entirely parted with its odour and its distin- guishing chemical properties, and cannot be expelled from the combination into which it has entered by the application of the highest temperature. The compounds formed in either instance being soluble, are also found to have acquired the peculiar taste 40, CHEMICAL EEACTIONS. which is well known as " saHne," and are no longer such power- ful chemical agents as their uncombined constituents. The remarks now about to be made apply chiefly to that class of bodies in which the opposed elements which constitute the salt are united simply in the relation of their saturating power, for to these the term " salt" or " saline combination" is almost ex- clusively applied; water (H^O), for example, is not the only oxide of hydrogen ; there is another, the peroxide of hydrogen (HjOj), iu which it will be observed that the double biatomie molecule 0^ (02= HJ is only combined with the double monatomic molecule of hydrogen, H^; the compound H^Oj cannot therefore be said to contain the elements hydrogen and oxygen in the simple relation of their saturating power, at least as that has been determined by such observations as those just detailed. Cases of combination of this nature will be presently adverted to. With regard, however, to this simplest class of compounds now under consideration, the perfect neutralization of the chemical properties of their constituents only holds good, as was just now stated, when the intensity of the antagonism of the two bodies is nicely balanced ; but regarded theoretically, the constitution of a salt does not depend upon the nice adjustment of this equilibrium, it simply requires the union of an acid with a basic element ; and viewed in this light, the combinations of oxygen with metals, or of hydrogen with salt-radicals, are true s alin e compounds, al- though with the more basic metals the feebly acid character of the oxygen is more than counterbalanced, and the compound remains basic, while the intensely acid character of the more powerful salt-radicals overcomes the weak basic properties of the hydrogen, and such combinations are therefore foimd to be acid. To illustrate these facts, and to exhibit the differences incident upon the varying apportioning of basic and acid element, the following cases are given : — Class I. Class II. Class III. Basic ? E;0 H3 N Neutral NaCl H,0 ? Acid HCl ? ? THE lAWS OP CHEMICAL COMBINATION. 41 In tte first of these classes the compound with, preponderance of base is wanting, because the intensely powerful acid element is capable of completely neutrahzing the most energetic basic element; ui the second class, the acid compound is defi.cient, because the less powerful acid element is iucapable of effecting more than the neutralisation of a less energetic basic element, hydrogen ; in the third class, the very weak acid element is in- capable even of the neutralization of the basic constituent, hydro- gen, and consequently both the acid and neutral compounds are absent ; at least it is probable that such is the case, although the inertness or insolubility of the members of this series ( Agj P, H3 As, &c.) does not allow accurate observations of their relations to neutrality to be made. Hitherto we have been regarding the multiplication of satu- rating power on the part of the acid elements only, but the same thing occurs also in the case of many basic elements. Two in- stances, those of the metals iron and copper, will suffice to show this, the comparison being made in each case with salts of the same acid-radical, and in which the monatomic molecule of the metal is supposed to exist either singly or multiplied. SALTS OP IKON. CHoride. Oxide. Phosphide. Ferrous* FeCl Fe,0 Fe^ P ? Ferric Fe.Cl, (Fe,)^ (Fe,)3 P3. SALTS OP COPPEE. Chloride. Oxide. Phosphide. Cuprous ....Cu, CI (Cu,),0 (Cu,)3P Cupric CuCl Cu,0 CUj'p. * It has been proposed by some chemists to assume, in the case of iron and of several other metals, two different atoms or equivalents, each conbining with the same weight of chlorine, &c., but themselves possessing a different weight. For instance, some have even said that the iron of a ferrous was not the same metal as the iron of a ferric salt : in the first case it would have the usual equivalent or atomic weight of 28, and in the second, the atomic weight 18'66, that is, ^rds of the first atom. The two molecules are respectively called ferrosum (Fe) and ferricum (fe), and are each equivalent to 1 atom of hydrogen, being each capable of combining with 1 atom of chlorine. Viewed 42 CHEMICAL EEACIIONS. From the above Table it will be seen that the conventional ex- pression for that salt vs^hicb contains the greater number of equi- valents of the basic, and the less number of equivalents of the acid element, is -ous salt, the other being termed the -io salt. But when we pass beyond the eases just cited, and examine the characters of compounds in which the basic element is com- bined with a yet larger quantity of the acid-radical, we find that the new compound is no longer neutral, but partakes of the acid character of the preponderating element. Thus, when in the imion of chromium or iron with oxygen, the oxygen amounts to two equivalents, we find the new body possessing powerfully acid properties, and capable of uniting as a compound acid- {i. e. salt-) radical with hydrogen or the metals, thus — HCrO^ chromic acid. KCrOj chromate of potassium. HFeOj ferric acid. KFeO^ ferrate of potassium. It must not be supposed that two equivalents is the largest quantity of oxygen that a compound acid-radical can contain: permanganic acid, for instance, is the hydrogen salt of a radical containing four equivalents of oxygen, thus — HMujO^ permanganic acid. KMn^O^ permanganate of potassium. A precisely similar result occurs when, on the other hand, there is a preponderating number of equivalents of basic element in a compound. The compound radical ammonium, containing one equivalent of nitrogen and four of hydrogen, partakes in a striking manner of the basic properties of the hydrogen, which in the light of this theory, the ferrous chloride remains PeCl, wliile tlie ferric chloride becomes feCl ; and so on with the various oxides. To the beginner tliis may perhaps be elucidated thus : — FeCl and 'Fe^ CI3 are not comparable, but 3(FeCl) or Fe^ CI3 is the true chemical representatire of Pe^ CI3. Therefore, Fe^ is equal in saturating power to Pe^, for Fe3=28x3, and Pcj = 28 X 2 are each equal to CI, = 35-5 X 3 : Therefore, say some, the metals are different and have different equivalents, which may be obtained by dividing each formula by 3, — ?52^=PeGl,- and ?£^=|(Pe)Cl; o o then Fe=28, and |Fe or fe = 18'66, are each equivalent to Cl = 3.3r>. THE LAWS OF CREJIIOAL COMBINATION. 43 constitutes so large a proportion of the compound ; and it is found to play the part of a base almost as energetically as potassium or sodium, combining with the acid-radicals to form very stable salts, the salts of ammonium. From the capability of the basic elements of combining with every acid element, and vice versa, whether the opposing ele- ments are unequal or equal in intensity of antagonism, results that large class of chemical changes known as " double decom- positions." They arise in many instances from bringing together a pair of salts the constituents of which are not well apportioned to each other, but which, by an interchange of their basic and acid elements, would become exactly, or at least more nearly ba- lanced in antagonism : let us take an extremely simple instance : — oxide of sodium or soda (Na^O) is a salt in which the basic properties of the sodium preponderate vastly over the acid ten- dency of the oxygen ; chloride of hydrogen or hydrochloric acid (HCl) is a salt in which the precise reverse obtains, as we have before seen ; now, if these compounds be mixed, the opposed elements of each being much more nearly the exact counterpart of one another, imite, forming two new compounds which are far more stable than those formerly existing, since the mutual antagonism of their components is more perfect : — Na,0+2HCl=H,0 + 2NaCl. This apparent election, which bodies make when they are, as it were, at liberty to choose with what they wOl combine, has been variously termed " elective affinity," " chemical affinity," and " chemical attraction." In reality, it is in every case the effect of many causes, — the resultant of many forces ; we cannot, how- ever, enter now into the details of their action, except so far as to state that in many double decompositions much depends upon insolubility, much upon volatility, and much upon inass. It has been lately shown that double decompositions are of far more frequent occurrence in chemistry than was formerly imagined ; it was thought that in many cases, especially where the elements were concerned, direct combination took place when bodies of opposite chemical characters were presented to each 44 CHEMICAL EEACTlOlirS. other : thus, when chlorine and hydrogen are mixed in the sun- light, and hydrochloric acid (HCl) results from their union, it was imagined that a kind of combination occurred, differing from that mentioned just now, inasmuch as it consisted in a direct Tuiion of the molecules of hydrogen and chlorine. Recent ex- periments, however, appear to show that the molecular arrange- ment of the elements is not expressed truly when written H and 01, but that their constitution is that of a binary molecule, a true salt, in fact, in which the hydrogen or chlorine, or what- ever the element may be, is both base and acid ; and that thus when HCl is formed by H and CI uniting, the action is as follows : — HH-1-C1C1=HC1+Ha Numerous instances might be adduced and proofs given, but are here imneeessary ; let it suffice to say that this view seems to give one reason why elements in the nascent state are more powerful agents than when liberated. It is argued — since the element has not yet united with itself to form a twin atom, therefore its combining tendency is stUl whoUy unsatisfied. It will at once be seen that if this law of binary combination and double decomposition be one of those most deeply impressed upon matter, it is likely to prevail in the more complex chemical compounds. By chemical analysis it is found, that though among the large number of bodies possessing the general characters of salts many consist of but two elements, and those of the opposed classes, yet that there are many which have by no means so simple a constitution; these, however, participate in the same double decompositions as their congeners of a simpler form ; and so, when their " elective afiinity" is allowed fuU play, we find that they transfer to each other their basic and acid compounds, just as we have seen the simpler types of salts mutually inter- change their basic and acid elements. The occurrence of basic compounds is rare ; the bodies of this constitution belong almost exclusively to the domain of organic chemistry, and the student ■wUl for the present have little or nothing to do with them ; with one, however, the compound base ammonium (NH,), he will IHE LAWS OF CHEMICAl COMBINATION. 45 speedily become acquainted ; it is a substance of great importance analytically, and is, moreover, a remarkable instance of the manner in wbich. the basic element hydrogen overcomes the feebly acid properties of nitrogen, and thus confers on their com- bination a basic character. The acid compounds are far more numerous and important, and are either produced by the union of the acid elements among themselves, or by their combination with basic elements in such proportion as to allow of the pre- ponderance of their own properties over those of the basic ele- ments. It is singular also that many of these acid compounds result from the combination of the two acid elements, sulphur and oxygen, with the remaining bodies of their own class ; the com- position of a few such compounds is given below, with the names which, by long usage, have become attached to them and cannot be desirably removed, although they must be regarded as wholly apart from any theoretical considerations touching the nature and constitution of the bodies which they designate ; the examples are given as existing in saline combination with hydrogen : — HNO3 HCIO HCIO3 Nitric acid. Hypochlorous acid. Chloric acid. H,SO, H,CO, H,C,0, Sulphuric acid. Carbonic acid. Oxalic acid. H3PO, H3Cfdy* H^CTt Phosphoric acid. Hydroferricyanic acid. Citric acid. "With regard to the nomenclature of these compounds, it may be as well remembered that (with one or two exceptions, as in the case of sulphocyanogen (CyS)), when the compound acid portion of a binary combination contains no oxygen or sulphur, the termination of its own name is altered into -ide when we wish to designate any compound which it forms with a basic element, thus : — CNCN Cyanogen. KCN Cyanide of potas- sium. CI CI Chlorine. NH.Cl Chloride of ammonium. SS PP Sulphur. Phosphorus. Fe,S Ag3P Sulphide of Phosphide of iron. silver. * Cfdy=Fe2 C»»6- t Cl = CjH5 0;. 46 CHEMICAL EEACIIONS. An exception is here made when these acid bodies luiite with the basic element hydrogen ; and though it is chemically correct to call such a compound as HCl " chloride of hydrogen," yet con- ventionality demands that it be also termed " hydrochloric or chlorhydrie acid ;" and thus with aU such compounds. Now, if oxygen be present in the acid compound, a totally distinct nomenclatiire is adopted ; these bodies combined with hydrogen constitute a very large section of the so-caUed acids, and receive either the termination -ie, as nitric acid (HNO3), or -ous, as hypochloroM acid (HCIO). When the hydrogen in one of these groups has been replaced by another basic element, the designation that previously terminated in -ic now ends in -ate, and that in -ous in -ite ; as nitra*« of potassium (KNO3), and hypoohloriie of calcium (CaClO). From the following Table of the hydrogen and potassium salts of some compound acid-radicals which contain sulphur and oxygen, the student will perceive the usage and changes of these terms : — Hyposulphurous acid H^ Sj O3 Hyposulphite of potassium K.^ S^ Og Sulphurous acid Hj SO3 Sulphite of potassium K, SO3 Sulphuric acid Hj SO4 Sulphate of potassium E^ SO4 Here is a similar list, containing the hydrogen and potassium salts of a series of compound acid-radicals formed by the union of chlorine and oxygen : — Hypochlorous acid ...HCIO Hypochlorite of potassium ... K CIO Chlorous acid HClOj Chlorite of potassium KCIO^ Chloric acid HCIO3 Chlorate of potassium KCIO3 Perchloric acid HCIO4 Perchlorate of potassium ...KClOj It wiU. have been observed, that in the Table of acids given at page 45 there are three classes of those bodies, distinguished by containing a difiPerent amount of hydrogen, that is, of basic ele- ment : these classes are the groups of monobasic, 5ibasic, and tri- basic acids which contain acid-radicals requiring these different amounts of basic element to satisfy their respective oombinino- powers ; and if the student wiU refer to what was said regardino' the three series of acid dements at page 38, he wiU at once per- ceive that these three series of compound acid-radicals accu- THE LAWS OF CHEMICAL COMBINATIOir. 47 Tately correspond with them, thus : — This relation may be exhibited m \ AciB Elements Acid J COMPODNDS 1 Series I. Series II. Series HI. Monatomie. Biatomic. Triatomie. AgCl Ag,S Ag3P Chloride of silver. Sulphide of silver. Phosphide of silver. Monobasic. Bibasie. Tribaeie. AgClO, Ag.SO, AgjPO, Chlorate of silver. Sulphate of silver. Phosphate of silver. The difference between a ferrous and a ferric, between a cu- prous and a cupric salt of an elementary acid-radical, has been already poiated out; it now only remains to transfer this di- straction to the corresponding salts of the compound acid-radicals. We will take potassium, iron, and bismuth as the basic elements in our salts ; and, for the compound acid-radicals, those existing ia the nitric, sulphuric, and phosphoric acids. Now, potassium is monatomie, i. e. K,=Hj ; and iron is sometimes sesquiatomic, t.e.rei=Hii, orFe2=H3; while bismuth is triatomie, i.e. Bii=Il3. TaMng these values, we arrive at the following formulae for the different salts of the same acids : — Series I. Monatomie. KNO3 Potassic nitrate. re,(X03)3 Ferric nitrate. Bi(N03)3 Bismuthic nitrate. Series II. Biatomic. K,SO, Potassic sulphate. (I'e,),(S0,)3 Ferric sulphate. Bi,(S0,)3 Bismuthic sulphate. Series III. Triatomie. K3PO, Potassic phosphate. Ferric phosphate. BiPO, Bismuthic phosphate. Here it is seen how the formula of the same description of salt varies, not only with the saturating power of the acid body, but also with the atomic function of the basic constituent. A word in explanation of a term in general use, the term " basic salt : " — when an absolutely perfect double decomposition does not occur, the precipitate produced, instead of being a pure salt, is a compound one ; this may be best illustrated by a hypo- 48 CHEMICAL REACTIONS. ttetical example, where M stands for a basic radical, such as one of the metals — 20MC1+19KHO=19(MHO),MC1+19KC1. ^— -V ' Basic salt. With regard to solvents ; — ^the action of these agents is exceed- ingly obscure ; they appear to fulfil an office intermediate between chemical imion and mechanical mixture. The student had better regard them simply as agents for presenting bodies in a liquid form, and as rarely participating in the chemical actions which take place in their very midst : of course they do occasionally exert very powerful chemical actions ; but these instances can be readily discrimiaated. The more stable the equilibrium of a body, the less chemical influence is it likely to exert ; and thus water is far less likely to Luterfere than the acids, and is for this reason always employed wherever it is practicable, as the solvent to which the least objection can be raised. CHAPTER V. OF REAGENTS. Reagents are those substances ■which by admixture we bring to act upon the bodies we desire to analyse, in such a manner as to produce certain phe- nomena which shall prOTe indubitably the presence of the substance sought for. If in such circumstances the expected effect is not produced, we must infer the absence of the object of our search. It is obviously, therefore, of the greatest importance that the reagents which are employed in chemical analysis should, if not absolutely pure, at least be free from substances which would interfere with the indications which they are employed to give. The amount and the nature of the impurities which they contain should be accurately known. Most of the reagents in common use aa-e met with in commerce of sufficient pm-ity to allow of their application in aU but the more delicate operations of analysis. For certain special oases, however, as in legal investigations for the purpose of ascertaining the presence or absence of poison, too much care cannot be bestowed upon the preparation of absolutely pure reagents ; and in such instances it is generally necessary for the chemist to ensure the purity of OF BEAaUNTS. 49 •the materials he employs by preparing, or at least scrupiilously purifying them himself. The ordinary methods of purification are briefly these : Sublimation, Cry- stallization, Precipitation, and Distillation. Sublimation can only be resorted to when it is desired to free a body solid at ordinary temperatures, but volatile at a higher degree of heat, from non- volatile impurities ; iodine is usually purified ia this way : many mercury and ammonium salts might also be thus freed from accompanying foreign matters which were not volatile. In the subHmation of many substances it is simply necessary to place the substance in a dish over which is fixed a tall beaker or bell-jar, which may be luted or otherwise attached to the dish below ; if the dish containing the substance is now heated, the volatile sub- stance (iodine, oxalic acid, &o., as the case may be) rises in vapour, — spee- dily however condensing on the cold surface of the receiver above. Crystallization is perhaps the most commonly adopted of all methods of purification. In general, substances dissolve more abundantly in hot than in cold solvents. If then at some given temperature a menstruum, as water, alcohol or sether, be saturated with any solid body («. e. supplied with it until no more is dissolved), the solution perfectly transparent at that degree of heat, will, as soon as the temperature diminishes, deposit some of the dis- solved matter in the solid form. In the same manner let a given bulk of a saturated solution of almost any substance be taken, and without increasing its temperature, let its volume be diminished to one half (as by slow sponta- neous evaporation), then a considerable portion of the BoHd matter before held ia solution wiU be foimd to have separated in the form of crystals. Upon these two facts is based the method of purification by crystallization. Salts differ much as to their solubility in the same menstruum ; and by taking advantage of the facts which experimenters have accumulated upon this point, we can separate different compounds with considerable accuracy by evaporating the solution containing the mixture, we will suppose of two salts, to that degree of concentration at which one of them will almost entirely separate, while the other will remain almost as whoHy in solution. By the repetition of this process upon the already partially purified product of the first crystallization, greater purity is attained. But vrith many articles of commerce one carefully conducted crystallization is often found suiEcient. The technical name for the liquid remaining after the separation of the crystals is " mother-liquor," while the successive products of the crystallizing process are spoken of as " crops" of crystals. Peecipitation is frequently employed when the substance constituting the impurity is known to form an insoluble compound on the addition of some reagent the introduction of which does not interfere with the efBcieney of the reagent we seek to purify. Let it be supposed that chloride of am- monium (NHj CI) is the substance with which we wish to deal. Sow the impurity which this salt commonly contains is chloride of iron (PeCl) ; to separate this the sixbstanoe is dissolved in water, and a few drops of sulphide D 50 CHEMICAL EE ACTIONS. of ammonium, (NH^), S, are added to the solution ; the black sulphide of iron (Fe^ S) is formed and precipitated, its remOTal being effected by passing the liquid through a filter, while the reagent added, so far from contaminating the chloride of ammonium by the decomposition, itself helps to form an ad- ditional quantity of that salt, the ammonium originally combined with the sulphur uniting with the chlorine of the chloride of iron (NHj)2S+2!E'eCl =Fe2S4-2NHjCl: if any excess of the alkaline sulphide has been added, by boiling the solution it may be volatilized and thus removed. However, it is not often possible thus to remove the excess of the substances introduced in order to precipitate impurities ; but care can then be taken that the foreign substances unavoidably brought in shall be such as do not interfere with the reactions which the purified substance is intended to exhibit. Sometimes, on the other hand, the pure substance is precipitated by an appropriate reagent, leaving the impurities in solution, being therefore just the reverse of the preceding process. Distillation is always used to separate a liquid which vaporizes at a cer- tain temperatiu-e from other liquid or solid matters which are not volatile at that temperature. Most liquids when heated to a certain point which is peculiar to each substance, boil and are converted into vapour, and in this condition of vapour they remain as long as that degree of heat is maintained, but no sooner does it diminish, than they again return to the liquid form of matter. The apparatus employed is generally the following : — A is the retort Fig. 3. in which the Uquid is placed, the temperature being indicated by the ther- mometer E, and regulated accordingly ; the only way of escape for the vapour which rises from the boiUng Hquid is thi-ough the neck C into tlie apparatus D D, which is a glass tube passed through an outer tube of zinc or copper, d d, the space between these two tubes being occupied by cold water ; the vapour is thereby cooled completely, and consequently reduced to the Hquid state, in which condition it flows through the adapter E, and issues fi-om the OF EEACENIS. 51 point F into the receiver G-. By this process of distillation several liquids of different degrees of volatility may be separated, the " distillates " being pre- served apart, while non-volatile substances, whether solids or liquids, in sus- pension or solution, may be removed, since they remain in the retort when the volatile matters have passed over ; this separation is of course more easily effected than that of volatile liquids from liquids of different volatility. We here give a list of the reagents employed in analysis, separating, how- ever, those commonly used from those employed for special purposes. LIST OF EEAGBNTS EMPIOTEB DT CHEMICAI ANALYSIS. The reagents to which an asterisk is afilxed are employed in the solid state : the remainder dissolved in water. General Reagents. BASIC ELEMENTS. *Zinc (Zn). SALTS OP POTASSIUM. *Nitrate of potassium (KNO3). Chromate of potassium (KCrOj). ♦Cyanide of potassium (KCN). Acetate of potassium (K A). ♦Hydrate of potassium (KHO). Ferrooyanide of potassium (K^ Cfy). ♦Carbonates of potassium and sodium (K,C03H-Na,C03). SALTS OP SODIUM. ♦Carbonate of sodium (NajCOj). ♦Biborate of sodium or borax (Na,Bo,0,). Phosphate of sodium (Na^HPO^). SALTS OP AMMONIUM. Chloride of ammonium (NH^ CI). Hydrate of ammonium (NH^ HO). Sulphydrate of ammonium (NH4HS). _ Carbonate of ammonium ([]SfH,],C03). Oxalate of ammonium ([NHJ^ O). SALTS OF EAKIUM. Chloride of barium (BaCl). Hydrate of barium (BaHO). Special Reagents. BASIC ELEMENTS. ♦Iron (Pe). ♦Copper (Cu). SALTS OF POTASSIUM. Iodide of potassium (KI). Sulphooyanide of potassium (KCNS). Silicate of potassium (KSiOj ?). Sulphydrate of potassium (KHS). Sulphate of potassium (K2 SO4). Acid metantimoniate of potassium (K,H,Sb,0,). Ferrieyanide of potassium (EjCfdy). SALTS OF SODIUM. Acetate of sodium (NaA). Hydrate of sodium (NaHO). Sulphydrate of sodiiun (NaHS). Sulphite of sodium (Na^ SO3). Phosphate of sodium and ammonium (NaNH^HPO^). SALTS OF AMMONIUM. Molybdate of ammonium (NH^ MoO^). Acetate of ammonium (NH^ A). Phosphate of ammonium ([NHJ,HPOJ SALTS OP BAUIUM. ♦Fluoride of barium (BaF). D 2 52 CHEMICAL EE ACTIONS . SALTS OP CALCIUM. Chloride of calcium (CaCl). *Oxide of calcium (OajO). Sulphate of calcium (Caj SO^). SALTS OF IRON. *Ferroua sulphate (Fe^ SO4). Ferric chloride (Fe^Clj). SALT OF COBALT. Nitrate of cobalt (C0NO3). SALT OF SILVER. Nitrate of silver (AgNOj). SALT OF LEAD. Acetate of lead (Pb A). SALT OP PLATINUM. Bichloride of platinum (PtCl^). SALT OF GOLD. Terchloride of gold (AUCI3). SALTS OF HYDROGEN. Hydrochloric acid (HCl). Nitric acid (HNO3). Acetic acid (H A). Water (H^O). Hydrosulphuric acid (Hj S). Sulphuric acid (H^ SO^). OxaHcaeid(H2C2 0J. ACID ELE3IENT. *Carbon (C). *Oxide of barium (Bag O). ^Carbonate of barium (BajCOj). SALT OF MAGNESIUM. Sulphate of magnesium (Mgj SO4). SALTS OF COPPER. Cuprous sulphate (Cu^ SO^). Cupric sulphate (Coj SO^). SALTS OP MERCURY. Mercurous nitrate (Hg^NOj). Mercuric chloride (HgCl). Mercuric oxide (HgjO). SALT OF BISMUTH. Oxyhydrate of bismuth (BiH3 03,Bi,03). SALT OF PALLADIUM. Chloride of palladium (PdCl). SALTS OP ETUYLE. Oxide of ethyle ([C^ H^J^ O). Hydrate of ethyle (C^ H5 HO). SALTS OP HYDROGEN. Sulphurous acid (Hj SO3). Carbonic acid (H2CO3). Tartaric acid (H, C, H^ O,). HydrofluosiKcic acid (H3 Si^Fg). ACID ELEMENTS. Bromine (Br). Chlorine (CI). TEST PAPBES. Blue litmus paper. Red UtmUB „ Turmeric „ Starch „ Acetate of lead „ OHGANIC BODIES. »Sugar(C,,H.,,0„). ^Gelatine ? ORGANIC BODY. *Slarch(C,2H,„0,„). OF KEAGENTS. 53 BASIC ELEMENTS. Iron (Fe). The purest iron met with in commerce is in the form of pianoforte wire : it should be preserved in a closely-stoppered bottle, together with some caustic lime to prevent oxidation. Zinc (Zu). One chief impurity of this metal is lead, which, however, does not ordi- narily interfere with its applications. The most detrimental impurity is arsenic, and the zinc employed in analysis should always be free from this substance : some specimens of commercial zinc are quite free from it. It should be either granulated or cut into small strips. Copper (Cu). The most convenient form in which to employ this metal is that of foil or turnings. SAiTS OF Potassium. Iodide of potassium (KI). This salt is found of sufficient purity in commerce for ordinary opera- tions : its chief contamination is carbonate of potassium (K^ CO3), which may be separated by digesting the crude salt in hot strong alcohol, filtering, and crystallizing out the iodide. To make a solution for the purposes of testing, 1 part of salt may be dissolved in 10 parts of water. Nitrate of potassium KNO3). Commercial nitre is sufficiently pure for ordinary use : its great impu- rities are chloride and sulphate of potassium, from which it may be freed by repeated crystallizations. Chromate of potassium (ECrOj). The salt met with in commerce is pure enough for the purposes to which it is applied. As the bichromate of potassium is a salt of more common occurrence, it may be used for the preparation of the neutral chromate by adding to every 100 parts of bichromate dissolved in water, 47 parts of dry carbonate of potassium (K^ CO3). The salt may then be crystallized. For use, 1 part of the crystals should be dissolved in 10 of water. Cyanide of potassium (K[C!N] or KCy). The cyanide prepared by throwing « mixture of 8 parts of dried ferro- cyanide of potassium with 3 of dried carbonate of potassium into a crucible heated to low redness, is sufficiently pure for ordinary analytical purposes. When so heated it decomposes thus, — 2(K., FeCyj) -t-K^ CO3 = 5KCy-l-KCyO -f 2Fe + CO^. When its contents are in a state of tranquil fusion the crucible is removed from the fire and allowed to stand, so that the particles of iron may subside : the fused mass is then poured out upon an iron plate. It consists of cy- anide and cyanate of potassium, and should be kept in a well-stoppered 54 CHEMICAL REACTIONS. bottle. The cyanide may be obtained pure by digesting the mass in hot alcohol, in which the cyanate is nearly insoluble. Sulphocyanide of potassium (K[CNS] or K [CyS] or KCsy). This salt is prepared by fusing 46 parts of ferrocyanide of potassium, 17 of carbonate of potassium, and 32 of sulphur in a covered iron crucible or pan. The fused mass, when cold, is boiled with alcohol ; the sulphocyanide crystallizes out on cooling. 1 part should be dissolved in 10 of water. Silicate of potassium (KSiOj ?). A solution of silicate of potassium made by fusing 1 part of pure quartz- sand (SijOj) with 4 parts of carbonate of potassium, and dissolving the re- sulting mass in boiling water, is occasionally employed in analysis. The fused mass should be first pounded and washed with cold water. Acetate of potassium (K.\G^'H.^O^ or KA.). The commercial salt is sufficiently pure for all ordinary analytical pur- poses. 1 part should be dissolved in 4 of water. Hydrate of potassium (KHO). The salt met with in commerce contains many impurities, of which the principal are the chloride, sulphate, and silicate of potassium ; these do not generally interfere with its use. But it also contains very frequently car- bonate of potassium, alumina (Al^Oj), and oxide of lead; the presence of these substances is often very troublesome in analytical processes. The last impurity is derived from the ilint-glass bottles in which the solution of hydrate of potassium is often kept: &erman glass bottles should be used instead. To obtain the pure hydrate, it is only necessary to dissolve the commercial salt in alcohol, in which its impurities are insoluble, and then by evaporating the clear part of the solution in a silver dish, the hydrate is ob- tained perfectly pure, if care has been taken to preserve it from the carbonic acid of the air. The following is a method of preparing a solution of this substance : — 10 parts of carbonate of potassium are dissolved in 100 parts of water and the solution heated to boiling in a silver or bright iron vessel pro- vided with a lid: 8 parts of good freshly bm-nt lime (Ca^O) are slaked in another covered vessel, and the hydrate formed added by degrees to the boihng solution of carbonate of potassium, the mixture being constantly stirred. The change may be represented thus : — K2C03-(-2(CaHO)=Ca2C03+2KHO. The mixture is boiled for a few minutes, the Ud of the vessel remaining on ; the liquid is then allowed to rest until all the carbonate of calcimn formed has settled, when the clear solution of potassa or hydrate of potas- sium is poured off into a well-stoppered bottle. Sulphydrate of potassium (KHS). This salt is prepared by passing sulphujett«d hydrogen (Hj S) into a solu- tion of hydrate of potassium until the liquid has a strong odour of the gas. Sulphate of potassium (K.^ SO.J. The commercial salt is sufficiently pm-e for analytical pui-poses ; it is OF REAGENTS. 55 Bometimes, however, expedient to reerystalKze it. For a solution for testing, 1 part is to be dissolved in about 12 of water. Acid metantimoniate of potassium {K-, H^ Sb„ O^). To prepare this salt, the neutral antimoniate is at first procured by throwing a mixture of 1 part of antimony (Sb) with 4 parts of nitre (KNO,) into a red-hot crucible ; when the mass is cold, the excess of nitre is removed from it by digesting the fused mass in tepid water ; the insoluble residue stiU left is then boiled with water for some time, and is thereby dissolved : its solution is then evaporated to the consistence of a syrup, and solid hydrate of potassium added to convert the antimoniate into metantimo- niate : the liquid is further evaporated until, upon a drop being taken out upon a glass rod, it readily crystallizes ; it is then allowed to cool, when a crystalline mass is obtained containing the acid and neutral antimoniates of potassium. The crystals are then dried on filter-paper and preserved dry in a stoppered bottle for use. When required for testing, 1 part is dissolved in about 20 of water at a gentle heat, the solution cooled and filtered. During this process of solution the neutral salt is converted by the action of water into the acid metantimoniate, hydrate of potassium being produced at the same time. Ferroeyanide of potassium (K2[FeC3N3] or KJFeCyj] or K.,Cfy+l^aq)». This salt is met with in great purity in commerce : its solution becomes some- what alkaUne on keeping. 1 part of salt should be dissolved in 12 parts of water. Carbonates of potassium and of sodium (KjCOj-fNajCOj). The separate salts are mixed in equivalent proportions. The mixture fuses at a lower temperature than either of its constituents. Ferricyanide of potassium (K3 [Fe^ Cj N^] or K3 [Fe^ CyJ or K^ Cfdy). The commercial salt is of suiKcient purity. This substance is prepared by passing chlorine gas into a solution of 1 part of ferrooyanide of potassium (Kj Cfy) in 9 parts of water until a drop of the Hquid no longer produces a blue precipitate or colour in a solution of perchloride of iron (Fe2Cl3). It should be crystallized several times: the crystals are of a fine deep red colour : 1 part of them should be dissolved in 10 of water for use as a test. Salts of Sodium. Acetate of sodium (Na[C2 H^ Oj] or WaA). This salt is met with in commerce of sufficient purity for ordinary ana- lytical operations. Being much cheaper than acetate of potassium, it is generally employed in its stead, although it cannot be so advantageously used in experiments where free oxaUc acid is present, since the oxalate of sodium which is then formed is comparatively insoluble. 1 part is to be dissolved in 4 of water. * The symbol aq=H20, and is generally employed to denote water of crystaUization. 56 CHEMICAL EEACTIOIfS. Hydrate of sodium (NaHO). This salt is frequently substituted for hydrate of potassium, on account of its greater cheapness. It is subject to the same impurities as the hydrate of potassium, and may be freed from them in a similar manner. Sulphydrate of sodium (NaHS). This salt is also used instead of the sulphydrate of potassium, and may be prepared in a similar manner. Sulphite of sodium (^32803 + 10 aq). This salt may be prepared by passing sulphurous acid gas (SOj) (pro- duced by boOing copper turnings in a flask with concentrated sulphuric acid, and passing the gas tlu-ough water in a wash-bottle) into an aqueous solution of carbonate of sodium, until carbonic acid gas is no longer evolved. The solution should be evaporated with as little exposure to the air as pos- sible, on account of the great tendency of the sulphite to pass into sulphate, and finally allowed to crystallize. The solution for testing should contain about 1 part of sulphite in 5 parts of water. Carbonate of sodium (Naj CO3). The commercial salt usually contains an admixture of sulphate and chloride of sodium, from which it is difficult to purify it. An easy method of preparing pure carbonate is by precipitating a comparatively pure specimen of a sodium salt with oxalic acid or a soluble oxalate. The oxalate of sodium is nearly insoluble, and by washing the precipitate obtained as before mentioned with water, only a small quantity of oxalate is lost, whilst the impurities are washed away. By ignition of this oxalate the pure carbonate is obtained, thus — Na2C2 0i=Na2C03-(-CO. Eiborate of sodium or borax (Na^ B04 O^ -I- 10 aq). The commercial salt may be employed for ordinary analytical operations, It can be purified by crystallization. Phosphate of sodium (Na2HPOi-l-12aq). For ordinary pm-poses the commercial phosphate may be employed ; it contains sulphate of sodium, from which it may be purified by crystallization. For use as a test 1 part is to be dissolved in 10 parts of water. Phosphate of sodium, ammonium and hydrogen, or microcosmic salt or phosphorus salt (NaNB[jHP0i-|-4aq). This salt is prepared by boiUng a solution of 6 parts of phosphate of sodium (the reagent just described) in 2 parts of water, and adding 1 part of pow- dered chloride of ammonium (NH^ CI). Chloride of sodium separates and is removed by filtration, while tlie filtrate on concentration yields crystals of microcosmic salt. Salts of Amjionium. Chloride of ammonium (NHj CI). The chief impurity of this salt as met with in commerce is chloride of iron ; this may be readily separated by precipitation, a few di-ops of sulphydi-ate of OP EEAGENIS. 57 ammonium (NH^ HS) being added to a solution of chloride of ammonium, and any black precipitate of sulphide of iron produced being filtered off ; hydrochloric acid is then added in quantity just sufficient to decompose any excess of sulphide of ammonium, and the liquid boiled till all odour of the sulphvu-etted hydrogen has left it : when the trifling excess of hydrochloric acid has been saturated with ammonia, the solution is evaporated and the salt crystallized. 1 part should be dissolved in about 8 parts of water. Molybdate of ammonium (NH, MoOj). In the preparation of this salt molybdic acid is at first prepared ; this is done by roasting native sulphide of molybdenum (MoS) in a platinum cru- cible at a low red heat, with constant stirring, as long as sulphurous acid (SOj) is evolved. The impure molybdic acid thus obtained is then dissolved with the aid of heat in ammonia. Much of its impurity is left undissolved, while more separates when the solution is evaporated to crystallize. By crystallization the bimolybdate is formed ([NH4]2Mo,jOy). Acetate of ammonium (NH.j C^ H^ O^ or NH^ A). This salt may be best prepared by neutralizing acetic acid with carbonate of ammonium. Hydrate of ammonium (NH, HO). Commercial ammonia may be advantageously used in analysis ; or it may be prepared by taking equal weights of freshly burnt lime (Ca^ 0) and powdered chloride of ammonium (NH4 CI), introducing them into a flask A, and adding a little water : the evolved gas is passed through a small quantity of water con- Fig. 4. tained in the first wash-bottle, represented in the annexed figure by B ; it is then conducted into a bottle, 4, or a series of bottles similarly fitted with tubes, and half-full of distilled water. The following equation represents the change : — NH4CH-CaHO=NH4HO-(-CaCl ; but although NH^ HO represents the hydrate of ammonium corresponding d5 58 CHEMICAI EEACTIONS. to the hydrate of potassium (KHO), and although for convenience and ana- logy sake we speak of this hydrate, yet it is more correct to regard the sub- stance so called as a solution of the gas ammonia (NH3) in water (HjO); for it wiB be seen that NH4HO=NH3+H20. Sulphydrate of ammonium (NH^ HS). This salt is prepared by passing hydrosulphuric acid (H^S) into a solution of hydrate of ammonium untfl the liquid is fully saturated and the gas escapes unabsorbed. The sulphide of ammonium ([NHJj S) is obtained by dividing a solution of hydrate of ammonium into two equal parts, and after having saturated one part with hydrosulphuric acid, adding the reserved part to it. Carbonate of ammonium ([NHJ2CO3). The commercial carbonate is a sesquicarbonate, but when dissolved in hot water the solution is said to contain the neutral carbonate. The coromon pre- parations of this salt are of sufficient purity for almost every analytical purpose. Oxalate of ammonium ([NHJaCjO.-l-aq or [NHJ^O+aq). _ This salt may be prepared by exactly neutralizing a solution of oxalic add by carbonate or hydrate of ammonium : 1 part of crystals should be dissolved in 24 parts of water for use as a solution for testing. Phosphate of ammonium ([NH4]2HP04). This salt may be prepared by decomposing the acid phosphate of calcium by carbonate of ammoniimi. Salts of Barium. Chloride of barium (BaCl+aq). This salt is generally found in commerce of sufficient purity for ordinary analytical purposes. It sometimes contains lead: it may be purified by crystallization. To prepare the solution for testing, 1 part should be dis- solved in 10 of water. This salt may also be readily made by dissolving the carbonate of barium (a commonly occurring mineral) in hydrochloric acid, and crystallizing the product. Fluoride of barium (BaF). This salt may be prepared by adding hydrofluoric acid (HF) to a solution of chloride of barium, containing hydrate of ammonium as long as a pre- cipitate is formed. The precipitate must then be quickly washed with water on a filter and dried. Oxide of barium or baryta (Ba^ O). This compound is best prepared fi-om nitrate of barium purified by re- crystallization. The nitrate, finely powdered, is introduced little by little into a crucible maintained at a bright red heat. After cooling, the crucible is broken, and the fused mass is separated from foreign matters and pre- served from the air. The decomposition is as follows : — 2BaN03 =Bai, O -I-N2 Oj-(- 0. Hydrate of barium (BaHO-|--t^ aq). This salt may be prepared by dissolving the oxide in boiling water, filtering the solution into a bottle or flask, and closing the latter by a cork to exclude OF EEAGENTS. 59 the air, which, from the carbonic acid gas which it contains, would soon oon- Tcrt the hydrate into the carbonate of barium. The above solution on cooling deposits the hydrate in large crystals, which may always, by a second or sometimes a third crystallizatiou, be obtained perfectly pure. This substance may also be prepared by heating to redness in a crucible a mixture of 6 parts of finely powdered sulphate of barium (Ba^ SO^) with 1 part of powdered charcoal and 1^ of flour, and boiling the resulting mass with water for-^a long time in a loosely-corked flask : the solution is to be filtered whilst hot with the same precaution as in the first process. The decompositions which occur are these : — (a) Ba2SOj-|-2C=Ba,S+2C02 (^) Ba^S +2(H20)=H, S+2(BaH0). As it is important that this reagent should be qmte free from the salts of the alkalies, the second process is a very convenient method, since, from the great insolubility of the sulphate of barium, it may be easily washed free from all soluble impurities, among which the alkaline salts are the most usual and most deleterious. For testing, a cold saturated solution of the crystal- lized hydrate may be employed. Carbonate of barium (Ba^COj). This salt occurs in a state of comparative purity as a mineral ; for ana- lytical purposes, however, it should always be precipitated by carbonate of sodium or ammonium from the pure chloride of barium (BaCl) ; the pre- cipitate is to be thoroughly washed, and then stirred with distilled water so as to form a pasty mass ; in this condition it should be preserved for use in a stoppered bottle. This salt, hke the preceding, should be absolutely free from soluble salts. Salts op Calcium. Chloride of calcium (CaCl). This may be preparad in the purest form by dissolving the finest white marble (Ca^ CO3) or precipitated carbonate of calcium, or, better still, small crystals of Iceland spar, in hydrochloric acid (HCl), the hydrochloric acid not being in sufficient quantity to dissolve the whole of the carbonate. Oxide of calcium (CajO). Freshly burnt quickHme just from the kiln should be taken, the white pieces selected and preserved in a well-stoppered bottle. Sulphate of calcium (Ca^ 80^+2 aq). This salt may be prepared by precipitating pure chloride of calcium with sulphuric acid (Hj SO^), washing the precipitate thoroughly, and then di- gesting the sulphate of calcium formed, with repeated agitation, in cold water. It is almost insoluble, and therefore the saturated solution may be used. Salt op Magnesium, Sulphate of magnesium (Mg^SO^-f 7 aq). The commercial salt (Epsom salts) is of sufficient purity for all ordinary analytical purposes. 1 part should be dissolved in 10 parts of water. 60 chemical eeactions. Salts of Iron. Protosulphate of iron or ferrous sulphate (Fbj SO4+7 aq). The commercial salt is of sufEcient purity for employment in analysis. The solution is made by agitating the crystals with cold water, out of contact with the air. Sesqui- or perchloride of iron, or ferric chloride (Fe2Cl3). This salt may be easily prepared by dissolving pianoforte wire (the pm-est form in wliich iron occurs commercially) in hydrochloric acid, boiling the solution, and adding nitric acid (HNO3) drop by drop until the original greenish-brown colour of the solution has changed to a bright yellow, or until a drop of the solution taken out on a glass rod is no longer precipi- tated blue on the addition of ferricyanide of potassium (Kg Cfdy). Excess of ammonia solution is then added, and the precipitate produced thoroughly washed with hot water ; it is then dissolved in hydrochloric acid, care being taken that enough acid is not added to dissolve the whole. Salt of Cobalt. Nitrate of cobalt (CoNOj-f-S aq). This salt may be purchased in a state fit for use : it is troublesome to pre- pare from cobalt ore. 1 part is to be dissolved in about 10 of water. Salt of Copper. Protosulphate of copper or cupric sulphate (COj SO4-I-5 aq). The commercial salt is always contaminated with ferric sulphate; for analytical purposes the metallic copper obtained by electrolysis may be dis- solved in hot sulphuric acid (II2 SO^) ; or the pure hydrate, oxide, or car- bonate may be taken, and heated with diluted sulphuric acid. The salt should be crystallized from its solution. 1 part should be dissolved in 10 parts of water. Salt of Silver. Nitrate of silver (AgNOj). This is best obtained by dissolving pure silver in nitric acid (HNO3) which has been diluted with about its own bulk of water, evaporating the solution to dryness, and gently fusing the residue. The fused mass may be dissolved in water when cold, and then crystallized. It is thus obtained quite free from acid. If silver coin («. e. silver alloyed with copper) p; g be employed, it is necessary, after dissolving it in nitric acid, to precipitate the silver as chloride by the addition of hydrochloric acid, to filter it, and then to wash it till it no longer contains a trace of the soluble copper salt. The pure chloride of silver is now to be placed in a small dish of porous earth- enware, placed in a larger dish or basin ; both vessels are then to be so far OF BE AGENTS. 61 filled with water, to which a few drops of hydrochloric acid liave been added, that their contents do not mix. A piece of zinc is to be laid under the inner vessel, and connected with the chloride of silTer by means of a bent platinum wire, when the desired action will at once commence, and after the lapse of a short time the whole of the chloride of sUyer will have been "reduced" to the metallic state : the change may be represented by the two equations — (1) HCl +Zn=ZnCH-H (2) AgCl+H =HC1 +Ag. The smaU dish is now to be removed, and the finely divided silver which it contains to be repeatedly washed with dilute hydrochloric acid, and, finally, with pure water. When quite free from hydrochloric acid, the silver is to dissolved in nitric acid, crystallized and fused as mentioned above*. For use, 1 part of the fused salt is dissolved in 20 parts of water. Salt of Lead. Acetate of lead (PbC^ H3 O^ or PbA+lJ aq). This salt is met with in commerce of sufficient purity : 1 part should be dissolved in 6 parts of water. Salts of Mercury. Protonitrate of mercury or mercurous nitrate (HgjNOj). This salt is obtained by leaving metallic mercury in contact with nitric acid (HNO3) without applying heat. In order to preserve it in the state of mercurous nitrate, some metallic mercury must always be kept in its solution. Percliloride of mercury or mercuric chloride (HgCl). The commercial salt is sufficiently pure. 1 part is to be dissolved in 16 parts of water. Peroxide of mercury or mercuric oxide (Hg^ O). This salt may be purchased tolerably pure. It should volatilize when heated without leaving a residue. Salt op Bismuth. Oxyhydrate of bismuth or mixed oxide and hydrate of bismuth (BiH3 03,Bi,03). The commercial basic nitrate of bismuth may be used instead of the basic hydrate (for the conversion of metallic sulpliides soluble in alkalies into oxides by boiling it with such alkaline solutions) : it must be free from arsenic (As). The metal bismuth may be purified from arsenic by fusing it with nitrate of potassiimi (KNO3) ; it may then be dissolved in dilute nitric acid, and the * By this fusion a portion of nitrite is said to be formed ; — ^this may be separated by dissolving the fused mass in cold water, evaporating and crystal- lizing afresh. 62 CHEMICAL EEACTIONS. solution diluted with water till a precipitate begins to form ; from this pre- cipitate the solution is filtered, and the filtrate evaporated until it is of suf- ficient concentration to crystallize. The crystals are then digested with water containing a little nitric acid, excess of ammonia solution added, and the precipitate of basic hydrate washed thorouglily and dried. Salt or Palladium. Protoohloride of palladium or palladious chloride (PdCl). The metal palladium is dissolved in nitro-hydrochloric acid, the solution evaporated to dryness on the water-bath, by wliich moans palladic chloride is first formed, but this salt (Pd^Clj) is converted into palladious eldoride (PdCl) with evolution of clilorine at the temperature employed : after the first evaporation, hydrochloric acid should be added, and the liquid again evaporated ; water is then to be poured on the salt, and the whole carried (o dryness once more on the water-bath. Salt op Tin. Protoohloride of tin (SnCl). This salt is obtained by dissolving the granulated metal in hydrochloric acid (the concentrated acid diluted with its own bulk of water) ; the mixture is to be heated, care being taken to stop the action before all the tin and hydrochloric acid have been consumed : the solution of the chloride is then to be decanted clear from the residual metal, and poured into a bottle con- taining a few fragments of pure tin : a little dilute hydrochloric acid should also be added. Salt or Platinum. Per- or bichloride of platinum or platinic clilorido (PtCl^). This salt is prepared in precisely the same manner as the palladious chloride. Salt of Q-old. Terohloride of gold or am-ie chloride (AuCl^). This salt may be prepared as the palladious chloride if the metallic gold is pure. If, however, the gold contains copper (Cu) or silver (Ag), the nitro- hydrochlorie solution is at once evaporated to dryness on the water-bath, and redisBolved in water, by which means the whole of the silver remains as chloride. The aqueous solution is then shghlly acidified with hydrochloric acid and boiled with a solution of oxaUc acid ; the gold is thus precipitated in the metallic form, while the copper remains in solution ; if, however, any copper still contaminates the gold in the form of oxalate of copper, it may be removed by treating the metal with ammonia solution. Salts op Etiiyle. Oxide of ethyle or ether ([C^HJ^O). This is obtained of sulHcient purity in commerce for the ordinary ana- lytical operations. If, however, ether free from water is required, it is OP HEAGENTS. 63 pbtained "anhydrous" by digestion with, and distillation from, caustic lime (Ca^O). For most purposes this is, however, unnecessary. The specific gravity of anhydrous ether is 0'73. Hydrate of ethyle or alcohol ([C^ Hj] HO). This is to be obtained of great purity as " rectified spirit," having the spe- cific gravity of 0'83 ; tliis, like commercial ether, contains water, from wliich it, too, may be freed by distillation with caustic lime. By other subsequent distillations with ignited carbonate of potassium (KjCOg), or anhydrous sul- phate of copper (CUj SO4), it may be rendered quite free from water. It is then termed " absolute," and has a specific gravity of 0'795. Por all ordinary purposes the alcohol recently introduced by the Excise, and known as " me- thylated spirit," may be employed. This spirit is simply alcohol inten- tionally and avowedly mixed with methyle alcohol to the extent of 10 per cent. Tliis is done in order to preclude its use as a beverage, without interfering with its applicability to most manufacturing and chemical purposes. Salts of Hydeogen. Cliloride of hydrogen or hydrochloric acid (HCl). Nitric and sulphuric acids and salts of iron are common impurities of commercial hydrochloric acid : it may, however, always be obtained of great purity in commerce. Its specific gravity should be 1-2. 1 part, by mea- sure, of acid diluted with 2 parts of water is often used in analysis as dilute hydrochloric acid. Nitrate of hydrogen or nitric acid (HNO3). The commercial acid generally contains a little hydrochloric and sulphuric acid (Hj SOj) ; it may, however, be obtained pure. The diluted acid should have the specific gravity of 1-12, and is made by mixing 1 volume of strong acid with 2 of water. Acetate of hydrogen or acetic acid (HCj H3 O^ or HA). This acid as obtained in commerce is of sufficient purity for most ana- lytical operations. It should have a specific gravity of 1'048. It occa- sionally contains sulphuric acid. Oxide of hydrogen or water (HjO). This substance, as it commonly occurs, holds various salts in solution, of which tlie principal are the chlorides, sulphates, and carbonates of potas- sium, sodium, calcium, and magnesium : from these impurities it may be separated by distillation. Sulphide of hydrogen or hydrosulphuric acid or sulphuretted hydrogen (H^ S). Thjs substance may be easily prepared by acting upon almost any me- taUic sulphide with hydrooliloric acid or with sulphm-ic acid ; in practice, however, the protosulphide of iron (Fe^ S) is almost invariably employed : the evolved gas is washed by passing it through a wash-bottle containing a 64 CHEMICAL EE ACTIONS. small quantity of water, and it may be afterwards dried by passing it through a tube containing chloride of calcium in small fragments. The solution of this gas in water may be prepared by passing the gas into distilled water as Fig. 6. long as it is dissolved, which may be ascertained by observing whether the bubbles as they pass through the liquid are dissolved, or whether they escape without diminution: a saturated solution of this gas is much employed in analysis. Sulphurous acid (Hj SO3). This acid is not known to us in the separate state, but only as a solution of the compound called sulphurous acid gas (SOj) in water (H^O). Sul- phurous acid gas is evolved when charcoal (C), copper (Cu), or mercvu-y (Hg) are boiled with concentrated sulphuric acid. The following changes occur: — 2(H2 S0„)+C=2(H, S03)+C02 2(11^ S0,)+2Cu=H, SO3+CU2 SO,-(-H, : but the sulphurous acid splits thus — H,S03=H,0+S0,. Sulphurous acid gas may be washed, and water may be saturated with it, just as in the case of ammonia gas. Sulphuric acid (H^ SO^). The common impui-ities of the commercial acid are lead (Pb) and arsenic (As) ; both are separated by passing a stream of sulphuretted hydro- gen through the diluted acid. For ordinary purposes a good specimen of commercial acid suffices, but for special cases, such as tlie detection of poisons in medico-legal investigations, it is necessary to employ an acid which is absolutely pure. The dilute acid employed in analysis is prepared or EEAGBNT8. 65 by mixing 1 part of the ooncenfa-ated acid (oil of vitriol) with 5 parts of water; the greater part of the lead is separated by this dilution. Carbonic acid (HjCOj). This acid is not known to us in the separate state, but only as a solution of carbonic acid gas (COJ in water (H^O), for H^ 003=002+112 0. The gas (OOj) can be easily prepared by decomposing any carbonate by an acid in an apparatus similar to that figured on page 64. Carbonate of calcium (marble) and hydrochloric acid (HCl) are usually employed: — Ca2 0Oj+2HCl=H2CO3+2CaCl ; but the carbonic acid is immediately decomposed into water and carbonic acid gas, which may be passed into water, in which a portion will dissolve, or into the solution to be submitted to its action. Oxalic acid (H^C^O^ or H^O). The commercial substance is of sufficient purity for ordinary operations. It may be purified by sublimation. 1 part of crystals should be dissolved in 20 of water. Sulphindigotio acid. The solution of indigo in oil of vitriol, or strong sulphuric acid, is called by this name. It is used in a very dilute state as a chemical test. Tartaric acid (HjC^HjOj or H^f). This acid is met with of sufficient purity for almost all analytical purposes. It may be purified by recrystalHzation. HydrofluosiHcic acid (H, Si^F,). This acid is prepared as follows: — A mixture of 1 part of sand (Si^Oj) and 1 part of fluoride of calcium (CaF) is introduced into the flask A ; 6 parts of con- centrated sulphuric acid are then added, and heat applied by means of a sand-bath. A glass delivery-tube passes through 4 parts of water placed in the jar B, and dips be- neath the surface of the mercury, C, at the bottom of the vessel. The following actions take place: — Hydrofluoric acid (HP) is generated by the action of the sulphuric acid on the fluoride of calcium (CaF), and in its turn this hydrofluoric acid acts upon the sand present, producing gaseous fluo- ride of silicon ; thus— 2(OaF)-|-H2SOi=2(HF) -(-Ca^SO^; and 6(HF)-1-Si2 03 =3(H2 0)-t-2(SiF3) Fluoride of silicon. The fluoride of silicon escapes through the mercury, C, into the superincum- bent layer of water, and by the latter it is instantly decomposed, silicic acid Fig. 7. 66 CHEMICAL EEACIIONS. being again formed and precipitated, while the hydrofluosilioio acid remains dissolved in the water ; thus — 6(SiB'3)+4H,0=2(HSi02)+2(H3Si,F3). The use of the mercury in prcTenting the access of water to the mouth of the deUvery-tube is obvious : the liquid should be filtered through a linen cloth to separate the gelatinous sUioic acid, and the filtrate preserved in a bottle of Oerman glass. Acid Elements. Carbon (C). The charcoal selected for blowpipe examinations should be made of sound beeehwood, and should be free from bark or knots. If the pieces are about IJ inch in diameter, they should be sawn into pieces of about 4 inches in length, and each piece should be divided longitudinally, the flat surfaces of the section being well adapted for blowpipe experiments. Bromine (Br). Tins salt-radical may be obtained in commerce of sufficient purity. Chlorine (CI). Chlorine may be easily prepared by one of the methods given on p. 19 ; if required dry it may be passed over fragments of fused chloride of calcium (CaCl) in a long tube, or over pieces of pumice-stone soaked in oil of vitriol. Test Papers. Vegetable blues, or at least most of them, possess the peculiar property of becoming red when moistened with an acid, i. e. the hydrogen salt of a simple or compound acid-radical, while their original colour is restored by an alka- line solution, that is, by the solution of a substance whose basic properties are definite. Some of the most delicate vegetable blues even assume a new colour when submitted to an alkaline liquid, becoming a brilliant green, whilst vegetable yellows, when dipped into alkaline solutions, become red- brown, but are not influenced by acids beyond the restoration of their original colour (boraeic acid being an exception, for it behaves like an alkali). These indications, although very valuable, must not be too implicitly relied on, since certain salts which are theoretically neutral produce changes of colour. Blue Utmus paper. The litmus of commerce should be dissolved in water, and very dilute sulphuric acid added to the clear blue solution until the colour has been changed to a reddish violet ; the blue colour is then restored by the addition of a small quantity of the original solution : wMte writing-paper, not highly glazed, is then to be painted with the blue liquid, on one side only, and the coloured pieces, when dry, are to be cut into narrow strips for use, and pre- served in a well-stoppered bottle. DETECTION OP THE BASIC RADICALS. 67 Eed litmuB paper. This may be prepared by using the blue liquid just mentioned, after having slightly reddened it with a drop of very dilute sulphuric acid. Dahlia paper. If the richly-coloured petals of the purple dahlia, or those of the hearts- ease, are boiled with alcohol, a red solution is obtained, which is of far greater delicacy than that produced by common Utmus ; it wiU become green also by the action of alkalies. Paper may be coloured with it as with the litmus solutions. Turmeric paper. An alcoholic extract of turmeric-root is of an orange-yellow colour, and becomes reddish brown when submitted to the action of alkaline solutions. Manganese paper. Strips of paper dipped in a moderately strong solution of manganous sul- phate (Mn^ SO^) are occasionally employed for the detection of ozone. Acetate of lead paper. Strips of paper steeped ia a solution of acetate of lead (PbCj Hj Oj) are very useful in the detection of sulphuretted hydrogen (Hj S). Starch paper. Strips of paper dipped in solution of starch made by boiling starch ia water, and kept somewhat moist, are very useful in the detection of bromine and iodine. Organic Bodies. Those forms of these bodies found in commerce may be safely employed, selecting, of course, the uncoloured variety of Starch (C^^ Hjj Oj„) ; the purest white Sugar (Cjj H^jOu), and that Mud of Gelatine known as isinglass. CHAPTER VI. DETECTION OF THE BASIC EADICALS IN THEIE COMPOUNDS. We have now introduced to the notice of the student the cha- racteristic features of the basic and acid elements, existing as elements in the uncombined state, and have remarked upon the peculiar properties which they manifest, and by means of which their identity can always be safely established. The considera- tion, however, of the laws of chemical combination will have 68 CKEMICAI EEACTIONS. rendered it apparent that, from the extremely energetic properties which have been impressed upon these classes of elementary matter, it must be a comparatively rare occurrence to find them existing in nature in the isolated or uncombined condition ; and therefore, if we are provided with no other means of recognizing them than those which apply to that state, these bodies must frequently elude us. Such means are not, however, wanting ; and it will be seen from the observations which follow, and from the details which will occupy this and the next chapter, that the tests which we can apply to prove the existence of these bodies in their compounds, are, if possible, stOl more copious and con- clusive than those which serve to assure us of their presence when they exist in the elementary state. In the present chapter we shall devote oiu'selves exclusively to the detection of the basic radicals in their convpounds ; reserving the description of the methods of distinguishing the acid radicals of compound bodies for a subsequent chapter. The principal means at our disposal for the recognition of a basic radical, is by the addition of some reagent to produce a saline combination which shall contain it, and which shall be at the same time easily identified by some remarkable physical or chemical characters. The majority of those compoimds, the formation of which is held to be most conclusive proof of the presence of a basic radical, are such as present some striking peculiarity of colour, or of iiisoluhility in certain menstrua, or of colour and insoluhility combined ; but there are others again which are gases of well-marked properties ; and these are equally recog- nizable, and no less certain criteria of the presence of the body sought for. The great mass of the basic radicals with which the student wiU have to do being elementary, no proof can be obtained of their presence from any decompositions which they might un- dergo ; the compound basic radicals, as ammonium, strychnine, morphiae, and quinine, being of complex constitution, may be thus recognized. Without further remark we wiU now proceed to state at DETECTION OF THE BASIC EADICALS. 69 length the various tests for the basic radicals when in combina- tion, pausing only to give a synoptical view of the subdivisions to be adopted, the members of each of which wUl be found identical with those given at page 3, as the subdivisions of the basic elements. In Subdivision III., however, three organic bases have been introduced. 1. Salts, the solutions of which are not precipitated by car- bonate of ammonium ; by a mixture of the chloride, hydrate, and sulphide of ammonium ; or by the passage of hydrosulphurie acid gas through their acid solution : — Salts op Potassium, Sodium, Lithium, and Ammonium. 2. Salts, the solutions of which are precipitated by carbonate of ammonium ; but not by a mixture of chloride, hydrate and sulphide of ammonium, nor by the passage of hydrosulphurie acid gas through their acid solution : — Salts op Baeium, Steontium, Calcium, and Magnesium. 3. Salts, the solutions of which are precipitated by carbonate of ammonium, and also by a mixture of chloride, hydrate and sul- phide of ammonium ; but not by the passage of hydrosulphurie acid gas through their acid solution : — Salts op Yiteium, Eebium, Teebium, Thoeinum, Ceeium, Lanthanium, Didymium, Zirconium, Glucinum, Alumi- nium, ChEOMIUM, UeANIUM, IeON, M^UfGANESB, CoBALT, Nickel, Zinc, Moephine, QurtrafB, Stexchnine. 4. Salts, the solutions of some of which are precipitated by car- bonate of ammonium, and by a mixture of chloride, hydrate and sulphide of ammonium ; but all of which, without exception, are precipitated by the passage of hydrosulphurie acid gas through their acid solution : — Salts op Cadmium, Coppee, Silvee, Meecuet, Lead, Bis- muth, Palladium, Tin, Antimony, Aesenic, Platinum, Ehodium, Euthenium, Ieidiuji, Osmium, Gold, Tungsten, Molybdenum, Vanadium, 70 CHEMICAL KEACTIONS. SUBDIVISION I. SALTS OF POTASSIUM, SODIUM, lithium, AND OF THE COMPOUND METAL AMMONIUM. The number of these combinations is of course only limited by the number of acid-radicak in existence, each of the above basic bodies (and the same observation is true of most of the basic radicals) having the property of forming salts with every acid radical. The stability of these combinations varies with the accurate opposition of the combining substances to each other ; if they are imequaUy matched, then a ready decomposition is effected, if a more appropriate combination can afterwards occur. Since the metals of this subdivision are the most powerfully basic bodies with which we are acquainted, the inequality of power, if there be any, is always on the side of the acid-radical, and such compounds are invariably decomposed when brought into contact with an acid-radical of more intense properties. The metallic chlorides (MCI), bromides (MBr), iodides (MI), and sulphates (Mj SO^) are among the more stable ; while the nitrates (MNO3), oxides (MjO), sulphides (M^ S), hydrates (MHO), sulphydrates (MHS), and carbonates (M2CO3), are examples of the more easUy decomposable salts of these metals. The decompositions take place as follows : — M,0 +2HC1 =H,0 -I-2MC1 M,C03+H,S0,=H,C03 + M, SO, MHO -l-HBr =H,0 -|-MBr. These observations also apply to the corresponding salts of almost every basic radical known. The salts of the metals of this group are remarkable for their great solubility in water ; and especially is it to be noted that their oxides, sulphides, carbonates*, sulphates, oxalates, and phosphates are soluble in that menstruum. The application of this statement vriU be seen when the salts of the other metals are considered, since many of their combinations with the acid radicals mentioned above are insoluble in water, * The rare metal lithium presents a remarkable exception here, its car- bonate and phosphate being msoluble. DETECTION OF THE BASIC EADICAIS. 71 There are certain conventional expressions applied to the salts of this group with which the student should familiarize himself : — 1. Their hydrates (MHO) are termed "the alkahes," or " the caustic alkaUes ;" and the hydrates of potassium and sodium are called " the fixed caustic alkalies," in contradistinction to the hydrate of ammonium, which is very volatile. 2. Their salts in general are called " aalts of the alkalies," or " alkaline salts ;" and such expressions as " the sulphates of the alkalies," or " an alkaUne acetate," are frequently em- ployed. There is a very striking family resemblance among the salts of this group of metals in many of their physical and chemical properties ; many of the combinations of the different members of.the group, with the same acid-radical, crystallize in the same form, or are isomorphous : they are aE colourless also, imless combined with a coloured acid-radical ; and in peculiarity of taste, and absence of actively poisonous properties, they possess a great similarity. Since the great object of analysis is continually to subdivide larger into smaller groups, untU at last each iadividual member is isolated, we will at once divide this group into two sections, by availing ourselves of the following properties of the different members : — Section I.— SALTS OF POTASSIUM, SODIUM, and lithium. Not volatilized by exposure in a dish to the heat of a naked flame, i. e. by ignition. Section II.— SALTS OF AMMONIUM. Eeadily volatilized by ignition. "We have comparatively slender means at our disposal for the detection of aU these metals, on account of the great solubility of most of their salts in aU menstrua ; for it must be remembered that our recognition of substances depends for the most part upon the formation of some insoluble salt of well-defined physical peculiarities of colour or form. The few salts which are insoluble 72 CHEMICAL EE ACTIONS. present, however, such striking features, as almost to defy mistake. SBCiioisr I. — Bodies not volatilized by ignition. SALTS OF POTASSIUM, SODIUM, and lithium. SAMS OF potassium:. Solution for the reactions : — chloride of potassium (KCl) in water. The metal potassium eomhiaes with oxygen in two proportions, forming a protoxide K^O, and a peroxide K^O^ ; oxygen is, however, the only acid-radical with which potassium is known thus to combine ; every other salt which it forms contains the basic and acid-radicals, either in the same relative proportion as they occur in the protoxide K^O, or in those in which they occur in the (proto-)ohloride KCl, they are therefore termed proto- salts ; and all may be referred to the two types of MCI and M^O. The potassium salts are white, unless the acid-radical contained in them, or an associated basic radical, is coloured; they are good examples of the taste known as saline, and are not usually poisonous, unless taken in very large quantities ; they are often employed in medicine. When heated before the blowpipe they frequently decompose, if their acid-radical is a compound ; and this decomposition is the more readily effected when they are heated in the presence of some powerful chemical agent, such as charcoal, which forms the usual support for substances undergoing the blowpipe exami- nation. This body, although inert generally at low temperatures, be- comes at high temperatures a very powerful chemical agent, and by its influence under such circumstances, a sulphate, for in- stance, would be converted into a sulphide, thus — K,SO,-f-2C=K3S+2CO,: or again, a nitrate would yield a carbonate by the joint effect of the heat and the carbonic acid produced by the combustion of the charcoal, thus — 4KNO3 -I- 5C = 2K:, CO3 + 3C0, -1- 4N. SALTS OF POTASSIUM. 73 Some salts, nevertheless, generally those which contain the elementary acid-radicals, but also a few others, as the cyanide and the carbonate, resist this method of decomposition. All potassium salts, however, when so heated, fuse, and, with but few exceptions, sink into the charcoal. They impart also a violet tinge to the blowpipe flame playing over them, — the cause of this is the volatilization of a small portion of the salt, and its subsequent decomposition by the carbonaceous constituents of the flame, with separation of potassium. Potassium, it wiU be remembered, when combining with oxygen, inflames, burning with a violet light ; to the trace of potassium-vapour produced in this experiment, and its immediate reoxidation on contact with the highly-heated air surrounding the flame, the reaction in this case is due. A good method of performing this experiment is to dip a loop of platinum wire (perfectly clean and imparting by itself n colour to the blowpipe flame) „. - into a solution of the potassium salt to be tested: the blowpipe flame should be as blue as possible, with no white streaks which would inter- fere with the observation of the colour : the woodcut shows the ar- rangement. If a potassium salt be mixed with good alcohol, and the mixture repeatedly stirred, upon setting it on fire the charac- teristic violet flame wiU be produced. Almost the only insoluble salts which potassium forms, and by means of which it may be recognized, are the follovraig : — the chloroplatinate, perchlorate, carbazotate, and acid tartrate. The Chloroplatinate is produced by the action of hydro- chloroplatuiic acid (HPtClg) [the so-called bichloride of pla- tinum (PtClj), with 1 equivalent of hydrochloric acid (HCl)] on solutions of potassium salts : it is a yeUow crystalline precipitate ; the crystals are octahedral, and belong to the regular system. The test, as is the case with most other Uquid tests, is applied by simply mixing it with the solution to be tested ; and if the 74 CHEMICAL EEAOTIOITS. precipitation of the insoluble salt does not occur immediately, it is -well to agitate the liquid by stirring, or by shaking the test-tube containing it. In the present instance, to hasten the change, a few drops of hydrochloric acid should be added at the same time as the test-liquid ; the presence of alcohol also renders the precipitate more insoluble. If so small a quantity of potas- sium should be present as to give no precipitate under these circumstances, the chloroplatinate of potassium may yet be ob- tained by evaporating the solution to which the reagent has been added jiist to dryness, and then digesting it with alcohol. The chloroplatinate being far more insoluble in that menstruum than in water, remains as a yeUow residue if but a minute trace only of potassium be present. The formula of the precipitate is KPtClg, in which the K is the basic and the PtClj the acid radical. The double decom- position which produces it is as follows : — KCl -I- HPtCl, = HCl + KPtCl,. yell. ppt. 1 part of this salt dissolves in 144 jjarts of cold water, but it is more soluble in hot water : 1 part requires about 3775 parts of rectified spirit for its solution. The Peechxobate is produced by the action of perchloric acid (HClOj) in solutions of potassium salts, if the latter are not too dilute : it is a white crystaUine precipitate ; the crystals are right rhombic prisms. Its formula is KCIO^. 1 part dissolves in 65 parts of water at 15° C, and in a less quantity of boilLng water. It is quite insoluble in alcohol. The Caebazotate is produced by the action of carbazotic acid* (HCgHjXgO) on solutions of potassium salts: it is a yellow precipitate which is crystalline, the crystals belonging to the rhombic system. Its formula is KC^H^XjO. 1 part re- quires 260 parts of water at 15° C. for its solution. It is in- soluble in alcohol. The Acid Tartrate is produced by excess of tartaric acid * X=N02, a radical wliich, in the nitro-substitution compounds, is found to replace H. SALTS OF SODItTM. 75 (HjCjH^Ou or H^T) added to solutions of potassium salts ; it is then precipitated rapidly, particularly if they be shaken or stirred. The delicacy of this test is much increased if a solution of the acid tartrate of sodium is added, instead of tartaric acid, to a neutral solution of the potassiiim salt. It is a white crystalline precipitate, the form of the crystals being that of the oblique prism with a rhombic base, and belonging to the monochnic system. The formula of the precipitate is KHC.H^O, or KHT ; the reaction producing it is as foUows : — KCl+H,T=HCl+KHf. white ppt. It is important that excess of tartaric acid shotdd be present, and not excess of the potassium salt, as in the latter case the neutral tartrate, K^ T, would be formed, and this is a perfectly soluble salt. The neutral tartrate is also produced by dissolving the acid tartrate in potash (KHO) solution, thus, — KHT+KHO=KKT+H,0. 1 part of acid tartrate of potassium dissolves in 240 parts of water at 10° C. : it is insoluble in alcohol. It dissolves in strong acids. The Silicofluokide is produced by the action of hydrofluo- sUicio acid (II3 Sij P,) ; a very slight gelatinous film at first appears in the liquid, but gradually thickens to a precipitate. Its formula is K, Si^ F,. It dissolves very sparingly in cold, but more readUy in hot water. The Acid Metantimos"iate is soluble. The tests most commonly employed for the detection of potas- sium are, the violet colour of the blowpipe flame, and the forma- tion of the chloroplatinate and the acid tartrate. SALTS OF SODITJM. Solution for the reactions : — chloride of sodium (NaCl) in water. The metal sodium resembles potassium very closely. It forms two compounds with oxygen, a protoxide (Na^O), and a per- oxide (Na^Oj) ; but among the numerous salts which this metal e2 76 CHEMICAL EEACIIONS. forms with other acid-radicals, none are found corresponding to the peroxide. The salts of sodium are therefore all regarded as formed after the types protoohloride (MCI), and protoxide (M^O), and so are called proto-salts. They are white, unless associated with a coloured acid-radical ; they possess in general no poison- ous properties ; one indeed, the chloride (NaCl), appears to he quite necessary to the well-being of the animal organism. When heated on charcoal before the blowpipe, sodium salts, like potassium salts, fuse and sink into the charcoal, and suffer similar decompositions. They impart to the blowpipe flame a briUiant yellow tinge, which is mtich more intense than the violet colour produced by potassium salts, the latter being less volatile than those of sodium. Thus, in a mixture of salts tested in this manner, the potassium flame is entirely masked by the sodium, unless the salt of the former metal is present in greatly preponderating quantity : if the sodium salt is mixed with even 20 or 30 times its weight of the potassium compound, the yeUow colour, though weakened, is still distinctly perceptible. The same colour is observed when alcohol is inflamed after digestion with sodium salts. The only insoluble salt by means of which sodium, can be recognized, is the acid metantimoniate ; but the test is not deli- cate, and is difficult of application. The Chioeoplatinate and the Peechloeate are soluble. The Caebazotaie is soluble; but a shght precipitate occurs in very concentrated solutions. The Acid Taeteaie is soluble ; but a slight precipitate occurs in very strong solutions. The Silicoeltjoeide is much more soluble than the correspond- ing potassium compoimd. The Acid lEetantimoniate is produced by the action of met- antimoniate of potassium (K^H^SbjO^-feaq). This reagent is liable to decomposition* by keeping its solution; it should * Metantimoniate of potassium (K^H^Sb^O,) passes readily into anti- moniate of potassium (KSbOg) by losing H^ O ; thus — K, H, Sb, 0,=2KSb03+H, O. SALTS OF llTHlrrM. 77 therefore be dissolved only just before applying the test. The precipitate separates in crystaUine grains, but does not appear immediately if the solution be dilute : the deposition is facilitated by agitation. Its formula is Na^H^SbjO^+Gaq. It is almost insoluble in cold water, but slightly soluble in booing water. It is quite insoluble in alcohol. In carbonate of potassium solution it dissolves, but not in other potassium The tests employed in practice for the detection of sodium are, the colour of the blowpipe flame, and the formation of the acid metantimoniate : the former of these is very delicate ; the latter, however, is httle used. SALTS OF LITHIUM. Solution for the reactions : — ehloride of lithium (LiCl) in water. Lithium diifers in many respects from the two preceding metals ; it forms two combinations with oxygen, but the salts of lithium are all proto-salts ; of these we may take the chloride (LiCl) and the oxide (Li^O) as types. The lithium salts are white when the acid-radical is colourless. They are more fusible than the potassium or sodium salts, and impart a very distinct carmine colour to the blowpipe flame; the presence of a large quantity of a potassium salt does not materially interfere with this reaction, but a small quantity of a sodium compound gives rise to a yellow The insoluble salts by which lithium may be recognized are these : — the carbazotate, the carbonate, the phosphate, and the silicofluoride. The Chloeoplatin ate and the Peechloeate are soluble. The Cakbazotate is produced by the action of carbazotic acid. The Carbonate is produced by the action of a very soluble neutral carbonate, e.g. carbonate of potassium (K2CO3), of sodium (NajCO^), or of ammonium ([NH4]2C03), upon rather concentrated solutions of salts of lithium : it is crystalline. Its formula is Lij CO3. 1 part requires 100 parts of cold water for its solution, but less of boiling water. By most acids it is decomposed and dissolved ; it is insoluble in alcohol. The Acid Taeteate is soluble. The Phosphate is produced by the action of phosphate of sodium (N 82 HPO4) on solutions of lithium salts : the precipitation takes place especially on ebullition. If the solution is then evaporated to dryness. 78 CHEMICAL REACTIONS. and the residue treated afresh with water, a perfect separation of the lithium is effected. This salt is a white powder. Its composition is said to be v&riable : some analyses give the formula LiNaHPOj. It is nearly insoluble iu water containing phosphate of soda, scarcely soluble in cold water, but more so in hot. It dissolTes in dilute nitric acid. The Silicofluoride is insoluble. The distinguishing features by which lithium salts are recognized are prac- tically these, — the carmine-coloured blowpipe flame, and the very insoluble phosphate of lithium and sodium. Section II. — Bodies readily volatilized by ignition. SALTS OF AMMONIUM. Solution for the reactions: — chloride of ammonium (NH_jCl) in water. Ammonium (NH^) is the first compound metal with which the student has to deal. It is not known in the separate state, but the salts in which it exists are very numerous : they are all proto-salts, I equivalent of NH^ being equal to 1 equivalent of H ; in other words, the basic radical ammonium is monatomic. All these salts are colourless, unless their constituent acid-radical is coloured ; they are not actively poisonous unless their acid-radical has very poisonous properties. When heated, ammonium salts entirely volatilize, and in so doing impart no colour to the flame (the chloride indeed tinges the flame blue, bu.t this is due to the chlorine). They may, however, be immediately recognized by their be- haviour when warmed gently with hydrate of potassium (KHO) ; a double decomposition occurs, thus, — NH, 01+ KHO = KCl -f NH.HO. The hydrate of ammonium thus produced decomposes into water (HjO) and ammonia gas (NH3). This gas has a most peculiar pungent odour, termed ammoniacal, but better known as that of hartshorn, or spirits of sal-volatile. The pungent odoui' is suffi- cient to reveal the presence of this gas, which may also be de- tected by holding over the mouth of a test-tube from which it is SAMS or AITMONIUM. 79 issuing, a stout rod moistened witli concentrated hydroclilorie or acetic acid, when dense ■white fumes will be seen about the rod, instead of the ordinary almost transparent vapour of the acid ; this effect is due to the formation of an ammonium salt, NH3 + HC1=KH,C1. White fume. The principal insoluble salt by which this metal is recognized is the chloroplatinate. The Chloroplatinate is produced by the action of chloroplatinic acid (HPtCl,) on solutions of ammonium salts. It is a yeUow crystalline precipitate, resembling the corresponding potassium salt in being octahedral, and belonging to the regular system. Its formula is ISTH, PtCl3. It is very insoluble in cold water, but more so in hot ; it is stiU more insoluble in alcohol, 1 part requiring 1405 parts of rectified spirit for its solution. It is more soluble in dilute acid than in pure water. The Peechlobate and the Caebazotatb are soluble. The Acid Tajbteate is only produced by tartaric acid (H^T), when added to very concentrated solutions of ammonium salts, especially of the hydrate. It is a white crystaUine precipitate of the same form as the corresponding potassium compound. Its formula is NH^HT. It is as readily soluble in the hydrate of ammonium (NH^ HO) as the potassium salt is in hydrate of potassium (KHO), the very soluble neutral tartrate being thereby formed. It is rather insoluble in cold water, but dissolves freely in boiling water ; it is more insoluble in alcohol, and more soluble in acids. The StticoPLTJOBrDE is soluble. The tests to be actually employed for the detection of ammo- nium obviously are, the volatUity of the salt, its ammoniacal odour when heated with solution of hydrate of potassium (EHO), or when mixed with moist hydrate of calcium (CaHO), and its pre- cipitation by chloroplatinic acid. 80 CHEMlCAl EEACIIONS. Reactions. K. Na. Li. NH4. Chloroplatinate . . . Perehlorate Carbaaotate Carbonate / yellow \ \ crystalline J white r yellow ] \ crystalline J f white \ crystalline r white \ gelatinous f white [ granular f yellow \ \ crystalline J white white f white \ \ gelatinous J yellow 1 crystaUine J f white 1 \ crystalline J Acid tartrate Phosphate Silioofluoride Acid metanti- moniate Colourimparted to blowpipe ■ flame violet yellow carmine — In order to avoid too much verbal recapitulation, and to stow the student the method of consecutively applying the tests above men- tioned when searching either for one or more of the basic radicals which the subdivision contains, the Table on the following page is annexed. Tables, it must be remembered, are not guides to be followed blhidly, but only indications of the kind of course which the student should pursue in analysis ; the best can after all be but descriptions of one series of methods, of which several may be equally good for the attaiament of the same end ; and the student should bind himself to no one formula, but seek frequently to vary his method of analysis by adopting other sequences of ex- periments. Greater scope will be afforded him in the succeeding subdivisions than in the present one for so doing ; and in the Tables which wUl be appended to each, we shall not always select that which is believed to be the best method of distinguish- ing a substance, if a slightly inferior one is more striking. Tables, nevertheless, which contain the most accurate methods are of great value, and a complete series of such will be found in the second part of the present volume : they wiU be constructed upon the sup- position that aU the substances occurring in their respective sub- divisions are present, whilst in those appended to each subdivision it wiU be assumed that one member only is to be detected. DEIECIION OP THE BASIC EADICALS. 81 Analysis of Subdivision I. The salt may be one of POTASSIUM, SODIUM, liihittm, or AMMONIUM. Ignite the substance ; if nothing Tolatilizes, we infer the absence of Ammonium, and confirm it by gently warming a fresh portion of the original sub- stance with solu- tion of hydrate of potassium. presence of Potassium, Sodium, or Lithium. Dissolve a portion of the ignited salt in a few drops of water, add one drop of hydrochloric acid and a few drops of bichloride of platinum, and stir ; if no preci- pitate is produced, even after the addition of alcohol, and the lapse of some time, we infer the absence of Potassium. presence of Sodium or Lithium. Dissolve the rest of the ignited salt in water, add solution of phosphate of sodium, and evaporate to dryness on a water-bath ; redissolve in a small quantity of cold water ; if an insoluble residue is left, we infer the absence of Sodium. presence of Lithium. SUBDIVISION II. SALTS OF BAEIUM, STRONTIUM, AND CALCIUM; AND OF MAGNESIUM. One great distinction between this and the first subdivision may be at once pointed out ; it is this : that a far smaller number of the salts of these metals is soluble in water ; and among the insoluble, or nearly insoluble salts, are found the sulphates, car- bonates, oxalates, and phosphates, nearly all of which are easily soluble in the first group, nearly all almost insoluble in the pre- sent. It is, however, especially to be remembered, that among the soluble salts of this subdivision the oxides and sulphides are ranked, because this constitutes a distinguishing feature between the first two and the last two subdivisions. If we desire to separate the metals of this group from those of the preceding one, we have only to form their carbonates, oxalates, or phosphates ; E 5 82 CHEMICAL EEACTIONS. the metal is thus precipitated in an iasoluble combination, and being collected on a filter, the clear liquid passing through mil contain the salts of the first subdivision. The way in which these insoluble salts are formed, is by adding a soluble salt of the required acid-radical to the solution which we wish to precipi- tate ; now almost the only soluble salts of the acid-radicals in question are the hydrogen salts (the so-called acids), and the salts containing the metals of the first subdivision (the alkaline salts) ; of these, for reasons which will soon be obvious, we prefer to employ the ammonium salts, and of the ammonium salts the neutral carbonate (]Sni^)2C03 is the most advantageous. Any salt thus chosen as the precipitant of an entire group is com- monly called the group-test or group-reagent ; in fact, we find in every subdivision that there is a certain reagent which preci- pitates every member of the group, to which this name of group- reagent has been applied. Afterwards other reagents are used, some of which exercise their action on several members, some on individuals only. Subdivision I. has no such general reagent; the entire group is not precipitated by any single substance, we are therefore obliged to resort to particular or special tests. Certain conventional expressions are attached to the compounds of this subdivision also. Their oxides and hydrates are called " the alkaline earths," and their other salts " the salts of the alkaline earths." The three first members of the subdivision bear a very strong resemblance to each other ; their salts are for the most part colour- less, except in those cases where the acid-radical is coloured. The compounds of barium are very poisonous, but those of stron- tium and calcium are not so. The fourth member, magnesium, differs in many respects from the others, many of its salts are far more soluble in water ; this difference is strikingly exhibited in the case of its sulphate, which is an extremely soluble salt, while the sulphates of the other three metals are almost in- soluble. The second subdivision is as readily broken up into two parts or sections as the first, although by different means. SALTS OP BAKIUIT. 83 Section I.— SALTS OF BARIXnVI, STRONTIUM, AND CALCIUM. Precipitated by carbonate of ammonimn ([NH^J^COj), and not' redissolved by the addition of chloride of ammonium (NH^Cl). Section IL— SALTS OP MAGNESIUM. Precipitated by carbonate of ammonium ([NHJ^COg), and re- dissolved by the addition of chloride of ammonium (NH^Cl). Since so many insoluble salts occur in this group, there is less difficulty in recognizing its different members than in the case of the preceding subdivision. The group-test is carbonate of ammonium ([NH^j^COj). Section I. — Precvpitated by Carbonate of ammonium (^[1STS.^^C0^, and w>t redissolved by Chloride of ammonium (NHjCl). SALTS OF BAEIUM, STRONTIUM, AND CALCIUM. SALTS OP BAEITJM. Solution for the reactions : — chloride of barium (BaCl} in water. Barium forms two combinations with oxygen, a protoxide (BajO) and a peroxide (BaAO^). The protoxide is the type of a large number of barium salts ; these are white unless the acid- radical in them introduces colour into the compound ; those which are soluble are extremely poisonous. When heated before the blowpipe, especially in the presence of a reducing agent such as charcoal, they are frequently converted into oxide ; in these cases the oxide remains infusible, and be- comes somewhat incandescent ; but if the salt resists decomposi- tion, as do the chloride, bromide, and iodide, it remains as a fused mass upon the charcoal. A platinum wire moistened with a solution of a barium salt imparts a yeUowish-green tinge to the blowpipe flame ; this may also be observed with insoluble salts if they are previously moistened with an acid, — hydrochloric acid for instance. Barium salts impart no colour to the borax-bead. The principal insoluble salts by means of which barium may 84 CHEMICAL REACTIONS, be recognized are these : — the chromate, hydrate, sulphate, car- bonate, phosphate, and silicofluoride. The Chromate is produced by the action of chromate of potas- sium (KCrO^ on solutions of barium salts ; in very dilute solu- tions it appears only after standing. It is a pale yellow preci- pitate. Its formula is BaCrOj- It is almost absolutely iasoluble in water, but is dissolved by inost acids. The Htdratb is produced by the action of the hydrates of potassium (KHO) or of sodium (NaHO) in moderately concen- trated solutions of barivim salts. The hydrate of ammonium (NHj HO) produces no precipitate. It is to be observed that the salts of potassium and sodium may generally be employed indif- ferently as reagents, as they almost invariably act in the same manner ; the salts of ammonium can only in certain instances be substituted for those of potassium or sodiimi, as in most cases they exercise an action peculiar to themselves. Many substances in fact are soluble in ammonium salts, but not in the salts of the fixed alkalies. The hydrate of barium is a white amorphous precipitate. , x The formula of the hydrate is BaMd£|-4iaq. Whenever H^O is written as aq, it is always to be understood to signify " water of crystallization," or water loosely combined with the substance : this water need never be taken into account in writing the equa- tion which represents the reaction ; in the present case, for in- stance, the change which takes place is simply a mutual trans- ference of acid and basic radical between the acting substances, and may be represented thus :-:- / \ , \ BaCl-|/KHQ=KClL-BaE:oJ , The hydrate of barium is comparatively soluble m water, 1 part dissolving in 35 parts of water at 13° C, and in 2 parts at 100° C. It is immediately dissolved by those acids whose barium salts are soluble, and it is decomposed by most others. The Sulphate is produced by the action of sulphuric acid (Hj SOJ, or of soluble sulphates on solutions of bariimi salts : in very dilute solutions it becomes evident only after standing SALTS OF BAEIUM. 85 for a few seconds. It is a white pulverulent precipitate, which glistens somewhat in the light. Its formula is Ba, SO^. It is one of the most insoluble substances known, 1 part dis- solving in 43,000 parts of water : its solubility is not perceptibly increased by the presence of chloride of ammonium or chloride of sodium, nor by acids, although there are circumstances in which certain salts of citric acid prevent the formation of the precipitate of sulphate of barium. The Carbonate is produced by the action of the neutral car- bonate of potassium or ammonium (KjCOj or [NHJ^COj) on solutions of bariiun salts. It is a white precipitate. The formula is Ba^C03. This salt is slightly soluble in solutions of ammonium salts (especially in chloride of ammonium) ; it is almost perfectly inso- luble in water, 1 part dissolving in 15,420 parts of water at the boiling temperature : it is readily decomposed by most acids ; but dissolves in solution of carbonic acid (H^COj), forming the soluble acid carbonate of barium (j^aHCOg), thus : — Ba^C03-f-H,C03=2(BaHC03). The Oxalate is produced by the action of the oxalate of potas- sium or ammonium (K^C^O^ or [NH^JjC^O^) on solutions of barium salts. It is a white pulverulent precipitate. Its formula is Ba^C^O^. It is slightly soluble in a solution of chloride of ammonium, and dissolves in 200 parts of water (either cold or boiling). It is readUy dissolved by most acids, but not by acetic acid (HA orHC,H3 0J. The acid oxalate is produced by the action of oxalic acid (HjCjOj) on solutions of barium salts; it appears, after standing for a few minutes, as a white crystaUine precipitate : the crystals are very acute rhombohedrons. Its formula is BaHC^O^. 1 part of this salt dissolves in 336 parts of water at 15°-5 C. ; it is more soluble in hot water, but less so in alcohol. It is dis- solved readily by most strong acids. The Feekocyanidb is produced by the action of ferrooyanide of Ob CHEMICAL EE4CTI0NS. potassium (K^Cfy) on concentrated solutions of barium salts. It is a dense pale yeUow and crystaUine precipitate. Its formula (disregarding its water of crystallization) is KBaCfy ; thus being in reality a ferrocyanide of potassium and barium. It is soluble in 36-38 parts of water at 14° C, and iu 11-85 parts of boiling water. The Phosphate is produced by tbe action of phosphate of sodium (Na^ HPO^) on solutions of barium salts. It is a white pulverulent precipitate. Its formula is Ba^HPO^. It dissolves easily in solutions of many ammonium salts, from which it is repreeipitated by the hydrate of ammonium (NH^ HO). 1 part dissolves iu 20,570 parts of water at 20° C. ; it is readily dissolved by most acids, even by acetic acid. The Silicofluoride is produced by the action of hydrofluosilicic acid (H3 m.-, Fj) on solutions of barium salts. It is a white, trans- parent and gelatinous precipitate, the separation of which is promoted by shaMng and stirring the liquid, and by the addition of alcohol to it. Its formida is Bn^ Si^ Eg. 1 part of this salt is soluble in 3802 parts of water at the ordinary temperature, or in 733 parts of water acidulated with hydrochloric acid : it is more soluble in hot water ; nearly in- soluble in alcohol. The special tests employed for the detection of the various members of the preceding subdivision produce no precipitates with solutions of barium salts. The special tests for barium which the student should parti- cularly remember are these : — the yeUowish-green blowpipe flame, the insolubility of the chromate and of the sulphate, and the pro- duction of the nearly insoluble sUicofluoride. SALTS OF STBONTIUM. Solution for the reactions : — ^nitrate of strontium (SrN03) in water. Strontium, lilce barium, forms two combinations with oxygen, a protoxide (S^O) and a peroxide (Si^O^). The protoxide may SALTS OP STEONTIUM. 87 be regarded as the type of the large number of salts which this metal forms. Salts of strontium resemble barium salts in most of their chemical characters, but differ from them in being desti- tute of poisonous properties. When heated before the blowpipe, strontium salts are for the most part converted into the oxide, which remains infusible, and becomes somewhat incandescent when the blowpipe flame is directed upon it. The chloride, bromide and iodide resist decom- position imder these circumstances, and remain fused, and not de- composed even on charcoal. A wire moistened with a solution of any strontium salt imparts a fine crimson colour to the flame, which, unlike the similar colour imparted by lithium, does not disappear after long heating. The borax-bead is colourless and transparent. The principal insoluble salts by which strontium is recognized are the hydrate, the sulphate, the carbonate, the oxalate, and the phosphate. The Cheomaie is soluble. The Htdbate is produced by the action of hydrate of potas- sium (KHO) on rather concentrated solutions of strontium salts : the hydrate of ammonium (NH^ HO) produces no precipitate. It is white and floeeulent,. Its formula is Si^(5y-4|aq. It is less soluble in water than the corresponding barium salt ; 1 part requiring 50 parts of cold water, or 2-4 parts of boiling water for its solution. It is dissolved by those acids whose strontium salts are solublCj and decomposed by most others. The Sulphate is produced by the action of sulphuric acid (H, SO^) or of soluble sulphates on solutions of strontium salts, unless they are extremely dilute. It is a white pulverulent precipitate. Its formula is Sr. 80^. It is somewhat more soluble than the corresponding barium salt. A solution of chloride of ammonium does not dissolve it ; but in a solution of chloride of sodium it is gradually but com- pletely taken up, although it is reprecipitated by the addition as CHEMICAL EEACTIONS. of sulphuric acid (H^ SO,). 1 part dissolves in 6895 parts of water at 14° C, and ia 9638 parts of boiliag water. The Carbonate is produced by the action of the neutral car- bonates of potassium or ammonium (K^CO^ or [NK^^CO^) on solutions of strontium salts : it is a white precipitate. Its formula is Sr^COj. This salt is more soluble in solutions of ammonium salts, espe- cially chloride of ammonium, than is the corresponding barium compound. It dissolves in 18,045 parts of water at the ordinary temperature, but in a much less quantity of boiling water ; it is readily decomposed by most acids ; but in solutions of carbonic acid gas (CO^) it dissolves without decomposition, in the same manner as the carbonate of barium, forming the analogous com- pound, namely, the acid carbonate of strontium (SrHCOj). The Oxalate is produced by the action of oxahc acid (H^CjO^), or of soluble oxalates, even in dilute solutions of strontium salts. It is a white precipitate. Its formula is Sr-C^O,. This salt is very soluble in hot aqueous solutions of chloride or nitrate of ammonium ; it is very sparingly soluble in cold water, but dissolves in 19-2 parts of boiling water ; it is dissolved readily by most strong acids, but not by acetic acid (HC^HjO^, or HA). The Feeboctanibe is soluble. The Phosphate is produced by the action of phosphate of so- dium (Na^HPOj) on solutions of strontium salts. Its formula is Sr^HPOj. It dissolves readily in most ammonium salts, but is repreoipitated by the addition of hydrate of ammonium (NH^HO). It is insoluble in water, but dissolves in most acids. The Silicoeltjoeide is soluble, especially iu the presence of acids. The special tests of the first subdivision are without well- defined action on salts of strontium. The special tests for strontium which the student should par- ticularly remember are these : — the blowpipe flame, the action of sulphates on soluble strontium salts, and the absence of the re- action with chromatos and silicofluorides ; by means of this last SALTS OP CALCITJM. test this metal is usually distinguished from barium, the reactions of which, in most other respects are so similar to its own. SALTS OF CALCITTM. Solution for the reactions : — chloride of calcium (CaCJ) in water. Calcium, hke the two preceding metals, forms two combinations with oxygen, a protoxide (Ca.O), and a peroxide (Ca^OJ ; it com- bines with almost every acid-radioal to produce salts ; which, like those of barium and strontium, are all proto-salts. They are colourless, except in cases where the acid-radical introduces colour. They are devoid of poisonous properties. These salts resemble those of the two preceding metals in their behaviour when heated before the blowpipe on charcoal, being for the most part decomposed into the oxide (Ume). This oxide remains infusible, and is remarkably incandescent, the light which it emits increasing with the intensity of the heat, and reaching its maximum only when the lime is stibjected to the highest temperature at our disposal — such, for instance, as that produced by the oxyhydrogen blowpipe. The light thus obtained has been utilized, and is known as the " lime Hght." The chloride, bromide, and iodide of calcium resemble the corre- sponding salts of barium and strontium in remaimng undecom- posed before the blowpipe flame on charcoal. A platinum vsdre, moistened with a solution of a calcium salt, tinges the flame of an orange-red colour ; the colour, however, imparted by a pure salt of calcium is a very pure red, the orange tint which it ge- nerally has being in fact owing to the presence of a trace of sodium ; the red of pure calcium salts may even be mistaken for the crimson of strontium compounds ; actual comparison, never- theless, shows the difference. The red colour may be observed even with the insoluble salts of calcium, by heating them before the blowpipe after they have been moistened with a strong acid, such as hydrochloric acid. The borax-bead is colourless. The principal insoluble salts of calcium are the hydrate, the sulphate, the carbonate, the ferrooyanide, and the phosphate. 90 CHEMICAL REACTIONS. The Cheomatb is soluble. The Hydrate is produced by the action of hydrate of potassium (KHO) on solutions of calcium salts ; the hydrate of ammonium (NHjHO) produces no precipitate. The hydrate is a white bulky precipitate. apO^ Its formula is CaL.v^^ This salt dissolves in about 730 parts of water at the ordinary temperature, but at temperatures about the boiling-poiiit, in from 1310 to 1350 parts, thus presenting the peculiarity of being less soluble in hot than in cold water. It dissolves readily in most acids. The Sulphate is produced by the action of sulphuric acid (HjSO^) or soluble sulphates on solutions of calcium salts, unless they are very dilute. It is a white, somewhat crystalline pre- cipitate. Its formula is Ca,S0^+2aq. The solubihty of this salt in water is increased by the presence of chloride of ammonium, or of other ammonium salts, and also by sodium salts, especially the chloride of sodium ; from its solution in water containing this latter compound it is not reprecipitated, as the sulphate of strontium is, by the addition of sulphuric acid (H^SO^). Sulphate of calcium is far more soluble in water than the corresponding salts of barium and strontium, 1 part re- quiring about 460 parts of water, either at the ordinary tem- perature or that of boihng water, for its solution. The Carbonate is produced by the action of the neutral car- bonate of potassium or ammonium (K^COj or [NH^]2C03) on solu- tions of calcium salts. It is a bulky white precipitate, but when seen under the microscope, is found (as is the case with many other precipitates) to be crystalline. It is a substance which is said to be dimorphous, for it is capable of assuming two distinct crystalline forms not belonging to the same system : the occurrence of these forms is determined by the temperature at which the salt is produced ; if precipitated in the cold, the crystals assume forms belonging to the rhombohedral system ; if at the temperature of boiling water, they belong to the right prismatic system. SALTS 01' CALCIUM. 91 Its formula is Ca.COg. When recently precipitated, it dissolves with comparative ease in concentrated solutions of chloride of ammonium and other ammonium salts ; it is also soluble to a slight extent in solutions of chloride of sodium. In water it is very slightly soluble, 1 part requiring 10,600 parts at the ordinary temperature, and 8834 parts of water at 100° C. for its solution. It is decomposed by most acids, and dissolved by solution of carbonic acid gas (CO^), with formation of the acid carbonate (CaHCOj). The Oxalate is produced by the action of oxalic acid (Rfifi^), or soluble neutral oxalates, on solutions of calcium salts ; when extremely dilute, appearing after the lapse of a few seconds. It is a granular precipitate. The formula of the salt dried at 100° C. is Ca,C,0^+aq. It is insoluble in chloride of ammonium and in water ; it is also insoluble in acetic acid (HA), but dissolves in the stronger acids, nitric and hydrochloric, readily. The Ferrocyanide is produced by the action of ferrocyanide of potassium (K^Cfy) on solutions of calcium salts, especially on standing, "and more quickly still by boiling. It is a dense white precipitate. Its composition is that of a ferrocyanide of potassium and calcium; it is KCaCfy+l^aq. This salt is more insoluble in the presence of chloride of ammonium and other salts ; it dis- solves in 795 parts of water at 15° C, and in 145 parts of boiling water : it is soluble in dilute, but insoluble in concentrated hy- drochloric acid. The Phosphate is produced by the action of the phosphate of sodium (Na^ HPO J on solutions of calcium salts. It is a bulky white precipitate. Its composition is probably Ca^HPO^. It is somewhat soluble in solutions of ammonium salts, and also in solutions of chloride of sodium. The SiLicoFLTjORTDB is soluble. The special tests of the preceding subdivision are without weU- deflned action on the salts of calcium. The special means of distinguishing calcium from strontium and barium which the student should remember are these : — the 92 CHEMICAL ENACTIONS. blowpipe flame and remarkable incandescence ; tbe comparative insolubility of the ferrocyanide, and the comparative solubility of the sulphate, as serving to distinguish calcium from both stron- tium and barium ; and the solubility of the chromate and sUico- fluoride as distinguishing it from barium. Section II. — Precipitated by Carbonate of ammonium ([NH^]2C03), and redissolved by Chloride of ammonium (NHjCl). SALTS OF MAaNESIUM. SALTS OF MAGNESIUM. This metal resembles the three preceding in forming one class of salts only, namely, proto-salts. These salts, although resem- bling those of barium, strontium, and calcium in many respects, yet differ from them in many chemical characters. They are white, unless when combined with a coloured acid-radical, and act powerfuLLy as purgatives when taken into the animal system. "When heated on charcoal they are for the most part decom- posed, and the oxide formed is as infusible and highly incan- descent as lime : the chloride, bromide, iodide, &c., if perfectly free from water, are not decomposed ; but if water be present, they too decompose by fusion thus — 2MgCl+H,0=Mg,0 + 2HCl: this decomposition will be found to obtain among many of the succeeding metals. Magnesium salts impart no colour to the blowpipe flame ; but when strongly heated in the oxidizing flame, after having been moistened vsdth solution of nitrate of cobalt (C0NO3), the mass is foimd on cooling to have acquired a very pale pink colour. The borax-bead is transparent and colourless. The principal insoluble salts by means of which this metal is recognized are — the hydrate, the carbonate, the ferrocyanide and the phosphate. The Cheomate is soluble. The Hydrate is produced by the action of the hydrate of po- tassium (KHO). It is a bulky white precipitate. The hydrate of ammonium (NHi HO) exerts a very peculiar action upon solu- SALTS OP magnesitjm:. 93 tions of magnesium salts, which must be here explained, as it is the type of a reaction which will be found to occur frequently between hydrate of ammonium and the salts of other metals. This reaction has its foundation in the fact that salts of am- monium containing strong acid-radicals, as CI and SO^, form double salts with magnesium salts, and that from these double salts the magnesium cannot be precipitated by the addition of hydrate of ammonium in excess. The hydrate of ammonium acts in the first place by ordinary decomposition upon a magnesium salt, producing the hydrate of magnesium ; but in so doing a salt of ammonium must be simultaneously formed, corresponding to the original magnesium salt ; thus — MgCl+NH, HO=]Sra[,Cl+MgHO. ^ Precipitate. The chloride of ammonium thus produced then unites with an- other equivalent of chloride of magnesium (supposing more to be present) ; and upon the double salt so formed (MgCl, NH^Cl) any excess of hydrate of ammonium wiU exert no decomposing action. Hydrate of ammonium, therefore, when added in excess to a solution of a magnesium salt, can never precipitate more than one-half of the magnesium ; and for every two equivalents pre- sent, the following wUl be the decomposition : — ■ , . 2MgCl+f2NH,Ho)==MgClisrH,cJ+Mgfeo)+(srH,Ho} A ^ ^ Solubledoubl/(^0^)^Cfy+4aq. It is but slightly soluble in cold water or alcohol, but far more soluble in these liquids at the boiHng temperature. The Feeeicyanide appears to be soluble. The Phosphate is soluble ; the Silicofluoeide does not exist, being re- h2 148 CHEMICAL EEACTIONS. solved, at the moment of its formation, into hydrofluate of strychnine and siKcic anhydride (Si^Og). The other special reagents of the present and two preceding groups are TABLE OF EEACTI0N8. Al. (see page 109) Cr. (see page 113) 'see page 117) Fe (see page 120) * yellow white 4- white * white blue-grey r yellow- } { brown J green + blue-green pale green green yellow yellow yellow black yellow yellow red-brown brown-red " Hght- ■) yellow J f reddish 1 \ brown J / yellow- 1 [ brown J / greenish "1 \ white J black f greenish "1 l- white J yellow pale blue deep blue f greenish "1 [ white J Chromate Hydrate Sulphide Carbonate Oxalate Ferrocyanide . . . Ferrieyanide . . . Phosphate BLOWPIPE REACTIONS. ' Incandescent residue, which, if moistened with C0NO3 and again heated, be- comes blue. The borax- bead is green in the inner, and emerald- green in the oxidizing flame. The borax- bead is yellow in the oxidiz- ing, green ia the reducing flame. The borax- bead is red- dish-brown in the oxidiz- ing flame, and bottle-green in the reduc- ing flame. Note. — -j- means that the precipitate formed by the reagent * means that a precipitate occurs, not of the salt TABLE OF EEACIIOirS. 149 not known to give any characteristic reactions with solutions of strychnine salts. Strychnine is usually detected by its reaction with chromic acid. BEACTIONS. Pe, Mn Co m Zn (see page 125) (see page 129) (see page 132) (see page 136) (see page 140) * / dirty \ yellow brown dirty pink. pale green white brown r reddish \ \ brown J r reddish 1 yeUow yellow red white olive green white black buff black black white red white r peach- "1 \ colour J pale green white yellow white rose f greenish I \ white J white ■ deep 1 1 blue J white pale blue / greenish "1 \ white J white ■ green \ solution J r brown- \ yellow j dark red f greenish 1 \ yellow / ' orange- 1 brown J white white blue pale green white Ferric salts With Na^COj The borax- The borax- With C0NO3 give the same a green mass. bead in either bead is red- the oxide as- blowpipe The borax- flame is deep brown in the sumes a green reactions as bead is grey blue. outer, and colour; with ferrous salts. in the inner, grey in the carbonate of and amethyst inner flame. sodium on in the outer charcoal, a flame. yellow incrus- tation, white when cold. added is similar in composition to that above it. indicated opposite in the first column, but of the hydrate. 150 CHEMICAL KEACTIONS. In the Table which we append to this group we have purposely unfrequently, but are ge9:eraUy asso- Analyds of The metals of more common occurrence only being included, lEON (ferrous or ferric), MANGAIfESE, Dissolve in hydrochloric acid ; boil with a few drops of nitric acid, and ammonia. A precipitate may contain Uranium, Aluminium, Chromium, or Iron. The precipitate is washed, and digested with carbonate of ammonium in the cold, then filtered ; if not wholly dissolved, we infer the absence of Uranium, confirmed by adding acetic acid and fer- rocyanide of potas- sium. presence of Aluminium, Chromium, or Iron. Redissolve in hydrochloric acid, and add excess of hydrate of potassium; if the precipitate at first formed is finally entirely dissolved, we infer the bsence of Iron. » presence of Aluminium or Chromium. Boil the solution. If no precipitate is pro- duced, we infer the absence of Chromium, possible presence of Aluminium, which may be ascertained by observ- ing whether the addition of chloride of ammonium produces a preci- pitate. * If a precipitate is in any case obtained, the reactions DEEECTION OT THE BASIC EADICALS. 151 omitted to mention the rarer metals, since they not only occur elated also with hut few other bodies. Subdivision III. the salt may be one of ubauium, ALUMINIUM, CHEOMIUM, NICKEL, COBALT, or ZINC. add some quantity of solution of chloride of ammonivun, and excess of No precipitate will indicate the presence of Manganese, Nickel, Cobalt, or Zinc. Add sulphide of ammonium, wash any precipitate which may form thoroughly, dissolve it in nitro-hydrochlorio acid, and add excess of hydrate of potassium ; the formation of any precipitate will indicate the absence of Zinc. This may be con- firmed by observing that hydro- sulphuric acid pro- duces no precipitate in this solution. presence of Manganese, Nickel, or Cobalt. Bedissolve in HCl, and add excess of carbonate of am- lonium ; the formation of no precipitate indicates the absence of Manganese. presence of Nickel or Cobalt. Acidify with acetic acid, add cyanide of po- tassium in excess, boU the solution, and add sHght excess of hydrochloric acid ; the formation of no precipitate indicates the absence of Nickel. * possible presence of Cobalt, which may be ascertained by evapo- rating to dryness, and observing whe- ther the residue colours the borax- bead blue in both flames. must be referred to, and confirmatory tests chosen. 152 CHEMICAL BEACTIOKS. SUBDIVISION IV. SALTS OF CADMIUM, COPPER, SILVER, MERCURY, LEAD, BISMUTH, PALLADIUM, TIN, ANTIMONY, ARSENIC, PLA- TINUM, EHODIUM, KITTHENIUM, IBIDIUM, OSMIUM, GOLD, TUNGSTEN, MOLTBDBNUM, AND VANADIUM. The metals of this subdivision bear a very great resemblance to those of the last group, both in the number and the composition of the insoluble salts which they form : two members, indeed, of the present subdivision, cadmium and copper, differ in but few particulars from the general chemical characters of iron, nickel, cobalt, and zinc ; but some metals of this class form in- soluble chlorides and iodides, as copper and mercury (cuprous and mercurous chlorides), and also sUver, lead, and platinum (argentic, plumbic, and platinous chlorides). As a general rule, however, the salts of the present and of the preceding subdi- vision correspond very closely in relative solubility and inso- lubility, — the chlorides, sulphates, siLicofluorides, &c. of the fourth subdivision beiag soluble like those of the third, while the chromates, hydrates, carbonates, sulphydrates, sulphides, &c. are iusoluble, at least for the most part, and thus resemble the similar salts of the third group. The great characteristic which enables us to arrange the metals whose names are given above into a distinct group, is the precipitation of their sulphides by hydro- sulphuric acid gas, not only from neutral, but also from acid solu- tions, — the ready solubility of the sulphides of the former sub- division in acids being, it will be remembered, one of its distinguishing features. But, in addition to this, a new pecu- liarity manifests itself in the deportment of the sulphides of the present group, by means of which its further division into sections is effected. The peculiarity alluded to, is the solubility of a great number of these sulphides in alkaline sulphides, and the insolubility (under the same conditions) of the remainder. A new feature is also to be observed in the members of this group, namely, their ready decomposition with precipitation of metal by the introduction of a sheet or bar of certain metals SALTS or CABMIUir, EIC. 153 into their solutions : the metals zinc and iron are especially active in this respect, they simply act by assuming the place of the precipitated metal, thus — CuCl+Fe=FeCl+Cu. The salts of the metals contained in this subdivision are some- times called " salts of the heavy metals." The first six metals of this subdivision are of frequent oc- currence ; and of the remainder, tin, antimony, platinum, and gold are the most important. The most abundant are copper, silver, lead, mercury, and tin; but others, such as cadmium, bismuth, and antimony, as well as some of quite the rarer ones, such as tungsten, molybdenum, and vanadium, exercise so very important an influence upon the commoner metals when alloyed with them, as to demand such attention from the student as may enable him to recognize these rarer bodies by their re- actions : it is equally, if not more important, that he should be able accurately to recognize the presence of platinum and gold, on account of the great value set upon those metals. It has just been mentioned that by the action of an alkaline sulphide, such as sulphide of ammoniiun (in which agent some of the sulphides of the present group are insoluble, while the remainder are soluble), we can separate this extensive subdivi- sion into two sections ; we shall adopt this method of arrange- ment, and here give a list of the members of each section. Another reaction is advantageously made use of for the still further subdivision of the former of these sections, namely, the formation of the insoluble argentic, mercurous, and plumbic chlorides by the addition of hydrochloric acid ; the other chlo- rides of the group being soluble, are thus separated from these three bodies, and are subsequently precipitated in the form of sulphides. Section I.— SALTS OP CADMIUM, COPPER, SILVER, MERCURY, LEAD, BISMUTH, and palladium. Salts of metals which form sulphides insoluble in sulphide of ammonium ([NH^], S). h5 154 CHEMICAL EEACTIONS. Section II.— SALTS OE TIN, ANTIMONY, ARSENIC, PLATINUM, BHODIUM, RUTHENIUM, IKIDIUM, OSMIUM, GOLD, TUNGSTEN, MOLYBDENUM, AND VANADIUM. Salts of metals whicli form sulphides soluble in sulpHde of ammonium ([NH^j^ S). The tests employed for the recognition of the members of this group are the following : — ^hydrochloric acid or a soluble chloride, iodide of potassium, cyanide of potassium, chromate of potas- sium, the hydrates of potassium and ammonium, sulphydrate and sulphide of ammonium, the carbonates of potassium and ammoniiun, oxahc acid and oxalate of potassium, sulphuric acid or a soluble sulphate, ferrocyanide and ferricyanide of potassium, phosphate of sodium, and hydrosulphuric acid. The group test is hydrosulphuric add (H^S) in an acid solution. Section I. — Salts of metals which form sulphides insoluble in Sulphide of ammonium ([NH^]^ S). SALTS OP CADMIUM, COPPER, SILVER, MEECUET, LEAD, BISMUTH, AND PALLADIUM. SALTS OF CADMrUM. Solution for the reactions ; — chloride of cadmium (CdCl) in water. Cadmium is a metal which presents so many features ana- logous to those of ziac, the last member of the preceding sub- division, that its most fitting place is at the beginning of the present group. Cadmium, like many of the succeeding metals, appears to form an oxide containing half as much oxygen as the common oxide (CdjO), and the formula of which consequently is Cd^O ; the former oxide (Cd^O) only is the representative or starting- point of the large number of salts which this metal yields. Salts of cadmium, when heated before the blowpipe on pla- tinum foU and in the oxidizing flame, undergo no change except- ing the separation of the red-brown oxide, which remains in- SALTS OE CADMITTM. 155 fusible; but if heated on a reducing surface such, as charcoal affords, and in the inner flame of the blowpipe, these com- pounds are reduced to the metallic state, while the metal volati- lizes, becoming oxidized as it passes through the flame iato the air, and then condenses on a distant part of the charcoal as a red-brown incrustation of oxide (Cd^O). It imparts no colour to the blowpipe flame ; when heated, however, with borax on a platinum wire and in the oxidizing flame, a transparent bead is produced, which, if saturated with the cadmium salt, becomes milk-white on cooling. In the reducing flame the metal is re- duced, and if sufficiently heated, volatilized; before this is effected, however, the wire wiU. probably be spoilt from the cadmium having formed a fusible alloy with the platinum. It yields no characteristic reaction with nitrate of cobalt. The salts of cadmium are white, unless the acid-radical introduces colour. The chief insoluble salts by means of which cadmiiim is recognized are the hydrate, the sulphide, the carbonate, the oxalate, the ferrocyanide, the ferricyanide, and the phos- phate. A bar or plate of metalUc iron introduced into the solution of a cadmium salt, does not precipitate the metal ; but a bar of zinc removes the cadmium from its solution, the zinc combining with the aoid-radical. The Chloeidb is soluble. The Iodide is readily soluble. The Cheomate is yellow. The Cyanide, according to some chemists, is soluble ; accord- ing to others, cyanide of potassium produces a precipitate with sulphate of cadmium (Cd^SO^), soluble in excess of the pre- cipitant and in warm ammonia-water, but insoluble in solu- tions of other ammonium salts. The Hydrate is produced by the action of hydrate of potas- sium, and is partially precipitated also by hydrate of ammonium : it is a white precipitate. Its formula is CdHO. It dissolves readily in hydrate of ammonium and in many 156 CHEMICAL EEACTIONS. other ammonium salts, and readily in acids, suffering decom- position. The Sulphide is produced by the action of hydrosulphuric acid or the sulphides of potassium and ammonium on solutions of cadmium salts ; it is precipitated even from solutions acidified by dilute mineral acids, and of course also separates from neutral or alkaline solutions. It is a brilliant rich yellow precipitate. Its formula is Cd^, S. It is very sKghtly soluble in hydrate of ammonium, but dis- solves easily in concentrated hydrochloric or nitric acids, and even in dilute hydrochloric at the boiling temperature, although precipitable from its acid solution by hydrosulphuric acid gas. The Sulphate is soluble. The Caebonaie is produced by the action of the neutral or acid carbonates of potassium or ammonium : it is a white preci- pitate. Its formula, dried at 100° C, is Cd^CO,. It is insoluble in water, and in excess of its precipitants, but readily soluble in solutions of ammonium salts, and with decom- position, in acids. The Oxalate is produced by the action of oxaHc acid or alka- line oxalates on solutions of cadmium salts : it is a white crystal- line powder. Its formula, dried at 100° C, is Cd,C,0, + 2aq. It dissolves ra the hydrate and in most other ammonium salts ; it is nearly insoluble in water, and in solution of oxalic acid. The Fereocyanide is produced by the action of ferrocyanide of potassium : it is a yeUowish-white precipitate. Its formula is Cd^Cfy. It is soluble in hydrate of ammonium, but does not completely dissolve in other ammonium salts. The Feeeictanide is produced by the action of ferricyanide of potassium : it is a pale yeUow precipitate. Its formula is CdgCfdy. It dissolves readily in hydrate of ammonium and in most other ammonium salts. SALTS OP COPPEE. 157 The Phosphate is produced by the aotion of phosphate of sodium : it is a white precipitate. Its formula is probably CdgPO^. It is iasoluble in water. The other reagents of the present and three preceding sub- divisions produce no characteristic reactions in solutions of cad- mium salts. The chief methods employed for the detection of cadmium are these, — the formation of the red-brown incrustation on charcoal, and the precipitation of the hydrate, readily soluble in ammonia, and of the brilliant yeUow sulphide, iasoluble in alkaline sulphides. SAITS OP COPPEE. The metal copper presents some analogy with cadmium, dif- fering, however, from it, among other characters, in forming two distinct and well-defined series of salts, the cuprous and cuprie salts, of which the oxides Cu^O and Cu^O, and the chlorides Cu^Cl and CuCl may be considered as representatives. Salts of copper when heated are converted into the oxide (Cu^O), and before the blowpipe on charcoal may be reduced to the metaUic state with the flame alone, although the reduction of the oxide may be much more readily effected if it be heated with carbonate of sodium. In this and in all eases in which it is sought to reduce a metal in order to ascertain whether the operation has been successful or otherwise, it is better to remove the mass from the charcoal, to powder it finely in a mortar, to stir up the powdered mass with water, and to allow the mixture to rest in order that the metallic particles may settle. Lastly, the liquid is to be poured off wbUe it stiU holds the impurities present in suspension, and the agitation with fresh quantities of water, and decantation, to be repeated until the metallic particles are at length obtained perfectly pure and free from the char- coal, &e. which at first obscured their presence and rendered it doubtful. By this process, also, the malleability or brittleness of the metal under examination can be ascertained ; for if, under the pestle, the globule of metal flattens out into a lamina, it may 158 CHEMICAL REACTIONS. be pronoxinced malleable ; and if, on the contrary, it is found to have been broken into minute fragments or powder, it must be considered brittle. Copper salts, when heated upon charcoal, give no incrustation, since neither copper nor its oxides are perceptibly volatile at the temperature employed; nevertheless many copper salts are sufficiently volatUe to impart a pure green colour to flame. Nitrate of cobalt gives no reaction with cupric oxide. When heated with borax on a platinum mre, salts of copper give in the oxidizing fiame a bead which is of a fine green colour while hot, and blue when cold, whilst, in the reducing flame, it becomes at first colourless, on account of the reduction of the cupric to the cuprous salts, or, if fully saturated, a brick-red bead is obtaiaed on cooHng. Copper salts are poison- ous. Cuprous salts are either colourless or red ; cupric salts are green, or if anhydrous, white : the former are converted into the latter on exposure while moist to the air, or to the action of such oxidizing substances as nitric acid, &c. The metals iron, zinc, and cadmium precipitate copper from cupric salts ; the two latter, however, precipitate a copper con- taining zinc or cadmium. Tia and lead also precipitate copper from some cupric salts ; and bismuth also, at the boiling tem- perature, precipitates a very impure metal. The presence of copper is frequently ascertained by immersing metallic iron in a solution of a copper salt. CUPKOUS SALTS. DI- OK SUB-SALTS OF COPPEK. Solution for the reactions: — cuprous chloride (Cu^Cl) in hydrooMoric acid. The principle insoluble salts by means of which the cuprous salts are re- cognized are these, — the hydrate, the sulphide, the ferrocyanide, and the ferricyanide. Many of the cuprous salts, such as the oxalate and the phosphate, either do not exist, or split, at the moment of their formation, into metallic copper and the corresponding cupric salt. The Chloride is obtained by the action of stannous chloride (SnCl) on a solution of cupric chloride (CuCl), when the following reaction takes place : — 2CuCl -I- SnCl = Cu, CI + SnCl,. cup. clilor. CTJPEOTTS SALTS. 159 This salt may also be prepared by boiling metallic copper with an acid solu- tion of cupric chloride. It is a white powder, which may, howeyer, be crystallized from its hydrochloric acid solution. It slowly becomes green on exposure to the air. The formula of this salt is Cu.^ CI. It is nearly insoluble in water, but easily soluble in hydrochloric acid, yielding a brown solution, from which a large volume of water precipitates the greater part of the salt ; it dissolves also in hydrate of ammonium, giving a colourless solution which rapidly becomes blue on exposure to the air, a cupric salt being formed, and oxygen absorbed. The Iodide is produced by the action of iodide of potassium on solution of cuprous chloride; also, it is said, by precipitating a cupric salt with iodide of potassiiun, iodine being liberated, thus — Cu2SO.,+2KI=:K2SOi+Cu^l4-I. It is a brown-red powder. Its formula is Cu^ I. It is somewhat soluble in hydrochloric acid. The Chromate is miknown. The Cyanide is produced by the action of cyanide of potassium on solu- tions of cuprous salts : it is a white curdy precipitate. Its formula is Cu^Cy. It dissolves in the hydrate and in many other ammonium salts ; it dis- solves also in strong hydrochloric acid, but is insoluble in warm dilute sul- phuric acid. The Hydrate is produced by the action of hydrate or carbonate of po- tassium upon solutions of cuprous salts : it is an orange-yellow powder. Its formula is that of an oxyhydrate, in which the oxide (Cu2)2 pre- dominates. It is soluble in hydrate of ammonium, yielding a colourless solution if the air be excluded ; it is said to dissolve in almost all acids, even in the weakest, without suffering a profound change, for such solutions still afford cu- prous salts by double decomposition. This hydrate is, however, only thus soluble in acids when moist, but when anhydrous, is at once decom- posed by them. The Sulphide is produced by the action of hydrosulphuric acid on acid, neutral, or alkaline solutions of cuprous salts ; it is a black pre- cipitate. Its formula is Cu^S or {Cn^.^^. It dissolves with diiRculty in strong boiling hydrochloric acid, but is at once decomposed by cold nitric acid into cupric nitrate and cupric sul- phide ; after ebullition with nitric acid, of course, all the copper exists in the form of cupric nitrate. The Sdlphate does not exist. The Caebonate is not known. The Oxalate is produced by the action of oxalic acid or oxalate of po- tassium : it is a white powder, which changes after a time to a blue-green. 160 CHEMICAL EEACTIONS. Its formula is not known. It dissolves readily in the hydrate and car- bonate of ammonium, but to a slight extent only in other ammonium salts. The Feebocyanide is produced by the action of ferrooyanide of potas- sium on solutions of cuprous salts : it is a white flaky precipitate, which becomes reddish brown from conversion into the corresponding cupric salt. Its formula is (Ca..^).^Cfy. It is soluble in the hydrate, but not in other ammonium salts. The Pbrricyanide is produced by the action of ferricyanide of potassium upon solutions of cuprous salts. It is a red-brown precipitate. Its formula is (Cu2)3 Cfdy. It dissolves readily in the hydrate, but is insoluble in other ammonium salts. The other special tests of the present and three preceding groups exert no characteristic or well-defined action on solutions of cuprous salts. The means usually employed for the detection of cuprous salts are these, — the formation, and behaviour with ammonia water of the insoluble chloride, and the precipitation of the iodide, hydrate, and sulphide. CtrPEIC SALTS. Solution for the reactions : — eupric sulphate (Cu^SO^) in water. The chief insoluble salts by means of which copper, in this form of combination, is recognized are these, — the chromate, the cyanide, the hydrate, the oxide, the sulphide, the carbonate, the oxalate, the ferrocyanide, and the phosphate. The Chloride is soluble. The Iodide does not exist. A cupric salt, with iodide of po- tassium, yields cuprous iodide and free iodine. The Cheomaie is produced by the action of chromate of po- tassium upon solutions of cupric salts. It is a dull yeUowish brown precipitate. Its formula is probably CuCrO^. It dissolves in hydrate of ammonium, forming a green solution, and is readily soluble also in dilute nitric acid. The Cyanide is produced by the action of cyanide of potassium on solutions of cupric salts. It is a brownish yeUow precipitate, which decomposes spontaneously, at ordinary temperatures, into CUPEIC SALTS. 161 cyanogen gas (CN) and a combination of cuprous and cupric cyanide (Cu^Cy, CuCy). Its formula is CuCy+aq. It is readily dissolved by excess of its precipitant. The Hydrate is produced by the reaction of equivalent quan- tities of a cold solution of hydrate of potassium or ammonium, and of a cold solution of a cupric salt. If the precipitant be de- ficient in quantity, a green basic salt is precipitated. The hy- drate is a flocculent blue precipitate. Its formula is CuHO. This precipitate is somewhat soluble ia excess of hydrate of potassium, from ■which solution it is completely reprecipitated by ebullition, in the form of the black or cupric oxide (Cu^O) ; it is also readily soluble in hydrate of ammonium, forming a deep blue solution. The state in which the copper exists in this ammo- niacal solution is very remarkable. The metal is believed to have replaced part of the hydrogen in the compound molecule NH^, and to constitute a new compound basic radical, known as cuprammonium (NHjCu). Other similar compound radicals have been obtained, in the form of salts ; and iu them two or more equivalents of the hydrogen in ammonium have been re- placed by copper. When the cupric sulphate is treated with hydrate of ammonium, it is the sulphate of cuprammonium* that is formed ; and so with other salts. The Oxide is produced by the action of a boiling solution of hydrate of potassium on solutions of cupric salts, or by boiling the hydrate with hydrate of potassium. It is a granular-black precipitate. Its formula is Cu^O. It is readily soluble in hydrochloric, sulphuric, or nitric acid. * The formula of this salt is| N N/'HgS | .SOj+aq; for it istobe observed that these compound ammoniums are rendered still more complex by the cuprammonium itself replacing 1 eq. of hydrogen in ordinary am- monium (NHj). 162 CHEMICAL ENACTIONS. The Sulphide is produced by the action of hydrosulphuric acid on solutions of cuprie salts, whether alkaliiie, neutral, or acid. It is precipitated in black flakes, which, when exposed to the air, absorb oxygen, passiag into cuprie sulphate. Its formula is Cu^ S. It is insoluble in the hydrates of potassium, sodium, or am- monium, and in the sulphides of potassium and sodium, but dissolves slightly in sulphide of ammonium; it is soluble in cyanide of potassium. Concentrated boUing hydrochloric acid dissolves it slowly, with evolution of hydrosulphuric acid, — ^while nitric acid decomposes it more readily, with separation of sulphur, and formation of sulphuric acid and of cuprie nitrate. The Sulphate is soluble. The Cakbonate is produced by the action of carbonate of potassium on solutions of cuprie salts ; it is a greenish blue pre- cipitate, which, by boiling, is converted into cuprie oxide. Its formula is that of a mixed carbonate and hydrate, Cu^COg, CuHO. It is slightly sohible in excess of its precipitant, forming a bluish solution ; in excess of carbonate of ammonium it dissolves perfectly, forming a deep blue solution (containing a salt of cuprammonium) : the carbonate dissolves also in other ammonium salts ; it is soluble in cyanide of potassium, is insoluble in water, but dissolves readily in acids, with decomposition. The Oxalate is produced by the action of oxahc acid, or of the alkaline oxalates, not added in excess (to avoid the formation of soluble double salts), on cuprie salts. It is a pale blue precipitate. Its formula is CUjCjO^+aq when dried at 100° C. It dissolves in excess of alkaline oxalates, in hydrate or car- bonate of ammonium, but is insoluble, or but sUghtly soluble, in other ammonium salts. It is insoluble in water or in oxalic acid, but soluble in hydrochloric acid. The Perrocyanide is produced by the action of ferrocyanide of potassium : it is a flocculent precipitate of a fine brownish red colour. SALTS OF SILVEB. 163 Its formula is CUjCfy. It is insokible in ammonium salts, also in water and in most acids ; but it is soluble in concentrated sulphuric acid, and repre- cipitable from the solution by water. The Febeictanide is produced by the action of ferricyanide of potassium on cupric salts: it is a greenish-yeUow preci- pitate. Its formula is believed to be CUjCfdy. It dissolves in hydrate and carbonate of ammonium ; but it is insoluble, or nearly so, in other ammonium salts. The Phosphate is produced by the action of phosphate of sodium : it is a greenish blue precipitate. Its formula is probably Cu, PO^. It dissolves but slightly in ammonium salts, is insoluble in water, but dissolves in almost all acids. The other special tests of the present and three preceding groups are without well-defined action on solutions of cupric salts. The means chiefly employed for the recognition of cupric salts are the precipitation of the black oxide, the sulphide, and the ferrocyanide. The blue colour of the ammoniacal cupric com- pounds is also very characteristic of these salts of copper. SALTS OF SILVEE. The salts of silver bear some resemblance to those of copper, — the principal points of resemblance being the formation of two series of salts, and the existence of similar relations in the case of both metals to the compound basic radical ammonium. The di- or sub-salts of silver, or argentous salts, are not by any means so numerous or well-defined as the cuprous salts ; and indeed the argentous oxide (Ag^O) is almost the only weU-known member of the series, — a series which is qaite unimportant in an analytical point of view, and which we do httle more than mention. The argentic salts wiU be described at length ; and of them the ar- gentic oxide (Ag^O) and the argentic chloride (AgCl) may be considered typical. Silver salts are poisonous, but are occasion- 164 CHEMICAL EE ACTIONS. ally employed in medicine : their taste is generally nauseous and metallic ; some, however, are excessively sweet. Salts of silver, when heated before the blowpipe on charcoal, are reduced very readily to the metaUic state, and still more readily in the presence of carbonate of sodium ; they furnish no incrustation upon the charcoal, nor do they impart any colour to the flame. When heated with borax, an opalescent or milk-white bead is produced : in the redueing flame the glass becomes grey from the reduced silver disseminated through it ; the borax af- terwards becomes clear, the metal running into a globule, which then aUoys with the platinum wire. With this and many subsequent metals this experiment is not usually tried, as it furnishes no decisive result except the destruction of the pla- tinum wire ; if the experiment be performed, it may be done on charcoal. Iron, zinc, cadmium, lead, and tin precipitate metallic silver from most soluble salts of that metal, and very generally, when placed in contact with insoluble sEver salts, equally eifeet their reduction, the silver appearing as a grey, brown, or black mass, usually spongy (see p. 60). Copper reduces silver in the form of minute spangles, while mercury forms an alloy with it. Other metals, as bismuth, antimony, and arsenic, also reduce silver, but less effectively. Many salts also, the metal of which has a ten- dency to pass into another and higher stage of combination, exert a similar action : ferrous sulphate and stannous chloride are ex- amples of these salts : — 3(AgN03) + 6(Fe, S0,)=3Ag+(re,X (N03)3+2([reJ, [SOJ3) ; Ferrous sulphate. Feme nitrate. Feme sulphate. AgNO, + 2SnCl= Ag+ S,nNO, + SnCl, Stannous chl. Stannic chl. AUGENTOUS SALTS. DI- OR SUB-SALTS OF SILVER. Of theBe the chloride and the oxide are almost the only examples known. The argentous chloride (Ag^Cl) is said to be produced by dissolviug the cor- responding oxide (Agj O) in hydrochloric acid ; and by some it is asserted to be the grey violet or blue compound produced by exposing argentic chloride AKGENTIC SAMS. 165 (AgCl) to the action of light while in the moist state : the latter is said to undergo the following decomposition : — 2AgCl=Ag,CH-Cl. AUGENIIC SAITS, OE SILTEE SALTS. Solution for the reactions: — nitrate of silver (AgNOj) in water. The chief insoliible salts which serve for the recognition of the compounds of silver are these, — the chloride, the chromate, the cyanide, the hydrate, the sulphide, the carbonate, the oxalate, the ferrocyanide, the ferricyanide, and the phosphate. The Chloride is produced by the action of hydrochloric acid or any soluble chloride on solutions of argentic salts ; it is a heavy white curdy precipitate, becoming violet and finally black by ex- posure to light. It fuses without decomposition, to a yellowish red hquid. Its formula is AgCl. It is soluble in cyanide of potassium, in the chlorides of the alkaline and some other metals, also Ln the alkaline hyposulphites ; it dissolves easUy in hydrate of ammonium, which, if concen- trated, deposits crystalline films of a compound containing chloride of sUver and ammonia. It is somewhat soluble in concentrated hydrochloric acid, but absolutely insoluble in water. In a solu- tion of mercuric nitrate (HgNOj) it dissolves. The Iodide is produced by the action of hydriodie acid or a soluble iodide on solutions of argentic salts. It is a yeUow curdy precipitate, which becomes of a deeper colour when heated, and may be fused at a higher temperature. Its formula is Agl. It is dissolved to a considerable extent by a concentrated solu- tion of the chlorides or iodides of potassium or sodium, but is in- soluble in water or acids. In hydrate of ammonium it is less readily soluble than the chloride or bromide of silver. The Cyanide is produced by the action of cyanide of potas- sium on solutions of argentic salts: it is a curdy white pre- cipitate. 166 CHEMICAL EEACTIONS. Its formula is AgCy. It is soluble in excess of its precipitant, and in the hydrate and other salts of ammonium ; it dissolves sparingly in boiling dilute nitric acid, and is decomposed by the concentrated acids, especially on boUuig. The Chromate i^ produced by the action of chromate of potas- sium on argentic salts : it is a granular precipitate, of a fine dark crimson. Its formula is AgCrO^. It is soluble in excess of its precipitant, also in hydrate of ammonium ; it is Lasoluble in water, but is dissolved by most acids. The Hydrate or Oxide is produced by the action of the hydrates of the alkaline metals or of barium : it is a precipitate of an olive- green colour, changing rapidly to a brown. The precipitate at first produced is believed to be the hydrate, which rapidly decomposes into water and the oxide, thus — 2(AgH0)=H,0 + Ag,0. It is readily soluble in cyanide of potassium and in hydrate of ammonium, and sufficiently soluble in water to impart to it a perceptible metaUie taste and an alkaline reaction ; it dissolves readily in most acids. Care should be taken, after experimenting, to precipitate the ammoniacal solution of argentic oxide which has been obtained, with hydrochloric acid (with formation of argentic chloride), since fulminating silver is occasionally de- posited from it, although it generally decomposes with separation of metallic sUver. The three formulae, NAgj, NAgH^, and FAgHj, have been assigned by different chemists to the body termed fulminating silver. The Sulphide is produced by the action of hydrosulphuric acid on alkaline, neutral, or acid solutions of silver salts ; it is a black precipitate. Its formula is Ag^ S. This salt is insoluble in cyanide of potassium and in hydrate of ammonium, which are the solvents for most sUvcr salts; it is also insoluble in alltaHne sulphides, in water, and in dilute acids : it dissolves in concentrated sulphui'ic and nitric acids. AEGENTIC SALTS. 167 The Sulphate is produced by the action of the alkaline and other soluble sulphates, and of sulphuric acid, upon strong solu- tions of sUver salts : it is a white crystaUine precipitate. Its formula is Ag^ SO^. This is by no means an insoluble salt, 1 part dissolving in 87 parts of water ; it is more soluble in nitric acid, and still more so in concentrated sulphuric acid, from which solution it is partly precipitated by the addition of water. The Caebonate is produced by the action of the neutral or acid carbonate of potassium : it is a white precipitate, which rapidly assumes a yellowish buff colour. Its formula is Ag^ CO3. This salt readily dissolves in cyanide of potassium, and is also soluble in the hydrate and carbonate of ammonium. It is in- soluble in water, but easily soluble in most acids. The Ox a late is produced by the action of oxalic acid on solu- tions of argentic salts : it is a white precipitate. Its formula is Ag^C^O^; but it contains a Httle water (2 per cent.) mechanically retained. It dissolves in the hydrate and carbonate of ammonium, and in warm solutions of other ammonium salts ; it is scarcely soluble in water, but dissolves in nitric acid. Tee FEEHOCTAifrDE is produced by the action of ferrocyanide of potassium : it is a white precipitate. Its formula is AgjCfy. It dissolves in cyanide of potassium and in hydrate of ammo- nium, but is insoluble in other ammonium salts ; it dissolves partly with decomposition in concentrated sulphuric or nitric acids, but is not acted on by other acids, not even by hydrochloric. The Febeictaiode is produced by the action of ferricyanide of potassium on argentic salts, or by the action of nitric acid on the ferrocyanide : it is an orange-yeUow precipitate. Its formula is AgjCfdy. It dissolves in a large proportion of cyanide of potassium, and easily in hydrate or in a hot solution of carbonate of ammonium, but not in other ammonium salts. 168 CHEMICAL BDACTIONS. The Phosphate is produced by the action of phosphate of sodium (Na^ HPOJ on solutions of argentic salts : it is a brilliant lemon- yeUoTv precipitate. Its formula is Agg PO^. It is insoluble in water, but dissolves in cyanide of potassium, also ia hydrate of ammonium, but less easily in other ammonium salts ; in most acids it dissolves readily. The other special tests of the present and three preceding sub- divisions exert no characteristic action upon solutions of argentic salts. The reactions usually employed for the detection of argentic salts are these, — the formation of the insoluble chloride, chromate, oxide, and phosphate, and the general solubility of these salts in hydrate of ammonium. SAITS OF MEECTTEY. Salts of this metal possess some features in common with those of silver, but at the same time are characterized by such pecu- Harities of their own as to render their detection very easy. Mercury, like copper and silver, enters into a compound ammo- nium ; and it also forms, Uke those metals, two series of salts, the mercurous and mercuric : the salts of both these series are generally colourless when neutral, unless the acid-radical is coloured, and of a yellow tint when basic. The mercurous salts are both more numerous and more important than the correspond- ing compounds of the two preceding metals. The formula of mercurous oxide is Hg^O, and of mercurous chloride Hg^Cl, while mercuric oxide is represented by the expression Hg^O, and mercuric chloride by HgCl. The metal itself being volatile, aU its salts are necessarily either volatile or decomposable by heat ; and consequently the ordinary blowpipe examiaation, by which metallic compounds are often recognized, fails ia this instance. This volatOity furnishes, how- ever, the best method for the detection of mercury when the following plan is adopted. The mercury salt is mixed with about three or four times its bulk of dry carbonate of sodium (NajCOj), SALTS OF MEECTJEr. 169 and the mixture introduced into a narrow tube (a) made of hard glass free from lead, and having a small stout bulb at its lower end ; the mixture should occupy about the space shown at A in the figure. The bulb and its contents are then heated strongly before the blow- pipe, when the following decompositions take place : — 2(HgCl) + m, CO3 = 2(]SraCl) + Hg, CO3, and Hg,C03=2Hg+CO,+0. The mercury condenses about B in figure 6, as distinct metallic globules if an appreciable quan- mirror on the inte- .•, J. i -J. ii j-j rior of the tube. tity ot mercury were present, or, if the quantity At a is a diity were very minute, as a grey subUmate, the par- " '"'"'* "■ tides of which may be easily collected into obvious globules by cutting the tube off below B, and inserting and turning roimd, in the tube cut off, a splinter of wood. Mercury compounds may also be recognized when in solution by adding to the liquid a few drops of hydrochloric acid to ori- ginate the action ; and then by immersing in the mixture a few fragments of copper foil, and boiling, the mercury is deposited upon the copper, thus — HgCl+Cu=CuCl-t-Hg. In the foregoing experiment the presence of nitric acid should be avoided, as it would dissolve all the mercury which would otherwise be liberated. The strips of copper used, when quite dry, may be placed in a narrow tube and strongly heated, when the mercury will volatilize and condense in the upper part of the tube in the form of the usual grey sublimate. Mercurous salts in solution are not acted on by iron, but are decomposed with separation of metallic mercury by zinc, cadmium, copper, lead, and bismuth, though at the commencement of the action a white or yellow precipitate is formed, consisting of a basic salt. Tin, antimony, and arsenic act less perfectly, while ferrous sulphate and stannous chloride act upon mercurous salts as they do upon those of silver. Upon solutions of mercuric salts the metals above mentioned act much in the same manner, but I 170 CHEMICAL EEACIIONS. more slowly, usually at first reducing tte mercuric to the mer- curous salt. The salts of mercury exert a very deleterious action upon the animal oeconomy ; they are employed in medicine. MBECUEOTJS SAITS, OE M- OE SUB-SALTS OP MEECUET. Solution for the reactions: — mercurous nitrate (Hg^WOj) in water. The principal insoluble salts of this series are these, — ^the chloride, the chromate, the oxide, the sulphide, the carbonate, the oxalate, the ferrocyanide, the ferricyanide, and the phosphate. The Chloride is produced by the action of hydrochloric acid or soluble chlorides on solutions of mercurous salts. It is a dense white precipitate. Its formula is Hg^Cl. It is insoluble in the hydrates of potassium and ammonium, but is decomposed by them with formation of oxide ; it is very triflingly soluble in the chlorides of the alkaline metals. It does not perceptibly dissolve in cold hydrochloric or nitric acid ; but it is dissolved by these acids after long boiling. It is easily soluble in nitrohydroohloric acid or in chlorine water, with formation of mercuric chloride. The Iodide is produced by the action of hydriodic acid or iodide of potassium upon solutions of mercurous salts, or by tri- turating an insoluble mercurous salt (Hg^Cl for instance) with those reagents. It is a dull-green powder. Its formula is Hg^ I. With excess of its precipitant it decomposes into mercuric iodide (Hgl) and mercury ; many other bodies which exert no solvent action act similarly. Boiling concentrated solutions of the chlorides of sodium and ammonium dissolve mercurous iodide to a slight extent. It is almost insoluble in water and acids. The CrANiDE does not exist. The Chromate is produced by the action of chromate of potas- sium on mercurous salts ; it is a precipitate of a bright red colour, turning black by exposure to Hght. MEECXmOTTS SAMS. 171 Its composition is tiat of a basic salt ; if boiled in nitric acid it is converted into tbe neutral cbromate Hg^CrO^. It dissolves sparingly in ammonium salts ; it is slightly soluble in cold water, but more so in boUing vater ; it also perceptibly dissolves in nitric acid. The Oxide is produced by the action of hydrate of potassium* on solutions of mercurous salts : it is a precipitate of a bro-wnish- black colour. Its formula is Hg^O, which, like other oxides of the same type, is perhaps more intelligible when written (IIg2)2 0. This salt is decomposed either by ebullition with its precipitant, or with solutions of many other salts, or even with water only, into mercuric oxide (Hgj,0) and mercury. The Sulphide is produced by the action of hydrosulphuric aeid upon alkaline, neutral and acid solution's of mercurous salts ; it is a black precipitate. Its formula is Hg^ S, which may be written (Hgj)^ S. When boiled with water or with solutions of various salts, it exhibits a similar tendency to that shown by the oxide, in dividing into mercuric sulphide (Hgj, S) and metallic mercury. It is in- soluble in sulphide of ammonium, but decomposed by sulphide of potassium into mercuric sulphide, which dissolves, and metallic mercury, which separates; it also behaves in a similar matter with hydrate of potassium. In dilute acids and in concentrated nitric acid it is insoluble ; but it is dissolved by nitrohydrochloric acid. The SuirPHATE is produced by the action of sulphuric acid or sulphate of sodium on mercurous salts (such as the nitrate) : it is a heavy white crystalline precipitate. Its formula is (Hg^X SO^. * When hydrate of ammonium acts upon solutions of mercurous salts, a black compound is formed similar in constitution to the compounds con- taining copper or sUver formed in the same way. In the case of the mer- curous salts, however, the compound ammoniums are generally insoluble ; if mercuric nitrate be employed, the following reaction takes place : — 3(Hg, N03)-f 3(NH, H0)=2(NH, NO,) -f-3H, -(-NHCHg,),, NO3. i2 172 CHEMICAL EEACTIONS. It dissolves in dilute nitric acid, from which solution it is precipitated by dilute sulphuric acid : it is very sparingly soluble in water; ia hot concentrated sulphuric acid it dissolves, but crystaUizee on coohng. The CAEBOifATB is produced by the action of carbonate of potassium ; it is a yeUow precipitate. It formula is (Hg2)jjC03. This salt decomposes spontaneously into mercurous oxide ([HgJjO) and the gas CO^ ; it is slightly soluble in excess of its precipitant and in many acids. Carbonate of ammonium produces in mercurous solutions a grey or black precipitate, which probably has a similar constitution to that of the hydrate of ammonium products. The Oxalate is produced by the action of oxalic acid or oxalate of potassium : it is a white precipitate. Its composition is (Hg2)2C2 0^+aq. It is scarcely soluble either in hot or cold water; it is in- soluble iu oxaUc, and in dilute nitric or sulphuric acid, but dis- solves slightly in the two latter acids when they are concentrated and warm. The Feeeoctanide is produced by the action of ferrocyanide of potassium : it is a dense white precipitate. Its formula is not known. The Peeeictanide is produced by the action of ferricyanide of potassium : it is a reddish-brown precipitate. Its composition is not known. The Phosphate is produced by the action of phosphate of sodium : it is a white precipitate. Its formula is not weU. ascertained ; but it seems to be a mix- ture of the mercurous and mercuric salts. It is somewhat soluble in chloride of ammonium solution : it is insoluble in water and in. phosphoric and tartaric acids. The other special tests of the present and three preceding groups do not give characteristic reactions with mercurous salts in solution. The tests usually employed for the detection of mercurous MEECUBIC SAIIS. 173 salts are these, — ^the precipitation of the chloride, the chromate. the oxide, and the sulphide, and the reactions mentioned in the preliminary remarks — although these are applicable to the detec- tion of mercury in any form. MEECTmiC SALTS. Solution for the reactions: — mercuric chloride (HgCl) in water. The principal Lasoluble salts by which mercury in this form is recognized are these, — the iodide, the chromate, the hydrate, the sulphide, the carbonate, the oxalate, the ferrocyanide, the ferricyanide, and the phosphate. The CnxoitrDE is soluble. The Iodide is produced by the action of hydriodie acid or iodide of potassium upon solutions of mercuric salts. It is a magnificent scarlet precipitate, known as geranium-colour : a modification of this salt exists, which possesses a fine yeUow tint. Its formula is Hgl. It is soluble in excess of iodide of potassium, and in mer- curic salts, forming colourless solutions ; it is very soluble in most ammonium salts, and ia chloride of potassium, also in many acids. 1 part requires 150 parts of cold water for so- lution. The Ctaktde is soluble. ■ The Chromate is obtained by the action of chromate of po- tassium on solutions of mercuric salts : it is a fine yellow pre- cipitate. Its formula is that of a basic salt Hg2 0,HgCr02. It is soluble in excess of many mercuric salts, and in most acids, even in acetic acid. The Hydrate is produced by the action of hydrate of po- tassium* on solutions of mercuric salts : it is a yellow preci- pitate. * Hydrate of ammonium exerts an action on mercuric salts analogous to that mentioned in the case of mercurous salts : it yields precipitates, gene- 174 CHEMICAL EEACTIONS. Its formula is HgHO, H^O, although, by many chemists, this precipitate is said to be the oxide (Hg^O), iato which compound the hydrate rapidly passes on drying, or by being kept. The hydrate dissolves very sparingly in water, conferring upon it a perceptible metalUe taste, and an alkaline reaction which may be detected by dehcate test-papers (prepared vsith an al- coholic tincture of violets) ; it dissolves in those acids which do not form insoluble mercuric salts. Like the iodide, the mercuric oxide exists in two modifications, a yellow and a red, which may be distinguished not only by their physical properties, but by their behaviour with reagents : oxalic acid, for instance, com- bines with the yellow modification in the cold, while with the red modification it produces no action. The Sulphide is produced by the action of hydrosiilphuric acid on acid or neutral solutions of mercuric salts: the addi- tion of a smaU quantity of this reagent produces a double salt, which is a white precipitate of the formula HgNOj, Hg^ S, or HgCl, Hg^ S, or Hgj SO^, SHg^ S, according to the acid-radical present ; by the addition of more of the precipitant, these salts become yellow, orange, brown, and finally black, from their conversion entirely into the black mercuric sulphide, which, indeed, like the iodide and the oxide, exists also in a red mo- flcation. Its formula is Hg^ S. It is insoluble in sulphide of ammonium, but dissolves com- pletely in sulphide of potassium. It is insoluble in hydrochloric or nitric acid, even at the boihng temperature, but dissolves readily in nitro-hydrochloric acid, with decomposition. The Sulphate, if formed by the double decomposition of neu- tral aqueous solutions of {e.g.) mercuric nitrate and sulphate of sodium, is immediately decomposed by the water present, espe- rally wliite, consisting of salts of compound ammoniums, the acid-radicals of which are those of the mercuric salts ; thus, with mercuric chloride, — 2HgCl+2(NH^HO) = N^^ C1+NH,C1+2H2 0. This compound was formerly much employed iu medicine, and was known by the name of " white precipitate." MEECTJEIC SALTS. 175 cially on boiling the mixture, with formation of a lemon-yeUow precipitate, formerly called twrhith mineral, the composition of which is that of a basic sulphate (Hg^SO^, 2[Hg2 0]), which dissolves in 2000 parts of cold, or 600 of boiling water, but is very soluble in acids. The Casbonatb is produced by the action of carbonate of potassium, or the carbonates of the alkaline earths, on solutions of mercuric salts : it is a brownish-red precipitate. Its formula is Hg.CO,, 3(Hg,0). It dissolves sparingly in solution of carbonate of potassium, and is soluble in chloride of ammonium ; it is also somewhat soluble in a solution of carbonic acid. The Oxalate is produced by the action of oxalic acid or oxa- late of potassium upon mercuric salts : it is a white precipitate. Its formula is Hg^CjO^+aq. It is soluble in chloride of ammonium, and in some other am- monium salts, insoluble in water, alcohol, or ether; slightly soluble in hot dilute nitric and sulphuric acids, but more soluble iu those acids when concentrated. The PEERocTAifrDE is produced by the action of ferroeyanide of potassium : it is a white precipitate, which becomes blue on standing. The composition of this precipitate is not accurately known ; by some chemists it is stated to be simply cyanide of iron (FeCy). The Eeebictan^ide is produced by the action of ferricyanide of potassium on certain mercuric salts, as the nitrate. It is a yeUow precipitate. Its composition is not known. The Phosphate is produced by the action of phosphate of sodium on certain mercuric salts, as the nitrate. It is a white precipitate. The formula of the salt dried at 100° C. is Hg^ P,0,. It is soluble in many ammonium salts, insoluble in water and alcohol, but dissolves in phosphoric and in hydrochloric acid. The other special reagents of the present and three preceding 176 CHEMICAL EEACTIONS. groups exert no defmite or characteristic action on solutions of mercuric salts. The chief reactions made use of for the recognition of mercuric salts are these, — the formation of the scarlet iodide, of the chxo- mate, the oxide, and the sulphide, — while the mercury they contain is readily detected hy the same processes as those em- ployed ia the case of the mercurous salts. SALTS OF LEAD. The metal lead forms a link between those members of the present subdivision which have been already considered, and those which are to follow. It forms several combinations with oxygen, as the suboxide (Pb^O), the (common) oxide (PbjO), and the peroxide (Pb^O^), together with some intermediate oxides. The peroxide partakes somewhat of acid characters. The sub- oxide of lead, like the suboxides of copper and mercury, decom- poses under the influence of acids, forming salts of a higher series. There are no compounds of other acid-radicals with lead corresponding to the peroxide (Pb^O^); and the large class of lead salts may all be referred to the series of which Pb^O is the oxide and PbCl the chloride. The salts of lead are poisonous ; many of them have a sweet taste. In general, salts of lead, when heated before the blowpipe on charcoal, are converted iato the oxide, which is of an orange- yeUow colour when hot, and yeUow when cold ; usually, too, a por- tion of the salt is reduced to the metallic state, and this takes place immediately, and with the greatest ease, if the substance be heated in the reducing flame or with carbonate of sodium. In aU cases an incrustation of the oxide (Pb^O) is formed upon the charcoal at a Httle distance from the salt, since metallic lead volatihzes at a red heat, and the oxide at a white heat. Lead salts impart no colour to the flame, nor do they give any characteristic reaction with nitrate of cobalt. "When fused with borax in the oxidizing flame, a cleai- yellowish glass is obtained, which remains transparent when cold, unless great excess of lead salt has been introduced; in the reducing flame metallic PLtfMBIC SALTS. 177 lead separates : this experiment should be performed on char- coal, to avoid the destruction of the platinum -wire. Salts of lead are decomposed by iron, the lead being deposited in an arborescent form ; the same effect is produced more rapidly by zinc, cadmium, and tin. PLUMBOUS SALTS, OK DI- OR SUB-SALTS OP LEAD. The only salts of this series which seem to exist are the oxide (Pb^O), and perhaps the sulphide (Pb^ S) : the former is produced by heating plumbic oxalate out of contact with the air, and the latter by igniting plumbic sulphate in a charcoal crucible. Dilute acids resolve plumbous oxide into plumbic salts and metallic lead. PLUMBIC SALTS, OR LEAD SALTS. Solution for the reactions : — plumbic nitrate (PbNOj) in water. The principal insoluble salts of this series are the chloride, the iodide, the chromate, the sulphide, the carbonate, the oxalate, the sulphate, the ferrooyanide, and the phosphate. The Chloride is produced by the action of hydrochloric acid, or soluble chlorides, on solutions of lead salts : it is a white pre- cipitate, which crystallizes in the form of sis-sided prisms. Its formula is PbCl. It is very soluble in the hydrate of potassium, and somewhat so in solutions of alkaline hyposulphites and of acetate of so- dium : it dissolves in 135 parts of water at 12°-5 C. ; but in water containing certain salts, as chloride of calcium, it is less soluble : it is much more soluble in boiling than in cold water. It is very sparingly soluble in alcohol ; of hydrochloric acid, cold and dilute, 1 part of plumbic chloride requires 1636 parts for solution, while in dilute nitric acid it is but very slightly soluble. Concen- trated hydrochloric acid dissolves this salt abundantly. Several compounds of chloride with oxide of kad are known ; they are prepared by precipitating hot solution of chloride of lead with the hydrates of ammonium or calcium. They vary much in composition : the formulae 2PbCl, Pb,0 ; 2PbCl, 7Pb,0 ; and PbCl, Pb^O have been assigned to three of these compounds. i5 178 CHEMICAL EEACTIONS. Wien a hot solution of chloride of lead is acted on hy lime- water (CaHO) a mixed chloride and hydrate is produced, having the formula PbCl, PbHO. The Iodide is produced by the action of hydriodic acid, or a soluble iodide, on solutions of lead salts : it is a golden- coloured crystalline precipitate. Its formula is Pbl. It is soluble in chloride of ammonium solution, especially on boiling; and it also dissolves in concentrated solutions of most soluble chlorides or iodides; it is insoluble, hovs^ever, in hydrate of ammonium and other ammonium salts generally. 1 part dissolves in 1235 parts of cold, or 194 parts of boiUng water. It is slightly soluble in ether, and dissolves somewhat more easily ia nitric acid. The Chromate is produced by the action of chromate of potas- sium on solutions of lead salts : it is a pale yeUow, lemon -yellow, or orange precipitate. Its formula is PbCrO^. This salt is slightly soluble in excess of its precipitant, and dissolves readily in hydrate of potassium ; in chloride of ammo- nium solution it is insoluble ; ia water also it is insoluble, but is decomposed by hydrochloric and sulphuric acids; in dilute nitric acid it dissolves slowly without decomposition. The CxAurDB is produced by the action of hydrocyanic acid, or soluble cyanides, upon many lead salts : it is a white pre- cipitate. Its formula is PbCy. It is soluble in hot solutions of chloride of ammonium and of some other ammonium salts ; it is insoluble, or nearly so, in water, but is decomposed by nitric or sulphiuic acid, with evolu- tion of hydrocyanic acid. The Hydrate or Oxide is produced by the action of the hydrates of potassium or ammonium on solutions of lead salts : it is a white precipitate, which, under the microscope, appears crystalline, the forms of tJie crystals varjing with the method of preparation. PLTJMBIC SALTS. 179 Its composition is 2(PbH0), Pb^O ; but it is generally a basic salt containing a portion of the acid-radical of tbe original salt. This salt is soluble in excess of hydrate of potassium, espe- cially on heating, but not in excess of hydrate of ammonium ; it is slightly soluble in water, but the presence of saline com- pounds diminishes its solubility to a great extent ; it dissolves easily in those acids which do not form insoluble lead salts. The hydrate of lead is converted into the oxide (Pb^O) by ex- posure to a gentle heat. The SiQphide is produced by the action of hydrosulphuric acid on acid, neutral, and alkaline solutions of lead salts. It is a black precipitate, although, under certain circumstances, and especially by the action of pentasulphide of sodium (Na^ S^), a bright red precipitate is obtained, which may, however, be a higher sulphide than the ordinary black precipitate. The composition of the black sulphide is Pb^ S. It is insoluble in alkaline sulphides, and in hydrate or cyanide of potassium ; in cold dilute acids it is insoluble ; but in strong boiling nitric acid it dissolves, with separation of sulphur, and in the fuming concentrated nitric acid it is converted into plumbic sulphate (Pb^SO^). It dissolves in boUing concen- trated hydrochloric acid. The Sulphate is produced by the action of sulphuric acid, or soluble sulphates, on solutions of lead salts : it is a white, cry- stalline, and heavy precipitate. Its formula is Pb^ SO^. It dissolves in hot solutions of the chloride and some other salts of ammonium ; it is also soluble in a hot solution of hydrate of potassium. 1 part of this salt dissolves in 22,816 parts of water at 11° C, and in 36,504 parts of dilute sulphuric acid ; in dilute acids it is but slightly soluble, dissolving, however, in larger proportion in concentrated acids, especially in sulphuric. The CAJEtBONATE is produced by the action of the carbonates of potassium or ammonium on lead salts : it is a dense, white, crystalline precipitate. 180 CHEMICAL BEACTIONS. Its formula is Pb2C03 when precipitated in tlie cold; if the liquid be boUed, the salt is a mixed hydrate and carbonate. It is very soluble in hydrate of potassium, and somewhat soluble ia solutions of ammonium salts ; 1 part requires 50,651 parts of water at 15° C. for its solution. It dissolves with de- composition in those acids which form soluble lead salts. The Oxalate is produced by the action of oxalic acid or alka- line oxalates on solutions of lead salts : it is a white crystalline precipitate. The formula of the salt dried at 140° C. is Pb,C,0,. It dissolves in hot solutions of chloride of ammonium and of many other ammonium salts, the hydrate and carbonate ex- cepted ; it is insoluble in water, very sparingly soluble in oxalic acid solution, dissolving more freely in nitric acid. The Fbehocyanibe is produced by the action of ferrocyanide of potassium on solutions of lead salts: it is a white preci- pitate. Its composition is Pb^Cfy-l-l^aq. It is partly soluble in hot hydrate of ammonium, and per- fectly in hot chloride of ammonium ; in water it is insoluble ; by sulphuric acid it is decomposed and slowly dissolved. The Febbictanide is comparatively soluble : it occurs in transparent brownish-red crystals. The Phosphate is produced by the action of phosphate of sodium : it is a white precipitate. This precipitate is a mixture of the two phosphates Pb^ PO^ andPb^HPO,. It dissolves in chloride of ammonium solution, but is repre- cipitated by the addition of hydrate of ammonium ; it dissolves in hydrate of potassium ; it is insoluble in water, but soluble in nitric acid; it is decomposed by hydrochloric or sulphuric acid. The other special reagents of the present and three preceding groups are without characteristic action on solutions of lead salts. The tests usually employed for the detection and recognition of SALTS OF BISMUTH. 181 lead salts are these, — the formation of the chloride, iodide, chro- mate, sulphide, and carbonate, and the reactions of lead com- pounds before the blowpipe. SAITS or BISMUTH. The salts of bismuth bear certain resemblances to those of lead, although, in many particulars, they dififer much from them. Bismuth forms several combinations with oxygen: — the sub- oxide, the composition of which is not accurately known ; the oxide which is usually met with, Bi^O,; an intermediate oxide; and, lastly, the oxide Bi^O,, which is frequently called anhy- drous bismuthic acid. The formula of the bismuthic chloride (BiClj), and that of the corresponding oxide (Bi2 03) may be taken as typical of the salts of bismuth, which may be termed proto-salts, and in reality correspond to the general formulse which we have found to represent the larger number of the series of salts already treated of ; for the metal bismuth is here " triatomic," that is, it corresponds to 3 equivalents of a mona- tomie (or monobasic) element, such as hydrogen (or chlorine), and to 1 equivalent of a tribasic radical, such as the phosphoric acid- radical (PO4). In combining with biatomic or bibasic bodies, 2 equivalents are equal or correspond to 6 equivalents of hy- drogen, and therefore to 3 equivalents of the biatomic molecules, — oxygen or the sulphuric radical (SO^). Bismuthic chloride then corresponds to 3 equivalents of hydrochloric acid, and the oxide to 3 equivalents of water, — a fact which is perhaps more clearly shown by the following formulae : — H HPO, H 1 eq. of phosphoric acid. We have been thus particular in explainiag the constitution of the salts of bismuth previously to giving the full details concern- ing those of them with which we are at present concerned, in CI HCl T,-0 H^O Bid HCl 1 eq. of bis- muthic oxide. H,0 BiPO^ CI 1 eq. of bis- muthic chloride. HCl 3 eqs. of hy- drochloric acid. 3 eqs. of water. 1 eq. of bis- muthic phosphate. 182 CHEMICAI, EEACTIONS. order ttat the student may see at a glance tte relations of their formulee to those of the corresponding salts of other metals. When heated before the blowpipe on charcoal and in the oxidizing flame, bismuth salts generally fuse to a brown mass, which, upon cooling, becomes pale-yellow; this is the oxide (BijOj) ; in the reducing flame, globules of metaUic bismuth are speedily produced, more easily in the presence of carbonate of sodium : in aU eases the surronading charcoal becomes covered with an incrustation of the oxide. This incrustation is more conspicuous when carbonate of sodium has been mixed with the bismuth salt under examination, on accoimt of the volatility of metallic bismuth being greater than that of the oxide. Bis- muth salts impart no colour to the blowpipe flame, nor do they yield any characteristic reaction with nitrate of cobalt. When fused with borax, a clear glass is obtained in the oxidizing flame, which is yeUow whilst hot, and colourless when cold, the colour deepening as the amount of bismuth is increased ; in the reducing flame (the action of which should be tried on charcoal) the bis- muth is reduced to the metallic state, and the bead remains clear and colourless. Bismuth salts exhibit a peculiarity which has already been seen to exist with one salt of lead (the chloride [PbCl]), which forms an oxychloride under the influence of hydrate of ammo- nium. Bismuth salts in general, by the action of water, yield salts of a si mil ar character and constitution, to which the name oxy-salts (oxychloride, oxynitrate, &c.) or hasic salts (basic chlo- ride, basic nitrate, &c.) has been applied : these compounds are very insoluble in water, but soluble in excess of acid. Thus water precipitates from neutral bismuth salts the corresponding basic or oxy-salts, — whilst in the solution an acid salt remains, or sometimes the original salt in small qviantities together with a portion of free acid. Disregarding those small portions of the original salts which remain dissolved and precluded from decom- position by the acid produced in the reactions, the following equations represent the action of water upon the chloride and the sulphate of bismuth respectively : — BISMUTH SALTS, OB BISMBTHIC SA1T8. ] 83 3BiCl3 + 3H, = BiCl3, Bi, 0, + 6HC1 ; oxychloride of Bism. 2(K,[S0j3) + 3H,0=Bi,(S0,)3, Bi,03+3H, SO, ; oxysulphate of Bism. and even the nitrate (nitrates are generally the most soluble of all salts) is decomposed in a similar manner, but a mixed hydrate and nitrate is in this case formed — 3(Bi[N03]3) + 6H,0=Bi(N03)3,2(BiH303) + 6HN03. mixed hydrate and nitrate of Bism. These precipitates, insoluble ia water, are readily dissolved by acids. The metal bismuth is precipitated from its salts quickly and completely by iron, zinc, cadmium, and tin, and appears as a dark grey powder : this reduction is also effected by lead and copper ; but the action is slow unless accelerated by heat. BISMUTH SAITS, OE BISMUTHIC SALTS. Solution for the reactions : — chloride of bismuth (BiCl,) iu dilute hydrochloric acid. In addition to the rasoluble oxysalts of bismuth, the under- mentioned are the chief compounds of this metal not dissolved by water, — the ehromate, the hydrate, the sulphide, the carbonate, the oxalate, the ferroeyanide, and the ferricyanide. The Chloeide is soluble iu slight excess of hydrochloric acid. The Iodide is produced by the action of iodide of potassium on bismuthic salts : it is a brown crystalline precipitate. Its formula is Bilj. It is soluble in hydriodio acid. The Chromate is produced by the action of chi-omate of potas- sium upon solutions of bismuthic salts : it is lemon-yeUow. Its formula is Bi(Cr02)3. It is insoluble in hydrate of potassium or ammonium, very slightly soluble in water, but soluble in dUute nitric acid. The Hydrate is produced by the action of the hydrates of potassium or ammonium, and also by the carbonates of barium, 184 CHEMICAL EEACIIONS. calcium, &c., in the cold, on solutions of bismuthic salts : it is a white floeculent precipitate. Its formula is that of the mixed hydrate and oxide (BiHjOj, It is insoluble ia excess of its precipitants, but readily dis- solves in acids. The Sulphide is produced by the action of hydrosulphurie acid on not too acid, or on neutral solutions of bismuthic salts : it is a brown-black precipitate. Its formula is Bi^ S3. It is insoluble in the hydrates, sulphides, or cyanides of po- tassium or ammonium, also in dilute acids ; but it is dissolved with decomposition by concentrated nitric acid. The Sttlphate is soluble. The Cabbonate is produced by the action of the carbonates of potassium or ammonium : it is a white floeculent precipitate. Its formula is that of a basic salt, — 812(003)3, SBi^Oj. It is somewhat soluble in excess of its precipitants, insoluble in water and in solution of carbonic anhydride (COj), although very soluble (with decomposition) in strong acids. The Oxaxaib is produced by the action of oxalic acid upon solutions of bismuthic salts, and is deposited on standing : it separates as a granidar crystalline precipitate. Its formula is 'Bi^{G^0J^ + 3a,q. The Fbekoctanide is produced by the action of ferrocyanide of potassium on solutions of bismuthic salts : it is a white pre- cipitate. Its formula is not known. It dissolves in nitric and hydrochloric acids, but is reprecipi- tated on the addition of water. The FEERicTANrDE is produced by the action of ferricyanide of potassium : it is a light bro"mi precipitate. Its formula has not been ascertained. The Phosphate is produced by the action of phosphate of sodium on solutions of bismuthic salts : it is a white precipitate. Its formula would appear to bo BiPO^. SAMS OP PAltADirM. 185 The otter special reagents of the present and three preceding suhdivisions give no characteristic reactions with solutions of bismuthic salts. The chief means employed for the detection of hismuth in its salts is the precipitation of the oxychloride, which is formed whenever a solution of bismuthic chloride is mixed with a large quantity of water. This (and so are the precipitates produced in a similar way with other salts of bismuth) is a salt which may be distiaguished from the precipitates formed under the same circumstances in solutions of antimony, by being insoluble in tartaric acid. The other chief insoluble salts by which bismuth is recognized are the chromate, the hydrate, and the sulphide ; the blowpipe reactions on charcoal are also characteristic. The insoluble bismuth salts, as the chromate, hydrate, or carbonate, may be easily distinguished from the analogous salts of lead or silver by their being insoluble either in hydrate of potassium or hydrate of ammonium. SALTS OP PALLADIUM. The metal palladium being of far rarer occurrence than the previously described members of the present group, its salts have not been so completely studied. The characteristics which these salts present differ from those of the salts already given, and more closely resemble those exhibited by tin and platinum compounds. Palladium forms two series of combinations with acid- radicals, the paUadious and the palladic : of the former, paUadious chloride (PdCl) and paUadious oxide (Pdj O) may be considered typical, while, of the latter, palladic chloride (PdClj) and palladic oxide (Pd2 02) are representa- tives. Palladic salts have a great tendency to form compounds the acid- radical of which contains palladium united with chlorine, iodine, &c. ; they yield these definite saline combinations with the chlorides and iodides of the metals of the first subdivision, as in the following instance : — PdCl^H-KClzrKPdClj. When heated before the blowpipe, pallewJium salts are reduced with the greatest ease either in the oxidizing or reducing flame, the heat alone being sufficient to decompose them with formation of metal ; owing to the difficult fusibility, however, of this element, no globules are seen, but only a black powder : they impart no colour to the blowpipe flame, nor do they give any reaction vrith nitrate of cobalt; when fused vrith borax, they are readily reduced in either flame. Palladium salts are reduced by the same metals as effect the reduction of silver salts, and also by ferrous sulphate. 186 CHEMICAL EEACTIONS. PALLADIOUS SALTS, OB PEOTO-SALTS OF PALLABIUM. Solution for the reactions : — palladious chloride (PdCl) in water. The principal insoluble salta of this series are the iodide, the cyanide, the chromate, the hydrate, the sulphide, the oxalate, the ferrooyanide, the ferri- cyanide, and the phosphate. The Chlokide is soluble. The Iodide is produced by the action of hydriodio acid or of iodide of potassium on solutions of palladious salts : in very dilute solutions a brownish red colour at first appears ; but after some time a black precipitate separates, which is the iodide. Its formula is Pdl. It is insoluble in water, alcohol, or ether ; neither is it dissolyed by hy- driodio acid. The Cyanide is produced by the action of cyanide of potassium, or mercuric cyanide, on solutions of palladious salts : it is a yellowish- whit« precipitate. Its composition is said by some to be PdCy ; when precipitated by mercuric cyanide the formula 2(PdCy, IIgCy)-|-aq has been assigned to it. It is extremely soluble in cyanide of potassium and in hydrate of ammo- niimi. It is soluble in hydrochloric acid unless very dilute. The Cheomate is produced by the action of chromate of potassium, but is not accurately known. The Hydrate is produced by the action of the hydrates of the alkaline metals on solutions of palladious salts ; it is also produced by the carbonates of potassium and sodium. Its composition is that of a basic salt. It is soluble in the hydrates of potassium or ammoniiim ; it also dissolves in strong acids with the aid of heat. The action of hydrate of ammonium on palladious salts varies : with some, as the nitrate, it produces no precipitate ; with others, especially the chloride, it gives a flesh-coloured precipitate, which is but slightly soluble in water, and less so in alcohol, but soluble in excess of its precipitants. This precipitate TT is NHj PdCl, or Np 3 CI, as it may be written, — i. e. the chloride of pallad- ammonium. The Sulphide is produced by the action of hydrosulphuric acid on alka- line, neutral, or acid solutions of palladious salts : it is a brownish-black precipitate. Its formula is Pd^ S. It is insoluble in sulphide of ammonium, but soluble in hydrochloric acid. The Sulphate is soluble. The Oaebonate does not exist ; for the soluble carbonates precipitate pal- ladious hydrate. The Oxalate is produced by the action of oxalate of potassium on solu- tions of palladious salts. PALLADIC SALTS, OE PEE-SALTS OP PALLADIUM. 187 Ite composition is not accurately known. When, however, oxalic acid is added to an ammoniacal solution of a palladious salt, a double oxalate is produced, having the formula PdNH4C2 0,i+aq when crystallized in short rhombic prisms, and the formula PdNH4C2 04+4aqwhen occurring in long The Febkocyanide is produced by the action of ferrocyanide of potassium on palladious salts, and is precipitated on standing : it is a yellowish brown precipitate. The Fekkicyanide is produced by the action of ferricyanide of potassium : it is a red-brown precipitate. The Phosphate is produced by the action of phosphate of sodium : it is a brown precipitate. This precipitate is said to be a basic phosphate. The other special reagents of the present and three preceding groups exert no characteristic aetion upon palladious salts. The formation of palladious iodide, hydrate, and sulphide, and the reduc- tion of the metal before the blowpipe, are made use of in analysis to detect palladious salts : the blowpipe reaction is, of course, applicable also to the recognition of the palladium in palladio salts. PALLAMO SALTS, OR PER-SALT8 OP PALLADIUM. Only a few representatives of this series exist ; they are almost confined to the chloride (PdCl^) and the oxide (Pd^ 0^) ; the former gradually gives off chlorine, especially on heating, and even when its aqueous solution is boiled, and is reduced to palladious chloride (PdCl). Wten combined with chloride of potassium, palladic chloride gives a salt which is very stable ; but the pal- ladium in it probably exists in the form of a compound acid-radical (PdClj) : this salt crystallizes in brownish-red octahedra. The oxide (Pd^O) may be obtained by acting on palladio chloride with the hydrate of potassium. The sulphide (Pd^ S^) cannot be obtained by passing hydrosulphuric acid into a solution of paUadio chloride ; for, if formed at all, it is immediately decomposed into palladious sulphide (Pd^ S) and sulphur. On aoooimt of the large number of important metals included in this Subdivision, we have not deferred giving the Table of Reactions until the end of the group, but have placed a synopsis of the reactions of the Ist Section on the following page ; and for the same reason, an Analytical Table will also be found appended. 188 CHEMICAL EE ACTIONS. TABLE OF Keactions. Chloride Iodide Cyanide Chromate ... Hydrate Oxide Oxychloride Sulphide Sulphate Carbonate ... Oxalate Ferrocyanide Ferricyanide Phosphate ... Cd. (see page 154) yellow white bright yellow white white white pale yellow white Cu. (see page 160) / brownish 1 \ yellow J f yellowish 1 \ brown / blue black black blue pale blue / brownish] \ crimson J / greenish \ \ yellow J greenish blue Ag. (see page 165) white pale yeUow white crimson buff brown black white white white white r orange "I \ yellow J yellow Blowpipe Beactions. With car- bonate of sodium on charcoal, a reddish brown deposit, the metal being reduced and yolatiUzed. With car- bonate of sodium on charcoal, malleable globules ; with borax in the oxidizing flame, a green, and in the reducing flame a red bead. With car- bonate of sodium on charcoal, malleable globule. TABLE or EEACTIONS. 189 REACTIONS. Hg2. Hg- Pb. Bi. Pd. (see page 170) (see page 173) (see page 177) (see page 183) (see page 186) white f yellow, changing ■ white — — dull-green bright yellow — black — [ to scarlet . white — r yellowish "1 \ white J orange-red dull-red yellow yellow — — yellow white white / yellowish "1 \ brown J ' brownish 1 black J yeUow — — — white white white — black black black r brownish "1 \ black J / brownish "1 t black / ■ yellowish ' white white white white — — brownish red white white — — white white white pale yellow — white white f yellowish "1 \ brown J — ' reddish "1 brown j yellow — light brown reddish brown white white white white brown Mixed with Same as the With car- With car- With car- carbonate of merourous bonate of bonate of bonate of sodium and salts. sodium on sodium on sodium on heated in a charcoal. charcoal, a charcoal, re- glass tube, malleable brittle globule duced to the the metal globule and yellow metaUic state. sublimes. and yellow incrustation. incrustation. 190 CHEMICAL EEACIIONS. ' We also give an Analytical Table for the 1st Section of this subdivision, on accoimt of the great number and importance of the metals it contains. Analysis of Subdivision IV. Section I. — Salts of metals which form Sulphides insoluble in Sulphide of Ammonium. The salt may be one of CADMIUM, COPPEE, SILVEE, MEECUET (mercurous or mercuric), LEAD, BISMUTH, or PALLADIUM. Ignite the substance ; if it does not Tolatilize, we infer the absence of presence of Mercury, Cadmium, Copper, SUrer, Lead, Bismuth, or Palladium. which may Dissolve the ignited residue in a Httle nitric acid, dilute be further with water, and add dilute sulphuric acid ; if no white pre- confirmed cipitate is produced, we infer the by heating the dry salt absence of presence of mixed Lead. Cadmium, Copper, Silver, Bismuth, or with dry Palladium. STa^CO. in a small To the same solution add dilute hydrochloric acid ; if no precipitate is produced, we infer the tube and observing absence of presence of the absence Silver. Cadmium, Copper, Bismuth, or of globules. Palladium. Add hydrate of ammonium in ex- cess ; if no white precipitate is pro- duced, we iufer the absence of presence of Bismuth. Cadmium, Copper, or Palladium. If the solution is blue, we infer the presence of Copper ; if colourless, of Cadmium or Palladium. Add hydrosulphm-ic acid ; if a yeUow precipitate is produced, we infer the presence of Cadmium ; if a brownish-black, of Palladium. SAXTS OP TIIT. 191 Section II. — Salts of metals which form sulphides soluble in Sulphide of ammonium ([NH^J^ 8). SALTS OF TIN, ANTIMONY, AESENIO, PLATINUM, rhodium, RUTHENIUM, OSMIUM, GOLD, TUNGSTEN, MOLYBDENUM, AND VANADIUM. SALTS OP TIN. The chemical characteristics of the compounds of this metal resemble to a certain extent those of the preceding : it forms two series of combinations with chlorine and acid-radicals in general, — the stannous chloride and oxide (SnCl and Sn^O) being repre- sentatives of the first, and the stannic chloride and oxide (SnCl^ and Sn^Oj) typifying the second series. Stannic salts, however, are far more numerous and important than palladic salts ; and so far from having, Kke them, a tendency to decompose into the acid- radical and the corresponding salt of the first series, they are actually produced easily from stannous salts, — ^half of the metal present being separated in the metallic state, while the portion of acid-radical previously imited with this half combines with the residual elements : thus stannous oxide, under peculiar circum- stances, passes into stannic oxide, thus — 2(Sn,0)=2Sn-l-Sn,0,. Besides these two series there is a third, which is, however, un- important, few members of it existing : it is intermediate between the stannous and stannic series, and has been called the stannoso- stannic series, while its members have been termed sesqui- salts. When salts of tin are heated in the oxidizing flame of the blowpipe, they are converted into an ratermediate oxide (Sn^Oj), at least for the most part ; several tin salts, however, as stannous chloride (SnCl), partially volatilize, while in the reduciug flame tia salts yield their metal ; but to efiect this requires some skUl in the operator, and may be taken as a test of proflcieucy in the use of the reduciug flame : fluxes, such as carbonate of sodium or cyanide of potassium, should not be employed, since the operation is deprived of all difficulty by their aid. Tin salts impart no colour to the flame ; hut with nitrate of cobalt the residjml oxide 192 CHEMICAL EEACTIONS. (SUJO3) assumes a bluish-green colovr, Wieii fused with, borax in the oxidizing flame, they yield a colourless transparent glass, which, if surcharged with the tin salt, becomes opaque and cry- stalline : in the reducing flame, part of the tin present is reduced to the metallic state ; this experiment should be performed on charcoal. Although the salts of tin are placed together in the second sec- tion of the present subdivision, that is, among those metals the sulphides of which are capable of forming sulphur salts with the alkaline sulphides, yet, properly speaHng, the stannous salts should belong to Section I., and the stannic salts to Section II., for the stannous sulphide (Sn^ S) does not dissolve as such in sulphide of ammonium, but only after its conversion into stannic sulphide by combination with the sulphur which sulphide of ammonium usually holds in solution ; thus Sn, S+(NH,), S+ S=(NHJ, Sn, S,. Stannous salts are reduced by iron under certain circumstances, readily by zinc and cadmium, slightly by lead. The same actions are observed with such stannic salts as are soluble. STANNOirS SALTS, OE PROIO-SALTS OP TIN. Solution for the reactions: — proto- chloride of tin (SnCl) in water. The principal insoluble salts of this series are the iodide, the cyanide, the chromate, the oxychloride, the hydrate, the sulphide, the oxalate, the ferrocyanide, the ferricyanide, and the phosphate. The Chloeide is soluble. The Iodide is obtained by the action of iodide of potassium in excess on solutions of stannous salts, especially after some time. It is a yeUovsdsh white precipitate ; but from warm solutions it separates in fine reddish yellow crystals. Its formula is SnI. It dissolves sparingly in cold water, but more readily in hot ; it is also soluble in a solution of stannous chloride. The Cyanide is produced by the action of cyanide of potassium on solutions of stannous salts : it is a white precipitate, which is STANNOUS SAMS, OB PBOTO-SALTS OF TIN. 193 said to be stannous hydrate, not stannous cyanide. A portion of tin salt remains in the solution of cyanide of potassium. The Chbomaxb is produced by the action of chromate of potas- sium in excess on solutions of stannous salts : if the stannous salt be in excess, a greenish white precipitate is obtained, which is thought to be chromic stannate (stannate of chromium), some of the oxygen contained in the chromic acid-radical being trans- ferred from the chromium to the tin, to form stannic acid. This precipitate dissolves in hydrochloric acid, forming a green solution. The Oxychloeide is produced by precipitating stannous chlo- ride with an insufB-cient amount of hydrate of potassium. It is a white precipitate. Its composition is 2SnCl, Sn^O, 3aq. It dissolves readily in most acids. The Hydrate is produced by the action of the hydrate or car- bonate of potassium or ammonium : it is a white precipitate. Its formula is SnHO. It is readily soluble in excess of hydrate of potassium, but not in excess of its other precipitants ; it dissolves readily in acids. If the potassic solution of this salt be boiled, one of those curious metamorphoses occurs similar to those which have been noticed before, and which results in part of the tin present pass- ing into a higher state of oxidation, at the expense of another part, which is reduced to the metallic state ; thus — 4SnH0-t-2KH0=K,Sn,03+2Sn-t-3H,0. The Sulphide is produced by the action of hydrosulphuric acid on neutral or acid solutions of stannous salts ; alkaline solu- tions are very partially precipitable. It is a brownish black precipitate. Its composition is Sn^ S, or possibly, when recently precipi- tated, SnHS. It dissolves in hydrate of potassium or sodiizm, but is repre- cipitated from these solutions unchanged by hydrochloric acid ; it is almost insoluble in protosulphide of ammonium ([NH^]^ S) and in sulphydrate of ammonium (NH^HS). When, however, 194 CHEMICAl EEACTIONS. the sulpHde of ammonium has become converted into one of the higher sulphides, as [NH^]^ S^, stannous sulphide dissolves in this reagent, producing sulpho-stannic acid, the ammonium salt of which is soluble, thus — 2SnHS+(NH,), S,=(NHJ, Sn, S3 + H, S. sulpho-stannate of ammoniuin. If hydrochloric acid be added to this solution, stannic sulphide (Sn^ Sj) is precipitated, — (NHJ, Sn, S3 + 2HC1=2NH,C1+Sn, S,+H, S. yellow ppt. Stannous sulphide dissolves in boiling hydrochloric acid, being converted into stannous chloride ; boiling nitric acid decomposes it with formation of stannic oxide (Sn^O^). The Sulphate is soluble. The Caebonaie does not exist. The Oxalate is produced by the action of oxalic acid on solutions of stannous salts ; the alkaline oxalates produce double salts, which are soluble. It is a white crystalline pre- cipitate. Its formula is Sn^C^Oj. It dissolves in hot solutions of chloride of ammonium and of other ammonium salts, and crystallizes out again on cooling ; it is but slightly soluble in cold or hot water, or in oxalic acid, or in dilute cold mineral acids, but in hot hydrochloric or nitric acid it dissolves. The FEKEOCxANrDE is produced by the action of ferroeyanide of potassium on solutions of stannous salts. It is a white precipi- tate, becoming yelLow by exposure to the air. Its formula is Sn^ Cfy. It is insoluble in the chloride and many other salts of ammo- nium, in water and in acids, but it dissolves in hydrate of am- monium. The Feericyanide is produced by the action of ferricyanide of potassium. It is a white gelatinous precipitate. Its composition is SnjCfdy. STiNNIC SALTS. 195 It dissolves in hydrate of ammonium, but not in other ammo- nium salts. The Phosphate is produced by the action of phosphate of sodium : it is a white precipitate. It is insoluble in chloride of ammonium and in water, but dis- solves in hydrochloric acid. The other special reagents of the present and three preceding subdivisions are not known to yield any characteristic reactions with stannous salts. The production of stannous hydrate and sulphide, and the re- action of the former salt when dissolved in hydrate of potassium and heated, are among the chief methods employed for the recog- nition of stannous salts. STAHNOSO-STANNIC SALTS, OR SESQUI-SALTS OP TIN. These salfa are thought by most chemists to be formed by the union of stannous and stannic salts. The Oxide, or more properly, the Hydrate, is obtained by acting on stannous chloride with ferric hydrate, — ferrous chloride and stannoso-stannic hydrate being the products of the change, which may be more simply repre- sented by assuming ferric oxide to be the ferric salt concerned — (FeJ^ O3 +4SnCl = (Sn,), O3 -t-4reCl. It is a yellowish- white precipitate, which dissolTes in hydrochloric acid with- out decomposition, if protected from the air. The Sulphide, or more properly, the SuLrHYDKATE, is said to be ob- tained by passing hydrosulphiu-ic acid through a solution of the hydi-ate in hydrochloric acid : it is a liver-coloured precipitate, haTing probably the formula (Sn2)2S3. STANNIC SALTS, OE BI- OK PER-SALIS OF TIN. Solution for the reactions : — stannic chloride (SnCl^) in water. This is the most stable series of the salts of tin, both of the preceding series possessing a great tendency to assume more acid-radical and pass into stannic salts. The decomposition of stannic salts under the influence of reagents is very peculiar, and wholly dependent upon the chemical nature of the substance presented to them : if the reagent be one possessing powerful k2 196 CHEMICAL EEACTIONS. basic properties, the stannic compound in combining with, it assumes the functions of an acid-radical, thus — 2SnH,0,+2KH0=K, Sn,03 +3H,0. stannate of potasBium. If, again, the same salt, stannic hydrate, be acted upon by a reagent possessed of powerful acid properties, the metal unites with the acid- radical of the acid to form a salt in which the tin plays the part of a base, thus — 2SnH,0,-h2H, S0,=Sn,(S0,X-|-4H,0. stannic sulphate. These or similar peculiarities have been described in the case of aluminium, chromium, and paUadinm. One important feature with respect to these salts is this : — there exist two modifications of them, which have been termed the stannic, and the metastannic salts ; the hydrate, however, and those other salts in which a compound of tin and oxygen is presumed to play the part of the acid-radical, are the only in- stances in which this " dimorphism" is strongly marked. The principal insoluble salts of this series are the cyanide, the ohromate, the hydrate, the sulphide, the ferrocyanide, and the phosphate. The Chloeide is soluble. The Iodide is not produced by iodide of potassium; but it separates in the form of orange or red crystals decomposable by water, when a solution of stannous chloride is boiled with iodine. The Cyanide is not produced by cyanide of potassium, the white precipitate obtained being believed to be only stannic hydrate. The Cheomate is produced by the action of chromate of po- tassium on solutions of stannic salts : it is a yellow precipitate. The Hydrate occurs in two distinct varieties, according to the method of its production ; in either form it is the hydrogen salt of a compound acid-radical, and yields .salts with the hydrates of the first subdivision, which contain the alkahne metals. STANNIC SALTS. 197 The two modifications are called respectively stannic and meta- stannic acids, 1. Stannic Acid is produced by the action of the hydrates or carbonates of potassium or ammonium, but it is precipitated in the purest form by the action of the carbonates of the second subdivision on solutions of stannic salts ; it is also produced by decomposing stannic chloride with water. It is a white gelatinous precipitate. Its formula is H^ Sn^Oj, while its known salts may be repre- sented by the formula M^Sn^Oj. Stannic hydrate when dried below 55° is, however, H^Sn^Oj, H^O, or more simply, SnH^O^. It dissolves readily in excess « ^^^- , ,. ^ J J At B small sphnters of talline ; and if an arsenic compoimd be s;entlv charcoal. ^ ° '' At A, a small lump heated m a tube open at both ends, and held of arsenious oxide. obUquely over the lamp, crystals distinctly visible to the naked eye, and readily seen to be octahedra by the aid of a. lens, con- dense towards the upper and cooler part of the tube. If the cirrrent of air be excluded, as would be the case were the tube closed at its lower extremity, most arsenical compounds would then volatiLLze unchanged: and thus, if the imcombined metal were present, a black mirror would be formed in the cool part of the tube ; if one of the sulphides, a yellow or an orange sub- limate ; if the iodide, red crystalline scales would be deposited ; — whilst it would condense as the oxide (As^Oj), only if it so existed in the original substance, or were produced by the decomposition of the compound in which it occurred. We now come to the consideration of the chief point in which arsenic resembles antimony, viz. the power which it possesses of combining in a similar manner with hydrogen. When arsenic compounds are exposed to the action of nascent hydrogen, they yield arseniuretted hydrogen (AsHj), thus — As,03 + 12H=3H,0+2AsH:3 ; and, as has been described in the section on antimony, this change is most conveniently effected by adding to the flask in which hydrogen is being rapidly generated the solution of the arsenical 212 CHEMICAL EEACTIONS. compound. The gas cannot be dried by passing tbrougb oil of vitriol, which decomposes it at ordinary temperatures ; but if re- quired dry, it may be passed through a tube containing fragments of porous chloride of calcium. The test for arsenic by means of the formation of arseniuretted hydrogen is called Marsh's test, from its inventor. The student should observe the foUowing properties of arseniuretted hydrogen, comparing them carefully with those of antimoniuretted hydrogen (see p. 200) : — a. The gas (which is colourless, has a specific gravity of 2-695, and at 40° C. condenses to a liquid, but has not yet been solidi- fied) possesses a most peculiar odour, resembling that of garlic : it is excessively poisonous if inhaled, and has often been fatal to human life through incautiously breathing it. If the gas be kindled at a fine jet, it bums with a pale bluish white flame, giving rise to the formation of water and arsenious oxide ; the latter may be seen as a white fume ascending in the current of heated air. (3. If a cold porcelain surface be depressed into the flame at the jet, a black lustrous spot of metallic arsenic will be produced, which is more readily volatilized by further heating than the corresponding antimony spot. It is caused by the cooliag down of the burning gas below the temperature at which arsenic enters into combination with oxygen. y. If the jet be replaced by a tube similar to that represented in fig. 11, and the gas, as it passes through, be strongly heated i an inch or so from the shoulder of the tube, the flame being urged by the blowpipe, there appears after some little time a metallic mirror at that part where the tube has been narrowed in order to confine the reduced arsenic to the smallest possible space, and so to render the least trace obvious. This mirror is more volatile than that of antimony, and may be driven about the tube by the application of heat with the greatest ease : it is produced by a simple decomposition of the gas into its con- stituents. g. The results hitherto given as peculiar to or indicative of arsenic are, it will be remembered, the precise counterpart of those SALTS or AESENIC. 213 yielded by antimoniuretted hydrogen ; and since we have already given the means of distiaguishing the antimony mirror and spots with certainty, we now proceed to state the methods of infallibly recognizing arsenic. 1. If an arsenic spot be dissolved in concentrated nitric acid, the acid perfectly driven off at the temperature of 100° C, and the residual white film moistened with nitrate of silver solution, its colour will change to yellow or red, according to the degree of oxidation which the arsenic has undergone : if it has been con- verted into arsenious acid, the colour wUl be yellow; if into arsenic, red. 2. An arsenic spot is immediately dissolved when moistened with a solution of hypochlorite of sodium (NaClO). 3. An arsenic spot remains undissolved when moistened with a solution of sulphide of ammonium containing excess of sulphur (antimony dissolves at once). To distinguish the arsenic mirror, the tube containing it is attached to an apparatus from which dry hydrosulphuric acid is being liberated ; and the mirror, being warmed by a spirit lamp, is speedily converted into the lemon-yellow tersulphide. If the tube be now removed to another apparatus from which dry hydrochloric acid gas is being transmitted, and the gas be passed through it at the ordinary temperature, no change occurs. If the student will now refer to the behaviour of the antimony mirror under the same treatment (p. 202), he wOl see how marked is the difference. But there is yet another means of discriminating between arsenic and antimony ; it is the test of Fresenius and Babo. An apparatus is taken similar to fig. 1 (p. 15), the tube (C) removed with its india-rubber connexion, and to the bent tube re- maining is attached a tube drawn out as in the annexed figure : — Fig. 11. A At A the heap of powder ; at B the mirror ; C is an opening at the extreme point. 214 CHEMICAL EEACTIONS. In the generating-flask some fragments of limestone or marble, together with some water, are placed, and in the washing-bottle a little concentrated sulphuric acid. Hydrochloric acid is then poured down the funnel-tube of the generating flask ; and the car- bonic acid gas evolved is thoroughly dried by its passage through the oU of vitriol. The best arsenic combination to be acted upon in the present arrangement of apparatus is the arsenious (or ter-) sulphide (As^ S3), a salt easily produced. The sulphide is dried at a temperature not exceeding that of boiling water, and mixed with about 12 times its bulk of a dry mixture (previously made) consisting of 3 parts of carbonate of sodium and 1 part of cyanide of potassium ; the powder is now carefully introduced into the tube at A by means of a paper gutter, and the whole apparatus left for a few minutes, in order that it may become entirely filled with carbonic acid gas. The arsenic tube is now very gently heated throughout its whole length, in order that every trace of moisture may be carried along and swept out of the apparatus by the advancing current of carbonic acid gas (carbonic anhydride), which should after- wards be allowed to pass at the rate of one bubble only per second. The part of the tube between B and A is now heated to redness with a spirit lamp, and the mixture itself also heated in the same manner with a lamp urged by the blowpipe. The arsenic, reduced by this means, condenses in the form of a mirror in the capOlary tube at B ; and it is said that a distinct mirror may be produced even when the quantity of arsenious sulphide ope- rated upon does not amount to more than -j-J^th of a grain. N antimony compound whatever yields a mirror under the same cir- cumstances. By the action of metallic plates, aqueous solutions of arsenious oxide are but slowly reduced, whUe hydrocliloric acid solutions deposit their metal more rapidly ; zinc, cadmium, and tin reduce more quickly than copper, lead, bismuth, or antimony. Iron does not reduce the metal. These actions are not so complete with arsenic acid. The combinations which arsenic in its basic capacity forms AKSENIOUS SALTS. 215 with salt-radicals are few ia number, and can scarcely be termed salts, using that word in its ordinary restricted signification: these combinations of arsenic are, as we have stated before, of two series, the first being the series of arsenious combinations, or AESBNIOUS SALIS, OE TEE-SALIS OF AESENIC. Solution for the reactions: — arsenious oxide (As^Oj) in hydros chloric acid. In those salts the combining equivalent of arsenic is supposed to be triatomic, resembhng in this respect the analogous anti- monious salts. They do not, however, resemble the latter bodies either in forming those peculiar compounds with certain organic acids into which the antimony enters as a basic radical (SbO), nor in suffering the same decompositions by the action of water which antimonious salts experience. The CHLOErDE is decomposed by the action of water, yielding arsenious oxide and hydrochloric acid. The Iodide is soluble in a considerable quantity of cold water. The Cyanide and the Cheomate do not appear to exist. The Oxide is obtained in commercial operations as a bye- product by heating the ores of metals contaioing arsenic in a current of air (roasting) : in these processes the arsenic is oxi- dized and volatilized as the oxide (As^ O3), which may then be collected and condensed in suitable chambers. This substance occurs in two well-defined varieties, — the vitreous and the cry- stalline. The first or glassy variety is produced when the oxide is fased under pressure, or sublimed and very slowly cooled ; it is quite transparent, and breaks with a conchoidal fracture : the second variety is obtained by subliming the former modification and rapidly cooling the vapour, or by simply keeping the first variety for some time ; it crystaUizes in the regular system, either as octahedra or tetrahedra. On account of its powerful tendency to yield salts ia which the arsenic is supposed to form part of a compound acid-radical, the oxide cannot be preci- pitated from arsenious salts by the addition of excess of the 216 CHEMICAL EEACTIONS. hydrates of potassium or ammonium, tte following reaction taking place, — ■ 2ASCI3 + lOKHO = 6KCH- K, As,0, + 5H, 0. arsenite of potassium. It is recognized as a compound acid-radical by the varied colours of the precipitates which its soluble combinations produce with different metallic salts : these are formed very readily by adding a solution of the desired metallic salt to a neutral solution of an alkaline arsenite, such as that of potassium (K^As^O.) or of ammonium ([NII^]^ As^ O5). The arsenite of copper (Cu^As^Oj) is called Scheele's green, and the arsenite of silver (Ag^ As^Oj) is yellow ; and these salts are perhaps the most remarkable arsenites. The composition of the arsenious oxide, or arsenious anhydride, is As^Oj : it does not appear to form any compound with water, i.e. no hydrogen salt of the acid-radical Aa^O^; many of its salts, with other basic radicals, are considered bibasic, and the formula M^ASjOj has been assigned to them. Arsenious oxide is very soluble in the hydrates and car- bonates of potassium and ammonium ; in water it does not dis- solve to any very great extent ; its physical condition also in- fluences its solubility. Thus 1 part of the opaque and crystalline variety dissolves in 7-72 parts of boiling water, whilst 1 pait of the vitreous oxide requires 9'33 parts for solution : as the tem- perature decreases, the greater portion of the substance is de- posited ; for 80 parts of cold water are requisite to hold 1 part of the opaque oxide in solution, and 103 of cold water axe required to dissolve 1 part of the vitreous variety. This substance is slightly soluble in alcohol. The presence of acids generally in- creases its solubility. Many arsenites dissolve in ammonium salts. No OxTCHioKinE exists. The Sulphide is produced by the action of hydrosulphuric acid gas on neutral or acid solutions of arsenious salts (e.c/. AsCl ), or acidified solutions of arsenites: it is a precipitate of a very fine orange colour, which occurs native as Orpiment. AESENIOUS SAMS. 217 Its formula is As^S^. It is very soluble in the hydrates, sulphides, and carbonates of potassium and ammonium. When dissolved in alkaline hy- drates or carbonates, it yields a mixture of arsenite and sulph- arsenite, perhaps thus— 2As, S3 + 5K,C03=K, As,,0, +K, As, S, -|-K, 8+600,. arsenite. sulpharsenite. When the sulphide is washed with cold water, a smaU quantity dissolves ; but it is decomposed to a very slight extent even by boihng water, a trace only of arsenious acid passing into solution at the same time that a minute quantity of sulphuretted hy- drogen escapes : this decomposition is shown more conspicuously if the sulphide be boiled with dilute sulphuric or hydrochloric acid, — boiling concentrated hydrochloric acid acting upon it with difficulty. This substance partakes to a great extent of the features of the oxide just described, particularly in giving rise to a series of well-defined sulphur salts, known as the sulpharsenites : they belong to three distinct series, aU produced from arsenious sulphide (As, S3), which we may here caU the sulpharsenious anhydride. Thus we have these formulae for the potassium salts of the three series — K^As^S^, KjAsSg, and EA.SS2 : the first series may perhaps be formed by the union of the second and third. Some further observations vnll be offered on this subject when treating of the acid-radicals containing arsenic. The Sitlphate, the Cabbonate, and the Oxalate do not exist. The Peeeootantde is said to be produced by the action of ferrocyanide of potassium upon a solution of arsenious oxide (AS2O3) in dilute hydrochloric acid. Its composition is unknovsm. It is decomposed by boihng nitric acid, but is iasoluble in water. The Febkictanibe and the Phosphate do not appear to exist. The other special reagents of the present and three preceding 218 CHEMICAL EEACTIONS. groups are not known to exert any characteristic or definite action upon arsenious combinations. The formation of the oxide and the sulphide, together with the characteristic properties of certain " arsenites," are the chief means employed for the recognition of arsenic in arsenious compounds. AESENIO COMBINATIONS, OB PENIA-SALTS OF AESENTC. Solution for the reactions : — arsenic oxide (As^Oj) in water. These compounds are closely allied to the penta-salts of anti- mony, hut partake more strongly of the acid character, and are, it would seem, confined to the forms of arsenic oxide (ASjOj), and arsenic sulphide (As^Sj), both of which may be considered anhydrous acids or anhydrides, and give rise to the salts termed " arseniates" and " sulpharseniates." The Oxide (As^Oj) is prepared by acting on arsenious oxide (As^Oj) with nitric acid : it probably unites with the elements of water to produce arsenic acid (HjAsO^), which, since it easily yields up water on the application of heat, cannot be isolated. Arsenic acid forms, however, an extensive class of salts, the general formida for which is M^AsO^; these contain water of crystallization, and are isomorphous with the tribasic phosphates. The arseniates are frequently of veiy characteristic colours ; the copper salt (Cu^HAsO^) is greenish blue, while the silver salt (Agj AsO^) is brownish red. The Sulphide is produced by the passage of hydrosulphuiic acid through acid solutions of arseniates : it is a lemon-yeUow precipitate. Its formula is As^ Sj. Athough quite insoluble in boiling water, it is very soluble in the hydrates, carbonates, and sulphides of potassium or ammo- nium, especially on the application of heat. "^Tien it dissolves in a soluble carbonate or hydrate, the solution contains a mix- ture of arseniate and sulpharseniate of the basic element intro- duced in the hydrate or carbonate employed. The following SALTS OF PLATINUM. 219 equation represents the action, assuming, for the sake of simpli- city, the presence of oxide of potassium (K^O) and the formation of arsenic salts with 3 equivalents of basic radical : — 4As, Sj + 12K, = 3K3 AsO, + 5K3 AsS,. arseniate. sulpharseniate. This substance, like sulpharsenious anhydride, yields three series of salts, which are termed sulpharseniates, and to which the formulae given below have been assigned : we take the po- tassium salts of the three series — K^ As^ S^, K, AsS^, and KAsS^ ; the first series may perhaps be formed by the union of the second with the third, for K3 AsS,-f KAsS3=K, As,S,. The other reagents of the present and three preceding sub- divisions do not appear to yield any characteristic reactions with a solution of arsenic acid ; and, in fact, the other salts of the present series are not known to exist. The chief means employed for the recognition of arsenic in the arsenic combinations are the precipitation and behaviour of the sulphide, and the formation of the coloured arseniates of copper and silver. SALTS OF PLATmUM. The metal platinum presents many features in common with palladium ; it also resembles in some respects the metal tin. Platinum forms two series of combinations with salt-radicals : — the platinous salts, of which the chloride (PtCl) and the oxide (PtjO) are types; and the platinic salts, which maybe repre- sented by the chloride (PtClj) and the oxide (Pt^O^). As in the case of palladium, the platinous salts must be regarded as the normal saline combinations of platinum, since the platinic com- pounds have a great tendency to yield bodies in which the plati- num constitutes part of the acid-radical contained in them. Like paUadic salts, platinic salts pass very readily into the lowe series of combinations. When heated before the blowpipe, either in the oxidizing or reducing flame, all platinum compoimds are reduced to the metallic state with the greatest ease ; but, owing to the infusi- l2 220 CHEMICAL EEACTIOirS. bility of the metal, no globule, but only a black or grey powder is obtained ; they impart no colour to the blowpipe flame, nor does the expeiiment with nitrate of cobalt yield any charac- teristic result. Fused with borax, platinum salts are merely reduced to the metallic state. Platinic chloride (PtClj) readily combines with chloride of potassium to form a salt in which the platinum is supposed to form part of the salt-radical, and which is known as chloro- platinate of potassium (KPtClg) ; the platinic iodide, bromide, oxide, and sulphocyanide behave in a precisely similar manner, and yield perfectly analogous products. The formation of the chloroplatinates of potassium and ammonium forms one of the best means of recognizing platinum ; they may always be pro- duced by bringing the platinum into the higher stage of com- bination as a platinic salt, and then adding hydrochloric acid and chloride of potassium (or ammonium), when the precipitate KPtClj (or ISTHj PtClg) forms, either immediately, or upon agita- tion or addition of alcohol to the liquid. Another test must be mentioned here as an important means of recognizing platinic salts : it is the action of stannous chlo- ride, which when added to a platinic salt produces at first a reddish brown tint, and subsequently a gelatinous precipitate of the same colour ; if the platinic solution be dilute, the colour of the Hquid and precipitate is yellow. These precipitates are soluble in hydrochloric acid, giving brown solutions. Platinic salts are reduced most quickly by iron, cobalt, zinc, cadmium, and copper, the platinum separating as a black powder, which aggregates into laminse. Tin effects the reduction quickly, but forms a compound with the platinum. Nickel, lead, silver, bismuth, antimony, and arsenic act more slowly. PLATINOUS SALTS, OR PKOTO-SALTS OP PLATINUM. Solution for the reactions : — platinous chloride (PtCl) in dilute hydro- chloric acid. The principal insoluble salts of this series are the cliloride, iodide, cyanide, hydrate, sulphide, and carbonate. The Chloride is obtained by heating platinic chloride, with constant PLATIHOUS SALTS. 221 stirring for some time, at the temperatm-e of melting tin (228° C). By the simple evaporation of the aqueous solution of platinic chloride at 100° C, this body is also to a certain extent produced. It is a greenish grey, or oc- casionally a brown powder. Its formula is PtCl. It is insoluble in water, but soluble in hydrochloric acid, and in a solution of platinic chloride. It does not dissolve in nitric or sulphuric acid. The Iodide is produced by the action of iodide of potassium on platinous chloride in the presence of water, the substances being heated together. It is said to be obtained also when iodide of potassium acts upon solutions of platinous salts, which in these cases remain at first colourless, then become deep brown, and after some time deposit the iodide as a heavy rich black precipitate, leaving the supernatant Uquid colourless. Its formula is PtI. It is acted upon by a hot solution of iodide of potassium, which forms iodoplatinate of potassium (KPtlj) and leaves metallic platinum. The same change is slowly effected by hydriodio acid in the cold, with formation of iodoplatinic acid (HPtl.,). It is insoluble in water or alcohol, and even in concentrated nitric, sulphuric, or hydrochloric acid. The Cyanide is produced by the action of cyanide of potassium on certain platinous salts, and by several other methods. It is a precipitate of a yel- lowish white colour. Its formula is PtCy. Its solubility in some menstrua varies with the method of its preparation ; it is, however, always soluble in excess of cyanide of potassium, and, it would seem, also in hydrate of ammo- nium. It is insoluble iu water and acids. The Chromate does not appear to exist. TuE Hydrate is produced by the addition of warm hydrate of potassium, not in excess, to solutions of platinous salts, if not too dilute. It is a bulky black precipitate. Its formula is probably PtHO ; but if precipitated by hydrate of sodium, the precipitate contains sodiimi. It is readily soluble in excess of its precipitants, forming green solutions, from wliich it may be reprecipitated by the addition of sulphuric acid, but which, if boiled, yield precipitates of metallic platinum. Boiling hydrochloric acid gives rise to the formation of chloroplatinic acid and metallic platinum. The Sulphide is produced by the action of hydrosulphuric acid or soluble sulphides on solutions of platinous salts : it is a brownish black pre- cipitate. Its formula is Ptj S. It dissolves in large excess of sulphide of ammonium, forming a brownish red solution. It is not altered by boiling hydrate of potassium ; the concentrated acids (nitrohydrochloric included) scarcely attack it even at the boiling temperature ; but fuming nitric acid dissolves it after long ebullition, yielding The Sulphate, a very soluble salt. The Carbonate is precipitated slowly when carbonate of potassium acts upon solutions of platinovis salts ; carbonate of ammonium cannot be sub- stituted for the potassium salt. It is a reddish brown precipitate, the formula of which is unknown. The Oxalate, the Fekkocyanide, the Fbrricyaxide, and the Phos- 222 CHEMICAL EEACTIONS. PHATE are not produced by their respective reagents, and if existing at all are soluble. The other special reagents of the present and three preceding subdiyisions are not known to give any characteristic reactions with platinous salts. The chief means employed for the recognition of this series of salts is the behaTiour of the chloride, and also the precipitation of the iodide and the sulphide. plathtic saxts, ok bi-salts op platintjii. Solution for the reactions : — platinic chloride (PtClJ in water. The principal insoluble salts of this series are the iodide, the cyanide, the ohromate, the hydrate, and the sulphide. The Chlokide (PtCl^) is soluble. The Iodide is produced by the action of iodide of potassium on solutions of platinic salts, and separates after standing, or more readily upon -warming the mixed solutions : it is a precipitate of a brown colour. Its formula is Ptl^. It dissolves in alcohol with partial decomposition, giving a yellowish green solution ; it is not decomposed by concentrated sulphuric acid in the cold. It dissolves readily in hydriodio acid. The Ctanldb is scarcely known, but appears to be soluble in cyanide of potassium, insoluble in acids. The Cheomate is produced by the action of chromate of potas- sium on solutions of platinic salts : it is a deep red precipitate, the formula of which has not been ascertained. The Hydrate is produced in a pure condition only when the hydrates of potassium or sodium, not in excess, are added to a solution of platinic nitrate ; these preoipitants throw down from most other platinic salts, potassium or sodium salts of one or other of the platinic acids. It is also produced by the action of the carbonates of the second subdivision. It is a black pre- cipitate. Its formula is PtH.O.^. This salt is soluble in excess of its precipitants, and from SALTS OF EHODIUM. 223 ttese solutions it is reprecipitated on the addition of acetic acid. It dissolves in the stronger acids. The Sulphide is produced hy the action of hydrosulphuric acid gas or soluble sulphides on neutral or acid solutions of all pla- tinic salts ; if the platinic solution be alkaline, partial precipi- tation only ooouxs. The chloroplatinates also yield platinic sul- phide. It is a precipitate of a bro'WTiish black colour. Its formula is Pt^ S^. It is soluble in large excess of alkaline sulphides, especially if they contain ter- or penta-snlphides ; it is iusoluble in hydro- chloric or nitric acid, but dissolves in nitro-hydrochloric. The Cahbonate does not appear to exist. The Oxalate exists, but is soluble. The Sulphate, the J^'ereoctaitide, the Feeeicyauide, and THE Phosphate do not appear to exist. The other special reagents of the present and three preceding subdivisions give no characteristic reactions -with platinic salts. The formation of the insoluble chloroplatinates of potassium and ammonium, as described on p. 220, constitutes the best test for the presence of the bi-salts of platinum. SALTS OF EHODICM. The metal rhodium is found associated with platinum in certain ores of the latter metal. It forms two series of combinations with salt-radicals, only one of which corresponds with a series of the platinum compounds, that is, the series of rhodious salts, of which the oxide is R^ 0, and the chloride KCl ; the other series, the rhodic salts, is represented by the oxide ([R2]2*-'3) ^^^ the chloride (R2CI3). Salts of rhodium are reduced to the metallic state when heated before the blowpipe in either flame, although, as the temperature is lowered, the finely- divided metal reoombines with oxygen. They impart no colour to the flame, nor do they give any reaction with solution of nitrate of cobalt ; with borax they are reduced. Most salts of rhodium have a pink or red colour. Besides the two series of salts mentioned above, there is another series of more oompKcated character, derived from the rhodic salts. Of this series the salt KjKjClj-f-aq may be taken as a representative: this salt, how- ever, as also that of ammonium ([NH^j^R^Clj-l-aq) is comparatively soluble in wat«r ; and therefore the addition of chloride of potassium or ammonium to rhodic chloride, although giving rise to the formation of these salts — the chlororhodiates of potassium or ammonium — does not constitute 224 CHEMICAL EEACTIONS. SO good a test for the presence of this metal as of platinum. The chloro- rhodiates are insoluble in alcohol. A salt of the formula K3 RjCl^+Baq also exists. The addition of a solution of staimous chloride to concentrated solutions of rhodic salts produces a brownish yellow precipitate, with more dilute solutions a yellow precipitate, and with eren the most dilute a yellow colouration. Rhodic salts are reduced to the metalho state by iron, zinc, copper, and mercury, but not by silver. EHODIOUS SALTS, OE PEOTO-SALTS OF EHODIUM. These salts are but little known ; all those which have been examined, or nearly all, are insoluble in water and acids, and are generally produced by decomposing rhodic salts. The Chloride, Oxide, Sulphide, and Sulphate are insoluble salts. EHODIC SALTS. These salts, although not corresponding in constitution with platinic salts, resemble them in one remarkable feature, viz. the power which the chloride and oxide possess of uniting with more chlorine or oxygen, and then, as a compound acid-radical, of assuming a basic constituent. The chief insoluble salts of this series are the iodide, the hydrate, and the sulphide. The Chloeide is soluble. The Iodide is produced by the addition of iodide of potassium, which darkens the solution, and produces, after a time, a slight yeUow precipitate. The Cyanide and Cheomate are not produced by the appropriate reagents. The Hydrate is produced by the action of hydrate of potassium on solu- tions of rhodic salts ; more slowly by carbonate of potassium. It is a yellow precipitate. Hydrate of calcium produces a reddish brown precipitate. Its formula is said to be EjHjOj-l-aq. It is soluble in excess of hydrate of potassium, and dissolves slowly in acids. The hydrate or carbonate of ammonium produces, after some time, in solutions of rhodic salts, a lemon-yellow precipitate of rhodiate of ammo- nium, which is soluble in hydrochloric acid. The Sulphide is produced by the passage of hydrosulphuric acid gas, or the addition of soluble sulphides to warm neutral or acid solutions of rhodic salts, or to solutions of those salts in which the metal exists as part of the aoid-radieal. It is a brown precipitate. Its formula is probably B. S . It is soluble in sulphide, and to some extent in hydrate of potassium, but it ia insoluble in excess of sulphide of ammonium ; it dissolves in hydrochloric or nitric acid. The Sulphate, the Caebonate, the Oxalate, the Feeeooyanide, the Peeeicyanide, and the Phosphate, are not produced by their several re- agents, or, if produced, are suluble. SALTS OF EuiirEH-nrM. 225 The other special reagents of the present and three preceding groups are not known to give any characteristic reactions with rhodic salts. The precipitation of the iodide, hydrate, and sulphide, and the reaction with stannous chloride, are the tests chiefly made use of for the detection of rhodic salts. SALTS OP KUTHBNIUM. This metal is found associated with platinum, and is obtained from that portion of the ore which is insoluble in nitro-hydrochloric acid. It unites to some extent the peculiarities of platinum and rhodium, since it forms three series of salts, of which the representative oxides and chlorides are respectively Ruj O and RuCl; (EUj)^03 and RU2CI3; Ku^O^ and EuCl,. The two latter series, like platinum and rhodiimi, yield other series of com- plicated constitution, in which the ruthenium is thought to constitute part of the acid-radical. In addition to these numerous compounds, this metal forms with oxygen another acid-radical, at present only known in the form of a potassium salt (KKuO^). The colours of ruthenium salts are very varied. Kuthenium has a greater tendency to combine with oxygen than any other of the metals resembUng platinum, with the exception of osmium ; conse- quently, when its salts are heated before the blowpipe, they are not reduced to the metallic state, the protoxide (Ru^ O) withstanding a white heat without parting with its oxygen. Kuthenium salts impart no colour to the flame, nor do they give any reactions with nitrate of cobalt or fused borax. This metal possessing two series of salts both capable of furnishing com- pound acid-radicals containing ruthenium, yields similar precipitates with solutions of the chlorides of potassium or ammonium as do the correspond- ing compounds of the two preceding metals. Thus, with ruthenium salts two classes of these combinations are formed : if the ruthenium be introduced as sesquichloride, the chlorides of potassium and ammonium produce in concentrated solutions dark brown crystalline precipitates (either IC, Eu^ CI3, or [NHJj Eu^ Clj), which are but slightly soluble in cold water, and insoluble in alcohol ; if, on the other hand, the bichloride of ruthenium be employed, the addition of a solution of chloride of potassium gives rise, particularly in the presence of alcohol, to the precipitation of a rose-coloured crystaUine salt (KEuClg). KUTHENIOUS SALTS. These salts are of trifling analytical importance ; the chloride is almost the only soluble salt known, while the oxide, which does not dissolve in acids, is almost the only well-defined insoluble salt which has been examined. SESQUI-SALTS OP KUTHENIUM. These are better defined, more numerous, and more stable than ruthenious salts : they are produced by dissolving the sesqui-oxide in acids ; the sesqui- oxide itself being obtained by heating the finely-divided metal before the blowpipe until it has acquired a bluish black colour. L 5 226 CHEMICAL EEACTIONS. The principal insoluble salts of this series are the hydrate and sulphide. The Ciilokide is soluble. The Cyanide * and the Cheomate do not appear to have been examined. The Hydrate is produced by the action of the hydrates or carbonates of potaasimn or sodium on sesqui-chloride of ruthenium ; it is also produced by a solution of phosphate of sodium, and even by one of borax, on heating. It is a blackish brown precipitate. Its formula is Eu^ H3 O3. It is insoluble in excess of hydrate of potassium. The Slllphide is produced by the passage of hydrosulphurie acid through a solution of the sesquichloride, or by the addition of sulphide of ammo- nium. Hydrosulphurie acid gives a result which is characteristic of ruthe- nium : if the gas be passed until the liquid appears nearly black, and the latter be then filtered, the filtrate will be found to have changed from, orange- yellow to a magnificent blue colour ; this change is said to be due to the reduc- tion of the sesquichloride to the state of protochloride. The sulphide is black : its formula is probably (Eu2)2 S3 ; it appears, however, always to contain an admixture of sulphur. It is not perceptibly soluble in excess of sulphide of ammonium. The Sulphate and the Oaebonate are not known, while the Ox.u,ate is not precipitated by oxalic acid, which only decolourizes the solution of the sesquichloride. The Fbreocyanide does not appear to exist ; ferrocyanide of potassium at first decolourizes the solution, and finally turns it bluish green. The Feeeicyanide and the Phosphate do not appear to exist. The other special reagents of the present and three preceding subdivisions are not known to exert any characteristic actions upon the sesqui-salts of ruthenium. KUTHENIC salts, OK BI-SALTS OF EUTHENIU.M. These salts are nearly as numerous and definite as the sesqui-salts of ru- thenium. The chief salt from which they are obtained is the sulphate (BUj [SOj]^), which is soluble in water, and is itself produced by digesting the sesqui-sulphide ([Eu^JaSj) iu nitric acid. The chief insoluble ruthenic salt is the hydrate. The Chloride is not known, except in combination with chloride of potassium, &c. The Cyanide and the Cheomate do not appear to have been obtained. The Hydrate is produced by evaporating a solution of the sulphate to dryness in the presence of hydrate of potassium or carbonate of sodium. It is a yellowish brown gelatinous precipitate: its formula is thought to be RuHj Oj ; it generally, however, retains a portion of its precipitant. It is soluble in acids, yielding solutions which are rose-coloui-ed when concen- trated, and yellow when dilute. * Mercuric cyanide colours a solution of sesquichloride of ruthenium blue, and produces a blue precipitate. lEIDIOUS SALTiJ. 227 A Sulphide of a yellowish brown colour is produced when hydrosulphuric acid is passed through the aqueous solution of the salt KBuClj ; but the liquid, unUke the solution of the sesquiohloride, remains rose-coloured. The Sulphate is soluble. The Carbonate, Oxalate, Pereooyanide, Pekeicyanide, and Phosphate do not appear to have been examined. The action of the other reagents upon solutions of ruthenic salts has not been ascertained. SALTS OF lEIDIUM. This metal also occurs associated with platinum, and is obtained from that portion of the ore which is insoluble ; it is also found, combined with osmium, in separate grains, occurring in the platinum ore. In many respects it re- sembles ruthenium, and forms a corresponding number of combinations with salt-radicals, viz. iridious salts, represented by the oxide Ir^ O, and the chlo- ride IrCl; sesqui-salts, represented by the oxide [Ir2]2 03, and the chloride Ir^ CI3 ; iridic salts, represented by the oxide Ir^ O,, and the chloride IrClj ; and even a fourth series, represented by one or two members only, the com- position of which does not, however, appear to have been accurately deter- mined hitherto. Salts of iridium, when exposed to a strong heat, are reduced to the metaUic state ; the metal, however, when exposed to a less elevated temperature, oxidizes. Its salts impart no colour to the blowpipe flame, are not affected by the nitrate of cobalt test, and yield no characteristic result by fusion with borax. The sesqui- and bi-salts of iridium present the same tendency which the corresponding platinum, rhodium, or ruthenium compounds exhibit, to yield salts containing an acid-radical of which the rare metal forms a constituent. Tlius, the addition of the chlorides of potassium or ammonium to sesqui- ohloride of iridium, causes the precipitation of salts, the composition of which, disregarding the water of crystallization in all cases, is K3 Ir^ Clg, or [NH,]3lr.,Clj, while the same reagents, if added to a solution of iridic chloride (IrCl^), produce the salts KlrCl^, orNH4lrCl3. These salts are comparatively soluble in water, but insoluble in alcohol. The colour of the former class of salts is olive-green ; of the latter, a very dark red, approaching to black. Iron, zinc, tin, and most other metals (excepting gold and platinum), par- tially precipitate iridium as a black powder. IRIDIOUS SALTS, OK PROTO-SALTS OF IRIDIUJl. The salts of this series are better defined than ruthenious salts. The chloride (IrCl) appears to be insoluble in water, but soluble in hydrochloric acid, while with alkaline chlorides it unites to form the salts K IrCl^, &c. The hydrate, the oxide, and the sulphide appear to be well-defined in- soluble salts. The Cyanide and the Chromate do not appear to exist. 2'28 CHEMICAL EBACIIONS. The Hydrate is produced by acting with the carbonates of potasBium or sodium upon solutions of the salts KlrClj or NalrClj : it is a greenish grey precipitate. Its formula is probably IrHO. It dissolves in excess of its precipitanta, yielding greenish yellow solutions ; it also dissolves in acids, with a green colour. The Oxide is produced by boiling the insoluble iridious chloride (IrCl) in solutions of hydrate of potassium : it is a black powder. Its formula is Ir^ 0. It dissolves slightly in excess of hydrate of potassium ; and the solu- tion, if exposed to the air, passes through a purple to a dark blue colour. It is but slightly soluble in boiHng acids. The Sulphide is produced by the action of sulphuretted hydrogen on iridious salts: when so prepared it is of a brownish-yellow colour. Its formula is Ir^ S. It is more soluble in sulphide of potassium than is the corresponding platinous salt : it is sHghtly soluble in pure water, imparting to it a reddish brown colour ; but this solubiUty is prevented by previously washing the sulphide with acidulated water, or a solution of chloride of ammonium. Nitric acid converts it into iridious sulphate. The Sulphate is soluble. The Carbonate, Oxalate, Feerocyanide, Fereicyanide, and Phosphate do not appear to have been examined. The other reagents of the present and three preceding groups are not known to exert any characteristic action upon solutions of iridious salts. SESQUI-SALTS OF lEIDIUM. These salts appear to be about as numerous as the preceding ; the chloride and sulphate are soluble, while the hydrate and sulphide are insoluble. The Hydrate is produced by the action of hydrate of potassium upon the sesquichloride : it is a bulky dark brown precipitate. This decomposi- tion does not, however, invariably occur, even when the mixture is heated ; but after a long time the liquid absorbs oxygen, becomes blue, and deposits iridic -hydrate, IrH^ 0.^. The brown sesquihydrate always contains potas- sium. It dissolves in acids, forming brown or dingy purple solutions. The Sulphide is produced by precipitating a sesqui-salt of iridium by hydrosulphuric acid gas : it is a brownish-black precipitate. Its formula is (Irj)2S3. It is somewhat soluble in solution of sulphide of potassium; in water also it dissolves slightly, colouring it yellow. Nitric acid converts it into the sesquisulphate. The Sulphate is soluble. The action of the other reagents of the present and three preceding groups upon sesqui-salts of iridium has not been ascertained. IRIDIC salts, oe bi-salts of iridium. These salts are more easy of formation than those of the preceding series, inasmuch as they may be easily produced from any of the iridium salts of the two kinds previously described, by merely boiling their solutions in PEE-IRIBIC SALTS. 229 vessels exposed to the air, or still more readily by the action of nitric acid. The anhydrous ii-idio salts are generally black, or red if powdered ; their solutions in water, red or dark brown when concentrated, and reddish yellow when dilute. The pi'inoipal insoluble iridic salts are the iodide, the hydrate, and the sulphide. Tub Chloride is soluble. The Iodide is produced by boiling iridic chloride with hydrochloric acid and iodide of potassium in solution : it is a black powder. Its formula is Irlj. It is insoluble in water and in acids. The Cyanide and tub Cheomatb are iminown. The Hydrate is produced by the action of hydrate of potassium not only upon solutions of iridic salts with the aid of heat, but also upon any of the chlorides of iridium at the boiling temperature : it is a bulky precipitate of an indigo colom-. Its formula is IrH^ O^ ; but it always retains a portion of its precipitant. It is almost insoluble in dilute nitric or sulphuric acid ; but it slowly dissolves in hydrochloric acid, the solution being at first blue, then green, and lastly of a reddish brown tint. Hydrate of ammonium produces a brown precipitate in solutions of iridic salts, but fails to precipitate the whole of the metal. The Sulphide is produced by the action of hydrosulphuric acid gas upon solutions of iridic salts, which at first are decolourized ; or by addition of sulphide of ammonium, not in excess, to solutions of iridic salts, or of salts in which the iridium forms part of the acid-radical : it is a brown precipitate. Its formula is Ir.^ S^. It is readily solable in excess of sulphide of ammo- nium ; it dissolves in sulphide of potassium also, and to a slight extent in water : by the action of nitric acid it is converted into iridic sulphate. The Sulphate is soluble. Tub Carbonate is said to be produced by the action of carbonate of potas- sium, not by carbonate of sodium, and is described as a reddish brown pre- cipitate which gradually redissolves, leaving traces only of a brownish black powder. The Oxalate does not appear to exist ; oxalic acid decolovu-izes solutions of iridic salts. The Feeeocyanide does not appear to exist; ferrooyanide of potassium only decolourizes solutions of iridic salts. The Feekicyanide and Phosphate do not seem to have been examined. The other special reagents of the present and three preceding subdivisions are not known to yield any characteristic reactions with solutions of iridic salts. The hydrate and sulphide are the most characteristic iridic salts ; and by their formation the metal in this form of combination may be recognized. PBR-IRIDIC SALTS, OR TEE-SALTS OP IRIDICM. Two only of these compounds are known, — the per-iridic chloride (IrClg) and the oxide (Ir^ O3). The chloride is soluble in water, giving a red solu- 230 CHEMICAL HEACIIONS. tion, while the oxide is a greenish-yellow precipitate, obtained by acting upoi. the salt Kg IrCl^ (3KC1, IrClj) with hydrate of potassium, — the salt Kg IrClj being formed by the union of chloride of potassium with per-iridic chloride. Per-iridic oxide is insoluble in water, and gives rise, under certain circum- stances, to the salts termed iridiates (MIrOj). SALTS OF OSMIUM. The metal osmium occurs alloyed with iridium, as already stated, in distinct grains, with platinum ores. In many of its chemical properties it is thought to resemble the arsenic, phosphorus, and nitrogen group of acid- radicals. It differs in many respects from the four preceding metals, and in no feature more remarkably than in the complete volatility of many of its compounds. Osmium forms no less than six compounds with oxygen, five of which exist in the isolated state. With other salt-radicals, such as sulphur, the combinations of this metal are not so numerous ; five compounds with sulphur are known, and but four with chlorine. The first three aeries only appear to partake decidedly of what has been termed the normal saline cha- racter. The oxides and chlorides of these three series are the following : — Osj O and OsCl ; (Os^)^ O3 and Os^ CI3 ; Os^ O^ and OsCLj. There are then three series which appear to possess in a marked degree the acid character ; two of these are represented by the following formulae — OSjOg and OsClj, OsjOj, while the third oxide, although termed osmic acid, or osmic anhydride, is scarcely known in combination with a basic radical, but generally appears as Osj 0,j. The colour of osmium salts is usually greenish, yellowish, brown, or black. When heated in the air, osmium compounds oxidize to osmic anhydride (OSjOj), which is a volatile compound having a pungent odour somewhat resembling that of chlorine or bromine. This conversion into a volatile com- pound precludes the application of the ordinary blowpipe test. Certain osmium salts present the usual characteristics of the allied rare metals, and yield, like them, salts in which the osmium forms part of the acid-radical. The best-defined of these salts is KCl,0sCl2, or rather KOsClj, which crystallizes in regular octahedra of a dark brown colour, which dissolve in cold water, more readily in hot, and are reprecipitated on the addition of alcohol, in the form of a vermilion-coloured crystalline powder. Osmium is precipitated from acid solutions of osmic anhydride (Os^ O^) by iron, zinc, cadmium, and tin, as a blue or reddish black powder, partiy sus- pended in the liquid, and giving it a blue or violet tint. On antimony, bismuth, lead, copper, mercury, and silver, osmium is deposited as a crust, without any blue colour. It is also reduced by ferrous sulphate, but not by stannous chloride. OSMIOUS SALTS. The Chloeidb (OsCl) is a green salt, soluble in water. The Hydrate is precipitated by the action of hydrate of potassium on a solution of the salt KOsClj, and probably also by alkaline carbonates acting QTJADEOXIDE OP OSMIUM. 231 upon osmioue salts. It is a greenish black precipitate, which dissolves slowly in acids, forming dull green solutions. The Sulphide is produced by hydrosulphuric acid gas acting upon solu- tions of osmious salts : it is a brownish yellow precipitate, slightly soluble in water, and which, by the action of nitric acid, yields The Sulphate, a soluble salt. The other osmious salts are either unknown or soluble in water. SESQUI-SALTS OF OSMIDM. The existence of these salts appears to be doubtful. OSMIC SALTS, OR BI-SALTS OF OSMIUM. The Chloride (OsClj) is very soluble in water, giving a reddish yellow solution, from which the other osmic salts may be prepared. The Hydrate is produced by the action of hydrate or carbonate of po- tassium on solutions of osmic chloride, osmic sulphate, or of the salt KOsCl^ : it is a black precipitate, wliich dissolves in excess of carbonate of potassium, forming a dark brown solution, from which it is reprecipitated by ebullition or on standing. It is insoluble in acids, excepting hydrochloric. The Sulphide (OSjSj) is precipitated by the action of hydrosulphuric acid gas on solutions of osmic salts : it is a dark yellowish brown precipitate, which is slightly soluble in hydrate of potassium and in water, at least when recently precipitated, and before drying. The Sulphate is soluble. The other osmic salts are either unknown or soluble in water. quadroxide of osmium. Osmic anhydride, or, as it is more commonly called, osmic acid, must be noticed here, as affording the principal means of recognizing osmium. The osm-iridium, or platinum to be tested for osmium, should be fused with three parts of nitre in a crucible, and the resulting dark red mass of osmiate of potassium just dissolved in water, the solution mixed with sulphuric acid which has been diluted with its own bulk of water, and then rapidly distilled. The body Os^ O^ (osmic anhydride) condenses as a white crystalline mass in the receiver, or fuses beneath the watery portion of the distillate if the temperature be but slightly raised. It boils and evaporates below 100° C, subliming at a slight elevation of temperature, and then condensing upon a cooler part of the receiver. Its taste resembles that of oil of cloves, and its odour that of chlorine or iodine. It is extremely poisonous and corrosive. It colours all organic substances black, from the reduction of osmium upon them. It is soluble in water. When an aqueous solution of this substance is mixed with excess of sul- phurous acid gas (sulphurous anhydride), a dark blue hquid is finally pro- duced, after the colour has passed through the stages of yellow, brown, and green. This blue compound is supposed to be an intermediate sulphate. CHEMICAL EEACTIONS. SALTS or GOLD. A considerable resemblance exists between gold and the im- mediately preceding metals; tbe compounds ■which it produces with salt-radicals are not, however, so numerous as those which the last five metals form. There are but two series of salts of gold, the aureus and auric salts ; of these the former series is represented by the oxide Au^O and the chloride AuCl, the latter by the bodies Au^Oj and AuClj. The latter series partakes to a great extent of the characteristics of the platinic, iridic, and similar compounds ; but, in addition to these combiaations, it seems probable that one member of a third series is known, per-auiic oxide, AujOj, which may be viewed as an anhydride. When gold salts are heated before the blowpipe, they are re- duced to the metallic state ; and by an intense heat, especially with the aid of a flux (borax), or carbonate of sodium, the metal may be fused into a malleable globule, the peculiar colour of which is easily recognizable. Gold salts impart no colour to the flame, nor do they yield any characteristic reaction with nitrate of cobalt. When fused with borax, they are reduced. Similarly to the metals recently considered, the second series of gold salts gives rise to compounds in which the gold is pre- sumed to form part of the compound acid-radical contained in them. Thus, auric chloride (AuClj) forms with chloride of po- tassium a salt KCl, AuCl,, or rather KAuCl^^ chloraurate of po- tassium, — while, if auric iodide be added to iodide of potassium, iodaurate of potassium (XAuIJ is formed. These salts, however, being very soluble in water, do not enable us to employ their formation as a means of recognizing gold. The reaction which auric chloride exhibits when treated with stannous chloride (SnCl), especially if the latter reagent contain a trace of stannic chloride (SnCl^), is the most valuable and characteristic indication of the presence of gold. The solution to be tested shoidd bo acidified with a few drops of nitric acid, or a few drops of a solution of ferric chloride (Ec , CI,) added to it, and then a small quantity of a solution of stannous chloride poured ATJEOtrS SALTS. 233 in : if gold be present, a reddish or purplish brown precipitate or cloud will be formed, marking the passage of the stannous solution as it mixes with the liquid under examination. It is better, in performing this experiment, to operate upon a considerable quantity of an extremely dilute gold solution (a di-op or two of auric chloride in a beaker of water). This precipitate is called "purple of CassitM" : when dry, and in fine powder, it has a dull blue tint. Its composition has been much discussed ; but the formula AuSn3 03+2aq seems a probable one. This compound may be prepared by placing an aqueous solution of auric chloride in contact with pure granidated tin. The purple of Cassius, when moist, is soluble in hydrate of ammonium, forming a solution of a mag-niflcent reddish piu-ple colour ; boiled in hydrate of potas- sium, however, or in water, it remains unchanged. BoiUng concentrated nitric or hydrochloric acids, or dilute sulphuric acid, act upon it but slowly, removing the tin. Most metals precipitate gold from its solutions in the metallic state, either as a biilliant metallic deposit, or in the form of a brown powder. Some metals yield a purple powder containing gold, oxygen, and the metal used as the precipitant. Phosphoms, sulphiu', and many reducing agents, separate metaUie gold from its solutions. One of the most characteristic tests for the presence of gold in a solution is the reduction of the metal effected by the addition of ferrous sulphate (Fe^SO^). If to a solution of gold containing 1 part of metal in 80,000 parts of water, a solution of ferrous sulphate be added, a bright blue tint is produced ; even if the mixture be diluted to 320,000 parts, a pale violet colour is apparent. AUROnS SALTS, OE PHOTO-SALTS OF GOLD. There appear to be no soluble salts of this series; the insoluble salts known are these, — the chloride, the iodide, the oxide, and the sulphide. The Chloride is obtained in variable quantity whenever auric chloride is evaporated to dryness. The latter salt is completely converted into this compound, with loss of chlorine, if it be heated for some time to the melting- point of tin (228° C), with continued stirring. It is a yellowish white 234 CHEMICAL EEACTIONS. powder. Its formula is AuCl. By water, especially on ebullition, it is resolved into auric chloride and metallic gold. The Iodide is produced by adding a solution of iodide of potassium, not in excess, to a neutral solution of auric chloride : it is a lemon-yeUow cry- stalline powder. Its formula is Aul. It is very soluble in excess of its precipitant. Water and acids are without action upon it in the cold ; but upon raising the temperature, they decompose it into iodine and gold. The Oxide is obtained by the action of boiling hydrate of potassium on a solution of auric chloride, or on the solid aureus chloride : it is a dark green powder. Its formula is Au^O. It is slightly soluble in hydrate of potas- sium ; hydrochloric acid converts it into auric chloride and metallic gold. The STllpMde is obtained by passing hydrosulphurio acid gas through a boiling solution of auric chloride : it is a brownish black powder. Its formula is Auj S. No other salts of this series are well known. ATJEIC SAITS, OE PEE-SALTS OF GOLD. Solution for the reactions : — auric chloride (AUCI3) in water. The principal insoluble auric salts are the iodide, the hy- drate, and the sulphide. The Chloeide (AuCl,) is soluble. The Iodide is produced when a solution of auric chloride is gradually added to a solution of iodide of potassium ; the liquid becomes green and deposits a green precipitate, which redis- solves on agitation. Its formula is Aulj ; but it is speedily resolved into aureus iodide and iodine. It is soluble in iodide of potassium solution. The Cyanide is produced by adding cyanide of potassium, not in excess, to a solution of auric chloride : it is a yellow precipi- tate. Or it may produced by adding an excess of cyanide of potassium, and then acidifying with hydrochloric acid. Its formula is probably AuCy,. It is insoluble, or nearly so, in dilute hydrochloric acid, but dissolves in excess of its precipitant, forming a salt to which the formula KAuCy, has been assigned, and which is much em- ployed ia electro-gilding. The Hydkate is produced by the action of hydrate of potas- AUEIC SALTS. 235 slum, not in exeess, and of the ordinary temperature, upon a solution of auric chloride. It is a reddish yeUow precipitate. Its formula is unkno'wn. It dissolves in excess of its precipitant, forming aurate of potassium, probably KAuO^. It is also soluble ia hydrochloric acid, and in. great excess of nitric or sulphuric acid. Carbonate or hydi-ate of ammonium added (not in excess) to a tolerably concentrated normal solution of auric chloride produces a reddish yellow precipitate of the so-called aurate of ammo- nium, or fulminating gold: it detonates most powerftdly after it has been carefully washed with hot water. Its constitution is obscure. The Sulphide is obtained by the action of hydrosulphuric acid gas upon auric chloride at the ordinary temperature, or by the action of sulphide of ammonium. It is a black precipitate. Its formula is Au^ S3. It dissolves in the sulphides of potassium and ammonium, and in hydrate of potassium, forming sulphaurates and aurates. From these solutions it is reprecipitated by acids in which it is insoluble. In nitro-hydrochloric acid, however, it dissolves. The Cabbonaie does not exist. The Oxalate does not exist. Oxalic acid acts upon solu- lutions of auric salts in a peculiar manner ; and this action con- stitutes one of the most characteristic tests for the presence of gold : when added to the gold solution (which should be pre- viously evaporated in the presence of hydrochloric acid to ensure the absence of nitric acid), and the mixture boiled, the metal separates in the form of an orange-brown powder, or in minute spangles ; for ^,jr^ 2AuCl3+3H,C,0,=2Au-F6HCl-l-6CO,. The Scxphate, the Febiioctanide, the FEEEicTANmE, and TEE Phosphate do not appear to exist. The other special reagents of the present and three preceding subdivisions give no characteristic reactions with auric salts. The presence of gold is usually recognized by the formation of the malleable yeUow globule, by the precipitation of the beau- 236 CHEMICAL BEACTIONS. tiful purple of Cassius, and by the reduction of the metal ef- fected by ferrous sulphate or oxalic acid. SALTS OF TUNGSTEN. To this and the remaining metals of the present subdivision, many of the remarks made on the characteristics of arsenic apply. These elements do not yield true normal salts, but, uniting with several equivalents of acid- radicals, produce bodies which present the features of acid anhydrides ; they are nevertheless noticed here, inasmuch as (Uke the analogous compounds of antimony and arsenic) they form certain insoluble combinationB, such as hydrates and sulphides, which may occur among the salts of the other metals. Tungsten forms three combinations with oxygen, two only of which are represented by combinations with other acid-radicals. These oxides are the binoxide (Wj O^) vrith the corresponding chloride (WClj), and the ter- oxide (WjOj) with the corresponding ter-chloride (WCI3) ; the remaining oxide is W,jOj, and seems to be formed by the union of the two former. Some of the salts of tungsten are volatile ; but those which are not, when heated before the blowpipe, are usually converted into tungstio oxide, which is yellow when cold, but becomes darker on heating ; in the reducing flame the oxide blackens, but does not fuse. When heated on platinum wire with carbonate of sodium, a dark yellow glass is obtained, which becomes paler, opaque, and crystalline, on cooling. Tungsten salts impart no colour t» the flame. With nitrate of cobalt no reaction is obtained. Fused with borax, however, on platinum wire, a clear colourless bead h formed in the oxidizing flarm ; but this, if the tungstic oxide be increased in quantity, becomes slightly yellow, and even somewhat opaque while in the flame, and on cooling, milk-white. In the reducing fiame with a moderate quantity of the oxide, the bead becomes darh yelhrn while hot, and brownish yellow on cool- ing. A more characteristic result is obtained if microcosmic salt be em- ployed instead of borax ; for in the oxidizing fla7ne the bead becomes paU yellow, while in the reducing flame it is clear blue. If, however, iron were present, as in testing the mineral Wolfram (tungstate of manganese and iron), the bead would have been of a bright red. With stannous chloride the salts of tungsten give a blue precipitate of the oxide WjOj. There are no tungsten compounds corresponding to the chloroplatinates, chloriridiates, and chloraurates. TUNGSTOCS SALTS. These compounds are but few iu number, and, with the exception of the sulphide, unstable ; they are also comparatively unimportant, as the analyst is almost entirely concerned with the tungstic series. The chief insoluble salts of this series are the oxide and the sulphide. The Chloride is a volatile liquid, decomposed by water. The Iodide, the Cyanide, and the Ciikosute, are unknomi. TTTNaSTIC SAMS. 237 The Oxide is produced both by decomposing the chloride (WClj) with water, and by acting on tungstic oxide (W^ O,) with nascent hydrogen : the latter method at first produces the blue oxide. This oxide may also be ob- tained by heating tungstate of ammonium in a closed vessel : it is a brown or violet brown powder. Its formula is W^ O^. It dissolves in hydrate of potassium, with evolution of heat and formation of tungstate of potassium (KTWO^,). Hydrofluoric is the only acid which attacks it. The SuLPHinB is obtained by the action of heat on tungstic sulphide. It also occurs in nature. Its formula is W^ S^. Nitrohydroehloric acid con- verts it into tungstic oxide and sulphuric acid. The Sulphate, the Carbonate, the Oxalate, the Fbkeooyanide, the Ferrictanide, and the Phosphate are iinknown. tungstic salts. These compounds are chiefly recognized by the insoluble oxide and sulphide. The Chloride is a volatile liquid, decomposed by water. The Iobide, the Cyanide, and the Chromate are unknown. The Oxide is obtained by decomposing the salts in which tungsten occurs as part of the acid-radical : thus the native tungstate of calcium, or the arti- ficial tungstate of sodium, yield the oxide when acted upon by hydrochloric acid. It is a yellow powder, becoming dull green when heated. Freshly precipitated it is gelatinous. Its formula is W^ O3. This substance is solu- ble in the hydrates of potassium and ammonium, forming tungstates ; from these solutions it is reprecipitated by nearly all acids, excess of which does not cause its re-solution (with the single exception of phosphoric acid). The organic acids, oxalic, citric, and tartaric, do not, however, effect the precipi- tation of tungstic oxide from tungstates, if added in excess. Tungstic oxide dissolves in the soluble sulphides of the alkaline metals. The Sulphide is obtained by saturating a solution of an alkaline tung- state with hydrosulphuric acid, and the subsequent addition of hydrochloric acid. It is produced also when the oxide is dissolved in an alkaline sulphide, and the resulting solution reprecipitated by an acid. It is a Hver- eoloured precipitate. Its formula is W^ S3. This compound is soluble in alkaline sulphides, forming a series of salts such as those described under antimony and arsenic : these solutions decompose in the air, finally yielding the tungstate and the sulphate of the alkaline metal. Tungstic sulphide dis- solves in hydrate and carbonate of potassium, and less readily in hydrate of ammonium : in these cases it forms a mixture of sulphotungstate and tung- state, just as arsenic sulphide yields under the same conditions a mixture of sulpharseniate and arseniate. Tungstio sulphide is slightly soluble in water, colouring it yellow or brown ; heat increases this solubility. The Sulphate, the Carbonate, the Oxalate, the Feekoctanidb, the Ferricyanide, and the Phosphate are unknown. 238 CHEMICAL EE ACTIONS. The other special reagents of the first and three preceding subdivisions give no characteristic reactions with tiuigstic salts. Tungstic salts are chiefly recognized by their oxide and sulphide ; but the formation of the indigo-blue oxide by the action of nascent hydrogen is also characteristic, although not peculiar to this metal. SALTS OF MOLYBDENUM. This metal bears a considerable resemblance to the preceding ; it forms, however, a larger number of compounds with oxygen and other salt-radicals, constituting several series, which are represented respectively by the oxides and chlorides MojO and MoCl; Mo^Oj and MoCl^; MO2O3 and M0CI3, while between the two latter oxides there exists one called the blue oxide, which is apparently intermediate or a compound of both (Mok, O5 ?). Some molybdenum compounds, as the chlorides, sublime at a gentle heat ; those which are fixed, usually yield the oxide Mo^ O3 when heated in the air. When heated on platinum vrire with carbonate of sodium, the oxide M02 O3 gives a glass which is clear while hot, and becomes nulk-white on cooling ; if the bead be transferred to charcoal, and heated on it, it sinks in, and if the mass be levigated, a steel-grey powder of the metal is obtained. Molybdenum compounds impart no colour to the blowpipe flame, nor does nitrate of cobalt yield any decisive result. With borax the bead is dark yel- low or red in the oxidizing flam^ whilst hot, and colourless or of a bluish grey opaline appearance when cold, according to the amount of molybdenum pre- sent ; in the reducing flame the bead becomes brown, vrith but a minute trace of molybdenum, and guite dark and opaque if a little more be added. With microcosmic salt in the oxidizing flame the bead is yellowish green when hot, and colourless when cold, and if transferred to charcoal, becomes opaque and bright green ; in the reducing flame the colour is of as fine a green as that of chromium. The salts of molybdenum, in which that metal exists as a compound acid- radical combined vrith potassium, sodium, or armnonium (alkaline molyb- dates), yield with a small quantify of stannous chloride (SnCl) a blue colouration ; with a larger quantity of the reagent, a blue precipitate ; and with a stiU larger amount, a green precipitate : the blue and green precipi- tates dissolve in sulphuric acid, yielding blue or green solutions. There ai-e no combinations of molybdenum known corresponding to the chloro- platinates and chloraurat«s. MOLVBDOUS SALTS. The soluble salts of this series are of a black or deep purple colour, or, if dilute, of a brownish green tint ; the insoluble salts are dark grey or black. They are generally obtained fi-om the oxide Mo^ O3, by dissolving it in hy- drochloric acid and adding zinc: the liquid becomes at first blue, then reddish brown, and finally black ; the molybdous chloride (MoCl) formed. MOLTBDIC s.u:,TS. 239 and present in the solution, is separated from the chloride of zinc by excess of hydrate of ammonium, which precipitates it as hydrate. Molybdous salts do not oxidize so readily as those of the next series. The principal insoluble molybdous salts are the chromate, the hydrate, the sulphide, the ferrocyanide, and the phosphate. The Chloride and the Iodide are soluble. The Cvaxide is unknown. The Chromate is produced by chromate of potassium. The Hydrate is obtained by adding the hydrates of potassium or am- monium, or the carbonates of potassium or sodium, to solutions of molyb- dous salts : it is a brownish black precipitate. Its formula is probably MoHO. It is insoluble in excess of alkaline hydrates, sUghtly soluble in the carbonates of potassium, sodium, and ammonium. Recently precipitated, it dissolves slowly in acids ; but after ignition, by which process it is converted into the oxide (Mo^O), it is quite insoluble in acids. The Sulphide is produced by the action of hydrosulphuric acid gas, as a brownish black, and by sulphide of ammonium as a yellowish brown pre- cipitate. Its composition has not been ascertained. It dissolves readily in sulphide of anunonium. The Sulphate, formed by dissolving molybdous hydrate in sulphuric acid, is soluble. The Carbonate is not known. The Oxalate is a dark grey precipitate, slightly soluble in excess of oxalic acid. The Ferrocyanide is produced by the action of ferrocyanide of potassium, as a dark brown precipitate. Its composition is unknown. It is soluble in excess of its precipitant, and also in excess of hydrate of ammonium, yielding dark brown solutions. From its ammoniacal solution it is reprecipitated upon the addition of chloride of ammonium. The Ferricyanide is produced by the action of ferricyanide of potassium, as a reddish brown precipitate. The Phosphate is produced by the action of phosphate of sodium, as a dark grey precipitate, soluble in excess of molybdous chloride. The action, on solutions of molybdous salts, of the other special reagents of the present and three preceding groups, has not been ascertained in all cases. Molybdous salts ai'e generally recognized by the formation of the insoluble hydrate and sulphide. MOLYBDIC SALTS. These salts are prepared by dissolving molybdic hydrate in the various acids. They may also be prepared by digesting excess of metallic molybdenum in a solution of per-molybdio oxide (Mo^Oj) in that acid whose molybdic salt we desire to obtain. In the anhydrous state these salts are black ; but when in solution, or combination with water, red or reddish brown. 240 CHEMICAL KEACTIONS. The principal insoluble salts are the ohromate, the hydrate, the sulphide, the ferrocyanide, and the phosphate. The Chloride and the Iodide are soluble. The Cyanide is unknown. The Ohromate is produced by the action of ehromate of potassium. It is precipitated in greyish yellow flakes, which are insoluble in water. The Hydrate is obtained by the action of the hydrates of potassium or ammonium, or of the carbonates of potassium or sodium, on solutions of molybdic salts. It is a reddish brown precipitate, which becomes nearly black on drying. The formula is probably MoH^Oj. It is insoluble in excess of the alkaline hydrates, but soluble in the carbonates ; slightly soluble in water, to which it imparts a yellow or red tint. It is reprecipitated from its aqueous solution by chloride of ammonium and some other salts. It dissolyes in acids. The Sulphide is produced after some time, by the passage of hydro- snlphurio acid gas through molybdic salts, as a brown precipitate, or by the addition of sulphide of ammonium, as a yellowish brown precipitate. Its formula is Mo^ Sj. It dissolves in sulphydrate of ammonium. It is easily soluble in nitric acid, while it is decomposed by sulphuric acid on ebullition, evolving the gas termed anhydrous sulphurous acid (SOj), and yielding a blue solution. The SciiPHATE and the Oxalate are soluble. The Carbonate does not appear to exist. The Ferrocyanide is produced by ferrocyanide of potassium, as a dark brown precipitate insoluble in excess of its precipitant, but soluble in hydrate of anunonium ; from this solution it is reprecipitated by chloride of ammonium. The Ferricyanidb is produced by ferrioyanide of potassium, as a dark brown precipitate insoluble in excess of its precipitant. The Phosphate is produced by phosphate of sodium, as a brownish white precipitate. The action, on bi-salts of molybdenum, of the other special reagents of the present and three preceding subdivisions, has not, in many cases at least, been well ascertained. The hydrate and the sulphide are the most characteristic salts of the series. Between the bi-salts and ter-salts of molybdenum, the characteristic blue Oxide of molybdenum occurs : it is obtained by the oxidation of the lower, or the reduction of the higher oxides. Its formxda is doubtful. It is soluble in water, but reprecipitated from its aqueous solution by chlo- ride of ammonium. ter-salts of molybdenum. The oxide of this series is commonly called molybdic acid ; it is reaUy anhydrous molybdic acid, or molybdic anhydride, and yields salts in which TEE-SALT3 OF MOLYBDENUM. 241 the molybdemun constitutes part of the acid-radical. Other ter-salts of molybdenum exist in addition to the oxide (Mo^Og): they are cliiefly formed by dissolving the latter in acids. The chief insohible compounds of this series are the oxide, the sulphide, the ferrocyanide, and the ferricyanide. The Chlohide, the Iodide, and the Cyanide, if existing at all, are pro- bably soluble. The Ciieomatb is unknown. The Oxide is produced by oxidizing one of the lower oxides or hydrates by nitric acid, or by roasting the native sulphide. It is a white crystalline body, which melts at a red heat to a yellow liquid. Its formula is MOjO^. It dissolves in the hyjirates of potassium and ammonium, forming the mo- lybdates KMoO,, and NHjMoOj. There are several series of molybdates — basic, normal, and acid ; the alkaline molybdates only, such as those just mentioned, are readily soluble in water. The oxide (Mo^Oj) dissolves in 500 parts of cold, or 960 of hot water ; before ignition it is soluble in many acids. The Sulphide is produced by saturating a solution of an alkaline molyb- date with hydrosulphuric acid gas, whereby an alkaline sulphomolybdate is first formed ( KMoO^ -I- 2112 S = KMoS, -|- 2H2 O ) ; the sulphomolybdate is then decomposed by the addition of hydrochloric acid (2KMoS2-l-2HCl=Mo2S, -|-H2S-(-2KCl). It is a brown precipitate. Acid solutions of molybdic an- hydride (MO2O3) are coloured blue when hydrosulphuric acid is first passed through them : after a time, a brown precipitate of the ter-sulphide contain- ing free sulphur occurs ; but the molybdenum is never wholly precipitated. The formula of the brown sulphide is MO2S3. It dissolves in the hydrates and sulphides of the first subdivision, forming the sulphomolybdates. The Sulphate, obtained by acting on molybdate of barium with sulphuric acid, is soluble. The Carbonate does not exist. The Oxalate is soluble. The Ferrocyanide is produced by adding ferrocyanide of potassium to an acid solution of molybdic anhydride (M^Oj), and appears as a reddish precipitate, which dissolves in excess of its precipitant, and also (with de- composition) in hydrate of ammonium. The Ferricyanide is produced by ferricyanide of potassium as a pale reddish brown precipitate, which is soluble in hydrate of ammonium. The Phosphate is scarcely known. The other special reagents of the present and three preceding subdivisions are not knovm to give any decisive results with solutions of ter-molybdic salts, or of the molybdates. The most characteristic salts of this series are the oxide and the sulphide, together with the derivatives of the oxide known as the " molybdates." 242 CHEMICAL EEACTIONS. SALTS OP VANADIUM. This metal resembles molybdenum in forming a considerable number of different combiaations with oxygen and other salt-radicals. The first series, that of Tanadious salts, is represented only by the oxide Vj O, which is dis- solved by nitric acid alone, and which, if exposed to the air, passes into vauadic oxide. The second series, that of vanadic salts, is represented by the oxide V^ Oj, and the chloride VCl^, — whilst the third series, that of the ter-salts of vanadium, is typified by the oxide Vj O3 (the anhydrous vana^ die acid) and the chloride VCI3. Between the oxides of the two latter series there are' certain other oxides of a blue or green colour. The metal zinc precipitates metallic vanadium from its solutions. VANADIC SALTS, OE BI-SALT3 OF VANADIUM. The anhydroas salts of this series are green or brown, while their solu- tions are of a blue colour, which varies in intensity with different salts, and which often changes to a green by oxidation. The oxide is prepared by the ignition of vanadite of ammoniiun ; it dissolves slowly in acids. The principal insoluble salts are the cyanide, the hydrate, the ferrocya- nide, and the ferricyanide. The Cyanide is formed by digesting the hydrate in a solution of hydro- cyanic acid, as a dark-brown gelatinous mass, which is soluble in cyanide of potassium. The Chlokide, the Iodide, and the Chbomate are soluble. The Hydrate is best produced by precipitating a vanadic salt (through the solution of which hydrosulphuric acid gas has been passed, in order to reduce the vanadic oxide) by slight excess of carbonate of sodium. The precipitate is greyish white ; and the Uquid should be left perfectly colour- less ; for if blue, carbonate of sodium enough has not been added, while, if green, vanadic oxide is present. The grey precipitate, if exposed to the air, speedily becomes brown. Its composition has not been ascertained. It dissolves in excess of alkaline hydrates, forming brown solutions containing vanadites ; from these solutions it is reprecipitated by more alkaline hydrate. In neutral or acid alkaline carbonates it dissolves, forming pale blue so- lutions. Solutions of vanadic salts (also the insoluble hydrate), when mixed with excess of hydrate of ammonium, yield a brown precipitate of vanadite of ammonium, in which the vanadium enters as a constituent of the acid- radical. Vanadite of ammonium is insoluble in hydrate of ammonium, but dissolves in water, with a brown colour. The Svilphide is not produced by hydrosulphuric acid gas ; but by the addition of alkaline sulphydrates (e. g. NH., HS) to solutions of vanadic salts, a brownish black precipitate is obtained. Its composition is V.^ S^. It dis- solves in excess of its precipitants, forming solutions of a beautiful purplish colour ; it dissolves also in a boiling solution of carbonate of sodium, with a brownish yellow colour. It is not affected by hydrochloric or sulphuric TEE-SALTS OF VANADITJlf. 243 acid; but by nitric acid it is converted into vanadic Bulphate, which is a soluble salt. The Carbonate and the Oxalate seem to be soluble. The PerrOCyanide is produced by the action of ferrocyanide of potas- sium : it is a bulky, lemon- yellow precipitate, which becomes green by expo- sure to the air. The Ferkioy aside is produced by ferricyanide of potassium, as a gelatinous yellow-green precipitate. The Phosphate is soluble. In most instances the other special reagents of the present and three pre- ceding subdivisions have been found to give no characteristic reactions with vanadic salts ; the action of others has not been aacertaiaed. The insoluble hydrate, sulphide, and ferrocyanide are the most character- istic vanadic salts. ter-salts of vanadium. The oxide of this series (V^ O^) plays the same part as the corresponding oxide of molybdenum ; and this metal occurs in nature in the form of a vanadiate, just as molybdenum occurs as a molybdate. Several salts, how- ever, containing other salt-radicals than oxygen, belong to the ter- or per- vanadic series. The vanadiates are colourless, yellow, or occasionally red, — while the ter-salts are also generally red or yellow, and give solutions of the same colour: by the action of reducing agents {e.g. HjS or HjO) they become blue. The Chloride (VCI3) is a liquid which dissolves in large excess of water, forming a pale yellow solution, which decomposes in a few days, becoming green or blue, and evolving chlorine, and forming the bichloride VCl^. The Iodide and the Chromate are unknown. The Oxide is produced by the action of nitric acid on the lower oxides, or directly from the ores ; it may also be obtained by the action of the hydrates of potassium or ammonium on vanadic salts. It is a reddish yellow or brick- red precipitate. Its formula is V2O3. It dissolves in the hydrates of potas- sium and ammonium, forming vanadiates, the solutions of which are yellow or brown (most metallic vanadiates are soluble). 1 part of ter-oxide requires 1000 parts of boiling water for solution. It dissolves readily in acids. The Sulphide is not produced by hydrosulphuric acid gas ; but by the addition of sulphydrate of ammonium a brown precipitate falls. Its formula is Vj S3. It dissolves in the hydrates, sulphides, and carbonates of the first subdivision, forming sulphovanadiates. It is not decomposed by sulphuric acid. The Sulphate is soluble. The Carbonate does not exist. The Oxalate is soluble. The Ferrocyanide is produced by ferrocyanide of potassium, as a beautiful green precipitate, which is insoluble in acids. m2 244 CHEMICAL EEACIIONS, The Feerioyanide is unknown. The Phosphate is yellow, and comparatively soluble in water. The other special reagents of the present and three preceding subdivisions have generally been found to give no characteristic reactions with ter-salts of vanadium. Ter-salts of vanadium may be recognized best by the formation and re- actions of the oxide, and also of the sulphide. SALTS OF SELENIUM AKT) TELLURIUM. These two bodies, which will be fully treated of in the next Chapter, are mentioned here because they are precipitated as sulphides from their acid solutions, in conjunction with the members of the fourth subdivision, by the passage of hydrosulphuric acid gas. The Sulphide of selenium is yellow. Its formula is SeSj. It dissolves in excess of sulphydrate of ammonium. If the sulphide be dissolved in nitrohydrochloric acid and evaporated to dryness, selenious anhydride (SeOj) will be obtained, which may be recog- nized by the following reactions : — a. If a portion be dissolved in water, with which it combines to form sele- nious acid (Hj SeO,), and some hydrochloric acid and a strip of zinc be then introduced into the solution, the zinc will become coated with a copper- coloured film, and subsequently red or red-brown fixicJcs of selenium are deposited. /3. If another portion of the selenious anhydride, or some of the precipi- tated selenium of experiment a. be dried at a gentle heat, and then volatilized before the blowpipe flame, a peculiar odour, res&mbling that of horse-radish, is perceived. The Sulphide of tellurium is a dark brown precipitate. Its formula is TeSj. It is soluble in excess of sulphydrate of ammonium, and in boiling solutions of the hydrates of potassium and sodium, yielding salts known as Bulphotellurites. We now subjoin a method for the analysis of the 2nd Section of this subdivision, supposing that we have one only of its im- portant members present. The Table for the 1st Section has been already given (p. 190). On pp. 246 and 247, the synopsis of reactions wUl be found. DETECTION OF THE BASIC EADICALS. 245 Analysis of Subdivision IV. Section II. — Salts of metals which form Sulphides soluble in Sulpliide of Ammonium. Tte salt may be one of TIN, ANTIMONY, AESENIC, PLA- TINUM, or GOLD. If, as ia probable, it is a sulphide, wash thoroughly ; add hydrochloric acid ; boil, and add, while boiling, a few drops of nitric acid, drop by drop, until the precipitate is dissolved. Pom- the solution down the funnel- tube of a hydrogen apparatus fitted with an " arsenic-tube" (see p. 21.3). •^PPly ^^ iisat of a spirit-lamp, urged by a blowpipe, to the arsenie-tube. The formation of a mirror after the lapse of a few minutes indicates the presence of Arsenic or Antimony. Dissolve the mirror out of the tube by a drop of hot nitric acid ; evaporate in a porcelain dish to dry- ness at 100° C. ; redissolve in a drop of water, and add nitrate of silver. A yellow or red precipitate indicates Arsenic ; no change indicates Antimony. If no mirror is obtained when the action in the hydro- gen apparatus has ceased, brush the black powder which is found, carefully from the surface of the zinc ; it may contain Tin, Antimony, Platinum, or Gold. Wash it by deoantatiou, boil it with hydrochloric acid, and filter. Any residue indicates the presence of Platinum or Gold. BoU in hydrochloric acid, and add a drop or two of nitric acid, just to dissolve ; boil to decompose any nitric acid remaining, then add some concentrated solution of oxalic acid, and keep warm for some time. A brown precipitate, or yellow metallic spangles, in- dicates the presence of Gold. If no pre- cipitate occm-s, the solution should be neutralized with ammonia; a yellow precipitate will indicate the presence of Platinum. Perfect solution indicates the presence of Tin or Antimony. Boil the hydrochloric solution, add a di-op or two of nitric acid, or a crystal of chlorate of potassium ; cool, and add excess of solution of sesqui- carbonate of ammonium : the formation of a precipitate insoluble in excess indicates the presence of Tin. This should be verified by re- ducing this precipitate by fusion with cyanide of potassium, dissolving the washed metal in hydrochloric acid, and test- ing it with pro- tochloride of mercury: a white or grey precipitate indicates Tin. The solution may contain Ajitimony. Pass hydro- sulphuric acid gas into it, and then acidify with hydrochloric acid: a reddish-orange precipitate indicates the presence of Antimony. 246 CHEMICAL BEACnONS. TABLE OF Eeactions. Chloride . . . Iodide Cyanide...... Chromate ... Hydrate Oxide Oxychloride Sulphide . . . Sulphate . . . Carbonate . . . Oxalate Ferrocyanide... Ferricyanide . . Phosphate Sn. (Stannous salts.) (see page 192) Sn. (Stannic salts.) (see page 196) f yellowish \ \ white J / 'yellowish "I [ white J white olive white r brownish "1 1 black ] /white cry- 1 [ staUine J white white white orange » yellow white white yellow r brownish 1 \ yellow J white Sb. (Antimonioua salts.) (see page 204) Sb. (Antimonic salts) (see page 207) / brownish 1 \ yellow J 4- white white orange-red white white white white white white / orange- \ \ yeUow J Blowpipe J Reactions. With carbonate of sodium in the reducing flame (on charcoal), stannous and stannic salts yield a mal- leable globule of tin. The incrustation on the char- coal is white. AYith carbonate of sodium in the reducing flame (on charcoal), antimonious and antimonic salts yield a brittle globule of anti- mony, and a bluish white incrustation. * Signifies that a precipitation occurs, but not 4. Signifies that the precipitate wliich is formed consists of TABLE 01' EEACTIONS. 247 EEACTIONS. As. As. Pt. Au. (Arsenious salts.) (Arsenic salts.) (Platinic salts.) (Auric salts.) (see page 215) (see page 218) (see page 222) (see page 234) — brown green — — ? yellow — — deep red — — black r reddish 1 \ yellow J white white — brown yeUow ? yellow / brownish 1 black * black * Arsenious and arsenic salts, when The metal is The metal is heated to redness on charcoal, in reduced, and reduced, and the reducing flame, emit a cha- appears as a black appears as a racteristic garlic odour, and, when or grey powder, malleableglobule. heated in a tube (closed at one end) when platinum if a sufficient with a mixture of carbonate of so- salts are heated temperature has dium and charcoal, give a black with carbonate of been attained. lustrous mirror. (See page 210.) sodium (or alone) in either flame. of the salt indicated in the horizontal column. the salt indicated in the horizontal column next below. 248 CHEMICAI EEACTIONS. CHAPTER VIL DETECTION OF THE AOID-EADIOALS IN THEIE COMPOUNDS. The reactions of the basic radicals iiaving been fuUy described in the preceding Chapter, the student may now acquaint himself with the tests by the application of ■which the presence or ab- sence of the acid-radicals is determined. The slightest consideration will show that, to a great extent, the same means which serve for the detection of the basic con- stituents of salts win also be ayaUable for the recognition of their acid-radical ; for it is obvious that, if a soluble chloride produces a white, curdy, insoluble precipitate in solutions of silver salts, a solution of a silver salt wOl prove an equally certain test for the presence of a soluble chloride. StiU, owing to the nu- merous broad distinctions, physical and chemical, which exist between the two classes of radicals themselves, other means of no less decisive nature are at hand in abundance, by the employ- ment of which, the class and also the individual characteristics of the acid constituent present in any given salt can be determined. A few remarks upon each of these methods of testing may not be out of place as an introduction to the present Chapter. And, firstly, — of the detection of the and-raclical by the foi-mation of certain saline compounds of well-defined chemical or physical pro- perties. As just now stated, a very large number of salts (easily recognizable by such characteristics as the following, — solubility in certain menstrua and insolubility in others, or insolubility in all, or again, the possession of some remarkable features of form or colour) are employed in common, as the products by the for- mation of which the presence either of the basic or of the acid- radical contained in them can be safely predicated. Thus chloroplatinio acid (HPtClg), usually employed as the test for the preeenee of potassium, may itself be recognized by the employment, as a reagent, of a soluble salt of potassium. Sulphmio acid, often employed to detect the presence of barium, may itself be recognized infallibly by a soluble DETECTION OP THE ACID-EADrCALS. 249 barium salt. The presence of mercury in a solution may be eyidenoed by tlie action of a soluble chromate, which, in ita turn, may be recognized by a mercury salt. Lead may be detected by hydrosulphuric acid, and hydro- sulphuric acid by lead. By these instances it may therefore be seen, that the same reaction differently applied may be used to indicate both a basic and an acid-radical. Nor, be it observed, is it necessary that the hydrogen salt of the acid-radical be employed ; in almost every instance (as in the third of the examples just given), any salt will be as eiEcient as the acid itself or salt of hydrogen, provided only it be soluble : thus, in the cases cited above, chloroplatiuate of sodium is as good a precipitant as chloroplatinate of hydrogen, i. e. cliloroplatinic acid ; the sulphides and sulphates of potassium, sodium, and ammonivmi act equally well with the acids themselves, i. e. the corresponding salts of hydrogen, the hydrosulphuric and sulphuric acids. And indeed it frequenUy happens that the desired reaction does not take place when the acid is employed, but only upon the addition of some other than the hydrogen salt ; the reason of this may be stated to consist in this, — that the hydrogen compound or acid liberated at the time of the formation of the new compound, either keeps that compound completely in solution, or prevents its entire precipitation. Thus, if hydi-osulphuric acid (H^S) be added to ferrous chloride (FeCl), no sulphide of iron (Fe, S) falls, since this ferrous sulphide is soluble in hydi-oohloric acid, the necessary complementary product of the reaction. But if, on the other hand, a soluble sulphide, such as the sulphide of potassium, sodium, ammonium, barium, strontimn, or calcium, be added to ferrous chloride, an immediate precipitation of ferrous sulphide occurs ; for it is no longer the chloride of hydrogen, i. e. hydro- chloric acid, which forms the secondary product of the reaction, but tlie chloride of a far more powerfully basic radical, a chloride therefore which exerts no decomposing or solvent action on the ferrous sulphide : in this case the reaction is as follows : — J E, S-f «FeCl=Fej S-|-2E:C1. ^ precip. Occasionally, as tlie student will have already observed in the reactions employed to detect the basic radicals, the recognition of substances does not depend upon the formation of a salt of ex- treme insolubility, or of remarkable physical features of form or colour, but upon the production of a body wJiich is readily vola- tilizable, and possessed of an easily recogniz-e-d odour. The detection of the basic radical ammonium depends upon a decomposi- tion of this kind, which the following equation will recall : — NHj Cl-|-KHO=NHj HO -l-KCl. In this case the hydrate of ammonium is resolved immediately into the gas ammonia (NHj) and water (H^ O) ; and ammonia is remarkable for a peculiar M 5 250 CHEMICAL EEACTIOKS. and pungent odour. Upon a similar formation of an odorous and volatile body depends, in great measure, the recognition of the presence of the acetic acid-radical. To the substance supposed to be or contain an acetate, sul- phuric acid and alcohol (C^ H, HO) are added, and the mixture heated. The former reagent will produce, with an acetate, acetic acid {i. e. acetate of hy- drogen) (HC2H3O2 or HA); and this, acting in the nascent state on the alcohol or hydrate of ethyle (0;, Hj HO, or EHO), yields a fragrant body, the acetate of ethyle, thus — ■ HA-(-EH0=H2 O-fEA. acetote of ethyle. The acetate of ethyle, or acetic ether, is volatilized at the temperature em- ployed, and, possessing a most peculiar and agreeable iruity odour, is easily identified. We win now consider briefly tie second method of detecting acid-radicals, by the actVMl elimination of the acid-radical itself, and the subsequent identification of its peculiar properties. And here it must be borne in mind, tbat a great distinction must necessarily exist between tbe bebaviour of tbe acid- and basic radicals, simply on accoimt of tbeir inherent nature. The basic radicals with which the student has been made acquainted, and which occur in great abimdance, are (with a few exceptions) elements, and, moreover, they are all (ammonium, mercury, and hydrogen only excepted) solid at the ordinary temperature. On the other hand, however, more than half of the acid-radicals of common occirrrence, and almost all the rarer ones, are compound bodies, which are characterized by great diversity of physical condition, several being gaseous, some liquid, and others soUd. The fact of a body beiag compound frequently adds to our facili- ties of recognizing it ; for, in addition to any peculiarities which it may exhibit as a compound, we have other clues to its pre- sence in the characteristic properties which its constituents may individually manifest when, by its decomposition, they have been set free. In fact, those acid-radicals which are complex cannot, with but few exceptions, be obtained in the isolated condition, but are resolved either into other and generally simpler com- pounds, or into their elementary constituents. Whilst, therefore, we indubitably prove the presence of an elementary acid-radical by DETECTION OF THE ACID -RADICALS. 251 obtaining it ia the free state and examining its properties, we no less distinctly show the existence of a compound acid-radical when we observe some of the weU-asoertained features of the decomposition which it undergoes when liberated. To illustrate the foregoing cases, we will take two examples. When chlorine acts upon a bromide, decomposition ensues, with separation of the element bromine, the peculiar features of which, such as the yeUow colour which it imparts to a solvent, or the orange tint which starch-paper exposed to its vapour assumes, or its peculiar suffocating odour, may be immediately re- cognized — MBr+Cl=MCl-l-Br. But if, on the other hand, we deal not with an elementary, but with a com- pound acid-radicaJ, such as that existing in the oxalates, by treating the salt in such a manner as to decompose it into new and characteristic products, the latter frequently furnish us with good proof of the previous existence of the compound acid-radical. These products, in the case of the oxalates, are the two gases carbonic anhydride (CO^) and carbonic oxide (CO) ; and they are obtained by the action of sulphuric acid upon oxalates, the decomposition being aided by heat, thus — M2C2 0,H-2H2SO,j=M:,SO,-|-H,SO.„H20-|-C02+CO. hydrate of sulphuric acid. The more easily recognizable gaseous product, or at least the more charac- teristic, is carbonic oxide (CO), which, when the carbonic anhydride (COj) has been removed by an appropriate agent, may be readily kindled on the application of a light, burning with a blue flame. The preceding hints will perhaps suffice to show the general principles upon which the detection of acid-radicals is based, and to exhibit the chief points in which their reactions resemble, and also those in which they differ from the reactions of the basic radicals. "We now proceed to detail these reactions, adopting the subdivisions which have already been chosen in the description of the acid elements. The classification of the acid-radicals is thus entirely founded upon the chemical characters of each group, and not upon their similarity ia an analytical point of view. 1. Salts containing the acid-radicals of Subdivision I. (page 17). Salts of Chloeine, BKOMUfE, Iodine, and Fluoeine, and of THE chief compound AOID-HADICALS INTO THE COMPOSITION OF WHICH THEY ENTEB. 252 CHEMICAL EEACTIONS. 2. Salts containing the acid-radicals of Subdivision II. (p. 18). Salts op Oxtgek, Stjlphtir, Selenium, and Tellueium, and OE THE chief COMPOITND ACID-BADICALS INTO THE COMPOSI- TION OF 'WHICH THET ENTEE. 3. Salts containing the acid-radicals of Subdivision III. (p. 18). Salts op Caebon, Boeon, Silicon, Tantalum, Niobium, Pelopium, and Titanium, and of the chief compound acid-eadicals into the composition op which thet entee. 4. Salts containing the acid-radicals of Subdivision IV. (p. 18). Salts op Niteogen, Phosphoeus, Aesenic, and Ajsttimont, and op the compound acid-eadicals into the composition of which thet entee. SUEDIYISION I. SALTS OF CHLORINE, BROMINE, IODINE, AND FLUO- RINE, AND OF THE CHIEF COMPOUND ACID-RADI- CALS INTO THE COMPOSITION OF WHICH THEY ENTER. The three first-named mcmbera of this Subdivision present the most striking resemblance to each other, both in the salts which they form by simple union with the basic radicals, and also in those in which they exist as a part only of a compound acid- radical. Fhioriue differs in many respects, and in none more decisively than in not forming compound acid-radicals similar to those which the other members of the group are known to yield. In the further arrangement of the present Subdivision, as also in the arrangement of those which follow, we take advantage of the differing chemical constitution of the members, and not of any analytical characteristics which they may present. In accord- ance vsdth this plan, we now proceed to divide the present group into three Sections, as follows ; — SALTS OP CHIOEHTE. 253 Section I.— SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE. The chlorides, bromides, iodides, and fluorides. Section II.— SALTS OF THE ACID-RADICALS WHICH CONTAIN CHLORINE, BROMINE, AND IODINE COMBINED WITH oxyaEN. The hypochlorites, chlorites, chlorates, perchlorates, hypo- hromites, bromates, iodites, iodates, and periodates. Section III.— SALTS OF THE ACID-RADICALS WHICH CONTAIN CHLORINE, BROMINE, AND IODINE COMBINED WITH METALS. The chloropaUadiates, chloroplatinates, chlororhodiates, ohloro- rutheniatcs, chloriridiates, and chloraurates. Section I. — The chlorides, bromides, iodides, and fluorides. SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE. The radicals of this Section are monobasic, and when com- bining with monatomic basic radicals yield compounds having the general formula MR. They are detected by both the methods described iu the preliminary observations to the present Chapter, i. 6. both by presenting to a soluble chloride, bromide, iodide, or fluoride a soluble salt of some basic radical known to form, with the acid element sought for, an insoluble salt of easUy recogniz- able properties, — and also by submitting the chloride, bromide, or iodide to such decomposing influences as are calculated to eliminate their acid-radical. SALTS OP CHIOEnrE, OE CHLOEEDES. These salts are for the most part soluble lq water, sparingly soluble in alcohol, and nearly insoluble in ether. Their formulse vary according to the atomic nature of the*combined basic con- stituent ; but the foUovring are the most usual : — M,C1, MCI, M,Cl3, MC1„ and MCI3. "When heated before the blowpipe on charcoal, the deportment 254 CHEMICAL EEACTIONS. of chlorides differs according to the nature of the combined basic radical: if the metal belongs to Subdivision I., the compound fuses, and sinks into the charcoal ; if to Subdivision II., it fuses and generally remains as a molten mass upon the charcoal : the chloride of magnesium is the exception here ; for, as it cannot exist in the presence of aqueous vapour, it suffers decomposi- tion, and leaves a white residue of oxide. Some of the remaining chlorides, such as those of silver and lead, fuse mthout change ; others again, as those of tin, antimony, and arsenic, volatilize, vfhUst others, such as those of platinum and gold, decompose into chlorine and the metal. If a bead of miorocosmic salt be fused upon a platinum wire, and cupric oxide (Cu^O) added to it until the bead is saturated, if a chloride be then introduced, and the bead submitted to the heat of the blowpipe jet, a blue colour will he imparted to thejlame. The Htdeooen Salt (HCl), or hydrochloric acid, is a trans- parent colourless gas at ordinary temperatures, which, at 45°-3 C, and under the pressure of 40 atmospheres, becomes a colourless Uquid, highly dispersive of light. 1 volume of water dissolves 480 volumes of the gas. The principal insoluble salts of this acid-radical are — as the student will readily recoUect — the cuprous, argentic, plumbic, mercurous, and platinous chlorides. The Cupeotjs Salt is produced by the action of a soluble cupric salt on a solution of stannous chloride. Its formula is Cu,Cl. It is insoluble in water, but soluble in most acids. The Argentic or Silver Salt is produced by the action of a soluble sUver salt on hydrochloric acid or any other soluble chloride : it is a white curdy precipitate, which assumes a grey tiuge on exposure to Hght. Its formula is AgCl. It is insoluble in water, soluble to a slight extent ia solutions of certain chlorides and in concentrated acids, and easily dissolves in hydrate of ammonium, in cyanide of potassium, and in hypo- sulphite of sodium. The Meectjeotts Sali is produced by the action of a soluble SALTS OF CHXORINE. 255 merciirous salt («. g. mercm-ous nitrate [Hg^ NO,]) on hydro- chloric acid, or a soluble chloride. It is a dense white precipi- tate. Its formula is Hg^Cl. It is but slightly soluble in water. The Lead Salt is produced by the action of a soluble lead salt on hydrochloric acid or any soluble chloride. It is a white cry- stalline precipitate. Its formula is PbCl. It is dissolved by a large quantity of cold water, but is soluble in a much smaller amount of boiling water. The platinous and other insoluble chlorides are not employed in testing for chlorine. Many of the remaining chlorides are soluble either in water or in dilute hydrochloric acid. The other methods by which this acid-radical is identified are the fonoAving : — a. Concentrated sulphuric acid and peroxide of manganese (Mn^Oj) are added to a chloride, and the mixture warmed: the sulphuric acid liberates hydrochloric acid — 21InCl-|-H, S0,=2HC1-|-Mn, SO, ; the peroxide then acts upon the hydrochloric acid — ■ ^^^^ 4HCl-|-Mn,0,=2MnCH-2H,0+2Cl. It is believed that bichloride of manganese (MnCl^) is first formed, and then decomposed into the protochloride (MnCl) and free chlorine. The free chlorine thus produced is recognized by its odom- and bleaching properties, while it is distinguished from bromine and iodine by the absence of any coloured reaction with starch. /3. When 1 part of chromate of potassium and 3 parts of oil vitriol are mixed with 1 part of the supposed chloride, and the resulting pasty liquid heated in a test-tube, to which a dry cork and bent tube have been fitted, the other end of the bent tube dipping into a test-tube free from any trace of water, and kept cool, a blood-red liquid distils over, to which the name chloro- chromic acid, and the formula CrClj, Cr^ O3, have been given ; — ♦SKCrO^-l-SNaCl-f 3H, S0,=CrCl3, Cr,03-f3KN"aSO,+ 311,0. * Possibly this reaction is more simple, — KC!r02+]SraCH-H2SOj=Ci-OCl+KNaSO,+H,0. In this case the product usually termed chlorochromic acid might be con- 256 CHEMICAL EEACTIONS. If to this red distillate a few drops of ammonia-water are added, a yellow liquid is obtained, whieh is a solution of chromate and chloride of ammonium, — • CrCl,, Cr,03 + 6NH, HO=3]SrH,Cl+3NH,CrO,-)-3H,0 ; and if into this solution, after the addition of a slight excess of acetic acid, a few drops of nitrate of silver he introduced, a beau- tiful crimson precipitate wiU be obtained, thus — NH, CrO, + AgNO, = NH, NO, + AgCrO,. crimson ppt. SALTS OP BEOMINE, OK BEOMIDES. The bromides hear the closest resemblance to the chlorides ; they are isomorphous with them. They are for the most part soluble in water, but sparingly soluble in alcohol, and nearly insoluble in ether. Bromine is monobasic ; but when combined with biatomic acid-radicals, it yields salts having the formulse already given as those of the various chlorides. Heated before the blowpipe on charcoal, the bromides exhibit the same deportment as the corresponding chlorides. They colour the flame green when fused with a bead of microoosmic salt satu- rated with cuprie oxide. The Htbeooen Salt (HBr), or hydrobromic acid, is a trans- parent colourless gas at ordinary temperatures, which, how- ever, Uquefles at 33°'3 C, and solidifies at — 37°'7. Hydro- bromic acid is very soluble in water, the solution possessing the property of dissolving a large quantity of bromine, forming a red liquid. The insoluble bromides are those which contain the same basic radicals as the insoluble chlorides, viz. the cuprous, argentic, mercurous, and plumbic bromides. The platinous bromide is unknown. sidered the chloride of a compound basic radical* chromyle (CrO), thus CrO, CI. The reaction of tliia body with hydrate of ammonium will be thus expressed in an equation : — CrO, 01+2NH, HO=NHj Cl+NIl, CrO,+H., 0. 3(CrO,Cl) = CrGl3,Cr2 03. SALTS OF BROMINE. 257 The Cupeous Salt is obtained by the action of a solutioii of a cuprovis salt on a soluble bromide. It is a white precipitate. Its formula is Cu^Br. It is insoluble in water, but soluble in hydrate of ammonium, and in hydrochloric and hydrobromie acids. In nitric acid it dissolves with decomposition ; but boiling sulphuric acid does not decompose it. The Argeatic or Silver Salt is produced by the action of a soluble silver salt on hydrobromie acid or other soluble bromides. It may also be obtained by adding the silver solution very cau- tiously to a mixture of hydrochloric and hydrobromie acids, when the bromide is iirst removed from the solution. It is a yel- lowish white curdy precipitate. Its formula is AgBr. It is slowly dissolved (but in considerable proportion) by a concentrated solution of ammonia ; it is but very slightly soluble in other ammonium salts ; it dissolves, however, to some extent iu a boiling solution of chloride of ammonium. It is slightly soluble in a concentrated solution of an alkaline bromide ; and when boiled with an alkaline iodide, it is whoUy converted into iodide of silver (Agl). Bromide of silver dissolves slightly iu concentrated hydro- chloric or hydrobromie acid ; boiling nitric acid has no decompos- ing action on it, but boiling sulphuric add alters it slightly. The MEECunoirs Salt is obtained by the action of a soluble mercurous salt (e. g. Hg^ NO,) on a soluble bromide : it is a yel- lowish white precipitate. Its formula is Hg^ Br. It is insoluble in ammonium salts, but, on ebullition with some of them, imder- goes decomposition into mercuric bromide and mercury. The Lead Salt is obtained by adding a soluble lead salt to hydrobromie acid or other soluble bromide. Its formula is PbBr. It is soluble in solutions of some ammonium salts, espe- cially on warming ; it is almost insoluble in cold water, and but sparingly soluble in hot. It is somewhat more soluble in dilute acids. The other insoluble bromides are not employed in testing for bromine. Many of the remaining bromides are soluble either in water or in hydro- bromie acid. 258 CHEMICAL REACTIONS. The other methods by means of which this acid-radical is identified are the following : — u. Bromine is readily distinguished by the properties which it possesses : it is eliminated from the bromides just as chlorine from the chlorides, by the joint action of sulphuric acid and bin- oxide of manganese. A remarkable peculiarity, however, belongs to the combinations of this substance with salt-radicals when they are treated with sulphuric acid, which, whether dilute or concentrated, when acting upon chlorides, liberates hydrochloric acid only ; but with the bromides the reaction varies with the strength of the acid employed : if the acid be weak, hydrobromic acid is set free, just as in the case of the chlorides — 2MBr-f-H, S0,=2HBr-l-M, SO, ; but if the acid be concentrated, the hydrobromic acid, which we may suppose to be first produced, is decomposed by a portion of the sulphuric acid, with formation of sulphurous acid and sepa- ration of bromine, thus — 2MBr 4-2H, S0,=2Br-|-H,0-|-H, SOj-FM, SO,. This is by no means the only method of liberating bromine ; for this element is set free equally weU when chlorine gas is passed (not in excess) into the solution of a bromide, or when to the latter a few drops of concentrated nitric acid are added : in the first case the bromine is set free by its place being occupied by the chlorine ; in the second process by a reaction similar to that exercised by sulphuric acid, given above in the form of an equation. The tests for the detection of bromine have been already given (p. 21), but may be here advantageously reca- pitulated. Besides its peculiar odour (which is very suffocating and of- fensive) and its bleaching properties, the colour of liquid and of gaseous bromine (a colour which it imparts to solvents) may be apphed for its recognition, in the following manner : — 1. Some chlorine water is added to the solution of the bro- mide ; the bromine is liberated, and dissolves in the water pre- sent, imparting to it a yeUow colour. To the coloured solution enough ether is now added to form a distinct stratum upon the SALTS OF BEOMDTE. 259 surface of the liquid, and the whole shaken in a narrow vessel, and then allowed to rest ia order to admit of the ether risiug to the surface and forming a layer there. This will contain all the free hromine of the solution, dissolved in it in virtue of the greater solubility of bromine ia ether than in water ; and its colour will vary from a pah yellow to a deep orange, according to the proportion of bromine present. The chlorine water in this experiment must be added cautiously; but if, after one treatment as above described, and separation of the etherial layer, the solution should still give a yellow colour with chlo- rine, the shaking with ether, &c. may be again repeated if it is desired to effect a perfect separation of the bromine. The etherial solution is shaken with a few drops of hydrate of potassium solution ; evaporated to dryness ; and then the ignition of the residue will give rise to the formation of bromide of potassium. Previously to the ignition, bromate of potassium would be present in addition: 6Br + 6KH0 = 5KBr + KBr03 + SHjj . bromide bromate of potas. of potas. 2. The starch-test is a good method of distinguishing bromine, as well as iodine, from chlorine. "When bromine -vapour is al- lowed to come into contact with starch paste (as by introducing a glass rod smeared vsdth this substance into a test-tube in which bromine vapour is being disengaged), a yeUow colour is produced if that acid-radical be present iu minute quantity, or, if iu larger proportion, a rich orange tint. Or the test may be applied by mixing the bromide with some starch paste in a porcelain dish, warming the mixture over the lamp, and dropping into its centre one drop of concentrated nitric acid : the liberated bromine im- mediately colours the starch. /3. When a bromide is distilled with ehromate or bichromate of potassium and sulphuric acid, a brown distillate passes over (p. 255), which dissolves in hydrate of ammonium, forming a colourless solution, which is precipitated white by nitrate of silver : this distillate is only bromine set free by the action of the 260 CHEMICAL EEACTIONS. sulpturic acid on the bromide; for there is no bromochromic acid kno'wn. SALTS OF IODISE, OB IODIDES. The iodides present the closest analogy with the bromides and chlorides, with which they are, for the most part, isomorphous. A large number of them are soluble in water ; a few, chiefly those of Subdivisions I. and II., somewhat soluble in alcohol ; but nearly all are insoluble in ether. Heated before the blowpipe on charcoal, the iodides behave in a similar manner to the corresponding bromides. They colour the flame of a fine green colour when fused with a bead of mi- crocosmic salt saturated with cupric oxide. The Htdeogen Salt (HI), or hydriodic acid, is a transparent colourless gas at ordinary temperatures, which, however, liquefies with cold, and soHdifles at about — 61° C. It is very soluble in water, the solution possessing the property of dissolving some quantity of iodine, forming a brown solution. The chief iodides possessing remarkable features are the cu- prous, argentic, plumbic, mercurous, mercuric, bismuthic, and paUadious salts. The platinotis iodide is also insoluble. The Cupeotts Salt is produced by the action of a soluble cuprous salt on a solution of an iodide. The cuprous salt em- ployed is often prepared extemporaneously, by adding to a solu- tion of the cupric salt sulphurous acid or ferrous sulphate, before mixing it with the iodide : the ferrous sulphate is most fre- quently employed for this purpose, and acts as foUows : — 2Cu, S0,+2Fe, SO,=(Cu,X SO,+(re,), (S0,)3. The cuprous iodide is a white precipitate, with a tinge of brown. Its formula is Cu^ I. It is shghtly soluble in hydro- chloric acid; but when heated with nitric or sulphuric acid, it is completely decomposed, with evolution of iodine. The Argentic or Silver Salt is produced by the action of a soluble silver salt on the solution of hydriodic acid or of a soluble iodide. It is a pale yellow precipitate. Its formula is Agl. SAITS OF lODrtTE. 261 It is soluble to a considerable extent ia concentrated solutions of chloride of potassium or ammonium, also in concentrated so- lutions of mercuric nitrate. It is scarcely soluble in concentrated hydrate of ammonium solution, 1 part requiring 2510 parts of the strongest ammonia-vater to dissolve it. Dilute acids are without action on it ; but concentrated nitric and sulphuric acids dissolve it with separation of a small proportion of iodine. The Mbkctteotts Salt is produced by the action of a soluble mercurous salt on hydriodic acid or a soluble iodide; but the salts should be mixed in equivalent proportions, to obtain a pre- cipitate free from metalhc mercury or a mercuric salt. Mer- curous iodide is a green precipitate. Its formula is Hg^ I. It dissolves partially in concentrated solutions of most soluble iodides, and in hydriodic acid ; but it is decomposed into mercuric iodide and mercury by the action of the reagents just mentioned, — by certain chlorides and by hydrochloric acid. It dissolves iu about 2375 parts of water, but is insoluble in alcohol. The Mercuric Salt is produced by the action of a soluble mercuric salt on hydriodic acid or a soluble iodide ; the addition of equivalents of the iodide and of the mercuric salt causes a perfect precipitation. It is a magnificent scarlet crystalline precipitate, which, when it begins to form, has a bright yeUow tint. Its formula is Hgl. It is very soluble in the alkaline iodides and chlorides, also in many ammonium salts; in most mercuric salts it is also very soluble. In water and ether it dissolves sparingly, but more abundantly in hot alcohol. It is soluble in hydriodic and hydrochloric acids. The Lead Salt is obtained by the action of a soluble lead salt upon hydriodic acid or a soluble iodide. It is an orange-yellow crystalline precipitate. Its formula is Pbl. It dissolves in concentrated solutions of most soluble iodides, also in chloride of ammonium, but not in other ammonium salts. 1 part dissolves in 1235 parts of cold, and in 194 parts of 262 CHEMICAL EEACTIONS. boiling water, and may ttus be purified from tbe oxyiodide, which is iasoluble in water; it is slightly soluble ui alcohol. Acids exert a slight decomposing influence upon it. The Bismuth Salt is produced by the action of a soluble salt of bismuth on a solution of a soluble iodide. It is a brown cry- stalline precipitate. Its formula is Bilj. The Falladious Salt is obtained by the action of paUadions chloride on hydiiodio acid or a soluble iodide. Its formula is Pdl. It is insoluble in water, alcohol, ether, and hydriodic acid. The other insoluble iodides are not employed in testing for iodine. Many of the remaining iodides are soluble in water or in hydriodic acid. The recognition of iodides by the separation of their acid- radical, is even more easy and certain than the detection of bromides by similar means. Iodine is liberated just as chlorine and bromine by the conjoint action of sulphuric acid and bin- oxide of manganese; but iodides differ from chlorides, and re- semble bromides, in the elimination of their acid constituents by the action of concentrated sulphuric acid employed without the addition of binoxide of manganese. a. Iodine, by whatever method liberated, may be recognized by the properties which have been already stated as belonging to this acid-radical (p. 22). 1. Not only by its characteristic odour may this element be detected, but, if it be present in some quantity in the substance under examination, it may be recognized by its separation in minute bluish black crystals when strong sulphuric acid is added to the aqueous solution of an iodide. If this solution become very hot on the addition of the acid, or if it be afterwards heated over the lamp, the beautiful rich violet-coloured vapour of iodine will float over the surface of the liquid, and gradually condense upon cooler parts of the test-tube in glistening crystals of a bluish black. If chlorine (not in excess) be passed into the aqueous solution of an iodide, and a little ether (or, better, ben- zole) be shaken up with the mixture, the ether or benzole ■\vill carry up the whole of the free iodine present to the surface of the SALTS OF FLuonnrE. 263 liquid, and appear there, after standing, as a red or beautiful violet- coloured stratum. The iodine may then be converted into iodide of potassium, and tested with nitrate of silver in the usual manner. 2. The starch-test is as good a test for iodine as for bromine, and perhaps more delicate. If a glass rod which has been dipped in starch paste be immersed into a tube containing the violet vapour of iodine, a blue colour will be produced, which passes into a black if much iodine be present. The same effect is arrived at by dissolving a small quantity of an iodide in water, adding a little starch paste, then a drop or two of pure sul- phuric acid, and lastly a very minute trace of nitrous acid, or of a soluble nitrite (». g. nitrite of potassium KNOj,), or else a very small quantity of chlorine water. /3. When an iodide is distUled with bichromate of potassium and sulphuric acid, no iodochromic acid is obtained, vapours of iodine only being evolved. SAXTS OF FLTJOEItfE, OE FLTJOEIDES. This acid-radical never having been isolated, the precise analogies which it may present to the three preceding elements are unknown ; its salts have, however, some features in common with the chlorides, bromides, and iodides, although presenting also many points of difference. The salts of fluorine are often isomorphous with these last-named salts, crystallizing generally in the regular system. Heated upon charcoal, many of the fluorides fuse, but without suffering decomposition. They impart no colour to the blow- pipe flame when added to a bead of microcosmic salt saturated with cupric oxide. The perfectly dry Hybbogen Sali of fluorine (HF), or hy- drofluoric acid, is behaved to be a transparent colourless gas under ordinary conditions, and to have no action on glass, &e. ; but, as usually obtained in the form of an aqueous solution, hydrofluoric acid is remarkable as one of the most powerful solvents known, dissolving such bodies as the silicic, titanic, 264 CHEMICAL EEACIIONS. molybdic, and tungstic anhydrides, •whicli are quite imattacked by all other acids. Fluorides vary considerably as to their solubility in water. The fluorides of the &8t subdivision are soluble; those of the second subdivision insoluble, thus exhibiting a remarkable con- trast with the chlorides, bromides, and iodides of the same group of metals. Most of the other protofluondes (MP) are insoluble, or but sparingly soluble m water, though slightly more soluble in aqueous hydrofluoric acid; they are often re- solved by excess of water, or on the application of heat, into oxyfluorides. The sesqui-, bi-, and terfluorides are very so- luble : the terfluoride of antimony, unlike the corresponding chloride, bromide, and iodide, is not decomposed by water with formation of the oxyfluoride. Since the fluorides of the second subdivision of the basic radicals axe insoluble, fluorine may be recognized by the for- mation of these salts, as also by that of the cuprous and plumbic fluorides. The Barium Salt is produced by the action of a soluble barium salt upon hydrofluoric acid or a soluble fluoride : it is a white precipitate. Its composition is BaF. It is insoluble in water, but readily dissolves in. hydrochloric, hydrofluoric, or nitric acid. The Steoniium Sam is produced by the action of a soluble strontium salt upon a solution of a fluoride : it is a white preci- pitate, insoluble in water and most acids. The Calcium Salt is produced by adding a soluble calcium salt to hydrofluoric acid or a soluble fluoride : it is generally a mere gelatiaous precipitate, hardly perceptible ; but on the addition of a little hydrate of ammonium, it becomes more visible. Its composition is CaF. This precipitate is somewhat soluble in solutions of ammonium salts; it is almost insoluble in water or in hydrofluoric acid, sparingly soluble in cold hydrochloric or nitric acid, but more soluble in these acids when hot. FLTJOBIBES. 265 The MAGNESruM Sam is produced by the action of a soluble magnesium salt on solutions of fluorides : it is a wbite pre- cipitate, nearly insoluble in water and acids. The Cuphous Sait appears to be insoluble both, in water and in hydrofluoric acid, but soluble in strong hydrochloric acid. The Siiteb Saxt is soluble. The Lead Salt is produced by the action of soluble lead salts upon hydrofluoric acid or a soluble fluoride : it is a white pre- cipitate, which easily fuses into a thick yellow liquid. Its for- mula is PbF. It is but slightly soluble in water or hydro- fluoric acid, more abundantly in hydrochloric or nitric acid. The MEECUEOTrs Salt is not produced by the action of soluble mereurous salts upon solutions of fluorides, but only by sublimation. The Mbbctjkic Salt is soluble. The Bismttth Salt appears to be soluble. The PLATHfOTJs and Palladiotjs Salts are not known. The other insoluble salts are not employed in testing for fluorine. Many of the remaining fluorine salts are soluble in water. Although the isolation of fluorine cannot be accomplished, we axe at no loss for a method of recognizing this elementary salt- radical, on account of the very remarkable affinity which it pos- sesses for silicon ; this fact is taken advantage of in two ways : — 1. In the etching test. A soluble or insoluble fluoride is placed in the dry state in a platinum capsule. A watch-glass is then taken to serve as a cover ; a little wax is melted in it, and al- lowed to run over every part, and through this coating a device is scratched with a wooden point, so as to expose the glass beneath. Several drops of strong sulphuric acid are then poured into the capsule, which is closed immediately afterwards -uith the coated glass, and then gently warmed, taking care not to melt the wax. The design traced on the cover wiU be found distinctly etched after the removal of the wax from the glass by means of tur- pentine or other solvent. The change described may be thus expressed, in the form of two equations : — 2MP+H, S0,=2HF-FM, SO, ; Si^O^ + 6HF=2SiF3-l-3H,0. 266 CHEMICAL KEACITONS. Thus the hydrofluoric acid first formed acts upon the silicoii contained in the glass, yielding water and the gaseous fluoride of siheon, the formation of which is itself an excellent test for fluorine. 2. The terfluoride of silicon test. A fluoride nuxed with some quantity of sand (81263) and of sulphuric acid, when heated, evolves, as has been already shown, gaseous terfluoride of silicon. The above mixture may be made in a test-tube (per- fectly dry), fitted with a cork and bent tube dipping under water in another glass vessel. When heat is applied, the tei-fluoride is immediately evolved, and, passing through the water, suffers the following decomposition : — 3SiF3-|-2H,0=HSiO,-|-H3 Si, F,. gelat. ppt. So rapid is the decomposition when the gas meets the water, that the aperture of the delivery tube soon becomes blocked with the silica deposited ; to avoid this, the point of the delivery-tube dips beneath a layer of mercury (fig. 7, p. 65). The formation of hydrofluosUicic acid (H3 Si, FJ, in the experiment just described, furnishes another proof of the presence of fluorine in the sub- stance examined ; this acid may be recognized by adding to the filtrate from the gelatinous precipitate of silica, a few drops of chloride of barium solution, when, after agitation, we obtain a gelatinous precipitate of silicofiuoride of barium (Ba, Si, F^), a salt with which the student has already become familiar. Sectiojt II. — The hypochlorites, chlorites, chlorates, perchhrates, hypobromltes, hromates, iodites, iodates, and periodates. SALTS or THE COMPOUND ACID-EADICALS WHICH CONTAIN CHLORINE, BROMINE, AJSTD IODINE COMBINED -WITH OXYOEN. Of the acid-radkrds containing chlorine comhined with oxygen, those existing in the acids or hydrogen salts, termed hypo- chlorous, chloric, and perchloric, are the most important in an analytical point of view. HTPOCHIOEITES. 267 SALTS OF THE HTPOCHLOEOTTS HABICAL, OK HTPOCHXOEITES. A few only of these salts are known ; they are extremely un- stable. The mode in which they are commonly produced is by passing chlorine either into a solution of hydrate of potassium or over solid hydrate of calcium ; the temperature of the materials must not be allowed to be more than lukewarm. 2CaH0 + 2a= CaClO + CaCa + H, 0. The hypochlorites are decomposed on a slight increase of temperature, and give no characteristic blowpipe reactions. The anhydrous hypochlorous acid (CljO) is a yellow gas, very soluble in water, and possessing a peculiar odour distinct from, and yet recalling, that of chlorine. Water dissolves more than 100 times its volume of the gas, and yields the hydrogen salt, or hypochlorous acid (HCIO). The gas (01,0) is a power- ful bleaching agent, yielding up both oxygen and chlorine, and indeed, from its great instability, decomposing readily, with ex- plosion, when gently heated. N'o insoluble hypochlorites are Tcnown; the aqueous solutions of the hypochlorites acquire a most sickly and disagreeable odour by contact with organic matter ; and in sunlight, or when heated, decompose into chloride and chlorate, with evolution of oxygen and chlorine. a. Hypochlorous acid, or a hypochlorite, may be immediately detected by warming the solution of the former, or by adding an acid to that of the latter, when, in either instance, their own peculiar odour is converted into the characteiistic odour of chlorine. The following equations represent the metamorphoses of a hypochlorite : — MClO -1- HC1= HCIO -I- MCI ; 2HC10=H,0+2Cl-|-0. /3. If a solution of a hypochlorite be mixed with a solution of a manganese salt, a brownish black precipitate of the bihydrate (MnH,0,) falls, thus— CaClO -F 2MnCl + 3H, = CaCl + 2MnH,0, -1- 2HC1. brown-black ppt. n2 268 CHEMICAL REACTIONS. y. If a solution of a typochlorite be mixed witt a solution of a lead salt, at first a white precipitate of plumbous chloride (PbCl) is produced (it must be remembered that hypochlorites are almost invariably accompanied by chlorides) ; this white pre- cipitate, however, speedily becomes brown, being converted, with evolution of chlorine, into the binoxide of lead (Pb^ OJ : 2PbCl + 2CaC10 = Pb, 0, + 2CaCl + 2C1. brown ppt. 3. If a solution of a hypochlorite be mixed with oxide of silver (Ag^O), the latter is rapidly converted into the chloride (AgCl) with violent evolution of oxygen, derived partly from the oxide of silver, and partly from the hypochlorite employed. If the same experiment be performed, only substituting the nitrate for the oxide of silver before used, a black precipitate, formerly believed to be peroxide of silver (Ag^O^), is deposited. e. The hypochlorites oxidize hydrosulphuric with formation of sulphuric acid and separation of sulphur ; by the addition of more hypochlorite, the sulphur is itself oxidized. The hypochlorites are recognized by the tests a, /3, y, and B, just described, and by their powerful bleaching action on indigo, litmus, and other vegetable colouring matters. SALTS OF THE CHLOROUS KADICAL, OK CHLOKITES. The chlorites do not occur in the course of analysis. The formula of the anhydrous acid is Cl^Oj, and that of the salts MClOj. Most of the known chlorites are readily soluble in water ; the argentic and plumbic chlo- rites are, however, nearly insoluble : the latter is a beautiful pale yellow precipitate, crystallizing in scales. The chlorites differ from the hypo- chlorites in the faet that their bleaching power is not destroyed by a solution of arsenious oxide in nitric acid. SALTS OF THE CHLOKIC EADICAL, OR CHLORATES. These salts are far more stable under ordinary circumstances than the hypochlorites ; the most common salt is that of potas- sium, which is generally prepared by passing chlorine into a solution of hydrate of potassium, and not preventing the conse- quent rise of temperature : GKHO -1- 6C1= KCIO3 -F 3H, -f SKCl. CHLOEATES. 269 The chlorates, when heated on charcoal before the blowpipe, deflagrate with great brilliancy, the charcoal being consumed and converted into carbonic anhydride, and a residue of chloride, oxide, or metal left, according to the nature of the basic radical present, unless indeed complete volatilization occur. The chlo- rate of barium imparts a green, that of strontium a crimson colour to the blowpipe flame. When heated alone in the solid state, the chlorates are decom- posed, any residue being either a chloride or an oxide, an evo- lution of oxygen also occurring. The Htdeogen Salt (IICIO3), or chloric acid, is only known dissolved in water ; in this state it is decomposed when heated above 40°. No insoluble chlorates are known ; some of the important re- actions of acids, &e. upon these salts are given in subsequent paragraphs. a. The chlorates are easily recognized by the peculiar decom- positions which their acid-radical suffers. When a chlorate is mixed with concentrated sulphuric acid, chloric acid (HCIO3) is evolved, thus — 2Ma03-|-H, S0,=2HC103+M, SO, ; as the temperature rises, the chloric acid decomposes, thus — 3HCIO3 = HCIO, + H, -t- CI, 0,. This decomposition is accompanied by a peculiar crackling noise, and the evolution of the greenish yellow gas, hypochloric an- hydride (Clj 0,), which, if the temperature rises too high, explodes with great violence. This gas has a most peculiar, almost aromatic odour, quite unlike that of chlorine ; but no sooner has the explo- sion and decomposition of the gas into oxygen and chlorine taken place, than the suffocating smeU of the latter gas may be directly perceived. Sulphuric acid acts much more readily upon chlorate of potassiiun when chloride of potassium is also present. /3. When a minute quantity of a chlorate is produced, and then rubbed gently in a mortar with a very small particle of sulphur, frequent and sharp detonations occur. 270 CHEMICAL REACTIONS. y. If a cUorate be mixed with an organic substance, such as sugar, the mass placed in a dish, and then a single drop of concentrated sulphuric acid allowed to fall from a glass rod upon the mixture, vivid combustion takes place, due, of course, to the liberation of chloric acid and its oxidizing effect upon the carbon and hydrogen of the sugar. S. A solution of a chlorate, even if somewhat dilute, when mixed cold with tiucture of litmus, and then a few drops of strong sulphuric acid added, bleaches the htmus. This test forms one of the best characteristics by means of which we can distinguish between the chlorates and nitrates. e. A solution of a chlorate mixed with a solution of indigo in sulphuric acid bleaches the indigo on the application of heat, just as a nitrate would do. ^. Hydrosulphuric acid does not decompose a solution of chlo- rate of potassium. The tests a. and S. are among those most usually employed for the recognition of the chlorates. SALTS OF THE PERCHLORIC RADICAL, OR PERCHLORATES. The perchlorates are remarkably stable ealfa ; the perehlorate of potassium withstands a higher temperature than the chlorate without decomposition, and is among the first products formed when chlorate of potassium is heated, since it is not itself resolved into chloride of potassium and oxygen, except at a more elevated temperature. Perchlorates, when fused upon charcoal, explode with violence ; but with combustible bodies in general they do not detonate so violently as the chlorates. The Hydrogen Salt (HCIO4), or perchloric acid, is a white crystalline solid, which melts at 45° C, and is very soluble in water. The potassic perehlorate is the only salt of the series which may be con- sidered comparatively insoluble. The Potassium Salt is obtained by the addition of certain soluble potassium salts (e.g. the carbonate [KjCOg]) to an aqueous solution of per- chloric acid, or by fusing chlorate of potassium at a gentle heat and for some time, and, after cooling, separating the chloride of potassium formed, from the perehlorate by water. It is a white crystalline powder. Its formula is KCIO4. It dissolves in 65 parts of water at 15° C, and in a smaller quantity of boil- ing water : it is quite insoluble in alcohol. BROMATBS. 271 The Ammonium Salt is produced by the addition of hydrate or carbonate of ammonium to aqueous perchloric acid : it is a white crystalline precipi- tate, very sKghtly soluble in alcohol, but requiring only 5 parts of cold water for solution. The barium and all the other known salts of the perchloric radical are soluble in water. The perchlorates are detected by the precipitation of the insoluble potas- sium salt, while they are distinguished from the chlorates by not becoming yellow on treatment with sulphuric acid (concentrated) in the cold. Of the acid-radicals containing bromine combined with oxygen, that existing in tlie acid (or kydrogen salt) termed bromic acid is the only important one in an analytical point of view. SALTS OF THE HYPOBBOMOnS KADICAL, OR HTPOBEOMITES. From the similarity of bromine to chlorine, and from the peculiar pro- perties of the solution formed when bromine is added to the carbonates or hydrates of potassium or sodium, the alkali being in excess, it is extremely probable that a series of hypobromites exist of the formula MBrO, pos- sessed of bleaching powers like the hypochlorites, and decomposing, When ignited, into bromide of the metal and oxygen. They are of no analytical importance. SALTS OP THE BEOMIO RADICAL, OR BROMATES. These salts resemble the chlorates in their general characters, and are produced generally by the action of bromine in excess on the hydrates and carbonates of the alkaline metals, with simultaneous formation of bromides. The bromates, when heated with charcoal or other combustibles, de- flagrate or detonate just as the chlorates. They are also decomposed when heated alone. The Hydrogeu Salt (HBrOj), or bromic acid, is known as dissolved in water ; but it is readHy decomposed upon the application of heat. The insoluble salts of this series which are most important are the ar- gentic, merourous, mercuric, and plumbic bromates. The Potassium and Ammonium Salts are soluble. The Barium Salt is produced by the action of a soluble barium salt on a moderately concentrated solution of bromate of potassium : it is a white crystalline precipitate, which requires 130 parts of cold, and 24 parts of boiling water for its solution. The Strontium, Calcium, and Magnesium Salts are soluble. The Cuprous Salt does not exist ; the Cupric Salt is soluble. The Argentic or Silver Salt is produced by the action of a soluble silver salt on a solution of bromic acid or other soluble bromate. Jt is a white precipitate. 272 CHEMICAL REACTIONS. Its formula is AgBrOj, This salt is insoluble, or nearly so, in water and in nitric acid, but dis- 6olTes in hydrate of ammonium. The Mbkcurous Salt is produced by the action of a soluble mercurous salt on solutions of bromates or of bromio acid : it is a yellowish white pre- cipitate. Its formula is Hg^BrOj. It is decomposed by washing with water, into bromic acid and a basic salt (HgjO, HgjBrOj) ; in hydrochloric acid it dissolves, with formation of mercuric chloride ; it is dissolred less easily by nitric acid. The Mercueic Salt is produced by the action of soluble mercuric salts upon solutions of bromic acid or of other bromates : it is a white precipitate. Its formula is HgBrOg+acj^. It is soluble in 650 parts of cold, and in 64 parts of boiling water ; it is dissolved by hydrochloric and by nitric acid. The Lead Salt is produced by the action of concentrated solutions only of lead salts on soluble bromates. It is a white precipitate, soluble in 75 parts of cold water ; and to it the formula PbBrOj -|-^aq has been assigned. Nearly all the remaining bromates that are known are insoluble in water. u. The bromates may be recognized, as easily as the chlorates, by the decomposition of their acid constituent ; but in their case, bromine, and not an oxide, is liberated. Thus, when sulphuric acid (concentrated), or even a dilute mineral or organic acid (such as acetic), is added to a solution of a bromate, oxygen and bromine are set free, and then the latter may be at once identified by its action on starch. p. A fragment of a bromate in powder, when rubbed in a mortar with such bodies as carbon, sulphur, or antimony, explodes or detonates. A similar result is obtained on heating the powdered mixture. y. Bromates mixed with sugar frequently cause the inflammation of the latter when the mixture is moistened with sulphuric acid. S. Bromates are decomposed by hydrosulphuric acid, — a white precipitate of sulphur being formed, and sulphuric and hydrobromic acids remaining in the solution. The bromates are recognized by the precipitation of the silver, mercury, and lead salts, and by the tests a. and /3. Of the acid-radicah containing iodine combined with oxygen, those existing in tlie acids or hydrogen salts, termed iodic and periodic acids are the most important in an analytical point of view. It is probable that the hypo-iodous (HIO) and iodous (HIO^) acids exist ; but nothing definite has as yet been ascertained con- cerning them. lODATES. 273 SALTS OF THE IODIC BADICAI,, OE lODATES. These salte are qmte analogous to the bromates, and may be prepared similarly, by the action of iodine on the alkaline hydrates and carbonates. They exist, however, in several closely -related modifications ; for, whUe to the ordinary iodates the formula MIO3 is assigned, there are also other salts represented by the formulse MjIiOn and MIjOj, all derivable from the action of iodic acid on metaUio oxides. A very remarkable series of salts will be found described in the observations upon the phosphates ; and we have already had peculiar instances among the sulpharseniates. Iodates, when heated, are converted either into iodides, with evolution of 3 equivalents of oxygen, or into oxides, with evolution of iodine and of a less proportion of oxygen or formation of periodates ; the former decom- position is that which the iodates of the first subdivision of basic radicals suffer, while the latter change is that experienced by the iodates of the second subdivision. The Hybbogen Salt, or iodic acid, may be made directly by heating iodine with nitric acid, or with nitric acid and chlorate of potassium. It is exceed- ingly soluble in water ; and the solution, which is syrupy, is extremely cor- rosive. Iodic acid, HlOg, when heated to 170° C, yields the iodic anhydride (Ij O5), which decomposes at a higher temperature into its constituents. The most important insoluble salts of this series are the argentic, mer- curous, and plumbic iodates. The Potassium and Ammonium Salts are soluble. The Barimn Salt is produced by the action of a concentrated solution of a barium salt on a soluble iodate ; it is a white granular precipitate. Its formula is BalOj-F^aq. It requires 1746 parts of water at 15°, and 600 parts of boiling water, to effect its solution ; it dissolves with difficulty in warm nitric acid. The Strontium Salt is soluble. The Calcium Salt is produced in the same manner as the barium salt : it is a white ciystalline precipitate, soluble in 260 parts of cold water, and in 75 of boiling water, but much more easily dissolved by nitric acid. The Magnesium Salt is soluble. The Cupeous Salt does not exist. The Cupeic Salt is produced by the action of cupric sulphates on iodate of sodium or iodic acid, and allowing the mixture to stand. If the precipitant were concentrated, the precipitate is bluish green ; if dilute, white. It dis- solves in 302 parts of water at 15°, or in 145 parts of boiling water, and is readily soluble in hydrate of ammonium. The Argentic or Silver Salt is obtained by the action of a soluble silver salt on a solution of a soluble iodate : it is a white precipitate. Its formula is AglOg. It dissolves in hydrate of ammonium, and sparingly in niti-ic acid ; by hydrochloric acid it is decomposed. N 5 274 CBBUICAL HEACIIONS. The Mebcueous Salt is obtained by the action of a soluble mercurous salt on solutions of iodic acid or iodates : it is a white precipitate, having a pearly lustre. It is slightly soluble in water, and is dissolved by most acids. The Meecuric Salt is soluble. The Lead Salt is produced by the addition of a soluble lead salt to a solution of an iodate or of iodic acid : it is a white precipitate, which dis- solves sparingly in water, and with difficulty in nitric acid. Most, if not all, of the remaining iodates that are known are compara- tively soluble in water. u. Iodates may be identified, with the same ease as bromates, by the de- composition of their acid constituent. This change is, however, generally effected by the action of a reducing agent, such as sulphurous acid gas (SOj), which separates iodine, this element being subsequently recognized by the usual tests. The strong acids generally liberate iodic acid from the iodates in solution. /3. Iodates detonate when heated with combustible bodies, or when the mixtures containing these bodies are struck ; the detonation is not nearly equal in violence to that of the chlorates, bromates, and nitrates when similarly treated. •y. If to a solution of an iodate a soluble iodide be added, and then a strong acid, the hydriodic and iodic acids, at the moment of liberation, act upon one another in the foEowing manner : — 7HI+HIOi=4H2 0-I-8I. The black precipitate, or brown colouration produced in the solution, is an excellent indication of the presence of iodine. S. Iodates are decomposed by hydrosulphuric acid, a white precipitate of sulphur being formed, and sulphuric and hydriodic acids remaining in the solution. The iodates are recognized by the precipitation of the barium, silver, and lead salts, and by the tests a, y, and d. SALTS OF THE PERIODIC RADICAL, OR PERIODATES. The periodates are, in some respects, similar to the perchlorates. They resemble the iodates in the faciUty with which they pass into new modi- fications possessing a different proportion of the basic constituent. The formula of the normal periodates would be MIO^ ; but others are known, to which the formula M^I^Oj, MjIO^, MjHjI^Ojj, &c., have been assigned. Most of the insoluble periodates belong either to the second or third of these classes. Heated on charcoal or with other combustibles, periodates detonate, but not violently ; when heated alone, they behave in a similar manner to the iodates. The Hydrogen Salt, or periodic acid, may be obtained in colourless PEEIODATES. 275 crystals (HI0j+2aq), which dissolve readily in water; the solution may be boiled without decomposition. Among the insoluble periodates the sodium, barium, SLlver, mercurous, mercuric, and lead salts are the most important. The Sodium Salt is obtained by passing chlorine through an aqueous solution of carbonate of sodium, and adding iodine ; also in other ways. It is a pearly, white, crystalline precipitate. Its formula is Na^I^O^+Saq. It is insoluble in cold, but sparingly soluble in hot water ; it is easily so- luble in acids. The normal salt (NalO,,) is very soluble in water. The Potassium Salts (KIO4 and KjI^Oj) are soluble. The Barium Salts (BajIO^ and Ba^HjIjOj^) are produced in several decompositions, generally by the action of the soluble periodates of sodium. They are insoluble in water, but dissolve in dilute nitric acid. The Strontium and Calcium Salts are not well known, but are believed to be insoluble. The Magnesium and Cupkous Salts are unknown. The Cupkic Salt is a light green precipitate, soluble in dilute nitric acid. The Argentic or Silver Salt is produced by the addition of nitrate of sUver to the solution of periodate of sodium in dilute nitric acid, and falls as a light yellow crystalline powder, to which the formula Ag^I^Og has been given. It is insoluble in water, sparingly soluble in nitric acid. The Mekcueous Salt is said to be produced by the action of mercurous nitrate on the Soluble periodate of sodium (NalOj). It is a yellow pre- cipitate, which when warmed becomes reddish brown ; it is easily soluble in dilute acids. The Meecueic Salt is said to be" produced by the action of mercuric nitrate on the soluble variety of periodate of sodium. It is a white pre- cipitate, which when heated becomes yellow ; it is soluble in dilute nitric acid. The Lead Salt is produced by the addition of a solution of plumbic nitrate (PbNOj) to an aqueous solution of the normal periodate of sodium, as a white precipitate, nearly insoluble in water, but soluble in dilute nitric acid. The Palladious and Platinous, and several other salts are unknown. Some of the remaining periodates that are known are soluble ; a few, chiefly belonging the class M4 Ij Og, are insoluble. The periodate of sodium (Na^I^Oj) is the most characteristic salt of the present series. 276 CHEMICAL KEACTIONS. Sbctiok III. — Th^ cklorocadmiates, chloropalladiates, chloroplaiinates, chloro- rhodiates, chlororutheniates, chloriridiates, and chlorawates, ^c. SALTS OF THE COMPOUND ACID-BADICALS WHICH CONTAIN CHLOBINE, BEOMINB, AND IODINE COMBINED "WITH METALS. The radicals contained in the salts of this section are monobasic; and consequently the general formula of these salts wiU be ME. The chloro- cadmiates are represented by the expression MCdClj, the chloropalladiates by MPdClj, the chloroplatinates by MPtClj, and the chloraurates by MAuClj. The other acid-radicals containing a metal and chlorine haye 3 equivalents of the latter element. Many corresponding compounds con- taining bromine and iodine combined with metals are also formed, but they are as yet but imperfectly known. TABLE OF SALTS. CI (see page 254) Br (see page 256) I (see page 260) (see page 263) Potassium ... — — — — Barium — — — white Strontium ... — — — white Calcium — — — white Magnesium . . Cuprous white white brownish 1 white J white red Cuprio — — — — Silver white white yellow white Mercurous . . . white white green white Mercuric . . . Lead white f white \ crystalline j scarlet orange- 1 yellow I crystalline J yellow white TABLE OP KEACTIONS. 277 These radicals may be recognized best by the insoluble salts which they yield with certain basic radicals, chiefly potassium, ammonium, and the organic compound ammoniums. These insoluble salts are almost all of a yellow, orange, brown, or red colour; and as they have been named or described under their respectiye metals, they need not be again noticed here. These radicals may also be identified by their deoompositiou into new products, &c. When, for instance, a stream of hydrosulphuric acid gas is passed through a neutral or acid solution of chloroplatinate of sodium, one of the products of the reaction is sulphide of platinum. This reaction, de- scribed in the appended equation, takes place with all the salts of the acid- radicals contained in this section : — 2KPtCa3-l-2H.,S=2Ka+4HCH-Pt2S2. REACTIONS. CIO CIO3 BrOa lOa PtCla (see page 267) (see page 269) (see page 271) (see page 273) (see page 220) — — ' white 1 crystalline J white orange- ] yellow crystalline J — : — r white 1 \ crystalline/ : ~'~' : : bluish green — — white white — — — f yellowish \ white white pearly — — — white — — — — white white — 278 CHEMICAL EEACTIONS. Analysis of Subdivision I. The acid-radicals of more common occurrence only being included, the salt may be a CHLOEIDE, BEOMIDE, IODIDE, FLU- OEIDE, HYPOCHLOEITE, CHLOEATE, BEOMATE, 10- DATE, or a CHLOEOPLATINATE. Evidence of the presence of any one of these salt-radicals may be ob- tained by adding to the solid salt, or its strong solution, some concen- trated sulphuric acid. The following effects vriU be produced, either immediately or on war min g the mixture : — Pungent colourless Tapours (of HCl) indicate a chloride. „ red-brown „ (of Br) indicate a bromide or bromate. ,, violet „ (of I) indicate an iodide or iodate. „ (of HI'), etching gla^s, indicate a fluoride. „ (of CljO), having the odour of bleaching- powder, indicate a hypochlorite. orange yellow „ (of Cl^ O^), explosive, indicate a chlorate. Further Analysis. Through the solution of the salt, pass hydrosulphuric acid gaa. A black precipitate of PtjSjWould indicate the presence of PtCL. If no precipitate, the solution may contain 01, Br, or I; any CIO, BrOj, or IO3, would have been decomposed by the passage of the hydrosulphuric acid. Boil to expel HjS ; add nitrate of silver. A white or yellow precipitate falls, of AgCl, AgBr, or Agl. Add ammonia, and warm. Yellow residue of Agl indicates I. If wholly dissolved, test a por- tion of the original solution by means of Mn, O, and H.SO . for CI or Br. SALTS or OXYGEN, ETC. 279 SUBDIVISION II. SALTS OF OXYGEN, SULPHUR, SELENIUM, AND TELLU- RIUM, AND OF THE CHIEF COMPOUND ACID-RADI- CALS INTO THE COMPOSITION OF WHICH THEY ENTER. Tlie members of this subdivision present many analogies with those of the preceding ; three of them, sulphur, selenium, and tellurium, bear the closest relation to each other, exhibiting a curious progression towards the basic character, whilst a fourth, oxygen, has a more distant resemblance. In addition to the salts which these form by direct combination with basic radicals, there are many others in which sulphur, selenium, and tellurium exist in the form of a compound acid-radical containing oxygen or a metal. The majority of the salts of this subdivision are bibasic ; some, however, are tribasic. Section I.— SALTS OF OXYaSN, SULPHUR, SELENIUM, AND TELLURIUM. The oxides, sulphides, selenides, and teUurides. SECTioif II.— SALTS OF THE COMPOUND ACID-RADICALS WHICH CONTAIN SULPHUR, SELENIUM, AND TELLURIUM COM- BINED WITH OXYGEN OR AMONG THEMSELVES, The hyposidphites, sulphites, hyposulphates, trithionates, tetra- thionates, pentathionates, and sulphates ; the selenites, seleniates, tellurites, and telluriates. Section IIL — SALTS OP THE COMPOUND ACID -RADICALS WHICH CONTAIN OXYGEN AND SULPHUR COMBINED WITH METALS. The aluminates, chromites, chromates, perchromates, ferrites, ferrates, manganates, permanganates, bismuthates, stannates, metastannates, platiaates, rhodiates, rutheniates, iridiates, os- mites, osmiates, aurates, tungstites, tungstates, molybdates, va- nadites, and vanadiates ; the sulphostannates, sulphoplatinates, 280 CHEMICAL BE ACTIONS. sulphorliodiates, siilphorutheniates, sulphiridiates, sulphosmiates, sulphaurates, sulphotungstates, sulphomolybdates, and sulpho- vanadiates. Sectioit I. — The oxides, sulphides, selenides, and tellurides. SALTS OP OXXaEN, SULPHUE, SELENIUM, AND TELLTIRnjM. We tave already seen that these four acid-radioals are bibasic, and that the following formulae are some of those which belong to the various combinations of metals with oxygen— (M2)2 0, MjO, (MJjOj, MjOj, M^Og, M2O5, — whUe, besides these common oxides, which can exist in the isolated condition, there are many others which play the part of acid-radicals, and are only known to us in combination with a basic constituent : such compounds are represented by the following formulae among others : — MO, M0„ MO3, MO^, M^O,, M,0„ &e. And in addition to these hy- pothetical compounds of metals with oxygen, there are numerous existing combinations of oxygen with other acid-radicals. What has been here said concerning oxygen, is true also as regards sulphur, and to a great extent with reference to selenium and tellurium. In common with other polybasic radicals, the members of the present subdivision possess the power of combining with, and uniting in one salt, separate single equivalents of two different basic radicals ; and although, in the class before us, one of these basic bodies is invariably hydrogen, yet, in salts containing more complex acid-radicals, two different metals are frequently com- bined with one and the same equivalent of acid-radical. The hydrates and sulphydrates already mentioned are salts in which this peculiarity occurs (1 eq. of hydrogen and 1 eq. of metal are united with a single equivalent of the biatomic radical oxy- gen) ; and they are comparable with the oxides and sulphides, in which 2 eqs. of metal are united with a single equivalent of the biatomic radical : — Oxides. Hydrates. Sulphides. Sulphydrates. MMO. MHO. MMS. MHS. OXIDES. 281 The salts of the present suhdivision may be recognized by the employment of the same means that are used for the detection of the members of the preceding subdivision : i. e., 1st, by the for- mation of insoluble compoimds ; 2nd, by their decomposition, and the subsequent recognition of their acid- element. SALTS OF OXTSEN, OE OXIDES. There are very many oxides known ; as a general rule they may be regarded as very stable salts. Many oxides are of bril- liant colours ; some are -white. Several of the oxides which occur in nature, and also of those which have been fused or crystallized, possess a metaUic lustre. Oxides, when heated upon charcoal, are frequently reduced to the metallic state ; some, indeed, are thus decomposed by heat alone, others by the joint action of heat and of the affinity, for the oxygen of the salt, which the carbon exerts. There are oxides, however, which can be decomposed only by the most powerful chemical agencies. The various blowpipe reactions of the metallic oxides have been already described under their re- spective metals. The Htdeaie of Hydrogen (HHO), hydric acid, or water, is a body too weU known to need description : it plays the part of an acid, exchanging 1 eq. of hydrogen, under suitable conditions, for an equivalent of a different basic radical ; but so nicely are the opposing properties Of its constituents balanced, that it is a very stable body, and is quite neutral with reference to a great many salts. This neutrality, combined with its vast solvent power on solids, liquids, and gases, renders water of the utmost service in chemical operations ; and in this capacity of a solvent it cannot be replaced by any known substance. The presence of water in certain salts as water of crystaUization or of hydration is little understood; but perhaps it is connected in some way with this neutrality of which we have been speaking. There is no oxide known which is soluble in water without de- compQsition ; for all the oxides upon which water seems to exert a solvent action are in fact decomposed by it. When water is 282 CHEMICAL EEACIIONS. viewed as hydric acid, this ciange becomes intelligible; with oxide of potassium it may be represented thus — KKO+HHO=KHO + KHO. Water, indeed, may be regarded as the normal oxide of hydrogen, but, being itself the universal solvent, cannot be regarded as soluble. The presence of oxygen cannot be well ascertained by double decompositions in which oxides and hydrates are precipitated ; it is always preferable to employ other means. Those me- thods which are admissible are of two kinds : in one we prove the absence of all other salt-radicals except oxygen ; and in the other we detect the oxygen by the decomposition of the salt under examination. For the sake of comparison with the salts of other acid-radicals, we give a few of the more important insoluble oxides and hy- drates, produced by the action of a solution of hydrate of potas- sium on the different metallic solutions, neither reagent being in excess. The Potassium, Sodium, and Ammonium Salts (hydrates) are very soluble in water. The Baeiitm, Stbontium, Calcium, and Magnesium Salts (hy- drates) are somewhat sparingly soluble. The Cupeous Salt ([Cu^J^O) is orange-yeUow. It is soluble in most acids. The Cupeic Salt (CuHO) is blue. It is soluble in hydrate of ammonium, and in most acids. The Silvek Salt (Ag^O) is brown. It is soluble in hydrate of ammonium, and in most acids. The Mercueous Salt ([Hg^J^O) is brownish black. It is soluble in most acids. The Mercuric Salt (HgHO, H^O) is yeUow. It is soluble in most acids. The Lead Salt (PbjHOj) is white. It is soluble in most acids. The other oxides and hydrates have been already described under their respective metals in Chapter YI. SITLPHIDES. 283 a. The negatiye evidence mentioned above as being employed in the identification of the compounds of oxygen, will not need further description; but the method of recognizing the salts of the radical now under consideration, by its elimination, may be here noticed. ft. The oxides which can be decomposed into metal and oxygen by the mere action of heat are few in number. Of these the oxygen salts of silver, mercury, and gold are the most important. Lead also, under certain circumstances, may be obtained by heating its oxide. If a small quantity of oxide of sUver (Ag^O) be heated in a dry test-tube, it wiU. readily split into metallic silver and oxygen gas, the latter being easily recognizable by the usual test, — ^the insertion, into the vessel used for the experiment, of the glowing end of a wooden match which has been previously Kghted, allowed to bum for a minute, and then blown out. If there has been only a small quantity of oxygen liberated, the red- hot end of the match wiH only glow more brightly ; but if a con- siderable amount, it will be rekindled. SALTS OP STJIPHUE, OE SULPHIDES. A great resemblance exists between these salts and the oxides, some of them possessing remarkably brilliant colours, others again being of an intense brown colour, or even black. When fused, or naturally ocourritig in crystals, many sulphides have a peculiar metallic lustre. To these salts belong the same formulae as those given under the salts of oxygen. When heated before the blowpipe, sulphides axe generally de- composed, the sulphur they contain being oxidized iato the sul- phurous or sulphuric radical, which remains combined with the metal ; but, on the other hand, when the sulphites and sulphates thus produced are heated on charcoal, they are for the most part reduced to the state of sulphide. Sulphides, when heated alone iu the air, often yield the oxide, and sometimes even the metal. The Hydeooen Salt (H^ S), hydrosulphurie or sulphydric acid or sulphuretted hydrogen, is a gas at ordinary temperatures and pressures, possessing a pecidiarly disagreeable and sickly 284 CHEMICAL REACTIONS. smell, and being very poisonous and narcotic. It may be con- densed, by combined cold and pressure, into a colourless transpa- rent liquid, more mobile and less adhesive even than ether, while by further cold it may be made to assume the solid form, and then appears as a white crystalline mass. The gas has a density of 1-191. Water dissolves about its own volume of sulphuretted hydrogen at the common temperature, forming a solution which, by exposure to the air, oxidizes, a deposit of sulphur taking place. The gas is combustible, burning vidth a blue flame, and may be ignited at a comparatively low temperature, as by a red-hot coal ; the products of its combustion are sulphurous anhydride (SO^) and water : H,S+30=H,0 + S0,. Most sulphides are insoluble in water, although many are soluble in acids. The sulphides of the first and second subdivi- sions are, however, soluble in water, though it may be presumed that they really undergo a decomposition during solution, be- coming partially converted into sulphydrates, just as certain oxides yield hydrates under similar circumstances : KKS -I- HHO =KHS + KHO. With hydrosulphuric acid solution instead of water only, 2 eqs. of the sulphydrate are formed : KKS-1-HHS=KHS4-KHS. The chief insoluble sulphides have been already described imder their respective basic radicals ; for the sake of comparison, however, with the salts of other acid-radicals, we give a list of the more important, premising that, of the insoluble sulphides given, all but the six first are precipitable from their neutral solutions by sulphuretted hydrogen. The PoTASsitTM, Sodium, Ammonium, Barium, Strontium, Cal- cium, and Magnesium Salts are soluble. The Ferrous (Fe^ S) and Ferric ([Fe J^ S3) Salts are black. The Manganous Salt (Mn^ S) is buff or flesh coloured, and soluble in dilute acids. The Cobait (Co^ S) and Nickel (Ni^ S) Salts are black, and soluble in dilute acids. SULPHIBES. 285 The Znrc Salt (Zn^ S) is ■white, insoluble ia water, but soluble in dilute acids. The Cabmujm Sam (Cd^ S) is bright yellow. The CuMiOTTS ([Cu^J^ S), Ctjpkic (CUj S), Siltee (Ag^ S), Meh- CTJROus ([Hgjj S), Meecttbic (Hgj S), Lead (Pb^ 8), and Palla- Dious (Pdj S) Salts are black or brownish black, and insoluble or nearly so La cold water and ia dilute acids. The cupric sul- phate is easily oxidized by atmospheric oxygen into the sulphate. The Stannoits Salt (Sn^ S) is brownish black. The Staiwic Salt (Sn^ S^)) is white, iacliaing to yeUow. The AsTTiMONioTrs (Sb^ S3), AifiiMoific (Sb^ S,), Abseniotjs (As^ Sg), and Absenic (As^ S^) Salts are of a fine orange yellow colour, inclining to red. The presence of sulphur in its compounds may be recognized also by processes of decomposition : — a. Most sulphides, when warmed with strong hydrochloric or sulphuric acid, decompose with evolution of hydrosulphuric acid gas (the odour of which is so characteristic), and occasionally also with separation of sulphur : M,S+H,SO,=H,S+M,SO,. When nitric acid is employed, the sulphide is generally oxidized and converted into the corresponding sulphate or nitrate (see 2.). jS. When an insoluble sulphide is fused with carbonate of sodium on charcoal, sulphide of sodium (Na^ S) is formed ; and if the mass be then scooped out, laid on a silver coin and moistened with water, a black stain (Ag^ S) is immediately produced. y. When hydrosulphuric and sulphurous acids meet in the presence of water, a white or very pale yeUow precipitate of sul- phur is produced, while the solution wiU be foimd to contain an acid known as pentathionic (H^ S^ Oj) : 5H, S-I-5H, S03=H, S,0, + 9H,0-|-6S. white ppt. 2. Very generally, when sulphides are boiled with nitric acid, a separation of sulphur takes place, and the latter substance often fuses and floats as an oily globule upon the surface of the liquid, solidifying, on cooling, in the form of a little circular cake. 286 CHEMICAL EEACTIONS. This action of nitric acid also gives rise to the simultaneous for- mation of sulphuric acid, and to the most highly oxygenated com- bination which the metal of the sulphide employed is capable of forming : thus with ferrous sulphide — ^^ 2^6, S-(-10HNO3=2re, (N03)3 + H, S0,-|-4H,0 + S+2N,0,. ferrous ferric nitrate, sulphuric ppt. sulphide. acid. e. A very exceEent test for the presence of sulphur in the form of a soluble sulphide (and by process /3. aU insoluble sul- phides may be made to yield the soluble sulphide of sodium) is found in a solution of nitroprusside of sodium. The most minute trace of sulphur is discoverable by the magnificent violet or purple colour which a drop of a dilute solution of this reagent imme- diately produces. Hydrosulphurio acid and other soluble salts of sulphur are usually detected by the formation of coloured metallic sulphides, and particularly by their action on lead salts (which, for this purpose, may be apphed in the form of aqueous solution to strips of white paper), and also by the tests a, p, y, e. SALTS or SELENIUM, OE SELENIDES. A most marked resemblance exists between the selenides and sulphides ; they do not, however, possess the same Tariety of brilliant colours, most of them, when freshly precipitated by hydroselenic acid (H^ Se) being brownish black or flesh-coloured. Natural selenides often possess a metallic lustre. When heated on charcoal in the air, the selenium of these salts burns slowly with a reddish blue flame, with evolution of a most powerful odour of horse-radish, due to the formation of a gaseous oxide of selenium, probably SeO. Selenium is more slowly expelled from selenides, by this process of "roasting," than sulphur from sulphides. The Hydrogen Salt (H^ Se), hydroselenic acid or seleniuretted hydro- gen, is a gas under ordinary circumstances, of specific gravity 2795. At first, its smell seems to resemble that of the corresponding sulphur acid ; but it subsequently painfully affects the mucous membrane of the nose, and destroys the sense of smell. It is intensely poisonous. It burns with a bluish flame. It is more soluble in water than hydrosulphuric acid ; the aqueous solution decomposes by exposm-e to the aii-, depositing seleniimi in red flakes. Most selenides are insoluble in water ; but they hare not been much studied. The Potassium and Sodium Salts are the best known soluble selenides. TELLTJErDBS. 287 The Barium and Stkontium Salts are soluble, the Calcium and Mag- nesium Salts nearly insoluble in water. The Manganese Salt is pale red, the Zinc Salt yellow ; they are both insoluble in water. The Cupeio, Silver, Mekcukio, and Lead Salts are black, beeoming grey on drying ; they are insoluble in water or neutral solutions. The presence of selenium in its compounds may be readily recognized by several processes of decomposition : — a. Upon treatment of a selenide with hydrochloric or sulphuric acid, hydroselenio acid is evolved, which may be recognized by its peculiar odour. Nitric acid generally converts selenides into selenites, with occasional sepa- ration of selenium. ;8. A selenide fused with carbonate of sodium on charcoal, transferred to a silver surface, and moistened with hydrochloric acid, will produce a black stain. y. Sulphurous acid produces, in an aqueous solution of hydroselenio acid, a bright reddish precipitate of selenium. 5. Selenides heated on charcoal with carbonate of sodium or miorocosmic salt, give the characteristic odour of horse-radish. 6. To detect traces of selenium, it is recommended to fuse the substance under examination with hydrate of potassium, to dissolve in water, filter, and expose the solution to the air ; if selenium be present it will slowly appear, causing a reddish turbidity, or it vrill separate in reddish flakes. Selenium may be conveniently recognized by the tests S. and e. SALTS OF TBLLUHIDM, OB TELLUEIDBS. These salts greatly resemble the selenides ; they, however, partake more of the character of alloys (or combinations of metals with one another) than of that of saline compounds. In teUurides the metallic appearance of the basic radical is scarcely masked by the tellurium ; even the potassium salt has a metallic lustre. The tellurides of the heavy metals, obtained by passing telluretted hydrogen through their aqueous solutions, are generally brown or black, and insoluble in water. When tellurides are heated on charcoal before the blowpipe, the tellu- rium burns with a blue flame edged with green, and emits a peculiar odour, different from that of selenium. The Hydeogen Salt (H^ Te), hydrotelluric acid or telluretted hydrogen, is a gas of specific gravity 4'489, its odour somewhat resembling that of the corresponding sulphur compound. It is poisonous. It is absorbed by water, imparting to that solvent a pale red colom- ; the aqueous solution, by exposure to the air, becomes brown, from separation of tellurium. Most tellurides are insoluble in water ; but they have not been much studied. The Potassium and Sodium Salts are soluble in water. The Cupeic, Silver, Mercuric, and Lead Salts are brown or black pre- cipitates, insoluble in water. 288 CHEMICAL EEACTIONS. The presence of tellurium in its compounds may be readily recognized by BCTeral processes of decomposition : — u. A telluride treated with hydrochloric acid CTolves telluretted hydrogen, the odour of which is characteristic. Nitric acid converts tellurides into tellurites. p. A telluride fused with carbonate of sodium on charcoal, transferred to a silver surface, and then moistened with hydrochloric acid, imparts a brown stain to the metal. y. Sulphurous acid and several other similar reagents produce, in aqueous solutions of hydrotelluric acid, a dark brown precipitate of tellurium. S. If a telluride be fused with hydrate of potassium, the fused mass dis- solved in water, and the solution exposed to the air, tellurium will be pre- cipitated. Section II. — The Jiyposvilphites, sulphites, hyposulphates, tri- thionates, tetrathionates, pentathwnates, and sulphates ; the selenites, seleniates ; tellurites, and telluriates. SALTS OF THE COMPOUND ACID-RADICALS WHICH CONTAIN SULPHUE, SELENIUM, AND TELLURIUM COMBINED WITH OXYGEN OR AMONG THEMSELVES. The aoid-radicals which contain oxygen, sulphur, selenium, and tellurium are hihasic, like these elements themselves. A sulphate, just like a sulphide, may contain two different basic radicals — 1 eq. of a metal, for instance, together with 1 eq. of hydrogen. With the sulphurous and several other acid-radicals of the present section, such compound or double comhinations are known to occur ; and the remainder have not as yet been sufficiently investigated. Of the acid-radicals containing sulphur combined with oxygen, those existing in the acids or hydrogen salts termed hyposul- phurous, sulphurous, and sulphuric are the most important in an analytical point of view. SALTS OF THE HYPOSULPHUROUS RADICAL, OR HYPOSULPHITES. The hyposulphites of the first and second subdivisions of the basic radicals are best known ; and from them most of the other hyposulphites may be pre- pared. They may be formed in various ways : when, for instance, an alkaline sulphite is boiled with sulphur, the sulphur is dissolved in considerable quantity, the following reaction taking place : — K,S03-|-S=K,S.,0,. HYPOSULPHITES. 289 The sodium salt is largely prepared, and may be made by boiling a strong solution of the hydrate with excess of sulphur, and then passing sulphurous acid gas (SO^), evaporating and crystallizing the solution. Many hyposulphites, when heated on charcoal, yield a large quantity of the corresponding sulphides. When heated alone with access of air, they yield water, sulphurous acid, and sulphates ; out of contact of air they are resolved into water, hydrosulphurie acid, and sulphur, which volatilize, while a mix- ture of alkaline sulphides, sulphites, and sulphates remains. The hyposulphites of the first and second subdivisions of the basic elements are tolerably stable if kept out of contact of air ; but the remainder are ex- ceedingly unstable, and can scarcely be said to exist. Hyposulphurous an- hydride (Sj (\) is itself a very unstable substance ; but its elements being capable of uniting in other proportions to form compounds of extreme stabi- lity, readily yield such products: any excess of sulphur left uncombined with oxygen is either precipitated or, by entering into combination with a portion of the metal present, produces a sulphide. Thus hyposulphite of silver (Ag2S2 03) undergoes the following cha-ngee on heatiug, or by standing : — Ag, S, 03-l-H,0=Ag, S-l-H, SO,. white black hyposulpliite sulphide of silver. of silver. The Hybeogen Salt (H^S^Oj), or hyposulphurous add, is believed to be produced when hyposulphites are decomposed by stronger acids, as when hyposulphite of lead is diffused in water at 0° C, and a stream of hydro- sulphuric acid gas allowed to act upon it, — sulphide of lead being precipi- tated, and hyposulphurous acid obtained in solution. This acid, however, speedily decomposes, thus — H2S,0,=H2S03-(-S. hypo- sulphurous sulphurous acid, acid. The hyposulphites may be recognized by the formation of certain insoluble salts, and by the decomposition of their acid-radical. The hyposulphites of the first and second subdivisions of basic radicals are soluble, with the exception of the barium salt. Neai-ly all the remaining salts are, as far as known, insoluble in water. The Potassium and Sodium Salts are soluble. The latter is much em- ployed in photographic processes, for dissolving iodide, bromide, and chloride of silver. The Barium Salt is produced by the action of a soluble barium salt on a tolerably concentrated solution of hyposulphite of sodium (Wa2S2 03). Its formula is Ba^ S^ O3 + aq. It is somewhat soluble in water, soluble in hydro- chloric acid, while with nitric acid it is converted into the sulphate. The Strontium, Calcium, and Masnesium Salts are soluble. The Ferrous, Cuprous, and Cupric Salts, also many other salts of the 290 CHBMICAI EJBACTIOIfS. metals contained in the third and fourth subdiviBions of the basic radicals, are soluble in water. The Silver Salt ia a white precipitate, which becomes yellow, red-brown, and finally black, sulphide of sUTer being produced. Its formula is Ag^ S^ O3. It is slightly soluble in water, and very soluble in alkaline hyposulphites ; if to this solution a soluble chloride be added, it gives no precipitate when excess of alkaUne hyposulphite is also present. The Mercueous Salt does not appear to exist, a black precipitate of sul- phide being produced. The Meecukic Salt is white or yellow, becoming brown or black on boiling, from formation of mercuric sulphide. The Lead Salt is a white precipitate, which becomes black below 100°- Its formula is Pb^ S^ O3. It is soluble in 3266 parts of water, and easily dissolves in alkaline hyposulphites. By nitric acid it is converted into the sulphate, which is very insoluble. The hyposulphites may also be recognized by the following processes of decomposition : — a. When an acid is added to a soluble hyposulphite, an immediate pre- cipitation of stdphur occurs, the hyposulphurous acid set free being at once resolved into sulphurous acid and sulphur : ]Sra2S2 03-(-2H01=2NaCl-|-H20-fS02+S. ppt. The sulphurous acid (H^ SO3) decomposes instantly into water and sulphu- rous anhydride, the latter being readily recognizable by its odour. /3. When a hyposulphite is fused with carbonate of sodium on charcoal, a sulphide is obtained which, when treated with an acid upon a silver surface, gives a black stain of sulphide of silver, while hyposulphites previous to fusion give no such result. y. When a soluble hyposulphite is brought in contact with a hydrochloric solution of stannous chloride, a brovm precipitate of stannous sulphide is produced. This radical is generally recognized by the decompositions which its various combinations so easily undergo. The changes which the hyposulphite of silver suffers, and the tests a, 13, and y. are perhaps the most characteristic examples of these methods of identification. SALTS OP THE STJLPHTJKOTJS EABICAI, OE StTLPHIIES. These salts are iDibasic. They are of much, easier production than the hyposulphites, and are much more stable. Sulphurous anhydride (SO^) is produced whenever sulphur is burnt in the air ; and from it the sulphites may in general be obtained. Sul- phites have a tendency to absorb oxygen from the air, especially when kept moist or ia solution, and by so doing pass into sul- phates : suiPHiTEs. 291 M,S03+0=M,S0,. On account of this property, sulphurous acid and other sulphites are employed as reducing agents. Heated on charcoal, many sulphites yield the corresponding sulphides, while others are reduced to the metallic state. The Htdeoqen Salt (H^ SO3), sulphurous acid, is known to exist only in comhination with water, the compound having the formula H^SO^ + Saq, and occurring in white crystals. It is decomposed with great readiness into the substance known as sulphurous anhydride, or sulphurous acid gas (SO^), and water. This gas has a density of 2 '222; its odour is most unpleasant, and produces a painful choking sensation. By a cold of —12° it may be liquefied, and at a lower temperature it may even be 8olidifi.ed ; it may also be rendered liquid by the pressure of from three to five atmospheres at the ordinary temperature. The sulphites may be recognized not only by the formation of insoluble salts, but also by the transformation and decomposition of their acid-radical. The majority of the sulphites are insoluble in water and in saline solutions. The sulphites of the alkaline metals and the acid sulphites (MHSOj) are, however, soluble. All sulphites are readily soluble in weak acids, the sulphurous acid being easily displaced. Of the iusoluble sulphites the most interesting and characteristic are the barium, cuprous, argentic, and plumbic salts. The Potassittm and Sobiteu: Salts are soluble. The Barium Salt is produced by the action of soluble barium salts on solutions of the alkaline sulphites. It is a white preci- pitate, having the formula Ba^SOg. It is scarcely soluble in water, but soluble in sulphurous, hydrochloric, and dilute nitric acid, if the sulphite were quite free from sulphate. Upon slightly heating the nitric acid solution, the sulphite of barium it con- tains is converted into sulphate, which, being very insoluble, is immediately precipitated. The Cuprous Salt is obtained when a eupric salt is mixed with an alkaUne sulphite, the cupric sulphite first formed spKtting o2 292 CHEMICAL EEACTIONS. into cuprous sulphite, cupric sulphate, and sulphurous an- hydride ; 3Cu, SO3 = (CuJ, SO3 + Cu, SO, + SO,, cuprous sulphite. It is a light brown precipitate, scarcely soluble in ■water, soluble in ammonia water and dilute sulphuric acid, but decomposed by most acids. The Argentic or Silver Salt is precipitated from silver salts by a soluble sulphite, as a white granular precipitate, which, when boiled in the solution from which it has been deposited, decom- poses into metallic silver, and sulphuric acid which remains in solution. The formula of the argentic sulphite is Ag, SO3. It dissolves in alkaline sulphites, and in ammonia water, but scarcely in sulphurous acid or water. The Meecuet Salts do not appear to exist. The Lead Salt is a white precipitate, which has the formula Pb, SO3, and which is insoluble in water, decomposed by strong acids, and by nitric acid especially ; with the aid of heat it is converted into sulphate. Sulphites may also be recognized by the decomposition of their acid-radical : — a. Sulphurous acid, when produced by the action of strong acids (such as hydrochloric acid) upon sulphites, decomposes in- stantly into sulphurous anhydride (SO^) and water, no sulphur being precipitated. /3. Sulphites fused with carbonate of sodium on charcoal yield sulphide of sodium, which may be recognized by its action on metallic silver. y. A hydrochloric solution of stannous chloride added to a soluble sulphite produces a gradually increasing precipitate of brown sulphide of tin. But if to the solution of a soluble sul- phite some quantity of hydrochloric acid be first added, and sub- sequently some stannous chloride, — and if, under the glass plate which covers the containing vessel, a slip of lead paper be sus- pended, this latter wiU speedily be blackened by the sulphuretted HiPosuLPHATEa. 293 hydrogen given off. The formation of the brown or brownish yellow precipitate of sulphide of tin, and the evolution of hydro- sulphuric acid, are due to the tendency which sulphites possess to pass into sulphates, by a change in which a portion of sul- phur already combined with oxygen parts vnth that element, in order to increase the proportion of oxygen in the remaining compound. The sulphur thus liberated unites either with tin or hydrogen, according to the conditions of the experiment. S. The action of sulphuretted hydrogen (H^ S) upon sulphurous anhydride (SO^) has been already described (p. 285, y). e. Soluble sulphites treated with zinc and hydrochloric acid evolve sulphuretted hydrogen, which may be tested in the usual way with lead paper. f. A soluble sulphite acidified with hydrochloric acid, de- colourizes permanganate of potassium (KMn^OJ, reduces ferric to ferrous salts, and in general exerts a powerful reducing action. The methods chiefly employed for the recognition of the sul- phites are these : — ^the precipitation and metamorphoses of the barium and silver salts, and the tests u, /3, y, S, t, ^ ; they are more particularly distinguished from the hyposulphites by the test a, in the case of the sulphites no precipitate occurring, while with the hyposulphites a deposit of sulphur takes place. SALTS OF THE HYPOSULPHUKIC KADICAt, OR HYPOSULPHATES. The manganese salt of this radical is generally prepared ; and from it the other compounds may be obtained. Binoxide of manganese suspended in water, and sulphurous acid gas (SO2) passed through it, yields hyposulphate of manganese tolerably free from sulphate if the temperature of the solution be low: Mn,0,+2S02=Mn2S20„. When heated, in some cases only to 100°, these salts evolve 1 eq. of sul- phurous acid gas, and leave a neutral sulphate : Mn^ S2 0e=Mn, SO^-I-SO,. The Hydrogen Salt (H^SjOj), or hyposulphuric acid, is a strongly acid liquid, which by exposure to the air is converted into sulphuric acid ; by ebullition it also decomposes, just as the other salts decompose, viz. — H,S,Oe=H,SO,+SO,. There are no known hyposulphates insoluble in water. 294 CHEMICAL EEACTIONS. The hyposulphatee may be identified by the decomposition of their acid- radical : — a. The addition of a strong acid to a hyposulphate Kberates hyposulphuric acid ; and if the solution be then boiled, sulphurous acid gas escapes, sulphuric acid remaining in solution, which may be tested in the usual manner : no deposit of sulphur tates place. p. Fused with carbonate of sodium on charcoal, hyposulphates yield sulphide of sodium. y. Dilute hyposulphuric acid, or a soluble hyposulphate acidified with hydrochloric acid, dissolves zinc without forming hydrosulphuric acid ; but after ebuUition it behaves as a solution of sulphurous acid would. S. Hyposulphuric acid does not decolourize permanganate of potassium, nor reduce ferric sulphate, nor precipitate sulphur from hydrosulphuric acid ; but after boiliug it behaves as sulphurous acid. Por the detection of this radical the tests just described may be used, while, for distinguishing it from the hyposulphurous and sulphurous radi- cals, the reactions described under y, and B. may be employed. SALTS OF THE TEITHIONIC EAnlCAL, OK TKITHIONATES. Of these salts, which are prepared with diificulty, that of potassium is the only one well known. The general formula of the salts is M.^ S3 O5 ; they are all soluble in water, and are easily destroyed. SALTS OP THE TETEATHIONIC RADICAL, OE TETEATHIONATES. Several tetrathionates are known, which are not very soluble in water, and much more stable than the trithionates. The Hydrogen Compouxd (HjS.jOj) may be boiled without decomposition, thus differing from tri- thionic acid. SALTS OF THE PENTATHIONIO EADICAL, OE PENTATHIONATES. The peutathiouates are very prone to decomposition. Their general for- mula is M2 Sj Og ; but one or two acid salts (MHSj j) are known. The Hydeooen Compound is very soluble in water, has an intensely acid taste, and gives precipitates with copper, silver, mercury, and lead salts, of various colours at first, but which speedily become dark brown or black, the sulphide being formed. SALTS OP THE SULPHUBIC EADICAL, OE SULPHATES. The salts of the sulphuric radical are more stable than those of any other acid-radical containing sulphur and oxygen ; and it is indeed remarkable in this respect among compound acid- radicals in general. It is in the form of combiaation which we ai-e now considering that sulphur exists, to a considerable ex- SULPHATES. 295 teat, in nature, and supplies the necessary quantity of this ele- ment to the a n imal and vegetable economy. The sulphates are, with few exceptions, soluble salts, and are met with in aU, or almost all, the diflferent varieties of water found in the earth. Many sulphates, when heated alone on charcoal, yield the metal ; others, such as those of magnesium and zinc, are resolved into metaUie oxides, — ^while some few give a residue of sulphide. In aJl cases, however, a mixture of sulphurous (SO^) and car- bonic (CO2) anhydrides is evolved. The Htdhogest Salt (H^SO^), or sulphuric acid, is a dense liquid, to which the common term " oil of vitriol" is by no means inappropriate. The density of the acid H^ SO^ is 1-848 ; it evolves great heat when mixing with water, and combines with it to form a hydrated sulphuric acid, which is strictly analogous to a sulphate with 1 equivalent of water of crystallization, has the formula H^ SO^ + aq, and crystallizes at 9° C. Other such hydrates are known, such as H^ S0^-|-2aq. There is an acid ob- tained by distilling ignited and oxidized ferrous sulphate and receiving the products in ordinary oil of vitriol, which is termed Nordhausen sulphuric acid, or fuming oil of vitriol : this liquid has a specific gravity of 1-896, and contains dissolved in it a substance which is known as anhydrous sulphuric acid, or sul- phuric anhydride (SO3), and which may be separated from the fuming acid by distOlation. Thus obtained, it occurs in long silky needles ; it bears the same relation to sulphuric acid (Hj SO^) as sulphurous anhydride (SOJ does to sulphurous acid (H.SO3). The great majority of the normal sulphates (M^ SO^), aU the acid sulphates (MHSO^), and all the so-called tersulphates are soluble in water. The few sulphates that are insoluble or spar- ingly soluble in water are dissolved to some extent by strong sulphuric acid. Sulphates may be recognized by the formation of insoluble salts, and by the decomposition of their acid-radical. The barium, mercuric, and lead salts are among the more im- portant insoluble sulphates. 298 CHEMMAt EEAcnoWS. ThS Potassiitm and Somwm Salts are soluble. The Barium Salt is produced by the addition of a soluble barium salt to sulphuric acid, or to a neutral or acid solution of any sulphate : it is a heavy white precipitate. Its formula is Ba^ SO^. It requires 43,000 parts of cold water for its solittion, and is but slightly more soluble in hot water, acids, or saline solu- tions, although there are circumstances in which certain organic salts, those of citric acid especially, prevent the precipitation of sulphate of barium. It dissolves sparingly in concentrated sul- phuric acid. The Steontium Sam is produced by the addition of a soluble strontium salt to sulphuric acid or to solutions of soluble sul- phates (even of sulphate of calcium) : it is a white precipitate. Its formula is Sr^ SO^. It is soluble in 6895 parts of water at 14°, and in 9638 parts of boiling water. The Calcium Salt is produced by the addition of a soluble calcium salt to sulphuric acid or to solutions of soluble sulphates. It is a white precipitate, to which the formula Ca^SO^+gaq has- been assigned. It is far more soluble than the corresponding strontium salt, 1 part requiring only 460 parts of boihng or cold water for its solution. The Magnesium, Fbheous, Feeeic, Manoakous, Cobalt, Nickel, Znrc, Cadmium, Cuprous, and Cupeic Salts are soluble. The Siltee Salt (Ag^SO^) is sparingly soluble, 1 part re- quiring 87 of water for solution ; it is more soluble in nitric acid, and very much more soluble iu sulphuric acid. The Meecueous Salt is produced by the addition of a so- luble mercurous salt to sulphuric acid or a soluble sulphate. Its formula is (Hg2)2 SO^. It is somewhat soluble in water ; but a basic salt is thereby produced. It dissolves in di- lute nitric acid, but is reprecipitated on the addition of dilute sulphuric acid. It dissolves abundantly in strong sulphuric acid. The Meecueic Salt is obtained by precipitating a mercuric salt with a soluble sulphate at a high temperature. It is a basic BTOPHATES. 297 salt (Hg,S04,2H:g2 0). It dissolves in 2000 parts of cold, or 600 of boiling water. The Leab Sali is obtained by tbe addition of a soluble lead salt to sulphuric acid or a solution of a soluble sulphate. It is a dense white precipitate. Its formula is Pb^ SO^. It dissolves in 22,816 parts of water at 10°, and in 36,505 of dilute sulphuric aeidj it is more soluble xa concentrated sulphuric acid, and also in nitric acid. Certain ammonium salts also dissolve it sparingly. The sulphates may also be recognized by the following tests : — a. When sulphates are acted on by strong mineral acids, no apparent liberation of the acid (H^ SO^) takes place, nor is any characteristic reaction produced. /3. Sulphates, when fused on charcoal with carbonate of so- dium, are reduced, in common with other salts of radicals con- taining sulphur and oxygen, to sulphides. y. Sulphuric acid and sulphates do not yield any trace of hydrosulphuric acid on the addition of hydrochloric acid and stannous chloride. 0. Sulphuric acid and sulphates give no characteristic reaction with sulphuretted hydrogen. e. Sulphuric acid and sulphates are not reduced to a lower stage of oxidation by hydrochloric acid and zinc. f . Sulphuric acid and sulphates exert no reducing action upon ferric salts, &c. ; nor do they decolourize permanganate of po- tassium. This radical is generally recognized by the formation of the insoluble barium salt, and by the test /3, — whUe it is distin- guished from the other radicals containing sulphur and oxygen, by the absence of reaction on the application of the tests «j 7) ^j f> f . Of the acid-radicals containing selenium coTnMned with osygen, only two are known — the selenious and selenic ; for the combination of Belenium with oxygen, the gas (SeO), to which is attributed the odour of horseradish produced whenever selenium or a selenium compound is heated strongly in the air, appears itself to possess no acid characters. o5 298 CHEMICAI EEACIIONS. SALTS or THE SELENI0U3 KADICAL, 08 SELENITBS. When selenium is burnt in air, or treated with nitric or nitrohydroohlorie acid, the compound SeO^ is produced, analogous to the gas SO2 ; the former compound is, however, a crystalline solid, which vapourizes at about 300° C, yielding a gas of the colour of chlorine. This body yields the salts termed selenites when brought into contact with basic oxides. Selenites easily de- compose with reducing agents, giving a deposit of selenium, but are not readily oxidized ; nitric acid does not convert them into seleniates. When heated alone on charcoal, selenites leave a residue of selenide, or, parting with the whole of their selenium, of metallic oxide. The Htdeogen Salt (HjSeOj), or selenious acid, may be obtained from the aqueous solution of the anhydride (SeOj) in crystals resembling those of nitre, and soluble in alcohol: when heated, selenious acid decomposes into water and selenious anhydride (SeOj), which subUmes. The majority of the normal selenites are insoluble in water ; the selenites of the alkaline metals and the acid selenites are, however, soluble. They may thus be recognized not only by products of decomposition, but also by the formation of insoluble salts. Of the insoluble selenites, the barium, cupric, silver, mercuric, and lead salts are the most remarkable. The Potassium and Sodium Salts are soluble. The Barium Salt is produced by the action of a soluble barium salt on a soluble selenite: it is a white precipitate. Its formula is BajSeOj. It is insoluble in water, but soluble in selenious, hydrochloric, or nitric add. It is not converted into seleniate by nitric acid, thus differing from the sulphite. The Strontium, Calcium, and Magnesium Salts are white precipitates, insoluble, or sparingly soluble, in water. The Ferrous, Ferric, Zinc, Cuprous, and maxy other Salts containing metals of the third and fourth subdivisions are white precipitates, insoluble in water. The Cupric Salt is a crystaUiae greenish blue precipitate, insoluble in water and selenious acid, but soluble in ammonia water. The Silver Salt is a white crystalline precipitate (Ag^SeOj) sparingly soluble in cold, more so in hot water ; it easily dissolves in nitric acid ; and from this solution water precipitates it. The Mercurous Salt is produced by the action of soluble mercurous salts upon solutions of selenites or selenious acid. It is a white precipitate, insoluble in water and selenious acid. The Mercuric Salt is a white precipitate, insoluble in water. The Lead Salt is precipitated by a soluble lead salt from solutions of selenites or selenious acid : it is a dense white precipitate. Its formula is PbjSeOj. It is almost insoluble in water or in selenious acid, and but sparingly soluble in hydrochloric or nitric acid ; it dissolves in hot nitric acid without decomposition. SELElflATES. 299 But selenites may also be readily recognized by the decomposition of their acid-radical : — a. Selenites heated on charcoal in the reducing flame giye a most power- ful odour of horseradish, and often a white incrustation of selenious an- hydride. p. Selenites do not give any characteristic reactions on the addition of strong acidB. y. Selenites fused with carbonate of sodium on charcoal, and the resulting mass placed on a silver coin and moistened with water, give a brown stain of selenide of silver. . S. Selenites are reduced, giving a red deposit of selenium, by a hydro- chloric solution of stannous chloride, by ferrous salts, and some other re- ducing agents. 6. Hydrosulphuric acid passed through the aqueous or acid solution of a selenite of the first and second subdivisions, gives a reddish yellow pre- cipitate of selenious sulphide (SeS^), which is soluble in sulphide of am- monium. S. If a solution of a selenite coutaining a metal of the fii-st or second subdi- vision be acidified with hydrochloric acid, and a plate of iron or zinc im- mersed in it, the selenium is deposited either as a copper-coloured film, or in red-brown or greyish-black flakes. J). If sulphurous acid gas be passed through a neutral or acidified so- lution of a selenite, a red precipitate of selenium is produced in the cold, a grey one if the solution be heated. 9. Selenites ignited in a hard glass tube with chloride of ammoniimi give a sublimate of selenium. The selenite of ammonium formed in the reaction decomposes in the following manner : — 3(NHJ2 SeOj =3 Se-(-4N-l-2NH3 -I-9H2 O. Selenites may be recognized by the formation of the insoluble barium and and lead salts, and by the tests a, 6, ?, 7), and 0, while they are more particu- larly discriminated from the sulphites by the tests fi, Z, and 9. SALTS OF THE SELENIC RADICAL, OK SELENIATES. By the action of fusing nitrate of potassiimi upon selenium, seleuides, or selenites, seleniates are formed ; the action of chlorine on solutions of alka- line selenites also yields the same products. Seleniates greatly resemble the sulphates. Seleniates thrown on glowing charcoal detonate and evolve the charac- teristic odour of horseradish, generally leaving a residue of selenide. The Hydrogen Salt (Hj SeO,), selenic acid, has never yet been obtained in the pm-e state ; for, as its aqueous solution evaporates, it exhibits a great tendency to decompose into selenious acid and oxygen. From this prone- ness to change, it has not yet been found possible to obtain the selenic anhydride (SeOj), corresponding to sulphuric anhydride (SO3), since the 300 CHEMIOAt EEACTIONS. solution of Beleuie acid (which has nearly the formula H^SeO^), when heated above 285°, decomposes rapidly into selenious anhydride, water, and oxygen. The concentrated acid erolves nearly as much heat when mixed with wat«r as sulphuric acid ; it also absorbs water from the air. The great majority of the selenlates are soluble in water. This radical may, however, be recognized not only by its decompositions, but by those few characteristic insoluble salts which it forms. Of the insoluble seleniates those of barium, strontium, and lead are the most characteristic. The Potassium and Sodium Salts are insoluble. The BarilUU Salt is produced by the action of soluble barium aalts upon solutions of selenic acid or of seleniates. Its formula is Ba^ SeO^. It is insoluble in water, and in hydrochloric or nitric acids ; by long boiling, however, with hydrochloric acid, it is gradually decomposed and dissolved, being converted into selenite, thus — BajSeOi+2HCl=Ba2 SeOg 4-H2 0+2C1, The Stkontium Salt is a white powder, nearly insoluble. The Calcium Salt is unknown ; the Magnesium Salt is soluble. The Fehkous, Zinc, Cupric, Silver, and many other Salts containing metals of the third and fourth subdivisions are soluble. The Lead Salt is a white precipitate, insoluble in water. Seleniates maybe recognized by the following processes of decomposition : — a. Seleniates heated before the blowpipe on charcoal detonate, emitting an odour of horseradish. The same odour is perceived when these salts are heated with borax or microcosmic salt. Heated with carbonate of sodium, they give the same results as selenitea. p. The strong acids in general exert no apparent decomposing influence upon selenites ; hydrochloric acid, however, long heated with selenic acid or seleniates, gradually reduces the acid to selenious acid, and the salts to selenitea. y. A hydrochloric solution of stannous chloride exerts no decomposing action upon seleniates. S. Sulphurous acid gas (SOj) or zinc with hydrochloric acid exert no decomposing action upon the selenic radical ; but both selenic acid and the seleniates give reactions of selenites, after their solutions have been boiled for some time with hydrochloric acid. Seleniates are most readily identified by the formation of the insoluble barium and lead salts, and by the action of boihng hydrochloric acid upon them (/3.). Of the acid-radicals containing teUuHum comMned with osyygen^ only two are known. These bear the closest analogy in composition to the compounds of selenium ; their hydrogen compounds are known as tellurious (H^TeOj) and telluric (H^TeO^) acids. TELlimiTES, 301 SALTS OF THE TILUJBIOUS lUDlCAL, OB TBLMKITES. Tellujium heated in the air or boiled with nitric ot sulphuric acid yields a body, tellurious anhydride (TeO^), the analogue of SOj and SeO^. It is a white crystalline body, volatile at a high temperature, and fusible at a low red heat to a yellow liquid. When brought in contact with water or metalUo oxides, saline combinations are formed, many of Which are easily decom- posed, even by the carbonic acid of the air. Tellurites, heated with charcoal, generally yield tellurium, and a white incrustation of tellurious anhydride ; they also impart a green colour to the flame. The HydeogeN Salt (tt^TeOg), or tellurious acid, occurs in white volu- minous Hakes, which are earthy when dry, redden litmus paper, and have a sharp metallic taste. This acid, when mixed with water, is resolved at 40° into water and the anhydride. The body TeO^ partakes much of the character of a metallic oxide ; and the corresponding sulphate and nitrate are also known. The tellurites, with the exception of those of the first subdivision, are in- soluble, or very sparingly soluble in water. The insoluble salts are in general dissolved by concentrated hydrochloric acid. The Potassium and Sodium Salts are soluble. The BariUin Salt is a white voluminous precipitate, very sKghtly soluble in water, but soluble in strong acids. It is produced by adding together solutions of chloride of barium and normal tellurite of potassium (JE^TeOj). The Stbohtium and Calcium Salts are sparingly soluble ; the Magnesium Salt much more so. The Feekous, Fbeeic, Zinc, and many other Salts containing the metals of the third and fourth subdivisions are yellow or white insoluble precipitates. The Cupeic Salt is a green precipitate, insoluble in water. The Silver Salt is a yellowish white precipitate, insoluble in water, but soluble in hydrate of ammonium. The Mekourous Salt is yellow when freshly deposited, but rapidly be- comes brown. The Meecubic Salt is a milk-white precipitate. The Lead Salt is white, and, though nearly insoluble in water, dissolves readily in acids. Tellurites may be recognized by the following processes of decomposition : — ■ a. When heated before the blowpipe on charcoal in the reducing flame, they impart a green colour to the light. (3. The addition of a few drops of acid, even of the weakest, to a soluble tellurite, decomposes it, liberating and precipitating the acid in white flakes. y. Most tellurites (the zinc, silver, and some other salts excepted), when fused with carbonate of sodium on charcoal, give a saline mass, which, when dissolved in water, forms a wine-red solution of telluride of sodium. d. A solution of staomoua chloride, added to solutions of tellurites, espe- 302 CHEMICAL KBACTIONS. oially on the addition of hydrochloric acid, produces a brown-blact pre- cipitate of tellurium, which, when pressed and rubbed, exhibits a metallic lustre. t. Hydrosulphurio acid precipitates, from solutions of tellurites, a black powder of sulphide of tellurium (TeS^), soluble in sulphide of ammonium. Z. The metals zinc, iron, copper, &c. precipitate tellurium from tellurites as a black powder ; lead precipitates it in dendritic masses. ij. Sulphurous acid produces a precipitate of tellurium. 6. Tellurite of ammonium does not decompose in the same way as the selenite. Tellurites may best be recognized by the formation of the barium salt, and by the teste (3, y, d, e, ?, t], — ^while they may be distinguished from the sulphites by the same experiments, and from the selenites by the test 0. SAMS OF THE TELLUKIO KADIOAI,, OK TELLURIATES. The most common telluriate, that of potassium, is made in the same way as the seleniate, by fusing teUurious anhydride, (TeOj) with nitrate of po- tassium, or by the action of chlorine on tellurite of potassium. Heated on charcoal before the blowpipe, many teUuriates yield tellurium, the reduction being frequently attended with slight detonation. When heated strongly alone, many teUuriates fuse, become yellow or brown, and evolve oxygen, yielding tellurites. The Hydkoqen Salt (H2Te04), or telluric acid, is prepared from the barium salt. It may be crystallized as the hydrated acid (H^TeO^+HjO). This, heated to 160°, gives the acid H2Te04 ; and this, if more strongly heated, yields the anhydride TeOj, an orange-yellow crystalline mass (the analogue of SO3 and SeOj). The crystallized acid is very soluble in water, but insoluble in alcohol. The teUuriates of the first subdivision are soluble ; the rest are insoluble, or nearly so. The Potassium and Sodium Salts are soluble. The Bariuin Salt is at first a bulky white precipitate, which graduaUy becomes denser. Its formula is BajTeO^. It is slightly soluble in cold water, more so in hot, and easily dissolves, without decomposition, in nitric acid. The Stkontium, Calcium, and Magnesium Salts are somewhat more soluble in water than the barium salt. The Fekrous, Fbkrio, and most othek Salts containing metals of the third and fourth subdivisions are insoluble, or nearly so, in water. The Cupeio Salt is pale green. TuE Silver Salt is deep yellow. It is soluble in hydrate of ammonium. The Meecurous Salt is yeUowish brown. The Mercuric Salt is a bulky white precipitate. The Lead Salt is a white, heavy, somewhat soluble precipitate. TeUuriates may also be recognized by the foUowing processes of decom- position : — AirilllfATES, CHEOMITES, ETC. 303 u. Telluriates, when heated on charcoal before the blowpipe in the reducing flame, impart to it a green colour, often detonating slightly and yielding tellurium and a white sublimate of tellurioua anhydride (TeO^). /3. By the action of boiling hydrochloric acid, telluriates are reduced to tellurites. y. With carbonate of sodium on charcoal, telluriates (like tellurites) give a mass containing telluride of sodium. S. Sulphurous acid gas (SO^), passed into a hot hydrochloric solution of a teUuriate, precipitates the tellurium. Telluriates may be recognized by the formation of seyeral insoluble com- pounds, such as that of barium, and by the tests a. and j3. Of the acid-radicals coutaioing tellurium combined with sulphur, only two are known. Their salts are termed sulphotelluritea and sulphoteUuriates. The sulphotellurites containing the metals of the first and second subdivisions are yellow crystalline salts, soluble in water : the insoluble salta of the third subdivision are white or yellow ; of the fourth, brown or black. The sulpho- teUuriates have scarcely been examined. SECTioif III. — The alwminates, chromites, chro'mates, perchromates, ferrites, ferrates, manganates, permanganates, bismuthates, stannates, metastannates, platinates, rhodiates, rutheniates, {relates, osniites, osmiates, aurates, tungstites, tungstates, molyhdates, vanadite^ and vanadiates ; the sidphostannates, sidplioplatinates, sulphorhodiates, sulphur utheiiiates, sulph- iridiates, sulphosmiates, sulphaurates, sulphomolybdates, and sulphovanadiates. SALTS OF THE COMPOmiTD ACID-EADICALS WHICH CONTAIN OXYaEN AND SULPHUE COMBINED WITH METALS. A very large class of compoimd acid-radieals, some of wHcli are extremely powerful, are produced by the imion of monatomic and biatomic molecules of certaiu basic radicals ■with a preponder- ating proportion of an acid element. Many of these bodies form salts of great stability — -witness the chromates, stannates, tung- states, and molybdates ; but their hydrogen compounds, or acids, are usually unstable. Some of these compound acid-radicals are monobasic, some bibasic, and others tribasic; the latter are kno^wn, in many instances, to yield acid salts containing 1 or 2 eqs. of basic hydrogen unreplaced by a metal. Most of these acid-radicals are very easy of detection. They 304 CHEMICAI. EBAOTIONS. form numeroiis msoluble compounds, some of wHoh are of ex- luiui ^u.u± jj;+^-„Ti fo this, the comparative tremely hrilHant colours; m addition to tnis, i- xrcmu^ M ,.,.,„ ^„„ hp caused to decompose, greatly readiness with which they may be canseu i ,& j facilitates their recognition. One compouftd acid^radioal containing aluminium and omen m known; M.«Tthe compound called hydrate of aluminium is considered to be an """•d ralmninio acid) ; and when this body is acted upon by hydrate of po- tassium, the potassium salt is formed. Viewed in this Ught, the formula H^Al. O may be assigned to the acid, and KH^AljOj to the potassium salt. Other modes of representing these compounds may be seen on referring to _ j^og^ 110. Several aluminates have been obtained. Of the acid-radicals containing chromium and oxygen, one only is of any analytical importance — that, namely, which is contained in chromic acid (HCrOj) ; the salts of the other acid-radicals, which are known as chromites and perohromates, are of rare occurrence. The chromites have the general formula MCr^Oj ; the potassium, magnesium, and iron salts are tolerably well known. SAXTS OF THE CHSOMlC HADlCAl, OB CHBOltAlES. These salts are usually made from the potassium salt, which is easily prepared by fusing chromic oxide ([CrJ^Oj) with nitrate of potassium in a crucible. The ehromates are often of a red or yeUow colour. Many ehromates, when strongly heated, yield chromic oxide and oxygen, while others {e.g. chromate of magnesium) yield chromites ; other blowpipe reactions of the compounds of chro- mium win be found on p. 111. The Htoeooew Sali (HCrOj), or chromic acid, has not yet been isolated ; when its aqueous solution is concentrated, fine crimson acicular crystals separate, which consist of the compound Cr^Oj, /. e. chromic anhj-dride*. This body possesses the propertj- of uniting with 2 eqs. of certain neutral ehromates to form new salts, which require no additional equivalent of basic radical. These salts have been called bichromates ; terchromates are also known, and some compounds oven which may be termed quadri- * Just as chlorocln.omio acid may be viewed as chloride of ohromyle ^ i" 'w '^'°^?y ' ''^''''""''' ""'^ ™^y ^'' considered as the oxide of that radical ([CrO],0) ; there is, however, some gi-ound for doubling the formula here assigned to ohromyle and the neutral ehromates. CEB0MATE8. 305 ckromates. All such, salts are usually of a darker colour than the simple chromates, which are generally yellow. The bichromates, &c. are thus formed : — 2KCrO,+Cr,03=K,Cr,0,. bichromate of potassium. The chromates of the first and second divisions of the basic elements are soluble, the barium salt excepted ; most of the other chromates are insoluble in water, but easily soluble in acids. The chromates may be recognized, not only by the formation of insoluble salts, but by several processes of decomposition. The most remarkable insoluble salts of this series are those of barium, silver, mercury, and lead. The Potassittm and Sodium Sams are soluble. The Barium Salt is produced by the action of a soluble barium salt on solutions of neutral chromates or of bichromates. Its formula is BaCrO^. It is a pale yellow precipitate, nearly as insoluble in water as the sulphate, but soluble in hydrochloric, nitric, or chromic acid, and in solutions of bichromates. The Steoniium, Calcium, and Magnesium Saxts are soluble. The Fekeic, Mafganous, and mant other Salts of the third subdivision are brown or yellow precipitates, nearly insoluble in water. The Cupeous Salt is unknown. The Cupeic Salt is produced by adding a cupric salt to a soluble chromate. "With bichromates no precipitate is produced. It is a yellowish brown precipitate. It is soluble in nitric acid, and in hydrate of ammonium. The Silver Salt is produced by the action of a soluble silver salt on a chromate. It is a crimson crystaUine precipitate. Its formula is AgCrO^. It is soluble in alkaline chromates, in hydrate of ammonium, and in acids. When formed in acid solutions, this precipitate is the bichromate (Ag^Cr^O^), and has a more brilliant colour. The Meecueous Salt is produced by a soluble mercurous salt when added to a solution of a chromate ; it is a red precipitate., 306 CHEMICAL EEACTIONS. Its formula is Hg^CrO^; but frequently the salt SHg^CrO^, (HgjXO is precipitated. It is slightly soluble in solutions of ammonium salts, in water, and ia nitric acid. The Meeoubic Salt resembles the mercurous salt very closely. It is soluble in excess of many soluble mercuric salts. The Lead Salt is produced by the action of a soluble lead salt on chromate or bichromate of potassium. It is a yellow precipitate. Its formula is PbCrO^. It is slightly soluble in excess of the chromate or bichro- mate of potassium, and in hydrate of potassium ; it is inso- luble in chloride of ammonium and in water, but soluble in nitric acid. This acid-radical may also be recognized by the following ex- periments : — a. Chromates, when heated before the blowpipe with a borax bead, give evidence of chromium ia the green tint produced ; care must, however, be taken that other interfering bases are absent. /3. "When boUed for some time with hydrochloric acid, chromates are reduced, yielding the sesquichloride (Cr^Cl,), with evolution of chlorine. If sulphuric acid be employed iustead, oxygen ia set free. y. The passage of hydrosulphuric acid through the aqueous solution of a chromate also effects its reduction, — a chromic salt with separation of sulphur being the results : 4KCrO, 4- 5H,S = 2Cr,H303 + 2K,S -|- 2H,0 -t- 3S. chromic hydrate, ppt. green ppt. Sulphurous anhydride (SO^) produces a similar effect, sulphuric and hyposulphuric acids being formed. Nascent hydrogen and many other reducing agents also give the same results. Numerous organic bodies are capable of rapidly reducing the chromates — such substances as alcohol, sugar, oxalic and tarta.ric acids. When warmed with alcohol and hydrochloric acid, a chromate decomposes thus : — PEECHROMATES. 307 4KCrO, + lOHCl + 3C,H„0 = 2Cr,Cl3 + 4KC1 + 8H,0 + 3C,H,0. alcohol. green aldehyde, c&omio chloride. The hydroclilorio acid acts partly as a solvent for the chromic hydrate, which we may suppose to be formed at first. S. Piised with carbonate of sodium many insoluble chromates yield the soluble chromate of sodium (see p. 112). The chromio radical is generally recognized by the formation of the insoluble silver and lead salts, and by the tests a. and (3. SALTS OF THE PEECHROMIC KADICAI/, OR PERCHROMATES. The hydrogen compound of tliis radical is known, but only as dissolved in ether : it is obtained by the action of a hydrochloric solution of peroxide of barium on bichromate of potassium ; the perchromic acid thus Hberated is taken up by ether, which becomes of a beautiful blue colour. It is imme- diately decomposed by hydrate of potassium, but may be made to unite with ammonium and certain organic bases, forming comparatively stable salts, from which acids separate the blue perchromic acid, which then speedily de- composes into chromic acid and oxygen. Of compound acid-radicals containing iron and oxygen, two are known, but they are of very slight importance. When carbonate of sodium and ferric oxide are strongly ignited, a compoimd termed ferrite of sodium is said to be obtained in very small proportion. Similar salts are believed to be formed when a solution containing ferric chloride and the chloride of an alkaline earth is precipitated (under certain conditions) by a hydrate of the first subdivision. But the only definite acid-radical of iron and oxygen is that contained in the ferrates (MFeOj). The ferrate of potassium is obtained by igniting iron or ferric oxide with hydrate or nitrate of potassium, by the action of chlorine on ferric oxide suspended in hydrate of potassium solution, or by the electrolytic evolution of oxygen gas from an iron plate immersed in a concentrated solution of hydrate of potassium. By all these methods the potassium salt is obtained, sometimes in the crystalline form ; it dissolves in water, forming a red-violet solution, which is instantly decomposed and de- colourized by ammoniacal salts and the weakest reducing agents, and even by a heat of less than 100° : the products of this decomposition are ferric oxide and oxygen. The hydrogen compound, or ferric acid, cannot be ob- tained, as any attempt at its hberation results in its instant decomposition. Of the acid-radicals containing manganese and oxygen, two are well known and easily produced. These are the manganic (MnO J and permanganic (Mn^O^) radicals. They are both monobasic. The potassium salt of the former is obtained by igniting man- 308 CHEMICAL EEACTIONS. ganese, or one of its oxides, -with hydrate of potassium in contact with, air, or with hydrate of potassium mixed with nitrate or chlorate of potassium. The manganates of the first and second subdivisions are known ; they are dark bluish green compounds, those of the alkaline metals dissolving ia water to form green solutions. The hydrogen compound is not known. Permanganic acid (HMn^ 0^) is produced by the action of dilute nitric acid on the aqueous solution of a manganate. Its colour is a beautiful violet ; the solutions of the alkaline permanganates have the same tiut. The permanganates, as far as known, are all soluble, no precipitates being formed with saUne solutions ex- cept ia cases where the latter act as reducing agents, and preci- pitate the peroxide of manganese (Mn^Oj). Of acid-radicals containing bismuth and oxygen, one only is known. When bismuthic oxide (Bi^ O3) is fuaed with hydrate of potassium, or when it is suspended in a concentrated solution of hydrate of potassium through which a current of chlorine is passing, a double salt of bisauthate of potassium and bismuth is formed, which contains the radical BiOg. One or two salts are known, and the hydrogen cotopound (HBiOj). Of acid-radicals containing tin and oxygen, two are known. Their hy- drogen compounds are stannic acid (H, Su^Oj) and metastanuic acid (HjHgSnijOij). The acids themselves being very insoluble bodies, no characteristic reactions can be obtained from them, except such as, by de- stroying the radical, prove the presence of its metallic constituent. Of the acid-radicals containing the rare metals of the fourth subdivision combined with oicygen, none are of analytical importance. The higher oxides of platinum, rhodium, ruthenium, iridium, osmium, and gold have the property of uniting with the elements of water to form acid compounds, and with the oxides of some few basic radicals, as those of the first subdivision, to form ealts. These salts, with the exception of the gold compounds, have not been thoroughly examined. The existence of a definite auric acid (HAuO^) is doubtful ; but the anhydride ( Au^ O3 ) is known : the aurate of potassium too has been obtained, crystallized, in small needles of a yellow colour, and having the formula KAuOj-t-Saq; a solution of this salt in water produces preci- pitates in many metallic solutions, proving that there are many insoluble aurates ; — insoluble, that is, in water, for they frequently dissolve in excess of of their precipitants to form double salts. It will be at once seen that these acid-radicals correspond closely to those mentioned under Section III. of the first subdivision of the acid-radicals (p. 276). Of the odd-radicals which contain tungsten combined with oxygen, one only TTTNGSIATES. 309 is of any analytical importance, although another is tnown to exist in a few compounds. The tungstie radical (WO^) is a very powerful one, and forms stable salts termed tungstates, which impart to water a bitter metallic taste. SALTS OF THE TUNGSTIO BADIOAL, OE TUNGSTATES. These salts are not decomposed by heat alone, unless their basic constituent is volatile or compoimd, and when heated on charcoal sometimes yield the brovm oxide, although they are reduced or decomposed in different ways according to the base present. The other blowpipe reactions of tungstie acid and tungstates will be found among the processes of decomposition employed for detecting the tungstie radical (see p. 236). The Hydeogen Salt (HTWOj) does not appear to be known ; for when the acid is liberated by the action of other acids upon solutions of tungstates in the cold, the white precipitate which occurs, though thought by some to be the acid, rapidly becomes yellow when the solutions are heated, or when the precipitate is allowed to stand. This yellow body has the formula W^Oj, and so bears the same relation to the acid (HWOj) as auric anhydride (AujOj) does to auric acid (HAuO^), or hypoohlorous anhydride (Cl^O) to to the acid (HCIO). Tungstie anhydride is lemon-yellow and crystalline. Recent researches hare shown that there are many modifications of tung- states, in which varying quantities of oxygen and tungsten are united to form aoid-radicals ; yet they will all group in a singular manner around the anhy- dride (W2O3), which may be produced by the decomposition of all. The union of the anhydride with normal tungstates gives, on the other hand, compound salts resembling the bichromates, &o. G?ungstates may be recognized by the formation of some of the most oha- rafiteristic insoluble salts, but are more usually identified by processes of decomposition. The tungstates of the first subdivision are soluble ; all the other salts, ex- cepting that of magnesium, are insoluble in water. The Barium Salt is produced by the action of soluble barium salts on the neutral tmigstate of potassium : it is a white precipitate. Its formula is BaWOj. It is insoluble in water and in phosphoric acid, but is decomposed by stronger acids ; it is dissolved by a boiling solution of oxalic acid. The Steontium and Calcium Salts are white precipitates, sparingly soluble in water. The Magnesium Salt is soluble. The Feeeous and many other Salts containing metals of the third and fourth subdivisions are insoluble, or nearly so, in water. The Cupeic Salt is obtained by the action of a soluble cupric salt on tungstate of sodium ; it is a grass-green precipitate. Its formula is CuWO.^. It is insoluble in water and oxalic acid, soluble in acetic and phosphoric acids. The Silvee Salt is a white insoluble powder, produced when a silver salt is added to a solution of bitungstate of sodium. Its formula is Ag^W^ O,. The MerCUrOUS Salt is produced by the action of a soluble mercurous 310 CHEMICAL EE ACTIONS. salt upon tungstate of potassium : it is a yellow precipitate, so insoluble in water as to be used for the guantitative estiTnatian of tungstic acid. The Mekcuric Salt is white if the mercury solution be in excess ; other- wise it is yellow, red, or brown. It is insoluble in water. The Lead Salt is a white precipitate, insoluble in cold water or cold nitric acid, soluble in hydrate of potassium. Tungstates are, however, most readily recognized by the decomposition of their acid constituent ; the following tests may be employed : — a. Tungstic anhydride (WjOj) does not volatilize when heated on char- coal, but yields a brown oxide of timgsten ; before the blowpipe, with micro- cosmic salt, this body ([W2O3] which, as we have seen, may be easily pro- duced from tungstates) gives in the reducing flame a fine bl'ue colour, which disappears in'the oxidizing flame ; if iron be present, a blood-red colour will be produced. /3. Solutions of the tungstates containing the alkaline metals are precipi- tated by hydrochloric, nitric, aeetic, sulphuric, and phosphoric acids ; and the precipitate is insoluble in all the above acids, excepting the last-named, which dissolves it readily. Oxalic, tartaric, and citric aoide do not separate the anhydride (W2O3). 7. When the body, W^ O3, is precipitated from a soluble tungstate by the addition of a mineral acid, a small quantity of tungstic acid remains in solution ; and if then a strip of zinc be introduced into the acid solution, the liquid wiU be coloured blue from the formation of the blue oxide of tungsten. This radical is usually recognized by the formation of the insoluble ba- rium and mercurous salts ; but more especially by the tests a. and y. (See aUo p. 237.) SALTS OF THE MOLYDDIC RADICAL, OR MOLYBDATES. The radical MoOj bears considerable resemblance to the radical WOj ; the soluble molybdates have a faint metallic taste ; several of the insoluble salts have a yeUow colour. Heated alone, they are fixed, unless their base is volatile or decomposable ; on charcoal, before the blowpipe, several molybdates are partially reduced, particularly in the presence of carbonate of sodium. The Hydrogen Salt (HMoO^) is not known ; when an attempt is made to liberate it by the action of acids on molybdates, the anhydride (MO2O3) separates as a white curdy precipitate. This body unites with molybdates to form bimolybdates, &c., analogous to the bichromates, bitungstates, &c. Molybdates are recognized by the formation of certain insoluble salts, and also by several processes of decomposition. The molybdates of the first subdivision are soluble in water ; the others insoluble, or sparingly soluble. The Potassium and Sodium Salts are soluble. The Barium Salt is produced by the action of soluble barium salts on molybdate of potassium : it is a white precipitate, probably having the VANADIATES. 311 formula BaMoOj. It is insoluble in wate*, but soluble in dilute nitric or hydrochloric acid. The Strontium and Calcium Salts are White, insoluble in water. The Magnesium Salt is comparatively soluble, particularly in hot water. The Febkous and many other Salts of the third and fourth subdi-pisions are yellow or brown precipitates, insoluble in water, soluble in hydrochloric or nitric acid. The Cupric Salt is yellowish green, insoluble[^(or nearly so) in water, de- composed by acids and alkalies. The Silver Salt is greenish white, slightly soluble in water and in dilute nitric acid. The Meecurous Salt is white, soluble in 500 or 600 parts of water, de- composed by nitric acid. The Lead Salt is produced by precipitating plumbic nitrate with normal molybdate of ammonium: it is a white insoluble precipitate. The native variety is the chief ore of molybdenum. Molybdatea may also be detected by several processes of decomposition : — a. Molybdic anhydride, when heated in the reducing flame on platinum wire, imparts a yeUowish green tinge to the light ; it also gives with micro- cosmic salt a fine green colour, and with borax a brown bead, when heated in the inner blowpipe flame. ;8. When to a neutral concentrated solution of a soluble molybdate, a few drops of hydrochloric or nitric acid are added, the anhydride (Mo^Oj) sepa- rates ; it dissolves, however, on the addition of more acid, or even upon dilu- tion with much water. Oxalic and phosphoric acids do not produce this efiect. y. Bj immersing a strip of zinc in a hydrochloric solution of a molybdate, a blue colour is produced, from separation of the blue oxide of molybdenum ; the colour gradually changes to green, and then becomes nearly black. S. By evaporating nearly to dryness a nitric solution of an alkaline phos- phate or of phosphoric acid, and adding a drop of molybdate of ammo- nium, a yellow precipitate is obtained, which is insoluble in hot nitric acid. e. A trace of hydrosulphurio acid produces in solutions of molybdates a blue colouration ; larger quantities of the gas give a brown precipitate of molybdous sulphide (MOj S^). Molybdenum is usually recognized, when existing as the molybdic radi- dical, by the precipitation of the barium and lead salts, and by the tests p. and S. (See also p. 241.) Of acid-radicals containing vanadium and oxygen, two are known ; of these the vanadic only is of any importance ; the vanadites are derived from the binoxide (V^ 0^). SALTS OP THE VANADIC RADICAL, OE VANADIATES. The acid-radical VO^ resembles the tungstic and molybdic radicals in many points : many of its salts are yellow or orange ; they have no cha- 312 CHEMICAL EEACTIONS. racteristie taste. Generally speaking, they are comparatiyely soluble in water. A red heat produces no change in the vanadiates, unless the basic con- stituent is volatile or decomposable. Vanadic anhydride (Vj^a) heated on charcoal is partially reduced to a lower oxide, and partly to vanadimn itself; vanadiates of the heavy metals yield alloys of vanadium. The Hydrogen Salt (HVO^) is unknown, the addition of an acid to a soluble vanadiate precipitating the anhydride (VjOj) in an impure state, as a yellow substance, soluble in acids, yielding yellow solutions. From the anhydride, vanadiates and bivanadiates are prepared. This radical may be recognized both by the formation of insoluble salts and by certain processes of decomposition. Many vanadiates are soluble in water. The Potassium and Sodidm Salts are soluble. The AuunOIiilUll Salt (WH^VO,) is remarkable for being quite in- soluble in a saturated solution of chloride of ammoniiun. The Banxun Salt is produced by the action of a soluble barium salt on an aqueous solution of vanadiate of ammonium : it is a yellow gelatinous precipitate, which becomes white and dense after standing. Its formula is BaVOj. It is slightly soluble in water, and dissolves with a red colour in suphuric acid. The Strontium Salt is a white crystaUine granular precipitate, more so- luble than the barium salt. The Calcium Salt is soluble, and the Magnesium Salt exceedingly so- luble in water. The Ferric, Nickel, and many Salts containing metals of the third and fourth subdivisions are yellow and soluble in water. The Cupeic Salt is soluble. The Silver Salt is obtained by the action of nitrate of silver on vana- diate of ammonium, and is a pale yellow or white precipitate, soluble in nitric acid and in hydrate of ammonium. The Meecceous, Mercuric, and Lead Salts are yellow and more or less soluble in water. The vanadic radical may also be recognized by processes of decompo- sition, &o. : — a. Vanadiates generally fuse when heated; the anhydride (VjOj) does not volatOize. With borax or microcosmic salt, the anhydride gives a green glass in the reducing, and a yellow in the oxidizing flame. /3. Vanadic anhydride dissolves in the stronger acids, forming yellow or red solutions, which often become colourless on ebullition, and yield red or yellow crystaUized compounds or salts of vanadic acid. The sulphate of vanadic acid is said to have the formula Vj (SOJj. y. Hydrosulphuric acid precipitates a mixture of binoxide of vanadium and sulphur from an acid solution of vanadic oxide. (5. Ferrooyanide of potassium produces a beautiful green precipitate with soluble vanadiates. TABLE OF KEACTIONS. 313 o. Solutions of vanadiates with tincture of galls yield a blackish blue or black mixture. Vanadiates are usually detected by the tests jS, S, and e. Of the acid-radicals which contain metals and sulphur, none are of suiS- cient importance to justify description here. They generally form yellow, reddish brown, brown, or brownish black salts, which correspond closely to the analogous salts containing the same metals combined with chlorine or oxygen. They are generally formed by the solution of the metallic sulphide in sulphide of potassium, sodium, &c. The salts formed by these radicals are termed sulphostannates (MjSujSj), sulphoplatinates (MjPtjS^), sulphorho- diates (MES^), sulphorutheniates (M^EUjSj), sulphiridiates (M2lr2S3), sulphosmiates (MOsS^), sulphaurates (MAuS^), sulphotungstates (MWS^), aulphomolybdates (MMoS^), and sulphoranadiates (MVSj). TABLE OF REACTIONS. Salts. (see page 281] s (p. 283) SO3 (p. 290) SO4 (p. 295) CrO. (p. 305) Barium white — white white pale yellow Strontium.. white — white white — Calcium . . white — white white — Magnesiiun white — — — — Ferrous .... r greenish \ white _| black — — / yellowish ] \ brown J Ferric red black — — brown Zinc white orange 1 yellow / black white black black r brownish l I red J — yellow ? ' yellowish I brown J Cuprous ... Cuprie Silver brown black white — crimson Mercurous .. ' brownish I black / black white white red Mercmc ... orange red black white white yellow Lead white black white white yellow 314 CHEMICAL BEACTIONS. Analysis of Subdivision II. The acid-radicals of more common occurreace only being in- cluded, the salt may be an OXIDE, SULPHIDE, SULPHITE, SULPHATE, CHROMATE, or TUNGSTATE. The addition of strong sulphuric acid to the solid salt or its concentrated solution may produce an efferTeeoence ; if so, the evidence sought will pro- bably be better obtained with a weaker acid, aided by heat. A gas having cm odour of rotten eggs (HjS) indicates a sulphide. „ ,, „ burning sulphur (SOj) indicates a sulphite. Further Analysis. Acidify the solution with hydrochloric acid, and warm for some time. A lemon-yellow precipitate of W2O3 would indicate the original presence of WO,. If no precipitate occurs, the solution may contain a chromate, sulphate, or oxide. Add a few (frops of al- cohol, and boil for some minutes ; if the liquid changes from a reddish yellow to an emerald-green colour, tiie previous existence of CrO^ may be inferred. Add excess of ammonia. A green precipitate of CrjHjOj would indioate the original presence of CrO,. If no green colour or precipitate oc- curs, add a few drops of chloride of barium. A white precipitate of Ba^SO^ would indicate the presence of SO,. If no precipitate occurs, and the sub- stance under exa- mination is obviously not a basic radical, i. e. a metal, we infer the presence of O as the acid-radical. SALTS OF CAEBON, ETC. 315 SUBDIVISION III. SALTS OF CARBON, BORON, SILICON, tantalum, NioBitrM, PELOPnjM, AND TITANIUM, AND OF THE CrilEF COM- POUND ACID-RADICALS INTO THE COMPOSITION OF WHICH THEY ENTER. This group, with the exception of its four latter and rarer members, presents but little analogy \vith either of the preceding subdivisions. One distinctive feature is, that no member of this subdivision combines directly vnth hydrogen to form a compound of acid properties, although they combine with almost aU metals to form salts. AU these acid-radicak, however, form, by union with oxygen, compound acid-radicals, which yield extremely stable salts with hydrogen and metals. Another great peculiarity of this group is the property possessed by carbon of uniting with hydrogen and oxygen, with hydrogen, oxygen, and nitrogen, and with other basic radicals, such as with iron and nitrogen, to form acid-radicals, many of which combine with basic radicals to form salts of great stability : most of such compounds are generaUy termed " organic," from their frequent occurrence in the animal and vegetable kingdoms, or from being obtained among the products of their decomposition. Examples of such compounds are — H,C,H,0„ H3C,H3N,0„ H3Co,C,Ne. succinic acid. uric acid. hydrocobalticyanio acid. Among these bodies many are monobasic, many bibasic, and some tribasic. Section I.— SALTS OF CABBON, BORON, SILICON, tantalum, nio- bium, PELOPIUM, AND TITANIUM. The carbides, borides, silicides, tantalides, niobides, pelopides, and titanides. Section II.— SALTS OF THE ACID-EADICALS WHICH CONTAIN CAEBON, BOEON, SILICON, tantalum, niobium, pelopiu.m, and titanium COMBINED WITH FLUOEINE, OXYGEN, OE SUL- PHITE. The borofluorides, sUieofluorides, carbonates, oxalates, borates, p2 316 CHEMICAL EEACUONS. silicates, tantalates, niobiates, pelopiates, titanates, and sulpho- carbonates. Section III.— SALTS OF THE ACID-EABICALS WHICH CONTAIN CARBON COMBINED WITH NITROGEN, WITH NITROGEN AND OXYGEN, WITH NITROGEN AND SULPHUR, WITH NITROGEN AND METALS, WITH OXYGEN AND HYDROGEN, AND WITH OXYGEN, HYDROGEN, AND NITROGEN. The cyanides, cyanates, and sulpbocyanides ; the ferrocyanides, ferricyanides, and cobalticyanides ; the formiates, acetates, ben- zoates, succinates, tartrates, lactates, citrates, gaUates, tannates, and urates. Section I. — The carbides, borides, silicides, tantalides, niobides, pelopides, and titanides. SALTS OF CARBON, BORON, SILICON, tantalot, niobium, pelopicm, AND TITANIUM. The radicals of this third subdivision, although they combine with metals, can scarcely be said to yield saline compounds, since it is with the greatest difficulty that the bodies are made to unite in definite proportions, and then the products of the union par- take more of the character of alloys. It is probable that their combinations, especially those of carbon and silicon (or of phos- phorus), with the metal, exist dififased through the mass of metal, which presents, in different specimens, different properties. Thus the varieties of commercial iron known as cast-iron and steel are entirely due to the presence of a small difference in the propor- tion of carbon present, which, after all, never rises above 2 per cent. It is thought that the known carbide of iron (Pe^ C) exists diffused in the mass, which also contains carbon in the form of graphite. Silicon and phosphorus again are known to exert a very dele- terious influence upon the quality of iron and of other metals, even when they are present in very small proportion. Numerous compounds of carbon -ndth hydrogen are luiown ; they are termed hydrocarbons. A compound of sUicon with hydrogen has been siLicopLTjonrDES. 317 discovered recently ; but aeither it nor the hydrocarbons possess acid properties or reactions. Section II. — The horofiuorides, silicofliMrides, carbonates, oxa- lates, borates, silicates, tantalates, niobiates, pelopiates, tita- nates, and sulphocarbonates. SALTS OF THE COMPOITOD ACID-RADICALS WHICH CONTAIN CARBON, BORON, SILICON, tantaldm, niobium, pelopium, and TITANIUM COMBINED WITH FLUORINE, OXYGEN, OR SUL- PHUR. The acid-radicals of the present section are for the most part powerful ; they possess different degrees of basicity. Those most important to the student will be found to be the compounds the acids of which are termed hydrofluosilicic, carbonic, oxalic, boracic, and sUieic. With the reactions of the five acids just named, the analyst should early make himself acquainted. Of acid-radicals formed hy the union of boron with fluorine, one only is known : it is the radical contained in the borofluorides, and is produced when the gas known as terfluoride of boron (B0E3) or its aqueous solution is mixed with a large quantity of water. The water effects a decomposition of the compouad B0P3, boric anhydride (Bo^Oj) being precipitated, and the com- pound HBoE^ remaining in solution : this compound is hydrofluoboric acid ; and the decomposition which gives rise to its formation is as follows : — 8B0E3 -t-SHj O =Bo2 O3 -I-6HB0E4. hjdrofiuoboric acidi The Hydrogen Salt (HB0E4) is not known in an isolated state, but only in aqueous solution. The fluoborides are all soluble in water, as far as has been ascertained. The radical must be recognized in its salts by processes of decomposition. SAMS or Sn-ICOrLtJOEINE, OE SIlICOELirOEIDES. This radical (that contained in the sUicofluorides) is of much greater importance than the preceding one, but is prepared in precisely the same manner. The method for its preparation has been already given (p. 65). When the gaseous body terfluoride of silicon (SiTj) is passed into water, the hydrogen compoimd of 318 OHEMIOAI. REACTIONS. the radical in question is obtained in solution, gelatinous silicic acid (HSiOj) being precipitated : 381^3 + 2H, = HSiO, + H3 Si, ¥,. Heated on charcoal, silicofluorides suffer various changes, ac- cording to the nature of the basic radical present. The Htdeogen Salt (HjSi^FJ is known only in aqueous solution. This radical may be recognized both by the formation of in- soluble salts and by processes of decomposition. The majority of the silicofluorides are soluble with greater or less facility in water ; it is remarkable, however, that those of the first and second subdivisions of the basic radicals are the least soluble. The Potassiitm Salt is produced by the action of a soluble potassium salt on hydrofluosilicic acid : it is a white gelatinous precipitate. Its formula is K^ Si^ Fg. It is very slightly soluble in cold water, but dissolves somewhat more freely in hot. The Barium Salt is produced by the action of a soluble barium salt upon hydrofluosilicic acid : it is a gelatinous precipitate, but appears crystalline imder the microscope. It is precipitated more speedily on stirring the solution. Its formula is Ba^ Sij Fg. It is but slightly soluble in cold water, 1 part requiring 3802 parts of pure water for its solution, and 733 parts of water aci- dulated with hydrochloric acid. In alcohol it is insoluble. The Steontium and Calcium Salts are comparatively soluble. The Magnesium Salt is exceedingly soluble. The Feeeous, Feeeic, Cupeous, Aegentic, and many othee Salts containing metals of the third and fourth subdivisions are soluble in water. The Meecueous Salt ([Hg^Jj Si, FJ is sparingly soluble. The Meecueic and Lead Salts are soluble. The salts of this acid-radical may be detected by the following processes of decomposition : — a. Hydrofluosilicic acid gradually decomposes when exposed to CAEBONArES. 319 the air in a glass vessel, terfluoride of silicon being given off, and the hydrofluoric acid thereby left attacking the glass and yielding another portion of the volatile terfluoride. In a glass bottle from which the air is always carefully excluded, and the volatihzation of any part of the gas SiF, thus prevented, no decomposition ensues. /3. Alkalies decompose hydrofluosilicic acid, yielding fluorides and sUioates. y. Strong sulphuric acid liberates gaseous terfluoride of silicon from hydrofluosUicic acid. From silicofluorides, acids separate a portion of sihoic acid, chiefly on ebullition. Of the acid-radicals which contain carbon and oxygen, two merit the attention of the student — the carbonic and the oxalic ; both are bibasic. The salts of the former radical are of very common occurrence in nature, forming (in addition to their general distribution through the earth's crust) extensive deposits, as the strata of limestones, of which they are practically the sole con- stituents. The salts of the latter radical, the oxalic, are of less frequent occurrence, although they also are found in nature, existing ia several members of the vegetable kingdom ; neverthe- less they are important as standing on what may be termed the neutral ground between the organic and inorganic domains of chemistry. The oxalates are also interesting, since they exhibit the simplification which complex organic molecules undergo in their gradual conversion into simpler forms. The oxalate is fre- quently the last stage of combination into which the carbon and oxygen of a complex body enter previously to their appearance as a carbonate, a salt which is very generally assumed to belong Lo inorganic nature. SAXTS OF THE CAEBOHTC EADICAL, OB CAEBONATES. These salts are not very numerous ; for the radical is one of such weak combining power that it is only when in union with the most powerful basic constituents (those of the first or second subdivisions), or where the salt is insoluble, that stable com- pounds are formed by it. For this reason, and on account of the 320 CHEMICAI EEACTIONS. facility -with which carbonates, especially on the application of heat, divide into metallic oxides or hydrates and carbonic anhy- dride (COj), it is found that many of the precipitates which in double decompositions should be carbonates, are in reality mixed carbonates and hydrates. Take, for example, the precipitate pro- duced by the action on carbonate of sodium of a zinc salt or any of the weaker bases, such as the triatomic molecules Al^, Cr^, Fe^, or Sb, some of which will not combine with this radical at all, or, if they do combine, yield salts which instantly or very rapidly decompose. All these precipitates of mixed hydrate and carbonate, even those which are insoluble in water, dissolve in the aqueous solution of carbonic acid gas ; and from the solution of acid carbonate so formed, crystals of neutral carbonate are often deposited : this is the case with the zinc precipitate : Zn^CO,, 3ZnH0 + 4H,C03=5ZnHC03 + 3H,0 ; mixed carbonate acid carbonate, and hydrate. the acid carbonate of zinc thus formed decomposes in the fol- lowing way : — 2ZnHC03=Zn,C03+H,0 + CO, crystalline precipitate. The alkaline carbonates, and those of barium and strontium, may be fused on charcoal vsithout decomposition ; all others are decomposed. The HroEOGEN Sam, or carbonic acid (II2CO3), is not known in the separate state. It is beheved to be formed when the gas COj is passed into water ; and the occiirrence of acid carbonates leaves little doubt of the existence of the acid, although, from its extreme instability and tendency to be resolved into water and carbonic anhydride, attempts to isolate it have not been successful. The gaseous anhydride has been condensed to a Uquid, and even to a solid. The following formulee represent the composition of carbonic acid and of the two varieties of ceirbonates : — H,C03, MHCO3, M^CO,. carbonic acid. acid carbonate. neutral (or normal) carbonate. CAEB0NATE8. 321 The carbonic radical may be recognized both by the formation of insoluble carbonates, and by a process of decomposition. The carbonates that have been obtained are almost all in- soluble, the salts of potassium, sodium, and ammonium being the only exceptions. The PoTAssruM, Sodixtm, and Ammostiiim: Saxts are soluble. The Barium Salt is a white precipitate. Its formula is Ba^COg. It is soluble in 141,000 parts of a solution of ammonia, or car- bonate of ammonium ; in 14,130 parts of pure water at 16° to 20°, or in 15,421 parts of boilitig water. It is soluble in carbonic and other acids. The STEONHtTM: Sam is a white precipitate, soluble in 18,045 parts of cold water, and readily dissolved by most acids. (See p. 88.) The Caicthm: Salt is a white precipitate, soluble in 10,600 parts of cold water, and readily dissolved by most acids. (See p. 91.) The MAGirEsruM Sait is a white precipitate, which requires 2493 parts of cold water for its sohition, and is readily dissolved by nearly all acids. (See p. 94.) The Fekeous and many otheb Saits of the third subdivision, if existing at all, decompose soon after formation as already de- scribed, or when exposed to the air or to a slight increase of temperature. The Cutbic Saxi is produced by the action of cupric sulphate upon soluble carbonates: it is a bluish green precipitate. Its formula is Cu2C03,2CuH0. It dissolves in ammonium salts and in acids, but is insoluble ia water. The SixvBE Salt is produced by the action of nitrate of silver on soluble carbonates : it is a white precipitate. Its formula is AgjCOg. It is soluble in ammonium salts and in acids, but in- soluble in water. The Mebcueoits Salt is produced by the action of mercurous nitrate on a solution of a carbonate : it is a yellow precipitate. Its formula is (HgJ^COj. p5 322 CHEMICAL EEACTIONS. The Meectjeic Salt is brownisli red. Its formula is Hg^COj, HgjO. It is slightly soluble in carbonate of potassium, soluble in chloride of ammonium and in. acids ; in water it is insoluble. The Lead Salt is white. Its formula is Pb2C03,2PbHO. It is soluble in 23,450 parts of water containing acetate, hydrate, or carbonate of ammonium, more soluble m water containing nitrate of ammonium ; it is readily soluble in many acids. 1 part dissolves in 50,551 parts of pure water at the ordinary temperature. This acid-radical may be readily recognized by the products of its decomposition. u. Almost any acid, however weak or dilute, when added to a soluble or insoluble carbonate, causes its decomposition ; and the resulting carbonic acid, by its resolution into water and the gaseous anhydride CO^, gives rise to the phsenomenon of effer- vescence. Eifervescence is caused by the escape of several other gases, such as hydrosulphuric acid or sulphurous anhydride, when certain sulphides or sulphites are similarly treated : but a pecu- liarity attends the formation of carbonic anhydride from carbo- nates ; for aU these salts, whether insoluble or not, and whatever basic radicals they may contain, are decomposed by acids, even the weakest, with evolution of the gas CO^. Now, although with the sulphides and cyanides of the first and second subdivisions, and with some few others, a somewhat similar evolution of gas takes place, yet it does not occur with all, and in many cases re- quires the employment of certain powerful acids. Chlorides too, especially alkaline chlorides, effervesce, evolving hydrochloric acid (HCl) when treated with concentrated sulphuric acid ; but weak suljahuric acid has no action upon chlorides unless heat also be appUed. ^ (3. The carbonic anhydride (CO^), usually called carbonic acid gas, which is obtained in the reaction of acids upon carbonates, may be recognized by its pecuhar smeE, but especially by its immediately forming a white precipitate of carbonate of barium when passed into baryta- water — a precipitate which, by the con- tinued passage of the gas, redissolves from formation of the soluble acid carbonate (BaHCOJ. The experiment may best be OXAIAIES. 323 made in the following manner : — Two small test-tubes are taken. Fig. 12. fitted with perforated corks and tubes, as in the annexed figure. Into the test-tube A, the suspected carbonate is to be placed, with only just sufficient water to cover the end of the tube at a. Sulphuric acid is then to be poured in at h, and the gas which issues from the tube c will then precipitate, from the baryta-water placed in the tube B, the white carbonate of barium. To assist in the detection of the gas where a small quantity only of material is pre- sent, the gas evolved may be drawn into the baryta- water by applying the mouth to the tube d, and so re- moving the original air from the test-tube B. SALTS OF THE OXAMC EADICAI,, OE OXALATES. The oxalates are very numerous, including salts of almost every basic radical, elementary or compound. Under ordinary conditions, oxalic acid and oxalates are very stable bodies. This radical forms an immense number of double salts, and many acid salts. The following formulae represent some of these com- pounds : — H,C,0, MHC.O, M,C,0, MH3C,0,. oxalic acid. acid oxalate, normal (or neutral) quadroxalate. oxalate. Oxalates, when submitted to a slightly elevated temperature, decompose, leaving a carbonate of the metal and evolving car- bonic oxide (CO), or leaving a residue of oxide and evolving both carbonic oxide and carbonic anhydride, thus : — Ca,C,0,=Ca,C03-|-C0 ; or Zn,C,0,=Zn,0 + C04-C0,. This difference in the products depends upon whether the car- bonate of a base can withstand the temperature at which the oxalate decomposes. The oxalates of potassium, sodium, and calcium are found in the juices of various plants ; and the hy- drogen compound of this radical is also a very common product of the action of oxidizing bodies upon complex molecules. 324 CHEMICAL EE ACTIONS. The Hybeo&en Salt (H^C^Oj, or H^O), or oxalic acid, is a white crystalline solid, wMoh sublimes between 100° and 162° without decomposition, and condenses in. slender colourless nee- dles : it is poisonous, and its vapour when breathed has a most irritating effect. The oxalic- radical may be detected both by certain insoluble salts, and by its decomposition. Many oxalates are iasoluble in water — ia fact, the majority of the neutral salts : many of the acid salts are more soluble ; but it is singular to find that, among the oxalates of the first subdivi- sion, the acid salt is generally less soluble than the neutral one. The Potassium and Sodium Salts are comparatively soluble iu water, although the latter (Na^C^O^) requires as much as 36'4 parts of cold, or 24-6 of boOing water for its solution. The Bamum Salt is precipitated by adding chloride of barium to solutions of oxalic acid or oxalates : if the acid be employed, crystals of the acid oxalate speedily separate ; if a soluble oxa- late, an immediate dense white precipitate of neutral oxalate will fall. The complete formula of the former salt is BaI[C2 0^-|-2aq ; of the latter, Ba^C^O^-l-aq. They are both sparingly soluble in cold water ; the acid salt dissolves more readily in hot water ; they both dissolve also in chloride of ammonium solution. (See p. 85.) The Steontittm: Salt is produced by the action of nitrate of strontium on oxahc acid or soluble oxalates. Its formula is Sr^CjO^. It is sparingly soluble in cold water, but only requires 19-2 parts of boiling water for solution. (See p. 88.) The Calcium Salt is produced by the action of soluble calcium salts on oxahc acid or oxalates: it is a white granular pre- cipitate. Its formula is Ca^CjO^-t-aq. It is insoluble in chloride of ammonium and in water ; it is also insoluble in acetic acid, but dissolves in the stronger acids readily. The Magnesium Salt is soluble. The Feekotts and some oihee Salts of the third and fourth subdivisions are soluble ; but the majority ai-e sparingly soluble. OXALATES. 325 The Cupsotjs Salt is white ; it is soluble in hydrate of am- monium. The Cupeic Salt is a greenish blue precipitate. Its formula is Cu^CjO^+aq. It is soluble in neutral alkaline oxalates, and in hydrate, carbonate, and succinate of ammonium, but not in other ammonium salts. It is insoluble in water, in oxalic acid, and in warm dilute nitric acid. It dissolves in warm concen- trated hydrochloric acid. The Silver Salt (Ag^C^O^) is a white precipitate. It dis- solves in hydrate and carbonate of ammonium, and in warm so- lutions of other ammonium salts. It is scarcely soluble in water, but dissolves in nitric acid. The Meectjkotjs Salt is precipitated by the action of mercu- rous nitrate on oxalic acid or soluble oxalates: it is a white precipitate. Its formula is (HgJ^CjO^+aq. It is but slightly soluble in water or in dilute acids. The MEEcrrEic Salt is a white precipitate. Its formula is HgjCjOj+aq. It is soluble in solutions of chloride and nitrate of ammonium, insoluble in water and dUute acids, somewhat soluble in sulphuric acid, and dissolved easily by other strong acids. The Lead Salt is a white precipitate. Its formula is Pb^CjO^ (dried at 140°). It is soluble in most ammonium salts, the hydrate and carbonate excepted ; it is insoluble in water and in acetic acid, but soluble in nitric acid ; it is somewhat soluble in oxalic acid. The oxalates may be detected by the decomposition of their acid-radical. a. When to an oxalate some strong sulphuric acid is added, and the mixture warmed, the oxalic acid thus liberated undergoes instant decomposition, partly from the tendency of sulphuric acid to form a hydrate : H,C,0,+H,SO,=H,SO„ H^O-t-CO-l-CO,. Considerable effervescence ensues from the escape of the carbonic anhydride and carbonic oxide gases ; and the latter gas wUl be found to bum with a blue flame. This action of sulphuric Bwjid, 326 CHEMICAL EEACTIONS. without any blackening of the substance under examination, poiats decisively to the presence of oxalic acid ; for though the salts of some of the more complex acid- radicals yield carbonic oxide also, they blacken simultaneously, the ferrocyanides ex- cepted. /3. If, instead of sulphuric acid alone, a mixture of binoxide of manganese (Mn^O^) and sulphuric acid be made to act upon oxalic acid, the sole gaseous product of the reaction is carbonic anhydride (CO^). SALTS OE THE BOEACIC RADICAL, OE BOHATBS. These salts are by no means of such frequent distribution in nature as the carbonates ; they occur in some few minerals, and in greater abundance in the hot lakes or boracic lagoons of Tuscany, into the waters of which the vapours are conveyed which rise from the volcanic bottom. These vapours, which are charged with boracic anhydride (Bo^Oj), yield it to the water, with which it combines to form boracic acid. It is generally met with in commerce combined as borax, the biborate of sodium. Most borates may be heated on charcoal without decomposi- tion. The use of borax as a blowpipe reagent is weU known. The Hyuko&en Salt crystallizes from a hot aqueous solu- tion ; but if these crystals be heated, they evolve water, and yield a fused glassy substance, which is the so-called anhydrous acid (BOjOg). This body bears the same relation to boracic acid as chromic anhydride does to chromic acid. "When dissolved to saturation in hot water, it separates on cooling, in the form of hexagonal laminae having a pearly lustre and the formula HBoOj+aq. It may be considered as the representative of what are called the monoborates, which have the formula MBoO^+naq. If these crystals be heated to a temperature considerably above 100°, they part with the elements of water, and another hydro- gen compound is obtained (Hg BojO,), which, when written with- out its 2 eqs. of accidental water, becomes H^ Bo^ 0„ and may then bo considered as the type of the biborates. The biborates may BOEATES. 327 also be viewed (like the bichromates) as combinations of the an- hydride (BOjOj) with the monoborates ; thus we have the following equation when we disregard water of crystaUization : — 2HBo02+Bo,03=H,Bo,0,. The rationale of the process whereby the biborates are pro- duced may be as follows : — ^we may suppose that, under the in- fluence of heat, 1 molecule of the anhydride (Bo^Oj) is formed from 2 equivalents of boracic acid, thus : — 2(HBoO„ H,0)=Bo,03+3H,0 ; the body, Boj O3, thus formed, then unites with 2 equivalents of undecomposed acid to form the biborate of hydrogen. Or we may merely express the change as foUows : — 4(HBoO„ H,0)=H,_Bo,0„ 2H,0-t-3H,0. Borates, then, may be of at least two classes, borates and bibo- rates. The latter salts are much more stable than the former — so much so, indeed, that even the potassium salt of the former series, by mere exposure to the air, absorbs carbonic anhydride, and becomes converted into the carbonate and biborate, thus — 4E:BoO,-FCO,=K,C03+K,Bo,0,. Nor are these the only classes of borates. Just as boracic an- hydride combines with borates to form biborates, so additional proportions of this body yield salts which have been caUed ter-, quadri-, and sex -borates. The formulae of the sodium (or potas- sium) salts of these compounds are — Borate Na Bo 0,. Biborate Na,Bo, 0, =2NaBoO,+ Bo,0, Terborate K. B03 0,„ =2KBoO, -F2Bo,0^ Quadriborate Na,Bo, 0,3: =2NaBo02+3Bo,0, Sexborate Na,Bo,,0,,: =2NaBoO,-t-5Bo,0, The borates, biborates, and sexborates are pretty well known ; but not so the others. The boracic radical may be recognized both by the formation of sparingly soluble salts, and by processes of decomposition. The normal borates are more soluble in water than the others. Of the biborates, which are the most common boracic salts. 328 CHEMICAL EEACTIONS. almost all, excepting those of tte first subdivision, are insoluble in water. The Potassiitm Salt (K^Bo^O^+Saq) is soluble. The Sodiitm Salt (Na^Bo^O^+lOaq), or borax, is soluble. The Babittm Salt is produced by the action of soluble barium salts on a solution of borax. It is a wbite precipitate. Its formula is Ba2Bo^O,+2aq. It is soluble in excess of cbloride of barium, also in ammonium salts ; it dissolves in 100 parts of cold -water, and in a smaller quantity of boiling water ; it is so- luble in acids. Before the blowpipe it fuses to a grey glass. The Sthontitjm Salt is produced by the action of a soluble strontium salt on a solution of borax : it is a white precipitate. It dissolves readily in cold solutions of chloride or nitrate of ammonium ; 1 part is soluble in 130 parts of boiling water. The Calcium. Salt is produced by the action of a soluble cal- cium salt on a solution of borax. Its formula is Ca^Bo^O^+aq after having been air-dried. It is scarcely soluble in water, but dissolves in acids. Before the blowpipe it fases to a glass. The Pbebotjs, Fekkic, and mant othee Salts of the third and fourth subdivisions are yellowish or white precipitates, insoluble in water. The Cupeic Salt is a pale green precipitate, slightly soluble in water, and dissolved easily by a solution of boracic acid. Before the blowpipe it fuses to a green opaque glass. The Silvee Salt is white : its formula, under all circum- stances, is AgBoOj. It is sparingly soluble in water. The Meecueous and Meecueic Salts do not appear to exist ; the biborates precipitate basic mercury compounds. The Lead Salt is obtained by the action of soluble lead salts on a solution of borax : it is a white precipitate. Its formula is Pbj Bo^O,. It is insoluble in excess of its precipitant, but slightly soluble in pure water. This acid-radical is also detected by the foUo'WTng experiments. u. When sulphuric acid is added to the aqueous solution of a borate, boracic acid separates in characteristic crystalline scales (HBoOj-l-aq). If the boracic acid be then dissolved in alcohol, SILICATES. 329 and the solution kindled, the flame produced -will have a darh green edge, best seen against a black background. In this ex- periment, the presence of chlorides and of copper salts should be avoided. /3. The most characteristic reaction of boracic acid is the action of its aqueous solution on turmeric paper. All other acids exert no influence upon ordinary yellow turmeric paper, or, if it has been browned by an alkali, they simply restore its original colour; but boracic acid behaves Kke an alkali, turning the yeUow of the paper to a reddish brown. The suspected borate is mixed with hydrochloric acid, and into the mixture a smaU. piece of turmeric paper is placed. The test is appUed in a white porcelain dish. y. Sulphuretted hydrogen and ferrocyanide of potassium pro- duce no characteristic actions upon boracic acid or soluble borates. SALTS OP THE SILICIC EABICAL, OE SILICATES. These salts are of universal distribution in nature : they form a very large proportion of the rocks constituting the earth's crust, and enter into the composition of many minerals. Heated before the blowpipe, most silicates fuse to a colourless or coloured glass. The HrDEOSEif Salt (HSiOJ, or sUicic acid, is not very well known ; it is believed that the body termed gelatinous silica has, when air-dried, this formula, but when dried at 100° the formula H^Si^O,, i.e. 2ES!iO^-^^i.fi^ : at a higher temperature it is resolved into water and sihcic anhydride (Si^Og). This body (SijOj), which bears the same relation to silicic acid (HSiOj) as boracic anhydride (Bo^Oj) bears to boracic acid (HBoOj), is of very common occurrence, and is familiar to every one under the forms of quartz, amethyst, sUieeous sand, flint, and chalcedony. Silicates are as various in their constitution as they are great in number ; but, as we have seen in the tung- states, ehromates, and especially in the borates, a number of acid-radicals may be buUt up by the assimilation of successive additions of the body which has been termed the anhydride. 330 CHEMICAL EEACTIONS. into -whicli and water all these complex acids are capable of splitting. Silicates are best recognized, not by the formation of insoluble salts, but by certain cbaracteristio products of decomposition which they yield. Silicates are very generally insoluble in water, the neutral and basic silicates of the first subdivision being almost the only ex- ceptions. The Potassittm Salts KSiO^, K^Si^O,, and K^Si^Oj^ are solu- ble in water; the salts K^SiijOj^, K^Bi^o 055 + 9aq, and K^Si^gO^ + 16aq are insoluble. The Sobium Salts NaSiO^-l-Saq, Na^Si^Oj^, and Na^SijOj, + 12aq are soluble in water ; those containing a larger addition of silicic anhydride are insoluble. The BAKruM, Calcium, and Magnesium Salts are white. They are insoluble in water, but soluble in acids. The Feeeous and othbe Salts of the third and fourth sub- divisions are insoluble in water. The Cupeic Salt is green ; the Silvee and Meecueotjs Salts white. The Meectteic Salt is tolerably soluble : it occurs in small dark crystals. The Lead Salt is precipitated from silicoiluoride of lead by hydrate of ammonium : it is a white precipitate, insoluble in water. This acid-radical is invariably recognized by the decomposition and behaviour of its salts. a. Many silicates, insoluble in water, are readily dissolved by acids ; others, again, are insoluble both in water and in all acids, the hydrofluoric excepted. The latter class of silicates may be converted into compounds quite soluble in acids and even in water, by the following process : — The insoluble silicate is mixed with four times its weight of hydrate or carbonate of potassium, or of the mixed carbonates of sodiiun and potassium, and the mix- ture fused for 15 minutes ; the mass should remain quite liquid for 10 minutes ; this fusion of course yields the alkaline silicate 8ILICATES. 331 by ordinary double decomposition. By the preceding process, a mass ■will be obtained ■which, in most cases, ■will dissolve .slo'wly in ■water, or at least the alkali and alkaUne silicate ■wiU. dis- solve, leaving a residue of metallic carbonate or oxide. In acids the fused mass ■will dissolve readily ; and then, if to the solution we proceed to add excess of acid (e. g. hydrochloric acid), a pre- cipitate of silicic acid will be formed, ■which, on the addition of a further portion of acid, again dissolves. If no^w the clear so- lution be evaporated to perfect dryness on a water-bath (at 100°), then moistened ■with water, and again evaporated to en- sure the expulsion of all free acid and moisture, the decompo- sition of the silicic acid iato water and silicic anhydride ■wUl have taken place, and the resulting white powder will be foimd per- fectly insoluble in water and in all acids except hydrofluoric. So perfect is this decomposition, that the most minute trace of silicic acid may be thus detected, and it is employed in the quantitative estimation of this substance. /3. An experiment already given on page 66, and also described as one of the tests for the presence of fluorine, serves for the detection of sUicon. A smaU. tube of lead closed at one end, perfectly dry, and fitted ■with a dry cork and leaden delivery- tube, is employed ; and into this vessel a mixture of equal weights of the substance to be tested for silicon and of fluoride of calcium is introduced, together -with, about t^wice the bulk of oil of ■vitriol. The delivery-tube should then be dipped under the surface of a small quantity of water contained in a cup of lead, and heat applied to the mixture : if silicon be present, the gaseous ter- fiuoride of silicon (SlF,) ■wiU be disengaged, which, coming in contact ■with water, ■will yield a gelatinous precipitate of silicic acid, and the solution wUl contain hydrofluosiLioic acid, recog- nizable by the usual tests. y. Wien gelatinous silicio acid is dried, it yields, as has been stated, the anhydride (Si^Oj), a fine white scaly powder of ex- treme lightness. If now a bead of carbonate of sodium be made on a platinum ■wire, and, when it is red-hot, silicic anhydride be added little by little, fusing the bead between each addition of 332 CHEMICAL EEACTIONS. substance, a period will arrive at which the bead no longer pre- sents the opacity of fused carbonate of sodium when cold, but remains perfectly pelliuiid. 8. If a bead of microcosmic salt be made, and some silica (SijOj) fused with it, the anhydride will remain undissolved, and float about the bead as a network or skeleton. t. Hydrosulphuiie acid and ferrocyanide of potassium give no characteristic reactions with silicic acid. This radical is usually detected by the tests a, /3, and y. Of compound acid-radicals containing tantalum and oxygen, two are known; they ocem' in a mineral termed "Tantalite," one variety of which consists of ferrous tantalise, 'Ee^a.fi^ ; other varieties are composed of ferrous tantalafo, FeTaOj. SALTS OF THE TANTALIO KADICAL, OK TANTALATES. Tantalic aeid, and many tantalates, when heated, yield tantalic anhydride (Ta^Oj). The Hydrogen Salt (HTaO^), or tantaUo acid, is known : it is ob- tained as a snow-white bulky precipitate, quite insoluble in water, and, when washed, but slightly soluble in many acids, except sulphuric acid, from its solution iu which, water reprecipitates it, and hydrochloric acid, which dissolves it somewhat more abundantly. It dissolves readily in the hydrate or the acid oxalate of potassimn, in boiling solutions of alkaline carbonates, and in hydrofluoric acid. The formula of the precipitate is HTaOj-faq. The tantalic radical is detected by the formation of insoluble salts, but especially by processes of decomposition. The alkaline tantalates are soluble in water, but are precipitated by or- dinary salts of ammonium. The sodium salt is also precipitated by the addition of excess of hydrate or carbonate of sodium, — a behaviour whereby tantalic acid is distinguished from all other acids (except niobic and pelopie), particularly from tnngstic acid, to which, iu many points, it bears a great resemblance. The Potassium Salt is soluble in pure water, nearly insoluble in cold carbonate of potassium solution. The Sodium Salt is sparingly soluble in cold water ; when the solution is boiled, it deposits a bitantalate. The Barium and Calcium Salts are white and insoluble. The Calcium, Magnesium, and Copper Salts are unknown. The Silver Salt is white and insoluble. The Mercury and Lead Salts are unknown. This acid-radical is detected by the following tests : — a. From soluble tantalates, hydrooliloric acid precipitates tantalic acid TITANATES. 333 (HTaOj), which, on addition of excess of the precipitant, is redissolved, but again separates on the addition of sulphuric add and subsequent ebullition, a compound of that acid with tantalic acid being produced. 13, If into the sulphuric acid precipitate (just mentioned) still remaining in the slightly acid liquid a strip of zinc be plunged, as it dissolves, a fine blue colour wiU be imparted to the liquid ; this tint will, however, change to a brown, and, finally, brown fiakes will separate, which, after some time, will become oxidized, and converted into tantalic acid. y. Precipitated tantalic acid is insoluble after ignition, in all acids, and must, like ignited silica (SijOj), be fused with hydrate or carbonate of sodium. d. Hydrosulphuric acid does not precipitate an acid solution of tantaUo acid. 6. In a slightly acidified solution of tantalic acid, ferrocyanide of potassium produces a yellow precipitate, and ferricyanide a white. Of compound acid-radicals containing niobium and oxygen, one is known, the radical of niobic acid. Of its salts, the niobiates, almost all that has been said regarding the tantalates equally well applies. The acid is, however, more completely separated from its salts than tantalic acid is from tantalates, on the addition of sulphuric acid, not requiring the aid of heat. Of compound acid-radicals containing pelopium and oxygen, one is known, that existing in pelopic acid. Its salts bear the closest resemblance to the tantalates and niobiates. SALTS or THE TITANIC EADIOAL, OK TITANATES. Two combinations of titanium with oxygen are known ; the lower oxide has not, however, been observed to manifest any tendency to pass iato an acid-radical. The titanic radical occurs in numerous minerals. In Titanite it occurs as titanate of calcium (Ca^TijOj) associated with silicate of calcium, while it is most frequently found in the varieties of titaniferous iron, one of which, Ilmenite, is the ferrous titanate (Fe^Ti^Og). Titanic acid when heated before the blowpipe yields the infusible titanic oxide Ti^Oj. The titanates are not generally decomposed by fusion, but, on the contrary, many salts of this radical are prepared by fusing titanic oxide vrith metallic carbonates. The Hydeogen Salt is prepared just as the analogous compound of sUicon, by the gradual addition of an acid. It is a white, flocculent, and bulky precipitate, and consists (when dried in vacuo over sulphuric acid) of the pure substance H^Ti^Og. The acid thus obtained, if washed with cold, not with hot water, dissolves readily in acids, but not in the hydrates of the first subdivision, and only to a trifling extent in alkaline carbonates. When the acid solution of titanic acid is diluted with much water and boiled, a precipitate occurs, probably of the body (TijO^) already mentioned as obtained by the ignition of the acid. It is a white precipitate, becoming yellow on heating. It is quite insoluble in water, and in all acids except hydrofluoric 334 CHEMICAL EEACTIONS. and boiling sulphuric acids. It occurs naturally in the minerals Kutile and Anatase. The titanates are, for the most part, insoluble in water. The monotitanates of the first subdivision are decomposed by water into a basic salt, which dis- solves, and an acid salt, which is precipitated. The barium, calcium, silver, mercury, and lead salts are unknown. This acid-radical is recognized by the following processes of decom- position : — a. When the hydrochloric solution of titanic acid is diluted and boiled, the oxide or anhydride (TijO^) separates as a white powder. |8. The oxide Ti^O^ requires fusion with carbonate of sodium to render it soluble. y. If into the hydrochloric solution of titanic acid a strip of ziuc be intro- duced, a blue solution will be obtained ; and from this a reddish or violet precipitate will separate, which gradually oxidizes into the white titanic acid. d. Titanic anhydride (Ti.fl^), when fused with microcosmie salt in the re- ducing flame, gives a violet-blue bead on cooUng : the colour is rendered more evident after the addition of tin. If iron be present, a yellow or blood- red bead will be produced in the reducing flame. c. Hydrosulphuric acid does not precipitate an acid solution of titanic acid. ?. Ferrocyanide of potassium gives a dense orange brown precipitate in a solution of titanic acid in weak hydrochloric acid. The precipitate is soluble in excess of the precipitant. SALTS OF THE SULPHOCARBONIC EADICAL, OK SULPHOCAKBONATES. These salts are usually of a yellow, red, or brown colour ; many of them decompose with rapidity into sulphides. They closely resemble the car- bonates in constitution, the oxygen of those salts being replaced by sulphur, thus — K,C,03, KjC^Sj. carbonate of sulphocarbonate of potaasium. potassium. On a slight increase of temperature, the sulphocarbonates decompose into bisulphide of carbon (CSj) and metallic sulphides. The Hydeogen Salt (HjCjSa) or sulphocarbonic acid, is a reddish brown, transparent, oily liquid, denser than water ; it has a very peculiar odour, and is prone to decompose into hydrosulphuric acid and the body CSj, which is the sulphocarbonic anhydride, and bears to sulphocarbonic acid the same relation that carbonic anhydride (CO,) bears to cai-bonic acid (H,C03). The sulphocarbonates may be recognized by certain insoluble compoimds, and also by their products of decomposition. The soluble sulphocarbonates have a saline and somewhat sulphureoiu taste ; those of the first and second subdivisions are soluble in water, as are also some members of the third subdivision. CTANIBES, CTANATES, ETC. 335 The P0TA88IUM, Sodium, Bakium, SiBONTinM, Caicium, and Magnesium Salts are soluble. The Cupeic Salt is red-brown when precipitated from sulphoearbonic acid, dark brown when from sulphoearbonate of calcium (CajCSj); it is soluble in excess of its precipitants ; it becomes black on drying. The Silver Salt is produced by the action of sulphoearbonate of calcium on silyer salts : it is a dark brown precipitate, which becomes black on dry- ing. It is soluble in excess of its precipitant. Tie Mercuric Salt is yellow when precipitated by sulphoearbonate of ammonium ([NHj]2CS3), black when the calcium salt is employed. The yellow salt passes from yellow to orange red and black, with evolution of bisulphide of carbon. The Lead Salt is dark brown when precipitated by sulphoearbonate of calcium, but red when sulphoearbonic acid or the ammonium salt is em- ployed ; it rapidly becomes black from separation of sulphide of lead (Pb^S). The sulphoearbonic radical may be readily distinguished by the following tests: — a. When to the solution of a sulphoearbonate a strong acid is added, the sulphoearbonic acid liberated is at once decomposed into hydrosulphuric acid and the oily body, bisulphide of carbon (CS2), both products being easily identified not only by their reactions but by their unmistakeable and unpleasant odour : /3. If the aqueous solution of a sulphoearbonate be evaporated two or three times with excess of sulphide of ammonium, and the resulting mass dissolved in water, filtered, and the solution then tested with ferric chloride (Fe^Clj), the magnificent blood-red colour of sulphoeyanide of iron wiU be produced. This radical is perhaps best recognized by the formation, &c. of the mer- curic and lead salts, and by the tests a. and /3. Section III. — TJie cyanides, cyanates, and suVphocyanides ; the ferrocyanides, ferricyanides, and cobalticyanides ; the for- miates, acetates, benzoates, succinates, tartrates, lactates, ci- trates, gallates, tannates, and urates. SALTS or THE COMPOimD ACID-BADICALS WHICH CONTAIN CAEBON AND NITEOGEN; CAEBON, NITEOGEN, AND OXY- GEN; CAEBON, NITEOGEN, AND SULPHUE; CAEBON, NI- TEOGEN, AND METAIiS ; CAEBON, OXYGEN, AND HYDEO- GEN; AND CAEBON, OXYGEN, HYDEOGEN, AND NITEO- GEN. To these salts the term " organic" is generally applied, from their naturally occurring almost solely in the organic kingdoms 336 CHEMICAL EEACTIONS. of nature. Many of these bodies do not, however, occur actually in nature, but are the artificial products of a chemical action upon natural substances. It was thought tDl recently that the building up of complex molecules from the common and simpler bodies at his disposal was not within the power of the chemist : but the experiments of recent years have shown this to be a fallacy ; for, by sldlful manipulation and ingenuity of contrivance, many most complicated substances have been artificially constructed. Nu- merous bodies have not yet been thus produced ; but their number is constantly diminishing. By a consideration of the members of this section, it will be seen that they are often arranged in series, somewhat after the manner of the borates, already alluded to ; and it needs but little discernment to predict that, if by a certaia process one member of such a series can be formed, by a slight variation of the experiment to suit the circumstances of the spe- cial case, every member of the group may probably be produced at will. The invention of a method is a discovery ; but the pro- duction of all subsequent members of the series is but the appli- cation of a principle. Of odd-radicals formed hy the union of carhon with nitrogen, one only is of any analytical importance, viz. cyanogen. SALTS OF CTANOOEN, OE CTASIDBS. These bodies occur in some few organic products ; and the radical may also be formed directly from its elements by exposing hydrate or carbonate of potassium to the joint action of carbon (or carbonic oxide) and nitrogen, at a high temperature. This action has been made to take place by employing charcoal saturated with the salts just mentioned, and heating it strongly in a vertical shaft to which the nitrogen, &c. of a furnace-flue was admitted by ap- propriate openings. The radical is thus obtained in combination with potassium. It may also be obtained by the decomposition of ferrocyanide of potassium. (See p. 63.) The cyanides of the first subdivision may be fused without de- composition, excepting the ammonium salt, which volatilizes un- changed ; the fusion may be effected on charcoal. The cyanides CYANIDES. 337 of the second subdivision also sustain a high temperature without change. Many other cyanides, however, decompose iato cyanogen gas and metal, or into cyanogen gas and a mixture of the metal with a paracyanide : such cyanides are the silver and mercuric salts. Others, again, are resolved into their elements — carbon, nitrogen, and metal ; e. g. cyanide of lead (PbCN or PbCy). The Hydeogen Salt (HON or HCy), hydrocyanic or prussic acid, is remarkable as being one of the most terrible poisons known. It is a transparent, colourless, mobile liquid of sp. gr. 0-705— 0-710 at 6° C; it freezes at —15°, boDs at 27°-5, and volatOizes ia the air with such rapidity, that the cold pro- duced by the evaporation of a portion freezes the remainder : it is inflammable, burning with a pale blue flame. In a state of great dilution, it is used in medicine. Pure hydrocyanic acid and its aqueous solution, if tolerably concentrated, rapidly decom- poses, yieldiag ammonia and a brownish black powder. The presence of a trace of miueral acid prevents this change ; but a large quantity of a strong acid itself causes a decomposition, the hydrocyanic acid then yielding an ammonium salt and formic acid, thus — HCN+HC1+2H,0=NH,CH-HCH0,. hydrocyanic formic acid. acid. This radical may be detected both by the formation of iasoluble salts and by its products of decomposition ; also by certain com- plex bodies which it may be made to yield. Eegarding the solubility of cyanides, it may be stated that the salts of the first and second subdivisions are readily soluble in water : for the bases of the first half of the third subdivision this radical exhibits little aflBnity; but the cyanides of iron, manganese, cobalt, nickel, and zinc, and those of the fourth subdivision, are for the most part insoluble in water. The insoluble cyanides aU. exhibit the peculiarity of dissolving in excess of alkaline cyanide, to form compounds in which a new, and often very stable, com- pound acid-radical is believed to exist. Such a change is repre- sented, in the case of iron, by the foUovnng equations : — Q 338 CHEMICAI, EEACnONS. KCy+reCl=PeCy+E:Cl ; ppt. reCy+2KCy=2E:Cy, reCy=K:,FeCy3. double cyanide ferrooyanide of potassium of potassium, and iron. The ferrocyanides are usually writteii M^Cfy. These changes have already been alluded to under iron and cobalt, pp. 120, 132. The Potassium, Sobitjm, Bakium, Sxeonhum, Caicittm, and Magnesium Salts are soluble. The Peeeotts Salt (FeCy) is a light reddish brown precipitate. (See p. 120.) The Cueeous Salt is white : it is generally produced by adding to a soluble cuprie salt, first, sulphurous acid, and then hydro- cyanic acid or cyanide of potassium. Its formula is Cu^Cy. It is soluble in cyanide of potassium, in the hydrate and many other ammonium salts, and ia concentrated hydrochloric acid. The Cupeio Salt is brownish yellow. It decomposes sponta- neously into eupro-eupric cyanide and cyanogen gas. Its for- mula is CuCy. It is soluble in excess of cyanide of potassium. The Silver Salt is a white curdy precipitate. Its formula is AgCy. It is soluble in alkahne cyanides and hyposulphites, in ferrocyanide of potassium, and in hydrate of ammonium. It is decomposed by strong hydrochloric, nitric, and sulphuric acids, more especially on boiling ; the dilute acids act but slightly on it. The Meecueous Salt is unknown : mereurous nitrate produces with cyanide of potassium a grey precipitate of metallie mercury, mercuric cyanide being formed and dissolved. The Meecueic Salt (HgCy) is soluble. The Lead Salt is white. Its formula is PbCy. It appears to be insoluble iu the cyanides of calcium and potassium. It is decomposed by cold dilute sulphuric acid, but not by dilute nitric acid. This acid-radical is also recognized by the foUowing changes and decompositions : — a. When hydrocyanic acid is set free by the action of a di- lute acid on its salts (dilute hydrochloric acid is found to answer CTAIflDBS. 339 best*), and heat applied to the liquid, the acid, as it escapes, may he seen to be inflammable by applying a light to the mouth of the tube. It bums with a blue flame. This vapour has also a most peculiar smell, resembling, when diluted with much air, the odour of peach-blossoms ; it also produces a singular sense of heat at the hack of the throat a few seconds after inhalation. These ex- periments, and the others about to he described, if performed at all, should be tried on a very small scale, and with the greatest precaution. /3. If the mercuric or silver salt be obtained, dried, and care- fully ignited in a short and very narrow tube, the gas cyanogen is disengaged, which, though generally considered to be the acid- radical itself, is, as we have previously shown, more probably the cyanide of cyanogen, CyCy. This gas, upon the appUcation of a light, bums with a violet Jlame. y. If a cyanide be decomposed by a drop or two of acid, in a watch-glass over which is inverted a second watch-glass moistened with a trace of sulphydrate of ammonium solution containing sulphur in excess, placed iu the centre of its concave surface (the circumferences of the two glasses accurately fitting), the hydro- cyanic acid evolved will be found, after the lapse of a few minutes, to have given rise, by its action on the sulphide, to the salt known as sulphocyanide of ammonium, thus — HCy -h NH.HS -I- S=NH,CyS -I- H,S. The sulphocyanide thus produced may be recognized by a ferric salt ; but, in order to ensure success, the upper watch-glass should be placed in a water-bath (that aU remaining sulphydrate of am- monium may evaporate), and to the residue a small quantity of a solution of ferric chloride added : the magnificent hlood-red colour of ferric sulphocyanide will be at once produced, and is indicative of the presence of cyanogen in the original substance tested. * When it ia desired to distinguish the odours of acids, concentrated re- agents should not in general be employed as liberators of the acids ; for nitric, hydrochloric, and several other acids, being themselves volatile, may completely mask all other odours by their own pungent vapours. a2 340 CHEMICAL EEACTIONS. S. If we take an alkaline cyanide (which may be made from any other cyanide by boiling the latter with hydrate or carbonate of potassium and filtering), and add to it a solution containing a ferrous and a ferric salt, warming the liquid at the same time, the excess of alkali present will of course produce a dense pre- cipitate, consisting apparently of ferrous and ferric hydrates only ; but if to the precipitate an excess of dilute hydrochloric acid be added, the presence of a blue compound, previously masked, win be rendered manifest. This precipitate is Prussian blue ([Fe^JjCfyj), or ferric ferrocyanide ; and its production is an ex- cellent indication of the original presence of cyanogen. A word of explanation with regard to the formation of the ferrocyanogen salts just described may be introduced here. The ferrous and ferric salts, though added simultaneously, may be more conveniently considered as acting separately; and the changes may be regarded as taking place in the following order : — f ECy +PeHO =PeCy+KHO ^ J ferrous ■I* "j hydrate. (.2KCy+FeCy=K,PeCy3=K,Cfy. ferrocyanide of potassium. ferric hydrate, prussian blue. e. Mixed solutions of hydrate and cyanide of potassium dissolve mercuric oxide (Hg^O) with great facUity ; and since this oxide is quite insoluble in a solution of hydrate of potassium which has been mixed with any other salt but an alkaline cyanide, this solvent power is therefore an indication of the presence of cyanogen. Cyanogen is most usually identified by the tests /3, y, and S. Of acid-radicals formed hy the union of carbon, nitrogen, and oxygen, one is known, the cyanic. SALTS OF THE CYANIC RADICAL, OR CYANATES. The salts are commonly obtained by the action of oxidizing agents upon cyanides. The potassium salt may be readily produced by fusing cyanide of potassium with the oxides of lead or copper ; " red lead" is frequently em- ployed for the purpose. SULPHOCTAIflDES. 341 Alkaline cyanates are not decomposed by simple fusion ; but, like all other cyanates, they are instantly decomposed when heated on charcoal. The Hydeogen Salt (HCyO), or cyauio acid, is a colourless liquid which has a peculiar odour intermediate between that of acetic acid and that of sulphurous anhydride (SOj). It presents the peculiarity of spon- taneously changing into a white solid called cyamelide. An aqueous solu- tion of the add yields, at ordinary temperatures, acid carbonate of ammo- nium, thus — HCNO-I-2H2 O=NH4H0O3. Most of the cyanates are more or less soluble in water, those of the first and second subdivisions dissolving readily. The Potassium, Sodium, Barium, Stkontium, Calcium, and Magnesium Salts are soluble. The Febeous Salt does not exist. The Cupeio Salt is a greenish brown precipitate. The Silver Salt is a white precipitate. Its formula is AgCyO. It is soluble in cyanide of potassium and in hydrate of ammonium ; it dissolves sparingly in boiling water, and is almost insoluble in cold water. It is de- composed by dilute nitric acid. The Mbecueous Salt is white. The Lead Salt is white. Its formula is PbCyO. It is slightly soluble in boiling water, and is dissolved, with decomposition, by dilute nitric acid. This radical may also be detected by its decomposition. a. When cyanic acid is set free by the action of an acid on a cyanate, it decomposes with an effervescence due to the escape of carbonic anhydride (CO2) : the pungent odour of cyanic acid, which in part escapes undecom- posed, will be very perceptible. If the liquid be tested for ammonium, additional evidence will be obtained of the original presence of the cyanic radical: the two reactions, which occur simultaneously when a cyanate is decomposed by an acid, may be represented in one equation, — Hj 0-f 2E:CN0+2H2 S0^=HCN0-l-KHS0i-l-KNH4 SOj+COj. j3. Hydrosulphuric acid is said to decompose cyanic acid. The cyanic radical is generally recognized by the test a. Of acid-radicals prodziced hy the union of carbon, sulphur, and nitrogen, one is well known, viz. the sulphocyanic. Its soluble salts are very useful as tests. salts op sulphoctauogen, ok sulphocyanides. The sulphocyanides are prepared much in the same way as the cyanates, substituting sulphur for oxygen : the potassium salt, for instance, is generally obtained by fusing ferrocyanide of potassium with carbonate of potassium and sulphur. (See p. 54.) 342 CHEMICAL EEACirONS. The sulphocyanides are all more or less easily decomposed when heated, and yield very varied and very numerous products. The Hydeogen Salt (HCNS or HCsy), hydrosulphoeyanic acid, may be produced by saturating hydrocyanic acid with hydrosulphuric acid, and exposing the liquid to the air. When pure, it is a colourless oily liquid, having a pungent odour like that of acetic acid: it freezes at 12°-5, boils at 102°-5. It is very poisonous. On keeping, it is speedily resolved into a new acid, hydropersulphocyanic acid, with evolution of hydrocyanic acid, thus — 3HCNS =HCN +H2 C^ N^ S3, yellow ppt, Sulphocyauogen may be recognized by the insoluble salts which it forms' by the remarkable colour of the ferric salt, and by the products of decompo- sition which its compounds yield. The majority of the sulphocyanides of the three first subdivisions are soluble in water. The chief insoluble compounds are the silver, mercurous, and lead salts. The Potassium, Sodium, BAKinM, Strontium, Calcium, and Magnesiuji Salts are soluble. The Ferric Salt, though soluble, is very characteristic : it imparts to water a magnificent blood-red colour. The Cupeous Salt is a white precipitate. Its formula is Cu^CNS (=Cu2CBy). It is scarcely altered by hydrochloric acid ; but nitric and sul- phuric acids decompose it. The Cupkic Salt does not separate from dilute solutions ; if concentrated solutions be employed, a precipitate is obtained which is grey from the ad- mixture of cuprous sulphocyanide. The pure cupric salt may be produced by adding some sulphuric acid to a concentrated solution of sulphocyamde of potassium, and then a saturated solution of cupric sulphate. A black crystalline precipitate, of the formula CuCNS or CuCsy wUl slowly separate. This substance is decomposed by pure water, but dissolved by ammonia water. Mtric, sulphuric, and hot hydrochloric acids dissolve it. The Silver Salt is a white precipitate. Its formula is AgCNS. It is soluble in hydrate of ammonium, very sparingly dissolved by boiling wat«r, and insoluble in dilute nitric acid. The Meeoueous Salt is white. Its formula is Hg^ CNS. It is scarcely attacked by nitric acid. The Meeoukio Salt is soluble. The Lead Salt separates gradually from the mixed solutions of plumbic acetate and sulphocyanide of potassium; it is more rapidly deposited on agitation : it is a pale yellow crystaUiue precipitate. Its formula is PbCNS. It is decomposed by pure water : warm nitric acid converts it into sulphate of lead. This acid-radical may also be detected by the decompositions which its compounds suffer. METALLO-CTANIBES. 343 a. When a Bulphocyanide (that of potassium, for instance) is boiled with nitric acid, or when chlorine gas is passed into the aqueous solution of a Bul- phocyanide, a yellow precipitate is produced, to which the name " pseudo- Bulphocyanogen" has been given : the probable constitution of this body is HC3N3S3. ;3. Most Bulphocyanides, when heated in a closed tube, yield a sublimate of sulphur, together with many other products. The ammonium suffers very remarkable changes, and yields, among other TolatQe bodies, bisulphide of carbon, sulphide of ammonium, hydrosulphurio acid, and sulphur. This acid-radical may be recognized by its insoluble sUTcr and lead salts, and by the decomposition described under a. Of add-radicah formed hy the union of cyanogen with metals, there are tliree wMcli more especially demand notice : tiey are known respectively as ferrocyanogen, ferricyanogen, and cobalti- oyanogen. The number of these compounds of carbon, nitrogen, and metals, or rather of cyanogen and metals, is, however, very great. They are generally formed by the direct union of two metallic cyanides, which, iustead of combining to form a double salt, appear to undergo a total change in the arrangement of their constituent molecules : — 2E:Cy-fPeCy=K,(reCy3). Some few of these compounds do, however, appear to partake far more of the characters of double salts than of simple salts which contain compound acid-radicals : such compounds are those formed by the cyanides of zinc and copper — KCy,ZnCy, and KCy, Cu^Cy ; while in other compounds, such as those of iron, manganese, cobalt, and platinum, so complete a metamorphosis has been effected, that no hesitation can be felt in ascribing to them a constitution differing from that of the others. The two com- pounds containing cyanogen and iron — ferrocyanogen (FeCy3) and ferricyanogen (Fe^Cyg) — are well known in combination vsdth basic radicals, forming very stable salts : the former of these radicals is bibasic, the latter tribasic. Chromium and manganese yield several radicals ; but their salts are not stable. The best known of these last mentioned compound radicals are chromi- cyanogen {Cvfij^) and manganicyanogen (Mn^Cy^), which are each tribasic. Cobalt forms a radical of the formula COjCy^, the 344 CHEMICAL REACTIONS. salts of which (cobaltieyanides) are very stable. The metals allied to platinum yield several radicals by imion with cyanogen. SAITS 01' PEEKOCTANOGEN, OR FEEEOCTANIDES. A ferrooyanide is produced when an alkaUne cyanide meets with iron, or an iron salt, imder appropriate conditions. Ferrocyanides are decomposed by heat : in most cases nitrogen gas is evolved, and a residue of iron and carbon left. The Hydkogen Sait (H^Cfy), or hydroferrocyanic acid, is pro- duced when hydrochloric acid is added to a concentrated solution of ferrocyanide of potassium. It separates on the addition of ether, in the form of minute white, yellowish, or bluish crystals floating ui the ether. It is soluble in water. This radical is best recognized by the formation of certain characteristic salts ; but it may also be identified by the products of its decomposition. The chief insoluble ferroeyanides are the calcium, ferrous, ferric, cupric, argentic, and lead salts. The Potassium and Sodhtm Salts are soluble. The Barium Salt dissolves in about 36 parts of cold water. The Steontitim: Salt is soluble. The Calcium Salt is a white precipitate. Its formula is KCaCfy+l|aq. It requires about 800 parts of cold water for its solution, and is even less soluble in water containing ammonium salts. The Magnesium Salt is a white precipitate. Its formula is Mg^Cfy+Gaq; but when an ammonium is present in the solutions employed, the precipitate appears to be MgNH^Cfy. It is insoluble in chloride of ammonium, readily soluble in hydrochloric acid. The Ferrous Salt is a white, or more usually a pale blue pre- cipitate, which is rapidly converted by the air or oxidizing agents into the ferric salt, becoming a deep blue in consequence. Its formula is KFe^Cfy,, or KFeCfy.Fe^Cfy. It is nearly insoluble in water. FEEEOCTANIDES. 345 The Ferric Salt is produced by the action of ferric salts on a solution of ferrocyanide of potassium. It is a deep blue preci- pitate, known as Prussian blue. Its formula is i^e^).JCij^. It is iasoluble in water, and in dilute hydrocbloric acid (see p. 126). The Cttpeous Salt is a white precipitate. Its formula is (^'"■2)fify- It is soluble ia the hydrate, but insoluble in the other salts of ammonium. The Cupric Salt is a brownish red precipitate. Its formula is Cu^Cfy. It is iasoluble in water, ammonium salts, and acids. The Silveb Salt is white. Its formula is Ag^Cfy. It is so- luble ia cyanide of potassium, ia the hydrate but not in the other salts of ammonium. Hydrochloric acid does not act upon it ; but nitric acid dissolves out one-fourth of its silver, convert- ing it into ferrioyanide. Sulphuric acid dissolves it. It is in- soluble ia water. The MEECtTEOtrs Salt is not known ; ferrocyanide of potas- sium precipitates yellowish white flakes (which contain no mer- cury) from solutions of merourous salts. The Meectiric Salt is white. The Lead Salt is white. Its formula is Pb^Cfy. It is sparingly soluble 'in. hot hydrate of ammonium, and entirely in chloride of ammonium, but not in the other common ammonium salts. It is insoluble ia water, but partially soluble ia sul- phuric acid. This acid-radical may also be detected by the following pro- cesses of decomposition : — a. If ferrocyanide of potassium or sodium be made by boiling any other ferrocyanide* vrith the hydrates or carbonates of potas- * Insoluble ferroeyanides may be thus decomposed, an alkaline salt of the radical, and an insoluble carbonate of the base being formed. Thus, to take two examples — (Fe2),Cfy3+6EHO=3K,Cfy+2Fe,H303 ; or Ba^Cfy+Na,C03=Na^Cfy+Ba,C03. a 5 346 CHEMICAL REACTIONS. siiim or sodium and filtering, and the resulting solution then eva- porated to dryness and ignited in a small covered crucible, a fused mass will be obtained, and, in that part of it soluble iti water, an aUialLne cyanide wUl be found, which may be identified by any of the usual tests, while the residue, insoluble in water, may, after due washing, be dissolved in hot hydrochloric or nitric acid and tested for iron. jS. When an alkaline ferrocyanide is heated with dUute sul- phuric acid, the characteristic odour of hydrocyanic acid is per- ceptible. y. But when powdered ferrocyanide of potassium (or of sodium) is heated with concentrated sulphuric acid, scarcely a trace of hydrocyanic acid is evolved, but only carbonic oxide gas (CO), according to the following equation :- — 2K, reC3 W3 + 6H, -I- 6H, SO, =2K, SO,-|-Fe, S0,+3[NHJ, S0,-F6C0. Ferrocyanogen is usually recognized by the formation of the ferrous and ferric salts ; occasionally also the cupric and uranium compounds are employed for this purpose, as well as the process given under a. SALTS OP PEEKICYANOGEN, OK FEEKI0TANIDE3. The potassium salt is obtained by passing chlorine into a solution of ferrocyanide of potassium, until a drop of the solution no longer produces a blue precipitate with a ferric salt. When heated, ferricyanides undergo decompositions rery similar to those of the ferrocyanides. The Hydeogen Salt (H3 Fe^ Cy^ or Hj Cfdy), or hydroferricyanic acid, is obtained by the action of hydrofluosiUcio acid upon ferrieyanide of po- tassium. This radical may be recognized by the formation of the ferrous, ferric, zinc, and silver salts. The Potassicm, Sodium, Barium, Strontium, Calcium, and Magnesium Salts are soluble. The Ferrous Salt is produced by the action of ferrieyanide of potas- sium : it is a blue precipitate. Its formula is FCj Cfdy. It is insoluble in water and in hydrochloric acid. The Ferric Salt is thought to be produced by the action of ferrieyanide of potassium. It is a very soluble salt, and only appeai-s in the form of a brownish green solution. COBALTICTANIBBS. 347 The Zinc Salt is produced by the action of ferricyanide of potassium : it is an orange brown precipitate. Its formula is Zn3 Cfdy. It dissolves in ammonium salts. The CupEons Salt is reddish brown. Its formula is (Cu^)3Cfdy. It is soluble in the hydrate, but not in other salts of ammonium ; it is insoluble in hydrochloric acid. The Cupeio Salt is brownish or greenish yellow. Its formula is Cuj Cfdy. It is soluble in the hydrate and carbonate of ammonium, but not in other ammonium salts, unless with the aid of heat. The Silver Salt is orange yellow. Its formula is Agj Cfdy. It dissolves in the hydrate, and in a hot solution of the carbonate of ammonium, but is insoluble in other ammoniiun salts. The Meroukous and Mekcdric Salts are yeUow. The Lead Salt is deposited gradually in dark brownish red crystals. Its formula is Pbj Cfdy. It is somewhat soluble in water. It is decom- posed by dilute sulphuric acid into sulphate of lead and hydroferricyanic acid. The constituents of this radical may be detected by its decomposition, in the manner described under ferrocyanogen ; but the formation of the charaeteristio ferrieyanides above mentioned must be relied on for its dis- tinction. SALTS OF COBALTICYANOGEir, OR C0BALTI0YANIDE8. These salts are produced by the direct action of an alkaline cyanide upon cyanide of cobalt. 4 eqs. of cyanide of potassium with 2 eqs. of cyanide of cobalt only differ from 1 eq. of cobalticyanide of potassium by 1 eq. of po- tassium, which in the reaction decomposes 1 eq. of water, producing 1 eq. of hydrogen and 1 eq. of hydrate of potassium : 4KCy-t-2CoCy-t-H,0=K3(Co2Cy,)-|-KHO-|-H. Cobalticyanogen, it will be observed, is analogous to ferricyanogen ; the cobalt compound corresponding to ferrocyanogen is unknown, or at least its existence is very doubtful. The Hydrogen Salt (HjCOjCy,, or 'R.^Coej), or hydrocobalticyanic acid, crystallizes in deliquescent needles. Heated above 100°, it is decomposed. It is soluble in water and in alcohol, but does not dissolve in ether. This acid-radical may be recognized both by the formation of insoluble salts, and by its decomposition. The Potassium, Sodium, Barium, Strontium, Calcium, and Magnesium Salts are soluble. The Ferrous Salt is a white precipitate. Its formula is Fe^ Cocy. The Ferric Salt is soluble. The Zinc Salt is a white precipitate. The Cuprous Salt is unknown. The Cupric Salt is produced by the action of soluble cupric salts on cobalticyanio acid: it is a sky-blue precipitate. Its formula is CUgCocy-(- 3|aq. It is soluble in hydrate of ammonium, insoluble in water and acids. 348 CHEMICAL EEACTIONS. The Silver Salt is a white curdy precipitate. Its formula is Agg Cocy. It is insoluble in water and acids. The Meeoukous Salt is a white precipitate. The Mekcoeic Salt is soluble. The Lead Salt is readily dissolved by water, but is insoluble in alcohol. Cobalticyanide of potassium gives with manganese and stannous salts white precipitates, and with cadmium salts a brown precipitate which be- comes white. It does not yield any results with titanic, uranic, and chromic salts. Cobalticyanogen may be recognized by its decomposition in a similar manner to the two preceding acid-radicals. Of acid-radicals containing carbon, oxygen, and hydrogen, a very large nimiber is known ; we shall, however, describe the salts of those only which are Kkely to come in the way of the student, viz. the acetates, henzoates, lactates, sueciaates, tar- trates, citrates, gallates, and tannates. SALTS OF THE ACETIC EAIICAL, OE ACETATES. The radical under consideration is an exemplar of a new class or order of compounds : it is a member of what is called " a ho- mologous series." Some approach to this form of combination has already been noticed in the case of the borates ; but among the compounds of carbon with hydrogen and oxygen, it is more completely and extensively developed. An immense number of acid-radicals has been discovered by degrees, each requiring the same amount of base for its saturation, and each dififering, from the term of the series next above or below it, only by the mole- lecule CHj. The foUowing list shows a few of the hydrogen compounds or acids of these radicals : — Formic acid HC H 0^. Acetic acid HC,H3 0,=HCH0,-f CH,. Propionic acid HC, H, 0, = ECHO, -f 2CH^. Butyiio acid HC, H, 0, = ECHO., -|- 3CH,. Valerianic acid HC„H,0,=HCH0J-t-4CH,. The series of which acetic acid is a member, is caUed " the series of fatty acids," because, as the amount of CH^ increases in them, they no longer exhibit the limpidity and perfect misci- bility with water characteristic of formic and acetic acids, but ACETATES. 349 become more and more oily, until, finally, tlie higher terms of the series reach the condition of solid fats. All these acids have certain features in common : they are volatile without de- composition; their boiling point increases regularly with each increment of CH^ ; they all yield similar products of decom- position, which vary only by CH^ ; and they may all be formed by the same agencies from a series of " alcohols" containing basic radicals, which bear a fixed and constant relation to the radicals of the acids. The acid of the acetic series is produced by the imperfect combustion of most organic bodies ; as " vinegar" it is produced by the slow oxidation of alcohol, and as " pyroHgneous acid" by the distillation of wood at a high temperature in iron retorts. The acetates of the first and second subdivisions, when heated, yield carbonates, and, if out of contact of air, a volatile liquid of peculiar odour, called acetone (CjHjO). Alkaline acetates, if mixed with excess of alkaHne hydrate and heated, are completely decomposed into the combustible gas known as "marsh-gas" and alkaline carbonates. The Hydkosen Salt (HC^HjO^), or acetic acid, is a colour- less crystalline solid at temperatures below 15° C. ; on this account it has received the name of glacial acetic add.* It boils at 120° C. It has the well-known taste and smell of vinegar in a most marked degree, and acts as an acrid poison. The normal or neutral acetates are almost without exception soluble in water ; the basic acetates are for the most part in- soluble. The Potassium, Sodium, Baeium, Steontium, Calcium, and Magnesium Sams are soluble. The Peeeous and Ferric Salts are soluble ; the latter, how- ever, if produced by adding a drop of ferric chloride to the solu- tion of an alkaline acetate, imparts a distinct brownish red colour to the liquid. If the coloured solution be then boiled, the neutral ferric acetate will be decomposed, a mixed hydrate * The hydrate of this acid, having the formula CjE^O^, H^O, boils at 104° C. 350 CHEMICAI, EEACIIONS. and acetate, or basic acetate, being produced, and the solution becoming gradually colourless. The Zinc and Cupeio Baits are soluble. The MERCimoirs Salt is obtained by adding mercurous nitrate to acetic acid or a soluble acetate : it is a white, scaly, crystal- line precipitate. Its formula is Hg^CjHjO;,. It dissolves readily iu excess of its precipitant : it is sUghtly soluble in water or acetic acid, especially on warming ; but a shght decomposition of the salt into mercuric acetate and mercury then occurs. The Silver Salt is produced by the action of soluble silver salts on the solution of an acetate : it is a white, beautifully cry- stalline precipitate, which becomes discoloured by exposure to light. Its formula is AgC^HjO^. It is soluble in hydrate of ammonium, but dissolves very sparingly in cold water or acetic acid, although it dissolves more abundantly in these liquids when hot, crystallizing out again on cooling. The Meecitbio Salt is soluble. The Lead Salt (PbC^HjO^) is soluble. The Basic Lead Salt is soluble, and is remarkable for having an alkaline reaction. Its formula is PbC,H3 0„ Pb,0. This acid-radical may also be detected by the following special processes : — a. When an acetate is warmed with dilute sulphuric acid, acetic acid is liberated, and, being volatile without decomposition, may be recognized by its peculiar odour and inflammability. /3. If an acetate be mixed with a small quantity of alcohol (Cj Hj HO or EHO, the hydrate of the compound basic radical ethyle) to which an equal bulk of sulphuric acid has been previ- ously added, a true salt wiU be formed, containing a compound basic and a compound acid-radical : this product is termed acetate of ethyle, or acetic ether, and may be at once recognized by its pe- culiar and agreeable aromatic odour. The reaction is as follows : — EHO + Hi=H,0-t-EA. y. When an acetate of the first or second subdivision is BENZOAIES. 351 heated in a test-tube, acetone, remarkable for its odour and in- flammability, is evolved ; the reaction is as follows : — 2BaC,H30,=Ba,C03 4-C3H,0. acetone. The acetic radical is generally recognized by the formation of the silver salt, and the test /3. SALTS OF THE BENZOIC EABICAl, OE BENZOATES. Just as acetic acid is the representative of the series of fatty acids, so benzoic acid is the type of " the series of aromatic acids." This group is by no means so numerous as the former ; but its members present the same regular differences of composition, and the same relations to other groups of con- nected bodies. Benzoic acid, though itself somewhat rare, is the member of this series most commonly met with. Beuzoates when heated decompose, generally giving rise to the formation of a volatile soHd body termed bemophenone, which is in reality the ben- zoate of phenyle (C^ H^, C, Hj O,). This radical may be recognized by the formation of insoluble salts, and by processes of decomposition. Thu Hydkogen Salt (HC, Hj 0^), or benzoic acid, is generally obtained by exposing " gum benzoin " and several other resins to heat, or by boiling them with an alkaline hydrate. It crystallizes in plates, and has an aromatic odour. At 120° C. it fuses, sublimes at 145°, and boils at 239°. Its vapour, if inhaled, provokes coughing. It is but slightly soluble in cold, more readily in hot water. In alcohol it is soluble. Nearly all benzoates are soluble in water ; the ferric salt is the most cha- racteristic insoluble benzoate. The Potassium, Sodium, Bakium, Strontium, Calcium, Magnesium, and Fekbous Salts are soluble. The Ferric Salt is produced by the action of ferric chloride upon solu- tions of benzoates. It is of a reddish yellow colour, and has the composition of a basic salt. It is dissolved by most acids. The Zinc Salt is soluble. The Cupkods Salt is unknown. The Cupric Salt is produced by the action of soluble cupric salts upon solutions of benzoates, as a blue precipitate. Its composition is CuC^ HjO^ with some water of crystallization. It is soluble in many acids. The Silver Salt is produced by adding a soluble silver salt to a solution of a benzoate, as a white curdy precipitate. Its formula is AgCj Hj O^. It dissolves in boiling water and in many acids. The Mercurous Salt is a curdy precipitate. The Mercuric Salt is a white curdy precipitate, slightly soluble in water and alcohol. The Lead Salt is a white precipitate of the formula PbC^HjOj with water of crystallization. 352 CHEMICAI EEACTIOITS. This acid-radical may also be detected by the following methods : — ■ a. When an acid is added to a soluble benzoate, a precipitate of benzoic acid is produced, which, if boiled in water, dissolTCS, and crystallizes out again on cooling. The acid, when separated, may be recognized by its fusi- bility, TolatOity, and remarkable odour. p. The dry cupric benzoate, when heated in a test-tube, decomposes, with the formation, among other products, of the benzoate of phenyle (Cj Hj, C^HjOj), which is a body possessing an odour resembling that of the geranium. SALTS OF THE LACTIC KADICAL, OB LACTATES. This radical is bibasic ; and the lactates known belong to the two series of acid and neutral salts : for the most part they dissolTC sparingly in water or alcohol, and are insoluble in ether. The Hydrogen Salt, or lactic acid, occurs in sour milk, in which it is produced by a fermeutive action upon the milk-sugar that liquid naturally contains, thus — CuH,„0„+2H,0=2C,Hi,0,. lactic acid. It is produced by the fermentation of other kinds of sugar. Its formula is HjCgHjjOj. It is a colourless syrupy liquid, which does not solidify at 24° C. It is inodorous, but has a biting acid taste. In presence of platinum it volatilizes without decomposition at about 200° C. Heated alone, it de- composes at about 130° C. into water and lactic anhydride (CijH^jOio). The latter is a pale yellow, bitter, and easily fusible solid. At high tempe- ratures, lactic acid decomposes into a great variety of products. Lactic acid dissolves in water in all proportions. The lactates of the first subdivision are very soluble in water ; those of the second subdivision require from 20 to 30 parts of water for solution, while the majority of the remaining salts dissolve easily. The Potassium, Sodium, Babiom, Strontium, Calcium, and Magnesium Salts are soluble. The Fekrous Salt is a nearly white precipitate. Its formula is Fe., L. It is soluble in 48 parts of water at 10° C, or in 12 of boiling water ; it is in- soluble in strong alcohol. The Ferric Salt is brown and soluble. The Zinc Salt is while, and crystallizes in four-sided prisms belonging to the right prismatic system. Its formula is Zn^ L. It is soluble in 58 parts of cold, or 6 of boiling water ; it is insoluble in alcohol. The Cupkio Salt is very soluble. The Silver Salt is soluble in 20 parts of cold water, nearly insoluble in cold, but very soluble in hot alcohol. The Mercurous Salt is a white precipitate consisting of fine needles. Its formula is (Hg.^)^ L-|-aq. It is sparingly soluble in cold, and is decomposed by boiling water. TriE Mercuric Salt is soluble. SUCCINATES. 353 The Lead Salt is soluble. Lactates may also be recognized by the following processes : — a. When the hydrogen compound, lactic acid, is heated to 130° C, water containing a little lactic acid distils, and the residue, on cooling, becomes a yellowish white sohd, of very bitter taste, almost insoluble in water, but easily soluble in alcohol or ether. It is called " laotide," and has the for- mula CgHidOs, and by long boiling with water is converted again into lactic acid. 13. If lactic acid be heated with concentrated sulphuric acid, almost pure carbonic oxide gas is given off, and a body resembling humin remains behind. SALTS OF THE SUCCINIC RADICAL, OB SUCCIHATEa. To the series of which succinic acid is a member, the name " oxalic acid series" has been applied. Oxalic acid, the first member, has been already described as a volatile and bibasic acid ; succinic acid and the other terms of the series, or honwlogues of oxalic acid, present the same characteristics. Succinic acid is obtained in many ways ; the most important of these are the dry distillation of amber, and the fermentation of malate of calcium. Succinates when heated yield numerous products of decomposition, car- bonic anhydride and acetic acid being among the number. The Hydkogen Salt (H.^ C,, H^ O^ or H^ S), or succinic acid, crystallizes in colourless prisms belonging to the obhque prismatic or monoclinio system. It is inodorous. It melts at 180° C, and boils at 235°, forming a most pungent vapour, which, if inhaled, excites violent coughing. It dissolves in 5 parts of water at 16° C, in 2-2 parts of boiling water, and in 1-37 part of strong alcohol. Many succinates are soluble in water ; the insoluble salts dissolve readily in acetate of potassium. The Potassium and Sodium Salts (KjC^HjO^j and Na^CjIIjOj) are soluble. The Barium and Strontium Salts are sparingly soluble in water, but dist solve in acids ; in alcohol they are insoluble. The Calcium Salt is precipitated on boiling concentrated solutions of chloride of calcium and succinate of ammonium. Its formula is Ca^C^ H^O^ -1-aq. It is soluble in succinic, acetic, and most other acids, but insoluble, or nearly so, in alcohol. The Magnesium Salt is soluble. The Ferrous Salt is a grey-green precipitate, insoluble in water, but soluble in acids. The Ferric Salt is a reddish brown precipitate of very variable consti- tution. It is insoluble in water, soluble in hot solutions of succinic or acetic acid, and in most other acids. The Cupeic Salt is green or blue. Its formula is Cuj 0^ H^ O4. It is soluble with difficulty in water or solution of succinic acid ; it dissolves in acetic and other acids. 354 CHEMICAL EEACTIONS. The Silver Salt is a white precipitate, produced by nitrate of silTer in neutral or alkaline solutions. It is soluble in hydrate of ammonium, and dis- solves slowly in water or acetic acid. It dissolves in most mineral acids. TuE Meecueous Salt appears to be soluble. The Meecueic Salt is a white precipitate. The Lead Salt is a white precipitate. Its formula is Pb^ C^ H^ O^. It is but sparingly soluble in water, in acetic, or boiling solution of succinic acid. In alcohol it is insoluble. The radical of the succinates may be recognized by the following tests : — u. Succinic acid, when heated in the air, evolves suffocating vapours, which burn with a pale flame. It may be subKmed in great part unchanged. /3. Succinates are not blackened when heated with strong sulphuric acid. SALTS OF THE TAETAEIO BADIOAI, OE TAETEATES. The potassium salt of this radical is found iu the deposit which occurs in wine casks, and which is termed " Tartar," or " Argol." This radical is not at present known to be a member of any homologous series ; it is bibasic ; none of its inorganic salts are volatile without decomposition. Tartrates when heated evolve the peculiar odour of burnt sugar, decomposing with formation of carbonic anhydride, oarburetted hydrogen gas, acetic acid, pyrotartaric acid, and other bodies. The Hxdko&en" Salt (H^C^H^O,, or H^T), or tartaric acid, is a substance which crystallizes in fine colourless prisms belonging to the oblique prismatic system. It melts at 170° C. to a trans- parent colourless liquid, but does not volatilize without decom- position. "When heated to a high temperature, new acids are obtained from tartaric acid. 1 part dissolves in ^ part of cold, and in a less quantity of boiling water. This acid has the pro- perty, in common with several others, of preventing the precipi- tation of many oxides by hydrate of potassium or ammonium. This radical may be recognized both by the formation of in- soluble salts and by processes of decomposition. The neutral tartrates of the first subdivision are almost the only soluble neutral salts of this radical, and their acid salts almost the only insoluble acid salts. The Barium Salt is produced by the addition of chloride of barium to the neutral or alka.liTie solution of a tartrate : it is a TAETEATES. 355 ■white precipitate. Its formula is Ba^C^H^Oj. It is easily soluble ia aU ammonium salts except the hydrate; it is also soluble in hydrochloric acid. The Steontium Salt is comparatively soluble in water, readily so in chloride of ammonium. The Calciimi Salt is produced by the addition of even the hydrate or sulphate of calcium in aqueous solution to tartrate of sodium ; it is produced in larger quantity by chloride of calcium. Its formula is CajC^H^Oj. Its precipitation is prevented, or at least retarded, by the presence of ammonium salts, in which it is easily soluble. This salt, if filtered and washed, is remarkable for its solubility in cold hydrate of potassiimi, its reprecipitation on boiling the alkaline solution, and its re-solution on the cooHng of the liquid. The MAGNEsrtna Saxi is comparatively soluble. The Feeeotjs Salt is a green precipitate. The Feeeic Salt appears to be soluble. The Zinc Saxt is soluble. The Cfpeic Salt is a green precipitate. Its formula is CUjC^ H^Oj 4-3aq. It is soluble in a boUiag solution of carbonate of sodium and ia acids. The Silver Salt is a white and crystalline precipitate. Its formula is Ag^C^H^Oj. It is insoluble in water; in hydrate of ammonium it dissolves, forming a solution which, when boiled, deposits a great portion of the silver it contains upon the sides of the containing vessel. With proper modifications, this constitutes Petitjean's silvering process. The Meecueotis and Meecueic Salts are white precipitates, insoluble in water, but soluble in acetic, tartaric, and mineral acids. The Lead Salt is white. Its formula is Pb^C^H^O^. It is soluble in chloride of ammonium, nearly insoluble in water ; it dissolves in acids. This acid- radical may be distinguished by processes of decom- position. u. Tartaric acid and tartrates, when heated on platinum foU, 356 CHEMICAL EE ACTIONS. char, and evolve inflammable gases and the peculiar odour of burnt sugar. The experiment may be performed in a test-tube open at both. ends. /3. When a tartrate is boiled with concentrated sulphuric acid, besides the odour of burnt sugar which is evolved, and the carbon which separates rapidly, carbonic oxide gas is also formed, and may be detected by the blue flame with which it bums when a lighted taper is applied to the mouth of the test-tube employed. The tartaric radical is usually recognized by the formation of the insoluble or sparingly soluble barium, calcium, and sUver salts, and by the tests a, and (3. SALTS OF THE CITEIC EADICAL, OE CITEATES. The citric radical belongs to no ascertained homologous series. It is tribasic. The acid is found in many plants, especially in the fruit of the Gitrus mediea, or lemon, and of the Citrus auran- tium, or orange. The citrates, when heated, begin to decompose at about 230° C, evolving many volatile products, and leaving a large quantity of charcoal. The Htdeo&en Salt (II3C3H5O, or Il3Ci), or citric acid, is a colourless crystalline body of the same form as the commercial acid HjCi-l-aq, which occurs in prisms belonging to the right prismatic system: these hydrated crystals effloresce in the air, and form the true acid. When heated to a high temperature, citric acid yields several new acids. The radical may be recognized both by the formation of in- soluble salts and by its decomposition. The majority of the citrates are insoluble in water. The salts of the first subdivision are, however, soluble. The Baeitjm Salt is a white precipitate. Its formula is BajCj H5O,. It is soluble in ammonium salts, iu a large propor- tion of water, and in acids. The Steontitjm Salt is a white precipitate of the formula SrjCjHjO,, soluble in many acids. The Calcium Salt is a white crystalline precipitate, which GALLATES. 357 is produced in dilute solutions only on boiling; the salt par- tially redissolves on the cooling of the solution. Its formula is CajCjHjO,. It is soluble iu chloride of ammonium solution; it dissolves more sparingly in boiling than ia cold water; it is soluble in acids and in most ammonium salts, excepting the hydrate. The Magnesittm Sam is soluble. The Zinc Salt is but slightly soluble in water. The Feeeic Sait is soluble. The Cttpeic Sait is precipitated on boiUng as a green crystal- line powder. Its formula is CujCi, CuHO-|-aq. The Siltee Salt is a white precipitate. Its formula is AgjCj H,0,. It is soluble in boiling water. The Meecueous and Meecueic Salts are white precipitates. The Lead Salt is a white precipitate, soluble in ammonium salts. This acid-radical may be distinguished by the following tests : — a. Citric acid, when heated in a tube open at both ends, evolves irritating acid vapours; heated on platinum foil, it chars and evolves combustible gases. /3. When boiled vdth concentrated sulphuric acid, citric acid evolves a trace of acetic acid and a large quantity of carbonic oxide, which may be kindled. A gradual separation of carbon also takes place. SALTS OF THE GALLIC RADICAL, OE GALLATES. The radical of these salts is obtained by the decomposition which tannic ^id undergoes when exposed in a moist condition to the action of the air or to the influence of a fermenting body. It is said to occur in the vegetable kingdom. Recent researches have shown it to be a tribasic radical. The radical is remarkable on account of the behaviour of its hydrogen salt (gallic acid) imder the influence of heat : at a temperature of from 210° to 215° C. it loses 1 eq. of carbonic anhydride, and is converted into 'pyro- galUc acid, thus — gallic acid. pyrogallic acid. The latter body sublimes in flattened needles : it is remarkable for its great affinity for oxygen, which it absorbs (especially when in solution), either from 358 CHEMICAI EEACTIONS. the atmosphere or from oxidizing agents, with the greatest avidity, becoming brown and ultimately black. The Hydrogen Salt, or gaUie acid (Hg, C, Hg O5), is a soKd body, crystal- lining in silky needles, which have no odour, but an astringent taste : 1 part dissolves in 100 parts of cold, or in 3 of boiUng water ; it is very soluble in alcohol, but less so in ether. The gallates generally formed are those which have the formuUe Hj M, C, H3 O5 and H M^,, C, H3 O5 ; those represented by M3 C^ Hg O5 are but rarely produced. The Potassium and Sodium Salts are soluble ; those of Barium, Steon- TiuM, and Calcium are but slightly soluble in water. They all have the general formula Hj M, G, II3 O5. The Magnesium and Zinc Salts are white precipitates, of the formula HM2, C^HjOj, and very shghtly soluble in water. The Ferrous Salt does not appear to have been obtained. The Ferric Salt is produced by the addition of a ferric salt tq a solution of a gallate ; the liquid instantly becomes of a bluish black colour. If this liquid be boiled, it decolourizes with escape of carbonic aeid gas and forma- tion of a ferrous salt. The Copper, Mercury, and Silver Salts appear to be unknown. The Lead Salt is produced by the action of a solution of acetate of lead upon a solution of gaUio acid, as a white precipitate having the composition HPbj, C, H3 O5, with water of crystallization. It dissolves easily (when recently precipitated) in concentrated acetic acid. Excess of this reagent is a perfect means of precipitating gallic acid. This acid-radical may be still further recognized by — a. Its rapid oxidation, with formation of a brown colouring matter, when an alkaline solution containing it is freely heated in contact with air. /3. It may be distinguished from tannic acid by its not producing a preci- pitate in solution of gelatine, unless previously mixed with a solution of gum. SALTS OE THE TAfTNIC BADICAX, OE TANNATES. Tannin or tannic acid is a name given to that large class of bodies which form the astringent principle in various parts of many plants. The individual acid here to be described, as most commonly met with, is that to which the name of gaUotannic acid has been given, from its occurrence in nutgaUs, from which it is always extracted by the joint action of ether and water. TheHybeogen Salt, tannic or gallotannic acid (HgC^^H^gOj,), is obtained as a white or slightly yeUow spongy mass, gUstening frequently from being an aggregation of crystals. It is very soluble in water, alcohol, or anhydrous etiier. TIEATBS. 359 The gallotaiinatea generally contain 2 eqs. of metal, but some- times 3 eqs. ; consequently their radical must be regarded as tribasic. The Potassittm and SoBitna: Salts are very soluble in water. The BAEruM Salt is white, almost insoluble ia. water. The Calcixtm: Salt dissolves ia pure water. The MAOirasnjM Salt is but slightly soluble. The Feheoits Salt is white and gelatinous, and sufficiently soluble in water not to be precipitated from dilute solutions. The Ferric Salt is produced by adding a ferric salt to a so- lution of a gallotannate : it is a bluish black precipitate. Its formula is probably Fe^'K,C^^'K^gO^^. The Zrsrc Salt is white. The Cttpeic Salt is brownish yellow. The Silvee Salt is reddish brown. The Meecueotjs Salt is yellow, and the Meectjeic Salt brick- red. The Leah Salt is white. Its composition is probably 2\, This radical may also be recogniiied and distinguished from that of the gallates by its property of precipitating gelatine : when an aqueous solution of gallotannic acid is mixed with an aqueous solution of gelatine, a fine filmy or gelatinous precipitate immediately forms. This is the reason of the employment of oak-bark, and other substances which contain these astringent principles, ia the process of tanning. Of acid-radicals produced hy the union of carhon with nitrogen, hydrogen, and oxygen, one only needs description here, viz. the uric. salts of the tteic eadical, oe tjbates. This radical is of animal origin : the chief source from which its salts are prepared is the excrement of serpents, which consists almost wholly of urate of ammonium. This radical is bibsisic. Fric acid and urates, when heated, ia common with nearly all organic bodies containing nitrogen, evolve the odour of bum- iag feathers. 360 CHEMICAL EEACTIONS. The Htbeogbn Salt (E^G^'N^'Kfi^or'E^V), or uric acid, occurs in delicate wMte needles ; it dissolves very sparingly ia cold water ; ia sulphuric acid it is soluble, forming a brown solu- tion, from wHch. water repreoipitates the uric acid. Urates, with the exception of the Potassitjm and Sodium Salts, are almost all insoluble in water : it is very remarkable that the Ammonium Salt is extremely insoluble in water ; it is, however, dissolved by chloride or phosphate (Na^ HPO^) of sodium, the sodium salt being formed. The Calcittm Salt is white; the Feeeic Salt brown; the CuPEic Salt green ; the Silvee Salt white, rapidly becoming black if the liquid be heated ; the Meecueic and the Lead Salts are white. The uric radical may be easily identified by the following pro- cesses of decomposition : — a. Uric acid, if heated alone, evolves the odour of burnt hair together with that of cyanide of ammonium, a carbonaceous re- sidue being left. /3. If uric acid or a urate be mixed with sohd hydrate of po- tassium and heated in a narrow tube, ammonia will be evolved, and cyanide or cyanate of potassiimi remain in the tube. The two latter products may be identified in the manner already pointed out (pp. 338-341). y. If uric acid be dissolved in dilute nitric acid, the solution evaporated just to dryness in a porcelain dish, and a glass stopper moistened with strong ammonia water be held over the residue in the dish, the magnificent purple colour of nmrexidc is pro- duced, which is quite characteristic. TABLE OH' BEACTIONS. TABLE OP EBACTIONS. 361 Salts. CO3. (p. 320) CA. (p. 323) B0O2. (p. 326) SiOa. (p. 329) C.H3O.. (p. 348) CHA. (p. 354) Potasaium ... white cryst. Sodiiuu — — — — — — Barium white white white white — white Strontium ... white white white white — white Calcium white white white white — white Magnesium .. white — white gelat. white — — Ferrous greenish white red yellow yellow white pale blue white pale yellow yellow white pale green white greyish green ? red green white blue white white greenish blue ? solution white green white Cupric Silver Mercurous . . . white crystal, white white Mercuric . . . white white — — — white Lead white white white aaky white — white In tte Table which immediately follows, as indeed in all similar Tables, reference must be made to the reactions for con- firmatory and discriminatory tests. 362 CHEMICAL EE ACTIONS. Analysis of Subdivision III. The aoid-radioals of somewhat common occurrence only being included, the salt may be a CAEBONATE, OXALATE, BO- EATE, SILICATE, CTANOGEN-COMPOUND, ACETATE, BENZOATE, STJCCINATE, TAETEATE, CITEATE, GAILATE, TAN- NATE, or UEATE. Some of these aeid-radicals maybe satisfactorily detected by the addition of concentrated sulphuric acid to the solid, or to its strong solution. The odours may, howcTer, be better detected by using dilute hydrochloric acid, aided by a gentle heat. Immediate effervescence indicates a carbonate. Effervescence with odour of peach-blossoms indicates a cyanide. The same odour (of HCy) may indicate a ferro- or ferricyanide. An odour of vinegar (of HC^HgOj) indicates an acetate. Separation of crystals from the solution may indicate a borate. ,, ,, with aromatic odour indicates a benzoate. ,, ,, with irritating vapour indicates a succinate. Blackening on warming, with odour of burnt sugar ^ indicates a tartrate. ,, „ ,, m a &SS Se^ree indicates a citrate. Evolution of carbonic oxide gas without blackening indicates an oxalate. Further Analysis. Carefully neutralize the solution with carbonate of sodium, then add one drop of hydrate of ammonium. Add solution of chloride of calcium until no more precipitate is formed. A precipitate would indicate the presence of O, B0O2, SiO,, or f. Wash thoroughly and divide into two parts. Shake with cold solu- tion of hydrate of potassium ; if the pre- cipitate dissolves, and is thrown down again on boiling the solu- tion, T is indicated. 11. If no solution takes place with I., add to the remainder of the precipitate acetic acid, and warm. An un- dissolved residue indicates 0. If it dissolves en- tirely, add hydro- chloi'io acid, and evaporate to perfect dryness. Redis- solve in hydro- drochlorio acid. A residue indicates SiO,. If entirely dissolved, BoOj is indicated If no precipitate occurs, boil the solution for some minutes. The forma- tion of a pre- cipitate indicates Ci, or perhaps SorCfy. If no precipitate is produced, add to the solution perchloride of iron. A pale red precipitate indicates BeorSl A bluish or greenish black indicates GorQt. A bright blue in- dicates Cfy. If no pre- cipitate, the solu- tion may be co- loured. A red colour indicates A or Csy. A green colour indicates Cfdy. SALTS OP NITROGEN, ETC. 363 SUBDIYISION IV. SALTS OF NITEOGEN, PHOSPHORUS, AESEXIC AND AN- TIMONY, AND OP THE CHIEF COMPOUND ACID- EADICALS INTO THE COMPOSITION OF ■WHICH THEY ENTEE. The three latter members of this subdivision present a re- markable similarity in properties ; nitrogen, although closely allied to them in many respects, exhibits, as we shall presently see, important differences, which may nevertheless be cleared away by future observations. In the preliminaiy observations made upon each section, we shaU enter more into detail con- cerning the chemical peculiarities of the radicals considered, since, although not strictly important in an analytical point of view, their knowledge will be of extreme use and interest to the student. This subdivision is divided into two sections : — Section I.— SALTS OF NITEOGEN, PHOSPHOEUS, ARSENIC, AND ANTIMONY. The nitrides, phosphides, arsenides, and antimonides. Section XL— SALTS OP THE ACID-EADICALS WHICH CONTAIN NITROaEN, PHOSPHORUS, ARSENIC, AND ANTIMONY COMBINED WITH OXYGEN OE SULPHUE. The nitrites, nitrates, hypophosphites, phosphites, phosphates, arsenites, arseniates, antimoniates ; sulpharsenites, sulpharse- niates, and sulphantimoniates. Section I. — The nitrides, phosphides, arsenides, and antimonides. SALTS OF NITEOGEN, PHOSPHOEUS, ARSENIC, AND AJSTIMONY. The elements considered in this group have the property of combining with many basic radicals, and are usually found to be triatomic, uniting with 3 equivalents of a monatomic molecule ; a few circumstances have, however, raised great obstacles to these combinations being considered truly saline. Their hydro- gen compounds, in the first place, are not possessed of manifesth- b2 364 CHEMICAL EEACTIONS. acid properties — they do not redden litmus; this may, never- theless, be accoiuited for by supposing that hydrogen, when com- bined in the proportion of 3 equivalents with the weak acid- radicals, nitrogen, phosphorus, or arsenic, forms a basic radical sufficiently powerful, in its counteraction, entirely to mask the acid properties of the nitrogen, phosphorus, or arsenic. These hydrogen compounds are also all gaseous bodies at common tem- peratures ; this is a great barrier to the perfect investigation of the properties of a substance ; and, what is more perplexing, they all (and the compound NH3 in the most marked manner) have a tendency to unite with a fourth equivalent of hydrogen to form a compound base, which again combines with acid- radicals to form stable saline compounds. With regard to the compounds produced by the union of these acid-radicals directly with metals, little is known ; and (as might be readily conjectured from the fact that hydrogen saturates their acid tendency so completely) those are the most stable, in which the weaker basic radicals exist combined. SALTS OF NITKOGEN, OE NITEIBES. These bodies have not been hitherto obtained by the action of ammonia (H3 N) either as gas or in solution upon saline bodies at ordinary tempera- ratures ; the only method which has successfully resulted in their produc- tion is that of passing the dry gas (H3 N) over the heated metal, the mole- cules of which we desire to substitute for those of hydrogen in the body H3 N. This, as might be expected when the triatomic character of nitrogen is con- sidered, does not always result in the formation of the substance M3 N ; but occasionally, as in the case of potassium, a compound is obtained, the for- mula of which represents a partial replacement. The oUve-greeu substance which potassium yields when gently heated in ammonia gas, has the com- position H2 KN ; it is known as amide of potassium, a name given by chemists who beheved its constitution to be K(NB[2), — NH^ being a hypothetical acid-radical which they called amidogen. This body, when heated to red- ness in a close vessel, decomposes into nitride of potassium and nitride of hydrogen, with the consequent separatiou of the latter (ammonia) : 3H,KN=K3N-|-2H3N. When, again, dry ammonia gas is passed over iron wire heated to redness in a tube for six or eight hours, a white brittle substance is obtained, the com- position of which nearly corresponds to the formula Fcg N^, that is, to a mix- NIIKIDBS. 365 tore of equivalents of nitride and dinitride of iron; for !Fe„N2=Fe3N+ (^62)3 N : this has no analogue among the combinations of iron with other aoid-radieals, although the probable existence of a disulphide of iron (Se^)^ S or Fe^S, and the well-known tendency of iron salts of different series to combine together, removes the improbability of its existence. The di- or Bubnitride of copper may be made by heating the precipitated oxide in dry ammonia gas ; its formula is CujN, that is, (Cu2)3N. Mercuric nitride is similarly produced ; it is a brown powder having the composition Hgj N, which explodes vrith great violence when struck or heated. The HrDEoaBif Compoottii of nitrogen (H, N), or ammonia, is almost always found in combiaation or union with, water : its great source is tlie decomposition of nitrogenized organic matters ; any such compounds, when heated with the hydrates of potas- sium or calcium, yield the whole of their nitrogen in the form of ammonia. The analogous compounds of phosphorus, arsenic, and antimony will he seen to he produced by the action of nascent hydrogen upon the element under experiment. This is not the case when the same agent meets with already eliminated nitrogen ; the gaseous condition of the latter body is, however, perhaps unfavourable to the success of the reaction. The gas ammonia has a very ptmgent odour, but is not corrosive ; it is slightly combustible, burning when a candle is applied to it, but the combustion ceasing upon the removal of the ignited body : when intensely heated it decomposes into its elements. It may be condensed to the liquid and even to the solid state by cold and pressure. The solid is colourless and crystalline, and melts at —75° C. : the liquid is colourless and very mobUe, of speeifle gravity 0-76 ; it boUs at — 33°-7 C. at about the ordinary pressure (0-7493"). The gas is absorbed by water with the greatest rapidity ; and, according to Ure, when the specific gravity of the solution is 0-8914 it holds 27-94 per cent, of H3 N in solution. No decomposition with formation of nitrides takes place when ammonia gas is passed into saline solutions, or when its aqueous solution is added to them -. this may, perhaps, be accounted for by the change which is very generally believed to occur whenever HjN meets with H^O, and which certainly takes place when it meets with more powerful acids — namely, its direct union with the acid, and formation of the corresponding salt of the basic radical ammonium : H3N-l-H^0=NHiH0; H3N+HCl=NHiCl. 366 CHEMICAL EEACTIONS. SAMS OP PHOSPHOKUS, OE PHOSPHIDES. These are more numerous than the analogous compounds of nitrogen, and may be more readily obtained by reason of the occurrence of phosphorus in the solid, Uquid, and gaseous forms within a conTCnient range of temperature, which is a circumstance most faTourable for a fuU investigation of the chemical properties of a body. The phosphides may be produced similarly with the nitrides ; but some are also formed by the action of phosphnretted hydrogen, Hj P (the ammonia of this series), upon saline solutions. The potassium salt is formed when its components are gently heated in an atmosphere of nitrogen ; it is a substance of a chocolate-brown colour. The calcium salt is produced, together with hypophosphite of calcium, when the Tapour of phosphorus acts on lime (Ca^ 0). Others, again, as the phosphides of iron, copper, and lead, are prepared by throwing phosphorus on the melted or red-hot metal, or by igniting the fiHngs of the metal with glacial phosphoric acid (HPO3). These compounds may also be formed by heating the metal in the gas H3 P ; and in some cases, by the passage of that gas through the aqueous solution of the metallic salt, the phosphide is slowly formed : thus cupric salts yield black phospliide of copper (Cuj P), mercuric salts a whitish yellow precipitate of a basic salt, and lead salts a brown precipitate. One thing is to be remarked in the phosphides, viz. that two distinct series of them are known, in one of which phosphorus plays the part of a bibasic, in the other of a tribasic radical ; thus we have two series of salts : — Ferrous. Ferric. Cuprous. Cupric. Bibasic Ca^P (Pe2)2P — — Cu^P Tribasic - - (FeJ^P (Cu,)3P Cu^P. It is interesting to know that whilst the majority, if not all, of the tribasic phosphides are produced by the vapour of a phosphorus (ordinary phos- phorus, see p. 34) upon metals, the bibasic cupric phosphide (Cu,P) is obtained by the reducing action of hydrogen gas at a high temperature upon the bibasic cupric phosphate ( Cu^ P^ O,) : it may be, that in the bibasic phosphides the /3 variety of phosphorus occurs. The Hydeogen CoMPOinfD (H3 P), or phosphuretted hydrogen, is usually obtained by the action of solution of hydrate of potas- sium upon phosphorus, or by the decomposing influence ■which water exerts upon the calcium salt (Ca, P) ; it is not obtained by the action of nascent hydrogen on solid phosphorus. As usually prepared, it is spontaneously inflammable in the air. In addi- tion to this gaseous body, there is another which is liquid, having the composition H^ P : this latter it is which is said to result from the action of water or other acids on the phosphide of calcium (Ca^ P) ; but by the agency of light it almost imme- AESENIBES. 367 diately splits up into the gas H, P, and a yellowish solid body, insoluble in water, which has the formula HP^: this decom- position is as follows : — j^ 6H:,P=HP,+3H„P. The liquid H^ P possesses an iutense spontaneous inflamma- bility in the air ; and the presence of a small portion of it is said to impart its inflammability to the gas Hj P, which is prepared from the phosphide of calcium : this is by no means improbable, since, when mixed with any combustible gas, it renders it spon- taneously inflammable when exposed to the air. The gas H, P is very slightly absorbed by water, but sufficiently so to impart to it a disagi-eeable smell and taste. The liquid H^ P is inso- luble in water. Solutions of Manganese, Zinc, or Ibon Salts are not precipi- tated by solution of phosphuretted hydrogen ; but this liquid does precipitate solutions of the salts of Coppbe, Siltee, Meecurt, Lead, and Gold. SALTS OF AKSENIO, OB AESENIDES. These also are both a numerous and important class of salts, although they hare not yet been much studied ; together with the phosphides, sili- eides and other similar compounds, they are of the utmost importance to the metallurgist, since their presence in minute quantity so much af- fects the character of the metals he produces. Arsenic occurs frequently combined with metals in nature; and these compounds begin to partate more of the characters of metallic alloys than those prefiously mentioned. The arsenides may be produced artificially, just as the phosphides — namely, by heating the add-radical itself or its oxygen compound As^ O5 with the metal, — ^by heating the metal under experiment with the gaseous hydrogen compound Hg As, or by passing the latter into solutions of some metallic salts. The constitution of the arsenides varies even more than that of the phosphides ; and they may be grouped into three series, in which a molecule of arsenic of the same atomic weight plays the part of a monobasic, a bibasic, or a tribasie radical respectively. Our surprise at such peculiarities is prevented by the remarkable instances of allotropy occurring among the elements, and of isomerism and polymerism among compoimd bodies. A few examples of arsenides may be given, the whole of which here quoted occur as minerals in nature — Ferrous. Cuprous. Cupric. Monobasic — ■ FeAs NiAs — — Bibasic MujAs — Ni^As (Cu^)2As — Tribasio — — NijAs — Cu^As. 368 CHEMICAL EEACTIONS. The compound acid-radicals into the composition of which arsenic enters retain this variable basicity, just as the well known and investigated com- pound acid-radicals containing phosphorus. The Htbeogen CoMPOiJin) (H3 As), or arseniuretted hydrogen, has been already spoken of at some length (p. 211) ; we will, however, here recapitulate its leading properties and characters. It is produced when an alkaline arsenide is dissolved in water, or the arsenide of a metal insoluble in water is dissolved in an acid ; it is formed most commonly by acting with nascent hy- drogen upon one of the oxygen compounds of arsenic. It is a coloiirless gas, of which the composition is II3 As ; it possesses a very offensive and peculiar odour, and is excessively poisonous when inhaled. The gas does not redden litmus. At a tem- perature of — 40° C. it condenses to a colourless liquid ; but it has not yet been solidified. Its specific gravity is 2-695 ; water dissolves one-fifth of its volume ; and the solution darkens solu- tions of many metallic salts. When heated, this gas is resolved iato its elements, hydrogen and arsenic; and when a light is applied to it in contact vdth the air, it bums with a bluish white flame, forming the oxide of arsenic (As^Oj) and water: if sufficient air is not present for the oxidation of the arsenic, the latter is deposited upon the sides of the containing vessel as a metallic film ; and the same end may be compassed by de- pressing a cold porcelain surface upon a jet of the burning gas. These features have already been spoken of as tests for arsenic (p. 212). In the decomposition of arsenide of potassium by water, a solid arseniuretted hydrogen is formed, which presents itself as a brown powder. Its formula appears to be H^ As. The salts of the two first subdivisions of basic radicals are not precipitated by the passage of arseniuretted hydrogen gas through their solutions ; those of iron also are not precipitated ; those of Manganese, Zinc, and Tin are very slowly decomposed ; but most salts of the fourth subdivision are precipitated, some in the form of arsenides, as Coppee and Plaiinum, whilst in other cases, as in those of Silver and Gold, the metal is thrown ANTIMONTDES. 309 down, and arsenious oxide formed, which remains in. solution, — thus, when this gas is passed into nitrate of silver — 12AgN03+2H3As + 5H,0=12HN03 + 12Ag+H,As,0,. Organic acid-radicals have some influence in preventing this precipitation, as is shown in. the instances of the acetate of lead and of the tartrate of antimonyle and potassium (tartar-emetic^ which are not acted upon by arseniuretted hydrogen. SALTS OP AlTTIMOlfT, OE ANTIMONIDES. The body antimony, as has been already stated, partakes almost more of the characters of a basic than of those of an acid- radical, and in its combinations with metals it produces bodies which far more nearly resemble alloys (or combinations of metals with each other) than true saline bodies, in which no physical characteristics of the basic or acid-elements are perceptible. It is thus not an easy matter to obtain, definite compounds, upon the formulae of which an opinion may be safely pronounced. The Htdeogen Compottito (H3 Sb), or antimoniuretted hydro- gen, is a very well defined body : it has been fully treated of at p. 200, and need be here but slightly noticed. It is obtained by the action of water on the antimonide of potassium, or by the action of nascent hydrogen on solutions of antimony salts. It is a gas which closely resembles H3 As ; its composition is H3 Sb : when ignited it bums with formation of antimonious oxide (SbjOj) and water; and if a cold porcelain surface be depressed upon the flame, a metallic spot is obtained : it is decomposed by a temperature below redness, into its elements antimony and hydrogen. This gas is not sensibly absorbed by water. A solid antimonide of hydrogen is also known. "When passed into alcoholic solutions of alkaline hydrates, a dark colour is produced, and, finally, brownish black flakes sepa- rate : this peculiarity distinguishes it from arseniuretted hydrogen. Solutions of salts of coppee, shvee, mbeotiet, and plaiintjm are precipitated by it more or less readily, with formation of bodies of the formula M3 Sb, thus — 3AgN03 + H3 Sb = 3HNO3 -1- Ag3 Sb. e5 370 CHEMICAL EEACIIONS. Section II. — The nitrites, nitrates, hypophospTiites, phosphites, phosphates, arsenites, arseniates, antimoniates ; sulpharsenites, sulpharseniates, sulphantimoniates. SALTS OF THE ACID-RADICALS WHICH CONTAIN NITROGEN, PHOSPHORUS, ARSENIC, AND ANTIMONY COMBINED WITH OXYGEN OR SULPHUR. Of acid-radicals containing nitrogen combined with oxygen, two only are of sufflcient importance to demand attention ; tliese are the nitrous and the nitric radicals (NO^ and NO3) : several other compounds of nitrogen and oxygen exist, but are of trivial importance in an analytical point of view. SALTS OE THE NITBOTJS KADICAL, OE NIXEITES. This radical is usually obtained in combination with potas- sium by heating the nitrate of potassium (KNO3) in a crucible, by which means the nitrite (KNOJ and oxygen are produced. Nitrites detonate when heated with combustible bodies ; they are either colourless or yeUow, and generally crystaUizable : the nitrite of silver is almost the only insoluble salt. This radical appears to have the property of assuming oxygen and trans- forming itself into monobasic, bibasic, and tribasic radicals, after the manner of the phosphoric acid-radical. The Htdbogen Salt (HNOj), or nitrous acid, is known only in solution in water, forming a blue liquid ; its anhydride (N^Og) is obtained as a gas when 1 part of starch is heated with 8 parts of nitric acid of specific gravity 1-25 : if the vapour is first dried by chloride of calcium, and then passed through a tube cooled to — 20° C, a very volatile liquid is obtained, green at the ordinary temperature, but colourless when exposed to extreme cold ; the vapour of this body is yellowish red. The Potassium, Sobiitm, Baehtm:, Steonthtm:, Calcium, Mag- nesium, Ieon", and Coppee Salts of this radical are soluble. The Silver Salt is obtained by adding nitrate of silver to a soluble nitrite (as the potassium salt) ; it is a yellowish white crystalline precipitate, the formula of which is probably AgNO . NIIHATE8. 371 It requires 300 parts of cold water for its solution, but is more soluble ia hot water ; and from its hot solution it crystallizes on cooUng. It is insoluble in alcohol. The Meecubic Salts are of doubtful existence ; and the Lead Salt is soluble. This radical is also detected by the following experiments : — a. By its liberation, even by weak acids (as acetic acid), in the form of the hydrogen compound, and the instantaneous de- composition of the latter, with formation of nitric oxide gas, which reddens on contact with air. /3. By the addition of a solution of ferrous sulphate and sul- phuric acid to the solution of a nitrite, a deep red liquid is ob- tained. y. Nitrites, when added to solutions of auric chloride or mer- curous nitrate, cause the precipitation of gold or mercury ; from solutions of manganous or ferrous salts, they precipitate manganic or ferric hydrate. S. When to a solution containing pure sulphuric acid, iodide of potassium, and starch, a minute portion of a nitrite is added, the characteristic blue iodide of starch is at once produced. SALTS OF THE KIIEIC EADIOAL, OE NITEATES. The abundant forms in which this radical occurs are its potas- sium, sodium, and calcium salts ; they are produced whenever nitrogenized organic matter is allowed to decompose in the presence of the hydrates of those basic radicals. Nitrates in general have a peculiar cooling taste ; they are all decomposed at a red heat : some, as the alkaline nitrates, yield nitrites in the first place ; but ultimately all are converted into oxides, with evo- lution of nitrogen and oxygen. Nitrate of aimnonium (NH^NOj) undergoes a peculiar decomposition under these circumstances, water and the gas called nitrous oxide (N^O) or laughing-gas being formed : NH,N03=2H,0-fN,0. Nitrates when fused on charcoal deflagrate, their oxygen uniting with the carbon to form carbonic acid gas, which then 372 CHEMICAL REACTIONS. takes oxygen, and converts the metal into a carbonate, if that salt is capable of withstanding the temperature to which it is exposed. When heated before the blowpipe with carbon and sulphur, with carbon and phosphorus, or with cyanide of potassium, a very violent and dangerous detonation ensues. The Hthbogen Compound (IINO3), or nitric acid, is an exceed- ingly corrosive liquid, and forms a most powerful solvent for metals, by reason of its ready decomposability. "When acting as a solvent, however, it differs from most acids hitherto considered, which simply part with their hydrogen and receive the replacing molecule of metal : nitric acid undergoes a more radical change ; for so comparatively feeble is the affinity which the nitrogen has for its 3 equivalents of oxygen, that the hydrogen of the acid iu escapiug decomposes a part of the aoid-radioal with the forma- tion of water and the evolution of one of the gaseous lower oxides of nitrogen. Thus, when it acts upon copper — 8HN03-l-6Cu=6CuN03 + W,0,+4H,0. nitric oxide. This property it is which imparts such a peculiar energy to the mixture of nitric and hydrochloric acids known by the names nitrohydrochloric acid and aqua regia : the oxygen of the nitric radical unites with the hydrogen of the hydrochloric acid; and among other products of decomposition, chlorine is set free, and, like all other nascent elements, exerts upon the body submitted to its action the most powerful effect : 2HNO3 -I- 2HC1 = 2H, + N, 0, -I- 2C1. In tbis way it is that this mixture of acids will dissolve the precious metals gold and platinum, which are attacked by chlo- riue, although not affected by either hydrochloric or nitric acids separately. The same reaction of course takes place when either hydrochloric acid is added in excess to a nitrate, or nitric acid in excess to a chloride ; for 2MNO3-I-4HCI =2MC1 -t-2H,0-|-]Sr,0,-t-2Cl or 2MC1 +4HN03=2MN03-|-2H,0 + N,0,-|-2C1; and it should be remembered that we always have it in. our power to convert one of these salts into the other by adding NITRATES. 373 excess of the acid which we wish to retain, since the other, be- coming decomposed into gaseous constituents, may he entirely removed by warming the solution. The nitric acid usually called " fuming " is generally red from the presence of N^O^, one of the products of its decom- position : its specific gravity is 1-536 ; and it solidifies at —49° C. to a very dark red mass. All nitrates are soluble in water j and therefore this radical cannot be recognised by the formation of any insoluble salts. It may, however, be identified by other processes : — a. By setting free the hydrogen compound (nitric acid) by the addition of concentrated sulphuric acid to a nitrate, and sub- jecting it to the immediate action of copper turnings, which must be added simultaneously with the sulphuric acid, decomposition of the nitric acid ensues, with disengagement of nitric oxide gas (NjOj). The latter is recognized by being itself colourless but capable of acquiring a peculiar brownish red colour by mix- ture with air ; it absorbs the atmospheric oxygen, and is con- verted into nitrous and hyponitric anhydrides (N^Oj and N^O^). /3. When nitric acid is produced from a nitrate by the action of concentrated sulphuric acid, the mixture cooled by immersion of the test-tube containing it in cold water, a crystal of ferrous sulphate added, and the whole allowed to rest, a dark halo is observed to form aroimd the crystal, which, upon the appUcation of heat, disappears vsrith a kind of effervescence. This is due to the formation of a very sing-ular combination of ferrous sulphate and nitric oxide having the formula 4re2S04, N^O^: heat de- composes this combination. The cause of its production is the decomposition of a portion of the nitric acid consequent upon the passage of the ferrous into the ferric salt, thus — lOFe, S0,+4H, SO,+2KN03=3(Fe,),(SOj3-l-K, SO, +4Fe,S0„N,0,+4H,0. brown compound, y. The nitrates do not reduce gold or mercurous salts; but when mixed with hydrochloric acid, they acquire the power of dissolving gold leaf 374 CHEMICAL KEAOTIONS. S. TJpon adding to a nitrate sulphuric acid and sulpliindigotic acid, the colour of the latter is destroyed. Of the acid-radicals containing phosphorus combined with oxy- gen, those existing in the phosphites and phosphates are of great analytical importance. The hypophosphites are rare. SALTS OF TnE IIYPOPHOSPHOROUS RADICAL, OE HYPOPHOSPHITES. _ This acid-radical is of rare occurrence, being only produced by artificial means. It is obtained in the decomposition of phosphide of barium by water, or by boiling phosphorus with an alcoholic solution of hydrate of potassium, or with the aqueous solutions of hydrate of barium or calcium, untU it disappears, and the vapour has no longer the odour of phosphuretted hydrogen. The phosphuretted hydrogen evolved during the process fre- quently causes dangerous explosions, which may be moderated by employing only a gentle heat. The barium or calcium salts thus obtained (BaH^POj or CaHj POj) are very crystaUizable. The Hydrogen Salt (H3 PO^), or hypophosphorous acid, is a viscid, rai- crystalhzable, very acid liquid, which when heated decomposes into phos- phuretted hydrogen and phosphoric acid, thus — 2IL^'P0^=H^'B+'K^'P0^. Although hypophosphorous acid is thus tribasic, one series of salts only is known, namely, the series of acid salts represented by the general formula MHj PO2 ; they generally occur with water of crystallization, and are all soluble in water, and many of them also in alcohol. This radical may nevertheless be recognized by several processes of de- composition : — a. When any dry hypophosphite is rather gently heated in a test-tube, decomposition of its radical occurs; phosphuretted hydrogen is evolved, which may be recognized by its odour and ready inflammabOify ; and a py- rophosphate of the metal remains behind. The lead salt exhibits this de- composition best : 4MH,P02=M^P,0.,-1-H20-|-2H3P. pyrophosphate. /3. When mixed with an acid, hypophosphites reduce silver and gold salts, precipitating silver and gold ; they also reduce mercuric and cupric salts. The same reactions take place more slowly with concentrated solutions of hypophosphites. y. When boiled with excess of hydrate of potassium, alkaline hypophos- phites evolve pure hydrogen gas : PHOSPHITES. 375 SALTS OF THE PHOSPHOEOTJS RADICAL, OE PHOSPHITES. This acid-radical is obtained ia combiaatioii -with hydrogen by the decomposition of terchloride of phosphorus (PCI3) by water, or by the slow oxidation of phosphorus in the air. The HrDEoaEN Salt (H3 PO3 ?), or phosphorous acid, is known in the liquid and also in the crystallized state ; when heated, it decomposes, thus — ^ 4H3P03=3H3PO,+H3P. The Alkaline Phosphites are soluble in water ; most other salts are insoluble or nearly so. The acid salts of the formula MHj PO3 are soluble in water ; the acid salts having the com- position MjHPOg are less so, whilst the neutral phosphites M3 PO3 are insoluble. The Baeitjm and Calcium Salts are slowly precipitated by the addition of alkaline phosphites to soluble barium or calcium salts, as white precipitates having the formula M^ HPO3 : by boiling, the precipitation is accelerated ; but the precipitate which then falls is M3 PO3, — MH, PO3 (the acid salt) remaining in solution. They are soluble in most acids, and by nitric acid are converted into phosphates. The Magnesium Salt is not precipitated when a dilute solution of a magnesium salt is added to a soluble phosphite in the pre- sence of the chloride and hydrate of ammonium. The Eekkous Salt is white, changing to red basic ferric phos- phate. The Fbeeic Salt is white. The Zinc Salt is soluble. The Cupeic Salt is blue. The Meectteous, Meecueic, and Silvee Salts do not exist. The Lead Salt is white. This radical may also be recognized as follows : — a. The majority of the phosphites do not evol-^g|ri|^miretted hydrogen, but pure hydrogen slightly contamin^Brwith it, when the dry salts are heated. The lead salt is an exception. 2Ba, HPO3 + H, = Ba^ P, 0, + 4H. 376 CHEMICAL EE ACTIONS. /3. Soluble phosphites reduce solutions of cupric, silver, mer- curic, or gold salts, and precipitate the metal. This takes place especially on boiling. y . Phosphites, when boiled with excess of hydrate of potassium, are not altered, nor does any evolution' of hydrogen occur. SALTS OP THE PHOSPHOEIC EADICAL, OE PHOSPHATES. The phosphates occur somewhat abundantly in nature ; they are found distributed in smaU quantities through the mineral and vegetable kingdoms, whence they pass into the bodies of animals, to which they are absolutely essential for the formation and renewal of their skeleton. The Hxbeogen Salt (H3 PO^), or phosphoric acid, is produced by the decomposition of these, or by the solution of phosphoric anhydride (the body PjjOj, which is the white crystalline solid obtained when phosphorus is burnt in oxygen or air) in water. The substance P^ 0^, when combining with water, produces three distinct acids, thus — PjOj + HjO =2HP03, meta- or monobasic phosphoric acid. 'P^0^+2K^0='K^F^0^ pyro- or bibasic phosphoric acid. P2 05 + 3H2 0=2Il3PO^, ordinary or tribasic phosphoric acid. These are each the representative of three distinct classes of salts, called respectively the metaphosphates, pyrophosphates, and phosphates, or the mono-, bi-, and ordinary phosphates : whether in these the three allotropic varieties of phosphorus exist, we do not know; but they singularly correspond to the two classes of phosphides previously mentioned (p. 366). The phosphates which ordinarily occur in nature are the tribasic phosphates. When the anhydride P^Oj is dissolved in abundance of water, and the solution heated, the latter of these acids is produced ; but if the phosphoric anhydride be allowed to dissolve in. cold water, l^^secM^ is obtained, — ^whUst, again, if the aqueous solu- tion of eTTOl ^. ' acid be evaporated in a platinum dish until water no longer is expelled, the residue solidifies on cooling into a glassy substance, which is caUcd " glacial" phosphoric acid, and which is in reality HPO^, or the monobasic acid. This wiU PHOSPHATES. 377 volatilize altogether at a red heat. The solution of the ordinary- acid (Hj PO^) may be evaporated without decomposition up to a temperature of 149° C, when it becomes of a syrupy consistence ; between that temperature and 213° C. it loses the elements of water, and is converted into pyrophosphoric acid ; and if cooled from that point, it solidifies in the form of a soft glass, or in small granular crystals ; if heated further, it again loses the ele- ments of water, and is converted into the monobasic acid, as has before been stated. Many phosphates behave in a characteristic manner when heated, owing to their peculiar constitution : thus with the tri- basic radical PO^, which forms the three series of salts, MH.PO, M,HPO, M3PO,. acid salt. acid salt. neutral salt. If heat is applied to the second of these acid salts, it decomposes into water and a neutral pyro- or bibasic phosphate, thus — 2M,HP0,=M,P,0,+H,0: and again, if the first acid salt be heated, water is again obtained and a meta- or monobasic phosphate ; for mh,po,=mpo3+h:,o. The pyrophosphates exhibit similar features. Notwithstanding, however, that the acid salts of the various phosphoric radicals are thus unstable, all neutral salts are but little affected by heat : the generality fuse to a glassy mass, and yield to few decompos- ing agents except carbon, which, at a high temperature, removes the oxygen from most phosphates except those of potassium and sodium, and eliminates the phosphorus, which then distUs and is suitably collected. (See p. 33.) Of neutral phosphates, those of the first subdivision are almost the only soluble ones; many of the acid phosphates, esnecially those of the formula MH^ PO^, are soluble in w^tt^fpt are soluble in acids. ^f^ The Baeium, Sthonthtm, and Calcium Saiis are white preci- pitates of the formula M^ HPO^ when produced by the action of ordinary phosphate of sodium (Na^HPO^). They are soluble in 378 CHEMICAL ENACTIONS. chloride of ammonium, insoluble in water, but soluble in acids, even in acetic. The neutral meta- and pyrophosphates of bariiiin are insoluble in chloride of ammonium, or water, and the latter also in acetic acid. The same salts of strontium are insoluble in water, and the former also in acids, the latter in acetic acid. The metaphosphate of calcium is a white viscous precipitate ; and the pyrophosphate does not dissolve in acetic acid. The MASNEsnjM Sam is formed but slowly by the addition of a salt of magnesium alone to a soluble phosphate — ^the precipitate imder such circumstances has the formula Mg^ HPO^ ; if, how- ever, chloride of ammonium and ammonia have been previously added, the subsequent mixture with a magnesium salt gives rise to an immediate crystaUine precipitate, which forms more rapidly on stirring : its formula is Mg^ NH^ PO^. It is soluble in 7548 parts of chloride of ammonium, in 44,330 parts of hydrate of ammonium, and in 15,627 parts of chloride of ammonium solution containing hydrate of ammonium. It is insoluble in water which contains any phosphate in solution, but dissolves in 15,293 parts of pure water, from which it may be precipitated by the addition of ammonia. It dissolves in acids. The meta- and pyrophosphates are scarcely produced except in the pre- sence of hydrate of ammonium. The Feseous phosphate and pyrophosphate are white. The Ferric Salt is white ; its formula is uncertain. It is in- soluble in ammonium salts, except the carbonate and sulphite, and it dissolves also in hydrate of ammonium in the presence of phosphate of sodium. It partially dissolves in carbonate of sodium. It is soluble in 1500 parts of water, and is easily dis- solved by dilute acids, even by sulphurous, but not by cold acetic acid. The metaphosphate is wliite, insoluble in water or dilute acids, but soluble in 8tro||H^y^ric acid. The^^^^^^hate is white, and is soluble in hydrate or carbonate of ammoniu^^^n phosphate of sodium ; it is insoluble in chloride of ammo- nium, and in hydrochloric or sulphurous acids. The Znsro Salt is a gelatinous precipitate which becomes cry- stalline on standing. It formula is Zn^ PO,. It dissolves in the PHOSPHATES. 379 hydrate and most ammonium salts, is insoluble in water, but soluble in acids. The metaphoaphate is soluble in water. The pyrophosphate is white, soluble in ammonia, but insoluble in water. The Ctjpeic Salt is bluisb green ; of tbe formula Cu^ HPO^, sligbtly soluble in ammonium salts, insoluble ia water, but soluble in acids. The metaphosphate is bluish white, insoluble in water or in dilute acids, but soluble in strong sulphuric acid. The pyrophosphate (Cu^P^O,) is greenish white, soluble in ammonia, phosphate of sodium, and acids. The Argentic or Silver Salt is yellow. Its formula is Agg PO^. It dissolves easily in tbe hydrate or carbonate of ammonium, but less so in other ammonium salts ; it is insoluble in water, but soluble in most acids. The metaphosphate is white, decomposed by water, soluble in nitric acid. The pyrophosphate is white, of the formula Ag^P^O,, soluble in hydrate of ammonium, insoluble in water or acetic acid, soluble in nitric acid, which, by boiling, conrerts it into the ordinary phosphate (Agj PO^). The Meectteous Salt is white, of the composition (^g^)^V^O,, insoluble in water and in many acids. By some acids it is de- composed. The pyrophosphate is white, and is decomposable by hydrochloric acid. The MBEotTEic Salt is white, it appears to be the pyrophos- phate (Hg^P^Oj). It dissolves in many ammonium salts, but very slightly in the hydrate. It is insoluble iu water, but soluble in many acids. The Lbab Salt is white, and variable in composition, being sometimes Pb^ HPO^, and at other times Pbg PO^. It dissolves in hydrate of potassium or chloride of ammonium, is insoluble iu water or acetic acid, but soluble iu nitric acid. This salt ex- hibits a great peculiarity: when heated on charooa before the blowpipe even the inner flame fails for some time to reduce it ; and upon removal from the flame, the colourless and transparent bead becomes opaque and orystaUine on cooUng ; the crystalline form is the dodecahedron. 380 CHEMICAL HEACTIONS. The metaphoBphate is white, insoluble in ammonia. The pyrophosphate (Pbj P^ O7) is white, soluble in hydrate of potaBsium or pyrophosphate of sodium, insoluble in hydrate of ammonium and in many acids, but soluble in nitric acid. Otter means of proving the existence of this radical are -want- ing, owing to its great stability; it may, however, be recog- nized by adding to the nitric solution of a phosphate (an alkaline phosphate is the best) some molybdate of ammonium (NH^ MoO^), evaporating to dryness, and just redissolving in nitric acid : a yellow crystalline residue is an evidence of the presence of a phosphate. Of acid-radicals containing arsenic and oxygen, two only are knovsm, those occurring in the arsenites and arseniates. SALTS OP THE ABSENIOTJS EAnlCAI, OE AESENITES. The arsenites are considered bibasic, and have the general for- mula Mj ASjOj ; they are sometimes colourless, but occasionally of beautiful colours. Most arsenites, when heated alone, decompose and leave the oxide of the basic radical, whilst the anhydride (ASjOj) volatiles; some, as the alkaline arsenites, decompose into an arseniate and arsenic. The HrDEoaEN Salt (H^As^Oj) is imknown; for when its supposed aqueous or acid solution is evaporated, the arsenious an- hydride (As^Oj) crystallizes out. The Alkaline Arsenites are soluble in water ; but most others are insoluble, although dissolved by acids and frequently by ammonium salts. The BAEitTM and Steontitjm Salts are precipitated only after being allowed to rest for some time. The Calcium Salt is precipitated immediately on mixing a soluble arsenite, or arsenious acid, with excess of the hydrate or other salt of calcium. It is a white precipitate. Dried in the air, its composition is Ca^ As.jOj-l-aq. It dissolves in ammonium salts, but is only slightly soluble in water ; in dilute acids, and even in an aqueous solution of arse- nious acid, it is soluble. AESENIAIES. ' 381 The Magnesium and Zinc Salts are scarcely known. The Cuprio Salt is bright green. Its formula is Cu^ As^O, ; it dissolves in ammonium salts and in acids. The Argentic or Silver Salt is lemon-yellow, of the foi-mula Agj As^Oj. It dissolves in ammonium salts and ia acids. The MEECtTHOirs, MEECimio, and Lead Saxts are white preci- pitates, insoluble in ammonium salts, but soluble in nitric acid. In addition to these means of detection, this radical may be recognized by other methods, previously detailed (p. 209), but which may be here briefly recapitulated : — a. By heatiag the arsenite in a bulb-tube with carbonate of sodium or charcoal, and observing the arsenical mirror. jS. By the action of nascent hydrogen, which produces the gas Hj As, by the subsequent decomposition of which the arsenical mirror may also be obtained. y. By the action of hydrosulphuric acid gas, which, when passed through the hydrochloric solution of an arsenite, yields the arsenious sulphide, which may be further tested by the me- thod of Fresenius and Von Babo (p. 213). SALTS OF THE AESENIC EADICAL, OE AESENIATES. The arseniates are tribasie, and bear a great resemblance to the phosphates ; they are produced by the action of nitric acid or other oxidiziag agents on arsenious anhydride or arsenites. The arseniates when heated are not so prone to decompose as the arsenites. The Hybeogen Salt (H3 AsO^ ?) is known ; it occurs in large crystals. By heating this body to fusion, a glassy substance, ar- senic anhydride (As^ O5), is obtained. The AiKALi:tfE Aeseniates are soluble ; most others are in- soluble. The Baeium, Steontium, Calcium, and Magnesium Salts are white, insoluble in water, but soluble in acids. The Zinc Salt is similar. The Cupeic Salt is bluish green, insoluble in water, but soluble in ammonia water and in the stronger acids. 382 CHEMICAL EEACTIONS. The Argentic or Silver Salt is dark brick-red ; its formula is AggAsO^; it is insoluble in water, but soluble in ammonium salts and in many acids. The Mbecueous Salt is white, changing to a fine red, a double salt being at first precipitated. Its composition is (Hg2)2 HAsO^ -|-aq. It is insoluble in most ammonium salts and in water, but soluble in nitric acid. The MEECimic Salt is yellow, soluble in nitric and arsenic acids. The Lead Salt is white, of the formula Pbj AsO^, insoluble in ammonium salts and in water, but soluble in nitric acid. This radical may be recognized in precisely the same manner as the preceding one, by processes of decomposition, a few pre- cautions being taken. a. Arseniates should be mixed with carbon, or carbon and boracic anhydride, before introducing into the bulb-tube in the blowpipe experiment. (See p. 210.) J3. With nascent hydrogen they act as arsenites. y. But before passing hydrosulphurie acid into their acid solution, the latter should be invariably treated with a current of sulphurous acid gas, in order to reduce the arsenic to an arsenious salt. This is necessary because the arsenic sulphide (As^ S^) forms and separates very slowly, whilst the arsenious sulphide (AsjSg) is much more rapidly produced. The liquid must be boUed until every trace of sulphurous acid gas is evolved, before any attempt is made to pass sulphuretted hydrogen. Of add-radicals formed by the union of antimony and oxygen, two only are known — those existing in the antimoniates and metantimoniates ; but of their combinations we are almost wholly ignorant. (See p. 207.) Of acid-radicals formed by the union of arsenic and antimony with sulphur, three are well defined — those existing in the sulph- arsenites, in the sulpharseniates, and in the sulphantimoniates ; but they are not of sufficient importance to demand a separate notice. (See pp. 208 and 217.) TABLE OF EEACTIONS. 383 TABLE OF REACTIONS. Salts. NO.. (see p. 370) NO3. (P-371) PO4. (p. 376) AS2O5. (p. 380) AsOi. (p. 381) Potassium Sodium... — — — - — Barium — — white white white Strontium ... — — white white white Calcium — — white white white Magnesium... — — ( white ] i crystal- ■ line J ? white Ferrous — — C white 1 • changing ■ to blue ? white Ferric. . . . — — C buff- ■ < white [ or white J f yellow- ] 1 ^^^ r [ brown J brown Zixic — — f white 1 i gelati- [ nous J — white Cuprio Silver C yellow- ■ < ish [ white J — f bluish \ \ green J yellow white r bright \ I green j f lemon- 1 \ yellow J white r bluish 1 t green J / brick- 1 1 red j white 1 • changing to red J MercuTous... Mercuric .... — — white white yellow Lead — — white white white 384 CHEMICAL BEACIIONS. Analysis of Subdivision IV. The acid-radicals of more common occurrence only being in- cluded, the salt may be a MTEATE, PHOSPHATE, AE- SENITE, or AESENIATE. ETidenoe of the presence of the first of these aeid-radioals may be ob- tained by adding concentrated sulphuric acid to the solid, or its strong solution, and heating. Pungent orange brown vapours indicate a nitrate. Proof of the presence of arsenic will have been obtained in the exami- nation for the basic radical, which in analysis always precedes the search for the acid-radiual. If the salt, when heated with carbonate of sodium and charcoal in a bulb tube (see p. 210), yields a metallic mirror, an arsenite or arseniate is indicated. Further Analysis, Acidify a portion of the solution of the salt with a few drops of dilute sulphiuic acid, and pass hydrosulphuric acid gas. A yellow precipitate of AsjSj or ^2^6 would indicate the presence of ASjOj or ASO4. To distinguish between these, the silTer .test must be resorted to, being applied to a, perfectly neutralized part of the original solution. AgjASjO. is yellow ; Ag3As04 IS brick-red. If no precipitate, or only a white one of sulphur (due to nitric acid), warm the solution, to expel every trace of hydrosulphuric acid; add excess of acetate of potassium, and a drop or two of perchloride of iron. A white pre- cipitate of Fe^PO,! would indicate the presence of PO.. If no precipitate, a fresh portion of the original solu- tion of the salt should be mixed with concentrated sulphuric acid (the test- tube being cooled at the time of mixture by immer- sion in water), a crystal of ferrous sulphate then added, and the whole allowed to rest: the formation of a reddish brown halo aromid the crystal, consisting of 4Pe2SO.„ NjOj, would indi- cate the presence of NO,. 385 Part II.— THE METHOD OF ANALYSIS. CHAPTER I. INTRODUCTION, 1 EERE8TEIAL matter, although consisting primarily of a de- finite numher of elements, is found, as the student will now have learnt, in an almost infinite variety of comhitiations. These comhinations or salts are formed, it will be remembered, by the union of two classes of bodies, which may be either simple or compound, and are distinguished as basic radicals, and acid- radicals. To test these combinations, that is, to identify their basic or acid constituent, is easQy accomplished by the employ- ment of any appropriate reaction which may elicit some charac- teristic feature of colour, odour, insolubility, &c. ; but to analyse such a combination, that is, to separate its basic and acid-radical either in an isolated condition or in a new form, is a more diffi- cult task. And this difficulty is, of course, enhanced when the process of separation has to be performed upon a complicated mixture of salts. Although complex bodies of mineral origin, almost without exception, as well as a vast majority of those derived from ve- getables and animals, are reasonably believed to be definite saline combinations of basic and acid-radicals, still several substances which occur abimdantly in organic structures, such as albumen, fibrine, starch, and gelatine, are composed of molecules so com- plex as to baffle all attempts made to catch a glimpse only of their constitution. These bodies, therefore, are not subjects for chemical analysis; at least, they cannot be resolved, like the saline combinations of compound radicals, into their proximate, but only into their several elementary constituents. 386 THE METHOD OP ANALYSIS. Smee, therefore, the processes of qualitative analysis to which the present ■work is confined have for their object the sepa- ration, recombination, and recognition of certain forms -of ele- mentary or of definite compound matter, i. e. the separate identi- fication, in the bodies termed salts, of their acid- and basic radi- cals, it is obvious that all indefinite compounds, to which ultimate analysis only is appUoable, are excluded from consideration. AR salts commonly met with (using the term salt in its widest sense, as including bases, oxides, acids, &c.) may, however, be considered as fit subjects for qualitative chemical analysis. It wUl be at once seen that the certainty of analysis depends much upon the simplicity or complexity of the bodies with which it has to deal. Thus, chemical analysis is most Kkely to be successful with bodies of mineral origin ; for in them, generally speaking, the elements exist in the simplest forms of combi- nation. These constituent elements of mineral substances are, moreover, possessed of most powerful chemical affinities, and, above all, are usually neither themselves gaseous at ordinary temperatiu'es, nor do they yield gaseous products. On the other hand, the bodies derived from the animal and vegetable kingdoms are compounds in which, for the most part, the foiu- elements, carbon, hydrogen, nitrogen, and oxygen, exist in large propor- tion. The ready deoomposability of these organic bodies depends in great measure upon the gaseous character, i. e. the volatility of their constituent elements, and upon the remarkable tendency which carbon and hydrogen, or carbon, hydrogen, and oxygen present, to imite in endless and ever- varying proportions. Other causes combine to render these substances unstable, such as the great afimity of carbon and of hydrogen for oxygen (CO., and H^O being thus formed), and of nitrogen for hydrogen (JSTHj being the product) : the gaseous character or ready volatility of the simpler compounds thus produced is also to be taken into ac- count. But the caiises of the instabUity of these organic sub- stances is not now the object of discussion ; it is merely adduced to show how smaD a hold upon them chemical analysis possesses, when we consider that its object is to separate a particular com- INTEODTJCTIOIT. 387 pound, which in these substances may slip, by a Protean meta- morphosis, through the fingers of the experimenter m the very process of detection. The action of reagents, themselves the means of analysis, is sufficient to decompose bodies such as these. But it is far otherwise with the elementary or simpler forms of matter which constitute mineral bodies. These are not so affected by reagents ; and if isolated, there is in most cases no danger of their volatilization at ordinary temperatures, and none of their decomposition : neither is their presence so concealed as to be undiscoverable ; for no known means, however energetic, can destroy their identity. It matters not whether they exist dissolved ia mineral waters, crystallized as distinct substances in masses of mineral, or diffused in minute quantity through various soils ; their recognition and separation is a matter of almost equal certainty. It is thus that mineral poisons are so much more easy of detection than those of vegetable or animal origin. The latter poisons are, ia the majority of cases, easily destroyed, and often cannot be satisfactorily pronounced to be the poison supposed without a quantitative determiaation of the proportions in which the carbon, hydrogen, nitrogen, and oxygen are present. Arsenic, lead, and copper, on the other hand, are subject to no such accidents. Whatever stage of decomposition the body poisoned by these substances may have reached, these minerals can still be recognized and separated from the moulder- ing remains. So far for the limits and the scope of qualitative analysis ; we wilL now speak of its method. The student vrill now have become acquainted with a certain number of tests, the apphcation of which, either singly or com- bined, cannot fail to assure him of the presence or absence of every basic or acid-radical. To analyse successfully, there is, however, one point to which he must invariably attend ; and that is, to preserve a weU-ordered sequence in the apphcation of the tests at his disposal. By the tables which have been appended to each subdivision of the basic and acid-radicals (in Chapters s2 388 THE METHOD OP ANALYSIS. VI. and VII.), the student has been somewhat prepared for this system, which, although at first sight it may appear to be a waste, is in reality an economy of time. The only true source of certainty in analysis consists, in fact, in this application of tests in a certain fixed order. The first step must always be to sepa- rate a group of substances (such as a subdivision of basic radicals) the members of which may always be removed together as one precipitate by the employment of a certain reagent. The labour is thus simplified : for if such a reagent fail to produce a preci- pitate, we know that an entire group of bodies is absent ; if, on the contrary, a precipitate is produced, we have an assurance that it can only contain certain members, and know therefore the limit of our search in that direction. This accomplished, a second group-test is applied, and the same course followed, until, having exhausted group-tests, we have ascertained in. what sub- division or subdivisions the substance or substances sought for exist. Then, by the apphcation of less general tests, we con- tinually subdivide the groups until the isolation of the individual members is accomplished. This principle applies to the analysis of simple salts or mixtures — to the detection of basic or acid- radicals. And the student cannot be warned too early of the extreme foUy of what maybe termed analytical "angKng" — of the promiscuous employment of tests which, when properly apphed, are extremely effective in detecting individual substances. Com- plicated results may thus ensue, to unravel which may baffle all the ingenuity of the student ; many substances, too, may thus be entirely overlooked, in consequence of the special test employed acting upon bodies other than the one sought for, and in a way not remembered. To take an instance from a frequent ocouiTenee in the laboratory. The student has a solution to analyse, the colour of which is green. He instantly concludes that the base is copper ; and instead of employing the ordinary sequence of group-tests, he devises a short and easy method. Knowing that hydrate of ammonium gives a characteristic reaction with copper salts, he adds it : a green precipitate is formed, and then redissolved ; but the solu- tion does not present the deep blue colour of cuprammonium salts. Thus he is disappointed ; but, still under the impression tliat he is dealing with a INTEODTJCTION. 389 copper salt, he tries the action of hydrate of potassium ? a green precipitate occurs, somewhat pale, it is true, but the student uerertheless regards it as confirmatory of his original supposition. Ferrocyanide of potassium is next added ; and the green precipitate which follows is a new perplexity. In despair at these results so conflicting and so contradictory of his original idea, he adds sulphide of ammonium : the black sulphide formed confirms his first supposition ; the doubts consequent upon the previous reaction clear away ; and he definitely pronounces the solution to contain copper. Why has nickel been thus obviously mistaken for copper ? Because the experi- menter, in defiance of the confliotirig evidence which the special tests have afforded, has entirely neglected all proper sequence of experiment, and omitted to apply the test which claims precedence of all — the group reagent, hydrosulphuric acid in an acid solution, by the employment of which he would at once have been able to decide the question about which so much time has been wasted. The student, however, should be equally careful not to trust too implicitly to a mechanical familiarity with the routine of analysis, and should learn by repeated trials to assign to each indication no more than its due value. The accumulation of evidence is also of the highest importance. Next to the accurate recollection of reactions characteristic of each basic and acid-radical, a scrupulous attention to the orderly application of tests is, as we have seen, most necessary to suc- cess in analysis ; and so, in order that the student may be well practised in this method, it is advisable that he should at first test substances for basic radicals only, reserving for a second stage the analysis of salts with a view to the detection of their acid-radicals : for these latter are, for the most part, identifiable only by a chain of circuitous evidence. And it must be remem- bered that, upon the knowledge of the basic radical present in a salt, the mode of testing for its acid constituent is frequently founded ; indeed, the presence of the latter is often ascertained in the examination for the former constituent. We now proceed, therefore, to details. 390 THE METHOD OF ANALYSIS. CHAPTER II. QUALITATIVE ANALYSIS OF A SESTGLE SALT. SECTloif I. — Examination for the basic constituent. The student wiU have learned, from the analytical schemes already given (Part I. Chapter VI., pp. 81, 97, 150, 190, 245), what basic radicals he should he prepared to find in any salt. In order to facilitate analysis, it has been found advisable to perform in the first place a few experiments, chiefly with the blowpipe, upon the dry salt. These experiments constitute what has been termed " the preliminary examination ;" and the results which it yields with a simple salt are often so decisive as at once to determine the nature of the basic radical present. Skill in this blowpipe analysis is of great service to the travelling mineralogist, since the apparatus necessary for conducting it may be packed in a small compass, and the results obtained afford a tolerably cer- tain and valuable guide iu examining the minerals of the country through which he passes. The student, however, who has the means of controlling these results by further analysis of a solu- tion of the substance, or " analysis by the wet method," should always consider the latter, as in truth it is, the mode of procedure most to be relied on, and should then employ the blowpipe ex- amination only as the preliminary step to a more accurate analysis. A convenient form of this examination is given in the following Table, in which, and in the other Tables which succeed, symbols are often employed in the place of words. Simple soluble salts for analytical examination may be selected from those mentioned under each basic radical in Chapter VI. For acid-radicals, their combinations with sodium, potassium, or ammonium may in general be vised. Examples of insoluble salts may be obtained from those printed in antique type. EXAMINATION FOE THE BASIC EADICAL. 391 Preliminary examination for the detection of the basic radical. EXPERIMENT. OBSERVATION. INFERENCE. Heat the powdered A. Entirely volatile. A. NH„ Cd, Hg, substance by the blow- As, certain salts pipe flame, allowing the of tin. flame to spread, on a flat surface of charcoal ; be- B*t. Not volatile ; no reduction of metal. [Al, Zn. 1 . Residue white on cooling. B. l.Subd. I.&II. gin with a gentle heat, ■fa. Fusible when heated. a. K,Na, perhaps and increase to intense Subd. II. ignition. 6. Infusible when heated. b. Subd. II., Al, Zn. 2. Cr,Fe,Mn,Co, 2. Residue coloured on cooling. C. Not volatile; reduction of metal. Ni. 1. Metallic globules malleable. C. 1. Pb, Ag, Sn, Cu, An. 2. Metallic globules brittle. 2. Bi, Sb. 3. Black metallic powder. 3. Pt. Allow the residue (if BriUiant incandescence. Ca, Mg, Al, Zn. any) to be heated by the Less brilliancy. Ba, Sr. central part of the flame. Colour imparted to 1 . Green ; 2, Red ; 3. Crimson ; l.Cu,2.Ca,3. Sr, the blowpipe flame in 4. Yellow-green; 5. Yellow; 6. Violet. 4,Ba,S.Na,6. K. the first experiment. Incrustation on the 1 . Dense white ; very distant. 1. HgaCl, HgCl, charcoal ; its distance nh'ci. 2. ASoOa. from thatend of the char- 2. White and crystalline ; distant. coal on which the sub- 3. Bluish white; distant. 3. Sb.,03, SnCl. stance has been placed ; 4. Yellowish white when hot, almost or 4. ZnaO, BigOa. its colour. quite white when cold ; less distant. 5. Orange hot, yellow cold ; less distant. 6. PboO. 6. Dense white; less dbtant. 6. SngO. 7. Reddish brown ; less distant. 7. CdgO. If A (see above), Heat with Nag CO3 in 1 . Sublimate is a black mirror. I. As. bulb-tube (see pp. l6g, 210). Heat with solution of 2. Sublimate is grey globules. 2. Hg. Pungent ammoniacal odour. NH4. KHO in test-tube (see p. 78). If B 1. 6 (see above). Heat with C0NO3 on Residue, originally white, becomes— l.Mg,2.Al,3.Zn. charcoal in oxidizing 1. pink; 2. blue; 3. green. flame. If B 2 (see above). O.F. E.F. Heat with borax on 1. Green. Green. 1. Cr. platinum wire in both 2. GVeere when hot. Colourless when hot 2. Cu. flames, and observe the Blue-green, cold. Reddish, cold. colour of the bead, both 3. Orange, hot. Colourless, hot. 3. Fe. when hot and when cold. Yellow, cold. Bottle-green, cold. 4. Blue. Blue. 4. Co. 6. Amethyst, Colourless. 5. Mn. 6. Red-brown. Grey. 6. Ni. * We cannot be sure that the substance belongs to B, and not to C, until we have also heated it on charcoal with NaaCOg or KCy. t Most salts containing water of crystallization fuse as soon as heated, from the solvent action of the water ; but the substance under examination can only be pronounced fusible when it continues so under the prolonged action of heat. 392 THE METHOD OF ANALYSIS. The student should make careful and ample notes of all ob- servations made, drawing up his results in the tabular form given above ; and having done this, he should proceed to make a solution of the substance under examination, preparatory to the actual analysis. ACTTTAI. ANALYSIS EOE THE DETECTION OF ONE BASIC EADICAL. If the substance be soluble in water, that liquid is the best solvent that can be employed, since all others entail more or less trouble in the subsequent treatment ; and so desirable is it that water should if possible be used, that in analysing a substance known to be a single salt only, if it is but slightly soluble in water, that aqueous solution may be taken in preference to an acid one. The solubility or insolubility of any substance in a given liquid may be ascertained very readily by boiling the solid and liquid together, allowing the mixture to cool, and then filter- ing it. A drop of the filtrate is now evaporated on a bright piece of platinum foil or in a watch glass, when, if a tolerable residue be visible, enough substance is contained in the solution for the purposes of the analyst. But if the residue be scarcely appreciable, or if none be present, the substance must be con- sidered insoluble, and another course adopted. If water fails to dissolve the substance, acids must be em- ployed. The incautious use of acids, however, leads not unfre- quently to failure in analysis ; great judgment is therefore neces- sary in dealing vsdth these solvents. The acids most commonly employed are hydrochloric and nitric, or a mixture of these ; but before proceeding to the selection of one of these solvents, the student must recall the results of his preliminary examination, if indeed the substance has been found insoluble in water. If, in the blowpipe experiments, a malleable globule of the lustre and colour of silver or lead, or a subhmate indicative of mercury has been obtained, nitric, not hydrochloric acid, must be employed. The reason of this is apparent. Hydrochloric acid, in dis- solving silver, mercurous, or lead salts, produces an insoluble chloride of those metaUie radicals, which wiU. baffle the student's DETECTIOIf OP ONE BASIC RADICAL. 393 attempts at analysis. The following equations represent the different results of acting upon an insoluble silver salt with hy- drochloric and with nitric acid : — Ag,C,0,+2HCl=H,C,0,+2AgCl. ppt. Ag,C,0, + 2HN03=H,C,0,+2AgN03. sol. Again, if a globule and incrustation iudioative of tin or antimony has been obtained in the blowpipe examination, hydrochloric, and not nitric acid, must be employed as the solvent of the compound, since soluble chlorides of the above-named metals wlU be thus produced, but with nitric acids the insoluble com- pounds, metastannic acid and antimonic anhydride. (See pp. 197, 207.) Sulphuric acid is but rarely employed as a solvent ; for when in the concentrated form, it is somewhat immanageable, and when dilute, it is not so advantageous as nitric or hydrochloric acid. A mixture of nitric and hydrochloric acids is seldom used. It is, however, the common solvent for certain alloys, and for the metals platinum and gold. It may be remarked that in most cases it is weU to act with as small a quantity as possible of a tolerably strong acid, and, after boiling the substance with it, to dilute with water and re- peat the ebullition ; for many of the salts formed by the action of acids imder these circumstances are easily soluble in dilute, although insoluble in strong acids : take the following instance — Pb,C03-l-2H]Sr03=2Pb]Sr03-|-H,0-l-C0, ; carb. of lead, nitrate of lead, insol. in water. insol. in strong acid. the nitrate of lead here formed would remain as a white crystal- line powder in the presence of excess of strong nitric acid, but on the addition of water would dissolve. But there exist substances insoluble in water and all acids, or which, if soluble in hot concentrated acids, are immediately pre- cipitated on dilution with water or cooling. All such substances require a special treatment to bring them into a condition fit for 394 THE METHOD OE ANALYSIS. analysis. The following are some of the more usual bodies of this class, arranged under their respective basic radicals : — Sn as stannic oxide, Sn^Oj. Ag as chloride, bromide, or iodide. Fe, Cr, Al as sesquioxides. Sb as antimoniate of antimony, Sb^Oj. Pb as sulphate. Ba, Sr, Ca as fluorides and sulphates. Almost aU basic radicals as silicates. To obtain these salts in a soluble form, it is necessary to mix the dry substance with five or six times its weight of Na^ CO3 + K^ CO, ; and to fuse the mixture on a fragment of porcelain, or, better, on a piece of platinum* foil for about ten minutes. If the body is a silicate, it should be fused with hydrate of barium in a silver* crucible at a low temperature. The fusion described in the preceding paragraph may produce several results. 1°. It may produce a double decomposition, and transference of the acid-radical — Ba, S0,-|-]Sra,C03=]S"a, S0,+Ba,C03. iusol. in H, O insol. iu H^ O, and in acids. but sol. iu acids. In this case we simply treat the fused mass with cold water, washing the residual Ba^COj perfectly free from soluble salts, and then dissolving it in dilute HCl. 2°. One of the salts produced in the decomposition may be itself decomposed — 2AgCH-]Sra,C03=2NaCl+2Ag+0 + CO,. insol. in water sol. in and nitric acid. nitric acid. The fused mass is treated as in 1° ; but the residue is dissolved in dilute HNO3. 3". The body may be unchanged in composition, but rendered soluble in acids — * PrcTious to the employment of platinum or sUver ressels, the absence of reducible metals in the substance under examination must be ascertained. DETECTION OF ONE BASIC KABICAL. 395 (re,X03 + Na,C03=(FeJ,03+Na,C0,. ignited oxide, soluble in insol. in acids. acids. The mass is treated as in 1°. 4°. The body yields an aoid-radieal, and unites with the sodium or potassium present — Sn,0,+N-a,C03=]Sra, Sn^O^ + CO,. In this case the fused mass mil entirely dissolve in water ; the aqueous solution must be acidified with HCl, and H^ S passed ; in fact, the proper group-test for Sn must be applied. In the ease of the compound S>\0^ the actions 1° and 4° will occur together. As a general rule, the nature of the salt-radical in. union with the base is perfectly immaterial, the oases being quite exceptional in which it affects the action of the tests employed. 1. Many organic acid-radicals, however, such as those of tar- taric and citric acids, entirely prevent the precipitation by hydrate of ammonium of certain metals, as aluminium, chromium, and iron, from solutions in which they exist. In the cases where these acid bodies interfere (and we always have an indication of their presence by the salt blackening when its solution is evapo- rated to dryness, and the residue heated), it is better, if no vo- latile metal be present, to ignite the substance so as thoroughly to carbonize it, to redissolve by boiling in hydrochloric acid, and to filter from the carbonaceous residue. In cases (as of poison- ing) in which a volatile metal, as mercury or arsenic, is mixed with organic acids or organic matter which obstruct the occur- rence of the reactions, it is usual to destroy the organic matter by the powerful oxidizing agents, nitric acid or hydrochloric acid with chlorate of potassium, which converting the carbon into carbonic anhydride, and the hydrogen into water, break up the constitution of the organic matter. 2. Another class of saline compounds requires peciiUar treat- ment also ; it is the large class of cyanogen compounds — the cyanides, ferrocyanides, ferricyanides, and sulphocyanides. These salts, if dissolved in acids, behave frequently in so peculiar a 396 THE METHOD OF ANALYSIS. manner with reagents, as to involve the analyst in endless per- plexity. It is better to decompose them at once by hoOing them vsdth hydrate of potassium solution to vchich a little carbonate of sodium has been added, in case of the presence of metals be- longiag to the second subdivision. The first solution thus ob- tained should be poured ofi' the residue, which latter should then be boiled twice or thrice with the same reagents as at first. The substance left should be washed vsdth water, and dissolved in acid. The decompositions in this process are extremely simple ; Prus- sian blue (the ferric ferrocyanide) may be taken as an instance — (Fe,),Cfy3 + 6KHO=3K,Cfy + (Fe,),03 +3H,0. 3. There is yet a third class of salts which may perplex the student, viz. such as, being insoluble in water, dissolve in acids without decomposition, and are repreeipitated in their original form when the acid is removed by neutralization. Thus, when phosphate of calcium is dissolved by hydrochloric or nitric acid, we have at least 2 saturating eqs. of acid-radical to every eq. of calcium present ; and in all such cases we cannot tell with cer- tainty with which radical the metal is combined. The salt may be simply dissolved ; or a double decomposition may have taken place, thus — • Ca, HPO, + 2HNO3 = H3 PO, + 2CaN03. At aU events, no sooner is the acid removed by neutralization, than the elements originally in combination appear as a precipi- tate of the original salt. Thus, if simple solution occurs, the reaction may be given thus — Ca, HPO, + 2HNO3 -I- 2NH, HO = Ca, HPO, + 2NH, NO, -1- 2H,0 ; in solution. repreeipitated. while, if a double decomposition is believed to take place, the equation wiU be as follows : — H3 P0,-l-2CaN03-|-2NH,H0=Ca,HP0,-l-2NH, N03-|-2H,0. repreeipitated. In the ordinary process of analysis, these salts therefore are precipitated as soon as the acid solution is rendered neutral ; and by a reference to the Tables which follow, this condition of things wiU be found to occur at the precipitation of Group III. in the BETECTION OF ONE BASIC EADICAL. 397 analytical arrangement of the metals. Consequently the preci- pitate which should contain only the hydrates of iron, chromium, and aluminium, may include all the insoluble salts of the kind just described which may be present in the solution. In the Tables for Group III., the influence which they exert, and the mode of deaUng with them, will be found described. Thxts we have endeavoured to point out the various means at our disposal for effecting the solution of a salt previous to its analysis ; we now proceed to the plan of analysis. GENBEAL TABLE SHOWDSra THE APPLICATION OF aEOUP- TESTS. To the solution add dilute HCl in excess, and warm gently. A preci- pitate in- dicates the presence of Pb, Examine by Table for Group I. If no precipitate occurs, pass excess of H^S through the solution, and warm gently. A preci- pitate in- dicates the presence of Hg,Sn, Pb, Sb, Bi, As, Cu, Pt, Cd,Au, Pd. Examine by Table for Q-KODP II. If no precipitate occurs, boil the solution to expel H^S, add a- little HNOj to peroxidize the Fe, boil again, evaporate to perfect dryness, ig- nite, redissolve in HCl ; then add some quantity of NH^Cl solution, and lastly excess of NH^HO. A preci- pitate in- dicates the presence of TJr, Al, Fe, Cr. Examine by Table for Q-EOUP III. If no precipitate occurs, (NH4)2S in small quantity. add A preci- pitate in- dicates the presence of Zn, m, Co, Mn. Examine by Table for G-EOUP III. a. If no precipitate oc- curs, boil off the (NHJ^S, filter if necessary from precipitate of S, add NH^Cl and (WHJ.COj, and warm. A preci- pitate in- dicates the presence of Ba, Sr, Ca. Examine by Table for Geoup IV. If no pre- cipitate occurs, the solution may contain NH„ Mg, K, Na. Examine by Table for Geoup V. 398 THE METHOD OP ANALYSIS. The student having now ascertained to which group the basic radical of the simple salt under examination belongs, must pro- ceed to discover which member of the group is present. The groups above given are almost identical with the subdivisions of the basic radicals described in Part I., the chief differences being the reversion of their order, and the division of the hydrosulphurie acid (Subdivision IV.) and sulphide of ammonium (Subdivision III.) groups respectively into two. The reason for reversing the order is obvious — it being far easier to separate at first those bodies which form the larger number of insoluble compounds, whilst, in the study of the reactions, it is simpler to begin vsdth those bodies which yield the smallest number of insoluble salts. The student may now proceed to examine the precipitates be- longing to the various groups, somewhat according to the fol- lowing Tables, in each case referring to the reactions given in Chapter VI. for confirmatory tests. TABLE FOR aROUP I. The precipitate produced by hydrochloric acid may contain PbCl, AgCl, or HgjCl. Collect on a filter, transfer the precipitate to a large test-tube, and heat with much water: if it entirely dissolves, the solution will contain PbCl. The presence of lead must be confirmed by the addi- tion of H,SO.j ; a white precipitate of PbjSO., indicates Pb. If a residue is left (it may be either AgCl or Hg^Cl), collect on a filter, remove to a test-tube, add IfHjHO and warm : if the residue dissolves entirely. the solution will contain AgCl. The presence of silver must be confirmed by the addi- tion of slight excess of HNO3 ; an insoluble white precipitate indicates Ag. If a black residue is left, it will consist of (Hg,),0. The presence of mercury must be confirmed by collecting the precipitate, drying it at 100° C, and mixing it with Na^COj and heating in a bulb-tube (see p. 169) ; a sublimate of grey globules indicates Hg. ANALYSIS OP GKOTJP II. 399 TABLE FOR GKOTJP II. The precipitate produced by hydrosulphuric acid may be Hg^S, BijS,, Pb,S, CilS, Cd,S, Pd.,S, Sn.,S, Sn^S,, Sb^S,, Sb^Sj, As.,S.„ As^Sj *PtjS„, *Au2S3, or S (if a ferric salt or ohromate were present). Collect on a filter, transfer to »• test-tube, and boil with (NH4)2S for five minutes : if a residue remains, it indicates — if brown or black, the presence of Hg.,S, Pb,S, BijSj, Cu,S, or Pd,S ; if yellow, of Cd^S (presence of Cd.)- Wash the brown or black pre- cipitate free from HCl, and boil in HNO,. A residue will be a trace of Pb,S, or will consist of HgS. Confirm (p. 169) the presence of Hg- If the precipitate entirely dissolTes, add excess of NH^HO. A preci- pitate formed and not redissolTed, will indicate Bi. If the so- lution is blue, it indicates the pre- sence of Cu; if colour- less, it contains PdCl. Add HjS : a brown precipitate indicates Pd. If the precipitate entirely dissolTes, Sn, Sb, or As must be sought for. Add slight excess of HCl and some H„S water ; collect the precipitated sulphide on a filter, wash, and dry it at 100° C Mix the dried precipitate with KlifOg and NajCO,, and fuse in a crucible. Digest the fused mass with cold water, neutralize exactly with HNO,: complete solution of the mass indicates the pre- sence of K2HASO4. Confirm by adding AgNO,: a preci- pitate of Ags^sO^ indicates As. If a residue and preci- pitate exist, collect and wash both, dry, mix with KCy, and fuse in a por- celain crucible. Wash the metallic globules or powder, boil them with HNO3, wash the white residue with water, and then digest it in HjT so- lution : if entirely dis- solTed, it indicates the presence ofHSbOj. AddH^Sian orange pre- cipitate indicates Sb. If a residue exists, it consists of Sn. * A separate examination must be made for platinum and gold, according to the plan given on page 245. 400 THE METHOD OP ANAXTSI3. TABLE rOR GROUP III. The precipitate produced by hydrate of ammomum may be TJrjHjOg, Pe^jOj, CrtH303, or MM^O, ; it may also be a phosphate or fluoride of Ba, Sr, Ca, or Mg, or a phosphate of IJr, Fe, Or, or Al. The oxalates wOl have been destroyed by ignition ; and the borates do not occur. It will be sufficient to ascertain the presence of the phosphoric radical by dissolving a small portion of the precipitate in the least possible quantity of dilute HNO,, in a watch-glass, adding a trace of NH^HO, to neutralize as far as possible the excess of IINO3 without reprecipitating the salt dissolved, and then introducing a few drops of AgNOg : the presence of II3PO4 is ascertained by the immediate precipitate of the yellow AgjPOj. The mass of the precipitate is then treated with sesquicarbonate of am- monium in the cold ; complete solution indicates the presence of TJr2H303. Eva- porate to dryness ,■ dissolve the yellow residue in HA, and add KjCfy : a brownish red precipitate or colour indicates XJr. If a residue is left, it is to be examined for Ee, Cr, or Al. Boil for five minutes with HjO, to separate Ba, Sr, and Ca as oxalates ; filter, aUow to cool, and add excess of KHO. A red or buff preci- pitate consists of EejHjOg orPe^PO^. Confirm the presence of iron by dissolving the precipitate in HA, and addmg K^Cfy ; a blue precipitate indi- cates Pe. Perfect solution indicates the presence of the chromic or aluminic hydrate or phosphate. Boil the solution. A green precipitate wiU be (Cr,),0 Confirm by fusion with borax: a grass- green bead indicates Cr. If no precipitate occurs, the solu- tion win contain AL,H303. Add NHjCl: a white precipitates indicates Al. ANALYSIS OF GKOtJPS III. a. IT. 401 TABLE FOB aEOUP III, «. The precipitate produced by sulphide of ammouium may be Zn„S, Mn,S, Ni,S, or Co,S. DissolTe it in concentrated HCl, adding one or two drops of concen- trated HWO3 when boiling. To the solution add excess of KHO. Perfect solution indicates the presence ofZn,S: add H^S to the solution, a white pre- cipitate of Zn,S indicates Zn. A precipitate of a flesh colour consists of Mn^S ; a black precipitate, of Ni^S or Co^S. _ Dissolve in concentrated HCl, add excess of KA, and pass HjS gas : the non-formation of a precipitate indicates the presence of Mn.S. Confirm by the addition of NHjHO, which will form'NHjHS, and give a flesh- coloured or buff precipitate of Mn^S, indicating ]y[ii. The occurrence of a precipitate proves the existence of Ni^S, or Co^S. Dissolve in concentrated HCl; add one drop of concentrated HNO3 when boiling, then KCy in excess. BoU the solution, and acidify with dilute HCl : a precipitate indicates the presence of nickel, which must be confirmed by fusion with borax : a red-brown bead indicates Ni. The absence of a pre- cipitate indicates cobalt, the presence of which must be confirmed by eva- porating the solution to dryness, and fusing a portion of the residue with borax : a blue bead indicates Co. TABLE FOR GROIJP IV. The precipitate produced by carbonate of ammonium, in the presence of NH^HO and NH^Cl, may be Ba^CO,, Sr^SO,, or Ca^COj. Dissolve in the smallest quantity of dilute "HCl, add KCrO^ in solution : the formation of a precipitate, after the lapse of a few minutes, indicates the presence of Ba. The absence of any precipitate indicates the presence of strontium or calcium. Divide the solution into two parts, dilute it with a small quantity of water. Add a saturated solution of Ca^SOj : a precipitate, after standing fifteen minutes, indicates Sr. If no precipitate occurs in 1. 'after fifteen minutes standing, add to 2. (NHJ2O: a white precipitate indicates Ca. 402 THE METHOD OP AITALYSIS. TABLE FOE GEOTJP V. If the variouB group-tests haTe produced no precipitate in the solution under examination, either NH^, Mg, K, or Na is present. Of these basic radicals, NH^ will have been already detected in the preliminary examina- tion (p. 391). DiTide the solution into two portions, one being thrice the bulk of the other. To the smaller portion add Na^HPO, and NH^^HO, agitate well, and allow to stand some time: a white orystalUne precipi- tate indicates Mg. 2. Evaporate the larger portion to dryness, ignite and test a small por- tion of the residue before the blow- pipe : a yellow colour imparted to the flame indicates Na. The remainder of the residue is to be dissolved in water, and then HCl and HPtClj added : a yellow crystal- line precipitate indicates Having now considered the method of detecting the basic radical in a simple salt, we proceed to give the details of — SeotiojST II. — The examination fo-r the acid constituent. The student must have already perceived that, although coin- pound basic radicals are extremely rare, the compound acid- radicals which occur in the course of analysis are very numei'ous. The latter bodies, though easily detected if they yield character- istic products of decomposition, are, however, in many cases re- cognized with great difficulty, particularly when of very great complexity. The recognition of the basic radicals by means of the blowpipe is comparatively easy, because in the majority of oases the acid-radical of the salt is expelled, or its basic consti- tuent is left in combination with oxygen only as an oxide, the characters of which are easily recognized ; but when we wish to detect the acid-radical present by the same means, the ready decomposability of the latter forms an insuperable obstacle. We have, however, at our disposal a method of Preliminary Examination which is of the greatest service in enabling us to form an idea concerning the nature of the acid-radical present,, and occasionally, indeed, affording us decisive proof of its exist- EXAMUfATION FOll THE ACID CONSIITTJENT. 403 enoe. One of the reactions thus employed consists in the de- composing influence which concentrated sulphuric acid exerts upon almost all saline combinations. The sulphuric radical unites with the basic constituent of the salt to form a sulphate, while the acid-radical in the substance either unites with the hydrogen to form a new acid which is liberated, or else splits up into characteristic products of decomposition. Whichever result takes place, its occurrence generally affords sufficient evidence of the nature of the acid constituent originally present. In addition to the experiment with concentrated sulphuric acid, decisive information concerning the nature of the acid- radical present in the substance under examination may often be obtained by gently warming the substance, or its solution, with dilute hydrochloric acid. AU concentrated acids, particularly concentrated nitric and hydrochloric, when heated, themselves evolve pungent vapours, which mask the otherwise characteristic odour of the newly liberated acid. In observing the action of sulphuric or hydrochloric acid upon a salt, it must be borne in mind that the nature of the basic radical present greatly influences the reaction. Thus the salts containing basic radicals of the first and second subdivisions united with weak acid-radicals, or with acid-radicals the hydro- gen salts of which are gaseous at ordinary temperatures, are much more readily decomposed by strong acids than are the salts of other subdivisions. To take an example of this difierenoe in the behaviour of salts. NaCl or BaCl is instantly decomposed by the addition of 'H.^ SO4, the HCl escaping with effervescence, — while AgCl is not acted upon. K^ S or Ca^ S is decom- posed in a similarly rapid manner by HCl even when dilute, while Fe^ S is but slowly acted upon, and Pbj S remains wholly intact. The varying solubility of the different compounds doubtless here influences the play of affinities. Carbonates and sulphites, the acids of which split, as soon as liberated, iato water and carbonic and sulphurous anhydrides, are decom- posed, perhaps without exception, even by weak acids, whatever may be the solubility of the individual salt operated on ; but here it is obvious that the decidedly gaseous character of the chief product of the action must exert a powerful influence in determining the decomposition. 404 THE METHOD OE ANALYSIS. Preliminary examination for the detection of the acid-radical. EXPERIMENT. OBSERVATION. INFERENCE. Heat the substance in a 1 Odour of burning sulphur 1 Presence of a sulphide, or tube open at both ends, and held obliquely (fig. 13). at A. free S. 2 Drops of liquid, neutral 2 Presence of a hydrate, or Fig. 13. A to test-paper, condense about B. water of crystallization. yOv 3 The substance carbon- 3 Presence of MgT. /^^^ izes, with odour of burnt ^/s^' sugar. J^T 4 The substance carbon- 4 Presence of M2U. izes, with odour of burnt ^^W B feathers. V^^^ 5 Substance changes co- 5 Probable presence of ox- /TiB!!— ^**^^P^ lour, regaining its first ides or chromates. k£^^^^^^ tint on cooling. ^^ 6 Yellow sublimate at B. 6 Presence of a volatile or other sulphide, or of free S. jl^^^. 7 Red sublimate at B. 7 Presence of Hgg S. J^^^^^^^^ft 8 Evolution of red fumes. 8 Presence of certain ni- ^^^^S^^ trates. Add to the solid salt, or its 1 Effervescence in the cold. 1. Presence of MCyO, aqueous solution, in a test- tube, dilute HCl, or dilute H2SO4. gases of characteristic Mg CO3, Ma SO3, or sul- odours being evolved. phides and cyanides of Subdivisions I. and II. 2. Occurrence of peculiar odour, without efferves- cence. 2. Presence of MA, certain cyanides, sulphides, se- lenides, and sulphites. Add to the solid salt, or its aqueous solution, in a test-tube, concentr. H2SO4 j 1. a. No blackening occurs. Crystals separate. 1. Presence of MB0O2, MBz, boil for some minutes. or MgS. 2. The liquid effervesces, pungent gases being 2. Presence of MA, MNO3, MNO2, M2CO3, M2SO3, MCyO, and frequently evolved. MCI, MBr, MI, MF, MCy, M2S, or MaSe. 3. Evolution of COj and CO. 3. Presence of MgCjO^. Presence of MClO, or 4. Evolution of CI. 4. MCIO3. 5. Evolution of CI, together with pecuhar crackling explosion. 5. Presence of MCIO3. 6. Evolution of 0. 6. Presence of MCrOg. 7. Evolution of gas which etches glass- 7. Presence of MF. 8. 1. Evolution of red vapours. ^. The substance blackens. Evolution of violet va- pours. 8. 1. Presence of MBr, or MNO3. Presence of MI. 2. Evolution of CO, with odour of burnt sugar. 2. Presence of tartrates or citrates. 3. No evolution of CO or peculiar odour. 3. Presence • of gallatea or tannates. Many acid-radicals being by no means distinctly recognized by analysis in tbe wet way, it will be weU for tbe student to foUow SPECIAL TESTS. 405 up the evidence lie has elicited by the foregoing prelimuiary examination, by testing specially for various acid-radicals before undertaking the actual analysis. SPECIAL TESTS. Any suspicion of the presence of Chlorine may be followed by direct testing (with H^ SO^ and Mn^OJ of the origiaal substance (see p. 255) ; of Bromine, by the starch test (see p. 259); Iodine, by the starch test (see p. 263) ; Fluorine, by the etching test (see p. 265) ; the Hypochlorous radical, by the lead test (see p. 268) ; the Chloric radical, by the action of concentrated Hj 80^ (see p. 269) ; Sulphur, by its odoui-, blue flame, and coloured salts ; Selenium, by its horse-radish odour (see p. 286) ; Sulphocyanogen, by ebullition with HNO3 (see p. 343) ; the Sulphurous radical, by the odour and action on H^ S, of SO^ the product of its decomposition (see p. 293) ; the Carbonic radical, by the action on BaHO solution of COj, the product of its de- composition; Cyanogen, by passing the vaporized acid, which bums with a blue flame, into a test-tube containing a drop of KHO solution, dividing the solution of KCy thus obtained into two parts, and applying to one the Prussian- blue, and to the other the sulphocyanide test (see p. 342); the Acetic radical, by the acetic-ether test (see p. 350) ; the Nitric radical, by mixing with a fresh portion of the strong solution of the substance an equal bulk of concentrated H^ SO,,, cooling the mixture, and then dropping in a crystal of FeSO^ — on standing qtdetly for some seconds, a brovra. halo will appear. "We may remind the student that every result obtained in the above preliminary examination should be as carefully recorded as those observed in the examination for basic radicals. It is, in- deed, more necessary to do this in the jjresent case, since the detection and distinction of acid-radicals is more dependent on the preliminary analysis and the special testings consequent thereon, than is the recognition of the basic radicals, previously treated of. 406 THE METHOD OF ANALYSIS. ACTUAL ANALYSIS FOE THE DETECTION OP ONE ACID-EADICAL. Attention to several points connected with this branch of the analysis of a salt is necessary to ensure success ; and — • 1. With regard to the solution of the substance under exami- nation. If it dissolve in vfater, one great source of difficulty is evaded ; but if not, it becomes a question in what acid it shaU be dissolved. To the use of HCl is presented a great objection — that it produces a dense precipitate with AgNO^, which is one of the principal reagents employed in the detection of acid-radicals. To the adoption, on the other hand, of HNO3 as the solvent for salts insoluble in water, a scarcely diminished objection exists ; for with many complex acids, if employed in sufficient strength to dissolve the salt, it oxidizes, and thus completely changes, the acid-radical. H^ SO^ too is rejected, because, if concentrated, it acts powerfully as an oxidizer, and even when dilute it produces precipitates nith BaCl and CaCl, two reagents frequently em- ployed Lq this course of analysis. Other acids, such as HP, HA, HjO, &c., are either too energetic, too weak, or too rare to be employed ; or else they form insoluble salts with the reagents used ; or, lastly, by their often complex constitution or ready deeomposabihty they increase the difficulties of the analysis. Thus somethiag may be urged against the use of each solvent acid ; and the student must bear in mind the evils and advantages which attach to each, and use his judgment in all cases, by em- ploying that solvent to which the fewest objections are attached. It is well that he should early learn that no strict rule can be laid down for his guidance in chemical analysis, and that this science demands of its practiser not only his whole manual skiU, but also his best mental faculties. On the whole, the best acid solvent for general use is dilute HNO3 ; in this form the acid does does not oxidize very rapidly, and has the immense advantage over most others, of not forming any insoluble salts. The salts of organic acid-radicals should not be boiled, but only heated gently with this acid. In addition to dilute HXO3, HCl. con- DETECTION OP ONE ACID-EADICAL. 407 centrated HNO3, and HA are advantageously employed in many special instances. 2. It will be seen presently that the method already adverted to in the detection of basic radicals may be employed for the recognition of the aeid-radical also, in the analysis of salts in- soluble in water. We allude to the mode mentioned (p. 395, § 2.) in which the decomposition is effected, and a soluble salt of the acid-radical thus obtained, by boiling the insoluble salt with a solution of NaHO or KHO. This method is frequently applicable where the attempt to make an acid solution would fail, and is especially used in the examination of cyanides, ferrocyanides, &c. The solid salt boiled with a concentrated solution of KHO, to which a little Na^CO^ has been added in order to precipitate any metal of Subdivision II. present as a carbonate, gives the following result : — mCy+KHO=KCy+NiHO ; an insol. a sol. ppt. cyanide. cyanide. 2CaKC!fy+Na2 CO, =K, Cfy+Na^Cfy + Ca^ CO3. an insoluble * soluble ferrocyanides. precipitate, ferrocyanide. This mode of decomposition may be very advantageously em- joloyed in the case of salts containing a complex acid-radical liable to decomposition if treated with HNO3. It is better to boil such salts with Na^COg, and not with the more powerful KHO. NaCOj, too, is an agent which almost invariably pro- duces an insoluble precipitate : for nearly aU carbonates are in- soluble in neutral solutions ; and in most other cases where an insoluble carbonate is not produced, an equally insoluble hydrate is the result, thus — Mn,C,Oj+Na,C03=Na2C,0,+]Mn2C03. an insoluble a soluble precipitate, oxalate . oxalate . 2Ba3 C3 Hj O^+SNa^ CO3 =2Na3 C^ H,- O^+SBa^ CO3. an insoluble citrate. a soluble citrate, precipitate. By such means we obtain a soluble in the place of an iiisoluhle salt of the acid- radical we wish to detect : nor is this the only object attained; we have an alkaline salt, i.e. a salt containing 408 THE METHOD OF AJTALTSIS. a metal belonging to the first subdivision. And this fact brings us to the consideration of a point of great consequence, viz. — THE ABSENCE OF ALL BASIC EABICALS EXCEPT POTASSIUM AND SODIUM. It has been already stated that the presence of acid-radicals often interferes most materially vnth the detection of the basic constituent of a salt ; the converse of this statement is true in even a more extended sense. The presence of metallic radicals other than potassium or sodium is found extremely inconvenient, chiefly on account of the insoluble salts which they form by union vsdth the acid-radicals of the salts added as reagents or tests. Ammonium indeed should, as a general rule, be excluded, on accoTmt of the interference which its salts {e.g. NH^Cl, NHj NO3, and [NH^]^ SO^) frequently exert by their solvent action on other saline combinations. Thus the borates and phosphates, the citrates and tartrates of barium and calcium (salts character- istic of their respective acid-radicals) are held in solution when reagents appropriate for their formation are added, if a salt of ammonium also be present in the liquid. It must, however, be stated here, that stable ammonium salts (NH^ HO and [NH^J^COj being thus excepted) do not inferfere with the action of two frequently employed reagents, viz. AgNO^ and Fe^CL,. The separation of the original basic constituent of a salt is sometimes very difficult, and in other cases very easy of accom- plishment. 1. If the salt is soluble in water, and the basic constituent belongs to Subdivision I., no such separation is needed, except in the special cases just mentioned, where the radicals of borates, phosphates, and organic salts are present, and we intend to em- ploy BaCl or CaCl as a test ; then, if ammonium be the base, it must be removed. This is accomplished by adding to the so- lution some KHO, and boiling the liquid imtil the addition of a few drops more of the alkah no longer produces an odour of NH3. 2. If the salt is soluble in water, and contains for its basic constituent a member of Subdivision II., it may be immediately DETECTION OF ACID-HADICALS. 409 converted to the requisite condition of a suitable alkaline salt by- boiling its solution with a solution of Na2C03 : 2BaBr+Na2 C03=2NaBr+Ba2 CO3. 3. If the salt contains a member of Subdivision II. as its basic radical, but is insoluble in. water though soluble in acids, the treatment with Na^COj may be employed. Care must, however, be taken to add a quantity of Na^ CO3 sufficient not only to neu- traUze the acid employed as solvent, but also to effect the decom- position of the original salt. If this precaution be not observed, the reagent will simply neutralize the solvent acid, and repreci- pitate the original salt, thus — Ba, R+2HN03 + ]Sra,C03=Ba, E+2]SraN03-|-H,C03 ; salt sol. in acid reprecipi- — v^ ' acid only, solrent. tated salt. solution. the search for the desired salt (Na^ E) in the solution will there- fore in this ease fail. But if enough NajCOj has been added, the reaction is as follows : — ■ Ba^ E-I-2HNO3 -|-2Na2 CO3 =Na2 E-l-2NaN03 -l-H, CO3 +Ba2 CO3, where the desired salt (Na^ E) is obtained. In these experiments the smallest possible quantity of acid solvent should be used. Moreover, in certain instances where Na^COj does not effect a rapid decomposition of the salt {e.g. BaCrO^, Ba^HPO^), it is weU to filter off the precipitate first formed, and to boU it with a fresh portion of ISTajCOj. 4. These observations and methods of treatment apply also generally to all salts, whatever basic radicals they contain, pro- vided that their acid constituent is not a complex organic radical containing C,H, and 0, or C,H,N, and 0. 5. But when we try to decompose salts containing the me- tallic radicals of the third and fourth subdivisions united with a complex organic constituent, we find that complete decompo- sition is not effected, that a perfect precipitation of the basic radical as carbonate is not made, but that in the filtrate the acid-radical to be detected exists in combination partly with Na, and partly with the original basic radical. Nor can this latter be removed by successive repetitions of the process; hero the T 410 TIO; METHOD OP ANALYSIS. analyst must use his judgment and the knowledge previously ac- quired. These organic radicals do not aUow of the perfect pre- cipitation of many bases belonging to the third and fourth sub- divisions by any reagents except oertaia combinations of sulphur (Hj S or JSTHj HS). Some of the sulphides thus formed are, it ■will be remembered, soluble in alkahne solutions, some in acids, while others are soluble in none of these reagents. The method of separation must therefore be adapted to the nature of the basic constituent present, which the student will have already recognized. If the sulphide of the radical be insoluble in acids, it is better to make a solution of the salt in HNOg as dilute as possible, and to pass Hj S through the acid solution till no more precipitate is formed. The sulphide should then be removed by filtration, and the residual H^ S expelled by gently warming the filtrate. The solution thus treated may then be immediately tested for acid-radicals. Should the sulphide of the radical in the salt be soluble in acids, but insoluble in alkaline solutions, Hj S is to be passed into the solution obtained by boiling the original salt with Na^COj (this plan is better, though longer, than adding NH^ HS) ; thus the removal of the small quantity of metallic radical retained in the alkaline solution is effected. Having filtered off the precipitate thus formed, the student must acidify the filtrate with dilute HNOj, to decompose the K"aHS present, and then gently warm the solution, to expel H„ S. By the means just described, or by a combination of them, acid-radicals may be separated from their original saline com- binations, and obtained in the form of an alkaUne salt, the base of which win not interfere ivith the effects produced by the re- agents employed. We now proceed to the method of testing the solution for acid-radicals — the actual analj-sis. But first it may be useful to give a list of the acids whose salts wc may expect to be pre- sent, distinguishing by smaU type those which are of rarer oc- currence. These, when they occur, are often reduced to simpler forms, or else are separated, in the preparation of the solution. They generally require for their recognition the employment of BETISCIION OF ACID-EADICAIS. 411 the special tests detailed in Chapter VII., although evidence of their existence is occasionally obtained in the preliminary exa- mination for the acid constituent (■which see) : — Subdivision I.— HGl, HBr, HI, HP ; HCIO, HCIO3, Hao,, HBrOj, HIO3, HIO.J, HPtClj, &o. Subdivision II.— H,0, H,S, H,Se, H,Te; H,S03, H,SO„ H^SeOj, H^SeO,, H.TeO^, H^TeO,; HCrO,, HWO„ HMoO,, HVO^. Subdivision III.— H3SijP„; H.COj, H,C,0„ HBoO„_HSiO, ; HCy, HCyO, HCyS, H,Cfy, H^Cfdy, HjCoey; HA, HBz, H^L, H,s; Hjf, HjCi, 'E.a, 'S.qt, H,U. Subdivision IV.— HNO„ HNO3, HjPO^, H3PO3, H3 PO^, H,As,0„ H3ASO,. Of these acid-radicals, some, as has been previously observed, can be detected in the preliminary examination, or by tests based upon the results of that examination. These are the radicals the acids of which are represented by the formulae HCIO, HCIO3; H,S, H^Se, H,S03; HCyO and HN'03. Some radicals, again, though found in analysing by the moist way, are best detected in the previous examination : the acids of these radicals are HCl, HBr, HI, HP, HCy, and HA. From the solution prepared as above directed, the original basic radical has been separated ; CO^ has also been expelled by a gentle heat applied to the liquid after it has been slightly acidified with dilute HNO3* : this expulsion of the CO^ is necessary, for its pre- sence in the liquid would falsify the results. The next step should be to exclude another class of metallic acids : they may all be removed by the passage of H^ S through the liquid ; but if this has been already done, it need not be here repeated. The H^ H gas is passed through the solution, which has been very slightly acidified with HITO3. By this means we remove the radicalsf * Unless tlie solution be very dilute, and the nitric acid very weak, HBz and Hj S may be here precipitated, while 'K.^V and H3 QtwiU certainly separate. t Chromic acid, and the other metallic acids in general, are detected and separated among the basic radicals by their behaviour with H^ S. t2 412 THE METHOD OP ANALYSIS. PtCl3, CrO„ 811,03, W0„ MoO,, VO,, As.O^, AsO, ; we also con- vert BrOj, IO3, and 10^ into the types MBr and MI ; and if cyanogen compounds be present, they mil generally be found to produce a sulphoeyanide, wkile feriicyanogen is changed to ferrocyanogen : these facts must be borne in mind when test- ing. The HjS remaining iu the liquid must now be remored by gently warmiug the solution placed in an evaporating dish. The list of radicals now existing as acids will be as follows : — Subdivision I.— HCl, HBr, HI, HF. Subdivision II.— H,SO^, H,SeO,i. Subdivision III.— H3Si2F„ H,C,0„ HBoO,, HSiO,; HCy (if not all expelled by warming the acid solution), HCsy; HjCfy, HjCfdy, HaCocy; HA (if not all expelled), HBF, and the other organic acids. Subdivision IV.— H, PO,. Wo reaUy good plan of detecting and separating the various acids has been yet devised ; and the Tables we are about to give must not be deemed in any way faiiltless. More reliance must be placed on the preliminary examination and special testings, than upon the actual analysis. To detect, then, with more or less certainty, in a single salt, the radical of any one of the above-mentioned acids, we may employ the foUowuig plan : — DETECTION OP ACID-EABICAXS. 413 Actual analysis for the detection of the acid comtitn^nt. To the solution add excess of HNO,. A precipitate indicates the presence of BoO, Sip, Bz S_ orXJ. If the plan described in tlie introductory remarks has been followed, the absence of a precipitate here might arise from the previous separation of the acid by the addi- tion of dilute HNO3. To the solution add BaNO,. A dense precipitate indicates the presence of SO, SeO,; a gelatinous precipitate indicates To the solution add slight excess of Na^COg and warm. A preci- pitate in- dicates the presence of BoO, SiO, T Ci orPO^. Examine by- Table for G-ROUP I. To the so- lution add BDNfO, and AgNO,,. A preci- pitate indi- cates the presence of CI, Br, I. Cy, Csy, Cfy, or Cfdy. Examineby Table for &K0UP II. To a fresh portion of the original solution, after careful neutral- ization with NH.HO, addFe,Cl,. A preci- pitate in- dicates the presence of Cfy Bz G orQt. A coloured : solution in- dicates the I presence of ) Csy ( A or Cfdy. , See Table for Geoup III. TABLE FOE GffiOIJP I. The precipitate may be BaF, Ba3Si,.Fg, Ba^O, Ba^T, Ba,Ci, BajPO^, BaBoOj, or BaSiO^. To the solution add dilute HCl, and then divide the liquid into two parts. I. Evaporate to dry- ness, add HCl, intro- duce a slip of turmeric- paper. A brown co- louration indicates B0O2 (or the green-alcohol flame may be obtained, see p. 329) ; .Ail insoluble residue indicates SiOo. If no results are obtained with I., boU the second portion vrith STaj CO, ; filter from the precipitate of Ba^COg, acidify with HA, and add CaCl. A preci- pitate in- dicates F or The solution may contain CaBoOj, Ca^T, Ca3a, or Ca^PO,. Divide into two parts. d (also indi- cated in the Prelim. Exam.). I. AddFe^Clj. A white precipitate indicates PO,. II. Boil the solution. A white precipitate (CagCi) indicates Solution may contain Ca^T (indicated in prelim, ex.). 414 THE METHOD OF ANAXTSIS. TABLE FOE aEOITP II. The precipitate may be AgCl, AgBr, Agl, AgCy, AgCsy, Agj Cfy, or Ag3 Cfdy. Add NH,HO, and warm. A residue may be Agl, AgCsy, or Ag iCfy. Boil it with concentrated XHO and a frag- ment of BUgar ; filter, neutralize with dilute HNO3, and divide into two parts. I. II. Test with HgCl. Test with A scarlet pre- 1-6013. cipitate of Hgl Ared colouration indicates indicates I. Csy; a blue precipitate Cfy. The solution may contain AgOl, AgBr, (traces of Agl,) AgOy, AgjCfdy. Add sUght excess of dilute HNOj ; collect the precipitate, wash, dry, and ignite it in a porcelain crucible : the Cy compounds are thus almost entirely re- duced to the metallic state. Boil the residue in dilute HNO,. A residue may be AgClor AgBr. Wash; add a fragment of zinc and a drop of dilute HjSOj ; allow to stand a quarter of an hour, filter : to the filtrate (neutralized and then concentrated) apply the starch-test. An orange colour indicates Br; the absence of colour indicates CI (to be confirmed as usual). The solution may contain AgNO^. AddHCl. A precipitate indicates the prcTious ex- istence of Cyor Cfdy. TABLE FOR GEOUP in. The precipitate may be Fe^Ofyj, which is a blue ppt. and in- Cfy. indicates Fe,B^3 Fe3G;_ FejQt blue black blue black Bz. Qt. The solution may contain Fe^Csyg, which is a soluble *>-ed salt, Csy. *broum red A- brown green Cfdy. and indicates Fei FeCfdy * These reds may be distinguished by adding HgCl ; when the colour of Fe^Csy, is discharged, and that of Fe^Ag remains. ANALYSIS OV MIXED SALTS. 415 CHAPTER III. ANALYSIS OF JIIXED SALTS. In the recognition of the various basic and acid-radicals which may he present in a mixture of salts, the plans described in the following Tables are to be adopted, with, however, such modifi- cations as the preHmiaary examinations may suggest. To the methods of preliminary examination already given (see pp. 391, 404) recourse must again be had ; indeed, the iadications which they afford are often of extreme value in the analysis of com- plicated mixtures. The methods for preparing the solution of the substance to be analysed will be the same as those already described. (See pp. 392, 408.) A few words may here be introduced concerning those combi- nations and mixtures of basic radicals vrith one another, known as alloys and amalgams. When once in solution, the manner of recognizing their constituents is identical with that adopted in the case of salts ; but nitric acid, moderately concentrated, which is usually employed as the solvent for alloys, leaves many metals unacted upon and undissolved {e.ff. platinum, gold, &c.), which require further treatment with hydrochloric or nitrohydrochloric acid. Nitric acid, moreover, partly separates tin. and antimony in the form of insoluble compounds, which must then be treated according to the plan described on p. 394. Throughout the Tables of the present and preceding chapter, the more common radicals are indicated by a conspicuous type. For the detection, &o. of the acid-radicals contained in a mixture of salts, the Tables already given may be employed (see pp. 413, 414) ; from these Tables, the rarer organic radicals, the reactions of which have been detailed in Chapter VII., are for the most part omitted, since they seldom occur together in the course of analysis, and generally require the employment of very special methods of separation. For these methods, reference must be made either to Chapter VII. or to a comprehensive treatise on Organic Chemistry. The preliminary examination of the mixture of salts having been accomplished, and its results recorded, the student vnll then proceed to the actual analysis. 416 THE irETHOB OP ANALYSIS. GENERAL TABLE FOE THE If HCl has been used for the solution of the substance, and no precipitate be assumed to be absent ; but if the substance has been dissolved in water addition as long as any precipitate is produced : when the precipitate ceases, ride of Bi or Sb, or any HSiOj, which may have been thrown down. Agitate The precipitate may contain PbCl,AgCl,orHgjCl; and also by thus acidi- fying their alkaUne so- lutions, the anhydride W,03 and the acids HSbOg H.SbjO, HBz HjS and H,U may be here precipit- ated, since they are but slightly soluble in water or acids. Examine according to Table for Group I. The filtrate is first freed from BTNOj by one or two separate Pt and the mass of the rarer aLhed metals, given in Table for Group II. If extremely acid, it suspected to contain As in the form of arsemc com- of the latter is expelled*, when a rapid stream of H^ S pitation of Pb, As, and Mo, it is well to warm the fil- time, with H^ S. A blue colour on the first passage of precipitate may be only S, due to the oxidizing action ever, a mass of S might easUy mask a small but impor- sufiered to pass unexamined. Collect and wash the The precipitate may contain Pb, S Sn, S, Hg,S SbjSj Bi^S, Sb,S5 Cu,S As;s Cd„S As,S, Pd,S Mo,S3t Sn,S Examine according to Table for Gkocp II. If the filtrate is of a previously formed, or evaporated to dryness at moistened with water and separation of HSiO, as sent, the residue should not be interfered with, a current of air : the only dered insoluble in acids ; bonaceous mass is left, well to bum the insoluble TABLE FOE THE AJSTALYSIS OF GEOUP I. The precipitates produced by the addition of HCl, and remaining undis- solved in excess of that reagent, may contain PbCl, AgCl, and Hg^ CI ; (he anhydride Wj O3 ; and the acids HSbOj, Hj Sbj 0;, HB0O2, HBz, H2S, andHjU. BoU the precipitate with several fresh portions of water, and wash it, when on the filter, with hot water. The solution may contahi PbCl, _ HB0O2, HBe and Hj S. Add dilute HjSO.,; a white precipi- tate indicates the presence ol' Pb. The acids will be found in the analysis for acid- radical. The residue may contain AgCl and Hg^ Ci ; W2O3; HSbOg, H4Sb2 07, andHgU. Warm with solution of KHO, filter and wash. The solution may contain KWO2 KSbOa K2H2Sb3 0; and KgU. The W may be detected by the blowpipe reartions ; the Sb by the H3 Sb series of experiments. The residue may contain AgCl and (Hg2)^0. Warm with solution of NH^ HO. The solution will contain AgCl. If a reprecipitation occurs on addition of HNO,, it indicatt's Ag. The residue will consist of (Hg,)„o,; the presence of wliieh may be proved by heating the dried substance with Na^ COj in a bulb-tube, and obtaming the metallic globules of Hg. ANALYTICAL TABLES. 417 EXAMINATION FOE BASIC EADICALS. either immediate or on cooling has been the result, the first gi-oup may or in HNOg or Hj SO.,, add a few drops of concentrated HCl, and repeat the add yet a few drops more of the concentrated acid, to redissolve any oxychlo- until the solution is clear, and then filter. evaporations on a water-bath with HCl ; it is then treated with NH^ 01, to and subsequently with HjO^O., to precipitate Au, according to the details should then be partially neutralized with Na^CO.,, still keeping it acid ; and if pounds, it must be saturated with SO, gas : it is then warmed imtil all excess gas is passed through it for at least half an hom\ To ensm-e the perfect preci- trate from the first H^S precipitate, and to saturate it a second, and even a third Hj S should lead the student to look for Mo. A white or very pale yellow of unexpeUed HNO3, of HCrO^, or of ferric salts upon the Hj S. Since, how- tant quantity of Sb^ S3 or As^ S^, or other bodies, no such precipitate must be precipitate completely. fine blue colour, special search for Ru should be made in the Pt precipitate Mo may be looked for again in the following group. The filtrate should be now 100° C. with HNO3 ; this process should be repeated, and the residue finally just again evaporated to perfect dryness : absolute desiccation ensures the complete Sij O3 ; it would otherwise be mistaken for Al^ H^ O3. If organic matter is pre- be more highly heated, in order that the detection of Al, Cr, Fe, Mn, &c. may It is well to bum organic bodies off entirely, by igniting the residue strongly in danger is, that by exposing sesquioxides to so high a temperature they are ren- a compromise is therefore frequently effected by heating until merely a car- whioh is boiled repeatedly with HCl, and the solution filtered. It would be residue white, to ascertain whether Sia O3 is present. To the HCl solution add some quantity of NH4 CI ; then almost neutralize with NHj HO ; place in a flask, and add (NHj)^ S until no more precipitate is produced : warm gently, allow to rest for some time in the corked flask, and filter, washing with water slightly impregnated with (NHj)^ S. The precipitate may contain Zn^ S AI2 H3 O3 Mn^S CrjH3 03 COj, S GI2 H3 O3 MphH^ O Ni^ S Zra H3 O3 QuHjO Pe' S Cea H3 O3 SchHaO V,S, YHO TliHO TaHjOj. Examine according to Table for G-eoup III. If the filtrate is brown, the presence of Ni may be inferred. First acidify with HA; warm, filter, and add the new precipitate to the one previously produced. The filtrate should be evaporated to expel excess of (NH J, S, and any precipitate of S resulting from its decomposition ascertained to be only S by its entire volatility. Solution of (NHJ^COj is then added untU the precipitation ceases ; me hquid warmed (not boiled, lest the precipitate should redissolve in the NH4CI) and filtered. The precipitate may contain Ba^COj Sr^COj Ca,C03. Examine according to Table for G-roup IV. The filtrate, containing NH4, Mg, K, and JSfa, is examined according to Table for Group V. « Certain sulphates, as those of Ba, Sr, and Ca, may be precipitated here, the SOj being pfinverted into Ho SO,. If insoluble in adds, such precipitate must be examined by fusion, t Mo is not ierfectlv precipitated unless HjS is passed into its alkaline solution, which is 418 THE METHOD OF ANALYSIS. TAELE FOR THE The filtrate from Group I. may contain all other basic Pb, Hg, Bi, Cu, Cd, Pd, Sn, Sb, As, It must be freed from HNO3 : this may be done by evaporating with slight To the HCl solution, which should be concentrated if it has been rendered too agitated, and aEowed to rest for some hours. A yellow crystalline precipitate of KPtCl; indicates Pt. The largest part of the rare metals R, Ru, Ir, and also some PdCl, would separate here in the same form. The filtrate should be mixed with a reasonable quantity of A precipitate con- sisting of yellow spangles, or of a brown yellow sponge, indicates All, Through the filtrate a current of second and even a third stream of thoroughly washed with hot water S ; the undissolved portion must be The residue may contain Hg^S, Pb,8, Bi^Sg, Cu S, Cd^S, and Pd^.S : it must be washed until quite free from CI, then boiled in concentrated HNO, vmtU all red fumes cease. The liquor is diluted with H^O, the residue allowed to settle, and dilute H^SO^ added until precipitation is complete ; it is then agitated and filtered. The residue and precipitate may contain Hg^S and PbjSO^. Divide it into two portions. Boil in HCl; add one or two drops of HNOj, and continue to boU. Drop in a bright fragment of copper foil. A silvery film on the foil indicates Hg. II. Ignite on a iragment of porcelain. A white non-volatile residue of Pb,SO.i indicates Pb. The filtrate may contain Bi, Cu, Cd, and Pd. Add some quantity of solution of KCl ; evaporate to dryness on a water-bath, adding a little ni- trohydrochloric acid towards the end of the operation. Kedissolve in a solution of E!C1, adding one drop of HCl ; filter and wash with KCl. A reddish yellow crystalline precipitate of KPdClj indicates Pd. iTo the filtrate add excess of XH^HO, A white precipitate ofBiHjOj indicates Bi. Confirm by theoxychlo-' ride test (seep. 182), The filtrate may con- tain Cu and Cd. Aci- dify with HCl, and saturate willi H^S ; fil- ter and wash the pre- cipitate with H,0 im- pregnated with H.,S. Boil the precipitate with dilute H^SO^, and filter qiiictlv. To the so- lution add excess of H,S. A yellow pre- cipitate indicates Cd. The pre- cipitate is Cu_S. Dissolve, and confirm by the NH,HO and KCfy tests for Cu. ATTALTTICAL TABLES. ANALYSIS OF GROUP II. 419 radicals ; in the present Group we separate the following : — Pt, B, Ru, Ir, 08», Au, and Mo. excess of HCl once or twice ; in so doing, any Os would escape as osmic anhydride*. dilute, a reasonable quantity of NH^Cl solution should be added, the liquid well concentrated solution of H^CjO,, and moderately heated for some hours. HjS should now be passed for a considerable time, the liquid warmed, and a H^S passed to ensure perfect precipitation. The precipitate must be collected, containing a little H^S, then boiled for a few minutes with (NII^)2S containing filtered off. The filtrate may contain Sn, As, and Sb, combined with S, in the form of acid-radicals. Keprecipitate them as sulphides by acidulating with HCl ; and, to prevent the HCl from decomposing a portion and dissolving it as chloride, pass a few bubbles of H^S through the solution. Collect and wash the precipitate ; boU it in HCl, and add, when boiUng, a very little HNO3, drop by drop, until it is dissolved. Introduce the solution into an apparatus from which H is being evolved by the action of H^SO^ upon Zn, both of these reagents having been ascertained to be free from As ; pass the evolved gases through a wash-bottle containing solution of PbA, and thence into a test-tube containing a somewhat strong solution of AgNO,, continuing the passage as long as any precipitate is produced in the AgNOj solution. When the action has ceased, a black residue will be found upon the surface of the Zn in the generator t. The black residue consists partly of Pb and other im- purities in the Zn; but it also contains the Sn and part of the Sb. It must be collected, boiled with HCl, filtered, diluted with H^O, and tested with a few drops of HgCl, when the forma- tion of a white or grey pre- cipitate indicates Sn. The solution of AgNOj is filtered, in order to collect the suspended precipitate. The filtrate may contain as Ag^ASjO, dissolved in excess of HNO3 Exactly neu- tralize with NHjHO, when a yellow precipitate indicates As. The precipitate may be Ag only, or Ag^Sb. Boil with H„T and filter. the residue will be The filtrate may contain Sb. Acidify with HNO3 and pass H^S, when an orange precipi- tate indicates Sb. * The separation of these four metals is most difficult : the process wiU be described in an Appendix to the present Table. t This process was, we believe, originated by Dr. Hofmann, and is employed by him in the Eoyal College of Chemistry. 420 THE METHOD OP ANALYSIS. TABLE FOE THE The precipitate produced by (NH4)jS in the Zn^S, Mn S, Pe-S, Co^, Ni^, U4S3 ; Cr^gOg, AUH3O3, gether with certain pKosphates of this group, and^rtain Boil the precipitate with HCl, and add a few drops of HNO3, drop by drop, excess of KTTO solution; The solution may contain Zn, Or, Al, Ta, and G. It is diyided into two portions. is acidified with H2C2O4, and infiision of galls added, when an orange colour or precipitate indicates the presence of Ta. II. is boiled for some time. A green preci- pitate indicates the presence of Cr. This may con- tain Pe, for which it must be examined. The solution may be acidified with HCl, then rendered alkaline with NH.HO, and the precipitate digested with (NHJ2CO3. The undissolved residue is AljTTjO^ , or AJ J>0^, and indicates Al. To ascertain whether the phos- phoric radical is present, dissolve the precipitate in HjT, add NH^HO in excess, then add NHjCl and MgjSO,, when the formation of a white crystalline precipitate would indicate the presence of PO,. The solution will con- tain the Cf which, if it is boiled, will be precipitated as Go H.> O3, Fe, Mn, and Y, and Dissolve in a few solution, previously The precipitate would contain the Fe as hydrate ; also Mn, Y, Ba, Sr, Ca, and Mg as carbonates. Dissolve in HCl, avoiding any excess, warm, and add (WHJ^S; filter. The filtrate will contain theBa, Sr, Ca, and Mg, and must be ex- amined ac- cording to the two succeeding Tables. The precipitate will contain the Fe, Mn, and Y. Dissolve in HCl, with the cautious addition of a few drops of HNO3 ; add excess of KA, and boil imtU aU the Fe is precipitated. The precipitate consists of Pe as basic acetate. This precipitate should be ex- amined for Cr. The solution contains the Mn and Y. Add NHjCl and excess of ]SrH,HO ; filter off any YHO which may precipitate, and add to the filtrate a few drops of Br. Allow to rest for twenty-four hours. The brown preci- pitate contains the Mn. The solution contains any dissolved Y, which may be pre- cipitated as oxalate. ANAlYTICAl TABLES. A^STALYSIS OF aEOTJP III. 421 filtrate from the H^S precipitate may contain TaHjO,, TijHjOa, G2H3O3, Zr^HjOa,, CbjH^Oj, LaHO, DiHO, ThHO, YHO, phosphates, borates, and fluorides of iBa, Sr, Ca, and Mg. to the boiling liquid ; filter from any residue of S. Add to the cooled solution filter, and wash with cold water. The precipitate may contain Mn, Fe, Co, Ni, U, Ti, Zr, Ce, La, Di, Y, and Th, together with the phosphates, borates, and fluorides. First dissolve in HCl, avoiding excess, and boil the solution for some time ; filter. A white pre- cipitate of TiaOj indicates the presence of Tl. To the filtrate, some quantity of a saturated solution of K2SO4 is added, the liquid allowed to rest for some hours, filtered, and the precipitate washed with cold saturated solution of K2SO4, The formation of a white, yellow, or red crystalline precipitate of double sul- phate would indicate the presence of Zr,Ce,La,Di,andTh. As all these rare bodies are never known to occur together, their separation is not a matter of prac- tical importance. The solution is boiled with a few drops of HWO3, slight excess of NH^HO added, and then a warm and concentrated solution of (NH4)2C03, with which the precipitate formed is digested at a moderate heat for some time. It is then filtered rapidly while hot, and the digestion with (N^j)2C0^ The preci- pitate will contain the also the phosphates, borates, and fluorides. drops of HCl, and drop into boiUng KHO mixed with a little !Na„Co,. The solution should be examined for phos- phoric, boracic, and hydrofluoric acids, by the appropriate tests. The filtrate will contain the U, Ni, and Co, and, if concentrated, will, on cooling, deposit fine lemon- yellow crystals of (U,0),C03, (NH,),C03, which may be separated. Add some NHjCl solution, and boil for some time. The precipitate will consist of (Ug 0)2 O, blowpipe for IT. Test by means of the To the filtrate add NajCOj, and boU until all odour of NH3 has ceased, then almost neutralize the S'a.COj with HCl. Add now, gradually, such a quantity of a weak solution of KCy as shall be exactly sufiicient to redissolvc the precipitate at first produced by it. Boil until HCy ceases to be evolTed ; filter, if necessary, and, when cold, add some excess of a strong solution of NaClO*. If no black precipitate or colour appears after the lapse of ten minutes, add a drop of HCl to facUitate its formation. Warm and filter. The precipitate will consist of (^12)203 Test by means of the blowjiipe for Ni. The filtrate will contaiu the Co. Eva- porate to dryness, and test by means of the blowpipe for Co. * This mode of separation was, we believe, first practised by Dr. Hofmaun. 422 THE METHOD OF ANALYSIS. TABLE FOE THE ANALYSIS OF aEOUP IV. The filtrate from the (NHJ.S precipitate freed from (NHJ^S by boil- ing and filtration, having been'mixed with (NH^)^ CO., and warmed in the presence of NH^ CI, may have yielded a precipitate consisting of the car- bonates of Ba, Sr, and Ca. The precipitate is dissolved in a few drops of HCl and divided into two portions. I. IL is mixed with some quantity of is mixed with some quantity of so- H3 Sij Fg, and evaporated to dryness. lution of Kj SOj, evaporated to dry- The mass is then treated with EHO. ness, and the mass boiled with water and filtered. A residue The filtrate is again consists of mixed with HjSijE,,, The residue To the filtrate, excess Ba^Si^Eg, and again evaporated consists of of NH4 HO is added. and indicates to dryness to ensure Ba, SO4 and and a few drops of Ba. the complete separa- Sr.SO,. (NHJ2O, when a tion of Ba. The so- white precipitate lution in EHO is re- indicates peated, the Hquid eva- Ca. porated to dryness, and the residue dis- solved in water and tested with solution of CajSO,,, when a white precipitate in- dicates Sr. TABLE EOE THE A]!fALYSIS OE GEOUP V. The filtrate from G-roup IV., or the solution in which the various group- reagents have failed to produce any precipitate, may contain NH^, Mg, K, and Na. Evaporate and ignite to expel NH^ salts, which will have been already detected in the preliminary examination ; mix the residue with mercuric oxide (Hg, O) in excess, and a drop of water ; ignite, extract with boiling water, and filter whilst hot. A residue will con- sist of MgHO, and in- dicates the presence of Mg. Evaporate the filtrate to dryness, test one por- tion of the residue before the blowpipe for Na; dissolve the remainder in dilute HCl, and add HPtCl^. A yellow crystalline precipitate of KPtClj indicates ANALYTICAL TABLES. 423 APPENDIX TO TABLE FOR THE ANALYSIS OF GROUP II., Exhibiting the general outline of the method of dealing with the metals Pd, Ir, E, Eu, and Os, which, together with some Fe and Cu, are found in platinum ore. The mineralis dissolved in a retort by means of a mixture of 5 parts of the most concentrated HCl with 1 part of fuming HNO3, and the acid which distils over as the liquid boils, collected in a receiver ; the distillate is returned and redistilled. The distillate will contain the Os as Osg O4. Saturate with solution of KHOj add EHO, and warm gently, when a fine red crystalline pre- cipitate forms, which is KOSO2. The syrupy residue in the retort is then filtered off from certain dark steel- coloured grains, which are not acted upon by the acid. The insoluble grains are called Osm-iridium, and contain Os, Ir, and Ru. These are pow- dered in a steel mortar, and fused with a mixture of equal parts of KHO and KCIO3. The mass is treated with water. The solution contains KOsO and KRuO, from which the Os may be sepa- rated by distilla- tion with nitro- hydro chloric acid. The residue consists of 1^2 0:j and grains unattacked, which must be again fused. The concentrated filtrate is mixed with about twice its bulk of EHO, and then with a warm solution of KCl until no more precipitate is formed. It should be allowed to rest for some time, filtered, and washed with weak EHO containing KCl. The yellow or red crystalline precipitate con- sists of KPtClg and KlrClg, with traces of Kg K^ CI3 and KPdClg. It is gently heated with an equal weight of NagCOgin a porcelain cru- cible until the mass becomes quite black. It is ' •< then boiled with and the residual black It is then digested water acidified with HCl powder of Pt and Ir^ O washed, with dilute nitrohydrochloric acid, in order to ex tract part of the Pt ; and this solution being pre- served, the insoluble residue of Pt {yet undissolved) and IrgO is mixed with NaCl and concentrated nitrohydrochloric acid, and evaporated to dryness. Water is then added, to dissolve the PtClg, and the solution filtered, the filter being washed with NaCl solution, and finally with NH4CI, to prevent the IrgO passing through the pores of the paper. The residue consists of Irg O3, which may be reduced to metal by heating in a current of H. The solution contains NaPtCIg and some Ir, which may be separated by a repeti- tion of the ignition with NaaCOa, &c. &c. The solution contains the R, Pd, and some It, together with the Fe and Cu. It is evaporated to dryness, the mass digested with concentrated nitrohydro- chloric acid, KCl added, and the eva- poration repeated. The mass is then washed with alcohol. The solution The residue, consisting will contain of Fes CI3 and Kg R3 CI5, CuCl. KPdCla, — — — ^-^ and KlrCL, is fused with K3Cr4 07, and the mass boiled with HoO. The residue con- The solution is tains a portion of acidified with HCl, Ir2 O3. and a piece of pure ■ ' Zn introduced. The black precipitate is washed and treated with HNO3. The solution contains the Pd. The residue consists of the R. 424 THE METHOD OF ANAtTSIS. The examination for acid-radicals is to be conducted in ac- cordance with the plans given on pp. 413, 414. Suitable mixtures for analysis may easily be made. For in- stance, at first two salts should be taken containing a common acid-radical and diflferent basic radicals belonging to different gToups ; then a mixture may be made, the basic constituents of which are four in number, two belonging to one group, and two to another. The student should then exercise himseK in effecting the more difficult and delicate methods of separation, gradually increasing the number and variety of the basic and acid-radicals to be detected. Trials should also be made with mixtures of soluble and insoluble salts, with aUoys, with salts incapable of remaining dissolved in the same solution, and with some of the substances met with in commerce or in common life, INDEX. Page Aoid elements 17 Acid-radicals, reactions and salts of 2^efseq. . . 348 207, 382 . . 369 . . 367 . 381 . . 380 234, 308 . . 351 . . 308 . . 316 . . 326 . . 256 . . 316 . . 318 . . 268 . . 253 255, 304 . . 268 . . 304 . . 356 . . 376 . . 340 osphoric . acetic . . antimonio antimony arsenic . arsenic . arsenious auric . . benzoic . bismuthic boron boracic . bromine . carbon , carbonic . chloric . chlorine . chlorochromic chlorous . chromic . citric . . common phi cyanic cyanogen ferric . . ferricyanogeu ferrooyanogen fluorine . . fluosiUcic gaUic . hydric . . hypochlorous hyponitric . hypophosphorous hyposulphuric hyposulphurous iodic . . iodine . . iridic . . . lactic . . . manganic . metantimonic metaphosphoric metastannic molybdic niobic . , 336 307 346 344 263 317 357 281 267 373 374 2 288 273 260 230, 308 352 307 207, 382 , 376 . 197 , 310 . 119 Acid-radicals {continued) niobium nitric . nitrogen nitrous osmic oxalic oxygen pelopium pelopic pentathionic perchloric perehromic periodic . permanganic phosphoric phosphorous phosphorus pyrophosphi rhodic . ruthenic . selenic . seleuious selenium silicic silicon . stannic succinic sulphantimonic sulpharsenic . sulpharsenious sulphocarbonie sulphotungstic . sulphur . sulphuric sulphurous tannic tantaUc . tantalum tartaric . telluric . tellurium teUurious tetrathionic titanic . titanium trithionic tungstic . Page . 119 . 371 . 364 . 370 . 308 . 323 . 281 . 333 . 333 . 294 . 270 . 307 . 274 . 308 . 376 . 375 366 376 . 308 . 308 . 299 . 298 . 286 . 329 . 316 197 . 353 208, 382 219, 382 217, 382 . . 334 237, 313 . 283 . 295 . 291 . 358 . 332 . 316 . 354 . 302 . 287 . 301 . 294 . 333 . 316 . 294 237, 309 426 INDEX. Page Acid, uric 359 Tanadic ... . 243,311 Acid-radicals, analytical classifi- cation of 251 general examination for . 413 preliminary examination for 404 schemes for detection of, 278, 314, 362, 384 special tests for .... 405 AiBuity 36,43 Alkalies 71 AlkaKne earths 82 Allotropy 26,28,34 Alloys, treatment of . . . .415 Almninates 109,304 Aluminium 7 Ammonia . .... 78, 365 Ammonium 78 Analysis of mixed salts . . .415 of simple salts . . . 390 method of . . 385 et seg. Anhydrides 267 et seq. Antimony .12 detection of . . . .200 Antimonyle . . ... 203 Aqueous fusion 391 Arsenic 12 detection of ... . 210 Arsenides ... ... 367 Atomic theory . . . 36 et seq. weights . 2, 37 Barium .... Baryta Basic bodies, organic . Basic elements . . Basic radicals, reactions salts of . . aluminivim . . ammonium antimony arsenic . barium bismuth cadmium calcium . cerium . chromium cobalt . copper . didymium erbium . ferric 3et and 67 et 6 58 143 seq. 108 78. 199 209 8;i 181 154 89 102 111 132 157 1(J.") 99 123 Basic radicals (continued) ferrous . glucinum gold . . hydrogen iridium . iron . . lanthanium lead . . . lithium . magnesium Page mercuric mercurous mercury molybdenum nickel . niobium osmium . palladium pelopium platinum potassium rhodium ruthenium silver sodium . strontium tantalum terbium . thorinmn tin uranium vanadium yttrium . zino . . zu'conium Basic salts Bismuth . . Borax . . . Borides . . Boron . Cadmium . Calcium . . Carbides . . . Carbon Carbonic acid gas Cerium . . CMorine Clu'omiimi Clironiyle, notes Cobalt 427 Page Combination, laws of . .36 et seq. by volume ... 37 by weight ... 37 Copper 10 Crystallization 49 purification by . 49 water of ... 55 Cyanides 336 Cyanogen ... .... 340 Decomposition, double ... 43 Diamond . . 29 Didymium 105 Distillation ... ... 50 Distilled water 63 Elective affinity 43 the resultant of many forces 43 Elements, classification of . . 1 Equivalent volumes .... 37 weights 37 Fluorides 263 Huorine 22 Eusion 394 Grlueinum 109 Gold . . 13 Graphite 29 Group reagents, use of . . . 388 Hydrates 282 Hydration, water of . . . 55, 281 Hydrogen . . 14 Insoluble substances . 392, 406 Iodides 260 Iodine ... 21 Iridiates ... . 230,308 Iridium . . . . . 227 Iron . . 8 Lanthanium . .... 104 Law of definite proportion 36 et seq. Laws of combination ... 36 Lead . 11 Lime . . .89 Lithia . . 77 Lithium . ... . . 5 Magnesium ... . 6 Manganates ... . 307 Manganese ... 8 Page Mercury 11 Method, importance of . . . 387 Molybdates 310 Molybdenum 310 Monatomic radicals .... 47 Monobasic radicals . . .46 Morphine 143 Nickel 9 Niobium 119 Nitrates 371 Nitrites 370 Nitrogen .31 Nitrohydrochlorio acid . . . 372 Nomenclature . . ... 45 Notation 38 Organic acid-radicals .... 319 Organic bases ... . 97, 143 Osmiates . . . 230,308 Osmium ... . 230 Oxalates 323 Oxides 281 Oxidizing action ... . 112 Oxygen ... .... 23 Oxy-salts 182 Palladium . ... 12 Pelopium . . .... 119 Pentathionates . . ... 294 Perchlorates ... ... 270 Perohromates 307 Periodates 274 Permanganates . . . . 308 Phosphates 376 Phosphides 366 Phosphites 375 Phosphorus .32 Platinates . ... .308 Platinum .13 Potassa .... ... 54 Potassium 4 Precipitation 49 Preliminary examination for acid-radicals 404 Preliminary examination for basic ra(£cals 391 Purple of Cassius . . . 233 Pyrophosphates . . . . 376 Qualitative analysis, method of . 385 preparing solutions for 392, 408 Quinine 144 428 INDEX. Reagents for qualitative am list of preparation of . . purification of . 49 Eeorystallizatiou Reduction .... by fusion on charcoal, Rhodium .... Ruthenium . . . definition Salts, definition of . Salt- or acid-radical, of. . Seleniates Selenides Selenites Selenium Silicates insoluble, analysis of suicides . . SUicofluorides Silicon . Silver . . . Soda . . . Sodium . . . Soluble salts . Solution . . of substances for ana- lysis . . . 392, Solvents various acids water. Stannates . Starch . . Strontium . Strychnine Sublimation Succinates . Sulphantimoniates Sulpharseniates Sulpharsenites Sulphates . . Sulphides . . Sulphites . . Sulphooarbonates Sulphotungstates "1 51 53 t seq. 49 124 394 157 223 225 39 17 298 286 299 27 329 394 316 317 30 11 56 5 49 49 406 392 392 49 197 67 6 146 49 353 208 219 217 295 283 291 3.04 237 Sulphur 25 Sulphur acids 313 Sulphuretted hydrogen . . 283 Sulphurous acid gas . . . 291 Symbols 2 Tables, analytical .... 81, 97, 150, 190, 245, 278, 314, 362, 384, 391, 397, 398, 399, 400, 401, 402, 404, 413, 414, 416, 418, 420, 422. of reactions . . . . 80, 96 148, 188, 246, 276, 313, 361, 383. Tannates ... .358 Tantalates .332 Tantalum . . .316 Tartrates . . .... 354 Telluriates 302 TeUurium 287 Terbium 99 Tests, special, for acid-radicals . 405 Tetrathionates 294 Thorinum 101 Tin 12 Titauates ... 333 Titanides ... .316 Titanium 316 Triatomie basic radicals ... 47 Tribasic acid-radicals ... 46 Trithionates ... . . 294 Tungstates . . . 237,309 XJrauates ... ... 11.8 Uranium ... ... 116 TJranyle . . 117 Urates ... . . 360 Vanadiates . . .311 Vanadium .13 Water 231 of crystallization ... 55 Ytfa-ium 99 Zinc. . . . 9 Zirconium . . . . 106 Taylor and Francis, Red Lion Court, Fleet Street. Catalogue of Books PUBLISHED BY MR. VAN VOORST. INDEX. Accentuated List of Lepidoptera . . . . p. 6 Adams & Baikie's Manual Nat. Hist. .. 11 Adams's Genera of MoUusca 5 Aikin's Arts and Manufactures 13 Anatomical RIanipulation 12 Ansted's Ancient World 9 Elementary Course of Geology .... 9 Geologist's Text-Book 9 Gold-8eeker'8 Manual 9 Scenery, Science, and Art 13 Babington's Flora of Cambridgeshire . . 7 Manual of British Bctany 7 Baptismal Fonts 13 Bate and Westwood's British Crustacea 4 Beale on Sperm Whale 3 Bell's British Quadrupeds 3 British Reptiles 4 British Stalk-eyed Crustacea 4 Bennett's Naturalist in Australasia .... 10 Bloomfield's Farmer's Boy 14 Boccius on Production of Fish 4 Bonaparte's List of Birds 3 Brightwell'a Life of Linnaeus 13 Burton's Falconry on the Indus 3 Church and Northcote's Cbem. Analysis 8 Clark's Testaceous Mollusca 5 Clermont's Quadrupeds & R. of Europe 3 Couch's Illustrations of Instinct 1 1 Cumming's Isle of Man 12 Cups and their Customs 13 Currency 15 Dallas's Elements of Entomology 5 Dawson's Geodephaga Britannica 6 Domestic Scenes in Greenland & Iceland 13 Douglas's World of Insects 6 Dowden's Walks after Wild Flowers . . 8 Drew's Practical Meteorology 10 Drummond's First Steps to Anatomy .. 11 Economy of Human Life 15 Elements of Practical Knowledge 13 England before the Norman Conquest. . 13 Entomologist's Annual 5 Fly Fishing in Salt and Fresh Water . . 4 Forbes's British Star-fishes 5 Forbes's Malacologia Monensis p. 5 and Hanley's British Mollusca . . •• 5 and Spratt's Travels in Lycia .... 12 Garner's Nat. Hist, of Staffordshire. ... V2 Gosse's Aquarium 12 Birds of Jamaica 3 British Sea-Anemones, &c 12 Canadian Naturalist 12 Handbook to Marine Aquarium . . 13 Manual of Marine Zoology 12 Naturalist's Rambles on Dev. Coast 12 Omphalos 9 Tenby 12 Gray's Bard and Elegy 14 Greg and Lettsom's British Mineralogy 9 Griffith & Henfrey's Micrographic Diet, 10 Harvey's British Marine Algae , 7 Thesaurus Capensis 7 Flora Capensis 7 Index Generam Algarum 7 Nereis Boreali- Americana 8 Sea-side Book 12 Henfrey's Botanical Diagrams 7 Elementary Course of Botany .... 7 Rudiments of Botany 7 Translation of Mohl 7 Vegetation of Europe 7 & Griffith's Micrographic Diet. , . 10 & Tulk*s Anatomical Manipulation 11 Henslow, Memoir of. . .,., 10 Hewitson's Birds' Eggs 3 Exotic Butterflies 6 Hunter's Essays, by Owen 10 Instrumenta Ecclesiastica 13 Jeffreys's British Conchology 5 Jenyns's Memoir of Henslow 10 Observations in Meteorology 10 Observations in Natural History . . 10 White's Selbomc 12 Jesse's Angler's Rambles 4 Johnston's British Zoophytes S Introduction to Conchology 5 • Terra Lindisfamensis 8 Jones's Aquarian Naturalist 10 JOHN VAN VOOEST, 1 PATEBNOSTEK EOW. BOOKS PUBLISHED BY MB. VAW^VDUBSTr 428 Eea^ Reel Bed Eho But Salt Salt oi Sele Sele Sele Sele Silii Sili. Silii SiU' SilY Sod Sod Soli Soil Jones's Animal Kingdom p. 11 Natural History of Animals 11 Knox's (A, E.) Rambles in Sussex 3 Knox (Dr.), Great Artists & Great Anat. 1 1 Latham's Descriptive Ethnology 11 — Ethnology of British Colonies 11 Ethnology of British Islands U Ethnology of Europe 1 1 Man and his Migrations 11 Varieties of Man 11 Leach's Synopsis of British MoUusca . . 5 Letters of Rusticus 12 Lettsom and Greg's British Mineralogy 9 Lowe's Faun^ et Florae Maderse 8 Manual Flora of Madeira 8 Malan's Catalogue of Eggs 3 Martin's Cat. of Privately Printed Books. 15 Melville and Strickland on the Dodo . . 3 Meyrick on Dogs 13 Micrographic Dictionary 10 Mohl on the Vegetable Cell 7 Moule's Heraldry of Fish 4 Newman's British Ferns 8 History of Insects 5 Letters of Rusticus 12 Northcote & Church's Chem. Analysis . 8 Owen's British Fossil Mammals 9 — — on Skeleton of Extinct Sloth 9 Paley'a Gothic Moldings 14 IManual of Gothic Architecture .... 14 Poor Artist 13 Prescott on Tobacco 13 Prestwich's Geological Inquiry 9 Ground beneath us 9 Samuelson'sEari;hwonn and Housefly 77. 10 Honey-Bee 1*> Sclater's Tanagers 3 Seemann's British Ferns at One View. . 7 Selby's British Forest Trees 8 Shakspeare's Seven Ages of Man 14 Sharpe's Decorated Windows 14 Shield's Hints on Moths and Butterflies 6 Siebold on True Parthenogenesis 6 Smith's British Diatomaceae 8 Sowerby's British Wild Flowers 6 Poisonous Plants 6 Spratt and Forbes' s Travels in Lycia .. 12 Stainton's Butterflies and Moths 6 History of the Tineina fl Strickland s Ornithological Synonyms. . 4 Memoirs 9 — - and Melville on the Dodo 3 Sunday Book for the Young 13 Tugwell's Sea-Anemones 5 Tulk and Henfrey's Anat. Manipulation 11 Vicar of Wakefield, Illustr. by Mulready 14 Wallich'a North-Atlantic Sea-Bed 10 Watts's Songs, Illustrated by Cope 14 Ward (Dr.) on Healthy Respiration 12 Westwood and Bate's British Crustacea 4 White's Selbome 12 Wilkinson's Weeds and Wild Flowers.. 7 Williams's Chemical Manipulation .... 8 Wollaston's Insecta Maderensia 6 on Variation of Species 11 Yarrell's British Birds 3 British Fishes 4 on the Salmon 4 Students' Class-Books. Sol Sta- sia; Str< Str Sul Sue Sul Sul Sul Sul Sul Sul Sul Sul MANUAL OF CHEMICAL QUALITATIVE ANALYSIS. By A. E. NoHTH- COTE, F.C.S., and Arthub H. Chtjech, F.C.8. Post 8vo, 10s. Bd. HANDBOOE OF CHEMICAL MANIPULATION. By C. Geeville Wil- liams. 15a. ELEMENTARY COURSE OF GEOLOGY, MINERALOGY, AND PHY- SICAL GEOGRAPHY. By Profeasor Ansted, M.A., &c. Second Edition, 12*. ELEMENTARY COURSE OF BOTANY: Structural, Phyaiologioal, and Sy- stematic. By ProfeBBor Henfbet. 12s. Gd. MANUAL OF BRITISH BOTANY. 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