FIRST DIVISION.

Special Reactions.

§ 126.

a. TEROXIDE OF GOLD (Au 0).

1. METALLIC GOLD has a reddish-yellow color and a high metallic lustre it is rather soft, exceedingly malleable, difficultly fusible: it does not oxidize upon ignition in the air, and is insoluble in hydrochloric, nitric, and sulphuric acids; but it dissolves in fluids containing or evolving chlorine, e.g., in nitrohydrochloric acid. The solution contains terchloride of gold.

2. TEROXIDE OF GOLD is a blackish-brown, its HYDRATE a chestnut brown powder. Both are reduced by light and heat, and dissolve readily in hydrochloric acid, but not in dilute oxygen acids. Concentrated nitric and sulphuric acids dissolve a little teroxide of gold; water reprecipitates it from these solutions. PROTOXIDE OF GOLD (Au O) is violet-black; it is decomposed by heat into gold and

oxygen.

3. OXYGEN SALTS of gold are practically unknown. The HALOID SALTS are yellow, and their solutions continue to exhibit this color up to a high degree of dilution. The whole of them are readily decomposed by ignition. Neutral solution of terchloride of gold reddens. litmus-paper.

OF

4. Hydrosulphuric acid precipitates from neutral or acid solutions the whole of the metal, from cold solutions as TERSULPHIDE GOLD, from boiling solutions as PROTOSULPHIDE OF GOLD (Au S). The precipitates are insoluble in hydrochloric and in nitric acid, but soluble in nitrohydrochloric acid. They are insoluble in colorless sulphide of ammonium, but soluble in yellow sulphide of ammonium, and more readily still in yellow sulphide of sodium or sulphide of potassium.

5. Sulphide of ammonium precipitates brownish-black TERSULPHIDE OF GOLD, which redissolves in an excess of the precipitant only if the latter contains an excess of sulphur.

6. Ammonia produces, though only in concentrated solutions of gold, reddish-yellow precipitates of fulminating gold. The more acid the solution and the greater the excess of ammonia added, the more gold remains in solution.

7. Protochloride of tin containing an admixture of bichloride (which may be easily prepared by mixing solution of protochloride of tin with a little chlorine water), produces even in extremely dilute solutions of gold, a purple-red precipitate (or coloration at least), which sometimes inclines rather to violet or to brownish-red. This precipitate, which has received the name of PURPLE OF CASSIUS, is insoluble in hydrochloric acid. It is assumed to be a hydrated compound of binoxide of tin and protoxide of gold with protoxide and binoxide of tin (Au O, Sn 0, + Sn O, Sn 0, +4 H O).

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8. Salts of protoxide of iron reduce the terchloride of gold in its solutions, and precipitate METALLIC GOLD in form of a most minutely divided brown powder. The fluid in which the precipitate is suspended

appears of a blackish-blue color by transmitted light. The dried precipitate shows metallic lustre when pressed with the blade of a knife.

9. Nitrite of potassa produces a precipitate of metallic gold. In very dilute solutions the fluid at first only appears colored blue, but in time the whole of the gold separates.

10. Potassa or soda added in excess to terchloride of gold leaves the fluid clear, but upon addition of tannic acid metallic gold separates. Warming assists the precipitation.

11. All compounds of gold are reduced in the stick of charcoal (p. 24). By triturating the charcoal afterwards, spangles of metal will be obtained, which are insoluble in nitric acid, but readily soluble in aqua regia.

§ 127.

b. BINOXIDE OF PLATINUM (Pt O2).

1. METALLIC PLATINUM has a light steel-gray color; it is very lustrous, moderately hard, very difficultly fusible; it does not oxidize upon ignition in the air, and is insoluble in hydrochloric, nitric, and sulphuric acids. It dissolves in nitrohydrochloric acid, especially upon heating. The solution contains bichloride of platinum.

2. BINOXIDE OF PLATINUM is a blackish-brown, its HYDRATE a reddish-brown powder. Both are reduced by heat; they are both readily soluble in hydrochloric acid, and difficultly soluble in oxygen acids. The PROTOXIDE OF PLATINUM (Pt O) is black, its hydrate brown; they are both by ignition reduced to the metallic state.

3. The SALTS OF BINOXIDE OF PLATINUM are decomposed at a red heat. They are yellow. BICHLORIDE OF PLATINUM is reddish-brown, its solution reddish-yellow, which tint it retains up to a high degree of dilution. The solution reddens litmus-paper. Exposure to a very low red heat converts bichloride of platinum to protochloride (Pt Cl); application of a stronger red heat reduces it to the metallic state. Solution of bichloride of platinum containing protochloride has a deep brown color.

4. Hydrosulphuric acid throws down from acid and neutral solutions, but always only after the lapse of some time, a blackish-brown precipitate of BISULPHIDE OF PLATINUM. If the solution is heated after the addition of the hydrosulphuric acid the precipitate forms immediately. It dissolves in a great excess of alkaline sulphides, more particularly of the higher degrees of sulphuration. Bisulphide of platinum is insoluble in hydrochloric acid and in nitric acid; but it dissolves in nitrohydro

chloric acid.

5. Sulphide of ammonium produces the same precipitate; this redissolves completely, though slowly and with difficulty, in a large excess of the precipitant if the latter contains an excess of sulphur. Acids reprecipitate the bisulphide of platinum unaltered from the reddish-brown solution.

6. Chloride of potassium and chloride of ammonium (and accordingly of course also potassa and ammonia in presence of hydrochloric acid) produce in not too highly dilute solutions of bichloride of platinum yellow crystalline precipitates of POTASSIO- and AMMONIO-BICHLORIDE OF PLATINUM, which are as insoluble in acids as in water, but are dissolved by heating with solution of potassa. From dilute solutions these precipi

tates are obtained by evaporating the fluid mixed with the precipitants on the water-bath, and treating the residue with a little water or with dilute spirit of wine. Upon ignition ammonio-bichloride of platinum leaves spongy platinum behind; potassio-bichloride leaves platinum and chloride of potassium. The decomposition of the latter compound is complete only if the ignition is effected in a current of hydrogen gas or with addition of some oxalic acid.

7. Protochloride of tin imparts to solutions containing much free hydrochloric acid an intensely dark brownish-red color, owing to a reduction of the bichloride of platinum to protochloride. But the reagent produces no precipitate in such solutions.

8. Sulphate of protoxide of iron does not precipitate solution of bichloride of platinum, except upon very long continued boiling, in which case the platinum ultimately suffers reduction.

9. On igniting a compound of platinum mixed with carbonate of soda on the loop of a platinum wire in the upper oxidizing flame, a gray spongy mass is obtained, which on trituration in an agate mortar yields silvery spangles, insoluble in hydrochloric and nitric acid, but soluble in aqua regia.

§ 128.

Recapitulation and remarks.-The reactions of gold and platinum enable us, at least partially, to detect those two metals in the presence of many other oxides, and more particularly where platinum and gold are present in the same solution. In the latter case the solution is most conveniently evaporated to dryness at a gentle heat with chloride of ammonium, and the residue treated with dilute spirit of wine, in order to obtain the gold in solution and the platinum in the residue. The precipitate will thus give platinum by ignition, and the gold may be precipitated from the solution by sulphate of protoxide of iron, after removing the spirit of wine by evaporation.

SECOND DIVISION.

Special Reactions.

§ 129.

a. PROTOXIDE OF TIN (Sn O).

1. TIN has a light grayish-white color and a high metallic lustre; it is soft and malleable; when bent it produces a crackling sound. Heated in the air it absorbs oxygen, and is converted into grayish-white binoxide; heated on charcoal before the blowpipe it forms a white incrustation. Concentrated hydrochloric acid dissolves tin to protochloride, with evolution of hydrogen gas; nitrohydrochloric acid dissolves it, according to circumstances, to bichloride or to a mixture of proto- and bichloride. Tin dissolves with difficulty in dilute sulphuric acid; concentrated sulphuric acid converts it, with the aid of heat, into sulphate of binoxide; moderately concentrated nitric acid oxidizes it readily, particularly with the aid of heat; the white binoxide formed (hydrate of metastannic acid, Sn O,, 2 H O) does not redissolve in an excess of the acid.

2. PROTOXIDE OF TIN is a black or grayish-black powder; its hydrate is white. Protoxide of tin is reduced by fusion with cyanide of potassium. It is readily soluble in hydrochloric acid. Nitric acid. converts it into hydrate of metastannic acid, which is insoluble in an excess of the acid.

3. The SALTS OF PROTOXIDE OF TIN are colorless; they are decomposed by heat. The soluble salts, in the neutral state, redden litmuspaper. The salts of protoxide of tin rapidly absorb oxygen from the air, and are partially or entirely converted into salts of binoxide. Protochloride of tin, no matter whether in crystals or in solution, also absorbs oxygen from the air, which leads to the formation of insoluble oxy-protochloride of tin and bichloride of tin. Hence a solution of protochloride of tin becomes speedily turbid if the bottle is often opened and there is only little free acid present; and hence it is only quite recently prepared protochloride of tin which will completely dissolve in water free from air, whilst crystals of protochloride of tin that have been kept for any time will dissolve to a clear fluid only in water containing hydrochloric acid.

4. Hydrosulphuric acid throws down from neutral and acid solutions a dark brown precipitate of hydrated PROTOSULPHIDE OF TIN (Sn S). This reagent does not precipitate alkaline solutions, or at least not completely. The precipitation may be prevented by the presence of a very large quantity of free hydrochloric acid. The precipitate is insoluble, or nearly so, in protosulphide of ammonium, but dissolves readily in the higher yellow sulphide. Acids precipitate from this solution yellow bisulphide of tin, mixed with sulphur. Protosulphide of tin dissolves also in solution of soda and potassa. Acids precipitate from these solutions brown protosulphide. Boiling hydrochloric acid dissolves it, with evolution of hydrosulphuric acid; boiling nitric acid converts it into insoluble hydrate of metastannic acid.

5. Sulphide of ammonium produces the same precipitate of hydrated

PROTOSULPHIDE OF TIN.

6. Potassa, soda, ammonia, and carbonates of the alkalies produce a white bulky precipitate of HYDRATE OF PROTOXIDE OF TIN (SO, HO), which redissolves readily in an excess of potassa or soda, but is insoluble in an excess of the other precipitants. If the solution of hydrate of protoxide of tin in potassa is briskly evaporated a compound of binoxide of tin and potassa is formed, which remains in solution, whilst metallic tin precipitates; but upon evaporating slowly crystalline anhydrous protoxide of tin separates.

7. Terchloride of gold produces in solutions of protochloride of tin and in solutions of salts of protoxide of tin mixed with hydrochloric acid a precipitate which varies in color between brown, reddish-brown, and purple-red, according to the presence of more or less bichloride of tin and the state of concentration (compare § 126, 7). In very dilute solutions a more or less brown or red coloration merely is produced.

8. Solution of chloride of mercury, added in excess, to solutions of protochloride or of protoxide of tin mixed with hydrochloric acid, produces a white precipitate of SUBCHLORIDE OF MERCURY, owing to the protosalt of tin withdrawing from the chloride of mercury half of its chlorine.

9. If a fluid containing protoxide or protochloride of tin and hydrochloric acid is added to a mixture of ferricyanide of potassium and sesqui

chloride of iron a precipitate of PRUSSIAN BLUE separates immediately, owing to the reduction of the ferricyanide (Fe, Cfdy) to ferrocyanide (Fe, Cfy,). Fe, Cfy,*+2H C1+2 Sn Cl= Fe, Cfy,+H, Cfy + 2 Sn Cl ̧. This reaction is extremely delicate, but it can be held to be decisive only in cases where no other reducing agent is present.

If

10. Zinc precipitates from solutions mixed with hydrochloric acid METALLIC TIN in the form of gray lamina or of a spongy mass. the experiment is made in a platinum capsule, the latter is not colored black.

11. If compounds of protoxide of tin, mixed with carbonate of soda and some borax, or better still, with a mixture of equal parts of carbonate of soda and cyanide of potassium, are exposed on a charcoal support to the inner blowpipe flame malleable grains of METALLIC TIN are obtained. The best way of making quite sure of the real nature of these grains is to triturate them and the surrounding parts of charcoal with water in a small mortar, pressing heavily upon the mass; then to wash the charcoal off from the metallic particles. Upon strongly heating the grains of metallic tin on a charcoal support the latter becomes covered with a coating of white binoxide. The stick of charcoal (p. 24) is also admirably adapted for the reduction of tin.

12. If to a borax bead colored slightly blue by copper a trace of a compound of tin is added and the bead is heated in the lower reducing fame of the gas lamp (p. 23), it will become reddish-brown to ruby-red in consequence of the reduction of the oxide of copper to suboxide (compare§ 120, 14). A compound of tin is essential to this reaction.

§ 130.

b. BINOXIDE OF TIN (Sn 0).

1. BINOXIDE OF TIN is a powder varying in color from white to straw-yellow, and which upon heating transiently assumes a brown tint. It forms two different series of compounds with acids, bases, and water. The hydrate precipitated by alkalies from solution of bichloride of tin dissolves readily in hydrochloric acid; whilst that formed by the action of nitric acid upon tin-hydrate of metastannic acid-remains undissolved. But if it is boiled for some time with hydrochloric acid it takes up acid; if the excess of the acid is then poured off, and water added, a clear solution is obtained. The aqueous solution of the common bichloride of tin is not precipitated by concentrated hydrochloric acid, whilst that acid produces in the aqueous solution of the metastannic chloride a white precipitate of the latter compound. The solution of the common bichloride of tin is not colored yellow by addition of protochloride of tin, as is the case in a remarkable degree if the solution contains metastannic chloride (LÖWENTHAL). The dilute solutions of both chlorides of tin give upon boiling precipitates of the hydrates corresponding to the chlorides.

2. The SALTS OF BINOXIDE OF TIN are colorless. The soluble salts are decomposed at a red heat; in the neural state they redden litmus-paper. Bichloride of tin is a volatile liquid, strongly fuming in

the air.

3. Hydrosulphuric acid throws down from all acid and neutral solu2 Fe, Cfdy Fe, Cfy; for Cfdy=C12V, Fe,= 2 Cfy.

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