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.

§ 129.

b. BINOXIDE OF TIN (Sn O).

1. Binoxide of tin is a powder varying in color from white to strawyellow, and which upon heating transiently assumes a brown tint. It forms two different series of salts 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. Upon boiling this solution, hydrate of metastannic acid separates from it; whilst from a solution of bichloride, largely diluted with water, common hydrate of binoxide separates upon boiling.

2. The salts of binoxide of tin are colorless; they are decomposed at a red heat. The soluble salts of binoxide of tin, in the neutral state, 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 solutions of salts of binoxide of tin, particularly upon heating, a white flocculent precipitate, if the solution of the binoxide is in excess; a faintly yellow precipitate, if the hydrosulphuric acid is in excess. The former (the white precipitate) may safely be assumed, in the case of a solution of bichloride of tin, to consist of a mixture of bichloride and bisulphide of tin (however, it has not as yet been analysed); the latter (the yellow precipitate) consists of hydrated BISULPHIDE OF TIN (Sn S2). Alkaline solutions are not precipitated by hydrosulphuric acid. The bisulphide of tin dissolves readily in potassa, alkaline sulphides, and concentrated boiling hydrochloric acid. It dissolves with some difficulty in pure ammonia, and is altogether insoluble in carbonate of ammonia. Nitric acid converts it into insoluble binoxide of tin. It is insoluble in a heated solution of acid sulphite of potassa and sulphurous acid. Upon deflagrating bisulphide of tin with nitrate and carbonate of soda, sulphate of soda and binoxide of tin are obtained. If a solution of bisulphide of tin in potassa is boiled with teroxide of bismuth, tersulphide of bismuth and binoxide of tin are formed, which latter substance remains dissolved in the potassa solution.

4. Sulphide of ammonium produces the same precipitate of hydrated BISULPHIDE OF TIN; the precipitate redissolves readily in an excess of the precipitant. From this solution acids reprecipitate the bisulphide of tin unaltered.

5. Potassa and ammonia, carbonate of soda and carbonate of ammonia, produce in solutions of salts of binoxide of tin white precipitates which, according to the nature of the solutions, consist of hydrate of binoxide of tin, or of hydrate of metastannic acid. Both dissolve readily in an excess of potassa.

6. Sulphate of soda, nitrate of ammonia (in fact, most neutral salts), when added in excess, throw down from solutions of both modifications

of binoxide of tin, provided they are not too acid, the whole of the tin as

HYDRATED BINOXIDE or HYDRATED METASTANNIC ACID.

7. Metallic zinc precipitates from solutions of bichloride or of salts of binoxide of tin, in the absence of free acid, white, gelatinous hydrate of binoxide; but in presence of a sufficient quantity of free hydrochloric acid, METALLIC TIN, in the shape of small gray scales, or as a spongy If the operation is conducted in a platinum dish, no blackening of the latter is observed (difference between tin and antimony).

mass.

8. The compounds of the binoxide of tin manifest the same deportment before the blowpipe as those of the protoxide. Binoxide of tin is also readily reduced when fused with cyanide of potassium in a glass tube.

$ 130.

c. TEROXIDE OF ANTIMONY (Sb 01).

lustrous;

1. Metallic antimony has a bluish tin-white color and is very it is hard, brittle, readily fusible. When heated on charcoal before the blowpipe, it emits thick white fumes of teroxide of antimony, which form a coating on the charcoal; this combustion continues for some time, . even after the removal of the metal from the flame; it is the most distinctly visible if a current of air is directed with the blowpipe directly upon the sample on the charcoal. But if the sample on the support is kept steady, that the fumés may ascend straight, the metallic grain becomes surrounded with a net of brilliant crystals of teroxide of antimony. Nitric acid oxidizes antimony readily: the dilute' acid converting it almost entirely into teroxide, the more concentrated acid into antimonic acid; both are nearly insoluble in nitric acid; still in the acid fluid filtered from the precipitate there are always found traces of antimony. Hydrochloric acid, even boiling, does not attack antimony. In nitrohydrochloric acid the metal dissolves readily. The solution contains terchloride of antimony (Sb Cl), or pentachloride of antimony (Sb Cl,), according to the degree of concentration of the acid and the duration of the action.

2. According to the different modes of its preparation, teroxide of antimony occurs either in the form of white, brilliant crystalline needles, or as a grayish-white powder. It fuses at a moderate red heat; when exposed to a higher temperature, it volatilizes without decomposition. It is almost insoluble in nitric acid, but dissolves readily in hydrochloric and tartaric acids, Teroxide of antimony is easily reduced to the metallic state by fusion with cyanide of potassium.

3. Antimonic acid (Sb O.) is pale yellow; its hydrates are white. Both the acid and its hydrates redden litmus paper; they are slightly soluble in water, and insoluble in nitric acid, but dissolve pretty readily in hot concentrated hydrochloric acid: the solution contains pentachloride of antimony (Sb Cl), and turns turbid upon addition of water. Upon ignition, antimonic acid loses oxygen, and is converted into antimonate of teroxide of antimony (Sb O,, Sb O). Of the antimonates the potassa and ammonia salts alone are soluble in water: acids precipitate hydrate of antimonic acid from the solutions, chloride of sodium throws down from them antimonate of soda (§ 89, 2).

4. Part of the salts of teroxide of antimony are decomposed upon ignition; the haloid salts volatilize readily and unaltered. The soluble neutral salts of antimony redden litmus paper. When treated with

a large amount of water, they are decomposed into insoluble basic and soluble acid salts. Thus, for instance, water throws down from solutions of terchloride of antimony in hydrochloric acid, a white bulky precipitate of basic terchloride of antimony (powder of Algaroth) Sb Cl,, 5 Sb O,, which after some time becomes heavy and crystalline. Tartaric acid dissolves this precipitate readily, and therefore prevents its formation if mixed with the solution previously to the addition of the water. It is by this property that the basic terchloride of antimony is distinguished from the basic salts of bismuth formed under similar circumstances.

5. Hydrosulphuric acid precipitates from acid solutions of teroxide of antimony the whole of the metal as orange-red TERSULPHIDE OF ANTImony (Sb S.). In alkaline solutions this reagent fails to produce a precipitate or, at least, it precipitates them only imperfectly; neutral solutions also are only imperfectly thrown down by it. The tersulphide of antimony produced is readily dissolved by potassa and by alkaline sulphides, especially if the latter contain an excess of sulphur; it is but sparingly soluble in ammonia, and-if it contains no free sulphur nor pentasulphide of antimony-almost insoluble in bicarbonate of ammonia. It is insoluble in dilute acids. Concentrated boiling hydrochloric acid dissolves it, with evolution of hydrosulphuric acid gas. It is not dissolved by heating with an aqueous solution of acid sulphite of potassa and sulphurous acid. When heated in the air, it is converted into a mixture of antimonate of teroxide of antimony with tersulphide of antimony. When deflagrated with nitrate of soda, it gives sulphate and antimonate of soda. If a potassa solution of tersulphide of antimony is boiled with teroxide of bismuth, tersulphide of bismuth precipitates, and teroxide of antimony dissolved in potassa remains in the solution. On fusing tersulphide of antimony with cyanide of potassium, metallic antimony and sulphocyanide of potassium are produced. If the operation is conducted in a small tube expanded into a bulb at the lower end, or in a stream of carbonic acid gas (see § 131, 12), no sublimate of antimony is produced. But if a mixture of tersulphide of antimony with carbonate of soda or with cyanide of potassium and carbonate of soda, is heated in a glass tube in a stream of hydrogen gas (compare § 131, 4), a mirror of antimony is deposited on the inner surface of the tube, immediately behind the spot occupied by the mixture.

From a solution of antimonic acid in hydrochloric acid, sulphuretted hydrogen throws down pentasulphide of antimony (Sb S.), which dissolves readily when heated with solution of soda or ammonia, and equally so in concentrated boiling hydrochloric acid, with evolution of hydrosulphuric acid gas and separation of sulphur.

6. Sulphide of ammonium produces in solutions of teroxide of antimony an orange-red precipitate of TERSULPHIDE OF ANTIMONY, which readily redissolves in an excess of the precipitant if the latter contains an excess of sulphur. Acids throw down from this solution pentasulphide of antimony (Sb S). However, the orange color appears in that case usually of a lighter tint, owing to an admixture of free sulphur.

7. Potassa, ammonia, carbonate of potassa, and carbonate of ammonia throw down from solutions of terchloride of antimony, and also of simple salts of teroxide of antimony-but not, or at least not immediately, from solutions of tartar emetic or analogous compounds-a white, bulky precipitate of TEROXIDE OF ANTIMONY, which redissolves pretty readily in an excess of potassa, but requires the application of heat for its

re-solution in carbonate of potassa, and is alogether insoluble in

ammonia.

8. Metallic zinc precipitates from all solutions of teroxide of antimony, if they contain no free nitric acid, METALLIC ANTIMONY as a black powder. If a few drops of a solution of antimony, containing some free hydrochloric acid, are poured into a platinum dish (the inside of a platinum crucible cover), and a small piece of zinc introduced, hydrogen is evolved and antimony separates, staining the part of the platinum covered by the liquid brown or black, even in the case of very dilute solutions : these new reactions I can therefore recommend as being delicate and characteristic. Cold hydrochloric acid fails to remove the stain, which, however, may be immediately removed by warm nitric acid.

9. If a solution of teroxide of antimony in solution of potassa or soda is mixed with solution of nitrate of silver, a deep black precipitate of SUBOXIDE OF SILVER forms with the grayish-brown precipitate of oxide of silver. Upon now adding ammonia in excess, the oxide is redissolved, whilst the suboxide is left undissolved (H. Rose). The following equation will explain the formation of the suboxide of silver in this process: KO, Sb Ò ̧ + 4 Ag 0 = K 0, Sb 0, + 2 Ag, O. This exceedingly delicate reaction affords us an excellent means of detecting teroxide of antimony in presence of antimonic acid.

3

10. If a solution of teroxide of antimony is introduced into a flask in which hydrogen gas is being evolved from pure zinc and dilute sulphuric acid, the zinc oxidizes not only at the expense of the oxygen of the water, but also at the expense of that of the teroxide of antimony, and the antimony separates accordingly in the metallic state; but a portion of the metal combines in the moment of its separation with the liberated hydrogen of the water, forming ANTIMONETTED HYDROGEN GAS (Sb H ̧). If this operation is conducted in a gas-evolution flask, connected by means of a perforated cork with the limb of a bent tube of which the other limb ends in a finely drawn-out point, pinched off at the top,* and the hydrogen passing through the fine aperture of the tube is ignited after the atmospheric air is completely expelled, the flame appears of a bluishgreen tint, which is imparted to it by the antimony separating in a state of intense ignition upon the combustion of the antimonetted hydrogen; white fumes of teroxide of antimony rise from the flame, which condense readily upon cold substances, forming spots on them which are not dissolved by water. But if a cold body, a porcelain dish, for instance, is now depressed upon the flame, METALLIC ANTIMONY is deposited upon the surface of the plate, in a state of the most minute division, forming a deep black and almost lustreless spot. If the middle part of the tube through which the gas is passing is heated to redness, the bluishgreen tint of the flame decreases in intensity, and a metallic mirror of antimony of silvery lustre is formed within the tube on both sides of the heated part.

As the acids of arsenic give under the same circumstances similar spots of metallic arsenic, it is always necessary to examine the spots produced, in order to ascertain whether they really consist of antimony or contain any of that metal. With spots deposited on a porcelain dish the object in view is most readily attained by treating them with a solution of chloride of soda (a compound of hypochlorite of soda with chloride of sodium, pre

* In accurate experiments it is advisable to use Marsh's apparatus. (§ 131, 10).

pared by mixing a solution of chloride of lime with carbonate of soda in excess, and filtering); which will immediately dissolve arsenical spots, leaving the spots proceeding from antimony untouched, or, at least, removing them only after a very protracted action. A mirror within the glass tube, on the other hand, may be tested by heating it whilst the current of hydrogen gas still continues to pass through the tube if the mirror volatilizes only at a higher temperature, and the hydrogen gas then issuing from the tube does not smell of garlic; if it is only with a strong current that the ignited gas deposits spots on porcelain, and the mirror before volatilizing fuses to small lustrous globules distinctly discernible through a magnifying glass, the presence of antimony may be considered certain. Or, better still, the metals may be identified by conducting through the tube a very slow stream of dry hydrosulphuric acid gas, and heating the mirror, by means of a spirit-lamp, proceeding from the outer to the inner border, and accordingly in an opposite direction to that of the gaseous current. The antimonial mirror is by this means converted into tersulphide of antimony, which appears of a more or less reddish-yellow color, and almost black when in thick layers. If a feeble stream of dry hydrochloric acid gas is now transmitted through the glass tube, the tersulphide of antimony, if present in thin layers only, disappears immediately; if the incrustation is somewhat thicker, it takes a short time to dissipate it. The reason for this is, that the tersulphide of antimony decomposes readily with hydrochloric acid, and the terchloride of antimony formed is exceedingly volatile in a stream of hydrochloric acid gas. If the gaseous current is now conducted into some water, the presence of antimony in the latter fluid may readily be proved by means of hydrosulphuric acid. By this combination of reactions, antimony may be distinguished with positive certainty from all other metals.

11. If a mixture of a compound of antimony with carbonate of soda and cyanide of potassium is exposed on a charcoal support to the reducing flame of the blowpipe, brittle globules of METALLIC ANTIMONY are produced, which may be readily recognised by the peculiar appearances attendant upon their oxidation (compare § 130, 1).

§ 131.

d. ARSENIOUS ACID (AS 0,).

1. Metallic arsenic has a blackish-gray color and high metallic lustre, which it retains in dry air, but loses in moist air, becoming covered with suboxide; the metallic arsenic of commerce looks therefore rather dull, the planes of crystallization appearing bronze-colored and feebly shining. Arsenic is not very hard, but very brittle at a dull red heat it volatilizes without fusion. The fumes have a most characteristic odor of garlic, which proceeds from the suboxide of arsenic formed. Heated with . free access of air, arsenic burns - at an intense heat with a bluish flame-emitting white fumes of arsenious acid, which condense on cold bodies. If arsenic is heated in a glass tube sealed at the lower end, the greater part of it volatilizes unoxidized, and recondenses above the heated spot as a lustrous black sublimate (arsenical mirror); a very thin coating of the sublimate appears of a brownish-black color. In contact with air and water arsenic oxidizes slowly to arsenious acid. Weak nitric acid converts it, with the aid of heat, into arsenious acid, which dissolves only