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 CI, 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: K O, Sb 0, +4 Ag 0= K O, Sb O, + 2 Ag, 0. 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 Alame 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 sparingly in an excess of the acid; strong nitric acid converts it partially into arsenic acid. It is insoluble in hydrochloric acid and dilute sulphuric acid; concentrated boiling sulphuric acid oxidizes it to arsenious acid, with evolution of sulphurous acid. 2. Arsenious acid generally presents the appearance either of a transparent vitreous or of a white porcelain-like mass. Triturated, it gives a heavy, white, gritty powder. When heated, it volatilizes in white inodorous fumes. If the operation is conducted in a glass tube, a sublimate is obtained consisting of small brilliant octahedrons and tetrahedrons. Arsenious acid is only difficultly moistened by water; it comports itself in this respect like a fatty substance. It is difficultly soluble in cold, but more readily in hot water. It is copiously dissolved by hydrochloric acid, as well as by solution of soda and potassa. Upon boiling with nitrohydrochloric acid it dissolves to arsenic acid. It is highly poisonous. 3. The arsenites are mostly decomposed upon ignition either into arsenates and metallic arsenic, which volatilizes, or into arsenious acid and the base with which it was combined. Of the arsenites those only with alkaline bases are soluble in water. The insoluble arsenites are dissolved, or at least decomposed, by hydrochloric acid. Terchloride of arsenic is a colorless, volatile liquid, fuming in the air, which allows the addition of a little water, but is decomposed by a larger amount into arsenious acid, which partly separates, and hydrochloric acid, which retains the rest of the arsenious acid in solution. 4. Hydrosulphuric acid precipitates solutions of arsenious acid aud of neutral arsenites slowly and imperfectly, except a free acid be present, in which case the precipitation is immediate and perfect. Alkaline solutions are not precipitated. The precipitates are of a bright yellow color; they consist of TERSULPHIDE OF ARSENIC (As S1), and are readily and completely dissolved by pure alkalies, alkaline carbonates and bicarbonates, and also by alkaline sulphides; but they are nearly insoluble in hydrochloric acid, even when concentrated and boiling. Boiling nitric acid decomposes and dissolves them readily. The deflagration of tersulphide of arsenic with carbonate of soda and nitrate of soda gives rise to the formation of arsenate and sulphate of soda. If a solution of tersulphide of arsenic in potassa is boiled with hydrated carbonate or basic nitrate of teroxide of bismuth, tersulphide of bismuth and arsenite of potassa are produced. If recently precipitated tersulphide of arsenic is digested with sulphurous acid and acid sulphite of potassa, the precipitate is dissolved; upon heating the solution to boiling, the fluid turns turbid, owing to the separation of sulphur, which upon continued boiling is for the greater part redissolved. The fluid contains, after expulsion of the sulphurous acid, arsenite and hyposulphite of potassa (2 As S, + 8 KO, SO2 = 2 K 0, As 0, + 6 K O, S, 0, + S ̧ + 7SO). Tersulphide of antimony and bisulphide of tin do not show this reaction, as I have already stated (§ 129, 3 and § 130, 5) (Bunsen). 3 2 2 3 If a mixture of tersulphide of arsenic with from 3 to 4 parts of carbonate of soda is made into a paste with some water, and this spread over small glass splinters, and after being well dried, rapidly heated to redness in a glass tube through which dry hydrogen gas is transmitted, a large portion of the arsenic present is reduced to the metallic state and expelled, if the temperature applied is sufficiently high. Part of the reduced arsenic forms a metallic mirror on the inner surface of the tube, the remainder is carried away suspended in the hydrogen gas; the minute particles of arsenic impart a bluish tint to the flame when the gas is kindled, and form stains of arsenic upon the surface of a porcelain dish depressed upon the flame. The fusion of the mixture of tersulphide of arsenic with carbonate of soda first gives rise to the formation of a double tersulphide of arsenic and sulphide of sodium, and of arsenite of soda (2 As S,+ 4 Na O, CO, = 3 Na S, As S, + Na O, As O, + 4 CO2). Upon heating these products the arsenite of soda is resolved into arsenic and arsenate of soda (5 As 0,= 2 As + 3 As O,), and the tersulphide of arsenic and sulphide of sodium into arsenic and pentasulphide of arsenic and sulphide of sodium (5 As O, 2 As + 3 As 0); and by the action of the hydrogen the arsenate of soda is also converted into hydrate of soda, arsenic, and water. With the exception, therefore, of that portion of the arsenic which constitutes a component part of the double pentasulphide of arsenic and sulphide of sodium formed in the process, a sulphur salt which is not decomposed by hydrogen, all the arsenic is expelled (H. Rose). 3 3 = 3 This method of reduction gives indeed very accurate results, but it does not enable us to distinguish arsenic from antimony with a sufficient degree of certainty, nor to detect the one in presence of the other. (Compare § 130, 5.) The operation is conducted in the apparatus illustrated by 6 Fig. 22. a is the evolution flask, b a tube containing chloride of calcium, c the tube in which, at the point d, the glass splinter with the mixture of tersulphide of arsenic and carbonate of soda is placed; this tube is made of difficultly fusible glass free from lead. When the apparatus is completely filled with pure hydrogen gas, d is exposed to a gentle heat at first, in order to expel all the moisture which may still be present, and then suddenly to a very intense heat,* to prevent the sublimation of undecomposed tersulphide of arsenic. The metallic mirror is deposited near the point e. Another method of effecting the reduction of tersulphide of arsenic to the metallic state, and which combines with the very highest degree of delicacy the advantage of precluding the possibility of confounding arsenic with antimony, will be found described in number 12. 5. Sulphide of ammonium also causes the formation of TERSULPHIDE In neutral and alkaline solutions, however, the tersulphide OF ARSENIC. * The flame of the blowpipe answers the purpose best. |