Special Reactions of the more commonly occurring oxides. FIRST DIVISION: OXIDES WHICH ARE PRECIPITATED BY HYDROCHI.O. RIC ACID. Special Reactions. a. OXIDE OF SILVER (Ag O). 1. METALLIC SILVER is white, very lustrous, moderately hard,. highly malleable, ductile, rather difficultly fusible. It is scarcely oxidized by ignition in the air. Nitric acid dissolves silver readily; the metal is insoluble in dilute sulphuric acid and in hydrochloric acid. 2. OXIDE OF SILVER is a grayish-brown powder; it is not altogether insoluble in water, and dissolves readily in dilute nitric acid. It forms no hydrate. It is decomposed by heat into metallic silver and oxygen gas. The SUBOXIDE OF SILVER (Ag, O) and the BINOXIDE (Ag O) suffer the same decomposition by ignition. 3. The SALTS OF OXIDE OF SILVER are non-volatile and colorless; most of them acquire a black tint upon exposure to light. The soluble neutral salts do not alter vegetable colors, and are decomposed at a red heat. 4. Hydrosulphuric acid and sulphide of ammonium precipitate from solutions of salts of silver black SULPHIDE OF SILVER (Ag S), which is insoluble in dilute acids, alkalies, alkaline sulphides, and cyanide of potassium. Boiling nitric acid decomposes and dis solves this precipitate readily, with separation of sulphur. 5. Potassa and soda precipitate from solutions of salts of silver the oxide of this metal in the form of a LIGHT BROWN POWDER, which is insoluble in an excess of the precipitant, but dissolves readily in ammonia. 6. Ammonia, when added in very small quantity to neutral solutions of oxide of silver, throws down the oxide as a brown precipitate, which readily redissolves in an excess of ammonia. Acid solutions of silver are not precipitated. 7. Hydrochloric acid and soluble metallic chlorides produce in solutions of salts of silver a white, curdy precipitate of CHLOride OF SILVER (Ag Cl). In very dilute solutions these reagents impart at first simply a bluish-white opalescent appearance to the fluid; by long standing, however, the chloride of silver separates. By the action of light, chloride of silver is slowly decomposed, losing chlorine, and acquiring at first a violet tint, but ultimately turning black; it is insoluble in nitric acid, but dissolves readily in ammonia as ammonio-chloride of silver, from which double compound the chloride of silver is again separated by acids. Concentrated hydro chloric acid and concentrated solutions of chlorides of the alkali metals dissolve some chloride of silver, more particularly upon application of heat; but the dissolved chloride separates again upon dilution. Upon exposure to heat, chloride of silver fuses without decomposition, giving upon cooling a transparent horny mass. 8. If compounds of silver, mixed with carbonate of soda, are exposed on a charcoal support to the inner flame of the blowpipe, WHITE, BRILLIANT, DUCTILE METALLIC GLOBULES are obtained, unattended with incrustation of the charcoal; or, if the blast be intense and prolonged, with the formation of a slight dark-red sublimate. $119. b. SUBOXIDE OF MERCURY (Hg, O). 1. METALLIC MERCURY is grayish-white, lustrous, fluid at the common temperature; it solidifies at -40°, and boils at 680° Fah. It is insoluble in hydrochloric acid; in dilute cold nitric acid it dis solves to nitrate of suboxide, in more concentrated hot nitric acid to nitrate of oxide of mercury. 2. SUBOXIDE OF MERCURY is a black powder which is readily soluble in nitric acid, and is decomposed by the action of heat, the mercury volatilizing in the metallic state. It forms no hy drate. 3. The SALTS OF SUBOXIDE OF MERCURY volatilize upon ignition; most of them suffer decomposition in this process. Subchloride and subbromide of mercury volatilize unaltered. Most of the salts of suboxide of mercury are colorless. The soluble salts in the neutral state redden litmus paper. Nitrate of suboxide of mercury is decomposed by addition of much water into a pale-yellow, insoluble basic, and a soluble acid salt. 4. Hydrosulphuric acid and sulphide of ammonium produce black precipitates of SUBSULPHIDE OF MERCURY (Hg, S), which are insolu ble in dilute acids, sulphide of ammonium, and cyanide of potassium. Protosulphide of sodium in presence of some caustic soda dissolves this subsulphide to sulphide, with separation of metallic mercury. Bisulphide of sodium dissolves the subsulphide to sulphide, without separation of metallic mercury. Subsulphide of mercury is readily decomposed and dissolved by nitrohydrochloric acid, but not by boiling concentrated nitric acids. 5. Soda, potassa and ammonia produce in solutions of salts of suboxide of mercury black precipitates, which are insoluble in an excess of the precipitants. The precipitates produced by soda and potassa consist of SUBOXIDE OF MERCURY; whilst those produced by ammonia consist of a BASIC DOUBLE SALT OF SUBOXIDE OF MERCURY AND AMMONIA, e. g. (N Hạ, N O5 + 2 Hg, O). 6. Hydrochloric acid and soluble chlorides precipitate from solu. tions of salts of suboxide of mercury SUBCHLORIDE OF MERCURY (Hg: Cl) as a fine powder of dazzling whiteness. Cold hydrochloric acid and cold nitric acid fail to dissolve this precipitate; it dissolves, however, although very difficultly and slowly, upon long protracted boiling with these acids, being resolved by hydrochloric acid into chloride of mercury and metallic mercury, which separates; and converted by nitric acid into chloride of mercury and nitrate of oxide of mercury. Nitrohydrochloric acid and chlorine water dissolve the subchloride of mercury readily, converting it into chloride. Ammonia and potassa decompose the subchloride of mercury, the first gives rise to the formation of amido-subchloride of mercury, (Hg, N H2, Hg, Cl) the latter separates black suboxide from it. 7. If a drop of a neutral or slightly acid solution of suboxide of mercury is put on a clean and smooth surface of copper, and washed off after some time, the spot will afterwards, on being gently rubbed with cloth, paper, &c., appear WHITE and LUSTROUS like silver. The application of a gentle heat to the copper causes the metallic mercury precipitated on its surface to volatilize, and thus removes the apparent silvering. 8. Protochloride of tin produces in solutions of suboxide of mercury a gray precipitate of METALLIC MERCURY, which may be united into globules by boiling the metallic deposit, after decanting the fluid, with hydrochloric acid, to which a drop of protochloride of tin may be added. 9. If an intimate mixture of an anhydrous compound of mercury with anhydrous carbonate of soda is introduced into a drawn-out glass tube, and covered with a layer of carbonate of soda, and the tube is then heated before the blowpipe, the mercurial compound invariably undergoes decomposition, and metallic mercury separates, forming a coat of gray sublimate above the heated part of the tube. The minute particles of mercury may be united into larger globules by rubbing this coating with a glass rod. § 120. c. OXIDE OF LEAD (Pb O). 1. METALLIC LEAD is bluish-gray; its surface recently cut exhi bits a metallic lustre; it is soft, malleable, readily fusible, and volatile at a white heat. Fused upon charcoal before the blowpipe, it forms a coating of yellow oxide on the charcoal. Hydro hloric acid and moderately concentrated sulphuric acid act upon it but little, even with the aid of heat; but dilute nitric acid dissolves it readily, more particularly on heating. 2. OXIDE OF LEAD is a yellow or reddish-yellow powder,* which *While hot, the oxide of lead appears red. upon exposure to a red heat fuses to a vitreous mass. Hydrated oxide of lead is white. Both the oxide and its hydrate dissolve readily in nitric and acetic acids. The SUBOXIDE OF LEAD (Pb, O) is black, MINIUM or red-lead (2 Pb O, Pb O) is red, the BINOXIDE Pb O is brown. These are all converted by ignition into oxide. The binoxide is insoluble in hot nitric acid, but dissolves on addi tion of alcohol, yielding nitrate of oxide of lead. 3. The SALTS OF OXIDE OF LEAD are non-volatile; most of them are colorless; the neutral soluble salts redden litmus paper, and are decomposed at a red heat. Chloride of lead when heated with access of air, partially volatilizes and oxychloride of lead remains behind. 4. Hydrosulphuric acid and sulphide of ammonium produce in solutions of salts of lead black precipitates of SULPHIDE OF LEAD (Pb S), which are insoluble in cold dilute acids, in alkalies, alkaline sulphides, and cyanide of potassium. Sulphide of lead is decomposed by boiling nitric acid. If the acid be sufficiently dilute the whole of the lead dissolves as nitrate of lead, and sulphur separates. Fuming nitric acid oxidizes the sulphur entirely to sulphuric acid, and all the lead separates as insoluble sulphate of lead. Nitric acid of medium strength causes the separation of a portion of the lead as sulphate, while the remainder remains in the form of nitrate. In solutions of salts of lead containing an excess of a concentrated mineral acid, hydrosulphuric acid produces a precipitate only after the addition of water or after neutralization of the free acid by an alkali. If a solution of lead is precipitated by hydrosulphuric acid, in presence of a large quantity of free hydrochloric acid, a red precipitate may be formed, consisting of chlo ride and sulphide of lead, which, however, is converted by an excess of hydrosulphuric acid into black sulphide of lead. 5. Soda, potassa and ammonia throw down BASIC SALTS OF LEAD in the form of white precipitates, which are insoluble in ammonia, and difficultly soluble in soda and potassa. In solutions of acetate of lead ammonia (free from carbonate,) does not immediately produce a precipitate, owing to the formation of a soluble triacetate of lead. 6. Carbonate of soda throws down from solutions of salts of lead a white precipitate of BASIC CARBONATE OF LEAD (e. g. 6 (Pb O, C O2) + Pb O, H O), which is insoluble in an excess of the precipitant and also in cyanide of potassium. 7. Hydrochloric acid and soluble chlorides produce in concen trated solutions of salts of lead heavy, white precipitates of CHLORIDE OF LEAD (Pb Cl), which are soluble in a large amount of water, especially upon application of heat. This chloride of lead Is converted by ammonia into oxychloride of lead (Pb Cl, 3 Pb O+HO), which is also a white powder, but almost absolutely insoluble in water. In dilute nitric and hydrochloric acids, chlo ride of lead is more difficultly soluble than in water. 8. Sulphuric acid and sulphates produce in solutions of salts of lead white precipitates of SULPHATE OF LEAD (Pb O, S O), which are nearly insoluble in water and dilute acids. From dilute solutions, especially from such as contain much free acid, the sulphate of lead precipitates only after some, frequently after a long time. It is advisable under all circumstances to add a considerable excess of dilute sulphuric acid, since sulphate of lead is more insoluble in this menstruum than in water. The separation of small quantities of sulphate of lead is best effected by evaporating, after the addition of the sulphuric acid, as far as practicable on the waterbath, and then treating the residue with water. Sulphate of lead is slightly soluble in concentrated nitric acid; it dissolves with difficulty in boiling concentrated hydrochloric acid, but more readily in solution of potassa. It dissolves also pretty readily in the solutions of some of the salts of ammonia, particularly in solution of acetate of ammonia; dilute sulphuric acid precipitates it again from these solutions. 9. Chromate of potassa produces in solutions of salts of lead a yellow precipitate of CHROMATE OF LEAD (Pb O, Cr O) which is readily soluble in potassa, but difficultly so in dilute nitric acid. 10. If a mixture of a compound of lead with carbonate of soda is exposed on a charcoal support to the reducing flame of the blowpipe, soft, malleable METALLIC GLOBULES OF LEAD are readily produced, the charcoal becoming covered at the same time with a slight yellow incrustation of oxide of lead. § 121. Recapitulation and remarks.-The metallic oxides of the first division of the fifth group are most distinctly characterized in their corresponding chlorides; since the different respective deportment of these chlorides with water and ammonia affords us a simple means both of detecting them and effecting their separation from one another. For if the precipitate containing the three metallic chlorides is boiled with a somewhat large quantity of water, or boiling water is repeatedly poured over it on the filter, the chloride of lead dissolves, whilst the chloride of silver and the subchloride of mercury remain undissolved. If these two chlorides are then treated with ammonia, the subchloride of mercury is converted into a black basic salt, insoluble in an excess of the ammonia; whilst the chloride of silver dissolves readily in that agent, and precipitates from this solution again upon addition of nitric acid. When operating upon small quantities, it is advisable first to expel the greater part of the ammonia by heat. In the aqueous solution |