Molybdate of *suboxide of siker (Ag.0,231o0.). Wohler forms this salt by passing hydrogen gas through an ammoniacal solution of molyb date of silver at It is a heavy brilliant black powder, in which occur regular octohedra. The tuvgstate of the suboxide is made in the same manner as, and much resembles, the molylxlate. Chromate of suboxide of silver is black and amorphous.
2. Protaride of silrer (AgO). A brown hydrated oxide of silver is thrown down when solution of potash, soda, baryta, or lime is added to solution of nitrate of silver. It becomes anhydrous when heated to 140° Fehr., and is reduced to the metallic state by increased heat, by light, hydrogen, or almost any deoxidising agent. It is a powerful base, forming salts, the chief of which are presently described.
3. Peroxide of silver occurs in dark gray acicular crystals when a solution of nitrate of silver is electrolysed. It accumulates on the positive pole, is a conductor of the electric current, but is very unstable.
Sulphide of surer. (AgS). The elements sulphur and silver have a great affinity for each other ; the compound produced by their union occurs native in largo quantities. [Sevin, in NAT. HIST. Div.] Sulphide of silver may be formed artificially by passing a stream of sulphuretted hydrogen gas through a solution containing sillier, or on adding a soluble sulphide to the silver solution, or, still more simply, by heating together sulphur and silver iu their equivalent proportions.
Sulphide of silver readily fuses and cools to a dark-gray, crystalline mama, that is somewhat soft and malleable. It is decomposed and dissolved when heated with concentrated sulphuric or nitric acids, and is also readily attacked by strong hydrochloric acid. Potash, soda, iron, copper, or lead reduce it, by the aid of heat, to the metallic state.
Chlorine and silver form two compounds, namely :— I. Subehloride of .Silrer (Ag,CI). When silver leaf is digested in solution of chloride of copper, or of perehloride of iron, black scales of subchloride of silver are produced. Nitric acid does not affect them, but ammonia resolves them into chloride of silver and metallic silver.
2. Proloaloride of Silver (AgCl), Chloride of Silver, or, Horn &her, found native. [SiLvEn, in NAT. HIST. Div.] It falls as n white, outblike precipitate when hydrochloric acid or any soluble chloride is added to an aqueous solution of silver salt.
Chloride of silver is insoluble in water or dilute acids, and is only very slightly acted on by strong nitric or hydrochloric acids. It is somewhat more soluble iu solutions of chlorides of 'alkalies or of alkaline earths, and is freely dissolved in solution of ammonia. It fuses when heated to about 500' Fahr., and on cooling forms a semi transparent horn-like mass. It is partially reduced to the state of aul?-chloride on exposure to light. A current of hydrogen removes the whole of the chlorine from heated chloride of silver ; zinc, iron, and some other metals also reduce it to the metallic state. Chloride of silver forms double salts with alkaline cyanides, sulphites, and hypo sulphites; the solutions of the last-named have a most intensely sweet taste, exceeding even that of sugar.
Bromide of Silver (AgBr) occurs native. It may be prepared artificially by precipitating nitrate of silver by bromide of potassium. It much resembles chloride of silver, but is less soluble in ammonia, and has moreover a yellow colour.
Iodide of Silver (AgI). This compound occurs native also. It falls as a yellow precipitate when an alkaline iodide is ridded to solution of nitrate of silver. It is insoluble in acids and rustily so in ammonia, but is very soluble in solution of iodide of potassium or hypoestdphite of soda.
Sulphate of Silver (A gOSO.). When silver is boiled in strong sulphuric acid, sulphate of silver is formed according to the following equation :— It is soluble in excess of the acid, but requires ninety !Arta of water to dissolve it.
Nitrate of Silrer (AgO,NO,). This salt, now so largely used in photography, and, when fused and cast into cylinders as an eacharotic, tinder the name of lunar caustic, by surgeons, is formed on dis solving silver in strong nitric acid. By evaporation of the solution, colourless, transparent right rhombic crystals are deposited. It has an unpleasant bitter metallic taste, is soluble in water or alcohol, and is not decomposed by exposure to light unless in contact with organic matter. Solution of ammonio-nitrate of silver is formed by adding ammonia to nitrate of silver until the resulting precipitate is nearly all redissolved.
The following are the principal remaining salts of silver that are of interest. They are produced by the ordinary process of double decom position.
The triphosphate (3AgO, PO.) is of yellow colour, alterable by time action of light, readily soluble in excess of nitric acid or of ammonia. The pyrophosphate is white and easily fusible.
The metaphosphate (AgO, occurs as a gelatinous mass, soluble in excess of nitrate of silver. The carbonate (AgO, is at first white, afterwards pale yellow. The borate (fig°, BOO forms white flakes which turn violet on exposure to light. The iodate (Ag0,10.) is white, and crystallises from ammonia in brilliant little rectangular prisms. The chlorate is soluble in water, and crystallises in white, opaque, four-sided prisms. The monochromate (AgO,Cr0.) is of a greenish-brown colour by reflected light and deep red by transmitted light. The bichromate is a purple-red crystalline preci pitate. The arseniate (3AgO, As0.) ls a dark brick-red precipitate, soluble in ammonia and in carbonate of ammonia.
For the salts which silver forms with organic acids, see the articles on those acids.
Testa for Silver. The production of the white curdy chloride on the addition of hydrochloric acid, the precipitate being insoluble in hot nitric acid but readily soluble in ammonia, forms the characteristic test for silver salts. Reduction on charcoal in the blow-pipe flame, a black precipitate by sulphuretted hydrogen, and a yellow one on the addition of an alkaline iodide, are confirmatory tests.
Estimation of Silver. This is accomplished as described under ASSAYING, or in the state of well-washed and fused chloride, 100 parts of which contain 75'27 of metal.