Prop., &c. Cyanide of silver is a white powder, soluble in ammonia, and decomposed by contact with vegetable substances; light turns it violet-coloured.—Dose, 1⁄16 to 1⁄8 gr.; in syphilis, &c. It has been proposed as a source of hydrocyanic acid. (Everitt.)
Silver Hyposul′phite of. Ag2S2O3. Syn. Argenti hyposulphis, L. A white substance, insoluble in water, and very prone to decomposition. It is very soluble in the alkaline hyposulphites,
forming compounds possessing an intensely sweet taste. See Hyposulphurous Acid.
Silver, I′odide of. AgI. Syn. Argentic iodide; Argenti iodidum, L. Prep. Precipitate a solution of nitrate of silver with another of iodide of potassium; wash the precipitate with distilled water, and dry it in the shade. Pale greenish-yellow; insoluble in water and in liquor of ammonia; soluble in a solution of hyposulphite of soda. Used in some of the French hospitals in the stomach affections of scrofulous subjects: also in epilepsy.—Dose, 1⁄12 to 1 gr.
Silver, Ni′trate of. AgNO3. Syn. Argenti nitras, L. This article is found in commerce under two forms:—
1. Crystallised. Prep. By dissolving grain silver in nitric acid diluted with about twice its weight of water, evaporating the solution until it is strong enough to crystallise on cooling, and then allowing it to cool very slowly. Colourless; transparent, anhydrous rhombic prisms or tables; soluble in an equal weight of cold and in half their weight of boiling water; soluble in alcohol; fuse when heated, and at a higher temperature suffer decomposition; blackened by light, and by contact with organic substances. Its solution in distilled water is not sensibly darkened by light, in the absence of organic matter. Used for solutions, and in photography.
2. Fused (Lunar caustic; Argenti nitras—B. P., Ph. L. & E., A. n. fusum—Ph. D.). Prep. (Ph. D.) Refined silver, 3 oz.; pure nitric acid, 4 fl. oz.; distilled water, 5 fl. oz.; mix in a glass flask, and apply in a gentle heat until the metal is dissolved; transfer the solution to a porcelain capsule (or a large porcelain crucible), decanting it off a heavy black powder which appears at the bottom of the flask, and, having evaporated it to dryness, raise the heat (in a dark room) until the mass liquefies; then pour it into a brass mould (iron moulds—Ph. E. & Ph. L. 1836), furnished with cylindrical cavities of the size of a goose-quill, and which then admits of being opened by a hinge; preserve the concreted salt in well-stopped bottles, impervious to the light. The formulæ of the Ph. E. & Ph. L. 1836 are similar.
Obs. In preparing this salt care should be had that the silver is free from copper. Pure nitrate of silver may, however, be prepared from silver containing copper, by evaporating the nitric solution to dryness, and cautiously heating the mixed nitrates to fusion. A small portion of the melted mass is examined from time to time, until a little dissolved in water, and treated with ammonia in excess, ceases to strike a blue colour. When this point is arrived at, the fused nitrate is allowed to cool, when it is redissolved in water, filtered or decanted from the insoluble black oxide of copper, and evaporated in the usual way.
The heat employed in preparing the fused nitrate should not exceed 420° Fahr., and the
fusion should be effected completely, but with moderate expedition, to prevent loss of nitric acid. Formerly, a mass of well-tempered white clay, perforated by means of a well-greased goose-quill, was used instead of metal moulds. In the Ph. E. & Ph. L. 1836 the moulds are ordered to be greased; when this is done, the sticks of caustic should be wiped clean before rolling them in paper. The moulds should be gently heated before pouring the fused nitrate into them. Mr Benzoin, the celebrated Danish pharmaceutist, recommends mould formed of the massive white Bohemian talc or of English slate.