A Manual of Photographic Chemistry, Including the Practice of the Collodion Process

by T. Frederick Hardwich

Iodide of Silver is reduced by Metallic Zinc in the same manner as the Chloride of Silver, forming soluble Iodide of Zinc and leaving a black powder.

THE PREPARATION AND PROPERTIES OF BROMIDE OF SILVER.

This substance so closely resembles the corresponding salts containing Chlorine and Iodine, that a short notice of it will suffice.

Bromide of Silver is prepared by exposing a silvered plate to the vapour of Bromine, or by adding solution of Bromide of Potassium to Nitrate of Silver. It is an insoluble substance, slightly yellow in colour, and distinguished from Iodide of Silver by dissolving in strong Ammonia and in Chloride of Ammonium. It is freely soluble in Hyposulphite of Soda and in Cyanide of Potassium.

The properties of the element Bromine are described in Part III.

CHEMISTRY OF THE OXIDES OF SILVER.

The Protoxide of Silver (Ag O).—If a little Potash or Ammonia be added to solution of Nitrate of Silver, an olive-brown substance is formed, which, on standing, collects at the bottom of the vessel. This is Oxide of Silver, displaced from its previous state of combination with Nitric Acid by the stronger oxide. Potash. Oxide of Silver is soluble to a very minute extent in pure water, the solution possessing an alkaline reaction to Litmus; it is easily dissolved by Nitric or Acetic Acid, forming a neutral Nitrate or Acetate; also soluble in Ammonia (Ammonio-Nitrate of Silver), and in Nitrate of Ammonia, Hyposulphite of Soda, and Cyanide of Potassium. Long exposure to light converts it into a black substance, which is probably a Suboxide.

The Suboxide of Silver (Ag₂O?)—This substance was obtained by Faraday on exposing a solution of the Ammonio-Nitrate of Silver to the action of the air. It bears a relation to the ordinary brown Protoxide of Silver similar to that which the Subchloride bears to Protochloride of Silver.

Suboxide of Silver is a black or grey powder, which assumes the metallic lustre on rubbing, and when treated with dilute Acids is resolved into Protoxide of Silver which dissolves, and metallic Silver.

SECTION II.