SILVER, OXIDE OF. There are three oxides of silver, viz. Suboxide 0 Protoxide . A g 0 Binoxidt A g 02 Of these the protoxide only forms salts.
Suboxide of silver is produced as a grey film when ammonio nitrate of silver is exposed to air. It is also produced when citrate of silver, (or any analogous organic salt of silver,) is exposed to the action of hydrogen at a temperature of 212°. The protoxide of silver contained in the citrate then loses one half of its oxygen, and the suboxide remains combined with one half of the acid. At least this is Wohler's theory ; but the probability is that the acid is also decomposed, and the compound not exactly a subcitrate of silver.
Dr. Graham says, " The solution in water of the suboxide salt is dark brown, and the suboxide is precipitated black from it by potass ; when the solution of the subsalt is heated it becomes colourless, and metallic silver appears in it. The salt dissolves of a brown colour in ammonia. Several other salts of silver, containing organic acids,
comport themselves in the same way as the citrate when heated in hydrogen." Protoxide of silver may be obtained by adding a dilute solution of caustic potass to a solution of nitrate of silver. It is thrown down as a dark olive coloured precipitate.
Protoxide of silver is, like oxide of lead, soluble to a slight extent in pure water, to which it communicates an alkaline reaction. The solution is reddened by exposure to light. This oxide is reduced to rit a dull red heat, and to black suboxide by the action of light. It stains glass of a yellow colour, and is used in painting on glass and enamel. Ammonia dissolves it completely, and forms a colourless solution called ammoniacal oxide of silver.
The peroxide of silver is a curiosity of no value in photography.