Properties of the Suboxide of Silver.—Suboxide of silver bears the same relation to the ordinary brown protoxide of silver that subchloride bears to protochloride of silver.
It is a black 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.
Symbol, AgCl. Atomic weight, 144.
Preparation of Chloride of Silver by double decomposition.—In order to illustrate this, take a solution in water of chloride of sodium or "common salt," and mix it with a solution containing nitrate of silver; immediately a dense, curdy, white precipitate falls, which is the substance in question.
In this reaction the elements change places; the chlorine leaves the sodium with which it was previously combined, and crosses over to the silver; the oxygen and nitric acid are released from the silver, and unite with the sodium: thus
Chloride of sodium + nitrate of silver = Chloride of silver + nitrate of soda.
This interchange of elements is termed by chemists double decomposition.
The essential requirements in two salts intended for the preparation of chloride of silver, are simply that the first should contain chlorine, the second silver, and that both should be soluble in water; hence the chloride of potassium or ammonium may be substituted for the chloride of sodium, and the sulphate or acetate for the nitrate of silver.
In preparing chloride of silver by double decomposition, the white clotty masses which first form must be washed repeatedly with water, in order to free them from soluble nitrate of soda, the other product of the change. When this is done, the salt is in a pure state, and may be dried, etc., in the usual way.