Very strong ammonia, in acting upon oxide of silver, converts it into a black powder, termed _fulminating silver_, which possesses the most dangerous explosive properties. Its composition is uncertain. In preparing ammonio-nitrate of silver by the common process, the oxide first precipitated occasionally leaves a little black powder behind, on re-solution; this does not appear, however, according to the observations of the author, to be fulminating silver. In sensitizing salted paper by the ammonio-nitrate of silver, _free ammonia_ is necessarily formed. Thus:-- Chloride of ammonium + oxide of silver in ammonia = chloride of silver + ammonia + water. Silver, Oxide of. Symbol, AgO. Atomic weight, 116. If a little potash or ammonia be added to solution of nitrate of silver, a 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. _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. Silver, Chloride of. 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.