Ammonium Chromous Carbonate, (NH₄)₂CO₃.CrCO₃

Ammonium Chromous Carbonate, (NH₄)₂CO₃.CrCO₃.H₂O, is deposited as a yellow crystalline powder when an ammoniacal solution of chromous acetate is acted upon, first by a current of carbon dioxide, and then by a stream of hydrogen. The salt is washed successively with dilute ammonia solution, alcohol, and finally ether, and then dried in a stream of hydrogen containing a little ammonia. It may also be prepared by boiling the ammoniacal solution of chromous acetate with a solution of sodium carbonate in an atmosphere of hydrogen. The salt is an energetic reducer. It gradually decomposes on exposure to air, giving blue chromic hydroxide; heated in the air or in hydrogen it yields green chromium sesquioxide. It is attacked by chlorine at red heat, giving chromic chloride; with hydrogen sulphide, the sulphide, Cr₂S₃, is obtained as a black crystalline powder. In absence of oxygen dilute mineral acids dissolve it, yielding blue solutions.