Chromic Cyanide, Cr(CN)₃

Chromic Cyanide, Cr(CN)₃, is formed when a solution of potassium cyanide is added in excess to a neutral solution of chromic chloride and the mixture brought to boiling. It appears as a light greenish-blue precipitate, insoluble in excess of potassium cyanide. A similar reaction occurs with a solution of chrome alum, except that the mixture immediately turns green. The precipitate can be dried, in absence of air, without decomposition, as, for example, by heating in a stream of hydrogen at 200° C. It dissolves in boiling hydrochloric acid, giving a green solution, from which it is again precipitated by ammonia. Hot potassium hydroxide decomposes it, with formation of chromic hydroxide and potassium chromicyanide.