Cuprous cyanide, CuCN

Addition of potassium cyanide to a solution of cuprous chloride in hydrochloric acid precipitates Cuprous cyanide, CuCN. The best method for its preparation is to mix cold aqueous solutions of potassium cyanide (65 grams) and cupric sulphate (130 grams), and expel cyanogen by warming the mixture under an efficient air-extractor. After settling, the cuprous cyanide is decanted, and washed with water, alcohol, and ether. References to other methods of preparation, and to Sandmeyer's process for aromatic nitriles, are appended.

Cuprous cyanide is a white solid, and is soluble with difficulty in water. It is dissolved readily by cold, concentrated hydrochloric acid, and is reprecipitated from this solvent by addition of an aqueous solution of potassium hydroxide. In contact with air, its colourless solution in ammonium hydroxide develops a blue tint. The salt is also dissolved by aqueous solutions of ammonium chloride, sulphate, and nitrate, and by warm, dilute sulphuric acid. None of its solutions has the power of absorbing carbon monoxide. The heat of formation of cuprous cyanide in the simple molecular form CuCN from carbon, solid copper, and gaseous nitrogen is 14.9 Cal.