Potassium cyanide, KCN

The Potassium cyanide, KCN, is manufactured by methods similar to those employed for the corresponding sodium derivative. Potassium ferrocyanide is heated either in absence of air, or with potassium carbonate and charcoal, or with sodium, the potassium cyanide being extracted by lixiviation with water or dilute alcohol. It is also obtained by the action of a mixture of steam and nitrogen on potassium carbonate or carbide, the manufacture of cyanides by the aid of atmospheric nitrogen being now an important industrial process.

The salt forms colourless cubes melting at 601.2° C., and of density 1.52. The heat of formation from the elements is given as 30.1 Cal. and 32.5 Cal. A solution in contact with excess of salt boils at 103.3° C. and contains 122.2 grams per 100 grams of water at that temperature. Owing to hydrolytic dissociation the aqueous solution has an odour of hydrocyanic acid and a strongly alkaline reaction. No hydrate has been isolated. Oxidation with sodium hypobromite converts the salt into cyanate, formate, and carbonate. Its strong reducing power at elevated temperatures renders it a valuable reagent in blowpipe analysis.

With gold, potassium cyanide forms complex derivatives, and it is employed in the extraction of the metal. As a double cyanide with other metallic cyanides, such as those of silver, gold, and nickel, it is an important reagent in electroplating. It is also employed in photography. Like hydrocyanic acid, it is extremely poisonous.