Cadmium Phosphide

A fused crystalline grey phosphide of cadmium is obtained by heating cadmium and phosphorus vapours in an atmosphere of hydrogen.

A brown powder is precipitated when a solution of cadmium oxide in potassium hydroxide is heated with phosphorus and some benzene. It evolves phosphine with hydrochloric acid and explodes with nitric acid. A grey crystalline mass of Cd₃P₂, with a metallic lustre, is produced by heating it in a current of hydrogen.

Renault obtained Cd₃P₂, which closely resembled the corresponding zinc phosphide in properties and was prepared similarly. He prepared the diphosphide, CdP₂, most easily by heating a mixture of ammonium phosphate (or phosphate of mercury or tin) with cadmium carbonate and carbon. After condensing the volatile products the cadmium phosphide was washed with dilute hydrochloric acid.

The diphosphide usually occurs in bright red crystals, though it is sometimes obtained in indigo-blue scales or plates. Its chief chemical difference from ZnP₂ is its ready decomposition by boiling hydrochloric acid.

Emmerling prepared the subphosphide, Cd₂P, by heating cadmium and phosphorus together. It is a greyish or silver-white mass consisting of fine needles. Hydrochloric acid evolves phosphine from it.