Alkaline Earth Phosphides

An impure calcium phosphide, made by exposing lime at a red heat to the vapour of phosphorus, was used in the preparation of phosphine. Calcium phosphide probably is also formed during the manufacture of phosphorus by the electric furnace method (q.v.). It has been prepared by heating calcium phosphate and lamp black in the electric arc furnace, and appeared as a crystalline reddish-black substance. Calcium phosphide prepared in this manner is only acted upon slowly by water at the ordinary temperature, but readily by aqueous solutions of strong acids. Concentrated nitric and sulphuric acids, and oxygen and chlorine, do not attack it at ordinary temperatures, but on heating it is oxidised, e.g. by chlorine above 100° C. and by oxygen above 300° C.

Strontium and barium phosphides have been prepared by similar methods.

Magnesium phosphide was first obtained from the metal and organic substances containing phosphorus, but is best prepared by heating the metal in phosphorus vapour or with red phosphorus in an atmosphere of hydrogen.

Phosphides of the alkali and alkaline earth metals are decomposed by water or dilute acids, giving the hydroxides or salts of the metals respectively, together with phosphine and other " hydro-phosphors." They are only slightly affected by oxidising agents such as concentrated nitric acid. They burn when heated slightly below a red heat in oxygen. They are also attacked by the halogens when heated.