Cadmium Arsenite, Cd₃(AsO₃)₂

Cadmium Arsenite, Cd₃(AsO₃)₂, is precipitated from a solution of cadmium chloride in 50 per cent, alcohol by a solution of potassium arsenite neutralised with acetic acid, or from a solution of cadmium sulphate by sodium metarsenite. The impure arsenite, precipitated by mixing solutions of cadmium sulphate and potassium arsenite, can be purified by solution in dilute acid and re-precipitation.

The white precipitate is slightly soluble in water, easily in ammonia solution or dilute acids, and can be converted into anhydrous Cd₃(AsO₃)₂ by heating at 100° C. in a stream of hydrogen. Alkalies do not attack it, and ignition leaves a residue of cadmium oxide contaminated with arsenic.