Cadmium Arsenites

When a solution of cadmium chloride in 50 per cent, alcohol is treated with potassium orthoarsenite solution neutralised with acetic acid, a white precipitate of cadmium orthoarsenite, Cd₃(NaO₃)₂, is formed. It is obtained anhydrous by heating at 100° C. in a stream of hydrogen. It is slightly soluble in water, easily soluble in aqueous ammonia or in dilute acids. Cadmium pyroarsenite, Cd₂As₂O₅, is obtained as a white precipitate by adding sodium metarsenite to a solution of cadmium sulphate. It is soluble in acids, unattacked by alkalis, and on ignition decomposes, leaving a residue of cadmium oxide contaminated with arsenic. A basic pyroarsenate, of composition Cd₂As₂O₅.3CdO.2H₂O, is obtained as a gelatinous precipitate by the addition of sodium orthoarsenite to a solution of a cadmium salt. The water may be removed by gently heating. Strong heat causes decomposition. It resembles the pyroarsenite in being readily dissolved by acids but unattacked by alkalis.