Chromic Arsenate, CrAsO₄

Chromic Arsenate, CrAsO₄, is formed as an apple-green precipitate when potassium arsenate is added to a solution of a chromic salt.

Double arsenates of chromium with the alkali metals have been described. When aqueous arsenious acid is added to a solution of potassium chromate, the liquid becomes green and soon coagulates to a tremulous jelly, which when dried at 100° C. yields a substance whose empirical formula is 4K₂O.3Cr₂O₃.3As₂O₅.10H₂O. The double arsenates, K₃Cr₂(AsO₄)₃ and Na₃Cr₂(AsO₄)₃, have been prepared by the addition of chromium sesquioxide to the fused alkali meta-arsenate. Crystallisation is accelerated by the addition of alkali chloride. Both compounds yield green transparent crystals. In the case of the potassium salt more than 7, and of the sodium salt more than 8, per cent, of the sesquioxide must be employed or a pyroarsenate is produced.