Cobalt Chromate, CoCrO₄

Cobalt Chromate, CoCrO₄, results as a greyish-black crystalline powder when a mixture containing cobalt carbonate (12.4 grams), chromium trioxide (20 grams), and water (20 grams) is heated for four hours in a sealed tube at 185° C. It is much more soluble than the corresponding nickel salt. The dihydrate CoCrO₄.2H₂O yields bronze-coloured acicular prisms.

Basic salts are produced when cobalt salts are precipitated with sodium chromate, or when the alkali-containing double salts first produced by precipitation with ammonium or potassium chromates are subjected to continued treatment with hot water. The following double salts have been described:

(NH₄)₂Co(CrO₄)₂.6H₂O; (NH₄)₂CrO₄.3CoCrO₄.2NH₃.3H₂O; K₂O.4CoO.4CrO₃.3H₂O and K₂Co(CrO₄)₂.2H₂O; Cs₂Co(CrO₄)₂.6H₂O.