Calcium Dichromate, CaCr₂O₇

Calcium Dichromate, CaCr₂O₇, may be obtained by treating a solution of the chromate with sulphuric acid, filtering off the calcium sulphate, and concentrating. Treatment of the neutral chromate with chromic acid, or partial saturation of calcium carbonate with chromic acid, also gives the dichromate as silky yellowish-brown crystals. Both a tetrahydrate, CaCr₂O₇.4H₂O, as yellowish-red prisms, and a tri-hydrate, CaCr₂O₇.3H₂O, forming deliquescent red crystals, are known. It is fairly soluble in water.