Mercuric Chromate, HgCrO₄

Mercuric Chromate, HgCrO₄, is formed by heating an equivalent mixture of mercuric oxide and chromic anhydride with a little water. It yields dark red rhombic prisms, which are decomposed by water with formation of the basic salt, 3HgO.CrO₃. Many basic salts have been described, but it has been shown from an investigation of the system, HgO-CrO₃-H₂O, that the above is the only one which exists as a separate chemical entity. It may also be produced by precipitation of mercuric nitrate solution with a dichromate, or by boiling mercuric oxide with potassium dichromate solution. The compound, 2HgCrO₄.HgS, formed by the action of a chromic acid solution of mercuric oxide on freshly precipitated mercuric sulphide, has explosive properties.