Mercury(I) chloride, Hg₂Cl₂, a covalent compound which is insoluble in water. The substance sublimes when heated. The formula weight is 472.086 and the specific gravity is 7.16 at 20°C (68°F). The material is a white, impalpable powder consisting of fine tetragonal crystals. Calomel is manufactured by precipitation when sodium chloride is added to a solution of mercury(I) nitrate or by direct combination of the elements.