Mercury(l) chloride, Hg2Cl2, a covalent compound which is not soluble 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 compound is a white, shadowy powder consisting of fine tetragonal crystals.
Calomel is used in preparing insecticides and medicines. It is well known in the laboratory as the constituent of the calomel reference electrodes which are commonly used in conjunction with a glass electrode to measure pH.