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.