Mercury(II) thiocyanate

Mercury(II) thiocyanate (Hg(SCN)₂) is an inorganic chemical compound, the salt of Hg²⁺ and the thiocyanate anion. It is a stable solid at room temperature that has the appearance of white powder with chunks; it can also be grey in color, depending on purity. Mercury compounds are extremely toxic and protective equipment should be used whenever working with mercury thiocyanate. However, it is commercially available, though expensive. Mercury thiocyanate is best known for its former use in pyrotechnics, as it will produce a large, winding “snake” when set on fire. This is known as the Pharaoh’s Serpent. Though some people still use it for this purpose, it is generally avoided because of the production of toxic gases when this reaction occurs.

Synthesis

The first synthesis of mercury thiocyanate was probably completed in 1821 by the chemist Jons Jacob Berzelius with evidence for the first pure sample occurring in 1866 prepared by a chemist named Hermes. Because of its ionic nature, there are several ways to synthesize the compound. Mercury(II) thiocyanate is made by reacting solutions containing mercury(II) and thiocyanate ions. The low solubility product of mercury thiocyanate causes it to precipitate. It is also soluble in several solvents...
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