Mercury(II) thiocyanate (Hg(SCN)₂) is a chemical compound. It was formerly used in pyrotechnics for the long snake-like ash Pharaoh's serpent that forms when a pellet of this compound, often with a small amount of a sugar such as glucose added to serve as supplemental fuel, is ignited. This is extremely dangerous because it produces poisonous mercury vapors.

Mercury(II) thiocyanate is made by reacting a mercury(II) salt (such as mercury(II) chloride) with a thiocyanate salt (such as potassium thiocyanate) in solution in water, producing a precipitate of mercury(II) thiocyanate.

Conditions/substances to avoid are: moisture, heat, light, aluminium and strong acids.

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