Mercury(II) thiocyanate

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Mercury(II) thiocyanate
IUPAC name
Mercury(II) thiocyanate
Other names
Mercuric thiocyanate
Mercuric sulfocyanate
Jmol-3D images Image
Molar mass 316.755 g/mol
Appearance White solid
Density 3.71 g/cm3
Melting point 165 °C (329 °F; 438 K) (decomposes)
Boiling point Decomposes
0.069 g/100 ml (at 25 ºC)
Solubility Soluble in dilute hydrochloric acid, anhydrous ammonia, KCN
Slightly soluble in ethanol, diethyl ether
Safety data sheet ScienceLab
Flash point 121 ºC
Lethal dose or concentration (LD, LC):
46 mg/kg (rat, oral)
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Mercury(II) thiocyanate is an inorganic chemical compound with the chemical formula Hg(SCN)2. When ignited, it will produce a large, expanding “snake”, effect known as the Pharaoh's serpent.



When ignited, mercury thiocyanate will decompose into an expanding residue, which has the form of a snake. The thermal decomposition is fairly complex and occurs in several stages:

2 Hg(SCN)2 → 2 HgS + CS2 + C3N4
CS2 + 3O2 → CO2 + 2 SO2
2 C3N4 → 3 (CN)2 + N2
HgS + O2 → Hg + SO2


Mercury(II) thiocyanate is a white solid, extremely poorly soluble in water, but somewhat soluble in other solvents and acids. It decomposes when heated above 165 °C. Its density at standard conditions is 3.71 g/cm3.


Mercury thiocyanate is sold by various chemical suppliers. It is sometimes sold on eBay.

Being a mercury compound, the sale of this compound is regulated in most countries.


Mercury(II) thiocyanate can be made by reacting a soluble thiocyanate salt, such as potassium thiocynate with mercury(II) nitrate:

Hg(NO3)2 + 2 KSCN → Hg(SCN)2 + 2 KNO3

Since Hg(SCN)2 is sparingly soluble in water, it will precipitate. Filter the precipitate and dry it, preferably in open air or in a desiccator. Avoid strong heat, as it cause it to decompose.


  • Pharaoh’s serpent



Mercury(II) thiocyanate is very toxic and proper protection must be worn when handling the compound.


Mercury(II) thiocyanate should be kept in a closed bottle, away from corrosive vapors. DO NOT STORE IT IN ALUMINIUM CONTAINERS!


Mercury(II) thiocyanate can be neutralized by turning it into mercury sulfide HgS, which is much less toxic. It then should be taken to special disposal centers.


Relevant Sciencemadness threads