NILERED / SCIENCE PHOTO LIBRARY NILERED / SCIENCE PHOTO LIBRARY
Mercury thiocyanate thermal decomposition. Sample of mercury (II) thiocyanate (Hg(SCN)2) forming snake-like structures during thermal decomposition, which is triggered by heat from a flame provided by the demonstrator. This effect is sometimes known as 'Pharaoh's serpent', and was used for entertainment value in the 19th century before it was discovered that the compound is toxic. This type of reaction, where a substance swells on exposure to heat, is known as an intumescent reaction.
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