Pharaoh's Serpent

An effect known as 'Pharaoh's Serpent' is a reaction that occurs during the combustion of mercury(II) thiocyanate.

When this white powder is lit by flame or strong heat, an exothermic reaction is started which produces the quick forming mass of coiling serpent-like solid you can see in this unique science experiment video. Mercury thiocyanate was once used in pyrotechnics but was ultimately banned when the toxic properties of the substance were found. Check out the video to see this crazy expanding substance in action!