Mercury thiocyanate was formerly used in pyrotechnics causing an effect known as the Pharaoh’s serpent or Pharaoh’s snake. When the compound is in the presence of a strong enough heat source, a rapid exothermic reaction is started which produces a large mass of coiling serpent-like solid. An inconspicuous flame which is often blue but can also occur in yellow/orange accompanies the combustion. The resulting solid can range from dark graphite grey to light tan in color with the inside generally much darker than the outside.[3]
This property was discovered soon after the first synthesis of mercury thiocyanate by Wohler in 1821: “winding out from itself at the same time worm-like processes, to many times its former bulk, a very light material the color of graphite…”.
http://en.wikipedia.org/wiki/Mercury...oh.27s_Serpent
