text: The Pharaoh's snake is a more dramatic experiment and it requires more safety precautions than the sugar snake due to the presence of toxic mercury vapor and other mercury compounds.
  This reaction was discovered by Friedrich Wöhler in 1821, soon after the first synthesis of mercury thiocyanate. It was described as "winding out from itself at the same time worm-like processes, to many times its former bulk, of a very light material of the color of graphite." For some time, a firework product called "Pharaoschlangen" was available to the public in Germany but was eventually banned when the toxic properties of the product were discovered through the deaths of several children who had mistakenly consumed the resulting solid.
  The Pharaoh's snake experiment is conducted in the same manner as the sugar snake experiment, however, the former uses mercury(II) thiocyanate (Hg(SCN)) instead of powdered sugar with baking soda. This must be done in a fume hood because all mercury compounds are hazardous.
  After igniting the reagents, mercury(II) thiocyanate breaks down to form mercury(II) sulfide (HgS), carbon disulfide (CS), and carbon nitride (CN). Graphitic carbon nitride, a pale yellow solid, is the main component of the ash.
  :2 Hg(SCN)(s) → 2 HgS(s) + CS(l) + CN(s)
  Carbon disulfide ignites into carbon dioxide (CO) and sulfur(IV) oxide (SO).
  :CS(l) + 3 O(g) → CO(g) + 2 SO(g)
  While carbon nitride (CN) will break down into nitrogen gas and dicyan
  :2 CN(s) → 3 (CN)(g) + N(g)
  When mercury(II) sulfide (HgS) reacts with oxygen (O), it will form gray mercury vapor and sulfur dioxide.  If the reaction is performed inside a container, a gray film of mercury coating on its inner surface can be observed.
  :HgS(s) + O(g) → Hg(l) + SO(g)