-  Mercury thiocyanate : Hg(SCN)2


         Take some Hg(SCN)2 (mercury is toxic, so wear
     gloves!) and set it on fire with lighter. The reaction
     starts immediately.
         The resulting "snakes" contain mostly carbon
     nitride, but the mercury is present as metal and is
     releasing mercury vapour, so the material has to
     be disposed by special chemical waste procedures.


         Certainly, one of the most spectacular and
     actually quite frightening reaction. Since
     mercury is toxic however, the experiment
     should only be conducted with extreme care
     and only if a proper waste disposal is available.
         The version described in experiment ME5 is
    by far not as breathtaking, but apart from the
    smoke not poisonous at all.

         Hg(SCN)2 decomposes into HgS, CS2, and C3N4
      with latter being the actual "snake". The products 
     decompose further:
          C3N4  →  3 NCCN + N2  ( → cyanide)
          HgS + O2  →  Hg + SO2
          CS2 + 3 O2  →  CO2 + 2 SO2
Initiation with flame.
Start of the reaction
Ongoing reaction