Mercury(II) thiocyanate is white insoluble solid, that can be obtained as a precipitate in the reaction of mercury(II) chloride or nitrate with potassium thiocyanate. Like all other mercury compounds it is highly toxic, so the experiment must be carried out in a fume hood.
When mercury(II) thiocyanate is ignited it decomposes, giving voluminous brownish mass that is insoluble in water. This formed product is mainly carbon nitride, C3N4. The main reaction is represented with the following equation:
Upon heating C3N4 partially breaks down to dicyan and nitrogen:
Mercury(II) sulfide produced in the reaction, further reacts with oxygen from air, while mercury vapors are liberated. If you look closely at the aquarium we used for performing this experiment, there is a grayish coating of condensed mercury on the glass left afterward:
Also, carbon disulfide (CS2) formed in the first equation, is a highly flammable compound, and combusts to carbon(IV) oxide and sulfur(IV) oxide: