The previous experiment demonstrated the combustion of coal (carbon) in molten potassium nitrate. This time, sulfur was chosen as the combustible substance instead of coal. The experiment started with the intense heating of the potassium nitrate. First, tehe salt melted and then decomposed due to the heat. Small bubbles of oxygen evolved from the molten salt:
2KNO3(l) → 2KNO2(l) + O2(g)
A small piece of sulfur was thrown into the molten salt where it started to burn vigorously in the oxygen released as a result of the decomposition of potassium nitrate:
S(s) + O2(g) → SO2(g)
As sulfur dioxide (SO2) is a toxic gas, the experiment was conducted under a fume hood.
1) OXYGEN: “Combustion of sulfur in air and oxygen”