What happens to the powdered sulfur when heat was applied?
It changes state or allotropic form. Below about 96 °C, rhombic sulfur is the more stable allotrope. On melting at about 118 °C, sulfur first forms a mobile, amber liquid containing S8 rings. If this is allowed to cool, monoclinic sulfur forms as crystallisation occurs above 96 °C. Monoclinic sulfur will turn slowly into the more stable rhombic form on standing below 96 °C. Further heating of the S8-containing liquid breaks the rings into S8 chains. These may join to form longer chains which tangle, causing an increase in viscosity. At higher temperatures, these chains break into shorter ones, perhaps as short as S2, and the viscosity decreases again. Rapid cooling of this liquid traps the resulting solid sulfur in the tangled chain state – this is plastic sulfur. On stretching, the chains uncoil and on releasing the tension they return to the partly coiled state.