Rhombic sulphur is a crystalline allotropic form of sulphur. It is also designated as α–sulphur. This is the most stable variety of sulphur. All other varieties of sulphur eventually revert to rhombic form on standing.

Preparation:
Rhombic sulphur is prepared by dissolving powdered sulphur in carbon disulphide at room temperature. The mixture is then filtered. The filtrate is then kept in a small beaker covered with a filter paper. The carbon disulphide will slowly evaporate away leaving behind large octahedral crystals of rhombic sulphur (or α–sulphur).

Properties:

• It exists as rhombic octahedral crystals.
• Its density is 2.06 g/mL.
• It melts at 112.8°C
• When slowly heated to 96°C, it changes into monoclinic or β–sulphur. However, when cooled below 96°C, it returns back to rhombic form.
• It is insoluble in water and soluble in carbon disulphide.

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