|The crude Sicilian sulphur, partly on account of the lack of fuel, is exported to be refined elsewhere. Sulphur Refining in the subsequent commercial purification the processes involved are decantation and sublimation or distillation. After melting in cylindrical vessels and allowing the mechanical impurities to settle, the sulphur is run into horizontal iron retorts which open into a large vaulted chamber. If distillation occurs slowly, the temperature of the receiving chamber will not attain the melting-point of sulphur and the vapour issuing from the retorts will condense directly to a solid powder, which constitutes " flowers of sulphur " or " sublimed sulphur." Rapid distillation will cause the temperature of the receiver to rise above the melting-point of sulphur and the vapour will then condense as a liquid, which is periodically tapped off into wet wooden moulds of rectangular or cylindrical shape, the resulting product being known as " roll sulphur." Moulds constructed of aluminium or its alloys have also been found suitable. |
In plant designed especially for the production of " flowers of sulphur," the condensing chambers may be of protected sheet iron and contain an arrangement of condensing surfaces, the entrained molten sulphur being separated by a baffle. The modern production of finely ground sulphur has lessened the demand for sublimed sulphur, although the latter is considered more suitable for vulcanisation and agricultural purposes.
"Chemically pure " Sulphur Refining can be performed from the foregoing products either by filtering whilst molten through glass wool and subsequently distilling under reduced pressure, or by repeated distillation in a current of pure carbon dioxide. For the removal of organic impurities it is sufficient to heat the sulphur for a period a little below its normal boiling-point.