"In some parts of the East, sulphur is separated from the earthy matter wherewith it is mixed in the soil, by heating the crude material very strongly in earthen pots, each covered with another similar pot inverted on it. The sulphur melts and then becomes gaseous and the gaseous, sulphur condenses in the upper pots, which are comparatively cool; the fine yellow powder which condenses is approximately pure sulphur; the earthy impurities remain in the lower pots."