Cerium persulphide, Ce₂S₄

Cerium persulphide, Ce₂S₄, is prepared by heating cerous sulphate to 580°-600° in a stream of dry hydrogen sulphide, the preparation being followed by weighing from time to time. The persulphide is a dark yellowish-brown, crystalline powder, moderately stable in air and cold water. It dissolves in cold hydrochloric acid, an odour of hydrogen persulphide being first noticed and subsequently a precipitation of sulphur. The compound therefore appears to be a polysulphide. At 720° it decomposes into the sesquisulphide and sulphur; it may be reduced to the sesquisulphide by heating in hydrogen at 400°.