Praseodymium sulphide, Pr₂S₃

Praseodymium sulphide, Pr₂S₃, cannot be prepared by the usual methods, if entirely free from cerium; the sulphate, when heated in hydrogen sulphide, giving only praseodymium oxysulphide, Pr₂O₂S. If, however, the praseodymium sulphate contains a little cerous sulphate, the trisulphide, Pr₂S₃, and persulphide, Pr₂S₄, may be obtained as in the cases of cerium and lanthanum. The trisulphide is chocolate-brown in colour and has a density of 5.042 at 11° (Muthmann and Stutzel). The persulphide begins to lose sulphur at about 650°.