Sulphides of Thallium

When mixtures of thallium and sulphur are fused, those rich in thallium separate into two non-miscible layers of thallous sulphide, Tl₂S, and thallium, while those rich in sulphur form two layers consisting of thallium pentasulphide and sulphur. Mixtures containing more sulphur than is required for thallous sulphide and less than is required for the pentasulphide form only one liquid phase, and solid solutions appear to separate when they are cooled. The nature of these solid solutions is not known; possibly a thallothallic sulphide, Tl₂S.Tl₂S₃, also exists, but has no melting-point.