Thallium pentasulphide, Tl₂S₅

Thallium pentasulphide, Tl₂S₅, is said by Pelabon to melt at 127°, but, if quickly cooled, to remain pasty at ordinary temperatures. When heated above the melting-point it readily loses sulphur. A crystalline pentasulphide is said to be formed by digesting thallous chloride with concentrated ammonium polysulphide solution; but, according to Hawley, there is no evidence that the substance thus obtained is a definite pentasulphide, but there exists a series of solid solutions containing thallium and sulphur, in which there is more sulphur than is required for a sesquisulphide.