Strontium Polysulphides

By boiling strontium monosulphide with sulphur and water, a tetra- and possibly also a penta-sulphide are formed.

On evaporating in vacuo at 15° C. to the consistency of a syrup the solution obtained with three molecules of sulphur to one of strontium sulphide, and keeping for several days at a fairly low temperature, red prismatic crystals of the Strontium Tetrasulphide, SrS₄.6H₂O, are obtained. It is very hygroscopic, dissolves readily in water and alcohol - the solution oxidising in the air - and melts at 25° C. At 100° C. it loses 4 molecules of water, giving a solid yellow mass of composition SrS₄.2H₂O. The same substance is formed as bright yellow crystals by evaporating the original syrup at a somewhat higher temperature, namely 25° C. instead of 15° C.