Caesium sulphides

In methods of preparation and properties the sulphides of caesium resemble closely the corresponding salts of rubidium. The monosulphide, Cs₂S, is prepared by heating sulphur with excess of caesium, and removing the uncombined metal by distillation in vacuum. It forms white needles, melting at the temperature of softening of glass, readily oxidized and combustible. It weathers in air, and dissolves in water with a hissing sound. It is more soluble than the monosulphide of potassium or rubidium, and the three sulphides are not isomorphous. Both the disulphide, Cs₂S₂, m.p. about 460° C., b.p. above 800° C., and the trisulphide, Cs₂S₃, m.p. 217° C., b.p. above 800° C., yield a monohydrate. The tetrasulphide, Cs₂S₄, is anhydrous. The pentasulphide, Cs₂S₅, melts at 204° to 205° C., and its density at 16° C. is 2.806.