Properties of fused polysulphides—IV. Cryoscopic studies on solutions of alkali metal polysulphides in potassium thiocyanate

Measurements have been made of the depression of the freezing point of fused KSCN by Na2S, Na2S4.4 and K2S5.9. Na2S gives a freezing point depression corresponding to three region particles. These are believed to be 2Na+ and CN−, the cyanide ion being formed by reaction of S2− with the solvent. Na2S4.4 and K2S5.9 give opaque solutions in KSCN which are initially dark blue-green, and which slowly lose sulphur vapour and change colour to blue and finally to pale yellow. The initial freezing point depressions correspond to 4 and 2 foreign particles respectively, but when sulphur evolution is complete the final depressions correspond to 2 and 0 foreign particles. The following schemes are consistent with the observations