Potassium polysulphides

The simplest method, in practice, for the production of the alkali polysulphides is supplied by the interaction of sulphur and the alkali sulphide in hot aqueous or alcohol solution.2 Liver of sulphur, obtained by fusing sulphur with potassium carbonate,3 is, when freshly prepared, mainly a mixture of potassium polysulphides with potassium thiosulphate. Solutions of the hydroxides of the alkali or alkaline earth metals also dissolve sulphur, yielding solutions of the polysulphides and thiosulphates of the corresponding metals (see p. 87). When a suspension of sulphur in aqueous ammonia is treated with hydrogen sulphide in the absence of air, a red solution is obtained, which on cooling yields yellow crystals of ammonium pentasulphide, (NH4)2S5.4 Bloxam claimed 5 to have separated tetra-, penta-, hepta- and nona-sulphides in this way, whilst Thomas and Riding,6 using alcoholic ammonia, obtained only what they considered to be di-, penta- and hepta-sulphides. Mills and Robinson, however, were unable to obtain evidence of the formation of any polysulphide other than the pentasulphide. 

Potassium, sodium and calcium sulphides are applied externally to soften the skin by dissolving the epidermis in diseases such as psoriasis, acne and seborrhea. Mixtures of calcium or potassium polysulphides and thiosulphate behave similarly and are also depilatories. Another common hair remover is barium sulphide, mixed with starch or zinc oxide, whereas selenium suphide and cadmium sulphide are applied topically, in shampoos, to control dandruff. 

Potassium polysulphides.—Several polysulphides have been described. According to Thomas and Rule,4 the complete series K Sa, exists, x being any whole number up to a maximum of 6. The values obtained for the molecular weights in alcoholic solution by the ebullioscopic method favour the simple formula K, and not K4Sa,. 

The heats of formation of the potassium polysulphides K2S , where n has values from 1 to 6, have been determined by solution calorimetry.213 The structures of the polysulphides BaS3, SrS3, BaS2, and SrS2 have been determined.214 The structures of the trisulphides contain symmetrical S2 groups with sulphur-sulphur bond distances between 2.076 and 2.050 A, and a bond angle at the central sulphur atom of 114.9 and 108.3°. In the disulphides the sulphur-sulphur bond distances were 2.126 and 2.08 A. 

M. Traube showed that the black product is a mixture of chromic sulphide and oxide. M. Traube obtained some sulphide by heating acid chromic sulphate in dry hydrogen sulphide A. Moulot heated the sulphate mixed with potassium polysulphide and K. Bruckner, with sulphur. H. Moissan heated chromic oxalate in hydrogen sulphide and R. Schneider heated the higher chromium sulphides—e-5 . Cr4S7=2Cr2S3+S. 

Scheele noted that the yellow solution of liver, of sulphur (potassium polysulphide) is converted on exposure to air into a colourless solution of vitrio-lated tartar (potassium sulphate), so that the alkali has attracted the acid of sulphur and the air the phlogiston ( 16). 

Sulphurated potash (Liver of Sulphur) consists of a mixture of potassium polysulphides, thiosulphate and other salts. It is standardised on its total sulphur content determined by the alkaline bromine oxidation method given above under Sulphur. 

Potassium sulphide Rhenium (VII) sulphide Silver sulphide Sodium disulphide Sodium polysulphide Sodium sulphide Tin (II) sulphide Tin (IV) sulphide Titanium (IV) sulphide Uranium (IV) sulphide... 

According to G. Calcagni, 100 c.c. of a cold 66 per cent, of sodium hydroxide dissolves 24 55 grms. of sulphur or 57 parts of sulphur per 23 parts of sodium while 100 c.c. of a similar soln. of potassium hydroxide dissolves 17 70 grms. of sulphur, or 59 35 parts of sulphur per 39 15 parts of potassium. The soln. reacts for sulphides, polysulphides, thiosulphates, and sulphites. The reaction between alkali hydroxides and sulphur is complex probably sulphides are first formed from which thiosulphates are produced, and by the dissolution of more sulphur, polysulphides the thiosulphates Ipse part of their sulphur forming sulphites. In the more cone. soln. of sulphur part of the latter appears to be uncombined because these soln. yield sulphur to hot benzene. All the soln. are decomposed by carbon dioxide yielding sulphur and hydrogen sulphide. 

Whilst the polysulphides of potassium, rubidium, and caesium resemble one another very closely, the sodium compounds exhibit notable differences. Thus, whilst the first-named three elements all form hexasulphides and stable pentasulphides, in the case of... 

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