Note 74 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

If instead of a sulphide we take an alkali hydroxide, a thiocarbonate is also formed, together with a carbonate—thus, 3BaH2O2 + 3CS2 = 2BaCS3 + BaCO3 + 3H2O. From the instability of the thiocarbonates of the alkaline metals we can clearly see the reason of the difficulty with which the salts of the heavier metals are formed, whose basic properties are incomparably weaker than those of the alkali metals. However, these salts may be obtained by double decomposition. Ammonia in reacting on carbon bisulphide gives, besides products like those formed by other alkalis, a whole series of products of as complex a structure as those substances which are produced by the action of carbonic anhydride on ammonia. In the ninth chapter we examined the formation of the ammonium carbonates, and saw the transition from them into the cyanides. It is not surprising after this that the action of carbon bisulphide on ammonia not only produces the above-mentioned salts, but also amidic compounds corresponding with them, in which the oxygen is wholly or partially replaced by sulphur. Thus ammonium dithiocarbamate is very easily obtained if carbon bisulphide be added to an alcoholic solution of ammonia, and the mixture cooled in a closed vessel. The salt then separates out in minute yellow crystals, CN2H6S2.

Carbon bisulphide not only forms compounds with the metallic sulphides, but also with sulphuretted hydrogen—that is, it forms thiocarbonic acid, H₂CS₃. This is obtained by carefully mixing solutions of thiocarbonates with dilute hydrochloric acid. It then separates in an oily layer, which easily decomposes in the presence of water into sulphuretted hydrogen and carbon bisulphide, just as the corresponding carbonic acid (hydrate) decomposes into water and carbonic anhydride. Carbon bisulphide combines not only with sodium sulphide, but also with the bisulphide, Na₂S₂, not, however, with the trisulphide, Na₂S₃.

The relation of carbon bisulphide to the other carbon compounds presents many most interesting features which are considered in organic chemistry. We will here only turn our attention to one of the compounds of this class. Ethyl sulphide, (C₂H₅)₂S, combines with ethyl iodide, C₂H₅I, forming a new molecule, S(C₂H₅)₃I. If we designate the hydrocarbon group, for instance ethyl, C₂H₅, by Et, the reaction would be expressed by the following equation : Et₂S + EtI = SEt₃I. This compound is of a saline character, corresponds with salts of the alkalis, and is closely analogous to ammonium chloride. It is soluble in water; when heated it again splits up into its components EtI and Et₂S, and with silver hydroxide gives a hydroxide, Et₃S·OH, having the property of a distinct and energetic alkali, resembling caustic ammonia. Thus the compound group SEt₃ combines, like potassium or ammonium, with iodine, hydroxyl, chlorine, &c. The hydroxide SEt₃·OH is soluble in water, precipitates metallic salts, saturates acids, &c. Hence sulphur here enters into a relation towards other elements similar to that of nitrogen in ammonia and ammonium salts, with only this difference, that nitrogen retains, besides iodine, hydroxyl, and other groups, also H₄ or Et₄ (for example, NH₄Cl, NEt₃HI, NEt₄I), whilst sulphur only retains Et₃. Compounds of the formula SH₃X are however unknown, only the products of substitution SEt₃X, &c. are known. The distinctly alkaline properties of the hydroxide, triethylsulphine hydroxide, SEt₃OH, and also the sharply-defined properties of the corresponding hydroxide, tetraethylammonium hydroxide, NEt₄OH, depend naturally not only on the properties of the nitrogen and sulphur entering into their composition, but also on the large proportion of hydrocarbon groups they contain. Judging from the existence of the ethylsulphine compounds, it might be imagined that sulphur forms a compound, SH₄, with hydrogen; but no such compound is known, just as NH₅ is unknown, although NH₄Cl exists.