Note 70 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

The fact should not be lost sight of that sulphur and charcoal are solids at the ordinary temperature, whilst carbon bisulphide is a very volatile liquid, and consequently, in the act of combination, referred to the ordinary temperature (Note 69), there is, as it were, a passage into a liquid state, and this requires the absorption of heat. And furthermore, the molecule of sulphur contains at least six atoms, and the molecule of carbon in all probability (Chapter VIII.) a very considerable number of atoms; thus the reaction of sulphur on charcoal may be expressed in the following manner: 3Cn + nS6 = 3nCS2—that is, from n + 3 molecules there proceed 3n molecules, and as n must be very considerable, 3n must be greater than 3 + n, which indicates a decomposition in the formation of carbon bisulphide, although the reaction at first sight appears as one of combination. This decomposition is seen also from the volumes in the solid and liquid states. Carbon bisulphide has a sp. gr. of 1·29; hence its molecular volume is 59. But the volume of carbon, even in the form of charcoal, is not more than 6, and the volume of S2 is 30; hence 36 volumes after combination give 59 volumes—an expansion takes place, as in decompositions.