Note 51 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

With an excess of snow, the hydrate H2SO4,H2O, like the normal hydrate, gives a freezing mixture, owing to the absorption of a large amount of heat (the latent heat of fusion). In melting, the molecule H2SO4 absorbs 960 heat units, and the molecule H2SO4H2O 3,680 heat units. If therefore we mix one gram molecule of this hydrate with seventeen gram molecules of snow, there is an absorption of 18,080 heat units, because 17H2O absorbs 17 × 1,430 heat units, and the combination of the monohydrate with water evolves 9,800 heat units. As the specific heat of the resultant compound H2SO4,18H2O = 0·813, the fall of temperature will be -52°·6. And, in fact, a very low temperature may be obtained by means of sulphuric acid.