IV. On evaporation and dissociation.— Part VIII . A study of the thermal properties of propyl alcohol

Abstract

In continuation of our investigations of the thermal properties of pure liquids, we have now determined the vapour-pressures, vapour-densities, and expansion in the liquid and gaseous states, of Propyl Alcohol, and from these results we have calculated the heats of vaporization at definite temperatures. The range of temperature is from 5° to 280°, and the range of pressure from 5 mms. to 56,000 mms. Preparation of pure Propyl Alcohol.—A sample of propyl alcohol was procured from Kahlbaum, of Berlin. It was dried with barium oxide, and then with small quantities of sodium; but in this case the results were not nearly so satisfactory as with methyl and ethyl alcohol, for propyl alcohol is soluble in water, forming a mixture or “hydrate,” which boils constantly at a lower temperature than the pure alcohol. It is not completely decomposed by sodium, and can be separated only by repeated fractional distillation. This hydrate was first described by Chancel (‘Comptes Rendus,’ vol. 68, 1867, p. 659), who, observing that it boiled with perfect constancy, assumed that it possessed a definite composition, and gave it the formula C 3 H 8 O, H 2 O. It has more recently been examined by Konowalow (Wiedemann’s ‘Annalen,’ vol. 14, 1881, p. 34), who has determined the vapour- pressures of varying mixtures of propyl alcohol and water at definite temperatures. Konowalow finds that the composition of the mixture, the vapour of which exerts the greatest pressure, is not the same at different temperatures, but that the mixture contains more alcohol at high temperatures than at low. From this it has been concluded that the composition of the “hydrate” must depend on the pressure under which the liquid is distilled. We have proved experimentally that this is the case (but we reserve a discussion of this interesting substance for a future paper), and we give the results of our experiments in an Addendum to this paper.