CII.Evidence of molecular changes in vapours and liquids

Abstract

Summary 1. (1) It is shown in this paper that the systems liquid-liquid (i. e., those which separate into two liquid layers) and systems liquid-gas are governed by identical laws.2. (2) Thus it is shown that the temperature changes in systems liquid-liquid also take place in a discontinuous manner; the discontinuous character appears very strongly if concentrations of two saturated layers are plotted against temperatures instead of densities. It appears that both temperature and concentration changes favour the formation of complex molecules.3. (3) The properties depending upon the number of molecules and not their nature, indicate that the number of molecules per unit volume remains the same with the increase of concentration in the critical regions and sometimes outside them. The formation of complexes is a necessary condition for separation into two phases.4. (4) The analogy between the two systems was extended to the conditions at the interface separating two phases. It was thus assumed that the law of difference must hold true for systems liquid-gas, with its natural consequence i. e., the number of molecules per unit volume in liquid is equal to the number of molecules in vapour. Or where δ l and δ v are densities of liquid and vapour, M the molecular weight, and x the association factor of liquid, and y that of vapour.5. (5) It is thus possible to calculate the association factor at all temperatures and to see that its value becomes fairly high at lower temperatures.6. (6) In both systems one can recognize definite molecular changes. The difference between systems liquid-liquid and liquid-gas is tlmt in the latter case these changes take place between molecules in a space not otherwise filled, whereas in the former they take place within a liquid acting as dissolvent.