On vapour-pressure and osmotic pressure of strong solutions

Abstract

1. The relations between vapour-pressure, osmotic pressure, and concentration of solutions are of great interest, and have been the subject of recent communications by Lord Berkeley and Hartley, by Spens, and by Porter. I propose in the present paper to develop a theory of solutions, based on a simple relation between the vapour-pressure and the concentration, which appears to give a very fair account of the phenomena observed in the case of strong solutions, and is at the same time a natural extension of the present theory as applied to dilute solutions. Before discussing the theory itself, I propose to give fresh proofs of some of the more important relations already accepted, for the sake of indicating clearly the order of approximation attempted, and of illustrating methods of proof which I have employed in teaching for many years, but which do not appear to be generally known. Relation between Vapour-pressure and Hydrostatic Pressure . 2. By considering the isothermal equilibrium of a liquid and its vapour in a capillary tube of radius r , Lord Kelvin deduced the well-known relation between the vapour-pressure p at the curved surface and the normal vapour-pressure p 0 at a plane surface, in terms of the surface tension T , and the densities of the liquid and vapour ρ and σ, p—p 0 = 2Tσ/r ( ρ —σ), (1)