The application of Dalton’s law of partial pressures to the osmotic pressures of mixtures of protein salts and diffusible salts has been discussed in a previous communication. The observed osmotic pressures of protein salts, measured with membranes permeable by water and other crystalloids but impermeable by the protein, are difficult to interpret until they have been analysed in terms of the partial osmotic pressures of protein ions and of diffusible ions. The partial osmotic pressure of the protein ions, symbolised p p , may be calculated from the observed osmotic pressure p by the formula p = p p + P i , in which P i represents the “ion pressure difference,” or the pressure due to the excess of diffusible ions inside the membrane. The provisional estimates of these partial pressures, p p and p i , published in the paper referred to above, depend upon a number of simplifying assumptions concerning the deviations from the ideal solution laws in mixtures of protein salts and diffusible salts, and the range of application of the approximate formulæ employed is restricted to mixtures in which the equivalent concentration of the protein salt is relatively small. In order to confirm the provisional results and to interpret the osmotic pressures of concentrated protein solutions, a more general method, based on Gibb’s fundamental equations, is developed in this paper.

The thermodynamic analysis of the observed osmotic pressures of protein salts in solutions of finite concentration. (1929). Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, 126(800), 16–24.