The potential difference occurring in a Donnan equilibrium and the theory of colloidal behaviour

Abstract

It is contended by Loeb that the Donnan Membrane Equilibrium, involving the presence of an indiffusible ion, is the basis of the colloidal properties of a protein solution. While the possibility of this conclusion is admitted, it is pointed out that one of the chief arguments employed in its favour by Loeb is incorrect. Loeb shows that the P. D. observed experimentally between a protein and a non-protein solution separated by a membrane agrees very exactly with that “calculated” from the difference in hydrogen-ion concentrations also observed experimentally, and concludes that this supports his theory. As a matter of fact, this equality is a necessary and inevitable consequence of the manner in which his observations were made and of general thermodynamical reasoning, and its proof is independent of any theory of the mechanism by which the P. D. is produced.