The Diffusion Constant of an Electrolyte, and Its Relation to Concentration

Abstract

A semi‐empirical equation is proposed which predicts for potassium chloride, sodium chloride and potassium nitrate in aqueous solution, differential diffusion constants which agree with the experimentally determined values for the three salts within the limits of error of the experiments. The relation of the effective diffusion constant determined in the Northrop‐McBain diaphragm cell to the differential diffusion constant is discussed; it is shown that Cole and Gordon's rule that the effective diffusion constant measured in such a cell is equal to the differential diffusion constant for the mean concentration, is still a valid approximation even when there is a nonlinear dependence of diffusion constant on cencentration, provided the total concentration range involved is less than 0.1 N.