Lars Onsager's Contributions to Electrolyte Theory

About one third of Onsager's scientific papers are devoted to electrolyte theory. He started his scientific career in this field in 1925, just after finishing his diploma thesis on absorption spectra in Trondheim. The first problem he attacked was the theory of conductivity of electrolytes. He was then 22 years old.

We have to remember that in the first quarter of this century one of the great open questions in physics and chemistry was the discrepancy between the experimentally observed data for conductance and thermodynamic functions of solutions and the theoretical formulae which were then available. The theory of solutions was at that time based on the work of Arrhenius and Van't Hoff and on Planck's theory of ideal solutions (see Falkenhagen¹). As a freshman chemist in Trondheim, Onsager was introduced to this theory, according to which the. properties of electrolytes should be additive with respect to the constituent ions. However the experiments by Kohlrausch and other workers had shown strong deviations from the theoretical curves and, in particular, a characteristic scaling of the deviations from the ideal theory with the square root of the concentration. Many of the leading physicists and chemists of that time considered the so-called anomalies of electrolytes as a great challenge for theorists…