Theory of Electrical Migration of Ions

Abstract

THE object of this note is to show that the theory of moving boundaries as developed by Kohlrausch and Weber overlooks the unequal transfer of the common ion at the boundary and consequently rests on a misconception of the conditions on the ‘indicator’ side of the boundary. For a stable boundary it is necessary that the slower moving ion follows the faster moving one and both should move at the same speed. This happens when the concentrations of the two electrolytes AR and BR on the two sides of the boundary are related as in the equation (1) α/n_A = β/n_B, where α and β are respectively the concentrations of the electrolytes AR and BR, and n_A and n_B are the transport numbers of the ions A and B in the electrolytes AR and BR.