Electrochemical properties of cellulosic ion-exchange membranes .2. Transport numbers of ions and electro-osmotic flow

Transport numbers of counter-ions in cellulosic cation- and anion-exchange membranes have been determined by both emf and Hittorf's methods for various (1:1)-electrolytes at different concentrations. The transport number derived from the emf data, in general, is lower than the value obtained by the Hittorf method, for any given external electrolyte concentration. This difference is attributed to transport of water occurring across the membrane. Electro-osmotic water transport across the membranes in equilibrium with several electrolytes has been determined at different concentrations. The data obtained have been interpreted in terms of the hydrated ion size of the counter-ions. Volume flow and electrical conductance across the membranes in the presence of various electrolytes have been measured at several electrical potential differences. The experimental results have been interpreted in terms of linear phenomenological equations. These relationships have been used to estimate the magnitudes of the phenomenological coefficients for volume flow and conductance across the cationic and anionic membranes. The validity of the phenomenological equation in volume flow across the membranes has been tested by comparison with the data obtained by direct measurements.