ON CATION AND WATER TRANSPORT NUMBERS IN CELLULOSE-ACETATE MEMBRANES

The cation transport number (tBAR+) and the water transport number (tBAR(w) of a cellulose acetate membrane separating two solutions of monovalent electrolytes have been determined. In order to get the true cation transport number, we have developed a new method for fitting the experimental emf data of a concentration cell (E*) as a function of the difference in osmotic pressure among the external solutions (DELTA-pi). The results show a strong dependence of tBAR+ and tBAR(w) on the external salt solution. The selectivity of the membrane decreases with concentration; tBAR+ even reaches a lower value than that corresponding to a free solution. Finally, it has been found that there is almost no influence of the electroosmotic water transport on the membrane potential.