Anions approach a cathode by diffusion and convection rather than by electrolytic migration in view of the adverse potential gradient. The rate of transport of anions of valence zj toward a cathode is decreased appreciably if the potential difference across the diffusion boundary layer is of the order of, or greater than, . This effect may account for the prevention of the reduction of hypochlorite at a cathode covered by a diaphragm of chromium oxide. Similarly, the rate of transport of cations toward an anode is decreased appreciably if the potential difference across the diffusion boundary layer is of the order of, or greater than .