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V. J. FRILETTE
The changes with time noted in Fig. 5 are greater than would be expected if the entire solution in each half-cell remained a t uniform concentration. Chloride ion transfer rates of the order of gram ions per hour are to be expected. Hence it is supposed that the major concentration changes resulting from diffusion must be limited t o small volumes adjacent to the membrane surfaces. This view is confirmed by the measurements illustrated in Fig. 6. I n this experiment the solution in the cell was stirred rapidly a t four minute intervals. The cell solutionb were not changed and the potentials were measured with the solutions at rest in the cell. As may be seen the original e.m.f. could be restored at will by mixing. However, it should be noted that on the basis of the above discussion the highest e.m.f. obtained is by no means the reversible e.m.f. for the cell reaction considered. I n the dilute solutions used for these measure-
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ments we concluded that reversible e.m.f. values within 0.1 mv. have been measured only for membrane cells exhibiting a potential >9S% of the ideal value. For these membranes the deviation is almost entirely because of reversible water transfer. The chloride transference number is almost negligible. For membrane cells showing a potential
