Oxygen was removed by a current of nitrogen, and a known weight of potassium iodide was added.The data for the cells made with these solutions are given in Table II. The reproducibility was better than for the first series; differences between duplicates were not larger than 0.09 mv., and the average was 0.03 mv.The quantity p in Table II is the ratio of the molality of un-ionized acetic acid to the molality of acetate ion. The values for Ejs were calculated by the equation4*1 K = Elf( y) = En + k log [KI] + k log p + k log XhOAo in which KHoac is the ionization constant of acetic acid for which the value 1.754 X 10-5 was used.6 The value of f(y) is small and should become zero when p = 0. The relation of E\[ to ionic strength is shown by Curve II of Fig. 2. Extrapolation to infinite dilution gives a value for £"5 in good agreement with the value from the first series of cells, and £25 = -0.0405 v. can be

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