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Vol. 75 to the electrode at a different rate than the symmetrical trans form. It follows that the migration current, and hence the limiting current, would be different for the cis ion than for the trans,2SThe situation in the absence of supporting electrolyte is complicated by the formation of electrolyte (nitrite ions, for example) during the reduction, as well as by stirring effects associated with maxima which may not completely disappear even at more negative potentials. Absolute values for limiting currents are, therefore, not reproducible.Experimentally, the cri-dinitrotetramminecobalt-(III) chloride has consistently given slightly higher limiting current values than the corresponding trans isomer in the absence of supporting elec-(28) H.

Müller and Baumberger1 and Müller2 have shown that the dropping mercury electrode can be used to measure the oxidation potential of the quinone-hydroquinone system. In their work the oxidation potential of the system was taken as that value of the potential of the dropping electrode at which the current flowing was zero. This procedure was found to give good results in the majority of practical cases where the solution used was reasonably well poised. However, when the same method was extended to very poorly poised (buffered) systems a fairly large error appeared to be made. Thus, in Müller's2 work, a 10_1 M phosphate buffer of pH 6.9 gave a zero current potential at the dropping electrode corresponding to a pH 7.7 when the buffer was diluted by a factor of 10,000. A more probable value of the pH of this buffer diluted under ordinary conditions would be of the order of 6.7. It is our purpose in the first part of the present paper to offer an explanation for the apparent deviation. 0.240 0.120 0 -0.120 -0.240 Potential of dropping electrode vs. S. C. E.

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