In the polarographic analysis of many, but not all, dyes representing reversible oxidation‐reduction systems, in addition to the “regular” wave with a half‐wave potential equal to the E o ′ of the system, a small wave, the anomalous wave, was found at a more positive potential. The separation of these waves varied with different dyes and was largest in the thiazines; it decreased under a variety of conditions in a similar way as anomalies (deviations from Beer's law) found in spectroscopic studies of such dyes, and thus suggests a common cause. In very dilute solutions only the anomalous polarographic wave was obtained, which reached a limiting height at concentrations of about 10 −4 M . At higher concentrations the second, “regular,” wave formed and increased without limit; the sum of the two waves was proportional to the concentration of the dye. A peculiar relationship between the height of the anomalous wave and the drop‐time of the dropping mercury electrode was found, pointing to a correlation between the polarographic results and known effects of dilution on potentiometrically determined potentials. The results are discussed in connection with Brdička's hypothesis of selective adsorption of the leuco form of the dyes. Included in this study are illustrations of: (a) the polarographic behavior of an oxidation‐reduction system in which the reductant is much less soluble than the oxidant; (b) the effect of temperature on semiquinone formation; and (c) the effect of ethyl alcohol on the diffusion current of reversible dyestuffs.
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O. Müller (1945) studied this question.