Vol. 61 homologs agree well with the suggestion that these compounds react with molecular oxygen to form quiñones and hydrogen peroxide.4. Hydrogen peroxide oxidizes the sulfite to sulfate.5. If the quinone formed has at least one nuclear hydrogen, it reacts with the sulfite with formation of the corresponding hydroquinone monosulfonate.6. The hydroquinone monosulfonate is autoxidized and the oxidation products undergo the reactions mentioned under (4), and, if the conditions are fulfilled, (5); thus, hydroquinone monosulfonate and toluhydroquinone monosulfonate form the disulfonates.7. The oxidation of hydroquinone in sulfite solution does not follow a simple first-order law. The dependence of the reaction rate on the con-centrations of oxidand and oxygen, and on the pH are in good agreement with a mathematical expression found on the assumption that the inhibitory action of sulfite is due to the removal of quinone which acts as a catalyst for the autoxidation.8. The linear dependence on the sulfite concentration which has been observed throughout the whole range of the experiments does not follow from this expression. 9. The inhibitory action of thiol compounds (cysteine, thioglycolic acid, thiocresol, etc.) also agrees with the assumption that their action is caused by the removal of the catalyzing quinone.10. The autoxidation of various reaction products of quiñones with thiol compounds has been measured.

Vol. 60 thiazine, thionol, with the values given by Clark3 for two other thiazines, Lauth's violet and methylene blue. At pH 7 the E'0 for thionol is 0.158, for methylene blue 0.011, and for Lauth's violet 0.062 at pH 6.967, and 0.045 at pH 7.517, which gives 0.061 at pH 7 by interpolation. These values place thionol appreciably closer to the oxygen electrode than the other two thiazines, being about midway between l-naphthol-2-sulfonate-indophenol and 2,6-dichlorophenol-indo-ocresol. This is in agreement with the observation that spontaneous oxidation of leuco thionol exposed to air occurs more slowly than is the case with methylene white at the same pH. Like-wise, the reducing power of a given sample of urine is more readily demonstrated with thionol than with methylene blue.

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