The potentiometric method was applied to the study of the influence of cyanide and of hydroxyl ion on methemoglobin. Both of these ions appear to combine with the iron of the methemoglobin molecule and reduce its oxidant activity. From the magnitude of the effect produced by cyanide and by variation in pH on the oxidation-reduction potential of the methemoglobin-hemoglobin system, it is concluded that cyanmethemoglobin and alkaline methemoglobin are undissociated ferric compounds, the first with cyanide and the second with hydroxyl.

Electronic formulas, based on the electrical properties of the hemoglobin derivatives, are suggested.

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