Oxidation-Reduction Potentials in Waterlogged Soils, Natural Waters and Muds

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Abstract
An attempt is made to correlate with other properties the potentials developed at bright platinum electrodes. In wet soils and muds, the diphenylamine reaction is positive and replaceable ferrous iron disappears above a potential of Eh+ 350 mV. (approx.) at pH 5. In natural waters, ferrous iron is only detectable below this potential, while below the same point ammonia tends to replace nitrate and sulphides to replace sulphates. Such potentials in natural waters are found at low oxygen concentrations, 8% of saturation or less. Data are given for the effects of oxygen on the drifts of potential. The apparent potentials estimated with various oxidation-reduction indicators agree with the electrode potentials in the critical range examined. The potentials appear to be related to ecologically reversible systems and suggestions are made as to their physico-chemical nature.

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