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Current‐voltage characteristics for the reduction of oxygen at silver and alloy electrodes formed with silver and elements having oxides of low electron affinity were studied in pre‐electrolyzed and in ordinary 15% KOH solution. In impure solutions or at the alloy electrodes straight Tafel lines were obtained, but with pure silver in pure solutions no such behavior was found. This is taken to indicate a dynamic surface of varying catalytic activity. With silver‐magnesium oxide surfaces, a potential about 100 mv higher than with pure silver was obtained at open circuit as well as under current drain. The possible mechanistic significance of the results is discussed in terms of the physical properties of the material and the behavior of the constituents in gas‐solid reactions.

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The rates of the magnetic ortho-para conversion of hydrogen adsorbed on some diamagnetic solids are determined and the true half lives are found by means of adsorption measurements. True half lives of 1 to 6 minutes are found with BaSOl and 2 samples of Ti02 at 90 ' IC. The appearance of a strong blue color in a sample of Ti02 due to loss of oxygen on heating in uacuo and disappearance of the color on contact with oxygen at room temperature is accompanied by changes in surface paramagnetism, as determined by the parahydrogen conversion. A method for estimating the number of extra-electrons due to surface defects is indicated ; for this, the found true conversion rate is compared with the true conversion rate in presence of measured amounts of molecular oxygen adsorbed on diamagnetic surfaces. The true half life on a solid D20 surface is found to be about 10 hours; this is shown to be'the expected order of magnitude if compared with conversion rates of hydrogen, dissolved in diamagnetic liquids.Charcoal a t liquid air temperatures is a good catalyst for the ortho-para conversion of hydrogen.a A short review of the work done on this type of reaction up to 1934 is found in Farkas' book.4 The "low temperature mechanism" in this case involves a nuclear spin inversion in the hydrogen molecule due to inhomogenous magnetic fields in the surface of the catalyst; the conversion is of the same type as found with paramagnetic The magnetic fields have been assumed to be due to "unsaturated valences" in the surface of the charcoal. The true half-lives of the conversion,* as measured in a static system, were between a few seconds and about 40 minutes for different charcoals. Conversions of a similar nature were also observed on other diamagnetic solid^.^ However, in most cases no quantitative conclusions can be drawn as adsorption data were not always given, and in some cases a chemical mechanism, analogous to the H2 + D P reaction, may have been involved.