With electrodes consisting of graphitized active carbon, active carbon, charcoal, soot and graphite, an anodic current was measured in 20% sulphuric acid at a temperature of 100°C and a constant potential of 1100 mV (reversible hydrogen potential = 0 mV). Soot and graphite yielded current densities smaller by factors of 10 and 100, respectively, than those furnished by the three first-mentioned carbon materials. The anodic oxidation is accompanied by evolution of carbon dioxide.After a consumption of approximately 0·5 F/mole, electrode carbon with a specific surface area of 200 m2/g reaches a potential of 1,070 mV in 20 per cent sulphuric acid at 100°C and 2·5 mA cm2. At 12·5 mA cm2, the polarization increases by 100 mV, whereas at 0·25 mA/cm2, the potential is 850 mV. After passage of about 1 F/mole, polarization increases rapidly.From the results obtained by anodic potentiostatic current/potential plots, anodic galvanostatic potential/time curves, cathodic reduction, gravimetric determination of degree of conversion, volumetric determination of carbon dioxide, chemical analysis, X-ray analysis and measurement of the electric resistance during the flow of current, it may be concluded that below the reversible oxygen potential the electrode carbon is almost directly oxidized to carbon dioxide and to a carbon-oxygen compound by about 80 and 20 per cent of the quantity of electricity, respectively, independent of the temperature (55 to 100°C), as well as the concentrations of sulphuric acid (20 to 70 per cent) or phosphoric acid (10 to 85 per cent). In potassium hydroxide solution carbonate is formed by corresponding reactions. The carbon-oxygen compound may contain up to 20 per cent by weight oxygen. Above the reversible hydrogen potential a major proportion of this compound cannot be reduced. It is thermally stable up to at least 130°C and after having been dried at this temperature does not contain water.A minor proportion of the carbon-oxygen compound can be reduced. This proportion does not depend on the degree of oxidation of the carbon and may therefore be regarded to be an oxidic surface layer. Futhermore the quantity of this reducible surface layer is not influenced by the medium used for the oxidation, which may be sulphuric acid, phosphoric acid or potassium hydroxide solution. The quantity, however, is only such that approximately every ninth carbon atom on the surface theoretically carries one elementary charge. The surface layer may, however, also contain a proportion of the non-reducible oxide, since oxygen can be incorporated in the electrode carbon in quantities up to an equivalent of 0·4 F/mole. On this assumption and by further assuming that the “oxide” is homogeneously distributed, every third carbon atom would formally carry one elementary charge, i.e. the atomic ratio of carbon to oxygen would be 6:1.