A com. active C, 20 g, was oxidized 3 h with 130 g aq. 65% HNO3 at room temp. or at the acid's b.p., washed until neutral, dried 3 h at 110degreesC, and studied by polarography (0.0 to -1.1 V), voltammetry (-2.0 to +1.5 V), potentiometry, and FTIR. The more oxidized was the C surface, the worse were the electrode properties. The higher the temp. of oxidation, the more oxygen groups occurred at the C surface. Complementary studies by instrumental methods are required to evaluate the C surface.