q ABSTRACTThe derivative discharge curves for ~-and 7-MnO2 down to ,~0.7V open cell voltage were resolved into one characteristic set of four normal distribution functions (peaks). Only peak positions shift to lower voltages for ~-compared to 7-MnO2. When the ratio of electrolyte to MnO2 is increased, the first peak increases while the other peaks decrease (the second passes through a maximum) and at a mass ratio above 14 only the first peak remains. The first peak represents direct reduction of Mn 4+ to soluble Mn e+ which ends at pH 7.5, the second is attributed to the formation of Mn(OH)~, and the third to the formation of MnOOH. Each reaction takes place throughout the depolarizer pellet before the next becomes significant. Electrochemical tests for the evaluation of the dry cell activity of MnO2 samples should be performed at the same mass ratio of electrolyte to MnO2 as used in commercial dry cells. Higher ratios lead to an overestimation of samples with Iow activity.