A study of the mechanism of the reduction of manganese dioxide in strongly alkaline electrolytes has shown that the rather complex process may be considered as occurring in three steps. The first is the simultaneous reduction to form a divalent manganese compound, presumably, normalMnfalse(OH)2 and an intermediate oxide tentatively identified as Mn4O7 ; the second step is the electrochemical reduction of Mn4O7 to form both Mn3O4 and normalMnfalse(OH)2 ; the final step is the electrochemical reduction of Mn3O4 to Mn3O4 and normalMnfalse(OH)2 . Both chemical and x‐ray diffraction analyses of cathodes at various stages of reduction are presented.

The reactions at the cathode of the Leclanch~-type dry cell are considered in terms of three heterogeneous chemical reactions for which there is advanced a plausible mechanism, leading to a unified theory of the cathode process. When reviewed in terms of this theory, the numerous observations of others that formerly have appeared to be incongruous are correlated and rationalized in terms of the over-all cathode reaction.

The cathodic reaction in the Leclanché dry cell has been described previously as consisting of two steps. The first of these steps is the electrochemical reduction MnIV to MnII. The second step is the chemical reaction of MnII produced in the first step with unreacted MnIV to form an insoluble MnIII compound. Two chemical reactions can occur producing normalMnOOH and normalZnO·Mn2O3 , manganite and hetaerolite, respectively. The latter reactions, termed recuperation reactions, have been subjected to analysis and rate studies to determine the effects of factors such as pH, concentration, and temperature. These reactions are found to be slow enough to limit dry cell operation under certain conditions. The more active depolarizers, such as electrolytic MnO2 , show more rapid recuperation reaction than the natural MnO2 ore. The basic concepts of heterogeneous chemical kinetics have been applied to this problem, and a simple mathematical equation was found which was applicable to all the data. These findings, correlated with previous results, support the cathodic reaction mechanism theory previously presented.

A new and improved separator medium for the aluminum dry cell is described. It provides an adhesive contact with the anode and a satisfactory electrolytic contact with the cathode. The method by which this separator is prepared involves a new technique which is described. The separator layer significantly improves the keeping quality and delayed service performance of the aluminum‐manganese dioxide cell.

The surface area of samples of manganese dioxide is shown to be an important factor in influencing its behavior. Four samples of MnO~ of widely different origins, electrolytic, activated, natural ore, and synthetic pyrolusite, with total surface area values of 52.8, 50.5, 7.4, and 1.6 mS/g, respectively, are used as examples. The rates of the recuperation reaction at temperatures of 21~ 50~ are shown to be related to the total surface area of the oxides by a complex relation, dependent on temperature and other factors. The product of the reaction MnOOH develops on the surface and in the pores of the original MnO~ particle, thus increasing the diameter and resulting in reduced pore volume, respectively. The MnOOH made under these conditions, from all four starting materials, appears as rod-shaped units in electron micrographs.