A Study of Equilibrium Reactions in the Leclanché Dry Cell

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Abstract
This paper deals with the equilibrium reactions in dry cells of the Leclanché type and the products formed as a result of discharge. X‐ray diffraction methods and the petrographic microscope have been employed for the identification of the solid phases under equilibrium conditions. The first part of the paper deals with the so‐called white compounds. The system and several simpler systems were studied over a wider range of compositions than would normally occur in dry cells. When is added to a solution similar to a dry‐cell electrolyte, the first solid phase to form is . With additional the second phase is basic zinc chloride, . No manganese oxides were present in these experiments. The second part of the paper deals with manganese oxides and the role of soluble divalent manganese in typical dry‐cell electrolytes over a wide pH range. Basic solutions contain little manganese in the divalent form. When is reduced in the presence of zinc, hetaerolite, , is formed and this is a product of discharge found in dry cells. The third part of the paper deals with the pH‐potential relationships of manganese dioxide electrodes. In solutions containing free the reduction of is accompanied by the formation of a salt, manganous chloride. The valence change is two. In more basic solutions the is reduced to a lower oxide, manganite, , or, if zinc is present, to hetaerolite mentioned above. The valence change in this case is one. The change in the potential that corresponds to a change of one unit of pH differs in acid and alkaline solutions. In the former it is 0.12 volt and in the latter 0.06 volt. The values observed agree with theoretical values for the reactions involved. In typical dry‐cell electrolytes and over the pH range usually encountered in dry cells, the results indicate that the most important equilibrium reaction is .

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