No abstract

A direct current method has been devised for measuring the internal resistance of dry cells. Data are presented which show that the internal resistance of a Leclanch6 type of dry cell is greater when measured at low current drains than at high current drains. This difference is believed robe due to a fihn formation on the zinc anode. It is also shown that during discharge the drop in terminal voltage of a dry cell owing to an increase in internal resistance is small. It is believed that pH changes of the electrolyte at the electrode surfaces and the change in the composition of the surface of the manganese dioxide electrode account for most of the potential drop when a Leclanch6 cell is discharged.Studies made m~ magnesium-manganese dioxide cells show that these cells undergo greater instantaneous voltage fluctuation than the conventional Leclanch6 cells. This voltage fluctuation is due to a high resistance coating on the magnesium anode. The direct current method for measuring internal resistances of dry cells described in this paper could be useful in the study of film formation on the surface of magnesium electrodes.