The equations necessary to calculate the potential drop across the diffuse layer and its differential capacity are derived for 1: 1 electrolytes on the basis of the Eigen and Wicke theory for concentrated electrolyte solutions. The results of this model are then compared. with Monte Carlo data for more concentrated solutions and solutions with ions of large diameters. It is shown that the Eigen-Wicke model is inadequate because it fails to consider the change in potential at a given ion due to its surrounding atmosphere.