'Physical chemists working in the 1880s and 1890s had begun to portray electrical potential as a product of the internal dynamics of battery cells. By introducing a semi-permeable membrane between differently-concentrated solutions of liquids, chemists argued, it was possible to model electrochemical phenomena in terms of the production and release of 'osmotic pressure': galvanic current was produced by the migration of ions between differently-concentrated regions of a battery cell (Barkan 1999, 46-57).'