Plane-parallel condenser with variable electrode spacing for determination of electric permittivity of highly conducting liquids below 1 MHz. Part 1.—Theoretical considerations

A method is described for the determination of the relative electric permittivity Iµx of highly conducting liquids below 1 MHz with a measuring cell consisting of a plane-parallel-plate condenser with variable electrode spacing. Both the electrode effects (due to the impedance of the diffuse double layer at the electrodes) and the edge effects (due to the perturbation of the uniform electric field near the edges of the plates) are taken into account in the expressions for the total capacitance and conductance of the cell. Using a series expression of the measured capacitance in negative powers of the spacing between the electrodes, Iµx can be computed from the coefficient of the linear term, if certain conditions are fulfilled. The correction methods for electrode effects only, as proposed previously by Fricke and Curtis or Shaw may lead to erroneous results.