Fur einen Kondensator der Kapazitat je Flacheneinheit C*, der tiber einen Widerstand dieser Charakteristik entladen wird, gilt dann . dQ* dU AIDie Integration dieser Differentialgleichung (mit der Randbedingung V = VA fur t = 0) ergibt: The pulse potentiostatic method for measuring of electrode capacitance was applied in the study of passivation and of properties of the passive film on iron in a neutral borate buffer solution, pH 8.41. Capacitance at the corrosion potential C = 38 (LF/cm l is considered to correspond to the double layer capacitance. At anodic polarization in the active dissolution range an adsorption isotherm, resembling to the Langmuir isotherm, was observed. The capacitance-potential relation under steady state conditions in the passive range and the thickness-capacitance plot derived from it were used to calculate the dielectric constant of the barrier layer of the passive film. The zero-field potential extrapolated from the capacitance-potential plot is in agreement with previous measurements. Additions of nitrate ions up to 0.50 mol/l do not have any effect both on the passivation characteristics and on the properties of the passive film. Sulphate ions, on the other hand, are responsible for the reactivation in the passive range, as well as for an increased conductivity of the film, attributed to incorporation of these ions in the film. The dynamic measurements of capacitance in the range of steady state film growth yielded a linear relation between capacitance and log of time, from the slope of which the field coefficient B was estimated.