Ar impedance measurements have been made at the vitreous carbon-sodium polysulphide (liquid) interphase at a temperature of 350°C. Molten Na2S3 and Na2S5 were employed. The impedance data confirm that the reaction is purely diffusion-controlled at relatively low overpotentials and that a film IS present on the electrode when the cathodic limiting current is reached. At extreme cathodic potentials, sodium deposition occurs. NOMENCLATURE parallel capacitance. double-layer capacitance. concentration of electroactive species in the bulk of the melt. concentration of electroactive species at the surface of the working electrode. diffusion coefficients. (Bo,R = 0.620 nFD$$ y~1/6 1 potential (uncorrected). standard potential. = (E -E,). reversible potential. overpotential (corrected for ohmic drop), Faradav constant. cm-rent-density. (-1p2 number of electrons involved in charge transfer. gas constant. ohmic resistance. zero frequency impedance of the melt. temperature (KeIvin). Warburg coefficient. minimum value of the Warburg coefficient. value of the Warburg co&cient at the equilibrium potential. kinematic viscosity. absolute viscosity. density. angular frequency. F/R7: RT/n'F= (ZD,."'. effective thickness of the Nernst diffusion layer. stoichiometric number of the oxidised speties, 0. stoichiometric number of the reduced species, R. ratio ol the diffusion coefficients, DdD,. Iz I COS +, real part of the impedance component, III Sin IJ, imaginary part of the impedance component. diffusion impedance. phase angle. rotation speed.