Approximate analytical methods are presented for the estimation of steady state electrolytic concentration and temperature profiles, and for the determination of stable behaviour under small perturbations in their inlet values. LIST OF PRINCIPAL SYMBOLS reactor width Tafel constants (j = 1 cathode reaction; j = 2 anode reaction) active electrode area electrolyte concertration; C, electrolyte concentration at the electrode surface specific heat of electrolyte Faraday's constant (96,487 C mol -') mass flow rate of electrolyte current density reactor length ith differential operator mass of electrolyte in the reactor molal mass of electrolyte number of electrons involved in electrode reaction (formerly called: valency) volumetric flow rate of electrolyte electrolyte resistance reactor height time electrolyte temperature; T. ambient temperature average overall heat transfer coefficient from dectrolyti to ambient potential drop between electrodes: V&, its minimum value (equilibrium value for the overall electrochemical process) dimensionless axial coordinate axial coordinate dimensionless electrolyte concentration perturbation variable associated with r heat of the electrode reaction dimensionless electrolyte temperature perturbation variable associated with 0 electrolyte density electrolyte conductivity dimensionless time Subscripts E reactor exit, steady state i reactor inlet ;: mean value taken over the reactor length magnitude at zero time of a perturbed variable s steady state (no variation with time) L axial distance. measured from reactor entrance