AWract-A flow cell electrode has been designed to measure diflusion coefficients in electrochemical solutions. Potassium ferri-ferrocyanide solutions containing different amounts of sodium carboxymethylccllulose were studied. The diffusion coehicient of ferricyanide ion and the rheologkal properties of these solutions were measured at various temperatures. NOMENCLATURE electrode area (cm') molar concentration of solute A diffusion coefficient (cm2 . s -') pipe diameter (cm) activation energy for diffusion (Cal. K -I) activation energy for viscous flow (Cal. K-') Faraday constant (C . mol-') limiting current (mA) rheological parameter, equation (2) (g, cm-' s*'-2, power law constant (g. cm-' .s"-') mass transfer coefficient (cm. s-') electrode length (cm) power law constant (dimensionkss) molar flow of the component A (mol. se1 cm-') absolute temperature (K) mean velocity in a pipe (cm. 5-l) number of electrons involved in the electrochemical reaction wall shear rate (s -I) fluid density (g .cn-') wall shear stress (g.cm-l.s-z) viscosity (g.cm-'.s-r) Reynolds number, equation (5) Sherwood number (k . d/D) Schmidt number, equation (6).