Аннотация:The authors studied the effect of formaldehyde on the adsorption behavior of cinnamaldehyde, which like formaldehyde is a surfactant component used in tin and tin-alloy electrodeposition. The authors measured electrocapillary ( sigma vs E) curves in aqueous-ethanolic 1 N Na//2SO//4 plus 1. 74 N H//2SO//4 solutions to which different amounts of cinnamaldehyde were added while formaldehyde was or was not present. The alcohol, in a concentration of 1 M, was added to the solution in order to raise the solubility of the cinnamaldehyde. Experimental results show in the cathodic region, measurements were possible only to a potential of minus 1. 0 v. At more negative potentials appreciable currents were observed due to cinnamaldehyde reduction. The cinnamaldehyde substantially lowers the interfacial tension of mercury, both in the absence and presence of formaldehyde. The curves recorded in the base electrolyte and insolutions with additive do not merge in the anodic region, probably since the cinnamaldehyde molecules which because of pi -electron interaction are in a flat position fail to desorb from the mercury surface.