Solvent extraction, as a chemical engineering method, has been the subject of a great deal of research during the past quarter century. The analogy between this operation and the other diffusional processes, distillation and gas absorption has long been recognized; common theoretical foundations have been found for all three processes. In each case mass is transferred from one fluid phase to another across an interface. Recent progress in the field of extraction has been in the direction of determining the quantitative data for the design of equipment in expanding and improving such industrial applications as have already been made, and in developing new modifications of the basic process of simple liquid extractions. Among these developments is that of fractional liquid extraction. The process of fractional liquid extraction is analogous to that of fractional distillation in that the components to be separated are distributed unequally between two fluid phases. In the case of fractional extraction the two phases concerned are the two solvents, and the components to be separated are distributed between these two phases in a manner which is dependent on their relative solubility in the solvents chosen. Somewhat better separation than that attainable by distillation is theoretically possible by fractional extraction in that two solvents are chosen, each of which has a preferential effect on certain components of the mixture to be separated. Yet even in the case of fractional extraction, the possibilities of economy inherent in the thermodynamic advantages of extraction over distillation apparently are not completely attained. The difficulty seems to be one of obtaining better contact between the two phases involved in this and other methods of extraction. The problem of securing intimate and continuous contact between the solvents and feeds involved is one that has greatly vexed the designers of extraction equipment, as evidenced by the numerous patents that have been obtained on ingenious designs. Many different combinations of sprays and baffles, with and without packing, have been developed, the former to produce the necessary dispersion of one liquid within another, and the latter to maintain this dispersed phase in contact with the continuous phase that constitutes the main body of liquid within the equipment. The question of interfacial tension between the two phases is intimately related to the question of contact in that it vitally affects the production and maintenance of the dispersed phase. The effect is mentioned qualitatively in the literature, but little data on the relationship of surface tension to extraction efficiency are found. It was the purpose of this investigation to study the effect of a wetting agent, sodium lauryl sulfate, on the efficiency of the fractional liquid extraction of a mixture of ethanol and ethanol and isopropanol with benzene and water. / Master of Science