The purpose of this investigation was to determine the effect of a homologous series of solutes on the overall mass-transfer coefficients for liquid-liquid extraction. The solutes used were ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The carrier solvent was water, and the extracting solvent was toluene. The phase diagrams for these systems were determined at 30 °C. The phase diagrams were found to be similar and to have maximum solubilities ranging from 69.9 to 76.7 weight per cent of solute.. Three of the systems exhibited solutropes, and the system containing tetraethylene glycol dimethyl ether approached a solutrope at a solute concentration of approximately 64 per cent. A countercurrent-flow, 1-1/2-inch diameter, horizontal, pyrex glass tube, eight feet long with an interfacial surface area of one square foot, was used for the extraction tests. The feed concentration ranged from 9.10 to 15.18 weight per cent of solute in water. The flow rates of the water phase varied from 15.20 to 34.72 pounds per hour, and the solvent phase flow rates varied from 18.86 to 33.83 pounds per hour. The overall mass-transfer coefficients based on the water phase were found to vary between 0.0098 and 0.0133, 0.0036 and 0.0051, 0.0035 and 0.0063, and 0.0023 and 0.0063, for the systems investigated. The solvent phase coefficients were found to vary between 0.0097 and 0.0149, 0.0057 and 0.0079, 0.0092 and 0.0172, and 0.0087 and 0.0237. The overall coefficients were not affected appreciably by changing the molecular weight of the solute. Also, experimentally determined values of the overall coefficients based on the solvent phase did not agree with those values of the coefficients calculated by previously determined equations. / Master of Science