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A modified hydration shell hydrogen bond model recently developed to account for some thermodynamic and spectroscopic properties of aqueous solutions of nonpolar molecules is extended to deal with the effect of a cosolvent that has no hydrophobic groups and that interferes minimally with the hydrogen-bonding behavior of water. The cosolvent is assigned the same molar mass and volume as urea

Fluorine chemical shifts are reported for water/oil/soap/butanol microemulsions in which the soap is potassium 11-(2,2,2-trifluoroethoxy)undecanoate and the oil is 1-(2,2,2-trifluoroethoxy)hexane or a mixture of this material with heptane. In many of the solutions the two fluorinated compounds appear to have identical microenvironments. This reinforces arguments presented recently by others to the effect that microemulsions do not always contain distinct oil-rich and water-rich domains separated by a well-defined interfacial layer.