The phase equilibria of dilute aqueous solutions are treated separately from those of dilute organic systems due to water's unique structure and hydrogen-bonding characteristics. As a result, traditional predictive methods (UNIFAC, ASOG, etc.) tend to be only moderately successful. In addition to inverse solubility measurements, we describe new direct and indirect techniques for precisely measuring these values which are more accurate. A database is compiled from data measured by using these techniques. The data were evaluated and suspect points removed. The data were correlated linearly with the solute solvatochromic R, , and π*, solute and solvent molar volume, solute vapor pressure, and the solute gas-liquid partition coefficient between hexadecane and an inert gas phase, log L 16 . The correlation fits the data to within an average absolute deviation of 0.294 ln units. The correlation provides a direct and relatively accurate method for estimating Henry's constants and thus limiting activity coefficients of nonelectrolytes in water.

A new measurement technique for activity coefficients at infinite dilution has been developed involving the construction of a very dilute vapor phase and the accurate determination of its dew point. This method is especially applicable to systems of low solute relative volatility, precisely where other methods such as differential ebulliometry and headspace gas chromatography become less precise. Data are reported for ym for N, N-dimethylformamide, dimethylsulfoxide, and Nmethyl pyrrolidone in water over a range of temperatures.