Salting Out Parameter Determination by Long and McDevit

In 1952, F.A. Long and W.F. McDevit (S15) presented the results of their extensive study of the activity coefficients of nonelectrolytes in aqueous salt solutions. Their results for the molar activity coefficients of undissociated nonelectrolytes in salt solutions were based mainly on solubUity, distribution and vapor pressure measurements. They noted that since the activity coefficient for any species i could be expressed as a power series to show the effects the concentrations of all solutes j in the solution  

Due to the low concentrations, interactions between the solutes would not be expected  

The ion-molecule interaction term, kg, is the one that is most often calculated. Long and McDevit felt that the nonelectrolyte self interaction term could safely be ignored only when the nonelectrolyte solubility was vei low as in the case of the nonpolar electrolytes hydrogen, oxygen and benzene. For the more soluble polar nonelectrolytes, such as ammonia, carbon dioxide and phenol, the self interaction term is of much greater importance and should be determined where data is available. 

Long and McDevit outlined the following methods for calculating the activity coefficient of a nonelectrolyte as a function of the salt concentration of the solution  

The data used by Long and McDevit was presented by many authors. It consisted of the saturation concentrations of nonelectrolytes in binary aqueous solutions and in salt solutions of varying concentrations. Both types of measurements can be found at different temperatures in the literature. 

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