Vol. 63 electric medium and the well known rule of electrostatic forces would apply.Equation 4 yields at «mo = 0 (pure glycol) the value In « = 0.207 and AH* = 5.4 kcal./mole. This predicts the dielectric constant of ethylene glycol at 25°to be 43 using the above assumption while the measured value is 37.7. Such agreement as this is satisfactory in view of the crudeness of the assumptions. Further investigation to determine the actual polymer phase composition (in terms of water content) and measurements of at varying temperatures to separate out entropy effects are needed to determine whether AH* actually inversely proportional to dielectric constant.If the linearity of log with amo observed is general to other solvating solutions, e.g., water plus alcohols, this simple rule will permit data on the diffusion of ions in ion-exchange polymers in partially non-aqueous media to be extended with a minimum of experimental effort.The present approach to the conductivity of a partially hydrated ion-exchange polymer may differ only formally from that of ion pair formation employed by Gregor19 and that of hydration shells employed by Glueckauf.20

Partial molal energy of mixing, kcal./mole (caled, by eq. 18a).functions for the pure hydrocarbons were not measured by Simons, et al., but were taken from other sources in the literature. In view of the agreement shown for the hydrocarbons in Fig. 1, it is probable that the vapor pressures used for the hydrocarbons are accurate while those measured for the fluorocarbons are not. ConclusionsThe heats of mixing paraffin hydrocarbons with fluorocarbons of the same carbon atom skeleton in liquid solution may be calculated by the Hildebrand-Scatchard theories when the interaction between unlike pairs of molecules in solution is properly evaluated. Insofar as the heats of mixing are concerned this interaction may be evaluated on the basis of London's dispersion forces, but the relatively large ratio of ionization potentials of hydrocarbons and fluorocarbons, heretofore neglected, must be taken into account as they appear in the London treatment. The correction to the calculated partial molal heats of mixing arising from the ratio of ionization potentials in the two systems w-C5Fx2:rc-C6Hi2 and n-C4Fi<>:«-C4Hio amounts to about 25% of the total calculated values.

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The empirical correlations of-the second virial coefficient of pure compounds as a function of temperature are shown to be satisfactory for mixtures of gases. From the London theory of dispersion attraction, the Lennard-Jones potential energy function, and the theory of corresponding states, the critical-pressure and critical-temperature characteristic of an unlike pair interaction are obtained in terms of the critical values of the two species involved in the pair interaction. These unlike pair critical values are

Formulas for the unlike-pair parameters in terms of the like-pair parameters for the Mie (n, 6) potential energy model are examined for their abilities to predict cross-term second virial coefficients. Formulas based on the London dispersion formula and an assumption of geometric mean repulsion energies are tested and shown to apply only for special cases. A geometric mean rule for each one of the parameters including the repulsion exponent, n, is shown to have far more general applicability and to give high accuracy in predicting the cross-term second virial coefficient. Potential energy parameters for several molecules are obtained using corresponding states relationships and the Dymond and Alder numerical potential energy function for argon. The geometric mean rule for the energy and distance parameter is shown to perform well for predicting the cross-term second virial coefficient for mixtures of molecules which obey the Dymond and Alder potential energy function.