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The method of studying molecular association by the use of Piekara factor (ΔIµ/E2) measurements together with electric permittivity (Iµ) is applied to the conformational equilibria in the liquid phase of 1,2-dichloroethane and dimethyl carbonate at several temperatures. Dipole moments of the gauche conformer in the first molecule as well as the temperature and solvent dependence of the equilibrium constant are in good agreement with other data. Results on dimethyl carbonate indicate the presence of 3 conformers in the liquid; the equilibria are studied by assuming values for the dipole moments.

A modification of Onsager's model taking into account molecular anisotropy is proposed for mixtures of polar liquids. Two formulae giving the concentration dependence of the electric permittivity and its variations under the influence of strong electric fields (dielectric saturation) are derived.Comparison with experimental results for several mixtures shows that the variation of the dipole moments determined with these formulae over the whole range of concentration of a polar compound dissolved in a non-polar as well as in a polar solvent is less than 5 %. An application to the study of molecular association is proposed.

The molecular theory of dielectric properties of liquid mixtures proposed earlier is extended to cases in which the components of the liquid interact chemically.The chemical equilibrium modifies the non-linear behaviour. The resulting equation provides the possibility of adding non-linear measurements to ordinary dielectric studies of associated liquids and therefore to investigate molecular interactions in more detail.The study of pyridine + chloroform mixtures is carried out as an example. Variations of equiibrium constant with the electric permittivity of the liquid are observed. They explain discrepancies between results obtained by different techniques (i.r., n.m.r.). Variation of the electrostatic part of the solvation energy explains this phenomenon satisfactorily.