Correlation of density and refraction index for liquid binary mixtures containing polyglycols. Use of the group contributions in the Lorentz-Lorenz, Gladstone-Dale and Vogel equations to evaluate the density of mixtures

Experimental density, ρ, and refractive index, n, of several simple compounds, polyglycols and their mixtures are correlated by the Lorentz-Lorenz, Gladstone-Dale and Vogel expressions in conjunction with the group contribution method. For several binary mixtures values of ρ are given as a function of known n at different mass fractions in the whole composition range. Values obtained by the different equations are comparatively analyzed. The linear mixing rule between specific refractions of mixture and those of pure compounds, provided by the above mentioned correlations, is extended to new correlations, where the specific refractions of pure compounds are evaluated from the different sets of group contributions corresponding to the Lorentz-Lorenz, Gladstone-Dale and Vogel expressions. Comparisons with the experimental results are reported with a discussion on the possible origin of the corresponding discrepancies.