The Thermal Conductivity of Organic Vapors. The Relationship between Thermal Conductivity and Viscosity, and the Significance of the Eucken Factor

The thermal conductivities of thirty‐one polar and nonpolar organic vapors have been determined at pressures up to one atmosphere, over a temperature range from 40 to 160°C. The relation between thermal conductivity and viscosity is discussed in terms of the expression: $$\frac{K^{0}M}{{\mathrm{\eta Cv}}_0}\mathrm{=f=}\frac{f_{\mathrm{trans}}{\mathrm{Cv}}_{\mathrm{trans}}{\mathrm{+f}}_{\mathrm{int}}{\mathrm{Cv}}_{\mathrm{int}}}{{\mathrm{Cv}}_0}$$ where, following a suggestion by Eucken, the ratio f is divided into separate components f_trans and f_int, corresponding to the different rates of transfer of translational and ``internal'' (vibrational and rotational) energies. Experimental values of f are not in accord with Eucken's original assumption that f_int=1. For nonpolar vapors f_int increases towards a high‐temperature limit which is close to the theoretical value of 1.3. For polar vapors f_trans appears to be less than the theoretical value of 2.5, the decrease depending on the polar character of the molecule. These results are discussed with reference to energy exchanges occurring during collisions between complex molecules.