Deviations from the principle of corresponding states

Certain intermolecular potential energies which are functions of the relative orientation of the molecules may be reduced to a form similar to that of simple spherical molecules by taking a statistical average over all orientations. Such an average energy is an explicit function of the temperature. Two such intermolecular potentials are used to calculate the difference in the equations of state of assemblies of elliptical molecules (part I), of dipolar molecules (part II), and an assembly of equivalent spherical molecules, which conforms to the principle of corresponding states. These calculations are compared with the observed deviations from this principle of the vapour pressure and rectilinear diameter of thirteen liquids.