New approximations to the virial equation of state for fluids

A simple equation of state for square-well (SW) molecules has been derived by approximating the radial distribution function in the virial equation by a corresponding function for hard spheres. If optimum parameters for the SW potential are chosen, experimental P-V-T data for methane, ethane, nitrogen and (liquid) octane can be quite satisfactorily described by the equation, except near the critical point.