Crossover from singular to regular thermodynamic behavior of fluids in the critical region

A procedure is presented for constructing equations for the thermodynamic properties of fluids in the critical region which incorporates the crossover from Ising-like scaled behavior near the critical point to regular (i.e., classical) behavior away from the critical point in a theoretically consistent manner. When the procedure is applied to a truncated classical Landau expansion, we obtain an accurate representation of the thermodynamic properties of carbon dioxide in both the asymptotic critical region and in the crossover regime.