A three parameter equation of state for gases

This paper presents an equation of state having the following features. It holds for many gases for temperatures from near critical to about five times critical, and for densities from zero to a little above critical, with the exception of the immediate vicinity of the critical point. It also holds for mixtures. Its accuracy is excellent, in most cases within experimental error. Exceptions are H₂O, CO₂, H₂ at high density. In the best cases the rms deviations in the compressibility factor are a few parts in ten thousand. In relatively poor cases the deviations are a few parts per thousand.The equation has a single reduced form for all gases, and requires only three characteristic parameters to identify each gas: a reducing parameter, T_B; a reducing density, d_o; and a dimensionless parameter, k_B. These three parameters are readily (though often not uniquely) evaluated from experimental data. Besides determining the PVT behaviour of a gas, including its virial coefficients, these three parameters are directly related to those in the common three-parameter intermolecular potentials.