The Second Virial Coefficient for Gas Mixtures

The second virial coefficients B for methane, normal butane, and three mixtures of these gases were evaluated from the experimental data, and the interaction term B12 computed for methane-n-butane from 150° to 300°C. The results were used to study the methods of combination of constants in an equation of state. Computation of B12 from a Lennard-Jones expression similar to that used for a pure gas with σ and θ evaluated as σ12=½(σ11+σ22) and θ12=θ11½θ22½ where the subscripts 1 and 2 refer to the pure components gave exceptionally good results. This suggested a new method of combination of constants in the equation of state which led to the best results of any method so far used.