EOS mixing rules and the quadratic concentration dependence of the second virial coefficient

The usual one-fluid mixing rule applied to the Alder-polynomial is generally not consistent with the required quadratic concentration dependence of the second virial coefficient. Consistency might have been achieved by refitting the constants, but it does not agree with argon data. The mixing rule written directly to the compressibility factor does not suffer from the consistency problem, but it involves separate mixing rules for different power combinations of u and V0.