Second virial coefficient of mixtures

The theoretical foundations of these rules are, however, rather weak the first one is supposed to result from a formula derived by London for dispersion forces between unlike molecules, the validity of which is actually restricted to distances much larger than r the second one would only be true for molecules acting as rigid spheres. Many authors tried to check the validity of the combination rules by measuring the second virial coefficients of mixtures. It seems that within the experimental accuracy (unfortunately not very high) both rules are roughly verified.24... 

Cruickshank A.J.B., Windsor M.L., Young C.L. (1966). The Use of Gas-Liquid Chromatography to Determine Activity Coefficients and Second Virial Coefficients of Mixtures. I. Theory and Verification of Method of Data Analysis, Proc. R. Soc. London, A, vol.295, n°1442, pp.259-270. ISSN 1471-2954... 

Chromatography to Determine Activity Coefficients and Second Virial Coefficients of Mixtures, Proc. R. Soc. 1966, A295, 259-270. 

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