A new approximation is presented for the thermal diffusion factor of an almost Lorentzian gas mixture (m2/m1Lt;1,x1rarr;1), which has better convergence properties than the Chapmanmdash;Enskog approximation. The results are given as the exact Lorentzian results plus correction terms in powers of the small quantitym2/m1. Numerical tables are given for the expminus;6, 12ndash;6, 9ndash;6, and 28ndash;7 potentials, and for repulsive exponential and screened Coulomb potentials. It is also shown that it is now possible to give simple formulas by which the thermal diffusion factor can be calculated accurately at all temperatures and compositions of ordinary interest, and for most values of the mass ratio. These formulas are summarized, and checked by comparison with experiment for Hesngbnd;Kr and Hesngbnd;Ar. Reversal of the calculation procedure gives a method for obtaining the ordinary diffusion coefficient from experimental measurements of the composition dependence of the thermal diffusion factor. Agreement with experiment is satisfactory.
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