Diffusion coefficients of gases from the rate of approach to the steady state in thermal diffusion

The rate of approach to the steady state in a convection-free two-bulb thermal diffusion experiment is treated in a more rigorous manner than previously available, in order that reliable ordinary diffusion coefficients may be derived from thermal diffusion measurements. The final results are of the same form as in the original simplified Jones and Furry treatment, but the parameters are now interpreted somewhat differently and a new correction term appears. Application to Nettley's measurements on H₂-N₂ mixtures removes an apparent discrepancy with the kinetic theory prediction of the composition dependence of the diffusion coefficient for this system.