Gaseous Diffusion in a Temperature Gradient

Abstract
The theory of diffusion in a temperature gradient has been tested by comparing the results of gas mixing experiments and gas unmixing experiments, the unmixing being caused by thermal diffusion. Both types of measurements have been carried out in the same apparatuses with the same temperature distributions, so that corrections cancel on taking ratios. Measurements are reported on H237Ar, H285Kr, D285Kr, T2‐N2, T2‐Kr, and T2‐CO2 over a maximum temperature range of about 195° to 435°K. The theory is confirmed within experimental uncertainty, provided that account is taken of the variation of the thermal diffusion ratio during the course of the diffusion. The ratio of the experimental results to their theoretical predictions is 0.991 ± 0.023. It is therefore possible to make reliable measurements of diffusion coefficients in the presence of temperature gradients.