The thermal diffusion of radon gas mixtures

In continuation of earlier experiments (Harrison 1937) in which the thermal diffusion in radon-hydrogen and radon-helium mixtures was measured, the thermal diffusion of mixtures of radon-neon and radon-argon has now been studied. The mean value obtained for the ratio of the proportion by volume of radon on the cold side at 0° C to that on the hot side at 100° C, after thermal diffusion, was 1·074 for radon-neon mixtures, and 1·008 for radon-argon mixtures. In order to calculate the repulsive force field,F 12 , between these two pairs of molecules, the present results were combined with measurements of ordinary diffiisirm of radon into neon and radon into argon (Hirst & Harrison 1939), and viscosity determinations at various temperatures of neon and argon (Trautz & Binkele 1930). The special theory, due to Chapman (1929), of thermal diffusion of a rare constituent in a binary mixture was used to derive Flt. The values obtained for the repulsive force field between the dissimilar molecules at collision were:F 12 (radon-neon) = 1·9 x 10-51 d -6·1 = (d /d 0 )-6·1 ,d 0 = 4·8 x 10-9 ,F 12 (radon-argon) = 2·1 x 10-43 d -5·1 = (d 0 )-5·1 ,d 0 = 4·3 x 10-9 ,d being the distance between the point centres of repulsive force andd 0 the value ofd at whichF 12 is 1 dyne. A comparison of the values obtained for the repulsive force index for radon-neon and radon-argon molecules with those obtained by Atkins, Bastick & Ibbs (1939) for binary mixtures of the first five inert gases shows that radon is the4 softest ’ of the inert gas molecules. Radon-argon molecules are the closest approach to the Maxwellian case yet studied experimentally.