The thermal diffusion of radon gas mixtures

A special theoretical treatment of thermal diffusion in mixtures of two gases, in which one component is rare, has been given by Chapman (1929). An interesting result which emerges from this theory is that this phenomenon may produce a large change in the quantity of the rare constituent on the cold and hot sides. Let M1 be the mass of the molecules of the rare and heavy constituent, M2 that of the light constituent, and r the ratio of the proportion by volume of the rare constituent on the cold to that on the hot side, after thermal diffusion. When M2/M1 is small, the formulae expressing the relationship between r and s12, the repulsive force index between unlike molecules, can be expressed in a simple form. In this case, the experimental value of the ratio, r, together with the coefficient of ordinary diffusion of the two gases and the coefficient of viscosity of the lighter gas, suffices to determine s12.