The use of approximate formulas for the viscosity of gaseous mixtures to determine diffusion coefficients has two advantages over the use of the rigorous expression. First, the resulting expression for the diffusion coefficient is simpler, and second, the diffusion coefficient can be written solely in terms of experimental quantities and one empirical factor. When the viscosity-derived diffusion coefficients were compared with ex¬perimental diffusion coefficients, the Buddenberg-Wilke equation failed if the masses of the components were very different, but the equations proposed by Brokaw and by Francis gave satisfactory results.
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