A generalized treatment of gas transport in porous media is presented as developed on the basis of the ``dusty-gas'' model, a model in which a porous medium is described as consisting of uniformly distributed, giant molecules (dust) held stationary in space. The problem is broken down into a series of special cases which involve the various combinations of gradients in composition, pressure, and temperature. Equations are given for the description of several well-known phenomena. These include isobaric, isothermal diffusion; diffusion under the influence of a pressure gradient; Poiseuille's flow equation, including the Knudsen minimum; the Kramers—Kistemaker effect; thermal transpiration; and the effect of pressure on the thermal-diffusion factor. The results are likewise applicable to capillaries by a suitable substitution for geometric parameters.

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The temperature dependence of the rotational collision numbers for O2, N2, CO, and CO2 was investigated in the range 47S-676°K by the thermal transpiration technique with the use of a novel apparatus design. In all cases the collision number was found to increase with temperature. For O2 and N2, where some comparison with theory is possible, the experimental rate of increase with temperature was found to be faster than the predicted behavior. The results for CO and CO2 are in general agreement with other transpiration measurements and with acoustic absorption results which were obtained at lower temperatures.

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Thermal transpiration results which were determined at an (assumed) characteristic temperature of 504°K are reported for all of the noble gases and for N2, O2, CO, and CO2. The helium data are found to be anomalous when viewed in terms of the dusty-gas model for thermal transpiration. Application of the model in the zeroth differential approximation yields the following rotational collision numbers for the polyatomic molecules: N2, 6.0; O2, 2.2; CO, 1.3; CO2, 1.9.