Knudsen diffusion in powders. Part I Critical examination of a gas diffusion relationship used in Knudsen flow permeametry

B. V. Derjaguin's treatment of gas diffusion in a porous medium under conditions of Knudsen flow is discussed. A semi-theoretical value obtained for the constant β in the general equation is tested experimentally. In opposition to previous conclusions, molecular diffusion seems best interpreted in terms of elastic collisions against the pore walls. The structure of the pore system is shown to be the controlling parameter of the gas flow, and the novelty of the present treatment consists in ways to take the pore structure into account.