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The flow rates of the vapors of benzene, ethyl chloride, diethyl ether, methanol, and water through activated carbon rods have been found to exceed, considerably, flow rates calculated by classical equations. The excess flow rates show maxima in widely different relative pressure regions and are ascribed t o flow of adsorbed material. An empirical equation is presented which correlates the observed flour rates with relevant adsorption isotherms. Classical equations of flow through elliptical and rectangular pipes are discussed with reference to flow through finegrained porous materials. I t is shown that equations of the Adzumi type are roughly valid as applied to line-grained porous bodies, but that without a knowledge of the frequency distributions of pore sizes and shapes, flow data cannot be related to pore dimensions in any literal sense. End effects are discussed.

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Total flow rates of gases through activated charcoal rods are regarded as consisting of the sums of comparatively independent flows through macropores and micropores. The flow rate through the macropore system is related to the relevant adsorptio~i isotherm by means of all empirical equation having three arbitrary constants. The empirical eqr~ations can be fitted to all of our observed results within the experitneatal error. Assunling that the adsorbate behaves as a one, cornpoltent fluid such as a gas in a gravitational field, it is shown that compresslve s~~r f a c e forces give rise to large fluid pressures within micropores. A very simple flow equation is derived which is qualitatively in agreement with observed results and which indicates a mean micropore diameter of the order of lo-' cm. The derived equation illustrates the nature of the physical factors involved and shows that surface forces may increase flow rates of adsorbable gases by \.cry large factors. The increased flow rates are due mainly to the greatly increased densities and to the increased pressure gradients resulting from the actiou of surface forces. A n~odel porous adsorbent is presented which exhibits many properties of real adsorbent systems and illustrates especially the relations between adsorbate densities and the various tensions and pressures existing within micropore systems. GENERAL CONSIDERATIONSThe flow rate in mass units, Q,,,, of a Maxwellian fluid through a pipe of circular cross section may be described by the equation, where d p / d z is the pressure gradient a t any point along the axis of the pipe; r ,

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