The Kinetics of Membrane Processes. III. The Diffusion of Various Non-Electrolytes through Collodion Membranes

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Abstract
Measurements have been made of the rates of diffusion of various non‐electrolytes, and of water, through a collodion membrane separating a dilute solution from pure water. The determinations were made by measuring the rate of rise and fall in a capillary tube in the solution, and analyzing the results using the procedure described in a previous paper. The work was done with 0.25N solutions of sucrose, lactose, raffinose and mannitol, and was carried out at different temperatures so that energies and entropies of activation could be determined. The energy of activation for diffusion through the membranes was found in all cases to be slightly less than for free diffusion, a result that is shown to be consistent with a positive heat of adsorption of the solute and solvent at the membrane. Analogously the entropies of activation for membrane diffusion are somewhat less than for free diffusion, since the process of adsorption brings about a decrease in entropy. The rate of diffusion of water through a membrane is shown to depend upon the nature of the solute diffusing, a result which arises from the fact that diffusion is a mutual process. An experiment is described in which there is an initial net flow from the solution into the solvent.
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