Studies on the Permeability of Membranes. Ii. Determination of Ionic Transfer Numbers in Membranes

I t has been shown (1) that the l,.m of a concentration chain, e . g . with two KCI solutions in the ratio 10:1, across a membrane of dried collodion, reaches its maximum value better the more dilute the KC1 solutions are, and that in higher ranges of concentrations, the effect of the membrane vanishes more and more. So in the latter case the P.W. approaches closely that established without a membrane. This is, in the case of KCI, practically equal to zero. The interpretation of the effect of the membrane was given as follows: Any potential difference between two aqueous solutions of different electrolytic content, in direct contact with each other, is due to the difference in the mobilities of the different kinds of ions. In the ultracapillary spaces of the membrane, the mobilities of the ions are not only changed with respect to their absolute value, but also to their relative value. In general, the mobility of the anion is considerably more decreased than the cation. Let us consider a very thin layer of the liquid content within a pore channel confined by two cross-sections through the channel, infinitely close to each other. Let the two sides of the membrane be in contact with two different solutions of the same kind of electrolyte consisting of two univalent ions. A transition zone will be formed across the membrane. Then the I~.D. between two infinitely close neighborLug cross-sections through this transition zone will be: