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An equation for the flux of electrolyte through a water-swollen cation-exchange resin membrane separating two solutions of the same electrolyte at different concentrations is derived on the basis of several assumptions regarding the physical nature of a swollen resinous exchanger. The complete flux equation contains three terms, one determined by the concentration difference across the membrane, another determined by the variation of the activity coefficient of the electrolyte with concentration in the membrane and a third concerned with the rate of osmotic or hydrostatic flow through the membrane. If ions in the resin are transported entirely in an internal aqueous phase, the mobilities required for the flux equation can be related to mobilities in aqueous solution and to the volume fraction of resin in the swollen membrane. The treatment is readily extended to anion exchangers.

Measured surfactant ion activities (al) and counterion activities (az) in solutions of sodium dodecyl sulphate (SDS) in the presence and absence of NaCl are reported. The results show that premicellar association is insignificant. Mean ionic activities of surfactant (a&) above the c.m.c. (critical micelle concentration) agree well with estimates from light scattering. This shows that the surfactant ion electrodes work well in the presence of micelles and that solubilisation of membrane constituents is unimportant. Comparison of a& values with estimates from surface tension studies suggests increasing surfactant adsorption above the c.m.c.At the c.m.c. in the presence of NaCl we find log a1 +O.795 log a2 = -3.185. (i)By putting (c')* = ml[ml+0.2(c-mml), (ii) where c and ml denote total and monomeric surfactant concentralion and c' is the concencration that would give the same activity as that in the solution of interest if no micelles formed, we found that increasing c leads to decreasing m l above the c.m.c. An attempt to obtain liquid junction potentials in solutions above the c.m.c. was unsuccessful. Differences between present and previous results are probably attributable to the non-Nernstian response of previous surfactant electrodes.

Various anomalies in the thermodynamic and kinetic properties of ion-exchange resins are attributed to a non-uniform distribution of the gegen-ions. It is suggested that some information on this distribution should be derivable from the correlation of a number of electro-kinetic properties of the resin. Electrical conductance and electro-osmosis have been studied using a highly swollen cation-exchanger and the results combined with previous determinations of ionic self-diffusion coefficients and transport numbers.At one temperature and concentration a fairly detailed application of the irreversible thermodynamic theory of membrane phenomena has been possible and this is tentatively extended to other concentrations. It appears that for resins containing little or no sorbed electrolyte the interaction between the gegen-ions and the matrix is important and also has the effect of concentrating the gegen-ions into regions of relatively high solution viscosity. In the presence of sorbed electrolyte these effects, per mole of cations, become less significant.The electro-osmotic permeability of the resin decreases by about 25 % as the external solution concentration is increased from 0.01 to 1-00 M. This suggests that the interaction between gegen-ions and matrix does not take the form of specific ion-pairing, association or incomplete dissociation, but that it is due to electrostatic interactions controlling the distributions of the ions in the pore solution. An analysis is given in terms of a general distribution of the gegen-ions which shows that these conclusions are consistent with the experimental data and electrostatic theory.The implications of these results with regard to the convection contribution to electrical conduction are considered in the light of the conductance and diffusion coefficient data. The difficulties in computing the convection current from the electro-osmotic permeability are pointed out and an attempt made to estimate the diffusion coefficient of H+ ions from the conductance of the H+-form resin.