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1. 1. The preparation of a series of sulfonated polystyrene-divinyl-benzene cation-exchange resins is described. 2. 2. Exchange capacities are found to be identical to all inorganic and organic univalent cations studied, with the possible exception of the tetra-(n)-butylammonium ion. The divalent cation capacities are slightly larger in every case. 3. 3. Studies of rates of uptake are presented, and diffusion coefficients calculated. The rate of uptake is correlated with both the ionic volume and the degree of cross-linking of the resin structure.

1. 1. The thermodynamic theory of ion-exchange processes predicts that the selectivity coefficient is determined by the ratio of the exchange ion activity coefficients in the resin phase, by differences in ionic volumes and by the thermodynamic osmotic pressure. 2. 2. The variation in selectivity coefficient with ionic composition of the resin phase appears to be, in the case of the alkali metal cations, primarily a pressure-volume effect. In the case of the quaternary ammonium ions, ion activity variations, resulting from adsorption of the organic ions on the resin matrix, appear to oppose the pressure-volume effects. 3. 3. The effects of temperature and concentration of the resin phase are consistent with the concept of ion hydration as it affects the pressure-volume term. The constancy of ionic activity ratios for the alkali metal cations is in accord with the Bjerrum, Harned, Stokes-Robinson theory. 4. 4. The selectivity coefficients are not a function of the ionic strength of the equilibrative solutions. In the absence of adsorption effects, the smaller ion is preferred. 5. 5. Selectivity coefficients for a pair of cations can be calculated from selectivity coefficient values for each of these ions with a third reference ion. This indicates that the thermodynamic osmotic pressure varies only slightly with different exchange cations for a given resin, and supports the view that the ionic activity coefficients are determined chiefly by the nature and concentration of the ion and not by interaction between the ions. 6. 6. Adsorption effects of the quaternary ammonium ions are more pronounced in the case of low capacity resins, due to the larger ratio of organic to polar groups.

The passage of a direct electric current across a fixed-charge membrane interposed between neutral electrolyte solutions can give rise to the production of hydrogen and hydroxide ions at the solution-membrane boundary in equivalent amounts, each of which can approach and equal the number of faradays passed. At this unique boundary, the electric field can inhibit the rate of recombination of hydrogen and hydroxide ions strongly enough to increase the dissociation constant of water and other weak electrolytes by several orders of magnitude. These observations lead to a model of the gastric secretory process wherein the gastric potential, primarily due to the activity of a chloride-ion pump, is applied across an adjacent ionselective membrane also present in the mucosa. The dissociating weak electrolyte can be water, to produce hydrogen ions in the stomach and hydroxide ions which combine with carbon dioxide in the blood, or it can be carbonic acid to produce bicarbonate directly.

1. 1. A study was made of the time required in which final, stable electrical resistances are established with three electrolytes—potassium chloride, lithium chloride, potassium sulfate—across three types of permselective oxidized collodion membranes, being originally in the acidic state. These periods vary from 15 min. to many hours. Equilibration is reached somewhat faster with membranes of higher porosity. A large noncritical ion does not seem to retard the establishment of the equilibrium to a significant extent. A large critical ion, however, seems to slow down equilibration. The concentration of the solution in contact with the membrane seems to be of little significance. The establishment of final, stable resistances requires much longer periods than those necessary for reaching final, stable concentration potentials under comparable conditions. 2. 2. The final, stable resistances of four types of permselective collodion membranes equilibrated with solutions of six electrolytes at three concentrations, 0.1, 0.01, and 0.001 N , were measured and tabulated. The data are evaluated as to the differences of the various types of membranes, the influence of the concentration on membrane resistance, and the influence of the nature of the electrolyte. A comparison is also made of the concentration function of the resistance of the same membranes equilibrated with solutions of different electrolytes; and of the concentration function of the resistance of different membranes with solutions of the same electrolytes. 3. 3. Certain shortcomings of the permselective oxidized collodion membranes, their deficiency in mechanical strength, and mainly their weak acid character are discussed, and possible ways of improving them are indicated.

Exchange equilibria, ohmic resistances, concentration and bi-ionic potentials, diffusion coefficients, and transport numbers were measured for the chloride–sulfate–oxalate system in anion-permeable membranes with quaternary ammonium and benzidine exchange sites. The benzidine membranes showed a greater selectivity for sulfate than chloride as compared with the quaternary ammonium membranes, but a lower transport number. These phenomena were interpreted in terms of an ion-binding mechanism. Fair agreement was observed between measured transport numbers and those calculated from selectivity coefficients, diffusion coefficients, and equivalent conductances.

1. 1. Water vapor sorption studies on a series of ion-exchange resins are presented. The systems investigated include sulfonic acid cation-exchange resins of various degrees of cross-linking, a carboxylic acid resin, and a quaternary ammonium anion-exchange resin. 2. 2. Some direct calorimetric measurements of heats of sorption are presented. Free energies, heats of sorption, and entropies are calculated. 3. 3. The sorption behavior of sulfonic acid resins is compared with that of sulfuric acid. It is concluded that the sulfonic acid groups are osmotically inactive. For the sulfonic acid resins, variations in sorption with ionic state are discussed and interpreted. The partial molal volumes of the hydrated resin systems are studied. 4. 4. The behavior of the cross-linked polystyrene sulfonic acid resins is discussed from the point of view of simple, strong electrolytes in aqueous media. This interpretation is valid for the range 0–75% relative humidity; the influence of cross-linking makes itself felt above this point.

Lithium ions, and, to a lesser extent, the sodium ions are bound by polyacrylic acid, as evidenced by pH titrations of polyacrylic acid in dilute (0.01 M) solutions of the alkali metal bases and solutions of their corresponding salts. The formation constant for the binding of lithium to polyacrylic acid was found to be 1.9. When dilute solutions of polyacrylic and polymethacrylic acids were titrated with quaternary ammonium bases, the polyacids became progressively weaker with increasing size of the counterion. These phenomena suggest that the counterions are largely held in close proximity to the polyanion chain, with distances of approach comparable to the sum of the ionic radii. Titrations of these acids with a mixture of a large and small cation also served to point up the increased chain potential in the presence of large cations. All of these effects are absent with the analogous low molecular weight acids.

Multilayer membranes composed of the alkaline earth salts of stearic and hexadecylsulfuric acids act as reversible electrodes to these cationic species only in mixed electrolytic solutions with even large excesses of alkali metal cations when the membrane is maintained at nearly constant volume by the imposition of a high pressure. Mixed electrolytic solutions of calcium or barium chloride with sodium or potassium chloride were studied at ionic strengths from 0.0003 to 1.5; these obeyed Harned's rule with slopes of zero at ionic strengths < 0.1, rising to -- 0.08 at ionic strength 1.5. Thus, thermodynamic activity coefficients of 2--1 electrolytes in mixed solutions with 1-- 1 salts were measured directly.

A study of the feasibility of using ion exchange resin systems for carbon dioxide absorption from gas streams was completed with the conclusion that such a system could compete very successfully with atmospheric control systems now in use. A detailed study of such a system based on polyethylenimine showed that this material is superior to any of the commercially available weak base resins tested. The kinetic data obtained correlated very well when a model was postulated that was based on diffusive transfer through a gas film, a water film, and the resin particle in series, with diffusion with the resin particle as the rate determining step.

A model has been developed to predict the selectivity of polyion gels for one counterion over another of a different size. The model, essentially an extension of the Kagawa—Gregor model is based on purely electrostatic interactions between the gel and the counterions and takes into account their differing distances of closest approach. This model was tested against experimental data involving cross‐linked polymethacrylic acid with Li+, Me4N+, and Et4N+ ions exchanging for K+; it was found to predict these selectivities to a good degree of accuracy, particularly with the unhydrated quaternary ammonium ions. The model correctly predicts the variation of selectivity with counterion size ratio and also correctly predicts the variation of selectivity with counterion concentration ratio. Discrepancies between theory and experiment attributable to pressure—volume effects were also evaluated and remaining differences were ascribed to adsorption phenomena.

Magnesium stearate and strontium stearate multilayer membrane electrodes were prepared. Inserted in solution chains (at concentrations up to 3 to 4 molal) of the corresponding chloride salts between reversible electrodes, they gave potentials that agreed within experimental error with those calculated from thermodynamic data. Magnesium stearate multilayer electrodes were also employed to measure the activity coefficient of magnesium chloride in a mixed electrolytic solution with potassium chloride; good agreement with Harned's rule was observed at a total ionic strength of 1.0. Using appropriate electrodes, the activities of the chiorides of magnesium and strontium were measured in mixtures of these two salts, and again Harned' s rule was observed, with the values of the two slopes being in agreement with derived thermodynamic relationships.

The enzyme-coupled ultrafiltration membrane system described by Gregor and Rauf (1) is characterized by a very high loading of bound enzyme, with the specific activity of the native enzyme largely retained. The system has unique advantages. Since the feed streams are pumped rapidly under pressure, the contact times are extremely short, such that diffusion control of the process is virtually eliminated. The nature of the membrane system lends itself to the use of high speed, repetitive processing.

Donnees sur l'utilisation de l'electrodialyse en vue de la production de solutions relativement concentrees de bases et d'acides faibles a partir des solutions salines correspondantes

The properties of a series of sulfonic acid fixed-charge membranes of graded porosity were described in terms of their fixed-charge molality, hydraulic permeability, concentration potential and rejection to a number of charged and uncharged solutes of differing molecular weight. Their use in ultrafiltration processes employing a number of test solutions and also solutions from the sewage-treatment, pulp and paper, and cheese industries was also described. The salient property of these membranes was their non-fouling character as exemplified by their ability to maintain their hydraulic flux and solute rejection properties with solutions known to foul conventional ultrafiltration membranes.

The contributions to this Advanced Study Institute on Charged and Reactive Polymers represented three different points of view of the same scientific subject. Some authors were concerned with solutions of polymers as whole entities, as for example the density of these solutions as reflecting the electrostriction of solvent by the polymer. A second group of authors was concerned with polymers per se, as with their general thermodynamic and dynamic properties as influenced by general considerations of ionic strength, etc., as with the configurational entropy entity of polymers. The third group of authors was not concerned with polymer systems as a whole but rather with a highly localized phenomenon, their binding to ions in solution, with a primary concern on the nature and extent of these bindings reactions.