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.
The preparation and properties of "permselective"2 collodion membranes which combine extreme ionic selectivity with high permeability have been described recently (3, 9), and a preliminary account was given of their usefulness in various types of physicochemical studies (6,8,9,10,15).The permselective collodion membranes were prepared (3) as follows: A solution of collodion in ether-alcohol was poured over test tubes which were rotated slowly in a horizontal position. The film thus formed was allowed to dry for several minutes; another layer was applied in the same manner, and yet another a few minutes after the second. After several more minutes the tubes were immersed in distilled water. The membranes, still on the tubes, were then oxidized in 1 Iff sodium hydroxide3 for measured lengths of time and then soaked in water to remove the base. Still on the tubes, the membranes were dried in air.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.