The electrochemistry of permselective membranes. III. The electrical resistance of permselective collodion membranes in solutions of various electrolytes

Abstract

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.