THERMAL MEMBRANE-POTENTIAL ACROSS CATION-EXCHANGE MEMBRANES FOR VARIOUS HALIDE SOLUTIONS

Thermal membrane potential across cation-exchange membranes was measured for various halide solutions. Linear relationships between thermal membrane potential (Delta psi) and temperature difference (Delta T) were observed, and the temperature coefficient of thermal membrane potential (Delta psi/Delta T) decreases with increase in the molality of the external solution as predicted by a theory reported. When counterions of membranes are hydrogen ions, the sign of the coefficients turns into minus near 0.01 mol/kg of the external solution for all membranes, although the coefficients are always positive for all the other forms. The dependence of the coefficients on the molality of the external solutions sometimes deviated slightly from the theory. This deviation is attributed to some change in water content of the membranes. A reproducible method of measuring water content of membranes was applied to discuss the change in the state of the membranes.