Heats of neutralization of H-exchange resins are approx. equal to AH for the formation of water from the ions. The heat of neutralization of base unsaturated bentonite is smaller, possibly due to the presence of exchangeable Al. Differences in heats of neutralization of H-resins with various metal hydroxides compare in magnitude with measured heats of ion exchange. Heats of ion exchange calculated from the temp. coeff. of the exchange equilibrium compare favorably with those measured calorimetrically. The biionic potential measured when an exchange resin or clay membrane separates equimolar solns. of two 1-1 electrolytes is tentatively identified with A F for the exchange of the cations concerned.