Mixtures of the radionuclides Na22and Na24, as the chloride salts, have been partially separated by chromatographic methods. A column 102 cm. in length containing the cation exchange resin Dowex 50 was used. The eluant was 0.7 Mhydrochloric acid. Na22is held more strongly by the resin than is Na24. The most effective separations were obtained at 25 °C and 5.5 °C.; experiments at 48 °C and 68 °C showed much smaller isotope effects.