The Separation of the Isotopes of Chlorine

Abstract

MR. D. L. CHAPMAN'S argument appears essentially to be similar to that already developed from a quite different point of view by Lindemann (Phil. Mag., 1919, vol. xxxvii., p. 523; vol. xxxviii., p. 173), that because isotopes are (theoretically) separable by physical means, they must also be chemically separable according to thermo-dynamical reasoning. The fact tliat the particular mode of separation by semipermeable membranes (assumption (3), NATURE, July 15, p. 611) is highly fanciful need not obscure the nature of the argument. Lindemann's conclusion that, though isotopes cannot be identical chemically, the difference may be reduced to an unmeasurable one of the second order of magnitude by suitable assumptions as to the “Nullpunktenergie,” seems to indicate the more hopeful line of advance. The chemical non-separability of isotopes, of which there is an accumulated mass of experimental evidence, seems to call for consequent adjustments in thermo-dynamic theory rather than the reverse.