Rays of positive electricity and their application to chemical analyses / [Sir J.J. Thomson].

  • Thomson, J. J. (Joseph John), 1856-1940.
Date:
1921
Catalogue details

Licence: In copyright

Credit: Rays of positive electricity and their application to chemical analyses / [Sir J.J. Thomson]. Source: Wellcome Collection.

    229/278 (page 213)
    No appreciable effect, however, was produced by this frac- tionation ; indeed, from an investigation by Lindemann and Aston, “Phil. Mag.” [6], 37, p. 523, 1919, it would seem that the effect which was to be anticipated was smaller than could have been detected by Aston’s experiments. Another method used by Aston was to allow the mixture to diffuse through a porous substance, like the stem of a clay tobacco-pipe, when the lighter constituent would get through a little more rapidly than the heavier one; he designed an automatic apparatus in which the diffusion went on uninterruptedly, but no decisive results were obtained. Mr. Aston has recently attacked the problem by quite a different method, based on the following considerations :— If the neon in the atmosphere contains two different constituents, then the atomic weight 20'2, determined by the measurement of the density of the gas, will not be the atomic weight of either constituent, but a mean value depending on the proportion in which the constituents are present. The measurement of the positive-ray photographs enable us to determine the atomic weight of the substance giving rise to any particular line, and if these measurements can be made with such accuracy as to enable us to say that neither of the lines has an atomic weight which corresponds to that of the atmospheric neon, this would prove that the neon in the atmosphere is a mixture. The evidence would be still stronger if the atomic weight of the mixture 20’2 agreed with the mean of the atomic weights of the constituents, the proportion between the constituents being determined from the relative intensities of the lines on the photographic plate. Mr. Aston determined, by the focus method described on page 36, the atomic weights of the substances producing the neon line, and its companion the line for which mje — 22.