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.

    75/278 (page 59)
    voltage very small compared with that necessary to give them velocities comparable with the io8cm./sec., which is the order of the velocity required by the positive rays. There must, therefore, be ways other than the ones we have discussed by which positive particles can produce ionization, and alternate between the charged and uncharged state. Let us consider, for example, the loss of charge by a positively charged particle. This might occur if the particle in its journey through the gas passed through a molecule of the gas and captured one of its electrons and carried it away with it. Again, a neutral particle passing through a molecule might have one of its own electrons captured and retained by the molecule, and emerge with one electron less, and therefore with a positive charge. We observe that in the first of these cases there is a positive ion produced in the gas and in the second a negative one, in neither case is a free electron produced : this distinguishes this process of ionization from that previously discussed. In this process a very high velocity of the particle is not necessary : in fact, if it had sufficient energy to pass through the molecule it would be more likely to capture one of its electrons if it were moving slowly. We could explain in this way the formation of secondaries by the heavier atoms : the fact that these are exceptional shows, I think, that this method of ionization is not so effective as the other. Another reason for this view is that if the second method took place to any large extent we should expect to find a considerable number of the particles with a negative charge. For consider the case when an uncharged molecule is moving rapidly through other molecules of the same kind : it is supposed to get its positive charge by a stationary molecule capturing one of its electrons, but since the effect depends only on the relative velocity of the two