The chemistry of the radio-elements / by Frederick Soddy.

  • Soddy, Frederick, 1877-1956.
Date:
1914
Catalogue details

Licence: In copyright

Credit: The chemistry of the radio-elements / by Frederick Soddy. Source: Wellcome Collection.

    16/64 (page 4)
    Table ; and, so far as can be ascertained, all the elements occupying the same place are chemically non-separable and identical. The diagram is interesting, not only as estab- lishing a fair presumption that the whole of these new changes have now been disentangled, but even more inter- esting because of the new light it sheds on what the Periodic Law means, and what the chemical elements themselves really are. The chemical non-separability and identity of different radio-elerpents, first definitely drawn attention to in the case of radium and mesothorium I,® and now shown to be the general characteristic of the radio-elements, becomes something more than the expression of experimental failures to separate and distinguish. Hitherto the terms have been employed to express matters of fact rather than of theory. These groups have been found experimentally to be chemically non-separable among themselves, and to possess a chemical character which apparently at least is identical. Nothing in this description necessarily implies that for all time they will remain chemically non-separable, or that some day slight differences of chemical character will not be discovered. The case of the rare-earths has often been quoted in this connection,’ but a fuller examination shows that there is no real analogy between the cases. In the first place, among the rare-earths the difficulty is probably less in their separa- tion, than to find means for determining what the effect has been of any attempt at separation. The only general test is the equivalent, and as the equivalents are close together the test is a very coarse one, so that separation of the constituents must already have proceeded to a considerable extent before it can be ascertained by such means. When, as in the case of praseodymium and neodymium, optical methods, such as the absorption spectrum, give an inde- pendent means of recognising the separate constituents of the mixture, the task of chemical separation is enormously simplified, whereas in the radio-elements extremely delicate and sensitive quantitative methods can always be devised to detect the least change in the ratio of a pair of non- separables in a mixture. The position with regard to the radio-elements is that more than one constituent is known to be there and yet they cannot be separated, whereas with