The electrolysis of solutions is, in many cases, a very powerful method of separating active products from one another, and its possibilities have not yet been exhausted. The main family of changes of the radio-elements, as far as they are known, have been investigated closely, and it is not likely that any product of comparatively slow rate of change has been overlooked. There is a possibility, however, that two radio-active products may in some cases arise from the disintegration of a single substance. This point is discussed further in section 260.
The remarkable way in which the disintegration theory can be applied to unravel the intricacies of the succession of radio-active changes is very well illustrated in the case of radium. Without its aid, it would not have been possible to disentangle the complicated processes which occur. We have already seen that this analysis has been instrumental in showing that the substances polonium, radio-tellurium and radio-lead are in reality products of radium.
After the radio-active substances have undergone the succession of changes traced above, a final stage is reached where the atoms are either permanently stable, or change so slowly that it is difficult to detect their presence by means of their radio-activity. It is probable, however, that the process of transformation still continues through further slow stages.
There is now considerable evidence that the elements uranium, radium and actinium are intimately connected together. The two latter probably result from the breaking up of uranium. The evidence in support of this idea is given in section 262, but there still remains much work to be done to bridge over the gaps which at present appear to separate these elements from one another.
After the series of transformations have come to an end, there will probably remain a product or products which will be inactive, or active only to a minute extent. In addition, since the α particles, expelled during the transformation, are material in nature, and are non-radio-active, they must collect in some quantity in radio-active matter. The probability that the α particles consist of helium is considered later in section 268.
The value of T, the time for a product to be half-transformed, may be taken as a comparative measure of the stability of the
