§ 92. Properties of Uranium and Thorium.
Uranium and thorium differ in one important respect from radium,
inasmuch as the first product of the decomposition of the uranium and
thorium atoms is in both cases solid. Sir William Crookes8 was able to separate from uranium salts by
chemical means a small quantity of an intensely radioactive substance,
which he called Uranium X, the residual uranium having lost most of its
activity; and M.
Becquerel, on repeating the experiment, found that the activity of the
residual uranium was slowly regained, whilst that of the uranium X
decayed. This is most simply explained by the theory that uranium first
changes into uranium X. It has been suggested that radium may be the
final product of the breaking up of the uranium-atom; at any rate, it is
quite certain that radium must be evolved in some way, as otherwise
there would be none in existence—it would all have decomposed. This
suggestion has been experimentally confirmed, the growth of radium in
large quantities of a solution of purified uranyl nitrate having been
observed. Uranium gives no emanation. Thorium probably gives at least
three solid products—Meso-thorium, Radio-thorium, and Thorium X, the
last of which yields an emanation resembling that obtained from radium,
but not identical with it.
