If, moreover, the bodies acted on are brought to a temperature of over 700 deg., they appear to lose by volatilisation certain substances condensed in them, and at the same time their activity disappears.
The other radioactive bodies behave in a similar way.

Bodies which contain actinium are particularly rich in emanations.

Uranium, on the contrary, has none.[37] This body, nevertheless, is the seat of transformations comparable to those which the study of emanations reveals in radium; Sir W.Crookes has separated from uranium a matter which is now called uranium X.This matter is at first much more active than its parent, but its activity diminishes rapidly, while the ordinary uranium, which at the time of the separation loses its activity, regains it by degrees.

In the same way, Professors Rutherford and Soddy have discovered a so-called thorium X to be the stage through which ordinary thorium has to pass in order to produce its emanation.[38] [Footnote 37: Professor Rutherford has lately stated that uranium may possibly produce an emanation, but that its rate of decay must be too swift for its presence to be verified (see _Radioactive Transformations_, p.

161) .-- ED.] [Footnote 38: An actinium X was also discovered by Professor Giesel (_Jahrbuch d.