of the vessel the upper layer of liquid becomes richer in uranium X. Since the β rays arise only from the product Ur X and not from the uranium itself, and the Ur X is mostly confined to the upper layer, a much greater proportion of the β rays escape than if the Ur X were uniformly distributed throughout the thick layer of uranium. When the amount of water added is just sufficient to supply the water of crystallization, the Ur X in the upper layer of crystals gradually diffuses back through the mass and, in consequence, the activity of the upper surface diminishes and of the lower surface rises. A similar explanation applies to the effects observed by Meyer and Schweidler. The water fraction, left behind after treatment with ether, contained all the Ur X. The first layer of crystals formed in it contained some Ur X, and this was for the most part confined to the top layer of crystals. The amount of β rays at first diminished owing to the gradual diffusion of the Ur X from the surface. In the first experiment, the amount of Ur X present was in radio-active equilibrium with the uranium, and, after the initial drop, the β ray activity remained constant. In the second experiment, the gradual rise is due to the fact that the crystals of uranium first formed contained less than the equilibrium amount of Ur X. After falling to a minimum, the β ray activity, in consequence, slowly rose again to the equilibrium value.
These effects exhibited by uranium are of great interest, and illustrate in a striking manner the difference in properties of Ur X and the uranium. The gradual diffusion of the Ur X throughout the mass of crystals is noteworthy. By measurements of the variation with time of the β ray activity, it should be possible to deduce its rate of diffusion into the crystallized mass.
Transformation products of Thorium.
207. Analysis of the active deposit. The radio-active processes occurring in thorium are far more complicated than those in uranium. It has already been shown in chapter vi that a radio-active product Th X is continuously produced from the thorium. This Th X breaks up,