294 RADIO-ACTIVE PROCESSES [CH. 
degree. With the electric method, on the other hand, the results 
obtained were exactly the reverse. The uranium freed from Ur X 
showed very little loss of activity while the activity of the Ur X 
was very small. The explanation of these results was given by 
Soddy! and by Rutherford and Grier?. The « rays of uranium are 
photographically almost inactive but produce most of the i1oniza- 
tion in the gas. The # rays, on the other hand, produce a strong 
photographic action, but very little ionization compared with the a 
rays. When the Ur X is separated from the uranium, the uranium 
does not at first give out any 8 rays. In the course of time, fresh 
Ur X is produced from the uranium, and 8 rays begin to appear, 
gradually increasing in intensity until they reach the original value 
shown before the separation of the Ur X. 
In order to determine the recovery curves of uranium after the 
separation of Ur X, it was thus necessary to measure the rate of 
increase of the @ rays. This was done by covering the uranium 
with a layer of aluminium of sufficient thickness to absorb all the 
a rays, and then measuring the ionization due to the rays in an 
apparatus similar to Fig. 16. 
Uranium has not yet been obtained inactive when tested by 
the electric method. Becquerel® has stated that he was able to 
obtain inactive uranium, but in his experiments the uranium was 
covered with a layer of black paper, which would entirely absorb 
the a rays. There is no evidence that the a radiation of uranium 
has been altered either in character or amount by any chemical 
treatment. The a rays appear to be inseparable from the uranium, © 
and it will be shown later that the other radio-active elements as 
well as uranium also possess a non-separable activity consisting 
entirely of a rays. The changes occurring in uranium must then 
be considered to be of two kinds, (1) the change which gives rise 
to the « rays and the product Ur X, (2) the change which gives 
rise to the @ rays from Ur X. 
The possibility of separating the Ur X, which gives rise to the 
8 rays of uranium, shows that the « and @ rays are produced quite 
independently of one another, and by matter of different chemical 
properties. 
1 Trans. Chem. Soc. 81, p. 460, 1902. 2 Phil. Mag. Sept. 1902. 
3 C, R. 131, p. 137, 1900. 
