﻿of the a Rays of Actii 



249 



tion was similar to that employed for the separation of 

 radiothorium from its products. The actinium solution was 

 precipitated successively five times with ammonia in order to 

 completely remove the actinium X. As in the case of radio- 

 thorium, the later precipitations are not complete, that is, 

 ammonia is not added to a sufficient extent to carry down the 

 actinium itself. By this procedure, the radioactinium is 

 concentrated in the first precipitate, while the actinium 

 remains for the most part in the solution. It is not difficult 

 to obtain a layer thin enough for the determination of the 

 ionization curve. 



3 4 



Ionization. 



Fig. 3 shows the curve for radioactinium when completely 

 freed from actinium X and also the active deposit. As the 

 activity of the specimen was not very strong, the scale of 

 abscissae is increased in the ratio 2'D ol that employed in the 

 other figures. 



It is seen that the curve of radioactinium has the charac- 

 teristic shape for a thin film of a single a. ray product. The 

 maximum range of the a rays is -±'8 cms., and this value is 

 probably correct within half a millimetre. Since radioactinium 

 at first increases in activity due to the production of 

 actinium X and its successive products, we should expect to 

 obtain evidence from the ionization curve of the presence of 

 these products. This is seen to be the case. 



