180 CONTINUOUS PRODUCTION OF RADIO-ACTIVE MATTER  [CH. 
ignition. A small residue was obtained which, weight for weight, was 
In some cases several thousand times more active than the thorium 
from which it was obtained, while the activity of the precipitated 
thorium was reduced to less than one half of its original value. 
This active constituent was named Th X from analogy to Crookes’ 
Ur X. 























0) 4 8 12 16 20 
Time in Days 
Fig. 34. 
The active residue was found to consist mainly of impurities 
from the thorium; the Th X could not be examined chemically, 
and probably was present only in minute quantity. It was also 
found that an active constituent could be partly separated from 
thorium oxide by shaking it with water for some time. On 
