
186 CONTINUOUS PRODUCTION OF RADIO-ACTIVE MATTER  [CH. 
the action of ammonia and ammonium carbonate. Ur X is com- 
pletely precipitated with the uranium in an ammonia solution 
and the filtrate is imactive. Ur X is separated by ammonium 
carbonate, while Th X under the same conditions is completely 
precipitated with the thorium. The Ur X and the Th X thus 
behave like distinct types of matter with well-marked chemical 
properties quite distinct from those of the substances in which 
they are produced. The removal of Ur X by the precipitation 
of barium is probably not directly connected with the chemical 
properties of Ur X. The separation is probably due to the 
dragging down of the Ur X with the dense barium precipitate. 
Sir William Crookes found that the Ur X was dragged down by 
precipitates when no question of insolubility was involved, and 
such a result is to be expected if the Ur X exists in extremely 
minute quantity. It must be borne in mind that the actual 
amount of the active constituents Th X and Ur X, separated from 
thorium and uranium, is probably infinitesimal, and that the 
greater proportion of the residues is due to impurities present 
in the salt and the reagents, a very small amount of active matter 
being mixed with them. 
123. Rate of production of Th X. If the recovery of 
the activity of uranium or thorium is due to the continuous 
production of new active matter, it should be possible to obtain _ 
experimental evidence of the process. As the case of thorium 
has been most fully investigated, a brief account will be given of — 
some experiments made by Rutherford and Soddy? to show that 
Th X is produced continuously at a constant rate. Preliminary 
experiments showed that three successive precipitations were suf- 
ficient to remove the Th X almost completely from the thorium. 
The general method employed was to precipitate a solution of 
5 grams of thorium-nitrate with ammonia. The precipitate was 
then redissolved in nitric acid and the thorium again precipitated 
as before, as rapidly as possible, so that the Th X produced in the 
time between successive precipitations should not appreciably 
affect the results. The removal of the Th X was followed by 
measurements of the activity of the residues obtained from suc- 
1 Phil. Mag. Sept. 1902. 
