Boltwood — Radio-activity of Uranium Minerals. 293 



rose at a rate corresponding to the growth of products in 

 actinium. At the end of 110 days the activity of the filin 

 was 4-05 div. per minute, which corresponded to 14/1 div. per 

 minute for the equilibrium value of the actinium separated 

 with the total oxides. The relative activity of the actinium 

 products obtained in this case was therefore 0*15 xU. 



Experiment 3. The amount of actinium in the mineral was 

 calculated from the rise in the activity of the film described 

 under "Experiment 4, Ionium." The activity of this film at 

 the end of 129 days was corrected for the activity of the thorium 

 products present. The initial activity (corrected for thorium 

 products) had been equivalent to 034xU; the final activity 

 (similarly corrected) was equal to 0*58 XU. The difference, 

 amounting to - 24xtJ, could be attributed to the actinium (and 

 products) in the mineral. 



Experiment 4. A portion of the oxides of the rare earths 

 separated as oxalates in " Experiment 1, Ionium," was made 

 into a film about six months later. Another small portion of 





















































































































" 



























the oxides was tested by the emanation method and found to 

 be free from appreciable quantities of radium. The activity 

 of the film corresponded to an activity of 0"71XU for the 

 total material separated, after a correction had been made for 

 the activity of the thorium products. It is regretted that the 

 activity of this film was not followed from the time when it 

 was first prepared, although a strict interpretation of any 

 variations which might have been noticed would have been 

 difficult owing to uncertainty as to the products contained in 

 it. Assuming that the final activity was clue to actinium and 

 ionium only, and deducting the maximum value of - 35xU 

 found previously for the ionium, gives a maximum value of 

 - 36xU for the relative activity of the actinium products in a 

 mineral. 



I am inclined for various reasons to believe that this is more 

 nearly the correct value. It has been observed by both Hahn* 

 and Levinf that the precipitation of actinium by ammonia is 



*Phil. Mag., xiii, 165, 1907. fPhys. Zeit., viii, 129, 1907. 



