714- Growth of Radiothorium from Mesotliorium 2. 



hydrogen peroxide. The value of! various reagents 

 effecting this separation was found as follows : — 



in 



Reagent. 

 Ammonia . 

 Methylamine . 

 m-Nitro- benzoic Acid 

 Amnion. Hydrazoate 

 Hydrogen Peroxide . 



Percentage of Meso- 

 tliorium 2 separated. 



. 16 



. 11 



. 100 



. 74 



. 100 



The hydrogen peroxide removes most of the ThB and part 

 of the ThC, but the last traces of these were removed by 

 adding lead and bismuth and precipitating out with H 2 S 

 several times. The filtrate was then evaporated down to 

 dryness and the ammonium salts ignited, leaving on a silver 

 tray a film of pure mesothorium 2. This tray was placed 

 between the poles of an electromagnet above which was an 

 electroscope. The brass base of the electroscope had a slot 

 cut out of it the size of the tray (7*7 cm. x 1*4 cm.). A 

 sheet of aluminium foil (thickness '00035 cm.) covered the 

 slot. The electroscope was provided with a mica screen 

 which could be slipped over the slot so as to absorb all the 

 a. rays without appreciably affecting the j3 or y activity. The 

 difference between two measurements made, one with the 

 mica off and one with the mica on (both being made with 

 the magnet on to deflect the /3 rays) gave the a activity. 



60 



40 



8 











/ 







7 ,'J 



\ // 



tstf / 







^oo 



400 



600 



T/ME /N HOURS. 



The variation of the a. activity with time is shown in the 

 figure, experimental points being indicated by the circles. 



