Radiotlwrium from Mesotlwrhim 2. 713 



The percentage of the total ionization due to one a ray of 

 each of the series was calculated from Geiger's * formula, 

 the figures being corrected for the magnet electroscope used 



-the equivalent of 1*5 cm. of air being subtracted from the 



range 



At a distance x along the range, the ionization i is 



£= a(R — x)$ 



where a is a constant. 



Then „ . 



If 5 = k(R- 1-5)3. 



This gives for the series : — 



RaTh 14^2 



ThX \6-b-) 



ThEm 19-6 [-58-3 



ThA 22-2J 



ThC ........ 6-0| 97 . 



ThC 21-5J Ai ° 



The a radiation is thus proportional to 



14-2X 2 B + 58'3X 3 C + 27*5X 5 E, 



where B, C, and E are the amounts, and X 2 , \ Z) and X 5 are 

 the radioactive constants of RaTh, ThX, and ThC re- 

 spectively. By calculating the amount of B, C, and E 

 present at any time in terms of their exponential functions 

 we get the ionization given by 



I = ]c[57'6-7-6e- Xlt -b5-6e- k3t +5-6e- Mt l, 



where k is a constant and X l5 X 3 , and X 4 the radioactive con- 

 stants of MesoTh 2, ThX, and ThB respectively. 



The mesothorium 2 was obtained in the following 

 manner : — The chemical methods were worked on the basis 

 of its analogy to actinium f . To a solution containing 

 mesothorium 1 associated with about 100 gms. of barium 

 chloride a few drops of thorium nitrate were added in acid 

 solution and the thorium precipitated out again by ammonia. 

 This brought down the mesothorium 2, the radiothorium, 

 and the thorium B and C present. The thorium and the 

 radiothorium were removed by dissolving the precipitate in 

 the smallest quantity of acid, neutralizing, and adding 



* Proc. Koy. Soc. A. lxxxiii. p. 513 (1910). 

 r Fleck, Trans. Chem. Soc. ciii. p. 381 (1913). 



