124 Ellen Gleditsch — Life of Itadium. 



and it is particularly free from all alteration products. It is 

 true that it contains some thorium ; in the way I determine the 

 radium content some thorium emanation may be brought into 

 the electroscope with the radium emanation. I have some- 

 times observed, that the current was higher the minute the 

 emanation was brought into the electroscope, than ten minutes 

 later. But the measurements are always taken three hours later, 

 when the current due to the radium emanation has reached 

 its maximum value, and during the same period the thorium 

 emanation has died away. Further, I have often demonstrated 

 that the activity of the active deposit from thorium can not 

 have influenced the results. Three hours after the removal of 

 the emanation, practically no activity is left in the electroscope, 

 and after 12 hours no trace whatever of activity can be 

 detected. 



It would certainly be of interest to confirm the result 

 obtained from broggerite by using other minerals. 



Conclusions. 



The growth of radium in solutions of ionium preparations 

 separated from different uranium minerals has been measured. 

 The results obtained for the most carefully prepared solutions 

 are : The disintegration constant of radium has a value of 



4-22 X 10- 4 (year)" 1 

 and 4-14 X 10~* (year)- 1 



The half-value period of radium indicated is accordingly : 

 1642 years and 1674 years. The result agrees very closely 

 with the value found by Sir Ernest Rutherford. 



In concluding, I wish to express my thanks to Mr. Boltwood 

 for the kindness with which he received me in his laboratory, 

 for his interest in the work and his many valuable suggestions. 



The work described in this paper was made possible through 

 the fact of my receiving a fellowship from the American 

 Scandinavian Foundation. I desire to express here my appre- 

 ciation of their generosity. 



Kristiania, Norway, October 11, 1915. 



