, 



480 A. S. Eve — Relative Activity of Radium and Thorium. 



plan for providing standards seems to be by comparison with 

 a sealed standard of radium bromide of known weight and 

 purity. 



Results. 



(1) Radium bromide is 4*5 X 10 6 times as active as Th0 2 , or 



radium is 6*9 X 10 6 times as active as thorium, meas- 

 ured by the 7-rays, when both are in radio-active equili- 

 brium. 



(2) The ratio of the quantity of radio-thorium per gram of 



thorium present in thorianite and in thorium nitrate has 

 been measured by Boltwood, using the a -ray method ; 

 by Dadourian, using the emanation method ; and, subse- 

 quently, by the writer, using the 7 -ray method. The 

 results obtained by these different methods are in good 

 agreement. 



With much pleasure I acknowledge the helpful advice of 

 Professor Rutherford. 



McGill University, Oct. 1906. 



