114 Ellen Gled'dsch-^-Life of Radium. 



has corrected the number according to the International Stand- 

 ard and gives the value as 1690 years. 



The disagreement between this value and the 2000 years 

 found by Boltwood is too large and makes it important to 

 redetermine the constant of radium. 



Mr. Boltwood suggested that I undertake this determination 

 and I have done it partly in the Sloane Laboratory at Yale 

 University, New Haven, Conn., partly at the University in 

 Kristiania, Norway. 



During the time elapsed since Mr. Boltwood made his 

 determinations of the period, nothing has been found that 

 might in any way make the method less reliable. The 

 determination of radium in solutions by measuring the activity 

 of the emanation has proved an absolutely sure and satisfactory 

 method. Later research concerning ionium seems to indicate 

 that this substance has a still longer life than was previously 

 supposed, which makes it still more fitted for our experiment. 

 And finally, later experiments concerning the ratio between 

 uranium and radium in minerals have shown that exceptions 

 from the constant ratio are to be found in minerals of later 

 origin, but at the same time the ratio proves to be extremely 

 constant in primary uraninites, 



Mr. Boltwood kindly permitted me to measure one of his 

 old solutions that had served for his determination in 1908. 

 It was the solution which he trusted most, given as Ionium 

 Solution 5 in his paper.* I made two measurements and 

 calculated the values from these and Mr. Boltwood's first 

 measurement made about 6 years earlier. 



\ T o. 



Days from start 



Growth of radium per day 



1 



2423 



0-00968 X 10" 9 



2 



2450 



0-00978 X 10" 9 



I give these values in terms of the international standard. 

 According to the standard used by Mr. Boltwood, they would 

 give: 



0-01016 X 10- 9 

 0-01027 X 10- 9 



Mr. Boltwood in his paper gives 0-0102 X 10~ 9 gram. 



The agreement is surprisingly good and proves in a delinite 

 way that the production of radium in ionium solutions is 

 constant and further that the rate of change of ionium is 

 very slow. It thus offers the best evidence of the reliability 

 of the method. 



Thus no fundamental objection can be raised against Bolt- 

 wood's method. 



*Loc. cit. 



