112 Ellen Gleditsch—*- Life > of Radium. 



Art. III. — The Life of Radium ; by Ellen Gleditsch. 



[Contributions from the Sloane Laboratory of Yale University.] 



Some years ago Professor B. B. Boltwood indicated a very 

 direct method for determining the disintegration constant of 

 radium, and also made some determinations of it.* It was at 

 that time generally recognized that radium was a disintegration 

 product of uranium ; it was known that the two elements 

 uranium and radium occurred in nearly constant proportion in 

 the uranium minerals. On the other hand several attempts to 

 prove the growth of radium in uranium solutions had failed, 

 so it was probable that the production of radium from 

 uranium-X was not a direct one, but took place through an 

 intermediate long-lived substance. Boltwood f succeeded in 

 1907 in finding a new substance in the radioactive minerals ; 

 this new element, ionium, produced radium at a measurable 

 rate. It therefore seemed possible to determine the constant 

 of change of radium from the growth of radium in ionium 

 preparations. Boltwood's experiments consisted in a separa- 

 tion of the ionium from known quantities of uranium 

 minerals and the comparison of the amounts of radium pro- 

 duced by the separated ionium in known periods with the 

 amounts of radium associated with it in the minerals. 



The radium present in a mineral was determined by meas- 

 uring the activity of the equilibrium amount of radium 

 emanation evolved from an average sample of the mineral and 

 by comparing it to the activity of the emanation from a solution 

 containing a known amount of radium. The solution contain- 

 ing the ionium from a mineral was sealed up in a glass bulb, 

 and from time to time the radium emanation which had 

 accumulated in it was boiled off and its activity measured. 

 The quantity of emanation present is a measure of the radium 

 present in the solution, though for short periods of accumu- 

 lation the quantities are not directly proportional. 



The mathematical discussion of the problem has been pub- 

 lished by Rutherford.:}: The amount of radium present in an 

 ionium solution at any time consists of two separate factors: 

 the quantity present with the ionium at the start and the quan- 

 tity formed by the ionium in the time passed since the start. 

 If a quantity of radium, q , is present in the ionium solution at 

 the start, the emanation will accumulate and after a time t 

 will be equal to 



where X is the disintegration constant of the emanation. 



* This Journal, xxv, 493, June 1908. 



t This Journal, xxii, 537, 1906 and xxiv, 370, 1907. 



JPhil. Mag., xiv, 733, 1907. 



