1912] 



on the Oriqin of Radium. 



405 



radium au intermediate product existed of period of life great by com- 

 parison with the time of the experiment. Such a product would 

 enormously retard the initial growth of radium. Its existence com- 

 plicates what first appeared as a very simple problem in many other 

 ways. It is no longer a question of simply detecting a growth of 

 radium. It is necessary to measure the form of the growth-curve 

 accurately. 



In the first place this intermediate parent must be present in 

 uranium minerals, and therefore, to greater or less extent, in com- 

 mercial uranium salts. The mere separation of radium therefrom 



120 



Fig. 3. 



initially, as in the first experiment, is not sufficient purification. In 

 addition every trace of the intermediate parent must also be sepa- 

 rated, or a growth of radium will not prove that uranium is the 

 parent. On this account, in conjunction with Mr. T. D. Mackenzie, 

 a fresh series of experiments were begun in Glasgow in 1905, in a 

 new laboratory uncontaminated by radium. Three separate quanti- 

 ties, each initially of 1 kilogram of uranyl nitrate, were purified by 

 repeated extraction with ether, which was considered to be the method 

 most likely to separate all the impurities, not merely the,, radium. 



2."E 2 



