406 



Mi\ Fredericlc Soddy 



[March 15, 



Observations on these preparations have now been in progress for six 

 or seven years. At the same time a portion of the impure fraction 

 sepai'ated from the origiuiil material was sealed up, freed from initial 

 radium by the barium sulphate method, and tested for radium from 

 time to time along with the pure uranium preparations. The diagram 

 (Fig. 3) shows the growth of radium in this impure fraction. The 

 unit used for expressing the quantity of radium is 10 ~^^ gram. It 

 confirms unequivocally the original observation that a substance is 

 present in commercial uranium salts capable of generating radium 

 and not removed from it by the barium sulphate method used first 

 for separating the radium, but separated, at least mainly, by the 

 ether method. 



The methods of stoiing the preparation, and of extracting the 

 emanation from the solutions and measuring it, are illustrated in 



«--^i— M :f/few^r:g»'^^ 



Fig. 4. 



Figs. 4 to 8. Figs. 4 and 5 represent a diagram and photograph 

 respectively of the ari'angement used for boiling out the emanation 

 from the uranium in the fl;isk A (Fig. 4) under reduced pressure, 

 and of collecting it in the bottle G, from which it is expelled into 

 the exhausted electroscope (Figs, fi and 7). The leak is taken after 

 P. hours, the electroscope being kept charged throughout the whole 

 interval. The electroscope is calibrated by similar tests with solutions 

 containing known small amounts of pitchblende of known ui-aniura 

 content. Fig. H represents a more recent experiment with a very 

 large quantity of uranium in which a reflux condecsor is sealed into 

 the flask. This addition makes it possible to work with large volumes 

 of fluid even nioi'e easily and accurately than for the older quantities. 



