Relation between Uranium and Radium. 275 



valuable preparations of uranium X which had been separated 

 and set up to be tested for the generation of radium. 



The investigation here described has not been confined 

 to the question whether radium is being produced from 

 uranium. Special experiments have also been started to see 

 whether uranium produces actinium, and whether actinium 

 produces radium. Several separations of uranium X from 

 uranium have also been made successively from the kilogram 

 of uranyl nitrate used in the old experiment, and one is 

 now under observation for the generation of radium. Finally > 

 all the residues that have survived from the various extrac- 

 tions of uranium with ether, and other methods of purification 

 attempted, have recently been separated very perfectly from 

 radium, by means of barium sulphate precipitations, and are 

 also being kept under observation for the regeneration of 

 radium. Up to the time of writing, however, all these ex- 

 periments have yielded only negative results, although in 

 one or two of the preparations a slight increase in the con- 

 tent of radium is recorded, too small however to be yet 

 certain of. 



Method of Testing for Radium. 



The method previously used for testing for the presence 

 of radium by bubbling air through the solution into the 

 electroscope, was, in the present work, employed only for 

 preliminary tests. It gives trustworthy indications of the 

 presence of radium, and a rough quantitative indication of 

 the amount, but is far inferior in accuracy to the methods 

 employed by Strutt (Proc. Roy. Soc. 1905, Ixxvi. A. p. 89) and 

 Boltwood (Am. Jour. Sci. 190-i, xviii. p. 379), which are cha- 

 racterized by the feature that the radium emanation present is 

 expelled from the solution by boiling. This secures the com- 

 plete expulsion of the emanation, whereas only a fraction of 

 the emanation is removed by bubbling air through the cold 

 solution, and this fraction depends somewhat upon the 

 conditions of the experiment. 



The method employed in the present work, which however 

 is being replaced more and more as opportunity offers by a 

 shorter and more convenient method, consisted in the removal 

 of the emanation from the solution by means of a mercury- 

 pump after boiling in vacuo, collecting the gas in a mercury 

 gas-holder, and expelling it into the electroscope. The 

 uranium solution, usually containing a kilogram of uranyl 

 nitrate, is contained in a three-litre flask, to the neck of 

 which is sealed a vertical all-glass condenser of the rapid- 

 cooling type. The end of the condenser is provided with a 



