Relation 1 etwein Uranium and Radium. 289 



started much later it already furnishes information equally 

 advanced to that in the first experiment. For the future it 

 will be much the more valuable of the two. 



It should be mentioned that to guard against the unknown 

 gas being absorbed by the mercury of the pump a side-tube 

 containing mercury was sealed on the flask. The soda-lime 

 and phosphorus-pentoxide tubes are not rejected when used 

 up, but sealed up and kept for future examination. 



Experiment III. 



The first disintegration product of uranium is known to be 



uranium X, discovered in 1900 by Sir William Crookes. Its 



period (in which one-half changes) is 22 days, and in this time 



a uranium solution after purification regenerates one-half of 



the equilibrium quantity of new uranium X. The experiment 



consisted in separating the uranium X regenerated by a 



solution of uranium in the course of some weeks after 



purification and setting it up on the mercury pump to be 



tested for the growth of radium. Such a growth is 



• • • 



theoretically to be expected, but it must necessarily be much 



less than in the case of uranium itself, in which there is 



a steady production of new uranium X replacing that 



disintegrating. 



The kilogram of uranyl nitrate employed was that used in 

 the former experiment and contained an excess of barium 

 nitrate. It was extracted with ether, which Crookes found 

 completely separated the uranium X, and tested for radium on 

 Dec. 16th, 1905, fifty- one days from purification. The leak 

 was 5'1 in an electroscope giving 2' 6 to the y-ray te>t. 

 An attempt made to separate the uranium X reproduced 

 in this interval by the ammonium carbonate process of 

 Crookes failed with the large quantity on account of the 

 insolubility of the uranium precipitate. The ammonium 

 salts were removed by evaporation with nitric acid, and 

 ignition in small quantities. An attempt was then made 

 with BecquerePs recently published method of removing 

 uranium X (Comjjt. Rend. 1905, vol. cxli. p. 485), and the 

 uranium-nitrate solution was boiled with, in all, eleven suc- 

 cessive quantities of Kahlbaunr's charcoal. This reduced 

 the /5 radiation, and therefore the uranium X present, to 

 20 per cent, of the initial, and further boiling with three 

 successive quantities of lamp-black did not reduce this amount. 

 Unfortunately these uranium X preparations were lost in the 

 explosion before mentioned. 



Ultimately the ether-extraction process was adopted. On 

 June 18th. 1900, after the uranium solution had been kept for 



