Boltwood — Production of Radium from Uranium. 243 



Tlie type of electroscope used in this investigation has 

 already been described (this Journal, xviii, 97). The ema- 

 nation from the radium associated with 0*1 gram of uranium 

 in a radio-active mineral caused a leak of approximately 21 

 divisions per minute. Assuming that the 100 grams of uranium 

 nitrate contained 48 grams of uranium, the leak correspond- 

 ing to the quantity of radium in radio-active equilibrium with 

 48 grams of uranium would be approximately 10,000 divisions 

 per minute. The normal air leak of the instrument was 0*012 

 division per minute, and an increase of 0*005 division per 

 minute could have been detected with certainty. The electro- 

 scope was therefore capable of indicating the presence of a 

 quantity of radium equal to 5 XlO -7 of the equilibrium quan- 

 tity. The actual quantity of radium equivalent to a leak of 

 0*005 division per minute was 1*7 XlO -11 gram.* 



On introducing the gases presentf in the uranium solution 

 into the electroscope no increase in the leak of the instrument 

 could be detected although the observations were continued 

 over a period of eight hours. The quantity of radium present 

 at the start was therefore less than 1*7 XlO -11 gram. 



The uranium solution in the bulb was allowed to cool, and 

 the neck of the bulb was again sealed. At the end of six 

 months from the start, in January, 1905, the uranium solution 

 was again tested under conditions identical with those under 

 which the first test was carried out. Entirely negative results 

 were obtained and the quantity of radium then in the solution 

 was still less than 1*7 XlO -11 gram. A similar test was con- 

 ducted on August 2, 1905, 390 days from the commencement, 

 and no evidence of the presence of radium emanation was 

 even then obtained. It can therefore be positively stated on 

 the basis of sound experimental data that in 390 days the 

 quantity of radium formed from 48 grams of uranium in a 

 uranium nitrate solution is less than 1*7X10 _U gram. 



The quantity of radium which can have been produced in 

 the given time is therefore less than one two-millionth of the 

 equilibrium quantity and less than one sixteen-hundredth of 

 the quantity which would be expected from the disintegration 

 theory if the value of \ for radium is taken as 8*8 XlO -4 

 (year) -1 . J The quantity is furthermore only about one-tenth 

 of the quantity assumed by Mr. Soddy to have been formed 

 from an equal quantity of uranium in his solution during an 

 interval of eighteen months. 



It is important to add that the whole series of measurements 

 has been conducted in a laboratory which has been carefully 



* Rutherford and Boltwood, this Journal, xx, 55. 



f At the end of the 30-day period. 



% Rutherford, Trans. Roy. Soc. London, (A) cciv, 215. 



