734 Prof. E. Rutherford on the 



parent, since it possessed a life long compared with radium 

 and was always found associated with it. There were two 

 obvious methods of attack to throw light upon this question, 

 one direct and the other indirect. The first consisted in an 

 examination to see whether in course of time radium ap- 

 peared in a solution of uranium initially freed from radium. 

 The second depended upon an examination of the relative 

 amount of radium and uranium in radioactive minerals. 

 According" to theory, if uranium is the parent of radium, the 

 ratio of the amount of radium in any mineral to that of 

 uranium should be constant. The constancy of this ratio 

 has been completely substantiated by the independent work 

 of Boltwood*, Struttj, and McCoy i; and there can be no 

 doubt that uranium and radium are genetically connected. 

 Rutherford and Boltwood § have found that for every gram 

 of uranium in a mineral, there is present 3*8 x 10~ 7 gram of 

 radium. 



The question of: the growth of radium in a uranium solu- 

 tion was first attacked by Soddy ||, and later by Boltwood If. 

 Without entering into the details of these important investi- 

 gations, it suffices to say that, in carefully purified uranium 

 solutions, no growth of radium has been observed, over the 

 space of the few years that observations have been in progress. 

 If radium is produced at all, it is certainly produced at less 

 than 1/1000 of the rate to be expected theoretically. This 

 result is not necessarily inconsistent with the view that 

 radium is a transformation product of uranium, for the 

 absence of observable growth of radium in a limited time is 

 to be expected, if one or more products of slow transformation 

 exist between uranium and radium. 



In the meantime, Boltwood** had approached the problem 

 from a different direction. B}^ a special method, the actinium 

 was separated from a kilogram of carnotite. A solution of 

 this actinium, initially containing very little radium, was 

 placed aside and examined 120 days afterwards. A notable 

 increase in the amount of radium was observed. In addition, 

 the rate of growth in this interval was about that to be ex- 

 pected if radium were half transformed in about 2000 years 

 — a result in conformity with calculations of the probable 

 life of radium. The work of Boltwood marks a definite and 



* Boltwood, Phil. Mag. April 1905. 

 t Strutt, Proc. Roy. Soc. March 2, 1905. 

 t McCoy, Ber. d. D. Chem. Ges. No. 11, p. 2641, 1905. 

 § Rutherford and Boltwood, Amer. Journ. Sci. July 1906. 

 || Soddy, Phil. Mag. June 1905, Aug. 1907. 

 ^[ Boltwood, Amer. Journ. Sci. Sept. 1905. 

 ** Boltwood, < Nature/ Nov. 15, 1906. 



