THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. I. — The Relative Proportion of Radium and Uranium 

 in Radio-Active Minerals • by E. Rutherford and B. B. 

 Boltwood. 



In the July number for last year of this Journal, the writers 

 gave an account* of measurements which had been made to 

 determine the amount of radium present per gram of uranium 

 in a natural mineral. Since previous experiments had shown 

 that the amount of radium in a mineral was always propor- 

 tional to its content of uranium, it was pointed out that the 

 weight of radium present per gram of uranium was a con- 

 stant of considerable practical and theoretical importance. 

 The method adopted depended on the preparation of a stand- 

 ard solution of radium bromide and the amount of radium 

 emanation formed in it was compared with that formed in a 

 radio-active mineral containing a known quantity of uranium. 

 Since the electrical comparison of the relative amounts of 

 radium emanation can be made with considerable precision, 

 the accuracy of the results obtained by the determination 

 mainly depended on the exactness with, which the solution of 

 radium taken as the standard had been prepared. 



The standard solution was prepared by Rutherford and Eve. 

 A crystal of radium bromide was taken from a stock which 

 previous experiments had shown to emit heat at the rate of 

 110 gram-calories per hour per gram and was consequently 

 probably nearly pure. The amount of radium bromide was 

 determined by direct weighing and also by comparing its 7-ray 

 effect with that produced by a known larger weight of the 

 same stock of radium bromide. The crystal of radium bro- 

 mide was then dissolved in distilled water and by successive 

 dilutions solutions were prepared to contain 10~ 2 , 10~ 4 and 



*This Journal, xx, 55, 1905. 



Am. Jour. Sci.— Fourth Series, Vol. XXII, No. 127.— July, 1906. 



1 



