56 Rutherford and Boltwood — Radium and Uranium. 



solution and was transferred to an air-tight electroscope, in 

 which its activity was measured. The observed activity corre- 

 sponded to the emanation from 1-584 Xl0~ 4 milligram of 

 radium bromide, which was assumed to be equivalent to 

 0-926 X 10" 4 milligram of radium. 



The activity of the maximum or equilibrium quantity of 

 emanation produced by the radium associated with one gram 

 of uranium in a radio-active mineral was determined by the 

 method which has already been described.* The mineral 

 chosen was a very pure sample of uraninite from Spruce Pine, 

 N. C, containing 74*65 per cent of uranium. 



The activity of the emanation from the standard radium 

 bromide solution was equal to 24*24 divisions per minute. The 

 activity of the emanation from 0*1 gram of the mineral was 

 equal to 14-45 divisions per minute, corresponding to 193*6 

 divisions per minute for each gram of uranium present. These 

 values indicate that " the qriantity of radium associated with 

 one gram of uranium in a radio-active mineral is equal to 

 approximately 7'4-XlO" 7 gram. One part of radium is there- 

 fore in radio-active equilibrium with approximately 1,350,000 

 parts of uranium. 



By the application of these numbers to the ordinary ores of 

 uranium it is possible to determine their actual content of 

 radium. Thus a high-grade pitchblende ore containing 60 

 per cent of uranium carries approximately 0*40 gram of 

 radium, equivalent to 0*69 gram of radium bromide, per ton 

 of 2,000 pounds. A low-grade 10 per cent uranium ore will 

 contain per ton approximately 0*067 gram of radium, equiva- 

 lent to 115 milligrams of radium bromide. 



The amount of radium occurring with uranium is about the 

 amount to be expected if uranium is the parent of radium, but 

 a satisfactory comparison of theory with experiment is not 

 possible until the relative activity of pure radium and pure 

 uranium is more accurately determined. Experiments in this 

 direction are in progress and the results will be given in a 

 later paper. A method has been devised for determining in 

 a radio-active mineral the proportion of the total activity due 

 to the presence of uranium, radium and the other radio-active 

 bodies. The results obtained lead to the conclusion that 

 actinium is not a direct product of uranium in the same sense 

 as is radium. An account of these experiments will be pub- 

 lished later. 



* Boltwood, loc. cit. 



