2S2 Boltwood — Radio-activity of Uranium Minerals. 



The average value of the ratios obtained from the first four 

 specimens is 4 - 69, a number differing by less than 4 per cent 

 from the value of the same ratio as determined by McCoy and 

 Ross. The results may be taken as indicating that tiie activity 

 of a uranium mineral containing its equilibrium amount of 

 emanation is about 4*7 times the activity of the uranium which 

 is present in the mineral.* 



Relative Activity of Radium and Uranium in Minerals. 



A solution was prepared by dissolving a few milligrams of 

 recrystallized radium-barium chloride in 250 cc of distilled water 

 containing a little free hydrochloric acid.f The emanation 

 produced by a portion of this solution was compared with 

 the emanation produced by a standard solution of radium 

 bromide.;}: The amount of the radium in one cubic centimeter 

 of the chloride solution was thus found to be 8'5xl0~ 10 gram. 

 By a comparison of the emanation formed in 10 co of this solution 

 with the emanation produced in known amounts of the analyzed 

 nraninites (Nos. 1, 2, 3, 4 and 5. Table IV) it was determined 

 that the radium in 10 c0 of the chloride solution was equal in 

 amount to that associated with 0*0250 gram of uranium in the 

 minerals. 



Portions of this solution 10 cc in volume were evaporated to 

 dryness in shallow glass dishes under conditions which insured 

 the complete removal of radium emanation and its immediate 

 active products. The activity of the residue remaining in the 

 form of a very thin film was then determined in the electro-, 

 scope. 



The following values were obtained for the activities : 



1-396, 1-373, 1-437, 1-341 ; average 1-386 div. per min. 



The activity of 0*0250 g. of pure uranium was equal to 124 X 0*25 

 -— 3-10 div. per min. 



1-386 



= 0-447 



3-10 



namely, the activity of the radium itself in the minerals was 

 0-447 that of the uranium present. 



Because of the variation shown in the separate results above 

 given, and particularly because of a slight uncertainty as to 

 the effect of the sides§ and non-conducting material of the glass 



* In a communication published in Nature for January 3, 1907, the value 

 5 3 was given for this ratio. This high and incorrect value was obtained 

 under the erroneous assumption that the substance obtained by moderately 

 heating the oxide of uranium in oxygen was pure U 3 O fl . 



f For further details concerning the preparation of this solution see this 

 Journal, xxi, 410, 1906. 



% Rutherford and Boltwood, this Journal, xxii, 2, 1906. 



§ 9 mm in height. 



