JBolUvood — Radio-activity of Uranium Minerals. 297 



uranium. The activity of one gram of pure, anhydrous radium 

 bromide (58 per cent Ra) over 30 days old and retaining all of 

 its emanation will therefore be the same as that of about 

 4,200,000 grams of pure uranium. These values are based on 

 the assumption that the radium bromide used by Rutherford 

 and Barnes,* for determining the heating effect of radium, 

 was pure, since this material was used in the preparation of the 

 standard solution. 



Dealers and manufacturers of radium bromide are in the 

 habit of using as a measure of the activity of the pure salt the 

 expression " 1,800,000 X Uranium." I have never found a 

 definite statement as to the exact meaning of this expression 

 or the manner in which the activity is determined. I have 

 observed,f however, , that thin films obtained by the evapora- 

 tion of dilute solutions of radium bromide may retain less than 

 fifty per cent of the emanation formed within them, so that 

 the number " 1,800,000 X Uranium" may express with a rough 

 degree of approximation the activity of pure radium bromide 

 measured under similar conditions. 



Summary of Mesults. 



The values for the relative activities of the uranium and the 

 various products contained in a uranium mineral which are 

 indicated in the preceding experiments can be expressed as 

 follows, the activity of the uranium being taken as unity : 



Element Activity- 

 Uranium .... 1 *00 



Ionium 0*34 



Radium 0-45 



Radium emanation 0'62 



Radium A 0-54 



Radium B 004 (?) 



Radium C 0-91 



Radium F (polonium) 0-46 



Actinium products - 28 



Total activity 4-64 X Uranium. 



If the value to be theoretically expected for the relative 

 activity, namely, - 49xU, be taken for radium F, and also 

 the maximum values found for the activity of ionium (0'35 XU) 

 and the actinium products (0 - 36xU), the sum of the separate 

 activities is equal to 4 "76 XU. These numbers are in good 

 agreement with the corresponding value of 4*69 XU found 

 from the direct measurement of the uranium minerals. The 

 numerical value of these different quantities will show more or 



*Phil. Mag., viii, 202, 1904. f This Journal, xxi, 414, 1906. 



