of Radium and Uranium. 5 



tion chamber with a capacity of about three liters. The 

 separation and collection of the radium emanation, its 

 transfer to the electroscope and the measurement of its 

 radioactivity were carried out according to methods 

 which have already been described. 11 



Ratio of the Activity of a Uranium Mineral to the Activity ofi 

 the Contained Uranium. 



The relation of the activity of the parent element, 

 uranium, associated with equilibrium amounts of all of 

 its disintegration products, to the activity of the parent 

 element alone, is a fundamental quantity of great impor- 

 tance to any consideration of the relations existing 

 between the individual products themselves. The ac- 

 tual progenitor of the series is uranium I, but this can 

 not be isolated from its invariable associate and isotopic 

 product, uranium II. The combined effect of these two 

 elements when mixed in equilibrium proportions can be 

 determined, however, and this can be compared with the 

 activity of a similar mixture containing all the other 

 disintegration products in equilibrium proportions. 



Such a mixture is furnished by a pure, primary, un- 

 altered uranite. A mineral containing a low proportion 

 of thorium is preferable since a correction must be made 

 for the activity of the thorium products present. A 

 specimen of uraninite from Spruce Pine in the posses- 

 sion of the authors was considered to fulfill all the 

 necessary requirements. It consisted of essentially un- 

 altered material selected with much care from a consid- 

 erably larger quantity. It contained less than 0*2% of 

 silica and residue insoluble in dilute nitric acid. A 

 determination of the uranium content was made by one 

 of the authors and by Ledoux and Co. of New York 

 City. 12 The mineral contained 1-9% of thorium oxide. 



In determining the activity of uranium a very pure 

 specimen of uranoso-uranic oxide was used. This had 

 been prepared from a specimen of especially pure ura- 

 nium nitrate obtained by fractional recrystallization of 

 a much larger quantity (see p. 3). The oxide was made 

 from the nitrate with all the precautions which have been 



u Boltwood, this Journal, 18, 378, 1904; Phil. Mag., 599, 1905. 



12 The authors wish to express here their obligation to Ledoux & Co. 

 for this favor and to state their appreciation of the value of this carefully 

 conducted analysis. 



