272 JBoltwood — Radio-activity of Uranium Minerals. 



mg varying proportions of thorium and uranium demonstrated 

 that the specific activity of the thorium and its products in a 

 mineral is constant* and furnished reliable data by which the 

 activity of a uranium mineral could be so corrected as to elimi- 

 nate that fraction of the total activity which was due to the 

 thorium contained in it. The conclusions with regard to 

 thorium were independently confirmed by Dadourian,f by 

 McCoy and Ross:]: and by Eve.§ 



The experiments described in this paper were begun over 

 two and one half years ago and have been steadily continued 

 throughout the intervening period. Various improvements 

 and modifications have suggested themselves from time to 

 time and much of the work has been frequently repeated in 

 order to insure greater accuracy and reliability. The results 

 are even now by no means so satisfactory as could be desired 

 and the repetition of some of the work would undoubtedly 

 lead to more trustworthy values. It is believed, however, that 

 the values as found are sufficiently accurate to permit certain 

 important deductions and conclusions to be drawn from them. 



It is of interest to note that the methods which were 

 employed in several cases depended on the quantitative chemi- 

 cal separation of a number of the radio-elements from the 

 complex mixture of active substances present in the mineral. 

 Information as to the exact chemical behavior of the radio- 

 elements other than uranium and thorium which can be found 

 in the literature is extremely meager and, as will be pointed 

 out later, is frequently untrustworthy. It has therefore been 

 necessary not only to work out the methods of separation 

 which were used, but to demonstrate that the separations were 

 more or less complete by confirmatory evidence of a purely 

 physical character. 



The Hadio-active Measurements. 



The measurements of the radio-activity of the different 

 minerals and preparations were made in an electroscope, a plan 

 of which in vertical cross-section is shown in fig. 1. The 

 ionization chamber was 14 tm in height, 19 cm in diameter at the 

 middle and 15 cm in diameter at the top and bottom. It was 

 made from two tin pans loosely fastened together by a single 

 copper rivet which permitted the lower pan to be swung to one 

 side for the introduction of the preparation to be measured. 

 The preparations were placed on the bottom of the lower pan 

 and the two sections of the ionization chamber were firmly 



* Boltwood, this Journal, xxi, 415, 1906. 



t This Journal, xxi, 427, 1906. % Ibid., xxi, 433, 1906. 



§Ibid., xxii. 477, 1906. 



