442 



McCoy and Boss — Thorium Compounds. 



All of the thorium activity measurements, as well as those 

 of uranium compounds and minerals, were made with a dis- 

 tance of 3 - 5 em between the active films and the charged elec- 

 trode. While this thickness of air is sufficient to absorb 

 practically all of the alpha rays of uranium, it is scarcely great 

 enough to absorb completely the more penetrating alpha rays 

 of some of the radium and thorium products." With a 

 greater distance than 3 - 5 cm between the films and electrode a 

 somewhat greater activity will be found for uranium and 

 thorium minerals. The general relationship between the 

 radio-activity and the composition of such minerals having 

 now been fully established, we are starting a new series of 

 measurements on minerals with the object of determining 

 their activities under conditions such that the maximum 

 ionizations due to the alpha rays can take place in the space 

 between the film and the electrode. 



In the analyses of the minerals the thorium was weighed as 

 dioxide. This was very pure, chemically. It had been sepa- 

 rated by JNTeish's method, having been precipitated once by 

 oxalic acid, once by potassium hydroxide and two or three 

 times by m-nitrobenzoic acid. The activity measurements of 

 three such samples, B, C, and D, were made from time to time 

 until after about one month the activities had reached con- 

 stant maximum values. The Th0 2 then contained the maxi- 

 mum amounts of ThX, Em, ThA and ThB. The results of 

 the maximum values are given in Tables XI to XIII with 

 a summary in Table XIV. 



Table XI. Thorium Dioxide B. 



E 



•2267 



61-4 



60-9 



•00372 



1-04 



1170 



40-2 



40-1 



•00292 



'('*) 



0673 



25-1 



25-1 



•00268 



(■8) 



l±\ 



= -00243 









Table XII. Thorium Dioxide C. 



K 



2634 



68-2 



67-8 



•00389 



1-04 



1292 



41-8 



41-7 



•00310 



(•5) 



0657 



24-1 



24-1 



•00273 



(•2) 



ea= 



00230 



* Rutherford Radioactivity, p. 135,1904; Bragg, Phil. Mag., viii, 

 1904; Bragg and Kleeman, Ibid., x, 318 and 600, 1905. 



721, 



