426 Boltwood — Thorium Minerals and Salts. 



shown in the results obtained by these two independent 

 methods is certainly striking, and would seem to warrant the 

 conclusions which have been reached in the matter. The 

 thorium nitrate from thorianite used by Mr. Dadourian was 

 prepared from the thorium oxide No. 6, mentioned on page 

 422 of this paper, and the thorium nitrate from North Caro- 

 lina monazite was prepared from the thorium oxide denoted in 

 the list as No. 7. The fact that Mr. Dadourian's values for 

 the thorium activities of these two preparations are quite 

 independent of any actinium or radium which might have 

 been present, adds a special significance to the numbers 

 obtained by him, as well as to the numbers which he obtained 

 for the other thorium preparations. The agreement of the 

 results obtained by both of us would appear to support the 

 suggestion made by Halm,* that the disintegration of thorium 

 itself is rayless. 



It affords me much pleasure to acknowledge my indebted- 

 ness to the Welsbach Light Company, and especially to their 

 chemist, Mr. H. S. Miner, for their great kindness and gener- 

 osity in supplying me with the greater part of the materials 

 used in these investigations. Their uniform courtesy and 

 liberality has been sincerely appreciated. 



Conclusions. 



1. The specific activity of thorium with its equilibrium 

 quantities of disintegration products is constant. 



2. Radio-thorium is a disintegration product of ordinary 

 thorium. 



3. Certain of the ordinary, commercial salts of thorium con- 

 tain only about one-half of the equilibrium quantity of radio- 

 thorium corresponding to the thorium present. 



4. The change undergone by thorium in disintegrating to 

 form radio-thorium is probably rayless. 



New Haven, Conn., April, 1906. 



*Loc. cit. 



