422 Boltwood — Thorium Minerals and Salts. 



"basic" sulphate of thorium separated. This was ignited to 

 a high heat to form the oxide. 



5. Thorium oxide prepared from thorianite by the analyti- 

 cal method described earlier in this paper. The mineral was 

 first dissolved in concentrated nitric acid. 



6. Thorium oxide which had been prepared from thorianite. 

 The mineral had been decomposed by fusion with sodium 

 bisulphate and. the thorium salts purified by conversion into 

 the double ammonium oxalate as in the case of No. 5 above. 



7. Thorium oxide obtained from North Carolina monazite 

 sand by the operations described under the analysis of this 

 mineral. 



8. Thorium oxide supplied by Mr. H. S. Miner, chemist of 

 the Welsbach Light Co., and stated by him to have been 

 obtained from monazite sands by the ordinary analytical opera- 

 tions in which the thorium was separated from the other rare 

 earths by repeated precipitation with sodium thiosulphate. 



All of the samples of oxides here mentioned had been pre- 

 pared at least one month previous to the time at which the 

 measurements given in the table were carried out, and all had 

 been subjected to the highest temperature of the blast lamp 

 at the time of their preparation. 





Table 



II. 











Activity 



per 



gram of oxide. 





Small 





Large 



Number. 



Source of oxide. 



electroscope. 



electroscope. 



1 



Mantel dust 



28 





50 



2 



Welsbach nitrate 



23 





41 



3 



a ie 



26 





46 



4 



a Li 



28 





49 



5 



Thorianite 



75 





124 



6 



a 



66 





116 



1 



N. C. monazite 



63 





113 



8 



Miner's oxide 



62 





110 



The activities of the oxides were determined for thin films 

 in exactly the same way that the activities of the minerals 

 were determined. • 



It is important to mention the fact that careful attention 

 was given to the question of the emanating power of both the 

 natural minerals and the separated thorium oxides described 

 in this paper. The minerals were chosen particularly because 

 of their low emanating power for both radium and thorium 

 emanations, which was not over one per cent for the highest. 

 Rutherford has shown* that the emanating power of ordinary 



*Phys. Zeit., ii, 429, 1901. 



