Boltwood — Thorium, Minerals and Salts. 415 



Art. XXXVIL— The Radio-Activity of Thorium Minerals 

 and Salts /* by Bertram B. Boltwood. 



The radio-activity of the element thorium has been the 

 cause of much discussion and the subject of many apparently 

 contradictory statements in the literature. Following the 

 original announcements by Schmidtf and by Mme. Curie,;}: 

 that the thorium minerals and salts possessed radio-active pro- 

 perties, Hofmann and Strauss published a paper§ in which it 

 was stated that they had separated an inactive thorium com- 

 pound from a specimen of the mineral euxenite. In a paper 

 by Hofmann and Zerban|| the claim was later made that an 

 inactive thorium preparation had been obtained from a Brazil- 

 ian monazite sand, and that thoria separated from broggerite, 

 cleveite and samarskite, although active when first prepared, 

 had lost its activity some months after its removal from the 

 minerals. Following this in another paper,^[ the same authors 

 claimed to have separated entirely inactive thorium oxide 

 from a specimen of Norwegian gadolinite. It has also been 

 stated by Baskerville and Zerban** that a new source of inac- 

 tive thorium had been found in a "rock" from South Amer- 

 ica. 



In apparent contradiction to the above we have the state- 

 ments of Rutherford and Soddy+f that ordinary commercial 

 thorium nitrate and the purest thorium nitrate obtainable gave 

 equal proportions of thorium-X ; the statements of Strutt^ 

 that he was able to obtain measurable amounts of thorium 

 emanation from solutions of all of the thorium-bearing min- 

 erals, including euxenite and a large number of others, which 

 he tested ; and the statements of Mine. Curie and a number of 

 other investigators who had in all cases detected radio-active 

 properties in the thorium minerals which they had examined. 



The announcement by Hahn§§ that he had obtained a 

 highly radio-active preparation, from certain residues sepa- 

 rated from the mineral thorianite, which was many thousand 

 times more active than ordinary thorium and which gave out 



* The general results and conclusions reached in this paper were presented 

 at a meeting of the American Physical Society held in New York City on 

 February 24, 1906. 



f Annal. d. Phys., Ixv, 141, 1898. 



iCompt. rend., cxxvi, 1101, 1898. 



§ Berichte d. cheni. Ges. , xxxiii, 3126, 1900. 



|| Berichte, xxxv, 531, 1902. 



«U Berichte, xxxvi, 3093, 1903. 



** Jour. Am. Chem. Soc, xxvi, 1642, 1904. 



ffProc. Chem. Soc, xviii, 120, 1902. 



iiProc. Roy. Soc. Lond., A lxxvi, 88 and 312, 1905. 



£§Proc. Roy. Soc. Lond., A lxxvi, 115, 1905. 



