Ashman — Radio- Activity of Thorium. 65 



Art. Y. — The Specific Radio- Activity of Thorium and 

 its Products ; by G. C. Ashman. 



The radio-activity of thorium compounds and minerals was 

 discovered by Schmidt* and independently by Mme. Curief; 

 StruttJ also found that all thorium minerals examined by him 

 showed radio-active properties. Debierne§ discovered actinium 

 while working up uranium ores containing thorium. The 

 similarity of the chemical properties of actinium and thorium 

 led to the suggestion by a number of chemists that the activity 

 of thorium is not due to thorium itself but to slight traces of 

 actinium, since actinium is very difficult to separate from tho- 

 rium and the other rare earths. This view is hardly tenable 

 in the light of the fact that thorium and actinium give emana- 

 tions with totally distinct properties : their rates of decay are 

 widely different, and their products are in no way identical. In 

 1902 Hofmann and Zerban|| announced that the} 7 had obtained 

 an inactive thorium preparation from a Brazilian monazite sand, 

 and that thoria prepared from various minerals, although 

 active at first, became inactive after a few months. Basker- 

 ville and Zerbanl" also claimed they had separated from a 

 South American mineral thoria which was perfectly inactive. 

 A little later Hahn** and Ramsayff extracted from the min- 

 eral thorianite a radio-active preparation several thousand 

 times more active than thorium itself and yielding a propor- 

 tionately larger amount of thorium emanation. This discovery 

 made it appear possible that the activity of thorium might be 

 due wholly to radiothorium since the latter possesses an extreme 

 tendency to retain its association with that element. Papers bear- 

 ing on this question were published simultaneously by Bolt- 

 wood,^by Dadourian,§§ and by McCoy and Ross||]|. The con- 

 cordant results of these three independent investigations proved 

 conclusively that the intensity of the radio-activity associated 

 with thorium in any mineral is directly proportional to the tho- 

 rium content of the mineral. This work, together with the 

 preparation of radiothorium from thorium minerals by Hahn and 



*Ann. d. Phys., lxv, 141, 1898. 



fC. R., cxxvi, 1101, 1898; 



iProc. Roy. Soc., London, lxxvi, 88 and 312, 1905. 



$C. R., cxxix, 593, 1899 ; cxxx, 206, 1900. 



||Ber. d. Chem. Ges., xxxv, 531, 1902. 



IT J. Amer. Chem. Soc, xxvi, 1642 1904. 



**Ber. d. Chem. Ges., xxxviii, 3371, 1905. 



ff J. de chim. phys., iii, 617, 1906. 



itThis Journal, xxi, 409, 1906. 



§§Ibid., xxi, 427, 1906. 



HI Ibid, xxi, 433, 1906. 



Am. Jour. Sci.— Fourth Series, Vol. XXVII, No. 157.— January, 1909. 

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