THE 



AMERICANJOURNALOFSCIENCE 



[FOURTH SERIES.] 



Art. VII. — On the Ultimate Disintegration Products of the 

 Radio-active Elements. Part II The Disintegration 

 Products of Uranium • by Bertram B. Boltwood. 



[Contributions from the Sloane Physical Laboratory of Yale University.] 



The general question of the nature of the ultimate disinte- 

 gration products of the radio-active elements, as indicated by 

 the occurrence of certain chemical elements in the radio-active 

 minerals, has been discussed in an earlier paper,* and it was 

 there pointed out that lead, bismuth and barium might per- 

 haps be included among the possible disintegration products. 

 As more recent experiments^ have indicated, however, that 

 actinium is probably an intermediate product between uranium 

 and radium, the number of possible ultimate products has 

 been correspondingly reduced. In addition to this careful 

 examinations have been made of specially selected samples of 

 typical primary uraninites from Branch ville, Conn., and Flat 

 Rock, ~N. C, and of thorianite from Ceylon, which have led 

 to the conclusion that neither bismuth nor barium can be con- 

 sidered as disintegration products in the main line of descent 

 from either uranium or thorium, at least on the basis of the 

 present disintegration theory. 



The conditions essential for the identification of the final 

 disintegration products of uranium from a study of the com- 

 position of the natural minerals which, contain this element 

 would appear to be the following : In unaltered primary min- 

 erals of the same species, and of different species from the 

 same locality, that is, in minerals formed at the same time and 

 therefore of equal ages, a constant proportion must exist 

 between the amount of each disintegration product and the 



*This Journal, xx, 253, 1905. f Ibid., xxii, 537, 1906. 



Am. Jour. Sci. — Fourth Series, Vol. XXIII, No. 134. — February. 1907. 

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