260 



B. B. Boltwood — Ultimate Disintegration 



tlieir detection by the ordinary electrical methods. It has been 

 pointed out by Rutherford* that the kinetic energy of certain 

 alpha particles approaches quite closely to the critical value 

 below which no ionization would be produced. It is moreover 

 quite interesting that the assumption of a difference of atomic 

 mass of 40 units between certain successive radio-active trans- 

 formation products would greatly facilitate their assignment to 

 vacant positions in the periodic system of the elements. 



Composition of Uraninite. 



The suggestions offered in the foregoing pages as to the pos- 

 sible nature of some of the disintegration products resulting 

 from the process of radio-active change can be more clearly 

 understood, and the basis of fact from which they have been 

 derived can be more correctly appreciated, by a consideration 

 of some of the results which have been obtained in the analysis 

 of radio-active minerals. 



The most accurate and reliable of the available data on the 

 composition of uraninite have been published by Hillebrand.f 



Table I. 



Locality 





Glastonbury, 



Donn. 



Bran 



chville, Conn. 



Colo. 



N. Carolina. 



U0 3 



uo 2 



1 

 22-08 

 59-13 



II 



23 35 



58-01 



in 

 22-22 

 59-31 



IV 



26-48 

 57-43 



V 1 VI 



23-0313-27 

 59-9372-25 



VII 



21-54 

 64-72 



VIII 



14-00 

 70-99 



IX 



2526 



5851 



X 



50-83 

 39-31 



XI 



44-11 

 46-56 



Total 



Uranium 



PbO 



Th0 2 



70$ 

 3-14 



70 

 3-24 



70 

 3-07 



72 



3-26 

 9-79 



72 | 74 



3-08 4-35 

 .... 7-20 2 



75 



'4-34 

 6-93 



74 



4-35 

 6-52 2 



72 

 0-70 



o-o 



77 



4-20 

 2-78 



77 

 4-53 



Total rare 



9-57 



10-24 



10-31 



10-37 



11-10 7-20 



7-26 



6-52 



7-81 



3-74 



3-04 



N, 1 



H 2 



Sp. G. 



0"-97 

 9-12 



9~-05 



---- 



~0~"61 



9-58 



2-41J .... 

 0-431 0-68 

 9-62 1 9-73 



b"-67 

 9-56 



2-63 



0-68 

 9-35 



0-15 

 1-96 



8-07 



0-37 

 1-21 

 9-08 



9-49 



Various important details such as the general character and appearance of the different 

 samples and the indication of alteration from external causes in a number of specimens will 

 be found in Hillebrand's papers. 



Blank spaces in the table signify that the indicated constituent was not determined. 



1 Hillebrand assumed that the inert gas present was nitrogen and the percentages of this 

 element shown in the table are calculated on the basis of that assumption. By dividing 

 these numbers by 7 a maximum value for the helium separated is obtained. 



2 Th0 2 + Zr0 2 ? 



The results of his analyses are given in a condensed form in 

 Table I. 



*Phil. Mag., July (1905). 

 f Bulletin of the U. S. Geological Survey, No. 

 xl, 384 (1890) ; ibid., xlii, 390 (1891). 



p. 43, 1891 ; this Journal, 



