256 B. B. Bolt/wood — Ultimate Disintegration 



I have been particularly impressed by the information 

 kindly supplied in a private communication by Mr. W. F. 

 Hillebrand of the U. S. Geological Survey, a recognized 

 authority on the analysis of uranium minerals, that so far as 

 his experience goes he does not remember to have found 

 uranium in any mineral without its being accompanied By 

 lead, and he adds: "the association has often caused me 

 thought." 



Additional weight attaches to these experimental indications 

 because of the theoretical considerations leading to a similar 

 conclusion. It has been pointed out by Rutherford,* that if 

 the alpha-ray particle consists of helium, since four alpha-ray 

 products intervene between radium and the final, inactive sub- 

 stance radium-Gr, the indicated atomic weight of radium-G is 

 sufficiently near to that of lead to be impressive. Thus one 

 alpha particle is expelled by each of the atoms Ra, Ra-Em, 

 Ra-A, Ra-C and Ra-F, making five particles in all. The loss 

 of five alpha particles with an atomic weight of 4 from the 

 atom of radium with an atomic weight of 225 would cause a 

 reduction of this by 4x5 = 20 units, with the formation of a 

 chemical element having an atomic weight of 205 or there- 

 abouts. This is not far from the accepted atomic weight of 

 lead, namely 206 "9. 



Thorium (Bare earths). 

 Another element which occurs quite commonly with uranium 

 is thorium, and the common association of these two elements 

 has been noted by Strutt and interpreted by him as indicating 

 that thorium is possibly the parent of uranium. f Aside from 

 the very doubtful hypothesis that the atomic weight of thorium 

 is greater than that of uranium, his conclusions would seem 

 open to serious objections. His statement that all thorium 

 minerals contain readily detectable quantities of uranium, while 

 some minerals containing notable quantities of uranium are 

 comparatively free from thorium, is manifestly in accord with 

 his experimental data, but it would appear that his thorium 

 minerals containing uranium are all old minerals, while his 

 uranium minerals containing no thorium are of relatively 

 recent origin. If his theory is correct, the existence of very 

 old minerals containing high percentages of uranium and no 

 thorium should be possible, but that such minerals have been 

 found is not indicated by any of the reliable analyses available. 

 The experimental data offered by Strutt, as well as those to be 

 derived from other sources, can all be much more consistently 

 interpreted by the assumption that thorium is a disintegration 

 product of uranium having a life considerably longer than that 



* Silliman Lectures, Yale University, 1905. Not yet published, 

 f Proc. Eoy. Soc. Lond. (A), lxxvi, 88 (1905). 



