THE TRANSFORMATION OF ELEMENTS 239 



Since he finds that all thorium minerals contain readily- 

 detectable quantities of uranium, while some uranium minerals 

 are practically free from thorium, Strutt concludes that uranium 

 is derived from thorium. Boltwood points out that in the 

 former case the minerals were much older than in the latter; 

 he thinks the evidence can be interpreted on the assumption 

 that thorium is a disintegration product of uranium having a 

 longer life. 



There is thus at least a possibility, so far as present evidence 

 goes, that uranium is the parent of all the radioactive elements. 



Since Ramsay discovered helium in the mineral cleveite, in 

 which it exists in comparatively large amount, and since Lord 

 Rayleigh proved its existence in the Bath waters, many workers 

 have turned their attention to the existence of the rare gases in 

 minerals and springs. Since Ramsay and Soddy showed that 

 helium is a disintegration product of radium, investigators have 

 tried to discover some relation between the amounts of radio- 

 activity and of rare gases present. Strutt and Moureu have paid 

 special attention to this problem. 



Strutt has made an exhaustive study of the composition of 

 radioactive minerals, especially to ascertain the relative propor- 

 tions of uranium-radium, thorium, and helium present. In his 

 initial experiments he heated the mineral with strong sulphuric 

 acid to obtain its gaseous constituents. These were analysed 

 by methods similar to those described in section 2. 



It has been mentioned already that Boltwood has considered 

 the presence of helium in minerals as derived from uranium, 

 neglecting the possible production from thorium. Strutt 

 strongly disputes this view, and his results bear out his opinion. 

 The following figures are taken from a paper which he published 

 in 1905 : 



