34 SODDY, Evolution of Matter by Radio-active Elements 



stituents by chemical analysis, E will not appear as a 

 transition-form like B^ C, D, but as a new radio-element, 

 whose activity is sensibly permanent. Whether E is 

 detected by its ordinary chemical reactions depends 

 simply on its quantity, and this we have seen is pro- 

 portional to its average life. If a sufficient number of tons 

 of the mineral are worked up, it will appear as a new 

 powerfully radio-active element. 



Viewed in this light it seems probable that the 

 new elements radium, actinium, and polonium are merely 

 slow changing transition-forms produced in the disintegra- 

 tion of the parent-element uranium. The quantity of 

 radium in pitchblende is about one-millionth part of that 

 of the uranium, and its average life as judged by the 

 activity of unit weight is about a million times less. For 

 polonium, if we assume, as seems probable, that Marck- 

 wald's work on radio-tellurium applies really to 

 Mme. Curie's element, the quantity present is less than 

 four milligrams to two tons of material. The average 

 life of polonium we know from the observations of 

 Mme. Curie is slightly greater than a year, or about one 

 thousandth of that of radium. These considerations are of 

 course not strictly quantitative in their application, but 

 apply to the order of the quantities that may be expected. 



The case of polonium may be first considered. Since 

 the activity of this type decays to half-value in about a 

 year, it follows without doubt that the existence of 

 polonium in pitchblende at the present time must be due 

 to its continuous production in the mineral. The only 

 question is as to the nature of the parent-element and the 

 stage of the disintegration at which polonium is produced. 

 There is a phenomenon recorded by Mme. Curie in her 

 thesis which perhaps has a bearing on this question. 

 When the " induced " radio-activity of radium decays, it 



