PRESENT PROBLEMS OF RADIOACTIVITY 



175 



simple and elastic, and is very useful in mathematical discussion of 

 the theory of successive changes. In the following table a list of the 

 products is given, together with the nature of the radiation and the 

 most marked chemical and physical properties of each product. The 

 time T for each of the products to be half transformed is also added. 



The changes which occur in the active deposits from the emanation 

 of radium, thorium, and actinium have been difficult to determine on 

 account of their complexity. For example, in the case of radium, the 

 active deposit, obtained as a result of a long exposure to the emana- 

 tion, contains quantities of radium A, B, and C. The changes occur- 

 ring in the active deposit of radium have been determined by P. Curie, 

 Danne, and the writer. The value of T for the three successive changes 



