64 Messrs. J. H. L. Johnstone and B. B. Boltwood on the 



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It is not proposed to discuss these schemes in detail or to 

 consider at any length certain minor points involved to which 

 exception might be taken. It is, however, difficult to under- 

 stand just what is implied by the dual transformation with 

 the expulsion of a-particles in both cases which is suggested 

 for U I. in the first scheme and for U II. in the second. It 

 would appear that the loss of an a-particle in each case 

 should lead to the production of one and the same kind of 

 matter, namely, to a single product and not to two different 

 products to be designated as U X x and U Y in one example 

 and as Io and U Y in the other. The main point under 

 consideration is, however, whether either of these schemes 

 gives us a clue to the explanation of the relative activities of 

 uranium and radium as they have been found in our experi- 

 ments, and it may be stated that they do not, since the first 

 scheme would suggest a ratio of l/*55 for the relative 

 activities of the uranium and the radium, while the second 

 scheme would imply a ratio of l/*53 for the same quantities. 



In order that Scheme I. might satisfactorily apply to the 

 ratio as found by experiment it would be necessary to assume 

 that about 26 out of every 100 atoms of U I- were trans- 

 formed in the mode leading to the production of actinium. 

 This in turn is contradicted by the relative activity of the 

 actinium products in an equilibrium mixture. 



In order to fulfil the conditions involved in Scheme II. 

 it would be necessary for 14 out of every 100 atoms of 



