112 CONCEPTION OF THE CHEMICAL ELEMENT 



first and most fundamental conclusion arrived at in 

 the study of radioactive change that the change is of a 

 transmutational character, involving the spontaneous 

 disintegration of the radio-element into others, it 

 would have been the chemists who would have been 

 most deeply interested, and who would have weighed 

 the evidence and pronounced a decision. Yet judg- 

 ment on the view, which was put forward more than 

 fifteen years ago, on evidence, in my opinion, even 

 then deserving of serious consideration, although 

 accepted and universally adopted by the workers in 

 the subject and by physicists, has gone by default so 

 far as the majority of chemists are concerned. From 

 the first, much of the most important evidence has 

 been of a singularly simple and convincing chemical 

 character. 



THE TRANSMUTATIONAL CHARACTER OF RADIO- 

 ACTIVE CHANGE. 



If a chemist were to purify an element, say lead 

 from silver, and found, on re-examining the lead at 

 a later date, that silver was still present, and, again 

 and again repeating the process, found always that 

 silver, initially absent, reappeared, would he not be 

 forced to conclude that lead was changing into silver 

 and that silver was being produced by lead? It is 

 because of the absence of evidence of this kind 

 that the doctrine of the unchangeability of the 

 elements has grown up. One positive example of 

 the kind in question and that doctrine would be at 

 an end. The conclusion to which, in 1902, Sir Ernest 

 Rutherford and I were forced with regard to the 

 element thorium was based on evidence of this 

 direct and simple nature. By simple purification, 

 by chemical and physical means, constituents respon- 

 sible for the greater part of the radioactivity of 



