340 



CARNEGIE INSTITUTION OF WASHINGTON. 



Because of the great interest attached to the supposed relation of 

 lead to radioactive change, and because Richards and Lembert and 

 others have found the atomic weight of radioactive lead to be lower 

 than that of ordinary lead, material from widely different geographical 

 sources was examined. The various specimens were all purified in the 

 same way, by several ciystallizations as nitrate and several as chloride. 

 Spectrographic examination in the visible and ultra-violet regions 

 failed to show the slightest difference between any of the samples. 



Series III. 



Furthermore, the original minerals in no case gave any indication of 

 radioactivity. This similarity of the different specimens is fully borne 

 out by the results of the chloride analyses, as shown in the table. 



The outcome of the investigation in its present stage is obviously 

 that ordinary lead does not vary in atomic weight to an extent capable 

 of detection by the most accurate analytical methods, and that the 

 atomic weight of lead is not far from 207.20 (Ag = 107.880). 



Further work upon the atomic weight of lead is planned with material 

 from still different sources, and by a radically different analytical 

 method. 



