



Mean 



206-68 





206*64 



206-34 





206-36 



206-59, 



206-55 



206-54 



20V-10 





207-08 



207-04 





207-01 



360 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Atomic Weight of Lead of Radioactive Origin. — The 

 facts connected with the spontaneous transformation of the radio- 

 active elements have led to the theoiy that some of the elements, 

 among which is lead, ma}^ consist of several individuals differing 

 considerably in atomic weight but not separable by chemical 

 means. According to this theory the lead found in different 

 kinds of radioactive minerals should show variations in atomic 

 weight from that of ordinary lead, as well as differences in the 

 various minerals. 



Maurice Curie has purified the lead from a number of min- 

 erals and has determined the atomic weights by converting the 

 metal into the nitrate with the following results: 



Pitchblende 206-60, 



Carnotite 206-38, 



Yttrotantalite .. . 206-49, 



Monazite 207*06, 



Galena 206-98, 



The atomic weight obtained from the lead of galena agrees well 

 with that at present accepted, but the atomic weight of lead from 

 uranium minerals is decidedly lower, and the lead from monazite 

 is slightly higher. 



A more elaborate and more anthoritative investigation of the 

 same subject has been made by Richards and Lembert, who 

 have obtained as many samples of radioactive lead as possible, 

 have purified the samples with the greatest care, and have deter- 

 mined the atomic weight of the lead in comparison with ordinary 

 lead with the high degree of skill that has been developed by 

 Professor Richards. The method used was the comparison of 

 lead chloride with silver and with silver chloride. The final 

 values found for the atomic weight of lead from different sources 

 were as follows : 



North Carolina uraninite _ 206*40 



Joachimsthal pitchblende (2 samples) 206*57 



Colorado carnotite (2 samples) .... 206*59 



Ceylonese thorianite (2 samples) 206-82 



English pitchblende _ 206-86 



Common lead ._- 207-15 



It is to be observed that these, results agree with those of Curie 

 in showing the atomic weight of the lead from the uranium minerals 

 to be much lower than that of ordinary lead. The authors say 

 that the result is amazing. Previous atomic weight determina- 

 tions made in Professor Richards's laboratory upon ordinary 



