﻿682 



Messrs. A. Holmes and R. W. Lawson on 



From the evidence of atomic weights, we can safely decide- 

 that the existence of uranium lead with a lower atomic weight 

 than that of ordinary lead has been proved. Moreover, the- 

 most recent results of Honigschmid show that this has an 

 atomic weight in almost perfect agreement with that theore- 

 tically to be expected. In the case of thorium lead the 

 evidence is much less certain, a fact undoubtedly following 

 from the instability of thorium lead (thorium E). 



The following table summarizes the evidence from atomic 

 weights up to the present time. 



Table VIII * 

 Atomic Weights of Lead from Radioactive Minerals. 



Type of 

 Lead. 



Experimenter. 



Source of material. 



Expected 



results. 1 



Actual 

 results. 



207-18 



Ordinary lead. 



Honigschmid. 





207-1* 





Eichards and 





207-1 



207 15 





Lembert. 









„ 



M. Curie. 



Galena. 



207-1 



20701 



206-74 



Uranium lead. 



Honigschmid and 



Uranium residues 



>206-2 





St. Horovitz. 



(Joachimstal). 







n 





Selected pitchblende 



> 206-2 



206-40 







(Joachimstal). 







>) >• 





Uraninite. 3 



2062 



20604 







(G. E. Africa). 







>» »> 



„ 



Broggerite (Norway). 4 



206-2 



206-06 



,, 



Eichards and 



Uraninite (North 



206-2 



206 40 





Lambert. 



Carolina). 







" >) 



" 



Pitchblende (Joachim- 

 stal). 



> 206-2 



206-57 



;> 





Carnotite (Colorado). 



>206-2 



206-59 



„ 



J? 



Pitchblende (Cornwall). 



> 206-2 



206-86 



,, 



Maurice Curie. 



Pitchblende. 



>206-2 



206-64 







Carnotite. 



>206-2 



206-36 



» 



" 



Yttrio-tantalite. 



> 206-2 



206-34 



208-40 



Thorium lead 5 . 



Soddy & Hyman. 



Thorite (Ceylon). 



208-24 



Thorium lead + 



Eichards and 



Thorianite (Ceylon). 



207-40 



206-83 



Uranium lead. 



Lembert. 









>> )> 



Maurice Curie. 



Monazite sand. 



<? 



207-08 



1 If thorium E and radium G are isotopic with lead, and are the respective- 

 stable end products of* the thorium and uranium families of radio-elements. 



2 International atomic weight. 



3 Marckwald, Centralblatt fur Min. u. Geol. 1906, p. 761 ; Chemisches 

 Centralblatt, 1907, i. p. 369. 



4 This result would appear to point to the stability of thorium E, if the 

 atomic weights of thorium E and radium G are respectively 208 - 4 and 2060. 

 Eemembering, however, that in all probability a small quantity of original 

 lead is present in this mineral, it is clear that we must be cautious in drawing 

 conclusions regarding the stability of thorium E from such a result, where 

 the mineral contained only 4 per cent, of thorium. Moreover, the theoretical 

 atomic weight of radium G, 206, is likely to be a minimum value. 



5 Theoretically 90 per cent. pure. 



* A revision of Table V. in Part I. p. 839. 



