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



extracted from the Joachimstal (Bohemia) uranium residues, 

 and found the value to be 206*736 + 0*009. Richards and 

 Lembert used lead chloride which had been obtained by- 

 working up (a) North Carolina uraninite, (b) Joachimstal 

 pitchblende, (c) Colorado carnotite, (d) Cornwall pitch- 

 blende, and obtained the following values respectively: — 

 206-4, 206-57, 206-59, and 206*86. The result for (a) is of 

 particular interest, because uraninite is less likely to contain 

 ordinary lead than pitchblende, which is a secondary form of 

 uraninite, and in which ordinary lead may probably be present 

 as impurity. The Joachimstal pitchblende is non-crystalline 

 in structure, and generally contains within its mass veins of 

 other minerals such as galena, and iron and copper pyrites. 

 The uranium residues, obtained from large quantities of the 

 ore, would thus be expected to have a larger content in 

 ordinary lead than selected samples of the pitchblende. This 

 fact is probably the cause of the difference in the atomic 

 weights 206-74 and 206*57 obtained for lead from Joachimstal 

 pitchblende by Honigschmid and St. Horovitz on the one 

 hand, and by Richards and Lembert on the other. For lead 

 which had been extracted from carefully selected samples 

 of pitchblende free from galena, the former experimenters 

 obtained an atomic weight 206*40 *. For ordinary lead 

 treated by the same method as their other materials, Richards 

 and Lembert obtained the value 207*15 ±001, a figure in 

 close agreement with that given in the International Table. 

 The preliminary results given by M. Curie vary between 

 206*36 and 206*64 for uranium minerals, whilst for ordinary 

 lead from galena he found the value 207*01. 



The results so far obtained clearly show that the lead 

 extracted from uranium minerals (in all the above minerals 

 the quantity of thorium present was very small) has a lower 

 atomic weight than ordinary lead, though the value is higher 

 than is to be expected from theory. It is quite possible that 

 the discrepancy is due to the presence of ordinary lead in 

 the minerals used, as well as to the presence of actinium lead, 

 of which the atomic weight is considered by Fajanst to be 

 about 207, and by other workers as high as 210. The pre- 

 sence of one or both of these elements would give an 

 increased atomic weight in the right direction, and so at 

 least in part explain the discrepancy. 



Still more recently Honigschmid and Fraulein St. Horovitz J 

 have determined the atomic weight of the lead extracted from 

 (a) Uraninite from Morogoro in German East Africa, and 



* Honigschmid and St. Horovitz, Wien. Anz. 9th July, 191 1 



t Fajans, loc. cit. p. 11 (1914). 



\ Honigschmid and St. Horovitz, Wien. Anz. 15th October, 1914. 



