24 SCIENCE PROGRESS 



INORGANIC CHEMISTRY. By C. Scott Garrett, D.Sc. 



Elements. — The question of the atomic weight and other 

 physical characteristics of lead from different radioactive 

 sources has been considerably advanced in papers which have 

 recently been published by Richards and Wadsworth (i and 2), 

 and by ^Echsner de Coninck and Gerard (3). As regards the 

 density at I9'94° C, lead from Norwegian cleveite showed a 

 density of 11*273, whilst Australian radio-lead gave a density 

 of 1 1*289, when determined in the same manner, as compared 

 with u '377 for ordinary lead not of radioactive origin. The 

 atomic weight of the Australian radio-lead was found to be 

 206*35, and that of the Norwegian lead 206*085, so that the 

 decrease in density is almost exactly proportional to the 

 decrease in atomic weight as between the lead from various 

 sources. The atomic volumes, therefore, of all three classes 

 of lead are practically constant, the figures being 18*281, 18*279, 

 18*277 for Norwegian, Australian, and ordinary lead respec- 

 tively. In their most recent paper, Richards and Wadsworth 

 have extended their results on the atomic weight of materials 

 of different origins. The new results are : 



Ordinary lead ...... 207*18 



Radio-lead (Colorado) .... 207*00 



Radio-lead (Australia) .... 206*34 



Radio-lead (broggerite, Norway) . . 206*12 



Radio lead (cleveite, Langesund, Norway) . 206*08 



The more carefully the samples were selected, the lower 

 were the figures obtained, so that the authors assume that 

 the higher results are due to accidental mixture with ordinary 

 lead. No new lines appear in the ultra-violet or visible spec- 

 trum of any of these samples. It can, therefore, be assumed 

 that lead has a dual structure. Further, no relation could be 

 traced between the magnitude of the radioactivity and the 

 lowering of the atomic weight below the figure for ordinary 

 lead. De Coninck and Gerard's results for the atomic weight 

 of lead tend to confirm the foregoing results. After careful 

 and extended determinations, these workers find that the 

 mean value of the atomic weight of ordinary lead is 206*98, 

 whilst that for lead from uranium minerals is 206*71 after 

 eliminating as far as possible all material of non-radioactive 

 origin. 



