350 CARNEGIE INSTITUTION OF WASHINGTON. 



taining lead of this sort. The atomic weight of each of these samples 

 was'^carefully determined by analyzing the chloride, according to the 

 method as elaborated in this special case by G. P. Baxter and his 

 assistants.^ It was found that the lead obtained from uraninite, car- 

 notite, or thorianite exhibited a lower atomic weight than ordinary 

 lead, the deficiency amounting in one case to as much as 0.75 unit. 



The atomic weight of lead from different sources. 



Lead from North Carolina uraninite (Sample R) 206.40 



Lead from Joachimstal pitchblende (Samples I and K) 206.57 



Lead from Colorado carnotite (Samples D and P) 206 . 59 



Lead from Ceylonese thorianite (Samples H and M) 206.82 



Lead from English pitchblende (Sample G) 206 . 86 



Common lead 207 . 15 



The ultra-violet spectrum of a typical specimen appeared to be 

 exactly identical with that of ordinary lead. The necessary inference 

 seems to be that lead from radioactive sources consists of a mixture of 

 at least two substances, of which one is ordinary lead; indeed, even 

 ordinary lead itself may be a mixture. The foreign substance must 

 give the reactions commonly ascribed to lead and must be very difficult 

 if not impossible to eliminate from it by chemical means; for many pre- 

 cautions were taken to purify the samples. This amazing outcome is 

 contrary to our experience with several other elements, notably copper, 

 silver, iron, sodium, and chlorine, each of which has been found to have 

 a constant atomic weight, no matter what the geographical source may 

 have been. The new results on radioactive lead are qualitatively 

 in accord with a recent hypothesis brought forward not long since 

 by Fajans and by Soddy, A note similar to this was published in 

 Science on June 5, 1914, and a preliminary paper, setting forth the 

 detailed methods and results, appeared in the July number of the 

 Journal of the American Chemical Society. 



2. Further Investigation of the Silver Voltameter (Coulometer). 



With the help of Mr. F. 0. Anderegg several unsettled points con- 

 cerning the silver coulometer as a measure of electrical quantity were 

 studied in detail. In every case the earlier work carried out at Harvard 

 twelve years ago was completely confirmed. It was found that the 

 silver precipitate always occludes more or less mother liquor and that 

 its true weight can not be found until this inclusion is determined 

 and allowed for. It was found also that the anode liquid is unques- 

 tionably surcharged with silver in a form capable of being deposited 

 upon a silver surface, but that this superfluous silver is oxidized in a 

 large volume of solution, or if exposed to the air for any length of time, 

 so that then the phenomenon does not appear. It was found, more- 

 over, that the porous cup surrounding the anode is the most convenient 

 method for removing the error due to the anode liquid, and that 

 Kohlrausch's form does not absolutely accomplish this result. The 



'Subsidized by the Carnegie Institution of Washington. 



