366 PROCEEDINGS OF THE AMERICAN ACADEMY. 



of uranium was probably 240 instead of 120.* The question was not 

 definitely settled until Zimmermann, in 1885, carried out the suggestions 

 of Mendeleeff, and by specific heat and vapor density determinations 

 confirmed the higher value.f 



Owing to the wide variations in the published results, the atomic 

 weight of uranium has long been considered one of the least satisfactorily 

 determined of the atomic weight values. A glance at the results thus 

 far obtained is sufficient to show the need for further work in this line. 

 A complete resume of the older work upon the subject is to be found in 

 Clarke's recent work on the atomic weights, t The following table 

 summarizes those investigations which seem to possess even a little 

 quantitative value : — 



Less Inaccurate Previocs Work on the Atomic Weight of Uranium. 



O =r 16.000 



1841 Peligot §— Analysis of Green Chloride 240. ± 



1842 Ebelmen II — Combustion of Oxalate 238. ± 



1843 Wertheim TT — Double Acetate of Sodium and Uranium 239. ± 

 1846 Peligot** — Combustion of Oxalate and Acetate . . 240. ± 

 1886 Zimmermann ff — Reduction of Oxide, UsOg to UO2 . 239.6 

 1886 Zimmermann H — Ignition of Double Acetate . . . 239.5 



The work of Ebelmen, Wertheim, and the early work of Peligot is neces- 

 sarily of little weight in assigning a probable value to the atomic weight 

 of uranium. lu some cases the material used was impure, and in others 

 the methods of analysis were faulty. Consequently it is not surprising 

 to find differences of whole units in the individual determinations of 

 each series. 



Peligot's later determinations from the oxalate is perhaps the best of 

 the early work. His material was carefully purified, and his method is 

 far preferable to the work of Ebelmen and Wertheim. By combustion 



* Annalen der Chemie u. Pharmacie, Supp. Vol. 8, 178 et. seq. 

 t Annalen der Cliemie u. Pliarmacie, 216, 1. 



} A Recalculation of the Atomic Weights, by F. W. Clarke, Smithson. Misc. 

 Coll., Constants of Nature, Part V. (1897), 263. 



§ Compt. Rend. 12, 735. Ann. Chira. Phys. (3) 5, 5 (1842). 



II J. prkt. Chem. 27, 385 (1842). 



1 Ibid., 29, 209 (1843). 



** Compt. Rend., 22, 487 (1846). 



tt Ann. d. Chem., 232, 299 (1886). 



Jt Ibid. 



