URANIUM. 263 



Hence tliere are six values for the atomic weight of tungsten, as follows : 



From (i) . W = 183.485, ± .0051 



From (2) . " = 182.638, ± .1248 



From (3) " =r 183 298, ± .0088 



From (4) " = 183.035, ± .1229 



From (5) . " = 182.268, zb .0663 



From (6) " = 182.647, zfc .0820 



General mean W = 183.429, ± .0044 



If = 16, W = 184.827. The rejection of all values except the first 

 and third raises the mean b}^ 0.009 ; that is, four of the ratios count for 

 almost nothing, and the work done in Smith's laboratory dominates all 

 the rest. The questions raised by Schneider in his latest determination, 

 however, are not yet answered, and farther investigation is required in 

 order to fully establish the true atomic weiglit of tungsten. 



URANIUM. 



The earlier attempts to determine the atomic weight of uranium were 

 all vitiated by the erroneous supposition that the uranous oxide was 

 really the metal. The supposition, of course, does not affect the weigh- 

 ings and analytical data which were obtained, although these, from their 

 discordance with each other and with later and better results, have now 

 only a historical value. 



For present purposes the determinations made by Berzelius,* by Arf- 

 vedson,t and by Marchand X may be left quite out of account. Berzelius 

 employed various methods, while the others relied upon estimating the 

 percentage of oxygen lost upon the reduction of U^Og to UO^. Rammels- 

 berg's § results also, although very suggestive, need no full discussion. 

 He anal^^zed the green chloride, UCl^; effected the synthesis of uranyl 

 sulphate from uranous oxide; determined the amount of residue left 

 vipon the ignition of the sodio and bario-uranic acetates ; estimated the 

 quantity of magnesium uranate formed from a known weight of UO,^, 

 and attempted also to fix the ratio between the green and the black 

 oxides. His figures vary so widely that they could count for little in 

 the establishing of any general mean ; and, moreover, they lead to esti- 

 mates of the atomic weight which are mostly below the true value. For 

 instance, twelve lots of U^Og from several different sources were reduced 

 to UO2 by heating in hydrogen. The percentages of loss varied from 3.83 

 to 4.67, the mean being 4.121. These figures give values for the atomic 



♦Schweigg. Jourii., 22, 336. 1818. Poggend. Annalen, i, 359. 1825. 

 fPoggend. Annalen, i, 245. Berz. Jahr., 3, 120. 1822. 

 X Journ. fiir Prakt. Chem., 23, 497. 1841. 



? Poggend. Annalen, 55, 318, 1842 ; 56, 125, 1842 ; 59, 9, 1843 ; 66. 91, 1845. Journ. fi'ir Prakt. Chem. , 

 29. 324- 



