URAMUM. 151 



established the controversy over the two rival values can 

 hardly be satisfactorily settled. 



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 weighings 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 Berze- 

 lius,* by Arfvedson,t and by Marchand,t 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 UgO^ to UO. Rammelsberg's|| 

 results also, although ver}' suggestive, need no full discus- 

 sion. He analyzed the green chloride, UCl , ; effected the 

 .synthesis of uranyl sulphate from viranous oxide ; determined 

 the amount of residue left upon the ignition of the sodio 

 and bario-uranic acetates ; estimated the quantity of mag- 

 nesium 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 estimates of the atomic weight 

 which are mostly below the true value. For instance, twelve 

 lots of U3O4 from several different sources were reduced to 

 UO 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 weight of uranium ranging from 92.G6 

 to 117.65, or, in mean, 107.50. Such discordance is due 

 partly to impurity in some of the material studied, and 

 illustrates the difficulties inherent in the problem to be 

 solved. Some of the uranoso-uranic oxide was prepared by 



* Schweigg. Journ., 22, 336. 1818. Poggend. Annal., i, 359. 1825. 

 t Poggend. Annal., i, 245. Berz. Jahr., 3. 120. 1822. 

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



II Poggend. Annal., 55, 318, 1842; 56, 125, 1842; 59, 9, 1843; 66, 91, 1845. 

 Journ. fiir Prakt. Chem., 29, 324. 



