264 



THE ATOMIC WEIGHTS. 



weight of uranium ranging from 184.33 to 234.05, or, in mean, 214.53. 

 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 calcining the 

 oxalate, and retained an admixture of carbon. Many such points were 

 worked up by Rammelsberg with much care, so that his papers should 

 be scrupulously studied by any chemist who contemplates a redetermi- 

 nation of the atomic weight of uranium. 



In 1841 and 1842 Peligot published certain papers* showing that the 

 atomic weight of uranium must be somewhere near 240. A few years 

 qater the same chemist published fuller data concerning the constant in 

 luestion, but in the time intervening between his earlier and his final 

 researches other determinations were made by Ebelmen and by Wer- 

 theim. These investigations we may properly discuss in chronological 

 order. For present purposes the early work of Peligot may be dismissed 

 as only preliminary in character. It showed that what had been pre- 

 viously regarded as metallic uranium was in reality an oxide, but gave 

 figures for the atomic weight of the metal which were merely approxi- 

 mations. 



Ebelmen 's f determinations of the atomic weight of uranium were 

 based upon analyses of uranic oxalate. This salt was dried at 100, 

 and then, in weighed amount, ignited in hydrogen. The residual ura- 

 nous oxide was weighed, and in some cases converted into U 3 8 by heating 

 in oxygen. The following weights are reduced to a vacuum standard : 



10.1644 grm. oxalate gave 7.2939 grm. UO 2 . 



12.9985 

 11.8007 



9.99 2 3 

 11.0887 

 10.0830 



6.7940 

 16.0594 



9-33 12 

 8.4690 



7- I 73 I 

 7.9610 



7.2389 

 4.8766 

 11.5290 



Gain on oxidation, .3685 



.3275 

 .2812 

 .3105 



453' 



Reducing these figures to percentages, \ve may present the results in 

 two columns. Column A gives the percentages of UO 2 in the oxalate, 

 while B represents the amount of U 2 3 formed from 100 parts of U0 2 : 

 A. , B. 



71-924 



71.787 103.949 



71.767 103.867 



71.621 103.920 



71.794 103.900 



71-793 



71.778 



71.790 103930 



Mean, 71.782, =b .019 



Mean, 103.9:3, =b .009 



*Compt. Rend., 12, 735. 1841. Ann. Chim. Phys. (3), 55. 1842. 

 t Journ. fur Prakt. Cheni., 27, 385. 1842. 



