374 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



weight of uranium ranging from 185.74 to 235.84, or, in mean, 216.17. 

 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 Eammelsberg with much care, so that his papers should 

 be scrupulously studied by any chemist who contemplates a redetermina- 

 tion 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 

 later the same chemist published fuller data concerning the constant in 

 question, 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 ' 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 UaOg by heating 

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



10.1G44 grm. oxalate gave 7.2939 grm. UO,. 



12.9985 " 9.3312 " Gain on oxidation, .3685 



11.8007 " 8.4690 " " .3275 



9.9923 " 7.1731 " " .2812 



11.0887 " 7.9610 " " .3105 



10.0830 " 7.2389 



6.7940 " 4.87G6 



16.0594 " 11.5290 " " .4531 



Reducing these figures to percentages, we may present the results in 

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

 while B represents the amount of UaOg formed from 100 parts of UOo : 



A. B. 



71.924 



71.787 103.949 



71.767 103.867 



71.621 103.920 



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

 2Journ. prakt. Chem., 27, 385. 1842. 



