1825.] Al. Berzeliitson Uranium. 267 



uranium are combined with 3*688 parts of oxygen. According 

 to the former of the above results, which M. Arfwedson consi- 

 ders as the most accurate, the ratio of the oxygen in the oxide 

 and oxidule is as 3 : 2 ; according to the latter, it is as 5 : 3. 

 As the oxide of uranium readily acts as a weak acid, it appeared 

 to me not unlikely that the latter ratio might be the true one, 

 and I thought it of importance to determine the point with pre- 

 cision. I undertook, therefore, an investigation of the compo- 

 sition of the oxide of uranium, in order by that means to ascer- 

 tain its saturating capacity as an acid ; * but the experimental 

 determination was accompanied with so many difficulties, that I 

 began to doubt its possibility. The oxide of uranium or its 

 hydrate cannot be obtained artificially in a state of purity. 

 If we attempt its preparation by means of nitric acid, it passes 

 into the state of oxidule just at the instant when we expel the 

 last portions of acid. If we precipitate it with an alkali, it 

 combines with the precipitant ; and when the latter is of a fixed 

 nature, the compound may be ignited without undergoing 

 decomposition. Owing to the presence of ammonia in the 

 hydrate precipitated by that alkali, it is impossible to analyse it 

 with such precision, that the proportion of oxygen will be deter- 

 mined to within less than t-t/W ^^ ^^^ weight of the oxide. 



I next hoped to gain my object by analyzing the carbonated 

 oxide. I therefore precipitated a solution of the nitrate of oxide 

 of uranium with carbonate of ammonia. No effervescence took 

 place at the commencement of the precipitation, and the preci- 

 pitate, on being collected upon a filter, appeared at firi^t to 

 admit easily of a complete edulcoration ; but it speedily became 

 whiter coloured, and at the same time so much of it passed 

 into solution, that it imparted a distinct yellow colour to the 

 filtered liquid. Tliis liquid became turbid on the application of 

 heat, and acquired a liijlit yellowish milky appearance, but many 

 days elapsed before the whole of the oxide of uranium subsided 

 ti) the bottom. The residue upon the filter dissolved in acids 

 without effervescence, and was therefore hydrate, instead of 

 carbonate of uranium. Thinking that this would prove pecu- 

 liarly serviceable for my purpose, I ignited a quantity in a suit- 

 able apparatus, in which the expelled gas was collected over 

 mercury, and the water by muriate of lime. By this means I 

 determined with precision the weight of the oxidule and of the 

 water ; but the gas greatly exceeded the quantity of oxygen 

 which ought to have been evolved, and proved to contain a 

 considerable proportion of carbonic acid and azote. Conse- 

 quently this hydrate was contaminated both with carbonic acid 

 and with ammonia : it is probable that these two substances 



• Before commencing this investigation, I examined the oxidule in the same man- 

 ner as had been done by M. Arfwedson, by reducing it with hydrogen gas, and found 

 it composed of 1 00 uranium + 3-086 oxygen. 



