268 M. Berxelius on Uranium. [April, 



were associated together, and were retained by the hydrate in 

 the state of carbonate of ammonia. 



I now examined the oxalate of the oxide. By submitting 

 this salt to distillation, I decomposed it in one experiment into 

 metaUic uranium, carbonic acid, and water ; and on the suppo- 

 sition that one-fourth of the oxygen of the carbonic acid had 

 been previously combined with the metal, it would have followed 

 that the oxide is composed of 100 uranium + 6-14 oxygen. 

 But in another experiment, I obtained a residue of oxidule of 

 uranium, and totally different proportions of carbonic acid and 

 water. In both cases the oxalate had been prepared with an 

 oxide purified in the manner recommended by M. Arfvvedson, 

 and precipitated by a long continued ebullition from its solution 

 in carbonate of ammonia. I shall return to the consideration of 

 this salt. I now ignited a mixture of determinate quantities of 

 the oxidule and of nitrate of lead, with the expectation of form- 

 ing an uranate of lead ; but by this treatment, only a small 

 portion of the oxidule combined with an additional dose of oxy- 

 gen. I mixed the two substances together therefore in the 

 state of solution, evaporated the mixture to dryness, and cal- 

 cined the residue; but during the evaporation, the nitrate of 

 lead crystallized in the first place, and the salt of the oxidule 

 concreted into a mass over it; and during the ignition, the lat- 

 ter salt first underwent decomposition, and the unequal mixture 

 of oxidule of uranium and nitrate of lead which remained, 

 afforded the same unsatisfactory result as in the first experi- 

 ment. I now dissolved a determinate quantity of magnesia in 

 nitric acid, expecting, with its assistance, to precipitate a solu- 

 tion of nitrate of the oxidule, by means of an excess of caustic 

 ammonia ; but both in this experiment, and when I mixed a 

 determinate quantity of magnesia with a solution of a determi- 

 nate quantity of the oxidule in nitric acid, evaporating the mix- 

 ture to dryness and calcining the residue, the results which I 

 obtained were equally varying and undecisive. 



I next had recourse to more indirect methods. M. Arfwedson 

 had found that oxide of uranium gives with sulphuric acid and 

 potash a double salt, in which its oxygen is to that of the potash 

 as 3 : 2. I determined therefore to examine this salt, and was 

 the more induced to do so by the uncommonness of this ratio 

 between the oxygen of the two bases. I mixed a saturated 

 solution of the oxide with a smaller quantity of sulphate of 

 potash than was necessary to form with it the double salt, and 

 committed the liquid to spontaneous evaporation. I considered 

 it not improbable that if the oxide of uranium contains 3 atoms 

 of oxygen, it might, like alumina and the oxides of iron and 

 manganese, form a salt crystallizing in a similar manner with 

 alum, which would have afforded a decisive proof of its atomic 

 constitution. But no such salt could be obtained, and the 



