1824.]' M. Arfwedson on Uranium. 265 



free from peroxide without undergoing decomposition. It is 

 probable, therefore, that M. Schonberg's experiments were made 

 upon a salt containing an excess of acid, in which case it is 

 obvious that he must have overrated the quantity of oxygen con- 

 tained in the basis. The peroxide employed in his second deter- 

 mination was obtained by decomposing pernitrate of uranium by 

 means of heat ; but this mode of experimenting cannot be deci- 

 sive, as from what has been stated it must be evidently impossible 

 to drive off the nitric acid completely from this salt without con 

 verting the basis partly into a protoxide. 



100 parts of uranium to form the protoxide combine with 

 3*688 oxygen. If this represents two atoms of oxygen, as is 

 probable, then an atom of uranium will weigh 5422*99. Peroxide 

 of uranium precipitated by a caustic alkali is insoluble in an 

 excess of the precipitating substance, and always contains a 

 little alkali, which cannot be washed out, but is found, together 

 with an earthy or metallic salt in ihe water, as the peroxide of 

 uranium is precipitated in combination with an earth or metallic 

 oxide. In alkaline carbonates, and in particular with carbonate 

 of ammonia, peroxide of uranium is easily soluble. The solution 

 has, a strong lemon colour, and even an inconsiderable portion of 

 peroxide of uranium is capable of giving that colour to water. 

 By boiling, the peroxide of uranium precipitates in the state of a 

 pale-yellow powder, which contains carbonic acid, and even 

 some ammonia. We must not, however, reckon upon obtaining 

 the whole oxide ; because however pure it may be, there always 

 remains a little in the water ; and when the carbonated oxide is 

 put upon the filter and washed, the water employed in the edul- 

 coration, especially towards the end, contains a good portion of 

 oxide in solution, which again falls when the liquid comes to be 

 mixed with the saline solution. The peroxide precipitated by 

 caustic ammonia acts in precisely the same way. Peroxide of 

 uranium, therefore, may be considered as slightly soluble in 

 water. This solubility is partly, but not entirely prevented by 

 washing it with water containing sal ammoniac dissolved in it. 

 On the other hand, if peroxide of uranium be united to an earth 

 or a metallic oxide, it is not in the least soluble in water. 



According to what has been already stated, peroxide of ura- 

 nium unites with the other earths and metallic oxides into a kind 

 of uraniates, in all cases, when the mixed solutions of both are 

 precipitated by caustic ammonia. These compounds may be 

 reduced by means of hydrogen gas to the state of alloys of 

 uranium, and the basis of the earth or oxide employed, even 

 when the earthy basis is barytes. These alloys again absorb 

 oxygen at the common temperature of the atmosphere, and the 

 oxidizement is accompanied by combustion. They constitute, 

 therefore, a peculiar kind of pyrophori not inferior to those 

 already known. The alloy of uranium and lead has been already 

 mentioned. An analogous body is obtained when uraniate of 



