1824.] M. Arfwedson on Uranium. 259 



with hot water, in either case we may generally expect to 

 find the whole after being dried in the state of peroxide 

 containing ammonia. Carbonate of ammonia throws down a 

 light-green precipitate of protocarbonate of uranium, which is 

 again dissolved if the precipitant be added in excess. If the 

 precipitate be heated in ammonia, we obtain protoxide of ura- 

 nium free from carbonic acid. The hydrated protoxide dissolves 

 very easily in acids ; and the precipitate by means of caustic 

 ammonia is easily dissolved again if a little excess of acid be 

 added to the liquid ; but if the precipitated hydrate be digested 

 for an hour in water, the chemically combined water is disen- 

 gaged, the matter concretes into a heavy powder of small bulk, 

 and is afterwards acted upon with great difficulty by acids. 



Yellow Oxide of Uranium. 



Peroxide of uranium, as is well known, has the property of 

 acting sometimes the part of an acid, and at others that of an 

 alkali ; and it has such a tendency to enter into combination 

 with other oxidized bodies, that I doubt the possibility of obtain- 

 ing it in an insulated state. For example, if we precipitate a 

 solution of this oxide in muriatic or nitric acid by means of 

 caustic ammonia, the precipitate is a chemical combination of 

 peroxide of uranium with water and ammonia, which last body 

 cannot be removed by washing the powder. The very same 

 result is obtained, if we precipitate the peroxide by means of 

 caustic potash. The hydrated uraniate of ammonia may be 

 heated without undergoing decomposition to 212°, or a little 

 higher. When raised to a still higher temperature, it gives out 

 water, azotic gas, and ammonia, and protoxide of uranium 

 remains behind. If we attempt on the other hand to heat per- 

 nitrate of uranium in order to disengage the acid, the decomposi- 

 tion of the salt does not cease till the whole mass is converted 

 into protoxide ; and this result takes place in what way soever 

 we regulate the temperature. 



Considering the small quantity of oxygen in the protoxide 

 of uranium, it was of the utmost importance in determining the 

 quantity of oxygen in the peroxide to employ a method which 

 was not liable to any uncertainty. It occurred to me that I 

 should obtain such a method if I combined peroxide of uranium 

 with a basis, the proportion of whose oxygen was accurately 

 known ; and then, by means of hydrogen gas, deprived both 

 substances of their oxygen. Knowing the proportions of per- 

 oxide of uranium and basis, and the proportion of oxygen on the 

 base, we should have the oxygen in the peroxide. To enable 

 me to employ such a method, some preliminary experiments 

 were undertaken, by which I found that when to a solution of 

 peroxide of uranium in muriatic acid any earthy or metallic 

 muriate is added, and then caustic ammonia is added to the 

 mixture, in all such cases the peroxide of uranium is precipitated 



