1824.] M. Aifwedson on Uranium* 253 



Article IV. 



A Contribution to a more accurate Knowledge of Uranium* 

 By J. A. Arfwedson. 



Uranium in the state of an oxide is occasionally found native 

 pretty pure, as, for example, in uran ochre and uran mica; but 

 the scarcity of these minerals has prevented them from being 

 employed for preparing oxide of uranium in any considerable 

 quantity. Chemists have, therefore, in their researches on this 

 metal, been obliged to employ the more abundant mineral called 

 pechblende, in which oxide of uranium is likewise found, mixed 

 with several other bodies from which it is with difficulty sepa- 

 rated. 



Klaproth found pechblende, from Joachimsthal, in Bohemia, 

 to contain, together with protoxide of uranium, silica, oxide of 

 iron, and sulphuret of lead. He extracted the protoxide of ura- 

 nium in the following way : The pulverised mineral was dissolved 

 in nitric acid, the silica and sulphur remaining undissolved. 

 From the filtered solution was separated by crystallization in the 

 first place, the lead, under the form of nitrate of lead. The liquid 

 being further evaporated, the nitrate of uranium crystallized, 

 which was finally decomposed by caustic potash. The oxide of 

 iron remained in the mother ley. 



Bucholz prepared his oxide of uranium in this manner. — The 

 pulverised pechblende was boiled with nitric acid, as long as 

 any thing was dissolved. The solution was evaporated at a high 

 temperature till fumes of nitrous acid were extricated, and this 

 was continued for a considerable time, taking care to stir the 

 matter continually. The salt of uranium was then taken up by 

 water, while the oxide of iron remained behind undissolved. 

 Bucholz found, however, that the solution contained likewise 

 copper and lime ; which were separated in this manner. The 

 liquid was decomposed by caustic ammonia added in excess, and 

 digested for some time along with the precipitate. By this pro- 

 cess the precipitate was freed from copper. It was washed and 

 heated to redness to drive off the whole of the ammonia. It was 

 again dissolved in nitric acid, and precipitated by caustic potash, 

 added as little as possible in excess. The oxide of uranium thus 

 obtained retained its yellow colour after being heated to redness, 

 and was considered as free both from lime and potash. 



From the knowledge of the subject which we at present .pos- 

 sess, it is easy to see that neither Klaproth nor Bucholz could 

 have obtained a perfectly pure oxide of uranium, on account of 

 the great variety of substances accidentally present in pech- 

 blende, the names of which I shall state below. 



• Tranblated from the Kongl. Vetenskaps Academiens Ilandlingar, for 1822, p. 404. 



