258 M. Arfwedson on Uranium. [Apr it, 



in nitric acid, the solution evaporated to dryness, and exposed 

 to a red heat ; but by this process no alteration whatever of the 

 weight was produced. 



The experiment was repeated with 1 -006 gramme of metal, 

 which increased in weight 0-0375 gramme, corresponding to 

 3*73 oxygen to the 100 of metal. 



These two experiments agreeing very well with each other 

 show plainly that the brown substance obtained when protoxide 

 of uranium was reduced by means of hydrogen gas, must like- 

 wise be in the metallic state. A hundred parts of the protoxide 

 lost 3*53 or 3-54 of their weight, leaving a remainder amounting 

 to 96-47 or 96-46. But 96-46 i 3-54 :: 100 : 3-67, which loss 

 quite corresponds with the augmentation of weight of the metal 

 when heated to redness. It was formerly remarked, that the 

 metal when obtained by reducing the protoxide by means of 

 hydrogen gas has a liver-brown colour; while on the other hand 

 the powder of the crystallized product is reddish-brown ; but 

 this may be owing to no other cause than a difference in the 

 fineness of the two powders. 



If the result of the reduction of the protoxide be compared 

 with that which is obtained by the combustion of the metal, 100 

 parts of protoxide of uranium are composed at a medium of 



Uranium 96-443 



Oxygen 3-557 



100-000 



and 100 parts of uranium combine with 3*688 parts of oxygen. 



The protoxide of uranium obtained from percarbonate is a 

 powder of a dirty-green colour. If the uranium salt be a second 

 time thrown down by caustic ammonia, and the precipitate be 

 heated to redness, the protoxide is obtained in the form of a 

 black metallic mass, the particles of which cohere together. 

 This mass is exceedingly hard, and is not without difficulty 

 reduced to powder. The powder has the usual green colour of 

 protoxide of uranium. Protoxide of uranium after having been 

 heated to redness, dissolves very sparingly in dilute muriatic or 

 sulphuric acid. The concentrated acids dissolve it better, and 

 when it is boiled in concentrated sulphuric acid, it dissolves 

 completely, a light-green coloured saline mass is obtained, which 

 dissolves in water with a deep bottle-green colour. If such a 

 solution be precipitated by caustic ammonia, the protoxide is 

 separated in the state of a hydrate, in brown flocks inclining to 

 purple. If these flocks be washed and dried at the temperature 

 of 212°, and then heated in a glass tube, they give out a consi- 

 derable portion of water, and become green. In general a por- 

 tion of the hydrate is likewise converted into peroxide, and it 

 becomes yellow before the end of the drying; and if it was 

 precipitated by ammonia in great excess, or if it was washed 



