260 M. Arfwedson on Uranium. [Aprij., 



in combination with the earth or metallic oxide in the form of a 

 uraniate, even when the base consists of a substance which, 

 when in an insulated state, is not precipitated by ammonia ; for 

 example, when it is lime or barytes ; and in this way a whole 

 series of uraniates may be obtained, which, however, do not 

 resemble other salts in their composition, as will be seen more 

 particularly hereafter. When peroxide of uranium is united to a 

 basis capable of withstanding the fire, it can resist a high tempera- 

 ture without losing any of its oxygen. When, on the contrary, 

 1 examined a uraniate having an easily reducible basis, the com- 

 position of which was known before, I in that case first reduced 

 the salt by means of hydrogen gas, which gave me the quantity 

 of oxygen contained in both oxides ; then determining the quan- 

 tity of oxygen in the basis I had that in the peroxide of uranium, 

 I employed for this purpose uraniate of lead as most suitable to 

 this kind of investigation. 



Analysis of Uraniate of Lead. 



The salt was prepared in this manner. Solutions of pernitrate 

 of uranium and nitrate of lead were mixed together, and precipi- 

 tated by caustic ammonia. The precipitate thus obtained was 

 washed, and exposed to a red heat. It probably contained an 

 excess of oxide of lead, in the form of subnitrate, as the nitrate 

 of lead had been added in considerable excess ; but this was of 

 no consequence. The precipitated compound after being heated 

 to redness and pulverized, had a cinnamon-brown colour, and it 

 gave a full lemon-yellow solution in muriatic acid ; showing that 

 the peroxide of uranium had lost none of its oxygen. 



1*969 gramme of uraniate of lead was reduced by means of 

 hydrogen gas in the same way as the analysis of the protoxide of 

 uranium was performed. As soon as it began to be red hot, it 

 gave out much water, and when this ceased the process was 

 stopped. The product consisted of a dark-brown powder, 

 which weighed 0*127 less than the uraniate of lead. But this 

 difference in weight could not be determined with accuracy, 

 because the apparatus while weighing was constantly increasing 

 in weight. The reduced mass became at the same time hot, and 

 when thrown upon paper, it took fire, and became quite ignited, 

 leaving uraniate of lead as a residue. 



This singular phenomenon, owing pVobably to the rapidity 

 with which the alloy of uranium and lead absorbed oxygen, was 

 so much the more unlooked for, as these metals, when in a 

 separate state, do not undergo any change in the common tem- 

 perature of the atmosphere. There miglit, in this case, have 

 been produced an electro-chemical process between them, which 

 occasioned their combustion. Meanwhile no accurate conclu- 

 sion could be drawn respecting the oxygen which the two metals 

 contained. The experiment, therefore, was repeated, with this 

 alteration, that the water was collected in a receiver, filled with 



