150 MixU /' — Heat of Formation of the 



The heat of formation of the dioxide lias heen regarded as 

 high hecause of difficulty of reducing it. Professor B. B. Bolt- 

 wood generously furnished an abundance of pure uranyl nitrate 

 for the investigation. 



Metallic uranium was prepared by a method of Moissan* 

 modified in some details. In the bottom of a steel cylinder 

 30 grams of sodium were placed and on top of it 40 grams in 

 small pieces of a mixture of the double salt, LTCl 4 2Na01, and 

 approximately two equivalents of sodium chloride. The latter 

 happened to be in excess when the double salt was made. The 

 cylinder was closed with a loose screw cap and heated to red- 

 ness for 15 minutes. Most of the excess of metallic sodium 

 volatilized and escaped about the screw cap ; the little 

 remaining in the cylinder was removed by alcohol. The 

 sodium chloride was dissolved in deaerated cold water and then 

 the metal was washed with water, alcohol, and ether, and dried 

 in vacuo, over sulphuric acid. The metal was in the form of 

 a friable mass. It was pulverized and passed through a milli- 

 meter mesh. The coarser portion ignited when rubbed in a 

 mortar. For analysis the metal was dissolved in aqua regia, 

 and the hydroxide precipitated by ammonia. 



0-3222 g. gave 0*3766 g. U 3 6 = 99'2$ U 

 0-9001 g. " 1-0144 g. U0 2 = 99-4$ TJ 



The metal contained a trace of sodium. The second analysis 

 was made nine days after the first one, and the results show 

 that the metal did not oxidize in the desiccator in which it was 

 kept. Nor did it gain weight for a time in ordinary air. The 

 brown coating of oxide was a protective coating. Another lot 

 of metal, made as before, gave on analysis the following : 



1-0378 g. metal; 1-543 g. U0 2 = 98-07$ IT 

 1-0336 g. " 1-1482 g. U(X, = 97-93$ U 



The metal was found to contain 0-07 per cent of sodium. Both 

 lots of uranium were free from chlorine and carbon, and both 

 dissolved slowly in hydrochloric acid and left a small residue. 

 This was an uranium compound soluble in aqua regia. The 

 metal was completely soluble in nitric acid. 



After completing the calorimetric work, a third lot of 

 uranium was made and the metal obtained was in fused pieces 

 and friable lumps. From the latter grains a half to one milli- 

 meter in diameter were separated. The analysis of these gave 

 U, 99' 7, Ka, 0-09 per cent. These grains were found to burn 

 incompletely in sodium dioxide in the bomb and to give low 

 results. Hence no further heat tests were made with this 

 sample of uranium. 



* C. E. cxxii, 1088. 



