Oxides of Vanadium and Uranium. 149 



dium by Ruff and Martin* appeared. They find for the heat 

 of formation of vanadium pentoxide 250,500°, a value much 

 lower than the writer's results indicate. For example, V 2 2 + 

 20 = 204,000° by the sodium dioxide method and confirmed, 

 as already stated, by combustion in oxygen, points plainly to 

 over 400,000° for the heat of formation of vanadium pentoxide, 

 for it must be assumed that the first two atoms of oxygen 

 give as much heat as the last two. 



In view of Ruff and Martin's result it seemed desirable to 

 burn vanadium in oxygen. The best material available was 

 preparation " C," which contained 89*7 per cent of vanadium 

 when first made, and 88*6 per cent four months later. It con- 

 tained a trace of magnesium. The determinations were made 

 as in Experiment 9, and the oxygen was at a pressure of 15 

 atmospheres. The product of a combustion formed a globule 

 in the bottom of the bomb, small drops adhering to the top, 

 and a dark red powder. The temperature of the combustion 

 was high, and in one instance the heavy platinum electrode 

 was fused. The following table indicates in part the details of 

 the work : 



15 16 17 



Metal taken (a) 1-141 1*428 1-695 gram 



Cotton " 0-075 0-069 0-071 " 



Heateffect 3419° 4172° 4578° 



" " of cotton 300 280 284 



" " of a (J) 3119° 389^° 4294° 



Oxygen taken up by a (c) 0-582 0-650 0-750 gram 



Heat effect of 1 gram of oxygen _ 5359° 5990° 5720° 



c 



Composition of product of com- 



bustion. V a 4 . 6 V 2 0,, V 2 4 . 2 



The average for 1 gram of oxygen combining with the oxi- 

 dized metal is 5690°. For 4 - 2 gram atoms of oxygen is 5690 X 

 16 X 4-2 == 382,000°. This is*" the heat effect of the oxidation 

 of a mixture of vanadium and vanadium oxide, containing a 

 large proportion of the latter. Hence the result is much less 

 than the pure metal should give. It is impossible to make 

 allowance for the oxide, but on any assumption the correction 

 will be large. 



Uranium. 



It is remarkable that. there are no thermal data on uranium 

 compounds since the metal and dioxide burn well in oxygen. 



*Zeitschr. f. angew. Ch., xxv, 49. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 200.— August, 1912. 

 11 



