Mixter — Oxides of Vanadium and Uranium. 141 



Art. XV. — Heat of Formation of the Oxides of Vanadium 

 and Uranium, and Eighth Paper on Heat of Combination 

 of Acidic Oxides with Sodium Oxide; by W. G. Mixter. 



[Contributions from the Sheffield Chemical Laboratory of Yale University.] 



The determination of the heat of formation of the oxides of 

 vanadium is simple calorimetric work provided the pure metal 

 in the form of a fine powder is available. This has not been 

 obtained and the results only show that the heat of oxidation 

 is very high. 



Vanadium. 



Roscoe obtained fairly pure metallic vanadium in small 

 quantities by reducing the chloride with hydrogen ; Moissan 

 reduced the oxide by carbon in the electric furnace and the 

 product contained several per cent of carbon. Other methods 

 have been tried, but, with possibly one exception mentioned 

 later, have yielded only impure metal. One specimen pur- 

 chased for electrolytic vanadium contains only 85 per cent of 

 the metal, and another marked "fused, c. p." 82 per cent. 

 Both specimens contain carbon. Weiss and Aichel* reduced 

 vanadium pentoxide with the mixed cerium metals and 

 obtained a fused metallic product which was brittle and 

 scratched quartz. For analysis they converted 0*2062 gram of 

 it into vanadyl sulphate, and made the solution to 500 cc . They 

 titrated 20 C0 of this solution containing 0*0082 gram and 

 obtained 0*0082 gram of vanadium. It is doubtful if an 

 analysis made with so small quantity gives an accurate result. 

 The writer has used for the determination of vanadium the 

 old method as follows : 0*2 to 0*5 gram of the metal or oxide 

 is dissolved in nitric acid and the solution evaporated to dry- 

 ness in a weighed platinum crucible, then heated slowly in an 

 electric furnace to a temperature a little under the melting 

 point of vanadium pentoxide. The heating was repeated 

 until a constant weight was obtained. It was found that 

 wetting the residue with nitric acid, drying and heating again, 

 did not increase the weight. A test of the method was made 

 by treating 0*5740 gram of vanadium pentoxide with nitric 

 acid. The weight was unchanged. The method presupposes 

 either the absence of substances that will leave a residue by 

 the treatment or the determination of them. 



It was found that magnesium and an oxide of vanadium 

 react violently when heated. With the hope of obtaining the 

 metal in a powder or a lower oxide the following was carried 



* Liebig's Ann., eccxxxvii, 380. 



