Oxides of Vanadium and Uranium. 145 



The average, l,432 c , multiplied by 150 equals 214,800 c for 

 the heat of the reaction of 1 gram molecule of vanadium 

 trioxide with sodium peroxide. 



Experiment 9. — The direct determination of the heat of 

 oxidation of vanadium trioxide was made by the method used 

 for finding the heat of combustion of titanium* ; 3 grams 

 of " F " were used. It was not completely changed to V 2 6 . 

 A weighed portion of the combustion product was oxidized by 

 nitric acid and the vanadium in it determined. From the data 

 obtained the atomic ratio of the vanadium to the oxygen was 

 found to be 1 to 2 - 2. The heat effect observed in the calori- 

 metric experiment is 1664°, that due to the cotton taken 558 c , 

 leaving 1104 c . Hence 1104 4- 3 X 150 = 55,200 c for the effect 

 of 1 gram molecule of vanadium trioxide burning to form the 

 tetroxide and some pentoxide. 



Vanadium Tetroxide. 



Vanadium tetroxide was made by heating to redness for 

 half an hour in an exhausted tube a mixture of equivalent 

 quantities of the tri- and pentoxide. The tube swelled some, 

 showing that oxygen was given off in small quantity. The 

 product was a coke-like mass. An analysis of it gave 61*1 per 

 cent of vanadium ; calculated 61*1 for V 2 4 . Yanadium 

 tetroxide burns readily with sodium dioxide without addition 

 of sulphur to the mixture. Two determinations in each of 

 which 4 grams were used gave respectively 1084 c and 1021°. 

 The mean is 1052 c or 174,600° for the reaction of one gram 

 molecule of vanadium tetroxide reacting with sodium dioxide. 



Vanadium Dioxide. 



Yanadium dioxide has been obtained in crystals by reducing 

 vanadium oxychloride, YOCl 3 with hydrogen. Berzelius-f 

 heated a mixture of vanadium pentoxide and potassium, 

 removed the soluble portion with water and regarded the 

 product as a metallic vanadium. Roscoe^: says it was a mix- 

 ture of oxides, and also§ that it was the dioxide. It is 

 commonly stated in the literature that vanadium dioxide may 

 be made by the method of Berzelius. It does not appear, how- 

 ever, to have been further investigated. Roscoe|| heated vana- 

 dium pentoxide and sodium in a closed iron crucible, washed 

 the product and obtained vanadium trioxide mixed with a 

 little higher oxide. The writer attempted the reduction with 



*This Journal, xxxiii, 45. f Pogg. Ann., xxii, 3. 



X Phil. Trans., clix, 687. 



SIbid, p. 690. 



J Eoscoe and Schorlemmer's Treatise on Chemistry, 4th ed., ii, p. 903. 



