Oxides of Vanadium and Uranium. 147 



to burn at the hole. The cylinder was cooled under water. 

 Yield 15 grams with vanadium content of 76*3 per cent. Tlie 

 water solution was reddish but lost color on standing, showing 

 that a vanadite was present which slowly changed to vanadate. 

 The reaction of potassium on vanadium trioxide evidently is 



V 3 3 + 2K = V 2 2 + K 2 



V 3 8 +K 3 0==K a V a 4 

 since, according to these equations the yield of 34 grams of 

 vanadium trioxide is 15"1 grams of the dioxide and 15 was 

 obtained. The first equation represents an endothermic reac- 

 tion since the heat of oxidation of vanadium dioxide to trioxide 

 is 145,000' and that of the oxidation of potassium is 97,000 c , 

 but the reaction of the system is exothermic and that of 

 V.O, + K 2 is greater than 97,000°. A portion of " K " was 

 placed in water in a tube through which a current of hydrogen 

 was passing to displace the air, the water was boiled, then 

 hydrochloric was added ; the substance dissolved forming a 

 green solution and no gas was evolved. I do not understand 

 the reaction for V s 2 should yield VC1 2 which should set free 

 hydrogen with formation of YC1 3 . 



In the following the calorimetric experiments preparation 

 " H" was used in 11 and " K " in 12 and 13. 



11 12 13 



Vanadium dioxide 1-7374 2-002 2-104 grams 



Sodium peroxide 6 8*3 8-6 " 



Water equivalent of system 2898 3093 3067 " 



Temperature interval -. 1-565° 1-589° 1-677° 



Heat effect 4535 4915 5143 



" " iron . —40 —40 —40 



" " oxygen evolved +109 +220 +230 



4604 5095 5333 

 For 1 gram "V^O, 2650° 2545° 2535 c 



Two determinations made with preparation " J. " which was 

 not very pure, gave 2810 and 2799 c . The results thus 

 obtained with different preparations vary somewhat, but those 

 of 12 and 13 are to be regarded as the best and give 340,000° 

 for the heat effect of one gram molecule of vanadium dioxide 

 reacting with sodium peroxide. 



Experiment lJf,. — 1-173 gram of " K " V 2 O a was burned in 

 oxygen as described in Exp. 9. Most of the product of the 

 combustion was in one globule which externally had the color 

 of the pentoxide but otherwise was black and crystalline. The 

 atomic ratio of the vanadium to the oxygen in it was found to 

 be 1 to 2 - 2. The heat effect observed less than of the cotton 

 used was 1819°. Hence 1819 + 1-173 X 134 = 208,000° for 

 the heat effect of V 2 2 burning chiefly to V 2 4 . 



