Mixter — Heat of Combination of Acidic Oxides. 135 



3^N T a 2 ° 2 + Cr 2 3 (crys.) = 2Na t Cr0 4 + Na 2 + 108000° 

 3Na 2 + 30 = 3Na 2 2 + 58200 c 



2Na 2 + Cr 2 3 + 30 = 2Na 2 Cr0 4 + 166200° 



2(Na 2 + CrO,) = 2Na 9 Cr0 4 + ... 154000° 



Cr 2 3 (crystalline) + 30 = 2Cr0 3 + 12200° 



2(Cr + 30) = 2Cr0 3 + --- 280000° 



Or 2 3 (ciys.) + 30 = 2CrO, + _ 12200° 



2Cr + 30 = Cr 2 3 (crystalline) + 267800° 



2Cr + 30 = Cr 2 3 (amorphous) 4- 243800° 



Amorphous C 2 8 = crystalline Cr 2 8 + 24000° 



Thomsen* found for Cr,H O e , 3 , aq = 2Cr0 3 + 18913 c and 

 Berthelotf gives Cr 2 3 precip. + 0+ean. = 2Cr0 9 crys. +16400°. 

 The changes in the oxidation of the hydroxide are different 

 from those in case of the oxide and hence the above results 

 can not be compared with that of the writer. They all, how- 

 ever, show that the heat of formation of chromium trioxide 

 from the sesqnioxide is small. BerthelotJ derived from reac- 

 tions in solution the following: CrO 3 +K 2 O = K 2 CrO 4 +47800 c . 

 This appears to be too low when considered in connection 

 with the 77000° found for JSa a + O0 3 = Na 2 O0 4 , since the 

 heat of formation of potassium salts is commonly greater than 

 that of sodium salts. 



Tungsten. 



Metallic tungsten used in the work was prepared by reduc- 

 ing the oxide with dry hydrogen at the highest temperature 

 attainable in a gas combustion furnace. Even after ten hours 

 a little water came off, showing that the reduction was not 

 complete. During the first hours occupied in the reduction 

 a little ammonia was formed from the atmospheric nitrogen 

 contained in the hydrogen, but the reduced metal was free 

 from nitrogen. The test was made by heating a mixture of 

 the metallic powder and soda-lime. So ammonia was given 

 off. The tungsten present in the metallic state was determined 

 by finding the increase in weight when a weighed amount of 

 the metal was oxidized by heating in air and finally in oxygen. 

 The tungsten equivalent to the oxygen taken up was 98'14 per 

 cent. Iron was present to the extent of 0*07 per cent, leaving 

 1*79 per cent by difference of oxide of tungsten as WO,. 

 Undoubtedly only the lower oxides were present and there 



* Therniocheinisclie Untersiicliuiigen, ii, 464. f Thermochemie, ii, 272. 

 \ Ann. Ch. Phys. (6), i, 195. 



