488 Mixter — Formation of the Oxides of Molybdenum, etc. 



Art. XLIII. — The Heat of Formation of the Oxides of Molyb- 

 denum, Selenium and Tellurium / and fifth paper on the 

 Heat of Combination of 'Acidic Oxides with Sodium Oxide; 

 by W. G. Mixter. 



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



Molybdenum. 



Thermal chemistry of molydenum is lacking, owing, per- 

 haps, to the difficulty of burning the metal completely in 

 oxygen. It is remarkable, however, that neither Thomsen nor 

 Berthelot recorded any experiments with it. The writer tried 

 burning molybdenum mixed with carbon for ignition and to 

 supply heat to volatilize the trioxide formed, and the result 

 was imperfect oxidation of the metal. Hence the indirect 

 method with peroxide was used. 



Metallic molybdenum for the work was prepared as follows : 

 Compact pellets of pure trioxide were heated in an electric 

 furnace in a porcelain tube through which pure dry hydrogen 

 was passed. The metal obtained was in the form of a gray 

 coherent mass and portions adhering to the tube were rejected.* 

 It was rubbed up in a mortar and passed through a fine sieve. 

 The purity of the metal was determined as follows : It was 

 oxidized by nitric acid, the acid removed by evaporation and 

 the residue cautiously heated until it ceased to lose weight. 

 The following are the analytical data : 



I II 



Metal taken __ 1-0505 1*1771 



Molybdenum trioxide obtained 1*5750 1*7653 



Oxygen taken up . _ 0*5245 0*5882 



Molybdenum equivalent to oxygen taken up 1*049 1*1764 

 Per cent of molybdenum as metal _ 99*86 99*84 



While the results indicate that the reduction by hydrogen was 

 not quite complete, very likely there was some loss in oxidizing 

 the metal or in heating the trioxide. Hence the metal was con- 

 sidered pure and no correction was made for 0*15 per cent of 

 oxygen which the above results indicate. The trioxide obtained 

 dissolved completely in ammonia, showing the absence of silica 

 and alumina. 



* Debray (C. R. lxvi, 732) found that molybdenum trioxide affects por- 

 celain at high temperatures. To avoid this the reduction was first tried 

 in a thin platinum tube contained in a porcelain tube. The platinum 

 was made quite brittle and the molybdenum obtained was very slowly acted 

 on by nitric acid. The reason of the action on the platinum was not inves- 

 tigated. In the reduction, where pellets of the trioxide were in contact with 

 the porcelain tube, the porcelain was slightly attacked and the molybdenum 

 adhering to it was found to have taken up a little iron. 



