tungsten compounds. 79 



The Chlorides of Tungsten. 



i. Tunysten Hexachloride, WC1 6 . — In the preparation 

 of this chloride in the pnre state it is absolutely necessary 

 to exclude every trace of oxygen or of moisture. For this 

 purpose the pure metal must be burnt in a current of per- 

 fectly dry and air-free chlorine, otherwise some red oxy- 

 chloride is invariably formed ; and this cannot be separated 

 from the chloride, owing to the slight difference existing 

 between their boiling-points. 



Metallic tungsten takes fire at a moderate heat in dry 

 chlorine, and the action goes on by itself until all the 

 chlorine disappears. In order to obtain the hexacbloride 

 in quantity, the metal was first ignited in a current of dry 

 hydrogen, then the hydrogen in the whole apparatus was 

 displaced by a current of dry carbonic- acid gas, and, lastly, 

 air-free chlorine was substituted for the carbonic acid, and 

 the tube or retort heated moderately. At the commence- 

 ment of the operation a slight sublimate of red needle- 

 shaped crystals of the oxychloride is frequently formed, 

 owing to the unavoidable presence of traces of oxygen ; but 

 this is easily driven to the end of the tube beyond the 

 point at which it is intended to collect the hexachloride. 

 On raising the temperature of the metal, a granular sub- 

 limate of dark violet opaque crystals of the hexachloride 

 makes its appearance. Prepared in quantity, the hexa- 

 chloride collects as a dark blackish-red liquid. In order 

 to saturate this liquid, it was slowly distilled in a current 

 of chlorine, by which means any traces of red oxychloride 

 were got rid of. 



The dark violet crystals decrepitate on cooling, and the 

 mass can thus be easily transferred to the tube in which it 

 is sealed up. When pure, the solid hexachloride does not 

 undergo any change even in moist air ; but in presence of 

 the slightest trace of the red oxychloride it at once absorbs 



