80 



with the corresponding bromine and iodine compounds, 

 appeared before all things necessary. 



The author then describes the mode employed for pre- 

 paring pure metallic tungsten, which was found to possess 

 a spec. grav. of 19 '2 61 at 12° C. 



The Chlorides of Tungsten. 



1. Tungsten Hexachloride, WClg. 



For the preparation of this chloride in the pure state it is 

 absolutely necessary to exclude every trace of air or moisture. 

 For this purpose the metal must be burnt in a current of 

 perfectly dry and air-free chlorine, otherwise red oxychloride 

 is formed, and this cannot be separated from the chloride, 

 owing to the slight differences in their boiling points. 



Metallic tungsten takes fire in chlorine at a moderate 

 heat. On heating the tube containing the metal a granular 

 sublimate of dark violet opaque crystals of the hexachloride 

 makes its appearance, which, when prepared in quantity, 

 collects as a dark blackish red liquid. In order to purify it 

 this liquid is distilled several times in excess of chlorine, 

 and then slowly rectified in a stream of hydrogen, by which 

 means any traces of adhering oxychloride can be got rid of. 



The dark violet coloured crystals decrepitate on cooling, 

 and the mass falls to a crystalline powder. When pure the 

 solid hexachloride does not undergo any change, even in 

 moist air, but in presence of the smallest trace of oxychloride 

 it at once absorbs moisture, evolving fumes of hydrochloric 

 acid, and changes from a violet to a brown colour. Cold 

 water also acts very slowly on the pure substance, but, 

 if impure, the mass is at once decomposed by cold water into 

 a greenish oxide. The hexachloride is readily soluble in 

 carbon disulphide, from which it is deposited in hexagonal 

 plates. On several occasions the tubes containing the crys- 

 talline chloride exploded on opening them with a file, the 

 crystals suddenly assuming the form of the decrepitated 

 substance. 



