80 PROF. H. E. ROSCOE ON CERTAIN 



moisture, evolving copious fumes of hydrochloric acid, and 

 the colour changing from a violet to a greenish brown. 

 Water does not act upon pure hexachloride of tungsten in 

 the cold ; but, on boiling, the decomposition into tungstic 

 acid and hydrochloric acid occurs. If, however, oxy chlo- 

 ride is present, the red needle-shaped crystals at once 

 become yellow, or, if an impure mass is employed, the 

 whole is suddenly decomposed by cold water into a green- 

 ish oxide. Tungsten hexachloride dissolves readily in dry 

 carbon disulphide, forming a dark brown solution, from 

 which the substance is deposited in six-sided plates ; but, 

 as the oxychloride is likewise soluble in this liquid, this 

 mode of preparation was not adopted. One of the tubes 

 in which the crystals thus obtained had been sealed, ex- 

 ploded with a loud report on opening with a file, the crys- 

 tals suddenly assuming the condition of the decrepitated 

 chloride. On decomposing the hexachloride with water, 

 a small quantity of chlorine is invariably retained by the 

 tungstic acid even on repeated distillation with water; 

 and, in order to obtain the whole of the chlorine, it was 

 found necessary to reduce the oxide to metal. The ana- 

 lysis was therefore carried out as follows : — the pure chlo- 

 ride was weighed in a porcelain boat, then carefully covered 

 with water, and the boat and contents quickly introduced 

 into a combustion-tube already fitted to a gas-furnace. 

 A current of purified hydrogen was delivered at one end 

 of the combustion -tube, whilst the other was connected 

 with a bent tube dipping into a flask containing water for 

 the absorption of the hydrochloric acid. On gently heating 

 the fore part of the tube (the greatest care being necessary 

 to avoid spirting) , the chloride is converted into the yellow 

 oxide, which, after being perfectly dried, is gradually heated 

 to as high a temperature as the tube will stand. The tung- 

 sten is thus obtained in the metallic state and the chlorine 

 as hydrochloric acid, which is estimated with silver. 



