TUNGSTEN COMPOUNDS. 87 



Vapour-density o/WCl s at 440 C. 



I. 11. in. 



Weight of bulb in air 19-4245 19-5200 19-6395 grms. 



Barometer 772 770 769 mm. 



Temperature 14 12 12 C. 



Weight of bulb and vapour, ] 



at o c _ / i9"979° 20-0100 20-3505 grins. 



Capacity of bulb * 106-02 9376 110-580.0. 



Hence vapour-density (H — 1) 186-4 1865 1857 



Vapour-density of WC1 5 at 350 C." 

 I. II. 



Weight of bulb in air 25-7517 25-8148 grms. 



Barometer 755-5 755-5 mm. 



Temperature I 3°'5 I 3°'5 C- 



Weight of bulb and vapour... 26-5370 26-3300 grms. 



Capacity of bulb 134-3 90-690.0. 



Hence vapour-density (H = 1 ) 179*9 175*6 



The formula WC1 5 requires a density of 180*7; hence 

 the density in the case of this compound is normal, the 

 mean experimental number being 182*8. 



3. Tungsten Tetrachloride, WC1 4 = 326. — The tetra- 

 chloride forms the non-volatile residue formed in the dis- 

 tillation of the hexachloride in hydrogen. In order to 

 obtain it in a pure state, the mixture of the two higher 

 chlorides is distilled at a low temperature (best in a bath 

 of sulphuric acid) in a current of dry hydrogen or carbonic 

 acid, and the volatile pentachloride distilled back again 

 once or twice over the residue to saturate the lower 

 chlorides or metal, which are always formed, up to the 

 tetrachloride. 



The tetrachloride of tungsten is a loose, soft, crystalline 

 powder of a greyish-brown colour. It is highly hygro- 

 scopic, but not so much as the pentachloride, and it is 

 partially decomposed by cold water into brown oxide and 

 hydrochloric acid, and also forms a greenish-brown solu- 



* The residual air was not measured ; expansion of glass not allowed for. 



