TUNGSTEN COMPOUNDS. 93 



I. II. 



Weight of bromide taken i'375° 1*6200 



„ tungsten obtained .. . 0-4570 0*5144 



„ silver bromide 2*0956 2*633 



„ metallic silver 0*0129 0*017:2, 



Percentage of tungsten 33' 2 4 3*75 



„ bromine 65*56 69*93 



Calculated. Found. 



Tungsten, W =184 31*51 3^*49 



Bromine, Br 5 =40o 68*49 67*74 



584 ioo*oo 100*23 



Reduction of Pentabromide in Hydrogen. — When penta- 

 bromide is strongly heated in a current of hydrogen, the 

 metal is reduced in the form of a fine black powder, which 

 takes fire spontaneously on exposure to air ; so that the 

 complete reduction of the bromides takes place much more 

 readily than in the case of the corresponding chlorides. 



If the pentabromide be treated with hydrogen at 350 

 for several hours, the resulting substance (which is not 

 homogeneous) consists of hard black crusts covered with 

 a velvety substance. It is scarcely acted upon by water, 

 and on analysis gave the following percentages : — 



I. II. III. 



Percentage of tungsten ... 43*53 44*48 45*35 



„ bromine 5°*3° 



The percentage of tungsten agrees nearly with that 

 needed for the formula WBr ? ; but that of the bromide is 

 too low, owing to admixture of oxybromide. 



2. Tungsten Dibromide, WBr 2 = 344. — This mixture, 

 when heated in a bath of fused zinc-chloride in a current of 

 hydrogen, gave off a large quantity of volatile bromide and 

 oxybromide, leaving a residue of a bluish-black velvety 

 colour. This latter substance is WBr 2 , tungsten dibro- 

 mide. The dibromide is decomposed by water, forming 

 a brown solution with evolution of hydrogen. Acted on 

 by nitric acid, tungsten trioxide is formed and bromine 



