92 prop. h. e. roscoe on certain 



Bromides of Tungsten. 



Bromine-vapour, or, more conveniently, carbonic acid 

 saturated with bromine, acts rapidly on red-hot tungsten, 

 forming dark bromine-like vapours, which condense to a 

 crystalline sublimate. Especial precautions, similar to 

 those necessary in the preparation of the chlorides, must 

 be employed with the bromides, as the oxybromide formed 

 in presence of air or moisture possesses very nearly the 

 same colour as the bromide, and therefore the detection 

 of an impurity is not so easy as in the case of the 

 chloride. 



i. Tungsten Pentabromide, WBr 5 = 584. — By the action 

 of excess of bromine on tungsten, a penta- and not a 

 hexabromide is obtained; indeed the pentabromide itself 

 evolves bromine on standing, showing that it is an un- 

 stable compound. Thus prepared, and distilled in excess 

 of bromine, the pentabromide forms dark crystals having 

 a metallic lustre, not unlike those of iodine ; these melt at 

 276 C. (corrected), and solidify at 273 , and the substance 

 boils at 333 . The pentabromide is at once decomposed by 

 excess of water into the blue oxide of tungsten and hydro- 

 bromic acid, and immediately undergoes decomposition on 

 exposure to moist air. On distillation, a small quantity of 

 a lower non-volatile bromide remains behind; and this 

 explains the slightly too high percentage of metal found in 

 the analysis. 



The body employed in Analysis I. was obtained directly 

 by the action of bromine on the metal ; for Analysis No. II. 

 the same body was employed after it had been heated for 

 eighteen hours at ioo° with excess of bromine, and this 

 distilled off at a low temperature. The analyses were con- 

 ducted as described for the chlorides, except that the hydro- 

 bromic acid and free bromine evolved were passed into a 

 solution of sulphurous acid. 



