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PEOFESSOE EOSCOE’S EESEAECHES ON VANADIUM. 
(trioxide), soluble in hydrochloric acid, which remains in suspension, and (2) a heavier 
grey powder (insoluble in hydrochloric acid), which is deposited, and which by repeated 
washing may be entirely freed from the lighter trioxide. This bright grey powder 
consists of metallic vanadium mixed with more or less oxide. If the finely divided 
metallic powder, after drying in vacuo , be reduced at a low red heat in a current of pure 
hydrogen, it takes fire spontaneously, when cold, on exposure to air or oxygen, a distinct 
flame being seen playing on the surface whilst water is formed. In one experiment 
a product thus prepared contained 91 T per cent, of metallic vanadium (0-354 substance 
gave 0-574 grm. V 2 0 5 ). This substance, exposed for some weeks to dry air, slowly 
absorbed oxygen, and on roasting gave a percentage increase of 53-75 (0-453 grm. 
yielded 0-6965 V 2 0 5 ), whilst 0-034 grm. or 7 - 5 per cent, of water was at the same time 
formed. This shows that the point of oxidation at which the metal containing hydrogen 
becomes stable in dry air nearly corresponds to the oxide V 2 O. 
A similar slow change in the appearance of the metal has been noticed in some of 
the portions of the metallic powder placed on microscopic slides. 
II. VANADIUM AND BEOMINE. 
1. Vanadium Oxytribromide or Vanadyl Tribromide, YOBr 3 , molec. wt.=307‘3. — 
When the vapour of perfectly dry and pure bromine is passed over vanadium trioxide 
(V 2 0 3 ) heated to redness, dense yellowish-white fumes of the oxytribromide are formed 
in the heated portion of the tube, and these condense together with the excess of bromine 
to form a dark red transparent liquid. In order to free the oxytribromide from excess 
of bromine, the mixed liquids must be rectified in vacuo, as the temperature of decom- 
position of the oxybromide lies (under the ordinary atmospheric pressure) below its 
boiling-point. By distilling under a pressure of 106 millims. of mercury in a current 
of perfectly dry air the whole of the bromine was got rid of before the thermometer 
rose to 45° C. The transparent liquid remaining in the retort had a dark red colour, 
gave off white fumes on exposure to moist air, and when thrown into water produced a 
light yellow-coloured solution of a vanadic salt. It is possible to distil the oxybromide 
under diminished pressure with but slight decomposition occurring, although when 
heated under the atmospheric pressure it suddenly solidifies at 180° C., splitting up into 
the oxydibromide and bromine. Under a pressure of 100 millims. of mercury the oxy- 
tribromide volatilizes without decomposition between 130° to 136° C. 
The following analytical results were obtained : — Analysis No. 1 was made from a 
portion of oxytribromide which had not been distilled, No. 2 from a portion of the 
same substance, after further treatment with dry air at 63°, No. 3 from another prepa- 
ration which had been distilled in vacuo, and in which the bromine determination is too 
high owing to traces of free bromine. 
