6 
PROFESSOR ROSCOE’S RESEARCHES ON VANADIUM. 
ammonium vanadate was separated by filtration from a residue containing silica, phos- 
phates, &c., and was crystallized by evaporation in platinum ; the pentoxide obtained 
from this salt was free from phosphorus. Another mode, which was adopted in order 
to obtain perfectly pure vanadium pentoxide, was to prepare the pure oxychloride, and 
this, on being decomposed by water, yielded the acid as a fine orange-coloured powder. 
In order to free this powder from any trace of obstinately adhering silica, it was mois- 
tened with sulphuric acid and exposed in a platinum vessel for some days to hydrofluoric- 
acid gas ; after expelling the sulphuric acid and on fusion, a mass of large transparent 
crystals of chemically pure vanadic acid was obtained. 
The vanadium minerals appear invariably to contain more or less phosphorus, and 
this fact in itself serves to establish the close relationship which exists between these 
two elements. The complete separation of this substance from vanadium is attended 
with great difficulty : if much phosphorus is contained with the vanadium, the method 
which has proved most effectual for its removal is to deflagrate the finely divided impure 
acid with its own weight of sodium in a well-covered wrought-iron crucible, and wash 
the resulting mixture of vanadium oxides by decantation until the wash-water ceases to 
give an alkaline reaction ; frequently this operation had to be repeated three times be- 
fore the molybdenum test ceased to indicate phosphorus. In other preparations, in 
which the phosphorus had been more completely removed by previous operations, the 
process described above, of repeated crystallization of the ammonium salt, was found 
capable of furnishing a product in which no trace of yellow precipitate was produced 
by molybdenum. 
The action of even traces of phosphoric acid on vanadic acid is most remarkable ; if 
present in quantities exceeding 1 per cent, of the weight of the vanadium, phosphoric 
acid altogether prevents the crystallization of the vanadic acid, and the fused mass pos- 
sesses a glassy fracture, and a black vitreous lustre ; this effect is not produced by the 
presence of either silica, arsenic, or the lower oxides of vanadium. Still more singular 
is the protective influence which even traces of phosphoric acid exert upon the reducing 
action of hydrogen on vanadic acid at a red heat. Thus a mixture of pure vanadic acid 
with 1 per cent, of phosphorus pentoxide weighing 1-5888 grm., on ignition in a current 
of hydrogen lost only 0-0007 grm. ; if no phosphorus had been present it must have lost 
0-2784 grm. 
III. ATOMIC WEIGHT DETERMINATION OF YANADIUM BY REDUCTION OF VANADIUM 
PENTOXIDE IN HYDROGEN. 
The method originally adopted by Berzelius for the determination of the atomic 
weight of vanadium, viz. the reduction of vanadic acid in a current of hydrogen, is per- 
fectly reliable, inasmuch as the reduced trioxide (the suboxide of Berzelius) does not 
undergo any further change when the temperature is raised to a bright-red heat, and the 
reduction of the pentoxide to trioxide at temperatures much below this is perfectly defi- 
nite. The number obtained by Berzelius according to this method was V=68‘5; the 
