322 
PROFESSOR ROSCOE’S RESEARCHES ON VANADIUM. 
is almost impossible to prevent traces of ammonium metavanadate from dissolving, and 
on ignition, even with the greatest care, some portions of the finely divided vanadium 
pentoxide are invariably carried off when the ammonia escapes. On the other hand, the 
volatilization of the comparatively large quantities of sal-ammoniac which must be em- 
ployed in order to ensure the complete precipitation of the vanadium, almost always 
entails a considerable loss of the fixed alkaline chlorides. A far more accurate plan for 
the separation of vanadium is the precipitation of the soluble vanadate by acetate of lead, 
when basic lead vanadate is precipitated, which is so insoluble that a portion when finely 
powdered and boiled in water did not dissolve in sufficient quantity to enable the lead 
reaction with sulphuretted hydrogen to be detected in the filtrate. This salt is also inso- 
luble in acetic, but it dissolves readily in nitric acid, liberating vanadic acid, which sepa- 
rates out, but dissolves completely when the liquid is warmed. In the analysis of a solu- 
ble vanadate this insoluble lead salt is collected on a filter, dried at 100° C. and weighed ; 
a given quantity of the dried salt is then dissolved in nitric acid, the lead precipitated 
by pure sulphuric acid, and the lead sulphate determined with the usual precautions of 
evaporation with addition of alcohol, &c. The lead sulphate thus obtained is (contrary 
to Berzelius’s statement) quite free from vanadium, whilst the vanadic acid in the 
filtrate is obtained perfectly pure, and well crystallized on evaporation and ignition. 
The filtrate from the lead vanadate, freed from excess of lead by means of sulphuric acid 
and evaporated, yields the alkaline sulphate not containing a trace of vanadium. 
Sodium Vanadates. 
1. Sodium Orthovanadate, Na 3 V0 4 + 16H 2 O. — When a mixture of three molecules 
of sodium carbonate and one molecule of vanadium pentoxide is fused until no further 
evolution of carbon dioxide is observed, three molecules of C0 2 have been expelled and 
a tribasic vanadate remains as a white crystalline mass. 
In one experiment in which a slight excess of sodium carbonate was taken 05785 
grm. V 2 0 5 liberated on fusion 0*4185 grm. C0 2 . According to the equation 
V 2 0 5 + 3Na 2 C0 3 = 2Na 3 V0 4 + 3C0 2 , 
the weight of C0 2 liberated by this quantity of vanadium pentoxide is 0*4182 grm. 
The mixture is easily fusible at first, but becomes less so as the reaction proceeds ; 
whilst to begin with the heat of a Bunsen’s burner is sufficient to melt the mass, it is 
necessary to apply the heat of a blowpipe-flame to keep up the fusion when the decom- 
position becomes more nearly complete. On cooling, the solidified mass acquires first 
a dark green colour, and then passes through yellow, until when cold it becomes per- 
fectly white, and is found to possess a crystalline appearance. It dissolves easily in cold 
water, but is insoluble in alcohol. Hot water must not be employed for dissolving the 
fused mass, and as little cold water as possible. The cold strong aqueous solution must 
be instantly mixed with excess of strong alcohol ; two layers of liquid are then formed, 
the upper one consisting of dilute alcohol, the lower one of the saline solution. After 
