12 
PEOEESSOE EOSCOE’S EESEAECHES ON VANADIUM. 
metal vanadium can be separated from its last atom of oxygen with such extreme diffi- 
culty, and the lowest oxide is found to enter as a radical into so many compounds, that to 
this oxide the name vanadyl (VO) may appropriately be given. 
Vanadium dioxide can be obtained in the dry state, as a grey powder possessing a 
metallic lustre, by passing the vapour of vanadyl trichloride (VO Cl 3 ), mixed with excess 
of hydrogen, through a combustion-tube containing red-hot carbon. Lower solid oxy- 
chlorides (see page 25) are found to be deposited in the further portions of the tube, 
whilst vanadium dioxide remains as a bright grey metallic powder mixed with the 
charcoal. On strongly igniting this mixture in a current of hydrogen, every trace of 
chlorine is removed, and a pure mixture of charcoal and dioxide remains. 
Vanadium dioxide possesses a grey metallic lustre, dissolves in acids without evolution 
of hydrogen, and yields a lavender-coloured solution which bleaches strongly. Vana- 
dium dioxide is insoluble in water. 
Preparation 1. Analysis 1. — 0-8650 grm. of a mixture of vanadium dioxide and car- 
bon, prepared as described, and freed from chlorine by heating in hydrogen, was treated 
with hydrochloric acid: the carbon, collected on a tared filter and dried at 120° C., 
weighed 0-6126 grm. ; the filtrate, evaporated to dryness with nitric acid, the residue 
fused and weighed, yielded 0-3605 grm. of vanadium pentoxide. 
Analysis 2. — Another portion of the same substance free from chlorine was burned in 
a platinum boat in a current of oxygen. The carbon dioxide formed was weighed, and 
the residual vanadium estimated as pentoxide: 0-0996 grm. substance yielded 0-2482 
grm. C0 2 , and 0-0416 grm. V 2 0 5 . Therefore the percentage of vanadium dioxide con- 
tamed in the grey powder is as follows: — No. 1, 105-3; No. 2, 96-1. 
Vanadium Dioxide in solution . — If the dark-red solution obtained by dissolving finely 
powdered vanadium pentoxide in strong boiling sulphuric acid be diluted with fifty 
times its bulk of water and then digested with metallic zinc, the liquid rapidly changes 
colour under the influence of the nascent hydrogen, passing through all shades of blue 
and green until, after lapse of some time, it assumes a permanent lavender or violet 
tint. The vanadium is then contained in solution in the lowest degree of oxidation 
(V 2 0 2 = 134-6) as sulphate, and this compound absorbs oxygen with such avidity as to 
bleach indigo and other vegetable colouring-matters as quickly as chlorine itself, and 
acts far more powerfully than any other known reducing agent. In order to estimate 
the degree of oxidation of the dissolved vanadium, a standard solution of potassium per- 
manganate w T as added to the reduced liquid until a permanent pink colour was produced, 
experiments with vanadium trioxide of known composition (given on page 15) having 
proved that this point is that of maximum oxidation (V 2 0 5 ), and that it can be accu- 
rately reached provided an excess of sulphuric acid be present*. 
* This method of estimation was proposed and used by Czudnowicz (Pogg. Ann. Bd. cxx. p. 37) ; the results 
described by him differ, however, altogether from my own. He did not obtain the lavender-coloured solution 
by th$ action of zinc, and it is clear that in his experiments the reducing action of the hydrogen was not com- 
plete. 
