PROFESSOR ROSCOE’S RESEARCHES ON VANADIUM. 
15 
atom of oxygen, and is transformed to small dark indigo-coloured crystals of tetroxide 
(see page 16). 
Vanadium Trioxide in solution . — The trioxide is insoluble in acids, but it may be 
obtained in solution as follows : — If solutions of vanadium pentoxide in sulphuric acid 
are diluted and treated with excess of metallic magnesium, the changes of colour which 
are observed when zinc, cadmium, or sodium amalgam are used do not continue beyond 
the green, and the liquid contains vanadium trioxide in solution. 
In order to ascertain the reliability of the method of analysis described, viz. oxidation 
by means of a standard permanganate solution, a known weight of vanadium trioxide was 
prepared by reducing vanadium pentoxide in a current of diy hydrogen with the pre- 
cautions which will be found described under the atomic weights determinations. 
The resulting trioxide was placed in a flask containing dilute sulphuric acid and filled 
with carbonic acid ; on the addition of permanganate the black finely divided oxide is 
rapidly oxidized, dissolving in the acid, and the point of complete oxidation can thus 
be accurately attained. 0*4043 grm. of vanadium pentoxide thus reduced required 50*4 
cub. centims. of permanganate solution (1 cub. centim. = 0*001413 grm. oxygen) for 
complete oxidation; this corresponds to a gain of 21*35 on 100 parts of trioxide; the 
theoretical gain in passing from trioxide to pentoxide is 21*24. 
The following numbers were obtained by the action of magnesium on the solution of 
vanadium pentoxide in sulphuric acid (1 cub. centim. standard solution represents 
0*001413 grm. oxygen): — 
Reduction with Magnesium . — 
Weight of V 2 0 5 taken 
Exp. 1. 
. 0*0759 
Exp. 2. 
0*1593 
Exp. 3. 
0*1025 
Exp. 4. 
0*1187 
Cub. centims. permanganate required 
. 9*4 
19*6 
13*0 
15*0 
Observed loss of oxygen on 100 V 2 0 5 
. 17*5 
17*38 
17*9 
17*9 
Ditto, calculated 
. 17*5 
17*5 
17*5 
17*5 
Solutions of vanadium trioxide can also be obtained by partial oxidation of the 
lavender-coloured solution of dioxide. If a current of air be passed through a reduced 
solution in which the free acid has been neutralized by excess of zinc, and the remaining 
metallic zinc removed, the liquid attains a permanent brown colour, which, on the addi- 
tion of a few drops of acid, turns to green. Both the brown and green liquids contain 
trioxide in solution, the dioxide having taken up one atom of oxygen, as the following 
analyses show : — 
(1) 0*1672 V 2 0 5 , reduced by zinc and oxidized by air passing through for one hour, 
required 21*9 cub. centims. of the foregoing permanganate solution for complete 
oxidation. 
(2) 0*1652 V 2 0 5 , treated in the same way, but exposed for four hours to a current of 
air, required 21*0 cub. centims. permanganate (1 cub. centim. = 0*001320 grm. 
oxygen). 
