8 
PROFESSOR ROSCOE’S RESEARCHES ON VANADIUM. 
the presence of the smallest quantity of phosphorus pentoxide rendering, as has been 
shown, the complete reduction of the vanadic acid impossible. Thus, for example, 
in two determinations it was found that 
(1) 2’9232grms. vanadium pentoxide yielded 2-4840 grms. trioxide, or V=65 - 4. 
(2) 4-2826 grms. yielded 3-5649 grms. trioxide, or V=55 - 4. 
On testing the residual oxide for phosphorus, the top layer of trioxide in the boat was 
found to contain phosphorus pentoxide, whereas the lower layers were free from it. 
In order to show that the reduction in these cases was incomplete, 3-4886 grms. of the 
reduced oxide from an experiment of the kind was treated in a tube with dry chlorine ; 
when all the chloride had volatilized, the residual vanadic acid was fused and found to 
weigh 2-165 grms. ; if the oxide had been completely reduced, the residual vanadic acid 
would have weighed 1-407 grm. 
No less than nine determinations of atomic weight were made with every possible pre- 
caution, in which the results varied from 52-2 to 65-4, owing solely to the employment 
of drying-tubes containing phosphoric anhydride. As soon as this source of error was 
removed and a sulphuric-acid tube substituted, the pentoxide was completely reduced 
to trioxide and the numbers became constant. 
The formula of vanadic acid being V 2 0 5 , and that of the oxide obtained by reduction 
V 2 0 3 , the atomic weight of vanadium is found from the equation 
8 (5 b -3a) 
X ~ a-b ’ 
where a = the weight of vanadic acid taken, and b = the weight of reduced oxide ob- 
tained. 
Determination No. 1. — The vanadic acid used in this and the following determina- 
tions was prepared from ammonium vanadate by roasting ; the acid thus obtained was 
found to contain traces of phosphorus and silica. To free it from these substances 
it was treated as follows : the powdered acid was first deflagrated with its own weight 
of metallic sodium in an iron crucible, the reduced oxide completely washed by decan- 
tation, treated with hydrochloric acid to free it from iron, and oxidized with nitric 
acid. This vanadic acid was then reduced in a current of hydrogen and converted into 
the oxychloride by heating in a current of chlorine ; after rectification the chloride 
was decomposed by water, and the resulting powdery acid dried and afterwards mois- 
tened with pure sulphuric acid and exposed in a platinum vessel for ten days to the 
action of hydrofluoric-acid gas. On fusing and cooling this purified acid, dark red 
transparent crystals, five to six centimetres in length, were obtained, stretching across 
the bottom of the basin. 
Platinum boat after first heating in air -f- tube* 19 6287 grms. 
„ „ second „ „ 19-6287 „ 
* The glass tube and stopper were frequently reweighed to ascertain if the friction of the stopper produced 
any appreciable diminution of weight. At the end of the series of determinations they were found to have 
