o 
PROFESSOR ROSCOE’S RESEARCHES ON VANADIUM. 
We are indebted to the researches of Berzelius for almost all we know concerning 
the chemical relations and composition of vanadium and its compounds. From his 
celebrated investigation on Vanadium* (1831), the results of which have since been 
more or less completely confirmed by ScHAFARixf and Czudnowicz $, it appears that the 
formula of vanadic acid is V 0 3 . Hence it is evident that we have here to do with either 
a case of dissimilarly constituted substances acting as isomorphous bodies and crystallizing 
together, or else the conclusions of Berzelius are erroneous, and the true formula of 
vanadic acid is V 2 0 5 , corresponding to the pentoxides of phosphorus and arsenic. The 
first of these alternatives has been properly accepted by most chemists as the only present 
solution of the difficulty, inasmuch as the definite experimental data given by Berzelius 
render the assumption of any other formula but V 0 3 for vanadic acid perfectly gratui- 
tous in the absence of experiments proving these data to be erroneous. 
Berzelius based his conclusions on the following experiments, viz. (1) the constant 
loss of weight which vanadic acid undergoes on reduction in hydrogen at a red heat ; 
(2) the action of chlorine on this reduced oxide, when a volatile chloride is formed and 
a residue of vanadic acid remains, which is found to be exactly one-third of the quantity 
originally taken for reduction in hydrogen. Hence Berzelius concludes .that the 
number of atoms of oxygen in the oxide is to that in the acid in the proportion of 
1 to 3 ; so that (assuming the lowest oxide to contain one atom of oxygen) the acid 
contains three atoms, a result which Berzelius finds borne out by its capacity of satura- 
tion. The question whether the acid contains one or two atoms of metal Berzelius 
decides in favour of the former view, by finding that no compound corresponding to the 
alums is formed when vanadic acid is brought together with sulphuric acid and potash. 
The analyses of the volatile chloride made both by Berzelius and Schafarik confirm 
this conclusion, and place beyond all doubt the fact that, if the atomic weight of vana- 
dium be taken to be 68‘5 and 0=8, the formula of vanadic acid is V 0 3 , that of the 
oxide prepared by reduction V O, and that of the chloride V Cl 3 . 
In the present communication I shall show that, whilst confirming these fundamental 
results in every particular, I still arrive at a totally different conclusion from Berzelius 
respecting the constitution of vanadic acid, and all the other vanadium compounds ; for 
I shall prove that the true formula of vanadic acid is V 2 0 5 (when 0 = 16), and the true 
atomic weight of vanadium 51-3, inasmuch as the substance supposed by Berzelius to 
be vanadium is not the metal but an oxide with an atomic weight of 67 ’3, nearly that 
of Berzelius’s metal, whilst the supposed terchloride is an oxychloride. 
The following are the grounds upon which I base my conclusions ; the experimental 
proofs are contained in the sequel : — 
(1) An oxide of vanadium exists which unites with three atoms of oxygen to form 
vanadic acid. Hence this latter substance must contain more than three atoms of 
oxygen. 
* Pogg. Ann. Bd. xxii. p. 1 (1831). t Ann. Ch. Pharm. cix. p. 84 (1859). 
i Pogg. Ann. Bd. cxx. p. 33 (1863). 
