1867.] 



Prof. Roscoe on Vanadium, 



221 



compounds been traced, that in many specimens these minerals have been 

 found to crystallize together in all proportions ; and Heddle describes a 

 crystal in his possession, the upper half of which consists of vanadinite and 

 the lower half of pyromorphite. 



Our knowledge concerning the chemical composition of the oxides of va- 

 nadium is derived from the accurate analytical results of Berzelius, to whose 

 celebrated research (1831) on vanadium we are indebted for almost all we 

 know of this metal and its compounds. From these experiments, more or less 

 completely confirmed by Schafarik and Czudnowicz, it appears that the for- 

 mula of vanadic acid is VOg. Hence it is evident that we have here to do with 

 either a case of dissimilarly constituted substances acting as isomorphous 

 bodies and crystaUizing together, or else the conclusions of Berzelius are 

 mistaken, and the true formula of vanadic acid is VgOg, corresponding to 

 phosphorus and arsenic pentoxides. The first of these alternatives has been 

 properly accepted by most chemists as the only present solution of the dif- 

 ficulty, inasmuch as the definite experimental data given by Berzelius ren- 

 der the assumption of any other formula but VO3 for vanadic acid perfectly 

 gratuitous 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 re- 

 mains, 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 pro- 

 portion of 1 to 3 ; so that (assuming the lowest oxide to contain one 

 atom of oxygen) the acid contains three atoms of oxygen, a result 

 which he finds borne out by its capacity of saturation. 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 Ber- 

 zelius and Schafarik confirm this conclusion, and place beyond all doubt 

 the fact that, if the atomic weight of vanadium be taken to be 68*5 and 

 0=8, the formula of vanadic acid is VO3, that of the oxide prepared by 

 reduction YO, and that of the chloride YCig. 



In the present communication the author, whilst confirming these funda- 

 mental results in every particular, still arrives at a totally different conclu- 

 sion from BerzeRus respecting the constitution of vanadic acid and all the 

 other vanadium compounds ; for he proves that the true formula of vanadic 

 acid is ^ when 0=16, and the true atomic weight of vanadium V= 51*2, 

 inasmuch as the substance supposed to be vanadium is not the metal but 

 an oxide, with an atomic weight of 67"2, nearly that of Berzelius's metal, 

 whilst the supposed terchloride is an oxychloride. 



VOL. XVI. X 



