496 ME. J. PEIESTLET ON THE PHYSIOLOGICAL ACTION OP VANADIUM. 
whose chemical characters and relations have been rigidly investigated ; they had 
shown that vanadium is to be ranked as a member of one of the most interesting 
families of elements, and yet not a single fact had been ascertained in reference to its 
physiological action. The hope that an elaborate examination of the physiological 
reactions of vanadium might cast some light upon the relations which may exist 
between the chemical and the physiological affinities of elements, and the fact that 
Professor Roscoe offered to furnish any vanadium compound which might be required, 
acted as inducements to undertake this research. 
Vanadium belongs to the group of pentad elements, which includes nitrogen, phos- 
phorus, arsenic, antimony, and bismuth. It would obviously be out of place here to 
examine in detail the grounds upon which this relationship of vanadium has been based — 
as, for example, the analogies between the oxides of nitrogen and vanadium ; the resem- 
blance of phosphates, arseniates, and vanadates ; the isomorphism of vanadinite and 
pyromorphite, &c. 
A glance at the atomic weights of the chief members of the arsenic group of elements 
shows that vanadium has an atomic weight which places it between phosphorus and 
arsenic : — 
N, Nitrogen 14 
P, Phosphorus 31 
V, Vanadium 51-2 
As, Arsenic 75 
Sb, Antimony 122 
Bi, Bismuth 210 
The fact that, in a family of which several members exert a highly poisonous action, 
a new metal could be found whose atomic weight was nearly the mean of that of the 
two members possessing the greatest toxicological interest appeared to render the 
research an important one ; and the interest was enhanced by the fact that vanadium 
possesses an atomic weight very nearly the same as that of a poisonous metal not 
belonging to the arsenic group, but whose compounds bear some resemblance to those 
of vanadium, viz. chromium : — 
Atomic weight of chromium . . . 52 - 2 
„ vanadium . . . 51 ‘2 
Vanadium forms four series of compounds. First, a pentad series, of which vanadic 
oxide, V 2 0 5 , may be taken as a representative ; this oxide forms soluble vanadates with 
the alkaline metals. Secondly, a series of hypovanadic compounds, represented by a 
tetrachloride, VC1 4 , and by hypovanadic oxide, V 2 0 4 . Thirdly, a triad, vanadous series, 
of which may be taken as a representative the trichloride, V Cl 3 , analogous to the arsenic 
and antimony compounds, but, unlike them, non-volatile. Fourthly, a diad, hypo- 
vanadous series, represented by VC1 2 and V 2 0 2 (hypovanadous oxide). 
Although it appeared desirable to investigate bodies belonging to the various groups 
