Encyclopædia Britannica, Ninth Edition/Vanadium

VANADIUM, a rare element discovered in 1830 by Sefström, when analysing a kind of iron obtained from the ores of Taberg in Sweden. Berzelius, in the course of an extensive investigation on vanadium, came to the conclusion that it is analogous to chromium, forming like it an acid trioxide, VanO₃, in which “Van” signifies 134.4^[1] parts of a radical analogous to the Cr = 52 parts of chromium in chromic acid, CrO₃. He succeeded in isolating this radical, and, as it exhibited semi-metallic properties, he had no doubt that it was the element vanadium itself. His results were universally adopted as correct until Roscoe (in 1867) found that Berzelius’s vanadium is an oxide containing O₂ = 32 parts of oxygen per Van, whence it followed that the presumed trioxide, VanO₃, is really a pentoxide, V₂O₅, where V₂ = 2 x 51.2 = 2 atoms of the real element. Our present knowledge of vanadium is based chiefly upon his investigations. Of vanadium minerals, which are all very rare, we name two only,—mottramite, (Pb,Cu)₃(VO₄)₂ + 2(Pb,Cu)(OH)₂, and vanadinite, 3Pb₃(VO₄)₂ + PbCl₂. This last is amorphous with apatite, which previous to Roscoe’s discovery was difficult to explain. See Chemistry, vol. v. p. 539.

Traces of vanadium are found in certain iron ores and in many other minerals. Roscoe utilized a kind of sandstone from Alderley Edge and Mottram in Cheshire which contains a small admixture of mottramite. Another suitable material is the “Bohnerz” of Steinlade and Haverloh, essentially a hydrated ferric oxide. For the extraction of vanadium from this latter mineral Wöhler recommends the following method. The finely powdered mineral is mixed with one-third of its weight of nitre and the mixture kept at a dull red heat for an hour. The ignited mass is powdered and lixiviated with water, which extracts the potash salts of the oxides V₂O₅, CrO₃, MoO₃, As₂O₅, P₂O₅, and SiO₂. The filtered solution is almost neutralized with nitric acid, but not completely, or else some of the V₂O₅ would be reduced by the nitrous acid to lower oxides; and the vanadic and most of the other acids named are precipitated as baryta salts by addition of chloride of barium. From the washed precipitate the acids are liberated by boiling dilute sulphuric acid, and the sulphate of baryta is filtered off. The solution is neutralized with ammonia, concentrated by evaporation, and, after cooling, kept in contact with a solid piece of sal-ammoniac more than sufficient to saturate the solution with this salt. Meta-vanadate of ammonia, V₂O₅(NH₄)₂O, being characteristically insoluble in sal-ammoniac solution, separates out as a yellowish crystalline precipitate. This is collected, washed with sal-ammoniac solution and after that with alcohol, and purified by re-crystallization or otherwise. The pure salt when heated to dull redness leaves the pentoxide, V₂O₅ (vanadic acid), as a red liquid, which freezes into a red-brown crystalline mass of sp. gr. 3.35 (J. J. Watts). It dissolves in about 1000 parts of water, forming a yellow solution which reddens litmus. The pentoxide, though capable of uniting with strong acids, e.g., with sulphuric into a salt, V₂O₂(SO₄)₃, behaves on the whole as an acid oxide analogous in its combining habits to phosphoric (see Phosphorus, vol. xviii. p. 818, and Chemistry, vol. v. p. 540). Solutions of vanadates are easily recognized: on addition of mineral acid they assume the yellow colour characteristic of the pentoxide, and if the mixture is then kept in contact with zinc it passes through all shades of (intense) green till it ultimately assumes a lavender colour. The solution then contains a chloride corresponding to the oxide V₂O₂ (Berzelius’s metal). It absorbs atmospheric oxygen with an extraordinary degree of avidity, assuming, in the absence of free acid, a dark brown colour. An acidified vanadate solution, if shaken with peroxide of hydrogen and ether, furnishes a dark red reduction product, which passes into the ethereal layer. One part of vanadic acid in 40,000 parts of water can thus be rendered distinctly visible (Werther). If a mixture of the pentoxide and charcoal is heated in dry chlorine, it is converted into an oxychloride, VOCl₃ (trichloride of Berzelius), which distils over and may be purified by re-distillation over sodium. It is a canary-yellow mobile liquid, freezing below -15° C. and boiling at 126°.7 C., and its sp. gr. at 14° C. is 1.841. Water decomposes it with formation of hydrochloric acid and pentoxide V₂O₅. If the vapour of this chloride is passed over red-hot charcoal in a current of chlorine, the tetrachloride VCl₄ is produced as a dark brown liquid, boiling at about 154° C. A mixture of the vapour of this chloride with hydrogen, when passed through a dull-red-hot tube, yields (more or less of “sesqui-” chloride, V₂Cl₆, and) the dichloride VCl₂ , which, if pure, forms apple-green, mica-like, hexagonal plates. From this dichloride Roscoe for the first time prepared the true metal by heating it to redness in hydrogen gas, a simple enough method in theory, but in practice one of the most difficult of operations, because the dichloride is very difficult to prepare and highly hygroscopic, and because the metal is extremely prone to take up oxygen. Even the purest product which Roscoe succeeded in obtaining contained an appreciable admixture of oxide. Vanadium is a light grey powder, which under the microscope appears crystalline and exhibits a silvery lustre, sp. gr.=5.5. Of its chemical properties the most remarkable is that it combines directly with nitrogen gas, N₂, into a bronze-coloured nitride, VN.

Rare and expensive as vanadium is, it has found a practical application in the production of aniline black. The black is produced from aniline by the action of chloric acid, aided by the presence of some oxygen carrier. Sulphide of copper is usually employed; but, as Lightfoot found, a mere trace of vanadic acid (or vanadate of ammonia) acts more energetically than any other available agent. According to Witz, 1 part of vanadic acid suffices for 67,000 parts of aniline salt.

1. Calculated from our present constants.