Chemically related to vanadium are the two elements tantalum and columbium or niobium.
Tantalum has in recent years been turned to economic service, being employed, in the same manner as tungsten, for the production of the filaments employed in incandescent electric lighting.
It is usually found associated with tantalum, the chief minerals containing these two elements being tantalite, columbite, fergusonite and yttrotantalite; it is also a constituent of pyrochlor, euxenite and samarskite.
It is then dissolved in hydrofluoric acid and heated in order to expel silicon fluoride; finally the columbium, tantalum and titanium fluorides are separated by the different solubilities of their double fluorides (C. Marignac, Ann.
Columbium pentoxide (columbic acid), Cb205, is obtained from columbite, after the removal of tantalum (see above).
Of minerals containing this element mention may be made of cassiterite or tinstone, Sn02, tin pyrites, Cu 4 SnS 4 + (Fe,Zn) 2 SnS 4; the metal also occurs in some epidotes, and in company with columbium, tantalum and other metals.
TANTALUM [[[symbol]] Ta, atomic weight 181 o (0=16)], a metallic chemical element, sparingly distributed in nature and then almost invariably associated with columbium.
Ekeberg discovered an element, tantalum, in some Swedish yttrium minerals.
Wollaston unsuccessfully endeavoured to show that columbium and tantalum were identical.
Tantalum is not affected by alkaline solutions, but is disintegrated when fused with potash.
In its chemical relationships tantalum is associated with vanadium, columbium and didymium in a sub-group of the periodic classification.
Tantalum tetroxide, Ta 2 0 4, is a porous dark grey mass harder than glass, and is obtained by reducing the pentoxide with magnesium.
Tantalum pentoxide, Ta205, is a white amorphous infusible powder, or it may be crystallized by strongly heating, or by fusing with boron trioxide or microcosmic salt.
Tantalum pentafluoride, TaF5, for a long time only known in solution, may be obtained by passing fluorine over an alloy of tantalum and aluminium, and purifying by distillation in a vacuum.
Tantalum pentachloride, TaC1 5, is obtained as light yellow needles by heating a mixture of the pentoxide and carbon in a current of chlorine.
The pentabromide exists, but tantalum and iodine apparently do not combine.
Tantalum forms a sulphide, TaS 2, and two nitrides, TaN 2 and Ta3N5, have been described.
Antimony, bismuth, selenium, tellurium, chromic iron ore, tin, nickel, cobalt, vanadium, titanium, molybdenum, uranium and tantalum are produced in the United States in small amounts, but such production in several cases has amounted to only slight discoveries, and in general they are of little importance in the market.
It is the hardest known substance (though tantalum, or an alloy of tantalum now competes with it) and is chosen as io in the mineralogist's scale of hardness; but the difference in hardness between diamond (io) and corundum (9) is really greater than that between corundum (9) and talc (1); there is a difference in the hardness of the different faces; the Borneo stones are also said to be harder than those of Australia, and the Australian harder than the African, but this is by no means certain.
The various improvements in electric illuminants, such as the Nernst oxide lamp, the tantalum and osmium incandescent lamps, and improved forms of arc lamp, enclosed, inverted and flame arcs, are described under Lighting: Electric. Between 1890 and 1900, electric traction advanced rapidly in the United States of America but more slowly in England.