ZIRCONIUM  [

symbol Zr, atomic weight 9o•6 (0=16)1, a metallic chemical element . Klaproth in 1789 analysed the mineral zircon or hyacinth and found it to contain a new earth, which he called " zirconia." The metal was obtained by Berzelius as an iron-grey powder by heating potassium zirconofluoride with metallic potassium . The amorphous metal also results when the chloride is heated with sodium; the oxide reduced with magnesium; or when fused potassium zirconofluoride is electrolysed (Wedekind, Zeit . Elektrochem., 1904, 10, p . 331) . Troost produced crystallized zirconium by fusing the double fluoride with aluminium in a graphite crucible at the temperature of melting iron, and extracting the aluminium from the melt with hydrochloric acid . It is more conveniently prepared by heating the oxide with carbon in the electric furnace . The crystals look like antimony, and are brittle, and so hard as to scratch glass and rubies; their specific gravity is 4.25 . The powdery metal burns readily in air; the crystalline metal re-quires to be heated in an oxyhydrogen flame before it catches fire . Mineral acids generally attack the crystallized metal very little even in the heat; aqua regia, however, dissolves it readily, and so does hydrofluoric acid . In its chemical affinities zirconium resembles titanium, cerium and thorium; it occurs in company with these elements, and is tetravalent in its more important salts . Zirconium oxide or zirconia, ZrO2, has become important since its application to the manufacture of mantles for incandescent gas-lighting .

For its extraction from zircon the mineral is heated and quenched in

water to render it brittle, and then reduced to a fine powder, which is fused with three to four parts of acid potassium fluoride in a platinum crucible . When the mass is quietly fusing, the crucible is heated for two hours in a wind-furnace . The porcelain-like melt is powdered, boiled with water, and acidified with hydrofluoric acid, and the residual potassium fluosilicate is filtered off . The filtrate on cooling deposits crystals of potassium zirconofluoride, K2ZrFs, which are purified by crystallization from hot water . The double fluoride is decomposed with hot concentrated sulphuric acid; the mixed sulphate is dissolved in water; and the zirconia is precipitated with ammonia in the cold . The precipitate, being difficult to wash, is (after a preliminary washing) re-dissolved in hydrochloric acid and re-precipitated with ammonia . Zirconium hydroxide, Zr(OH)4, as thus obtained, is quite appreciably soluble in water and easily in mineral acids, with formation of zirconium salts, e.g . ZrC14 . But, if the hydroxide is precipitated in the heat, it demands concentrated acids for its solution . The hydroxide readily loses its water at a dull red heat and passes into anhydride with vivid incandescence . Zirconia can be obtained crystalline, in a form isomorphous with cassiterite and rutile, by fusing the amorphous modification with borax, and dissolving out with sulphuric acid . The anhydrous oxide is with difficulty soluble even in hydrofluoric acid; but a mixture of two parts of concentrated sulphuric acid and one of water dissolves it on continued heating as the sulphate, Zr(504)2• Zirconia, when heated to whiteness, remains unfused, and radiates a fine white light, which suggested its utilization for making incandescent gas mantles; and, in the form of disks, as a substitute for the lime-cylinders ordinarily employed in " limelight." Zirconia, like stannic and titanic oxides, unites not only with acids but also with basic oxides .

For instance, if it be fused with sodium carbonate, sodium zirconate, Na2ZrO3, is formed . If the carbonate be in excess, the

salt Na4ZrO4 results, which when treated with water gives Na2Zr301 • 12H20, which crystallizes in hexagonal plates . When heated in a loosely covered crucible with magnesium the nitride Zr2N3 is formed (Wedekind, Zeit. anorg . Chem., 1905, 45, p . 385) . Zirconium hydride, ZrH2, is supposed to be formed when zirconia is heated with magnesium in an atmosphere of hydrogen . Zirconium fluoride, ZrF4, is obtained as glittering monoclinic tables (with 3H20) by heating zirconia with acid ammonium fluoride . It forms double salts, named zircono-fluorides, which are isomorphous with the stanni- and titani-fluorides . Zirconium chloride, ZrCla, is pre-pared as a white sublimate by igniting a mixture of zirconia and charcoal in a current of chlorine . It has the exact vapour-density corresponding to the formula . It dissolves in water with evolution of heat; on evaporation a basic salt, ZrOCl2.8H20, separates out in star-shaped acicular aggregates . Zirconium bromide, ZrBr4, is formed similarly to the chloride .

Water gives the oxybromide ZrOBr2 . Zirconium iodide, ZrI4, was obtained as a yellow, micro-crystalline solid by acting with hydriodic acid on heated zirconium (Wedekind,

Bee., 1904, 37, p . 1135) . It fumes in air; with water it gives ZrOI2.8H20; and with alcohol ethyl iodide and zirconium hydroxide are formed . The iodide combines with liquid ammonia to form ZrI4.8NH3; and with ether to give Zr14.4(C2H5)2O . Zirconium combines with sulphur to form a sulphide, and with carbon to form several carbides . The sulphate, Zr(SO4)2, is a white mass obtained by dissolving the oxide or hydroxide in sulphuric acid, evaporating and heating the mass to nearly a red heat . Since it forms a series of double sulphates, Ruer (Zeit. anorg . Chem., 1904, 42, p . 87) regards it as a dibasic acid, ZrOSO4•SO4H2, and that the crystalline sulphate is ZrOSO4•SO4H2.3H20 (not Zr(SO4)2.4H20) . Zirconium also forms double sulphates of the type Zr203(SO4M)2•nH2O, where M=K, Rb, Cs, and n=8 for K, 15 for Rb, 11 for Cs (Rosenheim and Frank, Be,'., 1905, 38, p . 812) .

The atomic weight was determined by

Marignac to be 90.03; Bailey (Prot . Roy . Soc., 189o, 46, p . 74) deduced the value 89.95 .