ZIRCONIUM, a rare element, closely allied to titanium. Klaproth in 1789 analysed zircon and found it to contain a new earth, which he called “zirconia.” Zircon is essentially a silicate of zirconia, ZrO 2 .SiO 2 . For the extraction from it of zirconia the mineral is first of all heated and quenched in water to render it brittle, and then reduced to a fine powder, which is fused up with three to four parts of acid fluoride of potassium at a gentle heat in a platinum crucible. When the mass fuses tranquilly and all the water is expelled, the platinum crucible is placed in a Hessian crucible; the two crucibles are then covered and kept for two hours at the highest temperature producible by means of a wind-furnace. The porcelain-like fuse is powdered, boiled in water, and acidified with hydrofluoric acid, and the residual fluosilicate of potassium is filtered off. The filtrate on cooling deposits crystals of fluozircon-ate of potassium, ZrF 6 K 2 , which are purified by re-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. Hydrated zirconia, Zr(OH) 4 , as thus obtained, is quite appreciably soluble in water and easily in mineral acids, with formation of zirconic salts, e.g., ZrCl 4 , analogous to SnCl 4 . But, if the hydrate is precipitated in the heat, it demands concentrated acids for its solution. The hydrate readily loses its water at a dull red heat and passes into anhydride with vivid incandescence. The anhydrous oxide, ZrO 2 , is with difficulty soluble even in ...