Zirconium oxide as an opacifier has been thoroughly investigated by Hartman[95] and by Grunwald[96] with promising results; and a number of foreign patents have been granted on the use of the oxide in white ceramic enamels. Zirconia seems to be especially suitable for the manufacture of refractory bricks, or it can be applied as a lining or surfacing to other less desirable refractories. Continental practice along this line is said to have been much more highly developed than practice in this country, one example quoted being actual practice tests of a Martin Siemens furnace with a zirconia-lined hearth. After four months of continuous operation at high temperatures the hearth was still in good condition and gave promise of lasting at least an equal length of time without renewal. Statistics compiled from these tests showed a saving of about 50 per cent. in actual maintenance costs in favor of zirconia over the other refractories ordinarily used for such purposes. Bradford[97] quoted Podszus[98] as claiming to have made a furnace with the pure oxide which had first been fused in an arc furnace and then ground; and in which temperatures of 2400° to 2500°C. were obtained by firing with gas and oxygen. [95] HARTMAN, AUGUSTUS, Zirconemail: Dissertations Arbeit: Techn. Hochschule, Munich, 1910. [96] Ueber Zirkonoxyd in der Emailindustrie: Sprechsaal, No. 5, 1911. [97] BRADFORD, LEOPOLD, Birmingham Metallurgical Society (British). [98] Podszus, Zeitsch. angew. Chem., Jahrg. 30, 1917, 1, pp. 17-19. The most important question regarding zirconium at the present time has to do with the remarkable properties that some of its advocates claim it imparts to steel. That the Germans have had this use in mind for some time is evidenced by the numerous patents they have obtained covering the use of zirconium and its alloys. Zirconium has been obtained in the amorphous and the graphitic state; and Wedekind has produced a metal of 99.8 per cent. purity resembling white cast iron in appearance, with a hardness of 7.8 (Mohs); specific gravity 6.40; specific heat, 0.0804; heat of combination, 1958 calories; and melting point, 1530°C. Numerous alloys of zirconium have been made and a number of foreign and domestic patents have been issued covering various alloys, both ferrous and non-ferrous. It is stated that ferrozirconium is finding a limited application in the steel industry as a scavenger for removing nitrogen and oxides. An English patent, No. 29,376, covers the use of zirconium as a scavenger, the alloy containing 20 per cent. of the element and being used in an amount equal to about 1 per cent. of the weight of steel treated.