YTTRIUM, the name of a rare element which in its character is closely allied to, and in nature is always associated with, cerium, lanthanum, didymium, and erbium (see LANTHANUM, vol. xiv. p. 291). For the preparation of yttrium compounds the best raw material is a rare Swedish mineral called gadolinite, which, according to Konig, consists of 22'61 per cent, of silica, 34•64 of yttria, Y203, and 42'75 of the oxides of erbium, cerium, didymium, lanthanum, iron, beryllium, calcium, magnesium, and sodium. Bunsen and Bahr, in 1866, elaborated a method for extracting the several rare oxides in the state of purity ; but the method is too complicated to reproduce here.1 Metallic yttrium is obtainable by reducing the chloride with potassium ; but this operation has never been carried out with pure chloride. Yttria, Y203, is a yellowish white powder, which at high temperatures radiates out a most brilliant white light. It is soluble, slowly but completely, in mineral acids. It is recognized most surely by its very characteristic spark spectrum. Solutions of yttria salts in their behaviour to reagents are not unlike those of zirconia. The atomic weight of yttrium, according to the latest researches," is 89'02, if 0 =16.