(dĭsprō'zēӘm) [Gr.,=hard to get at], metallic chemical element; symbol Dy; at. no. 66; at. wt. 162.500; m.p. 1,412 degrees Celsius; b.p. 2,562 degrees Celsius; sp. gr. 8.54 at 25 degrees Celsius; valence+3. Dysprosium is a lustrous silvery metal; it is very soft and can be cut with a knife. It is in Group 3 of the periodic table and is a member of the lanthanide series; all members of this series are rare-earth metals and resemble one another in their chemical properties. Dysprosium is stable in air at room temperature. It dissolves in both dilute and concentrated mineral acids; forms a white oxide known as dysprosia; and, with other elements, forms several brightly colored salts. It is commonly found with other rare-earth metals in several minerals, including gadolinite and euxenite. Dysprosium and its compounds are among the most highly susceptible to magnetization of all substances and are used in special magnetic alloys. A cermet of dysprosium oxide and nickel is used in nuclear reactor control rods. Dysprosium is used with argon in mercury-vapor lamps to give a higher light output and balance the color spectrum. Although dysprosium was discovered (but not isolated) in 1886 by P. E. Lecoq de Boisbaudran, a French chemist, it did not become available in relatively pure form until the 1950s.
(tûr'bēӘm) [from Ytterby, a village in Sweden], metallic chemical element; symbol Tb; at. no. 65; at. wt. 158.92535; m.p. 1,356 degrees Celsius; b.p
(ûr'bēӘm) [from Ytterby, a town in Sweden], metallic chemical element; symbol Er; at. no. 68; at. wt. 167.259; m.p. 1,529 degrees Celsius; b.p. 2,86
(yʊrō'pēӘm) [from Europe], metallic chemical element; symbol Eu; at. no. 63; at. wt. 151.964; m.p. about 820 degrees Celsius; b.p. about 1,600 degre