1911 Encyclopædia Britannica/Ytterbium
YTTERBIUM (Neo-Ytterbium) [symbol, Yb; atomic weight, 172.0 (O = 16)], a metallic chemical element belonging to the rare earth group. Mixed with scandium it was discovered by Marignac in gadolinite in 1878 (see Rare Earths). The oxide, Yb2O3, is white and forms colourless salts; the crystallized chloride, YbCl3·6H2O, forms colourless, deliquescent crystals; the anhydrous chloride sublimes on heating (C. Matignon, Ann. chim. phys., 1906 (8), 8, p. 440). In 1907 G. Urbain separated ytterbium into two new elements, neo-ytterbium and lutecium (atomic weight, 174.0); and in 1908 C. A. von Welsbach published the same result, naming his elements aldebaranium and cassiopeium (on the question of priority see F. Wenzel, Zeit. anorg. Chem., 1909, 64, p. 119).