Welsbach named them praseodidymium (green didymium) and neodidymium (new didymium). They came to be known as praseodymium and neodymium. In 1843 Mosander discovered terbium and erbium as components of yttria. However, this discovery was hotly contested. Spectroscopist Nils Johan Berlin denied that two elements existed, failing to confirm the existence of "erbia" and suggesting that its name be applied to "terbia". In 1864, Marc Delafontaine used optical spectroscopy to conclusively prove that yttrium, terbium and erbium were separate elements. Ironically, however, the confusion that had been introduced between the names continued. Mosander's proposed names were switched, giving the amethyst compound the name "erbium" oxide and the yellow substance the name "terbium" oxide, instead of the other way around as originally proposed. Mosander was elected a member of the Royal Swedish Academy of Sciences in 1833. Personal life and final years Mosander married Hulda Philippina Forsström on 20 December 1832. They had four children, two sets of twins. Mosander suffered from cataracts in later life. He died in 1858, at his summer house on the island of Lovön, Stockholm County. References 1797 births 1858 deaths People from Kalmar Swedish chemists Discoverers of chemical elements Academic staff of the Karolinska Institute Members of the Royal Swedish Academy of Sciences 19th-century Swedish scientists 19th-century chemists Lanthanum Erbium Terbium Rare earth scientists