Carl Gustaf Mosander

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Lore & Background

Mosander discovered lanthanum in 1838 from the Cerite-(Ce) from Bastnaes, Sweden, which at the time was the only abundant source for 'Cerium.' He partially decomposed ceria by heating it and treating the resulting salt with dilute nitric acid. He was hesitant to report his results, both for fear of embarrassing his mentor Berzelius, by showing that his discovery cerium was not an element; and because he was uncertain that he himself had reduced cerium to all of its components. Berzelius eventually suggested the name 'lanthan,' for 'hidden.' By 1840, Mosander had separated cerium oxide into yellow cerium oxide, white lanthanum oxide and a pinkish third component which he called 'didymium' meaning 'twin.' 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.

Reader's Guide

Mosander's significance lies in his pioneering work on rare earth elements, which revealed that previously accepted 'elements' were mixtures. In 1838, he discovered lanthanum by partially decomposing ceria from the mineral cerite, a finding that initially embarrassed his mentor Berzelius because it showed that cerium was not a pure element. Mosander also isolated didymium, later shown to be a mixture of praseodymium and neodymium. In 1843, he discovered terbium and erbium in yttria, though his findings were contested by spectroscopist Nils Johan Berlin. The confusion over names was eventually resolved by Marc Delafontaine in 1864, but the names were swapped from Mosander's original proposal. His work laid the groundwork for later rare earth separations by scientists such as Carl Auer von Welsbach. Mosander was elected to the Royal Swedish Academy of Sciences in 1833. He 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.

Did You Know?

• Mosander discovered lanthanum in 1838 from the Cerite-(Ce) from Bastnaes, Sweden, which at the time was the only abundant source for 'Cerium.'
• Berzelius suggested the name 'lanthan' for 'hidden' for Mosander's new discovery.
• Mosander isolated a pinkish third component from cerium oxide which he called 'didymium' meaning 'twin.'
• In 1843 Mosander discovered terbium and erbium as components of yttria, but his proposed names were later switched.
• Mosander married Hulda Philippina Forsström on 20 December 1832 and they had four children, two sets of twins.