praseodymium, neodymium (and didymium)

Praseodymium, element 59, and neodymium, element 60, have similar etymologies and their discovery, as well as their existence in nature, are bound up with one another. In 1841, Swedish chemist Carl Gustaf Mosander discovered a substance that he believed was an element. He dubbed it didymium, after the Greek δίδυμος (didymos), or twin, because the substance was found with cerium and lanthanium. Mosander was wrong about it being an element, but the name was apt, as didymium turned out to be a combination of the metals which would be known as praseodymium and neodymium. From an 1842 issue of the Chemical Gazette:

Mosander, the discoverer of lanthanium, has found that these metals are always mixed with a third new element (didymium), from which at present it is impossible to separate them.1

In 1885, Austrian Carl Auer von Welsbach succeeded in isolating the two elements that made up didymium. He named these praseodymium, from the Greek πράσιος (prasios), or leek-green from the color of the element’s salts, and neodymium, from the Greek νεο (neo), or new. The dymium he took from didymium. From an 1885 issue of the Journal of the Chemical Society:

By repeated crystallisation of a mixture of the double nitrates of lanthanum and didymium with ammonium, the lanthanum salt was obtained pure, whilst the didymium salt separated into the salts of two new elements, neodymium and praseodymium.2, 3

The chemical symbol of praseodymium is Pr, and that of neodymium is Nd.

1Oxford English Dictionary, didymium, 2nd Edition, 1989, Oxford University Press, accessed 15 October 2009,

2Oxford English Dictionary, praseodymium, 3rd Edition, March 2007, Oxford University Press, accessed 15 October 2009,

3Oxford English Dictionary, neodymium, 3rd Edition, June 2008, Oxford University Press, accessed 15 October 2009,

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