Castor and Pollux rescuing their sister Helen during the sack of Troy, Jean-Bruno Gassies, 1817, oil on canvas
28 June 2024
Praseodymium is a chemical element with atomic number 59 and the symbol Pr. Neodymium has atomic number 60 and the symbol Nd. Both are silvery, malleable metals that are found together in nature, making them twins of a sort. Both are widely used in the production of colored glass and magnets. Additionally, praseodymium is a component in a number of alloys, and neodymium is used to produce lasers of a certain wavelength.
Praseodymium and neodymium 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 later become known as praseodymium and neodymium. Mosander announced his discovery in July 1842, and his paper was translated into English and published in October 1843:
To the radical of this new oxide, I gave the name of Didymium (from the Greek word δίδυμος, whose plural δίδυμοι signifies twins), because it was discovered in conjunction with oxide of lanthanium. It is the oxide of didymium that gives to the salts of lanthanium and cerium the amethyst colour which is attributed to these salts; also the brown colour which the oxides of the same metals assume when heated to a red heat in contact with the air.
But in 1885 Carl Auer von Welsbach showed that the name didymium was appropriate for the ore but for a different reason than Mosander had ascribed to it. Didymium was not a single element but rather an ore made up of two other elements, which he dubbed praseodymium, from the Greek πράσιος (prasios), meaning 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:
Da sonach die exacte Zerlegung des Didyms in mehrere Elemente realisirt ist, so sehlage ich vor, die Bezeichnung Didym nunmehr ganz zu streichen und beantrage, für das erste Element, entsprechendder Grünfärbung seiner Salze und seiner Abstammung die Benennung:
Praseodym mit dem Zeichen Pr
und für das zweite, als das “neue Didym”, die Benennung:
Neodym mit dem Zeichen Nd.
(Since the exact decomposition of Didym into several elements has now been achieved, I propose to delete the name Didym completely and request that the first element be named according to the green color of its salts and its origin:
Praseodymium with the sign Pr
and for the second, as the "new Didym", the name:
Neodymium with the symbol Nd.)
Sources:
Miśkowiec, Pawel. “Name Game: The Naming History of the Chemical Elements: Part 2—Turbulent Nineteenth Century.” Foundations of Chemistry, 8 December 2022. DOI: 10.1007/s10698-022-09451-w.
Mosander, C. G. “On the New Metals, Lanthanium and Didymium, Which Are Associated with Cerium; and on Erbium and Terbium, New Metals Associated with Yttria.” London, Ediburgh, and Dublin Philosophical Magazine and Journal of Science, third series, 23.152, October 1843. HathiTrust Digital Archive.
Oxford English Dictionary, third edition, March 2007, s.v. praseodymium, n.; September 2003, s.v. neodymium, n.; second edition, 1989, s.v. didymium, n..
von Welsbach, Carl Auer. “Die Zerlegung des Didyms in seine Element.” Monatshefte für Chemie und verwandte Teile anderer Wissenschaften, 6, December 1885, 477–91 at 490. HathiTrust Digital Archive.
Image credit: Jean-Bruno Gassies, 1817. Wikimedia Commons. Public domain work as a mechanical reproduction of a public domain work.