Caesium-133 crystal stored in an ampule of argon
14 April 2023
Caesium, also spelled cesium, is a soft, silvery-gold alkali metal. Its atomic number is 55, and its symbol is Cs. It is the first element discovered through spectrography, when in 1860 Gustav Kirchhoff and Robert Bunsen identified it through its two distinct lines in the blue portion of the visible spectrum. The following year, when they published their research, they named the element after the Latin caesius or bluish-gray:
Die Leichtigkeit, mit welcher der nur einige Tausendstel eines Milligramins betragende, noch dazu mit Lithion-, Kali- und Natron-Verbindungen gemischte Stoff an dem blauen Lichte seines glühenden Dampfes als ein neuer und einfacher erkannt werden konnte, wird es wohl gerechtigt erscheinen lassen, wenn wir für denselben den Namen Caesium mit dem Symbol Cs vorschlagen, von caesius, welches bei den Alten vom Blau des heiteren Himmels gebraucht wird.
(The ease with which the substance, which amounts to only a few thousandths of a milligram and is also mixed with lithium, potassium and sodium hydroxide compounds, could be recognized as a new and simpler substance from the blue light of its glowing vapor, will make it appear justifiable that if we propose for it the name caesium, with the symbol Cs, from caesius, which is used by the ancients from the blue of the clear sky.)
Kirchhoff and Bunsen did not isolate the metal, however. That was first done by Carl Setterberg in 1882.
Sources:
Kirchhoff, Gustav and Robert Bunsen. “Chemische Analyse durch Spectralbeobachtungen.” Annalen der Physik und Chemie. 189.7 (1861), 337–381 at 338. HathiTrust Digital Archive.
Miśkowiec, Pawel. “Name Game: The Naming History of the Chemical Elements: Part 2—Turbulent Nineteenth Century.” Foundations of Chemistry, 8 December 2022 (online).
Oxford English Dictionary, second edition, 1989, s.v. caesium, n.
Setterberg, Carl. “Über die Darstellung von Rubidium- und Cäsiumverbindungen und Über die Gewinnung der Metalle Selbst.” Annalen der Chemie. 211.1 (1882), 100–116. HathiTrust Digital Archive.
Image credit: Dennis “S.K.”, 2008. Wikimedia Commons. Licensed under a Creative Commons Attribution 3.0 Unported license.