== Historie ==
Thallium (af [[græsk (sprog)|græsk]] ''θαλλός'', ''thallos'', dvs. "en grøn kvist")<ref>Liddell, Henry George and Scott, Robert (eds.) "[http://perseus.mpiwg-berlin.mpg.de/cgi-bin/resolveform?lookup=qallos&type=begin&lang=greek&searchText=&options=Sort+Results+Alphabetically&.submit=Submit&formentry=1&lang=greek θαλλος] {{Webarchive|url=https://web.archive.org/web/20160415174207/http://perseus.mpiwg-berlin.mpg.de/cgi-bin/resolveform?lookup=qallos&type=begin&lang=greek&searchText=&options=Sort+Results+Alphabetically&.submit=Submit&formentry=1&lang=greek |date=15. april 2016 }}", in ''[[A Greek–English Lexicon]]'', Oxford University Press.</ref> blev opdaget i 1861 ved hjælp af flammespektroskopi.<ref>Thallium blev opdaget af både William Crookes og Claude Auguste Lamy, der arbejdede uafhængigt af hinanden:
* Crookes, William (March 30, 1861) "On the existence of a new element, probably of the sulphur group," ''Chemical News'', vol. 3, [http://books.google.com/books?id=6QcAAAAAMAAJ&pg=PA193 pp. 193–194]; reprinted in: {{cite journal|url=http://books.google.com/books?id=OhyQnaPXF5QC&pg=RA1-PA301|date=april 1861|doi=<!-- 10.1080/14786446108643058 broken -->|title=XLVI. On the existence of a new element, probably of the sulphur group|volume =21|issue =140|pages =301–305|journal=Philosophical Magazine}}; {{en sprog}}
* Crookes, William (May 18, 1861) "Further remarks on the supposed new metalloid," ''Chemical News'', vol. 3, [http://books.google.com/books?id=6QcAAAAAMAAJ&pg=PA303 p. 303]. {{en sprog}}
* Crookes, William (June 19, 1862) "Preliminary researches on thallium," ''Proceedings of the Royal Society of London'', vol. 12, pages 150–159. {{en sprog}}
* Lamy, A. (May 16, 1862) "De l'existencè d'un nouveau métal, le thallium," ''Comptes Rendus'', vol. 54, [http://gallica2.bnf.fr/ark:/12148/bpt6k30115.image.r=Comptes+Rendus+Hebdomadaires.f1254.langFR pages 1255–1262]. {{fr sprog}}
</ref> Navnet skyldes thalliums klare grønne spektrallinje.<ref>{{cite journal| doi = 10.1021/ed009p2078| title = The discovery of the elements. XIII. Supplementary note on the discovery of thallium| year = 1932| last1 = Weeks| first1 = Mary Elvira|author-link1=Mary Elvira Weeks| journal = Journal of Chemical Education| volume = 9| issue = 12| page = 2078|bibcode = 1932JChEd...9.2078W }} {{en sprog}}</ref>
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