Wikipedia says that Ka was a symbol for potassium once.

Current symbol is K.

Name changed due to a standardization of, modernization of, or update to older formerly-used symbol.

When was the symbol for potassium changed from Ka to K? What was the rationale behind that?

Some findings. The INTERNET Database of Periodic Tables's first image with a symbol for potassium is of Charles Daubeny's system using K in 1831. Surprisingly I could not find any use of Ka. But there are many German-speaking books using Ka in the late 19th century, as well as some English ones. More recent findings of Ka: 1894, 1943, 2013

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    $\begingroup$ Probably better suited at History of Science and Mathematics $\endgroup$ Commented Mar 9, 2017 at 8:44
  • $\begingroup$ We already had a very competent answer to a similar question here. chemistry.stackexchange.com/questions/42561/… $\endgroup$
    – mhchem
    Commented Mar 9, 2017 at 9:06
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    $\begingroup$ Here is an image that shows Charles Daubeny used K in 1831. $\endgroup$
    – mhchem
    Commented Mar 9, 2017 at 9:16
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    $\begingroup$ There are many German-speaking books using Ka in the later 19th century. English KaCl findings (because that makes a better search term): 1894, 1943, 2013! $\endgroup$
    – mhchem
    Commented Mar 9, 2017 at 10:53
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    $\begingroup$ If guessing is OK I assume it is to avoid confusion with Potassium K and subscript a, like in pKa. There was no "K" so then the change is simple and easy. $\endgroup$
    – Stian
    Commented Mar 9, 2017 at 11:20

1 Answer 1


The symbol for potassium was mostly K in the English speaking world and even some old German book use K (as early as 1829 search Kalium in this book). So there was no official change from Ka to K, because both symbols were concurrently used in various parts of the world, just one symbol, Ka, wiped out of fashion. Perhaps the German logic was to retain (Ka)lium and (Na)trium. It is even interesting to see Ka and K being used in the same paper by no other than Bunsen and Kirchoff (the discoverer of rubidium and cesium). For example,


And their beautiful spectra, note Ka on the left. Available for free from Taylor and Francis or use Google Scholar. G*. Kirchhoff & R. Bunsen (1861) XLII. Chemical analysis by spectrum observations.— Second memoir , The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 22:148, 329-349, DOI: 10.1080/14786446108643164*

enter image description here

Humphrey Davy did not propose a symbol for sodium or potassium (from soda ash and potash, in 1807) because he was not 100% sure if they were elements. He implied that even if someone later shows that they are elements, the names can be retained as elements obtained from those metals.

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    $\begingroup$ "Available for free from RSC"? Where? $\endgroup$
    – mhchem
    Commented Oct 14, 2021 at 20:01
  • $\begingroup$ Google Scholar the DOI, and the first result is that paper. Sorry, it is from Taylor & Francis. $\endgroup$
    – ACR
    Commented Oct 14, 2021 at 20:55
  • $\begingroup$ Neither doi.org/10.1080/14786446108643164 nor doi.org/10.1039/QJ8611300270 are freely accessible for me. $\endgroup$
    – mhchem
    Commented Oct 15, 2021 at 21:10
  • $\begingroup$ If you really want to read this article, request a friend from a university. For some reasons, I could see pdf option in Google Scholar. $\endgroup$
    – ACR
    Commented Oct 15, 2021 at 21:27

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