Mullitkern · Element 19
This site collects what can be documented about the element: where it occurs in nature, what levels nutrient databases report, which instruments are used to measure it, and what wording regulators have approved for it.
Read the full guidePotassium, atomic number 19, sits in the first group of the periodic table. As a pure metal it is soft enough to cut with a knife, melts at around 63 degrees Celsius (145 °F) and is lighter than water. That very reactivity is why it never occurs in its native form in the Earth's crust, only in compounds.
The most important of these are sylvite, carnallite and kainite from salt deposits, along with the feldspars found throughout granite. Seawater contains roughly 390 milligrams per liter. From 1861 the mines at Stassfurt, Germany, first hauled these salts out as unwanted overburden — until it turned out they were worth more as a fertilizer raw material than the rock salt beneath them.
Information on the occurrence of the element in rock and seawater. No health claim is implied.
Health statements about nutrients cannot be phrased freely. In the European Union there is a positive list, and anyone who wants to put such a statement on a package or a web page must use the wording registered there. Rephrasing, shortening or sharpening it is not allowed.
For the link between potassium and nerve tissue, the list contains one entry. It appears here exactly as registered:
“Potassium contributes to normal functioning of the nervous system”
Per Regulation (EU) No 432/2012
The wording names an organ system as a whole. The annex does not list individual functions, and this text does not add any. The statement may also only be used for products that actually reach the minimum content required for labeling.
Long before anyone knew the metal, soap makers and dyers boiled wood ash in water and evaporated the solution in iron pots. What remained was a white salt named after the vessel it was made in: pot-ash. Chemically, it was potassium carbonate.
The Arabic word for plant ash, al-qalya, traveled through the word kali into German scientific language, while English potassium stayed with potash. That is why the same element carries two different names in two languages — and the symbol K, from the Latin kalium, is the compromise that stuck.
The full version of this story, including the electrolysis of 1807, is in the guide.
The complete written edition covers the history of the element, the content tables with their ranges, the measurement methods and the full regulatory framework — as a PDF file available once payment is received.
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Potassium is a macromineral, part of the group whose intake is counted in grams rather than micrograms. An adult body carries roughly 120 to 140 grams of it, the vast majority inside the cells. For food labeling in the United States, the FDA sets a Daily Value of 4,700 milligrams; the European Union uses a reference value of 2,000 milligrams per day.
These numbers are reference values for labels. They do not describe any individual's needs, and they deliberately differ from one another and from the estimates published by scientific bodies, because each serves a different purpose.
Anyone who scans content tables quickly notices a pattern: legumes, potatoes, cabbage-family vegetables, nuts and dried fruit sit near the top, with dairy and meat following at a clear distance. The reason lies inside the cell. Plants store potassium in their vacuoles while keeping sodium largely outside, so the ratio of the two ions in plant foods is very different from that in processed products with added table salt.
A second point concerns water. Because levels are given per hundred grams of product, values rise through drying alone: fresh apricots come to about 280 milligrams, dried ones to more than four times that. The difference says nothing about the fruit, only about how much water was removed.
Hardly any food is linked to this mineral as automatically as the banana. In the databases, at around 360 milligrams per hundred grams, it sits in the upper middle range, but potatoes, spinach, white beans, cocoa powder and tomato paste clearly beat it. Its reputation comes more from twentieth-century advertising than from laboratory data.
One more thing matters when reading such lists: variety, soil, fertilization and harvest time shift individual values considerably. Table figures are averages from series of measurements, not a property of the single piece of fruit in your shopping cart.
About 0.012 percent of natural potassium is the isotope potassium-40, which decays with a half-life of around 1.25 billion years. In geology, this decay is used to date rocks. In physiology it allows something else: because every body carries this fixed share, the total supply can be calculated back from the measured gamma radiation — in what is called a whole-body counter.
Alongside this elaborate method, laboratories use flame photometry and the ion-selective electrode. Both are routine, but both only measure what is in the sample submitted. The instrument does not decide what conclusion follows.
None of these numbers change the approved wording on nerve tissue. It still reads: “Potassium contributes to normal functioning of the nervous system” — per Regulation (EU) No 432/2012.
A description of analytical methods. It is not a guide to interpreting your own test results.
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