O potash tree, o potash tree

Rather out of season but here is a small forest of fir trees, once a major source of potash. Grown predominantly in the Baltic states Poland and Russia, the wood of these trees was burned in trenches and the resulting ash dissolved in boiling water. The liquor was then evaporated in copper pots (hence pot-ash) to leave the alkaline potassium salts. This process was the main source of potassium salts (used in glass-making, bleach, soap and gunpowder) until the discovery in the mid-nineteenth century of mineral deposits of potassium salts. By this time potassium salts were in high demand as Justus von Liebig had discovered that potassium is essential for plant growth and that many soils were deficient in potassium, thus kickstarting the fertiliser industry.

If you’re wondering why the symbol for potassium is K, it stands for kalium, the alternative name for the element which shares its root with the word ‘alkali’. Both come from the Arabic ‘al-kali’ meaning the ash that came from the burning of plants, from which sodium and potassium salts could be extracted. If the plants grew near the sea, then sodium salts predominated, and if they grew inland then potassium salts were the main product.

Credit for the idea for this one goes to Peter Wothers’ Antimony, Gold and Jupiter’s Wolf – how the elements were named

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