Potash, Kalium and Alkali

Potassium's names record an old craft: the leaching of wood and plant ashes to make potash, used for centuries in soapmaking, glass and bleaching. The Arabic al-qali, source of the symbol K and of the word alkali, ties the element to the vocabulary of early chemistry, where the alkalis stood opposite the acids as one of the great classes of matter. The metal itself belongs firmly to the nineteenth century and has no planetary or alchemical correspondence, but the substances it names, potash and the alkalis, were among the essential reagents of the pre-modern laboratory and workshop.

The acid-alkali distinction potassium's name preserves reaches back to the medieval Arabic alchemical tradition associated with Jabir ibn Hayyan, whose Latinised name, Geber, lent later European alchemy much of its technical vocabulary. Potassium nitrate, saltpetre, was in its own right the indispensable oxidiser of black powder, mined from cave deposits and manure heaps and fought over as a strategic resource for centuries before anyone understood it as a potassium salt; the element's alkaline and explosive faces, soap and gunpowder, both trace to the same humble ash and mineral chemistry of the pre-modern world.