potassium [E19th] Before potassium was isolated as a chemical it was known from potash [E16th], an impure form of potassium carbonate made by burning plant material, soaking it, and then evaporating the water in large iron pots—hence the name potash. This produced an alkali which could be used for making soap, glass, and in various other processes. Potass was a variant of the word and the name potassium was formed from this. One of the plants used in this process, glasswort, was known in the past as kali (derived from alkali), and it is from this that potassium gets its chemical symbol K.