When was potassium first isolated?

Potassium was first isolated in 1807 by Sir Humphry Davy, the same year he isolated sodium. Using electrolysis, Davy produced potassium as one of the first metals ever obtained from a compound rather than from ore in the old-fashioned sense. The element is highly reactive and belongs to the alkali metals, a group central to chemistry and biology. Potassium compounds are essential in fertilizers and in the human body.