Potassium is a silvery white metal, which will tarnish to grey in air. At temperatures below o° C. it is pretty hard and brittle; but at ordinary temperature it is soft enough to cut with a blunt knife. The symbol K is from kalium a word which has its root meaning in Arabic. The name potassium is from an English word, potash. Potassium reacts violently with water to produce hydrogen:
It was discovered by the British scientist Humphry Davy (1778 - 1829) in 1807. On placing a piece of potash on a platinum plate, connected to the negative of a powerful electric battery, and bringing a platinum wire, connected to the positive of the battery, to the surface of the potassium a vivid action was observed: gas was evolved at the upper surface of the fused globule of potash, whilst at the lower surface, adjacent to the platinum plate, minute metallic globules were formed, some of which immediately inflamed, whilst others merely tarnished. Davy danced around the room in glee and it was half an hour before he had calmed down enough to write his results in a notebook - it was the first time a metal had been isolated by electrolysis.