Discovered : 1807 by Sir Humphry Davy in London. Origin : The name is derived from the English potash (from which it was first isolated), and the chemical symbol comes from the Latin kalium, ‘potash’. Description : A soft, silvery metal that tarnishes within minutes. In water, it reacts rapidly to release hydrogen, which burns with a lilac flame. There are deposits of billions of tonnes of potassium chloride throughout the world and mining extracts about 50 million tonnes a year, mainly for use in fertilisers. Potassium is essential to all living things, and the average human consumes up to 7 grammes a day, and has a store of some 140 grammes (5 ounces) in the human body, mainly in the muscles. Normal diets contain enough potassium, but some foods such as instant coffee, sardines, nuts, raisins, potatoes and chocolate have more than average. Image : Alchemical symbol for potash.