Potassium nitrate is a chemical compound with the chemical formula KNO3. A naturally occurring mineral source of nitrogen, KNO3 constitutes a critical oxidizing component of black powder/gunpowder. In the past it was also used for several kinds of burning fuses, including slow matches. Potassium nitrate readily precipitates from mixtures of salts, and decomposing urine was the main commercial source of the nitrate ion, through various means, from the Late Middle Ages and Early Modern era through the 19th century. Its common names include saltpetre (saltpeter in American English), from Medieval Latin sal petrÃ¦: "stone salt" or possibly "Salt of Petra", nitrate of potash, and nitre (American niter). For specific information about the naturally occurring mineral, see niter. The name Chile saltpetre (American "Chile saltpeter") is applied to sodium nitrate, a similar nitrogen compound that is also used in explosives and fertilizers. The major problem of using the cheaper sodium nitrate in gunpowder is its tendency to go damp.