Potassium nitrate

Potassium nitrate (KNO₃), known historically as saltpeter or the mineral niter, is a common salt with multiple uses. It has been known since antiquity; an early appearance in the chemical literature was in 1872 US Patent 125,492, in which John Shannon of Palmyra, MO, included saltpeter in an ”improvement in medical compounds for treating hogs”. Six years later, in a more chemical account, British chemist J. W. Thomas included KNO₃ in an article about the action of hydrogen chloride gas on various metal salts.

As early as 300 BCE, KNO₃ was found on cave walls or other rocky surfaces. Until World War I, it was produced industrially via exchange reactions between nitric acid and various potassium salts. That method continues today, with potassium chloride as the most-used salt, or by the reaction of ammonium nitrate with potassium hydroxide or chloride.

Early uses of KNO₃ included an oxidant in gunpowder, a preservative for meats and other foods, and a medicine for treating asthma and high blood pressure. Some of these uses continue today; but KNO₃ is most widely used in agriculture as a water-soluble fertilizer that provides potassium and nitrogen, two of the three most important plant nutrients. Other modern uses include explosives and fireworks, a toothpaste ingredient that reduces tooth sensitivity, and certain usages in analytical chemistry labs.

KNO₃, as saltpeter, has long been purported to reduce libido, but this effect has never been scientifically demonstrated.