Potassium nitrate

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334 °C

400 °C decomp.

Potassium nitrate is a chemical compound with the formula KNO3. It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre (saltpeter in American English), from Medieval Latin sal petræ: "stone salt" or possibly "Salt of Petra" and nitrate of potash. The name Peru saltpetre or Chile saltpetre (American Peru saltpeter or Chile saltpeter) refers not to potassium nitrate but to a similar chemical sodium nitrate. Major uses of potassium nitrate are in fertilizers, rocket propellants and fireworks; it is one of the constituents of gunpowder. When used as a food additive in the European Union, the compound is referred to as E252.

Contents

History of production

The earliest known complete purification process for potassium nitrate was outlined in 1270 by the Arab chemist and engineer Hasan al-Rammah of Syria in his book al-Furusiyya wa al-Manasib al-Harbiyya ('The Book of Military Horsemanship and Ingenious War Devices'), where he first described the use of potassium carbonate (in the form of wood ashes).[2]

Into the 19th century, niter-beds were prepared by mixing manure with either mortar or wood ashes, common earth and organic materials such as straw to give porosity to a compost pile typically 1.5×2×5 meters in size.[3] The heap was usually under a cover from the rain, kept moist with urine, turned often to accelerate the decomposition and leached with water after approximately one year. Dung-heaps were a particularly common source: ammonia from the decomposition of urea and other nitrogenous materials would undergo bacterial oxidation to produce various nitrates, primarily calcium nitrate, which could be converted to potassium nitrate by the addition of potash from wood ashes.

A variation on this process, using only urine, straw and wood ash, is described by LeConte: Stale urine is placed in a container of straw hay and is allowed to sour for many months, after which water is used to wash the resulting chemical salts from the straw. The process is completed by filtering the liquid through wood ashes and air-drying in the sun.[3]

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