Potassium nitrate
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The chemical compound potassium nitrate is a naturally occurring mineral source of nitrogen, but makes up the critical oxidising component of gun powder, was necessary for burning fuse technologies including slow matches and since it readily precipitates, was widely "harvested" since the Late Middle Ages and Early Modern era through the 19th century from urine from which it was forced to crystallise in various odiferous ways. It is a nitrate with chemical formula KNO3.
Its common names include saltpetre (from Medieval Latin sal petrae: "stone salt" or possibly "Salt of Petra"), American English saltpeter, Nitrate of potash and nitre. The name Chile saltpetre is also applied to sodium nitrate, which while related to explosives as well, is a very different compound.
Description
Potassium nitrate is the oxidising component of black powder. Prior to the large-scale industrial fixation of nitrogen through the Haber process, a major source of Potassium nitrate was the deposits crystallising from cave walls or the drainings of decomposing organic material. Dung-heaps were a particularly common source: ammonia from the decomposition of urea and other nitrogenous materials would undergo bacterial oxidation to produce nitrate. It was and is also used as a component in some fertilisers. When used by itself as a fertiliser, it has an NPK rating of 13-0-44 (indicating 13%, 0%, and 44% of nitrogen, phosphorus, and potassium, by mass, respectively). Potassium nitrate was once thought to induce impotence, and was rumoured to be added to institutional food as an anaphrodisiac. If true, the treatment was ineffective, as potassium nitrate has no such properties.[1][1]
Manufacture
Historically[2], nitre-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 metres high by 2 metres wide by 5 metres long. 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. The liquid containing various nitrates was then converted with wood ashes to potassium nitrates, crystallised and refined for use in gunpowder. In more rural times, urine was collected and used in the manufacture of gunpowder. Stale urine was filtered through a barrel full of straw and allowed to continue to sour for a year or more. After this period of time, water was used to wash the resulting chemical salts from the straw. This slurry was filtered through wood ashes and allowed to dry in the sun. Saltpetre crystals were then collected and added to brimstone and charcoal to create black powder. Today, most potassium nitrate comes from the vast deposits of sodium nitrate (NaNO3, nitratine) in the Chilean deserts. The sodium nitrate is purified and then reacted in solution with potassium chloride (KCl, sylvite), from which the less-soluble potassium nitrate is precipitated out.
Applications
One of the most useful applications of potassium nitrate is in the production of nitric acid, by adding concentrated sulfuric acid to an aqueous solution of potassium nitrate, yielding nitric acid and potassium sulfate which are separated through fractional distillation.
Potassium nitrate is also used as a fertiliser, in model rocket propellant, and in several fireworks such as smoke bombs, in which a mixture with sugar produces a smoke cloud of 600 times their own volume. The ratio for smoke bombs using sucrose (powdered sugar) and potassium nitrate is 40(C12H22O11):60(KNO3). It can be used as is, or carefully melted together using a hot plate.
In the process of food preservation, potassium nitrate has been a common ingredient of salted meat, but its use has been deprecated. In the European Union, it is referred to as E252.
Potassium nitrate is also the main component (usually about 98%) of tree stump remover; it accelerates the natural decomposition of the stump.
It has also been used in the manufacture of ice cream and can be found in some toothpastes for sensitive teeth. Recently, the use of potassium nitrate in toothpastes for sensitive teeth has increased dramatically, despite the fact that it has not been conclusively shown to help dental hypersensitivity.[3]
Potassium nitrate is also one of the three parts of gunpowder, along with charcoal and sulfur. It contributes largely to gunpowder's explosive properties, but by itself is very hard to light. If sufficient heat is applied, however, KNO3 will ignite and burn with a very hot pink-orange flame, producing lots of smoke[citation needed].