POTASSIUM NITRATE

The chemical compound 'potassium nitrate' KNO₃ is a naturally occurring mineral source of nitrogen that constitutes a critical oxidising component of black powder gunpowder. In the past it was also used for burning fuse technologies including slow matches. It readily precipitates and 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 odorous ways.
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.

Contents

Description

Manufacture

Applications

See also

External links

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]

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.
Potassium nitrate could also be harvested from accumulations of bat guano in caves. This was the traditional method used in Laos for the manufacture of gunpowder for Bang Fai rockets.
During the 19th century and until around World War I, potassium nitrate was produced on an industrial scale from the deposits of sodium nitrate (NaNO₃, nitratine) in the Chilean deserts.This source of nitrates was replaced by synthetically produced nitrates, first by the Birkeland-Eyde process in 1905, and then later from ammonium produced by the much more efficient Haber process. The latter process came online during World War I, and supplied Germany with nitrates critical for the warfare that it otherwise had no access to the deposits of natural nitrate in Chile. It is assumed that this prolonged World War I. Today practically all nitrates are produced by ammonia from the Haber process.

Applications

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.^[3]
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.
It is commonly used in pre-rolled cigarettes to maintain an even burn of the tobacco.
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.^[4]
Potassium nitrate is also one of the three parts of black powder, along with powdered charcoal (substantially carbon) and sulfur. It acts as an oxidiser, oxidising the carbon and sulfur to their respective oxides.

See also

★ Nitric acid

★ Nitre

★ Black powder

★ Gunpowder

★ Sodium nitrate

★ Sodium nitrite

★ Potassium nitrite

External links

★ International Chemical Safety Card 018402216