The crystal structure of KNO3
is a
chemical compound with the
chemical formula KNO3. A naturally occurring mineral source of
nitrogen, KNO
3 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 petræ: "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
Peru saltpetre or
Chile saltpetre (American "Peru saltpeter" or "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.
Description
Potassium nitrate is the oxidising component of
black powder. Before the large-scale industrial
fixation of nitrogen through the
Haber process, major sources of potassium nitrate were the deposits crystallizing from cave walls and the draining 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 nitrates. These often contained calcium nitrate, which could be converted to potassium nitrate by the addition of
potash from wood ashes. It was and is also used as a component in some
fertilizers. When used by itself as a fertilizer, it has an
NPK rating of 13-0-38 (indicating 13.9%, 0%, and 38.7% of nitrogen, phosphorus, and potassium, by mass, respectively). Potassium nitrate was once thought to induce
impotence, and is still falsely rumored to be in institutional food (such as military fare) as an
anaphrodisiac; these uses would be ineffective, since potassium nitrate has no such properties.
However, potassium nitrate successfully combats high blood pressure and was once used as a hypotensive. Other nitrates and nitrites such as
glyceryl trinitrate (nitroglycerin), amyl nitrite and isosorbide derivatives are still used to relieve
angina.
History of production
Historically, 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 meters high by 2 meters wide by 5 meters 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 nitrate, crystallized and refined for use in
gunpowder.
Urine has also been used in the manufacture of saltpetre for gunpowder. In this process, stale urine placed in a container of straw hay 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.
Saltpetre crystals can then be collected and added to
sulfur 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.
The earliest known complete purification process for potassium nitrate is described 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) to remove
calcium and
magnesium salts from the potassium nitrate.
During the 19th century and until around
World War I, potassium nitrate was produced on an industrial scale, first by the
Birkeland–Eyde process in 1905, and then later from ammonia produced by the much more efficient
Haber process. The latter process came into use during World War I, and supplied Germany with nitrates critical for the warfare that it otherwise had no access to because the deposits of natural nitrate in
Chile were in British hands. It is assumed that this prolonged World War I. Today practically all nitrates are produced from the oxidation of
ammonia made by the
Haber process.
Uses
Potassium nitrate is also used as a
fertilizer, in amateur rocket propellants, and in several fireworks such as
smoke bombs.
In the process of
food preservation, potassium nitrate has been a common ingredient of salted meat since the
Middle Ages, but its use has been mostly discontinued due to inconsistent results compared to more modern nitrate and nitrite compounds. Even so, saltpetre is still used in some food applications, such as
charcuterie and the brine used to make
corned beef.
Sodium nitrate (and
nitrite) have mostly supplanted potassium nitrate's culinary usage, as they are more reliable in preventing bacterial infection than saltpetre. All three give cured
salami and corned beef their characteristic pink hue.
In the European Union, the compound is referred to as
E252.
It is commonly used in pre-rolled cigarettes to maintain an even burn of the tobacco.
As a fertilizer, it is used as a source of nitrogen and potassium, two of the
macro nutrients for plants.
Potassium nitrate is also the main component (usually about 98%) of tree stump remover, as it accelerates the natural decomposition of the stump.
Potassium nitrate is also commonly used in the heat treatment of metals as a solvent in the post-wash. The oxidizing, water solubility and low cost make it an ideal short-term rust inhibitor.
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 treating sensitive teeth has increased dramatically, despite the fact that it has not been conclusively shown to reduce
dentine hypersensitivity.
Potassium nitrate is also one of the three components of
black powder, along with powdered charcoal (substantially carbon) and sulfur, where it acts as an
oxidizer. When subjected to the
flame test it produces a lilac flame due to the presence of potassium.
Saltpetre is thought to decrease sex drive, but there is no scientific evidence to support that the substance causes such an effect.
See also
