potassium nitrate

Potassium nitrate[1]
Other names	Saltpetre Nitrate of potash Vesta powder
Identifiers
CAS number	7757-79-1 Y
PubChem	24434
UN number	1486
RTECS number	TT3700000
ChemSpider ID	22843
Properties
Molecular formula	KNO3
Molar mass	101.103 g/mol
Appearance	white solid
Odor	odorless
Density	2.109 g/cm3 (16 °C)
Melting point	334 °C
Boiling point	400 °C decomp.
Solubility in water	13.3 g/100 mL (0 °C) 36 g/100 mL (25 °C) 247 g/100 mL (100 °C)
Solubility	slightly soluble in ethanol soluble in glycerol, ammonia
Structure
Crystal structure	Orthorhombic, Aragonite
Hazards
MSDS	External MSDS
EU Index	Not listed
Main hazards	Oxidant
NFPA 704	0 1 0 OX
Flash point	Non-flammable
LD50	3750 mg/kg
Related compounds
Other anions	Potassium nitrite
Other cations	Lithium nitrate Sodium nitrate Rubidium nitrate Caesium nitrate
Related compounds	Potassium sulfate Potassium chloride
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

The crystal structure of KNO₃

Potassium nitrate is a chemical compound with the chemical formula KNO₃. A naturally occurring mineral source of nitrogen, KNO₃ 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.^{[citation needed]} 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.^[2] 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.^[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. 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.^[3] Saltpetre crystals can then be collected and added to sulfur and charcoal to create black powder.^[4] 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.^[5]

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,^[6] 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.^[7] 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.^[8]

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.^[9]

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.^[10] 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.^[11]

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.^[12]

Urban legend

A popular myth for generations, particularly among primarily male populations (armed services, schools, summer camps, prisons) holds that saltpeter, institutionally added to food, decreases sex drive and inhibits erection. There is no scientific evidence to support that the substance causes such an effect.

See also

• Nitric acid
• Niter
• black powder
• Gunpowder
• Sodium nitrate
• Sodium nitrite
• Potassium nitrite
• Nitrocellulose
• Potassium perchlorate
• nitroglycerine

References

Bibliography

• Dennis W. Barnum. (2003). "Some History of Nitrates." Journal of Chemical Education. v. 80, p. 1393-. link.
• Alan Williams: The production of saltpeter in the Middle Ages, Ambix, 22 (1975), pp. 125-33. Maney Publishing, ISSN 0002-6980.

External links

• International Chemical Safety Card 018402216
• "INSTRUCTIONS FOR THE MANUFACTURE OF SALTPETER" - by Joseph Leconte, professor of chemistry and geology in South Carolina College
• Confederate Gunpowder -- women contributed urine to the war effort.
• Worcester News: Bishop makes an unusual donation of urine for the gunpowder plot