|Jmol-3D images||Image 1|
|Molar mass||101.1032 g/mol|
|Density||2.109 g/cm3 (16 °C)|
decomposes at 400 °C
|Solubility in water||133 g/L (0 °C)
316 g/L (20 °C)
2460 g/L (100 °C)
|Solubility||slightly soluble in ethanol
soluble in glycerol, ammonia
|Refractive index (nD)||1.5056|
|Crystal structure||Orthorhombic, Aragonite|
|EU Index||Not listed|
|EU classification||Oxidant (O)|
|R-phrases||R8 R22 R36 R37 R38|
|S-phrases||S7 S16 S17 S26 S36 S41|
|Main hazards||Oxidant, Harmful if swallowed, Inhaled, or absorbed on skin. Causes Irritation to Skin and Eye area.|
|Other anions||Potassium nitrite|
|Other cations||Lithium nitrate
|Related compounds||Potassium sulfate
|Supplementary data page|
|n, εr, etc.|
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Major uses of potassium nitrate are in fertilizers, rocket propellants and fireworks. It is one of the major constituents of gunpowder (blackpowder) and has been used since the Middle Ages as a food preservative.
- 1 History of production
- 2 History of use
- 3 Production
- 4 Properties
- 5 Uses
- 6 In Folklore and Popular Culture
- 7 See also
- 8 References
- 9 Bibliography
- 10 External links
History of production
From mineral sources
The earliest known complete purification process for potassium nitrate was outlined in 1270 by the 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'). In this book, al-Rammah describes first the purification of barud (crude saltpetre mineral) by boiling it with minimal water and using only the hot solution, then the use of potassium carbonate (in the form of wood ashes) to remove calcium and magnesium by precipitation of their carbonates from this solution, leaving a solution of purified potassium nitrate, which could then be dried. This was used for the manufacture of gunpowder and explosive devices. The terminology used by al-Rammah indicated a Chinese origin for the gunpowder weapons about which he wrote. While potassium nitrate was called "Chinese snow" by Arabs, it was called "Chinese salt" by the Iranians/Persians.
At least as far back as 1845, Chilean Saltpeter deposits were exploited in Chile and California, USA.
A major natural source of potassium nitrate was the deposits crystallizing from cave walls and the accumulations of bat guano in caves. Extraction is accomplished by immersing the guano in water for a day, filtering, and harvesting the crystals in the filtered water. Traditionally, guano was the source used in Laos for the manufacture of gunpowder for Bang Fai rockets.
Perhaps the most exhaustive discussion of the production of this material is the 1862 LeConte text. He was writing with the express purpose of increasing production in the Confederate States to support their needs during the American Civil War. Since he was calling for the assistance of rural farming communities, the descriptions and instructions are both simple and explicit. He details the "French Method", along with several variations, as well as a "Swiss method". N.B. Many references have been made to a method using only straw and urine, but there is no such method in this work.
Niter-beds are 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. The heap was usually under a cover from the rain, kept moist with urine, turned often to accelerate the decomposition, then finally leached with water after approximately one year, to remove the soluble calcium nitrate which was then converted to potassium nitrate by filtering through the potash.
LeConte describes a process using only urine and not dung, referring to it as the Swiss method. Urine is collected directly, in a sandpit under a stable. The sand itself is dug out and leached for nitrates which were then converted to potassium nitrate via potash, as above.
From nitric acid
From 1903 until the World War I era, potassium nitrate for black powder and fertilizer was produced on an industrial scale from nitric acid produced via the Birkeland–Eyde process, which used an electric arc to oxidize nitrogen from the air. During World War I the newly industrialized Haber process (1913) was combined with the Ostwald process after 1915, allowing Germany to produce nitric acid for the war after being cut off from its supplies of mineral sodium nitrates from Chile (see nitratite). The Haber process catalyzes ammonia production from atmospheric nitrogen, and industrially produced hydrogen. From the end of World War I until today, practically all organic nitrates have been produced from nitric acid from the oxidation of ammonia in this way. Some sodium nitrate is still mined industrially. Almost all potassium nitrate, now used only as a fine chemical, is produced from basic potassium salts and nitric acid.
History of use
Potassium nitrates supplied the oxidant and much of the energy for gunpowder in the 19th century, but after 1889, small arms and large artillery increasingly began to depend on cordite, a smokeless powder which required in manufacture large quantities of nitric acid derived from mineral nitrates (either potassium nitrate, or increasingly sodium nitrate), and the basic industrial chemical sulfuric acid. These propellants, like all nitrated explosives (nitroglycerine, TNT, etc.) use both parts of the nitrate ion: the oxygen promotes rapid combustion (thermal energy), and the expansion of the previously solid nitrogen to N2 gas provides kinetic energy.
- NH4NO3 (aq) + KOH (aq) → NH3 (g) + KNO3 (aq) + H2O (l)
- NH4NO3 (aq) + KCl (aq) → NH4Cl (aq) + KNO3 (aq)
Potassium nitrate can also be produced by neutralizing nitric acid with potassium hydroxide. This reaction is highly exothermic.
- KOH (aq) + HNO3 → KNO3 (aq) + H2O (l)
On industrial scale it is prepared by the double decomposition reaction between sodium nitrate and potassium chloride.
- NaNO3 (aq) + KCl (aq) → NaCl (aq) + KNO3 (aq)
Potassium nitrate has an orthorhombic crystal structure at room temperature, which transforms to a trigonal system at 129 °C. Upon heating to temperatures between 550 and 790 °C under an oxygen atmosphere, it loses oxygen and reaches a temperature dependent equilibrium with potassium nitrite:
- 2 KNO3 → 2 KNO2 + O2
Potassium nitrate is moderately soluble in water, but its solubility increases with temperature (see infobox). The aqueous solution is almost neutral, exhibiting pH 6.2 at 14 °C for a 10% solution of commercial powder. It is not very hygroscopic, absorbing about 0.03% water in 80% relative humidity over 50 days. It is insoluble in alcohol and is not poisonous; it can react explosively with reducing agents, but it is not explosive on its own.
Potassium nitrate has a wide variety of uses, largely as a source of nitrate.
Potassium nitrate is an efficient oxidizer, producing a lilac-colored flame upon burning due to the presence of potassium. It is one of the three components of black powder, along with powdered charcoal (substantially carbon) and sulfur, both of which act as fuels in this composition. As such it is used in black powder rocket motors, but also in combination with other fuels like sugars in "rocket candy". It is also used in fireworks such as smoke bombs, made with a mixture of sucrose and potassium nitrate. It is also added to cigarettes to maintain an even burn of the tobacco and is used to ensure complete combustion of paper cartridges for cap and ball revolvers.
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, saltpeter 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. When used as a food additive in the European Union, the compound is referred to as E252; it is also approved for use as a food additive in the USA and Australia and New Zealand (where it is listed under its INS number 252).
In West African cuisine, potassium nitrate (salt petre) is widely used as a thickening agent in soups and stews such as Okra soup and Isi ewu. It is also used to soften food and reduce cooking time when boiling beans and tough meat. Salt petre is also an essential ingredient in making special porridges such as kunun kanwa literally translated from the Hausa language as 'salt petre porridge'.
- Used in some toothpastes for sensitive teeth. Recently, the use of potassium nitrate in toothpastes for treating sensitive teeth has increased and it may be an effective treatment.
- Used in some toothpastes to relieve asthma symptoms.
- Used in Thailand as main ingredient in Kidney Tablets to relieve the symptoms of cystitis, pyelitis and urethritis.
- Used historically to treat asthma.
- Combats high blood pressure and was once used as a hypotensive.
- Electrolyte in a salt bridge
- Active ingredient of condensed aerosol fire suppression systems. When burned with the free radicals of a fire's flame, it produces potassium carbonate.
- Component (usually about 98%) of some tree stump removal products. It accelerates the natural decomposition of the stump by supplying nitrogen for the fungi attacking the wood of the stump.
- In heat treatment of metals as a medium temperature molten salt bath, usually in combination with sodium nitrite. A similar bath is used to produce a durable blue/black finish typically seen on firearms. Its oxidizing quality, water solubility, and low cost make it an ideal short-term rust inhibitor.
- To induce flowering of mango trees in the Philippines.
- Thermal storage medium in power generation systems. Sodium and potassium nitrate salts are stored in a molten state with the solar energy collected by the heliostats at the Gemasolar Thermosolar Plant. Ternary salts, with the addition of calcium nitrate or lithium nitrate, have been found to improve the heat storage capacity in the molten salts.
In Folklore and Popular Culture
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; however, there is no scientific evidence for such properties.
- Record of Potassium nitrate in the GESTIS Substance Database from the IFA, accessed on 2007-03-09
- B. J. Kosanke, B. Sturman, K. Kosanke, I. von Maltitz, T. Shimizu, M. A. Wilson, N. Kubota, C. Jennings-White, D. Chapman (2004). "2". Pyrotechnic Chemistry. Journal of Pyrotechnics. pp. 5–6. ISBN 1-889526-15-0.
- Ahmad Y Hassan, Potassium Nitrate in Arabic and Latin Sources, History of Science and Technology in Islam.
- Jack Kelly (2005). Gunpowder: Alchemy, Bombards, and Pyrotechnics: The History of the Explosive that Changed the World. Basic Books. p. 22. ISBN 978-0-465-03722-3. "Around 1240 the Arabs acquired knowledge of saltpeter (“Chinese snow”) from the East, perhaps through India. They knew of gunpowder soon afterward. They also learned about fireworks (“Chinese flowers”) and rockets (“Chinese arrows”). Arab warriors had acquired fire lances by 1280. Around that same year, a Syrian named Hasan al-Rammah wrote a book that, as he put it, "treat of machines of fire to be used for amusement of for useful purposes." He talked of rockets, fireworks, fire lances, and other incendiaries, using terms that suggested he derived his knowledge from Chinese sources. He gave instructions for the purification of saltpeter and recipes for making different types of gunpowder."
- Peter Watson (2006). Ideas: A History of Thought and Invention, from Fire to Freud. HarperCollins. p. 304. ISBN 978-0-06-093564-1. "The first use of a metal tube in this context was made around 1280 in the wars between the Song and the Mongols, where a new term, chong, was invented to describe the new horror...Like paper, it reached the West via the Muslims, in this case the writings of the Andalusian botanist Ibn al-Baytar, who died in Damascus in 1248. The Arabic term for saltpetre is 'Chinese snow' while the Persian usage is 'Chinese salt'.28"
- Cathal J. Nolan (2006). The age of wars of religion, 1000–1650: an encyclopedia of global warfare and civilization. Volume 1 of Greenwood encyclopedias of modern world wars. Greenwood Publishing Group. p. 365. ISBN 0-313-33733-0. Retrieved 2011-11-28. "In either case, there is linguistic evidence of Chinese origins of the technology: in Damascus, Arabs called the saltpeter used in making gunpowder " Chinese snow," while in Iran it was called "Chinese salt." Whatever the migratory route"
- Oliver Frederick Gillilan Hogg (1970). Artillery: its origin, heyday, and decline. Archon Books. p. 123. "The Chinese were certainly acquainted with saltpetre, the essential ingredient of gunpowder. They called it Chinese Snow and employed it early in the Christian era in the manufacture of fireworks and rockets."
- Oliver Frederick Gillilan Hogg (1963). English artillery, 1326–1716: being the history of artillery in this country prior to the formation of the Royal Regiment of Artillery. Royal Artillery Institution. p. 42. "The Chinese were certainly acquainted with saltpetre, the essential ingredient of gunpowder. They called it Chinese Snow and employed it early in the Christian era in the manufacture of fireworks and rockets."
- Oliver Frederick Gillilan Hogg (1993). Clubs to cannon: warfare and weapons before the introduction of gunpowder (reprint ed.). Barnes & Noble Books. p. 216. ISBN 1-56619-364-8. Retrieved 2011-11-28. "The Chinese were certainly acquainted with saltpetre, the essential ingredient of gunpowder. They called it Chinese snow and used it early in the Christian era in the manufacture of fireworks and rockets."
- Major George Rains (1861). Notes on Making Saltpetre from the Earth of the Caves. New Orleans, LA: Daily Delta Job Office. p. 14. Retrieved September 13, 2012.
- Joseph LeConte (1862). Instructions for the Manufacture of Saltpeter. Columbia, S.C.: South Carolina Military Department. p. 14. Retrieved 2007-10-19.
- Eli S. Freeman (1957). "The Kinetics of the Thermal Decomposition of Potassium Nitrate and of the Reaction between Potassium Nitrite and Oxygen". J. Am. Chem. Soc. 79 (4): 838–842. doi:10.1021/ja01561a015.
- Agrawal, Jai Prakash (2010). High Energy Materials: Propellants, Explosives and Pyrotechnics. Wiley-VCH. p. 69. ISBN 978-3-527-32610-5.
- Amthyst Galleries, Inc. Galleries.com. Retrieved on 2012-03-07.
- Inorganic Additives for the Improvement of Tobacco, TobaccoDocuments.org
- Kirst, W.J. (1983). Self Consuming Paper Cartridges for the Percussion Revolver. Minneapolis, Minnesota: Northwest Development Co.
- "Meat Science", University of Wisconsin. uwex.edu.
- Corned Beef, Food Network
- UK Food Standards Agency: "Current EU approved additives and their E Numbers". Retrieved 2011-10-27.
- US Food and Drug Administration: "Listing of Food Additives Status Part II". Retrieved 2011-10-27.
- Australia New Zealand Food Standards Code"Standard 1.2.4 – Labelling of ingredients". Retrieved 2011-10-27.
- "Cook Clean Site Ghanaian Recipe". CookClean Ghana.
- Marcellina Ulunma Okehie-Offoha (1996). Ethnic & cultural diversity in Nigeria. Trenton, N.J.: Africa World Press.
- "Sensodyne Toothpaste for Sensitive Teeth". 2008-08-03. Retrieved 2008-08-03.
- Enomoto, K et al. (2003). "The Effect of Potassium Nitrate and Silica Dentifrice in the Surface of Dentin". Japanese Journal of Conservative Dentistry 46 (2): 240–247.
- R. Orchardson and D. G. Gillam (2006). "Managing dentin hypersensitivity". Journal of the American Dental Association (1939) 137 (7): 990–8; quiz 1028–9. PMID 16803826.
- Joe Graedon (May 15, 2010). "'Sensitive' toothpaste may help asthma". The Chicago Tribune. Retrieved June 18, 2012.
- LOCAL MANUFACTURED DRUG REGISTRATION FOR HUMAN (COMBINE). fda.moph.go.th
- Orville Harry Brown (1917). Asthma, presenting an exposition of the nonpassive expiration theory. C.V. Mosby company. p. 277.
- Adam Chattaway; Robert G. Dunster; Ralf Gall; David J. Spring. "THE EVALUATION OF NON-PYROTECHNICALLY GENERATED AEROSOLS AS FIRE SUPPRESSANTS". United States National Institute of Standards and Technology (NIST).
- Stan Roark (February 27, 2008). "Stump Removal for Homeowners". Alabama Cooperative Extension System. Archived from the original on March 23, 2012.
- David E. Turcotte; Frances E. Lockwood (May 8, 2001). "Aqueous corrosion inhibitor Note. This patent cites potassium nitrate as a minor constituent in a complex mix. Since rust is an oxidation product, this statement requires justification.". United States Patent. 6,228,283.
- Elizabeth March (June 2008). "The Scientist, the Patent and the Mangoes – Tripling the Mango Yield in the Philippines". WIPO Magazine. United Nations World Intellectual Property Organization (WIPO). Archived from the original on 25 August 2012.
- "Filipino scientist garners 2011 Dioscoro L. Umali Award". Southeast Asian Regional Center for Graduate Study and Research in Agriculture (SEARCA). Archived from the original on 30 November 2011.
- Juan Ignacio Burgaleta; Santiago Arias; Diego Ramirez. "Gemasolar, The First Tower Thermosolar Commercial Plant With Molten Salt Storage System" (Press Release). Torresol Energy. Archived from the original on 9 March 2012. Retrieved 7 March 2012.
- "The Straight Dope: Does saltpeter suppress male ardor?". 1989-06-16. Retrieved 2007-10-19.
- Richard E. Jones and Kristin H. López (2006). Human Reproductive Biology, Third Edition. Elsevier/Academic Press. p. 225. ISBN 0-12-088465-8.
- Dennis W. Barnum. (2003). "Some History of Nitrates." Journal of Chemical Education. v. 80, p. 1393-. link.
- David Cressy. Saltpeter: The Mother of Gunpowder (Oxford University Press, 2013) 237 pp online review by Robert Tiegs
- Alan Williams. "The production of saltpeter in the Middle Ages", Ambix, 22 (1975), pp. 125–33. Maney Publishing, ISSN 0002-6980.