Nitrate of potash
3D model (JSmol)
|E number||E252 (preservatives)|
|Molar mass||101.1032 g/mol|
|Density||2.109 g/cm3 (16 °C)|
|Melting point||334 °C (633 °F; 607 K)|
|Boiling point||400 °C (752 °F; 673 K) (decomposes)|
|133 g/L (0 °C)|
242 g/L (20 °C)
2439 g/L (100 °C)
|Solubility||slightly soluble in ethanol|
soluble in glycerol, ammonia
Refractive index (nD)
|1.335, 1.5056, 1.5604|
Heat capacity (C)
|95.06 J/mol K|
Std enthalpy of
|Main hazards||Oxidant, harmful if swallowed, inhaled, or absorbed on skin. Causes irritation to skin and eye area.|
|Safety data sheet||See: data page|
|H272, H315, H319, H335|
|P102, P210, P220, P221, P280|
|Flash point||non-flammable (oxidizer)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|1901 mg/kg (oral, rabbit)|
3750 mg/kg (oral, rat)
|Supplementary data page|
|Refractive index (n),|
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
It occurs in nature as a mineral, niter. It is a source of nitrogen, from which it derives its name. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpeter or saltpetre.
Major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants and fireworks. It is one of the major constituents of gunpowder (black powder) and has been used since the Middle Ages as a food preservative.
- 1 Etymology
- 2 Properties
- 3 History of production
- 4 Production
- 5 Uses
- 6 In folklore and popular culture
- 7 See also
- 8 References
- 9 Bibliography
- 10 External links
Potassium nitrate, because of its early and global use and production, has many names. Hebrew and Egyptian words for it had the consonants n-t-r, indicating likely cognation in the Greek nitron, which was Latinised to nitrum or nitrium. Thence Old French had niter and Middle English nitre. By the 15th century, Europeans referred to it as saltpeter and later as nitrate of potash, as the chemistry of the compound was more fully understood.
The Arabs called it "Chinese snow" (Arabic: ثلج الصين thalj al-ṣīn). It was called "Chinese salt" by the Iranians/Persians or "salt from Chinese salt marshes" (Persian: نمک شوره چيني namak shūra chīnī).
Potassium nitrate has an orthorhombic crystal structure at room temperature, which transforms to a trigonal system at 129 °C (264 °F).
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 (57 °F) 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.
- 2 KNO3 ⇌ 2 KNO2 + O2
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 saltpeter 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.
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 4 feet (1.2 m) high, 6 feet (1.8 m) wide, and 15 feet (4.6 m) long. 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 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 using 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 using 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).
- NH4NO3 (aq) + KOH (aq) → NH3 (g) + KNO3 (aq) + H2O (l)
An alternative way of producing potassium nitrate without a by-product of ammonia is to combine ammonium nitrate, found in instant ice packs, and potassium chloride, easily obtained as a sodium-free salt substitute.
- 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 displacement reaction between sodium nitrate and potassium chloride.
- NaNO3 (aq) + KCl (aq) → NaCl (aq) + KNO3 (aq)
Potassium nitrate has a wide variety of uses, largely as a source of nitrate.
Nitric acid production
Historically, nitric acid was produced by combining sulfuric acid with nitrates such as saltpeter. In modern times this is reversed: nitrates are produced from nitric acid produced via the Ostwald process.
The most famous use of potassium nitrate is probably as the oxidizer in blackpowder. From the most ancient times through the late 1880s, blackpowder provided the explosive power for all the world's firearms. After that time, small arms and large artillery increasingly began to depend on cordite, a smokeless powder. Blackpowder remains in use today 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. 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. It can also be heated to several hundred degrees to be used for niter bluing, which is less durable than other forms of protective oxidation, but allows for specific and often beautiful coloration of steel parts, such as screws, pins, and other small parts of firearms.
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 because of 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. 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 United States and Australia and New Zealand (where it is listed under its INS number 252). Although nitrate salts have been suspected of producing the carcinogen nitrosamine, in the United States both sodium and potassium nitrates and nitrites have been added to meats since 1925, though it is generally accepted that solid muscle products do not require the addition of nitrate for safety reasons.
In West African cuisine, potassium nitrate (saltpetre) 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. Saltpetre is also an essential ingredient in making special porridges, such as kunun kanwa literally translated from the Hausa language as 'saltpetre porridge'. In the Shetland Islands (UK) it is used in the curing of mutton to make "reestit" mutton, a local delicacy.
- Used in some toothpastes for sensitive teeth. Recently, the use of potassium nitrate in toothpastes for treating sensitive teeth has increased.
- Used historically to treat asthma. 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.
- 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.
- Works as an aluminium cleaner.
- 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.
- As a source of potassium ions for exchange with sodium ions in chemically strengthened glass.
- As an oxidizer in model rocket fuel called Rocket candy.
In folklore and popular culture
Potassium nitrate was once thought to induce impotence, and is still 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 of the Institute for Occupational Safety and Health, accessed on 2007-03-09.
- Gustafson, A. F. (1949). Handbook of Fertilizers - Their Sources, Make-Up, Effects, And Use. p. 25. Archived from the original on 2017-02-17.
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- Kolthoff, Treatise on Analytical Chemistry, New York, Interscience Encyclopedia, Inc., 1959.
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- Spencer, Dan (2013). Saltpeter:The Mother of Gunpowder. Oxford, UK: Oxford University Press. p. 256. ISBN 9780199695751.
- Peter Watson (2006). Ideas: A History of Thought and Invention, from Fire to Freud. HarperCollins. p. 304. ISBN 978-0-06-093564-1. Archived from the original on 2015-10-17.
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. Archived from the original on 2014-01-01. 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. Archived from the original on 2015-09-19.
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.
- Partington, J. R. (1960). A History of Greek Fire and Gunpowder (illustrated, reprint ed.). JHU Press. p. 335. ISBN 0801859549. Retrieved 2014-11-21.
- Needham, Joseph; Yu, Ping-Yu (1980). Needham, Joseph, ed. Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology, Part 4, Spagyrical Discovery and Invention: Apparatus, Theories and Gifts. Volume 5. Contributors Joseph Needham, Lu Gwei-Djen, Nathan Sivin (illustrated, reprint ed.). Cambridge University Press. p. 194. ISBN 052108573X. Retrieved 2014-11-21.
- 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.
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- 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. Archived from the original on 2016-05-11.
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.
- Major George Rains (1861). Notes on Making Saltpetre from the Earth of the Caves. New Orleans, LA: Daily Delta Job Office. p. 14. Archived from the original on July 29, 2013. Retrieved September 13, 2012.
- Joseph LeConte (1862). Instructions for the Manufacture of Saltpeter. Columbia, S.C.: South Carolina Military Department. p. 14. Archived from the original on 2007-10-13. Retrieved 2007-10-19.
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Salts and covalent derivatives of the nitrate ion