Potassium nitrate

Potassium nitrate[1]
IUPAC name
Potassium nitrate
Other names
Nitrate of potash
7757-79-1 YesY
3D model (Jmol) Interactive image
ChEMBL ChEMBL1644029 N
ChemSpider 22843 YesY
ECHA InfoCard 100.028.926
EC Number 231-818-8
E number E252 (preservatives)
KEGG D02051 YesY
PubChem 24434
RTECS number TT3700000
UN number 1486
Molar mass 101.1032 g/mol
Appearance white solid
Odor odorless
Density 2.109 g/cm3 (16 °C)
Melting point 334 °C (633 °F; 607 K)
Boiling point decomposes at 400 °C
133 g/L (0 °C)
316 g/L (20 °C)
2460 g/L (100 °C)[2]
Solubility slightly soluble in ethanol
soluble in glycerol, ammonia
Basicity (pKb) 15.3[3]
1.335, 1.5056, 1.5604
Orthorhombic, Aragonite
95.06 J/mol K
-494.00 kJ/mol
Main hazards Oxidant, Harmful if swallowed, Inhaled, or absorbed on skin. Causes Irritation to Skin and Eye area.
Safety data sheet See: data page
ICSC 0184
Oxidant (O)
R-phrases R8 R22 R36 R37 R38
S-phrases S7 S16 S17 S26 S36 S41
NFPA 704
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
1901 mg/kg (oral, rabbit)
3750 mg/kg (oral, rat)[4]
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
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Potassium nitrate is a chemical compound with the chemical formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3, and is therefore an alkali metal nitrate.

It occurs as a mineral niter and is a natural solid source of nitrogen. 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 (blackpowder) and has been used since the Middle Ages as a food preservative.


Potassium nitrate, because of its early and global use and production, has many names.

The Greeks used the term nitron, which was Latinised to nitrum or nitrium, while earlier Hebrews and Egyptians used words with the consonants n-t-r, which leads some to speculate that the Latin term is closer to the original than the Greek term. Middle English styled it nitre. Old French had niter. By the 15th century, Europeans referred to it as saltpeter[5] 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[6][7][8][9][10] or "salt from Chinese salt marshes" (Persian: نمک شوره چيني namak shūra chīnī).[11][12]


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]

Thermal decomposition

Between 550–790 °C (1,022–1,454 °F), potassium nitrate reaches a temperature dependent equilibrium with potassium nitrite:[13]

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.[14] 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.[15]

At least as far back as 1845, Chilean saltpeter deposits were exploited in Chile and California, USA.

From caves

A major natural source of potassium nitrate was the deposits crystallizing from cave walls and the accumulations of bat guano in caves.[16] 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.[17] 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.

French method

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.[17] 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.

Swiss method

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).


Potassium nitrate can be made by combining ammonium nitrate and potassium hydroxide.

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 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.


A demonstration of the oxidation of a piece of charcoal in molten potassium nitrate.

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.[18] It is also added to cigarettes to maintain an even burn of the tobacco[19] and is used to ensure complete combustion of paper cartridges for cap and ball revolvers.[20] 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.

Food preservation

In the process of food preservation, potassium nitrate has been a common ingredient of salted meat since the Middle Ages,[21] 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.[22] When used as a food additive in the European Union,[23] the compound is referred to as E252; it is also approved for use as a food additive in the USA[24] and Australia and New Zealand[25] (where it is listed under its INS number 252).[2] Although nitrate salts have been suspected of producing the carcinogen nitrosamine, both sodium and potassium nitrates and nitrites have been added to meats in the US since 1925, and nitrates and nitrites have not been removed from preserved meat products because nitrite and nitrate inhibits the germination of C. botulinum endospores, and thus prevents botulism from bacterial toxin that may otherwise be produced in certain preserved meat products.[26][27]

Food preparation

In West African cuisine, potassium nitrate (salt petre) is widely used as a thickening agent in soups and stews such as Okra soup[28] 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[29] literally translated from the Hausa language as 'salt petre porridge'. In the Shetland Islands (UK) it is used in the curing of mutton to make "reestit" mutton, a local delicacy.


Potassium nitrate is used in fertilizers as a source of nitrogen and potassium – two of the macronutrients for plants. When used by itself, it has an NPK rating of 13-0-44.[30][31]


Other uses

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.[45][46]

See also


  1. Record of Potassium nitrate in the GESTIS Substance Database of the IFA, accessed on 2007-03-09
  2. 1 2 3 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.
  3. Kolthoff, Treatise on Analytical Chemistry, New York, Interscience Encyclopedia, Inc., 1959.
  4. http://chem.sis.nlm.nih.gov/chemidplus/rn/7757-79-1
  5. Spencer, Dan (2013). Saltpeter:The Mother of Gunpowder. Oxford, UK: Oxford University Press. p. 256. ISBN 9780199695751.
  6. 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
  7. 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
  8. 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.
  9. 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.
  10. 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.
  11. Partington, J. R. (1960). A History of Greek Fire and Gunpowder (illustrated, reprint ed.). JHU Press. p. 335. ISBN 0801859549. Retrieved 2014-11-21.
  12. 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.
  13. 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.
  14. Ahmad Y Hassan, Potassium Nitrate in Arabic and Latin Sources, History of Science and Technology in Islam.
  15. 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.
  16. 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.
  17. 1 2 Joseph LeConte (1862). Instructions for the Manufacture of Saltpeter. Columbia, S.C.: South Carolina Military Department. p. 14. Retrieved 2007-10-19.
  18. Amthyst Galleries, Inc. Galleries.com. Retrieved on 2012-03-07.
  19. Inorganic Additives for the Improvement of Tobacco, TobaccoDocuments.org
  20. Kirst, W.J. (1983). Self Consuming Paper Cartridges for the Percussion Revolver. Minneapolis, Minnesota: Northwest Development Co.
  21. "Meat Science", University of Wisconsin. uwex.edu.
  22. Corned Beef, Food Network
  23. UK Food Standards Agency: "Current EU approved additives and their E Numbers". Retrieved 2011-10-27.
  24. US Food and Drug Administration: "Listing of Food Additives Status Part II". Retrieved 2011-10-27.
  25. Australia New Zealand Food Standards Code"Standard 1.2.4 – Labelling of ingredients". Retrieved 2011-10-27.
  26. Clostridium in food
  27. sodium nitrite and nitrate facts Accessed Dec 12, 2014
  28. "Cook Clean Site Ghanaian Recipe". CookClean Ghana.
  29. Marcellina Ulunma Okehie-Offoha (1996). Ethnic & cultural diversity in Nigeria. Trenton, N.J.: Africa World Press.
  30. Michigan State University Extension Bulletin E-896: N-P-K Fertilizers
  31. Environmental Impact of Fertilizer on Soil and Water. 2004. p. 40.
  32. "Sensodyne Toothpaste for Sensitive Teeth". 2008-08-03. Archived from the original on August 7, 2007. Retrieved 2008-08-03.
  33. 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.
  34. R. Orchardson & D. G. Gillam (2006). "Managing dentin hypersensitivity" (PDF). Journal of the American Dental Association (1939). 137 (7): 990–8; quiz 1028–9. doi:10.14219/jada.archive.2006.0321. PMID 16803826.
  35. Orville Harry Brown (1917). Asthma, presenting an exposition of the nonpassive expiration theory. C.V. Mosby company. p. 277.
  36. Joe Graedon (May 15, 2010). "'Sensitive' toothpaste may help asthma". The Chicago Tribune. Retrieved June 18, 2012.
  38. Reichert ET. (1880). "On the physiological action of potassium nitrite". Am. J. Med. Sci. 80: 158–180.
  39. Adam Chattaway; Robert G. Dunster; Ralf Gall; David J. Spring. "THE EVALUATION OF NON-PYROTECHNICALLY GENERATED AEROSOLS AS FIRE SUPPRESSANTS" (PDF). United States National Institute of Standards and Technology (NIST).
  40. Stan Roark (February 27, 2008). "Stump Removal for Homeowners". Alabama Cooperative Extension System. Archived from the original on March 23, 2012.
  41. 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.
  42. 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.
  43. "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.
  44. Juan Ignacio Burgaleta; Santiago Arias; Diego Ramirez. "Gemasolar, The First Tower Thermosolar Commercial Plant With Molten Salt Storage System" (PDF) (Press Release). Torresol Energy. Archived (PDF) from the original on 9 March 2012. Retrieved 7 March 2012.
  45. "The Straight Dope: Does saltpeter suppress male ardor?". 1989-06-16. Retrieved 2007-10-19.
  46. Richard E. Jones & Kristin H. López (2006). Human Reproductive Biology, Third Edition. Elsevier/Academic Press. p. 225. ISBN 0-12-088465-8.


Wikiquote has quotations related to: Potassium nitrate
Salts and covalent derivatives of the Nitrate ion
LiNO3 Be(NO3)2 B(NO3)4 C N O FNO3 Ne
NaNO3 Mg(NO3)2 Al(NO3)3 Si P S ClONO2 Ar
KNO3 Ca(NO3)2 Sc(NO3)3 Ti(NO3)4 VO(NO3)3 Cr(NO3)3 Mn(NO3)2 Fe(NO3)3 Co(NO3)2,
Ni(NO3)2 Cu(NO3)2 Zn(NO3)2 Ga(NO3)3 Ge As Se Br Kr
RbNO3 Sr(NO3)2 Y Zr(NO3)4 Nb Mo Tc Ru Rh Pd(NO3)2 AgNO3 Cd(NO3)2 In Sn Sb Te I Xe(NO3)2
CsNO3 Ba(NO3)2   Hf Ta W Re Os Ir Pt Au Hg2(NO3)2,
Tl(NO3)3 Pb(NO3)2 Bi(NO3)3
Po At Rn
Fr Ra   Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
La Ce(NO3)3,
Pr Nd Pm Sm Eu Gd(NO3)3 Tb Dy Ho Er Tm Yb Lu
Ac Th Pa UO2(NO3)2 Np Pu Am Cm Bk Cf Es Fm Md No Lr
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