Potassium nitrate is achemical compound with a sharp, salty, bitter taste and thechemical formulaKNO3. It is apotassiumsalt ofnitric acid. This salt consists of potassiumcationsK+ andnitrateanionsNO−3, and is therefore analkali metal nitrate. It occurs in nature as a mineral,niter (ornitre outside the United States).[7] It is a source ofnitrogen, and nitrogen was named after niter. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to assaltpetre (orsaltpeter in the United States).[7]
Nitre, or potassium nitrate, because of its early and global use and production, has many names.
As for nitrate, Egyptian and Hebrew words for it had the consonants n-t-r, indicating likelycognation in the Greeknitron, which was Latinised tonitrum ornitrium. Thence Old French hadniter and Middle Englishnitre. By the 15th century, Europeans referred to it assaltpetre,[9] specifically Indian saltpetre (Chilean saltpetre is sodium nitrate[10]) and later asnitrate of potash, as the chemistry of the compound was more fully understood.
The Arabs called it "Chinese snow" (Arabic:ثلج الصين,romanized: thalj al-ṣīn) as well asbārūd (بارود), a term of uncertain origin that later came to meangunpowder. It was called "Chinese salt" by the Iranians/Persians[11][12][13] or "salt from Chinese salt marshes" (Persian:نمک شوره چينیnamak shūra chīnī).[14]: 335 [15] TheTiangong Kaiwu, published in the 17th century by members of theQing dynasty, detailed the production of gunpowder and other useful products from nature.
InMauryan India saltpeter manufacturers formed the Nuniya & Labanacaste.[16] Saltpeter finds mention inKautilya'sArthashastra (compiled 300 BC – 300 AD), which mentions using its poisonous smoke as a weapon of war,[17] although its use for propulsion did not appear until medieval times.
A purification process for potassium nitrate was outlined in 1270 by the chemist and engineerHasan al-Rammah ofSyria in his bookal-Furusiyya wa al-Manasib al-Harbiyya (The Book ofMilitary Horsemanship and Ingenious War Devices). In this book, al-Rammah describes first the purification ofbarud (crude saltpeter mineral) by boiling it with minimal water and using only the hot solution, then the use ofpotassium carbonate (in the form ofwood 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.[18] This was used for the manufacture of gunpowder and explosive devices. The terminology used by al-Rammah indicated the gunpowder he wrote about originated in China.[19]
At least as far back as 1845,nitratite deposits were exploited in Chile and California.
Major natural sources of potassium nitrate were the deposits crystallizing from cave walls and the accumulations ofbat guano in caves.[20] 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 inLaos for the manufacture of gunpowder forBang Fai rockets.[21]
Calcium nitrate, or lime saltpetre, was discovered on the walls of stables, from the urine of barnyard animals.[10]
Potassium nitrate was produced in anitrary or "saltpetre works".[22] The process involved burial of excrements (human or animal) in a field beside the nitraries, watering them and waiting until leaching allowed saltpeter to migrate to the surface byefflorescence. Operators then gathered the resulting powder and transported it to be concentrated byebullition in the boiler plant.[23][24]
Besides "Montepellusanus", during the thirteenth century (and beyond) the only supply of saltpeter across Christian Europe (according to "De Alchimia" in 3 manuscripts of Michael Scot, 1180–1236) was "found in Spain in Aragon in a certain mountain near the sea".[14]: 89, 311 [25]
In 1561,Elizabeth I, Queen of England and Ireland, who was at war withPhilip II of Spain, became unable to import saltpeter (of which theKingdom of England had no home production), and had to pay "300 pounds gold" to the German captain Gerrard Honrik for the manual "Instructions for making saltpeter to growe" (the secret of the "Feuerwerkbuch" -the nitraries-).[26]
Anitre bed is a similar process used to produce nitrate from excrement. Unlike the leaching-based process of the nitrary, however, one mixes the excrements with soil and waits for soil microbes to convert amino-nitrogen into nitrates bynitrification. The nitrates are extracted from soil with water and then purified into saltpeter by adding wood ash. The process was discovered in the early 15th century and was very widely used until the Chilean mineral deposits were found.[27]
The Confederate side of the American Civil War had a significant shortage of saltpeter. As a result, theNitre and Mining Bureau was set up to encourage local production, including by nitre beds and by providing excrement to government nitraries. On November 13, 1862, the government advertised in the Charleston Daily Courier for 20 or 30 "able bodied Negro men" to work in the new nitre beds at Ashley Ferry, S.C. The nitre beds were large rectangles of rotted manure and straw, moistened weekly with urine, "dung water", and liquid from privies, cesspools and drains, and turned over regularly. The National Archives published payroll records that account for more than 29,000 people compelled to such labor in the state of Virginia. The South was so desperate for saltpeter for gunpowder that one Alabama official reportedly placed a newspaper ad asking that the contents of chamber pots be saved for collection. In South Carolina, in April 1864, the Confederate government forced 31 enslaved people to work at the Ashley Ferry Nitre Works, outside Charleston.[28]
Perhaps the most exhaustive discussion of the niter-bed production is the 1862LeConte text.[29] He was writing with the express purpose of increasing production in theConfederate States to support their needs during theAmerican 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".
Turgot andLavoisier created theRégie des Poudres et Salpêtres a few years before theFrench Revolution. Niter-beds were prepared by mixingmanure with eithermortar or wood ashes, common earth and organic materials such asstraw 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.[29] The heap was usually under a cover from the rain, kept moist withurine, turned often to accelerate the decomposition, then finallyleached with water after approximately one year, to remove the solublecalcium nitrate which was then converted to potassium nitrate by filtering throughpotash.
Joseph LeConte describes a process using only urine and not dung, referring to it as theSwiss method. Urine is collected directly, in a sandpit under a stable. The sand itself is dug out and leached for nitrates which are then converted to potassium nitrate using potash, as above.[30]
From 1903 until theWorld War I era, potassium nitrate for black powder and fertilizer was produced on an industrial scale fromnitric acid produced using theBirkeland–Eyde process, which used an electric arc to oxidize nitrogen from the air. During World War I the newly industrializedHaber process (1913) was combined with theOstwald 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 (seenitratite).
An alternative way of producing potassium nitrate without a by-product of ammonia is to combine ammonium nitrate, found ininstant ice packs,[31] andpotassium chloride, easily obtained as a sodium-freesalt substitute.
NH4NO3 + KCl → NH4Cl + KNO3
Potassium nitrate can also be produced by neutralizingnitric acid with potassium hydroxide. This reaction is highly exothermic.
KOH + HNO3 → KNO3 + H2O
On industrial scale it is prepared by the double displacement reaction betweensodium nitrate and potassium chloride.
Potassium nitrate has anorthorhombic crystal structure at room temperature,[32] which transforms to a trigonal system at 128 °C (262 °F). On cooling from 200 °C (392 °F), another trigonal phase forms between 124 °C (255 °F) and 100 °C (212 °F).[33][34]
Sodium nitrate is isomorphous withcalcite, the most stable form ofcalcium carbonate, whereas room-temperature potassium nitrate isisomorphous witharagonite, a slightly less stablepolymorph of calcium carbonate. The difference is attributed to the similarity in size betweennitrate (NO−3) andcarbonate (CO2−3) ions and the fact that the potassium ion (K+) is larger than sodium (Na+) and calcium (Ca2+) ions.[35]
In the room-temperature structure of potassium nitrate, each potassium ion is surrounded by 6 nitrate ions. In turn, each nitrate ion is surrounded by 6 potassium ions.[32]
Potassium nitrate is moderately soluble in water, but its solubility increases with temperature. The aqueous solution is almost neutral, exhibitingpH 6.2 at 14 °C (57 °F) for a 10% solution of commercial powder. It is not veryhygroscopic, 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 withreducing agents, but it is not explosive on its own.[2]
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 theOstwald process.
A demonstration of the oxidation of a piece ofcharcoal in molten potassium nitrate
The most famous use of potassium nitrate is probably as the oxidizer inblackpowder. From the most ancient times until 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 oncordite, asmokeless powder. Blackpowder remains in use today inblack powder rocket motors, but also in combination with other fuels like sugars in "rocket candy" (a popular amateur rocket propellant). It is also used in fireworks such assmoke bombs.[37] It is also added to cigarettes to maintain an even burn of the tobacco[38] and is used to ensure complete combustion ofpaper cartridges for cap and ball revolvers.[39] It can also be heated to several hundred degrees to be used forniter bluing, which is less durable than other forms of protective oxidation, but allows for specific coloration of steel parts, such as screws, pins, and other small parts of firearms.
Potassium nitrate has been a common ingredient of salted meat sinceantiquity[40] or theMiddle Ages.[41] The widespread adoption of nitrate use is more recent and is linked to the development of large-scale meat processing. The use of potassium nitrate has been mostly discontinued because it gives slow and inconsistent results compared withsodium nitrite preparations such as "Prague powder" or pink "curing salt". Even so, potassium nitrate is still used in some food applications, such as salami, dry-cured ham,charcuterie, and (in some countries) in thebrine used to makecorned beef (sometimes together with sodium nitrite).[42] In the Shetland Islands (UK) it is used in the curing of mutton to makereestit mutton, a local delicacy.[43] When used as a food additive in the European Union,[44] the compound is referred to asE252; it is also approved for use as a food additive in the United States[45] and Australia and New Zealand[46] (where it is listed under itsINS number 252).[2]
Since October 2015,WHO classifies processed meat as Group 1 carcinogen (based on epidemiological studies, convincinglycarcinogenic to humans).[47]
In April 2023 the French Court of Appeals of Limoges confirmed that food-watch NGO Yuka was legally legitimate in describing Potassium NitrateE252 as a "cancer risk", and thus rejected an appeal by the Frenchcharcuterie industry against the organisation.[citation needed]
Potassium nitrate is used infertilizers as a source of nitrogen and potassium – two of themacronutrients for plants. When used by itself, it has anNPK rating of 13-0-44.[48][49]
Component (usually about 98%) of sometree stump removal products. It accelerates the naturaldecomposition of the stump by supplying nitrogen for thefungi attacking thewood of the stump.[58]
Inheat 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. Itsoxidizing quality, water solubility, and low cost make it an ideal short-termrust inhibitor.[59]
Inglass toughening: molten potassium nitrate bath is used to increase glass strength and scratch-resistance.[60]
To induce flowering ofmango trees in the Philippines.[61][62]
Potassium nitrate was once thought to induceimpotence, and is still rumored to be in institutional food (such as military fare). There is no scientific evidence for such properties.[64][65]
In1776, John Adams asks his wife Abigail to make saltpeter for the Continental Army. She, eventually, is able to do so in exchange for pins for sewing.[66]
In the farming lore from theCorn Belt of the 1800s, drought-killed corn[67] in manured fields could accumulate saltpeter to the extent that upon opening the stalk for examination it would "fall as a fine powder upon the table".[68]
^abcB. J. Kosanke; B. Sturman; K. Kosanke; et al. (2004)."2".Pyrotechnic Chemistry. Journal of Pyrotechnics. pp. 5–6.ISBN978-1-889526-15-7.Archived from the original on 2016-05-05.
^Kolthoff, I.M.; Elving, P.A.; Sandell, E.B., eds. (1959).Treatise on Analytical Chemistry. New York: Interscience Encyclopedia, Inc.[volume & issue needed][page needed]
^Ema, M.; Kanoh, S. (1983). "[Studies on the pharmacological bases of fetal toxicity of drugs. III. Fetal toxicity of potassium nitrate in 2 generations of rats]".Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica.81 (6):469–480.doi:10.1254/fpj.81.469.ISSN0015-5691.PMID6618340.
^Cathal J. Nolan (2006).The age of wars of religion, 1000–1650: an encyclopedia of global warfare and civilization. Vol. 1 of Greenwood encyclopedias of modern world wars. Greenwood Publishing Group. p. 365.ISBN978-0-313-33733-8.Archived from the original on 2014-01-01. Retrieved2011-11-28.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."
^John Spencer Bassett; Edwin Mims; William Henry Glasson; et al. (1904).The South Atlantic Quarterly. Duke University Press. Retrieved22 February 2013.
^Alexander Adam (1805).A compendious dictionary of the Latin tongue: for the use of public Seminar and private March 2012. Printed for T. Cachorro and W. Davies, by C. Stewart, London, Bell and Bradfute, W. Creech.
^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.Bibcode:1957JAChS..79..838F.doi:10.1021/ja01561a015.
