Potassium nitrate is a chemical compound with a sharp, salty, bitter taste and the chemical formula KNO3. It is a potassium salt of nitric acid. This salt consists of potassium cations K+ and nitrate anions NO−3, and is therefore an alkali metal nitrate. It occurs in nature as a mineral, niter (or nitre outside the United States). It is a source of nitrogen, and nitrogen was named after niter. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpetre (or saltpeter in American English). Major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants and fireworks. It is one of the major constituents of traditional gunpowder (black powder). In processed meats, potassium nitrate reacts with hemoglobin and myoglobin generating a red color.
Etymology 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 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 saltpetre, specifically Indian saltpetre (Chilean saltpetre is sodium nitrate) 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, romanized: thalj al-ṣīn) as well as bārūd (بارود), a term of uncertain origin that later came to mean gunpowder. It was called "Chinese salt" by the Iranians/Persians or "salt from Chinese salt marshes" (Persian: نمک شوره چينی namak shūra chīnī). The Tiangong Kaiwu, published in the 17th century by members of the Qing dynasty, detailed the production of gunpowder and other useful products from nature.
History
Saltpeter Major natural sources of potassium nitrate were 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. Calcium nitrate, or lime saltpetre, was discovered on the walls of stables, from the urine of barnyard animals. In Mauryan India saltpeter manufacturers formed the Nuniya & Labana caste. Saltpeter finds mention in Kautilya's Arthashastra (compiled 300 BCE – 300 CE), which mentions using its poisonous smoke as a weapon of war, although its use for propulsion did not appear until medieval times.
Purification and production A 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 the gunpowder he wrote about originated in China. At least as far back as 1845, nitratite deposits were exploited in Chile and California.
Nitraries
Potassium nitrate was produced in a nitrary or "saltpetre works". 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 by efflorescence. Operators then gathered the resulting powder and transported it to be concentrated by ebullition in the boiler plant. 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". In 1561, Elizabeth I, Queen of England, who was at war with Philip II of Spain, became unable to import saltpeter (of which the Kingdom 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-).
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