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" () as well as
bārūd (), 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" ( ''
). 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. ==Historical production==
From mineral sources 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. 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.
From caves 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. 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-).
Nitre bed A
nitre 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 by
nitrification. 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. The Confederate side of the American Civil War had a significant shortage of saltpeter. As a result, the
Nitre 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. Perhaps the most exhaustive discussion of the niter-bed production 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".
French method Turgot and
Lavoisier created the
Régie des Poudres et Salpêtres a few years before the
French Revolution. Niter-beds were 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 high, wide, and long.
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). ==Modern production==