Niter or saltpeter (KNO3) is the mineral form of potassium nitrate. A soft substance easy to grind, it creates colorless to white crystals. Niter is found in arid climates or cave deposits where microbial activity and environmental conditions are right.
The mineral forms as potassium ions and nitrogen compounds (potassium nitrate) seep into porous substrates, eventually crystallizing as niter. History records its significance in various cultures, particularly in regions where it occurs naturally such as Egypt.
Highly soluble in water, niter has a variety of applications. Solubility arises from its ionic composition, which readily dissociates into potassium and nitrate ions in water. Niter is a soft mineral, between 1 to 2 on the Mohs hardness scale.
This softness makes it easy to grind into a powder, an attribute useful in numerous applications, including food preservation and agriculture. As a potent oxidizer, niter has a propensity to support combustion, leading to its historical use in gunpowder production.
Medieval alchemical friar Roger Bacon describes his encounter with Chinese firecrackers demonstrated by a traveling monk. He's amazed and sets out to (successfully) discover the composition.
He writes,
"... From the violence of that salt called saltpeter [together with sulfur and willow charcoal, combined into a powder] so horrible a sound is made by the bursting of a thing so small, no more than a bit of parchment [around it], that we find [the ear assaulted by a noise] exceeding the roar of strong thunder and a flash brighter than the most brilliant lightning ..."
In China the firecrackers frighten evil spirits. Beijing and other cities are banning home-made pyrotechnics displays in modern times due to the number of deaths and injuries each year. Deaths are primarily caused by over-enthusiastic unsafe setups.
During the US Civil War, a Confederate chemist solves a gunpowder shortage by using niter extracted from urine. Healthy urine contains nitrates, but these are converted to nitrites in the case of urinary tract infections. Their presence indicates the condition.
Historically, niter holds a significant place in the alchemy of medicine. Alchemists experiment with its properties, deriving nitric acid and various niter salts, both important to medical research. Niter is used to produce remedies for fevers and infections.
Discovery of Oxygen
Discovery of oxygen is attributed to later chemists but Michael Sendivogius (1566 - 1636) is the first to identify this element in air, by burning niter, which gives off gas as oxygen. He calls it the "food of life" and the "central niter". It receives the name oxygen in the 18th century.
Nitric Acid - the Acid Queen
Niter is also important to the production of nitric acid (HNO3), one of the most popular acids in both laboratory and industrial settings. Nitric acid is known as the Queen of Acids due to its power. With hydrochloric acid it forms fierce aqua regia, which can dissolve gold.
When niter is reacted with concentrated sulfuric acid (H2SO4), the result is nitric acid and potassium bisulfate. This reaction is used in manufacture of fertilizers, explosives, and various chemical products.
Nitric Salts
Beyond potassium nitrate, other nitric salts have significant applications in both industry and agriculture. Silver nitrate or lunar caustic is one example favored by alchemists. Sodium nitrate (NaNO3) and calcium nitrate (Ca(NO3)2) derive their properties from nitrate ions.
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