Saltpeter or Potassium Nitrate Facts

Saltpeter is a common chemical, used for many products and science projects. Here's a look at what exactly saltpeter is.

Saltpeter is the natural mineral source of the chemical potassium nitrate, KNO₃. It is an inorganic chemical that is soluble in water. Depending on where you live, it may be spelled "saltpetre" rather than 'saltpeter'. Before systematic naming of chemicals, saltpeter was called nitrate of potash. It has also been called 'Chinese salt' or 'Chinese snow'.

In addition to KNO₃, the compounds sodium nitrate (NaNO₃), calcium nitrate (Ca(NO₃)₂), and magnesium nitrate (Mg(NO₃)₂) are also sometimes referred to as saltpeter.

Sources of Saltpeter

Pure saltpeter or potassium nitrate is a white crystalline solid, usually encountered as a powder. Most potassium nitrate is produced using a chemical reaction of nitric acid and potassium salts. In the lab, it's easy to make potassium nitrate by reacting a mixture of ammonium nitrate and potassium chloride in water. Bat guano was an important historical natural source. Potassium nitrate was isolated from guano by soaking it in water, filtering it, and harvesting the pure crystals that grow. It may be produced in a similar manner from urine or manure.

Uses of Saltpeter

Saltpeter is a common food preservative and additive, fertilizer, and oxidizer for fireworks and rockets. It is one of the principal ingredients in gunpowder. Potassium nitrate is used to treat asthma and in topical formulations for sensitive teeth. It was once a popular medication for lowering blood pressure. Saltpeter is a component of condensed aerosol fire suppression systems, salt bridges in electrochemistry, heat treatment of metals, and for thermal storage in power generators. Adding potassium nitrate to meat causes a reaction between the hemoglobin and myoglobin in blood, making the meat appear red.

Saltpeter and Male Libido

It's a popular myth that saltpeter inhibits male libido. Rumors abound that saltpeter has been added to food in prison and military installations to curb sexual desire, but there is no evidence to support this has been done or would even work. Saltpeter and other nitrates have a long history of medical use, but it is toxic in high doses and can produce symptoms ranging from a mild headache and upset stomach to kidney damage and dangerously altered pressure.

History

Humans have been using saltpeter for thousands of years. One of the first written records mentioning it comes from an ancient Indian Sanskrit text (compiled between 300BC and 300AD) that mentions using its toxic smoke in warfare.

In 1270, Syrian chemist Hasan al-Rammah described a purification process for obtaining purified potassium nitrate from saltpeter. First, the saltpeter is boiled in a small amount of water and then reacted with potassium carbonate from wood ashes. This removes calcium and magnesium salts as precipitates, leaving a potassium nitrate solution. Evaporating the liquid yielded the chemical, which was used to make gunpowder.

Another process uses a nitrary. The process involves burying animal or human excrement in the ground and then watering it so that eventually saltpeter appeared on the ground from efflorescence. Then, workers scooped up the crystals and concentrated the chemical in a boiler.

Up until World War I, industrial production of potassium nitrate used the Birkeland-Eyde process. This is essentially industrial nitrogen fixation, where electric arcs react nitrogen and oxygen in air, making nitric acid and water. Reacting the nitric acid with a potassium compound yielded potassium nitrate.

Eventually, the Haber process and Ostwald process replaced the Birkeland-Eyde process.

Sources

Helmenstine, A.M. (2016). Where to Get Potassium Nitrate or Saltpeter. Science Notes.

LeConte, Joseph (1862). Instructions for the Manufacture of Saltpeter. Columbia, S.C.: South Carolina Military Department. p. 14. Retrieved 4/9/2013.

UK Food Standards Agency: "Current EU approved additives and their E Numbers". Retrieved 3/9/2012.

US Food and Drug Administration: "Food Additives and Ingredients". Retrieved 3/9/2013.

Snopes.com: The Saltpeter Principle. Retrieved 3/9/2013.