Potassium nitrate is the oxidizing component of black powder. Before the large-scale industrial fixation of nitrogen through the Haber process, major sources of potassium nitrate were the deposits crystallizing from cave walls and the draining of decomposing organic material. Dung-heaps were a particularly common source: ammonia from the decomposition of urea and other nitrogenous materials would undergo bacterial oxidation to produce nitrate.
Potassium Nitrate is manufactured by direct reaction of potassium chloride with concentrated nitric acid to produce potassium nitrate and chlorine.
Food Industry: In the process of food preservation, potassium nitrate has been a common ingredient of salted meat since the middle Ages, but its use has been mostly discontinued due to inconsistent results compared to more modern nitrate and nitrite compounds. Even so, saltpetre is still used in some food applications, as they are more reliable in preventing bacterial infection than saltpetre.
Agriculture Industry: Potassium nitrate is mainly used in fertilizers, as a source of nitrogen and potassium.
Mining and Oil Industry: Potassium nitrate is an efficient oxidizer, producing a lilac-colored flame upon burning due to the presence of potassium. It is one of the three components of black powder, along with powdered charcoal (substantially carbon) and sulfur, both of which act as fuels in this composition.
Medical Industry: Potassium nitrate is used in some toothpastes for sensitive teeth. Recently, the use of potassium nitrate in toothpastes for treating sensitive teeth has increased and it may be an effective treatment. Besides, Potassium nitrate is used historically to treat asthma as well as arthritis. Combats high blood pressure and was once used as a hypotensive.