Potassium nitrate has a wide variety of uses, largely as a source of nitrate.
Potassium nitrate is mainly used in fertilizers, as a source of nitrogen and potassium – two of the macro-nutrients for plants. When used by itself, it has an NPK rating of 13-0-44.
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. As such it is used in black powder rocket motors, but also in combination with other fuels like sugars in "rocket candy". It is also used in fireworks such as smoke bombs, made with a mixture of sucrose and potassium nitrate. It is also added to cigarettes to maintain an even burn of the tobacco and is used to ensure complete combustion of paper cartridges for cap and ball revolvers.
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, saltpeter is still used in some food applications, such as charcuterie and the brine used to make corned beef. When used as a food additive in the European Union, the compound is referred to as E252; it is also approved for use as a food additive in the USA and Australia and New Zealand (where it is listed under its INS number 252).
In West African cuisine, potassium nitrate (salt petre) is widely used as a thickening agent in soups and stews such as Okra soup and Isi ewu. It is also used to soften food and reduce cooking time when boiling beans and tough meat. Salt petre is also an essential ingredient in making special porridges such as kunun kanwa literally translated from the Hausa language as 'salt petre porridge'.
-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.
-Used historically to treat asthma. Used in some toothpastes to relieve asthma symptoms.
-Used in Thailand as main ingredient in Kidney Tablets to relieve the symptoms of cystitis, pyelitis and urethritis.
-Combats high blood pressure and was once used as a hypotensive.
-Electrolyte in a salt bridge
-Active ingredient of condensed aerosol fire suppression systems. When burned with the free radicals of a fire's flame, it produces potassium carbonate.
-Component (usually about 98%) of some tree stump removal products. It accelerates the natural decomposition of the stump by supplying nitrogen for the fungi attacking the wood of the stump.
-In heat treatment of metals as a medium temperature molten salt bath, usually in combination with sodium nitrite. A similar bath is used to produce a durable blue/black finish typically seen on firearms. Its oxidizing quality, water solubility, and low cost make it an ideal short-term rust inhibitor.
-To induce flowering of mango trees in areas like Philippines.
-Thermal storage medium in power generation systems. Sodium and potassium nitrate salts are stored in a molten state with the solar energy collected by the heliostats at the Gemasolar Thermosolar Plant. Ternary salts, with the addition of calcium nitrate or lithium nitrate, have been found to improve the heat storage capacity in the molten salts