Potassium nitrate in a watch glass. Potassium nitrate; KNO3; Molar mass 101.1032 g/mol. Also known as saltpeter, saltpetre, nitrate of potash, niter. Potassium nitrate??s a??hemical compound, an??onic salt??f??otassium ions??+??nd??itrate ions??O3-, an??lkali metal nitrate. It is found as the mineral niter, a source of??itrogen, and was once an important food preservative and its food additive number is E252 and is used in some charcuterie. It was one of the three components of gunpowder but today it is mainly used in fertilizer, rocket propellant and fireworks.