Saltpeter (potassium nitrate)
https://en.wikipedia.org/wiki/Nitre_and_Mining_Bureau

Potassium nitrate is a chemical compound with the chemical formula KNO3. This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitrate ions NO3?, and is therefore an alkali metal nitrate. It occurs in nature as a mineral, niter (or nitre in the UK). It is a source of nitrogen, and nitrogen was named after niter. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpetre (or saltpeter in the United States of America).

Major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants and fireworks. It is one of the major constituents of gunpowder (black powder). In processed meats, potassium nitrate reacts with hemoglobin and myoglobin generating a red color. https://en.wikipedia.org/wiki/Potassium_nitrate