"Saltpetre" is a word in ENGLISH

Potassium nitrate; niter; a white crystalline substance,
KNO3, having a cooling saline taste, obtained by leaching from certain
soils in which it is produced by the process of nitrification (see
Nitrification, 2). It is a strong oxidizer, is the chief constituent of
gunpowder, and is also used as an antiseptic in curing meat, and in
medicine as a diuretic, diaphoretic, and refrigerant.