Potassium nitrate (KNO3), also known as nitre and saltpeter, is composed of potassium, nitrogen, and oxygen.
Potassium nitrate is often used as a component in gunpowder. Captain James T. Kirk manufactured gunpowder in 2267 using potassium nitrate as a component while engaged in Metron-arranged combat with a Gorn. (TOS: "Arena")