Potassium nitrate
From Memory Alpha, the free Star Trek reference
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")
