Potassium nitrate, also known as saltpeter, is a water-soluble chemical compound with formula KNO3. It is a natural form of nitrogen fertilizer and is a key ingredient in gunpowder and fireworks. Potassium nitrate dissolves readily in water and its solubility depends on temperature - the higher the temperature, the more potassium nitrate will dissolve in water. At 20°C, 100 grams of water will dissolve 36.4 grams of potassium nitrate.