Why is Chile salt petre used in the manufacture of gunpowder?

Explanation

Gunpowder is a heterogeneous mixture of C, S and `KNO_(3)`. On heating `KNO_(3)` undergoes decomposition and liberates oxygen which supports combustion of carbon and sulphur. During combustion a huge amount of heat is liberated and pressure increases in side the small area. As a result explosion takes place.