Saltpeter is a preservative, and has been used in the making of brines and dry salt mixtures for hundreds of years. It has been found to be harmful when eaten in large quatntities, so it is probably wise to think twice before using it. Adding salt to water will raise the temperature at which it boils and lower the temperature at which it freezes. Adding a little salt balances the flavor of sweets like cakes, cookies, and candies. Boiling eggs in salted water makes them easier to peel.
Salt is a mineral, so it can be stored indefinitely without going stale.