Saltpeter was used to preserve food and in old explosives, so it carries two readings: keeping things as they are, and pent-up tension close to the surface.
Does the traditional reading fit your dream, or did it mean something else to you?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.