Salt-petre is separated from the brine which first affords it, or from the water with which it is washed out of nitrous earths, by the process commonly used in crystallizing salts. In this process, the brine is gradually diminished, and at length reduced to a small quantity of an unctuous bitter saline liquor, affording no more salt petre by evaporation, but, if urged with a brisk fire, drying up into a confused mass, which attracts water strongly, and becomes ?uid again when exposed to the open air.