Sublimation is the transition of a substance directly from the solid to the gas state without passing through the liquid state. Sublimation is a technique used by chemists to purify compounds. A solid is typically placed in a sublimation apparatus and heated under a vacuum. Under this reduced pressure, the solid volatilizes and condenses as a purified compound on a cooled surface (cold finger), leaving a non-volatile residue of impurities behind. Once heating ceases and the vacuum is removed, the purified compound may be collected from the cooling surface.
