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Sublimation apparatus is a piece of laboratory glassware used in the technique of sublimation usually used by chemists to purify compounds. Typically a solid is placed in a vessel which is then heated under vacuum. Under this reduced pressure the solid volatilizes and condenses as a purified compound on a cooled surface, leaving the non-volatile residue impurities behind. This cooled surface often take the form of a cold finger. Once heating ceases and the vacuum is released, the sublimed compound can be collected from the cooled surface.
More sophisticated setups use a temperature gradient that allows for the controlled recrystallization of different fractions along the glas tube. As thermodynamic processes follow a statistical distribution a gradient setup will yield different purities for the different zones within the glas tube. This is helpful in particular when the raw material contains a number of compounds (impurities) with similar sublimation points or pressure curves.