Sublimation is the change of a soldid substance directly to a vapor without passing through the liquid state. The term is also used to describe the reverse process of the gas changing directly to the solid again upon cooling. An exemple of sublimation is seen when iodine, on being heated, changes from a dark solid to a purplish vapor that condenses directly to a cristalline solid upon a striking a cool surface. In this way pure crystatls of iodine are prepared.
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