Sublimation: Direct conversion of solid to vapor without passing through liquid state (and vice versa: deposition). Occurs when the vapor pressure of the solid reaches atmospheric pressure below its melting point.

Common sublimable organic compounds (for JEE): Camphor, naphthalene, anthracene, benzoic acid, iodine, phthalic anhydride, salicylic acid.

Procedure: Place impure solid in china dish → cover with perforated filter paper → place inverted glass funnel on top → heat gently → sublimate deposits as pure crystals on the cool inner surface of funnel → non-volatile impurities remain in dish.

The perforated paper prevents already-deposited crystals from falling back into the impure residue. Cotton plug in funnel stem prevents crystal loss.

Limitation: Only works if the desired compound sublimes and the impurity does NOT (or vice versa). If both sublime, this technique fails. Also, the compound must not decompose before subliming.

Application in separation: Mixture of camphor + sodium chloride → camphor sublimes (pure), NaCl remains. Mixture of naphthalene + common salt → naphthalene sublimes.