The direct conversion of solid into vapour without passing through liquid state by heating is called sublimation.
Sublimation is used to purify solid substances. – Iodine, ammonium chloride, naphthalene, anthracene, and benzoic acid can sublime. A substance to be sublimed is taken in a watch glass covered with an inverted funnel. The funnel is plugged with wet cotton. The substance is heated slowly over a sand bath. The pure solid deposits on the inner side of the funnel.