Sublimation is used to separate a mixture of sand and ammonium chloride. Sublimation is a separation process that entails heating a mixture of solids, where one of the solids transitions from solid to gas without passing through the liquid state. The vaporized solid is then reclaimed by cooling the vapor which reverts back to its initial solid state.
In the case of ammonium chloride and sand, ammonium chloride is the sublimate and changes to vapor when heated. This process leaves behind the sand in its natural state. The ammonium chloride vapor is then condensed and reverts back to its solid state, resulting in the effective separation of the two solids.
To perform this technique, place the mixture in a china dish and cover it with a funnel with the narrow end pointing up. Cover the narrow end with some cotton wool and gently heat the china dish from below with a Bunsen burner or an alternative heat source. The ammonium chloride would change into vapor and rise through the funnel, eventually condensing and reverting back to its solid state on the cooler sides of the funnel.