How to show the sublimation of ammonium chloride???

Ammonium chloride when heated decomposes into hydrogen chloride and ammonia.

Experiment of sublimation of ammonium chloride.

Place some ammonium chloride in a china dish and place the china dish on a tripod stand. The china dish is covered with an inverted glass funnel. A loose cotton plug is placed in the upper, open end of the funnel to prevent the ammonium chloride vapours from escaping into the atmosphere. The china dish is heated by using a burner. On heating, ammonium chloride changes into white vapours. These vapours rise up and get converted into solid ammonium chloride on coming in contact with the cold, inner walls of the funnel. In this way, ammonium chloride changes directly from solid to gas and then collect at the funnel again changing its state from gas to solid. Ammonium chloride collected on the inner sides of the funnel in the form of a sublimate and can be removed.

In short:- Ammonium chloride sublimes because of dissociation of ammonium chloride into ammonia and hydrogen chloride in the vapour state. On cooling, ammonia and hydrogen chloride recombine to form Ammonium chloride again.