Boiling chips are frequently employed in distillation and heating. When a liquid becomes superheated, a particle of dust or a stirring rod can cause violent flash boiling. Boiling chips provide nucleation sites so the liquid boils smoothly without becoming superheated or bumping. Boiling chips should not be added to liquid that is already near its boiling point, as this could also induce flash boiling. The structure of a boiling chip traps liquid while in use, meaning that they cannot be re-used in laboratory setups. They also don't work well under vacuum; if a solution is boiling under vacuum, it's best to constantly stir it instead.