The filtrate is allowed to stand, cooling to room temperature when crystallisation is complete.
The solution should not be disturbed during this period so that crystallisation occurs slowly so that impurities are not co-crystallised with the desired product.
The re-crystallised solid is separated from soluble impurities using suction filtration (apparatus at the right).
The side-arm on the flask is connected to a vacuum source by a piece of thick-walled rubber tubing.