In chemistry, recrystallization is a procedure for purifying compounds. A crystal compound often has other compounds on it that make it less useful. To get rid of these extra items, the crystal is placed in a boiling liquid. Soon the crystal dissolves. The boiling solution, or the mix of the liquid and the dissolved crystal, gets colder. The crystal will form again. The unwanted compounds stay in the solvent, or the liquid. Now the crystal is pure and made of only the compound. Each type of compound works best in a certain type of liquid. Sometimes two or more liquids mixed together are needed to dissolve a crystal.