Crystal Growth by Slow Cooling of the Solvent
      Substances that are much more soluble in a solvent at high temperature than at low temperature are good candidates for crystal growth by slow cooling.
- Make a saturated, or nearly saturated, solution just below the boiling point of the solvent. Filter while hot if any solid remains. Allow the solution to cool slowly. Sometimes just turning off the heat and letting the solution slowly cool on the hot plate (without stirring, of course) works well. - If the solution cools too quickly, owing to the coolness of the room, you may surround the beaker with insulation. Commercial ovens are available, but a Styrofoam cup or packing base from acid bottles covered with metal foil may work as well to slow the rate of cooling. - With more volatile solvents, remove from the hot plate when dissolution is complete, and place on an insulated surface, such as a large cork, to cool. Most bench tops are relatively cold and the heat lost from the solution may be too rapid if the solution is placed on the bench top. - If the compound is rather soluble at room temperature, try putting the solution in the refrigerator to cool.