Boiling chips are small, insoluble, porous stones made of calcium carbonate or silicon carbide. These stones have pores inside which provide cavities both to trap air and to provide spaces where bubbles of solvent vapor can form. When a boiling chip is heated in a solvent, it releases tiny bubbles. These bubbles ensure even boiling and prevent bumping and boiling over and loss of the solution.

Always use a boiling chip when heating a solvent.

Never add a boiling chip to a hot solvent, because it can cause immediate boiling over of the solution. If you forget to add a boiling chip before you begin, you must cool the solution before adding one to prevent product loss. Boiling chips cannot be re-used since the pores inside these stones become filled with liquid on cooling.