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Short answer: Boiling stones, also called boiling chips or anti-bumping granules, are small porous, insoluble pieces of material added to a liquid before it is heated so that it boils evenly instead of bumping, boiling over and losing solution. They are added to a cool liquid, they work only once, and they do not help under vacuum or in liquids with precipitates.
This page is general laboratory reference for researchers and lab staff. It is not a substitute for your institution’s safety procedures or a method’s own instructions.
Definition and scope
A boiling stone is a small, porous, chemically inert piece of solid placed in a flask before heating. CU Boulder’s organic chemistry teaching site describes them as small, porous, insoluble stones of calcium carbonate or silicon carbide. The same item appears under several names, and all of them refer to the same function:
- Boiling stones, an alternative name for the same item.
- Boiling chips, the term used in most teaching-lab and supplier language.
- Anti-bumping granules, the name used for the same job in some catalogues and methods. The purpose of anti-bumping granules is the one described on this page: to promote steady boiling and prevent bumping.
This page covers the chip as a laboratory consumable. It does not cover kitchen or food uses of the word “stones”, and it does not cover sanitizing rocks (see the FAQ below).
What is the purpose of boiling stones in distillation?
Their purpose is to give a liquid a steady supply of small bubbles as it heats. According to CU Boulder’s technique page, the bubbles ensure even boiling and prevent bumping, boiling over, and loss of the solution. Bumping is the sudden, violent boiling that occurs when a liquid becomes superheated and then boils all at once. In a distillation or reflux setup that can throw liquid up the flask neck, spoil the separation and endanger the person at the bench.
The pores of the chip hold trapped air that releases as small bubbles when heated, which give the liquid places to start boiling. The same page’s rule is simple: always use a boiling chip when heating a solvent.
How boiling stones are used in practice
The two sources read for this page agree on the working rules:
- Add the chip while the liquid is cool. CU Boulder: never add a boiling chip to a solvent that is already hot. Lab Manager warns that adding one to a liquid that is already heated can cause it to erupt.
- If you forgot the chip, cool first. Let the solution cool before adding one, rather than dropping it into hot liquid.
- Do not reuse a chip. When the liquid cools, it fills the pores, and the chip loses its effectiveness if the liquid is reheated.
- Check the equipment. Lab Manager advises inspecting glassware and heating equipment for cracks and making sure no water or incompatible chemicals are in the system.
- Dispose of used chips by what they touched. Lab Manager notes that chips contaminated with hazardous material are hazardous waste, not ordinary trash and not drain disposal.
Round-bottom flasks are the usual vessel for this work; see what a round-bottom flask is and how its sizes and joints work. Where the boiling is done under reduced pressure, see how a rotary evaporator handles bumping.
Boiling stones versus stirring: a sourced decision table
Boiling stones are one way to provide nucleation sites. The table lays out where the two named sources say they work and where they do not. Every row comes from the Lab Manager article or the CU Boulder page listed under Sources.
| Situation | What the sources say | Source |
|---|---|---|
| Clear liquid at atmospheric pressure, heated from cool | A boiling chip is the standard tool: it ensures even boiling and prevents bumping. | CU Boulder |
| Liquid already hot | Do not add a chip; it can cause eruption. Cool the solution first. | CU Boulder; Lab Manager |
| Vacuum system | Chips are useless because the air trapped in their pores is rapidly removed. A magnetic stirrer is described as the most reliable method of providing nuclei. | Lab Manager |
| Liquid containing precipitates | Chips cannot prevent bumping. A paddle stirrer is suggested for dense precipitates. | Lab Manager |
| Reheating a liquid that was already boiled with a chip | The chip is spent: its pores fill with liquid on cooling. Do not reuse it. | CU Boulder |
For a stirring option, see the guide to hot plate stirrers.
Materials and related concepts
CU Boulder names calcium carbonate and silicon carbide as the materials of boiling chips. Reference summaries also list alumina, calcium sulfate, porcelain and carbon, and note that chips are often PTFE-coated and that teaching labs sometimes improvise with broken porcelain or glass. Whatever the material, it must be insoluble and non-reactive in the liquid being heated, which is why the choice follows the method being run.
Boiling stones address a physical problem (superheating) and are separate from the chemistry of the separation itself. For how distillation works as a technique, see fractional distillation. For boiling points of common solvents, see ethanol boiling point at 1 atm and under vacuum.
Where it matters for labs
For lab managers and instructors, the practical points from the sources are procedural rather than purchasing-related. Per CU Boulder, a chip is not reusable once its pores have filled with liquid. Waste handling follows the contamination of the used chips, not the chips themselves. Before heating, a short checklist drawn from the sources is: glassware free of cracks; no water or incompatible chemicals present; chip added to a cool liquid; stirrer chosen instead if the system is under vacuum or contains precipitate.
Common misunderstandings
- “A chip fixes any bumping.” It does not: Lab Manager lists precipitates and vacuum as cases where it fails.
- “Drop one in if it starts to bump.” Adding to hot liquid can trigger an eruption; cool the liquid first.
- “Chips can be reused after drying.” The sources describe them as not reusable once the pores have filled with liquid.
- “Boiling stones are the same as stones used to sanitize.” They are a laboratory consumable for steady boiling, not a sanitizing medium.
Frequently asked questions
What is the purpose of boiling stones in distillation?
They provide small bubbles that promote even boiling and prevent bumping, boiling over and loss of solution (CU Boulder). They are added to the cool liquid before heating.
What is the purpose of anti-bumping granules?
The same as boiling stones and boiling chips: to give the liquid nucleation sites so it boils steadily instead of bumping. The same limits apply, including that they do not work under vacuum and are single-use.
How long to boil rocks to sanitize them?
Boiling stones are a laboratory consumable, not a sanitizing medium. Sterilization or disinfection of any item follows the item manufacturer’s instructions or your institution’s procedure.
Can boiling stones be reused?
No. CU Boulder states that the pores fill with liquid on cooling, so the chip loses its effectiveness when reheated.
What should I do if I forgot to add a boiling chip?
Cool the solution first, then add the chip. Never add one to a solvent that is already hot.
Sources
- CU Boulder Organic Chemistry, “Boiling Chips”: orgchemboulder.com/Technique/Procedures/Distillation/Boilingchips.shtml (read 2026-11-08).
- Lab Manager, “3 limitations of using boiling chips in superheated fluids”: labmanager.com (read 2026-11-08).
- Wikipedia, “Boiling chip” (secondary; used only for the list of materials): en.wikipedia.org/wiki/Boiling_chip (read 2026-11-08).
