A boiling chip or boiling stone is a small, irregularly shaped piece of material added to liquids to make them boil

Boiling

Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. While below the boiling point a liquid...

 more smoothly. Boiling chips are frequently employed in distillation

Distillation

Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 and heating. When a liquid becomes superheated, a particle of dust or a stirring rod

Stirring rod

A stirring rod or "stir rod" is a piece of laboratory equipment used to mix chemicals and liquids for laboratory purposes. They are usually made of solid glass, about the thickness and slightly longer than a drinking straw, with rounded ends....

 can cause flash boiling. This very rapid boiling can be extremely violent and cause reagents to splatter, possibly causing severe burns, ruining an experiment, and damaging equipment. Boiling chips work by providing nucleation

Nucleation

Nucleation is the extremely localized budding of a distinct thermodynamic phase. Some examples of phases that may form by way of nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation...

 sites so the liquid boils smoothly without becoming superheated

Superheating

In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...

 or bumping

Bumping (chemistry)

Bumping is a phenomenon in chemistry where liquids boiled in a test tube will superheat and, upon nucleation, rapid boiling will expel the liquid from the container....

.

Use

Boiling chips should not be added to liquid that is already near its boiling point

Boiling point

The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

, as this could also induce flash boiling.

The structure of boiling chips traps liquid while in use, meaning that they cannot be re-used in laboratory setups.

Materials

Boiling chips are typically made of a porous material, such as alumina, calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

, porcelain

Porcelain

Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...

 or carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, and often have a nonreactive coating of PTFE. This ensures that the boiling chips will provide effective nucleation sites, yet are chemically inert

Inert

-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...

. In less demanding situations, like school laboratories, pieces of broken porcelainware or glassware

Laboratory glassware

Laboratory glassware refers to a variety of equipment, traditionally made of glass, used for scientific experiments and other work in science, especially in chemistry and biology laboratories...

are often used.