Bumping is a phenomenon in chemistry where liquids boil

Boil

A boil, also called a furuncle, is a deep folliculitis, infection of the hair follicle. It is always caused by infection by the bacterium Staphylococcus aureus, resulting in a painful swollen area on the skin caused by an accumulation of pus and dead tissue...

ed in a test tube

Test tube

A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top, usually with a rounded U-shaped bottom....

 will superheat

Superheating

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

 and, upon 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...

, rapid boiling will expel the liquid from the container.

This occurs when liquids are heated very rapidly and no nucleation occurs, thus when the liquid finally boils, a large vapor bubble

Bubble

-Physical bubbles:* Liquid bubble, globule of one substance encased in another, usually air in a liquid* Soap bubble, a bubble formed by soapy water * Antibubble, a droplet of liquid surrounded by a thin film of gas-Arts and literature:...

 is formed that pushes the liquid out of the test tube. Obviously, this expulsion of boiling liquid poses a serious hazard to others and oneself in the lab

Laboratory

A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...

.

Boiling chips alone may not prevent bumping and for this reason it is advisable to boil liquids in a boiling tube

Boiling tube

frame|A boiling tube looks much like a test tube.A boiling tube is a small cylindrical vessel used to strongly heat substances in the flame of a Bunsen burner...

. In addition, test tubes should always be pointed away from oneself while boiling, just in case bumping does occur.

A sealed capillary tube can also be placed in a boiling solution to provide a nucleation site, reducing the bumping risk and allowing its easy removal from a system.