Bell jar

This article is about the laboratory equipment. For the novel by Sylvia Plath, see The Bell Jar.

A bell jar is a piece of laboratory glassware in the shape of a bell.

Experiments using a bell jar

It can be sealed, which allows it to be used in a classroom science experiment involving an alarm clock and a vacuum pump. The air is pumped out of the sealed bell jar, and the noise of the alarm clock fades, thus demonstrating that the propagation of sound is mediated by the air. Deprived of its medium, the sound cannot travel.

Bell jars can also be used to simulate the vacuum of space. Hardware can be tested for performance issues in a bell jar which has been evacuated of air.