A bell jar is a piece of laboratory equipment that consists of a cylindrical or spherical glass vessel with an opening at the bottom and a knob or handle on the top for lifting. It is typically used to create a vacuum, as the jar can be placed over an object or chamber, and air can be removed using a vacuum pump. Bell jars are commonly used in chemistry, physics, and materials science experiments, such as to study the behavior of gases or to create a vacuum for processes such as thin film deposition. They can also be used to demonstrate the effects of air pressure on everyday objects, such as by placing a marshmallow or balloon inside the jar and then removing the air to show their changes in size. Bell jars can come in a range of sizes, from small tabletop versions for demonstrations to larger ones for more advanced scientific applications. They are typically made of borosilicate glass for durability and are designed to withstand changes in temperature and pressure