A vacuum bell jar is placed on a base which is vented to a hose fitting, that can be connected via a hose to a vacuum pump.
A vacuum is formed by pumping the air out of the bell jar.

The lower edge of a vacuum bell jar forms a flange of heavy glass, ground smooth on the bottom for better contact.
The base of the jar is equally heavy and flattened.
A smear of vacuum grease is usually applied between them.
As the vacuum forms inside, it creates a considerable compression force, so there is no need to clamp the seal.
For this reason, a bell jar cannot be used to contain pressures above atmospheric, only below.

Bell jars are generally used for classroom demonstrations or by hobbyists, when only a relatively low-quality vacuum is required.
Cutting-edge research done at ultra high vacuum requires a more sophisticated vacuum chamber.
However, several tests may be completed in a bell jar chamber having an effective pump and low leak rate.

Some of the first scientific experiments using a bell jar to provide a vacuum were reported by Robert Boyle.
In his book, New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects, (Made, for the Most Part, in a New Pneumatical Engine), he described 43 separate experiments, some of which were carried out with Robert Hooke, investigating the effect of reducing the air pressure within the bell jar on the objects contained within.
A vacuum bell jar is placed on a base which is vented to a hose fitting, that can be connected via a hose to a vacuum pump. A vacuum is formed by pumping the air out of the bell jar.
The lower edge of a vacuum bell jar forms a flange of heavy glass, ground smooth on the bottom for better contact. The base of the jar is equally heavy and flattened. A smear of vacuum grease is usually applied between them. As the vacuum forms inside, it creates a considerable compression force, so there is no need to clamp the seal. For this reason, a bell jar cannot be used to contain pressures above atmospheric, only below.
Bell jars are generally used for classroom demonstrations or by hobbyists, when only a relatively low-quality vacuum is required. Cutting-edge research done at ultra high vacuum requires a more sophisticated vacuum chamber. However, several tests may be completed in a bell jar chamber having an effective pump and low leak rate.
Some of the first scientific experiments using a bell jar to provide a vacuum were reported by Robert Boyle. In his book, New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects, (Made, for the Most Part, in a New Pneumatical Engine), he described 43 separate experiments, some of which were carried out with Robert Hooke, investigating the effect of reducing the air pressure within the bell jar on the objects contained within.
Bell jar