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This article is about the laboratory equipment. For the novel by Sylvia Bell jar book pdf, see The Bell Jar. This article relies largely...

This article is about the laboratory equipment. For the novel by Sylvia Bell jar book pdf, see The Bell Jar. This article relies largely or entirely on a single source. Relevant discussion may be found on the talk page.


Please help improve this article by introducing citations to additional sources. 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 that needs an ultra high vacuum requires a more sophisticated form of vacuum chamber. However, several tests may be completed in a chamber with an effective pump and low leak rate.

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