Büchner flask

A Büchner flask, also known as a vacuum flask,^[1] filter flask, suction flask, side-arm flask, or Bunsen flask, is a thick-walled Erlenmeyer flask with a short glass tube and hose barb protruding about an inch from its neck.

A Büchner funnel is attached to the flask via a black elastomer adapter. The hose barb is connected via vacuum hose to a vacuum source such as an aspirator. The flask should be clamped before use or the hose will likely cause it to tip.

Cross section of a Büchner Flask. Note the hose barb pointing right for attaching a vacuum source.

Description

The short tube and hose barb effectively act as an adapter over which the end of a thick-walled flexible hose (tubing) can be fitted to form a connection to the flask. The other end of the hose can be connected to source of vacuum such as an aspirator, vacuum pump, or house vacuum. Preferably this is done through a trap (see below), which is designed to prevent the sucking back of water from the aspirator into the Büchner flask. The purpose of applying a vacuum is to speed the filtration by providing a pressure differential across the filter medium that is greater than that produced by gravity alone.

Operation

The thick wall of the Büchner flask provides it the strength to withstand the pressure difference while holding a vacuum inside. It is primarily used together with a Büchner funnel fitted through a drilled rubber bung or an elastomer adapter (a Büchner ring) at the neck on top of the flask for the filtration of samples. The Büchner funnel holds the sample isolated from the suction by a layer of filter paper. During filtration, the filtrate enters and is held by the flask while the residue remains on the filter paper in the funnel.

The Büchner flask can also be used as a vacuum trap in a vacuum line to ensure that no fluids are carried over from the aspirator or vacuum pump (or other vacuum source) to the evacuated apparatus or vice versa.

Name

The flask is named after the industrial chemist Ernst Büchner, who invented it, despite the mistaken belief held by many people that it's named after chemist and Nobel Laureate Eduard Buchner.

Notes

^ The use of the term vacuum flask sometimes causes confusion with the thermos flask

References

Jensen, William B. (September 2006). "The Origins of the Hirsch and Büchner Vacuum Filtration Funnels" (PDF). Journal of Chemical Education. 83 (9): 1283. Bibcode:2006JChEd..83.1283J. doi:10.1021/ed083p1283. Archived from the original (PDF) on 2007-03-15. Retrieved 2006-09-08.

[vacflask-1] The use of the term vacuum flask sometimes causes confusion with the thermos flask

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