Büchner funnel
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A Büchner funnel (incorrectly, but often spelled Buchner funnel) is a piece of laboratory equipment used in filtration, especially in vacuum filtration.
Contents
Design
A Büchner funnel is a funnel shaped object, traditionally made of glazed porcelain, though glass and plastic funnels are also available. On top of the funnel-shaped part there is a cylinder with a fritted glass disc/perforated plate separating it from the funnel. Classical Büchner funnels have a long thin glass tube, to drain the filtered liquid, though some models have a ground glass joint or a lateral vacuum inlet tube, or both. Büchner funnels are often used with a side-arm flask (also known as Büchner or Kitasato flask) when doing vacuum filtration, though if vacuum adapters are used, ordinary flasks can also be used.
Jacketed Büchner funnels are a special type that are sometimes encountered in labs, often used when doing cold or hot filtering.
Hirsch funnel
Similar in construction to the Büchner funnel, the Hirsch funnel has an appearance almost identical to that of a classical funnel, with the walls of the funnel angle outward instead of being vertical. The funnel has a small diameter perforated disk near it's "neck". They are sometimes used for filtering smaller amounts of material or dilute suspensions.
Availability
Büchner funnels can be purchased from lab suppliers, both the porcelain and glass fritted disk models. Plastic Büchner funnels are also available. Aluminium or stainless steel Büchner funnels can be found in many hardware stores, as spare parts for coffee machines.
Hirsch funnels can also be purchased from lab suppliers and online. Plastic Hirsch funnels can sometimes be found in hardware stores, albeit of a lower quality.
Maintenance
Porcelain Büchner funnels should not be used to filter extremely corrosive reagents, as they might slowly corrode its protective enamel.
Büchner funnels with fritted disks are notorious for being hard to clean. If a base bath is used, they should never be left for more than a few hours as the base will gradually dissolve the glass bonding between the fritted glass particles, which eventually will cause them to crumble. A strong oxidizing solution, like aqua regia or in extreme cases, piranha solution, can be used to remove even the most persistent stains. These mixtures are among the few chemicals that can destroy graphite.
References
Relevant Sciencemadness threads
- Buchner funnels: which is best for what?
- The trouble with Buchner funnels
- 2 different buchner funnels. please help
- Ask a solution of Buchner funnel
- What vacuum funnel porosity to get?
- Trouble with vacuum filtration/better source of filter paper?
- Quick Question: Buchner funnel size
- Using a sintered buchner funnel
- Glass filter funnel question.
- cleaning glass frit
- sintered funnel VS. Buchner funnel
