Büchner funnel

A Büchner funnel is a tool for filtration in labs, typically made of porcelain, though glass and plastic versions exist. Its design features a cylinder above a funnel section, separated by either a fritted glass disc or a perforated plate. A similar device, the Hirsch funnel, works for smaller samples, with a much smaller plate and outward-angled walls instead of vertical ones.

To use it, a funnel with a fritted disc is ready right away. For one with a perforated plate, you place filter paper on the plate and wet it with liquid to stop early leaks. Then, pour the liquid into the cylinder and pull it through the plate or disc using vacuum suction. This method speeds up filtration by several orders of magnitude compared to gravity drainage. You must keep the liquid volume below the flask’s capacity to avoid overflow into the vacuum equipment; if a water flow device supplies the vacuum, overflow could spill hazardous liquid into wastewater, potentially breaking the law. A trap between the flask and vacuum source reduces both overflow risk and water backflow into the flask.

In organic chemistry labs, it helps collect recrystallized compounds. The suction dries the wet crystals, leaving pure dried crystals, though further drying in an oven or other means is often needed to remove residual liquid. It is commonly used with a Büchner flask, Büchner ring, and sinter seals. A vacuum-tight seal and stable flask and filter are crucial. A Büchner ring works with funnels, flasks, glass crucibles, and Gooch crucibles; its wide flange and large surface contact ensure a tight seal while being easy to remove and supporting even large funnels.

Despite common belief that it is named after Nobel Laureate Eduard Buchner, it actually honors industrial chemist Ernst Büchner.