Suction filtration

Suction filtration is a chemistry laboratory technique which allows for a greater rate of filtration. Whereas in normal filtration gravity provides the force which draws the liquid through the filter paper, in suction filtration a pressure gradient performs this function. This has the advantage of offering a variable rate depending on the strength of the pump being used to extract air from the Büchner flask. Care must be taken not to use such a strong vacuum that the filter paper rips (in which case all the solid will be lost back into the solvent) or in extreme cases the glass flask breaks.