Filter paper

Micro-photo of a paper coffee filter. The cellulose fibers are clearly visible. Pore size of the unsized paper around 5 µm .

Commercially available round filters for laboratory use

... in action in a nutscheer

Pleated filter folded

Pleated filter opened

Filter paper and filter paper-like materials are used in many areas to solids from liquids or gases to deposit ; physically, to separate a solid phase from an aqueous or gaseous one.

application areas

In the household

Separation of solid / liquid: tea bags made of tea bag paper , filter bags as coffee filters
Separation solid / gaseous: vacuum cleaner bag

In motor vehicles

Separation solid / liquid: oil filter , fuel filter
Separation solid / gaseous: air filter , pollen filter

In chemical and biological laboratories

Separation of solid / liquid: numerous applications with special filter papers (see next section)

Use in the chemistry laboratory

In the chemical laboratory, filter paper is important for preparative and analytical work. Papers with different pore sizes have been developed for the various purposes:

Filter shapes and pore sizes

Filter papers are designed as flat round filters or as pre- folded folded filters for the various funnel shapes .

Depending on the application, papers with different pore sizes are used, which are identified by color codes:

Black band filters are used for coarse precipitation (fast filtration)
White band filters are used for finer deposits (medium-fast filtration)
Blue band filters are used for very fine precipitation (slow filtration)

Ashless filter paper

Ash-free filters burn up practically residue-free when a filtered precipitate is dried and incinerated and therefore does not influence the sample weight during gravimetric analytical work, as is the case with conventional filters.

Use in the biology laboratory

Round filters are used here, but not for filtering, but for keeping z. B. of small-cut parts of plants in preparative work. As a rule, round filters of the appropriate size are placed in Petri dishes for this purpose .

Individual evidence

^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, pp. 412-413.
^ Gerhard Meyendorf: laboratory equipment and chemicals , people and knowledge Volkseigener Verlag Berlin, 1965, pp. 22-23.
^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 105-107, ISBN 3-211-81116-8 .

[ABC_Chemie-1] Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, pp. 412-413.

[Meyendorf-2] Gerhard Meyendorf: laboratory equipment and chemicals , people and knowledge Volkseigener Verlag Berlin, 1965, pp. 22-23.

[Wittenberger-3] Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 105-107, ISBN 3-211-81116-8 .