Filter paper

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Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid flow and is used to separate fine solids from liquids. In laboratories, filter paper is usually used with a filter funnel, Hirsch, or Buchner funnel.

[edit] Types

Filter paper comes in various porosities and grades:

Choice of filter paper for a given task depends on four parameters: strength, compatibility, efficiency and capacity. A coffee filter is an adequate example to evaluate these parameters and how they affect performance and results. If a coffee filter doesn't possess enough strength, many of the coffee grains will collect in the coffee pot. Compatibility, both heat and chemical, influence the same results as strength because a chemically or overheated medium is subject to structural failure. Efficiency is the retention of particles in a target category. The efficiency required is dictated by the particles or substances trying to be removed. A comparison of efficiency needs to could be compared by evaluating a screen door and filtering blood. Capacity is the ability to "hold" previously removed particles while allowing further flow. An overly efficient filter will plug up prematurely and cause excessive resistance or flow problems. A balance between particle capture and flow requirements must be met while ensuring integrity.