Filtration is the physical separation of solids from a fluid using a filtration medium. The filtration medium is chosen depending on the purpose of filtration, quantity, and particle size of the solid. In general, filtration efficiency increases with particle size. In simple filtration, the precipitate is first allowed to settle, and the mother liquor is decanted down a glass rod into a funnel fitted with filter paper. The precipitate is then transferred to the filter paper using a rubber policeman. Ashless filter paper can be ignited to recover the precipitate, when weighing is required. Alternatively, a sintered-glass funnel fixed to a Buchner flask, which has a sidearm that can be connected to a vacuum pump, is used to trap the precipitate.