Chapter 15 — chapter 15

Filtration separates an insoluble solid from a liquid using a porous filter medium (filter paper, cotton, glass wool, asbestos, sintered glass). The liquid collected is the filtrate and the solid left behind is the residue. Filtration through a conical funnel with folded filter paper is slow; it can be considerably increased using a fluted filter paper, folded into a fan-like arrangement with alternate elevations and depressions, giving more surface area. Filtration by suction through a crucible: a Gooch crucible is made of porcelain with a perforated bottom covered with paper pulp or filter paper; useful for precipitates which need to be ignited at high temperature, and with an asbestos mat for solutions that react with paper (conc. HCl, KMnO₄). A sintered glass crucible has a porous glass disc sealed in the bottom; no preparation is needed.