Stir Bars
A stir bar is the magnetic bar placed within the liquid wihich provides the stirring action. The stir bar's motion is driven by another rotating magnet or assembly of electromagnets in the stirrer device, beneath the vessel containing the liquid. Stir bars are typically coated in teflon, or less often in glass. Glass coatings are used for liquid alkali metals (except lye, which will eat through glass) and alkali metal solutions in ammonia. Both coatings are chemically inert and do not contaminate or react with the reaction mixture they are in.
They are bar shaped and often octagonal in cross-section (sometimes circular), although a variety of special shapes exist for more efficient stirring. Most stir bars have a ridge around the center (called a pivot ring) on which they rotate. The smallest are only a few millimeters long and the largest a few centimeters. A stir bar retriever is a separate magnet on the end of a long stick (usually coated with teflon) which can be used to remove stir bars from a vessel.
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