Magnetic stirrer
A magnetic stirrer is an electrical device that is used in the chemical laboratory to stir liquids . Usually the setting plate of the mixer is also a heating plate with which the liquid can be heated; one then speaks of a heating stirrer .
The magnetic stirrer was patented in 1944 by the American chemist Arthur Rosinger and developed independently a few years later by the Scottish chemist Edward McLaughlin .
The liquid is placed in a beaker , an Erlenmeyer flask or the like on a plate under which a magnet rotates at an adjustable speed. This magnet acts on a second, e.g. B. in the beaker, mostly rod-shaped magnets, the magnetic stir bar, and sets the liquid in motion through it. This so-called stirring bar or stirring magnet is mostly plastic (eg. B. PTFE ) or glass -coated, in order to reduce the friction and it chemically inert to make.
Magnetic stirrers enable liquids to be mixed even in closed vessels without being affected by problems with seals or lubricants from the drive - as is the case with stirrers with shafts. For example, you can work in a protective gas atmosphere or with substances that require isolation from the environment. The simple design of the stir bar also makes cleaning and sterilization much easier. To get the small magnet out of the vessel, use a 300 or 450 mm long, PP-encapsulated or a 150, 250 or 350 mm long, PTFE-encapsulated magnetic rod, also known as a stir-fish rod .
Using a magnetic heating stirrer has the advantage over heating over a Bunsen burner flame or a laboratory heating hood that the temperature can be set relatively precisely and can be regulated, for example, by a connected temperature controller. The supplied heat is quickly and evenly distributed in the contents of the vessel by the stirring movement, which avoids delayed boiling . In addition, many solvents such. B. in organic chemistry , should not be worked with an open flame, which is why you have to use a heating plate or a heater .
Connection for a contact thermometer (left-hand bush)
Magnetic stir bar (scale: cm)
Magnetic stir bars in use
Web links
Individual evidence
- ↑ Derek Lowe, Das Chemiebuch, Librero 2017, p. 338
- ^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, p. 66, ISBN 3-211-81116-8 .