A magnetic stirrer is a laboratory device that uses a rotating magnetic field to spin a magnetic stir bar (flea) placed inside a liquid, stirring it efficiently. The rotating magnetic field is generated either by a rotating magnet or stationary electromagnets positioned beneath the container holding the liquid.

Magnetic stirrers are commonly used in the fields of chemistry and biology, especially in situations where other stirring methods, such as motorized stirrers or manual stirring rods, are not feasible due to sensitivity or contamination concerns.

Stir bars are typically coated with PTFE (Teflon) or, less frequently, with glass. These coatings are chemically inert, preventing them from reacting with the liquid or contaminating the mixture during the stirring process. PTFE is commonly used, while glass is chosen in high-temperature or highly reactive chemical environments where PTFE may not be suitable.

A glass-coated stir bar would be preferred in situations where PTFE could be chemically attacked or damaged, such as in dissolving metal reductions (e.g., Birch reductions) involving alkali metals and primary amines. Additionally, glass is more suitable in cases where high heat or strong chemicals, like concentrated alkali solutions, could degrade PTFE.

Yes, glass can be attacked by strong alkali chemicals, such as lye, depending on factors like temperature, exposure time, and concentration. In such cases, careful consideration is required to ensure that the glass coating is appropriate for the application.