This is a device formed by a metallic bar (called the agitation bar) which is normally covered by a plastic layer, and a sheet that has underneath it a rotatory magnet or a series of electromagnets arranged in a circular form to create a magnetic rotatory field. Commonly, the sheet has an arrangement of electric resistances that can heat some chemical solutions.
During the operation of a typical magnetic agitator, the agitator bar is moved inside a container such as to dissolve a substance in a liquid. The container must be placed on the sheet, so that the magnetic field influences the agitation bar and makes it rotate. This allows it to mix different substances at high speeds.