Generally speaking, pipettes are divided into two kinds, one is the air displacement type; the other is the external piston type, often used as a special pipette, the application range is relatively narrow, and this type of pipette can be used to remove high viscosity samples. The so-called air displacement type is to press the piston, the air inside the lower end of the pipette out, and then when the piston is moved up, the pressure inside the lower end of the pipette is less than the external pressure, so that the liquid can be sucked up under the action of the external pressure. In short, the air goes out and the liquid comes in!