A Pasteur pipette is a type of eye dropper used in laboratory experiments. It was named after Louis Pasteur because he used them extensively in his research. Most pipettes are made cheaply from glass or plastic and are widely available. Typically, the main reason to use a Pasteur pipette is to transfer or remove small amounts of liquid from an experiment.
Louis Pasteur was a chemist who lived in the middle of the 19th century. After three of his children died of typhoid before reaching adulthood, Pasteur began searching for treatments and cures of various diseases in both men and animals. To keep liquids from being contaminated during an experiment, Pasteur invented a pipette; notably, he went on to develop several vaccines for diseases such as anthrax, fowl cholera, and rabies.
The Pasteur pipette is a standard piece of laboratory equipment consisting of a thin glass or plastic tube, usually topped by a rubber bulb. It holds about one milliliter of liquid, although precise measurements cannot be made with it. Pipettes are not graduated, meaning a scale is needed for exact measurements. They allow for the transfer of liquids without contaminating the experiment, and they can also be used to withdraw gases from micro-scale distillations.
To use a Pasteur pipette, the experimenter must first squeeze the bulb and then insert the open end of the tube into the liquid. The liquid will be pulled into the pipette when the bulb is slowly released; squeezing the bulb a second time will force the liquid out. Some pipettes lack a bulb, substituting a piece of cotton. The pipette is inserted into the liquid and a piece of cotton is used to cover the other end. When the cotton is removed, the liquid will spill out, though the cotton can also be used to filter solids out of the liquid.
Plastic pipettes, on the other hand, are made of one piece of plastic molded into both the tube and bulb; this type of pipette is suited for biology, since they do not have to resist solvents. In addition, plastic pipettes are typically considered disposable because they are inexpensive and difficult to sterilize. Before reusing a Pasteur pipette, it must be cleaned by rinsing out the tube with water. Since the rubber bulb contains many different contaminates, it should never touch the solutions; therefore, the bulb should not need cleaning. Pipettes are very inexpensive, so many scientists would rather dispose of a pipette instead of cleaning it.