Selecting a Burette on Amazon.com
A burette, also known as a buret or volumetric burette, is a long, graduated tube with narrow tip and a tap on the end for precise dispensing of liquid. It has a valve, known as a stopcock, for dispensing portions of a known volume at a desired rate, whereas a pipette delivers a known volume all at once. Capacity is most often measured in milliliters (mL), with 5mL to 100mL being the range of most common volumes. Many burettes can deliver volumes to the nearest 0.01mL. Since a burette is held vertically to deliver liquid from the bottom, it is calibrated to be read from the top down. The amount of liquid dispensed is the difference between the starting and the final volume. Because of its accuracy, a burette is often used for titration to add measured amounts of one substance to another until the reaction between them is complete.
Burettes are made of glass or plastic, particularly acrylic plastic, to provide optical clarity for observing the volume. Some glass burettes are manufactured to meet ASTM E287 standard specification for laboratory glass graduated burettes. This standard establishes specifications for construction and accuracy, designating Class A as precision grade and Class B as general purpose. A Class A burette meets tighter dimensional tolerance requirements. Because of its resistance to chemicals and solvents, PTFE (polytetrafluoroethylene) is the most common material for the stopcock.
Specialized types of burette include a Schellbach burette, which has a colored, vertical ribbon that clearly defines the position of the meniscus for accurate readings, and a piston or bottle-top burette, which is a syringe-like device that is usually electronic and has a digital readout to control dispensing. A burette clamp is designed to hold a burette and secure it to a laboratory stand, so that it can be suspended over a flask or other container. Burettes are commonly used in laboratory experiments and research applications.