A burette (also buret) is a vertical cylindrical piece of laboratory glassware with a volumetric graduation etched permanently on its full length and a precision tap, or stopcock with plug and bore, on the bottom. The commonly used stopcocks can be a ground-glass barrel or a plastic plug made of PTFE, depending on the liquid to be carried. It is used to dispense known amounts of a liquid reagent in experiments for which such precision is necessary, such as in a volumetric analysis. Burettes are extremely accurate, and have very small accuracy tolerances.
|Burette accuracy tolerances|
|Capacity, mL||Subdivision, mL||Class A and precision grade accuracy, ±mL||Class B and standard grade accuracy, ±mL|
Burettes measure from the top since they are used to measure liquids dispensed out the bottom. The difference between starting and final volume is the amount dispensed. Burettes are used primarily for titration, to deliver one reactant until the precise end point of the reaction is reached.