A buret (or burette) is a piece of volumetric glassware (some are plastic) for delivering precise amounts of fluid. A buret can be very precise; Class A and Class B burets have the following tolerances:
Capacity ml subdivisions, ml Class A accuracy ml Class B Accuracy, ml
10 0.05 0.02 0.04
25 0.10 0.03 0.06
50 0.10 0.05 0.10
100 0.20 0.10 0.20
Burets can have either PTFE or glass stopcocks. Some burets are self filling and have a reservoir so the operator does not have to keep filling with a funnel. Some have a 2 way stopcock so that they can be filled from a separate reservoir. Some are self zeroing as well so the operator does not have to spend time zeroing the buret. Serialized Class A burets are available with serial number and come with a certificate describing the accuracy of that particular buret.
Burets are mainly used in titrations involving determination of the concentration of a species by a well understood reaction. Known amounts of reagent are delivered until an endpoint in the reaction is reached. The volume of reagent required to reach this endpoint is directly related tot he concentration of an analyte. One example of this is the Karl Fischer reaction for determination of trace amounts of water. For an explanation of the technique for using a buret in a titration please see Use of A Buret