buret

A buret, also spelled burette in some variants, is a long, graduated glass tube with a valve or stopcock at its bottom. It is designed to measure and dispense precise volumes of liquid, most commonly for titrations in analytical chemistry. Common sizes include 50 mL and 100 mL; the glass is typically borosilicate to resist chemical attack, and the stopcock is often made of PTFE or similar materials to provide smooth control of flow.

The tube is graduated along its length. Readings are taken from the bottom of the liquid's meniscus, with zero at the top of the scale. Divisions are typically 0.1 mL, and readings are estimated to the nearest 0.01 mL. The buret is mounted vertically in a stand with a filling neck at the top and a spout at the bottom to deliver the liquid.

To use a buret, fill it with the solution to be delivered above the zero mark, ensure the stopcock is closed, and remove any air bubbles from the jet. Record the initial volume, then slowly open the stopcock to deliver the liquid, and record the final volume when the desired amount has been dispensed. The delivered volume is the difference between final and initial readings. In titrations, the endpoint is determined by an indicator or instrumental method.

Accuracy and care are important: calibration is affected by temperature, so volumes are specified at a standard temperature. Cleanliness is essential; after use, rinse with appropriate solvents and store dry. Leakage, cracks, or scratches can introduce error. Burets are essential laboratory tools for quantitative analysis and standardization.