A burette is a piece of laboratory equipment that is used to dispense small, precise volumes of liquid reagents. They are most commonly encountered in the process of titration where accurate measurements of liquid volumes are needed to determine the concentration of a reactant.
When used properly, a burette can be one of the most accurate pieces of lab glassware. However, it is important to understand how to read a burette before using it.
The reading from a burette is taken at the bottom of its curved surface, which is known as the meniscus. This is important to remember, because if you look at the reading from above or below the meniscus you will get an inaccurate reading. It is also important to keep your eye level with the meniscus to avoid parallax error, where you may think that you are reading a number higher or lower than it really is.
Before beginning a titration, ensure that the burette is rinsed and conditioned thoroughly. A dirty burette can give inaccurate readings, so it is crucial that it is thoroughly cleaned with a chemistry cleaning solution before each use. If the burette still has poor drainage after washing, it should be soaked in dichromate/sulfuric acid to ensure that it is free of any residue.
It is also recommended that a burette be read with a special card to improve its accuracy. This card contains a horizontal black strip, which should be held just under the meniscus so that the bottom of the meniscus is distinctly visible against a narrow zone of white behind it. This method is more repeatable than the alternative of looking at the last graduation on the scale, and will produce more accurate results.