A burette is a graduated glass tube with a tap at one end, for delivering known volumes of a liquid, especially in titrations. It is a long, graduated glass tube, with a stopcock at its lower end and a tapered capillary tube at the stopcock's outlet. The flow of liquid from the tube to the burette tip is controlled by the stopcock valve. There are two main types of burette; the volumetric burette and the piston burette. A

volumetric Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...

burette delivers measured volumes of liquid. Piston burettes are similar to

syringe A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...

s, but with a precision bore and a plunger. Piston burettes may be manually operated or may be motorized. A

weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a Euclidean vector, vector quantity, the gravitational force acting on the object. Others define weigh ...

burette delivers measured weights of a liquid.

Overview

A burette is a volumetric measuring glassware which is used in

analytical chemistry Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...

for the accurate dispensing of a liquid, especially of one of the reagents in a titration. The burette tube carries graduated marks from which the dispensed volume of the liquid can be determined. Compared to a

volumetric pipette A volumetric pipette, bulb pipette, or belly pipette allows extremely accurate measurement (to four significant figures) of the volume of a solution. It is calibrated to deliver accurately a fixed volume of liquid. These pipettes have a large bu ...

, a burette has similar precision if used to its full capacity, but as it is usually used to deliver less than its full capacity, a burette is slightly less precise than a pipette. The burette is used to measure the volume of a dispensed substance, but is different from a

measuring cylinder A graduated cylinder, also known as a measuring cylinder or mixing cylinder, is a common piece of laboratory equipment used to measure the volume of a liquid. It has a narrow cylindrical shape. Each marked line on the graduated cylinder represent ...

as its graduations measure from top to bottom. Therefore, the difference between the starting and the final volume is equal to the amount dispensed. The precision and control of the burette over other means of adding solution is beneficial for use in

titration Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant'' ...

Volumetric burette

A volumetric burette can be made of glass or plastic, and is a straight tube with a

graduation Graduation is the awarding of a diploma to a student by an educational institution. It may also refer to the ceremony that is associated with it. The date of the graduation ceremony is often called graduation day. The graduation ceremony is a ...

scale. At the tip of burette, there are a stopcock and valve to control the flow of the chemical solution. The barrel of the stopcock can be made of

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...

or the plastic PTFE. Stopcocks with glass barrels need to be lubricated with vaseline or a specialized grease. Burettes are manufactured for specific tolerances, designated as class A or B and this also is etched on the glass. Black_strip_2

Burette reading

In order to measure the amount of solution added in or drained out, the burette must be observed at eye level straight to the bottom of the

meniscus Meniscus may refer to: *Meniscus (anatomy), crescent-shaped fibrocartilaginous structure that partly divides a joint cavity *Meniscus (liquid) The meniscus (plural: ''menisci'', from the Greek for "crescent") is the curve in the upper surface ...

. The liquid in the burette should be completely free of bubbles to ensure accurate measurements. The difference in volume can be calculated by taking the difference of the final and initial recorded volume. Using the burette with a colorless solution may make it difficult to observe the bottom of the meniscus, so the black strip technique can make it easier to accurately observe and record measurements.

Specification

The specification of a volumetric burette indicates its properties, such as the nominal volume, volume unit, error limit, and accuracy class, plus other related details from the manufacturer. The nominal volume and error limit is usually given in units of mL or cm³. Another specification commonly found on burettes is the calibration mark "TD" or "Ex". This stands for "calibrated to deliver", indicating that the printed volume is accurate when the burette is used to deliver (rather than contain) a solution. Another commonly indicated specification is the accuracy class, including class A and class B. Class A is preferred to Class B when volumetric accuracy is important, as it has a narrower range of error with accuracy up to 0.1 percent compared to 0.2 percent in Class B burette. Specification of burette

Digital burette

Digital burettes are based on a

design. The barrel and plunger may be made of glass. With liquids that corrode glass, including solutions of

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

, the barrel and plunger may be made of

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...

or another resistant plastic material. The barrel is held in a fixed position and the plunger is moved incrementally either by turning wheel by hand, or by means of a step motor. The volume is shown on a digital display. A high-precision syringe may be used to deliver very precise aliquots. Motorized digital burettes may be controlled by a computer; for example, a titration may be recorded digitally and then subject to numerical processing to find the titer at an end-point.

History

The first burette was invented in 1845 by the French chemist

Étienne Ossian Henry Étienne-Ossian Henry (27 November 1798 in Paris – 26 August 1873) was a French chemist, son of Nöel Étienne Henry (1769–1832), and trained by his father, who was director of the Central Pharmacy of the Parisian hospitals and professor ...

(1798–1873). In 1855, the German chemist

Karl Friedrich Mohr Karl Friedrich Mohr (November 4, 1806 – September 28, 1879) was a German chemist famous for his early statement of the principle of the conservation of energy. Ammonium iron(II) sulfate, (NH4)2Fe(SO4)2.6H2O, is named Mohr's salt after him. Lif ...

(1806–1879) presented an improved version of Henry's burette, having graduations inscribed on the tube of the burette. The word "burette" was coined in 1824 by the French chemist

Joseph Louis Gay-Lussac Joseph Louis Gay-Lussac (, , ; 6 December 1778 – 9 May 1850) was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen (with Alexander von Humboldt), for two laws ...

(1778–1850). On p. 171, Gay-Lussac describes various figures that appear in a plate (illustration) that accompanies the article. From p. 171: ''" ''I'', burette destinée à mesurer la teinture d'épreuve: … "'' (''I'', burette intended to measure the test dye: … )

Additional images

File:Meniscus of water in burette.JPG, Meniscus File:Buret.png File:Stativ.svg File:Burette stand and burette .jpg, Burette with ring stand File:Stopcock .jpg, alt=plastic stopcock used in glass volumetric burette, Plastic stopcock used in glass volumetric burette

References

External links

Using a Burette
from ChemLab at Dartmouth College demonstrating how to use a burette correctly

{{Laboratory equipment, Glass Laboratory equipment Volumetric instruments French inventions