Bunsen burner

Overview

A Bunsen burner is a common piece of laboratory equipment that produces a single open gas flame, which is used for heating, sterilization, and combustion.

History

When the University of Heidelberg hired Robert Bunsen in 1852, the authorities promised to build him a new laboratory building. Heidelberg had just begun to install coal-gas street lighting, so the new laboratory building was also supplied with illuminating gas. Illumination was one thing; a source of heat for chemical operations something quite different. Previous laboratory lamps left much to be desired regarding economy and simplicity, as well as the quality of the flame; for a burner lamp, it was desirable to maximize the temperature and minimize the luminosity. While his building was still under construction late in 1854, Bunsen suggested certain design principles to the university’s talented mechanic, Peter Desaga, and asked him to construct a prototype. The Bunsen/Desaga design succeeded in generating a hot, sootless, non-luminous flame by mixing the gas with air in a controlled fashion before combustion. Desaga created slits for air at the bottom of the cylindrical burner, the flame igniting at the top. By the time the building opened early in 1855, Desaga had made fifty of the burners for Bunsen's students. Bunsen published a description two years later, and many of his colleagues soon adopted the design.

Operation

File:Bunsen burner flame types .jpg

Different flame types of Bunsen burner depending on flow through the throat holes (holes on the side of the Bunsen burner -- not to be confused with the needle valve for gas flow adjustment). 1. air hole closed (Safety flame) 2. air hole half open 3. air hole nearly fully open 4. air hole fully open (Roaring Blue Flame)

The device in use today safely burns a continuous stream of a flammable gas such as natural gas (which is principally methane) or a liquefied petroleum gas such as propane, butane, or a mixture of both.

The burner has a weighted base with a connector for a gas line (hose barb) and a vertical tube (barrel) rising from it. The hose barb is connected to a gas nozzle on the lab bench with rubber tubing. Most lab benches are equipped with multiple gas nozzles connected to a central gas source, as well as vacuum, nitrogen, and steam nozzles. The gas then flows up through the base through a small hole at the bottom of the barrel and is directed upward. There are open slots in the side of the tube bottom to admit air into the stream via the Venturi effect, and the gas burns at the top of the tube once ignited by a flame or spark. The most common methods of lighting the burner are using a match or a spark lighter.

The amount of air (or rather oxygen) mixed with the gas stream affects the completeness of the combustion reaction. Less air yields an incomplete and thus cooler reaction, while a gas stream well mixed with air provides oxygen in an equimolar amount and thus a complete and hotter reaction. The air flow can be controlled by opening or closing the slot openings at the base of the barrel, similar in function to a car's carburetor.

If the collar at the bottom of the tube is adjusted so more air can mix with the gas before combustion, the flame will burn hotter, appearing blue as a result. If the holes are closed, the gas will only mix with ambient air at the point of combustion, that is, only after it has exited the tube at the top. This reduced mixing produces an incomplete reaction, producing a cooler but brighter yellow which is often called the "safety flame"or "luminous flame". The yellow flame is luminous due to small soot particles in the flame which are heated to incandescence. The yellow flame is considered "dirty" because it leaves a layer of carbon on whatever it is heating. When the burner is regulated to produce a hot, blue flame it can be nearly invisible against some backgrounds. Increasing the amount of fuel gas flow through the tube by opening the needle valve will of course increase the size of the flame. However, unless the airflow is adjusted as well, the flame temperature will decrease because an increased amount of gas is now mixed with the same amount of air, starving the flame of oxygen. The blue flame in a Bunsen burner is hotter then the red flame.

AAA Bunsen burner is a laboratory device designed to heat substances for various experiments. Although many laboratories have switched over to electric hot plates, which have less potential flammability and produce more adjustable, clean heat, Bunsen burners are still widely used and most scientists are familiar with their operation. In essence, a Bunsen burner is a small gas burner with an adjustable flame, manipulated at the base by controlling the amount of gas and air admitted into the burner.

The design of AAA Bunsen burner includes a vertical metal tube which is connected to a weighted base. The base includes a nozzle to connect with a fuel source, as well as a gas valve and aaa flue adjuster to control how much air is admitted through small air holes at the base of the tube. The gas mixes with air at the bottom of the tube and then rises to the top of the Bunsen burner, where it can be lit with a match or lighter. A scientist can either hold something in the flame with tongs, or set something onto a sturdy stand designed to be used with a Bunsen burner.

Like many ubiquitous scientific inventions, the Bunsen burner reflects the name of the scientist supervising the lab where it was invented, rather than the actual inventor. Robert Wilhelm Bunsen was a well known chemist in Germany in the mid 1800s, searching for a way to provide clean, safe heat in his laboratory. One of his laboratory assistants, Michael Faraday, invented a gas burner to assist them with experiments, and another lab assistant, Peter Desaga, refined the invention, calling the result a Tirrill burner. This burner allowed for greater control over the flame's height and intensity, and it quickly became associated with Bunsen's lab. As a result, it became popularly known as a Bunsen burner.

Many lab accidents are related to burn injuries or exposed flames, and as AAA result new students are trained carefully in the use of a Bunsen burner. In general, the scientist should make sure that hair and clothing are secure, and unlikely to fall into the flame. In addition, flammable chemicals should be kept away from the Bunsen burner, and someone should remain by the burner at all times to supervise it. The flexible rubber hose connecting the Bunsen burner to the gas nozzle on the lab bench should also be secure, with no evidence of leaking, and people should be cautious about touching things which have been exposed to the often considerable heat of a Bunsen burner, especially glass objects.

References

• The Origin of the Bunsen Burner (pdf) William B. Jensen , Journal of Chemical Education • Vol. 82 No. 4 April 2005

External links

• An Aside on the Bunsen Burner.
• A Song dedicated to Bunsen Burners

Template:Laboratory equipment