Bunsen lighter

A burner or Bunsen burner is an instrument used in scientific laboratories to heat, sterilize or combust samples or chemical reagents.

It was invented by Robert Bunsen in 1857 and provides a very rapid transmission of intense heat in the laboratory. It is a burner of natural gas or liquefied gases from petroleum (normally propane, butane or a mixture of both), the flame being the product of the combustion of an adjustable mixture of air with one of these gases.

History

In 1852 the University of Heidelberg hired Bunsen and offered to assign him a new laboratory building. The city of Heidelberg had begun installing public lighting using gas streetlights, so the university was able to supply the new laboratory with a gas supply.

The building designers anticipated the use of gas not only for lighting, but also installed burners for laboratory operations. In laboratory burners it was desirable to maximize temperature and minimize luminosity. However, the laboratory burners existing at that time left much to be desired, both in terms of flame heat and their economy and simplicity.

While the building was under construction in late 1854, Bunsen suggested certain design principles to the university mechanic, Peter Desaga, whom he asked to build a prototype of a lighter. The Bunsen/Desaga design was very efficient in generating heat, reducing the soot generated and obtaining a non-luminous flame by mixing gas with air in a controlled manner before combustion. Desaga devised adjustable air slots at the bottom of the cylindrical burner, with the ignition flame at the top. By the time the building opened in early 1855, Desaga had built fifty of these burners for Bunsen's students. Two years later he published a description of the Bunsen burner, and many of his colleagues soon adopted this design.

Gustav Kirchhoff and Robert Bunsen built a spectroscope around 1860 for the analysis of light patterns generated by heating various substances with their burner, a procedure that made it possible to discover cesium (1860), rubidium (1861) in a very short time., thallium (1861) and indium (1863).

Similar principles had previously been used by Michael Faraday in the design of a burner, as well as in a device patented in 1856 by gas engineer R.W. Elsner, but they did not obtain the diffusion of the Bunsen/Desaga design.

Bunsen burners continue to be used today in laboratories around the world. However, the development of more modern laboratory instruments has relegated the Bunsen burner to the role of an auxiliary means, although it still has a great presence in laboratory practices. laboratory of many academic disciplines, where it is used in the basic training of students from numerous faculties and staff from all types of laboratories.

It is still used especially to facilitate the bending of laboratory glass and eventually to heat liquids (although other types of burners or electric heaters are usually more suitable). For spectrography tests, it has been systematically replaced by automatic analytical devices, which are much more precise as they do not depend on the manual adjustment of the starting conditions of the test to be carried out, nor on the interpretation made by a laboratory technician of the readings obtained.

Team assembly

• With the help of a hose connect the end at the gas output and the other end at the front of the lighter.(Check the correct connection)
• Verify that the key to the lighter is closed.
• Switch with the help of a phosphorus or phosphorera, open the keys for a long time until you have a yellow flame.
• Adjust the air inlet through the holes by turning that inlet until the flame becomes blue.

Description

The burner has a heavy base into which the gas supply is introduced. From there starts a vertical tube through which the gas flows through a small hole at the bottom of the tube. Some perforations on the sides of the tube allow air to enter the gas flow (thanks to the Venturi effect), providing a flammable mixture at the outlet of the gases at the top of the tube where combustion occurs, very effective for chemistry. advanced.

The Bunsen burner is one of the simplest heat sources in the laboratory and is used to obtain temperatures that are not too high (up to a maximum of around 1500 °C). It consists of a gas inlet (controlled by a needle valve, or without a regulator in the simplest models), an air inlet and a combustion tube. The combustion tube is screwed to a base through which the fuel gas enters through a rubber tube, with a stopcock that allows the gas flow to be opened or closed. It has two adjustable holes to regulate the air intake.

The amount of gas and therefore heat from the flame can be controlled by adjusting the size of the hole at the base of the tube. If more air is allowed to pass through to mix with the gas, the flame burns at a higher temperature (appearing blue). If the side holes are closed, the gas only mixes with atmospheric oxygen at the upper point of combustion, burning less efficiently and producing a flame with a colder temperature and a reddish or yellowish color, which is called "safe flame" #3. 4; or "luminous flame". This flame is luminous due to small incandescent soot particles. The yellow flame is considered "dirty" because it leaves a layer of carbon on the surface you are heating. When the burner is adjusted to produce high temperature flames, the bluish flames may become invisible against a uniform background.

If the gas flow through the tube is increased by opening the needle valve, the size of the flame will grow. However, unless the air intake is also adjusted, the flame temperature will drop because the increased amount of gas mixes with the same amount of air, leaving the flame low in oxygen. The blue flame on a Bunsen burner is hotter than the yellow flame.

The most common way to light the lighter is by using a match or a spark lighter.

Analysis of substances using the Bunsen burner flame

The different physicochemical properties of the characteristic regions of the Bunsen burner flame allow a series of tests to be carried out for the identification of various chemical or mineral substances. To do this, a tiny platinum ring attached to a wire of the same material (attached in turn to a glass rod) is usually used, which serves to place the pulverized samples (either directly or attached to a small pearl). of moistened borax salts that are previously formed by fusion at one end of the wire, a procedure called vitreous flow), at the desired point of the flame, being then able to study:

• Fussibility.
• Power to color the flame.
• Volatility.
• Behavior to oxidation and reduction.

In all these reactions the non-luminous gas flame is used. The gas usually contains small proportions of CO₂, O₂ and N₂; The rest are reducing substances, that is, they combine with oxygen during the combustion reaction. The luminosity of the flame is usually due to the presence in the gas of small traces of unsaturated hydrocarbons (such as ethylene, propylene or acetylene), which when heated decompose into methane and free carbon, which is the material that produces incandescence. the luminosity of the flame. When air is supplied to the gas in the appropriate proportion before burning, the flame tends not to be luminous.

The flame presents a series of characteristic regions, with different specific properties in each case:
Parts of the flame:

• I) The inner cone of the flame: There is no combustion, having a temperature too low; it contains gas without burning, with approximately 62% air.
• II) Flame cuff: formed by gas in combustion and air.
• III) Bright tip: appears when the air holes are partially closed.

At the same time, a series of specific points with specific properties are located:
Reaction zones:

• (1) Flame base: its temperature is relatively low, being in contact with outside air currents. It is used to investigate the presence of volatile substances that can color the flame, detecting in this area those that are volatile with lower temperatures.
• (2) Fusion zone: is the highest temperature zone, and is located just over a third of the height of the flame and in the center of the manguito (item II). It serves to investigate substances regarding their fussibility and volatility.
• (3) Lower oxidant zone: located on the outer limit of the Merge zone, is used for oxidation of dissolved substances in vitreous flow.
• (4) Lower reduction zone: located on the outer limit of the Area II; it presents a moderate reduction power, being used for reductions on charcoal or with a vivid flow.
• (5) Upper reducer flame: is the luminous tip of the inner cone of the flame, and gradually decreases the air access. It does not contain free oxygen, being rich in carbon free incandescent, which allows us to use this area to reduce oxides in the form of incrustations.
• 6) Upper oxidant call: is the tip of the non-light zone of the flame, it acts more effectively when the air input holes are completely open and used for oxidation tests, to trigger volatile products, and for oxidant processes that do not require excessively high temperatures.

Tests

Fusibility

The flame of the lighter allows us to determine the approximate temperature range at which numerous substances melt. Although the maximum theoretical temperature of the flame is about 2300 °C, in practice the maximum combustion temperature under optimal conditions of natural gas with one and a half times its volume of air is 1820 °C, normally obtaining lower temperatures (of between 1500 and 1000 °C) conditioned by various losses, by the quality of the fuel gas and by the volume and humidity of the mixed air. To identify the effective temperatures of each zone of the flame, the light emitted by a platinum wire when it glows inside the flame is usually analyzed:

As a guideline, the following melting points can be used as a reference:

Color communicated to the flame

The presence of certain chemical elements produces in many cases a certain color of the flame in which the samples are introduced (fuchsia-red for lithium, yellowish for sodium, orange for calcium, green for copper sulfate, violet for arsenic or lead lilac). This is a very basic test, which allows you to quickly and easily distinguish some specific minerals from others of similar appearance with different chemical composition.

Volatility

Using a closed glass tube, it is possible to separate the volatile substances contained in a sample by vaporizing them first by subjecting the tube to the flame, and waiting for them to condense on the walls of the tube once removed from the fire.

Oxidation and reduction

There are numerous oxidation and reduction tests that can be carried out with the flame of a Bunsen burner:

• Through vivid flows or pearls.
• Reduction with charcoal bars.
• Reducing test tube
• Reduction in the upper flame to form metal or oxide deposits.
• Reduction in charcoal.

Spectrometry

The Bunsen burner was also widely used in spectrometry tests, being a relatively simple method to achieve the incandescence of certain materials by heating them, which allows analyzing the corresponding refraction patterns.

This system has been widely used as a quick and economical analysis method, which allowed:

• Rapid qualitative analysis of the metal components of a substance.
• Precipitated review
• Checking the purity of certain laboratory analytical reagents.
• Detect the presence of rare metals, present in minimal quantities.
• Sample analysis of minimum quantities available.
• Quality control of the products of metallurgical plants.

For all these purposes, a series of spectrographic devices (both laboratory and pocket-sized) were developed, capable of providing more or less detailed information about the spectral patterns of the incandescent light produced by the burner.

Gas lighters

They work by combustion of a mixture of a flammable gas with air. They have a hole in the base through which air enters to form the mixture with the fuel gas. The most commonly used gas is natural gas, which is mostly methane gas (more than 90%), and to a lesser extent ethane.

The most common gas-fed laboratory burners, which are similar in principle to Bunsen burners, but differ in appearance, adjustment and control, are:

• Tirril: the base of the lighter has a needle valve that allows the regulation of the gas inflow directly from the lighter, instead of the gas valve. The maximum temperature of the flame can reach 1560 °C.
• Teclu: The bottom of the tube is conical, with a wheel dented at the base of that cone. The gap between the wheel and the end of the tube, regulates the airflow, similar to that made by the air window of the Bunsen lighter.
• Meker (or Meker-Fisher): the lower part of the tube has more openings than the Bunsen displaying a greater perpendicular section, admitting more air and improving the mixture of air and gas. The tube is wider and at its top is covered by a hole cricket, which separates the flame into a smaller flame matrix with a common envelope to them. This prevents the reverse of the flame to the bottom of the tube, which is a risk for high air/gas proportions, limiting the maximum flow of air that can enter. It can reach flame temperatures between 1100 and 1200 °C when used properly. Additionally, the output of the flame is silent unlike the Bunsen or Teclu lighters.