Jointly Robert Bunsen and Gustav Kirchhoff invented the spectroscope, which they used to identify spectra produced by sodium, lithium and potassium when
Jointly Robert Bunsen and Gustav Kirchhoff invented the spectroscope, which they used to identify spectra produced by sodium, lithium and potassium when they were heated to incandescence. This was possible only because previously with a lab assistant Bunsen had perfected a gas torch that did not emit interfering light. Their Bunsen burner has remained in use in laboratories since that time and is valued for its clean flame.
On today’s Burners, the hose barb typically connects via rubber tubing to a gas nozzle on the lab bench. The gas flows up through a small hole at the bottom of the barrel and is directed upward. Open slots in the side of the tube bottom admit air into the stream through the Venturi effect. Gas burns at the top of the tube once ignited by a flame or spark.
The amount of air mixed with the gas stream determines the completeness of the combustion. Less air causes an incomplete and thus cooler reaction, while a sufficiently airy mix provides a stoichiometric amount of oxygen and a complete and hotter reaction. The user controls the air flow by opening or closing slot openings at the base of the barrel.
Adjusting the collar at the bottom of the tube so more air mixes with the gas before combustion makes the flame burn hotter, appearing blue. Closing the holes allows the gas to only mix with ambient air at the point of combustion, after it has exited the tube at the top. The reduced mixing produces an incomplete reaction and a cooler yellow flame. The yellow flame is luminous because small soot particles in it are heated to incandescence. The yellow flame also leaves a layer of carbon soot on whatever it heats.
Opening the needle valve to increase the amount of gas flow through the tube makes the flame bigger. But unless the airflow is adjusted as well, the flame temperature drops because more gas now mixes with the same amount of air, starving the flame of oxygen.
Bunsen Burners are constructed differently depending on the type of gas supply. Some older Burners were set up for burning liquified petroleum gas (LPG), normally used for heating and cooking. The difference between LPG and natural gas burners is in the design of the jet. This is because LPG is delivered at a higher pressure than NG and it needs a different air-to-gas ratio for proper combustion: NG needs less oxygen than LPG.
There are other burners similar to the Bunsen Burner. Among the most widely used:
The lower part of the tube on a Teclu burner is conical, with a round screw nut
below its base. The gap, set by the distance between the nut and the end of the tube, regulates the air supply and functions like the open slots of the Bunsen Burner. The Teclu burner mixes air and fuel more effectively to yield higher flame temperatures (around 2,900°F) than the Bunsen Burner (around 2,000°F).
The lower part of the tube on a Meker burner has more openings with a larger total cross-section, letting in more air and better mixing the air and gas. The tube is wider and a wire grid covers its top. The grid divides the flame into an array of smaller flames with a common external envelope. It also prevents flashback to the bottom of the tube, a possibility at high air-to-fuel ratios. Flame temperatures can hit 2,200°F, and the flame also burns without noise, unlike Bunsen or Teclu burners.
Finally, the base of the Tirrill burner has a needle valve which regulates gas intake directly from the Burner, rather than from the gas source. Its flame can reach around 2,800°F.
The point to note about Bunsen and similar burners is that they allow adjustment of the amount of air that mixes with the gas. This lets the user tune the flame temperature as well as optimize conditions for complete combustion. In contrast, an ordinary gas stove doesn’t allow any adjustment of the air/fuel mix. The gas burner is set to always use the right air/gas mix to give complete combustion. And gas stove flames typically burn at around 3,560°F. But as with any flame, the exact temperature will depend on altitude (and thus oxygen content in the atmosphere).
Thus gas stoves can be used in a pinch for some types of lab heating tasks. One drawback is that cooking ingredients (especially salt) can contaminate the flame color, which may be important for certain kinds of tests.