The Bunsen burner is a foundational piece of laboratory apparatus, designed to safely produce a single open gas flame for scientific work. It was developed in 1855 by German chemist Robert Bunsen and his mechanic, Peter Desaga, to provide a clean and adjustable heat source for experiments. This device operates by mixing a flammable gas, such as natural gas or propane, with air in a controlled manner before ignition. The primary function of the burner is to provide heat for various laboratory processes, including heating substances, sterilization, and combustion studies.
Anatomy and Function of the Components
The Bunsen burner’s design is simple yet highly effective, built around interconnected components that regulate gas and air flow. The heavy base provides a stable foundation for the burner on the laboratory bench, preventing it from tipping over during use. A gas inlet, typically a small metal tube or hose barb, extends from the base, allowing the burner to be connected to the laboratory gas supply via flexible rubber tubing.
Resting vertically atop the base is the barrel, or chimney, a metal tube where the incoming gas and air are mixed. Near the bottom of the barrel are small openings, known as air holes, which allow atmospheric air to be drawn into the tube. The amount of air entering these holes is regulated by a moveable collar, a cylindrical ring that can be twisted to open or close the air vents. Controlling the ratio of gas to air determines the flame’s characteristics and temperature.
Understanding the Different Flame Types
The appearance and temperature of the flame depend directly on the amount of oxygen supplied through the air holes. When the collar fully closes the air holes, the flame produced is luminous, appearing yellow or orange in color. This color results from incomplete combustion, where insufficient oxygen causes the gas to burn poorly, creating glowing carbon particles. The luminous flame is relatively cool, reaching temperatures around 300 degrees Celsius, and is rarely used for heating because it deposits soot, or unburned carbon, onto objects.
When the air holes are fully or partially opened, the flame becomes non-luminous, appearing blue and transparent. This blue color signifies complete combustion, as a sufficient supply of oxygen ensures the fuel is fully oxidized. The non-luminous flame is significantly hotter and more stable, making it the standard for heating substances in the laboratory. This flame has distinct temperature zones, with the highest temperature, reaching approximately 1,500 degrees Celsius, located just above the tip of the pale blue inner cone.
Safe Lighting and Adjustment Procedures
The safe operation of a Bunsen burner begins with proper preparation of the workspace and the user. Long hair and loose clothing must be secured, and all combustible materials cleared from the immediate area. Before turning on the gas, the rubber tubing connecting the burner to the gas valve must be inspected for cracks or leaks and fitted securely onto the inlet and the gas source.
To light the burner, the air collar should be initially adjusted to mostly close the air holes, ensuring a visible, cooler flame upon ignition. A striker or long-nozzle lighter should be held slightly above the barrel’s opening before the gas is turned on at the source. Once the gas valve is opened, the gas must be ignited immediately with the sparker; if left on too long without ignition, it can accumulate, creating a hazard.
The initial yellow flame is then adjusted to the desired heating flame by slowly rotating the collar to introduce more air. As the air holes open, the flame transitions from yellow to a quieter, hotter blue flame with a distinct inner cone. The gas valve at the source or the burner’s needle valve can be used to control the height and intensity of the flame, ensuring it is appropriate for the task. A lit burner should never be left unattended. After use, the gas supply must be shut off at the source valve first, allowing the burner to cool before handling or storage.
Primary Laboratory Applications
The Bunsen burner’s primary role is to act as an adjustable heat source for various chemical and biological processes. Heating substances is its most common application, whether it involves boiling liquids in beakers, heating solids in crucibles, or warming solutions in test tubes. The ability to control the flame temperature is useful for experiments that require precise thermal conditions.
In microbiology, the burner is frequently used for sterilization, creating a sterile field by flaming the mouths of culture tubes or sterilizing inoculation loops before transferring microbial cultures. The upward flow of hot air created by the flame also helps maintain an uncontaminated work zone. Additionally, the burner is used in analytical chemistry procedures like flame tests, where the characteristic color produced by heating metal ions helps to identify their presence in a sample.