The Bunsen burner is a simple piece of laboratory equipment that produces a single, continuous, open flame for heating, sterilization, and combustion in scientific settings. Invented in the mid-19th century, this burner is named after German chemist Robert Bunsen, who, along with his mechanic Peter Desaga, refined an existing design to create a more efficient and controllable heat source for his new laboratory in 1855. The device’s design allows for the controlled mixing of fuel gas and air before ignition, securing its ongoing role in chemistry and biology laboratories.
Anatomy of the Bunsen Burner
The burner’s function relies on the interaction of its physical components. The heavy base provides stability and prevents the burner from tipping over during use. A rubber tube connects the gas inlet, or hose barb, located at the base, to the laboratory’s gas source, delivering fuel, such as methane or propane. Above the base sits the vertical metal tube known as the barrel or chimney, which elevates the flame and serves as the chamber where gas and air initially mix. At the bottom of this barrel, small air intake holes allow ambient air to enter the gas stream. An adjustable collar surrounds these openings, and rotating this component controls the amount of oxygen that mixes with the gas before ignition. This pre-combustion mixing allows the Bunsen burner to produce a hotter, more controlled flame.
The Science of Flame Types
The Bunsen burner’s flame control is rooted in the ratio of fuel gas to oxygen, regulated by the adjustable collar. As gas rushes upward through a small jet inside the burner, it creates a low-pressure area that draws air in through the side air holes, a phenomenon known as the Venturi effect. This suction pulls oxygen into the barrel, ensuring the gas-air mixture is prepared for combustion at the top.
When the air holes are completely closed, the flame is tall, yellow, and luminous, often referred to as the safety flame. This yellow color results from incomplete combustion due to insufficient oxygen, producing tiny, glowing carbon particles. This leads to a cooler temperature and the formation of soot. The luminous flame is typically used only as a visible indicator that the burner is operating, since its low temperature is inefficient for most lab work.
By opening the air holes slightly, the flame becomes a non-luminous blue, indicating a more complete and hotter combustion. Further adjustment to a fully open air hole creates the hottest setting, sometimes called the roaring flame. This flame is characterized by a loud noise and a distinct small, inner light-blue cone within a larger, darker-blue outer cone. This efficient reaction maximizes the heat output, with the hottest part of the flame located just above the inner cone, making it ideal for rapid heating.
Safe Operation and Procedure
Before operating a Bunsen burner, a user must observe several safety protocols. These include clearing the workspace of flammable materials and ensuring long hair and loose clothing are tied back. The rubber tubing must be inspected for cracks and securely attached to the gas jet and the burner’s inlet.
The procedure for lighting begins by ensuring the air collar is closed to produce the visible, cooler yellow safety flame first. The main gas valve at the lab bench is then opened, followed by a slight opening of the gas control valve on the burner itself, until a faint hiss of gas is heard. A flint striker or long-reach lighter is used to ignite the gas at the top of the barrel. Once the yellow flame is established, the user slowly rotates the collar to increase the air intake until the desired blue heating flame is achieved.
If the flame ever goes out, or if the flame appears to be burning inside the barrel (a condition known as “flashback”), the gas supply must be turned off immediately at the bench valve. Flashback occurs when the gas flow is too low or the air intake is too high, causing the flame front to travel down the barrel. After use, the gas supply is shut off at the bench, and the burner is allowed to cool completely.