A hot flame has always been the star of the laboratory and has the power to attract chemists like moths. Burning from the spout of a bunsen burner, the flame could be used for heating, sterilising and last but not least, combustion. Though it has not always been easy for a laboratory to access a clean hot flame to conduct their work.
In the 19th century, heating was an issue for chemists. Although furnaces and charcoal burners were practical for calcinations, they were impractical for heating situations requiring delicate temperature control like distillation. There were oil-based heaters but were complicated to use and the soot from the flame blackened flasks which not only obscured visual observation of the chemical reaction but also reduced the amount of heat being transferred to the flask.
The best available option was a spirit lamp. This was a glass filled bottle filled with alcohol that tapered to a narrow neck that held a cotton wick. Pure ethanol burns with a sooty flame so water was added to reduce the soot but this meant a lower temperature being delivered to the flask. Ethanol prices varied according to location. It was cheap to come by in Germany and France but expensive in Britain. So what to do?
In 1852, Robert Bunsen was hired by the University of Heidelberg with the promise of a new laboratory building. Something exciting was happening in Heidelberg. Coal gas street lighting was being installed which allowed the new laboratory to also be supplied with gas. After all the laboratory needed heating and illumination. Chemists were still chasing a high temperature flame that was clear and low luminosity.
As coal gas became available for the purposes of illumination, chemists began to use it to heat their reactions. Humphry Davy and his assistant Michael Faraday worked on determining the combustion of hydrocarbons and concluded that the flame temperature was not an intrinsic property of the gas but rather dependent on the rate of combustion. This led to a solution of coal damp explosions in coal mines where a metal frame was used to shroud a flame preventing it igniting any gas in the mine while changing appearance as a response to changes in gas concentrations.
In 1856, Robert Bunsen as a newly appointed professor at the University of Heidelberg asked the university’s instrument maker to build a burner. It was a simple design which allowed gas to flow from a small jet at the base of a chimney drawing air from a series of holes surrounding it. The result was a burner that produced a very hot non-luminous flame. The Bunsen Burner was born. Only 25 years earlier did Michael Faraday suggest a similar device that consisted of a metal tube with a movable conical chimney at the top. The higher this cone went, the better mixing of gas and air which led to a hotter and less luminous flame.For reasons unknown, this idea was not popular but the bunsen burner caught on as an idea and is now a permanent fixture in most laboratories from chemistry to physics and biology.
The bunsen burner enabled the foundations of spectroscopy research. The clear flame allowed that the colour light from flame tests to be analysed using a prism, something taken for granted with today’s technology and equipment. Despite the many advances in technology and equipment, the Bunsen burner is still one of the most convenient heat sources in laboratories.