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The man behind the burner: Robert Bunsen's discoveries changed the world of chemistry in more ways than one.

Let's play a little word association. Chemistry! What comes to mind? Beakers? Formulas? Molecules? Maybe. But chances are that "Bunsen burner" rolled off many a tongue. There is probably no other piece of equipment as closely associated with chemistry as that ubiquitous little burner. Turn on the gas, adjust the air intake, and we're ready to simmer, stew, or boil. But what do we know of the man behind the burner?

Robert Bunsen was a professor of chemistry at Heidelberg University in Germany during the second half of the 19th century. He became interested in the study of arsenic compounds--an interest that would cost him dearly. Since arsenic derivatives are smelly and poisonous, Bunsen devised a face mask to protect himself from inhaling the nasty vapours.

The mask had a glass shield and a long breathing tube which snaked out the window for access to fresh air. Unfortunately, not only are arsenicals poisonous, but many arsenic compounds ignite and explode spontaneously in dry air. Bunsen discovered this the hard way. One of his samples exploded, shattering his mask and blinding him in one eye. Undaunted, he pursued his chemical investigations.

Bunsen was a stickler for detail and for quality work. One day he was analyzing a sample of an ore for its beryllium content and was filtering the final precipitate that he had produced after putting the ore through a series of chemical reactions. The weight of this precipitate would be the key to the analysis.

Much to his horror, Bunsen saw a fly land on his filter paper and take off with some of his precious powder clinging to its landing gear. A traumatic scream brought his students running. They quickly captured the fly and presented its corpse to the master who cremated it in a platinum crucible. From the remains, Bunsen isolated the beryllium oxide with which the fly had absconded. After weighing the recaptured booty, he was able to arrive at a correct analysis for the beryllium content of the original sample. But beryllium, like arsenic, was highly poisonous, so Bunsen decided to switch the focus of his work. He began to play with fire.

Why was Bunsen so interested in fire? Because laboratory workers had long been plagued by sooty, hard-to-control flames. Bunsen of course knew that oxygen was necessary for combustion and that soot was the product of incomplete combustion. He therefore concluded that the secret to a clean flame lay in mixing the combustible gas with air in just the right proportion.

The prototype Bunsen burner consisted of a metal tube with strategically drilled holes through which air could enter and mix with the combustible gas flowing through the tube. A sliding metal cover allowed the operator to vary the number of open holes and thus control the character of the flame. Bunsen, however, never patented his invention. He did not believe that scientists should profit financially from their work; research was to be done for its own sake.

But why was Bunsen so interested in developing a clean flame? Because he had a passion for studying the diverse brilliant colours produced by sprinkling various substances into a fire. He had noted that throwing sodium chloride (ordinary salt) into a flame always resulted in a bright orange-yellow glow. The same colour appeared if sodium bromide, or indeed any compound of sodium, was cast into the flame. Other elements also produced characteristic colours. In fact, Bunsen discovered the existence of the elements rubidium and cesium through the colours they produced.

Over a hundred years earlier, Newton had shown how a prism can be used to separate white light into the colours of the rainbow. Bunsen now applied this principle to separate the colours of a flame into their individual components. The spectroscope, an instrument he developed together with the physicist Kirchoff, allowed unknown substances to be identified purely by the colours they produced when heated in the flame of a Bunsen burner.

So, who cares what colours are produced in a flame? Well, just think of the glorious colours of fireworks. Or the bright red strontium flame of an emergency roadside flare. Or the yellow glow of a sodium vapour highway light. The original studies that led to these applications were painstakingly carried out by Robert Bunsen.

After having long toiled with flames and spectroscopes in the laboratory, the great man spent years writing up his work for publication. The day the manuscript was finished, he left it on his desk and went out to celebrate. When he returned, Bunsen was horrified to see a smoldering pile of ashes where his treasured treatise had been.

A flask filled with water had been next to the papers and had acted as a magnifying glass, focusing the sun's rays and igniting the manuscript. A lesser man would have surrendered to fate at this point. But Bunsen, even at an advanced age, doggedly repeated the work and eventually published the results of his spectroscopic research so that all the world finally became aware of his burner and how it led to the right chemistry.

Popular science writer, Joe Schwarcz, MCIC, is the director of McGill University's Office for Science and Society. He hosts the Dr. Joe Show every Sunday from 3:00 to 4:00 p.m. on Montreal's radio station CJAD and on CFRB in Toronto. The broadcast is available on the Web at
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Title Annotation:Chemfusion
Author:Schwarcz, Joe
Publication:Canadian Chemical News
Geographic Code:4EUGE
Date:Jan 1, 2005
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