March 31st was National Bunsen Burner Day. Bunsen (1811-1899) should be remembered. After all, the “Bunsen Burner” is a typical symbol of chemistry. But there is more to Bunsen than just a burner.
Laboratory workers had long been plagued by sooty, hard-to-control flames and 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. Why was Bunsen so interested in developing a clean flame? Because he had a passion for studying the diverse brilliant colors 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 color appeared if sodium bromide, or indeed any compound of sodium was cast into the flame. Other elements also produced characteristic colors. In fact Bunsen discovered the existence of the elements rubidium and cesium through the colors they produced.
Over a hundred years earlier, Newton had shown how a prism can be used to separate white light into the colors of the rainbow. Bunsen now applied this principle to separate the colors 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 colors they produced when heated in the flame of a Bunsen burner.
So, who cares what colors are produced in a flame? Well, just think of the glorious colors of fireworks. Or the bright red strontium flame of an emergency roadside flare. Or the yellow glow of a sodium vapor 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, focussing 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.
