82 Atomic Light Signatures
tom of the day). Kirchhoff believed that this would let him find spikes in the radiation
coming from any burning gas.
However, the scheme did not work well. The flame he used to heat his gasses was too
bright and interfered with his observations.
Enter Robert Bunsen, the German-born chemist. In 1858, 47-year-old Bunsen had
been developing photochemistry—the study of light given off by burning elements. During
this work, Bunsen had invented a new kind of burner in which air and gas were mixed prior
to burning. This burner (which we still use and call a Bunsen burner) produced an extremely
hot (over 2700°F) flame that produced very little light.
Kirchhoff and Bunsen connected at the University of Heidelberg in 1859. Standing together, Kirchhoff barely reached Bunsen’s shoulder. The pair combined Kirchhoff’s prism
idea with Bunsen’s burner and spent six months to design and build the first spectrograph (a
device to burn chemical samples and use a prism to separate the light they produced into a
spectrum of individual frequencies).
They began to catalog the spectral lines (specific frequencies where each element radiated its light energy) of each known element and discovered that each and every element always produced the same “signature” set of spectral lines that uniquely identified the
presence of that element.
Armed with this discovery and their catalog of each element’s characteristic spectral
lines, Kirchhoff and Bunsen made the first complete chemical analysis of seawater and of
the sun—proving that hydrogen, helium, sodium, and half-a-dozen other trace elements
common on Earth existed in the sun’s atmosphere. This proved for the first time that Earth
was not chemically unique in the universe.
Kirchhoff and Bunsen had given science one of its most versatile and flexible analytical tools and had discovered a way to determine the composition of any star with the same
accuracy as we determine sulfuric acid, chlorine, or any other compound.
Fun Facts: Kirchhoff and Bunsen used their spectrograph to discover
two new elements: cesium in 1860 (they chose that name because cesium
means “sky blue,” the color of its spectrograph flame) and rubidium in
1861. This element has a bright red line in its spectrograph. Rubidium comes from the Latin word for red.
More to Explore
Clark, Donald. Encyclopedia of Great Inventors and Discoveries. London: Marshall
Cavendish Books, 1991.
Diagram Group. Facts on File Chemistry Handbook. New York: Facts on File, 2000.
Laidler, Keith. World of Physical Chemistry. New York: Oxford University Press, 1995.
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