Gustav Kirchhoff

Atomic Spectra (Gustav Kirchhoff)

For more than 200 years chemists have known that sodium salts produce a yellow color when added to a flame. Robert Bunsen, however, was the first to systematically study this phenomenon. (Bunsen went so far as to design a new burner that would produce a colorless flame for this work.) Between 1855 and 1860, Bunsen and his colleague Gustav Kirchhoff developed a spectroscope that focused the light from the burner flame onto a prism that separated this light into its spectrum. Using this device, Bunsen and Kirchhoff were able to show that the emission spectrum of sodium salts consists of two narrow bands of radiation in the yellow portion of the spectrum.

Kirchhoff noticed that the wavelength of the light given off when sodium salts were added to a flame was the same as the wavelength of the D line in Fraunhofer's spectrum of sunlight. He therefore concluded that absorption and emission spectra were related. Certain substances give off light when heated that has the same frequencies and wavelengths as the light they absorb under other conditions.