Image shows color bars along a wall. Text reads Chemistry + Color. See rest of page for full description of chemical event.

Chemistry and Color

Sub-basement level

Chemistry and Color: Spectroscopy

In the late 1600s Isaac Newton concluded that because daylight could be separated into different colors using a prism and the colors could be recombined to make white light, colors must be part of light, rather than being generated by an illuminated object. Newton designed a simple spectroscope—a scientific instrument that separated light into colors and allowed measurement of the brightness (intensity) of each color. The spectroscope was refined in the 1800s by William Hyde Wollaston, who used lenses to focus light onto a prism, and Joseph von Fraunhofer, who used a diffraction grating instead of a prism. Both Wollaston and Fraunhofer observed that the spectrum of the sun had many dark areas superimposed on the rainbow of colors.

In the mid-1700s chemists observed that different substances gave different colors when heated in a flame. By the mid-1800s chemists recognized that certain chemical elements produced flames with characteristic colors, such as the colors on the wall along this corridor. Copper and boron produce green flames, while sodium and calcium produce bright yellow or yellow-orange. Robert Bunsen and Gustav Kirchhoff systematically studied flame colors from different elements, which led to flame tests by which constituent elements in a sample could be identified. The famous Bunsen burner was designed to produce a steady, colorless, soot-free flame for measuring the spectra of elements.

Even a tiny quantity of an element can color a flame, and elements can even be detected in outer space. For example, the dark lines Wollaston and Fraunhofer saw in the spectrum of the sun were found to be due to hydrogen, which absorbed light of several colors, blocking those colors in the solar spectrum. In the 1860s astronomers Margaret Huggins and William Huggins used spectroscopy to show that elements in outer space were identical to elements found here on earth.

Characteristic flame colors can do more than show which elements are present. A greater quantity of an element produces a more intense flame color. Measuring the intensity of color indicates how much of the element is present. On the eighth floor of this building is an instrumentation laboratory where students in courses such as Chemistry 327 and Chemistry 329 use an inductively-coupled plasma atomic emission spectrometer to analyze samples quantitatively. This type of analysis can determine very small quantities of substances and is often used to detect environmental pollutants.

Are you interested in spectroscopy? If so, consider building your own spectroscope from an old DVD. Directions are available at this link.