Before the era of spectrophotometers, chemists used color in their research. With their eyes and with equipment like this colorimeter, chemists could crudely identify substances and measure their concentration by comparing the color of a reference sample with that of an unknown. The method was simple but imprecise and subjective. With the eye as a “detector,” colorimetry relied on individual perceptions of hue, saturation, and brightness.
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Merck litmus paper, 1934
©2010 Chemical Heritage Foundation