Analytical and environmental chemists are used to thinking about parts per million, tossing around the abbreviation ppm like it was no big deal. To help his students comprehend what ppm really means and how challenging it can be to detect things at ppm levels or below, Scripps chemistry professor John R. Yates III uses this jar filled with 1 million tiny beads. One bead out of 1 million is black—1 ppm. Yates says no one has ever found the one black bead in the 25 years he’s had the jar. “I did look, and the search can drive you crazy,” he says.
Credit: John R. Yates III
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