By Sam Kean

For a long time, I kept an eye out for the element Mercury (#80) at school and in books, as you might watch for a childhood friend’s name in the newspaper.

I’m from the Great Plains and had learned in history class that Lewis and Clark had trekked through South Dakota and the rest of the Louisiana Territory with a microscope, compasses, sextants, three mercury thermometers, and other instruments. They also carried with them six hundred mercury laxatives, each four times the size of an aspirin.

The laxatives were called Dr. Rush’s Bilious Pills, after Benjamin Rush, a signer of the Declaration of Independence and a medical hero for bravely staying in Philadelphia during a yellow fever epidemic in 1793. His pet treatment, for any disease, was a mercury-chloride sludge administered orally. Despite the progress medicine made overall between 1400 and 1800, doctors in that era remained closer to medicine men than medical men. With a sort of sympathetic magic, they figured that beautiful, alluring mercury could cure patients by bringing them to an ugly crisis — poison fighting poison.

Dr. Rush made patients ingest the solution until they drooled, and often people’s teeth and hair fell out after weeks or months of continuous treatment. His “cure” no doubt poisoned or outright killed swaths of people whom yellow fever might have spared. Even so, having perfected his treatment in Philadelphia, ten years later he sent Meriwether and William off with some prepackaged samples. As a handy side effect, Dr. Rush’s pills have enabled modern archaeologists to track down campsites used by the explorers. With the weird food and questionable water they encountered in the wild, someone in their party was always queasy, and to this day, mercury deposits dot the soil many places where the gang dug a latrine, perhaps after one of Dr. Rush’s “Thunderclappers” had worked a little too well.