Author Sam Kean recalls breaking a thermometer as a child. His mother corrals the spilled mercury droplets, pushing them together with a toothpick until they form one shimmery liquid ball, then deposits the ball into an old pill bottle. Kean has taken an interest in mercury, and all the elements, ever since.

Kean learns that the Lewis and Clark Expedition carried mercury pills to treat constipation. Today, archaeologists can locate many of the Expedition’s campsites: “mercury deposits dot the soil many places where the gang dug a latrine” (5). The mercury pills came from Dr. Benjamin Rush, a signer of the Declaration of Independence and doctor during the 1793 Philadelphia yellow fever epidemic, where his mercury treatments “no doubt poisoned or outright killed swaths of people whom yellow fever might have spared” (5).

Kean learns in science class that “the symbol for mercury, Hg, consists of two letters that don’t even appear in its name” but instead derive from the Latin hydragyrum, “water silver” (6). He discovers that the Mad Hatter of Alice in Wonderland probably had been poisoned from his use of mercury in the hat-making process. He also realizes that Dr. Rush’s mercury laxatives worked because “the body will rid itself of any poison, mercury included” (6).