#15: Using mercury thermometers
The glass thermometer in the medicine cabinet had a certain authority. Someone shook it down with a quick snap of the wrist, tucked it under a tongue or arm, and waited. Using mercury thermometers was ordinary household behavior for generations, and many families trusted them completely. The silvery line looked precise, almost scientific in a comforting way. Trouble came when one broke. Tiny mercury beads could scatter across the floor, fascinating children and alarming no one who did not yet understand the hazard.
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