2. Liquid mercury was regarded by ancient practitioners of medicine to possess great healing powers, but instead often just killed those who consumed or were exposed to the toxic metal.
Mercury is a naturally occurring element that, atypically for a metal, takes liquid form at room temperature. Dating its discovery to at least 1500 BCE, the substance has been used by almost every culture at some point throughout history ranging from Far-East Asia to the Americas. Despite the intense toxicity of mercury, capable of absorption through the human skin and lethal in cases of excessive or prolonged exposure, it was nonetheless used as part of longstanding medical treatments. Few of these treatments resulted in positive outcomes, with mercury poisoning highly lethal if not treated properly and swiftly.
Historically, ancient Chinese medicine believed the consumption of mercury had the power to prolong life, heal injuries, and maintain vitality; in fact, the consumption of mercury does almost precisely the converse. Most famously, the first emperor of China, Qin Shi Huang Di, is believed to have died after drinking a concoction made from mercury and powdered jade which resulted in liver failure and severe mercury poisoning precipitating a complete loss of brain function. Equally unhelpfully, Khumarawayh ibn Ahmad ibn Tulun, the second Tulunid ruler of Egypt (r. 884-896 CE), allegedly slept atop a basin filled with mercury to benefit from the presumed rejuvenative powers of the toxic substance.