4. Liquid mercury was believed by ancient medicine to possess the powers of rejuvenation, but actually often just killed those consuming or inhaling the toxic substance
Mercury, also known colloquially as quicksilver, is a naturally occurring metallic element that atypically for a metal takes liquid form at room temperature. Dating the discovery to at least 1500 BCE, with mercury identified in Egyptian tombs, the substance has been used by almost every culture at some point throughout history ranging from Far-East Asia to the Americas; among its many uses, mercury was until recently used in thermometers and is still used today in some sphygmomanometers and electrical circuitry. 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; it should be noted that limited quantities of mercury are still used in certain medical procedures, particularly in the United States and the developing world, typically as preservatives in vaccines and as part of topical antiseptics.
Historically, ancient Chinese medicine believed that 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 stupidly, 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.