Arsenic has been known as a poison for millennia. It was so commonly used during the Victorian Age it was called inheritance powder. (Seriously.) It occurs in nature and contaminates water and foodstuffs. (New Mexico has the dubious distinction of having high levels in their water and rice is particularly susceptible to absorbing arsenic.) A slightly sweet odorless and colorless powder, the symptoms of arsenic poisoning mimic cholera or some kind of intestinal distress. It has been used as a cause of death by many many mystery authors.
Women in the Elizabethan era used it in a paste to whiten their complexions. Of course it was absorbed through the skin and a lifetime of use must have meant serious health complications. (Talk about dying for fashion.)
What interests me, though, are the inadvertent poisonings. Napoleon’s hair was shown to have very high levels of arsenic. Was he poisoned by his nearest and dearest while on Elba? What about King George III, the so-called mad King who reigned during the Colonial period and Revolution? He had porphyria, a blood disease that results in dark urine and extreme sensitivity to the sun. (Some scholars think that porphyria was the original seed of the vampire legends.) Well, when they tested King George’s hair, it too displayed high levels of arsenic. Was he poisoned?
They were both probably poisoned by environmental factors. As that time a beautiful emerald green was all the rage for wallpaper. When George Washington built his house he ordered rooms papered in this fashionable color. The problem is that beautiful color was created by arsenic and in damp or humid weather the arsenic came out of the paper into the air. Instant poisoning.