Arsenic

The notoriously poisonous metalloid Arsenic or element # 33 on the Table of Elements was known as The Poison of Kings or "Inheritance Powder" during the Middle Ages and Renaissance because of its popularity as a murder weapon by the nobility. This was largely due to the fact that at the time it left no traceable elements in the body, and because it is a white, tasteless, and oderless powder that can easily be slipped into food. The first to prepare arsenic trioxide (the most common form used in murders) was an Arab Alchemist named Jabir in the 700s. Famous victims include Francesco I de Medici, Grand Duke of Tuscany and his wife; George III of Great Britain; Charles Francis Hall; Huo Yaun Jia; Clare Boothe Luce (although hers was unintentional and she only became extremely sick); and Napolean Bonaparte(there is no proof that he was intentionally poisoned). Also chronic arsenic poisoning could be behind Monet's blindness, Cezanne's development of severe diabetes, and Van Gogh's neurological disorders as the element was used in the making of a pigment frequently used by Impressionist painters called Emerald Green. Other inadverdent poisonings include arsenic being used in medication(quack and real); as a cosmetic for Victorian women who used it to help them become paler, when mixed with vinegar and chalk; and used in the frosting on pastries during the Victorian Era to make them look better.
Common symptoms include violent stomach pains, vomiting, diarrhea, convulsions and cramps, clammy sweats, red eyes, lividity of the extremities, delirium, and finally death.