Mad as a Hatter

Mercury is a very poisonous substance. In fact, Mercury is one of the most deadly poisons on Earth. Inhaling mercury vapors or gases, and eating or ingesting mercury can be very dangerous and even deadly. In the 1800's, mercury was used to manufacture felt hats in England and the Eastern United States. Many of the factory workers inhaled the mercury fumes. It damaged their brains and they became brain damaged or "mad." The term "mad as a hatter" comes from the hat makers that got brain damage from using mercury to make all those hats!