Mad as a hatter" is a colloquial phrase used in conversation to refer to a crazy person. In 18th and 19th century England mercury was used in the
production of felt, which was used in the manufacturing of hats common of the time. People who worked in these hat factories were exposed daily to
trace amounts of the metal, which accumulated within their bodies over time, causing some workers to develop dementia caused by mercury poisoning.
Thus the phrase "Mad as a Hatter" became popular as a way to refer to someone who was perceived as insane.
en.wikipedia.org...
Not good!


