Mad as a hatter - Crazy, demented
Reminds you of Alice's companion in her wonderland? I used to think the expression was Lewis Carroll's gift to the language just as jabberwocky is. Turns out the phrase was popular well before Carroll's "Alice in Wonderland" was published. "Mad hatter syndrome" was actually a medical affliction in Carroll's times.In the mid-1800s, hat makers used hot solutions of mercuric nitrate to shape wool felt hats and prolonged exposure to mercury vapors caused severe neurological damage ranging from uncontrollable muscular twitching (known as "hatter's shakes") to dementia. Hatters working in poorly ventilated workshops would breathe in (elemental) mercury vapor and in advanced cases, developed hallucinations and other psychotic symptoms.
Pic : www.rjohnwright.com