The Mad World of Hat Making

(via Amusing Planet)  Hat-making in the 18th and 19th centuries was a hazardous business, because it involved the use of many chemicals, one of which was the toxic substance mercury. Working in poorly ventilated rooms, hat-makers breathed in so much mercury fumes that a good number of them were driven out of their wits by mercury-induced brain damage. Mercury poisoning among hat-makers is widely believed to be the origin of the proverbial saying “mad as a hatter”.