Mad Hatters, Felt, and Mercury

Mad hatters.
Harry S. Truman Felt Fedora Hat – Image: National Park Service

Associated with the hat making business, how do felt and mercury produce mad hatters?

Felt hats have been produced from small animal pelts since about the 14th century. During the 19th century, fur was removed from the skin using camel urine. Some hatters usef their own urine, instead. The active ingredient in urine was nitrogen-rich urea.

Why Urine?

Those who used their own urine and were being treat for syphillis produced superior felt! This was due to the mercurous chloride (HgCl) they’d taken as medicine. Urine was replaced by the orange-colored mercuric nitrate Hg(NO₃)₂ solution.

Mad Hatters, an Occupational Hazard

The vats of solution and the drying process generated dangerous levels of mercury fumes. They were a source of chronic poisoning. Chronic mercury poisoning leads to tremors, mood disorders, and dementia.

Victims were called “mad hatters.” A mad hatter is one of the best known characters in Lewis Carroll’s Alice in Wonderland. The term mad hatter has become a synonym for a crazy person.

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