Mad Hatters, Felt, and Mercury

How is it mercury was associated with hats?
Harry S. Truman Felt Fedora Hat – Image: National Park Service

How did mercury ever come to be associated with the hat making business?

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 chose to use their own urine, instead. The active ingredient in urine is nitrogen-rich urea.

Why Urine?

Of those hatters using their own urine, any undergoing treatment for the sexually transmitted disease syphilis, oddly enough, were found to produce superior felt! Eventually it was realized this was due to the mercurous chloride (HgCl) they’d consumed as medicine. This led to the switching from urine to the orange-colored mercuric nitrate Hg(NO₃)₂ solution.

Mercury – 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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