How did the phrase mad as a hatter come about?

The phrase "mad as a hatter" is thought to have originated in the 17th century when hatters used mercury in the process of making a new top quality felt hats from beaver, mink, muskrat, raccoon, and hare felt. Mercury poisoning can indeed lead to neurological effects including irritability, memory loss, hallucinations, slurred speech, tremors, personality changes, delusions, violent behaviors, paranoia, depression, anxiety, as well as ataxia–loss of muscle coordination which causes problems with gait, motor control, and tremors, which could explain the association with madness and hat-making. The saying gained popularity in the 19th century with Lewis Carroll's use of the epithet in his literary children's novel Alice's Adventures in Wonderland where the Mad Hatter character often talks nonsense, drinks tea at all hours of the day, holds conversations with himself when alone, and refers to himself as both as Hatter and March Hare