Look at where technology was 200 years ago and where it is today, then try to tell me that someone in 1808 could have predicted the use of any material !
They might have told you that whalebone would be used in making very durable buggy whips !
There is no telling where good ol' Hg will be used.
Given the toxicity, and our continuing realization of how bad it is as a chronic low dose poison, and its effect on the growing brains of children, mercury is already on the way out.
The only large common use is in fluorescent light bulbs, and there it is being minimized. Long before 200 years from now I expect LEDs [currently nowhere near 100% efficient] to have blown fluorescent lamps out of the market.
Mercury is used in amalgam dental fillings, but polymer composite fillings are already starting to replace amalgam fillings.
Alkaline batteries use small amounts of mercury, but for environmental reasons this is under pressure.
Mercury is used in some explosive detonators, but only in small quantity.
I am not sure where else mercury is used [other than in high end vehicles from Ford {joke}], but I expect that environmental considerations will continue to reduce its use dramatically.
It is already illegal in the US to dispose of any industrial mercury bearing waste in a landfill; it must be recycled.
While a household can put fluorescent lights in the trash, unless they are special ultra low mercury ones, it is illegal for a business to do so.
