Forget about the feasibility of this question for the moment.
Could a column of mercury inside a tube of glass be used as an
antenna?

Sure, I don't see why not. You'd have to put up with a bit of tuning
drift, as the resonant frequency would drop in hot weather or after
you'd had your legal-maximum CW station running for a while :-)

There was a running gag over in rec.audio.high-end a few years ago,
about the ultimate speaker cables: mercury-filled surgical rubber
tubing.

Expensive, trouble-prone, toxic, and prone to cause unexpected visits
from the hazmat team. Be the first on your block!

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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