Subject: Mercury in a piston and cylinder.

Since mercury expands when heated, how much work could be done by 
allowing mercury in a cylinder to push a piston as the ambient 
temperature increases?

Could significant, useful work be done by allowing such a device, or a 
series of devices, to be cooled and heated by the fluctuations of 
daily temperature?

Do the laws regarding the conservation of energy say that the work 
output cannot exceed the heat energy going into the system?

Re: Mercury in a piston and cylinder.