how much heat can you apply to mercury so it becomes transparent?

This is not a task from my school, I'm just wondering if it can be done. Is it possible that if you had a transparent closed container (like a thermometer) which internal dimensions are 1 m wide, 1 mm thick and 200 m high (or infinite if you like), and you fill with 1 cm mercury (20 degrees Celsius). How much heat can you apply (suppose that the container can withstand a lot of heat) so the molecules of mercury spread so much it becomes transparent?