# The behaviour of a vacuum without the influence of air pressure?

1. Mar 20, 2013

### juniorcarty

2. Mar 21, 2013

### Staff: Mentor

Welcome to PF!

I think you can understand the situation better if you do not think of the vaccum as a thing. When flask A is open, mercury vapours will start floating around and some will end up in flask B. Equilibrium should be reached when the vapour pressure of mercury is the same in both flasks. But I don't see why there would be any flow of liquid mercury.

3. Mar 21, 2013

### jbriggs444

Assuming that the flasks are level with each other then there is a tiny pressure differential. The pressure of the mercury vapor at the bottom of the empty flask is slightly higher than it is at the top of the full flask. This is due to gravity.

If the vapor at the top of the full flask is in equilibrium with the liquid at the top of the full flask and if the vapor at the bottom of the empty flask is at a higher pressure than that then one would expect condensation at the bottom of the empty flask.