Question

Why mercury has its meniscus upward ??

Answer 1

This is a consequence of metallic bonding; and it is formally termed an ameniscus, or a convex meniscus (as opposed to the concave menisci, that water forms).

Explanation:

Mercury metal is more attracted to itself than to the walls of the glass manometer. Why? Because mercury still exhibits metallic bonding, even in the liquid state, and metal-metal interactions are stronger than the metal glass interactions.

When you spill mercury in the lab, you get perfect little spheres of mercury everywhere, rather than the puddles you get when you spill water. Again, this is a consequence of metallic bonding - mind you, should you spill mercury in the lab, you are going to get an enormous beat-down for clumsiness. This is a big clean-up job.