Why is the height of mercury independent to the mass?

Answer 1

If you have a sample of mercury in a tube, it has a definate mass, which will not increase or decrease based on the height in the tube. You can heat the tube, which would raise the height but would not increase the mass, thus the height of mercury is not dependant on the mass in the tube.

Answer 2

Because it is based on the density. So the mass and volume have to be considered.