Why is mercury used in Barometers?

1 Answer

t-nez's profile pic

t-nez | High School Teacher | (Level 3) Associate Educator

Posted on

Mercury is used in barometers because of its high density. At 13.9 g/cm^2, mercury is the most dense substance to exist as a liquid at room temperature. By comparison, water has a density of 1.00 g/cm^2. 

The Torricelli barometer, shown in the attached image, measures the barometric pressure by the distance that the atmosphere will push the mercury up an evacuated, closed-end tube. This distance is typically 760 mm or 29.9 inches at sea level.

So here's where the density becomes an important factor: The same atmospheric pressure will support a column of water in an evacuated tube at a height of about 10.4 meters. Using a very dense liquid allows the tube used for the barometer to be much shorter, which is an important matter of convenience when trying to fit it into a room.

This image has been Flagged as inappropriate Click to unflag
Image (1 of 1)