Why is mercury perferred as a barometric substance over water?

Explanation

The pressure P exerted by column of a liquid of height h, density of liquid `rho is P = h rho g` or `h prop 1.(rho)` (for a constant P). Since mercury is a most dense liquid available. Therefore by using it the barometric arrangement will be of very comvenient size. To understand it, let the atmospheric pressure be `1.01 xx 10^(5)Pa`. Then teh height of water barometer is
`h_(w) =(P)/(rho_(w)g) = (1.01 xx10^(5))/((13.6 xx 10^(3))xx 9.8) = 0.76 m`
This indicates that the tube required for water barometer should be long. which is very inconvenient, whereas the tube used in mercury barometer is small, which is convenient to use.