mercury is used in a barometer instead of water.give reason.

It has been found that atmospheric pressure can support 10.34m of water because density of water is 13.6 times less than mecury. Thus, a water barometer will support 10.34m of water. Since it is very diffcult to have a tube of 10.34m length, a water barometer is an impracticle idea. Moreover, water vaporises under vaccum conditions; therefore a water barometer will never show the true atmospheric pressure.