There are few reasons <span>why mercury is used in liquid barometer instead of water: 1. </span>Mercury (13.69 g/cm³) is more dense than water (1.00 g/cm³), so if we use water in barometar, <span>length of barometer would be much longer.</span><span> 2. </span><span>Mercury has lower vapor pressure than water. 3. </span>Mercury has lower freezing point (-38.83°C) than water (0°C)<span>.