# Why do we use a column of mercury rather than a column of water to measure pressure?

rho_(Hg) = 13.55*g*mL^-1; rho_("water") = 1.00*g*mL^-1;
One atmosphere will support a column of mercury $760$ $m m$ high. It would support a column of water approx. $10$ $m$ high. Sometimes, columns of water are used to measure osmotic pressures, which are much smaller than atmospheric pressures.