Question

Why would prefer to use the mercury instead the water in a sphygmomanometer?

Answer 1

Because `1*atm` supports a column of mercury `760` `mm` high..........

Explanation:

But given the density of mercury compared to water (`rho_"Hg"=13.55*g*cm^-3; rho_"water"=1*g*cm^-3`, it would require a column of water approx. `10*m` high to support a pressure of `1*atm`.

Now sphygmomanometers take blood pressure measurements; typically we measure `50-60*mm` above or below atmospheric pressure. A measurement of a water column would still be prohibitively high.