Water BarometerThe sketch shows a barometer for which the fluid is not mercury but water. The "pressure of the void" for water is the vapor pressure of water at 80°F. Calculate the reading of the barometer, that is the height of the column of water, H.

♦  In the atmosphere at the bottom of the barometer the pressure is atmospheric. An equation relating pressure change from the atmosphere through the water to the water pressure in the void is:

p_atm - ρ_waterg_oH = 0.5 lbf/in².

14.7(144)lbf/ft² - ρ_waterg_oH = 0.5(144) lbf/ft²

The above equation contains the single unknown quantity, the height of the column of water. We solve the equation taking proper care of units:

H = 32.8 ft

In pronciple water can be used in a barometer. However, the height, ~33 feet is impactical.