water barometer - easily In a water barometer the situation...

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The water will evaporate/boil at the top of the water column because there is a vacuum above it. This water vapor will depress the level of water in the water barometer. That is why mercury is used in a barometer. A mercury barometer has low vapor pressure and little evaporates into the vacuum. (The water barometer is also very cumbersome due to its height.) The Weather Glass, also known as a water barometer, was quite useful. However, it was more so an indicator of weather change rather than an air pressure measurement device. it was almost impossible to calibrate and was affected by evaporation of the water. Nevertheless, weather glasses were elegant instruments, and are still made today Mercury is most commonly chosen for a few reason. One, it is so dense that the column sustained by air pressure is of practicable height. In comparison, a barometer made with water, would have to be more than 34 ft (100 m) high. Also, mercury has a low vapor pressure, therefore it does not evaporate
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Unformatted text preview: easily. In a water barometer, the situation is quite different. Water's vapor pressure is much greater and the pressure exerted by water vapor at the top of the barometer would have to be taken into consideration. The vapor pressure exerted is pretty much a non-factor with a mercury barometer. However, with a mercury barometer, two additional components are necessary in order to increase the accuracy of a barometer. These two components are a vernier scale and a thermometer. The vernier scale allows for greater measurement accuracy than what is possible by just reading the scale itself. The thermometer is needed because the mercury's density (in addition to the density of other materials used in the assembly of the barometer) change with temperature. Many barometers come outfitted with thermometers attached to them....
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