Final answer:
It is necessary to use a nonvolatile liquid in a barometer or manometer because volatile substances evaporate, causing changes in measurements. Nonvolatile liquids ensure accurate and stable readings by avoiding fluctuations in the liquid column, crucial for pressure determination.
Step-by-step explanation:
The reason it is necessary to use a nonvolatile liquid in a barometer or manometer is because volatile liquids evaporate, affecting measurements. In devices such as barometers and manometers, the accuracy and stability of the liquid column are crucial for measuring pressure. Barometers measure atmospheric pressure using the height of a liquid column, typically mercury, within an inverted tube.
Manometers, which measure gas pressures, use a similar principle with a U-shaped tube. If a volatile liquid were used, its tendency to evaporate would cause fluctuations in the liquid column height, leading to incorrect pressure readings. This is why nonvolatile liquids, which have lower evaporation rates, ensure consistent and reliable measurements.
In the context of a closed-end manometer, the use of a volatile liquid would result in an inconsistent vapor pressure above the liquid column, thus affecting the pressure differential measurement between the gas sample and the external atmosphere.