Why isn water used as the liquid in the common thermometer?
If water was used in the common liquid thermometer we wouldn’t be able to measure anything over 100 °C (212 °F) or under 0°C (32 °F). These two temperatures represent the boiling and freezing points of water, respectively. Imagine for a moment that you have a common thermometer that uses water as its liquid. You go outside in the middle of winter and try to measure the air temperature. The water in the thermometer would freeze by the time it reached 0 °C and therefore wouldn’t be able to move down to the correct temperature. If you tried to measure the temperature of something above the boiling point of water, the imaginary thermometer would break as the water changed from liquid to gas. Mercury or alcohol are the liquids used in the common thermometer because both substances have a higher boiling point and a lower freezing point than typical Earthly temperatures.
