Mercury thermometers make use of the following properties of liquids:
- Liquids have no set shape. Because mercury has no set shape, it can conform to the shape of the glass tube that the thermometer is made from.
- Liquids expand when heated and contract when cooled. This is obviously very important for a thermometer. It is because of this property of liquid that the mercury can go up the thermometer tube as the temperature goes up.
Mercury is not the only liquid that can be used in a thermometer. However, mercury is ideal in part because it expands at a very constant rate over a large range of temperatures.
Thermometers - tools that are used to measure temperature. The most common consists of a tank with liquid and a graduated tube. Liquid from thermometers (usually mercury or alcohol) is expanding as the temperature rises and it rises within the tube. Clinical thermometers with mercury can be used to measure body temperature. They have an obstacle (a narrow neck) from the tube so that liquid is not coming back in the tank, immediately after the reading.
Usual thermometers - measure the temperature using the liquid expansion property: the more the temperature is higher, the more fluid is expanding more and increase the value indicated.
Mercury is used in thermometers because of its special properties. It can measure a wide range of temperatures from -40 to 356 ° C, and up to 570 ° C under pressure,in liquid state.
It expands regularly, proportional to the absolute temperature changes. Works well in capillary tubes, it does not "wet" them and it's easily obtained in pure form. Other substances used are alcohol-which can be used at temperatures lower than mercury (-80 ° C) and pentane (C5H12 ) - which can be used to -200 ° C.