With the exception of electronics, all thermometers are built on the principle that, by adding heat to a body, it expands; And when the heat is removed, it contracts.
Therefore, the operation of the mercury, alcohol, gas or metal mercury expansion thermometer is based on the principle of dilation and contraction of solid, liquid and gaseous bodies. The dilation and contraction of bodies are important notions for refrigeration. Generally temperature control in refrigerators, freezers, refrigeration counters, are applications of the principle of dilation and contraction, which can be explained as follows: depending on the amount of heat applied to a solid, liquid or gaseous body, its volume increases due to Mobility and greater intermolecular spacing. This phenomenon is called dilatation.
In the reverse process: depending on the amount of heat that is withdrawn from a body, its volume decreases, due to the lower mobility and intermolecular spacing. This phenomenon is called contraction.
This is the case of the mercury column that decreases as the temperature in the bulb goes down. To prove the dilation, you only have to bring the bulb of a mercury thermometer to a source of heat for a certain time. By pulling the bulb away from the thermometer from the heat source, the mercury column begins to drop, showing the contraction of the mercury. In this principle, it bases its construction of the main measuring instruments of temperature thermometer, the controls of operation of refrigeration and air-conditioning equipment thermostats and protection of electrical thermal protective equipment.
