Mercury-in-glass thermometer

A mercury thermometer is a liquid thermometer, the thermometer is used as liquid mercury. First mention is mercury in a work of Guillaume Amontons in which the change in the display of mercury barometers was described with the temperature. The importance of this was recognized in 1718 by the physicist Daniel Gabriel Fahrenheit, replacing the alcohol used until then by mercury. This had also already been doing other, but since he also anbrachte scales and his thermometer worked reliably and reproducibly by a calibration instruction and special manufacturing process, but he is considered the inventor of the mercury thermometer in particular also of the thermometer as a scientific measuring instrument in general.

Since mercury has a nearly temperature-independent coefficient of thermal expansion and the glass of the thermometer does not wet the tube, mercury thermometers were up in the 1970s, the most widely spread thermometer, especially for precise measurements. Mercury thermometers can be used in a temperature range of -38 ° C ( freezing point of mercury) and 350 ° C (boiling of mercury).

When the mercury thallium is added, the measurement range can be extended to -58 ° C.

The mercury thermometer may also be used to above its boiling point when the mercury nitrogens contains under high pressure. Thus, the measuring range can be extended to 750 ° C.

Since mercury is electrically conductive as the liquid metal, it is possible to build a mercury thermometer, which by a contact incorporated in the tube to perform switching operations when a certain temperature value, which may for example be used in thermostats.

Since the 1970s, are mercury thermometers due to the toxicity of mercury, especially mercury vapors occurring in case of damage, increasingly replaced by other types of thermometer, especially alcohol thermometer. In a clinical thermometer with mercury as an indicator is up to 1 g of mercury. At 20 ° C room temperature, this corresponds to a sphere of about 5.2 mm in diameter. Since April 2009, the sale of mercury thermometers is prohibited with the exception of scientific and medical area within the EU.