A mercury-in-glass thermometer, invented by German physicist Daniel Gabriel Fahrenheit, is a thermometer consisting of mercury in a glass tube. The thermometer is a device that measures Temperature or Temperature gradient using a variety of different principles it comes from the Greek roots Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the tube, which varies according to the heat given to it. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature To increase the sensitivity, there is usually a bulb of mercury at the end of the thermometer which contains most of the mercury; expansion and contraction of this volume of mercury is then amplified in the much narrower bore of the tube. The space above the mercury may be filled with nitrogen or it may be a vacuum. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner.
The thermometer was used by the originators of the Fahrenheit and Celsius temperature scales. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 The Celsius Temperature scale was previously known as the centigrade scale.
Anders Celsius devised the Celsius scale, which was described in his publication the origin of the Celsius temperature scale in 1742. Anders Celsius ( November 27, 1701 &ndash April 25, 1744 in Uppsala) was a Swedish astronomer.
Celsius used two fixed points in his scale: the temperature of melting ice and the temperature of boiling water. This wasn't a new idea, since Isaac Newton was already working on something similar. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements The distinction of Celsius was to use the melting temperature and not the freezing temperature. The experiments for reaching a good calibration of his thermometer lasted for 2 winters. By performing the same experiment over and over again, he discovered that ice always melted at the same calibration mark on the thermometer. He found a similar fixed point in the calibration of boiling water vapour (when this is done to high precision, a variation will be seen with atmospheric pressure). General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated At the moment that he removed the thermometer from the vapour, the mercury level climbed slightly. This was related to the rapid cooling (and contraction) of the glass.
The air pressure influences the boiling point of water. Celsius claimed that the level of the mercury in boiling water is proportional to the height of the barometer.
When Celsius decided to use his own temperature scale, he originally defined his scale "upside-down", i. e. he chose to set the boiling point of pure water at 0 °C (212 °F) and the freezing point at 100 °C (32 °F).  One year later Frenchman Jean Pierre Cristin proposed to invert the scale with the freezing point at 0 °C (32 °F) and the boiling point at 100 °C (212 °F). He named it Centigrade. 
Finally, Celsius proposed a method of calibrating a thermometer:
These points are adequate for approximate calibration but both vary with atmospheric pressure. Nowadays, the triple point of water is used instead (the triple point occurs at 273. In Thermodynamics, the triple point of a substance is the Temperature and Pressure at which three phases (for example Gas, Liquid 16 kelvins (K), 0. 01 °C).
A special kind of mercury thermometer, called a maximum thermometer, works by having a constriction in the neck close to the bulb. As the temperature rises the mercury is pushed up through the constriction by the force of expansion. When the temperature falls the column of mercury breaks at the constriction and cannot return to the bulb thus remaining stationary in the tube. The observer can then read the maximum temperature over a set period of time. To reset the thermometer it must be swung sharply. This is similar to the design of a medical thermometer. Medical thermometers are used for measuring human Body temperature, with the tip of the thermometer being inserted either into the mouth ( oral temperature
Mercury will solidify (freeze) at -38. 83 °C (-37. The Celsius Temperature scale was previously known as the centigrade scale. 89 °F) and so may only be used at higher temperatures. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 Mercury, unlike water, does not expand upon solidification and will not break the glass tube, making it difficult to notice when frozen. If the thermometer contains nitrogen the gas may flow down into the column and be trapped there when the temperature rises. If this happens the thermometer will be unusable until returned to the factory for reconditioning. To avoid this some weather services require that all mercury thermometers be brought indoors when the temperature falls to -37 °C (-34. 6 °F). In areas where the maximum temperature is not expected to rise above -38. 83 °C (-37. 89 °F) a thermometer containing a mercury-thallium alloy may be used. Thallium (ˈθæliəm is a Chemical element with the symbol Tl and Atomic number 81 An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has This has a solidification (freezing) point of -61. 1 °C (-78 °F).
Today mercury thermometers are still widely used in meteorology, however in other usage they are becoming increasingly rare, as many countries have banned them outright from medical use. Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the Some manufacturers use galinstan, a liquid alloy of gallium, indium, and tin, as a replacement for mercury. Galinstan is an Eutectic Alloy of Gallium, Indium, and Tin which is liquid at room temperature typically freezing at −19 ° Gallium (ˈgæliəm is a Chemical element that has the symbol Ga and Atomic number 31 Indium (ˈɪndiəm is a Chemical element with chemical symbol In and Atomic number 49 Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50
The typical "fever thermometer" contains between 0. 5 to 3 g (. For other uses of the words gram or gramme see Gram (disambiguation. 3 to 1. 7 dr) of elemental mercury. The avoirdupois (ˌævərdəˈpɔɪz French avwaʀdypwɑ system is a system of weights (or properly Mass) based on a pound of sixteen Ounces  Swallowing this amount of mercury would, it is said, pose little danger but the inhaling of the vapour could lead to health problems. 
In the United States both the American Academy of Pediatrics and the United States Environmental Protection Agency recommend that alternative thermometers be used in the home. The American Academy of Pediatrics ( AAP) is an organization of Pediatricians physicians trained to deal with the medical care of infants children and adolescents