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A mercury thermometer is a tool used for measuring temperature. Gabriel Fahrenheit invented it in 1714, and his basic model is still used today in medical and non-medical settings. Typically, such a device is a glass tube filled with mercury. The majority of this substance is found in a metal tip, which is used as a warming device for the thermometer.
Most of these thermometers hold between 0.02 ounces (0.5 g) and 0.1 ounces (3 g) of mercury. Thick glass generally encases the temperature-sensitive liquid metal. When a mercury thermometer is placed outdoors or in the body, the metal tip heats and mercury stretches along the length of hollow space within the tube. Higher temperatures cause mercury to grow longer, while low temperatures cause it to fall. These thermometers are usually marked with temperature readings on the Fahrenheit or Celsius scale.
These devices are commonly used in medicine and meteorology. Medical doctors often use the maximum mercury thermometer to measure human body temperature. This type can be used either orally or anally.
A maximum mercury thermometer works in much the same way as a standardthermometer, but the mercury does not shrink back into the tip when removed from a heat source. This allows temperature readings to be kept until mercury is forced back into the tip by centrifugal force, or shaking the thermometer with the head pointed toward the floor. Nitrogen gas in the glass tube is what holds the mercury in place.
A mercury thermometer may also be used by meteorologists to measure air temperature. Standard mercury freezes at -37.89°F (-38.83°C). In order to measure temperatures below this point, meteorologists will often mix mercury with thallium alloy. Thallium reduces the freezing point to -78°F (-61.1°C). If mercury freezes, nitrogen can be caught behind the metal causing the thermometer to stop working.
With only between 0.02 ounces (0.5 g) and 0.1 ounces (3 g) of mercury in eachthermometer, health risks from oral consumption are thought to be low. Inhalation of mercury at these levels could cause dangerous side effects, however. Due to the dangers associated with mercury poisoning ,many countries in Europe have chosen to ban mercury thermometers for medical use.
The United States has not banned mercury thermometers in a medical setting. The American Academy of Pediatricians and the United States Environmental Protection Agency, however, have suggested alternative temperature-measuring devices for personal use. There have been no U.S. bans, as of 2009, on mercury thermometer use in professional medical settings.
