Mercury-in-glass thermometer - AbsoluteAstronomy.com

A mercury-in-glass thermometer, also known as a mercury thermometer, was invented by German physicist Daniel Gabriel Fahrenheit in 1724 and is a thermometer

Thermometer

Developed during the 16th and 17th centuries, a thermometer is a device that measures temperature or temperature gradient using a variety of different principles. A thermometer has two important elements: the temperature sensor Developed during the 16th and 17th centuries, a thermometer (from the...

consisting of mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

in a glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

tube. Calibrated marks on the tube allow the temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

to be read by the length of the mercury within the tube, which varies (nearly linearly) according to the temperature of the mercury. 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

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

or it may be less than atmospheric pressure, which is normally known as a vacuum

Vacuum

In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

History

The thermometer was used by the originators of the Fahrenheit

Fahrenheit

Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

and Celsius

Celsius

Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...

scales.

Anders Celsius

Anders Celsius

Anders Celsius was a Swedish astronomer. He was professor of astronomy at Uppsala University from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germany, Italy and France. He founded the Uppsala Astronomical Observatory in 1741, and in 1742 he proposed the Celsius...

, a Swedish Astronomer, devised the Celsius scale, which was described in his publication the origin of the Celsius temperature scale in 1742.

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

Isaac Newton

Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

was already working on something similar. The distinction of Celsius was to use the condition of melting and not that of freezing. 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 to water vapour

Water vapor

Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

(when this is done to high precision, a variation will be seen with atmospheric pressure; Celsius noted this). 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.

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:

Place the cylinder of the thermometer in melting ice made of pure water and mark the point where the fluid in the thermometer stabilises. This point is the freeze/thaw point of water.
In the same manner mark the point where the fluid stabilises when the thermometer is placed in boiling water vapour.
Divide the length between the two marks into 100 equal pieces.

These points are adequate for approximate calibration but both vary with atmospheric pressure. Nowadays, the triple point

Triple point

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium...

of water is used instead of the freezing point (the triple point occurs at 273.16 kelvins (K), 0.01 °C).

Maximum thermometer

A special kind of mercury-in-glass 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 the set period of time. To reset the thermometer it must be swung sharply. This design is used in the traditional type of medical thermometer

Medical thermometer

Medical thermometers are used for measuring human body temperature, with the tip of the thermometer being inserted either into the mouth under the tongue , under the armpit , or into the rectum via the anus .-Liquid-filled:The traditional thermometer is a glass tube with a bulb at one end...

Maximum minimum thermometer

A Maximum minimum thermometer, also known as Six's thermometer, is a thermometer which can measure the maximum and minimum temperatures reached over a period of time, usually during a day. The traditional design contains mercury in the glass tube, but this is used solely as a way to indicate the position of a column of alcohol, and so it is not strictly a mercury thermometer.

Physical properties

Mercury will solidify (freeze) at -38.83 °C (-37.89 °F) and so may only be used at higher temperatures. Mercury, unlike water, does not expand upon solidification and will not break the glass tube (unlike water, when it is frozen then quickly heated, will break, 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-in-glass 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

Thallium

Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray poor metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy...

alloy

Alloy

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

may be used. This has a solidification (freezing) point of -61.1 °C (-78 °F).

Phase out

Today, many mercury-in-glass thermometers are still widely used in meteorology

Meteorology

Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...

; however, they are becoming increasingly rare for other uses, as many countries have banned them outright from medical use. Some manufacturers use galinstan

Galinstan

Galinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...

, a liquid alloy of gallium

Gallium

Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...

, indium

Indium

Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...

, and tin

Tin

Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...

, as a replacement for mercury.

The typical "fever thermometer" contains between 0.5 to 3 g

Gram

The gram is a metric system unit of mass....

(.3 to 1.7 dr

Avoirdupois

The avoirdupois system is a system of weights based on a pound of 16 ounces. It is the everyday system of weight used in the United States and is still widely used to varying degrees by many people in Canada, the United Kingdom, and some other former British colonies despite the official adoption...

) of elemental mercury. 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

American Academy of Pediatrics

The American Academy of Pediatrics is the major professional association of pediatricians in the United States. The AAP was founded in 1930 by 35 pediatricians to address pediatric healthcare standards. It currently has 60,000 members in primary care and sub-specialist areas...

and the United States Environmental Protection Agency

United States Environmental Protection Agency

The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

recommend that alternative thermometers be used in the home.

By the Philippines Department of Health

Department of Health (Philippines)

The Philippines’ Department of Health is the principal health agency in the Philippines. It is the executive department of the Philippine Government responsible for ensuring access to basic public health services to all Filipinos through the provision of quality health care and the regulation of...

’s Administrative Order 2008-0221, all mercury equipment from hospitals, including mercury-in-glass thermometers, will be phased out in the Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

by September 28, 2010. Even before the order was released, 50 hospitals have already banned mercury from their establishments. Among these fifty hospitals, the Philippine Heart Center

Philippine Heart Center

The Philippine Heart Center in Quezon City was established through Presidential Decree No. 673 issued by president Ferdinand E. Marcos in 1975. Its original name was the Philippine Heart Center for Asia and was changed to its current form in 1975. It was inaugurated on Valentine's Day, February 14,...

was the first one to do so. San Juan de Dios Hospital

San Juan De Dios Educational Foundation

San Juan de Dios Educational Foundation, Inc. is a private, non-stock, non-profit, joint institute of education and tertiary health sciences operating as a college and hospital within the City of Pasay, Philippines. Both the colleges and hospital are run by the Daughters of Charity.-History:The...

, Philippine Children’s Medical Center, San Lazaro Hospital, Ospital ng Muntinlupa, Lung Center of the Philippines, the National Kidney and Transplant Institute, Manila Adventist Medical Center

Manila Adventist Medical Center

The Manila Adventist Medical Center, , is an acute care, tertiary, non-stock, non-profit, and self-supporting private hospital that is located with in Pasay City of Metro Manila, Philippines. It was established on 1929 by a missionary doctor - Horace Hall...

and Las Piñas Hospital also made steps to ban the toxic chemical. The country was the first one to make a step to ban mercury from its health care system in Southeast Asia

Southeast Asia

Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

.

Taiwan wants to ban mercury-in-glass thermometers by 2011.

External links

EPA - guidelines for mercury spills removal