The alcohol thermometer or spirit thermometer has a similar construction and

theory of operation A theory of operation is a description of how a device or system should work. It is often included in documentation, especially maintenance/service documentation, or a user manual. It aids troubleshooting by providing the troubleshooter with ...

as a mercury-in-glass thermometer. However, the thermometric fluid of an alcohol thermometer is less toxic and evaporates quickly making it a safer alternative to mercury thermometers. The ethanol version is the most widely used due to the low cost and relatively low hazard posed by the liquid in case of breakage. An organic liquid is contained in a glass bulb which is connected to a

capillary A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the inn ...

of the same glass and the end is sealed with an expansion bulb. The space above the liquid is a mixture of nitrogen and the vapor of the liquid. For the working temperature range, the meniscus or interface between the liquid and gas/vapor is within the capillary. With increasing temperature, the volume of liquid expands and the meniscus moves up the capillary. The position of the meniscus shows the temperature against an inscribed scale. The liquid used can be pure

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

kerosene Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...

or isoamyl acetate, depending on manufacturer and working temperature range. Since these are transparent, the liquid is made more visible by the addition of a red or blue

dye Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy Fantasy is a genre of speculative fiction that involves supernatural or Magic (supernatural), magical ele ...

. One half of the glass containing the capillary is usually enamelled white or yellow to give a background for reading the scale. The range of usefulness of the thermometer is set by the

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envi ...

of the liquid used. In the case of the ethanol-filled

thermometer A thermometer is a device that measures temperature (the hotness or coldness of an object) or temperature gradient (the rates of change of temperature in space). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb ...

, the upper limit for measurement is 78 °C (172.4 °F), which makes it useful for measuring daytime, nighttime and body temperatures, although not for anything much hotter than these. Ethanol-filled thermometer are used in preference to mercury for

meteorological Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agriculture ...

measurements of minimum temperatures and can be used down to −70 °C (−94 °F).

British Standard British Standards (BS) are the standards produced by the BSI Group which is incorporated under a royal charter and which is formally designated as the national standards body (NSB) for the UK. The BSI Group produces British Standards under th ...

692:1990 ''Specification for Meteorological Thermometers'' The physical limitation of the ability of a thermometer to measure low temperature is the freezing point of the liquid used. Ethanol freezes at −114.9 °C (−174.82 °F). If an alcohol thermometer utilizes a combination of ethanol, toluene, and pentane, its lower temperature range may be extended to measure temperatures down to as low as −200 °C (−328 °F). However, the measurement temperature range c. −200 °C to 78 °C, is highly dependent upon the type of alcohol used.

History

The alcohol thermometer was the earliest efficient, modern-style instrument of temperature measurement. As is the case with many early, important inventions, several people are credited with the invention. These include

Ferdinando II de' Medici, Grand Duke of Tuscany Ferdinando II de' Medici (14 July 1610 – 23 May 1670) was Grand Duchy of Tuscany, grand duke of Tuscany from 1621 to 1670. He was the eldest son of Cosimo II de' Medici, Grand Duke of Tuscany, Cosimo II de' Medici and Archduchess Maria Mad ...

, who in 1654 made sealed tubes partly filled with alcohol, with a bulb and stem, depending on the expansion of a liquid, and independent of air pressure. Other sources, including the Encyclopædia Britannica, credit

Daniel Gabriel Fahrenheit Daniel Gabriel Fahrenheit FRS (; ; 24 May 1686 – 16 September 1736) was a physicist, inventor, and scientific instrument maker, born in Poland to a family of German extraction. Fahrenheit invented thermometers accurate and consistent enough t ...

with inventing the alcohol thermometer in 1709. Fahrenheit was a skilled

glassblower Glassblowing is a glassforming technique that involves inflating molten glass into a bubble (or parison) with the aid of a Blowpipe (tool), blowpipe (or blow tube). A person who blows glass is called a ''glassblower'', ''glassmith'', or ''gaffer'' ...

and his alcohol thermometer was the world's first reliable thermometer.Encyclopedia of World Biography "Gabriel Fahrenheit"
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References

{{DEFAULTSORT:Thermometers, Alcohol Thermometers Meteorological instrumentation and equipment 1709 in science fr:Thermomètre#Thermomètre à alcool