Alcohol thermometer
Encyclopedia
The Alcohol thermometer or spirit thermometer is an alternative to the mercury-in-glass thermometer
, and functions in a similar way. But unlike mercury-in-glass thermometer, the contents of an alcohol thermometer are less toxic and will evaporate away fairly quickly. An organic liquid is contained in a glass bulb which is connected to a capillary
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 vapour of the liquid. For the working temperature range, the meniscus
or interface between the liquid 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
or toluene
or kerosene
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
. 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
of the liquid used. In the case of the ethanol-filled thermometer the upper limit for measurement is 78°C, which makes it useful for measuring day and night-time temperatures and to measure body temperature, although not for anything much hotter than these. 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.
Ethanol-filled thermometers are used in preference to mercury for meteorological measurements of minimum temperatures and can be used down to -70°C.
, who in 1654 made sealed tubes part 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 German scientist Daniel Gabriel Fahrenheit with inventing the alcohol thermometer in 1709. Fahrenheit was a skilled glassblower and his alcohol thermometer was the world's first reliable thermometer.
Mercury-in-glass thermometer
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 consisting of mercury in a glass tube. Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the...
, and functions in a similar way. But unlike mercury-in-glass thermometer, the contents of an alcohol thermometer are less toxic and will evaporate away fairly quickly. An organic liquid is contained in a glass bulb which is connected to a capillary
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
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 vapour of the liquid. For the working temperature range, the meniscus
Meniscus
The meniscus is the curve in the upper surface of a liquid close to the surface of the container or another object, caused by surface tension. It can be either convex or concave. A convex meniscus occurs when the molecules have a stronger attraction to each other than to the material of the...
or interface between the liquid is within the capillary. With increasing temperature, the volume of liquid expands and the meniscus
Meniscus
The meniscus is the curve in the upper surface of a liquid close to the surface of the container or another object, caused by surface tension. It can be either convex or concave. A convex meniscus occurs when the molecules have a stronger attraction to each other than to the material of the...
moves up the capillary. The position of the meniscus
Meniscus
The meniscus is the curve in the upper surface of a liquid close to the surface of the container or another object, caused by surface tension. It can be either convex or concave. A convex meniscus occurs when the molecules have a stronger attraction to each other than to the material of the...
shows the temperature against an inscribed scale.
The liquid used can be pure ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
or toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
or kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
or Isoamyl acetate
Isoamyl acetate
Isoamyl acetate, also known as isopentyl acetate, is an organic compound that is the ester formed from isoamyl alcohol and acetic acid. It is a colorless liquid that is only slightly soluble in water, but very soluble in most organic solvents...
, depending on manufacturer and working temperature range. Since these are transparent
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...
, the liquid is made more visible by the addition of a red or blue dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
. 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
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
of the liquid used. In the case of the ethanol-filled thermometer the upper limit for measurement is 78°C, which makes it useful for measuring day and night-time temperatures and to measure body temperature, although not for anything much hotter than these. 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.
Ethanol-filled thermometers are used in preference to mercury for meteorological measurements of minimum temperatures and can be used down to -70°C.
History
The alcohol thermometer was the earliest, efficient, modern-style instrument of temperature measurement. As is the case with many early, important inventions, there are several people credited with its invention. These include Ferdinando II de' Medici, Grand Duke of TuscanyFerdinando II de' Medici, Grand Duke of Tuscany
Ferdinando II de' Medici was grand duke of Tuscany from 1621 to 1670. He was the eldest child of Cosimo II de' Medici and Maria Maddalena of Austria. His 49 year rule was punctuated by the terminations of the remaining operations of the Medici Bank, and the beginning of Tuscany's long economic...
, who in 1654 made sealed tubes part 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 German scientist Daniel Gabriel Fahrenheit with inventing the alcohol thermometer in 1709. Fahrenheit was a skilled glassblower and his alcohol thermometer was the world's first reliable thermometer.