Hydrometer

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Schematic drawing of a hydrometer. The lower the density of the fluid, the deeper the weighted float B sinks. The depth is read off the scale A. Areometer.svg
Schematic drawing of a hydrometer. The lower the density of the fluid, the deeper the weighted float B sinks. The depth is read off the scale A.

A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity.

Contents

A hydrometer usually consists of a sealed hollow glass tube with a wider bottom portion for buoyancy, a ballast such as lead or mercury for stability, and a narrow stem with graduations for measuring. The liquid to test is poured into a tall container, often a graduated cylinder, and the hydrometer is gently lowered into the liquid until it floats freely. The point at which the surface of the liquid touches the stem of the hydrometer correlates to relative density. Hydrometers can contain any number of scales along the stem corresponding to properties correlating to the density.

Hydrometers are calibrated for different uses, such as a lactometer for measuring the density (creaminess) of milk, a saccharometer for measuring the density of sugar in a liquid, or an alcoholometer for measuring higher levels of alcohol in spirits.

The hydrometer makes use of Archimedes' principle: a solid suspended in a fluid is buoyed by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid. The lower the density of the fluid, the deeper a hydrometer of a given weight sinks; the stem is calibrated to give a numerical reading.

History

Hydrometer from Practical Physics Hydrometer6455.png
Hydrometer from Practical Physics

The hydrometer probably dates back to the Greek philosopher Archimedes (3rd century BC) who used its principles to find the density of various liquids. [1] [2] An early description of a hydrometer comes from a Latin poem, written in the 2nd century AD by Remnius, who compared the use of a hydrometer to the method of fluid displacement used by Archimedes to determine the gold content of Hiero II's crown. [3]

Hypatia of Alexandria (4th-5th century AD), an important female Greek mathematician, is the first person traditionally associated with the hydrometer. [3] In a letter, Synesius of Cyrene asks Hypatia, his teacher, to make a hydrometer for him:

The instrument in question is a cylindrical tube, which has the shape of a flute and is about the same size. It has notches in a perpendicular line, by means of which we are able to test the weight of the waters. A cone forms a lid at one of the extremities, closely fitted to the tube. The cone and the tube have one base only. This is called the baryllium. Whenever you place the tube in water, it remains erect. You can then count the notches at your ease, and in this way ascertain the weight of the water. [4]

According to the Encyclopedia of the History of Arabic Science, it was used by Abū Rayhān al-Bīrūnī in the 11th century and described by Al-Khazini in the 12th century. [5] It was rediscovered in 1612 by Galileo and his circle of friends, and used in experiments especially at the Accademia del Cimento. [6] It appeared again in the 1675 work of Robert Boyle (who coined the name "hydrometer"), [3] with types devised by Antoine Baumé (the Baumé scale), William Nicholson, and Jacques Alexandre César Charles in the late 18th century, [7] more or less contemporarily with Benjamin Sikes' discovery of the device by which the alcoholic content of a liquid can be automatically determined. The use of the Sikes device was made obligatory by British law in 1818. [8]

Ranges

The hydrometer sinks deeper in low-density liquids such as kerosene, gasoline, and alcohol, and less deep in high-density liquids such as brine, milk, and acids. It is usual for hydrometers to be used with dense liquids to have the mark 1.000 (for water) near the top of the stem, and those for use with lighter liquids to have 1.000 near the bottom. In many industries a set of hydrometers is used (1.0–0.95, 0.95–.) to have instruments covering the range of specific gravities that may be encountered.

Scales

A NASA worker using a hydrometer to measure the brine density of a salt evaporation pond Brine concentration measurement.jpg
A NASA worker using a hydrometer to measure the brine density of a salt evaporation pond

Modern hydrometers usually measure specific gravity but different scales were (and sometimes still are) used in certain industries. Examples include:

Specialized hydrometers

Specialized hydrometers are frequently named for their use: a lactometer, for example, is a hydrometer designed especially for use with dairy products. They are sometimes referred to by this specific name, sometimes as hydrometers.

Alcoholometer

An alcoholmeter is a hydrometer that indicates the alcoholic strength of liquids which are essentially a mixture of alcohol and water. It is also known as a proof and Tralles hydrometer (after Johann Georg Tralles, but commonly misspelled as traille and tralle). It measures the density of the fluid. Where no sugar or other dissolved substances are present, the specific gravity of a solution of ethanol in water can be directly correlated to the concentration of alcohol. Saccharometers for measuring sugar-water mixtures measure densities greater than water. Many have scales marked with volume percents of "potential alcohol", based on a pre-calculated specific gravity. A higher "potential alcohol" reading on this scale is caused by a greater specific gravity, assumed to be caused by the introduction of dissolved sugars or carbohydrate based material. A reading is taken before and after fermentation and approximate alcohol content is determined by subtracting the post fermentation reading from the pre-fermentation reading. [10]

These were important instruments for determining tax, and specific maker's instruments could be specified. Bartholomew Sikes had a monopoly in the UK and Mary Dicas and her family enjoyed a similar monopoly in the US. [11]

Lactometer

A lactometer is used to check purity of cow's milk. The specific gravity of milk does not give a conclusive indication of its composition since milk contains a variety of substances that are either heavier or lighter than water. Additional tests for fat content are necessary to determine overall composition. The instrument is graduated into a hundred parts. Milk is poured in and allowed to stand until the cream has formed, then the depth of the cream deposit in degrees determines the quality of the milk. If the milk sample is pure, the lactometer floats higher than if it is adulterated or impure. [12] [13]

Saccharometer

A 20th century saccharometer Saccharometer, Merseyside Maritime Museum.jpg
A 20th century saccharometer

A saccharometer is a type of hydrometer used for determining the amount of sugar in a solution, invented by Thomas Thomson. [14] It is used primarily by winemakers and brewers, [15] and it can also be used in making sorbets and ice-creams. [16] The first brewers' saccharometer was constructed by Benjamin Martin (with distillation in mind), and initially used for brewing by James Baverstock Sr in 1770. [17] Henry Thrale adopted its use and it was later popularized by John Richardson in 1784. [18]

It consists of a large weighted glass bulb with a thin stem rising from the top with calibrated markings. The sugar level can be determined by reading the value where the surface of the liquid crosses the scale. The higher the sugar content, the denser the solution, and thus the higher the bulb will float.

Thermohydrometer

A thermohydrometer is a hydrometer that has a thermometer enclosed in the float section. For measuring the density of petroleum products, such as fuel oils, the specimen is usually heated in a temperature jacket with a thermometer placed behind it since density is dependent on temperature. Light oils are placed in cooling jackets, typically at 15 °C. Very light oils with many volatile components are measured in a variable volume container using a floating piston sampling device to minimize light end losses. [19]

Battery hydrometer

The state of charge of a lead-acid battery can be estimated from the density of the sulfuric acid solution used as electrolyte. A hydrometer calibrated to read specific gravity relative to water at 60 °F (16 °C) is a standard tool for servicing automobile batteries. Tables are used to correct the reading to the standard temperature. Hydrometers are also used for maintenance of wet-cell nickel-cadmium batteries to ensure the electrolyte is of the proper strength for the application; for this battery chemistry the specific gravity of the electrolyte is not related to the state of charge of the battery.

A battery hydrometer with thermometer (thermohydrometer) measures the temperature-compensated specific gravity and electrolyte temperature.

Antifreeze tester

Another automotive use of hydrometers is testing the quality of the antifreeze solution used for engine cooling. The degree of freeze protection can be related to the density (and so concentration) of the antifreeze; different types of antifreeze have different relations between measured density and freezing point.

Acidometer

An acidometer, or acidimeter, is a hydrometer used to measure the specific gravity of an acid. [20]

Barkometer

A barkometer is calibrated to test the strength of tanning liquors used in tanning leather. [21]

Salinometer

A salinometer is a hydrometer used to measure the salt content of the feed water to a marine steam boiler.

Urinometer

A urinometer is a medical hydrometer designed for urinalysis. As urine's specific gravity is dictated by its ratio of solutes (wastes) to water, a urinometer makes it possible to quickly assess a patient's overall level of hydration.

Use in soil analysis

A hydrometer analysis is the process by which fine-grained soils, silts and clays, are graded. Hydrometer analysis is performed if the grain sizes are too small for sieve analysis. The basis for this test is Stoke's Law for falling spheres in a viscous fluid in which the terminal velocity of fall depends on the grain diameter and the densities of the grain in suspension and of the fluid. The grain diameter thus can be calculated from a knowledge of the distance and time of fall. The hydrometer also determines the specific gravity (or density) of the suspension, and this enables the fraction of particles of a certain equivalent particle diameter to be calculated. [22]

See also

Related Research Articles

Density is a substance's mass per unit of volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:

<span class="mw-page-title-main">Relative density</span> Ratio of two densities

Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ; for gases, the reference is air at room temperature. The term "relative density" is often preferred in scientific usage, whereas the term "specific gravity" is deprecated.

<span class="mw-page-title-main">Meniscus (liquid)</span> Curve in a liquids surface due to adhesion to the container walls

In physics, the meniscus is the curve in the upper surface of a liquid close to the surface of the container or another object, produced by surface tension.

<span class="mw-page-title-main">Buoyancy</span> Upward force that opposes the weight of an object immersed in fluid

Buoyancy, or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and is equivalent to the weight of the fluid that would otherwise occupy the submerged volume of the object, i.e. the displaced fluid.

Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' principle is a law of physics fundamental to fluid mechanics. It was formulated by Archimedes of Syracuse.

<span class="mw-page-title-main">Alcohol by volume</span> Measure of how much alcohol is in a beverage

Alcohol by volume is a standard measure of how much alcohol (ethanol) is contained in a given volume of an alcoholic beverage. It is defined as the number of millilitres (mL) of pure ethanol present in 100 mL of solution at 20 °C (68 °F). The number of millilitres of pure ethanol is the mass of the ethanol divided by its density at 20 °C (68 °F), which is 0.78945 g/mL. The alc/vol standard is used worldwide. The International Organization of Legal Metrology has tables of density of water–ethanol mixtures at different concentrations and temperatures.

An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, allowing higher coolant temperature. However, all common antifreeze additives also have lower heat capacities than water, and do reduce water's ability to act as a coolant when added to it.

<span class="mw-page-title-main">Brix</span> Sugar content of an aqueous solution

Degrees Brix is a measure of the dissolved solids in a liquid, and is commonly used to measure dissolved sugar content of an aqueous solution. One degree Brix is 1 gram of sucrose in 100 grams of solution and represents the strength of the solution as percentage by mass. If the solution contains dissolved solids other than pure sucrose, then the °Bx only approximates the dissolved solid content. For example, when one adds equal amounts of salt and sugar to equal amounts of water, the degrees of refraction (BRIX) of the salt solution rises faster than the sugar solution. The °Bx is traditionally used in the wine, sugar, carbonated beverage, fruit juice, fresh produce, maple syrup and honey industries. The °Bx is also used for measuring the concentration of a cutting fluid mixed in water for metalworking processes.

The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks.

The Oechsle scale is a hydrometer scale measuring the density of grape must, which is an indication of grape ripeness and sugar content used in wine-making. It is named for Ferdinand Oechsle (1774–1852) and it is widely used in the German, Swiss and Luxembourgish wine-making industries. On the Oechsle scale, one degree Oechsle (°Oe) corresponds to one gram of the difference between the mass of one litre of must at 20 °C and 1 kg. For example, must with a specific mass of 1084 grams per litre has 84 °Oe.

The Baumé scale is a pair of hydrometer scales developed by French pharmacist Antoine Baumé in 1768 to measure density of various liquids. The unit of the Baumé scale has been notated variously as degrees Baumé, B°, Bé° and simply Baumé. One scale measures the density of liquids heavier than water and the other, liquids lighter than water. The Baumé of distilled water is 0. The API gravity scale is based on errors in early implementations of the Baumé scale.

<span class="mw-page-title-main">Refractometer</span> Measurement Tool

A refractometer is a laboratory or field device for the measurement of an index of refraction (refractometry). The index of refraction is calculated from the observed refraction angle using Snell's law. For mixtures, the index of refraction then allows to determine the concentration using mixing rules such as the Gladstone–Dale relation and Lorentz–Lorenz equation.

<span class="mw-page-title-main">Gravity (alcoholic beverage)</span>

Gravity, in the context of fermenting alcoholic beverages, refers to the specific gravity, or relative density compared to water, of the wort or must at various stages in the fermentation. The concept is used in the brewing and wine-making industries. Specific gravity is measured by a hydrometer, refractometer, pycnometer or oscillating U-tube electronic meter.

State of charge (SoC) quantifies the remaining capacity available in a battery at a given time and in relation to a given state of ageing. It is usually expressed as percentage. An alternative form of the same measure is the depth of discharge (DoD), calculated as 1 − SoC. It refers to the amount of charge that may been used up if the cell is fully discharged. State of charge is normally used when discussing the current state of a battery in use, while depth of discharge is most often used to discuss a constant variation of state of charge during repeated cycles.

In brewing, attenuation refers to the conversion of sugars into alcohol and carbon dioxide by the fermentation process; the greater the attenuation, the more sugar has been converted into alcohol. A more attenuated beer is drier and more alcoholic than a less attenuated beer made from the same wort.

When drinking beer, there are many factors to be considered. Principal among them are bitterness, the variety of flavours present in the beverage and their intensity, alcohol content, and colour. Standards for those characteristics allow a more objective and uniform determination to be made on the overall qualities of any beer.

The Twaddell scale is a hydrometer scale for reporting the measured specific gravity of a liquid relative to water. On this scale, a specific gravity of 1.000 is reported as 0, and 2.000 reports as 200. Concentrated sulfuric acid with a specific gravity of 1.8 has a Twaddell scale measurement of 160. The Twaddell scale is only used for liquids with specific gravity greater than that of water. The scale was used in the British dye and bleach manufacturing industries. While the Baumé scale was adopted throughout England, the Twaddell scale was used in England and Scotland.

Hydrostatic bubbles, also known as philosophical bubbles, gravity beads, aerometrical beads and hydrometer beads, are a type of hydrometer invented in 1757 by Alexander Wilson of Glasgow. The design was subsequently improved and patented by the glassblower and instrument maker Isabella Lovi of Edinburgh in 1805. The instrument, which consists of a set of glass beads, seems to have been particular to Scotland and was only used until the early 19th century, when it was largely superseded by more accurate methods.

<span class="mw-page-title-main">Mary Dicas</span>

Mary Dicas became Mary Arstall was a scientific instrument maker in Liverpool. Her company created thousands of hydrometers that were exported to America where Dicas & Co enjoyed a monopoly as the agreed instrument for calculating the tax on alcoholic beverages.

References

  1. ↑ Hornsey, Ian S. (2003). A history of beer and brewing. Cambridge: Royal Society of Chemistry. p. 429. ISBN   978-0-85404-630-0.
  2. ↑ Bendick, Jeanne (2011) [1962]. Archimedes And The Door Of Science. Literary Licensing, LLC. pp. 63–64. ISBN   9781258014889.
  3. 1 2 3 Bensaude-Vincent, Bernadette (2000). Holmes, Frederic L.; Levere, Trevor H. (eds.). Instruments and Experimentation in the History of Chemistry. Massachusetts Institute of Technology Press. p. 153. ISBN   9780262082822.
  4. ↑ FitzGerald, Augustine (1926). "Letter 15 - To the Philosopher (Hypatia)". The Letters of Synesius of Cyrene. Oxford University Press. p. 99.
  5. ↑ Rozhanskaya, Mariam; Levinova, I. S. (1996). "Statics". In Rushdī Rāshid; Régis Morelon (eds.). Encyclopedia of the History of Arabic Science, Volume 2 . Routledge. pp. 614–642 [ 639 ]. ISBN   978-0-415-12411-9 . Retrieved 2019-03-26.
  6. ↑ "In-depth Hydrometer". Museo Galileo. Retrieved 2024-01-01.
  7. ↑ Blondel, Claude-Joseph (2003). "Un enfant illustre de Beaugency : le physicien et aéronaute Jacques Charles (1746-1823)" [An illustrious child of Beaugency: the physicist and aeronaut]. Les Publications de l'Académie d'Orléans, Agriculture, Sciences, Belles-lettres et Arts (in French). Académie d'Orléans (4): 37.
  8. ↑ Denison, Merrill (1955). The Barley and the Stream: The Molson Story. Toronto: McClelland & Stewart. p. 132.
  9. ↑ Dick, William Brisbane (1975). "Degrees of Baum'e". Dick's Encyclopedia of Practical Receipts and Processes. New York: Dick and Fitzgerald, Publishers. ISBN   9780308101579.
  10. ↑ Rabin, Dan; Forget, Carl (1998). The dictionary of beer and brewing. London: Fitzroy Dearborn. ISBN   9781579580780 . Retrieved 2009-10-11.
  11. ↑ Morrison-Low, A. D. (2004-09-23). Dicas [married name Arstall], Mary (fl. 1800–1815), maker of scientific instruments. Vol. 1. Oxford University Press. doi:10.1093/ref:odnb/49542.
  12. ↑ Geisler, Joseph F. (1891). "Signification of Lactometer Tests". Journal of the American Chemical Society. 13 (2): 93–98. doi:10.1021/ja02124a009. ISSN   0002-7863.
  13. ↑ "Glass lactometer, England, 1875-1900". Science Museum Group Collection. Retrieved 2024-01-01.
  14. ↑ Thomson, Thomas (1840). Explanation of Allan's Saccharometer: Appointed by Act of Parliament for the Use of Distillers, & C. D. & W. Millar.
  15. ↑ Sambrook, Pamela (1996). Country House Brewing in England, 1500-1900. A&C Black. ISBN   9781852851279 . Retrieved 2009-10-11.
  16. ↑ Hanneman, Leonard J. (1993). Patisserie. ISBN   9780750604307 . Retrieved 2009-10-11.
  17. ↑ Mathias, Peter (1959). The Brewing Industry in England 1700-1830. University Press. Retrieved 2012-03-16.
  18. ↑ Bud, Robert; Warner, Deborah Jean; Chaplin, Simon; Johnston, Stephen; Peterson, Betsy Bahr (1998). Instruments of Science: An Historical Encyclopedia. Science Museum, London, and National Museum of American History, Smithsonian Institution. ISBN   9780815315612 . Retrieved 2009-10-11.
  19. ↑ Béla G. Lipták; Kriszta Venczel, eds. (2017). Instrument and automation engineers' handbook: measurement and safety (Fifth ed.). United States: Taylor & Francis Group, CRC Press. p. 1314. ISBN   978-1-4987-2764-8.
  20. ↑ "Acidometer". The Free Dictionary. Farlex. 2003. Retrieved 18 September 2010.
  21. ↑ Davis, Charles Thomas (1897). The manufacture of leather: being a description of all of the processes for the tanning and tawing with bark, extracts, chrome and all modern tannages in general use. H. C. Baird & co. Retrieved 2009-10-11. Barkometer.
  22. ↑ Fakhry A. Assaad, Philip Elmer LaMoreaux, Travis H. Hughes (ed.), Field Methods for Geologists and Hydrogeologists, Springer Science & Business Media, 2004 ISBN   3540408827, p.299

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