Editing Hydrometer (section)

==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.<ref>{{cite book |url=https://books.google.com/books?id=XRyxWu8rRnQC&q=Alcoholometer&pg=PA12 |title=The dictionary of beer and brewing|first1=Dan|last1=Rabin|first2=Carl|last2=Forget|publisher=Fitzroy Dearborn|place=London|date=1998 |isbn=9781579580780|access-date=2009-10-11 }}</ref>

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.<ref>{{Cite ODNB |last=Morrison-Low |first=A. D. |url=http://www.oxforddnb.com/view/10.1093/ref:odnb/9780198614128.001.0001/odnb-9780198614128-e-49542 |title=Dicas [married name Arstall], Mary (fl. 1800–1815), maker of scientific instruments |date=2004-09-23 |volume=1 |language=en |doi=10.1093/ref:odnb/49542|isbn=978-0-19-861412-8 }}</ref>

===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.<ref>{{Cite journal |last=Geisler |first=Joseph F. |date=1891 |title=Signification of Lactometer Tests |url=https://pubs.acs.org/doi/abs/10.1021/ja02124a009 |journal=Journal of the American Chemical Society |language=en |volume=13 |issue=2 |pages=93–98 |doi=10.1021/ja02124a009 |issn=0002-7863}}</ref><ref>{{Cite web |title=Glass lactometer, England, 1875-1900 |url=https://collection.sciencemuseumgroup.org.uk/objects/co154299/glass-lactometer-england-1875-1900-hydrometer-lactometer |access-date=2024-01-01 |website=Science Museum Group Collection |language=en}}</ref>

===Saccharometer===
{{about|the hydrometer|the optical instrument|Saccharimeter|section=yes}}
[[File:Saccharometer, Merseyside Maritime Museum.jpg|thumb|right|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 (chemist)|Thomas Thomson]].<ref>{{Cite book |last=Thomson |first=Thomas |url=https://books.google.com/books?id=6bUoAQAAMAAJ&q=Thomas+Thomson+saccharometer |title=Explanation of Allan's Saccharometer: Appointed by Act of Parliament for the Use of Distillers, & C |date=1840 |publisher=D. & W. Millar |language=en}}</ref> It is used primarily by [[winemaker]]s and [[brewing|brewers]],<ref>{{cite book |last1=Sambrook |first1=Pamela |url=https://books.google.com/books?id=vDEwIR0ZHGYC&q=Saccharometer&pg=PA64 |title=Country House Brewing in England, 1500-1900 |date=1996 |publisher=A&C Black |isbn=9781852851279 |access-date=2009-10-11}}</ref> and it can also be used in making [[sorbet]]s and ice-creams.<ref>{{cite book |url=https://books.google.com/books?id=D6YuI15dT74C&q=Saccharometer&pg=PA250 |title=Patisserie |isbn=9780750604307 |access-date=2009-10-11 |last1=Hanneman |first1=Leonard J. |year=1993 |publisher=Butterworth-Heinemann }}</ref> The first brewers' saccharometer was constructed by Benjamin Martin (with distillation in mind), and initially used for brewing by James Baverstock Sr in 1770.<ref>{{cite book |last1=Mathias |first1=Peter |url=https://books.google.com/books?id=PyU9AAAAIAAJ&pg=PA71 |title=The Brewing Industry in England 1700-1830 |publisher=University Press |year=1959 |access-date=2012-03-16}}</ref> Henry Thrale adopted its use and it was later popularized by John Richardson in 1784.<ref>{{cite book |last1=Bud |first1=Robert |url=https://books.google.com/books?id=1AsFdUxOwu8C&q=Saccharometer+John+Richardson&pg=RA1-PA312 |title=Instruments of Science: An Historical Encyclopedia |last2=Warner |first2=Deborah Jean |last3=Chaplin |first3=Simon |last4=Johnston |first4=Stephen |last5=Peterson |first5=Betsy Bahr |publisher=Science Museum, London, and National Museum of American History, Smithsonian Institution |year=1998 |isbn=9780815315612 |access-date=2009-10-11}}</ref>

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&nbsp;°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.<ref>{{Cite book|title=Instrument and automation engineers' handbook: measurement and safety|publisher=Taylor & Francis Group, CRC Press|year=2017|isbn=978-1-4987-2764-8|editor-last=Béla G. Lipták|location=United States|pages=1314|editor-last2=Kriszta Venczel|edition=Fifth}}</ref>

===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 {{Convert|60|F}} is a standard tool for servicing [[car battery|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]].<ref>{{Cite web |title =Acidometer |work =The Free Dictionary |publisher =Farlex |year =2003 |url =http://www.thefreedictionary.com/acidometer |access-date =18 September 2010 }}</ref>

===Barkometer===
A barkometer is  calibrated to test the strength of tanning liquors used in tanning [[leather]].<ref>{{cite book |last=Davis |first=Charles Thomas |url=https://archive.org/details/manufactureoflea00davi |title=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 |publisher=H. C. Baird & co. |year=1897 |quote=Barkometer. |access-date=2009-10-11}}</ref>

===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.

===Gallery===
<gallery mode="packed" heights="440px">
Hydrometer in a still (cropped).jpg|Alcohol meter to measure ethanol concentration of a water/ethanol mixture, shown in the "parrot head" of a still
Densimetro o galattometro con custodia - Musei del cibo - Parmigiano - 314a.jpg|Lactometer to measure the density of milk, indicating its fat content 
Battery condition indicator.jpg|Battery condition indicator to measure electrolyte density in a lead–acid battery, indicating its state of charge (~1985)
Coolant indicator.jpg|Antifreeze tester to measure engine coolant density, indicating its freezing point.
</gallery>