Editing Alcohol proof (section)

==History==
The term ''proof'' dates back to 16th century England, when [[liquor|spirits]] were [[Alcohol law#Taxation and regulation of production|taxed]] at different rates depending on their alcohol content. Similar terminology and methodology spread to other nations as [[Alcohol distillation|spirit distillation]], and [[Alcohol law#Taxation and regulation of production|taxation]], became common. In England, spirits were originally tested with a basic "burn-or-no-burn" test, in which an alcohol-containing liquid that would ignite was said to be "above proof", and one which would not was said to be "under proof".<ref>{{cite book |last=Klein |first=H. Arthur |year=1974 |title=The World of Measurements: Masterpieces, Mysteries and Muddles of Metrology |publisher=Simon and Schuster |isbn=9780671215651 |pages=564 |url=https://books.google.com/books?id=1SkFAAAAMAAJ |quote=The concept of a standard or normative 'proof' strength was operative in Britain from the early days of the burn-or-no-burn tests. It paralleled the normative concepts of applied to brewing...}}</ref> A liquid just alcoholic enough to maintain combustion was defined as 100 proof and was the basis for taxation. Because the [[flash point]] of alcohol is highly dependent on temperature, 100 proof defined this way ranges from 20% at {{Convert|36|C}} to 96% at {{Convert|13|C}} [[Alcohol by volume#Alcohol by weight|alcohol by {{Em|weight}} (ABW)]]<!--values from table in source-->; at {{Convert|24|C}} 100 proof would be 50% AB{{Em|W}}.<ref>{{cite web |author=<!--not stated--> |date=2005 |title=Ethanol Freeze Protected Water Solutions |website=Engineering Toolbox |url=https://www.engineeringtoolbox.com/ethanol-water-d_989.html |access-date=2020-05-12}}</ref>

Another early method for testing liquor's alcohol content was the "gunpowder method". [[Gunpowder]] was soaked in a spirit, and if the gunpowder could still burn, the spirit was rated above proof. This test relies on the fact that [[potassium nitrate]] (a chemical in gunpowder) is significantly more soluble in water than in alcohol.<ref>{{cite web |title=Alcohol Proof and Alcohol by Volume: Definitions and Explanations |date=10 April 2017 |publisher=alcoholproblemsandsolutions.org |url=https://www.alcoholproblemsandsolutions.org/alcohol-proof-and-alcohol-by-volume-definitions-and-explanations |access-date=3 October 2020}}</ref> While less influenced by temperature than the simpler burn-or-no-burn test, gunpowder tests also lacked true reproducibility. Factors including the grain size of gunpowder and the time it sat in the spirit impact the dissolution of potassium nitrate and therefore what would be defined as 100 proof. However, the gunpowder method is significantly less variable than the burn-or-no-burn method, and 100 proof defined by it is traditionally defined as 57.15% ABV.

By the end of the 17th&nbsp;century, England had introduced tests based on [[specific gravity]] for defining proof. However, it was not until 1816 that a legal standard based on [[specific density]] was defined in England. 100 proof was defined as a spirit with {{frac|12|13}} the [[specific gravity]] of [[Pure Water|pure water]] at the same temperature.<ref name=Jensen>{{cite journal|author1-link=William B. Jensen |last=Jensen |first=William B. |date=September 2004 |title=The Origin of Alcohol 'Proof' |journal=Journal of Chemical Education |doi=10.1021/ed081p1258 |volume=81 |issue=9 |pages=1258–1259 |bibcode=2004JChEd..81.1258J |url=http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/111.%20Proof.pdf |access-date=17 July 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140708232531/http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/111.%20Proof.pdf |archive-date=8 July 2014}}</ref> From the 19th century until 1 January 1980, the UK officially measured alcohol content by proof spirit, defined as [[liquor|spirit]] with a [[Gravity (alcoholic beverage)|gravity]] of {{frac|12|13}} that of water, or {{Convert|923|kg/m3|abbr=on}}, and equivalent to 57.15% ABV.<ref name=scotch>{{cite book |year=1995 |chapter=Section 6: Sale and Distribution |title=Scotch Whisky: Questions and Answers |publisher=Scotch Whisky Association |chapter-url=http://www.dcs.ed.ac.uk/home/jhb/whisky/swa/chap6.html |access-date=3 October 2020}}</ref>

The value 57.15% is very close to the fraction {{frac|4|7}} {{nowrap|≈ 0.5714}}. This led to the approximation that 100-proof spirit has an ABV of {{frac|4|7}}. From this, it follows that to convert the ABV expressed as a percentage to degrees proof, it is only necessary to multiply the ABV by {{frac|7|4}}. Thus pure 100% alcohol will have 100×({{frac|7|4}}) = 175 proof, and a spirit containing 40% ABV will have 40×({{frac|7|4}}) = 70 proof.

The proof system in the United States was established around 1848 and was based on percent alcohol rather than specific gravity. Fifty percent alcohol by volume was defined as 100 proof.<ref name=Jensen/> This is different from 50% [[volume fraction]] (expressed as a percentage); the latter does not take into account change in volume on mixing, whereas the former does. To make 50% ABV from pure alcohol, one would take 50 parts of alcohol and dilute to 100 parts of solution with water, all the while mixing the solution. To make 50% alcohol by volume fraction, one would take 50 parts alcohol and 50 parts water, measured separately, and then mix them together. The resulting volume will not be 100 parts but between 96 and 97 parts, since the smaller water molecules can take up some of the space between the larger alcohol molecules (see [[Alcohol by volume#Volume change|volume change]]).

The use of proof as a measure of alcohol content is now mostly linguistic and historical. Today, [[liquor]] is sold in most locations with labels that state its percentage alcohol by volume.