Editing Fahrenheit (section)

== History ==
Fahrenheit proposed his temperature scale in 1724, basing it on two reference points of temperature. In his initial scale (which is not the final Fahrenheit scale), the zero point was determined by placing the [[thermometer]] in "a mixture of [[ice]], water, and ''salis Armoniaci''{{NoteTag|1= "Sal Armoniac" was an impure form of ammonium chloride. The French chemist [[Nicolas Lemery|Nicolas Lémery]] (1645–1715) discussed it in his book {{lang|fr|Cours de Chymie}} (''A Course of Chemistry'', 1675), describing where it occurs naturally and how it can be prepared artificially. It occurs naturally in the deserts of northern Africa, where it forms from puddles of animal urine. It can be prepared artificially by boiling 5 parts of urine, 1 part of sea salt, and ½ part of chimney soot until the mixture has dried. The mixture is then heated in a sublimation pot until it sublimates; the sublimated crystals are ''sal Armoniac''. See:
* Nicolas Lémery, ''Cours de chymie'' […], 7th ed. (Paris, France:  Estienne Michallet, 1688), ''Chapitre XVII : du Sel Armoniac'', [https://books.google.com/books?id=4k54-UD6uR4C&pg=PT338 pp. 338–339].
** English translation:  Nicolas Lémery with James Keill, trans., ''A Course of Chymistry'' […], 3rd ed. (London, England:  Walter Kettilby, 1698), Chap. XVII: of Sal Armoniack, p. 383, available on-line at [http://dfg-viewer.de/show/?tx_dlf%5Bid%5D=http%3A%2F%2Fdigital.ub.uni-duesseldorf.de%2Foai%2F%3Fverb%3DGetRecord%26metadataPrefix%3Dmets%26identifier%3D1882311&tx_dlf%5Bpage%5D=431&tx_dlf%5Bdouble%5D=0&cHash=c8dd26af74e251df9bd96a6e4221344b Heinrich Heine University (Düsseldorf, Germany)].}} [transl. [[ammonium chloride]]] or even sea salt".<ref name=":1" /> This combination forms a [[eutectic system]], which stabilizes its temperature automatically: 0&nbsp;°F was defined to be that stable temperature. A second point, 96&nbsp;degrees, was approximately the human body's temperature.<ref name=":1">Fahrenheit, Daniele Gabr. (1724) [https://royalsocietypublishing.org/doi/abs/10.1098/rstl.1724.0016 Experimenta & observationes de congelatione aquæ in vacuo factæ a D. G. Fahrenheit, R. S. S] (Experiments and observations on water freezing in the void by D. G. Fahrenheit, R. S. S.),
''Philosophical Transactions of the Royal Society of London'', vol.&nbsp;33, no.&nbsp;382, page&nbsp;78 (March–April 1724). Cited and translated in  http://www.sizes.com:80/units/temperature_Fahrenheit.htm.</ref> A third point, 32&nbsp;degrees, was marked as being the temperature of ice and water "without the aforementioned salts".<ref name=":1" />

According to a German story, Fahrenheit actually chose the lowest air temperature measured in his hometown [[Gdańsk|Danzig]] (Gdańsk, [[Poland]]) in winter 1708–09 as 0&nbsp;°F, and only later had the need to be able to make this value reproducible using brine.<ref>{{cite web |url=http://www.deutscher-wetterdienst.de/lexikon/index.htm?ID=L&DAT=Lufttemperatur |title = Wetterlexikon - Lufttemperatur |publisher=[[Deutscher Wetterdienst]] |access-date=13 December 2013 |language=de |url-status=dead |archive-url=https://web.archive.org/web/20131015045624/http://www.deutscher-wetterdienst.de/lexikon/index.htm?ID=L&DAT=Lufttemperatur |archive-date=15 October 2013 |df=dmy }}</ref>{{failed verification|date=December 2023}}

According to a letter Fahrenheit wrote to his friend [[Herman Boerhaave]],<ref>Ernst Cohen and W. A. T. Cohen-De Meester. ''Chemisch Weekblad'', volume 33 (1936), pages 374–393, cited and translated in http://www.sizes.com:80/units/temperature_Fahrenheit.htm.</ref> his scale was built on the work of [[Ole Rømer]], whom he had met earlier. In [[Rømer scale]], brine freezes at zero, water freezes and melts at 7.5&nbsp;degrees, body temperature is 22.5, and water boils at 60&nbsp;degrees. Fahrenheit multiplied each value by 4 in order to eliminate fractions and make the scale more [[granularity|fine-grained]]. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90&nbsp;degrees); he adjusted the scale so that the melting point of ice would be 32&nbsp;degrees, and body temperature 96&nbsp;degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval 6 times (since 64 = 2<sup>6</sup>).<ref name="TMU">{{cite book |publisher=Cambridge University Press |isbn=978-0-521-71590-4 |last1=Frautschi |first1=Steven C. |author2=Richard P. Olenick |author3=Tom M. Apostol |author4=David L. Goodstein |title = The mechanical universe: mechanics and heat |date=14 January 2008 |page=502 }}</ref><ref>{{cite web
|url=https://www.straightdope.com/21342402/fahrenheit-scale-0-100-significance
|publisher=The Straight Dope
|title = On the Fahrenheit scale, do 0 and 100 have any special significance?
|first = Cecil |last = Adams |date=1989-12-15
}}</ref>

Fahrenheit soon after observed that water boils at about 212&nbsp;degrees using this scale.<ref>Fahrenheit, Daniele Gabr. (1724) [http://rstl.royalsocietypublishing.org/content/33/381-391/1.full.pdf+html "Experimenta circa gradum caloris liquorum nonnullorum ebullientium instituta"]. {{Webarchive|url=https://web.archive.org/web/20140629074815/http://rstl.royalsocietypublishing.org/content/33/381-391/1.full.pdf+html |date=29 June 2014 }} (Experiments performed concerning the degree of heat of some boiling liquids), ''Philosophical Transactions of the Royal Society of London'', '''33''' :  1–3.  For an English translation, see:  [https://web.lemoyne.edu/giunta/fahrenheit.html  Le Moyne College (Syracuse, New York)].</ref> The use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of [[Anders Celsius]], and these fixed points were adopted by a committee of the [[Royal Society]] led by [[Henry Cavendish]] in 1776–77.<ref>[[Hasok Chang]], ''Inventing Temperature: Measurement and Scientific Progress'', pp. 8–11, Oxford University Press, 2004, {{ISBN|0198038240}}.</ref><ref>{{cite journal | title=XXXVII. The report of the Committee appointed by the Royal Society to consider of the best method of adjusting the fixed points of thermometers; and of the precautions necessary to be used in making experiments with those instruments| last1 = Cavendish | first1 = Henry
| last2 = Heberden | first2 = William
| last3 = Aubert | first3 = Alexander
| last4 = Luc | first4 = Jean Andre De
| last5 = Maskelyne | first5 = Nevil
| last6 = Horsley | first6 = Samuel
| last7 = Planta | first7 = Joseph | journal=Philosophical Transactions of the Royal Society of London| volume=67 | date=28 December 1777 | issn=0261-0523 | doi=10.1098/rstl.1777.0038|doi-access=free| url=https://archive.org/details/paper-doi-10_1098_rstl_1777_0038| pages=816–857}}</ref> Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water was exactly 32&nbsp;°F, and the boiling point was exactly 212&nbsp;°F, or 180&nbsp;degrees higher. It is for this reason that [[normal human body temperature]] is approximately 98.6&nbsp;°F (oral temperature) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale).<ref>{{Cite journal |last1=Elert |first1=Glenn |title = Temperature of a Healthy Human (Body Temperature) |url=http://hypertextbook.com/facts/LenaWong.shtml |access-date=12 April 2008 |doi=10.1046/j.1471-6712.2002.00069.x |year=2002 |journal=Scandinavian Journal of Caring Sciences |volume=16 |pages=122–8 |pmid=12000664 |last2=Forsberg |first2=C. |last3=Wahren |first3=L.K. |issue=2 |url-status=dead |archive-url=https://web.archive.org/web/20100926162224/http://hypertextbook.com/facts/LenaWong.shtml |archive-date=26 September 2010 |df=dmy-all }}</ref>

In the present-day Fahrenheit scale, 0&nbsp;°F no longer corresponds to the eutectic temperature of ammonium chloride brine as described above. Instead, that eutectic is at approximately 4&nbsp;°F on the final Fahrenheit scale.{{NoteTag|Eutectic temperature of ammonium chloride and water is listed as −15.9&nbsp;°C (3.38&nbsp;°F) and as −15.4&nbsp;°C (4.28&nbsp;°F) in (respectively)
* {{cite journal
|journal = J. Fluid Mech.
|last1 = Peppin|first1=S. S.|last2=Huppert|first2=H. E.|last3=Worster|first3=M. G.
|year=2008
|title = Steady-state solidification of aqueous ammonium chloride
|volume = 159
|page = 472 (table 1)
|publisher = Cambridge University Press
|doi = 10.1017/S0022112008000219
|bibcode = 2008JFM...599..465P
|s2cid = 30271164
|url=http://www.itg.cam.ac.uk/people/heh/Paper209.pdf |archive-url=https://web.archive.org/web/20100119222017/http://www.itg.cam.ac.uk/people/heh/Paper209.pdf |archive-date=2010-01-19 |url-status=live
}}
* {{cite journal 
|journal = Procedia Materials Science
|doi = 10.1016/j.mspro.2014.07.288
|last1=Barman|first1= N.|last2=Nayak|first2= A. K.|last3=Chattopadhyay|first3= H.
|title = Solidification of a Binary Solution (NH<sub>4</sub>Cl + H<sub>2</sub>O) on an Inclined Cooling Plate: A Parametric Study
|volume = 7
|year = 2021
|page = 456 (table 1)
|url=https://cyberleninka.org/article/n/633625.pdf |archive-url=https://web.archive.org/web/20190115075817/https://cyberleninka.org/article/n/633625.pdf |archive-date=2019-01-15 |url-status=live
|doi-access = free
}}
}}

The [[Rankine scale|Rankine temperature scale]] was based upon the Fahrenheit temperature scale, with its zero representing [[absolute zero]] instead.