Editing PH (section)

== History ==
In 1909, the [[Danish people|Danish]] chemist [[S. P. L. Sørensen|Søren Peter Lauritz Sørensen]] introduced the concept of pH at the [[Carlsberg Laboratory]],<ref name="Sørensen2">{{cite journal |last1=Sørensen |first1=S. P. L. |year=1909 |title=Über die Messung und die Bedeutung der Wasserstoffionenkonzentration bei enzymatischen Prozessen |url=https://core.ac.uk/download/pdf/14517358.pdf |url-status=live |journal=Biochemische Zeitschrift |volume=21 |pages=131–304 |archive-url=https://web.archive.org/web/20210415205740/https://core.ac.uk/download/pdf/14517358.pdf |archive-date=15 April 2021 |access-date=22 March 2021 |quote=Original German: Für die Zahl p schlage ich den Namen Wasserstoffionenexponent und die Schreibweise p<sub>H</sub>• vor. Unter dem Wasserstoffionexponenten (p<sub>H</sub>•) einer Lösungwird dann der Briggsche Logarithmus des reziproken Wertes des auf Wasserstoffionenbezagenen Normalitäts faktors de Lösungverstanden.}} Two other publications appeared in 1909, one in French and one in Danish.</ref> originally using the notation "p<sub>H•</sub>", with H• as a subscript to the lowercase p. The concept was later revised in 1924 to the modern pH to accommodate definitions and measurements in terms of [[electrochemical cells]].<blockquote>For the sign ''p'', I propose the name 'hydrogen ion exponent' and the symbol p<sub>H•</sub>. Then, for the hydrogen ion exponent (p<sub>H•</sub>) of a solution, the negative value of the [[Common logarithm|Briggsian logarithm]] of the related hydrogen ion [[Equivalent concentration|normality factor]] is to be understood.<ref name="Sørensen2" /></blockquote>Sørensen did not explain why he used the letter p, and the exact meaning of the letter is still disputed.<ref>{{Cite journal |last=Francl |first=Michelle |date=August 2010 |title=Urban legends of chemistry |url=https://www.nature.com/articles/nchem.750.epdf |url-status=live |journal=Nature Chemistry |volume=2 |issue=8 |pages=600–601 |bibcode=2010NatCh...2..600F |doi=10.1038/nchem.750 |issn=1755-4330 |pmid=20651711 |archive-url=https://web.archive.org/web/20200806053215/https://www.nature.com/articles/nchem.750.epdf |archive-date=6 August 2020 |access-date=21 July 2019|url-access=subscription }}</ref><ref>{{cite web|last=Munroe|first=Randall|work=xkcd|url=https://xkcd.com/2943|title=Unsolved math Problems|date=June 7, 2024|access-date=June 10, 2024}}</ref> Sørensen described a way of measuring pH using ''potential'' differences, and it represents the negative ''power'' of 10 in the concentration of hydrogen ions. The letter ''p'' could stand for the French ''puissance,'' German ''Potenz,'' or Danish ''potens'', all meaning "power", or it could mean "potential". All of these words start with the letter ''p'' in [[French language|French]], [[German language|German]], and [[Danish language|Danish]], which were the languages in which Sørensen published: Carlsberg Laboratory was French-speaking; German was the dominant language of scientific publishing; Sørensen was Danish. He also used the letter ''q'' in much the same way elsewhere in the paper, and he might have arbitrarily labelled the test solution "p" and the reference solution "q"; these letters are often paired with e4 then e5.<ref>{{cite journal |last1=Myers |first1=Rollie J. |year=2010 |title=One-Hundred Years of pH |journal=Journal of Chemical Education |volume=87 |issue=1 |pages=30–32 |bibcode=2010JChEd..87...30M |doi=10.1021/ed800002c}}</ref> Some literature sources suggest that "pH" stands for the [[Latin language|Latin term]] ''pondus hydrogenii'' (quantity of hydrogen) or ''potentia hydrogenii'' (power of hydrogen), although this is not supported by Sørensen's writings.<ref name="Otterson2">{{cite journal |last1=Otterson |first1=David W. |date=2015 |title=Tech Talk: (11) pH Measurement and Control Basics. |journal=Measurement and Control |volume=48 |issue=10 |pages=309–312 |doi=10.1177/0020294015600474 |s2cid=110716297 |doi-access=free }}</ref><ref name="Lian2">{{cite journal |last1=Lian |first1=Ying |last2=Zhang |first2=Wei |last3=Ding |first3=Longjiang |last4=Zhang |first4=Xiaoai |last5=Zhang |first5=Yinglu |last6=Wang |first6=Xu-dong |date=2019 |title=Nanomaterials for Intracellular pH Sensing and Imaging. |url=https://www.sciencedirect.com/science/article/pii/B9780128144978000084 |journal=Novel Nanomaterials for Biomedical, Environmental and Energy Applications. |series=Micro and Nano Technologies |pages=241–273 |doi=10.1016/B978-0-12-814497-8.00008-4 |isbn=9780128144978 |s2cid=104410918 |access-date=16 June 2022|url-access=subscription }}</ref><ref name="Bradley2">{{cite news |last1=Bradley |first1=David |date=21 February 2018 |title=When it comes to caustic wit and an acid tongue, mind your Ps and Qs. |publisher=Materials Today |url=https://www.materialstoday.com/materials-chemistry/comment/caustic-wit-acid-tongues-mind-your-ps-and-qs/ |access-date=16 June 2022}}</ref>

In modern [[chemistry]], the p stands for "the negative [[Common logarithm|decimal logarithm]] of", and is used in the term p''K''<sub>a</sub> for [[acid dissociation constant]]s,<ref name="Jens2">{{cite journal |author=Nørby, Jens |year=2000 |title=The origin and the meaning of the little p in pH |journal=Trends in Biochemical Sciences |volume=25 |issue=1 |pages=36–37 |doi=10.1016/S0968-0004(99)01517-0 |pmid=10637613}}</ref> so pH is "the negative [[Common logarithm|decimal logarithm of]] H<sup>+</sup> ion concentration", while pOH is "the negative decimal logarithm of OH<sup>−</sup> ion concentration". 

American bacteriologist [[Alice Catherine Evans]], who influenced [[Dairy|dairying]] and [[food safety]], credited [[William Mansfield Clark]] and colleagues, including herself, with developing pH measuring methods in the 1910s, which had a wide influence on laboratory and industrial use thereafter. In her memoir, she does not mention how much, or how little, Clark and colleagues knew about Sørensen's work a few years prior.<ref name="Evans-Memoirs2">{{cite web |last1=Evans |first1=Alice C. |author-link=Alice Catherine Evans |year=1963 |title=Memoirs |url=https://history.nih.gov/archives/downloads/aliceevans.pdf |url-status=dead |archive-url=https://web.archive.org/web/20171215000804/https://history.nih.gov/archives/downloads/aliceevans.pdf |archive-date=15 December 2017 |access-date=2018-03-27 |website=NIH Office of History |publisher=National Institutes of Health Office of History}}</ref> She said:<blockquote>In these studies [of bacterial metabolism] Dr. Clark's attention was directed to the effect of acid on the growth of bacteria. He found that it is the intensity of the acid in terms of hydrogen-ion concentration that affects their growth. But existing methods of measuring acidity determined the quantity, not the intensity, of the acid. Next, with his collaborators, Dr. Clark developed accurate methods for measuring hydrogen-ion concentration. These methods replaced the inaccurate titration method of determining the acid content in use in biologic laboratories throughout the world. Also they were found to be applicable in many industrial and other processes in which they came into wide usage.<ref name="Evans-Memoirs2" /></blockquote>The first [[Electronics|electronic]] method for measuring pH was invented by [[Arnold Orville Beckman]], a professor at the [[California Institute of Technology]] in 1934.<ref>{{cite web |title=Origins: Birth of the pH Meter |url=https://eands.caltech.edu/origins-birth-of-the-ph-meter/ |url-status=dead |archive-url=https://web.archive.org/web/20181106180207/https://eands.caltech.edu/origins-birth-of-the-ph-meter/ |archive-date=6 November 2018 |access-date=11 March 2018 |website=Caltech Engineering & Science Magazine}}</ref> It was in response to a request from the local citrus grower [[Sunkist Growers, Incorporated|Sunkist]], which wanted a better method for quickly testing the pH of lemons they were picking from their nearby orchards.<ref>{{cite web |last1=Tetrault |first1=Sharon |date=June 2002 |title=The Beckmans |url=https://books.google.com/books?id=nf0DAAAAMBAJ&q=ph+caltech+beckman+sunkist&pg=PA96 |url-status=live |archive-url=https://web.archive.org/web/20210415222325/https://books.google.com/books?id=nf0DAAAAMBAJ&q=ph+caltech+beckman+sunkist&pg=PA96 |archive-date=15 April 2021 |access-date=11 March 2018 |website=Orange Coast |publisher=Orange Coast Magazine}}</ref>