Acid test
{{Short description|A process of distinguishing gold from base metals, with a figurative meaning}}
{{other uses}}
An acid test is a qualitative chemical or metallurgical assay utilizing acid. Historically, it often involved the use of a robust acid to distinguish gold from base metals. Figuratively, the term represents any definitive test for attributes, such as gauging a person's character or evaluating a product's performance.
Chemistry
Testing for gold with acid capitalizes on gold's status as a noble metal, resistant to corrosion, oxidation, or acid. The procedure includes rubbing the gold-colored item on black stone, leaving a visible mark. The mark undergoes scrutiny by applying nitric acid, which dissolves the mark of any item not gold, stainless steel, zinc, tungsten, aluminum, platinum, or palladium.{{cite web |title=How Do Jewelers Test Gold? |url=https://aalanddiamond.com/how-do-jewelers-test-gold/ |archive-url=https://web.archive.org/web/20200814161514/https://aalanddiamond.com/how-do-jewelers-test-gold/ |url-status=usurped |archive-date=August 14, 2020 |website=AaLAND Diamond Jewelers |date=22 June 2020 |access-date=13 April 2023 |quote=Nitric acid does not react to gold that’s 12 karats and above, nor does it react to stainless steel, zinc, tungsten, aluminum, or palladium.}} If the mark persists, further testing involves aqua regia (nitric acid and hydrochloric acid). If the mark dissolves, the item proves to be genuine gold. More precise assessment of fineness or purity is achieved using varying strengths of aqua regia and comparative testing against known fineness.{{cite book |title= Philosophy of Science: From Explanation to Justification|last= Bunge|first= Mario|authorlink= Mario Bunge|year= 1998|publisher= Transaction Publishers|isbn= 9780765804143|page= 343|url= https://books.google.com/books?id=ofcy8wZeLCoC&q=gold+test+aqua+regia}}{{cite book|title= Robert Boyle and Seventeenth-century Chemistry|last= Hall|first= Marie Boas|authorlink= Marie Boas Hall|year= 1958|publisher= CUP Archive|page= [https://archive.org/details/robertboyleseven0000hall/page/128 128]|url= https://archive.org/details/robertboyleseven0000hall|url-access= registration|quote= gold test aqua regia.}}{{Dead link|date=January 2022}}{{cite book |title= School science and mathematics, Volume 13|author1= School Science and Mathematics Association |author2=Central Association of Science and Mathematics Teachers |year= 1913|publisher= School Science and Mathematics Association|location= University of California|page= 732|url= https://books.google.com/books?id=XY8YAQAAIAAJ&q=gold+test+aqua+regia}}{{cite book |title= The Urban Treasure Hunter: A Practical Handbook for Beginners|last= Chaplan|first= Michael|authorlink= Michael Chaplan|year= 2005|publisher= Square One Publishers|isbn= 9780757000904|page= [https://archive.org/details/urbantreasurehun0000chap/page/194 194]|url= https://archive.org/details/urbantreasurehun0000chap|url-access= registration|quote= gold testing kit.}}
Geology
In geological applications, detecting the presence of calcite or other forms of calcium carbonate in alkaline soils or during lithological analysis involves using dilute hydrochloric acid and observing effervescence.{{cite web|last=Geology.com|title=The Acid Test for Carbonate Minerals and Carbonate Rocks|url=http://geology.com/minerals/acid-test.shtml|publisher=Geology.com|access-date=28 November 2016}}
Figurative meanings
The figurative usage of the expression gained popularity during and after the California Gold Rush,{{cite web|url=http://www.worldwidewords.org/backissues/wbi080517.txt|title=Q&A: Acid test|work=World Wide Words|access-date=2009-04-19|archive-url=https://web.archive.org/web/20110604064551/http://www.worldwidewords.org/backissues/wbi080517.txt|archive-date=2011-06-04|url-status=dead}} but had currency even before then. An example from the Wisconsin paper The Columbia Reporter, November 1845, illustrates this: "Twenty-four years of service demonstrates his ability to stand the acid test, as Gibson’s Soap Polish has done for over thirty years."{{cite web|url=http://www.phrases.org.uk/meanings/acid-test.html |title=Acid test |publisher=Phrases.org.uk |accessdate=2013-04-22}}
Other instances of the figurative use of the phrase include websites like Acid1, Acid2, and Acid3, designed to test web browsers for compliance with current web standards. Financial analysts also employ the "acid test" nickname for the quick ratio method, which assesses the liquidity of a business.
The term "acid test" took on a different meaning in the realm of experiences with the psychedelic drug LSD,{{cite web|url=http://www.cosmosmagazine.com/features/print/1690/the-acid-test |title=The acid test |accessdate=2007-02-01 |work=Cosmos Magazine |url-status=dead |archiveurl=https://web.archive.org/web/20080613014500/http://www.cosmosmagazine.com/features/print/1690/the-acid-test |archivedate=2008-06-13 }} popularized by the Merry Pranksters. This association stems from the drug's colloquial name, "acid" (which chemically it indeed was).