An acid test is a qualitative

chemical A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combin ...

metallurgical assay A metallurgical assay is a compositional analysis of an ore, metal, or alloy, usually performed in order to test for purity or quality. Some assay methods are suitable for raw materials; others are more appropriate for finished goods. Raw pre ...

utilizing

acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...

. Historically, it often involved the use of a robust acid to distinguish

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

from

base metals A base metal is a common and inexpensive metal, as opposed to a precious metal such as gold or silver. In numismatics, coins often derived their value from the precious metal content; however, base metals have also been used in coins in the past ...

. 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 A noble metal is ordinarily regarded as a metallic chemical element, element that is generally resistant to corrosion and is usually found in nature in its native element, raw form. Gold, platinum, and the other platinum group metals (ruthenium ...

, resistant to

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

, or

. The procedure includes rubbing the gold-colored item on black stone, leaving a visible mark. The mark undergoes scrutiny by applying

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

, which dissolves the mark of any item not gold, stainless steel, zinc, tungsten, aluminum, platinum, or palladium. If the mark persists, further testing involves

aqua regia Aqua regia (; from Latin, "regal water" or "royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar concentration, molar ratio of 1:3. Aqua regia is a fuming liquid. Freshly prepared aqua regia is colorless, but i ...

(nitric acid and

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

). If the mark dissolves, the item proves to be genuine gold. More precise assessment of

fineness The fineness of a precious metal object (coin, bar, jewelry, etc.) represents the weight of ''fine metal'' therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hard ...

or purity is achieved using varying strengths of aqua regia and comparative testing against known fineness.

Geology

In geological applications, detecting the presence of

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

or other forms of

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

in alkaline soils or during lithological analysis involves using dilute

and observing

effervescence Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from that release. The word effervescence is derived from the Latin verb ''fervere'' (to boil), preceded by the adverb ''ex''. It has the same l ...

Figurative meanings

The figurative usage of the expression gained popularity during and after the

California Gold Rush The California gold rush (1848–1855) began on January 24, 1848, when gold was found by James W. Marshall at Sutter's Mill in Coloma, California. The news of gold brought approximately 300,000 people to California from the rest of the U ...

, 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." Other instances of the figurative use of the phrase include websites like

Acid1 Acid1, originally called the Box Acid Test, is a test page for web browsers. It was developed in October 1998 and was important in establishing baseline interoperability between early web browsers, especially for the Cascading Style Sheets 1.0 ...

Acid2 Acid2 is a webpage that tests web browsers' functionality in displaying aspects of HTML markup, CSS 2.1 styling, Portable Network Graphics, PNG images, and data URIs. The test page was released on 13 April 2005 by the Web Standards Project. The ...

, and

Acid3 The Acid3 test is a web test page from the Web Standards Project that checks a web browser's compliance with elements of various web standards, particularly the Document Object Model (DOM) and JavaScript. If the test is successful, the results ...

, designed to test

web browser A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...

s for compliance with current

web standard Web standards are the formal, non-proprietary standards and other technical specifications that define and describe aspects of the World Wide Web. In recent years, the term has been more frequently associated with the trend of endorsing a set of ...

s. 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 Psychedelics are a subclass of hallucinogenic drugs whose primary effect is to trigger non-ordinary mental states (known as psychedelic experiences or "trips") and a perceived "expansion of consciousness". Also referred to as classic halluc ...

LSD Lysergic acid diethylamide, commonly known as LSD (from German ; often referred to as acid or lucy), is a semisynthetic, hallucinogenic compound derived from ergot, known for its powerful psychological effects and serotonergic activity. I ...

, popularized by the

Merry Pranksters The Merry Pranksters were followers of American author Ken Kesey. Kesey and the Merry Pranksters lived communally at Kesey's homes in California and Oregon, and are noted for the sociological significance of a lengthy road trip they took in the s ...

. This association stems from the drug's colloquial name, "acid" (which chemically it indeed was).

References

{{reflist , 30em Chemical tests Gold rushes California Gold Rush