Acid test

An acid test is any qualitative chemical or metallurgical assay which uses acid; most commonly, and historically, the use of a strong acid to distinguish gold from base metals. Figuratively, acid test is any definitive test for some attribute, e.g. of a person's character, or of the performance of some product.

Chemistry

The traditional acid test for gold consists of placing a small drop of a strong acid, such as nitric acid, onto the metal's surface. Most metals fizz or bubble, while precious metals remain unaffected. The acid test is thus decisive, immediate, cheap and simple to perform.

Figurative meanings

The figurative meaning of the expression, where it is applied to tests of character, or definitive tests to other materials, became popular during and after the California Gold Rush[1], but was current before then, as shown by this quote from the Wisconsin paper The Columbia Reporter, November 1845:

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 examples of the figurative use of the phrase are the web sites Acid1, Acid2 and Acid3, which are designed to test web browsers for compliance with current web standards. Another example is the quick ratio method, nicknamed "acid test", used by financial analysts to assess a business' liquidity.

The use of the term "acid test" for experiences with the psychedelic drug LSD was popularised by the Merry Pranksters, and derives from the drug's common name, "acid". Many users experience a dissolution between themselves and the "outside world", and such experiences are considered to be a test of ones character.