Q: I see the phrase “acid test” often used during the World Cup competition in Russia to mean a crucial test for a team. Did it once refer to a test with real acid?
A: Not only did the phrase once mean a literal acid test—it still does, though the figurative sense is much more common.
When the term first showed up in writing in the mid-18th century, the Oxford English Dictionary says, it meant a “chemical test involving reaction with an acid.”
The dictionary’s earliest citation, which refers to boric acid, is from a 1759 essay by the English chemist Robert Dossie: “It has not the acid test of changing the colour of vegetable tinctures.”
However, the figurative use of the phrase to mean a crucial or conclusive test—such as the test facing a team at the World Cup—was inspired by the use of nitric acid to test gold for purity, according to the OED:
“The test for gold from which the figurative use developed typically involves making a mark on a touchstone with a piece of the metal in question and treating this mark with nitric acid, which dissolves other metals more readily than gold.”
As the dictionary explains, “The effect of the acid in dissolving the mark is compared with its effect on marks made by specimens of known gold content.”
Interestingly, the first Oxford example for “acid test” used to determine the purity of a precious metal refers to silver, not gold:
“The gentleman would then offer to bet $5 that the quarter was good, and would stand the acid test, which, as it was good silver [it] would of course do” (from the July 29, 1844, issue of a Philadelphia newspaper, the North American and Daily Advertiser).
The OED’s first gold example is from the Nov. 14, 1860, issue of a Wisconsin newspaper, the Monroe Sentinel: “The outside film of gold, though less than the two hundred thousandth part of an inch in thickness, is yet enough to cover up the base metal, and protect it from the usual acid test.”
However, we’ve found an earlier gold example in the Chemist, a London journal, in which the word “nitric” precedes “acid test.”
In an Aug. 15, 1850, letter, William Griffiths, a goldsmith in Dublin, reports an example of “the alloying of metals so that they should present the appearance of gold and be capable of being apportioned, so as not only to resist the nitric acid test but to deceive the most experienced as to color and weight.”
The first OED citation for the figurative sense is from the Nov. 18, 1854, Columbia Reporter, a Wisconsin paper: “Twenty-four years of service demonstrates his ability to stand the acid test, as Gibson’s Soap Polish has done for over thirty years.”
Here’s a more recent example from Spectacles, Lorgnettes, & Monocles, a 1989 book by D. C. Davidson: “Even an expert would hesitate to distinguish 9 carat from 12 and 14 carat gold without resorting to an acid test.”
We’ll end with a July 2, 2018, headline from the Northern Echo, a regional daily in the English town of Darlington.
“World Cup 2018: England about to face their acid test.” (England passed the test, beating Colombia to reach the quarterfinals.)