litmus test

In chemistry, a litmus test is used to find out if a solution is an acid or a base. A special kind of paper is dipped in the liquid being tested during a litmus test.

A scientific litmus test can tell you the pH of a gas or liquid — in other words, it shows exactly how acidic the substance is. A litmus test uses litmus paper to test the substance; it turns red if it's acidic and blue if it's alkaline, or basic. The term litmus test is also used to talk about a simple, decisive test of something: "The vote was a litmus test of the voters' feelings about the economy."

Definitions of litmus test
  1. noun
    a coloring material (obtained from lichens) that turns red in acid solutions and blue in alkaline solutions; used as a very rough acid-base indicator
    synonyms: litmus
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    type of:
    acid-base indicator
    an indicator that changes color on going from acidic to basic solutions
  2. noun
    a test that relies on a single indicator
    “her litmus test for good breeding is whether you split infinitives”
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    type of:
    exam, examination, test
    a set of questions or exercises evaluating skill or knowledge
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