litmus paper

American  

noun

1. a strip of paper impregnated with litmus, used as a chemical indicator.

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Etymology

Origin of litmus paper

First recorded in 1795–1805

Example Sentences

The best way to confirm that the solution is neutralized is with litmus paper.

From Seattle Times

Watson recalls one telling advertising campaign: posters printed on litmus paper that said: “When acid rain is falling, you should see red” – offering a vivid illustration of the problem.

From The Guardian

Mr. Bradford views them as economic litmus papers for the poorest parts of the city, as companies laid off workers and stimulus checks ran out.

From New York Times

Testing kits come in all shapes and sizes, but when working with kids, it’s best to use a simple litmus paper test.

From Seattle Times

You have three basic options: a pH testing kit that uses litmus paper or an electronic pH tester, or you can send a soil sample into a lab.

From Seattle Times