litmus paper

paper covered in a special substance and used to detect acids and bases

Litmus may refer to:Litmus test (chemistry), a common pH testLitmus Zine, a web magazine devoted to creative science writingLitmus (Mozilla), a test case management tool maintained by Mozilla"Litmus" (Battlestar Galactica), an episode in the first season of the Battlestar Galactica television seriesLitmus (software), a WebDAV server protocol compliance test suiteLitmus Test of Medjugorje, a test of ecclesiastical obedience on part of the seers and the apparition of MedjugorjeLitmus test (language), an English colloquialism:Any kind of social indicator used to classify someone either favorably or unfavorablyLitmus test (politics), a question asked of a potential candidate
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Litmus is a water-soluble mixture of different dyes extracted from lichens, specially Roccella tinctoria. The mixture has CAS number 1393-92-6. It is often absorbed on to filter paper. The resulting piece of paper or solution with water becomes a pH indicator (one of the oldest), used to test materials for acidity. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic (i.e. alkaline) conditions, the color change occurring over the pH range 4.5-8.3 (at 25°C). Neutral litmus paper is purple in color. The mixture contains 10 to 15 different dyes (Erythrolein (or Erythrolitmin), Azolitmin, Spaniolitmin, Leucoorcein and Leucazolitmin). Pure Azolitmin does show nearly the same effect as litmus.
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Litmus paper n. An unsized white paper impregnated with litmus and used as a pH or acid-base indicator. [more]Litmus paper - Community and Resources

Noun
1. unsized paper treated with litmus for use as an acid-base indicator
(hypernym) paper
(substance-meronym) litmus, litmus test

Paper impregnated with litmus , usually cut in narrow strips. Dipping red litmus paper into a basic solution turns it blue; dipping blue litmus paper into an acidic solution turns it red.