Definition

1. Noun:
   • A natural dye used as a chemical indicator: Litmus is a water-soluble mixture of different dyes extracted from lichens. It is used to test whether a solution is acidic or basic (alkaline). Litmus turns red in acidic solutions and blue in basic solutions.

Usage

• Litmus is almost exclusively used in the context of chemical testing.
• It is typically used on a special absorbent paper called "litmus paper."
• The color change provides a simple, qualitative result (acidic or basic) but does not give a precise pH value.

Examples

• Noun:
  • The scientist dipped the litmus paper into the liquid to determine its pH.
  • A classic classroom experiment involves testing household substances with litmus.
  • If the litmus turns blue, the solution is alkaline.

Advanced Usage

• "Litmus test": A figurative idiom meaning a decisive test that produces a clear "yes/no" or "pass/fail" result, often used in politics, ethics, or decision-making.
  • His stance on the environmental bill became a litmus test for his political allies.
  • For many voters, this issue is the litmus test for any candidate.

Variants and Related Words

• Litmus paper (noun phrase): Paper impregnated with litmus, used for testing acidity or alkalinity.
  • She used a strip of litmus paper to test the water from the aquarium.
• Litmusless (adjective, rare): Not containing or not using litmus.

Synonyms

• Acid-base indicator: A more general scientific term for any substance that changes color to indicate pH.
• pH indicator: Another general term for substances like litmus, phenolphthalein, or universal indicator.

Related Phrases

• Turn litmus red/blue: A phrase describing the specific result of the test.
  • Vinegar will turn litmus red because it is acidic.

Related Idioms

• "A litmus test for (something)": As described in Advanced Usage, this is the primary idiom. It compares a situation to the definitive result provided by a litmus paper test.
  • The ability to work under pressure is often seen as a litmus test for this job.

Noun

1. 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