litmus paper

• Papier traité avec un colorant naturel qui change de couleur selon les conditions acides ou basiques, utilisé comme test chimique simple pour déterminer si une substance est un acide ou une base.

A type of paper treated with a natural dye that changes color in response to acidic or alkaline conditions, used as a simple chemical test to determine whether a substance is an acid or a base.

1. Chemical test paperB2formal

   A type of paper treated with a natural dye that changes color in response to acidity or alkalinity, used to test pH levels.

   papier de tournesol

   • The chemist dipped the litmus paper into the solution to check its pH.
   • Blue litmus paper turns red in acidic conditions.
   • Litmus paper is a simple tool for determining whether a substance is an acid or a base.

2. Decisive indicatorC1informal

   A figurative term for a test or situation that reveals the true nature or outcome of something.

   test décisif / pierre de touche

   • The election results were a litmus paper for public opinion on the new policy.
   • His reaction to the criticism was a litmus paper of his character.
   • This project will be a litmus paper for the team's ability to work under pressure.