Noun
unsized paper treated with litmus for use as an acid-base indicator
Source: WordNetWords are the litmus paper of the mind. Terry Pratchett
A playwright . . . is . . . the litmus paper of the arts. He's got to be, because if he isn't working on the same wave length as the audience, no one would know what in hell he was talking about. He is a kind of psychic journalist, even when he's gre. Arthur Miller
Words are the litmus paper of the minds. If you find yourself in the power of someone who will use the word "commence" in cold blood, go somewhere else very quickly. But if they say "Enter", don't stop to pack. Terry Pratchett
A swab of the discharge is put onto litmus paper to check its acidity. Source: Internet
It turned corks a yellow color and removed all color from wet, blue litmus paper and some flowers. Source: Internet