From Longman Dictionary of Contemporary Englishlitmus paperˈlitmus ˌpaper noun [uncountable] HCpaper containing litmus, used to test whether a chemical is an acid or an alkali
Examples from the Corpus
litmus paper• The use of litmus paper furnishes another example of such a transformation.• In a drawer the litmus paper mused upon which way to turn.• The litmus paper turned red when immersed in the liquid. 