''Litmus'' is one name for a lichen, whose extracts turn red in the presence of acids and blue in the presence of bases. Paper soaked in litmus extracts are used in traditional test for detecting acidity or alkalinity. The phrase ''litmus test'' has become part of the language, often in a social or political context. | ''Litmus'' is one name for a lichen, whose extracts turn red in the presence of acids and blue in the presence of bases. Paper soaked in litmus extracts are used in traditional test for detecting acidity or alkalinity. The phrase ''litmus test'' has become part of the language, often in a social or political context. |