Litmus is a substance that is commonly used in chemistry to indicate whether a solution is an acid or a base. It can be prepared in an acidic form, which is red, and in a basic form, which is blue. An acidic solution will turn blue litmus red, but will not affect red litmus. A basic solution will turn red litmus blue, but will not affect blue litmus. A neutral solution, which is neither acidic nor basic, will not change the color of either litmus.
Litmus may be dissolved in water or alcohol to make an indicating solution. Because litmus is an intensely colored substance, only a few drops of litmus indicator need to be added to a solution to tell whether it is acidic or basic. Litmus indicator is also used when a solution is being neutralized. For example, litmus indicator will turn an acidic solution red. In order to neutralize the acid, base is slowly added. When the solution becomes neutral, the litmus indicator will change to purple. If more base is added, the solution will become basic, and the litmus will turn blue.
Litmus may also be added to absorbent paper to make litmus paper. Litmus paper is blue or red, depending on which form of litmus is present. When a drop of solution is placed on the paper, the color will indicate whether the solution is acidic, basic, or neutral.
Litmus is extracted from organisms called lichens. It was once used as a dye and in coloring beverages. Today, litmus is also used as a stain to make specimens easier to view under a microscope.
