Litmus

litmus, organic dye usually used in the laboratory as an indicator of acidity or alkalinity (see acids and bases). Naturally pink in color, it turns blue in alkali solutions and red in acids. Commonly, paper is treated with the coloring matter to form so-called litmus paper. Litmus is extracted, chiefly in the Netherlands, from certain lichens (see archil), which are mashed, treated with potassium carbonate and ammonia, and allowed to ferment. The resulting product is mixed with various colorless substances, such as chalk or gypsum, and is sold in dark blue lumps, masses, or tablets. The active component of litmus, i.e., the part sensitive to acids or bases, is called erythrolitmin.

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litmus

Mixture of coloured organic compounds obtained from several species of lichens. In the form of a water solution or as litmus paper, it is the oldest and most-used indicator of whether a substance is an acid or a base. It turns red or pink in acid solutions and blue or purple-blue in alkaline solutions.

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litmus

a soluble powder obtained from certain lichens. It turns red under acid conditions and blue under basic conditions and is used as an indicator

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litmus [′lit·məs]

(materials)

Blue, water-soluble powder from various lichens, especiallyVariolaria lecanoraandV. rocella; turns red in solutions at pH 4.5, and blue at pH 8.3; used as an acid-base indicator. Also known as lacmus; lichen blue.

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litmus

An organic chemical indicator of acidity or alkalinity; is red in color for pH values below 4.5 and blue above 8.3.

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Litmus 

a dye extracted from certain species of lichen (for example, Roccella tinctoria).

The composition of litmus is complex and has not yet been fully established. The pigment component is the weak acid azolitmin, which yields blue salts. Litmus is used as an indicator: it turns red in an acid medium and blue in an alkaline medium. Test papers impregnated with the dye are generally the form used.