litmus

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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 A dye obtained from lichens of the genus Roccella. Litmus is used as a pH indicator, being red under acidic conditions and blue under alkaline conditions.

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lit·mus / ˈlitməs/ • n. a dye obtained from certain lichens that is red under acid conditions and blue under alkaline conditions.

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litmus Dye that is purple in neutral aqueous solutions; it is used to indicate acidity (turning red) or alkalinity (turning blue). It is most familiar in the form of litmus paper used as an acid-base indicator. The dye is extracted from lichens. See also pH

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litmus blue colouring matter from lichens. XVI. — ONorw. litmosi, f. ON. litr dye + mosi MOSS.

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litmus (lit-mŭs) n. a pigment used as an indicator of acids and alkalis. In the presence of acids it turns red; with alkalis it turns blue.