litmus

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

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

litmus

[′lit·məs]

(materials)

Blue, water-soluble powder from various lichens, especially Variolaria lecanora and V. 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.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

litmus

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

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.