Litmus is a watter-soluble mixtur o different dyes extractit frae lichens, especially Roccella tinctoria. It is eften absorbed ontae filter paper tae produce ane o the auldest furms o pH indicator, uised tae test materials for acidity. Blue litmus paper turns reid under acidic condeetions an reid litmus paper turns blue unner basic (i.e. alkaline) condeetions, wi the colour chynge occurrin ower the pH range 4.5-8.3 at 25 °C. Neutral litmus paper is purple. Litmus can an aa be prepared as an aqueous solution that functions similarly. Unner acidic condeetions the solution is reid, an unner basic condeetions the solution is blue.
- Manfred Neupert: Lackmus in Römpp Lexikon Chemie (German), January 31, 2013.