litmus: A water-soluble dye extractedfrom certain lichens. It turnsred under acid conditions and blueunder alkaline conditions, the colourchange occurring over the pH range4.5-8.3 (at 25°C). It is not suitable fortitrations because of the wide rangeover which the colour changes, but is used as a rough indicator of acidityor alkalinity, both in solution and aslitmus paper (absorbent paper soakedin litmus solution).
A natural pigment that
changes color when in contact with acids
and alkalis; above a pH of 8.3 it is blue and
below a pH of 4.5 it is red. Thus it gives a
rough indication of the acidity or basicity
of a solution; because of its rather broad
range of color change it is not used for precise
work. Litmus is used both in solution
and as litmus paper.
