Litmus

Name:
Litmus
Detailed information:

Chemistry name:	lichen blue
Properties:
A blue, amorphous powder frequently compressed into small cakes or strips (“paper”). Soluble in water; changes color with acidity of solution, red at pH 4.5, blue at pH 8.3.
Derivation:
By treating lichens (particularly Variolaria lecanora and V. rocella) with ammonia and potash and then fermenting the mass.
Use:
Indicator in analytical chemistry where precision is not required, soil testing.