Litmus Paper, Red

To the blue litmus extract, add dilute hydrochloric acid dropwise until the blue colour becomes red. Impregnate strips of filter paper with the solution and allow to dry.

Test for sensitivityImmerse a strip measuring 10 mm by 60 mm in a mixture of 10 mL of 0.02 M sodium hydroxide and 90 mL of water. On shaking the paper turns blue within 45 seconds.