Litmus Paper, Blue

Boil 10 parts of coarsely powdered litmus for 1 hour with 100 parts of ethanol (96%). Decant the alcohol and add to the residue a mixture of 45 parts of ethanol (96%) and 55 parts of water. After 2 days decant the clear liquid. 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 hydrochloric acid and 90 mL of water. On shaking the paper turns red within 45 seconds.