Litmus Paper, Red
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
—Usually about 6 x 50 mm in size. Red litmus paper meets the requirements of the tests for Phosphate, Residue on Ignition, and Rosin Acids, under Litmus Paper, Blue.
Sensitiveness: Drop a 10-to 12-mm strip into 100 mL of 0.0005 N sodium hydroxide contained in a beaker, and stir continuously: the color of the paper changes within 30 seconds. The 0.0005 N sodium hydroxide is prepared by diluting 1 mL of 0.1 N sodium hydroxide with freshly boiled and cooled purified water to 200 mL.
