• British Pharmacopoeia Volume V
  • Appendices
  • Appendix I A. General Reagents

Methyl Red Solution
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Methyl Red Solution

Dissolve 50 mg in a mixture of 1.86 mL of 0.1 M sodium hydroxide and 50 mL of ethanol (96%)and dilute to 100 mL with water.

Test for sensitivity To 0.1 mL of the methyl red solution add 100 mL of carbon dioxide-free water and 0.05 mL of 0.02 M hydrochloric acid. The solution is red. Not more than 0.1 mL of 0.02 M sodium hydroxide is required to change the colour to yellow.

Colour change pH 4.4 (red) to pH 6.0 (yellow).