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

Methyl Orange Solution
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Methyl Orange Solution

Dissolve 0.1 g of methyl orange in 80 mL of water and dilute to 100 mL with ethanol (96%).

Test for sensitivity A mixture of 0.1 mL of the methyl orange solution and 100 mL of carbon dioxide-free water is yellow. Not more than 0.1 mL of 1 M hydrochloric acid is required to change the colour to red.

Colour change pH 3.0 (red) to pH 4.4 (yellow).