1-Naphtholbenzein Solution

A 0.2% w/v solution of 1-naphtholbenzein in anhydrous acetic acid.

Sensitivity To 50 mL of glacial acetic acid add 0.25 mL of the naphtholbenzein solution. The solution is brownish-yellow. Not more than 0.05 mL of 0.1 M perchloric acid is required to change the colour to green.