Division 6.5 Titrate each distillate with standard volumetric solution (4.7.) until the pH is 4,6 ± 0,1, using a pH meter and if desired an automatic burette. Addition of an indicator helps to check whether the titration is proceeding correctly. Take each burette reading to the nearest 0.01 ml with the aid of a magnifying lens (5.10.) avoiding errors of parallax.
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The titrating may be carried out with the indicator only. Titrate until the colour of the distillate corresponds to that of a solution recently prepared from 150 ml of water to which has been added 50 ml of the boric acid solution and 0,20 ml of the indicator contained in a conical flask (5.8).