Acid-base titration. Image 2 of 3. Titrations are a method of volumetric analysis, in which a volume of one reagent is added to a known volume of another reagent until an end point. This end point can be measured by using an indicator, a substance that changes colour depending on its environment. This reaction is an acid-base titration, and the indicator used is methyl orange. The solution in the conical flask (bottom) has reached the end point, it is neutral (neither acid or alkali). For a sequence showing the change in colour at the end point, see images A500/348- 350.