The titration of an acid with a base. (a) The titrant (the base) is in the buret, and the flask contains the acid solution along with a small amount of indicator. (b) As base is added drop by drop to the acid solution in the flask during the titration, the indicator changes colour, but the colour disappears on mixing. (c) The stoichiometric (equivalence) point is marked by a permanent indicator colour change. The volume of base added is the difference between the final and initial buret readings.