Figure 2

H ₂ reduces MB (blue) to leucoMB (colorless). Early during the titration (MB-Pt reagent dropped into hydrogen-rich water), the solution contains more hydrogen than MB. Hence, MB is reduced to leucoMB and the solution is colorless. At the titration endpoint, the solution contains more MB than hydrogen; hence, it turns blue. 1. Drop an MB-Pt into hydrogen-rich water. 2. Hydrogen-rich water is colored by the blue of MB-Pt. 3. Immediately, blue turns colorless by hydrogen.