The Orthotolidine Reagent for Free Chlorine in Water. ORTHOTOLIDINE is most coomon test Reagent to detect Chlorine during Water distillation, Salts, Hypochlorite, Alkalinity process.
With small amounts of free chlorine, a deep yellow color is produced with the orthotolidine reagent.
During tratment with hypochlorite, a green color appeared which gradually deepened and changed to yellow and finally to deep red as the concentration of free chlorine increased.