Coagulation is affected by the chemicals, pH, and temperature of the system. Flocculation, settling and clarification are observed in the treatment of sulfur black dye waste. A combination of sulfuric acid and aluminum sulfate is used to obtain better settling with smaller quantities of chemicals than aluminum sulfate alone. Treatment with ferric chloride and hydrochloric acid has been studied more extensively because of the possibility of obtaining pH values that promote flocculation and rapid settling while reducing ferric chloride concentrations. In this case, clarification and settling are effected by the pH values and the order of addition of the chemicals.