When the pH value is below 7.8, settling is rapid, but clarification is not always complete, and ferric chloride must be added before the acid. When hydrochloric acid is added first, not only is the rate of settling slow, but the amount of free sulfur released also increases with increasing acid quantity. The quantities of free sulfur can be great enough that the liquid becomes milky. Treatment with ferrous sulfate and sulfuric acid or pickling liquor produces complete clarification, but it does not promote settling as rapidly as treatment with ferric chloride and hydrochloric acid.