Abstract: A wastewater clarificant very excellent in the powers for removing BOD, COD and SS is provided. The clarificant comprises an aqueous solution containing a polynuclear complex salt that is obtained by subjecting to isochoric heating an aqueous solution containing a mixture of sulfates of a plurality of metals selected from the group consisting of potassium, iron, calcium, sodium, magnesium and aluminum. Preferably, the clarificant comprises an aqueous solution containing a polynuclear complex salt that is obtained by subjecting to isochoric heating an aqueous solution containing a mixture of sulfates of a plurality of metals selected from the group consisting of, in molar concentration, 0.02 to 0.08 of potassium, 0.11 to 1.31 of iron, 0.003 to 0.030 of calcium, 0.004 to 0.040 of sodium, 0.27 to 0.81 of magnesium and 0.370 to 1.300 of aluminum.

Abstract: An fiber optic liquid level indicator with a floating reflector includes a reference scale provided with a reflector disposed in an upper space above the liquid level within a pressure vessel so that a reference distance usable to correct error due to pressure can be calculated on the basis of travel time of a laser beam pulse emitted from a laser generator and reflected from the reference scale reflector through an optical guide and lens. A beam change-over switch is used to selectively guide a laser beam pulse to either the floating reflector or to the reference scale reflector so that pulse travel time can be determined.