Reactive silica by formation of molybdosilicic acid, reduction to molybdenum blue and spectrophotometric measurement. Applicable to up to 50 $Gmg of SiO$d2 in up to 100 ml. Total silica by prior fusion to reactive silica. Applicable to up to 50 $Gmg of SiO$d2 in up to 50 ml. Suspended silica by prior filtration and fusion. Applicable to up to 50 $Gmg of SiO$d2 in up to 1 L.