This procedure determines the total silica, as bicarbonate-reactive silica, in filtered and unfiltered samples. The material which cannot pass through a 0.45 micron filter is considered particulate silica and measurable by the difference between the filtered and unfiltered samples. Silica reacts with a molybdate reagent in an acidic environment to form a yellow silicomolybdate complex. This complex is reduced by ascorbic acid to form the molybdate blue color. The color intensity is proportional to the silica concentration.