ISO 3361:1975

Specifies a reduced molybdosilicate spectrophotometric method for the determination of the soluble silica content of phosphoric acid for industrial use. The method can be used for the determination of 1 µg of soluble silica in the presence of 20 mg of phosphorus pentoxide. It is thus, for example, applicable to the determination of soluble silica contents greater than 30 mg/kg if the phosphoric acid contains 60 % of phosphorus pentoxide.