AbstractThe effect of various inorganic anions and cations on the determination of silica by the molybdenum‐blue method is studied. The following ions do not interfere:Anions:Carbonate, chloride, nitrate, sulphate.Cations:Aluminium, calcium, magnesium, manganese.The extent and nature of the interference caused by the following ions is discussed:Anions:Dichromate, phosphate.Cations:Copper, ferrous iron, ferric iron.The effect of copper is noteworthy, in that compound formation is indicated, the apparent ratio of copper to silica in the complex being 12 :