Summary: Rapid, accurate silica determinations have been made titrimetrically following decomposition by HClO₄-HF in a ‘Teflon’ vessel, the volatilized silicon tetrafluoride being precipitated as K₂SiF₆ in a HF-KF-glycerol-alcohol mixture. After filtration and washing with alcohol the precipitate is dissolved in boiling water, then titrated with NaOH. This method has many advantages over conventional gravimetric or spectrophotometric procedures.