Reference number
ISO 995:1975
ISO 995:1975
© ISO 2024
ISO 995:1975
Potassium hydroxide for industrial use — Determination of silica content — Reduced molybdosilicate photometric method
Edition 1
1975-09
1975-09
Retirada
Resumen
The method is applicable to products having silica contents exceeding 10 mg/kg. The principle is based on the formation of yellow oxidized silico-molybdic complex in a strongly acid medium, in the presence of boric acid to suppress interference by fluorides. Selective reduction of this complex with a mixture of aminonaphtholsulphonic acid (4-amino-3-hydroxynaphthalene-1-sulphonic acid), sodium metabisulphite and sodium sulphite, in the presence of oxalic acid and in a strongly acid medium so as to suppress interference by phosphates. Photometric measurement of the blue-coloured complex at a wavelength of about 795 nm.