Silicon content can be determined in the range of 0,2 % (m/m) to 1 % (m/m). The principle is dissolution of a test portion in acid, filtration and aspiration of the test solution into a nitrous oxide-acetylene flame of an atomic absorption spectrometer, combustion of the filter, volatilization of silica, fusion of the residue, dissolution of the melt in dilute acid, aspiration of this second solution into another such flame, measurement of the absorbance of the resonance line energy from the spectrum of aluminium and comparison with that of calibration solutions at 309,3 nm.