Tschermak, in 1878, regarded them as isomorphous mixtures of the following fundamental molecules: H 2 KA1 3 (SiO 4) 3, corresponding with muscovite; Mg 6 Si 3 0 12, a hypothetical polymer of olivine; and H4S15012, a hypothetical silicic acid.
In 1858 he pointed out the isomorphism of the fluostannates and the fluosilicates, thus settling the then vexed question of the composition of silicic acid; and subsequently he studied the fluosalts of zirconium, boron, tungsten, &c., and prepared silicotungstic acid, one of the first examples of the complex inorganic acids.
A certain proportion of soda ash (carbonate of soda) is also used in some works in sheet-glass mixtures, while " decolorizers " (substances intended to remove or reduce the colour of the glass) are also sometimes added, those most generally used being manganese dioxide and arsenic. Another essential ingredient of all glass mixtures containing sulphate of soda is some form of carbon, which is added either as coke, charcoal or anthracite coal; the carbon so introduced aids the reducing substances contained in the atmosphere of the furnace in bringing about the reduction of the sulphate of soda to a condition in which it combines more readily with the silicic acid of the sand.
Water decomposes it into silicofluoric acid and silicic acid: 3SiF 4 +3H 2 0 =2H2SiF6+ H 2 SiO 3.
Water decomposes it into hydrochloric and silicic acids.