| http://www.w3.org/ns/prov#value | - As is known, they are obtainable, for example, by precipitating silica from waterglass using an acid, washing the ionic constituents out of the hydrogel formed, displacing the water by a lower-boiling, water-soluble organic liquid, especially an alcohol such as methanol, heating the resulting alcogel containing the alcohol under supercritical pressure to a temperature above the critical temperat
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