Precipitated Silica: Hot Water Glass Carbonated, Then Acidified to pH 6.75 (Allen 1957)

Bubble carbon dioxide through hot dilute water glass and the silica comes down as an extremely fine white powder rather than a gel. Edward Allen of Columbia-Southern made it this way as a white reinforcing filler for rubber; this follows his Example XI, which gave a powder of 148 m² per gram. Source: E. M. Allen (Columbia-Southern), US 2,805,955 (1957), Example XI. The percentages are our arithmetic; the filter, mill and indicator are ours. Picture drawn by Youblob.