It is well known to chemists that when silicates are decom- posed, by acids or other agents, in the presence of water, that the silicic acid thus produced is soluble to a large amount in that fluid; but that it may again be easily brought to an insoluble condition, as it exists in flint or sand, by the subse- quent separation of the water; and this fact, with the demon- stration of the exudation f