unwrap tool 1.4 download

MnO trace trace Loss on ignition 19.3 Another theory, due to von Buch and Daubree, of the origin of clay should be mentioned. It is that the felspar has been attacked by acid vapours, chiefly hydrofluoric acid, from below. Collins, in 1887, claimed to have CERAMIC CHEMISTRY. 7 obtained kaolinite in 96 hours by treating orthoclase with dilute hydrofluoric acid. But it is much easier to suppose that the fluorides are already present in the granite as a mica, and that the acid has been liberated by carbonic acid. This theory is really part of a wider one, the pneuma- tolytic theory, which supposes post-volcanic emanations of fluorine, sulphur or boron compounds. Possibly isolated beds of clay have been formed by such means and by many other agencies, such as swamp waters alone. It is, in fact, impossible to generalise on every clay, but weathering, with or without chemical agents, is undoubtedly the safest hypothesis yet advanced. Besides the felspathic granites, clay may also be formed from augitic, zeolitic, and volcanically metamorphosed minerals. However original rocks may differ in com- position, the residual clays formed by their weathering tend to bear a striking chemical resemblance to each other,