The Calculation of the “Rational Analysis” of Clays

Introduction.There are comparatively few clays used in the ceramic industries which consist of pure kaolin, AhO3.zSiO2.zH20,or of those other closely similar hydrated aluminum silicates, which, collectively, have been called "clay substance" and by other similar names.'By far the greater number of clays contain other minerals as well; of these, the most important are quartz, feldspars, and micas.The two most common micas, the purely potassic muscovite and the ferro-magnesian biotite, are, however, not present in large amount in any but a few clays that are of commercial value, particularly for the finer ceramic purposes.Besides the above-named minerals, numerous other minerals have been observed in clays,z but these, almost without exception, are present in such small amounts in clays of any notable commercial value that they may be regarded as practically negligible.Only four minerals, then, kaolin, quartz, feldspar, and mica, need be considered for the present.As each of these influences the "burning" and other properties of a clay and of the finished products, it is of importance to be able to estimate the relative amounts of each present in any given clay, so that the proper mixtures may be made or the proper temperature and other conditions may be controlled.The ceramist endeavors to accomplish this by what is known technically as the "rational" analy~is.~