A PRELIMINARY REPORT ON CLAYS OF FLORIDA 79

 The ultimate analysis does not indicate what compounds are present in a clay, but at the same time some data can be derived from it. Ries1 lists the following facts as obtainable from chemical analysis:
 "1. The purity of the clay, showing the proportions of silica, alumina, combined water and fluxing impurities present. High-grade clays often show a percentage of silica, alumina, and chemically combined water approaching quite closely to kaolinite.
 2. The approximate refractoriness of a clay; for other things being equal, a clay with high total fluxes, is commonly less refractory than one with low total fluxes. In this connection it is to be remembered that texture, irregularity of distribution of the constituents, and condition of kiln atmosphere are among conditions affecting the result.
 3. The color to which the clay burns. This must be judged with caution. Assuming the constituents to be evenly distributed, then a clay with 1 per cent or less of ferric oxide is likely to burn white, but at high temperatures titanium if present produces discoloration. One with 2-3 per cent of ferric oxide is likely to burn buff ; one with several per cent or more of ferric oxide will usually burn red if there is no excess of lime or alumina: It should be remembered that condition of 'the kiln atmosphere, texture of the clay, and sulphur in the fire gas may all affect the results.
 4. The quantity of chemically combined water. Clays with a large amount sometimes show a high shrinkage, but there are many exceptions to this.
 5. Excess of silica. A high percentage of silica (80-90 per cent) may indicate a sandy clay, and possibly one of low shrinkage, but does not necessarily point to a very lean one. High silica in a fire clay usually shows only moderate refractoriness provided it is evenly distributed.
 6. Organic matter. This should be determined, as it causes trouble in burning if present to the extent of several per cent, requiring thorough oxidation in firing before the clay is allowed to pass to the vitrification stage.
 7. Sulphur trioxide. Since this may be the cause of swelling in improperly burned wares, and also indicate the presence of soluble sulphates, it should always be determined.
 1Ries, H., Clays, Their Occurrence, Properties and Uses, p. 62, 1908. New Jersey Final Report, Vol. VI, p. 50, 1904.