A PRELIMINARY REPORT ON CLAYS OE FLORIDA 
79 
The ultimate analysis does not indicate what compounds are pres¬ 
ent in a clay, but at the same time some data can be derived from it. 
Ries 1 lists the following facts as obtainable from chemical analysis: 
“1. The purity of the clay, showing the proportions Of silica, alumi¬ 
na, 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 excep¬ 
tions 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 im¬ 
properly burned wares, and also indicate the presence of soluble sul¬ 
phates, it should always be determined. 
iRies, H., Clays, Their Occurrence, Properties and Uses, p. 62, 1908. New 
Jersey Final Report, Vol. VI, p. 50, 1904. 
