A PRELIMINARY REPORT ON CLAYS OV FLORIDA 193


 Sedimentary kaolin occurs in numerous places in the vicinity of Dade City and in at least one point near San Antonio. For a full discussion of this clay see Chapter IX.
 A grayish-brown, sandy clay occurs on the property of the Crystal Springs Colony near Crystal Springs. It contains some cherty fragments. This clay is red-burning and has good plasticity and working qualities. Soluble salts are present to a detrimental extent and form an irregular white efflorescence on the ware when exposed to moisture. If precautions are taken to overcome the soluble salts this clay may be used for a fair grade of common brick, but the production of a vitrified product would be impracticable. Its physical properties are:

 Physical Properties of Crystal Springs Clay (Lab. No. o-69).
 Plasticity, judged by feel........... Excellent.
 W ater of plasticity................. 20.60%
 Pore water ........................ 5.35%
 Shrinkage water .................. 15.25%
 Linear air shrinkage............... 9.4 %
 Volume air shrinkage.............. 28.8 %
 Modulus of rupture, average........ 317.7 pounds per square inch.
 Slaking test ....................... 10 minutes.
 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 950*C. 0.4 14.31 31.90 Brick red.
 1050 0.6 13.40 32.80 Brick red.
 1150 1.0 12.02 31.80 Brick red.
 1190 1.0 12.39 30.40 Brick red.
 1230 1.6 12.30 28.65 Brick red.
 1310 2.4 12.98 22.80 Brick red.

 A gray, plastic clay occurs one mile north of Dade City, between the Seaboard track and the highway. This clay is irregular in extent, is underlain by limestone and averages about nine feet in thickness. The overburden consists of about two feet of sandy soil.
 This clay has a high air-shrinkage and cracks badly in drying and burning. It is not desirable for the manufacture of burned products. Its physical properties are:

 Physical Properties of Seaboard Clay, Dade City (Lab. No. 0-22).
 Plasticity, judged by feel........... Fair.
 W ater of plasticity................. 52.90%
 Linear air shrinkage............... 13.90%
 Volume air shrinkage.............. 40.45%
 Modulus of rupture, average........ 180 pounds per square inch.
 Slaking test ....................... 3 minutes.
 Overfires at cone 9.