A PRELIMINARY REPORT ON CLAYS OF FLORIDA 137





















 Fin. 9.-Circular duw n-draft kili. Gamble and S ockton Brick and Tile Co., South Jacksonville, Duval County.


 The lower blue clay has an extremely high modulus of rupture. It has a high air shrinkage which is a disadvantage, but on the other hand it dries easily \VithOtut warping and cracking. It alone can he used for face brick, hollow blocks, roofing tile, drain tile, etc. It has the following
physical properties:

 Physical Properties of Gamble and Stockton Blue Clay (Lab. No. 0-32).
 Plasticity, judged by feel....... ......Excellent.
 Water of plasticity ..................30.50%
 Pore water ..........................0.51%
 Shrinkage water ....................29.99%
 Linear air shrinkage.................13.0 %
 Modulus of rupture, average... ..... 1593.1 pounds per square inch.
 Slaking test........................1 hour.
 Steel hard at cone 05.
 Overfires at cone 12.
 Fire tests:
T temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 9500C. 0.5 13.95 20.75 Brown.
 1050 4.0 7.91 20.40 Brick red.
 1150 9.0 5.26 19.80 Brick red.
 1190 4.0 3.50 15.30 Brick red.
 1230 9.0 3.25 14.20 Brick red.
 1310 4.5 1.94 13.20 Brick red.


 A brownish, sandy surface clay from the Platt Bros. brick plant,
now abandoned, about two and one-half miles east of South Jackson-