A PRELIMINARY REPORT ON CLAYS OE ELORIDA 137 
Fig. 9.—Circular down-draft kiln. Gamble and Stockton 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 without warping and cracking. It alone can be 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 
Steel hard at cone 05. 
Overfires at cone 12. 
Fire tests: 
1 hour. 
iperature. 
Linear Shr. 
Per Cent. 
A bsorption. 
Per Cent. 
Porosity. 
Per Cent. 
Col 
950°C. 
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- 
