16 FLORIDA GEOLOGICAL SURVEY-SEVENTH ANNUAL REPORT. 
A portion of the samples was tempered with water and wedged on 
a marble slab until it acquired stiff mud consistency. 
“Preparation of Test Pieces. —Twenty-four briquettes were 
molded from each clay by pressing in the stiff mud condition on a 
hand repress machine, the test pieces being numbered consecutively 
from i to 24. Test pieces Nos. 1, 2, 3, and 4 from each batch were 
weighed in the moist state and after drying, and the water of plas¬ 
ticity calculated in terms of the dry weight of the clay. Linear 
measurements were also made on test pieces Nos. 1, 2, 3, and 4 and 
the linear shrinkage in terms of the wet length of the briquettes de¬ 
termined. 
“Drying Treatment .—Each series of briquettes were allowed to 
dry at room temperatures until they had acquired leather hard con¬ 
sistency, the (final drying being in an electrically heated drying oven 
at 75 0 and no° C. 
“Burning. —The test pieces were burned in a down-draft test 
kiln fired with natural gas. The duration of burning was about 36 
hours, the kiln temperature being increased at the rate of 25 0 C. 
per hour above 850° C. The kiln temperatures were measured by 
platinum-platinum rhodium thermocouples and recording millivolt 
meters. Four burns were made on the 24 samples. The twenty- 
four test pieces molded from each sample were arranged in the kiln 
so that two could be drawn at regular temperature intervals. Thus 
two briquettes from sample No. 1 were drawn at 850° C, 950° C., 
980° C., and so on to the final burning temperature. The briquettes 
were dropped into hot sand as they were drawn from the kiln. 
“Porosity Determinations. —The porosities of the briquettes 
burned to the different temperatures were determined by the use of 
W-D 
the formula,-x 100 = % porosity, in which W = the weight 
W-S 
of the briquette saturated with water, D = the dry weight of the 
briquette, and S = the suspended weight of the briquette. Before 
determining the wet weights the pieces were boiled two hours in 
water in vacuo.” 
The examination of the clay samples thus prepared included the 
determination of : The molding behavior ; the water of plasticity in 
percentage of dry weight; the drying behavior; the linear drying 
shrinkage in terms of wet length; the linear burning shrinkage in 
terms of dry length; the color after burning; and the percentage of 
