A PRELIMINARY REPORT ON CLAYS OE ELORIDA 
101 
placed on a screen having four meshes to the inch and carefully immersed 
in water. The time required for the clay to disintegrate and fall through 
the screen is noted. 
The plasticity of certain clays is increased by weathering which thus 
facilitates tempering. The slaking test indicates the weathering quality 
of a raw clay and may be employed to ascertain whether or not weather¬ 
ing would facilitate handling. Also a clay which slakes readily is more 
easily washed than one requiring a long time for slaking. 
In the case of high-grade clays a mixture of 50 per cent clay and 50 
per cent potter’s flint is made into test pieces and slaked. This is one 
indication of the bonding strength of the clay. 
In the determination of volume air-shrinkage the volume of the test 
piece is determined in cubic centimeters. Then it is allowed to dry at 
room temperature followed by a period of drying at 110° C. until con¬ 
stant in weight. The volume in cubic centimeters is again determined 
and the loss in volume is calculated in percentage terms of the dry 
volume. 
The linear air shrinkage is computed by determining the reduction 
during drying in the length of a line of known length marked upon the 
test piece when freshly molded. This shrinkage is expressed in per¬ 
centage terms of the original plastic length. 
The volume fire shrinkage is determined after firing at the respec¬ 
tive temperatures. The reduction in volume after the completion of the 
air shrinkage is determined in cubic centimeters and calculated in per¬ 
centage terms of the original dry volume. 
The linear fire shrinkage is determined after firing at the various 
temperatures in the same manner as the linear air shrinkage. It is ex¬ 
pressed in percentage terms based upon the wet length of the mark. 
Both the linear air and fire shrinkage may also be calculated from 
the volume shrinkage formula. The volume and linear shrinkage are 
simply two different methods of expressing the same property of a 
clay. The shrinkage of a clay both in drying and in firing is obviously 
an important factor. 
The absorption test is made to determine the amount of water a 
clay will absorb. The weight of the test pieces after each firing is de¬ 
termined, after which they are immersed in water at room temperature 
for twenty-four hours and weighed again. The absorption is the amount 
