A PRELIMINARY REPORT ON CLAYS OE ELORIDA 99 
absorb and in this way influences the amount of air-shrinkage. Porosity 
also influences the rate at which the ware can be dried. The larger the 
pore space the more rapidly the water can escape. Also in the burning 
process a clay remains porous until the point of vitrification is reached. 
A low porosity in burned products is usually desired. 
TRANSVERSE STRENGTH 
The transverse strength is the resistance which an air-dried clay 
offers to rupture or breakage. It is usually expressed as modulus of rup¬ 
ture in pounds per square inch. It was formerly the custom to determine 
the tensile strength of a clay in much the same way that cements are 
tested. It has been shown, however, that the tensile strength stands in 
direct relation to the transverse strength. 1 The transverse strength test 
is in reality a closer approximation of the conditions to which the ware 
is subjected before burning, and for that reason is the test commonly 
applied in modern clay investigation. The transverse strength is an index 
of the ability of the clay to withstand the shocks and strains of handling 
incident to its molding, drying, and preparation for firing. A clay of 
high strength will suffer less loss from breakage in the manufacturing 
process than a clay of low strength. 
BONDING STRENGTH 
The bonding power of a clay is its ability to withstand the addition 
of non-plastic material. A clay which will allow the addition of a large 
amount of sand, for example, without seriously affecting its strength is 
said to have a high bonding power. The bonding power of a clay Is of 
practical importance because in the manufacture of high-grade wares 
as electric porcelain, chinaware, etc., non-plastic ground flint and feld¬ 
spar are often added. 
!Ries & Allen, Trans. Am. Ceramic Soc., Vol. XII, p. 141, 1910. 
Bleininger and Loomis, Trans. Am. Ceramic Soc., Vol. XIX, p. 601, 1917. 
