A PRELIMINARY REPORT ON CLAYS OF FLORIDA 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 rupture 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 feldspar 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.