BRICK.
Nature of the Problems Involved—In Holland brick has been used for street paving for more than a century, and in the United States for over thirty years. During this period, ceramics, or the study of clay working, has been developed as a science to such an extent as to become, especially in the last decade, a prominent factor in the technical advance that has been made in the various clay industries. The application of pure sci ence, notably physics and chemistry, has solved a great many practical problems that clay workers have met in their endeavor to keep pace with the ever increasing requirements for better quality and greater adaptations of ware.
Ceramics, or the application of pure science to clay working, has been developed chiefly along two lines : first, the applications of mechanics to the evolution of methods of winning raw materials, and manufactur ing of wares; second, the application of physical and chemical prin ciples to the selection and mixing of clays and minerals.
Along these two lines ceramics has attained its greatest development in the pottery, floor and wall tile, and kindred industries where white burning-clays and pure minerals are blended in the manufacture of wares. The compounding of the white ware mixtures and the processes for their manufacture can now be said to have emerged from the strictly empirical stage and to have reached a degree of perfection that cor rectly merits the designation of "applied science." In the brick, tile and kindred industries which use more complex clays—clays that naturally contain sufficient fluxes to produce the requisite degree of hardness in the burned ware—ceramics has de veloped principally along the first line, the application of mechanical principles to the processes of manufacture. In this, ceramics has kept abreast of the demands. Along the second line, the application of pure science to the determination and control of the properties of body mixtures, but very little progress has been made. In this, science has been baffled by the complexity of the mineral mixture which nature has compounded and man calls clay.
Complexity of properties is the natural result of complexity of min eral composition. If this complexity of mineral composition resulted simply in variation of chemical constituent, the problem would be com paratively simple, but the physical properties of each of the several minerals are nearly, if not equally, as potent factors in complicating the problems, as the chemical.
The science of ceramics is making rapid progress in the solution of these problems; but today the question of what physical and chemical properties raw clay must possess that it might be suitable for use in the manufacture of paving brick is still unanswerable. Chemical analysis alone is not a safe criterion by which to decide this and similar ques tions, for, as can be shown in nearly, if not all, geological survey re ports on clays, the analyses of clays that are known to be suitable for paving brick have their counterparts in analyses of building brick clays. Indeed in range of variation in chemical constituents, these two types of clays overlap one another to a very large extent: There are possibly one or two characteristics in the chemical composition of paving brick clays that are not common to those used for building brick, and yet no fixed rule has been, or so far as the writer can perceive, can be, laid down at present, by which to identify paving brick clay by chemical analysis.
Physical testa on green or unburned clay, so far as is now known, would not lead one any nearer the possibility of fairly judging a pav ing brick clay than would chemical analysis. Possibly an exception should be made of determinations of fineness of grain. Plasticity, tensile strength, bonding power, slaking properties, etc., are found to vary widely in different paving brick clays, so that no dependence can be placed upon any of them, taken alone. The determination of fine ness of grain, however, does give a negative test that seems to be of some value.