BURNING BRICK.
In Chapter III. we have already described the method of burn ing hand-made brick, and as that method is analogous to the process employed in the burning of tempered-clay machine made brick, no special description is therefore necessary.
We shall, consequently, in the present instance, confine our selves to no regular description, but shall collate only such informamation as may be of practical value to the manufac turers of all classes of tempered-clay machine-made brick.
Fire is the chemically mixing of certain combustible sub stances with a supporter of combustion in such a way as to produce light and heat. Just what these elements are, and the most effective manner and means of bringing them together so as to produce the greatest amount of available heat, are among the most difficult questions with which the practical brick man ufacturer has to deal.
The most critical period in the process of brick-making is the burning of the kiln. Clay, sand, weather, and all other
conditions necessary to the evolution of the perfect brick may be never so favorable, but without a successful burning all is failure. The burning with wood is both uncertain and expen sive. These difficulties consist largely in the inability to con trol the heat, which is often unavoidably too high or low, and in the great cost of fuel and the labor necessary to care for a kiln after it has been fired. The arch brick are frequently much damaged by over-burning, the ends exposed to the fire being twisted, cracked, or even melted down, thus rendering them of little value. Then the percentage of soft brick, that is, brick insufficiently burned, is often a big item of loss to the brick maker. These are found in the outside and upper courses.