Page:The American Cyclopædia (1879) Volume III.djvu/274

268 BRICK d. Valves of cast iron are made to close at plea- sure the orifices of the flues. Movable sluices in the dividing walls allow of communication to be made or closed between the chambers ; h h are plugs through which the coal, in powder, is introduced, undergoing calcination. The advantages of this furnace lie in its great economy of fuel. The heat is very equable, and no smoke is generated, the fuel being burnt while falling to the bottom of the fur- nace. The immense consumption of bricks in cities has made it an important object to re- duce the labor employed in their manufacture as much as possible, and consequently much ingenuity has been expended in devising ma- chinery for grinding and moulding the clay. A great number of machines have been patent- ed in this country and in Europe, but it has been found exceedingly difficult to render them practically successful. Two kinds of machines have been made, one by which it is sought to prepare the brick from clay which contains so little moisture that they may be immediately taken to the kiln, and another which moulds it in so soft a state that it requires to be dried before baking. The difficulty with the first method is that the bricks do not seem to pos- sess the strength of those which are made of moister clay, and from the immense power re- quired to press them to the proper size in the moulds some parts of the machinery are liable to break. Those machines which employ moist clay have been utilized in manufacturing pipe and tile and peculiar forms of brick ; but in making common brick the saving of labor has not been found sufficient to make them take the place of hand labor, by which process nearly all the bricks used in building are made. The red color of bricks is owing to the peroxidation of the iron contained in the clay. If the iron is de- ficient or only partially oxidized through insuffi- cient heat, the bricks are of a pale color. The clay in the vicinity of Milwaukee, Wisconsin, is remarkably free from iron, and the bricks made of it are of a delicate straw color. Other colors may be imparted to brick, provided that of the oxide of iron does not overpower all other coloring matters introduced. American bricks vary in size in the different states, run- ning from 7f to 8J inches in length, 4 to 4 in width, and from 2J to 2J in thickness. The weight is commonly reckoned at 4 Ibs. to the brick ; but this varies with the size, the amount of pressure to which the clay has been subject- ed, and the heat applied in baking. English bricks are commonly 9 inches long, 4J wide, and 2^ thick. Floating Bricks. A very light silicious earth is occasionally met with, of which bricks have been made that float upon the water. Clay may be added to the silica, if required to bind the material together. Such bricks were made in ancient times, and were described by Posidonius and Strabo, and particularly commended by Vitruvius, Pollio, and Pliny. In 1791 they were again brought into notice by Giovanni Fabroni in Tuscany, who after many trials succeeded in making bricks which would float upon water. Their strength was but little inferior to that of ordinary bricks. They are remarkable not only for ex- treme lightness, but also for their infusibility, and for being very poor conductors of heat. They may bo held by one end while the other is red-hot. As an experiment Fabroni con- structed the powder magazine of a wooden ship with these bricks. The vessel, being set on fire, sank without explosion of the powder. In 1832 Count de Nantes and Fournet, a min- ing engineer, used them in constructing powder magazines and other parts of ships, lessening danger from fire. Kutzing found the material from which these bricks were made to con- tain immense numbers of microscopic silicious shells of infusoria. Similar earth has been dis- covered in France and at Berlin, and it is prob- ably the same whitish substance that is often found under our peat bogs. Fire Brick. When bricks are required to withstand high tempera- tures, they are made of the most infusible clays, such as contain from 63 to 80 per cent, of silica, with from 18 to 25 per cent, of alu- mina, and the remainder water. Oxide of iron may be present, but the light color of fire brick shows that this is in very small quan- tity. Lime would render the mixture fusible, and this is necessarily always absent. Such clays are of common occurrence in the bitu- minous coal measures, where they are found making the floor or underlying stratum of the coal beds. The material is indurated, so that it is broken up like a soft stone. When used, it is ground in a mill, and mixed with fragments of previously baked fire brick, or of some refractory stone, or with a coarse, clean silicious sand and gravel. The materials are made into a paste with water, moulded in hand moulds, and baked in permanent kilns at a very high tem- perature. Good clay for fire bricks is also found associated with other clays of more re- cent formations. The potters' clay formation found at South Amboy, N. J., contains beds of excellent quality, together with others of very pure sand, suitable for mixing with the clay. The manufacture of fire brick has long been carried on at this locality. At Athens, oppo- site Hudson, on the Hudson river, good fire bricks have long been made. At Bennington, Vt., an excellent clay is found of the character of kaolin, from which fire bricks of very refrac- tory quality are made by mixing with it stones that withstand heat, crushed sufficiently fine. These bricks are extensively employed at the blast furnaces in that part of the country. It is for the lining of such furnaces that fire bricks are principally in demand, and for this use they are prepared of a variety of sizes and shapes, adapted to fit the curves in the lining of the stacks and the arches of the flues. The stan- dard size to which all the larger bricks are re- ferred in reckoning their number, is that of the common rectangular fire brick, which measures 9 inches iu length, 4^- in breadth, and 2J in