Of the 4,215 concerns in the United States that may properly be termed manufacturers, about 50 per cent use what is known as the °stiff plastics process. If the material to be worked is of a hard or flinty nature (shale), it is first ground in a °dry-pan,° after which it is raised by means of a cup elevator and passed through a screen to the pug-mill, or mixer, the tailings from the screens being re turned to the dry-pan. If the material is suf ficiently open, as good brick clay should be, it can be run direct to the pug-mill with little disintegration or grinding. The pug-mill is usually 10 or 12 feet long and contains a series of mixing knives, by which the clay and water are mixed to a proper consistency. From thSs mixer the clay passes into the brick machine, where it is compressed by a heavy auger into a solid and continuous column, being forced on to the cutting-table through a die of proper size. The cutting is done by fine steel piano wires on a revolving wheel, working automatic ally. One of these machines is capable of turn ing out an average of 100,000 bricks per day. A belt traveling a little faster than the column in moving separates the severed cubes and car ries them to the re-press. This latter squares their corners and edges, gives them a smooth, polished surface and imprints upon them any lettering or design desired. The cubes are not put through the re-press unless intended for front or face-brick. The common, rough brick go immediately from the cutting-table to the dryer, which may consist of a series of tunnels built of brick .4 feet wide and 5 feet high by 120 feet long. These tunnels are heated by a furnace underneath, by steam pipes or (in large plants) by a blower which conveys the waste heat from the cooling kiln. The cubes are loaded on little cars and run into these tunnels, where they remain till drawn out at the end of 24 hours thoroughly dried. Each tunnel holds about 5,000 bricks. The bricks are then ready for the kilns, which are of various de signs. The down-draft is a favorite modern method of construction. This requires small structures, round, 10 or 12 feet high and 30 feet in diameter, held in place by heavy iron bands to prevent warping from the intense heat. The floors are made of perforated blocks. Super heated air from the furnaces is forced from the top down through the brick piled within, through the floor, and either out through a chimney or into other kilns or dryers. The interior of these kilns under fire is a solid sheet of twist ing flame and heat, turning the brick a cherry red, if of common clay. This is kept up for from 6 to 10 days, when the fires are drawn and the mass allowed to cool. The continuous kiln of from 16•to 22 chambers has produced economical results. This stiff plastic method .enables the handling of the clay cubes as they leave the cutter without preliminary drying. This and its simplicity make it very popular.
There are three methods of brick manufac ture, the °soft-mud° process, astiff-mud° proc ess and °dry-clay" process. The stiff mud is most widely used, the soft mud almost as ex tensively and the dry clay claims only a small percentage of the output. Soft-mud brick, be ing made with a very trifling pressure, are less dense than stiff-mud brick and theoretically seem weaker and less calculated to withstand the weather, but in practice, when well made, they last indefinitely. The stiff-mud brick, though more solid, may contain laminations or planes of separation that weaken them. The soft-mud brick requires more time to dry but is easier to burn. The stiff-mud brick process
seems to have a little preference because the bricks are dryer and can go to the kiln more quickly.
About 40 per cent of the manufacturers use the soft-mud process. Clays of a short, sandy nature, or those with a disposition to excessive lamination, are readily treated by the soft-mud process, and beautiful sand-faced brick results. As a rule the Hudson River yards use this system, as well as many in New England and the Middle West. The clay passes first through the separator to free it of lumps, whence it is elevated to the pug-mill compartment of the brick machine. In the pug-chamber it is thor oughly mixed and water added to make it of the proper consistency to mold easily. The machine presses it into wooden molds, which are sanded to prevent adhesion of the clay to the mold, and are removed automatically. They are then placed on a revolving dumping-table, where they are dumped on to pallets, the empty mold being again sanded and passed to the machine for use again. Then the brick goes to the dryer and afterward to the kiln. It takes much longer to make brick by this mold method, but a very fine brick is produced, with a per fectly homogeneous body to it.
Not more than 10 per cent of the manufac turers can or do use the expensive °dry-press° or °dry-clay° method, which takes the finer clays and presses them with a force of 20,000 pounds to the square inch into steel molds. The clay is nearly dry when this is done, so that the cakes can be handled with ease at once. The objection urged by some against this method is that the brick resulting is too porous and apt to absorb moisture, and °sweat" or disintegrate. Still, for the finer clays this method possesses undoubted advantages. The beautiful clays of Staten Island and in portions of New Jersey and Pennsylvania are nearly white, very fine and smooth in texture. These work up into most artistic front and face-brick for the exterior of fine buildings or for dec orative mantel and chimney work in the tenors. Hollow brick is much used for par titions. It is made in large sizes and so can be erected very rapidly. .It is, inexpensive, and since it provides considerable air space is a good non-conductor, thus tending to keep in the heat as well as to keep the. cold out of a building. Paving brick, which were once very common, are going into disuse because the concrete pavement is more sightly, more satis factory and more permanent.
Tiles, being made of the same material as brick, are commonly produced in the same es tablishments. Tile is really nothing but vitri fied or glazed brick. This gives a beautiful surface for interior decoration and a water resisting surface for roof-tile and sewer-pipes. The United States census classes the brick and tile industry as one, and in the 1910 census lists 4,215 factories. It is probable that there are several thousand more small makers of brick using hand processes who escape notice and are not listed. Those included in the census report give employment to 85,746 people, have an invested capital of $174,673,000, make prod ucts valued at $92,776,000, of which $69,040,000 is value added to the materials in course of manufacture. Illinois is the leading State in the brick industry, with 340 factories; Indiana, Iowa, Missouri, Georgia, Kansas, California and Alabama follow in the order named. For further information regarding the uses of brick, see BUILDING MATERIALS; BRICK-MAKING MA.. CH INERY ; CLAY-WORKING MACHINERY; MA SONRY.