Page:The American Cyclopædia (1879) Volume VII.djvu/326

 318 FORGE FORGERY they are also called forges from the hammering or rolling which succeeds the reduction pro- cess in the furnace. The term forging is equally applicable to the working of other mal- leable metals, as gold, silver, and copper, when these are heated and hammered into desired shapes. The immense variety of articles into which iron is fashioned requires forges of va- rious dimensions, and many of them adapted for special uses. They agree, however, in the general character of the apparatus with which faey are furnished. The smith's forge, fitted for all sorts of small work, is the best repre- sentative of the smaller forges. It is provided, first, with a small open fireplace or hearth, upon a sort of table in brickwork, 2 to 2 ft. high. A chimney, open at the base, stands at one end, and a hood of sheet iron prevents the escape into the room of the vapors from the fire. Two fires are sometimes arranged under the same hood, and a double hearth is again obtained by building two hearths back to back, the same chimney having a flue for each fire. In the back wall of each hearth is fitted a cast-iron plate or back through which the perforated nozzle of the tuyere, or piece form- ing the extremity of the blast pipe, projects into the fire. The pipe connects with the bel- lows, which is so placed that the smith can work it with one hand, as he attends to the fire upon the hearth and the articles heating in it with the other. The fuel may be char- coal, bituminous coal, coke, or anthracite. Good hard-wood charcoal is an excellent ma- terial, not only for its great calorific property, but more particularly for its freedom from sul- phur, the presence of which in the mineral fuels often results in serious detriment to the iron exposed to its action. Upon the hearth are laid the various kinds of tongs required for holding the differently shaped pieces of iron. At the end opposite the chimney is a trough for water, into which the tools and work are dipped, as may be convenient, to cool them. It serves also, if kept scrupulously free from grease, for tempering articles of steel ; and the water is also frequently sprin- kled with a broom dipped in it over the fire, to check the combustion of the fuel at the sur- face. A stock of fuel is kept on the hearth by the trough, and as wanted it is drawn forward upon the fire. Conveniently near the hearth, and at the same height, is set the anvil, upon which the smith places the heated iron as he takes it from the fire. As the smith holds the hot iron upon the anvil with his left hand, he hammers it with the right, directing his blows and turning the work to receive the precise effect in a manner to be acquired only by long practice. If the work is heavy, he requires an assistant to aid the forging by striking with a heavy sledge, while he turns the piece to re- ceive the blows, and strikes himself in turn with his hand hammer, tapping it at last upon the face of the anvil as the signal, universally adopted, for the blows to cease. Hammers are employed of a great variety of shapes and sizes adapted to the different kinds of work. There are also punches for driving holes through the soft iron, chisels of numerous shapes, and swaging tools, which are generally in pairs, and called top and bottom tools, the latter fit- ting by a tang into a hole in the anvil. The great forges in which are fabricated the im- mense wrought-iron shafts for ocean steamers present the same class of operations, with some new appliances, however, adapted to the gi- gantic scale upon which the work is done. The fires in these forges are either large reverbera- tories or close furnaces, blown by a powerful fan blast. The work is commenced by intro- ducing 15 to 20 pieces of square iron bound to- gether, making, it may be, a bundle 6 ft. long and 2 ft. square, into the furnace. When one end is brought to a welding heat the mass is swung out suspended in chains from the great crane and subjected to the blows of a heavy hammer, of 5 or 10 tons weight, moved by its own gravity, or a lighter hammer is used, moved by steam. One long rod is left pro- jecting on the line of the axis of the mass, and serves when swung in the crane as a guide rod, or porter, as it is called. By means of the pulleys which sustain the load running forward and back upon the jib of the crane, the mass is brought to any desired point within the area traversed by the swing of the crane ; and by means of a cross lever or handle fixed to the end of the porter the men are enabled to turn the mass of iron while the other end of it is receiving upon the anvil the blows of the ham- mer. When the iron has been sufficiently hammered, it is returned to the furnace to be again heated, so as to extend the weld through- out the whole mass. After this a slab of wrought iron, called by the workmen a use, is welded on one side at the end of the piece, and under the hammer the shaft thus built up is drawn down to the required size. New addi- tions are repeatedly made in this way until the desired length is obtained. Only the end of the shaft is thrust into the furnace, and the aperture which remains open around it is stopped during the heating by fire brick and clay. The end outside remains supported in the chains from the crane. The weight of the intermediate paddle shaft of the Great Eastern, which was launched at the end of January, 1858, is upward of 22 tons, and that of the cranks 11 tons. Its length is 23 ft., and its diameter 2 ft. 2 in., and it is 2 ft. in diameter at the main bearings. The cranks are 7 ft. long between the centres. The screw shaft is 2 ft. in diameter and about 178 ft. long, and its whole weight about 135 tons. FORGERY, in general, the illegal falsification or counterfeiting of a writing. Although this offence is the subject of a great variety of cases in England and the United States, the definitions do not quite agree. That given in East's "Pleas of the Crown" (vol. ii., p. 852) is : "A false making of any written instrument