BLOWING MACHINES. Bellows, or ma chines for dircting a current of air upon a fire, to excite the requisite intensity of com bustion for metallurgical and otheroperations, are of very early origin. Rosellini represents an Egyptian painting in which a man is en gaged in working two pairs of bellows with his feet, having strings to assist in raising the boards of the exhausted pair to admit a fresh supply of air. Bellows consist, essen tially, of an air-tight chamber capable of alter nate expansion and contraction, and furnished with two valves, one opening inwards to admit air while the chamber is expanding, and the other opening outwards into a pipe or muzzle, to allow the air to escape when the chamber is compressed. In some of the recent Expo sitions of Manufactures, bellows have been exhibited which show great beauty in form and ornament.
The blast from common bellows being ne cessarily intermittent, and variable in inten sity, it is necessary, when a continuous blast is required, either to employ two or more separate bellows or pairs of bellows, working alternately ; or, where more perfect equability is required, to direct the air expelled from the bellows into a second chamber of variable di mensions, which is kept under a constant and uniform pressure, and from which the blast is directed into the nozzle. In forge-bellows of this construction three boards are used, con nected by leather sides, which are kept in re gular folds by hoops of cane. The middle board, to the upper side of which the nozzle is attached, is fixed in a horizontal position, and the upper and lower hoards are moveable, forming two chambers, of which the lower one is kept distended by weights excepting when the board is raised by a lever and chains, and forms the part analogous to ordinary bellows; while the upper one, which is constantly com pressed by weights attached to the top board, constitutes the air-chamber or reservoir. In the best smith's bellows the boards are circu lar, instead of being pear-shaped like the do. mastic machine, and in some helical springs are used instead of weights. Very simple and efficient bellows may be made of wood alone, on the model of common bellows, by the use of two boxes sliding upon one another so as to constitute, jointly, a chamber of variable dimensions ; and the missionary Williams, in the absence of leather for ordinary bellows, con structed an efficient blowing-machine of wood, consisting of two square boxes with pistons arranged to rise and fall alternately. Woodew.
bellows are sometimes used in large organs.
The trombe, or trompe, is a blowing engine often referred to by old writers, in which a shower of water, in its fall down a large verti cal tube, draws with it so much air as to pro duce a powerful current, which is conducted from the bottom of the tube, where it is sepa rated from the water, to the furnace. The most important blowing-machines however for metallurgical operations, are those in which the air is alternately drawn into and expelled from large cylinders resembling those of a steam-engine, by the action of pis tons impelled either by waterwheels or by steam-engines. The first machines of this character were constructed by Smeaton for the Carron Foundry about 1700. The cylin ders, of which any number may be employed, usually force the air into large air-chests, or chambers of iron or masonry, from which it is conducted to the blast-pipes, which are called tuyeres or tweers. The force of the blast may be regulated either by a contrivance resembling a safety-valve, allowing the air to escape when the pressure exceeds a given' degree, or by connecting with the air-chest an ! apparatus similar to a gasometer.
One of the largest blast-engines or machines ever constructed is now in use at ' the Coltness Iron Works in Scotland. The high pressure cylinder is 54 inches in diam eter, 9 feet stroke, and weighs 10 tons ; the blowing cylinder is 122 inches in diameter, 9 feet stroke, and weighs 31 tons. The beam is 30 feet long, 0 feet broad in the centre, and weighs 30 tons. The connecting rod gives 14 strokes per minute, with a stroke of 12 feet. The fly-wheel is 30 feet in diameter, and with its shaft weighs 35 tons. The steam pipes are 21 inches in diameter. The working me chanism is supported on two columns and entablature, weighing 221 tons. The pedes tals on which the machine stands are com posed of 1900 tons of solid masonry. This gigantic machine was constructed to supply a blast to ten iron furnaces.