BLOWING-MACHINES. 19S BLOWING-MACHINES. on both the forward and the return stroke of the piston. Often the steam-cylinders are compound- ed. The air from the air-cylinJor passes some- times into a receiver, but more often directly into the blast-pipes, vhioh are made hu;;e enoujih to act as a receiver or reservoir for maintaining a steady supply of air to the furnaces. The foUowino; are brief descriptions of a num- ber of representative modern hlowing-engines : A blowing-engine built for the Hernadthaler Iron-Works at Krompach. Hungary, in 1898, is a horizontal cross-compound engine, with a high- pressure steam-cjiinder 35 inches in diameter, a low-pressure cylinder .54 inches in diameter, and an air-cylinder 7(i inches in diameter, all with a stroke of 55 inches. The contract with the build- ers required that this engine should have a ca- pacity of 28,250 cubic feet of air at 10 pounds pressure, with a steam-pressure of 112 pounds, and making 52i^ revolutions per minute. Among the more important vertical blowing-engines are those for the Dominion Iron and Steel Company of Sydney, Cape Breton, Canada, to supply the blast for the five blast-furnaces built in lilOO. These engines have high-pressure steam-cylinders SO inches in diameter, low-pressure steam-cylin- ders 06 inches in diameter, air-cylinders 96 inches in diameter, and a piston-stroke of 60 inches. The largest gas-engine blower ever built is that conslructed by the John Coekcrill Company, of Seraing, Belgium, and exhibited at the Paris Exposition of 1900. Tliis engine is of 600 horse- power: the gas-cylinder is 51.2 inches in diame- ter, with a piston-stroke of 55.1 inches; the air-cylinder is 66.9 inches in diameter, with a piston-stroke of 55.1 inches, and the engine is horizontal, with the air-cylinder ahead of the power-cylinder. Disk Blowers. Disk blowers consist of an axle carrying several blades arranged something like the blades of a screw propeller and re- volving concentric with and inside of a cylin- drical casing open at both ends. This form of blower is used chiefly for ventilating purposes, Fig. 1. DISK BLOWER. and in such cases is set in the wall of a biildiiig with one end of the cylindrical casing opening into the building and the other end opening to the outside air. In this position the axle and blades are rotated by means of an electric motor or belt, and by means of this rotation suck or force the vitiated air from the room into the outer atmosphere. By .setting the l)lower so that it faces into the buihling. ficsli air from the out- side may l)c forced into the room instead of the foul air being drawn out. The familiar "electric fan' is a form of disk blower. Disk blowers are built of varying sizes, from 1 foot to 8 feet in diameter, and have a capacity of from 1500 cubic feet to 00,000 cubic feet of air per minute, depending upon their size and the s])eed at which they are run. Fans. Fans are a form of rotary blower, something like a disk blower, except that the axle carries radial arms or spokes, to the ends oi FlO. 2. POSITIVE BLOWEB. which are fastened fiat blades parallel to the a.xle. These blades revolve inside a chest or casing so arranged that the air is sucked in through circular oritices at the sides and is expelled through an outlet in the periphery. Several modern forms of rotary fan blowers have curved blades instead of flat paddles, as described al)ovc. Positive Bi.oweks. A recent form of rotary blower much used is the positive blower, of which the Uoot bhiwer, sliown in Fig. 2, is the most familiar form. This blower consists of two en- cased 'revolvers,' shaped something like a figure 8 and carried l>y two liorizontal shafts, which are connected by gear-wheels outside of the casing, so that their relative motion is invariable. Tliese 'revolvers' lit the casing closely, an<l also mesh closely with each other when revolving. As is clearly shown by the engraving, the air is taken in at tile bottom of the casing and forced out at its top. These blowers are capable of dcvelo])ing considerably greater pressure than fans or disk blowers. •Jet Bi.oweks. A jet of steam or of water forced through a pipe of small diameter inserted in an air-pipe of larger diameter, ojien at both ends, creates a current of air through the air- pipe in the direction of the escaping jet, which is often use<l for blowing purposes, 'riie most fa- miliar forms of sleam-jet, blowers arc the exhaust nozzles u.scd in the smokestacks of locomotives and fire-engines. In these instances the exhaust steam from the engine-cylinders is employed to furni.sh the steam-jet. A water-jet blower, called a Iroinpc. was frecpiently used in the early days of metallurgy' to furnish the blast for iron-fur- naces. In this device a stream or jet of water
