Page:Collier's New Encyclopedia v. 02.djvu/94

LEFT BLOWING MACHINE 72 in the flesh of animals, thus making tumors arise. Several species of cal- liphora do this, so do breeze flies, etc. BLOWING MACHINE, an apparatus for producing an air blast for metallur- gical purposes. The earliest blowing ma- chine was, doubtless, some form of the common bellows. Blounng Engines. — For blast furnaces and for Bessemer steel converters, blow- ing engines of large size are employed. In the former, the strength of the blast sometimes is as high as 10 pounds per square inch. For the Bessemer converter, where a much greater pressure is re- required, it occasionally reaches 30 pounds per square inch. A blowing en- gine consists of a steam cylinder, an air cylinder, and a large air chamber, to in- sure a uniform blast. Sometimes the latter is dispensed with, and large main pipes used instead. The blowing cylinder is of cast iron, with an air-tight piston, which, as it ascends and descends with the motion of the engine, alternately in- hales and expels the air at each end. Trompe. — In the Catalan forges of Spain, the south of France, and some parts of the United States, there is a very ingenious water blowing machine in use called a trompe; but it can only be ad- vantageously employed where a fall of a few yards of water is available. A cistern to act as a reservoir for the water; pipes (generally two in number), through which it descends; and a wind chest to allow the air and water to separate, con- stitute the essential parts of the appara- tus. It is put in operation by lifting the wedge with a lever ; this allows the water to rush down the pipe, and, in doing so, draws in air through sloping holes, called aspirators, at the throat of the pipe. A continuous current of water and air is thus supplied to the wind chest, which is provided with an opening for the escape of the water, while the air passes out in a regular stream by the nozzle pipe. The height from which the water falls deter- mines the tension of the blast; but the height seldoms exceeds 27 feet, which gives a pressure of from 1^/^ to 2 pounds to the square inch. The separation of the air from the water is greatly pro- moted by the current impinging on the platform. Fans. — The fan is another machine for producing blasts of air. It is em- ployed for such purposes as the melting of pig iron in foundries and for forge fires. It is also used as an exhaust to withdraw full air from mines, public buildings, and ships. For mines it is oc- casionally of a very large size. The win- BLOWPIPE nowing of corn is another application of it. The common blast fan is like a wheel with the arms tipped with vanes or blades, instead of being joined by a rim, and it is placed usually in an ec- centric position, inside a chest, with cen- tral openings on each side for the ad- mission of air. It is generally driven by steam power, and as it revolves, air is sucked in at the center, drawn toward the tips, and impelled forward through the exit pipe. Rotary Pressure Blowers. — These are machines introduced in comparatively re- cent years. They act by regular displace- ment of the air at each revolution, since their pistons or drums closely fit their cases. In this respect they differ from fans, because, although there were no outlet for the blast, a fan could be kept revolving, but in such a case a pressure blower would stop. BLOWPIPE, a small instrument used in the arts for glass blowing and solder- ing metals, and in analytical chemistry and mineralogy, for determining the na- ture of substances by the action of an intense and continuous heat. Its utility depends on the fact, that when a jet of air or oxygen is thrown into a flame, the rapidity of combustion is increased, while the effects are concentrated by diminish- ing the extent or space originally oc- cupied by the flame. The blowpipe generally consists of a conical tube of metal, about eight inches long, closed at the wider or lower end, but open at the narrow or upper end, which latter constitutes the mouthpiece, and is turned over to admit of the lips closing perfectly round it. Near the lower end, a small tube, fitted with a small platinum tip, is inserted in the large tube — the space below being intended as a chamber for condensing the moisture of the breath, and through this tip a fine current of air can be projected against the flame experimented with. Where high temperatures are required mechanical blowpipes are resorted to. Substances under examination before the blowpipe are generally supported either on wood-charcoal or platinum — the latter in the condition of wire or foil. In applying the blowpipe test, the body to be examined is either heated alone, or along with some flux or fusible sub- stance; this being added, in some cases, for the purpose of assisting in the reduc- tion of metals from their ores and other compounds : in others, for the production of a transparent, glassy bead, in which different colors can be readily observed. When heated alone, a loop of platinum wire, or a piece of charcoal, is generally