. A manual of veterinary hygiene. Veterinary hygiene. Fig. 13.—Boyle's air - pump ex- tractor. curved bell-mouth arrangement ' B,' in which a large body of air is collected and forced into the narrow annular space ' C,' at which point, owing to the com- pression of the air, which cannot otherwise escape or free itself, it attains a greatly ac- celerated velocity, and, in passing over the slip ' D,' creates an induced current, exhaust- ing the air with rapidity from the central chamber ' E.' The foul air immediately rushes up the shaft to supply the place of the air extracted, and is in its tur
. A manual of veterinary hygiene. Veterinary hygiene. Fig. 13.—Boyle's air - pump ex- tractor. curved bell-mouth arrangement ' B,' in which a large body of air is collected and forced into the narrow annular space ' C,' at which point, owing to the com- pression of the air, which cannot otherwise escape or free itself, it attains a greatly ac- celerated velocity, and, in passing over the slip ' D,' creates an induced current, exhaust- ing the air with rapidity from the central chamber ' E.' The foul air immediately rushes up the shaft to supply the place of the air extracted, and is in its turn drawn off, thus creating a continuous upward current in the shaft connected with the place being ventilated. An exhaust cowl constructed on these prin- ciples may also be employed in ship venti- lation. The extracting power of this and similar contrivances lies in the size of the head; the head should always be about double the diameter of the tube to which it is connected. Tubes or shafts may be used either as inlets or outlets. The golden rule is never to employ them if they can be avoided, and never to use a long one if a short will serve the same purpose. Air passing along a tube suffers loss from friction, and in consequence its velocity is diminished ; the narrower the tube the greater the friction. Angles or bends in tubes are more important causes of loss ; for example, if a current be pass- ing along a tube at a velocity of 10 feet per second, on meeting with a right angle its velocity is reduced to 5 feet per second, a second right angle will reduce it to 2^ feet per second. Thus a right angle diminishes the velocity by half, this is. Fig. 14.— Plan of Boyle's air- pump. Digitized by Microsoft®. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Smith, Frederick 1857-1929. New York : W. R. Jenk
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