Air Bladder, or Swim Bladder

( Zool.). An organ somewhat generally po e ed by fishes, though absent in many cases, consisting of a large sac filled with a gas largely composed of nitrogen, which is secreted into the bladder from its walls. The bladder varies considerably in size and shape, being sometimes a small and simple sac, and at other times large and complex in structure. In some cases it opens by a tube into the air-pa ages. It is probably useful to some extent in swimming, but seems to be a surviving remnant of the cellular air-bladder found in the ganoid fishes, from which, also, the lung of air-breathing animals is supposed to have been derived. Very probably, the original form of this organ was developed as a primitive lung, which in one direction unfolded into the existing lung, and in the other degenerated into the air-bladder, and in many instances completely disappeared. This hypothesis was originally suggested by Prof. Charles Morris, in a paper published some years ago in the Proceedings of the Academy of Natural Sciences of Philadelphia, in which the probable origin of the bladder in a primitive air-breathing invagination of the œsophagus, which developed into a lung-like organ, was suggested and sustained by facts and reasonings. This view was widely accepted by scientists as a very Air-brake. ( Mech .) The nece ity of having some effective means of stopping railroad trains was felt as soon as it was found po ible to run them at any considerable speed. The problem of how to stop a train was therefore presented simultaneously with the introduction of locomotives. As the speed and length of trains increased, the importance of placing them under the control of the locomotive runner became with each accident and its accompanying horrors more evident. For years, therefore, inventors have been exercising, more or le succe fully, their ingenuity in endeavoring to devise some means which would enable the man who runs the engine to apply the brakes instantly on the whole train behind him. The first system, however, which may be said to have come near to fulfill. ing the requisite condition of an automatic brake, is the Air - brake , or Atmospheric - brake , invented and pat ented in 1869 by Mr. George Westing house, and manu, factured in Pittsburgh, Pennsylvania. It may be summarily described as follows: On the right side of the locomotive, and in full view of the engineer, an airpump is fastened to the locomotive frame. It is propelled by steam drawn from the boiler, is self-acting, and is motionle only when the expansive force of the compre ed air in the reservoir, which hangs beneath the cab (a cylinder of boiler iron suitable to the dimensions of the locomotive), becomes equal to that of the steam. Thus as the pre ure of steam increases, the air-pump works, and the expansive force of compre ed air is augmented. When the steam is high, and the po ible demand for great force of the brake consequently increased, the pre ure of steam and air in the reservoir must correspond. This relation of expansive force is always maintained. Pipes to convey the compre ed air extend from the reservoir beneath the locomotive-cab back under the whole train. Midway beneath each car is a fixed cylinder with piston so contrived as to act directly on the lever of the ordinary hand-brake, and does not prevent the use of the latter brake in conjunction with the air-brake, or separate from it if required. The continuity of air-pipe between the cars is preserved by heavy rubber-hose connected by a most ingenious bra coupling, so devised that, when coupled, valves are open and the compre ed air can move from the reservoir unimpeded to exert its force; if any cars are detached, thereby sundering the connecting pipe after the force has been applied, the coupling accommodates itself to the exigency by unjointing, valves instantly close, precluding the escape of the compre ed air, and the brake remains effective on each separate car. When the engineer applies the brake (by opening a valve and permitting the escape of the compre ed air from the reservoir through the conducting pipes) its force is exerted simultaneously and equally upon every wheel of the train. The engineer has entire control of the quantity of force exerted, and can graduate it to satisfy the demand. The term Vacuum Brakes is used to distinguish that particular cla of brakes which are operated by atmospheric pre ure from those operated by compre ed air. Both are, properly speaking, air-brakes, the atmosphere being the means employed to convey the power used in both cases, vacuum-brakes operating by external, and air-brakes, so called, by internal pre ure. The Eames vacuum-brake consists of a steam ejector, located upon the engine, and diaphragms upon the cars. The ejector, which the inventor of the brake, Mr. F. W. Eames, has greatly improved over the before existing patterns, is operated by steam directly from the boiler, through a graduating valve, making it po ible to admit as little or as much steam as may be desired, the valve being controlled by a lever within convenient reach of the engineer. The e ential part of the ejector consists of a double tube, the outer space of which communicates with the steam valve, and the inner with the train air pipes. Steam being admitted to the outer space, it escapes past the end of the inner tube in such a way as to form an approximate vacuum at that point, which the air from the train pipes constantly rushes to fill, and the steam and air are thrown out together at the top of the ejector. The Eames ejector produces, at sea level, a vacuum corresponding to 24 inches of mercury, or, approximately, a pre ure of 12 pounds to the square inch. Immediately below the air tube above described is a check-valve, to prevent the inflow of air, and the consequent destruction of the vacuum, until such time as the engineer desires to release his brakes. He does this by means of another valve, called the release valve, the handle of which is placed in near proximity to that which controls the admi ion of steam. These three valves-the steam, release, and check valves-are the only moving parts of the ejector, the two former only requiring to be operated by hand, and it is therefore a very simple piece of mechanism, and not likely to get out of order. The diaphragm is made of rubber, suitably strengthened by cloth insertion, and moulded to proper shape. It is clamped by the edges to the diaphragm shell. The lat ter is of cast iron and approaches a hemisphere in shape, over the open side of which the rubber diaphragm is fastened. The air being exhausted from this shell, the diaphragm will be pre ed in with a force proportionate to the area of the diaphragm. The Eames diaphragm is furnished in different sizes, according to the service required, for light or heavy cars, and varying in area from 180 to 500 square inches. The diaphragm shell is preferably fastened to the truck of the car, its proportionately large area and short stroke peculiarly fitting it for this place. The diaphragm has an eye-bolt attached to its centre, by which motion is communicated to the brake lever. For connecting the ends of the air pipes between the cars, rubber suction hose is used, each piece of hose being provided with a coupling of peculiar construction, also an invention of Mr. Eames, The two halves of this coupling are exactly alike, and consequently any single half coupling will couple with any other one. The coupling is provided with a valve which closes automatically in case of the separation of the train, thus making such portion of the train as may be still attached to the locomotive as fully under control of the engineer as before the separation. The first railroad fitted with the Eames brake was the Callao, Lima, and Oroya, of Peru, S. A., which cro es the Andes at an elevation of 15,645 feet above the sea. The grade averages nearly 31⁄2 feet in every hundred, and in some places is 42 feet. The requirements of a train brake were therefore very severe. The Eames brake was applied on this road in 1876, and has since been constantly in use there. At a trial made on that road in August, 1876, a train consisting of locomotive, ten der, and three cars, moving down a grade of four feet in a hundred, at the rate of 20 miles per hour, was stopped in 17 seconds' time and 380 feet distance after the brakes were applied. The elevated railroads of New York city are entirely equipped with the Eames brake, it having been found to best answer the requirements. The service is very severe, the number of stops made by all the engines in a month aggregat ing more than a million. The Eames brake has also been applied to horse, cable, and electric cars. slower in action than the pre ure brake, but has compensating advantages, and is largely used in foreign countries. The Westing house brake is almost universally used in the U. S., and to a large extent abroad. The Westing house quick-acting freight train brake, perfected in 1887, will stop a 50 car train in 320 to 350 feet. Pa enger trains moving 40 m. an hour can be stopped in 600 feet, and those of 60 m. an hour 'n from 900 to 1,000 feet. By a law of the U. S., pa ed in 1893, power brakes and automatic couplers are required for freight cars. Brakes are applied not only to the wheels of the cars, but also to the driving and tender wheels of locomotives and sometimes to those of the engine trucks. In addition to air power, brakes to operate by steam, hydraulic power, weights, springs, and electricity have been invented, but the air-brake still continues the one chiefly used. It is