Abbildungen der Seite
PDF
EPUB

extremity of the external cylinder was heated by a fire to 650° Faht., as indicated by the pyrometer, and was maintained at that temperature.

A second, or charging cylinder was provided, which by the motion of its working piston, alternately withdrew and returned the same air to the first cylinder. The capacity of the charging cylinder was 24 cubic feet, and its piston made 18 strokes per minute: about two-thirds of its contents, or 16 cubic feet of air of atmospheric pressure, passed with each stroke, to and fro through the respirator, and all the heat carried away was absorbed by the sides of the cylinder. After 24 hours' working, the temperature of the charging cylinder was raised from 60° to 110° Faht. (50°). Its capacity for heat had been previously ascertained, by suddenly admitting steam, and weighing the condensed water obtained (in heating it from 60° to 210° Faht.) (150°), which amounted to about 54 lbs. The quantity of air which passed from the respirator into the cylinder was 43,200 cubic feet, and its weight 3360 lbs.: this, if multiplied by its specific heat 0.267, is equal to 897 lbs. of water-power of

50

absorbing heat. The heat given off was 1000 = 18000

150

units, and consequently the air left the respirator, each time, at 18000 a temperature of = 2001° higher than that at which it 897 entered. Adding to this, for loss of heat by radiation during the experiment, which according to established rules may be taken at 50, the entire loss of heat by the respirator amounts to 25° Faht. when air is employed. In using steam it does not exceed 10° Faht., owing to the greater conducting power of that fluid.

The regenerator condenser, which was designed and executed some years ago by the Author, is an illustration that water may be also subjected to respirative action.

The Paper is illustrated by a series of diagrams from whence Plate 3 is compiled.

[Mr. C. MANBY

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][graphic][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small][subsumed]

Mr. C. MANBY, Secretary, read some quotations from a letter addressed by M. Regnault to Colonel Sabine, Treas. Royal Society, (dated April 1853), in which he stated, that he was about to publish, immediately, a series of elaborate experimental researches, on various subjects connected with the effects of heat on elastic fluids; the results of which would solve many questions long in dispute, and by means of which engineers might accurately calculate the effect of a given amount of fuel, in whatever way it was applied. M. Regnault communicated in anticipation, that he had arrived at the number 0.237, for the specific heat of air, at constant pressure, and at 0.475, for that of steam, under atmospheric elasticity, the specific heat of water being taken in each case as unity.

Mr. SIEMENS explained, that the diagrams were chiefly intended to illustrate the peculiar functions of the "respirator," or as Mr. Ericsson had termed it, the "regenerator." Very conflicting opinions had been expressed regarding this most essential element in Ericsson's engine. Some thought that, by its agency, the heat used to effect a stroke of the engine could be wholly recovered, except accidental losses, and that, theoretically, it involved the accomplishment of a perpetual motion. Others, on the contrary, contended that the regenerator was only an obstruction to the passage of the air, and of no utility whatever. He had endeavoured to prove in his Paper, that neither the one extreme view, nor the other was correct; that, indeed, the respirator might be usefully employed, to recover that portion of heat which presented itself at the exhaust part of the engine, in the form of free, or sensible heat, but that neither the respirator, nor any other possible contrivance, could recover the heat that was lost in the expansion of the air behind the working piston. He had adopted the new "dynamical theory of heat" for his argument, because that theory enabled him to calculate the absolute quantities of heat, that must inevitably be sacrificed, to produce a given mechanical effect, and to separate the same from the other and much larger quantity, that served only to form the elastic medium behind the working piston, and which might be recovered, by means of a respirator, unless, as he had shown in the Paper, it was all converted into power, by the expansive action being carried to its last (but impracticable) limits. Ericsson himself seemed to incline to the idea, that he

could recover the whole of the heat by means of his " regenerator," for it would be difficult otherwise to account for the extraordinary insufficiency of heating surface he had provided. Mr. Siemens could speak confidently as to the mechanical efficiency of action of the respirator, having applied a precisely similar contrivance to a steam engine of his design, some years previously.

Mr. HAWKSLEY contended, that in the caloric engine, the so-called "regenerator" was productive of no mechanical effect, as might be shown, by reducing the engine to a primitive form, so as to get rid of all the complexity consequent upon the employment of valves and flaps, and air under compression. In this form the engine might be assumed, for the sake of illustration, to consist of an upper and a lower cylinder, bearing the proportions, in regard to area, of 1 to 2; the upper cylinder acting as the pump, or receiver, of cooled air, and the lower cylinder as the expansion, or working vessel. It might also be assumed, that the air was expanded and contracted alternately, from 1 volume into 2 volumes, and from 2 volumes into 1 volume, by the operation of the regenerator placed in the connecting pipe of the two cylinders. In this case it would readily be seen, that even if the regenerator should actually operate in the manner alleged, yet that no mechanical effect would be produced, because the space vacated by the motion of the lower piston would be exactly equal to the amount of expansion consequent upon that displacement. Therefore, if in this single case no mechanical effect was produced, à fortiori no mechanical effect would result from mere complexity of arrangement, involving no change of principle. The machine, in point of fact, involved a mechanical fallacy, closely allied to the fallacy of perpetual motion, and of quite as simple a character. The motion of the machine created the space to be filled by the air, after its expansion by the restored heat of the regenerator; whereas it had been most erroneously imagined, that the expansion was the cause, rather than the consequence of the motion. Had the design of the machine been scientifically correct, it would have been the wonder of the age,-whereas, by the confusion of cause and effect, (an easy thing to do in a case of this kind), an endeavour had been made, though with great ingenuity, to realize an impossibility. Nevertheless, in contra

« ZurückWeiter »