« ΠροηγούμενηΣυνέχεια »
8 79 40 80 43 79 52 76 55 77 16 77 52 78 40 65 13 63 41 67 59 68 18 69 7 68 32 65 40 67 27 63 4 57 40 56 43 56 16 52 3 48 40 46 30 45 30 45 14 42 45 42 3 39 12 39 3 38 37 36 23 34 57 34 51 35 17 44 4 44 23 48 30 50 0 50 9 51 14 55 15 58 49 60 3 62 46 64 48 67 1 68 8 68 82 70 9 71 50 72 15 74 17 74 47 75 40
ON PHYSICS OR NATURAL PHILOSOPHY.
pump, and thus rendered the working of the machine more No. XXI.
Fig. 93. (Continued from page 292.) PNEUMATIC AND HYDRAULIC MACHINES. Rarefaction and Compression of Gasos.-The rarefaction of the air is effected in the following manner, by means of a suction. premp, fig. 93, in which p is the suction-pipe. This pipe communicates, at its lower extremity, with the receiver or vessel in which the air is to be rarefied; and at its upper extremity, with the barrel or body of the pump D. The piston P, which moves up and down in the barrel by means of the piston-rod, is furnished with a valve in the middle, just under the semicircular piece to which the rod is fastened, and similar to the valve 8 (seen in the figure at the bottom of the barrel), which covers the upper extremity of the suction. pipe. Both valves open upwards and close downwards. When the piston p is raised, the valve 8 opens, the air contained in the receiver passes through the tube p into the barrel, and is there rarefied or expanded. When the piston is lowered, the valve s, closes, and the air in the barrel between this valve and the piston is condensed; it then forces open the valve in the piston and escapes through the spout B, into the atmosphere. In this manner, every stroke of the piston rarefies the air in the re. ceiver. Thus, it appears that the common suction-pump is in its principle and construction a veritable air-pump, as will appear by the description of the latter in the following para. graph. Nevertheless, for ordinary purposes, many simple and handy air-pumps are made on the principle just described. In order to construct a pump which shall condense the air or any other gas, we have only to construct the valves so that they shall work in an opposite direction to that in which they work in fig. 93 ; but this, also, will be more fully explained in a rapid and less laborious, the atmospheric pressure which acted subsequent paragraph.
on both pistons tending to produce an equilibrium.
The Air.Pump.—The air-pump is an apparatus which is The air.pump, as now constructed, is composed of two brau employed to make a vacuum in a given space, or, more cylinders (strong glass in our engraving to show the construc: strictly speaking, to rarefy the air in that space'; for it cannot tion), in each of which works a piston r, fg.94, formed of sereral produce an absolute vacuum. This machine was invented by discs of leather, put one above another, and greased so as to Otto de Guericke, burgomaster of Magdeburg, in 1650, a few completely exclude the air while moving up and down in the rears after the discovery of the barometer. "Hawksbee, in cylinders. To each piston is fastened å rack, in the teeth of England, was the first, who added two cylinders to the air which a pinion H, fig. 95, is made to work alternately from