- 1 28 CoiiJIruBion of an Air Pump iv'tth MclalUc Valves. 



Uotted line, tlirough which the air pafTes from the valves to the pipe. This Fig. is defigned 

 cliiefly to fliew the pbces in which the valves play, as at I. 



Fig. 1 1, is a fuie view of the pump, (hewing the fituation of the valve pump and handle of 

 (lie cock } where A is tiie pump, and B the handle. 



Fig. 12, Plate VII. is a pcrfpective view of Cuthbertfon's pump, with its two principal 

 gauges fcrewed into their places : thcfe need not be ufed together, except in cafes where the 

 utmofl e.\aclnefs is required ; for in common experiments either of the two may be taken 

 away, and a (lop fcrtw put into its place. When the pear gauge is ufed, a fmall round plate, 

 large enough for the receiver to iland upon, mufl firft be fcrewed into a hole at A ; but 

 when this gauge is not ufed, this hole muft be clofed with a flop fcrew. When all three 

 gauges are made ufe of, and the receiver is exhaufted, the Hop fcrew B, at the bottom of the 

 pump, mud be unfcrewed, to admit the air into the receiver ; but when the gauges arc not 

 all ufed, the flop fcrew at A, or either of the other two which are in the place of the gauges, 

 may be unfcrewed for this purpofe. 



In Figure i, CD rcprefents one of the barrels of the pump, F the collar of leathers, G a 

 hollow cylindrical velTel to contain oil ; R is alfo an oil vedel, which receives the oil that is 

 driven with the air through the hole a a, when the pifton is drawn upwards ; and when this 

 is full, the oil is carried over with the air along the tube T into the oil veflel G. c c is a wire 

 which is driven upwards, from the hole a a, by the paflage of the air ; and as foon as this 

 has efcaped, falls down again by its own weight, fhuts up the hole, and prevents any air 

 from returning by that way into the barrel : at d d are fixed two pieces of brafs, to keep the 

 wire c c in fuch a diredlion as may preferve the hole air-tight. H is a cylindrical wire which 

 carries tlie plflon I, and is made hollow to receive a long wire q q that opens and clofes the 

 hole L, which forms the communication with the receiver (landing on the plate, m is part 

 of a pipe, one end of which is fcrewed into L, and the other into the centre of the receiver 

 plate. M is a (lop fcrew, ferving only to clofe that hole. OP is a fmall (led fcrew, one end 

 of which is fcrewed into the wire q q, that opens and (liuts the hole L ; and upon the other 

 end O is fcrewed a nut, which, flopping in the fmalled part of the hole, prevents the wire 

 •from being lifted or carried too high. This wire and fcrew are more clearly (hewn in Fi- 

 gure 2 and in Figure 6 ; they (lide through a collar of leathers r r. Figure 2 and Figure 5, 

 in the middle piece of the piUon. Figures 4 and 5 are the two main parts wliich compofe 

 the pidon ; and when the pieces in Figures 3 and 6 are added to it, the whole is reprefented 

 by Figure 2. Figure 5 is a piece of brafs, turned in a conical form, with a (lioulder or ledge 

 at the bottom ; a long female fere* is cut in it, about two thirds of its length ; and the re- 

 maining part of the hole, in which there is no fcrew, is about the fame diameter as the fcrew 

 part, except a thin plate at the end, which is of a width exa£lly equal to the thfcknefs of q q. 

 That part of the infide of the conical piece of brafs, in which no tliread is cut, is filled with 

 oiled leathers with holes in them, through which q q can Aide air-tight ; there is alfo a male 

 fcrew with a hole in it, which is fitted to q q, and ferves to prefs down the leathers r r. In 

 Figure 4, a a a a is the outfide of the pidon, the infide of which is turned exa£lly to fit the 

 outfide of Figure 5. b b are round leathers, about 60 in number ; c c is a circular plate of 

 brafs, of the fize of the leathers; and d d is a fcrew, which ferves to prefs them down as 

 tight as is necedary. The male fcrew at the end of Figure 3, is made to fit the female fcrew 

 in Figure 5 ; now if Figure 6 be pulhed into Figure 5, this into Figure 4, and Figure 3 



fcrewed 



