A I R 



A I R 



tlic leathers which clofe them may be covcrdl willi oi! tn 

 prevent leaking. The lowei- pai't of the pump is fitted with 

 drawers to contain the neceiTary apparatus. 



A jjerfpeftlve view of a double-barrelled pump, made by 

 Air. Jones, according to the conftruilion of Mr. Prince, 

 may be feen in P/,iie vii. Piic-umnlics, Jig. 48. A, A, are 

 two brafa barrels in which the pillons move ; the barrels 

 c>)mmunicate with the receiver placed on the pump by means 

 of the pipe B C, and canal D E ; the rods of the pillons 

 ;ue feen at F, G ; each of thcfe is connefted with a rack or 

 piece having teeth on one fide. At I th.ere is a wheel, 

 whofe teeth are laid hold of by thofe of the rack ; fo that 

 by tui-ning the handle H the piftons are alternately raifed or 

 depreffed, and the air is exhaulted out of the receiver K L, 

 the tube B C, and the canal 1) E, which communicate 

 with one another. At the top of each barrel is a plate, on 

 which is A boK m n, containing a collar of leathers ; through 

 this the cylindrical part of the pifton rod moT.e3, air-tight ; 

 o 9 is the place of the valve on the top plate, into which a 

 pipe is foldered that conveys the air from the valves to the 

 duft, pafiing under the valve-pump P, which is dcllgntd for 

 preventing the prefl'ure of the atmofphere from ailing on tlse 

 valve of the top plate. Q^is the pifton rod of this pump, 

 and R the handle by which it is worked. Y is a cock to 

 cut off occalionally the communication between the receiver 

 and the working parts of the pump. At S is a fcrew, 

 whic'i clofes the orifice of the canal D E, by unfcrewing 

 which the air may be admitted when required. Z is an oil- 

 veilel for receiving the oil driven over by the a£lion of the 

 pump ; and there (hould be ahvays a fmall quantity of oil in 

 the cups of the boxes m, it, that hold the collar of leathers 

 through which the pillon rods move ; n b c h the barometer- 

 gage ; d e the box or ciftern containing the mercury ; and 

 there is a divided box-fcale affixed to the tube, for afcertain- 

 ing the rife or fall of the mercur)' ; a fmall ivory tube en- 

 compaffes the lower end of the glafs tube, and floats upon 

 the quickfilver in the ciftern ; the upper end of this is 

 always to be brought to coincide with the lower divifion of 

 the box fcale, by means of the fcrew under the ciftern ; and 

 whjn it thus coincides, the divillons on the fcale give the 

 true diftance from the furfacc of the mercury in the bafon. 

 The key f ferves for tightening or loofening the fcrews of 

 the pump. When either pifton is down, in the operation of 

 this- pump, there is a free communication from the receiver 

 through the tubes and the canal to the part of the barrel 

 above the pifton ; when the pifton rifes, it forces out the air 

 above it through the valve in the top plate ; and as this 

 valve prevents the air from returning into the barrel, when 

 the pilton defcends, a vacuum is formed between it and the 

 imder furface of the top plate; as foon, therefore,as the pifton 

 has defcended below the holes communicating, by the tubes 

 and pipe, with the receiver, the airnifties into the exhaufted 

 tarrel ; on the next afcent of the pifton, this air is forced 

 out as before. To prevent the pifton from meeting any re- 

 fiftance in its defcent, there is a valve in it through which 

 the air paffes as the pifton defcends ; but the air does not 

 -neceifarily depend upon a paffage through the pifton in order 

 to get into the barrel. By thefe means the pifton defcends 

 as eafily as in any other conftra^ion, w^hile the valve in it 

 does not impede the rarefaction. The valve pump P is, as 

 we have obferved, ufed for taking off the prelTure of the 

 atmofphere trom the valve on the top plate of the pump, 

 and for forming a more perfeft vacuum between this plate 

 and the pifton, that nothing may prevent this inftrument 

 fj-om exhaufting as far as its expanfive power will admit. 

 The barometer gage a b c, ferving to meafure the exhauftion 

 «f ihe receiver, confitts of a tube, divided by an annexed fcale 



of inches and fraftional parts of an inch, wliofe higher orifice 

 communicates with the receiver, and the lower is inimcrfid 

 in a ciftern of mercmy. Before any exhauftion lias t.ikeii 

 place the mercury in the tube and ciftern is upon the f;iiiie 

 level ; and after any number of turns of the handle oi" the 

 pump, the air in tlie lube and receiver i.s equ.'.Uy rarefied, 

 and the mercury will afcend in the tube till the wciglit of the 

 column above the furface of that in the cillern, and elafticity 

 of the air in the receiver, taken together, be equivalciit to 

 the' weight of the atmofphere ; and if the altitude of the 

 column is equal to the ftaudc.rd altitude, the vacuum in the 

 receiver, and that above the mercury in tlje barometer, arc 

 the fame. Eor an account of the fyphon-gagc, occalionally 

 fubftituted for the barometer gage, and the pear gage ; fee 

 Gage. 



In a contrivance, fuggefted by an ingenious workman of 

 the late Mr. Adams, and annexed to the pumps conllrufted 

 by Mr. Jones, one of the lower flexible oil-feins, or leather 

 valves in the two barrels, is attached to a brafs ring, which 

 is allowed an interval of motion of -j'^th of an inch ; a long 

 wire is fixed to a bar over the diameter of the ring, which 

 wire pafles along the body of the pifton and rod turough a 

 collar of Icatlurs in the pifton. By the friction of thefc 

 leathers upon the rod, asrthey move up and down, the lower 

 valve is occalionally raifed and deprclfed ; and thus a com- 

 munication is ojjciied with the barrel and receiver, and of 

 courle the cxhauli c 1 is carried to as great a degree a the 

 nature of the air itfelf appears to admit. By a comparifon 

 of the height of the merjuiy in a good barometer tube, Mr. 

 Jones did not oblerve the 4'?;th of an inch difference between 

 this and that of the barometer gage to the pump ; and con- 

 fequently the rarefaftiou was about 1 200 times ; and hence 

 he concludes that it was equal in power to that of Mi\ 

 Cuthbertlon or any pi:mp .whatever. 



We fliall now defcribe more minutely the parts of which 

 Mr. Prince's improved air-pump confifts. Fig. 49. Pl^ile 

 vii. reprcfents a perpendicidar fcftion cf one of the ban-els, 

 the two eifterns, condenfing gage, &c. ; where A B is the 

 barrel, C 1) is the ciftern on which it ftands, a a a a the 

 leathered joint, funk into e focket,and buried in oil ; E F i« 

 the pifton, with the cylindrical rod pafiing through a collar 

 of leathers, G G, in the box H I. K Ihews the place of 

 the valve on the top plate K, covered by the crofs piece M 

 M, into which is foldered the pipe O O, that conveys the air 

 from the valves to the duel going under the valve pump, as 

 maybe feen mfg. 51. : is part of the faid duft ; p is the 

 joint funk into a focket in the crofs piece P P, wliich con- 

 neils the eifterns, and has a duct through it leading to 

 them. Into this duft open the dufts q and r, the firll 

 leading to the gage in front of the pump, and the other to 

 the cock and receiver. The other bane! is left out of the 

 figure, except Q-, which is the top of it bmught down 

 out of its place for tlie purpofe of fliewir.g the top plate 

 that fliuts up the barrel, feparated from the box, which 

 contains the collar of leathers. S is one of the holes in tlie 

 plate over which the valve lies, and which is covered I^y K 

 in the crofs piece. V V is the pifton fticwing the valve o.peu 

 on the toji, which is to prevent labour wlien the pump con- 

 denfes. W X is the ciftern, in which is more diftinctly feen 

 the flioulder for the leather, which clofes the point between 

 this and the barrel, and alfo the focket in which the oil lie* 

 over the leather. Y Z is the condenfing gage, with the 

 orifice of the tube raifed above the furface of the quick- 

 filver ; c If is the collar of leathers, through which the glaf$ 

 tube moves ; and / is a fmall pipe coming up through the 

 quickfdver to form a communication between the valves and 

 the gage. In^fj^- 50. is feen the tipper furface 01 the top 

 3 P 2 plate 



