for compressing Gases or other elastic Fluids. 15 



means of the crank (n) and the slings [mm). D is the pneu- 

 matic chamber, at the top of which are placed the induction 

 valve (e) and the eduction valve (c): over the latter is placed 

 a small vessel (g) with the pipe h leading to the receiver. 



Now when the plunger C is at the bottom of the stroke, 

 as shown in fig. 2, the pneumatic chamber D is then to be 

 quite full of oil or some other non-elastic fluid ; and for further 

 security a small quantity of oil is also to be above the eduction 

 valve (c) : — when the plunger C is drawn back, the oil in the 

 chamber D will sink to the level of (rs), and the space will 

 then be filled with the gas, which will rush from the gasome- 

 ter through the pipe {f) and valve (<?): but when the plunger 

 is again forced down, the oil will rise to the same height as 

 before, again filling up the whole capacity of the chamber D, 

 and forcing out every particle of gas through the valve (c) ; 

 and so on alternately. 



If, through the increased pressure, or from some other 

 cause, the oil in the chamber D should not be quite sufficient 

 to fill up the whole cavity on the return of the plunger, it is 

 of no consequence, because the moment the valve (c) rises 

 ever so little, the oil which was above the valve will descend 

 and displace the gas in the chamber D. The vessel g is a 

 small reservoir for the oil, and to receive any drainage from 

 the gas : the tube (k) is for ascertaining that the proper quan- 

 tity of oil is in the apparatus, or for supplying more when re- 

 quired. 



It is possible that a trifling leak may take place through 

 the valve (c); but this will be of little consequence, as the 

 escape of a small quantity of a non-elastic fluid back into the 

 chamber D is not attended with a twentieth part of the in- 

 convenience to which the escape of the same volume of com- 

 pressed gas would be subject. 



Now the particular advantage of this pump is, that the full 

 charge of gas is forced through the valve (c) at every stroke of 

 the piston, whether the pressure be equal to 1, 10, or 50 at>- 

 mospheres. Indeed there are no limits to the degree of com- 

 pression of which this pump is capable ; provided the parts of 

 the machine be sufficiently strong to withstand the strain, and 

 an adequate power be employed ; while it is supposed that 

 the operation of the common pump is not capable of extend- 

 ing beyond a pressure of 30 or 40 atmospheres. 



The following diagram will furnish an easy method of as- 

 certaining the power required to work the above pump suffi- 

 ciently near for all practical purposes. 



Thus let the straight lino A H be divided into 82 equal 



parts ; 



