146 PNEUMATICS. 



Plate 6. fig. 12. represents a machine of this 

 kind ; it consists of a brass-barrel containing a 

 piston, with a valve opening downwards; so that, 

 as the piston is raised, the air passes through the 

 valve ; but as the piston is pushed down, the air 

 cannot return, and, is therefore, forced through a 

 valve at the bottom of the barrel that allows it to 

 pass through into the receiver B, but prevents it 

 from returning. Thus, at every stroke of the pis- 

 ton, more air is thrown into the receiver, which is 

 of very thick and strong glass. The receiver is 

 held down upon the plate C by the cross-piece 

 D, and the screws E F. The air is let out of 

 the receiver by the cock G, which communicates 

 with it. 



A great variety of experiments may be per- 

 formed by means of condensed air. 



1. The sound of a bell is much louder in con- 

 densed than in common air. 



2. A square phial may be broken by condens- 

 ing the air round it, provided the condensed air be 

 prevented from getting within the phial. 



3. A very beautiful fountain may be made by 

 condensed air. Procure a strong copper vessel 

 (Plate 7« %• !•) having a tube that screws into the 

 neck of it, so as to be air-tight, and long enough 

 to reach near to the bottom. Having poured a 

 quantity of water into the vessel, but not enough 

 to fill it, and screwed in the tube, adapt to it a 

 condensing syringe, and condense the air in the 

 vessel ; shut the stop-cock, and unscrew the sy- 

 ringe ; then, on opening the stop-cock, the air 

 acting upon the water in the vessel will iforce it 

 out into a jet of great height. A number of dif- 

 ferent kinds of jet pieces may be screwed on the 



