PNEUMATIC COCK. 107 



The cock is of a bended form, that the key may be situated 

 below the receiving orifice D, so that on opening the cock, 

 the fluid may run into the nozzle with sufficient rapidity to fill 

 its full bore ; which is essential to the principle of the instru- 

 ment. For the same reason the bore of the nozzle tapers a 

 little from the key at E, towards the orifice at F. 



As the fixed air generated within air-tight casks containing 

 vinous liquors; sometimes more than counteracts the pressure of 

 the atmosphere, and forces these fluids through every aperture 

 which may be made for them; it is in such cases necessary 

 while the cock remains open, to close the orifice A, of the up- 

 per perforation with the thumb, which may be done with great 

 facility, while the fingers are employed in holding the key. 



That the structure of the cock may be compleatly under- 

 stood, Fig. 2, affords a separate view of the key, and of those 

 parts of the upper and lower perforations, which lie within it. 



Fig. 3, is a representation of a cock executed in wood, on 

 the same principle with that above described. The dotted 

 lines A B C, D E F, represents the tracks of the upper and 

 lower perforations, of which the latter comes out through the 

 key. This is made unusually long in order to depress the de- 

 livering orifice, and thereby increase the velocity of efflux. 

 The lower perforation is considerably inclined below the hori- 

 zontal line, in order that on opening the cock the fluid may 

 run into the key with rapidity sufficient to fill the bore full. 



This as before observed being essential to the action of the 

 pneumatic cock, Fig. 4, is a separate view of the wooden 

 key, with the parts of the perforations which lie within it. 



