105 
Steam Engine. 
extremity ; and there covered by a clack-valve, called 
the snifting-valve, which has a little dish round it, to hold 
water for keeping it air-tight. 
There proceeds also from the bottom of the cylinder, a 
pipe g, of which the lower end is turned upwards, and is 
covered with a valve r. This part is immersed in a cis- 
tern of water, called the hot- well, and the pipe itself is call- 
ed the eduction-pipe. 
Lastly, the boiler is furnished with a safety valve, call- 
ed the puppet-clack, in the same manner as in Savary’s en- 
gine. This valve is generally loaded with one or two 
pounds on the square inch, so that it allows the steam to 
escape when its elasticity is one-tenth greater than that of 
the atmosphere. Thus all risk of bursting the boiler is 
avoided, the pressure outwards being very moderate. 
When the cistern for the injection- water i, cannot be 
supplied by pipes from some more elevated source, water 
is raised by the machine itself. A small lifting-pump s, 
is worked by a rod v, suspended from a small arch upon 
the great beam ; this forces water through the pipe t into 
the injection-cistern. 
The parts of the engine being now described, the ope- 
ration is as follows : 
Suppose the piston and lever in the position represent- 
ed in the plate, and the water in the boiler in a state of 
ebullition, the steam and injection-cocks being shut. 
Having opened the steam-cock n, the steam from the 
boiler will immediately rush in, and flying all over the 
cylinder, will mix with the air. 
Much of it will be condensed by the cold surface of the 
cylinder and piston, and the water produced from it will 
trickle down the sides, and run oif by the eduction-pipe. 
This condensation and waste of steam will go on until 
the whole cylinder and piston be made as hot as boiling- 
water. 
Vol. II. 
O 
