106 
Steam Engine, 
When this happens, the steam will begin to issue 
through the snifting-valve, slowly at first, and cloudy, be- 
ing mixed with much air ; but, by degrees, it will be- 
come more transparent, having carried off* the greatest part 
of the air which filled the cylinder. 
When the attendant perceives that the blast at the snift- 
ing-valve is strong and steady, and the boiler is supplied 
with a steam of proper strength, appearing by the renewal 
of its discharge at the safety-valve, which had stopped 
while the cylinder was filling, he shuts the steam-cock n, 
and opens the injection- cock 1. The pressure of water 
in the injection-pipe forces some out into the cylinder, 
which condenses the steam and forms a partial vacuum, 
as explained above. 
The upper side of the piston is now exposed to the 
whole pressure of the atmosphere, which, not being coun- 
terbalanced on the under side, will act with its whole force 
on the piston, and, provided there be not too much weight 
on the other end, will raise it, the piston going to the bot- 
tom of the cylinder. 
When the piston has gone down as low as necessary^, 
the injection-cock is shut, and the steam-cock opened. 
The steam, which has been accumulating above the wa- 
ter in the boiler, during the time of the descent of the pis- » 
ton, and is nov/ issuing through the puppet- clack, as soon 
as the steam-cock is opened, rushes violently into the cy- 
linder, having a greater elasticity than that of the air. It 
therefore immediately blows open the snifting-valve, 
through which it drives out the air that had been disen- 
gaged irom the injection- water. 
At the same time, the water which had been injected 
be for : , and the condensed steam, run out through the 
eduction-pipe g, and lifting up the valve r, flow into the 
hot-well. 
