21<i HYDRAULICS. 



When this happens, the steam will begin to issue 

 through the snifting-valve, slowly at first, and 

 cloudy, being mixed with much air ; but, by de- 

 grees, it will become more transparent, having 

 carried off the greatest part of the air which filled 

 the cylinder. 



When the attendant perceives that the blast at 

 the snifting-valve is strong and steady, and the 

 boiler is supplied with steam of a 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, /. The pressure of water in 

 the injection-pipe forces some out into the cylin- 

 der, 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 counterbalanced 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 bottom 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 accu- 

 mulating above the w r ater in the boiler, during the 

 time of the descent of the piston, and is now 

 issuing through the puppet-clack, as soon as the 

 steam-cock is opened, rushes violently into the 

 cylinder, 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 disengaged from the injection-water. 



At the same time, the water which had been in- 

 jected before, together with the condensed steam, 



