260 EXAMPLES. 



p the pressure of the steam in the condenser. Then the 

 total resistance upon the piston is K \F + L (1 +./) + p\, 

 and therefore the work expended per minute in overcoming 

 this resistance 



= NK[F+L(l +/) +p\ (A, - c). (4) 



When the mean motion of the piston of the engine is uni- 

 form, the work of the resistance will be equal to the work 

 of the steam ; therefore, by equating (3) and (4), and re- 

 ducing by (1), we have 



ft 



f(P) 



t -c), (5) 



from which the value of the useful load L is readily de- 

 termined. 



EXAMPLES. 



1. If a blowing machine changes per second 10 cubic feet 

 of air, at a pressure of 28 inches, into a blast at a pressure 

 of 30 inches, find the work to be done in each second. 



Herep z , from (8a) of Art. 129, = 0.4913& ; .-. etc. 



Ans. 1366.7 foot-lbs. 



2. If under the piston of a steam engine, whose area is 

 201 square inches, there is a quantity of steam 15 inches 

 high and at a pressure of 3 atmospheres, and if this steam 

 in expanding moves the piston forward 25 inches, find the 

 work of the expansion per second. Ans. 10866 foot-lbs. 



3. The air in a reservoir is at a temperature of 120 C., 

 and at a pressure corresponding to a height of the manom- 

 eter of 5 inches, while the barometer marks 29.2 inches. 

 Find (1) the theoretical velocity of efflux, and (2) the theo- 

 retical discharge through an orifice 1 inches in diameter. 



Use (9) of Art. 129. 



Ans. (1) 645.12 feet ; (2) 7.917 cubic feet, 



