4SI On the Advantages of High Pressure Sieam, [Dec. 



II 

 III 



IV 



V 



VI 



VII 



VIII 



Suppose we have to work at a pressure of 10 lbs. 

 on the inch. 



Let the steam be raised to a force of 80 lbs. on the 

 inch, and let in ith of the stroke ; then stop the 

 communication, the piston being at I. 



We have thus ith at 80 lbs. 



When the steam has expanded to II, the volume 

 is doubled, and the force reduced to 40 lbs. (suppos- 

 ing the cylinder to keep the temperature constant), 

 the mean from I to II being 60 lbs. 



Hence we have -|-th at 60 lbs. 



When the piston reaches IV, the volume is again 

 doubled, and the force reduced to 20 lbs. the mean 

 from II to IV being 30 lbs. 



This gives i-th stroke at 30 lbs. 



On reaching VIII, the volume will again double itself, and 

 the force will be reduced to :^-, thus becoming 10 lbs. on the 

 inch as proposed ; but the mean, from IV to the bottom, is 15 lbs. 



Which makes V stroke at 15 lbs. 



Adding these quantities together, we have 



I. 4- at 80 lbs. = lOlbs. 

 I to II. i at 60 lbs. = 7-5 



II to IV. ± at 30 lbs. = 7-5 

 IV to VIII. ^ at 15 lbs. = 7-5 



32*5 lbs. on the inch. 



for the mean impetus communicated to the fly-wheel by each 

 stroke of the piston : and as the cylinder full of steam is at a 

 density of only 10 lbs. on the inch, the power thus gained appears, 

 at first view, enormous. 



But against this must be set, the irregularity of the impulse 

 communicated to the fly, and of the temperature supplied to the 

 cylinder ; beside the additional weight and friction of the 

 machinery, and other considerations ; involving too many theo- 

 retical principles to allow of a satisfactory estimate from calcu- 

 lation, without direct and repeated experiment. 



Enough, however, is known, to prove both in practice and 



theory, that great profit is attainable l)y working steam at high 



temperatures ; and the limit of economy appears to me the 



degree at which water is decomposed by the containing vessels. 



I am, Gentlemen, your very humble servant, 



John Pridraux. 



