Perkins'' Steam Engine. 59 



the fire. These partitions might be constructed of rough 

 boards in such a manner that they could be removed when 

 the boiler required cleaning, and would rather favor, than 

 retard the process of making steam. 



The bursting of the boiler of the iEtna, was attributed to 

 the supply pipe being choked. To this then the theory is 

 perfectly applicable. 



Your obedient servant, 



Erskine Hazard. 



Philadelphia, April 16, 1827. 



5. On the Economy of using highly Elastic Steam Expan- 

 sively ; by Jacob Perkins, Esq.* 



[See the Plate.] 



The diagram, figs. 1 and 2, in the plate, will show the 

 economy of using steam expansively, and also the method 

 of compensating for the inequality of the pressure on the 

 piston, which, if steam of 400lbs. to the square inch is 

 used, and stopped off at the quarter stroke, will end its 

 stroke at lOOlbs. per inch. The diagram will also show 

 that the velocity of the piston is continually varying, while 

 the crank is uniform in its motion.t 



From repeated experiments and much reflection, I am 

 led to believe that there is great economy in using very high 

 steam, and that expansively ; that the higher you can prac- 

 tically use the steam the sooner you may cut it off. The di- 

 agram shows the gain in cutting off the steam at quarter 

 stroke. Let the piston, which is represented by the line h. 1 

 «., fig. 1, descend to i. &., being one quarter of the stroke, 

 with a constant pressure of 400lbs. per square inch. At this 

 point, let the steam be cut off and expand to double its 

 volume ; when it arrives at h. c. it will be exerting a pressure 

 of 200lbs. per inch, producing a mean of 300lbs. per inch, 

 through the quarter stroke. Let the steam again expand to 

 double its volume, and the piston will finish its stroke at jf. e. 

 at lOOlbs. per inch, giving a mean of 150lbs. per inch for 



* The above article is subjoined to that on the Explosion of Boilers, 

 in the pamphlet received from Mr. Perkins.-^-Sd. Franklin Journal. 



t It is not pretended that this diagram is mathematically accurate ; 

 the object being merely to explain to the practical mechanic, in a suf- 

 ficiently clear and concise manner, the principle of the advantage gain- 

 ed by using steam expansively. 



