Manchester Memoirs, Vol. xlv. (1901), No. 10. 7 



fraction -^ — 77- once. The volume occupied by the clear- 

 ance steam at any pressure during expansion will then be 

 the total volume given by the card multiplied by ^^^^^^ - 



In this manner the expansion curve GHJ has been 

 constructed down to J, at the pressure corresponding to 

 release pressure. 



Between J and K the expansion line must be put in 

 by guesswork. It may be somewhat as shewn by the thick 

 line JK, or may proceed by expansion to I and evapora- 

 tion at approximately constant pressure to K, or it may 

 follow the expansion curve CD, thus necessitating com- 

 pression back to the pressure of K before the re-evapora- 

 tion at constant pressure takes place. In the diagram, 

 the simplest line JK has been assumed to avoid compli- 

 cating the figure, especially since, as previously explained, 

 it does not affect those parts of the diagram from which 

 information is required. Thus the clearance steam diagram 

 is GHJ K AG, and its area gives the net work done on 

 the clearance steam per pound of cylinder feed, together 

 with the loss due to partially resisted expansion of admis- 

 sion steam if compression is not complete. 



If the compression is complete up to admission 

 pressure, this latter loss is eliminated, but there is still a 

 resultant transference of heat to the cylinder walls by 

 means of the work done on the clearance steam, and this 

 could only be zero if the dryness of the clearance steam 

 during expansion and compression were the same at each 

 stage ; that is to say, if the curves coincide. 



The elimination of the clearance steam is obtained by 

 setting back each point P and / in Fig. i by the volume 

 «H occupied by the clearance mixture at that pressure. 

 The area of the indicator diagram is unaltered, and the 



