4 Wilson and Noble, Entropy Diagrams. 



clearance steam. Considering in general the proportion 

 that the clearance steam bears to the total quantity in the 

 cylinder, it seems not unnatural to suppose it to follow 

 the same law of expansion as the main body of the steam. 

 The authors, therefore, have made this assumption, viz., 

 that during expansion the clearance steam follows the 

 same law as the rest of the steam in the cylinder, and 

 hence its expansion curve will have its volumes propor- 

 tional to those shown by the diagram for the total 

 mixture.* This assumption has the advantage of giving 

 dryness fractions which agree with those calculated by the 

 method of weights, being, in fact, a graphical translation of 

 the same, and in general will show the steam drier than if 

 the saturation curve is adopted, whilst the net work done 

 upon the clearance steam will be increased. Of course, 

 the curve thus assumed cannot be continued below a 

 pressure corresponding to release with any certainty, and 

 must between that point and compression be filled in by 

 conjecture, but this uncertainty will not affect those parts 

 of the diagram which are important, and applies in an 

 equal degree to any other curve which may be assumed 

 for expansion. It remains, therefore, to indicate the 

 method of reduction of the indicator diagrams and their 

 transference into entropy diagrams. 



In Fig. I, ABCDKA is an indicator diagram drawn 

 on a volume scale such that the area represents the net 

 work done per pound of cylinder feed, i.e., per pound of 

 mixture passing through the engines. EF represents the 

 volume swept through by the piston per pound of mixture, 

 OE represents the clearance volume per pound of mixture, 

 ST is a portion of the saturation curve for one pound of 

 steam, and is set out with respect to OX and OY as axes 



* The method of constructing the entropy diagram will apply whatever 

 assumption is made as to the expansion of the clearance steam. 



