Manchester Memoirs, Vol. xlv. (1901), No. 10. 3 



water in the cylinder. To do this, the dryness of the 

 mixture must be known at some point during expansion 

 or compression. In the absence of definite information, 

 the usual practice seems to be that of assuming a certain 

 value for the dryness fraction at the point of compression. 

 From this assumption, the weight of clearance mixture 

 shut in at compression can be obtained, and the indicator 

 card then placed in its true position with respect to the 

 saturation curve for the steam and water present in the 

 cylinder. 



The method adopted by Professor Reynolds, which is 

 fully explained in the paper to which reference has 

 already been made, can be found in standard text- 

 books on the steam engine. Shortly stated it is as follows. 

 Through the compression-point in the diagram an ideal 

 compression-curve is drawn for the clearance steam. 

 The volumes obtained in this manner for the clearance 

 steam are then deducted from the total volume of clearance 

 and cylinder steam as shewn by the diagram, that is to 

 say, the diagram is " set back " by these quantities. 



It would seem that the question is one of the relative 

 conditions of clearance steam and cylinder steam during 

 expansion. The experiments of Callendar and Nicolson* 

 show that steam in holes and crannies of the cylinder 

 may be superheated during most parts of the stroke. 

 This would apply in particular to the ports, but how far 

 it would affect the total clearance steam is doubtful. In 

 the same experiments, temperature measurements made 

 in the main body of the steam did not show this to nearly 

 such a marked extent. At first sight it might appear 

 that discussion of the point is immaterial, but quite 

 appreciable differences in the dryness fraction will result 

 according to the law of expansion assumed for the 

 * Proc. Inst. C.E. Vol. cxxxi., p. i68. 



