34 MR. J. H. OR1NDLEY ON AN KXPF.K1MKXT.M. INVESTIGATION OF 



may be used in a simple manner to determine the specific volume v in superheated 

 steam at any temperature and pressure, the value of A for this particular pressure 

 being calculated from known data of the saturated condition. 



It would appear, however, from Section XVI., p. 25, that the maximum volume 

 which steam can occupy at the temperature of saturation under a certain pressure is 

 not that given in the usual steam tables for the volume of dry saturated steam under 

 that pressure and temperature, as the dry saturated steam used in the experiments 

 does not become superheated with the slightest amount of wiredrawing. A correction, 

 which is usually very small, could be found for the specific volume of the dry saturated 

 steam as obtained from tables, to bring it to the specific volume of steam when a 

 maximum at the temperature and pressure of saturation considered, i.e., when no 

 further increase of volume can occur at that pressure without superheating. Thus, 

 taking an actual example, it is shown on p. 25 that at 236*4 the maximum amount of 

 heat the steam can contain at this temperature of saturation without becoming super- 

 heated is equal to the total heat of evaporation of the steam at 239 '2 F. as given by 

 the steam tables, i.e., the latent heat required to create the maximum volume at 

 236 '4 F. is greater than that required to bring the steam to the dry saturated 

 condition by the amount 



0-305(239-2 236'4) or 0'854 B.T.U., 



and hence the ratio of the specific volume of dry saturated steam to the 

 maximum volume obtainable under the same conditions of pressure and temperature 



* s = QK.n.*iA 949'52 being the latent heat of evaporation in B.T.U.s of steam 

 you*o 1 4 



at 236 '4, for, according to RANKINE'S formula for calculating the specific volumes 

 of saturated steam, the volume is proportional to the latent heat. 



The maximum volume being obtained in this manner by substituting it in the 



equation 



v + CKf 



T " 



it is possible to find A, and hence to find v for any other temperature T under the 

 same pressure, the units of CK P being altered as required. 



By calculations of the preceding nature the volumes have been obtained of super- 

 heated steam at various pressures, and at temperatures which enable a direct 

 comparison with HIRN'S experimental results to be made. These experiments of 

 HIRN on the densities of superheated steam do not give very consistent results amonic 

 themselves, but they are the only ones as yet made which cover such a range of 

 pressure and temperature as is the case in the present research, and hence are the 

 only ones with which a comparison can be made. The experiments of FAIRBAIRN and 

 TATE,* however, furnish us with direct evidence that a very large expansion of 



* ' Phil. Trans.,' 1860-2, "On the Law of Expansion of Superheated Steam." 



