THK THERMODYNAMICAL PHOPKRTIKS OF SUPERHEATED MT.AM. 



29 



TABLE V. 



Hence as regards the values of the specific heat under constant pressure of super- 

 heated steam the results of the experiments show that a very large variation in its 

 value occurs with temperature, but its value is practically independent of the 

 pressure. 



We see therefore that since the " perfect gas" condition is never obtained in the 

 steam in the experiments, it is impossible to calculate the constants in equation 8, 

 p. 4, or to in any way use RANKINE'S formula 7 for the total heat of gasification of 

 steam anywhere within the limits of pressure and temperature used in these experi- 

 ments. 



SECTION XVII. Added October 4, 1899. 

 Comparison with previous experiments. 



It has been suggested to the author that a comparison of the experimental results 

 with those of previous experimenters would be of interest, and for the sake of com- 

 parison, HIRN'S experimental results have been taken, as no others have been made 

 which enable even a small comparison to be made. It may be remarked, however, 

 that experiments such as those by PARENTY,* or by PEABODY and KuHNHARDT,t 

 though not undertaken with the same object as in the present ones, emphasise the 

 difficulty of obtaining accurate results in this class of experiments. As regards the 

 lii v i, r h values which have been obtained for the value of the specific heat under con- 

 stant pressure in superheated steam in the present experiments, though in view of 

 KKUNAULT'S experimental result of 0'4805 for the mean specific heat between 248 F. 

 and 430 F. they seem highly improbable, there is no direct evidence that a very 

 large variation in its value does not occur, what evidence exists tending in fact to 

 show that very large variations do actually occur; thus, DELAROCHE and BERARD* 

 found that K P = 0'847, while recently the value 0'38 has been calculated for the 



* ' Ann. do Chimie et <lc Physique', 7me serie, tome xii., 1897. 

 t ' Proceedings American Society of Mech. Engineers,' 1890. 

 \ Vide ZUENKR'S ' La Chaleur,' p. 422. 



