THK THKHMODYNAMICAL PROPERTIES OF sl'l'l .I;HK \ 1 i;i> ^\\:\M. 31 



As will be seen from the lust column in this table, the values of K P deduced from 

 1 1 1 UN'S experiments are very inconsistent with one another, a careful examination of 

 them showing, however, that as a rule the variations of K P shown by H ut.s's results 

 is greater than that deduced from the present experiments, and further that HIRN'B 

 results show a distinctly higher value for K P under atmospheric pressure and about 

 300 F. 



SECTION XVIII. Added October 4, 1899. 

 On the Cooling Effects observed in the Wiredrawn Steam. 



It will be seen on Diagram 5 that the fall of temperature along a line of free 

 expansion is not exactly proportional to the difference of pressure, the lines of free 

 expansion being slightly convex upwards. 



Again, in the experiments of JOULE and THOMSON on the cooling effects observed 

 by wiredrawing different gases through a porous plug, it was observed that the 

 cooling effect was almost proportional to the inverse square of the absolute tempera- 

 ture. To observe how far this was true for steam, there were obtained from 

 Diagram 5 various values of the cooling effect 86/8p, or, as we will in future call 

 it, C, and by plotting the logarithms of these values of C and of the absolute tempera- 

 tures T, it appeared that C varied approximately as (1/T) 3 ' 8 , the index 3 '8 being very 

 different to the value 2 obtained by JOULE and THOMSON. 



SECTION XIX. On certain Thermodynamical Relations existing between the Cooling 

 Effect, the Specific Heat K P , and Density of Superheated Wiredrmvn Steam. 



It early suggested itself to the author that some simple relation existed between 

 the variations in the value of K P with pressure and temperature, and an examination 

 showed that the cooling effect C(= 80/8p) was connected to K P in the following 

 relation 



......... (a), 



showing that the variation in the value of K P with the pressure is equal to, but of 

 opposite sign, to the variation with temperature of the product of K P with the cooling 

 effect. This formula may be deduced in the following manner. From THOMSON'S 

 formula* for the cooling effect produced by wiredrawing, we have 



CK 



TAIT'S ' Heat,' (1892), p. 340. 



