EXPERIMENTAL STUDY OF HEAT LEAKAGE. 799 



In Goodenough and Mosher's ammonia equation, the constant a is 

 zero and the constant c is negative. This accounts for the difference 

 as to sign between the vahie of {dfx/dp)r just calcuhited and that 

 derived from the ammonia ecjuation. 



If the pressure coefficient of ju is actually negative, the right hand 



ends of all fx vs. plots should be tilted upward, decreasing slightly 



the heat-leak effect. If it is positive, as the writer believes and as 

 Goodenough's steam equation indicates, the extrapolated jit's will all 



be slightly increased. In the case of the plot of yJ against - for plug S, 



for which the effect would be greatest, a reduction of all /x"s to 3. 87 

 kgm./cm.^on the assumption that {diJL/dp)T = + 0.028 °C. cm.Vkgm- 

 raises the four plotted points by 0.006, 0.003, -0.002 and -0.008 °C. 

 cm.Vkgm. respectively, counting from the one for the smallest value 

 of 1// outward in order, and the extrapolated value of /u is increased 

 from 3.182 to 3.200 — about 0.56 per cent. It is doubtful whether 

 the actual correction is as great as half of this. 



i. Comyarison with the results of other experimenters. 



Only three accounts of Joule-Thomson experiments by other 

 investigators on superheated steam over ranges of temperature which 

 include 165° C. have been published. These experiments were 

 conducted by Peake,^^ Grindley ^'^ and Griessmann.^^ All were what 

 engineers usually call 'throttling' or 'wire-drawing' experiments, — 

 that is, experiments in which steam known or assumed to be dry and 

 saturated is throttled to various lower pressures under conditions of 

 negligible loss of energy during the throttling process. The curve 

 which passes through a set of points representing the states of the 

 fluid on the low side of the plug for a number of different pressure- 

 drops from the same original high side pressure, is called a 'throttling 

 curve,' and is a curve of constant total heat, if the throttling has l)een 

 performed without gain or loss of energy. In all of the experiments of 

 Grindley and in some of those of Peake, the steam on the high side 

 was not devoid of moisture; hence, in these experiments, the state 



16 Pror. lloy. Soc, 76 A,lS.5-20.5 (1905). 



17 Phil. Trans. 194A, l-;:;(i (1900). 



18 ZS. des Vcreines d. Ing., 47, 1852-1857 uiid 1880-188-1 (1903). 



