EXPERIMENTAL STUDY OF HEAT LEAKAGE. 797 



of the curves corresponding to the 2, 3 and 10 atmosphere ammonia 

 curves, of a sort indicating that the Joule-Thomson coefficient does not 

 vary with the pressure so rapidly as their equation demands. 



The reduced mean coordinates of the runs with the set-up S are 

 0.0172 for the pressure and 0.676 for the temperature. The corre- 

 sponding pressure and temperature for ammonia are respectively 

 29.05 lbs./in.2 abs. and 495° F. abs. On differentiating equation (p) 

 of Goodenough and Mosher's paper with respect to the pressure at 

 constant temperature, and inserting the above values of pressure and 

 temperature, the values of the various constants as given by the 

 authors and their values of Cp and its pressure-deri\'ative as given by 

 their equation (9), one finds the value -0°.0832F. in.yib.^ for (dfx/dp)t 

 for ammonia in the state specified. Multiplication of this by (1690)-/ 

 (460 + 273), which is the ratio of the square of the critical pressure 

 of ammonia in Ibs./in.^ to its critical temperature in °F. abs. gives 

 — 11.96 as the value of the derivative in question in reduced units. 

 This value may be checked by reference to Figs. 9a and 9b of Good- 

 enough and Mosher's paper. (Figs. 9a to 9e inclusive, except the 

 lower part of Fig. 9e, of this paper, are all incorrectly labelled; 9a and 

 9b are for reduced pressures of 0.0174 and 0.0261 respectively, instead 

 of 0.0S70 and 0.0783. A first glance at this set of figures gives the 

 impression that jj, increases with increasing pressure at constant 

 temperature, which is in contradiction of the equation (p) of the paper.) 

 Finally if -11.96 be multiplied by 648/(225.0)^, we find -0.152 °C. 

 cm.ykgm.^ for {dij./dp)Jor steam under the conditions of the runs of 

 set-up S, by this somewhat round-about invocation of the law of 

 corresponding states. 



There is no doubt that this result is far too large as regards its 

 magnitude, and possibly incorrect in sign. Its only justification is 

 that at other pressures the throttling experiments used by Davis 

 verify Goodenough and Mosher's ammonia equation. The actual 

 observations in the A'icinity of the pressure we are here concerned 

 with are not in agreement with this equation. If the experiments 

 made by Dodge, which exhibit much larger accidental errors than 

 those of the other observers, are neglected, it may fairly be doubted 

 whether even the negative sign of the pressure derivative of (jl is ^'eri- 

 fied. At all events, the accidental errors of the experimental work 

 are so large compared with the effect sought that any quantitative 

 estimate would be hazardous, and none will be here attempted. Of 

 course the very good verification obtained by Goodenough and Mosher 

 at higher pressures raises the presumption that at the pressure of the 



