SPECIFIC HEAT OF AMMONIA. 327 



I. Introduction. 



The investigation described in this paper and carried on in the 

 Laboratory of Physics of Northwestern University during the years 

 1914-15-16, is a continuation of measurements on the thermodynamic 

 properties of ammonia, (NH3), made in the Research Laboratory of 

 Physical Chemistry of the Massachusetts Institute of Technology 

 in 1912-13. 



The work at the Massachusetts Institute of Technology was divided 

 into two parts: the equation of state for ammonia was determined 

 by Keyes and Brownlee,^ while Keyes and the writer made measure- 

 ments of the specific heat. The mean specific heat capacity of liquid 

 ammonia was determined by a parallel method of mixtures, using 

 water as a reference substance, between 0°— 20° C. and between 

 20° — 50° C.^ Realizing the unsuitability of this method for higher 

 temperatures, where the specific heat varies rapidly with temperature, 

 Keyes devised a "point" method which gave the mean specific heat 

 over very small temperature ranges.^ By this method some rough 

 measurements were made betw^een 25° — 95° C, but the data was not 

 considered of sufficient accuracy to warrant publication. 



The investigation described in this paper is an elaboration of this 

 latter method. 



II. Experimental Method. 



The specific heat capacity at constant volume, of a mixture of 

 ammonia, liquid and vapor, (XH3), has been determined over a tem- 

 perature range from 30° to 125° C, by an absolute method, which 

 consists of heating the ammonia, by measured amounts of electrical 

 energy, through temperature ranges of about 1° C, from various 

 initial temperatures. 



The calorimeter contains the calorimetric fluid, a heater, a ther- 

 mometer, and a sealed tube enclosing the ammonia. When the 

 calorimeter has been brought to some initial temperature, a measured 



1 "Thermodynamic Properties of Ammonia," Keyes and Brownlee. John 

 Wiley and Sons. (1916). Also Frederick G. Keyes, Amer. Soc. of Refrig. 

 Eng. Jour., 1, 9 (1914). 



2 Keyes and Babcock, Amer. Chem. Soc. Jour., p. 1524, .39-, (1917). 



3 " Thermodvnamic Properties of Ammonia," Keyes and Brownlee. John 

 Wiley and Sons. (1916), p. 29. 



