408 BABCOCK. 



X A constant denoting the rate of temperature change due to 



stirring alone. 



T A parameter used in Equation 35. 



8 Used as a symbol for an increment. 



8c Constant in the Callendar-Griffith's equations (19) and (20). 



8k A function in Keyes equation of state, (32). 



a A constant in Keyes equation of state, (32). 



/ A constant in Keyes equation of state, (32). 



Abstract. 



The specific heat-capacity at the constant specific volume 2.6593 

 ccm./gm. of a mixture of the liquid and vapor phases of ammonia 

 (NH3), has been determined in the temperature range 30° — 125° C. 

 The method employed consists of transferring to a calorimeter meas- 

 ured amounts of electrical energy, each sufficient to raise the tempera- 

 ture of the system approximately one degree. These changes of 

 temperature were measured by means of a platinum resistance ther- 

 mometer. The heat capacity of the system was measured first when 

 the apparatus was loaded with ammonia, and again when the appara- 

 tus was empty. At any particular temperature, the difference of these 

 heat capacities is the heat capacity of the ammonia, and knowing the 

 mass of ammonia present, the specific heat capacit}^ is computed. 



The calorimeter was a steel tube containing mercury, in which were 

 immersed the ammonia container, a thermometer and a heating coil, 

 the whole being jacketed in a Dewar vacuum flask, enclosed in a 

 vessel and totally submerged in an oil bath whose temperature could 

 be controlled. A special calorimetric Wheatstone Bridge was used 

 in connection with the platinum resistance thermometer. 



A special method of computing the calorimetric curves and the 

 cooling correction was developed. 



The experimental results consist of two curves, giving the heat 

 capacities of the apparatus when loaded with ammonia, and when 

 empty, as a function of the temperature. The values of the specific 

 heat of the particular mixture of liquid and vapor mentioned above, 

 are computed and the results given in Table II. 



Equations are given which permit the computation of any other 

 specific heat in the liquid-vapor region, or on the boundary of that 

 region, from the experimentally determined values of the specific 

 heat at constant specific volume. 



