SPECIFIC HEAT OF AMMONIA. 



329 



constant, so that the specific heat so obtained is at constant volume.^ 

 This specific heat is denoted b}^ Cv^z- The subscript ,, signifying "at 

 constant volume," and the subscripts i and 2, denoting "of a mixture 

 of hquid and vapor," subscript 1 referring to the vapor phase and sub- 

 script 2 to the hquid phase. To be exact, it is necessary to specify 

 the numerical vahie of the particular specific volume at which the 

 measurements were made. We have then 





and for the laboratory equation 



8H2 



'l'12 



(1) 



(2) 



M V 89 86 



in which the terms in the brackets are functions of the temperature, 6. 

 Equation 2 gives the specific heat at any temperature 6, in terms of 



VAPOR REGION 



UQUID-VAPOR 

 REGION 



V 



Figure 2. 



the mass of ammonia and the heat capacities of the apparatus full 

 and empty, measured at the same temperature 6. The methods of 

 measuring 8H1, 8H2, 86, and M, will be described in detail hereafter. 

 Given values of c^jj as a function of the temperature 6, at some 



5 Measurements were made to determine the temperature dilatation of the 

 container, and this quantity was found to be negligible. 



