22 PROPERTIES OF STEAM AND AMMONIA 



Accurate values of T w are given in the steam tables; hence, if the con- 



stants c and k are known, values of T a are readily calculated. Using 



the graphical method suggested by Moss, Mosher plotted the avail. iNr 



experimental values and established the following \ .ilues of the constants 



c- 1.70 - 0.000224 - 



Values of T. thus obtained represent with satisfactory accuracy the most 

 rrliablr of the experimcMit^. 



Specific Volume of Liquid Ammonia. For the temperature range 

 -60 to 160 F., Mosher, following Avenarius, assumed an equation of 

 the form 



t/a-&log(/*-/), 



to express the relation between the liquid volume and the temperature. 

 In this equation /* denotes the critical temperature of ammonia, which is 

 taken as 273.2 F. With the constants a 0.06335, b = 0.016, the equa- 

 tion represents satisfactorily the experiments of Dieterici, Lange, and 

 ulriVff. Above 160 F. the liquid volumes were determined by the 

 law of thr 'Straight diameter." 



Specific Volume of Saturated Ammonia Vapor. Latent Heat. By 

 a combination of the equation expressing Ramsay and Young's law with 

 tin- Clapeyron equation, the following relation is obtained: 



The subscript w refers to water, the subscript a to ammonia. The 

 ratio - is 0.0001316. At any given pressure the term in the first mem- 



ber of this equation and the bracketed term in the second member may 

 be found from the known properties of steam. Hence the quotient 



" i/ 



- for ammonia may be calculated. 



With reference to the numerator v" v f , satisfactory values of v' 

 are available and Dieterici's experiments give acceptable values of v" 

 within the range 3O-222 F. Hence tentative values of the latent heat r 

 may be calculated and compared with the experimental values. Follow- 

 ing this procedure, Mosher deduced the following formula: 

 log r - 1.856064+ 0.37 log (273.2 - /). 



The curve r - /(/) representing this equation fits the discordant experi- 

 mental points at least as well as any of the other proposed curves and the 

 form of the equation is such as to justify extrapolation to very low tem- 

 peratures. 



With this equation for r available the process just described may be 

 reversed, and values of v" - v' may be calculated. Values of v" up to 

 160 F. were thus obtained. For temperatures above 160 F., values of 

 v" were obtained from the law of the straight diameter. 



