4 PROPERTIES OF STEAM AND AMMONIA 



However, such equations cannot be extended over any considerable tem- 

 perature range without change of constants, and it is, of course, desinil.K 

 that ihr rniire range 32 F. to the criiic.il temperature be represented 

 by a single equation with the same constants. 



ter a number of trials the preceding equation was written in the 

 form 



A (A) 



wh< IT 



A - O.00002 IO 



/ 



Thr addition of thr term A amounts to the inclusion of terms in T* 

 livi F 1 in the general formula. The constants an 



A - 10.5688080 log D =- 3.6088020 



log B - 3.688 1 209 log E = 6. 1 463000 



c- 0.0155 r=/+ 459.6 



The agreement between the formula and the experimental values is 

 shown in Fig. I. The equation is used as a standard of reference and 



Temp. F. 

 Ftc. i. PRESSURE AND TEMPERATURE OF SATURATED STEAM. 



orrlinates represent the relative deviation of the experimental values of p 

 (taken from the preceding tables) from the calculated values. From 

 200 to 700 degrees the agreement is remarkably good, the deviations 

 for the most part being less than I in 2000. Below 200 degrees the 

 discrepancies are relatively larger but absolutely very small. Thus the 

 discrepancy at 122 F. between the last Scheel and Heuse point and the 

 first Holborn and Henning point, which looks large in the figure, is only 

 mm. of mercury. The equation gives an intermediate value at 

 this temperature. At 32 degrees the equation gives 4.587 mm., while 

 the value generally accepted is 4.579 mm. of mercury. So far as pres- 

 sures are concerned the discrepancy is unimportant. The significant 



fact is that the derivative is quite uncertain at low temperatures. 



