Starkweather — Thermodynamic Relations for Steam. 131 



sions of interest. A p-v-T equation should be of the form 



P 



RT 



V— a 



-/(T) + W 



In this R must have its theoretical value deduced from the 

 chemical composition of water, while a, on account of the 

 extreme incompressibility of water, should have a value not 

 much less than 0*001, v being in cubic meters per kilogram. 



Moreover, <j>(v) must be sensibly — for large values of v. 



The writer has formed the following equation, to hold for 

 volumes not much less than 0*12 cubic meters per kilogram. 

 At such volumes it should not be used when the pressure much 

 exceeds 11700 mm , although for larger volumes it maybe applied 

 to higher pressures. 



RT A 



P — 1 — i • 



v — a Tv% (v^ +y) 



Li p is expressed in millimeters and v in cubic meters per 

 kilogram the constants are 



log R = 0*539990 a = 0*0008 



log A = 4-632127 y = 1*20484 



The value of R is that given by Yan Laar,* modified by the 

 fact that he places the absolute zero at — 273°*2 instead of 

 — 273°*7, as assumed here. 



How well the equation agrees with 

 shown by the following table. In the 



the saturation line is 

 first column is given 

 the temperature absolute, in the second the pressure, p G , calcu- 

 lated from the formula by means of the saturation volumes, 

 in the third the pressure according to Regnault, p^ and in the 

 fourth the fractional deviation, d, of p c from^? K . 



T 



Pc 



PR 



d 



T 



pc 



p K 



d 



313*7 



55-11 



54-91 



+ •0036 



403-7 



2026-4 



2030-3 



— •0019 



323*7 



92-37 



91-98 



+ •0042 



413-7 



2712-2 



2717-6 



— •0020 



333*7 



149-34 



148-79 



+ •0037 



423-7 



3573*3 



3581-2 



— •0022 



343*7 



233-66 



233-08 



+ •0025 



433-7 



4641-7 



4651-6 



— •0021 



353-7 



355-04 



354-62 



+ •0012 



443-7 



5950-9 



5961*7 



— •0018 



363-7 



525-64 



52539 



+ •0005 



453-7 



7538-1 



7546-4 



— •0011 



373-7 



760-01 



760-00 







463-7 



9442-7 



9442-7 







383-7 



1074-6 



1075-4 



— •0008 



473-7 



11700 



11689 



+ •0009 



393-7 



1489-5 



1491-3 



— •0012 











With the exception of those near 323°*7 the variations are 

 insignificant, but the change in sign at 463° "7 shows that the 



* Zeitschr. fur Phys. Chem., xi, p. 433, 1893. 



