350 Tables 94—97 



SATURATION VAPOR PRESSURE TABLES 



Resolution 164 of the Twelfth Conference of Directors of the International Meteoro- 

 logical Organization (Washington, 1947) adopted the Goff-Gratch 1 formulation for the 

 saturation vapor pressure in the pure phase over plane surfaces of pure water and pure ice : 



logics = - 7.90298 (7\/T — 1) + 5.02808 logm(T,/7) (1) 



- 1.3816 X lO- 7 (10 11 - 3Mn - r/r * ) - 1) 



+ 8.1328 X l0- 3 (10- : " 9149(^ ' /y - 1, - 1) + log**.., 



and 



logics = -9.09718(7y:r-l) - 3.56654 log, (T„/T) (2) 



+ 0.876793(1 - T/To) + log,o*«o, 

 where : 



e w = saturation vapor pressure over a plane surface of pure ordinary liquid water 



(mb.), 



d = saturation vapor pressure of a plane surface of pure ordinary water ice (mb.), 

 T= absolute (thermodynamic) temperature (°K.), 

 T t = steam-point temperature (373.16 C K.), 

 To = ice-point temperature (273.16 °K.), 

 ?«• = saturation pressure of pure ordinary liquid water at steam-point temperature 



(1 standard atmosphere = 1013.246 mb.), 

 do = saturation pressure of pure ordinary water ice at ice-point temperature 

 (0.0060273 standard atmosphere = 6.1071 mb.). 



The Goff-Gratch formulas are based on integration of the Clausius-Clapeyron equation 

 considering the deviations from a perfect gas, and on modern experimental data. The 

 stated range of validity of (1) is 0° to 100 C C. Since there is a dearth of experimental 

 data on vapor pressure over supercooled water and the necessary thermodynamic data 

 for an exact integration of the Clausius-Clapeyron equation do not exist, no completely 

 satisfactory formula exists for the vapor pressure over liquid water at temperatures 

 below °C. However, direct extrapolation of (1) gives values of e v in the middle of 

 the range suggested by other investigators and has been adopted for the range 0° to 

 — 50 °C. pending further research. 



Values for each half degree centigrade and whole degree Fahrenheit were computed 

 from (1) and (2), and values for each 0.1° were obtained by interpolation (Newton's 

 method)? with the exception of the few values in Table 94 for 7> 100 °C, which were 

 computed from Keyes 3 formula : 



logio^w (mm. of mercury) = — 2892.3693/7 



- 2.892736 logioT - 4.9369728 X 10" 3 r -f- 5.606905 X lO'T 



- 4.645869 X 10- 9 r 3 + 3.7874 X lfrT + 19.3011421. 



The small difference between e w and ei at °C. (32 °F.) arises from the fact that the 

 triple point for water is 0.01 °C. 



1 Goff, J. A., and Gratch, S., Trans. Amer. Soc. Heat, and Vent. Eng., vol. 52, p. 95, 1946. Also 

 see Tables 84-92. 



2 Keyes, F. G., Journ. Chem. Phys., vol. 15, No. 8, pp. 602-12, 1947. 



SMITHSONIAN METEOROLOGICAL TABLES 



