260 



TABLE 241.— SIMPLE GAS LAWS (concluded) 



Vapor pressure and the effect of vapor pressure upon the measurement of gas. — 



If a volatile liquid is introduced, a portion evaporates and exerts a pressure on the con- 

 fining walls. The amount evaporated and the pressure exerted are independent of the 

 presence of any other gas. If there is enough so that not all evaporates and if time is 

 allowed for equilibrium, the pressure is independent of the volume of space and of the 

 amount of liquid left unevaporated ; but it does depend upon the temperature. For each 

 volatile liquid there is therefore a definite saturation pressure or vapor pressure cor- 

 responding to every temperature. See Tables 360-369. 



When any gas is in contact with a volatile substance, the measured pressure is the 

 pressure exerted by the gas plus the vapor pressure of the volatile material. With no 

 change of temperature, this vapor pressure remains constant no matter how we change 

 the total pressure. Hence for the purposes of volume conversion the saturated gas may 

 be considered as a dry gas, the pressure of which is the partial pressure of the gas, or its 

 equivalent, the difference between the total pressure and the saturated vapor pressure of 

 the volatile material. 



TABLE 242.— VOLUME CONVERSIONS, FACTOR Z, FOR HIGH PRESSURES* 



In the measurement of gases at high pressures the quantity PV is no longer constant 



at constant temperature but varies with the pressure by amounts that differ for each gas. 



P\V P V PV 



Consequently the relation * = " 2 no longer holds. As a correction factor, Z = -== 



n 1 1 K 1 1 Kl 



is given for different values of some one or more of the variables. The values of Z for 



different gases as given in the table are for different pressures and temperatures. The 



values extend to pressures of 100-200 atm and to temperatures of 200 C C. Values of this 



factor of hydrogen for temperatures ranging from 16°K to 600°K and for pressures 



ranging from a small fraction of an atmosphere (.01) to 100 atm are given in Table 254, 



Part 2. n The value of this factor can be calculated for a wide range of pressures using 



the data given in some of the following tables. 



This tables gives values of volume correcting factor Z (V = 1 at 1 atm pressure and 



0°C). 



Argon 



Atm 



10 

 25 

 50 

 75 

 100 



Atm 



10 

 25 

 50 

 75 

 100 

 200 



Atm 



10 



50 



100 



150 



200 



0°C 50°C 



.9952 .9997 



.9877 .9987 



.9782 .9996 



.9722 1.002 



.9712 1.0077 



Helium 



100°C 



1.0021 

 1.0044 

 1.0100 

 1.0191 

 1.0253 



200°C 



1.0061 

 1.0084 

 1.0177 

 1.0277 

 1.0382 



o°c 

 .9921 

 .9784 

 .9577 

 .9403 

 .9262 



Hydrogen 



50°C 100°C 



.9973 1.0000 



.9918 .9984 



.9842 .9971 



.9783 .9971 



o°c 

 1.0050 

 1.0129 

 1.0260 

 1.0392 

 1.0524 



so°c 

 1.0042 

 1.0108 

 1.0218 

 1 .0329 

 1 .0440 



Nitrogen 



100°C 

 1.0035 



1.0092 

 1.0185 

 1.0279 

 1.0372 



o°C 

 1.0062 

 1.0156 

 1.0316 

 1.0480 

 1.0646 

 1.1333 



50°C 100°C 



1.0056 1.0051 

 1.0141 1.0127 

 1.0285 .1.0255 

 1.0429 1.0384 

 1.0575 1.0514 

 1.1168 1.1036 



Methane 



200°C 



1.0042 

 1.0105 

 1.0209 

 1.0315 

 1.0419 

 1.0839 



0°C 50°C 100°C 



.9975 1.0015 1.0035 



.9835 1.0035 1.0125 



.9835 1.0145 1.0295 



1.0015 1.0385 1.0546 (.730) .873 .943 1.004 



0°C 50°C 100 C C 200°C 



.978 .989 .993 .999 



.883 .941 .971 .997 



.781 .896 .951 .998 



200°C 



1.0023 

 1.0044 

 1.0084 

 1.0138 



Neon 

 0°C 



1.0045 

 1.0119 

 1.0235 

 1.0358 



.9746 .9990 1.0197 (1.0492) 



Oxygen 



0°C 20°C 50°C 100 C 



.9908 .9933 .9965 .9993 



.9771 .9835 .9908 .9980 



.9562 .9685 .9831 .9968 



.9378 _ .9771 .9971 



.9231 — .9733 .9983 



1.0686 1.0836 



— .873 .950 1.020 



* Adapted from data furnished by J. Hilsenrath, National Bureau of Standards. 



78 Woolley, Scott, and Brickwedde, Nat. Bur. Standards Res. Pap. RP 1932, vol. 41, 1948. 



SMITHSONIAN PHYSICAL TABLES 



