261 



TABLE 243.— RELATIVE GAS VOLUMES AT VARIOUS PRESSURES 



(Deduced by Cochrane, from the pv curves of Amagat and other observers.) 



Relative volumes when the pressure is reduced from the value given at the head of the 

 column to 1 atmosphere; see also Nat. Bur. Standards Circ. 279. 



Gas 

 (Temp. = 16°C) 



"Perfect" gas 



Helium 



Hydrogen 



Nitrogen 



Air 



Argon 



Oxygen 



Oxygen (at 0°C). . . 

 Carbon dioxide . . . 



Relative volume the gas will occupy when the pressure 

 reduced to atmospheric from 



* Carbon dioxide is liquid at pressures greater than 90 atmospheres. 



TABLE 244.— VAN DER WAAL'S CONSTANTS FOR IMPERFECT GASES 70 



Van der Waal developed an equation to represent the pressure, temperature, and volume 

 relation of a real gas. One form of this equation is 



[p + a(y} 2 ~\(V — nb) = nRt 



n = number of molecules 

 (V — nb) = effective volume 



o= internal pressure constant [(dynes/cm 2 ) X (cm 3 /mol)] 

 b = reduction in effective volume (V) per molecule (cm 3 /mol) 



P (dynes/cm 2 ), V (cm 3 /mol), R t and T have their usual meanings. 

 The value of these constants (a and b) for various gases are given in the table. If Van der 

 Waal's equation were correct, V c /3 = b {V c critical volume). 



79 Slater, J. C, Introduction to chemical physics, page 408, 1939, McGraw-Hill Book Co. Used by 

 permission of the publishers. 



(continued) 



SMITHSONIAN PHYSICAL TABLES 



