ADIABATIC CHANGES OF MOIST AIR NEUHOFF 445 



then we obtain the equation for the adiabat in the following simple 

 form 



p' T a a 



log-,-»,,-log^ + ^--, 



which may be written 



a a 



lo g P' ~ T, ~ w n lo g T = lo g Po - T7 - w a lo g T - constant (9) 



The factor a which may be designated the condensation factor 

 is a function of the temperature only and therefore behaves 

 analogously to the vapor tension e m of aqueous vapor. The law of 

 variation with temperature followed by a is also analogous to that for 

 e m . The graphic representation of this quantity shows a curve 

 analogous to the curve of elastic pressure for aqueous vapor. 



In order to determine from equation (9) the value of p' expressed 

 as a height of a column of mercury we must also express the 

 pressure e m by its corresponding height in mercury. 



The values of the coefficient a are given for the corresponding 

 temperatures for each degree from o° to 30 in table 5, column 5, 

 and can be taken from this by using the argument /. Intermediate 

 values can easily be determined by linear interpolation. For 

 instance, for t = iy°, io°, and o° we have the corresponding values 

 a = 115. 71, 75.98, and 39.99- 



The volume (V) of the mixture is obtained from the equation of 

 condition for dry air Vp' = RT. The quantity of vapor present x 

 is obtained from the corresponding equation 



e m 



x = e — r 

 P' 



If in equation (9) by the use of the last-mentioned relation we 

 express the atmospheric pressure p' in terms of x then we may 



