438 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



column the values of the vapor pressure e m of saturated aqueous 

 vapor corresponding to the different temperatures according to 

 the data given by Guldberg and Mohn in their "Etudes, " p. 15. 



The table for x here given differs from that previously devised 

 by von Bezold, 13 in that the latter determined in grams the quantity 

 of moisture in the form of vapor contained in a kilogram of satu- 

 rated air and which therefore corresponded to the idea of the 

 specific moisture of saturated air. 



The quantity 



or (1 + 1.608 x) R = f (x) can appropriately be called the 

 mixing constant as [it is dependent on the mixing ratio, x. In 

 column 3 of table 4 are given the auxiliary quantities needed 

 for the computation of the mixing constant corresponding to 

 values of the mixing ratio from o up to 30 grams; we have only 

 to substitute Rp for R, so that, for example, for dry air Rp = 2.1528 

 and for x = 12.5 grams we have R'p = 2.1960. 



If the quantity of heat d Q is given to any gas then its change of 

 condition is expressed by the thermal equation 



dQ = c v dT + Apdv 

 or since we have 



c v = c p - AR and pv = RT 



hence 



dQ = c p dT - Avdp = c p dT - ART _?. 



P 



We make use of this latter form of equation in order to obtain 

 the equations for pressure and temperature, and therefore for any 

 change of condition of the mixture we obtain the following equa- 

 tions for the changes in the individual components, the dry air 

 and the aqueous vapor, which we distinguish by means of the 

 superscript indices prime and double prime. 



dQ' = c'dT - ART dp - 

 p p' 



dQ" = xc' p dT -xA R T^ 

 p e p" 



13 von Bezold : Zur Thermodynamik der Atmosphftre. Sitsb. Berlin Akad, 

 1890, p. 239 or 390, or Mechanics of the Earth's Atmosphere, 1S91, p. 287. 



