(79) 



(6) 



a' = — wi' 



a" = - mi' 



(80) 



{() 



FUNDAMENTAL EQUATIONS OF IDEAL GASES 365 

 (a) {—) = (—\ 



Kdmi'/p, I, mj' \dm-i' ) p, t, mi' 



\dnii/p, t, TBj" \9w2 / p, t, mi" 



' f— -\' 1 



\dmi / p, t, m^' 



\dmi" ) p, t. tnj" , 

 ~; I dm\ 



l\ J p, t, mj' 



(:; — -, ) dm2', 



drrh /p. t, Tn,' 



\a7n2 / p, t, m,' 



The following equations may now be written, where Xi, X2 are 

 the quantities of heat required to evaporate a unit quantity of 

 constituent 1 or 2 from the mixture, and Aiv, 1^20 are the corre- 

 sponding changes in volume of a unit of components 1 or 2 in 

 passing into vapor: 



dni = dyL\ 

 + 



\dmi 



(81) 



Xi 

 t 



h 



t 



dt = Aivdp - a'dr' + a"dr", 

 dt 



, dr' „ dr" 

 L^vdrt + a' — - Vi" —^^ 

 r r 



(82) 



(83) 



21. Application to "Gas-Streaming" Method of Measuring 

 Vapor Pressures. An instance of some practical importance in 

 the application of these equations will now be discussed. The 

 determination of vapor pressures by the "streaming method" 

 was referred to earlier in connection with the Poynting effect, ' 

 but a fuller discussion was postponed until the Gibbs-Dalton 



