276 PROCEEDINGS OP THE AMEBIl \N V LDEMT. 



state of infinitely attenuated vapor. We will denote this quantity by 

 Y. It beaTS the Bame relation to the value v of a pure suhsta 

 the quantity v doea to w. We may call it the partial "ideal heat of 

 evaporation.'' 

 The above equation then becomes, 



/ainA _V-/V 



V cr )p,n i;r- ' 



which is a general equation for the influence of temperature upon the 

 activity uf one of the constituents of a mixture when the pressure and 



the composition are constant. 11 



Just as equation X was proved we may show that for one mol of the 

 mixture, 



Y = jVjY, + XS' 2 . XIII 



Hence we obtain an equation analogous to equation XI, namely 



/ N l d\a& + .\V 1 . , i, \ _ Y- I'r 



Here as before v is the volume occupied by one mol of the mixture 

 and Y the increase in internal energy when one mol of the mixture 

 converted into infinitely attenuated vapor, or in other words when it 

 evaporates in a vacuum. 12 



11 The approximate equation for the vapor pressure of one constituent 

 binary mixture obtained from equation XII is, 



\ OJ Jr.s- "/./-' 



where Q is the partial heal of vaporization (including the external work). This 

 i> in a Bimpler form than the equation obtained by Kirchhoff, 



( ";:\ i 



\ OJ'Jr.x' I. I- 



I I 



\'< rnst, Theoretische Chemie, -1 Edit., p. 1 18). 

 12 Equation X 1 1 bears the Bame relation to X IV that the equation of Kirchhofl 

 does t « > one obtained by Nernst, namely, 



rfln^H ,,/ln ... 



p v__ _ k 



dT 11 i- 



(Nernst Theor. Chem., i Edil , p. 117). 



