( 280 ). 



will now have lo suffer some niodilication too, and as I shall show in 



a 

 dl — 

 1 da b 1 db b 11 db 



another communication, be equal to ; ——--— = — h "tt v T" ' 



a dx b b da dx o b dx 



but the difference is slight — and this factor and others of a similar form 



dT dT 



occurrino- in the \alue of , the value of , calculated on the 



" Tdx Tdx 



supposition of b variable, may be considered as sufïicientlj accurate. 



We must therefore not expect to find a perfectly complete dis- 



cnssion of the problem in what precedes. If this was wanted, a closer 



investio-ation would be required for the determination of t- and 



\bxj, 



, if we take b dependent, not only on x, but also on v — , and 



(ix dv 

 hence put : 



b = b, {l + «(^*^) + ^(^*^Jete.|, 



while b^ = (^'i^^ (1 — '^O + ('''Jx •^' is put. But in the following com- 

 munication I shall show that in this particular case, the component 

 being in critical circumstances, we can determine the value of these 

 quantities without entering into a closer investigation. 



Physics. ''The properties of the sections of the surf ace of saturation 

 of a binary mixture on the side of the components." By 

 Prof. VAN DER Waals. 



I have brought the differential equation of the 7),.??, T-surface of a 

 binary mixture into the following form : 



In this equation ^ — - is equal to -^—z :rz-^ — . 



fè'^\ /d>A MRT 

 For X. infinitely small v^^^=i\ — v^, ^ — - = I ^ — - :=— 71 : 



and for i(\^ w^e may substitute the molecular heat of evaporation 

 of the component, which we shall denote by Jfr. The above equation 

 is then simplified to 



