( 171 ) 



llio o(|Uiili()ii (>r llie nielliiiji,-|)()iiil liiio iit xarviiig' vapour pi-ossiiro 

 from tlio difïei'Giitiiil eqiuilioiis di-awii up bv van dku Waai,s for 

 two-phaso (Mpiilihiia in a l»iiiai'V sysleni. 



If we combine llie foUowiiiu- two e(pialioiis: 



ai ld 



{ h% \ 



(1 



.^) 



i.e. if we seek llie iiilerseetioii of Ihe two n<pii(l surfaces, we get 

 au eipiatiou for the three phase e([uilibiMiiui ^ -\- /> -|- ^i- If as 



r/,77 dit 



here, we want to tiud the e(nuitioii of — , we eUmiuate , which 



(piautitv for the ecpiilibrium between Hcpiid and vapour in the case 

 under consideration is equal to that foi- the ecpiilibi-iiim between 

 solid and liquid. 



So from the equations (1) and (2) follows: 



0-^ A '^''7, »/.s7. '''.'/ — -''a f 0-s ^ "'•'■ 



,7 -f -— ■ 



"■'^L V>-'*'"lJpt'^'^^ '\SL %L \<'''",Ji.pdT r ^^ 



L %L 



01 



dw 



M"SL~-'lSL%L 



dT 



If finally instead of the decrease of entrop}' we write thedeveloj)- 

 nient of heat divided b}' the absolute temperature, we get the 

 ecpuitioii which will be applied in the further discussion. 



As we wish (o apply this equation up to tein|)eratures at which 

 critical phenomena appear, it deserxes re(*onimeiidatioii to write /;.,/■ 

 and //'.,/• instead of i\f and w^j., so that the equation takes the 

 followinu' form : 



dwL 



T — = 



dT 



1 



'-''„L • ^'-^y - "-y ' ^,L 



f ^^ (.'^. - "'/ ) z;^/^ - (.7;,/-./;/^) V,f 



Vö.r/^V/>7 



K^) 



Now with regard to the sign of the tpiantities /',,./ iind w^f, we 

 must I'cfer to the relation indicated bv the etpiation : 



or;/., 



in which {jt^f),- denotes the loss of energy that takes place when 

 1 gr. mol. of the solid phase is dissolved in an inlinilely large 



"'•-y 



'•./• H- (^z)'- 



(4) 



