( (^56 ) 



If we draw the «f^^- and /^.^/ as ordinates and jj as abscis we obtain 

 two curves which obviously touch each other at one point ; it is 

 difficult, however, to define this point of contact precisely. If the 

 same is done with p^j^ and jj^pi, the determination of the point of 

 contact of the two curves is even less certain, owing to the circum- 

 stance that, according to the table above, for x = 0,4035 =. p^-k ^Pxpi, 

 which surely follows from the inaccuracy of the method. And the 

 deduction of this point of contact from a graphical representation 

 of the Vxk and i\-f,i is quite impossible because these volumes are 

 known bv no means with sufficient accuracy. 



Therefore it seems to me that the best method is that of Quint 

 who deduced the composition of the special mixture from the shape 

 of the plaitpoint curve by searching on this curve the point where 

 the bordercurve, Avhich terminates at that point, touches the plaitpoint 

 curve. That point may be determined fairly accurately : we find 

 for its coordinates 7/j =r 29'',0 and vk = Q^,S atms., whence again 

 .,., = 0,44 and vt = 0,00500. 



By means of the gi-aphical representations of the t^^, jjj-j^ and v^k 



I find in the neighbourhood of .i-^- = 0,44, — ^ =:: — 20, — =— 30 



da; dx 



and — = 0,0020; hence « = — 0,07 /? = —0,50 and r = 0,40, so 



dx 



that the relations y = a — /? in - := 7,3 are confirmed in a satisfac- 



a 



tory way. 



By means of Quint's observations, by intei-- or extrapolation, partly 

 also by using the law of corresponding states and the values of 

 txk') pxk, ^xk found above, I have drawn the isothermals for the 6 

 eX'-values considered, at the critical temperature 29". C. of the special 

 mixture x = 0.44. Those isothermals are represented in the annexed 

 figure, which thus shows the ^?-?;-diagram of the mixtures at the 

 temperature 29°. C. The dot-dash line is the critical x = 0.44 with 

 the critical point in C. The isothermal x = 0.40 is a dash line in 

 the unstable part; owing to their small curvature the experimental 

 isothermals are represented by straight lines. The border curve is 

 a complete line like the observable parts of the isothermals. 



Under the p, t'-diagram I have represented the projection on the 

 V, A'-surface. The critical isobar (63.8 atms.) is represented by a dot- 

 dash line; some other isobars are drawn, like the projection of the 

 connodal line (also projection of the afore-mentioned border curve), 

 while the isobars in the unstable part, i. e. within the projection, are 

 dotted. The temperature 29° being lower than the critical temperature 



