( 293 ) 



Fig'. I shows the system of isotliermal lines '). At temperatures 

 below 27^.50 I observed separation into two phases; 27.50 is the 

 temperature of the critical point of contact of the mixture. The 

 isothermals of 15°.30 and 21". 50 show distinctly a discontinuity in 

 slope resulting' from the separation into two phases. 



In the diagram the points where condensation begins and ends 

 are connected by a curve, which forms the limit between the area 

 where there is only one phase and the area where there are two. 

 The common tangent to the border-curve and the isothermal is 

 not horizontal as in the case of a pure substance. As for the 

 course of the border-curve at still smaller volumes, it is bound 

 to show a point of inflection somewhere and to be reversed 

 finally towards the axis of the volumes. In the figure however the 

 convex side is turned towards this axis, so that the reversing will 

 probably occur only at a very high pressure. I observed that at a 

 temperature of 27°. 10 at a decrease of volume the meniscus became 

 more and more indistinct and disappeared at last in the middle of 

 the tube as a mist when the volume 0,004063 and the pressure 

 91.85 atm. were reached. And so this point is the plaitpoint for the 

 composition .('^0,0494. The critical point of contact cannot be deduced 

 with accuracy from the experiments themselves; the best way is to 

 find out from the figure the point of contact of the critical isothermal 

 and the border curve. In doing so we find with pretty great certainty 

 the elements of the critical point of contact for the composition 

 ,rz= 0,0494; < = 27°.50; v = 0.0048; p =87.4 atm. 



The value of the coefficient of pressure for different volumes can 

 be determined from the isorhermals above the critical isothermal. These 

 coefficients of pressure within the narrow limits of the temperature 

 may be considered as constant, and the observations at large volumes 

 point to this fact. These coefficients of pressure are: 



V = 0.0338 (—) — 0.13S 



\dUv 



281 0.170 



225 0.216 



203 0.245 



180 0.283 



158 0.336 



conimunicatioii, the iiumbers here given and others occuriug m this coiiiiniiniL-atiou 

 do not exactly agree with tliose published in the dutch communicatiou. The volumina 

 uuderliued are those where separatiou in two phases takes place. 



1) Fig. 1 has been constructed at an arbitrary scale. The exact one we oljtaiii by 

 multiplying the abscissae by I,i2'i7, and the ordinates bv 0,99. 



20 



Proceediugs Roval Acad. Amsterdam. Vol. 1. 



