( m ) 



is as has been indicated by van der Waals 1 ). The points of intersec- 

 tion of these two curves are the centre Q of the isobars and the 

 double point of (lie pressure curve at, P. 



b. The ^'-surface for 20°. Fig. 1, pi. Ill denotes the ^-curves 

 and the connode. Pig 2, pi. Ill the if\. y-curvcs and the connode. 

 Fig. 3 gives the projection on the x y-plane of the connode, of 

 the tangent chords and of some isobars. The connode is denoted by 

 _. PI. I fig. 2 gives a representation of the model. 



c. The ty' -surface for 26°. Fig. 1 pi. IV gives the if', /-curves, fig. 2 

 pi. IV gives the critical states, k\ and K, the isobars and the con- 

 nodes for the mixtures which are taken as homogeneous, and whose 

 gas branch as well as whose liquid branch is almost a straight line. 

 Though in the calculations (see § 2) the plaitpoint x Tp and the criti- 

 cal point of the homogeneous mixture ,vn-, have been considered 

 as coinciding, a distance has now been given between these points 

 which has been fixed by estimation 2 ). The dotted parabola has been 

 taken from Verschaffflt's calculation, Suppl. N°. 7, p. 7, though 

 properly speaking it holds only for the case that the maximum 

 pressure falls in P 1 or l\ ; the produced connode denotes the probable 

 course of this part by approximation. PI. I, fig. 3 gives a repre- 

 sentation of the model. All this refers to a small region of .randt'; 



fig. 3 pi. IV, however, indicates by the connode accord ing 



to the construction for the mixtures taken as homogeneous all over 

 the width of the ^'-surface. The square drawn denotes the extension 

 of the just treated part of the if/-surface. 



d. The contraction and the subsequent splitting up of the plait 

 appears from tig. 4 PI. Ill, where the ^-projections of the connode 

 and some connodal tangent chords of the three models have been 

 drawn on the same scale after the ^-figures for 5°, '20° and 26° 

 mentioned under abc. 



v ) Prof, van der Waals was so kind as to draw our attention to a property 

 which might also have been represented in the figure, when also the curve for 



3 — ^- = had been drawn, viz. that the minimum volume in the vapour branch, 

 Ov 2 0.v 



■ • • d 3 <// 



and the maximum volume in the liquid branch lie on the curve ^--<~ =0 which 



ov*d,v 



ÖV 



has a course similar to that of the curve ^— =.— = 0, more particularly it has the 



same asymptotes, and it deviates from it only in this, that with greater density 

 the curve passes over larger volumes. 



'-) Here the representation of the plait must come into conflict with the theory 

 or with the simplification introduced at the basis of the calculation. With a view 

 to the illustration of the theory by figures the latter has been chosen. 



