( 670 ) 



not pursued it any further. Thus the represented part of the ip-surfece 

 for 26° from #=0.35 to #=0,65 and from r=0.0038 to r=0.0070, 

 has been given by us chiefly to demonstrate how exceedingly small 

 the influences must be on which a plait depends, and how much 

 care is required to determine a plait experimentally which is not at 

 all to be seen on the surface. The curves drawn on the surface, 

 which relate to the plait, were found by indirect ways, partly by 

 construction, partly by calculation. To facilitate a comparison of the 

 models inter se the region of .c and v, on which the model for 20° 

 and that for 26° extends, has been indicated on the model for 5°, 

 on the model for 20° that for 26°. 



§ 6. Further remarks on the different models and drawings obtained 

 by construction. 



a. The tfr '-surface for 5°. The model, pi. I, fig. 1, and the drawings 

 pi. II, tigs. 1, 2 and 3 show curves of equal concentration, \}\,r, 

 equal volume and equal pressure, the connode and the connodal 



do/ 



tangent chords. As— -— =p— 25, some pressures are represented 



by negative slopes on the stalde part of the ^''-surface, in consequence 

 of which the character of this i|«'-surface does not in this respect imme- 

 diately express that of the ^'-surface, where all the slopes are positive. 

 A connodal tangent-chord, near the concentration with maximum 

 pressure, almost touches the tfv-line. With the concentration of 

 maximum pressure this would be just the case. Just as the connodal 

 tangent chords the isobars are traced in the projection on the x r-plane 



(PI. II, tig. 3) in full lines, the connode is denoted by 



For the isobars l ) we may note several peculiarities, to which 

 van der Waals has drawn attention in his theory of ternary 

 systems 2 ). The isobar which touches the connode on the liquid and 

 vapour side, belongs to the pressure p = 36,6, which is found for 

 the mixture which when behaving as a simple substance should 

 have a maximum coexistence pressure. The pressure curve rr 

 determines the transition between the continuous isobars (taking 

 the region outside the drawing into consideration) and those 

 split up into two branches. The parts of the continuous isobars 

 which point to P, have each a point of inflection on either 



d> d 2 ip- 



side of the top. The shape of the curves ^— — = and - T - = 



1 ) Cf. the sketch by Hartman, Leiden Gomm., Suppl n°. 3, pi. II, fig. 5. 



2) These Proc. March J 902, p. 540. 



