( 665 ) 



four figures *) ; one of them gives the critical quantities from which 

 we shall start in our deduction, and the border curves for mixtures 

 of different concentration; the three others, which represent the xv- 

 projection of the connode with the connodal or tangent chords at 

 the temperatures 20° C, 25° C, 26° C, show the contraction of the 

 transverse plait with rise of temperature, and finally its splitting up 

 into two plaits. 



We have thought that we could obtain a better comparison of 

 observation and calculation, when representing the observations by 

 the .^-figures for 5° C., 20° C. and 26° C, and the pT-tigure, instead 

 of by the .ir-figures at the before mentioned temperatures and the 

 pT-figure. 



§ 2. Basis of the calculation. Law of the corresponding states 

 and reduced equation of state. We start (cf. Suppl. N°. 8, These 

 Proc. Sept. 1904 § 1) from the supposition that the law of the 

 corresponding states — at least within the region of the observations 

 — holds as well for C 3 H 6 and N 2 as for their mixtures. As reduced 

 equation of state we chose equation V. s. 1 of Comm. N°. 74 2 ) p. 12 

 For a region of reduced temperature and pressure which incloses 

 the region which corresponds to that of the observations under in- 

 vestigation, this equation is as closely as possible adjusted to C0 2 , 

 which in thermical properties has much in common with N,0, and 

 there is no reason to suppose that this will not be the case with C 2 H 6 . 



In the application we are, however, confronted by this difficulty, 



that V. s. 1 deviates most strongly from the observations on C0 3 



exactly in the neighbourhood of the critical state. (Cf. Comm. N°. 74 



and later Keesom, Comm. N°. 88). If from V. s. 1 3 ) the point is 



derived, for which 



dp d'p 



^- = and — - = , 



d» do' 



we find f = 1.010595, to = 1.0407. 10-», p = 1,06566. Keksom's 

 observations, Comm. N°. 88, give for the critical volume, when it 

 is sought by the application of the law of the rectilinear diameter, 

 for CO, 



v k = 0.00418 and for X = P -^ — 1.0027.10-3. . . (1) 



Tk 



1 ) Where it was necessary, Kuenen's figures have been rectified in accordance 

 with the results of observation given by him. 



2 ) Arch. Néerl. Vol. Jubil. Bosscha. Serie II, tome 6, 1901. 



3 ! In the calculations 7' is put 273°,04 for the freezing point of water, because 

 V. s. 1 was calculated with this value. 



45* 



