( 436 ) 



the question in one of his hist papers : inltdl is the eqaatioit of state, 

 after all, that corresfxmds to the fact of the ''straight diameter ' — ■ 

 hut that this fad ah-eady follows from the simple equation of van 

 DER Waaj.s with I) constant, as a special particularity that the coefii- 

 eient of direction of the curve ^/^{d -\- d') = fm) does not deviate 

 much at its initial and its final point from the coefficient of the 

 direction of the straujut line connecting them, so that the curve, as 

 it were, winds about the straight line, and nowhere moves away 

 from it considerably. 



This alone is the reason of the said curve being almost straight, and 

 it is (|uite unnecessary to look for a very special equation of state 

 which was to account for this fact. And for this reason we took the 

 trouble to demonstrate this iu the above with respect to the "ideal" 

 VAN DER Waals' e([uation. For there already we meet with the 

 so-called '\^tr(ii</ht" diameter. And ihis fact continues to exist also 

 for the ecpiatiou of state modified by us when the molecules of the 

 substance have joined to greater molecule-complexes by association. 

 Only the coefficient of directioji will then not be 0,4 to 0,5, but 

 abont twice as large, viz. 0,9 to 1, as we shall ])rovc in a following 

 communication. 



Verv near the critical point d and d' (see also the above table) 

 will be represented according to the idi'>d ecpialion of state by 



whereas in reality a much greater divergeiice of the two phases is 

 found, when m becomes slightly smaller than 1. Then the coefficient 

 2 should be replaced by about 3,6, as follows from the values d 

 and d' for the standard noruial substance tluorben/.ene, and also 

 from that of SO,, which latter values very recently were determined 

 by Cardoso with great accuracy in the iuimediate neighbourhood 

 of the critical [>oint. 



With respect to C\,H,F we have the following table (p. 437) 

 (see also Kuenex, Die Zustandsgleichung, p. 99). 



So the deviations from the straight line betw^een \'„ {d -\- d') = 1 

 and 1,274 are iu reality even (jreater than according to the ideal 

 equation of state of van der Waals ; further the curve now winds 

 about the straight line in exactly the reversed way from that in the 

 ideal case : near the critical point the curve deviates to the liquid 

 side ; further on to the \apour side. The straight line has 0,9 as 

 coefficient of direction ; the curve at the critical point 1,1. The 

 so-called "straight" diameter exhibits even a perceptible curvature 

 close to the critical point, where it turns its convex side to the vapour 



