(152) 



Here too, we find therefore values for the ratio in question, vvliich 

 are not in contradiction with its empirical value. 



Doubling the molecular formula of the solvent is therefore no 

 longer necessary, and we may, therefore, say that the formula found 

 by us (3(2) or approximated (^h) represents the molecular rise of the 

 lower critical temperature very satisfactorily. 



Finally I may point out, that the experiments — of Centnerszwer 

 as well as those of Büchner — are not so accurate that the difference 

 between 1,9 and 2,2 for naphtaline is of much importance. 



The reason of this is easy to see; it is exceedingly difificult 

 to observe the critical plaitpoint temperature accurately. For it 

 is required for this purpose, that the corresponding volume be 

 accurately known beforehand, and that the volume of the tubes used 

 be chosen accordingly. Else, of course, not the plaitpoint temperature 

 sought, is found, but another temperature, situated more or less in 

 its neighbourhood. And this too can be a source of inaccuracies ^). 



From all that precedes it sufKiciently appears that van 't Hoff's 

 assertion that the value of A is constant, and equal to about 3, is 

 altogether incorrect. For the value of A is quite determined by the 

 ratio <9 of the critical temperatures. 



If & should happen to be in the neighbourhood of 2,3, then 

 A = /9{^—l) will lie in the neighbourhood of 2,3X1,3=3. 

 And now it has been very misleading, that really for the examined 

 substances the values of <9 lie nearly all near 2,3. (For the five 

 substances mentioned examined by Büchner the mean value of 6 is 

 2,25, for the substances investigated by Centnerszwer this is also 

 the case). If & = 3, we should find about 6 for A, so this is twice 

 as much! Hence there is no question of constancy. 



1) Also Centnerszwer calls attention to this in his paper (Z. f. Ph. Ch. 46, 

 p. 427-501 (1903). See specially p. 446, 459, 464— 466, 469-470, 489— 492 and 

 497 — 499. It appears from these passages, how much trouble he has taken to 

 determine the exact "Fiillungsgrad", and in this way to get as near as possible to 

 the critical plaitpoint temperature. As the determination of the rise of the critical 

 temperature was only of minor importance to Büchner, the values given by him, 

 cannot — as he himself states — lay claim to the accuracy reached by Centnerszwer. 



