616 



tlie OH-groups is substituted by an oxalkjl-gruiip, as e.g. with 

 monovieihylresorcinol and giutjacol. These difïereiic'es liowes'er are 

 (•oinpletely reduced to the size found in the case of' the above 

 mentioned substituted hydrocarbons, if all //-atoms of the O/Z-groiips 

 present are esterified : between ortho-, and para-Nitrodnisol e.g. the 

 deviation of tiie two curves is already much weaker, as in the case 

 of oriho-, and para-N^itrophenoI itself, while it is yet more consider- 

 ably diminished in the case of Veratrol, Dhia'lliyllnjdruiiuuione, where 

 the f(-^curves of the two last named substances even coincide almost 

 over their full length. If we now observe so much stronger ditferences 

 between e.g. ortho-, and para-Nilioplwnol, than between their cor- 

 res|)0Mding anisols, this could probably be considered as an indication, 

 til t the internal equilibrium in the li(piid between the molecules with 

 the conatitntion of the |)seudo-acid, and between those with the true 

 nitrophenol-formula, may bo siiuated in the case of the ovlho- 

 compound in such a way, that it much more approaches to the 

 side of the pseudo-acid, than in the case of the /^ara-conipound : a 

 circumstance pi'oliably caused by the more immediate vicinity of 

 ()/7-groups and iV^^^"!'^*^'*^"^' >" 'l^^ case of the orthi)-nitroj)henoL In 

 the case of the corresponding iinisoh, they might then be sup|)Osed 

 to [)0ssess a quite analogous structure, no freely movable //-atom 

 being any more present. 



Even in the cases, where the .«-/-curves of such isomerides, approach 

 each other relatively closely, it can be ofien obser\c<l, that the valuer of 



the temperature-coefficient ^- are evidently ditferent, which thus deter- 



at 



mines the steeper or flatter shape of the curves. 



Besides in the case of the jj/iéj/jo/*-, also somewhat greater ditferences 

 may be stated between isomeric aromatic bases, and between the 

 cresols. Tlie al)norinal shape of the curves with some of the considered 

 bases, undoul)tedly must be partially explained by the alterations 

 and decompositions, which seem more easily to occur in the case 

 of these compounds at higher temperatures, than with other substances. 

 Finally we can draw^ attention to the fact, that within the series 

 of the halogenniirobenzenes, just as within that of the hahgenated 

 benzenes themselves, the values of;* at the same temperatures appear 

 to be the greater, the higher the atomic weight of the halogen-atom 

 is. This fact is of course just opposite to that observed in the case 

 of I he molten halogenides of the alcali-metals. 



A general rule considering the relative magnitude of ft in the 

 case of ortho-, mcta-, and /)a/'a-monosubstitutionproducts, could not 

 be formulated. " I 'niveisitg-Laboratory for Inorganic 



Groningen, August 19J5. and Physical Chemistry. 



