116 Dr. E. Obach on Relationship between Specific 



exist, viz. for the various esters of fatty acids and for the 



alcohols. 



Tables I. a, II. a, III. a, and IV. a contain the results of these 



X r 

 calculations, they show that the constancy of the quotient ^ 



is quite as good as in the corresponding tables containing the 

 observed values of X. We are, therefore, justified in regarding 

 the results obtained for the benzoic-acid esters given in 

 Table Y. with the same degree of confidence as those of the 

 other series, and to conclude that these compounds also show the 

 direct relationship between inductive capacity and latent heat. 

 This is the more interesting, as the benzoic esters belong to 

 the entirely distinct class of aromatic compounds. 



It will be observed from Tables I. a and II. a that the latent 

 heats of the free acids, calculated with Schiff 's constant 20*8, 

 differ widely from those actually found, and in order to 

 obtain a better agreement the constant would have to be 

 reduced to 15*1 ; but if in place of the boiling-temperatures 

 actually observed, those which would follow from the position 

 of the acid in the particular ester series were employed, viz. 

 283° for formic and 311° for acetic acid, the resulting latent 

 heats of vaporization would become 128 and 108 respectively * ? 

 which is in better accordance with the experimental results, 

 and gives for K the more probable values 13*1 and S'8. How- 

 ever, the higher members of the series, viz. butyric and valeric 

 acid, also examined by Favre and Silbermann, do not conform 

 to this rule. Table VI. gives, for direct comparison, the mean 



X X' 



values of the ratios ^ and ^ for all five series hitherto con- 

 sidered, and it will be seen that there is practically very 

 little difference between them. There is also only little 

 difference between the mean ratios of the formic and benzoic 

 esters, and, again, between those of the acetic esters and the 

 esters of the higher acids, whereas the alcohols give a notably 

 lower ratio. 



* Trouton (I. c. p. 5) increases the theoretical vapour-density of formic 

 acid in the ratio 2*68 : 1*62, and that of acetic acid in the ratio 3 - 19 : 2 - 08, 

 for the calculation of his constant. If the molecular weights are similarly 

 increased, the latent heats, calculated from the actual boiling-temperatures 

 with Schiff 's mean constant, are about 20 per cent, below the observed 

 values ; but if the constant derived from water, which I applied to the 

 alcohol series, is taken, the results are practically the same as those given 

 above, viz. 127 and 110 respectively. 



