( 285 ) 



was 0,455 normal. Kept at the ordinary temperature it did not 

 change its titre perceptibly for many months. As Goldschmidt showed 

 that the constants are proportionate to the concentration of the 

 catalyzer, they were all recalculated to a concentration of normal 

 hydrochloric acid. Owing to the large excess of alcohol the equation 

 for unimolecular reaction could be applied. The velocity measure- 

 ments were executed at 25°, 40'^ and 50°. At these last two tempera- 

 tures, the titre of the alcoholic acid very slowly receded (formation 

 of ethylchloride) and a correction had, therefore, to be applied. The 

 strength of the alcohol used was 98.2 7o by volume. 



In order to be able to compare not only the esterification-constants 

 E of the dinitrobenzoic acids with each other but also with those of 

 benzoic acid and its mononitroderivatives, the constants for those acids 

 were determined at 25° under exactly the same circumstances as 

 in the case of the dinitroacids. The results obtained are shown 

 in the subjoined table : 



As will be seen, E is by far the largest for benzoic acid and each 

 subsequent substitution decreases its value. 



On peinising this table it is at once evident that in the dinitroben- 

 zoic acids two groups can be distinguished. Those with an ortho- 

 placed nitro-group have a much smaller constant than the other two. 

 Whilst therefore the dissociation constant for acids with an ortho- 

 placed nitro-group is the largest their esterification constant is the 

 smallest. As shown from the subjoined table, this phenomenon 

 proceeds quite parallel ; the acids whose dissociation constant is 

 greatest have the smallest esterilication constant and vice versa. 



