( 283 ) 



CO,H( 



orCH, 



on 1 ' toluenes 



e.<-ters 



3.4 

 3.5 

 2.3 

 2.5 

 2.4 

 2.6 



1.2594 

 •1.2772 

 1.2625 

 1.2820 

 1.2860 

 1.28:3 



1.2791 

 1.2935 

 1.2825 

 1.2859 

 1.2858 

 1.2923 



Water at 4° as unity. Corrected for upward atmospheric pressure 

 and for expansion of glass. 



Conductivity jwwer. This was determined in the usual manner 

 with a Wheatstone-bridgë and telephone at 25° and at 40°. As the 

 acids are soluble in water witli diflieulty v =: 100 or 200 was taken 

 as initial concentration; the end concentration was ?; = 800 or 1600. 

 In the subjoined table the dissociation constants are shown. 



On comparing these figures it is at once evident that the acids 

 with ortho-placed nitro-group possess a much greater dissociation 

 constant than the other two, so that in this respect, they may be 

 divided into two groups. In the acids without an ortho-placed nitro- 

 group, the value of the dissociation constant is fairly well the same. 

 In the other four, the position of the second group seems to cause 

 fairly large differences. That second group increases the said con- 

 stant most when it is also pliiced ortho : in N/mo solution 2-6-dinitro- 

 benzoic acid is ionised already to the extent of 90 °/g. Again, a NO^-group 

 in the para-position increases the dissociation constant more than one 

 in the meta-position ; and for the two acids 2,3 and 2,5 which both 

 have the second group in the meta-position, K is considerably larger 

 for 2,5, therefore for the non-vicinal acid than for the vicinal one, so 

 that here an influence is exercised, not only by the position of the 



19* 



