ELECTRICAL CONDUCTIVITIES, ETC. 139 



strength of that acid, depends upon the position of the group. Benzoic acid at zero 

 and t> = 128 has a value of (* = 18.49. M c for salicylic or orthohydroxybenzoic acid 

 = 62.65, for metahydroxybenzoic = 20.48, while for parahydroxybenzoic at 128 and 

 0,m,= 18.29. 



The introduction of the second hydroxyl group raises the conductivity, the amount 

 depending on the position of those groups. At zero and v = 128, /x for 1, 2, 4 dihy- 

 droxybenzoic acid = 44.74, while n v for 1, 2, 5 dihydroxybenzoic = 66.18. 



Gallic acid, or trihydroxybenzoic acid, has an interest of its own. For zero and 

 t> = 128, n v = 14.01. The third hydroxyl, instead of raising, lowers the conductivity 

 below that of benzoic acid itself. 



The presence of the amino group lowers the strength of the acid, as would be 

 expected. Thus, benzoic acid at and v = 64, //= 13.42. For orthoaminobenzoic 

 acid ju r = 3.07; while for paraaminobenzoic acid /* = 3.71. 



The four sulphonic acids studied are all strong, as are sulphonic acids in general. 



Of the three toluic acids, the ortho is much stronger than the benzoic, while the 

 other two are of the same order of strength. Cinnamic acid is slightly stronger than 

 hydrocinnamic. 



When we come to the dibasic phthalic acid, we have a much stronger compound 

 than the monobasic acid. Thus, at and y = 64, n v for phthalic acid =55.98. 

 The introduction of the second carboxyl thus increases the strength of the acid. 



DISSOCIATIONS OF ORGANIC ACIDS. 



It is not necessary to consider the dissociations of the several acids in detail. It 

 is better to take up the constants calculated from the dissociations, since these are 

 the quantities so often desired in connection with the organic acids. Some conclu- 

 sions have, however, been reached, especially by White and Wightman, in connec- 

 tion with the dissociations of these compounds, and these will be given. 



The conductivity of most of the organic acids is a parabolic function of the tem- 

 perature, as is shown by comparing the values found with those calculated from 

 interpolation formula. Several of the amino acids are exceptions to this relation, 

 their conductivities not being a parabolic function of the temperature. 



The effect of rise in temperature on the dissociation of organic acids can be for- 

 mulated thus: The dissociation of some of the organic acids decreases regularly with 

 rise in temperature from 0. Maxima occur in the dissociation of many of the 

 organic acids. In some cases the maximum appears between 15 and 25; in others 

 between 25 and 35, while in still other cases it falls at a higher temperature, i. e., 

 around 50. This is apparently not in accord with the Thomson-Nernst hypothesis, 

 which connects the dissociating power of a solvent with its dielectric constant, and 

 the dielectric constant decreases with rise in temperature. 



The strong organic acids do not obey the Ostwald dilution law and, therefore, 

 "dissociation constants" could not be calculated for them by means of this law. 



Isomeric acids are not always dissociated to the same extent, and their dissocia- 

 tions change differently with rise in temperature. 



The migration velocities of mctameric ions are identical. The migration veloci- 

 ties of the anions of organic acids are a function of the number of atoms present in 

 the anions. This fact is utilized to find the values of u* for the dibasic organic acids. 



