56 CONDUCTIVITIES AND DISSOCIATIONS 



The results of the conductivity measurements are tabulated in the 

 following pages. The molecular conductivities (/!) are expressed in 

 Siemens units. Temperature coefficients are expressed in both conduc- 

 tivity units and percentages. The former are obtained by the equation 



(Hn At,) / (1 conductivity units ; 

 the latter by the equation 



Gufi M/) /W^i~0 = per cent temperature coefficient 1 



where t= the lower temperature, t\ the next higher temperature, ju, 

 and fri the conductivities of the same solution measured at tempera- 

 tures t and ti, respectively. 



Obviously the percentage dissociation may be expressed as 



a=^ B /M 



The dissociation constants are obtained from Ostwald's dilution law 



a 2 /(l-a)V = K 



This is found to hold for the weaker organic acids. In the tables 

 where no values are given for XX10 4 , the acids were so strong that 

 they did not obey the law. 



The following acids were tested, but were found to be either too 

 slightly soluble to work with, or to undergo decomposition : 



Nitrocinnamic acid (insoluble). 



/3-Naphtholdisulphonic acid (insoluble). 



Terephthalic acid (insoluble). 



Aminosalicylic acid (insoluble). 



Aminophenolsulphonic acid (decomposed). 



p- and o-nitro- and dinitro-phenols were studied, but the conductivi- 

 ties found were so small that the results were not reliable, since the per- 

 centage error due to unavoidable experimental errors was relatively large. 



In table 18 omitted values have been determined by other investi- 

 gators, especially those whose values are given at only the higher 

 temperatures. 



It has been shown by the work of Ostwald, Jones, and others in 

 this field, that the Ostwald dilution law does not hold for strongly 

 dissociated acids. The "constants" of acids of this class have been 

 omitted. In the tables that were secured in the experimental work, 

 irregular constants are frequently given. These are of value only in 

 determining the relative strengths of such acids. 



It had been previously observed that as a rule the percentage dis- 

 sociations of the organic acids decreased with rise in temperature, but 

 that the values of percentage dissociation of certain acids increased with 

 rise in temperature. In this work, however, it was found that in each 

 case the increase has been at a diminishing rate, and further study 

 showed that the maximum dissociation was reached in all cases except 

 citric acid. 



!Zeit. phys. Chem., 2, 561 (1888). 



