I 4 2 



Conductivity of Aqueous Solutions. Part V. 



The discussion, given in section 55, of the change of conductivity of 

 hydrochloric acid with the concentration is substantially also a discussion 

 of the change of ionization ; for the three functions there considered, pro- 

 vided each be assumed to hold down to zero concentration and therefore 

 to give the true value of A , may be written in the forms : 



1 y = KC i ; l y = K(C y y and C(l y) = K(Cy)i 



The conductivity functions corresponding to the first two of these have 

 been shown to express the results fairly satisfactorily in all cases; but 

 this is not true, especially at the higher temperatures, of the function cor- 

 responding to the last of these expressions. It was in fact shown that 

 the exponent in the expression corresponding to the general exponential 

 function C(i y) = K(Cy) n has both for hydrochloric acid and sodium 

 acetate values differing from 1.5 and varying somewhat with the tempera- 

 ture (see table 39). 



The question of the applicability of the mass-action law to the results 

 with acetic acid at the higher temperatures is of considerable interest. 

 The values of its ionization-constant (multiplied by 10 6 ) calculated from 

 the data of table 41 by the equation K = Cy 2 /(1 y) are given in table 

 42, the concentration used in the calculation and given in the table being 

 expressed in equivalents (not milli-equivalents) per liter. 



Table 42. I onisation-constants (10 6 /C) for acetic acid. 



It is evident from these results that the mass-action law holds true, at 

 least approximately, for this acid at 218, just as it does at 18. The 

 values given in the last rows those for the more concentrated solutions 

 are doubtless the best values of the constant. 



It will be seen from table 41 that the ionization of all these substances 

 decreases steadily with rising temperature. In 0.1 normal solution the 

 decrease between 18 and 218 is nearly the same (9 to 11 per cent) for 

 the first three substances, and consequently their relative degrees of ioniza- 

 tion are not much different at the higher and lower temperatures. The 

 decrease in the case of acetic acid is very great, the ionization at 218 being 

 only about one-third of that at 18 ; moreover, the decrease is especially 

 rapid above 100. Correspondingly, its ionization-constant (given in table 

 42) has decreased at 100 to about 0.6 and at 218 to about 0.1 of its value 

 at 18. 



