140 



Conductivity of Aqueous Solutions. Part V. 



It will be seen from the table that as in the case of the salts previously 

 investigated, the cube-root function of Kohlrausch expresses the results 

 almost perfectly at the three higher temperatures, but that at 18 the de- 

 viations reach 0.25 per cent. That of Barmwater is nearly, but not quite, 

 as satisfactory. On the other hand, the function of van't Hoff well rep- 

 resents the data at 18, but does so less and less perfectly the higher the 

 temperature, so that at 218 the deviations reach 0.7 per cent. 



We have also determined graphically, by plotting 1/A against (AC)" -1 

 (see section 17, Part II), what value of the exponent n in the function 

 C(A A) =K(CA) n best expresses the results at the different tem- 

 peratures both for hydrochloric acid and sodium acetate (unhydrolyzed 

 values). The results are given in table 39. 



Table 39. Values of the exponent n in the function 

 C(A A)=zK(CA)n 



The effect of temperature is mainly of interest when considered with 

 reference to the conductivity values extrapolated for zero concentration ; 

 for this effect then consists solely in a change in the migration velocity of 

 the ions, while at higher concentrations upon this the change in ionization 

 is superposed. To show the character of this effect, we have calculated 

 the mean absolute temperature-coefficient of the conductivity at zero con- 

 centration AA /A/ between 18 and 100, 100 and 156, and 156 and 

 218. These coefficients are given in the following table, together with the 

 value of the equivalent conductance at 18. The coefficients for sodium 

 acetate are based on the conductance values corrected for hydrolysis. 



Table 40. Mean temperature-coefficients of the 

 equivalent conductance at zero concentration. 



It is evident from the preceding table that the temperature-coefficient of 

 sodium acetate, like that of the other uni-univalent salts discussed in 

 Parts II and IV first increases rapidly,* attains a maximum, and then 



According to Arrhenius (Ztschr. phys. Chem., 4, 99, 1889) its absolute tempera- 

 ture-coefficient for the interval 18-52 is 2.08, thus much smaller than that from 

 18 to 100. 



