Section 96. Change of Conductance with Temperature. 265 



The change of the A -values with the temperature deserves considera- 

 tion only in the cases of nitric acid, phosphoric acid, hydrochloric acid 

 and barium hydroxide; for only for these substances were they directly 

 derived. Table 112 contains the ratios of these A - values to those pre- 

 viously given for potassium chloride and for some other substances. 



Table 112. Ratio of the A u -values to those for 

 potassium chloride and other substances. 



The ratio HC1 :KC1 at 306 was found to be 1.27; its value at lower 

 temperatures was found by Noyes and Cooper to be as follows : 2.91 at 

 18, 2.05 at 100, 1.73 at 156, and 1.53 at 218. It will be observed 

 that the ratio of the values for hydrochloric and nitric acids is not far 

 from unity at all temperatures, showing that the chloride and nitrate 

 ions always move at nearly the same rate. The values of the other ratios 

 show that the velocities of the hydrogen and hydroxide ions approach 

 those of each other and of the neutral-salt ions as the temperature rises. 



Table 113 contains the values of the mean temperature-coefficients of 

 the conductance at zero concentration (AA /A) for the substances 

 included in this investigation. It will be seen that all these values steadily 

 decrease, showing that the conductance-temperature curve is concave 

 toward the temperature axis and that it has no points of inflexion, as is 

 the case with neutral salts. 



Table 113. Mean temperature-coefficients of the conductance 

 at zero concentration. 



With reference to the effect of temperature on the conductance values 

 at the higher concentrations, attention may be called to the fact that 

 maximum values are reached in the cases of all the acids investigated, 

 namely, near 75 with 0.1 molal and near 128 with 0.002 molal phos- 

 phoric acid, between 15G and 218 with 0.08 normal nitric acid, and 



