NOYES AND COOLIDGE. — ELECTRICAL CONDUCTIVITY. 215 



It will be seen that the differences in the case of sodium chloride are 

 in opposite directions at 140 and 218°; they are therefore doubtless in 

 large part, if not entirely, due to experimental errors ; aud therefore, 

 within the limits of these, the conductivity at infinite dilution is a linear 

 function of the temperature in the case of this salt. # With potassium 

 chloride the deviation at 140°, though probably real, since it falls upon 

 the smooth curve drawn through all the values, amounts to only 0.7 per 

 cent. At the higher temperatures the deviations are seen to be much 

 larger, though still of secondary magnitude. This approximate pro- 

 portionality between the increase of migration velocity and that of the 

 temperature has, up to 100°, already been observed by Schaller.f 



The values of the percentage temperature-coefficients referred to the 



value at 18° ( -r— ■? ] are 2.74 for potassium chloride (between 18 



\(A )i 8 A*y v 



and 218°) and 3.05 for sodium chloride. These are much higher than 



those observed on dilute solutions (0.01 — 0.001 normal), by Kohlrausch 



between 18 and 26° (2.21 aud 2.38), by Deguisne between 18 and 34° 



(2.28 and 2.40), by Arrhenius between 18 and 52° (2.33 and 2.53), 



and by Krannhals between 18 and 99.4° (2.40 and 2.62)$. This is due 



in part to the facts that the values of some of these investigators were 



not corrected for the expansion of the solutions upon heating and that 



they refer to solutions not infinitely dilute ; § but it also undoubtedly 



arises in part from the fact that the temperature function is not perfectly 



linear until temperatures considerably above 18° are reached. 



The ratio of the limiting conductivity of potassium chloride to that of 

 sodium chloride is 1.19 at 18°, 1.13 at 140°, 1.08 at 218°, 1.06 at 281°, 

 and 1.04 at 306°. The migration- velocities of the potassium and sodium 

 ions are therefore slowly approaching equality. 



The conductivity curves (see Figs. 10 and 11) at the higher concentra- 

 tions recede more and more from that for zero concentration as the 

 temperature rises, owing to a decreasing dissociation tendency (see 



* This is also clearly shown by the values of a calculated for the four suc- 

 cessive temperature-intervals 18 - 140, 140 -218, 218 - 281, and 281 - 306° ; these 

 are 3.30, 3.47, 3.21, and 3.75 (this last value being much in error because the inter- 

 val is small). 



t Ztschr. phys. Chem,, 25, 512, 523 (1898.) 



I These data are taken from Kohlrausch and Holborn's Leitvermiigender Elek- 

 trolyte, 197-199. 



§ Thus, the temperature-coefficient between 18° and 140° of our 0.01 normal 

 NaCl solutions is 2.90, while that at infinite dilution is 3.05. 



