MüNb and Üruckrr ') suggested the value 338 at 25°; and tlieh 

 Druckkr ') used the value 312 at 18° aiul 345 at 25°. Again, 

 Drucker "), Goodwin and Haskkll "), and Whetham ''), hj combining 

 their niolectilar conductivity measurements with the transference 

 ratios oblained by Jahn and his pupils, and Towek deduced the 

 mean value for hydrion equal to 313 at 18" or 346 at 25°. Kohl- 

 rausch ") again, and Jahn and his pupils '), declared the most 

 probable value of hydrion to be 315 at 18" or 348 at 25°. Gorke *) 

 obtained the value 353 at 25' from measurements of picric acid. 

 NoYKs and Kato ') came to the value 315 at 18° or 348 at 25° 

 from migration ratios of nitric and hydrochloric acids. Druckeb and 

 K1SN.IAIR '") again gave the \;ihie 313 at 18° or 346 at 25°. It 

 would be quite evident from these that the value for hydrion is 

 far from being correctly known. 



Now, by applying Kohi.rausch's formula for the temperature 

 coefficient of mobility we can get the values of ions at 0° from the 

 values given at 18 or 25°. But this empirical formula holds good 

 with rigidity in the neighbourhood of 18°; so results deduced at 

 are rather uncertain. Moreover Kohlrausch himself has changed 

 these values of temperature coefficients many times. For comparison, 

 are added below the tables (see p. 416) of temperature coefficients (n) 

 as published by Kohlrausch") in 1901, and 19(38. 



Thus extrapolation to 0° is rather uncertain. With a view to deter- 

 mine exactly the ionic velocities at 0°, this investigation was under- 

 taken. NoYE,s and Falk ") have given very accurate tables collected 

 from the work of numerous investigators for the transference numbers 

 of various substances at almost infinite dilution and at 0°. From the 

 molecular conductivity determination at 0°, the sum of the ionic 



velocities at is obtained (since (it 00 = u -{- v), and - is taken 



V 



from NoYEs and Falk's tables ; thus u and v are obtained. 



1) Zeit. Phys! Ghem. 1903, 46, 827. 



2) Zeit. Phys. Ghem. 1904, 49, 563. 



8) Zeit. Eleklrocliem. 1907, 13. 81. 



+) Proc. Amer. Acad. 1904, 40, 399. 

 5) Zeit. Phys. Ghem. 1906, 55, 200. 

 «) Zeit. Elelitrochem. 1907, 13, 333. 

 7) Zeit. Phys. Ghem. 1907, 58, 641. 

 ») Zeit. Pliys. Gliem. 1908, 61, 495. 



9) Zeit. Phys. Ghem. 1908, 62, 420. 

 1") Zeit. Phys. Ghem. 190S, 62, 731. 



") Sitzungsbcr. d. Beil. Akad. 1901, 102G; 1902, 572; Proc. Roy. Soc. 71, 338 

 (1903). Zeit. Elektrochem. 14 (1908\ 129. 

 1-) loc. cit. 



