Page:Text-book of Electrochemistry.djvu/156

in the law is also approximately true for the molecular conductivity at any given dilution, v, but only with each single group of electrolytes ; attention was also called to this point by Kohlrausch.

Transport Numbers and Ionic Mobilities.— As already mentioned, Hittorf had confirmed his own views on this subject in his famous experiments on the migration of the ions. The data found by him refer for the most part to concentrations at which the transport numbers vary with the dilution. The data contained in the following table, which may be regarded as the most exact known at the present time, have been taken from the comprehensive investigations of Jahn (9) and his pupils, and refer to very dilute solutions at 18°. The table gives under u_o (observed) the observed transport number of the cation, and under u_c (calculated) the value calculated from Kohlrausch's results for λ₃₀ and the Hittorf numbers —

Salt U_o (obaerved). Observer. U_c (calculated). |- |NaCl||0.396||Bogdan||0.399 |KCl||0.497||Template:Didto||0.497 |KBr||0.496|| Template:Didto|| |AgNO3||0.464||Metelka||0.478 | ||0.472||Mean value of various observers |CuSO4||0.375||Metelka||0.412 |BaCL2||0.447||Metelka„||0.412 |CdCl2||0.433||Metelka„||0.40 |CdI2||0.442||Metelka„||0.40

The influence of temperature on the transport number of some cations is shown by the following results obtained by Bein (10):—