solutions in another solvent than water. Only few investi- gations have been carried out with a view to ascertaining the relationships in this respect. Eablukoff {19) investigated solutions of hydrochloric acid in various media, and found that benzene and other hydrocarbons give the poorest con- ductors ; solvents in which the conduction is better are ethyl ether and higher alcohols; and in ethyl alcohol, methyl alcohol, and water the salts conduct best. This influence is, however, not solely dependent on the differences of the frictions against the various liquids, but depends far more on the degree of dissociation of the electrolyte in the solvent ; only after these two actions have been differentiated will it be possible to gain some exact knowledge about the influence of additions on the friction of the ions in solution. The same may be said of the conductivity of fused salts.
Many attempts have been made to directly measure the velocities of the ions, particularly by Lodge and Whetham. Lodge (20), for instance, filled a long glass tube, R (Fig. 37), with sodium chloride solution, which was deeply coloured with some cdkali and phenolphthalein. In order to avoid disturbances in the solution, agar-agar was added. This is a gelatinous substimce which acts like a fine network in the pores of which is the solution, like water in a sponge. The ends of the tube were immersed in sul- phuric acid solution, contained in the vessels S and 8\, A current from the battery B was sent in the direction from Sto Si through R, so that the hydrogen ions of the sulphuric add gradually passed along B, and caused decolorisation as they went. The results obtained for the velocity of migration of the ions in the tube B corresponded with those predicted by theory.
It must be noted that in these experiments it is not the true ionic mobility which is measured, but the product of ionic mobility and degree of dissociation, because the free
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