53 
indication of the idea of the purely directive character of the applied 
electro-motive force, taking advantage of dissociation to produce chemical 
separation. 
The energy side of the problem now began to attract attention and the 
development of what may be called the thermo-dynamics of electro- 
chemistry began. Among the most prominent workers in the field have 
been Joule, Helmholtz, Gibbs, Kelvin, Bosscha and Faure. In 1853 Hit- 
torf made quantitative determinations of the change of concentration 
near the electrodes when a current is passed through a solution. His work 
is of historical interest because his work and conclusions formed prac- 
tically the starting point for what may be called the modern view of 
electrolysis. Hittorf’s experiments extended over several years and served 
practically to establish the theory of the migration of the ions in the solu- 
tion. Hittorf communicated the following laws: 
“The change in concentration due to current is determined by the mo- 
tion which the ions have in the unchanged solution. 
“The unlike ious must have different velocities to produce such change 
of concentration. 
“The numbers which express ionic velocities mean the relative distance 
through which the ions move between the salt molecules, or express their 
relative velocities in reference to the solution, the change in concentration 
being a function of the relative ionic velocities.” 
Hittorf’s analyses enabled him to give numerical values to these rela- 
tive velocities. The experiments of Nernst, Loeb and others have ex- 
tended Hittorf’s results and haye shown that in dilute solutions the 
relative velocities of the ions are independent of the difference of poten- 
tial between the electrodes and are only slightly, if at all, influenced by 
temperature. Hittorf pointed out that a knowledge of the conductivity of 
electrolytes should give valuable information in reference to the nature 
‘of electrolytic action. A great deal of work has been done in this direc- 
tion by Horsford, Weidemann, Beez, the Kohlrausches and others. The 
most notable, perhaps, was the work of P. Kohlrausch, who devised a 
method of measurement, using alternating currents, by which results of 
high accuracy were obtained. WKohlrausch’s results give the sum of the 
ionic velocities, and thus combined with the results of Hittorf on change 
of concentration, which gave the ratios, the absolute velocities can be ob- 
tained. It appears from these results that the velocity of the ions in very 
dilute solutions depends only on its own nature and not upon the nature of 
