THE DEVELOPMENT OF ELECTRICAL SCIENCE. 233 



Hittorf's analyses enabled him to give numerical values to these 

 relative velocities. The experiments of JSTernst, Loeb, and others have 

 extended Hittorf's results, and have 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 conduc- 

 tivity of electrolytes should give valuable information in reference to 

 the nature of electrolytic action. A great deal of work has been done 

 in this direction by Horsfordj Wiedemann, Beetz, the Kohlrauschs, and 

 others. The most notable, perhaps, was the work of P. Kohlrausch, 

 who devised a method of measurement using alternating current, by 

 which results of high accuracy were obtained. Kohlrausch'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 abso 

 lute velocity can be obtained. It appears from these results that the 

 velocity of the ion in very dilute solutions depends only on its own 

 nature and not upon the nature of the other ions with which it may be 

 associated. For example, the velocity of the chlorine ion is the same 

 when determined from solutions of KC1, NaCl, or HC1. The impor- 

 tant general law has also been found that the conductivities of neu- 

 tral salts are additively made up of two values, one dependent on the 

 positive, the other upon the negative ion. If, then, the velocities of the 

 ions themselves be known, the conductivity of a salt may be calculated. 

 Tue results of Kohlrausch received strong confirmation from some very 

 ingenious experiments by Lodge and Whetham, in which the migration 

 of the ions was made to produce a change of color in the solution, and 

 could thus be directly observed. 



In 1887 the theory was advanced by Arrhenius and Ostwald that 

 dissociation is directly effected by solution or fusion and that in very 

 dilute solutions the dissociation is practically complete. Arrhenius 

 holds that the ions carry charges of electricity, positive or negative, 

 dependent upon their nature, but of equal quantity in every ion. The 

 remaining part of the theory is similar to that of Clausius and others. 

 According to this theory the ratio of electric conductivities for different 

 densities of solution gives a measure of the relative dissociation or 

 ionization. If the act of solution effects the dissociation necessary to 

 admit of electrolysis, chemically pure substances ought not to be decom- 

 posed by the electric current, and this is found to be the case. It is 

 curious that two substances like hydrochloric acid and water, which 

 separately are insulators, should, when mixed, conduct readily, and 

 that practically only one of them should be decomposed. This, how- 

 ever, is only one of the many problems still to be solved. Another 

 question is how do the ions obtain their electric charge? Still another, 

 what is the nature of the force which causes ionization? There are 

 many more. 



When we turn to the commercial application of electro-chemistry we 



