CONDUCTION PROCESS IN ELECTROLYTES 21 



themselves, in his theory, he associated the charge with certain atomic 

 complexes, which complexes in fact do not exist. Present day concep- 

 tions regarding the constitution of chemical compounds do not differ in 

 many respects from those of Berzelius save that it is assumed that the 

 charge is associated with the atoms. In recent years, as a result of ex- 

 perimental methods which have enabled us to gain an insight into the 

 structure even of the atoms themselves, it is becoming more and more 

 apparent that, in their compounds, the elements exist not in an atomic, 

 but in an ionic, that is, in a charged, state. Under ordinary conditions 

 this state of the elements in a compound is not clearly evidenced, except 

 in the case of such compounds as are electrolytes when dissolved in 

 suitable solvents or when in a fused state. From the standpoint of chem- 

 istry, the study of the properties of electrolytes is therefore not so much 

 an end as a means. In other words, the study of the properties of 

 electrolytes constitutes a convenient method of acquiring knowledge 

 regarding the constitution of various chemical compounds. 



Faraday was not content to merely state the results of his observa- 

 tions and to combine these observations in the form of general laws. 

 He attempted to gain an insight into the mechanism of the processes 

 involved. It is often assumed that the ionic theory dates from the 

 time when Arrhenius co-ordinated the work of earlier investigators and 

 suggested a means for determining the relative amount of carriers present 

 in an electrolytic solution under given conditions. The ionic theory, 

 however, is much older than this. Its foundation was laid by Faraday, 11 

 who recognized that in an electrolyte the current is carried by positive 

 and negative electrical charges associated with definite material com- 

 plexes moving in opposite directions through the solution. The terms 

 which we now employ to describe the phenomena observed in the pas- 

 sage of the current through an electrolyte are due to Faraday, and in 

 themselves contain the concept of motion. The chief contribution of the 

 later ionic theory consisted in devising methods which made it possible 

 to determine the number of carriers present in an electrolytic solution. 

 Whether or not these methods, in fact, give us a true measure of the 

 number of ions present under various conditions in no wise affects the 

 correctness of the more general conceptions upon which the ionic theory 

 is based. 



2. Concentration Changes Accompanying the Current: Hittorf's 

 Numbers. The concentration changes in the neighborhood of the elec- 

 trodes were first investigated by Hittorf. 12 The fundamental conception 



"Faraday, "Experimental Researches," Vol. 1. 

 "Hittorf, Pogg. Ann. 89, 177 (1853). 



