Chapter XIV. 



Systems Intermediate Between Metallic and Electrolytic 



Conductors. 



1. Distinctive Properties of Metallic and Electrolytic Conductors. 

 Substances which possess the power of conducting the electric current 

 are, in the main, sharply divided into two classes; namely, metallic 

 and electrolytic conductors. The members of each of these two classes 

 of conducting substances have many properties in common with one 

 another, which properties serve to distinguish the members of one class 

 from those of the other. It is in their optical and electrical properties 

 that the members of the two classes exhibit the greatest contrast. While 

 electrolytic systems, in general, are transparent, metallic systems are 

 non-transparent and exhibit metallic reflection. Electrolytic systems 

 conduct the current with the accompaniment of material effects, while 

 metallic systems conduct the current without attendant material effects 

 of any kind. Nevertheless, the view has been gradually gaining ground 

 that the conduction process in the two systems is similar in that conduc- 

 tion is effected by the motion of charged particles. While we possess a 

 more or less comprehensive theory of the mechanism whereby the transfer 

 of the charge is affected in electrolytic systems., a similar theory does 

 not exist for metallic systems. Such knowledge as we do possess regard- 

 ing the existence of charged particles in metals is founded chiefly on 

 observations on the properties of metals other than those relating imme- 

 diately to the conduction process. There exists little direct evidence 

 showing that the passage of the current through the metals is effected 

 by the motion of charged particles. 



The great difficulty in the way of a direct attack on the problem of 

 metallic conduction lies in the absence of material effects accompanying 

 the passage of the current. In addition, there has been a complete lack 

 of systems exhibiting properties intermediate between those of metallic 

 and electrolytic conductors. Conducting systems fall sharply into 

 one of two classes; namely, metallic and electrolytic conductors. In 

 recent years, however, a class of solutions has been subjected to investi- 

 gation which appears to bridge the gap between metallic and electrolytic 

 conductors; in other words, which exhibits properties, on the one hand, in 



366 



