14 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



radiations, we have systems which are not in a state of equilibrium. 

 These systems will not be further considered here, since they have been 

 treated extensively in treatises dealing with the conduction of gaseous 

 systems. In what follows we shall treat only such systems as are nor- 

 mally in a conducting state. These may be divided into two classes; 

 namely, metallic and electrolytic conductors. 



3. Metallic Conductors. Metallic conductors are characterized by 

 the absence of material effects when a current passes through a system 

 comprising one or more conductors of this class alone. In this respect 

 metallic conductors are for the most part sharply differentiated from 

 electrolytic conductors, in which concentration changes or other material 

 effects accompany the passage of the current through any surface of 

 discontinuity. It does not follow, however, that metallic and electro- 

 lytic conduction are entirely unrelated and that the two processes of 

 conduction may not take place more or less simultaneously. Certain 

 substances apparently conduct electrolytically when in one condition and 

 metallically when in another. In other cases, a portion of the current 

 appears to be carried by a process similar to that in the metals and 

 another portion by a process similar to that in electrolytes. 



Metallic conductors are also characterized by the relatively high 

 value of their conducting power. While a few metals exhibit a value 

 of the conductance comparable with that of electrolytes, the conductance 

 of most metals is many times greater than that of electrolytes. If this 

 is true at ordinary temperatures, it is even more true at lower tempera- 

 tures where the resistance may ultimately fall off to practically zero. 

 The problem of metallic conduction is one possessing great interest and 

 one whose solution cannot but prove to be of great importance in the 

 development of chemistry and molecular physics. At the present time, 

 however, its solution appears far from complete. While metallic con- 

 ductors come within the scope of the present monograph, it is not in- 

 tended to treat this subject exhaustively. 



4. Electrolytic Conductors. Electrolytic conductors are character- 

 ized, in the first place, by the fact that the passage of the current through 

 them is accompanied by a transfer of matter. In a homogeneous elec- 

 trolytic conductor this transfer of matter within the body of the con- 

 ductor does not become apparent, but at any point of discontinuity 

 material effects make their appearance. The material effects accom- 

 panying the current are subject to certain definite laws commonly known 

 as Faraday's Laws. Conductors for which Faraday's Laws hold true 

 within the limits of the experimental error are termed electrolytic con- 

 ductors. We have here to consider two classes of electrolytic conductors: 



