Chapter XIII. 

 Pure Substances, Fused Salts, and Solid Electrolytes 



1. Substances Having a Low Conducting Power. In the preceding 

 chapters, the properties of solutions of electrolytes have been discussed. 

 We shall now consider, briefly, the properties of pure substances in the 

 liquid state. Nearly all substances in the fused condition exhibit a 

 measurable, though often small, conducting power for the electric cur- 

 rent. Even such substances which we ordinarily class as insulators con- 

 duct the current in some degree. What the nature of the conduction 

 process is in these substances has not been shown, but in all likelihood 

 the process is an ionic one; that is, the current is carried by particles of 

 atomic or molecular dimensions. A typical example of this class of con- 

 ductors, or perhaps more properly insulators, is found in the hydrocar- 

 bons. It has been shown that the conductance of substances of this type 

 is materially affected by the presence of small amounts of impurities. 

 The specific conductance of nearly all poorly conducting substances is 

 materially decreased by careful drying and fractionation. Evidently, 

 therefore, in part at least, the conductance of this class of substances is 

 due to the presence of other substances, as a result of which their con- 

 ductance is materially increased. We have, however, no knowledge of 

 the nature of the charged particles by means of which conduction is 

 effected. * 



In the case of petroleum ether and hexane, it has been found possible 

 to carry the process of purification so far that the effect of impurities is 

 almost entirely eliminated. It has been found that the residual con- 

 ductance in these solvents is chiefly due to the action of radiations from 

 surrounding bodies, as a result of which the solvent itself is ionized. 1 

 The conductance under these conditions was found to be altered by sur- 

 rounding the conductance vessel with screens which absorb the external 

 radiation. The conductance of pure hexane, therefore, is lower than that 

 due to the ions produced by the radiation from surrounding bodies and 

 it is possible that the conductance of this substance is in effect zero. 

 Under ordinary conditions, the conductance of the hydrocarbons is due 

 primarily to impurities. 



*Jaff6, Ann. d. Phys. 32, 148 (1910). 



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