PURE SUBSTANCES, FUSED SALTS, SOLID ELECTROLYTES 357 



tive ion. Among those substances which may be classed strictly as fused 

 salts are the glasses. A glass is to be considered as a supercooled liquid 

 which is mechanically rigid. Usually, glasses consist of mixtures of 

 silicates of the alkali metals and the metals of the alkaline earths. What 

 the nature of the compounds is in these systems is not known. Doubt- 

 less, the silica is present in the electronegative constituent. It is well 

 known that ordinary glasses are excellent conductors of the current at 

 high temperatures, the conductance increasing with the temperature. In 

 general, the conductance-temperature curve is exponential in form. 



In the following table are given values of the resistance of ordinary 

 soda-lime glass at different temperatures. 11 



TABLE CXL. 

 RESISTANCE OF ORDINARY SODA GLASS AT DIFFERENT TEMPERATURES. 



Temperature C.... 325 355 404 469 484 500 540 

 Resistance 9200 1900 687 172 133 89 2.4 



It will be observed that, even at temperatures as low as 325, glass con- 

 ducts the current with measurable facility, while in the neighborhood of 

 its softening point, 540, it conducts extremely well. To what the great 

 increase in the conductance of glass is due is uncertain. We shall see 

 below that the ionization of a glass varies only little as a function of the 

 temperature and consequently the increased conductance must be due 

 to the increased speed of the ions. The nature of the frictional resist- 

 ance which the ions meet in their motion through a glass is, however, 

 uncertain. At temperatures below 400, glasses of this type appear to 

 be entirely rigid and consequently the increased conductance is not 

 simply related to the mechanical rigidity of the glass. 



The conduction process in the case of the glasses is electrolytic in 

 character. 1111 If a current is passed through a glass tube from a sodium 

 nitrate anode to a mercury cathode, metal is transferred from the sodium 

 nitrate to the mercury through the glass in accordance with Faraday's 

 law and no change whatever takes place in the glass itself. This indi- 

 cates that the conduction process in such glasses is due to the motion 

 of the sodium ion and is not due to the motion of an electronegative ion. 

 This type of conduction is characteristic of many rigid electrolytic con- 

 ductors. Since positively charged carriers are present within the glass, 

 it is obvious that negative carriers must likewise be present. The nega- 

 tive carriers, however, must form a substantially rigid system, since they 

 take no part in the conduction process. It is also evident that, in the 



"Darby, Thesis, Clark University (1917). 



" LeBlanc and Kerschbaum, Ztschr. f. phys. Chem. 12, 468 (1910). 



