PURE SUBSTANCES, FUSED SALTS, SOLID ELECTROLYTES 359 



While these values are not very precise, nevertheless, they clearly indi- 

 cate that about three- fourths of the sodium present in these glasses may 

 be electrolyzed out and replaced by another metal. The effective ioniza- 

 tion of the sodium in soda glass, therefore, is of the order of magnitude 

 of 75 per cent. This is apparently the only direct determination which 

 has thus far been made of the relative amount of a substance actually 

 concerned in the conduction process in an electrolyte. If so large a 

 proportion of the sodium in soda glass is actually concerned in the con- 

 duction process, it is reasonable to assume that the fused salts are very 

 nearly completely ionized. It is interesting to note that, as the tempera- 

 ture rises, the ionization of sodium in glass increases slightly. 



Since the penetration of the silver is determined solely by the rate 

 of motion of the ions and since the conduction is due entirely to the posi- 

 tive ion, it follows that the depth of penetration should be proportional 

 to the specific conductance or inversely proportional to the specific resist- 

 ance of the glass. This condition is in general fulfilled. 



From the preceding data it is possible to calculate the speed of the 

 sodium ion in glasses; that is, the speed with which this ion moves under 

 a potential gradient of one volt per centimeter. In the following table 

 are given values of the absolute speed of the sodium ion at different 

 temperatures. 



TABLE CXLIII. 



ABSOLUTE SPEED OF THE SODIUM ION IN SODA GLASS AT DIFFERENT 



TEMPERATURES. 



278 4.52 X 10- 8 



295 1.46 X 10- r 



323 3.26 X 10' 7 



343 5.9 X 10- 6 



It will be observed that, as might be expected, the absolute speed of the 

 sodium ion is relatively very low. On the other hand, corresponding to 

 the greatly increased conductance of glass with increasing temperature, 

 the speed of the sodium ion increases largely with temperature. 



4. Solid Electrolytes. Solid substances, both crystalline and amor- 

 phous, conduct the electric current with more or less facility. In the 

 case of the insulators, where the conductance is of an extremely low 

 order, it is not unlikely that conductance is due to the presence of traces 

 of impurities. The only substance for which this has actually been 

 shown is crystalline quartz, in which the conductance is due to the pres- 

 ence of traces of sodium as impurity. 12 Here the current is carried by 



Warburg and Tegetmeier, Ann. d. Phys. 35, 455 (1888). 



