362 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



point, where a discontinuity occurs, a large increase taking place on 

 fusion. Silver iodide, however, forms an exception to this rule. This 

 substance exhibits a transition point at 144.6. Below this temperature 

 the conductance of silver iodide increases with temperature in a manner 

 similar to that of silver chloride and bromide. At the transition point, 

 the specific conductance increases from a value of 3.4 x 10~ 4 to 1.31. 

 Beyond the transition point, the conductance of silver iodide increases 

 slowly with the temperature, the temperature coefficient being not greatly 

 different from that of fused salts, as may be seen from the figure. It 

 will be observed, furthermore, that at the melting point the conductance 

 of solid silver iodide is markedly higher than that of the fused salt, the 

 conductance on melting decreasing from 2.64 to 2.36. Even at the tran- 

 sition point, at a temperature as low as 144.6, the specific conductance 

 of solid silver iodide is of the order of magnitude of that of fused salts. 

 This is a remarkable phenomenon and shows that the power of con- 

 ducting the current with facility is by no means restricted to the liquid 

 state. Thus far, however, silver iodide is the only solid salt whose con- 

 ductance in the solid state has been found to be comparable with that 

 in the liquid state far below its melting point. 



The conduction process in solid salts of this type is purely electrolytic, 

 as follows from the fact that Faraday's Law holds true within the limits 

 of experimental error. In the following table are given the observed 

 amounts of silver precipitated on electrolysis, together with the amounts 

 of silver precipitated in a silver coulometer carrying the same current. 14 



TABLE CXLV. 

 TEST OF FARADAY'S LAW IN SOLID ELECTROLYTES. 



Ag Ag 



Dissolved Precipitated 

 Electrolyte Temperature at Anode in Coulometer % Dif. 



Silver Iodide 540 0.7212 0.7139 + 1.20 



" " 540 0.5642 0.5623 +0.34 



150 0.7841 0.7804 +0.48 



150 0.7767 0.7706 +0.80 



Silver Bromide 400 0.5883 0.5842 + 0.70 



Silver Chloride 430 0.3779 0.3751 +0.75 



Considering the small amount of silver precipitated or dissolved and 

 the difficulty of carrying out the experiments, the agreement between 

 the observed and the calculated values of the amount of silver dissolved 



"Tubandt and Lorenz, loo. cit. 



