PURE SUBSTANCES, FUSED SALTS, SOLID ELECTROLYTES 365 



In the following table are given values of the specific conductance of 

 lithium hydride at different temperatures. 



TABLE CXLVII. 



SPECIFIC CONDUCTANCE OF LITHIUM HYDRIDE AT DIFFERENT 

 TEMPERATURES. 



t p t |i 



443 2.124 X10- 5 661.5 2.018 X 1Q- 2 



507 2.113 X10- 4 685 3.206 X 10~ 2 



556 8.447 X 10" 4 725 7.59S X 10" 2 



570 1.491 X 10- 3 734 1.125 X 10' 1 



597 3.225X10- 3 754 1.01 



638 1.139 X 10- 2 



The values of the specific conductance may be represented by means 

 of a sum of terms in ascending powers of the temperature. It is interest- 

 ing to note that the same equation applies both above and below the 

 melting point of lithium hydride, which is 680. Apparently, therefore, 

 there is no discontinuity in the conductance of this hydride at its melt- 

 ting point. This behavior is exceptional. 



This salt exhibits polarization when a direct current is passed through 

 it, and it has been shown that, on the passage of the current, lithium is 

 deposited at the cathode and hydrogen evolved at the anode. The cur- 

 rent is therefore conducted by either one or both of the ions Li + and H~. 

 This salt, therefore, presents a very interesting case, not only in that the 

 conductance of the solid is the same as that of the liquid at its melting 

 point, but, also, in that hydrogen appears here as a negative ion. This 

 is the only case so far. observed in which hydrogen has been shown to 

 function in this manner. 



The behavior of hydrogen in lithium hydride is thus very similar to 

 that of certain metallic elements in their compounds with the alkali 

 metals in liquid ammonia, referred to in a preceding chapter. We saw 

 there that, for example, in a solution containing lead and sodium, lead 

 is dissolved at the cathode and precipitated at the anode. In the pres- 

 ence of very electropositive elements, less electropositive elements tend to 

 take up negative electrons and function as anions. This dual function 

 of many elements, which ordinarily act as cations, is very significant 

 from the standpoint of the constitution of many compounds in which 

 these elements are involved. 



