396 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



Other alloys of this type exhibit a similar behavior at low temperatures. 



At high temperatures, the resistance curves of many of the alloys of 

 this type are very -complex, often exhibiting both maxima and minima 

 and the temperature coefficient at times becoming negative. 13 * The curve 

 for manganin wire, for example, exhibits two maxima at approximately 

 25 and 475 C. and two minima at 360 and 525 C. respectively. In a 

 few instances, the temperature coefficient is very nearly zero over a large 

 range of temperature, as, for example, in the case of advance wire, for 

 which the temperature coefficient varies very little up to a temperature of 

 250 C. Taken all together, the resistance curves of solid solutions of 

 metals are very complex at higher temperatures. 



c. Solid Metallic Compounds. The conductance of a solid compound 

 of two elements is always lower than that of one of the constituents and 

 is often lower than that of both. The specific resistance of a compound 

 relative to that of the constituent elements depends upon the nature of 

 the elements and upon tne nature of the compound formed. In general, 

 the more stable the compound, the higher is its resistance relative to 

 that of the constituent elements. Compounds between strongly electro- 

 positive and strongly electronegative metallic elements, as a rule, exhibit 

 a very high specific resistance. In the following table are given values 

 of the specific conductance of a number of compounds at room tem- 

 peratures. 



TABLE CLIX. 

 SPECIFIC CONDUCTANCE OF A NUMBER OF METALLIC COMPOUNDS. 



It will be observed, from the table, that the compound between mag- 

 nesium and tin has a very low specific conductance. Where two ele- 

 ments form a number of different compounds, that compound, in gen- 

 eral, has the lowest specific conductance which corresponds to the normal 

 electronegative valence of the less metallic element. Thus, the specific 

 conductance of Cu 4 Sn is much lower than that of Cu 3 Sn or of CuSn. 

 The low value of the specific conductance is well shown in the case of the 

 alloys of magnesium and tin which form the compound Mg 2 Sn. The 



Somerville, Phys. Rev. 31, 261 (1910). 



