THE PROPERTIES OF METALLIC SUBSTANCES 



399 



and tin likewise exhibits singularities, which indicate the formation of 

 compounds. The temperature coefficients of these compounds are 

 negative. 



It may be concluded that liquid alloys, in which compounds are 

 formed, exhibit properties which differ markedly from those of alloys in 

 which compounds are not formed. When the compounds formed are 

 very stable, the conductance of the resulting alloy is usually less than 

 that of the pure components. The temperature coefficient of fused metal- 

 lic compounds is, as a rule, either very small or negative. 







Hg 



?0 2O JO 



6O 70 80 90 700 



B 



Weight Per Cent B 



FIG. 70. Conductance of Liquid Amalgams as a Function of Composition. 



6. Variable Conductors. Within this class are included those ele- 

 mentary substances which lie upon the border line between metallic and 

 nonmetallic elements. There are also included a considerable number 

 of metallic compounds in which one of the constituents is strongly electro- 

 negative. The elementary substances comprised within this class often 

 appear both in a metallic and in a nonmetallic state. Carbon is a typi- 

 cal example of this type which, in the form of diamond, is a noncon- 

 ductor, and, in the form of graphite, a relatively good conductor. Many 

 of the metallic compounds, also, may appear both in a conducting and in 

 a nonconducting state, as, for example, various sulphides and oxides 



