THE PROPERTIES OF METALLIC SUBSTANCES 397 



specific conductance of this compound at 25 is 0.0912, as compared with 

 8.65 for tin and 22.73 for magnesium. 



While the conductance of inter-metallic compounds is thus, in gen- 

 eral, very low, the temperature coefficient of these compounds is of the 

 same order of magnitude as that of pure metals. While, therefore, the 

 addition of a second metallic component increases the resistance of the 

 metallic alloy, whether a compound or a solid solution is formed, so that 

 it is at times difficult to distinguish between these two cases by this 

 means, the temperature coefficient of the resulting alloy will, in general, 

 differ widely in the two cases. The high value of the temperature coeffi- 

 cient of metallic compounds and the low value of this coefficient for 

 homogeneous alloys afford a delicate method of detecting the presence 

 of solid solutions in metallic alloys. 



d. Liquid Alloys. The properties of liquid alloys differ greatly from 

 those of homogeneous solid alloys. On the addition of a second com- 

 ponent, the conductance of a liquid metal may either increase or de- 

 crease. The relative conductance of the two substances does not deter- 

 mine the magnitude and sign of the initial conductance change. If the 

 specific conductance of two metals is nearly the same, the conductance 

 curves often exhibit maxima or minima and sometimes both maxima and 

 minima. In Figure 70 are shown the conductance curves for mixtures 

 of mercury with bismuth, lead, tin and cadmium. Small additions of 

 these elements to mercury cause a relatively large initial rise of the 

 conductance curve. This rise is particularly noteworthy in the case of 

 bismuth, which itself is a relatively poor conductor. The four curves are 

 evidently similar. With bismuth and lead, whose specific conductances 

 are relatively low, both a maximum and a minimum occur in the con- 

 ductance curve. With tin the maximum and minimum have disappeared, 

 but an inflection point is present in the conductance curve. The curve 

 for alloys of cadmium and mercury exhibits a constant curvature. The 

 four elements, the conductance of whose amalgams are shown in the 

 figure, do not form compounds with mercury according to their melting 

 point diagrams. 



The behavior of amalgams, in which compounds are formed, differs 

 markedly from that of amalgams in which compounds are absent. The 

 addition of small amounts of lithium, calcium and strontium increases 

 the conductance of mercury, while that of potassium, sodium, caesium 

 and barium reduces its conductance. 14 With increasing temperature, the 

 relative effect of such addition is increased. According to Hine, 15 the 



14 H. Fenninger, Dissertation, Freiberg, 1914 ; J. Koenigsberger, loc. cit. t p. 654. 

 Hine, J. Am. Chem. Soc. 39, 890 (1917). 



