THE PROPERTIES OF METALLIC SUBSTANCES 



391 



the present time it is not possible to reach any certain conclusion as to 

 the nature of these phenomena. 



The mean temperature coefficients a for a number of elementary sub- 

 stances are given in Table CLIII above. In the following table are 



1 dfy 

 given values of the temperature coefficient a = -=- for a number of 



tit Ut 



metals at different temperatures. 



TABLE CLVI. 



TEMPERATURE COEFFICIENT ^ -5 FOR METALS AT DIFFERENT 



R t tit 



Temperature Ag 



25 0.0030 



100 0.0036 



200 0.0039- 



300 0.0040 



400 0.0042 



500 0.0044 



600 0.0046 



700 0.0047 



800 0.0052 



900 0.0058- 



1000 



1075 . 



Mg 



0.0050 

 0.0045 

 0.0041 

 0.0043 

 0.0040 

 0.0036 

 0.0100 

 0.0250 

 at 625 



Cu 



0.0036 

 0.0038 

 0.0040 

 0.0041 

 0.0042 

 0.0043 

 0.0044 

 0.0047 

 0.0053 

 0.0057 

 0.0062 



It will be observed, from the table, that the temperature coefficient in- 

 creases with increasing temperature. The magnitude of the coefficients 

 of different metals differs considerably, particularly those of the magnetic 

 metals, iron and nickel. It is interesting to note that, as the transition 

 point of these metals is approached, the temperature coefficient increases 

 very largely. The temperatures at which the transition points are 

 reached are indicated in the table by heavy type. Beyond the transition 

 points, the temperature coefficients fall back to normal values, in the 

 case of both iron and nickel. A somewhat similar phenomenon is ob- 

 served in the neighborhood of the melting point, which is illustrated in 

 the case of aluminium and magnesium, particularly in the case of the 

 latter element. The temperature coefficient increases considerably as the 

 melting point is approached. Beyond the melting point, the coefficients 

 are, in general, smaller than below this temperature. 



The temperature coefficients of elementary liquid metals vary within 



