392 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



wide limits. The coefficients are greatest for the alkali metals, in which 

 case they differ very little from those of the solids. In other cases, the 

 temperature coefficients reach extremely small values, as, for example, 

 in that of zinc. As a rule, the temperature coefficients of liquid metals 

 have values in the neighborhood of one fifth that of the solid metals. In 

 the following table are given the mean temperature coefficients of a 

 number of liquid metals referred to their resistance at the lowest tem- 

 perature given. 



TABLE CLVII. 

 TEMPERATURE COEFFICIENT OF LIQUID METALS. 



Temperature 

 Metal a Interval 



Sodium 38.5 X 10" 4 M.P. 



Potassium 41.8 X 10~ 4 " 



Lithium 27.3 X 10' 4 178-230 



Tin 5.9 X 10' 4 M.P.-350 



Bismuth 4.1 X 10' 4 



Thallium 3.5 X 10~ 4 



Cadmium 1.3 X 10- 4 



Lead 5.2 X 10~ 4 



Copper 4.12 X 10' 4 1084-1500 



Aluminium 5.42 X HH 653-1250 



Iron 3.66 X10- 4 1055-1650 



Nickel 1.67 X 1Q- 4 1451-1650 



Zinc 0.3 XIO' 4 419-500 



Tin 4.68 X 10' 4 232-1600 



Cadmium 2.26 X 10~ 4 500-650 



Antimony 1.37 X 10" 4 631-800 



The temperature coefficients here given cannot be directly compared 

 with those of the solid metals at ordinary temperatures, since the coeffi- 

 cients are referred to the resistance of these metals at higher tempera- 

 tures. In a number of instances values have been extrapolated to ordi- 

 nary temperatures, in which case the coefficients are invariably smaller 

 than those of solid metals. For example, the values for copper, 

 aluminium and iron are 7.45 X 10~ 4 , 8.40 X 10' 4 and 8.15 X 10' 4 , re- 

 spectively. 



The temperature coefficient as commonly measured is the resultant 

 effect of temperature change and volume change. The temperature coef- 

 ficient at constant volume differs materially from that at constant pres- 

 sure, depending upon the influence of pressure upon the resistance of the 

 conductor in question. In solid metals, the pressure effect is relatively 



