150 



BRIDGMAN. 



Theoretical Bearings. 



Since the purpose of this paper is primarily the presentation of 

 new data, I cannot more than touch on two matters of theoretical 

 interest suggested by considerations of the previous papers. 



It has been known for some time that the temperature coefficient 

 at constant volume of liquid mercury is negative instead of positive, 

 as is the coefficient at constant pressure. In my previous theoretical 

 paper ^^ I suggested reasons for this. It is now of interest to find 

 whether the other liciuid metals have the same property. 



The coefficient of resistance at constant volume is given by the 

 relation 



Hence in addition to the pressure and temperature coefficients of 

 resistance, which have been determined in the present work, values of 

 the thermal expansion and compressibility are also needed. These 

 have not been determined experimentally for any of the metals above, 

 but in some cases an intlirect estimate may be made with the help of 

 various data from the melting curve. I have previously given an 

 estimate of the dift'erence of compressibility and thermal expansion 

 between solid and licjuid sodium, potassium, and bismuth. ^^ With 

 these data, the temperature coefficients at constant \'olume may be 

 computed, as is shown in Table XXI. The fundamental data are 



TABLE XXI. 



The Temperature Coefficient at Constant Volume of Liquid Metals at their 



Melting Points. 



