146 BRIDGMAN. 



resistance and pressure means a pressure coefficient becoming less 

 at the higher pressures. This is what one might at first expect, but 

 this is the first time that we have found it in a substance with positive 

 coefficient. Since the pressure coefficient is independent of tempera- 

 ture, the temperature coefficient is independent of pressure over the 

 range of the measurements. 



Relative Behavior of the Sa7ne Metal in the Solid and the Liquid States. 

 This is a matter of considerable importance as suggesting the relative 

 parts played in the mechanism of conduction by the crystalline struc- 

 ture and the properties of the atoms as such. It will in the first place 

 pay to recall the fact already well known that the direction in which 

 the resistance changes when a metal melts is also the direction in 

 which the volume changes. If the metal expands on melting, as is 

 normal, the specific resistance increases on melting, and if the metal 

 expands on freezing, the resistance of the liquid is less than that of the 

 solid. This rule is without exception. Gallium and bismuth are the 

 only two metals known at present in the second class; the data for 

 antimony do not as yet seem well established. In the present work 

 I was able to add lithium to the list of substances which obey this rule. 

 This is of interest, because solid lithium is abnormal. 



With regard to the magnitude of the change of resistance on melt- , 

 ing there have been a number of theoretical proposals. The inaccu- 

 racy of the experimental results has allowed considerable latitude here. 

 Thus theoretical considerations have been based on the assumption 

 that the ratio of the resistance of the solid to that of the liquid is 

 approximately an integer. ^^ There is perhaps a tendency for the 

 values to cluster about the figure 2, but it is now certain that within 

 the limits of error the ratio is not integral. Attempts have been 

 made to connect quantitatively the volumes of solid and liquid with 

 the resistance, as would be suggested by the above general rule. Thus 

 Professor Hall ^* has suggested that if the resistance of the solid is 

 extrapolated to such a temperature that the volume expansion is 

 sufficient to bring the volume of the solid up to the volume of the 

 liquid at the melting temperature, the resistance of the solid will be 

 found to be the same as that of the liquid. Of course any such long- 

 range extrapolation must always be open to question, and it is prob- 

 able that the numerical agreement found is no more significant than 

 the general rule relating to volume already mentioned. 



The above measurements under pressure bring out a fact that could 

 not have been known before, namely that the ratio of the resistance 

 of solid to liquid is approximately a constant characteristic of the 



