ELECTRICAL RESISTANCE UNDER PRESSURE. 



81 



Ti 



1 



2 3 



4 5 6 7 8 9 



Pressure, Kg. /Cm.' X 10' 

 Sodium 



Figure 4. Relative resistances of sodium at constant temperature as a 

 function of pressure. 



of Bernini, and appreciably higher than that of Northrup. Doubt- 

 less the freedom from constraint of the bare wire is in large part 

 responsible. As the solid sodium expands in the glass container it 

 will exert a pressure on the walls, which will have the effect of decreas- 

 ing the resistance, and making the temperature coefficient appear too 



low. 



For the temperature coefficient of the liquid, Bernini ^ found 

 between 100° and 1 10° 0.00279 of the resistance &t 100°. Northrup's ^ 

 mean value between 100° and 140° is 0.00330 of the resistance at 100°. 

 My mean value between 100° and 120° is 0.00325, slightly lower than 

 the value of Northrup. It is not yet established whether the purer 

 liquid metal usually has a higher temperature coefficient than the 

 impurer or not. 



