THERMO-ELECTRIC QUALITY UNDER PRESSURE. 



315 



the purer material, and beyond the minimum the rise is much more 

 rapid, so that at 12000 kg. "tlie e.m.f. has become +0.2 X lO^^ This 

 change of sign was not found until 50° with the purer sample. In 

 general, the tendency towards positive values is much greater with 

 this specimen than with the purer material. At 75°, the e.m.f. is 

 1.7 X 10'^ at 12000 kg., against 1.0 X 10~« of the purer. One is 

 tempted to generalize and say that the effect of increasing impurity 



TABLE XV. 



Aluminum (Commercial). 



Thermo-electromotive Force, volts X 10". 



is to obliterate the peculiarities characteristic of aluminum itself and 

 make the beha\'ior approach that of a normal metal. 



The Peltier heat of the impurer metal is much like that of the purer, 

 but it passes through a greater range of values, from negative to 

 positive, and the curvature is not so uniform. The Thomson heat is 

 throughout positive, but much more, irregular. The range of values 

 is about the same as before, but there are maxima with respect to 



