THERMO-ELECTRIC QUALITY UNDER PRESSURE. 



325 



The niinuTical results are shown in Tables XX and XXI and 

 Figures 21 and 22. At constant temperature the e.m.f. curves are 

 nearly linear, but are slightly concave toward the pressure axis, as 

 is natural. At constant pressure the e.m.f. curves are convex toward 

 the temperature axis. The thermal e.m.f. is positive, rises regularly 

 with pressure and temperature to 3.546 X 10"^ volts at 100° and 12000 

 kg. The Peltier heat is positive and rises with pressure and tempera- 

 ture. The Thomson heat is zero at the lower pressures, becomes 



TABLE XX. 



Copper. 



Thermo-electromotive Force, volts X 10^. 



positive at the higher, and at each constant pressure passes through 

 a minimum with rising temperature. 



The value found by Wagner between 0° and 100° at 300 kg. was 

 -\- 3.2 X lO""^^ volts per degi'ee per kg. against 2.9 X lO"'^^ indicated 

 by interpolation of the data above. 



Copper is one of the metals for which Cohen^^ finds allotropic 

 forms. No evidence of this has been found by Burgess and Kell- 

 berg,-^^ however, from measurements of electrical resistance, and my 

 thermal e.m.f. measurements above also suggest nothing of the kind. 



11 E. Cohen and W. D. Helderman, ZS. phys. Chem. 89, 638-639, 1915. 



12 G. K. Burgess and I. N. Kellberg, Jour. Wash. Acad. Sci. 5, 657-662, 

 1915. 



