THERMO-ELECTRIC QUALITY UNDER PRESSURE. 293 



were perfectly steady, and the permanent change of zero was almost 

 imperceptible. The maximum departure of any point from a smooth 

 curve was 0.4% of the total effect. It was very gratifying that this 

 soft substance showed no permanent zero change, since permanent 

 distortions must very easily be introduced into it. 



The numerical results are shown in Tables III and IV, and Figures 

 4 and 5. The e.m.f. is positive and increases regularly with pressure 

 and temperature; the Peltier heat between compressed and uncom- 

 pressed metal is also positive and increases with pressure and temper- 

 ature, and the Thomson heat increases with pressure, except at the 

 maximum temperature and pressure, but decreases regularly with 

 rising temperature. 



There are no previous measurements whatever on this substance 

 for comparison. 



Cadmium. This was a piece of new wire 0.02 inch diameter, from 

 the same original piece as the resistance wire. It was extruded at a 

 temperature of 180°, and seasoned after extrusion by several hours 

 at 120° in an electric oven. 



The thermo-electric behavior at atmospheric pressure against 

 lead may be represented by the formulas: 



E = (12.002 f ^- 0.1619/-) X lO"*^ volts, 



P = (12.002 + 0.3238 1) {t + 273) X lO"*^ volts, 



(7 = 0.3238(/ + 273) X 10"^ volts/°C. 



The pressure effect is not regular, and the readings were never 

 steady, indicating an incomplete state of internal equilibrium. The 

 material was seasoned by two preliminary applications of 12000 at 

 room temperature, and five runs were made, at 25°, 50°, 75°, 95° and 

 25° again. There was much hysteresis; this was larger at the higher 

 temperatures, and amounted at the maximum to 5% of the total 

 effect. The run at 25° was repeated in order to find whether the 

 hysteresis would disappear by accommodation after several runs at 

 different temperatures, but it did not change. The first run at 25° 

 almost exactly repeated itself, hysteresis and all. Wagner found 

 similar effects over so low a range as 300 kg.; he found an abnor- 

 mally long time required to reach equilibrium and a hysteresis which 

 never disappeared, no matter how long he waited. 



It will be recalled that Cd is one of the metals for which Cohen '' 

 claims different allotropic forms. The evidence of this paper corro- 



7 E. Cohen and W. D. Helderman, Proc. Amster. Acad. 17, 1050-1054, 1915. 



