THERMO-ELECTRIC QUALITY UNDER PRESSURE. 



371 



seasoned by baking at 140° for several hours, and by several applica- 

 tions of 12000 at room temperature. After this seasoning there was 

 no appreciable change of resistance after a run under pressure. At 

 0° and 25° the pressure coefficient of resistance is practically the same; 

 as it is also at 50°, 75° and 100°, but between 25° and 50° there was 

 an increase of coefficient of 0.7%. However, the measurements 

 were not as good as they might be, and the isolated change between 

 25° and 50° is probably not real. 



The e.m.f. measurements under pressure were made in the regular 



40° 50° 60° 

 Temperature 

 Manganin 



Figure 44. Manganin. Thermal E.M.F. of a couple composed of one 

 branch of uncompressed metal, the other compressed to the pressure in kg./cm.^ 

 indicated on the curves, the junctions being at 0°C and the temperature 

 plotted as abscissae. 



way. The effect is small and negative. The wire was seasoned for 

 the e.m.f. measurements by baking to 140° at atmospheric pressure, 

 and by one application of 12000 kg. at room temperature. The 

 measurements at the lower temperatures were regular, but at the 

 higher temperatures the irregularities increase very rapidly. This is 

 as one would expect in an alloy. The greatest discrepancy was shown 

 by the final zero point at 97° which lies off a smooth curve by 18% of 

 the maximum effect at 97°; at this temperature the average arith- 

 metic departure is 7.7%; at 75° the maximum departure is at 8000 



