Table 386. 

 THERMOELECTRIC POWER. 



317 



The thermoelectric power of a circuit of two metals is the electromotive force produced by one degree C difference 

 of temperature between the junctions. The thermoelectric power varies with the temperature, thus: thermoelectric 

 power = Q = dE/dt = A + Bt, where A is the thermoelectric power at 0° C, B is a constant, and / is the mean tem- 

 perature of the junctions. The neutral point is the temperature at which dE/dt = o, and its value is — A/B. When 

 a current is caused to flow in a circuit of two metals originally at a uniform temperature, heat is liberated at one of 

 the junctions and absorbed at the other. The rate of production or liberation of "heat at each junction, or Peltier effect, 

 is given in calories per second, by multiplying the current by the coefficient of the Peltier effect. This coefficient in 

 calories per coulomb = QT/J, in which Q is in volts per degree C, T is the absolute temperature of the junction, and 

 3f = 4.19. Heat is also liberated or absorbed in eacli of the metals as the current flows through portions of varying 

 temperature. The rate of production or liberation of heat in each metal, or the Thomson effect, is given in calories 

 per second by multiplying the current by the coefficient of the Thomson effect. This coefficient, in calories per coulomb 

 = BTd/y, in which B is in volts per degree C, T is the mean absolute temperature of the junctions, and is the differ- 

 ence of temperature of the junctions. (BT) is Sir W. Thomson's "Specific Heat of Electricity." The algebraic signs 

 are so chosen in the following table that when A is positive, the current flows in the metal considered from the hot 

 junction to the cold. When B is positive, Q increases (algebraically) with the temperature. The values oi A, B, and 

 thermoelectric power in the following table are wi/h respect to lead as the other metal of the thermoelectric circuit. 

 The thermoelectric power of a couple composed of two metals, i and 2, is given by subtracting the value for 2 from 

 that for i; when this difference is positive, the current flows from the hot junction to the cold in i. In the following 

 table, A is given in microvolts per degree, B in microvolts per degree per degree, and the neutral point in degrees. 



The table has been compiled from the results of Becquerel, Matthiessen and Tait; in reducing the results, the 

 electromotive force of the Grove and Daniell cells has been taken as i.gs and 1.07 volts. The value for constantan was 

 reduced from results given in Landolt-Bomstein's tables. The thermoelectric powers of antimony and bismuth alloys 

 are given by Becquerel in the reference given below. 



Substance. 



Aluminum 



Antimony, comm'l pressed wire 



axial 



" equatorial 



Argentan 



Arsenic 



Bismuth, comm'l pressed wire. . 

 " pure " " . . . 



" crystal, axial 



" " equatorial . . . . 



Cadmium 



" fused 



Calcium 



Cobalt 



Constantan 



Copper 



" commercial 



" galvanoplastic 



Gallium 



Gold 



Iron 



" pianoforte wire 



" commercial 



Lead. . ._ '. 



Magnesium 



Molybdenum 



Mercury 



Nickel 



" (-18° to its") 



" (2SO°-300°) 



" (above 340°) 



A 

 Microvolts. 



-o. 76 



+2.63 



+1-34 



+2.80 

 +I7-IS 



-f2.22 



-21.8 

 -83.57 

 —3.04 



B 



Microvolts. 



-fo.oo39 



—0.0506 



+0.0424 



+0.0094 



+0. 



OIOI 



0482 



.0000 

 .0094 



+0 



— o 



0506 



2384 



0506 



Thermoelectric power 



at mean temp, of 

 junctions (microvolts). 



20° C 



-0.68 



+6.0 



+ 22.6 



+ 26.4 



-12.9s 



-13.56 

 —97.0 

 -89.0 

 -65.0 

 -45.0 

 +3.48 



— 22 



+1.52 

 +0. 10 

 +3.8 

 — o. 2 

 +3.0 

 + 16.2 

 +17-5 



+ 2.03 



+5-9 

 -0.413 



So'C 



-0.56 



-14.47 

 -12.7 



+4.75 

 +2.45 

 +8.9 



-19-3 

 +1.81 



+3.30 

 + 14-74 



+ 12.10 



+9.10 



0.00 



+1-75 



-3.30 

 -15-50 

 -24-33 



Neutral 

 point 

 _ ^ 

 B 



+ 195 



— 236 



[-277] 

 +356 



+236 



[-431] 



Author- 

 ity. 



T 

 B 



S' 

 M 



T 

 M 



S 



T 



T 



M 



B 



T 



S 

 MB 



Smithsonian Tables. 



