Thermo-electric Series

The arrangement of po ible thermoelectric elements, q. v., in a table in the order of their relative polarity. Bismuth and antimony form a couple in which when their junction is heated the bismuth acts as the positive or negatively charged element and antimony as the negative or positively charged. Between these two extremes according to Seebeck the series runs as follows: Antimony,   Silver, Copper,   Arsenic, Gold,        Platinum, Iron,       Molybdenum, Palladium, Steel, Tin,         Cobalt,   Cadmium, Lead,        Nickel,   Tungsten, Mercury,     Bismuth. Zinc,       Manganese, A differential temperature of 1° C. (1.8° F.) in a bismuth-antimony couple maintains a potential difference of 103 micro-volts. Matt hies sen gives a different series; it is arranged in two columns; the first column has positive coefficients annexed the second has negative. On subtracting the greater one from the le er, which, if the two elements are in different columns, of course amounts to adding after changing the negative sign, the relative potential difference due to the combination is obtained. + -   Bismuth 25      Gas Coke          0.1 Cobalt 9 Zinc 0.2   Pota ium 5.5 Cadmium           0.3 Nickel 5 Strontium         2.0 Sodium      3. Arsenic           3.8 Lead        1.03 Iron 5.2 Tin 1      Red Phosphorous   9.6 Copper 1 Antimony          9.8 Silver 1 Tellurium       179.9   Platinum 0.7 Selenium        290 Thus the relative E. M. F. of a bismuth-nickel couple, as both are in the + column, would be 25 - 5 = 20; that of a cobalt-iron couple, one being in the + column the other in the - column, would be 9 + 5.2 = 14.2. Alloys are not always intermediate to their constituents, and small amounts of impurities affect the results largely. This may account for the discrepancies of different observers. Other compounds could be introduced into the series. Artificial silver sulphide has been used by Becquerel in a thermo-electric battery. 535   STANDARD ELECTRICAL DICTIONARY.