Thermo-electric Series.
The arrangement of possible 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.
Matthiessen 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 lesser, 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
Potassium 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.