al and liquid
couple, the metal has not been previously rendered electro-polar by
contact with a different one, and is therefore in a somewhat different
state. When a voltaic combination, in which the positive metal is
thermo-negative, and the negative one is thermo-positive, is heated,
the electric potential of the couple diminishes, notwithstanding that
the internal resistance is decreased.

Magnesium in particular, also zinc and cadmium, were greatly depressed
in electromotive force in electrolytes by elevation of temperature.
Reversals of position of two metals of a voltaic couple in the tension
series by rise of temperature were chiefly due to one of the two
metals increasing in electromotive force faster than the other, and in
many cases to one metal increasing and the other decreasing in
electromotive force, but only in a few cases was it a result of
simultaneous but unequal diminution of potential of the two metals.
With eighteen different voltaic couples, by rise of temperature from
60 deg. to 160 deg. F., the electromotive force in twelve cases was increased,
and in six decreased, and the average proportions of increase for the
eighteen instances was 0.10 volt for the 100 deg. F. of elevation.

A great difference in chemical composition of the liquid was attended
by a considerable change in the order of the volta-tension series, and
the differences of such order in two similar liquids, such as
solutions of hydric chloride and potassic chloride, were much greater
than those produced in either of those liquids by a difference of 100 deg.
F. of temperature. Difference of strength of solution, like difference
of composition or of temperature, altered the order of such series
with nearly every liquid; and the amount of such alteration by an
increase of four or five times in the strength of the liquid was
rather less than that caused by a difference of 100 deg. F. of
temperature. While also a variation of strength of liquid caused only
a moderate amount of change of order in the volta-tension series, it
produced more than three times that amount of change in the
thermo-electric tension series. The usual effect of increasing the
strength of the liquid upon the volta-electromotive force was to
considerably increase it, but its effect upon the thermo-electro-motive
force was to largely decrease it. The degree of potential of a metal
and liquid thermo-couple was not always exactly the same at the same
temperature duri