Circles with Sulphuret of Potassium 259

theory meet, include, combine, and even predict, the numerous
experimental results! When there is a current there is also
chemical action; when the action ceases, the current stops (870,
873, 882); the action is determined either at the anode or the
cathode, according to circumstances (1027, 1029), and the
direction of the current is invariably associated with the direc-
tion in which the active chemical forces oblige the anions and
cations to move in the circle (697, 1040).

864. Now when in conjunction with these circumstances it
is considered, that the many arrangements without chemical
action (813, etc.) produce no current; that those with chemical
action almost always produce a current; that hundreds occur in
which chemical action without contact produces a current
(1005, etc.); and that as many with contact but without
chemical action (855) are known and are inactive; how can
we resist the conclusion, that the powers of the voltaic battery
originate in the exertion of chemical force?

^f iii. Active Circles excited by Solution of Sulphuret of
Potassium

865. In 1812 Davy gave an experiment to show, that of two
different metals, copper and iron, that having the strongest
attraction for oxygen was positive in oxidising solutions, and
that having the strongest attraction for sulphur was positive in
sulphuretting solutions.1 In 1827 De la Rive quoted several
such inversions of the states of two metals, produced by using
different solutions, and reasoned from them, that the mere
contact of the metals could not be the cause of their respective
states, but that the chemical action of the liquid produced
these states.2

866. In a former paper I quoted Sir Humphry Davy's ex-
periment (678), and gave its result as a proof that the contact
of the iron and copper could not originate the current pro-
duced; since when a dilute acid was used in place of the sul-
phuret, the current was reverse in direction, and yet the contact
of the metals remained the same. M. Marianini3 adds, that
copper will produce the same effect with tin, lead, and even
zinc; and also that silver will produce the same results as
copper. In the case of copper he accounts for the effect by

1 Elements of Chemical Philosophy, p. 148.

*Annales de Chimie, 1828, xxxvii. 231-237; xxxix. 299.

3 Memorie della Societd, Italiana in Modena, 1837, xxi. p. 224. suit the real results, these