as the wire; it was then connected in turn with
the conductor of the machine, or with the voltaic apparatus (369.), so as
always to form the positive pole, and at the same time retain a
perpendicular position, that it might rest, with its whole weight, upon the
test paper to be employed. The test paper itself was supported upon a
platina spatula, connected either with the discharging train (292.), or
with the negative wire of the voltaic apparatus, and it consisted of four
thicknesses, moistened at all times to an equal degree in a standard
solution of hydriodate of potassa (316.).

374. When the platina wire was connected with the prime conductor of the
machine, and the spatula with the discharging train, ten turns of the
machine had such decomposing power as to produce a pale round spot of
iodine of the diameter of the wire; twenty turns made a much darker mark,
and thirty turns made a dark brown spot penetrating to the second thickness
of the paper. The difference in effect produced by two or three turns, more
or less, could be distinguished with facility.

375. The wire and spatula were then connected with the voltaic apparatus
(369.), the galvanometer being also included in the arrangement; and, a
stronger acid having been prepared, consisting of nitric acid and water,
the voltaic apparatus was immersed so far as to give a permanent deflection
of the needle to the 5-1/3 division (372.), the fourfold moistened paper
intervening as before[A]. Then by shifting the end of the wire from place
to place upon the test paper, the effect of the current for five, six,
seven, or any number of the beats of the watch (369.) was observed, and
compared with that of the machine. After alternating and repeating the
experiments of comparison many times, it was constantly found that this
standard current of voltaic electricity, continued for eight beats of the
watch, was equal, in chemical effect, to thirty turns of the machine;
twenty-eight revolutions of the machine were sensibly too few.

[A] Of course the heightened power of the voltaic battery was
necessary to compensate for the bad conductor now interposed.

376. Hence it results that both in _magnetic deflection_ (371.) and in
_chemical force_, the current of electricity of the standard voltaic
battery for eight beats of the watch was equal to that of the machine
evolved by thirty revolutions.

377. It also follows that for this case of electro-chemical decomposition,