Faraday's Researches

had been set free at p, that when the drop was stirred the
whole became colourless.

51. A drop of solution of iodide of potassium mingled with
starch was put into the same position at p and n; on turning
the machine, iodine was evolved at p, but not at n.

52. A still further improvement in this form of apparatus
consists in wetting a piece of filtering paper in the solution to
be experimented on, and placing that under the points p and n,
on the glass: the paper retains the substance evolved at the
point of evolution, by its whiteness renders any change of
colour visible, and allows of the point of contact between it and
the decomposing wires being contracted to the utmost degree.
A piece of paper moistened in the solution of iodide of potas-
sium and starch, or of the iodide alone, with certain precautions
(58), is a most admirable test of electro-chemical action; and
when thus placed and acted upon by the electric current, will
show iodine evolved at p by only half a turn of the machine.
With these adjustments and the use of iodide of potassium
on paper, chemical action is sometimes a more delicate test
of electrical currents than the galvanometer (9). Such cases
occur when the bodies traversed by the current are bad con-
ductors, or when the quantity of electricity evolved or trans-
mitted in a given time is very small.

53. A piece of litmus paper moistened in solution of common
salt or sulphate of soda was quickly reddened at p. A similar
piece moistened in muriatic acid was very soon bleached at p.
No effects of a similar kind took place at n.

54. A piece of turmeric paper moistened in solution of sul-
phate of soda was reddened at n by two or three turns of the
machine, and in twenty or thirty turns plenty of alkali was
there evolved. On turning the paper round, so that the spot
came under p, and then working the machine, the alkali soon
disappeared, the place became yellow, and a brown alkaline
spot appeared in the new part under n.

55. On combining a piece of litmus with a piece of turmeric
paper, wetting both with solution of sulphate of soda, and
putting the paper on the glass, so that p was,on the litmus and
n on the turmeric, a very few turns of the machine sufficed to
show the evolution of acid at the former and alkali at the latter,
exactly in the manner effected by a volta-electric current.

56. All these decompositions took place equally well, whether
the electricity passed from the machine to the foil a, through
water, or through wire only; by contact with the conductor/transmitted through water ord