286	Faraday's Researches
 961.	When the tube was arranged, as in fig. 72. with water
or dilute acid on one side only, and the wires were immersed
not more than one-third of an inch, the effects were greatly
diminished; and more especially if, by a little motion with a
platinum wire, the acids had been mixed at m} so that the transi-
tion from weak to strong was gradual instead of sudden.    In
such cases, even when the wires were moved, horizontally, in
the acid, the effect was so small as to be scarcely sensible, and
not likely to be confounded with the chemical effects to be
described hereafter.    Still more surely to avoid such inter-
ference, an acid moderately diluted was used instead of water.
The precaution was taken of emptying, washing, and rearrang-
ing the tubes with fresh acid after each experiment, lest any of
the metal dissolved in one experiment should interfere with the
results of the next.
 962.	I occasionally used the tube with dilute acid on one
side only, fig. 72, and sometimes that with dilute acid on both
sides, fig. 73.    I will call the first No. i, and the second No. 2.
 963.	In illustration of the general results I will describe a
particular case.    Employing tube No. i with strong and dilute
nitric acid,1 and two Copper wires, the wire in the dilute acid
was powerfully positive to the one in the strong acid at the
first moment, and continued so.    By using tube No. 2, the
galvanometer-needle could be held stiffly in either direction,
simply by simultaneously raising one wire and depressing the
other, so that the first should be in weak and the second in
strong acid; the former was always the positive piece of metal.
 964.	On repeating the experiments with the substitution of
platinum, gold, or even palladium for the copper, scarcely a
sensible effect was produced (961).
 965.	Strong  and dilute  nitric  acid.1—The  following  single
metals being compared with themselves in these acids, gave
most powerful results of the kind just described with copper
(963);   silver, iron, lead, tin, cadmium, zinc.    The metal in
the weaker acid was positive to that in the stronger.    Silver
is very changeable, and after some time the current is often
suddenly reversed, the  metal  in  the  strong acid becoming
positive:  this again will change back, the metal in the weaker
acid returning to its positive state.    With tin, cadmium, and
zinc, violent action in the acid quickly supervenes and mixes all
1 The dilute acid consisted of three volumes of strong nitric acid and two
volumes of water.