428 Dr. Wollaston’s Experiments on 
equally, if the other wire consists of a metal on which the acid 
has no effect. 
Exper. 2. If zinc, iron, or copper, are employed with gold, in 
dilute nitric acid, nitrous gas is formed, in the same manner, 
and under the same circumstances, as the hydrogen gas in the 
former experiment. 
Exper. 3. Experiments analogous to the former, and equally 
simple, may also be made with many metallic solutions. If, 
for instance, the solution contains copper, it will be precipitated 
by a piece of iron, and appear on its surface. Upon silver merely 
immersed in the same solution, no such effect is produced ; but, 
as soon as the two metals are brought into contact, the silver 
receives a coating of copper. 
In the explanation of these experiments, it is necessary to 
advert to a point established by means of the electric pile. 
We know that when water is placed in a circuit of conduc- 
tors of electricity, between the two extremities of a pile, if the 
power is sufficient to oxidate one of the wires of communica- 
tion, the wire connected with the opposite extremity affords 
hydrogen gas. 
Since the extrication of hydrogen, in this instance, is seen to 
depend on electricity, it is probable that, in other instances, 
electricity may be also requisite for its conversion into gas. 
It would appear, therefore, that in the solution of a metal, 
electricity is evolved during the action of the acid upon it ; 
and that the formation of hydrogen gas, even in that case, 
depends on a transition of electricity between the fluid and the 
metal. 
We see, moreover, in the first experiment, that the zinc, 
without contact of any other metal, has the power of decom- 
