GALVANISM. 
merits, that the galvanic phenomena are es- 
sentially promoted, by having two metallic 
surfaces so situated, that one shall be oxy- 
dated, and that the other shall be situated 
as near it as possible, for the purpose of re- 
ceiving its electricity. We have shewn, 
that the current is not only interrupted by 
distance, but that it is essential the passage 
should be a direct line. 
In Dr. Wollaston’s experiments, when 
the wires were placed in a metallic solution, 
such as that of copper and silver, and the 
contact formed between the zinc and silver 
wires, no hydrogen was evolved by the lat- 
ter, the contrary of which was the case 
with the dilute acid ; but the metal in solu- 
tion became reduced upon the silver. 
There does not appear any thing myste- 
rious in the reduction of the metal, since 
the hydrogen does not appear, being em- 
ployed in the deoxydation of the metal. 
A further proof that this is the case, is, that 
no other metals can be reduced in this way, 
but such as do not decompose water. This 
singular process enables us to account for 
several facts which have hitherto appeared 
anomalous. If a glass plate be smeared 
over with a solution of nitrate of silver, and 
a common pin be laid in the middle of the 
plate, beautiful ramiiications of metallic sil- 
ver will soon appear, as if vegetating from 
the pin. If the process be examined by a 
magnifying glass, the ramifications of silver 
may be fairly seen to grow from their ends. 
Though the more oxydable metal, the 
pin, may, in the first instance, have reduced 
a portion of silver, it does not account for 
the vegetative appearance which is after- 
wards observed. The pin cannot reduce 
the silver at so great a distance from itself, 
which is sometimes more than an inch. In 
order to prove, that the agency of the oxy- 
dable metal was not essential to the reduc- 
tion of the metal, the writer of this article 
covered one half of the plate with liquid ni- 
trate of silver, and the other half with di- 
lute muriatic acid, suffering the liquids to 
touch each other ; a wive of zinc was laid 
in the dilute acid, and one of platina in the 
nitrate of silver. As soon as the opposite 
ends of the wires were brought in con- 
tact, beautiful ramifications of silver soon 
began to appear from the platina wire, but 
no gas was observed. 
If a solution of gold be used, instead of 
that of silver, the platina becomes speedily 
gilt. The experiment producing what is 
called the lead- tree, cannot be accounted 
for in any other way : it consists in filling a 
bottle with a solution of acetate of lead, in 
the upper part of which is suspended a 
piece of metallic zinc : in the course of a 
day or two, metallic lead is observed in 
shining filaments, suspended from the piece 
of zinc. The same difficulty occurs in this, 
as in the last experiment : the filaments of 
lead constantly grow from the ends at a dis- 
tance of many inches from the zinc. In 
order to prove that this experiment is simi- 
lar to the last, that is, that the lead is re- 
duced by the hydrogen, take a tube, A B, 
fig. 3, at one end of which, tie a piece ot 
bladder so tight that the tube may hold wa- 
ter; let a cork be inserted at A, through 
which the platina wire, P p, is passed ; the 
tube being set up right in the zinc, cup, D, 
containing dilute muriatic acid, and a con- 
nection formed at P, the platina soon be- 
comes covered with brilliant crystals ot me- 
tallic lead ; hence it would appear, that the 
platina had the power of reducing the lead 
into its metallic state, or that some sub- 
stance had been transmitted through the 
biailder adequate to that effect. If, instead 
of the acetate of lead, the tube be filled 
with dilute acid, upon the connection be- 
ing formed at P, the platina becomes co- 
vered with bubbles of hydrogen: need we, 
therefore, hesitate in concluding, that the 
lead owes its reduction to the hydrogen. 
The method of whitening brass and cop- 
per, by boiling them with cream of tartar 
and tin, is a process of this kind ; the cream 
of tartar, and the metallic, tin, answering 
the purpose of the zinc and acetate of lead, 
in the last experiment: a portion of the tin 
in solution is reduced upon the copper or 
brass, rendering it white, by the hydrogen 
which is produced during the galvanic con- 
tact of the copper or brass, with the tin. 
In all the experiments, the zinc wire is, 
during its contact with that of the platina, 
silver, &e. undergoing an increased oxyda- 
tion, which is proportionate to the quantity 
of hydrogen evolved at the platina wire ; 
since the oxygen of that, and hydrogen, both 
of which are derived from the water, are dis- 
posed of in the oxydation of the zinc. The 
hydrogen passes from the zinc to the oppo- 
site wire, with the greatest facility, through 
a direct liquid communication, the shorter 
the better. It becomes much interrupted 
by having to turn sharp angles, or in passing 
through small apertures. It passes with 
more or less freedom through solid bodies, 
when moistened with water, but does not 
pass at all, except when moisture is pre- 
sent. 
