442 ELECT 
the thighs of the frog, which are held by the third and 
fourth perfons, will be violently convulfed.” 
Aldini and Humboldt have both obferved, that, if the 
legs of a prepared frog be immerfed in mercury, and the 
nerves be brought in contact with the external furface of 
that fluid, the convulfion will take place every time the 
circuit is formed. From this experiment thefe phyflolo- 
gifts have .deduced, that diflimilar metals are no ways 
neeeflary. The celebrated Volta properly obferves that,, 
although one metal is tints apparently employed, the 
different dates in which the mercury is found, conftitute 
what.may be confidered as two diflimilar metals. As 
mercury, the inltant it is expofed to the air, becomes 
oxydated, a part of the animal being in contact with the 
fluid in its metallic (late, and the fciatic nerve being 
equally fo with the oxydated furface, convulfions will 
neceffarily enfue. From all the experiments hitherto 
brought forward, in which convulfions have been pro¬ 
duced by the influence of diflimilar metals, it would ap¬ 
pear that the difengaged electricity is from the oxydated 
Jurface of the metal ; and that the mufcular fibres of the 
frog are, in confequencc of their exquifite fenfibility, con¬ 
vulfed by the trammiffibn of the electricity from the non- 
oxydated plate to the oxydated plate. 
ft has been already obferved, that a fimple galvanic 
combination may either confift of two diflimilar metals, 
and an interpofed fluid, or of a Angle metal placed be¬ 
tween two different fluids, one of which aCls on the me¬ 
tal without its being influenced by the other. Let A B, 
fig. 27, in the fame engraving, represent two glaffes, one 
Tilled with a diluted folution of nitrous acid, and tha 
other with water. It thefe two veflels be connefted by 
a,copper arc, ab y a fimple galvanic combination will be 
formed. The part of the copper in the diluted folution 
of nitrous acid will be oxydated, while the portion in 
the veil'd of water will not be aCted on. If one of the 
extremities of a prepared frog, as at F, be placed in one 
of the liquids, as foon as the other extremity is brought 
in contact with the liquid in the other veflel, convulfions 
will enfue. This effeCt is more ffrongly produced in the 
experirnent-repi efented at fig. 28, in which B D is a glafs 
di!h filled with a folution of the fulpluire of pot-a(h ; and 
A, a filver cup, or a falt-cellar, placed withinfide, and 
neatly filled with a weak folution of nitric acid. By this 
arrangement a pcrfcEl galvanic combination is produced ; 
as foon as a prepared frog is made to form a communica¬ 
tion between one of the fluids and the other, it will be 
convulfed. 
Upon the principles of fimple galvanic combinations, 
many curious phenomena are explicable. Formerly, in 
applying copper (heets to the bottoms of (hips, it being 
the ufage to employ iron bolts, it was obferved that the 
copper foon became loofened in the part where the two 
metals were in contaft. This arrangement conftituted a 
fimple galvanic combination of two diflimilar metals, and 
an interpofed fluid. In this cafe the interpofed fluid was 
the fea-water, or a folution of the muriat of foda, and the 
metallic fubffances, the iron and copper. In a fimilar 
arrangement, the iron, the moff oxydable metal, in be¬ 
coming oxydated in the part more immediately in contaft 
with the copper, is foon deffroyed, and detached from 
the latter fubftance. In 1795, Creve firft (hewed that, 
in every fimple galvanic combination, water is decom- 
pofed. The oxygen, in thefe combinations, enters into 
union with the metal; and the hydrogen is evolved. 
The difcoloration of a filver fpoon, in the aft of eating 
eggs, is a curious galvanic operation. Mr. Carlifle, by 
a very ingenious analyfis, has proved the exiffence of 
fulphur, both in the yolk and in the albumen of an egg. 
A tea-fpoon left immerfed in either of thefe fubffances, 
undergoes no difcoloration ; but the above remarkable 
phenomenon takes place in the aft. of eating the egg; 
the bowl of the fpoon which is mod in the mouth, being 
always found to be difcoloured. In this cafe the galva¬ 
nic combination confifts of the fulphurated folution, the 
LICIT Y. 
filver tea-fpoon, and the faliva. In every galvanic ope¬ 
ration Creve has (hewn that water is decojupofed. The 
nafeent hydrogen, readily uniting with the fulphur, forms 
fulphurated hydrogen gas, which produces the difcolora¬ 
tion. It is this gas, evolved from our coals in the aft of 
combuftion, which occafions a fimilar tarnilh to the filver 
employed for domeftic purpofes. 
Mr. Davy, chemical profeffor at the royal inllitution 
of London, obferves, that charcoal pofieffes a fimilar pro¬ 
perty with metals, of forming a galvanic combination 
with two diflimilar fluids. Suppofing, according to him, 
A and B, fig. 29, to reprefent two glades, one filled with 
nitric acid, and the other with water: if a communica¬ 
tion be formed, by means of an angular piece of charcoal 
CD, a galvanic combination will be produced. Charcoal 
is an excellent conduftor of electricity, and ranks next to 
metallic fubffances. It has been aliened, that it was firft 
employed by Fontana as a conduftor of galvanifm ; but 
the earlieff experiment was made by Volta. 
Humboldt having noticed that the Lydian (tone is a 
conduftor, fufpefted it to poffefs that properly in confe- 
quence of a certain portion of carbon it contains. On 
burning it with cauftic pot-a(h, in an open veflel, the 
pot-alh became mild, and effervefeed with acids. A proof 
was thus obtained of its having acquired carbonic acid. 
From this obfervation we may perceive how delicate a 
teft galvanifm is, in detefting carbon in a fubftance in 
which the prefence of that principle was not even fuf¬ 
pefted. So great, at the fame time, is the fenfibility of 
galvanifm to good condufting media of this defcription, 
that it evinces inffantaneonfly the exiffence of the final left 
portion of carbon. All fubffances which have this prin¬ 
ciple diifufed through them, become galvanic conduftors. 
Some perfons have fuppofed galvanifm to differ from 
eleftricity, becaufe the • condufting powers of charcoal 
have been found to be greater for the former than for the 
latter principle. This is, however, far from being the 
cafe. Charcoal preferves the fame rank in the order of 
conduftors, both for eleftricity and for galvanifm. That 
it is found fuperior to metals, in the deflagration of the 
latter fubffances by galvanic precedes, does not depend 
upon its condufting power, but upon its aiding principle 
of combuftion. 
Volta has obferved, that various parts of animals can 
be excited without the aid of metals ; and feveral inge¬ 
nious methods have been propofed by Galvani for this 
purpofe. In the opufculi of Milan, an account is given 
of Aldini’s experiments, made in the prefence of the in- 
ftitute of Bologna, in 1794. A prepared frog having been 
immerfed in a flrong folution of tiie muriat of foda, and 
removed from thence, the learned profeffbr held one of 
the extremities in his hand, and allowed the other to 
hang freely down. While the animal was in this petition, 
he raifed up the nerves with a glafs rod, on fiiddenly re¬ 
moving which, as often as the nerves touched the muf- 
cular parts, convulfions were produced. 
Animal fubffances, as conduftors of eleftricity, have 
their capacities proportioned to their condufting powers. 
No change can be induced in thefe fubffances, without an 
adequate change in their capacities. Both the mufcular 
fibre, and the nervous fubftance, in their healthy living 
Ifate, and connefted with the fources by which their ener¬ 
gies are preserved, are, with refpeft to eleftricity, in a 
precife balance with each other. When a portion of ani¬ 
mal fubftance is detached and feparated, changes are in¬ 
duced, and decompofitions effefted. In cold-blooded ani¬ 
mals, the procefs being very flow, the mufcular fibres 
remain for a long time fufceptible to So pervading a fti- 
mulus as eleftricity. When the fubftance is immerfed in 
a folution of the muriat of foda, the nervous and 'mufcu¬ 
lar parts feem not to undergo equal changes. The part 
which is the moft rapidly afted on, will leave the other 
in a negative date of eleftricity; and, on the communica¬ 
tion being formed, convulfions will be produced. If the 
communication be made through the medium of a warm¬ 
blooded 
