803 
2. The simplest combinations capable of 
producing galvanic effects, (viz. to convulse 
the prepared limbs of a frog, or to excite 
the taste upon the tongue, &c.) must consist 
of three different conductors; for two con- 
ductors only will not produce any sensible 
effect.. If the three conductors are all of the 
first class, or all of the second, then the effect 
is seldom sensible. In this case such con- 
ductors of the second class as differ more 
from each other, are more likely to produce 
a sensible effect than those of the first class. 
Tut a proper active simple combination must 
consist of three different bodies; viz. of one 
conductor of one class, and tsvo different 
conductors of the other- class. Thus (de- 
noting the bodies of the first class by means 
of large capital letters, and those of the se- 
cond class by small letters) the combinations 
of fig. 5 and 6, are active ; but those of fig. 7, 
8, 9, 10, and 1 1, are not active ; because that 
of tig. 7, 8, or 9, consists of two bodies only, 
and that of fig. 10, or 1 1, consists of three 
bodies, of which two are of the same sort, 
and of course act as a single body. 
When .two of the three bodies are of the 
first class, and one is of the second, the com- 
bination is said to be of the first order ; other- 
wise it is said to be of the second order. 
In a single active galvanic combination, 
or, as it is commonly called, in a simple 
galvanic circle, the two bodies of one class 
must touch each other in one or more points, 
at the same time that they are connected to- 
gether at other points by the body of the 
other class. Thus, when a prepared frog is 
convulsed by the contact of the same piece 
of metal in two different places ; then the 
fluids of those parts, which must be some- 
what different from each other, are the two 
conductors of the second class, and the me- 
tal is the third body, or the conductor of 
the first class, If two metals are used, then 
the fluids of the prepared animal, differing 
but little from each other, may be considered 
as one body of the second class. Thus also, 
when a person drinks ont of a pewter mug, 
the saliva or moisture of his under lip is one 
fluid or one conductor of the second class, 
the liquor in the mug is the othexy and the 
metal is the third body, or conductor of tire 
first class. 
3. It seems to be indispensably requisite, 
that in a simple galvanic circle, the con- 
ductor or conductors of one class should have 
some chemical action upon the other con- 
ductor or conductors ; without which cir- 
cumstance the combination of three bodies 
will have either no galvanic action at all, or 
a very slight one. Farther, the galvanic 
action seems to be proportionate to the de- 
gree of chemical agency ; which seems to 
shew that such chemical action is the pri- 
mary cause of the electric phenomena. 
T he most active galvanic circles of the 
first order, are when two solids of different 
degrees of oxidability are combined with a 
fluid capable of oxidating at least one of the 
solids. Thus gold, silver, and water, do 
not form an active galvanic circle ; but the 
circle will become active if a little nitric 
acid, or any fluid decomposable by silver, is 
mixed with the water. 
A combination of zinc, silver, and water, 
forms an active galvanic circle ; and the 
water is found to oxidate the zinc, provided 
the water holds some atmospherical air, as it 
GALVANISM, 
commonly does, and especially if it contains 
oxygen gas. But zinc, silver, and water 
containing a little nitric acid, form a more 
powerful galvanic circle, the fluid being ca- 
pable of acting both upon the zinc and upon 
the silver. 
The most powerful galvanic combinations 
of the second order, are when two conduct- 
ors of the second class have different che- 
mical actions on the conductors of the first 
class, at tlxe same time that they have an 
action upon each other. Thus copper, or 
silver, or lead, with a solution of an alkaline 
sulphuret, and diluted nitrous acid, forms a 
very active galvanic circle. 
The present state of knowledge relative 
to this subject, does not enable us accurately 
to determine the particular powers of all 
sorts of galvanic combinations; the follow- 
ing lists, however, contain an useful arrange- 
ment of the best combinations, disposed in 
the order of their powers, and commencing 
with the most powerful. 
Table of galvanic circles of the first order, 
viz. which consist of two conductors of 
the first class, and one of the second. 
Zinc, with gold, or charcoal, or silver, or 
copper, or tin, or iron, or mercury ; and 
water containing a small quantity of any of 
the mineral acids. 
Iron, with gold, or charcoal, or silver, or 
copper, or tin, and a weak solution of any 
of the mineral acids, as above. 
Tin, with gold, or silver, or charcoal, and 
a weak solution of any of the mineral acids, 
as above. 
Lead, with gold, or silver, and a weak acid 
solution, as above. 
Any of the above metallic combinations, 
and common water, viz. water containing at- 
mospheric air, or especially water contain- 
ing oxygen air. 
Copper, with gold, or silver, and a so- 
lution of nitrate of silver and mercury ; or 
the nitric acid ; or tlxe acetous acid. 
Silver, with gold, and the nitric acid. 
Table of galvanic circles of tiie second order, 
viz. which consist of one conductor of the 
fii'st class, and two of the second. 
with water, or and a solu- 
Charcoal, or with a solution tion of ni- 
Copper, or of any hydro- trous acid. 
Silver, or genated alka- or oxygenat- 
Lead, or line sulphur- ed muriatic 
Tin, or ets, capable of acid, &c. ca- 
Iron, or acting on the pable of act- 
Zinc, first three nxe- ing upon all 
tals only ; the metals. 
Tlxe action of a simple galvanic circle 
seems to be in sonxe measure dependant 
upon the quantity of surface of contact be- 
tween the acting bodies. A higher tem- 
perature, within certain limits, renders the 
activity of the circle greater than a lower 
temperature. 
The activity of a galvanic circle is not al- 
tered by the interposition of such conductors 
as have no action upon the adjoining con- 
ductors of tlxe circle. Thus, if a circle con- 
sists of zinc, gold, and water ; and if you in- 
terpose a piece of iron, or of silver, or both, 
between the zinc and the gold ; the activity 
of the circle will not be altered. Ilence it 
appears that the action of a galvanic circle 
may be conveyed through extraneous con- 
ductors to a considerable distance ; but it 
S 1 ' 2 
must be observed, that the activity is weak- 
ened by tlxe great length of the conductors, 
especially if they are of an imperfect nature. 
4. When the three bodies which foi'm a 
galvanic circle of tlxe first order are laid one 
upon the other, hut the lower and the up- 
per one do not touch eaclx other ; then 
these two extremes are in opposite electric 
states, viz. the extremity which is next to 
that metallic surface that touches the body 
of the second class, is positive, and the op- 
posite extremity is negative. Thus let cop- 
per, zinc, and moistened leather, be laid one 
upon the other, as in fig. 12, 'and (he upper 
end W, viz. the wetted leather, will be found 
possessed of positive electricity ; whilst the 
lower end C, or the copper, will be found 
negative. 
5. The galvanic effects may be increased 
to almost any degree, by connecting several 
of the above-mentioned active combinations, 
or by a repetition of the same simple galva- 
nic combination (the most active simple com- 
binations forming tlxe xxxost powerful bat- 
teries, axxd vice versa) provided the simple 
combinations are disposed so as not to couix- 
teract each other. 
Those batteries are said to be of the first 
or of the second order, according as the 
simple combinations, of which they consist, 
are of the first or of the second order. Thus, 
if a piece of zinc is laid upon a piece of cop- 
per, and a piece of moistened card upon 
the zinc ; then a similar arrangement of 
three other such pieces laid upon them, and 
a third arrangement upon this, &c, all in 
the same order ; the whole will form a bat- 
tery of the lirst order. But if the arrange- 
ment is lxxade by connecting a piece of cop- 
per with a piece of cloth xnoistened with wa- 
ter; the latter with a piece of cloth moist- 
ened with a solution of sulphuret of potass, 
and this again with another piece of copper, 
&c. the whole will form a battery of the se- 
cond order. 
Mr. Davy distinguishes the batteries of 
the second order into the following three 
classes : 
1. The most feeble is composed, whenever 
, single metallic plates, or arcs, are arranged 
in such a manner, that two of their surfaces, 
or ends opposite to each other, are in con- 
tact with different -fluids, one capable and 
j the other incapable of oxidating the metal. 
And regular series of such combinations are 
formed. 
2. When the single combinations or ele- 
ments of the series consist each of a single 
! plate or arc of a metallic substance capable 
| of acting upon sulphurated hydrogen, or 
upon sulphuret dissolved in water, accompa- 
nied with portions of a solution of sulphurets 
of potass on one side, and water on the other. 
3. The most powerful class is formed when 
metallic substances oxidable in acids, and 
capable of acting on solutions, of sulphurets, 
I ai'e connected, as plates, with oxidating 
fluids and solutions of sulphuret of potass, in 
such a manner that the opposite sides of 
every plate may be undergoing different che- 
mical changes, the mode of alternation 
being regular. 
T he above-mentioned restriction, viz. that 
the parts of a battery must not counteract 
I each other, will be easily understood by 
1 considering that every simple, but interrupt- 
] ed galvanic combination, Ixas a positive axxd 
