98 GALVAWNISM 
Theory. . stated by Volta: (Nicholson’s Journ. Svo. ii. 281.) In 
—— the experiments of Bennet and Cavallo, where electri+_ 
city was induced upon metallic bodies by contact, it is. 
to be observed, that they were no longer in contact 
“when they manifested signs of electricity, and it ap- 
pears not easy to conceive how two metals can be in 
We shall quote the account which Dr Henty gives of: 
this hypothesis, as it appears to afford a correct, and: 
at the same time a concise view of it. wc 
“« To the efficiency of the pile, two circumstances are Henry’s 
essential ; that the electric fluid should be disengaged, count of 
and that it be confined and carried forward in i 
PLATE 
Chemical 
hypothesis. 
Cuthbert. 
son’s opi- 
nion. 
extensive contact, without communicating their elee- 
tricity to each other, so as to acquire precisely the same 
state. The experiments of De Luc, on the dissection 
of the pile, seem to be strongly adverse to the electric: 
hypothesis. In the second distribution of the ternary 
groups, the two metals are in contact, and therefore 
any electrical effect might be produced, which would 
arise from this circumstance; there was also the fluid 
between them, which would serve as a conductor of 
electricity, yet because the apparatus was so arranged 
that this fluid could not act upon the zine and oxidate 
it, no proper galvanic effect ensued. 
As we have already remarked, Dr Wollaston was the 
first who decidedly pronounced the chemical action of 
the pile to be the primary cause of its effects; but in 
establishing this point, he did not proceed to explain the 
nature of the operation, or show what was the train of 
events which contributed to the final result. This was 
attempted by Mr Cuthbertson, who, in the essay to 
which we referred above, after pointing out the inac- 
curacy of the experiments that were brought forward 
by Volta in favour of ‘the electric hypothesis, offers 
‘some observations in support of the contrary opinion. 
He conceives that the chemical action of the interposed 
fluid upon the zine, alters the electric properties of the 
metal, and disposes it to part with electricity ; that this 
evolved electricity cannot enter into the remainder of 
the zine which has not been acted upon, because it re~ 
trated form, than before. 
rection, so as to be cencentrated at the end of the/ap+ ccLXIt 
paratus. The first object is fulfilled by the oxidizes Fig. 21. 
: 3 
ment of the zine; the second, as Dr Bostock supposes, 
is effected by the union of the evolved electricity with 
nascent hydrogen, and by the attraction of the next 
copperplate for electricity. At the surface of this platey 
the hydrogen and electricity are to separate ; 
the hydrogen to be disengaged in the state'of gas, and: 
the electricity to be conveyed onwards to the next zine 
plate. Here, being in some degree accumulated, it is’ 
extricated in larger quantity, and in a more éoncen- 
By a répetition of the same 
train of operations, the electric fluid continues to ac’ 
cumulate in each successive pair ; until, by a sufficient 
extension of the arrangement, it may be made to exist’ 
at the zine end of the pile, in any assignable degree of 
force.” For a farther account of this hypothesis, we 
must refer our readers to the original essay, and more 
especially to that part of it where the author explains 
the action of the interrupted circuit in the decomposi« 
tion of water, and the evolution of the gases at the ex- 
tremities of the two wires: (Thomson’s Ann, iii, 88.) 
It must be admitted that it satisfactorily ins the 
henomena, and that it accords with all the facts that 
ve hitherto been ness but it labours under the 
great objection of being founded upon a gratuitous 
position, of which there is no pooh wine the facility 
with which it explains the ces, 
\ 
tains its former electric state, but that itis ‘ propelled 
forwards from the zinc, through the menstruum, to the 
next adjoining copper in the pile or trough. This ef- 
fect; however, can only happen in a progressive man 
ner, because the fluid is but an imperfect. conductor ; 
and to this he ascribes many of the peculiar phenomena 
of the apparatus. . Dr Henry, in a judicious essay “| On 
the Theories of the Excilement of Galvanic Electricity,” 
(Manchester Mem. ii. 293, 2dSeries), observes, that “the 
explanation of Mr Cuthbertson is unequivocally a valu-: 
able supplement to the theory of Volta, imasmuch’as it 
takes into account the efficiency of chemical menstrua.” 
But, as he farther remarks, it is defective, because it 
does not explain why “ the action. of the menstruum 
is chiefly, if not entirely, exerted in oxidizing and 
dissolving the zinc plates, and why the evolution of 
hydrogen gas, or of nitrous gas, occurs chiefly at 
the copper surface.”| This deficiency was attempted:to 
be supplied by Dr Bostock, who, about the same time, 
published am essay on the action of the galvanic pile, 
which he has since considerably extended and modified 
in such a manner, as to’ accord with the recent discos 
veries. (Nich. Journ. iii. 8vo. 9. and 69. Thomson's 
Annals, iii. 32.) He proceeds upon the principle which 
which is called galvanism. psa: 
Bostock’s 
hypothesis. 
platés, he obeerved, that although some-of theseffects. 
was laid down by Dr Wollaston, that electricity isevol- ’ 
ved by the oxidation of metals; and generalizes it so far 
as to conclude, chat the electric fluid is always libera- 
* ted when an oxidable substance is united to oxygen. 
In addition to this principle, he proposes to admit the 
two following postulates, that the electric fluid has a 
strong attraction for hydrogen, and that when in passin; 
through a chain of conductors, it leaves the oxidable 
substance to: be conveyed through water, it combines 
with’ the hydrogen, and is again disengaged from it, 
whenever it again enters into an oxidable substance, 
were rendered more powerful by employing a solutiom 
of salt, yet-the electrometer was not more effected than’ 
with simple water. He evem asserts, that im many’ 
trials on gto agro scale, for example, with 1000 
pairs of is, he has ‘ found the electrical effects’ 
greatest when the chemical effects have been least.” 
He relates other facts of a similar kind, which appear 
to place this matter beyond all doubt, and to establish’ 
a decisive difference between these two operations of 
the instrument. See Singer's Elem. p. 330. 
M. De Lue’s experiments confirm’ and ‘illustrate this De Lue 
view of the subject; for they not enly show this want expe 
XPerk 
ment 
