THEORY OF GALVANISM, 
ms 
to be the cause , and not the effect, of the evolution of electric 
city. In the solution of a metal (it has been observed by Dr. 
Wollaston*,) it would appear, that electricity is evolved by the 
action of the acid upon the metal ; and, in cases where hydro- 
gen is disengaged, that this evolution is required to convert the 
hydrogen into gas. When a piece of zinc and Another of sil- 
ver, are immersed in very dilute sulphuric acid, the zinc is’ dis- 
solved, and yields hydrogen gas 3 the silver, having ho power 
of decomposing water, is not acted upon. But as soon as the 
two metals, placed under the diluted acid, are made to touch, 
hydrogen gas arises also from the surface of the silver. In this 
case, it is added, we have no reason to suppose that the contact 
of the silver imparts any new power 3 but merely that it serves 
as a conductor of electricity, and thereby occasions the forma- 
tion of hydrogen gas. 
The chemical theory of the galvanic pile, though already 
suggested in general terms, may be considered, however, as 
having been a mere outline, till Dr. Bostock undertook to give 
it greater distinctness and consistency*. To the extended hy- 
pothesis which he has proposed, it is necessary to admit, as a 
ground-work, the three foliowing postulates : lstly, that the 
electric fluid is always liberated or generated, when a metal or 
other oxidizable substance unites with oxigen ; 2dly, that the 
electric fluid has a strong attraction for hydrogen 3 and 3dly, 
that when the electric fluid, in passing along a chain of con- 
ductors, leaves an oxidizable substance, to be conveyed through 
water, it combines with hydrogen, from which it is again dis- 
engaged when it returns to the oxidizable conductor. 
To the efficiency of the pile, two circumstances, it is ob- 
served by Dr. Bostock, are essential 3 that the electric fluid be 
disengaged 3 and that it be confined and carried forward in 
one direction, so as to be concentrated at the end of the appa- 
ratus. The firs object is fulfilled by the oxidizement of the 
zinc j the second, Dr. Bostock supposes, is effected by the 
Dr. Bostock 51 ! 
theory, viz. 
oxidation li- 
berates elec- 
tricity, 
which be- 
comes united 
xvi tli hydro- 
g n, 
and is convey- 
ed by it to 
the next ox. 
conduct®!-. 
Explanation. 
* Phi!. Trans, 
* Nicholson’s Join nal, 8v0. iii. 9. 
Vol. XXXV.— No. 164. T 
union 
