THEORY OP GALVANISM. 
269 
metal, becomes oxidized, but if of a non-oxidable metal 
oxygen gas is evolved from it, whilst, in both cases, a stream of 
hydrogen gas proceeds from the negative wire. Why, it may Why are the 
be asked, do the elements of water, thus disunited, arrange adis^ 
themselves at a distance'from each other ? If the particle of tance. 
water, which has been decomposed, be imagined to have been in 
contact with the extremity of the positive wire, the hydrogen 
must have been transmitted in an invisible state to the negative 
wire : but if the decomposed water were in contact with the 
negative pole, then the oxygen must have passed imperceptibly 
to the positive wire. 
These appearances have been explained by Dr. Bostock on Invisible 
the same hypothesis, by which he has accounted for the pheno- 
mena of the pile. The electric fluid, he imagines, enters the elements, 
water by the positive wire, and is there instrumental either in 
oxidizing the metal or in forming oxygen gas. In either case, 
the decomposition of the water must furnish hydrogen, which, 
uniting with the electric fluid, is carried invisibly to the negative 
pole, the attraction of which for electricity again occasions the 
separation of hydrogen, and its appearance in a gaseous state. 
This theory, however, is liable to some objections. 
1. It explains the decomposition of those bodies only, which Remarks cm 
contain hydrogen as one of their elements. And though it has tllis 
been ably contended by Mr. Sylvester, that the presence ot 
water is, in every case, essential to’ Galvanic decompositions, 
yet the fact does not appear to be sufficiently established. Even 
if it were verified, the agency ot moisture might be supposed to 
consist in its giving that peculiar interrupted transmission, on 
wjiich the efficacy of Galvanic electricity in disuniting the 
elements of bodies seems much to depeud. 
2. If the postulate of Dr. Bostock be granted, that electricity 
is evolved by oxidation, we shall be entitled to assume the 
reverse as equally true, viz. that electricity is absorbed when 
oxygen passes to the state of gas. In cases, where the positive 
wire is of an oxidable metal, the phenomena accord sufficiently 
with the theory ; for by its oxidation, electricity may be suppos- 
ed to be liberated, and to form the required combination with 
hydrogen. 
