to
Sir Humphry Davy's paper in the Philosophical Transactions, 1807, p.
31, that that philosopher, in repeating Wollaston's experiment of the
decomposition of water by common electricity (327. 330.) used an
arrangement somewhat like some of those I have described. He immersed
a guarded platina point connected with the machine in distilled water,
and dissipated the electricity from the water into the air by
moistened filaments of cotton. In this way he states that he obtained
oxygen and hydrogen _separately_ from each other. This experiment, had
I known of it, ought to have been quoted in an earlier series of these
Researches (342.); but it does not remove any of the objections I have
made to the use of Wollaston's apparatus as a test of true chemical
action (331.).

P ii. _Influence of Water in Electro-chemical Decomposition._

472. It is the opinion of several philosophers, that the presence of water
is essential in electro-chemical decomposition, and also for the evolution
of electricity in the voltaic battery itself. As the decomposing cell is
merely one of the cells of the battery, into which particular substances
are introduced for the purpose of experiment, it is probable that what is
an essential condition in the one case is more or less so in the other. The
opinion, therefore, that water is necessary to decomposition, may have been
founded on the statement made by Sir Humphry Davy, that "there are no
fluids known, except such as contain water, which are capable of being made
the medium of connexion between the metals or metal of the voltaic
apparatus[A]:" and again, "when any substance rendered fluid by heat,
consisting of _water_, oxygen, and inflammable or metallic matter, is
exposed to those wires, similar phenomena (of decomposition) occur[B]."

[A] Elements of Chemical Philosophy, p. 160, &c.

[B] Ibid. pp. 144, 145.

473. This opinion has, I think, been shown by other philosophers not to be
accurate, though I do not know where to refer for a contradiction of it.
Sir Humphry Davy himself said in 1801[A], that dry nitre, caustic potash
and soda are conductors of galvanism when rendered fluid by a high degree
of heat, but he must have considered them, or the nitre at least, as not
suffering decomposition, for the statements above were made by him eleven
years subsequently. In 1826 he also pointed out, that bodies not containing
water, as _fused litharge_ and _chlorate of pota