LEC'T.   V.

HISTORY OF CHEMISTRY

71

current into its constituents, hydrogen and oxygen, but that
no other kind of change occurs in the water ; and that all
observations of the apparent occurrence of such change are
to be explained either by some action upon the vessel in
which the experiment has been conducted, or by some im-
purity in the water.
This enquiry is comparable, in many respects, with the first
of Lavoisier's investigations.^12 In both cases an endeavour is
made to refute a statement based upon inaccurate observation,
and that not simply by speculation, or by the assertion that it
is in contradiction to general views. In opposition to the
earlier superficial experiments, new ones are adduced which
have been carried out with the most minute attention to all the
conditions. In both cases the purpose is attained, and the
older inaccurate view is replaced by a correct one. Such
results as those obtained in these cases by Lavoisier and by
Davy are often called negative, but most people will agree with
me when I assert that they may be of great positive value.
Davy, however, does not stop here. He next investigates
the decomposition of salt solutions, and finds confirmation of
the statements of Berzelius and Hisinger. But he proceeds
with still greater circumspection, and endeavours to follow up
the phenomena more exactly. All the means are at his com-
mand, and he does not fail to avail himself of them.
Direct observation shows Davy that hydrogen, the alkalies,
the metals, etc., are separated by means of the current at the
negative pole, and oxygen and the acids at the positive pole.
From this he concludes that the former substances possess a
positive, while oxygen and the acids possess a negative electri-
cal energy; that in this case,as usual, the oppositely electrified
bodies attract each other; and that, in consequence, the posi-
tive substances separate at the negative pole, and vice versa.
In this assumption Davy had arrived at a conception, or, shall
I say, an explanation of the phenomena of decomposition ob-
served in the galvanic circuit. But he goes a step further, and
^18 See p. 22,